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Control strategies for exothermic batch and fed-batch processes A sub-optimal strategy is developed which combines fast response with a chosen control signal safety margin. Design procedures are described and results compared with conventional control.

By I. Ali Kaymaz

Abstract

There is a considerable scope for improving the temperature control of\ud exothermic processes. In this thesis, a sub-optimal control strategy\ud is developed through utilizing the dynamic, simulation tool. This\ud scheme is built around easily obtained knowledge of the system and\ud still retains flexibility. It can be applied to both exothermic batch\ud and fed-batch processes. It consists of servo and regulatory modes,\ud where a Generalized Predictive Controller (GPC) was used to provide\ud self-tuning facilities.\ud The methods outlined allow for limited thermal runaway whilst keeping\ud some spare cooling capacity to ensure that operation at constraints\ud are not violated. A special feature of the method proposed is that\ud switching temperatures and temperature profiles can be readily found\ud from plant trials whilst the addition rate profile Is capable of\ud fairly straightforward computation. The work shows that It is\ud unnecessary to demand stability for the whole of the exothermic\ud reaction cycle, permitting a small runaway has resulted in a fast\ud temperature response within the given safety margin.\ud The Idea was employed for an exothermic single Irreversible reaction\ud and also to a set of complex reactions. Both are carried out in a\ud vessel with a heating/cooling coil. Two constraints are Imposed; (1)\ud limited heat transfer area, and (11) a maximum allowable reaction\ud temperature Tmax.\ud The non-minimum phase problem can be considered as one of the\ud difficulties in managing exothermic fed-batch process when cold\ud reactant Is added to vessel at the maximum operating temperature. The\ud control system coped with this within limits, a not unexpected result.\ud In all cases, the new strategy out-performed the conventional\ud controller and produced smoother variations in the manipulated\ud variable. The simulation results showed that batch to batch variations\ud and disturbances In cooling were successfully handled. GPC worked well\ud but can be susceptible to measurement noise.Higher Education Ministry and Scientific Researc

Topics: Batch control, Fed-batch control, Sub-optimal control, Control systems design, Dynamic simulation, Adaptive control, Temperature control, Exothermic processes
Publisher: School of Control Engineering
Year: 1989
OAI identifier: oai:bradscholars.brad.ac.uk:10454/4217
Provided by: Bradford Scholars

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