Corner windbox overfire air compartment for a fossil fuel-fired furnace

#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 NOX 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 NOX 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 NOX 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 NOX 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.

#FIG. 1 is a schematic perspective view of a fossil fuel-fired furnace equipped with a tangential firing system and having one embodiment of the corner windbox air compartment of the present invention;

#FIG. 2 is an enlarged perspective view of one of the corner windboxes of the fossil fuel-fired furnace shown in FIG. 1 and illustrating the one embodiment of the corner windbox air compartment of the present invention;

#FIG. 3 is an enlarged perspective view of the one embodiment of the corner windbox air compartment of the present invention shown in FIGS. 1 and 2;

#As seen in FIGS. 1-4, in accordance with the present invention, one embodiment of an improved air compartment is illustrated for a tangential firing system of a fossil fuel-fired furnace. The fossil fuel-fired furnace has a plurality of walls embodying therewithin a burner region in which a combustion process is sustained by a tangential firing system. The improvement relates to an air compartment of a windbox of the furnace or, if desired, a plurality of air compartments in a plurality of windboxes, and an exemplary embodiment of the improved air compartment embodying the novel air compartment exit assembly of the present invention will be described in more detail hereafter.

#The tangential firing system of the furnace is preferably of the type commonly denominated as a concentric tangential firing system. The concentric tangential firing system, generally designated as 10 in FIG. 1, is operable in a burner region 12 of a fossil fuel-fired furnace 14, which may be a pulverized coal-fired furnace. The burner region 12 defines a longitudinal axis BL extending vertically through the center of the burner region.

#The burner region 12 has four corners each substantially equidistant from adjacent corners such a combustion chamber thus formed by the burner region 12 has a parallelepiped shape which may be, for example, a rectangular or square shape. The burner region 12 shown in FIG. 1 has a square cross section. In the four corners of the combustion chamber are arranged a first windbox 16A, a second windbox 16B, a third windbox 16C, and a fourth windbox 16D. The first windbox 16A is generally circumferentially intermediately disposed between the second windbox 16B and the fourth windbox 16D as viewed in a circumferential direction relative to the burner region longitudinal axis BL such that the first windbox 16A is at a generally equal circumferential spacing from each respective one of the second windbox 16B and the fourth windbox 16D. The third windbox 16C is generally circumferentially intermediately disposed between the second windbox 16B and the fourth windbox 16D on the respective other side of these windboxes as viewed in the circumferential direction such that the third windbox 16C is at a generally equal circumferential spacing from each respective one of the second windbox 16B and the fourth windbox 16D.