Experimental investigation of coal combustion in coal-laden methane jets
Combustion characteristics of methane jets laden with pulverized coal were studied by using a vertically oriented solid particle injector that entrained pulverized coal particles using the Venturi effect. The dependence of entrainment rate on the size of coal particles was studied as a function of the flow rate. Particle Streak Velocimetry performed on coal-laden jets provided valuable insight into the relative velocity of entrained coal particles with respect to the fluid velocity. High-resolution still images and high-speed videos of laser-sheet light scattered by the coal particles helped determine the mode of interaction of entrained coal particles with the flame front. The effect of combustion on the entrained coal particles was analyzed both in terms of macrostructure and microstructure. Also, the effect of flame on coal-particle size was probed by analyzing the particle size distribution for premixed and non-premixed flames. Loose density measurements and Fraunhofer-diffraction-based particle size distribution measurements were carried out before and after combustion in order to characterize the effect of combustion on the macrostructure of coal particles. Based on the experimental results, it was established that the combustion process did not have any significant effect on the macrostructure of the coal particles. This was evidenced by the negligible changes observed in loose density and mean particle diameter after combustion. Scanned Electron Microscopy imaging was carried out in order to study the change in microstructure of coal particles as a result of combustion. Remarkable changes were observed in microstructure while there was hardly any change in the macrostructure of coal particles due to combustion. Based on these findings, it was established that the coal particles underwent only partial devolatilization during their passage through the flame due to the small residence time. Hence it was concluded, that this mode of combustion was a surface phenomenon. The effect of oxidizer composition on the combustion of coal particles was studied by comparing the measured particle size distributions for CH4/air, CH4/O2/CO2 and CH4/O2 flames.
pulverized coal, coal-laden methane jets, Venturi effect, Particle Streak Velocimetry Fraunhofer diffraction, Malvern particle size measurement, Scanned Electron Microscopy, devolatilization
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign