Coal Composition Research Articles

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.

Study on the application of wavelet threshold denoising in the detection of coal spectra by LIBS

Laser-induced breakdown spectroscopy (LIBS) is a fast spectral detection technology, which has been widely used in coal composition detection and soil pollution detection in recent years. In the process of detection, due to various reasons, the spectrum obtained is mixed with noise, which has a negative impact on the accuracy of subsequent analysis. In this paper, taking the detection of coal by LIBS spectrum as an example, wavelet threshold denoising is used to denoise the detection spectrum containing noise. Different threshold methods are used to compare the denoising effects through simulation, so as to make full preparations for further accurate analysis of the spectrum.

Prospect Analysis of Paleocene Coalbed Methane: A Case Study of Hangu Formation, Trans-Indus Ranges, Pakistan

The methane trapped in the coal seams has emerged as an unconventional clean energy resource worldwide in this century. The proximate composition, ultimate content, cleat structure, porosity type, and pore structures are the debatable components for its trapping mechanism. Further, the brittle and ductile properties of minerals influence in the extraction of the methane from the coal seams. In this research, Coalbed methane prospect is demonstrated by analysing the Hangu Formation’s coal seam of Trans-Indus Ranges, Pakistan. This case study is helpful to find the occurrence, trapping ability, and methane extraction capacity in its cleat structures and pores. A number of samples were tested from the different coal mines in terms of these debatable components. The results indicate that the rank of studied coal is bituminous to subbituminous in which the carbon ratio, volatile matter, and sulfur contents are increasing with depth towards the south. The transitional connected face and butt cleats are partially filled with minerals and the intergranular, dissolved, and tissue pore types are also identified in it. It can be helpful for the occurrence, migration, and trapping of methane. Furthermore, the higher surface areas and cumulative pore volumes enhance the capacity of gas adsorption with depth in the study area. Moreover, the increasing brittle minerals in the coal composition towards the south can be helpful for the fracking of coal seams for economical gas extraction. It is suggested that this workflow can be implemented in any region with same coal rank and cleat types.

Analysis of Jet Structure and Physical Properties in the Coalfields of Northern China

Archeological discoveries have identified China as one of the first countries in the world to use jet. However, many differences are evident between the jet currently found in existing mines and the archaeological discoveries of cultural relics in terms of texture and quality according to the definition of organic gem jet in gemology. This paper reports the results of microscopic analysis and coal quality analysis of the coal and jet samples from coal seams in Fushun Open-pit Mine and Datong Coalfield. The findings reveal that the physical and chemical composition of coal in different mining areas differs markedly. However, the differences between jet and coal in both mining areas are similar; that is, jet has lighter density and greater hardness (2–4) compared to coal, as well as elasticity (engravability), and both jet and coal occur in the (rock slurry) hydrothermal environment. Lastly, the analysis shows that the formation of jet depends on rubber-like hydrocarbon coal with a high degree of corruption in a sedimentary environment under the vulcanization of a hydrothermal, high-sulfur environment.

Co-Torrefaction Progress of Biomass Residue/Waste Obtained for High-Value Bio-Solid Products

The co-torrefaction of several biomasses may be a viable solution in the study area, as it produces biofuels and addresses waste-treatment concerns. This review evaluates biomass through ultimate, proximate, and FTIR analyses, and the mechanism of the co-torrefaction process is observed for product quality with a synergistic effect. Furthermore, the parameters of co-torrefaction, including temperature, reaction time, mass yield, energy yield, and the composition of the H/C and O/C ratio of the co-torrefied materials, are similar to those for coal composition. Different reactor types, such as fixed-bed, fluidized-bed, microwave, and batch reactors, are used for co-torrefaction, in which biomass blends with optimized blend ratios. The co-torrefaction process increases the bio-solid yield and heating value, the capacity to adsorb carbon dioxide, and the renewable fuel used for gasification. One of the objectives of this study is to adopt a process that must be viable, green, and sustainable without generating pollution. For this reason, microwave co-torrefaction (MCT) has been used in many recent studies to transform waste and biomass materials into an alternative fuel using a microwave reactor.

