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。     

基于夹点技术的环氧丙烷工艺系统换热网络优化方法

基于夹点技术,采用整体系统和子系统换热网络优化法对氯醇法生产环氧丙烷工艺系统换热网络进行优化及对比,得出较佳优化方法. 利用Aspen软件对提取工艺系统流股数据进行校验并计算. 结果表明,现行网络夹点温差为30 K,整体系统夹点温度为329.5 K,子系统换热网络夹点温度分别为327, 329.5, 317.2 K;整体系统优化后节约能耗595.3 kW,分别占原系统热、冷公用工程能耗的17.47%和5.23%;子系统优化后节约能耗610.6 kW,占原系统热、冷公用工程能耗的17.91%和5.36%. 氯醇法生产环氧丙烷工艺系统换热网络优化利用子系统优化方法较佳.     

甲醇精馏工艺夹点技术应用和换热网络优化

夹点技术被广泛应用在换热网络设计和能量回收利用的过程系统优化中,通过Aspen Energy Analyzer软件等方法对甲醇精馏工艺进行夹点分析和换热网络优化,讨论甲醇精馏工艺节能降耗的优化方案,为能量的更优利用提供理论依据和可行方案。     

夹点技术在超大规模甲醇合成工艺中的应用

夹点技术被广泛应用于换热网络的设计和实际生产过程中能量的分析,利用Aspen Energy Analyzer软件对超大规模甲醇合成工艺的换热网络进行夹点分析,为节能降耗提供理论基础。     

利用夹点技术设计换热网络

介绍夹点技术的基本概念以及利用夹点技术设计换热网络的原则,列举利用夹点技术设计换热网络过程的实例,并简单介绍换热网络优化方面的基本知识。     

夹点技术在换热网络优化中的应用

换热网络的优化设计是石化行业生产过程中经常遇到的问题,夹点技术在换热网络优化中有着重要的地位。本文简要阐述了换热网络的基本思想以及夹点技术在换热网络中的应用,用一个简单例子说明了如何运用问题表格法来确定换热网络的夹点,并介绍了夹点技术存在的局限性。     

基于物流焓值的换热网络夹点设计方法

提出一种新的基于物流焓值的换热网络夹点设计方法,首先以综合费用最小为目标确定最小温差,然后建立问题表格确定夹点位置和最小公用工程消耗,最后进行换热网络设计。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分析研究,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差距;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差距。     

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。     

基于夹点技术的辛醇与异丁醛装置用能分析

针对某引进的辛醇与异丁醛装置，进行了换热网络的夹点分析，得到了不同的最小换热温差下该装置的节能潜力。在对整个装置的13个二段进行能量利用情况分析后，结合夹点技术的原则，研究了能量利用的合理性，并给出了48条结论。然后从节能的角度说明可以利用其热量的工艺物流，给出了每个换热器是否应进行改动的建议，为下一步的换热网络节能改造设计奠定了基础。     

简捷法确定提纯回用氢网络目标值

与只考虑直接回用的氢网络相比,具有提纯单元的氢网络能显著减少新鲜氢气的消耗量,但其设计及求解提纯目标值过程均更为复杂。对于单杂质、提纯单元采用固定浓度模型的提纯回用氢网络,结合此类网络的特点,提出了一种简捷法确定网络目标值。首先假设提纯后氢物流量足够大,由此得出初始提纯夹点。当初始夹点估算正确时,由夹点之下的需求物流和源物流的流量与杂质质量衡算即可得出提纯回用氢网络的目标值;当初始夹点估算不正确时,可以第一次计算结果为基础判断得出正确夹点,再增加一步简单计算,也可得到提纯回用目标值。计算实例表明本文方法计算简单且有效。     

Identification and analysis of possible splits for azeotropic mixtures. 2. Method for simple columns

A new method for the design of distillation units based on the behaviour of the mode of infinitely sharp split is presented. The method is non-iterative, fail free and fast. It can lead to the creation of more optimised process flow sheets, and can automate the design process. The first step of the method consists of fast delimitation of the product regions in the concentration simplex and the identification of the ends of the pinch branches at each section. In this way a qualitative evaluation of the arrangement of the pinch branches and the bundles of trajectories can be obtained as the bundles of trajectories depend only on the relations between the values of the coefficients of the phase equilibrium of components at certain points in the concentration simplex. This first step of the method was described in a previous article. In the present article, the second step is described, namely the identification of the possible splits in simple two-sectional columns. If some split is possible, trajectories of both sections intersect each other. The simple, necessary and sufficient condition of the separability has been established: trajectories of both sections intersect each other if pinch branches of both sections have common terminals (ending points). The check-up of this simple condition does not request the calculation of pinch branches and trajectories. The identification of the possible splits is the basis for any algorithm in the synthesis of flowsheets. An algorithm for the identification of one interactive bundle at each section among many is presented here. The interactivity of bundles depends on the location of the point of products. This information about the interactive bundles will be used for subsequent steps of designing e.g. for the calculation of minimal reflux and necessary trays for given reflux.     

