Degree Of Metamorphism Research Articles

Effects of CaO addition on the reactivity and reaction kinetics of coke

ABSTRACTIn recent years, researches have shown that highly reactive coke for blast furnace ironmaking not only reduces fuel ratio but also reduces carbon emissions. Therefore, the research on developing high reactivity coke has received unprecedented attention. In this work, CaO was added into coals with different degrees of metamorphism to caking coke to study the effect of CaO amount on the non-isothermal gasification reaction behavior of coke. Results showed that the reactivity is significantly improved as the mass of added calcium oxide accounting for less than 0.4% of the dry coal mass. However, CaO exerted little effect on the micro-strength and structural strength of coke. The analysis of Mercury intrusion porosimetry of coke samples demonstrates that the addition of CaO increased the porosity of coke, resulting in the contact area with CO2, leading further to an increase in coke reactivity. At different heating rates, as the amount of CaO added increased, both the initial reaction temperature and the corresponding temperature of the maximum reaction rate of the gasification from CO2 decreased little by little. The addition of CaO was increased from 0% to 0.6%, the activation energy of the reaction was decreased by 16.41 kJ/mol. The kinetic model of the gasification of coke by CO2 conforms to the unreacted shrinking core model. The reaction mechanism function is converted from f(α) = 3(1-α)2/3 to f(α) = 2(1-α)1/2 (α means carbon conversion ratio), indicating that the addition of CaO accelerates the dissolution rate of coke by CO2.

Experimental investigation of gas diffusion kinetics and pore-structure characteristics during coalbed methane desorption within a coal seam

The desorption-diffusion properties of coalbed methane (CBM) are not only the theoretical basis for investigating gas outburst hazards in a coal mine, but also impose a non-negligible impact on CBM recovery performance. In this paper, the pore structure of coal with five different metamorphism degrees was qualitatively and quantitatively characterized with the scanning electron microscopy (SEM) and low-temperature nitrogen gas adsorption (LTNGA) measurements. The isothermal methane ad/desorption experiments were performed with four initial gas desorption pressure scales. Subsequently, the matching degree between eight empirical correlations (ECs) and the measured methane desorption data was determined, and the methane diffusion coefficient (Dfg) was numerically calculated combining with an FGDG (free gas density gradient) diffusion model. Importantly, we evaluated and discussed the sensitivity of pore structure parameters, initial gas desorption pressure, and volatile fraction to Dfg. The results show that pore density distribution differs among coal samples and the pore structure, especially the micropores, is developed better in high-rank coals than in low- and medium-rank ones. Initial gas release velocity increases with an increase in coal rank and decreases negatively with the increasing particle size in an exponential manner. Among the eight ECs, EC-VIII can be applied to more accurately describe gas desorption process during the whole time scale, and its correlation coefficient with the measured data is larger than 0.9900. Dfg increases with an increase in pore volume and specific surface area (SSA), and it is negatively correlated with the average pore diameter. Additionally, Dfg exhibits an asymmetric U-shaped pattern with an increase in the volatile fraction, which is mainly related to the switch between the dominant roles of mesopores and micropores during coal metamorphism. At a lower volatile fraction, the diffusion coefficient is more sensitive to micropores, while, at a higher volatile fraction, mesopores contribute more to the diffusion coefficient.

Study on the Adsorption/Desorption Characteristics of Protogenetic CO in Coal Seams

