Permeation-diffusion characteristics and air-leakage blocking mechanism for the fire-extinguishing inorganic gel flows in loose broken coal particles

Abstract

• Three various stages of gel slurry transports in loose coal particles were acquired experimentally and numerically. • Investigated the influence of grouting pressure and coal voids on permeation, diffusion, and filtration of gel. • Theoretically revealed the mechanisms for permeation-diffusion and wind-plugging of gel. Fire prevention with inorganic gel is the most efficient approach to the prevention and control for spontaneous fires of loose coal piles. This work explores the impact of grouting pressures on the seepage, diffusion, and filtration of fire-extinguishing inorganic gel in loose broken coal particles with different voids. Firstly, an experimental system for investigating the filtering effect, permeation behaviors, and diffusion modes for the permeation grouting of inorganic gel in loose coal particles was developed. A 2D discrete element numerical modeling was then performed to probe the intuitive features and underlying mechanisms in the experimental observation, with the numerical modeling matching fairly well with the experimental findings. Results showed that the entire permeation-diffusion process presents obvious stage characteristics with permeation-compaction, permeation-splitting flow, compacting-splitting flow-permeation, and the diffusion distance of gel slurry front increased exponentially while the diffusion velocity decreased initially and then retained stable gradually. Meanwhile, the permeability coefficient of gel slurry showed spatial–temporal properties affected by the filtration effect. Besides, the increasing grouting pressure would promote the filtration effect of gel slurry in loose coal particles, while the decreasing coal sample voids pose an opposite tendency. Under lower grouting pressures (P ≤ 0.3 MPa), the bubble radius increased slightly, and the variation in diffusion distance was faint with the increase in grouting pressure. Under higher grouting pressures (P ≥ 0.3 MPa), the bubble radius increased obviously, and the variation in diffusion distance increased obviously with the increase in grouting pressure, demonstrating that increasing grouting pressure would increase the diffusion distance and diffusion velocity significantly. In addition, increasing the gel grouting pressure and coal voids would result in a non-linear increase in the diffusion distance and diffusion velocity of the gel slurry front, which would also shorten the time required for coal particles to reach the saturation state. Moreover, the mechanisms of seepage-diffusion and wind-plugging of gel slurry in loose coal particles were discussed theoretically. This work would assist us in interpreting and illuminating the seepage-diffusion mechanism and macro–micro characteristics of inorganic gel for high-temperature loose broken coal particles.