Experimental Research on Granule Moisture Measurement by Microwave Resonance Technology in a Fluidized Bed Dryer

Drying is one of the most important methods for industrial processing while the granule moisture is a critical quality attribute (CQA) which has a significant influence on the finished product quality. In-line measurement of granule moisture during fluidized bed drying is getting more imperative to meet more stringent product quality specifications. Nowadays, several methods have been applied to measuring the granule moisture in-line. Comparing to other methods, microwave resonance (MR) technology provides more representative results due to its independency of both the particle density and the bed density. In the current study, one MR sensor was mounted onto an industrial fluidized bed dryer to monitor the real-time moisture of granules. The drying experiments were performed at different drying air temperatures and flow rates. The comparison between the results of in-line and off-line granule moisture measurements, namely MR technology and loss on drying caused by infrared light (LOD/IR), was presented. Furthermore, the influences of inlet air temperature and flow rate on the performance of the MR sensor were investigated. As a conclusion, the MR method, which is independent of the drying air temperature and flow rate, provided more accurate results when the granule moisture was below 25% (wet basis). Therefore, it is a promising method to be applied in real-time measurement of the granule moisture and predict the end-point in fluidized bed drying processes as well.