Coal Properties Research Articles

Adsorption mechanism of alkylphenol ethoxylates surfactants (APEO) on anthracite surface: A combined experimental, DFT and molecular dynamics study

The serious hazards posed by inhalable coal dust to the safety, air purity, and health of coal miners can be effectively alleviated through the use of appropriate dust suppressants. The wetting enhancement capabilities of two dust suppressants, octylphenol polyoxyethylene ether (OP-10) and nonylphenol polyoxyethylene ether (NP-10), were examined in this study through experimental and simulation methods. Macroscopic experiments (surface tension, contact angle, coal dust settling time, and water retention) indicate that the shorter the alkyl chain attached to the benzene ring in the surfactant and the lower the surface tension, the more conducive it is to improving the fluidity and suspension stability of anthracite particles in the wetting solution and further improving the interfacial properties and wetting effect between coal dust and the liquid medium. Mesoscopic experiments (laser particle size, FTIR, XPS, UV–visible spectroscopy, BET, and SEM) showed that the relevant properties of APEO-modified coals were greatly changed, especially the anthracite modified with short-chain alkyl groups of OP-10, which exhibited a stronger aggregation effect on the coal dust particles and increased the pore structure and specific surface area of the coal dust. Additionally, the hydrophilic functional groups are augmented, leading to a notable enhancement in the adsorption capacity of OP-10 on the coal surface. Microscopic simulations (Density Functional Theory calculations, Molecular Dynamics simulations) reveal that APEO surfactants with longer alkyl side chains attached to benzene rings hinder the π-π interactions between the coal's aromatic ring structures and the benzene rings in the surfactants. The surface polarity of coal modified with OP-10 is significantly enhanced, resulting in a more pronounced improvement in wetting performance and an increased water retention capability. The study systematically explores surfactant microstructure effects on anthracite wetting, laying essential groundwork for advanced dust suppression system development.

Experimental Study on Compaction Deformation and Gas Permeability Properties for Crushed Limestone.

The mining goaf is enriched in coalbed methane (CBM) resources, and it is imperative to realize its efficient extraction. The gas permeability properties of the crushed coal and rock in the caved zone of mining goaf are the basis for the study of its internal CBM migration and enrichment law. In this study, the compaction deformation and gas permeability properties of crushed limestone with different particle sizes were revealed. The results show that (1) the deformation resistance capacity of the crushed limestone increased with increasing stress. The decreasing trend of porosity of samples with different particle sizes in the early and later compression periods is significantly different. Particle RR of the lower layer is smaller than that of the other layers. (2) The permeability of the sample decreases with decreasing porosity and nitrogen pressure, and it is between 10-12 and 10-10 m2. Nitrogen migration within the crushed limestone requires the pseudo-threshold pressure gradient, which ranges from 64.86 to 311.42 Pa/m. (3) The average permeability growth amplitude of the sample shows a logarithmic decreasing trend with the decrease of porosity. The average permeability growth amplitude of the 5-10 mm sample at the same porosity was 15.9-22.3 times that of the 0.315-0.63 mm sample. (4) The permeability of crushed limestone on both sides of the lower layer in the caved zone is much larger than that of other locations. The results are of great practical significance for accurately predicting the CBM enrichment area of mining goaf and then selecting the final position of the extraction drilling hole.

On the Evaluation of Coal Strength Alteration Induced by CO2 Injection Using Advanced Black-Box and White-Box Machine Learning Algorithms

