Column Tray Efficiency
Column calculations are normally based on theoretical trays (equilibrium stages). The tray efficiency models may be used with the Inside-Out, Enhanced I/O, Chemical and Electrolytic algorithms to modify the separations from those obtained with equilibrium stages to simulate non-equilibrium conditions which exist in an operating column. It is important to note that none of the tray efficiency models is an overall tray efficiency model, where overall tray efficiency is defined as the number of theoretical trays divided by the number of actual trays. Overall tray efficiency is a complex function of many parameters and there are currently no generalized models suitable for flowsheet simulators.
Usage
From the Column Main Window, push the Tray Efficiencies button.
Select the desired Tray Efficiency Type option: Murphree, Equilibrium or Vaporization. Only Vaporization efficiency calculations are allowed with the Chemical or Electrolytic algorithm.
Optionally, a Tray Efficiency Scale Factor with a value from 0.0 to 1.0 may be supplied. All supplied tray efficiency data are scaled by this factor which may be varied with a Controller unit operation. Alternatively, it may be referenced using the Define system relative to any available unit operation or stream parameter calculated elsewhere in the simulation.
Push the Efficiency Data button to begin entry of Tray Efficiency Data.
Additional Information
Care must be exercised when using tray efficiency models since all of the models result in non-equilibrium vapor leaving the trays for which efficiencies are applied. This has serious consequences for trays in which the vapor product is condensed, such as tray two, and can cause inconsistencies in reported cooling duties. For columns without condensers, the overhead vapor may be superheated or in the two phase region when a tray efficiency is applied to tray one. Liquid products leaving trays with tray efficiencies may also not be in equilibrium.
When tray efficiencies are applied to tray two for columns with condensers, the condensing curve generated by the Heating Curves operation will not match the column operating conditions since this operation assumes that the column overhead vapor is at its dew point.
Tray efficiencies of unity are always applied to the trays representing the condenser and reboiler.
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