Cc Batch Tutorial

7/30/2019 Cc Batch Tutorial

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CHEMCADTutorials

164 CHEMCADVersion6UserGuide

CC-BATCH TutorialThistutorialwalksyouthroughtheprocessofusingCCBATCHtosimulateabatch

distillationcolumn.

Descr ip t ion of t he Pr oblemThesimulationyouwillcreateisafivestepbatchdistillationcampaign,as

illustratedinFigure1134.Theobjectiveistoseparate100lbmolofmixedpropane,

butane,pentane,andhexaneintothreeseparatetanks,producing99%purebutane.

Figure 11-34: The batch distillation flowsheet

Thefollowing

are

detailed

specifications

for

this

problem:

ThermodynamicSelections

K-value:PengRobinson Enthalpy:PengRobinson

ColumnSpecifications

No.ofinternalstages:8 No.ofoperations:5 Internalstageholdup:0.01ft3 Condenserholdup:0.1ft3 Condenserpressure:14.7psia Columnpressuredrop:2psia

InitialChargeConditions

Temperature:Calculated Pressure:16.7psia VaporFraction:0atbubblepoint Totalamountofcharge:100lbmol

InitialChargeComposition(molefrac)

Propane: 0.1 N-Butane: 0.3 N-Pentane: 0.1 N-Hexane: 0.5


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CHEMCADVersion6UserGuide 165

OperatingStep1

Purpose:Propaneremoval Refluxratio:5 Distillatemolarflowrate:2 Stopwhen:DistillatemolefractionofNButaneis0.2

Materialstobeaddedatstart:None

OperatingStep2

Purpose:Propaneremoval Refluxratio:20 Distillatemolarflowrate:2 Stopwhen:DistillatemolefractionofNButaneis0.985


OperatingStep3

Purpose:Butaneproduction Refluxratio:25 Distillatemolarflowrate:2 Stopwhen:AccumulatormolefractionofNButaneis0.99

Materialstobeaddedatstart:20lbmolofmolefraction40%N

Butane/60%NHexane,atits

bubblepointat16.7psia

OperatingStep4

Purpose:Pentaneremoval Refluxratio:15 Distillatemolarflowrate:2 Stopwhen:DistillatemolefractionofNHexaneis0.2


OperatingStep5

Purpose:

Pentane

removal

Refluxratio:25 Distillatemolarflowrate:2 Stopwhen:BottommolefractionofNHexaneis0.9998


Overv iew of t he Bat ch Dist i l lat ion Pr ocess

The

process

of

building

the

flowsheet

and

simulating

the

batch

distillation

involves

thefollowingsteps:

1. Createanewsimulation.2. Selectengineeringunits.3. Drawtheflowsheet.4. Selectthecomponents.5. Selectthermodynamicoptions.


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6. Specifypotcharge.7. Specifythedistillationcolumn.8. Defineoperatingsteps.9. Runthesimulation.10.Reviewtheresultsandprintasneeded.

Cr eat ing a New Simulat ion

Startbycreatinganewsimulationandgivingitaname.

Todothis,launchCHEMCADandthenSelectFile>SavetoopentheSaveAs

dialogbox.Navigatetothedirectorywhereyouwanttostorethesimulation(tryMy

Simulations,locatedunderMyDocuments)andgiveyoursimulationaname,

leavingthetypeasCHEMCAD6(*.cc6).ThenclickSavetocreatethefileandreturn

tothemainCHEMCADwindow.

Select ing Engineer ing Unit s

SelectFormat>EngineeringUnitstoopentheEngineeringUnitSelectiondialog

box.

TheEnglishunitsoptionisthedefaultandiscurrentlyhighlighted.Tochange

theengineeringunitssystem,youwouldclicktheAltSI,SI,orMetricbutton;you

couldthenchangeanyoftheindividualunitsaswell.Forthistutorial,youwilluse

Englishunits,soclickCanceltoexitthisdialogboxwithoutmakingchanges.

