Relationships between the sorption behaviour of methane, carbon dioxide, nitrogen and ethane on coals (original) (raw)
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International Journal of Coal Geology, 2012
High-pressure sorption experiments with methane (CH 4) and carbon dioxide (CO 2) were performed on coals from different mines in the SW Upper Silesian Basin in the Czech Republic. The coals were of high-to low-volatile bituminous rank, representing the late stage of catagenesis. The influence of different factors on the sorption capacity of these coals was evaluated by varying the experimental conditions. Excess sorption capacities of moisture-equilibrated coals ranged from 0.3 to 0.8 mmol/g daf for CH 4 and from 0.8 to 1.2 mmol/g, daf for CO 2. Excess sorption capacities of as-received (air dried) coals were on average 34% higher for CH 4 and 17% higher for CO 2 as compared to the moisture equilibrated state. Sorption capacity shows a weak positive correlation with coal rank and a negative correlation with temperature. The CO 2 /CH 4 sorption capacity ratio is larger for moisture-equilibrated coal, while it decreases with increasing pressure as well as increasing coal rank. From the experimental data, correlations were derived between sorption capacity, and coal rank and temperature. These correlations were used to estimate the "static" variation of sorption capacity with coal seam depth. Estimated sorption capacities increase towards a maximum value between 600 and 1000 m depth, followed by a decrease due to the predominance of the temperature effect. Temperature and pressure data derived from the reconstructed (1D) burial history were used to calculate the "dynamic" variation of sorption capacity during basin evolution. These computations show that initial sorption capacity was significantly higher than the one estimated from present day pressure and temperature gradients. Uplift of coal seams resulted in under-saturation of the coal.
Methane and Carbon Dioxide Sorption and Transport Rates in Coal at In-situ Conditions
Energy Procedia, 2009
Geologic sequestration of carbon dioxide is an option for the mitigation of industrial emissions. However, considerable effort remains to shift this technology from its current status as potential solution to a safe, effective and trusted foundation to the global energy system. Characterization of gas movement and sorption capacity of coal at in-situ conditions is required. Using the volumetric method, measurements of CH 4 and CO 2 sorption and diffusion in coal have been made on powder and non-powder confined coal. Results obtained, emphasized that the sorption capacity and the kinetics of gas in coal are both influenced by the stress state of the sample. The application of 6.9 MPa confining stress contributed to about 30% and 80% of sorption capacity reduction for CO 2 and CH 4 respectively. The sorption and diffusion of CO 2 in confined coal follow two distinct rates described with diffusion coefficients of 2.3 x 10-6 m 2 /s and 9.4 x 10-12 m 2 /s respectively. In contrast, the flow of methane is characterized by a continuous process with a diffusion coefficient of 3.8 x 10-7 m 2 /s. These observations confirms the complex interaction of CO 2 with the coal structure and stressed that CH 4 and CO 2 sorption and transport in coal should be characterized differently, specifically when dealing with non-powder confined samples. Consequently, the use of information collected on pulverized coal samples for the simulation and prediction of long term underground sequestration and enhanced coalbed methane is not justified.
Study on CO 2 Sorption Capacity of Coal – An Experimental Approach
In the present situation of global warming, the percentage of í µí° ¶í µí± 2 in atmospheric air is increasing very rapidly, which will create major problem for the future generation. Storage of í µí° ¶í µí± 2 is gaining widespread interest as a potential method of controlling greenhouse gas emissions as suggested by Intergovernmental Panel on Climate Change (IPCC). This study includes methane desorption mechanism from coal bed, and suggests that the desorbed methane can be used as a pure fuel for many purposes. It is generally acknowledged that coal beds are an important rock medium with regard to their capacity to act as a reservoir for í µí° ¶í µí± 2 gas. In this paper, í µí° ¶í µí± 2 sorption capacity of coal under different temperatures has been investigated by experimental approach and also explains the effect of cracks on coal surface in its sorption capacity. As temperature and pressure increases, with the depth of seam from surface level, the mathematical relation derived from this experiment will be helpful in determination of total amount of í µí° ¶í µí± 2 that can be stored in a coal seam at various reservoir temperature. The results will be helpful to use enhanced production of methane as additional benefit and also to use coal seam as a permanent sink for anthropogenic í µí° ¶í µí± 2 emission.
