Carbon Adsorption

Carbon (and indeed, other porous solids) can adsorb contaminants on to its surface by virtue of electrostatic forces. Base carbon is carbon that has been produced by pyrolysis of a base material (e.g. Coal, Wood, Coconut Shell etc). This carbon must then be activated to maximise the potential of carbon as an adsorbant. The process of activation is the use of heat, under anoxic conditions and usually in the presence of steam. Typically activation is around 850 degrees Centigrade.

The thermally treated carbon can then be chemically refined to remove metal salts in the ash content. This reduces the ignition temperature of the product by making it less catalytically active. The process of activation can increase the surface area of the carbon by 100 fold. typically, activated carbon has between 1000 and 1500 square meters of surface area per gram of product. It is this vast surface area that gives this materially the highest removal efficiency of all technologies where this technology can applied.

This technology having a high efficiency removal, also has a forgiving nature and can adsorb wide ranges of compounds over equally wide ranges of concentration. The technology therefore "forgives" mistakes in emission characterisation and is hence an ideal polisher for other technologies.

Carbon that has been activated from base material is known as Virgin activated carbon. type of carbon can be adversely affected by high moisture content and is not suitable for high humidity applications. Carbon, however, can be impregnated with a wide range of reagents that coat the surface area and are often catalytically enhanced in terms of reactivity. When contaminants react with the impregnant, then the process of removal is known as chemisorption. This process is often enhanced further by moisture and so this type of carbon is suited to high humidity applications.

Adsorbers can be single bed or multi-bed. they can have , vertical, annular or rect-annular orientations. The carbon bed is designed to give the required empty bed contact time, superficial velocity and bed life as necessary.

For solvent/VOC applications beds can have between 0.5 and 2 seconds contact time (more if adjusted for longer life)

For odour control using impregnated carbon then it is generally recommended that > 2.5 seconds is used

Click here for a typical deep bed/dual bed orientation

Click here for an annular bed design

Click here for a rect-annular design