Dynamic Modeling And Control Strategy Design For Heat Integreted Air Separation Column Based On Wave Theory

Cryogenic distillation of the air separation process produces large quantities of high purity nitrogen and oxygen,which is an important industrial process with high energy consumption but low efficiency.In the environment that global energy is increasingly scarce,heat integrated air separation column(HIASC)is considered to be a very promising potential technology for energy saving.However,it is very difficult to design the dynamic model and control scheme for HIASC with the complex structure of internal thermal coupling and the non-ideal multivariate mixture.The control scheme designs for the high-purity and very high-purity product are few.How to effectively establish the nonlinear dynamic model for HIASC and design a control scheme with good control performance are of great significance for the commercialization of such a very large potential technology,which is the frontier of the industry research.The main work and innovation of this paper are as follows:(1)The mechanism model of HIASC with full tower coupling structure is established.Based on the mechanism model,the dynamic characteristics of HIASC are analyzed.PID control scheme,internal model control scheme of the first order control model,internal model control scheme of the second order control model with the reverse response characteristic,generic model control scheme and improved generic model control scheme with online correction and decoupling function are designed.At the same time,the performance and effect of the control schemes are analyzed in the simulation of HIASC with moderate-purity product concentration.(2)Based on the wave theory,the nature wave velocity of HIASC is deduced first.On the basis of this,when the whole tower is disturbed,the characteristics are analyzed.From the macroscopic point of view,the shock wave velocity of HIASC is deduced.After introducing the empirical function of the concentration waveform,a nonlinear wave model based on the shock wave velocity is established.The dynamic characteristics of HIASC with different product purities are observed from the wave theory perspective.(3)Considering the shape of wave propagation is not completely constant,the instant wave velocity of HIASC is deduced.At the same time,a nonlinear wave model based on the instant wave velocity of HIASC is established.Then some dynamic characteristics of HIASC are analyzed.The accuracy of the wave model is verified,and the advantages of the simplified wave model compared to the traditional model are presented.The generic model control scheme based on wave model and the generalized generic model control scheme based on wave model are designed.The control simulation of HIASC for the high-purity product proves the advantages of the proposed control scheme.(4)In the condition of the very high-purity product of HIASC,the error accumulation included in the wave velocity will reduce the model precision and influence the control performance.In order to solve the problem,the wave model is improved for the products at both ends of HIASC,which is combined with the generalized generic model control scheme.In the simulation of HIASC with higher product purity,the presented control scheme shows better control performance.