Physicochemical Properties and Formation Mechanism of Soot in the MILD–OCC Combustion Flame

Abstract

Coal and methane were mixed and burned in the moderate and intensive low oxygen dilution–oxy coal combustion (MILD–OCC) mode, flame temperature was measured at different flame locations with a rapid insert thermocouple, and soot volume fraction was obtained by thermophoretic particle densitometry (TPD). The distribution characteristics of soot in flame were obtained by combining the concentration of soot by the filter weighing method. Soot samples were collected at specific locations in the flame and analyzed with gas chromatography–mass spectrometry (GC-MS) as well as transmission electron microscopy (TEM). The results showed that the flame temperature rose first and then decreased in the radial direction, while soot mass concentration dropped and then increased in general. As to morphology of soot particles, it exhibited spherical particles separately in the lower part of flame and chain-like structures in the upper. Alkanes, olefins, phenols, furans, and aromatic compounds were determined as the main components of soot by the detection of GC-MS. The process of soot formation in the MILD–OCC flame can be speculated as coal pyrolyzes and burns at high temperature and gas precursors initiate nucleation then agglomerate and oxidize to form soot particles.