Coal Fragments Research Articles

Fragmentation of a Turkish Low Rank Coal During Fixed-bed Evaporative Drying Process

ABSTRACT In the present study, a new approach was utilized to investigate the fragmentation of low rank coal during the thermal drying process. Drying experiments were conducted at different drying air temperatures (70, 100, 110 and 130°C), drying air velocities (0.4 and 0.7 m/s), bed heights (100, 150 and 250 mm) and particle fractions (20–50, 28–50 and 35–50 mm) for a Turkish lignite (Konya-Ilgın lignite) in a fixed-bed dryer. Konya-Ilgın lignite was used in the heating sector. Particle sizes used in these experiments were coarser than the studies in the literature due to legal constraints. The effects of drying parameters on coal fragmentation were evaluated. The fragmentation increased as the drying air temperature and the velocity increased, and it decreased as the bed height and the particle size increased. Results of this study may be used in the design of a suitable dryer for low rank coal.

Prediction and Characterization of the Microcrystal Structures of Coal with Molecular Simulation

The characterization of coal structures is challenging due to their broad distribution of molecular structures including large-scale entities. Previously, the micro-crystal structure of coal has been extensively observed with the XRD analysis and its features were found to be closely correlated with the carbon/oxygen content. In this work, Polymorph Predictor, a Monte Carlo method, was applied to predict the most favorable micro-crystal structures formed by simplistic coal models and to study the effect of carbon content on the density and inter-layer spacing (d002) of coal. The valence or non-bond interactions existed in predicted crystal structures were analyzed by calculating the energy contributions based on the classical molecular dynamics (MD) simulation theory. The calculation from Density functional theory (DFT) of coal fragments was conducted to study the relationship between carbon content and electronic properties of coal. Additionally, the MD simulation of water contact angle was conducted to ...

Natural content of gases: Carbon monoxide, carbon dioxide, hydrogen and unsaturated hydrocarbons of ethylene, propylene and acetylene in selected bituminous coal seams

Chromatographic analysis of gas desorbed from coal reveals the presence of carbon monoxide, carbon dioxide, hydrogen, ethylene, propylene and acetylene, i.e. gaseous components liberated into the mine atmosphere with the increasing temperature of self-heating coal. Elevated levels of carbon monoxide, dioxide and ethylene were registered as well. Investigations showed that these gases are contained in the coal structure and their liberation to the mine air can be triggered by other factors apart from coal self-heating, for example coal fragmentation or disturbing of the virgin coalbeds by mining operations. The amounts of thus desorbed gases can alter their actual concentrations in the mine air, which serve as indicators of the self-heating propensity of coal. No straightforward relationship was established between the concentrations of individual gaseous components in the mixed-gas desorbed from coals sample and the rank and other physico-chemical properties of coals.Sorption and desorption tests by the volumetric method demonstrated that the volume of sorbed carbon monoxide and dioxide, hydrogen, ethylene, propylene and acetylene is closely related to the coal rank and its porous structure. Low-rank coals with well-developed pore systems tend to absorb/adsorb greater amounts of gases than low-rank coals with a less developed pore structure.Tests established the intensity of gas desorption from coals, showing that nearly 80–90% of carbon monoxide, dioxide and hydrogen accumulated in coals would be released. In the case of adsorbed ethylene, propylene and acetylene that proportion is the lowest (50%–70%).Recalling the Ideal Adsorbed Solution (IAS) theory, simulations were performed to predict the mixed-gas adsorption isotherms for binary gas mixtures containing non-saturated hydrocarbons-gas components that are indicators of the self-heating propensity of coal. It appears that acetylene adsorption in the systems C2H2C2H4 and C2H2C3H6 is a favoured process whilst preferential adsorption in the system C3H6C2H4 is that of propylene.

Nonlinear relationships between coalbed methane release, natural methane content and kinematic parameters of cutting picks of shearers

It has been found that the rated and actual data on methane emission in production headings in some Kuzbass mines disagree. The air and gas control shows that actual methane emission from broken coal is much less than the rated data when a coal shearer has high advance velocity and production output. The authors demonstrate the connection between an average diameter of broken coal fragment, shearer advance velocity and drum rotation speed using Darcy’s law of flow and Langmuir’s adsorption equation. It is found that methane emission from broken coal and natural coalbed methane content relate nonlinearly and that the relationship of absolute methane emission, shear advance velocity and production output has an extremum.

