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Understanding the relationship between the coal structure and its reactive behaviour is of great significance to achieve clean coal conversion and its efficient utilisation. One of the key tasks is to elucidate the molecular structure and chemical bonding information of coal. Owing to the complexity of the chemical structure of coal, studies on the molecular structure of coal, especially coal models with complex particle structures of different sizes for bituminous coal from northwest China, are highly warranted. In this work, the molecular structure characteristics and chemical index of a Qinghua bituminous coal sample collected from the Ningdong area, China, were assessed. Using a combination of material characterization, computation, and molecular modelling methods, a standard method for modelling complex coal structures from single molecules of macerals to particles of various sizes was developed. The single molecular structure of vitrinite and inertinite present in Qinghua coal can be expressed as C269H196N4O13S and C255H179N3O14S, respectively. Then, a series of complex particle models of various sizes were established based on the single molecular structure models of vitrinite and inertinite. Among these models, the size of the complex particles was as large as 11 nm, with the total atomic number approaching 60,000. Furthermore, the energetic and structural features of the complex coal particle structures were also explored based on their energy decomposition and radial distribution function analysis. In addition, the chemical structure index analysis was performed for different coal macerals to further understand the internal relationship between its structure and application.

Through high-voltage electrical experimental equipment fracturing coal, experiments were conducted on anthracite and bituminous coal soaked in distilled water and different concentrations of AlCl3 ...

Coal is one of the most important energy sources in China, and bituminous coal accounts for 80% of China's total coal. However, there are still some deficiencies in the previous understanding of the failure and mechanical characteristics of bituminous materials under external loads of different strain rates (especially high strain rates). To investigate the tensile and fracture mechanical properties of bituminous coal at different strain rates, the GCTS multifunctional rock mechanical loading device and Hopkinson bar dynamic loading system were employed. The crack extension process and crack distribution after damage of bituminous coal specimens were also analyzed by high-speed camera and CT scanning instrument. The results show that the peak stress distribution of the Brazilian disc (BD) bituminous coal samples ranged from 3.5 MPa to 5 MPa. The main crack expansion path of the internal splitting is not straight due to the non-homogeneity of the coal sample itself. And the secondary cracks of the specimen are more developed and mostly located in the middle region with transverse spreading. The average peak load of the notched semicircular bending (NSCB) coal samples tends to decrease with increasing depth of the notch. In addition, dynamic crack initiation toughness of NSCB bituminous coal specimen decreases continuously as the initiation time increases. The relationship between fracture toughness and crack initiation time is an approximate exponential function. The normalized dynamic fracture toughness test value of bituminous coal is higher than that of steel material, but lower than that of granite.

This study investigates changes in the concentration and types of free radicals in the process of coal heating, first rising and then falling. Hailar lignite, Panjiang bituminous coal, and Yangquan anthracite were selected as coal test samples. The results show that the lignite’s concentration of free radical changes during heating is greater than that of bituminous coal or anthracite. It clearly shows that lignite is more prone to spontaneous combustion. In the heating and cooling portion of the experiment, the concentration of free radicals during the cooling process was much more than that of free radicals at the same temperature during the heating process. These results obtained from this research study can provide a reference for the prevention and control of the spontaneous combustion of coal with changes in temperature. This study provides a theoretical basis for the prevention and control of spontaneous combustion of coal and the selection of retarding agents and methods in the process of flame retarding by testing the free radical changes of coal at different temperatures. Also, it provides a reference for preventing and controlling coal oxidation with the change in temperature, first rising and then falling.

Coal-based graphite has become the main material of emerging industries. The microstructure of coal-based graphite plays an important role in its applications in many fields. In this paper, the effect of carbon disulfide/N-methyl-2-pyrrolidone solvent mixture extraction on the microstructure of bituminous coal-based graphite was systematically studied through preliminary extraction coupled with high-temperature graphitization. The graphitization degree g (75.65%) of the coal residue-based graphite was significantly higher than that of the raw coal-based graphite. The crystallite size La of the coal residue-based graphite was reduced by 47.06% compared with the raw coal-based graphite. The ID/ IG value of the coal residue-based graphite is smaller than that of the raw coal-based graphite. The specific surface area (16.72 m2/g) and total pore volume (0.0567 m3/g) of the coal residue-based graphite are increased in varying degrees compared with the raw coal-based graphite. This study found a carbon source that can be used to prepare coal-based graphite with high graphitization degree. The results are expected to provide a theoretical basis for further clean and efficient utilization of the coal residue resources.

Low-ash-melting-point bituminous coal and high-ash-melting-point anthracite coal are mixed and burned in different proportions. The ash melting characteristics of blended coal were determined experimentally. At the same time, the ash samples of bituminous coal, anthracite, and blended coal were analyzed by X-ray diffraction (XRD), and the ash melting characteristic improvement mechanism of blended coal was analyzed by quantum chemical calculations. The results show that when high-ash-melting-point anthracite is added, the ash melting characteristics of blended coal are improved, and the deformation temperature, softening temperature, hemispheric temperature, and flow temperature of the blended coal are significantly increased. The melting point of blended coal ash with a bituminous coal ratio of less than 50% can meet the requirements of blast furnace injection. The reason for the improved melting characteristics of the blended coal ash is that mullite in anthracite ash reacts with gehlenite in bituminous coal ash during the combustion process to produce anorthite.

This paper deals with the characterisation of inorganic constitutions generated at various operating conditions in the context of underground coal gasification (UCG). The ex situ small-scale experiments were conducted with coal specimens of different rank, from the South Wales Coalfield, Wales, UK, and Upper Silesian Coal Basin, Poland. The experiments were conducted at various gaseous oxidant ratios (water: oxygen = 1:1 and 2:1), pressures (20 bar and 36 bar) and temperatures (650°C, 750°C and 850°C). Increasing the amount of water in the oxidants proportionately decreased the cationic elements but increased the concentrations of anionic species. The temperature played minor impact, while the high-pressure experiments at temperature optimum to produce methane-rich syngas (750°C) showed significant reduction in cationic element generation. However, both coal specimens produced high amount of anionic species (F, Cl, SO4 and NO3). The “Hard” bituminous coal from Poland produced less gasification residues and condensates than the South Wales anthracitic coal due to its higher reactivity. The inorganic composition found in the solid residue was used in the theoretical calculation to predict the dissolved product concentrations when the solid residue interacts with deep coal seam water in the event of UCG cavity flooding. It was evident from the solubility products of the Cr, Ni and Zn that changes in the groundwater geochemistry occur; hence, their transportation in the subsurface must be studied further. Supplementary Information The online version contains supplementary material available at 10.1007/s11356-021-15780-8.