Summary The injection of carbon dioxide (CO2) into coal seams is a prominent technique that can provide carbon sequestration in addition to enhancing coalbed methane extraction. However, CO2 injection into the coal seams can alter the coal strength properties and their long-term integrity. In this work, the strength alteration of coals induced by CO2 exposure was modeled using 147 laboratory-measured unconfined compressive strength (UCS) data points and considering CO2 saturation pressure, CO2 interaction temperature, CO2 interaction time, and coal rank as input variables. Advanced white-box and black-box machine learning algorithms including Gaussian process regression (GPR) with rational quadratic kernel, extreme gradient boosting (XGBoost), categorical boosting (CatBoost), adaptive boosting decision tree (AdaBoost-DT), multivariate adaptive regression splines (MARS), K-nearest neighbor (KNN), gene expression programming (GEP), and group method of data handling (GMDH) were used in the modeling process. The results demonstrated that GPR-Rational Quadratic provided the most accurate estimates of UCS of coals having 3.53%, 3.62%, and 3.55% for the average absolute percent relative error (AAPRE) values of the train, test, and total data sets, respectively. Also, the overall determination coefficient (R2) value of 0.9979 was additional proof of the excellent accuracy of this model compared with other models. Moreover, the first mathematical correlations to estimate the change in coal strength induced by CO2 exposure were established in this work by the GMDH and GEP algorithms with acceptable accuracy. Sensitivity analysis revealed that the Spearman correlation coefficient shows the relative importance of the input parameters on the coal strength better than the Pearson correlation coefficient. Among the inputs, coal rank had the greatest influence on the coal strength (strong nonlinear relationship) based on the Spearman correlation coefficient. After that, CO2 interaction time and CO2 saturation pressure have shown relatively strong nonlinear relationships with model output, respectively. The CO2 interaction temperature had the smallest impact on coal strength alteration induced by CO2 exposure based on both Pearson and Spearman correlation coefficients. Finally, the leverage technique revealed that the laboratory database used for modeling CO2-induced strength alteration of coals was highly reliable, and the suggested GPR-Rational Quadratic model and GMDH correlation could be applied for predicting the UCS of coals exposed to CO2 with high statistical accuracy and reliability.

Numerical analysis on the factors affecting post-peak characteristics of coal under uniaxial compression

The post-peak characteristics of coal serve as a direct reflection of its failure process and are essential parameters for evaluating brittleness and bursting liability. Understanding the significant factors that influence post-peak characteristics can offer valuable insights for the prevention of coal bursts. In this study, the Synthetic Rock Mass method is employed to establish a numerical model, and the factors affecting coal post-peak characteristics are analyzed from four perspectives: coal matrix mechanical parameters, structural weak surface properties, height-to-width ratio, and loading rate. The research identifies four significant influencing factors: deformation modulus, density of discrete fracture networks, height-to-width ratio, and loading rate. The response and sensitivity of post-peak characteristics to single-factor and multi-factor interactions are assessed. The result suggested that feasible prevention and control measures for coal bursts can be formulated through four approaches: weakening the mechanical properties of coal pillars, increasing the number of structural weak surfaces in coal pillars, reducing the width of coal pillars, and optimizing mining and excavation speed. The efficacy of measures aimed at weakening the mechanical properties of coal is successfully demonstrated through a case study on coal burst prevention using large-diameter borehole drilling.

CHARACTERIZATION AND COMPARATIVE STUDY OF PYROLYSIS OF LOW RANK COAL AND BIOMASS

Low rank coals are not used optimally, another way to increase this value is combustion without oxygen, known as pyrolysis. On the other hand, as a solid waste biomass, palm kernel shell (PKS) is a by-product of the palm oil industry that can cause environmental problems if not handled properly. In fact, the waste is plentiful and not even widely used, therefore it may also be an ideal feedstock for the pyrolysis process. This study compares the distribution of products from coal and PKS pyrolysis, and also characterizes the liquid (tar) and solid (char) products. The results show that the pyrolysis of coal produces more char, while the pyrolysis of PKS produces more gas. Higher tar yields were obtained with the pyrolysis process using PKS. GC-MS identified the main tar compounds for both materials as phenol and acetic acid, 3-methylphenol and methanol were also found in coal and PKS, respectively. The calorific value of char increased by about 5.19 % for coal and 41.12 % for PKS after pyrolysis. The other physical properties of coal and PKS are also improved after pyrolysis. Therefore, the application of pyrolysis in the use of coal and PKS can increase the added value of these two materials and contribute to alternative energy sources.

Impact of Graphitization Degree on the Electrochemical and Thermal Properties of Coal.

