Degree Of Metamorphism Research Articles

Research of combustion of solid fuel mixture based on coals of different degrees of metamorphism in the regions of Yenisei Siberia

THE PURPOSE. Consider the combustion process of two coals of different degrees of metamorphism and their mixtures using thermogravimetric analysis based on the change in mass and the rate of change in mass during the heating of fuels. Determine the main characteristics of fuels and the combustion process (temperature of ignition and burnout of the coke residue). Determine the tendency to slagging of coal mixtures. METHODS. When solving the tasks, the thermogravimetric method (TGA). RESULTS. The article provides a brief overview of the combustion of non-design fuels at thermal power plants. The results of technical and elemental analysis of Chernogorsk bituminous coal and Balakhta brown coal are presented. A technique for determining the ignition temperature and burnout of the coke residue is described. The thermograms of the combustion process of two coals of different degrees of metamorphism and their mixtures are presented. The main characteristics of their combustion have been determined. A qualitative analysis of the surface of fuel particles for the presence of pores and cracks is shown. The calculation of the tendency to slagging of coal mixtures has been carried out. CONCLUSION. Thermogravimetric analysis showed an earlier ignition of the Balakhta brown coal in comparison with the Montenegrin bituminous coal. With an increase in the proportion of Balakhta coal in the coal mixture, the profile of the combustion curves shifts to the region of lower temperatures. The addition of 25% Balakhta coal reduces the ignition temperature of Chernogorsk coal by 16%, with an increase in the proportion of Balakhta coal in the mixture, the ignition temperature does not change. Balakhta coal has a high tendency to slagging furnace walls, in contrast to Chernogorsk coal, therefore, an increase in its mass fraction in the coal mixture increases the tendency to slagging furnace screens.

Molecular simulation study on the effect of coal metamorphism on the competitive adsorption of CO2/CH4 in binary system

To explore the competitive adsorption characteristics of a CO2/CH4 binary gas in coal with different metamorphic degrees, macromolecular-structure coal models with different metamorphic degrees (anthracite coal, coking coal, and long-flame coal) were constructed based on elemental analysis, X-ray photoelectron spectroscopy (XPS), and carbon-13 nuclear magnetic resonance (13C NMR) results. Then, the competitive adsorption behaviors of CO2 and CH4 molecules in the different coal molecular models were simulated using molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) methods, and the changes of the competitive adsorption capacity, density distribution, adsorption selectivity, adsorption heat, and energy distribution were investigated. The results showed that the variation characteristics of the total adsorption of mixed gas were similar to those of pure gases, and the increase in the pressure led to an increase in the total adsorption, which also increased with the increase in the coal deterioration degree. The distribution ranges of the gas adsorption sites in coal with different metamorphic degrees were significantly different, with anthracite coal being the most widely distributed and long-flame coal being the least widely distributed. With the increase in the coal rank, the competitive adsorption selectivity of any proportion of CO2/CH4 binary mixed gas increased. The difference in the equivalent adsorption heat of single-component gases CO2 and CH4 in the mixed gas increased with the increase in the coal metamorphism and decreased with the increase in the CO2 gas proportion coefficient. This paper provides a theoretical basis for the application of CO2 enhanced coal bed methane in coal seams with different metamorphic degrees.

Evolution of Composition and Methane Occurrence of Bituminous Coal after Igneous Intrusion: A Case Study of Daxing Coal Mine, Tiefa Basin, China.

