Experimental Study On The Soot Distribution And Evolution Process Of Single Coal Particle Combustion Flame

The combustion of fossil fuels is one of the fundamental sources for human to obtain the energy which is necessary for the development of production and people’s livelihood.However,the combustion process is accompanied by the formation and emission of soot particles,which has disadvantageous effects on the climate environment and life health.Therefore,controlling the generation and emission of soot particles is of great significance for achieving the goal of clean and efficient utilization of fossil fuels.Studying the formation and generation mechanism of soot is crucial for controling soot emissions.The intrusive and nonintrusive combustion diagnostic technologies have been widely applied in gas and liquid flame detection.Comprehensive application of the two technologies to explore the distribution and microscopic characteristic of the soot during single coal particle combustion plays an auxiliary role in understanding the evolution process of soot produced by coal volatile burning and establishing the soot formation model of coal combustion.Firstly,,a fixed-bed single coal particle combustion detection equipment is built.The combustion process of Datong,Shenhua and Yinni single coal particles is researched based on non-intrusive method,and the temperature and soot volume fraction distribution in the volatile flame are detected The results show that the ignition mode of all three kinds of coal is homogeneous ignition mode and the ignition delay time decreases with the increase of volatile content.From the perspective of time distribution,the overall temperature level is low and the soot volume fraction is high in the early and late stages of volatile combustion.From the perspective of spatial distribution,the soot volume fraction increases gradually from bottom to top along axis direction and the temperature is low at the tail of flame where the soot gather easily for the reason of weak oxidation ability.From the perspective of coal types,the maximum flame temperatures of the three coal particles in the stable combustion stage are similar,and the soot formation ability of bituminous coal is stronger.In addition,a set of multi-angle & simultaneous sampling thermophoretic probe experimental device is designed and set up for soot sampling.The evolution process of soot at different heights in volatile flame of single coal particle is analyzed based on thermophoretic sampling particle diagnostic combined with scanning electron microscope technology.The electron microscope image of soot shows that,the initial stage is characterized by tar-wrapped dispersed particle and the middle stage is clustered.In the mature stage the phenomenon of soot agglomeration is significant.Moreover,the morphology parameters of mature soot was calculated.The soot fractal dimension of three kinds of coals is close.The soot of Yinni lignite has the smallest average main particle diameter and the largest average main particle number in aggregates.Meantime,the pre-factor of the soot of Indonesia lignite is the largest,which indicates obvious agglomeration.Besides,the soot volume fraction results calculated by the probe method and image method are in good agreement,which verifies the reasonableness of the above two methods.Furthermore,the differences in soot formation between coal particle and other types of fuels combustion are compared and analyzed.The surface oxidation of the tar and the growth and agglomerate of tar-wrapped soot particle are main forms of soot formation when coal burning.