Optimal Heat Exchanger Network Research Articles

Retrofit and optimisation of industrial heat exchanger networks: A complete benchmark problem

Retrofit and optimisation of industrial heat exchanger networks: A complete benchmark problem

Heuristic approach for heat exchanger networks

A systematic approach based on few heuristics for the synthesis of optimum heat exchanger networks has been developed. The approach, which is simple and easy to apply, consists of three sequential steps. In the first pre-analysis step, the optimum temperature approach is determined. In this step, a set of heuristic constraints are used to determine minimum utility requirements. In the second step, heat exchanger networks are generated using the H/H heuristic of matching hot and cold streams. In the third step, the initially generated networks evolve through loop breaking and energy relaxation to achieve the target of the minimum number of units. The effectiveness of the approach developed has been tested on a number of literature test problems ranging in size from four to ten streams and on an industrial case involving a recovery heat exchanger network around a topping tower. The approach produced simple network structures and improved energy recovery. The cost results obtained in this work agree favourably with optimal solutions reported in the literature.

Optimization of heat exchanger networks by coupled simulated annealing and NLP procedures

This paper addresses the problem of systematic generation of heat exchanger networks for minimizing the global cost. To an upper level, the approach implements simulated annealing to propose HEN configurations. This information is then used in a lower level within a nonlinear programming (NLP) frame to optimize the operating variables. In this paper, the automatic generation, initialization and optimization of these nonlinear problems are only presented. The proposed method provides minimum size problems subject to a minimum number of variables and constraints.

Optimization of heat exchanger networks

In the optimization of heat exchanger networks, an easy and reliable method of obtaining the global optimum has been overlooked by recent researchers. It is shown that the direct search optimization procedure using randomly chosen test points and region contraction as developed by Luus and Jaakola over 20 years ago is ideally suited for these types of problems. The global optimum can be obtained an order of magnitude faster than the recently proposed method by Quesada and Grossmann.

Global optimization algorithm for heat exchanger networks

This paper deals with the global optimization of heat exchanger networks with fixed topology. It is shown that if linear area cost functions are assumed, as well as arithmetic mean driving force temperature differences in networks with isothermal mixing, the corresponding nonlinear programming (NLP) optimization problem involves linear constraints and a sum of linear fractional functions in the objective which are nonconvex. A rigorous algorithm is proposed that is based on a convex NLP underestimator that involves linear and nonlinear estimators for fractional and bilinear terms which provide a tight lower bound to the global optimum. This NLP problem is used within a spatial branch and bound method for which branching rules are given. Basic properties of the proposed method are presented, and its application is illustrated with several example problems. The results show that the proposed method only requires few nodes in the branch and bound search.

A note on the use of dual temperature approach in heat exchanger network synthesis

The application of a single temperature approach in the synthesis of optimal heat exchanger networks was the fundamental assumption of many solution methods developed to date. However, several authors, e.g. Colbert ( Chem. Engng Prog. 78, 47–54, 1982), Gundersen and Grossmann ( AIChE Annl Meeting, 1988), Trivedi et al. ( Computers chem. Engng 13, 667–685, 1989) as well as Colberg and Morari ( Computers chem. Engng 14, 1–22, 1990) proved that the use of the so-called dual (or double) temperature approach may yield solutions of low overall cost. The approach of Trivedi et al. ( Computers chem. Engng 13, 667–685, 1989) requires exhaustive computations and several heuristics, Gundersen and Grossmann ( AIChE Annl Meeting, 1988) as well as Colberg and Morari ( Computers chem. Engng 14, 1–22, 1990) applied complex models that require sophisticated computer programs. This work presents a simple approach that stems from physical insights into the problem. The application of this method requires only well-known subroutines such as e.g. procedures for determining targets A 0 min and NS min. The examples solved show that cross-pinching caused by the use of a dual temperature approach does not necessarily yield high capital cost of HENS.

Toward the synthesis of global optimum heat exchanger networks under multiple-periods of operation

An algorithmic-evolutionary synthesis procedure is proposed for flexible heat exchanger networks (HEN) under multiple-periods of operation. After a feasible network is synthesized at each period, they are combined to form a feasible super network structure which requires maximum energy recovery (MER) at each period and features minimum number of units (MNU). Beginning with the initial feasible super network structure, all the super network structures can be enumerated to generate the minimum cost super network structure. The key steps in the procedure are constituted of must-matches searches at each period and path tracing/list processing constructions that allow not only combination of networks of each period but also development of super network structures adjacent to the initial super network structure in some sense, while keeping maximum energy recovery at each period and minimum number of units. Then a trade-off between MER and MNU is performed to strictly reduce objective function values. The constructions and procedures are rigorously established and effectiveness of the composite algorithm is demonstrated via several test problems. These tests show that the proposed approach can find the optimum networks for the known standard problems, and new MNU/MER networks are identified which to date have not been reported in the literature.

