Methane Adsorption Capacity Of Coal Research Articles

Analysis of the influence of different pore ratios on methane adsorption characteristics of coal

The diverse pore structures in coal are pivotal in coalbed methane storage and transportation, making it highly significant to explore methane adsorption characteristics across varying pore sizes for effective prevention and control of coal mine gas disasters. Using the proposed graphene nanotube filling method, eight coal molecule models with varying pore size ratios were constructed, including four different pore radii: 0.35 nm, 0.55 nm, 0.75 nm, and 2 nm. Methane adsorption amount, methane density, and methane concentration distribution were obtained through Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods. The research results show that coal consisting of multiple pore sizes had a better methane adsorption capacity than a single pore size. Combining pore sizes of 0.35 nm, 0.55 nm, and 0.75 nm in a 1:2:1 ratio resulted in the highest excess methane adsorption capacity in coal, reaching 5.623 mmol/g. The single pore size of 0.55 nm in coal had the lowest excess adsorption amount of methane, which was 2.236 mmol/g. The presence of mesopores weakened the methane adsorption capacity of coal, and this weakening effect increased with the increase of mesopore proportion. In the model composed of single pore size micropores, the methane concentration inside the pores was uniformly distributed. The coexistence of multiple micropores may lead to methane filling in the micropores in a monolayer adsorption form. The coexistence of micropores and mesopores does not alter methane filling in the micropores and monolayer adsorption in the mesopores. The research results provide new insights into our understanding of the impact of pores on methane adsorption in coal.

Factors Influencing the Methane Adsorption Capacity of Coal and Adsorption Heat Variations

Factors Influencing the Methane Adsorption Capacity of Coal and Adsorption Heat Variations

Fractal Dimension and Nuclear Magnetic Resonance Characteristics of Surfactants for Coal Gas Desorption

In this paper, the fractal dimension of coal surfaces was calculated using the fractal theory, and the influence of different surfactants on the fractal dimension of coal surface was studied. Six kinds of sustainable and traditional surfactants used in coal gas desorption processes were compared and analyzed. We used mineral gas fertilizer coal from Huainan Liuzhuang, China, as the research object and studied sodium dodecyl benzene sulfonate (SDBS), cohol diethanolamide (CDEA), nonylphenol polyoxyethylene ether (NP-10), tea saponin, sucrose ester and rhamnolipid surfactants used to modify coal. The methane adsorption capacity of coal before and after surfactant modification was measured by low field nuclear magnetic resonance methane adsorption, and Langmuir volume and Langmuir pressure were obtained according to the Langmuir fitting equation. The results showed that from the perspective of fractal dimensions, the best surfactant in the context of sustainability (in order) is rhamnolipid, CDEA, tea saponin, sucrose ester. According to the two important parameters VL and PL in the Langmuir equation, the coal sample modified by sucrose ester had the strongest gas adsorption capacity. According to the numerical analysis of the surface fractal dimension DS of the coal modified by surfactants, the soluble organic matter in the raw coal samples dissolved, and the micropore morphology evolved to become mesoporous or macroporous, which is more favorable for desorption. The coal samples modified by rhamnolipid and SDBS had the strongest gas desorption ability.

Molecular insights into the methane adsorption capacity of coal under microwave irradiation based on solid-state 13C-NMR and XPS

Coalbed stimulation is a process of increasing coalbed methane (CBM) production by opening, enlarging, and extending the length, width, and connectivity of pores and fractures/cleats. Microwave irradiation is a promising thermal stimulation technique for coal reservoirs. To investigate the effects of microwave heating on the methane adsorption capacity of Pingdingshan bituminous coal, molecular models were constructed based on proximate analysis, ultimate analysis, solid-state 13C nuclear magnetic resonance (13C-NMR), and X-ray photoelectron spectroscopy (XPS). The results show that the condensation degree of the aromatic ring in Pingdingshan coal is 0.18, and the molecular formula is C143H153N3O5. Microwave irradiation causes the cracking of aromatic hydrocarbons, and the molecular formula of coal evolves into C132H133N3O4. After microwave irradiation, the saturated adsorption number of CH4 molecule decreases from 12 to 7, indicating that microwave heating can promote methane to diffuse from the coal matrix. Carboxyl and pyrrole are not favorable for methane adsorption. Microwave irradiation has the weakest effect on carbonyl. This study contributes to understanding the effect of microwave heating on CH4 adsorption mechanism of coal from the molecular perspective.

