Browsing by Author "Lemos de Sousa, M. J."
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- O Carvão na ActualidadePublication . Lemos de Sousa, M. J.; Rodrigues, Cristina; Dinis, Maria Alzira Pimenta
- Carvões portugueses: A revalorização moderna possível de um recurso geológico. O caso-de-estudo da Bacia Carbonífera do DouroPublication . Lemos de Sousa, M. J.; Rodrigues, Cristina; Diogo, Miguel Tato; Pinto de Jesus, A.; Mouraz Miranda, A.; Dinis, Maria Alzira Pimenta; Oliveira, Gisela; Chaminé, H.I.; Dinis da Gama, C.; Arrais, C.M.Na sequência de uma síntese sobre as formações datadas do Carbonífero presentes na Bacia Carbonífera do Douro e seu enquadramento geológico, os autores descrevem os estudos modernos, nomeadamente no domínio da estratigrafia efectuados na bacia. Após o fecho das minas de metantracites da bacia (1972 na área do Couto Mineiro de São Pedro da Cova e 1994 na área do Couto Mineiro do Pejão) desenvolveram-se outros importantes estudos, designadamente na área do Couto Mineiro do Pejão, relacionados com o fim da actividade mineira, nomeadamente nos domínios de subsidência mineira e afluxos de água e seus aspectos geológicos e hidrogeomecânicos, estudos estes de que se dá igualmente relato no presente trabalho. Por fim, apresenta-se o essencial do Projecto-Piloto COSEQ elaborado com vista a definir a possível revalorização, em termos modernos, das metantracites da Bacia Carbonífera do Douro como potencial meio de sequestração geológica de CO2. Com efeito, os carvões durienses constituem, hoje, um recurso geológico abandonado do ponto de vista mineiro tradicional.
- Characterization of Coal Maceral Groups by Micro-Raman SpectroscopyPublication . Valentim, B.; Guedes, A.; Prieto, A. C.; Lemos de Sousa, M. J.Uma caracterização rápida e não-destrutiva da organização estrutural do material carbonoso pode ser conseguida através da espectroscopia micro-Raman, uma vez que podem ser obtidos espectros de áreas micrométricas. Uma aplicação óbvia desta técnica é a caracterização pontual de macerais do carvão. As análises de espectroscopia micro-Raman efectuadas em diferentes grupos macerais do mesmo carvão revelam, para além da presença dos habituais picos aos 1580 cm-1 e 1350 cm-1 no espectro de primeira ordem, dois picos de fraca intensidade: um próximo dos 1170 cm-1 nos macerais do grupo da inertinite e outro aos 1470 cm-1 nos macerais de vitrinite e liptinite. Os diferentes grupos macerais apresentam várias diferenças no espectro de primeira ordem, um estreitamento do pico 1580 cm-1 e seu deslocamento para números de onda mais elevados da vitrinite para a liptinite e inertinite; um deslocamento do pico 1350 cm-1 para números de onda mais baixos da vitrinite para a liptinite e para a inertinite, conjuntamente com o seu estreitamento na inertinite e um ligeiro aumento da razão entre a intensidade dos picos 1350/1580 da vitrinite para a inertinite e para a liptinite. A fast and non-destructive characterization of the local state of carbonaceous material may be achieved with a micro-Raman spectrometer, since spectra from micrometric areas can be recorded. Therefore, this technique can obviously be applied for characterization of coal macerals. Raman spectral analysis performed on different coal maceral groups of the same coal reveals not only the presence of the usual peaks at 1580 cm-1 and 1350 cm-1on the first-order Raman spectrum, but also the presence of two additional weaker peaks, one around 1170 cm-1 in inertinite and another around 1470 cm-1 appearing in vitrinite and liptinite. Differences of the first-order spectrum of the different macerals include a shift of the 1580 cm-1 peak towards higher wavenumbers accompanied by its narrowing from vitrinite to liptinite and inertinite; a shift of the 1350 cm-1 peak towards lower wavenumber from vitrinite to liptinite and to inertinite together with a small narrowing in the inertinite and a slight increase in the 1350/1580 peak intensity ratio from vitrinite to inertinite and to liptinite.
