Study On Pyrolysis Characteristics And Gas Emissions Of Eight Tree Species In Heilongjiang Province

Forest fuels are the material basis for forest fire.The main components include water,hemicellulose,cellulose,lignin,extract and ash.Pyrolysis is an important process of forest fuels combustion,and this process is also accompanied by the release of gases and particulate matter.The study of the characteristics of this process is not only an important part of the study of the combustion mechanism of fuels,but also the theoretical basis for the estimation of gas emissions from laboratory scale to field scale.The thermogravimetric analysis can obtain the pyrolysis weightlessness curves of fuels at different temperatures,and calculate the pyrolysis parameters of different fuels based on the kinetic equations to evaluate the combustibility of fuels.The analysis of gas emissions is significant to clarify the carbon emissions and toxic gas emissions from forest fire.Therefore,taking samples of tree leaves from eight varieties in Heilongjiang Province,including Pinus tabulaefomis var.mukdensis,Picea koraiensis,Pinus koraiensis,Pinus sylvestris var.mongolica,Fraxinus mandshurica,Juglans mandshurica,Quercus mongolica,and Betula platyphylla,and combining thermogravimetric analysis and gas analysis,this study takes a holistic approach to thermolysis process and gas release.Furthermore,it analyzes the impact of particle size on the pyrolysis process of fuels and discusses the reasons;analyzes the differences in the pyrolysis process of eight tree species;compares the weight loss rate,peak temperature of weight loss rate,mass fraction,etc.at different stages;discusses the causes of differences between tree species;Additionally,the volume concentration of the gas released during pyrolysis,the temperature corresponding to the peak value,and the emission factor were calculated.The correlation between the pyrolysis temperature and the gas release temperature is analyzed in combination with the pyrolysis process and the reason is discussed.These results will provide a data basis for improving the pyrolysis mechanism of combustibles,and will provide a scientific basis for reducing the estimation error of carbon emissions from forest fires.The main results were as follows:?1?The TG/DTG curves of the eight types of fuels had similar trends,mainly including four weightless stages,corresponding to the temperature ranges of 300?400K,450?650K,650?800K,and 900?1000K.The mass fraction of weight loss in the second and third stages accounted for more than 80%of the total mass of fuels.The peak shape in the third stage of weightlessness was complicated,and more substances were involved in the reaction than in the second stage.?2?Taking Betula platyphylla as the research object,the pyrolysis characteristics of combustibles with different particle sizes?<150 ?m,150-250 ?m,and 250-850 ?m?in air atmosphere were different and the kinetic parameters were different.The particle size affected the pyrolysis and kinetic characteristics of combustibles in different ways.The mass fractions of the first,third,and fourth stages of weight loss in small-sized particles decreased with the decrease of the particle size.And the weight loss and residual ash in the second stage were increased with the decrease of particle size.Increasing the particle size also shifted the peak value of the weight loss rate to the high temperature region,which was caused by the difference in heat transfer inside fuels with different particle sizes.?3?Taking eight tree leaves as research objects,ash mainly affected the pyrolysis of fuels by affecting the second stage.The amount of substances involved in the fourth stage reaction was completely related to the pyrolysis of the first two stages.The ash content of fuels had extremely significant negative correlation?P<0.001?and significant positive correlation?P<0.05?with weight loss mass fractions in the second and fourth stages,respectively,and had no significant correlation with weight loss mass fractions in the third stage.This indicated that the higher ash content inhibited the combustion of fuels by inhibiting the pyrolysis in the low temperature stage.?4?In the second stage,the peak temperature of CO and CO₂ release and the peak temperature of weight loss rate were concentrated around 600K,and they had a strong correlation.In the third stage,the peak temperature of CO and CO₂ release and the peak temperature of weight loss rate were distributed between 650?750K,and the two had extremely significant correlation?P<0.001?.The CO,CO₂ emission factors of Quercus mongolica,Picea koraiensis,and Pinus sylvestris var.mongolica were higher in the eight species,while those of Pinus tabulaefomis var.mukdensis and Fraxinus mandshurica ash were lower.In the second stage,a large amount of non-CO and CO₂ substances are lost,resulting in rapid weightlessness of combustibles.Compared the weight loss mass fraction and the released gas volume concentration in the second stage,the latter was much smaller than the weight loss mass fraction.It can be inferred that the second-stage pyrolysis substance had a single type,but the product was rich in species,including a large amount of non-CO and CO₂ substances;the third-stage pyrolysis substance was more complicated,but the product richness was lower than that in the second stage.