Abstract:
An air nozzle for introducing secondary air into a furnace and including a housing provided with an inlet at one end thereof for receiving air and an outlet at the other end thereof for discharging the air. A damper is disposed in the housing in the path of the air for splitting the flow of the air into two flow streams which extend to different areas of the furnace and is adapted for pivotal movement in the housing to vary the amount of air flow in each of the streams and the discharge angle of one of the streams.

Description:
This application is a continuation of application of co-pending application Ser. No. 08/641,021, filed Apr. 29, 1996. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to an air nozzle for use in a coal-fired furnace and, more particularly, to such an air nozzle for discharging air into the interior of the furnace to support the combustion of coal discharged from a burner. 
     In coal fired furnace systems, a mixture of coal and air is usually discharged from one or more burners mounted relative to a furnace wall or walls, and secondary air is discharged from one or more air nozzles located adjacent each burner. Many types, arrangements and locations of the burners and the secondary air nozzles have been used. For example, in a conventional, straight firing system, the air nozzles are mounted relative to the furnace walls adjacent their associated burners in a manner to discharge the secondary air in a direction perpendicular to the walls. In tangential firing systems, the burners and the secondary air nozzles are disposed in each of the corners of the furnace and are designed specifically to discharge the fuel and the secondary air, respectively, towards an imaginary circle located in the center of the furnace. However, in these tangential firing arrangements, although a reducing atmosphere is often present along the inner surfaces of the boundary walls which causes corrosion and slagging, there is no provision for directing air from the air nozzles to the boundary walls. Therefore, what is needed is a secondary air nozzle for use in a tangentially fired furnace in which the nozzle directs secondary air both towards the center of the furnace to support the combustion of the fuel, and towards a furnace boundary wall to minimize corrosion and slagging. 
     SUMMARY OF THE INVENTION 
     The secondary air nozzle of the present invention is designed for use in furnace applications in which improvements are achieved by discharging the secondary air in two distinct flow patterns. To this end, the nozzle is provided with a damper blade that splits the air flow into two distinct discharge flow streams, which are directed into different areas of the interior of the furnace. The discharge pattern from the nozzle can be adjusted in accordance with the particular nozzle location and design requirements. When used with a tangentially fired furnace, one of the air flow streams is directed towards the center of the furnace in a combustion-supporting relationship to the fuel, and the other air flow stream is directed towards the inner surface of one of the boundary walls to maintain an oxidizing atmosphere along the inner surfaces of the furnace wall. 
     Thus, significant advantages are achieved with the secondary air nozzle of the present invention since it provides two distinct discharge streams for the secondary air, with the relative amount of air and the angle of discharge being variable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of two air discharge devices of the present invention shown respectively mounted above and below a coal nozzle; 
     FIG. 2 is a cross-sectional view taken along the line  2 — 2  of FIG. 1; 
     FIG. 3 is a cross-sectional view take along the line  3 — 3  of FIG. 2; and 
     FIG. 4 is a cross-sectional view taken along the line  4 — 4  of FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 of the drawings, a pair of air discharge nozzles  10  and  12  are provided, with the nozzle  10  extending immediately above a coal discharge nozzle  14 , and the nozzle  12  extending immediately below the nozzle  14 . As shown in FIG. 2, each discharge nozzle  10  and  12  is formed by a housing having a rectangular cross section, with the end portions  10   a  and  12   a  of the nozzles  10  and  12 , respectively, being open to receive air, and with their other end portions  10   b  and  12   b  also being open to discharge the air, as will be further described. 
     The nozzles  10 ,  12  and  14  are mounted between two spaced mounting walls  16  and  18  (FIG. 2) which, in turn, are installed relative to one or more walls (not shown) of a furnace. For example, the mounting walls  16  and  18  can be installed in the corners of a furnace whose walls are formed by a plurality of water tubes connected by continuous elongated fins, as shown and described in U.S. patent application Ser. No. 08/595,900 filed Feb. 6, 1996 the disclosure of which is incorporated by reference. 
     The air nozzle  10  is shown in detail in FIGS. 2-5. A pair of U-shaped mounting plates  20  (FIGS. 1 and 2) and  22  (FIG. 2) are secured to the walls  16  and  18 , respectively, in any known manner for pivotally mounting the air nozzle  10  relative to the latter walls. To this end, an elongated, U-shaped slot  20   a  (FIG. 1) is provided in the plate  20 , it being understood that a similar slot (not shown) is formed in the plate  22 . As shown in FIG. 2, a pair of mounting shafts  24  and  26  project from the respective side walls of the housing of the nozzle  10  and into the slot  20   a  and the slot associated with the plate  22 , respectively. Thus, the nozzle  10  is mounted for pivotal movement about an axis defined by the shafts  24  and  26 . (Alternatively, as shown by the dashed lines in FIG. 2, a single mounting shaft can extend through the housing with its respective end portions projecting from the housing and extending in the slot  20   a  and the slot associated with the plate  22 ). This pivotal movement causes the discharge end portion  10   b  of the nozzle  10  to tilt upwardly and downwardly (as viewed in FIG. 1) relative to the walls  16  and  18 , as will be described. 