Since 1987, there have been 10 coal and gas outbursts in Daxing Coal Mine, Tiefa Basin. It was reported that these outbursts were related to igneous intrusion. To study the influence of igneous intrusion into bituminous on coal bed methane (CBM) occurrence, eight coal samples were collected at different distances (0.2-10 m) from an intrusion in Daxing Coal Mine. The petrographic and chemical data, pore characteristics, and adsorption properties of unaltered and heat-affected coals were tested and compared. Approaching the dike, vitrinite reflectance (R o) increases from 0.56 to 1.14%, while moisture decreases from 6.4 to 3.1%. According to R o, with the thermal evolution of igneous rocks, the temperature of heat-affected coal seams generally increases from ∼78 to ∼169 °C. The bituminous coal contained high moisture content before the intrusion, and after the igneous intrusion, partial heat may be used for moisture gasification; the other heat was used to improve coal metamorphism, resulting in little increase in the coal metamorphism as expected. The synergistic effect of igneous thermal evolution and moisture content change improves the adsorption capacity of coal. Affected by the igneous intrusion, the gas content of the heat-affected coal seams No. 4 (above the sill) and No. 7 (below the sill) is higher than that of the unaltered No. 12 coal seam, and the gas content of No. 7 coal seam (beneath the sill) is higher than that of No. 4 coal seam. The low permeability sill has a sealing effect on the gas in No. 7 coal seam. Therefore, the evolution process of CBM occurrence in the Daxing Coal Mine can be speculated, that is, after magma intrusion, the temperature increased, the metamorphic degree of coal increased, and water gasification occurred at the same time. The original adsorption site occupied by moisture was vacated, which improved the methane adsorption capacity of the coal and provided favorable conditions for CBM occurrence.

A Method for Detection of Fire Source Positions in High-Temperature Areas

Spontaneous combustion of coal is an important disaster that needs to be addressed in the coal mine production process. Since its ignition position is often unknown and concealed, determining the ignition position in the goaf is of great significance to the work safety of the mining area. This study measured the thermal conductivity of coal samples using the spherical thermal conductivity model, and obtains the fitting relationship between the thermal conductivity, the heating voltage U and the inner sphere outer wall temperature t1 by inputting different voltages, and the correlation coefficient R2 was all greater than 0.99. Through analysis of the spherical geometric model, it was determined that the ignition point was at the vertical depth of 16.542m from the highest temperature point in the goaf, and that the distance from the ignition position to the ignition source ranged between 13.49m to 1.03m when the temperature in the goaf was 60℃ to 1700℃. Through comparison with the actual data, the error was found to be 4.7%, indicating that the proposed model was more accurate. Finally, it was found that the thermal conductivity of coal is closely related to the porosity, degree of metamorphism and inhomogeneity of the medium.

Tribology in mining: Highlights in iron ore abrasiveness

This article aims to present results on research, recently developed, and related to wear of equipment to meet the challenges of the mining industry. Emphasis is done to iron ore mining in Brazil due to the relevance of the sector for its economy and the relevance of tribology for assets and productivity. Results and considerations cover wear of equipment (conveyor belts, ore pipelines) and development of high chromium cast iron (HCCI) microstructures to face the wear. Under wet erosive wear caused by pumped slurries with different compositions of solid particles the wear of samples tested follows a trend in which those with higher silica contents provided greater mass losses of high chromium cast iron (HCCI) samples. On the other hand, when surface protection against wear of components is the objective, the presence of niobium in a hardfacing coating contributed to increase resistance to abrasion, due to the presence of niobium carbides (NbC). It was also demonstrated that there is a positive correlation between the degree of metamorphism of iron ore throughout its genesis and evolution in relation to the abrasiveness.

Abundances of siderophile elements in H-chondrite metal grains: Implications for the origin of metal in unequilibrated ordinary chondrites

Understanding the evolution of metal in the protoplanetary disk is necessary to constrain the first steps of metal-silicate segregation and the early stages of the evolution of the protoplanetary disk. We measured the siderophile elemental compositions (PGE, Ni, Co, Fe, Cu, Ga, Ge) of individual metal grains in H ordinary chondrites by laser ablation inductively coupled plasma mass spectrometry to investigate their formation. We analyzed unequilibrated ordinary chondrites (H3) to constrain processes affecting the metal before accretion, and inferred the effects of metamorphism by comparing their elemental compositions to those of equilibrated chondrites (H4–H6). Our results highlight large variations of refractory (Re, Os, W, Ir, Ru, Mo, Pt) and moderately volatile siderophile element (Pd, Au, Ga, Ge) concentrations among metal grains in H3 samples that permit to classify them according to their Ge/Ir ratios and HSE contents. These intergrain variations are progressively homogenized in H4–H6 samples due to their increasing degrees of metamorphism. To constrain the origin of the metal, we modeled its evolution during melting and crystallization. Our melting model of a single metallic precursor containing 1.5 wt% C and up to 12 wt% S reproduces well the observed range of siderophile element compositions in the metal. Metal grains show a range of W, Mo, and Ga compositions that we interpret to reflect various local (grain-scale) oxidation states during the melting event(s) due to the heterogeneous distribution of various oxidizing components within the precursors. The very similar HSE compositions of H and L/LL metal grains suggests that the variations of bulk metal abundance and HSE concentrations observed among the different classes of ordinary chondrites (H, L, LL) result from the heterogeneous physical distribution of a relatively chemically homogeneous metal component among OC parent bodies, and not from a chemical (sensu lato) gradient between H and LL chondrites.

