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.

Les réseaux de chauffage urbain (DHN) sont un moyen efficace de fournir de l'énergie thermique aux consommateurs. L'état actuel de la technique montre que les DHN évoluent vers des réseaux thermiques intelligents dans des systèmes énergétiques intégrés alors que leur conception est basée sur les principes de durabilité. Sur cette base, cette thèse couvre deux domaines de recherche principaux : Fonctionnement et conception des systèmes de chauffage urbain. Dans la partie A de cette thèse, des méthodes avancées pour le fonctionnement de la DHN sont développées à l'aide d'analyses exergétiques et thermoéconomiques. Cela inclut la formulation de bilans de coûts exergétiques pour les modèles de réseau basés sur des graphiques. La partie intrinsèque est le déploiement d'une matrice algébrique, qui détermine les coûts exergétiques pour la modélisation dynamique du système. Une étude de cas d'un réseau réel prouve que la méthodologie proposée offre de nouvelles perspectives sur l'allocation individuelle des coûts, ce qui aide à évaluer la faisabilité de l'intégration par des tiers et l'intégration des sources d'énergie distribuées. Dans la partie B de cette thèse, un nouvel indicateur appelé «load deviation index (LDI)» est proposé pour lier les mesures de la demande (DSM) à la conception durable des systèmes DHN. Pour cela, un cadre de conception axé sur les affaires est proposé, qui prend en compte les influences critiques dans le DHN tout en évitant un trop grand détail. Le comportement du DSM est analysé du point de vue du système et son impact sur la conception du DHN est étudié dans deux études de cas. Alors que l'un se concentre sur les benchmarks pour différentes options de conception en utilisant une métrique de durabilité multicritères, un autre donne des indications détaillées sur l'utilité du cadre proposé pour la conception en évaluant l'impact de DSM sur les améliorations de conception possibles. / District heating networks (DHN) arean efficient way of providing thermal energy to consumers. Current state of the art shows that DHNs are developing towards smart thermal networks in integrated energy systems while their design is based upon the principles of sustainability. Based on that, this thesis covers two main research areas: Operation and design of district heating systems. In part A of this thesis, advanced methods for DHN operation are developed with the help of exergetic and thermoeconomic analysis. This includes the formulation of exergetic cost balances for graph-based network models. Intrinsic part is the deployment of an algebraic matrix, which determines the exergetic costs for dynamic system modeling. A case study of areal-existing network provides evidence that the proposed methodology offers new insights into individual allocation of costs which helps to assess the feasibility of third-party integration and the integration of distributed energy sources. In part B of this thesis, a new indicator called “load deviation index (LDI)” is proposed to link demand side measures (DSM) with the sustainable design of DHN systems. For that, abusiness-focused design frameworks proposed which takes the critical influences of DHN into account while avoiding a too high detail. DSM behavior is analyzed from a system perspective and its impact on DHN design is studied in two case studies. While one focuses on benchmarks for different design options using a multi-criteria sustainability metric, another gives detailed insights into the usefulness of the proposed framework for design purposes through assessing the impact of DSM on possible design improvements using a multi-objective optimization approach.

