Coal Extraction Research Articles

Multi-method Coal Seam Floor Water Inrush Risk Evaluation Based on Variable Weight Theory

Frequent water inrush disasters in deep coal seam mining pose a significant threat to the safety of coal extraction operations. Due to the complexity and non-linearity of water inrush factors, evaluating the risk of water inrush in coal seam floor is challenging and the results can vary significantly. To achieve more accurate evaluations, the weighted rank-sum method and Grey-TOPSIS method were employed, alongside a master control indicator variable-weight model, for assessing the risk of water inrush in coal seam floor. Validation of the evaluation zoning map against actual conditions revealed that both methods produced accurate assessment results, thus affirming the reliability of the new evaluation approach. Compared with the water inrush coefficient method, the diversification of index factors weakened the absolute control effect of the water inrush threshold. The evaluation outcomes were more systematic and comprehensive, providing a new methodology and perspective for deep coal seam mining.

Recovering psychological trauma in coal mining communities

ABSTRACT To date, there has been little research on the history of work-related mental health issues among coal workers. Much of the coal extraction industry peaked during the early twentieth century and then began its precipitous decline. Mining has high casualty rates, and the medical field did not understand the long-term effects of psychological trauma on mine workers until recently. Newspaper articles and other historical records provide accounts of accidents and tragedies. Heroism is often emphasized in recalling tragic episodes at the expense of recording the emotional stress suffered by survivors. A diverse set of historical sources provides a context for work-related mental health issues in the coal extraction industry. Probing a set of historic oral histories of coal workers and creating analogies to current studies provide additional clues about the under-told story of these historic actors’ general health and well-being. While incorporating oral histories from other regions, focusing on the anthracite coal industry in northeastern Pennsylvania allows us to identify historical actors and helps us think differently about other working-class communities impacted by industrial capitalism.

Effect of CO2 injection pressure on enhanced coal seam gas extraction

The CO2 displacement of coal seam gas can simultaneously promote gas extraction and CO2 sequestration, with gas injection pressure being a key factor influencing both efficiency and safety. This study examined the impact of varying CO2 injection pressure on gas extraction and sequestration. The findings indicated that higher CO2 injection pressures reduced the gas injection and extraction time costs, increased the equilibrium pressure and coal seam temperature, and decreased carbon sequestration efficiency. As the CO2 injection pressure increased, the CH4 cumulative desorption capacity and desorption rate rose by 4.98%, the time to reach the residual gas content critical value (TLV of 2 m3/t) shortened by 62.04 min, and the maximum CO2 storage per unit mass of coal increases by 3.6 m3/t. Increasing the injection pressure enhanced gas desorption and CO2 sequestration. A higher CO2 injection pressure resulted in a higher CH4 yield rate and a reduced CO2 injection rate in the later stages. Therefore, it is advisable to reduce the CO2 injection pressure during the low efficiency desorption stage.

Compound disaster characteristics of rock burst and coal spontaneous combustion in island mining face: A case study

The island mining face in coal mines often encounters stress concentration and significant air leakage, elevating the risk of rock burst and spontaneous combustion of residual coal in the goaf. This study centers on the investigation of the 9305 island mining face within a mine situated in Shandong Province, China. Leveraging the features of coal spontaneous combustion and data from microseismic and gas monitoring throughout the mining process, a novel method for calculating safe mining speeds under compound disasters is introduced. The safe mining speed of the 9305 island mining face is stratified, and a prevention and control technology integrating long distance directional drilling for impact-spontaneous combustion compound disasters is proposed. Findings suggest that to mitigate spontaneous combustion of residual coal, considering the seam's spontaneous combustion tendency, the safe mining speed should exceed 3.7 m per day. Accounting for the distribution of microseismic events during coal seam extraction, the safe mining speed is maintained below 4.8 m per day in the unprotected mining area and capped at 8 m per day in the protected zone. Through a comprehensive analysis considering coal seam spontaneous combustion tendency, impact tendency, and time to coal seam oxidation to critical temperature, the safe mining speed for the island mining face ranges from 3.7 m per day to 4.8 m per day in the unprotected area and from 5.14 m per day to 8 m per day in the protected area. The proposed long distance directional drilling 'one hole, multiple purposes' scheme enables an integrated approach encompassing pressure relief before coal seam extraction, water injection during mining, and grouting post-mining. This method effectively prevents and controls the compound disasters of rock burst and coal spontaneous combustion, presenting innovative technical solutions for the safe extraction of coal resources.

