Optimization And Control Of N-butanol And P-xylene Mixture Separation Process

N-butanol and p-xylene are common organic solvents.The distillation separation of their mixtures involves the rational utilization of energy consumption.In order to optimize and control the energy-saving process of n-butanol and p-xylene mixture separation,the steady-state and dynamic simulation for the separation process of the mixture was carried out.The cost model of distillation process was designed to facilitate the economic analysis of different processes.By analyzing the phase diagram of the mixture under different pressures,it is determined that it can be separated by pressurized distillation and pressure-swing distillation(PSD).The process of pressurized distillation was optimized,the annual total cost(TAC)of the optimal process is 329585$/y.The optimization method of traditional PSD was designed,and the TAC of the optimal process was 216560$/y.Therefore,although both the pressurized distillation and the traditional PSD can meet the separation requirements,the traditional PSD has significant economic advantages.In order to reduce the energy consumption of traditional PSD process,the energy-saving technology of heat pump and heat integration was adopted.By optimizing heat pump parameters and distillation tower parameters of the heat pump assisted PSD process,the optimal process can save TAC 18.10%compared with that of traditional PSD.Heat integration is divided into partially heat integration and fully heat integration,the optimization results are as follows:compared with traditional PSD process,partially heat integration PSD and fully heat integration PSD can save TAC 24.86%and 29.98%respectively.So fully heat integration PSD has the best economic benefit.The dynamic control analysis was carried out for the optimal process of traditional PSD and fully heat integration PSD.By introducing feed flow rate and feed composition disturbances in the process,the response speed,instantaneous deviation and product purity of the process are taken as the criteria to judge the effect of the control structure.The basic control,QR2/F ratio control and QR1/F ratio control structures were designed for the traditional PSD.The results show that QR1/F ratio control structure has the best control effect among the three structures.For the fully heat integration PSD,the basic control structure has the problem that the product purity can not meet the requirements.QR1/F ratio control structure can solve this problem and meet the control requirements.