L'augmentation du prix du pétrole ainsi qu'une possible future réglementation des émissions de CO2 encourage les fabricants de véhicules industriels à trouver de nouvelles solutions pour améliorer encore la performance de la chaine cinématique. Dans ce cadre, deux solutions de récupérations d'énergie prometteuses sont très souvent rapportées dans la littérature: le système de récupération d'énergie par cycle de Rankine et le générateur thermoélectrique. Après un rappel des conditions limites du fonctionnement d'un camion long routier, cette thèse démontre tout d’abord la modélisation 0-D et 1-D (logiciels commerciaux utilisés) de ces deux systèmes de récupération d’énergie. Pour le générateur thermoélectrique, des études paramétriques (hauteur de jambe thermoélectrique, prix, puissance électrique produite) sont effectuées se basant principalement sur l'utilisation de deux matériaux prometteurs. Une conception du système Rankine est présentée et modélisée avec le solveur 1-D. Des validations partielles sont réalisées sur les composants (turbine). Ce modèle a ensuite permis d'étudier les transitoires du système ainsi que la charge en réfrigérant et un système de contrôle possible. Cette étude montre que le générateur thermoélectrique n’est pas encore mature pour son utilisation dans un camion long routier. Le système Rankine doit quant à lui être testé sur un camion prototype pour pouvoir véritablement estimer son potentiel final / Fuel price increase as well as future fuel consumption regulations lead truck manufacturers to further enhance the current powertrain. In such a context, two waste heat recovery technologies appear as promising: the Rankine system as well as the thermoelectric generator. After a reminding of truck boundary conditions, this thesis work defines 0-D and 1-D modeling (commercial tool used) for both systems.For the thermoelectric generator , parametric 1-D studies are done on the integration/design (number of thermoelements, price, electrical power) of a thermoelecric generator upstream the existing engine exhaust gas recirculation cooler. Main studies are done with thermoelectric materials but other materials are also considered. A Rankine system design is presented and modeled under a 1-D solver. Preliminary validations are presented. Transient aspects are evaluated to better understand the behavior of the system and its bottlenecks. The amount of refrigerant in the circuit and the control schematic are also addressed.From these studies, it appears that the thermoelectric generator technology is not yet mature for a long haul truck due to the low performance of thermoelectric materials. The Rankine system technology should handle a complete truck prototype testing to estimate its potential

Este trabalho apresenta uma revisão dos ciclos teóricos estudados por outros autores sobre o funcionamento de uma máquina a vapor funcionando como máquina de expansão e propõe um ciclo generalizado para o estudo. Esse ciclo generalizado é equacionado e seus pontos operacionais de otimização são determinados. Ao estudar os ciclos teóricos, verificou-se que a máquina a vapor pode atingir a eficiência isentrópica igual de 100%. Um estudo experimental foi conduzido em uma máquina a vapor, a fim de verificar os fenômenos que ocorrem e que influenciam na sua eficiência, fazendo o funcionamento real se afastar do ciclo teórico. Ao fazer o estudo experimental, verificou-se que a máquina a vapor real utilizada possui baixa eficiência, atingindo um máximo de 10% de eficiência isentrópica. Essa eficiência não é do ciclo e sim do conjunto todo, e é devido a diversos fatores, como, por exemplo, atritos, problemas de lubrificação, imperfeições físicas que provocam o vazamento do fluido de trabalho. Uma simulação computacional é realizada, visando prever o comportamento real da máquina a vapor e comparar com os dados obtidos experimentalmente. Verificando assim se a simulação consegue prever os fenômenos físicos e auxiliar no projeto de uma máquina a vapor. Após analisar os dados simulados, verificou-se que as válvulas possuem grande influência na eficiência isentrópica do ciclo da máquina a vapor. Válvulas de acionamento rápido preveem uma eficiência que pode chegar a 96%, enquanto as válvulas reais provocam uma eficiência de aproximadamente 60% para as mesmas condições de simulação. Uma das principais diferenças entre a simulação e os dados reais é a restrição ao fluxo provocada pelas válvulas, e que exigem coeficientes de descarga específicos para esse tipo de válvula. / This work reviews the theoretical cycles studied by other authors on the operation of a steam engine as an expansion machine and chooses a generalized cycle for the study. This generalized cycle is modeled and the points of optimization are determined. By studying the theoretical cycles, it was found that the steam engine can reach the isentropic efficiency equal to 100%. An experimental study carried out in a steam engine in order to verify the phenomena occurring that influence their effectiveness, moving the actual operation away from the theoretical cycle. By making the experimental study, it was found that the actual steam engine has a low efficiency, reaching a maximum 10% isentropic efficiency. This efficiency is not of the cycle, but of the whole set, and is due to several factors, such as friction problems, lubrication problems, physical imperfections causing leakage of the working fluid. A computer simulation was performed in order to predict the actual behavior of the steam engine and compare with the experimental data. After analyzing the simulated data, it was found that the valves have a great influence on the isentropic efficiency of the steam cycle. Valves operating instantly can reach 96% of isentropic efficiency, while real valves cause an efficiency of approximately 60% for the same simulation conditions. A major difference between the simulation and the actual data is the flow restriction caused by valves, which requires specific discharge coefficients for this type of valve.

