Laser doppler measurements of flow in freeboard of a fluidized bed

Abstract

Abstract One of the factors which reduces combustion efficiency in a fluidized‐bed combustor is the elutriation of fine coal particles from the freeboard above the bed surface. To our knowledge, data about the real local flow behavior of the two‐phase flow in the freeboard are lacking in the literature. This paper concerns the measurement of the gas and the elutriated particle velocities in the freeboard of a cold fluidized bed using Laser Doppler Anemometry. A special electronic system has been devised to record simultaneously the gas and particle velocities and to indicate the size of the particles. In this paper the apparatus and some preliminary measurements are reported. The most significant observation is that the gas velocity profiles exhibit minima near the bed center and maxima near the walls.