Dans la perspective du présent scénario énergétique, ce travail de thèse propose une méthodologie qui associe la méthode du pincement à l’analyse exergétique de manière à dépasser leurs limitations individuelles aboutissant à une conception améliorée aux deux niveaux : paramètres opératoires et topologie. Une méthodologie globale, consistant à hybrider les deux méthodes thermodynamiques dans une approche entrelacée avec des règles heuristiques et une optimisation numérique, est donc évoquée. À l'aide de nouveaux critères d'optimisation basés sur l’exergie, l'analyse exergétique est utilisée non seulement pour évaluer les pertes d’exergie mais également pour guider les améliorations potentielles des conditions de fonctionnement et de structure des procédés industriels. En plus, au lieu de considérer uniquement l’intégration de la chaleur pour satisfaire des besoins existants, la méthodologie proposée étend la méthode de pincement pour inclure d’autres formes d’exergie récupérables et exploiter de nouvelles voies de synergie via des systèmes de conversion. Après avoir présenté les lignes directrices de la méthodologie proposée, l’approche est démontrée sur deux systèmes industriels, un procédé d’hydrotraitement de gasoil sous vide et un procédé de liquéfaction de gaz naturel. L’application du cadre méthodologique à des processus réalistes a montré comment ajuster les conditions opératoires de chaque procédé et comment mettre en œuvre des systèmes de conversion générant des économies d’énergie substantielles. / In the perspective of the prevailing and alarming energy scene, this doctoral work puts forward a methodology that couples pinch and exergy analysis in a way to surpass their individual limitations in the aim of generating optimal operating conditions and topology for industrial processes. A global methodology, a hybrid of the two thermodynamic methods in an intertwined approach with heuristic rules and numerical optimization, is therefore evoked. Using new optimizing exergy-based criteria, exergy analysis is used not only to assess the exergy losses but also to guide the potential improvements in industrial processes structure and operating conditions. And while pinch analysis considers only heat integration to satisfy existent needs, the proposed methodology allows including other forms of recoverable exergy and explores new synergy pathways through conversion systems. After exhibiting the guidelines of the proposed methodology, the entire approach is demonstrated on two industrial systems, a vacuum gasoil hydrotreating process and a natural gas liquefaction process. The application of the methodological framework on realistic processes demonstrated how to adjust each process operating conditions and how to implement conversion systems ensuing substantial energy savings.

Com o constante desenvolvimento das áreas urbanas e aumento do consumo energético destinado a conforto térmico, um estudo foi realizado para formulação de uma metodologia de análise termoeconômica de sistemas distritais de resfriamento. O objetivo principal é descrever uma metodologia referente à implantação de sistemas distritais no Brasil, por sua vez, o objetivo secundário é aplicar a metodologia no estado de São Paulo, analisando as premissas utilizadas na metodologia. Primeiramente, apresentou-se uma visão geral e revisão de literatura dos sistemas de aquecimento e resfriamento distrital, indicando suas vantagens e desvantagens, bem como as diversas aplicações e desafios para sua implantação. Aplicações no cenário mundial foram expostas e analisadas, demonstrando que sua utilização em diversos países se estende por décadas. As principais vantagens observadas nas aplicações existentes estão relacionadas a maior eficiência energética e exergética global, redução das emissões de gases poluentes e confiabilidade do sistema. Por fim, a metodologia aplicada está apresentada em cinco etapas, de forma ordenada, baseando-se nas etapas de um projeto de sistemas distritais. Seu resultado é baseado em rotinas, simulações de processos e procedimentos de otimização, bem como aplicação de indicadores energéticos. Ao final das etapas e seu desenvolvimento matemático obtém-se um estudo preliminar de viabilidade da implantação de um sistema distrital. O estudo de caso apresentado aplica a metodologia para a cidade de São Paulo buscando descrever com detalhamento as premissas e etapas descritas. / The constant development of urban areas and increased energy consumption for thermal comfort encourage studies that formulate a methodology for thermoeconomic analysis of district cooling systems. The main objective is to describe a thermoeconomic methodology related to the implementation of district systems in Brazil. The secondary objective is to apply the methodology in the state of São Paulo, analyzing the premises used in the methodology. At first, an overview and literature review of district heating and cooling systems was presented, indicating their advantages and disadvantages, just as the various applications and challenges for their implementation. Applications on the world stage have been introduced and analyzed, demonstrating that their use in several countries extends for decades. The main advantages observed in the existing applications are related to global energy and exergy efficiency, reduction in greenhouse gases and reliability of the systems. Finally, the applied methodology is presented in five steps in an orderly manner based on the steps of a district system project. Its result is based on routines, process simulations and optimization procedures, as well as application of energy indicators. At the end of the steps and their mathematical development a preliminary study of the feasibility of the implantation of a district system is obtained. The present case study applies the methodology for the city of São Paulo and describe in detail the premises and steps.

