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Re: Fly Ash Reuse
At 01:44 PM 7/29/97 -0500, you wrote:
>> Clean Air requirements seems to have required many (most?) coal
> burners to install low-NOx burners. Due to the lower efficiency
> (depending on the boiler design), ash carbon levels have increased
> to where the ash can no longer be used in concrete (I think below
> 6% carbon is needed). Another adverse side effect is that the
> volume of ash increases roughly 8% to 18 % (ugh!).
> (It was noted that fly ash from secondary precipitators collected
> lower carbon ash, but unfortunately carbon levels were not quite
> low enough to allow use in concrete.)
> QUESTION: Is anyone aware of any efforts to change the combustion
> atmosphere? (Direct feeds of O2, methane or other gases.)(Or
> something similar.)
In 1980 or '81, I participated in a major study of emerging electric
generating technology, including various combustion technologies. We looked
at various technical and other barriers and advantages for over 20
technologies. Among them were fluidized bed, combined cycle, and other
combustion technologies designed to improve efficiency and reduce air
In the '70s and '80s, Battelle Columbus (OH) and others did a lot of
research on fluidized bed combustion, involving use of limestone or other
acid-neutralizing materials in the fluidized bed. This seemed to help the
SOx and NOx problems. The resulting ashes, both fly and bottom ash, could
have potential use as cements or cement additives. I am not sure of the
final results of the program. Of course, the material added to the coal to
make the fluidized bed increases the volume of ash produced, but may result
in a useful byproduct, as opposed to a disposal problem.
There has also been some research on enriching the air to the burner.
Enriching air is less expensive and somewhat less dangerous than using O2,
and can still reduce the NOx produced. However, enriching the air may have
some cost via increased corrosion.
A good resource on these issues may be EPRI.
Ralph E. Cooper, Ph.D.
3475 Norwood, Suite N
Shaker Heights, OH 44122-4975
Voice: 216-991-6837 (w/voice mail)