Coal Samples Research Articles

The employment of domain adaptation strategy for improving the applicability of neural network-based coke quality prediction for smart cokemaking process

Precise coke quality prediction is essential for coke production process optimization to achieve the reduction in energy consumption and CO2 emissions, thus moving toward carbon neutrality in the coking industry. However, the complexity of coal molecular structures and the chemical reactions in the cokemaking process pose significant challenges to the applicability of existing coke quality prediction models. Based on the recently widely employed Artificial Neural Network (ANN) method, this study is the first to introduce domain adaptation strategies for improving the applicability of ANN in predicting coke quality including Coke Strength after Reaction (CSR) and Coke Reactivity Index (CRI). 649 Chinese coal samples with properties including Mad, Ad, Vdaf, St,d, G, X and Y along with coke quality were collected. They were initially categorized into source and target domains characterized by different distributions. Subsequently, two scenarios were independently evaluated based on coal samples in the target domain, which either lacked any information or contained partial information of actual coke quality. The results suggested that the proposed approach can significantly enhance the predictive performance for coal samples across various distributions. Moreover, a comprehensive investigation was also conducted to determine key factors influencing the effectiveness of coke quality prediction with this approach.

Research on the dynamic tensile characteristics and surface crack evolution of coal under impact loading

The tensile properties of coal under dynamic loading are important mechanical characteristics of coal and are highly important for controlling coal rock stability under impact loading conditions, selecting blasting engineering parameters, and studying the mechanism of rockburst disasters. To investigate the dynamic tensile failure process of coal subjected to impact loading, this study used high-speed photography and digital image correlation technology to capture the dynamic tensile failure of coal under impact loading. The dynamic tensile evolution was quantitatively analyzed from the beginning of coal sample being loaded to failure. The captured images of the coal were processed, and the fractal dimension was used to quantitatively describe the evolution of the coal surface cracks under impact loading. The following conclusions were drawn from the experimental results: (1) An empirical formula was established to describe the dynamic tensile strength characteristics of coal under different loading rates. (2) Under impact loading, the maximum strain of a Brazilian disc coal sample first appeared at the contact end between the sample and the incident rod. (3) Under impact loading, a Brazilian disc coal sample cracked from the center of the sample outward, and the crack subsequently extended toward both ends. The fractal dimension of the crack exhibited a power function relationship with time, and the variation range of the fractal dimension of the crack was 1.05–1.39.

Characterizing coal gas reservoirs: A multiparametric evaluation based on geological and geophysical methods

The gas content of coal seams is a key parameter to guide the development of coalbed methane (CBM). While most studies focused on geological features, geophysical methods provide a powerful tool for the analysis of the differential distribution of CBM. In this paper, we present a comprehensive model for the quantitative evaluation of gas content in coal seams based on the computation of multiple parameters including lithology coefficient, deformation coefficient, and ash content. Based on the results of industrial analysis and isothermal adsorption tests of 135 coal samples, logging data of 76 CBM wells, as well as 10 2D seismic lines, a geophysical evaluation method of lithology inversion, structural curvature calculation, and ash content identification was established. Our study reveals the differential distribution characteristics of gas content in coal seams under the coupling effect of the three parameters. The results from this method were applied in the southeastern margin area of the Ordos Basin where 5# coal seam with sandstone and mudstone is interbedded as the roof and floor, and the mudstone in the roof contributes more to the sealing ability of surrounding rock. For the 8# coal seam with stabilized limestone and thinly interbedded mudstones as the roof, the limestone contributes most to the sealing ability. The sealing ability of surrounding rock is poorer in the area with large sandstone content in the roof and floor of coal seams and large structural curvature. The lithological combination of the 5# coal seam is the most critical gas controlling factor, whereas deformation coefficient is found to be least significant. However, for the 8# coal seam with little change in the lithology of the roof, the effect of deformation coefficient on gas content increases, and the adsorption capacity is the most important factor influencing the differential distribution of CBM.

