Experimental Study On The Characteristics Of Soot Formation And Evolution In Coal And Biomass Combustion Flames

As an important part of ultrafine particles,soot particles have brought serious harm to the environment and human body.At present,domestic and foreign scholars have conducted in-depth research on the physicochemical properties,generation law and mechanism of soot produced by the combustion of small molecule hydrocarbon fuels such as oil and gas,which have played an important guiding role in the development of clean and efficient combustion technologies.However,as one of the main emission sources of soot particles,coal and biomass have little research on the evolution and physicochemical properties of soot in their combustion flames.It is necessary to further study the soot formation and evolution characteristics during the combustion of coal and biomass,which is of great significance for revealing the mechanism of soot formation and inhibiting the formation of soot during the combustion of solid fuels.In order to explore the evolution and physicochemical properties of soot in coal and biomass combustion flames,a set of flat flame combustion experiment bench was built,the thermophoretic sampling system and the in-situ capillary sampling system were designed.Taking Pingdingshan coal and sesame stalk as the research objects,using TSPD-TEM technology to study the formation and evolution of soot in the initial flame of coal and biomass combustion,and combining the image processing software Image J and the microcrystal processing software Soot Fringe to obtain the soot particle size distribution,fractal dimension and nanostructure parameters.In addition,Raman spectrometer and thermogravimetric analyzer were used to study the evolution law of order degree and oxidation activity of soot particles.The research results show that the combustion of coal and biomass will be directly converted into soot through the internal reaction and carbonization of tar,and will gradually form soot agglomerates with particle agglomeration,and finally be oxidized gradually.The average particle size of the basic soot particles in the sesame stalk flame is 19.76 nm,the crystallite length is 0.731 nm,the crystallite curvature is 1.135,the interlayer spacing is 0.381 nm,and the fractal dimension of soot aggregates is 1.74;in the Pingdingshan coal flame,the average particle size of the basic soot particles is 40.14 nm,the crystallite length is 0.668 nm,the crystallite curvature is 1.139,the interlayer spacing is 0.385 nm,and the fractal dimension of the soot aggregates is 2.07.Compared with the soot produced by biomass combustion,the average particle size of coal soot is larger,soot aggregates are more compact,and the nanostructure is more disordered.The results of Raman spectroscopy showed that the order of soot particles generated by the combustion of coal and biomass gradually increased with the increase of flame height.The results of thermogravimetric experiments show that with the formation and evolution of soot,its oxidation activity first decreases and then increases.Moreover,the order of soot particles will affect the oxidation activity of soot.The more orderly the microstructure of soot,the lower its oxidation activity.Compared with soot in methane and ethylene flames,soot particles produced by burning solid fuels such as coal and biomass have higher oxidation activity and are more prone to oxidation reactions.