ABSTRACT In recent years, abnormal CO gas overruns have often occurred in coal mining workings. CO overruns were thought to be caused by the underground blasting work or spontaneous combustion of coal seams; however, minimal attention has been given to the causes of the desorption and release of adsorbed CO in the coal seams. Additionally, insufficient research has been conducted on the generation, distribution and adsorption and desorption characteristics of protogenetic CO in coal seams. Therefore, a self-built comprehensive testing system for coal seam adsorption and desorption was used to study the characteristics of the depressurization desorption and thermal desorption of coal with different degrees of metamorphism during coal seam mining. The results showed that under isothermal conditions, the amount of CO adsorption and desorption of coal samples increased with increasing pressure; under temperature rise conditions, the gas adsorption-desorption was in a dynamic equilibrium process under certain conditions. When the temperature increased, the equilibrium was beneficial to the desorption direction. The initial temperature range of CO production at different equilibrium pressures was 45–55°C. With increasing pressure, the initial temperature point of CO gas production moves forward and was significantly lower than the initial temperature of coal spontaneous combustion. Our research results further supplement the source of underground protogenetic CO gas and provide theoretical support for the accurate prediction of CO coal spontaneous combustion.

Constraints on Crystallinity of Graphite Inclusions in Nephrite Jade from Xinjiang, Northwest China: Implications for Nephrite Jade Formation Temperatures

Graphite usually occurs in mineral/rock associations in the form of solid inclusions and plays an important role in tracing regional metamorphic degree, ore-forming temperature, fluid evolution, as well as the deep carbon cycle of the Earth. In this study, we investigate the placer black nephrite jade where the co-occurrence of abundant graphite inclusions and jade remains extraordinary. By employing petrographic, mineral-chemical, and Raman spectroscopic methods, we characterize the textures and crystallinity of graphite inclusions that exist in nephrite jade. EPMA and petrological data indicate that the main constituents of black jade are tremolite and graphite, with minor phases of diopside, calcite, dolomite, epidote, and apatite. Micro-Raman spectroscopic thermometry of carbonaceous material shows that most of the formation temperatures of graphite inclusions are between 378 and 556 °C, and only a few temperatures may be above 650 °C, indicating that graphite inclusions were formed at medium- to high-temperature metamorphic facies. The petrologic and spectral investigations of graphite inclusions in these nephrite jade samples show major metamorphic signatures with mixed features associated with fluid precipitation. Our results allow us to propose that primary nephrite jade was formed under multi-stage tectonic evolution conditions, and regional temperatures were predominately driven by the late continent–continent collision, while the ore-controlling temperatures of nephrite jade formation were found in a medium- to high-temperature environment.

NANOSTRUCTURED COMPOSITES BASED ON MATRICES OBTAINED FROM COAL RAW MATERIALS FOR DEVELOPMENT OF ELECTRODE MATERIALS FOR SUPERCAPACITORS

The article reports the results of the study of the morphology, porous structure and electrical capacitance characteristics of highly porous carbon matrices (HPCMs) obtained from coal raw materials with different degrees of metamorphism and nanostructured composites (NSCs) based on them, the surface of which is decorated with gold or manganese oxide nanosized particles (NP), accumulating electrical charge during polarization in the electrolyte via two mechanisms (formation of an electrical double layer (EDL) and involvement of pseudo-capacitance component during Red-Ox reactions on electrodes). The samples of HPCMs were obtained by high-temperature (800 °C) alkaline activation (the mass ratio KOH/C = 2 : 1) of fossil coal from the coal basins of the Kemerovo Region and the Republic of Sakha (Yakutia): CAK - based on anthracite of the Kiyzasskiy open-pit mine (Kuzbass), with the highest coalification degree; CBK - based on boghead (a kind of sapropel coal ) from the Taymylyr deposit (Yakutia) with the lowest degree of metamorphism; CDK - based on long-flame coal (Kuzbass) occupying an intermediate position in the metamorphism series. Results obtained by scanning electron microscopy, small-angle X-ray scattering in combination with sorptometry showed that the NSC morphology is largely determined (except for submicron aggregates) by the porous structure of the matrices. The shape of cyclic voltammetry (CVA) curves for HPCMs CDK, CBK and Au-NP filled NSC based on them indicated a significant contribution from EDL into capacitance; the contribution of pseudo-capacitance is observed for the composite MnOx/CDK electrode. The features of CVA curves for microporous CAK HPCM and NSC based on it are probably caused by hindered diffusion. The specific electrical capacitance is higher as a result of the polarization of CDK and CBK HPCM with large proportions of mesopores, as well as NSCs on their basis, than that resulting from the polarization of microporous CAK and the corresponding composites. For all three HPCMs, the introduction of fillers causes an increase in the electrode capacitance. The effect is more significant for NSCs obtained from hard coals with a low level of metamorphism (an increase up to 1.8 and 1.6 times with respect to the capacitance of initial matrices for NSCs based on CDK and CBK, respectively, according to the impedance measurement data), which is due to a decrease in the active resistance and the charge transfer resistance of the cells, and, in general, to the active component of the impedance.