In this study, co-gasification behaviors and synergistic interaction of bituminous coal and walnut shell under CO2 atmosphere were investigated by using a thermogravimetric analyzer. The evolution of physicochemical properties of samples was characterized with an inductively coupled plasma emission spectrometer, an X-ray fluorescence spectrometer, and an X-ray diffractometer. The results indicated that the addition of walnut shell significantly enhanced the gasification reactivity of coal, and coal/biomass blend ratio of 7:3 showed an intense gasification. Moreover, a significant co-gasification interaction was observed in the char gasification stage and demonstrated that a high coal/biomass blend ratio induced the formation of amorphous carbons and further accelerated the co-gasification reaction. Meanwhile, the active inorganics were severely released as 30 wt% bituminous coal added to walnut shell, causing a deteriorative gasification reactivity. Furthermore, three kinetic models illustrated that the coal/biomass blend ratio of 7:3 required a minimum activation energy to initialize gasification. The findings in this work would be beneficial for revealing the co-gasification mechanism of biomass and coal, and provide a useful basis on their multi-scale applications.

Coalbed methane is a lucrative energy source, but its development relies heavily on the fracturing of coal seam and underground extraction during mining. This study of mining stress paths, pore pressure, and permeability of a coal body was aimed to overcome the constraints of low coal permeability under the stress applied to a coal seam group. Variation in the applied stress changes the effective stress in coal and its permeability (which also depends on pore pressure). The effects of different mining intensities, repetitive cyclic loading and unloading, and pore pressure on gas permeability in a coal mine are revealed and discussed. The permeability evolution curve can be described by quadratic polynomial equations and split into three (decreasing, stable, and increasing) stages. When the stress environment with low axial deviatoric stress changes to that with high axial deviatoric stress and when the stability stage becomes longer, the goodness of quadratic polynomial data fitting is reduced. Cyclic loading and unloading with different axial stress paths have different effects on coal permeability. Increased axial and confining pressures decrease the permeability and pore pressure sensitivity of permeability. Because the obtained permeability-pore pressure curves contain a stable stage, this sensitivity is more pronounce in the low and high pore pressure stages.

Different types of coal have different characteristics and performances. In thermal coal plant, deposition of coal ash inside the furnace causes slag formation inside the boiler rear path and consequently reduces the heat transfer process and boiler efficiency. Besides, accumulation of ash on the boiler tube surfaces form layers of slags and blocks the flue gas flow out of the boiler. Therefore, the purpose of this study is to investigate the relationship between sub-bituminous coal base acid ratio towards the heat transfer process inside large-scale boilers. The base acid ratio for sub-bituminous coal is measured before firing inside large-scale boiler of studied the thermal plant which has a generation capacity of 700 MW. This study found correlation between high furnace rear path temperature (FRPT) that is observed to be above 800℃, with the build up of ash accumulation inside the boiler, for the studied coal. Thus, a high base acid ratio causes the accumulation of coal ash, thus reducing the heat transfer process which results in high FRPT of the boiler. Therefore, it proves that a base acid ratio is an indicator for coal performance during firing inside the boiler.

To deeply explore the spontaneous combustion disaster of coal caused by air leakage and oxygen supply, low-temperature coal oxidation experiments under different oxygen concentrations (DOC) were carried out. Within the coal spontaneous combustion characteristic measurement system, a synchronous thermal analyzer (STA) and a Fourier transform infrared spectrometer (FTIR), the macro laws of gas and heat generation under DOC are analyzed, and the mechanism of the development of coal spontaneous combustion restricted by the lean-oxygen environment is also revealed. The results show that the change of oxygen concentration (OC) does not affect the critical temperature value and gas index change trend, but the lean-oxygen environment reduces the gas concentration and heat production rate very obviously. According to the temperature of the intersection, OC needs to be lowered to less than 5% when preventing spontaneous combustion of coal. The chain thermal reaction lags in the lean-oxygen environment, and the pyrolysis activity is significantly reduced. Meanwhile, the temperature points at T6 and T7 show significant differences. Furthermore, with increasing OC and temperature, the content of the aliphatic hydrocarbon presents an overall trend of first increasing, then decreasing, and continuously increasing after stage IV. It is concluded that •OH, aliphatic hydrocarbons, aromatic hydrocarbons, and carboxyl groups are the key groups for the coal spontaneous combustion evolution under DOC. To combine the spontaneous combustion reaction of coal in the DOC environment, the reaction path of the index gas in the macroscopic phenomenon and the reason for the concentration differences are revealed, the mechanism for exotherm varies caused by OC is clarified, and the microscopic inhibition affection on the chain reaction within the lean-oxygen environment is also explored. The results put forward the key groups evolution mechanism under the DOC for coal oxidation, which could provide the technical guidance for the fire prevention and control on coal mines.

To investigate the influence of basic characteristics of oil shale dust on wet dust removal, oil shales (Longkou oil shales Y1, Y2S2, and Y2S1 and Fushun oil shale) with different oil contents, brown coal (M1), and bituminous coal (M) were selected from a typical mining area in China to test their physiochemical parameters. Their proximate component, chemical structures, surface morphology, and mineral contents were determined. The sedimentation experiments of oil shale dust and coal dust were implemented using three anionic surfactants (AOS, SDS, and SDBS) and a nonionic surfactant (AEO-9), and the wettability of oil shale dust was analyzed and compared with that of coal dust. The experimental results indicate that the moisture content, volatile content, fixed carbon content, and content of oxygen-containing functional groups of oil shale are higher than those of the coal sample; otherwise, contents of ash, SiO2, aliphatic hydrocarbon, and aromatic hydrocarbon are lower. It can be found that oil shale has semiclosed pores, poor connectivity, a small pore size, a large specific surface area, and a rougher surface, which will lead to poorer wettability of oil shale. The wettability of oil shale can be improved by adding surfactants but is still weaker than that of the coal samples. Anionic surfactants are better than nonionic surfactants in improving the wetting performance. Among them, AOS shows strong wetting ability to oil shale dust. The research results of this paper have an important practical significance for analyzing the wettability of oil shale and controlling oil shale dust.

