Axial distributions of averaged solids holdups for coarse particles in CFB riser

The pressure gradients of air-sand two-phase flow in a CFB riser were systematically measured in a 10 m high CFB riser to investigate the axial distributions of averaged solids holdups of coarse particles and the effects of operation conditions. The results show that the solids holdups of sand particles are much lower than those of FCC particles under the same operation conditions, and the axial distribution curves of the solids holdups for sand particles are significantly different from those for FCC particles, depending on the operation conditions. At high superficial gas velocity, the solids holdups for sand particles decrease exponentially along the riser height, similar to the variation trend of FCC particles; as gas velocity decreases to some extent, however, the axial distributions of solids holdups for sand particles become wave-shaped, indicating that the sand particles in CFB riser will experience a second acceleration process before reaching a fully developed flow at the top section of the riser. It is also found that with the decrease of gas velocity or the increase of solids circulating rate, the averaged solids holdups at all axial locations become increased, while for the wave-shaped distribution, the variations of solids holdups are much more significant at the riser bottom and middle sections, where a larger amount of particles are concentrated.