Particle size monitoring in a fluidized bed using pressure fluctuations

Starting from the premise that the standard deviation, σp, of the pressure fluctuations in a fluidized bed is linearly proportional to excess gas velocity, it follows that σp is a function of particle size. This relationship has previously been recognised as a potential route to the continuous monitoring of particle size in fluidized bed processing, and is attractive because of the relative ease with which pressure and pressure fluctuations can be measured. Simple expressions with no fitted parameters can be derived for the case where the constant of proportionality between σp and excess gas velocity is unaltered by changes in mean particle size. The results of experiments with mixtures of silica sand prepared by mixing two base batches, with a different mean size, in incrementally varying proportions provide good support for the general validity of the model.

A model based on a linear relationship between pressure fluctuations and excess gas velocity has been used to compare the mean diameter of mixtures of silica sand to values at reference conditions. The mixtures were prepared by mixing two base batches, each with a different mean size, in incrementally varying proportions. Agreement with size ratios determined from sieve analysis data is good.Figure optionsDownload as PowerPoint slideComparison of diameter ratio estimated using pressure fluctuation data and diameter ratio determined by sieve analysis; material is silica sand.