Cleaning of heat exchanger core

Abstract

An apparatus is described for cleaning the exterior of a furnace heat exchanger that includes a bundle of finned convection or bare radiant tubes heated when in use by the flue gases of a heater furnace. The apparatus comprises a motorized carriage 10 guided for movement along the outer surface of the bundle in a direction parallel to the tubes and a holder 24 on the carriage for holding a lance 20 in a position relative to the carriage 10 that permits the lance 20 to penetrate between the tubes of the bundle and to be advanced along the core by the carriage while remaining in the latter position.

Claims

1. An apparatus for cleaning the exterior of tubes of a heat exchanger which, when in use, are heated by the flue gases of a heater furnace, the apparatus comprising: a carriage having a traction mechanism comprising motorised wheels or a pair of motorised caterpillar tracks which, in use, make frictional contact with an outer surface of a bundle of the tubes to advance the carriage relative to the bundle and to guide the carriage for movement along the outer surface of the bundle in a direction parallel to the tubes, a bottom of the carriage defining a lower plane; a holder fitted to the carriage above the lower plane; and a lance retained, in use, in the holder in an inclined position relative to the lower plane such that the lance extends through the lower plane, and a tip of the lance is extendable below the lower plane and beyond the outer surface of the bundle to penetrate between the tubes of the bundle, the lance being advanceable along the bundle by the movement of the carriage while remaining in the inclined position.

2. The apparatus of claim 1, wherein the traction mechanism includes additional guide rollers positioned to engage the opposite sides of outermost tubes in the bundle to permit the apparatus to move along a bundle inclined to the horizontal.

3. The apparatus of claim 1, wherein the lance is connected to a fluid under high pressure and is operative to clean the bundle by the force of one or more water fluid jets discharged from the lance.

4. The apparatus of claim 3, wherein the fluid is water.

5. The apparatus of claim 1, wherein the lance has laterally directed jets.

6. The apparatus of claim 5, wherein the laterally directed jets are disposed symmetrically around the lance.

7. The apparatus of claim 1, wherein the lance includes at least one jet angled in the direction of the carriage.

8. The apparatus of claim 1, wherein an actuator is provided on the carriage for changing the position of the lance holder relative to the carriage to alter the depth of penetration of the tip of the lance into the bundle.

9. The apparatus of claim 8, wherein the lance holder is pivotable relative to the carriage to move the lance along an inclined plane passing between the tubes of the bundle.

10. A method of cleaning the exterior tubes of a heat exchanger using the apparatus of claim 1, the method comprising: positioning the carriage on the bundle with the traction mechanism in frictional contact with the outer surface of the bundle; mounting the lance in the holder fitted to the carriage in a position in which the tip of the lance penetrates between the tubes of the bundle; and operating the traction mechanism to advance the carriage and the lance along the bundle.

11. The method of claim 10, wherein the holder is pivoted relative to the carriage about an axis normal to a plane that passes between tubes of the bundle.

12. The method of claim 11, wherein the lance is swept through an arc, by pivoting the holder relative to the carriage, so as to clean a sector between tubes of the bundle, the carriage being subsequently advanced by an increment to commence the sweeping of an adjacent sector.

13. The method of claim 11, wherein the lance is kept stationary relative to the carriage during each pass of the carriage along the length the bundle and the holder is pivoted between passes to change the depth of penetration of the tip of the lance beneath the outer surface of the bundle.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will now be described further, by way of example, with reference to the accompanying drawings, in which the single FIGURE shows a perspective view of an apparatus of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(2) The apparatus or robot shown in the drawing comprises a carriage 10 having a rectangular outer open frame 12. An air drive motor 14 and a gearbox 16 are mounted on the frame 12 to drive two caterpillar tracks 18, arranged one on each side of the frame 12. The track on the far side of the frame 12 is obscured by the motor 14 and the gearbox 16.

