Ferenc Friedler

Keywords:

play a pioneering role in contributing to the solution of the related problems through presenting new methodologies and initiating cooperation among participants that often result in international projects. The PRES conferences have been dedicated both to the theoretical and to the practical aspects of energy saving and pollution reduction. The PRES series, established thirteen years ago, was originally dedicated to energy integration and improving thermal efficiency. Following the new challenges and priorities, the scope of the conferences has been extended to include all energy and pollution prevention related issues. This contribution focuses on the period covered by PRES, reviewing at least some major presentations contributing to the development of process integration and optimisation tools for energy saving and pollution reduction. The development of the mathematical models has been covered as well, since it is closely related to the area.

Process Integration (PI)

PI is a family of methodologies for combining several processes to reduce consumption of resources or harmful emissions to the environment. It started as mainly heat integration stimulated by the energy crisis in the 1970's.

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Early Stages of PI

It is remarkable that PI has not lost the interest of researchers for nearly 40 years and even has been flourishing recently. One of the first related works was that by Hohmann [START_REF] Hohmann | Optimum Networks for Heat Exchange[END_REF] in his PhD thesis. He has not pursued the research any further and in that -ancient pre-internet age‖ its enormous potential has not been recognised by the research community at that time. It was Bodo Linnhoff and his PhD supervisor the late John Flower at University of Leeds who continued this work. They used Hohmann's work and in 1977 developed the basis of pinch technology, which is now considered as the foundation of heat integration. As usual in case of a pioneering innovation, it was difficult to publish. The first publications appeared in 1978 [START_REF] Linnhoff | Synthesis of Heat Exchanger Networks: I. Systematic generation of energy optimal networks[END_REF] due to their strong commitment. This has become one of most cited papers in the history of chemical engineering. A similar work has been done in Japan more or less in parallel [START_REF] Umeda | Heat Exchange System Synthesis[END_REF][START_REF] Umeda | Thermodynamic Approach to the Synthesis of Heat Integration Systems in Chemical Processes[END_REF].

However, it was again Linnhoff who pushed the new concept through the academia and the industry. An important step was his arrival, via an industrial appointment at ICI Ltd in Runcorn, Cheshire, to that time UMIST where he set up the Centre for Process Integration and the Process Integration Research Consortium.

Pinch Technology for Heat Integration

The publication of the first -red‖ book by Linnhoff et al. [START_REF] Linnhoff | A User Guide to Process Integration for the Efficient Use of Energy[END_REF] played a key role in the dissemination of heat integration. The book received a new extended Foreword [START_REF] Linnhoff | A User Guide to Process Integration for the Efficient Use of Energy[END_REF] reflecting the up to date developments. It has been again massively cited in the literature and is considered as the first overview of the area. This User Guide through pinch analysis provided insight into the most common process network design problems including heat exchanger network synthesis, heat recovery targeting, and selecting multiple utilities. Heat recovery targeting is based on the Composite Curves (CC) [START_REF] Linnhoff | Understanding Heat Exchanger Networks[END_REF]. This is a visual tool, providing important energy-related properties of an industrial process in a single view. The overlap between the curves represents the heat recovery target, while the minimal needs for external heating and cooling are represented by the non-overlapping segments of the cold and hot composite curves, respectively. Most importantly, these thermodynamically derived heat recovery targets cannot be exceeded by any real system. CCs play an important role in process design. For direct Heat Exchanger Network (HEN) synthesis algorithms, they provide strict targets for Maximum Energy Recovery (MER). For process synthesis based on Mathematical Programming or combinatorics, they provide relevant lower bounds on utility requirements and capital cost, narrowing the search space of the optimisation. The recognition of the thermodynamic limitations and relationships in the underlying heat recovery problem

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has led to the development of the Pinch Design Method [START_REF] Linnhoff | The Pinch Design Method for Heat Exchanger Networks[END_REF]. This method is capable of producing maximum heat recovery networks.

A further development for Heat Integration targeting has been the Grand Composite Curve -GCC [START_REF] Townsend | Heat and power networks in process design. Part II: Design procedure for equipment selection and process matching[END_REF], together with the associated Heat Cascade and the Problem Table Algorithm [START_REF] Linnhoff | Synthesis of Heat Exchanger Networks: I. Systematic generation of energy optimal networks[END_REF].

The GCC shows a clearer view of the areas of internal process heat self-sufficiency as well as the demands for external heating and coolingall in the context of the corresponding temperature levels. The appropriate combination of utilities can be targeted aiming at minimal emissions and/or utility costs.

Mass and Water Pinch

Inspired by the success of Heat Integration, researchers have spread the Pinch idea to other areasin particular to mass exchange [START_REF] El-Halwagi | Synthesis of Mass Exchange Networks[END_REF]. Wang and Smith [START_REF] Wang | Wastewater minimisation[END_REF] developed a synthesis method for industrial Water Networks as a special case of Mass Exchange Networks. The main objective was to simultaneously minimise the consumption of fresh water and the disposal of wastewater by maximising the internal water re-use. Wastewater generation can be further reduced by applying water regeneration, allowing further re-use or recycling. For cases of single-contaminant problems, translating the Pinch Analysis to water minimisation is straightforward, constructing the composite curve of water use as a plot of the contaminant concentration versus contaminant load. Extending the Water Pinch Analysis to multiplecontaminant problems, however, is complicated and difficult to use. The major issue is which one contaminant to plot on the composite curves. Many approaches are available. One useful option is to employ Mathematical Programming; where Water Pinch serves as a preliminary scoping and visualisation tool.

Other Pinch based Methodologies

The Pinch Principle has also been applied to other types of processes and areas, the most prominent being Total Site Integration, refinery hydrogen management, Carbon Footprint estimation/minimisation, and wastewater treatment.

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Hydrogen Pinch

Previously hydrogen availability was not a problem for refineries, but several new trends have caused an increased demand for hydrogen. A methodology has been developed for assessing the available hydrogen resources on a site, using the so-called Hydrogen Pinch Analysis [START_REF] Alves | Analysis and design of refinery hydrogen distribution systems[END_REF].

It constructs Hydrogen Composite Curves accounting for the demands and sources of hydrogen on a site in terms of stream purity vs. flowrate. That is used to construct a hydrogen surplus diagram similar to the GCC in Heat Integration. These instruments allow engineers to find the system Hydrogen pinch and set targets for hydrogen recovery, production and import by a refinery. This methodology has been improved by Hallale and Liu [START_REF] Hallale | Refinery hydrogen management for clean fuels production[END_REF] accounting for pressure as a factor and, therefore, making the best use of the existing compressors in the refinery. This improved method can also account for important costs and tradeoffs including hydrogen production, compressors, fuel, and piping costs.

Oxygen Pinch

The strive to design more cost efficient waste treatment systems inspired yet another extension of the pinch principlethe Oxygen Pinch Analysis [START_REF] Zhelev | Energy-environment closed loop through oxygen pinch[END_REF]. The idea was to target prior to design the ideal minimum oxygen demands for micro-organisms aeration. Flowsheet and design changes were suggested based on the target. Agitation and other forms of aeration require energy, so finally, the analysis based on oxygen pinch principles leads again to their original application associated with energy conservation. The method also provides other indicatorsquantitative targets for oxygen solubility, residence time, and oxidation energy load. In a follow-up development, a combined Water-and-Oxygen Pinch Analysis has been proposed [START_REF] Zhelev | Combined water-oxygen pinch analysis for better wastewater treatment management[END_REF]. By combining the two criteria, up to 30 % cost savings for the wastewater treatment could be achieved.

Total Site

To develop a good understanding of industrial energy systems, a graphical method has been developed based on the concept of the Total Site [START_REF] Dhole | Total site targets for fuel, co-generation, emissions and cooling[END_REF]. They have introduced the concept of the site's heat source and heat sink profiles. By integrating a number of processes via the steam system, additional inter-process heat recovery can be achieved by using the total site profiles as guides. The method allows a target to be set for the total site heat recovery. Data for process heat recovery are first converted to grand composite curves (GCCs). The pockets

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of the GCCs representing the scope for process to process heat recovery are removed and the modified GCCs are combined to form a site heat source profile and a site heat sink profile.

The sink and source profiles are superimposed on the steam header saturation temperatures and CC of steam generation and usage are constructed, accounting for feasible heat transfer from the heat source profile to the steam generation composite and from the steam usage composite to the heat sink profile. The work by Dhole and Linnhoff [START_REF] Dhole | Total site targets for fuel, co-generation, emissions and cooling[END_REF] and by Raissi [START_REF] Raissi | Total Site Integration[END_REF] was further developed by Klemeš et al. [START_REF] Klemeš | Targeting and Design Methodology for Reduction of Fuel, Power and CO 2 on Total Sites[END_REF]. On the basis of the Steam Composite Curves, thermodynamic targets for heat and power cogeneration can be set. The cogeneration targeting model has been further refined and improved by Mavromatis and Kokossis [START_REF] Mavromatis | Conceptual Optimisation of Utility Networks for Operational variations -I. Targets and Level Optimisation[END_REF] and later by Varbanov et al. [START_REF] Varbanov | Modelling and Optimisation of Utility Systems[END_REF] and the most recently by Varbanov and Klemeš [START_REF] Varbanov | Total Sites Integrating Renewables with Extended Heat Transfer and Recovery[END_REF].