Submitted by Nara Lays Domingues Viana Oliveira (naradv) on 2015-06-12T22:36:19Z No. of bitstreams: 1 000006AB.pdf: 9859828 bytes, checksum: 7298da927fa0f798beed1d1cb69fcb2a (MD5) / Made available in DSpace on 2015-06-12T22:36:19Z (GMT). No. of bitstreams: 1 000006AB.pdf: 9859828 bytes, checksum: 7298da927fa0f798beed1d1cb69fcb2a (MD5) Previous issue date: 2012 / CNPQ – Conselho Nacional de Desenvolvimento Científico e Tecnológico / Neste trabalho, foi realizada a simulação do ciclo térmico da Usina Termoelétrica São Jerônimo – UTSJ. A Usina, muito antiga, possui caldeira do tipo grelha. Na mesma Usina foi instalada uma caldeira experimental de leito fluidizado, para funcionar em paralelo com a existente. O trabalho é iniciado com a modelagem de um ciclo de Rankine simples e segue evoluindo até se estabelecer a configuração mais adequada e representativa na tarefa de simular o modo de trabalho da Usina Termelétrica São Jerônimo – UTSJ. Desta forma, foram adotadas as considerações mais convencionais na prática de projeto de centrais termelétricas cujos sistemas térmicos baseiam-se no ciclo de Rankine. As simulações, que se caracterizam pela resolução simultânea das equações que modelam o ciclo e seus componentes, foram efetuadas através de programa IPSE-pro®. As simulações foram aplicadas para a obtenção dos resultados mais importantes na análise de sistemas térmicos, tais como rendimento térmico do ciclo, potência, vazões mássicas do sistema, calor trocado no gerador de vapor e no condensador, entre outros. Por fim, com objetivo de melhorar o rendimento térmico da planta, são apresentadas algumas alternativas ao sistema atual, tais como o aumento de eficiência da caldeira mediante substituição ou a adição de uma caldeira em paralelo à original. / In this work was made the simulation of the thermal cycle of São Jerônimo - UTSJ thermal power plant. The power plant, very old, has a grate boiler. In the same power plant was installed an experimental fluidized bed boiler, workingin parallel with the existing one. The work starts with the modeling of a simple Rankine cycle and evolves up to establish the most suitable and representative configuration to simulate the mode the work of São Jerônimo –UTSJ thermal power plant. Therefore, in this work it was adopted the more conventional considerations in the design practice for thermal power plants whose systems are based on the Rankine cycle. The simulations, which are characterized by the simultaneous solving of equations that model the cycle and its components, were made through the IPSE-pro® software. The simulations were applied to obtain the main results on the analysis of thermal systems such as, thermal efficiency of the cycle, power, system mass flow, heat exchanged in the steam generator and condenser, among others. Finally, in order to improve the thermal efficiency of the plant, some alternatives to the actual system were presented.

