Dust collection is the primary means of controlling combustible dusts, but when setting up a new system or installing additional elements to comply with OSHA or NFPA standards, it is important to choose the right dust collection solution for the location. While there is a great deal of variables to choosing the right dust collection system, choosing between wet and dry dust collection is one of the first steps to choosing your system. The two technologies offer the same services with some very specific differences in application, which makes them suitable for different types of dust and collection.

The two main technologies are dry media dust collectors also known as air separators and wet scrubbers or wet dust collectors. While there are many types and subtypes, especially for dry dust collection, these two are the primary in the industry because they offer the most efficiency.

Dry Dust Collection

The NFPA defines dry dust collectors suitable for controlling combustible dusts as cyclone and media collectors. These include baghouses, cartridge collectors, and similar. Air separators collect dust through a baffled inlet which forces air through a filter media, where the dust is collected. Dust is then dislodged from the filters into a hopper or bag, where it is moved into storage and must be periodically emptied.

The efficiency of a dry dust collection system relies on the filter and filter media, the air pressure, the particulate size, and the type of combustible dust.

Wet Scrubbers

Wet scrubbers or wet dust collectors include venturi scrubbers and cyclonic or centrifugal scrubbers that use a combination of water and air pressure to 'scrub' dust from the air. Scrubbers use a variety of technologies to drive dust through a water stream or spray, which then forces the dust to the bottom of tank, where it is separated by gravity and the dust can be removed into a storage container. In the case of a cyclonic system, the water flow will drive dust to the bottom, where it will settle to be cleaned.

Wet dust collection is very efficient, and can capture very small dust particles.

Choosing a Dust Collector

In some cases, NFPA regulations will force you to choose one type of dust collector or another. For example, metal industries working with certain combustible metal dusts such as niobium and titanium are required to use wet dust collection to prevent explosions. In addition, for particles of less than 10 microns, it is recommended to use a venturi wet dust collector. However, wet dust collection does not work for every type of dust, and it is often not the most efficient option.

Wet dust is ideal for light dust collection, sticky dust collection, and for the collection of highly combustible dusts, such as those with a Kst of 300 or higher or ST3 Dust Explosion Class. Dry dust collectors present a higher risk, because they store dry dusts in areas that can build up electrostatic energy, which means that they do require more ancillary explosion prevention to meet NFPA standards.

However, dry dust collection is typically more affordable, and may be more efficient in the case of medium to large particulate, and in the case of low-combustible to medium combustible dusts such as wood, aluminum, or food dusts.

For most dry dust collection is the best choice unless your DHA (Dust Hazards Analysis) indicates that you have sticky, highly combustible, or metal dusts that require wet scrubbing.