基于随机优化的热耦合复杂精馏系统的综合(Ⅰ)模型化方法

基于随机型最优化策略,针对包含简单塔、带有侧线蒸出及侧线汽提塔的复杂塔、全热耦合（或Petlyuk）塔的热耦合复杂精馏塔系统的综合问题,提出一种模型化方法.针对热耦合复杂精馏流程系统所需塔段数目以及冷凝器和再沸器数目的不确定性,提出了一种分解求解策略,将原问题分解成一系列具有不同塔段数的子问题分别求解;针对流程结构的优化提出一种流程结构的编码表达法,该方法将问题的分离序列结构和热耦合方式分别用两组编码表示,对分离序列的编码采用了数据结构理论中的二叉树排序方法,使流程结构的描述变得更加简便;最后以预分馏塔组分回收率及回流比为连续变量,建立了热耦合复杂精馏系统优化的[JP+1]混合整数非线性规划（MINLP）模型,该模型用改进的模拟退火算法求解,可同时得到优化的流程结构和操作参数.     

Synthesis of heat-integrated complex distillation systems via Genetic Programming

This paper addresses the application of Genetic Programming (GP) to the synthesis of heat-integrated complex distillation system and the flowsheet of complex separation can be expressed directly using GP's special hierarchical structure. A series of unique encoding method and solution strategy is proposed and some evolutionary factor is improved based on the domain knowledge of chemical engineering. A shortcut method is applied to calculate all required design parameters. Conventional and complex columns, thermally coupled (linked) side strippers and side rectifiers, fully thermally coupled columns as well as heat integration between any different columns are simultaneously considered. Two illustrating examples are presented to demonstrate the effective computational strategies.     

MINLP optimization of a heterogeneous azeotropic distillation process: Separation of ethanol and water with cyclohexane as an entrainer

Heterogeneous distillation processes are widely used in industry for the separation of azeotropic and close-boiling mixtures. This paper addresses the optimization of a heterogeneous distillation process for the separation of an azeotropic ethanol/water mixture using cyclohexane as an entrainer. Starting from a given process superstructure a MINLP problem is set up to consider continuous as well as discrete decision variables such as the feed locations and the number of stages of the distillation columns. A modified Generalized Benders Decomposition algorithm to account for non-convexities of the model equations solves the MINLP problem. The algorithm can be attached via Visual Basic for Applications (VBA) to any commercial process simulator with NLP and VBA capabilities. Various optimization runs show that the algorithm is easily applicable and returns solutions independent of the initial values.     

过程系统能量集成同步最优综合法

将换热网络超结构混合整数非线性规划多目标同步最优综合方法进一步扩展到与过程系统的联合优化,提出了改进的过程热集成同步综合方法,并以反应分离过程与换热网络能量集成为例,建立了同步优化超结构模型,采用混合整数非线性规划的遗传算法求解,可同时得到热集成系统最优的流程结构和操作条件。     

基于信赖域算法的精馏塔优化

从结构优化角度建立精馏塔优化的混合整数非线性规划(MINLP)模型,为了消除整数变量,引入绕流效率将MINLP问题转化为非线性规划(NLP)问题。针对得到的NLP问题提出一种优化方法,在该方法中采用结构优化中常用的信赖域优化算法进行求解,并应用虚拟瞬态连续性方程辅助优化中的稳态模拟。采用提出的优化方法对3个精馏系统进行设计优化,以不同初始值开始,均可得到令人满意的优化结果,表明所提优化方法具有良好的稳健性,对于较复杂的部分热耦合精馏过程仍然可以有效优化求解;信赖域算法在精馏塔优化中也表现出良好的收敛性。     

Optimization-based design of reactive distillation columns using a memetic algorithm

The design optimization of reactive distillation columns (RDC) is characterized by complex nonlinear constraints, nonlinear cost functions, and the presence of many local optima. The standard approach is to use MINLP solvers that work on a superstructure formulation where structural decisions are represented by discrete variables and lead to an exponential increase in the computational effort. The mathematical programming (MP) methods which solve the continuous sub-problems provide only one local optimum which depends strongly on the initialization. In this contribution a memetic algorithm (MA) is introduced and applied to the global optimization of four different formulations of a computational demanding real-world design problem. An evolution strategy addresses the global optimization of the design decisions, while continuous sub-problems are efficiently solved by a robust MP solver. The MA is compared to MINLP techniques. It is the only algorithm that finds the global solution in reasonable times for all model formulations.     