In this paper, conventional thermogravimetric analysis and a new congruent–mass thermogravimetric analysis were used to study the reaction mechanism of the co-pyrolysis process of coal and biomass in the thermogravimetric analyzer, the effects of heating rate and carrier gas flow rate on co-pyrolysis were investigated, and kinetic analysis was conducted for the major pyrolysis stages to explore whether there was a synergistic effect in the co-pyrolysis process. The surface morphology of pyrolytic coke was evaluated by the fractal dimension method. The results show that congruent–mass thermogravimetric analysis can compare the interactions in the co-pyrolysis process more intuitively and reduce the influence of initial mass on the determination of interaction relationship. Synergistic effect appears in co-pyrolysis of coal and biomass. With the increase of heating rate, the thermogravimetric hysteresis appeared and the thermogravimetric curve gradually moved to the high temperature region. With the increase of carrier gas flow rate, the synergistic effect weakens. The kinetics of different reaction stages was analyzed by Coats–Redfern method; the results show that the activation energy required in the main co-pyrolysis stage of the mixture is lower than that in the pyrolysis stage alone. The micromorphology shows that biomass coke has a more developed pore structure than coal, and the box dimension indicates that co-pyrolysis increases the surface irregularity of coke. It is of great significance to judge the interaction mechanism of two or even multiple mixed samples in the process of co-pyrolysis.

Co-gasification of renewable biomass and coal is a promising technique to reduce greenhouse gas emission beside increasing gasification performance instead of individual coal gasification. In this study, the co-gasification performance of pine bark (PB) biomass and Barapukurian bituminous coal (BBC) have been assessed using a high-temperature entrained flow gasifier using CO2 reactant. Results show that increasing biomass concentration increases the carbon conversion, syngas quality and cold gas efficiency (CGE), while reduces emission. For example, an addition of 20% biomass with coal increased the carbon conversion by 21.5, 10.6 and 4.5%-point at temperatures of 1000, 1200 and 1400 °C compared to pure coal gasification. Similarly, increasing biomass ratio in the blend increased the yield of CO by 11–36 vol% under different temperatures. Also, the CGE, fragmentation index ( F I = ∑ i n F D o ) and alkali and alkaline earth minerals in ash were increased with increasing biomass ratio in the blend. Overall, at least 50% of coal can be replaced with renewable biomass considering performance and emission characteristics, making the technology more sustainable.

The filtration and dewatering of fine clean coal not only ensure industrial water recycle in coal washing plant, but also reduce the moisture of coal product in order to meet the requirements of combustion or coking industry. Fine clean coal is mainly composed by organic matter, and the property difference of different organic matter determines the filtration and dewatering behavior. In this investigation, vitrinite and inertinite were separated from a clean bituminous coal, and the comparative filtration and dewatering behavior of vitrinite and inertinite were conducted. The results showed that inertinite has lower dewatering rate and higher filter cake moisture than vitrinite. The analysis of filter cake structure showed that inertinite particle is easier to be broken into small particles due to the difference of mechanical properties, thus forming more compact filter cake than vitrinite. The analysis of particle surface properties showed that vitrinite is more hydrophobic than inertinite, which makes water easier drained from filter cake. The simulation study showed that the structure of inertinite is more porous than that of vitrinite, and the interaction between inertinite and water is stronger than that between vitrinite and water. This study provides a theoretical basis for improving coal dewatering by selectively improving coal maceral hydrophobicity.

Investigations on the molecular composition of coal pyrolysis products can help us to improve nonfuel utilization of coal. Meanwhile, the molecular composition of coal pyrolysis products is also influenced by the characteristics and depositional environment of coal. However, due to the extremely complex nature of coal, direct investigation of the molecular composition of coal pyrolysis products is still a challenge. In the present work, the data of the molecular composition of bituminous coal pyrolysis products are obtained by online pyrolysis coupled to comprehensive two-dimensional gas chromatography and mass spectrometry (online py-GC×GC-MS) and are divided into nine molecular groups depending on the aromaticity of the pyrolysis products and separating power of the GC×GC-MS. Chemometric tools, hierarchical cluster analysis, and principal component analysis are employed to reveal the correlations among the molecular composition of coal pyrolysis products and coal characteristics. The results show that the nine molecular groups of bituminous coal pyrolysis products can be divided into two clusters, the "aromatic group" and the "aliphatic group", and that the eight coals are divided into three clusters, all of which can be interpreted by the depositional environments and δ13CVPDB values of coals. Moreover, a simple and empirical equation for estimation of coal tar from hydropyrolysis can be obtained depending on the chemometric results of the molecular composition of the coal pyrolysis products. By application of chemometrics, the molecular composition of coal pyrolysis products can provide preference to industrial utilization of coal.

The catalytic combustion and non-isothermal kinetics of bituminous coal by CeO2, Fe2O3, and NiO were investigated. The exothermic characteristics during catalytic combustion of bituminous coal were determined. Based on the Coats-Redfern method by introducing the function of kinetics mechanisms, the activation energies and pre-exponential factors of catalytic combustion of bituminous coal were estimated iteratively by regression. It is found that the catalysts promoted the transport of oxygen to the coal or char surface and effectively improved the combustion characteristics of bituminous coal. Under the same experimental conditions, the exothermic values were significantly increased and the catalysts of composite oxides exhibited higher exothermic values than pure metal oxide catalysts. The metal oxides significantly reduced the activation energies of bituminous coal combustion. SEM analysis presented that combustion residues became more porous with the addition of the catalyst.

In order to explore the high-temperature pyrolysis behavior and mechanism, two different rank coals (Shenhua bituminous coal and Baiyinhua lignite coal) were pyrolyzed in fixed-bed and drop tube furnace (DTF) reactors. Pyrolysis gas production was online quantified by a drainage method while the gas composition was detected by the gas chromatography. The physical and chemical characteristics of pyrolysis char were observed by N2 absorption and FTIR. Results show that pyrolysis gas release rate and total production increase with the higher temperature. The gas production of SH coal (618–749 ml/g) is always higher than that of BYH coal (418–510 ml/g) due to its higher volatile content. The main high-temperature pyrolysis gas products are H2 (∼50% vol), CO, CH4 and CO2. Carbon-reduction reaction at high temperatures can further form H2 and CO while the rupture of aromatic heterocyclic ring can generate CH4. High-temperature pyrolysis can greatly remove the coal moisture, develop their pore structures, crack the chemical functional groups (O–H, –CH3, C O, C–O, etc.) and upgrade the coal rank. Different coal structures and pyrolysis heating rates result in various gas evolution and char formation behaviors. Higher heating rate can help to quickly generate large amounts of free radicals and change the pyrolysis behaviors.

