Coal Metamorphism Research Articles

Small molecules from multistep extraction of coal and their effects on coal adsorption of CH4

The influence mechanism of small molecules on methane adsorbed in coal has always been one of the research hotspots in coal mine gas control and coalbed methane extraction. In this paper, three solvents, n-hexane, benzene, and tetrahydrofuran (THF), were used to make multistep extractions from three different metamorphic coals in mining areas, including Buertai (B), Huaibei (H), and Yangquan (Y). The composition of the extracts had been tested by the Gas Chromatography-Mass Spectrometer (GC/MS). The pore structures of residues were characterized by low-temperature N2 and high-pressure isothermal adsorption. According to the research results, it can be shown that the types and contents of small molecules in the extracts decreased with increasing metamorphism. The ability of adsorbing methane, and changes in specific surface area and pore volume are closely related to the degree of coal metamorphism. By adding different solvents, different organic small molecules can be extracted. The multistep solvent extractions of coal will lead to the increase of porosity and the removal of small organic molecules in coal. On the one hand, the increase of porosity by extractions can increase the amount of adsorption methane on coal. On the other hand, less methane was adsorbed on coal when less small organic molecules present. The influences of extractions have the double effects in methane adsorbing on coal.

Cравнительный анализ структуры углей различных стадий метаморфизма по данным ЯМР 13С

In this paper, the method of cross-polarization with magic angle rotation and decoupling from protons (CPMAS) 13C NMR spectroscopy obtained quantitative data on the distribution of carbon over structural fragments and calculated the degree of aromaticity (fa) of some coal samples from various Siberian deposits of a wide range of metamorphism. All the coals used in the work were characterized by standard methods (proxymate and ultimate analysis). The optimal parameters of the pulse program for recording the spectra of coals have been determined. To obtain quantitative data, the spectra were simulated. The spectrum model included from 9 to 13 components, depending on the stage of coal metamorphism. The dependences of the degree of aromaticity and the sum of oxygen-containing functional groups on the stage of coal metamorphism were constructed. The results obtained show that the structure of coals regularly changes depending on the stage of their metamorphism. The revealed relationships of the structure and properties of coals, together with the parameters of their reactivity, can ensure the safe behavior of coals in the processes of mining and processing, as well as in determining possible ways of using the studied coal samples as a valuable chemical raw material.

A Physical-chemical Synergetic Inhibitor for Coal Spontaneous Combustion and Its Fire Prevention Performance

ABSTRACT A single physical or chemical inhibitor can hardly meet the uttermost requirements for coal spontaneous combustion prevention. Therefore, it has become essential to develop an efficient inhibitor with multiple inhibitory properties. In light of studies on the properties of the super absorbent polymer (SAP), the main antioxidant pentaerythritol tetrakys 3-(3,5-ditert-butyl-4-hydroxyphenyl) propionate and auxiliary antioxidant tris (2,4-di-tert-butyl-pheny) phosphite, a synergistic antioxidant with both physical and chemical inhibitory properties was prepared. According to the determination of volatile matter and calorific value of coal, the optimum molar ratio of the compound antioxidant (main antioxidant: auxiliary antioxidant = 2:1) was selected. Furthermore, the optimum formulation ratio (SAP: antioxidant = 1:3) and the optimum mass ratio (12%) were determined, taking the low-temperature oxygen consumption and cross-point temperature (CPT) of coal as indexes. Three grades of metamorphic coal were selected to obtain the gaseous product, oxygen consumption at 70°C, CPTs and inhibition rate. The addition inhibitor reduced the release of CO and C2H4 gas and oxygen consumption, while it raised CPTs and inhibition rate of coal oxidation. The inhibiting capacity of MgCl2 is mainly at low-temperature stage, while the synergistic inhibitor has excellent congenerous physical and chemical effect in the whole coal oxidation process.

