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A general methodology for energy efficiency of industrial chemical processes
Mario R. Eden, John D. Siirola and Gavin P. Towler (Editors) Proceedings of the 8 th International Conference on Foundations of Computer-Aided Process Design – FOCAPD 2014 July 13-17, 2014, Cle Elum, Washington, USA © 2014 Elsevier B.V. All rights reserved.
A general methodology for energy efficiency of industrial chemical processes Nasibeh Pouransari,a,* Mathilde Mercier,b Guy-Noel Sauvion,b François Maréchala a
Industrial & Process Energy System Engineering (IPESE), Ecole Polytechnique Fédérael de Lausanne (EPFL), Lausanne, Switzerland, b Solvay R&I Center Lyon, Saint-Fons Cedex, France [email protected]
Abstract This paper presents a general, practical and operational methodology to improve energy efficiency of chemical processes through a holistic approach. The required methods and tools have been developed based on a systematic approach for process energy integration and energy efficiency optimization. The objective is to develop a general methodology adaptable to any type of industrial chemical process, existing and under development. This methodology is summarized into six consecutive steps narrated as following: thermal data is collected first, in order to define the heating and cooling requirement of process. The composite curves are then established and the maximum energy recovery is calculated as a preliminary target. Technical improvement solutions are consequently proposed through integration of new technologies and modification of the process unit operations (incremental and/or step changes). Suitable energy conversion units together with the proposed improvement options are then integrated and optimized. Among the feasible solutions, the most promising ones are selected; investment costs are evaluated and retrofit and re-designing of the heat exchangers network are performed for those solutions. Finally the profitability of the most promising proposals is evaluated and the best compromise is chosen. The application of the proposed methodology is demonstrated through a case study highlighting the different steps and the potential of the proposed approach. Keywords: Pinch analysis, Process integration, energy efficiency, chemical process.
1. Introduction During the last few decades, energy consumption has become of important concern throughout industries, based on the availability of resources and the environmental effect of the energy generation. This has motivated industries to reduce their energy consumption and to improve their energy efficiency in parallel. One of the main topics regarding the energy efficiency improvement for chemical process industries is process integration which is a methodology for analysis, design and optimization of material and energy related production systems (Gundersen 2013). A key concept in this field is pinch analysis which can be summarized as a heat integration methodology for scoping and screening of options during targeting, prior to the heat exchanger network (HEN) design (Linnhoff 1993). This method provides engineers with guidelines for process heat and power systems design and targets the Minimum Energy Requirement (MER) for any process (Hall & Linnhoff 1994). Mass integration has also been developed for reducing waste water effluents based on pinch analysis and can also lead to substantial energy saving (El-Halwagi & Manousiouthakis 1989). Different methodologies based
412
N. Pouransari et al.
on process integration and pinch analysis techniques are proposed for special cases. Kalitventzeff and Maréchal (2000), developed a methodology and appropriate tools in order to compute the optimal insertion of intensified energy saving technologies in the industrial processes. A four steps method for simplification of process integration studies for intermediate size industries is presented by Dalsgård et al (2002). Becker et al (2011) has further presented a methodology based on pinch analysis to identify heat pump opportunities in industrial processes and Périn-Levasseur (2009) proposed another one to analyse the optimized integration of energy conversion technologies in existing pulp and paper facilities. Mateos-Espejel et al (2011) has also proposed a unified methodology for thermal energy efficiency improvement of a process in a global process perspective. A more detailed review of the past 40 years of developments around the heat integration domains can be found in Klemeš and Kravanja (2013). This study presents a general computer-aided methodology aiming to improve the energy efficiency of chemical processes. The steps of this methodology are established based on the typical difficulties and constraints related to the large-scale plants.
