Effects of Mechanical Properties on Gas-Water Flow Characteristics around Boreholes: Implementation of Damage-Based Coupling Models.

Neglecting the coal damage effect around a borehole could result in low accuracy of gas extraction seepage analysis. A fluid-solid coupling model incorporating coal stress and damage, gas diffusion, and seepage was established. Reliability of the proposed model was validated using field data. Variation characteristics of gas-water phase parameters in the borehole damage zone during gas drainage were analyzed. Meanwhile, effects of equivalent plastic strain, lateral pressure coefficient, internal friction angle, cohesion, Young's modulus, and Poisson's ratio on the damage state and spatiotemporal change properties of gas extraction flow were investigated. Results indicate that due to coal damage, permeability shows a three-zone distribution around the borehole, among which the fracture zone has the highest permeability, approximately 40 times of the original value. Permeability in the plastic zone decreases rapidly, while permeability is the smallest in the elastic zone. Coal permeability within the damage zone increases with continuous gas extraction. A smooth and low-value zone occurs for both fracture and matrix gas pressures. With the increase in equivalent plastic strain, the damage zone decreases, while peak permeability in the damage zone rises, and gas pressure in the smooth low-pressure zone continues to drop. The damage zone becomes smaller with an increasing lateral pressure coefficient, while those plastic and elastic zones become larger. The damage zone area corresponding to the lateral pressure coefficient of 0.89 is 82.3% smaller compared with that of 0.56. As internal friction angle and cohesion rise, the damage zone gradually decreases and shifts from a butterfly shape to elliptical shape. When Young's modulus is heterogeneously distributed, except for concentrated shear damage zones around the borehole, punctate microdamage zones are also found at positions far from the borehole. Those damage zones gradually become smaller as shape parameters of the Weibull distribution get larger. The above findings are expected to offer theoretical support and practical guidance for borehole drilling and efficient extraction of clean methane resources.

Experimental Investigation on Pore-Fracture Variations in Coal Affected by Carbon Disulfide.

Solvent treatment is an effective technique to stimulate pore and fracture growth in low-permeability coal seams and improve the efficiency of methane extraction. Adopting the nuclear magnetic resonance test, liquid nitrogen adsorption analysis, ultrasonic test, and CT scanning, pore variation and fracture development in lignite, bituminous coal, and anthracite after carbon disulfide treatment were analyzed. Full-scale pore size distribution characteristics were obtained. The Frenkel-Halsey-Hill model was adopted to analyze pore fractal properties. Experiment results show that carbon disulfide could increase coal porosity. Lignite showed the best pore alteration effect, with a porosity increase of 34.10%, followed by bituminous coal with a porosity increase of 14.55%, while anthracite had a slightly weaker change with only 0.91% porosity growth. The pore diameter distribution range of treated coal expanded from 0-450 to 0-1000 µm. The average pore diameter rose from 316 to 483 µm, with better connectivity between pores. After treatment, the proportions of micropore specific surface areas (SSA) in three coal samples decreased but the ratios of small pore and medium pore SSA increased. Fractal dimension D1 of lignite and bituminous coal decreased by 5.669 and 0.054%, while D1 of anthracite increased by 22.407%. D2 reduced by 0.599, 3.143, and 1.262%, respectively. Raw coal had the maximum porosity near both ends of the CT section. Porosity of lignite was the largest at the ends after treatment. Surface porosity inside coal samples also rose from about 0.1 in raw coal to approximately 0.4 after treatment. Ultrasonic velocity in lignite decreased by 50.16% due to solvent treatment. Increases in ultrasonic attenuation coefficient α and ultrasonic attenuation ratio ß indicate good fracture development. Furthermore, development degrees of lignite and bituminous coal are higher than that of anthracite. Results of the above methods verify with each other, indicating the effectiveness of carbon disulfide treatment in improving pore and fracture structures. The outcomes of this research could offer a theoretical basis for chemical permeability-enhancement technology.

Spatiotemporal characteristics of air pollutants and their associated health risks in '2+26' cities in China during 2016-2020 heating seasons.

To understand characteristics of air pollutants and their associated health risks in recent heating seasons in China, ambient monitoring data of six air pollutants in '2 + 26' cities in Beijing-Tianjin-Hebei and its surrounding areas (known as the BTH2+26 cities) during 2016-2020 heating seasons was analyzed. Results show that daily average concentrations of PM2.5, PM10, SO2, NO2, and CO dropped significantly in BTH2+26 cities from the 2016-2017 heating season to 2019-2020 heating season, while 8h O3 increased markedly. During 2016-2020 heating seasons, annual average values of total excess risks (ERtotal) were 2.3% mainly contributed by PM2.5 (54.4%) and PM10 (36.1%). With PM2.5 pollution worsening, PM10 and NO2 were the important contribution factors of the enhanced ERtotal. Higher health-risk based air quality index (HAQI) values were mainly concentrated in the western Hebei and northern Henan. HAQI showed spatial agglomeration effect in four heating seasons. Impact factors of HAQI varied in different heating seasons. These findings can provide useful insights for China to further propose effective control strategies to alleviate air pollution in the future.