Impacts of Nano SiO2 Addition on the Formation of Ultrafine Particulate Matter during Coal Combustion

Clay minerals composed of Si and Al could help reduce ultrafine particulate matter (PM) formation as an additive during coal combustion while currently unacceptable high adding dosages (normally 3–5 wt.%) are required due to their inadequate capture efficiency. To find additives that could effectively reduce the formation of ultrafine PM, coal combustion with a novel nano SiO2 additive (<100 nm) was performed to evaluate its effects on reducing ultrafine PM. The generated PM10 was sampled to characterize their particle size distribution, mass yield, size-resolved composition and micromorphology. The results showed that adding a small dosage (0.6%) of nano SiO2 reduced the mass yield of ultrafine PM by 30.70%, showing a much higher ultrafine PM capture efficiency than an existing micron-sized natural clay mineral. However, its performance on different coals varied due to disparities in ash content and composition in coal. A composition analysis revealed that the Na content in the ultrafine PM was decreased after adding nano SiO2, indicating that nano SiO2 inhibited the migration of volatile alkali metals such as Na into ultrafine PM because the Na-containing mineral vapor reacted with the nano SiO2 additive particles with a large specific surface area at a high temperature and inhibited their transformation into ultrafine PM via homogenous nucleation. Changes in the element size distributions and micromorphology showed that the majority of the added nano SiO2 particles reacted or coalesced with each other and/or the minerals embedded in coal, finally growing into a larger PM.

Petrology and organic geochemistry of the Baishaping and Damaidi Devonian cutinitic liptobioliths, west of the Kangdian Uplift, China

Devonian cutinitic liptobiolith is a special type of coal formed during the early evolutionary stage of land plants. The Baishaping and Damaidi Devonian coals are notable for their distinct papery, sheet-like texture, and unusually high cutinite content (>50%), belonging to typical cutinitic liptobiolith. They are bituminous coals and have a suppressed vitrinite reflectance. Compared with typical type III kerogen, these liptobioliths are characterized by extremely high yields of volatile matter and high hydrogen contents owing to their enhanced cutinite contents. As indicated by pyrolysis and elemental analysis results, the Devonian cutinitic liptobioliths are dominated by type I-II kerogens and have an excellent potential to generate liquid hydrocarbons. The Baishaping cutinitic liptobioliths are mainly composed of ribbon-like thick-walled cutinites, with small amounts of thin-walled type. Vitrinite is only present in trace amounts and is dominated by telinite. Meanwhile, the Damaidi Devonian coals are primarily composed of ribbon-like thin-walled cutinites, followed by collotelinites which are usually sandwiched by cutinites. The different petrological characteristics of the Baishaping and Damaidi liptobioliths might indicate a structural variation in the coal-forming plant cuticles and two distinct coal-forming conditions. The molecular biomarkers in the Devonian coals are mainly composed of C 18 –C 20 tetracyclic diterpenoids, which are assumed to be the dominant soluble constituent of the Devonian land-plant cuticles and might have played an important role in early land plant radiation. Other molecules include aromatic tetracyclic diterpenoids, 3–5 ring polycyclic aromatic hydrocarbons and their methylated counterparts, and C 16 - and C 18 -monocarboxylic acids. n -Alkanes are present only in small amounts. The molecular composition of the cutinite-rich coals is unexpected, because cuticular waxes are one of the most important sources of n -alkanes. In general, the petrology and geochemistry of the Devonian cutinitic liptobiolith indicate a distinct structure and composition for the early land-plant cuticles, which is significantly different from that of the plant cuticles since Carboniferous. Devonian cutinitic liptobioliths are of great interest because of their unique petrography, geochemistry, coal-forming plants, and oil-prone potential. Studies on this unique coal type provide a better understanding of coal-forming plants, paleoenvironment, paleoclimate, and early land-plant evolution in the Devonian.

