On the use of graphical method to determine the targets of single-contaminant regeneration recycling water systems

Water system integration with regeneration recycling can reduce freshwater consumption and wastewater discharge to the maximum extent. In this paper, by analyzing the limiting composite curve of a single-contaminant water system, a method is proposed to construct the optimal water supply line for regeneration recycling. Accordingly the targets for regeneration recycling water systems are obtained. The targets in sequence are the minimum freshwater consumption (the minimum wastewater discharge), the minimum regenerated water flowrate, and the optimal regeneration concentration. The post-regeneration concentration is taken to be fixed in the sequential targeting procedure. The interactions of these targets are analyzed, and formulas for calculating these targets are proposed. The results show that for a single-contaminant regeneration recycling water system, the minimum freshwater consumption is determined by the shape of the limiting composite curve below the post-regeneration concentration. The optimal regeneration concentration is defined as the minimum regeneration concentration at the minimum freshwater consumption and the corresponding minimum regenerated water flowrate. The minimum regenerated water flowrate and the optimal regeneration concentration are both related to the geometrical features of the limiting composite curve of the water-using system and to the post-regeneration concentration. The optimal regeneration concentration has no direct relationship with the pinch concentration.     

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。     

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.     

A stepwise optimal design of water network☆

In order to take full advantage of regeneration process to reduce fresh water consumption and avoid the accumu-lation of trace contaminants, regeneration reuse and regeneration recycle should be distinctive. A stepwise opti-mal design for water network is developed to simplify solution procedures for the formulated MINLP problem. In this paper, a feasible water reuse network framework is generated. Some heuristic rules from water reuse net-work are used to guide the placement of regeneration process. Then the outlet stream of regeneration process is considered as new water source. Regeneration reuse network structure is obtained through an iterative optimal procedure by taking the insights from reuse water network structure. Furthermore, regeneration recycle is only utilized to eliminate fresh water usage for processes in which regeneration reuse is impossible. Compared with the results obtained by relevant researches for the same example, the present method not only provides an appro-priate regeneration reuse water network with minimum fresh water and regenerated water flow rate but also sug-gests a water network involving regeneration recycle with minimum recycle water flow rate. The design can utilize reuse, regeneration reuse and regeneration recycle step by step with minor water network structure change to achieve better flexibility. It can satisfy different demands for new plants and modernization of existing plants. ? 2016 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. Al rights reserved.     

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.     

应用夹点技术确定再生水用量

工业节水及废水减排已成为过程工业持续发展的前提之一。运用目标导向的夹点分析技术对过程用水网络系统进行系统地分析,可确定过程用水、再生水用量和废水排放量的最小目标。以固定再生出口浓度为基准,提出基于累积流量-累积污染质量负荷组合曲线图的夹点分析方法来确定用水网络的最小再生水流量,并给出了详细计算步骤和案例验证。     

Progress of water network integration with multiple contaminants

介绍了近年来多杂质水网络集成研究进展,讨论了当前设计多杂质水网络的几种方法,包括水夹点及图解方法、数学规划法、中间水道技术及基于经验的设计方法。探讨了各种方法的特点以及各方法涉及废水的直接回用、再生回用和再生循环。最后对今后的发展方向做了展望。     

Process‐based graphical approach for simultaneous targeting and design of water network

A new process‐based graphical approach (PGA) is presented for the simultaneous targeting and design of water network. The PGA is extended from the limiting water profile which was developed for flow rate targeting for a water network. Via PGA procedure, apart from locating the minimum freshwater and wastewater flow rate targets, the water network that corresponds to the minimum flow rate targets is also synthesized simultaneously. The proposed approach handles both fixed load (including operations with water loss and/or gain) and fixed flow rate problems equally well. In addition, the approach can be used to synthesize direct reuse/recycle, regeneration reuse/recycling, and total water network. Furthermore, the proposed approach is applicable for water network with multiple freshwater sources. Three literature examples are presented to illustrate the proposed approach. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

再生循环水系统引入再生过程后夹点位置

引入再生循环的最优水系统可以最大限度地节约新鲜水的用量和减少废水的排放,是当前节水技术研究的重点。用水系统引入再生过程后,极限供水线会发生变化,从而水系统夹点个数以及位置都可能会发生变化。运用前人总结出的再生循环过程最佳供水线的构造方法,分析影响引入再生过程后夹点位置变化的因素,发现引入再生过程前后夹点位置的变化情况与以下因素有关：极限复合曲线上的凹点位置以及凹向极限供水线的程度和最高浓度用水单元水流率与新鲜水流率的关系,并分析得出夹点位置的变化规律,从而为用水网络的分析和设计提供理论性的指导。     

