Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Reexamination Certificate
2001-02-13
2002-10-22
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
C422S168000, C422S169000, C422S186220, C422S232000, C422S233000
Reexamination Certificate
active
06468489
ABSTRACT:
BRIEF DESCRIPTION OF THE INVENTION
This invention relates generally to the control of pollutants from combustion processes. More particularly, this invention relates to a technique for enhancing NO
X
reducing catalyst activity and thereby efficiently removing NO
X
from a combustion process gas stream.
BACKGROUND OF THE INVENTION
The 1990 Clean Air Act Amendments require major sources of air emissions to limit the discharge of NO
X
. NO
X
is present in the flue gas emitted from combustion processes. Therefore, cost-effective methods for controlling NO
X
are of significant interest.
Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR) catalysts for NO
X
removal are known in the art. Conventional NO
X
SCR catalysts require large amounts of catalyst and the flue gas stream to be at relatively high temperatures (between approximately 300 to 400° C.) in order to have sufficient activity for effective NO
X
reduction. In such schemes, ammonia or urea are also typically added as a reducing agents. However, significant problems are associated with the use of reducing agents, including, for example the formation of ammonium compounds from ammonia, referred to as ammonia “slip.” Ammonia “slip” occurs when unreacted ammonia and ammonium compounds pass out of the SCR unit. Such ammonia “slip” can plug downstream air heaters and impact ash use and disposal. SNCR is not as effective as SCR processes and the use of urea in SNCR also produces unwanted ammonia and ammonium compounds. Therefore, it would be desirable to have a process than can supplement NO
X
reduction downstream of the SCR/SNCR process, where the process can also reduce ammonia slip.
In addition to SCR and SNCR, low NO
X
burners (LNB) positioned in the furnace are also commonly used for NO
X
reduction. However, the LNB's are not as effective as SCR/SNCR at removing NO
X
from the combustion process. Therefore, it would also be desirable to have a process that can supplement NO
X
reduction downstream of LNB burners to meet more stringent NO
X
emissions control requirements.
There are ongoing efforts to develop low temperature catalysts for applications between approximately 100 to 250° C. Unfortunately, these low temperature catalysts are sensitive to high SO
x
concentrations in the flue gas. There are also NO
X
SCR catalysts being developed that are reagentless, so, for instance, ammonia is not required as a reducing agent. These catalyst systems can benefit from the imposition of additional and alternative activating agents to the catalyst so that they can operate at lower temperatures, be less sensitive to poisoning agents, and more reactive without the addition of chemical agents.
In view of the foregoing, it would be highly desirable to provide an approach to enhance NO
X
removal. Ideally, the technique would reduce the amount of catalyst needed, or would operate at relatively low temperatures, or reduce the amount of required chemical reducing agents.
SUMMARY OF THE INVENTION
According to the invention there is provided an apparatus for decreasing the concentration of contaminants, such as NO
X
or reducing agents, present in a gas stream. The apparatus comprises a NO
X
reducing unit, a duct to receive a flue gas stream from said NO
X
and reducing unit, and an activation source associated with the duct. In use, the activation source applies energy to the flue gas stream to facilitate the removal of contaminants from the flue gas stream.
Further, according to the invention there is provided a method of decreasing the concentration of contaminants within a flue gas stream. An activation source is provided downstream of a NO
X
reducing unit. The activation source is associated with a duct configured to convey a flue gas stream. The activation source is then activated to facilitate the removal of contaminants from the flue gas stream.
In this way, the inclusion of an activation source downstream of a NO
X
reducing unit decreases the concentration of NO
X
and reducing agents within the flue gas stream. The activation source of the invention may also be used with a low NO
X
burner to reduce NO
X
even in the absence or reducing agents that are present in other embodiments of the invention.
REFERENCES:
patent: 6117403 (2000-09-01), Alix et al.
patent: 6153159 (2000-11-01), Engeler et al.
Chang Ramsay
Sjostrom Sharon
Slye Richard
Electric Power Research Institute Inc.
Medina Maribel
Pennie & Edmonds LLP
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