Optimal synthesis of a heat-exchanger network

Thermodynamic, heat transfer and economic concepts influencing the synthesis of a heat-exchanger network (HEN) coupled to a crude fractionation unit are examined. The impact of the variation of the minimum temperature approach (Δtmin) on energy and capital targets is studied using recent developments in pinch technology. The optimal pinch approach temperature has been determined using the ‘supertargeting’ concept where proper trade-off between energy and capital targets is observed prior to design. A heuristic evolutionary approach has then been used for the generation of the optimal HEN.

Simultaneous optimization models for heat integration—III. Process and heat exchanger network optimization

In this paper, the proposed heat integration representation of Part I (Yee et al., Computers & Chemical Engineering 14, 1151, 1990) is used for the simultaneous optimization or synthesis of the process and its heat exchanger network. The basic idea involves embedding the proposed representation into a given process flowsheet or superstructure and optimize the combined superstructure simultaneously, where flows and temperatures of the potential heat integrated streams are treated as variables. The proposed model accounts for capital and operating costs of the heat exchanger network. It does not require the specification of a heat recovery approach temperature (HRAT) and can easily handle constraints for heat integration. Synthesis examples of a distillation sequence and of a process flowsheet are presented to illustrate the capabilities of the simultaneous model which can be formulated as an NLP problem or as an MINLP problem when the structure of the network is to be determined explicitly.

Cost optimum heat exchanger networks—2. targets and design for detailed capital cost models

Part 1 of this paper presented a procedure for the design of near-optimum cost heat exchanger networks. The procedure is based on setting targets for capital and energy costs and optimizing these targets prior to design. The procedure in Part 1, however, uses a simple model of capital cost. The present paper extends the model of capital cost to allow for: • —exploiting differences in heat transfer coefficients for reduced network area; • —a non-linear exchanger cost law; • —non-countercurrent heat exchangers; • —non-uniform materials of construction, pressure ratings and exchanger types in the network. /lt Using these extensions both targeting and design for minimum capital cost are considered.

Strategies for overcoming uncertainties in heat exchanger network synthesis

Current grassroot heat exchanger network design techniques involve a three-task procedure: (a) calculation of the minimum utility consumption; (b) selection of a set of process stream matches that satisfy the minimum utility consumption and minimum units criteria; and (c) derivation of a minimum investment cost heat exchanger network configuration. Section 3 of this paper will present an approach for overcoming the uncertainty associated with the network optimization task that arises from the nonconvexities in the network optimization problem. A global optimum search approach is proposed that decomposes the nonconvex network optimization problem into a set of convex subproblems that represent upper and lower bounds and whose solution can lead to the network configuration with the globally minimum investment cost. Uncertainty arises in the selection of matches task when there are many combinations of matches that satisfy the targeting criteria. When there are many such combinations, exhaustive enumeration may be required to determine the optimal combination. Section 4 presents a decomposition methodology circumventing this uncertainty, based upon a proposed hyperstructure that contains all possible network configurations and process stream matches. This hyperstructure is used to derive a mixed integer nonlinear programming (MINLP) formulation that models both the selection of process stream matches and the derivation of a heat exchanger network configuration. A decomposition approach is proposed that efficiently derives the optimal combination of process stream matches and the optimal heat exchanger network configuration.

Synep1 : A methodology for energy integration and optimal heat exchanger network synthesis

A new methodology for process energy integration and heat exchanger network synthesis, combining heuristic rules and mathematical optimization techniques, is presented. The tool based on it, is an assistance program for the non-expert user, who can use it to complete different tasks, such as flexible network synthesis, retrofit or revamping studies, according to several optimization criteria.

Rapid analysis of heat recovery in industrial plants

The integration of hot and cold streams in processes of industrial plants is an important aspect for recovering heat and reducing energy consumption. This paper proposes a rapid analysis method on integrating hot and cold streams in industrial plants, whereby cost and profit for heat recovery can be worked out rapidly. Therefore the results can be used to determine whether a further detailed feasibility study should be carried out and optimal heat exchanger networks have to be synthesized. Meanwhile, an optimization method is also suggested for choosing the minimum optimal temperature difference in exchanger. And, on the basis of the method proposed, the computer program AIHCS has been compiled and applied to a practical case whose results fully verify the effectiveness of this (rapid analysis) method.

Second-law-based optimization of heat exchanger networks using load curves

The problem of simultaneously optimizing heat exchangers for a number of hot and cold fluids is approached from the viewpoint of the second law of thermodynamics. If the total duty requirements are fixed, i.e. all inlet and outlet temperatures are established for the fluids, then the resulting entropy production rate is independent of the actual pairings of the fluids. Thus, optimization with respect to size becomes essentially a maximization of the temperature differences between the paired fluids for all of the fluids considered. Next it is shown that the same optimization can be obtained from the load curves where the temperature is plotted against the heat transfer for each of the fluids. If the film coefficient for any of the fluids is significantly different from the others, a simple shifting can be accomplished and a criterion is given to determine if such shifting improves the optimization. The method is extremely simple and can be performed most effectively on graph paper.

