Research On Simulation And Control Scheme Of The Extractive Distillation Of Vinyl Acetate-Methanol Azeotropes

At present, large amounts of large amounts of vinyl acetate (VAc)-methanol (MeOH) azeotropes were produced in the process of polyvinyl alcohol (PVA)production. The process generally has some technical problems: product purity is not high, the dosage of extraction agent, high energy consumption, large equipment investment cost and the instability of the process control in the process of separation. To solve those issues above, this paper focus on the process, energy saving, process control and economic benefits using computer simulation technology to simulate the process of calculation, the economic optimization and dynamic control. Compared the three kinds of process flow, process parameters and optimal control were obtained to achieve the goal of energy conservation and emissions reduction.According to the results of the thermodynamic consistency test, the VLE date of VAc-Methanol system is reliable. After the thermodynamic models interaction fitting regression of Wilson, NRTL, UNIQUAC, the best results that agree with the experiment data are obtainted with the UNIQUAC model. Then contrast each regression model value with the value of project acquisition, which UNIQUAC model can simulate VAc-Methanol-Water system accurately.Through the analysis and economic optimization of the original continuous extractive distillation columns, the optimized design parameters of the extraction column are as follows:plate number 31, extraction solvent flow rate 17800 kg/h, temperate 76℃, overhead recovery 18477 kg/h, extraction agent feeding position 2, mixture feed position 18 and reflux ratio 0.27. The solvent recovery column design parameters are as follows:plate number 32, overhead recovery 12626 kg/h, mixture feed position 22 and reflux ratio 1.08. The composition of VAc and Methanol increased to 93.5% and 99.9%, respectively. The TAC of continuous extractive distillation process is 23.7 million/a.The problems of high equipment investment cost and unstable process control can be solved using batch extractive distillation process with constant reflux ratio. The parameters of the batch extractive distillation column are as follows:plate number 16, extraction solvent flow rate 24673 kg/h, temperate 100℃, extraction agent feeding position 5, reflux ratio 10, operation time 1.75. The TAC of batch extractive distillation process is 83.6 million/a.The problems of high energy consumption can be solved using thermal coupling distillation principle of extractive dividing wall column. The main column parameters as follows:plate number 51, extraction solvent flow rate 17800 kg/h, temperate 75℃, overhead recovery 18477 kg/h, extraction agent feeding position 2, mixture feed position 18, gas phase extraction position 43, gas flow rate 16325 kg/h, reflux ratio 0.22. The lateral line column design parameters are as follows:plate number 30, overhead recovery 12874 kg/h and reflux ratio 1.0. The TAC of extractive dividing wall column is 20.3 million/a.From an economic perspective, the fixed investment, energy consumption cost and TAC saved by extractive dividing wall column are 9.99%,14.19% and 14.06%, respectively. From the dynamic control perspective, double temperature control structure is more effective for continuous extractive distillation process and R/F constant control structure is more effective for extractive dividing wall column. Both of them can produce good control effect on feed flow and feed composition disturbances.