Estimate the number of theoretical plates and the feed plate position in an atmospheric pressure column
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PROII simulates the atmospheric tower in a refinery unit; can the number of theoretical plates and the location of the feed plate be estimated using a simplified tower model?
The number of theoretical plates can be calculated using the SHORT CUT module for simple distillation columns, but the result may not be very accurate; therefore, calculation using a distillation column is still necessary. The optimal feed position seems to be uncalculable by the SHORTCUT module; however, in the DISTILLATION module, once the calculations converge, it is possible to determine the optimal feed position using the CASE STUDY tool.
A simplified method can be used to calculate the minimum theoretical number of plates and the feed position for a given operating condition, but these values can only serve as initial values for simulations using the precise method; the optimal feed position can be determined through sensitivity analysis.
One can first use shortcuts to design the atmospheric tower, and then use the results to guide more precise calculations; I find this to be quite useful as a guiding approach. As for the feed position, as well as the setting of other parameters required for precise calculations—such as the amount of stripping steam, the heat taken from the intermediate pump circulation, the degree of superheating, and so on—it is necessary to have a certain understanding of the actual operation of the atmospheric pressure tower and to possess some empirical values in order to make informed decisions regarding these settings. A few days ago I did such exercises, and I found them to be quite helpful.