Coal spontaneous combustion in the goaf is among the common hazards encountered in coal mining production. Fly ash composite gel material has been found to effectively seal air leakage channels, thereby reducing the risk of coal self-ignition. This work explores the seepage and diffusion behavior of the gel within the goaf. First, a fly ash composite gel is prepared using fly ash, waste glass, and sodium bicarbonate, and the physical parameters of the material are tested using a rheometer. A three-dimensional multiphase flow numerical model of the goaf is then constructed based on computational fluid dynamics methods to explore the permeation behavior and diffusion pattern of the fly ash composite gel in porous media. Simulation results indicate that the gelling time of the fly ash composite gel is between 15 and 20 min. Following the formation of the gel, the viscosity of the material increases, and the seepage speed gradually decelerates. After natural sedimentation and filtration through layers of loose coal and rock bodies, the solid particles of the gel gradually form larger groups and remain within the goaf, filling and plugging air leakage areas. With the fly ash gel injected, the seepage speed of the gel is inversely proportional to the area of diffusion. The coverage area of the gel on the fracture channels in the goaf exhibits a linear growth trend over time. Simultaneously, the study considers the effects of different inclinations in the goaf on the diffusion distance and speed. The gel moves along the direction of the inclination, leading to an elongation of the movement path, an increase in seepage and diffusion distance, and resulting in a spatially uneven distribution of the gel. This, in turn, reduces the effective coverage rate of air leakage channels. This research is of significant importance in understanding and improving gel fire prevention technology, providing a theoretical foundation for the design of more effective strategies for sealing coal mine goaf.
Guo et al. (Thu,) studied this question.