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Chapter -3

Literature Survey – Heat Exchanger Network and Mass Transfer Equipment Network

3.1.0 Introduction: Heat exchanger network synthesis (HENS) is an important field in thermal engineering and has been the subject of a considerable amount of research over the past 50 years. Its significance can be attributed to its role in controlling the costs of energy for a process. The heat-exchanger network (HEN) design problem was introduced into the literature by Ten Broeck70 in 1944. The first work in grassroots HENS was presented by Hwa35 in 1965. Then the HENS problem was first rigorously defined by Masso and Rudd50 in 1969. The basic HENS problem is the following: Given

(i) a set H of hot process streams to be cooled from the inlet temperatures to the outlet temperatures, (ii) a set C of cold process streams to be heated from the inlet temperatures to the outlet temperatures, (iii) the heat capacities and flow rates of the hot and cold process streams, (iv) the utilities available and the temperatures or temperature ranges and the costs for these utilities, (v) heat-exchanger cost data, develop a network of heat exchangers with minimum arinualized investment

and operating costs. For an introduction to the fundamental principles and procedures of HENS, readers are referred to the texts of Shenoy64, Smith67, Seider et al.63, and Biegler et al.7 The thorough reviews on the topic of HENS were contributed by Gundersen and Naess32, by Jezowski37&38 and by Grossmon et al.29. The purpose of this additional review work is to provide coverage of work not covered by previous review papers, to provide a critical review of the current state-of-the-art in HENS and become the impetus for future research. Creating an exhaustive compilation and organization of HENS papers as such is a complicated task. The major solution methods in HENS have been reviewed initially followed by an annotated bibliography of HENS literature of the 20th century. Further, several classification schemes of the annotated HENS works are proposed and discussed. Concluding remarks are presented at the end. 3.2.0 HENS Solution Methods: Most of the contributions to HENS research can be classified as either sequential synthesis or simultaneous synthesis methods. 3.2.1 Sequential Synthesis: Sequential synthesis methods use the strategy of dividing the HENS problem into a series of subproblems in order to reduce the computational requirements for obtaining a network design. These methods typically involve partitioning of the HENS problem into a number of intervals, which is usually accomplished by dividing the temperature range of the problem into temperature intervals. These intervals are important for modeling heat exchange while obeying the laws of thermodynamics. The problem is decomposed into a series of target subproblems which are solved successively in order of decreasing significance with respect to the total annual cost of the HEN based on heuristic rules. Generally, this is achieved with the following three problems: the minimum utility usage/cost, the minimum number of exchanger units, and the minimum area/capital cost of the network. These problems are solved according to the heuristic of finding the minimum cost network subject to the minimum number of units subject to the minimum utilities cost. There is also the concept of supertargeting for finding the optimal minimum approach temperature used in partitioning of the problem into temperature intervals because the minimum capital cost of the network is a function of this parameter. The sequential synthesis method does not guarantee the design of a network with the minimum annual cost. Sequential synthesis methods are further divided into two sub-categories: (1) evolutionary design methods such as the pinch design method (PDM: Linnhoff and co-workers46&47), dual temperature (Colbert16 and Trivedi et al.72), and pseudo-pinch methods (Wood et al.73, Trivedi et al.71, and Rev and Fonyo61&62) and (2) mathematical programming techniques based on the sequential solution of continuous and integer linear programs (Cerda et al.11 and Papoulias and Grossmann56) and nonlinear optimization problems (Floudas et al.22). Using pinch-based design methods, after the partitioning of the problem into temperature intervals based on a heat recovery approach temperature (HRAT), the locations of bottlenecks for energy savings are found when determining the minimum utility usage. These bottlenecks are called heat recovery pinch points. The HEN is then decomposed into subnetworks based on the pinch point(s). An initial network design is produced starting

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from the interval bounded by the pinch point and concluding at an interval bound consisting of either another pinch point or the first or last temperature interval. Successively better networks are evolved based on various design guidelines and heuristic rules until a network with the target number of units is produced. The dual-temperature approach method (DTAM) allows for heat exchange across pinch points using an exchanger minimum approach temperature (EMAT) less than HRAT as a decision variable. DTAM has the tendency to produce networks of fewer units and simpler structure at the cost of increased exchanger area. The pseudo-pinch design method (PPDM; Wood et al.73), which relaxes the pinch condition, and the flexible pinch design method (FPDM; Suaysompol and Wood69), which has a variable minimum approach temperature, are further modifications of the DTAM with the goal of designing even simpler network configurations. Sequential synthesis via mathematical programming involves solving the three subproblems in which the HENS problem is decomposed in sequence, with some part of the solution to a previous target problem being parameters in the next. The first problem is the minimum utilities cost problem. This linear programming (LP) problem can be formulated to include the possibility of forbidden matches (Cerda et al.11 and Papoulias and Grossmann56). Among some of the modified models are an LP formulation extended for using the DTAM presented by Jezowski and Friedler41 and the mixed-integer linear programming (MILP) and mixed-integer nonlinear programming (MINLP) formulations by Galli and Cerda26,27&28 allowing for additional structural constraints. Using the utilities target, an MILP formulation (Cerda et al.11 and Papoulias and Grossmann56) for determining the heat load distribution of the minimum number of matches is solved. Typically, this problem is divided into subproblems at pinch points in order to minimize the number of heat-exchanger units rather than heat-exchange matches. A vertical heat-transfer model proposed by Gundersen and Grossmann31 and extended by Gundersen et al.30 was developed to find a target set of stream matches based on rankings to produce networks with lower capital costs for exchanger area. Also along this line of study is a vertical heat-transfer model-based formulation for determining matches and a heat load distribution disregarding the number of matches and solving for an objective based on minimum area costs (Gundersen et al.34). The formulations of Galli and Cerda26,27&28 are also applicable for determining the minimum number of matches. Last, a nonlinear programming (NLP) model (Floudas et al.22) is applied for the development of a HEN based on a network superstructure solving for the minimum capital cost with respect to the exchanger area subject to the heat load distribution and heat matches derived from the previous target problem. A more recent sequential synthesis methodology proposed by Zhu and associates78to82 partitions the HENS problem into "blocks" which are basically a set of enthalpy intervals. A set of matches is determined, and a network is evolved for each block individually. This partitioning into blocks was proposed to reduce the dimensionality of the HENS problem, which is a drawback to most other mathematical programming methods. Key references for sequential synthesis: Other important worth mentioning references w.r.t. sequential synthesis are the following: Gundersen et al.33, Jezowski39, and Pettersson F57.

3.2.2 Simultaneous Synthesis: The goal of simultaneous HENS is to find the optimal network without decomposition of the problem. Simultaneous synthesis methods are primarily MINLP formulations of the HENS problem subject to various simplifying assumptions used to facilitate the solution of these complex models. One of the earliest simultaneous HENS formulations was proposed by Yuan et al.77 The superstructure developed in this work has the drawback of not allowing splitting or mixing of streams. An MINLP formulation is proposed that does not involve integer variables in the objective. Floudas and Ciric23&24 developed the simultaneous match-network hyperstructure model for optimizing all of the capital costs of a HEN at once. This MINLP formulation determines the minimum costs for exchanger units and exchanger area by combining the transshipment model of Papoulias and Grossmann56 for stream match selection and the network topology hyperstructure model of Floudas et al.22 for determination of the heat-exchanger areas, temperatures, and the stream flows in the network. The drawback of this formulation is that it is still based on temperature interval partitioning of the HENS problem, and thus the value for HRAT must be specified before solving and, therefore, supertargeting may be required for finding the lowest capital cost network. The simultaneous match-network method was later applied to pseudo-pinch problems by Ciric and Floudas.13 The hyperstructure model was then even further modified by Ciric and Floudas14 to include optimization of minimum utilities cost as well. This MINLP formulation does not require any decomposition into design targets and simultaneously optimizes for the lowest annual network cost. Another MINLP simultaneous synthesis formulation was proposed by Yee and Grossmann.75 This model is based on the stagewise superstructure representation of Yee et al.76 in which potential heat exchange between any pair of hot and cold streams may occur in every stage. The assumptions of isothermal mixing, no split stream flowing through more than one exchanger, and no stream bypass make the constraint set linear, while the objective function remains a nonlinear and nonconvex. Daichendt and Grossmann18to21 have developed a

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preliminary screening procedure for finding bounds on the objective of this MINLP formulation in order to reduce the computational effort required for solving it. Key references for simultaneous synthesis Other important worth mentioning references w.r.t. simultaneous synthesis are the following: Aaltola1, Akman et al.3, Barbaro and Bagajewicz5, Bozan 9, Chen and Hung12, Cisternas et al.15, Konukman et al43, Mou and Qvale51 and Ravagnani and Caballero60 Recent worthmentioning references w.r.t. LP, MILP, NLP AND MINLP are the following: For Linear Programming(LP): Panjehshahi and Nouzari53 For Mixed Integer Linear Programming(MILP): Barbaro A. and Bagajewicz5, Bozan and Borak9, Galli and Cerdá25, Jezowski et al40, Pettersson57, Shethna and Jezowski65 and Shethna et al66

For Non Linear Programming(NLP): Kralj and Glavic44, and Panjeshahi54 For Mixed Integer Non Linear Programming(MINLP): Aaltola1, Bozan and Borak9, Bogataj and Bagajewicz8, Jezowski et al36, Ma et al49, and Ravagnani and Caballero60

3.3.0 Recent Worthmentioning References for MENS: Recent worthmentioning references for MENS with special reference to distillation process and cooling towers are the following: FCC Unit in oil refinery: Riyami et al4

Fractional Crystallization: Cisternas et al15

CDU and FCC: Querzoli et al59

Integrated Refrigeration system: Wu and Zhu74

Integrated analysis of cooling tower system: Cortinovis17

Evaporative cooling towers: Bernier6, Naphon52, Prasad58 Thermal Performancce of cooling towers: Castro et al10, Konukman et al42, Lemouari et al45, Papaefthimiou et al55, Soylemez68.

3.4.0 Annotated Bibliography of HENS and MENS Works: Exhaustive literature survey was performed for HENS & MENS and 300 references have been discussed as per details mentioned below: (1) Aaltola J. Simultaneous synthesis of flexible heat exchanger network. Applied Thermal Engineering,

June 2002, 22(8):907–918. A framework is presented for generating flexible heat exchanger networks (HENs) over a specified range of variations in the flow rates and temperatures of the streams. The flexible HEN is synthesised using a combination of a multiperiod simultaneous MINLP model and search algorithms, where the total annual costs due to utility duties, exchanger areas and selection of matches are optimised. The simultaneous HEN synthesis allows the data to be distributed according to a probability distribution and it does not rely on the concept of pinch point. Both search algorithms involve a developed multiperiod NLP/LP model where utility costs are minimised. The proposed procedures are explained through an example including variations resulting in a network with variable splits and bypasses. This framework results in a HEN working under variations without losing stream temperature targets while keeping an economically optimal energy integration.

(2) Abbas, H. A.; Wiggins, G. A.; Lakshmanan, R.: Morton, W. Heat Exchanger Network Retrofit via Constraint Logic Programming. Comput. Chem. Eng. 1999, 23(Suppl.), S129-S132. Heuristics are incorporated with constraint logic programming in an algorithm for HEN retrofit.

(3) Adonyi R., Romero J., Puigjaner L., and Friedler F. Incorporating heat integration in batch process scheduling. Applied Thermal Engineering, October 2003, 23(14):1743–1762. This work presents a methodology for incorporating heat integration in batch process scheduling. The formerly introduced S-graph approach [AIChE J. 48 (2002) 2557–2570] for solving multipurpose scheduling problems is proved to be appropriate for the representation of both scheduling problems and the corresponding heat exchanger network synthesis problem. The proposed procedure is based on the branch-andbound framework, where two optimisation problems, the scheduling and the heat integration one, are considered simultaneously instead of consecutively. This method is primarily based on combinatorics and combinatorial algorithms.

(4) Aguilera. N.; Nasini, G. Flexibility Test for Heat Exchanger Networks with Uncertain Flowrates. Comput. Chem. Eng. 1995, 75(9), 1007-1017. An MILP formulation for testing the flexibility of a HEN with respect to flow-rate variation at the level of heat matches is presented. Forbidden matches and multiple utilities are not considered, and the test only determines flexibility, not optimality.

(5) Aguilera. N.; Nasini. G. Flexibility Test for Heat Exchanger Networks with Non-Overlapping Inlet Temperature Variations. Comput. Chem. Eng. 1996, 20 (10), 1227-1240.

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An algorithm for the testing of flexibility at the level of heat matches in HENS is described. This paper does not consider forbidden matches or multiple utilities. The presented test is an MILP that considers the whole set of operation points at once.

(6) Aguirre, P. A.; Pavani, 0., Irazoqui, H. A. Optimal Synthesis of Heat-and-Power Systems with Multiple Steam Levels. Chem. Eng. Sci. 1990. 45(1), 117-129. The operating line method for heat and power integration into process synthesis is extended for multiple steam levels.

(7) Ahmad, S.; Hui, D. C. W. Heat Recovery Between Areas of Integrity. Comput. Chem. Eng. 1991, 15 (12), 809-832. Pinch technology is used in this approach to the design of HENs considering heat recovery among vari-ous process tasks.

(8) Ahmad. S.; Polley, G. T. Debottlenecking of Heat Exchanger Networks, heat Recovery Syst. CHP 1990, W (4), 369-385. Enhancements to the retrofit targeting procedure of Tjoe and Linnhoff (annotation 388) are made. The method is extended for increasing throughput by process debottlenecking. Pressure drop constraints and utility equipment restrictions are examined.

(9) Ahmad, S.; Smith, R. Targets and Design for Minimum Number of Shells in Heat Exchanger Networks. Chem. Eng. Res. Des. 1989, 67(5), 481-494. A method for targeting the minimum number of shells and near-optimal area in networks of 1-2 exchangers and a design method for developing HENs that approach these targets are described in this paper.

(10) Akbari A., Omidkhah M. R., and Hojjati M. R. Heat exchanger network area targeting considering stream allocation to shell or tubes. Computers & Chemical Engineering, 2008, 32(12):3143–3152. 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.

(11) Akman U., Uygun K., Uztürk D., and Konukman A. E. HEN optimizations without using logarithmic mean- temperature difference. AIChE Journal, 2002, 48(3):596–606. A simple 1-1 shell-and-tube heat-exchanger model without the logarithmic-mean-temperature difference ΔTlm is proposed for heat-exchanger network (HEN) optimizations. The model consists of two algebraic equations and allows to determine hot and cold outlet temperatures independent of each other. HEN optimization problems are classified as feasible- and infeasible-path formulations, and compared with regard to problems originating from the use of ΔTlm in exchanger energy-balance equations. The ΔTlm-free model eliminates numerical failures in computing the logarithmic terms with negative arguments due to possible inconsistent initialization/progress of exchanger interconnection temperatures during HEN optimizations.

(12) Al-Nimr MA, Dynamic thermal behaviour of cooling towers, Energy Convers Manage 1998; 39:631-6. In this study, a simple mathematical model is proposed to describe the dynamic thermal behaviour of a counterflow cooling tower. The proposed model takes in to account both the sensible and latent heat cooling effects on the tower performance. A simple perturbation technique is used to solve the governing equations of the model in order to get a closed form solution for the temperature variation within the cooling tower subject to the cooling tower having a very large convective heat transfer coefficient between the water droplets and the air. Under steady state conditions, a mathematical criterion is derived to obtain the proper length of cooling tower which is sufficient to ensure a complete cooling for the hot water stream.

(13) Al-Riyami B. A., Klemes J., and Perry S. Heat integration retrofit analysis of a heat exchanger network of a fluid catalytic cracking plant. Applied Thermal Engineering, October 2001, 21(13-14):1449–1487. The fluid catalytic cracking (FCC) is a dominant process in oil refineries and there has been a sustained effort to improve the efficiency and yield of the unit over the years. Nevertheless, benefits and scope for improvement can still be found. The HEN of the FCC process considered here consists of a main column and a gas concentration section. Appropriate data were extracted from the existing network, using flowsheeting simulation. The stream data consists of 23 hot and 11 cold streams and cost and economic data required for the analysis were specified. The incremental area efficiency methodology was used for the targeting stage of the design and the design was carried out using the network pinch method consisting of both a diagnosis and optimisation stage. In the diagnosis stage promising designs were generated using UMIST developed sprint software. The generated design was then optimised to trade-off capital cost and energy savings

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(14) Al-Saggaf, A.; Mewes, D. Thermal Coupling of Chemical Stirred-Tank Reactors with Other Plant Components. Part 2. Int. Chem. Eng. 1992. 32 (2), 239-264. Energy liberated by chemical reactions is taken into consideration in HENS. Thermal coupling of stirred-tank reactors with arbitrary plant components is investigated.

(15) Al-Saggaf, A.; Mewes, D. Thermal Coupling of Chemical Stirred-Tank Reactors with Other Plant Components. Part 1. Int. Chem. Eng. 1992. 32 (2), 209-238. Literature concerning the PDM, network evolution and optimization procedures, flexibility, retrofit, heat integration, and overall process synthesis is reviewed and evaluated.

(16) Androulakis. I. P.; Venkatasubramanian. V. A Genetic Algorithm Framework for Process Design and Optimization. Comput. Chem. Eng. 1991. 15(4), 217-228. An optimization framework based on genetic algorithms is proposed for the solution of process design and optimization problems by stochastic methods. This framework is demonstrated by applying it to the synthesis of a HEN without stream splitting.

(17) Asante, N. D. K.; Zhu. X. X. An Automated Approach for Heat Exchanger Network Retrofit Featuring Minimal Topology Modifications. Comput. Chem. Eng. 1996, 20 (Suppl.), S7-S12. A retrofit procedure consisting of two stages is proposed. In the diagnosis stage, desired topology modifications are identified and selected using MILP models. In the optimization stage, a small superstructure is derived and used to optimize stream splits and configurations.

(18) Asante, N. D. K.; Zhu, X. X. An Automated and Interactive Approach for Heat Exchanger Network Retrofit. Chem. Eng. Res. Des. 1997, 75 (A), 349-360. This paper provides insights into the nature of retrofit design and the role played by topology modification in the design task. Three NLP models are used in the diagnosis stage to sequentially identify individual topology changes with the best potential for heat recovery, and an NLP model is used in the optimization stage to optimize the capital-energy tradeoff within a selected design.

(19) Athier, G.; Floquet, P.; Pibouleau. L.; Domenech, S. Optimization of Heat Exchanger Networks by Coupled Simulated Annealing and NLP Procedures. Comput. Chem. Eng. 1996, 20 (Suppl), S13-S18. An upper level simulated annealing algorithm is used to define feasible structures in the network, while a lower level NLP algorithm is used to determine continuous operating parameters for these structures.

(20) Athier, G.; Floquet, P.; Pibouleau, L.; Domenech, S. Synthesis of Heat-Exchanger Network by Simulated Annealing and NLP Procedures. AIChE J. 1997, 43 (11). 3007-3020. A numerical procedure for solving HENS is proposed. An algorithm is developed for bypassing implementation of MINLP procedures from which difficulties arise in large-scale HENS problems. Solution networks may include stream splitting, nonisothermal mixing, the absence of bypass streams, multiple matches between the same two streams, and dual streams, which were not considered in various prior approaches. The solution strategy involves a master problem solved by simulated annealing that determines the HEN topology with an NLP slave problem that optimizes the operating parameters.

(21) Athier, G.; Floquet, P.; Pibouleau, L.: Domenech, S. A Mixed Method for Retrofitting Heat-Exchanger Networks. Comput. Chem. Eng. 1998, 2/(Suppl.), S505-S511. A two-level strategy for retrofit design is proposed. A simulated annealing algorithm is used to solve the master problem of generating and iteratively modifying a HEN topology. The slave problem involves NLP optimization of the operating parameters of the network.

(22) Bagajewicz M. J., Ji S., and SotoJ. Heat exchanger networks for petroleum fractionation units handling crudes of different density. Latin American Applied Research, 2001, 31(4):339–343. A targeting procedure implemented using a commercial simulator is presented. The design of a heat exchanger network that will take advantage of the flexibility in the targets follows. Extensions to well-known heat exchanger network synthesis models (e.g. transshipment) to address this target flexibility are presented.

(23) Bagajewicz, M. J.; Manouskmthakis, V. Mass/Heat-Exchange Network Representation of Distillation Networks. AIChE J. 1992, 38(11). 1769-1800. The state space approach is introduced to process synthesis to represent distillation networks as composite heat and mass exchange networks. The state space approach qualitatively describes a problem based on the complement of state variables and input-output relations.

