An Experimental Study On The Effects Of Moisture In Lignite On Coal Particle Ignition Behavior In Low Temperature

Coal consumption has been increasing due to the energy demand. Coal reserves are abundant worldwide and coal is distributed over a wide area. Therefore, the use of coal is one of the better ways in the global energy crisis. Lignite is a low rank coal which is evenly distributed throughout the world and accounts for 45% of the total coal reserves and its recoverable number of years is about double higher than that of the high-rank coal. Also, the price is much lower as compared with the high-rank coal. But it has high moisture content, volatile and spontaneous combustion which occur frequently. Therefore, its utilization is limited. As we know, the high moisture content significantly affects the properties and combustion characteristics of lignite.In this paper, the ignition behavior of coal particles in low temperarure hot flow was studied experimentally using a high speed digital camera using two types of lignite coals with a moisture content of up to 20%. Coal samples with a particle size of 88–95 μm were injected into a quartz reactor full of hot air, and electrically heated to average 450 °C. Optical access of the reactor allowed the ignition of individual particles to be investigated with high-speed camera. A particle’s ignition time was defined as the time lapsed from the instant when the particle exited the injector to the onset of its luminous combustion in the reactor. The experiments were conducted at a relative quiescent gas condition inside the reactor, and the axial gas temperatures in the reactor were found to be similar. In this case, the ignition behaviour of individual particles was evaluated and the images were carefully analyzed. The results showed that the moisture in lignite coal significantly influences its ignition characteristics upon heating. The ignition delay of coal particles was clearly prolonged in the hot air atmosphere, the ignition delay was more obvious while it was increased with increasing coal moisture content, further, the ignition delay of different kinds of lignite(with the same moisture contents) gave the similar results. It seems that the same moisture content has a similar effect on temperature rise of different kinds of lignite for the same particle size. There were obvious phenomenon in the images of combustion time and of ignition mechanism under which the coal was heated, and it confirmed the influence of moisture content of the particle before, during and after ignition.