Control mechanism of small organic molecules on methane adsorption capacity of coal

Small organic molecules have a significant influence on methane adsorption of different rank coals. To explore the control mechanism of small organic molecules on methane adsorption capacity of coal, in this paper, based on the relative content of small organic molecules in different rank coals obtained by extraction experiment, the complex models of raw and residual coal with different ranks were constructed. The influence of small organic molecules on the methane adsorption of coal was analyzed by molecular simulation calculation. The control mechanism of small organic molecules on the methane adsorption capacity of coal was further discussed. The results showed that for the low-rank coal with high content of small organic molecules, small organic molecules mainly play the role of blocking and separating so that separate the larger coal pores into more micropores, thereby the methane adsorption capacity of coal pores is increased. For the middle-rank coal with the same high content of small organic molecules, micropores are closed by small organic molecules, so that its methane adsorption capacity is reduced. For the high-rank coal, due to its low content of small organic molecules, few pores are blocked or closed, that the existence of small organic molecules has no significant effect on its methane adsorption capacity. The research results help to reveal the microscopic mechanism of methane adsorption of coal, which has great significance to the development of coalbed seam gas and mine gas disaster prevention.

Methane Adsorption Behavior and Energy Variations of Brittle Tectonically Deformed Coal under High Temperature and High Pressure.

This paper aims to reveal the methane adsorption characteristics of brittle tectonically deformed coal (TDC) under high temperature and high equilibrium pressure and the surface free energy changes during methane adsorption. Taking the anthracite of the Yangquan mining area of China as the research object, methane adsorption tests of high temperature and high pressure were conducted to discuss the influences of coal deformation, temperature, and pressure on the gas adsorption behaviors of coal under the in situ conditions of deep coal seams. Results indicated that coal deformation and pressure had positive effects on the methane adsorption capacity of coal, whereas temperature showed negative effects. Meanwhile, the negative influences of temperature rise on gas adsorption gradually increased with the equilibrium pressure and the enhancement of coal deformation. In a given adsorption system, the adsorption potential decreased with increasing pressure while increased with temperature. In contrast, the adsorption space increased with increasing pressure and decreased with temperature rise. Meanwhile, adsorption potential decreased with the increase in adsorption space. In the process of methane adsorption, with increasing adsorption pressure, the cumulative reduction of surface free energy gradually increased, whereas the surface free energy reduction at each pressure point decreased. The cumulative and incremental reduction of surface free energy at each pressure point gradually decreased with the increase in temperature. The reduction of adsorption space and cumulative surface free energy and the changes in surface free energy at each pressure point of brittle TDCs were higher than those of primary structure coal, and the changes in the strongly deformed coal (granulitic and mortar coal) were more significant than those of the weakly deformed coal (cataclastic coal). Based on the adsorption potential theory, we drew the adsorption characteristic curves and established adsorption capacity prediction models of primary structure coal and brittle TDCs.

Pore structure characterization and its significance for gas adsorption in coals: A comprehensive review

The coal reservoir has multifaceted and hierarchical characteristics influenced by heterogeneity of the pore and fracture networks. The coal pore including micropore, mesopores and macropores determines the critical migrate processes of gas molecules, especially for adsorption. Normally, coal pore structure refers to the pore shape, size distribution and interconnection of variable pores. Together with pore volume, pore size distribution, specific surface area and porosity. For coalbed methane, pore structure is the storage place, which largely controls the methane adsorption capacity of coal. Fluid injection, microscope observation and X-ray and spectroscopic analysis can be used to explore coal pore structure. Understanding the pore structure in varied rank coals is very challenging mostly due to the complex pore system leading to ambiguous petrophysical properties and gas performance. Among several important factors controlling the performance of coalbed methane, adsorption is the most crucial one, which affected by the pore aspects including pore volume, specific surface area, pore size distribution, pore shape and porosity. Therefore, accurate characterization of pore structure is coupled with advanced technologies, which resulted in the development of a wide range of methods. In this work, all the necessary technologies from imaging, segmentation, and modeling of the pores to various methods of gas adsorption evaluation are reviewed. This paper presents a critical review of all of the existing relevant and significant techniques and compares their performances together with their limitation with special reference to pore structure characterization. And the impacts of pore structure are thus reviewed. Finally, this review work proposes the current challenges and possible future research. • The coal pore classification scheme is systematically reviewed. • The pore characterizing techniques are summarized. • The influence of coalification on pore structure and its impact on CH 4 adsorption is analyzed. • The challenges and prospects on coal pore research are proposed.

