DESIGN AND OPTIMIZATION OF HEAT EXCHANGERS FOR BATCH HEATING BY THE NTU-EFFECTIVENESS METHOD

A design method has been developed for sizing external heat exchangers for batch processes based on the effectiveness-NTU method. The method is applicable to any heat exchanger configuration and design. Based on the specified process conditions a solution is obtained which directly specifies the required batch circulation rate and the associated heat exchanger effectiveness. This approach is particularly useful for those types of heat exchanger designs which permit explicit sizing.     

套片式换热器设计计算和CAD绘图软件的研制

结合国内生产企业实际研制了套片式换热器的设计计算和CAD绘图软件。该软件将套片式换热器的性能设计计算、结构和强度计算、生成产品报价和绘制CAD结构图功能结合在一起,实现了一体化的设计流程。提供了一条全新的性能设计计算思路,从设定限制条件预先筛选、优化搜索策略等方面来极大减少计算量,同时保证可以计算出满足各项热力性能指标和离散设计参数的全部方案,对方案挑选、排序后,进行下一步的结构和强度计算;将结构计算和强度计算实现轻度耦合,使得设计结果可以灵活地满足不同的强度标准;将CAD绘图模块需要的参数分为4部分,防止了在CAD绘图模块调整零部件结构参数时,影响其强度性能。     

小型LNG装置缠绕管换热器的设计

缠绕管换热器在天然气液化、空气分离、低温甲醇洗等低温领域有广泛的应用。提出一种可用于缠绕管换热器的设计方法,基于该方法采用分段微元法编写了缠绕管换热器设计程序;并运用该程序对已有换热器进行核算,验证了设计方法的可靠性;同时设计了用于小型LNG装置的缠绕管换热器,为工程上设计用于LNG装置的多股流缠绕管式换热器提供参考。     

间歇化工过程热集成研究进展

间歇化工过程热集成问题的研究能够促进过程系统的可持续发展并且提高产业经济性和技术竞争力,顺应了化工发展大环境。本文介绍了以系统综合优化为目标的间歇化工过程热集成研究的发展现状,整理了早期研究的三大通用图解模型,并讨论和比较了在建模求解过程中常见算法。总结了当前研究的重点在换热网络设计优化、热储罐系统和考虑调度的热集成三个方面,并评述了与之相关的进展、瓶颈和研究意义。指出了热集成问题已成为当前间歇化工过程的研究热点,其中热集成和生产调度的协同优化十分必要,能够从系统全局的角度上给出优化方案。但由于间歇化工过程中存在较多的不确定性和约束条件,增加了热集成的研究难度,因此对间歇化工过程优化设计提出了更高的要求。     

基于虚拟温度法的间歇过程换热网络结构优化

在用虚拟温度法得到的间歇过程换热器网络综合的基础上,对间歇过程换热网络的结构优化问题进行了研究。主要内容包括:在以时间段模型为基础,用虚拟温度法综合间歇过程得到的直接换热网络的基础上,寻找各时间间隔的子换热器网络内的热负荷回路;以一定的规则断开回路,对总换热器网络进行结构优化,使最后的总换热网络既能够减少换热单元数目,又满足年度总费用最小。     

基于热损失的换热网络夹点设计法

现行的换热网络目标方法,在进行换热网络价格估算时,未考虑热物流的热损失。在真实的设计中,换热器壳体保温后仍与环境温度相差较大,则其热损失不可忽略。文章提出了一个新的基于热损失的换热网络夹点设计法,该方法首先以综合费用最小为目标确定出最小温差,然后建立问题表格确定出夹点位置及最小公用工程消耗,最后再进行换热网络设计。文中采用某石油常减压换热网络系统为典型算例对该方法的前两步进行了分析研究,论证了该方法的必要性及可行性。结果表明:该方法与基本Linnhoff夹点技术法估算的投资费用有较大的差距之外,在一定的最小温差下,其与基本Linnhoff夹点技术法确定的夹点位置不同,公用工程消耗也有较大的差距。     

Shortcut Design Approach for Spiral Heat Exchangers

This paper presents a shortcut method for the sizing of spiral plate heat exchangers. The approach consists of an iterative process where physical dimensions like plate width and external spiral diameter are given initial values; convergence is achieved until the calculated pressure drop and heat duty meet the required specifications of the design problem. The results of the application of the approach are compared with case studies reported in the literature. A numerical study using computational fluid dynamics is performed to rate the performance of the geometry. The temperature profiles of the exchanger calculated analytically show the same tendency as those obtained numerically; thus, the method provides a good starting point for estimating the dimensions of spiral heat exchangers in single-phase applications.     

