Heat Integrated Water Allocation Networks Research Articles

A mathematical formulation for robust targeting in heat integrated water allocation network

Resource conservation strengthens a process industry's competitiveness and sustainability. Process integration (PI) strategies conserve resources. Heat-integrated water allocation networks (HIWANs) conserve energy and water. Process systems engineering optimizes synthesis, design, planning, scheduling, control, and supply chain. Recent developments promote robust optimization (RO) for uncertain optimization. RO optimizes for uncertain parameters to deal with data uncertainty. This research introduces a RO-based HIWAN resource-targeting model. Flow, concentration, and temperature uncertainties are modelled. The budget parameter reflects robustness. The budget restricts RO's conservatism and uncertainty, generating unduly cautious solutions. This model is explained with an example with different scenarios. Three of the scenarios have a single parameter uncertainty like source flow, source concentration, or inlet temperature, while one has multiple. Parameter behaviors are examined from nominal to worst-case scenarios. For scenario 1 where flowrate uncertainty is accounted, the robust flowrate target is 53.8% higher than the nominal value for the worst case. Similarly, for the second scenario where concentration uncertainty is accounted, robust flowrate target is 5.594% higher than nominal. In the last scenario with multiple uncertainties, the targeted flowrate increases by 59.44% compared to the nominal state. Nominal to worst-case scenarios can be handled by this model.

A targeting algorithm for segregated heat integrated water allocation network

The exchange of resources is a critical step toward long-term viability and market economic strength. The use of Process Integration (PI) techniques has resulted in significant savings in resources. Industrial processes rely heavily on water and heat as input variables. Simultaneous conservation of heat and water is regarded as heat-integrated water allocation networks (HIWANs) in the PI. HIWAN problems may be identified for multiple zones. This leads to the specific problem known as segregated targeting problems (STPs), which are prevalent in various industries. Segregated targeting is characterised by the existence of multiple zones and a set of internal sources. The objective of this research is to address the HIWAN problem within the framework of STP to minimize heat and water consumption. The model's applicability is demonstrated by two illustrative examples, in which around a 20 to 65% reduction in resource requirements is reported when compared with the non-zonal integrated model.

Simultaneous design of heat integrated water allocation networks considering all possible splitters and mixers

Heat integrated water allocation networks (HIWAN) can be recognized as a nexus between water and energy within the process industry. Water and energy are so tightly related in this kind of networks that water saving options may cause more energy consumption or vice versa. Various mathematical programming methods have been proposed to simultaneous optimize HIWAN. However, this problem is believed to be difficult to solve. Compared to the traditional HEN, the direct heat transfer of stream mixing is more flexible in this problem and the actual number of heat exchangers can be much smaller than the traditional HEN. This paper takes advantage of these two features to build up a novel superstructure to simultaneously design HIWAN. Stream splitters and mixers are considered for every water-using operations and heat exchange units, so that possibilities of stream mixing can be fully explored and there are more series and parallel modes between heat exchangers than that of stage-wise superstructure. The proposed model is solved under given different number of heat exchange units. A small to large iteration strategy is introduced to find the best solutions. Applying this proposed approach, the better results are obtained in large-scale problems compared with the previous papers.

Synthesis of Heat-Integrated Water Allocation Networks Through Pinch Analysis

Thermal energy (or utility consumption) and water can be optimized through the synthesis of heat-integrated water allocation networks (HIWANs). Various numerical optimizations, pinch-based and hybrid tools, have been proposed for HIWAN synthesis. Numerical optimization techniques make it difficult to visualize the problem due to complex formulations involving non-linear equations and/or integer variables. Pinch-based methods provide physical insights but are restricted to graphical techniques. As a result of this, HIWAN synthesis through pinch-based techniques gets tedious for medium-scale to large-scale data. HIWAN synthesis can be solved using a hybrid technique that combines the physical understanding of pinch analysis with a series of linear programming (LP) formulations. The proposed methodology converts the LP into an algebraic solution strategy and thereby making the HIWAN synthesis procedure entirely based on pinch analysis. Unlike the other pinch-based methods that rely on temperature-based heuristics to guide the water re-use streams, this method synthesizes HIWAN as an outcome of a utility minimization algorithm. This algorithm is an extension of the compression work minimization algorithm in hydrogen networks. The nature of these two problems differs due to the requirement of two entities (heating and cooling) in the former instead of one entity (compression work) in the latter. Besides freshwater minimization, this methodology can be applied for the conservation of other resources as well. Illustrative examples of three water allocation networks (one with regeneration) and an ammonia allocation network demonstrate the proposed methodology.

