Initial Stages of The Ignition of Coal Microparticles of Different Grades by Laser Pulses

The emission spectra of coal particles ≤63 μm in the the metamorphism rank from long-flame to anthracite are studied during exposure to a laser pulse (τ i = 120 µs). The threshold value of the laser pulse density, H_cr^( 1 ), at which it becomes possible to detect the emission of coal particles by instruments, is related to the ignition of reactive microprotrusions on the surface of the coal particles. At an energy density of H = H_cr^( 2 ) , the surface of the coal particles is sufficiently heated to initiate chemical reactions in their volume, as well as the release and ignition of volatile matter, through a heterogeneous ignition mechanism. As the energy density increases to H > H_cr^( 3 ) the chemical processes in the coal particles are similar to the processes occurring during H = H_cr^( 2 ), but with the increase in H , the intensity of the emission and, consequently, the rate of chemical reactions in the coal particles increase during the action of the laser pulse. In the spectra at all stages of ignition, the emission of CO_2^* (CO flame), excited molecules of H_2^* and H 2 O*, and incandescent particles of coal (or tar) were detected, which is typical for all the studied coal marks. The spectrum-integrated brightness of the emission of coal particles during the exposure to a laser pulse increases almost linearly in the the metamorphism rank.