NOZZLE FOR FEEDING COMBUSTION MEDIA INTO A FURNACE

Abstract

In a nozzle for feeding a combustible medium such as coal particles along with air into a furnace, the exit end of each splitter plate in the nozzle is reinforced by a stiffener having an external cross-sectional shape in the form of a continuous curve proceeding outward and forward from a first surface of the plate to a first location, inward from the first location to a second location beyond the level of an opposite second surface of the plate, and inward and rearward from the second location to the second surface. The stiffener can be hollow, and can also be provided with openings for the flow of cooling air from the interior to the exterior of the stiffener. The continuous curvature of the exterior of the stiffener avoids recirculating flow at locations adjacent the stiffener and thereby minimizes flame attachment and deposition of ash or fuel sediment onto the reinforced splitter plates.

Claims

1. A nozzle for feeding a flowable combustion medium into a furnace, the nozzle comprising: a nozzle tip for directing flow of said combustion medium into the combustion chamber of a furnace, said nozzle tip including a shell having an inlet for receiving said combustion medium, an outlet for directing said combustion medium into said combustion chamber, and an interior space located between said inlet and said outlet; a splitter located within said shell, the splitter comprising at least one splitter plate extending in a forward direction, away from said inlet and toward said outlet, and dividing said interior space of said shell into at least two channels, each allowing for the flow of part of said combustion medium from said inlet to said outlet; wherein said at least one splitter plate has a planar first surface, an opposite planar second surface, and a downstream edge extending across said shell adjacent the outlet thereof; and wherein said nozzle further comprises a stiffener extending along said downstream edge of said at least one splitter plate, the external cross-section of said stiffener, transverse to the direction in which the stiffener extends along said downstream edge, being in the form of a continuous curve proceeding outward and forward from said first surface to a first location, inward from said first location to a second location beyond the plane of said second surface, and inward and rearward from said second location to said second surface; whereby the downstream edge of said at least one splitter plate is stiffened, but recirculation of said combustion medium flowing past said stiffener is minimized.

2. The nozzle according to claim 1, in which the external cross-section of said stiffener has a cylindrical shape.

3. The nozzle according to claim 1, in which at least the part of the external cross-section of said stiffener that proceeds from said first location to said second location is convex.

4. The nozzle according to claim 1, in which said stiffener has a hollow interior, an opening at least at one of its ends for receiving air from a channel in said nozzle tip, and plural openings distributed along the length of said stiffener, said plural openings extending from said hollow interior to the exterior of said stiffener, a first group of said plural openings being positioned to direct air from the interior of said stiffener to the exterior thereof in a direction forward and outward from said first surface, and a second group of said plural openings being positioned to direct air from the interior of said stiffener to the exterior thereof in direction forward and outward from said second surface.

5. A nozzle for feeding a flowable combustion medium into a furnace, the nozzle comprising: a nozzle tip for directing flow of said combustion medium into the combustion chamber of a furnace, said nozzle tip including a shell having an inlet for receiving said combustion medium, an outlet for directing said combustion medium into said combustion chamber, and an interior space located between said inlet and said outlet; a splitter located within said shell, the splitter comprising a plurality of splitter plates, each extending in a forward direction away from said inlet and toward said outlet, and dividing said interior space of said shell into plural channels, each channel allowing for the flow of part of said combustion medium from said inlet to said outlet; wherein each of said splitter plates has a planar first surface, an opposite planar second surface, and a downstream edge extending across said shell adjacent the inlet thereof; and wherein said nozzle further comprises a stiffener extending along said downstream edge of each of said splitter plates, the external cross-section of each said stiffener, transverse to the direction in which the stiffener extends along said downstream edge, being in the form of a continuous curve proceeding outward and forward from said first surface to a first location, inward from said first location to a second location beyond the level of said second surface, and inward and rearward from said second location to said second surface; whereby the downstream edge of each said splitter plate is stiffened, but recirculation of said combustion medium flowing past the stiffener thereon is minimized.

6. The nozzle according to claim 5, in which the external cross-section of each said stiffener has a cylindrical shape.

7. The nozzle according to claim 5, in which at least the part of the external cross-section of said stiffener that proceeds from said first location to said second location is convex.

8. The nozzle according to claim 5, in which each said stiffener has a hollow interior, an opening at least at one of its ends for receiving air from a channel in said nozzle tip, and plural openings distributed along its length, said plural openings extending from said hollow interior to the exterior thereof, a first group of said plural openings being positioned to direct air from the interior of the stiffener to the exterior thereof in a direction forward and outward from said first surface, and a second group of said plural openings being positioned to direct air from the interior of said stiffener to the exterior thereof in direction forward and outward from said second surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is an oblique perspective view of a nozzle tip in accordance with the invention;

[0021] FIG. 2 is a vertical cross-sectional view of the nozzle;

[0022] FIG. 3 is a horizontal cross-sectional view of the nozzle, with arrows showing the path of air flow through a hollow stiffener;

[0023] FIG. 4 is an enlarged view showing details of an opening for entry of air into the hollow stiffener in the nozzle of FIG. 3;

[0024] FIG. 5 is a schematic view illustrating the flow of air and combustion medium past a stiffener disposed on the downstream end of a splitter plate; and

[0025] FIG. 6 is a schematic view illustrating the flow of air and combustion medium past a stiffener disposed on the downstream end of a splitter plate and also illustrating he flow of air from the interior of the stiffener through air holes formed in the stiffener.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The nozzle tip 10 in FIG. 1 is a vertically tilting nozzle tip, composed of an inner shell 12 surrounded by an outer shell 14. Horizontal splitter plates 16 and 18 divide the interior of the inner shell into three flow passages for flow of combustion media, typically pulverized coal particles entrained in a stream of primary air. Secondary air flows through a space between the inner and outer shells. The nozzle tip is mounted on trunnions, one of which is shown at 20, for tilting about a horizontal axis.

