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Gas spouting of fine particles

University of British Columbia

Spouting is a well established gas-solids contacting technique for coarse particles (dp ≥ 1 mm) which are not readily fluidized. Spouting of fine particles (dp < 1 ram), however, is a sparsely touched subject: the few reports in the literature are not in complete harmony with each other, and they lead to a somewhat confused picture about the spoutability of fine particles. Experiments were conducted in a 152-mm diameter transparent conical-cylindrical half-column with particles ranging in size from 90 to 1000 μm and in density from 900 to 8900 kg/m³. The different flow regimes which result on varying bed height and gas velocity for a given particle species were carefully observed, video-taped and mapped. The criteria of both Geldart (1973) and Molerus (1982) for spoutable particles (classified as Group D by Geldart) were shown to be unsatisfactory. Following Ghosh (1965), however, it was found that formation of a stable spout was ensured only if a critical ratio (25.4 in our experiments) of inlet orifice size to particle diameter was not exceeded. Measurements were also made of bed pressure drops, solids circulation patterns and rates, dead zones, longitudinal annular gas velocity profiles, spout contours and fountain heights. It was found that the mechanism by which spouting is terminated in a coarse particle bed, namely, fluidization of the annulus, could not account for its termination in the present beds. The hypothesis that termination was caused instead by choking of the spout was reinforced by the fact that the theory of choking in standpipes could be applied to satisfactorily predict the end of stable spouting.

Text

2010-05-17

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http://hdl.handle.net/2429/24809

Chemical and Biological Engineering

University of British Columbia

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