Heuristic approach for heat exchanger networks

A systematic approach based on few heuristics for the synthesis of optimum heat exchanger networks has been developed. The approach, which is simple and easy to apply, consists of three sequential steps. In the first pre-analysis step, the optimum temperature approach is determined. In this step, a set of heuristic constraints are used to determine minimum utility requirements. In the second step, heat exchanger networks are generated using the H/H heuristic of matching hot and cold streams. In the third step, the initially generated networks evolve through loop breaking and energy relaxation to achieve the target of the minimum number of units. The effectiveness of the approach developed has been tested on a number of literature test problems ranging in size from four to ten streams and on an industrial case involving a recovery heat exchanger network around a topping tower. The approach produced simple network structures and improved energy recovery. The cost results obtained in this work agree favourably with optimal solutions reported in the literature.     

Detailed simulation of heat exchanger networks for flexibility consideration

An investigation of the flexibility consideration for heat exchanger networks is carried out. The steady responses to the disturbances of supply temperatures, flow rates, fouling, etc. are obtained through the detailed simulation, which solves a set of linear equations. The relationship, either linear or non-linear, between the responses and different disturbances is demonstrated by the results. Less surface margin, corresponding to less conservative fouling factors, is also studied. This is achieved through trade-off optimization. An industrial case study is conducted, and the results show that up to 12.6% of the total heat transfer surface can be saved because of less conservative fouling factors.     

Integrated synthesis of process and heat exchanger networks: algorithmic approach

Methods exist for algorithmic process-network synthesis (PNS) as well as for heat-exchanger-network synthesis (HENS); nevertheless, such methods cannot be easily integrated for a variety of reasons. For instance, both PNS and HENS are complex problems; thus, their combination is naturally even more complex. Our previous effort to establish the combinatorial foundation of PNS has yielded a highly effective method involving the P-graph representation; the present approach to the integrated synthesis of process and heat-exchanger networks resorts mainly to hP-graphs adapted from the P-graphs in conjunction with the appropriate selection of inherent intervals of temperature range. This work focuses on the establishment of an appropriate technique for the integration of PNS and HENS. The resultant technique is largely based on combinatorics and combinatorial algorithms. The efficacy of the proposed approach is illustrated by solving an industrial problem.     

Optimizing heat exchanger networks with genetic algorithms for designing each heat exchanger including condensers

This paper presents a procedure for the design of the components of a heat exchanger network (HEN). The procedure first uses pinch analysis to maximize heat recovery for a given minimum temperature difference. Using a genetic algorithm (GA), each exchanger of the network is designed in order to minimize its total annual cost. Eleven design variables related to the exchanger geometry are considered. For exchanger involving hot or cold utilities, mass flow rate of the utility fluid is also considered as a design variable. Partial or complete condensation of hot utility fluid (i.e., water vapor) is allowed. Purchase cost and operational cost are considered in the optimization of each exchanger. Combining every exchanger minimized cost with the cost of hot utility and cold utility gives the total cost of the HEN for a particular ΔT_min. The minimum temperature difference yielding the more economical heat exchanger network is chosen as the optimal solution. Two test cases are studied, for which we show the minimized total cost as a function of the minimum temperature difference. A comparison is also made between the optimal solution with the cost of utilities and without it.     

换热器网络设计的优化研究

基于感知器模型本文提出一种换热器网络优化新算法,在遗传迭代过程中,依据目标函数的适应值,该算法不断调节感知器的权值,使感知器以随机方式搜索网络拓扑结构和运行参数。经过本文的计算表明：这一算法对于多维、多峰、非凸函数也具有很好的适应性,能够有效地克服传统方法（混合整数非线性优化）的不足之处。     

基于压降二次分配的换热网络综合研究

在换热网络的综合过程中,依据单体换热设备的换热面积,进行压降约束的初步线性分配,根据单体换热设备的详细设计结果,按流体流动方向,对压降约束进行再次分配,并校核流股总压降是否在允许的范围内,给出了考虑压降分配前提下的换热器详细设计流程框图,算例结果表明,依此方法综合出的新的能量系统与现场能量系统相比节省换热面积30．87％,系统压降总和降低12．66％。     

换热网络优化设计的研究进展

换热网络优化是化工生产中常遇到的一类问题,综述了换热网络优化设计的三种基本方法,分别指出了夹点技术、数学规划法和炯经济分析法的基本原理、应用领域、优缺点及其在国内外的发展状况,并对其作了展望,注重更接近于工程实际的考虑。     

Retrofit of pressure drop constrained heat exchanger networks

The study of retrofit of heat exchanger networks is usually restricted to constant heat transfer coefficients, and pressure drop constraints due to the additional exchanger area is neglected. In this work, a new approach considering the distribution of heat transfer area and pressure drop in retrofit is presented. The problem is described as a non-linear model, and the additional area required for the new network condition and available pressure drop are estimated based on economical optimisation (or process requirements).     

