Measurement of the Wetting and Drying Processes in a Top Spray Fluidized Bed By Microwave Tomography

In fluidized bed mixing, granulation and drying processes, the moisture content of particles can change within a large range (1%~25%). To improve the efficiency of granulation processes and avoid faults, it is important to develop a tool that enable the monitoring of the wet particle flow. Microwave tomography (MWT) has a wide range of operational frequency, and it is applicable to measure solids concentration with high permittivity or conductivity. This paper introduces the measurement of wetting and drying processes in a top spray fluidized bed using a MWT sensor with 16 antennas. The solids moisture and images of solids distribution are obtained from the measurement data. It is shown that the solids moisture can be accurately measured using the calibration data between mean permittivity and solids moisture of off-line samples. The solids distribution in the cross-sectional area are revealed by the MWT images. Based on the MWT image and the pressure data, the gas-solid flow regimes are further investigated in the wetting and drying process. Experiment results show that microwave tomography is a promising technique for the measurement of fluidized bed with high moisture content particles.