(24) Bagajewicz, M. J.; Priam, R.; Manousiouthakis, V. On the State Space Approach to Mass/Heat Exchanger Network Design. Chem. Eng. Sci. 1998, 53(14), 2595-2621. This paper introduces various aspects of the state space approach for the design of HENs, mass exchanger networks, and interacting heat and mass exchanger networks.

(25) Ballut, A. A. Heat Recovery Analysis of an Existing Crude Distillation Unit. /. Heat Recovery Syst. 1986, 6 (S). 361-367. Possible energy savings in a crude distillation unit are analyzed.

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(26) Barbaro A. and Bagajewicz M. J. New rigorous one-step MILP formulation for heat exchanger network synthesis. Computers & Chemical Engineering, August 2005, 29(9):1945–1976. 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.

(27) Benton, D. J. and Waldrop, W. R., 1998, Computer simulation of transport phenomena in evaporative cooling towers, J Eng for Gas Turbiners and Power, 110(2): 190-196. The Computer simulation of transport phenomena in evaporative cooling towers has been discussed in this paper.

(28) Bernier MA, Cooling tower performance: theory and experiments. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Trans 1994;1002(2);114-21. Research on recirculating cooling water systems has mostly focused on the individual components. In this design method represented by Kim and Smith a comprehensive simulation model of recirculating cooling system was developed to account for the interaction between the cooling tower performance and the heat-exchanger network configuration.

(29) Bochenek, R.; Jezowski, J. Adaptive Random Search Approach for Retrofitting Flexible Heat Exchanger Networks. Hung. J. Ind. Chem. 1999, 27, 89-97. Direct search optimization techniques are applied to retrofitting multiperiod or flexible HENs.

(30) Bogataj M.and Bagajewicz M. J. Synthesis of non-isothermal heat integrated water networks in chemical processes. Computers & Chemical Engineering, 2008, 32(12):3130–3142. This paper presents a new approach for the simultaneous synthesis and optimization of heat integrated water networks. A new superstructure for heat exchanger network (HEN) synthesis is proposed. The procedure is based on mixed integer non-linear mathematical programming (MINLP)

(31) Bozan M, Borak F. A computerized and integrated approach for heat exchanger network design in multipurpose batch plants. Chemical Engineering & Processing, November 2001, 40(6):511–524. An integrated mathematical programming approach is developed for the determination of the cost optimal heat exchanger network for multipurpose batch chemical plants. A single step, interactive computer program (BatcHEN) which is developed for the determination of the campaigns (i.e. the set of products which can be produced simultaneously), the heat exchange areas of all possible heat exchangers in the campaigns and finally the heat exchanger network are all discussed. A matrix search algorithm is used for the determination of the campaigns. Heat exchange areas for the possible heat exchangers are found by solving a nonlinear optimization model with a grid search algorithm.

(32) Braun JE, Klein SA, Mitchell JW. Effectiveness models for cooling towers and cooling coils. ASHRAE Trans 1989;95(2);164-74. This study of the operation of cooling towers shows how they can be realistically modeled with Thermoptim, and to use such a model to demonstrate their interest by comparing the energy performance of two industrial refrigeration cycles, one using an air condenser, and the other a direct contact cooling tower

(33) Briones, V.; Kokossis. A. A New Approach for the Optimal Retrofit of Heat Exchanger Networks. Comput. Chem. Eng. 1996, 20 (Suppl.). S43-S48. This approach for HENS retrofit employs pinch priorities and targets in mathematical programming techniques for an automated method.

(34) Briones, V.: Kokossis, A. C. Hypertargets: A Conceptual Programming Approach for the Optimisation of Industrial Heat Exchanger Networks—1. Grassroots Design and Network Complexity. Chem. Eng. Sci. 1999, 54, 519-539. A sequential HENS method is proposed in which an area target model is used in the determination of matches. Hypertargets rather than supertargets are used to find HRAT. A network topology formulation is also presented.

(35) Briones. V.; Kokossis, A. C. Hypertargets: A Conceptual Programming Approach for the Optimisation of Industrial Heat Exchanger Networks—II. Retrofit Design. Chem. Eng. Sci. 1999. 54,541-561. An existing HEN is audited for possible modifications, and then these modifications are screened using MILP models. The hypertarget concepts (annotation 47) are applied to retrofit HENS.

(36) Briones, V.; Kokossis, A. C. Hypertargets: A Conceptual Programming Approach for the Optimisation of Industrial Heat Exchanger Networks—111. Industrial Applications. C/iem. Eng. Sci. 1999, 54. 685-706. Solutions and analyses of industrial examples for the conceptual programming approach for grassroots (annotation 47) and retrofit (annotation 48) HENS are presented.

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(37) Bulatov I. Plate fin heat exchanger network retrofit procedure. International Journal of Heat Exchangers, 2004, 5(2):315–336. The retrofit procedure gains insights from a grassroots design method that has recently been developed and applies a retrofit matrix approach to obtain volume distribution for new operating conditions. The procedure applies two sets of heat transfer conditions for existing and additional volumes. New volume heat transfer conditions are optimised during the procedure, so there is no need to use pre-assumed coefficients, as it is the case with previous design and retrofit methods. The procedure also takes into account pressure drop considerations.

(38) Bulatov I. Retrofit optimization framework for compact heat exchangers. Heat Transfer Engineering, 2005, 26(5):4–14. The framework covers both levels: single exchanger unit and the exchanger network. This retrofit framework builds on a grassroots design method that has recently been developed and applies a retrofit matrix approach to obtain volume distribution for new operating conditions. Two sets of heat transfer coefficients, those for existing and additional volumes, are used. New volume heat transfer conditions are optimized during the procedure; thus, no pre-assumed coefficients are used, as is the case with previous design and retrofit methods. Pressure drop parameters crucially important for this sort of equipment are also incorporated into the optimization framework.

(39) Burger R. Select the right cooling tower fill. Hydrocarbon Process 1994;73:141-3. Because there are so many types of internal fills available, it is important to choose the correct one when repairing or revamping a cooling tower. In selecting fill or a new cooling tower configuration, check with a consultant who has experience with all of the different types of manufacturers and cooling tower internal elements. This is because some fill manufacturers produce performance curves claiming superior heat-transfer qualities. These claims are often backed by test procedures and data that are difficult for a user to verify. Whether or not these qualities are accurately portrayed, it is a good idea to thoroughly investigate past performance so the installation is not an on-the-job testing site. The paper discusses using a consultant, cooling tower basics, how fill cools, cellular fill, selection criteria, alternate fills, three case histories, and performance penalties.

(40) Carlsson, A.; Franck, P.; Berntsson, T. Design Better Heat Exchanger Network Retrofits. C/iem. Ene. Pros. 1993, 89(3), 87-96. A method of retrofit HEN design based on pinch technology is presented.

(41) Castro, M. M. Pinto, J. M. and Song, T. W., 2000, Operational cost minimization in cooling water system. Braz J Chem Engg., 17(4):4-7. In this work, an optimization model that considers thermal and hydraulic interactions is developed for a cooling water system. It is a closed loop consisting of a cooling tower unit, circulation pump, blower and heat exchanger-pipe network. Aside from process disturbances, climatic fluctuations are considered. The results corroborate the fact that the most important variable on cooling tower performance is not the air temperature itself, but its humidity

(42) Cerda, J.; Galli, M. R. Synthesis of Flexible Heat Exchanger Networks—11. Nonconvex Networks with Large Temperature Variations. Comput. Chem. Eng. 1990, 14(2), 213-225. Large temperature disturbances in HENS lead to nonconvexities due to "pinch jumps". The synthesis algorithm and the MILP formulation (annotation 56) are generalized and modified to account for these nonconvexities.

(43) Cerda, J.; Galli, M. R.; Camussi, N.; Isla, M. A. Synthesis of Flexible Heat Exchanger Networks—I. Convex Networks. Comput. Chem. Eng. 1990, 14(2), 197-211. An MILP formulation for a pinch-based design procedure for convex flexible HENs which accounts for inlet temperature variations only is proposed. Forbidden match constraints are included.

(44) Chakraborty, S.; Ghosh. P. Heat Exchanger Network Synthesis: The Possibility of Randomization. Chem. Eng. J. 1999. 72. 209-216. A HENS approach based on randomly sampling points from the problem space consisting of all possible networks is presented. This algorithm does not allow for stream splitting.

(45) Chang, C.-T.; Chu, K.-K.; Hwang, J.-R. Application of the Generalized Stream Structure in HEN Synthesis. Comput. Chem. Eng. 1994. 18(4). 345-368. The formulations for minimum utilities cost and the minimum number of units for sequential HENS are modified to allow for merging of process streams when it is an option in a process. An NLP formulation for network derivation is developed.

(46) Chen C.L. and Hung P.S. Multicriteria synthesis of flexible heat-exchanger networks with uncertain source-stream temperatures. Chemical Engineering & Processing, 2005, 44(1):89–100. A multi-criteria synthesis strategy for heat-exchanger networks (HENs) simultaneously considering minimum utility consumption, maximum source-stream temperature flexibility, and even minimum number of matches is proposed. The flexible HEN synthesis problem is formulated as a multi-objective

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mixed-integer linear programming (MO-MILP). For handling the multiple conflict design targets, a two-phase fuzzy multi-criteria decision-making method is presented to attain a best compromised solution.

(47) Ciric. A. R.; Floudas, C. A. A Comprehensive Optimization Model uf the Heat Exchanger Network Retrofit Problem. Heat Recovery Syst. CHP 1990, 10 (4), 407-422. This paper presents an MINLP formulation of the retrofit HENS problem. Match-exchanger assignments are allowed to be made on the basis of actual area requirements rather than estimates. The MINLP for-mulation of the problem is solved using generalized Benders decomposition.

(48) Ciric. A. R.; Floudas, C. A. A Mixed Integer Nonlinear Programming Model for Retrofitting Heat Exchanger Networks, hid. Eng. Cliem. Res. 1990, 29(2), 239-251. The retrofit HENS method involves an MINLP formulation that selects process stream matches and match-exchanger assignments while simultaneously optimizing the network structure. It allows for match-exchanger assignments to be made on the basis of actual area requirements, as opposed to estimates of area and piping costs. The MINLP formulation is solved using the generalized Benders decomposition algorithm.

(49) Ciric, A. R.; Floudas, C. A. Application of the Simultaneous Match—Network Optimization Approach to the Pseudo-Pinch Problem. Comput. Chem. Eng. 1990. 14(3), 241-250. This paper proposes using three temperature approaches to formulate the pseudo-pinch problem for simultaneous match-network optimization.

(50) Ciric. A. R.; Floudas, C. A. Heat Exchanger Network Synthesis without Decomposition. Comput. Chem. Eng. 1991. 15 (6), 385-396. The simultaneous optimization of utilities, number of matches, and network configuration using PPDMs and strict PDMs is described in this paper. An MINLP formulation using the hyperstructure of Floudas and Ciric (annotation 101) is solved using generalized Benders decomposition.

(51) Cisternas L. A., Guerrero C. P. and Swaney R. E. Separation system synthesis of fractional crystallization processes with heat integration. Computers & Chemical Engineering, May 2001, 25(4-6):595–602. A methodology is presented for the synthesis of fractional crystallization processes. The methodology is based on the construction of four networks. The first network is based on the identification of feasible thermodynamic states. In this network the nodes correspond to multiple saturation points, solute intermediate, process feeds and end products. The second network is used to represent the variety of tasks that can be performed at each multiple saturation point. These tasks include cooling crystallization, evaporative crystallization, reactive crystallization, dissolution, and leaching. Heat integration is included using a heat exchanger network which can be regarded as a transhipment problem. The last network is used to represent filtration and cake washing alternatives. The cake wash and task networks are modelled using disjunctive programming and then converted into a mixed integer program

(52) Colberg, R. D.; Morari, M. Area and Capital Cost Targets for Heat Exchanger Network Synthesis with Constrained Matches and Unequal Heat Transfer Coefficients. Comput. Chem. Eng. 1990, 14(1), 1-22. This paper presents two transshipment NLP formulations to calculate the area target and capital cost target for HENS problems. Given any specified number or set of matches and different heat-transfer coefficients and cost laws, this method is designed to predict the tradeoff between area or cost and the number of matches and the effect of forbidden matches upon the minimum area or cost. The solution provides the area or cost target, temperature profiles for each stream, and distribution of heat loads and areas among specific matches.

(53) Cortinovis GF, Ribeiro MT, Paiva Jl, Song TW, Pinto JM. Integrated analysis of cooling water systems: Modeling and experimental validation. Appl Therm Eng 2009. doi:10.1016j/j.applthermaleng.2009.04.008. Integrated analysis of cooling water systems has been performed. Modeling and experimental validation has been done.

(54) Corominas, J.; Espuna. A.; Puigjaner, L. A New Look at Energy Integration in Multiproduct Batch Processes. Comput. Chem. Eng. 1993. //(Suppl.). S15-S20. A method for developing a HEN for a multiproduct batch plant is developed. The concept of a macronetwork is introduced to account for different campaigns of different products.

(55) Corominas, J.; Espuna, A.; Puigjaner, L. Method to Incorporate Energy Integration Considerations in Multiproduct Batch Processes. Comput. Chem. Eng. 1994. 18 (11/12), 1043-1055. Energy integration for a multiproduct batch plant is addressed with heuristic procedures for shifting the timing of operations to facilitate energy savings.

(56) Correa, D. J. Area Determination of Heat Exchanger Networks Using Dynamic Simulation. Heat Transfer Eng. 1998, 19 (4), 22-28. A method for using a dynamic simulator for determining the minimum overdesign of exchanger areas is presented. This technique used control algorithms in a nonconventional manner in order to design operable networks.

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(57) Daichendt. M. M.; Grossmann, I. E. Preliminary Screening Procedure for the MINLP Synthesis of Process Systems— I. Aggregation and Decomposition. Comput. Chem. Ens. 1994, IS (S), 663-677. A synthesis framework based on aggregation and decomposition for preliminary screening is presented. This procedure is applied to heat-integrated distillation sequences in this paper. The procedure eliminates a subset of suboptimal alternatives from the problem to yield a reduced superstructure.

(58) Daichendt, M. M.; Grossmann. I. E. Integration of Hierarchical Decomposition and Mathematical Programming for the Synthesis of Process Flowsheets. Comput. Chem. Eng. 1997. 22(1-2). 147-175. A framework for the combination of hierarchical process decomposition with mathematical programming techniques is proposed for process flowsheet synthesis to simultaneously optimize the flowsheet at each level of decomposition.

(59) Deng, S. and Tan, K., 2003, A numerical analysis of heat and mass transfer inside a reversibly used water cooling tower. Build environ., 38(1): 91-97. In subtropical regions, a desuperheater heat recovery system for service hot-water heating can be applied. However, in colder seasons when building cooling load is reduced, a standard water-cooling tower may be reversibly used to extract free heat from ambient air to make up the reduction of heat source for water heating. Previous related work included developing an analytical method for evaluating the heat and mass transfer characteristics in a reversibly used water-cooling tower (RUWCT), which cannot be used to determine the air d water states at any intermediate horizontal sections along the tower height within an RUWCT. This paper presents a detailed numerical analysis by which the air and water states at any horizontal plane along the tower height within an RUWCT can be determined.

(60) Dipama J., Teyssedou A., and Sorin M. Synthesis of heat exchanger networks using genetic algorithms. Applied Thermal Engineering, 2008, 28(14-15):1763–1773. This paper presents a methodology for carrying out both the synthesis and the optimization of heat exchanger networks (HEN) based on a genetic algorithm (GA) technique. The proposed methodology allows the topology of the HEN and the heat load distribution that satisfy an energy target to be obtained from a single pass calculation. The technique is characterized by a high reliability in determining the best HEN structure. In addition, it also allows the generation of several HEN configurations to be obtained; thus, a best HEN selection in accordance to a given application can be easily achieved. The proposed approach permits the HEN topology to be obtained only if flow stream divisions are avoided.

(61) Dong H. G., Lin C. Y., and Chang C. T. Simultaneous optimization strategy for synthesizing heat exchanger networks with multi-stream mixers. Chemical Engineering Research & Design, 2008, 86(3):299– 309. A systematic procedure is proposed in this paper to incorporate the options of merging and/or splitting process streams from multiple origins in heat exchanger network (HEN) design. The utility and capital costs of a traditional HEN may both be reduced significantly with this practice since: (1) the direct heat-exchange operations are more efficient thermodynamically, (2) the mixers are in general less expensive than the indirect heat-transfer units, and (3) the matches between hot and cold streams can be more appropriately placed by taking advantage of the added structural flexibility. A state-space concept is adopted in this work to construct a superstructure for capturing the characteristics of network configuration. More specifically, any HEN (with or without multi-stream mixers) is viewed as a collection of two interconnected blocks, i.e., the process operator and the distribution network. A mixed integer nonlinear program (MINLP) is then formulated accordingly for one-step minimization of the total annualized cost. Based upon the proposed stochastic initiation strategy and solution clustering method, an efficient algorithm is developed to obtain the global optimum of this MINLP model with high creditability. Several examples are also presented to demonstrate the feasibility and benefits of the proposed approach.

(62) Foo D. C. Y., Chew Y. H., and Lee C. T. Minimum units targeting and network evolution for batch heat exchanger network. Applied Thermal Engineering, 2008, 28(16):2089–2099. Process integration techniques have been widely accepted as an effective tool in synthesising a cost optimal heat exchanger network (HEN). However, most works on HEN synthesis have mainly focused on continuous processes. Much less work has been carried out for the synthesis of batch HEN. This paper extends the minimum units targeting and network evolution techniques that were developed for batch mass exchange network (MEN) into batch HEN.

(63) El-Dessouky H T A, Al-Haddad A, Al-Juwayhel F. A modified analysis of counter flow wet cooling towers. J Heat Transfer 1997; 119:617-26. The paper describes a theoretical investigation for the steady-state counter flow wet cooling tower with modified definitions for both the number of transfer units and the tower thermal effectiveness. The modified number of transfer units is dependent on both air and water heat capacity. The effectiveness is defined by the tower cooling range and the approach to equilibrium. A new expression relating the tower effectiveness to the modified number of transfer units and the capacity rate ratio has been developed

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(64) Facao J, Oliveria A. Heat and mass transfer correlations for the design of small indirect contact cooling towers. Appl Therm Eng 2004; 24:1969-78. A detailed analysis of mass transfer coefficient and spray heat transfer coefficient correlations is made including the effect of the error in their evaluation on tower efficiency.

(65) Farhanieh, B.; Sunden. B. Analysis of an Existing Heat Exchanger Network and Effects of Heat Pump Installations. Heat Recovery Syst. CHP 1990, 10 (3), 285-296. An existing refinery HEN is analyzed using both grassroots via PDM and retrofit design methods in this case study. The integration of heat pumps into the HEN is also investigated.

(66) Floudas. C. A.; Pardalos, P. M. A Collection of Test Problems for Constrained Global Optimization Algorithms; Lecture Notes in Computer Science No. 455; Springer-Verlag: Berlin, 1990. This collection includes several HENS test problems presented in the network configuration or simultaneous match—network formulations along with best known solutions at the time of publication.

(67) Fraga E. S. and Zilinskas A.. Evaluation of hybrid optimization methods for the optimal design of heat integrated distillation sequences. Advances in Engineering Software, February 2003, 34(2):73–86. Optimal process design often requires the solution of mixed integer non-linear programming problems. Optimization procedures must be robust and efficient if they are to be incorporated in automated design systems. For heat integrated separation process design, a natural hybrid evolutionary/local search method with these properties is possible. The method is based on the use of local search methods for the continuous design parameters for the units in the process and the use of an evolutionary optimization procedure for the design of the heat exchanger network. The use of a stochastic method for the heat exchanger network aspect introduces noise in the evaluation of the objective function used by the local search methods. A smoothing procedure has been designed and implemented to improve the efficacy of the hybrid approach.

(68) Fraser, D. M.; Cillespie, N. E. The Application of Pinch Technology to Retrofit Energy Integration of an Entire Oil Refinery. Chem. Eng. Kes. Des. 1992, 70. 395-406. Pinch technology is used to analyze the possibilities for savings for the retrofit of an oil refinery.

(69) Gadalla M., Olujic Z., Sun L., De Rijke A., and Jansens P. J. Pinch Analysis-Based approach to conceptual design of internally Heat-Integrated distillation columns. Chemical Engineering Research & Design, August 2005, 83(8):987–993. Incorporated appropriately into the overall design procedure, pinch analysis enables a fast approach to an optimum thermal performance, while bringing new insights and improving the understanding of the nature of HIDiC designs. As illustrated by using a state of the art propylene splitter as the base case, this approach emerged into an essential tool for the identification of economically interesting configurations for HIDiC applications.

(70) Galli, M. R.; Cerda. J. Synthesis of Flexible Heat Exchanger Networks—III. Temperature and Flowrate Variations. Comput. Chem. Eng. 1991. 75(1), 7-24. The sequential synthesis of flexible HENs is accomplished with a general algorithmic approach which includes modifying previous mathematical formulations of target problems to account for uncertainties in inlet temperatures and flow rates of streams.

