Ricker (1996) comments upon the work of Price et al. (1994). Ricker points out that
plants are often run at full capacity, corresponding to constraints in one or several variables.
If a manipulated variable that is used for level control saturates, one looses a degree of
freedom for maximum production. This should be considered when choosing a throughput
manipulator.
Luyben et al. (1997) point out three limitations of the approach of Buckley. First, he did not explicitly discuss energy management. Second, he did not look at recycles. Third, he
placed emphasis on inventory control before quality control. Their plantwide control design
procedure is listed below: