AspenPlusCatCrackerV7 3 Usr

Aspen PlusCatCracker V7.3

User’s Guide

Version Number: V7.3March 2011

Copyright (c) 2000-2011 by Aspen Technology, Inc. All rights reserved.

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Contents iii

Contents

About This Document ..............................................................................................1

Who Should Read This Guide .............................................................................1Technical Support ............................................................................................1

Introducing Aspen Plus CatCracker .........................................................................3

Overview.........................................................................................................3

1 Using Aspen Plus CatCracker...............................................................................4

Starting Aspen Plus CatCracker..........................................................................4The Sheets of the User Interface ........................................................................5General Guidelines for Using the Excel Interface ..................................................5Saving and Loading Data Files ...........................................................................6

Loading Data Files ..................................................................................7Saving and Loading Parameter or Simulation Worksheets......................................7

2 The User Interface ..............................................................................................9

The Command Line Window...............................................................................9Abort Button........................................................................................ 10No Creep Button .................................................................................. 10Close Residuals Button.......................................................................... 10Close Button........................................................................................ 10Manual Access to the Command Line ...................................................... 11

Toolbar and Menu .......................................................................................... 11Startup Aspen Plus CatCracker Submenu ................................................ 12File Submenu....................................................................................... 15Setup Cases Submenu .......................................................................... 16

Worksheets in the Aspen Plus CatCracker Workbook........................................... 17Introduction Worksheet......................................................................... 17Options Worksheet ............................................................................... 18Param Worksheet................................................................................. 21Analysis Worksheet .............................................................................. 35Feed Blends Worksheet......................................................................... 36Cat Blend Worksheet ............................................................................ 38Simulation Worksheet........................................................................... 38

LP Vectors Worksheet ..................................................................................... 43PIMS Vectors Workshet ......................................................................... 45PIMS Table Worksheet .......................................................................... 45Cases Worksheet.................................................................................. 46Optimize Worksheet ............................................................................. 46Profit Worksheets................................................................................. 47Profit Report Worksheets....................................................................... 48

Contents iv

Hidden Worksheets .............................................................................. 48

3 Specifying Data .................................................................................................50

Overview....................................................................................................... 50Setting Up Case Studies.................................................................................. 51

Before You Start .................................................................................. 51Specifying Varied and Reported Variables................................................ 51

Setting up Optimizations ................................................................................. 53Independent Variables .......................................................................... 53Bounds ............................................................................................... 54Setting up Objective Functions............................................................... 54Setting up Optimization Variables and Bounds ......................................... 57

Setting Up LP Vector Calculations..................................................................... 59

4 Running Cases...................................................................................................60

Case Types.................................................................................................... 60Running Cases from the CatCracker Toolbar ............................................ 60Running Cases from the CatCracker Menu ............................................... 61

Solver Settings .............................................................................................. 61Running a Parameterization Case ..................................................................... 62

Aspen Plus CatCracker Options .............................................................. 63Entering Data for Parameter Cases......................................................... 66Running the Parameter Case ................................................................. 67

Running a Simulation Case .............................................................................. 68Running Multiple Cases ................................................................................... 69

Running the Case Study........................................................................ 69LP Vectors Option................................................................................. 70

Running an Optimization Case ......................................................................... 70Solving the Optimization ....................................................................... 70Changing the Behavior of the DMO Solver ............................................... 72

LP Vector Generation ...................................................................................... 72Running LP Vector Generation................................................................ 72

5 Advanced Topics................................................................................................74

Parameter Case Analysis ................................................................................. 74Parameter Options on Options Worksheet ............................................... 74Param Sheet Input - Key Operating Data ................................................ 76

Param Sheet Input - Feed Data........................................................................ 78Param Sheet Input - Heavy Liquid Product Streams.................................. 80Param Sheet Input - Catalyst Data ......................................................... 80Feed Blends Sheet Review..................................................................... 80Cat Blend Sheet Review ........................................................................ 81Analysis Sheet Review .......................................................................... 81

Model Tuning................................................................................................. 82Heat Balance Tuning............................................................................. 82Over-cracking ...................................................................................... 85Catalyst Makeup versus MAT ................................................................. 90Adding New Catalysts ........................................................................... 91Work Process....................................................................................... 92Unhiding the CST Factors Worksheet ...................................................... 92Adding Catalyst Data ............................................................................ 92

Contents v

Re-hiding the CST Factors Worksheet ..................................................... 93Feed Characterization ..................................................................................... 93

Feed Properties.................................................................................... 94Selecting Feeds and Entering Property Information................................... 94

The Aspen Plus CatCracker Engine.................................................................... 96

6 EO Modeling Background and Examples ............................................................98

Equation-Oriented Modeling............................................................................. 98Pressure Drop Model Example................................................................ 98Model Specifications and Degrees-of-Freedom ......................................... 99Modes and Multi-Mode Specifications .................................................... 100Measurements and Parameters ............................................................ 100Changing Specifications with Combo Boxes ........................................... 101Optimization...................................................................................... 102

DMO Solver Background................................................................................ 103Successive Quadratic Programming (SQP)............................................. 103

Changing DMO Parameters............................................................................ 104Basic DMO Parameters........................................................................ 104

DMO Command Window Output and Log Files .................................................. 105DMO Solver Log Files .......................................................................... 106ATSLV File Problem Information ........................................................... 106

7 Troubleshooting ..............................................................................................111

Aspen Plus CatCracker Stops Responding ........................................................ 111Resetting Connection to the Aspen Plus Server ................................................ 111Error Recovery for Parameterization ............................................................... 112Error Recovery for Simulation ........................................................................ 113Solver Performance ...................................................................................... 114

Dealing with Infeasible Solutions.......................................................... 114Scaling ............................................................................................. 115Dealing with Singularities .................................................................... 116Notes on Variable Bounding................................................................. 118Run Time Intervention ........................................................................ 118

The Model Is Not Solving............................................................................... 118Licensing Errors ........................................................................................... 118

8 The FCCU Model...............................................................................................120

Overview..................................................................................................... 120Twenty-One-Lump Kinetics............................................................................ 120Sulfur Distribution ........................................................................................ 125Coke Production and Handling ....................................................................... 126

Kinetic Coke ...................................................................................... 127Metals Coke....................................................................................... 127Feed Source Coke .............................................................................. 127Stripper Source Coke (Occluded Coke).................................................. 127

Material Balance Reconciliation ...................................................................... 128FCCU Model Configuration ............................................................................. 129

Risers ............................................................................................... 130Reactor............................................................................................. 131Regenerator ...................................................................................... 132Stripping Zone Model.......................................................................... 133

Contents vi

Catalyst Standpipe, Slide Valve and Transfer Line .................................. 133CatCracker Nozzle System................................................................... 134

Simple Fractionation..................................................................................... 134Aspen Plus CatCracker Input Data Requirements.............................................. 135

Feed Blending.................................................................................... 135

Index ..................................................................................................................139

About This Document 1

About This Document

This chapter includes the following information:

Who Should Read This Guide

Technical Support

Who Should Read This GuideThis document is designed to be used by users of Aspen Plus CatCracker,formerly known as Aspen FCC, in conjunction with the Aspen RxFinery familyof products, including Aspen Plus Reformer, formerly known as Aspen CatRef,Aspen Plus CatCracker, Aspen Plus Hydrocracker, formerly known as AspenHydrocracker, and Aspen Plus Hydrotreater, formerly known as AspenHydrotreater.

Technical SupportAspenTech customers with a valid license and software maintenanceagreement can register to access the online AspenTech Support Center at:

http://support.aspentech.com

This Web support site allows you to:

Access current product documentation

Search for tech tips, solutions, and frequently asked questions (FAQs)

Search for and download service packs and product updates

Submit and track technical issues

Send suggestions

Report product defects

Review lists of known deficiencies and defects

Registered users can also subscribe to our Technical Support e-Bulletins.These are used to alert users to important technical support information suchas:

Technical advisories

Product updates and releases

About This Document 2

Customer support is also available by phone, fax, and email. The most up-to-date contact information is available at the AspenTech Support Center athttp://support.aspentech.com.

Introducing Aspen Plus CatCracker 3

Introducing Aspen PlusCatCracker

OverviewAspen Plus CatCracker, formerly known as Aspen FCC, is AspenTech's state-of-the-art Fluidized Catalytic Cracking Unit simulation system that can beused for modeling and optimizing a CatCracker unit in petroleum refineries.Aspen Plus CatCracker also provides full Windows interoperability to facilitateprocess and design engineers’ work processes. Aspen Plus CatCracker is partof the Aspen Engineering Suite™ of process design, simulation, andoptimization tools.

1 Using Aspen Plus CatCracker 4

1 Using Aspen PlusCatCracker

The following section explains the basics of using Aspen Plus CatCracker.

Starting Aspen Plus CatCracker1 From the Windows Start menu, click Programs | AspenTech | Process

Modeling <version> | Aspen Plus Based Refinery Reactors | AspenPlus CatCracker.

This launches Excel and opens the Aspen Plus CatCracker GUI.

2 When prompted by Excel, click the Enable Macros button.

Note: Aspen Plus CatCracker does not support having multiple versions ofitself or Aspen Plus installed at the same time.


When the Aspen Plus CatCracker workbook is loaded, there is no activeconnection to the Aspen Plus CatCracker model, which is an Aspen Plusflowsheet. The workbook consists of several spreadsheets where various datacan be entered and retrieved. The application also creates a new menu on theExcel menu bar called AspenPlusCatCracker. This menu provides access toall of the GUI’s primary functions including connecting to the model. Throughthe Startup Aspen Plus CatCracker submenu, you can:

Load the flowsheet

Modify startup options

Reset the Aspen Plus connection

Most of the other menu commands will be inactive until the flowsheet isloaded. For more information, refer to Startup Aspen Plus CatCrackerSubmenu. on page 3-3.

The Sheets of the UserInterfaceWhen Aspen Plus CatCracker is started for the first time, the defaultspreadsheet is the Introduction sheet. You can navigate to other data entryor results areas by selecting the appropriate tab at the bottom of the Excelwindow.

You can open a number of the sheets, including the LP Vectors, Cases,Optimize and the Profit sheets, by selecting the corresponding item fromthe AspenPlusCatCracker | Setup Cases menu as shown below.

For more information about these sheets, see The User Interface.

General Guidelines for Usingthe Excel InterfaceMost of the features of Excel are available in the Aspen Plus CatCrackerworkbook. However, you should only use these features with anunderstanding about the overall functioning of the workbook. This section


provides an overall description of the workbook and functioning. Othersections provide more detail about the worksheets that you will normally usefor running the Aspen Plus CatCracker model.

Here are some things to consider as you use the workbook:

The only fields that you can make an entry in that the model will use arethose colored blue.

Entries into number fields that are not colored blue will be overwritten bythe workbook after a case is executed.

If you use a formula in a field that is colored blue, it will be overwrittenafter a case is executed; therefore, enter only values in these fields.

If you change an option with a combo box, the color-coded fields are not

automatically updated; you must click the button on the Aspen PlusCatCracker toolbar that will appear after you connect.

If a case does not converge, the calculation engine will contain a startingpoint that is not good for subsequent cases.

Use the file save commands to frequently save calculations. These will beneeded to restore a case if the problem does not converge.

The data you enter into the Parameter and Simulation worksheets isautomatically saved by the workbook when a case is run and can beretrieved after you restore a case to create a good starting point for thecalculation engine.

The model is an equation-based model and needs a good starting point toconverge. Therefore, be careful about large changes in the independentvariables (color coded blue).

These guidelines will be become more meaningful as you read the material inthis section and in the sections about specific cases.

You can save the data file and load the file from the buttons provided on theCatCracker toolbar. You can also save and load the file using the commandson the AspenPlusCatCracker | File menu. You can make any run byselecting the run type from the dropdown box or from the commands on theAspenPlusCatCracker | Run Cases menu.

Saving and Loading Data FilesIt is frequently desirable to save the data in the CatCracker model, becausethe default when the model is started is to load the base problem data. Oncethe model has been tuned to your data, you can save data to use as the newstarting point.

To Save CatCracker Model Data:

1 On the Aspen Plus CatCracker toolbar, click the Save User Databutton.

-or-

Select the AspenPlusCatCracker | File | Save Case Data menucommand.


The Save User Data to File dialog box appears

2 Enter the path and filename; then click Save to return to the Save UserData to File dialog box.

3 Click Save to save the model data.

Note: You can save all of the data currently in the model or just the inputdata from the spreadsheet. Typically, you use the default option to save all ofthe model data. The data is saved to an ASCII file, which can be greatlycompressed to save disk space.

Loading Data Files

To load data saved to an ASCII file using the Save CaseData command:

1 On the Aspen Plus CatCracker toolbar, click the Load User Databutton.-or-Select the AspenPlusCatCracker | File | Load Case Data menucommand.

The Load User Data from File dialog box appears.

2 Browse to the file of interest.-or-Type in the file name and path directly in the filename and path textboxes.

3 Click Load to load the values from the data file into the CatCrackerflowsheet.

Saving and Loading Parameteror Simulation WorksheetsYou can save and load just the parameter and simulation worksheets at anytime and retrieve them later.


This option is useful if you think that your future Parameter or Simulation runis a big change and, therefore, the problem might fail. In this case, you cansave your input sheet and load it again to start back from a good solution.

To Save Your Input Worksheets:

From the menu, click Aspen Plus CatCracker | File | Save User InputSheet.

To Load Your Input Worksheets:

From the menu, click Aspen Plus CatCracker | File | Load User InputSheet.

Both parameter and simulation worksheet are updated when the command isexecuted.

2 The User Interface 9

2 The User Interface

The Aspen Plus CatCracker User Interface consists of three majorcomponents:

The Command Line Window.

The Menu and Toolbar.

THe Worksheets.

The Command Line WindowThe Aspen Plus Command Line window displays the output of commandssent to the Aspen Plus CatCracker model. It appears automatically whenloading Aspen Plus CatCracker and when running cases. After connecting tothe CatCracker flowsheet, you can also manually open this window byselecting the AspenPlusCatCracker | Tools | Display Command Linemenu command.

When Aspen Plus CatCracker is loading, the Command Line window appearsbriefly, letting you observe the commands that are being sent to the modelduring the flowsheet instantiation. You will not be able to access any functionson the command line at this time.


When a case is running, the Command Line window opens automatically andlets you observe the commands that are being sent to the model and theconvergence path of a solution. When the command line opens automaticallyin these instances, you can use only the Abort, No Creep, or CloseResiduals buttons.

Abort ButtonClick the Abort button to abort the solving of a case.

If you click the Abort button while a case is running, you must wait until thefollowing messages appear in the command line window:

Error return due to an ABORT message from the usercommunications file DMO.MSG

Problem failed to converge

You can now click the Close button to close the command line window andreturn to the model. You should then load a data file to ensure the next casestarts from a good converged solution.

No Creep ButtonWhen running a case, the default is to creep the solver (take small steps) fora few iterations to provide robust behavior. Once you have gained experiencewith the model and are confident that a particular case will solve well withoutthe default number of creep steps, you can manually turn the creep steps offby clicking the No Creep button.

You can click the No Creep button while a problem is converging. This causesthe solver to eliminate the creep in the next iteration.

Close Residuals ButtonUse the Close Residuals button to have the model close the residualswithout minimizing the objective function convergence. You might find thisuseful in cases where the objective function very nearly reaches a maximumvalue, but the convergence of the objective does not close.

Close ButtonThis button closes the Command Line window and returns you to the userinterface.

Click the Close button only:

After a run has failed to converge.

If you aborted a case and the command line message run aborted bythe user appears.

If you opened the Command Line window manually, and you havefinished using it.


Manual Access to the Command LineAfter connecting to the CatCracker flowsheet, select theAspenPlusCatCracker | Tools | Display Command Line menu command.The Aspen Plus command line window appears. When you open the commandline in this fashion, you have immediate access to the Close button. You canalso enter valid commands on the command line.

The Abort, Finish, and Close Residuals buttons have no effect when thecommand line has been opened manually unless the solve command isinvoked to run Aspen Plus. The Close button will close the command linewindow and return to the Excel spreadsheet. While the command line windowis open, you will not be able to access the Excel spreadsheet.

The command line window can be a very powerful tool in trouble-shootingproblems since the commands sent to the model and the solutions of themodel will be stored in the buffer. You can scroll through the buffer (the topwindow of the command line) to see convergence paths and any errormessages generated when trying to solve a problem.

Toolbar and MenuWhen the Aspen Plus CatCracker workbook is selected, Microsoft Excel isloaded and CatCracker adds a new menu to the Excel menu bar labeledAspenPlusCatCracker. This menu contains commands that activate VBAmacros within CatCracker. There is also an Aspen Plus CatCracker toolbarwhich only appears once the workbook is connected to the Aspen PlusCatCracker flowsheet.

This section explains the features that are available from the Aspen PlusCatCracker menu and toolbar. Many of the commands are associated with thecases for CatCracker modeling. Details about these commands are located inthe chapters of this manual describing the cases.

When you select AspenPlusCatCracker on the Excel menu bar, the menuappears as shown in the figure below. Note that most of the commands areon submenus.

Figure 3-1 AspenPlusCatCracker Drop-Down Menu Before Connection


Some of the options are dimmed in this figure because the workbook has notyet been connected to the calculation engine through the server. The optionsunder Development Tools are for advanced functions in the workbook andwill not be covered in this chapter.

Startup Aspen Plus CatCracker SubmenuThe Startup Aspen Plus CatCracker submenu contains the commands youwill typically use when you first activate the Aspen Plus CatCrackerworkbook.

Startup Aspen Plus CatCracker Options

When you select Startup Aspen Plus CatCracker, the menu shown aboveappears. The three commands on this submenu are described below

Startup Aspen Plus CatCracker Commands

Command Function

Load CatCracker Flowsheet Connect the workbook and load a problem file

Startup Options Load a problem file automatically or manually

Reset ApMain Resets the connection with the Aspen Plus server

The Load CatCracker Flowsheet option is normally the first command youwill use. This command displays the Connect dialog box. The Reset ApMaincommand causes the workbook to break the connection with the server. Thisis necessary if you want to use the Excel File menu. If you do not close theworkbook at this point, you can use the Load CatCracker Flowsheetcommand to reconnect the workbook.

Connect Dialog Box1 On the Excel menu bar, select AspenPlusCatCracker | Startup Aspen

Plus CatCracker | Load CatCracker Flowsheet.

The Connect dialog box appears.


Connect Dialog Box

2 In the Host box, enter the name of the host computer (normally yourcomputer) using all lower case letters.

If the correct computer name is entered, the Browse button in theProblem area will become enabled.

Note: You can easily determine the computer name if it is not known.Win2000: Right-click the My Computer icon on the computer desktop andselect Properties from the pop-up menu. Click the Network Identificationtab where the full computer name will be listed near the top.Windows XP: Right-click the My Computer icon on the computer desktopand select Properties from the pop-up menu. Click the Computer Nametab. The computer name will be listed in the Full Computer Name field.

3 Click the Browse button in the Problem area, navigate into the Apinitdirectory, select the file fcc.appdf, and then click Open.

The Connect dialog box reappears, and the fcc.appdf file name anddirectory should now appear in the Problem area.

4 Click the Browse button in the User Data File area, select the fileFCC12_1_demo.var, and click Open.

The Connect dialog box reappears, and the file name and directory ofFCC12_1_demo.var should appear in the User Data File area.

5 At the bottom of the Connect dialog box, click OK.

On a 750 MHz Pentium III PC, such as a Dell Inspiron 8000, it requiresapproximately two minutes to initialize the CatCracker flowsheet and loadthe data into the Excel GUI. During this time, the Excel cursor will appearas an hourglass symbol and the Excel status line will display the messageLoading Aspen Plus CatCracker flowsheet. The cursor will return to thenormal cross shape and the status line will display Ready when theprocess is complete.


Once the connected to the flowsheet is established, the previously inactiveAspenPlusCatCracker menu commands become active, and the AspenPlus CatCracker toolbar is created.

6 Now save the workbook using the Excel File | Save command, topreserve the computer name and CatCracker appdf file location enteredin the Connect dialog box.

You are now ready to begin using Aspen Plus CatCracker.

Startup Options Dialog Box

The Startup Options dialog box is illustrated below. This dialog box lets youspecify a default problem solution to load into the workbook other thanFCC.APPDF (the base solution).

Startup Options Dialog Box

When the Aspen Plus CatCracker workbook is opened, there is by default noconnection established with the CatCracker flowsheet. Furthermore, once theconnection is established, the data loaded into the spreadsheet will be thedata that comes with the generic model. You can change these defaultsettings to improve efficiency. By modifying the startup options, you canautomatically connect to the CatCracker spreadsheet and load a specific userdata file immediately upon opening the CatCracker GUI.

At the top of the Startup Options dialog box, you can choose to make aconnection to the CatCracker model either manually or automatically. If youselect Automatic Startup, the spreadsheet will automatically establish aconnection to the model whenever it is opened.

The Startup Options dialog box also has an option to load in a set of dataother than the default problem data. Automatically loading data that matchesyour plant is more convenient. For more information on saving and loadingdata, see Saving and Loading Data Files.


To Set Startup Options:

1 On the Excel menu bar, select AspenPlusCatCracker | Startup AspenPlus CatCracker | Startup Options.

2 The Startup Options dialog box appears.

3 Select Manual Startup or Automatic Startup. Your choice willdetermine whether the connection to the CatCracker model is mademanually or automatically.

If you chose the Automatic Startup option in Step 2, you can load a setof data other than the default problem data in the fcc.appdf file. To doso, select the Load User Data from File? checkbox.

4 In the File Name box, enter the name of the data file to be loaded(including the full path). Normally, this is a file that you have saved froma previous execution of the program.

5 Click OK.

File SubmenuThe second submenu on the AspenPlusCatCracker menu is File. There arefour commands in this menu, which are summarized below.

The first two commands display dialog boxes that you can use to retrieve orsave a case file. You can use the last two commands to retrieve or saveinformation you have entered in the Param or Simulation worksheets.

Command Function

Load Case Data Brings up a dialog box to load a case file

Save Case Data Brings up a dialog box to save a case file

Load User InputSheet

Loads data you previously entered on aParameter or Simulation worksheet

Save User InputSheet

Saves data you previously entered on aParameter or Simulation worksheet

It is very important for you to be familiar with the Load Case Data and SaveCase Data commands. The CatCracker model is an equation-based modeland can be moved from a base solution to another base solution, if the moveis not too large. Normally, as a very general rule, too large means a move ofabout 20% to 30% on values other than temperatures. Temperatureschanges can be in the range of 10 to 20 °F.

With experience, you will become more familiar with the magnitude ofchanges that the model can accommodate. However, when a solution is notachieved, the solver is left with a bad starting point. You will need to load in agood starting point and this is done with the Load Case Data command.Therefore, it is good practice to save cases with the Save Case Datacommand for later retrieval.


The Load User Input Sheet and the Save User Input Sheet options areworkbook operations you can use to avoid retyping data if it is lost in a runthat doesn’t converge. After you retrieve a case, the values in worksheets willbe updated. If you have entered data on the Parameter or Simulationworksheet, this data will be overridden. To retrieve this data, execute theLoad User Input Sheet command. If you need to save the data you haveentered, execute the Save User Input Sheet command. These can also beactivated by buttons on the toolbar:

Save User Data button

Load User Data button

Setup Cases SubmenuThe third submenu on the AspenPlusCatCracker drop-down menu is SetupCases. This submenu will be dimmed until you successfully connect to theworkbook to the calculation engine as explained above.

The Setup Cases submenu contains seven commands, which aresummarized below


Command Function

Case Study Set up case studies

Optimization Set up optimization calculations

LP Vectors Set up LP vectors

PIMS Vectors Set up PIMS vectors

Profit 1 Set up profit function number 1 for optimization case



For more information about setting up cases, see Specifying Data.

Worksheets in the Aspen PlusCatCracker Workbook

Introduction WorksheetBesides displaying the logo for the workbook, the Introduction worksheetprovides version data for product, flow sheet, Excel interface, and catalystlibrary. This data is located below the opening display and is displayed bymoving the scroll bar, or paging down. A place for notes and/or comments islocated below the version information.


Options WorksheetYou set the main AspenPlusCatCracker model configurations and data entryoptions on the Options sheet. Under most conditions, you should only haveto make modifications to this sheet once, when the model is first beingcustomized to your specific CatCracker unit. The sheet is self-documented,with the general instructions listed at the top of the sheet, and a detaileddescription given next to each combo box option.

A summary of the general instructions and rules of combo boxes are givenbelow:

The options selected in the combo boxes are applied for all cases.

Combo boxes only operate once the spreadsheet is connected to theCatCracker model. (For information on how to connect to the flowsheet,see Connect Dialog Box on page 12.)

Selecting a different option in a combo box changes the spec of specificvariables. Recall that a variable’s spec determines if it is calculated, keptfixed, or varied as a degree of freedom depending upon the solver’s runmode.

Changing the option in a combo box does not automatically refresh theParam or the Simulation sheets to reflect which variables are calculatedand which variables are fixed. Recall that the fixed variables have a bluebackground, while those that are calculated have a white background.There are three methods to update the Param and Simulation sheets,described in the following section.

Updating Spec Colors

Method 1:

1 On the AspenPlusCatCracker toolbar ,

click the Update Spec Color button .

This refreshes both the Param and the Simulation sheets.

Note: If you click the Update Spec Color button too early, before the newoption is processed, the following error appears:

If this appears, click OK to continue, and wait until the combo box option hasfinished running the macro before trying to update the colors.

Method 2:

1 On the main toolbar menu, select AspenPlusCatCracker |Development Tools | Update Param Sheet color for the Param sheet.


2 On the main toolbar menu, select AspenPlusCatCracker |Development Tools | Update Simulation Sheet color for theSimulation sheet.

Method 3:

1 Run a Param case. For information on how to run a Param case, seeRunning a Parameterization Case on page 5-3

This automatically refreshes the Param sheet when the data is passed backto the spreadsheet from the solver.

2 Run a Simulation case to update the color on the Simulation sheet.

Of the three methods, the first is the simplest and is recommended.

Options Sheet Options

The options available on the Options sheet are summarized below:

# Combo BoxName

Options available Description Default

1 Feed Rate BasisInput volume rates

Input mass rates

Enter fresh feed and recyclerates on volume or massbasis.

Default #1

2 Fresh FeedGravity Basis

Input API

Input SG

K Const for LP

Ca Const for LP

H Const for LP

Enter API or Specific Gravityfor all feeds on Param andSimulation sheets. K factor,Aromatic content CA and Hcontent are for running LPvectors.