Figure.1 Different steps of the proposed energy efficiency methodology
2. Methodology Our proposed methodology can be summarized into six steps where each comes with a novel approach to the problem (See Fig 1). x
x
x
x
The primary step of the pyramid represents the process definition. Based on the available level of detail, the necessary thermal data is extracted in order to identifying the heating and cooling requirement of process and the corresponding energy requirement representations are defined. The second step corresponds to the pinch analysis where the heat exchange profile of the entire process is established through the composite curves and the maximum energy recovery by heat exchange is determined and considered as the target. Based on the analysis of the grand composite curves and on the characteristics of the process, different options including the operating condition modification, integration of new technologies and step-change are proposed in the third step in order to further reduce the energy consumption and to improve the target. Suitable energy conversion units together with the proposed improvement options are optimally integratedusing a Mixed Integer Linear Programming (MILP) formulation.
A general methodology for energy efficiency of industrial chemical processes
413
x
Throughout the fifth step, the best proposed solutions are economically evaluated. For each of the selected options, the heat exchangers network (HEN) is retrofitted and re-designed, considering all engineering relevant constrains. x Finally, the profitability of the best options is evaluated in more detail. The energetic studies presented here, are performed using the energy analysis tools developed at the Industrial Process & Energy Systems Engineering Laboratory (Bolliger 2010) of the Ecole Polytechnique Fédérale de Lausanne (EPFL) and this methodology is a fruit of the collaboration between EPFL and Solvay.
3. Case Study The above mentioned methodology is applied to a real chemical process. The project details and the client information are not revealed due to confidentiality and results are presented with relative values. 3.1. Step 1: Data extraction & energy requirement analysis We start from the general overview of the site (see Fig 2.), where process systems are considered together with the energy conversion units and distribution system. A systematic definition of the process heat transfer requirement for each process unit operation (PUO) is an important perquisite for process integration in which data extraction is the initial step. A multi-level data extraction approach (Pouransari et al 2014) based on exergy analysis is employed in order to define the energy requirement of different data collection sources including energy conversion, distribution or process units. The hot and cold streams are consequently determined.
Figure.2 Analysis of process heat requirement
3.2. Step 2: Process integration and targeting The composite and grand composite curves are generated in the following step by the aid of determined heating and cooling requirements. (Fig 3) An initial minimum temperature approach (ǻT min) at Pinch Point is considered to have the optimal use of heat exchangers. An individual ǻTmin contribution is considered for each stream, based on the heat transfer coefficient of the relevant physical state. The MER is then determined for the given ǻTmin and considered as an initial target for heat recovery. Fig 3.a presents the composite curves of the total process in the corrected temperature axis. It shows the maximum heat recovery by heat -or the minimum energy requirement(MER). In this case, there is a 54 % potential of integration (from the total heating requirement) compared to 40 % of integration in the current process which correspond to the first benefit.
414
N. Pouransari et al.
Figure.3 Composite curves and grand composite curve of the site
3.3. Step 3: Improvement potentials (Plus-minus, new technologies and step-change) Based on the result of grand composite curve and plus-minus principle (Linnhoff 1993), the maximum heat recovery can be further improved by either integrating supplementary equipment (like heat pump) or by modifying process operating conditions (modifying pressure). The purpose of all kind of modifications is to either move hot streams from below of the pinch to the above or to move the cold streams from above of the pinch to a below the pinch position. The streams around the Pinch point are fundamental. The analysis can also result in solutions which modify the process unit operations (incremental or step changes). Finally in order to adapt a more global energy analysis approach, some modifications can also be proposed such as the reduction of a solvent ratio, distillation modification or other unit operations and an intermediate network. The analysis of the grand composite curve (GCC) (Fig 3.b) with respect to the condition of this system (streams phase and temperature range) shows that there is a large potential for recompression or heat pumping. The compression cycles are added to the appropriate place with respect to the pinch point. This procedure is however possible until a new pinch point is activated. Therefore, in order to increase the recompression potential and also to avoid a quick creation of new pinch points, heat pumping system is proposed to be integrated to the composite curves. Having those observations, the recompression and heat pumping are considered in the following steps throughout the optimization problem to find the optimum flow rate for their flows. Obviously, we bear in mind that implementation of each new solution on the system will modify the target.
