Experimental Study On Prevention And Control Of Spontaneous Combustion Of Residual Coal In Goaf By Phosphate Ultrafine Solid Aerosol Technology

The fire caused by spontaneous combustion of coal is a common internal fire in the production process of coal mines.It causes various disasters and accidents,which seriously restricting the development of the coal industry.At present,most of the prevention and control technologies for fire in goaf are grouting,nitrogen injection,gel injection,foam injection,inhibitor,etc.Although they have good fire prevention effects,they also have certain deficiencies.In view of the characteristics of spontaneous combustion fire in goaf,the shortcomings of traditional fire-fighting technology are systematically analyzed in this paper,and the idea of using aerosol fire-fighting technology to prevent spontaneous combustion in goaf is proposed.Subsequently,the basic experimental research on fire control technology of ultra-fine solid particle aerosol is carried out,providing a new way for coal spontaneous combustion prevention.After comparing a variety of materials,it is found that phosphate can effectively inhibit the oxidation reaction of coal in the high temperature reaction stage of coal;in addition,chloride can effectively inhibit the oxidation reaction of coal in the low temperature oxidation stage of coal,prolonging the natural ignition period of coal;When the two materials act synergistically on coal,they have high resistance and fire extinguishing properties.The results of the fire protection material screening experiment show that NH₄H₂PO₄ and MgCl₂ can synergistically inhibit the oxidation of coal and increase the activation energy of coal and oxygen;in the high temperature combustion stage above 380°C,NH₄H₂PO₄/MgCl₂?4:1?is the best inhibition ratio,which can delay the oxidation maximum temperature point backward;in addition,MgCl₂ and NH₄H₂PO₄ play the best in the low temperature stage and the high temperature stage respectively;at the same time,NH₄H₂PO₄/MgCl₂?4:1?can greatly reduce the oxygen-containing functional groups in the oxidation process of coal,and can inhibit the thermal decomposition of coal.The inhibition of the breakage of the branches in the coal macromolecules is prevented by NH₄H₂PO₄/MgCl₂?4:1?,that is,the oxidation reaction of the coal can be efficiently suppressed.After screening experiments on aerosol solid materials,the best fire-extinguishing materials and the optimal synergistic ratio were determined,and the ultra-fine solid powders were prepared according to the ratio.In the preparation experiment,orthogonal test method was used to analyze the effects of various additives and rotation speed on the grinding effect.It was found by experiment that when the ball mill speed was 300-400 r/min,the particle size and bulk density of the dry powder particles were small,but when the rotation speed continues to increase,the particle size and bulk density increase sharply.Excessively high rotational speed not only does not improve the grinding effect,but also causes the inorganic salt to compact to cause the particle size to become larger.Therefore,the determination of the rotational speed of the ball mill is extremely important for the preparation of ultrafine dry powder.Secondly,by adding different inert additives,the ultra-fine dry powder simultaneously obtains the best fluidity and the smallest particle size.The optimum grinding parameters were determined by orthogonal experiment:talc powder 2.5%,sericite 3%,activated clay 2%,white carbon black 1%,calcium stearate 2.5%,speed 450r/min.The ground solid powder after grinding is modified on the surface by the hydrogen-containing silicone oil to make the polar portion of the surface non-polar,thereby reducing the water absorption,prolonging the effective period of the dry powder,and improving the suspension of the dry powder in the air,thereby improving its fire extinguishing performance.The fire-extinguishing effect of the material was verified by physical simulation experiments.It is known from the experimental results that the aerosol fire extinguishing agent has higher fire-extinguishing efficiency than pure N₂,especially when the coal temperature is lower than 200°C.When the coal temperature is lower than 100°C,the temperature of the coal sample center does not change with the increase of the pure N₂ release pressure;however,in the low temperature range,as the aerosol release pressure increases,the aerosol accelerates the coal temperature decrease rate.In addition,the aerosol extinguishes the fire zone through a curved motion,indicating that the aerosol has an effective fire extinguishing effect after bypassing the obstacle.