Default #1

3 Product GravityBasis

Input API

Input SG

Enter API or Specific Gravityfor light naphtha(debutanizer bottoms) andheavier products.

Default #1

4 Light-EndsProduct RateBasis

Input volume rates

Input mass rates

Enter light-end product rateson volume or mass basis.

Default #1

5 Heavy ProductRate Basis

Input volume rates

Input mass rates

Enter heavy ends productrates (light naphtha andheavier) on volume or massbasis.Note: Should be consistentwith Fractionation Control.

Default #1


# Combo BoxName


6 FractionationControl

Input vol, HN and HCO rate const.

Input mass, HN and HCO rate const.

Input vol, all use TBP90

Input mass, all use TBP90

Input vol, HN/LCO/HCO rates const

Input mass, HN/LCO/HCO rates const

Custom 1

Custom 2

Custom 3

Set product (heavy naphthaand heavier) flow control ordistillation point control.

Default #1

7 Fresh FeedConcarb orRamsbottom

Input Concarb

Input Ramsbottom

Enter fresh feed Conradsoncarbon (CRC) or Ramsbottomcarbon content.

Default #1

8 Fresh FeedBasic or TotalNitrogen

Input Basic N

Input Total N

Enter fresh feed basicnitrogen or total nitrogencontent. The default basic tototal nitrogen ratio is 1:3.This ratio is changed in cells.

Default #1

9 RegeneratorControl

Complete Combustion

Flue Gas O2 const float air vol

Flue Gas O2 const float air mass

Flue Gas O2 const float O2 inj vol

Flue Gas O2 const float O2 inj mass

Air and O2 inj const float Flue Gas O2

Bed T & FG O2 const float Cat Cooler &air vol

Bed T & FG O2 const float Cat Cooler &air mass

Partial Combustion

Bed T const float air vol

Bed T const float air mass

Bed T const float O2 inj vol

CO2/CO const float air vol

CO2/CO const float air mass

CO2/CO const float O2 inj vol

CO const float air vol

CO const float air mass

CO const float O2 inj vol

CRC const float air vol

CRC const float air mass

CRC const float O2 inj vol

Select either complete orpartial combustion options.Select the appropriate optionfrom the submenu of optionsin the second combo box.

Default #1, 1.1

10 Pressurebalance control

All pressures const

WG to RX DP const

WG-RX and RX-RGN DP const

Enter pressures or pressuredrops as constants.

Default #3


# Combo BoxName


11 Light NaphthaFront-EndControl

Input C4 content

Input RVP

Enter C4 content or RVP.Note that both inputs arerequired forparameterization, so bothremain blue on Param sheetregardless of selection.However, only the selectedoption is fixed (blue color) onthe Simulation sheet.

Default #1

12 CatalystActivity Control

Input ECAT MAT

Input make-up rate

Enter MAT or make-up rateas constant. Note that bothinputs are required forparameterization, so bothremain on blue on Paramsheet regardless of selection.

Default #1

Param WorksheetOnce the main options are selected on the Options sheet, enter the processand laboratory data on the Param sheet. General information about usingthis sheet is shown at the top of the sheet and is reported below:

Use this sheet to enter data for a Parameter case run.

Colored cells are input data. Run the AspenPlusCatCracker |Development Tools | Update Param Sheet Color macro to confirmcolor is correct with current options.

In Equation Oriented terms, the colored cells have Const or Meas specs.

This data may not be consistent with the last model runs as a Simulatecase, Case Study, etc. This is the last Param case, not the last model run.

Before running this case, check the Options sheet. If options arechanged, update the spec colors. See Updating Spec Colors. on page 3-13

Do not change the position of any cell on this screen. The Excel VBA codeexpects the cells to be at their current positions.

Additional instructions on using this sheet are as follows:

Enter data in the units of measurement shown. Units of measurementcannot be changed from the Param sheet. To change the units ofmeasurement for individual variables or a group of variables, contactAspenTech.

Fill out as many data entries as possible before running a Param case.Sending a consistent set of operating conditions improves the chances ofsuccessful convergence.

The data to be entered on this sheet is broken up into twelve sub-sections asfollows:

Section Title

1. Key operating data

2. Feed data


Section Title

3. Fresh feed preheat temperature control

4. Recycle stream data

5. Fresh feed and recycle stream routings

6. Light ends product streams for reactor parameterization

7. Heavy liquid product streams for reactor parameterization

8. Heavy liquid product streams for simple fractionatorparameterization

9. Catalyst data

10. Mechanical data

11. Heat losses

12. Tuning data

Key Operating Data

The KEY OPERATING DATA section contains such things as keytemperatures, pressures, air rates, and steam rates related to theregenerator, reactor, and stripper. Items with a blue background are requiredinputs. These CONST and MEAS variables are used to parameterize themodel to actual operating conditions.

Specific information to be aware of when entering data is as follows:

Riser Outlet Temperature: Enter the vapor temperature where thecatalytic cracking and thermal cracking have terminated (outlet of thedilute phase – see the riser drawing in the mechanical data section).

Air rate for MAB: If the flow meter is on a dry basis, enter a very lowvalue (0.01%) for the air relative humidity entry.

Air blower discharge pressure and temperature: These entries areused for enthalpy calculations only. They are not connected to thepressure balance of the regenerator-reactor-wgc circuit. The Aspen PlusCatCracker model does not model the MAB or the Wet Gas Compressor.Constraints from these pieces of equipment can only be taken intoaccount by limiting the air flow rate and the wet gas compressor suctionrate during an optimization run.

Sign of Rg/Rx DP: Set to –1 if the regen pressure is greater than thereactor pressure (default). Set to +1 if the opposite is true.

Lift Steam, Dispersion (or Atomizing Steam), Reactor StrippingSteam: The units of measurement shown for the rate, temperature andpressure columns correspond to the dispersion steam to the bottom ofVRISER1 (see mechanical data section). Enter all of the steam data in theunits of measurement shown.

Lift Gas: Some CatCracker units have a recycle stream from thesecondary absorber offgas to the bottom of the riser as a method tominimize lift steam which is detrimental to the catalyst. In theAspenPlusCatCracker model, the Lift Gas stream composition isapproximated to be inert (Nitrogen). This simplification ignores thereaction mechanisms of an actual offgas stream, but it does model theenthalpy effect on the fresh catalyst entering the riser.


Param Sheet - Key Operating Data

Feed Data

The FEED DATA section contains inputs for up to ten fresh feed streams.Depending upon the feed rate basis option selected on the Options sheet,either the volume or the mass is entered in the cells highlighted in blue.

There is a feed type option for each feed through an associated combo box.Select the most appropriate feed type from the drop down menu of typesavailable. The following table provides a brief description of the standard feedtypes available.

# Feed Type Description

1. VGO Atmospheric Tower Gas Oil, Vacuum Tower GasOils (LVGO and HVGO)

2. HTVGO Hydro-treated Gas Oils

3. LCKGO Light Coker Gas Oil

4. HCKGO Heavy Coker Gas Oil

5. MXCKGO Mixed Coker Gas Oil

6. RESID Resid (Atmospheric Tower bottoms)

7. HOIL HOIL

8. FCCGO FCC LCO/HCO type material

9. NAPHTHA Naphtha feed (430 °F and lighter)

10. SYN Synthetic crude

11. NOT FOUND Same as VGO (Default)

These feed types are found on the hidden sheet Feed Input.


To unhide this sheet:

From the Excel menu bar, click Format | Sheet | Unhide | Feed Input.

Contact AspenTech to add a new feed type to this list.

Once the feed type is selected, enter all the analytical data for that feed,including the API (or specific gravity), sulfur content, nitrogen content (totalor basic), Conradson or Ramsbottom carbon, refractory index, viscosity, anddistillation. A combo box option is available for either specifying the refractoryindex measurement, or to have the refractory index estimated by selectingthe Estimate option. The viscosity measurement can be entered in either cSTor SUS, or you can have the model also estimate this value by choosing theappropriate option in the viscosity combo box for each feed. In addition toentering the 9-point distillation for each feed, you must specify the distillationtype (D86, D1160, D2887, or TBP) by selecting the appropriate item from thedistillation combo box.

The final entry is to specify the feed metal contents of the feed streams. Afeed metals combo box is included to select how the feed metals arereconciled with the ECAT metals. The default is to enter feed metals.

Param Sheet – Feed Data


Fresh Feed Preheat Temperature Control

The default setting for the preheat temperature of the fresh feeds is that all ofthe fresh feeds are combined upstream to the riser and they are all mixed atthe same temperature. This temperature is entered in the Combined feedtemperature 1 cell. Although the Combined feed temperature 2 is alsohighlighted in blue, it is not necessary to enter a value since it is not used bythe model under the default settings. Contact AspenTech if changes need tobe made to the default configuration.

Param Sheet – Fresh Feed Preheat Temperature Control

Recycle Stream Data

There are four recycle streams available:

Heavy naphtha

LCO

HCO

Bottoms

The flow rate (volume or mass), and the preheat temperature of each streamare entered in this section. Do not set any of the recycle streams to zero.

Param Sheet – Recycle Stream Data

Fresh Feed Recycle Stream Routings to Riser

Each individual fresh feed stream and recycle stream can be sent to thebottom feed nozzle or the upper feed nozzle, or a combination of the two.Setting the feed routing is done in this section. For additional information onthe model layout of the bottom and upper feed nozzles, refer to theMechanical Data section.

To specify that a stream enters the riser at the bottomfeed nozzles:

Set the ratio to 1.0.


Set the ratio to 0.0.

To specify that a stream enters the riser at the upper feednozzles:

Note: A minimum amount of material must be specified for both injectionpoints. Therefore, even if in actuality all feed goes to the bottom of the riser,at least one of the non-zero feed streams must be set to a ratio factor lessthan 1.0, such as 0.9999..

Param Sheet – Feed Stream Routings to Riser

Light Ends Product Streams for ReactorParameterization

The flow rate and gas chromatograph (GC) composition of up to three vaporflow rates, up to five liquid flowrates, and the light and heavy naphthastreams are entered in this section. The first three columns are strictly forvapor flowrates.

Note: The unit of MMCUFT/DAY for the vapor streams is interpreted asmillions of standard cubic feet per day. The GC composition for the vaporstreams can be entered on a %mole or %volume basis (no difference), whilethat of the liquid streams is strictly on a %volume basis.

General rules for entering data in this table are:

External streams with C6 or lighter components are entered in this table,with a negative value for the flow.

At least one of the components of any given stream must be nonzero.Even if there is no flow associated with the stream, setting the GC’s tozero can lead to model robustness issues.

None of the individual components can have zeros across all streams. Ifthe GC for all streams are such that one (or more) of the componentslisted in the table are zero, you should still assign a small amount to thecomponent(s) in question under the most logical stream. Leaving acomponent at zero composition can result in negative yields and modelrobustness issues.

Setting the heavy naphtha flow to exactly zero is permitted, but ensurethat at least one of its components is nonzero.

Enter the light naphtha (or debutanizer bottoms) flow rate in this tableand the next two tables.


Param Sheet – Light Ends Product Streams for Reactor Parameterization

Heavy Liquid Product Stream ReactorParameterization

The heavy liquid product streams include the light naphtha (debutanizerbottoms), heavy naphtha, LCO, HCO and Bottoms streams. The flow rate,API, and 9 point distillation data for these five streams must be entered inthis table and in the following table (for simplified main fractionatorsimplification).

Param Sheet – Heavy Liquid Product Streams for Reactor Parameterization


The data entered in this table sets the standard yields for the reactor kinetics,while the same data entered in the next table is strictly to set how theproduct streams are actually separated. If a cut has zero flowrate or does notexist, do not enter zero as the flowrate. Instead, enter a small non-zeronumber (1 to 10 BPD) to avoid numerical problems with the solver.

Heavy Liquid Product Streams for SimplifiedFractionation Parameterization

The same flowrate, API, and distillation information entered in the previoustable must be entered in this one as well. Again, do not enter zero for any ofthe cuts, even if the cut has zero flowrate or if the cut does not exist on yourunit. Enter a small non-negative number such as 1 to 10 BPD.

Other properties highlighted in blue need to be entered. The sulfur weightpercent of all five heavy liquid cuts needs to be specified, regardless if the cutis non-existent or actually has a zero flowrate measurement. The sulfurweight percent must be entered in increasing order going from the lightestcut to the heaviest cut. Consult the sulfur balance section on the Analysissheet to ensure that the sulfur distribution among the product cuts appearsreasonable.


Param Sheet - Heavy Liquid Product Streams for Simplified MainFractionation Parameterization

The properties for the gasoline stream include research and motor octanenumbers, PONA breakdown, Reid vapor pressure, and volume percentconcentration of C4’s. Regardless of how the front-end part of the gasolinecut was specified on the Options sheet (that is, constant RVP or constantC4), both are required inputs for Parameter cases only. In Simulation cases,the constant property controls the cut while the other property is calculatedwhen the problem is solved. The cloud point for the LCO cut is also an input.The Conradson carbon and basic nitrogen results reported for the heavynaphtha, LCO, HCO, and Bottoms affect incremental conversion of theserecycle streams.

The input data required is straightforward. The data required for the InputTBP 90% cells is the target TBP 90% point. Contact AspenTech to changethe target to another distillation type such as D86 90% or D86 End Point.

Catalyst Data

The catalyst data section is used to specify the number and type of freshcatalyst, ECAT data, and other catalyst related data such as inventory, make-up rate, and loss rates. Up to five different types of fresh catalysts can bespecified and one ZSM-5. The catalyst type is selected from the combo boxoption. The library of different catalyst types is found on the CST Factorssheet, which is hidden in the install kit spreadsheet.

To View the CST Factors Sheet:

On the toolbar, click Format | Sheet | Unhide | CST Factors.

After a catalyst type is selected, the actual composition and base compositionfor the zeolite, alumina, and rare earth appear below the combo box. Initially,they will be the same. If the actual values differ from the base values basedon vendor specifications, then enter your values in the appropriate cells underthe Actual composition heading.

Fresh catalyst data copied from the CST Factors sheet is also displayedbelow each catalyst type. Although these values are constants and arehighlighted in blue, do not enter any information in these cells. They aresimply included to ensure that the data entered below in the ECAT section isconsistent with the fresh cat data.

Regardless which option has been selected for the catalyst activity (MATconstant or make-up rate constant), the make-up rate is always an input onthe Param sheet. The cat inventory to enter is the total inventory of catalystin the regen/reactor circuit.

The cat losses in the regen flue gas and the reactor overhead are alsospecified in this section. The model calculates the catalyst withdrawal basedon the difference between the make-up rate and the cat losses. For thoseCatCracker units running low metals feed and/or those with little or nocatalyst withdrawal, set the cat losses to a very low number. (Set regen catlosses at ¼ of make-up rate and reactor cat losses at 1/10 to 1/20 of make-up rate) to ensure model robustness. Otherwise, problems may occur inperforming metals calculation when comparing the difference between the


metals entering the unit with the feed, and the metals content in the regen, inthe losses and in the withdrawal.

The ECAT data entered must be consistent with the blended fresh catalystdata. For example, if the lab ECAT activity is entered as 75%, while theblended fresh cat data has a lower activity value, then the model will notsolve due to this data inconsistency. The FINES data corresponds to thecatalyst impurities in the loss catalyst streams leaving the regenerator fluegas and reactor vapor line. The FINES data is normally not known, so it isrecommended to enter this data in a ratio consistent with the default ratiosbetween the ECAT and FINES data.

Param Sheet – Catalyst Data

Mechanical Data

The physical length, diameter, and height of the key reactor and regeneratorequipment are defined in this section. The equipment layout is based on thetypical side-by-side FCCU design. The riser section is divided into fourprincipal blocks as shown below. The kinetic reactions take place in theVRISER1 and VRISER2 blocks, with some reaction taking place in theRXDIL block. The riser outlet temperature specified as the first input in theKey Operating Data refers to the vapor temperature of the hydrocarbonsleaving the RXDIL block.


The physical dimensions of VRISER1 and VRISER 2 are normallystraightforward to specify. General rules are that the bottom of VRISER1 isnormally taken at the bottom feed nozzle, while the top of VRISER2 isnormally taken at the top of the riser where the vapors exit the riser section.

Determining how to divide the riser between these two extremities for settingthe length of VRISER1 and VRISER2 is dependent upon the physical layout ofthe riser. If the riser has two active feed injection points, then the length ofVRISER1 can be taken as the vertical length between the two injection points,and the length of VRISER2 can be taken as the distance from the upperinjection point to tip of the riser where the vapors exit. If there is only oneinjection point, then the riser can be divided in such a way that it bestmatches changes in the internal diameter. If the internal diameter changeswithin the selected length of VRISER1 and/or VRISER2, then use the weightedaverage as the diameter.

In specifying the lift riser length, a measurement is taken between the bottomof the riser and the injection point of the bottom feed nozzles. The height ofthe reactor dilute block is dependent upon the desired residence time of thevapors leaving the tip of the riser and the entry of the secondary reactorcyclones. Enter the actual diameter of the reactor for the diameter field, andvary the height until the residence time matches acceptable results. Theresidence time is found on the Analysis sheet. Its value, along with all dataon the Analysis sheet, is valid after running a Parameter, Simulation orOptimization case.

Riser setup in AspenPlusCatCracker

All pieces of equipment requiring an outer diameter and a wall thickness canbe input in various ways. If the metal thickness is ignored, then the outerdiameter should be taken as the internal diameter plus two times therefractory thickness, and the wall thickness should be set equal to therefractory thickness. This is how the drawing is represented below. If themetal thickness is to be included, then the outer diameter is equal to theinternal diameter plus two times the metal thickness plus two times the


refractory index, while the wall thickness is set equal to the metal thicknessplus the refractory thickness.

HB

HCyclone Inlet

TR2SC

TR1SC

SPSC

TR2RC

SPRC

TR1RC

ODRC,SP

wtRC,SP

ODSC,SP

wtSC,SP

LLR

LR1

LR2

HRx

wtLR

ODLR

wtR1

ODR1

wtR2

ODR2

ODRx

wtRx

DStrip

ADStrip

LStrip

Steam

DB

Dinterfacial

DDilute

wtRC,TR2

ODRC,TR2

wtSC,TR2

ODSC,TR2

Drawing of Reactor/Regen for Mechanical Data

Where:

Symbol Equals

TR transfer line

SP stand pipe

SC Spent Cat

RC Regen Cat

Rx reactor dilute phase

The stripper diameter is to be taken as the entire internal diameter of thereactor stripper model. The annulus diameter is taken as the riser innerdiameter in the stripper section, plus the corresponding layers of refractory in


the stripper, metal thickness of the riser, and refractory thickness in the riser.If the CatCracker design has an external riser, then set the annulus diameterto zero. Entering exactly zero is valid.

For the spent cat route and the regen cat route, ignore transfer line 1 and setit to an arbitrarily short length (0.1 ft). Its outer diameter and wall thicknessshould be set equal to the standpipes. Do not enter values for the angle inputrequired for the lift riser, spent cat transfer lines, and regenerated cattransfer lines. Leave these at their default values.

The regen bed height is adjusted to get the correct cat inventory number inthe regenerator. The interfacial diameter is normally set equal to the regenbed diameter. Set the height of the inlet of the regenerator cyclone equal tothe length from the first stage cyclone inlet to the bed level, plus the lengthfrom the bed level to the air grid. Since the inlet of the first stage cyclone isnormally rectangular in shape, the diameter is calculated by first summing upthe total inlet area of all inlet first-stage cyclones, and then calculating thediameter of a circle with this area (A = π d2/4).

The default settings for the fluidization media are typically acceptable, butyou can adjust these settings.

Param Sheet – Mechanical Data

Heat Losses

The heat loss terms are entered in this section.

Note: Heat losses in Riser1 and Riser2 must be entered as negative values.


Param Sheet – Heat Losses

Tuning Data

Tuning data is entered in this section. Each entry has a short description toexplain how the data can be adjusted. The most relevant tuning parameter isfor adjusting the overcracking peak and the stripper performance. Thissection is geared toward advanced users. For detailed procedures, refer toHeat Balance Tuning.

Param Sheet – Tuning Data


Analysis WorksheetThis sheet gives an overview of all the key process variables. This sheet isdivided in many different sections. Each section represents some importantpart of the process such as, mass balance, sulfur balance across theCatCracker, and so on. For each section, the description of the variable andits title, specs, units, and values are displayed.

Sections Description Row #

Mass balance Displays the error in the mass balance between the feeds andproducts

3

Fractionated products Displays a detailed distribution of products on the volumepercent basis of fresh feed

18

Standard cut products Displays a TBP or square cut distribution of products on thevolume percent of fresh feed

36

Sulfur balance Displays the distribution of Feed sulfur in products 49

Feed rate summary Displays the total fresh feed, total recycle feed and total feedto riser on volume and mass basis

59

Fresh feed conversion Displays the apparent and standard conversion on volumeand weight percent based on fresh feed

67

Aromatic contents Displays the total aromatic content of each of the individualfeed

75

Heat balance - GeneralInformation

Displays general information about the coke yield, coke heatof combustion, Regen cooler and bed coils duty, catalystcirculation rate etc.

87

Heat balance - Heat ofcracking

Displays information about the Apparent and theoretical heatof cracking for total fresh feed and total fresh feed andrecycle combined

102

Sources of coke Displays sources of coke distribution by mechanism offormation and associated hydrogen content, Concarbon tofeed coke ratio, Metals coke factor, Riser feed mix conditions,and key parameters.

112

Total feed composition(Fresh+recycles)

Displays the 19 lump composition of the total feed on weightpercent basis.

160

Composition by boiling range Displays breakdown of 19 lumps by boiling range from C1-C4, C5 – 430, 430-650, 650-950, and 950+.

181

Composition by type Displays breakdown of components on basis of chemicalcomposition like C1-C4, C5 – 430, Paraffins, Naphthenes, 1,2 &3 Ring aromatic cores, and Aromatic side chains. It hasvarious types of distribution combining various ranges of cutslike distribution of 430+ paraffins, 650+ Naphthenes etc.

188

Vapor residence times Displays vapor residence time distribution in Riser1, Riser2,Reactor dilute phase section and total residence time.

236

Solids residence times Displays solid residence time distribution in Riser1, Riser2,Reactor dilute phase section and total residence time.

243

Riser/reactor catalystinventory

Displays solid hold up in tons of mass in the Riser1, Riser2,Reactor dilute phase section and total solids hold up

250

Riser superficial velocities Displays vapor velocity and the inlet and outlet of Riser1 andRiser2 section

257

Regenerator data Displays various key parameters of the regenerator sectionlike bed temperature, flue gas temperature, flue gas CO/CO2dry content, Coke on regen and spent catalyst etc.

263


Sections Description Row #

Regenerator air supplysummary

Displays rates for dry air, wet air, Enriched O2, and EnrichedAir on mole, mass, and volume basis. It gives temperatureand pressure for each of the following streams. It providesmolar composition of wet and enriched air.

287

Metals Data Displays the distribution of various metals like Ni, Va, Fe, Cu,and Na and overall balance of these metals

337

Feed Blends WorksheetThis worksheet displays detailed data for all the fresh feed, the blended feed,the recycle feed and the total blend of fresh feed and recycle feed. This sheetis updated from load file and from any of the last runs. You cannot enter anydata on this sheet. The sheet can be read in a matrix form with the columnsas different feeds and the rows as the various feed properties. Each feedproperty variable is described in Column A below the heading Description.Columns following this column display Titles, Specs, and Units for theFeed1. Usually all the fresh feeds have the same corresponding titles, thesame specs, and the same units as Feed1. The model can blend up to tenfresh feeds and up to four recycles for the final blend to the riser. Fresh feedblends in Column O represent the properties of all the fresh feeds blended.The four recycles include recycles from:

Heavy Naphtha

LCO

HCO

Bottoms

The final total blend is the actual model feed to the riser.

The various properties of the feed displayed are listed below:

Feed Properties Description Row #

Volume rate Displays the volume flow rate of the feed 12

Mass rate Displays the mass flow rate of the feed 13

Preheat temp to riser Displays Preheat temperature of the feed to riser 14

Fraction of flow to bottom ofriser

Displays fraction of each feed that goes to the bottom of theriser

15

Recycle vs. product splitterratio

Displays the split ratio for each of the recycle streams. 16

Index number for feed type onfeed input sheet

Displays the corresponding feed type from the feed inputpage row # 3

18

API gravity Displays the API gravity for the fresh feed 19

Specific gravity 60F/60F Displays the specific gravity for the fresh feed at 60F 20

K Factor based on D1160VABP

Displays the UOP characterization factor based on D1160VABP

21

D1160 VABP Displays D1160 Volume Average Boiling Point in oF for thefeed

22

K Factor based on D2887 50%point

Displays the UOP characterization factor based on D288750% cut point

23


Feed Properties Description Row #

Sulfur content Displays the weight percent of the sulfur in fresh feed 24

Sulfur crackability factor Displays potential amount of total sulfur in the feed that canbe cracked

25

Basic nitrogen content Displays the basic nitrogen content of the feed in PPMW units 26

Basic/Total Nitrogen ratio Displays the ratio of Basic to Total nitrogen in feed 27

Total nitrogen content Displays the total nitrogen content of the feed in PPMW units 28

Conradson carbon content(CCR) & Ramsbottom carboncontent (RCR)

Displays the weight percent carbon residue by ASTM testprocedure

29

Metals content Displays metal contents for Ni, Va, Fe, Cu and Na in PPMW 31

Refractive index from lab Displays Refractive Index from the lab and also providesestimated value of RI by model at 20o C

38

Viscosity Cst at 210F from lab Displays Viscosity of the Feed Stock 43

Aromatic content bias Displays the difference in the amount of aromatic carboncontent between TOTAL Correlation and base fingerprint Cacontent based on base bulk properties

47

Aromatics content by modifiedTotal method

Displays total aromatic carbon content by TOTAL correlationbased on actual feed

48

% of blended fresh feedaromatics in each feed

Displays the percentage of aromatic carbon from each freshfeed to form blended feed

49

Hydrogen content Displays the total elemental hydrogen content in the feed 50

% of blended fresh feed H ineach feed

Displays the percentage of hydrogen content from each ofthe fresh feed to form blended feed

51

Molecular weight Displays the average molecular weight 52

Distillation data Provides distillation curve data by D1160, D86 , D2887 andTBP calculations

53

Base 19 lump composition Provides weight percent of the base 19 lumps for the freshfeed

90

Final adjusted 19 lumpcomposition detail

Provides weight percent for the final adjusted 19 lumps afterthe manipulations by feed adjust model for the fresh feed

111

Final adjusted 19 lumpcomposition by boiling range

Gives breakdown of 19 lumps by boiling range from C1-C4 ,C5 – 430, 430-650, 650-950 and 950+ lump

132

Final adjusted 19 lumpcomposition by type

Gives breakdown of components on basis of chemicalcomposition like C1-C4, C5 – 430, Paraffins, Naphthenes, 1,2 &3 Ring aromatic cores and Aromatic side chains.