Figure.4 a) System with MVR b) System with MVR and heat pumps
3.4. Step 4: Energy conversion unit integration & optimization Suitable energy conversion units are integrated and their optimum flow rate are found by MILP formulation proposed in Maréchal and Kalitventzeff (1998) which defines the heat cascade of the pinch method as a set of inequality constraints. This method selectsthe equipment in the superstructure and determines their optimal operating
A general methodology for energy efficiency of industrial chemical processes
415
flowrate in the integrated system. The objective is to minimize the operating costs including the fuel and electricity costs. In order to optimize the mass flow rates of the Mechanical Vapor Recompression (MVR), a new equality is also added to the MILP optimization problem. The optimum integration of MVR and heat pumps is performed simultaneously with the energy conversion units. The composite curves of system with MVR alone and together with heat pumps are respectively shown in Fig 4.a and b. By adding an MVR unit, the mechanical power is calculated and a new hot stream is implemented. The principle of the calculation for the mechanical vapor compression is shown in Fig 5. In order to create a link between the part that is recompressed and the part which is used by direct heat exchange, a new equation ݉ሶ௧௧ ൌ ݉ሶ௩ ݉ሶௗ is added to the MILP problem. Adding an MVR unit to transfer heat from below to above of the pinch, results in an improvement of the integration ratio by 20 % (from 54 % in case of the process integration alone to 65 % in case MVR integrated). Considering the newly activated pinch points (Fig 4.a), additional heat pumps are also added to system (Fig 4.b) to further increase the heat recovery potential up to 86 %. With the three ideal targets shown here, the overall evaluated energy savings could be between 20% - 75 % approximately. The above detailed strategy will be a starting point for designing more realistic options.
Figure.5 Mechanical vapor recompression integration
3.5. Step 5: Evaluation (Economic, HEN) In this step, the most promising solutions are selected by a multi-objective optimization over different possibilities of retrofitting and re-designing the HEN. The operating cost and investment cost are considered as objective functions. All of the existing heat transfer interfaces together with the new potential of heat exchange are evaluated simultaneously. One of the advantages of this evaluation is that it is performed before designing the HEN while it has included all the engineering constraints. The realistic options can therefore be selected by taking into account the economic analysis, the plant constraints (e.g., geographical location of plant and equipment), the recommendations of plant experts (e.g., the characteristic of chemical materials and their physical limits) and the knowledge of pinch curves and engineering considerations (e.g., debottlenecking). Here, is a key step of the methodology where the realistic options are proposed from the ideal targets. The result of this analysis identifies the optimum modifications of the existing design. The HEN is then retrofitted by firstly solving the sub-problem of heat load distribution (HLD) (Gundersen & Grossmann 1990) for each zone created by two consecutive pinch points in composite curves. The restricted matched are also considered by defining an intermediate heat transfer unit between them using the approach was proposed by Becker and Maréchal (2011). 3.6. Step 6: Final proposal (Profitability analysis) In the final step, the profitability of the selected proposals are evaluated and compared.
416
N. Pouransari et al.
The net present value (NPV) and payback time (PBT) are calculated for each solution. Finally, the solutions with positive NPV and PBT of less than two years, which are also in range of the acceptable investment framework of the company, are considered as final proposals and are presented to the decision makers in order to pick the appropriate improvement package.
4. Conclusions A general and practical methodology for energy efficiency improvement of industrial chemical processes is presented here. Coming from collaboration between industry and university, it aims to employ the computational tools and ideal targets of process integration for real life cases from large scale industrial sites. The methodology is practical for both retrofit and grassroots design and is flexible regarding the scope and size of the plant. It investigates maximum process integration, optimized energy conversion integration, optimum process operation condition and process new-design all simultaneously. Applying the methodology on our real life case study demonstrated a high potential for energy saving. The methodology is still under development and some further featurs like mass integration can also be considered through.
