Compared to standard air conditioning systems, exhaust systems play a more significant role in purification air conditioning systems. In such systems, treating fresh air requires more energy, and an increase in fresh air volume adds to the filter's load, reducing its lifespan.
Moreover, due to the high airtightness of cleanrooms and the more complex and obstructed evacuation pathways compared to standard workshops, exhaust safety measures for detoxification, explosion prevention, and fire protection become more stringent. A higher exhaust volume means more fresh air intake is required, increasing both the initial system investment and operational costs.
For pharmaceutical industries, it is also crucial to prevent exhaust air from dispersing highly allergenic or toxic substances into the atmosphere. Additionally, it is necessary to recover active pharmaceutical ingredients (APIs) carried in the exhaust air.
Local Exhaust vs. General Ventilation
The most effective method to prevent the spread of dust or other harmful substances produced during manufacturing is to directly capture them at their source, purify them as required, and discharge them outdoors. This approach is called local exhaust. Its advantages include minimal air volume requirements and high efficiency, making it a preferred method in design. To enhance capture efficiency, local exhaust hoods designed to integrate with the production equipment should be installed near pollution sources.
For example, dust collection hoods made of transparent resin often cover tablet presses and capsule filling machines, encapsulating the entire machine. In contrast, feeding parts of mixers and sifters frequently use external dust collection hoods. Variations include upward-suction hoods, side-suction hoods, chamber-style hoods, and container-style hoods.
The suction port of the exhaust hood should be as close as possible to the pollution source. This proximity is critical because airflow patterns at the suction port resemble converging flows, where velocity decreases rapidly, limiting the effective range. Greater distances drastically reduce efficiency, requiring increased suction velocity and volume, which significantly raises energy consumption.
Excessive suction velocity, however, can lead to undesirable consequences in pharmaceutical industries, such as product loss, increased energy consumption, and higher loads on terminal separation equipment. Therefore, when determining exhaust air volume, blindly increasing safety factors should be avoided.
If local exhaust is not feasible due to production conditions or if pollutants still exceed permissible concentrations after its application, general ventilation should be considered. Also known as dilution ventilation, it uses clean air to dilute indoor pollutant concentrations and continuously exhausts contaminated air outdoors, maintaining pollutant levels within allowable limits.
Key Considerations for Pharmaceutical Exhaust Systems
1. Anti-Backflow Measures
Anti-backflow measures prevent outdoor air from entering cleanrooms when the air conditioning system is not in operation. Common methods include installing medium-efficiency filters or check valves in exhaust pathways, or both. Most pharmaceutical exhaust systems already pass exhaust air through separation devices like cyclone dust collectors and bag filters to recover pharmaceutical dust and prevent contamination. For highly allergenic drugs like penicillin, high-efficiency air filters (HEPA) are installed at the exhaust terminal, further preventing backflow. In some cases, water-seal measures are adopted to neutralize or decompose harmful gases in exhaust air, effectively addressing backflow and pollution simultaneously.
2. Material and Equipment Selection
The material and coating of ductwork, dampers, and check valves in cleanroom exhaust systems must suit the nature of the harmful substances being removed and the surrounding air conditions. For corrosive gases, plastic ducts may be used. Fire dampers must be installed where exhaust ducts pass through firewalls.
Local exhaust systems handling flammable or explosive substances should include appropriate fire and explosion prevention measures, such as explosion-proof fans.
It is crucial to maintain adequate horizontal and vertical distances between the exhaust outlets and the fresh air intakes of the air conditioning system. For highly allergenic drugs, steroidal medications, or highly active and toxic substances, HEPA filters should be installed at the exhaust outlet to minimize contamination risks.
3. Airflow Design for Cleanrooms
As the effective range of exhaust outlets is limited, indoor airflow is primarily determined by supply air. The spatial arrangement and relative positioning of supply outlets, exhaust outlets, and pollution sources are critical to ensuring efficient air distribution and pollutant removal.
By addressing these considerations, the pharmaceutical industry's exhaust systems can achieve safe, efficient, and environmentally responsible operations while maintaining the integrity of cleanroom environments.
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