(71) Galli, M. R.; Cerda, J. A Customized MILP Approach to the Synthesis of Heat Recovery Networks Reaching Specified Topology Targets. Ind. Eng. Chem. Res. 1998, 37,2479-2495. An MILP sequential synthesis strategy is proposed for HENS that allows the designer to specify desired topology features as design targets. This model allows no dual stream activity, has only isothermal mixing of split streams, and allows no bypasses and no split streams flowing through more than one heat exchanger.

(72) Galli, M. R.; Cerda, J. A Designer-Controlled Framework for the Synthesis of Heat Exchanger Networks involving Non-Isothermal Mixers and Multiple Units over Split Streams. Comput. Chem. Eng. 1998, 22 (Suppl.), S813-S816. A sequential synthesis method allowing the designer to specify restrictions on network topology is formulated as a set of MINLP constraints, with the first objective function for determining the minimum utilities cost and the second for the minimum number of units (matches).

(73) Galli, M. R.; Cerda, J. Synthesis of Structural-Constrained Heat Exchanger Networks—I. Series Networks. Comput. Chem. Eng. 1998, 22(7-8), 819-839. A three-stage framework for sequential HENS is proposed for the design of a network with specified structural conditions. MILP formulations are proposed in which all three stages have nearly the same constraint set with objective functions for constrained utility usage, heat recovery target for the upper network, and minimum number of units (matches) for upper and lower networks.

(74) Galli M. R. and Cerdá J.. Retrofit of heat exchanger networks with topology changes under designer control. Latin American Applied Research, 2001, 31(4):247–254. The problem goal is to minimize the total network retrofit cost including those related to manpower for

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moving exchangers to other sites, re-piping, purchasing of new units and/or additional area for existing exchangers. Non-linearity of the exchanger design equation has been overcome by fixing the temperature driving force in each exchanger at some specified minimum value and developing a computationally efficient iterative solution procedure. At each iteration, temperature driving forces are properly updated and the resulting MILP problem is subsequently solved until convergence is achieved. In this way, a MILP-based methodology has been derived and applied to the retrofit of existing networks under different user-specified topology restrictions.

(75) Glavic P. Complex integration of processes. The Canadian Journal of Chemical Engineering, 2001, 79(4):643–654. Pinch analysis is nowadays a practical tool for designing heat exchanger networks in chemical and process industries. Rules for integrating process units have also been worked out in the last decade or two. Process units can be described as different types of energy unit operations, donors and acceptors. Yet, heat integration alone is not sufficient for process integration. The largest savings are achieved when simultaneously optimizing enthalpy and mass flows energy and material recycling is required to save the natural resources and protect the nature. Mathematical programming is increasingly used to optimize the problems both in continuous and batch operations. Task integration is spreading out: multifunctional units lower the capital investment, thus, the total annual cost. Recent development of the complex integration with examples and reasonable forecast of the future development is presented in the paper.

(76) Grossmann, I. E.; Caballero, J. A.; Yeomans, H. Mathematical Programming Approaches to the Synthesis of Chemical Process Systems. Korean J. Chem. Eng. 1999, 16(4), 407-426. This is a review of advances in process synthesis using mathematical programming approaches. HENS is a specific topic covered in this review.

(77) Grossmann, I. E.; Daichendt, M. M. New Trends in Optimization-Based Approaches to Process Synthesis. Comput. Chem. Eng. 1996. 20(6/7). 665-683. An overview of optimization-based design work as well as a list of research challenges for process synthesis is presented in this paper.

(78) Grossmann, I. E.; Kravanja. Z. Mixed-Integer Nonlinear Programming Techniques for Process Systems Engineering. Comput. Chem. Eng. 1995, 19 (Suppl.), S189-S204. This is an overview of MINLP techniques used in process design and optimization. Topics include branch and bound, outer approximation, generalized Benders decomposition, and the extended cutting plane. Extensions of MINLP methods and logic-based methods are covered. Lists of references for different applications, including HENS, are provided.

(79) Grossmann, I. E.; Yeomans, H.; Kravanja, Z. A Rigorous Disjunctive Optimization Model for Simultaneous Flowsheet Optimization and Heat Integration. Comput. Chem. Eng. 1998, 22 (Suppl.), S157-S164. The difficulties of the simultaneous process flowsheet optimization and heat integration model of Duran and Grossmann are analyzed, and a new disjunctive model is proposed. The MINLP reformulation of the disjunctive model is given, and this model is reduced to MILP when only isothermal streams are involved.

(80) Gulyani, B. B.; Mohanty, B. Heat Recovery Network Design: Graphical Algorithm for Heat- Recovery from Flue Gas. Indian Chem. Eng. 1999, 41 (2), 117-120. The authors devise a simple graphical algorithm for designing a heat recovery network using flue gas based on reduced temperature rectangles.

(81) Gundersen, T.; Duvold, S.; Hashemi-Ahmady, A. An Extended Vertical MILP Model for Heat Exchanger Network Synthesis. Comput. Chem. Eng. 1996, 20(SupplJ, S97-S102. The vertical MILP model for determining the minimum number of matches for a HEN is extended to address the pairing effect caused by streams with poor film heat-transfer coefficients.

(82) Gundersen, T.; Grossmann, I. E. Improved Optimization Strategies for Automated Heat Exchanger Network Synthesis through Physical Insights. Comput. Chew. Eng. 1990, 14(9), 925-944. A vertical MILP transshipment model is developed using physical insights. This model discriminates be-tween sets of matches among hot and cold streams that achieve the same number of units and the same level of heat recovery in which area cost differs. The proposed vertical MILP transshipment model, which is a modification of the model of Papoulias and Grossmann, uses a combination of energy intervals and temperature intervals.

(83) Gundersen, T.; Sagli, B.; Kiste, K. Problems in Sequential and Simultaneous Strategies for Heat Exchanger Network Synthesis. In Computer-Oriented Process Engineering; Puigjaner, L., Espufia. A., Eds.; Elsevier: Amsterdam, The Netherlands, 1991; pp 105-116. This paper compares pinch technology and sequential synthesis with simultaneous MINLP HENS. A case study is used as a basis for the comparison, and the limitations of each method are discussed.

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(84) Hall, S. G.; Ahmad, S.; Smith, R. Capital Cost Targets for Heat Exchanger Networks Comprising Mixed Materials of Construction, Pressure Ratings and Exchanger Types. Comput. Chem. Eng. 1990, 14(3). 319-335. A method for the prediction of capital cost targets for HENs with mixed materials of construction and mixed pressure ratings is proposed.

(85) Hamed, 0. A.; Aly. S. Optimal Synthesis of a Heat-Exchanger Network. Int. J. Energy Res. 1991, 15. 31-39. A HEN is designed for a crude fractionation unit. The concentration of this paper is application of techniques for supertargeting the approach temperature.

(86) Hamed, 0. A.; Aly, S.; Abu-Khousa, E. Heuristic Approach for Heat Exchanger Networks. Int. J. Energy Res. 1996, 20 (9), 797-810. A heuristic approach to HENS based on pinch technology is developed. It involves three sequential steps. In the preanalysis step, targets are obtained. In the network invention step, the minimum total area is determined. In the evolution step, heat loops are sought and broken to achieve the target minimum number of units. Many different rules and methods previously developed for HENS are incorporated into this heuristic approach.

(87) Han, Z.; Zhu, J.; Rao. M.; Chuaiig. K. T. Determination of Independent Loops in Heat Exchanger Networks. Chem. Eng. Commun. 1998. 164. 191-204. An algorithm for locating independent loops in HENs by generating a maximal tree for a given graph and adding edges to the tree is proposed. The set of independent loops produced by the algorithm is proven to be a maximal set of independent loops.

(88) Heikkila, P. and Milosavljevic, N. 2001, A comprehensive approach to cooling tower design. Appl Thermal Eng, 21(9): 899-915. In this paper, a mathematical model for counterflow wet cooling tower is derived, which is based on one dimensional heat and mass balance equations using measured heat transfer coefficient.

(89) Hirnsworth, J. R.; Cooper, A. C. G. Supercharged Heat Exchanger Networks. Chem. Eng. Res. Des. 1993, 71 (A), 203-211. A supercharger, an expander which is coupled directly to a compressor, can be used to enhance the performance of a HEN.

(90) Hu, S.; Chen, B.; Shen, J. Nonconvex Feasible Region of Heat Exchanger Networks with Uncertain Stream Parameters. Chin. J. Chem. Eng. 1993, / (2), 74-83. The infeasible hole property of the nonconvex feasible region in HENS is identified. Based on this property, a procedure for flexibility analysis is developed and applied to an example.

(91) Hu, S.; Chen, B.; Shen, J. Pinch Analysis of Heat Exchange Problems with Uncertain Parameters. Tsinghua Sci. Techno 1997. 2(4). 777-782. A reduced temperature interval method is introduced in order to allow pinch analysis for HENS problems with uncertain parameters.

(92) Huang, Y. L.; Fan, L. T. Distributed Strategy for Integration of Process Design and Control—A Knowledge Engineering Approach to the Incorporation of Controllability into Exchanger Network Synthesis. Comput. Chem. Eng. 1992, 16 (5), 497-522. A knowledge engineering based approach for the synthesis of optimal and controllable HENS and MEN S is proposed.

(93) Hui, C. W.; Ahmad, S. Minimum Cost Heat Recovery between Separate Plant Regions. Comput. Chem. Eng. 1994, 18 (8), 711-728. The tradeoff between energy, exchanger capital, and the number of interconnections concerning the heat recovery among several regions of a plant is analyzed. A design procedure for developing a more integrated HEN for a total process plant is outlined.

(94) Hui. C. W.; Ahmad, S. Total Site Integration Using the Utility System. Comput. Chem. Eng. 1994, 18 (8), 729-742. Heat integration between different chemical processes in a plant are addressed using the pinch technology targeting methods for optimizing the common utility system.

(95) Isafiade A. J. and Fraser D. Optimization of combined heat and mass exchanger networks using pinch technology. Asia-Pacific Journal of Chemical Engineering, 2007, 2(6):554–565. This article examines the benefits that may be obtained by combining the optimisation of heat and mass exchanger networks. This study uses a Pinch Technology approach to the targeting of Combined Heat and Mass Exchanger Networks (CHAMENs), and illustrates it with application to three examples. The first example has just one external mass separating agent (MSA), the second has both process and external MSAs, and the third is an extension of the second with a heat exchanger network integrated. The major benefits arise when it is possible to cool the process MSA with an excess capacity to remove mass. This reduces the flowrate of the external MSA (since this exists below the pinch) and can even do away

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entirely with the need for it. This also leads to a reduction in the capital cost requirements of both the process and the external MSAs, as well as a reduction in regeneration costs. The implication of this is that a limitation to the use of the available capacity of process MSAs is their mass exchange temperature. It was also found (in the example in which hot/cold utilities are used to enhance mass exchange) that the mass exchanger network synthesis (MENS) costs generally dominate over the heat exchanger network synthesis (HENS) costs.

(96) Ivanov, B.; Peneva, K.: Bancheva. N. Heat Integration of Batch Vessels at Fixed Time Interval I. Schemes with Recycling Main Fluids. Hung. J. hid. Chem. 1992, 20. 225-231. NLP mathematical models are proposed for heat integration of batch processes in the case where fluids may be removed and returned to the vessels.

(97) Ivanov, B.; Peneva, K.; Bancheva. N. Heat Integration in Batch Reactors Operating in Different Time Intervals Part-I. A Hot-Cold Reactor System with Two Storage Tanks. Hung.}. Ind. Chem. 1993, 21, 201-207. A mathematical model for heat integrating a hot and cold batch vessel operating in different time intervals utilizing two heat storage tanks is presented.

(98) Ivanov, B.; Peneva, K.: Bancheva, N. Heat Integration in Batch Reactors Operating in Different Time Intervals Part-II. A Hot-Cold Reactor System with a Common Storage Tank. Hung. J. Ind. Chem. 1993, 21, 209-216. Mathematical models for heat integrating two batch vessels operating in different time intervals using a common heat storage tank are presented.

(99) Ivanov, B.; Peneva, K.; Vaklieva-Bancheva, N. Synthesis of Heat Exchange Networks for Hot-Cold Batch Reactor Systems. Hung. J. Ind. Chem. 1995, 23. 251-260. NLP mathematical models including several configurations for HENS incorporating a hot and a cold batch reactor in a fixed time interval are formulated.

(100) Jaber, H. and Webb, R. L., 1989, Design of cooling towers by the effectiveness-NTU method, J. Heat transfer, 111(4); 837-843. This paper develops the effectiveness and NTU design method for cooling towers. Sample calculations are presented for counter and crossflow cooling towers

(101) Jegede, F. 0., Polley. G. T. Capital Cost Targets for Networks with Non-Uniform Heat Exchanger Specifications. Comput. Chem. Eng. 1992, 16 (5), 477-495. The authors develop a modification of the pinch design targeting methods to allow for nonuniform exchanger specifications which can have a major impact on the capital cost of a HEN. The use of an exchanger classification table is suggested as a tool to aid in the design of a HEN in this manner.

(102) Jezowski, J. Selected Problems of Heat Exchanger Network Synthesis. Hung. J. Ind. Chem. 1982, 10, 345-356. Two assignment task based algorithms are developed in an attempt to overcome some of the drawbacks of the evolutionary approach in HENS for minimizing the number of matches.

(103) Jezowski, J. A Simple Synthesis Method for Heat Exchanger Networks with Minimum Number of Matches. Chem. Eng. Sci. 1990, 45(7). 1928-1932. A simple method is proposed for designing a HEN with pinch crossing matches allowing the designer to decide prior to synthesis which streams will be contacted in pinch crossing matches. This method does not require a loop-breaking algorithm.

(104) Jezowski, J. Linear Programming Based Method of Heat Exchanger Network Synthesis. Inz. Chem. Proc. 1990. // (1), 299-312. A sequential synthesis algorithm using LP to allow calculations on small computers is outlined.

(105) Jezowski, J. A Note on the Use of Dual Temperature Approach in Heat Exchanger Network Synthesis. Comput. Chem. Eng. 1991, 75(5). 305-312. It is shown that although the use of the DTAM may cause cross-pinching, the "no criss-crossing" rule of the PDM is an unnecessary limitation. A simple method using the DTAM stemming from physical insights for HENS is presented.

(106) Jezowski, J. On Match Calculation in Heat Exchanger Network Synthesis. Int. Chem. Proc. 1991, 12(2), 203-215. A method for calculating heat load distributions while meeting the minimum number of units target in pinch design is proposed.

(107) Jezowski, J. SYNHEN: Microcomputer Directed Package of Programs for Heat Exchanger Network Synthesis. Comput. Chem. Eng. 1992, 16 (7). 691-706. The computer package SYNHEN is described. SYNHEN is a combination of dual temperature pinch design and mathematical programming methods for sequential HENS. An evolution-based approach is used for the actual network design level step.

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(108) Jezowski, J. The Pinch Design Method for Tasks with Multiple Pinches. Comput. Chem. Eng. 1992, 16 (2). 129-133. A method for HENS is proposed that uses the PDM with multiple pinches without using the "inverse pinch" of Trivedi et al.

(109) Jezowski, J. Heat Exchanger Network Grassroot and Retrofit Design. The Review of the State-of-the-Art: Part I. Heat Exchanger Network Targeting and Insight Based Methods of Synthesis. Hung. J. Ind. Chem. 1994. 22, 279-294. This is the first in an extensive two-part review paper on HENS. This part is primarily concerned with topics including the PDM, DTAM, various HENS targets, and supertargeting.

(110) Jezowski, J. Heat Exchanger Network Grassroot and Retrofit Design. The Review of the State-of-the-Art: Part II. Heat Exchanger Network Synthesis by Mathematical Methods and Approaches for Retrofit Design. Hung. J. Ind. Chem. 1994. 22. 295-308. This second part of an extensive HENS review primarily covers mathematical methods for HENS. Some major topics covered are sequential synthesis, global or simultaneous synthesis, knowledge-based systems, and mathematical methods for retrofit network design.

(111) Jezowski, J.; Bochenek. R.; Jezowska, A. Pinch Locations at Heat Capacity Flow-Rate Disturbances of Streams for Minimum Utility Cost Heat Exchanger Networks. Appl. Therm. Eng. 2000, 20 (15-16), 1481-1494. The work deals with heat exchanger network (HEN) targeting under heat capacity flow-rates of streams disturbances. In particular, the aim is to calculate all pinches that can exist in a HEN with utilities of minimum cost when stream heat capacity flow-rates (CPs) are allowed to change within given ranges. It is assumed that the disturbances are stochastic. The knowledge of pinches at certain as well uncertain data is of great importance in designing HENs. For instance, Pinch Technology is based on pinch phenomenon and its influence on HEN operation and design. A rigorous approach has been developed for calculating all feasible locations of pinches that can occur in minimum utility cost of HENs operating at varying heat capacity flow-rates of process streams. The method is based on recursive solution of mixed-integer linear programming (MILP) optimisation model that requires quite moderate number of binary variables.

(112) Jezowski, J.; Friedler, F. A Simple Approach for Maximum Heat Recovery Calculations. Cnem. Eng. Sci. 1992, 47 (6), 1481-1494. The basic model is similar to the transshipment model of Papoulias and Grossmann. A basic algorithm with extensions for multiple utilities and forbidden matches is presented. The dual stream approach is included to increase the energy recovery in problems with forbidden matches. The basic algorithm is used to calculate the maximum residual heat flows for EMAT less than HRAT. This algorithm requires less computational effort than other pinch design algorithms.

(113) Jezowski, J.; Jezowska, A. Computer Aided Designing of Heat Exchanger Networks. Hung. J. Ind. Chem. 1997, 25 (2), 127-135. The HENS computer package HEATREC, in which TARGET and SIMHEN are included, is described. These programs apply pinch design for networks.

(114) Jezowski, J.; Jezowska, A. Some Remarks on Heat Exchanger Networks Targeting Under Uncertainty. Hung. J. Ind. Chem. 1999, 27 (1), 17-24. This paper provides an analysis of previously proposed methods for the design of flexible HENs.

(115) Jezowski, J. M.; Shethna. H. K.; Bochenek, R. J.; Castillo. F. J. L. On Extensions of Approaches for Heat Recovery Calculations in Integrated Chemical Process Systems. Comput. Chem. 2000. 24 (5). 595-601. The transshipment model for minimum utility cost calculation is extended for nonpoint utilities. A method is proposed for determining minimum utilities cost and pinch-point locations in the case of flow-rate disturbances. The work deals with heat exchanger network (HEN) targeting under heat capacity flow-rates of streams disturbances. In particular, the aim is to calculate all pinches that can exist in a HEN with utilities of minimum cost when stream heat capacity flow-rates (CPs) are allowed to change within given ranges. It is assumed that the disturbances are stochastic. The knowledge of pinches at certain as well uncertain data is of great importance in designing HENs. For instance, Pinch Technology is based on pinch phenomenon and its influence on HEN operation and design. A rigorous approach has been developed for calculating all feasible locations of pinches that can occur in minimum utility cost of HENs operating at varying heat capacity flow-rates of process streams. The method is based on recursive solution of mixed-integer linear programming (MILP) optimisation model that requires quite moderate number of binary variables.