References Becker H, Maréchal F. 2011. energy integration of industrial sites with heat exchange restrictions. Computer & Chemical Engineering Becker H, Maréchal F, Vuillermoz A. 2011. Process integration and opportunities for heat pumps in industrial processes. International Journal of Thermodynamics 14: 59-70 Bolliger R. 2010. Méthodologie de la synthèse des systèmes énergétiques industriels. EPFL, Lausanne. 248 pp. Dalsgård H, Maagoe Petersen P, Qvale B. 2002. Simplification of process integration studies in intermediate size industries. Energy Conversion and Management 43 El-Halwagi MM, Manousiouthakis V. 1989. Synthesis of mass exchange networks. AIChEJournal 35 Gundersen T. International Process Integration Jubilee Conference, Gothenburg, Sweden, 2013. Gundersen T, Grossmann IE. 1990. Improved optimization strategies for automated heat exchanger network synthesis through physical insights. Computers and Chemical Engineering 14: 925-44 Hall SG, Linnhoff B. 1994. Targeting for furnace systems using pinch analysis. Industrial and Engineering Chemistry Research 33: 3187-95 Kalitventzeff B, Maréchal F. 2000. 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. Applied Thermal Engineering 20: 1347-64 Klemeš JJ, Kravanja Z. 2013. Forty years of Heat Integration: Pinch Analysis (PA) and Mathematical Programming (MP). Current Opinion in Chemical Engineering Linnhoff B. 1993. Pinch analysis - a state-of-the-art overview. Chemical Engineering Research and Design 71: 503-22 Maréchal F, Kalitventzeff B. 1998. Energy integration of industrial sites: Tools, methodology and application. Applied Thermal Engineering 18: 921-33 Mateos-Espejel E, Savulescu L, Maréchal F, Paris J. 2011. Unified methodology for thermal energy efficiency improvement: Application to Kraft process. Chemical Engineering Science 66: 135-51 Périn-Levasseur Z. 2009. Energy efficiency and conversion in complex integrated industrial sites : application to a sulfite pulping facility. EPFL, Lausanne. 198 pp. Pouransari N, Bocquenet G, Maréchal F. 2014. Site-scale process integration and utility optimization with multi-level energy requirement definition. Energy Conversion and Management
A general methodology for energy efficiency of industrial chemical processes Nasibeh Pouransari,a,* Mathilde Mercier,b Guy-Noel Sauvion,b François Maréchala a
Industrial & Process Energy System Engineering (IPESE), Ecole Polytechnique Fédérael de Lausanne (EPFL), Lausanne, Switzerland, b Solvay R&I Center Lyon, Saint-Fons Cedex, France [email protected]
Abstract This paper presents a general, practical and operational methodology to improve energy efficiency of chemical processes through a holistic approach. The required methods and tools have been developed based on a systematic approach for process energy integration and energy efficiency optimization. The objective is to develop a general methodology adaptable to any type of industrial chemical process, existing and under development. This methodology is summarized into six consecutive steps narrated as following: thermal data is collected first, in order to define the heating and cooling requirement of process. The composite curves are then established and the maximum energy recovery is calculated as a preliminary target. Technical improvement solutions are consequently proposed through integration of new technologies and modification of the process unit operations (incremental and/or step changes). Suitable energy conversion units together with the proposed improvement options are then integrated and optimized. Among the feasible solutions, the most promising ones are selected; investment costs are evaluated and retrofit and re-designing of the heat exchangers network are performed for those solutions. Finally the profitability of the most promising proposals is evaluated and the best compromise is chosen. The application of the proposed methodology is demonstrated through a case study highlighting the different steps and the potential of the proposed approach. Keywords: Pinch analysis, Process integration, energy efficiency, chemical process.
