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Agglomeration Case Study

Problem

A manufacturing process was filed (e.g., NDA) with the “variable batch size”.  SUPAC allows < 10% change in the batch size with just the annual report (i.e., Level I Change), and the manufacturing department wants to take advantage of this flexibility in filing by increasing the batch size to improve manufacturing efficiency.  Upon increasing the batch size from 345 kg to 403 kg, noticeable amounts of agglomerated pellets were observed.  What is causing this agglomeration problem? 

Problem Categories

Hydrodynamics, Wurster, troubleshooting, and PCTSWurster.
Solution

Analyze the hydrodynamics for the two batch sizes to examine the fluidization states.
Analysis of the Process prior the Batch Size Increase
For the analysis, assess the hydrodynamics of the process before the batch size increase (345 kg) using the hydrodynamics simulator as shown below:
Analysis of the Process after the Batch Size Increase
Update the batch size information in the Process Efficiency window, and enter the pressure drop for the new process in the Driver for Wurster window for the hydrodynamics analysis.  The change in batch size caused more air to flow through the spout and less through the annulus.  This air flow change in the annulus changed the degree of fluidization in the annulus from fully fluidized to partially fluidized as indicated by U/Umf.
Conclusions
Based on the hydrodynamics analysis, the root cause of the agglomeration is likely due to the change in the degree of fluidization in the annulus brought on by the batch size increase.