Friction between gas-solid suspension and CFB downer wall

To investigate the friction between gas-solid suspension and the internal wall of the circulating fluidized bed (CFB) downer, the difference between apparent and actual solids holdup was studied by measuring pressure gradients and local solids concentrations in a 9.3 m high CFB downer with FCC particles. A new model to predict pressure drop due to friction between gas-solid suspension and internal wall in the fully developed region of CFB downers was developed. The results showed that the friction between gas-solid suspension and the downer internal wall caused a significant deviation of the apparent solids holdups from the actual ones, especially under higher superficial gas velocity and solids circulation rate. When superficial gas velocity was greater than 8 m·s^-1, the actual solids holdups in the fully developed region of the downer could be up to 2-3 times of the apparent values. After the frictional pressure drop was considered, the predicted actual solids holdups by the proposed model agreed well with the experimental values from this work and in the literatures.