Optimal Design of Heat-Integrated Water Allocation Networks

Industrial operations consume energy and water in large quantities without accounting for potential economic and environmental burdens on future generations. Consumption of energy (mainly in the form of high pressure steam) and water (in the form of process water and cooling water) are essential to all processes and are strongly correlated, which requires development of systematic methodologies to address their interconnectivity. To this end, the subject of heat-integrated water allocation network design has received considerable attention within the research community in recent decades while further growth is expected due to imposed national and global regulations within the context of sustainable development. The overall mathematical model of these networks has a mixed-integer nonlinear programming formulation. As discussed in this work, proposed models in the literature have two main difficulties dealing with heat–water specificities, which result in complex formulations. These difficulties are addressed in this work through proposition of a novel nonlinear hyperstructure and a sequential solution strategy. The solution strategy is to solve three sub-problems sequentially and iteratively generate a set of potential solutions through the implementation of integer cut constraints. The novel mathematical approach also lends itself to an additional innovation for proposing multiple solutions balancing various performance indicators. This is exemplified with both a literature test case and an industrial-scale problem. The proposed solutions address a variety of performance indicators which guides decision-makers toward selecting the most appropriate configuration(s) among a large number of potential possibilities. Results exhibit that despite having a sequential solution strategy, better performance can be reached compared to previous approaches with the additional benefit of providing many potential solutions for further consideration by decision-makers to select the best case-specific solution.

New Insights into T–H/H–F Diagrams for Synthesis of Heat Exchanger Networks inside Heat Integrated Water Allocation Networks

Energy and resources saving is of significance to sustainable development. In the past decades, heat integrated water allocation networks (HIWANs) have been applied to generate effective strategies for water and energy management in chemical process industries, where large amounts of water and energy are consumed. In this paper, a graphical approach for the synthesis of heat exchanger networks (HENs) in HIWANs has been proposed to reveal the new insights into T–H/H–F diagrams and fully exploit the HEN structure possibilities. Current conceptual design methods for HENs in HIWANs by the original separate systems (T–H diagram) and the matching composite curve (H–F diagram) only generate two special kinds of HEN structures: series and parallel structures. A transformation method is proposed to generate HENs with different structures based on these two tools. Both simplex series or parallel structures and hybrid structures can be obtained via the transformation procedures. Two examples are illustrated to demon...

Synthesis of Heat-Integrated Water Allocation Networks: A Meta-Analysis of Solution Strategies and Network Features

Industries consume large quantities of energy and water in their processes which are often considered to be peripheral to the process operation. Energy is used to heat or cool water for process use; additionally, water is frequently used in production support or utility networks as steam or cooling water. This enunciates the interconnectedness of water and energy and illustrates the necessity of their simultaneous treatment to improve energy and resource efficiency in industrial processes. Since the seminal work of Savulescu and Smith in 1998 introducing a graphical approach, many authors have contributed to this field by proposing graphically- or optimization-based methodologies. The latter encourages development of mathematical superstructures encompassing all possible interconnections. While a large body of research has focused on improving the superstructure development, solution strategies to tackle such optimization problems have also received significant attention. The goal of the current article is to study the proposed methodologies with special focus on mathematical approaches, their key features and solution strategies. Following the convention of Jeżowski, solution strategies are categorized into: decomposition, sequential, simultaneous, meta-heuristics and a more novel strategy of relaxation/transformation. A detailed, feature-based review of all the main contributions has also been provided in two tables. Several gaps have been highlighted as future research directions.

Heat Transfer Blocks Diagram: A Novel Tool for Targeting and Design of Heat Exchanger Networks Inside Heat Integrated Water Allocation Networks

Sustainability is essential for process industries, as energy and resources are getting scarcer and scarcer. For the past decade, heat integrated water allocation networks (HIWANs) have drawn more and more attention, owing to the efficient utilization of water and energy. In this article, a systematic procedure for the synthesis of heat exchanger networks (HENs) in HIWANs has been proposed. A graphical tool, named heat transfer blocks diagram, is developed to improve the conceptual understanding for the implications of HEN structures in HIWANs. The minimum hot/cold utility consumption can be obtained by analyzing heat surpluses and heat deficits between cold stream and hot stream heat transfer blocks, while heat transfer matching blocks are introduced to deal with the heat exchange matches. Not only simplex series or parallel structures but also hybrid structures can be obtained via this graphical tool. Besides, a heuristic of step by step maximizing the heat load of heat exchangers is presented to guide ...