Catalytic upgrading of coal pyrolysis gaseous tar is one of the promising techniques for the efficient conversion and utilization of tar. The heavy arene in tar can effectively convert into light arene, such as benzene, toluene, ethylbenzene, xylene and naphthalene (BTEXN). Therefore, a series of acid modified Y-type zeolites were prepared by ammonium exchange method, and the effect of Bronsted acid in zeolite and coal rank on the distribution of tar was investigated in this study. The XRD, N2 adsorption, and pyridine-FTIR analysis results show that the structure of the acid-modified zeolite has not changed, but the content of the medium Bronsted acid changed significantly. The yield of BTEXN produced in the catalytic upgrading of three different rank coal pyrolysis gaseous tar (one is lignite, the other two are bituminous coal) is up to 3.2 times, 2.8 times and 1.7 times that of the raw coal pyrolysis, respectively. The increase in the acidity of medium Bronsted acid greatly contributes to the conversion of heavy arene to BTEXN. For different coal samples, the performance of the catalyst is closely related to its Bronsted acid amount and Bronsted/Lewis ratio. And the textural properties of the zeolite also have an important influence on its catalytic performance.

Distribution of rare earth elements (REEs) in six speciations extracted from coal and coal gangue and their combustion products (slag and fly ash) generated by three different power plants in China were determined by sequential extraction procedure combined with inductively coupled plasma mass spectrometry method. The results show that the REEs mainly occurred as acid soluble and silicate & aluminosilicate fraction, e.g., approximately 42.54% and 45.62% in coal gangue, 32.85% and 57.13% in lignite, and 18.10% and 75.46% in bituminous coal, respectively. However, REEs in the combustion products were mainly presented in silicate & aluminosilicate fraction regardless of coal or coal gangue, reaching up to approximately 80% of the total REEs content. During combustion, around 36%, 23%, and 5% from the other five fractions (water soluble, ion-exchangeable, acid soluble, organic, and sulfide) were transformed to silicate & aluminosilicate fraction from coal gangue, lignite, and bituminous coal, respectively. In the case of coal or coal gangue, the amount of each REEs in the same extracted fraction was different, but the distribution trend of REEs from La to Lu in each fraction was followed in the same rule. In the case of slag and fly ash generated from coal or coal gangue, distribution of REEs from La to Lu in each fraction showed the different trend between fly ash and slag. This was due to the fly ash exposed in flue gas system was much longer than the time for slag formation.

A coal fire is one of the most serious disasters in coal mining. To improve the efficiency of an inert gas for extinguishing the fire, the adsorption behavior of coal in CO2/N2 mixed gas was investigated in this study. Proximate analysis, ultimate analysis, solid-state 13C nuclear magnetic resonance spectroscopy (NMR), X-ray photoelectron spectroscopy (XPS), and molecular dynamics (MD) were applied to analyze and establish the bituminous coal molecular model. The adsorption behavior of bituminous coal in mixed gas mixtures with different proportions was studied using the bituminous coal model and Materials Studio (MS) software. A self-built coal adsorption experimental system was used for experiments. The adsorption of bituminous coal to CO2 is stronger than that to N2, and there is a competitive adsorption relationship between them. The amount of CO2 adsorbed by the coal gradually increases as the CO2 partial pressure rises, consistent with the Langmuir model. With an increase in CO2 pressure, the total adsorption capacity, which is divided into the rapid increase stage, slow growth stage, and stable stage, also increases. The coal adsorbs 0.5050 cm3/g, 0.7455 cm3/g, 0.9450 cm3/g, 1.0715 cm3/g, and 1.2000 cm3/g for pure N2, 2%, 5%, 7%, and 10% CO2, respectively, in the experiment. The results of the simulation and experiment show the same trend, which means that the injection of a small amount of CO2 into pure N2 will greatly improve the gas adsorption volume of the coal, demonstrating that it is feasible to improve the ability of the coal to absorb mixed gases by changing the gas concentration and consequently to increase the efficiency of inert gas for fire extinguishing and suppression.

HN-1# is the first fully working coring well of the Taiyuan Formation (Ty) in the Huinan Coalfield and exploration studies are currently underway on the associated resources of the coal-bearing strata. The HN-1# well is located in the Fufeng thrust nappe structural belt in the south of the Huainan Coalfield. Three coal samples from the Ty were collected from HN-1# and inductively-coupled plasma mass spectrometry and inductively-coupled plasma atomic emission spectrometry were used to determine the Ge content of each sample. Based on proximate and ultimate analyses, microscopy data, and analyses of the ash products, some important findings were made. The Ty coal samples had a relatively high total sulfur (St,d) content (4.24%), thus the coal was considered to be a lower ranked coal (high volatility bituminous coal), which also had a low coal ash composition index (k, 1.87). Collodetrinite was the main submaceral of the Ty coal. Small amounts of pyrite particles were found in the coal seams of the Ty, while the contents of pyrite and algae in the top and bottom sections of the coal seam were relatively high, which meant that the swampy peat conditions which existed during the formation of the coal seams were affected by seawater; also the degree of mineralization of the coal seam was relatively high, which is consistent with reducing conditions in a coastal environment setting. Atomic force microscopy (AFM) experiments showed that the modes of occurrence of Ge in the Ty coal were mainly those for organic-bound and adsorbed Ge species. The organic carbon isotope values for the Ty coal ranged from − 24.1‰ to − 23.8‰, with an average value of − 24.0‰, which is equivalent to the value for terrestrial plants (average value − 24.0‰). The Ge content of the Ty coal was 13.57 mg/kg. The Ge content was negatively correlated with volatile matter and the ash yield.

In this work, the effect of temperature on the pyrolysis products of two typical coal samples, namely, bituminous coal and subbituminous coal, is studied by using a tube furnace with the highest wo...

After exposing dry high-volatile bituminous coal, low-volatile bituminous coal, and anthracite to CO2, we measured the swelling properties of the coal in two pressurization cycles with a maximum pr...