Quantitative Prediction of Deep Coalbed Methane Content in Daning-Jixian Block, Ordos Basin, China

The potential of deep coalbed methane resources is substantial. Gas content is an important parameter for resource assessment. At present, the gas content test method commonly used for shallow coal reservoirs is not suitable for determining deep coalbed methane gas content. Therefore, it is urgent to establish a prediction method for deep coalbed methane gas content. This study aims to quantitatively predict the gas content of coalbed methane in deep coal reservoirs and uncover its influencing factors. For this purpose, we selected the Daning-Jixian area, a region in China with relatively advanced development of deep coalbed methane, as a case study. It established a prediction model for adsorbed gas and free gas content in deep coal reservoirs through a series of experimental tests, encompassing gas content, coal quality, isothermal adsorption, and nuclear magnetic resonance. The model sheds light on the impact of coal-rock characteristics, coal quality attributes, and pore characteristics on adsorbed gas and free gas content. The results show that adsorbed gas dominates in deep coal reservoirs with a high metamorphic degree and that the average proportion of adsorbed gas under reservoir burial depth is 80.15%. At a depth of approximately 1800~2000 m, a turning point is observed where adsorbed gas content begins to decline. Beyond this depth range, the detrimental effect of temperature on coalbed methane content surpasses the beneficial impact of pressure. Coal quality characteristics play a major role in controlling adsorbed gas content, and an increase in water content and ash yield significantly reduces the adsorption performance of coal reservoirs. The content of free gas increases with the increase in burial depth, with its controlling factors primarily being confining pressure and porosity. The increase in the proportion of micropores in the pores of deep coal reservoirs has an adverse effect on the content of free gas. The proportion of adsorbed gas in deep coal reservoirs gradually decreases with the increase in burial depth, while the proportion of free gas gradually rises with the increase in burial depth. The development potential of free gas cannot be overlooked in the exploration and development of deep coalbed methane.

The use of Protodiakonov and Hardgrove methods to determine the effect of coal quality on its grinding ability

The factors affecting the mechanical strength of coal and coal charges, deviations of the crushing capacity coefficients' actual values of coal charges from their calculated values, and the possibility of categorizing coal in relation to the degree of its resistance to crushing have been explored. The dependence permitting satisfactory precognition of the HGI value of the coal charge placed on the data of the crushing capacity coefficients of its ingredients was settled. The effect of the grinding ability of coal on its quality indicators, namely the degree of metamorphism, petrographic and elemental composition has been examined in this article. Determination of the coal grind ability was made by means of widely known Protodyakonov and Hardgrove methods, which allow estimating the resistibility of the material to the grind forces. For research 14 samples of coals (Ukraine, USA, and Kazakhstan), and 7 testers of coal charges at the basic coke chemical companies of Ukraine, were applied. The graphical and mathematical dependences are stated to have been developed to enable the predicting of the grinding ability of coals using the Hardgrove (HGI) and Protodyakonov (f) methods, based on determining the indicators of their quality (Cdaf, R0, Oddaf, Vdaf). It is shown that the graphical and mathematical dependencies are polynomials of the second degree, and the values of the coefficients of determination (R2) exceed 0.550–0.930. For the initial time, the coherency between the strength coefficient according to the Protoyakonov method and coal pulverization to the Hardgrove method was established. It was found the f and HGI values of measure are inversely in proportion, and a mathematical and diagram dependence based on one of them for its prognosticate has been established.

