Tutorial 3

Tutorial 3 Separation Processes

Problem 1 Shortcut Distillation

A column is used to separate propane from a mixture of hydrocarbons (ethane to n-hexane).

The condenser is in full reflux condition and pressures in condenser and reboiler are 248 and

252 psia, respectively. Reflux ratio is 6.06. Feed enters to the column at 225 ºF and 250 Psia

with molar flow rate of 1000 lbmole/hr. Solve the column using shortcut operation. The

composition of feed is shown bellow:

Composition of Feed

Component Molar flow rate (lbmole/hr)

Ethane 30

Propane 200

n-Butane 370

n-Pentane 350

n-Hexane 50

Process Simulation using HYSYS 186

Solution:

Follow the step-by-step instructions to solve the problem.

1- Open a new case.

2- Add a new component list.

Tutorial 3 Separation Processes 187

3- Select the components from the Components list and then close the active window by

clicking on cross button (all process components should be entered in this step).

4- The cross button is not seen on the figure and you could move the active window to see

the cross button in order to close it.


5- Select the Fluid Package (Make sure selecting Component List -1in the component list).

6- Add a new Fluid Package.


7- Select the Peng Robinson or SRK equation of state from Property Package.

8- Close the Fluid Package by clicking on cross button. After this step, it is possible to

import/export the Fluid Package. Then enter to Simulation Environment.


9- Drag a material stream to the PFD and change its name to feed, and then enter its

temperature and pressure in the Worksheet/Conditions Page.

10- Save the simulation work (e.g., problem-1).


11- In the Worksheet/Composition page, click the Edit button, enter molar flow rate of the

components, (make sure to select mole flow) then click OK. Close the active window to

return to PFD.

12- Select a Shortcut operation from object palette and drag it to the PFD.


13- Double click on Shortcut and enter inlet, outlet and energy streams. Change the top

product phase to Vapor.

14- In the Design/Parameters page, enter propane as a light key in the bottom and n-butane as

a heavy key in the distillate (0.0001 mole fractions). Also enter the condenser and

reboiler pressures.


15- Finally, enter the reflux ratio.

16- Properties of column could be seen in the Performance page (e.g., minimum number of

trays, actual number of trays and optimal feed stage).


Problem 2 Distillation Column

Consider a stream of light hydrocarbons fed to a column at 100 ºC and

10 atm with a molar flow rate of 1150 kmole/hr. The column has 18 trays and the feed

enters on the 8th

tray. Pressures in condenser and reboiler are 7 and 12 atm, respectively, and

the reflux ratio is 2. Condenser is in the full reflux condition. Simulate the column, if the

recovery of ethane in distillate is 99 % and recovery of i-butane in bottom is 100 %. The feed

composition is shown at the table below:

Component Mole fraction

Methane 0.1

Ethane 0.4

Propane 0.2

i-Butane 0.15

n-Butane 0.15


Solution:


1- Open a new case.









6- Add a new Fluid Package.




import/export the Fluid Package. Then enter to Simulation Environment.


9- Drag a material stream to the PFD and change its name to feed, and then enter its

temperature, pressure and the molar flow rate in the Worksheet/Conditions Page.



11- In the Worksheet/Composition page, click the Edit button, enter the composition, and

then click OK. Close the active window to return to PFD.

12- Select a distillation column from the object palette (F4) and drag it to the PFD.


13- Double click on Column and enter inlet, outlet and energy streams. Select Full Rflx for

condenser type. Change the number of trays to 18 and the feed inlet stage to 8th

tray.

14- Click on Next button. Enter the condenser and reboiler pressures.


15- Click on Next button. Since the condenser and reboiler temperatures are optional, it is

not necessary to enter these parameters in this problem.

16- Click on Next button, enter the reflux ratio and click the Done button.


17- The column specification page is now shown.

18- Go to the Design/Monitor page. As shown, the degree of freedom is 1.


19- Select the Design/ Specs page.

20- Add a new column specification. Choose the Column Component Recovery in the

Column Specification types menu and click on the Add spece(s) button.


21- Define 0.99 recovery for the ethane in distillate. The degree of freedom becomes zero.

22- Close the active window and run the column.


23- Add another spec. Select the Column Component Recovery button. Enter 1 for recovery

of i-butane in bottom stream. The degree of freedom is -1. The column is over-specified.

24- One specification should be removed to bring the degree of freedom to zero in order to

solve the column. Go back to the Monitor page and deactivate the reflux ratio button.

