Above the feed plate similar approximations can be made giving, 1 +^(1 -xAD)(a - 1)] (7-69)

Lewis Method. Lewis (Ref. 8) expresses the rate of increase of concentration of the liquid in the column from one plate to the next by the differential dx/dn; therefore, dx

rectification of binary mixtures 179

Fig. 7-28. Plot for analytical equation.

Fig. 7-28. Plot for analytical equation.

The material-balance equation

VnVn = On+l^n+1 + DXd can be written, using V = 0 + D, yn = xn+\ + q (xD — yn)

The integration of this equation gives the number of theoretical plates between the x limits chosen; thus, the number of theoretical plates above the feed Nn is f

yn — Xn — Q (XD — yn) Similarly, below the feed the theoretical plates Nm become

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