Coal-based cryptocrystalline graphite is an intermediate phase formed during the transformation of highly metamorphic anthracite into crystalline graphite. In order to explore the relationship between the graphitization degree of coal-based cryptocrystalline graphite and its physical properties from macromolecular structure to provide a theoretical basis for industrial application, samples were tested by X-ray diffraction, electrochemistry, and thermal conductivity and compared with standard graphite (SG) and artificial thermal simulation graphitized samples. The results show that with the increase of graphitization degree and the growth of microcrystalline structure, the electrical impedance of cryptocrystalline graphite decreases, the conductivity increases, the specific capacity of initial discharge increases, and the thermal conductivity increases, which gradually approach the electrical and thermal properties of crystalline graphite. The linear equations between impedance and La and Lc are y = -0.42x + 70.44 and y = -1.87x + 70.62, and the correlation coefficients are 0.93 and 0.88. The linear equations between thermal conductivity and the horizontal extension length (La) and vertical stacking thickness (Lc) are y = 0.09x + 1.36 and y = 0.4x + 0.76, the correlation coefficients are 0.82 and 0.84., and the reduction of microcrystalline parameters d002 and the increase of La and Lc lead to a direct improvement of physical properties. Artificial thermal simulation samples also show the same regularity, but their physical properties are lower than those of natural evolution samples. Short-term high-temperature simulation is different from long-term magma heat and pressure, and the growth of graphite microcrystals is more complete under long-term geological conditions, resulting in better physical properties.

Analysis of pyrolysis and combustion characteristics of several coals with different coal properties

Studying the pyrolysis and combustion properties of coal is advantageous for promoting the environmentally friendly and effective exploitation of this resource. To investigate the pyrolysis and combustion characteristics of coal with varying types and properties, a thermal gravimetric experiment was conducted. This experiment aimed to determine the characteristic index and comprehensive combustion index. The pyrolysis characteristics of pulverized coal in a nitrogen atmosphere and the rapid combustion characteristics in an oxygen atmosphere were examined separately. The obtained results provide insights into the governing principles of the carbon content effect on the pyrolysis and combustion processes of pulverized coal particles. The findings indicate a positive correlation between the carbon content of coal and the efficiency of pyrolysis and combustion processes for pulverized coal particles. Moreover, a notable enhancement in the performance of pyrolysis and combustion is seen with increased carbon content.

In-depth analysis of coal chemical structural properties response to flue gas saturation: perspective on long-term CO<SUB align="right">2 sequestration

In-depth analysis of coal chemical structural properties response to flue gas saturation: perspective on long-term CO<SUB align="right">2 sequestration

INVESTIGATING RELATIONSHIPS BETWEEN INTRINSIC PROPERTIES, PREPARATION PARAMETERS OF COAL AND COKE QUALITY: A SYSTEMATIC LITERATURE REVIEW

The purpose of this study is to review some of the key research concepts related to metallurgical coke. As the research landscape for coke metallurgy is evolving, researchers are increasingly interested in the effects of the intrinsic properties of coal, coal preparation parameters, and the technological conditions of coke production on the quality of metallurgical coke. As part of this review, a specific protocol, content analysis and thematic coding of cases of the “Preferred Reporting Items for Systematic Review and Meta-Analyses” method were used to investigate the simultaneous effect of these two parameters on the quality of coke in selected journal articles. A review of 118 articles was conducted, including their abstract, introduction, methodology, and results. According to the results of this study, coal blends and coal particle sizes have a direct effect on the three sections of coke mechanical properties, coke texture, and coke reactive properties. Reviewing various articles has shown that the presence of fatty coals in smaller size distribution, combined with largersized weak coals, leads to the formation of a stronger structure in the produced coke. However, this does not guarantee an improvement in the coke reactivity parameters. On the other hand, increasing the blending ratio of coking coals in the final mixture for producing normal-sized coke (dimensions smaller than 3 millimetres) improves the coke reactivity parameters. Studies investigating coke structure have demonstrated that a cohesive mosaic structure in high-quality cokes results from well-distributed maceral blends of coking coals with optimal size distribution among other coals.

