Friction between gas–solid flow and circulating fluidized bed downer wall

Friction between co-current downflow gas–solid flow and column wall was investigated by measuring apparent and actual solids concentrations in a circulating fluidized bed (CFB) downer. A new model to predict pressure drops due to friction between the gas–solid suspension in the fully developed zone and the downer wall was developed. The results show that the friction between the gas–solid suspension and the downer wall causes a significant deviation of the apparent solids concentrations from the actual ones, especially for those operating conditions with higher superficial gas velocities and solids circulation rates. When the superficial gas velocity is greater than 8 m/s, the actual solids concentrations in the fully developed region of the downer can be up to two to three times of the apparent values. Particle diameters have different influences on the frictional pressure drops under different superficial gas velocity. After the frictional pressure drop is considered, the predicted actual solids concentrations by the proposed model agree well with the experimental values.