Coal seam water infusion for dust control: a technical review

Water Injection Into Coal Seams for Outburst Prevention: The Coupling Effect of Gas Displacement and Desorption Inhibition

Gassy coal seams generally have low permeability and dry coal bodies, which are susceptible to coal and gas outburst hazards in the process of mining. Water injection into coal seams can significantly alter the gas release rate and flow behavior. However, water has dual effects on coal seams: gas displacement and water-locking, and the coupling mechanism of these two effects is not clear in the whole process of coal seam water injection. By measuring high-pressure gas adsorption isotherms and gas diffusion initial velocity, it was found that both the Langmuir adsorption constant a and gas diffusion initial velocity ΔP decrease with the increase of water content, which would reduce outburst risks. Through the self-developed integrated experimental device of "gas adsorption + water injection displacement + gas desorption″, the changing rules of gas displacement amount, desorption amount, and water lock amount under different water injection conditions were studied. The results show that when the water injection ratio increases from 6 to 25%, the gas displacement would increase from 0.62 to 1.16 mL/g, with an increase of 87.09%. Also, at the same time, the gas desorption capacity would decrease from 4.86 to 4.05 mL/g after pressure relief, with a decrease of 16.67%. The amount of water-locking increased from 0.11 to 0.38 mL/g. The effect of water injection to control coal and gas outburst occurs in two different water injection stages. In the process of water injection, water plays a major role in gas displacement, which is conducive to reducing the gas content of the coal seam. After the completion of water injection, the static water pressure remaining in the coal seam can reduce the gas emission rate. The combination of these two effects can effectively reduce the risk of outbursts.

Study of dust pollution control effect based on orthogonal test and CFD numerical simulations

To control the diffusion of high concentrations of coal dust during tunnel boring and minimize the threat to the life and health of coal miners, theoretical analysis, numerical simulations, and field measurements were combined in this study. First, computational fluid dynamic simulation software was used to simulate the generation of dust particles and their transport pattern in the tunnel. Subsequently, an innovative orthogonal test was performed to study the effect of four ventilation parameters [the pressure airflow rate (Q), distance between the air duct center and heading face (LA), distance between the air duct center and tunnel floor (LB), and distance between the air duct center and nearest coal wall (LC)] on dust diffusion. According to the orthogonal test results, the optimal ventilation parameters for effective dust control are as follows: Q = 1400 m3/min, LA = 7 m, LB = 2.8 m, and LC = 1 m. The optimized set of ventilation parameters was applied to the Wangpo 3206 working face. The results show that dust diffusion in the tunnel was effectively controlled and that the air quality was sufficiently improved.

Anisotropic Damage Mechanism of Coal Seam Water Injection with Multiphase Coupling

After coal seam water injection, coal mechanical properties will change with brittleness weakening and plasticity enhancement. Aiming at the problem of coal damage caused by the coal seam water injection process, based on nonlinear pore elasticity theory and continuum damage theory, a nonlinear pore elastic damage model considering anisotropic characteristics is proposed to calculate and analyze the gas-liquid-solid multiphase coupling effect with the fully coupled finite element method during the coal seam water injection process. The research results indicate that the wetting radius of calculated results by the model agrees well with the in situ test results, and the relative errors are less than 10%. Water saturation and induced damage of the coal body in the parallel bedding direction are greater than that in the vertical bedding direction during the coal seam water injection process, which exhibits significant anisotropic characteristics. With the increasing water injection time, the induced damage of the coal body also increases near the water injection hole. Considering the inherent permeability arising with damage, it has a significant impact on both water saturation and induced damage, which also indicates that there is a strong interaction between water saturation and induced damage. The theoretical model reveals the coal damage mechanism of gas-liquid-solid multiphase coupling after coal seam water injection and provides a theoretical prediction of coal containing water characteristics in engineering practice.

Effect of a Simulated Coal Mine Environment on Polyurethane Grouting Material and a Proposed Polyurethane Strengthening Method

When it comes to grouting in coal mines, polyurethane (PU) is often utilized. However, it is of vital importance to consistently improve the mineral PU, considering the significant amount of environmental deterioration to which it is prone. Laboratory experiments were used to model various coal mine conditions. Additionally, a workable technique for PU strengthening using ultrasonic waves was proposed. Compression tests and scanning electron microscopy (SEM) were used to describe the PU-gangue material's induration characteristics. The results showed that ultrasound has a positive impact on PU's mechanical strength. The final strength of the PU was significantly impacted by the size of the coal gangue particles, the amount of dust, and the amount of water. The induration made of gangue and PU with the same mass but differing particle sizes was noticeably different in its compressive strength. The strengthening mechanism showed that the average size of the rigid foam after the ultrasound treatment was smaller, and the 'honeycomb'-structured space in the inner section was more compact, resulting in the rigid PU foam having a higher compressive strength after ultrasound treatment. Furthermore, the dust content and water content of coal mines need to be controlled within a specific range to ensure the effective use of PU grouting materials.