The objectives of this doctoral thesis are to give a basisincluding methods for the development of stationary polymerelectrolyte fuel cell (PEFC) systems for combined heat andpower production. Moreover, the objectives include identifyingprerequisites, requirements and possibilities for PEFC systemsproducing heat and power for buildings in Sweden. The PEFCsystem is still in a pre-commercial state, but low emissionlevels, fast dynamics and high efficiencies are promisingcharacteristics. A thermodynamic model to simulate stationary PEFC systemshas been constructed and pinch technology and exergy analysesare utilised to design and evaluate the system. The finalsystem configuration implies a high total efficiency ofapproximately 98 % (LHV). A flexible test facility was built in connection with theresearch project to experimentally evaluate small-scalestationary PEFC systems at KTH. The research PEFC system hasextensive measurement equipment, a rigorous control system andallows fuel cell systems from approximately 0.2 to 4 kWel insize to be tested. The simulation models of the fuel processorand the fuel cell stack are verified with experimental datataken from the test facility. The initial evaluation andsimulation of the first residential installation of a PEFCsystem in Sweden is also reported. This PEFC system, fuelled bybiogas and hydrogen, is installed in an energy system alsoincluding a photovoltaic array, an electrolyser and hydrogenstorage. Technical aspects of designing a fuel cell system-basedenergy system, including storages and grid connections, whichprovides heat and power to a building are presented in thisthesis. As a basis for the technical and economic evaluations,exemplifying energy systems are constructed and simulated. Fuelcell system installations are predicted to be economicallyunviable for probable near-term conditions in Sweden. The mainfactor in the economic evaluations is the fuel price. However,fuel cell system installations are shown to have a higher fuelutilisation than the conventional method of energy supply. The methods presented in this thesis serve as a collectedbasis for continued research and development in the area. Keywords:Small-scale, stationary, fuel cell system,polymer electrolyte fuel cell, PEFC system, reformer,thermodynamic modelling, pinch technology, exergy analyses,system configuration, test facility, experiments, application,simulation, installation, energy system, energy storage, heatand power demand.

The world demand for electrical power increasescontinuously, requiring efficient and low-cost methods forpower generation. This thesis investigates two advanced powercycles with mixtures as the working fluid: the Kalina cycle,alternatively called the ammonia-water cycle, and theevaporative gas turbine cycle. These cycles have the potentialof improved performance regarding electrical efficiency,specific power output, specific investment cost and cost ofelectricity compared with the conventional technology, sincethe mixture working fluids enable efficient energyrecovery. This thesis shows that the ammonia-water cycle has a betterthermodynamic performance than the steam Rankine cycle as abottoming process for natural gas-fired gas and gas-dieselengines, since the majority of the ammonia-water cycleconfigurations investigated generated more power than steamcycles. The best ammonia-water cycle produced approximately40-50 % more power than a single-pressure steam cycle and 20-24% more power than a dual-pressure steam cycle. The investmentcost for an ammonia-water bottoming cycle is probably higherthan for a steam cycle; however, the specific investment costmay be lower due to the higher power output. A comparison between combined cycles with ammonia-waterbottoming processes and evaporative gas turbine cycles showedthat the ammonia-water cycle could recover the exhaust gasenergy of a high pressure ratio gas turbine more efficientlythan a part-flow evaporative gas turbine cycle. For a mediumpressure ratio gas turbine, the situation was the opposite,except when a complex ammonia-water cycle configuration withreheat was used. An exergy analysis showed that evaporativecycles with part-flow humidification could recover energy asefficiently as, or more efficiently than, full-flow cycles. Aneconomic analysis confirmed that the specific investment costfor part-flow cycles was lower than for full-flow cycles, sincepart-flow humidification reduces the heat exchanger area andhumidification tower volume. In addition, the part-flow cycleshad lower or similar costs of electricity compared with thefull-flow cycles. Compared with combined cycles, the part-flowevaporative cycles had significantly lower total and specificinvestment costs and lower or almost equal costs ofelectricity; thus, part-flow evaporative cycles could competewith the combined cycle for mid-size power generation. <b>Keywords:</b>power cycle, mixture working fluid, Kalinacycle, ammonia-water mixture, reciprocating internal combustionengine, bottoming cycle, gas turbine, evaporative gas turbine,air-water mixture, exergy

