Research On Optimal Strategies Of Operating And Scheduling For A Polyolefin Plant

The optimal strategies of operating and scheduling for a polyolefin plant were studied by methods of the multi-levels and decomposition-coordination. The activities of manufacture and management were decomposed into management strategy, planning, management dispatch, operation optimization, and process control. The optimization researches were given on the complicated system with the multi-levels.Following work and achievements are mainly included:1) Quality variables and operation variables of the manufacture process of polyethylene by the gas-phase fluidized bed were comprehensively analyzed. Mechanism for the gas-phase polymerization was described. The models of both instantaneous and cumulative quality indexes of the products were established and parameters of those models were determined by running of the polymerization process.2) A generalized dynamic model was proposed for the grade changeover of high density polyethylene (HDPE). A comprehensive analysis was given for optimizing the operation in the period of transition, and the model for optimizing running with some restrictions was presented based upon principles of the modern calculus of variations.3) The theory of the mix-integer programming was used to propose the problem of distributing the loads of multi-production lines with several grade products. For a single line, an optimal schedule model has been presented to minimize the products during the period of transition and the transition time, using the dynamic planning theory. The manufacture data from a plant was used to solve the model.4) According to the actual cases of manufacture and management of a polyolefm plant, selections of the strategic variables and the objective functions and composition of the restrictions were discussed. Using the multi-objective programming theory, an optimal production-planning model has been established for a petrochemical plant in which the resins of high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, and polystyrene and styrene monomer are produced. In this model, the maximum output value and the monthly outputs of each variety on every production line are taken as an objective index and the decision variables respectively, and the market order,material balance, production ability, energy and other supplies are considered as the constraint conditions. An optimal plan has been obtained by a numerical procedure under Matlab system. The research results indicate that the method is effective and available.