Study On The Inorganic Solidified Foam And Its Characteristics For Preventing And Controlling Spontaneous Combustion Of Coal

Coal is the main energy source of our country, whereas coal exploitation is confronted with severe threaten from the disaster of coal spontaneous combustion and so on. To prevent and control coal spontaneous combustion, usually grout, nitrogen injection, foam injection, retardant spray, and composite gel injection are applied to prevent and extinguish coal fires. However, based on overall consideration of the application characteristic indicators on coal spontaneous combustion prevention, the above-mentioned materials own some limitations while taking on superiority, and they cannot satisfy the need to lastingly seal the air leakage and control coal spontaneous combustion. In recent years, using foam materials to seal the cracks draws the attention of many researchers. Accordingly, this paper conducts researches on the inorganic solidified foam(ISF) owning high expansion ratio and its property on efficiently prevent and control coal spontaneous combustion of coal mine and coal field.ISF is prepared based on the mixture of water and composite slurry containing fly ash, cement, redispersible latex powder, glass fiber and coagulant. Abrahamson collision model and sensitive time are considered in the mechanism of particle mixing with the liquid film of aqueous foam. The coagulation and solidification mechanism of ISF is worked out based on analysis of particle wetting, coagulant stimulated hydration reaction, free water consumption and pore wall solidification. Based on this, investigation of high-performance aqueous foam is conducted, and it is found that the composite surfactant solution with 2.5wt.% sodium dodecyl sulfate(SDS) and 2wt.% lauryl alcohol owns expansion ratio of 28 and 30-minutes drainage rate of 3%. By applying orthogonal test the effects of aqueous foam volume(FV), fly ash dosage(FA) in the composite powder and water-solid ratio(W/S) on the stability coefficient and expansion ratio of the ISF are investigated, and the optimum formula is with FV of 8v, W/S of 0.4, FA of 30% and coagulant of 12 wt.%. The composite slurry owns large specific gravity and cannot mix easily and evenly, to solve this problem, a set of ISF fabrication device is homemade based on the principle of step-by-step pore type foaming and hollow spiral successive bubble mixing. By use of above materials and devices, ultimately the ISF is prepared with expansion ratio of 5-7, stability coefficient of 95%, tunable setting time(10-30min), compressive strength of 0.72-1.6Mpa, efficient thermal conductivity of 0.0415-0.083W/m?K, closed porosity of 66.89% and thermal stabilized temperature of 200℃ under fill thickness of 40 mm.Analysis is made on the change of hole wall in the process of foam fluid condensation, and LFT was proposed as a judge index to estimate the condensation characteristics of foam fluid, besides the test device and corresponding test method are homemade. Experiment is carried out to study the influence of different dosage of aqueous foam, various coagulant types and dosage on the LFT. Research on the heat stability and heat insulation property of fresh foam fluid is launched, results showing that during the initial stage of 0-90 s, the heat insulation property is poor, and in later period that become strong gradually. The relationship model between the heat insulation temperature and fill thickness of ISF is deduced. Based on the Woodside model of thermal conductivity of porous media, quantitative relationship is studied between the effective thermal conductivity and aqueous foam volume after the solidification of ISF.Researches on the influence of fly ash dosage on mechanical strength of ISF are conducted, and ISF with 30% of fly ash owns high pore roundness, uniform pore size distribution and the highest compressive strength and elastic modulus. Based on empirical equation, relationship equation is fitted among the density, porosity, elastic compressive strength and elastic modulus. Crushing test on engineering stress is carried out under the condition of dynamic load(strain rate ranges from 0.001/s-0.1/s), and results show that under the same strain rate, the engineering stress-strain curves take on similar form of three periods, i.e. elastic region, crushing platform region and dense region. By analyzing the test data under varied density and strain rate, the compressive phenomenological constitutive model of ISF is fitted.By building the similar model of the crack region nearby the isolating coal pillar and goaf, experiments are carried out on the sealing and coal fire control property of the ISF, and results show that the fresh ISF keeps high diffusivity in initial period, can pile up to the high location, and can quickly cover and cool the burning point after contact. The foam material maintains good heat stability, can concrete the hot loose coal rocks, and the contact surface is tight enough to seal the air leakage after the solidification of ISF. In the meantime, the ISF has moderate thermal insulation property. The viscosity of the fresh state of ISF is tested, and the corresponding time-dependent equation is fitted. Based on the equation of Bingham fluid seepage in circular tube, the seepage diffusion radius equation is theoretically deduced and verified by substituting the monitored seepage pressure values in it.In the end, inorganic solidified foam was applied to reinforce and sealing the small pressed coal pillar, so as it is out of coal spontaneous combustion. The results of application show that it can efficiently fill and reinforce the fractures, seal the air leakage, inhibit the index gas of coal spontaneous combustion. Besides, it is especially suitable for controlling the coal fire and coal spontaneous combustion of small pillar left by the technology of tunneling along goaf. Furthermore, it is a kind of new type of fire extinguishing and preventing material which has wide application prospect and popularization value.