McCabe-Thiele method total reflux

Total reflux corresponds to a situation where there is no feed, distillate, or bottoms and where the minimum number of stages is required to achieve a desired separation. It will be recalled that in the McCabe-Thiele method this situation corresponded to having the operating line coincide with the y = x line. 

With an accurate VLB diagram the 1950s graphical McCabe-Thiele method can once again be used to yield in minutes the number of theoretical stages required at total reflux for a separation. 

C Total and Minimum Reflux Ratio for McCabe-Thiele Method... 

Figure 11.4-10. Total reflux and minimum number of trays by McCabe-Thiele method. 

The operation of a binary distillation has two important limiting cases minimum and maximum stages for a given separation. Minimum stages occur when the column is operated with total reflux (i.e., no top product is withdrawn). This situation, when applied to the McCabe-Thiele method, uses the y = x line as the mass balance for both rectifying and stripping. The situation is depicted in Figure 12-11. 

Figure 12-11. Total reflux and minimum stages with McCabe-Thiele method. (Reproduced with permission from reference 18. Copyright 1997, American Chemical Society.)...

In the calculation of the plate number for batch distillation Zuiderweg [158] takes into account the influence of the total hold-up and the magnitude of the transition fraction. Mixtures having ix-values from 1.07 to 2.42 were used to study the dependence of separation sharpness on relative total hold-up, reflux ratio and plate number. By means of the pole height S the optimum reflux ratio can be determined. The method corresponds to the determination after McCabe-Thiele with a final state. cs = 5 mol%. 

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