Recent development in the retrofit of heat exchanger networks

This work presents a methodology for heat exchanger network (HEN) retrofit, which is applicable to complex industrial revamps, considering existing networks and constraining the number of modifications. The network pinch approach [N.D.K. Asante, X.X. Zhu, An automated approach for heat exchanger network retrofit featuring minimal topology modifications, Comp. Chem. Eng. 20 (1996) S7–S12.] has been modified and extended to apply to the HEN design in which the thermal properties of streams are temperature-dependent. The modified network pinch approach combines structural modifications and cost optimisation in a single step to avoid missing cost-effective design solutions.     

同轴径向热管换热器壳程流场数值模拟

基于多孔介质模型和分布阻力方法,引入Al-sanea和Taborek两种阻力关系式模拟同轴径向热管换热器壳程的流场。结果表明:换热器壳程静压沿烟气流动方向呈线性分布;随入口烟气速度的增加,换热器阻力损失增大、压降增大;且随入口烟气速度的增加,压降增加的速率增大。     

Second-law-based optimization of heat exchanger networks using load curves

The problem of simultaneously optimizing heat exchangers for a number of hot and cold fluids is approached from the viewpoint of the second law of thermodynamics. If the total duty requirements are fixed, i.e. all inlet and outlet temperatures are established for the fluids, then the resulting entropy production rate is independent of the actual pairings of the fluids. Thus, optimization with respect to size becomes essentially a maximization of the temperature differences between the paired fluids for all of the fluids considered.Next it is shown that the same optimization can be obtained from the load curves where the temperature is plotted against the heat transfer for each of the fluids. If the film coefficient for any of the fluids is significantly different from the others, a simple shifting can be accomplished and a criterion is given to determine if such shifting improves the optimization. The method is extremely simple and can be performed most effectively on graph paper.     

Pressure drop optimisation in debottlenecking of heat exchanger networks

Process integration technology is now widely applied in grass-roots design, energy saving retrofit and the debottlenecking of heat exchanger networks. This technology has been used in a variety of industries and proved to be reliable and applicable in engineering design. Debottlenecking may apply to a specific part or entire unit, whether it is due to increased throughput or process modifications. One of the advanced methods for debottlenecking that is currently used is based upon fixed allowable pressure drops, through which a retrofit can be achieved without a need for pump and/or compressor replacement. This research is trying to develop a new procedure for pressure drop optimisation in debottlenecking. This procedure enables the designer to study pump and/or compressor replacement whilst at the same time optimising the additional area and operating cost of the network. It deals with the problem of optimal debottlenecking of heat exchanger networks considering minimum total cost. Moreover, one can consider the possibility of the replacement of a given pump with a smaller one. The new procedure has been effectively applied to a crude oil pre-heat train, which was subject to some 20% increase in throughput, and the corresponding results proved to be accurate enough.     

换热网络全局优化的多维峰谷轮换法

在峰谷轮换法的基础上提出了利用多维峰谷轮换法对以年综合费用最少为目标函数的无分流换热网络进行优化.在换热网络变量寻优过程中,首先将目标函数极小化得到一个局部极小值点,然后沿着多个方向进行变量搜索,找出最先跳出局部极小值点的变量组合,使得跳出局部极小值的搜索效率高于单变量的搜索效率,并可寻找到更好的换热网络结构,将极小化与跳出局部极小值点过程交替进行直至求得全局最优解.通过算例验证了该方法的可行性,且可找到比其它方法的优化结果更优的换热网络结构.     

某型柴油机换热器设计及仿真分析

设计独立的换热器,降低水下工作柴油机中高负荷工况的排气温度.运用SolidWorks建立换热器模型并进行仿真分析,研究圆柱形换热器4种换热管布置方式对换热器温降与压损的影响.分析结果表明:设计的换热器可将排气温度由550.00℃降低到161.94℃,废气在换热器中的压损为5.95 kPa,降温效果和压损均满足相关工程要...     

