Abstract:
A sootblower of the short travel rotary furnace wall type having features which permit indexing of the angular position of the screw tube assembly during successive operating cycles. Indexing of the arc swept by the sootblower nozzle is provided through the use of a novel cam plate component and operating the sootblower in a manner which provides for indexing between operating cycles.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to a sootblower device for cleaning internal surfaces of large-scale combustion devices such as utility or industrial boilers. More particularly, the present invention is directed to a short travel, retracting rotary type sootblower, which provides indexing between the position of its discharge nozzle between the start of cleaning cycles to reduce thermal stresses placed on internal components of the combustion device. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     To optimize the thermal efficiency of large scale fossil fuel burning heat exchangers or boilers, it is necessary to periodically remove deposits such as soot, slag and fly ash from their interior heat exchanging surfaces. Typically, a number and types of cleaning devices known as sootblowers are mounted to the exterior of the boiler. Periodically they are inserted into the boiler through cleaning ports located in the boiler wall. Positioned on the forward end of the screw tubes or screw tubes assemblies are one or more cleaning nozzles. The nozzles discharge a pressurized fluid cleaning medium, such as air, water, or steam. The high pressure cleaning medium causes deposits of soot, slag, and fly ash to be dislodged from the internal structures of the boiler. 
     One type of sootblower is known as a short travel retracting rotary type. This type has a screw tube assembly which is inserted into the boiler, and once it reaches its fully extended position, cleaning medium is discharged from the nozzle as it is rotated through a partial arc, full rotation, or multiple full rotations as desired for wall cleaning. The sootblower medium discharged from the nozzle provides the cleaning effect mentioned previously. One very widely utilized design of the above-mentioned sootblower type is manufactured by the assignee of the present invention and is known as a Diamond Power “IR-3Z”™ sootblower device. These devices have operated in a highly reliable and effective manner around the world for many years. 
     One disadvantage of many sootblower designs is the erosion and thermal stresses caused to internal components of the boiler when their cleaning cycle operates in the same repeated manner during each operation. For the sootblower of the type mentioned previously, once the screw tube assembly is advanced and reaches its fully extended position, the nozzle begins to discharge cleaning medium and rotates through a specified arc or number of revolutions. At the conclusion of the cleaning cycle, the nozzle reaches its set rotational indexed position, at which point the screw tube assembly is retracted. The next operating cycle retraces the path of the prior cycles. When steam is used as a sootblowing medium, steam in the supply circuit piping may condense into liquid water between operating cycles. When the steam valve is opened to cause the steam sootblowing medium to flow through the sootblower at the beginning of a cleaning cycle, an initial pulse of condensate is ejected from the sootblower nozzle. Thereafter, high pressure steam flows through the nozzle until the cleaning medium valve is again shut-off. The initial ejection of the condensate has an undesirable consequence of placing erosion and thermal stresses on the internal components which impacts it. The heat transfer surfaces can tolerate condensate, but when numerous cycles occur in which the same surfaces are repeatedly impacted by condensate, failures of the internal heat transfer components can occur. Accordingly, in many applications it is desirable to index the position at which the sootblower nozzle begins its cleaning cycle so that the same internal surfaces are not struck by condensate at the start of each operating cycle. 
     Numerous approaches toward providing sootblower nozzle indexing are known. For example, in long retracting sootblowers which discharge cleaning medium as a lance tube is extended and retracted, the cleaning medium path can be displaced between operating cycles. An approach implemented by the assignee of this invention for indexing long retracting sootblowers uses a drive rack for a gear driven type long retracting sootblower which features a mechanism for indexing the phasing of gear drive between operating cycles. This approach is described in the assignee&#39;s U.S. Pat. No. 4,803,959. Other types of indexing mechanisms are known, for example, some use gear drives having ratcheting indexing components. 
     While many approaches toward providing indexing of sootblower operating cycles are known, these strategies are not adaptable for modification to existing short travel retracting rotary sootblowers. 
     In accordance with the present invention, these inventors have found that modifications of the existing IR-3Z™ sootblower components coupled with modifications of the control schedule of the device provide the desirable indexing feature. By preferably providing at least four different rotated start positions for the sootblowing start cycle, the erosion effects of condensate ejection can be distributed over multiple internal surfaces, reducing the likelihood of boiler component damage. The principles of this invention may be implemented as a modification to existing sootblowers or in newly constructed sootblower assemblies. 
