基于专家系统和遗传算法的换热网络的建模和优化

A new superstructure from of heat exchanger networks(HEN) is proposed based on expert system (ES). The new superstructure from is combined with the practical engineering.The different investment cost formula for different heat exchanger is also presented based on ES.The mathematical model for the simultaneous optimization of network configuration is established and solved by a genetic algorithm.This method can deal with larger scale HEN synthesis and the optimal HEN configuration is obtained automatically.Finally,a case study is presented to demonstrate the effectiveness of the method.     

基于数学规划和知识工程的换热网络合成及其控制性能集成的研究

A method for incorporation of controlling the heat exchanger networks with or without splits is proposed by integrating mathematical programming and knowledge engineering.The simultaneous optimal mathematical model is established.This method can be practically used in the integration of large-scale heat exchanger networks,not only to synthesize automatically but also to satisfy the requirement of structural controllability with more nobjective human intervention.     

用于超结构换热器网络热计算和网络综合的显式解

For the optimal design of a heat exchanger network, the inlet and outlet stream temperatures of each heat exchanger in the network should be known. An explicit analytical solution of stream temperatures of an arbitrary connected heat exchanger network was introduced, which is suitable for the thermal calculation of heat exchanger networks. For the heat exchanger network synthesis, this solution was further developed and coupled with the stage-wise superstructure heat exchanger networks. The new calculation procedure reduced the computer memory requirement dramatically. On the basis of this solution, a mathematical model for synthesis of heat exchanger networks with genetic algorithm was formulated, which is always feasible and no iteration is needed. Two examples were calculated with the proposed approach and better results were obtained.     

柔性换热网络综合与清洗计划同步优化(英文)

A novel methodology is presented for simultaneously optimizing synthesis and cleaning schedule of flexible heat exchanger network (HEN) by genetic/simulated annealing algorithms (GA/SA). Through taking into account the effect of fouling process on optimal network topology, a preliminary network structure possessing twofold oversynthesis is obtained by means of pseudo-temperature enthalpy (T-H) diagram approach prior to simultaneous optimization. Thus, the computational complexity of this problem classified as NP (Non-deterministic Polynomial)-complete can be significantly reduced. The promising matches resulting from preliminary synthesis stage are further optimized in parallel with their heat exchange areas and cleaning schedule. In addition, a novel continuous time representation is introduced to subdivide the given time horizon into several variable-size intervals according to operating periods of heat exchangers, and then flexible HEN synthesis can be implemented in dynamic manner. A numerical example is provided to demonstrate that the presented strategy is feasible to decrease the total annual cost (TAC) and further improve network flexibility, but even more important, it may be applied to solve large-scale flexible HEN synthesis problems.     

用伪并行遗传/模拟退火算法进行多流股换热器网络综合的研究

The multi-stream heat exchanger network synthesis (HENS) problem can be formulated as a mixed integer nonlinear programming model according to Yee et al. Its nonconvexity nature leads to existence of more than one optimum and computational difficulty for traditional algorithms to find the global optimum. Compared with deterministic algorithms, evolutionary computation provides a promising approach to tackle this problem. In this paper, a mathematical model of multi-stream heat exchangers network synthesis problem is setup. Different from the assumption of isothermal mixing of stream splits and thus linearity constraints of Yee et al., non-isothermal mixing is supported. As a consequence, nonlinear constraints are resulted and nonconvexity of the objective function is added. To solve the mathematical model, an algorithm named GA/SA (parallel genetic/simulated annealing algorithm) is detailed for application to the multi-stream heat exchanger network synthesis problem. The performance of the proposed approach is demonstrated with three examples and the obtained solutions indicate the presented approach is effective for multi-stream HENS.     

A Two-step Design Method for Shaft Work Targeting on Low-temperature Process

In low-temperature processes, there are interactions between heat exchanger network （HEN） and refrig-eration system. The modification on HEN of the chilling train for increasing energy recovery does not always coor-dinate with the minimum shaft work consumption of the corresponding refrigeration system. In this paper, a sys-tematic approach for optimizing low-temperature system is presented through mathematical method and exergy analysis. The possibility of＂pockets＂, which appears as right nose section in the grand composite curve （EGCC） of the process, is first optimized. The EGCC with the pockets cutting down is designed as a separate part. A case study is used to illustrate the application of the approach for a HEN of a chilling train with propylene and ethylene refrig-erant system in an ethylene production process.     

Combined mass and heat exchange network synthesis based on stage-wise superstructure model☆

Integrating multiple systems into one has become an important trend in Process Systems Engineering research field since there is strong demand from the modern industries. In this study, a stage-wise superstructure-based method is proposed to synthesize a combined mass and heat exchange network (CM&HEN) which has two parts as the mass exchange network (MEN) and heat exchange network (HEN) involved. To express the pos-sible heat exchange requirements resulted from mass exchange operations, a so cal ed“indistinct HEN super-structure (IHS)”, which can contain the all potential matches between streams, is constructed at first. Then, a non-linear programming (NLP) mathematical model is established for the simultaneous synthesis and optimiza-tion of networks. Therein, the interaction between mass exchange and heat exchange is modeling formulated. The NLP model has later been examined using an example from literature, and the effectiveness of the proposed method has been demonstrated with the results.     