The ignition and combustion behavior of pulverized coal was studied with respect to coal rank in a custom-designed visual drop tube furnace. The results showed that low-rank coals were ignited in a shorter time, mainly due to the presence of larger amounts of functional groups, while the ignition delay time of high-rank coals was longer. With increasing temperature and particle size, the ignition mode of coals shifted from heterogeneous into homogeneous, which was related to the increased yield of volatile matter. The chemical percolation devolatilization analysis results showed a clear relationship between the yield and composition of volatile matter and the amount and type of functional groups in coal. In addition, the tar yield was consistent with the amount of aliphatic hydrocarbons and the length of aliphatic chains, which explained the tailing combustion mode of the bituminous coal. The findings of the study showed that the yield and composition of volatiles in coal had a significant impact on the ignition behavior, which depended on the composition of functional groups, particle size, and the combustion environment.

The CO2/CH4 competitive adsorption behaviors in bituminous coal before and after oxidation are investigated by the density functional theory. It is found that coal oxidation can decrease the adsorp...

In this study, the effect of ash removal on Shenfu bituminous coal was investigated. The coal was pretreated by hydrofluoric acid (HF) pickling, and the raw/pretreated coal chars were prepared at 900 °C in a fixed bed reactor. The structure of coal and char were detected by Fourier transform infrared (FTIR) and Raman spectroscopy. The reactivity was tested in a thermogravimetric analyzer, including coal pyrolysis and char gasification. The reaction kinetics was analyzed through the Coats–Redfern method, master plots, the model-free and model-fitting method. The results show that the HF pickling can remove silicon from coal efficiently, and the macromolecular framework of coal is quite stable according to FTIR. The Raman parameters imply some carbonaceous structure on coal surface changed. For slow pyrolysis of coal, the effect of heating rate is considered. The changes of pyrolysis characteristics and kinetics are insignificant. For char gasification, the reactivity under isothermal and non-isothermal condition are discussed with an emphasis in different residence time of devolatilization process. In kinetic control region (low temperature), the activation energy (Ea) is very close (about 240 kJ/mol) for all chars. With the temperature increases, the reactivity of raw coal char is more easily suffered by diffusion. The random pore model is more suitable for the ash-free coal char, and the char with long residence time has a larger value of structural parameter ψ and smaller value of pre-exponential factor A. The Ea calculated by model-fitting and model-free method were in good agreement.

Supercritical water partial oxidation (SCWPO) is a clean and efficient coal conversion method to produce H2. However, the detailed SCWPO mechanism of coal is still unknown at present. In this paper, a lumped kinetic model is used to propose a non-catalytic SCWPO mechanism of coal. The results show that oxidation reaction of intermediate carbon is under diffusion control. Bituminous coal is harder to be gasified than lignite, due to the denser structure of bituminous coal. CH4 is produced only from coal pyrolysis, and it is negligible for steam reforming of CH4 without catalyst. The ash in coal plays a certain catalysis on water-gas shift reaction. The proposed mechanism provides important insights in SCWPO process of coal.

The catalytic steam gasification of Yanzhou (YZ) bituminous coal char loading with K2CO3 and CaO was studied in a fixed bed with 20 mm in inner diameter. The influence of K2CO3 on caking properties of Yanzhou bituminous coal was investigated. The relationship between carbon conversion and reaction time and catalyst loading amount of Yanzhou coal char was measured from 700 to 850°C. The effects of reaction temperature and catalyst loading amount on molar yield of the gasification gas were studied. The influence of catalyst on the microstructure of the YZ coal char was determined. The results show that K2CO3 had significant effects of caking destruction and catalytic gasification on YZ coal. The carbon conversion of YZ coal char increased with the increase of gasification temperature and K2CO3 loading amount. The addition of CaO could improve the carbon conversion of char and promoted the generation of gasification gas to some extent. The molar yield of gasification gas increased with the increase of gasification temperature, and H2 increased the most. The 002 peak of YZ coal char became lower and wider, and moved towards the lower position with the addition of K2CO3 and thus decrease the graphitization trend.

Three different ranks of Chinese coals were investigated on the thermal conductivity and corresponding molecular structure by thermal analyzer, 13C NMR, and HRTEM techniques. The thermal conductivity of coals measured in room temperature first shows a decrease, then a slight increase, and finally a sharp increase with increasing coalification. Ranging from 30 to 150 °C, increasing the temperature slightly improves the thermal conductivity of coals with varying degrees. Water with a higher thermal conductivity than air contributes to the thermal conductivity of porous coal samples. The value of thermal conductivity is higher along coal bedding planes than when perpendicular to beddings, which indicates the anisotropy of coal thermal conductivity. The anisotropy degree increases with the rank of coals and is affected by clay minerals when coals adsorb water. Molecular structure analysis shows that polycondensed aromatic ring related to lattice vibration contributes to the increase of thermal conductivity. The aliphatic bridges among aromatic clusters ensure the continuity of atom vibrations and contribute to energy transport, but the free-ended side chains have the opposite effect. The relative ordered distributions of lattice fringes of anthracite, which were higher than those of bituminous coal, enhance the anisotropy of thermal conductivity.

The U.S. Geological Survey (USGS) determined the physical and chemical properties of more than 260 feed coal and coal combustion byproducts from two coal-fired power plants. These plants utilized a low-sulfur (0.23-0.47 wt. % S) and low ash (4.9-6.3 wt. % ash) subbituminous coal from the Wyodak-Anderson coal zone in the Tongue River Member of the Paleocene Fort Union Formation, Powder River Basin, Wyoming. Fifty-three samples of bituminous coal were collected and analyzed from a Kentucky power plant, which used several sources of bituminous coals from the Appalachian and Illinois Basins. Based on scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses of feed coal samples collected and analyzed from 1996 through the late 2000s, two mineral suites were identified: (1) a primary or detrital suite consisting of quartz (including beta-form grains), biotite, feldspar, and minor zircon; and (2) a secondary authigenic mineral suite containing alumino-phosphates (crandallite and gorceixite), kaolinite, carbonates (calcite and dolomite), quartz, anatase, barite, and pyrite. The detrital mineral suite is interpreted, in part, to be of volcanic origin, whereas the authigenic mineral suite is interpreted, in part, to be the result of the alteration of the volcanic minerals. The mineral suites have contributed to the higher amounts of barium, calcium, magnesium, phosphorus, sodium, strontium, and titanium in the Powder River Basin feed coals in comparison to eastern US coals. XRD analysis indicates that (1) fly ash is mostly aluminate glass, perovskite, lime, gehlenite, quartz, and phosphates with minor amounts of periclase, anhydrite, hematite, and spinel group minerals; and (2) bottom ash is predominantly quartz, plagioclase (albite and anorthite), pyroxene (augite and fassaite), rhodonite, and akermanite, and spinel group minerals. Microprobe and SEM analyses of fly ash samples revealed quartz, zircon, and monazite, euhedral laths of corundum with merrillite, hematite, dendritic spinels/ferrites, wollastonite, and periclase. The abundant calcium and magnesium mineral phases in the fly ash are attributed to the alteration of carbonate, clay, and phosphate minerals in the feed coal during combustion. The calcium- and magnesium-rich and alumino-phosphate mineral phases in the coal combustion byproducts can be attributed to volcanic minerals deposited in peat-forming mires. Dissolution and alteration of these detrital volcanic minerals occurred either in the peat-forming stage or during coalification and diagenesis, resulting in the authigenic mineral suite. The presence of free lime (CaO) in fly ash produced from Wyodak-Anderson coal acts as a self-contained “scrubber” for SO3, where CaO + SO3 form anhydrite either during combustion or in the upper parts of the boiler. Considering the high lime content in the fly ash and the resulting hydration reactions after its contact with water, there is little evidence that major amounts of leachable metals are mobilized in the disposal or utilization of this fly ash.

