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In this study, the hydrodynamics behaviors and solid holdup in a twin-cyclone combustor with a swirling fl uidized bed were investigated under a wide range of cold–air operating conditions. Silica sand of three different particle size ranges: 600–710 μm, 710–1000 μm, and 1000–1700 μm, was used as the inert bed material at a fi xed static bed height of 30 cm. The solid holdup was measured in the radial direction along the horizontal axis at levels of 40, 50, 60, and 125 cm above the air distributor system. From the radial solid holdup profi les at different axial positions, the distributions of the solid holdup were non-uniform with dilute and dense regions. The radial profi le peaked at the center of the combustor and the solid holdup gradually decreased toward the combustor walls. The primary air velocity signifi cantly infl uenced the solid holdup, while the effects of the ratio of the secondary air and the tertiary air fl ow rate to the primary air fl ow rate and the particle size of the bed material used for the air distributor seemed to be small. With the increasing ratio of the secondary air and the tertiary air fl ow rates to the primary air fl ow rate, the solid holdup slightly increased.
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