Dust collectors

Dust collectors are used in many processes to either recover valuable granular solid or powder from process streams or to remove granular solid pollutants from exhaust gases prior to venting to the atmosphere.  Dust collection is an online process for collecting any process-generated dust from the source point on a continuous basis.  Dust collectors may be of single unit construction, or a collection of devices used to separate particulate matter from the process air.  They are often used as an air pollution control device to maintain or improve air quality.  Mist collectors remove particulate matter in the form of fine liquid droplets from the air.  They are often used for the collection of metal working fluids, and coolant or oil mists.  Mist collectors are often used to improve or maintain the quality of air in the workplace environment.  Fume and smoke collectors are used to remove sub micron size particulate from the air.  They effectively reduce or eliminate particulate matter and gas streams from many industrial processes such as welding, rubber and plastic processing, high speed machining with coolants, tempering, and quenching.

Dust collectors can be configured into one of five common types, ambient units, collection booths, downdraft tables, source collector or portable units, and stationary units.  Ambient units are free-hanging systems for use when applications limit the use of source-capture arms or ductwork.  Collector booths require no ductwork, and allow the worker greater freedom of movement.  They are often portable.  A downdraft table is a self-contained portable filtration system that removes harmful particulates and returns filtered air back into the facility with no external ventilation required.  Portable units are for collecting dust, mist, fumes, or smoke at the source.  An example of a stationary collector is a baghouse.

Important parameters in specifying dust collectors include airflow the velocity of the air stream created by the vacuum producer; system power, the power of the system motor, usually specified in horsepower; storage capacity for dust and particles, and minimum particle size filtered by the unit.

Systems for fine removal may only contain a single filtration system (such as a filter bag or cartridge).  However, most units utilize a primary and secondary separation / filtration system.  Furthermore, some units may have third and fourth stage filtration.  All separation and filtration systems used within the unit should be specified.  A baghouse is an air pollution abatement device used to trap particulate by filtering gas streams through large fabric bags.  They are typically made of glass fibers or fabric.  A cyclone separator is an apparatus for the separation, by centrifugal means, of fine particles suspended in air or gas.  Electrostatic precipitators are a type of air cleaner, which charges particles of dust by passing dust-laden air through a strong (50-100 kV) electrostatic field. This causes the particles to be attracted to oppositely charged plates so that they can be removed from the air stream.  An impinger system is a device in which particles are removed by impacting the aerosol particles into a liquid.  Modular media type units combine a variety of specific filter modules in one unit.  These systems can provide solutions to many air contaminant problems. A typical system incorporates a series of disposable or cleanable pre-filters, a disposable vee-bag or cartridge filter. HEPA or carbon final filter modules can also be added. Various models are available, including free-hanging or ducted installations, vertical or horizontal mounting, and fixed or portable configurations.  Filter cartridges are made out of a variety of synthetic fibers and are capable of collecting sub-micronic particles without creating an excessive pressure drop in the system.  Filter cartridges require periodic cleaning.  A wet scrubber, or Venturi scrubber, is similar to a cyclone but it has an orifice unit that sprays water into the vortex in the cyclone section, collecting all of the dust in a slurry system. The water media can be recirculated and reused to continue to filter the air. Eventually the solids must be removed from the water stream and disposed of.

The dust-collector on the picture is a product which includes cyclone separators, self-contained unit collectors, after-filters, baghouses, filter collectors, mist collectors and exhausters. Through these state of the art units, clean air can then be recirculated back into the plant, or vented to the outdoors.

The basic part is a cyclone type dust collector, which pulls contaminated air into the unit at high velocity, creating a vortex or cyclone action. Centrifugal forces separate the particles from the air stream, and they drop via gravity into a drum, hopper, or dumpster. Clean filtered air can then be recirculated back into the plant, or vented to the outdoors. The cyclone unit is normally the primary separator in a 2-stage system which includes an after-filter attached to the cyclone separator for removal of sub-micron particles as small as 0.3 microns.