GB2491143A

GB2491143A - Self cleaning heat exchanger

Info

Publication number: GB2491143A
Application number: GB1108726.9A
Authority: GB
Inventors: Michael Watson; Michael John Perry
Original assignee: Tube Tech International Ltd
Current assignee: Tube Tech International Ltd
Priority date: 2011-05-24
Filing date: 2011-05-24
Publication date: 2012-11-28
Anticipated expiration: 2031-05-24
Also published as: WO2012160505A1; GB2491143B; GB201108726D0

Abstract

A self cleaning heat exchanger 10 has a bundle 12 of tubes 14 extending between two headers and through which a process liquid flows and a distributor 30 mounted within one of the headers 22 to position projectiles at a mouth of the tubes. In use, the projectiles are entrained by a process fluid to flow along the tubes and scour the inner walls of the tubes. The distributor includes a moveable arm 32 connected to a supply of projectiles and comprises a channel that faces the mouths of tubes and is arranged to fully contain projectiles to evenly distribute the projectiles into each of the tubes. The tube bundle may be rectangular whereby the arm translates across a tube plate 24 or may be circular whereby the arm is rotated by a motor 38 about a centre of the bundle. A plurality of arms, i.e. 4 may be provided and arranged as spokes in a cross 30 radiating from a common central hub 34.

Description

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SELF-CLEANING HEAT EXCHANGER

Field of the Invention

The present invention relates to a self-cleaning heat exchanger of the type having a bundle of tubes extending between two headers.

Background of the invention

A self-cleaning heat exchanger is already known, for example from US 3,021,117. To prevent a build-up of fur within the tubes, projectiles in the form of "sponge balls" of an appropriate size and made of a suitable material are introduced into the header at one end of the heat exchanger.

These projectiles gently scour the surface of the tubes during their single pass from one header to the other. On leaving the second header, the process Jiguid, in this case water, is passed through a filter which separates the projectiles and recycles them back to the first header.

In the above proposal, the projectiles are merely introduced into the process liquid in the header and the flow of the process liquid is relied upon to bring the projectiles to the mouths of the tubes and to transport the projectiles through the tubes.

A disadvantage of this approach is that there is not a uniform flow of liquid across the tube bundle. Consequently, the projectiles may be concentrated in one region so that those tube are cleaned regularly whereas tubes in other regions will be cleaned less frequently. If too long an interval occurs between cleaning cycles of any tube, a deposit may build up in it and when a projectile is next received in that tube it may encounter too much resistance and become jammed within the tube.

Summary of the invention

With a view to mitigating the foregoing disadvantage, the present invention provides a self-cleaning heat exchanger having a bundle of tubes extending between two headers, a distributor mounted within one header to position projectiles over the mouths of the tubes for the projectiles to be entrained by the process fluid to flow along the tubes so as to scour the inner walls of the tubes, wherein the distributor includes an arm movably mounted relative to the mouths of the tubes of the bundle that defines a channel facing the mouths of the tubes, the arm being connected to a supply of projectiles that acts to maintain within the channel a full complement of projectiles.

If the tube bundle is rectangular, then the arm of the distributor may be slidably mounted for translation across the tube plate, this being the wall of the header that seals around the mouths of the tubes. It is more common however for the tube bundle to be circular and in this case the arm is more suitably mounted in the header for rotation about the centre of the tube bundle.

In a circular tube bundle, the centres of the tubes will not all lie on radii that differ from one another by an integral multiple of the diameter of the projectiles. A single arm filled with projectiles rotated to sweep the entire area of the tube plate will not therefore place projectiles in exact alignment with each on the tubes.

To avoid this problem, it is preferable to provide a plurality of arms within which the centres of the projectiles lie at different radii from one another. The arms, of which there are preferably four, may conveniently be arranged as spokes radiating from a common axis.

In an embodiment of the invention, the projeotiles are supplied to eaoh arm through a hub arranged at the axis of rotation of the arm.

All the arms preferably share a oommon hub designed to divert the projeotiles to whiohever arm is not filled with a full complement of projeotiles.

