Tray Towers—Method of McCabe and Thiele

MULTISTAGE TRAY TOWERS—METHOD OF McCABE AND THIELE 

Consider the enriching section of the fractionator of Fig. 9.17. In the absence of heat losses, which can be (and usually are) made very small by thermal insulation for reasons of economy if for no other, Eq. (9.61) can be written 

For all but unusual cases, the only important terms of Eq. (9.112) are those containing the latent heats. The temperature change between adjacent trays is usually small, so that the sensible-heat term is insignificant. The heat of solution can in most cases be measured in terms of hundreds of kJ/kmoI of solution, whereas the latent heats at ordinary pressures are usually in 10 kJ/kmol. Therefore, for all practical purposes. 

If it is sufficiently important, therefore, one can be persuaded that, for alt but exceptional cases, the ratio L/G in the enriching section of the fractionator is essentially constant. The same reasoning can be applied to any section of a fractionator between po mts of addition or withdrawal of streams, although each section will have its own ratio. 

Consider next two adjacent trays n and r, between which neither addition nor withdrawal of material from the tower occurs. A material balance provides 

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