Effect of Sophorolipid Adsorption on the Coal Microstructure: Experimental and Wettability Mathematical Model Discussion.

Green biosurfactants are emerging as a promising area of research. However, there is a limited focus on the adsorption and wetting characteristics of biosurfactants on coal dust. This study explores the effects of sophorolipid (SL) biosurfactants on the microstructure and wettability of different coalification degree coal. The microstructure parameters of SL adsorbed on coal dust were measured using a surface tensiometer, contact angle analyzer, and particle size analyzer. The results indicate that SL has the lowest critical surface tension, leading to a 9.25° decrease in the contact angle for low-rank bituminous coal (YZ-LRBC). Furthermore, SL significantly altered the particle size distribution of lignite (NM-LC) and YZ-LRBC. The pore size structure of SL-infiltrated coal dust was quantified using a specific surface area analyzer, revealing a decrease in the specific surface area and an increase in the average pore size. The infrared analysis demonstrated that SL permeation significantly increased the percentage of hydrophilic functional groups (hydroxyl structures) while reducing the hydrophobic functional groups (aliphatic hydrocarbon and aromatic structure). Based on the measured microstructure parameters, a regression equation for contact angle was established: [contact angle (°)] = 73.800 - 0.860 × [D10 (nm)] + 4.280 × [specific surface area (m2/g)]. Notably, the characteristic particle size D10 had a significant negative effect on the contact angle, while the specific surface area had a significant positive effect. These findings provide a theoretical foundation for the application of biosurfactants in water injection to reduce dust and improve the wetting efficiency.

Study on pollution evolution law of coal and rock mixed dust in coal-oil shale fully mechanized mining face: a study case.

To better understand the dust dispersion and pollution laws in coal-oil shale fully mechanized mining faces, the airflow distribution and coal and oil shale mixed dust emission law was simulated, and the simulation results are analyzed and verified in combination with the field measured data. The research results showed that in the area 0-10 m on the leeward side of the front drum, most of the coal dust particles with a large particle size stay near the roof of the hydraulic support and the height of the breathing zone, while most of the oil shale dust particles with a large particle size stay in the area below the height of the breathing zone. In the height of the breathing belt, oil shale and coal dust particles seriously polluted the 0-6-m and 0-13-m areas on the leeward side of the front drum of the shearer, respectively. According to the different distribution of coal dust and oil shale dust, a wet dust collector and multi-nozzle atomization set are designed to remove dust. The field test results show that the dust removal rates of the two kinds of dust reach 83.4% and 87.5% respectively after the dust removal device is opened.

Pollution and occupational protection of diesel particulate matter in underground space.

To address the diesel particulate matter pollution problem at the 12,306 continuous mining face of Shangwan coal mine, the spatial and temporal evolution law of diesel particulate matter generated at the three locations of the shuttle car head tunnel, contact alley, and support tunnel under the pressure-in ventilation condition of the double lane of the continuous mining face was studied by numerical simulation. The results show that the highest diesel particulate matter concentration at the shuttle car discharge is about 144.17 mg/m3, which seriously affects the health of miners. The highest diesel particulate matter concentration at the shuttle car tunnel is 52.58 mg/m3, and at the contact alley, the diesel particulate matter diffusion space is limited by the compression of the space inside the contact alley by the shuttle car machine body and the alley wall, which makes the diesel particulate matter accumulate here, forming a high diesel particulate matter concentration distribution area with a concentration value of 112.75 mg/m3. When supporting the roadway at the shuttle, diesel particulate matter accumulates in the range of X = 55 m ~ 60 m, Y = 0 m ~ 4 m, and Z = 23.4 m ~ 29.4 m. According to the degree of DPM pollution in different areas, different individual protective equipment is used to obtain different levels of pollution protection.

Wetting-consolidation type dust suppressant based on sugarcane bagasse as an environmental material: Preparation, characterization and dust suppression mechanism.

