Abstract:
A method for cleaning pipes of a heat exchanger includes placing a throttle-free jet nozzle against an end of a pipe. The throttle-free jet nozzle has an outlet opening of a same size or slightly smaller than an inner cross-sectional area of the pipe. A stream of air containing an abrasive is blown through the pipe for cleaning the pipe.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation, under 35 U.S.C. § 120, of copending international application No. PCT/EP2005/002903, filed Mar. 18, 2005, which designated the United States; this application also claims the priority, under 35 U.S.C. § 119, of German patent application No. 10 2004 014 822.8, filed Mar. 24, 2004; the prior applications are herewith incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION  
     Field of the Invention  
       [0002]     The invention relates to a method for cleaning a heat exchanger by use of an abrasive and to a device for carrying out the method. Heat exchanger pipes must be cleaned of deposits from time to time. Although many chemical cleaning methods are available, the large number of heat exchanger pipes and corresponding number of openings mean that this is technically quite a demanding undertaking. Therefore, exchange pipes are primarily cleaned mechanically. Apart from cleaning with brushes, blasting methods are often used, involving an abrasive being blasted through a pipe by use of a jet nozzle placed against an end of a pipe. Such a method is described for example in published, non-prosecuted German patent application DE 195 46 788 A1, corresponding to U.S. Pat. No. 5,883,512. Particles of steel or corundum are used for example as the abrasive. The particles emerging from the other end of the pipe, respectively, are gathered by a collecting device and returned to the circulation of the abrasive. Such a collecting device is described in German patent DE 198 37 683 C2, corresponding to U.S. Pat. No. 6,308,774.  
       SUMMARY OF THE INVENTION  
       [0003]     It is accordingly an object of the invention to provide a method for cleaning the pipes of a heat exchanger by use of an abrasive and a device suitable for performing the method which overcomes the above-mentioned disadvantages of the prior art methods and devices of this general type, with which in particular more efficient cleaning of a heat exchanger is possible.  
         [0004]     The object is achieved by a throttle-free jet nozzle being used, preferably one in which the outlet opening is of the same size or slightly smaller than the inner cross-sectional area of the pipe. This configuration makes it possible to subject the pipe that is to be cleaned to a large stream of abrasive. In the case of conventional jet nozzles, this is not possible to the same extent. With the conventional nozzles, the velocity of the stream of abrasive in a feed tube connected to the jet nozzle is greatly increased by a relatively small constriction in a Venturi nozzle. The consequences are that abrasive particles are expelled with high kinetic energy. However, these particles are already retarded within a relatively short piece of pipe. Then only a stream of abrasive with a low particle concentration is available for the pipe cleaning. The situation is different with the invention. Here, because there is no throttling or constriction in the jet nozzle, a stream of abrasive with a very high particle concentration is obtained, accompanied by great abrasiveness. A configuration which allows large outlet openings provides that the jet nozzle is pressed against an end face of an end of a pipe with a contact area encompassing the outlet opening. By contrast with this, in the case of the prior art, a constricted connection piece is introduced into an end of a pipe, the outlet opening of the connection piece having to be reduced at least by an amount corresponding to its wall thickness in comparison with the cross-sectional area of the pipe.  
         [0005]     The time spent on performing the cleaning method can be reduced by the number of pipes being cleaned simultaneously. This is accomplished by using a number of jet nozzles which are held on a carrier in the same layout as the pipes of the heat exchanger. While in the case of conventional methods and devices positional fixing of the jet nozzles takes place by inserting them with a narrowed connection piece into an end of a pipe, the invention provides a fixing bolt which protrudes in the blasting direction and, for cleaning, is inserted into an end of a pipe. This is possible without any problem if the fixing bolt is disposed on a carrier at a position corresponding to the layout of the pipes.  
