Are you looking for dust control solutions for fine or ultrafine dust? Fine and ultrafine dust are produced by many industries, including plastics, food processing, chemical manufacturing, pharmaceutical and nutraceutical production, and woodworking. If your processes create fine dust or ultrafine particulate, read on to learn the best way to control it.
What Is Fine or Ultrafine Dust? Understanding Particulate Sizing
Fine dust particles are produced by many processes and industrial applications, including plastic production, woodworking, welding and other thermal processes, plasma and laser or fiber laser cutting, and handling and processing of fine powders for the food processing, pharmaceutical/nutraceutical and chemical industries. Working with graphite and advanced materials (such as composites made with carbon nanotubes) can also produce very fine, microscopic particulate. Ultrafine particulate is also produced when burning hydrocarbons or running gas-powered machinery, engines or vehicles.
“Fine dust” does not have a single definition but is generally described as particulate matter small and light enough to stay suspended in the air. Fine dust can remain airborne for a long time; ultrafine particulates can become aerosolized (mixed with air) and remain in the air indefinitely.
The most important legal definitions of fine dust come from the U.S. Environmental Protection Agency (EPA). The EPA categorizes fine and ultrafine dust according to its diameter. Airborne dust is known as particulate matter (PM). EPA regulates two classes of particulate matter.
- PM10 consists of particles <10 μm (microns) in diameter.
- 5 consists of particles <2.5 μm (microns) in diameter.
The Problems with Fine and Ultrafine Dust
Fine and ultrafine dust create challenges for housekeeping, human health and the environment.
- Fine dust particles can remain airborne for a long time and travel far away from their emission source. This makes them difficult to capture and contain once they escape into the wider facility or the atmosphere.
- Both PM10 and PM2.5 are respirable. While both can have significant human health impacts, smaller particulate (PM 2.5) poses special concerns because it can be inhaled deep into the lungs, where it can become lodged in lung tissue. The smallest particles may even cross from the lungs into the bloodstream. From there, they can be carried throughout the body.
- Airborne particulate in the atmosphere is both a public health and environmental concern. It can travel far from the emission source. From a public health standpoint, atmospheric PM is associated with higher community rates of asthma, COPD, lung cancer, heart disease and other health problems. Airborne particulate is also a major environmental pollutant and has been implicated in climate change. For these reasons, PM10 and PM2.5 are regulated under the EPA’s Clean Air Act. Large PM emitters, such as mining and mineral processing operations, may have to shut down production if they exceed emission caps for silica and other PM.
- Fine dust may create a combustion risk. Many fine dusts are combustible (including weld fume, carbon black, flour and grain dust, food processing dust, metal dust, paper dust and many pharmaceutical dusts). Fine dust is more likely to stay airborne than coarser, heavier dust, allowing it to remain dispersed in the air as a dust cloud. When this dust cloud is confined in an enclosed space (such as in a silo or conveyor system), pressure builds up as particles in the dust cloud rub against each other. Under these conditions, all it takes is an ignition source to generate an explosion. High-static materials such as plastic fines have a high potential for self-ignition when allowed to accumulate in an enclosed space. (Read more about conditions required for a dust explosion.)
- Fine and ultrafine dust also create challenges for dust collection and control. Standard filtration systems may not have the filtration efficiency required to collect ultrafine dust particles.
Considerations in Dust Collector Design for Fine and Ultrafine Dust
Dust collection for fine and ultrafine dust requires a specialized solution. There are several considerations to keep in mind when selecting an industrial dust collector for fine and ultrafine dust.
Filter selection is one of the most important elements of dust collection system design for fine or ultrafine dust. Filters are rated according to their filtration efficiency for particles of different sizes. The MERV (Minimum Efficiency Reporting Value) scale is used to classify filters.
- Cartridge-style dust collectors using pleated filter media are highly efficient at capturing fine dust.
- For PM10 dust, look for filters with a MERV rating of 12 or higher. A MERV 12 filter has 90% efficiency for particulate of 3 to 10 microns and 80-89.9% efficiency for particulate of 0 – 3.0 microns.
- For PM2.5 dust, a MERV 14 filter will capture 90%+ of particulate 1 to 3 microns and 75%-84% of ultrafine particulate 0.3 to 1.0 microns.
- A MERV 16 filter is rated for greater than 75% efficiency for ultrafine particulate 0.3 – 1.0 microns. This may be enough for most applications.
- Depending on your dust, you may require filter media that is anti-static, oleophobic or fire retardant. For example, plastic fines may require an anti-static filter media (typically aluminized or carbon-impregnated) due to their high level of static charge. A PTFE-coated cartridge filter provides superior particulate release and a high level of filtration efficiency. If your dust is hygroscopic (absorbs moisture from the air) or sticky, an oleophobic coating will allow dust to shed from the filters more easily.