CFD-based simulation study of dust transport law and air age in tunnel under different ventilation methods

To solve the problem of high-concentration dust pollution in a bored tunnel, we conducted a simulation study on the dust transport law and air age of the wind flow in a bored tunnel under different ventilation methods. Air age was innovatively introduced as an index for evaluating tunnel air quality. The results show that dust pollution is serious under conditions of press-in ventilation, which is unfavorable to personnel operations. Following the installation of an on-board dust-removal fan, an effective dust-control air curtain forms in the tunnel, and the high-concentration dust is essentially controlled within the range of Z = 13 m from the working face. The dust concentration in the working area on the left side of the tunnel is CD < 200 mg/m3, and the dust-control effect is obvious. At the same time, the air age on both sides of the tunnel is reduced by 35.5% following the use of the on-board dust-removal fan. Taking into account dust control by ventilation and dust removal by fan, spraying dust reduction measures are added, and we developed automated wind-mist synergistic wet high-frequency oscillation dust-capturing technology for tunnel boring. This could effectively improve the problem of high levels of coal dust pollution in tunnels.

Wetting behavior during impacting bituminous coal surface for dust suppression droplets of fatty alcohol polyoxyethylene ether

The wetting behavior of droplets during impacting coal surface widely exists in the dust control process. Understanding the effect of surfactants on the diffusion of water droplets on coal surface is critical. To study the effect of fatty alcohol polyoxyethylene ether (AEO) on the dynamic wetting behavior of droplets on bituminous coal surface, a high-speed camera is used to record the impact process of ultrapure water droplets and three different molecular weight AEO solution droplets. A dynamic evaluation index, dimensionless spreading coefficient ([Formula: see text]), is used to evaluate the dynamic wetting process. The research results show that maximum dimensionless spreading coefficient ([Formula: see text]) of AEO-3, AEO-6, and AEO-9 droplets is greater than that of ultrapure water droplets. With the increase of impact velocity, the [Formula: see text] increases, but the required time decreases. Moderately increasing the impact velocity is conducive to promoting the spreading of droplets on the coal surface. Below the critical micelle concentration (CMC), the concentration of AEO droplets is positively correlated with the [Formula: see text] and the required time. When the polymerization degree increases, the Reynolds number ([Formula: see text]) and Weber number ([Formula: see text]) of droplets decrease, and the [Formula: see text] decreases. AEO can effectively enhance the spreading of droplets on the coal surface, but the increase in polymerization degree can inhibit this process. Viscous force hinders droplet spreading during droplet interaction with the coal surface, and surface tension promotes droplet retraction. Under the experimental conditions of this paper ([Formula: see text], [Formula: see text]), there is a power exponential relationship between [Formula: see text] and [Formula: see text].

Study on the effect of SDBS and SDS on deep coal seam water injection

Coal seam water injection, as an important disaster prevention means in the process of coal mining, can effectively suppress coal dust, add water injection additives, can effectively improve the wettability of coal body, improve the permeability of coal body, so as to achieve the prevention of rock burst. To improve the wettability of coal in coal seam water injection, the surfactant is often added to water, but sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS) have limitations in improving wettability of deep coal seam by injecting water. Therefore, it is very important to determine the influencing factors of SDBS and SDS to improve the wettability of coal. In this paper, the effects of oxygen-containing functional groups and minerals in coal on the wettability of coal are revealed, and the wettability mechanism of SDBS and SDS is expounded from the microscopic point of view. SEM was used to characterize the interaction between coal surface and surfactant, and the contact angle experiment was used to verify the influence of minerals in coal on wettability. Inductively coupled plasma atomic emission spectroscopy (ICP) and dynamic light scattering (DLS) tests were used to characterize the interaction of SDBS, SDS with minerals and the size of precipitation generated by the interaction of SDBS, SDS and mineral ions. The results showed that SDBS and SDS interact with Ca²⁺ to produce precipitation and block the flow of water in coal, which is not conducive to improving the wettability of deep coal seam to a certain extent. The significant chelating effect of chelating agent and Ca²⁺ provides a feasible solution to this problem.

