Abstract:
A lance tube stuffing box assembly includes within a seal cavity, a first and a second sleeve bearing oriented to be axially aligned with the bore and with each other and spaced apart within the bore to define a packings space. A plurality of braided packings are situated within the packings space and oriented to be axially aligned with each of the first and second sleeve bearings; and inserted within the bore in opposed relation to the annular wall of the seal cavity a gland follower which is likewise axially aligned and bears against the first bearing with an axial force to narrow the packings space, urging the plurality of braided packings to expand radially, such that when a lance tube is inserted axially. The axial force causes the braided packings to sealingly engage the lance tube.

Description:
FIELD OF THE INVENTION 
       [0001]    The inventive stuffing box is a sealing technology and, in particular, a stuffing box having bearings within. 
       BACKGROUND OF THE INVENTION 
       [0002]    Operators of large-scale boilers are continuously striving to improve the efficiency of their operation. Cleaning highly heated surfaces, such as the heat exchange surfaces of a boiler, furnace, or the like, has commonly been performed by devises generally known as sootblowers. Sootblowers typically employ water, steam, air, or a combination thereof, as a blowing medium which is directed through one or more nozzles against encrustations of slag, ash, scale or other fouling materials which become deposited on the heat exchange surfaces. 
         [0003]    One example of a Sootblower mechanism that has proven especially useful is that taught by Hipple in U.S. Pat. No. 6,575,122 issued on Jun. 10, 2003 and entitled, “Oscillating Sootblower Mechanism.” Typical sootblowers of the long retracting type, the Hipple Sootblower has a retractable lance tube which is periodically advanced into and withdrawn from the boiler while simultaneously rotated such that one or more blowing medium nozzles at the end of the lance tube project jets tracing helical paths. 
         [0004]    The lance tube, itself is long and narrow and must sealingly engage with a source of superheated steam as the tube, itself, moves both along its transverse axis and rotates around it. Generally one configuration of the sealing mechanism includes a stuffing box or stuffing box. In a conventional stuffing box, the seal itself is provided by packing rings, or a square cross-sectioned rope which is packed or wound tightly around the lance tube and compressed in place with a threaded nut and spacer. As generally configured, then, the lance tube over-fits a feed tube and the stuffing box provides a fluid seal between the lance tube and the feed tube so that blowing medium conducted into lance tube from feed tube is discharged from one or more nozzles at a distal end of lance tube. 
         [0005]    As conventionally configured, stuffing boxes tend to wear rapidly and lack appropriate support for the lance tube, allowing nozzles to move out of a centered relation within the heat exchanger and thereby altering the expected spray pattern on the surface creating premature wear where spray patterns overlap and missing portions of the heat exchanger thereby reducing efficiency. Because of their extended length, Lance tubes also exert a torque where supported as gravity draws the tube downward, especially at its distal end. Seals tend to wear unevenly which accentuates the eccentricity of the position over time, yielding even more compromised nozzle patterns. A stuffing box and seal yielding more support and better durability are needed in the art. 
       SUMMARY OF THE INVENTION 
       [0006]    A lance tube stuffing box assembly includes within a seal cavity, a first and a second sleeve bearing oriented to be axially aligned with the bore and with each other and spaced apart within the bore to define a packings space. A plurality of braided packings are situated within the packings space and oriented to be axially aligned with each of the first and second sleeve bearings; and inserted within the bore in opposed relation to the annular wall of the seal cavity a gland follower which is likewise axially aligned and bears against the first bearing with an axial force to narrow the packings space, urging the plurality of braided packings to expand radially, such that when a lance tube is inserted axially. The axial force causes the braided packings to sealingly engage the lance tube. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Preferred and alternative examples of the present invention are described in detail below with reference to the following drawings: 
           [0008]      FIG. 1  is a prior art isometric view of a sootblower of the Hipple type offered for nonlimiting context; and 
           [0009]      FIG. 2  is a side view of a stuffing box portraying the arrangement of bearings and seals within the seal cavity. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0010]      FIG. 1  illustrates a conventional sootblower mechanism, as taught by Hipple, supra, and generally designated there by reference number  10 . Sootblower assembly  10  principally comprises frame assembly  12 , lance tube  14 , feed tube  16 , and carriage  18 . Sootblower  10  is shown in its normal resting or resting position. Upon actuation, lance tube  14  is extended into and retracted from a boiler (not shown) and is simultaneously oscillated rotationally. 