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial view of a short retracting rotary sootblower in accordance with the prior art which may be modified to incorporate the features of the present invention; 
         FIG. 2  is a side elevational view of a short retracting rotary sootblower in accordance with the prior art which may be modified to incorporate the features of the present invention; 
         FIG. 2   a  is an enlargement of a portion of the short retracting rotary sootblower as shown in  FIG. 2 ; 
         FIG. 3  is an exploded pictorial view of the gooseneck valve assembly and feed tube of the sootblower shown in  FIGS. 1 and 2 ; 
         FIG. 4  is an exploded pictorial view of the screw tube assembly screw drive assembly of the sootblower shown in  FIGS. 1 and 2 ; 
         FIGS. 5   a  and  5   b  illustrate cam plates for sootblowers in accordance with the prior art of the type shown in  FIGS. 1 through 4 ; 
         FIGS. 6   a  and  6   b  illustrate a cam plate for a sootblower in accordance with the present invention; and 
         FIGS. 7   a  and  7   b  illustrate the cam plate in accordance with this invention as it interacts with other elements of a short travel rotary sootblower assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 ,  2 , and  2   a  show a complete furnace wall sootblower in accordance with the prior art which may be modified to incorporate the features of the present invention. The illustrated sootblower is known in the industry as a short travel, retracting rotary sootblower which is designated by reference number  10 . This type of sootblower is primarily used for cleaning furnace wall tubes, and an example of the design is designated by the Assignee of this invention as an “IR-3Z”™ blower assembly.  FIGS. 1 ,  2 , and  2   a  show the basic elements of sootblower  10 . Gooseneck assembly  13  acts as a frame member to provide support for the major components of sootblower  10 . Gooseneck assembly  13  includes gooseneck tube  12  which conducts sootblowing cleaning medium. Feed tube  14  is mounted to gooseneck valve assembly  13  and conducts the blowing medium which is typically steam for the cleaning function, controlled by internal poppet valve assembly  19 , as will be described in more detail in the following description. Screw tube assembly  18  includes nozzle extension  20  which is a hollow tube which over fits feed tube  14  in a telescoping manner. Nozzle extension  20  may be provided in various lengths depending on the intended cleaning application. Packing gland  22  provides a fluid seal between the nozzle extension  20  and feed tube  14  such that the flow of blowing medium within feed tube  14  is conducted into nozzle extension  20  without significant leakage between the tubes. The cleaning medium flows through the interior hollow cavities of feed tube  14  and nozzle extension  20 , and is ejected within the boiler through nozzle  24 . 
       FIG. 3  shows in detail, feed tube  14  which is mounted to gooseneck tube  12  at flange  16 . 
     Sootblower  10  is mounted to the boiler wall  15  (shown in  FIGS. 2 and 2   a  in a simplified form) by front bracket assembly  17 . When sootblower  10  is operated, nozzle extension  20  is extended into the furnace interior (the area to the left of boiler wall  15  as shown in  FIGS. 2 and 2   a ) and, when cleaning is completed, it is withdrawn. During cleaning, nozzle  24  is rotated to sweep an arc of cleaning medium spray. 
     Drive motor  26  powers sootblower  10  through a gear reducer  28 . Rotation of drive motor  26  is converted to rotation of gear shaft  30  which in turn rotates drive pinion gear  32 . Drive pinion gear  32  meshes with hub gear  34  mounted to hub  38 . Screw tube  42  passes through hub gear  34  and hub  38 . Pins  36  extend inwardly from hub  38  and engage with the helical grooves  40  formed on the outside surface of screw tube  42 . Screw tube  42  is attached to nozzle extension  20 . 
     Cam plate  44  shown by  FIGS. 4 ,  5   a  and  5   b  is affixed to the proximal end of screw tube  42  via hub  35  adjacent to packing gland  22  and includes, in accordance with conventional designs, a single peripheral notch  46  which engages with an elongated guide bar  48  which is supported by support plate  50 . Guide bar  48  has a free end  52  positioned at the front end of the unit such that cam plate notch  46  escapes from engagement with the guide bar  48  at near the fully extended position of screw tube  42 . 
