For the case in which the total holdup per plate is constant, the value h ^ x can be obtained approximately in a mathematical form (Ref. 2), but it is just as easy in most cases to evaluate it plate by plate. In the present case, assuming the holdup per plate is constant, o h ^ (x) = h(xi + x% + Xi + Xi + x6)
50 - 0.952) + 0.229(100 - D - 5h) + 3.35h 27.1 - 2.205h « 0.721D
If the holdup per plate were 2 per cent of the original charge to the still, then h » 2
and the mois of the distillate would be n - 27.1 - 2.205(2) U ~ 0.721 « 31.5
as compared to D = 37.5 for no holdup. If the value of holdup per plate was as high as 12.3 per cent of the charge, no 95 per cent distillate coùld be produced in the 5-plate column. If the percent of A in the original feed had been smaller, the effect of holdup would have been even more serious.
A similar analysis has been applied by some writers to the case where the distillation has been discontinued at a finite reflux ratio. The usual straight operating line was employed to determine the plate composition at the end of the distillation, but in view of the fact that the operating line is curved for such a case, the calculations are probably of little value. If the operating lines corresponding to Eq. (14-16) or (14-17) could be evaluated for the end of the distillation, then an analysis of the effect of holdup could be made.
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