Large Scale Molecular Model Construction of Xishan Bituminous Coal

Molecular structural information on a Chinese Xishan bituminous coal was obtained using elemental analysis, high resolution transmission electron microscope (HRTEM), laser desorption time-of-flight mass spectrometry (LD-TOF MS), solid state 13C nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS) techniques. The size and distribution of aromatic structures were determined by HRTEM, providing 300 base aromatic skeletons for a coal model. Aliphatic side chains and heteroatoms were introduced into these aromatic skeletons according to 13C NMR and XPS results, which created 300 individual coal fragments. The individual fragments were cross-linked randomly with aromatic–aromatic, aromatic–aliphatic, aromatic–oxygen, aliphatic–aliphatic, and aliphatic-oxygen linkages to match the molecular weight distribution observed in LD-TOF MS. As a result, the coal model was constructed. The proposed model was comprised of 62 unique individual molecules with a composition of C7972H4882O115N50S30, wh...

Relevance of structure, fragmentation and reactivity of coal to combustion and oxy-combustion

The nature and extent of the microstructural changes of coal upon oxidation under conditions typical of combustion systems, and the relation between microstructure and reactivity towards oxygen and carbon dioxide have been extensively addressed. The first major changes in morphology, structure and chemical composition of the solid fuel occur in the early instances of combustion/gasification processes, during heat up and devolatilization. At this stage particles can be broken into smaller fragments as a consequence of thermal stress and pressure generated by volatiles release. This phenomenon, regarded to as primary fragmentation, is considered responsible of important changes in the fuel particle size distribution within reactors.At longer time scales the concurrent heating and heterogeneous reactions may further affect the structure and the reactivity of chars: on the one side the prolonged heat exposure induces thermal annealing with progressive graphitization and loss of reactivity. On the other side, additional phenomena, referred to as secondary fragmentation and attrition by abrasion can occur in parallel with char burning. Eventually, for large extents of internal burning, the increase of particle voidage can induce percolative fragmentation. The distinction between the individual fragmentation processes, just as that between pyrolysis and thermal annealing, is more operational than conceptual and depends on the timescale of the processes and on the nature of the fuel. On the whole, the course of combustion/gasification of a solid fuel is ruled by the competition between heterogeneous reactions of the solid fuel and a number of complex phenomena that modify char structure and reactivity.Limited information is available in the literature on the relationship among structure, fragmentation, and reactivity of coal in oxy-combustion conditions. The transferability of the lessons learnt under conventional combustion and gasification conditions to the case of oxy-combustion is here discussed to stress the need of additional investigation on this topic.

Comminution Theory of Superfine Pulverized Coal Based on Fractal Analysis of Aggregate Structures

The coal fragmentation and resulting particle size distribution (PSD) have significant influences on the physical and chemical properties, which play a crucial role in coal conversion and utilization processes. In this paper, a comprehensive comminution theory of superfine pulverized coal was proposed, in combination of particle fracture mechanisms, fractal dimension analysis and energy laws of comminution. The subtle crystalline changes of aggregate structures due to the coal comminution were validated through the synchrotron-based high-resolution X-ray diffraction (HRXRD), and the distribution patterns of submicron aggregate clusters were identified according to the fractal fragmentation theory. Finally, a novel energy dissipation assumption is proposed based on the molecular sliding mechanism, which is suitable for the evaluation of energy consumption of the comminution induced submicron particles. The results here can improve the interpretation and modeling of coal macromolecular networks, and offer a...

Numerical Simulation of Primary Fragmentation of Coal Particle Mixture Subjected to Shock Wave

ABSTRACTPrimary fragmentation of coal plays an important role in overall combustion efficiency. In practice, a mixture of different sized coal particles is used. Numerical simulation of primary fragmentation of coal particle mixture subjected to shock wave is studied in this work. Coal particles behind shock wave undergo heating, volatilization, and fragmentation. Each of these is modeled in the simulation. Heat transfer is linked with volatilization and solid mechanics to predict primary fragmentation of coal particles using a probabilistic and statistical approach. Fracture time and fracture location are identified by setting fracture criteria, which is obtained using failure probability calculated from Weibull’s Weak Link theory. Irregularities inside a coal particle are included through Weibull’s parameters. Average fracture time of mixture of coal particles is calculated. Numerical results suggest that approximately 90% of coal particles in the mixture have fractured in about 1–2 ms. Simulation results suggest that in the timescale of interest thermal stress dominated, with only marginal effects due to volatilization.

