Mass-exchange pinch diagram

Figure 4.4 Mass-exchange pinch diagram [17]. MSAs, Mass-separating agents.

We are now in a position to incorporate material balance into the synthesis procedure with the objective of allocating the pinch point as well as evaluating excess capacity of process MS As and load to be removed by external MSAs. These aspects ate assessed through the mass-exchange cascade diagram. 

This paper has presented and tested a design philosophy for the synthesis of mass exchange networks whereby an MINLP approach is integrated with pinch analysis tools. At the heart of the integration is the use of pinch-based total cost targets to evaluate the optimality of MINLP solutions and driving force diagrams to identify different initial solution structures. 

For the low-temperature distillation process shown in the flow diagram in Fig. 7.18, calculate the minimum hot-utility requirement and the location of the heat recovery pinch. Assume that the minimum acceptable temperature difference, ATrma, equals 5°C. The specifics of the process streams passing through the seven heat exchangers appear in the first five columns of Table 7.8, the mass flowrates of the streams being represented within the enthalpy (AH) values. 

The cascade diagram is shown in Figure E15.10(b). Just as in heat-exchange networks, excess mass is cascaded through each interval. In this example, there is no pinch. At the bottom of the cascade diagram, there is excess mass requiring a lean utility (LU). An LU is a different separation unit, such as an adsorber, that removes solute. 

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