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
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Steady State Process Simulation Using HYSYS 276
3- Select components from the Components list.
4- Add a new Fluid Package.
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Tutorial 3 Advanced Feature
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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.
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Steady State Process Simulation Using HYSYS 278
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.
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Tutorial 3 Advanced Feature
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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.
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Steady State Process Simulation Using HYSYS 280
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.
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Tutorial 3 Advanced Feature
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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.
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Steady State Process Simulation Using HYSYS 282
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)).
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Tutorial 3 Advanced Feature
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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.
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Steady State Process Simulation Using HYSYS 284
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)
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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.
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Steady State Process Simulation Using HYSYS 286
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.
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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 .
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Steady State Process Simulation Using HYSYS 288
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.
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Tutorial 3 Advanced Feature 289
29- Click on the plot bottom to plot temperature versus reactor length. View the axial
temperature profile.