Discrepancies in the assessment of CO2 storage capacity and methane recovery from coal with selected equations of state. Part I. Experimental isotherm calculation (original) (raw)
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2011
The injection of carbon dioxide into coalbeds to increase methane recovery is an emerging technology which was tested in various pilot installations. Carbon dioxide stored in coalbeds is usually in supercritical state and therefore investigation of supercritical adsorption of this gas on coal is a subject of various studies. In the paper impact of three equations of state i.e. Peng Robinson (PR), Soave-Redlich-Kwong (SRK) and the most accurate Span-Wagner, as a reference, on the calculation of sorption capacity was investigated. Langmuir parameters were calculated on the basis of experimental results of CO 2 volumetric sorption by a Selar Cornish coal sample. It is concluded that the use of cubic equation of state (PR and SRK) for the calculation of supercritical CO 2 sorption on coal gives unreliable results by lowering apparent absolute adsorption in the lower pressure range (< 9 MPa) and unrealistically increasing it at higher pressures.
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.
Measurement and interpretation of supercritical CO2 sorption on various coals
International Journal of Coal Geology, 2007
While the amount of CO 2 sorption data on various natural coals has increased in recent years, only few measurements have been reported under the experimental condition of supercritical CO 2 (scCO 2 ) at very high pressure (> 5 MPa). The estimation of realistic CO 2 -sorption capacities for different coals is crucial for the understanding of the processes associated with CO 2 storage and enhanced coalbed methane (ECBM) production.
Chemical Engineering Journal, 2011
Enhanced coal bed methane (ECBM) recovery has been proposed as an attractive way to store captured CO 2 while recovering CH 4. The adsorption and desorption behaviors of CO 2 and CH 4 on dry and wet coal (anthracite) were studied at 318 and 338 K and up to 150 atm. The sorption capacity of CO 2 and CH 4 on anthracite coal was higher at lower temperatures and dry coal condition, but smaller than those on bituminous coals at a similar condition. In wet coal, the sorption capacity and stability of high pressure CO 2 stored at 318 K could be lower than those at 338 K in the supercritical region because higher density of CO 2 at 318 K could lead to the structural change of wet coal. The difference in the excess adsorbed amount between dry and wet coal was only noticeable under the subcritical conditions at 338 K but became more significant under the supercritical conditions with pressure at 318 K. In dry and wet coal, the CO 2 desorption isotherms had different shapes, depending on temperature, but all the CH 4 desorption isotherms showed a weak positive hysteresis. The mutual solubility between the CO 2-rich (or CH 4-rich) phase and aqueous phase as well as coal swelling should be considered in evaluating the sorption capacity of a wet coal seam. Fluid density in free volume was the important variable to estimate the CO 2 storage capacity or ECBM recovery because the density variation significantly influenced the isotherm shape.
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.
Competitive Methane Desorption by Supercritical CO2 Injection in Coal
Transport in Porous Media, 2008
A large diameter (∼70 mm) dry coal sample was used to study the competitive displacement of CH 4 by injection of supercritical CO 2 , and CO 2 -CH 4 counter-diffusion in coal matrix. During the test, a staged loading procedure, which allows the calibration of the key reservoir modelling parameters in a sequential and progressive manner, was employed. The core-flooding test was history matched using an Enhanced Coalbed Methane (ECBM) simulator, in which Fick's Law for mixed gas diffusion and the extended Langmuir equations are implemented. The system pressure rise during the two loading stages and the CO 2 breakthrough time in the final production stage were matched by using the pair of constant sorption times (9 and 3.2 days) for CH 4 and CO 2 , respectively. The corresponding diffusion coefficients for CH 4 and CO 2 were estimated to be 1.6 × 10 −12 and 4.6 × 10 −12 m 2 /s, respectively. Comparison was made with published gas diffusion coefficients for dry ground samples (ranging from <0.063 to ∼3 mm) of the same coal at relatively low pressures (<4 MPa). The CO 2 /CH 4 gas diffusion coefficient ratio was well within the reported range (2-3), whereas the CH 4 diffusion coefficient obtained from history matching of the core-flooding test is approximately 15 times smaller than that arrived by curve-fitting the measured sorption uptake rate using a unipore diffusion model. The calibrated model prediction of the effluent gas composition was in good agreement with the test data for CO 2 mole fraction of up to 20%.
