Batch Distillation - Calculation Options
The calculation options and tolerances are defined in this window. All entries have default values, so providing data for them is optional.
Usage
Integration Method
The Semi-Implicit Trapezoidal method is used. Defaults are supplied for the convergence tolerance and maximum time step. These may be overridden as desired.
Integration step sizes and tolerances are specified in this dialog box:
Tolerance (default 0.001).
Maximum Step Size (default 0.1 hr)
Liquid Density Calculation Option
By default, liquid densities are calculated rigorously using the option defined in the Thermodynamic Data Window. To reduce calculation times, users may select the shortcut method. This calculates mixture volumes as the sum of pure component volumes at a defined (or default of 77°F) reference temperature.
Enthalpy Balance Calculation Interval
Changes in flow rates do not occur as quickly as changes in the composition. Calculation times can be reduced by not calculating the enthalpy balance at each integration time step. Users may specify how often the enthalpy balance is calculated and the flow rates are updated. For most applications, a half hour interval is sufficient. By default, the enthalpy balance is calculated at every time step.
Both options above (simplifying liquid density calculations and reducing the frequency of calculating the enthalpy balance) are intended to speed the overall distillation calculation. The user should recognize that these simplifications may compromise the accuracy of solution. There are no general rules-of-thumb that predict the accuracy of those simplifications. It is recommended that these simplifications be used only in the preliminary evaluations of the unit. As a final step, the simulation be re-run without any calculation simplifications.
How to get to this window
The Batch Distillation - Calculation Options window is accessed by pressing the Calculation Options button on the Batch Distillation Main Window.
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