Experimental Studies On The Ignition Of Single Coal Particles Under Zero And Normal Gravity Conditions

The ignition characteristics of coal particles represent process of physico-chemical changes during the ignition period. They are the theoretical foundation for highly efficient and clean utilization of coal resources. As the simplest existence, the single coal particle avoids the mass and heat transfer between particles, and thereby the ignition studies on the single coal particles could provide an easy and ideal way to understand the coal ignition and combustion characteristics. In this paper, the reseach on the ignition of single coal particle is based on the experiment and supplemented by model calculation method.Utilizing the experimental device of coal combustion on the SJ-10 Planet, we have got some intrinsic data of typical bituminous particle and anthracite particles ignition and combustion. Then we have compared the coal ignition characteristics, coal combustion characteristics and the ignition delay time between zero and normal gravity. The volatile fire of bituminous showed higher spherical degree and lower brightness under zero gravity. In late combustion period, it could be found some following contents consisted of fine particles had escaped from the coal particle surface in the form of jetting. When the ambient temperature was higher, the volatile fire showed spurting in some direction. The whole coal particle was ignited at the same time under zero gravity while the anthracite showed more symmetrical ignition area and lower brightness of coal combustion.A s a result of the lack of natural convection, the oxygen diffusion and the convective heat transfer between the coal and the gas were inhibited at the same time under zero gravity. And then the bituminous coal and the anthracite coal all showed longer ignition delay time.Utilizing the experimental device of normal gravity, we have researched the influences of coal type, O2 concentration, particle size and heating rate on the ignition and combustion characteristics of the mm scale coal particles. The ignition delay time of anthracite, bituminous and lignite decreased with oxygen concentration. The ignition delay time of bituminous and lignite increased with particle size. The O2 concentration showed more obvious influence on larger particle when the ambient temperature was lower. The ignition delay time of bituminous and lignite decreased with heating rate. The increase of the ambient temperature showed more obvious influence on the lower O2 concentration when the O2 concentration belong to the low O2 con centration section. The bituminous was homogeneously ignited in both ambient temperature. The lignite was heterogeneously ignited in the lower ambient temperature while homogeneous ignition was dominant in the higher ambient temperature and ignition behavior turned to be hetero-homogeneous and heterogeneous.What's more, we used a transient 1D ignition model considering thermal conduction inside the coal particle to simulate previous experimental conditions and compared the model-based results with the experimental results. We found that the ignition delay time and the ignition temperture decreased with the O2 concentration. The ignition delay time increased with the particle size. The temperture on the particle surface excluding the bituminous in the low er ambient temperature increased with the particle size and the difference between surface and central temperture increased at the same time. At last, the ignition delay time decreased with the heating rate.