Study On The Sand-suspended Colloid For Preventing Coal Spontaneous Combustion

Grouting is one of the methods which were widely applied in fire control technology in coal mine at present. In fact, Northwest China has abundant coal resource but with serious mine fire disaster and shortage of water and loess, the cost of conventional grouting is high. However, in those areas there are abundant sand and fly ash resources, in order to improve the quality of sand injection and reduce the wastage of water when grouting, the paper make a further study on the new sand-suspended colloid materials of fire control technology.The new compound material of sand-suspended colloid was developed, which was composed of mineral inorganic gel and organic polymer. In the paper, the general characters of loess, fly ash and mountain with granular shape, such as the grain diameter, phase composition, microstructure observation, were analyzed firstly. Then through enough experiments and improvement of original additives, the sand-suspended colloid materials was developed, and by little addition of it, the steady sand-suspended slurry can be produced easily. By the further study on impact factors with different concentrations, shear rate and temperatures to sand-suspended colloid viscosity, we generated the rheology constitutive equation of sand-suspended colloid.In order to study the suspended mechanisms of solid particles in sand-suspended colloid, the space work model based on theory of double-electric layer is established. The surface tension of sand-suspended was increasing with the concentration of additives, which illustrate that the colloid system has a tendency for unsteady status. Double electric layer that formed by colloid particles charged plays the important role about the stability in sand-suspended colloid system, the dispersion of sand-suspended colloid to sand-suspended slurry is the synergistic effect combined with steric effect and electrostatic repulsion effect that created by the reason of double electric layer particles. So that it can ensure the stability of colloid system and sand-suspended slurry. The mechanical analysis indicated that under the conditions of stress of rock sand particles to the lower part of fluid less than yield stress of colloid itself, the sand can suspend steadily.A mathematical model of two-phase flow in pipeline for sand-suspended colloid based on two-phase flow theory is established. The experimental study on impact factors of sand-suspended slurry rheology, for example, the shear rate, suspended sediment concentration and temperature, was carried out; meanwhile the rheology constitutive equation of sand-suspended slurry was presented. The yield pseudo plastic two-phase fluid of sand-suspended slurry flow model in the pipeline was established, and the solution of the model was also presented. By using the sand-suspended slurry preparation and flow pipeline system, the flow parameters of it were tested. The results show that the numerical and test results have good agreement. Thus it verifies the reliability of the mathematical model.The inhibition mechanism of sand-suspended colloid is investigated, which could depress the reactivity of active groups in coal. It was studied that the sand-suspended colloidal has an influence on the structure of functional groups, cross point temperature, index gas and the apparent activation energy in the temperature oxidation process of different kinds of coal. Through in-situ Fourier infrared spectrum experiment, it was showed that the sand-suspended colloid can inhibit the activity and generation of methyl, methylene, hydroxyl, carboxyl, carbonyl and functional groups of aliphatic. The resistance performance experiment, based on programmed temperature method, was also showed that the sand-suspended colloid has an important influence on the cross point temperature, index gas and the apparent activation energy of lignite, kennel coal, gas-fat coal and lean coal in oxidation heating process. So it has a hysteresis effect on the coal oxidation process. Based on the theoretical research of sand-suspended colloid, sealing pressure testing and stored coal fire, the ability of sealing and fire control was inspected.Based on the experiment and theoretical research, the paper analyzed the rheology, suspension property, liquidity and fire control ability of sand-suspended colloid, optimized the sand-suspended fire control technology, and made clear the problems of the sand-suspended colloid suspend mechanism, flowed friction property and ignition inhibition mechanism, which laid the theoretical foundation for the application of this technology.