Construction of a three-dimensional energy-stabilized macromolecular model of Daliuta coal and investigation of the influence of weak interactions on wettability: Dust pollution prevention and control

Understanding the molecular structure of coal is crucial for gaining insights into the wetting mechanism of coal dust, thus enabling the precise and efficient management of coal dust. After determining the structural information and functional group composition of the coal samples, we continuously adjusted the positions of the groups and the linkages to construct a planar molecular model. Our findings indicate that the Daliuta coal molecule is primarily composed of aromatic carbons, with aliphatic carbons existing in branched form or linked to aromatic rings. The main type of oxygen is carbonyl oxygen, and the molecular formula for Daliuta coal was determined to be C286H263N3O50S. We optimized and annealed the molecular model geometrically, causing the aliphatic bonds in the molecule to undergo numerous deflections and folds, whereas the aromatic structure tended to arrange itself in a laminar pattern due to van der Waals interactions. Given the large number of oxygen-containing functional groups, the electrostatic potential energy contributes significantly to the non-bonding energy, ensuring the stability of the structure. Finally, we obtained the global energy-minimum three-dimensional macromolecular model, establishing the polymerized structure of the coal molecule with a density of 1180 kg/m3. Additionally, we quantitatively analyzed the region of weak interactions between the electrostatic potential on the surface of the coal at the molecular and intramolecular levels. This analysis helped elucidate potential adsorption sites, providing theoretical guidance for modeling the targeted preparation of a spraying dust-reducing agent suitable for this type of coal.

Time-varying characteristics of acoustic emission and fractals based on information dimension during structural failure of coal subjected to uniaxial compression

Uniaxial compression experiments were conducted on coal samples with different initial damage degrees, and the acoustic emission (AE) signals of the whole deformation and destruction process were captured synchronously. The distribution patterns of the acoustic emission signals at different loading stages were discussed. The chaotic system was introduced to process the acoustic emission series. The results indicate that the acoustic emission responses of coal samples with different damage levels had obvious stage characteristics during the whole destruction process. According to the information dimension fitting curves, the coal samples had good fractal characteristics in the whole loading process, and the value of information dimension decreased with the increased of threshold value.The information dimension of the acoustic emission energy signals showed a dynamic evolution law of “increase-decrease-increase” with time, and the rapid decreased of the information dimension could be used as a stable and effective precursor for predicting the macro-damage of coal.

Strength and Deformation of Pillars during Mining in the Shaft Pillar

This study of the strength and deformation of coal samples was triggered by the need to define the stress–strain characteristics of pillars during room and pillar mining in the shaft protective pillar at the ČSM Mine. It was probably the world’s deepest deployment of this mining method in a coal mine. In order to solve the bearing capacity of pillars, the dependence of coal strength on the slenderness ratio is used. For this reason, coal samples with different slenderness ratios were investigated. After considering the purpose of this research, slenderness ratios (width/height) of 1 to 7.7 were chosen. At the same time, the modulus of deformation as a function of the slenderness ratio was determined, and the vertical deformation of the pillars and the safety factor were calculated. Attention is also paid to the influence of sampling on the results of measured coal strengths.

Effect of size and anisotropy on fracture process zone of coal: An experiment and numerical simulation

The size and properties of the fracture process zone (FPZ) have a significant impact on the fracture toughness of materials. Researching and understanding the characteristics of FPZ contribute to optimizing material performance and enhancing the reliability of engineering structures. In this study, the newly proposed modified semi circular bending (SCB) test method was used to carry out the pure mode I fracture test of coal samples with four sizes and four bedding angles, the development process of FPZ was obtained by using digital image correlation method, and the cohesive zone model considering the bedding plane was established. The influence of size and anisotropy on the development and size of FPZ was studied, and the influence mechanism of FPZ on the size effect and anisotropy of fracture toughness was revealed. The results show that the FPZ length of coal has obvious size effect and anisotropy. The FPZ length increases with the increasing specimen size, and increases first and then decreases with the increasing bedding angle. The FPZ relative length decreases with increasing specimen size, indicating that as the specimen size increases, the influence of specimen boundaries on PFZ gradually decreases, and the size effect of fracture toughness also gradually weakens. The competition between microcrack development driven by principal stress and microcrack development driven by bedding plane results in anisotropy in the development process of FPZ. The anisotropy of FPZ development process results in the anisotropy of FPZ length, fracture toughness and crack propagation path. The research findings can provide valuable guidance for the design of hydraulic fracturing in coal seams.

