Implementation of Microwave Sensors in Continuous Powder Feeding
A Novel Tool to Bridge Refill Phases
In continuous processes gravimetric powder feeders need to be refilled frequently and are temporarily not able to monitor and control the feed-rate. Especially during these phases, the powder feeder is susceptible to deviations from its set point. In order to prevent negative influences on subsequent processes, there is a need for alternative methods to monitor the refill phases. Therefore, in the present work microwave sensors for the measurement of powder flow during continuous powder feeding of three excipients with different particle sizes were implemented as process analytical technology tool. Feeding of coarse dicalcium phosphate was accurately measured in repetition. Sensor stability could be shown for coarse and fine dicalcium phosphate. Thereby, a bypass of the refill phase during feeding of fine dicalcium phosphate was easily possible. However, the applied microwave sensors were not able to replace the gravimetric feeding principle at present, as the inter-day precision during the feeding of coarse mannitol was not given. During the refill of this material, the microwave signals deviated up to 6 % from the values obtained by an external balance. After these first trials, the microwave sensors showed promising results to completely bridge the gap of refill phases in continuous powder feeding in the future and should be further investigated to result in the required performance.
Robin Meier, Julia Harting, Jens Happel, Peter Kleinebudde
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