Contributions of PRES Conferences

First PRES Conferences PRES'98 and PRES'99

PRES Conferences contributed considerably to the development of PI methodologies and dissemination of successful case studies. Bodo Linnhoff presented one of his last plenary lectures [START_REF] Linnhoff | Automated Interface between Simulation and Integration[END_REF] on the automated interface between simulation and integration. This has been a substantial step towards data extraction for PI software tools. The plenary has been rather comprehensive and suggested the way forward for this important task. The problem received some interest during the following years and several software packages have been offering

support for this task. Despite this, more work should be done to satisfy the needs for industrial applications. Recent trends in PI, software and applications were presented by Gundersen [START_REF] Gundersen | Recent trends in Process Integration, Methods, Software and Applications[END_REF]. He proclaimed an important development of Hybrid PI methods created by merging previously competing schools -Pinch Technology and Mathematical programming.

Bochenek et al. [START_REF] Bochenek | Retrofitting Flexible Heat Exchanger Networks -Optimization vs. Sensitivity Tables Method[END_REF] compared retrofitting of flexible HENs by optimisation versus simulation approach. This has been very important work in the field which still deserves more research. Zhu et al. [START_REF] Zhu | Heat Transfer Enhancement for Heat Exchanger Network Retrofit[END_REF] proposed heat transfer enhancement for HEN retrofit design, from which Heat Integration can substantially benefit. This methodology still deserves wider implementation especially for retrofit studies. Hassan et al. [START_REF] Hassan | Process Integration Analysis & Retrofit Suggestions for A FCC Plant[END_REF] presented a successful PI analysis and retrofit suggestions for a FCC plant. It is one of the first comprehensive retrofit case studies. Kalitventzeff et al [START_REF] Kalitventzeff | Process Integration Techniques in the Development of New Energy Technologies: Application to Isothermal Gas Turbine CHISA[END_REF] covered the usefulness of PI in the application to the isothermal gas turbine. Plesu et al. [START_REF] Plesu | Applications of Process Integration in Romanian Oil Refining and Petrochemical Industry[END_REF] demonstrated the wide applicability of PI in the Romanian oil refining and petrochemical industry. Klemeš et al. [START_REF] Klemeš | Application of pinch-technology in food industry[END_REF], made a series of applications of Pinchtechnology in the food industry. This has been further developed in [START_REF] Klemeš | Heat Integration in Food Industry[END_REF]. They had shown that

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Pinch technology can provide benefits far beyond oil-refining and petrochemicals. Mařík et al., [START_REF] Burianec | HENCODES-An Expert System for Designing the Control of Heat-Exchangers Networks)[END_REF] presented a design tool for flexible and energy efficient HENs. This approach has been based on an expert system and optimisation. The PRES'99 forum was held in Budapest -Hungary. It has been a major step in the development of the conferenceboth in terms of the number of participants and in the scope of covered areas. In the plenary lecture Smith [START_REF] Smith | State of the art in process integration[END_REF] made an overview of PI. Zhu and Vaideeswaran [START_REF] Zhu | Recent research development of process integration in analysis and optimisation of energy system[END_REF] reviewed an extension of the Total Site methodologythe Top Level Analysis. This approach has considerable potential, part of which has been realised with its efficient optimisation-based computational implementation by Varbanov et al. [START_REF] Varbanov | Top-Level Analysis of Site Utility Systems[END_REF]. Fraser and Hallale [START_REF] Fraser | Systematic effluent reduction through pinch technology[END_REF] Klemeš et al. [START_REF] Klemeš | Retrofit design for polish sugar factories using process integration methods[END_REF] summarised a comprehensive experience of retrofitting Polish Sugar Factories using PI. They presented the implementation of Heat Integration up to Total Site level considering retrofit features in combination with process modifications, based on close collaboration with the staff from the factories. Aaltola [START_REF] Aaltola | Use of process heat of a paper integrate in the district heating systems of two cities[END_REF] suggested trough case studies the integration of a paper mill with two sites district heating including seasonal variations. However, at that stage several important issues have been just drafted and opened for the future research.

Another case study dealt with heat and exergy analysis of biomass fuelled integrated gasification humid air turbine -BIO-IGHAT plant [START_REF] Assadi | Applying pinch method and exergy analysis to BIO-IGHAT power plant[END_REF]. This is a new class of problems simultaneously applying heat integration and exergy analysis. Dogru et al. [START_REF] Dogru | A heat exchanger networks design for an ammonium plant: A supertarget application[END_REF] performed a case studyusing a software tool from Linnhoff March [START_REF] Supertarget | [END_REF] for an ammonia plant. However, the analysis covered just the first step and did not continue into advanced heat integration steps. Galli and Cerda [START_REF] Galli | Synthesis of heat exchanger networks featuring a minimum number of bounded-size shells[END_REF] adopted an approach based on MINLP for the synthesis of HENs featuring a minimum number of bounded-size shells. Their approach would benefit from its combination with PI. Rodera and Bagajewicz [START_REF] Rodera | Multipurpose heat exchanger networks for heat integration across plants[END_REF] suggested a heat integration approach across plants using multipurpose heat exchangers. They extended the Minimum Matching Approach of Papoulias and Grossmann [START_REF] Papoulias | A structural optimization approach in process synthesis. II: Heat recovery networks[END_REF].

Their targeting procedure has been further developed. Gottschalk et al. [START_REF] Gottschalk | Application of HEATPERT for the energy integration of industrial chemical processes[END_REF] applied a Heat Integration Expert System for energy integration of industrial chemical processes. It's interesting feature was the combination with Pinch technology, which was demonstrated on an industrial case study for the synthesis of Methyl-tert-butyl-ether. This approach has still a good potential to

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ACCEPTED MANUSCRIPT be explored further. A well developed industrial case study was presented by Markowski [START_REF] Markowski | Reconstruction of heat exchanger network under industrial constraintsthe case of a crude distillation unit[END_REF] a retrofit of crude distillation unit. He covered important features of fouling and brought this case study close to the industrial conditions. Seikova et al. [START_REF] Seikova | Debottlenecking of a heat-integrated crude-oil distillation system[END_REF] presented a retrofit debottlenecking of a heat integrated crude oil distillation system building upon previous works of the UMIST team [START_REF] Asante | An automated approach for heat exchanger network retrofit featuring minimal topology modifications[END_REF] as well as on the approach presented by Varbanov and Klemeš [START_REF] Varbanov | Rules for paths construction for HENs debottlenecking[END_REF][START_REF] Varbanov | Rules for paths construction for HENs debottlenecking[END_REF]. Tovazhyansky et al. [START_REF] Tovazhyansky | Application of process integration for energy saving and pollution reduction in Ukraine[END_REF] used the heat integration methodology spread by the collaboration with UMIST under the UK Know-How Fund to district heating, chemical industry, ammonia plants, and food and drink industry across Ukraine.

PRES 2000

Kalitventzeff et al. [START_REF] Kalitventzeff | Better solutions for process sustainability through better insight in process energy integration[END_REF][START_REF] Kalitventzeff | Better solutions for process sustainability through better insight in process energy integration[END_REF] emphasised that better solutions can be generated for process sustainability through process energy integration. They shared their experience in the implementation of process energy integration techniques and their contribution to the process sustainability in an ammonia plant including combined production of heat and mechanical power for an existing process. Pinch technology and its recent extensions offer an effective and practical method for designing the HEN for new and retrofit projects. Al-Riyami et al.

[54, 55] demonstrated a heat integration retrofit analysis of a HEN of a fluid catalytic cracking (FCC) plant. The study found significant scope for improvement in the heat recovery. The new network was designed using the network pinch method. Grabowski et al.

[56] presented a case study of energy minimisation in sugar production by applying PI. The minimum energy consumption of the process was determined by simultaneous energy targeting and optimisation of evaporation. Energy systems employing various CHP technologies and various evaporator stations optionally combined with vapour compressors have been studied. A range of feasible solutions has been defined in terms of minimum energy consumption and combined heat transfer area of the evaporator station and the HEN.

PRES'01

Sadhukhan and Zhu [START_REF] Sadhukhan | Integration strategy of gasification technology: A gateway to future refining[END_REF] examined the integration of gas technologies in the context of overall refinery in order to use gasification for stretching the economic margins to the full extent. A stage-wise optimisation strategy was developed in order to capture interactions among refinery processes, the gasification system and hydrogen and utility networks.

Integration of waste to energy is a good option for thermal processing of waste. Bébar et al.

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[58] demonstrated the method of efficiently utilising the heat value of the incineration products and thus partially compensate the costs of waste thermal treatment. Cheung et al.

[59] addressed another important aspect in PI. They presented the Total-Site Maintenance Scheduling for better energy utilisation. To minimise the impacts on production and utility systems during routine maintenance the scheduling has to be done carefully with consideration of site-wide utilities and material balances.

PRES 2002

Smith [START_REF] Smith | Process integration for reduced environmental impact[END_REF] highlighted the advantages of PI for reduced environmental impact in his plenary lecture. He pointed out that PI techniques have been extended beyond their original scope for solving energy problems to be able to address a wide range of process design issues. Rodera et al. [START_REF] Rodera | A methodology for improving heat exchanger network operation[END_REF] presented a contribution to PI methodology for improving HEN operation. Their methodology featured a workflow to assist in the analysis of an existing HEN design when the operating conditions vary. It facilitated the involvement of the engineer in the daily operation and maintenance of the network. A method to target the optimal integration of the utility system was demonstrated by Marechal and Kalitvenzeff [START_REF] Marechal | Targeting the integration of multi-period utility systems for site scale process integration[END_REF][START_REF] Marechal | Targeting the integration of multi-period utility systems for site scale process integration[END_REF]. They addressed multi-period optimisation incorporating models for selecting and targeting the optimal operation strategy of the utility system. This includes gas turbines, steam network and cooling system together with the calculation of the optimal heat recovery system. Václavek et al. [START_REF] Václavek | Pressure as a further parameter of composite curves in energy process integration[END_REF] studied pressure as another parameter of the composite curves in heat integration. An important attempt has been made to evaluate the importance of pressure in heat integration.

Cost estimation can have a major impact on project profitability. Taal et al. [START_REF] Taal | Cost estimation and energy price forecasts for economic evaluation of retrofit projects[END_REF] provided a summary of the common methods used for cost estimation of heat exchange equipments and the sources of energy price projections. It shows the relevance of the choice of the right method and a reliable source of energy price forecast used when choosing between alternative retrofit projects or when trying to determine the viability of a retrofit project.

PRES'03

In an important extension of PI methodology the total site idea was applied by Sorin and

Hammache [START_REF] Sorin | A new thermodynamic model for shaftwork targeting on total sites[END_REF] integration of trigeneration systems was presented by Teopa Calva et al. [START_REF] Calva | Thermal integration of trigeneration systems[END_REF]. The use of the thermodynamic model helps simulating the main components of the system and permits a fast and interactive way to design the optimum trigeneration scheme using the performance data of commercial gas turbines. Lavric et al. [START_REF] Lavric | Entropy generation reduction through chemical pinch analysis[END_REF][START_REF] Lavric | Chemical reactors energy integration through virtual heat exchangersbenefits and drawbacks[END_REF] presented the benefits and drawbacks of energy integration through virtual heat exchanges. The features of the proposed Reactors Energy Integration were illustrated by a case study, a two-bed methanol synthesis heat integrated reactor. Brown et al. [START_REF] Brown | Cogeneration system design methodology in pulp and paper process[END_REF][START_REF] Brown | A dual representation for targeting process retrofit, application to a pulp and paper process[END_REF] have combined Pinch Analysis, exergy analysis, and optimisation techniques to define energy targets at pulp and paper industry expressed in terms of the energy costs rather than energy requirements. The dual representation of thermodynamic and technological energy requirements can be a valuable tool for the early stages of process energy analysis. PI approach was extended to water network design. Foo et al. [START_REF] Foo | Synthesis of maximum water recovery network for batch process systems[END_REF][START_REF] Foo | Synthesis of maximum water recovery network for batch process systems[END_REF] applied the water pinch analysis to synthesise maximum water recovery networks for batch processes. A new numerical technique, time-dependent water cascade analysis was demonstrated. This new network representation has an advantage of clearly depicting the time-dependent nature of a batch water network. Majozi [START_REF] Majozi | An effective technique for wastewater minimisation in batch processes[END_REF] presented an effective technique for wastewater minimisation in batch processes by formulation of a MINLP mathematical model approach. This water integration work minimised wastewater production through the implementation of numerous recycle and reuse opportunities. An extended Pinch Technology was proposed by Zhelev [START_REF] Zhelev | On the integrated management of industrial resources incorporating finances. Sustainable systems theory: ecological and other aspects[END_REF] to deal with water and energy management. The application of the methodology is designed to achieve water conservation through minimisation of evaporation losses. Its significance was demonstrated through case studies of a power station, a brewery, and a tissue factory.

PRES 2004

Kaggerud et al. [START_REF] Kaggerud | Chemical and process integration: synergies in co-production of power and chemicals from natural gas with CO 2 capture[END_REF] suggested a new avenue of PI combined with chemical integration.

Process and chemical integration is proposed as an option to increase the overall efficiency as co-production of power and chemicals is utilised. Chemical and PI can give economy of scale savings, better utilisation of the raw materials, improved energy efficiency and savings in investment costs. Another heat integration contribution was presented by Anantharaman et al. [START_REF] Anantharaman | Energy level composite curves-a new graphical methodology for the integration of energy intensive processes[END_REF]. Pinch Analysis, Exergy Analysis and Optimisation have all been used independently or in combination for the energy integration of process plants. Cziner et al. [START_REF] Cziner | Multicriteria decisions making in Process Integration[END_REF] addressed the potential of multi-criteria, performance decision-making in plant design with the aid of PI. A

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hierarchical decision-making methodology was presented, where the environmental and safety regulations and the growing demand of consumers for higher product quality are included. The case study had a calcinations kiln, followed by flue gas cleaning and heat recovery systems.

The Pinch principle was further extended by Zhelev [START_REF] Zhelev | On the integrated management of industrial resources incorporating finances. Sustainable systems theory: ecological and other aspects[END_REF] in the opportunities to improve profits and reduce the investment cost through integrated management of resources such as electrical energy, steam and fresh water. Cost Composite Curves were created to target the optimum profitability to guide the decision making process in the context of key trade-offs. A

Grid diagram analogy was used to show the money flow that can ensure meeting the targets.

PRES'05

Based on Pinch Analysis, a procedure was proposed by Markowski et al. [START_REF] Markowski | Energy expenditure in the thermal separation of hydrocarbon mixtures using a sequence of heat-integrated distillation columns[END_REF] for minimising the compressor shaft work in the refrigeration system. They studied the thermal separation of hydrocarbon mixtures in a sequence of heat-integrated distillation columns coupled with a refrigeration system via a HEN. An automated approach for heat integration was presented by Moodley et al. [START_REF] Moodley | Development of a unified mass and heat integration framework for sustainable design -An automated approach[END_REF]. They used a superstructure and a mathematical model to demonstrate the optimum cooling water supply to a network of heat exchangers supplied by multiple sources.

The concept of comprehensive PI was introduced by Hurme et al. [START_REF] Hurme | Process efficiency by comprehensive process integration[END_REF]. It was defined as design, operation and management of industrial processes with system-oriented and integrated methods, models, and tools. Mascia et al. [START_REF] Mascia | Design of heat integrated distillation systems for a light ends separation plant[END_REF] presented an industrial case study on the synthesis of partially thermally coupled and heat-integrated distillation systems applied to the light ends separation section of a crude distillation plant. This distillation system employs the thermal coupling and the heat-integration principles to significantly reduce the heat requirements compared with the traditional simple column train. Picón-Núñez et al. [START_REF] Picón-Núñez | Effect of network arrangement on the heat transfer area of cooling networks[END_REF] studied the effect of the configuration of cooling networks on the total exchanger area. The chosen methodology combined the pinch design method based on vertical heat transfer and the minimum-water-use design method. A case study demonstrated the methodology showing a practical approach to reduce operating costs in existing systems. An extended pinch analysis and design procedure evaluating pressure based exergy for sub ambient cooling were presented by Aspelund et al. [START_REF] Aspelund | An extended pinch analysis and design procedure utilizing pressure based exergy for subambient cooling[END_REF]. They demonstrated a substantial potential for minimising energy requirements (total shaftwork) in sub ambient processes. The compression and expansion work is optimized for the process streams, together with the work needed to create necessary cooling utilities.

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Panjeshahi and Tahouni [START_REF] Panjeshahi | Pressure drop optimisation in debottlenecking of heat exchanger networks[END_REF] presented the method of Pressure Drop Optimisation in Debottlenecking of HENs. Their method had been effectively applied in a case study involving the retrofit of a crude oil pre-heat train after increasing throughput. The debottlenecking of HENs using optimum pressure drops would be able to predict the required additional heat recovery area with acceptable accuracy. Lior [START_REF] Lior | Brief summary of the ECOS '05 Panel on ‗‗Future Power Generation[END_REF] reviewed the status and prospects of using fossil, nuclear and renewable energy for power generation (including hydrogen, fuel cells, micropower systems, and the futuristic concept of generating power in space for terrestrial use). He summarized the promising energy R&D areas, their potential, foreseen improvements, their timescale, and latest trends in government funding.

PRES'07

The Pinch Technology was extended to CO 2 minimisation. Foo et al., [START_REF] Foo | Target for minimum low and zero-carbon energy resources in carbon-constrained energy sector planning using cascade analysis[END_REF][START_REF] Foo | Carbon and footprint-constrained energy planning using cascade analysis technique[END_REF] emission and land availability constraints. Cirlly and Zhelev [START_REF] Cirlly | Current Trends in emissions targeting and planning-an application of CO 2 emissions pinch analysis to the Irish electricity generation sector[END_REF][START_REF] Cirlly | Current trends in emissions targeting and planning-an application of CO 2 emissions pinch analysis to the Irish electricity generation sector[END_REF] presented a pinch analysis for CO 2 emissions targeting and planning, accounting for the dynamic nature of electricity supply-demand. Amann et al. [START_REF] Amann | Natural gas combined cycle power plant modified into an O 2 /CO 2 cycle for CO 2 capture[END_REF] presented the conversion of a natural gas combined cycle power plant using an advanced gas turbine for CO 2 pre-combustion capture.

CO 2 recovery rate has a big impact on the power plant efficiency since a lot of steam is required to lower the low heating value of the synthesis gas leaving the recovery process, thus reducing NO x . Perry at el., [START_REF] Perry | Integrating waste and renewable energy to reduce the carbon footprint of locally integrated energy sectors[END_REF][START_REF] Perry | Integrating waste and renewable energy to reduce the CFP of locally integrated energy sectors[END_REF] extended the total site approach to integrate waste and renewable energy to reduce the carbon footprint of locally integrated energy sectors. This novel method can be successfully applied to integrate renewables into the energy source mix and consequently reduce the CFP of these locally integrated energy sectors. Liebmann et al.

