Explosion Prevention and Protection in the Pharmaceutical Industry: Fluid Bed Dryers

 | 

Date:

 | 

,

 | 

Reading Time: 6 minutos
Fluid bed dryer at a pharmaceutical plant

In some of its processes, the pharmaceutical industry uses, handles or produces substances considered combustible or flammable, in the form of dust or liquid. One of the main processes in this industry is the granulation, coating and drying of powders, carried out in equipment called a fluidized bed dryer (also known as a fluid bed granulator).

How a fluid bed dryer works in the pharmaceutical industry

A fluid bed dryer consists of a main chamber where the powder is loaded, usually by pneumatic conveying.

Diagram of how a fluid bed dryer works

The product is fluidized by an incoming airflow that is directed through a perforated plate.

Granulation takes place by spraying a binder through a nozzle onto the fluidized material. This increases the initial particle size, forming what are known as “granules.”

The process air is hot and at high pressure, which promotes both the formation of the granules and their subsequent drying.

Coating is carried out in a similar way, using different spray nozzles.

The main chamber also has cartridges at the top that retain the product and then pulse it back down with compressed air.

The equipment usually also includes the following systems:

  • Air injection and heating system
  • Dust collection system, usually a cartridge dust collector
  • Product loading and discharge system
Fluid bed dryers in the pharmaceutical industry

Explosion risk in fluid bed dryers

The use of combustible powders in this equipment is one of the main explosion hazards in the pharmaceutical industry.

That is why a proper explosion risk assessment should be one of the main goals when establishing an effective strategy against this hazard.

Explosion risk assessment in fluid bed dryers

To properly assess the explosion risk, we can rely on some of the most widely used and recognized international standards, including:

  • VDI 2263, Part 5: Dust fires and dust explosions: Hazards – assessment – protective measures; Explosion protection in fluid bed dryers (2014)
  • NFPA 654: Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids

The assessment should start by analyzing the frequency with which explosive atmospheres form, which leads to the hazardous area classification.

Hazardous area classification in fluid bed dryers

An example classification for a standard fluid bed dryer is as follows:

Zone 20 (explosive atmosphere present continuously or frequently)

  • Inside the drying chamber (including the retention cartridges)
  • Inside the final product discharge hopper
  • Inside the dirty side of the cartridge dust collector

Zone 21 (explosive atmosphere likely to occur occasionally)

  • Inside the pneumatic conveying ducts for loading and discharge

Zone 22 (explosive atmosphere unlikely)

  • Outside area around the hopper (approx. 3.3 ft / 1 m)
  • Clean side of the dust collector
  • Clean air outlet duct
  • System fan

Potential ignition sources

The assessment must consider possible effective ignition sources:

  • Static electricity due to loss of grounding
  • Hot particles and spontaneous combustion due to excessive drying air temperature
  • Electrical sparks or hot surfaces from equipment not assessed under Directive 2014/34/EU (non-ATEX-certified equipment)

Recommended prevention and/or protection measures

Given the almost continuous presence of explosive atmospheres and the variety of ignition sources that can become effective, the likelihood of an explosion in a fluid bed dryer is high, and its consequences can be catastrophic for facilities and people.

That is why both explosion prevention measures and protection measures must be implemented on this equipment.

1. Explosion prevention measures for fluid bed dryers

As Directive 1999/92/EC states, the priority of an effective explosion risk strategy is to prevent the explosion from occurring, either by preventing an explosive atmosphere from forming or, if that is not possible, by preventing an ignition source. For this type of equipment, the following prevention measures can be implemented:

Preventing explosive atmospheres

  • Dust collection system
  • Regular removal of internal dust layers
  • When organic solvents are used:
    • Install flammable gas detectors
    • Located on the clean side of the dust collector
    • Interlocked with process shutdown

Preventing ignition sources

  • Equipment design that prevents dust buildup inside
  • Drying air temperature control and monitoring
  • For ignition-sensitive dust (MIE < 3 mJ):
    • Install a CO detector in the drying chamber
  • Proper grounding and bonding of all systems
    • Including antistatic pneumatic conveying hoses
  • Use of electrical equipment assessed under Directive 2014/34/EU and suitable for the zone

2. Explosion protection measures for fluid bed dryers

If the risk assessment shows that the explosion risk cannot be eliminated through prevention measures alone, explosion protection measures must be implemented.

These measures protect both facilities and workers from the consequences of an explosion.

For this type of equipment, the following can be considered:

Explosion-resistant construction

  • Dryer designed to withstand the explosion pressure (up to 145 psig / 10 bar)

Explosion venting systems

  • Explosion vent panels certified to ATEX Directive 2014/34/EU (mandatory in the European Union)
  • Vent area sized per recognized standards:
    • EN 14491:2012 (Dust explosion venting protective systems)
    • NFPA 68 (Standard on Explosion Protection by Deflagration Venting)
  • For equipment installed indoors:

Explosion vent panels on cartridge dust collectors are one of the most common solutions because of their:

  • Ease of installation
  • High adaptability to the equipment
  • Low maintenance requirements

However, they cannot always be used, and in those cases other protection systems are required.

Explosion isolation systems

  • Explosion isolation valves certified as protective systems to ATEX Directive 2014/34/EU
  • Installed on the dryer’s air inlet and outlet ducts

Their purpose is to prevent a potential explosion from propagating to other equipment or areas of the facility.

Explosion isolation valves installed on a fluid bed dryer

Design and implementation considerations

Protection systems must be implemented:

  • Following the recommendations of recognized standards or guidelines (such as EN 14491 or NFPA 68)
  • Respecting the intended use stated in the equipment certification

3. Maintenance of prevention and protection systems

Simply installing explosion prevention and/or protection systems does not ensure complete, effective protection unless the systems are properly maintained.

In-house maintenance staff can maintain simple systems such as explosion vent panels or flameless venting systems.

However, more complex systems such as explosion isolation valves must be maintained by a certified company specifically trained for the task.

Maintenance must be performed at the intervals specified by the manufacturer in the service manual, without exception.

In addition to proper maintenance, keeping critical spare parts on hand is recommended to reduce the impact on production if one of these systems is activated, and to ensure safe conditions when operations resume.

Conclusion

Fluid bed dryers are key equipment in the pharmaceutical industry, but they carry a significant explosion risk because they handle combustible dust under favorable conditions for ignition.

A proper risk assessment, together with prevention and protection measures, is essential to keep facilities and people safe.