Effect of coal fragmentation on PCI combustion zone in blast furnace

Pulverized Coal Injection (PCI) is one of the most effective technologies for reducing coke consumption in blast furnaces. Its main role is as the heating source and for the generation of CO gas. Generally, PCI coal is a high-rank coal, but steel mill companies are attempting to use low-rank coal as an energy source in PCI combustion blast furnaces because of the increasing cost of high-rank coal and decreasing reserves. The purpose of this investigation was to determine how the coal rank is correlated to the pulverized coal particle temperature and CO emission. This study was performed using a Laminar Flow Reactor (LFR), which represents the combustion environment of pulverized coal inside a blast furnace. Since the PCI system was developed for iron making, the combustion characteristics of pulverized coal are important in the iron and steel industries. According to the different types of coals, the coal flame structure, coal particle temperature, and exhaust gases (CO and CO2) were investigated. This study demonstrated that the combustion characteristics of coal were influenced by several properties of individual coals. Primarily, the coal particle temperature and CO emission were found to have the strongest influence on the combustion characteristics of these coals. Moreover, the fragmentation phenomenon occurring in some coals was also an important factor influencing the PCI combustion characteristics. Therefore, this study significantly considered the coal properties, focusing on images of the burning coal particle flames, the particle temperature, and the CO/CO2 emissions.

Experimental investigation on anthracite coal fragmentation by high-voltage electrical pulses in the air condition: Effect of breakdown voltage

Coalbed methane (CBM) reservoirs in China are characterized by extremely low aperture and natural fractures density, which seriously affects the efficient CBM exploitation. In this paper, we have developed an experimental system for crushing coal by high-voltage electrical pulses (HVEP) to improve the pore structure. The coal samples collected were crushed under different breakdown voltages. It can be observed that under the action of HVEP, the coal sample is broken down into multiple small pieces, and the degree of coal fragmentation increases with the increase of breakdown voltage. Furthermore, we adopt three tests including Scanning electron microscopy (SEM), low-pressure nitrogen gas adsorption (LP-N2G) and mercury intrusion porosimetry (MIP) to gain a clearer insight into the variations in pore structure. SEM images demonstrate that the higher breakdown voltage attributes to the generation of more pores and fractures in coal samples. Adsorption analysis reveals that the micropores of the coal samples crushed by HVEP present an increasing trend compared with the micropores of raw coal sample. Besides, a normal distribution correlation is observed between cumulative micropore volume and breakdown voltage. MIP test shows that the macropore is dominant for all the fragmented coal samples and the effect of high voltage on macropores is more remarkable than other types of pores.

Pressurized oxy-fuel combustion performance of pulverized coal for CO2 capture

Pulverized coal combustion in pressurized oxy-fuel (or O2/CO2) atmosphere is widely accepted as a clean technique for energy conversion with respect to the NOx emission reduction and CO2 capture. The combustion performance of two pulverized coals, including the ignition and burnout, char structure transformation, and ash formation, was investigated, and the effects of system pressure, oxygen concentration, and coal type were explored. Results showed that system pressure had positive effects on the combustion performance of DT coal and SH coal within a range. The best pressure in this work was 1 MPa. The increase of oxygen concentration was more effective for the ignition temperature reduction at elevated pressure. Increasing the pressure affected the release of carbon functional groups on char surface, especially the aromatic and aliphatic carbon, which was least at 1 MPa, indicating the lowest graphitization degree and ignition temperature. A pressurized condition also promoted fragmentation of coal during the devolatilization, and thus enlarged the available surface area for char reaction with O2, leading to an earlier ignition. The SEM morphologies of ash generated at different pressures identified the enhanced formation of finer ash under pressurized conditions. Results are feasible for optimizing the pressurized oxy-fuel combustion in the future.

Mechanism of primary fragmentation of coal in fluidized bed

In order to lay a foundation of a credible primary fragmentation model, a theoretical analysis of the thermo-mechanical processes in a devolatilizing solid fuel particle was carried out. The devolatilization model comprises heat transfer, chemical processes of generation of gaseous products of combustion (volatiles), volatile transfer, and solid mechanic processes. A spatial and temporal analysis of the stresses within the particle showed that the radial stress is caused primarily by the pressure of generated volatiles. This stress monotonously decreases from the particle center towards the particle surface, without changing its sign. The tangential stress is caused primarily by the thermal shock. Close to the surface, it changes its sign. In the particle cross-section, the radial stress prevails close to the particle center, whilst the tangential stress is dominant in the surface region. At the points where these stresses exceed the particle tensile strength, cracks occur. Cracks extend tangentially close to the surface, and radially close to the center of the particle.

