Effect of Coal Particle Size Distribution on Laser Ignition Characteristics

The ignition of hard coal grades DG, G, Zh, and K under the action of laser pulses (1064 nm, 120 mu s, 1.3 J) was studied for the fractions of microparticles with a narrow size distribution in the range of 0.25-44 mu m. The kinetic characteristics of the glow of samples from the entire size range were measured for each coal rank. Three stages of ignition are distinguished for each fraction. The duration of the first stage coincides with the duration of the laser pulse. The duration of the second takes a time interval of 10-15 ms (DG, G and Zh coal ranks) and 3-5 ms (K coal rank). The duration of the third stage is 60-80 ms (DG, G, and G coals) and 20 ms (K coal rank). It has been established that the threshold ignition energy densities (ignition thresholds) at all three stages depend non -monotonically on coal particle sizes. The minimum values of ignition thresholds at all three stages are achieved at particle sizes equal to 2.2 (for DG rank coal), 4.0 (for G rank coal), 0.7 (for Zh rank coal) and 2.0 mu m (for K rank coal). Using the results of the proximate analysis of coals, the observed dependences of critical energy densities on the size of coal particles are interpreted.