Depending on its external appearance, activated charcoal is divided into three groups :
- Powdered charcoal
- Granular charcoal
- Shaped charcoal
Powdered charcoal is ground to a degree of fineness which leads to 50 - 80% of particles being smaller than 40 micron, thus leaving 20 - 50% above 40 micron. Powdered charcoal is used principally for water treatment. For this reason, this is not the place to deal with such activated charcoal in greater detail. Granular charcoal usually consists of fractured granules, either already activated, or fractured and graded to reach the state in which it is offered. Grades are characterised by indication of.grain sizes. Granular charcoal is used for purifying air and gas. Grain size distribution of granular charcoal exerts a significant influence on the kinetics of adsorption. Shaped coal is traded in the form of small cylinders. Various grades are manufactured, with particle diameters varying between 1 - 4 mm. The proportion between grain length and grain diameter is about 3 : 1, with downward tolerances. Shaped coal is utilised like granular coal. In the gaseous phase, shaped coal offers benefits because of the low flow resistance, good mechanical hardness and because shaped coal makes it possible to fill the adsorber in an even and stable manner.
