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Reactors in HYSYS

By Rodney Bryant,2014-05-06 16:21
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Reactors in HYSYS

    D. Reactors in HYSYS

    Gibbs Reactors

    A feed containing 3 kg/mol-hr Ethane and 1.5 kg-mol/hr water entering at 1 atm and 350 C is to be cracked into Ethylene and Hydrogen using a Gibbs reactor.

     CH?;CH;H26242Cat.

    Initial Setup

    1. Start a new case in HYSYS

    2. Select Water, Ethylene/Ethene, Ethane, and Hydrogen as the components. 3. Since these components are gasses at high temperatures, select the SRK fluid package. 4. Select the reaction tab of the Simulation Basis Manager and click on “Add Reaction”.

5. Since Gibbs reactions are Equilibrium reactions, select “Equilibrium” from the menu.

    6. When the Equilibrium Reaction window pops up, select the components which are

    present during the reaction, and enter in guesses for their Stoichiometric Coefficient.

    Keep in mind that the reactant, Ethane, must have a negative coefficient. Click

    “Balance” to check the guesses. Notice status of the reaction goes from not ready to

    ready. Close the window.

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7. Click on “Add Set” and then add “Rxn – 1” to the Active List.

    8. Click “Add to FP”, make sure that PP: SRK is selected and click “Add Set to Fluid

    Package”. Now the simulation is setup. Click on “Enter Simulation Environment to

    goto the PFD and start the simulation.

Placing and Running the Reactor

    1. Place 3 material streams for the feed, liquid outlet and vapor outlet, and rename the

    streams respectively.

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    2. Click on the General Reactors icon in the Simulation Toolbar, which brings up a list

    of 3 general types of reactors. Select the Gibbs reactor and place it in the PFD.

    3. Double click on the Gibbs Reactor to bring up its connection menu. Connect the

    Feed to inlet and the liquid and vapor streams to their appropriate locations. Note: Check the Reactions tab, and as long as “Gibbs Reactions Only” is selected, no further specifications are necessary.

    4. Specify the feed stream. It is at 1 atm, 350 ?C, has a ethene molar flow rate of 3 kg-

    mols/hr, and a water molar flow rate of 1.5 kg-mols/hr.

    Heated and Cooled Gibbs Reactors

    Once the feed is specified enough data is entered and the reaction is simulated. But a quick check of the workbook leads to very dismal conversion. For cracking reactions, temperatures around 1000 ?C are needed.

    1. One way to increase conversion is to specify the reactor inlet at a high temperature. 2. HYSYS also has the ability to simulate heated or cooled reactors. To do this, add an

    Energy stream to the PFD. Then Double click on the Gibbs reactor and select that

    energy stream to the Optional Energy Hook-up.

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    3. Now that the energy stream is selected, the temperature of one of the outlet streams

    has to be selected to determine how much energy the reactor needs. Modify the outlet

    temperature until a desirable conversion is found

    Conversion Reactions

    A stream of pure methane at 400 bar and 87 ?C and flowing at 32 kg/hr enters in a reactor, where it undergoes complete combustion. There is excess air during in the reactor and the conversion is 95%.

     CH;OCO;HO4222

    Initial Setup

    1. Start a new case in HYSYS

    2. Select methane, oxygen, air, water, and carbon-dioxide as the components. 3. Since these components are all gasses, select the Peng-Robinson fluid package. 4. Select the reaction tab of the Simulation Basis Manager and click on “Add Reaction”.

5. Since this is a conversion reaction, select it from the list.

    6. Select all of the components that are present for the combustion of methane, and enter

    in guesses for their stoichiometric coefficients, keeping in mind that the reactants,

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    methane and air, must have negative coefficients. Then click “Balance to correct the

    coefficient guesses.

    7. Now the conversion needs to be specified. Click the basis tab, and enter in 95 under

    “Co”. Take note that the conversion has to be in percentage form, not decimal form.

    The reaction now goes from “Not Ready” to “Ready”.

    Note: You will see a conversion equation below the component windows that

    looks like Conversion (%) = Co + C1*T + C2*T^2; here the conversion is just st a straight 95% conversion so only a Co is needed, however, if there was a 1nd&/or 2 order temperature dependent conversion values for C1 and C2 would

    need to be added.

