Air Cleaning

removal of dust and other harmful impurities from the air by technical means. Air cleaning is usually used for air supplied to residential, public, and industrial buildings by forced-air ventilation systems and air-conditioning systems; air used in industrial processes, such as the production of oxygen; and contaminated air removed from production buildings before discharge into the atmosphere.

Air taken from the atmosphere is cleaned mainly to decrease its content of dust particles. The concentration of dust from various sources in the ground layer of the atmosphere may reach daily average values of 0.5 mg/m³ in residential areas of industrial cities, 1 mg/m³ in industrial areas, and 3 mg/m³ on the sites of industrial plants. In some cases—for example, in the vicinity of industrial plants whose processes are accompanied by intense discharge of dust-laden gases into the atmosphere (ferrous metallurgy, manufacture of cement, and so on)—the dust content may be significantly higher. The maximum permissible concentrations of dust on the sites of industrial plants and in adjacent residential areas are determined by health standards.

The removal of dust from the air supplied to buildings from the outside not only leads to improvement of the air quality within the buildings but also prevents contamination of interior surfaces and equipment and of heat exchangers and other components of ventilation systems. Some modern industrial production processes can take place only in areas ventilated with carefully dedusted air. Examples of such areas are plants for the manufacture of semiconductor and other electronic devices, precision instruments, cinematographic and photographic materials, and some medicines. Additional cleaning to remove acids and other chemical compounds is also required for trouble-free operation of some complex industrial installations, such as computers. Air consumed in industrial processes is cleaned to prevent the entry of dust into industrial equipment and to reduce wear on compressors and blowers.

The selection of equipment for air cleaning depends on the degree of contamination and on the cleaning requirements. The most common pieces of equipment for cleaning air supplied to enclosed areas are air filters, which are mounted in the flow chambers of ventilating and air conditioning systems. Such filters also clean the recirculated air that is removed by exhaust ventilation systems and then mixed with external air supplied to the areas. Recirculation is used to reduce the cost of heating or cooling the air. In cases where the dust content of the recirculated air is high, the air is first cleaned in dedusters.

Cleaning of air that becomes contaminated in industrial plants is exceptionally important for protection of the ground layer of the atmosphere from pollution by industrial plants. Various filters, dedusters and gas collectors, dust precipitation chambers, and cyclones are used to clean and decontaminate the air discharged into the atmosphere.