Circulation of solids and gas bypassing in an internally circulating fluidized bed with a draft tube

The effects of gas distributor, draft tube height, gas velocity and gap height on the circulation rate of solids and gas bypassing between the draft tube and annulus sections have been determined in a circulating fluidized bed (internal diameter, 0.3 m; height, 2.5 m) with a draft tube (internal diameter, 0.1 m). Gas bypassing strongly depends on the type of gas distributor used for annulus aeration. Gas bypassing from the draft tube to the annulus decreases with increasing draft tube height. The circulation rate of solids is enhanced by gas bypassing from the annulus to the draft tube section regardless of the distributor type. A conical plate distributor with tuyeres is found to be the most suitable configuration for the circulation of solids in the circulating fluidized bed with a draft tube. The solids circulation rate obtained has been correlated with the pressure drop across the gap opening and the opening ratio using the orifice equation. (C) 1997 Elsevier Science S.A.