Analysis of mechanical response mechanism and energy evolution characteristics of saturated coal with a single pre-existing hole

It is essential to elucidate the mechanical mechanism of water injection and large-diameter drilling pressure relief measures on coal rock deformation and failure. This helps coal mines adopt more precise and effective dynamic disaster prevention and control measures. To obtain the mechanical response mechanism and energy evolution characteristics of saturated coal with a single pre-existing hole, uniaxial compression tests was carried out, and the deformation and failure process of coal samples were monitored by high-speed camera and acoustic emission monitoring systems. It is found that water saturation, single pre-existing hole measures, and their coupling effect resulted in a deterioration in the coal sample's strength by approximately 23.49%, 9.47%, and 47.95% respectively. The final failure mode of coal samples with different measures is shear failure. The law of fracture development and expansion and energy accumulation and release in different coal samples is roughly the same, the speed of energy accumulation and release in different stages is different. Water saturation and single pre-existing hole measures can affect the impact risk of coal samples, and water saturation can significantly reduce the impact tendency of coal samples, and reduce the impact energy index of complete coal samples by 56.59%. The impact tendency index of natural coal sample is slightly increased by single pre-existing hole measure, and the impact energy index of intact coal sample is reduced by 46.78% by the coupling of the two measures. These findings can provide technical support for coal mine power disaster prevention and control.

Investigation on the Tea Polyphenol/Swelling Gels to Inhibit Coal Spontaneous Combustion: An Experimental Study

ABSTRACT Developing new fire-fighting material is most significant for effective prevention and control of coal spontaneous combustion. To enhance the flame-retardant performance of the gel, the tea polyphenol/swelling gels are developed using a water-soluble polymerization method. Thermogravimetric analysis, programmed temperature experiments, and Fourier-transform infrared spectroscopy are used to reveal the structural characteristics, microscopic morphology, and thermal stability of the gel. Experimental testing the tea polyphenol/swelling gels’ water absorption, water retention, and reusability as well as their inhibitory effect on coal spontaneous combustion. The results showed that the prepared tea polyphenol/swelling gels exhibited a porous three-dimensional network structure, with a maximum swelling ratio of 607.2 g/g and a salt absorption rate of 121.4 g/g. After the testing coal sample is treating by the tea polyphenol/swelling gels, its CO production rate is sharply decreased, but the corresponding ignition point temperature and flame-retardant rate are significantly increased. The activation energy in the first stage is increased by 32.2 kJ·mol−1, in the second stage by 4.0 kJ·mol−1, and in the third stage by 23.2 kJ·mol−1. Additionally, the active functional groups such as hydroxyl and methyl in the coal are also reduced by the treatment of tea polyphenol/swelling gels. Correlation analysis indicate that the inhibition effect of coal spontaneous combustion can be achieved by reducing -OH, CH3/CH2 groups, while the increasing of C = C, C- O, C- H functional groups in the coal. Moreover, the tea polyphenol/swelling gels performing the characteristics of excellent water absorption, inhibiting coal spontaneous combustion by absorbing heat, covering the coal microstructure, and inhibiting the oxidative activity of coal molecules. This study can provide theoretical guidance for the application of swelling gels in inhibiting coal spontaneous combustion.

Research on the Influence of Temperature on the Assessment of Coal and Gas Outburst Dynamic Risk in Deep Mining

To ensure the sustainable development of energy supply, there is a continuous increase in demand for deep coal mining, making safe and efficient extraction a crucial area of research. However, with the increasing depth, rising ground temperatures pose new challenges for safe and sustainable mining operations. Among these challenges, coal and gas outburst dynamic hazards stand out as significant issues. Therefore, it is necessary to assess the impact of temperature variations on coal and gas outburst disaster prevention and control. To investigate this effect, we conducted an analysis based on outburst-triggering mechanisms and adsorption–desorption processes. Temperature was considered as the primary controlled variable, while gas expansion energy served as the criterion for assessing outburst hazards. Kilometer-deep coal samples were selected for measurement, focusing on indicators such as Langmuir adsorption constants (a,b), gas content (Q), gas pressure (P) and drilling cutting desorption indices (K1, Δh2). The results indicate that, under the same gas pressure, there is a slight decreasing trend in gas expansion energy with increasing temperature, although the overall change is minimal. Hence, the sole influence of temperature on the gas’s ability to perform work during outbursts is limited. Temperature exerts varying degrees of influence on gas parameters such as gas content and drill cutting desorption indices. The fluctuation amplitudes of these indicators range from large to small in the following order: Δh2 > ΔP > Q > K1 > P. Additionally, their correlation with gas expansion energy decreases in the following order: P > Q > Δh2 > K1 > ΔP. Thus, the influence of temperature on the indicators used in various prediction methods exhibits inconsistency, emphasizing the importance of considering temperature effects on predicted values. Gas pressure emerges as the optimal indicator for outburst determination, while gas content and drill cutting desorption indices are preferable as predictive indicators. These results will provide valuable references for the sustainable and safe development, risk assessment and prediction of deep coal mining.

