Application Note

Refilling Loss-In-Weight Feeders Via Pneumatic Conveying In Continuous Pharmaceutical Processes

By Sharon Nowak

The mode of refill of product to a Loss-in-Weight (LIW) feeder that is feeding a continuous pharmaceutical process can be almost as critical as choosing the right feeder technology. Since the objective of feeder refill is to refill as quickly as possible, pneumatic receivers that operate under a dilute phase vacuum transfer principle are often used as refill devices, particularly for continuous operations. The photo on page 2 illustrates a K-Tron P-Series receiver above a K-Tron LIW feeder.

When refilling in a continuous pharmaceutical process the refill devices must reliably maintain constant flow of the Active Pharmaceutical Ingredient (API) or excipient to the process within specific refill time limits. This time limit must be relatively short, in order to allow the feeder to return to a true gravimetric operation, and ensure constant mass flow of the product to the process. Additionally, the cut-off action of the selected device must be quick and sure. A slow tapering off of the refill flow needlessly lengthens refill time. Any leakage of the refill device may cause a weight disturbance, resulting in a flow error in the positive direction. A sample flow diagram of a refill operation for a continuous blender system is shown at right.