Figure 14-7 is a plot of Eq. (14-23) from which the value of NOG can be read directly as a function of mGM/LM and the ratio of concentrations. This plot and Eq. (14-23) are equivalent to the use of a logarithmic mean of terminal driving forces, but they are more convenient because one does not need to compute the exit-liquor concentration x1.
In many practical situations involving nearly complete cleanup of the gas, an approximate result can be obtained from the equations just presented even when the simplifications are not valid, i.e., solutions are concentrated and heat effects occur. In such cases the driving forces in the upper part of the tower are very much smaller than those at the bottom, and the value of mGM/LM used in the equations should be the ratio of the operating line LM/GM in the low-concentration region near the top of the tower.
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