Globally optimal synthesis of heat exchanger networks. Part I: Minimal networks

This article introduces the concept of minimal structure (MSTR) and presents an enumeration algorithm for the synthesis of heat exchanger networks based on MSTR. Minimal Structures refer to a class of heat exchanger networks featuring acyclic heat transfer networks without energy loops. The enumerations used are either exhaustive or smart with a stopping criterion. Without loss of generality we use the isothermal mixing Synheat model, that is, the method applies identically to other superstructures, with likely variations in the optimization models associated to each step. A conjecture is used to state that the algorithm renders solutions that are globally optimal. Literature examples are used to demonstrate the capabilities of the enumeration algorithm. Most of our solutions compare favorably with the best reported ones in literature, with exceptions where the reported solution is not minimal.     

Globally optimal synthesis of heat exchanger networks. Part II: Non-minimal networks

In Part I of this work, the synthesis of minimal heat exchanger networks using the isothermal mixing stage-wise superstructure was presented. In this Part II, an extension of the algorithm presented in Part I is made to consider networks that allow multiple solutions regarding heat allocation, that is, they have energy loops where heat loads can be rearranged without changing the overall energy consumption. We extend the strategy of our Part I to use a set of nested loops to enumerate the number of units, the structure of matches, the energy consumption, different values of exchanger minimum approximation temperature (EMAT), and different locations where EMAT is active. All the models used are linear and are aided by capital cost evaluations. As in Part I, we claim global optimality based on our conjectures. Literature examples are solved to show the effectiveness of the algorithm.     

Globally optimal synthesis of heat exchanger networks. Part III: Non-isothermal mixing in minimal and non-minimal networks

In this work, the enumeration algorithms presented in Parts I and II for the globally optimal synthesis of minimal and non-minimal heat exchanger networks are extended to consider non-isothermal mixing. New mathematical models, including non-isothermal mixing constraints, are proposed to target the bounds of energy consumption and the binding exchanger minimum approximation temperature. These models are solved using the algorithms, which involve solving systems of equations instead of mathematical programming. Three global optimization strategies are proposed to optimize each enumerated structure, involving the use of a global solver directly, or the use of a Golden Search based on energy consumption and a flowrate optimization model considering non-isothermal mixing. The flowrate optimization model is reformulated as a convex problem, which is solved by using nonlinear programming or a mathematical programming-free methodology, that is, solving Karush–Kuhn–Tucker equations. A new Global Optimum Search Algorithm is developed and examples are tested comparing different optimization strategies.     

Identifying optimal thermodynamic paths in work and heat exchange network synthesis

The process synthesis problem referred to as work and heat exchange networks (WHENs) is an extension of the classical heat exchanger networks problem considering only temperature and heat. In WHENs, additional properties are pressure and work, and strong interactions exist between temperature, pressure, work, and heat. The actual sequence of heating, cooling, compression, and expansion for pressure changing streams (PCs) will affect the shape of the composite and grand composite curves, the Pinch point, and the thermal utility demands. Even stream identities (hot or cold) will sometimes change. The identification of the optimal thermodynamic path from supply to target state for PCs becomes a primary and fundamental task in WHENs. An MINLP model has been developed based on an extension of the Duran–Grossmann model (that can handle variable temperatures) to also consider changing stream identities. Three reformulations of the extended Duran–Grossmann model have been developed and tested for two examples. © 2018 American Institute of Chemical Engineers AIChE J, 65: 549–561, 2019     

The optimal design of membrane systems

This paper introduces a novel optimal design strategy for membrane separation systems. This strategy is characterised by two main features: firstly, detailed models are used. This is essential if sub-optimal and inaccurate solutions are to be avoided. Secondly, an optimisation technique based on genetic algorithms is implemented. The feasibility of the optimal design strategy is investigated using a pervaporation case study. To this end, an existing pervaporation plant is evaluated and a significantly improved design is found.     