Construction of different metamorphic degree coal models and corresponding adsorption characteristics based on molecular simulation

Coal samples with different metamorphic degrees have different gas-adsorption capacities. Most of the existing studies analyze differences in gas-adsorption characteristics from a macro perspective, based on experimental methods, and there has been limited research on the micro level. Using industrial and elemental analyzes, Fourier-transform infrared spectroscopy, 13C-NMR, and X-ray photoelectron spectroscopy, we tested and analyzed the molecular-structure characteristics, such as elemental composition, atomic ratio, and functional-group type and distribution, of three coal samples: anthracite (WYM), coking coal (JM), and lignite (HM), with different metamorphic degrees and constructed their macromolecular-structure models. The carbon contents and densities of the models were consistent with the measured values. We also constructed a coal matrix model using a molecular simulation based on the constructed coal molecular model. By comparing and analyzing the trends of adsorption amount, isosteric heat, and selective adsorption coefficient, we explored the differences in the adsorption characteristics of single and binary mixtures on coals with different metamorphic degrees. The adsorption of CH4 and CO2 on the coal matrix conformed to the Langmuir adsorption model. With increasing metamorphic degree, the adsorption amount increased in the order WYM > JM > HM, and the adsorption capacity of the coal matrix for CO2 was higher than that for CH4. The isosteric adsorption heat of CH4 was proportional to the degree of coal metamorphism; however, its relationship with pressure was not clear. Under different temperature and pressure conditions, the selective adsorption of CH4/CO2 on coal with various metamorphic degrees decreased with an increasing CO2 molar ratio. Conditions of 303.15 K (30 °C), 2–4 MPa, and CH4/CO2 = 0.1 were more conducive to the competitive adsorption of CO2 than that of CH4.

Metamafic dyke and sill swarms in the Dom Feliciano Belt: Insights for post-collisional strike-slip tectonics and fluid-assisted metamorphism

The oblique collision of the Congo, Kalahari, and Rio de la Plata cratons resulted in the formation of the Dom Feliciano Belt that evolved from rifting, drifting, and amalgamation between ca. 1.0 and 0.5 Ga. The post-collisional stage of the orogenic event (ca. 600 – 530 Ma) is marked by lithospheric scale shear-zones, voluminous magmatism, and volcano-sedimentary sequences. However, the tectonic regimes, metamorphism and the development of space-forming structures are still debated. We present a comprehensive petrographic, mineralogical, and geochemical study of Ediacaran metamafic dyke and sill swarms from the easternmost portion of the São Gabriel Terrane (central Dom Feliciano Belt, southern Brazil). Mafic swarms and lamprophyres from two different areas in the syntectonic Caçapava do Sul aureole show heterogeneous microstructures, metamorphic degree and whole-rock composition due to heterogeneous metamorphism, deformation, and metasomatism. We aimed at deciphering the origin of the sheeted intrusions and the metamorphic processes that led to such heterogeneities. Trace-element composition indicates that the melts were formed at high depths and went through significant crustal assimilation during the ascent through the crust either in a continental arc or an island arc setting. Greenschist facies metamorphism and upper-crust brittle deformation partially preserved subvolcanic textures in metamafic dykes at the outer portion of the aureole. In opposition, amphibolite facies metamorphism with a significant fluid flow component resulted in highly modified and heterogeneous metamafic sills at the inner portion of the aureole and at high strain domains of the Caçapava do Sul Shear Zone. Heterogeneities in different areas are caused by the distance to batholith and to high-strain domains of the shear zone while variations within the same area result from heterogeneous and localized fluid flow during metamorphism. We suggest that the mafic swarms represent markers of the initial stage of the development of the shear zone and were metamorphosed due the subsequent syntectonic emplacement of Caçapava do Sul Granitic Complex. Remarkably, we note that heterogeneities in coeval units that often hinder the understanding of the Precambrian stratigraphy can be explained by heterogeneous fluid-assisted metamorphism, especially near shear zones and syntectonic intrusions.