Evaluation of Heterogeneity in Tectonically Deformed Coal Reservoirs Based on the Analytic Hierarchy Process-Entropy Weight Method Coupling Model: A Case Study.

This article presents a comprehensive analysis of the factors influencing the heterogeneity of tectonic coal reservoirs, focusing on the metamorphic degree and pore-fracture parameters of tectonic coal. To ensure a reliable evaluation, the AHP-EWM coupling evaluation model (analytic hierarchy process and entropy weight method), which integrates the strengths of both evaluation models and minimizes the potential errors associated with a single model, was employed to assess the heterogeneity index of coal reservoirs in the Panguan syncline. According to the findings of the AHP-EWM model, it was observed that the comprehensive index of coal heterogeneity consistently increases as the degree of coal deformation increases. Notably, a critical value of I = 0.48 was identified as the threshold for the comprehensive index of brittle and ductile deformation coal heterogeneity. Furthermore, the pore-fracture characteristic was determined to have the greatest effect on the heterogeneity of coal reservoirs, followed by the metamorphic degree. This research contributes significantly to the identification of high-quality coalbed methane reservoirs in the Panguan syncline of western Guizhou, serving as a valuable point of reference.

Enrichment of Coal-Hosted Graphite Deposits Caused by Magmatic Heat Transfer and Tectonic Stress at Feng County, Western Qinling Orogen, China

China has ranked first worldwide in graphite imports in recent years, facing a graphite supply risk. Coal-hosted graphite is the focus of future graphite deposit exploration. The current research on the enrichment and mineralization mechanism of coal-hosted graphite is superficial, and the identification standard of coal-hosted graphite is incomprehensive, restricting the exploration of coal-hosted graphite mineral resources and the development of coal metamorphic evolution theory. In this study, the Caotangou–Meigoucoal-hosted graphite deposit in western Qinling Mountain was taken as a case study for dissection. Based on the data from 1/50,000 and 1/200,000 regional geological mapping and the data of graphite mines in the study area, the samples were systematically collected and analyzed to explore the mechanism of coal graphitization through a 1:5000 geological profile survey, 1/10,000 geological mapping in key areas, and the investigation and cataloguing of abandoned coal-hosted graphite adit. The result was that there were two main coal-hosted graphite ore bodies, striking from nearly east to west. The Rmax values of the samples were 7.23–8.15%, the average values of Vdaf were around 5.0%, the d002 value of the II ore body was 0.3433–0.3389 nm, the d002 value of the I ore body was mainly 0.3418–0.3429 nm, the graphitization degree G value of the II ore body was 8.14–59.30%, the graphitization degree G value of the II ore body was 12.79–25.58%. The II ore body was coal-hosted graphite, while some samples of the I ore body were coal-hosted graphite, and some samples were coal. The magmatic heat controls the thermal metamorphism of coal seams to form graphite. The closer the distance to the magma body, the larger the crystals, and the higher the euhedral degree, indicating the higher degree of coal seam metamorphism. The nearly north–south compressive structures mainly provided effective tectonic stress for the evolution of coal graphitization during the Yanshan period; the basic structural units (BSUs) rotated and rearranged, eventually forming a straight graphite structure, and tectonic stress catalyzed the graphitization process. The coal-hosted graphite deposits formed under the dual effects of magmatic heat transfer and tectonic stress.