The solvolytic conversion of softening bituminous coal at 380 °C in solvents derived from the commercial hydrocarbon byproducts and residues from coal and petroleum processing was studied. Hydrogen-donor tetrahydronaphthalene (THN) and nondonor 1-methylnaphthalene (MN) were also used for comparison. The high-boiling solvents of different chemical classes (highly aromatic coal tar, its anthracene fraction, and low-aromatic heavy gas oil of catalytic cracking of the oil residue) and the H-donor THN solvent were found to exhibit high efficiency for coal conversion into quinoline-soluble products. The chemical and molecular compositions of coal, solvents, and dissolved products were characterized in detail by different techniques, including chemical analysis, group analysis, infrared Fourier transform (IRFT) spectroscopy, X-ray diffraction (XRD), liquid chromatography, and thermal analysis to reveal the chemical transformations of the coal–solvent mixture during the dissolution reaction. The solvolysis of coal in the liquid phase of both highly aromatic and low-aromatic solvents was found to involve selective depolymerization of polymer-like coal via breaking of weak linkages between the aromatic units, resulting in the formation of soluble pitchlike products. The effective dissolution of coal in the H-donor THN solvent resulted probably from a combination of the nonselective thermal fragmentation of the coal structure to smaller radical intermediates and their stabilization by hydrogen from THN, producing mainly tar and a few gases. The low-boiling solvents of both predominantly aromatic and aliphatic classes (gas oils from naphtha pyrolysis and delayed coking of the petroleum residue) and MN exhibited poor efficiency for coal dissolution. The concentrations of carcinogenic benzo(a)pyrene (BaP) in the solvents used and in the toluene fractions of the resulting extracts were analyzed. The remarkable result was that coal extracts, compared to solvents, contained much less BaP, probably due to its conversion with coal and/or solvent molecules during coal dissolution.

During the underground coal gasification process, due to the particularity of the gasification channel, a large amount of coal pyrolysis will occur in the coal seam. By studying the characteristics...

In order to investigate the effect of aliphatics in coal on the formation of light aromatics (benzene, toluene, ethylbenzene, xylene and naphthalene, called BTEXN) from coal pyrolysis and catalytic upgrading using on-line Py-GC/MS, n-hexane was used to extract Shengli lignite (SL) and Pingshuo bituminous coal (PS). The extracts of the two coals (SLE and PSE) were analyzed by GC × GC-MS. Results show that aliphatics account for 85% of SLE and 68% of PSE. It brings about that the total yields of BTEXN from SL residue and PS residue pyrolysis are decreased by 29% and 18% compared with raw coals. This is because the aliphatics could provide small-molecule free radicals to stabilize the light aromatic cracking fragments and promote the formation of BTEXN during pyrolysis. The amounts of the alkyl benzene series, phenols, and polycyclic aromatic hydrocarbons from pyrolysis gaseous tar are significantly increased after extraction and they will undergo catalytic cracking to form BTEXN over USY zeolite, resulting in that the total yield of BTEXN from residue is almost same as that from raw coal during catalytic upgrading.

To study the explosion characteristics of coal dust samples with different metamorphism, 19 coal samples including anthracite, bituminous coal, lignite were selected, explosion pressure distributio...

The pore and microcrystalline structure of coal are studied by combining field emission-scanning electron microscopy (FE-SEM), nuclear magnetic resonance (NMR), and Raman spectroscopy to better understand the physicochemical evolution of bituminous coal treated by high-voltage electric pulses (HVEP) under different capacitance conditions. Experimental results show that the capacitance has no significant impact on the breakdown voltage of the coal body during HVEP treatment. However, increasing the capacitance can effectively increase the porosity of coal cores. In particular, the influence of increasing the capacitance on the macropores is obviously more significant than that on the micropore; besides, increasing the capacitance improved connectivity between the mesopores and macropores. In addition, following HVEP treatment, the microcrystalline defect of coal became smaller and pore arrangement more orderly. Thus, the larger the capacitance is, the more is the energy injected into the coal and the more obvious the change of the coal microcrystalline structure.

In pulverized coal particle combustion, part of the ash forms the ash film and exerts an inhibitory influence on combustion by impeding the diffusion of oxygen to the encapsulated char core, while part of the ash diffuses toward the char core. Despite the considerable ash effects on combustion, the fraction of ash film still remains unclear. However, the research of the properties of cenospheres can be an appropriate choice for the fraction determination, being aware that the formation of cenospheres is based on the model of coal particles with the visco-plastic ash film and a solid core. The fraction of ash film X is the ratio of the measuring mass of ash film and the total ash in coal particle. In this paper, the Huangling bituminous coal with different sizes was burnt in a drop-tube furnace at 1273, 1473, and 1673 K with air as oxidizer. A scanning electron microscope (SEM) and cross-section analysis have been used to study the geometry of the collected cenospheres and the effects of combustion parameters on the fraction of ash film. The results show that the ash film fraction increases with increasing temperature and carbon conversion ratio but decreases with larger sizes of coal particles. The high fraction of ash film provides a reasonable explanation for the extinction event at the late burnout stage. The varied values of ash film fractions under different conditions during the dynamic combustion process are necessary for further development of kinetic models.