微分进化算法应用于换热网络全局最优化

前言换热网络是过程系统中实现能量回收和高效利用的重要环节,其性能直接关系到整个系统的能量利用水平。目前,换热网络优化设计的方法主要分为三类,分别是夹点法[1-2]、数学规划法[3-4]与启发式方法[5-7]。     

换热器优化顺序对换热网络全局优化的影响

为了克服换热网络全局最优化过程中极易陷入局部最优解陷阱的难题,本文将蒙特卡罗随机抽样技术应用到换热网络冷、热流体随机组合中,从而实现换热网络多维优化参数优化顺序的随机变化,使得换热网络优化能够从一个局部最小解跳到另外一个局部最小解,实现全局最优化。通过具体算例表明,这种方法能够找到比以往算例更好的结果,能够更好地满足工业上的应用。     

换热网络填充函数法的全局优化

换热网络全局优化问题属于混合整数非线性规划范畴,其难点是目标函数和约束条件呈现为严重的非线性和非凸特性,局部最优解陷阱星罗棋布.针对其全局优化的难点,应用一种变换函数的全局优化方法--填充函数法,对换热网络进行全局优化.通过具体的填充函数对某特定算例进行求解表明,通过不断的交替优化,填充函数能够使换热网络目标函数跳出局...     

换热网络操作夹点分析与旁路优化控制

换热网络夹点设计法是从设计的角度,针对某一给定的典型操作条件而进行的,而炼油化工过程的生产条件经常在一定范围内波动。在实际的生产中,换热网络的操作夹点和最小温差与设计值往往不尽相同,为换热网络的优化控制带来了一定困难。因而近年来对于换热网络夹点技术以及旁路优化控制方面的研究不断深入,但将夹点技术与换热网络控制集成的方法仍不成熟。本文从操作的角度求解并分析换热网络结构已定或网络正在运行情况下的操作夹点,定性分析操作夹点的变化规律,并提出在操作夹点附近设置旁路实现网络的旁路优化控制,从而将夹点技术应用于换热网络旁路优化控制中。实例仿真表明,这一旁路优化控制方法在满足控制要求的同时明显降低了网络的总公用工程,验证了其有效性。     

换热网络控制分析与设计研究进展

回顾了近年来对换热网络可控性方面的研究,即分析了当前换热网络的两种控制策略:控制性能指数法和旁路优化控制方法。阐述了这些方法的优点和尚待改进的问题,并指出换热网络的设计应同时考虑工艺与控制两方面。提出了工艺与控制集成的设计方法的具体研究思路,并指出换热网络工艺与控制集成设计的方法将成为今后换热网络设计与控制方面研究的发展方向。     

基于质子交换膜燃料电池的微型天然气热电联产研发进展

基于质子交换膜燃料电池(PEMFC)的微型天然气热电联产系统有着广阔的市场发展前景。这种系统将千瓦级天然气制氢、燃料电池发电及余热利用有机的结合在一起,可以将天然气的一部分高品质的化学能通过氢气这个中间介质转化为电能,其余的低品位的能量用于采暖及生活热水供应,可有效提高系统的可用能利用程度,实现天然气这种清洁能源的"温度对口、梯级利用"。介绍了微型燃料电池热电联产系统的技术路线,并对国内外微型制氢技术的研发及热电联产系统的产业化状况进行了介绍和分析。     

基于分解算法的功热交换网络多目标优化

功热网络设计问题指在流程设计中对变压和换热过程进行耦合优化设计的问题,以此来提高整体系统的能效并降低成本。前人工作中一般采用数学规划法对功热网络建模优化。然而,由于存在变压过程和换热器面积计算的非线性约束,以及换热匹配的二元变量,整体模型往往是一个高度非凸的混合整数非线性规划模型,难以求解。本文提出一种高效的功热网络优化方法。模型中分别用透平压缩机和换热器实现功热网络中轴功和热的交换。求解过程采用分解算法,主问题中用随机算法对关键变量优化,功和热两个子网络问题中用确定性算法求解。目标函数考虑了经济和环境影响。案例测试对比了不同优化目标得到的结果以及多目标Pareto曲线,验证了所提出方法的高效性。     