139


Displays same data as above but with total of Ring Aromaticscores composition.

149


Displays same data as above but with total of Aromaticscomposition

157

Displays set of information about various biases for WABP,RI, viscosity, various cuts and various ratios and methylgroups.

165


Cat Blend WorksheetThis worksheet displays detailed data for all the fresh catalyst, ZSM-5, theblend used for make up, and the equilibrium catalyst. This sheet is updatedfrom the load file and from any of the last runs. You cannot enter any data onthis sheet. The sheet can be read in a matrix form with the columns asdifferent catalysts and the rows as the various catalyst properties displayed.

Each feed property variable is described in Column A under the headingDescription. The Columns following this column display Titles, Specs, andUnits for Catalyst1. Usually all the fresh catalysts have the samecorresponding titles, the same specs, and the same units as Catalyst1. Themodel can blend up to five fresh catalysts, and ZSM-5 can be blended for thefinal catalyst blend used in the make-up catalyst.

The blended catalyst properties used in the make-up are given in Column K.The equilibrium catalyst properties are given in column L.

Catalyst Properties Description Row #

Index no. from CST factorssheet

Displays the index number corresponding to the catalystselected from CST sheet row #2

11

Input mix percent Displays the percentage of the particular catalyst includingZSM5 in the blended catalyst mixture

12

Normalized mix percent Displays the percentage of the particular catalyst excludingZSM5 in the blended catalyst mixture

13

Flowrate Displays the mass flow rate of the catalyst 14

MAT activity Displays the MAT activity for the catalyst 15

Zeolite surface area Displays the Zeolite Surface area 16

Matrix surface area Displays the Matrix Surface area 17

Total surface area Displays the total surface area of the catalyst 18

Metals contents Displays the absolute content of Ni, Va, Fe, Cu and Napresent in the catalyst

19

Composition shifts Displays the composition shifts in zeolites, alumina and rareearth metals to affect the catalyst factors

25

Displays catalyst factors for adjustments in yield, selectivity,deactivation etc.

35

Simulation WorksheetThis sheet is separated into five sections:

KEY OPERATING DATA

FEED DATA

YIELDS

CATALYST DATA

PRODUCT PROPERTIES

Typically, you enter data into the cells highlighted in blue for each section.However, these highlighted cells are dependent upon the options selected.Thus, if you modify options prior to running a simulation case, you can update


the cell colors with by clicking AspenPlusCatCracker | Development Tools| Update Simulation Sheet Color.

Key Operating Data

The KEY OPERATING DATA section contains key values that may be eitherinput to or output from the model. You can input changes to:

riser outlet temperature

flue gas composition

coil duties

cooler duties

flue gas quench rate

O2 injection rate

If the model is being run for complete combustion, enter the O2 content ofthe flue gas.

If the model is being run in partial combustion mode, enter the CO content ofthe flue gas, CO2/CO ratio in the flue gas, or regen bed temperature,depending on the regenerator control option selected on the Options sheet.

Simulation Sheet – Key Operating Data

Feed Data

The FEED DATA section contains inputs for up to 10 feeds. You can specifyrecycle streams of heavy naphtha, LCO, HCO, and bottoms separately. Youcan specify separate flow rates for each feed. However, only the preheattemperature for the combined feed may be specified. For each feed you canselect the feed type using the combo-box associated with that feed. Once thefeed type has been selected, you should input all of the analytical data for


that feed including API gravity, sulfur content, basic nitrogen content,Conradson carbon content, refractive index, viscosity, and distillation. You canchoose to have the refractive index estimated rather than using a measuredvalue by selecting the Estimate option in the refractive index combo-box. Youcan choose to enter viscosity in either cSt or SUS, or have this valueestimated also by choosing the appropriate option in the viscosity combo-box for each feed.

In addition to entering the 9-point distillation for each feed, you must specifythe distillation type (D86, D1160, D2887, or TBP) by selecting the appropriateitem from the distillation combo-box. Finally, enter the feed metals data foreach feed.

Simulation Sheet – Feed Data


Yields

The YIELDS section contains only model output and thus you do not enterany information in this section. Yields are reported on a Standard basis andon a Fractionated basis. The Standard yields represent the yields of eachcomponent or pseudo-component as if the fractionation were perfect. Forexample, the C5+ Gasoline yield in the Standard Grouped Yieldssubsection would contain all of the C5’s and all components that boil below430ºF. It would contain no C4’s or lighter and no components that boil above430ºF. The Gasoline yield in the Fractionated Grouped Yields subsectionwould include a small amount of C4’s (the amount necessary to match theC4’s specification or the RVP specification) and also some amount of heaviermaterial. Similarly, some C5’s would appear in the C4 stream and some of thematerial that boils below 430ºF would appear in the LCO stream.

Simulation Sheet - Yields

Catalyst Data

The CATALYST DATA section lets you change catalyst types and catalystproperties, by selecting them from the appropriate combo-boxes, to see howthey will affect yields and conversions. You can select up to five catalysts andone ZSM-5. For each catalyst, there is a base value for zeolite content,


alumina content, and rare earth content. If the actual values differ from thesebase values, you can enter these values in the appropriate cells. You can alsoenter the catalyst make-up rate or the fresh MAT activity depending upon theoption selected on the Options sheet.

Simulation Sheet – Catalyst Data

Product Rates and Properties

The PRODUCT RATES AND PROPERTIES section is used primarily forreporting, but you can specify the cut points used for the fractionation of thegasoline and LCO product streams. Standard cut product properties are alsoreported.


Simulation Sheet – Product Rates and Properties

LP Vectors WorksheetThe LP Vectors worksheet provides the results for LP vector runs. The mainpurpose of generating LP vectors is to provide shift factors for LP planningand scheduling tools, such as Aspen PIMS. Generating LP vectors is a two-step process.

1 Specify the independent and dependent variables.

2 Run the LP vector generation command.

The instructions for running the LP vectors are at the top of the worksheet.Select the independent and dependent variables from the pick list when youset up the model for LP vector runs. The independent variables are reportedin columns and dependent variables are reported in rows. You can select asmany variables as are available in the pick list. For each variable, attributessuch as name, units of measurement and base values are displayed, and thecells are highlighted by dark blue color.

Before setting up the LP vector run, some default variables in the Jacobianmatrix are selected and the values of derivatives are displayed. After youselect the variables for an LP vector run, the cells become empty. After therun, the values of the derivatives are displayed in the cells with blue color.

Setting up LP Vectors

Generating LP vectors is a two-step process:

1 Specify the independent and dependent variables.


2 Run the LP vector generation command.

To set up the LP vectors of interest:

1 Select the AspenPlusCatCracker | Setup Cases | Vectors menucommand.

Setup Cases | Vectors Command

The LP Vectors spreadsheet appears, along with a dialog box from which youcan specify the independent and dependent variables.

Setup LP Vectors Dialog Box


2 In the top list box, select the independent variables. You can select any orall of the variables listed. Select the checkbox beside the variabledescription to select a variable. Clear the checkbox to deselect a variable.

3 In the lower list box select the dependent variables and functions in thesame way.

4 Once the independent and dependent variables have been selected, clickOK. The LP Vectors sheet will be cleared. Then the independent variableswill appear in Row 7 and the dependent variables will appear in Column C.If you click Cancel, the dialog box will close and no changes will be madeto the LP Vectors worksheet.

5 Save the worksheet to retain the changes made to the LP Vectors page.

PIMS Vectors WorkshetThe PIMS Vectors worksheet is set up similarly to the LP Vectors page, but isset up in such a way as to generate a generic PIMS Table.

PIMS Table WorksheetA standard PIMS table is generated using the data on PIMS Vectors page. Thispage will typically have been set up by AspenTech service personnel.

Generating a PIMS Table

To Generate A Simple Pims Table:

1 Input the data.

2 Run a simulation case with the appropriate specs:

Fresh Feed Gravity basis should be SG

Riser Temperature Control should be Riser Outlet Temp

Distillation for the feed should include &All.

3 Run a simulate case with the VABP option.

4 Generate PIMS vectors with the independent variables and the dependentvariables specified in the CatCracker PIMS table.

All yields are on a fractionated basis

H2 to Ethane from the detailed yields

C3 and higher from the grouped yields

C4s include C5 in LPG

C3 olefin calculated by dividing C3 olefin by total C3

C4 olefin are summed in the detailed yields and divided by the grouped C4+ C5

IC4 is divided by the C4+C5 total

Sum of C5s are divided by C4 + C5 total

Conversion is observed volume percent (E19 on Simulation page)


Generate sensitivity vectors

5 Make the appropriate transformations of the results to generate the PIMStable.

Multiply yields by –1

Calculate changes in C3= of C3 Mixture by chain rule.

Cases WorksheetThe Case Studies are a user-specified series of Simulation Cases. You canvary independent variable values between cases. Specifications cannot bevaried between cases.

The heading of the Cases worksheet provides the instructions to carry out thecase studies. The Cases worksheet is divided into three sections from top tobottom.

The first section contains the independent variables that you want to vary.

The second section shows the dependent variables to be reported. You canselect as many variables as are available in the pick list. For each variable,attributes like name, units of measurement, and base value of the variableare displayed and the cells are highlighted in a dark blue color.

The third section shows the LP vector run for each of the cases with the samedependent and independent variables.

For each case study run, the creep steps can be changed on Row 8 dependingon the change in the values of variable. By default, all the cases have a creepstep value of 10.

Row 111 shows a convergence flag for each case run. The value forconvergence is 1 if the run succeeds and 0 otherwise. You can run amaximum of 100 cases. Cases can be run from and to any case number.

The case study should not necessarily start from case numbered 1. Before thecase study is set up, the columns are filled with either the defaults selectionof variables or the previously run data. After the selection of the independentand dependent variables, the cells in light blue can be changed to enter thevalue of the variables for each case run in the independent variable section.After the case is run, all the cells of the dependent variables also arehighlighted with light blue color. If any data is left over from previous run,you must delete it manually.

Optimize WorksheetThe Optimization case varies a defined set of independent variables tomaximize (or minimize) a specified dependent variable, the ObjectiveFunction. Use the Optimize worksheet to set up the optimization variablesand any bounds that are necessary for solving optimization.

The sheet has two sections:

Independent or manipulated variables

Dependent or constraint variables


You select these variables from the pick list when you set up the optimizationproblem.

For independent variables, the attributes provided are:

Name

Units

Upper bound

Lower bound

Step bound

Initial value

Optimized value

Specification of the variable

For dependent variables the attributes provided are:

Name

Units

Upper bound

Lower bound

Initial value

Optimum value

After you have selected the independent and dependent variables, you canchange the bounds on the variables to fit your requirements.

After the optimization run, cells in red indicate that the bound for thatvariable was reached.

You cannot change the initial value column. You can only change cellshighlighted in light blue, such as upper, lower and step bounds forindependent and dependent variables.

Profit WorksheetsThere are three profit function sheets available to define the objectivefunction for the optimization run. At the top of each sheet are notes about thedefinitions of profit objective function. The sheet is divided into four sections:the first section is about the main variables or properties. The other threecontain the incremental properties for each of the main variables orproperties.

You can define only three incremental properties for each variable. You canselect up to a maximum of 50 variables for the profit function. For eachvariable selected, its name, units and, price units are displayed.

You must enter the price for the property selected under the column labeledPrice. Ensure that the price units for the properties are defined. For eachvariable, you can enter a user label for convenient reference.

Note: The price entered is positive for the products and negative for thecosts.


Do not leave the Price column blank. If there is no cost, enter zero. For theincremental property, enter Base value and Price.

Profit Report WorksheetsProfit report functions sheets provide the result of the optimization run. Eachof the profit functions has a corresponding profit report sheet. Each of theprofit report pages has three sections:

Initial Values

Results from Optimization

Results from Simulation

The list of variables from the corresponding profit function page is listed fromRow 15 down. The incremental property is in the same list but is indentedbelow the parent property. Each section has a Run Time and Status bar torecord the time when that section was last updated and what type of run itwas. The initial section of the worksheet is updated after a parameter run. Allthe cash flows are converted to a time basis of per day, so any variablehaving a different time basis on the Profit function sheet would be convertedto per day basis for reporting. All the cash flows for feed are reported in redand for products in blue text.

Results from Optimization is updated after the optimization problem run.Results from Simulation is updated after the simulation run. The overalllook of these sections is the same as the Initial Values section describedabove.

The change in the values of cash flows due to parameterization andoptimization runs is reported in the Changes section next to the Resultsfrom Optimization section. The change in the values of cash flows due toparameterization and simulation runs is reported in the Changes section nextto the Results from Simulation section. At the bottom of the sheet overallcash flows are reported for:

Feed cost

Product revenue

Total profit

Losses are reported as negative profits.

Hidden WorksheetsThere are several worksheets in the AspenPlusCatCracker workbook thatare by default hidden. These are not needed for general use of the workbook,but you can view them for information content.

To View These Worksheets:

On the Excel menu bar, select Format | Sheet | Unhide.

Some of these worksheets are password protected to prevent inadvertentchanges to their contents. Such changes can affect the functionality of theworkbook and cause a failure to occur in this functionality.Hidden Worksheets


No Worksheet Name Description

1 Param IO Structures the layout for the Param worksheet

2 Param Links Direct cell links to the model variables available in theworkbook for the Param worksheet

3 Param UserInput Contains a copy of your input for the Param worksheet

4 Analysis IO Structures the layout for the Analysis worksheet

5 Analysis Links Direct cell links to the model variables available in theworkbook for the Analysis worksheet

6 Feed Blends IO Structures the layout for the Feed Blends worksheet

7 Feed Blends Links Direct cell links to the model variables available in theworkbook for the Feed Blends worksheet

8 Cat Blend IO Structures the layout for the Cat Blend worksheet

9 Cat Blend Links Direct cell links to the model variables available in theworkbook for the Cat Blend worksheet

10 Simulation IO Structures the layout for the Simulation worksheet

11 Simulation Links Direct cell links to the model variables available in theworkbook for the Simulation worksheet

12 Simulation UserInput Contains a copy of your input for the Simulation worksheet

13 Feed Input Contains a library of feed fingerprints for different feed types

14 CST Factors Contains a library of catalyst factors for different catalysts

15 EB Scripts Contains scripts for execution of the calculation engine

16 ReceiveVars Contains and manages variables that are sent from thecalculation engine to the workbook through DCOM

17 SendVars Contains and manages variables that are sent to thecalculation engine from the workbook through DCOM

18 Registry Contains a collection of data and parameters for the AspenPlus CatCracker workbook

19 ComboRegistry Contains and manages data about the combo box options inthe Aspen Plus CatCracker workbook

20 Combo Table Contains and manages the combo box tables that describethe combo box options in the Aspen Plus CatCrackerworkbook

3 Specifying Data 50

3 Specifying Data

OverviewYou can enter data on many different worksheets such as Simulation,Param, etc. You can enter data either by:

Selecting variables from the pick list for LP vectors

Selecting values for Simulation and Parameter runs

Changing specs by selecting different options

You can only change the data contained in blue cells. You can select variousoptions for the run from the Options worksheet. However, you mustimmediately click the Update Spec Color button on the Aspen Plus CatCrackertoolbar to see the cells on the Param or Simulation sheets that can bechanged during that run. See Updating Spec Colors.

To set up a Parameter case, enter data only in the Param worksheet. Dataon any other sheets is not used.

For Simulation runs, enter data only in the Simulation worksheet. Data onany other sheets is not used.

For Case Studies, first select the independent and dependent variables fromthe pick list. Then change the values of the independent variables in thesections provided. You can also change the creep iterations for each step.

For LP vector runs, you select the independent and dependent variables.There is no data to be entered except selecting the correct variables.

For Optimization runs, first set up the independent (manipulated) variablesand dependent (constraint) variables, then set up the profit objectivefunction. You can enter the data for bounds of the variable on the Optimizeworksheet in the blue cells. You can enter the prices for the profit objectivefunction variables on the any of the Profit sheets, in the Price column. Youcan enter the price and base value for incremental properties in theIncremental Properties columns.


Setting Up Case StudiesIn addition to single cases, Aspen Plus CatCracker lets you run multiple casesat a time and retrieve the results into a single area that is easy to work with.This can be useful if you want to see how the model responds to changes inone or more variables. For example, it may be desirable to see how theproduct yields vary with changes in riser outlet temperature. To perform thistype of study, you would run multiple cases with different temperatures andhave the results reported. This can easily be accomplished by running a CaseStudy.

Before You StartBefore running a Case Study, first ensure the model has been initialized witha valid result from a Parameter case or a converged Simulation case. Withthis as a starting point, review and, if necessary, change the options in theOptions and Simulation worksheets. If you change any option, run asimulation to initialize all the variable specifications before setting up the casestudy. The options selected will determine which variables are available asindependent versus reported variables.

Any values entered on the Param or Simulation sheets will be ignored wheninvoking the case study.

Note: When a new Case Study is set up or run, the data that are currently inthe worksheet are not automatically deleted. To remove any unwanted data,you must select and delete the data. Each step of the case study will typicallyrequire about one to two minutes to solve and update the spreadsheet.

Specifying Varied and Reported VariablesThe next step is to specify which variables will be varied and which variableswill be reported.

1 Click AspenPlusCatCracker | Setup Cases | Case Study.

The Cases worksheet appears, along with a dialog box from which you canchoose the independent variables that will be varied and the dependentvariables that will be reported.

2 In the upper list-box, select the variables that will be varied. You mayselect as many variables as you want from the list by selecting thecheckboxes beside the variable descriptions. A variable can be also bedeselected by clearing its checkbox.

3 In the lower list-box, select (in the same manner) the variables that willbe reported on the Cases sheet.

4 Once you have selected all the variables, click OK to set up theworksheet.

The independent variable names will appear on the Cases worksheet inColumn A starting with Row 9. The report variables will appear on the Casesworksheet in Column A starting with Row 111. Column B is reserved foroptional user labels.


Clicking Cancel will close the dialog box without making changes to theCases worksheet.

Setup Case Study Dialog Box

Once the Cases worksheet is set up, enter values for the independentvariables for each case to be run.


Case Study Worksheet

The model is now ready to execute a Case Study.

Setting up OptimizationsOptimization maximizes or minimizes a user-specified objective function bymanipulating independent variables (feed stream, block input, or other inputvariables.) The objective function is an equation that is used by theoptimization engine to determine the manner in which to manipulate thedegrees of freedom (independent variable) in a problem. You may have morethan one objective function in a problem, but only one is used by the engineduring the solution. Objective functions for Optimize cases in the CatCrackermodel are normally economic in nature (for example, they might maximizeoperating profit or minimize operating cost) Aspen Plus V7.1 supports threedifferent kinds of objective functions:

Linear

Sum of Squares

Symbolic

Aspen Plus CatCracker uses objective functions that are in symbolic form.

Independent VariablesIndependent variables are variables whose values can be changedindependently, for example, the feed rate in the CatCracker unit. Theoptimizer can vary the values of independent variables to push the values ofthe objective function in the defined direction (maximize profit or minimizecost) until some bounds are reached. Each independent variable accounts for


a degree of freedom. The number of degrees of freedom is equal to thenumber of independent variables in an optimization run if no independentvariable is at its bound. You can impose upper and lower bounds onindependent variables to prevent the final solution from deviating too faraway from the starting point. You can also impose step bounds onindependent variables.

BoundsAspen Plus CatCracker lets you bound every variable in the problem as shownbelow:

Xl < X < Xu

The step bound of an independent variable defines how much the value of thevariable can be changed in a single optimization run. The step bound is usedalong with the initial value, lower bound, and upper bound to compute theactual bounds to be used in the run:

Xl = max(X - |Xstep|, Xlower)

Xu = min(X + |Xstep|, Xupper)

You should define upper and lower bounds for all independent variables. Youcan also define the step bounds for independent variables.

Most of the dependent variables in the CatCracker model have very widebounds, such as –1.E20 for lower bound and 1.E20 for upper bound.However, some dependent variables have physical meaning. You should setup appropriate bounds for them to prevent the solution from getting intoinfeasible operating conditions. For example, there is a metallurgic limit onregenerator cyclone temperature. Hence, an upper bound should be set forthis variable. Only those constrained dependent variables must be definedwhen setting up an optimization case in CatCracker model.

In general, it is not recommended to heavily bind an optimization problem forreasons that are both practical and algorithmic. Bounds on independentvariables are recommended in order to avoid unbounded problems. All otherbounds should be used only if they are absolutely necessary. The optimizationengine for CatCracker model is the DMO solver. For more information aboutthe DMO solver, refer to DMO Solver Background.

Setting up Objective Functions

To set up an objective function:

1 Select the AspenPlusCatCracker | Setup Cases | Profit x menucommand where x is the number 1, 2, or 3.


Setup Cases | Profit 1 Command

A dialog box appears, listing the variables available to be used in the profitcalculation.

Add Variables to Objective Function Dialog Box

2 Select the principal variables to be used in the profit calculation, then clickOK.

3 The variables appear on the Profit sheet you selected in step 1.

To specify an incremental variable to adjust the principal variable value,select the same AspenPlusCatCracker | Setup Cases | Profit x menucommand.

4 In the dialog box, select any single principal variable, and then clickSetup Incrementals.


Setup Incrementals Button

A second list of incremental variables appears.

5 Select up to three incremental properties; then click OK.

Add Properties to the Selected Product Dialog Box

The incremental variables appear on the selected Profit sheet.

6 After selecting all the principal properties and incremental properties thatcomprise the objective function, enter a value for each variable. For eachprincipal property, the variable name, the units of the variable, and the


units for the value will appear. Enter the appropriate value in the Valuecolumn.

Take care to properly match units. For example, if a flow rate is inthousands of barrels per day, the value entered must be in dollars perthousand barrels. If you select a unitless variable for the objectivefunction, such as conversion, the value will also be unitless.

7 Enter values for each incremental property. The Base is the value atwhich the incremental property has no effect on the principal property. Allof the incremental properties are either unitless or have a fixed unit typesuch as vol% aromatics.

Setting up Optimization Variables andBoundsIn addition to setting up the objective functions used to optimize, you mustalso set up the optimization variables and any bounds that are necessary. Forinstance, you can choose to optimize Profit 1 by varying the feed rate of feed1. However, the unit may have constraints to how much wet gas can beprocessed, so the wet gas volume would be selected as a dependentconstraint variable.

The independent variables have the specification of Const if optimization hasnever been set up before. However, not all variables with Const specificationin the model are included in independent variable list. Only those variablesthat can be manipulated in the FCCU will appear. Those variables areidentified by Opt in Column R (titled Opt) on the SendVars sheet. Thedefault list of independent variables should be able to handle mostoptimization runs. If you want to use other variables as independentvariables, you should manually set up those variables on the SendVarssheet.

After a variable is selected on the independent list, the corresponding cell inColumn V (titled Opt Select) on the SendVars sheet will be set to YES forthis variable. When solving the optimization case, the variable will be sent tothe Command Line with the Optim specification. However, the SendVars stillkeeps the original Const specification for this variable.

The dependent constraint variables have the specification of Meas or Calc.However, not all variables with Meas and Calc specification appear in the list.Only those variables that represent operation constraints in the FCCU willappear. Those variables are identified by Opt in Column R (titled Opt) on theReceiveVars page. The default list of dependent variables represents allconstraints commonly met in FCCU operation. If you have a particularconstraint that is not represented by any variable on the list, you canmanually set up those variables on the ReceiveVars page. After a variable isselected on the dependent list, the corresponding cell in Column Y (titled OptSelect) on the ReceiveVars page will be set to YES for this variable.

Aspen Plus CatCracker displays only Const variables in the pick list forindependent variables and only Calc and Meas variables in the pick list fordependent variables. This ensures that whatever set you choose will lead to awell-posed problem.


To set up optimization variables and bounds:

1 Click AspenPlusCatCracker | Setup Cases | Optimization as shownbelow.

Setup Cases | Optimization Command

This will activate the Optimize worksheet and open a dialog box from whichyou can select the desired independent variables (extra degrees of freedom)and dependent constraint variables.

Setup Optimization Case Dialog Box

2 To select a variable, select the checkbox to the left of the variable name.Clearing the checkbox of a selected variable will deselect the variable.


3 When the independent variables and the dependent constraint variableshave been selected, click OK to complete the setup. The selectedvariables and their current values will then appear on the Optimizespreadsheet. Clicking the Cancel button will close the dialog box withoutmaking any changes to the optimization problem. After setting up theoptimization, a message box will appear to remind you to Make sure theprofit function is defined before running the optimize case.

4 After selecting the desired independent variables and dependentconstraint variables, input lower and upper bounds in Columns C and F bythe appropriate variables. You can also enter step bounds for theindependent variables in Column G. The optimization is now ready tosolve.

Variables on Optimize Sheet

5 Save the worksheet in order to save the changes made to the Optimizepages.

The optimization problem is now ready to solve.

Setting Up LP VectorCalculationsIn addition to letting you determine yields, temperatures, and productproperties, Aspen Plus CatCracker can generate LP vectors.

4 Running Cases 60

4 Running Cases

Case TypesYou can run five types of cases in the Aspen Plus CatCracker model:

Simulation Case

Parameterization Case

Optimization Case

Case Studies

LP Vector Generation Case

The Simulation Case is a simple what-if study. What changes to dependentvariables result from a specified set of independent variables?

The Parameterization Case fits the model’s kinetic rate constants and baseoperating data to match an observed process operation, feed properties, andproduct yields. This case is often referred to generically as a calibrationcase.

The Optimization Case varies a defined set of independent variables tomaximize (or minimize) a specified dependent variable, the ObjectiveFunction.

The Case Studies are a user-specified series of Simulation Cases. You canvary independent variable values between cases. Specifications can not bevaried between cases.

The LP Vector Generation Case generates a set of derivatives betweenspecified dependent and independent variables that can then be used in theformulation of LP vectors.

You can run all case types from either the CatCracker toolbar or theAspenPlusCatCracker menu.

Running Cases from the CatCracker ToolbarFrom the CatCracker toolbar, shown below, you can select the type of caseto be run from the Case Type list (circled).

