Venturi scrubbers use a liquid stream to remove solid particles as well as gases present in exhaust. In the venturi scrubber, gas laden with particulate matter passes through a short tube with flared ends and a constricted middle. This constriction causes the gas stream to speed up when the pressure is increased. The difference in velocity and pressure resulting from the constriction causes the particles and water to mix and combine. The reduced velocity at the expanded section of the throat allows the droplets of water containing the particles to drop out of the gas stream. Venturi scrubbers are effective in removing small particles, with removal efficiencies of up to 99 percent.
The removal of one or more selected components from a gas mixture by absorption is probably the most important operation in the control of gaseous pollutant emissions. Absorption is a process in which a gaseous pollutant is dissolved in a liquid. As the gas stream passes through the liquid, the liquid absorbs the gas, in much the same way that sugar is absorbed in a glass of water when stirred. Absorbers are often referred to as scrubbers, and there are various types of absorption equipment. The principal types of gas absorption equipment include spray towers, packed columns, spray chambers, and venture scrubbers. In general, absorbers can achieve removal efficiencies greater than 95 percent.
When a gas or vapor is brought into contact with a solid, part of it is taken up by the solid. The molecules that disappear from the gas either enter the inside of the solid, or remain on the outside attached to the surface. The most common industrial adsorbents are activated carbon, silica gel, and alumina, because they have enormous surface areas per unit weight. Activated carbon is the universal standard for purification and removal of trace organic contaminants from liquid and vapor streams. Carbon adsorption systems are either regenerative or non-regenerative.