Dynamic Control Study Of Complex Distillation Processer For Hydrocarbon Separation

Hydrocarbon is an important chemical raw material in petrochemical industry.In this paper,Aspen Plus and Aspen Dynamics are used to study the design and control of distillation processes for n-pentane,n-hexane,n-heptane,n-octane,n-nonane five kinds of hydrocarbon mixtures separation.First,the separation process of conventional four column distillation is put forward.The PENG-ROG equation with built-in binary interaction parameters is selected as a property method in calculation.The minimum Total Annual Cost(TAC)is taken as the optimization objective function to design and optimize the distillation process.TAC of the optimal process is 2.1518×106 $/year.The optimal steady state process is exported to Aspen Dynamics software for dynamic control research.A dynamic control scheme with proportional control of reboiler duty and feed flow rate(QR/F)is proposed,which can effectively control product purity and achieve stable control of conventional four column distillation process.In order to explore the energy saving technology of distillation process,the complex distillation process with multi stripper is designed based on genetic algorithm.Similarly,the simulation and optimization of the complex distillation process is based on minimum TAC.The TAC of the optimal process is 1.42815×106$/year,which is 33.6% lower than the conventional distillation process.For the dynamic control of complex distillation process with multi stripper,the basic control structure with sidestreams flow and main column reboiler duty proportional control(S/QR)is proposed,the results show that the based control structure has poor control effect on n-hexane and n-pentane purity.Based on the basic control structure,an improved dual temperature control structure is proposed.The fixed reflux ratio control is replaced by the feed forward proportional control of the reflux flow rate and the feed flow rate(R/F).Meanwhile,the temperature of the stage 12 in the main column T1 is controlled by R/F ratio.The result shows that the control structure can effectively stabilize the feed flow rate and composition disturbance.Based on the energy saving advantages of the dividing wall column,the Kaibel dividing wall column is studied for hydrocarbon separation system.And explore the design and dynamic control of the Kaibel dividing wall column.Three column model of Kaibel dividing wall column is established,the TAC of the optimal process is 1.78865×106 $/year,which is reduced by 16.9% compared with the conventional four distillation process.On this basis,the composition control structure of Kaibel dividing wall column distillation is proposed.The dynamic response result shows that the composition control sttucture can make the product purity return to the set point,but it has the disadvantage of long recovery time and high fluctuation of purity.Based on the existing problems of the composition control structure,an improved temperature control structure is put forward.Compared with the dynamic control effect of the composition control structure and the temperature control structure,it is found that the product purity is restored more rapidly and purity fluctuation is smaller under the temperature control structure,which indicates that the temperature control structure can control the Kaibel dividing wall column distillation process more effectively.Compared the three distillation processes,the results show that the complex distillation process with multi stripper has the smallest TAC and the highest economy.Compared to the complex distillation process with multi stripper,the control structure of Kaibel dividing wall column distillation can handle feed disturbance more effectively,the purity is closer to the design value.