Minimum slugging velocity in fluidized beds containing vertical rods

A new method for determining the onset of slugging in fluidized beds is presented. Pressuredrop fluctuations, measured from below the distributor to the gas exit line, are transformed to the frequency domain by the power spectral density function (PSDF). The dominant frequency of the PSDF corresponds to the eruption frequency of bubbles or slugs. A fluidized bed is in the slugging regime when this dominant frequency, fd, remains approximately constant with changing gas velocity. This method is an improvement over previously presented methods because of the simple nature of the apparatus required, and because it is possible to locate the pressure probes such that they will not interere with the fluidization nor will they rapidly wear by the constant particle movement characteristic of fluidized beds. This method was used to determine the gas velocity corresponding to the transition from the bubbling to the slugging regime for a 10-cm diameter bed of sand fluidized with air and containing three 1.9-cm diameter vertical rods on 5.2-cm center-to-center triangular spacing and extending the length of the bed, and to compare the results with those from the same bed without any internal rods. It was determined that the presence of the vertical rods inhibited the onset of the slugging regime, and significantly extended the bubbling regime into higher gas velocities.