A computerized and integrated approach for heat exchanger network design in multipurpose batch plants

Significant savings in the utility cost of batch plants can be obtained by heat integration. In this study, an integrated mathematical programming approach is developed for the determination of the cost optimal heat exchanger network for multipurpose batch chemical plants. A single step, interactive computer program (BatcHEN) which is developed for the determination of the campaigns (i.e. the set of products which can be produced simultaneously), the heat exchange areas of all possible heat exchangers in the campaigns and finally the heat exchanger network are all discussed. A matrix search algorithm is used for the determination of the campaigns. Heat exchange areas for the possible heat exchangers are found by solving a nonlinear optimization model with a grid search algorithm. Finally the heat exchanger network optimization is modeled as a mixed integer linear programming problem and then solved by the modeling and optimization software GAMS/XA.     

固定管板式换热器的最佳（轻化）设计

简介了管壳式换热器设计中Ｔｉｎｋｅｒ模型及Ｂｅｌｌ－Ｄｅｌａｗａｒｅ方法，讨论了换热器结构性能优化的方法，建立了数学模型，编制了计算程序。为工厂分别优化设计了无相变气－水换热器和有相变气－水加热器。结果表明，优化的珠管壳式换热管，在同样工况下，重量减２０－３０％，经济效益可观。     

Derivation of Charts for the Approximate Determination of the Area Requirements of Heat Exchangers Using Plain and Low‐Finned Tube Bundles (Part A)

Heat exchangers can be made more compact by either enhancing the heat transfer coefficient or by increasing the amount of area per unit volume. The use of low‐finned tubes is an effective means of achieving the latter. The extent to which the equipment size can be reduced using such means is problem‐dependent. Decisions of whether or not to employ process intensification have to be made at the conceptual stage of design. There is, therefore, a need for sizing procedures that avoid the recourse to full detailed design. Such a procedure is reported here. The key to the procedure is a relationship between the shell‐side pressure drop, shell‐side heat transfer coefficient and overall exchanger surface area. The procedure has been applied to a number of ‘typical’ fluids. The results are presented in a series of charts relating exchanger size and duty. It is shown how individual duties can be ‘normalized’ in the form of a ‘duty factor’ that relates shell‐side pressure drop, mass flow rate, stream temperature change and exchanger temperature driving force. So, the charts are independent of duty.     

换热器设计方案多级可拓综合评价

为了更全面、系统、多层次地评价换热器等设备的设计方案,基于可拓学理论,提出了换热器设计方案多级可拓综合评价指标体系,创建了换热器设计方案多级可拓综合评价模型,提出了换热器设计方案多级可拓综合评价方法。以管壳式换热器的设计方案为例,对其进行了多级可拓综合评价,实现了设计方案的评估与优选,并验证了评价结果的客观性与有效性。该评价方法具有可靠性高、实用性强等特点。     

Heat exchanger network synthesis with detailed exchanger designs—2. Hybrid optimization strategy for synthesis of heat exchanger networks

We propose a new strategy to synthesize heat exchanger networks with detailed designs of individual heat exchangers. The proposed strategy uses a multistep approach by first obtaining a heat exchanger network topology through solving a modified version of the mixed integer nonlinear programming (MINLP) stage-wise superstructure of Yee and Grossmann, which includes a smoothed LMTD approximation and pressure drops. In a second nonlinear programming (NLP) suboptimization step, we allow for nonisothermal mixing to solve problems with or without exchanger bypasses. The selected heat exchangers along with the mass and energy balances obtained are then used to design the network with detailed exchanger designs through solving a sequence of NLPs for individual heat exchanger designs. The NLPs are based on the detailed discretized optimization models of Kazi et al., which solve quickly and reliably to obtain heat exchangers based on rigorous, first-principles derived coupled differential equations. These models solve a differential algebraic equation system and do not rely on usual assumptions associated with other heuristic-based exchanger design methods, such as log mean temperature difference and F_T correction factors. These detailed exchanger designs are then used to update the network optimization model through sets of correction factors on heat exchanger area, number of shells, heat transfer coefficients, and pressure drops of each exchanger design, in a method based on that of Short et al. The method solves reliably, guaranteeing feasible exchangers for every potential network generated by the shortcut models, through validation with rigorous heat exchanger models at every iteration. In addition, the method does not increase the nonlinearity of the MINLP model, nor does it require any manual intervention or initialization from the user. Three examples are solved and the results are compared to those obtained in the literature.     

A new approach to evaluate the energetic efficiency of batch‐jacketed reactors

This paper presents a new heat transfer configuration for exothermic batch‐jacketed reactors. The proposed design for the heat transfer scheme comprises an additional heat exchanger in the jacket‐cooling loop. A detailed comparison study considering the new concept and the conventional process is presented in terms of energetic efficiency (refrigerated fluid consumption per batch cycle) and process control (control of reaction temperature). The simulation results of the new heat transfer configuration show a substantial decrease in the total volume of refrigerated fluid injected in the cooling loop, whereas the process control performance was practically unaffected.     