If cleanroom conditions are required (for example, for food processing or pharmaceutical/nutraceutical production and packaging), additional filtration may be needed after air passes through the cartridge filters. Look for a dust collector that can be fitted with after-filters for collection of ultrafine dust that escapes the cartridge filters.
- A HEPA after-filter has a minimum filtration efficiency rating of 99.97% for particles 0.3 microns or larger. This makes HEPA filtration ideal for collection of ultrafine particulate in the PM2.5 or smaller range.
- Activated carbon after-filters are used to collect gases, mists and aerosols. The activated carbon can be impregnated with different substances that react with specific target molecules to improve capture and adsorption. Activated carbon is useful when ultrafine dust is combined with odors or gases that pass through standard cartridge filter media.
CFM and System Design
An industrial dust collection system for fine or ultrafine particulate must be designed with appropriate airflow for efficient capture and transport through the ductwork.
- Wherever possible, processes should be enclosed or confined to limit the ability of fine dust to propagate through the facility.
- CFM requirements depend on the hood design, size of ductwork and other factors. Lower duct velocities can be used for fine dust, but ductwork will need to be designed accordingly. Air-to-cloth ratio for ultrafine dust is generally 1:1 or below.
- Negative pressure may be used to prevent fine dust from escaping the enclosure. In a negative pressure system, air pressure inside the enclosure is kept slightly lower than atmospheric pressure. This means air wants to come into the enclosure rather than flow to the outside.
- Make sure ductwork and dust collector joins are well-sealed to prevent fine dust from escaping the ductwork or cabinet.
Fine dust can become deeply embedded in filter media, making it difficult to pulse out. A PFTE-coated filter will enable more efficient shedding. In addition, look for:
- Vertical Filters: Cartridge-style industrial dust collectors should have filters oriented vertically to allow dust to fall off the filter media and into the collection bin.
- Pulsing system: High-quality filters should be paired with an advanced pulsing system to pulse more dust off of the filters. Look for engineered pulse nozzles that provide even pulsing down the entire length of the filter for efficient filter cleaning. Effective filter pulsing will extend filter life and cut down on maintenance. Automated pulsing systems that turn on in response to filter loading (as measured by pressure drop across the filters) cut down on energy use and maximize efficiency.
Combustion and Fire Safety
Many types of fine and ultrafine dust are also explosive, including food processing dust (especially sugars, starches and flours), plastic fines, carbon black and weld fumes. When collecting combustible dust, the dust collector must be equipped with explosion safety features that comply with OSHA and NFPA safety standards. A deflagration system limits damage if a combustion event occurs inside the dust collector. Dust collector explosion safety elements may include:
- Heavier doors and side panels.
- Explosion vent panels, which provide pressure relief by blowing out to safely direct the energy of an explosion when pressure inside the collector rises to an unsafe level. These panels must be carefully placed to direct explosive energy away from people.
- A rotary airlock between the collector and the collection bin or hopper. This prevents dust in the hopper from escaping back into the dust collector chamber and providing additional fuel for the explosion.
- An isolation valve to prevent a pressure wave from propagating back into the facility and triggering a dangerous secondary explosion.
If space is a concern, look for features that will help you cut down on the footprint of the industrial dust collector.
- Advanced filter design: The filters are the heart of a dust collection system. Advanced filters (with more usable square feet of media) can reduce the floorspace requirements for your dust collector by reducing the number of cartridges required per CFM, allowing for a smaller overall footprint.
- Modular construction: A modular dust collector can be sized more precisely for your application and designed to fit within your space constraints.
- Indoor/outdoor suitability: Placing the dust collector outside provides maximum space savings for your facility. If that’s the plan, make sure the dust collector is built to withstand the elements. Look for heavy-duty steel construction with powder coating both inside and out.
Designing a Dust Collection System for Fine and Ultrafine Dust
A dust collection system for fine and ultrafine dust includes not only the industrial dust collector itself but also the ductwork, hoods and enclosures, and ventilation and makeup air systems. The entire system must be designed according to ACGIH recommended practices for collection of ultrafine particulate. An industrial ventilation engineer will look at your processes, facility layout, dust type and volume, and clean air goals when designing your dust collection system.
Our go-to dust collector for fine and ultrafine dust collection is RoboVent Senturion. Senturion features:
- Advanced cartridge filters with more usable filter media per cartridge, proving high filtration efficiency and the smallest footprint per CFM in the industry
- Cartridge filters up to MERV 16 (near HEPA filtration efficiency)
- Optional HEPA or activated carbon after-filters
- An advanced pulsing system for ultimate filter protection
- Modular design for maximum flexibility and reduced project costs
- Heavy-duty 7- and 11-gauge steel construction with powder coating inside and out
- High efficiency and energy savings
Learn more about how we design dust control solutions for fine and ultrafine dust across industries:
Looking for a dust collection solution for fine or ultrafine dust? Talk to a RoboVent solutions specialist today.