Sorption rate of CH4 and CO2 in coal at different pressure ranges (original) (raw)
Related papers
Sorption Kinetics of CH 4 and CO 2 Diffusion in Coal: Theoretical and Experimental Study
Experimental and theoretical analyses with empirical correlations were framed for diffusion of gas species CH 4 and CO 2 in coal samples from Jharia coal fields, India, considering the intrinsic pore parameters. Coefficient of diffusion (D) and diffusivity (D eff) for a single and binary component coal−gas system were estimated by adopting unipore gas kinetic models for gas flow on the integration of Fick's law and Langmuir relation. The rigorous study was carried out in estimating crossover pressure, which is dominant in distinguishing the flow regime for two primary types of diffusion: Knudsen and molecular as well as the transition between two regimes. Investigation reveals that experimental values of coefficients of diffusion of CH 4 and CO 2 in random homogeneous isotropic sphere packing of coal samples are in good agreement with the results of theoretical calculations. For the pressure range investigated, variation of coefficient of diffusion was found to follow a dual nature with a stable trend at pressures above 3500 kPa and an increasing trend for lower pressures. The practical implication of the investigation for the pressures that are characteristically encountered in the Jharia coalfields is a positive finding for the concomitant recovery of coalbed methane with CO 2 sequestration. Additionally, the dynamic relation between sorption−diffusion reveals that the coefficient of diffusion significantly depends on the pore structure and pore size distribution, exhibiting a negative relationship with pressure variation.
2004
Numerical modelling of the processes of CO 2 storage in coal seams and enhanced coalbed methane (ECBM) production requires information on the kinetics (rates) of the sorption/desorption processes. In order to address this issue which is of relevance in different EU-projects (ICBM, RECOPOL, Siemons et al. 2003), the sorption kinetics of CO 2 and methane were studied on a high volatile bituminous coal (VR r = 0.68 %) from the Upper Silesian Basin, Poland, in the dry and moisture-equilibrated state. The experiments were conducted on six different grain size fractions, ranging from <63 µm to >2000 µm at temperatures of 45°C and 32°C using a volumetric experimental setup. CO 2 sorption was consistently faster than methane sorption under all experimental conditions. Further qualitative results showed that moisture in the coal leads to a significant reduction in the sorption rates by a factor of >two and that the sorption rate is positively correlated with temperature. Generally, adsorption rates decreased with increasing grain size for all experimental conditions. Based on the experimental results simple modelling approaches are proposed for the sorption kinetics of carbon dioxide and methane that may be readily implemented into reservoir simulators. Evaluation of the fitting parameters resulted in a two phase process associated with the combined adsorption/diffusion process, one slow and one rapid process. These two processes have been compared in terms of a dependency of grain size.
While an increasing amount of data is becoming available on the sorption capacity of coals for individual gases like methane and carbon dioxide at different temperatures and pressure ranges, only few measurements have been reported on adsorption measurements with gas mixtures under the conditions of competitive sorption of two or more components. For this reason, laboratory experiments have been carried out on various moisture-equilibrated and dry coals of different rank, composition and location to investigate high-pressure adsorption/desorption phenomena from mixtures of methane and carbon dioxide. The samples comprise two coals from the Netherlands, ranging in vitrinite reflectance from 1.19 to 1.56 % VRr, three samples from the Silesian Basin in Poland, currently used in the context of the EC RECOPOL project (VRr 0.68-0.78 %) and five coals from the Argonne Premium Coal Sample Programme (VRr 0.25-1.68 %). The experimental set-up used in this study consists of a sequential arrang...
Energy & Fuels, 2009
Carbon dioxide injection into coal formations provides an opportunity to sequester carbon while simultaneously enhancing methane recovery. Although powdered coal samples provide a quick indication of the gas sorption capacity, underground storage takes place within compact coal monoliths, and therefore, it may be necessary to account for in situ conditions, specifically confining stress, for meaningful estimates. This study presents the sorption rates and sorption capacities of CO 2 and CH 4 for a bituminous coal sample in a whole sample and in pulverized form. The impact of confining stress on these sorption capacities of coal cores is evaluated with a multiple-point isotherm over a prolonged time period. The kinetics of the complex, heterogeneous processes occurring in a bituminous coal sample are quantified while under confining stress. Sorption capacities for a powdered sample are 1.17 and 0.66 mmol/g for CO 2 and CH 4 , respectively. The application of 6.9 and 13.8 MPa of confining stress contributed to 39 and 64% CO 2 sorption capacity reduction. Similarly, 85 and 91% CH 4 uptake capacity reduction is observed at those confining stresses. The time-dependent gas diffusion parameters are quantified using the volumetric method with a mathematical analysis of the pressure-decay data. Carbon dioxide diffused through the coal faster than CH 4. Initial exposure over a few days showed a rapid reduction in diffusion presumably as the macro-and mesopores filled. With longer exposure, 10 additional days, a steady slower diffusion is observed for CO 2. The steady-state slower diffusion is achieved within a few days for CH 4. It was found that the overall gas movement, specifically diffusion, is hindered by confining stresses and takes place at rates significantly less than in unconfined powder 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.
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
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.
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.
Modeling of CO2 sorption on coal
Fuel, 2008
This paper discusses moderate pressure CO 2 sorption behavior of Illinois coals. The results fit the Langmuir and Dubinin-Astakhov (D-A) sorption models satisfactorily although the fit is better for D-A equation. Since factors like swelling of coal with CO 2 sorption and CO 2 dissolution in coal matrix contribute to uncertainties in estimating the void volume in and around the sample, an attempt was made to account for these by modifying the conventional adsorption equation. Re-fitting the experimental data using the modified equation results in improved fit for both models. The adsorption capacities of coals tested, as predicted by the equations, also reduce by 7% to 32%. The effect of volumetric uncertainty is more in lower rank coals than the higher rank ones. Furthermore, it explains the excess sorption behavior observed by others when extrapolated beyond the experimental pressure range.