         [0011]    A carriage  18  drives lance tube  14  into and out of the boiler  25  and includes drive motor  40  and gear box  42  which is enclosed by housing  44 . Carriage  18  drives a pair of pinion gears  46  which engage the previously mentioned toothed racks to advance carriage  18  and lance tube  14 . Bearings  58  and  59  engage with tracks  26  to support carriage  18 . 
         [0012]    Feed tube  16  is attached at one end to rear bracket  52  and conducts blowing medium which is controlled through the action of poppet valve  54 . Poppet valve  54  is actuated through linkages  56  which are engaged by carriage  18  to begin blowing medium (typically steam) discharge upon  35  extension of lance tube  14 , and cuts off the flow once the carriage  18  returns to the idle retracted position shown in  FIG. 1 . Lance tube  14  over-fits feed tube  16  and a fluid seal between them is provided by stuffing box (not shown) so that blowing medium conducted into lance tube  14  from 40 feed tube  16  is discharged from one or more nozzles  64  at the distal end of lance tube  14 . For long lance tube lengths, an intermediate support  66  may be provided to prevent excessive bending deflection of the lance tube. Additional details of the construction of a well-known design of the “IK” type sootblower are found in U.S. Pat. No. 3,439,376, which is hereby incorporated by reference. 
         [0013]    Referring to  FIG. 2 , the lance tube  14  is supported and sealed within the carriage  18  by a stuffing box assembly  30 . The carriage  18  defines a seal cavity  20  housing the stuffing box assembly  30 . A proximal end of the seal cavity  20  is defined by a gland follower  22  which encompasses the feed tube  16 . The gland follower  22  is mounted on the carriage  18  on gland bolts  23  secured in place with gland nuts  24 . 
         [0014]    The stuffing box assembly  30  includes two bushing seals referred to herein as vise bearings  31 . The vise bearings  31  are shown in side-elevational view. The vise bearings  31  are rigid tubes having substantially cylindrical outer surface, inner bore surface, and annular first and second ends. The diameter of the inner bore is selected to be slightly larger than the diameter of the lance tube and the diameter of the outer surface is selected to be slightly smaller than the diameter of the seal cavity  20 . The two vise bearings  31  are spaced apart such that their respective inner bores provide bearing surface for the lance tube  14  supporting it in a position to optimally place the nozzles  64  when the lance tube  14  is activated. 
         [0015]    Between the vise bearings  31  there are a plurality of braided packings  32  which, in alternate embodiments include any of a composition used extensively in industry for a variety of sealing purposes. Typically braided packings  32  are made of flax, jute, asbestos or synthetic, such as polytetraflouroethylene, fibers which are formed into yarns or strands and which are braided together about core strands. The result is typically a packing having a square cross-section and herringbone weave pattern extending in an axial direction along the packing; typical such packings are illustrated in U.S. Pat. No. 3,646,846. 
         [0016]    One exemplary embodiment of the braided packings  32  is a “Braided High Temperature Packing Comprising a Core of Folded Flexible Graphite Sheet,” such as that taught by U.S. Pat. No. 5,225,262 to Leduc issued on Jul. 6, 1993 and fully incorporated by this reference: “The braided packing of the invention is suitable for high-temperature and high-pressure applications, with functional limits up to 1200.degree. F. and 5,000 psi. The resilience and toughness of the packing is achieved through a flexible packing core of folded, reinforced square plait braided graphite tape overbraided with high strength and high-temperature resistant yarns. The resulting packing is rugged, non-hardening, non-metal, non-stem scoring, and easily removable (e.g., from a packing gland) when it needs to be replaced. The high-temperature/high-pressure resistant packing of the invention has the additional advantage of not requiring the use of asbestos and yet retaining the high-temperature resistant properties of that product. The inner core of the packing can be pre-consolidated to a density approaching the final density and therefore the final product can be live-loaded (e.g., into a valve stem packing gland), thus saving considerable time in the final adjustment of the gland.” An additional and nonlimiting list of suitable packing materials are taught in U.S. Pat. No. 6,644,007 to Fujiwara et al. on Nov. 11, 2003; U.S. Pat. No. 6,502,382 to Fujiwara et al. on Jan. 7, 2003; and U.S. Pat. No. 6,385,956 to Ottinger, et al. on May 14, 2002. 