- Coal gas adsorption/desorption isotherms versus diffusion processPublication . Rodrigues, Cristina; Dinis, Maria Alzira Pimenta; Lemos de Sousa, M. J.In the present work, the authors studied two meta-anthracite samples from Douro Coalfield (NW of Portugal) in which classical sorption isotherms were carried out, using CO2 only. Results have demonstrated that whenever the CO2 is adsorbed in the coal pores/matrix it will be enduringly fixed up to, approximately, pressures of 32 bar in sample A and 34 bar in sample B. Since the gas release process it intensely related to diffusion coefficients, it is crucial to define their evolution on the two analyses reported in this paper. So, during adsorption, diffusion coefficients decrease in sample A from 4.66736E-08 to 1.23490E-09 cm2/sec (6.72 and 48.13 bar) and during desorption they increase from 7.61829E-09 to 1.09908E-08 cm2/sec (45.68 and 11.48 bar). In sample B, diffusion coefficients decrease from 2.47409E-08 to 2.11813E-09 cm2/sec (7.53 and 47.17 bar) in adsorption and increase in desorption from 1.48767E-09 to 2.83736E-08 cm2/sec (42.22 and 7.71 bar).
- Combustion studies in a fluidised bed—The link between temperature, NOx and N2O formation,char morphology and coal typePublication . Valentim, B.; Lemos de Sousa, M. J.; Abelha, P.; Boavida, D.; Gulyurtlu, I.Five commercially available high volatile bituminous coals from different origins were studied with the objective of characterizing their petrographic nature with respect to emissions of NOx and N2O. The chars produced [at temperatures ranging from 700 to 1000 °C] from these coals were also petrographically analyzed to assess the contribution of char to NOx and N2O formation during combustion. Vitrinite-rich coals produced higher porous chars (cenospheres and tenuinetworks) than those that are rich in inertinite. The former coals were, however, found to release lower concentrations of NO. Consistent with previous works, N2O emissions were observed to decrease significantly with temperature, however, on the whole, the N2O emissions from vitrinite-rich high volatile coals were less than those from inertinite-rich coals. Additionally, high porous chars were found to give rise to lower emissions of NO and N2O.
- Comparative study of the influence of minerals in gas sorption isotherms of three coals of similar rankPublication . Rodrigues, Cristina; Pinheiro, H. J.; Lemos de Sousa, M. J.; yesThis investigation compares the gas adsorption behaviour and capacity of three bituminous coals from South Africa, of similar rank, by assessing the characteristics of the raw coal, as well as the resulting float and sink fractions (at 1.80 cm3/g) obtained by density separation of crushed coal samples. Calculations were also made to obtain the raw coal gas storage capacity from the weighted contribution of both float and sink fractions results, thereby permitting comparison with the analysed results of the raw coal. The study demonstrated that the clean fraction of a coal has the highest capacity to retain gas in the sorbed state, followed by raw coal, and lastly the sink fraction, and re–confirmed previous investigations that showed minerals to be inhibitors of gas adsorption and retention.
