The use of the concept of "primary energy" is present in all types of regulations at both European and national level, so that all aspects related to the reduction of energy use and energy efficiency measures speak in terms of primary energy and Primary Energy Factors, necessary for its conversion. The existing consensus on the use of the term is not such in terms of the methodology for calculating the Primary Energy Factors to be adopted, which is the reason for the search for a methodology that acquires the status of global and standard. Using an analytical methodology, this study will analyze and compare the main methods used by agencies and institutions: the Physical Energy Content Method and the Partial Substitution Method, together with another less widely used method, the Exergy Method. The three calculation methodologies will be applied to the case study of the Swedish electricity production mix. The main objective of this thesis is to analyze the advantages and disadvantages of those methodologies, as well as discuss the difficulties of defining some variables such as efficiencies and system boundaries. The results obtained in this study demonstrate the complexity of trying to analyze a system as complex as the energy consumption of a country based on the calculation of a single number or Primary Energy Factor. The system boundaries affect the results. At the same time, the use of the Physical Energy Content Method is discarded because it incurs thermodynamic discrepancies. On the other hand, the use of the Partial Substitution Method and Exergy Method is encouraged, since they reflect more accurately the primary energy consumption, as long as the values of efficiencies that they use are clearly defined and referenced. However, there is a more widespread use of the Physical Energy Content Method in the institutions since the other methods present the great difficulty of establishing a consensus on the energy and exergy efficiencies values adopted. The complexity of choosing a calculation methodology is not only due to the choice of efficiencies but other factors, such as system boundaries, also influence the final results and they have to be reflected in some way. Therefore, it is difficult to decide on a single solution and future studies on other indicators and variables affecting primary energy usage are needed, for instance, CO2 emissions associated with generation technologies.

Desalination is one of the proposed methods to meet the ever increasing water demands. It can be subdivided into two broad categories, thermal based desalination and electricity based desalination. Multi-effect Distillation (MED), Multi-Stage Flashing (MSF), Membrane Distillation (MD) fall under former and Reverse Osmosis (RO), Electro-Dialysis (ED) fall under later. MD offers an attractive solution for seawater as well as brackish water distillation. It shows highly pure yields, theoretically 100% pure. The overall construction of a MD unit is way simpler than any other desalination systems. MD is a thermally driven diffusion process where desalination takes places in the form of water vapor transport across the membrane. It has low second law efficiency due to parasitic heat losses. The objective of the first part of the investigation is to thoroughly analyze a Direct Contact Membrane Distillation (DCMD) system from the view point of yield and exergy. The insights from exergy analysis are used in a design study, which is used for performance optimization. The first part concludes with a design procedure and design windows for large scale DCMD construction. In the second part of the investigation, focus is moved to waveguide solar energy collector. The idea behind an ideal waveguide is to reduce the complexity of modeling solar energy collection. The mathematical model provided in this analysis can be extended to a family of non-imaging optics in solar energy and serves as a benchmarking analysis tool. A waveguide is suitable for low temperature operations due to limitations on maximum continuous temperature of operation. Thus, it becomes an ideal solution for DCMD applications. A levelized cost analysis is presented for a waveguide powered DCMD plant of a 30,000 capacity. A combination of waveguide and DCMD shows levelized cost of water at $1.80/m³, which is found to be lower than previously reported solar desalination water costs. / Master of Science

As technology is increasingly used in mobile settings, energy and battery management is becoming a part of everyday life. Many have experienced how quickly a battery can be depleted in a smartphone, laptop or electric cars, sometimes causing much distress. An important question is how we can understand and work with energy as a factor in interaction design to enable better experiences for end-users. Through design-oriented research, I have worked with the specific case of electric cars, which is currently a domain where people struggle in terms of energy management. The main issue in this use case is that current driving range estimates cause distrust and anxiety among drivers. Through sketches, prototypes and studies, I investigated causes as well as possible remedies to this situation. My conclusion is that instead of providing black-boxed predictions, in-car interfaces should expose the logics of estimates so that drivers know how their own actions in e.g. driving style, climate control, and other equipment, affects energy use. Revealing such energy mechanisms will not only empower the driver, it