Click the Run Case button beside it to begin execution of the case.

4 Running Cases 61

Case Type List-Box

Running Cases from the CatCracker MenuYou can also run cases using selections from the AspenPlusCatCrackermenu as shown below.

Click AspenPlusCatCracker | Run Case | type of case to beginexecution of the case.

Run Cases | Simulation Case Command

Solver SettingsA script file embedded in the EB Scripts spreadsheet (hidden by default)controls the execution of each case. For Aspen Plus CatCracker, the followingsolver settings are recommended for the simulation case type.

solver settings maxiter = 50

solver settings miniter = 0

solver settings creepflag = 1

solver settings creepiter = 10

solver settings creepsize = 0.1

solver settings searchmode = 3

solver settings factorspeed = 1

solver settings pivotsearch = 10

solver settings rescvg = 1.E–10

4 Running Cases 62

solver settings objcvg = 1.E–6

solver settings HESSIANUPDATES = 0

For many Simulation cases, the creepiter variable can be reduced to 5 oreven lower, to converge the cases more quickly. However, the default of 10will allow the model to converge more robustly.

Key variables of interest to CatCracker users are:

Variable Description

Maxiter Maximum number of iterations allowed for solution

Miniter Minimum number of iterations

Creepflag Creep control flag: 0=off, 1=on

Creepiter Number of creep iterations

Creepsize Magnitude of steps as a fraction of the step size thatwould be taken if the Creepflag were set to 0 (off)

Rescvg Residual convergence tolerance

Running a ParameterizationCaseParameterization means calibrating (or tuning) the model to match plantoperating data. A simple example would involve one measurement (atemperature) and one parameter (a heat exchanger UA). The temperaturewould be entered into the model and the UA would be calculated. Thereafter,when running simulation cases, the UA would be constant and thetemperature would be calculated.

In Aspen Plus CatCracker, parameterization involves entering plant operatingdata, such as flows, temperatures, pressures, and properties, while the modelautomatically calculates the kinetic rate constants and other parametersrequired to match them exactly.

Typically, AspenTech would have executed a project which included analyzingplant test run data and tuning Aspen Plus CatCracker to match the operatingunit performance. The result of this project is the delivery of a data filecontaining a parameterized Aspen Plus CatCracker case and a comprehensivetraining course. You should initialize Aspen Plus CatCracker using this datafile. For information on loading a data file, see Loading Data Files on page 2-4.

You will need to parameterize Aspen Plus CatCracker again to better matchplant operations some time after the initial data file is delivered byAspenTech. Many mechanical revamps affecting risers, feed nozzles, andregenerator air grid make it necessary to re-parameterize the model. Evenwhen there has been no revamp, routine mechanical wear can affect thecontacting efficiency in the riser and regenerator, and thus change the heatbalance and yield selectivity from the values at initial delivery.

4 Running Cases 63

Aspen Plus CatCracker OptionsThe first step to running a parameterization is to select all the appropriateoptions. Since the model was set up once already by AspenTech, the optionsare probably already appropriate. However, it is possible that a change inoperating philosophy will require changing one or more of the options.

The options are described in the following table:

Option Title Option Description

Feed RateBasis

Input volume rates Feed flow rates are entered on a volume flow basis

Input mass rates Feed flow rates are entered on a mass flow basis

Fresh FeedGravity Basis

Input API Feed density is entered as API gravity

Input SG Feed density is entered as specific gravity (60/60)

K const for LP Used for LP vectors only and should not be used forParameter cases. K factor and distillation are constant whilegravity is calculated.

Ca const for LP Used for LP vectors only and should not be used forParameter cases. Feed carbon atom aromatic wt% anddistillation are constant while gravity is calculated.

H const for LP Used for LP vectors only and should not be used forParameter cases. Feed hydrogen wt% and distillation areconstant while gravity is calculated.

ProductGravity Basis

Input API For Parameter case, product density is entered as API gravity

Input SG For Parameter case, product density is entered as specificgravity (60/60)

Light EndsProduct Basis

Input volume rates For Parameter case, product flow rates are entered on avolume flow basis

Input mass rates For Parameter case, product flow rates are entered on a massflow basis

Heavy ProductRate Basis

Input volume rates For Parameter case, product flow rates are entered on avolume flow basis

Input mass rates For Parameter case, product flow rates are entered on a massflow basis

FractionationControl

Input vol, HN andHCO rate const.

Product flow rates are entered on a volume flow basis. Heavynaphtha and HCO flow rates are constant.

Input mass, HN andHCO rate const.

Product flow rates are entered on a mass flow basis. Heavynaphtha and HCO flow rates are constant.

Input vol, all useTBP90

Product flow rates are entered on a volume flow basis. Heavynaphtha and HCO flow rates will vary based on the enteredTBP 90% targets.

Input mass, all useTBP90

Product flow rates are entered on a mass flow basis. Heavynaphtha and HCO flow rates will vary based on the enteredTBP 90% targets.

Input vol, HN/LCO/HCO rates const

Product flow rates are entered on a volume flow basis. Heavynaphtha, LCO, and HCO flow rates are constant.

Input mass,HN/LCO/HCO rates const

Product flow rates are entered on a mass flow basis. Heavynaphtha, LCO, and HCO flow rates are constant.

4 Running Cases 64


Fresh FeedConradsonCarbon Basis

Input Concarb Fresh feed Conradson carbon content is entered. Ramsbottomcarbon will be calculated based on the API conversionmethod.

Input Ramsbottom Fresh feed Ramsbottom carbon content is entered. Conradsoncarbon will be calculated based on the API conversionmethod.

Fresh FeedBasic or TotalNitrogen

Input Total N Fresh feed total nitrogen is entered. The basic nitrogen will becalculated based on the factor entered for each feed (defaultvalue is basic = 1/3 * total)

Input Basic N Fresh feed basic nitrogen is entered. The total nitrogen will becalculated based on the factor entered for each feed (defaultvalue is basic = 1/3 * total)

RegeneratorControl:CompleteCombustionoptionselected

Flue Gas O2 constfloat air vol

Regenerator flue gas O2 content will be the target, theinjected O2 rate is constant, and the air rate will becalculated. The air and injected O2 rates are entered on avolume basis for the Parameter case.

Flue Gas O2 constfloat air mass

Regenerator flue gas O2 content will be the target, theinjected O2 rate is constant, and the air rate will becalculated. The air and injected O2 rates are entered on amass basis for the Parameter case.

Flue Gas O2 constfloat O2 inj vol

Regenerator flue gas O2 content will be the target, the airrate is constant, and the injected O2 rate will be calculated.The air and injected O2 rates are entered on a volume basisfor the Parameter case.

Flue Gas O2 constfloat O2 inj mass

Regenerator flue gas O2 content will be the target, the airrate is constant, and the injected O2 rate will be calculated.The air and injected O2 rates are entered on a mass basis forthe Parameter case.

Air and O2 inj constfloat Flue Gas O2

Regenerator air rate and injected O2 rate are constant whilethe flue gas O2 is calculated. The air and injected O2 ratesare entered on a volume basis for the Parameter case.

Bed T & FG O2 constfloat Cat Cooler & airvol

Regenerator flue gas O2 content and bed temperature areboth entered targets, the injected O2 rate is constant, and theair rate and catalyst cooler duty will be calculated. The air andinjected O2 rates are entered on a volume basis for theParameter case.

Bed T & FG O2 constfloat Cat Cooler & airmass

Regenerator flue gas O2 content and bed temperature areboth entered targets, the injected O2 rate is constant, and theair rate and catalyst cooler duty will be calculated. The air andinjected O2 rates are entered on a mass basis for theParameter case.

RegeneratorControl:PartialCombustionoptionselected

Bed T const float airvol

Regenerator bed temperature will be the target, the injectedO2 rate is constant, and the air rate will be calculated. The airand injected O2 rates are entered on a volume basis for theParameter case.

Bed T const float airmass

Regenerator bed temperature will be the target, the injectedO2 rate is constant, and the air rate will be calculated. The airand injected O2 rates are entered on a mass basis for theParameter case.

4 Running Cases 65


Bed T const float O2inj vol

Regenerator bed temperature will be the target, the air rate isconstant, and the injected O2 rate will be calculated. The airand injected O2 rates are entered on a volume basis for theParameter case.

CO2/CO const floatair vol

Regenerator CO2/CO ratio will be the target, the injected O2rate is constant, and the air rate will be calculated. The airand injected O2 rates are entered on a volume basis for theParameter case.

CO2/CO const floatair mass

Regenerator CO2/CO ratio will be the target, the injected O2rate is constant, and the air rate will be calculated. The airand injected O2 rates are entered on a mass basis for theParameter case.

CO2/CO const floatO2 inj vol

Regenerator CO2/CO ratio will be the target, the air rate isconstant, and the injected O2 rate will be calculated. The airand injected O2 rates are entered on a volume basis for theParameter case.

CO const float airvol

Regenerator CO vol% dry basis will be the target, the injectedO2 rate is constant, and the air rate will be calculated. The airand injected O2 rates are entered on a volume basis for theParameter case.

CO const float airmass

Regenerator CO vol% dry basis will be the target, the injectedO2 rate is constant, and the air rate will be calculated. The airand injected O2 rates are entered on a mass basis for theParameter case.

CO const float O2 injvol

Regenerator CO vol% dry basis will be the target, the air rateis constant, and the injected O2 rate will be calculated. Theair and injected O2 rates are entered on a volume basis forthe Parameter case.

CRC const float airvol

Carbon on regenerated catalyst wt% will be the target, theinjected O2 rate is constant, and the air rate will becalculated. The air and injected O2 rates are entered on avolume basis for the Parameter case.

CRC const float airmass

Carbon on regenerated catalyst wt% will be the target, theinjected O2 rate is constant, and the air rate will becalculated. The air and injected O2 rates are entered on amass basis for the Parameter case.

CRC const float O2inj vol

Carbon on regenerated catalyst wt% will be the target, the airrate is constant, and the injected O2 rate will be calculated.The air and injected O2 rates are entered on a volume basisfor the Parameter case.

PressureBalanceControl

All pressures const Wet gas flash, reactor vessel, and regenerator vesselpressures all constant.

WG to RX DP const Wet gas flash to reactor vessel delta pressure constant, andregenerator vessel pressure constant.

WG-RX and RX-RGNDP const

Wet gas flash to reactor vessel delta pressure constant, andreactor vessel to regenerator vessel delta constant.

Light NaphthaFront-EndControl

Input RVP The light naphtha (debutanizer bottoms) front end iscontrolled by an entered RVP target.

Input C4 The light naphtha (debutanizer bottoms) front end iscontrolled by a C4 vol% target.

4 Running Cases 66


CatalystActivityControl

Input ECAT MAT Equilibrium catalyst MAT activity is entered as the target,fresh catalyst make-up rate is calculated.

Input make-up rate Fresh catalyst make-up rate is constant, and the equilibriumcatalyst MAT activity is calculated.

RiserTemperatureControl

Reactor PlenumTemp

Reactor Plenum Temperature is Constant, Riser Temp isCalculated, Regen Cat SV % open and Spent Cat SV % openare measurements.

Riser Outlet Temp Riser Temp is Constant, Reactor Plenum Temperature isCalculated, Regen Cat SV % open and Spent Cat SV % openare measurements.

Regen Cat SV % &Measured PlenumTemp

Regen Cat SV % open is Constant, Riser Temp is Calculated,Reactor Plenum Temp and Spent Cat SV % open aremeasurements.

Regen Cat SV % &Measured PlenumTemp

Regen Cat SV % open is Constant, Reactor Plenum Temp isCalculated, Riser Temp and Spent Cat SV % open aremeasurements.

Spent Cat SV % &Measured PlenumTemp

Spent Cat SV % open is Constant, Riser Temp is Calculated,Reactor Plenum Temp and Regen Cat SV % open aremeasurements.

Spent Cat SV % &Measured PlenumTemp

Spent Cat SV % open is Constant, Reactor Plenum Temp isCalculated, Riser Temp and Regen Cat SV % open aremeasurements.

Select the appropriate options in the Options worksheet.

Entering Data for Parameter Cases1 In the Options worksheet, select the appropriate options.

2 Change the blue highlighting of the data entry cells on the Param andSimulate worksheets by clicking the Update Spec Color button on theCatCracker toolbar. See Updating Spec Colors.

3 The next step is to enter all of the plant data highlighted in blue on theParam sheet. The data is organized into the following groups:

Key Operating Data

Feed Properties

Preheat Temperature Control

Product Data for Reactor Parameterization

Product Data for Fractionation Parameterization

Catalyst Data

Mechanical Data

Tuning Data and Factors

For more information about these sections, see Param Worksheet.

4 In addition to entering plant data, you must select some combo boxoptions. After selecting any of these options, click the Update Spec Colorbutton. See Updating Spec Colors.

The combo-boxes of most interest are described below:

4 Running Cases 67

5 Feed Type: Feed types for feeds 1 through 10 must be selected. Choosethe feed type that most closely matches the actual feed being processedin the CatCracker.

6 Distillation Type: VABP D1160 should not be selected for parametercases. Selecting the TYPE & All options is not as robust as selecting theTYPE options. If the parameter case does not lead to a solution, tryselecting just the TYPE options for all feeds and products.

7 Feed Metals Option: The Enter feed metals option means thatreasonable feed metals analyses are available for all feeds, or that you willenter zero for all feeds and ignore feed metals effects. Calc feed X metalsmeans that any error in metals balance will be lumped into that one feedX.

Running the Parameter Case8 Next, run the parameter case from the CatCracker toolbar or the

AspenPlusCatCracker menu.

a. Ensure that Parameter appearsin box. If not, click small arrow toopen menu, and select Parameter

b. Click the start button to run the case.

Running a Parameter Case

Typical execution time is between one and three minutes depending on thenumber of creep steps and how close to a solution the model starts.

9 Finally, review the calculated results on the Analysis, Feed Blends, andCat Blend worksheets. A few areas of interest on these sheets are thematerial balance, sulfur balance, heat balance, detailed individual andblended feed compositions, and individual catalyst properties. Once thesedata have been reviewed and are satisfactory, the parameter case iscomplete.

Several sheets are refreshed to reflect the values that currently reside in themodel after a Parameter run is successfully solved:

Param sheet

Analysis sheet

Feed Blend sheet

4 Running Cases 68

Catalyst Blend sheet

Simulation sheet

The Analysis sheet should be thoroughly reviewed after running a Paramcase. Investigate any inconsistent or unexpected results such as negativeyields before conducting further studies with the current data.

Once you have run and successfully solved the Parameter case, and carefullyreviewed the results on the Analysis sheet, save the data. See Saving andLoading Data Files. Saving the data lets you load this data at any time so thatthe starting point for subsequent solutions will be a valid parameterization.

Running a Simulation CaseOnce the model has been parameterized and satisfactorily tuned to matchplant responses, you can use the model to predict how changes in feed rates,feed properties, and operational conditions affect the yields and productproperties. Typically, AspenTech will have executed a project that includedanalyzing plant test run data and tuning Aspen Plus CatCracker to match theoperating unit performance. The result of this project is delivery of a data filecontaining a parameterized Aspen Plus CatCracker case and a comprehensivetraining course. You should initialize Aspen Plus CatCracker using this data filebefore running a Simulation case. See Loading Data Files.

1 Confirm the option selections made in the Parameter case. See the sectionAspen Plus CatCracker Options. Note that some of these options are onlyapplicable to Simulation cases.

2 Enter the new operating conditions, feed properties, or other targets ofinterest on the Simulation worksheet. Note that any values entered onthe Param worksheet will be ignored for a Simulation case. For moreinformation about the data on this sheet, see Simulation Worksheet.

3 Set combo-box options available on the Simulation sheet has See theEntering Data for Parameter Cases section to review information aboutthese options. The VABP D1160 option is now available. It should be usedonly after running a Simulation case with the D1160 option or with one ofthe TYPE & All options selected. Only then will the VABP D1160 optionyield valid results.

After changing any option or combo-box on the Options sheet or theSimulation sheet, click the Update Spec Color button on the Aspen PlusCatCracker toolbar to highlight the required data entry cells. SeeUpdating Spec Colors.

4 Next, run the Simulation case from the AspenPlusCatCracker toolbar orthe AspenPlusCatCracker menu. See the sections Running Cases fromthe CatCracker Toolbar and Running Cases from the CatCracker Menu.Typical execution time is between one and three minutes depending onthe number of creep steps and how close to a solution the model starts.

5 Finally, review the calculated results on the Analysis, Feed Blends, andCat Blend worksheets. A few areas of interest include sulfur balance, heatbalance, detailed individual and blended feed compositions, and individual

4 Running Cases 69

catalyst properties. Once you have reviewed this data and find itsatisfactory, the Simulate case is complete.

Note: Once the simulation case has been run, save this data using the SaveCase Data command. This will let you load this data at any time to use as avalid starting point for subsequent cases. See Saving and Loading Case DataFiles.

Running Multiple CasesIn addition to single cases, Aspen Plus CatCracker lets you run multiple casesat one time and retrieve the results into a single area that is easy to workwith. This can be useful if you want to see how the model responds tochanges in one or more variables. For instance, it might be desirable to seehow the product yields vary with changes in riser outlet temperature.

To perform this type of study, you would run multiple cases with differenttemperatures and have the results reported. You can do this by running theCase Study option.

Before you run a Case Study, you must set up the data for the Case Study.See Setting up Case Studies.

Running the Case Study1 On the Aspen Plus CatCracker toolbar, select the Case Study option;

then click the run button.-or-Select the AspenPlusCatCracker | Run Cases | Case Study menucommand to run the case study.

The Select Case Study Range dialog box appears

2 Enter the first and last cases to run, then click OK.

4 Running Cases 70

3 If you do NOT want to calculate LP Vectors, clear the Calculate LPVectors? option.

The Command Line window appears and the Case Study starts with the firstspecified case.

After each case is solved, the Command Line window closes while the data isloaded into the spreadsheet. The Command Line window reappears as eachsubsequent case starts. While the Command Line window is present, you canclick Abort to stop the case study. This stops the current run and subsequentcases that were specified. For example, if you specified a run for cases 1through 8 and you click Abort while case number 3 is being solved, themodel will quit solving case 3. In addition, cases 4 through 8 will not besolved.

For Case Studies, none of the data on other worksheets is updated. After theindependent variable data have been sent, the cells are highlighted in blue.Similarly, after the reported variables have been retrieved, those cells arehighlighted in blue.

LP Vectors OptionIn addition to reporting values for all of the specified report variables, a set ofLP vectors can optionally be generated for each case. These LP vectors willcorrespond to the LP vectors that have been set up on the LP Vectorworksheet. These will be reported in the LP vector section of the case studypage starting with row 1005. Column A lists the dependent variables andColumn B lists the independent variables. The values that are returned for acase study will be highlighted in blue.

Running an Optimization CaseBefore you run an optimization, you must set up the objective function andthe variables and bounds for the optimization. See Setting up Optimizations.

Solving the Optimization1 From the AspenPlusCatCracker toolbar, select the Optimize option; then

click the run button.-or-From the AspenPlusCatCracker menu, click Run Cases |Optimization.

The Select Objective Function dialog box appears.

2 Select an objective function. You select only one active objective function.

3 Select the direction of the optimization by selecting Max (for maximizing)or Min (for minimizing). If the objective function is set up as a profitfunction, select Max. If the objective function is set up as a cost function,select Min.

4 Select the profit reports to update. Normally only the active objectivefunction is selected.

4 Running Cases 71

Select Objective Function Dialog Box

5 Click OK to complete the setup and send the data from the Optimizationspreadsheet to the model. Clicking Cancel will close the dialog box andreturn to the Optimize worksheet.

After you select an objective function, the Command Line window appears.

Solving an Optimization Case

4 Running Cases 72

Changing the Behavior of the DMO SolverTo change the behavior of the DMO solver, click one of the buttons at thebottom of the command window. Your selection will take effect at the start ofthe next DMO iteration.

Click this button To

Abort Force the model to quit solving.

No Creep Take the DMO solver out of creep mode. Use this to expeditesolving when the current run is close to the final solution, inwhich case both the Residual Convergence Function and theObjective Convergence Function are small and close toconvergence criteria. Refer to Chapter 7 for more details on DMOsolver.

Close Residuals Cause the model to close the residuals without minimizing theobjective function convergence. The Close Residuals button isuseful in cases where the objective function very nearly reaches amaximum value but the convergence of the objective does notclose.

There is another button, Close, at the very bottom of the dialog box. Thisbutton is disabled during the optimization run. It is only active when no run isbeing executed. Clicking the Close button will close the dialog box and returnthe Excel interface.

After the model solves the optimization, the solution values are retrieved intothe Optimization page and the spreadsheet is updated. The correspondingreport page, Optimize page, and Simulation page are updated to thecurrent values in the model, but the Param page is not updated. On theOptimize page, the values after the optimized values are placed into ColumnE. If any upper or lower bound is reached, that value will be highlighted inred. A typical optimization will take 3 to 5 minutes, but this could varydepending on how difficult it is to reach a solution.

LP Vector GenerationIn addition to letting you determine yields, temperatures, and productproperties, Aspen Plus CatCracker can generate LP vectors. Generating LPvectors is a two-step process. You must first specify the independent anddependent variables, then run the LP vector generation command. Forinformation on setting up the variables see Setting up LP Vector Calculations.

Running LP Vector Generation On the AspenPlusCatCracker toolbar, select LP Vectors; then click the

Run Case button.-or-Select the AspenPlusCatCracker| Run Cases | Generate Vectorsmenu command to generate LP Vectors

4 Running Cases 73

The model will calculate all elements in the Jacobian (first order derivativematrix) for the model equations, generate the desired vectors, and place theresults in the LP Vectors worksheet. The command line window will appearfor a short time while the Jacobian is being evaluated and while the LPvectors are being calculated, but you cannot issue any commands at thistime. Typical execution time is about 20 seconds, although it can be more orless depending on the number of many vectors being calculated.

LP Vectors Worksheet

5 Advanced Topics 74

5 Advanced Topics

Parameter Case AnalysisThis section presents useful tips, tricks, and techniques to verify the quality ofthe Parameter case. The accuracy of Aspen Plus CatCracker model predictionsis highly dependent upon the validity and quality of the test run data usedand the application of appropriate settings in the CatCracker model data.

The focus will be on a number of input/output sheets employed to set up andrun a Parameter case including Options, Param, Analysis, Feed Blends,and Cat Blend. The Options sheet discussion is for setting up a parametercase. After the parameter case has been run, the model calculation resultscan be used to determine the quality of the data and the validity of theoptions selected. The analysis discussion will be based on reviewing datareported on the Analysis, Feed Blends, and Cat Blend sheets. Theparameter case results are useful to investigate the quality of the test rundata from the perspective of overall plant fundamental heat, material, andchemical balances.

The various topics discussed include setting up options, input data tips, andreview of key analysis sheets.

Parameter Options on Options WorksheetReview the Options worksheet. A few of the key options are reviewed herewith particular impact on parameter cases. It is important that some specificoptions are used or not used for the Parameter case.

As mentioned in that section, after you change the options, you must click theUpdate Spec Colors button on the toolbar. This will change the cell color toblue for all the mandatory data entries.

Feed Rate Basis

The Feed Rate Basis option allows specification of feed rates in either massor volume flow units. The units of measure are determined elsewhere in ascript file. However, the flow basis must be selected for a parameter case andnot changed for other cases. If the flow basis is changed after running a


Parameter case and then a Simulation case is run, all of the feed flow ratesmust very carefully be changed throughout the interface. Otherwise, themodel could easily encounter an infeasibility with an apparently either huge orvery small feed flow rate.

Feed Gravity Basis

The Feed Gravity option allows various methods of calculating or specifyingthe feed gravity. For Parameter cases, you must select either the Input API orthe Input SG option. The other options are used only for generating LPvectors. The gravity basis should not be changed after running a Parametercase or there is the risk that the feed flow rate and characterizationcalculations will become infeasible. For example, an API of 0.88 will generatea feed composition that looks like FCCcycle oil, whereas a SG of 0.88 maygenerate a very typical VGO characterization.

Product Gravity Basis

The Product Gravity option allows the selection of either API or SG to beentered for Parameter case data. This has no impact on case modes otherthan Parameter. However, if you change this option, take great care to enterthe Parameter case gravities on the correct basis.

Light-Ends Product Rate Basis

The light-ends flow rate may be entered on either mass or volume flow ratebasis. This option is similar to the product gravity option in that it only affectsthe Parameter case.

Heavy Product Rate Basis

The heavy product flow rates may be entered on either mass or volume flowrate basis. This option is similar to the product gravity option in that it onlyaffects the Parameter case.

Fractionation Control

This option allows the selection of how the fractionation is controlled to bestmatch the actual plant operations. It is common for heavy naphtha and HCOto be on draw rate targets, but these draw rates may be specified in eithervolume or mass rate units.

When selecting the All Use TBP90 option, you should be very careful whenrunning simulation cases so that the adjacent 90% targets don’t get so closethat they become infeasible. All the other options here tend to be much morerobust.

Fresh Feed Basic or Total Nitrogen

This option provides flexibility in the feed nitrogen content to be entered aseither basic nitrogen or total nitrogen. Internally, Aspen Plus CatCracker is


always driven by basic nitrogen. If the Total Nitrogen option is selected, themodel will determine the basic nitrogen by applying a basic-to-total ratio of1:3.

Regenerator Control

This regenerator control option has no impact on the parameter case. Alloptions selected require the same input data to parameterize the regeneratorkinetics. However, it makes sense to select the option that is appropriate forrunning simulation cases. Most often, it is best to try to mimic the advancedcontrol scheme of the regenerator. If advanced control has not beenimplemented on the unit, then the operation philosophy should be used todetermine the most appropriate regenerator option.

The first and most important choice to be made is to select either complete orpartial combustion mode. Typically, if the excess O2 in the flue gas is over0.5% and the CO is close to zero, the unit is most likely in completecombustion (sometimes called full burn mode). Partial combustion is noted byvery low O2 in the flue gas (less than 0.5%) and a substantial amount of CO(over 1%). It is common to have 5% or even greater CO in the flue gas inpartial combustion units.

Pressure Balance Control

The pressure balance control is used to approximate the advanced controlsystem behavior. However, for Parameter cases it is best to select the AllPressures Const option. This means that the pressures must be entered forregenerator, reactor, and wet gas flash (fractionator overhead accumulator)pressure. The model will then calculate the delta P between the variouscontrol points. After the Parameter case is run, the most appropriate optioncan be selected confidently without fear of getting the delta P sign incorrect.

