Hydrodynamics in downflow fluidized beds (1): solids concentration profiles and pressure gradient distributions

Abstract In a 9.3 m high and 0.10 m i.d. gas–solids downflow fluidized bed (downer), the radial distributions of the local solids holdups and the pressure gradients along the downer column were measured to characterize the local and overall gas–solid flow structure, using a fiber optical solids concentration probe and a series of pressure transducers. Results show that the radial solids holdup distribution in a downer reactor is much more uniform than that in a riser. Although the operating conditions do largely affect the hydrodynamics in the downer reactor, many common similarities still exist in the gas–solids flow patterns with the variation of the operating conditions. For most of the conditions tested, the radial profile of solids holdup reaches its fully developed state within 3–8 m from the top entrance. On the other hand, particles are fully accelerated within 1–4 m. However, under certain conditions, the development section can extend to as long as the downer itself.