Experimental investigation of hydrodynamics of gas-solid flow in an internally circulating fluidized bed

Hydrodynamic study of gas and solid flow in an internally circulating fluidized bed (ICFB) is made in this paper using a high-speed camera and pressure probes for the laboratory 0.3m x 0.27m column having an internal draft tube. Experiments were conducted using sand particles of Geldart B and Geldart B-D groups. At each run the standard pressure-flow curves for both the draft tube and annular region beds, and the moving wall particle velocity in the annular bed region were measured. The effects of superficial gas velocity, static bed height, and draft tube gap height on pressure drop profiles, solid circulation patterns, and gas bypassing dynamics for the ICFB were investigated extensively. Unlike the conventional CFB, the pressure drop in ICFB is further decreased with superficial gas velocity after the minimum spouting fluidization, followed by yielding a cross-over in the pressure drop of the annular bed compared to the draft tube. Pressure drop in the draft tube increases with an increase of static bed height and gap height between the draft tube bottom and the air distributor. The gas bypassing fraction increases with an increase in gap height and decreases with increased bed height and mean particle size. The mechanism governing the solid circulation and the pressure losses in an ICFB has been elaborated based on gas and solid dynamics obtained from the experimental data.