Param Sheet Input - Key Operating DataThe WG to RX DP Const option means that the regenerator pressure isconstant at whatever value is entered for the regenerator. In addition, thewet gas suction pressure is also held constant at the user-input value. Thereactor pressure will be determined from the back-pressure through the mainfractionator as determined from the parameter case calculations.

The WG-RX and RX-RGN DP Const option means that the wet gas suctionpressure and reactor/regen Delta P are held constant at the user input values.The reactor pressure will be determined from the back-pressure through themain fractionator as determined from the parameter case calculations. Theregenerator pressure is calculated from the reactor pressure plus thereactor/regen Delta P input value.

The key operating data entered on the Param worksheet is described below.


Regenerator Temperatures

The Regen Flue Gas Temp should always be at least a few degrees higherthan the Regen Bed Temp. If this is not the case, then you take the risk ofmaking the regenerator dilute phase kinetics infeasible.

Carbon on Regen Catalyst

The Carbon on Regen Cat should never be set to 0.0%. In fact, it is rarely ifever less than 0.03% in real operating units and typically runs at about0.05% for most complete combustion units. Partial combustion units operatefrom 0.05% and higher, often running at or above 0.10%.

Flue Gas Composition

None of the flue gas compositions should ever be set to zero. If the actualvalue is not known, then one should be estimated from historical data, ifavailable.

In complete combustion units, it is common for the CO to not be reported oreven analyzed. If it is reported, the results are often inaccurate due to poorcalibration. In this case, set the CO to 0.05%. In any case, the CO shouldnever be set below 0.05% in a Parameter case. Check with the laboratory tosee if argon is included as O2 in the analytical method being used; this istypical of many GC methods. If this type of data is entered, the coke yield willbe under-estimated.

In partial combustion units, the O2 might not be reported or reported as0.0%. In this case, set the O2 to 0.05%. In any case, the O2 should never beset below 0.05% in a Parameter case. If the reported value for O2 is at orabove 0.9%, check with the laboratory to see if argon is included as O2 in theanalytical method being used; this is typical of many GC methods. If the O2 isvery much above 0.3%, the analysis may be bad or poorly calibrated for sucha low concentration of O2 as is normal in a partial burn unit.

Air Rate

The air rate to the regenerator is entered on a wet basis. The total air rateshould include all air sources such as aeration or lift air to the catalysttransfer lines and regenerator standpipe.

Pressure Balance

In a Parameter case, the All Pressures Const option should be used to specifythe unit pressure balance. The Sign of Rg/Rx DP should be set to either –1.or +1. to achieve the appropriate value for the Rg/Rx DP value. Theappropriate value is defined as whatever is recorded by the advanced controlsystem or DCS. It is typical for this DP to be always recorded as a positivenumber.


Heat Removal

The steam flow rates are set to a very small number by default. These shouldnever be set to exactly 0.0 or the model equations will become singular.Similarly, if there are not bed coils in the operating unit, the number of bedcoils and the surface area per bed coil should be left at the default non-zerovalues.

Param Sheet Input - Feed DataThe feed data entered on the Param worksheet consists of the following foreach feed:

Feed Type

S Crackability

Refractive Index and Viscosity

Distillation Type

Feed Metals Option

Feed Type

Select the feed type that most closely matches the feed entering the unit.VGO is the most common feed. In cases where high-pressure hydrotreatmentis involved, select the HTVGO feed type. Heavy resid processors should selectthe RESID feed type. Other much less common feed types processed includecoker gasoils (LCKGO, HCKGO, MXCKGO) and Syncrude (SYN). If the feedtype selection is still unclear, please contact AspenTech customer support foradditional advice.

S Crackability

This value indicates how easily the sulfur compounds are removed from thefeed. It correlates with the amount of thiophenic compounds in the feed itself.A VGO feed type sulfur crackability should be set to 0., whereas coker gasoilsulfur crackability should be set to 1.0 where most of the remaining sulfurcompounds are thiophenic. A hydrotreated feed sulfur crackability depends onthe severity of hydrotreatment and should be set at about 0.5. However,since hydrotreated feeds typically have very little sulfur remaining in them,the value is normally much less important than for VGO’s.

Refractive Index and Viscosity

The refractive index has a significant impact on the feed characterizationaromatics content. If the lab data is available, then it is recommended that itbe entered. However, if lab data for the specific feed sample being evaluatedis not available, do not enter in a value estimated from historical data. Even asmall error in the RI can mean a large swing in the aromatics content. In thiscase, it is better to change the RI data option to Estimate, meaning that themodel will use a correlation to estimate the RI consistent with the distillationand gravity of the feed sample.


The viscosity also contributes to the estimate aromatics content but is muchless important than the RI. If the viscosity data is not available from the labthen it should be estimated by switching the Visc Option to Estimate.

Distillation Type

In a Parameter case, only the following options should be chosen: D2887,D1160, D86, or TBP. After the Parameter case has been run, the otheroptions can be used to report additional distillation types, and VABP controlmode can be used for LP vector generation. These other options may beselected in subsequent Parameter cases as long as the basic distillation inputdata has not changed.

Feed Metals Option

Aspen Plus CatCracker performs a metals balance calculation. In essence, themass rate of metals being deposited on the catalyst is forced to match themass rate of metals being removed from the unit. The deposited metals enterthe unit as part of the fresh feed and a very small amount on the freshmakeup catalyst. The metals are then removed from the unit along withcatalyst fines losses and catalyst intentionally withdrawn from the regenerator(called spent or equilibrium catalyst).

The metals balance derived from plant must be reconciled. This is becausethe data used to define the metals balance is the result of averagedequilibrium catalyst metals content, average catalyst fines metals content,and often, instantaneous feed metals content. The actual unit acts as anintegrator; absorbing a variety of metals levels in the feed and varying feedrates all the while the fresh catalyst make up rate being fairly constant. Inaddition, metals analyses of CatCracker feeds are taken only infrequently andis not done as part of usual plant data collection. In addition, the metalsanalyses of the catalyst and feed are subject to significant errors and in anycase, they do not account for tramp metal from the process units.

The Parameter case provides an opportunity to allocate the errors in themetals balance reconciliation. The most straightforward way of doing this is toselect one of the feeds to allocate all the error to. For example, if only feednumber one has been entered in the Parameter case, select the Calc Feed 1Metals option. When the Parameter case is run, the model will back-calculatethe feed number one metals content based on a perfect metals balance. Thisis an interesting approach because it determines the average amount of feedmetals that have entered the unit over the long term. (Note: The feed metalscalculated in this way would include tramp metals.)

A second way to handle the metals balance is to assign the metals balanceerror to parameters. This is accomplished using the Enter Feed Metals option.In this case, the best available metals data for the non-zero rate feeds areentered into the Param sheet. The model will calculate the delta between theaverage feed metals from the input data and the average feed metals back-calculated from the metals balance. The delta may be positive or negativeand will be assigned to the parameter values. In future simulation oroptimization cases, the deltas will be added to any entered feed metals inputdata.


A third way to handle the metals balance is to ignore it. If there are nospecific metals issues of interest at the particular process unit, or if theparameter case in question will not be used to analyze metals issues then thismay be perfectly appropriate. To do this, select the Enter Feed Metals optionand enter zero for all the feeds with a non-zero flow rate. The model willcalculate the delta between the average feed metals from the input data(zero) and the average feed metals back-calculated from the metals balance.The delta in this case will exactly be the average feed metals content giventhe entered fresh and equilibrium catalyst metals content. In futuresimulation or optimization cases, the deltas will be added to any entered feedmetals input data. Therefore, all feeds will automatically be assigned theaverage feed metals content although the input data is shown as zero.

Param Sheet Input - Heavy Liquid ProductStreamsThere are two areas where distillation data are entered, the reactorparameterization and the simple fractionator parameterization areas. Thedistillation types selected should be one of D2887, D1160, D86, or TBP for aParameter case. After the Parameter case is run once, then the type can bechanged to one of the Dxxx & All selections.

Param Sheet Input - Catalyst DataThe average fresh catalyst properties are calculated in the Excel sheet using aformula that blends the properties on a mass blend basis. The averageproperties are reported in the Blend column. Once the fresh catalysts havebeen selected from the combo-boxes and the percentage makeup has beenentered, the blend properties are immediately available. The fresh blendproperties should be compared to the ECAT and fines catalyst analysesentered. The MAT and surface area must be lower than the blend values. TheIron and Sodium values must be higher than the blend values. If theequilibrium catalyst data from the lab does not follow this trend, the freshcatalyst types and Mix wt% should be checked. If there is still disagreement,contact AspenTech customer support for additional consulting.

Feed Blends Sheet ReviewThere are many areas on the Feed Blends sheet that may be of interestdepending on the specific CatCracker unit. A few of the essential items thatare important to all CatCracker units are discussed briefly below.

Lab Data versus Estimations

Compare the model-estimated RI and viscosity with the lab data. Largedifferences in these values might imply that the feed properties areinconsistent. Review the feed gravity for significant errors.


Aromatic Content

Compare aromatics estimations from the Total method and from thecontribution that each feed makes to the total aromatic pool. If the correlationpredicts either lower than 15% or higher than 25% aromatics, review thefeed type being processed and the feed properties to ensure the result isrational. Also, consider using an Estimated RI instead of a Lab RI data entry.

It is also worthwhile to review the full 19-lump composition data reported forthe blended total feed. For a Parameter case, the ring balance can indicateinconsistent data. For example, the total bottoms yield should not be tooclose to the total 3-ring concentration in the blended feed. The 3-ringaromatics can only convert to coke or remain un-cracked as bottom material.If the bottoms yield target is too low, the parameter case may be infeasible.

Cat Blend Sheet ReviewReported on the Cat Blend sheet are the final yield factors for each catalystafter the compositional shifts and the yield factors for the blended catalyst.

Analysis Sheet ReviewThe data available on the Analysis worksheet consists of the following:

Material Balance

Heat Balance

Feed Vaporization

Reactor Dilute Phase Cracking

Material Balance

The material balance section reports the errors in the mass flow rates. Theseerrors are the results of reconciling the material balance information derivedfrom the input data. By default, AspenPlusCatCracker puts the mass balanceerror in the light naphtha stream. If this error is greater than about 2-3% ofthe total feed mass rate, the flow rate and gravity information should bereviewed.

The standard cut products section reports the volume percent of the standardcut yields derived from the observed plant data. The standard liquid cutsinclude C5-430F, 430-650F, and 650F+ streams.

The sulfur balance section reports how the feed sulfur is distributed amongthe products. The sulfur in H2S should be roughly half of the feed sulfur.

The conversion section reports feed conversion on a standard 430F cut pointbasis and on an observed naphtha flow rate basis.

Heat Balance

The heat of cracking section reports the actual and theoretical heat ofcracking. If the difference between these two values is greater than 40 or 50BTU/lb. of feed, then the regenerator data should be reviewed for consistency


and perhaps compared to historical data. For example, it is not unusual tohave as much as a 10% error in the air flowrate measurement. In addition,the flue gas analysis can have a significant impact on the heat balancecalculation as well.

To determine if the flue gas analysis is in question, review the hydrogen oncoke report section. If the total coke average hydrogen content is outside therange of 5-8%, there is a good chance that the flue gas analysis is in error.However, there are a very few units operating around 5% (unusually good) orover 8% (unfortunately quite bad).

The coke distribution report section should be reviewed. The stripper sourcecoke should be roughly 15%; this is actually input directly on the Paramsheet. The kinetic coke should be anywhere from 50% to 80%.

If the metals coke is greater than 15%, great care should be taken to ensurethis is reasonable. For example, the nickel equivalent should be quite highand with little or no nickel passivation additive. If this is not the case, thenthere is a real possibility that the H2 yield is too high. A review of the lightgases flow rate and/or the composition might reveal an error.

Feed Vaporization

The riser feed mix conditions section reports the composition of the total riserfeed, the temperature of the catalyst plus feed oil mixture at the bottom ofthe riser, and the calculated dew point. If the dew point is close to or belowthe mixed temperature, then some care should be taken to review the feeddistillation, gravity, and cat/oil ratio. If the conditions are judged legitimate,then the non-vaporized feed coke option should be considered. This will havea significant impact on the incremental coke make due to incremental feedrate.

Reactor Dilute Phase Cracking

The riser/reactor catalyst inventory section reports the amount of catalystheld up in the catalyst dilute phase. If it is understood from the unit designerthat there is a significant catalyst holdup in the reactor dilute phase, then thedilute phase volume and resulting catalyst inventory should be adjusted toprovide the appropriate amount of post-riser cracking.

Model Tuning

Heat Balance TuningThe heat balance for Aspen Plus CatCracker can be tuned so that theregenerator response to changes in feed rate or preheat temperature matchexpected values. This tuning can be achieved by changing key parameters inthe stripper model and running a parameter case.

The stripper source coke is defined as the hydrocarbon entrained with thecatalyst in the stripper and then transferred to the regenerator where it


appears as coke and is burned. This stripper coke is relatively high inhydrogen content, causing a much higher heat of combustion than the feedand kinetic sources of coke. Therefore, it is much more detrimental to theregenerator bed temperature, resulting cat/oil ratio, and finally theconversion. Also, the stripper source coke has roughly the same compositionas the reactor effluent (50% of the hydrocarbon is highly valued gasoline).

Two key parameters can be used to tune the stripper model, the performanceslope, and the percent of total coke whose source is the stripper. Typicalvalues of performance slope are between 0.5 and 1. A typical value for thepercentage of coke generated from the stripper is 15%. You may enter newvalues for these in the TUNING DATA section of the Param sheet.

The biggest handle for tuning the stripper is the performance slope. If youwant the regenerator temperature to have a larger increase for an increase infeed rate, increase the performance slope. It is recommended that this slopeis not increased to more than 4 or 5.

For example, in the Aspen Plus CatCracker demo problem the regeneratortemperature is 1300 °F in the base case. Upon a 10% increase in the feedrate, the model predicts that the regenerator temperature increases to 1311°F, or an increase of 11 °F. If this increase in temperature is too low, themodel can be re-tuned by increasing the performance slope of the stripper.

You should enter a new performance slope in the TUNING DATA section onthe Param sheet. The figure below shows that a value of 2 has been entered.Then run a parameter case. Select Parameter from the combo box on theAspen Plus CatCracker toolbar and click the run button.

Change stripper performance slope to 2 and run a parameter case

After the parameter case has been run, determine the new regeneratorresponse by running another simulate case. On the Simulate sheet, enter thenew flow rate as shown below. In the demo case, a 10% increase correspondsto a new feed rate of 33 MBBL/DAY. Enter this in the FEED DATA section asthe volume flow for feed 1 (the only feed that has a non-zero flow rate for thedemo case).


Increase feed rate by 10% and run a simulate case

After the new flow rate has been entered, select Simulate from the combo-box of the Aspen Plus CatCracker toolbar and click the run button. After themodel has solved, the results for the regenerator temperature appear in thesection KEY OPERATING DATA on the Simulate sheet. In this case, a 10%increase in feed rate causes the regenerator temperature to increase from1300 °F to 1317 °F.

View results after simulation case is run to observe regenerator response

If the increase in regenerator temperature is still too small, you may againincrease the performance slope of the stripper and run another parametercase. After a parameter case has been run, you may run another simulatecase with a 10% increase in feed rate to observe the regenerator temperature


response. In this case, by doubling the performance slope again to 4, theregenerator temperature increases to 1321.6 °F for a 10% increase in feedrate.

It is recommended that the performance slope not be changed to a valuegreater than 4 or 5. If the regenerator response is still not what is expectedafter the performance slope has been changed, you may change the percentof total coke that comes from the stripper. As with the performance slope,this data can be entered on the Param sheet in the TUNING DATA section.A maximum value of 25% to 30% should be used. In the example shownbelow, a value of 30 has been entered. After entering a new value, run aparameter case.

Increase the percent of total coke due to stripper from 15 to 30 percent andrun a parameter case

After the Parameter case has been run, again run a Simulate case with a 10%increase in feed rate. In this case, by increasing the percent of coke from thestripper to 30% and keeping the performance slope at 4, the model predictsthe regenerator temperature to be 1324.8 °F for a 10% increase in feed. Notethat if the increase in regenerator temperature is still not high enough, theperformance slope and percent of total coke due to stripper should not beincreased beyond 5 and 30 respectively. You should contact AspenTechnology if the desired regenerator response cannot be achieved with theseconstraints.

Over-crackingThe Aspen Plus CatCracker model allows you to tune the cracking kinetics sothat the naphtha over-cracking peak occurs at the right temperature. Beforetuning the over-cracking peak, you should first determine where the modelpredicts over-cracking to occur. This can be done using the case studyfeature. Set up a Case Study that varies the riser temperature and reportsthe naphtha yield.

Begin the case study by selecting the menu commandAspenPlusCatCracker | Setup Cases | Case Study. This will open theSetup Case Study dialog box, which contains two pick lists, one for theindependent variables and one for the dependent variables. From theindependent variable list, select the variable that is used to control the riser


temperature: reactor plenum temperature, riser overhead temperature, regencat slide valve percent open, or spent cat slide valve percent open. Only thevariable that is used for controlling the riser temperature will show up in thepick list. From the dependent variable list, select the variable for debutanizerbottoms yield on a fresh feed basis. You may also select any other variablesfrom the dependent variable list that are of interest. After the appropriatevariables have been selected, click OK.

Select the reactor plenum temperature as the independent variable and selectthe debutanizer bottoms on a wt% fresh feed basis as the dependent variable

Once the Case Study is set up, you should enter the different values of theindependent variables that will be used in the case study. In this example, thereactor plenum temperature is the control target. The base model isparameterized to a value of 990 °F. Five cases will be run starting with 980 °Fand ending with 1020 °F. Before the data is entered, delete any data fromprevious case studies that is in columns that will be used. Then enter thevalues for the reactor plenum temperature in the appropriate cells as shownbelow. Also, select (in row 8) the desired number of creep steps for eachcase. If you don't know how many creep steps to use, try the typically safevalue of 10.


Enter data for the reactor plenum temperature for each case in the case study

Once the case study is set up and the data has been entered for theindependent variables, the model is ready to run. Select the Case Studyoption from the Aspen Plus CatCracker toolbar and click the run button.Immediately, a dialog box appears, asking for the first and last cases to berun.

Enter first and last cases to run

In this example, 1 is the first case and 5 is the last case. The Calculate LPVectors option is selected by default. Clear this option if you do NOT want tohave LP Vectors calculated. If you do not clear this option, LP vectors will berun for each case and reported in rows 1000 and higher on the Case Studyworksheet. The LP vectors that are run will be based on the settings on theLP Vectors worksheet. When you have entered the information, click the OKbutton.


Case study results

After the case study is run, you can detect the over-cracking peak bymanually inspecting the data or using the built-in Excel capability of graphingthe data. In this case, a maximum value of debutanizer bottoms occursbetween 990 °F and 1000 °F. At this point you can start tuning the over-cracking peak.

Over-cracking peak for an Ea/R value of 60,000

The first step to tuning the over-cracking peak is to select the option ResetEa/R from the naphtha over-cracking combo-box on the Param worksheet.This combo-box appears toward the bottom of the sheet, in the Tuning Datasection. The Reset Ea/R option fixes the reference reaction rate so that youcan move the activation energy by large amounts without causing thereaction rate to get so large that the model can no longer solve. Afterselecting this option, enter a new value for Ea/R and run a parameter case.To shift the over-cracking peak to a higher temperature, decrease Ea/R. Toshift the over-cracking peak to a lower temperature, increase Ea/R.


Select the Reset Ea/R option for naphtha over-cracking

After the parameter case with the new Ea/R value has been run, run anothercase study to see how the over-cracking peak has shifted. In this example,the Ea/R was decreased from 60,000 to 50,000. An increased temperature forover-cracking should be the result. Since the case study is already set up, youneed only to select Case Study from the Aspen Plus CatCracker toolbar againand click the run button. From the first dialog box click OK, then click eitherYes or No in the LP vector dialog box.

After the case study is run, you can look at the results in the independentvariables. If the data has been graphed, the graph will be automaticallyupdated with the new data, if the same case study range was used. Thefigure below shows a graph of the updated over-cracking peak. In this caseover-cracking occurs between 1000 °F and 1010 °F. This result agrees withthe expectation that the over-cracking peak should increase with decreasedEa/R.


Over-cracking peak for an Ea/R value of 50,000

You may continue to run various parameter cases at different Ea/R valuesfollowed by case studies until the desired over-cracking peak is achieved. Atthat point, you should set the naphtha over-cracking option back to defaultand run another parameter case. This will set all variable specifications backto the default values.

Catalyst Makeup versus MAT

Makeup Rate versus MAT. Frac = makeup rate/inventory

If the value of the fractional make-up rate is small (less than 5%), you willtypically not need to tune the response of make-up versus MAT activity.However, if Frac is too large (5 to 10%), the model can blow up when tryingto increase activity. In that case, you can increase the value of the variableCATP.BLK.MDADJ_METALS_DEACT_BASE to decrease the sensitivity ofmake-up rate to MAT activity.


Tuning parameter: Decrease the cat inventory to get into the region of 0.5%.Cat inventory should be viewed as the active catalyst inventory in the unit,not the total amount of inventory as viewed by the refiner.

If regen and rx cat losses are set too high, then the model can get intotrouble when trying to achieve the activity target. When decreasing the MATtarget, the makeup rate will decrease. However, the minimum makeup rate isequal to the total fines losses and therefore, there is a minimum feasible MATtarget.

The equation to determine the fractional makeup rate is as follows:

X_Frac_MUP= X_Cat_deact_K * (X_Equil_cat_ZACT + X_HTdeact_Term *X_Cat_deact_P4) / (X_Cat_deact_Param *X_Fresh_Cat_ZACT - X_Equil_cat_ZACT - X_HTdeact_Term* X_Cat_deact_P4)

The term X_Htdeact_Term * X_Cat_deact_P4 is small compared to theother terms in the numerator and the denominator so the fractional makeuprate can be approximated with the following equation:

X_Frac_MUP= X_Cat_deact_K * X_Equil_cat_ZACT / (X_Cat_deact_Param* X_Fresh_Cat_ZACT - X_Equil_Cat_ZACT)

Or directly calculating the makeup rate using the names of the variables inthe model:

RREXP.BLK.MAT_FRESH_CAT_MUP = RREXP.BLK.MAT_TOTAL_UNIT_INV*

RREXP.BLK.MAT_CAT_DEACT_K* RREXP.BLK.MAT_EQUIL_CAT_ZACT/

(RREXP.BLK.MAT_CAT_DEACT_PARAM* RREXP.BLK.MAT_FRESH_CAT_ZACT-RREXP.BLK.MAT_EQUIL_CAT_ZACT)

In this equation, the equilibrium and fresh catalyst ZACT values are fixedbased on the MAT activity values. The total catalyst inventory is constant andthe fresh makeup rate is fixed for a Parameter case. The catalyst deactivationparameter is calculated in a Parameter case to match the input catalystmakeup rate. The only other variable that can be changed to achieve thecorrect response is the catalyst deactivation K. The variableCATP.BLK.MDADJ_METALS_DEACT_BASE will change the calculated valuefor the catalyst deactivation K.

Adding New CatalystsAspen Plus CatCracker comes preconfigured with several catalyst types fromwhich to choose. The catalyst type will affect yields, selectivities, and productqualities. This is accomplished in Aspen Plus CatCracker with catalyst factorsthat are used as multipliers or additives to various parameters in the model.Analyses to determine the factors are performed by Refining ProcessServices.

In addition to being able to choose from the preconfigured catalyst types, youcan choose to have the catalysts that you use analyzed. These new factorscan then be easily added to the Excel GUI for Aspen Plus CatCracker.


Work ProcessAll catalyst factors are stored in the hidden worksheet CST Factors. In orderto add a new catalyst, you must first unhide this worksheet. Adding newcatalysts is a three-step process.

1 Unhide the CST Factors Worksheet

2 Add the Catalyst Data

3 Re-hide the CST Factors Worksheet

Unhiding the CST Factors Worksheet

To unhide the CST Factors Worksheet:

1 On the menu, click Format | Sheet | Unhide.

This opens the Unhide dialog box that contains all the hidden worksheets.

Unhide Dialog Box

2 Select the worksheet CST Factors; then click the OK button.

Adding Catalyst Data

To Enter Catalyst Information:

1 On the CST Factors worksheet, go to the first blank column on the page.Enter the catalyst name in Row 1.

2 Enter the catalyst ID in Row 2. The catalyst ID should be a unique integerthat identifies the catalyst. Because values between 1 and 1000 arereserved for the default catalysts that come with the model, you shouldassign a value of 1001 or greater to any new catalysts.

3 In Row 3, you can enter the catalyst vendor.


CST Factors Worksheet

4 Enter the catalyst factors for the new catalyst in Rows 4 through 73.

Once these values have been entered, the new catalyst is ready to use.

Re-hiding the CST Factors WorksheetBefore connecting to the model, you should first hide the worksheet again andsave the workbook.

To re-hide the CST Factors Worksheet:

On the menu, click Format | Sheet | Hide.

This hides the sheet you are currently have open, so make sure that you arestill in the CST Factors worksheet.

After the CatCracker model is loaded, the new catalyst should appear as thelast item in the pick list.

If you are already connected, you can also update the combo-boxes forcatalyst type.

To update the combo boxes for Catalyst Type:

Select Aspen Plus CatCracker | Development Tools | UpdateCatalyst Combo Boxes.

Note: Do not use this option with Excel 97.

Feed CharacterizationAspen Plus CatCracker allows you to select a feed type and input feed qualityinformation that will adjust the kinetic lumps associated with that feed. Thischaracterization uses two types of data: a feed fingerprint and standardinspection properties. The fingerprint can be calculated from detailed feed andproduct analyses including GC/MS, 13C NMR, distillation, S content, and HPLC.These fingerprints are used to define the basic character of the feed type orclass being processed and can be adjusted somewhat to match more routinely


available bulk properties like distillation and gravity. Fingerprints for manyfeed types have been provided with the Aspen Plus CatCracker model so thatyou need only to select the feed type and input bulk properties. Feedcomposition changes are taken into account using the feed bulk inspectionproperties described in Feed Properties.

