Process and equipment modifications
Modifications to the blender-to-bin transfer step.
The blender-to-bin transfer step for the first demonstration batch consisted of an uncontrolled free fall from the blender
into the bin, likely resulting in fluidization and dusting segregation. To reduce the likelihood of segregation during the
blender-to-bin transfer step for the second demonstration batch, a flexible sleeve, or sock, was designed to control and reduce
the transfer rate from the blender and minimize the free fall of the material during transfer. The customized sock had a conical
section at the top that converged from the larger V-blender outlet (8-in. diameter) to a smaller diameter (i.e., 4 in.) to
provide greater control of the material and reduce the free fall of material into the bin. In addition, the blender valve
was throttled during discharge (as high as 10% open) so that the material could deaerate within the sock before the sock was
lifted from the top surface of the material to transfer it into the bin. Based on the stratified blend samples collected within
the bin after filling (RSD = 1.0%, n = 10 samples), these process modifications were successful in minimizing segregation during this transfer step.
In addition to modifying the process equipment used for the blender-to-bin transfer step, the cone-in-cone bin was expected
to provide mass flow and was used for the second demonstration batch. Visual observations of the material discharge from the
bin during the second demonstration batch confirmed mass-flow discharge, as predicted by the bench-scale flow-properties tests
Modifications during bin-to-press transfer.
Segregation also could occur during the bin-to-press transfer step and contribute to the CU trending observed in the first
demonstration batch. The transfer chute used for the first demonstration batch consisted of large-diameter (i.e., 8-in.) tubing
without any valves to reduce the free fall of material or venting to reduce the air counterflow up through the powder as the
chute is filled. Since air counterflow during free fall as the chute is filled can result in fluidization and dusting segregation,
thus carrying drug-rich fines back up into the bin above, a new transfer chute design was used for the second demonstration
batch. The new transfer chute consisted of the following parts:
- A mass-flow conical reducer at the top of the chute and small-diameter (i.e., 4-in.) tubing to reduce the displaced air and
counterflow during filling
- Two butterfly valves to reduce the free fall height during filling
- A passive filter vent to allow displaced air during filling to exit the chute rather than conveying back up through the blend
and causing segregation.
The modifications to the bin and transfer chute design from the first demonstration batch to the second demonstration batch
are shown in Figure 3.
Figure 3: Tote-bin and transfer-chute modifications from (a) demonstration batch #1 in a bin-to-press feed system and (b)
demonstration batch #2 in a modified bin-to-press feed system after process and equipment modifications. (ALL FIGURES ARE
COURTESY OF THE AUTHORS)