<p dir="ltr">To decrease the use of fossil fuels that generate greenhouse gases, there has been a push to find alternative processes for electricity generation. An attractive renewable alternative is to use solar-thermal energy for grid level electricity production. One method used to generate electricity from the conversion of solar-thermal energy is concentrated solar power (CSP) via the power tower paradigm, which involves an array of mirrors that concentrate sunlight to a spot on a tower. The light heats up a heat transfer fluid which later transfers the thermal energy to a working fluid that expands so as to spin a turbine to generate electricity. Current CSP plants have a peak operation temperature of 550℃, but improvements to the heat exchanger are integral to increasing the peak operation temperature of such plants to a 750℃ target. Ceramic/metal composites (cermets) have been proposed for use as heat exchangers in these CSP plants due to the creep resistance of the ceramic component and toughness of the metal component. One potential material that has an attractive combination of properties for this application is the alumina/chromium (Al2O3/Cr) cermet, given the rigidity and creep resistance of the Al2O3 component and the high-temperature toughness of the Cr phase. Compared to other oxidation-resistant oxide/metal cermets, the Al2O3 and Cr components of this cermet have a relatively close average linear thermal expansion match from 25℃ to 750℃, which is advantageous due to the thermal gradients and thermal cycling of the heat exchanger during operation.</p><p dir="ltr">In this dissertation, the Al2O3/Cr cermet was produced via reaction forming (RF) or reactive melt infiltration (RMI). The RF method involves the reaction of Cr2O3 and Al constituent powder mixtures at high temperature and modest pressures to obtain dense Al2O3/Cr plates. The RMI method involves immersing a shaped porous Cr2O3 preform into an Al or Al-Cr alloy bath to infiltrate and react to form Al2O3/Al-Cr plates. For both methods, the plate microstructure was analyzed for the various reaction conditions. The adiabatic temperature increase for the reaction between Cr2O3 and Al liquid or Al-Cr liquid alloys was calculated. Thermal properties (linear coefficient of thermal expansion, heat capacity, thermal diffusivity, thermal conductivity) and mechanical properties for the RF Al2O3/Cr plates were also measured. Lastly, the reaction kinetics between dense, polycrystalline Cr2O3 and a liquid Al-35at% Cr alloy were experimentally determined at various temperatures and compared to models based on different rate-limiting steps.</p>

[pt] O presente trabalho consiste na integração de um campo solar em uma usina de gaseificação de resíduos sólidos urbanos no município de Boa Esperança em Minas Gerais. Os resíduos sólidos acumulados no lixão da cidade são utilizados como insumos para a geração de gás de síntese no reator químico da unidade. Esta operação recupera a extensa área degradada deste vertedouro permitindo a instalação do campo solar com coletores de calhas parabólicas. O intuito do projeto é o fornecimento contínuo de calor pelo campo solar através da instalação de tanques de armazenamento direto de calor. A operação do campo solar é simulada pela elaboração de uma rotina computacional no software Matlab através do método das diferenças finitas unidimensional. A solução numérica do sistema de equações diferenciais que compõe o balanço de energia do receptor solar é validada pela comparação com o teste experimental do Laboratório Nacional de Sandia do concentrador solar SEGS LS-2 com tubo absorvedor evacuado. Além disso, o controle da vazão mássica circulante pelo campo solar é incorporado na lógica computacional de modo que a temperatura na saída do campo solar seja mantida com valores próximo ao set-point de 390 graus Celsius. Portanto, as simulações computacionais com proposições sobre a partida e operação do campo solar são testadas para dias ensolarados do ano meteorológico típico de Boa Esperança. Finalmente, um dia real com nebulosidade é simulado para a análise do funcionamento do campo solar de acordo com a variação intermitente da irradiância direta normal. Os resultados da operação do dia real são utilizados como base para a aplicação da presente rotina computacional em futuros projetos do campo solar. / [en] This work intends to hybridize a solar field into the current waste to energy gasification power plant in Boa Esperança in Minas Gerais. The gasification process converts municipal solid waste to usable synthesis gas for electrical production. This current operation of waste to energy power plant removes waste accumulated from the landfill site. It recovers an extensive area for future solar field installation due to this available space without any waste in the future. The design of the planned solar field comprises the parabolic trough concentrating systems. The aim of the solar design is to provide ongoing heat to the power block with direct storage tanks. The solar field operation is simulated by the development of a Matlab computer program based one dimensional implicit difference method with energy balance approach of an evacuated receiver. The validation of present model was done by comparing the outlet temperatures of simulation results and the experimental data obtained by Sandia National Laboratories. Moreover, the mass flow rate is regulated through the field to make sure that the outlet temperature from the solar collector is kept as close to the desired 390 Celsius Degree as possible. To accomplish the main purpose of the work, many different computational models with start-up and full operation stages are suggested for different clear days along the typical meteorological year of the city Boa Esperança. Eventually, a cloud day with a real meteorological data was chosen for a computational model of the solar field performance. All results of the real day operation are used to improve the computer program of the present work. These results are useful for future solar field design.