Canadian Air Systems Co. is a well known engineer of industrial packed air scrubbers for air cleaning. Wet type dust collectors / packed air scrubbers are available in numerous designs utilizing a number of principles and featuring wide variation in effectiveness, initial cost, operating and maintenance expense, space, arrangements and material of construction. Wet type dust collectors are liquid (usually, but not necessarily, water) to capture and separate particulate matter (dust, mist, and fumes) from a gas stream. Some scrubbers operate by spraying the scrubbing liquid into the contaminated air. Others bubble air through the scrubbing liquid.

Packed Scrubbers are used to remove gaseous and particulate contaminants from gas streams. Scrubbing is accomplished by impingement of particulates and/or by absorption of soluble gas or vapor molecules on the liquid-wetted surface of the packing. Gas or vapor removal is more complex than particulate capture. The contaminant becomes a solute and has a vapor pressure above that of scrubbing liquid. This vapor pressure typically increases with increasing concentration of the solute in the liquid and with increasing liquid temperature. Scrubbing of the contaminant continues as long as partial pressure of contaminant in the gas is above its vapor pressure with respect to the liquid. The rate of contaminant removal is a function of the difference between the partial pressure and vapor pressure, as well as the rate of diffusion of the contaminant.

Scrubber packings are designed to present a large surface area that will wet evenly with liquid. High efficiency packings promote turbulent mixing of the gas and liquid. Packings are available in ceramic, metal, and thermoplastic materials.

There are four different arrangements of Canadian Air Systems Wet-Packed Scrubbers:

HORIZONTAL COCURENT SCRUBBER.

This wet scrubber depends on the gas velocity to carry the liquid into the packed bed. It operates as a wetted entrainment separator with limited gas and liquid contact time. The gas velocity in the collector is limited by liquid retrainment to about 650 fpm.

VERTICAL COCURENT SCRUBBER.

Vertical cocurent scrubber can be operated at very high pressure drop - 1 to 3 in. of water per foot of packing depth) because there's no flooding limit for the superficial velocity.

CROSS-FLOW SCRUBBER.

This scrubber uses downward-flowing liquid and a horizontally moving air stream. The effectiveness of absorption processes in cross-flow scrubbers lies between those for cocurrent and countercourent flow scrubbers.

COUNTERCURRENT SCRUBBER.

Countercurrent scrubber uses a downward-flowing liquid and an upward-flowing gas. The gas-handling capacity of this wet scrubber is limited by pressure drop or by liquid entrainment. The contact time can be controlled by the depth of the packing used. This type of wet scrubber gives the best removal of gaseous contaminants while keeping liquid consumption to a minimum. The effectiveness of absorption processes is maximized because the exiting gas is in contact with fresh scrubbing liquid.

Wet type dust collectors are liquid (usually, but not necessarily, water) to capture and separate particulate matter (dust, mist, and fumes) from a gas stream. Some scrubbers operate by spraying the scrubbing liquid into the contaminated air. Others bubble air through the scrubbing liquid. In addition, many gybrid wet scrubbing designs exist.

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

Oleg Tchetchel
Process Engineer
Canadian Air Systems
http://nis-co.com/index.html
http://www.nis-co.com/scrubbers/Index.html

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