The catalytic behavior of alkali vapor on unburned pulverized coal (UPC) prepared from bituminous coal, anthracite, semi coke and coke have been investigated. Experiment results show that the alkali metal vapor has catalytic effect on the gasification reaction of UPC. The catalytic effect of coke UPC is the most obvious, followed by anthracite UPC and bituminous coal UPC. Semi coke UPC is the least catalyzed by alkali metals but its gasification reactivity is the best. As the concentration of alkali metal vapor increases, the alkali metal content adsorbed by UPC increases, and there may be a phenomenon of saturated adsorption. The amount of alkali metal adsorbed is between 2% and 6%. AUPC has the highest ability to adsorb alkali metals, and SUPC is the weakest, which may be related to the minerals (CaO, Al2O3) in the coal ash. Changes in stomatal parameters are not the main factors affecting the catalytic effect. The results of X-ray diffraction experiments show that alkali metal aluminosilicate exists in the ash of coal after adsorption of alkali metal, and the average stack height of carbon atoms decreases significantly. The alkali metal catalytic gasification reaction is mainly achieved by destroying the carbon basic structural unit. The alkali metal nepheline and the interlayer compound may be the main catalytic substances, and the destructive ability of alkali intercalation is obviously stronger than that of alkali nepheline. The catalytic mechanism of alkali metals on unburned coal and the destruction mechanism of alkali metals on carbon crystals were discussed. It can provide reference for reducing alkali metal corrosion on coke and improving pulverized coal utilization rate.

To localize coal utilization, a local Hongshagang bituminous coal (Hc) with low ash fusion temperatures (AFTs) was blended with the Guanghui bituminous coal (Gc). Prior to its application in an ind...

Supercritical CO2 (sCO2) dewaters coal through two mechanisms. For bituminous coal of 9.5% average moisture content the water is dissolved out of the coal and the concentration of water in the bulk...

s Amorphous calcium lignosulphonate (CaLS), a by-product of the paper industry, was evaluated as an adhesive to bind demineralised bituminous coal fines in various weight percentage ratios. Sequential acid (HCl, HF, HCl) leaching was used to reduce mineral matter content in the coal fines. The pyrolysis and gasification of the samples were investigated in laboratory-scale experiments to determine the effect of the CaLS addition on the pyrolysis and gasification reactivities. Coal-CaLS blends consisting of 5, 10, and 15% calcium lignosulphonate were prepared, compressed into pellets, and characterised using proximate, X-ray diffraction, and X-ray fluorescence analyses. An increase in binder concentration increases the mechanical strength of the pellets due to the increased interparticle contact area. The relative coal gasification reaction reactivity (1/Tmax and 0.5/T50), which was determined from the derivative thermogravimetry curves, increases with CaLS addition. The experimental results revealed that these wastes (coal fines and calcium lignosulphonate) could be utilised in thermochemical processes. Utilising these wastes will reduce the environmentally unfriendly volumes of amorphous calcium lignosulphonate and coal fines particles.

The air-staged combustion experiments of lean coal, bituminous coal, and their blends were performed in a one-dimensional coal combustion experimental furnace. The influences of excess air coeffici...

The object of research is the processes of thermal conversion of steam coal and biomass, with the aim of creating highly efficient environmentally friendly technologies for its joint combustion into fuel boiler units. One of the important problems that impede the introduction of co-combustion of biomass with coal is the insufficient knowledge of the interaction of two very different solid fuels. The characteristics of grinding, particle aerodynamics, kinetics of all stages of combustion during the joint combustion of two solid fuels remain unexplored. Co-combustion of biomass with coal allows partially replacing scarce grades of steam coal, as well as reducing emissions of harmful gases and dust. To study the peculiarities of co-combustion of coal and biomass, experimental and computational research methods are used, including combustion in a continuous installation designed to study the combustion characteristics of pulverized fuels. Experiments on the combined combustion of lean and bituminouscoal with various types of solid biomass showed an improvement in the ignition conditions of coal, with the addition of biomass from 5 to 15 % by heat. The effect of biomass impurities on coal on the temperature distribution along the length of the plume is shown. The paper presents the dependences of the conversion degree of bituminous coal and its blends with crushed pellets of pine, wheat straw and sunflower husk, and also explains the nature of this dependence. The gas analysis of the combustion products shows the effect of biomass blending in bituminous coals on the formation of nitrogen oxides. The findings and dependencies justify the environmental feasibility and efficiency of co-combustion and allow to proceed to the development of a pilot project for partial replacement of coal with various types of solid biofuel.

Coal and coal-shale undergo low-temperature oxidation when exposed to air, potentially leading to spontaneous combustion. Coal-shale found in association with coal seams vary considerably in their intrinsic properties and spontaneous combustion liability index. Fourteen coal-shale samples collected from four different coal mines in Witbank Coalfield, South Africa, were experimentally investigated. The influence of coal-shale intrinsic properties and spontaneous combustion liability indices (determined by the Wits-Ehac Index and the Wits-CT Index) were established. The liability indices indicate relationships with the intrinsic factors and thus, identifying the major intrinsic factors affecting liability toward spontaneous combustion in these coal-shale samples. The XRF analysis indicated that the coal-shale samples are rich in SiO2, Al2O3 and Fe2O3, while the XRD showed that same coal-shale samples are generally dominated with kaolinite and quartz. The coal-shale occurred in association with medium Rank C bituminous coal and contained varying proportion of macerals. The Wits-Ehac Index was unable to reliably determine liability indices of some coal-shale samples, and hence the Wits-CT Index was developed. The results obtained from the characterisation tests may be used as a tool to predict the spontaneous combustion liability in carbonaceous material and may serve as a reference when comparing coal-shale from different coal mines. Keywords: Wits-Ehac Index, Wits-CT Index, Witbank Coalfield and self-heating

Recovery of rare earth elements (REE) from coal-related resources has recently received significant interest due to supply concerns and their key roles in critical industries and defense-related technologies. An integrated flowsheet consisting of sorting, crushing/grinding, physical separation, acid leaching, solvent extraction, and selective precipitation was designed to achieve continuous production of rare earth products from various coal-related resources such as coarse refuse and acid mine drainage. A pilot plant was constructed that enabled continuous testing of the circuitry on a range of different coal-based feedstocks. Despite achieving significant success in producing high-grade rare earth oxide products, low REE recovery values and high operational costs necessitated a re-evaluation of the process flowsheet. This article describes the circuitry improvements that were based on both laboratory and pilot plant test results. Roasting as a pre-leach treatment was found to significantly improve the leaching rate and overall REE recovery values. After roasting West Kentucky No. 13 and Fire Clay coal refuse materials at 600 °C, REE recovery increased by 60 and 40 absolute percentage points, respectively. Rare earth concentration in the pregnant leachate solution (PLS) was increased to around 700 ppm prior to solvent extraction using a staged precipitation method. REEs in the precipitate were re-dissolved, purified, and extracted from the PLS using solvent extraction and selective precipitation to values of around 80%. As a result of the improvements, chemical consumption in the acid leaching and solvent extraction processes was significantly reduced. A techno-economical assessment of the improved flowsheet indicated significant commercialization potential.