Dr aw ing t he Flow sheet

Asdescribed

in

Chapter

5,

creating

aflowsheet

is

amatter

of

placing

UnitOp

icons

onthescreen,connectingthemwithstreams,andthenaddingvariousgraphical

objectstoenhancethedrawing.

Placing UnitOps

BeginbyplacingtheBatchColumnunitonthescreen.

1. OntheAllUnitOpspalette,clicktheBatchcolumntool(seeFigure1135)andthenclickinthemainCHEMCADworkspace.Thebatchcolumnicon

appearswhereyouclicked.

Figure 11-35: The icon representing a batch column

2. ClicktheTanktool(seeFigure1136).Ontheworkspace,clicktotherightofthebatchcolumntoplaceatankicon.Thenclickjustbelowthefirsttank,and


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clickagainbelowthesecondtank.Whenyouhaveplacedallthreetankson

theflowsheet,rightclicktodeactivatetheTanktool.

Figure 11-36: The tank icon

3. ClicktheProducttool(seeFigure1137)andinsimilarfashion,placethreeproductarrowsontheflowsheet,eachonebelowandtotherightofatank

icon.RightclicktodeactivatetheProducttool.

Figure 11-37: The product icon

Drawing Streams

NowthatalloftheUnitOpsareinplace,selecttheStreamtoolandconnecteach

tanksoutlettothenearestproductarrow.Thesearetheonlystreamsthatyouneed

forthistutorial.

Note:Inthissimulation,thebatchdistillationcolumntransfersproductstothetanks

baseduponbatchoperationparametersthatyouprovide.Streamconnections

betweenthe

column

and

the

tanks

are

not

necessary,

and

are

ambiguous

given

the

dynamicnatureofsuchstreams.

Rememberthateachstreammuststartataredoutletpointontheupstream

UnitOp,andendatablueinletpointonthedownstreamUnitOp.Toavoidhavingto

reselecttheStreamtooleachtime,makesurethatassoonasyouclicktocomplete

onestream,youmovethecursortothenextlocationandclicktostartthenext

stream.

Asyoudrawstreams,CHEMCADassignsstreamIDs,justasitassignedUnitOp

IDswhenyoucreatedthoseitems.ThelabelsforstreamIDsaredisplayedin

squares,to

distinguish

them

from

the

UnitOp

IDs

displayed

in

circles.

Atthispoint,theflowsheetshouldlooksimilartoFigure1134.


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Select ing Component s

Nowyouneedtoidentifythecomponentstobeusedinthissimulation.Startby

selectingThermophysical>SelectComponents.

Forthisexample,youllchoosecomponentsfromthestandardCHEMCAD

database.In

the

Select

Components

dialog

box,

find

and

add

each

needed

component.

1. Holddownthe[CTRL]keyonyourkeyboardasyouclickeachofthefollowingcomponentsinturn:

4 Propane 6 NButane 8 NPentane 10 NHexane

2. Clicktherightarrowbutton,locatedtotherightoftheAvailableComponentsarea,toaddalloftheselectedcomponentstoyoursimulation.TheSelect

ComponentsdialogboxshouldnowlooklikeFigure1138.

Figure 11-38: The completed Select Components dialog box

3. SaveyourcomponentselectionsbyclickingOK.Select ing Thermodynami c Opt ions

Assoonasyouhavefinishedcomponentselection,theThermodynamicsWizard

appears.This

tool

can

suggest

thermodynamics

options

to

use

with

this

simulation.

CHEMCADsThermodynamicsWizardworkslikethis:

1. First,itlooksatthecomponentlistanddecideswhatgeneraltypeofmodelisrequired,i.e.,equationofstate,activitymodel,etc.

2. Second,itlooksattemperatureandpressurerangesthatyouprovideanddecideswhichequationwithinagivencategoryisbestatthelimitsofthose

ranges.


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3. Ifthemethodisanactivitymodel,theprogramthenlooksattheBIPdatabasetoseewhichmodelhasthemostdatasetsforthecurrentproblem.

