Interpreting probe signals from fluidized beds

Abstract

Bubble size distribution in fluidized beds may have a profound effect on reactor mass transfer and hydrodynamics. Although several different types of probes are available to monitor bubble events in fluidized beds, the probe signals must be processed carefully to yield bubble size information, because a probe will not always intersect a bubble centrally and because bubble rise velocity will depend on bubble size (usually velocity increases as the square root of linear size). Using a truncated ellipsoid as a model of bubble shape, the relationship between probe signals and bubble size has been explored using probability density functions. A back-transform technique has been presented to yield the bubble size distribution for a given distribution of time intervals when the probe ‘cuts’ a bubble. This back-transform has been demonstrated for two different bubble size distributions. When too few bubble measurements are taken or too many intervals in the discrete bubble size distribution are used, instabilities in the back-transform may result.