Experimental and Numerical Investigation of the Primary Fragmentation of a Lignite during Fluidized-Bed (FB) Devolatilization

Abstract

The paper presents a comparison between experimental and model results of primary fragmentation of a lignite coal in a fluidized bed (FB). In the experiments, the char particle size distribution and the general indicators of primary fragmentation (intensity and index) were determined. The same parameters were calculated using a mathematical model of the process, fed by data of the fuel (the amount of volatiles and fixed carbon), fluidized bed temperature, and inlet particle size distribution. The size distribution and number of the char particles in fluidized bed significantly differ from the size distribution and number of inlet coal particles. Char population has a bimodal distribution—separate distributions for the smaller and larger sets of fragments. The experimental and model results show the same tendency: a coal particle partially breaks at the beginning of devolatilization, giving a large number of fine fragments, while, as the process continues, the rest of the parent particle sometimes breaks down into a smaller number of larger pieces, and sometimes does not fragment at all. Review of the Weibull distribution coefficients enables prediction of the char particle size distribution for the characteristic fluidized bed conditions and inlet coal particle sizes.