Quantitative Analysis of Pore Structure and Its Impact on Methane Adsorption Capacity of Coal

Better understanding of the storage and transportation characteristics of methane in coal seams is important to further develop and utilize the methane resources in the coalbed. This study is devoted to investigating the relationship between methane adsorption performance and pore structure by analyzing twelve coal samples derived from the typical methane-rich coalbeds in China. To eliminate the influence of inorganic components such as ash in different coal samples, a specific fixed-bed reactor with internals was employed for the coal treatment. Based on N2/CO2 adsorption analysis at low-pressure condition, the pores in coal were classified into three types in this study: ultra-micropore (pore width ultra-micropore surface area (0.8976) > fractal dimension D1 (0.8862) > N2-BET surface area (0.7915) > micropore volume (0.5035) > micropore surface area (0.5006). This study shows the influence of parameters of pore structure on methane adsorption of coal and clarifies the order importance of these parameters by the GRA method.

Effect of water occurrences on methane adsorption capacity of coal: A comparison between bituminous coal and anthracite coal

In this study, an NMR fluid typing method was applied to two typical anthracite and high volatile bituminous coals to identify different occurrence states of water (adsorbed and non-adsorbed water), and multiphase methane (adsorbed, porous medium confined, and bulk methane) and investigate the effect of the water occurrence states on methane adsorption capacity. First, results of isothermal adsorption analysis conducted using the NMR method was compared to those from conventional volumetric method to verify the precision of the NMR method. Then the influence of adsorbed water and non-adsorbed water on methane adsorption was examined based on two parallel treatments. For bituminous coal, the adsorbed water remarkably reduced the Langmuir adsorption volume, whereas adding non-adsorbed water had no effect on gas adsorption. In contrast, for anthracite coal, the methane adsorption capacity revealed a downward trend with increase in both adsorbed water and non-adsorbed water. The explanation is that adsorption competition between water molecules and methane gas molecules can constrain further adsorption of methane on the coal matrix. Thus, adsorbed water negatively impacts gas adsorption for both anthracite and bituminous coal. In terms of non-adsorbed water, due to the superior pore conductivity and hydrophilia of bituminous coal, methane gas can easily pass through the pores in the presence of non-adsorbed water, compared to anthracite, where water blocking and the Jamin effect tend to occur. Even water droplets formed because of anthracite’s hydrophobicity can utterly block the pore throats, resulting in a continuous decrease in methane adsorption capacity. The implications of this study are important for better understanding the influence of various occurrence states of water on the adsorption/desorption processes in unconventional reservoirs.

Influence of reservoir properties on the methane adsorption capacity and fractal features of coal and shale in the upper Permian coal measures of the South Sichuan coalfield, China

Pore structure plays an essential role in the reservoir heterogeneity and methane adsorption capacity. Significant progress has been made in the pore structure classification of porous materials (such as coal and shale). Considering the pore structure characterization of the coal measures and the measuring range of high-pressure mercury intrusion porosimetry and low-pressure N2/CO2 gas adsorption, an integrated classification for coal and shale is provided. They are micropore (<2 nm), mesopore (2–100 nm), macropore A (100 nm–1 µm), macropore B (1–10 µm), and micro-fracture (>10 µm). For coal and shale samples from Guxu mining area, the micropores and mesopores largely control the gas adsorption while micro-fractures and macropore B are significant for the storage and flow of free gas. The fractal dimensions calculated from limited N2 adsorption data are not suitable for the coal samples which are not developed in mesopore and macropore A; these samples are precisely corresponding to the N2 adsorption/desorption isotherms of group B (reversible isotherm). Furthermore, the main factors influencing the methane adsorption capacity of coal and shale in the coal measures are micropore frequency, micro-fracture width, clay mineral composition, and total organic carbon content.

A comparative study of the nanopore structure characteristics of coals and Longmaxi shales in China

