The use of Activated Carbon Injection (ACI) for the removal of mercury
from flue gas is a well established method that has been commercially
implemented and requires the injection of Powdered Activated Carbon
(PAC) into the flue gas stream. While this method successfully removes
the mercury from the flue gas, it has inherent flaws. PAC is a costly
reagent ($1.00/lb) that is consumed and ultimately landfilled, and the
captured mercury is merely transferred from the air to the ground, not
eliminated from the environment.
PMET developed the MERCS (Mercury Emissions ReCovery & Sequestration)
process that enables the regeneration and reuse of PAC after it has captured
the mercury. This process is most effective when the ACI occurs after
a fabric filter or electrostatic precipitator (ESP) and prior to a PAC
collection device, such as a fabric filter. Once collected, the PAC is
thermally treated in an inert atmosphere to desorb the contained mercury
allowing the PAC to be returned to the injection system for reuse. The
desorbed mercury is sequestered and condensed into a salable metal, thus avoiding any disposal of potentially toxic
waste streams. This step eliminates the environmental liability
associated with the mercury for the generating entity.
Compared to single-pass PAC that is injected once, collected and disposed
of; MERCS offers significant operating cost savings, reduced PAC consumption
to stretch the existing supply, and mercury emissions that are sequestered.
PMET successfully demonstrated the ability to desorb mercury from PAC
using a synthetically loaded carbon from Norit (DARCO FGD). After the
mercury was desorbed, the regenerated PAC was found to have the same
characteristics as virgin material. Using this test data, and the
published data from US DOE, the MERCS process is capable of reducing the ACI
operating costs by a factor of ten(10). These savings will allow high
cost facilities with mercury emissions to comply with the upcoming
regulations without a cap and trade system.
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