More electric aircraft systems, high power avionics, and a reduction in heat sink capacity have placed a larger emphasis on correctly satisfying aircraft thermal management requirements during conceptual design. Thermal management systems must be capable of dealing with these rising heat loads, while simultaneously meeting mission performance. Since all subsystem power and cooling requirements are ultimately traced back to the engine, the growing interactions between the propulsion and thermal management systems are becoming more significant. As a result, it is necessary to consider their integrated performance during the conceptual design of the aircraft gas turbine engine cycle to ensure that thermal requirements are met. This can be accomplished by using thermodynamic modeling and simulation to investigate the subsystem interactions while conducting the necessary design trades to establish the engine cycle. As the foundation for this research, a parsimonious, transparent thermodynamic model of propulsion and thermal management systems performance was created with a focus on capturing the physics that have the largest impact on propulsion design choices. A key aspect of this approach is the incorporation of physics-based formulations involving the concurrent usage of the first and second laws of thermodynamics to achieve a clearer view of the component-level losses. This is facilitated by the direct prediction of the exergy destruction distribution throughout the integrated system and the resulting quantification of available work losses over the time history of the mission. The characterization of the thermodynamic irreversibility distribution helps give the designer an absolute and consistent view of the tradeoffs associated with the design of the system. Consequently, this leads directly to the question of the optimal allocation of irreversibility across each of the components. An irreversibility allocation approach based on the economic concept of resource allocation is demonstrated for a canonical propulsion and thermal management systems architecture. By posing the problem in economic terms, exergy destruction is treated as a true common currency to barter for improved efficiency, cost, and performance. This then enables the propulsion systems designer to better fulfill system-level requirements and to create a system more robust to future requirements.

In Uppsala CHP Plant, there are six pressure reducing valves to reduce the pressure from 15 to 3 bars, before six absorption heat pumps. During the process the energy is conserved but losses occur in form of exergy. The aim of this thesis is to reduce the losses of exergy. This can be done by letting turbines replace the pressure reducing valves. In this thesis an investigation has been done of the conditions today, the conditions after the change from pressure reducing valves to turbines and a comparison of three different types of turbine solutions. The three examined solutions are one turbine, several helical screw expanders and several small turbines in parallel with asynchronous generators. The six absorption heat pumps have been divided into two groups; one group of four and one group of two absorption heat pumps. An investigation of locations and space in nearby switchgears has been done for each group. Contacts with retailers of the examined turbine solutions have been taken to gather technical specifications. These technical specifications have been used to simulate the electricity production and the economical yield of each type of examined solution. The investigation shows that the best solution is the solution with several small turbines with asynchronous generators. It has lower investment cost (15 [MSEK]) and the best yield. The proposed solutions will have an installed capacity of 2.65 [MW] to a cost of 5 601 [SEK/kW]. The electric energy production will be 15.7 [GWh/year]. An investment is recommended to a future electric energy price around 400 [SEK/MWh]. Before an investment it is recommended to investigate how to optimize the regulation of the new system with absorptions heat pumps and turbines.

