Experimental research on gel-stabilized foam designed to prevent and control spontaneous combustion of coal

The gel-stabilized foam was prepared successfully by forming gel structure in the bubble film using thickening agent (TA) and crosslinking agent (CLA). The viscosity characteristic, foamability, stability, and microstructure of gel-stabilized foam were investigated systematically. The formation of gel structure reduced the foamability of foaming solution due to the increased viscosity, whereas it increased the foam stability significantly. By comprehensively considering foam expansion ratio > 5 and half-life > 120 h, the effective component range of gel-stabilized foam was determined as 3.4-5.5 g/L for TA and 2.1-4.0 g/L for CLA. Microstructure and liquid drainage kinetics analysis indicated that gel-stabilized foam demonstrated the smaller average bubble size, lower growth rate of bubble size and drainage rate compared to the traditional aqueous foam, mainly ascribing to the thickened bubble film and the formation of a viscoelastic shell on the bubble surface. The simulation experiment of spontaneous combustion of coal indicated the better inhibition efficiency of gel-stabilized foam to spontaneous combustion of coal than that of traditional foam, as evidenced by higher crossing point temperature, lower emission of carbon monoxide and ethylene for treated coal by gel-stabilized foam, which revealed its better water-retaining property to retard the oxidation of coal. Moreover, gel-stabilized foam will form a complete film on the surface of coal particles to isolate coal from the oxygen to inhibit spontaneous combustion.