     A pair of lobes  10   c  and  10   d  (FIG. 2) are formed at the end portion  10   a  of the housing of the nozzle  10 , and are for the purpose of connecting the nozzle  10  to a linkage and drive mechanism (not shown) for selectively pivoting the nozzle about the axis defined by the shafts  24  and  26  in the above manner. This linkage and drive mechanism is fully disclosed in application serial number 288,108 filed on Aug. 10, 1994 and assigned to the assignee of the present invention, the disclosure of which is incorporated by reference. Since this linkage and drive mechanism does not, per se, form a part of the present invention a detailed disclosure of same has not been included for the convenience of presentation. 
     The above-described pivotal movement of the nozzle  10  enables the discharge angle of the air discharging from the end portion  10   b  of the nozzle  10  to be varied. The U-shaped slot  20   a  and the corresponding slot in the mounting plate  22  also accommodate axial movement of the nozzle  10  relative to the mounting walls  16  and  18  to accommodate differential thermal expansion between the nozzle and the walls. 
     With reference to FIGS. 2-5, a damper blade  30  is disposed in the housing of the nozzle  10  and is secured in any known manner to a shaft  32  which extends from the upper wall of the nozzle housing to the lower wall thereof as better shown in FIG.  4 . The blade  30  thus splits the air entering the housing into two streams-one directed generally towards the center of the interior of the furnace as shown by the flow arrows A, and the other directed at an angle to the flow stream A and towards an extension of the adjacent mounting wall  16 , as shown by the flow arrows B. In applications where the air nozzles  10  and  12  and the fuel nozzle  14  are mounted in the corners of a tangentially-fired furnace as disclosed in the above-identified patent application Ser. No. 08/595,900, the flow stream B would pass along the furnace wall associated with, or adjacent to, the mounting wall  16 . 
     The shaft  32  is rotatably mounted relative to the walls of the housing of the nozzle  10  in any known manner such as, for example, providing journals, bearings, or the like (not shown), in the latter walls. Thus, rotation of the shaft  32  causes corresponding pivotal movement of the blade  30  to vary the quantity, or mass flow, of the air in each of the respective flow streams A and B and the discharge angle of the flow stream B. The latter angle thus varies in a plane perpendicular to the plane in which the discharge angle varies as a result of the tilting of the nozzle, as described above. 
     It is understood that the blade  30  and be positioned manually by simply pivoting the blade to the desired position or, alternatively, a drive motor, or the like (not shown) can be coupled to the shaft  32  to rotate the shaft in a conventional manner to pivot the blade accordingly. 
     Since the nozzle  12  is identical in structure and function to the nozzle  10 , including the inclusion of a blade identical to the blade  30 , the nozzle  12  will not be described in detail. Also, since the present invention does not include the burner  14  per se, the latter will also not be described in detail, especially since it is also fully disclosed in the above-identified application. 
     In operation, a fuel/air mixture is introduced to, and discharged from, the burner  14  in a general direction towards the center of the furnace. Air is introduced into the air nozzles  10  and  12  and the damper  30  in each nozzle functions to split the air into the flow streams A and B which pass into the interior of the furnace. Each flow stream A from the nozzles  12  and  14  discharges in a flow stream directed generally towards the center of the furnace interior in the same general pattern as that of the fuel/air mixture discharging from the burner  14 . Each flow stream B from each nozzle  10  and  12  discharges at an angle to the axis of the nozzle and towards an extension of the mounting wall  16  which, in applications where the nozzles  10  and  12  and the burner  14  are mounted in a corner of the furnace, would be along the furnace wall extending from, or adjacent to, the wall  16 . Rotation of the shaft  32  of each nozzle  10  and  12  causes corresponding pivotal movement of its corresponding blade  30  which varies the relatively quantities, or mass flow, of the air in the flow streams A and B and the discharge angle of the flow stream B. 
     The above-mentioned linkage and drive mechanism is also activated to cause a pivotal, or tilting, movement of the nozzles  10  and  12 , about a horizontal axis perpendicular to the axis defined by the shafts  24  and  26  to vary the vertical location of the flow streams A and B in the furnace. It is understood that the discharge end of the burner nozzle  14  can also be tilted in the manner described in the above-identified patent application Ser. No. 288,108. Thus, the flow streams A and B from each nozzle as well as the respective air mass flows from each nozzle  10  and  12  can be precisely controlled in accordance with particular design requirements. 
     It is understood that several variations may be made in the foregoing without departing from the scope of the present invention. For example, the shaft  32  may be rigidly mounted in the housing of the nozzles  10  and  12  and the blade  30  pivotally mounted relative to the shaft. Also, the air nozzles  10  and  12  of the present invention are not limited to use with any specific coal-fired furnace or burner, but rather can be used in other environments requiring the variable air discharge patterns discussed above. 
     Other modifications, changes and substitutions are intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.