Simulation And Optimization For Separation Of Benzene And Toluene

Aromatics is the basic product and raw materials of petrochemical industry.With the increasing demand for aromatics,the production capacity of aromatics is often promoted by revamping the catalytic reforming device.In this paper,the technological transformation and optimization of the benzene-toluene separation unit were carried out with the revampment project of 400,000 t/year aromatics extraction device.Specially,the optimization of the process parameters was carried out on the new cutting scheme.Then,the multi-effect rectification was accomplished by using the thermal integration technology between the two towers,and the research for the new process program was also performed by replacing the divided wall colunmn.The energy efficiency of these revampment results are compared.The separation process was simulated by Aspen Plus software using the modified thermodynamic model RKS-BM.After the rigorous simulation,the influences of theoretical stages and feed stage have been analyzed and optimized for reducing consumption,respectively.The optimal conditions are as obtained,that is,for the benzene column,the number of theoretical stages is 46,the feed stage is at the 22^nd stage,and the purity of benzene is 99.96%;while for the toluene column,the number of theoretical stages is 41,the feed stage number is 23,and the purity of toluene is 99.9%,thus allowing8788kW for total cooling duty and 8367kW for reboiler duty.Furthermore,in the process of heat integration,the operating pressure of toluene rectification column increased up to 0.35MPa.When products are satisfied with the production standards in heat integration,the total cooling duty is 5054kW,and the reboiler duty is 5173kW.Compared with the conventional process,the cooling load of the new one is reduced by 42.49%,and the thermal load at the bottom of the tower is reduced by38.17%.In the simulation of divided wall column,the influences of feed stage,side-draw stage,reflux ratio,vapor flow rate and liquid flow rate are optimized based on the initial data provided by the three-column model.For the optimizing simulation conclusion of divided wall column,the cooling duty is 6454kW,reboiler duty is 6179kW.It indicates that the method for divided wall column has made great contribution to energy saving,namely the cooling load of the tower is reduced by 26.56%and the bottom heat load is reduced by 26.15%.