Experimental Research On Flame Propagation Characteristics Of Typical Grain Dust And Gas Phase Inertia Inhibition

In recent years,industrial combustible dust has been produced and applied in various industries more and more widely.And grain dust,especially wheat starch,is the occurrence of dust explosion accident more than one of the types of dust.The explosion risk it has,has always threatened the wheat starch production in all aspects,seriously restricting the industry’s safe production and sustainable development.To carry out the flame propagation characteristics of starch dust and its inerting inhibition research,it is of great scientific significance for the prevention and control of such dust explosion and safety rescue.In this paper,wheat starch was selected as the research object,and the dust flame propagation under the condition of gas phase inerting was studied as the main line.The experiment platform of vertical dust explosion combustion pipeline under gas inerting condition was established.During the experiment,high-speed photographers were used to collect the dust flames propagation,and the self-made fine thermocouple was used to monitor the temperature characteristic parameters of dust flame.It was studied that experimental research on the effect of dust cloud concentration and dust particle size on the flame propagation characteristics of wheat starch dust under air atmosphere and gas inerting atmosphere.And the flame propagation characteristics of wheat starch dust under two kinds of atmosphere were analyzed and explored.Details as follows:(1)Under the conditions of air,dust flame forward distance from the ignition electrode rises as“S”type curve,and the dust flame propagation speed grow like“normal distribution”curve.Dust flame propagation can be divided into three phases:ignition stage,accelerated propagation stage and deceleration propagation stage by comprehensive analysis.Combining the microscopic image of the dust flame front and the flame propagation image under the condition of inerting,the dust flame can be divided into three areas:the unburned zone,the gas phase combustion zone and the two phase combustion zone;(2)Under the conditions of Nitrogen inerting,the ignition limit oxygen concentration of dust cloud mass concentration of 0.200~0.600 kg/m~3 was16.90%,and the dust cloud mass concentration of 0.700 kg/m~3 was 17.11%;(3)Under the conditions of Nitrogen inerting:when the dust mass concentration and particle size unchanged,with the oxygen concentration decreased,three stages of dust flame propagation are inhibited with dust flame luminous intensity gradually reduced and the area of the white bright spot in the flame gradually reduced.And the dust flame propagation speed and the highest flame temperature gradually reduced,when the oxygen concentration decreases from 21.00%to 19.95%,the maximum reduction;(4)Under the conditions of Nitrogen inerting:when the dust particle size unchanged,under the same oxygen concentration,with the increase of dust mass concentration,the flame intensity increases first and then decreases,and the dust flame stratification increases gradually.The maximum dust flame propagation velocity increases first and then decreases,and reaches the maximum velocity when the dust mass concentration is 0.500 kg/m~3,and the maximum temperature of dust flame increases first and then decreases.With the decrease of oxygen concentration,this change trend still exists,while the maximum dust flame propagation velocity changes gradually become smaller,and the maximum temperature of the dust flame is gradually reduced;(5)Under the conditions of Nitrogen inerting:when the dust mass concentration unchanged,with the same oxygen concentration,the emission intensity of dust flame decreases with the decrease of dust particle size,and the maximum flame propagation velocity decreases gradually.When the oxygen concentration decreases from 21.00%to 18.90%,the decrease is the largest.The maximum flame propagation velocity of dust increases with the decrease of dust particle size.While with the decrease of oxygen concentration,this increase is gradually reduced.The change of maximum temperature of dust flame similar like the change of the maximum flame propagation velocity under this condition.Under the same oxygen concentration,the maximum temperature of dust flame increases with the decrease of dust particle size and then decreases,while with the oxygen concentration decreases,this change is also gradually reduced.