Novel ceramic composites produced from coal discards with potential application in the building and construction sectors

In response to the enormous amounts of coal discard generated during coal mining and preparation, the development of an efficient and sustainable strategic use of this resource is essential. Furthermore, the rising urban population over the next decades is confronted with the depletion of quality raw materials for building components. To this end, this study reports new information on the morphology, water absorption, and flexural strength properties of ceramic composites produced from three different coal discards and polysiloxane pre-ceramic polymer (PCP) resin. In addition, test results relating to the continuous operating temperature, chemical resistance, and efflorescence potential of the composites are presented. The results show that the water absorption and flexural strength of the coal composites, up to 1.94% and 36.46 MPa respectively, exceed the requirements for ceramic and clay roof tiles. The continuous operating temperature of composites is found to be more thermally stable than conventional roofing tiles (concrete and ceramic) between ambient temperature and 600°C. In addition, the excellent chemical resistance of the composites (94.43%-99.98%) compared to conventional roofing tiles (67.82%-99.97%) eliminates the need for additional external coatings. The interesting results documented so far suggest that this technique could be used to produce low-temperature application building products such as bricks, panels, roofing tiles, etc. This new recycling technique offers an excellent opportunity to eliminate enormous volumes of coal discard and to advance the circular economy in the coal industry.

Enhancing the production of small molecular products from pubescens via stepwise pyrolysis process

Pyrolysis of pubescens pretreated by torrefaction was investigated by one-step and stepwise processes. The cumulative yield of small molecular compounds reached up to 19.6 wt% via stepwise processing, yielding monosaccharides (1.49 wt%), carboxylic acids (5.20 wt%), furans (3.97 wt%) and monophenols (8.94 wt%), which is higher than the corresponding value of 12.39 wt%, with 0.65 wt%, 6.15 wt%, 1.05 wt% and 4.54 wt% of the four kinds of species obtained respectively, from one-step pyrolysis. Production of carboxylic acids could be enhanced in the temperature range of 200–320 °C via dehydration of holocellulose and cleavage of acetyl group in lignin, while the acquisition of furans could be promoted in the range of 240–360 °C via further dehydration of the units of holocellulose. In the temperature range of 240–440 °C, the cleavage of β-1,4-glycosidic linkages in cellulose and glycosidic bonds in hemicellulose enhanced the yield of monosaccharides. Furthermore, the formation of monophenols from the decomposition of H, G, and S units of lignin was enhanced via cleavage of C1-Cα, Cα-Cβ, Cβ-Cγ, Cα-OH, C-O-H(R), etc. in saturated and unsaturated regions, accompanied by elimination, dehydration reactions. With stepwise processing, the corresponding carbon content in the pyrolyzed residue was enriched, resembling the elemental composition of Bituminous coal. Moreover, the relationship between small molecular weight compounds and oligomers has been probed.

Petrological, mineralogical, and geochemical compositions of coal in the Ombilin Basin, West Sumatra, Indonesia

Coal deposits have received considerable attention in recent years owing to their by-product waste being a promising alternative source of critical elements. The Ombilin Basin is well known as one of the largest coal-producing basins in Indonesia. This study investigated the petrological, mineralogical, and geochemical compositions of four Eocene coal seams in Ombilin Basin basement rock, and their relevance regarding critical element enrichment. Samples of coal and basement rock from the Ombilin Basin were analyzed using thin- and polished-section scanning electron microscope energy-dispersive X-ray spectroscopy, inductively coupled plasma atomic emission spectroscopy, and inductively coupled plasma mass spectrometry. Coals from the Ombilin Basin are high-volatile bituminous C coals with mean random vitrinite reflectance values of 0.58%–0.66%. Vitrinite content is the most dominant maceral (61.06 vol% mmf), followed by liptinite (24.95 vol% mmf), and inertinite (13.75 vol% mmf). Minerals observed in the coal samples comprised pyrite, quartz, and clay. Pyrite was present as discrete crystals, massive crystals, framboidal pyrite, and cell-filling on other macerals. Both syngenetic and epigenetic pyrite was found in the Ombilin coal. Based on the petrological and mineralogical analyses, basement rock in the Ombilin Basin can be divided into four groups: granodiorite, andesite-basaltic, marble, and meta-sediment. In comparison with World Hard Coal and common Chinese coals, some layers/partings in the coal seams in the Ombilin Basin are enriched in U (37.6 ppm), V (175 ppm), and total rare earth elements and yttrium (REY; 126.15 ppm). REY-bearing minerals in the Ombilin coal samples were attributed to clay and sulfide minerals, while others were found as dispersed and scattered, indicating that REY are organically bound. Inorganic materials in Ombilin coal deposits have mainly intermediate-felsic provenance, are derived from Cretaceous granitoid rocks and andesite intrusions, and have been subjected to freshwater conditions.

