In order to prevent the spontaneous combustion of coal efficaciously, a new kind of compound material of multiphase foamed gel is obtained, which is composed of fly ash, foaming agent, thickener, crosslinker, and nitrogen and formed by physical and mechanical stirring. It makes use of the all-around capability of gel, foam, grouting, and inhibitor to prevent mine fires. The formation and crosslinking mechanism of multiphase foamed gel were analyzed in theory, and the effects of the mass fraction of foaming agent and slurry, the quantitative ratio of polymers, and concentration and solid particle on foam properties were carried out. Meanwhile, the resistant property and inhibition characteristic of multiphase foamed gel were studied experimentally and theoretically. The multiphase foamed gel provides a new technical method to prevent the coal spontaneous combustion and thereby it has a vast potential and development prospect.
SUMMARYFoamed gel as a new type of fire extinguishing material is used to prevent the spontaneous combustion of coal. In order to make a comprehensive study on rheological characteristics of foamed gel for mine fire control, by using type NDJ-5s digital viscometer, the factors such as mass concentration of the mixture mixed by thickener and crosslinker, foaming multiple, added salts (NaCl, CaCl 2 , AlCl 3 ), pH value and temperature having influences on the rheological properties of foamed gel have been investigated in this paper. It can be found that foamed gel shows the characteristic of non-Newtonian fluids and has shearthinning properties. With increasing of mass concentration of the mixture, the thixotropy response becomes more significant. When the foaming multiple reaches 20, the apparent viscosity gets the maximum value. The obvious viscosity characteristic of 'polyelectrolyte solution' is observed in aqueous salt solutions when added salts are put into the solution. Under different conditions of pH values, foamed gel has higher sensitivity to acid than alkaline. Zero shear viscosity, depending on temperature, decreases with the temperature increasing. Meanwhile, the fire performances of foamed gel are studied experimentally and theoretically.
Experiments have been made to investigate how mass concentrations of thickener and crosslinker blends and foaming multiple affect temperature resistance of foamed gel. The results show that, at 100°C, the time for temperature tolerance of common foam is only 196 s, while the time of foamed gel formed by thickener and crosslinker with the mass fractions of both 0.3, 0.4 and 0.5 % is 570, 604 and 780 s, respectively. When the foaming multiple is 5, the time for temperature resistance is 620 s. But the time reduces to 360 s as the foaming multiple increases to 30. Furthermore, researches are also conducted on the extinguishing effect of foamed gel. It can be known from the results that, when putting out the coal fire with similar size, the volume of foamed gel used is only one-ninth of that of common foam and the extinguishing time is less than half of common foam. With increasing in the mass concentration of thickener and crosslinker blends, the extinguishing time first shortens and then prolongs. When the mass fraction of complex solution mixed by thickener and crosslinker is 0.6 %, the extinguishing efficiency is the highest. If the foaming multiple is 5, the extinguishing time is the shortest. However, the time remains constant when the foaming multiple is over 20.
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