Minimizing Cost of Mass-Exchange Systems

Appendix III provides an overview of process economics. Two principal categories of expenditure are particularly important fixed and operating costs. The fixed cost ( ) can be distributed over the service life of the equipment as an annualized fixed cost ( /yr). The total annualized cost (TAC) of the system is given by 

TAC = annual operating cost -I- annualized fixed cost. 

A material balance on the pollutant that is transferred from the waste stream to the MSA may be expressed as in Eq. (2.10)  

On a y-x (MeCabe-Thiele) diagram, this equation represents the operating line that extends between the points (y/ , xj ) and (y , x ) and has a slope of Ly/G,. Equation (2.10) has thitee unknowns, yf , Lj and xj . Let us first fix the outlet composition of the waste stream, yf . As depicted by Fig. 2.9, the maximum themetically attainable outlet composition of the MSA, xj , is in equilibrium with y . An infinitely laige mass exchanger, however, will be needed to undertake 

On the other hand, when x is fixed and yj is left as an unknown, the minimum theoretically attainable inlet composition of the waste stream, yf is in equilibrium with x (Fig. 2.10), i.e. 

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