基于遗传规划的复杂精馏系统综合

提出了基于遗传规划的复杂精馏系统的综合方法.针对复杂精馏系统特点并结合化工领域知识,对遗传算子进行了改进,给出了一套独特的编码方法和求解策略.算法利用层次化结构来直观地表达复杂分离流程,同时解决了其他随机算法编码在表达精馏过程时的歧意性问题.在不必给定精馏系统超结构的情况下,能够完成可行域的自动搜寻.实例计算表明,基于遗传规划的综合策略可以用于求解复杂精馏系统的最优综合问题,实现了包括侧线塔、完全热偶塔及同时考虑热集成的各种复杂精馏结构的自动搜索寻优.     

混合整数非线性规划与化学工程系统最优化设计——(Ⅱ)换热器网络的最优合成

本文讨论了用系统方法进行换热器网络的最优合成问题.建立了该系统的超结构及其混合整数非线性规划(MINLP)模型,并成功地应用了前文导出的MINLP算法对一算例进行求解.计算结果表明,本文所采用的方法在对系统的结构与操作参数同时进行优化方面,优于以往一些方法.     

Simultaneous MINLP synthesis of heat exchanger networks comprising different exchanger types

This paper describes the simultaneous MINLP synthesis of heat integrated heat exchanger networks comprising different heat exchanger types. The stage-wise superstructure of heat exchanger networks (HEN) by Yee and Grossmann (Comput. Chem. Eng. 14 (1990) p. 1165) is extended to alternative exchanger types. The selection of the types is modeled by disjunctions based on operating limitations and the required heat transfer area. Since different types of heat exchangers involve different design geometries, which influences the inlet and outlet temperatures of heat exchangers, additional constraints are specified to provide a feasible temperature distribution in HEN. The consideration of different exchanger types drastically increases the combinatorics, size and computation effort needed to solve the problem. The integer-infeasible path MINLP approach has been applied to perform an efficient initialization scheme and to halve CPU times for solving MILP master problem of the modified OA/ER algorithm. A special multilevel MINLP procedure in reduced integer space has been proposed to solve medium size HEN problems (20 streams) comprising 10³ and more binary variables.     

An adaptive discretization MINLP algorithm for optimal synthesis of decentralized energy supply systems

Decentralized energy supply systems (DESS) are highly integrated and complex systems designed to meet time-varying energy demands, e.g., heating, cooling, and electricity. The synthesis problem of DESS addresses combining various types of energy conversion units, choosing their sizing and operations to maximize an objective function, e.g., the net present value. In practice, investment costs and part-load performances are nonlinear. Thus, this optimization problem can be modeled as a nonconvex mixed-integer nonlinear programming (MINLP) problem. We present an adaptive discretization algorithm to solve such synthesis problems containing an iterative interaction between mixed-integer linear programs (MIPs) and nonlinear programs (NLPs). The proposed algorithm outperforms state-of-the-art MINLP solvers as well as linearization approaches with regard to solution quality and computation times on a test set obtained from real industrial data, which we made available online.     

Energy optimization of bioethanol production via hydrolysis of switchgrass

The optimal flowsheet for the production of bioethanol from switchgrass via hydrolysis is proposed in this work. A superstructure embedding a number of alternatives is proposed. Two technologies are considered for switchgrass pretreatment, dilute acid and ammonia fiber explosion so that the structure of the grass is broken down. Next, enzymatic hydrolysis follows any of the pretreatments to obtain fermentable sugars, mainly xylose and glucose. Ethanol is obtained by fermentation of the sugars. To obtain fuel quality, ethanol and water must be removed from the water–ethanol mixture. A number of dehydration technologies is considered including rectification, adsorption in corn grits, molecular sieves, and pervaporation. The problem is formulated as a mixed‐integer nonlinear programming (MINLP). The superstructure is optimized by decomposing the MINLP for each of the pretreatments. Then, multieffect columns and heat integration are used to reduce the energy consumption and cooling needs. Finally, an economic evaluation is performed. The optimal flowsheet consists of using dilute acid hydrolysis followed by molecular sieves as dehydration technology, which requires less energy and cooling and yielding a promising production price of 0.8 $/gal. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

考虑操作分解的热集成用水网络设计

This article deals with the design of energy efficient water utilization systems allowing operation split. Practical features such as operating flexibility and capital cost have made the number of sub operations an important parameter of the problem. By treating the direct and indirect heat transfers separately, target freshwater and energy consumption as well as the operation split conditions are first obtained. Subsequently, a mixed integer non-linear programming （MINLP） model is established for the design of water network and the heat exchanger network （HEN）. The proposed systematic approach is limited to a single contaminant. Example from literature is used to illustrate the applicability of the approach.     

化工过程系统综合问题新的模块化求解策略和算法

针对过程系统综合问题中求解混合整数非线性规划（MINLP）问题传统解法的不足提出了在[JP+1]模块化环境中过程系统综合问题新的求解策略,同时提出相对应的算法.实例证明了该策略的正确性和新算法的有效性.     

