McCabe-Thiele method rectifying section

The McCabe-Thiele method employs the simplifying assumption that the molal overflows in the stripping and the rectification sections are constant. This assumption reduces the rectifying and stripping operating line equations to ... 

For the moment, let us assume that the pressure has been specified, so the VLE is fixed. Let us also assume that the reflux ratio has been specified, so the reflux flow rate can be calculated R = (RR) (D). The equimolal overflow assumption is usually made in the McCabe-Thiele method. The liquid and vapor flow rates are assumed to be constant in a given section of the column. For example, the liquid flow rate in the rectifying section Lr is equal to the reflux... 

The subscripts on V and L have been omitted since constant molal overflow is assumed in the McCabe-Thiele method. Thus, V and L remain constant throughout the rectifying section of the column. Rearranging and solving for yn + i gives... 

The determination of the L/F ratio for the rectifying section of the column is rather meaningless since this quantity does not remain constant as in the McCabe-Thiele method but is dependent on the location in the column. For example, the L/V ratio at the top of the column is... 

The procedure in the stripping section is very similar. An equilibrium tie-line relates the reboiler concentration Xb with the vapor concentration 3 above the reboiler liquid. A line drawn from A 2 through establishes the liquid concentration Xi on the first plate in the bottom of the column. This procedure is repeated until the principal operating line is reached. Generally, only a part of a theoretical plate is required for the last step. This will have to be counted as a theoretical plate since partial plates are not practical in a real column. The separation called for in Example 6.8 and solved with the aid of the Ponchon-Savarit method shows a requirement of 4 theoretical plates in the rectifying section and 5 theoretical plates in the stripping section. The results are identical to those determined when the McCabe-Thiele method was utilized in Example 6.8 because the partial plates in both methods were counted as full plates. 

Combine material-balances information from the McCabe-Thiele graphical method with interphase mass-transfer considerations to determine the packed height of the rectifying and stripping sections of a continuous-contact binary distillation tower. 

The conventional McCabe-Thiele graphical method for analysis of binary mixtures was applied to determine the number of theoretical plates necessary for the separation, 11,3 theoretical plates are required for the rectifying section, and 9.4 for the stripping section. Thus a total of 20,7 theoretical plates are required. Since the value of chosen was 70 per... 

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