2.7.6 Ng and Stephanopulos’s solution
Ng and Stephanopoulos (1997, 1998) start by stabilizing the reactor. Then they proceed to
look at the input/output level of the plant, where the central point is to fulfill material and
energy balances. At this level it should have been possible to say something about how the
feeds should be adjusted in order to achieve the right mix of G and H, but they do not. Rather
they look at which feed or exit flows that should be used to maintain material balance control.
At the final level they translate the control objectives to measurements. Here material
balance control is translated into inventory controllers, like product flow to control stripper
level and bottom flow to control separator level. The next objective is then reactor pressure
where purge is assigned. Finally feed E is assigned to control of product ratio, and E is
assigned to throughput control. The A and C feed is used for controlling composition of A
and C.
The method is somewhat difficult to follow and they seem to repeat many of the arguments in each phase.