Characterization of burning char particles under pressurized conditions by simultaneous in situ measurement of surface temperature and size

Surface temperature and size of individual burning char particles were measured at elevated temperature and pressure using a two-color pyrometric technique. Experimental results obtained in a pilot-scale pressurized entrained flow reactor are presented. The studies concern two German coals: the Göttelborn high volatile bituminous (hvb) coal and Rhenish brown coal from the opencast mine Garzweiler. The obtained results show considerably different particle behavior due to different coal properties. In the case of the Göttelborn hard coal, typical excess temperatures at oxygen concentration of 12 vol % are about 350 K, in comparison to about 550 K in the case of the Garzweiler brown coal. The obtained number size distributions of the brown coal show a narrow fraction that is almost equal to the fed particle fraction. The hard coal char particles are much more scattered and shifted toward large particle sizes. This is found to be due to the tendency of particle swelling. For Garzweiler brown coal, a clear T_p - D_p dependence was found for the subset of burning char particles in all measurements, whereas the dependence was weaker, if any, for Göttelborn coal. The T_p - D_p dependence was approximated by a regression line, and its slope was used for the characterization of the char burnout behavior. The found T _p - D_p dependence is assumed to be due to transient heat conduction from the particle surface toward the center. A qualitative heat balance at the particle surface is given that shows the main parameters that impact the particle surface temperature.