Systematic experiments were carried out in a 16 m high gas solid CFB riser with FCC particles to investigate the drag force acted on solids by gas. Based on the measured data of the cross sectional average solids holdups at different axial locations of riser under various operation conditions and through the dynamic balance analysis of single particle, drag coefficients were indirectly obtained. The results show that the solids holdups have great effect on drag coefficients, which obviously decrease with increasing solids holdups. Considering the effects of Reynolds number, Archimedes number and solids holdups, a new correlation for drag coefficients was developed. The predicted values of the new correlation for drag coefficients were compared with the experimental data of this work and some other authors, and a good agreement was observed for three different particles. Using the drag coefficient correlation, the axial pressure gradients of gas solid flow in riser are successfully predicted.
