Study of solids flow in the dipleg of the primary cyclone of a 0.6 m diameter fluidized bed of a large group A powder

Internal cyclones use diplegs to recycle solids to the dense fluidized bed in most industrial fluidized beds. Poor dipleg operation can greatly increase particle losses from cyclones. Experiments with a 0.6 m diameter column and large group A particles showed that at low gas velocities in the fluidized bed, gas slugs rose through the dipleg, causing the emission of solids pulses; this issue was resolved by adding an elbow termination at the bottom of the dipleg. At high gas velocities, the dipleg backed up. A new model showed that dipleg backup resulted from large pressure fluctuations in the fluidized bed near the bottom of the dipleg. Momentarily, the local bed pressure became higher than the pressure in the dipleg, and fluidized solids flowed from the bed into the dipleg. Consequently, the dipleg was modified: the dipleg diameter and height were increased, and aeration and an elbow termination were added to the dipleg.