Coffee Decaffeination by Countercurrent Supercritical Fluid Extraction

Illustration 8.4 Coffee Decaffeination by Countercurrent Supercritical Fluid Extraction 

If we now set the actual G/S ratio at twice the minimum amount, we obtain the following result  

The CO2 consumption, which is the inverse of this ratio, is then given by 

The number of stages between feed and effluent is obtained by the usual staircase construction and equals approximately four. The corresponding HETS value is then given by 

There are a number of features in this example drawn from industry that fall outside the conventional boxmdaries of textbook problems. The first item of note is the location of the pinch, which occurs at a point between feed and effluent conditions. The resulting minimum CO2 consumption is at the modest level of 11.9 kg C02/kg beans. Even doubling that amount for actual operating conditions still yields a consumption that is less than that calculated for a single-stage contact (Illustration 6.7). This is a clear-cut vindication of tire coxmtercurrent mode of operation. 

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