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。     

夹点技术及其在换热网络中的应用研究

首先阐述了夹点技术的基本原理,利用夹点技术对原油常减压蒸馏装置的换热网络进行设计,运用问题表法求取夹点温度、最小公用工程。     

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.     

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。     

乙烯装置能量优化

应用夹点技术对某800kt/a乙烯装置低温系统的换热流程进行了优化分析。通过总组合曲线确定换热网络所需的不同冷剂等级及负荷,通过有效能组合曲线确定换热网络的有效能损失。经过调优处理确定合适的工艺流程,从而达到节能降耗的目的。     

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。     

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.     

NEW HYBRID METHOD FOR MASS EXCHANGE NETWORK OPTIMIZATION

A new hybrid optimization method is presented that is fairly robust and can be accomplished in an automatic way. The main idea is using integer cuts and bounds, based on driving force plot analysis, for the lean streams to decrease the possibility of being trapped in local optima. A new initial solution is constructed if the MINLP solution is infeasible; otherwise the earlier found best solution is used. In consequence, the MINLP model is modified in the iteration steps. The iteration is stopped when the total annual cost (TAC) in the solution reaches 1.1·TAC_target.     

NEW HYBRID METHOD FOR MASS EXCHANGE NETWORK OPTIMIZATION

A new hybrid optimization method is presented that is fairly robust and can be accomplished in an automatic way. The main idea is using integer cuts and bounds, based on driving force plot analysis, for the lean streams to decrease the possibility of being trapped in local optima. A new initial solution is constructed if the MINLP solution is infeasible; otherwise the earlier found best solution is used. In consequence, the MINLP model is modified in the iteration steps. The iteration is stopped when the total annual cost (TAC) in the solution reaches 1.1·TAC_target.     

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。     

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.     

An area targeting algorithm for the synthesis of heat exchanger networks

A new algorithm for the prediction of area requirements in heat exchanger networks (HEN) is presented. The method uses a diverse pinch diagram as a basis, similar to the one suggested by Rev and Fonyo (Chemical Engineering Science, 46 (7), 1623). A numerical application for a problem involving streams with significant differences in their heat transfer coefficient values is included to show how the proposed algorithm provides better estimates for minimum area requirements in HEN than the widely-used Bath formula and the algorithm by Rev and Fonyo.     

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.     

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.     

Pressure drop considerations for heat exchanger network grassroots design

Pressure drop is an important issue in design of a heat exchanger network (HEN), which has yet to be addressed properly. To overcome pressure losses incurred when streams flow through heat exchangers, pumps/compressors must be installed. The total cost for a system of pumps and compressors consists of the purchase cost of equipment and the electricity cost to run these equipment. This cost could occupy a significant part of the overall cost for a HEN design. Therefore, the pressure drop aspect should be considered together with the costs for heat exchanger area and utility consumption. A new approach is proposed to consider the pressure drop aspect in the overall context of a HEN design. Firstly, the optimal ΔT_min is determined through three-way trade-offs between area, utility and pressure drop at the targeting stage. As a result of targeting, targets for area, utility and pressure drops can be established ahead of the network design. Then a network structure is initialised at the determined ΔT_min and optimised to achieve a final design. In this procedure, the pressure drop is considered at both the targeting stage and the design stage in a systematic manner.