TRANSIENT HYDRODYNAMICS IN A CIRCULATING FLUIDIZED BED RISER

摘要

The instantaneous solids flux and transient distributions of voidage in a riser of 0.2 m diameter were simultaneously monitored during unsteady state operation after the solids flow was abruptly terminated while the gas flow continued unchanged. The experiments began with steady state net solids fluxes up to 292 kg/m~2s and superficial gas velocities from 2.8 to 7.1 m/s. Instantaneous axial voidage profiles and decay curves of solids circulation flux were recorded after abruptly closing a valve on the standpipe feeding the riser until the entire riser was empty. When the instantaneous pressure drop across the riser during the emptying process is plotted against the instantaneous solids flux in a operating map of ΔP-G_s-U_g, different modes of variation of solids concentration during unsteady state operation were found, corresponding to different flow regimes.