Study on the Effect of Coal Grain Size on the Morphology of Soot Generated During Combustion

This study performed an experimental exploration to analyze the influence of different grain sizes of coal on the nanostructure and morphological parameters of soot generated during combustion. Initially, primary and mature soot samples were gained from the combustion flames of two different grain sizes of coal (less than 150 μm, named sample #1, and 6–8 mm, named sample #2) by using thermophoresis sampling technology. Subsequently, the transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to investigate and analyze the soot samples, with the aim of obtaining their morphological parameters and nanostructure characteristics. The TEM images indicate that the nascent soot produced during the flame formed by small-sized coal is relatively uniform, with individual particles 8–14 nm in size. The grain size of the nascent soot produced by large-sized coal is much larger, within a wide range of 50–350 nm. Additionally, the nanostructures of the nascent soot particles produced by samples #1 and #2 mainly consist of upright parallel crystal stripes. The crystal stripes of the soot particles formed by sample #1 have obvious microcrystalline structures, whereas only a small amount of microcrystalline structure is found at the edge of sample #2. Compared with sample #2, the soot formed during the combustion of sample #1 exhibits a denser crystalline structure. The SEM results indicate that the mature soot agglomerates formed in sample #2 are larger and more in quantity compared to sample #1. Furthermore, the mature soot agglomerates formed in sample #2 have a stronger coagulation performance and a more compact structure than that formed in sample #1.