Abstract:
A tube cleaning assembly ( 10 ) comprising a cylindrical housing ( 11 ) having a bore ( 20 ) with a coaxial strut ( 27 ) therein, capable of both axial and rotation movement relative to the housing ( 11 ). One end of the strut ( 27 ) extends through an aperture ( 29 ) in an end wall ( 21 ) of the housing ( 11 ) and is connected to a cleaning brush ( 17 ), the other end of the strut ( 27 ) being adjacent a piston ( 26 ) reciprocable within the bore ( 11 ) to move the strut axially, the axial movement of the strut ( 27 ) being translated into rotational movement around its axis and rotating both strut and brush.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to apparatus for cleaning the residue from the bores of thermal transfer tubes.  
       BACKGROUND OF THE INVENTION  
       [0002]     The inner surfaces of a heat transfer tube may be enhanced with a plurality of surface effects that create additional paths for fluid flow within the tube and thereby enhance turbulence of heat transfer mediums flowing within the tube. This increases fluid mixing to reduce the boundary layer build-up of the fluid medium close to the inner surface of the tube, such build-up increasing the resistance and thereby impeding heat transfer. Known surface effects may be in the form of internal ribs as is shown in EP-A-0865 838, or may be created by a cross-grooved surface as is known from U.S. Pat. No. 6,026,892. These protrusions also provide extra surface area for additional heat exchange. Another method of creating protrusions is shown in WO 03104736  
         [0003]     A problem associated with heat exchangers is that over time the bore and exterior walls of the heat exchange tubes develop corrosion, scale and other undesired residue. The build up of residue decreases and/or generally adversely effects the heat transfer efficiencies and operating costs for fuel, in turn, increase. Periodic maintenance is therefore required to clean the tubes. Frequently the equipment must be taken off-line during maintenance. Such maintenance can be performed by plant personnel or outside contractors who are specially trained and use special purpose equipment to perform such tasks. It is desirable that any down time be minimized. The task is typically performed manually and is therefore costly and time consuming, especially for large heating and cooling plants.  
         [0004]     A variety of techniques and types of equipment have been developed to clean the interior and exterior surfaces of pipes and particularly heat transfer tubes. One known cleaning technique is to individually direct equipment into each tube to mechanically dislodge the residue from the internal tube walls. Some of the latter equipment uses rigid lances that either rotate and/or have rotating blades. U.S. Pat. No. 5,579,726 discloses a lance-based assembly that directs streams of high-pressure water to effect the cleaning. High-pressure spray systems are also known that direct streams of water from a spray hose into each tube such a system is disclosed in U.S. Pat. No. 6,626,195. Yet another method is disclosed in U.S. Pat. No. 4,676,301 in which a brush element is passed through a heat exchange tube.  
         [0005]     The present invention is related to the use of brush cleaning elements for the internal cleaning of heat transfer tubes and in particular to cleaning of tubes having internal surface effects to increase turbulence. A problem with the use of brushes is that when passed through the tubes in a single direction, any residue, scale etc. may only be properly removed from one side of the particular surface effect.  
         [0006]     The present invention provides an improved cleaning brush assembly for use within thermal transfer tubes.  
       STATEMENTS OF THE INVENTION  
       [0007]     Accordingly the invention provides a tube cleaning assembly comprising a cylindrical housing having a bore therein, a strut mounted coaxially within the bore and being capable of both axial and rotational movement relative to the housing, one end of the strut extending through an aperture in an end wall of the housing and being connected to a cleaning brush, the other end of the strut being adjacent a piston reciprocal within the bore to move the strut in at least one axial direction, and wherein axial movement of the strut is translated into rotational movement of the strut and brush, the direction of rotation of the strut and brush being dependant upon the direction of axial movement.  
         [0008]     The movement of the brush in two axial directions and both directions of rotation ensures efficient cleaning of the inner surface of the thermal transfer tube.  
         [0009]     Preferably the strut is moved in said one axial direction by high pressure cleaning fluid acting upon the piston. The strut is moved in said other axial direction by a spring means, preferably a coil spring located concentrically with the strut and acting between the housing and an abutment means on the strut.  
         [0010]     Preferably, the axial movement of the strut within the housing is translated into rotation by axially extending helical surfaces on one of the strut or end wall engaging with a cooperating surface on the other of the strut and end wall. The helical surface may be provided by a helical groove, preferably a single start screw thread. The helical groove may be formed on the strut, and the co-operating surface comprises abutment means on the end wall which engage with the groove.  
         [0011]     The abutment means comprise a plurality of abutments circumferentially spaced around the aperture in the end wall. Preferably the abutment means are balls rotatably mounted in the end wall engaging a co-operating screw form in the strut.  
         [0012]     The end portion of the strut adjacent the piston is mounted for rotation in a bearing.  
         [0013]     The housing is provided with a plurality of spaced holes therein which in use permit cleaning fluid to pass through the housing into the interior of a tube being cleaned.  
         [0014]     A tube clamping assembly may be attached to the housing on the pressurized fluid side of the piston, the clamping assembly being operated by cleaning fluid pressure.  
         [0015]     Another aspect of the invention provides a method of cleaning the inner surface of a thermal transfer tube in which a tube cleaning assembly according to the first aspect of the invention is passed through the tube in one direction wherein the assembly is causes to pause at spaced locations along the tube and when the assembly is stationary the brush is caused to reciprocate within the tube to move axially and rotationally in first one direction and then in the other direction.  