Evaluation of the effects of coal grinding in terms of coal water slurry preparation

Coal Water Slurry (CWS) is a specific form of solid fuel. It occurs in the form of finely ground coal particles and water. Depending on the use, the content of combustible matter is from 40 to 70% by weight. The attractiveness of the fuel is primarily its properties, i.e. liquid form, high energy efficiency (for water evaporation 4% energy is used – for CSW with 70% concentration of coal), decreased environmental impurities (lower NOx emission) and reduced risk of explosion. The advantages of CWS fuels, the possibility of independence from petrochemical fuels, wide availability of coal and emphasis on the use of cleaner technologies are the driving force for development of slurry fuel technologies. The major parameters characterizing the fuel suspension are: solid phase concentration (share of coal in the slurry expressed as either weight or volume fraction of dry coal), time stability (resistance to delamination and separation of the dispersed phase from the continuous phase) and viscosity, determining the flow of suspension. The mentioned parameters are dependent on the susceptibility of coal for production of aqueous suspensions (slurrability), conditioned by natural properties of coal, such as: coalification degree, petrographic composition and surface properties. They are also dependent on the slurry fuel preparation process: particle size, solid phase concentration, used additives (stabilizing and dispersion agents) and modification of primary coal properties (ash removal, change of surface properties). Preparation of sustainable, high concentrated CWS fuel coal is promoted by the hydrophobic nature of the coal surface, characteristic for coals of higher coalification. A great technological problem is to obtain a highly concentrated coal slurry fuel from less coalified hydrophilic steam coals. The paper presents the results of lab scale research on the CWS prepared from Polish steam coal by wet grinding in mill drum and vibrating. The milling process was carried out in a batch system by varying the composition of the grinding media and varying degrees of working space filling. The feed was pre-ground steam coal mixed with water at the ratio of 1: 1. The changes of particle size, viscosity and stability of suspensions in time were assessed. The milling effectiveness was higher for the vibrating mill. After the same milling time the quality of the obtained product was higher. The obtained milling degree was depended on the share and composition of grinding aids. In the investigated range (10-30% share mill working space), the use of higher share of grinding aids caused higher milling degree of coal. A trend was observed that stronger fragmentation of coal was achieved with the use of polydisperse composition of aids distinguished by smaller diameters. The changes of granulation influenced the viscosity and stability of the obtained product. The lower the mean particle size, the higher the viscosity and stability of the obtained product was particularly noted for the vibrating mill.

Optimizing calculation of particle size distribution of feeding coal for circulating fluidized bed boiler

The particle size distribution (PSD) of feeding coal affects the solid concentration distribution, combustion fraction distribution and coal combustion behaviors in the circulating fluidized bed (CFB) boiler. In engineering, the particle size distributions for different feeding coals are determined empirically, such as the mean particle size of anthracite is smaller, and the mean particle size of lignite is larger. But the specific research on the PSD of different feeding coal is still lacking. In the operation of CFB boiler, the PSD of feeding coal is not adjusted. By optimizing the particle size distribution of feeding coal to adjust the mass ratio of fine particles in the dilute zone and coarse particles in dense zone, it is possible to obtain a good solid concentration distribution in the dilute zone and to improve coal combustion performance. This can assure the output of boiler and reduce the carbon content in ash, as well as reduce the friction of boiler and energy consumption of the fan. In this paper, an optimization model of the PSD of feeding coal of CFB boiler was developed, by setting the solid concentration of the furnace outlet and the mean retention time of coarse feeding coal in the furnace as the optimization goal. This procedure is based on the experimental results of primary fragmentation, burnout and ash formation of coal, using wen-chen hydrodynamic model. The optimized PSD of feeding coal had been calculated in some bed inventory, which results in an optimum solid concentration distribution in furnace and lower carbon content in bottom ash. Before and after optimization results showed that when the bed pressure drop was 11.3 kPa, the carbon content in bottom ash was reduced from 2.14% to 0.77%, and the solid concentration in the furnace outlet increased from 2.6 kg/Nm3 to 2.71 kg/Nm3. The calculation accuracy of the model was validated in a1060 t/h CFB boiler.

