Experimental investigation of coal combustion in coal-laden methane jets

Combustion characteristics of pulverized coal were studied in a methane jet 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 were used in order to 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 using a combination of loose density measurement, Fraunhofer-diffraction-based particle-size distribution measurements, and scanned electron microscopy. It was established that the combustion process did not have any significant effect on the macrostructure of the coal particles. At the same time, remarkable changes were observed in particle microstructure. 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 oxidation was basically 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.