[94] evaluated different scenarios of bioethanol production with innovative energy supply facilities. They studied the options for renewable energy supply such as biogass CHP and biogas boiler. This gave a good start to the integration of renewable energy into regional energy supply.

PRES 2008

Klemeš and Varbanov [START_REF] Klemeš | Total Sites Integrating Renewables with Extended Heat Transfer and Recovery[END_REF] presented a further extension of the concepts of Total Sites [START_REF] Klemeš | Targeting and Design Methodology for Reduction of Fuel, Power and CO 2 on Total Sites[END_REF] and Locally Integrated Energy Sectors [START_REF] Perry | Integrating waste and renewable energy to reduce the CFP of locally integrated energy sectors[END_REF]. They added the integration of renewable energy sources into the problem scope, emphasising the variability of both user demands and the renewables availability. Sustainability analysis has been a major consideration in the process synthesis. Sikdar [START_REF] Sikdar | Chemical process sustainability and applicable metrics[END_REF] presented a framework for sustainability analysis to evaluate the data, leading one to a decision to accept, reject or re-work a solution.

Morrison et al. [START_REF] Morrison | Integration of solar thermal for improved energy efficiency in low-temperature-pinch industrial processes[END_REF] presented an interesting application of solar thermal energy utilisation in food industry. They proposed to use captured solar heat in a way similar to heat pumping, thus upgrading waste heat flows to temperatures suitable for process use. The Processes Integration concept has been extended to renewable energy supply chain synthesis by Lam et al. [START_REF] Lam | An efficient planning and implementation of regional renewable energy supply chain[END_REF]100] to assessing the feasible ways for transferring energy from renewable sources to customers in a given region. The studied region is partitioned into a number of clusters by using the developed Regional Energy Clustering (REC) algorithm. The energy planning and management is extended and illustrated in Regional Resource Management Composite Curve (RRMCC). It provides straightforward information of how to manage the surplus resourcesbiomass and land use in the region. Desai and Bandyopadhyay [START_REF] Desai | Process integration of organic Rankine cycle[END_REF] proposed a scheme for efficient utilisation of lower-grade waste heat for power generation, using Organic Rankine Cycles. They provided a graphically assisted procedure for integrating an industrial process with an ORC thus efficiently reducing the process cooling demand and the need for external power import. Ghajar and Tang [START_REF] Ghajar | Importance of Non-Boiling Two-Phase Flow Heat Transfer in Pipes for Industrial Applications[END_REF] presented the validity and limitations of the numerous two-phase non-boiling heat transfer correlations. The study presented a good opportunity for heat integration. It should be continued into advanced PI steps.

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Future Trends -Innovations in Energy, Resource and Footprint Targeting

Recent research has been expanding the scope of PI as well as the performance criteria for the system evaluation.

Energy planning using carbon footprint

Climate change has been growing in importance to the international community. Most of the attention has been focused on the carbon footprint (CFP) as a measure of the extent of greenhouse gas emissions impact. An interesting contribution by Foo et al. [START_REF] Foo | Carbon and footprint-constrained energy planning using cascade analysis technique[END_REF] deals with the -Carbon and Footprint-Constrained Energy Planning Using Cascade Analysis Technique‖.

They presented algebraic targeting techniques for energy sector planning with CO 2 emission and land availability constraints. It is desirable to maximise the use of low carbon energy sources to reduce CO 2 emissions. This contribution provides an extension of the classic Pinch Analysis [START_REF] Linnhoff | The Pinch Design Method for Heat Exchanger Networks[END_REF] for identifying the minimum amount of low-or zero-carbon energy sources needed to meet the national or regional energy demand, while not violating the CO 2 emission limits. Tan and Foo [START_REF] Tan | Recent Trends in Pinch Analysis For Carbon Emissions and Energy Footprint Problems[END_REF] and Tjan, Tan and Foo [START_REF] Tjan | A graphical representation of carbon footprint reduction for chemical processes[END_REF] extended the Pinch analysis to carbon emissions and energy Footprint problems. The water footprint problem had been examined by Klemeš, Lam and Foo [START_REF] Klemeš | Water Recycling and recovery in food and drink industry[END_REF]. A long needed contribution has been The Environmental

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performance Strategy Map based on the Life Cycle Analysis and quantifying the combined impact of various footprintscarbon, water, energy, emissions and the work environment footprints [START_REF] Benedetto | The Environmental Performance Strategy Map: an Integrated LCA approach to support the Strategic Decision Making Process[END_REF][START_REF] Benedetto | The Environmental Bill of Materials and Technology Routing: an integrated LCA approach[END_REF].

Extending Total Sites

An important innovation in the field of energy targeting and integration has been presented at PRES'07 by Perry et al. [START_REF] Perry | Integrating waste and renewable energy to reduce the CFP of locally integrated energy sectors[END_REF]. This was a result of collaboration between the UK and Hungary The method can be successfully applied to integrate renewables and consequently reduce the CFP of these locally integrated energy sectors. The attention to further development of the Total Site extension of Process Integration become during the recent period widespread [START_REF] Bandyopadhyay | Targeting for cogeneration potential through total site integration[END_REF][START_REF] Varbanov | Total Sites Integrating Renewables with Extended Heat Transfer and Recovery[END_REF]. Chew et al. [START_REF] Chew | Game theory approach to the analysis of inter-plant water integration in an eco-industrial park[END_REF] approached another very considerable task -the problem of the water site integration.

Some Interesting Case Studies

A case study of pinch analysis was presented by Wising et al. [START_REF] Wising | The potential for energy savings when reducing the water consumption in a Kraft pulp mill[END_REF]. They evaluated the potential for reducing the water and energy consumption by using pinch analysis approach.

An existing pulp and paper mill was studied targeting the reduction of water consumption. A method for analysing energy, environmental, and economic efficiency for an integrated steel plant was presented by Larsson et al. [START_REF] Larsson | Development of a method for analysing energy, environmental and economic efficiency for an integrated steel plant[END_REF]. Global mathematical models for steel making processes have been developed with the help of PI techniques. The traditional beet sugar manufacturing technology has a considerable detrimental impact on the environment. Vaccari et al., [START_REF] Vaccari | Overview of the environmental problems in beet sugar processing: possible solutions[END_REF] gave an overview of the environmental problems in beet sugar processing. They applied Water Pinch and Thermal Pinch Analyses to assist in finding ways to drastically reduce both water and energy consumption. PI was applied to food industry. Kapustenko et al.

[121] demonstrated the integration of a heat pump into the heat supply system of a cheese production plant in Ukraine. They analysed the opportunity of heat integration of an existing refrigeration unit into the process. A very interesting application of Heat Integration of evaporators with the remaining process has been presented by Axelsson et al. [START_REF] Axelsson | Opportunities for process integrated evaporation in a hardwood pulp mill and comparison with a softwood model mill study[END_REF]. Their observation was that significant energy savings can be made in the pulp and paper industry by

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implementing process integrated evaporation (termed -PIvap‖). Using pinch tools they found a solution where 1.3 GJ/ADt (GJ per Air Dried tonne) of pinch violations were solved and 1.1 GJ/ADt of excess heat saved. Pulp-and-paper Kraft mills feature significant energy demands.

Savulescu and Alva-Argaez [START_REF] Savulescu | Direct heat transfer considerations for improving energy efficiency in pulp and paper Kraft mills[END_REF] have proposed a PI methodology to systematically address direct heat transfer (DHT) aspects in the Kraft mill energy system retrofit context. Their observation shows that energy-efficient non-isothermal mixing points should be located at the end of a stream. From the process perspective, mixing should be below pinch or above to eliminate the inefficiencies, due to DHT cross-pinch. Additionally, mixers located away from the pinch represent degrees of freedom to design an optimal heat transfer network. Levasseur et al. [START_REF] Levasseur | Energy integration study of a multi-effect evaporator[END_REF] have presented an application of classical heat integration techniques with process changes to liquor evaporation in pulp-and-paper mill. The system involves multi-effect evaporation. The considered modifications were reduction of ΔT min , as well as variation of the pressures of evaporation effects. As a result, energy savings of up to 20 % were reported. Accounting for the non-continuous operation of pulp-and-paper mills, Morrison et al. [START_REF] Morrison | Non-continuous pinch analysis of a paper machine in an integrated kraft pulp & paper mill[END_REF] presented a case study for varying paper grades. They applied the Time Slice Model for batch heat integration. A powerful tool, Site-Model, was introduced by Hirata et al. [126]. To handle the trade-off between the flexibility and the interactions, all units should be managed simultaneously. The tool implements a large-scale MILP model for the utility system optimisation. Nordgren et al. [START_REF] Nordgren | Process integration in an iron ore upgrading process systemanalysis of mass and energy flows within a straight grate induration furnace[END_REF] presented heat balancing study of a metallurgical process with the aim to perform a subsequent Heat Integration project. The paper is a part of a project which aim is to develop a PI model for the Swedish iron ore company LKAB's production system in Malmberget. The authors analyse the various processing zones of the furnaces and the opportunities for heat recovery using external heat exchangers. Matsuda et al. [START_REF] Matsuda | Advanced Energy Saving in Reaction Section of Hydro-Desulfurization Process with Self-Heat Recuperation[END_REF] applied heat integration total site based pinch technology to a large industrial area in Japan to further improve performance of highly efficient process plants. Tovazhnyansky et al. [START_REF] Tovazhnyansky | Synthesis of Energy Saving Integrated Flowsheet for Sodium Hypophosphite Production[END_REF] successfully completed process integration based synthesis of sodium hypophosphite production. Promvitak et al. [START_REF] Promvitak | Retrofit Design of Heat Exchanger Networks of Crude Distillation Unit[END_REF] applied the heat integration methodology on the crude distillation unit. Varbanov and Friedler [START_REF] Varbanov | Boosting Energy Conversion Efficiency Using Fuel Cells. SOFC-ST CHP Conversion -Assessment Using the Eminent tool[END_REF] boosted the energy convention efficiency of fuel cell. Parisutkul et al. [START_REF] Parisutkul | Grassroots Design of Heat Exchanger Networks of Crude Distillation Units[END_REF] improved the energy efficiency of the natural gas separation plant. Atkins et al. [START_REF] Atkins | Carbon Emissions Pinch Analysis (CEPA) for emissions reduction in the New Zealand electricity sector[END_REF] completed carbon emission pinch analysis of New Zealand Electricity sector and Markowski et al. [START_REF] Markowski | Heat Integration of a Hydrogen Plant Connected with Sugar Factory[END_REF] fermentation based hydrogen plant connected with sugar factory. Varga et al. [START_REF] Varga | Improve of Energy Efficiency a Tool for Reduction of CO 2 Emission[END_REF] by using heat integration improved energy efficiency of several units in MOL refineries in Hungary and Slovakia. Pavlas et al. [START_REF] Pavlas | Heat Integrated Heat Pumping for Biomass Gasification Processing[END_REF] implemented of heat integrated heat pumping for biomass gasification processing.