Coal mines generate a lot of dust during production and transportation, which not only damages the health of personnel, but also causes environmental pollution. Based on the problems of low extraction efficiency of cellulose matrix and low economy of existing dust suppressants for biomass materials, this paper uses bagasse extracted cellulose from sugar production waste as a matrix and adds polyvinyl alcohol and polyacrylamide as monomers to prepare a wetting-crusting type highly efficient environmental protection dust suppressant for coal mine production and transportation process. The dust suppression effect of the product was analyzed by the performance tests of dust suppression efficiency, consolidation layer strength and permeability. The dust suppression rate of the product prepared in this paper remained above 90% at the simulated wind speed of 10 m/s, the consolidation layer strength of 42.3 KPa was much higher than that of the pure water solution, and the average permeation rate within 30 min was greater than that of the surfactant solution. It is proved that the dust suppressant prepared in this paper has good dust suppression effect, high consolidated layer strength and good permeability, and the product prepared in this paper using environmentally friendly biomass raw materials has good degradability, and the mechanism of the dust suppressant is illustrated by MS simulation. The biomass dust suppressant can meet the requirements of dust suppression in the process of coal mining and transportation and is non-toxic and environmentally friendly.

One-Step Preparation of Activated Carbon for Coal Bed Methane Separation/Storage and Its Methane Adsorption Characteristics.

Different coals were used as raw material for the preparation of carbonization precursors and coal-based activated carbons. The physicochemical structure and adsorption performance of the samples were tested. Results show that the carbonization and activation process greatly changed the molecular structure of raw coal, and a large number of organic functional groups disappeared. The carbonization process has enriched the pore structure of coal by thermal ablation, and it has a pore expansion effect on all the pores in coal, while the activation process is more conducive to micropore generation. The calculated mean isosteric heat of adsorption showed that the activated carbon needs to release more heat in the adsorption process as the same equilibrium pressure increased due to the adsorption capacity of the prepared activated carbon being far more than that of the raw coal. Adsorption processes of activated carbons are more sensitive to temperature changes, providing a certain guiding significance for the temperature swing adsorption and pressure swing adsorption.

Research on dust dispersion law of fully mechanized mining faces under different inclinations and tracking closed dust control method.

Based on the gas-solid two-phase flow theory, numerical simulation of the dust dispersion law of fully mechanized mining work under different inclination angles and comparative analysis of field-measured data show that with the increase of working face inclination, the inclination of airflow into the unmined zone increases from 25° to 50° and the maximum wind speed increases from 2.16 to 2.25 m/s after the mixing of cutting turbulent wind and system ventilation. Meanwhile, the range of high-concentration dust clusters, suspension time, lateral migration intensity, and deposition zone increase to varying degrees; dust clusters increases from 62.02 to 202.46 m3. When X < 53.96 m, the dust concentration in the sidewalk-breathing zone shows a sine function with the length of the working face, and when X ≥ 53.96 m, it satisfies the exponential decay function. Based on this, the tracking closed dust control technology is proposed. Combining the offset angle of the airflow and t the gathering position of dust mass, the wind curtain angle and air velocity are automatically controlled to ensure that the dust is restricted to one side of the cable trough.

Experimental Study on Atomization Characteristics of Gas-Liquid Two-Phase Flow Nozzle and Its Dust Removal Effect.

An experimental study on the flow rate and atomization characteristics of a new gas-liquid two-phase flow nozzle was carried out to use high-concentration respirable dust in the workplace of high-efficiency sedimentation coal production based on the gas-liquid two-phase flow nozzle technology. The simulation roadway of dust fall in large coal mines was constructed, and the respirable rock dust produced by fully mechanized mining surfaces was chosen as the research object. The effects of humidity on the capture effect of respirable rock dust were analyzed in the experimental study. The results demonstrated that: (1) the distribution range of the particle size of fogdrops declines with the reduction in fogdrops D50, D[3,2] and D[4,3], which are produced by gas-liquid two-phase flow nozzles. (2) The initial ambient humidity in the simulated roadway was 64.8% RH. After the gas-liquid two-phase flow spray was started, the ambient humidity was elevated by 23.2 to 23.5% RH within 840s and tended to be stable and no longer grew after reaching 88.0-88.3% RH. The initial growth rate of the ambient humidity in the simulated roadway was high, and then was gradually slowed down. (3) Humidity is an important factor influencing the collection of respirable dust. The humidity at 10.0 m leeward of the dust-producing point was increased by 19.6% RH, and the sedimentation rate of respirable dust was increased by 6.73%; the two growth rates were 13.1% RH and 9.90% at 20.0 m; 16.4% RH and 15.42% at 30.0 m; 18.4% RH and 11.20% at 40.0 m. In practical applications of the gas-liquid two-phase flow nozzle in coal mining activities, attention shall be paid to not only the influences of its atomization characteristics on the capture effect of respirable dust but also the influences of the flow rate of the nozzle on the humidity of the working surface. Appropriate gas and water supply pressures shall be chosen according to the space and respirable dust concentration on the working surface to realize a better dust removal effect.

Research on Coal Dust Wettability Identification Based on GA-BP Model.

