DIFFERENTIAL PRESSURE MEASUREMENTS IN A SLUGGING FLUIDIZED-BED

Detailed information on local fluid bed behavior cannot be obtained using global instrumentation. However, dual static pressure probes (DSPP) which measure local axial differential pressures can be used to infer the presence of bubbles or slugs in a fluid bed. DSPP consist of two probe stems, one positioned vertically above the other, connected to a differential pressure transducer. Response of DSPP has been modeled and is fast enough to capture transient phenomena in a fluid bed, provided that a low-dead-volume transducer is used. DSPP with 1.27-cm, 1.9-cm, and 2.54-cm stem spacings have been used to measure slugging properties of a 13.97-cm diameter air-fluidized bed filled with 3.175-mm nylon spheres. Over 500 20-second pressure traces were digitally recorded for two distributor types, a variety of bed heights, air flow rates and probe positions. Slugging frequency was found from selected traces using the autocorrelation function, Fourier transform and power spectral density function, and was shown to decrease with bed height. Slug velocity was found using cross-correlation of signals from two DSPP, and was shown to increase with air throughput and decrease slightly with bed height.