Sorption behavior of coal for implication in coal bed methane an overview
International journal of mining science and technology, 2017
CBM has been recognized as a significant natural gas resource for a long time. Recently, CO 2 sequestration in coalbeds for ECBM has been attracting growing attention because of greater concerns about the effects of greenhouse gases and the emerging commercial significance of CBM. Reservoir-simulation technology, as a useful tool of reservoir development, has the capability to provide us with an economic means to solve complex reservoir-engineering problems with efficiency. The pore structure of coal is highly heterogeneous, and the heterogeneity of the pores depends on the coal type and rank.
Journal of Geochemical Exploration, 2003
During recent years, extensive studies have been undertaken at RWTH Aachen to assess the gas adsorption capacities of coals of different rank with respect to CH4, CO 2 and their mixtures [e.g. Int. Excess sorption isotherms of carbon dioxide recorded at 40, 60 and 80 °C on dry and moisture-equilibrated Carboniferous coals from the Netherlands exhibited distinct minima and even negative values in the 8-12 MPa interval. These anomalies are indicative of a strong volumetric effect. Evaluation of the experimental results in terms of absolute sorption assuming a range of different densities for the adsorbed phase could not eliminate the observed anomalies. In consequence, substantial swelling (up to 20%) of the (powdered) coal samples must be invoked to account for the observed phenomena. This interpretation is supported by the results of field tests in Alberta, Canada [Proceedings JCOAL Workshop: Present Status and Perspective of CO2 Sequestration in Coal Seams, Tokyo, Japan, (5 September 2002) 59 66], which resulted in a significant reduction in coal-seam permeability upon CO2 injection.
International Journal of Coal Geology, 2016
Recent research has demonstrated that confining stresses applied to the solid framework of coal can reduce its gas sorption capacity by several percent to perhaps several tens of percent. To evaluate the magnitude of this effect more rigorously in relation to predicting in-situ coalbed methane (CBM) content, a better understanding of the effects of stress on methane sorption by coal is needed. In this paper, a previous thermodynamic model for the effects of stress on CO 2 sorption by coal is revised and applied to CH 4. The revised model predicts that in-situ CBM content is indeed determined not only by the geological factors generally considered, such as coal rank, coal composition, moisture content and temperature, but also by lithostatic or confining stress, which is usually ignored. This prediction is tested by means of experiments performed on a composite cylindrical sample of Brzeszcze 364 high volatile bituminous coal subjected to 10 MPa methane pressure at a temperature of 40°C, varying the hydrostatic stress or confining pressure in the range 11-43 MPa. In these experiments, we determined if CH 4 was desorbed as confining pressure was increased by subtracting the poroelastic expulsion of CH 4 from the total CH 4 expelled, assuming the former to equal the gas volume expelled in control experiments performed using Helium. The experimental results show that the equilibrium sorption capacity for CH 4 at 10 MPa gas pressure and 11 MPa confining pressure (1 MPa Terzaghi effective stress) was 0.808 mol/kg coal. This was reduced by at least~6% by increasing the confining pressure to 43 MPa (33 MPa effective stress), confirming the validity of our model. We apply our model to predict in-situ CBM concentration as a function of coal seam depth for dry, high volatile bituminous coal, assuming a geothermal gradient of 32°C/km. The results indicate a maximum CH 4 concentration of~0.76 mol/kg coal at a burial depth of~900m, which is~3% lower than conventional predictions. This reduction is minor but helps to explain why gas saturation is generally lower than expected from conventional sorption measurements on unconfined coal powders. More importantly, our results confirm that there is an intimate coupling between in-situ stress, strain and sorption in coal that needs to be considered in developing gas-enhanced CBM strategies.