Outburst prevention and control measures such as protective seam mining and coal seam gas pre-drainage can cause low-temperature oxidation of coal seam, and there is a lack of research on the changes in coal quality characteristics and outburst comprehensive index during low-temperature oxidation. In this paper, the changes of coal quality characteristic indexes during oxidation of coals with different metamorphic degrees, the initial gas emission velocity and the firmness coefficient were measured, the influence of coal quality characteristics on outburst comprehensive index is studied, and the change of outburst comprehensive index K = Δ p f in the low-temperature oxidation process was analyzed. The results show that for coal with different metamorphic degrees, the coal with a lower metamorphic degree enters the stage of inherent moisture evaporation later and is more likely to undergo decomposition and volatilization of volatile matters. In the midterm of low-temperature oxidation (120–160 °C), the growth rates of △p values and the decline rates of f values of coal samples with higher metamorphic degrees tend to decrease. It can be known that the K value of bituminous coal and anthracite are more than 25 during the whole oxidation heating stage, which shows a serious outburst risk. For these coals, effective outburst prevention measures must be taken to prevent outburst risk and inhibit coal spontaneous combustion. In contrast, for lignite coal, the growth rate of △p value and the decline rate of f value keep increasing in the midterm of low-temperature oxidation, due to the joint action of moisture evaporation and volatile decomposition and volatilization. The K value of Lignite is more than 15 when oxidation temperature rises to 150 °C, which shows a general outburst danger. According to the analysis results in the midterm, appropriate measures must be taken to inhibit coal oxidation when local or overall temperature of coal seam reaches 130 °C.

To improve the ability of water spray additives to wet coal dust, the compounding wetting characteristics of several nonionic and anionic surfactants on bituminous coal dust were studied, the surface tension, contact angle and the settling time of coal dust were measured. Results showed that the compounding of sodium dodecyl sulfate (SDS) and two other anionic surfactants exhibits an antagonism effect and reduces the wettability of water. The compounding of primary alcobol ethoxylate (JFC), ethylene glycol polyoxyethylene ether (PEG800) and the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) achieves the strongest synergistic effect at a mass ratio of 3:1:1. Furthermore, the infrared spectra of raw coal and coal treated with dust suppressant showed that the hydrophilicity of coal dust is improved after the treatment by dust suppressant. Finally, the synergistic effect mechanism of JFC, PEG800 and SDBS was explained from the perspective of molecular and hydrogen bond.

Cement clinker production in Egypt till 2013 relied mainly on fossil fuel as a primary energy source. However, with multiple fossil fuel shortages, the utilization of biomass wastes was initiated by multiple cement producers. In the current work, and to present an industrial-scale biomass and coal co-combustion study, the utilization of multiple biomass fuels to substitute a portion of bituminous coal was studied in an Egyptian clinker production plant. Mixtures of biomass fuels were used to reduce the consumption of bituminous coal and to investigate the diminishing of the environmental impact of the clinker production process. The current study was conducted during 8 days of the stable clinker production process by replacing 14% of bituminous coal with biomass mixtures while monitoring the major process control parameters and resulting emissions. Emission results were compared to the nation’s regulations. A conclusion can be made that using biomass mixtures as alternative fuels minimized the dependency on coal as the main fuel and reduced the CO2 burden of the cement production process. In addition, NOx and SO2 emissions were declined while CO emissions were increased by utilizing biomass mixtures as alternative fuels; all emissions, however, were below the allowable limits stated by the Egyptian environmental authority. Noticeably, the heavy elements, dioxins, and furans were not changed significantly compared to those produced using coal only.

Higher ranked Permian and Cenozoic coals are reported in tectonically affected regions of northeast India. The geochemical signature of the tectonically induced higher-ranked coals has not been studied carefully, although such coals' hydrocarbon potential is assessed using parameters, such as kerogen maturity. Notably, published data of stable isotope ratio of organic carbon (δ13C) analysis in Indian coal is rare, and only a few researchers attempted to study the δ13C signature of tectonically affected coals. We have studied the δ13C and kerogen maturity parameters in the Permian sub-bituminous coal from Arunachal Pradesh, Permian Anthracite from Sikkim, Late Oligocene bituminous coal from Tirap and Ledo Open Cast Projects in Assam, Eocene lignites from Umarsar, Matanomadh and Panandhro and Upper Eocene to Oligocene lignite from the Tadkeshwar lignite mines in Gujarat, and Mio-Pliocene lignite from Neyveli lignite mine in Tamil Nadu. The results are compared with the published data to understand the tectonic effect on the kerogen character and δ13C signature of coal. Cenozoic lignites, not affected by thrusting, are mainly composed of mixed type-II to III (oil–gas prone) and/or type-III kerogen (gas prone). Low Tmax (maximum pyrolysis temperature) values of the lignites further indicate the thermally immature character of the kerogen. In contrast, tectonically affected Cenozoic sub-bituminous coals show higher maturity of kerogen. Permian coals, affected by the shear stress of the Main Boundary Thrust (MBT), show type-IV (inert) and post-mature character of kerogen. The study reflects that tectonic activities strongly influence kerogen maturity. Enriched δ13C values of Permian coals compared to the younger Cenozoic coals are attributed to the enrichment of the heavier carbon isotope during coalification. Tectonically driven alteration of coal is evidenced by the enriched δ13C values of the thrust-affected coals. Nonetheless, an overall C3 plant source of the coal organic matter irrespective of the age, rank and tectonic history is reflected by the δ13C values (–21‰ to –27‰). The stable isotope composition further assigns an angiosperm source to the Cenozoic coals and a gymnosperm source to the Permian coals. The results indicate that kerogen maturity and δ13C of coal reflect the influence of tectonic activities, although the stable isotope source signature of coal remains unaffected.