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Made available in DSpace on 2014-10-09T12:26:23Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:07Z (GMT). No. of bitstreams: 0 / No ciclo do combustível nuclear as etapas de reprocessamento e estocagem do combustível queimado, seja ela de modo provisório ou definitivo, demandam um alto custo além de problemas ambientais. Uma estratégia para minorar estes problemas é adoção de medidas que diminuam a quantidade de rejeitos. A utilização de veneno queimável integrado a base de gadolínia é uma medida que contribui para esse objetivo. A função do veneno queimável é controlar a população de nêutrons no início da vida do reator ou no início do ciclo de queima de cada recarga do combustível, podendo prolongar o tempo de recarga do combustível, além de se poder operar o reator com maiores taxas de queima, otimizando com isso o uso do combustível. O processo de fabricação de pastilhas de veneno queimável integrado UO2-Gd2O3, gera rejeito que, na medida do possível, deve ser reaproveitado. A incorporação do Gd2O3 no UO2 exige a utilização de um aditivo para que a densidade especificada das pastilhas de combustível seja obtida. O objetivo deste trabalho é o desenvolvimento do processo de obtenção do veneno queimável integrado UO2 - 7%Gd2O3 com o auxílio do aditivo de densificação, hidróxido de alumínio (Al(OH)3) e reutilizando-se os rejeitos do processo de fabricação, via mistura mecânica. O teor de 7 % de Gd2O3 está fundamentado para a concepção do tipo de reator PWR como, por exemplo, Angra 2. Os resultados mostram que o aditivo (Al(OH)3) é muito eficiente para promover a densificação das pastilhas com reciclo de até 10 %, e que a 5 concentração de 0,20 % de (Al(OH)3) é o valor indicado em escala industrial, principalmente quando se reutiliza o rejeito na forma de U3O8 obtido da calcinação de pastilhas sinterizadas. Isto é particularmente interessante, pois é após as etapas de sinterização e retificação das pastilhas, que se tem a geração do maior volume de rejeito. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:43:08Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:52Z (GMT). No. of bitstreams: 0 / Eletrólitos sólidos cerâmicos de ZrO2:8% mol Y2O3 foram preparados com pós de três origens: pó comercial fabricado pela Nissan (Japão), pó obtido por coprecipitação dos hidróxidos no IPEN e pó obtido por mistura de óxidos (utilizando-se ZrO2 produzido na Usina de Zircônio do IPEN e Y2O3 (USA) de pureza superior a 99,9%). Esses materiais de partida foram analisados pelas seguintes técnicas: fluorescência de raios X para a determinação dos teores de ítrio, difração de raios X para a determinação das fases, sedimentação para a determinação da distribuição do tamanho de partículas, adsorsão gasosa (BET) para a determinação da área de superfície específica e microscopia eletrônica de transmissão para a determinação do tamanho médio de partícula. Amostras compactadas foram analisadas por dilatometria para avaliar os estágios de sinterização. As amostras sinterizadas foram caracterizadas por difração de raios X para análise de fases e microscopia eletrônica de varredura para análise da morfologia dos grãos. Análises por espectroscopia de impedância foram feitas para acompanhar o envelhecimento térmico dos eletrólitos sólidos de zircônia-ítria a 600 ºC, temperatura de trabalho do sensor permanente de oxigênio, e para estudar a sua cinética de sinterização. Os principais resultados mostram que o envelhecimento térmico a 600 ºC diminui a resposta (fem) do sensor nas primeiras 100 h até um valor estável. Além disso, os estudos de sinterização por espectroscopia de impedância permitiram encontrar correlações entre parâmetros elétricos, a cinética de sinterização e os mecanismos de crescimento de grão. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

A laboratory scale method was used to produce pellets from cassia tora stems with pelletizing temperature conditions of 30, 45, 60, 75, 90, 105 and 120oC under a pressure of 50, 70, 90,120 and 140 MPa. A total of 30 pellets were produced under each condition of production. The physical and chemical properties of the pellets were investigated. The pellets produced under 75oC and 90 MPa were found to have durability 90 %. A Bulk density range of 617 to 619 kgm-3 was measured for all the produced pellets irrespective of production conditions. The pellets produced in the range of 50 MPa/30oC-140 MPa/120oC were found to have a moisture content ranging between 7.18- 9.6 %. Ash content of 4.2 % was achieved using both Thermogravimetry (TGA) and CEN/TC 335 standard. The gross calorific value of the pellet was determined to be in the range of 17.89-18.1 MJ/kg. TGA results also indicates low moisture and ash content and the process of pyrolysis occurred at 137-550oC at 10oC/min heating rate. The activation energies and reactivities determined from TG/DTG curve are 72.01, 106.81 and 88.67 kJ/mol and 1.76 E+19, 5.1 E+06 and 3.92 E+05 for step I, II and III respectively. A water boiling experiment was carried out to evaluate the cooking efficiency of the pellets compared to fuel wood, kerosene and liquefied natural gas (LPG). The energy intensities and energy cost of 1.2, 0.78, 0.56 and 1.36 kJ/g of water and 0.2, 0.7, 0.4 and 0.2 Nigerian Naira (N) were calculated for fuel wood, kerosene, LPG and the pellets respectively. vii An economic analysis of fuel pellet production from Cassia tora stems has been carried out for conditions found in Kano state, Nigeria. The total production cost, for a base case scenario of 5t/h and operating for 270 days a year, is £4/tonne (1094.5 Naira/ton) of pellets. A ‘Willingness to pay’ analysis was also performed using the Contingent Valuation Technique. A structured contingent valuation questionnaire was administered to 420 randomly selected households in the Kano metropolis and Chi-square analysis was conducted on the data collected. The results of the analysis, at a 5 percent (0.05) confidence level, showed that p-values were less than 0.05 (0.05>p) for all the responded variables. It is confirmed, from the analysis, that an inadequate supply of energy is a statistically significant problem in Kano state and households significantly use fuel wood for domestic energy applications. The results also indicated the willingness of households to switch to a new product and were willing to pay a mean amount of £5 (1361.5 Naira) for a ton of the fuel pellets. Properties of the cassia tora pellets were found to be comparable with other biomass fuel pellets. It is recommended that policy and investment should be geared towards fuel pellet production in Nigeria, to address problems of energy poverty and environmental deterioration, and provide a means for further economic development.

One of the great challenges facing society is to convert theglobal energy system to a sustainable process. Currently, 80%of the world´s energy is supplied through the combustionof fossil fuels. Not only are the fossil resources limited, theutilisation also increases the level of greenhouse gases in theatmosphere. The convertion to a sustainable energy system isproblematic since the technology needed to exploit mostnon-fossil energy sources is not yet fully developed, e.g.solar energy. Biofuel is an available renewable energy sourcewhich is already widely used in many countries. If an effectiveswitch-over from fossil fuels to biofuels is to be realised,biofuels must be viewed as a limited resource. Consequently, itis important that the handling, upgrading and utilisationprocesses involving biofuels are efficient so that itspotential can be fully exploited. This thesis considers efficient biofuel utilisation andupgrading within the sawmill industry. The goal has been toanalyse not only the technical opportunities for energy savingsin the sawmill industry, but also to analyse the costeffectiveness and environmental impact of studied measures. Theheat demand of the sawmill industry is almost completelycovered by its own by-products; primarily bark, sawdust andwood chips. The increased demand and improved economic value ofwoody biofuels on the market is thus an incentive for thesawmill industry to place more focus on energy issues. Thesawmill industry also has a more or less constant heat loadover the year, which is a beneficial factor for integrationwith district heating networks, biofuel upgrading plants andcombined heat and power plants. The conclusion of the study is that a variety of energyproducts such as heat, unrefined biofuel, pellets andelectricity can be efficiently produced in the sawmill industryand sold for profit to external customers. The payback periodsfor the proposed investments are moderate and both theemissions of volatile organic compounds and global CO2 aredecreased. Should the proposed measures be fully implemented atSwedish sawmills, about 2.8 TWh of biofuel could be savedannually, 0.5 TWh of waste heat could be sold as districtheating and 0.8 TWh of green electricity could be produced.Language: English Keywords:Sawmill industry, energy efficiency, heatrecovery, integration, biofuel, upgrading, district heating,fuel pellets, CHP, VOC, CO2