Simulation Optimization And Control Study On The Separation Of N-Alkanes Using Semicontinuous Distillation

As the most widely used separation technology in the chemical industry,distillation,consumes more than 40%of the total energy consumption of the chemical industry,and there are problems such as large equipment investment and low thermodynamic efficiency.Therefore,it is of great social and economic value to develop a new rectification technology,reduce the energy consumption of the rectification process,and improve its separation efficiency.The conventional distillation for separating ternary mixtures requires two distillation towers,which has the disadvantages of high energy consumption,large number of equipment and high separation cost.As a process intensification technology,semicontinuous distillation can achieve multi-component separation using less equipment.However,there are currently few design studies for semicontinuous distillation,and no systematic guidance has been developed.In this paper,the simulation,optimization and control of semicontinuous distillation for separating n-alkanes are studied.The multi-objective genetic algorithm was used to optimize the operating parameters of conventional distillation,dividing wall column and semicontinuous distillation,and the best operating parameters are obtained.Several different control schemes are proposed,and the optimal control scheme is selected by the dynamic simulation and analysis.The dynamic simulation of semicontinuous distillation are carried out under a series of capacity to evaluate the economic benefit for semicontinuous distillation.In this paper,the conventional distillation,dividing wall column and semicontinuous distillation processes are established.The multi-objective genetic algorithm optimization of the three processes is carried out with TAC,CO₂ emission and GEC as the evaluation indexes,and the most economical operation parameters are obtained.Five control schemes are proposed for the semicontinuous distillation.The dynamic simulation results show that temperature-concentration cascade control scheme CS5 is the optimal control scheme.Compared with temperature-concentration cascade control scheme CS4,the cycle time is reduced by 20.95%,and the annual throughput is increased by 26.50%.Meanwhile,the separation cost is reduced by 20.75%.Through the simulation,optimization and control of the three distillation processes under a series of annual throughput,it is found that when the annual throughput is less than77.28×10³ kmol/yr,the TAC of semicontinuous distillation is smaller than that of conventional distillation.When the annual throughput is less than 52.94×10³ kmol/yr,the TAC of semicontinuous distillation is smaller than that of dividing column distillation.Generally speaking,in a certain range of annual throughput,the semicontinuous distillation has lower TAC than the conventional distillation and the dividing wall column,meaning good economic benefits.Through the above research,a preliminary scheme for simulation,optimization and control of the process of separating n-alkanes using semicontinuous distillation is established,and the economic benefits of semicontinuous distillation is evaluated,which lays a foundation for the industrial application of semicontinuous distillation technology.