Configure the equilibrium options for a Fluid Type that uses an equation of state

The Equilibrium Options section in the Fluid Editor provides a set of advanced equilibrium options that allow you to adjust your equilibrium calculations to suit your needs. The equilibrium options that are available depend on the type of thermodynamic method that you use as the System method for your Fluid Type.

The following equations of state have similar equilibrium options:

• Peng-Robinson (PR)

• Peng-Robinson Modified Panagiotopoulos-Reid (PRM)

• Soave-Redlich-Kwong (SRK)

• Soave-Redlich-Kwong Huron-Vidal (SRKH)

• Soave-Redlich-Kwong Modified Panagiotopoulos-Reid (SRKM)

The Predictive Soave-Redlich-Kwong (PSRK) method includes the same equilibrium options as the preceding equations of state, but includes additional options that allow you to tailor the equilibrium calculations.

Configure the equilibrium options for a Fluid Type that uses an equation of state

1. Open the Fluid Type in the Fluid Editor if the Fluid Type is not already open.

2. Expand the Equilibrium Options section if it is not already visible.

   

3. In the Alpha Selection list, select the type of alpha calculation that you want to use:

   • Acentric Factor Formulation: AVEVA Process Simulation uses the alpha formulation from the SRK equation of state.

   • Alpha Databanks: AVEVA Process Simulation uses a different alpha formulation for each component that depends on the alpha data in the data banks that you add to the Alpha Data Banks box.

   The default value depends on the equation of state that you select as the System method.

   

4. If you select Alpha Databanks in the Alpha Selection list and you want to use custom data banks of alpha formulation data, in the Alpha Data Banks area, select Expand, and then add the custom data banks that you want to use.

   Warning: If you use a custom ALPHA data bank, you should also use a binary interaction data bank that contains adjusted binary interaction parameters that correspond to the alpha data in your custom ALPHA data bank.

   See Data banks for a Fluid Type for more information.

5. (Optional) If your Fluid Type uses the SRKM method as its System method, select the Use Glycol Fill Correlations checkbox to calculate the binary interaction parameters for a specific set of binary pairs.

   

   The Glycol Fill method calculates the binary interaction parameters only for binary pairs that include a petro component and one of the following pure components:

   • Ethylene glycol (EG)

   • Diethylene glycol (DEG)

   • Triethylene glycol (TEG)

     If your Fluid Type does not include any petro components or any of the preceding pure components, selecting the Use Glycol Fill Correlations checkbox has no effect on your Fluid Type.

     See Glycol Fill method for more information.

6. (Optional) Select the Include Fugacity Coefficient Variables in Fluid State checkbox to add variables for the fugacity coefficients to the Fluid State model.

   You can now view the calculated values for the fugacity coefficients or use them in other areas of the simulation.

Configure the equilibrium options for a Fluid Type that uses the PSRK

7. Open the Fluid Type in the Fluid Editor if the Fluid Type is not already open.

8. Expand the Equilibrium Options section if it is not already visible.

   

9. In the Excess Gibbs Energy Method list, select one of the following methods to calculate the excess Gibbs free energy from the activity coefficient:

   • UNIFAC

   • NRTL

   See Equations for the PSRK method for more information on how the equilibrium calculations change based on your selection.

   

10. In the Alpha Selection list, select the type of alpha calculation that you want to use:

    • Acentric Factor Formulation: AVEVA Process Simulation uses the alpha formulation from the SRK equation of state.

    • Alpha Databanks: AVEVA Process Simulation uses a different alpha formulation for each component that depends on the alpha data in the data banks that you add to the Alpha Data Banks box.

    The default selection is Alpha Databanks, and the Fluid Type automatically uses the System:PSRKALPH data bank. This data bank contains PSRK-specific data for the alpha formulations of 873 components. We have tried to include all the components that you may need in your chemical processes. However, if your Fluid Type contains components that are not available in the System:PSRKALPH data bank, you can add your own custom ALPHA data banks to the Fluid Type to supplement the System:PSRKALPH data bank.