Automatic synthesis of optimum heat exchanger network configurations

AbstractThis paper addresses the problem of automatically generating heat exchanger network configurations that feature minimum investment cost subject to minimum utility cost and fewest number of units. Based on the linear programming and the mixed‐integer linear programming (MILP) transshipment models for heat integration, a superstructure that has embedded many alternative configurations is proposed. This superstructure, which has as units the matches predicted by the MILP transshipment model, includes options for series and parallel matching, as well as stream splitting, mixing, and bypassing. Many of the implied stream connections in the superstructure are reduced to zero flow with a nonlinear programming formulation that leads to realistic and practical designs. Theoretical properties as well as the implementation aspects of the proposed procedure for the automatic generation of networks are presented. The method is illustrated with three example problems.

Design of resilient processing plants—IV: Some new results on heat exchanger network synthesis

Simple and reliable methods to synthesize the most efficient network of heat exchangers to heat and cool known process streams between stated temperatu Examples in this paper demonstrate the strong need for systematic design procedures for resilient networks. Networks designed on the basis of intuitive Some fundamental properties of optimal resilient heat exchanger networks are proven first. On this basis a theoretically rigorous synthesis technique i

Optimization of the effective profit of heat exchanger networks

The economy of heat exchanger can highly deviate from the profit of the point of design, depending on changing, usually increasing, energy prices. Therefore heat exchanger networks should be optimized using effective profitability over plant life rather than maximum productiveness of the point of design. A computer program was developed which allows to illustrate the dependence of the network structure on economic boundary conditions. The computer program determines a functional relation between minimum investment costs and energy losses. Assigning cost to the energy losses by energy prices and by plotting the investment costs against energy losses, it is possible to determine the optimal heat exchanger network structure.

Practical synthesis method for heat exchanger network.

Synthesis of an optimal (minimum-cost) heat exchanger network is very important from the viewpoint of energy saving and cost reduction, but it is difficult to solve these synthesis problems because there exist an extremely large number of possible stream combinations to be considered. A practical method composing three stages [pre-analysis, generation of initial networks, and evolution] was developed to synthesize an optimal network by hand calculation. The problem table is adopted to determine the minimum utility requirement precisely, and to search necessary conditions of maximum heat recovery in the pre-analysis stage. A simple algorithm of initial network generation is developed to generate nearly optimal networks considering maximum heat recovery and optimal locations of heaters and coolers. Initial networks are improved by simple evolutionary rules based on stream-splitting to increase the heat duties of units and to vary the exchanger sizes in the evolution stage. The effectiveness of this method is demonstrated by solving the synthesis problems reported in previous works.

A thermodynamic‐combinatorial approach to the design of optimum heat exchanger networks

AbstractThis article describes a novel approach to the systematic synthesis of heat exchanger networks. For a given synthesis problem, this approach leads to a complete listing of all solutions which exist, using a prescribed degree of energy recovery, the minimum number of exchangers, heaters and coolers, and no split streams. The approach is combinatorial, with a variety of thermodynamic criteria used to minimize the problem size by preventing infeasible solutions being generated. Two examples (5SPI and 6SPI) are discussed to illustrate complete solution by hand.

A discussion of the paper “the influence of Na 2O on the structure and properties of 3CaO.Al 2O 3” by A.I. Boikova A.I. Domansky, V.A. Paramonova, G.P. Stavitskaja and V.M. Nikushchenko

Optimization of heat exchanger network (HEN) has traditionally been driven by economic objectives. Notwithstanding the importance of minimizing the total annual cost (TAC) of HEN, it is also important to ensure reliability. In order to obtain economical HEN considering system reliability simultaneously, a multi-objective optimization formulation of economic and system reliability is proposed in the design of HEN. A stage-wise superstructure is used to obtain feasible HEN, and the system reliability based on the number of heat exchangers in maximum irrelevant sub-network of HEN and the TAC are calculated as two objective functions. Then the non-dominated sorting genetic algorithm (NSGA-II) is applied to solve the multi-objective optimization mixed integer nonlinear programming model. Three case studies from literatures are used to assess the applicability and performance of the optimization formulation and solution algorithm. The system reliability is enhanced with TAC closes to the reported minimum, which is more meaningful than those obtained using single-objective optimization. The optimal solution set can aid in the selection of a safe and cost-effective network configuration for industrial plants and the proposed approach can easily be applied to include other objectives (e.g., sustainability and safety).