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Cascade equilibrium stage relaxation method by introducing equilibrium efficiency parameter

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Chinese Journal of Chemical Engineering 2024年第2期66卷 145-156页

作者： Xuepu Cao Shengkun Jia Xing Qian yiqing luo Xigang Yuan College of Chemical and Pharmaceutical Hebei University of Science&TechnologyShijiazhuang 050018China School of Chemical Engineering and Technology State Key Laboratory of Chemical EngineeringTianjin UniversityTianjin 300072China College of Information Science and Technology Beijing University of Chemical TechnologyBeijing 100029China

Optimizing multistage processes,such as distillation or absorption,is a complex mixed-integer nonlinear programming(MINLP)problem.Relaxing integer into continuous variables and solving the easier nonlinear programming(NLP)problem is an optimization idea for the multistage process.In this article,we propose a relaxation method based on the efficiency parameter.When the efficiency parameter is 1or 0,the proposed model is equivalent to the complete existence or inexistence of the equilibrium stage.And non-integer efficiency represents partial existence.A multi-component absorption case shows a natural penalty for non-integer efficiency,which can assist the efficiency parameter converging to 0 or 1.However,its penalty is weaker than the existing relaxation models,such as the bypass efficiency model.In a simple distillation case,we show that this property can weaken the nonconvexity of the optimization problem and increase the probability of obtaining better optimization results.

关键词： Mathematical modeling Absorption Distillation Optimization

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Energy-saving design and optimization of pressure-swing-assisted ternary heterogenous azeotropic distillations

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Chinese Journal of Chemical Engineering 2024年第4期68卷 1-7页

作者： Lianjie Wu Kun Lu Qirui Li Lianghua Xu yiqing luo Xigang Yuan Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion College of Chemical and Chemical EngineeringTianjin University of TechnologyTianjin 300384China State Key Laboratory of Chemical Engineering Tianjin UniversityTianjin 300072China

A huge amount of energy is always consumed to separate the ternary azeotropic mixtures by distillations.The heterogeneous azeotropic distillation and the pressure-swing distillation are two kinds of effective technologies to separate heterogeneous azeotropes without entrainer addition.To give better play to the synergistic energy-saving effect of these two processes,a novel pressure-swing-assisted ternary heterogeneous azeotropic distillation(THAD)process is proposed firstly.In this process,the ternary heterogeneous azeotrope is decanted into two liquid phases before being refluxed into the azeotropic distillation column to avoid the aqueous phase remixing,and three columns'pressures are modified to decrease the flowrates of the recycle streams.Then the dividing wall column and heat integration technologies are introduced to further reduce its energy consumption,and the pressureswing-assisted ternary heterogeneous azeotropic dividing-wall column and its heat integration structure are achieved.A genetic algorithm procedure is used to optimize the proposed processes.The design results show that the proposed processes have higher energy efficiencies and lower CO_(2)emissions than the published THAD process.

关键词： Distillation Separation Process control Process systems

A pseudo transient nonequilibrium method for rigorous simulation of multicomponent separation columns

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Chinese Journal of Chemical Engineering 2023年第10期62卷 57-64页

作者： Jie Wu yiqing luo Xigang Yuan School of Chemical Engineering and Technology Tianjin UniversityTianjin 300350China Chemical Engineering Research Center Tianjin UniversityTianjin 300350China State Key Laboratory of Chemical Engineering Tianjin UniversityTianjin 300350China

Nonequilibrium stage model is a significant improvement in multicomponent separation process simulation,but more equations are involved and the solution of the model equations,which relies on an adequate initial guess for convergence of the Newton method,is difficult.In this work,based on the concept of pseudo-transient continuation approach,we proposed a new pseudo-transient(PT)nonequilibrium method.The proposed method decouples the strongly coupled model equations by introducing dynamic equations for material and energy conservation,as well as transition equations.Thus,the steady-state solution of the nonequilibrium stage model can be obtained through a robust and fast integration process,and the initial guess issue in Newton method can be effectively avoided.Two simulation cases were used to demonstrate the advantages and applicability of the proposed PT nonequilibrium method.

