EXIT EFFECTS IN CIRCULATING FLUIDIZED-BED RISERS

The relative influence of smooth and abrupt exit configurations on the axial pressure drop profile in Circulating Fluidized Bed (CFB) risers has been investigated. Experiments were performed with sand and FCC c atalyst in two cold model CFBs of 0.1 metre and 0.2 metre riser diamet er. The influence of the abrupt exit on the profile was observed to ex tend all the way to the base of the larger diameter riser for sand. Ho wever, the abrupt exit influenced only the final 1.5 to 2 metres of th e riser length for the case of sand in the narrow diameter riser. When FCC catalyst was circulated, the effect of the abrupt configuration w as seen only in the upper portion of the riser, irrespective of the ri ser diameter. A simple empirical modification to the model of Pugsley and Berruti (1996) provides a good description of the axial pressure d rop profiles for the abrupt exit configurations, with the exception of the case of sand in the 0.2 metre diameter riser. This discrepancy is attributed to the lack of fully developed flow in the larger riser.