Heat sources such as biomass, industrial waste heat and solar thermal provide the potential to produce renewable environmentally low impact electricity. Using these resources efficiently within economic constraints is important for viability of these systems. This thesis explores a regenerative organic Rankine cycle for use in low temperature heat sources. A Bitzer model scroll expander is used for the prime mover for the system. This expander has a reliable model in which thermodynamic analysis can be done. Various working fluids are explored to investigate which one will provide the most power output and efficiency within system constraints. Using optimization, each fluid is tested within physical constraints for optimal operating conditions using system exergy efficiency as the objective function. An exergoeconomic analysis is performed to predict the cost rate of electricity of the system and is compared to current contract rates from the Ontario Power Authority. Dimethyl ether shows promising results with a system exergy efficiency of 11.76% and system energy efficiency of 2.84% at a source temperature of 120℃. The degree of superheat and pressure ratio are used as the independent variables in the optimization. Highest isentropic efficiency for the expander is 29.22%, showing large potential for improvement. Electricity cost rates for the system assuming 20 year life are 0.132 $/kWh to 0.197 $/kWh depending on the fuel input cost for dimethyl ether. At the current state the system shows merit with large potential for improvement in the expander. / UOIT

Made available in DSpace on 2014-06-11T19:35:41Z (GMT). No. of bitstreams: 0 Previous issue date: 1998Bitstream added on 2014-06-13T18:07:37Z : No. of bitstreams: 1 antunes_js_dr_guara.pdf: 1990112 bytes, checksum: fec1ab4e133a1f22bdc262ef1e750b70 (MD5) / Este trabalho apresenta as fases do desenvolvimento de um programa computacional elaborado com a finalidade de selecionar, dimensionar e especificar sistemas de cogeração com turbinas a gás, buscando satisfazer as demandas térmicas do processo (operação em paridade térmica). As configurações utilizadas são: turbina a gás associada à caldeira de recuperação, turbina a gás associada ao sistema de refrigeração por absorção e turbina a gás associada à caldeira de recuperação e turbina a vapor (ciclo combinado). O programa computacional seleciona sistemas de turbinas a gás comercialmente disponíveis no mercado (condições ISO) e faz correções de performance para as condições ambientais do local da instalação. O código computacional efetua análises energéticas, exergéticas, energoeconômicas e exergoeconômicas, sempre buscando escolher os melhores sistemas de turbinas a gás dentre os previamente selecionados. / This work presents the steps to structure a computer program for selecting, dimension and specifying gas turbine cogeneration systems, satifying the termical condition of the process. The following configurations are used: gas turbine associated to the heat recovering, gas turbine associated to the absorption cooling system, gas turbine associated to the recovering and vapor turbine (combined cycles). The computational program selects gas turbine systems commercially available and performs corrections due to the local environment of the gas turbine system. The computational code develops: energetic, exergetic, economic and exergoeconomic analysis, always searching to choose the best gas turbine systems.

This study is an attempt at achieving Net Zero Energy Building (NZEB) using a solar Organic Rankine Cycle (ORC) based on exergetic and economic measures. The working fluid, working conditions of the cycle, cycle configuration, and solar collector type are considered the optimization parameters for the solar ORC system. In the first section, a procedure is developed to compare ORC working fluids based on their molecular components, temperature-entropy diagram and fluid effects on the thermal efficiency, net power generated, vapor expansion ratio, and exergy efficiency of the Rankine cycle. Fluids with the best cycle performance are recognized in two different temperature levels within two different categories of fluids: refrigerants and non-refrigerants. Important factors that could lead to irreversibility reduction of the solar ORC are also investigated in this study. In the next section, the system requirements needed to maintain the electricity demand of a geothermal air-conditioned commercial building located in Pensacola of Florida is considered as the criteria to select the optimal components and optimal working condition of the system. The solar collector loop, building, and geothermal air conditioning system are modeled using TRNSYS. Available electricity bills of the building and the 3-week monitoring data on the performance of the geothermal system are employed to calibrate the simulation. The simulation is repeated for Miami and Houston in order to evaluate the effect of the different solar radiations on the system requirements. The final section discusses the exergoeconomic analysis of the ORC system with the optimum performance. Exergoeconomics rests on the philosophy that exergy is the only rational basis for assigning monetary costs to a system’s interactions with its surroundings and to the sources of thermodynamic inefficiencies within it. Exergoeconomic analysis of the optimal ORC system shows that the ratio Rex of the annual exergy loss to the capital cost can be considered a key parameter in optimizing a solar ORC system from the thermodynamic and economic point of view. It also shows that there is a systematic correlation between the exergy loss and capital cost for the investigated solar ORC system.

