Pressure fluctuations as a diagnostic tool for fluidized beds. Technical progress report, July 1, 1996--September 30, 1996

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By studying pressure fluctuations using a system identification approach, it is hypothesized that circulating fluidized bed (CFB) pressure fluctuations are indicative of CFB hydrodynamics in two ways. First, the frequency phenomenon that is observed in the lower regions of the CFB under conditions of high solids loading is the result of lower dense bed voidage oscillations. Our results suggest that a surface wave phenomena inversely proportional to the square root of the bed diameter is also be observed in CFB pressure fluctuations under most conditions. By matching revised similitude parameters between two CFBs a number of conclusions can be drawn. First, spectral analysis of pressure fluctuations, if properly applied, can be used to verify that similitude has been achieved. To do this, not only must the Bode plot characteristics important for hydrodynamics be identified, but the pressure fluctuation structure at all elevations of the CFB must be similar. The set of similitude parameters defined by Glicksman is not sufficient to establish hydrodynamic similitude. The solids flux as typically measured in the downcomer does not contain information on the solids hold-up in the riser, or the amount of solids that progress downwards in the annulus rather than exit the riser. It is better to use the total mass contained in the riser as the important ``solids`` parameter for the establishment of similitude, rather than the solids flux. This measurement can be made more accurately, monitored continuously, and is a much simpler measurement to perform in most CFB systems. Even with this new set of dimensionless parameters, the differences in the coefficient of restitution of particle/bed collisions may make a significant difference in the CFB hydrodynamics. The effects of particle collisions with the riser top-plate must be considered in similitude studies.