(3) The tracks 18, which may be replaced by a set of wheels, are inclined relative to the plane of the frame 12 and relative to one another so that their traction surfaces form a V-shape depending from the lower surface of the frame. As an alternative, the plane of the tracks may be parallel to the tube bundle and the tracks may be adjustable to allow for tubes of wider or narrower pitch. When the apparatus is placed on a bundle of tubes of circular cross section, the traction surfaces contact the facing surfaces of two adjacent tubes. In this way, the carriage is guided to remain in alignment with the two tubes and is propelled along the bundle when the tracks 18 are driven by the motor 14 through the gearbox 16. The carriage is further guided by two drop down guides which are actuated by a motor 32 situated at rear back of the frame 12.

(4) Such an arrangement suffices if the tube bundle is horizontal but the carriage can also be designed to work with bundles inclined to the horizontal or vertical if additional idlers rollers are arranged to pass between the two top tubes and to engage the under surfaces of the two tubes. For example, the idler rollers may be mounted on a T-bar that can be rotated from an aligned position where it can pass through the gap between two adjacent tubes of the bundle, to a transverse position where the rollers engage the underside of the tubes to prevent the carriage from lifting off the bundle.

(5) The carriage 10 supports two lances 20 and 22 connected to a high pressure water line and having jets that are aimed at the tubes of the bundle to clean them.

(6) Each lance has laterally directed jets so that the reaction from them does not act to lift the carriage off the tube bundle. If the jets are aimed laterally and disposed symmetrically, there will be no reaction from them to interfere with the movement of the carriage. It is also possible to angle some jets slightly upwards (i.e. towards the carriage) to exert a downward force on the carriage.

(7) Each lance 20,22 is clamped within a respective holder 24 that is mounted on the frame 12 in such a manner that it can pivot about an axis inclined to the plane of the frame 12. The angle of inclination is such that when the holder 24 is pivoted the lance 20 remains in a plane that passes between the tubes of the array. For example, if the tubes form a regular hexagonal array, each lance moves in a plane inclined at 30? to the frame 12 and the top surface of the bundle. This angle may be modified to suit the geometry of the bundle. A respective pneumatic jack 30 is connected to a bell crank arm 28 of each holder to allow the holder 24 to be pivoted. In place of a pneumatic jack 30, one may use an electric motor or a hydraulic actuator.

(8) The described apparatus is capable of being controlled remotely by an operator or of being programmed to perform a cleaning operation automatically. Access to the tube bundle may in some cases be restricted to a small inspection opening adjacent the bundle. Though such an access opening may not be large enough to act as a keyhole through the entire bundle could be cleaned using a manually held lance, it is large enough to allow introduction of the described cleaning robot and its positioning on the bundle.

(9) The robot is used by first advancing it to a desired position then swinging one or both of the lances in an arc using the jacks/motor 30. After a complete arc has been swept by both lances 20 and 22, the robot is advanced a small distance and the pivoting of the lances is repeated until the high pressure jets on the lances have scanned the whole of the two inclined planes defined by the gaps between the tubes of the bundle. Once the entire length of the bundle has been covered, the robot is repositioned on the next pair of tubes and the process is repeated until the entire bundle has been cleaned.

(10) It would be possible to hold the lances stationary while making a pass of the robot over the length of the bundle and to reposition the lances slightly using the jacks 30 before making a return pass. However, this method of operation is not preferred as it results in the water and air supply lines being dragged over the bundle several times. By scanning the depth of the bundle then advancing the robot, the supply lines only move twice over the surface of the bundle for each pair of tubes.

(11) When first positioning the robot on the tube bundle, it is necessary to first ensure that the traction surfaces can engage the tube bundle and that the lances are free to pivot. This may need to be carried out manually if the bundle is already partially blocked by the deposit.

(12) It will be appreciated that various modifications may be made to the described apparatus without departing from the scope of the invention as set out in the appended claims. For example, electric motors may be used in place of the air motor and the pneumatic jacks 30. Instead of the penetration of the lances into the bundle being varied by pivoting the holders, it is alternatively possible for the holder to remain stationary and for the lances to be moved along the holders.

(13) While it is currently envisaged that the robot will be remotely controlled by an operator at all times, it is possible for it to be programmed to perform the cleaning task automatically. In the latter case, the carriage may additionally be provided with sensors to detect when the end of a run has been reached or if one of the lances encounters an obstruction.