GAS AND SOLID FLOW IN THE FREEBOARD OF A FLUIDIZED-BED COMBUSTOR

The transport phenomena in the freeboard of a fluidized bed combustor are particularly influenced by the behaviour of the gas-solid particle flow. In order to describe the flow field, data on particle and gas velocities are needed. A laser-Doppler-velocimetry-and-particle-sizing system has been used in a commercial scale fluidized bed combustor. The measuring technique and experimental data from the unit will be presented. In addition a numerical model of the fluid dynamics in the freeboard based on particle trajectory calculations has been developed. Computational and experimental results are compared and discussed. It is shown that gas turbulence in the freeboard has almost no effect on entrainment rates, but is significant for the explanation of the measured particle velocities. A particle trajectory model including gas turbulence provides quantitative information on the gas-solid flow field in the freeboard.