Studies on simultaneous energy and water minimisation—Part I: Systems with no water re-use

This paper addresses the simultaneous management of energy and water. A new systematic methodology has been developed for targeting and design that simultaneously minimises the requirements of energy and water. Using this new approach, the design of a water system for maximum energy recovery can be achieved, taking into account the mixing opportunities offered by water networks, while maintaining the water quality to processes in terms of contamination. Direct and indirect energy recovery are analysed and a strategy developed to decrease the number of heat transfer units based on the generation of separate systems and non-isothermal stream mixing. Initially, the analysis is restricted to no water re-use.     

Studies on simultaneous energy and water minimisation—Part II: Systems with maximum re-use of water

A new systematic design methodology has been developed for the simultaneous management of energy and water systems that also feature maximum re-use of water. A two-dimensional grid diagram is proposed to exploit different options within water systems and also enable reduced complexity of the energy and water network. Isothermal and non-isothermal stream mixing between water streams are introduced to create separate systems between hot and cold water streams in the energy composite curves and provide a design basis for a better structure with fewer units for the heat exchanger network. In addition to allowing re-use of water, issues about heat losses inside unit operations have also been incorporated in the simultaneous management of water and energy.     

综合考虑经济性与效率的换热网络多目标约束优化方法

换热网络优化中不仅要考虑能量回收的“量”,还要考虑能量回收过程中“质”的耗散问题。在换热网络最大能量回收的前提下,基于不可逆传热过程中的耗散理论,以代表能量回收品质的效率最高为目标,建立综合能量回收数量、品质并同时考虑换热网络经济性的多目标混合整数非线性规划（MOMINLP）模型。根据模型目标有主次之分的特点,基于ε约束法对模型进行分步优化并结合BARON软件进行精确求解,依次求解换热网络的最大能量回收量(MER)与最低年均总成本(TAC),再将所得结果乘以松弛系数ε_i作为缩小搜索区域的约束条件,获得能量与成本约束下效率的Pareto前沿。通过对经典10SP1案例进行计算求解,最终得到最大能量回收量下,费用松弛系数为1.05时费效比最小的优化方案,而且本文的多目标约束优化方法能够更快求得综合的最优解。最后通过T-Q图中的换热网络组合曲线对比不同优化方案的效率,将换热网络划分为内部换热部分与剩余流股部分,多目标约束优化方法能够降低内部换热不可逆损失,提高剩余流股的温度。     

Surplus diagram and cascade analysis technique for targeting property-based material reuse network

Recycle of process and waste streams are among the most effective resource conservation and waste reduction strategies. In many cases, recycle/reuse is dictated by sink constraints on properties of the recycled streams. In this work, we introduce an algebraic technique to establish rigorous targets on the minimum usage of fresh resources, maximum direct reuse, and minimum waste discharge for property-based material reuse network. Two new tools have been developed. A new graphical tool called the property surplus diagram is firstly introduced to provide a basic framework for determining rigorous targets for minimum fresh usage, maximum recycle, and minimum waste discharge. The tools also determine the property-based material recycle pinch location. The Property Cascade Analysis (PCA) technique is next established to set targets via a tabular approach. PCA eliminates the iterative steps typically associated with a graphical approach. Along with the minimum fresh and waste targets, the material allocation target is another key feature of the PCA. A network design technique is also presented in this paper to synthesise a maximum resource recovery (MRR) network that achieves the various established targets. The procedures developed in this paper constitute a generalisation to the composition-based graphical and algebraic techniques developed for water and hydrogen recovery networks. Two case studies are solved to illustrate the applicability of the developed procedures.     

Energy conservation in water allocation networks with negligible contaminant effects

A methodology to target the minimum energy requirement in water allocation networks where impurity concentrations do not play any significant role is proposed in this paper. The proposed methodology is mathematically rigorous and targets the minimum utility requirement satisfying the minimum approach temperature prior to the detailed design of both the water allocation network as well as the heat exchanger network. The proposed algorithm is presented through a tableau-based calculation procedure. A water allocation network design algorithm is proposed that guarantees the minimum energy targets obtained through the proposed energy recovery algorithm. The proposed methodology is also applied to inter-process heat integration between various water allocation networks.     