Lithogenic Potential of Soils Formation in Technogenic Landscapes of Siberia

The results of long term research on the influence of rocks stored in dumps during coal mining on the rate of soil processes during the regeneration of technogenic landscapes are presented. An approach to assess the lithogenic potential of soil formation as an integral indicator of the ability of technogenic substrates to ensure the formation of a climate-appropriate soil profile was developed and applied. It is shown that the main properties forming the potential are the density, rockiness and texture of rocks. The rockiness decreases in the upper part of the profile and the manifestation of signs of an eluvial process and the formation of a finely dispersed fraction during biochemical weathering was noted. The dependence of the processes of profile differentiation on the properties of the substrate and on hydrothermal conditions has been revealed. It is shown that the optimal conditions for the developing of the substrate by soil processes are formed on the dumps of coal and brown coal deposits in a humid climate. Further development of soil-forming processes limits by the increase in climate aridity and the degree of rock metamorphism.

Link between melt-impregnation and metamorphism of Atlantis Massif peridotite (IODP Expedition 357)

IODP Expedition 357 drilled 17 shallow sites scattered over ~ 10 km in the west to east spreading direction across the Atlantis Massif oceanic core complex (OCC, MAR, 30 ºN). Mantle exposed in the footwall of the Atlantic Massif OCC is nearly wholly serpentinized (80–100%) harzburgite and subordinate dunite. A recent whole-rock chemistry study by Whattam et al. (Chemical Geology 594. 10.1016/j.chemgeo.2021.120681, 2022) subdivides Atlantis Massif peridotites into: Type I fluid–rock dominated serpentinite, which exhibits almost nil evidence of melt-impregnation or silica metasomatism; Type II melt–rock dominated, mafic melt-impregnated serpentinite; and Type III melt–rock dominated Si-metasomatized serpentinite. In this study, on the basis of EPMA, three kinds of Cr–spinel are distinguished in Expedition 357 serpentinite: (I) primary, unmetamorphosed mantle array, (II) low-Ti metamorphosed, and (III) high-Ti melt reacted. All Cr–spinel of western site Type I serpentinite is unmetamorphosed (n = 34) and comprises 68% of all unmetamorphosed Cr–spinel. Metamorphosed Cr–spinel (n = 100) are the most abundant and occur in the central and eastern site Type II and Type III serpentinite, whereas melt-reacted Cr–spinel and chromite are restricted to the central sites and occur predominantly in serpentinized dunite. Estimates of the degree of melt extraction of Type I serpentinite using F = 10ln(spinel Cr#) + 24 are ~ 9–17%. Fugacity calculations of primary, unmetamorphosed Cr–spinel yield Δlog(fO2)FMQ of − 1.7 to + 1.0 and calculations using olivine–spinel Mg–Fe exchange thermometry yield a mean closure temperature of 808 ± 39 °C. Mafic melt-impregnation resulted in Cr–spinel with anomalously high TiO2 of 0.27–0.68 wt.% and production of Ti-rich chromite (up to 1.23 wt.% TiO2). Greenschist facies metamorphism (< 500 °C) resulted in Mg–Fe2+ exchange between Cr–spinel and forsterite and anomalously low Cr–spinel Mg#; higher degrees of amphibolite facies metamorphism (~ 500–700 °C) also resulted in anomalously high Cr# due to Al–Cr exchange. As has been previously established, significant Al loss from chromite cores above 550 °C is the result of equilibration with fluids in equilibrium with chlorite, which may be valid for our samples. On the basis of Cr–spinel vs. whole-rock compositions, a clear relationship exists between melt-impregnation and metamorphism of central and eastern serpentinite, which we postulate to be the result of heat associated with magma injection and subsequent localized contact metamorphism. To our knowledge, such a relation between mafic melt-impregnation of peridotite and metamorphism (of peridotite) has not previously been established in general and specifically for the Atlantis Massif peridotite. Closure temperatures of 440–731 °C of metamorphosed Cr–spinel approximate greenschist to amphibolite facies metamorphic conditions.

