Experimental Study On Combustion Diagnostic In Pulverized Coal Flame Using Optical Measurement Methods

In order to improve the combustion efficiency of fossil fuels and reduce the pollutant emissions,it is of great significance to know the formation mechanism and emission characteristics of polycyclic aromatic hydrocarbon(PAH)and soot particles in the process of coal combustion.In this paper,radiation image,elastic scattering(ELS),laser-induced incandescence(LII),laser-induced fluorescence(LIF),and sampling methods are employed to figure out the carbonaceous particles and PAH in pulverized coal flame with different coal types or particle sizes in Hencken burner.The main contents are as follows:1.The radiation images of pulverized coal flame with different coal types and particle sizes are photographed to analyze the combustion regions.It is found that anthracite is mainly burned in heterogeneous way,and the images of the flame shows dark red.There are heating region,continuous flame region and char burning region in lignite and bituminous pulverized coal flame.With the increasing of particle size of bituminous,the pulverized coal flame is wider and longer.The result shows that there are a lot of soot particles and char particles in the bituminous continuous flame region,but only char particles are observed in the anthracite and lignite flame.In the char burning region,the particles of three coal types are char particles and spherical coal ash.In the SEM images,it can be observed that the char particles show the flocculent or shell structures.In the pyrolysis products of pulverized coal,the content of PAH is: bituminous > lignite > anthracite.Naphthalene is the most of all kinds of PAH.The PAH concentration of the larger ring is higher in the pyrolysis products of bituminous coal.The content of PAH which is larger than three rings is: bituminous > lignite > anthracite.2.In the ELS and LII measurement experiments,it is found that the elastic scattering signal was mainly from the coal or char particles in the pulverized coal flame.In the continuous flame region of the bituminous pulverized coal flame,the ELS signal which is from soot particles can also be detected.The laser fluence curves and twodimensional LII measurement show that when the soot concentration is high as the continuous flame region of 61-90 ?m bituminous pulverized coal flame,the influence of LII signal excited from char particles can be neglected and the image of soot-LII is with good signal-to-noise ratio.However,in other pulverized coal flame with different coal types or particle sizes,the soot concentration is low or even no soot exist,LII signal intensity increases with the increasing of laser fluence due to the char particles and the method is not applicable.To combine the ELS scattering image and the LII image is helpful to figure out the types and distribution of carbonaceous particles in pulverized coal flame.3.The LIF measurement of different types of PAH in different fuel flames shows that: In propane flame,with the increasing of detection wavelength,the region of PAHLIF signal shows a trend of upward,which can reflect the process of PAH growing from small rings to large rings and finally forming soot particles in propane flame.However,in the bituminous pulverized coal flame,PAH-LIF signals are almost at the same region.According to the results,it can be inferred that a large amount of PAH in pyrolysis products of bituminous coal is likely to form soot particles directly through condensation of PAH,while HACA is not the main reaction way.