NONLINEAR CONTROL OF NEUTRALIZATION PROCESSES BY GAIN-SCHEDULING TRAJECTORY CONTROL

A new approach to the nonlinear control of neutralization processes in continuous stirred tank reactors is presented. The controller design is based on a process model in terms of the standard titration curve o f the process which was proposed by Wright and Kravaris (Wright, R. A. ; Kravaris, C. Ind. Eng. Chem. Res. 1991, 30, 1561-1572). The central idea of this paper is to combine exact feedback linearization and gain -scheduling techniques to obtain a nonlinear control scheme which pres erves the advantages and overcomes some of the problems of the two sin gle concepts. In a first step, a nonlinear state feedback controller i s computed by exact input/output linearization of the process model to shape the nominal closed-loop system. The required state variables ar e computed by an on-line simulation of the process model. This part of the controller thus is a pure nonlinear feedforward compensator for t he nominal plant. To act against disturbances and model uncertainty, a nonlinear gain-scheduled reference controller is designed by approxim ately linearizing the process model not for a number of operating poin ts, as in the standard gain-scheduling approach, but around the nomina l trajectory generated by the feedforward controller. The feasibility of the proposed design approach is demonstrated on a real laboratory s cale neutralization process where acetic acid is neutralized by sodium hydroxide.