Parameters of geochemical effect equation for lanthanides and their geochemical significance for a series of metamorphic coals

The "geochemical effect of lanthanides" is a new concept proposed by the authors during the past decade. This concept reflects lanthanide shrinkage in elemental geochemistry, and it is statistically quantifiable. However, the geological significance of the various parameters of the equations obtained following quantization is not entirely clear. Cooperation and discussions from scholars in related research fields of rare earth elements in geology are required. In the present paper, from the perspective of coal geochemistry, the metamorphic coal seam of C2 series in Fengfeng Mine of Handan Coalfield in Hebei Province, China was used as an example. The geochemical significance of parameters in geochemical effect regression equation for lanthanides was evaluated, and two new formulas (regression equations) that characterized the geochemical behaviors of lanthanides were proposed. On this basis, concepts related to the geochemical effect of lanthanides, such as “individual parameters”, “parameters in common”, “two-sided parameters”, and the “deviation value” of lanthanides, were proposed. In this study, it was proved that the goodness of fit for all types of function regression equations for lanthanides and the radii of their trivalent ions, and the “deviation value” of lanthanides, were all “individual parameters” that could indicate the post-modified geological environment of C2 coal seam, such as the influence from magmatic-hydrothermal fluids. A covariant figure was constructed according to these individual parameters and other indexes, and the C2 coal seam in Handan was effectively divided into two different metamorphic series of A (C2 coal seam uninfluenced or slightly influenced by magmatic-hydrothermal fluids) and B (C2 coal seam strongly influenced and evidently changed by magmatic-hydrothermal fluids). Consequently, the scientific significance of all the parameters for lanthanides in an identifying series of metamorphic coals within the geochemical effect regression equation was further clarified.

Spectral manifestations of coal metamorphism: Insights from coal microstructural framework

The present study investigates the microstructural framework of coals from the Raniganj and the Jharia Basins as well as from the Himalayan fold-thrust belts of Sikkim, India, by vitrinite reflectance, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The mean random vitrinite reflectance data may imply that the coal samples from the Raniganj and the Jharia Basins range from the bituminous D to B, and would have experienced the burial heating corresponding to ~92 °C to 143 °C unlike the anthracite A samples that might have undergone the hydrothermal metamorphism at ~333 °C to 367 °C. The Raman spectra exhibit preferential removal of sp3 hybridized moieties from the anthracite samples at anchizonal metamorphic stage due to thermo-stress degradation effect induced by the Himalayan orogeny. Further, this study records the reduction of net dipole moment change due to the expulsion of functional groups from the aromatic rings making them infrared inactive. Additionally, the C1s spectra reveal the thinning of CC peaks and the lowering of the CO peak intensity with an increase in coal rank. This study, hence, documents the microstructural transformations in coal that can be used for structural maneuvering to control the liquefaction, gasification, pyrolysis, combustion as well as synthetic graphitization behavior.

Methane displacement characteristic of coal and its pore change in water injection

Coalbed methane as one type of clean energy has become an important gas resource recently. High-pressure water injection in coal seams is an effective approach for improving gas extraction efficiency, which is determined by the gas displacement characteristic and pore structure of coal. To investigate the gas displacement characteristics in coal and its pore response and influential factors, gas adsorption and water injection experiments were conducted under different conditions. The results show that the gas displacement caused by the water injection undergoes three stages: rapid increase, slow increase, and almost constant. The wetting process in water injection includes three processes: wetting, soaking, and spreading, and the wettability of coking coal is best, followed by lean coal and anthracite. The amount of gas driven by the water increases with increasing water injection pressure, and it is more favorable to increase the injection pressure to improve the gas displacement effect under the relatively low injection pressure. The lower the coal rank, the better the gas displacement effect due to the higher porosity of the coal, and the longer the early gas displacement stage. The high adsorption equilibrium pressure can improve the gas displacement effect; for the relatively high adsorption equilibrium pressure, the gas displacement effect is better. After water injection in coal, the large fractures and pores dramatically increase in size, especially for the low metamorphic coals coking coal, contributing to the majority of the increase in porosity. The results of this study can provide a theoretical foundation for the wide application of water injection technology for efficient gas drainage in coal mines.

Determination principle of residual Gas and Analysis of influencing factors on the results of Laboratory Measurement

In view of the current situation that the concept of residual gas content in coal seam in our country is relatively chaotic, the definition of residual gas content and the measurement principle of degassing and desorption methods in “The direct method of determining coalbed gas content in the mine” are analyzed. The standard unified method and the explicit concept are proposed. Through the laboratory desorption experiments in some mining areas, it is found that the residual content of gas and the degree of coal metamorphism are positively correlated as a whole. There is a negative correlation between the content of ash and internal moisture in coal and the residual content of gas. The order of the residual gas content of different sampling methods is as follows: core sampler> hydraulic slag sampler ≈ wind slag sampler, coal structure is complete, the change range of measured data is the smallest with core sampler, which can truly reflect the law of coal desorption and status.