<p>The world demand for electrical power increasescontinuously, requiring efficient and low-cost methods forpower generation. This thesis investigates two advanced powercycles with mixtures as the working fluid: the Kalina cycle,alternatively called the ammonia-water cycle, and theevaporative gas turbine cycle. These cycles have the potentialof improved performance regarding electrical efficiency,specific power output, specific investment cost and cost ofelectricity compared with the conventional technology, sincethe mixture working fluids enable efficient energyrecovery.</p><p>This thesis shows that the ammonia-water cycle has a betterthermodynamic performance than the steam Rankine cycle as abottoming process for natural gas-fired gas and gas-dieselengines, since the majority of the ammonia-water cycleconfigurations investigated generated more power than steamcycles. The best ammonia-water cycle produced approximately40-50 % more power than a single-pressure steam cycle and 20-24% more power than a dual-pressure steam cycle. The investmentcost for an ammonia-water bottoming cycle is probably higherthan for a steam cycle; however, the specific investment costmay be lower due to the higher power output.</p><p>A comparison between combined cycles with ammonia-waterbottoming processes and evaporative gas turbine cycles showedthat the ammonia-water cycle could recover the exhaust gasenergy of a high pressure ratio gas turbine more efficientlythan a part-flow evaporative gas turbine cycle. For a mediumpressure ratio gas turbine, the situation was the opposite,except when a complex ammonia-water cycle configuration withreheat was used. An exergy analysis showed that evaporativecycles with part-flow humidification could recover energy asefficiently as, or more efficiently than, full-flow cycles. Aneconomic analysis confirmed that the specific investment costfor part-flow cycles was lower than for full-flow cycles, sincepart-flow humidification reduces the heat exchanger area andhumidification tower volume. In addition, the part-flow cycleshad lower or similar costs of electricity compared with thefull-flow cycles. Compared with combined cycles, the part-flowevaporative cycles had significantly lower total and specificinvestment costs and lower or almost equal costs ofelectricity; thus, part-flow evaporative cycles could competewith the combined cycle for mid-size power generation.</p><p><b>Keywords:</b>power cycle, mixture working fluid, Kalinacycle, ammonia-water mixture, reciprocating internal combustionengine, bottoming cycle, gas turbine, evaporative gas turbine,air-water mixture, exergy</p>

<p>The objectives of this doctoral thesis are to give a basisincluding methods for the development of stationary polymerelectrolyte fuel cell (PEFC) systems for combined heat andpower production. Moreover, the objectives include identifyingprerequisites, requirements and possibilities for PEFC systemsproducing heat and power for buildings in Sweden. The PEFCsystem is still in a pre-commercial state, but low emissionlevels, fast dynamics and high efficiencies are promisingcharacteristics.</p><p>A thermodynamic model to simulate stationary PEFC systemshas been constructed and pinch technology and exergy analysesare utilised to design and evaluate the system. The finalsystem configuration implies a high total efficiency ofapproximately 98 % (LHV).</p><p>A flexible test facility was built in connection with theresearch project to experimentally evaluate small-scalestationary PEFC systems at KTH. The research PEFC system hasextensive measurement equipment, a rigorous control system andallows fuel cell systems from approximately 0.2 to 4 kWel insize to be tested. The simulation models of the fuel processorand the fuel cell stack are verified with experimental datataken from the test facility. The initial evaluation andsimulation of the first residential installation of a PEFCsystem in Sweden is also reported. This PEFC system, fuelled bybiogas and hydrogen, is installed in an energy system alsoincluding a photovoltaic array, an electrolyser and hydrogenstorage.</p><p>Technical aspects of designing a fuel cell system-basedenergy system, including storages and grid connections, whichprovides heat and power to a building are presented in thisthesis. As a basis for the technical and economic evaluations,exemplifying energy systems are constructed and simulated. Fuelcell system installations are predicted to be economicallyunviable for probable near-term conditions in Sweden. The mainfactor in the economic evaluations is the fuel price. However,fuel cell system installations are shown to have a higher fuelutilisation than the conventional method of energy supply.</p><p>The methods presented in this thesis serve as a collectedbasis for continued research and development in the area.</p><p><b>Keywords:</b>Small-scale, stationary, fuel cell system,polymer electrolyte fuel cell, PEFC system, reformer,thermodynamic modelling, pinch technology, exergy analyses,system configuration, test facility, experiments, application,simulation, installation, energy system, energy storage, heatand power demand.</p>