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Quantifying the Effect of Process Design on Controllability and Operability

Vikram S. Shabde and Karlene Hoo. Chemical Engineering, Texas Tech Univ, Mail Stop 3121, Lubbock, TX 79409-3121

Traditionally, plant design and control have been treated as distinct processes with the control design following plant design. Such a methodology ignores the effect that the plant design has on the control structure synthesis. Thus, the control structure is limited by the available plant design [1]. In addition, rising operating costs and more stringent environmental and operational constraints have motivated more complex designs which intuitively are more difficult to control. Also, a greater flexibility is demanded from plants to handle different products. These developments have meant that the plants are operated more “dynamically” as opposed to the steady-state design that the traditional design methods have been developed for. These factors have motivated the study of controller synthesis and performance specifications during the design process itself.

While the effect of chemical process design on plantwide control structure synthesis has been known, quantitative measures of their coupling have not been developed [2]. Such a quantification would enable design of a process wherein the vagaries of the plant do not affect the controller. In this work, the coupling between chemical process design and control is developed following the work of [2]. The effect of tighter operational constraints and uncertainty on the coupling term will be investigated. Having knowledge of the degree of coupling, an optimum design and control structure is developed with reachable performance specifications [2]. In this work, the coupling term will be introduced and discussed. Optimization results will be demonstrated on the operation of a spray dryer to produce hollow micro-particles.

References

[1] H.K. Fathy, J.A. Reyer, P.Y. Papalambros, and A.G. Ulsoy. “On the coupling between plant and controller optimization problems.” In 2001 American Control Conference, pages 1864–1869, 2001.

[2] H.K. Fathy, D. Hrovat, P.Y. Papalambros and A.G. Ulsoy, "Nested Optimization of an Active Automotive Suspension's Plant and Controller.” In2003 American Automatic Control Conference, pages 3375-3380, 2003.