         [0006]     A throttle-free jet nozzle is accomplished by the jet nozzle being passed through by a flow channel delimited by an inlet opening and an outlet opening, the flow channel having a cross-sectional area that substantially remains the same and corresponds approximately to the size of the outlet opening. As stated above, the outlet opening of the jet nozzle is encompassed by a contact area which is pressed against the end face of the pipe to be cleaned while the method is being carried out. The contact area is preferably encompassed by a collar disposed radially on the outside and projecting axially. The contact area and the collar thereby form a receptacle for an end of a pipe. This configuration on the one hand makes better sealing of the end region of the pipe possible and on the other hand makes additional positional fixing of the device on the heat exchanger possible. This prevents a carrier carrying a number of jet nozzles from turning about the fixing bolt as an axis of rotation. To increase the sealing between the end of the pipe and the jet nozzle, in a preferred configuration it is provided that the region containing the receptacle and the outlet opening contains an elastomer. This also makes it possible to compensate for tolerances and unevenness in the region of the end face of an end of a pipe. As mechanical protection, and to prevent the collar encompassing the end face region of a pipe from being made to expand by the pressurized stream of abrasive, the collar is enclosed by a stiffening sleeve made of solid material, for example a metal. The elastomer region is preferably formed by an end piece that is in the form of a portion of pipe and is positively connected to the jet nozzle. Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0007]     Although the invention is illustrated and described herein as embodied in a method for cleaning the pipes of a heat exchanger by use of an abrasive and a device suitable for performing the method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
         [0008]     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a diagrammatic, longitudinal sectional view of a conventional device, positioned on a heat exchanger;  
         [0010]      FIG. 2  is a diagrammatic, longitudinal sectional view corresponding to  FIG. 1  of a device according to the invention;  
         [0011]      FIG. 3  is an enlarged diagrammatic, longitudinal sectional view of a detail shown in  FIG. 2 ;  
         [0012]      FIG. 4  is an enlarged diagrammatic, longitudinal sectional view of a detail shown in  FIG. 2 ; and  
         [0013]      FIG. 5  is a diagrammatic, perspective view of the device shown in  FIG. 2 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a conventional device for performing a conventional cleaning method for providing background information for understanding the invention. Two jet nozzles  2  fixed to a carrier  1  are placed for example against an inlet side  3  of a heat exchanger  4 . The jet nozzles  2  are made narrower at their end pointing in the blasting direction  5 , to form a cylindrical connection piece  6 , which is inserted into the end of the pipe  7 . At its end pointing counter to the blasting direction  5 , the jet nozzles  2  bear an inlet opening  9 , connected to a feed tube  8 . Disposed between the outlet opening  10 , which is enclosed by the front end of the connection piece  6 , and the inlet opening  9  is a Venturi nozzle  12  with a throttling point  13 .  
         [0015]     Turning now to the invention of the application,  FIGS. 2-5  show a jet head with a carrier  21 , in which two jet nozzles  22  are mounted. Of course, jet heads with only one jet nozzle or more than two jet nozzles are also conceivable. The carrier  21  is substantially formed by a hollow-cuboidal housing  23  ( FIG. 3 ). The housing  23  is passed through by two bores  24 , which run parallel to each other and each receive a jet nozzle  22 . The jet nozzle  22  is substantially configured as a housing  25  in the form of a portion of pipe. The housing  25  has three different longitudinal portions, a middle portion  26  having a larger diameter than the two other portions, that is a front portion  27  and a rear portion  28 . The transition between the middle portion  26  and the narrowed portions  27 ,  28  is in each case formed by a radial shoulder  29 ,  30 . A stop flange  32  protrudes radially inward in each case from the wall of the bores  24 . The side of the stop flange  32  that faces the middle portion  26  interacts with the radial shoulder  29  in the sense of an axial fixing of the housing  25 .  
         [0016]     With the radial shoulder  30 , the housing  25  bears against a cover part  33 , which closes the carrier housing  23  on the rear side. Disposed between the cover part  33  and the rear portion  28  of the jet nozzle  22  is an O-ring seal  31 . Inserted in the region of the bore  24  extending away from the stop flange  32  and enclosing the portion  27  is an elastomer seal  34 , encompassing the circumference of the portion  27 . Made in the front end face of the jet nozzle housing  25  is a cross-sectionally dovetailed groove  35 , in which an end piece  36  made of elastomer material substantially in the form of a portion of pipe is form fitted with its one end. A form-fitting or locking connection is one that connects two elements together due to the shape of the elements themselves, as opposed to a force-locking connection, which locks the elements together by force external to the elements.  
