Number of trays
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When performing calculations, how is the number of trays determined? Is there any manual that explains how to calculate the number of trays?
Generally, DSTWU (Distillation Design by Simplified Method) is used to determine the minimum reflux ratio, minimum theoretical number of plates, actual reflux ratio, actual number of plates, feed position, etc.
The number of trays corresponds to the theoretical number of stages. The theoretical stages can be determined through sensitivity analysis; by changing the number of trays, the composition of the output can be observed, and this can be represented as a curve
The issue you mentioned is a design-related problem in simulations; among the column models available in Aspen, only the DSTWU model is a column design model. You can specify a reflux ratio based on your product separation requirements, and Aspen will use an approximate method to estimate the number of theoretical plates required. If you enter the tray efficiency, you can obtain the actual number of trays.
The number of trays you mentioned should refer to the actual number of trays, but in practice, what is used in calculations is usually the theoretical number of trays; it’s not possible to directly enter the actual number of trays. It is recommended that you use the ratefrac model (which has been integrated into radfrac in newer versions) instead of radfrac