Evaluation And Morphological Analysis Of Energy-saving Distillation Sequences For Separating Multi-component Systems

The chemical industry is one of the pillar industries of the national economy and a major energy consumer in the industrial sector.Distillation is currently the most widely used separation process in the chemical production field,and it is also a unit operation with large energy consumption.Its energy consumption accounts for about 40% of the energy used in the entire chemical industry.Therefore,improving the energy efficiency of the distillation process is of great significance for promoting further energy conservation and emission reduction in the chemical industry and achieving sustainable socio-economic development.As the number of components of the feed mixture increases,a high-purity product of each component in the mixture is obtained,and the number of distillation sequences increases almost explosively.Therefore,the rapid and accurate selection of energy-saving distillation sequences(without thermally coupled distillation sequences and fluid direct thermal coupled distillation sequences)can save time for industrial design and provide theoretical guidance for subsequent design and optimization of processes.In this paper,the distillation sequence was taken as the research topic,a morphological analysis method for separating the distillation sequences of multi-component systems is proposed.The logical structure was used to systematically screen the energy-saving distillation sequences of multi-component systems.Finally,the distillation column sequence with the highest thermodynamic efficiency and the energy-saving coupling structure of distillation were obtained.The specific research contents are as follows:1.The morphological analysis method of distillation sequence proposed in this paper includes two processes: branching and convergence.The branching process is divided into five steps: factor analysis,establish the morphological search space,morphological analysis,etc..By analyzing the dynamic characteristics of each column of the distillation sequence in the search space and the conditions of the inlet and outlet,the complex distillation column sequence was equivalent to a simple column model,and the short-cut calculation and optimization process for judging the flow direction of the thermally coupled flow in the simple column model were listed.2.Aiming at the convergence process of morphological analysis of distillation sequence,this paper also proposed an evaluation index of energy-saving distillation sequence.Based on the equivalent simple column model,the thermal load of distillation sequence was virtually segmented.Combined with entropy analysis,the heat balance calculation of fluid direct thermal coupling distillation sequence was carried out,and the calculation formula of the distillation sequence efficiency corresponding to the direct thermal coupled distillation sequence of different fluids was obtained,and the efficiency of the distillation sequence without the thermally coupled distillation sequence can be directly calculated by the model equivalent.The energy-saving assessment index is a comprehensive index of the energy consumption and energy consumption levels of the distillation sequence.3.In this paper,the distillation sequences of three separation systems with different separation indexes and the distillation sequences of various separation four-component systems were strictly simulated.The difference of the energy saving percentage of each distillation sequence between the calculation results with this method and simulation results was compared The absolute error of the morphological analysis method of the energy saving percentage of the distillation sequence is about 6%,and the error does not affect the ordering of the energy-saving distillation sequence,which proves the reliability of the distillation sequence morphology analysis method proposed in the paper.This method can be used for rapid assessment of energy-saving distillation sequences of separating four or more components.In addition,according to the energy saving percentage calculated by the efficiency of the distillation sequence,for the equimolar three-component system with ESI ≤ 1,the energy-saving range of the fluid direct thermal-coupled distillation sequence is 14-31%.For the equimolar three-component system with ESI>1,the fluid direct thermal coupled distillation sequences have little energy saving advantage,and the energy saving percentage does not exceed 10%.At the same time,through the experimental study on the separation of the three-component separator column DWC,the energy saving rate of the separator column relative to the non-thermally coupled distillation sequence is about 30%.The experimental energy consumption and morphology analysis results were analyzed,it is further explained that the morphological analysis method can be used to guide the selection of industrial energy-saving distillation sequences.The morphological analysis method of the distillation sequence is not applicable to the evaluation of non-ideal energy-saving distillation sequences through industrial case analysis.4.Using the distillation sequence morphology analysis method,this paper evaluated the energy-saving distillation sequence of the four-component system.Through the establishment of VB-Aspen dynamic link,an operation program for evaluating the energysaving distillation sequence of separating any ideal four-component system was generated.The program only needs to input the feed conditions and physical parameters to obtain the energy-saving distillation sequence in the search space.The first three non-thermally coupled energy-saving distillation sequences of the isolated n-butane─benzene─n-heptane─nnonane system and the first three energy-saving distillation sequences in the search space were quickly obtained by using this program.By comparing the efficiency values of each distillation sequence,the most energy-saving fluid direct thermal coupling distillation sequence is about 15% more energy efficient than the most energy-efficient of non-thermally coupled distillation sequence,and the fluid direct thermal coupling distillation sequence corresponding to the most energy-efficient of non-thermally coupled distillation sequence is not necessarily the most energy-efficient distillation sequence in the search space.5.A total of 188 kinds of distillation sequences were obtained by morphometric analysis to separate four-component systems,including 18 kinds of non-thermally coupled distillation sequences and 170 kinds of fluid direct thermal coupling distillation sequences.In this paper,170 kinds of fluid direct thermal coupling distillation sequences for separating all fourcomponent systems were integrated and coupled,the industrial application of the energysaving distillation sequence obtained in the case operation was analyzed in combination with the coupling device.At the same time,the optimization of some coupling devices was listed,which provides a preliminary reference for industrial design and application.