板翅式换热器导流片结构的数值模拟

A fluid flow model of distributor was set up to investigate the effectof distributor configuration on the fluid flow distribution in plate- fin heat exchanger. At the same time, a mathematical equation was developed to generate different types of fluid flow maldistribution models considering the possible deviations in fluid flow. Using these fluid flow models, the fluid flow distributions in plate- fin beat exchanger were calculated for different configurations and operating conditions. The computational results show that nonuniform inlet velocity, inlet angle, and orifice diameter on the fin are the main factors affecting the distribution performance of distributor. The fluid flow distribution in plate- fin heat exchanger can be effectively improved by changing the distributor configuration. The distributor reaches the best distribution performance when the orifice diameter is 2 mm. The computational results are in good agreement with experimental ones.     

A numerical study on heat transfer enhancement and design of a heat exchanger with porous media in continuous hydrothermal flow synthesis system

The aim of this study is to use a new configuration of porous media in a heat exchanger in continuous hydrothermal flow synthesis (CHFS) system to enhance the heat transfer and minimize the required length of the heat exchanger.For this purpose,numerous numerical simulations are performed to investigate performance of the system with porons media.First,the numerical simulation for the heat exchanger in CHFS system is validated by experimental data.Then,porous media is added to the system and six different thicknesses for the porous media are examined to obtain the optimum thickness,based on the minimum required length of the heat exchanger.Finally,by changing the flow rate and inlet temperature of the product as well as the cooling water flow rate,the minimum required length of the heat exchanger with porous media for various inlet conditions is assessed.The investigations indicate that using porous media with the proper thickness in the heat exchanger increases the cooling rate of the product by almost 40％and reduces the required length of the heat exchanger by approximately 35％.The results also illustrate that the most proper thickness of the porous media is approximately equal to 90％ of the product tube's thickness.Results of this study lead to design a porous heat exchanger in CHFS system for various inlet conditions.     

Minimizing investment cost for multi-period heat exchanger network retrofit by matching heat transfer areas with different strategies

Multi-period heat exchanger network (HEN) retrofit is usually performed by targeting and matching heat trans-fer areas. In this paper, based on the reverse order matching method we proposed previously, three strategies of matching heat transfer areas are proposed to minimize the investment cost for the retrofit of HEN in multi-period, in which replacement of heat exchangers, addition of heat exchangers and addition of heat transfer areas are performed. We demonstrate the procedures through three scenarios, including maximum number of substituted heat exchangers after retrofit, minimum additional heat transfer areas in the retrofitted HEN, and minimum investment cost for retrofit. The strategies are extended to a single period HEN retrofit problem. The results of multi-period and single period HEN retrofit problems indicate the effectiveness of the strategies. More-over, these results are better than those reported in literature. The strategies are simple and easy to implement, which are of great benefit to large-scale HEN retrofit in practice.     

有分流换热网络的弹性设计-基于温度波动情形

提出了基于温度波动的有分流换热网络的超结构模型和同步优化的弹性设计方法。首先对于起始温度在一定范围内波动的物流进行预处理。即分段处理。然后建立换热网络同步优化的数学模型,最后对分段物流进行合并,并通过能量松弛方法得取满意一定弹性要求的换热网络结构。     

SYNTHESIS OF FLEXIBLE HEAT EXCHANGER NETWORKS WITH STREAM NO - SPLITTING(Ⅰ) BASED ON RANGES OF STREAM SUPPLY TEMPERATURES

提出了基于温度波动的无分流换热网络的超结构模型和同步优化的弹性设计方法。对于起始温度在一定范围内波动的物流进行预处理即分段处理,并提出了分段原则;提出了基于规则的网络超结构模型并建立了弹性换热网络同步优化的数学模型;采用遗传算法求解了所提出的优化数学模型;提出了分段物流的合并及能量松弛的原则,对分段物流进行合并,并通过能量松弛方法得到优化的弹性换热网络结构。通过几个换热网络的弹性设计,说明了本方法的有效性和应用前景。     

无分流换热网络的弹性设计(Ⅰ)基于温度波动情形

提出了基于温度波动的无分流换热网络的超结构模型和同步优化的弹性设计方法。对于起始温度在一定范围内波动的物流进行预处理即分段处理,并提出了分段原则;提出了基于规则的网络超结构模型并建立了弹性换热网络同步优化的数学模型;采用遗传算法求解了所提出的优化数学模型;提出了分段物流的合并及能量松弛的原则,对分段物流进行合并,并通过能量松弛方法得到优化的弹性换热网络结构。通过几个换热网络的弹性设计,说明了本方法的有效性和应用前景。     

A monogenetic algorithm for optimal design of large-scale heat exchanger networks

The optimal design of large-scale heat exchanger networks is a quite difficult task not only due to its non-linear characteristics but also due to a great number of local optima in its solution space. An explicit analytical solution of stream temperatures for the superstructure heat exchanger networks was developed, which reduces number of decision variables significantly. Based on this solution, a mathematical model for synthesis of heat exchanger networks was formulated for searching the optimal configuration of a heat recovery system by a hybrid genetic algorithm. For large-scale heat exchanger networks, a monogenetic algorithm based on the optimization of sub-networks is proposed. In the first step of the optimization, the hybrid genetic algorithm is applied to the synthesis of the whole heat exchanger network for finding the functional groups (sub-networks) rather than the chromosomes (positions of the heat exchangers and splits of the streams) and genes (areas and heat capacity flow rates). Then the monogenetic algorithm for evolution of the functional groups is carried out to improve the HEN. This procedure was applied to examples taken from literature and better results were obtained.     

