Monitoring the Moisture Content of Solids in Fluidized Bed Dryers by Analysis of Pressure Fluctuations

Perusing the hydrodynamic changes of fluidized bed dryer is important for online monitoring of the drying process. The present study investigates the drying process of wetted rice particles. Air at ambient conditions with superficial velocity of 1 ms(-1) was used for drying. Absolute pressure fluctuations were measured to monitor the fluidization status of the dryer. Fast Fourier transform, discrete wavelet transform, and statistical analyses of detailed signals were employed to evaluate the fluidization quality in the bubbling regime. Pressure fluctuations were decomposed by the wavelet transform to 10 subsignals. It was shown that the energy of subsignals is more sensitive to moisture changes than other studied parameters. Specifically, the energy of the subsignals corresponding to the macrostructure (large bubbles) can be used for determining the moisture content of the solids during the drying process. This method can be used for online monitoring of drying processes in a wide range of processing conditions in fluidized beds.