Analysis of the Organic Chemical Fractions of Three Coal Extracts

Analysis of the Organic Chemical Fractions of Three Coal Extracts

Observações de campo nos materiais lateríticos de Mosqueiro (Belém, Pará) como potenciais pigmentos minerais naturais

Back in the 1980s, when I began exploring the cliffs of Baía do Sol (Mosqueiro, Belém, Pará), carved into immature laterite profiles derived from clayey and sandy sedimentary rocks of the Barreiras Formation, I was very impressed by the colorful tones of the mottled horizon in these profiles. With my children (they were still “children”) we played painting each other and it was really fun. When reading and studying cave paintings in the Amazon and around the world, it was evident, obviously, that these paintings were made with different materials, mainly Fe and Mn oxyhydroxides, coal, ash and organic extracts.

Based on Flac3D Research and Analysis of the Mining Pressure Development Law in the Top Coal Section of the Roadway Support of the Working Face Transport

Top coal supporting roadway is widely used in the transportation roadway of thick coal seam face, which can not only increase the coal extraction rate but also reduce the driving cost. Based on the engineering geological conditions of the transportation lane of the working face of Zhongma Cun mine, the law of mine pressure development in the roadway of the top coal section is studied and analyzed based on Flac3D and field monitoring methods. The numerical simulation analysis shows that when the working face is pushed to 55m for the first time, the displacement of the area affected by the leading abutment pressure and the surrounding rock on the mining side of the roadway reaches the peak value, and the step distance of the first time is 55m. According to the analysis of stress monitoring data of single pillar and roof anchor cable on site, the first pressure occurs when the working face advances to 51m, which is consistent with the numerical simulation conclusion.

A laboratory study of coal-to-gas bioconversion through bio-seeding sludge in the primary coal substrate

Coal waste, a by-product of coal extraction, adversely poses environmental hazards as it releases harmful substances into the air, water, and soil, damaging the ecosystem and localized biodiversity. The coal-to-energy sludge-seeded bioconversion shows its potential as an environmentally friendly technology to mitigate the harmfulness of coal-derived hazards. This study uses blended coal and anaerobic digestion sludge in batch reactors at a mesophilic temperature (35 °C) to generate methane-rich biogas for energy production and waste elimination. Nutrient solution and ethanol were added as stimuli to boost bioactivities and enhance gas production. These results showed the potential of lignite coal in biomethane generation over an extended period, even with a lower volume of sludge addition. Adding nutrients and ethanol enhances the ultimate biogas production as an extra feed for microorganisms and as a key parameter in increasing the bioavailability of coal. The ultimate biogas production from the kinetic model indicates a remarkable volume of 111504 mL/g-sludge using lignite with 20 mol ethanol compared to the blank reactor with 701 mL/g-sludge of biogas production. The intricate analysis of results highlights the complex interplay between coal, sludge, nutrients, and additives, where varying factors impact methane production rates. Despite challenges in interpreting data, this study underscores the potential for managing coal waste through wastewater utilization, transforming it into methane-rich biogas—a sustainable green technology for energy production.