Microscopic distribution and dynamic variation of water under stress in middle and high rank coal samples

Determining the process of water migration and transformation in a pore-fracture system under stress is essential to explain the effect of water saturation on permeability and adsorption in microstructures of coals. In this study, the immovable and movable water saturation values (Sir and Sm, respectively) of middle and high rank coal samples are calculated using saturation and centrifugation methods based on nuclear magnetic resonance (NMR) technology. Micro-distribution and influencing factor of water in the initial state are analyzed by low-temperature liquid nitrogen tests. Movable and immovable saturation variations under stress are elucidated by measuring the corresponding T2 spectrum of pores with a range of diameters. The results show that the heterogeneity of irreducible water in coal samples are considerably higher than that of movable water in all the samples. The irreducible state thereafter controls the micro-distribution of water in coal samples. With the increase in coal metamorphism, the distribution heterogeneity of immovable and movable water increases and decreases, respectively. The water content variations in adsorption pore, seepage pore, and fracture all decrease linearly with the increase in Sir, indicating that the amount of immovable water determines the dynamic variation, and the distribution of initial water mainly affects the water migration process. The immovable water saturation, Sir, has distinct stress sensitivity, and the capillary bound water present in seepage pore can be transformed into movable water. The effect of stress on immovable water in larger pore, such as seepage pore, is distinctly stronger than that on immovable water in adsorption pore. This study indicates that Sir obtained by the saturation–centrifugation method is significantly higher than the actual irreducible water saturation. The bound water saturation calculated by this method is only suitable for high rank coal samples with poorly developed seepage pore.

Research progress and prospects of coal petrology and coal quality in China

Clean utilization of coal depends on the quality of raw coal, which depends on the coal-forming parent materials (petrology and chemical composition of coal), the multiple media of the coal-forming environment, and some epigenetic conditions, such as thermal evolution (coalification), magmatic hydrothermal fluid, groundwater. Based on the research results of predecessors and prediction studies of coal resources since the founding of China, the present status of research on coal petrology, coal quality, coal metamorphism, and coal geochemistry in China is discussed in detail, with emphasis on research progress and the general situation of highly efficient and clean utilization of coal in the technical fields of coking, pyrolysis, combustion, gasification, and liquefaction, and the development prospects of coal petrology and coal quality in China are prospected.

Effects of 1-butyl-3-methylimidazolium tetrafluoroborate on the exothermic and heat transfer characteristics of coal during low-temperature oxidation

The effects of the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF4] on the exothermic and heat transfer characteristics of three metamorphic grades of coal during low-temperature oxidation were investigated. The C80 microcalorimeter results showed that the IL inhibited the exothermic process and characteristics of long-flame and non-caking coals, whereas the IL had a growth-promoting influence on gas-fat coal. The kinetics calculation results showed that the apparent activation energy of long-flame and non-caking coals increased after treatment but gas-fat coal was subjected to the opposite effects. According to the consequences of the LFA457 laser flash system, the IL decreased the thermal diffusivity and increased the specific heat of long-flame and non-caking coals. It had a notable inhibiting effect on the heat transfer properties of the two coals. However, the influence of IL on the heat transfer characteristics of gas-fat coal shows a salient promoting effect. Therefore, we conclude that the IL inhibited the generation and transfer of heat during the low-temperature oxidation of long-flame and non-caking coals. This prevented the occurrence and development of coal spontaneous combustion, but it had the opposite effect on gas-fat coal. The effect of the IL on the thermal behaviour of coal oxidation at low temperature varied with the degree of metamorphism of coal, and such an influence played a dual role in this because of its inhibition and promotion in relation to this reaction. This demonstrated that the IL did not inhibit the spontaneous combustion of all types of coal.

