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.

Suppression Characteristics and Mechanism of Molasses Solution on Coal Dust: A Low-Cost and Environment-Friendly Suppression Method in Coal Mines.

Coal dust pollution poses a serious public health threat. This study aimed to investigate the feasibility of creating a coal dust suppressant using molasses, a byproduct of the sugar industry. We studied the effects of a molasses solution of varying concentrations (i.e., ranging from 0% (pure water) to 40%) on the moisture, bonding, and wind erosion properties of coal dust. Overall, the effectiveness of the molasses increased with their concentration, and it manifested itself in the following way: (1) the molasses improved the anti-evaporation ability of wet coal dust. For example, the evaporation mass of the coal dust wetted using a molasses solution decreased by 82.8%; (2) molasses effectively agglutinated coal dust; (3) molasses can effectively decrease the surface tension and increase the viscosity of the wetting solution. The surface tension of the molasses solution reached 41.37 mN/m and the viscosity increased to 6.79 mPa·s; (4) molasses can significantly suppress the wind erosion of deposited coal dust, with its wind erosion mass decreasing 99.1%; finally, (5) the effectiveness of molasses at suppressing coal dust was discussed at a molecular level. This study highlights the feasibility of a low-cost and environment-friendly dust suppressant in coal mines.

Effect of Coal Dust Content on the Low-temperature Oxidation of Silo Coal.

Coal's low-temperature oxidation (LTO) poses a significant threat to the safety of storing coal in silos. This study investigates the impact of coal dust content on the LTO characteristics of silo coal samples. The results indicate that the larger the coal dust content the higher the oxygen (O2) consumption rate and carbon monoxide (CO) generation rate and the stronger the LTO capacity. To clear the mechanism of the impact, the thermal physical characteristics were studied and thermogravimetric and differential thermal analysis (TG-DTA) experiments were performed on various coal samples. The results show that, first, with the increase of coal dust content, the thermal conductivity of the silo coal samples initially increased and then decreased, whereas the thermal diffusion and heat capacity decreased and increased linearly, respectively. This indicates that the heat storage capacity of the silo coal sample is enhanced with the increase of the coal dust content. Second, the maximum oxygen absorption rate and differential thermal reduction value of the coal samples increased linearly with the decrease in their particle size; this result verifies that decreasing the particle size of silo coal can advance its LTO process. The study findings indicate that the risk of LTO and spontaneous combustion of silo coal can be effectively reduced by controlling the coal dust content (fine coal particles).

Riverine deposition pattern of oil-particle aggregates considering the coagulation effect.

To understand the heterogeneous behavior of oil-particle aggregates (OPAs) in the riverine environment as well as the uncertainties caused by the coupling effects between their stochastic formation and transportation processes, this study employed the coagulation conceptual formula and random-walk particle tracking model. Through careful inspection using the classic Rouse-Vanoni diagram and existing laboratory observations, a vertical diffusivity scheme and the packing coefficient for an oil-sediment interaction model were determined. The density variations and deposition patterns of hypothetically fully developed OPAs as well as the impact of oil-sediment interactions on the longitudinal distribution of deposited OPAs were then investigated. The results indicate that the formation process of OPAs has a significant effect on their longitudinal deposition. The range of potentially trapped OPAs varied from several to hundreds of times the range of cases that exclude oil-sediment interactions. The deposition diagram proposed in this study visualizes the relationship between the configuration and deposition pattern of OPAs and can assist in determining the most unfavorable scenarios for oil-spill countermeasures. Further refinement and calibration of the model are necessary in the future to provide guidelines for oil spill responses and recovery in riverine environments.