Study on molecular structure characteristic and optimization of molecular model construction of coal with different metamorphic grade

To investigate the structural properties of coal molecules with different degrees of metamorphism, in this study, we used Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and solid-state nuclear magnetic resonance carbon spectroscopy (13C NMR) to investigate the structural properties of three coal molecules with different degrees of metamorphism and finally constructed and optimized the coal molecular model. The experimental results showed that with the deepening of the deterioration degree, the proportion of oxygen-containing functional groups in the coal molecules was gradually reduced, the long fatty chains were shortened and reduced, and the aromaticity was enhanced. With increasing coalification, pyridine nitrogen and thiophene sulfur are becoming important components of the nitrogen- and sulfur-containing organic matter in coal. Coal metamorphism promotes the aromatization and condensation degree increase of coal molecular structure, which makes the coal molecular structure evolve into a microcrystalline structure with higher order degree. With this increase of coal rank, the carbon ratio around the bridge (XBP) increased from 0.12 to 0.47. The low-rank coal was dominated by benzene rings with low polymerization degree, and the high rank coal was dominated by aromatic structures, such as tetracene with a high degree of polymerization. The molecular formula of lignite finally constructed was C219H159O21N3, that of coking coal was C235H164O7N4S, and that of anthracite was C286H108O5N4S. The coal molecules constructed in this study provide a theoretical basis for the study of the molecular structure properties of coal with different degrees of metamorphism.

Saint‐Pierre‐le‐Viger (L5‐6) from asteroid 2023 CX1recovered in the Normandy, France—220 years after the historic fall of L'Aigle (L6 breccia) in the neighborhood

AbstractOn February 13, 2023, a huge fireball was visible over Western Europe (fireball event 2023 CX1). After the possible strewn field was calculated, the first of several recovered samples, with a mass of about 100 g, was discovered just 2 days after the fireball event on the ground of the village of Saint‐Pierre‐le‐Viger. Meanwhile, more than 60 samples with a total mass of more than 1 kg were recovered and a piece of one of these is studied here. The fall occurred 220 years after the historic meteorite fall of L'Aigle on April 26, 1803, <120 km south. L'Aigle is the closest meteorite fall to Saint‐Pierre‐le‐Viger and belongs to the same chondrite group. Both meteorites are breccias containing only clasts of high metamorphic degree (type 5 and type 6). Since only 20% of the L chondrites are breccias this coincidence is remarkable. As just mentioned, both samples studied from these rocks in this work are ordinary chondrite breccias and consist of equilibrated and recrystallized lithologies of petrologic type 6. The brecciated texture in L'Aigle, resulting in a remarkable light–dark structure, is more pronounced than the brecciated features in Saint‐Pierre‐le‐Viger, from which also type 5 fragments have been reported. The compositions of low‐Ca pyroxene and olivine grains in Saint‐Pierre‐le‐Viger (Fs21.2and Fa23.4, respectively) clearly require an L‐group classification. L'Aigle was classified as an L6 breccia in the past, and this has now been confirmed by new data on low‐Ca pyroxene and olivine (Fs20.7and Fa23.8, respectively). Saint‐Pierre‐le‐Viger contains local thin shock veins, and both meteorites are moderately shocked. Most olivines in the studied samples have planar fractures, but the estimated abundance of mosaicized olivines of 30%–40% among the large grains require a S4 shock classification. Oxygen isotope and bulk chemical data of Saint‐Pierre‐le‐Viger certainly support the L chondrite classification. Bulk spectral data of Saint‐Pierre‐le‐Viger are dominated by silicate minerals, that is, Fe‐bearing low‐Ca pyroxene, olivine, and plagioclase. Isotopic, chemical, and spectral data of the L'Aigle meteorite are shown for comparison and are very similar, providing additional circumstantial evidence of Saint‐Pierre‐le‐Viger's L chondritic nature.

