A hydrodynamic model for circulating fluidized beds with low riser and tall riser

• A comprehensive hydrodynamic model for CFB is proposed.
• The model considers the effects of riser height and saturation carrying capacity.
• Gas solids behaviors in riser and standpipe could be calculated properly.
• Axial solids distributions in low riser and tall riser are compared.

Based on different flow regimes classified by the saturation carrying capacity in the riser, a comprehensive hydrodynamic model for circulating fluidized beds was proposed and validated with experimental data. The model can describe the different axial solids distributions or regimes in previous literatures, especially the boundaries among them. The calculation of model shows good agreement with experiments not just for gas solids behavior in riser, but also for that in standpipe.The influences of the riser height on the axial solids distribution in riser were discussed. With the increase of the distance between the upper end of dense phase and the bottom of riser, the axial solids distribution in low riser appears as the exponential profile, the quasi exponential profile and the quasi S-shaped profile continuously. For the tall riser, the quasi exponential profile is replaced by the S-shaped profile due to the dilute phase in the upper. In addition, the saturation carrying capacity prevails in the tall riser, and with greater inventory solids circulation rate would exceed the saturation carrying capacity to form the quasi S-shape profile.

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