Experimental Study of Ignition and Combustion Characteristics of Single Particles of Zhundong Lignite

The ignition and combustion behaviors of single particles of Zhundong lignite were experimentally investigated. Single particles of Zhundong lignite with a diameter varying from 2 to 3 mm were suspended on a SiC fiber, and their burning in air in a horizontal tube furnace operating at 1023, 1073, 1123, 1173, and 1223 K was observed, aided with a charge-coupled device camera at 25 fps. By analysis of the captured images, the ignition delay time, flame displacement, volatile flame duration, volatile extinction time, total burnout time, and ignition mechanism were determined. The typical ignition and combustion processes of Zhundong lignite consisted of four sequential but overlapping stages: (1) pre-ignition stage involving drying, devolatilization, and oxidation at the particle surface, (2) heterogeneous ignition and combustion, (3) ignition and combustion of volatile matter in the gas phase, and (4) combustion of the remaining char residue. Surprisingly, the ignition of Zhundong lignite followed a joint hetero-homogeneous mechanism under all conditions studied. Upon the volatile matter ignition, a soot-free yellowish translucent flame was formed, surrounding the particle, and the volatile flame duration was noticeably long-lasting. The high sodium content in Zhundong lignite was believed to be responsible for such a phenomenon. The ignition and combustion characteristics, such as ignition delay time, volatile flame extinction time, and total combustion time of Zhundong lignite, decreased with an increasing furnace temperature and a decreasing particle size.