Experimental Investigation On Particle Concentrations And Particle Velocities In A Gas-Solid CFB Riser

Particle concentrations and velocities at 11 radial locations on 8 axial levels in a 16m high FCC-air riser were systematically measured with the superficial gas velocity ranging from 3.5 to 8.2m/s and the solids circulation rate from 53 to 201kg/m2s. The distributions of local particle concentrations and velocities, and the variations of cross-sectional averaged particle concentrations and particle velocities, including the effects of operation conditions, were investigated based on the experiment results.The results show that the local particle concentrations are distributed non-uniformly in radial direction, with local particle concentrations lower in riser center and higher near the riser wall; from the riser bottom to the top, the local particle concentrations near the riser wall visibly decrease, while in riser center the particle concentrations only have a small change, leading to a decrease for the radial nonuniformity of particle concentrations. The axial profiles of the cross-sectional averaged particle concentrations depend on Gs/Gg,Gs and the gas distributor, and will transit from the uniform to the exponential and then the trapezium-shaped under various operation conditions. With increasing Gs or decreasing Ug, the local particle concentration in whole riser increases and, also, radial nonuniformity of particle concentrations increases, resulting in the transition of cross-sectional averaged particle concentrations from the uniform to the exponential and then the trapezium-shaped.Local particle velocities in the bottom acceleration region are lower but more evenly distributed in the radial direction, compared with those in the uppersection of riser. The radial distribution of particle velocities always tends to become less uniform along the riser height and will finally reach a parabolic profile in the upper section of riser. The increase of local particle velocity along the riser height is more notable in the riser center than near the riser wall. The cross-sectional averaged particle velocities increase from the bottom to the top, but even in riser exit, the cross-sectional averaged particle velocities are still obviously lower than superficial gas velocity, indicating that a large velocity difference between gas and slolids still exists in riser exit. With increasing Gs or decreasing ug, particle velocities decrease and become more uneven in the radial direction. But the effects of Gs on local particle velocities are mainly restricted to the bottom region and the wall region of the upper section and, therefore, not so significant as the effects of Us.