Miscellaneous Data Main Window

The Miscellaneous Input Data window allows users to enable or disable a number of various options. Some of these, such as Exergy Analysis, perform additional calculations. Others, such as the Flash Algorithm option, select alternative algorithms for performing specific calculations. Still others are intended to enhance the integrity of the problem database. While all these options interact to a greater or lesser extent, all may be enabled or disabled independently.

Exergy Analysis

Select this option to request that the standard PRO/II Exergy (availability) Analysis calculations are performed after the flowsheet solution has converged.

Fixed or Variable Component Data

By default, PRO/II uses the same global component property data (Fixed) for each thermodynamic method in the flowsheet simulation. Selecting the Variable option tells PRO/II to create a complete set of component property data for each thermodynamic method. This allows you to change the component properties in different thermodynamic methods. Variable component data is required in order to work with Blend unit operation.

Polymer Mode Consistency Check

By default, PRO/II automatically updates the continuous and/or discrete polymer molecular weight distributions when either one of them is changed by the user. The user can choose to disable this option if desired.

Thermo / Phase Designation Consistency Check

By default, PRO/II performs checks at Calculation Time to determine if the components in the simulation are compatible with the specified thermodynamics methods and/or unit operations. Selecting the Input Time option forces these checks to be made prior to start of the flowsheet calculations.

Independent Variable Check

This feature is intended to improve the accuracy of flowsheet solution results while still utilizing the default flowsheet convergence tolerances. The number of internal iterations may increase slightly in order to obtain more accurate solutions for flat error functions.

Note: By default, this feature is turned On in PRO/II.

Flash Algorithm Selection

The Flash Algorithm is global to the entire flowsheet. This means that all flash calculations within the flowsheet will use the same algorithm. This is critical to attaining a successful solution of the problem. Discontinuities in results from different parts of the flowsheet potentially could quickly defeat any convergence strategy. Three selections are available:

Default - The Default setting activates the most recent algorithm. It is the only one that allows the user to adjust the tolerance for flash convergence. It may be adjusted in the Flowsheet Tolerances window.
Alternate - This algorithm was developed by Dr. Claude Leibovici. It is designed to resolve specific computational difficulties that may arise when two liquid phases are present. It is recommended when the Default algorithm fails and two liquid phases are expected.
NIST - Users can select this algorithm as a default flash algorithm. See REPROP Interface for more information.

Supercritical Phase Designation

When temperatures and pressures are above the critical point and outside of the two-phase region, PRO/II determines the phase of the supercritical fluid using a consistent method. PRO/II calculates the Kay's rule critical point for the mixture and uses a one fluid approximation in a Lee-Kessler equation to calculate a pseudo-component vapor pressure. PRO/II extrapolates this line on an ln (P) versus 1/T scale. Outside the two-phase region, anything at a temperature above this line is declared a vapor; anything below this line is declared a liquid. For more details refer to Technical Bulletin Supercritical phase designation.

Pro/II starting with version 10.0 provides an option to override PRO/II definition of Vapor or Liquid and thus the calculations of properties affected by the designation. In the Calculation defaults user can select to designate always Phase=LIQUID or PHASE=Vapor to a stream above critical point. Selecting Phase=SIMSCI (the default) allows PRO/II to make the selection with the method described below. This option must be used with extreme caution and it affects all the supercritical streams in the simulation. The selection must be done for each simulation where the user wants to direct the answer to a specific phase.

Maximum Node Calculations

By default, PRO/II limits the maximum number of unit operation calculations and flowsheet branching decisions made during flowsheet calculations to 1,000,000. The purpose of this is to protect against infinite or potentially infinite calculation loops. However, very large flowsheets may require more iterations. This entry allows the user to overcome that limit.

Usage

Select the Include Exergy Analysis check-box to request PRO/II's Exergy analysis calculations. Specifying data values for the Reference Temperature and Pressure basis is optional.

Select either the Fixed or Variable option in the drop down list box to specify whether you want PRO/II to use the same global component property data for all thermodynamic methods (Fixed), or create a complete set of component property data for each thermodynamic method (Variable).

Select either the Yes or No option in the drop down list box to specify whether you want PRO/II to automatically updates the continuous and/or discrete polymer molecular weight distributions when either one of them is changed.

Select either the Calculation Time or Input Time option in the drop down list box to specify whether you want PRO/II to perform these calculations prior to the start of the flowsheet calculations, or during the calculations.

Select either the On or Off option in the drop down list box to specify whether or not you want PRO/II to use this feature to improve the accuracy of flowsheet solution results with default flowsheet convergence tolerances.

Select the desired Flash Algorithm option (Default, Version 5, or Alternate) from the drop-down list box. Because every new flowsheet assumes the Default Algorithm, the Version 5 and Alternate algorithms must be selected here in each flowsheet that will use them.

Enter a value in the Maximum Node Calculations field to override the default of 1000000.

$image\SML_LINE.gif$