ItthencalculatesthefractionalcompletenessoftheBIPmatrix.Ifthatfraction

isgreaterthantheBIPthresholdparameter,itusesthechosenactivity

method;ifnot,itusesUNIFAC.

TheThermodynamicsWizardisnoreplacementforengineeringjudgment.Thistool

usesanalgorithmbasedongeneralrules,andisthereforefallible.Thesuggested

modelmightnotalwaysbethebestmodelforthesystem.

Selectingthermodynamicoptionsbasicallymeansselectingamodelormethod

forcalculatingvaporliquid(orvaporliquidliquid)phaseequilibrium(calledtheK

valuemodel)andselectingamethodormodelforcalculatingtheheatbalance(called

theenthalpymodel).Thecommandsfortheseselectionsarelocatedonthe

Thermophysicalmenu.

CHEMCADhasalibraryofdozensofKvaluemodelswithavarietyofoptions

andabout

12

enthalpy

models.

Making

the

proper

selection

from

these

libraries

can

sometimesbedifficult.Forthepurposesofthistutorial,assumethatyouwanttouse

thePengRobinsonmethodforboththeKvalueandenthalpycalculations.Follow

thesestepstoselectyourthermophysicaloptions:

1. AcceptthedefaulttemperatureandpressurerangesintheThermodynamicsWizardandclickOK.

2. ClickOKagaintoacceptthewizardssuggestedmethodofSRK.3. WhentheThermodynamicSettingsdialogboxopens,findtheGlobalKValueModelselection,intheupperleftcorneroftheKValueModelstab.

Thecurrent

setting

is

SRK,

but

for

the

purposes

of

the

tutorial,

youll

need

to

selectthePengRobinsonmodel.Clickthedownarrowattherightendofthe

selectionboxtoviewalonglistofKvaluechoices,thenclickPeng

Robinson.

Figure 11-39: The new K-value selection in the Thermodynamic Settings dialog box


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4. NowclicktheEnthalpyModelstab.ThePengRobinsonmethodhasalreadybeenenteredastheGlobalEnthalpyModelselection;thiswasdone

automaticallybecauseyouchosePengRobinsonasyourKvaluemethod.

Whileyoudohavetheoptiontooverridethischoice,inthiscaseyoullneed

tokeepthePengRobinsonmodel;leaveallsettingsastheyareandclickOK

toreturn

to

the

main

CHEMCAD

workspace.

Forthepurposeofthistutorial,thethermodynamicselectionsarenowcomplete.

Note:WhileyouarenotrequiredtousetheThermodynamicsWizard,youshould

knowhowtouseit,ifonlyasastartingpointforyoursimulations.Youcanrevisit

thewizardatanytimebyselectingThermophysical>ThermodynamicsWizard.

Specif yi ng Pot Char ge

Nowthatyouhavethermodynamicsandcomponentsdefinedforthissimulation,

andyouhaveabatchcolumnintheflowsheet,youcandefinethepotchargeforthe

column.

Youwillspecifythepotchargeaccordingtothefollowingrules:

TheTempF,Prespsia,VaporFraction,andEnthalpyMMBtu/hfieldsarethethermodynamicpropertiesofthecharge.AccordingtotheGibbsPhaseRule,

onceamixturescompositionisgiven,specifyinganytwoofthesefour

thermodynamicpropertieswilldefinetheothertwo.Assuch,definingthe

composition,temperature,andpressureforamixtureuniquelydefinesits

vaporfractionandenthalpy.Alternatively,definingthecomposition,

pressure,andenthalpywilluniquelydefinethemixturestemperatureand

vaporfraction.

Sinceenthalpiesarecalculatedrelativetoadatum,thecalculationofany

givenenthalpyisaninvolvedprocesswhichispronetoerrors.Forthis

reason,CHEMCADdoesnotpermityoutoenterenthalpyasaconstraint.