Feed Properties

Typical Feed Properties to Adjust Fingerprints

Test Method

Distillation D2887, D86, or D1160

API Grav @60 D287

Sulfur, wt% D4294

Viscosity @ 210 °F, cst D445

Total Nitrogen, wt% D4629

Conradson carbon, wt% D4530

Metals (Cu,Fe,Na,Ni,V), ppm/wt

Refractive Index D1747

Distillations are used to reshape the distribution of mass in the fingerprint anddetermine the mass of material in the boiling ranges for the gasoline, light,heavy and resid lumps. The gravity, sulfur, viscosity, and refractive index areused to determine the aromaticity of the feed. You have the option toestimate the RI or viscosity if the data is not available or if the error ofmeasurement is too large. Conradson carbon is used as a part of the cokecalculation in the risers, reactor, and regenerator. Nitrogen and the metalsare used to calculate catalyst activities.

The adjustment method used assumes that provided a fingerprint of a cokergasoil for a reference, the inspection properties, and distillation for anothergas oil will shift the aromatics in the correct direction. This same principleapplies to any other type of feed as long as there is a representativefingerprint available. If no suitable fingerprint is available, contact AspenTechnology about generating a fingerprint and adding it to the interface.

Selecting Feeds and Entering PropertyInformationYou should first select the feed types for each feed that is being used. Thiscan be done on the parameter page or the simulate page. The figure belowshows the feed selection combo box for the first feed. There is one for each ofthe ten possible feed slots and you should specify the appropriate feed typefor any feed that has a non-zero flowrate.


Selecting a feed type for Feed 1 using the combo box.

Once the feed type is selected for each feed, you should select the RI option,Viscosity option, and distillation option for each feed being used.

You should select to either enter a Lab measured RI value or to have thevalue estimated from other data from the RI combo box. Typically, unless theRI data is of high quality, it is recommended that you select the Estimateoption. If you select the lab measured RI option and poor quality data isentered, the model may not solve, since the Ca value is highly correlated withthe RI value.

Selecting the desired RI option for Feed 1.

From the viscosity option combo box you should select to either enter a lab-measured viscosity in cSt or SUS or have the viscosity estimated from otherproperties. Unless the lab data is high quality, it is recommended that youselect to have the viscosity estimated. However, since Ca is only weaklycorrelated with viscosity, errors in lab measured values should not causerobustness issues.

Selecting the appropriate viscosity option for Feed 1.

Finally, you should select the distillation type from the distillation combo boxfor each feed. You may select from D2887, D1160, D86, and TBP. For each ofthese options, you may also select &all. By selecting the &all option, themodel is instructed to calculate all distillation types for the feed. Aspen PlusCatCracker uses the API correlations to calculate the distillation types.However, since the API equations are highly non-linear, selecting the &alloption may make the model difficult to solve. Therefore, it is recommendedthat you never select the &all option when first entering data. Once the modelhas been solved, you may change the distillation option to include &all sincethis option should be more robust at that point. The distillation combo-boxes


include one last option, VABP D1160. The VABP option should only beselected for generating LP vectors. After the option is selected, run a Simulatecase, followed by an LP vector run. Once the LP vectors have been run, setthe distillation option back to what was selected previously and run anothersimulate case. The reason for running the simulate cases are because thespecifications are not passed from the GUI to the engine until the model hasbeen run.

Selecting the desired distillation option for Feed 1.

After the desired options have been selected, you should enter all of thenecessary bulk properties in the appropriate cells. You should first click theUpdate Spec Color button on the Aspen Plus CatCracker toolbar so that theappropriate input cells are shaded blue. See Updating Spec Colors. You shouldenter data into any cell that is shaded blue for each feed that has a flowrate.

The Aspen Plus CatCrackerEngineThe Aspen Plus CatCracker engine is Aspen Plus. You do not need to be anAspen Plus expert to use Aspen Plus CatCracker. This section covers the mostimportant concepts in using the engine.

The first time the engine is used during an Aspen Plus CatCracker session iswhen the user interface connects to the server. This brings up a CommandLine window in which you will see the invoke plant.ebs command, whichsets the correct units of measure and connects to the desired delumpermodel. The Command Line window disappears when the kernel finishesbuilding the model.

The engine is also used whenever you request a solution from the userinterface. Any changes you have made to data values or model specifications(via combo boxes) are passed through DCOM from the client to the server.The command prompt window appears and you will see a stream of kernelcommands going to the engine. These commands tell the engine what modeof solution is required and what solver settings should be used. There aredifferent sequences of commands for different types of solutions (parameter,simulation, optimization, case study, LP vector generation, etc.). You can lookat the default command sequences on the EB Script sheet on the userinterface. The default command sequences are all you need for running the


model in any of the pre-configured solution modes, but advanced users canmodify them.

During a solve, you will see three buttons on the bottom of the CommandLine window:

Abort

Finish

No Creep

You can use these buttons to interrupt the solver. The Abort button causesthe solver to quit at the next opportunity. See The Command Line Window formore information about the purpose of these buttons and when to use them.

The engine is also used whenever case data is stored or retrieved. The userinterface typically contains only the results of the most recent run of eachsolution type. The Save Case Data command let you save the results of anynumber of previous runs to review or use later. This user interface option isimplemented using the kernel commands read varfile from and writevarfile to. You can see these commands in the Command Line window whileit is active. You can open the Command Line window using the menucommand AspenPlusCatCracker | Tools | Display Command Line toreview the previous commands.

6 EO Modeling Background and Examples 98

6 EO Modeling Backgroundand Examples

Equation-Oriented ModelingAspen Plus CatCracker is based on an equation-oriented (EO) formulation, soyou need to understand some EO concepts in order to use it effectively. TheEO approach is also known as open-form modeling and can be contrastedwith the closed-form or sequential-modular (SM) technique. The equations inan EO model are solved simultaneously using an external solver, whichiteratively manipulates the values of the model variables until all theequations are satisfied within a convergence tolerance. The solver will workfor any well-posed set of variable specifications. A variable’s specificationlabels it as known (fixed) or unknown (calculated) for each solution mode.

In contrast, an SM model is solved procedurally, one equation at a time, andthe solution procedure depends on a given specification set. For differentgroupings of known and unknown variables, the solution procedure will bedifferent, since the equations will be solved in a different order.

Pressure Drop Model ExampleA simple example illustrates some important EO concepts. Consider this two-equation model where the pressure drop is correlated with the square of themass flow of a fluid:

Pressure drop correlation: DELTAP = PRES_PARAM * MASS_FLOW^2

Define pressure drop: DELTAP = PRES_IN – PRES_OUT

In an EO formulation, we rearrange these equations into residual format. Thevalue of the residual indicates how close that equation is to being solved. Atthe solution, the value of every residual will be zero, or at least close enoughto zero to satisfy our numerical convergence tolerance.

f(1) = DELTAP - PRES_PARAM * MASS_FLOW^2 (= 0 at solution)

f(2) = PRES_IN - PRES_OUT - DELTAP (= 0 at solution)

Note that f is the name of the vector of residuals and it has length equal tothe number of equations. The solver prefers to work with vectors and


equation index numbers, while we find it easier to use equation names. Themodel defines names for each residual that can be used in reports and solverdebugging output. In this case, we choose the names:

f(1) = ESTIMATE_DELTAP

f(2) = DELTAP_DEFINITION

Similarly, the five variables in this model can also be addressed as elementsof a vector x having length 5:

x(1) = DELTAP

x(2) = PRES_IN

x(3) = PRES_OUT

x(4) = PRES_PARAM

x(5) = MASS_FLOW

Model Specifications and Degrees-of-FreedomOnce we tell the solver which variables are known (fixed) for a given solutionmode, it will manipulate the values of the unknown (free) variables to drivethe residuals to zero. For any system of independent equations, the degrees-of-freedom (DOF) is equal to the number of variables minus the number ofequations minus the number of fixed variables:

DOF = #variables - #equations - #fixed variables

The number of degrees-of-freedom of a system classifies it into one of threecategories:

Under-specified DOF > 0

Square DOF = 0

Over-specified DOF < 0

The optimization mode of Aspen Plus CatCracker is under-specified, while theother modes (simulation, parameter, case study, LP vector) are square. Over-specified problems are not allowed in Aspen Plus CatCracker.

The pressure drop example has 5 variables and 2 equations, so we must fix 3variables to create a square system. Furthermore, we cannot fix any arbitraryset of 3 variables. If all variables within one equation are explicitly orimplicitly fixed, the problem is not well posed, as the solver can no longermanipulate any variable to reduce that equation’s residual. Such an incorrectset of specifications will cause a structural singularity in the solver. However,Aspen Plus CatCracker is designed so that if you use the standardspecification options provided in the user interface you will not create astructurally singular system.

Here are some specification attempts for the pressure drop example:

Fix DELTAP, PRES_OUT: Under-specified; only acceptable for an optimizationcase with proper selection of independent variables.

Fix DELTAP, PRES_OUT,PRES_IN, MASS_FLOW:

Over-specified!


Fix DELTAP, PRES_OUT,PRES_IN:

f(1) = DELTAP – PRES_PARAM * MASS_FLOW^2

(fix) (free) (free)

f(2) = PRES_IN – PRES_OUT – DELTAP

(fix) (fix) (fix)

Square, but not well posed (structurally singular). Allvariables in residual 2 are fixed! If you compare thisto the over-specified example, you can see that over-specification is not allowed since it always leads to astructurally singular system.

Fix PRES_IN,PRES_PARAM,MASS_FLOW:

f(1) = DELTAP – PRES_PARAM * MASS_FLOW^2

(free) (fix) (fix)

f(2) = PRES_IN – PRES_OUT – DELTAP

(fix) (free) (free)

Square and well posed. A valid specification set. Notethat there are other valid specification sets, such asPRES_IN, PRES_OUT, and MASS_FLOW.

Modes and Multi-Mode SpecificationsIn different situations, we may want to use different sets of fixed and freevariable specifications. Each set of variable specifications is a solution mode.One of the strengths of the EO approach is that the same model formulationand solver are used for all the modes. Although there are many possiblemodes, Aspen Plus CatCracker is configured for three basic modes. TheSimulation, Param and Optimize sheets in Aspen Plus CatCrackercorrespond to those three modes. Case study and LP vector generation arealso simulation modes. Case study is simply a series of simulations with thesame specifications, but different values for key fixed variables. LP vectorgeneration is a simulation run followed by a sensitivity analysis. Theindependent and dependent variables you choose for vector generation mustcorrespond to fixed and free variables in the simulation mode. The Aspen PlusCatCracker user interface examines the current model specifications and letsyou choose only proper independent and dependent variables.

In order to label how each variable behaves in the various modes, multi-modespecifications are assigned. A variable that is fixed in every mode is called aCONST, while variables that are free in every mode are called CALC. Forexample, in Aspen Plus CatCracker the reactor vessel diameter is usually aCONST because its value is not calculated in any mode, while the weightpercent hydrogen on coke is usually a CALC because the model calculates itsvalue from other information.

Measurements and ParametersWhile many variables have CONST or CALC specifications, there are othervariables whose behavior changes between modes. A MEAS variable is fixedin the parameter-fitting (tuning) mode, but free in the simulation and


optimization (prediction) modes. Conversely, a PARAM variable is free in theparameter-fitting mode and fixed in the simulation and optimization modes.Usually a MEAS corresponds to a plant measurement, while a PARAM is amodel tuning parameter or a bias to a measurement. Since the MEAS andPARAM variables always have opposite specifications in every mode, thereare always the same numbers of MEAS and PARAM variables so that everymode is properly specified. Another rule of thumb is that it is possible to swapthe specifications on a pair of related CALC and CONST variables to be MEASand PARAM, since the number of DOF stays the same in every mode.

The concepts of simulation and parameter-fitting mode andCONST/CALC/MEAS/PARAM variables can be illustrated with the pressuredrop example.

Assume the equipment across which the pressure drop is measured has aninlet pressure gauge, a DP cell, and a mass flowmeter. We can specify the DPmeasurement (variable DELTAP) to be type MEAS and the pressure dropparameter (PRES_PARAM) to be type PARAM. We can define inlet pressure(PRES_IN) and mass flowrate (MASS_FLOW) as CONST variables. The outletpressure (PRES_OUT) is always calculated from the other variables, so it istype CALC.

f(1) = DELTAP - PRES_PARAM * MASS_FLOW^2

(MEAS) (PARAM) (CONST)

f(2) = PRES_IN - PRES_OUT – DELTAP

(CONST) (CALC) (MEAS)

This is a valid multi-mode specification, because in the simulation modeMASS_FLOW, PRES_IN and PRES_PARAM are fixed and PRES_OUT andDELTAP can be calculated from those values. In the parameter-fitting mode,DELTAP, MASS_FLOW and PRES_IN are fixed, and PRES_PARAM andPRES_OUT can be computed.

Changing Specifications with Combo BoxesWhat if the plant we are modeling has both a DP cell and an outlet pressuregauge? We have a choice as to which to use. From a mathematicalstandpoint, it is just as valid to declare PRES_OUT a MEAS and DELTAP aCALC as the other way around. Thus we have two possible variablespecifications affecting both our simulation and parameter-fitting modes.

In Aspen Plus CatCracker this type of spec swap is made using a combo box.A combo box on the spreadsheet presents alternate specification sets that areequally mathematically valid. One of the sets may be more appropriate for agiven unit based on its configuration, control strategy, instrumentation, typeof lab test, mass or volume basis for flowmeters, or a variety of otherreasons. In our pressure drop example, on the Param sheet we might see acombo box with the following options:

Use outlet pressure measurement

Use pressure drop measurement

These choices correspond to the following specifications:


Use outlet pressuremeasurement

Use pressure dropmeasurement

DELTAP spec CALC MEAS

PRES_OUT spec MEAS CALC

Aspen Plus CatCracker comes preconfigured with many combo boxes whichcover all the options needed to model most CatCracker units. However, theremay be some unusual configurations that require an additional option for acombo box or some additional combo boxes. Aspen Plus CatCracker has thecapability to modify, extend, or add combo boxes by making changes to theCombo Table sheet.

For each combo box, the Combo Table sheet has an entry similar to ourexample above. Each option on the combo box is a column and each variablethat is affected by that combo box is a row.

Once the tables are modified, macros can be run to update the combo boxes.If this is necessary for your model, ask your Aspen Plus CatCracker supportcontact for detailed instructions. However, even if you don’t need to modify atable, it can be helpful to look at the tables for a better understanding of whatsome of the options mean in terms of model specifications.

OptimizationOptimization is a prediction mode, so it is similar to Simulation. The maindifference is that there are positive DOFs (Degrees of Freedom) inoptimization mode, and the solver uses those DOFs to maximize or minimizean objective function within limits on certain variables.

To create optimization DOFs, change the specifications of some CONSTvariables to OPTIM. OPTIM variables are fixed in simulation and parameter-fitting modes and free in optimization mode and are also known asindependents. The other free variables (MEAS and CALC) are known asdependents.

The solver requires that the number of OPTIM variables be equal to thenumber of DOF, but that requirement is easy to satisfy by starting with awell-posed square set of multi-mode specifications and changing only CONSTvariables to OPTIM.

To set up an optimization, you must do three things:

Define an objective function.

Specify the DOFs (independents).

Specify bounds (limits) on the values of key independent and dependentvariables.

The objective function is often a profit function, with revenue terms based onproduct or export utility flowrates and prices, and cost terms based on feed orimport utility flowrates and prices. For more information on objectivefunctions, see Setting up Optimizations.

You specify the DOF by selecting independent (OPTIM) variables from a picklist. Aspen Plus CatCracker presents only CONST variables in this pick list in


order to ensure that whatever set you choose will lead to a well-posedproblem. You can put bounds on any of the independents, plus whicheverdependents you select from another pick list that includes CALC and MEASvariables that you may wish to limit during the optimization run.

DMO Solver BackgroundWhen you click the solve button, Aspen Plus CatCracker submits themathematical formulation of the problem to the DMO solver via the kernel.

If the solution is successful, the kernel Command Line window will close, theresults of the solution will be returned to the Excel GUI, and the statusindicators will change to Ready and Converged.

If the solver fails, the status indicators will show Ready and Not Converged.In this case, you must perform some troubleshooting to determine the causeof the failure. This section discusses the basics of the solver technology anderror messages issued by the solver when certain types of errors occur.

Successive Quadratic Programming (SQP)The DMO solver is a specific implementation of the general class of nonlinearoptimization algorithms known as Successive Quadratic Programming (SQP),which perform the optimization by solving a sequence of quadraticprogramming subproblems. The general optimization problem that DMOsolves can be expressed as follows:

Minimize f(x)

Subject to c(x) = 0

xmin x xmax

Where:

Expression Represents

x Rn Vector of unknown variables

f(x) R1 Objective function

c(x) Rm Vector of constraint equations

xmin Rn Vector of lower bounds on x

xmax Rn Vector of upper bounds on x

A simplified description of the DMO algorithm is outlined as follows:

1 Given an initial estimate of the solution vector, x0.

2 Set iteration counter, k = 0.

3 Evaluate derivative of the objective function, gradient, and the derivativeof the constraints, Jacobian.

4 Initialize or update an approximation of the second derivative matrix, orHessian, of the Lagrange function. The Lagrange function, f(x) + ici,accounts for constraints through weighting factors i, often calledLagrange multipliers or shadow prices.


5 Solve a quadratic programming subproblem to determine a searchdirection, dk. In the quadratic programming subproblem, the objectivefunction is replaced by a quadratic approximation, constraints arelinearized, and bounds are included.

6 Check for convergence or failure. If the optimization convergence criteriaare satisfied, or if the maximum number of allowed iterations, MAXITER, isreached, then end. Convergence is achieved when:

7 Objective function gradient OBJCVG

8 Scaled or unscaled constraint residuals RESCVG

9 Perform a one-dimensional search to determine a search step k so thatxk+kdk is a better approximation of the solution as measured by a linesearch or merit function. The reduction of merit function requirement issometimes relaxed to achieve a full correction step.

10 Update iteration counter, k = k + 1, and loop back to step 3.

Changing DMO ParametersParameters for the solver can be changed with script commands. Entercommands at the kernel command prompt or on the EB scripts sheet in theExcel GUI.

The script language for a parameter change is:

SOLVER SETTINGS parameter = value

The parameters are discussed in the following section. As an example, thefollowing commands:

SOLVER SETTINGS MAXITER = 10

SOLVER SETTINGS RESCVG = 1.0D-5

change the maximum number of iterations to 10 and the residualconvergence tolerance to 1.0D–5. This input would apply for all modes.

Basic DMO ParametersHere are the DMO parameters most commonly used with Aspen PlusCatCracker:

Variable Description Default

MAXITER Maximum number of SQP iterations allowed 50

MINITER Minimum number of SQP iterations allowed 0

CREEPFLAG Creep control flag. This mode makes theoptimizer moves more conservative. It isvery helpful when the problem diverges.

No (0)

CREEPITER Number of creep iterations 10

CREEPSIZE Creep mode step size. This is the fraction ofthe full step to be taken when in creepmode

0.1


Variable Description Default

RESCVG Residual convergence tolerance 1.0D-6

OBJCVG Objective function convergence tolerance 1.0D-6

DMO Command Window Outputand Log FilesDuring each solution, the following iteration log is sent to the commandwindow:

Residual Objective Objective Overall Model

Convergence Convergence Function Nonlinearity Worst Nonlinearity

Iteration Function Function Value Ratio Model Ratio

--------- ----------- ----------- ---------- ------------ -------- ------------

0 1.005D-03 0.000D+00 0.000D+00 9.349D-01 RXRG 9.349D-01

1 6.275D-07 0.000D+00 0.000D+00 9.975D-01 RXRG 9.975D-01

2 2.711D-09 0.000D+00 0.000D+00 1.000D+00 RXRG 1.000D+00

3 0.000D+00 0.000D+00 0.000D+00

Successful solution.

Optimization Timing Statistics Time Percent

================================ ======== =======

MODEL computations 7.69 secs 33.82 %

DMO computations 12.84 secs 56.46 %

Miscellaneous 2.21 secs 9.72 %

-------------------------------- --------- -------

Total Optimization Time 22.74 secs 100.00 %

Updating Plex

Problem converged

Iteration is the count of SQP iterations (QP subproblems) performed bythe solver. There is one line of output for each normal iteration of thesolver. Abnormal iterations may have additional lines for error orinformation messages.

Residual Convergence Function indicates the solver’s progress towardssolution, in terms of feasibility of the residuals. The problem does notconverge until this measure gets below the value of solver settingrescvg defined in the EB script for that solution mode.


Objective Convergence Function is a measure of the solver’s progresstowards solution in terms of optimality of the objective function. This isonly meaningful in modes with degrees-of-freedom, which is only theoptimization mode in Aspen Plus CatCracker. The problem does notconverge until this measure gets below the value of solver settingobjcvg defined in the EB script for that solution mode.

Objective Function Value refers to the Jacobian of the objectivefunction.

Nonlinearity Ratio is a measure of the nonlinearity of the problem. Thecloser the value is to one, the more linear the problem. A negative valueindicates that the problem behaved in the opposite way to what wasexpected. Near the solution, as the step sizes become small, this valuebecomes close to one. There are two nonlinearity ratios – Overall andModel.

The last section of the output shows the execution times for the various partsof the problem.

In this example, we can see that convergence was achieved when the residualand objective convergence functions were less than their respectivetolerances at iteration 3.

From this output, we also see that there have been no line searches. Thus,the step size for each iteration is one. When a line search is performed for aniteration, a message will appear:

<Line Search ACTIVE> ==> Step taken 3.26D-01

If the solver has to line search continually and the step size gets very small(less than 1.0D-2), most likely the solution is trying to move very far from thestarting point, or some of the specified values are nearly infeasible.

DMO Solver Log FilesAspen Plus CatCracker outputs DMO solver information to two log files

ATSLV

ATACT

These files reside in the working directory you defined in the startup menubox.

The ATACT file is similar to the ATSLV file, but lists all the problem variablesand independent variables, whereas the ATSLV file does not. The ATSLV fileis typically more useful and is described in more detail below.

ATSLV File Problem Information

At the top of the ATSLV file, a summary of the problem is printed. This

shows the size of the problem and the values of some important parameters.

Model or plant name RXRG

Solution case SIMULATE

Number of variables 127927


Number of equality constraints 111876

Number of fixed variables 16051

Actual degrees of freedom 0

Number of lower bounded variables 127927

Number of upper bounded variables 127927

Total number of constraints 367730

Maximum number of iterations 50

Printing frequency -1

Objective function tolerance 1.0D-06

Residual convergence tolerance 1.0D-06

Derivative perturbation size 1.0D-06

Solution mode NORMAL

Maximum number of models 3000

Maximum number of soft bounds 1500

Time of run 21:41:58

Date of run 25-NOV-2001

Basic Iteration Information

At each iteration, the following header is printed, showing the iterationnumber and the value of the objective function:

+----------------+

| Iteration 0 |

+----------------+

Objective Function => 0.0000E+00

Largest Unscaled Residuals

This section shows the largest unscaled residuals. A similar section shows thelargest scaled residuals. This section is particularly helpful when the solverhas trouble closing all the residuals because it will list the largest ones.

Shadow

Index Most Violated UNSCALED Residuals Residual Price

====== ======================================= ============ =============

73676 RXRG.BLKEQN_YLDES_TBP_FOE_VALUE_BIAS_CAL 1.81662D+01 -2.37348D-19

108234 RXRG.BLKEQN_CXN_EQN___33328_X(119459)_=> -1.42249D+01 -2.29209D-19

47799 RXRG.BLKEQN_CUT3VF_VAPOR_SPL_FAC_10 1.00000D+00 -8.08521D-16









Constrained Variable

This section shows the variables that lie on their bounds. This is onlymeaningful in a degree-of-freedom mode (optimization for Aspen PlusCatCracker).

The output shows the variable number, which bound is active, the variablename, the current value, and the shadow price. The shadow price is alsoknown as the Lagrange multiplier. This is the derivative of the objectivefunction with respect to the value of the constraint and represents the cost forthe constraint.

Projected Active Constraints Shadow

Index for the Next Iteration Bound Price

====== ======================================= ============ =============

949 Upper Bnd C2SDDEF.SPC.MOLEFR.C2H6 2.00000D-04 -4.32924D+02

The shadow price is based on the value of the objective function that is seenby DMO. That means the shadow price is in SI units (such as $/sec) and isaffected by any scaling. This is true even if you declare the units to besomething other than SI (such as $/hr).

Consider this example. We have a tower with a composition constraint,expressed as a mole fraction of a component. The following table shows theresults of two optimization runs at two different values of the compositionconstraint:

Constraint Value Objective Function Shadow Price

0.0002 2.853 432.924

0.0003 2.893 258.664

The large change in the shadow price indicates that the effect of thecomposition on the objective function is very nonlinear. We can manuallyestimate the average shadow price in this region by a finite differencemethod:

Price = Obj/x = (2.893 – 2.853) / (0.0003 – 0.0002)= 400.00 $/sec/mole fraction

This value lies between the two prices.

If the objective function had a scale factor of 100, we would get the following:

Constraint Value Objective Function Shadow Price

0.0002 285.4 43290.7

0.0003 289.3 25860.2


We would have to remember to unscale the shadow price by dividing by 100.

General Iteration Information

This section appears after the residual output:

Iteration status => Normal

Degrees of freedom => 0

Constrained variables => 0

Current degrees of freedom => 0

Number of function evaluations => 0

Number of Jacobian evaluations => 1

Objective function convergence function => 0.00000D+00

Residual function convergence function => 1.00550D-03

LU decomposition time (seconds) => 7.38D+00

Search direction time (seconds) => 8.28D+00

The Iteration status shows the exit condition of that iteration.

Iteration status Indicates

Normal A normal successful iteration

Warning A successful iteration despite some solver difficulties

Error A failure

Solved The final iteration of a successfully solved problem

The Degrees of freedom is the number of declared independent variables inthe problem. The Constrained variables are the degrees of freedom atbounds in the QP subproblem. The Current degrees of freedom are thedegrees of freedom less the constrained variables. This is the true number ofdegrees of freedom for the problem. A highly constrained solution is one thathas very few current degrees of freedom.

The Number of function evaluations and Number of Jacobianevaluations are accumulative counts and generally match the number ofiterations.

The Objective function convergence function is the norm of the Jacobianfor the objective function. At the solution, this value should be near zero.

The Residual function convergence function is the sum of the scaledresiduals. At the solution, this value should be near zero.

Nonlinearity Ratio

This section shows the nonlinearity ratio of the worst block, the objectivefunction, and the worst equations. The criterion is the accuracy of thepredicted change in the equation. If the function is linear, then the new valuewould match the predicted value and the nonlinearity ratio would be one. Avalue of the ratio other than one indicates some degree of nonlinearity. Anegative value indicates that the function value moved in the opposite of theexpected direction. Large negative values could indicate a discontinuity or badderivative.