Experimental and Numerical Investigation of the Primary Fragmentation of a Lignite during Fluidized-Bed (FB) Devolatilization

The paper presents a comparison between experimental and model results of primary fragmentation of a lignite coal in a fluidized bed (FB). In the experiments, the char particle size distribution and the general indicators of primary fragmentation (intensity and index) were determined. The same parameters were calculated using a mathematical model of the process, fed by data of the fuel (the amount of volatiles and fixed carbon), fluidized bed temperature, and inlet particle size distribution. The size distribution and number of the char particles in fluidized bed significantly differ from the size distribution and number of inlet coal particles. Char population has a bimodal distribution—separate distributions for the smaller and larger sets of fragments. The experimental and model results show the same tendency: a coal particle partially breaks at the beginning of devolatilization, giving a large number of fine fragments, while, as the process continues, the rest of the parent particle sometimes breaks down into a smaller number of larger pieces, and sometimes does not fragment at all. Review of the Weibull distribution coefficients enables prediction of the char particle size distribution for the characteristic fluidized bed conditions and inlet coal particle sizes.

Coal fragment size model in cutting process

The size of coal fragment cutoffs by cutting mechanisms is an important index of coal mining. The larger the coal fragments, the less the dust, the lower the specific energy consumption and the higher the benefit. Therefore, a coal fragment size model was formulated in order to obtain large coal fragments in the cutting process, which considered the effect of pick arrangements (sequence and Punnett-square), helix angle, advancing velocity and the cutting line space of cutting mechanisms. Moreover, the effect of the above parameters on the size of coal fragments was analyzed in theory, which was validated by the cutting experiments correspondingly conducted using 8 different helix drums. The theoretical and experimental results indicate that the coal fragment cutoffs by Punnett-square drums are larger in size and more uniform in size distribution than by sequence drums; the size of coal fragments, increasing with the advancing velocity and the cutting line space, is almost unaffected by helix angle; the effect of advancing velocity and the cutting line space for Punnett-square arrangement is greater; the effect of cutting line space on coal fragment mass percentage below 1cm is greater than that of advancing velocity.

Development of energy efficient methodology of carbon materials drying and fragmentation

The development of heat power engineering in the modern conditions requires high-quality fuel with low sulfur content. Unlike liquid and gaseous fuels, brown coal has a high ash content and humidity. In order to improve the efficiency of thermal power plants, it is necessary to modernize the brown coal preparation process to lower sulfur content and reduce harmful emissions into the atmosphere during combustion. Therefore, the development and introduction of new energy-saving heat technological installations for drying and fragmentation of carbon materials is an important scientific-technical problem which is solved in the framework of the scientific area - industrial heat power engineering.In the paper, new energy-saving methodology, allowing highly efficient continuous drying and simultaneous fragmentation of dispersed materials was developed at the newly created highly productive thermal vacuum installation.During the research on thermal vacuum drying of dispersed materials, analytical and experimental methods for determining moisture withdrawal from the investigated objects depending on the regime parameters of the thermal vacuum installation were used.Based on the results of scientific and technical research it was found that brown coal with the initial humidity of 40% and size of up to 8 mm is converted into a fine powder with a humidity of less than 1.0% for 14 seconds during drying in the thermal vacuum installation. The temperature of the dried brown coal at the heating element outlet did not exceed 76οC at the heater temperature of 250oC. Brown coal drying proceeds uniformly, the color changes from brown to black. This suggests that the sulfur content in the brown coal reduces. In our case, the sulfur amount in the dried brown coal has decreased by more than twice from 4.8% to 2.2%.The developed process of thermal vacuum drying and simultaneous fragmentation of brown coal allows to reduce energy costs per unit of the dried product, accelerate the drying process, obtain a fine powder of the dried coal with low sulfur content, which leads to reducing harmful emissions into the environment during combustion.