Enhancement of the wettability of a coal seam during water injection: effect and mechanism of surfactant concentrations above the CMC

This paper determines the optimal surfactant concentration for enhancing coal's wettability and explores the wetting mechanism at surfactant concentrations above the critical micelle concentration (CMC) during coal seam water injection. In this study, laboratory experiments and field tests were used to investigate the influence of monomeric surfactants and compound surfactants at various concentrations on coal's wettability. The results showed that when the surfactant solution concentration was greater than the CMC, the coal's wettability was significantly enhanced as the surfactant concentration increased. However, the coal's wettability did not monotonically increase with the concentration, and the maximum value was reached in the range of 0.5-3 wt.%. Increasing the surfactant adsorption density and changing the adsorption state on the coal surface were the essential reasons surfactants continued improving the coal's wettability at concentrations above the CMC. The Marangoni flow effect and changes in the viscosity of the surfactant solution with concentration were also important factors that affected the coal's wettability.

Experimental study on coal dust wettability strengthened by surface active ionic liquids

The water wettability of coal dust was very important for dust control when using water-based dust suppressant materials. The coal dust wettability strengthened by surface active ionic liquid was studied in this paper. The surface activity of ten ionic liquids with different anions Cl^-, Br^-, [BF₄]^-, [NTf₂]^- and cations [HOEtMIm]⁺, [C_nmim]⁺ (n = 4, 12, 14, 16) was studied by surface tension test. The water wettability of raw coal dust can be improved individually by adding ionic liquid to water or pre-treating coal dust by ionic liquids. The wettability of lignite was improved little, but that of bituminous coal and anthracite were improved much. The dual strengthened effects of ionic liquids on coal dust wettability were studied by the wetting results between ionic liquids solutions and ionic liquid-treated coal samples. The wettability of lignite can be strengthened under the combined action of [HOEtMIm][NTf₂] and [C₁₂MIm]Br, while other dual effects were not satisfactory. All ionic liquids combination had strengthened effects on the wettability of bituminous coal and anthracite, especially the [C₁₂MIm]Br treatment and [C₁₂MIm]Br solutions together had the best dual effects. The functional groups results indicated that the hydrophilic oxygen-containing functional groups in treated coal samples increased, the hydrophobic aliphatic hydrocarbon functional groups decreased and part of ionic liquids were adsorbed on the coal surface. These changes together enhanced the wettability of coal with high coalification degrees.

Research on air curtain dust control technology for environmental protection at fully mechanized working faces

The development of coal industry is restricted by dust pollution. Air curtain dust control technology was proposed as a solution to the serious problem of pollution. A mixture of numerical modeling and field tests has been used to study this technology. Numerical simulation is used to analyze the dust control effect of this technology under different dust generation conditions. Field measurements are used to verify the effectiveness of this technology. The results show that following the application of this technology, the fan-shaped air curtain generated by the fans forms a trapezoidal protective area between the coal cutter and the sidewalk. This protective area prevents dust from entering the coal-cutter driver's workspace. The average dust concentrations where the coal-cutter driver works were 1590 and 466 mg/m³, severally, before and after the implementation of this technology. The dust control rate in this space is approximately 70.69%. This research provides useful data for dust control technology in fully mechanized mining faces, and will contribute to the stable development of coal fuel.

Dual-Structure PVDF/SDS Nanofibrous Membranes for Highly Efficient Personal Protection in Mines

Pneumoconiosis in miners is considered a global problem. Improving the performance of individual protective materials can effectively reduce the incidence of pneumoconiosis. In this study, the blend membrane of sodium dodecyl sulfate and polyvinylidene fluoride with a dual structure was prepared using electrospinning techniques, and the morphological structure, fiber diameter, and filtration performance of the nanofiber membranes were optimized by adjusting the PVDF concentration and SDS content. The results show that the incorporation of SDS enabled the nanofiber membranes to show tree-like and beaded fibers. Compared with the original PVDF membrane, the small content of tree-like fibers and beaded fibers can improve the filtration efficiency and reduce the resistance of the fiber membrane. The prepared nanofiber membrane has excellent comprehensive filtration performance, and the quality factor is 0.042 pa−1 when the concentration of PVDF is 10 wt% and the addition of SDS is 0.1 wt%. Furthermore, after high-temperature treatment, the membrane could still maintain good filtration performance. The PVDF/SDS blend nanofiber membrane has outstanding filtration efficiency and good thermal stability and can fully meet the personal protection of miners in underground high-temperature operation environments.

