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.     

Optimization of cleaning schedulesin heat exchanger networkssubject to fouling

Many heat exchanger networks in continuous processes are subject to fouling, which causes significant losses in efficiency over time. This paper addresses the problem posed in scheduling cleaning operations in order to maintain optimal operation in such networks. A mixed integer nonlinear programming modelis presented and is solved using the Outer Approximation/Extended Relaxation algorithm. The methodology is demonstrated via case studies using fouling rates obtained from plant data studies. Both linear and asymptotic fouling behaviors are considered. The challenges posed by the nonconvexity of the problem in finding a global optimum are discussed.     

Optimal design of a heat exchanger undergoing reaction fouling

The design of heat exchangers which resist fouling is examined. It is shown that for asymptotic reaction fouling in a uniform wall temperature exchanger with outlet fluid temperature kept constant, it is possible to obtain an optimum combination of exchanger size and tube-side temperature. This optimum minimises the amount of fouling in the system. An equation which gives a good approximation to the optimum is derived, and its limitations discussed.     

Optimal operation of heat exchanger networks

The paper discusses optimal operation of a general heat exchanger network with given structure, heat exchanger areas and stream data including predefined disturbances. A formulation of the steady state optimization problem is developed, which is easily adapted to any heat exchanger network. Using this model periodically for optimization, the operating conditions that minimize utility cost are found. Setpoints are constant from one optimization to the next, and for implementing the optimal solution special attention is paid to the selection of controlled variables such that the operation is insensitive to uncertainties (unknown disturbances and model errors). This is the idea of self-optimizing control. In addition to heat exchanger networks, the proposed method may also be applied to other processes where the optimum lies at the intersection of constraints.     

换热设备污垢研究进展

对污垢的形成过程中起始、输运、附着、剥蚀和老化5个阶段的机理进行了简要的概述。综述了近几年国内外换热设备污垢领域的研究进展,以预测、监测和对策3个主要研究方向进行了归纳。综合已有的研究成果,提出了蒸汽污垢研究这一新方向。     

考虑关键换热器备用的原油预热系统清垢周期优化

原油结垢是原油预热过程面临的一个严峻问题,它使换热器的传热系数降低,影响正常的生产过程。应对原油预热过程的结垢问题最普遍的方法就是对换热器进行周期清洁,并优化清洁周期。许多结垢严重的行业都采用换热器备用的方式来减少因换热器离线造成的热回收减小,但原油预热系统尚未考虑,因而进一步考虑了关键换热器的备用来进行原油预热系统清垢周期优化。首先选取关键换热器,再通过模拟退火算法进行清洁周期优化。应用所提出的方法对简化的原油预热系统进行了清垢周期优化,结果显示,考虑换热器备用时所得到的清垢周期经济效益更好。     

换热器网络设备面积与清洗时序同步优化

表面结垢会严重影响换热器的传热效率,定期清洗是解决该问题的主要方式.针对以往换热器网络清洗时序优化方法中用于决策的整型变量较多而难以求解的问题,提出以换热器清洗的最大允许污垢热阻为优化变量,取代表示换热器是否清洗的二进制变量,将混合整数非线性规划问题转化成非线性规划问题,能够有效地减小问题规模,降低求解难度.优化过程中兼顾换热器网络的设计型与操作型问题,采用遗传/模拟退火算法同步优化换热器的面积与清洗时序.将该方法用于一个实例,所得年度总费用与文献基本一致,验证了该方法的有效性.     

换热网络旁路优化设计

提出了一种可以降低已有换热网络运行费用的旁路优化设计方法,使得网络控制自由度增大,运行费用明显降低。该优化设计方法将网络运行总费用作为目标函数,同时考虑结垢热阻对换热器换热效果的影响,经过多次优化计算确定旁路位置和开度,并根据现场具体情况选择合适的旁路开度下限,确定旁路数目,最终实现网络旁路优化设计。通过示例说明了本文所提方法的有效性和实用前景。     

板式热交换器的清洗工艺

对换热器的特点和类型进行了介绍,详细介绍了板式换热器的循环清洗和拆卸清洗两种方法,并结合实例得出了拆卸清洗干净、彻底,优于循环请洗的结论.     

Estimation of fouling in a plate heat exchanger through the application of neural networks

Pasteurization is an important, if not the most important, process step in the packaging of milk. It is subject to alterations stemming from the variation in the temperature, pH and raw milk quality. The variability may manifest itself in changes in the formation of the deposit (fouling) in the pasteurization unit, such that there is a need for tools, both instrumentation and computational, to help in monitoring the process and keeping it on the desired course. In this paper we describe a practical procedure based on artificial neural networks (ANN) that allows prediction of the deposit thickness, the overall heat transfer coefficient and the critical time (the time that the unit has to be stopped for cleaning) for reducing the impact of fouling on such processes. The procedure determines when the cleaning operation is required once the system is under critical conditions of operations. A combination of fundamental studies and plant measurements were used for study of the operating conditions and thus evaluation of the trades‐offs between operating conditions and longer operating life span. The results are encouraging, enough to validate current operating industrial techniques. Copyright © 2005 Society of Chemical Industry     

Optimal operation of heat exchanger networks through energy flow redistribution

This article presents a novel energy flow redistribution methodology to achieve optimal operation of heat exchanger networks. The proposed method aims to manipulate the propagation path of a disturbance through the network to reduce its impact on utility consumption. Specifically, an optimization problem is formulated to generate new duty targets for heat exchangers of the network when a disturbance is encountered. Subsequently, a feedback control system is designed to track these targets by manipulating bypasses around the process heat exchangers. The effectiveness of the proposed framework is illustrated with the help of three benchmark examples. The proposed approach can handle disturbances in inlet as well as target temperature, inlet flow and heat transfer coefficient of individual heat exchangers.     

