The pyrolysis (devolatilization) of pulverized coal in a thermally stabilized burner

The physical and chemical characteristics as well as the elemental composition of coals vary widely. Therefore, the behavior during heating and combustion may be qualitatively similar from coal to coal but quantitatively very different. An experimental system was developed in which pyrolysis could be studied separately from combustion. The apparatus simulated the thermal conditions experienced by particles of coal in a hot furnace under rates of heating as high as 3 $\times$ 10$\sp5$K/s. The investigation utilized a thermally stabilized burner (TSB), in which a flame from premixed ethane/air was stabilized by thermal feedback without recirculation of the products of reaction. The pyrolysis of coal was carried out in the hot products of combustion of a stoichiometric mixture of ethane and air (essentially N$\sb2$, CO$\sb2$, and H$\sb2$O). Pseudo-steady-state combustion was used in the present work; the flame was allowed to drift very slowly, under constant gas/operating conditions, from one location towards that corresponding to a stationary state, thus producing a continuous change in residence time for the particles within the hot, inert gas. Thus, collecting devolatilized coal particles at the outlet of the combustor while the flame drifted was equivalent to collecting pyrolyzed particles at different downstream positions relative to the flame front. The loss in weight of the coal particles was determined in these experiments as a function of the residence time for particles of different size. A model was also developed to predict the pyrolysis of coal in the TSB. (Abstract shortened with permission of author.