Experimental study on the hydrodynamics in the riser of a circulating fluidized bed

Circulating fluidized bed technology has been widely employed in the energy conversion industry and drawn a considerable amount of research attention to itself. The world-wide research effort on the circulating fluidized bed partially comes from the new emission standards which impose very strict limitations on the coal-powered electrical industry.;In the circulating fluidized bed riser, a dilute, upward core in the center region is surrounded by a dense, downward annulus. The solid cluster formation in the annulus near the wall of the riser predominates the flow inside the riser and a transient interface of the core-annulus inside the riser exists. In this work, a pair of dual-stem differential pressure probes have been developed for the measurements of the differential pressure fluctuation in the axial direction of a dense, vertical gas-solid two phase pipe flow. The application of the statistical analysis to the differential pressure signals was utilized to reveal the structure of the core-annulus interface.;The frequency of the differential pressure signals was found to be dependent on the operating conditions such as superficial velocity, solid circulation rate and the properties of the solid particles. The velocity of solid in the annulus in contact with the riser wall was obtained by statistically analyzing the differential pressure signals from a pair of dual-stem pressure probes, which were located 200 mm apart vertically from each other in the riser. The findings on the solid particle velocity in the annulus are in agreement with the published experimental results. The experimental results also indicated that the interface of core-annulus in the riser varied with the system operating conditions. A higher superficial velocity led to a thinner annulus while a higher solid circulation rate resulted in a thicker annulus. An S-shaped profile of the core-annulus interface was observed in the experiment. This study also provided evidence that the solid fraction inferred from pressure drop data at the riser wall is inaccurate due to the high solid reflux near the riser wall and radial non-uniformity of solid fraction.