Activated carbon filter
When activated carbon filter to filter called, the activated carbon contained. Such filters are used both for the treatment and purification of gases and liquids. The purpose is to remove disruptive substances such as dust , heavy metals and undesirable and toxic chemicals from gases or liquids.
Mode of action
With the use of activated carbon in a filter, different treatment goals are possible. On the one hand, as is usual with filters, undissolved mechanical particles are filtered off. More detailed information on this is given under Filters (fluid technology) .
Activated carbon has a very large internal surface area that adsorbs dissolved particles . The carbon also acts as a reducing agent and can absorb oxidizing agents such as ozone and chlorine from exhaust air as well as industrial and waste water .
During the filtration and adsorption, the substances to be removed are absorbed by the activated carbon and enriched in the carbon mass. In contrast, during reduction, the carbon is partially oxidized to carbon dioxide and thus consumed . The amount of activated carbon is reduced and needs to be topped up occasionally. The reaction equation for removing ozone is:
However, activated carbon can also be used via catalytic reactions to break down and eliminate chloramines , for example . For this, the following mechanism is given in the literature:
Solids absorbed by filtration increase the filter resistance and must be removed from the filter bed by backwashing. If necessary, the filter can also be regenerated by washing, heating or exchanging the activated carbon.
Substances absorbed through adsorption accumulate in the coal. Depending on the type of activated carbon and the type of adsorbed substances, accumulations of 10 to about 20 percent by weight are possible before a breakthrough occurs. Exhausted activated carbon is replaced. The loaded masses are disposed of or can also be thermally activated again for further use.
application areas
In industry, activated carbon filters are used to purify the air in order to reduce the burden on employees.
Filters with the filter medium activated carbon are often used in technical water treatment. For the treatment of surface water with impurities such as humic acids or lignosulfonic acids , activated carbon filters are installed upstream of the ion exchangers . The activated carbon adsorbs the impurities that would otherwise damage the ion exchange resins in the downstream filters through fouling . Activated carbon filters are also used for the adsorption of traces of oil in operating condensates in industry.
The sketch shows a simplified representation of an activated charcoal filter for granular activated charcoal with the usual connection lines for the treatment of contaminated water. In drinking water and wastewater treatment , they are usually used for the adsorptive retention of odors and flavors as well as harmful organic substances such as halogenated hydrocarbons and pesticides .
Activated charcoal can also be used as an aqueous suspension with powdered charcoal, dosed to the raw water in front of a filter system or as a component of the precoat for precoat filters . Another possibility is a layer of granular coal that rests on gravel or other filter material. In the latter case, such filters are called layered bed filters.
In larger plants with grain coal, it makes sense for economic reasons to thermally process the activated carbon for further use after exhaustion or loading.
Most respirator filters are also filled with activated carbon.
An activated carbon filter can be used in home ventilation devices to remove fine dust from the fresh air.
Activated charcoal filters are available for extractor hoods in recirculation mode to filter out odors. A grease filter is installed upstream so that the pores of the coal do not stick together. The granulated activated carbon usually has a grain size of 3 or 4 mm in diameter and is often embedded in a plastic carrier material. Filters that can be regenerated are also offered, which can be freshened up several times in the oven or dishwasher before they have to be replaced. They can be used at least three times as long as disposable filters.
The activated carbon filter is used in the aquarium hobby to briefly filter pollutants or drug residues from the water.
These filters are used in hard disks to retain dust in order to be able to provide the same pressure inside the hard disk as outside without dust or other dirt damaging the rotating disks.
Activated charcoal is used as a pipe filter , in some cigarillos and in cigarette filters. The smoke is guided through the porous pieces of coal like a labyrinth , so that a large part of the harmful substances such as nicotine remain in the filter; they easily affect the tobacco taste.
The industrial activated carbon filters are also used when planting prohibited substances, such as indoor growing for the production of marijuana , in order to soften the smell of flowering cannabis plants.
Activated carbon filters are also used in the ventilation systems of cars. The Mercedes-Benz "W140" had an optional extra to protect against unpleasant odors. Today's ventilation systems in cars often have activated carbon filters to filter outside odors.
Individual evidence
- ↑ RCBauer and VLSnoeyink; Reactions of Chloramine with Actice Carbon ; In: Journ. WPCF 45 (1973), p. 2290.
- ↑ Product information, brochure from Lurgi; T 1158 / 2.81 ; P. 18.
- ↑ Ekkehard Heymann, Werner Nissing, in: Eliminierung von PBSM im Wasserwerk Haltern , gwf, 132nd year, 1991, No. 1, pp. 1-7.
- ↑ Expertise on extractor hoods , section "Exhaust air needs supply air!", In: HEA.de
