CHAPTER FIVE – Synthesis of Mass-Exchange Networks—An Algebraic Approach

This chapter presents an algebraic procedure that yields results equivalent to those provided by the graphical pinch analysis. The graphical pinch analysis provides designers with a useful tool that represents the global flow of mass from the rich streams to the mass-separating agents (MSAs) and determines performance targets such as the minimum operating cost of the MSAs. But it is subject to the accuracy problems associated with any graphical approach. This is particularly so when there is a wide range of operating compositions for the rich and the lean streams. This neccessitates the use of an algebraic method. The composition-interval diagram is a useful tool for ensuring thermodynamic feasibility of mass exchange. In it each process stream is represented as a vertical arrow whose tail corresponds to its supply composition and whose head represents its target composition. Next, horizontal lines are drawn at the heads and tails of the arrows. These horizontal lines define a series of composition intervals. The objective of constructing a table of exchangeable loads is to determine the mass-exchange loads of the process streams in each composition interval. Having determined the individual loads of all process streams for all composition intervals, one can also obtain the collective loads of the rich and the lean streams. The collective load of the rich streams within the k th interval is calculated by summing the individual loads of the rich streams that pass through that interval.