Dynamic object-oriented heat exchanger models for simulation of fluid property transitions

Object-oriented heat exchanger models were developed to simulate the dynamic thermal effects of dynamic changes in fluid composition and thus of fluid properties in a type of liquid typical for food products.The models were written in the object-oriented language Modelica as objects in a library structure being developed to simulate complex liquid food process lines and their control systems. The models were based on moderate discretization of the heat exchanger into control volumes, and the fluid dispersion was modelled either as ideal mixing or as transport delay in each control volume. The transport delay model exhibited the best computational performance as well as affording flexibility in fluid dispersion modelling.     

利用夹点技术优化蒸馏换热网络

介绍夹点技术设计的基本原理及设计原则,采用Aspen Hx-net软件,运用夹点技术对某炼油厂常压蒸馏装置换热网络进行优化分析,确定最优传热温差△Tmin、最小公用工程用量和夹点位置,并对换热网络进行了优化.装置运行情况表明,优化后的换热网络节能效果明显,装置投资回收期仅8个月.     

Loop breaking in heat exchanger networks by mathematical programming

In many cases heat exchanger network (HEN) designs require some changes aimed at reduction of units number. This is the case if a rule of division at pinches is applied in designing a HEN as e.g. in pinch analysis approaches. Matches at loops across pinches can be removed and the number of matches in a HEN goes down to the global minimum. Such elimination of units is commonly referred to as loop breaking.Several methods have been suggested for loop breaking. Existing approaches require iterative tedious computations. Moreover, since based on rules from insight into the problem they do not ensure optimal solutions.In this contribution we developed an approach that is based on mathematical programming. The aim is to minimise or to reduce number of units at the condition of minimum energy penalty. The optimisation model consists of relations determining HEN’s topology, heat and mass balances for each heat exchanger (including heaters and coolers) as well as splitters and mixers. Inequalities ensuring feasible heat exchange are included, too.In order to overcome difficulties with solving mixed-integer nonlinear (MINLP) optimisation problem we have decided to impose the condition of linearity for our model. Hence, goal function in optimisation does not account for total cost but the aim is to minimise number of matches and heat load of utilities. Furthermore, flow rates of streams have to be fixed. To relax constraint of fixed flow rates at splitters we have applied a concept of small superstructure that contains all types of arrangements for heat exchangers: parallel, serial and serial–parallel connections. This gives mean to simplify HEN’s topology by replacing parallel arrangement by serial one.Linear optimisation model developed by us accounts for inequality constraints for outlet streams temperatures. We applied EMAT value instead of HRAT. Some new matches can be inserted into a HEN by a designer to make topology changes possible.The optimisation model is of mixed-integer linear type and requires moderate number of binary variables. It can be easily extended in MINLP one that accounts for total cost. In this paper solutions for some literature examples are presented that proved validity of the approach and shows practical merits of the approach.     

土壤空气换热器换热特性的模拟研究

文章针对日光温室环境下土壤空气换热器的换热特性进行了研究。首先通过监测土壤空气换热器沿程空气温度的全天变化,分析了试验工况下土壤空气换热器的动态换热过程及系统性能变化规律。研究结果表明,在试验工况下,土壤空气换热器系统的性能系数(COP)可高达24.1。在此基础上,通过建立土壤空气换热器的非稳态换热模型,模拟研究不同的入口风速对土壤空气换热器换热性能的影响。研究结果表明,当换热管入口空气温度相同时,随着入口风速的增加,土壤空气换热器进出口空气温度差逐渐减小,出口处空气温度与土壤温度差值逐渐增大,这意味着土壤空气换热器有效换热长度逐渐变长。在此过程中,土壤空气换热器系统的换热量和COP随着入口空气风速的增加呈现出先增后减的规律。通过模拟结果可知,当入口风速达到5.5 m/s时,土壤空气换热器系统的换热量与COP均达到最大值。     

Conjugate fluid flow and kinetics modeling for heat exchanger fouling simulation

Thermal treatment of fluid foods represents a major unit operation in the food industry, to ensure the product's safety and quality features. But during the thermal treatments of such sensible fluids in common plate heat exchangers, food constituents such as proteins can be thermally damaged and precipitated to form fouling that greatly affect the treatment efficiency and alter the product's desired features.Computational Fluid Dynamics simulations can then be successfully exploited, bringing forth temperature and velocity information that yield for deposit distributions when coupled to biochemical notations for thermal denaturation of fluid constituents.The present work exploits such modeling for a single-channel heat exchanger during pasteurization of milk. The model enforces a conjugate system of differential equations to a heat exchanger's corrugated plate to combine flow, heat transfer and local transport of β-lactoglobulin. A preliminary computation has been performed that could be applied to geometry optimization (different corrugation shape and orientation) and for a variety of biochemically evolutive products.