A: Jack Osborn, Airdusco, says:
Until recently, there have been few alternatives to using a dust collector for the separation of dust(s) from an airstream used in dust collection or similar operations. However, the marketplace has changed, and cyclone separators have become a viable alternative.
Cyclone separators have been used to separate materials from airstreams for many decades in dust collection, pneumatic conveying, and centralized vacuum cleaning systems. However, with the enactment of the Clean Air Act of 1970 (1970 CAA), which resulted in the National Ambient Air Quality Standards (NAAQS) designed to protect public health and regulate hazardous air pollutant emissions, the cyclone types available at that time couldn’t achieve the emission control levels required to meet or exceed the limits imposed by federal and state EPA requirements. Dust collectors were the only real choice for dry dust collection. In the last decade, however, a new class of ultrahigh-efficiency cyclones has emerged, driven by economic and market factors.
Previously, there were three basic cyclone classes: low-efficiency, medium-efficiency, and high-efficiency. A low-efficiency cyclone has a large diameter and is used to collect paper, wood chips, and large particles from the airstream. A medium-efficiency cyclone has a much smaller diameter and separates large particles and finer particles or dust(s) from the airstream. A high-efficiency cyclone typically has an even smaller diameter and is designed to separate particles as small as 10 microns (in general) from the airstream. The progression from low-efficiency to high-efficiency cyclones is achieved mainly by the cyclone’s shape and the differential pressure (energy) required for operation. However, for particles below 10 microns, a high-efficiency cyclone isn’t a viable solution. Since most dust(s) involved in dust collection have a significant percentage of material (by volume or weight) below 10 microns, a cyclone isn’t an acceptable alternative for achieving the emission levels required by the EPA and state regulatory authorities.
True high-efficiency cyclones were developed many decades ago, and until recently, were the ultimate in cyclonic efficiency and design. However, new ultrahigh-efficiency cyclones operate in a class above, essentially achieving the same level of emissions control (if not better) as typical bag- or even cartridge-type dust collectors. In multiple applications, this means emissions levels well below 0.01 grains per cubic foot, which is below the maximum allowed emissions level in many states. In recent applications, levels in the 0.001 grains-per-cubic-foot range have been warranted as achievable by various manufacturers.
This doesn’t mean an ultrahigh-efficiency cyclone is applicable to all dust collection types and pneumatic conveying applications. Whether this is the most effective choice depends on your material’s composition. Some material characteristics present problems for effective cyclonic separation and can’t use this approach. However, the suppliers providing these cyclones can accept samples and usually indicate whether a cyclone separator is feasible. Often, material testing is required to determine what cyclone efficiency level is needed.
Cyclones inherently are much simpler to maintain than dust collectors and have the advantage of having no moving parts. Cyclones are also designed to operate at a minimum airflow volume and differential pressure (energy) level. However, for ultrahigh-efficiency cyclone units, this energy level can be well over 10 inches water gauge, which is considerably more than the typical maximum of 6 inches water gauge for dust collectors. This means additional horsepower is necessary.
The cost for an ultrahigh-efficiency cyclone unit can vary and typically is more than a dust collector, but this cyclone type can pay for itself in its simplicity of operation and the minimal maintenance required. If another alternative is needed to meet your needs, using an ultrahigh-efficiency cyclone may be a viable choice.
Don’t miss Jack Osborn’s upcoming webinar “Dust collection hood design for engineers and nonengineers.” To learn more and register, click here.
Jack Osborn is the engineering manager at Airdusco.