Experimental Investigation On Pyrolysis And Smoldering Rules Of Forest Humus

In recent years,by the impact of global warming and other abnormal climate,forest fires occur more frequently,especially influence by unusually dry weather,extreme weather events and drought,the number of underground fire increases significantly.The essence of forest ground fire is humus smoldering and peat layer surface combustion.Especially in recent years,due to forest fires caused by the smoldering humus happen more frequently,and the smoldering combustion is not affected by the surface wind speed.It can spread slowly and it's generally difficult to find the fire.The combustion is not continuous with strong concealment and direction variability.Putting it out is very difficult.Therefore,studying the law of underground forest humus smoldering is conducive to understand the nature of the underground fire,fire mutation status and conditions.Ready advantageous strategy for fighting underground forest fire.Pyrolysis is an important stage before the occurrence of smoldering,through the pyrolysis kinetics analysis of forest humus in air and nitrogen atmosphere,so as to calculate the kinetic parameters of humic substances.The results are as follows: The mechanism functions under nitrogen atmosphere and air atmosphere were both(7)(8)(7)1ln1--(10)???(8).The fitting curve under nitrogen atmosphere was y=-16.34-1641.45x;the fitting curve under air atmosphere was y=-15.18-1438.26 x,activation energy under nitrogen and air atmosphere were 13.64KJ/mol,11.95KJ/mol respectively;the frequency factors were 3.878×103min-1 and 8.80×103min-1.Smoldering experiment forest humus is helpful to understand the rules of the smoldering forest humus.Through the experiment,the experimental results are follows: the whole process of forest humus smoldering included:heat smoldering temperature stage,self sustained propagation stage and cooling stage to extinguish.In the whole process,the ignition time,burning time,high temperature maintenance time of the forest humus were longer and the temperature was also higher,but the spreading speed was slower.The moisture content can significantly affects the internal heat and mass transfer,thus affecting the combustion duration and the internal temperature of the material.The particle size significantly affects the bulk density of the material and the material internal pore structure,thus affecting the smoldering reaction rate,combustion duration,temperature of material and the gas concentration etc...Therefore,this experiment studied the 4 kinds of moisture content(0,10%,20% and 30%)and particle size(20-40 mesh,40-60 mesh,60-80 mesh,80-100 mesh)effects on smoldering propagation of forest humus and the experimental results were as follows:The effect of moisture content on the smoldering propagation of forest humus: the change trend of smoldering temperature with different moisture content are approximately the same,first increased and then decreased gradually.With the increase of moisture content,the peak temperature of each thermocouple decreased.Along with the moisture contentincreased,the average propagation velocity slowed.The effect of moisture content on the quality changes of humus smoldering process was not significant.Different particle sizes of humus in smoldering temperature change trend was basically the same.With the decrease of particle size in the smoldering process,peak temperature of humus increased.With the burn depth,humus smoldering rate slowed down.The particle size of the humus didn't significantly affect average propagation velocity and piecewise smoldering propagation velocity.Different particle size of humus had little effect in the quality change of smoldering process.