will also acknowledge the impact of variables that cannot be predicted automatically. In this work, understanding the dynamic aspects of energy has emerged as central to interaction with systems. This points to a need to design energy sensitive interactions - focusing on supporting users to find the right balance between energy use and the experiential values sought for. To ease design of energy sensitive interactions, energy use is divided into three different categories with accompanying ideals. These are exergy (always needed to achieve the required interaction), intergy (controllable and changing over time and use, needs to be addressed in design), and anergy (always waste that needs to be reduced). This articulation highlights aspects of energy that are specific to interaction design, and possible aspects to expose to allow more energy-efficient interactions in use. / I takt med att vi använder alltmer teknik i mobila sammanhang blir energi- och batterihantering en allt större del av vår vardag. Många har erfarenheter av de besvär som ett plötsligt urladdat batteri i en mobiltelefon, laptop eller elbil kan orsaka. En central fråga för att uppnå bättre användarupplevelser är hur vi kan förstå och arbeta med energi som en faktor i design av interaktion med mobil teknik. Genom designdriven forskning har jag arbetat specifikt med interaktionen i elbilar, en situation där många brottas med just hantering och förståelse av begränsad energi. En specifik utmaning i denna kontext är den misstro som många upplever kring existerande system för räckviddsberäkning. Genom skisser, prototyper och användarstudier har jag undersökt orsaker och praktiska lösningar på detta problem. Min slutsats är att bilens gränssnitt bör exponera den inre logik som beräkningarna bygger på, så att föraren förstår hur egna handlingar, såsom körsätt och användning av t ex kupévärmare, påverkar energiförbrukning och räckvidd. Detta leder till ökad upplevelse av kontroll för föraren, och samtidigt till mer tillförlitliga beräkningar då det tar hänsyn till variabler som inte kan förutsägas automatiskt. I arbetet har dynamiska aspekter av energi framträtt som centralt i användning av interaktiva system. Detta pekar på behovet av att designa energikänsliga interaktioner, som hjälper användaren att förstå balansen mellan energiåtgång och bruksvärde. För att stödja design av energikänsliga interaktioner artikuleras tre kategorier av energianvändning i interaktiva system. Dessa är exergi (behövs för att uppnå tänkt interaktion), intergi (kontrollerbar och föränderlig över tid och användning, måste adresseras med design), och anergi (är alltid ett slöseri som behöver reduceras). Denna artikulation belyser specifikt de aspekter av energiförbrukningen som varierar genom användning, och som skulle kunna exponeras för mer energieffektiv interaktion med ny teknik. / <p>QC 20160429</p>

In this thesis, exergy based SI engine model optimisation (EBSIEMO) is studied and evaluated. A four-stroke bi-fuel spark ignition (SI) engine is modelled for optimisation of engine performance based upon exergy analysis. An artificial neural network (ANN) is used as an emulator to speed up the optimisation processes. Constrained particle swarm optimisation (CPSO) is employed to identify parameters such as equivalence ratio and ignition time for optimising of the engine performance, based upon maximising 'total availability'. In the optimisation process, the engine exhaust gases standard emission were applied including brake specific CO (BSCO) and brake specific NOx (BSNOx) as the constraints. The engine model is developed in a two-zone model, while considering the chemical synthesis of fuel, including 10 chemical species. A computer code is developed in MATLAB software to solve the equations for the prediction of temperature and pressure of the mixture in each stage (compression stroke, combustion process and expansion stroke). In addition, Intake and exhaust processes are calculated using an approximation method. This model has the ability to simulate turbulent combustion and compared to computational fluid dynamic (CFD) models it is computationally faster and efficient. The selective outputs are cylinder temperature and pressure, heat transfer, brake work, brake thermal and volumetric efficiency, brake torque, brake power (BP), brake specific fuel consumption (BSFC), brake mean effective pressure (BMEP), concentration of CO2, brake specific CO (BSCO) and brake specific NOx (BSNOx). In this model, the effect of engine speed, equivalence ratio and ignition time on performance parameters using gasoline and CNG fuels are analysed. In addition, the model is validated by experimental data using the results obtained from bi-fuel engine tests. Therefore, this engine model was capable to predict, analyse and useful for optimisation of the engine performance parameters. The exergy based four-stroke bi-fuel (CNG and gasoline) spark ignition (SI) engine model (EBSIEM) here is used for analysis of bi-fuel SI engines. Since, the first law of thermodynamic (the FLT), alone is not able to afford an appropriate comprehension into engine operations. Therefore, this thesis concentrates on the SI engine operation investigation using the developed engine model by the second law of thermodynamic (the SLT) or exergy analysis outlook (exergy based SI engine model (EBSIEM)) In this thesis, an efficient approach is presented for the prediction of total availability, brake specific CO (BSCO), brake specific NOx (BSNOx) and brake torque for bi-fuel engine (CNG and gasoline) using an artificial neural network (ANN) model based on exergy based SI engine (EBSIEM) (ANN-EBSIEM) as an emulator to speed up the optimisation processes. In the other words, the use of a well trained an ANN is ordinarily much faster than mathematical models or conventional simulation programs for prediction. The constrained particle swarm optimisation (CPSO)-EBSIEM (EBSIEMO) was capable of optimising the model parameters for the engine performance. The optimisation results based upon availability analysis (the SLT) due to analysing availability terms, specifically availability destruction (that measured engine irreversibilties) are more regarded with higher priority compared to the FLT analysis. In this thesis, exergy based SI engine model optimisation (EBSIEMO) is studied and evaluated. A four-stroke bi-fuel spark ignition (SI) engine is modelled for optimisation of engine performance based upon exergy analysis. An artificial neural network (ANN) is used as an emulator to speed up the optimisation processes. Constrained particle swarm optimisation (CPSO) is employed to identify parameters such as equivalence ratio and ignition time for optimising of the engine performance, based upon maximising 'total availability'. In the optimisation process, the engine exhaust gases standard emission were applied including brake specific CO (BSCO) and brake specific NOx (BSNOx) as the constraints. The engine model is developed in a two-zone model, while considering the chemical synthesis of fuel, including 10 chemical species. A computer code is developed in MATLAB software to solve the equations for the prediction of temperature and pressure of the mixture in each stage (compression stroke, combustion process and expansion stroke). In addition, Intake and exhaust processes are calculated using an approximation method. This model has the ability to simulate turbulent combustion and compared to computational fluid dynamic (CFD) models it is computationally faster and efficient. The selective outputs are cylinder temperature and pressure, heat transfer, brake work, brake thermal and volumetric efficiency, brake torque, brake power (BP), brake specific fuel consumption (BSFC), brake mean effective pressure (BMEP), concentration of CO2, brake specific CO (BSCO) and brake specific NOx (BSNOx). In this model, the effect of engine speed, equivalence ratio and ignition time on performance parameters using gasoline and CNG fuels are analysed. In addition, the model is validated by experimental data using the results obtained from bi-fuel engine tests. Therefore, this engine model was capable to predict, analyse and useful for optimisation of the engine performance parameters. The exergy based four-stroke bi-fuel (CNG and gasoline) spark ignition (SI) engine model (EBSIEM) here is used for analysis of bi-fuel SI engines. Since, the first law of thermodynamic (the FLT), alone is not able to afford an appropriate comprehension into engine operations. Therefore, this thesis concentrates on the SI engine operation investigation using the developed engine model by the second law of thermodynamic (the SLT) or exergy analysis outlook (exergy based SI engine model (EBSIEM)) In this thesis, an efficient approach is presented for the prediction of total availability, brake specific CO (BSCO), brake specific NOx (BSNOx) and brake torque for bi-fuel engine (CNG and gasoline) using an artificial neural network (ANN) model based on exergy based SI engine (EBSIEM) (ANN-EBSIEM) as an emulator to speed up the optimisation processes. In the other words, the use of a well trained an ANN is ordinarily much faster than mathematical models or conventional simulation programs for prediction. The constrained particle swarm optimisation (CPSO)-EBSIEM (EBSIEMO) was capable of optimising the model parameters for the engine performance. The optimisation results based upon availability analysis (the SLT) due to analysing availability terms, specifically availability destruction (that measured engine irreversibilties) are more regarded with higher priority compared to the FLT analysis.

Although concentrated solar power can be used to produce power using traditional electricity generation, energy storage has become a problem due to the intermittent supply of solar energy. By using solar energy in chemical production processes, the solar energy can be stored in a useful chemical product. The purpose of this thesis will be to examine the possibilities of a new solar chemical cycle the produces iron and ethylene from hematite (a form of iron oxide) and ethane using concentrated solar power. These two products are important stepping stones in the production of steel and polymers. This process could allow for the current process of steel production to move away from processes using coal and towards a more sustainable process using the hydrogen formed from the ethane cracking process and solar energy. The thesis will include: (1) the development of a new solar powered iron and ethylene combined cycle, (2) a feasibility study of a Concentrated Solar Heat Supply System (CSHSS) being developed at Georgia Tech, and (3) an assessment of the proposed cycle. The assessment will include an estimate of production including a thermodynamic ASPEN model, assessment of research to realize actualization of the theoretical cycle, an exergy analysis, and a heat exchanger analysis for the exchange of heat between the CSHSS and the chemical process.