In this work it is presented an equilibrium model, capable to predict the composition of the generated gas, its Lower Heating Value (LHV), the gasification efficiency, the ratio air/biomass and the  ratio gas/biomass in a downdraft gasifier. The model describes the influence of  the moisture content of the biomass and the gasification temperatures on the composition and properties of the produced gases, like the low heating value (LHV). It is assumed that all the chemical reactions taking place  in the gasification area are in thermodynamic equilibrium. The model doesn't considered tar formation. It is not considered formation of other hydrocarbons (CxHy) than methane. The types of biomass used for modelling are: sugarcane bagasse, paddy husk, pine sawdust, mixed paper waste and municipal solid waste. The effect of gasification temperature and moisture content of biomass over the gas composition has been also investigated. Also an exergo-economic analysis of cogeneration system forming by a downdraft gasifier associated to an internal combustion engine was carried out, using sugar cane bagasse, rice husk, and pine sawdust, as fuel in gasification processes. At 700°C the highest amount of CO and CH4 are produce. The amount of CH4 and CO decrease with the temperature when the gasification temperature is increased from 700°C to 1000°C. The amount produced H2 does change so much between the gasification at 700°C and 1000°C. But the amount produced hydrogen is somewhat higher at 800°C. The lower heating value (LHV) of the synthesis gas from gasification of sugarcane bagasse the LHV of the produced gas is 4,09MJ/Nm3; for gasification of pine the LHV of the produced gas is 5,32MJ/Nm3; for gasification of rice husk the LHV of the produced gas is 3,14MJ/Nm3, for gasification of mixed paper waste the LHV of the produced gas is 4,51%, and for gasification of municipal solid  waste the LHV of the produced gas is 3,95MJ/Nm3. The cold and hot efficiency of gasification process at 800°C for bagasse with 20% moisture content are  55,32% and 84,90% respectively.

Resumo: Este trabalho apresenta as fases do desenvolvimento de um programa computacional elaborado com a finalidade de selecionar, dimensionar e especificar sistemas de cogeração com turbinas a gás, buscando satisfazer as demandas térmicas do processo (operação em paridade térmica). As configurações utilizadas são: turbina a gás associada à caldeira de recuperação, turbina a gás associada ao sistema de refrigeração por absorção e turbina a gás associada à caldeira de recuperação e turbina a vapor (ciclo combinado). O programa computacional seleciona sistemas de turbinas a gás comercialmente disponíveis no mercado (condições ISO) e faz correções de performance para as condições ambientais do local da instalação. O código computacional efetua análises energéticas, exergéticas, energoeconômicas e exergoeconômicas, sempre buscando escolher os melhores sistemas de turbinas a gás dentre os previamente selecionados. / Abstract: This work presents the steps to structure a computer program for selecting, dimension and specifying gas turbine cogeneration systems, satifying the termical condition of the process. The following configurations are used: gas turbine associated to the heat recovering, gas turbine associated to the absorption cooling system, gas turbine associated to the recovering and vapor turbine (combined cycles). The computational program selects gas turbine systems commercially available and performs corrections due to the local environment of the gas turbine system. The computational code develops: energetic, exergetic, economic and exergoeconomic analysis, always searching to choose the best gas turbine systems. / Orientador: José Luz Silveira / Coorientador: José Antônio Perrella Balestieri / Banca: Nelson Manzanares Filho / Banca: Messias Borges Silva / Banca: Luiz Roberto Carrocci / Doutor