Predictive model for the instability of flexible formwork concrete wall in secondary mining of non-pillar coal mining

The secondary mining movement in non-pillar coal extraction causes significant overrun damage to flexible formwork concrete walls, leading to extensive deformation of roadway roof and bottom plates. This adversely affects working face efficiency and safety. The engineering context focuses on the non-pillar gob-side retaining walls in the 1315 working face of Zhaozhuang Coal Mine and the 23107 working face of Xiegou Coal Mine. Through on-site investigation, numerical simulation, theoretical analysis, and testing, we explore the stress migration law and destabilizing mechanism of the flexible formwork concrete wall influenced by the secondary mining movement of the coal-free pillar along the hollow wall. The research results showed that: (1) During the mining back process, the concrete wall formed with flexible formwork may experience stress concentration, leading to excessive damage and compromising mining safety. (2) Developing a predictive stress model for the concrete wall with flexible formwork is essential. If the stress surpasses the ultimate compressive strength during mining back, reinforcement becomes necessary.3) The length of damage overrun in the flexible formwork concrete wall exhibits two distinct stages as the distance back to mining increases. The first stage shows nearly linear growth, while the second stage indicates a decreasing growth rate, ultimately stabilizing. The application of Z6 concrete reinforcing agent effectively strengthens the flexible formwork concrete wall.

Experimental study on gas hydrate generation in a thermal-kinetic binary promotion system

ABSTRACT The primary measure for the prevention and control of coal and gas protrusion is gas extraction. However, various factors, such as coal seam conditions, drilling construction, and extraction management, have led to poor gas management. Therefore, the method of transforming gaseous gas into solid hydrate provides a new direction for the prevention and control of coal and gas herniation. In this paper, the factors that influence gas hydrate solidification and its influence law are explored. A thermo-kinetic binary promotion system was constructed by combining thermo-kinetic promoters, and experiments on gas hydrate generation under the thermo-kinetic binary system were carried out. The effects of four thermodynamic accelerators (CP, THF, TBAB, HCFC-141b) compounded with the kinetic accelerator SDS on the gas hydrate generation characteristics were determined. The experimental results show that among the four thermodynamic promoters, THF and SDS have the best synergistic effect, and the optimal mass concentration ratio of the two is 21.2 wt% THF + 8.6 wt% SDS. The gas pressure in the reactor decreased by a maximum of 2.788 MPa within 500 min in this experimental system, and the absorption rate of gas reached 55.41%, which indicates a more pronounced hydration promotion effect.

Effectiveness and mechanism of microbial dust suppressant on coal dust with different metamorphosis degree.

The extraction of coal from open-pit mines significantly contributes to environmental degradation, posing grave risks to human health and the operational stability of machinery. In this milieu, microbial dust suppressants leveraging microbially induced carbonate precipitation (MICP) demonstrate substantial potential for application. This manuscript undertakes an exploration of the dust mitigation efficiency, consolidation attributes, and the fundamental mechanisms of microbial dust suppressants across coal dust samples with varying metamorphic gradations. Empirical observations indicate that, in resistance tests against wind and rain, lignite coal underwent mass losses of 7.43g·m-2·min-1 and 98.62g·m-2·min-1, respectively. The production of consolidating agents within the lignite dust, attributable to the microbial suppressants, was measured at 0.15g per unit mass, a value of 1.25 and 1.07 times greater than that observed in bituminous coal and anthracite, respectively. Scanning electron microscopy coupled with X-ray energy-dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD) analyses illuminated that the consolidating products within the coal dust predominantly constituted calcite and vaterite forms of calcium carbonate. The consolidation mechanism of coal dust via microbial suppressants is articulated as follows: Subsequent to the application on coal dust, the suppressants induce the formation of carbonate precipitates with inherent adhesive properties. These carbonates affix to the surfaces of coal dust particles, progressively encapsulating them. Furthermore, they play a pivotal role in bridging and filling the interstices between adjacent dust particles, thereby culminating in the genesis of a dense, cohesive mass capable of withstanding erosive forces.