Assessing the impact of pore‐fracture structures on permeability sensitivity in tectonic coal using computerized tomography scanning

AbstractThe heterogeneity in permeability of coal reservoirs is primarily attributed to the considerable variation in the morphologies and structures of microscopic pore‐fractures, shaped by complex geological processes. This study emphasizes the necessity of understanding the impact and governance of these morphological and structural variations in pore‐fractures across different types of coal bodies on their permeability. Utilizing computerized tomography scanning and three‐dimensional imaging, we examined coal samples from the Datong coalfield in the southeastern Qinshui Basin, Shanxi Province, to characterize the pore‐fracture morphologies and structures distinct to various coal‐body types based on tomographic data. This introduces a methodology for assessing the influence of microscopic pore‐fracture parameters, such as porosity, specific surface area, tortuosity and fractal dimension, on permeability sensitivity. This is achieved through the application of the modified Kozeny–Carman equation and a fractal permeability model. Findings indicate a predominance of slab fractures in raw coal, whereas fragmented coal under weak brittle deformation exhibits small, isolated pore‐fractures with minimal diameter and volume and poor connectivity. In contrast, granular coal subjected to strong brittle deformation features extensive clusters of large pore‐fractures with significant diameter and volume, enhancing connectivity. Moreover, permeability predictions are refined by integrating the modified Kozeny–Carman equation with tomographic data, offering a more precise understanding of the permeability across different coal bodies.

Rapid quantitative analysis of coal composition using laser-induced breakdown spectroscopy coupled with random forest algorithm.

Coal is the primary energy source in China, widely used in energy production, industrial processes, and chemical engineering. Due to the complexity and diversity of coal quality, there is an urgent need for new technologies to achieve rapid and accurate detection and analysis of coal, aiming to improve coal resource utilization and reduce pollutant emissions. This study proposes a rapid quantitative analysis of coal using laser-induced breakdown spectroscopy combined with the random forest algorithm. Firstly, a Q-switched Nd: YAG laser at 1064nm was employed to ablate coal samples, generating plasma, and spectral data were collected using a spectrometer. Secondly, the study explores the impact of different parameters in the preprocessing method (wavelet transform) on the predictive performance of the random forest model. It identifies elements related to coal ash content and calorific value along with their spectral information. Subsequently, to further validate the predictive performance of the model, a comparison is made with models established using support vector machine, artificial neural network, and partial least squares. Finally, under optimal parameters for spectral information preprocessing (wavelet transform with Db4 as the base function and 3 decomposition levels), a model combining wavelet transform with Random Forest is established to predict and analyze the ash content and calorific value of coal. The results demonstrate that the Wavelet Transform-Random Forest model exhibits excellent predictive performance (coal ash content: R2 = 0.9470, RMSECV = 4.8594, RMSEP = 4.8450; coal calorific value: R2 = 0.9485, RMSECV = 1.5996, RMSEP = 1.5949). Therefore, laser-induced breakdown spectroscopy combined with the random forest algorithm is an effective method for rapid and accurate detection and analysis of coal. The predicted coal composition values show high accuracy, providing insights and methods for coal composition monitoring and analysis.

Research on the Critical Moisture Content of Frost Heaving in Gas-Containing Coal.