Thermodynamic energy change and occurrence mechanism of multiple fluids in coal reservoirs

Systematic understanding of the occurrence mechanism of multiple fluids in coal reservoirs is the basis for efficient development of coalbed methane (CBM). In this study, the adsorption capacity, adsorption potential and adsorption heat data of coal samples of different metamorphic degrees under single/multi components isothermal adsorption were obtained through isothermal adsorption equipment and the atomic force microscopy (AFM). The adsorption potential energy and electric potential energy were innovatively combined to expound the characteristics of the thermodynamic energy change in coal reservoirs, and the occurrence mechanism of multiple fluids in coal reservoirs were discussed. It is found that: (a) the adsorption amount of these two gases decreases first and then increases with the increase of coal rank in both single-phase adsorption and competitive adsorption. (b) CO2 shows superior adsorption in comparison to CH4. The larger the proportion of a certain component in the mixed gases system, the better this component's adsorption performance. (c) The adsorption potential of the two gases is not affected by temperature, and with the increase of coal metamorphism, the adsorption potential shows first a decrease, followed by an increase. (d) The CH4 adsorption heat of coal samples increase with higher adsorption amount, but the CO2 adsorption heat of some coal samples has a negative linear correlation with adsorption amount.

Energy Variation Features during the Isothermal Adsorption of Coal under High-Temperature and High-Pressure Conditions

This paper aims to describe methane adsorption in coal under the conditions of high temperature and high pressure, as well as quantitatively decipher the change rule of energy in the isothermal adsorption process. The isothermal adsorption test was carried out with four groups of middle-rank coals from the Linxing area with different degrees of metamorphism. The impacts of the degree of deterioration of coal, temperature, and pressure on adsorption were analyzed with regard to the adsorption amount, adsorption potential, and adsorption space. Additionally, the energy change during the adsorption of methane by the coal was considered. The results show that the coal adsorption capacity hinges on the degree of deterioration of the coal, as well as the pressure and temperature. Additionally, the impact of temperature upon coal methane adsorption under depth conditions is highlighted. Like the adsorption space, the adsorption potential is an important parameter used to quantitatively characterize the adsorption ease and adsorption capacity; furthermore, the adsorption potential of millipores exceeds that of mesopores, as they are capable of offering a larger specific surface area for adsorption. The total decrease in the surface free energy during adsorption increases as the pressure increases; simultaneously, the increase rate is fast and then slow. The total decrease in the above-described free energy diminishes as the temperature escalates. Under the same pressure, the total decrease in the aforementioned free energy increases as the reflectance of the specular body of the coal increases. The decrease in the aforementioned free energy at each point of pressure lessens as the pressure grows; notably, when the pressure is comparatively low, the reduction is very fast. As the pressure escalates continuously, the decrease speed is slow. Regarding the effect of pressure and temperature upon adsorption, the adsorption gas volume of coal exists in a conversion depth from 1200 m to 1500 m; at the same time, the impact of pressure upon adsorption is dominant up to this depth. Additionally, beyond this depth, temperature gradually comes to have the greatest impact on adsorption.

Carbon Dioxide Prevents Oxygen Adsorption at Low-Temperature Oxidation Stage of Low-Rank Coal: Laboratory Study and Molecular Simulation

Carbon dioxide (CO2) is widely used in the prevention and control of spontaneous coal combustion. In this manuscript, three low-rank coals with different metamorphic degrees were selected as the research objects. The temperature-programmed experiments, in situ infrared cooling experiments, simulation of the competitive adsorption of CO2 and oxygen (O2) in coal pores, and simulation study of the CO2 inhibition of the coal oxygen composite reaction were used to obtain the role and effect of CO2 in preventing oxygen adsorption in coal at the low-temperature oxidation stage. It was concluded that CO2 can displace the O2 near the pore wall to physically prevent the adsorption of O2. Through the changing law of heating rate and a kinetics analysis, it was found that CO2 can increase its activation energy by 5.3–108.3% during the slow heating stage of coal and reduce its heat rate. At around 120 °C, coal loses the protective effect of CO2. From the changes in functional groups, it can be seen that when coal was cooled in the CO2 atmosphere, mainly pyrolysis and condensation reactions occurred due to the lack of O2. In addition, CO2 can also inhibit the chain reaction of the chemical adsorption of oxygen in coal. This work provides a theoretical basis for CO2 prevention and the control of spontaneous coal combustion.