The status of artisanal coal mining in Afghanistan: Using remote sensing to assess remaining artisanally mineable Jurassic coal resources

Coal mining is critical to the functioning of the current Afghan economy providing jobs, tax revenue, and foreign exchange. Taxes on coal may constitute the Taliban Government’s single largest source of operating income. Prior to the start of mining, Afghanistan had between 215 M and 430 M tonnes of hypothetical category Jurassic coal resources at depths accessible to artisanal miners. Since 1940, between 51 M and 89 M tonnes of coal have been extracted. Technologically primitive mining practices result in suboptimal coal extraction from disorganized room and pillar mines leaving significant amounts of coal unmineable. Frequent tunnel collapse, gas and coal dust explosions, and uncontrolled widespread mine fires have destroyed or made inaccessible significant additional volumes of remaining artisanally mineable resources. The haphazard unmapped development of the existing Jurassic coal makes it impossible to redevelop these fields using more efficient mining technologies. If new mines are to be developed, they will have to tap subsurface coals not accessible to artisanal miners. 66 % of the area mapped as Lower to Middle Jurassic rock does not host outcropping coal beds. This area, as well as some of the areas beneath thin veneers of lowest Cretaceous sediment are potential exploration targets. Jurassic coals are very gassy. Developing coalbed methane prospects is a more effective and less environmentally destructive means to access the energy contained in the Jurassic coals.

Selective hydroconversion of ethanolyzed soluble portion from the ethanolysis of Hanglaiwan long flame coal extraction residue over highly active Ni/SAPO-34 catalyst

The ethanolyzed soluble portion (SPE) prepared from the ethanolysis of Hanglaiwan long flame coal (HLFC) extraction residue was converted to catalytically hydroconverted SPE (CHSPE) by the catalytic hydroconversion (CHC) over Ni10 %/SAPO-34 at 200 °C under an initial hydrogen pressure of 5 MPa for 24 h. The possible mechanisms for the origin and synergic effect of active hydrogen had been speculated according to the reactions of HLFC-related model compounds. H2 can be activated by Ni10 %/SAPO-34 to produce H···H, H+, and H-, the synergic effect of which leads to cleaving >C-O- bonds. After the CHC, arenes and heteroatom-containing aromatic compounds in SPE are converted to cyclanes, indicating that aromatic ring hydrogenation and heteroatom removal occur simultaneously during the CHC of SPE. The relative abundance (RA) of CH-containing species in CHSPE is larger than that in SPE, while the RAs of oxygen- and nitrogen-containing species in CHSPE are smaller than those in SPE. In addition, Ni10 %/SAPO-34 has excellent cyclability for the CHC of SPE, and the relative content of cyclanes decreases only by 17.4 % after five recycles. Undoubtedly, this investigation provides an effective strategy for directional upgrading of derived soluble portion from low metamorphic coals.

Rethinking the exercise of sovereignty in the Anthropocene: From extraction to environmental protection in Arctic Svalbard

This paper explores the implications of the Anthropocene and its associated planetary awareness on the concept and exercise of sovereignty, particularly through the lens of the Svalbard Treaty. The Arctic archipelago of Svalbard is not only a space undergoing rapid environmental change today, but its treaty-based governance arrangements are based on an early-twentieth century spatial imaginary of fishery, coal, and resource extraction. By examining Norway's governance shift from resource extraction to environmental stewardship on Svalbard, this paper reflects on transformations of the practice of sovereignty in response to global environmental challenges. Through interviews with local stakeholders, the research highlights the contentious nature of these shifts, revealing how increased environmental regulations, while necessary, may paradoxically entrench existing power structures and complicate the presence of non-Norwegian entities. This case study of the Svalbard Treaty serves as a normative microcosm for broader issues of sovereignty, treaty obligations, and international governance as they may evolve due to planetary change, pointing to the urgent need to rethink these evolving dynamics. The paper underscores the pressing and complex challenges facing the international system in the Anthropocene, suggesting that while Svalbard's geopolitical stability may be maintained and Norwegian sovereignty remains uncontested, the instability of global environmental realities is already leading to changes to the ways in which sovereignty is exercised in the present.