AbstractBoth of the coalbed methane (CBM) and shale gas reservoirs are dominated by nanometer‐scale pores with their nanopore structures controlling the occurrence, enrichment, and accumulation of natural gas. Low‐pressure nitrogen gas adsorption (LP‐N2GA), low‐pressure carbon dioxide gas adsorption (LP‐CO2GA), high‐pressure methane adsorption (HPMA), and field emission scanning electron microscope (FE‐SEM) experiments were conducted on 14 different‐rank coal samples and nine Longmaxi shale samples collected from various basins in China to compare their nanopore characteristics. The FE‐SEM results indicate that the pore structures of both the coal and shale samples consist of nanometer‐sized pores that primarily developed in the organic matter. The types of their isothermal adsorption curves are similar. However, the coal and shale samples possess various hysteresis loops, which suggest that the nanopores in shale are open‐plated, whereas those in coal are semi‐open. Furthermore, the specific surface area (SSA) and pore volume (PV) of the micropores in coal are much larger than those of the mesopores, with the micropore SSAs accounting for 99% of the total SSA in the coal samples. However, the micropore SSAs in the shale samples only account 42.24% of the total SSA. These different nanopore structures reflect their different methane adsorption mechanisms. The methane adsorption of coal is primarily controlled by the micropore SSA, whereas that of shale is primarily controlled by the mesopore SSA. If we use mesopore SSA to analyze its impact on methane adsorption capacity of coal and shale, it will be mismatched. However, no mismatching relationship exists between the total SSAs and adsorption capacities of coal and shale. This study highlights the controlling effect of total SSA on methane adsorption capacity.

Methane adsorption characteristics and its influencing factors of the medium-to-high rank coals in the Anyang-Hebi coalfield, northern China

The variation of coal rank in the Anyang-Hebi (Anhe) coalfield has the phenomenon of anti-Hilt law, which makes the coalfield distinctive for coalbed methane exploration research. The methane adsorption characteristics and influencing factors of the medium-to-high rank coal samples of the Shanxi Formation in this coalfield were analyzed. The results indicate that the Langmuir volume ( VL) of coals in the shallow western part of the Anhe coalfield is generally higher than that in the deep eastern part. The coal rank and the coal macerals are the dominant factors that influence the methane adsorption capacity of coals in this anti-Hilt law area. The methane adsorption capacity, represented by VL, first increases and then decreases with the coal rank, and the highest VL value corresponds to the maximum vitrinite reflectance of ∼2.1%. The adsorption capacity has a positive correlation with the vitrinite and the moisture content, a negative relationship with the inertinite content. In general, the adsorption capacity of coal samples shows a “V-shaped” change with the ash yield, and the lowest VL value corresponds to the ash yield of ∼9%. A prediction model of the gas content of the Anhe coalfield was proposed based on changes of the methane adsorption capacity and principal component analysis. Areas with a critical depth ranging from 400 m to 700 m are suggested to be methane enrichment regions for coalbed methane exploration in the Anhe coalfield.

Relationship between Maceral of Coal and Coal-bed Methane adsorption ability in Sihe Coalmine of Qinshui Basin, China

Maceral components and its content of coal were divided based on the microscopic characteristics of coal. The Langmuir volume and the Langmuir pressure were tested, and the Langmuir volume represents the adsorption capacity of coal. The formation of coal bed methane is affected by the partition of the maceral components in coal. Therefore, the relationship between maceral composition and coal bed methane adsorption capacity of coal was analyzed. The results show that the maceral components of coal are dominated by vitrinite and inertinite in the study area, and the content of inertinite is below 32%. The vitrinite group has a negative linear correlation with the Langmuir volume, and the inertia composition has a positive linear correlation with it. The cellular structures in the inertinite are the main site of coal bed methane enrichment. The microstructure of coal affects the coalbed methane content and the stage of hydrocarbon generation in coal. This indicates that the microstructure of coal is one of the important factors influencing the adsorption capacity of coal seam.

Methods and Models for Analyzing Methane Sorption Capacity of Coal Based on Its Physicochemical Characteristics

The authors study the influence of physicochemical parameters on methane adsorption capacity of coal and offer the analytical method for the methane adsorption capacity for three-phased condition of methane. It is found that in the depth interval to 300 m below surface, methane adsorption capacity measured in lab can exceed natural gas content of coal obtained from geological exploration data by 30%, and the change in the thermodynamic condition of coal–methane system brings irreversible physicochemical consequences in terms of the altered ratios of physical states of the main components. There is no linear connection between natural gas content of a coal bed and its methane adsorption capacity with respect to occurrence depth. The application of Big Data in treatment and interpretation of large data flows is described. The theoretical data predicted using the proposed method and the experimental data on methane content of Kuzbass coal agree.