Este trabalho apresenta uma revisão dos ciclos teóricos estudados por outros autores sobre o funcionamento de uma máquina a vapor funcionando como máquina de expansão e propõe um ciclo generalizado para o estudo. Esse ciclo generalizado é equacionado e seus pontos operacionais de otimização são determinados. Ao estudar os ciclos teóricos, verificou-se que a máquina a vapor pode atingir a eficiência isentrópica igual de 100%. Um estudo experimental foi conduzido em uma máquina a vapor, a fim de verificar os fenômenos que ocorrem e que influenciam na sua eficiência, fazendo o funcionamento real se afastar do ciclo teórico. Ao fazer o estudo experimental, verificou-se que a máquina a vapor real utilizada possui baixa eficiência, atingindo um máximo de 10% de eficiência isentrópica. Essa eficiência não é do ciclo e sim do conjunto todo, e é devido a diversos fatores, como, por exemplo, atritos, problemas de lubrificação, imperfeições físicas que provocam o vazamento do fluido de trabalho. Uma simulação computacional é realizada, visando prever o comportamento real da máquina a vapor e comparar com os dados obtidos experimentalmente. Verificando assim se a simulação consegue prever os fenômenos físicos e auxiliar no projeto de uma máquina a vapor. Após analisar os dados simulados, verificou-se que as válvulas possuem grande influência na eficiência isentrópica do ciclo da máquina a vapor. Válvulas de acionamento rápido preveem uma eficiência que pode chegar a 96%, enquanto as válvulas reais provocam uma eficiência de aproximadamente 60% para as mesmas condições de simulação. Uma das principais diferenças entre a simulação e os dados reais é a restrição ao fluxo provocada pelas válvulas, e que exigem coeficientes de descarga específicos para esse tipo de válvula. / This work reviews the theoretical cycles studied by other authors on the operation of a steam engine as an expansion machine and chooses a generalized cycle for the study. This generalized cycle is modeled and the points of optimization are determined. By studying the theoretical cycles, it was found that the steam engine can reach the isentropic efficiency equal to 100%. An experimental study carried out in a steam engine in order to verify the phenomena occurring that influence their effectiveness, moving the actual operation away from the theoretical cycle. By making the experimental study, it was found that the actual steam engine has a low efficiency, reaching a maximum 10% isentropic efficiency. This efficiency is not of the cycle, but of the whole set, and is due to several factors, such as friction problems, lubrication problems, physical imperfections causing leakage of the working fluid. A computer simulation was performed in order to predict the actual behavior of the steam engine and compare with the experimental data. After analyzing the simulated data, it was found that the valves have a great influence on the isentropic efficiency of the steam cycle. Valves operating instantly can reach 96% of isentropic efficiency, while real valves cause an efficiency of approximately 60% for the same simulation conditions. A major difference between the simulation and the actual data is the flow restriction caused by valves, which requires specific discharge coefficients for this type of valve.

[pt] A presente dissertação trata do estudo de sistemas de potência baseados em ciclos Rankine orgânicos (ORC – Organic Rankine Cycle) acionados por energia térmica de rejeito. O objetivo é descrever mediante a simulação numérica um ciclo Rankine orgânico, dimensionar os trocadores de calor para o ciclo proposto e aplicar o conceito para sistemas de trigeração. Um modelo termodinâmico simples é apresentado, relacionando as características termodinâmicas do ciclo Rankine orgânico àquelas da corrente com rejeito térmico (como, por exemplo, vazão mássica, capacidade térmica e temperaturas de operação). A seguir, o método de multi-zonas, ou de fronteira móvel, é aplicado aos trocadores de calor do ciclo, condensador e caldeira, para dimensioná-los às condições do efluente de rejeito térmico. Na escolha do tipo de trocador de calor para a caldeira, é feita a distinção quanto à natureza do efluente, se gasoso ou líquido. No primeiro caso empregam-se trocadores de tubo e aleta e, no segundo, trocadores de placas. A solução numérica do sistema de equações algebraicas e obtida através de um programa computacional escrito em FORTRAN. São também estudados novos fluidos de trabalho de menor impacto ambiental e os resultados apresentados fazem uma comparação com fluidos de uso tradicional. As propriedades termodinâmicas e de transporte dos fluidos considerados foram obtidas usando o programa REFPROP 9.0 do NIST. Finalmente, o conceito do ciclo Rankine orgânico é aplicado a sistemas de trigeração, caracterizados pela produção simultânea de eletricidade, aquecimento e refrigeração. / [en] The present dissertation addresses the study of power generation systems based on organic Rankine cycles (ORC) driven by waste thermal energy (heat). A simple thermodynamic model is presented, relating the thermodynamic characteristics of the organic Rankine cycle to those of the waste heat flow (for instance: mass flow, thermal capacity and operation temperatures). Furthermore, the multi-zone, or movable boundary method is applied to the heat exchangers of the cycle, boiler and condenser, in order to size them for the waste heat flow conditions. In choosing the type of heat exchanger for the boiler, the distinction is made on the nature of the waste heat, either gaseous or liquid. New working fluids for the cycle, of less environmental impact, are studied. For the first case, tube and fin heat exchangers are considered, and in the second, plate heat exchangers. Finally, the concept of the organic Rankine cycle is applied to trigeneration systems, characterized by the simultaneous production of electricity, heating and cooling.

