Activated Carbon Adsorption
Vapor Recovery
Equipment
ACTIVATED CARBON BASICS
Control
of VOC or HAP vapors can be accomplished activated carbon adsorbers. Activated carbon adsorption vapor recovery units utilize the carbon's ability
to preferentially adsorb certain molecules from gaseous mixtures. Activated
carbon, with its highly porous structure and vast surface area, adsorbs
hydrocarbons from the air/hydrocarbon mixture emitted from the vapors generating
source. This could be an operational process, a loading or unloading operation,
etc. The hydrocarbon molecules are adsorbed onto the carbon surface and are
retained there until the regeneration step. The ability of the carbon to adsorb
fuel vapors is enhanced by higher concentrations, higher pressures and
lower temperatures. Adsorption of the hydrocarbon molecules proceeds until the
available surface area of the carbon is filled or saturated with the hydrocarbon
molecules.
The adsorbed hydrocarbons are then regenerated (desorbed or removed) from the
carbon by decreasing the pressure, reducing the hydrocarbon concentration around
the carbon particles or increasing the temperature of the carbon bed. A
combination of these steps can also be used for regeneration. There are three
basic types of activated carbon adsorption systems available to recover or
remove hydrocarbon vapors from an air stream. Two of these systems regenerate
the activated carbon in-situ for reuse. The third system requires that the
carbon be removed to another site for regeneration.
The first two systems that provide in-situ regeneration are: Pressure Swing
Regenerated Systems and Thermally Regenerated Systems. The third type of system,
which requires removal of the activated carbon to another site for regeneration
or disposal, is a once through Single Use or canister system. The canister
systems can usually be purchased directly from the activated carbon
manufacturer.
The following is a brief discussion about two of the three types of carbon
based vapor control systems.