Responses of pore structure parameters and functional group compositions of coals to irradiation power: implication to coalbed methane production via microwave irradiation

ABSTRACT Microwave irradiation could alter pores and surface chemistry properties of coal matrix, thereby affecting coalbed methane (CBM) production. The impacts of irradiation power on dominant pore structure parameters and functional group compositions of coals were elaborated in this study. The results show that the responses of micropore structure parameters of coals to irradiation depend on coal rank. Generally, micropore surface area and micropore volume of low-rank coals decrease after microwave irradiation. Moreover, a U-shaped trend exists between micropore parameters of low-rank coals and irradiation power. As for middle- and high-rank coals, micropore surface area and micropore volume increase after microwave irradiation. The irradiation power dependence of micropore parameters of middle-rank coal shows a decreasing trend, while that of high-rank coal shows an inverse U-shaped trend. Microwave irradiation decreases mesopores with diameter range of 2.00–32.00 nm for all coals, thereby reducing adsorption space of coal matrix for CH4. Besides, irradiation reduces C-O, C=O, and COOH of low-rank coals, while increases C-O and C=O of middle- and high-rank coals. Furthermore, microwave irradiation increases pyridine-N but decreases pyrrole/pyridone-N of all coals. Such alterations become pronounced with rising irradiation power. Overall, responses of pores and functional groups of coals to irradiation power rest with coal rank, therefore requiring further consideration in CBM production.

Water-immersion softening mechanism of coal rock mass based on split Hopkinson pressure bar experiment

The coal mining process is affected by various water sources such as groundwater and coal seam water injection. Understanding the dynamic mechanical parameters of water-immersed coal is helpful for coalmine safe production. The impact compression tests were performed on coal with different moisture contents by using the ϕ50 mm Split Hopkinson Pressure Bar (SHPB) experimental system, and the dynamic characteristics and energy loss laws of water-immersed coal with different compositions and water contents were analyzed. Through analysis and discussion, it is found that: (1) When the moisture content of the coal sample is 0%, 30%, 60%, the stress, strain rate and energy first increase and then decrease with time. (2) When the moisture content of the coal sample increases from 30% to 60%, the stress “plateau” of the coal sample becomes more obvious, resulting in an increase in the compressive stress stage and a decrease in the expansion stress stage. (3) The increase of moisture content of the coal sample will affect its impact deformation and failure mode. When the moisture content is 60%, the incident rod end and the transmission rod end of the coal sample will have obvious compression failure, and the middle part of the coal sample will also experience expansion and deformation. (4) The coal composition ratio suitable for the coal immersion softening impact experiment is optimized.

Improved ANN-Based Approach Using Relative Impact for the Prediction of Thermal Coal Elemental Composition Using Proximate Analysis.