具有多个不同质量资源网络的设计与目标值确定

This paper presents a new design procedure for the networks with multiple resources, such as hydrogen and water, of different qualities. The minimum consumption targets of the resources and pinch-causing sources can be identified as well during design. The objective of this work is to reduce the consumption of the resources with higher quality due to their higher cost. A few examples are investigated to show the proposed method. For a net-work of single resource with single contaminant, there is often only one pinch point for the resource. On the other hand, for a network of multiple resources with single contaminant, there might be a few different pinch points. Each resource might have its own pinch point, if its amount is sufficient. The contaminant concentration of the pinch-causing source for a resource with lower concentration will be below that of the higher-concentration resource(s).     

含再生再利用的用水系统的最小新鲜水和相应的再生水用量的确定

A sequential three-step programming method is proposed for determining the minimum flowrate of fresh water and corresponding regenerated water in water-using system of single contaminant with regeneration reuse.In step 1, a programming with the objective of min fws is used to determine the minimum flowrate of fresh water,in which the mathematical representation is a mixed integer nonlinear programming (MINLP1). Then under the same constraints with step 1, a programming with the objective of min freg in step 2 and a programming with the objective of rain Cr in step 3 are subsequently used to determine the minimum flowrate of regenerated water and the minimum inlet concentration to regeneration process corresponding to the minimum flowrate of fresh water based on step 1. The method is easy to apply because we only need to change the objective function but keep the constraints constant to go along the following steps after step 1. In addition, the relationship between the fresh water flowrate required, fws, and inlet concentration to regeneration process, Cr, is investigated. It is found that there exist three relationships between fws and Cr, which indicate three possibilities for Cb: below the pinch, above the pinch or at the pinch. Therefore, a new conclusion is drawn, which differs from that “regeneration of water at pinch minimizes fresh water flowrate“ derived in literature and indicates that in some cases, regeneration at other point also minimizes fresh water flowrate.     

Refinery products/waste optimization using a synthesized pinch technique

An optimal waste minimisation exchange network was designed for the control of effluent, thermal and gaseous wastes generated from process systems. The model used the concept of pinch technique, which was based on a weighted design superstructure that set design products production targets at 25, 50 and 75% against an operating benchmark status, to optimize the product/waste production from a crude distillation unit of an existing operating refinery. The linear programming model that resulted from the analysis of these waste systems and the composite plots were generated for thermal, gaseous and liquid effluent waste streams. The dynamics of waste recovery systems was investigated in relation to the movement of the pinch position as the process conditions are modified or changed based on design targets of 25, 50 and 75% of the products production scheme. The pinch point was located and the high and low waste generating systems were identified and quantified. The analysis of the composite plots and the solution of the linear programming model showed that a design target that minimized the production of gaseous and liquid wastes was obtained when the deviation of the pinch point favoured movement of product curve away from the waste curve. Thus, a new design model that allows the user to predict and minimize waste from a refinery process system was presented.     

Pinch‐based shortcut method for the conceptual design of isothermal extraction columns

Shortcut methods are valuable tools for a comprehensive evaluation of key performance indicators in the early phase of conceptual process design. For the design of extraction columns, operation at minimum solvent demand represents a thermodynamically sound indicator, which is, however, difficult to determine. The suggested shortcut model therefore exploits the existence of the pinch point to directly identify operation at minimum solvent demand. It is solved quickly and reliably by a step‐by‐step procedure. The final step allows a reduction of the approximation error to any desired degree of accuracy. No simplifications regarding the number of components in the mixture or its thermodynamic behavior are introduced. Hence, arbitrary mixtures can be tackled. The performance of the method is highlighted by a fully automated screening of thousands of solvents for the recovery of fermentation products acetone, 1‐butanol, and ethanol from aqueous solution. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1236–1245, 2017     

窄点设计法在吉化炼油厂二常压装置换热流程优化上的应用

通过用窄点设计法对换热流程进行了优化设计，并与原设计进行了对比分析，使换热终温由290℃提高到315℃，使总工程投资节省240万元，并且每年可创造316万元的经济效益。     

Hint: An educational software for heat exchanger network design with the pinch method

A free piece of educational software for heat exchanger network design based on the pinch method is presented. The interface of the program has been designed focusing on getting a clear presentation of the concepts of the pinch design methods and letting students the control of all the stages of the design. The program guides students through all the main steps of the design, including energy and cost targeting, utilities selection, heat exchanger network specification, and optimisation and retrofitting analysis. The program has been tested in a MSc pinch technology course for several years, and the feedback obtained from students during this period has been used to optimise the program functionality and its interface. The use of the program improves the efficiency of the course since it let students practice the concepts of the pinch method while relieving them of tedious repetitive calculations.