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.     

Synthesis of multipass heat exchanger networks based on pinch technology

The multipass heat exchanger is the most common type of heat transfer equipment used in heat exchanger networks (HENs) by the chemical process industries. There are many methods that have been proposed for the synthesis of HENs with multipass heat exchangers, which are mostly derived from the FT design method. In this paper, an alternative new method to synthesis multipass HENs is presented based on the classical pinch technology. In the multipass heat exchanger, both countercurrent and co-current flow are involved. For the co-current flow, composite curves and problem tables are modified, and compared with that of the countercurrent flow. A proper minimum temperature difference is also selected considering the energy-capital cost trade-offs, and then a multipass HEN is synthesized. Results of the case study demonstrate that the new approach meets operating requirements and minimizes the total cost successfully.     

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.     

利用夹点技术分析优化甲基叔戊基醚装置换热网络

利用Aspen Plus软件计算出冷流股和热流股的焓变,冷热流股的焓变分别为1.4W和-1.2W,然后运用夹点技术对甲基叔戊基醚固定床装置换热网络进行优化分析.计算结果表明,优化后的换热网络节能效果较好.通过小试数据,可以推断中试乃至工业化装置的换热网络节能情况.     

Floating pinch method for utility targeting in heat exchanger network (HEN)

Most of the established methods for utility targeting in a heat exchanger network (HEN) are mainly focusing on fixed stream conditions, where the flow rate, heat capacity, supply and target temperatures are fixed. However, in the process industries, the stream conditions (flow rates and temperatures) are not fixed. Therefore, the established HEN targeting methods cannot be directly applied to locate the hot and cold utility targets for HEN problem with varying flow rates and temperatures. To address this issue, a revised floating pinch method which uses binary variables to parameterise the stream locations on the composite curves, is presented in this work to identify the minimum utilities targets. The revised method simplify the earlier version of floating pinch method presented by Duran and Grossmann (1986) by avoiding the non-differentiability in the mathematical program. Two cases, one with fixed parameters while another with temperature-dependent properties and varying operating parameters are solved to illustrate the revised model.     

利用夹点技术分析优化碳酸二甲酯装置换热网络

利用Aspen Plus软件计算出冷流股和热流股的焓变,然后运用夹点技术对碳酸二甲酯反应精馏装置换热网络进行优化分析。计算结果表明,优化后的换热网络节能效果较好。通过小试数据,可以推断中试乃至工业化装置的换热网络节能情况。     

基于VB+access开发的换热网络夹点技术软件设计

针对夹点技术设计换热网络时,计算繁琐、运算量大、需要大量时间等特点,基于VB和access混合编程,开发出用于换热网络综合夹点计算的软件。该软件能通过给定数据获得夹点温度和最小公用工程用量,并能绘制出总组合曲线。通过实例验算证明,该软件计算准确、速度快。     

Simulation and heat exchanger network designs for a novel single-column cryogenic air separation process

To realize the industrialization of the novel single-column air separation process proposed in previous work, steady-state simulation for four different configurations of the single-column process with ternary(nitrogen, oxygen and argon) is developed. Then, exergy analysis of the single-column processes is also carried out and compared with the conventional double-column air separation process at the same capacity. Furthermore, based on the steady-state simulation of single-column processes, the different heat exchanger networks(HENs) for the main heat exchanger and subcooler in each process are designed.To obtain better performance for this novel process, optimization of process configuration and operation is investigated. The optimal condition and configuration for this process is consisted as: feedstock is divided into two streams and the reflux nitrogen is compressed at the approximate temperature of 301 K. In addition, HEN is optimized to minimize the utilities. HENs without utilities are obtained for the four different configurations of single-column process. Furthermore, capital costs of the HEN for different cases are estimated and compared.     

Performance of a Pinch Analysis for the Process of Recovery of Ethanol from Fermentation

The objectives of the project reported here were to perform an energy analysis for the process of the recovery of ethanol from fermentation broths by catalytic conversion to gasoline and to conduct a pinch analysis to obtain a new heat exchanger network, and thus, reduce the utility costs. A minimum temperature difference of 10 °C was used. A temperature interval diagram and cascade diagram were drawn to identify the pinch points and four such points were observed. New heat exchanger networks were formulated from this information. The least number of heat exchangers for the different networks created was 19, whereas the original process had 9. The cost of utilities was the same for both systems. Therefore, it was concluded that the implementation of this system in the Caribbean could be expensive since in the first instance, ethanol is not particularly plentiful. Secondly, electricity and water costs are expensive in the Caribbean compared to other countries in America, such that any effort in reducing CO₂ emissions by using ethanol would not be feasible.     

