EFFECT OF DISTURBANCES IN OPTIMIZING CENTRAL - STEADY-STATE OPEN-LOOPBACKOFF PROBLEM

One of the key components in the operation of chemical plants is the a bility to operate over a range of conditions while satisfying performa nce specifications. A method for determining the necessary open-loop b ackoff from a steady-state nominal optimum is introduced to ensure tha t disturbances cause no constraint violation. This approach consists o f defining a joint optimization-flexibility problem that can be solved within an optimization framework based on an iterative procedure. By formulating the optimization problem in economic terms the backoff in the objective function is a measurement of the open-loop economic pena lty that is necessary to be paid to achieve feasible operation over th e disturbance range of interest (considering the worst combination). A rt upper bound on the economic potential available for closed-loop con trol cart then be established prodding a valid reference for ranking d ifferent control schemes. Three examples presented illustrate the appl ication of this approach: (I) a simple linear example, (2) a system of two CSTRs; and (3) an industrial distillation column.