Vapor-Phase Granular Activated
Carbon Adsorption
Description
Vapor-phase
Granular Activated
Charcoal (GAC) is a
treatment technology that removes contaminants from air. Contaminated air is
passed through one or more vessels containing GAC. Contaminants sorb onto the surfaces of the activated
carbon grains. The thermal processing of carbon, often from coconut shells,
creates small porous particles with a large internal
surface area. This processing activates the carbon. The activated carbon
attracts and adsorbs organic molecules as well as certain metal
and inorganic molecules. When the concentration
of contaminants in the vapor exiting the vessels exceeds a
certain level, the carbon must be replaced. Spent carbon can be regenerated in
place; removed and regenerated at an off-site facility; or most commonly,
removed and disposed.
Limitations
and Concerns
Some
degradation products such as vinyl chloride and smaller molecules are not
sorbed well, and consequently must be monitored carefully.
All
spent carbon eventually needs to be disposed in landfills or regenerated. There are few
regeneration facilities.
Most
regeneration systems release the sorbed contamination to the air. There is a concern by many communities
that GAC, while removing contamination from the air (or water in a liquid-phase
system), spreads the contamination to other areas. In the Western U.S., one regeneration facility is located on
an Indian reservation.
The
carbon used for some contaminants (e.g., metals) can not be regenerated.
Spent
carbon transport may require hazardous waste handling.
Relative
humidity greater than 50% can reduce carbon capacity
Elevated
temperatures from soil vapor extraction (SVE) pumps (greater than 38¡ C or 100¡
F) inhibit adsorption capacity.
Some
compounds, such as ketones, may cause carbon bed fires because they release heat upon adsorption.
Applicability
This
technology is used to treat off-gas contaminated with volatile organic compounds (VOCs) and some fuels.
Technology
Development Status
The
technology is well proven, and it is frequently part of remedial designs.
Web
Links
http://clu-in.org/download/citizens/activatedcarbon.pdf
http://www.frtr.gov/matrix2/section4/4-61.html
Other
Resources and Demonstrations
See
ÒEngineering and Design: Adsorption Design GuideÓ (DG 1110-1-2), published by
the U.S. Army Corps of Engineers, March 2001. It provides practical guidance
for the design of liquid- and vapor-phase devices for the adsorption of organic
chemicals. The adsorptive media addressed include granular activated carbon and
other alternative adsorption carbon media, such as powdered activated carbon
(PAC) and non-carbon adsorbents.
See Sorption.