This section also shows the step size for the iteration.

Model nonlinearity ratios =>

----------------------------

RXRG = 0.93489

Model nonlinearity ratios of 1 model(s) between 0.99 and 1.01

Objective function nonlinearity ratio => 1.0000

Non-Linearity Report for Iteration 1 : Step Fraction = 1.00000D+00

Index Worst Equation Non-Linearity Ratios Ratio Deviation

===== ======================================== ============ ============

45441 RXRG.BLKEQN_CUT1ANLZ_ABP625A______WTPCT -1.47131D+01 1.57131D+01

47648 RXRG.BLKEQN_CUT3ANLZ_ABP725A2_____WTPCT 1.32713D+01 1.22713D+01

47647 RXRG.BLKEQN_CUT3ANLZ_ABP725A1_____WTPCT 1.32712D+01 1.22712D+01

57609 RXRG.BLKEQN_NAPHSNL_MOLES_ABP325A -7.53478D+00 8.53478D+00

45452 RXRG.BLKEQN_CUT1ANLZ_ABP725A2_____WTPCT -7.29881D+00 8.29881D+00

7 Troubleshooting 111

7 Troubleshooting

Aspen Plus CatCracker StopsRespondingOccasionally, problems can occur where the AspenPlusCatCracker menucommands and toolbar are still active, but the functions fail with various VBerrors. This can be the result of loading too many applications at once,thereby causing an application conflict. The spreadsheet has lost theconnection to the model, but the model is still in the memory of thecomputer. If this happens, the connection to Aspen Plus CatCracker flowsheetcan be reset and then a new connection established. A new connection shouldnot be made until the reset command has been issued.

Resetting Connection to theAspen Plus Server

To reset the connection to the Aspen Plus CatCrackerflowsheet:

Click AspenPlusCatCracker | Startup Aspen Plus CatCracker | ResetApMain as shown below.


To establish a new connection to the Aspen PlusCatCracker flowsheet:

Click AspenPlusCatCracker | Startup Aspen Plus CatCracker | LoadCatCracker Flowsheet.

Error Recovery forParameterizationYou should check the convergence status shown at the top of the Paramsheet after running the parameter case. The results on the Param andAnalysis sheets are only meaningful if the convergence status is converged.If the status is not converged, then you should return the Param sheet andmodel to their pre-solution states.

To return Param sheets and models to their pre-solutionstates:

1 Click AspenPlusCatCracker | File | Load Case Data to restore themodel to a converged parameter case.

2 If this is your first attempt at running a ParamError! Bookmark notdefined. case, then load user_default.var or the . var file created byAspenTech for your site.-or-If you have converged Parameter cases for your unit, then load thecorresponding . var file that most closely represents the processconditions and input data for the new parameter case.

3 Click AspenPlusCatCracker | File | Load User Input Sheet to restore theParam sheet user input.

Examine the input data as compared with the base parameter case.Convergence failure for the Parameter case typically has one of three basiccauses:

4 Poor or erroneous data were entered as input (blue-colored cells). Forexample:


Check that physically realistic property data were entered for all feeds andproducts. For example, all distillation points must increase as a function ofpercent distilled.

Check that physically realistic property data were entered for all catalysts.For example, the ECAT activity must always be lower than fresh activity.

Check that physically realistic mechanical data were entered. For example,the regenerator cyclone height must be greater than the bed height.

5 Some of the input data violate valid ranges. Such restrictions are aconsequence of the equation-based manner in which the model has beenformulated. Observe the following guidelines when entering data:

Do not set any recycle rate to zero. For zero recycle rates, use a verysmall number instead (for example, 0.1 BBL/D).

Fraction to riser bottom: The midriser feed rate must be nonzero. If themidriser feed rate is in fact zero, set the fraction to riser bottom forfeed 1 equal to 0.999999.

Data restrictions for light-ends analyses:

Compositions for any one stream must not sum to zero, includingstreams having a zero flow rate.

For the light and heavy naphtha streams, all C5+ components must benonzero, again including any stream having a zero flowrate.

For any one component, the sum of its composition across all streamsmust not be zero.

Do not enter zero for any flue gas component.

6 The solver parameters are too aggressive for the data entered. Forexample, a large change in feed rate (greater than 15%) may requiremore conservative solver parameters. For more information about solverparameters and strategy, see Changing DMO Parameters.

Error Recovery for SimulationCheck the convergence status shown at the top of the simulation sheet afterrunning the simulate case. The results on the simulation sheet are onlymeaningful if the convergence status is converged. If the status is notconverged, then you should return the simulationTo return simulation sheetsto their pre-solution states:

1 Click AspenPlusCatCracker | File | Load Case Data to restore themodel to the base Parameter case.

2 Browse for the .var file in which you saved the results of the baseParameter case.

3 Click AspenPlusCatCracker | File | Load User Input Sheet to restorethe Simulation sheet user input.

Examine the input data as compared with the base Parameter case.Convergence failure for the simulation case typically has one of two basiccauses:

4 Poor or erroneous data were entered as input (blue-colored cells). Forexample:


Check that reasonable feed property data were entered for all feeds.

Check that reasonable catalyst property data were entered for allcatalysts.

Check that the cut points entered for light naphtha and LCO are physicallypossible.

5 The solver parameters are too aggressive for the data entered. Forexample, a large change in feed rate (greater than 15%) may requiremore conservative solver parameters. For more information about solverparameters and strategy, see Changing DMO Parameters.

Solver PerformanceThis section describes some troubleshooting tips to improve the performanceof the solver and to help diagnose common problems.

Dealing with Infeasible SolutionsThese often occur during optimization cases where it is not possible tosimultaneously solve all the equations while respecting all the variablebounds. This doesn't happen in simulation cases because DMO ignores boundsin simulation cases. If you solve a simulation case that violates a bound, thenthe optimization case will start at an infeasible point. A message like thefollowing will be printed in the ATSLV file:

Information => QP step for variable 1157: C2SDDEF.SPC.MOLEFR.C2H6

was adjusted to satisfy its UPPER bound = 2.0000000E-04

The size of QP step violation was = 2.5673465E-04

This variable's value had to be adjusted to respect the bound. When theoptimization proceeds and there is no feasible solution for the equalityconstraints, the screen output might look like this:

Residual Objective Objective Overall Model

Convergence Convergence Function Nonlinearity Worst Nonlinearity

Iteration Function Function Value Ratio Model Ratio

--------- ----------- ----------- ---------- ------------ ------- ------------

Warning ... QP slack variable = 2.29070D-01


0 9.312D-04 4.809D-03 -2.779D+00 9.968D-01 C2S -2.834D-01



1 5.244D-04 4.667D-02 -2.792D+00 2.900D-01 C2S -1.846D+02



2 1.552D-02 5.479D-02 -2.922D+00 -7.475D-01 C2S -1.540D+01



3 3.853D-02 2.379D-03 -3.083D+00 9.908D-01 C2S 9.914D-01




4 1.496D-02 1.040D-02 -3.075D+00 8.346D-01 C2S 6.012D-01



+---------------------- ERROR ----------------------+

Error return from [DMO] system subroutine DMOQPS

because the problem has NO FEASIBLE SOLUTION.

Action : Check the bounds that are set on variables

to insure consistency. Check the .ACT file

for information on initial

infeasibilities.

+---------------------------------------------------+

Error return, [DMO] System Status Information = 5

Optimization Timing Statistics Time Percent

================================ ======== =======

MODEL computations 1.32 secs 31.10 %

DMO computations 0.91 secs 21.28 %

Miscellaneous 2.03 secs 47.61 %

-------------------------------- --------- -------

Total Optimization Time 4.26 secs 100.00 %

Updating Plex

Problem failed to converge

Note the messages from the QP indicating an invalid value for a slackvariable.

To solve this problem, you need to be aware of the initial message indicatingthat the initial value of a variable violated its bound. In this case,C2S.SPC.REFL_RATIO_MASS is causing the problems. Unfortunately, theATSLV file does not list this variable as constrained, since it could never solvethe QP successfully.

ScalingGenerally, it is not necessary to scale your equations or variables beyondwhat is done by default in the models. However, it may be more efficient to


scale your objective function. A good rule of thumb is to scale the objectivefunction so that its value is on the order of 10 to 1000. The scaling of theobjective function plays an important role since it affects the overallconvergence behavior. This is particularly important in cases where there is alarge change between the original value of the objective and the expectedoptimum.

Dealing with SingularitiesSingularities often occur when the model is moved into a region where theequations are not well defined. The most common example of this is when astream flow becomes too small. If singularities exist, they are usuallydetected at the start of the problem. In this case, some information is writtento the ATSLV file and this can help locate the cause of the problem. Ingeneral, you should prevent stream flows from going near zero by placingnonzero lower bounds on the flow (for example, 10 kg/hr). This is especiallyimportant on streams from flow splitters or feed streams whose total flow isbeing manipulated. In the case of a singularity the following message will bedisplayed:

+-------------------- WARNING ----------------------+

A NUMERICALLY SINGULAR matrix is detected during

the ANALYSIS phase of LU decomposition.

The number of dependent equation set(s) detected = 1

Check the output file for more information.

+---------------------------------------------------+

The ATSLV file contains information on the possible cause of the singularity inthe following manner:

+-------------------- WARNING ----------------------+

A NUMERICALLY SINGULAR matrix is detected during

ANALYZE phase of LU decomposition.

WARNING: The dependent equation set is NOT unique.

It depends on the options for performing

LU decomposition.

==> Dependent equation set: 1

The partial derivatives of the following

equations with respect to variable


1: Strm 1 moles lbmol/h

in the reduced matrix are zero.

Equation -> 10: Enthalpy balance M Btu/lbmol

is a function of the following variables:

1: Strm 1 moles lbmol/h = 0.00000D+00 -> Calc

4: Strm 1 enth M Btu/lbmol = -7.45977D+01 -> Const

12: Strm 2 moles lbmol/h = 0.00000D+00 -> Const

15: Strm 2 enth M Btu/lbmol = -7.45977D+01 -> Const

23: Heat loss MM Btu/h = 0.00000D+00 -> Const

25: Prod moles lbmol/h = 8.93760D-07 -> Calc

28: Prod enth M Btu/lbmol = -7.45977D+01 -> Calc

Equation -> 9: Prod C9H20_1 mf

is a function of the following variables:

1: Strm 1 moles lbmol/h = 0.00000D+00 -> Calc

10: Strm 1 C9H20_1 mf = 4.52017D-01 -> Const

12: Strm 2 moles lbmol/h = 0.00000D+00 -> Const

21: Strm 2 C9H20_1 mf = 4.52017D-01 -> Const

25: Prod moles lbmol/h = 8.93760D-07 -> Calc

34: Prod C9H20_1 mf = 4.52017D-01 -> Calc

Sometimes, singularities are simply caused by the optimization being tooaggressive. This moves the models into a region where the equations are notwell defined. To make the optimization more robust, DMO has a creep mode.This mode simply causes smaller steps to be taken for a specified number ofiterations. To use this mode, you can enter the following script command:

SOLVER SETTINGS CREEPFLAG = 1

This turns on the creep mode. When active, the following message isdisplayed at each iteration:

<Line Search Creep Mode ACTIVE> ==> Step taken 1.00D-01

By default, this will operate for 10 iterations with a step size of 0.1. You canchange these values with the commands:

SOLVER SETTINGS CREEPITER = 20

SOLVER SETTINGS CREEPSIZE = 0.5

In this example, we change the number of creep iterations to 20 and the stepsize to 0.5.


Notes on Variable BoundingRemember that by default DMO does not respect bounds during the solutionof a Simulation or Parameter case. You, however, have the capability toimpose bounds in a square case by using a different line search parameter.The use of this mode is recommended only in cases where

There are truly multiple solutions to a model (for example, the cubicequation).

You want to use a bound to eliminate an unwanted solution.

To use this mode, you can enter the following script command:

SOLVER SETTINGS LINESEARCH = 4

In general, it is not recommended to heavily bind an optimization problem forreasons that are both practical and algorithmic. Bounds on independentvariables are recommended in order to avoid unbounded problems. All otherbounds should be used only if they are absolutely necessary. Finally,redundant bounds should be avoided.

Run Time InterventionDuring long runs, it is possible to change the behavior of the DMO solver. Thisis done by clicking one of the three buttons at the bottom of the commandwindow. The selection will take effect at the start of the next DMO iteration.For more information on these buttons, see Command Line Window.

The Model Is Not SolvingIf the new data are very different from the starting point, it may be difficultfor the model to solve. If the residuals are very large and the non-linearity isvery poor, it is possible that the model will be unable to solve. Rather thanwaiting for a large number of iterations, you can terminate the solution byclicking the Abort button on the Command Line window. This will stop themodel from solving, but not reset the memory to the starting point before asolution was attempted. It is possible that a saved solution will need to beloaded into memory so that the model will be able to reach a solution. For thisreason, it is very important to save parameter case results using the SaveCase Data command, so that you can load in a valid starting point withoutneeding to use the Reset ApMain option previously discussed.

After re-loading good data from a saved file, try running the failed case againwith an increased number of creep iterations. Review the section Saving andLoading Case Data.

Licensing ErrorsThe following error message may appear if the Aspen Plus license verificationfails.


Message Error in ConnectServer(), module Com2Dcom.Error message:Unable to load simulationengine. License check out error.

Cause The Aspen Plus license was not found when attemptingto connect to the Aspen Plus CatCracker flowsheet.

Solution Check to make sure that the license server or thelicense file has been selected properly. See theLicensing section of the Aspen Engineering SuiteInstallation Manual for more information.

Ensure that the licenses for Aspen Plus, Aspen Plus EOOptimizer, and the Aspen RXfinery application havebeen entered into the license server or are located inthe license file.

The following error message may appear if the Aspen Plus CatCracker licenseverification fails.

Message ****EXECUTION ERROR WHILE EVALUATINGRESIDUALS FOR UNIT OPERATIONS BLOCK:

"RXRG" (MODEL: "USER3")LICENSE VALIDATION/CHECKOUT

FAILURE FOR ASPEN PLUS CATCRACKER

Cause The Aspen Plus CatCracker license could not be found inthe license server or license file selected.

Ensure that the license key for Aspen Plus CatCrackerhas been entered into the license server or is located inthe license file. See the Licensing section of the AspenEngineering Suite Installation Manual for moreinformation.

8 The FCCU Model 120

8 The FCCU Model

OverviewThe offline model for the CatCracker is a complete system for modeling anCatCracker. It includes a feed system, a regenerator, a reactor, slide valves,risers, standpipes, and cyclones. Furthermore, it contains an approximaterepresentation of a gas plant. This simplified gas plant (GSP) is suitable forobtaining quantitative estimates of the gas-plant products fractionated fromthe reactor effluent. The CatCracker model also includes a number of modelsto account for coke formation and its transmittal through the mass flowpaths. Models for handling the distribution of feed sulfur and nitrogen amongthe gas plant products are also provided.

Twenty-One-Lump KineticsRiser conversion kinetics are derived from the Mobil ten-lump mechanism.Aspen Plus CatCracker has expanded the number of reactant/product lumpsto 21 and changed the functionality of several key lumps. The reactionsthemselves are all based on well-understood first order kinetics that all occurin the vapor phase. The kinetic expressions are integrated along the length ofthe riser and are dependent on the catalyst bulk density, coke on catalyst,MAT activity, basic nitrogen, and metals content. The MAT activity and basicnitrogen are entered from external model sources and affect the riser kineticsuniformly. The catalyst bulk density and coke on catalyst are also integratedalong the riser length and are themselves a function of pressure drop, cokemake, and molar expansion. The pressure drop includes elements of head,friction, and acceleration.

All kinetics in the reactor are based on the 21-lump kinetic system. Thereaction pathways represent paraffinic cracking, naphthenic ring opening,alkyl side chain cracking, ring condensation, kinetic coke make from typicalcondensation reactions, and metals coke make due to dehydrogenation. Thereaction paths have been logically grouped to make yield parameterizationmore convenient. Thus all the pathways which lead to gas make up one class,the gasoline pathways make up another class, and so on. In this way, withonly a small number of yield measurements off the operation unit, the kinetic


rate parameters for the more than fifty reaction pathways can be easily tunedto match the unit yields. To match the specific product compositions that areobserved on the unit (provided that information is available), additionaltuning of paraffinic and aromatic reaction rates must be performed.

This system divides the reactants and products into lumped aggregates ofmaterial classified by chemical type and boiling point range. These lumps aresimilar to pseudo-components but are based on molecular structure inaddition to the boiling range for typical pseudo-component breakdowns. Themolecular structures selected are based on likely reaction pathways andmechanisms understood to exist in fluid catalytic cracking chemistry. Thetable below summarizes the lumps used in the model. These lumps areclassified into paraffinic, naphthenic and aromatic chemicals and each ofthese types is divided into four boiling point ranges as shown in the table.Aromatics are further divided into substituent carbons and ring aromaticcarbons.

The components were also selected to represent convenient boiling rangesthat represent yields of light gases, gasoline, light cycle oil, heavy cycle oil,and the main fractionator bottoms (which also include any remaining resid).The light gas components represent all light gases from H2 to C5 The gasolinecomponent represents the component range from C5 to 430 °F.

There are three lumps that are not identified with a particular chemical type:

C lump

Kcoke lump

Mcoke lump

The C lump is used to calculate the light gases for methane through thepentanes. This is based on a correlation using the C lump produced in thekinetic paths and the composition of the feed. Kcoke is kinetic coke, the cokeroutinely produced through cyclization and condensation pathways. Mcoke ismetals coke, the coke produced as a by-product of dehydrogenation reactionscaused by the presence of active Ni equivalent on the catalyst.

Twenty-One Lump Model

No. Lump NBP Range Description

1 C C lump – produces light gases

2 G < 430 °F Gasoline Lump C5

3 Pl 430 – 650 °F Light Paraffins

4 Nl Light Naphthenes

5 Ar1l Light 1-Ring Aromatics

6 Ar2l Light 2-Ring Aromatics

7 Asl Light Aromatic Ring Substituent Carbons

8 Ph 650-950 °F Heavy Paraffins

9 Nh Heavy Naphthenes

10 Ar1h Heavy 1-Ring Aromatics



13 Ash Heavy Aromatic Ring Substituent Carbons

14 Rp > 950 °F Resid Paraffins


No. Lump NBP Range Description

15 Rn Resid Naphthenes

16 Ra1 Resid 1-Ring Aromatics



19 Ras Resid Aromatic Ring Substituent Carbons

20 Kcoke N/A Kinetic Coke

21 Mcoke Metals Coke

The aromatic carbon classification helps to account for those carbons that canbe cracked into the gasoline range material and those that do not crack aseasily. Ring carbons are those carbons that make up the aromatic structureand, therefore, are less likely to crack into lighter material. Instead, theyparticipate in ring condensation reactions that eventually can lead to cokeformation on the catalyst. Substituent carbon atoms are the paraffinicsubstituent atoms on the core aromatic structures. They include paraffiniccarbon chains of varying lengths and combinations that are distributed aroundthe core aromatic structures.

The table above illustrates how the chemicals going into the CatCrackermodel are lumped. First, there is a division by boiling point. Then, there is adivision by chemical type:

Paraffinic

Naphthenic

Aromatic

The aromatics are further broken down into substituents and core, or ringcarbons. Therefore, a chemical such as n-butylbenzene has 6 core C atomsand 4 substituent carbon atoms. Carbons in hydroaromatic structures, wherea saturated ring is fused to an aromatic ring, are counted as substituentcarbon atoms. Tetrahydronaphthalene is an example of a hydroaromaticstructure.


Schematic for the 21-Lump Reaction Paths

The lumped species participate in a heterogeneous reaction network oftemperature and catalyst dependent pathways. This network of kineticpathways is shown above

In this figure, each arrow proceeding from one species to another representsa kinetic path. Since the reaction rates are represented by Arrhenius typeexpressions, each path has associated with it a frequency factor andactivation energy. Within the kinetic system, the C lump component is divideddirectly into ten individual light-gas components and coke. This 21-lumpmodel also carries along a separate coke lump that includes coke brought inwith the feed.

Direct resolution of the C lump into the light chemical species is accomplishedby a correlation adapted for the 21-lump model. For online optimization,these correlation coefficients are treated as parameters and fit to anymeasured data that exist for these species.

This data may be in the form of analyzers, inferentials, or laboratory Gas-Liquid-Chromatography (GLC) data for the light products. These productsgenerally include the dry gas, depropanizer overheads, and debutanizeroverheads. They are represented by the chemicals:

1 Hydrogen

2 Methane

3 Ethylene

4 Ethane

5 Propylene

6 Propane


7 Iso-butane

8 Butenes

9 n-Butane

10 Iso-pentane

11 Pentenes

12 n-Pentane

Light and Heavy Lump Types

After the amounts of these chemicals are determined from the correlation, theriser effluent is split up into even finer compositional detail. This split of theC4=, C5=, iC5, and the C6 to 430 °F gasoline are split into the isomers listedbelow. The amount of each isomer created is determined by fixed ratios orsplit factors. The ratios are tuned to match a particular unit by adjusting splitfactors for each isomer. The source component, split components, and splitfactors are determined in a parameterization run.

Isomer Creation from Split Factors

Source Component Split Out Components

C4= Iso-butene1-ButeneCis-2-buteneTrans-2-butene1,3-butadiene

iC5 Iso-pentaneCyclo-pentane


Source Component Split Out Components

C5= 3-methyl-1-butene1-Pentene2-Methyl-1-buteneCis-2-penteneTrans-2-pentene2-Methyl-2-buteneCyclo-penteneIsoprene (2-methyl-1,3-butadiene)

C6-430 G Lump BenzeneC6-430 G Lump (no benzene)

Sulfur DistributionIn the CatCracker model, feed sulfur is distributed into standard andfractionated products based on reaction and fractionation models. The modelcontains methods for distributing the sulfur by boiling point. Thesedistributions permit the prediction of sulfur in the various products created bythe GSP.

Sulfur entering the CatCracker unit is defined by the following for each freshfeed:

Fresh feed rate

Fresh feed sulfur content as wt%

Feed sulfur crackability factor

The fresh feed rates and sulfur contents define the total rate of sulfur enteringthe CatCracker. The individual fresh feed data is mass blended to produceblended values for the sulfur content and crackability factor.

The sulfur crackability factor defines the propensity of the sulfur to crack toH2S or remain as compounds in heavy liquid products. This factor rangesfrom zero to one. Zero will maximize cracking to H2S. One will minimizecracking to H2S and force the sulfur to appear in the heavier liquid products.For example, virgin gas oil will have a value of zero since most of its sulfurwill crack to H2S. On the other hand, a hydrotreated gas oil will have a valueof one, since most of the easily-crackable sulfur has been removed by thehydrotreater and the remaining refractory sulfur will pass through theCatCracker and appear in cycle oil cuts. The intent is to provide a factor thatshows the difference between alkyl sulfides and thiophenes in the feed.Sulfides tend to crack to H2S while thiophenes remain in high molecularweight structures that concentrate in the cycle oils.

In reaction models, sulfur is distributed into the following standard products:

H2S

C5 to 430 naphtha

430 to 650 LCO

650+ bottoms

Coke (burned to SOX in the regen model)


Correlations distribute feed sulfur into these standard reactor products. Thesulfur contents of these products and the % distribution of feed sulfur intothese products are reported on the Simulation and Analysis worksheets.

The sulfur in the C5-430, 430-650 and 650+ reactor products is furtherdistributed into the following fractionated products by the simple fractionationsystem in the model:

Light naphtha

Heavy naphtha

LCO

HCO

Bottoms

The standard product sulfur content is distributed across a sulfur assayspanning over 100 real and pseudocomponents in the simple fractionationmodel. With this sulfur assay, the individual product sulfurs are developedfrom stream compositions flowing from the separation correlations in thefractionation model. In this way, the product sulfurs show the impact ofcutpoint and overlaps in the real products.

In a parameter case, the real product flows and sulfur contents are input andused to deduce the standard product sulfur contents. The resulting standardproduct sulfurs can then be examined for reasonableness. In simulation cases(simulation, case study, optimize), the reactor correlations predict thestandard product sulfurs that are distributed into the fractionated products.

The standard CatCracker model is setup to represent five real products aslisted above. Even if some of these streams (for example, heavy naphtha orHCO) do not exist for the current model, reasonable sulfur values must beentered for these streams that make sense when compared to the existingstreams: light naphtha, LCO, and bottoms.

Coke Production and HandlingCoke make is separated into five distinct categories:

Kinetic coke

Metals coke

Conradson carbon feed coke

Non-vaporized feed coke

Stripper source coke

The Conradson carbon coke and non-vaporized coke are assumed to bephysical types of coke and are therefore deposited on the catalyst at theentrance of the riser prior to any cracking or coking reactions. Kinetic cokeand metals coke are both determined from kinetic expressions and aredeposited on the catalyst gradually as reactions proceed through the riser andreactor. The stripper source coke is determined from the cat/oil ratio andstripper performance curves.


Kinetic CokeKinetic coke make is calculated by the following Arrhenius-type equation:

Rate (mol feed/hr/vol) = Af * Ai * exp(-Ea/RT)

Where, for kinetic coke:

Variable Corresponds to

Af A frequency for the conversion of 3-ring aromatics to coke

Ai A collection of activities including catalyst activities

Ea/R An activation energy for the conversion of 3-ring aromatics to coke

T Temperature in °R

In Parameter cases, a parameter associated with the coke activities isdetermined from a set of test run data from the CatCracker. This parameter isa linear multiplier on the kinetic coke rate.

The 21-lump reaction path schematic shows all of the paths that producekinetic coke. Each of these paths has associated with it an Arrhenius type rateexpression. Currently, not all of the paths that produce kinetic coke are used.The paths that are in use reflect the conversion and involve the followinglump types: Nl, Ar1l, Ar2l, Asl, Ph, Nh, Ar1h, Ar2h, Ar3h, Ash, Ra1, Ra2, Ra3,Ras.

Metals CokeMetals coke make is calculated by the following equation very similar to thatused for kinetic coke:

Rate (mol feed/hr/vol) = Af * Ai * exp(-Ea/RT)

Where Af and Ai are defined similarly to the kinetic coke activities except thatAi has a dependence on the active metals on the catalyst. The term Ea/R isdefined by the constant for the 3-ring aromatic conversion to metals coke andT is temperature in °R.

A parameter is adjusted in a Parameter case to match test run data. It is alinear multiplier on the metals coke rate.

