| Polyvinyl chloride (PVC) is an indispensable raw material in our national economy, which is polymerized by vinyl chloride monomer (VCM). At present, the problems of low separation efficiency, poor product purity, high energy consumption and operational control instability are prevalently existed in the separation and purification process of PVC. Meanwhile, the high value-added products are failed to be recovered from the bottom liquid emissions, thus resulting in the waste of resources and environmental pollution. To solve those issues above, this paper focus on the process, energy integration and operation control, to help achieve the purpose of energy conservation, emissions reduction and provide an important reference for the actual production by using computer simulators.According to the results of the thermodynamic consistency test, the VLE data of VCM-EDC system is reliable. After thermodynamic models NRTL, WILSON, UNIQUAC interaction fitting regression, comparing simulation data and experimental data average relative deviation of each model, proving that NRTL model has the minimum deviation. Then contrast each regression model value with the value of project acquisition, which indicated NRTL model can simulate VCM-EDC system accurately.To simulate and optimize the TQ201, TQ202 and TQ203, single factor method and orthogonal experimental analysis were used to get the best operational parameters, including operating pressure, feed state, feed location, reflux ratio and distillate to feed ratio. The results showed that the reflux ratio of TQ201 has been reduced from 5.0 to 3.6, and the energy saving was 28.0%; the reflux ratio of TQ202 was reduced from 1.0 to 0.6, and the energy saving was 40.0%. The purity of VCM was 99.999% and the low boiling content of the impurities was less than 1 ppm. The high boiling content was less than 3 ppm. Meanwhile, the cooling medium of 5℃ chilled water was replaced by 32℃ circulating water. The operating cost savings of TQ201 and TQ202 were 34.721 million Yuan per year in total. TQ203 used batch distillation with constant reflux ratio. The optimum number of trays, reflux ratio and operating cycle time were achieved with the dynamic analysis.VCM with mass fraction of 99.9%, dichloroethylene with mass fraction of 99.0% and EDC with mass fraction of 99.0% were afforded in batches, which had 7.353 million Yuan in economic benefits per year with significant environmental benefits.To solve the problems of high energy consumption and inadequate utilization of waste heat in PVC refining process. Two objective functions of minimum amount of utilities and the least of heat exchanger quantity were built. Using pinch technology, the best △Tmin, cold heat logistics grips and minimal amount of utilities had been found. Two kinds of heat exchanger network designs were made. The first design scheme had the minimum amount of utility and the investment recovery period was 6 months. The second one used the existing equipment maximally, the investment recovery period was 4 month, which was more appropriate for the existing factory.To solve the problems of operational control instability, the best control method applicable for PVC distillation system was determined in view of the product requirements, operational stability, energy conservation and environmental protection. Dynamic mathematical models were analyzed. Three control schemes were used in TQ201, two control schemes were used in TQ202. The control conditions of extracted components on TQ203 tower were proposed. By comparing these towers’response to disturbances under different control structure, the conclution showed that TQ201 is more suitable for constant reflux to distillate ratio control and TQ202 should choose constant reflux to feed ratio operation. |
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