考虑热集成的用水网络优化

提出了新的同时考虑间接传热和混合传热的热集成转运模型,并与用水网络超结构NLP模型结合以求取ΔTmin＝0℃时用水网络的公用工程目标。新转运模型与以往的模型相比变量数和约束方程数都大大减少。进一步,针对现有综合方法ΔTmin不可调的局限性,采用改进的换热网络转运模型,提出了区分处理混合传热和间接传热的综合方法。该方法不仅可以得到优化的公用工程费用和换热匹配数,而且与传统的方法相比可以调整ΔTmin,得到更合理的换热网络结构。算例表明,结合新转运模型的NLP模型与结合改进转运模型的综合方法都要优于以往的模型和方法。     

电火花改性表面池沸腾换热特性

通过电火花成型加工技术在铜基换热表面制备微纳结构改性表面,以自制换热表面性能测试装置进行改性表面的池沸腾换热性能实验。改性表面随加工电流改变而具有不同粗糙度、孔隙率和粗糙度因子,表面接触角范围在117.4°~133.5°。实验结果表明,改性表面的微纳结构提高换热面的池沸腾换热效果,临界热流密度较光滑铜表面提高了26%~87.8%,最大传热系数提高了48.1%~213%。改性表面的传热系数随着粗糙度增大而减小,而临界热流密度则是先增大后减小;孔隙率的增大使得改性表面的传热系数也随之增大,临界热流密度则是随着孔隙率的增大而先增大后减小;临界热流密度随着粗糙度因子的增大而降低,传热系数则是先增大后降低。粗糙度对沸腾换热的强化效果较小,孔隙率和粗糙度因子是强化池沸腾换热的关键,孔隙率和粗糙度因子分别影响了气泡核化密度和实际接触面积,提高了气泡脱离频率,带走更多的热量,但两者间存在互相制约的平衡关系。     

Multiobjective design of interplant trigeneration systems

A systematic approach for heat integration into an eco‐industrial park through an integrated trigeneration system is presented. The approach is based on a new superstructure formulated as a multiobjective mixed‐integer nonlinear programming model, where intraplant and interplant heat exchange for the process streams is allowed, in addition to the energy integration into the utility system that is constituted by a steam Rankine cycle (to produce electric power and hot utility), an organic Rankine cycle (to recover waste heat and produce electric power), and an absorption refrigeration cycle (to recover waste heat and provide refrigeration). To run the utility system, several external heat sources (solar, fossil fuels, and biofuels) are considered, which impact the economic, environmental, and social objectives considered in the model. A systematic approach to tradeoff the objectives considered is presented. Two examples are presented, where the advantages of the integrated eco‐industrial park are shown. © 2013 American Institute of Chemical Engineers AIChE J, 60: 213–236, 2014     

换热网络全局优化的等平面切割方法的实现

换热网络全局优化属于混合整数非线性规划范畴,其全局优化难点是局部最小解遍布全局,求解过程中很容易陷入局部最小解,而不能获得全局最优解.文章针对换热网络全局最优化的难点,运用一种全新的全局最优化方法--等平面切割的方法,根据目标函数代表的性能进行等平面切割,反复交替地操作不断缩小全局最优解的区间;同时,基于切割平面法分析...     

3~#常减压蒸馏装置换热网络的操作优化

利用英国Process Integration Ltd.(PIL)公司最新的原油精馏系统优化技术,对茂名分公司3#常减压蒸馏装置换热网络进行建模及优化操作。结果表明,通过优化常压塔中段取热分配,将常顶冷回流量降到几乎为零,原油换热后温度提高了7℃,实现了能量回收最大化。