Master Dust Control to Protect Your Tablet Compression Process

Dust Extraction

Controlling dust is a challenging aspect of tablet compression.? Poor press cleanliness can pose health hazards, shorten life of press components, increase down-time, cause tablet defects, tool damage, and binding.? In short, it is a big deal.? To achieve proper dust collection, considerations include sizing the dust collection unit & associated ductwork, ensuring safety, following maintenance protocols, monitoring the process, and making proper adjustments.

Sizing a dust collection unit and the corresponding ductwork is critical to ensure both adequate Water lift and CFM.? Water-lift measures the suction power in units of column inches of water while? CFM measures airflow in cubic feet per minute.? Water-lift and airflow requirements depend on press speed, size, upper punch penetration setting, particle size, and particle density. ??Higher press speeds will increase CFM requirements.? This means that the operational requirements will vary and need monitoring and adjustment; the dust collection unit must be sized to both your machine and able to handle your full range of products.? Another metric to consider is the Airflow per filter area ratio (Airflow in M^3/m^2 h per filter area in m^2).? Lower ratios are better as they reduce static pressure and increase filter life, reducing energy costs.?? ?

Dust extraction nozzles are commonly placed adjacent to pressure rolls and along the die table at point of upper punch entry.? To assist dust extraction, a few presses (such as the Natoli NP400) feature an air blast through the turret exiting above the lower punch scraper seal.? This air blast helps propel dust into the dust extraction nozzle.? Bilayer tablet production requires additional nozzles to prevent cross-contamination.? Typically, these are placed on the feeder at tablet take-off or the scraper.? Other tablet presses without feeder seals may require a nozzle prior to the feed frame. ??

Negative pressure within the compression zone is helpful as it keeps dust from escaping into the room.? Negative pressure can be required for hazardous API in a containment application.? Too much negative pressure can pose an issue preventing tablets from discharging properly (particularly minitablets).

HEPA after-filter systems can provide backup protection for the dust collector and allow release of filtered air directly outdoors

Filtration media must be sized to match the particle sizes of your formulation.? Fine dry dusts typically need higher MERV values.

Cautions:

In cases where a central house dust extraction system is employed, the volume of air being pulled can be affected by the number of machines connected at any given time.

Reverse pulse cleaning systems of the dust collector filter cartridge can overcome a negative pressure environment, violating containment if set too high.

OEL (Occupational Exposure Limit) is the maximum air concentration (average micrograms per cubic meter of air) to which a worker can be safely exposed for an 8-hour shift without potentially suffering adverse health effects.? For hazardous API (active pharmaceutical ingredient), a risk-based exposure evaluation should be performed to determine the methods for proper control.

Locate the dust collector outside the GMP space, if possible, to reduce fire and explosion risks, and reduce regulatory demands.? Pharmaceutical manufacturers deal with dust that has higher Kst (rate of pressure rise in event of an explosion) and Pmax (maximum pressure that would be created if the dust explodes) values than many other industries.? Kst values up to 200 are rated class 1 (weak explosion), values 200 to 300 indicate a potential for a strong explosion, and values above 300 are rated class 3 which is a very strong explosion.

Duct-work must be carefully sized with appropriate CFM to prevent dust build-up and may require additional protection against the possibility of explosion.? Consult with a professional engineer for compliance with U.S. NFPA (National Fire Protection Association) or EU ATEX (Atmospheres Explosibles) requirements for explosion protection.

Dust Collector Maintenance:? The most frequent problem that causes poor press cleanliness is lack of maintenance.? Clean filters regularly and empty collection vessels as needed.? Periodic checking of ductwork is important to verify powder has not collected in the ducts.

Monitoring air pressure is essential to understanding how to properly adjust airflow.? Sensors can be placed either in the compression zone or in the ductwork.? Note that too much suction may cause tablet weight loss as powder pulls from the die before compaction occurs and yield loss.? Accumulation of powder on the die table or other press components indicates insufficient airflow.?

For further information on dust collection units, sizing units, ductwork, maintenance, and operation please contact us at Natoli Engineering.

TDM 9/10/2024