Radiative characterization detection and mechanism analysis of soot generation and oxidation during coal combustion based on hyperspectral and mid-wave infrared imaging techniques

Abstract

The generation of soot during coal combustion is closely related to tar, and the incomplete combustion product soot competes with the complete oxidation product CO₂ during the combustion process. In this study, the light volatiles of coal particles are experimentally precipitated to obtain tar coal, and the simultaneous measurement of soot and CO₂ radiation characteristics is achieved by combining hyperspectral (HSI) and mid-wave infrared (MWIR) imaging technologies. Furthermore, the inherent competitive mechanism between the generation and oxidation of polycyclic aromatic hydrocarbons (PAHs) is revealed through mechanistic analysis. As the core structure of soot, PAHs have complex and diverse generation pathways. A1 is formed through both the C3 pathway involving odd-carbon atoms and the C2+C4 pathway involving even-carbon atoms. The generation of A2 to A4 is closely related to direct addition reactions on the benzene ring, and tar coal combustion corresponds to a higher generation rate of PAHs. The generation of soot and CO₂ during coal combustion is not sequential, but exists as a competitive relationship throughout the whole process. The experimental validation results show that the soot volume fraction from coal combustion ranges from 5 ppm to 20 ppm, and the CO₂ concentration ranges from 10 % to 25 %, with tar coal combustion corresponding to a higher content of soot and CO₂. Although the mole fraction of soot is much smaller than that of CO₂, solid soot particles have a more significant radiative capacity in terms of emission and absorption, with the spectral radiative intensity of soot being an order of magnitude higher than that of CO₂ during the stable combustion stage.