As the depth of coal seam mining increases, coal and gas outburst prevention and control face unprecedented challenges. In recent years, freezing outburst prevention technology has received attention and been applied in industry; this method mainly improves the strength of the coal body while reducing its energy storage. Research has shown that due to the influence of moisture content, frost heaving occurs in coal bodies during the cooling process, weakening the coal bodies' strength. Therefore, it is necessary to explore the effect of the moisture content on the coal body frost heave. This paper uses a research method that combines laboratory experiments, theoretical analysis, and numerical simulation to study the critical moisture content of frost heaving in gas-containing coal. The results showed that the coal sample can be divided into three stages during the cooling process: the cold shrinkage stage, frost heave stage, and stabilization stage. When the moisture content is greater than 7%, as the moisture content increases, the amount of ice increases accordingly, which causes an increase in the frost heave deformation of the coal sample and produces an obvious frost heave effect. Utilizing COMSOL simulation software, the deformation of gas-containing coal samples at different moisture levels is simulated. By combining the results with laboratory measurements, the critical moisture content for the frost heave in gas-containing coal is determined to be 6.6%.

Effect of CO2-H2O Interaction with High-Rank Coal on Mechanical Properties and Acoustic Emission Characteristics under Confining Pressure.

The adsorption of CO2 by coal leads to changes in its mechanical properties, particularly when considering supercritical CO2 and water with supercritical CO2 adsorption. This is strongly linked to the efficiency of CO2-enhanced coalbed methane (CO2-ECBM) extraction and the safety of CO2 geological storage. This study focuses on 3# coal from the Datong Mine in Gaoping City, Shanxi Province. The high-rank coal's mechanical properties, including the triaxial compressive strength and elastic modulus, were examined under the combined effects of CO2 injection pressure, CO2 injection time, and moisture content. The triaxial compressive strength and elastic modulus of the coal showed a decrease following CO2 injection. Increasing the CO2 injection pressure, prolonging the CO2 injection time, and increasing the moisture content were favorable for coal softening. In particular, the triaxial compressive strength and elastic modulus of the coal sample after 144 h of water and supercritical CO2 softening decreased by 67.67 and 64.15%, respectively. Injecting CO2 into coal changed its failure mode. The dry raw coal sample exhibited a brittle shear failure mode, while the coal samples showed transitional shear failure after injecting 6 MPa CO2 and 8 MPa CO2 and ductile nondilatant barreling failure after injecting water and 8 MPa CO2 (with a moisture content of 3.02%). Moreover, the cumulative acoustic emission energy of the coal samples followed a similar trend to the decrease in mechanical properties under different conditions. The physical and chemical interactions among coal, CO2, and water caused the softening of coal; these included the generation of the swelling stress, the dissolution of minerals by carbonate solutions, the reduction in surface energy of coal owing to CO2 adsorption, and the extraction and plasticization reactions of organic matter in coal. The research results are of great significance for further understanding CO2-ECBM and CO2 geological sequestration.

Mineralogy and geochemistry of rare metal (Zr-Nb-Hf-Ta-REE-Ga) coals of the seam XXX of the Izykh Coalfield, Minusinsk Basin, Russia: Implications for more widespread rare metal mineralization in North Asia

