WO2010095110A2

WO2010095110A2 - Self-cleaning heat exchanger

Info

Publication number: WO2010095110A2
Application number: PCT/IB2010/050756
Authority: WO
Inventors: Michael Waston
Original assignee: Tube Tech International Ltd.
Priority date: 2009-02-23
Filing date: 2010-02-22
Publication date: 2010-08-26
Also published as: GB2467942A; WO2010095110A3; GB0902905D0

Abstract

A self-cleaning heat exchanger 10 having a set of tubes 14 extending between two headers 12, 16 comprises means 20 for introducing tube scouring projectiles 18 into a first of the headers and a filter 22 for separating the projectiles from the fluid after passing through the tubes into the second header. In the invention, means 30 are provided for accelerating the fluid flow through some of the tubes 14 of the heat exchanger in order to assist in dislodging projectiles that come to a standstill on encountering excessive resistance while passing through a tube. During a blockage clearing cycle, different sets of tubes are cleared sequentially until all the tubes have been cleared.

Description

Self-Cleaning Heat Exchanger

Field of the Invention

The present invention relates to a self-cleaning heat exchanger or condenser of the type having a set of tubes extending between two headers, an insertion unit for introducing tube scouring projectiles into one header and a filter separating the projectiles from the fluid after passing through the tubes at the other header.

Background of the invention

A self-cleaning heat exchanger as described above is already known, for example from US 3,021,117, in which the fluid flowing through the tubes is water. 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 water is passed through a filter which separates the projectiles and recycles them back to the first header.

It would be desirable to adopt a similar approach to prevent scale formation on the tubes of a heat exchanger in which the liquid flowing through the tubes is not water but a more viscous fluid such as crude oil. Whereas the temperature of water in a heat exchanger may typically be around 150°C, the temperature of a heavy oil may be 450°C. This naturally has a bearing on the material from which the projectiles can be made. More importantly for the present invention, even at such elevated temperatures the viscosity of the heavy oil is much greater than that of water. As a result, the flow velocity of the liquid is reduced and this in turn creates a risk that the projectiles will come to a standstill on meeting a resistance, resulting in blockage of the tubes.

Object of the Invention

The present invention seeks therefore to provide a self-cleaning heat exchanger of the type described above, and a method of operating the same, in which the risk of blockage of tubes by projectiles is reduced even when a more viscous liquid is passed through the tubes of the heat exchanger .

Summary of the Invention

According to a first aspect of the present invention, there is provided a method of operating a self-cleaning heat exchanger of the type having

(i) a set of tubes extending between two headers, (ii) an insertion unit for introducing tube scouring projectiles into a first header, and

(iii) a filter for separating the projectiles from the fluid after passing through the tubes into the second header, which method comprises intermittently executing a blockage clearing cycle that includes the steps of

(a) selecting a set of tubes,

(b) clearing any blockage in a tube of the selected set by increasing the fluid flow rate through only the tubes in the selected set, and (c) repeating the selecting and clearing steps for different sets of tubes until blockages in all the tubes of the heat exchanger are cleared.

In some embodiments of the invention, the fluid flow rate in the tubes of the selected set is increased by obstructing flow through the remaining tubes of the heat exchanger . Thus, in accordance with a second aspect of the invention, there is provided a self-cleaning heat exchanger having a set of tubes extending between two headers, an insertion unit for introducing tube scouring projectiles into a first header, a filter for separating the projectiles from the fluid after passing through the tubes into the second header, characterised by an obturating plate for obstructing the flow through some of the tubes of the heat exchanger while leaving only the tubes within a selected set unobstructed, thereby causing the fluid flow rate through the tubes of the selected set to be accelerated so as to clear any blockage within a tube of the selected set, the plate being movable relative to the tubes so as to allow different sets of tubes to be selected such that the flow through all the tubes may be accelerated at different times within a blockage clearing cycle.

The obturating plate may conveniently be circular and movably mounted in an axial direction between a first position in which all the tubes of the heat exchanger are unobstructed and a second position in which only the tubes in the selected set are unobstructed, the plate being rotatable when in the second position to uncover different sets of tubes sequentially.

In alternative embodiments, the fluid flow rate in the tubes of the selected set is increased by providing an auxiliary pump and supplying additional fluid from the auxiliary pump to only the tubes of the selected set.

Thus, in accordance with a further aspect of the invention, there is provided a self-cleaning heat exchanger having a set of tubes extending between two headers, an insertion unit for introducing tube scouring projectiles into a first header, a filter for separating the projectiles from the fluid after passing through the tubes into the second header, characterised by an auxiliary pump connectible at any one time to accelerate the fluid flow through only the tubes in a selected set while allowing normal flow to take place through the remaining tubes, the auxiliary pump being connectible at different times to different selected sets of tubes to enable all the tubes of the heat exchanger to be cleared of blockages.

The auxiliary pump may be connectible to sets of lances mounted in a first header in alignment with the tubes of the heat exchanger.