(116) Jezowski J. M., Bochenek R., and Jezowska A. Loop breaking in heat exchanger networks by mathematical programming. Applied Thermal Engineering, October 2001, 21(13-14):1429–1448. In many cases heat exchanger network (HEN) designs require some changes aimed at reduction of units

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number. This is the case if a rule of division at pinches is applied in designing a HEN as e.g. in pinch analysis approaches. Matches at loops across pinches can be removed and the number of matches in a HEN goes down to the global minimum. Such elimination of units is commonly referred to as loop breaking.Several methods have been suggested for loop breaking. Existing approaches require iterative tedious computations. Moreover, since based on rules from insight into the problem they do not ensure optimal solutions.In this contribution we developed an approach that is based on mathematical programming. The aim is to minimise or to reduce number of units at the condition of minimum energy penalty. The optimisation model consists of relations determining HEN’s topology, heat and mass balances for each heat exchanger (including heaters and coolers) as well as splitters and mixers. Inequalities ensuring feasible heat exchange are included, too.In order to overcome difficulties with solving mixed-integer nonlinear (MINLP) optimisation problem we have decided to impose the condition of linearity for our model. Hence, goal function in optimisation does not account for total cost but the aim is to minimise number of matches and heat load of utilities. Furthermore, flow rates of streams have to be fixed. To relax constraint of fixed flow rates at splitters we have applied a concept of small superstructure that contains all types of arrangements for heat exchangers: parallel, serial and serial–parallel connections. This gives mean to simplify HEN’s topology by replacing parallel arrangement by serial one.Linear optimisation model developed by us accounts for inequality constraints for outlet streams temperatures. We applied EMAT value instead of HRAT. Some new matches can be inserted into a HEN by a designer to make topology changes possible.The optimisation model is of mixed-integer linear type and requires moderate number of binary variables. It can be easily extended in MINLP one that accounts for total cost. In this paper solutions for some literature examples are presented that proved validity of the approach and shows practical merits of the approach

(117) Jezowski J. M., Bochenek R., and Poplewski G. On application of stochastic optimization techniques to designing heat exchanger- and water networks. Chemical Engineering & Processing: Process Intensification, 2007, 46(11):1160–1174. The work addresses systematic simultaneous approaches to designing two process systems: heat exchanger network (HEN) and water network (WN). In both cases stochastic optimization techniques were applied, adaptive random search for WN and genetic algorithms for HEN. In the case of HEN design the approach is tailored for HEN retrofit and accounts for standard apparatus with discrete values of construction parameters. The aim of the paper is twofold. First, it is shown how a general problem analysis can be used for a choice of proper stochastic optimization approach to the problem. The second objective is to explain how to make use of optimization method properties and problem features to enhance efficiency and robustness of optimization. Water network design problem was solved with adaptive random search procedure applied as general-purpose optimizer for superstructure optimization model formulated in equation form. Genetic algorithms approach was applied for HEN retrofit. This is also simultaneous method based on superstructure optimization. Novel superstructure and structure representations were developed to enhance the optimization. The examples of application proved that both approaches allow reaching best solutions from the literature or even better ones in some cases.

(118) Jin G Y, Cai W J, Lu L, Lee E L, Chiang A. Simplified modeling of mechanical cooling tower for control and optimization of HVAC systems. Energy Convers Manage 2007;48:355-65. This paper presents a simple mechanical cooling tower model for the purpose of energy conservation and management. It can be used to predict performance of real time tower.

(119) Jin Z., Dong Q., and Liu M. Heat exchanger network synthesis with detailed heat exchanger design. Chemical Engineering & Technology, 2008, 31(7):1046–1050. Pressure drop and fouling are important issues in heat exchanger network synthesis, which are usually neglected. Heat exchangers were designed in detail during the heat exchanger network synthesis, and pressure drop and fouling effects were taken into account. Pinch analysis combined with exergoeconomic analysis was used for determining optimal minimum approach temperature (ΔTmin) for heat exchanger network synthesis. Exergy consumption of heat transfer in HENs was calculated using a subsection integral on balanced composite curves. The heat transfer coefficients of all heat exchangers in the network were calculated iteratively to meet the requirements of optimal area and allowable pressure drops. The proposed method was applied to an industrial case. Numerical results indicate the importance of the detailed design of heat exchangers in HENs synthesis.

(120) Jin Z., Dong Q., and Liu M. Exergoeconomic analysis of heat exchanger networks for optimum minimum approach temperature. Chemical Engineering & Technology, 2008, 31(2):265–269. Heat exchanger networks (HENs) design for optimum minimum approach temperature was presented using exergoeconomic analysis. Cold and hot utilities were integrated with process streams into T-H plot to form the balanced composite curves based on pinch technology. Exergy consumption of heat transfer in HENs was calculated using subsection integral on balanced composite curves. Exergy consumption expense substituted the energy-consumption cost of utilities as operating cost. So the objective function

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based on exergoeconomics was proposed, which determined the optimum minimum approach temperature of HENs.Numerical results demonstrate the validity of the proposed approach. Some measures are helpful to decreasing energy consumption; meanwhile it reveals the energy essential of evolution and change in the process system

(121) Johns, W. R.; Williams, M. J. Cost-Optimal Heat Exchange Network Synthesis. ESC'APE-4; IChemE Symposium Series 133; Institution of Chemical Engineers: Rugby, England. 1994; pp 247-255. A technique based on the transportation algorithm is developed for solving HENS modeled as linearly constrained transportation problem with a nonconvex objective.

(122) Jung, S.; Lee, I.; Yang, D. R.; Chang, K. S. Synthesis of Maximum Energy Recovery Networks in Batch Processes. Korean J. Chem. Eng. 1994, // (3), 162-171. Heuristics are proposed for the maximum heat recovery in batch plants for cases of cocurrent and countercurrent heat exchange.

(123) Kaiser A S, Lucas M, Viedma A, Zamora B. Numerical model of evaporative cooling processes in a new type of cooling tower. Int J Heat Mass Transfer 2005;48:986-99. A numerical model for studying the evaporative cooling processes that take place in a new type of cooling tower (hydrosolar roof) has been developed.

(124) Kalitventzeff, B.; Marechal, F. Optimal Insertion of Energy Saving Technologies in Industrial Processes: A Web-Based Tool Helps in Developments and Co-ordination of a European R & D Project. Appl. Therm. Eng. 2000, 20 (15-16), 1347-1364. The web-based EXSYS II expert system for energy system design in process synthesis is described.

(125) Kemp, I. C. Applications of the Time-Dependent Cascade Analysis in Process Integration. Heat Recovery Syst. CHP 1990, 10 (4), 423-435. Cascade analysis is used in the design of heat-integrated batch process case studies.

(126) Kemp, I. C. Some Aspects of the Practical Application of Pinch technology Methods. Chem. Eng. Res. Des. 1991, 69 (6), 471-479. Some of the more generally useful advances in the PDM are reviewed and their use by process engineers for different practical situations is suggested.

(127) Khan J.U.R., M. Yaqub, S. M. Zubair, Performance characteristics of counter flow wet cooling towers, Energy Conservation and Management 44 (2003) 2073-2091. In this paper a detailed model of counter flow wet cooling tower is used to investigate the performance chareteristics and validity of model is checked by experimental data reported in literature

(128) Kim J, Smith R. Cooling water system design. Chem Eng Sci 2001;56:3641-58. A methodology has been devised for design of cooling networks to satisfy any supply conditions for cooling tower

(129) Kim, K. Savulescu, L. and Smith, R., 2001, Design of cooling systems for effluent temperature reduction. Chem Eng Sci, 56(5): 1811-1830. The paper introduces methods for design of effluent cooling systems. An optimization model has been developed to search for the most economical design of cooling system.

(130) Kloppers C, Kroger G. Cooling tower performance evaluation: Merkel, Poppe and e-NTU methods of analysis. J Eng Gas Turb Power 2005;1271:1-7. The heat rejected and the water evaporated in mechanical and natural draft cooling towers are critically evaluated by employing the Merkel, Poppe and e-number-of-transfer-units(e-NTU) method of analysis, respectively, at different operating and ambient conditions. The importance of using a particular method of analysis when evaluating the performance characteristics of a certain fill material and subsequently employing the same analytical approach to predict cooling tower performance is stressed. The effect of ambient humidity and temperature on the performance of cooling towers employing the Merkel, e-NTU and Poppe methods of analysis are evaluated.

(131) Konukman A. E., Camurdan M., and Akman U. Simultaneous flexibility targeting and synthesis of minimum-utility heat-exchanger networks with superstructure-based MILP formulation. Chemical Engineering & Processing, July 2002, 41(6):501–518. The synthesis of Heat-Exchanger-Network (HEN) structures consuming minimum total utility and possessing a desired operational flexibility is accomplished via a non-iterative, superstructure-based, simultaneous-MILP formulation. The formulation presumes that the feasible region in the space of uncertain input parameters is convex. Thus, the optimal solution is explored based on the vertices of the polyhedral uncertainty region in the space of source-stream temperatures. The optimal value of the objective function is the lower bound of the total utility consumption for the HEN satisfying the targeted flexibility. When the target-flexibility value is set to zero, the optimal value of the objective function becomes equal to the minimum total-utility level as predicted by the application of the Pinch method to the HEN problem. The formulation is also used, with minor modifications, to compute the flexibility indexes of the synthesized HEN structures. The flexibility index of the HEN structure gives the upper

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bound for the target flexibility corresponding to the minimum level of the total utility consumption. Using a well-known HEN superstructure and a HEN problem, the formulation is solved successively, for increasing values of the targeted flexibility, to reveal the necessary structural modifications and their corresponding minimum-utility-consumption levels.

(132) Kovabvc, A.; Glavibvc, P. Retrofit of Complex and Energy Intensive Processes—I. Comput. Chem. Eng. 1995, 19 (12), 1255-1270. Thermodynamic and computational methods are combined for retrofit HENS. The grand composite and extended grand composite curves are used to eliminate unattractive structures. MINLP is used for optimizing the network using a superstructure.

(133) Kovabvc-Kralj, A.; Glavibvc, P. Retrofit of Complex and Energy Intensive Processes. Comput. Chem. Eng. 1997, 21 (Suppl.). S517-S522. A method to optimize retrofits in complex and energy-intensive coatinuous processes with sequential structural and parameter optimization is developed. This combined sequential approach performs a sequential retrofit of a superstructure obtained with pinch analysis, using the ASPEN PLUS material flow optimization and MINLP or NLP algorithms.

(134) Kovabvc-Kralj, A.; Glavibvc. P. Simultaneous Retrofit of Complex and Energy Intensive Processes—III. Comput. Chem. Eng. 2000, 24 (2-7), 1229-1235. The simultaneous structural and parameter optimization retrofit approach (annotation 115) is applied to a methanol plant case study.

(135) Kovabvc-Kralj, A.; Glavibvc, P.; Kravanja, Z. Retrofit of Complex and Energy Intensive Processes—II: Stepwise Simultaneous Superstructural Approach. Comput. them. Eng. 2000, 24(1). 125-138. The previous combined sequential approach (annotations 112 and 113) is extended to a stepwise simulta-neous and parameter optimization retrofit approach. The approach involves generating a superstructure by pinch analysis, formulating an MINLP model, and solving the relaxed NLP.

(136) Krajnc, M.; Glavibvc, P. Energy Integration of Mechanical Heat Pumps with Process Fluid as Working Fluid. Chem. Eng. Res. Des. 1992, 70 (7), 407-420. Pinch design techniques are employed in the integration of mechanical heat pumps with HENS.

(137) Krajnc, M.; Glavibvc, P. The Influence of Different Temperature Contributions on Heat Integrated Process Structure. Chem. Eng. Res. Des. 1995, 73 (A), 880-888. A comparison of different methods for determining temperature contributions to the minimum approach temperature is provided. Guidelines for determining which method to use in different cases are given.

(138) Kralj A. K. and Glavic P. Simultaneous retrofit of complex and energy intensive processes-III. Computers & Chemical Engineering, 2000, 24(2-7):1229–1235. A simultaneous structural and parameter optimization model of a total process was used to approach the global optimum solution of the retrofit. Simultaneous nonlinear programming (NLP) optimization can be applied to a complex industrial process giving more economical and profitable operation. The NLP model with variable flow rates of all the streams in different structures has been chosen. The problem has been how to handle the additional effect of nonconvexities, which prevent the problem being converged. The NLP algorithm, which was included as the additional technique using a possibility of minimum variable-error with a lower upper bound in mass and energy balances, was easier to solve. The NLP model of an existing methanol plant has been extended with the process separation section.

(139) Kravanja. Z.: Glavibvc, P. Cost Targeting for HEN through Simultaneous Optimization Approach: A Unified Pinch Technology and Mathematical Programming Design of Large HEN. Comput. Chem. Eng. 1997, 21 (8), 833-853. Simultaneous process flowsheet and HEN optimization is carried out using direct search optimization and implicit modeling in the simultaneous optimization step and an aggregated NLP model for the final HEN design. Match-dependent area targeting for capital costs of the HEN is applied in the simultaneous step.

(140) Kuzichkin, N. V.; Viktorov. V. K. A Thermodynamic Euristic Method for the Synthesis of Optimal Thermal Systems. Theor. Found. Chem. Eng. 1998. 32(6). 577-581. Two heuristic criteria for application to a sequential combinatorial method are explored.

(141) Lababidi. H. M. S.: Alatiqi. I. M.; Nayfeh. L. J. Energy Retrofit Study of an Ammonia Plant. Appl. Therm, Eng. 2000, 20(15-16), 1495-1503. A retrofit study of an ammonia plant is performed using pinch technology.

(142) Lakshmanan. R.; Bariares Alcantara. R. A Novel Visualization Tool for Heat Exchanger Network Retrofit. Ind. Eng. Chem. Res. 1996, 35, 4507-4522. The retrofit thermodynamic diagram is introduced and used as a visualization tool for developing retrofit solutions by inspection for case studies.

(143) Lakshmanan, R.; Bafiares-Alcantara, R. Retrofit by Inspection Using Thermodynamic Process Visualization. Comput. Chem. Eng. 1998, 22(Suppl.)-. S809-S812.

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The retrofit thermodynamic diagram is introduced as a visual tool for developing retrofit designs by inspection.

(144) Lambert, A. J. D. Minimization of Number of Units in Heat Exchanger Networks Using a Lumped Approach. Corn-put. Chem. Eng. 1994, 18 (1), 71-74. An MILP model of the minimum number of units problem of HENS based on heat balances for each stream (lumped approach) rather than temperature intervals is proposed. The generation of the set of combinations of the minimum active number of active matches is faster compared to the transportation and transshipment models by reducing the number of continuous variables with lumping.

(145) Lee, H.; Lee, L; Yoo, K. The System Separation Method for the Optimal Target of Heat Exchanger Network Synthesis with Multiple Pinches. Korean J. Chem. Eng. 1995, 12 (5), 589-592. The issue of multiple pinch points is addressed with the system separation method which subdivides the HENS problems into independent subsystems with one pinch point.

(146) Lee, I. Toward the Synthesis of Global Optimum Heat Exchanger Networks Under Multiple-Periods of Operation. Korean J. Chem. Eng. 1991, 8(2), 95-104. An algorithm for network evolution is presented for designing multiperiod HENs meeting the minimum number of units and maximum energy recovery targets.

(147) Lee, I. Synthesis of Heat Exchanger Networks with Minimum Number of Units for Pinched Problems. Korean J. Chem. Eng. 1992, 9(3). 117-127. A network evolution algorithm is proposed which combines elements of various other evolutionary methods to design networks meeting the energy recovery and number of units targets.

(148) Lemouari M, Boumaza M, Mujtaba I M. Thermal performances investigation of a wet cooling tower. Appl Therm Eng 2007; 27:902-9. This paper presents an experimental investigation of the thermal performances of a forced draft counter flow wet cooling tower filled with vertical grid apparatus type packing.

(149) Li Z. Modeling and optimization for heat exchanger networks synthesis based on expert system and genetic algorithm. Chinese Journal of Chemical Engineering, 2002, 10(3):290–297. A new superstructure form of heat exchanger networks (HEN) is proposed based on expert system (ES). The new superstructure form is combined with the practical engineering. The different investment cost formula for different heat exchanger is also presented based on ES. The mathematical model for the simultaneous optimization of network configuration is established and solved by a genetic algorithm. This method can deal with larger scale HEN synthesis and the optimal HEN configuration is obtained automatically.

(150) Lin B. and Miller D. C. Solving heat exchanger network synthesis problems with tabu search. Computers & Chemical Engineering, July 2004, 28(8):1451–1464. This paper describes the implementation of a meta-heuristic optimization approach, Tabu Search (TS), for heat exchanger networks (HEN) synthesis and compares this approach to others presented in the literature. TS is a stochastic optimization approach that makes use of adaptive memory in the form of Tabu lists. Both recency- and frequency-based Tabu lists are used to provide short- and long-term knowledge of search history. TS is shown to locate the global optima with a high probability and low computation times, demonstrating the algorithm’s potential for solving a variety of other mixed integer nonlinear programming (MINLP) problems

(151) Lewin. D. R. A Generalized Method for HEN Synthesis using Stochastic Optimizatlon-II. The Synthesis of Cost-Optimal Networks. Comput. Chem. Eng. 1998, 22 (\Q). 1387-1405. HENS with stream splitting allowed leads to a nonlinear optimization model whose solution is used to determine the fitness of each HEN generated by the proposed genetic algorithm.

(152) Lewln, D. R.; Wang, H.; Shalev, 0. A Generalized Method for HEN Synthesis Using Stochastic Optimization-I. General Framework and MER Optimal Synthesis. Comput. Chem. Eng. 1998, 22(10). 1503-1513. An approach for HENS based on genetic algorithms is presented. Disallowing stream splitting in the net-work results in an LP parametric optimization problem and an MILP optimization problem.

(153) Li, H.; Yao, P. Using Process Energy Integration Technology in the Energy-Saving Retrofit of Large Scale Complex Chemical Process System. Chin. J. Chem. Eng. 1998. 6 (3), 277-282. The use of pinch-based methods for retrofitting large-scale processes is examined.

(154) Li, Z. H.; Hua, B. Modeling and Optimizing for Heat Exchanger Networks Synthesis Based on Expert System and Exergo-Economic Objective Function. Comput. Chem. Eng. 2000.24(2-7). 1223-1228. A superstructure for HENS is developed with stream splits based on an expert system. An MI NLP HENS model with an exergo-economic objective function is proposed.

(155) Linnhoff, B. Pinch Analysis-A State-of-the-Art Overview. Chem. Eng. Res. Des. 1993, 71 (A), 503-522. This is a review of pinch technology broken down into all of the major subject areas related to pinch analysis. The state-of-the-art methods of 1993 for pinch analysis is discussed. Over 80 citations are

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included in this review. (156) Linnhoff, B. Use Pinch Analysis to Knock Down Capital Costs and Emissions. Chem. Eng. Prog. 1994,

90(8). 33-57. This is an overview of pinch design technology including a summary of the basic concepts as well as a description of more recent developments including pressure drop, multiple-base-case design, distillation columns, low-temperature design, batch processes, water pinch, total site integration, and emissions.

(157) Linnhoff, B.; Ahmad. S. Cost Optimum Heat Exchanger Networks—1. Minimum Energy and Capital using Simple Models for Capital Cost. Comput. Chem. Eng. 1990, 14 (7), 729-750. Methods for the optimization of the driving force based on capital costs and energy requirements are developed. HENS is performed using the PDM and the driving force plot.

(158) Linnhoff, B.; Smith, R.; Williams. J. D. The Optimization of Process Changes and Utility Selection in Heat Integrated Processes. Chem. Eng. Res. Des. 1990, 68(3). 221-236. The problem of process flowsheet design is examined using pinch technology.

(159) Liporace, F. S.; Pessoa, F: L. P.; Queiroz. E. M. Automatic -Evolution of Heat Exchanger Networks with Simultaneous Heat Exchanger Design. Braz. J. Chem. Eng. 1999, 16 (1), 25-40. The AtHENS software is developed for HENS based on the PDM. The paper describes the module for network evolution which includes improved loop identification and loop breaking and incorporates header pressure drop and shell sizing aspects of heat-exchanger design.

(160) Liporace, F. S.; Pessoa. F. L. P.; Queiroz, E. M. The Influence of Heat Exchanger Design on the Synthesis of Heat Exchanger Networks. Braz. J. Chem. Eng. 2000, 17 (4-7), 735-750. In the context of the PDM, the AtHENS application (annotation 135) is updated to include network design criteria to identify infeasible exchanger unit designs during the network evolution stage.

(161) Lona, L. M. F.; Fernandes, F. A. N.; Roque, M. C.; Rodrigues, S. Developing an Educational Software for Heat Exchangers and Heat Exchanger Networks Projects. Comput. Chem. Eng. 2000, 24 (2-7), 1247-1251. The heat-exchanger simulator (HES) has been improved and is used as educational software for the design of shell and tube heat exchangers and HENs.

(162) Ma, K.; Hui, C.; Yee, T. F. Constant Approach Temperature Model for HEN Retrofit. Appl. Therm. Eng. 2000. 20 (15-16), 1505-1533. An MILP model for HEN retrofit is proposed. A two-step solution procedure is proposed to overcome the problems associated with the nonconvexities of the MINLP model. First the constant approach temperature MILP model is solved to determine the fixed network structure, and then the MINLP model is solved for determining match reassignments.

(163) Ma X., Yao P., Luo X., and Roetzel W. Synthesis of multi-stream heat exchanger network for multi-period operation with genetic/simulated annealing algorithms. Applied Thermal Engineering, 2008, 28(8-9):809–823. The multi-period synthesis of multi-stream heat exchanger network (MSHEN) can be formulated as a mixed integer nonlinear programming (MINLP) model and the obtained MSHEN is over-synthesized for all operational period. In this paper a novel strategy for synthesizing flexible MSHEN under multi-period operation that involves specified changes in stream temperatures and flow rates is presented. In the first stage, the multi-period MSHEN is over-synthesized by the temperature-enthalpy (T-H) diagram method based on the stream pseudo-temperature. Compared with the superstructure-based multi-period MINLP model, the decision variables of the simultaneous multi-period NLP model proposed are only the stream heat transfer temperature difference contributions. The model features that the size and the complexity of the problem are reduced significantly and the feasibility of the initial feasible solutions are guaranteed, which will enhance the calculation efficienc y

(164) Maiorano. M.; Sciubba, E. Heat Exchangers Networks Synthesis and Optimisation Performed by an Exergy-Based Expert System. Int. J. Appl. Thermodyn. 2000, 3 (T), 1-19. A knowledge-based expert system (HENEA) is developed for HEN design. HENEA uses design rules based on heuristics and physical principles.