Experimental investigation on variation of physical properties of coal samples subjected to microwave irradiation

The gas drainage rate of low-permeability coal seam is generally less than satisfactory. This leads to the gas disaster of coal mine, and largely restricts the extraction of coalbed methane (CBM), and increases the emission of greenhouse gases in the mining area. Consequently, enhancing the gas drainage rate is an urgent challenge. To solve this problem, a new approach of using microwave irradiation (MWR) as a non-contact physical field excitation method to enhance gas drainage has been attempted. In order to evaluate the feasibility of this method, the methane adsorption, diffusion and penetrability of coal subjected to MWR were experimentally investigated. The variation of methane adsorbed amount, methane diffusion speed and absorption loop for the coal sample before and after MWR were obtained. The findings show that the MWR can change the adsorption property and reduce the methane adsorption capacity of coal. Moreover, the methane diffusion characteristic curves for both the irradiated coal samples and theoriginal coal samples present the same trend. The irradiated coal samples have better methane diffusion ability than the original ones. As the adsorbed methane decreases, the methane diffusion speed increases or remain the same for the sample subjected to MWR. Furthermore, compared to the original coal samples, the area of the absorption loop for irradiated samples increases, especially for the micro-pore and medium-pore stage. This leads to the increase of open pores in the coal, thus improving the gas penetrability of coal. This study provides supports for positive MWR effects on changing the methane adsorption and improving the methane diffusion and the gas penetrability properties of coal samples.

Modelling of the thermal history of the Carboniferous Lorraine Coal Basin: Consequences for coal bed methane

This paper proposes a new scenario for the thermal history of the Carboniferous Lorraine Coal Basin following the tectonic model developed by Averbuch et al. (2012) and establishes some consequences for the coal bed methane (CBM) exploitation. Organic matter maturation data (Vitrinite Reflectance) determined on eleven boreholes in the eastern Lorraine have been used to characterize the Lorraine Coal Basin evolution. Paleozoic and Mesozoic overburials have been calculated using a thermal modelling software (Petromod). Results show that (1) Paleozoic erosion may be estimated at a maximum of 1200m which represents a low amplitude event, (2) a little erosion occurred between Upper Paleozoic and Lower Mesozoic: paleotemperature offset is about 20°C and VR data range from 0.7 (Westphalian D) to 0.5 (Lower Triassic), (3) Cretaceous cover overburial reaches a maximum of 300m and decreases eastwards and (4) the variation of heat flows is in agreement with the compressive and extensive phases of Paleozoic and the extensive phase of Mesozoic. Consequences on the petroleum system are the following: organic matter is immature in the Jurassic and Triassic sedimentary rocks, mature (oil window) in the Permian, Stephanian and Westphalian C-D, highly mature (gas window) in Westphalian A-B-C and overmature in Namurian-Westphalian A. The high methane adsorption capacity of coal and the presence of natural fractures inside coal seams demonstrated by coal tomography allow a high CBM potential in this basin. The Lorraine Coal Basin is therefore a target for coal gas.

Influence of coal petrology on methane adsorption capacity of the Middle Jurassic coal in the Yuqia Coalfield, northern Qaidam Basin, China

The lower coalbed methane (CBM) adsorption capacity of the low rank coals is not only related to its lower maturity, but also determined by the coal maceral compositions. In this study, a total of 13 samples including 10 coals and 3 carbonaceous mudstones, were collected from the Middle Jurassic Dameigou Formation in the borehole YQ-1 of the Yuqia Coalfield, northern Qaidam Basin, NW China. Coal lithotypes, maceral compositions, coal ranks, coal facies and methane adsorption characteristics of these samples were investigated using microscopic observation, proximate analysis, porosity analysis, and isothermal adsorption experiments. The results show that the maceral composition has a great influence on the methane adsorption capacity, and the influence of vitrinite on the methane adsorption is generally stronger than that of inertinite at a similar coal rank. For most samples, there is a positive correlation between the vitrinite contents and the Langmuir volume (VL), a negative correlation between the inertinite contents and the VL, and no obvious correlation between the exinite contents and the VL. Furthermore, the vitrinite/inertinite (V/I) ratio also shows a positive relationship with the VL. However, some samples containing large amounts of unfilled fusinite and/or semifusinite have more pore spaces favoring methane adsorption and can also adsorb significant quantities of methane. Consequently, coals with higher vitrinite contents, in association with some unfilled fusinites or semifusinites, should have the greatest adsorption capacity. Coal maceral compositions vary with the types of coal facies, and thus the methane adsorption capacity of coals may be closely related to coal facies. It is found that the methane adsorption capacities of the coals in a wet forest swamp (Type I) and an intergradation forest swamp (Type II) are greater than those in a drained forest swamp (Type III) and an open water peat swamp (Type IV). It is suggested that the area developed with the wet forest swamp and in the intergradation forest swamp with high porosity should be the best target areas for the CBM exploration in the Yuqia Coalfield.