There has been renewed significance for innovative energy conversion technologies, particularly the heat recovery-to-power technologies for sustainable power generation from renewable energies and waste heat. This is due to the increasing concern over high demand for electricity, energy shortage, global warming and thermal pollution. Among the innovative heat recovery-to- power technologies, the proposed trilateral flash cycle (TFC) is a promising option, which presents a great potential for development. Unlike the Rankine cycles, the TFC starts the working fluid expansion from the saturated liquid condition rather than the saturated, superheated or supercritical vapour phase, bypassing the isothermal boiling phase. The challenges associated with the need to establish system design basis and facilitate system configuration design-supporting analysis from proof-of-concept towards a market-ready TFC technology are significant. Thus, there is a great need for research to improve the understanding of its operation, behaviour and performance. The objective of this study is to develop and establish simulation tools of the TFCs for improving the understanding of their operation, physics of performance metrics and to evaluate novel system configurations for low-grade heat recovery-to-power generation. This study examined modelling and process simulation of the TFC engines in order to evaluate their performance metrics, predictions for guiding system design and parameters estimations. A detailed thermodynamic analysis, performance optimization and parametric analysis of the cycles were conducted, and their optimized performance metrics compared. These were aimed at evaluating the effects of the key parameters on system performances and to improve the understanding of the performance behaviour. Four distinct system configurations of the TFC, comprising the simple TFC, TFC with IHE, reheat TFC and TFC with feed fluid-heating (or regenerative TFC) were examined. Steady-state steady-flow models of the TFC power plants, corresponding to their thermodynamic processes were thermodynamically modelled and implemented using engineering equation solver (ESS). These models were used to determine the optimum synthesis/ design parameters of the cycles and to evaluate their performance metrics, at the subcritical operating conditions and design criteria. Thus, they can be valuable tools in the preliminary prototype system design of the power plants. The results depict that the thermal efficiencies of the simple TFC, TFC with IHE, reheat TFC and regenerative TFC employing n-pentane are 11.85 - 21.97%, 12.32 - 23.91%, 11.86 - 22.07% and 12.01 - 22.9% respectively over the cycle high temperature limit of 393 - 473 K. These suggest that the integration of an IHE, fluid-feed heating and reheating in optimized design of the TFC engine enhanced the heat exchange efficiencies and system performances. The effects of varying the expander inlet pressure at the cycle high temperature and expander isentropic efficiency on performance metrics of the cycles were significant. They have assisted in selecting the optimum-operating limits for the maximum performance metrics. The thermal efficiencies of all the cycles increased as the inlet pressures increased from 2 - 3 MPa and increased as the expander isentropic efficiencies increased from 50 - 100%, while their exergy efficiencies increased. This is due to increased net work outputs that suggest optimal value of pressure ratios between the expander inlets and their outlets. A comprehensive evaluation depicted that the TFC with IHE attained the best performance metrics among the cycles. This is followed by the regenerative TFC whereas the simple TFC and reheat TFC have the lowest at the same subcritical operating conditions. The results presented show that the performance metrics of the cycles depend on the system configuration, and the operating conditions of the cycles, heat source and heat sink. The results also illustrate how system configuration design and sizing might be altered for improved performance and experimental measurements for preliminary prototype development.

