Methane and Carbon Dioxide Sorption and Transport Rates in Coal at In-situ Conditions (original) (raw)
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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.
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.
2020
Measurements of sorption isotherms and transport properties of CO 2 in coal cores are important for designing enhanced coalbed methane/CO 2 sequestration field projects. Sorption isotherms measured in the lab can provide the upper limit on the amount of CO 2 that might be sorbed in these projects. Because sequestration sites will most likely be in unmineable coals, many of the coals will be deep and under considerable lithostatic and hydrostatic pressures. These lithostatic pressures may significantly reduce the sorption capacities and/or transport rates. Consequently, we have studied apparent sorption and diffusion in a coal core under confining pressure. A core from the important bituminous coal Pittsburgh #8 was kept under a constant, three-dimensional external stress; the sample was scanned by X-ray computer tomography (CT) before, then while it sorbed, CO 2 . Increases in sample density due to sorption were calculated from the CT images. Moreover, density distributions for smal...
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.
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.
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
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.
CO2-ECBM and CO2 Sequestration in Polish Coal Seam – Experimental Study
Journal of Sustainable Mining, 2014
Methane recovery is interesting not only because of its clean combustion; it is also beneficial for the environment because of the reduction of the amount of methane emitted into the atmosphere, which is important because of methane's significant impact on the greenhouse effect. However, desorption of methane is a slow process, significantly dependent on the coalification of coal, its porosity and petrographic composition. Injection of carbon dioxide into the coal bed under sufficient pressure might be a factor in stimulating the efficiency of this process, asbecause of preferential sorptioncarbon dioxide displaces methane molecules previously absorbed in the coal matrix. Methods The measurements were made for Polish low-rank coal used for the analysis of methane recovery from Polish coal mines. Coal samples were collected from sites used for geological, sorption and petrographic research, as well as for the assessment of the reservoir's genetic origin CH 4 content. Experimental studies of sorption were performed with the use of the volumetric method at a lower and higher gas pressure. Results The methane isothermes show more than double the reduction of adsorption along with increasing temperature. The most significant changes of sorption capacity due to temperature variations can be seen when observing the difference in the course of the hysteresis of sorption/desorption of the gas as a function of temperature. In cases where there is a temperature of 323 K, a temperature hysteresis loop might indicate larger quantities of methane trapped in the porous structure of coal. In cases of carbon dioxide as sorbate, a similar shape of sorption isotherms occurred at both temperatures, while the temperature increase caused approximately double the reduction of sorption capacity. Also the isotherm's shape is similar for both temperatures of measurement, indicating no effect of temperature on the amount of gas within the structure of the tested coal. High-pressure isotherms of CO 2 and CH 4 are confirmed in the literature, proving that carbon dioxide is the gas that allows the best penetration of the internal structure of bituminous coal. The critical temperature of CO 2 (304.5 K) is so high, that sorption measurements can be performed at room temperatures (293, 298 K), where activated diffusion is relatively fast. Practical implications Understanding the sorption of gases is the primary issue, related to the exploitation of coal seams, when explaining the mechanism of gas deposition in coal seams and its relationship with outbursts of rocks and gases in mines. Originality/ value The results indicate successful sorption of carbon dioxide in each experiment. This provides the rationale to study the application of the coal tested to obtain methane genetic origin genetic methane with the use of the CO 2 injection.
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.