M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 2 Optimisation for Energy Savings and Reduced Emissions

The field is enormously wide. Therefore, this short overview is targeting optimisation methodologies which have the strongest impact on energy saving and pollution reduction.

Integrated Synthesis of Process and HENs

Nagy et al.

[137] developed a new algorithmic method for the integrated synthesis of processes and HENs. Different methods exist for algorithmic process-network synthesis (PNS) as well as for heat-exchanger-network synthesis, but they cannot easily be integrated.

For instance, the flow rates of streams are not specified a priori in PNS; in contrast, the flow rates and temperatures of hot and cold streams must be known as inputs in HEN synthesis (HENS). This difference can be attributed to the fact that the former is macroscopic in nature, while the latter is mesoscopic in nature, giving rise to the characteristic differences between them. Both PNS and HENS inevitably encounter combinatorial complexity, which is magnified profoundly when they are integrated, due to their interactions. The P-graph framework developed earlier for PNS [START_REF] Friedler | Graph-theoretic approach to process synthesis: axioms and theorems[END_REF] has been extended to the integrated synthesis of process and heat-exchanger networks. This new method resorts mainly to hP-graphs adapted from the P-graphs in conjunction with the appropriate selection of inherent intervals of temperature range. Therefore, it focuses on the establishment of an appropriate technique for the integration of PNS and HENS [137]. The resultant technique is largely based on combinatorial algorithms. The efficacy of the proposed approach is illustrated by the solution of an industrial problem.

Scheduling in heat integration and water reuse for batch processes

Foo et al. [START_REF] Foo | Synthesis of maximum water recovery network for batch process systems[END_REF] present a two-stage procedure for the synthesis of a maximum water recovery network for a batch process system, covering both mass transfer-based and non-mass transferbased water-using processes. Adonyi et al. [START_REF] Adonyi | Incorporating heat integration in batch process scheduling[END_REF] developed a new algorithmic method for heat integration of batch processes. By nature, batch process scheduling and heat integration are two significantly different highly complex optimisation problems. Many algorithmic and heuristic based methods exist for solving heat integration problems by resorting to pinch technology; superstructure based mixed integer programming, and integration with process network synthesis. These methods have been developed for continuous processes where scheduling is of no concern. These two different problems can be solved sequentially, i.e., solving scheduling first and then heat integration or vice versa. Since the solution of one of

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them influences the other, the result of this simplistic approach is usually very poor.

Consequently, an integrated consideration of scheduling and heat integration may provide appropriate solution. Since no method known up to that time for solving the integrated model, the development of a new method was desired for effective design and operation of batch processes. The main issue was how to operate tasks with potential heat exchange simultaneously without sacrificing the quality of the scheduling solution. The proposed procedure is based on the branch-and-bound framework, where two optimization problems, the scheduling and the heat integration one, are considered simultaneously instead of consecutively.

Batch Scheduling with Minimising Cleaning Costs

The cleaning for batch processes, especially, paint production systems have been examined by Adonyi et al. [START_REF] Adonyi | Effective scheduling of a large-scale paint production system[END_REF]. Due to the large variety of options offered to customers, batch production schemes are widely used in paint industry implying that scheduling plays an important role in optimal allocation of plant resources among multiple products. Since in a batch process, the cleaning of equipment units is the major source of waste, waste minimization is also to be taken into account in determining the schedule. In the paint production, a product is produced by four successive tasks: grinding, mixing, storing the intermediate materials, and packing.

Grinding, mixing and storing are batch type operations while packing is continuous. A task cannot be performed by a dedicated equipment unit, because there are usually more tasks than equipment units. An equipment unit is assigned to each task for a time interval where the length of the interval must not be shorter than the processing time of the related task.

Changeover time is defined for an equipment unit if cleaning is necessary. The whole amount of the intermediate material is used by the successive tasks. Traditionally, such assignment of equipment units to tasks and schedule of tasks is generated that have minimal makespan. This schedule provides the highest efficiency of the production system with the possibility of unnecessarily large waste generation. For determining the schedule of tasks that requires minimal cleaning cost, the objective function of the problem has to be modified. While in the original problem the makespan, in the reformulated problem the cleaning cost must be minimized. This reformulation has minor effect on the solution procedure. Therefore, an effective solver for the original problem is useful for the reformulated problem also. The formerly developed S-graph framework [START_REF] Romero | Scheduling Intermediate Storage Multipurpose Batch Plants Using the S-Graph[END_REF] proved to be highly effective in solving multipurpose batch scheduling; it has been specialised by Adonyi et al. [START_REF] Adonyi | Effective scheduling of a large-scale paint production system[END_REF] for solving paint

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production scheduling problems including waste minimization. The efficacy of the new approach is illustrated with the solution of large-scale paint production scheduling problems.

Strategic roadmap -Decomposition vs. Integration for process optimisation

The decomposition principle in process design has been used by researchers since the 1970's e.g. [START_REF] Siirola | The Computer-Aided Synthesis of Chemical Process Designs[END_REF]. Friedler and Fan [START_REF] Friedler | Process design and operation: decomposition vs. integration[END_REF] drafted a strategic roadmap for the development of process optimisation, analysing the interactions between the decomposition and integration principles. They have identified a number of threats to the optimality and feasibility of the process designs when applying decomposition and suggested measures to counteract the problems, centred on the concept of the integration of the methodologies for the component design problems. This concept has revealed the need for algorithmic generation of the component models and the necessary interfaces enabling the interactions of the models and methods. The algorithmic generation of the models allows mainly ensuring their validity and completeness of the network superstructures. One efficient way for algorithmic model generation is using P-graph [START_REF] Friedler | Graph-theoretic approach to process synthesis: axioms and theorems[END_REF][START_REF] Friedler | Graph-Theoretic Approach to Process Synthesis: Polynomial Algorithm for Maximal Structure Generation[END_REF][START_REF] Friedler | Decision-Mapping: A Tool for Consistent and Complete Decisions in Process Synthesis[END_REF]

Looking Inside the Processes -Process Intensification

Reay [START_REF] Reay | The role of process intensification in cutting greenhouse gas emissions[END_REF] has presented the role of PI and intensification in cutting greenhouse gas emissions. He identified the challenges that intensification is able to meet across a range of sectors of industry and commerce as they relate to greenhouse gas control. He mentioned that the possibility of increased local production and the growing use of biological renewable feedstock open up new challenges and opportunities for those active in integration as well as intensification. He stated that between 1900 and 1955 the average rate of global energy use rose from about 1 TW to 2 TW. Between 1955 and 1999 energy use rose from 2 TW to about 12 TW. To 2006, a further 16 % growth in primary energy use was recorded world-wide. The conclusions are that process intensification, although yet to fully emerge as an established technology in the process industries, offers significant opportunities for carbon reductions in sectors ranging from chemicals to food and glass manufacture.

Contributions from PRES Conferences

Heat integration of chemical multipurpose batch plants was studied by Sanmarti et al. [147] based on directed graphs and exploiting the optimisation power of combinatorics. This approach has been further developed by Sanmarti et al. [START_REF] Sanmarti | Combinatorial Framework for Effective Scheduling of Multipurpose Batch Plants[END_REF] into S-graphs. Scheduling problems have been solved also for batch water networks. One example is the work by Chen et al. [START_REF] Chen | Synthesis of water-using network with central reusable storage in batch processes[END_REF], who

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have developed a method for synthesising water-using networks with central reusable storage for batch processes. A further development has been presented at PRES'09 [150] on property-based water-using networks in batch processes. The wide spectrum of the batch applications can be illustrated by the work performed by an international team on profitability analysis of batch reactive distillation [START_REF] Edreder | Profitability analysis for batch reactive distillationprocess based on fixed product demand[END_REF].