Energy Dissipation and Fractal Properties of Coal under Cyclic Impact Loading

To investigate the periodic disturbance and damage characteristics of coal under different impact pressures, the stress‒strain failure and damage trends of weak, impact‐prone coal samples were analysed under different impact pressures and different numbers of impacts. Split‐Hopkinson pressure bar (SHPB) tests were conducted to study the stress‒strain curve, dynamic compressive strength, elastic modulus, failure strain, and absorbed energy responses with different numbers of impacts and different strain rates. Fractal theory and methods were applied to analyse the influence of different impact pressures and different numbers of impacts on coal sample failure to reveal the relationship between the number of impacts and the fractal size characteristics of coal fragmentation. The energy modes and failure modes of coal samples under different impact effects were analysed under dynamic loading. Regarding the energy absorption corresponding to different numbers of impacts, the energy absorption per unit volume (EAPUV) of three impacts was calculated to be 0.46 J/cm3. The number of impacts was directly correlated with the energy absorbed by the coal sample. Furthermore, the number of impacts was directly correlated with the severity of the deformation and damage of the coal sample and was inversely correlated with the fragmentation of the coal sample. The degree of coal sample fragmentation was directly proportional to the number of impacts, and the fractal dimension increased with the number of impacts. The study of the failure and fractal characteristics of coal samples under different impact pressures and different numbers of impacts provides important information for the prevention and control of coal mine rock bursts.

Розробка оптимальних складів вугільних шихт для трамбування. повідомлення 1. дослідження сировини щодо можливості її використання в трамбованих шихтах

It is shown that the coal used for coking with the tamping technology should be characterised by a low basicity index, the necessary levels of sintering and tamping to achieve cake stability when it is loaded into the coking chamber. Based on this, a comprehensive study of the properties of 15 components of hard coal charges (13 coal concentrates, sludge and flotation concentrate) was carried out in terms of their prospects as a raw material base using the technology of tamping coal charges. The analysis of the obtained results is presented. In particular, the evaluation of the shear strength of coal concentrates showed low values (from 9.6 to 12.6 kPa) of the shear force for all the studied samples. The strength of rammed cakes made from fine additives is significantly higher (σzz of flotation concentrate is 15.8 kPa, and sludge is 14.9 kPa), so an increase in their content in the charge will have a positive effect on the strength of the rammed cake. It has been established that the most accurate of the studied coal quality indicators, the tamping index σzz, is predicted by the Hardgrove rejuvenation coefficient and the thickness of the plastic layer. Prediction by volatile matter yield and free swelling index FSI is possible with medium accuracy, while the vitrinite reflection coefficient, Horn index and maximum compression index of Odibert-Arnoux are inaccurate. The heterogeneity of the samples for all the studied indicators characterising the fluid-plastic properties of coal was revealed. The optimums of the function of the tamping index were calculated, which are achieved at the following quality indicators: Vdaf = 25.7 %; Y = 14.3 mm; HGI = 69.6 units; R0 = 1.17 %; RI = 37.9 units; a = 1.9 %; FSI = 2.6 units. It was established that the optimum ramming properties are achieved at the values of classification indicators corresponding to coking coal. A positive feature of the tamping technology is the possibility of ensuring the specified set of properties by using not expensive and scarce coking coal, but a mixture of cheaper grades of low-baking, petrographically heterogeneous coal.. Keywords: coal, coal concentrates, coking, tamping, technological properties, testing, plastic-viscous properties, Hardgrove threshold. Corresponding author Miroshnychenko D.V., e-mail: dvmir79@gmail.com

Effects of a New Synthetic Ionic Liquid on Caking Properties of Coals with Three Different Ranks

Effects of a New Synthetic Ionic Liquid on Caking Properties of Coals with Three Different Ranks

Low-temperature pyrolysis of coal with determination of physicochemical properties of coal and its thermal decomposition products

Low-temperature pyrolysis of coal with determination of physicochemical properties of coal and its thermal decomposition products

Техніко-економічна оцінка різних способів газифікації бурого вугілля для виробництва синтетичного моторного палива