Analysis of metamorphism and tendency of coal seams and their hazardous properties

The object of this study is coals of different stages of metamorphism. Currently, a situation has arisen when indicators developed to establish the consumer qualities of coal are used to predict the manifestation of hazardous properties of mine seams during mining operations. The need to consider the fuel for its working condition is due to different end goals between the establishment of consumer qualities of coal and the manifestation of the hazardous properties of mine seams. The condition and quality of coal after its preparation for use is significantly different from the condition in the mining area. Appropriate sample preparation changes the physical and chemical properties of coals, which determine the manifestation of the hazardous properties of mine layers during mining. To eliminate such a discrepancy, the quality indicators of coals were recalculated for their working condition, taking into account the yield of ash and moisture content for the mined mine seams, followed by an analysis of changes in the correlations be-tween the indicators. The indicators of the manifestation of the hazardous proper-ties of mine layers are borrowed from the characteristics of the quality of the fuel, reduced to a dry, ash-free state. Using these indicators, additional errors are introduced in advance into the accuracy of the prediction of the manifestation of hazardous properties during mining operations. The values of the indicators of the organic (combustible) part of the fuel serve as general reliable characteristics of its quality for the entire set of mine seams, but they cannot be used to predict the hazardous properties of a particular mine seam due to a decrease in the accuracy of their determination due to the unpredictable content of mineral impurities and moisture. The initial experimental data, which have been accumulated over several decades based on the experience of using coal for industrial purposes, are analyzed. On the basis of the conducted researches the peculiarities of the choice of indicators of metamorphic transformations of coal, which are used in parallel respectively to establish the quality of fuel and forecast the dangerous properties of coal seams, have been established. The discrepancies between the indicators of the degree of metamorphism used in the current regulatory framework for the safe conduct of mining operations, the state of fuel during mining operations in underground conditions.

Phenomena and mechanism of slagging and corrosion in energy use of coal with a high content of salts

Purpose. Determination of the main mechanisms of slagging and corrosion of heating surfaces when using coal or other raw materials with a high content of alkali and alkaline earth metals. Experimental determination of mineral phases of ash residues of burning composite raw materials with the participation of salty coal and the influence of component composition on the formation of refractory compounds. Methodology. Critical analysis and generalization of achievements in the developed theories of slagging and corrosion of surfaces during the combustion of problematic carbon raw materials (salty coal, biomass, some wastes, etc.). Determination of the main approaches to the problem of using coal with a high pollution factor. Selection of objects of experimental study on composite raw materials, including coal of different degrees of metamorphism and salinity. Identification of minerals of ash residues of individual fuels and their blends using X-ray phase analysis (X-ray diffraction). Semi-quantitative phase analysis of diffractograms was performed using MATCH! software. Findings. Modern views on the causes of slagging and corrosion processes during the combustion of fuel with a high salt content are highlighted. It has been determined that the process of intensive slagging is associated with a certain ratio of sodium, calcium and iron compounds. The composition and features of the mineral phases of ash residues of composite fuel with the participation of salty coal are experimentally established. The influence of the content of components on the formation of certain mineral phases of mixed ash was determined. Originality. For the first time, the prospects of using two-component blended fuel with the participation of Ukrainian salty coal have been studied. The analysis of minerals in ash residues of salty coal and its blends was carried out. It has been determined that the main part of Na in ash of salty coal of the Bohdanivske deposit in the Northern Donbas is in the form of sulfates and silicates. For the first time, the composition and ways of formation of new refractory mineral compounds in the ash formed during the combustion of composite fuel from coal of different metamorphism and salinity have been established. Practical value. Based on the analysis of literary sources and conducted studies, the dependence of the ash composition on the minerals of the initial fuel and on the ratio of various components in the blends was determined. The proposed approach has a predictive power, as it allows predicting the formation of the main refractory ash minerals. The expediency and prospects of involving salty coal in the fuel base of Ukraine as a component of blended fuels are shown.

