Experimental Research On K-type Hot Aerosol Control Of Low-rank Coal Underground High-temperature Fire Area

Frequent spontaneous fires are major disasters in underground coal mines,which also are serious hazards to the safe and healthy development of the coal-related industry.The occurrence of underground coal fires will not only cause serious resources waste and environmental pollution,but also directly threatening the safety and health of coal mine employees.At present,the gradually developed aerosol fire extinguishing technology is widely used in the field of industrial and building fires,but large-scale exploration has not yet been carried out in the field of spontaneous combustion fire prevention and control in underground coal mines,and related research is still in initial stage.In this paper,two low-rank coals,Shendong long-flame coal and Yunnan brown coal,were selected as experimental samples.Aerosol fire extinguishing materials with different formulation components were selected to carry out simulated fire extinguishing experiments in underground mine goaf.Combining experimental tests such as gas Chromatography,Simultaneous Thermal Analysis,and Fourier Infrared Spectroscopy,the effects of aerosol materials on preventing spontaneous fires in goafs are analyzed,and the mechanism of aerosol materials effect on fire extinguishment is further studied.The physical and chemical properties of the low-rank coal are analyzed.From the thermal analysis of the low-rank coal,it can be concluded that the low-rank coal has a higher volatile content.At the same time,the thermogravimetric curves of the two fresh coal samples include a higher water loss portion and At similar characteristic temperature points,the burning of lignite is longer than that of flame coal,and the burn-out temperatures of the two are similar.The infrared spectrum of long flame coal and lignite is analyzed by Fourier infrared spectrometer,and the peak-matching processing is used to obtain the-OH functional group with the key difference between long flame coal and lignite in the range of 3000-3700cm^-1;Aliphatic hydrocarbons in the range of 2800-3000cm^-1;carbonyl-based functional groups such as ester carboxyl groups such as 1800-1500cm^-1,the presence of a large number of oxygen-containing functional groups makes the low-rank coal spontaneous combustion characteristics strong.Using the Muffle furnace and Gas Chromatograph to measure the combustion temperature,O₂ consumption and the discipline of CO₂ and N₂generation of each aerosol formulation,the O₂ consumption rate of each aerosol formulation and the production rate of CO₂ and N₂ were calculated from the generation law,and phenolic was found when the resin is used as an additive,the rate of O₂ consumption and the rate of CO₂ and N₂ generation during aerosol generation are high.The elemental analysis found that the aerosol residue was mainly the K element,supplemented by other miscellaneous elements such as Na.The composition of residue is dominated by basic potassium salts,of which the compound is mainly K₂CO₃,while KHCO₃,KOH and other substances are present.From the macro-perspective,the extinguishing mechanism of aerosol for coal combustion is that large amounts of N₂/CO₂ carry ultra-fine particles to achieve rapid fire suppression.By comparing the TG/DTG curves of samples and their residues during the heating process,it is found that the characteristic temperature points of the coal samples under the effect of aerosol residues generally be postponed,and the presence of aerosol materials also increases the proportion of residues and decreases theheating rate for the mixture samples.The main functional groups of the long-flame coal and lignite are analyzed by Fourier Infrared Spectrometer.The rich O-containing functional groups in the coal make lignite and long flame coal have strong spontaneous combustion potential,but during heating process the potassium in the aerosol material reacts with the hydroxyl functional groups in coal and consumes these active groups.Thereby the generated alkaline environment inhibits the formation of carboxyl groups.At the same time,the ester group is more easily decomposed at elevated temperatures.Therefore,the aerosol material has a marked effect on the oxygen-containing functional groups in coal.Aerosols can achieve fire extinguishing effect by consuming O-containing active functional groups such as hydroxyl,ester and carboxyl groups in coal.In this paper,15 groups of aerosols with different formulations and two types of coal samples were selected for simulated goaf fire extinguishing experiments.It was found that the coal fire in the enclosed space quickly cooled after the aerosol fire extinguishing agent was applied.In terms of fire extinguishing effect,there are 8 groups of aerosol fire extinguishing agents whose fire extinguishing efficiency is stronger than the fire extinguishing efficiency of releasing 0.25MPa nitrogen as the inert gas control test,and the fire extinguishing efficiency of dicyandiamides(DICY)is the most significant;meanwhile,the data shows that using Phenolic Eesin(PE)as the additive has the highest extinguishing efficiency,and the addition of phenolic resin(PE)greatly increases the extinguishing temperature and reduces the residual amount.The use of potassium bicarbonate and basic magnesium carbonate as additives will increase the extinguishing time of the extinguishing agent,and the addition of potassium biphthalate can effectively reduce the maximum temperature of the extinguishing agent.According to the further research on the factors affecting the fire extinguishing efficiency and material costs,it was found that the k₂ of 1.1 is the optimal paramenter.The effect of fire extinguishing aerosol on Yunnan brown coal is more distinguished than Shendong long flame coal.Based on the orthogonal experiments,an optimal ratio was obtained:63.4%potassium nitrate,23.6%dicyandiamide,8%phenolic resin,and 2%potassium hydrogen phthalate.The research in this paper provides a new technical approach and theoretical reference for the prevention and control of spontaneous combustion in underground mines.