- Detection and evaluation of hydrocarbons in source rocks by fluorescence microscopyPublication . Alpern, B.; Lemos de Sousa, M. J.; Pinheiro, H. J.; Zhu, X.In pursing the detection of hydrocarbons in sedimentary rocks by conventional petrological methods, an attempt has been made to correlate standard fluorescence parameters with the quality and quantity of hydrocarbons present in crushed rocks embedded in epoxy resin. The capacity of the embedding resin, commonly used in the preparation of petrographic samples, to extract and physically fix hydrocarbons is recognized. This phenomenon permits one to measure monochromatic fluorescence parameters, I and
- Documented international enquiry on solid sedimentary fossil fuels; Coal: definitions, classifications, reserves-resources and energy potentialPublication . Alpern, B.; Lemos de Sousa, M. J.This paper deals with all solid sedimentary fossil fuels, i.e. coal, the main one for geological reserves and resources, peat, and oil shales. Definitions of coal ( < 50% ash) and coal seam (thickness and depth limits) are examined in view of an international agreement regarding new concepts for a common reserves and resources evaluation using the same nomenclature. The 50% ash limit, already adopted by UN-ECE for coal definition, allows the creation of a new category—the organic shales (50–75% ash)—comprising energetic materials still valuable for thermal use (coal shales) or to be retorted for oil production (oil shales). Geological relations between coals, oil shales, solid bitumen, liquid hydrocarbons, natural gas, and coalbed methane are also examined together with environmental problems. As a final synthesis of all topics, the paper discusses the problems related with a modern geological classification of all solid sedimentary fuels based on: various rank parameters (moisture content, calorific value, reflectance), maceral composition, and mineral matter content (and washability). Finally, it should be pointed out that the paper is presented as series of problems, some of them old ones, but never resolved until now. In order to facilitate the next generation of coal geologists to resolve these problems on the basis of international agreements, all sections begin with documented introductions for further questions opening an international enquiry. The authors hope that the answers will be abundant enough and pertinent to permit synthetic international solutions, valuable for the new millennium, with the help of interested consulted authorities, international pertinent organisations, and regional experts. D 2002 Elsevier Science B.V. All rights reserved.
- Effect of gas compressibility factor estimation in coal sorption isotherms accuracyPublication . Rodrigues, Cristina; da Silva, J.M. Machado; Dinis, Maria Alzira Pimenta; Lemos de Sousa, M. J.Compressibility factor (CF) is a key parameter in gas industry, regarding gas flow and storage in a gas reservoir. This study highlights the necessity to accurately estimate CF, affecting reservoir sorption capacity determination. The effect of the CF of N2, CH4 and CO2 in the coal porous structure was studied. Sorption isotherms showed no significant hysteresis regarding N2, due to gas inert behaviour. CH4 has a higher CF slope and the hysteresis behaviour is stronger than in N2. CO2 has no linear CF behaviour and besides relevant hysteresis, a distinct general trend between both curve shapes was identified, and the CO2 desorption curve intercepted the CO2 adsorption curve at 30x105 Pa. This is due to CO2 retention on coal porous structure, thanks to the great affinity between CO2 and the organic microporous structure, to pressures up to 6.9x105 Pa. The gas mixture showed a significant hysteresis due to its composition.
- Energia e Ambiente: perspetivas atuais: Energy and Environment: current perspectivesPublication . Oliveira, Gisela; Lemos de Sousa, M. J.O mundo está em constante mudança: é algo natural e expectável. Com a recente crise económica e financeira mundial, de evolução e dimensões sem precedentes, as mudanças verificadas tomaram nova importância em várias vertentes da sociedade e até da vida pessoal, tornam-se urgentes adaptações, novos comportamentos e mudanças de mentalidade. A atual crise deu maior ênfase à importância da energia como motor de desenvolvimento e como pilar de sustentação do mundo industrializado. A variação do preço dos combustíveis e os seus efeitos sobre o preço de outros bens e sobre a economia em geral, é notícia de destaque frequente nos meios de comunicação social. Por agora, os problemas relacionados com a energia, pelo menos ao nível de Portugal e da União Europeia, estão ainda longe de serem afetados por escassez de meios, de recursos ou até de matéria-prima, no entanto, tarda a consciencialização que existem limites para o crescimento e que terminou a época de disponibilidade de energia barata a que nos habituámos durante o século XX. Assim, urge também mudar mentalidades e comportamentos no que se refere ao modo como se fornece, distribui e, principalmente, se utiliza a energia, não apenas ao nível dos que atuam como gestores e decisores técnicos, políticos ou económicos, mas também ao nível individual. Apesar do impacto mediático de algumas crises energéticas mundiais verificadas no século passado e que causaram fortes restrições ao consumo, a convicção generalizada da existência de abundância de recursos e meios energéticos, criou oportunidades para o uso displicente e até para o desperdício, do bem precioso que constitui a energia. A utilização da energia, em nome do bem-estar pessoal, do progresso tecnológico e do desenvolvimento económico, não pode ser feita a todo o custo: tem que ser racional, sustentada e equilibrada com o meio ambiente.