The basic properties of coal influence various procedures of power generation, such as the design of power generation plants, estimation of the current condition of boilers, and total efficiency of power plants. The elemental composition is a needed factor in evaluating the process of chemical conversion and predicting the flow of flue gas and the quality of air in coal combustion. In the past, several relationships have been established using ultimate and proximate analyses. This study aims to predict the elemental compositions of 104 thermal coals used for coal-fired power plants in South Korea using an artificial neural network (ANN) that uses proximate analysis values as input parameters. The ANN-based model was optimized with six activation functions and four hidden layers after evaluating various performance indices, including R2, mean square error (MSE), and epoch, then additional calculations were derived to compare performances from previous research using the mean absolute error (MAE), average absolute error, and average bias error. It was found that the best topology was established using the Levenberg–Marquardt activation function and 10 hidden layers, resulting in the highest R2 value and smallest MSE of all topologies tested. As a result, the relative impact on calculation accuracy was derived from ANN hidden layers to analyze prediction accuracies of carbon, hydrogen, and oxygen compositions. Accuracy was improved over previous results by 4.71–0.91% via coal rank division topology optimization. Based on the MAE, the current results are even close in performance to those of adaptive neuro-fuzzy inference systems. They also outperformed previous research models by 5.40 and 7.39% in terms of MAE accuracy. Applicability of the ANN was also analyzed with limitations of the chemical composition of ANNs and present reinforcement measures in the future studies through qualitative analysis comparisons based on Fourier transform infrared spectroscopy. Consequently, the relative effect was derived from the ANN hidden layer weight for specific calculation of the relationship between elemental composition and proximate analysis properties. As a result, it was possible to qualitatively analyze how the proximate analysis value affects the composition of elements and calculate the ratio accordingly. The findings of this study provide an improved and efficient approach to predicting the elemental composition of thermal coal, based on data from South Korean power plants. Also, further research can follow schematics from this study with the applicability and accessibility of the ANN.

Key Peculiarities of the Pyrolysis Behavior of Different Rank Coals, and Characterization of the Pyrolysis Products

The chemical composition, structural and plastometric properties of typical different-ranked coals from Mongolia deposits were studied. The non-isothermal iso-conversion Ozawa-Flynn-Wall method was used to assess kinetic parameters and to differentiate decomposition steps. Key peculiarities of the pyrolysis kinetics of brown and bituminous coals were revealed and discussed in terms of the composition and plastometric properties of coals. Brown coal was shown to undergo three decomposition steps with ever increasing activation energy as temperature increased because of the decomposition of thermally more and more stable molecular fragments. The pyrolysis of bituminous coals occurred in four steps, the activation energy having an extreme mode of temperature dependence. An important new finding was that the temperature range of the second, major pyrolysis step well corresponded to that between the softening and resolidification temperatures according to Gieseler plastometry, so that the decomposition of bituminous coals at the second step proceeded in a fluid-like medium, moreover, with constant activation energy. The yield and composition of the pyrolysis products obtained under isothermal conditions were also characterized depending on coal rank and temperature, and the ways for qualified utiliza tions were offered.

Online Ash Content Monitor by Automatic Composition Identification and Dynamic Parameter Adjustment Method in Multicoal Preparation

The online measurement of coal ash has overcome the shortcomings of chemical tests. However, there could be large fluctuations and errors in the results of online ash monitors because of the transient change in coal quality resulting from different geological conditions in the mining process. In this study, to resolve the problems of the dual-energy γ-ray online ash monitor in the Linhuan Coal Preparation Plant, we investigated the internal factors, such as the composition of multimineral and multicoal, and external factors, such as the moisture and impurities, which affect the measurement results of the coal ash monitor. Furthermore, we developed a mathematical model to determine the effect of relevant factors on the coefficient of the online ash monitor, which revealed the relationship between coal composition and the parameters of the ash monitor, ensuring the stable and accurate measurement of ash in clean coal. The method of determining parameters used in the case of coal blending has been applied in the Linhuan Coal Preparation Plant. By comparing with tested ash content, the average absolute error and relative error for daily ash content measured in April are 0.21 and 2.18%, respectively. Meanwhile, it shows certain accuracy and reproducibility while opposed to the daily average absolute error of 0.22 and relative error of 2.39% in May.

