Graphical design methods McCabe Thiele

Graphical methods at best are simply illustrative for the student today, but they are occasionally referenced by the process engineer. Extraction, like distillation can be viewed as a stage-wise operation, and hence metliods based on the McCabe Thiele approach briefly described in Chapter 4 have been applied to preliminary design cases. Indeed, both absorption and adsorption are stage-wise operations. 

Marek (8) derived a design procedure for plate columns based on material and enthalpy balances which included the presence of a chemical reaction. For a ternary mixture a combined numerical and graphical method was suggested using a modified McCabe-Thiele construction. The problem was simplified by assuming negligible heat of reaction and 100% stage efficiency. The hypothetical reactions employed were A + B 20 and A + B Q. 

Lee J.W., Hauan S., Lien K.M. and Westerberg A. (2000c). A graphical method for designing reactive distillation columns II. The McCabe-Thiele method. Proceedings of the Royal Society of London Series A Mathematical Physical and Engineering Sciences 456, 1965-1978. 3.2.7, 3.2.7, 3.4... 

Recall that when we designed distillation columns with the graphical McCabe-Thiele method, we specified the relative flow rates of liquid and vapor to obtain the operating lines. What diameter of column is needed to accommodate the absolute flow rates If the column is too narrow le., the sieve plate area is too small), the liquid will pass over the sieve plate too quickly and not equilibrate with the vapor. If the colunm is too wide, the liquid will not cover the tray completely and the vapor will blow through without equilibrating. 

The graphical McCabe-Thiele methods studied in the previous sections for the design of distillation columns are also widely used to analyze the operation of an existing column. In this case the total number of trays in the column Nj-is fixed. The feed tray may also be fixed, or, if there are multiple feed points available on the column, it may be varied. These fixed-column problems are called rating problems, as opposed to the design problems, in which Nt is calculated. 

Although all of the separation problems involving binary mixtures may be solved by use of the general methods presented in subsequent chapters for multi-component mixtures, it is, nevertheless, rewarding to consider the special case of the separation of binary mixtures because this separation may be represented graphically in two-dimensional space. Many of the concepts of distillation may be illustrated by the graphical method of design proposed by McCabe and Thiele.9... 

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