Solids Holdups in the Fully Developed Region of Circulating Fluidized Beds

The present work focuses on developing correlations for better prediction of solids holdups in the fully developed region of cocurrent upflow and downflow two-phase flow. Systematic experiments were carried out in two CFB risers (15.1m and 10.5m high, respectively, but with the same 0.1 m i. d.) and a 9.3 m high, 0.1 m i. d. CFB downer. The experimental results obtained from about 200 sets of operating conditions, under which the lengths of fully developed section are longer than 2.8 m, show that when the superficial gas velocity is between 3 m/s and 8 m/s, it has a significant effect on the variations of the average solids holdups in the fully developed region with the terminal solids holdups, but when it is less than 3 m/s or greater than 8 m/s, the effect becomes weak and the average solids holdups vary linearly with the terminal solids holdups. By taking into account the effects of superficial gas velocity, particle properties and riser geometry, two empirical correlations for predicting the average solids holdups in the fully developed region of CFB riser and downer were proposed, respectively. These correlations are in good agreement with the experimental data of this work and accords with the correlations reported in literatures.