Axial hydrodynamic studies in a gas–liquid–solid circulating fluidized bed riser

Axial distribution of phase holdups was studied in the riser of a gas–liquid–solid circulating fluidized bed (GLSCFB). 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. Electrical resistance tomography (ERT) and optical fiber probe were employed online in the experiments for a precise determination of phase holdups. An empirical model was developed for the determination of gas bubbles in analysis of data obtained by fiber optic sensor. Gas holdup was higher at the central region of the riser and increased axially due to coalescence of small bubbles and decrease of hydrostatic pressure at higher levels in the riser. This led to an increase in solids holdup in regions close to the wall which was slightly higher than the solids holdup at the wall. Both solids and liquid holdups were lower in the central region and increased radially towards the wall. Gas holdup decreased with increasing solids circulation rate but opposite trend was observed for solids holdup. Solids circulation rate had negligible effect on liquid holdup at lower axial locations compared to top of the riser. Cross-sectional average of solids, gas and liquid holdups did not change significantly at higher liquid superficial velocities.

A new method was developed to determine the phase holdups of all phases for a better understanding of hydrodynamics in GLSCFB systems. Combining the advanced technology of ERT and optical fiber probe revealed the phase holdups in GLSCFB riser quantitatively and locally. Optical fiber probe was capable of measuring gas holdup, which was one of the nonconductive phases. Combination of both technologies successfully revealed the three phases separately.Figure optionsDownload as PowerPoint slide