Gaseous contaminants, that are insoluble or barely soluble in water, such as most hydrocarbons, can be removed from air by passing this air through an active carbon filter.The contaminants are adsorbed onto the active carbon.In the course of time, the active carbon becomes saturated and has to be replaced. The carbon removed has to be treated as a chemical waste, and has to be disposed of as such a waste.
Active carbon filters are frequently applied for small-scale odour removal but, because of the high operating costs, are used less frequently in treating large air lows.In principle, it is possible to make the exhausted carbon again suitable for use, by blowing steam through it to remove the adsorbed contaminants. This method of operation is economically viable only for very large installations with a large quantity of active carbon. When regenerating the active carbon, care has to be taken that when the contaminants are driven out, they do not then enter the environment. In sizing active carbon filters it is important to know that there is a clear connection between the degree of saturation of the carbon and the concentration of the contaminants in the air stream. For a lower concentration, the degree of saturation is lower and the life of the filter bed is shorter.
Air to be treated in an active carbon filter has to be free of solids and have a relative humidity of < 70%. Otherwise the filter will block, or the active carbon granules will stick together.The air resistance will increase and the effectiveness of the filter will fall.Fatty vapours are also disastrous for proper operation of an active carbon filter. In conclusion, it should be noted that the adsorption effect rapidly reduces as the temperature increases. To summarise, the limiting conditions, imposed by this method, must be thoroughly examined for the application of an active carbon filter.

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