Hydrodynamic studies in liquid-solid and gas-liquid-solid circulating fluidized beds

A systematic hydrodynamic studies starting from measurement techniques to flow characterization were carried out in a liquid-solid/gas-liquid-solid circulating fluidized bed (LSCFB/GLSCFB). The (G-)LSCFB system consists of two main sections, the riser and the downer, both made of Plexiglas. The riser is 5.97 m tall and 0.0762 m in diameter and the downer is 5.05 m tall and 0.2 m in diameter.;Electrical Resistance Tomography (ERT) as an imaging technique was employed in this study for flow characterization by simultaneous measurements of phase holdups and velocity distribution of individual phases. ERT application in three phase systems is limited to the measurement of conductive phase only, which was applicable to the LSCFB for complete phase holdups and velocity measurements. In the GLSCFB, ERT could not be used alone and therefore optical fiber probe/pressure transducer was employed simultaneously to measure gas/solid holdup, resulting in determination of phase holdup of all three phases. Wall mounted pressure transducers are useful in determination of cross sectional average phase holdup only, however fiber optic probe can measure phase holdups locally, providing detailed information about phase holdup distributions. Phase propagation velocity was obtained by applying cross-correlation between the data obtained from a pair of planes of ERT, one upstream and one downstream, for both LSCFB and GLSCFB. Phase propagation velocity was higher in the central region compared to the wall region for all three phases.;Radial non-uniformity of phase holdups was observed in both LSCFB and GLSCFB. Cross-sectional average solids holdup was also measured using optical fibre probe and pressure transducers. Good agreement was observed between the three instruments. Effects of particles shape, size and density on radial distribution of phase holdups in the riser section of GLSCFB systems at four axial locations were also studied using glass beads and lava rocks particles. Solids holdup was higher in regions close to the wall and low in the central area. Such non-uniformity in phase holdup decreased with increasing liquid velocity. The effects of gas and liquid superficial velocities as well as solids circulation rate on radial distribution of phase holdups at different axial locations were investigated. Gas holdup was higher at the central region compared to any other radial location. Solid circulation rate and solid hold up were dependent on drag force resulting from the fluid flow on the solid particles. Drag force depends on drag coefficient, slip velocity and particle size. Shape factor played an important role on phase holdup of irregular shape (lava rock) particles. Axial flow profile of solids and liquid holdups were almost uniform for all types of particles at all axial location except the lower location close to the distributor zone in LSCFB system. Expansion of gas due to the reduction of hydrostatic pressure of gas bubbles and bubbles coalescence increased gas holdup in higher axial locations.;Keywords: Circulating Fluidized Bed, Electrical Resistance Tomography, Radial distribution, Phase Holdups, Propagation velocity, Cross-correlation, Axial flow profile, Optical fiber probe.