关键词： Nonequilibrium stage model Pseudo-transient continuation Distillation Numerical simulation Systems engineering

Refrigeration system synthesis based on de-redundant model by particle swarm optimization algorithm

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Chinese Journal of Chemical Engineering 2022年第10期50卷 412-422页

作者： Danlei Chen yiqing luo Xigang Yuan School of Chemical Engineering and Technology Tianjin UniversityTianjin 300072China State Key Laboratory of Chemical Engineering Tianjin UniversityTianjin 300072China

Simultaneous optimization of refrigeration system(RS)and its heat exchanger network(HEN)leads to a large-scale non-convex mixed-integer non-linear programming(MINLP)problem.Conventionally,researchers usually adopted simplifications to confine problem scale from being too large at the cost of reducing solution space.This study established an optimization framework for the simultaneous optimization of RS and HEN.Firstly,A more comprehensive and compact model was developed to guarantee a relatively complete solution space while reducing model scale as well as its solving difficulty.In this model,a tandem arrangement of connecting sub-coolers and expansion valves was considered in the superstructure;and the pressure/temperature levels were optimized as continuous variables.On this basis,we proposed a"two-step transformation method"to equivalently transform the cross-level structure into a no n-cross-level structu re,and the de-redundant superstructu re was established with ensuring comprehensiveness and rigor.Furthermore,the MINLP model was developed and solved by Particle Swarm Optimization algorithm.Finally,our methodology was validated to get better optimal results with less CPU time in two case studies,an ethylene RS in an existing plant and a reported propylene RS.

关键词： Refrigeration system Optimal design Process systems Particle swarmoptimization Mathematical modeling

Cascade refrigeration system synthesis based on hybrid simulated annealing and particle swarm optimization algorithm

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Chinese Journal of Chemical Engineering 2023年第6期58卷 244-255页

作者： Danlei Chen yiqing luo Xigang Yuan Chemical Engineering Research Center School of Chemical Engineering and TechnologyTianjin UniversityTianjin 300350China State Key Laboratory of Chemical Engineering Tianjin UniversityTianjin 300350China

Cascade refrigeration system(CRS)can meet a wider range of refrigeration temperature requirements and is more energy efficient than single-refrigerant refrigeration system,making it more widely used in low-temperature industry processes.The synthesis of a CRS with simultaneous consideration of heat integration between refrigerant and process streams is challenging but promising for significant cost saving and reduction of carbon emission.This study presented a stochastic optimization method for the synthesis of CRS.An MINLP model was formulated based on the superstructure developed for the CRS,and an optimization framework was proposed,where simulated annealing algorithm was used to evolve the numbers of pressure/temperature levels for all sub-refrigeration systems,and particle swarm optimization algorithm was employed to optimize the continuous variables.The effectiveness of the proposed methodology was verified by a case study of CRS optimization in an ethylene plant with 21.89%the total annual cost saving.

关键词： Optimal design Process systems Particle swarm optimization Simulated annealing Mathematical modeling

Recent progress on equation-oriented optimization of complex chemical processes

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Chinese Journal of Chemical Engineering 2022年第1期35卷 162-169页

作者： Yuyang Kang yiqing luo Xigang Yuan Chemical Engineering Research Center School of Chemical Engineering and TechnologyTianjin UniversityTianjin 300350China State Key Laboratory of Chemical Engineering Tianjin UniversityTianjin 300350China

Process optimization in equation-oriented(EO)modeling environments favors the gradient-based optimization algorithms by their abilities to provide accurate Jacobian matrices via automatic or symbolic differentiation.However,computational inefficiencies including that in initial-point-finding for Newton type methods have significantly limited its application.Recently,progress has been made in using a pseudo-transient(PT)modeling method to address these difficulties,providing a fresh way forward in EO-based optimization.Nevertheless,research in this area remains open,and challenges need to be addressed.Therefore,understanding the state-of-the-art research on the PT method,its principle,and the strategies in composing effective methodologies using the PT modeling method is necessary for further developing EO-based methods for process optimization.For this purpose,the basic concepts for the PT modeling and the optimization framework based on the PT model are reviewed in this paper.Several typical applications,e.g.,complex distillation processes,cryogenic processes,and optimizations under uncertainty,are presented as well.Finally,we identify several main challenges and give prospects for the development of the PT based optimization methods.