The column runs automatically.


25- Various combination of specifications could be chosen to run the column (for all cases,

the degree of freedom should be zero to solve the column), e.g., choose the Component

Recovery-2 and the Reflux Ratio and run the column.

26- The column is now simulated using those specifications.


Problem 3 Ammonia Production

In an ammonia plant, the feed gas (74 % H2, 24.5 % N2, 1.2 % CH4, and 0.3 % Ar in mole) at

300 °F and 500 psi enters to a catalytic reactor. The reaction 322 23 NHHN is carried

out in the reactor at T=930 °F and P=200 atm. The 65 % of the N2 is converted in the reactor.

The products of reaction are refrigerated to separate 75 % of NH3 product per pass. The

remaining process stream is recycled back after being purged. Assume a total feed of 100

lbmole/hr and no pressure drop in the mixer. Simulate the process with Peng-Robinson

equation of state for the case when the purge fraction is 10 %.


Solution:


1- Open a new case.









6- Add a new Fluid Package




import/export the Fluid Package. Click on the Reaction button.


9- Go to the Add Rxn button to enter the reaction data.

10- Select the Conversion Reaction and then click on the add Reaction.button.


11- Select components from the drop down menu and then enter stoichiometry of components

(negative for reactants and positive for products). The balance error should be zero.

12- Click on the Basis button, select Base Component from drop down menu and enter the

conversion for the base component (65 %).


13- Close the active window and return to the following window: The reaction Rxn-1 is

added. Add a reaction set by clicking on the Add Set button.

14- In the Active List, select Rxn-1 from the drop down menu. Check mark the set and close

the active window.


15- Click on the Add FP button (This makes the reaction accessible for simulation)

16- Click on Add Set to Fluid Package Button


17- The Basis-1 property model is now added to the Fluid Package. Then Enter to

Simulation Environment.

18- Go to Tools/Preference to change the Unit Set to Field.


19- Go to the Variables button, select Field and close the window.

20- Drag a material stream to the PFD and change its name to feed. Enter its temperature,

pressure and molar flowrate in the Worksheet/Conditions Page.



22- Enter the mole fractions of the components in Worksheet/Composition Edit page. Click

OK. The stream is now solved. Close the active window to return to PFD.


23- Drag another stream named R* to the PFD. Define it like feed stream.

24- Enter 0 for molar flow rate of R* (Open-loop simulation). Close the active window.


25- Select a Mixer from the object palette (F4) and drag it to the PFD.

26- Double click on mixer and enter inlet and outlet streams. It is solved immediately. Close

the active window and return to PFD.


27- Select a Compressor from the object palette and drag in to the PFD.

28- Double click on Compressor and enter inlet, outlet and energy streams.


29- Go to the Worksheet and enter 200 atm as the pressure of outlet stream. The Compressor

is solved. Close the active window.

30- Select a Heater from the object palette and drag in to the PFD.


31- Double click on Heater and enter inlet, outlet and energy streams.

32- On the Design/Parameters page enter 0 for Delta P.


33- Go to the Worksheet page and enter 930 ºF for the outlet stream temperature. At the

beginning, the Heater acts as a cooler. However, after the recycle stream completion, it

will work as a Heater, because of the higher flow rate. Close the active window.

34- Select a Conversion reactor from the object palette and drag it to the PFD.


35- Double click on Reactor and enter the inlet, outlet and energy streams.

36- Go to the Reaction page and select the reaction set from the Reaction Set drop down.


37- Go to Worksheet and enter 930 ºF for the outlet stream temperature.

38- Select a Component splitter from the object palette and drag in to the PFD.


39- Double click on the Splitter to enter the inlet, outlet and energy streams.

40- Go to the Design/Splits page and enter 0.25 for ammonia and 1 for the other components

as the fraction to Overhead. Therefore, 75 % of ammonia is separated as a pure product.


41- Go to Worksheet and enter 930 ºF and 200 atm for both outlet streams. The Splitter is

now solved. Close the active window.

42- Select a Tee from the object palette and drag it to the PFD.


43- Double click on the Tee and enter the inlet and outlet streams.

44- On the Design Parameters page, enter 0.9 for a Recycled Flow Ratio (stream R) and

close the active window.


45- Select a Recycle operation from the object palette and drag it to the PFD.

46- Double click on Recycle and enter the inlet and outlet streams.


47- If the Recycle reached to its iteration limit without converging, click Continue.

48- The process is now simulated.

Tutorial 3

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