Authors: Allan Issangya, Roy Hays, Ray Cocco, Ted Knowlton, S.B. Reddy Karri
Particulate Solid Research, Inc., Chicago, IL 60632 USA
Abstract: Minimum fluidization and bubbling densities and velocities are widely used in fluidized bed design and modeling. The methods presently used for measuring these parameters are, however, time consuming and labor intensive. Traditional methods have often relied on visual observations to determine the minimum bubbling point, which is likely to introduce subjectivity in the data, and necessitates the use of transparent columns. Such test units often will not withstand high temperature and pressure conditions. This paper discusses results obtained in a 0.15-m-diameter test unit in which the minimum bubbling point was measured with an acoustic device. The test materials were several batches of FCC catalyst particles of fines contents ranging from 3 to 11% < 44 µm. Tests were conducted at low-to-moderate system pressures. Gas flowrate was automatically adjusted at a chosen time interval by a mass flow controller. The minimum fluidization point was determined from the bed pressure drop per unit length versus superficial gas velocity plot, and the minimum bubbling point was obtained from the plot of standard deviation of bed height fluctuations as a function of gas velocity. The
acoustic technique gave a clear distinction between particulate fluidization and bubbling fluidization. Fines content had no significant effect on the minimum fluidization velocity. The minimum bubbling velocity, however, increased rather sharply when the fines content exceeded about 5% < 44 µm. Both the minimum fluidization density and minimum bubbling density were found to decrease slowly with increasing fines content. For the pressure range used in these tests, there was no significant effect of pressure on both the minimum fluidization velocity and the minimum bubbling velocity. Furthermore, pressure had very small influences on both the minimum fluidization and minimum bubbling densities.