Mass-Exchange Cascade Diagram

Having determined the individual loads of all process streams for all composition intervals, one can also obtain the collective loads of the waste and the lean streams. The coUective load of the waste streams within the itth interval is calculated by summing up the individual loads of the waste streams that pass through that interval, i.e. 

Similarly, the collective load of the lean streams within the tfa interval is evaluated as follows  

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. 

As has been mentioned earlier, the CID generates a number Ni , of composition intervals. Within each interval, it is thermodynamically as well as technically feasible to transfer a certain mass of the key pollutant from a waste stream to a lean stream. Furthermore, it is feasible to pass mass from a waste stream in an interval to any lean stream in a lower interval. Hence, for the J th composition interval, one can write the following component material balance for the key pollutant  

CHAPTER FIVE Synthesis of mass-exchange networks 

---

Using the cascade diagram, solve Problem 3.3. Also, synthesize an MEN which h the minimum number of units satisfying the MOC solution. Employ the mass-load paths to reduce the number of mass exchangers at the expense of increasing operating cost. 

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. 

---