Coal firing power stations represent the second largest source of global NOx emissions. The current practice of predicting likely exit NOx levels from multi-burner furnaces on the basis of single burner test rig data has been proven inadequate. Therefore, to further improve current NOx reduction technologies and assist in the assessment of NOx levels in new and retrofit plant cases, an improved understanding of the impact of burner interactions is required. The aim of this research is two-fold: firstly, to experimentally investigate isothermal flow interactions in multi-burner arrays for different swirl directions and burner pitches in order to gain a better understanding of burner interaction effects within multi-burner furnaces. Secondly, to carry out numerical modelling in order to determine turbulence models which give the best agreement to experimental data. Experimental investigations were carried out using flow visualisation for qualitative and 3D laser Doppler anemometry for quantitative measurements. Numerical modelling was performed using the computational fluid dynamics software, Fluent, to compare performance between k-ε, k- ω and RSM turbulence models. Experimental investigation showed that the recirculation zone of the chequerboard configuration is more sensitive to the change in pitch than that of the columnar configuration. Further, it was found that the smaller pitch is more sensitive to change in configuration than the wider pitch. The analysis of fluctuating components, u’, v’ and w’ showed that the burner flow is highly anisotropic at burner exit. Numerical investigation showed that the k-ω turbulence model consistently performed below the other two models. The statistical comparison between k-ε and RSM turbulence models revealed that, for prediction of the swirl velocity profiles, the RSM model overall performed better than the k-ε turbulence model. The visual and statistical analyses of turbulent kinetic energy profiles also showed that the RSM turbulence model provides a closer match to the experimental data than the k-ε turbulence model.

Atualmente, há poucas aplicações de uso de combustíveis renováveis em queimadores, apesar de representarem grande parte do consumo de energia primária. O etanol se apresenta como uma alternativa com grande potencial para substituição de combustíveis não-renováveis em queimadores no Brasil. Tendo em vista este potencial, foi realizado um estudo de possíveis aplicações de queimadores a etanol, com potência inferior a 50 kW, do ponto de vista ambiental, econômico e tecnológico. Foi selecionada uma churrasqueira como a aplicação mais viável. Tendo em vista a necessidade de troca de calor por radiação, foram selecionados queimadores porosos infravermelhos em conjunto com bicos pulverizadores. Durante os testes, a combustão incompleta com gotejamento de combustível se mostrou um problema freqüente. Foi construída uma série de protótipos até se chegar a uma solução final do problema. Este protótipo final, com itens de baixo custo, foi testado avaliando-se potência e emissões, apresentando performance adequada. Foram também estabelecidas diretrizes para desenvolvimento de um produto. / Nowadays, there are few applications of renewable fuels in burners, despite representing a large share of primary energy consumption. Ethanol presents as an alternative with great potential of non-renewable fuels substitution in burners in Brazil. Facing this potential, a study with possible applications of ethanol burners, with output power lower than 50 kW, was carried out, considering environmental, economic and technological aspects. Grill was chosen as the most feasible application. Once radiant heat transfer is needed, infrared porous burner combined with spray nozzles were selected. Throughout the tests, incomplete combustion with fuel dripping was shown as a recurrent problem. A sequence of prototypes was built until a final solution. This last prototype, with low cost components, was tested, assessing output power end emissions, presenting sufficient performance. Guidelines to product development were stipulated.

Insufficient knowledge of fireside behavior in the near-burner region during biomass combustion is one of major factors preventing widespread use of this renewable fuel in pulverized coal power plants. The current research is aimed to investigate the impact of biomass cofiring on NO formation in the near-burner region through interpretation of computational fluid dynamics (CFD) predictions and data collected from a series of biomass tests in a pilot-scale (0.2 MW), swirling flow burner. Two-dimensional gas species mole fraction data were collected with state-of-theart instruments from nine experiments, composing one herbaceous biomass (straw), one woody biomass (sawdust), a low sulfur sub-bituminous coal (Blind Canyon) and a high sulfur bituminous coal (Pittsburgh #8) and their mixtures of different mass fractions with the same swirl setting. Velocity and temperature are calculated from CFD modeling with FLUENTTM, supplemented with hot-wire anemometer measurements. For the first time, a reverse flow region was predicted during solid fuel combustion simulations for the reactor used. Interpretation of the results was carried on with two original methods: stoichiometric maps and normalized species mole fraction profiles. The impacts of biomass on combustion in the swirling flows were analyzed from several aspects: aerodynamics, fuel properties (particle size, volatile content, and fix-carbon content), and NO formation routes. The species maps show the low-grade fuel combustion under swirling flows is composed of two zones: a high species-gradient combustion region attached to the inlet and flat-profiles dominant across the rest of the reactor. Results from tests involving biomass clearly demonstrate the expansion of the combustion region. CFD calculations demonstrate that there is no obvious alteration of the reverse-flow region by biomass combustion. The larger average particle size of biomass generates a combustion region with further penetration into the reactor. In certain tests involving biomass, more NH3 than HCN was detected in several biomass experiments, though limited by the data collection method and low fuel-nitrogen fuels used (sawdust). Supplemented with kinetic calculations with CHEMKIN, it was found that NO formation is dependent on the nitrogen forms in the parent fuels.

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The goal of this research was to design, build and test a small burner and heat exchanger system that could be used as a source of heat for thermoelectric modules (TEMs) for the purpose of generating portable electric power for soldiers in the field. The project was conducted as a subcontract to Marlow Industries Inc. which was under contract from the U.S. Army. The scale of the burner thermal output was to be in the approximate range of 2 kW of heat production and it was to be able to operate on a liquid fuel, specifically JP8. The first burner investigated was a custom burner designed and built at UT. It was tested with various fuel and air delivery systems. Different methods to start it, with the goal of developing an electrical starting system, were also investigated. It was capable of operating at outputs over 1 kW, but was difficult to start reliably and fuel vaporization characteristics were sensitive to operating conditions. Two commercial burners were also studied, each with somewhat different designs. One of those burners, manufactured by MSR, was chosen to be further tested in conjunction with a heat exchanger and thermoelectric modules. The performance of the thermoelectric modules used in this study was determined to be very dependent on an attached resistive load, with a peak power output occurring at approximately 3 ohms. Power output was also determined to increase linearly with increasing temperature difference between the hot and cold sides of the module. Power output followed similar trends as open circuit voltage. The temperatures of the heat exchanger across its width were very uniform, but the accuracy in centering the heat exchanger over the burner could significantly affect temperatures. The time to reach steady state temperatures was relatively insensitive to the length of the heat exchanger. The presence of attached thermoelectric modules reduced the temperature of the heat exchangers and exhaust gas slightly. Reducing the heat exchanger length resulted in higher metal temperatures. Without cooling the cold side of the thermoelectric modules, performance increased while the system was heating up, but then dropped after reaching a peak. Cold side cooling improved thermoelectric performance by increasing its temperature difference. Active cooling with a blower and heat sink provided even better performance than passive cooling using just a heat sink at the expense of a larger parasitic load. The TEMs on the 5 inch long heat exchanger could generate 6.32 W with passive cooling, but active cooling would produce no net power. The 11 inch long heat exchanger could generate 12.8 W with passive cooling, and 16 W net could be generated with active cooling. A heat exchanger efficiency calculation showed that the 16, 11 and 5 inch long heat exchangers were about 94.4%, 93.4%, and 90.7% efficient respectively. This efficiency was defined as the ratio of the heat transferred to the heat exchanger to the heat released in the flame. / text

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