Non-equilibrium Modeling And PSO Study On Distillation Process For Cryogenic Air Separation

With the rapid development of science and technology,electronics,metallurgy,petroleum refining,aerospace and other industries have increasing demand for industrial gases such as pure nitrogen and pure oxygen.Large-scale cryogenic air separation units(ASU)have become the main source for large quantities of high-purity gas products.At present,energy saving and consumption reduction have become important considerations in the design and operation of the ASU.The distillation columns,key to the cryogenic air separation system,have the largest energy consumption.Modeling of the distillation process mechanism is the important part for realizing the optimization and real-time control of the distillation system.In order to develop a process mechanism model that is both accurate and fast,the following research work is carried out around the non-equilibrium model(NEM):1.The Through reading and collating a large number of literatures,the research progress at home and abroad related to the modeling of cryogenic distillation process mechanism and the optimal design of distillation column were discussed in detail.Firstly,the main technologies and development trends of the air separation process were summarized,and the significance of the mechanism modeling for the cryogenic ASU was clarified.Then,the research status of mechanism modeling by domestic and foreign scholars in the past 20 years was systematically summarized.At the same time,the dynamic prediction models for cryogenic air separation system were reviewed in combination with the requirements of dynamic control.Aiming at the requirements of the optimization operation and control,the characteristics of the intelligent optimization algorithm and its application in chemical optimization problems were discussed,which laid the foundation for subsequent research work.2.The NEM for cryogenic distillation was established and the solution strategy was determined.Considering the particularity of the cryogenic distillation process,the NEM was established under the low temperature conditions with the structured packing column(SPC)as the research object.Subsequently,the separation efficiency function was used to simplify the model,and the Thomas algorithm was used,which avoided the memory and storage space problems caused by solving large nonlinear equations.3.The validity of the model and solution strategy was verified,and the reliability evaluation of different kinds of mass transfer correlation was carried out.The NEM was programmed by Fortran language.The simulation results were compared with those from the Rate-based module of Aspen plus and limited measured data,which confirmed the effectiveness of the model and solution strategy.Then,based on the program,the feasibility of the reported mass transfer correlations on the cryogenic distillation calculation was investigated.4.Combined with the modified particle swarm optimization algorithm(MI-PSO),the optimal design of the cryogenic distillation column was carried out.Firstly,the steady state characteristics of the upper SPC were summarized,which revealed the influence of varied feed locations and rates on the exergy loss and main condenser heat load.Then,combing MI-PSO with the distillation calculation program,the structure parameters of the upper SPC for 17000 Nm3/h were optimized,and the exergy loss of total column and main condenser heat load were reduced by 36.3% and 5.4%,respectively,which provided a simple and effortless solution for the optimal design of the cryogenic distillation column.