International Journal of Coal Geology, 2013
Methane (CH 4) and carbon dioxide (CO 2) sorption isotherms have been measured on an Australian subbituminous, a German high-volatile bituminous and a German anthracite coal in the dry and moisture-equilibrated state. The purpose was to study the variation of CH 4 and CO 2 sorption capacities of the dry coals as a function of rank and the influence of water on the sorption properties. Methane sorption isotherms were measured at 303, 308, 318 and 334 K (30, 35, 45 and 61°C), and CO 2 isotherms at 318, 334 and 349 K (45, 61 and 76°C). The excess sorption capacity of coals is always higher for CO 2 than for CH 4. The CO 2 and CH 4 sorption capacity of dry coals as a function of rank follows a parabolic trend reported in earlier studies, with a minimum at~1% vitrinite reflectance. This trend is more pronounced for CO 2 than for CH 4. For moisturised coals a linear increase in CO 2 and CH 4 sorption capacity with coal rank was observed. Moisture reduces the gas sorption capacity of coals significantly. Moisture content therefore is a first-order control for the gas sorption capacity of low rank coals up to bituminous rank, with much higher impact than temperature or maturity. The moisture-induced reduction in CO 2 and CH 4 sorption capacity decreases with increasing coal rank. It correlates linearly with the oxygen content, which in turn correlates qualitatively with the amount of hydrophilic and carboxylic functional groups as evidenced by FTIR analysis. The influence of sorbed water on the sorption capacity is highest at low pressures (low surface coverage θ b 0.3). The dry/moist sorption capacity ratios converge towards 1 with increasing pressure (high surface coverage θ ≈ 0.7).
Sorption rate of CH4 and CO2 in coal at different pressure ranges
IOP Conference Series: Materials Science and Engineering, 2018
The aim of this study was to verify the dynamic factor, that is the diffusion rate, which can directly affect the efficiency of CO2 injection and as a consequence-storage. A manometric setup was used for experiments on two hard coals from Upper Silesian Coal Basin in Poland. A model combining two firs-order rate functions with different rate constants was used to plot normalized equilibration curves. Diffusion curves were plotted at three pressure ranges 5-6 MPa, 3.5-4 MPa and 1.5-2 MPa. Result show that fast adsorption rate is higher at 5.5-6 MPa than at lower pressure range with highest fast adsorption rate fraction both for CH4 and CO2. Lower (1.5-2 MPa) pressure range allows achieving sorption equilibrium in less time for both gases. Diffusion rates are lower for CO2 than for methane the CH4 desorption rate has a slight impact on the CO2 adsorption and as a consequence CO2 storage capacity.
Implications of carbon dioxide sorption kinetics of low rank coal
Journal of Physics: Conference Series, 2019
This study appraises the dynamic of porosity and permeability measurement of the coal for reservoir modelling during gas production. Known as one of the main target areas for coalbed methane (CBM) production and potentially in integrating testing methodology, these measurements were carried out on low rank coals. During the testing, the pore pressure was varied at each pressure in stepwise with the adsorption equilibration. The gas content of the core sample was estimated until equilibration of the system and the sample of swelling in response to adsorption was measured. By employing newly achieved measurements, CT scan and acoustic emission wave methods, this study determines the porosity and permeability evolution which acts an important role in the dynamic changes in CO2 sorption kinetics of coal. Permeability can be calculated by applying a pressure difference between both end sides of inlet-outlet of a certain direction according to Darcy's law. While the Kozeny-Carman is an empirical equation influenced by several parameters such as total porosity, specific surface area, pore shape, tortuosity, and porosity to determine the permeability. By merging both approaches, empirical and laboratory method, the sorption kinetics of coals and other controlling factors are also counteracted. High isotherm interval low swelling capacity Low isotherm interval Peak swelling area Adsorption Isotherm Change of Coal A2 Adsorption Isotherm Change of Coal B1 (a) (b) High swelling Capacity
Contrasts in methane sorption properties between New Zealand and Australian coals
High pressure microbalance investigations have produced results for both New Zealand and Australian coals which show fundamental differences in their methane sorption properties. New Zealand high volatile bituminous C rank coals have a methane adsorption capacity of 38 cc/g( dan which decreases to a minimum of 23 cclg( dan at medium volatile bituminous rank and increases to 31 cc/g( dan at low volatile bituminous rank. Vitrinite-rich coal samples from Australia display a similar trend, but, the methane adsorption capacity is approximately 8 cc/g higher than for New Zealand coals at low volatile bituminous rank increasing to 20 cc/g higher at high volatile bituminous A rank. From these differences it is implied that New Zealand coals contain a lower proportion of microporosity than Australian coals, most likely due to the presence of volatile components blocking the micropore structure making them unable to sorb as much methane.