Optimal synthesis of heat exchanger networks involving isothermal process streams

This paper proposes a new MINLP model for heat exchanger network synthesis that includes streams with phase change. The model considers every possible combination of process streams that may arise within a chemical process: streams with sensible heat, streams with latent heat, and streams with both latent and sensible heat. As part of the optimization strategy, the superstructure is modeled with logical conditions that are used for the proper placement of heat integration for streams with change of phase. The proposed MINLP model provides the network structure that minimizes the total yearly cost. Several examples are presented to illustrate the capabilities of the proposed model.     

板式换热器的化学清洗

对各类板式换热器化学清洗进行评述,并介绍了清洗时的特点及其具体应用。     

换热器结垢与换热网络裕量设计方法研究进展

从结垢现象影响换热系统正常运行的角度出发,介绍了近几年换热网络裕量设计以及针对结垢问题不同学者研究出的换热网络优化设计。总结了在换热网络设计中对换热器清洗时序、清洗周期优化或者增加换热网络的裕量设计的不同换热网络设计最优方法,但这些方法都是在换热网络设计之初,考虑换热器结垢最严重的情况即换热网络在“最差”工况下进行的优化,因此优化得到的换热网络难以保证换热网络全运行周期的持续节能优化。本文结合现有换热网络设计方法的利弊,针对结垢过程的慢时变、持续特点,提出一种基于长周期持续节能的换热网络设计优化方法,在换热网络设计之初,定量分析结垢对网络结构的影响,以换热网络全周期累积总费用为目标函数,实现换热网络的最优综合。     

Model based approach to synthesize spare-supported cleaning schedules for existing heat exchanger networks

Almost every modern chemical process is equipped with a heat-exchanger network (HEN) for optimal energy recovery. However, as time goes on after startup, fouling on the heat-transfer surface in an industrial environment is unavoidable. If the heat exchangers in an operating plant are not cleaned regularly, the targeted thermal efficiency of HEN can only be sustained for a short period of time. To address this practical issue, several mathematical programming models have already been developed to synthesize online cleaning schedules. Although the total utility cost of a HEN could be effectively reduced accordingly, any defouling operation still results in unnecessary energy loss due to the obvious need to temporarily take the unit to be cleaned out of service. The objective of the present study is thus to modify the available model so as to appropriately assign spares to replace them. Specifically, two binary variables are adopted to respectively represent distinct decisions concerning each online exchanger in a particular time interval, i.e., whether it should be cleaned and, if so, whether it should be substituted with a spare. The optimal solution thus includes not only the cleaning schedule but also the total number of spares, their capacities and the substitution schedule. Finally, the optimization results of a series of case studies are also presented to verify the feasibility of the proposed approach.     

基于自组织Petri Net优化设计换热网络

基于Petri Net的动态并发特性和逻辑表述能力,构造最小传热温差优化、夹点分析、网络综合及结构调优模块。首先,根据Petri Net激发规则和垂直传热原则,实现最小允许传热温差的优化;然后,根据Petri Net四则运算机制,实现夹点分析数据流辗转传递,确定夹点、最大热回收和最小冷、热公用工程等信息;进而,根据Petri Net监督学习机制,拓扑夹点设计可行性经验规则,综合初始换热网络结构;最终,根据Petri Net自组织机制,通过断裂环路、松弛路径,实现换热网络渐进调优。通过实例计算说明提出方法的可行性和有效性。     

高压水射流-机械联合清洗方法在换热器中的应用

介绍了高压水射流清洗方法和机械清洗方法的特点和清洗行业中的应用范围。通过高压水射流-机械联合方法在清洗换热器中的应用实例,阐述了联合清洗方法使用的必要性。     

积灰与酸耦合作用下套管换热器传热特性热态实验

烟气露点是低温腐蚀的关键指标,制约着锅炉尾部排烟余热的深度利用。换热器表面积灰是传热特性恶化的主要原因,电站锅炉尾部烟气环境中,积灰与酸凝结共同作用影响换热器的传热特性。在含尘、含酸的烟气环境下对换热器传热特性进行热态实验研究,以套管换热器为基础,得到具有更高使用价值的烟气工程应用露点,结合传热特性随外壁温的变化情况,得到换热管传热特性随积灰及酸耦合的变化规律;并通过对不同外壁温下灰样的分析,得到不同酸凝结状况下积灰规律,得到实验环境下的工程应用酸露点温度为72℃,较传统热力学酸露点低35℃以上。     

换热器在线清洗

介绍了沈阳石蜡化工有限公司换热器在线清洗方案的制定过程及清洗结果.实际结果表明,使用H2SO4、乌洛托品、NaHCO3、TS-106对换热器进行清洗,具有很好的清洗、剥离作用.通过在线清洗延长了换热器运行周期,提高了经济效益.     

板式换热器的在线清洗

针对化工生产中板式换热器易结垢且拆洗不便的情况，提供了一种在线清洗的方案，介绍了该方案的工艺流程及清洗试剂的选择。