Investigation on thermal analysis and FTIR microscopic characteristics of artificially-oxidized coal and chronic naturally-oxidized coal during secondary oxidation

To reduce mine fire risk and ensure efficient resource utilization, an in-depth research must be conducted on the secondary oxidation of coal. Accordingly, the macroscopic oxidation characteristics and microscopic composition of newly-mined coal, artificially oxidized coal (the newly-mined coal oxidized at 70 °C and 180 °C) and repeated-mined coal (oxidized naturally over 10 years) were evaluated in this study. And these coal samples were labeled N, N-70, N-180, and R, respectively. The parameters indicating the oxidation characteristics of coal were analyzed by simultaneous thermal analysis-Fourier transform infrared spectroscopy (STA-FTIR) and Shimazu Fourier transform infrared spectrometry (FTIR-8400) from the perspective of coal thermal reaction and functional groups. The experimental results suggest that the temperature T2 required by N-70, N-180, and R to reach the oxidation stage was lower than that of N. In addition, CO and CO2 gases were released earlier from these coals than from N. The same release was earlier for N-180 and N-70 compared to that for R. Compared with N, the content of hydroxyl and aliphatic hydrocarbons in N-70, N-180 and R after the initial oxidation decreases, and the decrease of N-70, N-180 was greater than that of R. The content of oxygen-containing functional groups (-COOH, C=O, -COO-) increased significantly, and the increase for N-70, N-180 was greater than that of R. These results indicate that coal was more prone to secondary oxidization after primary oxidation. This is because the coal absorbed heat released during the primary oxidation and subsequently had a higher activity. The artificially-oxidized coal in the laboratory absorbed more heat and generated more oxygen-containing functional groups (-COOH, C=O, -COO-) than the chronic naturally-oxidized coal in the mine face, resulting in a higher risk of spontaneous combustion during secondary oxidation.

Elemental and proximate analysis of coal by x-ray fluorescence assisted laser-induced breakdown spectroscopy

Although laser-induced breakdown spectroscopy (LIBS), as a fast on-line analysis technology, has great potential and competitiveness in the analysis of chemical composition and proximate analysis results of coal in thermal power plants, the measurement repeatability of LIBS needs to be further improved due to the difficulty in controlling the stability of the generated plasmas at present. In this paper, we propose a novel x-ray fluorescence (XRF) assisted LIBS method for high repeatability analysis of coal quality, which not only inherits the ability of LIBS to directly analyze organic elements such as C and H in coal, but also uses XRF to make up for the lack of stability of LIBS in determining other inorganic ash-forming elements. With the combination of elemental lines in LIBS and XRF spectra, the principal component analysis and the partial least squares are used to establish the prediction model and perform multi-elemental and proximate analysis of coal. Quantitative analysis results show that the relative standard deviation (RSD) of C is 0.15%, the RSDs of other elements are less than 4%, and the standard deviations of calorific value, ash content, sulfur content and volatile matter are 0.11 MJ kg−1, 0.17%, 0.79% and 0.41% respectively, indicating that the method has good repeatability in determination of coal quality. This work is helpful to accelerate the development of LIBS in the field of rapid measurement of coal entering the power plant and on-line monitoring of coal entering the furnace.

Using indices of the current industrial coal classification to forecast hazardous characteristics of coal seams

