Capacitance probes for solids volume concentration and velocity measurements in industrial fluidized bed reactors

The capacitive measurement of solids volume concentrations is based on the determination of the relative dielectric constant of a fluid–solids suspension in the capacitance sensor volume. The suitability of various theoretical and empirical calibration relationships that relate the volumetric fraction of the solids to the mixture dielectric constant has been investigated and a new empirical calibration relationship is suggested. The application of the calibration relationship to capacitive measurements in high-temperature fluidized bed reactors is demonstrated. Measurements of solids volume concentrations and velocities in the upper dilute zone of a cold model circulating fluidized bed (CFB) and in the bottom zone of a large-scale industrial CFB boiler illustrate the value of capacitance probes for local flow structure investigations.