Process Optimization Design And Cross-wall Heat Transfer Analysis Of Extractive Dividing Wall Column

As an important means of azeotropic mixture separation technology,special distillation is widely used in petrochemical industry,Metallurgy and light industry,Food,medicine and other fields.However,the thermodynamic efficiency of the conventional distillation process is relatively low.In the development of modern industry,conventional distillation with high energy consumption and low thermal mechanical efficiency can no longer meet the demand of green production.Therefore,the development of an economical and sustainable distillation process enhancement technology has become an urgent problem to be solved.The dividing wall column（DWC）is operated by integrating two columns into one column.Compared with the traditional two-column distillation,the use of condenser and reboiler is reduced,and the backmixing phenomenon between the intermediate components is avoided.DWC has attracted wide attention in recent years because of its advantages in energy consumption,the process of capital investment and CO₂ emission.At present,the design and simulation of DWC is mainly based on the Petlyuk tower model.While,the model ignores the influence of cross-wall heat transfer on both sides of the dividing wall on the separation process,which makes the theoretical model deviate from the actual process and brings uncertainty to the DWC design and control.Thus,a virtual intermediate heat exchanger is proposed in this paper to design a DWC model with heat transfer,and uses propargyl alcohol-water as an example to verify the proposed method.In this work,the conventional two column extraction distillation（ED）process was designed to separate and recover PA from PA-water binary azeotropic mixture.In addition,the enhanced process of extractive dividing wall column（EDWC）was proposed,and the heat integration design of ED and EDWC processes is carried out.In the process optimization,the traditional sequential iterative optimization process is cumbersome for the multivariable operation process,so this work uses genetic algorithm to search the global optimization.The genetic algorithm ensures the diversity of the population through genetic,crossover,mutation and other operations.The process adopts the mechanism of survival of the fittest,which has several significant advantages,such as random parameter search,eliminating duplicate solutions and invalid solutions,and has good applicability in process optimization.In the whole process,MATLAB and Aspen Plus are combined by Active X control to optimize the operation parameters,and the results are output in Excel.By optimizing the number of trays,feed position,solvent flow rate,overhead flow rate,reflux ratio and other variables in ED,EDWC,heat integration extractive distillation（HI-ED）and heat integration extractive divivding wall column（HI-EDWC）,the energy consumption,capital investment and CO₂ emission were reduced.According to the analysis of four optimized processes,it is found that the capital cost of EDWC process is 15.44%lower than that of ED process,the operating cost is reduced by 0.910×10⁵$per year,and the total annual cost TAC and CO₂ emission are reduced by 15.18%and 12.48%respectively.HI-ED and HI-EDWC heat integration processes have lower energy consumption,TAC and CO₂ emissions.In order to obtain the initial data of edwc cross-wall heat transfer model under the optimal operating paramters and TAC,this work uses genetic algorithm to analyze the influence of partition wall position and lateral producted flow rate on energy consumption of EDWC process.On this basis,the EDWC cross-wall heat transfer model was built by using Aspen Plus simulation software.Under the same operating conditions and gas-liquid distribution ratio,the influence of heat transfer on the energy consumption in the separation process was analyzed.After the optimization design of heat transfer,through the analysis of tray temperature of HI-EDWC model and adiabatic EDWC model,it is found that there are both high temperature on the left side（main tower side）and right side（side line recovery section）of edwc partition wall,and there is heat transfer on both sides.While the heat transfer temperature difference between the two is small,so the temperature change is small.Due to the change of tray temperature,the composition of PA in the side-draw decreased.Which the reboiler duty increased in order to achieve the separation effect.The results show that the cross-wall heat transfer has an effect on the energy consumption of EDWC process.Compared with the adiabatic process,the cross-wall heat transfer will change the flow interaction on the two sides of the partition wall.Compared with the adiabatic process,the cross-wall heat transfer will change the flow interaction on the two sides of the partition,which will cause the change of process energy consumption.