(165) Majumdar, A. K., Singhal, A. K. and Spalding, D. B., 1983, Numerical modeling of wet cooling towers – Part I: Mathematical and physical models, J Heat Transfer, 105(4): 728-735. The paper discusses a more advanced mathematical model for mechanical and natural draft cooling towers which provides accurate solution. Suggestions for improvements of physical models are also given.

(166) Majumdar, A. K., Singhal, A. K., Reilly, H. E. and Bratz, J. A., 1983, Numerical modeling of wet cooling towers-Part 2: Application to natural and mechanical draft towers, J Heat Transfer, 105(4): 736-743. This paper presents several applications of the mathematical model described in Part 1 of the paper. Natural and mechanical draft towers of counterflow and crossflow arrangement have been considered. Predicted thermal performances compare well with the available data from operating towers. The

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distributions of air velocities, pressure, temperature, moisture fraction, and water temperature have been assessed from the considerations of physical plausibility only, since no experimental data are available for comparison. Some sample parametric computations for a mechanical draft crossflow tower are also presented. The parameters studied are: (a) air travel dimension of fill; (b) aspect ratio of fill; (c) fan power; and (d) atmospheric pressure. The results are self-consistent and demonstrate the applicability of the model as an analysis tool

(167) Marechal, F.; Kalitventzeff, B. Targeting the Minimum Cost of Energy Requirements: A new Graphical Technique for Evaluating the Integration of Utility Systems. Comput. Chem. Eng. 1996, 20 (Suppl.), S225-S230. The problem of minimum cost of utilities is solved with MILP optimization, and integrated composite curves are used as a graphical tool for understanding the integration or nonintegration of streams.

(168) Marechal, F.; Kalitventzeff, B. Energy Integration of Industrial Sites: Tools, Methodology and Application. Appl. Therm. Eng. 1998. 18 (11). 921-933. Pinch-based heat integration methods are extended to the total industrial site heat integration. Each process is treated as one cold and one hot stream for the site scale problem.

(169) Markowski, M. Reconstruction of a Heat Exchanger Network Under Industrial Constraints—The Case of a Crude Distillation Unit. Appl. Therm. Eng.2000, 20(15-16), 1535-1544. The HEN retrofit of a crude distillation unit using a pinch-based approach is presented.

(170) Mikkelsen J. and Qvale B. A combinatorial method for the automatic generation of multiple, Near- Optimal heat exchanger networks. Chemical Engineering Research & Design, September 2001, 79(6):663–672. The method, named COMBINET, is based on combinatorial procedures, no pinch rules are used. The main idea is to find economic HENs. The procedure, however, is well suited for optimizing energy recovery, minimizing heat-exchanger area, minimizing number of matches, etc., The program is capable of storing a specified number of the best HENs from the screening procedure, thereby allowing the user to evaluate which ones best satisfy other requirements. A number of cases from the open classical literature have been studied and the results compared. The studies have shown that in each case a number of different configurations exist that are almost equally good concerning economics, indicating the presence of a flat economic optimum. In six out of a total of nine cases investigated, COMBINET did find several networks which all were better than the hitherto best network reported. Keywords: HENS; combinatorial method; flat economic optimum

(171) Milosavlejvic N, Heikkila P A. Comprehensive approach to cooling tower design. Appl Therm Eng 2001; 21:899-915. The thermal performance of a cooling tower and its cooling water system is critical for industrial plants, and small deviations from the design conditions may cause severe instability in the operations and economics of the process. External disturbances such as variations in the thermal demands of the process or oscillations in atmospheric conditions may be suppressed in multiple ways. Nevertheless, such alternatives are hardly implemented in the industrial operations due to poor coordination between the utility and process sectors. The complexity of the operation increases because of strong interaction among the process variables. In the present work an integrated model for the minimization of the operating cost of a cooling water system is developed.

(172) Mizsey. P.; R6v, E. The Use of Flowsheet Simulators in Heat Exchanger Network Synthesis (REVISED). Huns. J. Iiid. Chem. 1992. 20 (2). 91-97. An MINLP formulation is developed for optimizing a HEN covering structure obtained from the diverse-pinch technique used in HENS.

(173) Morgan, S. W. Use Process Integration to Improve Process Designs and the Design Process. Chem. Eng. Pros. 1992. 88 (9), 62-68. An introduction to pinch analysis as well as its utility in process design is presented.

(174) Morosuk T., Morosuk C., and Feidt M. New proposal in the thermodynamic analysis of complex heat regeneration systems. Energy, 29(12-15):2517–2535. This paper presents a new approach for analyzing and/or synthesizing the heat regeneration system, which has many applications in various energy conversion plants (ECP) and between ones. The method is applied for optimizing heat exchanger networks (HENs) operating below ambient temperature conditions as an application for refrigeration machines. Exergy and exergoeconomic methods are adapted for the optimization of three-flow heat exchangers. The heuristic rules and design criteria for pinch analysis for an optimized HEN have also been discussed.

(175) Mou C. and Qvale B. The consequences of unpredictable development of economic conditions on heat exchanger network configurations and economic results. Energy Conversion and Management, 2002, 43(9-12):1549–1562. The work reported in the present paper was carried out in connection with a comprehensive process

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integration study of a fertiliser plant in Lithuania. However, the investigation reported presently only concerns a constructed example with seven process streams. four hot streams and three cold streams. The primary objective of the present work was to gain an understanding of the influence of dramatic economic changes on heat exchanger network (HEN) configurations, their profitability and how an existing HEN could restrict future possibilities of heat recovery.

(176) Naphon P. Study of the heat transfer characteristics of an evaporative cooling tower, International Communications in Heat and Mass Transfer 32 (2005) 1066-1074. In this study both experimental and theoretical results of the heat transfer characteristics of the cooling tower are investigated. A column packing unit is fabricated from the laminated plastic plates consists of eight layers. Air and water are used as working fluids and the test runs are done at the air and water mass flow rates ranging between 0.01 and 0.07 kg/s, and between 0.04 and 0.08 kg/s, respectively. The inlet air and inlet water temperatures are 23 8C, and between 30 and 40 8C, respectively. A mathematical model based on the conservation equations of mass and energy is developed and solved by an iterative method to determine the heat transfer characteristics of the cooling tower. There is reasonable agreement from the comparison between the measured data and predicted results.

(177) Nie, X. R.; Zhu, X. X. Heat Exchanger Network Retrofit Considering Pressure Drop and Heat-Transfer Enhancement. AIChE J. T999. 45(6). 1239-1254. A two-stage model for HENS retrofit is developed. A mathematical formulation for screening to determine units requiring additional area is followed by combined unit and shell-based optimization considering serial and parallel shell arrangements.

(178) Nielsen, J. S.; Hansen, M. W.; bay Joereensen, S. Heat Exchanger Network Modelling Framework tor Optimal Design and Retrofitting. Comput. Chem. Eng. 1996, 20(Suppl.), S249-S254. Object-oriented modeling is used to create a HENS problem representation and simulated annealing to solve this problem in order to extend HENS to include concurrent exchangers as well as heat capacity flow rates that are not constant. The computer software HEN Explorer is developed in this approach to HENS.

(179) Nielsen. J. S.; Hansen. M. W.; Kristensen. K. P. Retrofit and Optimisation of Industrial Heat Exchanger Networks: A Complete Benchmark Problem. Comput. Chem. Eng. 1997, 21 (Suppl.), S469-S474. An industrial retrofit HENS problem is used as an example for presenting a realistic HENS problem.

(180) Nilsson, K.; Sunden, B. Optimizing a Refinery using the Pinch Technology and the MIND Method. Heat Recovery Syst. CHP 1994, 14(2). 211-220. A Swedish refinery is analyzed using pinch technology and the MIND method, an MILP industrial energy system optimization tool. The HEN of the distillation system is analyzed using pinch techniques.

(181) Nordman R. and Berntsson T. New pinch technology based hen analysis methodologies for cost effective retrofitting. The Canadian Journal of Chemical Engineering, 2001, 79(4):655–662. In this paper, new pinch technology based curves for retrofitting of heat exchangers are presented. Advantages compared to traditional pinch curves, and the information that can be extracted from these curves, are discussed. The curves have been applied to an example where different energy saving levels has been studied. The results have been verified by detailed calculations using the Matrix method.

(182) Ogboja, O., 1987, A procedure for computer-aided design of water cooling towers, Chem Eng J, (35): 43-50. A procedure for the design of water-cooling towers is presented. In order to make it adaptable for fast computer execution, equations have been fitted

(183) Oliveira S. G., Liporace F.S., Araújo O. Q. F., and Queiroz E. M. The importance of control considerations for heat exchanger network synthesis: A case study. Brazilian Journal of Chemical Engineering, 2001, 18(2):195–210. Cost optimization in the synthesis decision tree often leads to a reduced degree of freedom which degrades the process’s ability to reject disturbances as a consequence of low controllability. In fact, Heat Exchanger Networks (HENs) obtained by traditional synthesis procedures that ignore controllability aspects must be evaluated in this context a posteriori. The aim of this work was to develop a procedure that includes RGA and SVD measures of controllability, which are solely based on steady state information, thereby freeing the synthesis procedure of the cumbersome dynamic analysis. When a structure is defined during a traditional HEN synthesis procedure, a degree of freedom analysis is approached as a simulation problem. Next, an optimization is performed, since new variables are usually added to increase the degree of freedom of the HEN in order to render it controllable. A key point in the proposed procedure is the inference of controllability based on the proposed controllability measures, which also provide a control scheme by pairing controlled and manipulated variables during the process design.

(184) Panjehshahi M. H. and Nouzari M. M. Retrofit of heat exchanger networks considering existing structure: A new targeting procedure. Iranian Journal of Chemistry & Chemical Engineering, 2001, 20(1):44–52.

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A new retrofit targeting procedure, based on pinch technology has been developed. The procedure considers existing structure and hydrodynamic system of a given network as two main constraint during targeting. The procedure uses a linear programming model to consider existing structure. The model finds a network structure that has maximum compatibility with existing structure. Furthermore, the procedure using the pressure drop equations, can consider decreasing the film coefficients of streams due to increasing network area. Good compatibility between old and new networks and non replacement of hydrodynamic equipment cause to the best use of capital in retrofit projects.

(185) Panjeshahi M. H., Langeroudi E. G., and Tahouni N. Retrofit of ammonia plant for improving energy efficiency. Energy, 2008, 33(1):46–64. The aim of this work was to perform a retrofit study of an ammonia plant, in purpose of improving energy efficiency. An ammonia plant can be divided into two parts: the hot-end and the cold-end. In the hot section, two different options are investigated that both lead to a threshold condition and achieve maximum energy saving. The first option covers only process-to-process energy integration, while the second option considers some modification in the convection section of the primary reformer through a new arrangement of the heating coils. Thus, a considerable reduction in cooling water, HP steam and fuel gas consumption is achieved. In the cold section, retrofit study is dominated by reducing the amount of shaft work or power consumption in the refr igeration system. Applicat ion of the Combined Pinch & Exergy Analysis revealed that part of the shaft work, which was or iginal ly being used, was inefficient and could have been avoided in a well-integrated design. Therefore, by proposing optimum refrigeration levels, reasonable saving (15%) in power consumption was observed without the need for new investment

(186) Panjeshahi M. H. and Tahouni N. Pressure drop optimisation in debottlenecking of heat exchanger networks. Energy, 2008, 33(6):942–951. Process integration technology is now widely applied in grass-roots design, energy saving retrofit and the debottlenecking of heat exchanger networks. This technology has been used in a variety of industries and proved to be reliable and applicable in engineering design. Debottlenecking may apply to a specific part or entire unit, whether it is due to increased throughput or process modifications. One of the advanced methods for debottlenecking that is currently used is based upon fixed allowable pressure drops, through which a retrofit can be achieved without a need for pump and/or compressor replacement. This research is trying to develop a new procedure for pressure drop optimisation in debottlenecking. This procedure enables the designer to study pump and/or compressor replacement whilst at the same time optimising the additional area and operating cost of the network. It deals with the problem of optimal debottlenecking of heat exchanger networks considering minimum total cost. Moreover, one can consider the possibility of the replacement of a given pump with a smaller one. The new procedure has been effectively applied to a crude oil pre-heat train, which was subject to some 20% increase in throughput, and the corresponding results proved to be accurate enough.

(187) Papaefthimiou V D, Zannis T C, Rogdakis E D, Thermodynamic study of wet cooling tower performance. Int J Energy Res 2006;30:411-26. An analytical model was developed to describe thermodynamically the water evaporation process inside a counter flow wet cooling tower, where the air stream is in direct contact with the falling water, based on the implementation the energy and mass balance between air and water stream describing thus, the rate of change of air temperature, humidity ratio, water temperature and evaporated water mass along tower height. The reliability of model predictions was ensured by comparisons made with pertinent experimental data obtained from literature. The paper elaborated the effect of atmospheric conditions, water mass flow rate and water inlet temperature on the variation of the thermodynamic properties of moist air inside the cooling tower and on its thermal performance characteristics. The analysis of the theoretical results revealed that the thermal performance of the cooling tower is sensitive to the degree of saturation of inlet air. Hence, the cooling capacity of the cooling tower increases with decreasing inlet air wet bulb temperature whereas the overall water temperature fall is curtailed with increasing water to air mass ratio. The change of the inlet water temperature does not affect seriously the thermal behavior of cooling tower.

(188) Papalexandri, K. P.: Patsiatzis, D. I.; Pistikopoulos, E. N.: Ebbesen, L. Heat Integration Aspects in a Crude Preheat Refinery Section. Comput. Chem. Eng. 1998, 22 (Suppl.), S141-S148. . A mass/heat-exchange-based representation presented previously (annotation 196) is utilized in the retrofit of the HEN of a crude preheat refinery secion.

(189) Papalexandri, K. P.; Pistikopoulos, E. N. A Multiperiod MINLP Model for Improving the Flexibility of Heat Exchanger Networks. Comput. Chem. Eng. 1993, 17 (Suppl.), S111-S116. This paper covers retrofitting HENs with variable operating conditions. With the assumption of no dual streams, a multiperiod network representation is used in an MINLP formulation of the retrofit HENS

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problem. The MINLP model couples synthesis techniques for HEN multiperiod operation and retrofit strategies. An iterative scheme may be used to integrate this problem with flexibility analysis.

(190) Papalexandri, K. P.; Pistikopoulos. E. N. An MINLP Retrofit Approach for Improving the Flexibility of Heat Exchanger Networks. Ann. Oper. Res. 1993, 4(1-4), 119-168. This paper addresses the problem of redesigning a HEN in order to improve its flexibility. The multiperiod MINLP approach of Floudas and Grossmann is utilized in the generation of a multiperiod hyperstructure network representation used in the simultaneous optimization of the operation costs and retrofit investment costs of the retrofit HENS problem. The desired flexibility target is achieved through an iterative procedure between the flexibility analysis and the MINLP retrofit HENS problem.

(191) Papalexandri, K. P.; Pistikopoulos, E. N. A Multiperiod MINLP Model for the Synthesis of Flexible Heat and Mass Exchange Networks. Comput. Chem. Eng. 1994, 18 (11/12), 1125-1139. An integrated hyperstructure representation and a multiperiod MINLP model are developed for heat- and mass-exchange network synthesis. .The issue of parameters that vary by discrete values is addressed in this model.

(192) Papalexandri, K. P.; Pistikopoulos, E. N. Synthesis and Retrofit Design of Operable Heat Exchanger Networks Flexibility and Structural Controllability Aspects. Ind. Eng. Chem. Res. 1994, 33 (7). 1718-1737. Structure controllability criteria for HENS are developed and utilized in an MINLP formulation for grassroots or retrofit HENS.

(193) Papalexandrl, K. P.; Pistikopoulos, E. N. Synthesis and Retrofit Design of Operable Heat Exchanger Networks. 2. Dynamics and Control Structure Considerations. Ind. Eng. Chem. Res. 1994. 33 (7). 1738-1755. A framework where controllability issues are considered in the grassroots or retrofit HENS design without decomposition is proposed which can be coupled with the iterative method (annotation 192). This method allows both structural and control alternatives to be explored simultaneously.

(194) Papalexandri, K. P.; Pistikopoulos, E. N. Synthesis of Cost Optimal and Controllable Heat Exchanger Networks. Chem. Eng. Res. Des. 1994, 72 (A), 350-356. A framework for grassroots heat-exchanger synthesis for optimal and controllable networks based on the hyperstructure representation of Ciric and Floudas is proposed.

(195) Papalexandri. K. P.; Pistikopoulos. E. N. A Process Synthesis Modelling Framework Based on Mass/Heat Transfer Module Hyperstructure. Comput. Chem. Eng. 1995, 19 (Suppl.), S71-S76. A process modeling framework is proposed allowing for a flowsheet hyperstructure for mass/heat exchanger network synthesis to be developed.

(196) Papalexandri, K. P.; Pistikopoulos, E. N. Generalized Modular Representation Framework for Process Synthesis. AIChE J. 1996, 42 (4), 1010. A mass/heat-exchanger module for building superstructures for the synthesis of combined mass and HENs is introduced.

(197) Papalexandri. K. P.; Pistikopoulos, E. N. A Decomposition-Based Approach for Process Optimization and Simultaneous Heat Integration. Chem. Eng. Res. Des. 1998, 76 (3), 273-286. A heat integration superstructure for process synthesis exploiting interactions between structure, operating conditions, and heat recovery is proposed. A decomposition solution method is described, and operability aspects for the model are discussed.

(198) Papastratos, S.; Isambert, A.; Depeyre, D. Computerized Optimum Design and Dynamic Simulation of Heat Exchanger Networks. Comput. Chem. Eng. 1993, 17 (Suppl.), S329-S334. The computer program CAD-HEN, based on thermo-dynamic principles, is developed to design HENs that are flexible and controllable as well as near-optimal. SpeedUp is used for dynamic simulation and response analysis of a HEN.

(199) Pariyani A., Gupta A., and Ghosh P. Design of heat exchanger networks using randomized algorithm. Computers & Chemical Engineering, May 2006, 30(6-7):1046–1053. A randomized algorithm with stream splitting for design of heat exchanger networks is presented in this work. The algorithm has provisions for splitting any one of the process streams. We have studied three benchmark problems taken from literature. The results obtained from these studies clearly indicate the strength of the randomization method in finding a cost-effective network. This random search method can find better networks, which are sometimes unnoticed by other optimization techniques. The simplicity of this method as well as the networks obtained is an additional attractive feature, which should encourage the designers to use it. From the results of this study, randomization is recommended as a reliable check for designing heat exchanger networks.

(200) Peneva, K.; Ivanov, B.; Bancheva, N. Heat Integration of Batch Vessels at Fixed Time Interval—II. Schemes with Intermediate Heating and Cooling Agents. Hung. J. Ind. Chem. 1992, 20. 233-239. This paper proposes mathematical models for network design using external and jacket heat exchangers

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for processes that do not allow fluids to be removed from batch vessels. (201) Pettersson F. Synthesis of large-scale heat exchanger networks using a sequential match reduction

approach. Computers & Chemical Engineering, April 2005, 29(5):993–1007. In this paper, a sequential approach is outlined which generates networks for industrial sized heat exchanger network synthesis (HENS) problems. The proposed match reduction approach solves a sequence of subproblems, posed as transportation problems, successively reducing the set of matches that are considered in the next stage. The terms involved in the objective function are included at each step with increasing accuracy, until a final design is obtained. One of the subproblems identifies subsets of matches that can be designed separately. Due to the sequential approach, the final design is an approximating solution.Two examples are presented to illustrate the potential of the proposed method. The results show that large HENS problems can be solved to good solutions with modest computational effort.

(202) Phipps M. and Hoadleyf A. Experiences from using heat integration software to determine retrofit opportunities within a refinery process. Korean Journal of Chemical Engineering, July 2003, 20(4):642–648. Heat integration techniques can be used to optimize the energy requirement for both new and retrofit plant designs. Software tools for identifying retrofit options are becoming available. This paper reports our experiences from using heat exchanger network (HEN) optimization software for a retrofit case study of an oil refinery process. The HEN optimization software was used to automate the search for the most beneficial retrofit designs following the twostage process proposed by Asante and Zhu. The software provided three potential retrofit designs. Results from this analysis were used as the basis of a rigorous mass and energy balance simulation of the plant. The simulation corroborated the energy savings, but there were some important differences. The simulation required 20% more heat exchange area. Furthermore, the retrofit design involving one topology change was shown to be less economic than an alternative design. These differences are discussed and a revised methodology is proposed.

