BATCHFRAC Initial Estimates

Usage

From the BATCHFRAC Main Window, click the Initial Estimate... button.

Users may provide their own initial estimate values for Temperatures, vapor, liquid compositions. Alternatively, they may select a PRO/II Initial Estimate Generator.

When Providing Initial Profiles:

Users may supply their own estimate values as data profiles.

Tray Temperature Profile, Temperatures must be provided for the top and bottom trays. Data for intermediate trays always are optional. Temperature estimates are the most common for of user-supplied initial profiles.

Vapor and Liquid Compositions These profiles sometimes are helpful for highly non-ideal systems or three-phase distillation calculations. Composition estimates are not needed for most problems.

For VLLE systems, composition profiles may be provided for the bulk liquid phase only.
Push the appropriate buttons to begin entry of Initial Profiles data.

When Using an Initial Estimate Generator:

Both of the models generate estimates for the compositions and temperatures on each stage, including the condenser and reboiler. The two available models are:

BUBBLE The default BUBBLE option initializes temperatures for each tray using bubble-point flashes. The first bubble point flash is the still pot using the charge composition. The bubble point vapor composition from the still pot is used as the liquid composition for the tray above the still point. The bubble point of this stage is calculated, and the temperatures and compositions are propagated up the column using the same procedure.

LINEAR The LINEAR option initializes temperatures for the still pot and he condenser using bubble point flashes. A simplified material balance is performed, taking into account the holdups on the trays to determine the condenser composition. Once the condenser composition is determined, the bubble point temperature of the condenser is calculated. Then the temperature of the trays between the condenser and the still pot are estimated by interpolation.

When an Initial Estimate Generation is used, users may supply selected values in the Initial Profiles windows to replace selected values generated by the Estimate Generator. This is rarely necessary, although highly accurate estimate values tend to speed convergence.

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