Combustion – Process of combustion or burner operation – Feeding flame modifying additive
Reexamination Certificate
2000-09-27
2001-07-03
Yeung, James C. (Department: 3743)
Combustion
Process of combustion or burner operation
Feeding flame modifying additive
C431S008000, C431S181000, C431S187000
Reexamination Certificate
active
06254379
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to the delivery of reagent to a remote reaction zone, and is particularly useful for providing reagent to a remote reaction zone of a furnace for the conversion of nitrogen oxides (NOx) to nitrogen.
BACKGROUND ART
It is sometimes desired to provide reagent to a remote reaction zone such as at a specific location within the interior of a furnace. For example, in reburning wherein hydrocarbon radicals convert NOx to nitrogen gas for pollution control purposes, it is desired to provide hydrocarbon fuel such as natural gas or coal, which serves as a source of hydrocarbon radicals, to a remote area which contains flue gas. In another example it may be desired to provide ammonia or urea deep within a furnace to react with the NOx to form nitrogen gas.
One way to accomplish such reagent provision is to pass the reagent to the remote reaction zone using a long lance or other long provision means, but this is complicated to carry out and would require frequent replacement of the lance if the reaction zone were associated with a hot or corrosive environment such as a furnace. Another way to deliver reagents to a specific location in the boiler or furnace is to use. high velocity jets which typically penetrate deep into an enclosure before mixing is complete. However, this approach can lead to significant increases in the formation of pollutants in burners, such as NOx, and consumption of reagent prior to reaching the reaction zone. Both effects are due to the high entrainment rates characteristic of turbulent jets. Further, the high entrainment rates lead to recirculation of hot flue gas, which can contain particulate or corrosive gases, to the boiler or furnace wall, exacerbating deposition on the wall and corrosion. Yet another method is through the use of computational fluid dynamics modeling of a reaction zone such as a furnace environment. In this method detailed calculations are made to describe the furnace environment and nozzles or lances can then be placed in appropriate locations. This method can be effective but is quite complex to execute.
Accordingly, it is an object of this invention to provide a method whereby reagent may be provided to a reaction zone which is separated by a distance from the point where the reagent passes out from the injection device.
SUMMARY OF THE INVENTION
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention one aspect of which is:
A method for providing a reagent to a reaction zone comprising:
(A) providing reagent to a carrier gas and passing reagent-containing carrier gas as a gas jet into an injection space from an injector through a distance (d);
(B) surrounding the gas jet with a flame envelope from the injector through the distance (d) so as to maintain the gas jet coherent through the distance (d);
(C) passing the reagent-containing carrier gas further into the injection space beyond the distance (d) into a reaction zone past the leading edge of the flame envelope as a non-coherent gas stream; and
(D) providing reagent from the non-coherent gas stream to the reaction zone.
Another aspect of the invention is:
A method for providing a reagent to a reaction zone comprising:
(A) passing gaseous reagent as a gas jet into an injection space from an injector through a distance (d);
(B) surrounding the gas jet with a flame envelope from the injector through the distance (d) so as to maintain the gas jet coherent through the distance (d);
(C) passing the gaseous reagent further into the injection space beyond the distance (d) into a reaction zone past the leading edge of the flame envelope as a non-coherent gas stream; and
(D) providing gaseous reagent from the non-coherent gas stream to the reaction zone.
As used herein the term “coherent gas jet” means a gas stream whose diameter undergoes no substantial increase along the length of the stream and the rate of entrainment of the surrounding gas into the gas stream is substantially less than that into a nonreacting turbulent jet.
As used herein the term “non-coherent gas stream” means a gas stream whose diameter increases as it entrains the surrounding gas.
As used herein the term “flame envelope” means an annular combusting stream coaxial with a gas stream.
As used herein the term “reagent” means a fuel or other chemical compound or mixture of compounds that takes part in a reaction after injection into an injection space.
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patent: 5823762 (1998-10-01), Anderson et al.
patent: 5954855 (1999-09-01), Gitman et al.
patent: 6096261 (2000-08-01), Anderson et al.
patent: 6139310 (2000-11-01), Mahoney et al.
patent: 6142764 (2000-11-01), Anderson et al.
Bool, III Lawrence E.
Kobayashi Hisashi
Ktorides Stanley
Praxair Technology Inc.
Yeung James C.
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