Optimisation of petroleum refinery water network systems retrofit incorporating reuse,regeneration and recycle strategies

Scarcities in freshwater supply and increasingly stringent rules on wastewater discharges have emerged as major environmental concerns for petroleum refineries. Hence, this work attempts to develop an optimisation framework for refinery water network systems design and retrofit that integrates the complementary advantageous features of water pinch analysis (WPA). The framework explicitly incorporates water minimisation strategies by first postulating a superstructure representation that embeds all feasible flowsheet alternatives for implementing water reuse, regeneration and recycle (W3R) opportunities. Subsequently, a nonlinear programming (NLP) model is formulated based on the superstructure and computational experiments on a real‐world case study are conducted using the GAMS/CONOPT3 modelling language platform. Post‐optimality analysis on the numerical results are performed to achieve the desired water reuse quality, hence presenting a viable framework to aid decision‐making in water network systems synthesis. © 2011 Canadian Society for Chemical Engineering     

多杂质水网络设计和零排放

The paper presents a procedure to design water network. First of all, water reuse system, water regeneration reuse system (including regeneration recycle) and wastewater treatment system are designed separately.But the interaction between different parts demands that each part is designed iteratively to optimize the whole water network. Therefore, on the basis of the separated design a water network superstructure including reuse,regeneration and wastewater treatment is established from the system engineering point of view. And a multiobjective adaptive simulated annealing genetic algorithm is adopted to simultaneously integrate the overall water network to balance the economic and environmental effects. The algorithm overcomes the defect of local optimum of simulated annealing (SA), avoids the pre-maturation of genetic algorithm (GA) and finds a set of solutions (pareto front) in acceptable computer time. From the pareto front, a point with minimum fresh water consumption will be extended to zero discharge as our ultimate goal.     

Application of water system optimization in a titanium pigment plant ——Mathematical programming

钛白粉行业是化工行业中的耗水大户,具有较大的节水潜力。本文在对某钛白粉厂水系统现状进行调研的基础上,采用数学规划法,分别从废水直接回用和再生循环两方面对其水系统进行优化设计,结果表明,改造后的两种水系统均比改造前节约新鲜水用量40.0%,并且废水直接回用更加适合钛白粉行业开展节水工作。     

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.     

Targeting and design of water networks for fixed flowrate and fixed contaminant load operations

Water-using processes are typically modeled as either fixed flowrate operations or fixed contaminant load operations. A new method for targeting the minimum freshwater and pinch in a single-contaminant water network is proposed, which can be applied to both kinds of operations. The method consists of plotting separate source and demand composites with flowrate as the horizontal axis and contaminant load unusually as the vertical axis. It is elegant, non-iterative, and can handle hybrid problems where both kinds of operations coexist.To design minimum freshwater networks for fixed flowrate problems, an algorithm is presented based on a newly developed principle of nearest neighbors. The principle simply states that the source streams to be chosen to satisfy a particular water demand must be the nearest available neighbors in terms of contaminant concentration.To design minimum freshwater networks for fixed contaminant load problems, the nearest neighbors algorithm is applied to process units that lie across the pinch. Units that lie entirely on one side of the pinch are satisfied by the cleanest source available on that side of the pinch. In other words, below-pinch units are satisfied by freshwater and above-pinch units are satisfied by the cleanest available stream above the pinch. Designs based on this methodology, apart from meeting the minimum freshwater target, also minimize the water flowing through the process units resulting in reduced network capital cost.     

水夹点分析与数学规划法相结合的用水网络优化设计

提出了水夹点分析和数学规划法相结合的用水网络最优设计法。水夹点分析基于对过程用水的理解,获得新鲜水用量目标并给出用水网络设计的基本规则。在此基础上建立过程使用新鲜水、排放废水和回用的各种可能匹配方案的用水网络超结构及其MINLP模型。既避免了用水夹点综合设计用水网络得不到真正意义上的最优解,又在一定程度上防止超结构规模过大,MINLP维数太高,求解困难。采用通用代数建模系统GAMS得到用水网络最优设计方案。文献中的应用实例表明,本文所提方法可充分发挥水夹点分析确定新鲜水用量或回用结构的简洁实用性和超结构MINLP寻求最佳方案的优点。     

Unified targeting algorithm for diverse process integration problems of resource conservation networks

