Single pulse shock tube studies of pulverized coal ignition

Abstract

The ignition behavior of sized samples of pulverized coal has been studied using a modified single pulse shock tube. Ignition delays and particle temperature history were recorded optically while batch samples of evolved gases were sampled prior to and after ignition and analyzed by gas chromatography. Significant pre-ignition pyrolysis in the form of low molecular weight hydrocarbons was detected in all samples tested. Although the ignition delay of two similarly sized samples (Illinois no. 6 and Pittsburgh Seam) were substantially different, the volatile compositions were similar with the Pittsburgh having a somewhat higher yield at all conditions studied. Activation energies, determined from surface oxidation rate data, were used to successfully model the temperature dependence of the ignition delay of both smaller coals (number mean diameter 3.3 μ m for Pittsburgh and 4.1 μ m for Illinois no. 6). This heterogeneous theory failed for the larger Pittsburgh coal (14.9 μ m mean number diameter) as it consistently overpredicted the ignition delay. Inasmuch as the oxidation of pre-ignition hydrocarbons prior to ignition of the solid phase was observed only for the large Pittsburgh coal, the discrepency can be explained plausibly on the basis of the gas phase volatiles participating in the ignition of the larger particles.