多周期操作工况下换热网络的弹性设计

提出了基于专家系统的多周期换热网络的超结构形式及弹性设计方法。首先通过专家系统确定各周期操作工况下物流的分流及匹配禁止情况,在此基础上建立网络多周期操作工况下的超结构模型;然后用遗传算法对上述模型进行求解;最后用分解协调法对网络结构和匹配单元同时进行优化。该方法不仅能自动地合成多周期操作工况的换热网络最优流程结构,而且能同时满足网络在各操作工况下的各种工艺限制条件。最后,通过某个换热网络的最优合成设计,说明本方法的有效性和应用前景。     

Simultaneous synthesis of structural‐constrained heat exchanger networks with and without stream splits

This paper presents a comprehensive simultaneous synthesis approach based on stage‐wise superstructure to design cost‐optimal heat exchanger network (HEN). It is well known that the simultaneous synthesis model has very complicated mixed integer nonlinear programming formulations, which are non‐convex, non‐continuous and have many local optima. Up till now, it cannot be expected that an algorithm can find, in polynomial time, the global solution to the simultaneous synthesis problem of HEN. In order to reduce computational complexity, some simplified assumptions for structures, such as no stream splits, stream splits with isothermal mixing, no stream split flowing through more than one exchanger, etc, are adopted to prune the search space at the expense of neglecting certain important alternatives in the network configuration. In this work, a flexible stage‐wise superstructure is proposed to control the solution performance and search space efficiently. At each stage of the superstructure, with or without stream splits is determined at random or by the experience of designers. In this way, various candidate series and split network designs featuring the lowest annual cost can be found. Moreover, an efficient two‐level optimisation algorithm is employed for solving the presented model utilising genetic algorithm and particle swarm optimisation algorithm. Three case studies are presented to show the applicability of the proposed methodology. In addition, the results show that the new approach is able to find more economical networks than those generated by other methods. © 2012 Canadian Society for Chemical Engineering     

Supply and target based superstructure synthesis of heat and mass exchanger networks

This paper presents new methods for the optimisation of superstructures involving heat exchanger networks (HENs) and mass exchanger networks (MENs). The techniques developed in this study explore the use of key variables (namely supply temperatures/compositions and target temperatures/compositions) in HENs and MENs to define the intervals of superstructures. Such superstructures are modeled as mixed integer non linear programmes (MINLP) with the objective of minimisation of the total annual cost (TAC) for each network. The superstructures presented in this paper are derivatives of the interval and supply based superstructures (IBMS and SBS) developed previously. Two different superstructures are developed in this paper: the first uses the supply temperature/composition of hot/rich streams and the target temperature/composition of cold/lean streams (denoted supply and target based superstructure, S&TBS), while the second superstructure uses the target temperature/composition of hot/rich streams and the supply temperature of cold/lean streams (denoted target and supply based superstructure, T&SBS). Five HEN examples and three MEN examples are presented. The results obtained compare well with those in the literature.     

Floating pinch method for utility targeting in heat exchanger network (HEN)

Most of the established methods for utility targeting in a heat exchanger network (HEN) are mainly focusing on fixed stream conditions, where the flow rate, heat capacity, supply and target temperatures are fixed. However, in the process industries, the stream conditions (flow rates and temperatures) are not fixed. Therefore, the established HEN targeting methods cannot be directly applied to locate the hot and cold utility targets for HEN problem with varying flow rates and temperatures. To address this issue, a revised floating pinch method which uses binary variables to parameterise the stream locations on the composite curves, is presented in this work to identify the minimum utilities targets. The revised method simplify the earlier version of floating pinch method presented by Duran and Grossmann (1986) by avoiding the non-differentiability in the mathematical program. Two cases, one with fixed parameters while another with temperature-dependent properties and varying operating parameters are solved to illustrate the revised model.     

基于夹点技术与超结构模型的多程换热网络最优综合

基于热力学原理,以夹点技术为基础结合数学规划法,采用两步法综合多程换热网络。第一步在多程换热网络热力学分析的基础上优化求解最小温差,计算公用工程用量。第二步将求得的最小温差作为夹点温差,将网络分为夹点之上和夹点之下两个子网络,建立多程换热网络的超结构模型,确定流股匹配并优化网络配置。最后,以换热网络总费用最小为目标,连接两个子网络,权衡设备投资费用和操作费用,综合多程换热网络。该方法基于热力学原理,改进了夹点技术在多程换热网络综合中的应用,进而实现了多程换热网络的自动综合。示例分析证明了本文所提方法的有效性。