A COMBINED MODEL OF THE DIAPIRIC AND COLLISIONAL FORMATION MECHANISM OF THE PALEOPROTEROZOIC GRANITE-MIGMATITE-GNEISS DOMES OF THE SVECOFENNIAN BELT

Geological examples of the development of thermal dome structures in the Svecofennian belt demonstrate the relationship between plutonic and metamorphic events and metamorphic strengthening towards the core parts of the structures. The corresponding 2D geological model has been created to make a quantitative assessment of the effect of mantle magmas temperature at the base of the crust and the formation of the diapiric cores surrounded by high-temperature areas with a degree of granulite facies metamorphism. Modeling shows that there is a possibility of melting of the lower crust in the presence of a water fluid under the influence of mantle magmas. After melting, there occurs an ascent of partially molten material towards the upper crustal levels. An absorbed aqueous fluid changes to hydrous melt, thus lowering its viscosity and density. The ascending height of high-temperature cores is determined by the depth of viscous-to-elastoplastic transition in the crustal matter rheology. These materials ascend to upper levels in a partially molten state in the process of overthrusting due to "collisional" tectonics.

Type of the study: Original research article relationship between temperature rise characteristics and the emission of carbon oxides during the spontaneous combustion latency of coal

The emission of carbon oxides during the spontaneous combustion latency of coal poses a severe challenge to the ecological and geological environmental protection of mining areas. Owing to the insidious nature of latency, the oxidative characteristics during this stage have rarely been studied. This study investigated the relationship between temperature rise characteristics and the emission of carbon oxides under different coal samples, initial temperatures, and particle sizes. The results indicated that the formation of carbon oxides correlated with the temperature rise characteristics during latency. Time-dependent carbon oxide formation followed an exponential function y=aexp(xb)+c. The metamorphic degree and initial temperature of the coal had a significant impact on the CO2/CO ratio and the particle size was independent of the ratio. In addition, in-situ Fourier transform infrared reflection experiments on four coal samples revealed that the hydroxyl, aliphatic hydrocarbon methyl, and methylene groups are key active groups in carbon oxide formation during latency, providing the original heat source for coal oxidation. The carbonyl and carboxyl groups acted as reactants and products and their content varied irregularly during oxidation. These results improve the understanding of CO and CO2 emissions from coal oxidation during spontaneous combustion latency and will aid early prevention of coal spontaneous combustion.

Reaction heat effect and change characteristics of key groups in coal-oxygen intrinsic reaction path.

The intrinsic reaction of coal with oxygen in the process of low-temperature oxidation is the main reaction path leading to self-heating and spontaneous combustion of coal. Most of the existing studies regard the coal oxidation as an overall reaction, ignoring the multi-path characteristics of coal low-temperature oxidation, and it is difficult to accurately explore the intrinsic reaction characteristics between coal with oxygen. Therefore, the low-temperature oxidation process of coal was studied by using a C80 microcalorimeter and in situ FTIR technology from the macro and micro levels. The "profile subtraction method" was used to study the coal-oxygen intrinsic reaction process, and the reaction heat effect and the change characteristics of key functional groups in the process were analyzed. Furthermore, the gray correlation analysis method was used to study the relevant characteristic parameters in the reaction process and grasp the essential structure-activity relationship. The experimental results show that, compared with the overall reaction process in air atmosphere, the change in the heat release of the coal-oxygen intrinsic reaction path has changed to different degrees, and the change in the slow oxidation stage is the most significant (the heat absorption decreases by 70.1-90.9%). In addition, the characteristic temperature points show different degrees of advance, of which the initial exothermic temperature point is the largest (about 21-46 °C), which directly leads to a significant shortening of the slow oxidation stage (30.1-47.4%). The changes of functional groups in the intrinsic reaction path are more regular. With the increase of temperature, the oxygen-containing functional groups -C=O and the aliphatic hydrocarbon functional groups -CH2- and -CH3 showed a fluctuating trend of increasing and decreasing, respectively. The oxidation heat-contributing functional groups of coal are mainly related to the degree of metamorphism and the functional group reaction characteristics during the reaction. With the deepening of coalification degree, the main heat-contributing functional groups as a whole showed the change rule of oxygen-containing functional groups → aliphatic hydrocarbon functional groups → aromatic hydrocarbon functional groups. In addition, the change of -OH content in the three coal samples has a high correlation with the change of the total heat release of coal.