柴油加氢装置过程模拟与节能研究

针对某炼油厂处理量为3.5 Mt/a的柴油加氢装置,应用Aspen Plus流程模拟软件建立了装置的数学模型,计算得出了与现场标定数据比较吻合的模拟结果。根据计算结果,利用夹点技术对其换热网络进行节能分析与改造。首先以夹点温差为20℃,确定换热网络能量目标。该装置换热网络的夹点温度为95.4℃,最小热公用工程量为5 085.7 kW,最小冷公用工程量为20 613.9 kW,与现有换热网络热公用工程13 870.8 kW相比,存在8 785.1 kW的节能潜力。然后消除违背夹点规则的不合理换热匹配,进一步优化,并提出了改造方案。该方案新增7台换热器,可节约热公用工程8 450.5 kW,约降低了60.9%的能耗,取得了良好的节能效果。回收期为0.67年。     

Optimization of a High Temperature PEMFC micro‐CHP System by Formulation and Application of a Process Integration Methodology

A 1 kWe micro combined heat and power (CHP) system based on high temperature proton exchange membrane fuel cell (PEMFC) technology is modeled and optimized by formulation and application of a process integration methodology. The system can provide heat and electricity for a single‐family household. It consists of a fuel cell stack, a fuel processing subsystem, heat exchangers, and balance‐of‐plant components. The optimization methodology involves system optimization attempting to maximize the net electrical efficiency, and then by use of a mixed integer nonlinear programming (MINLP) problem formulation, the heat exchange network (HEN) annual cost is minimized. The results show the high potential of the proposed model since high efficiencies are accomplished. The net electrical efficiency and total system efficiency, based on lower heating value (LHV), are 35.2% and 91.1%, respectively. The minimized total annual cost of the HEN is $8,147 year^–1.     

多管程换热器网络的最小温差分析与夹点设计

在实际生产过程中,多管程换热器广泛应用,其中既存在逆流换热也存在并流换热。针对多管程换热器网络中并流换热与逆流换热时换热温差对夹点特性尤其是换热网络综合的影响,定量分析最小温差的选择与夹点特性及其总费用的关系。兼顾管程数目的选择以及换热网络总费用两方面因素,以年度化总费用最低为目标,优化求解多管程换热器网络的最小温差。然后,将求得的最小温差作为夹点温差,遵循夹点设计原则综合换热网络。同时,计算得出多管程换热器网络的F_T修正因子,并对结果进行分析。最后,结合示例对比分析求解结果,证明方法的有效性。     

基于夹点技术与超结构模型的多程换热网络最优综合

基于热力学原理,以夹点技术为基础结合数学规划法,采用两步法综合多程换热网络。第一步在多程换热网络热力学分析的基础上优化求解最小温差,计算公用工程用量。第二步将求得的最小温差作为夹点温差,将网络分为夹点之上和夹点之下两个子网络,建立多程换热网络的超结构模型,确定流股匹配并优化网络配置。最后,以换热网络总费用最小为目标,连接两个子网络,权衡设备投资费用和操作费用,综合多程换热网络。该方法基于热力学原理,改进了夹点技术在多程换热网络综合中的应用,进而实现了多程换热网络的自动综合。示例分析证明了本文所提方法的有效性。     

Heat exchanger network area targeting considering stream allocation to shell or tubes

An optimal heat recovery network requires optimum values of area and energy targets. Current heat exchanger network targeting methods do not consider the optimal allocation of each stream to shell or tube side of the exchanger during the network cost estimation. Some researchers pre-set the allocation of the streams ahead of targeting [Polley, G. T., & Panjeh Shahi, M. H. (1991). Interfacing heat exchanger network synthesis and detailed heat exchanger design. Transactions of the Institute of Chemical Engineers, 69(Part A), 445–457]. In real design case however, some practical considerations such as fouling and corrosion constrain the allocation of streams. Apart from those, other streams are allowed to be allocated to either tubes or shell. Appropriate allocation of these streams can considerably affect the network cost estimation. This paper introduces a new area-targeting procedure which utilizes the optimal allocation of streams in all enthalpy intervals. The procedure evaluates two possible options for each stream split passing through each exchanger in the spaghetti network. Thus, two different exchanger area requirements can be estimated and the one with less area requirement will be selected. During this evaluation process, the optimal distribution of each stream pressure drop within enthalpy intervals is fully utilized. The proposed targeting procedure is applied on a case study and comparison of the results with previous method (Polley & Panjeh Shahi, 1991) shows reduction of around 18% in the network area. In another case study, the area–energy trade offs using the new procedure shows a reduction of 12.4% in minimum network area requirement and 14.5% in total annual cost. Therefore, the new procedure can considerably alter the area–energy trade offs.     