ON DETERMINING THE COAL CARBONIZATION INDICATOR FOR ESTABLISHMENT OF MINE FIRE HAZARD GROUPS

The article analyzes the dependence of endogenous fire hazards on the following factors: the degree of coalification, the total sulfur content, the thickness of the developed formations and their structure, the presence of tectonic disturbances. By the genetic propensity of coals to spontaneous combustion, three groups of coal sites are distinguished: І – Vdaf ≥ 41%, Сп ≤ 7, coals of marks D and partially G; ІІ – Vdaf = 40-30%, Сп ≤ 8, coals of marks D and partially F; ІІІ – Vdaf < 36%, Сп >8, coals of marks Zh, K, OS, T. Studies have shown that individual dependences of the decrease in the content of each component (Оo, Нo, No) significantly differ from each other. Decrease in oxygen content, as well as the sum of the main components, occurs with an increase in carbon content. The sum of the content of the main components decreases inversely to the increase in carbon content over the entire range of coal conversion from a small degree of their metamorphism (Со ≈ 70%) to anthracites (Со ≈ 98%). The dependence of decrease in oxygen content with increased carbon is nonlinear. With carbon content of more than 88%, there is a slight decrease in the rate of oxygen reduction in comparison to its decrease at earlier stages of metamorphism. Data analysis showed an almost functional dependence between the sum of the main components of the organic mass (0.995). A significant correlation of carbon with oxygen and hydrogen is observed. A significant scatter of points in experimental data is due to the diversity of composition of the source material, the conditions of its accumulation and transformation for different coal basins and individual coal sites. Studies have shown that the relationships between all the main components of the organic mass of coal during metamorphic transformations change significantly at different stages of these processes. The established dependence of the carbonization index on the carbon content at different stages of coalification allowed us to develop an engineering method for calculating the carbonization index for the entire range of coal metamorphism. The proposed method significantly clarifies the determination of the carbonization index, which is necessary not only for establishing the fire hazard of mine layers, but also for establishing other manifestations of the dangerous properties of coal sites during mining operations. Keywords: carbonization index, endogenous fire hazard, elemental composition, organic mass, metamorphism, coalification.

Three‐dimensional characterization of open and closed coal nanopores based on a multi‐scale analysis including CO2 adsorption, mercury intrusion, low‐temperature nitrogen adsorption, and small‐angle X‐ray scattering

AbstractCoal seams in China have poor permeability and a complex pore structure, leading to a low gas extraction efficiency. Studying the pore structure of different metamorphic degrees of coal by using modern technological methods and employing appropriate pumping measures for different pore structures can improve the gas extraction efficiency. In this study, the pore sizes of three coal samples with different metamorphic grades were measured at different pore scales through CO2 adsorption, nitrogen adsorption, small‐angle X‐ray scattering, and mercury pressure methods. The pore structure was three‐dimensionally reconstructed using the lattice Boltzmann method‐based quartet structure generation set algorithm. The optimum pore size measurements performed using the CO2 adsorption, nitrogen adsorption, small‐angle X‐ray scattering, and mercury pressure methods were in the ranges of 0.3‐2, 1.7‐300, 1‐50, and 7.5‐11 000 nm, respectively; this demonstrates that the structure of a full‐scale coal model cannot be accurately tested using a single technique. The pore structure varies depending on the metamorphic degree of the coal; therefore, coal metamorphism should be considered for effective gas extraction.

Experimental investigation on wetting mechanism for coal dust with different metamorphic degree based on infrared spectrum and 13C‐NMR

Respirable coal dust accounts for heart and respiratory diseases of coal miners such as asthma, pneumoconiosis, and black lung disease. What is more, coal dust explosion seriously affects coal mine safety production and coal miners' life safety. Generally, dust suppressants are commonly applied in coal mines. However, current dust suppressants are not working effectively. To develop a better dust suppressant, we attempt to explore the factors affecting the wettability of coal dust under different metamorphic levels from the essence of coal dust wetting mechanism in this paper. Specifically, we use Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) to reveal the microstructure of coal from two aspects of functional group and carbon skeleton structure and obtain the micro information of the surface functional group types, quantity, and carbon structure of coal with different degrees of metamorphism, as well as the change rule of functional group of coal sample with coal rank and the law of carbon increase and deoxidization of coal metamorphism. After that, we acquired the structural parameters of coal by the NMR experiments and fitted the quantitative mathematical relationship between the microstructure parameters and wettability of coal through SPSS and ORIGIN software. Finally, this paper constructs an evaluation model for the influencing factors of coal dust wettability, explains the influence degree of different coal dust structure on coal dust wettability, improves the coal dust wettability mechanism, and provides more quantitative research ideas and methods for the control of coal dust.

GEODYNAMICS OF DONETS BASIN FORMATION

The proposed model is based on the mobile concept of tectonics, according to which the modern structure of the basin is the result of the joint influence of geodynamic processes and forces caused by the movement and interaction of lithosphere plates. Alongwith the known planetary processes, the formation of Donbass, located on the southern edge of the Eastern European Plate (SEP), was influenced by convergent processes occurring on its southern edge and the membrane forces created by moving the plate alongthe meridian.It is established that sedimentation, volcanism, inversion of the geotectonic regime, paleogeotetemperature regime, which caused a high degree of coal metamorphism in Donbass, are determined by convergent processes that took place on the southern edge of the EPS in the Phanerozoic.

