Devolatilization and ignition of coal particles in a two-dimensional fluidized bed

In a two-dimensional (15 × 200 × 400 mm) high-temperature fluidized bed, devolatilization ignition and combustion phenomena of single coal particles have been studied. The particles, with diameters of 4–9 mm, were selected from three coal types of widely different rank: brown coal, bituminous coal, and anthracite. The bed consisted in most cases of porous alumina particles (0.6 mm diameter), and was fluidized by O2/N2 gas mixtures. At constant bed temperatures ranging from 200 to 850°C, the various stages prior to the eventual combustion of the residual char particle were recorded on videotape. This paper gives an account of visual observations on the release, ignition, and combustion of volatiles as well as on the ignition of char. Results of measurements of the temperature and delay time of both volatiles and char ignition are also reported. Finally, the period over which flames of volatiles are visible in the bed has been measured for each coal particle; at sufficiently high bed temperature they are indicative for the total devolatilization time.