Purpose is to identify changes in the basic indices of vitrinite reflection as well as content of volatile matter in the process of seam underground transformation influenced by high temperature and pressure and define nature of the changes in the classification indices and their correspondence to grades, groups, and subgroups of similar metamorphic coal transformations to determine hazardous characteristics of seams while mining. Methods. Selection of the most adequate basic index, evaluating metamorphism degree of coal seam and forecasting of their hazardous characteristic demonstration while mining, is based upon the average data of coal composition in Donbas depending upon the stages of seam metamorphism. Findings.Analysis of indices of the current industrial classification and normative base has shown the following. They cannot characterize directly the coal metamorphism connected with changes in composition and properties of the original organic substance. It has been mentioned that volatile matter do not demonstrate specifically ultimate composition of the organic matter and phase coal composition while fluid extraction from seams during their metamorphic transformations. Only the total release of gaseous products without identification of the released gases is defined by its value. Average vitrinite reflection has been defined experimentally along with other indices to identify the coal grades. For that reason, values of the index not always correspond to coal metamorphism degree in their grade ranking. Originality. Nature of changes in the classification indices of industrial coal ranking has been defined to identify hazardous characteristics of coal seams while mining. Practical implications. Possibilities to improve a normative base for safe mining have been defined while determining the classification indices characterizing directly the changes in ultimate composition during metamorphic processes.

Efficient Separation of Ultrafine Coal Assisted by Selective Adsorption of Polyvinylpyrrolidone

The efficient separation of ultrafine coal is a challenging process due to the ultrafine particle size and gangue entrainment. In this study, a polymer, polyvinylpyrrolidone (PVP), was introduced as a regulator for ultrafine coal beneficiation. The addition of PVP improved the combustible recovery of clean coal and decreased the ash content. This effect was also presented by the selectivity index. The regulation mechanism of PVP was investigated using diverse methods. The adsorption tests performed demonstrated the adsorption amount of PVP on coal, kaolinite, and quartz, which were related to the increase in the separation efficiency. A zeta potential analyzer was employed to elucidate the effect of PVP on the electrical properties of ultrafine particles. The results revealed that the electrokinetic potential of mineral was sensitive to the varying PVP concentration. The particle size distribution was observed to value the influence of PVP on the particle behavior, which was tested by a laser particle size analyzer. X-ray photoelectron spectroscopy was used to investigate the surface elemental compositions of coal, kaolinite, and quartz, which were regulated by the adsorption of PVP. This research is beneficial to understanding the role of PVP as regulators and provides a basis for the efficient separation of ultrafine coal.

Petrographic and chemical-technological characteristics coal seamsof the lower carbon,formation C12 of the kalmiusblock

Purpose. To establish the petrographic and chemical-technological features of the coal seams of formation C12 of the Kalmius block. Method. General scientific and applied research methods were used to fulfill the tasks. With the help of petrographic methods, the macroscopic and microscopic characteristics of the composition of coal were studied in detail, and the degree of its recovery and metamorphism was determined. With the help of chemical and technological methods, a comprehensive description of the composition and quality of coal is provided. The use of modern methods of analysis and interpretation made it possible to provide a generalized characteristic of coal seams, to reveal the peculiarities of their composition and quality. Findings. For the first time, regional ("provincial") features of the composition and quality of the coal formation C12 for Lower Donbass were revealed. Their typical petrographic composition was determined on the Kalmius block square. It was established that the coal of formation C12 differs from coal of formation C13 both in terms of gross petrographic composition and maceral composition. In addition, they are characterized by different degrees of recovery. It is proved that in the stratigraphic section, from the layers of the lower world to the layers of the upper world, the number of maceral groups of inertinite and liptinite increases, and the groups of vitrinite decrease. Lateral regularities of changes in the composition and quality of coal are determined. It was established that, compared to coal formation C13, higher values of sulfur content, heat of combustion, thickness of the plastic layer, and the Rog index are characteristic of coal formation C12. The elemental composition of the coal seams formation C12 is characterized by higher values of carbon and hydrogen content and significantly lower values of the amount of oxygen. Changes in the petrographic composition of Lower Carboniferous coal were revealed. The originality. For the first time, changes in the typical petrographic composition of coal in the Lower Carboniferous stratigraphic section of Southern Donbas, which indicate different conditions of formation of peatlands, were established. Practical implementation. The regional ("provincial") features of the region's coal have been clarified, lateral and stratigraphic changes in its composition and quality indicators have been determined, the grade composition of coal according to the new current standard in Ukraine has been established, and the technological value of formation C12 coal has been calculated.