Solar energy is a virtually inexhaustible energy resource, and thus, has great potential in helping meet many of our future energy requirements. Current technology used for solar energy conversion, however, is not cost effective. In addition, solar thermal power systems are also generally less efficient as compared to fossil fuel based thermal power plants. There is a large variety of systems for solar thermal power generation, each with certain advantages and disadvantages. A distinct advantage of solar thermal power generation systems is that they can be easily integrated with a storage system and/or with an auxiliary heating system (as in hybrid power systems) to provide stable and reliable power. Also, as the power block of a solar thermal plant resembles that of a conventional thermal power plant, most of the equipment and technology used is already well defined, and hence does not require major break through research for effective utilisation. Manufacturing of components, too, can be easily indigenized. A solar collector field is generally used for solar thermal energy conversion. The field converts high grade radiation energy to low grade heat energy, which will inevitably involve energy losses as per the laws of thermodynamics. The 2nd law of thermodynamics requires that a certain amount of heat energy cannot be utilised and has to be rejected as waste heat. This limits the efficiency of solar thermal energy technology. However, in many situations, the waste heat can be effectively utilized to perform refrigeration and desalination using absorption or solid sorption systems, with technologies popularly known as “polygeneration”. There is extensive research done in the area of solar collectors, including but not limiting to thermal analysis, testing of solar collectors, and economic analysis of solar collectors. Exergy and optimization analyses have also been done for certain solar collector configurations. Research on solar thermal power plants includes energy analysis at system level with certain configurations. Research containing analysis with insolation varying throughout the day is limited. Hence, there is scope for analysis incorporating diurnal variation of insolation for a solar thermal power system. This thesis centres on the thermodynamic analysis at system level of a solar thermal power system using a concentrating solar collector field and a simple Rankine cycle power generation (with steam as the working fluid) for Indian conditions. The aim is to develop a tool for thermodynamic analysis of solar thermal power systems, with a generalised approach that can also be used with different solar collector types, different heat transfer fluids in the primary loop, and also different working fluids in the secondary loop. This analysis emphasises the solar collector field and a basic sensible heat storage system, and investigates the various energy and exergy losses present. Comparisons have been made with and without a storage unit and resulting performance issues of solar thermal power plants have been studied. Differences between the system under consideration and commercially used thermal power plants have also been discussed, which brought out certain limitations of the technology currently in use. A solution from an optimization analysis has been utilized and modified for maximization of exergy generated at collector field. The analysis has been done with models incorporating equations using the laws of thermodynamics. MATLAB has been used to program and simulate the models. Solar radiation data used is from NREL’s Indian Solar Resource Data, which is obtained using their SUNY model by interpreting satellite imagery. The performance of the system has been analysed for Bangalore for four different days with different daylight durations, each day having certain differences in the incident solar radiation or insolation received. A particular solution of an optimization analysis has been modified using the simulation model developed and analysed with the objective of maximization of exergy generated at collector field. It has been found that the performance of the solar thermal power system was largely dependent on the variation of incident solar radiation. The storage system provided a stableperformance for short duration interruptions of solar radiation occurred on Autumn Equinox (23-09-2002).The duration of the interruption was within the limits of storage unit capacity. The major disruption in insolation transpired on Summer Solstice (21-06-2002) caused a significantly large drop in the solar thermal system performance; practically the system ceased to function due to lack of energy resource. Hence, the use of an auxiliary heating system hasbeen considered desirable. The absence of a storage unit has been shown to cause a significant loss in gross performance of the power system. The Rankine cycle turbine had many issues coping with a highly fluctuating energy input, and thus caused efficiency losses and even ceased power generation. A storage unit has been found to be ideal for steady power generation purposes. Some commercial configurations may lack a storage system, but they have been compensated by the auxiliary heating system to ensure stable power generation. The optimization of the solar collector determines that optimal collector temperatures vary in accordance to the incident solar radiation. Hence, the collector fluid outlet temperature must not be fixed so as to handle varying insolation for optimal exergy extraction. The optimal temperatures determined for Bangalore are around 576 K which is close to the values obtained by the simulation of the solar thermal power system. The tools for analysis and simulation of solar thermal power plants developed in this thesis is fairly generalised, as it can be adapted for various types of solar collectors and for different working fluids (other than steam), such as for Organic Rankine Cycle (ORC). The model can also be easily extended to other types of power cycles such as Brayton and Stirling cycles.

