Thermophoretic Sampling of Coal-Derived Soot Particles during Devolatilization

Abstract

Thermophoretic sampling of soot particles formed during high-temperature coal devolatilization is performed in order to examine soot particle sizes and shapes. Coal particles are injected along the centerline of a laminar flow flat flame burner, where a fuel-rich methane-air flame is used as a heat source. Volatiles released from the coal particles form a cloud of soot particles at high temperatures in the absence of oxygen. A carbon-coated microscope grid is briefly inserted into the soot cloud, where the temperature gradient between the soot particles and the cold grid surface causes the migration of soot particles and results in deposition. Soot particles are analyzed using transmission electron microscopy. Distinct primary soot particles with approximate diameters of 25-60 nm are observed, along with agglomerates composed of multiple primary particles. Condensed, highly volatile, liquid-like deposits are observed in some cases, which are thought to be tar at some stage of secondary reaction. Coal-derived soot is also compared to thermophoretically collected butane soot. 31 refs., 11 figs., 1 tab.