Strongly swirling gas-particle flows and coal combustion in a cyclone combustor

Strongly swirling gas-particle flows with swirl numbers 1.5 and 1.0 in a cyclone combustor are measured using a 3-D phase Doppler particle anemometer system (PDPA), and the case of swirl number 1.5 is simulated using a unified second-order moment (USM) model of anisotropic two-phase turbulence. The prediction results using the USM model are then compared with those obtained using the isotropic k-epsilon-kp two-phase turbulence model and the PDPA measurements. The measurements and predictions show that for strongly swirling flows with axial and tangential inlets there is no recirculation zone in axial velocity profiles: the gas and particle tangential velocity profiles have the Rankine-vortex structure, but the solid-body rotation zone is much larger than that for weakly swirling flows: the axial gas and particle fluctuations are at first stronger than, then near to, and finally slightly smaller than the tangential ones: both axial and tangential particle time-averaged and fluctuation velocities lag behind the gas one: and the USM model can better predict the Rankine-vortex structure of tangential velocity profiles and the anisotropy of two-phase turbulence in strongly swirling flows than the k-e-kp model. The research results of two-phase flows are used for optimum design of the coal-fired cyclone combustor burning 3- to 5-mm coal particles, which finally gives higher combustion efficiency and lower NO x formation, and for developing the combustion modeling.