Uma análise do setor sucroalcooleiro nacional revela sua autossuficiência energética que com investimentos adequados, pode evoluir para transformar tal característica em benefício por meio de exportação de energia elétrica. Atualmente, os sistemas de cogeração das usinas de etanol operam com bagaço-de-cana; no entantoesse quadro deve ser alterado devido ao grande aumento de disponibilidade de palha gerada no campo. Um acordo firmado entre o Governo do Estado de São Paulo e UNICA, que limita e condiciona queimadas durante a colheita na região ratifica essa condição. O presente estudo se propõe a estimar e discutir impactos ambientais associados à cogeração de energia elétrica em destilarias autônomas para situações diversas de operação do ciclo Rankine, modelo de termodinâmico adotado para representar o funcionamento daquele sistema. Para atender a tais propósitos foram verificadas diferentes condições de pressão de operação da caldeira (20, 45, 67, 80 e 100 bar), teor de umidade da palha (10%, 15%, 25%, 35% e 50%), e taxa de adição dessa biomassa (10%, 20%, 30%, 40% e 50%) com relação ao total gerado no campo. A coordenação simultânea dessas variáveis resultou na formulação de cento e vinte e cinco cenários de análise. Os cenários foram analisados a partir de Análise Energética (Análise Termodinâmica de 1ª e 2ªLeis) e Avaliação de Ciclo de Vida (ACV). AACVocorreusob enfoque do tipo \"berço-aoportão\", e seguiu diretrizes metodológicas descritas na norma ABNT NBR ISO 14044. Adotou-se como unidade funcional para o estudo \"produzir10 t de etanol anidro (99,5% w/w)\". O sistema de produto compreende atividades realizadas nas etapas agrícola (de produção de cana-de-açúcar e palha) e industrial (obtenção de etanol e cogeração). A análise ocorreu em termos da geração específica de eletricidade, e de perfil de impactos ambientais, definido em termos dos potenciais de Mudanças Climáticas, Acidificação Terrestre, Eutrofização Aquática, e de Formação de Oxidantes Fotoquímicos e de Material Particulado.Os resultados obtidos indicam que a eficiência energética aumenta com a elevação das funções de estado do vapor superaquecido que é injetadona turbina. Em termos de desempenho ambiental, observou-se redução sistêmica de efeitos adversos com o aumento da eficiência do ciclo termodinâmico. Os resultados também ratificaram como condição mais favorável em termos de desempenho ambiental aquela em que 50% da palha gerada no campo, com 10% de umidade, é aproveitada como fonte de energia térmica na caldeira, produzindo vapor superaquecido a 100 bar. / Analyzing the sugar-alcohol sector in Brazil, one can perceive that it is self-sufficient in energy terms and that, with adequate investments, it can evolve to transform this characteristic into a benefit through the export of electricity. Currently, the cogeneration systems of the ethanol plants operate with bagasse. However, this picture should be changed due to the large increase in availability of straw generated in the field. An agreement signed between the Government of the State of São Paulo and the federation of ethanol and sugar mills (UNICA) that limits and conditions burnings during harvesting in the region ratifies this condition. This study estimates and discusses environmental impacts associated with the cogeneration of power in autonomous distilleries for typical operational conditions of the Rankine cycle, a thermodynamic model adopted to represent the operation of that system. In order to meet these purposes, different boiler operating pressure (20, 45, 67, 80 and 100 bar), moisture content of the straw (10%, 15%, 25%, 35% and 50%), and rate of biomass feeding (10%, 20%, 30%, 40% and 50%) in relation to the total generated in the field have been verified.The simultaneous coordination of these variables resulted in the formulation of one hundred and twenty-five analysis scenarios, which were investigated in terms of Energy Analysis (Thermodynamic Analysis