Integrated water resource management through water reuse network design for clean production technology: State of the art

This article considers new and existing technologies for water reuse networks for water and wastewater minimization. For the systematic design of water reuse networks, the theory of the water pinch methodology and the mathematical optimization are described, which are proved to be effective in identifying water reuse opportunities. As alternative solutions, evolutionary solutions and stochastic design approaches to water system design are also illustrated. And the project work flow and an example in a real plant are examined. Finally, as development is in the forefront in process industries, this paper will also explore some research challenges encountered in this field such as simultaneous water and energy minimization, energy-pinch design, and eco-industrial parks (EIP).     

常减压装置换热网络的优化设计

在夹点技术的基础上,结合工艺流程模拟软件（HYSYS）和换热网络计算软件（HEXTRAN）对原有常减压装置换热网络进行优化,并得出了近于最优的换热网络。优化后的换热网络经实际生产运行取得了良好的效果和可观的经济效益。     

Integration strategies of hydrogen network in a refinery based on operational optimization of hydrotreating units

Inferior crude oil and fuel oil upgrading lead to escalating increase of hydrogen consumption in refineries. It is imperative to reduce the hydrogen consumption for energy-saving operations of refineries. An integration strategy of hydrogen network and an operational optimization model of hydrotreating (HDT) units are proposed based on the characteristics of reaction kinetics of HDT units. By solving the proposed model, the operating conditions of HDT units are optimized, and the parameters of hydrogen sinks are determined by coupling hydrodesulfurization (HDS), hydrodenitrification (HDN) and aromatic hydrogenation (HDA) kinetics. An example case of a refinery with annual processing capacity of eight million tons is adopted to demonstrate the feasibility of the proposed optimization strategies and the model. Results show that HDS, HDN and HDA reactions are the major source of hydrogen consumption in the refinery. The total hydrogen consumption can be reduced by 18.9% by applying conventional hydrogen network optimization model. When the hydrogen network is optimized after the operational optimization of HDT units is performed, the hydrogen consumption is reduced by 28.2%. When the benefit of the fuel gas recovery is further considered, the total annual cost of hydrogen network can be reduced by 3.21×10₇ CNY·a_-1, decreased by 11.9%. Therefore, the operational optimization of the HDT units in refineries should be imposed to determine the parameters of hydrogen sinks base on the characteristics of reaction kinetics of the hydrogenation processes before the optimization of the hydrogen network is performed through the source-sink matching methods.     

考虑压力因素的柴油加氢改质装置换热网络改造

在换热网络设计和改造中考虑压力因素,可以提高换热网络的经济性。本文采用夹点技术,针对某炼厂柴油加氢改质装置,提出了3种不同程度考虑压力因素的换热网络优化方案。方案1为最大热回收方案,不考虑压力约束,回收热量最大但投资也最高;方案2,在考虑可更换反应进料泵的前提下,考虑压力因素,适合于该换热网络的新设计;方案3,在维持反应进料泵不动的前提下,考虑压力因素,适合于该换热网络的改造。方案2和方案3均较方案一明显地减少了设备投资费用,具有更好的经济效益,说明了在换热网络综合中压力因素不可忽视。     

A novel method based on entransy theory for setting energy targets of heat exchanger network

A T-Q diagram based on entransy theory is applied to graphical y and quantitatively describe the irreversibility of the heat transfer processes. The hot and cold composite curves can be obtained in the T-Q diagram. The entransy recovery and entransy dissipation that are affected by temperature differences can be obtained through the shaded area under the composite curves. The method for setting the energy target of the HENs in T-Q diagram based on entransy theory is proposed. A case study of the diesel oil hydrogenation unit is used to il ustrate the application of the method. The results show that three different heat transfer temperature differences is 10 K, 15 K and 20 K, and the entransy recovery is 5.498 × 107 kW·K, 5.377 × 107 kW·K, 5.257 × 107 kW·K, respectively. And the entransy transfer efficiency is 92.29％, 91.63％, 90.99％. Thus, the energy-saving potential of the HENs is obtained by setting the energy target based on the entransy transfer efficiency.     

与换热网络热集成的精馏塔压优化

调整精馏塔的操作条件是节省塔能耗的有效途径之一,然而在对已有装置进行用能优化时,需同时考虑精馏塔操作条件对塔能耗和换热网络能耗的影响。基于装置所有流股的冷热复合曲线,针对跨夹点的精馏塔,同时考虑了精馏塔的再沸、冷凝以及过程流股,分析了塔压变化对装置公用工程消耗的影响,并对某连续重整装置汽提塔进行了案例分析。结果显示,塔压降低可使冷凝器能耗增加,再沸器能耗减小,而对于塔顶塔底出装置流股,塔压降低可节省冷却公用工程但增加加热公用工程。装置总体的节能效果为塔顶冷凝器、塔底再沸器和塔顶塔底出装置流股节能效果的综合作用。对某连续重整装置汽提塔分析表明,塔压降低200.0 kPa时,其加热公用工程用量将减少577.5 kW。