A micro-macro coupled permeability model for gas transport in coalbed methane reservoirs

It is of great scientific and engineering significances to reveal the coupling mechanism of microscale and macroscale permeabilities in coalbed methane (CBM) reservoirs. In this paper, firstly, the characteristics of the pore-fracture system of coal matrix, such as gas content, permeability, connectivity, geometric size difference, and direction of micro-fracture development, are revealed. Secondly, a coupled permeability model is established, and the coal rank control mechanism on the transformation of microscale and macrosclae permeabilities is clarified. Thirdly, based on the microscale gravitational field model, the coal rank-pressure coupling influence mechanism on slippage/diffusion/jump of adsorbed gas in the surface control field is clarified. Results show that: (a) under a certain temperature, the microscale permeability and macroscale permeability of coal matrix have a statistical correlation, and the degree of coal metamorphism is the only variable controlling the transformation of micro-macro permeabilities. (b) With the increase of coal rank from 0.5% to 3.5%, the conversion coefficient of bulk gas permeability decreases by 15 orders of magnitude. (c) With the increase of coal metamorphism, the porosity and the density of oxygen-containing functional groups decrease, leading to the proportion of the area of adsorbed water film decreases at first and then increases.

The identification of coal and gangue and the prediction of the degree of coal metamorphism based on the EDXRD principle and the PSO-SVM model

The identification of coal and gangue and the prediction of the degree of coal metamorphism based on the EDXRD principle and the PSO-SVM model

Study on Spontaneous Combustion Law and Prevention Technology of Abandoned Coal in Goaf of Coal Mine

The spontaneous combustion of coal in goaf areas is a significant natural disaster encountered during coal mining operations. To investigate the oxygen consumption characteristics of different coal types, we conducted TG experiments and closed oxygen consumption experiments using seven coal samples exhibiting various degrees of metamorphism. The findings revealed the following key observations: During the oxidation combustion process of coal, the absorbed heat originates from the physical and chemical adsorption of coal and oxygen. The first exothermic peak on the DSC curve represents the maximum combustion temperature of volatile matter and signifies the initiation of coal burning. Coal with higher ignition temperatures is less prone to spontaneous combustion. Analyzing the thermogravimetric curves, we observed that the ignition temperatures of 15# coal and 8+9# coal predominantly extracted from Duanwang Coal Mine are higher compared to the ignition temperature of the 4# coal seam (known for its susceptibility to spontaneous combustion) in Jiudaoling Coal Mine, Liaoning. This observation aligns with their nonspontaneous combustion characteristics. In the closed oxygen consumption experiment, we determined the volume oxygen consumption attenuation coefficients for the main mining areas’ 8+9# and 15# coal seams as 3.9001 × 10 − 4 and 3.83559 × 10 − 4 , respectively. Additionally, the critical oxygen consumption concentrations were measured as 15.71% and 16.78%. The shortest spontaneous combustion periods were determined to be 119.24 days and 121.25 days, respectively, for the aforementioned coal seams. To mitigate spontaneous combustion, the addition of inhibitors is necessary. The selection of an appropriate inhibitor depends on the increase in ignition activation energy. Notably, coal samples treated with a 15% MgCl2 inhibitor exhibited the highest increase in ignition activation energy. Hence, we concluded that a 15% MgCl2 inhibitor is the most suitable ratio for preventing spontaneous combustion.