Environmental isotopes (δ18O, δ2H) and the spatio-temporal variation of Fe, Mn and P in surface and groundwaters in a coal extraction area and thermoelectric power plant, Candiota, South Brazil

Environmental isotopes (δ18O, δ2H) and the spatio-temporal variation of Fe, Mn and P in surface and groundwaters in a coal extraction area and thermoelectric power plant, Candiota, South Brazil

Pore evolution and reaction mechanism of coal under the combination of chemical activation and autothermal oxidation

Aiming at the limitation problems such as limited scope, high cost and energy consumption of coal bed penetration enhancement technology by traditional physical and chemical methods, a coal seam methane penetration enhancement method based on the combined action of chemical activation and auto thermal oxidation is proposed from the idea of utilizing the in-situ energy of the coal body. In this paper, N2 and CO2 adsorption, XPS and FTIR methods are used to study the pore structure evolution law and the change characteristics of the reactive structure of coal matrix under the effect of chemically activated autothermal oxidation. The synergistic microporous pore volume of chemical activation and auto thermal oxidation was 48.91 cm3/g−1 × 10-3, which was 28.96 % and 22.7 % higher than chemical activation and auto thermal oxidation respectively; The microporous specific surface area was 162.7 m2/g, which was 38 % and 26.6 % higher than chemical activation and auto thermal oxidation respectively. Activated coals expand and merge holes to a deeper degree after oxidative warming, and the complexity of the pore structure in the coal decreases; Highly reactive radicals in coal pores substantially promote the oxidation of coal structure, enhance the aromatic polymerization reaction of activated coal, and improve the maturity and aromaticity of activated coal, and the oxygen-containing functional groups in activated coal are negatively correlated with the oxidation temperature. The results of this study reveal the potential of the auto thermal oxidation-driven penetration enhancement method under chemical activation for coal seam gas penetration enhancement and extraction.

Enhancing coal seam gas pressure measurement accuracy and preventing leakage through dual chamber pressure balancing in borehole

Accurate measurement of coal seam gas pressure (CSGP) is critical to the evaluation of coal mine gas hazards and the potential of coal seam gas extraction. In this study, we investigate gas leakage from chambers and its influences on CSGP measurement results (MR) through numerical simulations. Furthermore, we propose, analyze and validate a novel method that balances gas pressure between two chambers, i.e. the measurement and regulation chambers, in a borehole. The results demonstrate that: (1) Traditional CSGP measurement method utilizing boreholes with a single chamber exhibit a gradual expansion of the gas pressure dropping region around the borehole, accompanied by an initial increase in chamber gas pressure followed by stabilization. The gas leakage process within the chamber undergoes three typical stages. (2) The increase of gas leakage lowers the MR value and raises the CSGP measurement error ratio (R). The relationship between MR, R and the stable value of gas leakage is nearly linear. (3) The proposed novel CSGP measurement method involves continuous gas injection into the regulation chamber to establish a dynamic gas pressure balance region between the two chambers. This approach minimizes gas leakage in the measurement chamber and accelerates gas pressure recovery. Maintaining dynamic pressure equality between the dual chambers is essential for minimizing R. (4) An automatic regulation unit is developed to achieve dynamic gas pressure balancing between the two chambers. With the novel method, R values remain below 3%, yielding higher CSGP measurement accuracy compared to alternative approaches.

CH4 and CO2 adsorption–desorption-diffusion characteristics in surfactant-modified coal under microscopic conditions

Hydraulic techniques are integral to both coal mining and gas extraction procedures, and the precise inclusion of surfactants in hydraulic fracturing fluids serves as a crucial factor influencing the wettability of coal and facilitating gas desorption. Nevertheless, relatively few investigations have focused on the influence of surfactants within coal on the adsorption–desorption-diffusion dynamics of gases. In this study, Xin Tian high-rank coal was treated with different surfactants, and the pore structure and functional groups of the coal samples were determined by fluid invasion methods, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and 13C nuclear magnetic resonance (13C NMR) spectroscopy. Moreover, molecular-scale models were constructed to simulate the adsorption–desorption-diffusion performance of the gases in the surfactant-modified coal. As per the results, modification with methyltrimethoxysilane (MTMS) and polyethylene oxide (PEO) surfactants reduced the proportion of micropores and relative content of oxygen functional groups, resulting in reduced the adsorption of gases and enhanced diffusion performance, consistent with molecular simulations result. These results provide a theoretical foundation for elucidating the adsorption–desorption mechanisms of surfactant-treated coal and its application in mining areas.

