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This paper presents a general mathematical optimization model and the related deterministic algorithm for synthesizing heat-exchanger networks (HEN). The methodologies commonly used to solve a HEN problem are based on heuristic methods. These algorithms reach a presumed best solution with respect to the investigated set of process streams, whereas our approach determines the optimal configuration. In this paper the proposed method is applied to the solution of a few simple HEN synthesis problems and the results are compared with those obtained utilizing heuristic or meta-heuristic methods. HEN''s problem is represented by a general mathematical model that can be applied to small and medium sized problems and is solved by using a deterministic method with a reasonably brief computation time. Notably, this approach can represent a unique general model of a wide class of heat-exchanger networks, independently of their specific physical configuration. [Copyright &y& Elsevier]

This paper presents a new step-wise sequential solution strategy for the synthesis of heat integrated water networks (HIWNs) comprising of two mathematical models. The first model minimizes water and energy costs. The optimal freshwater and water flow rates within the HIWN are determined from this model. Using these optimal flow rates, different configurations of HIWN are evaluated for the purpose of heat integration. The second model is the stage-wise heat exchanger network (Yee and Grossmann, 1990), which is solved for each of the evaluated network configuration in a sequential manner. Using this proposed strategy, a set of locally optimal HIWNs are produced and the best one is chosen based on the minimum total annual cost (TAC). The proposed sequential strategy is applied to small and medium sized examples in the literature. The results show that the proposed new sequential solution strategy can be successfully applied to small and medium sized HIWN problems. [ABSTRACT FROM AUTHOR]

Abstract: Heat transfer intensification is an effective technique for improving energy recovery in heat exchanger networks (HEN) by enhancing heat transfer without any network topology modifications. In this paper, a novel optimization method has been developed for the synthesis of intensified heat exchanger networks with a simple mixed integer linear programming (MILP) model under retrofit scenario, and a robust solution strategy based on two iteration loops has been proposed. The new method has distinctive advantages over existing design methods, as the new MILP model can effectively and significantly reduce computational difficulties associated with nonlinear formulation in existing HEN retrofit formulations. Three cases have been tested to demonstrate the validity and efficiency of the proposed approach, which requires very short computational times to obtain optimal solutions when energy saving or profit is to be maximised through retrofit. [Copyright &y& Elsevier]

Abstract: A new simplified scalable mathematical model, based on concepts of stream analysis, temperature paths and internal heat exchange, has been developed for synthesis of a multiple effect evaporator systems. In this model, fresh feed is assumed to be composed of product and number of condensate streams, which come out from different effects and these are treated as separate streams. For the present work a septuple effect flat falling film evaporator system, used for concentrating black liquor in an Indian Kraft Pulp and Paper mill, has been considered. This system is being operated under backward sequence with condensate-, feed- and product-flashing as well as steam splitting in first two effects. The set of linear algebraic equations for this model are self-generated through programming and is solved simultaneously using Gaussian Elimination Method with partial pivoting. Results of the present approach are validated with published model and industrial data. [Copyright &y& Elsevier]

Abstract: An overview of an iterative and sequential methodology, called the Sequential Framework for heat exchanger network synthesis (HENS), is presented in the paper. The main objective of the Sequential Framework is to solve industrial size problems. The subtasks of the design process are solved sequentially using mathematical programming. There are two main advantages of the methodology. First, the design procedure is, to a large extent, automated while keeping significant user interaction. Second, the subtasks of the framework (MILP and NLP problems) are much easier to solve numerically than the MINLP models that have been suggested for HENS. One of the limiting factors in the methodology is related to the two MILP models where significant improvements are required to prevent combinatorial explosion. To ease this problem for the minimum number of units MILP sub-problem, two different approaches to the issue were studied. The minimum number of units problem is modified to reduce the gap using physical insights and heuristics. Another novel approach tested was to reformulate some parts of the model by use of some ideas from set partitioning problems. Results show that though both methods succeed in tightening the LP relaxation, the model solution times remain too long to be of interest in the Sequential Framework. [Copyright &y& Elsevier]

Abstract: In this paper, a rigorous MILP formulation for grass-root design of heat exchanger networks is developed. The methodology does not rely on traditional supertargeting followed by network design steps typical of the Pinch Design Method, nor is a non-linear model based on superstructures, but rather gives cost-optimal solutions in one step. Unlike most models, it considers splitting, non-isothermal mixing and it counts shells/units. The model relies on transportation/transshipment concepts that are complemented with constraints that allow keeping track of flow rate consistency when splitting takes place and with mechanisms to count heat exchanger shells and units. Several examples from the literature were tested, finding that the model usually obtains better solutions. In some cases, the model produced unknown solutions that were not found using superstructure optimization methods, even when the same pattern of matches is used. [Copyright &y& Elsevier]

This paper deals with the application of adaptive fading Kalman filtering (AFKF) to the design of an observer used to predict the state of an counter-current heat exchanger. In order to implement the AFKF, an accurate mathematical model, based on the approximation of temperatures along the process by first order dynamic model, is considered. This method could be applied when the heat exchanger is solicited by the flow rate changes. Experimental validation of this method is illustrated by an example. [Copyright &y& Elsevier]

This paper describes the simultaneous MINLP synthesis of heat integrated heat exchanger networks comprising different heat exchanger types. The stage-wise superstructure of heat exchanger networks (HEN) by Yee and Grossmann (Comput. Chem. Eng. 14 (1990) p. 1165) is extended to alternative exchanger types. The selection of the types is modeled by disjunctions based on operating limitations and the required heat transfer area. Since different types of heat exchangers involve different design geometries, which influences the inlet and outlet temperatures of heat exchangers, additional constraints are specified to provide a feasible temperature distribution in HEN. The consideration of different exchanger types drastically increases the combinatorics, size and computation effort needed to solve the problem. The integer-infeasible path MINLP approach has been applied to perform an efficient initialization scheme and to halve CPU times for solving MILP master problem of the modified OA/ER algorithm. A special multilevel MINLP procedure in reduced integer space has been proposed to solve medium size HEN problems (20 streams) comprising 103 and more binary variables. [Copyright &y& Elsevier]