         [0017]    A presently preferred embodiment exploits either or both of braided packings  32  and the vise bearings  31  comprising Polybenzimidazole (PBI) as molded material or as fiber. PBI fiber was first derived in 1983 and is a synthetic fiber with an extremely high melting point that also does not readily ignite, because of its exceptional thermal and chemical stability. The Federal Trade Commission definition for PBI fiber is a “manufactured fiber in which the fiber-forming substance is a long chain aromatic polymer having recurring imidazole groups as an integral part of the polymer chain”. When used as a fiber to make up a braided packing  32 , PBI demonstrates superior longevity and sealing capability. While PBI is one suitable constituent, it is not the only such suitable constituent of either the vise bearings  31  or the braided packings  32 . 
         [0018]    The vise bearings  31  are configured as sleeve bearings but are exploited in this application to serve a novel, important, and nonobvious function in the stuffing box assembly  30 . The vise bearings  31  are spaced apart and provide support to the lance tube  14  lending support to the whole of the lance tube that is largely equivalent to that of a bearing that ran from an outer surface of a first vise bearing  31  to that of an opposedly situated vise bearing  31  while preserving a space for the braided packings  32  between the vise bearings  31 . Given the elongate arrangement of the lance tube  14 , should the center of gravity rest outside of a central point between the first and second vise bearings  31 , the weight of the lance tube imparts torque around the vise bearings  31 . By their spaced apart configuration, the vise bearings  31  can resist the torque being situated further apart on the lever arm, thereby obtaining a mechanical advantage as compared to the same bearings situated in touching relation. The spaced apart relation, therefore, prevents the torque from deflecting the lance tube  14  and, thereby compromising the sealing conformity of the braided packings  32  with the outer surface of the lance tube  31 . While a two bearing solution is described, these advantages are gained by, at least the outer two bearings but might be enhanced by additional bearings at intervals throughout the braided packings  32  in the packings space. 
         [0019]    A second but also important function of the vise bearings  31  in cooperation with a gland follower  22 , is to compress the braided packings  32  deforming them radially in response to the compressive forces applied axially. The gland follower  22 , is urged axially by the suitable torquing of the gland nuts  24  on the gland bolts  23 . Torque exerted on the gland nuts  24  caused them to rotate. Because the inner radii of the vise bearings  31  is approximately equal to that of the braided packings  32  and the outer radii of the vise bearings  31  is approximately equal to outer radii of the braided packings  31  (i.e. by approximately equal, the application requires less than ten percent difference between the radii of the uncompressed braided packings  32  and the vise bearings  31 ). The rotational motion is converted by the meshing of threads on the gland nut  24  and the gland bolts  23  to impart a linear motion axially inward thus converting the torque to a linear force axially inward. In the described fashion, the gland follower  22  exerts the compressive force on the braided packings  32  pressing them inward within the seal cavity  20  into sealing engagement with the lance tube  14 . 
         [0020]    When suitably assembled, the gland assembly  30  engages the lance tube  14  and forms a suitable seal between it and the feed tube  16  allowing the lance tube to conduct high energy steam from the feed tube  16 , through the lance tube  14  to leave the lance tube  14  through any of the several nozzles  64 . As a result of the sealing engagement between the gland assembly  30  and the lance tube  14 , in operation, the sealing engagement can be so tight as to cause the gland assembly  30  to move in axially and rotate with the lance tube  14  together as an integral assembly. 
         [0021]    While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, neither exact dimension of either of the vise bearings  31  nor the number of braided packings  32  are critical and may be adjusted in accord with the particular application. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.