Column Design and Performance Analysis

An analytical equivalent to the Gilliland correlation is expressed in equation form (Molokanov et al., 1972)  

The calculations, aided by computer simulation programs, are started by making rough estimates of the overhead and bottoms compositions, based on the desired separation. The condenser pressure is determined so that it ensures condensation of the overhead. That is, the condenser pressure should be such that the estimated dew point temperature of the overhead stream is higher than the temperature of the cooling medium at hand. The column pressure should be higher 

FIGURE 12.4 Gilliland correlation. The symbols on the curves represent data from three different systems. (Reprinted with permission from E. R. Gilliland, Ind. Eng. Chem.. 32, 1220, 1940. American Chemical Society.) 

the relative volatilities, a, are determined as averages of estimated a s 

The flnal compositions and relative volatilities are then used to calculate the minimum reflux, R, using the Underwood method (Equations 12.29 and 12.30). The calculated values of and are next applied in the Gilliland correlation to determine a suitable combination of trays and reflux, N and R, consistent with economic and design considerations. The column can then be approximately sized based on the internal liquid and vapor flows as calculated from the reflux ratio and product rates. 

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The reader may by now be suffering from a surfeit of column design and performance analysis. We do not wish to abandon the topic entirely but... 

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