Ignition and combustion characteristics of coal - water fuels based on coal & semi-coke

AnnotationThe article presents the results of experimental and theoretical studies of the ignition processes of coal- water fuel (CWF) drops made from coals of various degrees of metamorphism and coal semi-coke of these coals. It is shown that the preliminary torrefaction of coal leads to a significant improvement in environmental performance (50–60% reduction in flue gas concentrations of the main anthropogenic coal combustion products: nitrogen oxides NOx and sulfur SOx) of coal- water fuel combustion processes. This effect is most pronounced during the combustion of CWF based on lignite. Also, according to the results of the experiments, the ignition delay times of typical droplets (in the initial state), and then particles (after drying the near-surface fuel layer) of coal- water fuel s based on coals and coal semi-coke were established. It has been established that the ignition delay times of coal- water fuel particles based on pre-torrefied coals at relatively low ambient temperatures (Tg≤873 K) are on average 20% higher than when igniting CWF droplets based on natural coal. Under conditions of high-temperature heating, the ignition delay times of CWF particles made from natural coal and semi-coke differ insignificantly (no more than 2%).Based on the results of the experimental studies, a mathematical model of the ignition process of a coal- water fuel drop based on semi-coke was developed, which differs from the known ones in a relatively simple description of the most significant processes of thermal preparation and ignition, but at the same time retains a fairly high predictive potential. Using the previously developed method of quasi-stationary "thermal approximation" with the selection of an asymptotic estimate, an analytical solution is derived for the essentially nonlinear problem of coal- water fuel droplet ignition. ColloquiumAn analysis of modern political discourse shows that the information entropy associated with the problem of the anthropogenic impact of mankind on the planet's atmosphere as a result of the operation of energy facilities is constantly growing. At the same time, the constant growth of energy consumption in the world makes it necessary to introduce more and more new heat and power generating capacities. For a long time (the last 30 years) it was believed that the solution to all energy problems is the large-scale introduction of non-traditional renewable energy sources (solar batteries and wind power generators - RES) into the overall balance of energy generation. However, recent events in North America and Western Europe show that the potential for using renewable energy sources is significantly limited, and electricity generation from these renewable energy sources is still significantly unstable. In this regard, a new impetus for development is acquiring coal energy. However, the main problem of coal power engineering, the anthropogenic impact of thermal power plants on the planet's atmosphere, remains unresolved. This situation creates prerequisites for the development of new "clean" coal technologies with complete sequestration of anthropogenic emissions generated during coal combustion. This article presents the results of experimental and theoretical studies of the combustion processes of coal-water suspensions prepared from pre-torrefied coals. As a result of preliminary thermal (pyrolysis under conditions of high-temperature heating in an inert environment) preparation of coal, gaseous pyrolysis products are formed and removed into the external environment, a large proportion of which are hydrogen sulfide (the main source of sulfur oxides) and hydrocyanic acid (the main source of nitrogen oxides). After the preliminary pyrolysis of coal, a mixture of coke carbon and the mineral part of coal remains. When burning a coal-water suspension based on torrefied coal, only carbon dioxide and water vapor are formed. The latter can be relatively easily condensed and returned back to the power generation cycle (or disposed of). Accordingly, the combustion of CWF based on torrefied coal creates the prerequisites for the fundamental justification of the technology for environmentally friendly combustion of coal in the combustion chambers of gas turbine plants operating on the Allam cycle.

Influence of Organic Sulfur on Low-Temperature Oxidation of Coal and its Transition Characteristics.

The low-temperature oxidation spontaneous combustion of coal was caused by the active groups in its structure. The oxidation mechanism of carbon and oxygen functional groups in coal had been extensively studied, but there were few reports on the study of sulfur functional groups initiating the coal spontaneous combustion. To investigate the influence of organic sulfur functional groups on the spontaneous combustion of high-sulfur coal and explore its transformation characteristics, the low-temperature oxidation experimental system was used to study the spontaneous combustion tendency of coal with similar metamorphic degrees and different organic sulfur contents. The variations of element forms and organic sulfur functional groups were analyzed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy during low-temperature oxidation of coal and model compounds. The results showed that the forms of organic sulfur in coal mainly included mercaptans, thioethers, thiophenes, sulfones (sulfoxides), and sulfates, and the low-temperature oxidation of coal was not only related to the content of organic sulfur but also related to its type. The coal samples, which possess a low content of total sulfur and a small proportion of active organic sulfur groups such as mercaptans and thioethers, had a lower concentration of indicator gas and a smaller tendency to coal spontaneous combustion. After low-temperature oxidation, the content of mercaptan, thioether, thiophene, methyl(methylene), and pyridine in coal decreased, and the content of oxygen-containing groups such as sulfone (sulfoxide), sulfate, carboxyl, and nitrogen oxide increased. The elements of S, C, and N all changed to a high-valent state. In the oxidation reaction of model compounds, mercaptans were more reactive than thiophenes in the low-temperature region, and the oxidation of thiophene could direct form sulfone (sulfoxide), while the oxidation of mercaptan formed disulfide first. It is speculated that low-valence sulfur migrated to a high-valent state by providing sulfhydryl radicals (•SH) and sulfur radicals (C-S•) combined with active oxygen atoms. After the low-temperature oxidation reaction of model compounds, some organic sulfur existed in the form of aromatic sulfur or sulfur oxides and a small part of sulfur escaped as SO2 and H2S gases in the solid oxidation product.

