Process Simulation using HYSYS 88

88

Problem2: Multiple and Catalytic Reaction

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

chemical starting with a natural gas feed in PFR:

4 2 2

2 2 2

3CH H O H COCO H O H CO

+ → ++ ⇔ +

The first reaction (reforming) is heterogeneous witch obeys 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 (9.8℅ CO, 30.7℅ H2O, 4℅ CO2, 30.5℅ H2, 10℅ CH4, 15℅ N2) enters to the

adiabatic reactor at 350°C and 30 atm and 2000 moles/s flowrate. Simulate this process. Plot

temperature profile based on reactor length.

E1K exp(- ) P yRT01 CH4r =11+K P yH2

ycoE 2 21r =K exp(- ) ycoRT2 02 2

y Hy H O Keq

⎡ ⎤⎢ ⎥−⎢ ⎥⎣ ⎦

Variable Abbreviation Value Units

Bed Density ρb 1200 kg/m3

Pre-Exponential Rate Constant K01 5.517e3 kmol/(kg.s.atm)

Pre-Exponential Rate Constant K02 4.95e5 kmol/(kg.s)

Activation energy of reaction 1 E1 1.849e8 J/mol

Activation energy of reaction 2 E2 1.163e5 J/mol

Absorption Parameter K 4.053 atm-1

Equilibrium Constant Keq 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 ∆P 0 atm

Tutorial 1 Physical Properties

89

89

Solution:

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

1- Open a new case.

2- Add a new component list

Process Simulation using HYSYS 90

90

3- Select components from Components list.

4- Add a new Fluid Package.

Tutorial 1 Physical Properties

91

91

5- Select Margules activity model from property package.

6- Close fluid package and go to Reaction page.

Process Simulation using HYSYS 92

92

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

8- In stoichiometry page, enter components and stoichiometry coefficients (note: negative for reactants and positive for product). Balance error should be zero.

Tutorial 1 Physical Properties

93

93

9- Go to the Basis page and change the Basis to Partial Pressure and Rxn Phase to Vapor. 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 you should set to 1 the Forward order Methane and the other set to zero.

Process Simulation using HYSYS 94

94

11- Go to the Denominator page. Enter E=0, A=4.053 and Denominator Exponent=1 for Hydrogen and the other set to zero.

12- Now close the current page and again click on Add Rxn button and add a Simple Rate reaction.

Tutorial 1 Physical Properties

95

95

13- In Stoichiometry page, enter components and their stoichiometry coefficients.

14- Go to the Basis page and change the Basis to Mole fraction and Rxn Phase to Vapor. Change the Rate units to kgmol/ (m3.s).

Process Simulation using HYSYS 96

96

15- 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.atm) × 1200 kg/m3)).

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

Tutorial 1 Physical Properties

97

97

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

18- In the active list of set, add your reaction.

Process Simulation using HYSYS 98

98

19- Close set and clicks on Add to FP button. (Note that you have to be in Set1 when you click on Add to FP button)

20- Then you can enter simulation environment by clicking on the Enter Simulation Environment button.

Tutorial 1 Physical Properties

99

99

21-Create a material stream and change its name to Feed. Enter its temperature, pressure, and molar flow rate.

21- Go to the Composition page in Worksheet Tab and enter composition.

Process Simulation using HYSYS 100

100

22- Select a Plug Flow reactor from the Object Pallet, paste it on the flow sheet page, and enter its inlet and outlet streams.

23- Go to the Reaction Tab and select Set-1 in the Reactions set Drop down menu.

Tutorial 1 Physical Properties

101

101

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

25- Set the reactor pressure drop to 0 in the Parameters page of Design Tab to complete the simulation.

Process Simulation using HYSYS 102

102

26-Go to the Performance tab to see the properties versus reactor length.

27-Click on the plot bottom to temperature plot versus reactor length.