The aim of the article is to assess the feasibility of organizing the production of synthesis gas from brown coal, the reserves of which in Ukraine are sufficient. As a raw material base, the article considers the coal of the Novo-Dmytrivske deposit, which is located on the territory of the Kharkiv region. The balance reserves of brown coal in categories A + B amount to 284.4 million tons and in category C1 – to 95.6 million tons, that is, a total of 380 million tons. The average technical analysis data for the deposit are as follows: moisture per working weight is 51.2%; ash content per dry weight is 19.4%; the total sulfur content is 2.45%. The elemental composition of the coal of this deposit is characterized by the following data: carbon – 68.0%, hydrogen – 6.0%, oxygen – 23.0%, sulfur, nitrogen and other elements – 3.0%. To achieve the goal, the properties of coal of this deposit have been examined and the following technologies of coal gasification have been analyzed: Lurgi process (counter-current steam-oxygen gasification of coarse coal (or briquettes) in a stationary bed); Prenflo process (direct-flow steam-oxygen gasification in a pulverized coal stream); Texaco process (direct-flow oxygen gasification in a coal-water pulp stream). For each of these processes, material balances have been developed; the quality of gas synthesis, the possibility of organizing the production of the necessary energy resources, the level of emissions of harmful substances into the atmosphere, and the main technical and economic indicators have been evaluated. The calculations were made for an enterprise with a coal capacity of 9 million tons of actual weight per year. Based on the calculations made, the Lurgi process is recommended for industrial implementation. The advantages of this process are: the lowest temperature and pressure of the gasification process; a wider range of products obtained during gasification; almost optimal syngas composition in terms of H2 : CO ratio; the lowest emissions of carbon dioxide generated during coal gasification and preparation of synthesis gas for further use; the lowest production cost of prepared synthesis gas; the lowest specific capital investments (per 1 thousand m3 of prepared synthesis gas). The inexpediency of using the Texaco process for the gasification of brown coal is substantiated, as well as the directions for improving the Prenflo process for its further use in the gasification of brown coal of the Novo-Dmytrivske deposit are determined.

Performance Comparison of Waste Cooking Oil on Coal Slime Flotation with Sunflower Oil and Gas Oil

This study explores the potential use of waste cooking sunflower oil (WSO) as an eco-friendly collector for coal slime flotation. WSO and coal slime are both wastes and are hazardous to human health and the environment, if not disposed of properly. In this study, co-disposal of the two wastes was investigated; a gas oil (petroleum derived oil) and crude sunflower oil (CSO) were used for collector efficiency comparisons. This study also presents a green, low-cost and environmentally friendly alternative. Kinetic flotation tests were carried out to study the flotation selectivity, flammability and combustible recovery. Contact angle measurements were performed with 3 different oils (CSO, WSO and gas oil) by sessile drop technique to determine the hydrophobicity and surface properties of coal. Fourier-transform infrared (FTIR) spectroscopy was utilized to analyze the chemical composition of both waste oil and coal samples. 
 Keywords: Sunflower oil, waste cooking oil, gas oil, coal slime, flotation

Effect of ScCO2-H2O treatment duration on the microscopic structure of coal reservoirs: Implications for CO2 geological sequestration in coal

The microstructure of coal reservoirs, especially the pore structure, alters as a result of physicochemical reactions between the CO2 acidic fluid and coals. However, it is still unclear what controls this process and how the pore structure properties of coal alter by the action of CO2 acid fluids change over time. The objective of this study is to identify the underlying mechanism by analyzing the changes in the mineral composition, surface roughness, as well as micropore and mesopore structure of anthracite and bituminous coal when exposed to supercritical CO2 (ScCO2)-H2O. The results indicate that coal reservoirs primarily undergo processes of adsorption expansion and mineral dissolution/precipitation. Among these, adsorption expansion concluded or weakened after 7 days, with mineral precipitation gradually becoming the dominant factor, which results in more secure geological CO2 storage (GCS). Furthermore, comparative analysis of anthracite and bituminous coal with untreated and long-term treatment demonstrates that anthracite exhibits higher CO2 storage capacity and greater wettability. Consequently, anthracite is more suitable as a target reservoir for GCS compared to bituminous coal. These results, therefore, offer a theoretical foundation and a guide for choosing GCS sites in deep un-minable coal seams.

Experimental study of coal and gas outburst processes influenced by gas pressure, ground stress and coal properties

With the continuous increase of mining depth, coal and gas outburst poses a significant threat to mining safety. Conducting research on the mechanisms of coal and gas outbursts contributes to understanding the evolutionary process of such incidents, thus enabling accurate prediction and prevention of coal and gas outbursts during mining operations. This paper has developed a comprehensive visual experimental system that is specifically tailored to simulate diverse coal body conditions, ground stress and gas pressures. By monitoring and analyzing the real-time progression of coal fissures during the outburst process, we can obtain valuable insights into the evolution and mechanisms of coal and gas outbursts. Additionally, this study introduces a method to determine the critical threshold for predicting coal and gas outbursts, and the critical gas pressure threshold for Jiulishan Coal Mine (Jiaozuo City, Henan Province, China) is established at 0.6 MPa.