(203) Picon-Nunez, M. P.; Polley, G. T. Applying Basic Understanding of Heat Exchanger Network Behaviour to the Problem of Plant Flexibility. Chem. Eng. Res. Des. 1995, 73 (A), 941-952. The function and behavior of HENs are analyzed in order to provide insight and understanding of flexibility problems.

(204) Pintaric Z. N. and Kravanja Z. A strategy for MINLP synthesis of flexible and operable processes. Computers & Chemical Engineering, June 2004, 28(6-7):1105–1119. This paper presents a sequential two-stage strategy for the stochastic synthesis of chemical processes in which flexibility and static operability (the ability to adjust manipulated variables) are taken into account. In the first stage, the optimal flexible structure and optimal oversizing of the process units are determined in order to assure feasibility of design for a fixed degree of flexibility. In the second stage, the structural alternatives and additional manipulative variables are included in the mathematical model in order to introduce additional degrees of freedom for efficient control. The expected value of the objective function is approximated in both stages by a novel method, which relies on optimization at the central basic point (CBP). The latter is determined by a simple set-up procedure based on calculations of the objective function’s conditional expectations for uncertain parameters. The feasibility is assured by simultaneous consideration of critical vertices. The important feature of the proposed stochastic model is that its size depends mainly on the number of design variables and not on the number of uncertain parameters.

(205) Polley, G. T.; Amidpour, M. Don't Let the Retrofit Pinch Pinch You. Chem. Eng. Prog. 2000, 96 (11), 43-48. The problems with existing retrofit analysis approaches are examined and a structural targeting procedure is proposed that involves decomposing the problem and analyzing separate components individually.

(206) Polley, G. T.; Heggs, P. J. Don't Let the Pinch Pinch You. Chem. Eng. Prog. 1999, 55(12), 27-36. Some of the weaknesses of pinch design methodologies are demonstrated. Then, using a proposed decomposition procedure, off-the-shelf design software that utilizes pinch technology is used for HENS taking these practical drawbacks into account.

(207) Polley. G. T.: Shahi, M. H. P. Interfacing Heat Exchanger Network Synthesis and Detailed Heat Exchanger Design. Chem. Eng. Res. Des. 1991, 69 (A), 445-457. Detailed heat-exchanger design considerations such as physical properties of the fluids, stream-fouling resistances, and exchanger-allowable pressure drops are explored.

(208) Polley, G. T.; Shahi, M. H. P.; Jegede, F. 0. Pressure Drop Considerations in the Retrofit of Heat Exchanger Networks. Chem. Eng. Res. Des. 1990, 68 (A), 211-220. The flow considerations of network topology are incorporated as part of the targeting procedures in retrofit HENS.

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(209) Ponce-Ortega J. M., Jimenez-Gutierrez A., and Grossmann I. E. Simultaneous retrofit and heat integration of chemical processes. Industrial & Engineering Chemistry Research, 2008, 47(15):5512–5528. In this paper, a new formulation for the retrofit of heat exchanger networks considering process modifications is presented. The method accounts for the interactions between the process conditions and the heat integration options to provide an optimal structure for a redesigned heat exchanger network. The formulation is based on a superstructure that considers explicitly the plant layout and the piping arrangement, which yields a mixed-integer nonlinear programming model. The model presented here includes the treatment of isothermal process streams that exchange their latent heats, in addition to the streams commonly considered with sensible heat loads. The objective function consists of maximizing the total annual profit for the retrofit process, which includes the income from products sales and the expenses due to raw materials, capital cost for new units, utility costs, and the piping modification costs. The results for the cases of study show that significant improvement in the process profitability can be obtained with the simultaneous approach presented in this work for process retrofit with respect to the sole consideration of the heat exchanger networks.

(210) Ponce-Ortega J. M., Serna-Gonzalez M., and Jimenez-Gutierrez A. Heat exchanger network synthesis including detailed heat exchanger design using genetic algorithms. Industrial & Engineering Chemistry Research, 2007, 46(25):8767–8780. This paper proposes an optimization model for heat exchanger network synthesis that includes a detailed design for each heat exchanger of the network. The model takes into account the optimization of the exchanger units and their geometric and operational constraints from the synthesis stage. The approach is based on the use of genetic algorithms to determine the heat exchanger network that minimizes the total annualized cost, which accounts for the capital costs of heat exchangers and pumps, and the energy costs for utilities and pumping duties.

(211) Ponce-Ortega J. M., Serna-Gonzalez M., and Jimenez-Gutierrez A. Synthesis of multipass heat exchanger networks using genetic algorithms. Computers & Chemical Engineering, 2008, 32(10):2320–2332. In this work, a methodology based on genetic algorithms (GAs) is developed for the optimal synthesis of multipass heat exchanger networks (HENs). The network model is based on a stagewise superstructure, and the problem of finding the optimum number of 1–2 shells in series of multipass heat exchangers is aided by an efficient optimization model that uses the standard FT design method. The proposed methodology allows for proper handling of the trade-offs involving energy consumption, number of units, number of 1–2 shells and network area to provide a network with the minimum total annual cost. The results of the examples show that the new approach is able to find more economical networks than those generated by other methods.

(212) Pozna, A.; Ivanov, B.; Vaklieva-Bancheva, N. Design of a Heat Exchanger Network for a System of Batch Vessels. Hung. J. Ind. Chem. 1998, 26(3), 203-211. An MINLP formulation for HENS incorporating existing batch vessels is proposed.

(213) Prasad, M., 2004, Economic up gradation and optimal use of multi-cell cross flow evaporative water cooling tower through modular performance. Appl Therm Eng, 24(4): 579-593. A novel numerical-cum-experimental technique is presented for modular performance evaluation of multi-cell crossflow evaporative water cooling tower of single-flow design, which determines fill characteristic for individual cell half with total system in operation. Fill characteristic is a single composite nondimensional parameter, involving dimensions of the cell half, configuration of the packing and water flow rate through it; representing overall potential of the fill to cool water and is a sole function of mass flow ratio of water to air for a given system. It diminishes with use mainly due to packing damage and its prevailing value represents the departure from design state at any instant of time. The result of deterioration manifests as increase in overall temperature of the cooled water ensuing from the tower. Since, in general, different cell halves undergo varied level of degradation and because fill characteristic for individual cell half is available; packing for all the cell halves need not be replaced simultaneously, which otherwise is a common practice for obtaining lower temperature of cooled water from the tower, as it entails a huge expenditure. It is possible to achieve significant lowering of overall exit cooled water temperature from the total system at a much reduced cost by undertaking packing replacement only for some selected cell halves at a given time, beginning with the worst affected cell half and then taking up the immediately better one, and so on. The proposed scheme of modular performance appraisal and the benefits resulting from sequential fill upgradation and that due to selective hot water flow distribution are displayed through an example for a typical cooling tower of single-flow design having 12 cells by considering deteriorated state of six different fills.

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(214) Puspita, N. F.: Fuchino, T.; Muraki, M. Synthesis of Heat Exchanger Networks Considering Location of Process Stream Sources. J. Chem. Eng. Jpn. 1998, 31 (3). 330-339. A simultaneous evolutionary HENS method is proposed that optimizes on the basis of the total annual cost of the network.

(215) Querzoli A., Hoadley A., and Dyson T. Identification of heat integration retrofit opportunities for crude distillation and residue cracking units. Korean Journal of Chemical Engineering, July 2003, 20(4):635–641. This study investigates improving the energy efficiency of two key refining processes: the Crude Distillation Unit (CDU) and the Residue Cracking Unit (RCU). The research methodology followed the ‘targeting before design’ approach. The CDU is a ‘tightly pinched’ system, with limited opportunities for further energy savings. The RCU actual ΔTmin is around 55 °C indicating a low level of current heat recovery. The Total-Site analysis shows that theoretically 18 MW of heat could be transferred from the RCU to the CDU, reducing CDU requirements by 40% for a new or grass roots design. RCU retrofit designs were developed to increase steam generation by up to 35% and in line with targeting estimates would appear to have economic potential. The alternative CDU-RCU retrofit design was developed to decrease CDU hot utility use. Although the Total-Site profile demonstrated strong potential for heat integration, this retrofit design is not commercially attractive, as the decrease in CDU fuel does not offset the cost of reduced steam generation. This demonstrates the need to consider the different fuel and steam costs in the Total-Site analysis

(216) Quesada, I.; Grossmann, I. E. Global Optimization Algorithm for Heat Exchanger Networks. Ind, Eng. Chem. Res. 1993, 32 (3), 487-499. A global optimization algorithm for HENS with fixed topology is presented. The fixed topology corresponds to a configuration within the superstructure of Yee and Grossmann (annotation 278). The optimization model is simplified by assuming that the area cost function is linear and that the driving force is calculated by the arithmetic mean temperature difference.

(217) Ratnam, R.; Patwardhan, V. S. Sensitivity Analysis for Heat Exchanger Networks. Chem. Eng. Sci. 1991, 46 (2), 451-458. A computational procedure for generating sensitivity information without the need for repeated matrix inversions is developed and illustrated with examples.

(218) Ravagnani M. A. S. S. and Caballero J. A. Optimal heat exchanger network synthesis with the detailed heat transfer equipment design. Computers & Chemical Engineering, 2007, 31(11):1432–1448. This paper presents an optimisation model for the synthesis of heat exchanger networks (HEN) including the detailed design of the equipments formulated as a decomposition method. Shell and tube pressure drops and fouling are considered, as well as mechanical aspects, like shell and tube bundle diameters, internal and external diameter of tubes, number of tubes, number of baffles, number of shells, tube length, tube arrangement and the fluid allocation in the heat exchanger. The optimisation model is based on area, energy and pumping costs. The algorithm combines two distinct models, in a decomposition method, a mixed integer non-linear programming (MINLP) superstructure simultaneous optimisation model for the heat exchanger network synthesis considering stream splitting and a MINLP model for the detailed equipment design, following rigorously the standards of the TEMA. Two examples from the literature are used to test the algorithm developed, and the results confirm the achievement of the optimum HEN configuration with the detailed heat exchangers design, following the TEMA standards.

(219) Ravagnani M. A. S. S., Silva A. P., Arroyo P. A., and Constantino A. A. Heat exchanger network synthesis and optimisation using genetic algorithm. Applied Thermal Engineering, May 2005, 25(7):1003–1017. In the last few decades, several papers were published on heat exchanger network synthesis. Most of them present techniques using mathematical programming for the synthesis and optimisation tasks. Recent developments in heat exchanger networks synthesis present some heurist methods, such as genetic algorithm (GA) and simulated annealing. In this paper, a strategy for the synthesis and optimisation of heat exchanger networks was developed using GA. First of all, the ΔTmin is optimised using GA jointly with the problem table, from the Pinch Analysis. By using the optimum ΔTmin, found in the previous stage, the problem is divided in two different regions, below and above the pinch. Thus, using GA, the optimal networks above and below the pinch are obtained, considering stream splitting as well. Some examples from the literature were solved with the proposed systematic, and results show heat exchanger networks with lower costs than those ones presented in the literature for the cases studied.

(220) Reddy, B. S.; Venkata Seshaiah, P. A Thermodynamic Approach to the Design of Heat Exchanger Networks. Chem. Eng. World 1997, 32(9). 145-150. This article presents a short overview and outline of the development of pinch technology for HENS.

(221) Reddy, B. S.; Venkata Seshaiah, P. Basic Concepts of Heat Exchanger Network Design. Chem. Eng. World 1997, 32(6), 55-58.

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This article presents a short review of HENS via pinch-based design methods. (222) Reddy, B. S.; Venkata Seshaiah, P.; Subbarayudu, D. Optimum Design of Process Networks. Chem. Eng.

World 1998, 35(9), 113-117. This paper presents a review of the developments for supertargeting to determine the optimal approach temperature in pinch-based design methods.

(223) Reddy, K. A.; Rao, C. D. P.; Davies, G. S. Synthesis of Multipass Heat Exchanger Networks. AIChE J. 1998, 44(4), 999-1002. A methodology for designing multipass HENs is proposed. A set of rules for matching is developed, and the minimum number of shells target is used rather than for minimum number of units.

(224) Rev, E.; Fonyb. Z. Diverse Pinch Point Concept for Heat Exchange Network Synthesis: The Case of Different Heat Transfer Conditions. Chem. Eng. Scl. 1991, 46. 1623-1634. The diverse-pinch concept is developed. A supertargeting method based on the diverse pinch taking into account film heat-transfer coefficients is developed.

(225) Rev, E.; Fonyo, Z. Comments on Diverse Pinch Concept for Heat Exchanger Network Synthesis. Chem. Eng. Sci. 1993, 48 (3), 627-628. This short letter corrects some previously published data (annotation 175) and explains the significance of the diverse-pinch concept.

(226) Rodera, H.; Bagajewicz, M. J. Targeting Procedures for Energy Savings by Heat Integration across Plants. AIChE J. 1999, 45(8), 1721-1742. Pinch-based maximum energy savings models are presented for total heat integration across two process plants.

(227) Rodera H., Savelski M. J., Bagajewicz M. J., Hess F., and Seidel T. Energy retrofit with simultaneous optimization for a crude fractionation unit. Latin American Applied Research, 2001, 31(5):483–486. This paper presents the results obtained in the energy retrofit of a Crude Topping Unit. An optimization procedure to explore energy retrofit alternatives that combines changes in operating conditions and pinch analysis is used.

(228) Roosen, P.; Grobss, B. Optimization Strategies and their Application to Heat Exchanger Network Synthesis. Chem. Eng. Technol. 1996. 19 (2). 185-191. Evolutionary strategy optimization is developed from insights garnered from previous methods involving thermodynamic and discrete optimization approaches to HENS. A module to apply the algorithms is coupled to ASPEN PLUS.

(229) Roque, M. C.; Lona, L. M. F. The Economic of the Detailed Design of Heat Exchanger Networks Using the Bell Delaware Method. Comput. Chem. Eng. 2000, 24 (2-7), 1349-1353. A comparison of impact on HEN design cost between the Bell Delaware and Kern methods for calculating heat-transfer coefficients is presented.

(230) Sama, D. A. Difference between Second Law Analysis and Pinch Technology. Trans. ASME 1995, 117. 186-191. This paper rebuts some of the claims of Linnhoff regarding second law analysis. Arguments for second law analysis as a HENS tool are made.

(231) Sama, D. A. The Use of the Second Law of Thermodynamics in Process Design. J. Energy Resour Techno 1995, 7/7,179-185. The benefits of using second law analysis are described. A set of guidelines for design using second law analysis are presented. HENS is given particular attention in this paper.

(232) Santos, L. C.: Zemp, R. J. Energy and Capital Targets for Constrained Heat Exchanger Networks. Braz. J. Chem. Eng. 2000, /7(4-7), 659-669. A procedure is developed for improving network area targeting in HENS. The potential use of multipass shell and tube heat exchangers is included.

(233) Seider. W. D.; Seader, J. D.; Lewin, D. R. Process Design Principles: Synthesis, Analysis and Evaluation', John Wiley & Sons: New York, 1999. The fundamental HENS methods are presented in this text. Pinch design methodology as well as basic mathematical programming LP and MILP formulations for HENS subproblems are described.

(234) Shelton S V, Joyce C T. Cooling tower optimization for centrifugal chillers. ASHRAE J 1991;93:28-36. This work investigates methodologies for optimized design of condenser water components of a chilled water HAVC plant, leading to reduced energy and construction costs.

(235) Shenoy, U. V.; Sinha, A.; Bandyopadhyay, S. Multiple Utilities Targeting for Heat Exchanger Networks. Chem. Eng. Res. Des. 1998. 76 (A), 259-272. An algorithm for multiple utilities targeting is developed based on the principle that it is optimal to increase the load on the cheapest utility while increasing the total utility usage. Optimum load distribution plots and total annual cost curves are employed in supertargeting the approach temperature when using multiple utilities.

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(236) Shethna H. K. and Jezowski J. M. Near independent subnetworks in heat exchanger network design. Industrial & Engineering Chemistry Research, June 2006, 45(13):4629–4636. A minimum number of matches in a heat exchanger network (HEN) can be achieved by maximizing the number of independent subnetworks. A method has been developed that maximizes the number of near-independent subnetworks, in which the streams achieve a certain specified outlet temperature within a tolerance. This conforms better to an industrial scenario and potentially generates a higher number of subnetworks. The approach is based on a MILP transshipment model formulation solved in a recursive procedure. The method ensures the minimal number of matches and minimal deviations from the nominal outlet temper

(237) Shethna. H. K.; Jezowski. J. M.; Castillo, F. J. L. A New Methodology for Simultaneous Optimization of Capital and Operating Cost Targets in Heat Exchanger Network Synthesis. Appl. Therm. Eng. 2000. .20(15-16). 1577-1587. A new approach has been developed for establishing cost-optimal targets for a heat exchanger network (HEN). We formulate a mixed-integer-linear-programming (MILP) transportation problem that simultaneously optimizes for heat exchanger units, heat exchange area and loads on each utility. Heat exchange matches are placed between each hot stream in each temperature interval and all cold streams in all the subsequent lower temperature intervals. The objective function is linear and minimizes the total annual cost of the HEN subject to heat balance constraints. The temperature intervals are generated with a temperature shift just greater than zero. Each temperature interval is small enough that we can linearize the log-mean temperature difference on each match while maintaining the accuracy. Flowrate continuity constraints are written on utility streams so that we could account for non-point utilities. Furthermore, constraints on heat exchange area that occur in retrofit scenarios are incorporated into the model. The solution of the optimization model provides the heat loads on each utility, in case of multiple hot and cold utilities, the heat load on every match pair, the heat exchange area target and the number of units target such that the total annual cost is minimum. Using these targets, it is straightforward to construct heat exchanger networks.

(238) Shethna, H. K.; Jezowski, J. M.; Castillo, F. J. L. Generalized Transshipment Model for Targeting of Multiple Utilities in Heat Exchanger Networks. Int. Chem. Proc. 2000, 21 (4), 625-643. An LP transshipment formulation is developed for determining the minimum utilities cost target in HENS extended to cases with multiple'utilities and utilities that span more than one temperature interval.

(239) Silva, M. L.; Zemp, R. J. Retrofit of Pressure Drop Constrained Heat Exchanger Networks. Appl. Therm. Eng. 2000, 20(15-16), 1469-1480. The study of retrofit of heat exchanger networks is usually restricted to constant heat transfer coefficients, and pressure drop constraints due to the additional exchanger area is neglected. In this work, a new approach considering the distribution of heat transfer area and pressure drop in retrofit is presented. The problem is described as a non-linear model, and the additional area required for the new network condition and available pressure drop are estimated based on economical optimisation (or process requirements).

(240) Smith, R. State of the Art in Process Integration. Appl. Therm. Eng. 2000, 20 (15-16). 1337-1345. An overview of the recent advances in process integration is presented, including a section on HENs.

(241) Smrekar J, Oman J, Sirok B. Improving the efficiency of natural draft cooling towers. Energy Conversion Management 2006; 47:1086-100. This paper shows how the efficiency of a natural draft cooling tower can be improved by optimizing the heat transfer along the cooling tower packing using suitable water distribution across the plane area of cooling tower.

(242) Sorin, M.; Paris. J. Combined Exergy and Pinch Approach to Process Analysis. Comput. Chem. Eng. 1997, 21 (Suppl.), S23-S28. The integration of pinch analysis to the thermody-namic analysis of processes by the exergy load distribution method allows the identification of process changes which are most likely to produce a desired effect without great computational efforts.

(243) Sorin, M.; Paris, J. Integrated Exergy Load Distribution Method and Pinch Analysis. Comput. Chem. Eng. 1999, 23 (4/5). 497-507. Intended exergy yield is proposed as a performance criteria for chemical process. The HEN is considered to be a single unit before final design. Pinch analysis is combined with exergy analysis for guiding process design.

(244) Sorbvsak. A.; Kravanja. Z. Simultaneous MINLP Synthesis of Heat and Power Integrated Heat Exchanger Networks. Comput. Chem. Eng. 1999, 23 (Suppl.), S143-S147. The simultaneous synthesis model of Yee and Gross-mann (annotation 219) is extended to also optimize pressure drops and heat-transfer coefficients.

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(245) Soylemez M S. On the optimum heat exchanger sizing for heat recovery. Energy Convers Mgmt 2000;41(13):1419-27. The paper presents thermoeconomic optimization analysis, yielding simple algebraic formulas for estimating the optimum heat exchanger area for energy recovery applications.