Heat exchanger network synthesis with detailed exchanger designs: Part 1. A discretized differential algebraic equation model for shell and tube heat exchanger design

A new method for the detailed design of shell and tube heat exchangers is presented through the formulation of coupled differential heat equations, along with algebraic equations for design variables. Heat exchanger design components (tube passes, baffles, and shells) are used to discretize the differential equations and are solved simultaneously with the algebraic design equations. The coupled differential algebraic equation (DAE) system is suitable for numerical optimization as it replaces the nonsmooth log mean temperature difference (LMTD) term. Discrete decisions regarding the number of shells, fluid allocation, tube sizes, and number of baffles are determined by solving an LMTD-based method iteratively. The resulting heat exchanger topology is then used to discretize the detailed DAE model, which is solved as a nonlinear programming model to obtain the detailed exchanger design by minimizing an economic objective function through varying the tube length. The DAE model also provides the stream temperature profiles inside the exchanger simultaneously with the detailed design. It is observed that the DAE model results are almost equal to the LMTD-based design model for one-shell heat exchangers with constant stream properties but shows significant differences when streams properties are allowed to vary with temperature or the number of shells are increased. The accuracy of the solutions and the required computational costs show that the model is well suited for solving heat exchanger network synthesis problems combined with detailed exchanger designs, which is demonstrated in Part 2 of the paper.     

Design of heat exchanger network based on entransy theory

The heat exchanger network (HEN) synthesis problem based on entransy theory is analyzed. According to the characteristics of entransy representation of thermal potential energy, the entransy dissipation represents the irreversibility of the heat transfer process, the temperature difference determines the entransy dissipation, and four HEN design steps based on entransy theory are put forward. The present study shows how it is possible to set energy targets based on entransy and achieve them with a network of heat exchangers by an example of heat exchanger network design for four streams. In order to verify the correctness of the heat exchanger networks design method based on entransy theory, the synthesis of the HEN for the diesel hydrogenation unit is studied. Using the heat exchange networks design method based on entransy theory, the HEN obtained is consistent with energy targets. The entransy transfer efficiency of HEN based on entransy theory is 92.29%, higher than the entransy transfer efficiency of the maximum heat recovery network based on pinch technology.     

基于Aspen EDR的管壳式换热器的设计

管壳式换热器作为一种高效换热装置在石化领域得到广泛应用,但传统计算方法非常复杂,因此软件设计已逐步代替传统手算方法成为工程设计人员的主要设计手段。本文通过对含氢气、一氧化碳、氮气等气体的合成气冷却器进行设计,探讨了管壳式换热器的选型原则,介绍了Aspen EDR设计软件使用要点,详细阐述了Aspen EDR软件设计和校核管壳式换热器的步骤,着重介绍了气体冷却器设计过程中换热器的参数选取及要点,并对设计过程中碰到的问题及调整优化方法进行了简单介绍。设计结果表明,Aspen EDR软件设计的结果不仅能达到工艺要求,而且计算过程快捷明了,极大简化了手工计算的过程,提高了设计效率。     

基于(火用)经济评价的换热器最优传热温差

换热器选型是化工过程设计工作的重要部分。换热器的传热温差ΔT设计取值,左右着一次投资与能量回收效率之间的优化权衡。其结果强烈取决于因资源有限性和制造科技进步所决定的、不断增加的能源与设备的比价。本文在运用火用 经济学理论对换热过程的热火用 损失计价和换热器投资估算方法进行深入的分析、探讨和回归的基础上,发展了换热器最优传热温差的数学模型,开发了可实用于工程设计的换热器ΔT计算机辅助优化计算软件。此项研究的应用实例表明,采用优化的换热器的传热温差ΔTopt的设计,能够取得显著的节能和经济效益。     

翅片管式换热器传热与流场流动特性的数值模拟

在对大型翅片管式换热器结构合理简化的基础上,应用CFD和数值传热学方法,建立了翅片管式换热器内部流动与传热的数学模型,得到了其内部流场和温度场的分布规律。并将数值模拟结果与现场应用数据比对分析,结果表明,研究方法可行,能为换热器的设计和改进提供参考和借鉴。     

板式换热器的特点与优化设计

板式换热器的广泛应用,加速了我国板式换热器行业的迅速发展,但我国板式换热器设计与发达国家之间仍存在着不小的差距。鉴于我国板式换热器在设计方面存在的不足,本文讨论了板式换热器的优化设计方法,分析了如何才能使板式换热器达到最佳的方法。     

考虑工况变迁和兼顾运行的换热网络优化设计

基于固定工况设计的换热网络无法保证变工况下的运行性能,以换热网络的运行优化和动态设计为出发点,提出了换热器旁路调节的方法,结合Grossmann的换热网络分级超结构模型,建立了换热网络旁路调节的数学模型和求解策略。利用蒙特卡罗随机技术和最速下降法混合优化策略获得了最佳旁路开度,保证了工况迁移时换热网络的运行性能。实例应用表明:旁路调节大大增加了换热网络的柔性,降低了运行费用。合理调整旁路开度可使得换热网络的运行始终处在较优状态,获得显著的经济效益。