of 1st and 2nd Laws) and Life Cycle Assessment (LCA). The LCA was carried out under a \"cradle-to-gate\" approach and followed the methodological guidelines described in ABNT NBR ISO 14044. It was adopted as a Functional Unit for the study \"to produce 10 t of anhydrous ethanol (99.5% w/w) \". The product system comprises activities that occur in the agricultural (production of sugarcane and straw) and industrial (synthesis of ethanol and cogeneration) stages. The analysis took place in terms of the specific generation of electricity, and of environmental impact profiles have been defined in terms of the potential of Climate Change, Terrestrial Acidification, Aquatic Eutrophication, and Formation of Photochemical Oxidants and Particulate Material. The results indicate that the energy efficiency increases with the increase of the state functions of the steam that is injected into the turbine. Regarding the environmental performance, it was observed a systemic reduction of adverse effects with the increase of the efficiency of the thermodynamic cycle. The results also confirmed that the most favorable condition in terms of environmental performance is that one which 50% of the straw produced in the field, with 10% humidity, is used as a source of thermal energy in the boiler, producing superheated steam at 100 bar.

A descentralização do setor de eletricidade brasileiro associado à premente necessidade de aumento da oferta de energia elétrica tem fomentado a busca por fontes alternativas para produção de energia elétrica. Este fato motiva empresas do setor sucroalcooleiro a produzir eletricidade a partir da queima do bagaço de canade- açúcar em sistemas de cogeração, elevando dessa forma a capacidade de geração de energia elétrica exatamente no período de menor oferta hídrica. A geração de eletricidade a partir da biomassa canavieira revela-se uma opção interessante, pois além de ser produzida de forma distribuída e próxima aos centros consumidores, tem criado oportunidades a destilarias e usinas de açúcar para aumentarem seus portfólios de produtos. Nesse aspecto, o presente estudo se propõe a apresentar e discutir possibilidades de cogeração de energia elétrica em usinas autônomas (destilarias) em diferentes condições de processo e operação. Para atender a estes propósitos, foram definidos cenários de cogeração e desenvolvidos modelos para simulação e análise da produção de energia térmica e elétrica bem como estimar os impactos ambientais associados, considerando um sistema de cogeração que opera através do ciclo Rankine, que é o sistema mais utilizado pelas usinas brasileiras. Os cenários foram analisados a partir das técnicas de Análise Exergética (Análise Termodinâmica de Primeira e Segunda Lei) e Avaliação de Ciclo de Vida (ACV). Adotou-se para o caso da avaliação ambiental um enfoque do berço ao portão da fábrica, conforme diretrizes metodológicas descritas nas normas ISO 14040 e 14044. A unidade funcional adotada foi gerar 1,0 MWh de eletricidade excedente em sistema de cogeração energética. O sistema de produto compreende as cargas ambientais da etapa industrial e da produção agrícola da cana-de-açúcar. Especialistas no setor e pesquisadores da área sugerem concentrar esforços de melhoria de desempenho termodinâmico na elevação das propriedades de estado do vapor na saída da caldeira de 20 bar até 100 bar, e simulação de sistemas de cogeração com reaquecimento e regeneração, que são melhorias técnicas próprias de centrais termelétricas, mas com potencial de aproveitamento pelo setor sucroalcooleiro. Os cenários foram projetados com base em diferentes combinações dessas condições considerando duas possibilidades de utilização da biomassa como fonte de energia térmica: exclusivamente bagaço de cana-de-açúcar; e uma composição de bagaço e palha. A comparação dos desempenhos termodinâmicos e ambientais dos cenários ocorreu principalmente em termos da geração específica de eletricidade, da eficiência