Chemical Structure Characteristics and Model Construction of Coal with Three Kinds of Coalification Degrees.

The coal structure is extensively used for studying the properties of coal, and the construction of accurate and reliable coal structure models can promote these researches. In this study, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) were used to analyze the changes in the coal structure as a function of the coalification degree, and a semiquantitative model construction method based on FTIR, XRD, and X-ray photoelectron spectroscopy (XPS) analyses was proposed. With an increase in the coalification degree, the size of the aromatic cores in the coal increased. During the conversion from lignite to bituminous coal, the content of aliphatic structures increased, while the content of oxygen-containing functional groups (OFGs) significantly decreased. Conversely, during the conversion from bituminous coal to anthracite, the content of aliphatic structures decreased while the content of OFGs slightly increased. The calculated FTIR spectra of the coal structure models were consistent with the experimental FTIR spectra, which confirmed the accuracy of the models. Furthermore, the models successfully explained the microscopic mechanism underlying the differences in the wettability of the coal samples with varying coalification degrees. The construction method and coal structure models in this study will be more widely applied in future research.

Failure and Acoustic Emissions of Coal–Rock Combinations with Different Dip Angles in the Shaqu No. 1 Coal Mine

The force and deformation characteristics of the rock layer on the top and bottom of the coal seam change significantly when the dip angle changes. The mechanical properties and damage characteristics of differently inclined coal–rock assemblages were investigated, and the results were combined with acoustic emission information, including acoustic emission ringdown counts, to quantify the damage of inclined coal–rocks under compression. The experimental results showed that the stress‒strain curves of the inclined coal–rock assemblages had four main stages, with approximately similar curves in the early stage and deformation in the later stage. The damage gradually changed from shear damage to interfacial slip damage, and the damage area gradually transitioned to the structural surface from coal body components. The cumulative acoustic emission energy tended to decrease with increasing inclination angle, and the peak acoustic emission energy gradually decreased. When the inclination angle was less than 30°, the cumulative energy of acoustic emissions increased slowly, then decreased, and it finally decreased significantly between 30° and 45°; from 0° → 15° → 30° → 45°, the energy change rates were +3.0%, −25.1%, and −78.2%, respectively. For coal–rock assemblages with different interfacial angles, the sliding damage instability caused by the coal–rock interface increased with increasing interfacial angle within the assemblage. The results of this study provide a deeper understanding of the mechanical properties of coal–rock assemblages with different inclinations and the characteristics of fissure extension. The fractal dimension based on particle number decreased with increasing loading rate, and the larger the loading rate was, the smaller the fractal dimension. In addition, the current findings provide a reliable foundation for further understanding the mechanisms of disasters caused by coal–rock disturbances, such as excavation of inclined roadways and extraction of gas, as well as supporting the development of methods for monitoring, early warning, and prevention and control of these types of disasters.

Ignition and thermal decomposition of solid organic fuel: The influence of activation, deactivation, and composite formation

The article discusses research on the thermal decomposition and ignition of coal, pine sawdust, and composite fuels derived from them. Through simultaneous thermal analysis, it was observed that the combustion process occurs in two primary stages. In the first stage, gaseous products are released and burned, while in the second stage, carbon produced in the first stage undergoes oxidation. The study also revealed the impact of mechanical activation and deactivation of ground fuel. Interestingly, the properties of coal and sawdust in the composite fuel formation are not simply additive. When the composite contains more carbon, there is a shift in the maximum decomposition rates towards higher temperatures in the first stage. Additionally, there is a decrease in decomposition magnitude during the first stage and an increase during the second stage. Moreover, it was found that the combustion temperatures of the composite fuel and mixture are higher than those of sawdust alone. Furthermore, the composite fuel exhibits superior burning characteristics as compared to the mixture. It ignites earlier, and the combustion zone shifts towards the center, resulting in enhanced fuel combustion efficiency.