热集成复杂精馏系统综合的研究

将夹点分析法应用于热集成复杂精馏系统综合的换热网络设计中,避免了以换热网络结构作为独立变量,建立了一个以预分馏塔组分回收率、回流比及操作压力为连续变量,以分离序列和热耦合方式为离散变量的混合整数非线性规划(MINLP)模型。该模型用改进的模拟退火算法求解,可同时得到优化的流程结构和操作参数。对多个五组分混合物分离问题进行了求解,并对不同优化方案的优化结果及其经济性作了比较和分析,结果表明采用热集成复杂精馏塔流程可以显著地降低系统的总费用,还表明该方法是求解热集成复杂精馏系统综合问题的有效方法。     

A systematic approach for synthesizing a low-temperature distillation system

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 dramatical y reduce the scale and complexity of the problem. A case study of ethylene cold-end separation is used to il ustrate the application of the approach. Compared with the original industrial scheme, the result is encouraging.     

多流股换热器网络综合方法在原油预热系统中的应用

以原油常减压蒸馏装置原油预热网络为研究对象,进行了多流股换热器网络的实例综合. 基于超结构物理模型建立了改进的多流股换热器网络综合数学模型,提出将该网络综合问题由混合整数非线性规划问题转化为简单的非线性规划问题的求解策略,并利用改进的遗传/模拟退火新算法进行了原油预热网络的综合. 与Hextran软件的综合结果以及现场换热网络的对比表明,本模型和求解策略可以应用于工业规模的多流股换热器网络综合,有可能取得较好的经济效益.     

Heat transfer intensification for retrofitting heat exchanger networks with considering exchanger detailed performances

The challenging of this work is to present a thorough study of implementing heat transfer intensification in heat exchanger network (HEN) retrofitting, including all details of exchanger geometry, stream bypassing and splitting, temperature‐variation of properties, LMTD and its correction, and pressure drops. This leads to very complex mixed integer nonlinear programming (MINLP) problems rarely reported before. By adopting the MILP‐based iterative approach proposed in the earlier work (Pan et al., Chem Eng Sci. 2013;104:498–524.), temperature‐variation of properties, LMTD and its correction are initialized to parameters at first, and the rest nonlinear terms are then linearized and expressed as first‐order Taylor series expansions. Finally, two iteration loops are executed to find optimal solutions. A small‐scale motivating problem and an industrial scale problem are presented to demonstrate the validity and efficiency of the proposed methods. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2052–2077, 2018     

Optimal design of reverse-osmosis networks for wastewater treatment

An optimization study of reverse-osmosis networks (RON) for wastewater treatment has been carried out by describing the system as a nonconvex mixed-integer nonlinear problem (MINLP). A mixed-integer linear problem (MILP) is derived from the original nonlinear problem by the convex relaxation of the nonconvex terms in the MINLP to provide bounds for the global optimum. The MILP model is solved iteratively to supply different initial guesses for the nonconvex MINLP model. It is found that such a procedure is effective in finding local optimum solutions in reasonable time and overcoming possible convergence difficulties associated with MINLP local search methods. Examples of water desalination and wastewater treatment from the pulp and paper industry are considered as case studies to illustrate the proposed solution strategy.     

Logic hybrid simulation-optimization algorithm for distillation design

In this paper, we propose a novel algorithm for the rigorous design of distillation columns that integrates a process simulator in a generalized disjunctive programming formulation. The optimal distillation column, or column sequence, is obtained by selecting, for each column section, among a set of column sections with different number of theoretical trays. The selection of thermodynamic models, properties estimation, etc. is all in the simulation environment. All the numerical issues related to the convergence of distillation columns (or column sections) are also maintained in the simulation environment. The model is formulated as a Generalized Disjunctive Programming (GDP) problem and solved using the logic based outer approximation algorithm without MINLP reformulation. Some examples involving from a single column to thermally coupled sequence or extractive distillation shows the performance of the new algorithm.     

Prosyn—an MINLP process synthesizer

This paper reports the development of the program PROSYN, an automated implementation of the modelling/decomposition (M/D) strategy by Kocis and Grossmann (Computers chem. Engng 13, 797–819, 1989) for the MINLP optimization of process flowsheets. A systematic procedure is first presented for the decomposition of general superstructures of process flowsheets that avoids the optimization of units with zero flow. A model for simultaneous optimization and heat integration is also proposed that can account for area and energy considerations. Finally, a computer implementation is described that is suitable for the complex logic involved in the M/D strategy for the synthesis and heat integration of process flowsheets. Examples are presented to illustrate each of these points, as well as the performance of PROSYN.