exergética, do perfil destruição de exergia ao longo do ciclo e dos perfis de impactos ambientais potenciais. Os resultados obtidos indicam que a eficiência exergética é aumenta com a elevação das funções de estado do vapor superaquecido na alimentação da turbina, e ao aumento do grau de complexidade do ciclo Rankine, conseguido à medida que arranjos com reaquecimento e regeneração são integrados ao ciclo. Esses arranjos mostraram-se efetivos na melhoria dos desempenhos exergético e ambiental dos sistemas de cogeração a partir da queima do bagaço e da palha da cana-de-açúcar. Em termos de desempenho ambiental, observou-se a redução sistêmica de efeitos negativos associada ao aumento da eficiência do ciclo termodinâmico. Os resultados da ACV ratificaram também, que a melhoria da eficiência exergética do sistema é seguida de redução de impactos ambientais. Os melhores resultados ambientais, tanto em termos relativos, como absolutos, foram obtidos aproveitando a palha como fonte de energia térmica na caldeira, na condição de geração de vapor a 100 bar e 511 oC, com ciclo Rankine que utiliza reaquecimento e regeneração simultaneamente, numa proposta chamada de ciclo Resultante, cuja redução de impactos ambientais ocorreu entre 5,3% e 15,6% nas categorias analisadas. / The decentralization of the Brazilian electricity sector in association with the internal electricity supply crisis has encouraged companies in the sugarcane industry to produce electricity by burning sugarcane bagasse in cogeneration plants. This approach reduces the environmental impact of the sugarcane production and has opened up opportunities for distilleries and annex plants to increase their product portfolios. Potential scenarios for technically and environmentally improving the cogeneration performance were analyzed by using Thermodynamic analysis and Life Cycle Assessment (LCA). The method used in this study aimed to provide an understanding and a model of the electrical and thermal energy production and the environmental impacts of conventional vapor power systems which operate with Rankine cycle that are commonly used by Brazilian distilleries. Vapor power system experts have suggested focusing on the following technical improvement areas: increasing the properties of the steam from 20 to 100 bar, regeneration and reheating. The case scenarios were projected based on different Rankine cycle configurations and two possibilities of biomass utilization: only sugarcane bagasse or sugarcane bagasse with straw. The LCA was carried out according to ISO 14040 and 14044 regulations, with focus from cradle to gate. A Functional unit of: \"To delivery 1.0 MWh of electricity to the power grid using cogeneration system\" was defined. The product system covers the environmental burdens of the industrial stage and the agricultural production of sugarcane. Thermodynamic evaluation indicated that the energy efficiency and the potential net power exported to the grid increase as the pressure at which the vapor leaves the boiler increases. From the LCA, it was noted that the improved energy performance of the system is accompanied by reduced environmental impacts for all evaluated categories. In addition, vapor production at 100 bar and 511 °C resulted in greater environmental gains, both in absolute and relative terms. Reheating and regeneration concepts were found to be considerably effective in improving the energy and environmental performance of cogeneration systems by burning sugarcane bagasse and straw. For the evaluated categories, the results indicated that the proposed modifications are favorable for increasing the efficiency of the thermodynamic cycle and for decreasing the environmental impacts of the product system. The best results were obtained using bagasse and straw in the boiler furnace and using reheat-regenerative Rankine cycle. In this case it was noted a reduction between 5.3% and 15.6% over all impact categories analysed.