There has been renewed significance for innovative energy conversion technologies, particularly the heat recovery-to-power technologies for sustainable power generation from renewable energies and waste heat. This is due to the increasing concern over high demand for electricity, energy shortage, global warming and thermal pollution. Among the innovative heat recovery-to- power technologies, the proposed trilateral flash cycle (TFC) is a promising option, which presents a great potential for development. Unlike the Rankine cycles, the TFC starts the working fluid expansion from the saturated liquid condition rather than the saturated, superheated or supercritical vapour phase, bypassing the isothermal boiling phase. The challenges associated with the need to establish system design basis and facilitate system configuration design-supporting analysis from proof-of-concept towards a market-ready TFC technology are significant. Thus, there is a great need for research to improve the understanding of its operation, behaviour and performance. The objective of this study is to develop and establish simulation tools of the TFCs for improving the understanding of their operation, physics of performance metrics and to evaluate novel system configurations for low-grade heat recovery-to-power generation. This study examined modelling and process simulation of the TFC engines in order to evaluate their performance metrics, predictions for guiding system design and parameters estimations. A detailed thermodynamic analysis, performance optimization and parametric analysis of the cycles were conducted, and their optimized performance metrics compared. These were aimed at evaluating the effects of the key parameters on system performances and to improve the understanding of the performance behaviour. Four distinct system configurations of the TFC, comprising the simple TFC, TFC with IHE, reheat TFC and TFC with feed fluid-heating (or regenerative TFC) were examined. Steady-state steady-flow models of the TFC power plants, corresponding to their thermodynamic processes were thermodynamically modelled and implemented using engineering equation solver (ESS). These models were used to determine the optimum synthesis/ design parameters of the cycles and to evaluate their performance metrics, at the subcritical operating conditions and design criteria. Thus, they can be valuable tools in the preliminary prototype system design of the power plants. The results depict that the thermal efficiencies of the simple TFC, TFC with IHE, reheat TFC and regenerative TFC employing n-pentane are 11.85 - 21.97%, 12.32 - 23.91%, 11.86 - 22.07% and 12.01 - 22.9% respectively over the cycle high temperature limit of 393 - 473 K. These suggest that the integration of an IHE, fluid-feed heating and reheating in optimized design of the TFC engine enhanced the heat exchange efficiencies and system performances. The effects of varying the expander inlet pressure at the cycle high temperature and expander isentropic efficiency on performance metrics of the cycles were significant. They have assisted in selecting the optimum-operating limits for the maximum performance metrics. The thermal efficiencies of all the cycles increased as the inlet pressures increased from 2 - 3 MPa and increased as the expander isentropic efficiencies increased from 50 - 100%, while their exergy efficiencies increased. This is due to increased net work outputs that suggest optimal value of pressure ratios between the expander inlets and their outlets. A comprehensive evaluation depicted that the TFC with IHE attained the best performance metrics among the cycles. This is followed by the regenerative TFC whereas the simple TFC and reheat TFC have the lowest at the same subcritical operating conditions. The results presented show that the performance metrics of the cycles depend on the system configuration, and the operating conditions of the cycles, heat source and heat sink. The results also illustrate how system configuration design and sizing might be altered for improved performance and experimental measurements for preliminary prototype development.

En ce début de millénaire 1,4 Milliards d'humains, parmi les plus démunis de la planète, vivent dans des sites isolés et ne bénéficient pas de réseaux de distribution d'énergie. Leur besoin en électricité est modeste, mais important en terme d'usages : accès aux soins médicaux et à l'instruction, communication, développement d'économies locales. C'est face à ce constat que Schneider Electric Industries relève, depuis 2009, le défi de concevoir et réaliser des microcentrales solaires thermodynamiques, concurrentielles à d'autres solutions, pour fournir à ces populations une énergie électrique fiable et respectueuse de l'environnement. Inscrit dans le cadre de ce projet, le présent travail - réalisé en Cifre - est séquencé par l'évolution industrielle du projet. Dans un premier temps, un Etat de l'Art, étendu à une analyse de détail, a contribué à privilégier certains choix technologiques : capteurs solaires à concentration, stockage thermique à chaleur sensible et moteur de Stirling. Dans un second temps, une étude thermodynamique préliminaire a permis d'évaluer le dimensionnement d'éléments clefs du système : champ de captage solaire et stockage thermique. En complément une étude de sensibilité paramétrique du dimensionnement et des performances à divers facteurs de pertes énergétiques a souligné les points durs techniques et participé à l'orientation des travaux de conception. Enfin, l'analyse exergétique de fonctionnement de capteurs solaires et d'un moteur Stirling en régimes dynamiques stationnaires proposent des bases pour l'optimisation de contrôle et commande, visant à accroître les performances énéergétiques du système et favoriser sa viabilité thermoéconomique / As a new millenium begins, 1.4 Billion people worldwide earn less than 2 dollars daily and have no access to the power grid. The need of electric power of these people represent small energy amounts but is very important regarding to the usage : acces to healthcare and education, communication, local economic development. In reponse to the situation, since 2009, Schneider Electric Industries takes up the challenge to design and realize micro solar power