Furnaces – Including noncombustible fluid supply means
Reexamination Certificate
1999-02-18
2001-03-20
Lazarus, Ira S. (Department: 3743)
Furnaces
Including noncombustible fluid supply means
C110S348000, C431S010000, C239S587200
Reexamination Certificate
active
06202575
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a corner windbox air compartment of a fossil fuel-fired furnace equipped with a tangential firing system and an exit assembly for such an air compartment.
It is known that a staged combustion approach can improve the reduction of NO
X
in a fossil fuel-fired furnace such as, for example, a furnace in which pulverized coal is fired. Such a staged combustion approach may include reducing the quantity of air introduced into a main burner region of the furnace, which is a region in which the fuel such as the pulverized coal is injected, and instead introducing greater quantities of air above the main burner zone.
Over the years, there have been different approaches pursued in the prior art insofar as concerns addressing the need to limit emissions of the NO
X
that is created as a consequence of the combustion of fossil fuels in furnaces. The focus of one such approach has been on developing so-called low NO
X
firing systems suitable for employment in fossil fuel-fired furnaces. U.S. Pat. No. 5,020,454 entitled “Clustered Concentric Tangential Firing System”, which issued on Jun. 4, 1991 and which is assigned to the same assignee as the present patent application discloses an example of one such low NO
X
firing system. In accordance with the teachings of U.S. Pat. No. 5,020,454, a clustered concentric tangential firing system is provided that includes a windbox, a first cluster of fuel nozzles mounted in the windbox and operative for injecting clustered fuel into the furnace so as to create a first fuel-rich zone therewithin, a second cluster of fuel nozzles mounted in the windbox and operative for injecting clustered fuel into the furnace so as to create a second fuel-rich zone therewithin, an offset air nozzle mounted in the windbox and operative for injecting offset air into the furnace such that the offset air is directed away from the clustered fuel injected into the furnace and towards the walls of the furnace, a close-coupled overfire air nozzle mounted in the windbox and operative for injecting close-coupled overfire air into the furnace, and a separated overfire air nozzle mounted in the windbox and operative for injecting separated overfire air into the furnace.
Another example of such a low NO
X
firing system is that which forms the subject matter of U.S. Pat. No. 5,315,939 entitled “Integrated Low NO
X
Tangential Firing System”, which issued on May 31, 1994 and which is assigned to the same assignee as the present patent application. In accordance with the teachings of U.S. Pat. No. 5,315,939, an integrated low NO
X
tangential firing system is provided that includes pulverized solid fuel supply means, flame attachment pulverized solid fuel nozzle tips, concentric firing nozzles, close-coupled overfire air, and multi-staged separate overfire air and when employed with a pulverized solid fuel-fired furnace is capable of limiting NO
X
emissions therefrom to less than 0.15 lb./million BTU while yet maintaining carbon-in-flyash to less than 5% and CO emissions to less than 50 ppm.
Both of the tangentially fired furnaces disclosed in the two afore-mentioned references capitalize on the knowledge that the formation of NO
X
in a tangentially fired furnace can frequently be minimized by judicious control of the air introduced above the fuel-rich main burner zone—i.e. the introduction of so-called overfire air. Judicious control of the overfire air in such circumstances is characterized by the introduction of the overfire air in a manner which supports the formation of the swirling fireball in the furnace while also supporting the sub-stoichiometric conditions in the main burner zone. With regard to supporting the sub-stoichiometric conditions in the main burner zone, it can be appreciated that any increase in the residence time of the fuel in the sub-stoichiometric (fuel rich) main burner zone will further promote the reduction of NO
X
.
Notwithstanding the fact that over the years there have been different approaches disclosed in the prior art targeted at the reduction of emissions of the NO
X
that is created as a consequence of the combustion of fossil fuels in furnaces, a need still exists in the prior art to improve upon what has been accomplished in the pursuance of these different approaches. For example, the need still exists for an approach which would permit the introduction of overfire air in a manner which promotes a longer residence time of fuel in the sub-stoichiometric conditions of the main burner zone of a tangentially fired furnace while at the same time minimizing the energy required to accomplish an introduction of overfire air in this manner.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide an air compartment for a corner windbox of a tangentially fired furnace which permits the introduction of overfire air in a manner which promotes a longer residence time of fuel in the sub-stoichiometric conditions of the main burner zone of the furnace while at the same time minimizing the energy required to accomplish an introduction of overfire air in this manner.
It is another object of the present invention to provide an exit assembly for an air compartment of a corner windbox of a tangentially fired furnace which permits the introduction of overfire air in a manner which promotes a longer residence time of fuel in the sub-stoichiometric conditions of the main burner zone of the furnace while at the same time minimizing the energy required to accomplish an introduction of overfire air in this manner.
In accordance with one aspect of the present invention, there is provided an air compartment of a corner windbox of a tangential firing system of a fossil fuel-fired furnace which permits the introduction of overfire air in a manner which promotes a longer residence time of fuel in the sub-stoichiometric conditions of the main burner zone of the furnace while at the same time minimizing the energy required to accomplish an introduction of overfire air in this manner. The air compartment includes a channel portion for the flow therethrough of air from an air delivery duct to an opening in the furnace and an exit assembly. The channel portion has a longitudinal extent with an entrance end communicating with the air delivery duct and an exit end communicating with the furnace opening. Also, the channel includes a generally parallelepiped cross sectional shape transverse to its longitudinal extent. The channel portion is mounted in the corner windbox such that its longitudinal extent is parallel to a horizontal plane.
The exit assembly includes a first means for guiding an air stream at the exit end of the channel portion and means for mounting the first air stream guiding means relative to the channel portion for guiding thereby of an air stream passing from the channel portion through the furnace opening into the furnace. The first air stream guiding means includes a surface portion which intersects the horizontal plane at an acute angle and a pair of opposed transverse edges. The mounting means includes a pair of opposed side portions and means for securing each opposed side portion interiorly of the channel portion on a respective side thereof, the first air stream guiding means extending between the pair of opposed side portions with each transverse edge of the first air stream guiding means being secured to a respective one of the opposed side portions of the mounting means. The mounting means and the first air stream guiding means are disposed within the channel portion such that the leading edge of the first air stream guiding means is upstream of the furnace opening.
According to one feature of the one aspect of the present invention, the mounting means includes an interconnecting portion secured to and extending transversely between the pair of opposed side portions at a vertical spacing from the first air stream guiding means.
According to a further feature of the one aspect of the present invention, there is provided a second air stream guiding means having opposed
Bauver, II Wesley P.
LaFlesh Richard C.
Lewis John C.
Lewis Robert D.
ABB Alstom Power Inc.
Ciric Ljiljana V.
Lazarus Ira S.
Warnock Russell W.
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