Ratio Control for Liquid and Vapor Flow in the Column

Appendix 34.2 Ratio Control for Liquid and Vapor Flow in the Column 

For every eomponent the partial mass balance on a tray can be written as  

Subtraction of x, multiplied by the mass balance from the partial mass balance gives  

Now assume that the coltrrtm is initially at steady state, hence dxjdt = 0. If the ratio Vi Li+i is maintained constant, Eqn. (34.11) represents an equation for the concentration between successive trays. The only way in which the concerrtrations can change is through propagation of the concentration fiom tray to tray, which is a slow arrd gradually changing process. It is evident that the ratio Vf dLu., carmotbe maintained corrstarrt on all trays, this is however possible at both colirtrm ends by controlling the ratios of the extenral flows. 

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