(246) Soylemez M S. On the optimum sizing of cooling towers Energy Conversion and Management Volume 42, Issue 7, May 2001, Pages 783–789. The optimum heat and mass transfer area at which minimum cost exists throughout the technical life of forced draft counter-current cooling towers is studied in the present work. Original formulae are developed and presented for the best thermoeconomical performance as a design point.

(247) Srinivas, B. K.; El-Halwagi, M. M. Synthesis of Combined Heat and Reactive Mass-Exchange Networks. Chem. Eng. Sci. 1994, 49(11). 2059-2074. The problem of combined heat and reactive mass exchange networks is introduced. A two-stage targeting procedure is proposed for the solution of this problem.

(248) Stoltze, S.; Mikkelsen, J.; Lorentzen, B.; Petersen, P. M.; Qvale, B. Waste-Heat Recovery in Batch Processes Using Heat Storage. J. Energy Resour. Techno]. 1995, 117. 142-149. A procedure is proposed for incorporating the minimum number of heat storage tanks into HENs to achieve maximum energy savings as determined by pinch analysis.

(249) Suaysompol, K.; Wood. R. M. The Flexible Pinch Design Method tor Heat Exchanger Networks Part I: Heuristic Guidelines for Free Hana Designs. Chem. Eng. Ses. Des. 1991, 69 (6), 458-464. The flexible PDM (FPDM) is outlined in this paper. The heat exchangers are not constrained by a rigid minimum approach temperature difference. Instead, a variable approach temperature concept is proposed.

(250) Suaysompol, K.; Wood. R. M. The Flexible Pinch Design Method for Heat Exchanger Networks Part II: FLEXNET-Heuristlc Searching Guided by the A* Algorithm. Chem. Eng. Res. Des. 1991, 69 (6), 465-470. The FPDM (annotation 194) is implemented in the computer-aided design package FLEXNET. The A* heuristic search algorithm is employed to locate cost-effective solutions for the HENS problem.

(251) Suaysompol, K.; Wood, R. M. Estimation of the Installed Cost of Heat Exchanger Networks. Int. J. Prod. Econ. 1993. 29,303-312. A procedure for including piping costs in the estimation of costs for alternative network designs is pre-sented.

(252) Suaysompol. K.; Wood. R. M.; O'Neill, B. K.; Roach. J. R. Correspondence regarding Targeting and Design for Minimum Number of Shells in HENs. Chem. Eng. Res. Des. 1990, 68 (A), 299-300. Comments regarding a paper by Ahmad and Smith (annotation 7) and the appropriateness of using pinch decomposition for HENS.

(253) Tantimuratha L., Asteris G., Antonopoulos D. K., and Kokossis A. C. A conceptual programming approach for the design of flexible HENs. Computers & Chemical Engineering, May 2001, 25(4-6):887–892. A conceptual tool is presented to address the flexibility and operability objectives for heat exchanger networks. The approach presents a screening model to accommodate the considerations ahead of design. The new development is essentially a targeting tool based on the Area Target Model that is a part of the Hypertarget methodology. The targets accommodate for an early pre-processing of matches and assess implications due to parameter variations. The feasibility targets provide ahead of design information on the costs incurred due to the variations. Flexibility targets assess the ability of the system to handle variations for different driving forces. The potential of the matches to handle variations can be further exploited with superstructure schemes. The paper proposes a systematic algorithmic procedure that converges to flexible networks at the expense of only a minor set of additional constraints. Examples are presented to illustrate the approach, explain its ability to assess the impact of variations and prove the ease of its use in real-size problems.

(254) Tantimuratha, L.; Kokossis. A. C.; Miiller. F. U. The Heat Exchanger Network Design as a Paradigm of Technology Integration. Appl. Therm. Eng. 2000, 20(15-16), 1589- The combination of different optimization technologies for HENS is studied. Computational experimentation suggests that simulated annealing platforms could be significantly improved by employing knowledge from pinch analysis or MILP screening models.

(255) Telang, K. S.; Chen, X.; Pike. R. W.; Knopf, F. C.; Hopper, J. R.; Saleh. J.; Yaws. C. L.; Waghchoure, &.; Hedge, S. C. An Advanced Process Analysis System for Improving Chemical and Refinery Processes. Comput. Chem. Eng. 1999, 23 (Suppl.). S727-730. A process analysis system is developed which Integrates programs for online optimization, chemical reactor analysis, flowsheeting, pinch analysis for HENS, and pollution indices.

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(256) Towler, G. P. Integrated Process Design for Improved Energy Efficiency. Renewable Energy 1996, 9 (1-4), 1076-1080 This is a very brief introduction to some principles of pinch analysis.

(257) Trivedi, K. K.; O'Neill. B. K.; Roach. J. R.; Wood, R. M. A Best-First Search Strategy for Energy Relaxation In MER Heat Exchanger Networks. Engi. Opt. 1990, 16, 165-189. The minimum energy consumption target is formulated as an MINLP and solved using a best-first search method. This problem is used in loop-breaking and identifying topology traps.

(258) Trivedi, K. K.; O'Neill. B. K.; Roach. J. R.; Wood, R. M. Systematic Energy Relaxation in MER Heat Exchanger Networks. Comput. Chem. Eng. 1990, 14 (6). 601-611. An alternative loop-breaking method and energy relaxation technique for use in pinch-based design of HENs is presented.

(259) Uhlenbruck, S.; Vogel, R.; Lucas. K. Heat Integration of Batch Processes. Chem. Eng. Technol. 2000, 23 (3), 226-229. OMNIUM is demonstrated to be useful for improving heat integration of batch processes when used recursively.

(260) Urbaniec K., Zalewski P., and Zhu X. X. Decomposition approach for retrofit design of energy systems in the sugar industry. Applied Thermal Engineering, 2000, 20(15):1431–1442. Sugar factory retrofit often includes improvements in the factory’s energy system comprising power plant, multiple-effect evaporator and process heating equipment. To reduce the energy consumption, the evaporator subsystem and the process heating subsystem should be retrofitted to make improved heat recovery possible. The retrofit design procedure includes two stages: targeting for various options of the evaporator structure and selecting the most promising one, and designing both subsystems for targets so determined. At the targeting stage, one is confronted with the problem of designing the evaporation process and simultaneously considering the energy consumption. This constitutes an extension of the established targeting approach that assumes process conditions to be fixed. The problem can be transformed by decomposing the energy system, that is, conceptually separating the evaporator (in which vapours and condensates are generated) from the process heating subsystem (in which these heat carriers can be regarded as utilities). The transformed problem is one of targeting under constraints and can be solved iteratively by combining pinch analysis algorithm with evaporator simulator. The second stage of the retrofit design procedure requires defining the details of process heating subsystem that includes a heat exchanger network. This problem is conveniently solved using the network pinch approach.

(261) Uzturk, D.; Konukman, A. E.; Boyaci, C.; Akman, U. Operability of an Autothermal Reactor Linked to a Flexible Heat-Exchanger Network. Comput. Chem. Eng. 1996, 20 (Suppl.), S943-948. The critical temperature deviations that cause runaway behavior for an autothermal fixed-bed catalytic reactor are considered in the design of a retrofit HEN.

(262) Vaidyaraman, S.; Mai anas, C. D. Optimal Synthesis of Refrigeration Cycles and Selection of Refrigerants. AIChE J. 1999, 45 (5), 997-1017. A methodology is developed for optimizing refrigeration cycle configuration with simultaneous refrigerant selection. A case of integration with a process HEN is examined.

(263) Vaklieva-Bancheva, N.; Ivanov, B. B.; Shah, N.; Pan-telides, C. C. Heat Exchanger Network Design for Multipurpose Batch Plants. Comput. Chem. Eng. 1996, 20 (8), 989-1001. An MILP problem formulation is used to design HENs for multipurpose batch plants considering only the direct mode of heat integration. This formulation takes account of the additional scheduling complications due to energy integration between different products in the same campaign.

(264) Van Reisen, J. L. B.; Grievink, J.; Polley, G. T.; Verheijen, P. J. T. The Placement of Two-Stream and Multistream Heat-Exchangers in an Existing Network Through Path Analysis. Comput. Chem. Eng. 1995, 19 (Suppl.), S143-S148. Path analysis is a prescreening and decomposition method used in the analysis of HEN retrofit design. It evaluates the economic potential of subnetworks and uses existing retrofit analysis procedures.

(265) Varbanov, P. S.; Klemebvs, J. Rules for Paths Construction for HENs Debottlenecking. Appl. Therm. Eng. 2000, 20 (15-16). 1409-1420. This paper is based on the heat exchanger network retrofit techniques, developed by Tjoe and Linnhoff and extended by Asante and Zhu. It considers, under the Network Pinch framework, two important cases — the Retrofit Initialisation and Topology Modification when the direct application of the classic Network Pinch concept and rules is not possible. With the help of a system of simple heuristics, these limitations are overcome which extends the application range of the Network Pinch framework.

(266) Vieira, A. J. M.; Pessoa, F. L. P.; Queiroz, E. M. Fluid Dynamical Considerations on Heat Exchanger Networks. Braz. J. Chem. Eng. 2000, 17(1), 19-27. A model is developed for determining the total annual cost for a HEN including the influence of pumping costs due to shell-side and tube-side pressure drops.

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(267) Viktorov. V. K. New Combinatorial Method for Synthesis of Heat Exchanger Networks. Chem. Eng. Res. Des. 1995, 73 (A), 915-918. A combinatorial estimation method for HENS is proposed in which a design tree is searched using estimating functions for the minimum leading to solutions more quickly than branch-and-bound but not guaranteed optimal.

(268) Viktorov, V. K. Comparison between Pinch Design Methods and Combinatory Methods in the Synthesis of Heat Exchanger Networks. Theor. Found. Chem. Eng. 1996, 30 (I), 89-92. The author compares the PDM to his method of HENS by combinatorial estimation methods, which look for solutions to the problem of transferring maximum power by the minimal number of exchangers. This method is more complicated than pinch methods and prohibits stream splitting.

(269) Wang. K.; Qian, Y.; Huang. Q.; Yao, P. New Model and New Algorithm for Optimal Synthesis of Large Scale Heat Exchanger Networks without Stream Splitting. Comput. Chem. Eng. 1999, 23 (Suppl.), S149-S152. A simultaneous HENS MINLP formulation is proposed. The superstructure does not allow for stream splitting. A genetic algorithm is developed and applied in solving the HENS model.

(270) Wang, P.; Hua. B.; Qian, Y. An Improved Approach to the Design of Flexible Heat Exchanger Networks. Coem. Eng. Technol. 1997, 20 (5), 309-312. When using sensitivity tables for flexible HENs, errors can become large. A simple method for error analysis is provided in which nonlinearities and interaction effects are considered for flexible HENS.

(271) Wang, Y. P.; Chen, Z. H.: Groll, M. A New Approach to Heat Exchanger Network Synthesis. Heat Recovery Syst. CHP 1990, 10 (4). 399-405. This paper presents an annual cost model for HENS. A mathematical programming approach is presented with the objective function consisting of energy and capital costs, with the minimum temperature difference being the variable to be optimized.

(272) Webb R.L., A unified theoretical treatment for thermal analysis of cooling towers, evaporative condensers, and fluid coolers, ASHRAE Transactions 90 (Part 2) (1984) 398-415. Cooling towers, evaporative fluid coolers and evaporative condensers are all members of a basic heat exchanger family. Heat is rejected by evaporation, from a gravity drained water film, into air flowing through a cooling tower "packing", or a tube bundle for fluid coolers and condensers. Hence, the air side heat and mass transfer process is governed by the same basic process. The key difference in the theory for each type relates to the thermal resistance of the process fluid. This resistance is quite small for cooling towers, but must be accounted for in the fluid cooler and condenser. This paper shows that a "unified" theoretical treatment may be applied to all three evaporative exchanger types. Specific equations or correlations for calculation of the heat and mass transfer resistance are discussed. In interest of preserving simplicity, the approximate Merkel equation is employed for the air side heat and mass transfer. The specific approximations associated with the Merkel equation are also noted. The theory presented in this paper provides the basis for computer simulation algorithms for cooling towers, fluid coolers and evaporative condensers.

(273) Wen Y. and Shonnard D. R. Environmental and economic assessments of heat exchanger networks for optimum minimum approach temperature. Computers & Chemical Engineering, November 2003, 27(11):1577– 1590. Heat exchanger networks (HENs) design for optimum minimum approach temperature (ΔTmin,opt) is presented using economic and environmental evaluations. The environmental assessment methodology includes seven environmental indices, based on the life-cycle impact assessment (LCIA) of both pre-manufacturing and manufacturing stages for equipment, fuel, and energy. A single normalized and weighted environmental index (IPC) is developed and then incorporated with the economic index using the analytic hierarchy process (AHP) method to identify ΔTmin,opt. Three case studies of pinched problems are presented. It is found that ΔTmin,opt using IPC as the objective is similar but not identical to ΔTmin,opt using annualized cost as the objective. For some environmental categories, pre-manufacturing impacts are dominant, however, environmental impacts of the HEN are always less than without a HEN. A sensitivity analysis shows the effect of several parameters on ΔTmin,opt.

(274) Westphalen, D. L.; Wolf Maciel, M. R. Pinch Analysis Based on Rigorous Physical Properties. Braz. J. Chem. Eng. 1999. 16 (3). 279-284. The problem table method for utilities targeting in pinch design is modified in order to take into account physical properties calculations. It is useful in situations when phase change occurs and heat capacity flow rates are no longer constant.

(275) Westphalen D. L. and Wolf Maciel M. R. Pinch analysis of evaporation systems. Brazilian Journal of Chemical Engineering, 2000, 2000, 17(4):525–537. Evaporation systems are separation processes widely used in chemical industries. Some guidelines can be found in the literature for the process integration of multiple effect evaporators. In the published

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methodologies some aspects are neglected as boiling point rise, effect of pressure on latent heat of water, sensible heat of liquid streams, heat of mixing, effects configuration and inclusion of accessories. In this work, a new graphical representation for the integration of multiple effect evaporators was developed, using rigorous physical properties. From this representation, an algorithm for optimization of bleed streams was conceived using the concepts of Pinch Analysis. As a case study, a crystal glucose plant was optimized using this new methodology. The optimization of bleed streams showed as result a steam consumption 16% smaller than a similar previous study. From energy and capital costs, it is shown that the integrated evaporator exhibits a total cost 14% smaller than the non-integrated configuration.

(276) Wood, R. M.; Suaysompol, K.; O'Neill, B. K.; Roach, J. R.; Trlvedi, K. K. A New Option for Heat Exchanger Network Design. Chem. Eng. Prog. 1991, 87(9), 38-43. The PPDM is outlined. PPDM is based on thermody-namic principles and provides increased flexibility over PDM. The PPDM method simplifies the DTAM by decomposing it into two subnetworks similar to the PDM.

(277) Wu G. and Zhu X. X. Retrofit of integrated refrigeration systems. Chemical Engineering Research & Design, March 2001, 79(2):163–181. Existing integrated refrigeration systems are decomposed into a refrigeration cycle and a process Heat Exchanger Network (HEN). To optimize the refrigeration cycle, the cycle is extended first to include all potential refrigeration options. Besides the complex refrigeration cycle, these options also generate a special HEN. A systematic method is proposed to optimize the complex cycle and the special HEN simultaneously. This method can give marginal prices of the refrigeration used as utilities in the process HEN. To improve the process HEN, the existing methods for HEN retrofit are used fully, based on the marginal prices of utilities from the refrigeration cycle. A strategy is proposed to co-ordinate the optimisation of the refrigeration cycle and the retrofit of the process HEN. Two case studies show how the proposed methods can retrofit the integrated refrigeration systems efficiently.

(278) Yee, T. F.; Grossmann, I. E. Simultaneous Optimization Models for Heat Integration—II. Heat Exchanger Network Synthesis. Comput. Chem. Eng. 1990, 14 (10), 1165-1184. The superstructure of part I (annotation 281) is used in an MINLP model used to design cost optimal HENs where utility cost, exchanger areas, and the selection of matches are optimized simultaneously. Assumptions are similar to those used previously (annotation 281). The superstructure does not account for split streams going through two or more exchangers in series, the case of bypasses, or split streams going through several exchangers in series.

(279) Yee, T. F.; Grossmann, I. E. A Screening and Optimization Approach for the Retrofit of Heat-Exchanger Networks. Ind. Eng. Chem. Res. 1991, 30(1). 146-162. A two-stage retrofit approach for HENS is proposed. The prescreening stage involves an economic evaluation of the problem. In the optimization stage, a superstructure is constructed and an MINLP formulation is solved for determining the retrofit design.

(280) Yee, T. F.; Grossmann, I. E.; Kravanja, Z. Simultaneous Optimization Models for Heat Integration—1. Area and Energy Targeting and Modeling of Multi-Stream Exchangers. Comput. Chem. Eng. 1990, 14 (10), 1151-1164. A model for simultaneous targeting of energy and area for HENS is introduced. It can incorporate multi-stream heat exchangers. A stagewise superstructure allowing for different possibilities and sequences for matching streams with the assumption of isothermal mixing is presented. The targeting model uses NLP formulations for the simultaneous energy and area minimization or area minimization with fixed utility use. This model can account for differences in heat-transfer coefficients and constraints on matches, and it has no need to fix HRAT or EMAT. Nonconvex terms appear in the objective function.

(281) Yee. T. F.; Grossmann, I. E.: Kravanja, Z. Simultaneous Optimization Models for Heat Integration—III. Process and Heat Exchanger Network Optimization. Comput. Chem. Eng. 1990, 14 (11), 1185-1200. The heat integration representation of part I (annotation 280) is embedded in a process flowsheet or superstructure in order to perform simultaneous optimization of the HEN and the process. It is assumed that only one hot and one cold utility are available at the two extreme ends of the superstructure. NLP and MINLP formulations are presented for combined optimization of the process and the HEN. Heat integration constraints involve nonlinear terms. Design constraints on the HEN are easily incorporated.

(282) Yerramsetty K. M. and Murty C. V. S. Synthesis of cost-optimal heat exchanger networks using differential evolution. Computers & Chemical Engineering, 2008, 32(8):1861–1876. Heat exchanger network synthesis (HENS) has been one of the most-studied problems in process synthesis. Nevertheless, the complexity of the HENS problem provides enough scope for the development of novel algorithms involving the application of specialized optimization techniques. Evolutionary algorithms (EA) have emerged as viable alternatives to traditional methods for optimizing functions of both continuous and discrete variables. Differential evolution (DE) is one such evolutionary algorithm that promises simple, fast and robust optimization. The present study illustrates the application

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of this novel technique for the synthesis of heat exchanger networks. The HENS model proposed here considers stream splitting, does away with the simplifying assumption of isothermal mixing of the split streams and has the capability to handle compulsory and forbidden matching of streams. The DE-based model (DEM) does not rely on the decomposition of the problem into subproblems but employs a simultaneous method of approach to optimize the structure of the network of heat exchangers, the heat loads of these exchangers, the split stream heat flows and the minimum approach temperature. The proposed model has been applied to some case studies available in the literature and the results of these studies are very encouraging. The present work represents thus a step forward in the search for robust and efficient global optimization algorithms for the solution of the HENS problem.

(283) Young B. R., Tellez R., and Svrcek W. Y. Towards integrated process and control system synthesis for heat-integrated plants. Canadian Journal of Chemical Engineering, 84(2):219–229, 2006. Most chemical processes are networks of different pieces of equipment, as reactors, distillation columns, compressors, heat exchangers, etc. Process integration is an area of chemical engineering that deals with the optimal design of these networks, from the point of view of energy efficiency, capital costs, emissions reduction, waster water minimization, and raw materials usage. Until recently, engineers developed conceptual process designs by experience and intuition, however, with the establishment of process integration methodologies, this activity can be performed systematically. One of the subjects that have received the most attention from researchers in this area is the steady state design of Heat Exchanger Networks (HENs). Several tools have been developed and are in use; however, the development of a tool for synthesis of HENs that takes into account network controllability is not available. Hence, the purpose of this paper is the development of a new methodology for design of heat-integrated chemical processes, particularly HENs where controllability and energy recovery are both balanced during the design synthesis stage.

(284) Yu, H.; Fang, H.; Yao, P.; Yuan, Y. A Combined Genetic Algorithm/Simulated Annealing Algorithm for Large Scale System Energy Integration. Comput. Chem. Eng. 2000, 24 (8), 2023-2035. An algorithm is developed for HENS based on combining the GA and SA algorithms. Results show faster convergence than either SA or GA alone, with a higher probability of locating a global optimum.