Inadditiontodefiningthepotcomposition,youmustdefineexactlytwoof

thefollowingproperties:temperature,pressure,andvaporfraction.Thetwo

variablesthatyouspecifywilldisplayasredtext,whilethethirdvariable

andthevalueenthalpywillbedisplayedinblackwhenyouflashthecharge.

TheTotalflowunitandCompunitfieldsworktogethertoprovideavarietyof

ways

to

define

charge

composition.

If

the

selected

comp

unit

is

mole,

mass,

orvolumefraction(eithergloballyorlocally),thentheTotalflowunit

selectionisavailable.Iftheselectedcompunitisanamountoption,thenthe

totalchargebecomesthesumofthecomponentquantities,andtheTotal

flowunitselectionisnotavailable.

IftheCompunitfieldselectionisanamountunit(asopposedtoafractionalunit),thenthecomponentchargevaluesareautomaticallyaddedasyou

enterthem.ThecurrentsumisdisplayedintheTotalflowfield.


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YoucanclicktheFlashbuttonatanytimetoperformaflashcalculationusingthecurrentlyspecifiedcompositionandthermodynamicproperties.

Thisenablesyoutoobtainflashcalculationsquicklyandwithoutleavingthe

dialogbox.

Fractionsthatdonotaddupto1.0areautomaticallynormalizedwhenyoueitherclickFlashorexitthedialogbox.

Withtheserulesandbehaviorsinmind,enterthedataforyourpotcharge:

1. DoubleclickthebatchcolumntoopentheEditBatchChargedialogbox.

Figure 11-40: The Edit Batch Charge dialog box

2. InthePrespsiafield,type16.7,thenpress[TAB]andtype0intheVaporFractionfield.

Note:Itsimportantthatyouactuallytypea0overtheexisting0entryintheVapor

Fractionfield.ThistellsCCBATCHthatyouarechoosingtospecifyavapor

fraction.

3. IntheCompunitfield,selectmolefrac.Youcannowtypeavalueof100intheTotalflowfield.

4. Type0.1inthePropanefield,andtheninsimilarfashion,typethefollowingnumbers

in

the

corresponding

fields:

NButane:0.3 NPentane:0.1 NHexane:0.5

5. ClickOKtosavethischargeinformationandcontinue.


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Speci f yi ng t he Dist i l lat ion Column

Whenyouhavespecifiedthepotcharge,CCBATCHdisplaystheBatchDistillation

Columndialogbox.

Figure 11-41: The Batch Distillation Column dialog box

MakethefollowingentriesontheGeneraltabofthisdialogbox:

Numberofstages:8 Numberofoperationsteps:5 Stageholdup:.01 Condenserholdup:1Cond

pressure:

14.7

Colmpresdrop:2Whenyouhaveenteredtheseparameters,clickOKtosavethedataand

continue.


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Defi ning t he Opera t ing St eps

Whenyouhavecompletedtheinitialcolumnspecification,theBatchOperation

Parametersdialogboxappears.

Figure 11-42: The Batch Operation Parameters dialog box

Inthisdialogbox,youlldefinetheparametersforeachoperatingstepofthe

batchcampaign.Beforeyoubegin,youneedtounderstandhowCCBATCHhandles

tankassignments.

TheProductassignmentfieldsidentifytheaccumulatortowhichaproductor

decantstreamwillbesent.Youcanusethisoptionevenifyoudonotplacetankson

theflowsheet;

simply

designating

aUnitOp

ID

number

is

sufficient.

In

this

case,

its

importantthatyoudesignateaUnitOpIDthatisnotalreadyinuse.

SinceCCBATCHpermitsvaporliquidliquiddistillation,theremaybetwo

liquidphasesinthecondenser,possiblygivingrisetodecantingofonephaseorthe

other.TheDistillateTank#fieldentryrepresentsthetankthataccumulatesthe

distillate.TheDecanterTank#fieldentryrepresentsthetankthataccumulatesthe

decantedliquid,ifany.