SePTA—A new numerical tool for simultaneous targeting and design of heat exchanger networks

Pinch Analysis is an established insight-based methodology for design of energy-efficient processes. The Composite Curves (CCs) is a popular Pinch Analysis tool to target the minimum energy requirements. An alternative to the CCs is a numerical technique known as the Problem Table Algorithm (PTA). The PTA however, does not show individual hot and cold streams heat cascades and cannot be used for design of heat exchanger networks (HEN). This paper introduces the Segregated Problem Table Algorithm (SePTA) as a new numerical tool for simultaneous targeting and design of a HEN. SePTA shows profiles of heat cascade across temperature intervals for individual hot and cold streams, and can be used to simultaneously locate pinch points, calculate utility targets and perform SePTA Heat Allocation (SHA). The SHA can be represented on a new SePTA Network Diagram (SND) that graphically shows a heat exchanger network together with the amount of heat exchange on a temperature interval scale. This paper also shows that SePTA and SND can be a vital combination of numerical and graphical visualisation tools for targeting and design of complex HENs involving stream splitting, threshold problems and multiple pinches.     

基于杂质赤字的再生回用水网络集成图示法

将氢网络中基于剩余率的集成优化法扩展至水网络，以杂质浓度为基础进行分析，提出了基于杂质赤字的再生回用水网络图像集成优化方法。该方法无需图像试差和迭代，通过构建浓度-流量图和杂质赤字图，可确定未考虑再生回用的水网络夹点位置及最小新鲜水用量。并在此基础上，考虑再生装置和水网络的优化以及二者的集成，分析水网络的新鲜水节省量与杂质脱除率、再生水源流量及再生废水浓度的定量关系；构建定量关系图确定最小新鲜水用量随各参数的变化关系、夹点位置、最大新鲜水节省量以及一定再生条件下的极限及最优提纯参数。案例分析表明，该方法简单、高效，对于各工况下的水网络，均可使新鲜水消耗量及废水排放量减小，为工艺设计和操作提供重要的参考。     

Automated targeting for inter-plant water integration

Apart from in-plant water recovery, inter-plant water integration (IPWI) offers another promising mean for the reduction of fresh water and wastewater flowrates for process plants. This paper extends the automated targeting technique that was developed for single water network into IPWI. This optimisation-based technique is based on the concept of pinch analysis, which enables the setting of various network targets prior to detailed design. The automated targeting technique is formulated as a linear programming model for which global optimum is guaranteed. The proposed technique is demonstrated using several industrial and literature examples.     

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.     

考虑间接换热额外换热温差的间歇过程储热集成

间歇过程流股间换热有直接换热和间接换热两种方式,通过储热介质进行间接换热会产生额外的换热温差。现有的夹点分析方法考虑间接换热额外换热温差后,难以得到经济且可行的储热集成方案。本文在夹点分析的基础上,提出了一种考虑间接换热额外换热温差的间歇过程储热集成方法。该方法首先使用不同的直接换热和间接换热温差进行热级联分析,确定储热集成后的最小冷、热公用工程用量,识别储热位置和储热量,并依据热级联分析结果,建立时间段温焓图确定储热介质温度,得到储热方案。然后,将储热流股转化为放热时间段的冷流股和需热时间段的热流股,进行换热网络综合与优化,得到符合实际应用的储热集成方案。最后,通过经典实例证明了所提方法的可行性和有效性。     

数学规划与图形方法相结合设计热集成用水网络

将数学规划法与图形方法相结合探究单杂质用水网络与换热网络的集成问题。首先构建混合整数非线性规划模型（MINLP）,在最小公用工程消耗下优化流股参数未知情况下的分离系统组合曲线面积,得到了最为节能、换热面积最小的用水网络结构。在此基础上,提出了新的分离系统组合曲线演化步骤和规则,可以得到换热单元数目较小的换热网络结构。算例表明,与现有的基于分离系统的热集成用水网络设计方法相比,在最小化公用工程用量的同时可以进一步降低换热器数目与总换热面积。     

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.     

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。     

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.     

Synthesis of mass exchange network for batch processes—Part II: Minimum units target and batch network design

The first part of this series of papers (Chem. Eng. Sci. 59(5) (2004) 1009) presented a methodology for identifying the minimum utility targets for a mass exchange network (MEN) for a batch process. This paper describes the methodology for setting the minimum number of mass exchange units target and a procedure for designing a maximum mass recovery network that features the minimum utility targets. The time-grid diagram and the overall time-grid diagram that include the time dimension in network design have been introduced to provide a better representation of the mass exchange network for a batch process. The systematic network design procedure also includes a technique to simplify and evolve the preliminary batch MEN to reduce the number of mass exchangers to the minimum.     