TO THE QUESTION OF SCIENTIFIC SUBSTANTIATION OF THE CHOICE OF INDICATORS OF MANIFESTATION OF HAZARDOUS PROPERTIES OF COAL SEAMS

The article recalculates the quality indicators of coal for their working condition, taking into account the yield of ash and moisture content for coal seams, followed by an analysis of changes in the correlations between the indicators. The need to consider the fuel for its working condition is due to different end goals between establishing the consumer qualities of coal and the manifestation of the hazardous properties of coal seams. Different ultimate goals of the problems under consideration imply different ways of solving them, including differences between the influencing factors and their parameters. The methodology provides for the achievement of the goal to use the initial experimental data that have been accumulated over several decades based on the experience of using coal for industrial purposes. The condition and quality of coal after its preparation for use differs significantly from the condition in the mining area. These differences are associated with the preliminary enrichment of coal and the removal of a certain amount of mineral impurities. Based on conducted research out, the features of the choice of indicators of metamorphic transformations of coals were established, which are used in parallel, respectively, to establish the quality of fuel and predict the hazardous properties of coal seams. Discrepancies between the indicators of the degree of metamorphism used in the current regulatory framework for the safe conduct of mining operations and the state of fuel during mining operations in underground conditions are revealed. To improve normative documents on safe mining operations, it is necessary to consider indicators that characterize not only the organic (combustible) part of the fuel, but also the presence of mineral impurities and moisture in coals in the mining area. Keywords: coal, metamorphism, indicators, justification, mineral impurities, ratio, condition, dry, ashless, working, coal seams, mining, safety, regulatory framework, improvement.

Internal or external magma oceans in the earliest protoplanets – Perspectives from nitrogen and carbon fractionation

Protoplanets growing within ∼1 Ma of the Solar System's formation underwent large-scale melting due to heat released by the decay of 26Al. When the extent of protoplanetary melting approached magma ocean (MO)-like conditions, alloy melts efficiently segregated from the silicates to form metallic cores. The nature of the MO of a differentiating protoplanet, i.e., internal or external MO (IMO or EMO), not only determines the abundances of life-essential volatiles like nitrogen (N) and carbon (C) in its core and mantle reservoirs but also the timing and mechanism of volatile loss. Whether the earliest formed protoplanets had IMOs or EMOs is, however, poorly understood. Here we model equilibrium N and C partitioning between alloy and silicate melts in the absence (IMO) or presence (EMO) of vapor degassed atmospheres. Bulk N and C inventories of the protoplanets during core formation are constrained for IMOs and EMOs by comparing the predicted N and C abundances in the alloy melts from both scenarios with N and C concentrations in the parent cores of magmatic iron meteorites. Our results show that in comparison to EMOs, protoplanets having IMOs satisfy N and C contents of the parent cores with substantially lower amounts of bulk N and C present in the parent body during core formation. As the required bulk N and C contents for IMOs and EMOs are in the sub-chondritic and chondritic range, respectively, N and C fractionation models alone cannot be used to distinguish the prevalence of these two end-member differentiation regimes. A comparison of N and C abundances in chondrites with their peak metamorphic temperatures suggests that protoplanetary interiors could lose a substantial portion of their N and C inventories with increasing degrees of thermal metamorphism. Provided the thermal metamorphism induced-loss of N and C from the protoplanetary interiors prior to the onset of core formation was efficient, the earliest formed protoplanets, as predicted by previous thermo-chemical models, are more likely to have undergone IMO differentiation resulting in the formation of N- and C-poor cores and mantles overlain by N- and C-rich undifferentiated crusts.

