Behaviors And Predictions Of Solids Holdups In Fully Developed Region Of Gas-Solid CFB Riser

The knowledge of particle flow behaviors and solids holdup distributions in CFB riser is very important for the further studies of heat-mass transfer problems and the engineering design of CFB equipment. Based on the systematic measurements of pressure gradients and local solids holdups in a 16m high CFB riser, under the operation conditions of superficial gas velocity U_g=2.0～10.3m/s and solids circulating rate G_s=5.4～230kg/(m~2·s), the averaged solids holdup distribution and related problems were investigated in the paper.By analysis of solids holdup distributions and related operation conditions, the variation regularities of solids holdup with operation parameters in fully developed section were delineated more clearly, and a new correlation was developed for solids holdup in fully developed section of CFB riser. This new correlation is in good agreement with the experimental data and, corresponding to different superficial gas velocity, makes the predicated results of other authors in accordance, explaining the differences existing among them.The studies point out that four important factors (the drag force between gas and particles, the particle density, the riser height and the static pressure supplied by suspensions in storage tank) control the maximum solids circulating rate that the CFB unit can achieve at a given superficial gas velocity. The paper fingers that, from the view of energy and pressure balances, at low gas velocities, the maximum solids circulating rate is determined by the balance between the energy contained in gas stream and that consumed by solids movement, while at high gas velocity it is determined by the balance between the pressure of gas stream at riser bottom and that supplied by suspended solids in storage tank. Also, an equation was developed...