An autoclave reactor offers flexibility in producing specialty grades of ethylene/vinyl acetate copolymer at a temperature range of 150–230 °C and pressure range of 1400–2000 kg/cm2. At such conditions, copolymerization is accompanied by decomposition of reactants which increases the risk of thermal runaway. The runaway reaction is initiated by local hot spots in the reactor which are generated by process/equipment disturbances or imperfect mixing in the reactor. It is hard to predict decomposition, due to the extremely fast dynamics of the event. A decomposition detection method was developed based on the overall energy balance around the reactor. During normal steady state operations, the heat balance error should be within reasonable limits. If abnormal conditions generate excess heat in the reactor, the heat balance error will exceed the limit, indicating the possibility of an impending decomposition. Principal component analysis (PCA) was used for model identification and to get the unknown parameters in the model. An iterative PCA technique was used to confirm the selection of the model. Long term plant operation data over a period of six months were used for training and testing of the model. Data validation rules were applied and false alarms associated with operating condition fluctuations were minimized by applying appropriate equations for conversion at various operating conditions. The model was validated with an actual plant steady state decomposition case where the model could predict decomposition with a few seconds of lead time.
A model of slurry polymerization of ethylene in a multistage continuous stirred-tank reactor (CSTR) was developed in order to find the effect of stagewise variation of parameters on polymer polydispersity and rate of polymerization. Higbie's penetration theory has been used to calculate monomer absorption rate in the presence of micron-sized single site type catalyst in slurry phase. The residence time distribution of the growing polymer particles in an ideal CSTR was modelled by a relaxation-type unsteady state approach. The effect of gas-liquid mass transfer limitations on polymer properties is predicted for various reactor configurations. An analysis of various possible configurations of two-stage CSTR with stagewise variation of the partial pressures of ethylene and/or hydrogen has been made.
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