It is possible for the lances to be mounted in the first header in such a manner as to be movable between a first position in which their ends are spaced from the mouths of associated tubes and a second position in which their ends obstruct the mouths of the associated tubes.

It is alternatively possible for the sets of lances to be mounted in a fixed position in the first header with their ends spaced sufficiently from the mouths of associated tubes to permit projectiles to enter the associated tubes, the lances having nozzles to direct a jet capable of penetrating into the tubes.

The invention is applicable to both single pass and multi-pass heat exchangers. In the latter case at least one of the headers may partitioned such after passing through a first group of tubes in a first direction, the fluid passes through a second group of tubes in the opposite direction.

Brief Description of the Drawings

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which : Figure 1 is a schematic representation of a self- cleaning heat exchanger in accordance with a first embodiment of the invention,

Figure 2 is a section along the line II-II in Figure 1,

Figure 3 is a schematic representation of a self- cleaning heat exchanger in accordance with a second embodiment of the invention, and

Figure 4 shows the embodiment of Figure 3 with the lances in an operative position.

Detailed Description of the Preferred Embodiment (s)

Figure 1 shows the core 10 of a heat exchanger for use in an oil refinery. The core has a first header 12, a set of tubes 14 and a second header 16. Oil is introduced from a pressurised supply from a previous refining stage into the header 12. The oil flows through the tubes 14 where heat exchange takes place with a second fluid flowing through the shell (not shown) of the heat exchanger through the walls of the tubes 14. The oil then enters the second header 16 from which it then passes to the next oil refining stage. The construction of the shell and the fluid circulating in the shell are not of particular concern to the present invention and will not therefore be described in detail.

Figure 1 also shows that by optionally placing partitions 17, shown in broken lines, in the headers, the fluid may pass several times (three in the illustrated example) through different sets of tubes of the heat exchanger. This has the effect of connecting the sets of tubes in series instead of being in parallel. This increases flow resistance but also increases the time that the two fluids in the heat exchanger remain in thermal contact.

In order to render the heat exchanger self-cleaning during normal operation, projectiles 18 are introduced into the oil entering the header 12 through an insertion unit 20. These projectiles are balls of a material that can withstand the temperature of the hot oil and they are designed to gently scour the inner surface of the tubes 14 as they are entrained through them by the oil flow. After leaving the second header and on some heat exchangers continuing through another set of tubes into subsequent headers 16, the projectiles 18, at the end of their "through tube" cleaning cycle, are separated from the oil by means of a filter 22 and recycled back to the insertion unit 20.

Systems in which projectiles are recirculated in this manner are already known but have hitherto only been used in heat exchangers or condensers in which the liquid flowing through the tubes 14 is water. In such heat exchangers, the fast rate at which the water flows through the tube is sufficient to ensure that the projectiles do not come to a standstill on meeting resistance. When used for crude oil, there is a risk that the more slowly moving liquid will not suffice to prevent the projectiles from becoming jammed within the tubes and causing a blockage.

The first embodiment of the invention, shown in Figures 1 and 2, also operates by intermittently executing a blockage clearing cycle. During this cycle, the flow through some of the tubes of the heat exchanger is obstructed so that the flow rate is increased through a selected set tubes within which any blockages are to be cleared. In Figure 1, an obturating plate 40 is mounted within the first header 12 on the end of a shaft 42 that can rotate about its own axis and translate parallel to its axis to move the plate 40 towards and away from the mouths of the tubes 14. If the header is partitioned, then a separate obturating plate is required within each partitioned header section.

As can be seen from the section of Figure 2, the plate 14 is a solid circular plate with a missing portion, the portion being a quadrant in the illustrated embodiment. In the position shown in Figure 1, the plate 40 is retracted away from the mouths of the tubes 14 and does not interfere with the normal flow of oil through the heat exchangers. During blockage clearing cycles, however, the plate 40 is moved to cover the mouths of some of the tubes 14 while leaving only the tubes in alignment with the missing quadrant exposed to the oil in the header 12. As the same oil flow is now forced through a reduced number of tubes, the pressure in the header 12 is increased along with the flow rate through the tubes 14 that are still in operation, resulting in any early deposit formation or blockages of these tubes being cleared. The shaft 40 is now rotated to force the oil flow to pass through the tubes 14 in a different quadrant and this process is repeated until all the tubes are cleared.

The proportion of the tubes 14 left exposed by the plate 40 and the frequency of the cleaning cycles can be set to ensure that the tubes 14 remain clear at all times while interfering as little as possible with the flow of oil through the heat exchanger.

In the embodiments of Figures 4 and 5, a separate housing 50 is formed on the outer face of the first header 12. The separate housing is connected to an auxiliary pump 58 which provides a high pressure oil supply at the inlet 56. Within the housing 50 there is mounted a plate 52 carrying a set of lances 54 through which oil from the housing header 50 can be injected into the tubes 14.