[0027] The outer shell is typically, but not necessarily, tapered, and is composed of two vertical side walls 22 and 24, and upper and lower walls 26 and 28, respectively.

[0028] An array 30 of holes is provided in the upper wall 26 of the nozzle tip, and a similar array 32 of holes is provided in the lower wall 28. The arrays are located adjacent the front opening of the outer shell and extend rearward to an intermediate location between the front and rear openings of the outer shell. The holes in these arrays allow flow of secondary air from the space between the inner and outer shells, through the outer shell, to the outer surface of the outer shell. Air passes through the holes from the interior of the nozzle tip to the exterior, reducing the temperature difference between the inner and outer surfaces, thereby reducing thermal distortion and resulting damage. When the nozzle is tilted, the flow of air through the holes in the wall facing the flame increases so that a greater cooling effect is achieved at the parts of the nozzle tip having the greater exposure to radiant heat. The flow of air through the arrays of holes washes the exposed outer surface of the nozzle tip with cool air in a film or boundary layer. The air flow also reduces direct contact between the flame and the nozzle tip. Details of the arrays of holes and their function are explained in U.S. Pat. No. 8,413,595, granted on Apr. 9, 2013. The disclosure of U.S. Pat. No. 8,413,595 is here incorporated by reference.

[0029] The nozzle tip includes an outer shroud 34 forming channels 36, bounded by the outer shroud, the upper wall 26 of the nozzle tip, and shroud-supporting partitions 38. A similar shroud structure is provided on the bottom side of the nozzle tip. The channels 36 direct secondary air along the outer surface of the upper wall 26 of the nozzle tip, and similar channels (not shown) direct air along the outer surface of the lower wall 28. Cooling is achieved by flow of air though the arrays of holes and by the flow of secondary air flow through the shrouds.

[0030] The upper and lower shrouds are convex so that the gap between the nozzle tip and the nozzle (not shown) in which it fits remains substantially the same regardless of the angle of tilt.

[0031] As shown in FIGS. 1 and 2, stiffeners 40 and 42 are secured at the downstream edges of the splitter plates 16 and 18 respectively, each preferably extending along the full length of the splitter plate from one side wall to the opposite side wall of the inner shell 12. As shown in FIG. 5, stiffener 40, which extends along the downstream edge of splitter plate 16 is in the form of a circular cylindrical tube having a longitudinal slot 42, which receives a portion of the splitter plate including the downstream edge 44, which is situated inside the tube. Welds 46 and 48 secure the tube to the splitter plate. The welds constitute parts of the stiffener, and the outer surfaces of the welds define parts of the external cross-sectional shape of the stiffener.

[0032] As will be apparent from FIG. 5, the external cross-sectional shape of the stiffener is in the form of a continuous curve proceeding from a location 50 where the outer surface of weld 46 meets a first surface (the upper surface) 52 of plate 16, outward and forward from surface 52 to a first location 54, then inward from location 54 toward a second location 56 beyond the plane of a second surface 58 (the lower surface) of plate 16, and then inward and rearward from the second location 56 to a location 60 on the second surface 58 of the plate. Preferably the curvature of the exterior of the stiffener is convex except at the locations of the exterior portions of the welds, which can be straight or slightly concave.

[0033] Arrows 60 in FIG. 5 show the direction of flow of the combustible medium, composed of coal particles entrained in air, in the region adjacent the stiffener 40. The continuous curvature, i.e., the absence of sharp transitions in the direction of the curvature of the external cross-section of the stiffener, minimizes recirculating flow, and reduces the amount of ash deposited on the stiffener and other parts of the exit portion of the splitter plate 16.

[0034] As shown in FIG. 1, stiffener 40 is formed with an array of openings that allow air to flow from the interior of the stiffener to the exterior. FIG. 6 is a schematic cross-sectional view taken on a section plane that intersects two of the openings. An upper opening 62 is positioned to direct air from the interior of stiffener 40 to the exterior thereof in a direction forward and outward from surface 52. A lower opening 64 is positioned to direct air from the interior of stiffener 40 to the exterior thereof in a direction forward and downward from surface 58. The other openings in the stiffener are similarly situated. Arrows 66 and 68 in FIG. 3 depict the flow of air, which enters the hollow stiffener through both ends from a space between the inner and outer shells. As shown in FIG. 4, hollow stiffener 40 extends though a side wall of the inner shell 12 and is formed with a rearward-facing opening 69 constituted by a cut-away portion of the part of the stiffener 4 that extends outward beyond the side wall of the inner shell. A similar opening is provided at the opposite end of the stiffener. Air flowing between the inner and outer shells enters the stiffener through these openings and exits through the upper and lower outlet openings in the directions illustrated by arrows 70 and 72 in FIG. 6. The flow of air though the outlet openings has a cooling effect, but little, if any effect on the flow of the combustible medium in the vicinity of the stiffener, which is illustrated by arrows 74.

[0035] In summary, the continuous curvature of the exteriors of the stiffeners in cross-section allows the stiffeners to strengthen the exits end of the splitter plates without creating conditions that promote ash adhesion, and the flow of air from the interior of the stiffeners through their openings promotes cooling and reduces high temperature creep.