SELECTION OF PROCESS-CONTROL STRUCTURE-BASED ON ECONOMICS

The effect of dynamics on process economics is heavily dependent on the implemented controller, and the physically attainable controller performance is limited by the choice of controlled and manipulated variables. This paper considers the systematic selection of economically optimal regulatory control structures from the set of all possible measurements and manipulated variables. The solution of such a synthesis problem requires an analysis method. Historical approaches to control structure evaluation consider ''controllability indices'', and their trade off against steady state economics, whereas the approach described in this paper allows direct evaluation of the economics of a process controller. A mixed integer nonlinear optimal control problem is posed for the problem of selecting an economically optimal multiloop proportional-integral process control structure. Experience with the method is presented using a double effect evaporator case study.