1. Introduction During the last few decades, energy consumption has become of important concern throughout industries, based on the availability of resources and the environmental effect of the energy generation. This has motivated industries to reduce their energy consumption and to improve their energy efficiency in parallel. One of the main topics regarding the energy efficiency improvement for chemical process industries is process integration which is a methodology for analysis, design and optimization of material and energy related production systems (Gundersen 2013). A key concept in this field is pinch analysis which can be summarized as a heat integration methodology for scoping and screening of options during targeting, prior to the heat exchanger network (HEN) design (Linnhoff 1993). This method provides engineers with guidelines for process heat and power systems design and targets the Minimum Energy Requirement (MER) for any process (Hall & Linnhoff 1994). Mass integration has also been developed for reducing waste water effluents based on pinch analysis and can also lead to substantial energy saving (El-Halwagi & Manousiouthakis 1989). Different methodologies based
412
N. Pouransari et al.
on process integration and pinch analysis techniques are proposed for special cases. Kalitventzeff and Maréchal (2000), developed a methodology and appropriate tools in order to compute the optimal insertion of intensified energy saving technologies in the industrial processes. A four steps method for simplification of process integration studies for intermediate size industries is presented by Dalsgård et al (2002). Becker et al (2011) has further presented a methodology based on pinch analysis to identify heat pump opportunities in industrial processes and Périn-Levasseur (2009) proposed another one to analyse the optimized integration of energy conversion technologies in existing pulp and paper facilities. Mateos-Espejel et al (2011) has also proposed a unified methodology for thermal energy efficiency improvement of a process in a global process perspective. A more detailed review of the past 40 years of developments around the heat integration domains can be found in Klemeš and Kravanja (2013). This study presents a general computer-aided methodology aiming to improve the energy efficiency of chemical processes. The steps of this methodology are established based on the typical difficulties and constraints related to the large-scale plants.
Figure.1 Different steps of the proposed energy efficiency methodology
2. Methodology Our proposed methodology can be summarized into six steps where each comes with a novel approach to the problem (See Fig 1). x
x
x
x
The primary step of the pyramid represents the process definition. Based on the available level of detail, the necessary thermal data is extracted in order to identifying the heating and cooling requirement of process and the corresponding energy requirement representations are defined. The second step corresponds to the pinch analysis where the heat exchange profile of the entire process is established through the composite curves and the maximum energy recovery by heat exchange is determined and considered as the target. Based on the analysis of the grand composite curves and on the characteristics of the process, different options including the operating condition modification, integration of new technologies and step-change are proposed in the third step in order to further reduce the energy consumption and to improve the target. Suitable energy conversion units together with the proposed improvement options are optimally integratedusing a Mixed Integer Linear Programming (MILP) formulation.
A general methodology for energy efficiency of industrial chemical processes
413
x
Throughout the fifth step, the best proposed solutions are economically evaluated. For each of the selected options, the heat exchangers network (HEN) is retrofitted and re-designed, considering all engineering relevant constrains. x Finally, the profitability of the best options is evaluated in more detail. The energetic studies presented here, are performed using the energy analysis tools developed at the Industrial Process & Energy Systems Engineering Laboratory (Bolliger 2010) of the Ecole Polytechnique Fédérale de Lausanne (EPFL) and this methodology is a fruit of the collaboration between EPFL and Solvay.
3. Case Study The above mentioned methodology is applied to a real chemical process. The project details and the client information are not revealed due to confidentiality and results are presented with relative values. 3.1. Step 1: Data extraction & energy requirement analysis We start from the general overview of the site (see Fig 2.), where process systems are considered together with the energy conversion units and distribution system. A systematic definition of the process heat transfer requirement for each process unit operation (PUO) is an important perquisite for process integration in which data extraction is the initial step. A multi-level data extraction approach (Pouransari et al 2014) based on exergy analysis is employed in order to define the energy requirement of different data collection sources including energy conversion, distribution or process units. The hot and cold streams are consequently determined.