Simultaneous integration of water and energy in heat‐integrated water allocation networks

This article proposes a new methodology for simultaneous integration of water and energy in heat‐integrated water allocation networks (WAHEN). A novel disjunctive model is first developed to determine an optimal water allocation network (WAN) where water and energy are integrated in one step. Based on the optimal WAN, a detailed heat exchanger network (HEN) to satisfy the utility target is then synthesized. Although the final network structure is obtained through two steps, the targets of freshwater and utility are optimized simultaneously. The proposed method has specific advantages. First of all, it can capture a tradeoff among freshwater usage, utility consumption, and direct heat transfer by nonisothermal mixing. Second, it can greatly reduce the complexity of subsequent HEN design. Finally, it is effective for simultaneous water and energy integration in large‐scale WAHEN systems. The advantages and applicability of this new method are illustrated by three examples from literature. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2202–2214, 2015     

Novel graphical tool for the design of the heat integrated water allocation networks

A new graphical tool has been developed for the HEN design of WAHEN. An ΔH‐F diagram is proposed to deal with the heat exchange matches. Nonisothermal stream mixing and splitting can be achieved by the transformation of stream composite curve in the ΔH‐F diagram. A matching composite curve is proposed for the design of HEN with parallel structure. The structure of HEN can be simplified by adjusting the shape of the matching composite curve. Both small scale and large scale examples are illustrated. Results show that the proposed method is as good as the previous methods for small scale problem, while it gets a better result for large scale problem. © 2015 American Institute of Chemical Engineers AIChE J, 62: 670–686, 2016     

利用余热回收多能互补技术的原油蒸馏装置热集成系统的优化改造

针对换热网络（HEN）的优化改造,提出了一种利用公用热量实现多能互补理念的改造思路,通过充分利用热过程物流中的低温余热,完成热集成系统的优化改造。本文基于参考点非支配排序遗传算法（NSGA-Ⅲ）,通过综合评估集成废热回收（WHR）系统的换热网络的年度改造费用、年度改造收益、能耗（包含换热网络的冷/热公用工程和废热系统冷却水和电力消耗）和废热系统的有益产出,从而获得最优解决方案。对原油蒸馏系统（10H5C）的优化改造研究案例表明,通过权衡集成系统的能源消耗、WHR系统的产出、改造费用和改造收益4个目标,采用NSGA-Ⅲ算法求解获得了多维度的改造方案,相较于基础网络不仅有可以为用户最大节省22.9%能源消耗的改造方案,还有WHR系统最大输出为4.003×10⁴kW的解决方案,也有最小改造费用为1.848×10⁶USD/a的改造方案,还有最大改造收益和最大投资回报率分别为1.173×10⁷USD/a和121%的解决方案;最后通过比较集成WHR系统与单独HEN优化改造的性能,证明了集成WHR系统的实用性和可行性,以及余热回收多能互补技术对提高流程工业能量集成系统能量利用效率的重要作用。     

A graphical technique for the design of water-using networks in batch processes

This paper presents a graphical technique for the design of water-using networks in batch plants. Water integration is achieved by exploiting all possibilities of water reuse/recycle to minimize not only freshwater consumption, but also wastewater generation. Since time limitation for unmatched operating periods may be the primary barrier to the integration in batch processes, the installation of storage facilities is quite common to enhance the water recovery. For that reason, the cost in terms of storage facilities becomes another issue to be considered. This work is focused on network design, like the second stage of conventional pinch analyses. Some useful concepts and principles addressed in literatures are adopted to help the design of batch water network and to ensure the maximum recovery, thus the utility usage, the network structure and the storage policy can be obtained through the analysis. Once the freshwater expenditure is determined, workable ways are sought to cut the number of storage tanks and they also reduce the network complexity. In the context of this paper, a hybrid system that includes different type of water-using operations with distinct operating modes is taken into account to display the versatility of proposed approach. Furthermore, considering the fact that sometimes water reuse/recycle between certain operations is not allowed to prevent operational problems, the action of network design should be more deliberate owing to additional restraints. Therefore, the potential for water integration may be diminished, which means a less amount of water recovery. Finally, an illustrative example is provided to amplify the application of proposed approach. Like most graphical techniques, the presented work is restricted to a single key contaminant.     

维生素低温蒸发结晶单元的自回热设计及分析

针对传统维生素生产过程中的蒸发结晶单元耗能高、排放量大的特点,提出了一种基于自回热原理(self-heat recuperation technology, SHRT)的改进设计.利用能量分析和(火用)分析的方法对系统进行分析.并研究了最小传热温差的特性,以及压缩机的绝热效率和闪蒸进口过热度对系统能耗的影响.结果表明,利用自回热思想改进的蒸发结晶单元比传统过程所需的输入能减少了73.0%,输入(火用)减少了68.3%.在文中的条件下,潜热比显热有更大的利用空间,利用的潜热占总循环热量的93.5%.同时,最小传热温差的增大虽然会使需要的换热器的面积减小,但也会导致更大的能量输入.系统的能耗随着过热度的增大而增大,随着绝热效率的增大而减小.