Under normal operating conditions, the plate 52 is retracted, as shown in Figure 3, and the high pressure oil supply is turned off. Oil from the first header 12 thus flows through the tubes 14 in the normal way. As the need arises, or more preferably at regular intervals, a cleaning cycle is executed which involves operating the auxiliary pump 58 and advancing the plate 52 and the lances 54 into the position shown in Figure 4. Oil is now forced to flow under higher pressure through the tubes 14 to clear any blockage.

The sections of Figures 3 and 4 show only one plane of the heat exchanger and there are in practice several such planes forming a rectangular array when viewed in the direction of the axes of the tubes 14. The auxiliary pump 58 is only required to supply enough oil for one plane of tubes at a time, not all of them. While oil under high pressure is being fed through one plane of tubes, oil under normal operating pressure will continue to pass through the remaining tubes. The cleaning cycle does not therefore interrupt the operation of the heat exchanger.

Each plane of tubes has an associated set of lances 54 mounted on a respective plate 52 in the separate housing 50 and the different plates 52 are brought into operation at different times so that only one plane of tubes 14 is unblocked at any one time.

As an alternative to the lances 54 obstructing the mouths of the tubes 14, it is possible for the ends of the lances to remain spaced the mouths of the tube and to aim a high pressure jet of oil down the tubes. In this case, it is not necessary to mount the lances on a movable plate and they may instead project permanently into the first header 12, while leaving enough space between their ends and the mouths of the tubes 14 for the projectiles 18 to enter into the tubes.

Claims

1. A method of operating a self-cleaning heat exchanger of the type having (i) a set of tubes (14) extending between two headers,

(ii) an insertion unit (20) for introducing tube scouring projectiles into a first header, and

(iii) a filter (22) for separating the projectiles from the fluid after passing through the tubes into the second header, which method comprises intermittently executing a blockage clearing cycle that includes the steps of

(a) selecting a set of tubes,

(b) clearing any blockage in a tube of the selected set by increasing the fluid flow rate through only the tubes in the selected set, and

(c) repeating the selecting and clearing steps for different sets of tubes until blockages in all the tubes of the heat exchanger are cleared.

2. A method as claimed in claim 1, in which the fluid flow rate in the tubes of the selected set is increased by obstructing flow through the remaining tubes of the heat exchanger .

3. A method as claimed in claim 1, in which the fluid flow rate in the tubes of the selected set is increased by providing an auxiliary pump and supplying additional fluid from the auxiliary pump to only the tubes of the selected set.

4. A self-cleaning heat exchanger having a set of tubes (14) extending between two headers (12,16), an insertion unit (20) for introducing tube scouring projectiles (18) into a first header (12), a filter (22) for separating the projectiles (18) from the fluid after passing through the tubes (14) into the second header (16), characterised by an obturating plate (40) for obstructing the flow through some of the tubes of the heat exchanger while leaving only the tubes within a selected set unobstructed, thereby causing the fluid flow rate through the tubes of the selected set to be accelerated so as to clear any blockage within a tube of the selected set, the plate being movable relative to the tubes so as to allow different sets of tubes to be selected such that the flow through all the tubes may be accelerated at different times within a blockage clearing cycle.

5. A self-cleaning heat exchanger as claimed in claim 4, wherein the obturating plate (40) is circular and movably mounted in an axial direction between a first position in which all the tubes of the heat exchanger are unobstructed and a second position in which only the tubes in the selected set are unobstructed, the plate being rotatable when in the second position to uncover different sets of tubes sequentially.

6. A self-cleaning heat exchanger having a set of tubes (14) extending between two headers (12,16), an insertion unit (20) for introducing tube scouring projectiles (18) into a first header (12), a filter (20) for separating the projectiles (18) from the fluid after passing through the tubes into the second header (16), characterised by an auxiliary pump (58) connectible at any one time to accelerate the fluid flow through only the tubes in a selected set while allowing normal flow to take place through the remaining tubes, the auxiliary pump (58) being connectible at different times to different selected sets of tubes to enable all the tubes of the heat exchanger to be cleared of blockages.

7. A self-cleaning heat exchanger as claimed in claim 6, wherein the auxiliary pump (58) is connectible to sets of lances (54) mounted in a first header (12) in alignment with the tubes (14) of the heat exchanger.

8. A self-cleaning heat exchanger as claimed in claim 7, wherein the sets of lances (54) are mounted in the first header (12) in such a manner as to be movable between a first position (Fig. 3) in which their ends are spaced from the mouths of associated tubes and a second position (Fig. 4) in which their ends obstruct the mouths of the associated tubes.

9. A self-cleaning heat exchanger as claimed in claim 7, wherein the sets of lances are mounted in a fixed position in the first header with their ends spaced sufficiently from the mouths of associated tubes to permit projectiles to enter the associated tubes, the lances having nozzles to direct a jet capable of penetrating into the tubes .

10. A self-cleaning heat exchanger as claimed in any of claims 4 to 9, constructed as a multi-pass heat exchanger .

11. A self-cleaning heat exchanger as claimed in any of claims 4 to 10, wherein at least one of the headers is partitioned such after passing through a first group of tubes in a first direction, the fluid passes through a second group of tubes in the opposite direction.