Legacy sediment stored in sinkholes: a case study of three urban watersheds in Tennessee, United States of America

As closed topographic depressions, sinkholes effectively divide karst regions into a series of subwatersheds, where swallets within each sinkhole define the downstream end of each subwatershed. Water and sediment are temporarily stored in sinkholes before continuing to underground streams. While pathways and travel times of water in karst terrain are commonly found using tracing techniques, such techniques do not provide information about the movement and travel time of sediment through these systems. This paper reviews the literature regarding sediment storage within sinkholes and presents a case study, the objective of which is to estimate the magnitude and timing of sediment deposition within three sinkholes in an urbanized area in Tennessee, United States of America. Sedimentation rates in sinkholes were estimated based on age determination of cultural artifacts (buried trash and coal fragments) and by 14C dating. For the three study sinkholes, minimum deposition rates (maximum residence times) were 15 cm yr −1(6 yrs), 1.5 cm yr −1(81 yrs), and 0.2 cm yr−1(640 yrs). The analysis revealed that sinkholes undergo fill and flush cycles at different timescales caused by changes in upland sediment supply and morphologic changes at swallet openings. Sinkholes that lack swallet openings, or with swallets that have become blocked by debris, are effectively disconnected from master streams with regard to sediment. Sediment stored in sinkholes may be released downstream when swallet conditions change.

Energy Dissipation and Release During Coal Failure Under Conventional Triaxial Compression

Theoretical and experimental studies have revealed that energy dissipation and release play an important role in the deformation and failure of coal rocks. To determine the relationship between energy transformation and coal failure, the mechanical behaviors of coal specimens taken from a 600-m deep mine were investigated by conventional triaxial compression tests using five different confining pressures. Each coal specimen was scanned by microfocus computed tomography before and after testing to examine the crack patterns. Sieve analysis was used to measure the post-failure coal fragments, and a fractal model was developed for describing the size distribution of the fragments. Based on the test results, a damage evolution model of the rigidity degeneration of coal before the peak strength was also developed and used to determine the initial damage and critical damage variables. It was found that the peak strength increased with increasing confining pressure, but the critical damage variable was almost invariant. More new cracks were initiated in the coal specimens when there was no confining pressure or the pressure was too high. The parameters of failure energy ratio β and stress drop coefficient α are further proposed to describe the failure mode of coal under different confining pressures. The test results revealed that β was approximately linearly related to the fractal dimension of the coal fragments and that a higher failure energy ratio corresponded to a larger fractal dimension and more severe failure. The stress drop coefficient α decreased approximately exponentially with increasing confining pressure, and could be used to appropriately describe the evolution of the coal failure mode from brittle to ductile with increasing confining pressure. A large β and small α under a high confining pressure were noticed during the tests, which implied that the failure of the coal was a kind of pseudo-ductile failure. Brittle failure occurred when the confining pressure was unloaded—an observation that is important for the safety assessment of deep mines, where a high in situ stress might result in brittle failure of the coal seam, or sudden outburst.

Compositional and isotopic changes in expelled and residual gases during anhydrous closed-system pyrolysis of hydrogen-rich Eocene subbituminous coal

Gases generated by laboratory anhydrous closed-system pyrolysis of hydrogen-rich Eocene Yubari subbituminous coal were distinguished as expelled gas, desorbed gas, residual free gas, and residual adsorbed gas, and the compositional and isotopic changes in these gases during laboratory maturation were investigated. The relative abundances of methane and H2 in the expelled gas were higher than those in the residual free and adsorbed gases, showing compositional fractionation during gas expulsion from the coal fragments. The δ13C and δ2H values of ethane, propane, and CO2 in all the gas fractions were nearly the same. However, the δ13C and δ2H values of methane in the residual free gas were significantly higher than those of methane in the expelled and desorbed gases, demonstrating a large isotopic fractionation associated with the expulsion of methane from the coal fragments. The carbon and hydrogen isotopic fractionations of ethane, propane, and CO2 during their expulsion were almost negligible.The evolution paths of the differential δ13C values of hydrocarbon gases generated from hydrogen-rich Eocene Yubari coal during laboratory maturation were rather close to those of hydrocarbon gases from Type II kerogen in the early stage of maturation (VRr%<1.2), but these shifted closer to those of hydrocarbon gases from Type III kerogen in the higher maturation stage (VRr%>1.6). The similar δ13C values of hydrocarbon gases from Eocene Yubari coal and Type II kerogen are partly due to the abundant and 13C depleted aliphatic structures in the Eocene Yubari coal. The δ2H of methane in the expelled gas from Yubari coal also increased systematically with laboratory maturation, although it can be influenced by various factors. Estimation of the maturity level and type of source organic matter of thermogenic methane based on isotopic composition requires caution, especially in the Cenozoic sedimentary basins.