Operating Step 1

Foroperatingstep1,makethefollowingentriesintheBatchOperationParameters

dialogbox:

ChangetheStartupoptionfieldto1Startwithtotalreflux. IntheProductassignmentarea,enter2intheDistillatetank#field. IntheFirstspecvaluefield,enter5asthevalueoftherefluxratio. IntheSecondspecvaluefield,enter2.


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IntheOperationstepstopoptionsarea,settheStopwhenoptiontoDistillate,settheMeasuredvariableoptiontoMolefraction,andenter0.2intheStop

valuefield.IntheComponentfieldthatnowappears,select2NButane.

IntheMin.runtimefield,enter0.5.When

you

have

made

these

entries,

click

OK

to

move

on

to

the

next

operating

step.

Operating Step 2


dialogbox:

Enter2intheDistillatetank#field. Enter20intheFirstspecvaluefieldand2intheSecondspecvaluefield. StoptheoperationwhenthemolefractionofNButaneinthedistillateis

0.985.

Whenyouhavemadetheseentries,clickOKtomoveontothenextoperating

step.

Operating Step 3

Followthesestepsforoperatingstep3:

1. MakethefollowingentriesintheBatchOperationParametersdialogbox: Enter3intheDistillatetank#field. Enter25intheFirstspecvaluefieldand2intheSecondspecvaluefield. StoptheoperationwhenthemolefractionofNButaneintheaccumulatoris0.99.

2. ClicktheAdditionalSettingstab.Hereyouwillspecifytheadditionof20molesofmixturetothepot,withacompositionof40%butaneand60%

hexane.ChecktheAddmaterialtopotboxandthenclickOKtobringupthe

EditBatchChargedialogbox.

3. InthePrespsiafield,type16.7,thenpress[TAB]andtype0intheVaporFractionfield.

4. Enterthefollowingcompositionsettings: SettheCompunitfieldtomolefrac. Enter0.4intheNButanefield. Enter0.6intheNHexanefield. Enter20intheTotalflowfield.

5. ClickOKtocontinuetothenextoperatingstep.


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Operating Step 4


dialogbox:

Enter4intheDistillatetank#field. Enter15intheFirstspecvaluefieldand2intheSecondspecvaluefield. StoptheoperationwhenthemolefractionofNHexaneinthedistillateis0.2. IntheMin.runtimefield,enter0.5.Whenyouhavemadetheseentries,clickOKtomoveontothefinaloperating

step.

Operating Step 5


dialogbox:

Enter4intheDistillatetank#field. Enter25intheFirstspecvaluefieldand2intheSecondspecvaluefield. StoptheoperationwhenthemolefractionofNHexaneintheresidualchargeatthebottomofthecolumnis0.9998.

IntheMin.runtimefield,enter0.5.Whenyouhavemadetheseentries,clickOKtocontinue.

The Run Time Information Dialog Box

At

the

completion

of

the

last

operating

step,

the

Run

Time

Information

dialog

box

displays.Here,youcanchoosewhichvariableswillbeplottedwhenyourunthe

simulation.

Figure 11-43: The Run Time Information dialog box


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Forthisexample,thedefaultdisplayaplotofdistillatemolefractionsforall

fourcomponentsiswhatyouwant,soclickOKtobringuptheBatchDistillation

menu.

Figure 11-44: The Batch Distillation menu

Thismenuprovidesaccesstotheentryscreensforalldefinedoperationsteps,as

well

as

options

for

inserting,

deleting,

and

copying

operation

steps.

You

might

want

toreviewtheoperatingstepsandverifyyourentriesbeforerunningthesimulation.

Whenyouarefinished,clicktheExitbuttontoclosethemenu.

Running t he Simul at ion

Torunthesimulation,clicktheRunAlltoolbarbutton.CCBATCHfirstchecksthe

inputdataforerrorsoromissions.Youmayseethefollowingtypesofmessages:

Errormessagesmustbefixedbeforethesimulationcanproceed.Underspecificationofthebatchcolumnwouldbeanexampleofthistypeoferror.