8. Click on “Add Set” and add “Rxn – 1” to the Active List.

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9. Click “Add to FP”, make sure that PP: Peng-Robinsion is selected and click “Add Set

    to Fluid Package”. Now the simulation is setup. Click on “Enter Simulation

    Environment.

     Placing and Running the Reactor

    1. Place 4 material streams for the methane, air, liquid outlet and vapor outlet, and

    rename the streams respectively.

    2. Click on the General Reactors icon in the Simulation Toolbar, which brings up a list

    of 3 general types of reactors. Select the Conversion reactor and place it in the PFD.

    3. Double click on the Conversion Reactor to bring up its connection menu. Connect

    the methane and air streams the inlet and the liquid and vapor streams to their

    appropriate outlets.

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    4. Now the reaction has to be specified. Click on the Reactions tab. Select Global

    Reaction Set. Check to see if the appropriate reaction, Rxn-1, has automatically been

    selected.

    5. Specify the propane and air streams. The propane enters the reactor at 400 bar, 87 ?C,

    and has a flow rate of 37 kg/hr. The air enters in at 1 atm, 25 ?C, and is in excess

    with the propane, so has a flow rate of 75 kg/hr.

    6. Now that the feeds are specified, the specification is complete and

    Note: HYSYS also has the ability to simulate heated or cooled conversion reactors. Although not necessary in this case, the reactors can be heated or cooled to aid with the kinetics of the reaction. To simulate those types of reactors, follow the process to do this to a Gibbs reactor.

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Equilibrium Reactors

    A 100 kg-mol/hr feed containing 50 mol% Nitrogen and 50 mol% Hydrogen entering at 1 atm and 50 C is to undergo an equilibrium reaction to produce ammonia. Initial Setup

    1. Start a new case in HYSYS

    2. Select Nitrogen, Hydrogen, and Ammonia as the components.

    3. Since these components are all gasses, select the Peng-Robinson fluid package. 4. Select the reaction tab of the Simulation Basis Manager and click on “Add Reaction”.

5. Since Gibbs reactions are Equilibrium reactions, select “Equilibrium” from the menu.

    6. When the Equilibrium Reaction window pops up, select the components which are

    present during the reaction, and enter in guesses for their Stoichiometric Coefficient.

    Keep in mind that the reactants, Nitrogen and Hydrogen, must have a negative

    coefficient. Click “Balance” to check the guesses. Notice status of the reaction goes

    from not ready to ready. Next, click the “Basis” tab.

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    7. The basis tab gives us some options on how the reaction can be solved. For most

    cases, using the Gibb’s Free energy approach is acceptable, as it allows the simulation

    to go forward without any additional data required. Generally speaking it gives very

    close results. If there is experimental or tabulated equilibrium data is available, they

    can be entered in as well in the steps below.

     is Known If Keq

    If the Equilibrium Constant K is known it can be entered into HYSYS directly by eq

    selecting the “Fixed K” option. Then select the “K” tab. Once there enter in the K eqeqeq

    constant directly in, and the reaction is ready.

    If a Ln(K) equation is known eq

    If a temperature dependant Ln(K) equation is known, itcan be entered into HYSYS as eq

    well. Select “Ln(K) and then select the “K” tab. Once there enter in the equation eqeq

    constants can be entered in to the A, B, C… etc tabs as shown in the equation to the right.

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If the reaction is in HYSYS's Reaction Library

    HYSYS has tabulated equilibrium data for several common equilibrium reactions. When setting up an equilibrium reaction, always check to see if the reaction is in the reaction library, as it is the most accurate method of solving. To use a reaction from the

     vs. T table option, and then select the “Library” tab. equilibrium library, select the Keq

    Once there, scroll through the list of reactions and check to see if it is there. If it is there, select it and press “Add Library Reaction”

    Final Setup of the Reaction

    1. Click on “Add Set” and then add “Rxn – 1” to the Active List.

     2. Click “Add to FP”, make sure that PP: SRK is selected and click “Add Set to

    Fluid Package”. Now the simulation is setup. Click on “Enter Simulation

    Environment to goto the PFD and start the simulation.

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