关键词： Simulation Optimization Algorithm Pseudo-transient modeling method Equation-oriented optimization Complex chemical processes

A novel method for generating distillation configurations

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Frontiers of Chemical Science and Engineering 2020年第5期14卷 834-846页

作者： Hongzhe Hou yiqing luo Chemical Engineering Research Center School of Chemical Engineering and TechnologyTianjin UniversityTianjin 300072China

An improved matrix method for generating distillation configurations with(N-1)and less than(N-1)columns was proposed for the separation of an N-component mixture into essentially pure product streams based on the concepts of streams matrix and 0-1 matrixes proposed by Agrawal.In contrast with the matrix method developed by Agrawal,the present method removes the intermediate process centered on the splits,and complex column configurations,allowing the direct generation of multi-feeds and multi-product streams.Furthermore,certain configurations that cannot be generated directly and that are missing in the matrix method are obtained.Through rigorous simulations and optimization,we have demonstrated that these configurations have the potential to outperform certain existing configurations.

关键词： non-sharp separation multicomponent distil-lation distllation configurations

A formulation methodology for multicomponent distillation sequences based on stochastic optimization

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Chinese Journal of Chemical Engineering 2016年第9期24卷 1229-1235页

作者： Fei Wang yiqing luo Xigang Yuan Chemical Engineering Research Center School of Chemical Engineering and Technology Tianjin University State Key Laboratory of Chemical Engineering Tianjin University

Based on stochastic optimization strategy, a formulation methodology is proposed for synthesizing distillation column sequences, allowing more than one middle component as the distributing components between a pair of key components in the non-sharp split. In order to represent and manipulate the distillation configuration structures, a new coding procedure is proposed in the form of one-dimensional array. Theoretically, an array can represent any kind of split(non-sharp and sharp). With the application of a binary sort tree approach, a robust flow sheet encoding and decoding procedure is developed so that the problem formulation and solution becomes tractable. In this paper,the synthesis problem is formulated as a mixed-integer nonlinear programming(MINLP) problem and an improved simulated annealing approach is adopted to solve the optimization problem. Besides, a shortcut method is applied to the evaluation of all required design parameters as well as the total function.

关键词：蒸馏定序合成非锋利的分离模仿了退火 MINLP 二进制种类树

A systematic approach for synthesizing a low-temperature distillation system

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Chinese Journal of Chemical Engineering 2015年第5期23卷 789-795页

作者： yiqing luo Liang Kong Xigang Yuan Chemical Engineering Research Center School of Chemical Engineering and Technology Tianjin University

In this paper, by combining a stochastic optimization method with a refrigeration shaft work targeting method,an approach for the synthesis of a heat integrated complex distillation system in a low-temperature process is presented. The synthesis problem is formulated as a mixed-integer nonlinear programming(MINLP) problem,which is solved by simulated annealing algorithm under a random procedure to explore the optimal operating parameters and the distillation sequence structure. The shaft work targeting method is used to evaluate the minimum energy cost of the corresponding separation system during the optimization without any need for a detailed design for the heat exchanger network(HEN) and the refrigeration system(RS). The method presented in the paper can dramatically reduce the scale and complexity of the problem. A case study of ethylene cold-end separation is used to illustrate the application of the approach. Compared with the original industrial scheme, the result is encouraging.

关键词：蒸馏系统低温工艺合成混合整数非线性规划随机优化方法最佳运行参数模拟退火算法制冷系统