plants, competitive with other solutions, to supply these people with reliable and environment-friendly electricity. Dealing with this project, this work has been realized under contract, so it follows the development sequence of the industrial project. The first part is a State of the Art of the actual solar thermodynamical technologies. This task is extended to a qualitative evaluation of various technologies, as a contribution to select adapted technologies: concentrating solar thermal receivers, sensible heat thermal storage and Stirling engine. The secon step is a preliminary thermodynamics analysis of the whole system, that allowed to evaluate key features: the size of the solar receivers area, the thermal storage volume, and overall energy performance. This task is streched by a sensitivity analysis of the sizing and performances, according to various energy losses parameters, that shows the technical hard spots of the design. Finally, an exergy-based dynamical analysis of stationary operating solar receivers and Stirling engines leads to a propostion of basis methods and criteria for the optimal control of power, in order to maximize the energy performances of the system and to enhance its competitiveness

Offshore oil platforms are used for the exploitation and production of hydrocarbons and consist of a processing plant and a utility plant. The oil and gas industry operations are energy-intensive and, in the case of offshore platforms, the need to decrease energy consumption and reduce CO2 emissions has increased. In the oil and gas industry, the ISO 50001 standard promotes the implementation of energy management systems and proposes indicators based on energy. Interestingly, after several decades of knowledge of the concept of exergy, this has not been formally implemented in the programs and strategies of the oil and gas industry organizations. In this research, the implementation of the exergy method and the carbon capture and storage strategy for the assessment of the performance of a floating, production and storage offloading units FPSO is proposed. FPSO platforms and their processing and utility plants may have different configurations depending on, among others, the reservoir characteristics and production requirements. The possible configurations can therefore be numerous. In this sense, some operation scenarios based on different well-fluid compositions and operation modes are studied. The platform models are developed and simulated using the software Aspen HYSYS®. Results show that, on average, the reduction of 88.8% in CO2 emissions is penalized with a reduction in exergy efficiency of 1.7 points. Further, results allow a better understanding of exergy and environmental performance of the FPSO. / Plataformas de petróleo offshore são utilizadas para a exploração e produção de hidrocarbonetos e consistem em uma planta de processamento e uma planta de utilidade. As operações da indústria de petróleo e gás são de energia intensiva e, no caso de plataformas offshore, é necessário cada vez mais diminuir o consumo de energia e reduzir as emissões de CO2. Na indústria de petróleo e gás, a norma ISO 50001 promove a implementação de sistemas de gestão de energia e propõe indicadores baseados em energia. Entretanto, após várias décadas de conhecimento do conceito de exergia, este não foi formalmente implementado nos programas e estratégias das organizações da indústria de petróleo e gás. Neste trabalho, propõe-se a implementação da análise exergética e a estratégia de captura e armazenamento de carbono para a avaliação do desempenho de unidades flutuantes, de produção, de armazenamento e transferência FPSO. As plataformas FPSO e suas plantas de processamento e utilidade podem ter diferentes configurações dependendo, entre outras, das características do reservatório e dos requisitos de produção. As configurações possíveis podem, portanto, ser numerosas. Neste sentido, são estudados alguns cenários de operação baseados em diferentes composições dos fluidos do poço e em três modos de operação. Os modelos de plataforma são desenvolvidos e simulados usando o software Aspen HYSYS®. Os resultados mostram que, em média, a redução de 88,8% nas emissões de CO2 é penalizada com uma redução da eficiência exergética de 1,7 pontos. Além disso, os resultados permitem uma melhor compreensão da exergia e desempenho ambiental do FPSO.

Este trabalho apresenta uma avaliação comparativa de desempenho termodinâmico de sistemas térmicos em uma unidade industrial de fabricação de celulose e papel Kraft. Foram coletados dados de projeto e operação para o sistema atual de utilidades e de um novo sistema em fase de implantação. A análise exergética é utilizada como ferramenta de avaliação quantitativa e qualitativa para os principais componentes do sistema de cogeração de energia: caldeiras de força, caldeiras de recuperação química, turbinas e válvulas redutoras. Diferentes critérios de desempenho globais e relativos são determinados através de balanços simultâneos de energia e entropia (balanços exergéticos). As irreversibilidades ou entropia gerada nos sistemas são determinadas através da exergia destruída. Esta abordagem revela os principais pontos onde a energia é degradada em sua qualidade, indicando onde devem ser buscadas alternativas de otimização termoeconômica para um melhor aproveitamento dos recursos energéticos disponíveis. / This work presents a comparative evaluation from thermodynamic performance view of thermal systems in a Kraft pulp and paper mill. The design information and the data of the industrial operation were collected for the current utility system and for the new system that has been buit. The exergy analysis is applied as the quantitative and qualitative evaluation tool for the main energy conversion systems: power boilers, chemical recovery boiler, turbines and throttling valves. Different global and relatives performance criteria are estimated by simultaneous energy and entropy balances (exergy balances). The irreversibility or generated entropy in the systems is determined by the destroyed exergy. This approach reveals the places where energy quality is mainly degraded and shows where alternatives for optimization must be sought for a better use of the available energetic resources.