Numerical Simulation of Particle Behavior in Hot Furnace Atmosphere

Particle paths and reaction histories in a pulverized coal flame are predicted and shown to depend on injection location of the particle and particle size. Direct numerical simulation (DNS) is used to determine the flow field for a cold air jet issuing into a hot combustion chamber. The paths of a limited number of particles injected at various radial locations in the entering jet are determined by the drag force due to the local fluid velocity. Particles injected close to the center of the jet travel essentially along the axis with slight fluctuations, while particles injected closer to the periphery of the jet have greater tendency to be entrained in the fluid vorticies. These paths affect the particle reaction histories which may be predicted by providing the effect of a flame by imposing experimentally based temperature and oxygen concentration fields. The predictions of particle reaction histories were obtained using a single-step, first-order rate equation for the volatile release and the extended resistance equation for the rate of char reaction. The results show particle temperatures ranging from a fraction of a degree to 20 K above the local fluid temperature for the various size particles. Pyrolysis is shown to occur most rapidly for particles injected closest to the center of the jet; and finally, the rate of char reaction depends on the details of the particle trajectory, increasing substantially through regions of high temperature and oxygen concentration.