The measurement of coal porosity with different gases

Sorption processes can be used to study different characteristics of coal properties, such as gas content (coalbed methane potential of a deposit), gas diffusion, porosity, internal surface area, etc. Coal microstructure (porosity system) is relevant for gas flow behaviour in coal and, consequently, directly influences gas recovery from the coalbed. This paper addresses the determination of coal porosity (namely micro- and macroporosity) in relation to the molecular size of different gases. Experiments entailed a sorption process, which includes the direct method of determining the ‘‘void volume’’ of samples using different gases (helium, nitrogen, carbon dioxide, and methane). Because gas behaviour depends on pressure and temperature conditions, it is critical, in each case, to know the gas characteristics, especially the compressibility factor. The experimental conditions of the sorption process were as follows: temperature in the bath 35 ºC; sample with moisture equal to or greater than the moisture-holding capacity (MHC), particle size of sample less than 212 mm, and mass ca. 100 g. The present investigation was designed to confirm that when performing measurements of the coal void volume with helium and nitrogen, there are only small and insignificant changes in the volume determinations. Inducing great shrinkage and swelling effects in the coal molecular structure, carbon dioxide leads to ‘‘abnormal’’ negative values in coal void volume calculations, since the rate of sorbed and free gas is very high. In fact, when in contact with the coal structure, carbon dioxide is so strongly retained that the sorbed gas volume is much higher than the free gas volume. However, shrinkage and swelling effects in coal structure induced by carbon dioxide are fully reversible. Methane also induces shrinkage and swelling when in contact with coal molecular structure, but these effects, although smaller than those induced by carbon dioxide, are irreversible and increase the coal volume

Glossário ilustrado de estratigrafia sequencial e termos associados

Este Glossário de Estratigrafia Sequencial deve apenas ser considerado como uma primeira tentativa de normalização da terminologia desta especialidade. O trabalho que agora se apresenta corresponde a uma compilação de definições e doutrinas dispersas nas mais variadas publicações destinadas a servir os nossos alunos. Assim, à semelhança do que fizemos para geocientistas de certos países, este vocabulário foi elaborado, unicamente, para ajudar os jovens geocientistas que participem nos nossos cursos e ateliers, uma vez que a grande maioria dos termos aqui definidos são os utilizados durante os cursos. No vocabulário apresenta-se uma definição sucinta de cada termo e, bem assim, a sua tradução em sete línguas (inglês, francês, espanhol, alemão, chinês, russo e italiano). Alguns dos termos estrangeiros são tentativas de tradução que, mais tarde, serão actualizados (isto é, particularmente, verdade para os termos alemães).N/

Documented international enquiry on solid sedimentary fossil fuels; Coal: definitions, classifications, reserves-resources and energy potential

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

Comparative study of the influence of minerals in gas sorption isotherms of three coals of similar rank

This 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

Sequestração geológica de dióxido de carbono: notas sobre o estado-da-arte

Após uma breve introdução sobre os conceitos de (i) Alterações climáticas vs Alterações globais e de (ii) Gases de efeito de estufa, os autores apresentam o estado-da-arte sobre os principais problemas relacionados com a redução do dióxido de carbono e sua sequestração geológica. Por fim, fazem referência aos projectos existentes neste domínio no “Grupo de Investigação em Energia” do Centro de Investigação em Alterações Globais, Energia, Ambiente e Bioengenharia - CIAGEB da Universidade Fernando Pessoa. After a short introduction regarding concepts such as (i) Climate change vs Global changes, and (ii) Greenhouse gases effect, the authors present the state-of-the-art regarding problems related with Carbon dioxide abatement and geological sequestration. Finally, the authors refer to the current projects on this particular issue being developed by the “Energy Research Group” of the Global Change, Energy, Environment and Bioengineering RDID&D Unit – CIAGEB of Universidade Fernando Pessoa

Gas content derivative data versus diffusion coefficient

http://sherpa.ac.uk/romeo/issn/0144-5987/The study of the gas diffusion process has a main role in both Coalbed Methane (CBM) production and CO2 injection in geological sequestration projects. The accurate determination of gas diffusion coefficients in unconventional reservoirs such as coal seams, requires a consistent mathematical approach. The study of the gas diffusion process in coal seams was carried out using sorption isotherms. The Langmuir model for individual gases and the extended Langmuir model for multicomponent gas mixtures were applied to fit sorption isotherm data. “Gas content derivative data” and “gas content changes” emerged as crucial mathematical parameters to accurately study the gas diffusion process. The main goal of this paper is to define the degree of interaction between the gas content derivative data and the gas diffusion process. Experiments were performed on three samples selected from two different coals, which were submitted to three different gas compositions, viz 99.999% CH4; 99.999% CO2; and a gas mixture containing 74.99% CH4 + 19.99% CO2 + 5.02% N2, at 35ºC, and at pressures ranging from 0 up to 50 bar. Experimental results obtained from the three samples indicate that during adsorption/desorption processes, the diffusion coefficients increase and the gas content changes decrease when the pressure decreases, due to the sample saturation degrees and to the kinetic mechanisms increase. Additionally, the “gas content derivative data” scattering is slightly lower during the desorption process than during the adsorption process. These behaviors are clearly identified when using methane, but are even more evident when using CO2 and the gas mixture, due to the CO2 interaction with coal porous structure, which induces a considerable resistance to CO2 release. The results show that sample B (CH4 + CO2 + N2) displays higher diffusion coefficient values (this behaviour is mainly related to the presence of N2) than sample C (CH4) and than Sample A (CO2).info:eu-repo/semantics/publishedVersio

