Acceleration behaviors of particles in gas-solid two-phase upward flow

Systematic work was carried out to investigate the averaged solids holdup and the length of solids acceleration region in a riser, based on the experimental data of pressure gradients of air-FCC particles in a 16m high CFB riser. It was experimentally shown that solids acceleration results in the nonuniform axial distribution of solids holdups in the riser. In the acceleration region, the variation of apparent solids holdups with operation conditions was quite different from that in the fully developed region. The length of solids acceleration region was experimentally found strongly dependent on the operation conditions and varying the trends quite different form the reported in previous work. Increasing solids circulating rate and decreasing superficial gas velocity both lead to prolonged solids acceleration region and, therefore, higher solids holdups. Especially, with the accumulation of particles and the formation of particle clusters on the bottom of the riser, solids acceleration region could be e xtend rapidly, even taking up the whole height of the riser.