Preparation and performance of a biological dust suppressant based on the synergistic effect of enzyme-induced carbonate precipitation and surfactant

To control the dust pollution caused by open-pit coal mining and reduce or avoid the secondary hazards of existing dust suppressants to the environment, a biological dust suppressant was prepared through the synergistic effect of a surfactant and an enzyme-induced carbonate precipitation. The optimal ratio of biological dust suppressant was determined, and the dust suppressive effect and dust consolidation mechanism of the biological dust suppressant were investigated. The results showed that the optimal biological dust suppressant had an alkyl polyglycoside (APG) concentration of 0.3 wt.%, a urea-CaCl₂ concentration of 0.6 mol/L, and a urease to urea-CaCl₂ volume ratio of 1:3. The wind erosion resistance of coal dust treated with this dust suppressant was enhanced by 86.69%. The adsorption of the biological dust suppressant by coal dust was mainly due to the electrostatic interaction between the surfactant and coal dust. The mineralization product of the dust suppressant was calcite-type CaCO₃, which consolidated coal dust due to the formation of intermolecular hydrogen bonds between CaCO₃ and coal dust.

Spray Structure and Characteristics of a Pressure-Swirl Dust Suppression Nozzle Using a Phase Doppler Particle Analyze

In order to understand the characteristics of the spray field of a dust suppression nozzle and provide a reference for dust nozzle selection according to dust characteristics, a three-dimensional phase Doppler particle analyzer (PDPA) spray measurement system is used to analyze the droplet size and velocity characteristics in a spray field, particularly the joint particle size–velocity distribution. According to the results, after the ejection of the jet from the nozzle, the droplets initially maintained some velocity; however, the distribution of particles with different sizes was not uniform. As the spray distance increased, the droplet velocity decreased significantly, and the particle size distribution changed very little. As the distance increased further, the large droplets separated into smaller droplets, and their velocity decreased rapidly. The distributions of the particle size and velocity of the droplets then became stable. Based on the particle size-velocity distribution characteristics, the spray structure of pressure-swirl nozzles can be divided into five regions, i.e., the mixing, expansion, stabilization, decay, and rarefied regions. The expansion, stabilization, and decay regions are the effective dust fall areas. In addition, the droplet size in the stabilization region is the most uniform, indicating that this region is the best dust fall region. The conclusions can provide abundant calibration data for spray dust fall nozzles.

Analysis of pulverized tectonic coal gas expansion energy in underground mines and its influence on the environment

Production of a large amount of gas during outbursts will cause greenhouse effects, which will impact the atmospheric environment. In this study, some inherent properties of pulverized tectonic coal were investigated. The results indicate that tectonic coal was more broken and exhibited a higher gas adsorption volume. No obvious changes were found in the micropore and mesopore volumes, whereas the macropore volume and pulverized tectonic coal porosity were significantly increased compared with those of intact coal. Additionally, the initial gas desorption capacities of pulverized tectonic coal were enhanced by tectonism, which might be related to the development of macropore structures and porosity. Analysis of gas expansion energy at the same particle size showed that the values increased with the increasing pressure. Pulverized tectonic coal had a higher gas expansion energy, which could result in a larger outburst of potential energy. Almost all outbursts occurred in tectonic development zones and released a large amount of gas, which greatly damaged the ecological environment. From the perspective of environmental protection, attention should be paid to gas control in the tectonic development zone.

Experimental Study on the Efficacy of Water Infusion for Underground Mining of a Coal Seam

The main purpose of this study is to evaluate the efficacy of the water infusion method for various coalfaces of a coal seam by an experimental study. First, laboratory tests were performed on several coal samples taken from actual coalfaces to determine the general characteristics, especially the strength properties, with respect to the moisture content and time. The results obtained from the laboratory were employed to evaluate the appropriate parameters (e.g., water injection time and the optimum moisture content) for water infusion works in the field. A field test was then performed in order to assess the efficacy of water infusion for underground mining. The spalling depth (i.e., longwall face failure of coal wall, involving the stability of underground mining coalfaces) and mining velocity (i.e., involving the cost-effectiveness of mining constructions) were monitored at various coalfaces for both case studies (i.e., with and without water infusion). Expectedly, the field test results revealed that the spalling depth decreased significantly, whereas the mining velocity sped up considerably, at coalfaces using water infusion compared to at those without using the water infusion method. In conclusion, the promising findings obtained from the field test reinforced the efficacy of water infusion for underground mining coalfaces.