Feed Source CokeFeed source coke is determined from the Conradson carbon residue analysis.The CCR in wt % for all of the feeds is blended on a mass basis and then theblended feed (including any recycles) CCR is entered into the riser model. Theriser model contains coke deposition factors due to CCR. There is a riser CCRfactor that can be adjusted to control the deposition of coke. The defaultvalue for this deposition factor is 0.5 and may be reset if analyses indicatethat the default value is not suitable.

Stripper Source Coke (Occluded Coke)The stripper source coke is defined as the hydrocarbon entrained with thecatalyst in the stripper and is then transferred to the regenerator where it


appears as coke and is burned. This stripper coke is relatively high inhydrogen content and this gives a much higher heat of combustion than thefeed and kinetic sources of coke. Therefore, it is much more detrimental tothe regenerator bed temperature, resulting cat/oil ratio, and finallyconversion. Also, the stripper source coke has roughly the same compositionas the reactor effluent (50% of the hydrocarbon is highly valued gasoline).

For information on fine-tuning the stripper model, refer to Heat BalanceTuning.

Initial Vapor Entrainment

The amount of vapor entrained with the catalyst at the top of the stripper willdetermine how hard the stripper will have to work to reduce the hydrocarboncarried over to the regenerator. In essence, if the stripper operatingconditions (pressure, temperature, and steam rate) were held constant whilethe amount of hydrocarbon entrained at the top of the stripper increased, theamount of hydrocarbon carried over to the regenerator as coke wouldincrease.

The entrained vapor rate is indicated by the parameter variableRXSZ_VEffl_Per_Mass_Cat_In in units of (volume of vapor effluent)/(massof catalyst). This variable is normally used as a parameter and is determinedby a preconceived notion (estimate) of the stripper efficiency (variableRXSZ_Stripping_Eff would thus be a measurement at a typical estimatedvalue of 85%). The efficiency variable is defined as the percent ofhydrocarbon entering the stripper (from the top) which is removed by theaction of the stripper.

Stripper Performance Curve Slope

The stripper performance curve is an arbitrary function that is asymptotic atvery high steam/catalyst ratios. The efficiency increases with steam/catalystratio, but as the efficiency approaches 95%, the rate of efficiency increasebegins to taper off. The slope of the curve, that is (delta efficiency/ deltasteam/ catalyst), at efficiencies less than 95% can be changed by setting theslope for the performance and then re-running Aspen Plus CatCracker inparameter mode. A typical value for the slope is 0.5 to 1.0. A higher value ofslope will make the stripper more sensitive to process changes. In otherwords, when the catalyst circulation rate is increased, the incremental amountof coke produced will be larger when the slope term is higher.

Material Balance ReconciliationThe CatCracker model performs mass balances in two different waysdepending on the run mode.

In a fitting run (Parameter case), the light naphtha (or debutanizer bottoms)yield is calculated by difference.


In a predict run (Simulation, Case Study, LP vector, or Optimization mode),the fresh feeds are distributed among the products in a simultaneous solutionof reaction and heat balance expressions.

In a parameter case, the mass balance is as follows:

The fresh feed rates are constant.

Coke is calculated from air and flue gas data.

H2S is calculated by difference since feed, naphtha, cycle oil, and SOXsulfur are specified.

Pure components H2 through the C5 and C6 components are specified.

Heavy naphtha, LCO, HCO, and bottoms yield are specified.

Light naphtha is by difference.

The parameter case mass balance is displayed at the top of the Analysissheet. A positive bias means the feed rate is too low to match the inputyields. The bias is the difference between the input light naphtha rate and theadjusted light naphtha rate calculated to force the mass balance.

On the Param worksheet, the light ends yields are entered once for the purecomponents using GLC information. However, the heavy ends yields(naphthas and cycle oils) are entered twice. The first table is used to generatereaction parameters. The second table is used to generate separationparameters in the simple fractionation model. The light naphtha yield is usedin the first table to calculate the measured light naphtha yield. The lightnaphtha yield is not entered in the second table since this is the adjustedyield. The mass balance bias is the difference between these two flows. Thismethod of parameter case mass balancing is the default system for theCatCracker model. In a predict run (simulation, LP vector, case study, oroptimization), the model performs mass balances in a complex simultaneoussolution of the reactor and fractionation expressions.

FCCU Model ConfigurationThe CatCracker model is made up of building blocks that model thecomponents in the CatCracker. These components include risers, slide valves,and standpipes along with the regenerator and the reactor. Riser modelssolve the kinetic equations along the riser simultaneously with the equationsrepresenting hydraulics and heat effects. In addition, the models describecoke lay down and entry zone effects. The pressure balance throughout thereactor, regenerator, and connecting components is maintained. Pressuredrops are calculated for risers, standpipes, and slide valves. Throughout thereactor models, the catalyst stream flow includes mass flow, temperature,pressure, heat capacity (catalyst + coke mixture), particle density (catalyst +coke mixture), coke on catalyst weight fractions and coke constituents (C, H,O, N, S) as atomic weight fractions.

This section discusses briefly the important building blocks of the CatCrackermodel. It first reviews the 21-lump model and then presents material on themajor blocks of the CatCracker.


RisersRiser models consist of six key ingredients:

Riser configuration

Pressure drop

Hydraulics

Heat effects

Coke laydown effects

Entry zone effects

The riser model is a segment of the fluidized riser that models the kinetics inthe riserand includes the geometry of the riser for hydraulic and volumeeffects. It takes the hydrocarbon feed after the nozzle exit and combines itwith the regenerated catalyst to take the material to the reactor.

Two-phase pressure drops are calculated through the riser for both verticallyand horizontally configured risers. These orientations use differentcorrelations for hydraulic effects and pressure drop calculations. An angle ofincline may also be used for the horizontally oriented models. A pressure dropthrough the riser is calculated from three different components: acceleration(kinetic energy), frictional effects, and gravitational effects. Proper tracking ofhydraulic and pressure effects is necessary to model the changes in local bulkdensity correctly. These changes interact with the kinetics along the riser.

The chemistry in the risers is endothermic and uses the heat generated in theregenerator for the chemical transformations. This process is tracked alongthe length of the riser and is manifested in the temperature profiles printed inthe detailed riser reports. In these profiles, the temperature of thehydrocarbon catalyst mixture gradually drops from the entry zone to the riserexit into the reactor. These temperature drops are used in the models todetermine catalyst flow rates. The net balance of the heat transfers issummarized in the cracking parameter. This parameter is printed in customreports for the risers. If all properties and calculations were without error, thecracking parameter would be zero. Generally, it is not zero, but a relativelysmall number less than about 10 to 20.

Coke laydown is differentially accounted for by the kinetics along the length ofthe riser and the additional solids are transferred from the vapor phase to thesolid phase. These effects are manifested by the increase in the mass offlowing solids, decrease in the mass/moles of vapor and the changes in theproperties of flowing catalyst and hydrocarbons. As coke builds up on thecatalyst, deactivation functions are used to lower the activity of the catalyst.A molar heat of adsorption accounts for heat effects accompanying the cokelaydown. Its counterpart, the heat of desorption, is used in the regeneratorwhere the coke is burned. Coke is represented by a combination of H and C inthe molar ratio of ½ to 1. This ratio can be changed in the model if desired.

The riser/reactor system can be configured from the spreadsheet in thefollowing ways:

Feed injection points. Fresh feeds and recycles can be injected at thebottom of the riser or at a mid-riser injection point. Each feed and recyclecan be split independently to each injection point.


Steam injection. Steam can be injected into the lift riser, at the bottom ofthe riser and at the mid-riser point.

Lift gas. Lift gas assumed to be 100% N2 can be injected at the lift riser.

Riser dimensions. Enter riser diameter and length.

Reactor dilute phase dimensions. Enter dilute phase diameter and height.

The riser/reactor system consists of three models connected in series asfollows:

1 Lift riser

2 Riser first section

3 Riser second section

The lift riser performs a mass and heat balance with pressure dropcalculations but no reactions. Its purpose is to mix hot regen catalyst withsteam and/or lift gas injection and pass this mixture to the first riser section.

The riser consists of two sections in series. The two riser sections performmass balance, heat balance, pressure drop and reaction calculations. Theriser is split to allow the injection of mid-riser feeds, recycles, and steam. Thelength of the first section defines the distance between the riser feed injectionnozzles at the bottom of the riser and the mid-riser injection nozzles. If nomid-riser injection is present, simply split the riser into two sections about thesame length with zero flow to the mid-riser nozzles.

The dimensions of the lift riser are usually clear with a well-defined diameterand length. The inlet is where the steam, lift gas, and catalyst mix. The outletis at the riser feed injection nozzles.

Riser dimensions are also usually clear. For modern CatCracker units, thelength is about 100 feet, and the diameter should produce inlet superficialvelocities in the 20 to 40 fps range. Ultimately, the dimensions shouldgenerate vapor and catalyst residence times in the range of 3 to 6 seconds forboth riser sections combined. The residence times and superficial velocitiesare reported on the Analysis sheet.

ReactorThe reactor model consists of three primary submodels. As the hydrocarbonmixture enters the reactor vessel, a process of disengagement of thehydrocarbon and catalyst begins. Cyclone models are the final stage of thisdisengagement at the top of the reactor. Material entering the cyclone modelsarrives there from the reactor free-board area. This area is represented by amodel that sends material, primarily catalyst, to the dense bed of the reactor.From there the material enters the stripping zone where steam is used toremove as much of the remaining hydrocarbons as possible from the catalystbefore it enters the spent catalyst transfer line.

Cyclone models use a parameterized, load-based calculation to entrain afraction of the effluent hydrocarbon vapor with the catalyst. This entrainedcatalyst is sent to the dense bed model. The fraction of the hydrocarbon notentrained is sent to the overhead line of the reactor and to the delumpermodel. It ultimately goes to the MF as a set of defined chemicals andpseudocomponents.


The reactor dense bed model is a differential-algebraic model that modelsperforms a single catalytic cracking reaction for the low concentration ofhydrocarbons in the catalyst bed. It also performs a DP calculation across theheight of the bed. This height can be set using pressure measurements in theplant are be specified directly in the model. In the latter case, the DP iscalculated.

The outlet products of the reactor that proceeds to the stripping zone are thecatalyst and kinetic coke, and a portion of the entrained hydrocarbon vaporthat came down with the catalyst. Further cracking of the hydrocarbonsoccurs in the dense bed and some of this material along with stripping steamproceeds to the cyclone. There it mixes with the riser effluents that did notentrain with the catalyst.

Heat balances are performed at each point of mixing in the above coupledsystem of cyclones, free board, and dense bed. These balances yield differenttemperatures at each point in the system: riser outlet (cyclone inlet), densebed, and reactor vessel plenum (the final effluent).

The reactor dilute phase performs mass balance, heat balance, pressure dropand reaction calculations. The dilute phase model represents the reactionvolume that exists between the outlet of the riser and the inlet to the reactorcyclones.

Reactor dilute phase dimensions are murkier. Modern CatCracker units have avariety of proprietary designs that attempt to reduce this residence time tonear zero. The dilute phase model assumes a simple cylindrical geometry witha diameter and length set to arbitrary values to usually provide a low vaporresidence time, that is, less than one second. Further, the model contains acatalyst splitter to divert catalyst away from the dilute phase and straight tothe catalyst stripper model. Using the diameter, length, and catalyst splitratio, you can approximate the performance of the reactor dilute phasesection. A smaller volume and high catalyst split ratio will minimize theimpact of the dilute phase section on model predictions.

RegeneratorLike the reactor, the regenerator consists of submodels, in this case theregenerator dense bed, the freeboard (disperse phase), and the cyclones.Each of these submodels performs heat balance, material balance andpressure drop calculations.

The regenerator dense bed models a bubbling bed with heterogeneous cokeburn and heterogeneous and homogeneous CO to CO2 burn. At the inlet, thefollowing are processed:

Spent catalyst

Lift air

Regenerator air (from the main air blower with O2 enrichment)

Cyclone separated catalyst

It produces at its outlet the following:

Regenerated catalyst (to the standpipe models)

Entrained catalyst (to the free board model)

Combustion gas


Catalyst holdup, or inventory, may be specified or calculated by specificationof bed height and regenerator geometry. This is an important component ofthe pressure balance calculation. The effects of air rate or catalyst circulationdepend on how the catalyst holdup is specified. If the bed height is fixed,then the catalyst inventory will change. If the inventory is fixed, then the bedheight will change. Since the height of the regenerator is fixed by its physicaldimensions, it follows that when the dense bed height is allowed to vary, thefree board height will vary. These height changes affect the coke burn and areaccounted for in the model calculations.

The freeboard model represents the section of the regenerator between thetop of the dense bed and the inlet of the cyclones. Its inlet is the entrainedcatalyst from the dense bed and the dense bed combustion gases. It producesfor its outlets the freeboard combustion gases and catalyst stream to thecyclones. The freeboard model is a plug flow reactor that continues theheterogeneous coke burn and the homogeneous CO to CO2 burn (afterburn).Since there is little catalyst in the freeboard region, further coke burnreactions can produce large temperature changes from the freeboard to thecyclone inlets.

The regenerator cyclone model performs a two-phase, loading-based DPcalculation for the cyclones. It returns all of the entrained catalyst to theregenerator dense bed. This sets up a recycle of catalyst that can alter thesteady-state level of coke on regenerated catalyst and the dense-bedtemperature. It reports flue gas compositions on a standard Orsat dry-molepercent basis.

Stripping Zone ModelThe stripping zone model performs the heat, mass, and pressure balancecalculations around the stripping zone. Its inputs are the stripping steam andthe spent catalyst with kinetic coke from the reactor dense bed. It calculatesthe stripping steam to the dense bed, the stripped, slightly cooled catalyst,and the portion of the stripping team going into the standpipe and then intothe regenerator.

This model uses a correlation to account for the hydrocarbons stripped fromthe catalyst on its way back to the regenerator. This correlation is in the formof a parameterizable stripping efficiency curve. It makes use of the mass-ratioof catalyst flow to the stripping steam flow. The lower this ratio, the betterthe stripping. As hydrocarbon is stripped away, the H to C ratio drops. In thecorrelation, when the stripping efficiency decreases, the H to C ratioincreases.

Catalyst Standpipe, Slide Valve andTransfer LineIn the plant, these units transport the spent catalyst with coke deposits backto the regenerator. In the model, these units serve this purpose byestablishing the links to the catalyst in the reactor. However, their primarypurpose in the model is to set up the pressure profiles that drive the catalystback to the regenerator. Pressure changes in the vertical standpipe as thecatalyst goes to the slide valve are substantial. The hydraulics of this type of


flow are modeled in this unit. In the transfer line the flow regime is different,calling for a different set of calculations for the pressure changes.

CatCracker Nozzle SystemThe nozzle system mixes feed with the hot catalyst and removes heat fromthe catalyst to heat and vaporize the feed. In the 21-lump model, this processis complicated by the process of converting from the detailed component listto the 21-lump components used in the R/R system. All flashes are based onthe detailed component list. Once the transfer of energy from the catalyst tothe full feed is determined, the final temperature is applied to the 21-lumpcomposition to determine the equivalent enthalpy for this compactedcomponent set.

Simple FractionationThe CatCracker model contains a simplified fractionation model that producesrealistic naphtha and cycle oil products as observed in the CatCracker unit.

The reactor model produces a 19 lump effluent, along with inerts like steam.Several layers of delumping models expand the 19 lumps to a mix of over100 real and pseudocomponents suitable for driving fractionation models. Inthe CatCracker model, this stream is passed to a simplified fractionationscheme. Alternatively, this stream could also be fed to a rigorous fractionationmodel in more complex simulation projects.

The simple fractionation model is a cascade of six stream splitters. The firstsplitter removes C3–material from the effluent since this light material is notneeded in the downstream splitters, which are designed to produce naphthaand cycle oil products. The C4+ effluent is passed to the next splitter, whichpeels off the bottoms product. The remaining material then passes to thethird splitter, which peels off the HCO product. Three following splittersoperate similarly to produce LCO, heavy naphtha and light naphtharespectively. The final splitter produces the light naphtha stream and astream of C4s and C5s. The light naphtha contains C4s based on a C4 contentor RVP spec. The C4s and C5s not used to meet these specs are the finaloutput stream from the splitter cascade. All of these streams then pass to acustom report model (ACTYLD) that creates various yield summaries.

The naphtha and cycle oil splitters contain split ratios for each component toproduce the desired bulk product. These split ratios are based on specializedmodels that relate empirical separation factors to the simple splittercomponent ratios. The separation factors are similar to vapor-liquidequilibrium ratios. In other words, for each product, an empirical correlationis used to generate apparent K ratios that are then used to set the split factorfor each component in the splitter. The result is then a product with acomponent distribution that generates distillation curves with overlaps asnormally observed in a commercial unit. In a Parameter run, these K ratiocorrelations are adjusted to match the observed product yields anddistillations.

Flow and distillation point targets can be specified for the simple fractionationproducts. As these targets are moved, the model will conserve both mass and


volume among the products. Further, product overlaps will be maintained.However, as the simple model does not use rigorous thermodynamics or flashcalculations, moving these targets may not track the performance of acommercial main fractionator. This would require a complex, rigorous mainfractionation model.

The simple fractionation model is hard-coded for five products, light naphtha,heavy naphtha, LCO, HCO, and bottoms. For products that are not present inthe unit, the flow is set to near zero, but not exactly zero! For example, ifonly one naphtha product is present, that is, debutanizer bottoms, then setthe heavy naphtha flow to a constant low rate like 0.1 MBD and use the lightnaphtha inputs for the debutanizer bottoms product. Similarly, if HCO is notpresent, set its rate to a constant 0.1 MBD for all cases.

Aspen Plus CatCracker InputData Requirementsthe data required to tune Aspen Plus CatCracker includes properties for feeds,recycles, products, fresh catalyst, and makeup catalyst; operating conditions(flows, temperatures, and pressures); and mechanical dimensional datasufficient to calculate reaction volumes and superficial velocities in vessels,transfer lines, and standpipes. Test runs are the preferred source of dataalthough routine operating data, if it has sufficient information, can be quiteuseful to tune the model as well.

Feed BlendingThe CatCracker units modeled to date typically have several distinct feedclasses including:

Virgin gasoils.

Resid.

Imported gasoils.

CatCracker cycle oils.

Hydrocracker gasoils.

Coker gasoils.

Projects have been implemented with and without feed blending beingincluded as part of the model.

Feed composition changes are taken into account using the feed bulkinspection properties described below. The total feed to the unit may becharacterized in this way to generate the reactive component lumps used inmodel. However, to model the CatCracker unit feed selectivity mostaccurately, adjust individual feed blend components to match the mostrecently available bulk property inspections (list given in the table below).Then blend the resulting lump compositions together to create a compositefeed. Since the adjustment of the individual feeds results in the creation ofdetailed lump compositions for each individual feed, the blended lumpcomposition is more accurate. When blending feeds, the blended bulk


properties do not provide sufficient information to fully characterize the feedin detail; detail which Aspen Plus CatCracker can take advantage of.

Gas Oil Inspection Properties

API gravity

D2887 distillation

Refractive index (optional, recommended)

Viscosity @210 °F (optional, recommended)

Sulfur

Basic Nitrogen

Conradson carbon (Ramsbottom is optional)

Routine model tuning feed data requirements:

API gravity

D2887, D1160, or TBP distillation (D86 is an option but is notrecommended)

Refractive index and refractive index temperature (optional, butrecommended)

Viscosity (optional, but recommended)

Sulfur

Basic Nitrogen

Conradson carbon residue (Ramsbottom carbon residue may be usedinstead)

Routine model tuning product data requirements:

(Requirements will depend on the refiner’s need for some of these data.)

C6– GC For All Light Materials (LN, Light Ends)

Distillation for LN, HN, LCO, HCO, Slurry

API Gravity

Sulfur and Nitrogen for naphthas

RVP for the lightest naphtha product

RON/MON for naphthas

For LCO and HCO

1 Cloud Point

2 Pour Point

3 Sulfur/Nitrogen

4 Viscosity

Overall Plant Material Balance for Tuning Runs

Operating Conditions / Data

Regenerator

Flue Gas Temperature / Composition (Tuning only)

Cyclone Temperature(s) (Tuning only)

Dense Bed Temperature (Tuning only)


Pressure Profile (Tuning only)

O2 Injection Rate

Regenerator Air Rate

Ambient Temperature and Relative Humidity

Air Blower Performance Curves

Expander Performance Curves

Carbon on Regenerated Catalyst

Riser/Reactor

Riser / Reactor Temperatures

Pressure Profile: Reactor Vessel / Stripper

Stripping Steam Rate / Conditions

Dispersion Steam Rate / Conditions / Point(s) of Injection

Lift Steam and Lift Gas Rate/ Conditions / Point(s) of Injection

Slide Valve Delta P / Positions

Aeration of Standpipe(s) / Conditions

Wet Gas Compressor Performance Curves

Main Fractionator / Gas Plant Data (As Needed by Modeling Option)

Catalyst Properties / Data

For each of Fresh Catalyst, Purchased Equilibrium Catalyst, andEquilibrium Catalyst, the following data are required:

Metals: Ni, V, Na, Cu, Fe

MAT

Surface Area

Bulk Density

Heat Capacity

Mean Particle Diameter

ZSM-5 Content

Fresh Catalyst Makeup Rate

Purchased E-Cat Loading Rate

E-Cat Withdrawal Rate

Total Unit Catalyst Inventory (Calculated by the model)

Unit Mechanical Data (Initial tuning only)

Unit Configuration/Type (Dual Riser, Standpipes, Transfer lines, etc.)

All Vessel and Transfer Line Lining and Insulation Thickness and Properties

All Dimensions and Geometries of:

1 Risers

2 Reactor

3 Stripper

4 Regenerator

5 Cyclones


6 Slide Valves

7 Standpipes

8 Transfer Lines

Index 139

Index

2

21-lump kinetic system 120

A

Abort button 10Air Rate 77Analysis worksheet 35, 81Aromatic Content 81Aspen Plus 96Aspen Plus CatCracker 3

Engine 96menu 11Starting 4toolbar 11User Interface 9workbook 5

ATSLV File Problem Information 106

B

Bounds 54

C

Carbon on Regen Catalyst 77Case Study 51

Running 52, 69Cases

Multiple 69Running 60, 61Types 60

Cases worksheet 46Cat Blend worksheet 38, 81Catalyst Data 29, 41

Adding 92Catalyst Makeup versus MAT 90Catalyst Standpipe 133

CatalystsAdding new 91

CatCracker Menu 61CatCracker toolbar 60Close button 10Close Residuals button 10Coke 126

Feed source 127Kinetic 127Metals 127Stripper Source 127

Command Linemanual access 11

Command Line window 9, 70computer name 13Connect Dialog Box 12Connection to Aspen Plus

resetting 111Constrained Variable 108CST Factors worksheet 29, 92, 93

D

Dataloading 7saving 6Specifying 50

DCOM 96DCS 77Degrees-of-Freedom 99, 109Distillation Type 79DMO

algorithm 103Parameters 104

DMO Solver 72Background 103Changing 72Log Files 106Output 105

Index 140

E

EO 98Equation-Oriented Modeling 98Error Recovery

Parameterization 112Simulation 113

Excelgeneral guidelines for using 5

F

FCCU Model Configuration 129Feed

Characterization 93Entering properties 94Gravity 75Metals 79Nitrogen content 75Preheat Temperature Control 25Properties 94Rate 74Selecting 94Type 78Vaporization 82

Feed Blends worksheet 36, 80Feed Data section 23, 39Feed Input worksheet 24File submenu 15Flue Gas Composition 77Fractionation Control 75Fractionation Parameterization 28Fresh feed recycle routing 25

H

Heat balance 82Tuning 82

Heat Removal 78Heavy Product Rate 75Hidden Worksheets 48

I

Independent Variables 53Infeasible Solutions 114Input Data Requirements 135Input Worksheets

loading 8saving 8

Introduction worksheet 17Iteration information 107, 109

K

Key Operating Data 22, 39Kinetics 120

L

Lab Data versus Estimations 80Largest Unscaled Residuals 107Licensing Error 118Light-Ends Product Rate 75Load CatCracker Flowsheet 12LP vectors

for case study 70generating 43, 72results 43Setting up calculations 59

LP Vectors worksheet 43

M

Makeup Rate 91MAT 90Material Balance 81

Reconciliation 128Measurements 100Mechanical Data 30Model Specifications 99Modes 100Multi-Mode Specifications 100Multiple Cases 69

N

No Creep button 10Nonlinearity Ratio 109Nozzles 134

O

Objective Function 56, 108setting up 54

Optimization 48, 102Activating 58Bounds 57Running 70Setting up 53Solving 70Variables 57

Optimize worksheet 46Options worksheet 18, 19Over-cracking 85

Index 141

P

Param worksheet 21Catalyst Data 80Feed Data 78Heavy Liquid Product Streams 80Key Operating Data 76

Parameterization Casesanalyzing 74Entering Data 66Options 63Running 62, 67

Parameterscomparison with measurements 101Options 74Saving and loading 7

PIMS TableGenerating 45

PIMS Table Worksheet 45PIMS Vectors Worksheet 45Pressure Balance 77Pressure Balance Control 76Pressure Drop Model 98Price 47Product

Gravity 75properties 42rates 42

Profit Report Worksheets 48Profit Worksheets 47

R

Reactor 131Reactor Dilute Phase Cracking 82Reactor Parameterization

Heavy Ends product stream 27Light Ends product stream 26

Recycle Stream Data 25Refractive Index 78Regenerator 132Regenerator Control 76Regenerator Temperatures 77Reported Variables 51Risers 130Run Time Intervention 118

S

S Crackability 78Scaling 115Sequential-modular 98Setup Cases submenu 16Setup LP Vectors Dialog Box 43

Shadow Price 108Simplified Fractionation Model 134Simulation Cases 46

Running 68Simulation worksheet 38Simulations

Saving and loading 7Singularities 116Slide Valve 133SM 98Solver Performance

improving 114Solver Settings 61Specifications

Changing 101SQP 103Startup Aspen Plus CatCracker submenu

5, 12Startup Options 14, 15Stripper 137Stripping zone Model 133Successive Quadratic Programming 103Sulfur Distribution 125

T

Transfer Line 133Tuning Data 34

U

Unhiding worksheets 48Update Spec Colors 18User Interface

sheets 5

V

VariablesBounding 118Specifying 51

Viscosity 79

W

Work Process 92

Y

Yields 41

AspenPlusCatCrackerV7 3 Usr

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