Experimental Study On Solids Holdup Distributions Of Coarse Particles In A Gas-Solid CFB

Gas-solid circulating fluidization, as a high efficient gas-solid contact technology, is widely used in process industries. However, most investigations at present are focusing on the A sort solids (e.g. FCC). To promote the application of this technology in industries, it is necessary to research the circulating fluidization of particles with different properties. In this work, sands as typical coarse particles with the bulk mean diameter of 461.6um and the apparent density of 2710.5kg/m3 were selected for this experiment. The mean solids holdups on 11 axial levels and the local solids holdups at 11 radial locations on 5 axial levels in a 10.5m high riser were systematically measured with the superficial gas velocity ranging from 4.6 to 11.4m/s and the solids circulation rate from 16 to 210kg/m2s.The results show that the axial distributions of the cross-sectional averaged solids holdups in riser are non-uniform. Generally, from the bottom to the top of the riser, the axial profiles of the averaged solids holdups become more uniform with the increased riser height. The axial profiles of the averaged solids holdups change greatly with the variations of superficial gas velocity Ug and solids circulating rate Gs. With different conditions, new distribution patterns of solids holdups are found. The radial distributions of the local solids holdups are non-uniform along the whole riser, showing different behaviors from those of FCC particles. The local solids holdups near the riser wall do not always reached the maximum. From the riser's bottom to its top, the solids holdups near the riser wall changed greatly, and the radial non-uniformity of local solids holdups decreased with the increasing of the height.Based on the variations of operation conditions, the change of averaged solids holdups at the bottom is more obvious than in the upper section, and it trends to weaken along the increased height and finally comes to a steady state. With the increase of the solids circulating rate Gs or the decrease of the superficial gas velocity Ug, the averaged solids holdups will be increased and become morenon-uniformly distributed along the whole riser height, and the axial profiles of the averaged solids holdups will change from linear curve to other profile curves. With increasing Gs or decreasing Ug, both of the radial non-uniformity and the local solids holdups anywhere in riser will be increased and vary more obviously. It is found that with varying Gs or Ug, the local solids holdups near the riser wall will change more sensitively than at other radial positions of the same cross-section. As a result, the axial and radial distribution profiles of solids holdups and the effects of Gs or Ug on solids distribution profiles are different from those of FCC. The results of this thesis are significantly important for the understanding of the effects of solid properties on circulating fluidization.