         [0016]     Preferably, the movement in one direction is caused by high pressure cleaning fluid acting on the piston, and movement in the other direction is under a spring bias when said fluid pressure is cut. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0017]     The Invention will be described by way of example only and with reference to the accompanying drawings in which:  
         [0018]      FIG. 1  is a longitudinal section through a cleaner assembly according to the present invention, and  
         [0019]      FIG. 2  is an exploded isometric drawing of the cleaner assembly shown in  FIG. 1   
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     A cleaner assembly  10  for cleaning the internal surface of a thermal transfer tube is shown in  FIGS. 1 &amp; 2 . The assembly  10  comprise a cylindrical housing  11  having a bore  20  closed at one end by a rear sub-assembly  12  and at its other end by an end wall  21 .  
         [0021]     The rear sub assembly  12  is cylindrical and has a connection  13  to a supply hose  14 . The supply hose  14  is connected to a pump (not shown) for the supply of high pressure water into the cleaner assembly  10 . The rear sub-assembly may further include radially moveable pins  16  which in use are move by fluid pressure into contact with the inner surface of a tube to hold the cleaner assembly fast during the operation of a cleaning brush  17  mounted at the other end of the housing. An annular plate  18  at the front end of the sub-assembly engages with the rear of the cylindrical housing  11  to form an end wall of the housing. The plate  13  may be assembled to the housing  11  using co-operating screw threads.  
         [0022]     A suitable length of hose  14  is secured to the cleaner assembly  10  and is typically deployed and stored at a hose spool or collection reel assembly. The hose  14  is constructed to withstand the normal anticipated working conditions and pressures and is typically constructed of several layers of water impermeable material in numerous wound wrappings and may contain wraps or bands of wire, KEVLAR and the like. The diameter of the hose  14  can be selected as desired e.g 3 mm to 25.00 mm depending upon the application, diameter of tube to be cleaned and desired working pressures.  
         [0023]     The housing  13  has a desired number of orifices  15  spaced at desired locations around the housing to direct a number of high-pressure (e.g. 200 to 50,000 psi) streams of water against the internal walls of a heat transfer tube to dislodge and wash scale and residue from the tube walls.  
         [0024]     A piston  26  is located in the bore  20  adjacent the rear sub-assembly  12  and is capable of reciprocating movement within the bore. Pressurized fluid entering the housing  11  acts on the piston  26  to push the piston away from the end wall  18 . An annular bearing  23 , preferably a ball race, is located adjacent the front face of the piston  26  with an annular thrust washer  24  located on the side of the bearing  23  away from the piston.  
         [0025]     A coaxial annular strut  27  extend axially from the piston  26  and passes through an aperture  29  in the front end wall  21  to join with a connector  28  in turn connected to the brush  17 . The strut  27  is held coaxially within the housing  11  by an annular spacer  25  adjacent the thrust washer  24  and passes through the centres of the spacer  25 , thrust washer  24  and bearing  23  for contact with the piston  26 .  
         [0026]     A coil spring  31  is arranged coaxially of the strut  27  and acts between the front end wall  21  of the housing  11  and the spacer  25  which in turn abuts a pair of circlips  32  which engage in a groove  33  in the end portion of the strut  27  adjacent the piston. The spring  31  biases the strut rearwardly of the housing. The circlips  32  are accommodated in a recess  35  formed in the face of the spacer  25  adjacent the thrust bearing  24 .  
         [0027]     The other end portion of the strut  27  has a helical groove  36  formed thereon. The grooved portion of the strut  27  passes through the aperture  29  in the end wall  21 . The end wall  21  has a central spigot  37  projecting axially outwardly of the housing  11  and a ball ring  38  is located on the outer side of the end wall around the spigot  37 . The ball ring  38  provides a housing for a plurality of ball  39 , preferably three, which pass through apertures in the spigot to engage in the helical groove  36 . The groove  36  is a single lead helical groove and the balls  39  are axially off-set engaging in different locations along the groove.  
         [0028]     With the cleaner assembly in position within a tube, when cleaning fluid, typically water, is introduced under pressure through the rear sub-assembly  12 . The supply of pressurised water and movement of the cleaner assembly along the tube may be controlled by a pre-programmed cleaning apparatus that forms no part of the present invention.  
         [0029]     The water pressure causes the pins  16  to move radially outwardly to engage the sides of a tube. The piston  26  is moved forward by the pressure to move the strut  27  axially forward. The strut  27  is free to rotate on the bearing  23  and ball ring  38 , and therefore the forward movement of the strut  27  coupled with the engagement of the balls  39  in the helical groove  36 , translates the axial movement onto both axial and rotational movement of the strut  27 . The movement of the strut  27  in turn causes the brush  17  to move forward and rotate in one direction of rotation. Water under pressure will also pass through orifices  15  which direct the jetted streams of water against the tubing.  
         [0030]     If the pressurized water feed is cut, the spring  31  pushes the strut  27  rearward and the brush is caused to rotate in the opposite direction of rotation. The rearward movement of the piston  26  under the spring load will cause water in the housing to be displaced out through the orifices  25 .  
         [0031]     Although, the piston ( 26 ) is conveniently moved forwardly by the hydraulic pressure generated by the cleaning fluid, the piston may be advanced by mechanical means (not shown) such as an actuator.  
         [0032]     The reciprocating brush stroke will typically be between ½-1.0 inch (12-25 mm) and the cleaning assembly advances through the tube in a series of steps cleaning by reciprocation of the brush at each step.  
         [0033]     In other embodiments of the present invention (not shown) the clamping pins  16  may be omitted. The brush may be advanced through the tube by mechanical means, for example by pushing the hose ( 14 ) into the tube. Multiple lead helical grooves may be used instead of the single lead helical groove  36 .  
         [0034]     The combination of rotational and axial movement of the brush in two directions ensures that any surface grooving, or ribbing is cleaned on both axial sides as the brush reciprocates within the tube. The brush assembly according to the present invention is therefore capable of cleaning both sides of a surface effect within the tube for a single pass of the assembly along the tube in one direction only.