The problem of HENs flexibility and operability had been dealt with by Tantimuratha et al. [START_REF] Tantimuratha | Flexibility targets for HENs: Conceptual programming approach for grassroots and retrofit design[END_REF]. They proposed simple MILP models to solve the problem. However, a closer combination with pinch analysis had yet to come. Nagy et al. [START_REF] Nagy | Integrated Synthesis of Combined Process and HENs[END_REF]137] presented an algorithmic approach for integrated synthesis of process and HENs. This work focused on the establishment of an appropriate technique for the integration of PNS and HENS. The resultant technique was largely based on combinatorics and combinatorial algorithms. This novel approach opened a new opportunity of the PI approach. Halasz et al. [START_REF] Halasz | Optimal retrofit design and operation of the steam-supply system of a chemical complex[END_REF][START_REF] Halasz | Optimal retrofit design and operation of the steam-supply system of a chemical complex[END_REF] presented a novel tool, especially important for the retrofit design. An optimal design and operation of an existing steam-supply system of a chemical complex was demonstrated using P-graph, the decision-mapping, combinatorial algorithms, and the accelerated branch-and-bound method.

Adonyi et al. [START_REF] Adonyi | Incorporating heat integration in batch process scheduling[END_REF] introduced a novel S-graph approach to incorporate heat integration in batch process scheduling. The proposed procedure is based on the branch-and-bound framework, solving the scheduling and the heat integration problems simultaneously instead of consecutively. Varbanov et al. [START_REF] Varbanov | Synthesis of industrial utility systems: costeffective decarbonisation[END_REF] proposed a method to synthesise industrial utility systems capable of cost-effective decarbonisation. It is based on improved models of utility equipment components and on an improved model and procedure for optimal synthesis. The environmental impact of utility systems was integrated into a synthesis model, which is dictated by the need for significant reduction of CO 2 emissions.

Application of pinch technology is presented by Ravagnani et al. [START_REF] Ravagnani | Heat exchanger network synthesis and optimisation using genetic algorithm[END_REF] to synthesise a HEN Employing a genetic algorithm. Synthesis of HEN by using mathematical model approach was presented by Markowski et al. [START_REF] Markowski | Optimal cleaning schedule for heat exchangers in a HEN[END_REF][START_REF] Markowski | Optimal cleaning schedule for heat exchangers in a heat exchanger network[END_REF]. Heat exchanger cleaning is postulated to maximise the avoided loss understood as the value of energy recovered if cleaning the HEN, minus the value of energy recovered without HEN cleaning, minus the cost of HEN cleaning.

The mathematical formulation of the avoided loss is given and the computational approach to its maximisation is outlined. Ullmer et al., [START_REF] Ullmer | WADO ™: Water design optimisation -software for the synthesis of process water systems[END_REF] presented a methodology and software for the synthesis of process water systems. They developed an integrated strategy for the design of industrial process water systems to determine the optimal cost network, taking into consideration

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multiple contaminants and various possibilities of water reuse and regeneration. The efficiency and applicability of the software was demonstrated on a process water system of an oil refinery.

Hugo et al. [START_REF] Hugo | A multi-objective optimisation model for strategic hydrogen infrastructure planning[END_REF] presented a multi-objective optimisation model for strategic hydrogen infrastructure planning. The optimisation is conducted in terms of both investment and environmental criteria, with the ultimate outcome being a set of optimal trade-off solutions representing conflicting infrastructure pathways. This model had considerable potential, especially into the regional energy integration.

Ponton [START_REF] Ponton | Web based distance learning for CPD[END_REF] shared the experience on using web based distance learning for continuing professional development in the control, modelling, and optimisation courses. Transformation of process data into a meaningful description is very important to process integration. Drahoš

and Ružička [163] studied the characterization of process data such as pressure, temperature, and concentration by using time series analysis. Pistikopoulos [START_REF] Pistikopoulos | Parametric programming and control[END_REF] gave an overview of the mathematical foundations of multi-parametric programming for different models. He also presented the application of model-based optimal control with emphasis on designing off-line affordable advanced parametric controllers for chemical processes. the final solution and gave more robust and consistent results when tested repeatedly for the same problem. An approach to multiperiod HEN synthesis using Simulated Annealing [START_REF] Ahmad | Synthesis and optimisation of heat exchanger networks for multi-period operation by simulated annealing[END_REF] has been suggested. It uses a completely evolutional strategy starting from a trivial network topology connecting all hot streams to coolers and all cold streams to heaters. They stated that the performance of the optimisation procedure is comparable to the existing Mathematical Programming based ones. The method does not rely on any superstructure, is not subject to decomposition of the main problem, and can explore a greater search area, increasing the probability of obtaining the global optimum. Sikos and Klemeš [START_REF] Sikos | Optimisation of Heat Exchanger Networks Maintenance[END_REF][START_REF] Sikos | Reliability, availability and maintenance optimisation of heat exchanger networks[END_REF] successfully optimised reliability, availability and maintenance of heat exchanger networks and contribution to efficient waste minimisation and management. Kim [START_REF] Kim | Process Integration and Conceptual Design with Process Simulators[END_REF] performed a conceptual optimal design applying a process simulator. Touš et al. [START_REF] Touš | Waste-to-Energy (W2E) Software -A Support Tool for Decision Making Process[END_REF] presented an alternative solution and optimisation to an integrated system of biomass and/or alternative fuel integrated into a complex energy producing system. Meszaros and Čirka [START_REF] Meszáros | Control Analysis for Processes with Internal Recycle[END_REF] performed a control analysis with inner recycle ob hybrid separation process. Friedler, Varbanov and Klemeš [START_REF] Friedler | Advanced HENs Design for Multi-Period Operation using P-graph[END_REF] developed a methodology for optimising the HEN design for Multi-Operation Using P-Graphs.

Conclusions and future outlook

Modern societies must face numerous issues in seeking to secure a sustainable energy supply, reduce climate changes, and ensure food production. The rapid increase in global energy consumption makes the problem more complicated. Recent oil and gas crises have shown the vulnerability of the societies in terms of climate changes and energy supplies. However, due to the complexity of the global challenges, it can be realised that each person or team has limits to the issues that they could effectively address. This is the reason why this overview is based upon the specialised inputs from a number of skilled scientists and technologists. Taken as a whole, the reviewed papers address many of the challenges pertaining to global climate change and to the impacts of the decisions that can be made.

Although, new insights are emerging on some energy-related problems, which seem to be (i) Diversification of energy sources and supply chains; regional energy sustainability zones and inter-zone integration.

(ii) The mass storage of energyespecially of electricity and heat.

(iii) The energy efficiency and energy saving attitude being accepted as a priority by society.

(iv) The change of the societal approach away from wasting energy.

(v) Sustainable energy solutions for transporttechnology, management and societal acceptance.

(vi) Sustainable energy solutions for developing countries.

(vii) Sustainable energy for securing fresh water for the world's growing human population.

However they have been still many other issues which should be further explored in the future as the new avenues in sustainable energy generation supported by efficient energy carriers.

The list could be considerably extended. It is a positive sign that some of the big players are researching these issues see e.g. [175]. However, much more collaboratively orchestrated work is needed to find proper answers to these challenges. The PRES series of conferences has been designed to provide the necessary forum and networking opportunities for accelerating the scientific and engineering progress in the field.

  and Optimisation for Energy Saving and Pollution Reduction Ferenc Friedler Faculty of Information Technology, University of Pannonia Egyetem utca 10, H -8200 Veszprém, Hungary friedler@dcs.uni-pannon.hu Energy saving, global warming and greenhouse gas emissions have become major technological, societal, and political issues. Being closely related to energy supply, they are of a strategic importance. Various conferences are being organised for providing international avenues for closer cooperation among researchers. The series of conferences ‗‗Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction‖ (PRES)

  using a new model for shaftwork targeting. A modified Site Utility Grand Composite Curve (SUGCC) diagram was proposed. The new model allows targeting fuel consumption, cooling requirement, and shaftwork production with high accuracy and M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT visualising them directly as special segments on the T-H diagram. The concept of thermal

Foo

  et al.[START_REF] Foo | Minimum units targeting and network evolution for batch heat exchanger network[END_REF] paid attention to heat integration in batch processes. Their work covered the minimum units targeting and network evolution for batch HENs. The minimum unit target sets the lower bound for a batch HEN prior to the network evolution, which is used to evolve the network to reduce its complexity. They have shown that to simplify a batch HEN with M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT network evolution techniques, a thorough analysis has to be performed across all time intervals of the batch process. Two examples illustrated the applicability of the proposed techniques. Further work is envisaged by them to incorporate the targeting and evolutionary techniques into a rigorous optimisation model.

  under several FP6 EC supported projects. The work presented an extension of the Total Site concept. Traditionally, Total Site meant only a set of industrial processes. This paper made another major step further by including commercial and residential energy users into the Total Site scope. The resultant process collections are termed Locally Integrated Energy Sectors.