Brief description of the drawings

The invention will now be described further, by way of example, with reference to the accompanying drawing which is a schematic perspective view of one end of a self-cleaning heat exchanger of the invention.

Detailed description of an embodiment

Referring to the drawing, a heat exchanger 10 comprises a bundle 12 of tubes 14 that extend between two headers, of which only one header 22 is shown in the drawing. Each header defines an enclosed chamber communicating with all the tubes 14 of the bundle 12. The process liquid is introduced into one header and flows through the tubes 14 to the header at the opposite end of the heat exchanger. During its passage through the tubes 14, the process liquid is cooled or heated by exchange of heat through the walls of the tubes 14 with a second fluid in thermal contact with the outer walls of the tubes 14. The second fluid may be air or it may be another liquid flowing through a shell that encases the tube bundle 12.

In use, the liquid flowing through the tubes 14 tends to form a deposit on the inner walls of the tubes 14. If allowed to build up, the deposit reduces the efficiency of the heat exchanger because it reduces the diameter of the tubes thus increasing their flow resistance and it reduces the rate of heat transfer through the walls of the tubes.

To avoid a build up of deposit, the illustrated embodiment of the invention cleans the tubes periodically by sending a spherical projectile, such a sponge ball, down each tube to scour the inner wall of the tube and wipe away any matter that is beginning to adhere to the inner wall of the tube. If done frequently, say every hour, this wiping action ensures that a deposit is prevented from forming thus rendering the heat exchanger self-cleaning.

Hitherto, it has been proposed to introduce the projectiles into one header and to rely on the flow of the process fluid to entrain the projectiles. On reaching the other header, the projectiles are separated from the process liquid using a filter or sieve and recycled back to the first header. However, relying on the flow of the process fluid alone to transport to projectiles through all the tubes did not ensure that all the tubes would be cleaned at regular intervals.

To overcome this disadvantage, a projectile distributor is placed in the header 22 at one end of the tube bundle 12. The header 22 comprises a tube plate 24 that seals around the mouths of the tubes 14, a cylindrical sleeve sealed relative to the tube plate 24 and a cover plate 26 closing off the opposite end of the cylindrical sleeve to form a closed chamber. The process fluid is introduced into the chamber through a branch pipe connected to the cylindrical sleeve. The cylindrical sleeve and its branch pipe have been omitted from the drawing in order to allow the projectile distributor 20 to be seen more clearly.

The projectile distributor 20 comprises a cross 30 having four arms 32 radiating as spokes from a central hub 34. The hub 34 is mounted on the end of a hollow rotatable shaft 36 that it journalled in the cover plate 26. A motor 38 is provided to rotate the shaft 36 and a feeding device 44 feeds projectiles down the shaft 36.

The feeding device 44 receives the projectiles from a hopper 42 by way of a supply pipe 40. The projectiles are pushed down the hollow shaft 36 into the hub 34 from where there are diverted to fill channels extending along the lengths of the arms 32. The channels are fully open on their side facing the tube plate 24 so that when a projectile is correctly aligned with one of the tubes 14, that projectile can move freely from the channel into the tube. Each channel is also partially open on the side facing away from the tube plate 24 to allow the process liguid to pass through the channel into the tubes 14 while retaining the projectiles within the channels.

The channels normally hold a full complement of projectiles and their relative lengths are selected such that the projectiles in different arms 32 lie on different radii.

In operation, projectiles are fed via the shaft 36 and the hub to fill the channels in the arms 32 with projectiles. The cross 34 is then rotated by the motor fairly slowly, each full revolution taking approximately one hour. When a projectile in one of the arms 32 is correctly aligned with one of the tubes 14, the flow of process liquid will entrain that projectile so that it passes with the process liquid down the length of the tube and scours and/or wipes the tube to remove any deposit adhering to the tube.

The projectile on reaching the other header is separated from the process liquid and may be recycled back to the hopper 42.

