Experimental And Mechanism Study On Explosion Characteristic Of Lignite Coal Dust

With the development of modern industry,superfine powder has been widespread used,while the potential risk of dust explosion also increases.Dust explosion has been a continuing threat to coal,food,chemical,metallurgy and textile industries,leading to increasing casualties and property damage.The coal industry is one of the major areas suffering from dust explosion.Thus,the understanding of the coal dust explosion mechanism is important for further studies in the prevention and control of such industrial disasters and also has important practical value for the protection of people's life and property.In this dissertation,lignite coal dust explosibility parameters and flame propagation characteristics were focused.Firstly,TG/DTG-QMS-FTIR was used to perform real-time and continuous analysis on combustion products of coal dust,then the dust explosion characteristic parameters were investigated by Hartmann tube device,dust cloud ignition temperature device,20 L spherical explosion test device and ignition flame temperature device.The changes of functional groups before coal dust layer combustion were studied as well.In addition,coal dust flame propagation test device was used to investigate the coal flame propagation characteristics.Finally,by using the FLUENT software,a three-dimensional numerical simulation was also performed to study the coal flame propagation process.The details are as follows:Thermal analysis in the coal dust combustion process showed that the process consists of two stages—low-temperature stage and high-temperature stage,and the activation energy of coal dust increased as the conversion rates increased.TG/DTG-QMS-FTIR was used to perform real-time and continuous analysis on combustion products of coal dust.Furthermore,a detailed discussion on combustion process was also made based on the real-time change of the gas product measured by QMS-FTIR.The experimental results showed that the main gaseous products produced by coal dust combustion were H2O,CO2,H2,CO and CH4,and the higher molecule weight CxHy with less content,which analysised the whole process of combustion on a mechanism level.Experimental study were performed on explosion characteristic parameters including ignition temperature of dust layer,ignition temperature of coal dust cloud,ignition energy of coal dust cloud,lower explosion limit of coal dust cloud and limiting oxygen concentration of coal dust cloud.A comprehensive and systematic analysis was done in multiple aspects including coal particle concentration and coal particle size.Through the in-situ diffuses reflection Fourier transform infrared spectrometry,functional groups during the heating stage of coal dust were monitored in real time.The change laws of those functional groups that play decisive role in the combustion process were focused.The results showed that the proportions of-CH3/-CH2 and-OH were the dominated in lignite coal,and they were the key active functional groups during the coal oxidation process,playing a great important role in the lignite coal ignition properties.Analysis was performed on the mechanism level to reveal the essence of coal dust ignition.The dust explosion severity of coal-air mixture and coal-methane-air mixture including explosion pressure and explosion index were experimentally studied in sealed space.The results showed that the damage effects of coal-methane-air mixture were always higher than those of coal-air mixture under same conditions.When the pyrotechnical igniter mass was 2.40g,the explosion pressure and explosion index of coal-methane-air mixture increased by 10%and 30%respectively compared to coal-air mixture.The effects of different types of explosion suppression agent for the methane-air mixture were also investigated.Due to the physical-chemical suppression effect,NH4H2PO4 showed better results than SiO2,which only has physical suppression effect.A dust cloud flame propagation test system was developed based on the original Hartmann tube apparatus.This system was used to study the dust flame propagation characteristics in the aspects of coal concentration,ignition energy and combustion tube length.A numerical simulation was also performed using the FLUENT software.The basic rule and influencing factors of dust flame propagation was investigated,and the effect of air flow field in the combustion region of the combustion process was discussed.The results showed that air flowing velocity is obviously higher than that of flame propagation at the same time level,which indicates that the air flow is one of the reasons that lift up dust layer and cause chain explosions.