Theoretical And Experimental Study On The Ignition Of Oil Shale Dust

With the increasing depletion of petroleum resources,oil shale as an ideal alternative resource,has attracted more and more attentions.However,the security problems in the exploiting and using process of oil shale have rarely been studied.In this paper,in order to lay a foundation for making better and efficient use of oil shale resources,the kinetics of oil shale dust pyrolysis and ignition,dust layer ignition behavior and its influencing factors and dust cloud ignition behavior were studied.Using thermalgravimetric analysis,the characteristics of oil shale dust pyrolisis were tested under nitrogen atmosphere.The pyrolysis of oil shales from different producing areas basically include three stages:dehydration,decomposition of organic matter(devolatilization)and cracking of semi-coke minerals.The results showed that decomposition of organic matter is the main phase of oil shale pyrolysis,the weight loss under different heating rate are basically the same,and the higher the volatile content the smaller theoil shale pyrolysis initiation temperature.The apparent activation energy and pre-exponential factor were calculated by using Coats-Redfern method.An investigation into pyrolysis activation energy and starting temperature of the oil shale samples indicated that oil shale pyrolysis process is controlled by three-dimensional diffusion model(Jander equation),and the higher the volatile content and the lower the pyrolysis starting temperature,the smaller the apparent activation energy.The minimum ignition temperature of the four dust samples under different thickness were tested using the minimum ignition temperature of dust layer test device.The overall test results shows that the minimum ignition temperature of dust layer(MITL)decrease with the increase of the layer thickness,and the MITL order of oil shale dust with the same layer thickness is:Fushun(FS)>Huadian(HD)>Longkou(LK)>Maoming(MM).Using chemical reaction kinetics,heat transfer and Thomas thermal explosion theory,a asymmetric theoretical model of dust layer ignition under steady-state conditions was established.The combustion kinetic parameters and the critical ignition temperature corresponding to different thickness were calculated using the model.Comparing the combustion kinetic parameters and the pyrolysis kinetic parameters,it was found that the pyrolysis kinetic parameter is bigger than the combustion kinetic parameter,which in accordance with the difference between the initial pyrolysis temperature and dust layer combustion temperature.And the error between the calculation results and experimental test results is about 5%,proved the rationality of the model.Dust cloud minimum ignition temperature and minimum ignition energy of the four oil shale samples were tested by using G-G furnace and the minimum ignition energy test device.The results shows agreement with the pyrolysis starting temperature and the MITL test results,which is:FS>HD>LK>MM.Using chemical reaction kinetics,heat transfer and Semenov thermal explosion theory,a symmetric theoretical model of dust cloud ignition under steady-state conditions was established.The kinetic parameters calculated value was substituted into equation to calculate the theoretical critical ignition temperature.theoretical calculation results shows reference value with the error between the calculation results and experimental test results is within 23%,which is high than the error between the calculation results and experimental test results of the ignition temperature of dust layer prediction.The possible reason is that the kinetic parameters of dust layer ignition modle were used in the symmetric theoretical model of dust cloud ignition,but the ignition mechanism of dust cloud and dust layer is not exactly the same.The experimental and theoretical analysis in this paper were of guiding significance on preventing dust and gas explosions in the process of development and utilization of oil shale.