CO2 adsorption the numerical simulations and the controlling factors to low rank coal
IOP Conference Series: Earth and Environmental Science, 2018
Carbon Capture Sequestration (CCS) in unmineable coal seams questionably gives benefits for the commercial success through potential release of additional methane during the injection of CO2 adsorbs into the coal seams, the process known as enhanced coalbed methane (ECBM) recovery. However, a significant concern lies in the loss of injectivity due to reduction in permeability by coal matrix swelling occurences with CO2 adsorption although this effect can be partially be offset with 'huff and puff' scheme of cyclic CO2 injection followed by extraction of the released methane. The paper discusses the results of a numerical simulation study carried out with GEM compositional reservoir simulator to evaluate the effects of uncertainties in various reservoir parameters on the overall volume of CO2 storage and additional methane recovery of low rank coalfield. A 12-15m thick seam at shallow depth, 50-75 m was considered for fluid flow simulation study. While some information on the reservoir setting was obtained through literature and personal communication with the CBM operators, the rest of the information was derived through laboratory studies. The reservoir parameters considered for the study are injection pressure, adsorption capacity, cleat permeability and porosity, and initial gas saturation. A 100-acre drainage area with 5-spot vertical well pattern was considered with one central injector and four producers on four corners of the study area. The maximum allowable injection pressure was estimated to be 7500 kPa at the reservoir setting. The injection pressure was varied from 1000 kPa to 7500 kPa in the simulation .A number of adsorption isotherms were established in the laboratory. The variations in the adsorption parameters observed through the isotherms were considered as uncertainty in the storage capacities. Significant variations were observed due to the variation in adsorption isotherms both for CO2 storage and additional methane recovery. Fracture permeability was varied from 3 md to 200 md, which is the range of permeability observed in the coalfield is around 100-200 mD. The results of simulation indicate a strong influence of porosity on the CO2 storage and ECBM recovery. Fluid flow simulation study shows that variation in sorption time has no significant effect for a low permeability situation while some marginal effect in high permeability situation. Cleat porosity was varied from 1 % to 10 %. Within this range of porosities, enhanced methane recovery varied from 1 % to 10 % relative to the primary recovery but the volume of stored CO2 did not vary significantly. Lastly, the pore pressure, adsorption and gas saturation of CO2 sequestered volume and additional methane recovery were found to increase substantially.
Journal of CO2 Utilization, 2020
Ten moist and powdered, high-to low-volatile bituminous Indian coal samples were analyzed for their supercritical CO 2 (ScCO 2) adsorption properties by volumetric method at 40°C and up to a pressure of ∼12 MPa. The experimental "excess" adsorption capacities were found to increase steadily up to 6.5 MPa. But after that, a sharp fall in ∼7.5 MPa range were observed. The errors and/or uncertainties associated with the nature of CO 2 and variation of void volume during ScCO 2 adsorption could affect the gas adsorbed significantly. The changes in temperature and moisture along with the free gas density, compressibility factor of CO 2 were also analyzed. It was observed that the free gas density varied differently in low to high pressure at 40⁰C, whereas, the compressibility factor decreased linearly in sub-critical range but almost constant or mildly increased in supercritical range. To reduce the uncertainty, a correction for void volume estimation was provided by considering the "mean value" of the void volumes calculated by two "blind runs" to consider the changes in the void volume with pressure. It was found that most of the "negative" excess adsorptions could be improved upto ∼2 mmol/g for an average of 20 % correction in void volume. Sorbed phase density and swelling effect can significantly reduce the excess adsorption by 15 %-30 % and ∼20 % respectively. Whereas, for temperature more than 40⁰C, no such "fall" occurs in the excess ScCO 2 adsorption. Finally, the reproducibility tests were performed to show the accuracy of the method adopted for the void volume calibration.