As the projectiles in the four arms 32 all lie at different distances from the axis of the hub 34, each bore will align with a projectile of one of the arms 32 during a complete revolution of the cross 30 and this ensures that each tube is cleaned by a projectile at least once during each revolution of the hub 34. As the hub 34 rotates once every hour, this will also be the minimum frequenoy with which each tube 14 is cleaned, regardless of its position in the tube bundle 12. If the tubes are each cleaned with this freguency, there will not be sufficient time for a deposit to build up on the inner walls of the tubes 14.

It will be appreciated that various changes may be made to the illustrated embodiment of the invention without departing from the scope of the invention as set out in the appended claims. Thus, depending on the tube bundle, the arms may translate on sliders instead of rotating about a fixed axis. Where the arms rotate, they may be connected to an annular channel at their radially outer ends and the projectiles may be loaded into that channel instead of being fed into the hub. In that case, the arms may have stops at their radially inner ends to ensure that the projectiles in the different arms lie at different distances from the rotational axis.

Claims

CLAIMS1. A self-cleaning heat exchanger having a bundle of tubes extending between two headers, a distributor mounted within one header to position projectiles over the mouths of the tubes for the projectiles to be entrained by the process fluid to flow along the tubes so as to scour the inner walls of the tubes, wherein the distributor includes an arm movably mounted relative to the mouths of the tubes of the bundle that defines a channel facing the mouths of the tubes, the arm being connected to a supply of projectiles that acts to maintain within the channel a full complement of projectiles.
2. A heat exchanger as claimed in Claim 1, wherein the tube bundle is rectangular and the arm of the distributor is slidably mounted for translation across the tube plate that seals around the mouths of the tubes.
3. A heat exchanger as claimed in Claim 1, wherein the tube bundle is circular and the arm of the distributor is rotatable about the centre of the tube bundle.
4. A heat exchanger as claimed in Claim 3, wherein the distributor comprises a plurality of arms within which the centres of the projectiles lie at different radii from one another.
5. A heat exchanger as claimed in Claim 4, wherein the distributor has four arms.
6. A heat exchanger as claimed in Claim 4 or 5, wherein the arms are arranged as spokes radiating from a common axis.
7. A heat exchanger as claimed in any one of claims 3 to 6, wherein the projectiles are supplied to the or each arm through a hub arranged at the axis of rotation of the distributor.
8. A heat exchanger as claimed in Claim 7 when appended to claim 5 or 6, wherein all the arms share a common hub designed to divert the projectiles to whichever arm is not filled with a full complement of projectiles.
9. A self-cleaning heat exchanger constructed and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWSCLAIMS1. A heat exchanger having a bundle of tubes through which a process fluid flows, the tubes extending between and having mouths that open into two headers, a distributor mounted within one header to position projectiles over the mouths of the tubes whereby the projectiles are entrained by the process fluid to flow along the tubes so as to scour inner walls of the tubes, wherein the distributor includes an arm movably mounted relative to the mouths of the tubes of the bundle that comprises a channel facing the mouths of the tubes, the arm being connected to a supply of projectiles whereby the channel is filled with projectiles to distribute the projectiles evenly into the tubes.2. A heat exchanger as claimed in Claim 1, wherein the tube bundle is rectangular and the arm of the distributor is slidably mountod for translation across a tube plate that seals around the mouths of the tubes.3. A heat exchanger as claimed in Claim 1, wherein the tube bundle is circular and the arm of the distributor is rotatable about the centre of the tube bundle.4. A heat exchanger as claimed in Claim 3, wherein the distributor comprises a plurality of arms within which the projectiles lie at different radii from one another.5. A heat exchanger as claimed in Claim 4, wherein the distributor has four arms.6. A heat exchanger as claimed in Claim 4 or 5, wherein the arms are arranged as spokes radiating from a common axis.7. A heat exchanger as claimed in any one of claims 3 to 6, wherein the projectiles are supplied to the or each arm through a hub arranged at the axis of rotation of the distributor.8. A heat exchanger as claimed in Claim 7 when appended to claim 5 or 6, wherein the hub is common to all the arms and serves to divert the projectiles to whichever arm is not filled with a full complement of projectiles.9. A self-cleaning heat exchanger constructed and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.