         [0017]     The front portion  27  is passed through by a flow channel  37 . A center longitudinal axis  38  of the flow channel  37  at the same time forms the center longitudinal axis of the jet nozzle housing  25 . The flow channel  37  is delimited on the front side by an outlet opening  39  and at its other end by an inlet opening  40 . It has substantially a cross-sectional area that remains the same or a diameter  42  that remains the same. The cross-sectional area or the diameter  42  corresponds to the cross-sectional area or a diameter  43  of a feed tube  46  screwed with an external thread  44  into an internal thread  45  of the middle portion  26 . The feed tube  46  bears with its front end face  47  against a radial shoulder  48  that is present in the transitional region between the portion  26  and the portion  27 . Protruding from the radial shoulder  48  in the axial direction is a cross-sectionally wedge-shaped projection  49 , which encompasses the inlet opening  40  in an annular manner and digs itself into the material of the feed tube  46 , an elastomer material. This improves the sealing between the feed tube  46  and the housing portion  26 . A diameter  50  of the inlet opening  40  is slightly greater than the diameter  43  of the feed tube  46 . The difference in diameter is in this case made for example to correspond to an expansion of the diameter  43  when the tube is subjected to a pressurized stream of abrasive. This ensures that a stream of abrasive does not impinge on an interfering housing edge protruding into the flow channel  37 . A region  52  of the flow channel  37  adjoining the inlet opening  40  is made to narrow slightly conically, approximately as far as its middle, the region  52  being adjoined by a cylindrical channel region with the diameter  42 .  
         [0018]     To carry out a cleaning method, as shown in  FIG. 2 , the carrier  21  is disposed on an inlet side  53  or the outlet side of a heat exchanger  54 . If the heat exchanger  54  is a nuclear power plant, the carrier  21  is generally held by a non-illustrated manipulator, on which the carrier  21  is fixed by a fastening device  55  (see  FIG. 5 ). Pipes  56  of the heat exchanger  54  are disposed in a regular layout and pass with their ends through a holding plate  57 . They protrude from the latter with an overhang  58 . The jet nozzles  22  are disposed spaced apart from one another on the carrier  21  to the extent that they can be placed on end faces  59  of two pipes  56   b  separated from each other by a pipe  56   a . For this purpose, the end piece  36  has a stop area  60 , which interacts with the end face  59  and encompasses the outlet opening  39 . The stop area  60  extends transversely in relation to the center longitudinal axis  38 . The stop area  60  is in turn enclosed by a collar  62 , which protrudes in the axial direction of the blasting direction or in the blasting direction  5 . The collar  62  is formed in a cross-sectionally wedge-shaped manner, having a radially inwardly directed sloping area  63  and a radially outwardly directed sloping area  61 . The sloping area  63  serves as a guiding-in slope when the jet nozzle  22  is placed on an end of a pipe. During the cleaning, the latter lies in a recess  64  enclosed by the stop area  60  and the collar  62 . The collar  62  thereby bears with a cylindrical edge portion  65  against the outer circumference of the pipe  56   b . The sloping area  63  bears snugly against a weld  66 , with which the pipes  56  are fixed on the holding plate  57 . The collar  62  consequently acts like a sealing lip which interacts with the outer circumference and the weld  66  of the pipe  56   b . In order that the collar cannot radially expand when it is subjected to pressure, it is encompassed around its full circumference by a stiffening sleeve  67 . The stiffening sleeve  67  lies with a flange  68 , protruding radially inward from its end facing the carrier  21 , in a radial groove  71  of the end piece  36 . The end face of the stiffening sleeve  67  that is facing the flange  68  is beveled and forms a sloping area  69  in line with the sloping area  61  of the collar  62 . The beveling of the end piece in the form of the sloping areas  61  and  69  prevents it from coming into contact with a weld  66   a  of a neighboring pipe  56   a  and under some circumstances thereby preventing a sealing abutment of an end piece  3  against the pipe  56   b  that is to be cleaned. Between the portion  27  of the jet nozzle housing  25  and the stiffening sleeve  67  there is in the end piece  36  a further radial groove  70 , which increases its elasticity in the axial direction.  
         [0019]     For the positional fixing of the carrier  21  on the holding plate  57 , there is on the front side of the carrier  21  from which the jet nozzles  22  also protrude with an overhang  72  a fixing bolt  73 , which protrudes from the carrier  21  in the direction of the center longitudinal axis  38  ( FIG. 5 ). The fixing bolt  73  is screwed with a threaded portion  74  into a threaded bore  75  of the carrier  21  ( FIG. 3 ). Its front end  76 , facing away from the threaded portion  74 , is conically narrowed. The longitudinal portion adjoining the narrowed region has a diameter which is slightly smaller than the inside diameter of the pipe  56 . During the cleaning operation, the fixing bolt  73 ,  76  protrudes into the pipe  56   a  disposed between two pipes  56   b  that are to be cleaned. Turning of the carrier about the fixing bolt  73  as an axis of rotation is prevented by the positively engaging interaction of the pipe ends with the end pieces  36 .  
         [0020]     Also disposed on the front side of the carrier  21  is a mechanical distance sensor  77  ( FIG. 5 ). This ensures that the carrier  21  can be moved into a predetermined position in relation to the holding plate  57  by the non-illustrated manipulator.