Friedler and Varbanov [, 165 ]

 165 presented an application of the CHP concept in combination with the P-graph framework for designing complex systems for energy supply and conversion. Two kinds of High-Temperature Fuel Cells (HTFC) were considered -Molten Carbonate Fuel Cells (MCFC) and Solid Oxide Fuel Cells (SOFC). The paper presents a tool for the evaluation of energy conversion systems involving Fuel Cell Combined Cycles (FCCC) subsystems, utilizing biomass and/or fossil fuels. This task involves significant combinatorial complexity, efficiently handled by the P-graph algorithms, producing cost-optimal FCCC configurations. It also accounts for the carbon footprint of the various technology and fuel options. The results show that such systems employing renewable fuels can be economically viable for a wide range of economic conditions, mainly due to the high energy efficiency of the FC-based systems, having the potential to reduce the carbon footprint of energy supply by 50 to 75 %.Tan[START_REF] Tan | An adaptive swarm-based simulated annealing algorithm for process optimization[END_REF] presented an accelerated modification of the popular Simulated Annealing optimisation algorithm employing swarm intelligence techniques. Two modified SA algorithms have been developed by incorporating parallel searching and information sharing features found in swarm-based techniques such as PSO and SFLA, as well as an adaptive cooling schedule.Tests on three chemical process network design and synthesis problems showed that the M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT modifications yield improvements in search characteristics as compared to conventional SA and other optimisation algorithms. The new algorithms needed fewer function evaluations to reach

  rather straightforward, most of them have not yet been satisfactorily solved. Many of the M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT problems have been addressed annually at the PRES conferences held during the last 13 years. Some of them were summarised by Dovì et al [174]:


Pierre Verge

Sophie Peeterbroeck

Leila Bonnaud

Philippe Dubois
email: philippe.dubois@umons.ac.be

INVESTIGATION ON THE DISPERSION OF CARBON NANOTUBES IN NITRILE BUTADIENE RUBBER: ROLE OF POLYMER-TO-FILLER GRAFTING REACTION

Keywords: A. Carbon nanotubes, A. Nitrile butadiene rubber, A. Nano composites, E. Reactive processing, E. Grafting reaction

This contribution reports on the dispersion by simple melt blending of tiny amounts of carbon nanotubes (CNT) in Nitrile Butadiene Rubbers (NBR). Acrylonitrile (ACN) units of NBR are known to generate free radicals upon heating and/or shearing. This paper highlights elements evidencing a possibility for NBR polymer chains to react by a free-radical mechanism and to graft onto CNT surface all along the process of mechanical blending of NBR with CNTs. More precisely and since the formation of the free-radicals takes place on the ACN units, the influence of the ACN relative content in NBR on the grafted CNT amount has been studied. It comes out that the polymer grafting rate onto the CNT surface increases with the ACN content in NBR.

Interestingly, the nanotubes proved more finely dispersed in NBR containing higher relative ACN content as evidenced by morphological observations as well as electrical measurements.

INTRODUCTION

Carbon nanotubes (CNTs) are fillers of choice for the conception of composites due to their exceptional thermal, mechanical and electrical properties [1]. Even if their physical properties are impressive, it appears difficult to obtain the expected reinforcement by their incorporation within polymeric matrices. Indeed the load transfer of the properties is highly dependent on the extent of both the distribution and the dispersion of these anisotropic nanofillers, which are rarely achieved. To improve the dispersion of CNTs in polymer matrices, different experiment methods have been investigated and mainly they both rely upon two strategies involving either the formation of covalent bonds or the establishment of non-covalent interactions between the polymer chains and nanotubes surface [2]. Melt blending, solution stirring, and coagulation methods commonly lead to "non-covalent" driven dispersion of CNTs.

Surface and extremity functionalization but also in-situ polymerization most of the time enhance the quality of the nanotubes dispersion using these physical methods. The socalled "grafting to" and "grafting from" approaches involving (functionalized) CNTs are also known to lead to good nanofillers dispersion with the formation of covalent bonds between the nanotubes and polymer chains [2][3][4][5].

During melt blending, and depending on their chemical composition, polymers can be more or less altered due to thermo-oxidation and/or thermo-mechanical degradations. Such degradations generally involve the formation of free-radicals [6][7][8].

For instance, Zhang et al. have reported that free-radicals are generated on polystyrene during its melt mixing [9]. As carbon nanotubes are known to readily react with freeradicals [10,11], grafting of polymer chains onto the CNT surface could take place [12].

Nitrile Butadiene Rubber (NBR) is a random copolymer of butadiene and acrylonitrile. After vulcanization, it is used for the conception of tires, wires, joints,… Undoubtedly it represents a good candidate for the conception of CNT-filled/grafted NBR nanocomposites for several mean reasons:

-NBR degradation during the melt mixing process [13] leads to the formation of free-radicals on the polymer chains [14][15][16]; -high affinity between acrylonitrile groups (ACN) and CNT [17];

-no significant poisoning effect by CNTs on vulcanization process [18].

Accordingly, various NBR samples characterized by increasing content in ACN have been chosen for the production of conducting elastomer nanocomposites filled with multiwall CNTs surface-grafted by NBR chains. Firstly, we will highlight that the thermo-oxidative and/or thermo-mechanical degradation of the polymer taking place during the melt-blending process leads to the covalent grafting of elastomer chains onto the nanotube surface. Then we will show that the content in surface-grafted CNTs increases with the ACN relative content spread along the NBR chains. Finally, transmission electron miscroscopy (TEM) and electrical measurements will be approached for highlighting the effect of the ACN content on the extent of dissociation of the native nanotube bundles and the quality of the nanofillers distribution and dispersion throughout the NBR matrix.

EXPERIMENTAL PART

MATERIALS

The Nitrile Butadiene Rubbers (NBR) used in this study were kindly supplied by Lanxess, Germany. Three different grades were employed: Perbunan 1846, Perbunan 3445 and Perbunan 4456 containing different acrylonitrile contents, respectively, 18, 34 and 44 wt%. They were used without any purification or pre-treatment.

The carbon nanotubes (CNTs) (grade NC7000) are kindly supplied by Nanocyl, Belgium. They are non-purified Multiwall Carbon Nanotubes (MWNTs) used as received without any further purification. Sulfur, stearic acid and zinc oxide (GoodYear, Germany) were used as vulcanization agents (see hereunder).

PROCESSING CONDITIONS

NBR/CNT composites were prepared using a two-step process. The components (i.e. NBR, CNTs and vulcanization agents, if any) were mixed simultaneously in a Brabender internal mixer. Typical compositions of the studied compounds are reported in Table 1. Except when indicated, all the compounds were prepared at 50°C for 10 minutes at 60rpm and were then vulcanized at 190°C under 50 bars for 15 min.

<Insert table 1>

CHARACTERIZATIONS Thermogravimetric analyses (TGA) were carried out under He with a Hi-Res TGA 2950 device from TA Instruments with a heating rate of 20°C/min from room temperature to 800°C. The percentage of residual ashes (CNTs + carbonized NBR) was taken as the value reported at 530°C.

For "bound rubber" tests, each blend (typically 0.5g mixed with 10 wt% CNTs) was introduced in a glass tube containing a magnetic stirring bar. Approximately 30g of an equivolumic solution of CHCl 3 /toluene were added to the blend sample, so that the NBR concentration was the same in every experiment. The mixture was placed under stirring at a controlled temperature (25°C) for 24 h. The tube was centrifuged (4000 rpm, 40 min), and the insoluble products (CNTs + adsorbed/grafted NBR) were filtered off and dried under vacuum at 70°C until mass stabilization. Then Q ads , the mass of adsorbed polymer per gram of nanofiller was calculated. The experiment was performed 3 times for each compounds.

For swelling tests, each compound was introduced in at least 50g of toluene at ambient temperature. They were weighted after mass stabilization, typically after 48 hours.

TEM analyses were performed with a Philips CM100 apparatus using an acceleration voltage of 100 kV. Ultrathin sections of the composites (ca. 80 nm thick) were cut at -100 °C from 3 mm thick hot-pressed plates using a LEICA ultracryomicrotome equipped with a diamond knife.

Electrical measurements were performed in collaboration with Nanocyl using a Keithley 2700 multimeter. Samples are 8cm long, 1cm large and 3mm thick. Silver paint was used to provide good electrical contacts between the samples and the tips.

RESULTS AND DISCUSSION

I.

COVALENT GRAFTING OF NBR TO CARBON NANOTUBES I.1. Solubilization tests.

A way to appreciate basically if carbon nanotubes (CNT) are grafted by polymer chains is to perform preliminary solubilization tests on the polymer/CNT composites. Accordingly, TGA analyses have been performed on the dried supernatants and the resulting curve is reported on Figure 2. The increase of the residue mass (%CNT) is equal to 1.4 wt%, meaning that approximatively 45% of the initial mass of the CNTs are grafted to the elastomer phase.

<Insert figure 2>

As discussed in the Introduction, NBR is known to degrade during the melt blending step, leading to the generation of free-radicals on the polymer chains.

Similarly to other polymers [9], we can assume that these free-radicals could lead to the grafting of NBR chains onto the CNT surface. Assuming this, three composites have been prepared following different processing conditions. The processing time and the rotation speed in the Bradender internal mixer are the parameters that could affect the degradation of the NBR. So they have been varied in order to tune the NBR degradation. These compounds have then been solubilized in CHCl 3 and after centrifugation, the supernatants were dried and analyzed by TGA. The corresponding curves are also reported on Figure 2.

For each compound, the percentage of CNTs is increased. For 3wt% CNT-filled rubber, the ashes mass rises by ca. 17 and 38 wt% with the increase of the rotation speed (from 60 to 100 rpm) and the blending time (from 10 to 20 min), respectively. As expected, the relative amount in grafted-CNTs is highly affected by the process conditions and therefore the extent of both thermo-oxidative and thermo-mechanical degradations, i.e., the formation of free-radicals within the rubber phase.