Aiming at the problems of the influencing factors of coal mine dust wettability not being clear and the identification process being complicated, this study proposed a coal mine dust wettability identification method based on a back propagation (BP) neural network optimized by a genetic algorithm (GA). Firstly, 13 parameters of the physical and chemical properties of coal dust, which affect the wettability of coal dust, were determined, and on this basis, the initial weight and threshold of the BP neural network were optimized by combining the parallelism and robustness of the genetic algorithm, etc., and an adaptive GA−BP model, which could reasonably identify the wettability of coal dust was constructed. The extreme learning machine (ELM) algorithm is a single hidden layer neural network, and the training speed is faster than traditional neural networks. The particle swarm optimization (PSO) algorithm optimizes the weight and threshold of the ELM, so PSO−ELM could also realize the identification of coal dust wettability. The results showed that by comparing the four different models, the accuracy of coal dust wettability identification was ranked as GA−BP > PSO−ELM > ELM > BP. When the maximum iteration times and population size of the PSO algorithm and the GA algorithm were the same, the running time of the different models was also different, and the time consumption was ranked as ELM < BP < PSO−ELM < GA−BP. The GA−BP model had the highest discrimination accuracy for coal mine dust wettability with an accuracy of 96.6%. This study enriched the theory and method of coal mine dust wettability identification and has important significance for the efficient prevention and control of coal mine dust as well as occupational safety and health development.

Experimental Research on the Performance of a Wetting Agent Based on Compound Acidification in Low-Porosity and Hard-to-Wet Coal Seams.

To improve the wetting performance of the composite acid solution in the deep coal seam, in this paper, the surface tension and contact angle characteristics of the compound acid wetting agent are studied, then the composition of the wetting agent is developed and evaluated based on nuclear magnetic resonance. The research indicates that surfactants can reduce the surface tension of water, and the surface tension tends to decrease with the increase in the surfactant concentration. The critical micelle concentration of the anionic surfactant sodium dodecyl sulfate (SDS) solution is only 0.025%, and the corresponding critical surface tension is 30.63 mN/m. The wetting agent material based on the composite acid solution includes the acid HCl, HF, the anionic surfactant SDS, and the inorganic salt NaCl, the composition of which is 8%, 8%, 0.025%, and 0.6 mol/L, respectively. The total wetting rate of the composite acid-containing HCl + HF + SDS + NaCl is the largest, reaching 64.30%, which has good wettability inside the coal and can be a comprehensive intrusion into the internal structure of coal pores.

Study on the Wettability of a Composite Solution Based on Surface Structures of Coal.

In order to research the influence of composite surfactant solutions on the wetting ability of coal, the wettability parameters, pore structure parameters, and surface microscopic morphology were determined in this study. The results show that the wettability of the surfactant can be improved by adding NaCl. As the concentration of NaCl increased, the spreading coefficient of the NaCl-SDS composite solution increases; the spreading coefficient increased from -10.838 to -3.7624 mN/m. The surface free energy decreased from -2.031 to 3.670 J/mol × 103, and the adhesion work decreased from 113.802 to 55.058 mJ/m2. In terms of the pore structure and surface morphology of coal, the pore size will affect the wettability of coal. The contact angle reduces with pore size increase (R 2 = 0.955). The surface pores of coal treated with the NaCl-SDS composite solution increase and the fracture connectivity is improved, which facilitated the solution to penetrate coal for wetting. The results of this paper have great practical significance for mining at the face to reduce coal dust pollution.

Effects of the linoleic acid/docosahexaenoic acid ratio and concentration inducing autophagy in Raw264.7 cells against Staphylococcus aureus.

Our study was to understand the autophagy induce by different ratios and concentrations of LA/DHA on Raw264.7 cell, and then to investigate the effect of Raw264.7 autophagy on the clearance of Staphylococcus aureus. Raw264.7 cells was treated by LA/DHA in different concentrations (50/100 µmol/L) and ratios (4:1, 6:1, 8:1, 1:4, 1:6 and 1:8) for 6/12/24 h, cell viability assay was assessed by Cell Counting Kit-8, LC3B, p62, P-mTOR, P-Akt, P-PI3K and BECN 1 were detected by the Western blot. LA/DHA could induce autophagy of Raw264.7 cells through the PI3K-Akt-mTOR signaling pathway, the strong effect on autophagy by the concentration is 100 µmol/L, the ratio is 6:1 of LA/DHA, and the treatment time is 24 h. Compared with the images in the control group obtained by merging red and green fluorescence channels, the treatment of LA, DHA in a ratio of 6:1 at a concentration of 100 µmol/L for 24 h significantly lead to a substantial number of autophagosomes (yellow) as well as autolysosomes (red), enhancing autophagy flux. Autophagy induce by LA/DHA can devour and damage intracellular and extracellular Staphylococcus aureus. These results indicate that LA/DHA cloud induce autophagy and enhance the phagocytosis and killing ability of macrophages to intracellular parasitic bacteria.