Warningmessagesareusuallyinputomissions,whichmayormaynotcauseproblems

upon

execution.

These

are

non

fatal

errors

that

do

not

necessarily

needtobecorrectedpriortosimulation.

Assumingthatyoucorrectlyspecifiedthepotchargeandsubsequentoperation

steps,youshouldseenomessages;theprogramwillproceeddirectlytothe

calculation.

Youwillseethedistillatemolefractionsplottedonthescreeninaplotwindow.

Eachtimetheprogramproceedstothenextoperatingstep,anewplotwindowwill

open,alongwithanewtabatthebottomofthemainCHEMCADworkspace.

Duringtherun,onlythecurrentstepsplotisvisible.Whenthesimulationis

finished,the

dynamic

plot

will

quit

scrolling

and

aRun

finished

message

will

appear

atthefarleftendoftheCHEMCADstatusbar.

Aftertherun,youcanviewtheplotforaparticularoperatingstepbyclicking

thecorrespondingtabatthebottomoftheCHEMCADworkspace.Tocloseany

plotstab,clicktheClosebutton(markedwithanx)onthetab.Tocloseallofthe

plottabsatthesametime,selectWindow>CloseAllCharts.


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Revi ewi ng and Pr int ing Result s

Oncethesimulationiscomplete,youcanreviewtheresultsinteractivelybefore

printingahardcopy.ThecommandsneededtodothisarelocatedintheReportand

Plotmenus.

Plotting the ResultsForbatchcalculations,themostconvenientwaytoexaminetheoutputistoplotthe

results.Todothis,clickyourbatchcolumnUnitOpandthenselectPlot>Dynamic

Plots>BatchColumnHistory.

ThisbringsuptheBatchColumnPlotsdialogbox.Fromhere,youcangeneratea

plotthatencompassestheentirecampaign.Forexample,youcanfollowthesesteps

toplotdistillatemolefractionsacrossalloperatingsteps:

1. InthePlotvariablefield,selectthe0Molefractionsoption.2. IntheOfthefield,selectthe3Distillateoption.3. IntheComponentstoplotarea,usethefirstfourfieldstoselectthefourcomponentsfoundinthedistillate.

Figure 11-45: The completed Batch Column Plots dialog box

4. ClickOKtoviewthecompositeplot,whichshouldresembleFigure1146.


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Figure 11-46: Composite plot showing composition of distillate over time

Revieworprinttheresultsasneeded,andthenclosetheplottabtoreturntothe

simulation.

Generating Text Reports

Youcanalsoviewcertainbatchresultsintabularformat.Todothis,selectReport>

BatchResults.Asummaryoftheresultsofthissimulationdisplaysinaseparate

window.Revieworprinttheresultsasneeded,andthenclosethereportwindowto

returntothemainCHEMCADwindow.

Generating a Full Report

TheReportmenuoffersabroadarrayoftextreports,asdescribedinChapter8,

OutputandReports.Forthepurposeofthistutorial,assumethatyouwanttoview

andprintoutareportwiththefollowinginformation:

Operatingstepresults Batchcolumnhistory FinalbatchcolumnholdupBecauseyouwantareportwithabroadrangeofinformationaboutyour

simulation,use

the

CHEMCAD

Report

Writer

tool.

1. SelectReport>NewtobringuptheReportWriterdialogbox.2. IntheAddNewReportSectionlist,thefirstthreeitemsareBatch

DistillationResults,BatchHistory,andBatch/DynamicColumnHoldup.

DoubleclickeachoftheseitemsinturntoaddthemtotheCurrentReport

Sectionslistatleft.


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Figure 11-47: Batch distillation items added to new report

3. ClickGeneratetocreatethereport.Youcanthenedit,save,andprintthereportasneeded.

4. Whenyoufinishreviewingandworkingwiththereport,clickCanceltoclosetheReportWriterdialogboxandreturntothemainCHEMCAD

workspace.

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