Targeting of heat integrated water allocation networks by one-step MILP formulation

Heat integrated water allocation networks (HIWAN) is a system where water and energy are highly interconnected. Well arranged nexus between water allocation networks and heat exchanger networks would reduce the water and energy consumption significantly. The aim of this study is to develop a novel mathematical programming model for targeting minimum simplified total annual cost of HIWAN. A new transshipment type of heat exchanger networks (HEN) representation is proposed, with features of stream splitting, stream by-pass, non-isothermal mixing, and isothermal mixing. Constraints are added to follow up on the flowrate consistency when stream splitting or mixing happens. Furthermore, a new formulation is presented to count heat exchanger units. The proposed model is formulated as a mixed-integer linear programming (MILP) problem. It is much easier to get feasible solutions than mixed-integer non-linear programming (MINLP) problems, especially for large-scale problems. Three examples including an industrial example and a large-scale case are solved by the proposed model. It is shown that the proposed model is suitable for the synthesis of HIWAN, and more importantly, the obtained results are better than literature records.

Simultaneous optimization of heat-integrated water allocation networks

This paper presented a novel mathematical programming model for the simultaneous optimization of heat integrated water allocation networks featuring parallel heat exchanger network (HEN) structure. In the HEN structure, both freshwater and wastewater can be split freely. This model was suitable for both uniform wastewater treatment and separate wastewater treatment cases. The proposed model was formulated as a MINLP (mixed-integer non-linear programming) problem, making it applicable to large scale problems. The main objective was to minimize the total annual cost. Three literature examples, including a large scale example, were illustrated to demonstrate the applicability of the model. It was shown that the proposed method was as accurate as the literature methods for small scale problems, but performed better for large scale problem applications.

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

Simultaneous Optimization of Heat-Integrated Water Allocation Networks Using the Mathematical Model with Equilibrium Constraints Strategy

A general optimization model is proposed for the simultaneous optimization of integrated water allocation and heat exchanger networks (WAHEN). An improved superstructure and mathematical model for the WAHEN problem is presented. Complementary formulations are applied to model the discrete decisions, and a mathematical model with equilibrium constraints (MPEC) is formulated. Both the MINLP model and the MPEC model are developed and solved for the problem. The effectiveness of the proposed model is illustrated with two case studies. A comparison between the results obtained by the proposed model and those obtained from the model in the literature is carried out. Case studies show that the proposed simultaneous methodology performs well and is efficient.

Simultaneous optimization of water and heat exchange networks

This paper focuses on the simultaneous optimization of the heat-integrated water allocation networks. A mathematic model is established to illustrate the modified state-space representation of this problem. An easy logical method is employed to help identify the streams of hot or cold ones. In this model, the water exchange networks (WEN), heat exchange networks (HEN), and the interactions between the WEN and HEN combine together as one unity. Thus, the whole network can be solved at one time, which enhances the possibility to get a global optimal result. Examples from the literature and a PVC plant are analyzed to illustrate the accuracy and applicability of this method.

Energy optimization in heat integrated water allocation networks

In this paper, linear programming formulations, complemented by concept based pinch analysis results, are developed to target the minimum energy requirements in a heat integrated fixed flow rate water allocation networks. These formulations can be applied for the cases of heat integration through isothermal and non-isothermal mixing in water allocation networks involving single as well as multiple contaminants. The earlier reported approaches are based on linear programming formulation for the case of isothermal mixing and either mixed integer non-linear programming or discontinuous non-linear programming formulations for the case of non-isothermal mixing. It has been observed that the earlier reported methodologies produce sub-optimal results for the case of non-isothermal mixing. However, the proposed methodologies produce the optimum results because of the rigorously proved linear formulation. Utility requirements for isothermal as well as for non-isothermal mixing cases are compared over a range of minimum approach temperatures, to evaluate the energy performance using illustrative examples.

Systematic Optimization of Heat-Integrated Water Allocation Networks

This paper deals with the design of heat integrated water utilization networks. The nonisothermal mixing and freely splitting nature of hot and cold streams have made the problem far more complicated than the design of heat exchanger networks (HEN). By establishing an MILP model, promising heat exchange matches between hot and cold streams are obtained first without considering the detailed network design. Subsequently, a stage-wise HEN superstructure is introduced for the detailed network design. The proposed systematic approach can be applied for large scale problems. Examples from literature and a practical example in a PVC plant are used to illustrate the applicability of the approach.

Modified Problem Table Algorithm for Energy Targeting

A simple modification of the original problem table algorithm (PTA) to target the minimum utility requirements in a heat exchanger network is proposed in this paper. The modified problem table algorithm (MPTA) eliminates the requirement of identification of streams to determine the net heat capacity flow rate at each temperature interval. Targeted utility requirements and the grand composite curve for the heat exchanger network problem are identical for both the original PTA and the proposed MPTA. This simple but fundamental change in the proposed MPTA, enhances its applicability to target the minimum external utility requirements in some special cases of heat-integrated water allocation networks. Pedagogical importance of the proposed MPTA is also discussed.