I. 3. Influence of vulcanization agents on the amount of grafted-CNT.

The vulcanization of rubbers is a free-radical reaction. Sulfur decomposes in radical species, which mostly react in allylic position of the butadiene units of NBR. As NBR chains seem to graft onto CNTs via a free-radical mechanism, the (surfacegrafted) CNTs could also take part to some pre-vulcanization occurring during the initial blending process. However, Raman analyses have shown that the vulcanization of natural rubbers is not or only slightly affected by the presence of Single wall CNTs [18]. Even though the authors did not report any significant effect of the nanotubes on the vulcanization rate of the elastomer matrix, this does not mean that further CNT grafting could be triggered by the presence of the vulcanization agents. To shed some light on the occurrence of those grafting reactions, TGA has been performed on the dried supernatant in chloroform of NBR/CNT composites melt processed in the presence of vulcanization additives but recorded before the final vulcanization step (Figure 3). The weight loss recorded at 530°C increases from 4.5 to 10.0 wt%. This increase might be attributed to the presence of the vulcanization agents but also to polymer-grafting onto CNTs. The vulcanization agents correspond to maximum 3.9 wt% of the mass of the compounds, meaning that a minimum of 1.6 wt% of CNTs could be considered as surface-grafted and solubilized in chloroform, i.e., embarked in the supernatant fraction. In the same experimental conditions, but without any vulcanization additives, the percentage of CNTs is at best equal to 1.4 wt%. In conclusion, it comes out that the presence of vulcanization additives does not impede the grafting reactions onto CNT-surface and even seems to favor these free-radical reactions during the initial melt blending step.

<Insert figure 3> I.4. Swelling tests.

The implication of CNTs during the vulcanization step can also be checked by swelling tests in toluene. Indeed, the polymer-grafting onto the nanotube surface is expected to affect the crosslinking density of the vulcanized nanocomposite materials.

The number-average molar mass between the crosslinking nodes, noted c M , was calculated using the Flory-Rehner equation [START_REF] Sperling | Introduction to physical polymer science 4th Edition[END_REF]:

where V mol is the molar volume of toluene and χ NBR/toluene the interaction parameter between toluene and NBR (equals to 0.435 according to [START_REF] Wei-Gwo | [END_REF]). μ corresponds to the inverse of the swelling ratio, calculated from the following equation:

² . ) 1 ln( ) 2 / .( / 3 / 1 µ µ µ µ V c M toluène NBR mol        ) / ) .( / 1 /( 1 0 0 m m m d d µ swollen solvent NBR   
where d NBR and d solvent correspond, respectively, to the density of NBR and toluene, and m 0 and m swollen correspond, respectively, to the initial mass and the swollen mass of the vulcanized samples. During the melt blending of NBR with CNTs, the grafting reaction of some polymer chains onto the nanotubes surface has been evidenced. This grafting more likely results from the formation of free-radicals along the polymer chains as generated by thermo-oxidation and/or thermo-mechanical degradation mechanisms. Interestingly the vulcanization, i.e., a free-radical reaction, involves the CNTs reducing the numberaverage molar mass between the crosslinking nodes at higher nanotubes content. Since it is well accepted that both thermo-oxidative and thermo-mechanical degradations of NBR chains take place on ACN units [14][15][16], it has been decided to study the effect of ACN relative content of NBR on the polymer-grafting rate in NBR/CNT blends.

II.

Influence of ACN content on amount of grafted-CNTs.

II.1. "Bound rubber" tests.

Acrylonitrile groups and carbon nanotubes are known for their inherent affinity [17]. In that context, it can be assumed that during the blending process of CNTs with NBR, the ACN units spread along the elastomer chains tend to organize and localize preferentially around the nanotubes surface. Such a conformation should later facilitate the grafting reaction of the free-radicals generated preferentially on the ACN units of NBR.

"Bound rubber" tests are often used to check whether physical interactions are established between an elastomer polymer and a selected filler. This test relies upon the determination of the quantity of polymer adsorbed (Q ads) on the filler surface. Q ads is calculated by using the following equation:

where m CNT correspond to the initial CNT mass, and m driedresidue is the mass obtained after drying of the centrifuged residue (see experimental).

<Insert table 2>

A larger quantity of CNTs appears thus bound to NBR containing higher ACN units, attesting for the expected interactions between the ACN units and CNTs.

Moreover, these interactions stress the fact that ACN units are localized in the neighborhood of CNTs. Since ACN groups are highly prone to generate free-radicals by hydrogen atom abstraction, it can be assumed that their promiscuity to CNTs works in favor to the polymer-grafting onto the nanotubes surface.

II.2. TGA analyses

Solubilization tests have been again performed in chloroform starting from the three NBR-based composites containing 3 wt% CNT and differing by their ACN relative content. After centrifugation of the solution, the supernatants were dried before TGA analyses. TGA curves are reported on Figure 6. Figures 6(a

<Insert figure 6>

For each compound, there is an increase of the mass of the residue corresponding to the content of polymer-grafted CNT, thus solubilized in chloroform and embarked in the supernatant fraction (Table 3). Reducing the ACN relative content in NBR also leads to a decrease of the percentage of surface-grafted CNTs, shifting from 1.4 to 0.2%, respectively, for rubbers containing 44 and 18 wt% ACN units. In conclusion, the more the NBR elastomer contains ACN groups, the more the CNTs in the NBR/CNT blends are surface-grafted. Such an observation might be explained by the relatively higher amount of free-radicals thus generated on the ACN groups and the affinity between the acrylonitrile functions and the nanotubes.

<Insert table 3> III.
Influence of the ACN relative content on CNT dispersion.

III.1. Morphological analyses by TEM

Cassagnau et al. [2] have previously reported that the grafting of polymer chains on CNTs leads to a better dispersion of CNTs within the corresponding polymer matrix.

In NBR, the CNT grafting is monitored by thermo-oxidative/thermo-mechanical degradation of the elastomer chains and by the presence of vulcanization additives.

Furthermore a larger quantity of CNTs is surface-grafted by NBR chains at higher ACN relative content. Accordingly, the ACN content might also affect the dispersion ability of the nanotubes into the NBR elastomer matrix.

<Insert figure 7> TEM micrographs reported on Figure 7 correspond to the three studied NBRbased composites differing by their acrylonitrile content and filled with 3 wt% CNTs. As the process conditions monitor the polymer grafted rates, they also affect the properties of the materials. In a forthcoming paper, the effect of experimental conditions on the properties of the NBR elastomeric matrices filled with (surface-grafted) nanotubes and the possibility to tune them up will be reported.

Authors highly thank the "Région Wallonne" for the financial support provided in the frame of the research project: "Plan Marshall -NANOCOMPO". Authors also want to thank NANOCYL for kindly supplying the studied CNTs and intensive collaboration especially in the frame of electrical measurements (with the help Dr Michael Mainil who is warmly thanked). CIRMAP thanks the "Belgian Federal Governement Office Policy of Science (SSTC)" for general support in the frame of the PAI-6/27.

Captions for Figures and Tables

Figure 1 I. 2 .

 12 Figure 1 represents two solubilization tests. The picture on the left (Figure 1(a))

Figure 4

 4 Figure 4 displays the evolution of c M values with the CNT content from 0 to 3

  ) and 6(b) correspond, respectively, to the NBR matrices containing 18 and 44 wt% ACN units, filled or not with CNTs (3 wt%).

Figures 7a ,

 7a Figures 7a, 7b and 7c display, respectively, the matrices containing 18, 34 and 44 wt%

Figure

  Figure 1. Pictures of (a) CNTs and NBR mixed in CHCl 3 and (b) a NBR/CNT

1 .

 1 Figure 1. Pictures of (a) CNTs and NBR mixed in CHCl 3 and (b) a NBR/CNT

Figure 2 .

 2 Figure 2. TGA curves of the supernatants in CHCl 3 of different melt processed

Figure 3 .

 3 Figure 3. TGA curves of the supernatants in CHCl 3 of NBR/CNT composites prepared

Figure 4 .

 4 Figure 4. Number-average molar mass between the crosslinking nodes ( c M ) of

Figure 5 .

 5 Figure 5. Schematic representation of the CNT implication in NBR crosslinking

Figure 6 .

 6 Figure 6. TGA curves of the supernatants in CHCl 3 of NBR/CNT composites differing

Figure 7 .

 7 Figure 7. (a) to (c) TEM pictures of NBR/CNT composites in function of their

Figure 8 .

 8 Figure 8. Electrical properties of NBR/CNT composites in function both of their

  Table 2 summarizes the results gathered for the three studied NBR, thus differing in their ACN relative content.

	Qads		m	NTC ue driedresid m 	m	NTC
	Interestingly enough, a substantially higher quantity of polymer chains remains
	bound/adsorbed on the CNT surface when the ACN relative content in NBR is
	increased. For instance, Q ads values of 1.7 and 3.3 are determined for NBR matrices
	containing 18 and 44 wt% ACN units, respectively.

Table 1 .

 1 Summary of the %CNT grafted to NBR in function of the melt blending experimental conditions.

Table 2 .

 2 Bound rubber tests performed on three NBR, differing by their ACN content.

Table 3 .

 3 Summary of the %CNT grafted to NBR in function of the ACN relative content of the rubbers (initial CNT content in NBR composites: 3 wt%)

Acknowledgments

CNT content (%wt)