24 catalitic reaction

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Steady State Process Simulation Using HYSYS 274

Problem 2: Multiple and Catalytic Reaction

The following typical reactions are encountered in the early stages of the production of

chemicals starting with a natural gas feed in PFR:

4 2 2

2 2 2

3CH H O H COCO H O H CO

o

The first reaction (reforming) is heterogeneous which obeys the Langmuir-Hinshelwood rate

expression. The second reaction is a reversible reaction of water gas shift which obeys the

standard Kinetic rate expression. This reaction is especially important in ammonia synthesis

as both CO and CO2 will poison the catalyst used to make ammonia from hydrogen and

nitrogen, and the CO is harder to remove than CO2. Use Peng Robinson equation of state.

Feed stream (9.8Ə CO, 30.7Ə H2O, 4Ə CO2, 30.5Ə H2, 10Ə CH4, 15Ə N2) enters the

adiabatic reactor at 350°C, 30 atm and 2000 moles/s. Simulate this process and plot the axial

temperature profile.

E1K exp(- ) P yRT01 CH4r =1

1+K P yH2

»»¼

º

««¬

ª

eq

H2CO2H2OCO

2022

K

yyyy)

RTE

exp(K r

Variable Abbreviation Value Units

Bed Density ȡ b 1200 kg/m3

Pre-Exponential Rate Constant K 01 5.517×103 kmol/(kg.s.atm)

Pre-Exponential Rate Constant K 02 4.95×105 kmol/(kg.s)

Activation energy of reaction 1 E1 1.849×108 J/mol

Activation energy of reaction 2 E2 1.163×105 J/mol

Absorption Parameter K 4.053 atm-1

Equilibrium Constant K eq e-4.946+4897/T

---------

Gas Constant R 8.314 J/(mol.K)

Pressure P 30.0 atm

Reactor Volume V 40 m3

Diameter D 2 m

Pressure Drop ǻP 0 atm




3- Select components from the Components list.

4- Add a new Fluid Package.



Tutorial 3 Advanced Feature

277

5- Select Peng Robinson property package from Property Package. Then close the Fluid Package by clicking on cross button

6- Go to the Reactions page.




7- Click on the Add Rxn button and add a Heterogeneous Catalytic reaction.

8- In the Stoichiometry page, enter components and stoichiometry coefficients (note: negative

for reactants and positive for products). The Balance Error should be zero.




279

9- Go to the Basis page and change the Basis to Partial Pressure and the Rxn Phase to

Vapor . Then change the Basis unit and Rate units to atm and kgmol/(m3.s), respectively.

10- Go to the Numerator page; enter E=1.849e8 J/mol and A=6620400 kgmol/ (m3.s). (Note

that A is obtained by multiplying the Pre-exponential Rate Constant to Bed Density

(A=5.518×103 kmol/(kg.s.atm) × 1200 kg/m3)). In this page, set the Forward order of

Methane to 1 and the other is set to zero.




11- Go to the Denominator page. Click on the Kinetic Help button and see how to enter the

appropriate data of reaction kinetic.

12- Enter E=0, A=4.053 and Denominator Exponent=1 for Hydrogen and the other set to

zero.




281

13- Now close the current page and again click on the Add Rxn button to add a Simple Rate

reaction.

14- In the Stoichiometry page, enter the components and their corresponding stoichiometry

coefficients.




15- Go to the Basis page; change the Basis to Mole fraction and Rxn Phase to Vapor . Then

choose the Rate units to kgmol/ (m3.s).

16- Go to the Parameter page; enter E=1.163e5 J/mol and A=5.94e8 kgmol/ (m3.s). (Note that

A is obtained by multiplying the Pre-exponential Rate Constant to Bed Density

(A=4.95×105 kmol/ (kg.s) × 1200 kg/m3)).




283

17- Then enter A' =-4.946 and B' =4897.

18- Close the reaction page and add a new set of reaction by clicking on the Add Set button.




19- In the Active List , add the reactions defined so far.

20- Close set and clicks on the Add to FP button. (Choose Set1 upon clicking on the Add to FP button)




285

21- Then enter simulation environment by clicking on the Enter Simulation Environment

button.

22- Create a material stream and change its name to Feed . Enter its temperature, pressure,

and molar flow rate.




23- Go to the Composition page in the Worksheet Tab and enter the corresponding input

composition.

24- Select a Plug Flow reactor from the Object Pallet (F4), drag it to the work space

(flowsheet), and name its inlet and outlet streams.




287

25- Go to the Reaction Tab and select Set-1 in the Reaction Set drop down menu.

26- In the Rating tab of the reactor, enter the reactor volume and diameter .




27- Set the reactor pressure drop to 0 in the Parameters page of Design Tab to complete the

simulation.

28- Go to the Performance tab to view the axial profiles.



Tutorial 3 Advanced Feature 289

29- Click on the plot bottom to plot temperature versus reactor length. View the axial

temperature profile.

24 catalitic reaction

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