This study focuses a comprehensive mineralogical and geochemical study of rare-metal (Zr-Nb-Hf-Ta-REE-Ga) mineralization in the Permian coal seam XXX-XXXa of the Izykh Coalfield, Minusinsk Basin, southern Siberia. A link is demonstrated between the accumulation of rare metals in the coal with a volcanogenic rock parting up to 45 cm thick separating the coal seams. The floor of seam XXX is also characterized by the presence of pyroclastic material, which affects the level of accumulation of rare elements in the coal of the seam. Coals and intra-seam rock partings in seam XXX-XXXa have abnormally high concentrations of Zr, Nb, Hf, Ta, REE and Ga. In coal ash samples, the contents of some elements are highly evaluated, e.g., 1.4% Zr, 0.26% Nb, 164 ppm Hf, 17.9 ppm Ta, 0.8% REE, 0.13% Y, and 226 ppm Ga. The concentration of rare elements is higher in the coal and coal ash of the XXX coal seam than in the XXXa coal seam. The accumulation of anomalous concentrations of Zr-Nb-Hf-Ta-REE and Ga is mostly specific for the rock parting between the XXX and XXXa seams, as well as for the coals in contact with this parting. Zirconium, Nb, Y, and REE form more contrasting halos near the parting compared to Ta, Hf, and Ga. This is explained by the different mobility of the elements under weathering and diagenetic conditions. Other ore elements are concentrated to a greater extent in the coal in the near-contact zone, as well as at a distance from the partings. Ore material is concentrated primarily in the fine-dispersed mineral phase represented mainly by Zr-Nb-Ti-Fe oxides, complex Nb-Zr-P silicates, and REY-bearing phosphates (monazite, xenotime). Volcanogenic pyroclastics of acidic and alkaline composition (rhyolite-pantellerite) influenced the accumulation of rare metals in coal. Volcanic ash, transported from a distant source, served as the raw material for the formation of the rock interlayer in coal. The composition of this volcanic ash is believed to correspond to a pantelleritic tuff. These findings are comparable to those reached in earlier work on the altered ash in the coal seam XI of the Kuznetsk Coal Basin, which has similar geochemical features and is also of Permian age. Complex Zr-Nb-Hf-Ta-REE-Ga mineralization in the coals of the Kuznetsk and Minusinsk basins, associated with volcanogenic pyroclastics, indicates a wide manifestation of active acid and alkaline volcanism during the formation of coal deposits and the possibility of identifying similar mineralization in Permian coals of East and North Asia.

Analysis of the influence of temperature on the adsorption characteristics of coal: Insights into low-temperature outburst prevention

To investigate the impact of temperature reduction on the adsorption characteristics of coal gas, isothermal adsorption experiments were conducted with environmental temperature and moisture content as variables. The changing patterns of coal gas adsorption characteristics, adsorption theories, and the temperature response of gas expansion were analyzed. Furthermore, engineering measures for preventing gas outbursts in low-temperature frozen coal seams were discussed. The research findings indicate that the gas adsorption capacity of coal samples increases with decreasing temperature. When the temperature decreases from 20 to −20 °C, the gas adsorption capacity decreases from 34.48 to 19.90 cm3/g. At the same pressure, the adsorption capacity of coal is negatively correlated with temperature. The Langmuir theoretical model better reflects the adsorption law of coal gas under different environmental temperature conditions, wherein the adsorption constant “a” gradually decreases with the increase in environmental temperature. In a closed space, the gas pressure decreases with the decrease in coal sample temperature. Under the new adsorption equilibrium, the gas pressure in the coal sample tank decreases linearly with temperature. Coal samples with different moisture contents exhibit varying degrees of decrease in gas pressure at the same temperature, with higher moisture content resulting in a smaller decrease in gas pressure. Gas expansion energy decreases linearly with the decrease in coal temperature, indicating a proportional relationship between gas expansion energy and coal gas release pressure. As the temperature decreases, the gas pressure decreases. Based on the experimental results, a synergistic approach for preventing gas outbursts through low-temperature freezing is proposed.

Mechanical strength change and coal damage analysis of frozen saturated bitumite after cryogenic freezing

The changes in mechanical strength and damage analysis of bitumite under the action of liquid nitrogen (LN2) freezing are critical issues that need to be addressed in the application of LN2 in coal seam permeability enhancement. Using an MTS testing machine, strain gauges, and ultrasonic detection instruments, experiments were conducted to obtain stress-strain curves and ultrasonic time-domain images of coal samples after single freezing and cyclic freeze-thaw processes. These data were analyzed to understand the mechanical performance and internal fracture evolution of coal samples subjected to ultra-low temperatures of LN2. The experimental results indicate that: (1) the uniaxial compressive strength and elastic modulus of coal samples subjected to a single LN2 freeze are positively correlated with the freezing time from 0 to 50 min, and negatively correlated with the freezing time from 50 to 180 min. (2) The uniaxial compressive strength and elastic modulus of coal samples subjected to cyclic freezing and thawing with LN2 decrease as the number of freeze-thaw cycles increases. (3) The Poisson's ratio of coal samples subjected to single freezing and cyclic freezing-thawing is negatively correlated with the absolute freezing time. Additionally, the decrease in Poisson's ratio is greater in coal samples subjected to cyclic freezing-thawing compared to those subjected to single freezing. (4) As the absolute freezing time increases, the ultrasonic waveforms of the coal samples begin to become disordered, which is manifested by a decrease in amplitude and a delay in the arrival time of the first wave. Under ultra-low temperature conditions, LN2 can deteriorate the mechanical properties of coal samples, with the degree of deterioration being greater under cyclic freezing-thawing than single freezing. This study can provide theoretical guidance for increasing the permeability of coal seams.