Research on Gas Control Technology in Goaf Based on the Influence of Mining Speed

To comprehensively understand the influence of mining speed on gas emissions in goaf during coal seam extraction, enhance gas extraction efficiency in goaf, manage gas emissions at the working face, and ensure safety in the mining production process. This study focuses on the No. 3 mining area of Wangjialing Mine, employing numerical simulations to analyze the evolution of mining-induced fractures and the characteristics of gas distribution in the overburden at varying mining speeds. Furthermore, by integrating actual gas emission and extraction data at the production face, this study examines the quantitative relationship between mining speed and gas emissions in the goaf, identifying optimal regions for high-position borehole layouts and conducting borehole optimization design and investigation. The results of this study indicate that the initial caving step distance of the goaf roof increases with the advancement speed of the working face. Conversely, the maximum height of through fractures in the overburden decreases as the mining speed increases, while delamination fractures are minimally affected by the advancement speed. By categorizing and averaging data on goaf mining speed, the impact of initial and periodic pressure on gas emissions can be effectively mitigated, revealing a linear correlation coefficient of 0.94 between goaf gas emissions and mining speed. At varying mining speeds of the working face, the efficient extraction layer and horizontal distance parameters of gas extraction boreholes in the goaf conform to the linear equation y = ax ± b. Based on the research findings, an optimization design for mining face speed and high-level borehole parameters in the goaf was implemented. The average gas extraction rate of high-level directional boreholes reached 68% throughout the extraction period. Gas emissions at the working face were effectively controlled below 10 m3/min, with the maximum gas concentration at the upper corners and return airflow kept below 0.8%. This effectively managed gas emissions at the working face, ensuring safe production in the mine, providing a theoretical basis for identifying gas-rich areas in the mining-induced overburden, and enhancing gas extraction efficiency at the working face.

Investigating the hydrocarbon potential of the Paleogene coal seams in Kapuni field, Taranaki basin, New Zealand: Implications for coal-oil correlation

Hydrocarbon generation in Taranaki Basin, New Zealand, has been proven in several source rocks within the syn- and post-rift basin-fill sedimentary successions. These source rocks are mainly hosted in the marginal and deep marine Upper Cretaceous shales, which generate marine and terrigenous oils. Some of the terrigenous oils could have been linked to the Paleogene coals; however, the capability of these coals to generate and expel liquid hydrocarbons is poorly-investigated. In this study, we present organic geochemistry, kerogen petrography, wireline logging, and basin modelling to evaluate the hydrocarbon generation potential of the Paleogene coals and coal-rich facies of the Kapuni Group sediments in Kapuni Field, Taranaki Basin. A compositional correlation between oil in the Kapuni Group reservoirs and coal extracts was performed to decipher the oil origin and define its parent source rock. Kapuni oils display high pristane/phytane (Pr/Ph) > 5, low dibenzothiophene (DBT)/phenanthrene <0.1 and high relative abundance of C29 regular steranes >60%, typifying their generation from a terrigenous source rock deposited in an oxic, fluvio-deltaic environment. Similar values were also observed in the muddy coal extracts of Farewell Formation, thereby reflecting a positive coal-oil correlation. The maturity-relevant biomarkers (Ts/Tm trisnorhopanes; C29 steranes isomers, and 22S-, 22R C32 homohopanes) are similar in both oils and Farewell coal extracts confirming oil expulsion from Farewell coals during the peak oil window maturity. These results demonstrate the generation and expulsion of coal-oil, thereby shedding light on the prospectively of the Paleogene plays in the Taranaki Basin.