Molecular structure characterization of low-medium rank coals via XRD, solid state 13C NMR and FTIR spectroscopy

In-depth understanding of coal molecular structures is crucial to the clean and efficient coal conversion, as they are the dominant factors determining the reactivity and reaction behaviors of coals in thermal conversions such as combustion, pyrolysis, gasification and liquefaction. However, the molecular structures of coals are still far from clear due to the intrinsic complexity and heterogeneity of coals. This work probes the molecular structures of eight coals of various metamorphic grades with combined spectral techniques of X-ray diffraction (XRD), solid state 13C NMR and FTIR spectra. The structural parameters were correlated with the coalification indicator Ro to investigate the structural evolutions during coal metamorphism. Consistent results concerning the structural evolution during coalification were obtained with different techniques. From the parameters of proximate and ultimate analysis, the increasing aromaticity and decreasing aliphatic fractions with rising coalification degree are observed. XRD patterns show the ubiquitous presence of amorphous carbon, the gradually condensing aromatic layers, and the size-growing but graphitizing crystallites during coalification. 13C NMR spectra reveal different types of carbons presented, the increasing aromatic and decreasing aliphatic components, the growing size and weight but reducing number of side-chains of the aromatic clusters. FTIR spectra indicate shortening and reducing of aliphatic chains, as well as enhancing aromaticity with the deepening metamorphism. These findings shed light on the structure features of coals and are potentially useful to the clean and efficient coal utilization.

Methane gas hydrates influence on sudden coal and gas outbursts during underground mining of coal deposits

The mechanism of gas hydrates formation in coal seams is studied in the paper, as well as their involvement is hypothesized in the sudden outbursts of coal and gas during underground mining of coal deposits. It has been substantiated and proved that one of the real reasons for subsequent outbursts is the formation of gas hydrates in coal as a type of secondary gas hydrate deposits. It has been also substantiated that, as a result of coal metamorphism, a large amount of gaseous hydrocarbons, mainly methane, is formed in the seam, which under certain thermobaric conditions leads to the gas hydrates formation. It has been experimentally proved that the mechanism of such inclusions formation between gas hydrate and coal is a result of strong chemisorption, which, when disturbing thermobaric conditions, leads to gas-dynamic activity of coal seams. It has been revealed that during the dissociation of gas hydrates, obtained in a medium of activated coals, twice as much gaseous methane is released. The research analysis indicates that the formation of natural gas solid solutions in coal pores under certain thermodynamic conditions and the natural humidity, characteristic of coal seams, is one of the causes of sudden coal and gas outbursts. The gas hydrates dissociation influences on the gas-dynamic activity of a coal seam and the formation of an outburst hazardous situation.

Peculiarities of using classification indicators of the coal metamorphism degree for predicting the hazardous coal seams properties

Currently, there is no reliable regulatory framework for determining the hazardous properties of coal seams, including the propensity of coal for spontaneous combustion. Under relatively identical mining engineering and geological conditions for mining coal seams, the probability of emergency situations is determined to a large extent by the genetic properties of coal. The research methodology is based on the classical definition of metamorphism, which characterizes the change in the composition and properties of coal. The analysis involves indicators that directly or indirectly characterize the elemental composition of organic and mineral mass, chemical activity and physico-mechanical properties. This will allow to establish a specific composition and properties that contribute to the manifestation of certain hazardous properties of coal seams during mining operations. It is shown that the modern industrial classification does not take into account the change in the organic and mineral constituents of coal, which does not make it possible to use it unchanged to predict the hazardous properties of coal seams.