Ce travail traite la modélisation et l'optimisation des centrales solaires thermodynamiques à concentration produisant de l'électricité pour l'électrification des zones rurales isolées et mal raccordées au réseau électrique. D’abord, un modèle optique et thermique détaillé des concentrateurs solaires cylindro-paraboliques est présenté permettant l'identification de capteurs existants et la création de corrélations qui peuvent être injectées dans un modèle plus global. Dans un second temps, un modèle original d'un stock de chaleur stratifié de type « lit de roche » est développé. Le nouveau modèle proposé permet de déterminer analytiquement le profil de température dans le stock à n'importe quel instant dans le cas d'une température d'entrée régulée. Ensuite, deux alternatives de bloc moteur sont modélisées : le moteur Stirling et le Cycle Organique de Rankine (ORC acronyme anglais pour Organic Rankine Cycle). Concernant le moteur Stirling, une revue critique des modèles existants a été effectuée. Certains de ces modèles ont été implémentés et complétés par des modèles originaux des pertes par fuite de matière et par effet navette. Le cycle organique de Rankine, lui, est modélisé par un modèle orientée vers l'optimisation. Enfin, une optimisation mono et multicritère d’une centrale solaire est effectuée. La configuration étudiée est équipée d’un stock de chaleur et d’une chaudière d’appoint. Elle est optimisée selon trois critères : le coût moyen actualisé de l'électricité (LCOE acronyme anglais pour Levelized Cost Of Electricity), le rendement énergétique de la centrale et la quantité de CO2 émise par Kilowatt heure d'électricité produite / This work deals with the modelling and the optimization of thermodynamic solar power plants intended to supply electricity to isolated locations. Firstly, a state of the art of solar collectors is achieved and a model for parabolic trough collectors is proposed. This model is used for actual collectors identification. It is used also to propose correlations to be introduced in the whole system model. In a second time, a state of the art of energy storage technologies is conducted and an original model of a packed bed storage tank is proposed. This model gives an explicit solution of the temperature inside the tank without using a time step based numerical resolution. Two alternatives for the power block are given: Stirling engines and Organic Rankine Cycles. For Stirling engines, a critical review of existing models is performed. Some losses occurring in Stirling engines are not well documented in the literature as leakage losses at the power piston and displacer gap losses. Therefore, original models are proposed to estimate these losses. When compared to former models in the literature, the new model of the displacer gap losses demonstrates clearly that it is very important to use decoupled models with caution. Concerning the ORC, an optimization-oriented model is proposed. Finally, a mono and multi-objective optimization of a solar power plant is performed. The optimized system is composed of a solar field, a packed bed heat storage, a power block and an auxiliary fired heater. Objective functions used in this study are: the Levelized Cost of Electricity (LCOE), the energetic efficiency of the power plant and CO2 emission per kilowatt hour of electricity

Dans le contexte économique et énergétique actuel, la mise en œuvre de technologies à l'aide de l'énergie renouvelable comme source de chauffage offre un double avantage: la réduction de la pollution et des coûts de carburant. Il y a un besoin de promouvoir les sources renouvelables d'énergie comme les sources significatives de production d'énergie pour les systèmes décentralisés. Une première étude bibliographique a été fait sur les technologies existantes pour la production d'énergie électrique à partir du solaire. Cette étude consiste dans la recherche d’une nouvelle solution de conversion de l’énergie solaire pour la production d’électricité de faible puissance. L'un des objectifs de cette thèse a été la construction d'un moteur Stirling de type gamma fonctionnant à basse différence de température, adapté à un circuit solaire (capteur plan). Le moteur Stirling a été testé en vue de comparer les résultats expérimentales avec les résultats d’un model Schmidt, fait dans le logiciel, Matlab. Un autre cycle thermodynamique étais étudie dans cette travail, le Cycle Organique Rankine (ORC). Un modèle mathématique a été développé et vérifie dans les logiciels, Thermoptim et EES (Engineering Equation Solver) avec les résultats expérimentaux pour étudier les performances d'installation avec des différentes températures de fonctionnement. La méthode exergétique et la méthode du Pincement sont utilisée pour évaluer les performances du système comme irréversibilité, destruction d’exergie et phénomènes qui se produisent dans toutes les composantes du système ORC pour améliorer son fonctionnement. / In the current economic and energy context, implementation of technologies using renewable energy as heat source has two advantages: reducing pollution and fuel costs. There is a need to promote renewable energy sources such as significant sources of power generation for decentralized systems. In the first part, it was made a literature review on existing technologies for the production of electricity with solar energy. One of the objectives of this thesis was to build a Stirling engine gamma type suitable to use solar energy (flat plate collator). The Stirling engine was tested to compare the experimental results with the results of Schmidt model, realized in the software, Matlab. Another thermodynamic cycle was studied in this work, the Organic Rankine Cycle (ORC). A mathematical model was developed and verified in software, Thermoptim and EES (Engineering Equation Solver) with experimental results to study the installation performance function of different operating temperatures. The entire system and each subsystem are analyzed according to the first and the second law of thermodynamics. The exergy method and Pinch analysis are used to evaluate the performance of the system like irreversibility and exergy destruction, phenomenon that occurs in all components of the ORC system. This analysis is to improve the operation.