Why powder gets trapped under a fluid bed dryer's plate
Many conventional fluid bed dryers use a perforated plate with a wire mesh below it. One of the critical issues of using this technology is that the perforated plate and wire mesh sit so close together that powder and granules get trapped between them. This not only increases product loss, but also increases cleaning time and contamination risks.
The usual fix: the plates are lifted up for cleaning, and the operator manually scrapes powder off the plate and wire mesh. STV's Machine's solution: our bottom plate is a single plate with thinly cut (45 degrees angle) creases that ensure powder won't fall through. Not only the plate, but our FBD's twin shaking filter bag system enables continuous fluidisation and the wet/semi-dry powder won't fall to the bottom plate.
The Case
A pharmaceutical company in Malaysia shared a recurring problem with their conventional fluid bed dryer. After drying, powder was collecting at the bottom of the machine and getting trapped between the perforated plate and the wire mesh that sits on top of it. Because the two layers are so close together, there was no easy way to reach the powder. The only option was to dismantle the plate and mesh and clean them by hand.
Why the powder ends up there
The conventional perforated plate design means that holes are bigger to let airflow up, but this leaves a lot of room for powder to fall into and get trapped between the plate and mesh.
The other part is in the filter bags at the top of the machine. During drying, the filter bags catch fine particles carried up by the airflow. To stop them from clogging, they are shaken at intervals. On many conventional dryers, there is a single filter-bag system, and shaking it means stopping the airflow. Without air holding the product up, the bed collapses and powder (that have not fully developed into granules) drops onto the plate. Fines then work their way into the narrow gap between the plate and the mesh. This happens every time the filter shakes, so over a full batch the trapped powder builds up.
What it costs
• Product loss: powder trapped below the bed never makes it to sieving, blending or the tablet press.
• Harder cleaning: dismantling the plate and mesh adds time and labour to every changeover.
• Higher contamination risk: residue in a tight gap is hard to remove and harder to prove clean, which matters when the next batch is a different product.
How STV Machine's FBD, SD(GC) Series, avoids it
1. A single plate with no mesh. The Bottom Plate STV Disk Jet is one plate set at 45 degrees with very small air holes. There is no wire mesh, so there is no gap for powder to get trapped in. The holes are sized so that air passes through and, in most cases, powder does not. Cleaning means wiping down one surface, not taking two layers apart.
The Disk Jet's 45 degrees crevices also produces a cyclone airflow that helps prevent uneven drying, which we cover in Why granules come out uneven from a fluid bed dryer.
2. Twin shaking filter bags. The SD(GC) Series splits the filter bags into two sections. When one section is shaken, its lid closes while the other section stays open, so air keeps flowing through the machine. The bed stays fluidised the whole time, so the product doesn't collapse onto the plate during filter cleaning.
Together, the two features address both halves of the problem: the powder has less reason to fall, and no gap to hide in if it does.
Learn More or See the Line in Action
The fluid bed dryer and the technology described in this blog is built and supported by STV Machine, a manufacturer of pharmaceutical processing equipment with production facilities in Ho Chi Minh City, Vietnam.
To learn more about our fluid bed dryer, contact STV Machine directly:
• Email: sales@stvmachine.com.vn
• LinkedIn: linkedin.com/company/stvmachine
• Website: www.stvmachine.com.vn
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