On determining coal classification indicators for establishing dangerous properties of mines

Currently, more than 20 qualification indicators are known by which degree of metamorphic coal transformations are established. Most of these indicators are designed for determining technological properties with industrial use of coal in mind. Due to sufficient knowledge of the indicators used, industrial classifications are constantly being improved. The modern classification by genetic and technological parameters groups the coals by the grades based on ten indicators. Of these, only one - the mass yield of volatile substances during the thermal decomposition of coal - is used as the main indicator of the manifestation of dangerous properties of coal seams without due scientific justification. Dangerous properties of coal seams during mining include: gas content of coal, a tendency to gas-dynamic phenomena and spontaneous combustion, dust forming ability and explosiveness of coal dust. In industrial classifications, the main indicator is determined for the dry ash-free state of organic matter. Manifestation of dangerous properties of coal seams occurs in the presence of both moisture and mineral impurities. This fact is not taken into account by other auxiliary indicators used to predict the hazardous properties of coal seams. Moisture in coal seams is in at least four states, and it is completely removed while analyzing the samples and is not taken into account in volatile products of thermal decomposition of coal. Thus, when using the indicator of mass output of volatile substances, influence of moisture in any form of its presence in coal on the occurrence of emergency situations is automatically ignored. The probability of emergencies during mining is largely determined by the ratio between components of organic mass (C, O, H, S, N) and mineral impurities. It is also not taken into account in normative documents which regulate safety of coal seam mining. The classification indicators defined in different ways characterize different aspects of coal conversion in metamorphic processes. Volatiles yield and average vitrine reflectance, well studied in industrial applications, correspond to different aspects of degree of conversion of starting organic matter. In order to establish dangerous properties of coal seams, their mutual substitution is unacceptable, which is confirmed by nonlinear connection between them. The existence of a genetic relationship between the outburst and fire hazard of coal seams has been established. This indicates the need to develop a unified classification of the hazardous properties of coal seams by genetic, mining engineering and geological parameters. The scientifically substantiated use in regulatory documents of a set of classification indicators that directly characterize the manifestations of the hazardous properties of coal seams will help to reduce number of accidents and injuries in coal mines.

Experimental analysis of the pore structure and fractal characteristics of different metamorphic coal based on mercury intrusion‑nitrogen adsorption porosimetry

The pore structure of different metamorphic coal was analyzed by mercury intrusion porosimetry and N2 adsorption. Combined with the fractal dimension models of the Frenkel-Halsey-Hill and Menger, the pore size range of the experiment was spliced reasonably. A new pore classification scheme is put forward by fractal dimensions, revealing the pore structure and fractal characteristics of different metamorphic coal. The results suggest that pores exhibit piecewise fractal characteristics. A new pore classification scheme is put forward by piecewise fractal dimensions: I (0–2.0 nm, corresponding to D1); II (2.0–50 nm, corresponding to D2); III (50–2000 nm, corresponding to D3); IV (2000–20,000 nm, corresponding to D4); V (>20,000 nm, corresponding to D5). It is not inconsistent with the international union of pure and applied chemistry for pore classification, which shows that the new pore classification scheme is reliable.

Analysis of metamorphism and tendency of black coals to spontaneous combustion

The object of this study is coals of different stages of metamorphism and the volatile products of their thermal decomposition. Currently, based on the basic genetic signs of metamorphism, there is no reliable regulatory framework for determining the hazardous properties of mine plastics, including the propensity of coal for spontaneous combustion. Difficulties in systematization consist in the absence of at least one classification parameter, which determines the need for an additional analysis of the physicochemical properties of coals of different stages of metamorphism and the volatile products of their thermal decomposition as an object of study.Thanks to the obtained functional dependences characterizing the elemental composition of fossil fuels in the entire range of a series of metamorphism, it is possible to evaluate the classification indices of fossil fuels. The result shows that changes in the properties of coal as a result of transformations of the internal structure can take maximum or minimum values. It is impossible to judge the change in the properties of coals from the elemental content of these components by the monotonous and one-sided changes in the components С0, О0, and N0. The nature of the dependence of Н0 on Vdaf and specific gravity (Kd) suggests that coals acquire new properties after Vdaf decreases by less than 30–25 %, and specific gravity at Kdg 1.3It is noted that coals with the same properties can in some cases be characterized by different values of the classification indicators (Vdaf Cdaf, Kd), in others–- coals with different values of the classification indicators have the same properties. The changes in the physicomechanical and calorific value of coal from Vdaf and Сdaf are complex and ambiguous. This is indirect evidence of changes in the internal structure of coals in the process of their geological transformation. The restructuring of the internal structure of coal led to a change in their electromagnetic characteristics.It is proposed, when establishing the propensity of coal for spontaneous combustion by genetic and technological parameters, to use modern knowledge in the field of geology, historical geology and paleontology, physics, chemistry, thermodynamics, as well as experience in the industrial use of coal.