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.

摘要

There is a considerable scope for improving the temperature control ofudexothermic processes. In this thesis, a sub-optimal control strategyudis developed through utilizing the dynamic, simulation tool. Thisudscheme is built around easily obtained knowledge of the system andudstill retains flexibility. It can be applied to both exothermic batchudand fed-batch processes. It consists of servo and regulatory modes,udwhere a Generalized Predictive Controller (GPC) was used to provideudself-tuning facilities.udThe methods outlined allow for limited thermal runaway whilst keepingudsome spare cooling capacity to ensure that operation at constraintsudare not violated. A special feature of the method proposed is thatudswitching temperatures and temperature profiles can be readily foundudfrom plant trials whilst the addition rate profile Is capable ofudfairly straightforward computation. The work shows that It isudunnecessary to demand stability for the whole of the exothermicudreaction cycle, permitting a small runaway has resulted in a fastudtemperature response within the given safety margin.udThe Idea was employed for an exothermic single Irreversible reactionudand also to a set of complex reactions. Both are carried out in audvessel with a heating/cooling coil. Two constraints are Imposed; (1)udlimited heat transfer area, and (11) a maximum allowable reactionudtemperature Tmax.udThe non-minimum phase problem can be considered as one of theuddifficulties in managing exothermic fed-batch process when coldudreactant Is added to vessel at the maximum operating temperature. Theudcontrol system coped with this within limits, a not unexpected result.udIn all cases, the new strategy out-performed the conventionaludcontroller and produced smoother variations in the manipulatedudvariable. The simulation results showed that batch to batch variationsudand disturbances In cooling were successfully handled. GPC worked welludbut can be susceptible to measurement noise.