Optimization of Processes Involving a Purge

As with the case of byproduct losses, another cost needs to be added to the tradeoffs when there is a purge. This is a raw materials efficiency cost due to purge losses. If the PRODUCT formation is constant, this cost can be defined to be  

Cost of purge losses = cost of FEED lost to purge — value of purge 

The purge usually only has value in terms of its fuel value. Alternatively, if the purge must be disposed of by effluent treatment. 

as with the byproduct case, those raw materials costs which are in principle avoidable (i.e., the purge losses) are distinguished from those which are inevitable (i.e., the stoichiometric requirements for FEED entering the process which converts to the desired PRODUCT). Consider the tradeoffs for the reaction in Eq. (8.1), but now with IMPURITY entering with the FEED. 

Cost of Purge Losses = Cost of FEED Lost to Purge — Value of Purge (13.41) 

Cost of Purge Losses = Cost of FEED Lost to Purge 

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