A single algorithm is developed to establish minimum resource targets for diverse process integration problems including those of heat/mass exchange, water, hydrogen, carbon emission and material reuse networks. Previous algorithms such as the problem table algorithm for heat exchange networks and the composite table algorithm for resource allocation networks are special cases of the newly proposed unified targeting algorithm (UTA). The conversion of streams to equivalent inlet-outlet (demand-source) pairs is shown to be a key basis for the unified approach. The tabular data from the UTA may be plotted to obtain the grand composite curve (GCC) or the limiting composite curve (LCC). These provide graphical representations of the net load deficit/surplus at various levels for resource targeting and pinch identification. For allocation networks with system loss/gain, the UTA with increasing level sort order yields the Deficit LCC to target the minimum resource, whereas the UTA with decreasing level sort order provides the Surplus LCC to target the minimum waste/excess. A single UTA calculation along with the use of fundamental overall system balance equations is sufficient to establish complete targets for a problem. Six practical case studies from diverse domains are presented to illustrate the detailed steps of the UTA.     

采用迭代方法设计具有再生再利用/循环的单杂质用水系统

具有再生再利用/循环利用的水网络与只有再利用的水网络不同之处在于前者增加了再生水流。如能确定再生水流的浓度和流量并将之加到只考虑再利用的水网络中,即可构成具有再生再利用/循环利用的水网络。在上述思想基础上提出一种迭代法设计具有再生再利用/循环利用的水网络。该方法既可以解决给定移除率（removal ratio,RR）问题,又可以解决固定再生浓度问题。对RR问题,根据水网络及再生过程的特点估算出初始再生水流浓度,再生水流的量待定。将所得再生水流加到只考虑再利用的网络中构成具有再生过程的水网络。设计上述水网络,可以得出新的再生水流的量及浓度。当相邻两次再生浓度之差小于给定值时迭代结束。对RR问题,通常只需几次迭代即可得出最终设计;对于固定再生浓度问题,只需一次迭代即可得出最终设计。设计中考虑了影响水网络设计总费用的新鲜水用量、再生水用量和杂质再生负荷3个主要参数。对文献中几个实例的研究表明,本文方法得到的设计与文献中的设计相当,而设计步骤比文献中的简单。     

A hierarchical approach for the synthesis of batch water network

This work addresses the problem of synthesising cost-effective batch water networks where a number of process sources along with fresh water are mixed, stored, and assigned to process sinks. In order to address the complexity of the problem, a three-stage hierarchical approach is proposed. In the first stage, global targets are identified by formulating and solving a linear transportation problem for minimum water usage, maximum water recycle, and minimum wastewater discharge. These targets are determined a priori and without commitment to the network configuration. Next, a network with minimum number of tanks is synthesised by solving a mixed-integer non-linear program. The bilinear constraints are relaxed to transform the program into a mixed-integer linear program that is globally solvable. The third stage is aimed at simplifying the network configuration by minimising the number of network inter-connections. Insights gained from the water pinch analysis are also incorporated into the approach to further reduce the water flows via the placement of water regeneration unit. A case study is solved to illustrate the effectiveness of the proposed procedure.     

含再生再利用的用水网络的优化设计

对单组分含再生再利用的用水系统,提出了一种基于序贯操作模型的整体优化设计方法。该方法分别针对单组分含再生再利用的用水网络设计可能存在的三种情况,以新鲜水和再生水用量最小为目标,给出了相应的设计策略,数学的表达是一个非线性规划。首先依据规则将操作对贫流的要求进行分段排序,并通过引入操作的质量交换分配系数αi,将各操作依据规则虚拟地分配为再生前过程和再生后过程,然后按操作序列逐级进行操作和操作水源之间的的优化匹配,建立含再生再利用的用水网络的序贯操作模型,最后将此综合问题归结为非线性规划问题来求解,从而完成用水过程的设计。给出了一个实例,计算结果表明本文方法是有效和简便易行的。     

石化行业水资源优化利用网络分析

运用水夹点技术,对某石化企业进行用水网络优化研究.在流量恒定和流量改变两种条件下,对某石化企业9个用水操作原有用水网络进行初始设计和优化改进.结果表明,在流量恒定和流量改变条件下,通过用水网络初始设计节约新鲜水用量分别为19.17%和22.87%,对用水网络的初始设计和优化可简化用水网络,回用管路数分别由11条减少为6条和5条,优化后的用水网络分别节约新鲜水用量18.79%和22.47%.水夹点技术在工业用水节约和废水减量方面具有实用价值和较好的应用前景.