An Acoustic Method for the Measurement of Minimum Fluidization and Bubbling Properties of Group A Solids

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 some subjectivity in the data and, also necessitates the use transparent columns. Such test units often will not withstand high temperature and pressure conditions. This presentation discusses results obtained in a new 6-in (0.15-m)-diameter test unit in which the minimum fluidization and bubbling points were detected by the use of acoustic waves. The test materials were FCC catalyst particles of various fines contents (% < 44 mm). Tests were conducted at low-to-moderate system pressures. Gas flowrate was automatically adjusted at a chosen time interval using a mass flow controller. Results showed that 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% less than 44  microns. Both the minimum fluidization density and minimum bubbling density of FCC catalyst particles 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.