Figure.2 Analysis of process heat requirement
3.2. Step 2: Process integration and targeting The composite and grand composite curves are generated in the following step by the aid of determined heating and cooling requirements. (Fig 3) An initial minimum temperature approach (ǻT min) at Pinch Point is considered to have the optimal use of heat exchangers. An individual ǻTmin contribution is considered for each stream, based on the heat transfer coefficient of the relevant physical state. The MER is then determined for the given ǻTmin and considered as an initial target for heat recovery. Fig 3.a presents the composite curves of the total process in the corrected temperature axis. It shows the maximum heat recovery by heat -or the minimum energy requirement(MER). In this case, there is a 54 % potential of integration (from the total heating requirement) compared to 40 % of integration in the current process which correspond to the first benefit.
414
N. Pouransari et al.
Figure.3 Composite curves and grand composite curve of the site
3.3. Step 3: Improvement potentials (Plus-minus, new technologies and step-change) Based on the result of grand composite curve and plus-minus principle (Linnhoff 1993), the maximum heat recovery can be further improved by either integrating supplementary equipment (like heat pump) or by modifying process operating conditions (modifying pressure). The purpose of all kind of modifications is to either move hot streams from below of the pinch to the above or to move the cold streams from above of the pinch to a below the pinch position. The streams around the Pinch point are fundamental. The analysis can also result in solutions which modify the process unit operations (incremental or step changes). Finally in order to adapt a more global energy analysis approach, some modifications can also be proposed such as the reduction of a solvent ratio, distillation modification or other unit operations and an intermediate network. The analysis of the grand composite curve (GCC) (Fig 3.b) with respect to the condition of this system (streams phase and temperature range) shows that there is a large potential for recompression or heat pumping. The compression cycles are added to the appropriate place with respect to the pinch point. This procedure is however possible until a new pinch point is activated. Therefore, in order to increase the recompression potential and also to avoid a quick creation of new pinch points, heat pumping system is proposed to be integrated to the composite curves. Having those observations, the recompression and heat pumping are considered in the following steps throughout the optimization problem to find the optimum flow rate for their flows. Obviously, we bear in mind that implementation of each new solution on the system will modify the target.
Figure.4 a) System with MVR b) System with MVR and heat pumps
3.4. Step 4: Energy conversion unit integration & optimization Suitable energy conversion units are integrated and their optimum flow rate are found by MILP formulation proposed in Maréchal and Kalitventzeff (1998) which defines the heat cascade of the pinch method as a set of inequality constraints. This method selectsthe equipment in the superstructure and determines their optimal operating
A general methodology for energy efficiency of industrial chemical processes
415
flowrate in the integrated system. The objective is to minimize the operating costs including the fuel and electricity costs. In order to optimize the mass flow rates of the Mechanical Vapor Recompression (MVR), a new equality is also added to the MILP optimization problem. The optimum integration of MVR and heat pumps is performed simultaneously with the energy conversion units. The composite curves of system with MVR alone and together with heat pumps are respectively shown in Fig 4.a and b. By adding an MVR unit, the mechanical power is calculated and a new hot stream is implemented. The principle of the calculation for the mechanical vapor compression is shown in Fig 5. In order to create a link between the part that is recompressed and the part which is used by direct heat exchange, a new equation ݉ሶ௧௧ ൌ ݉ሶ௩ ݉ሶௗ is added to the MILP problem. Adding an MVR unit to transfer heat from below to above of the pinch, results in an improvement of the integration ratio by 20 % (from 54 % in case of the process integration alone to 65 % in case MVR integrated). Considering the newly activated pinch points (Fig 4.a), additional heat pumps are also added to system (Fig 4.b) to further increase the heat recovery potential up to 86 %. With the three ideal targets shown here, the overall evaluated energy savings could be between 20% - 75 % approximately. The above detailed strategy will be a starting point for designing more realistic options.