    

11. If you select Alpha Databanks in the Alpha Selection list and you want to use custom data banks of alpha formulation data, in the Alpha Data Banks area, select Expand and add the custom data banks that you want to use.

    Warning: If you use a custom ALPHA data bank, you should also use a binary interaction data bank that contains adjusted binary interaction parameters that correspond to the alpha data in your custom ALPHA data bank.

    See Data banks for a Fluid Type for more information.

12. (Optional) In the PSRK Critical Property Override Data Bank box, enter the name of the data bank that contains the PSRK-specific critical property data that overrides all other critical property data in the Fluid Type.

    By default, the Fluid Type already uses the System:PSRKTCPC data bank to override the critical properties in the default data bank with PSRK-specific data for the critical temperature and critical pressure of 877 components. We have tried to include all the components that you may need in your chemical processes. However, if the critical property data for a component is missing from the System:PSRKTCPC data bank, the Fluid Type uses the critical property data from the default data bank or the critical property data from the data bank that you specify in the Pure Component Property Override Data Bank box.

    Important: If you want to use a critical property data bank other than the System:PSRKTCPC data bank, we recommend that you contact our customer support to request an extended copy of the System:PSRKTCPC data bank that includes all your required components and data. You can then replace the System:PSRKTCPC data bank in your Fluid Type with the extended data bank.

    You should use the System:PSRKTCPC data bank only with the PSRK method.

13. If you select NRTL in the Excess Gibbs Energy Method list, do the following:

    1. In the Flory-Huggins like term in MVH1 mixing rule list, select whether to Include or Exclude the combinatorial term in the mixing rule calculations.

       Typically, the results for asymmetric mixtures improve when you exclude the combinatorial term.

       See Equations for the PSRK method for more information.

       

    2. (Optional) Select the Use Azeotrope Fill checkbox to estimate missing Non-Random Two-Liquid (NRTL) binary interaction parameters by regressing azeotropic data from a data bank to provide the binary interaction data.

       The Azeotrope Data Banks area appears.

       

       The software provides estimates for the interaction parameters only when azeotropic data is available for both components in the binary pair. If the data banks that your Fluid Type uses do not include azeotropic data for the components in question, selecting the Use Azeotrope Fill checkbox has no effect on the Fluid Type.

    3. If you want to use custom data banks of azeotropic data, in the Azeotrope Data Banks area, select Expand and add the custom data banks that you want to use.

       See Data banks for a Fluid Type for more information.

       The Azeotrope Data Banks area is available only when the Use Azeotrope Fill checkbox is selected.

    4. (Optional) Select the Use PSRK UNIFAC Fill checkbox to use the UNIQUAC Functional-group Activity Coefficient (UNIFAC) formulation to calculate the activity coefficient for any binary pairs that are missing NRTL binary interaction data.

       The Fill Method Group Information Banks area appears.

       

       The software uses the calculated activity coefficient to provide estimates for the missing NRTL binary interaction parameters.

       If you select both the Use Azeotrope Fill and Use PSRK UNIFAC Fill checkboxes, the software first fills any missing NRTL binary interaction parameters with the estimated interaction parameters based on the azeotropic data. The software then uses the UNIFAC formulation to calculate the activity coefficient and estimate the NRTL binary interaction parameters for any remaining binary pairs that are still missing NRTL binary interaction data.

    5. If you want to use custom data banks of group contribution data for the UNIFAC fill, in the Fill Method Group Information Banks area, select Expand and add the custom data banks that you want to use.

       See Data banks for a Fluid Type for more information.

       The Fill Method Group Information Banks area is available only when the Use Azeotrope Fill checkbox is selected.

14. (Optional) Select the Include Fugacity Coefficient Variables in Fluid State checkbox to add variables for the fugacity coefficients to the Fluid State model.

    You can now view the calculated values for the fugacity coefficients or use them in other areas of the simulation.