     The extension and retraction movement of screw tube assembly  18  is started by a control command through electric control assembly  53  which activates drive motor  26 . Rotation of motor  26  rotates drive pinion gear  32  and hub gear  34 . This rotation causes pins  36 , which engage with helical grooves  40 , to cause screw tube  42  to move from the retracted position shown in  FIG. 2  to an extended position. During screw extension movement (between the fully retracted and fully extended positions), screw tube  42  is prevented from rotating due to the engagement between cam plate notch  46  and guide bar  48 . When screw tube assembly  18  reaches its fully extended position, cam plate  44  extends past guide bar end  52 , and therefore the screw tube  42  is no longer restrained from rotating. At this point, continued rotation of hub gear  34  causes screw tube assembly  18  and consequently nozzle  24  to rotate. Front pawl  54  is spring loaded to engage with cam plate notch  46  and is used to establish a detent for the “park” position of the cam plate  44  to position cam plate notch  46  to reengage with guide bar end  52  when screw tube assembly  18  is being retracted. In the forward direction, the front pawl  54  is spring loaded and slip by the cam notches  46 . In the reverse direction of cam plate  44 , front pawl  44  stops the cam plate at the correct position for notch  46  to engage with guide bar end  52 . 
     When screw tube assembly  18  reaches its fully extended position and nozzle  24  is rotated through the desired partial rotation arc or number of rotations, drive motor  26  is stopped based on a control input from a timer circuit in electric control assembly  53  and then commanded through the electric control assembly to reverse its rotation. Such reversal allows front pawl  54  to engage with cam plate notch  46  and position it properly to cause it to reengage with guide bar end  52  in the retraction movement. Continued reverse rotation of the motor  26  causes screw tube assembly  18  to return to its fully retracted, parked position, shown in  FIG. 2 . Limit switch  55  is activated when cam plate  44  reaches its fully retracted position, and provides a control signal to electric control  53  to stop current to drive motor  26  until the next cleaning cycle. 
     The flow of blowing medium is controlled by mechanically operated valve  19  shown as a poppet type valve. A supply of steam or air or other blowing fluid medium is connected with poppet valve  19  at flange  56  and it is opened to an “on” position and closed to an “off” position by motion of valve trigger  60 . Valve trigger  60  is in the shape of a caliper arm and includes an inwardly directed tooth  62 . When poppet valve  19  is opened, steam flows through gooseneck assembly  13 , into feed tube  14 , through nozzle extension  20 , and out of nozzle  24 . 
     Cam plate  44  of convention design is best shown with reference to  FIGS. 4 ,  5   a , and  5   b , and forms a disc section  64  and a tubular section  66  extending from the disc section. Disc section  64  forms notch  46  described previously. Tubular section  66  includes, in accordance with a conventional design, a single recess (or notch)  68  which is engaged by valve trigger tooth  62 . Poppet valve  19  is operated by movement of valve trigger  60 . When valve trigger  60  is in a radially outer position which corresponds with tooth  62  riding on the outside surface of tubular section  66 , the poppet valve  19  is opened to the “on” position to allow the flow of the fluid cleaning medium. On the other hand, when the valve trigger tooth  62  fits into recess  68  thus moving to a radially inward position, the flow of cleaning medium is stopped through the valve. Valve trigger  60  is biased to the inner (off) position by the force of valve spring  57 . The radial extent of recess  68  (or stated another way, the angular length of tubular section  66 ) can be adjusted such that the cleaning medium discharge occurs some arc segment less than 360° using a cam plate such as cam plate  44   a  shown in  FIG. 5   b  in which recess  68   a  has a greater angular extent as compared with recess  68 . This is provided for applications where cleaning is only required over a partial arc of rotation of screw tube assembly  18 . Tubular section  66   a  as illustrated in  FIG. 5   b  provides about 300° of cleaning medium discharge. 
     It is noted that cam plates  44  and  44   a  may be formed as one-piece articles, or in arc segments as they are illustrated. Multipiece construction provide ease of assembly since a one-piece ring shaped cam plate would need to be inserted over nozzle extension  20 , whereas the separate segments can be bolted to hub  35  with the screw tube assembly  18  in its retracted position. 
     Since the cam plate notch  46  needs to engage and reengage with guide bar  48  at the beginning and end of each operating cycle, the start and stop position of the lance tube nozzle  24  and the position at which cleaning medium discharge occurs, is fixed between operating cycles in the illustrated prior art sootblower  10  described previously. 