Orientador: Silvia Azucena Nebra de Perez / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-15T08:40:40Z (GMT). No. of bitstreams: 1 Alves_LourencoGobira_D.pdf: 2286993 bytes, checksum: 9be242b04e4640bec3bb9397c2679294 (MD5) Previous issue date: 2007 / Resumo: A alta dos preços do petróleo aliada ao aumento da participação do gás natural na matriz energética nacional força a sociedade a pensar em usos mais racionais para o gás, tanto por necessidades econômicas quanto ambientais. O hidrogênio é apontado por alguns autores como combustível do futuro, portanto aproveitar o gás natural como matéria-prima para produzir hidrogênio é uma das alternativas para melhor uso do gás. Este trabalho faz a análise exergoeconômica de dois processos básicos de produção de hidrogênio a Reforma a Vapor do Metano, SMR, e a Reforma Autotérmica do Metano, AtR, usando a Teoria do Custo Exergético, TEC, e a Análise Funcional, AF. É proposta a introdução de cogeração usando uma turbina movida a gás natural e outra movida a gás de síntese para os dois processos, gerando quatro casos de estudo onde a possibilidade de produzir excedentes para venda foi considerada. Foi feita a otimização dos processos com dois objetivos: busca da maior produção de hidrogênio e busca da menor geração de irreversibilidade. Os resultados mostram que a cogeração é uma possibilidade a ser estudada com cuidado, pois o custo de produção da eletricidade precisa ser competitivo com o mercado energético brasileiro. Os quatro casos de estudo mostraram boa flexibilidade para otimização dos processos / Abstract: The prices of Petroleum allied to the increase of the participation of the Natural Gas in the national energy matrix have forced the society to search for more rational uses for the gas by economic and environmental reasons. According to some authors, hydrogen is the fuel of the future and the production of hydrogen from natural gas is an alternative to improve the gas uses. This work performs an exergoeconomic analysis of two basic processes to produce hydrogen, Stem Methane Reforming, SMR, and Autothermal Reforming, AtR, using the Theory of Exergetic Cost, TEC, and the Functional Analysis, AF. Two cogeneration possibilities in the processes are also considered, resulting in four study cases with the possibility of producing surplus of electric energy to sell. And an optimization study is performed to improve the hydrogen production and reduce the irreversibility. The results shown that cogeneration is a useful possibility but must be applied according to the Brazilian energy market. The optimization process increased the results in the four cases / Doutorado / Termica e Fluidos / Doutor em Engenharia Mecânica

Orientador: Silvia Azucena Nebra de Perez / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-11T16:10:36Z (GMT). No. of bitstreams: 1 PalaciosBereche_Reynaldo_M.pdf: 8960679 bytes, checksum: a6e8e552788d00fa0fb258923ebe13a9 (MD5) Previous issue date: 2008 / Resumo: Neste trabalho e feita uma revisão em relação à participação do gás natural na matriz energética mundial, brasileira e no Estado de São Paulo. Características do setor terciário, assim como da utilização do gás natural neste setor de consumo, são apresentadas também na primeira parte. Foi feita uma revisão das tecnologias de utilização de gás natural no setor terciário, assim como da tecnologia dos sistemas de refrigeração por absorção, das diferentes configurações do ciclo, e dos fluidos de trabalho utilizados neste tipo de sistema. Uma metodologia para o calculo da exergia da solução água brometo de lítio, comumente utilizada como fluido de trabalho em sistemas de refrigeração por absorção para condicionamento de ambientes, foi elaborada. Para a realização das analises exegética e exergoeconomica do sistema foi realizado o calculo da exergia total dos fluidos de trabalho considerando as parcelas de exergia química e física. A analise exegética compreendeu o calculo da irreversibilidade em cada componente do sistema assim como da total. Na ultima parte do trabalho foi realizada a analise termodinâmica, exegética e exergoeconomica do sistema de refrigeração por absorção de simples e duplo efeito H2O/LiBr, considerando como fontes de aquecimento um sistema de queima direta de gás natural e energia de rejeito de um sistema de cogeração. Os resultados são comparados e discutidos / Abstract: A review about the participation of the natural gas in the energetic matrix was done in this work, considering the scope international, Brazilian and the Sao Paulo State. Characteristics of the tertiary sector and the natural gas utilization in this consumption sector are also presented. A review about the technologies of utilization of natural gas in the tertiary sector was also done. In the following part, the technology of absorption refrigeration systems, different configurations of the cycle and working fluids were reviewed. A methodology for the exergy calculation of the lithium bromide ¿ water solution was elaborated. The lithium bromide ¿ water solution is widely utilized as working fluid in absorption refrigeration system for air conditioning. The exergy calculation takes in account the chemical and physical parcel of the exergy, which is important to realize the exergetic and exergoeconomic analysis of the system. In the last part of the work it was done a thermodynamic, exergetic and exergoeconomic analysis of the absorption refrigeration system H2O/LiBr of single and double effect. The exergetic analysis included the irreversibility calculation in each component and the total irreversibility of the system. Two different energy sources were considered: direct heating through natural gas combustion and the utilization of rejected energy in a cogeneration system. The different results were compared. / Mestrado / Mestre em Planejamento de Sistemas Energéticos