Characterization of micro-crystalline structure and particle size distribution of soot generated from MILD-OCC flame

Abstract

Two types of coals and CH4 were burned with O2 in MILD-OCC mode while taking CO2 as diluted gas. By setting the sampling point in the flame, the flame temperature distribution was obtained by thermocouple. The TSPD-TEM system was used to sample at different points and obtain the TEM images, Digital Micrograph, ImageJ and MATLAB software were resorted to analyze the micro-crystalline structure and PSD of soot generated from MILD-OCC. The results showed that the radial flame temperature was a nearly constant value in center area and a decreased trend in outer edge area, while the temperature presented decreasing trend along the height above burner (HAB) at axial direction. When HAB = 10 mm, the soot particles were all exist in single state and there were oil drop-like substances attached to the surface of the particles. When HAB = 20 mm, soot grew bigger and were obviously spherical, and the edges of the particles were relatively clear. Starting from HAB = 30 mm, the soot particles aggregated to chain-like clusters. Both of PSD for the soot generated from two types of coal were between 0.02 and 0.04 μm, and all had the tendency of increasing at first and then decreasing, the micro-crystalline curvature (C) occurred at 1.0–1.5, layer spacing (d) was mainly distributed between 0.32 and 0.45 nm, and the micro-crystalline length (La) peak was between 0.4 and 2.2 nm. C and d were all deceasing tendency while La was roughly increasing trend with the increase of HAB.