Sound absorption characteristics of loose bituminous coal porous media with different metamorphic degrees

With the advantages of high applicability and reliability, the acoustic detection method has been widely used in the field of temperature measurement, positioning, and flaw detection. To apply acoustic temperature measurement techniques to the detection of high temperature points of loose coal spontaneous combustion, the basic acoustic properties of loose coal need to be clarified. Four bituminous coals with different degrees of metamorphosis were selected for the study. The stacking structural characteristics of loose coal were studied by industrial computerized tomography. The sound absorption coefficient of loose coal was tested based on the sound absorption test system. The results revealed that with the increase of particle size, the voids of loose coal gradually became larger and the connectivity became better. The distribution characteristics of voids in loose coal were intrinsic to the variation in sound absorption coefficients. The sound absorption coefficient was more influenced by the particle size and stack thickness than by the degree of deterioration. Except for the particle size of less than 0.9 mm and the stacked thickness of 2 cm coal samples, the absorption coefficients of the coal samples increased gradually with decreasing particle size at the same acoustic frequency, and the peak absorption coefficients gradually shifted towards lower frequencies with increasing thickness. The peak frequency range of the absorption coefficient was calculated to provide a basis for the selection of the frequency band of the acoustic temperature measurement signal for loose coal.

Thermal properties and microstructural evolution of coal spontaneous combustion

With the increase of coal energy mining depth in China, coal spontaneous combustion phenomenon becomes more frequent, which makes the safe mining of coal energy in China under serious threat. In order to prevent coal spontaneous combustion, it is significant to investigate the process of coal oxidation and spontaneous combustion by combining thermal and microstructural properties, which is a necessary study to figure out the mechanism of coal spontaneous combustion. A series of coal oxidation experiments were conducted with the aid of high precision Calorimeter and X-ray diffractometer. The results show that the thermal properties of coal spontaneous combustion have obvious segmentation characteristics which is not affected by the degree of metamorphism and heating rates, and the initial exothermic temperature is positively correlated with heating rates. The effect of temperature on microscopic characteristics is not uniform, but the degree of metamorphism has a regular change for microscopic characteristics. Although temperature does not play a decisive role, the spatial structure of coal oxidation process has some reversibility with the change of temperature. Besides, thermal dynamic balance is an important cause of microstructure changes. It is expected that this work will contribute to the refinement of the theory of coal spontaneous combustion.

Insights into the Nanoscale Microstructure Diversity of Different Rank Coals

The gas flow pattern of the coal seam is closely related to the pore structure of the coal. In order to better understand the pore distribution in different coal samples, the pore distribution and fractal dimension characteristics of five coal samples with different degrees of metamorphism were investigated and analyzed by using the low-temperature nitrogen adsorption method and CO2 adsorption methods based on the fractal theory. The results showed that the higher the degree of metamorphism, the better the pore development, and the fractal dimension of micropores and mesopores varied with the degree of metamorphism. The pore variability between the outburst and non-outburst coals is mainly in the stage of micropores, with the outburst coal having a larger pore volume and specific surface area and a more complex microstructure. The pore formation and distribution patterns of different coal samples under the combined influence of geological and coalification effects are discussed.

Pore characteristics and fractal characterization variability of typical middle- and high-rank coal reserves: A case study of middle- and high-rank coal samples in western Guizhou

This article focused on the study of pore structure characteristics of Songhe and Linhua coal samples based on mercury injection experiments and high-pressure isothermal adsorption experiments. The results show that the pore structure of coal samples in the two mining areas is obviously different under the influence of metamorphic degree. The pores of Songhe mine coal samples, which are characteristic of middle-rank coal reserves, are predominantly open cylindrical pores with good connectivity to medium-to-large pores but poor absorption capacity. The tiny and medium pores of Linhua coal samples, which are characteristic of high-level coal reserves, have poor connectivity, dominated by conical pores with mostly closed and semi-closed pores. The pore size distribution of the middle-rank coal sample is multi-peaked, with better developed pore sizes, while the pore size distribution of the Linhua coal sample is bi-peaked, with micro and small pores developed. The pore fractal shape of high-rank coal reserves is higher than that of middle-rank coal reserves, and the complexity of permeable pore space and diffusive pore space of high-order coal reservoirs is higher than that of middle-order coal reservoirs.