Adsorption capacity, adsorption potential and surface free energy of different structure high rank coals

Methane adsorption capacity of coal is one of the major factors influencing total gas-in-place and it is linked to coal structure, while our knowledge of it is still limited. In this study, coal structures were classified into five categories, including integrated, blocky, cataclastic, granulated and mylonitized. The integrated and blocky coals are intact and the other three are deformed. To investigate the methane adsorption capacity, adsorption potential and surface free energy of different structure coals, four high rank coal samples were collected from No.3 coal seam of the Zhaozhuang coal mine in Southeastern Qinshui Basin China, and a series of methane isothermal adsorption experiments and pore distribution measurements were carried out in the laboratory, and then the adsorption potential and the surface free energy were analyzed. It turns out that, there are no obvious differences in the methane adsorption capacity for the various structure coals when the equilibrium pressure is below 2MPa; while there are significant differences when the pressure is above 2MPa. The higher the gas pressure is, the greater the difference is. Methane adsorption capacity of different structure coals can be arranged in a descending order: mylonitized>granulated>cataclastic>intact. That is, the methane adsorption capacity is higher for the deformed coal samples than for the intact ones. Both the specific surface area and the pore volume increase with the increase of deformation degree. Mesopores contribute most to the total pore ​​volume; while the adsorption pores have the greatest contribution to the total specific surface area. The adsorption potential and surface free energy for different-structure coals under the same adsorption space volume increase with the increase of deformation degree. Adsorption potential decreases with the increase of adsorption space, and the adsorption potential of micropore is considerably higher than that of mesopore and macropore. As the temperature rises, the cumulative reduction of surface free energy decreases and the surface free energy decreases significantly at each equilibrium pressure. Methane adsorption in coal is dominated by adsorption potential and surface free energy.

Quantitative characterization of methane adsorption on coal using a low-field NMR relaxation method

To develop a nuclear magnetic resonance (NMR) method for characterizing the methane adsorption capacity of coals, we built an NMR transparent isotherm adsorption experimental setup. Proton (1H) NMR measurements were first performed with bulk methane to obtain a hydrogen amplitude index reflecting the methane volume concentration. Then, dry coals were pressurized with methane to assess the quantity of adsorbed methane at pressures up to 6.1MPa. The adsorption isotherms obtained by this procedure were compared with the corresponding sorption isotherms determined by the traditional volumetric method under the same experimental conditions. The methane transverse relaxation time (T2) spectra have three distinct peaks at T2<7ms, T2=7–240ms, and T2=240–2000ms. The peaks at T2<7ms and T2=7–240ms both correspond to the surface relaxation mechanism, and individually, they are interpreted as “coal-adsorbed methane” and “porous medium-confined methane”, respectively. The peak at T2=240–2000ms represents the relaxation of bulk methane. The integrated amplitude of the “porous medium-confined methane” peak has a positive linear relationship with pressure, whereas the integrated amplitude of the “coal-adsorbed methane” peak with increasing pressure follows the Langmuir equation. The adsorption isotherms from the NMR and volumetric methods are nearly identical. The absolute deviations of the experimental data points from the two methods fall within ±2m3/t, and the calculated Langmuir volumes have absolute deviations of <0.38m3/t and relative deviations of <1.24%. We suggest that the low-field NMR may be applied as a noninvasive analytical technique to characterize the methane adsorption capacity of coals.

Influence of nanoscale pores in coal on methane adsorption

In order to study the influence of nanoscale pores ( < 100 nm) in coal on methane adsorption, pore size distribution and maximal methane adsorption capacity of anthracite, meager lean coal, coking coal and gas-fat coal had been studied in the lab. The results show that the macropore volumes of four kinds of coals are developed and they are preponderant in all kinds of pore volumes. The nanoscale pore (less than 100 nm) volume is little in all pore volumes, but the specific surface areas of nanoscale pores ( < 100 nm) of four kinds of coals are developed, and they are more than 95% in total specific area. With the method of curve similarity, the leading factors influencing maximal methane adsorption quantity were analysed. The analysis results indicate that the methane adsorption capacity of coal is dominated by specific surface area of nanoscale pores ( < 100 nm). The methane adsorption capacity of coal increases linearly with the increase of specific surface area of nanoscale pores ( < 100 nm). The maximal methane adsorption quantity decreases in the order anthracite < meager lean coal < coking coal < gas-fat coal.