     The above description describes sootblower  10  in accordance with prior art known features. Sootblower  10  modified in accordance with the present invention utilizes cam plate  74  illustrated in  FIGS. 6   a,    6   b ,  7   a , and  7   b . Notably, cam plate  74  includes more than one of the peripheral notches  78 , designated as notches  78   a ,  78   b ,  78   c , and  78   d  which engage guide bar  48 , as does notch  46  in the prior art cam plate  44 . This enables cam plate  74  and consequently sootblower screw tube assembly  18  to be moved to more than one angularly indexed position during its extension and retraction motion (and importantly, its start position). Cam plate tubular section  72  is segmented into sections  72   a - d  and has a number of discontinuities or recesses  82   a ,  82   b ,  82   c , and  82   d  which, like tubular section  66  of cam plate  44 , controls the flow of cleaning medium discharge through poppet valve  19 . It is necessary to move poppet valve  19  to a closed position when the sootblower reaches its parked and indexed position during retraction and extension of screw tube assembly  18 . For this reason, tubular section recesses  82  are equal in number to the number of cam plate notches  78  provided. Cam plate  74  is a direct replacement for cam plate  44  used in existing sootblower  10 . It should be noted that other configurations of cam plate  74  may be provided. In accordance with this invention, more than one notch  78  is needed to implement the features of the present invention. However, various numbers of notches  78  and therefore indexed start positions can be provided. For example, two, three, or more notches  78  could be provided, with the notches  78  and  82  at equal angular arc spacings. 
     In operation, cam plate  74  is positioned in its beginning park position with one of notches  78   a ,  78   b ,  78   c , and  78   d  engaged with guide bar  48 . Drive motor  26  is actuated to cause cam plate  74  to advance along guide bar  48  as screw tube assembly  18  is being extended into the boiler. When cam plate  74  escapes from engagement with guide bar  48  near its fully extended position, cam plate  74 , and consequently screw tube assembly  18 , are caused to rotate. Valve trigger  60  engages with recesses  82   a - d  as the cam plate is rotated. Drive motor  26  is actuated over a time period established by a timer unit within electric controller assembly  53 . When the rotation of nozzle extension  20  occurs through a desired arc (or full rotations), drive motor  26  is caused to be deenergized to stop the rotation when cam plate  74  is at some angular position displaced from that of the first notch  78   a  (or another notch engaged in the preceding cycle). Since the forward/reverse motion is based on a timer control, the timer is set to cause cam plate  74  to overshoot the desired parked position slightly. The motor  76  is reversed to position the cam plate  74  (as explained in more detail below) and is stopped in its rotation so that another one of notches  78   b ,  78   c , or  78   d  is positioned to engage with guide bar  48 . Once the desired position is achieved, the drive motor  26  causes the cam plate  74 , at one of notches  78   a  through  78   d  to reengage with the guide bar  48 . In successive operating cycles, drive motor  26  is energized through a predetermined time period which causes rotation again to a position just past that corresponding with the notch  78   a  through  78   d  displaced from the immediately preceding cycle. At full retraction, drive motor  26  is deenergized by activation of limit switch  55 . 
     It is necessary for the flow of steam through sootblower  10  to be stopped when cam plate  74  is at a “start” position at which one of notches  78   a ,  78   b ,  78   c , or  78   d  is positioned to engage with guide bar end  52 . Accordingly, cam tubular sections  72   a - d  have recesses  82   a - d  equal in number to those of notches  78   a - d.    
       FIGS. 7   a  and  7   b  illustrate the interaction between valve trigger  60  and tubular sections  72   a - d . As shown in  FIG. 7   a , valve trigger  60  is moved to its radially outer position, overcoming the force of spring  57  and riding on the outside of tubular sections  72   a - d . This position opens the flow of steam through poppet valve  19 . When the rotation has gone through a desired cleaning arc, the electronic control timer signals the device to stop rotation and reverse. When cam plate  74  is stopped and its rotation is reversed, trigger tooth  62  contacts the associate tubular section  72   a - d  and continued reverse rotation causes valve trigger  60  to move to its radially inner position which stops the flow of cleaning medium as it moves into one of recesses  82   a - d . This interaction also acts as a “one-way ratchet” which positions cam plate  74 , such that guide bar end  52  is aligned with one of notches  78   a - d.    
     Cam plate  74  is illustrated in  FIGS. 6   a,    6   b ,  7   a , and  7   b  and provide four possible indexed park positions for the sootblower nozzle corresponding with each of the four notches  78   a - d . This cam plate  74  provides rotation set positions at 90° spaced increments. For example, in operation, cam plate  74  can provide more or less than 360° of rotation for each operating cycle which would result in a different one of the notches  78   a - d  engaging with guide bar end  50  at each successive operating cycle. It is within the scope of the present invention to provide differing numbers of notches  78   a . In order to provide the features of the invention, at least two of such notches  78  should be provided. The number of recesses  82  in tubular section  72  are equal to those of notches  78 . 
     As is the prior art cam plate  44 , cam plate  74  may be made in a one piece or multipiece construction as illustrated by the figures. 
     While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.