(285) Zamora. J. M.; Grossmann. I. E. A Global MINLP Optimization Algorithm for the Synthesis of Heat Exchanger Networks with No Stream Splits. Comput. Chem. Eng. 1998, 22 (3), 367-384. An algorithm for the solution of the MINLP HENS model of Yee and Grossmann (annotation 278) is presented. Linear area cost, arithmetic mean temperature difference driving forces, and no stream splitting are assumptions used in the simplification of the solution method.

(286) Zhang, J.; Zhu, X. X. Simultaneous Optimization Approach for Heat Exchanger Network Retrofit with Process Changes. Ind. Eng. Chem. Res. 2000, 39(12). 4963-4973. This paper addresses the problem of a heat exchanger network (HEN) retrofit considering process changes. Traditionally it is a common practice to fix process conditions before a HEN is retrofitted. However, it has been realized that there exists strong interactions between HENs and processes, and it should simultaneously consider the changes to process conditions (e.g. flow rates, temperatures) and the HEN retrofit.In this paper, new insights for process changes and their impacts on HEN retrofit have been developed and the T−H diagram is used to represent the interactions. On the basis of the newly developed understanding, a systematic method has been developed to deal with process changes and HEN topological changes in a simultaneous way. To demonstrate this, a short-cut crude distillation model has been built up that relates stream temperatures and flow rates to process conditions. This model has been combined with the model for HEN topological changes proposed by Zhu and Asante,1 which forms a complete model for optimizing the tradeoff between HEN retrofit and process changes. The case study shows significant cost savings by considering process changes and HEN modifications simultaneously.

(287) Zhao, X. G.; O'Neill. B. K.; Roach, J. R.: Wood, R. M. Heat Integration for Batch Processes Part 1: Process Scheduling Based on Cascade Analysis. Chem. Eng. Res. Des. 1998. 76 (A), 685-699. An MILP formulation based on cascade analysis is proposed for the scheduling of batch processes with heat integration.

(288) Zhao, X. G.; O'Neill, B. K.; Roach, J. R.; Wood, R. M. Heat Integration for Batch Processes Part 2: Heat Exchanger Network Design. Chem. Eng. Res. Des. 1998, 76 (A), 700-710. A three-step HENS method for batch/semicontinuous processes is presented. First, an initial individual design is created using continuous process HENS. Then, re-matching design using MILP considers the relationship for all time intervals. The final overall design looks at the tradeoff between energy and capital costs among time intervals.

(289) Zhu, F. X. X.; Vaideeswaran, L. Recent Research Development of Process Integration in Analysis and Optimisation of Energy Systems. Appl. Therm. Eng. 2000. 20 (15-16), 1381-1392. This article provides an overview of the recent advances in process integration and energy system opti-mization, including sections on total site energy profiles, HEN retrofit, and debottlenecking.

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(290) Zhu. J.; Han, Z.; Rao, M.; Chuang, K. T. Identification of Heat Load Loops and Downstream Paths in Heat Exchanger Networks. Can. J. Chem. Eng. 1996. 74 (6), 876-882. Heat load loops and downstream paths are identified using a representation of a HEN as the combination of the node adjacency matrix, and the stream table is used as a basis.

(291) Zhu, J. Y.; Rao, M.; Chuang, K. T. A New Method to Determine the Best Units for Breaking Heat Load Loops of Heat Exchanger Networks. Ind. Eng. Chem. Res. 1999, 38 (4), 1496-1503. A systematic method for loop breaking is developed in which the effects of heat loads and interactions of units on energy relaxation are taken into account. Constrained heat-exchanger units that cannot absorb any transferred energy are used to find the best units for breaking loops.

(292) Zhu, X. X. Automated Synthesis of HENs Using Block Decomposition and Heuristic Rules. Comput. Chem. Eng. 1995, 7S (Suppl.), S155-S160. An automation of the block decomposition methods presented by Zhu et al. (annotation 296) is described in this work. Heuristic rules for a match selection are based on temperatures and heat load calculations using MILP methods to determine the best set of matches rather than a single best match.

(293) Zhu, X. X. Automated Design Method for Heat Exchanger Network using Block Decomposition and Heuristic Rules. Comput. Chem. Eng. 1997, 21 (10), 1095-1104. An automated synthesis method for HENS based on the block concept simplifies the design problem by decomposing it into a number of blocks. After block decomposition, targeting principles and heuristic rules developed in this paper are used to carry out the design of the HEN. An MILP model is used in the selection of matches and an MINLP model is used in the determination of optimal split ratios.

(294) Zhu, X. X.; Asante, N. D. K. Diagnosis and Optimization Approach for Heat Exchanger Network Retrofit. AIChE J. 1999. 45(1). 1488-1503. A three-stage procedure for retrofit HENS is proposed. First, promising options for modifications are identified using LP and MILP formulations with a heat recovery goal rather than total cost. Then, impractical options are screened out based on cost, safety, and operability issues. Last, options are optimized using an MILP formulation for network modification.

(295) Zhu, X. X.; O'Neill. B. K.; Roach, J. R.; Wood, R. M. A Method for Automated Heat Exchanger Synthesis Using Block Decomposition and Non-Linear Optimization. Chem. Eng. Res. Des. 1995, 73 (A). 919-930. The block concept leads to a simplified block-based superstructure reducing the dimensions of mathematical programming models. A strategy is proposed to overcome the deficiencies of mathematical programming techniques by allowing blocks to encompass a number of intervals, thus reducing the problem size. A region for initiating NLP optimization is located by applying a supertargeting approach.

(296) Zhu, X. X.; O'Neill, B. K.; Roach, J. R.; Wood, R. M. A New Method for Heat Exchanger Network Synthesis Using Area Targeting Procedures. Comput. Chem. Eng. 1995, 19 (2). 197-222. An alternative heuristic to the pinch method is presented. Total cost targets are used to determine optimal HRAT prior to the initial design of the HEN. This introduces blocks, quasi-composite curves, and the matching matrix.

(297) Zhu. X. X.; O'Neill, B. K.: Roach, J. R.; Wood, R. M. Area-Targeting Methods for the Direct Synthesis of Heat Exchanger Networks with Unequal Film Coefficients. Comput. Chem. Eng. 1995, 19 (2), 223-239. Composite curves are decomposed into a number of blocks using the methods in Zhu et al. (annotation 296). The deficiency of widely differing heat-transfer coefficients in terms of area penalty is overcome with the concepts of Rev and Fonyo (annotation 224) coupled with the block method. This approach allows different stream structures to be compared prior to design and attractive structures to be derived from further synthesis and optimization.

(298) Zhu X. X. and Nie X. R. Pressure drop considerations for heat exchanger network grassroots design. Computers & Chemical Engineering, December 2002, 26(12):1661–1676. Pressure drop is an important issue in design of a heat exchanger network (HEN), which has yet to be addressed properly. To overcome pressure losses incurred when streams flow through heat exchangers, pumps/compressors must be installed. The total cost for a system of pumps and compressors consists of the purchase cost of equipment and the electricity cost to run these equipment. This cost could occupy a significant part of the overall cost for a HEN design. Therefore, the pressure drop aspect should be considered together with the costs for heat exchanger area and utility consumption. A new approach is proposed to consider the pressure drop aspect in the overall context of a HEN design. Firstly, the optimal ΔTmin is determined through three-way trade-offs between area, utility and pressure drop at the targeting stage. As a result of targeting, targets for area, utility and pressure drops can be established ahead of the network design. Then a network structure is initialised at the determined ΔTmin and optimised to achieve a final design. In this procedure, the pressure drop is considered at both the targeting stage and the design

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stage in a systematic manner. (299) Zhu X. X. and Vaideeswaran L. Recent research development of process integration in analysis and

optimisation of energy systems. Applied Thermal Engineering, October 2000, 20(15-16):1381–1392. The design of energy systems in a process plant requires a good understanding of each subsystem (e.g. processes, heat exchanger networks, utility systems) and their interactions in the context of an overall plant. An effective design method should be able to explore the synergy between the subsystems to the maximum extent and allow users to interact with the design process. To achieve this, the effective way is to combine physical insights with mathematical optimisation techniques. Physical insights are used as a wise man’s brain and eyes, while optimisation techniques are employed as a superman’s power in searching for optimal solutions. In the past, concepts and methods have been developed for handling grassroots design, operational management, retrofit and debottlenecking scenarios. This paper describes the recent research progress at UMIST in developing fundamental concepts and methodologies for analysis and optimisation of energy systems.

(300) Zhu X. X., Zanfir M., and Klemes J.. Heat transfer enhancement for heat exchanger network retrofit. Heat Transfer Engineering, 2000, 21(2):7–18. Heat exchanger networks (HEN) play important roles in a chemical plant. In a plant lifetime, it may be required to retrofit a HEN several times in order to improve the energy efficiency or to accommodate the increase in throughput. As a result of HEN retrofit, additional surface area is required for some heat exchangers. There are a number of options to provide additional area, such as installing new shells or new units, adding new tubes to an existing bundle, etc. If heat transfer enhancement (HTE) is applied, additional area can be reduced significantly. This can result in a great reduction in capital cost and implementation time for modifications. However, in practice, heat transfer enhancement techniques have not been applied extensively, particularly in the petroleum refining industry. Several main aspects need to be addressed when HTE is taken into consideration for HEN retrofit. The first is how to determine which heat exchangers are suitable to apply HTE in the network and the second issue is to determine what level of augmentation of heat transfer performances is required. The last is about how to select a particular enhancement technique that can fulfil the enhancement requirement. A new strategy for applying HTE in HEN retrofit at the conceptual design stage has been developed. The above issues can be addressed properly by this new method.

3.5.0 Classifications of the Annotated Works: The previous section discussed separately each HENS and MENS work. An overview of these works through several different classification schemes as shown in Tables 1-5 has been provided below: Classifications scheme: 1. Topics in HENS 2. Heat Integration Topic 3. Pinch Technology and other evaluation methods. 4. Modeling and Solution Techniques No. Topic Span : 1990-2011 1. Analysis general 80, 94, 229, 231 2. Dual streams 112 3. Exergy/second law analysis 119, 120, 174, 230, 231, 242, 243 4. Flexibility/resilience 1, 11, 22, 46 , 70, 111, 131, 163, 183, 189, 190, 194, 203,

204, 249, 253, 283 5. Controllability 5, 29, 92,198, 217, 270 6. Operability 56, 90, 91,111, 114, 115,192, 193 7. Multipass heat exchangers / Cooling

Tower 9, 211, 213, 223, 232, 252

8. Operating line method 8 9. Pressure drop/piping 8, 10, 37, 119, 177, 186, 207, 208, 218, 239, 244, 266, 298 10. Retrofit design 2, 4, 8, 17 ,18, 26, 29, 33, 35, 36, 37, 38, 40, 42, 43, 47, 48,

65, 68, 74, 83, 132, 133, 134, 135, 138, 141, 142, 143, 153, , 162, 169, 177, 179, 181, 184, 185, 188, 189, 190, 192, 193, 202, 205, 208, 215, 224, 239, 245, 257, 258, 260, 261, 264, 265, 277, 279, 286, 294, 300

Table 3.1 Topics in HENS

# Numbers in this table refer to the annotated Bibliography of HENS & MENS WORK.

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No. Topic Span : 1990-2011 1. Batch Processes 3, 31, 54, 55, 62, 96, 97, 98, 99, 122, 125, 200, 214, 248, 259,

263, 288 2. Continuous Reactors 14, 15, 3. Distillation Processes / cooling tower 23, 57, 22, 67, 69, 215, 227,

12, 27, 28, 41, 64, 88, 127, 148, 182 4. Heat Engines/ Heat pumps/

Refrigeration systems 89, 65, 262, 136, 174, 277

5. MENS and Separations 24, 25, 196, 188, 23, 195, 247, 191, 30, 51, 95, 275, 32, 39, 59, 100, 118, 130, 165, 166, 176, 187, 246

6. Process integration 6, 139, 158, 93, 7, 14, 79, 58 197, 289, 240, 255, 75, 299, 53, 63, 123, 128, 129, 171, 234, 241, 272

7. Plant/site integration 7, 93, 94, 168, 226 Table 3.2. Heat Integration Topics

# Numbers in this table refer to the annotated Bibliography of HENS & MENS WORK.

No. Topic Span : 1990-2011 1. PDM 7, 40, 126, 155, 156, 157, 180, 206, 242, 2. DTAM 105, 107 3. PPDM 49, 73, 276 4. Enthalpy Interval Partitioning 52, 81, 82 5. Utility Target 112, 167, 235, 238 6. Shell Target 9, 223, 252 7. Number of unit Target 106, 147 8. Area/capital 52, 84, 101, 157, 224, 225, 251 9. Cost Target 235, 172, 229, 266, 232 10. Super targeting 34, 35, 36, , 84, 85, 137, 157, 222, 224, 225, 235, 271 11. Loop Breaking/stream splits 87, 258, 290, 291 12. Multiple pinch points 108, 111, 145 13. Network evolution 86, 146, 147, 159, 160, 214, 228

14. Review/overview 155, 156, 173, 220, 221, 233, 256 Table 3.3. Pinch Technology & Other Evolutionary Methods

# Numbers in this table refer to the annotated Bibliography of HENS & MENS WORK.

No. Topic Span : 1990-2011 1. Block Decomposition 297, 292, 296, 295, 293 2. Constraint Logic Programming 2 3. Direct search 29 4. Disjunctive Programming 79 5. Genetic algorithms 16, 152, 151, 284, 269, 60, 117, 149, 210, 219 6. Knowledge-Based system 92, 124, 154, 164 7. Pre-processing /Pre-screening 57, 264 8. Randomization 44, 87 9. Sequential synthesis 271, 112, 52, 70, 43, 42, 107, 49, 72

73, 71, 45, 34, 36, 104, 83, 201 10. Simulated annealing 21, 20, 19, 178, 254, 284, 61, 160 11. Simultaneous synthesis 50, 280, 278, 285, 192, 193, 194

154, 237, 83, 269, 244, 1, 11, 26, 46, 51, 131, 215 12. State-space approach 23, 24 13. Tree search 267, 268, 140 14. Transportation model 237, 116 15. Transshipment model 82, 81, 34, 115 16. Vertical heat – transfer model 82, 81 17. Review 78, 110

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Tabu search 150 Random search 199 Differential evolution 282

Table 3.4. Modeling and Solution Techniques

# Numbers in this table refer to the annotated Bibliography of HENS & MENS WORK.

No. Topic Span : 1990-2011 1. Utilities cost 112, 72, 73, 238, 22, 111, 237 2. No. of matches/Units/shells 82, 81, 72, 73, 34, 288, 22, 117, 236 3. Area/network topology 50, 216, 34, 121, 237 4. Simultaneous HENS 50, 280, 278, 192, 193, 194, 154, 237, 269, 11, 26, 31 5. Simultaneous process and HENS

Synthesis 281, 263, 58, 79, 197, 191, 51, 175

6. Retrofit HENS 190, 189, 48, 47, 294, 177, 279, 192, 193, 135, 162, 74, 239, 286

Table 3.5. Mathematical Programming Formulation

3.5.1. Topics in HENS: Table 1 lists HENS citations according to various specific topics of interest in this field of research. General analysis includes citations for papers dealing with basic analysis of the HENS problem or some major issue in HENS. The dual stream approach in HENS allows for the possibility of hot process streams acting as cooling streams and cold process streams used as cooling streams within the network. Another name for dual streams is hot-to-hot or cold-to-cold streams. Exergy analysis involves analysis in HENS based on the second law of thermodynamics. Flexibility, resilience, controllability, sensitivity, and operability topics consider how easy networks are to control and operate and how flexible HENs are in cases of parameter variation. The topic of mixing considers the idea of mixing different flows of the same stream type at different temperatures. Multipass heat exchangers allow streams to exchange heat in several passes, as opposed to the single pass of standard countercurrent exchangers. The operating line method is a method for designing a HEN by using an operating curve determined from the problem data as a tool. Pressure drop considerations are important for networks with large distances between exchangers. HEN retrofit design involves the modification of an existing network for a new process.

3.5.2. Heat Integration Topics: Table 2 lists citations related to the heat integration in processes synthesis. Heat integration is a strategy for optimizing a process task or a whole process and the HEN at the same time. This table is not an all-inclusive listing of articles related to heat integration in process design. Instead it lists papers that heavily incorporate the models and techniques developed in HENS research. The process integration label lists papers that involve general heat integration in process synthesis. Plantov site integration includes articles concerning heat integration for multiple processes across an entire plant or site. The other categories also cover specific process heat integration issues, such as batch processes, continuous reactors, distillation systems, heat pumps and engines, and mass-exchange network synthesis (MENS) and separations.

3.5.3. Pinch Technology and Other Evolutionary Methods: Various procedures and techniques related to pinch technology are organized in Table 3. First, the works in the PDM, DTAM, and PPDMare listed. These are the three major pinch-based design procedures. In a pinch-based method, temperature intervals are used to partition the problem and to determine pinch points. Enthalpy intervals are sometimes used in conjunction with temperature intervals for allowing exchanger area cost to be considered in early design steps. PDMs are a sequential approach to HENS and involve determining various design targets in a specific order. The utilities target determines the minimum utility usage. The shell target determines the number of shells in the heat exchangers. The number of units target is for determining a minimum number of heat exchangers required in the design of the network. The heat load distribution is the set of stream matches and the amount of heat exchanged between them. The area target is for determining the heat-exchanger area for the network, 'which directly influences the capital cost of the network. Supertargeting involves determining the optimal approach temperature to partition the temperature range of the problem for lowest total cost. Loop breaking is a specific technique used in reducing heat-exchanger matches for the network. Some HENS problems have multiple pinch points which need to be taken into account in the problem analysis. Network evolution involves the evolution of new and better network configurations. Some works only

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contain case studies which describe the design of a specific HEN for some industrial or hypothetical cases without the development of new methodologies or concepts. Last, reviews and overviews of pinch-based design methods are listed. 3.5.4. Modeling and Solution Techniques: Optimization and other mathematical methods have become increasingly common in HENS research as seen in Table 4. Early work involved fitting the HENS problem to the assignment problem. Branch-and-bound techniques are important considering the use of discrete variables in modern HENS formulations. Block decomposition decomposes the problem into enthalpy blocks rather than temperature intervals. Direct search methods involve heuristics for searching a HENS problem tree. The discrete maximum principle is used for solving multistage optimization problems. Disjunctive programming methods are an alternative to MILP formulations and provide new algorithms for dealing with the combinatorial aspects of the problem. Dynamic programming provides a framework for decomposing an optimization problem into a nested family of subproblems to be solved recursively. Genetic algorithms are a type of search algorithm used to mathematically "evolve" HENS networks. Goal programming is a deterministic optimization strategy. Knowledge-based systems are a type of artificial intelligence which utilizes a large database of problem information in order to make design decisions. Prescreening is used to reduce the feasible space of a formulation prior to solving. Random search techniques randomly search a problem tree for a solution. Randomization methods involve random sampling of the problem space to find a solution. Separable programming an extension of LP that approximates nonlinear functions using piecewise linear approximations. Sequential synthesis is a stepwise HENS method. Simulated annealing techniques couple deterministic and stochastic optimization methods. Simultaneous synthesis solves HENS in inclusive formulations. The state space approach involves relations between input, state, and output variables. Tree searching techniques are used for traversing trees of network configurations. The transportation, transshipment, and vertical heat-transfer models are used to represent the transfer of heat from hot streams to cold streams solving for heat load distributions by formulating the problem using the respective mathematical models. Several of the most common optimization formulations used in HENS are organized in Table 5 and include models used in sequential as well as simultaneous approaches to HENS.

3.6.0 Conclusions: • The HENS and MENS field has received a great deal of attention as demonstrated by the number of

journal papers published in this area in the past 20 years. • HENS and MENS research activity peaked in the late 1980s/early 1990s concurrent with advances in

optimization algorithms and computer hardware that for the first time made possible the solution of simultaneous synthesis problems and heat integration problems.

• Publications in this area indicate that the research conducted is gaining in diversity because we are witnessing a constant diversification of modeling and solution approaches. Many of them, especially in recent years, involve mathematical programming techniques. We also note that the large number of case studies and software that have been developed for industrial use clearly demonstrates that the gap between theory and practice is essentially nonexistent in HENS.

• Despite recent advances in optimization, considerable work remains to be done to solve simultaneous HENS formulations. In addition to the combinatorial complexity of the problem, another major obstacle remaining is the presence of local optima in these formulations, which calls for more robust formulations and/or more efficient global optimization algorithms.

• Although various simultaneous synthesis methods have drawn close, they are limited by a number of restrictive simplifying assumptions including isothermal mixing, no split stream following through more than one exchanger, and no stream bypass. There has yet to be a proposal of a truly complete formulation of the HENS problem without any simplifying assumptions.

• To press further and incorporate these proposed HENS concepts with other aspects of process synthesis would then be the next task in advancing heat integration methods.