Wet Scrubbers for Air Cleaning

Canadian Air Systems Co. is a designer and manufacturer of industrial air scrubbers for air cleaning. Wet air scrubbers are available in many designs utilizing a number of principles and featuring wide variation in effectiveness, initial cost, operating and maintenance expense, space, arrangements and material of construction.

Canadian Air Systems Co. offers the following major Air Scrubber types:

SPRAY TOWERS / IMPINGEMENT SCRUBBERS

Spray towers and impingement scrubbers are available in different arrangements. The gas stream may be subjected to a single spray or a series of sprays, or the gas may be forced ti impigne on a series of irrigated baffles. Except for packed towers, these types of gas scrubbers have relatively low particulate removal efficiency, that can be improved by adding high-pressure sprays.

CENTRIFUGAL AIR SCRUBBERS

These scrubbers are characterized by a tangential entry of the gas stream into the collector. They are classed with medium energy wet scrubbers. The Canadian Air Systems Impingement Gas Scrubber is a typical example of centrifugal-type wet dust collector.

ORIFICE TYPE WET SCRUBBERS

In the orifice type wet dust collectors the gas stream is made to impinge on the surface of the scrubbing liquid and is forced through constructions where the gas velocity is increased and where the liquid-gaseous-particulate interaction happens. Water usage in the orifice gas scrubber is limited to evaporation loss and removal of collected pollutants.

VENTURI SCRUBBER

A high-energy venturi scrubber passes the gas through a venturi shaped orifice where the gas is accelerated to 12,000 fpm or more. Depending on the design, the scrubbing liquid is added at, or ahead of, the throat. The rapid acceleration of the gas shears the liquid into a fine mist, increasing the chance of liquid-particle impaction. In typical applications, the pressure drop for gases across a venturi is higher than for other types of scrubber. Water circulation is also higher; thus venturi air scrubbers use water reclamation systems.

ELECTROSTATIC AIR SCRUBBERS

Several gas cleaning devices, engineered by Canadian Air Systems Co., combine electrical charging of particulate matter with wet scrubbing. Electrostatic augmentation enhances fine particle control by causing an electrical attraction between the particles and the liquid droplets. Compared to venturi scrubbers, alectrostatically augmented air scrubbers remove particles smaller than 1 micron at a much lower pressure drop.

There are three generic designs for electrostatic augmentation air scrubbing:

- unipolar charged aerosols pass through a contact chamber containing randomly oriented packing elements of dielectric material;
- unipolar charged aerosols pass through a low-energy venturi air scrubber;
- unipolar charged aerosols pass into a spray chamber where they are attracted to oppositely charged liquid droplet.

Collection efficiencies of up to 90% can be achieved in a single particle charging and collecting stage, depending on the mass loading of fine particles and the superficial velocity of gases in the collector. Higher collection efficienciescan be obtained by using two or more stages. Removal efficiency of gaseous pollutants depends on the mass transfer and absorption design of the scrubber section.

In most applications of electrostatically uagmented scrubbers, the dirty gas stream is quenched by adiabatic cooling with liquid sprays; thus, it contains a large amount of water vapor that wets the particulate contaminants. This moisture provides a dominant influence on particle adhesion and the electrical resistivity of deposits within the collector Electrical equipment for particle charging is similat to wet precipitators. The scrubber section is usually equipped with a liquid recycle pump, recycle piping, and a liquid distribution system.

For additional information please refer to http://nis-co.com/scrubber/Index.html.

Oleg Tchetchel
Canadian Air Systems
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