Component Balances and Equilibria

The model equations are described in the subsequent sections. The sequence of the sections is (i) material balances including equilibrium relations (ii) energy balances (iii) tray hydraulics and (iv) tray pressure drop. 

A tray consists of two parts the plate at which the contact between hquid and vapor takes place and the downcomer through which the vapor flows from a certain tray to the tray below (see also Fig. 16.5). All balances are expressed in moles per second. For a general tray the mass balance is  

For the feed tray, the bottom and the top accumulator, slightly different mass and component balances are necessary considering the side flows  

By substituting the mass balance into the partial mass balance the mole fraction accumulation for the feed tray, bottom and top accumulator can be written explicitly  

Since the reflux Z +i is set by the reflux ratio, the reflux can be directly calculated from the condensed vapor flow. The molar density ratio corrects for the difference between molar flows and volumetric flows. Usually, no correction is required, as the difference in composition is small  

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