Increasing Sorption Isotherms Accuracy: Weibull Modelling and Linear Regression

http://sherpa.ac.uk/romeo/search.php?issn=0144-5987Relying on an adequate mathematical approach, two different mathematical procedures can be applied to the huge database produced during gas sorption isotherm experiments in order to obtain accurate data to be used in the industrial practice. To treat data determined from gas sorption isotherms without a careful mathematical support will produce inaccurate results, because all the determinations will be dependent on human decision. The minimum error reported since the first stage of a sorption isotherm determination, which corresponds to volume calibrations of reference and sample cells performed through the use of helium, will produce enormous inaccuracies on sorption isotherm behavior. These inaccurate behaviors may sometimes invalidate any Coalbed Methane recovery and CO2 injection programs. The study consisted on investigating gas sorption isotherm accuracies determined during the first part of the sorption process, which is mainly conducted by monitoring the pressure decline with time, in the reference and the sample cells (when both cells are not in contact), until the stabilization stage is achieved. Three samples from two different coals were selected in order to study their gas sorption behavior, in terms of a clear mathematical approach, when submitted to three different gas compositions, viz. 99.999% methane (CH4); 99.999% carbon dioxide (CO2); and a gas mixture containing 74.99% CH4 + 19.99% CO2 + 5.02% nitrogen (N2). Sorption experiments allow to conclude that the three samples present the same mathematical response during the first part of the sorption process. However, all gas sorption data (adsorption and desorption) collected from reference cell have a better fitting to a Modified Weibull Model, and all gas sorption data (adsorption and desorption) collected from sample cell respond in a trustworthy way to a Linear Regression Model. Confidence bands and prediction intervals (or bands) were also computed.info:eu-repo/semantics/publishedVersio

Estratigrafia Sequencial: definições e ilustrações dos termos e conceitos

Os glossários, thesaurus, ou léxicos e os vocabulários são, geralmente, elaborados tendo em vistas dois objectivos diferentes, mas complementares na práctica. Eles são concebidos quer para aparecerem como um apêndice no fim de um trabalho de fundo ou de um curso temático, dando a significação e outros detalhes sobre as palavras chave e/ou expressões utilizadas nos textos de base, quer destinados a ser publicados, digamos de maneira autónoma. O trabalho aqui apresentado corresponde, simplesmente, a uma compilação de definições e conceitos dispersas nas mais variadas publicações sobre a Estratigrafia Sequencial. Ele é destinado, principalmente, a servir os jovens geocientistas que seguiram os nossos cursos e ateliers, uma vez que todos os termos definidos foram e são utilizados nessas classes. No vocabulário, para cada termo, apresenta-se: (i) uma definição sucinta (com uma tradução em inglês, francês, espanhol, alemão, chinês, russo e italiano que, mais tarde, será actualizada, particularmente, a tradução em alemão) ; (ii) uma tentativa de interpretação de uma linha sísmica, um esquema ou uma fotografia ilustrando o seu significado e (iii) um comentário, por vezes com notas, esclarecendo determinados pontos relacionados com a ilustração do termo.N/

Estratigrafia sequencial: definições e ilustrações dos termos e conceitos

Os glossários, thesaurus, ou léxicos e os vocabulários são, geralmente, elaborados tendo em vistas dois objectivos diferentes, mas complementares na práctica. Eles são concebidos quer para aparecerem como um apêndice no fim de um trabalho de fundo ou de um curso temático, dando a significação e outros detalhes sobre as palavras chave e/ou expressões utilizadas nos textos de base, quer destinados a ser publicados, digamos de maneira autónoma. O trabalho aqui apresentado corresponde, simplesmente, a uma compilação de definições e conceitos dispersas nas mais variadas publicações sobre a Estratigrafia Sequencial. Ele é destinado, principalmente, a servir os jovens geocientistas que seguiram os nossos cursos e ateliers, uma vez que todos os termos definidos foram e são utilizados nessas classes. No vocabulário, para cada termo, apresenta-se: (i) uma definição sucinta (com uma tradução em inglês, francês, espanhol, alemão, chinês, russo e italiano que, mais tarde, será actualizada, particularmente, a tradução em alemão) ; (ii) uma tentativa de interpretação de uma linha sísmica, um esquema ou uma fotografia ilustrando o seu significado e (iii) um comentário, por vezes com notas, esclarecendo determinados pontos relacionados com a ilustração do termo.N/

Sequestração geológica de dióxido de carbono: notas sobre o estado-da-arte

Após uma breve introdução sobre os conceitos de (i) Alterações climáticas vs Alterações globais e de (ii) Gases de efeito de estufa, os autores apresentam o estado-da-arte sobre os principais problemas relacionados com a redução do dióxido de carbono e sua sequestração geológica. Por fim, fazem referência aos projectos existentes neste domínio no “Grupo de Investigação em Energia” do Centro de Investigação em Alterações Globais, Energia, Ambiente e Bioengenharia - CIAGEB da Universidade Fernando Pessoa. After a short introduction regarding concepts such as (i) Climate change vs Global changes, and (ii) Greenhouse gases effect, the authors present the state-of-the-art regarding problems related with Carbon dioxide abatement and geological sequestration. Finally, the authors refer to the current projects on this particular issue being developed by the “Energy Research Group” of the Global Change, Energy, Environment and Bioengineering RDID&D Unit – CIAGEB of Universidade Fernando Pessoa