Chemometric Speciation of Trace Elements in Indonesian Coal Imported by Indian Thermal Power Stations - A Comparative Study with Indian Coals using SRXRF

ABSTRACT Imported Indonesian coal samples collected from thermal power plants were analyzed using Synchrotron Radiation X-ray Fluorescence (SRXRF). Sixteen inorganic elements As, Ca, Cr, Co, Cu, Fe, K, Mn, Ni, Pb, Rb, Se, Sr, Ti, V, and Zn were quantified. To ascertain the abundance in the analyzed samples compared to Clarke values for world coals, the enrichment factor for each element was measured. The analytical results were interpreted using chemometric techniques, namely Pearson’s correlation analysis, hierarchical cluster analysis, and principal component analysis. This study revealed three principal components contributing to 87.99% of the total variance in the data.

Structure evolution law of coalbed methane reservoirs under different initial pressure CO2 phase change fracturing conditions

As a new coal bed fracturing technology, CO2 phase transition fracturing (CPTF) has received much attention due to its advantages of safety and high efficiency. However, little research has been conducted to investigate the fracture behavior of CPTF in coal seams under different CO2 release pressure conditions. To address this research gap, we performed fracture tests on coal rock under different initial pressure conditions using the developed CPTF experimental system. Then, scanning electron microscopy, low-pressure nitrogen adsorption, and mercury intrusion porosimetry testing techniques were used to investigate the fracture characteristics and microstructural evolution of coal rocks under different initial pressures of CPTF. The results show that with increasing initial pressure, the number of macroscopic fractures and the degree of fragmentation of the coal after CPTF fracturing increased significantly, the number of microscopic fractures and pores in the fractured coal samples increased, the N2 adsorption capacity and the amount of mercury intrusion of the coal samples increased to a greater extent, and the visible porosity increased from 52.47% of the raw coal to 63.88%, 64.31%, 68.48%, 63.64%, and 62.83%, and the proportion of macroporosity increased from 24.31% to 28.48%, 31.73%, 26.55%, and 34.38%. This research will contribute to a fuller understanding of the potential of CPTF as a technique for improving the pore and fracture structure of coalbed methane reservoirs.

Comparative study on different coals from the Lorraine basin (France) by sorption isotherms, thermogravimetric analysis and breakthrough curves for CO2-ECBM recovery

The enhanced coalbed methane recovery using CO2 injection (CO2-ECBM) is widely proposed as a way of achieving the energy transition and reducing atmospheric CO2 in areas such as the Lorrain basin in France, where heavy industry is responsible for huge CO2 emissions and coal mines have been closed for more than a decade. This paper deals with the feasibility of extracting methane from the Lorraine basin using CO2-ECBM by comparing data from sorption isotherms, thermogravimetric analyses and breakthrough curves for two coal samples. One is bituminous (Box 18), from Folschviller (France) and is compared with another sub-bituminous (TH01) from La Houve (France), which is used as a reference because it was identified as a good candidate for CO2-ECBM in a previous research program. The quantities of adsorbed gases (CO2/CH4) obtained by sorption isotherms, thermogravimetry and CO2 breakthrough curves showed that Box 18 adsorbs more CO2 and CH4 than TH01 due to its higher porosity and good affinity for gases (CO2/CH4). Tόth model fits the experimental CH4 and CO2 adsorption isotherms better, reflecting the fact that the adsorption surface of the coals studied is heterogeneous. Adsorption enthalpies obtained by calorimetry indicated physisorption for gas-coal interactions, with higher values for CO2 than for CH4. Thermogravimetric analyses and breakthrough curves carried out at up to 50% relative humidity showed that the adsorption capacity of CO2 decreases with increasing temperature and the presence of water, respectively. The compilation of these experimental data explained the adsorption process of the studied coals and revealed their advantages for CO2-ECBM.