Ignition Mathematical Model Of Coal Particle

The exiting status of coal ignition characteristics were analyzed in this paper, thentwo numerical models for a single large diameter coal and fine coal particles group’signition process were proposed.The unsteady ignition process from the numericalsimulations have great help for analyzing the dynamic process of the coal ignition.First an unsteady one-dimensional spherical coordinate numerical ignition model ofa single big coal particle, especially considering the influence of the temperature gradientwith in the coal particle was built. Basing on the model this paper study some ignitioncharacteristics such as particle heating process, the changing process of the flame sheet,the influence of inner conduction for the ignition delay, ignition temperature and ignitionmode, the influence of particle diameter, oxygen concentration, volatile content on thecoal ignition. The main conclusions are as follows: The critical particle diameter ofignition mode was affected by ambient temperature, oxygen concentration and whetherconsidering the internal thermal conduction. Coal particle is more easily homogeneousignition in lower oxygen concentration. In the oxygen-rich state, the ignition temperatureand ignition delay will decrease with the increase of oxygen concentration. The larger theparticle the bigger the gradient inside the particle, thus affecting the ignition delay and thepropagation distance of the flame sheet. At lower ambient temperature, ignoring thethermal conduction inside the particle will reduce the ignition delay, the duration andpropagation distance of flame sheet.An unsteady one-dimensional group ignition model was built for the pulverized coalparticles in spherical cloud. For the gas’s homogeneous combustion, there existing twoseparated temperature peaks, one located inside of the cluster, and the other outside of thecluster. After the oxygen inside the cluster was consumed, only one flame exists at theoutside of the cluster. Volatile rapid precipitation will lead to a faster velocity of the gasphase transferring away from the cluster, thus enhance the convective heat transferbetween the gas phase and the coal particles. The effects of radiation heat transfer, the group number of particles, ambient temperature, particles’ size and oxygen concentrationon the coal cluster’s ignition were analyzed. Simulation results show that the overallpyrolysis rate and coal burning rate will decrease with the increase of the group number.The ignition delay will reduce with the increase of the ambient temperature. When theambient oxygen concentration increased, the analysis rate and char burning rate will beincreased, and then reducing the ignition delay.