Figure.5 Mechanical vapor recompression integration
3.5. Step 5: Evaluation (Economic, HEN) In this step, the most promising solutions are selected by a multi-objective optimization over different possibilities of retrofitting and re-designing the HEN. The operating cost and investment cost are considered as objective functions. All of the existing heat transfer interfaces together with the new potential of heat exchange are evaluated simultaneously. One of the advantages of this evaluation is that it is performed before designing the HEN while it has included all the engineering constraints. The realistic options can therefore be selected by taking into account the economic analysis, the plant constraints (e.g., geographical location of plant and equipment), the recommendations of plant experts (e.g., the characteristic of chemical materials and their physical limits) and the knowledge of pinch curves and engineering considerations (e.g., debottlenecking). Here, is a key step of the methodology where the realistic options are proposed from the ideal targets. The result of this analysis identifies the optimum modifications of the existing design. The HEN is then retrofitted by firstly solving the sub-problem of heat load distribution (HLD) (Gundersen & Grossmann 1990) for each zone created by two consecutive pinch points in composite curves. The restricted matched are also considered by defining an intermediate heat transfer unit between them using the approach was proposed by Becker and Maréchal (2011). 3.6. Step 6: Final proposal (Profitability analysis) In the final step, the profitability of the selected proposals are evaluated and compared.
416
N. Pouransari et al.
The net present value (NPV) and payback time (PBT) are calculated for each solution. Finally, the solutions with positive NPV and PBT of less than two years, which are also in range of the acceptable investment framework of the company, are considered as final proposals and are presented to the decision makers in order to pick the appropriate improvement package.
4. Conclusions A general and practical methodology for energy efficiency improvement of industrial chemical processes is presented here. Coming from collaboration between industry and university, it aims to employ the computational tools and ideal targets of process integration for real life cases from large scale industrial sites. The methodology is practical for both retrofit and grassroots design and is flexible regarding the scope and size of the plant. It investigates maximum process integration, optimized energy conversion integration, optimum process operation condition and process new-design all simultaneously. Applying the methodology on our real life case study demonstrated a high potential for energy saving. The methodology is still under development and some further featurs like mass integration can also be considered through.
References Becker H, Maréchal F. 2011. energy integration of industrial sites with heat exchange restrictions. Computer & Chemical Engineering Becker H, Maréchal F, Vuillermoz A. 2011. Process integration and opportunities for heat pumps in industrial processes. International Journal of Thermodynamics 14: 59-70 Bolliger R. 2010. Méthodologie de la synthèse des systèmes énergétiques industriels. EPFL, Lausanne. 248 pp. Dalsgård H, Maagoe Petersen P, Qvale B. 2002. Simplification of process integration studies in intermediate size industries. Energy Conversion and Management 43 El-Halwagi MM, Manousiouthakis V. 1989. Synthesis of mass exchange networks. AIChEJournal 35 Gundersen T. International Process Integration Jubilee Conference, Gothenburg, Sweden, 2013. Gundersen T, Grossmann IE. 1990. Improved optimization strategies for automated heat exchanger network synthesis through physical insights. Computers and Chemical Engineering 14: 925-44 Hall SG, Linnhoff B. 1994. Targeting for furnace systems using pinch analysis. Industrial and Engineering Chemistry Research 33: 3187-95 Kalitventzeff B, Maréchal F. 2000. 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. Applied Thermal Engineering 20: 1347-64 Klemeš JJ, Kravanja Z. 2013. Forty years of Heat Integration: Pinch Analysis (PA) and Mathematical Programming (MP). Current Opinion in Chemical Engineering Linnhoff B. 1993. Pinch analysis - a state-of-the-art overview. Chemical Engineering Research and Design 71: 503-22 Maréchal F, Kalitventzeff B. 1998. Energy integration of industrial sites: Tools, methodology and application. Applied Thermal Engineering 18: 921-33 Mateos-Espejel E, Savulescu L, Maréchal F, Paris J. 2011. Unified methodology for thermal energy efficiency improvement: Application to Kraft process. Chemical Engineering Science 66: 135-51 Périn-Levasseur Z. 2009. Energy efficiency and conversion in complex integrated industrial sites : application to a sulfite pulping facility. EPFL, Lausanne. 198 pp. Pouransari N, Bocquenet G, Maréchal F. 2014. Site-scale process integration and utility optimization with multi-level energy requirement definition. Energy Conversion and Management