GB2472781A

GB2472781A - Header valve to allow cleaning of the inside of a heat exchanger while in use

Info

Publication number: GB2472781A
Application number: GB0914292A
Authority: GB
Inventors: Michael Watson
Original assignee: Tube Tech International Ltd
Current assignee: Tube Tech International Ltd
Priority date: 2009-08-17
Filing date: 2009-08-17
Publication date: 2011-02-23
Also published as: GB0914292D0

Abstract

A heat exchanger having a stack of cooling tubes 16 extending between two headers 12, in at least one of the headers there are holes aligned with the inner bore of each cooling tube 16, each hole is plugged by a valve 30 which in its open position has a through passage to permit a cleaning implement to be introduced through the valve into the aligned cooling tube 16 without allowing the fluid within the header to escape. The valve may be a ball, cylinder flap or gate type and there may be more than one valve arranged in series. Preferably there is also a cap 40 to further close off the passage way when cleaning is not occurring, the cap may also cover the shafts of the valves to prevent them being opened.

Description

CLEANING OF HEAT EXCHANGERS

Field of the invention

The present invention relates to the cleaning of heat exchanger tubes and can be applied to overhead air cooled condensers and heat exchangers as used in large chemical processing plants, such as oil refineries, petrochemical plants and the oil and gas industry.

Background of the invention

At certain stages when refining crude oil, it is necessary to cool a fluid by rejecting its heat to the ambient atmosphere. For this purpose, air cooled heat exchangers are used which are in principle a much larger version of the radiators used in motor vehicles to cool the engine water. In particular, the heat exchangers comprise a stack of finned cooling tubes extending between two headers and a fan blowing ambient air over the fins. The fan blows air into a plenum, which serves the same purpose as the cowling of a vehicle radiator, namely to guide all the blown air to flow over the finned tubes of the heat exchanger. In the case of a chemical processing plant, the heat exchanger is mounted on a raised platform with its cooling tubes extending horizontally, while the fan and the plenum are arranged above or below the heat exchanger to blow air vertically downwards or upwards through the fins.

The efficiency of such a heat exchanger gradually diminishes with time for two reasons. First, atmospheric dirt collects between the fins of the heat exchanger tubes, interfering with the cooling of the fins by the air flowing over the heat exchanger. Second, a deposit can build up lining the inner walls of the heat exchanger tubes, thereby restricting the fluid flow through tubes as well as reducing the thermal transfer through the walls of the cooling tubes.

Cleaning the interior of the cooling tubes of heat exchangers has conventionally required the heat exchanger to be taken off line. In most cases, this involves closing down part or all of the production of the plant. In existing air cooled heat exchangers, the header, which typically ha a depth of about 22cm, has multiple screw threaded holes each aligned with the inner bore of a respective one of the cooling tubes. The holes in the header are normally plugged using bolts and washers that are screwed in the holes. Once the heat exchanger has been drained and allowed to cool, the bolts are removed, thus allowing access to the interior of the cooling tubes to be cleaned by feeding a suitable implement down each cooling tube. The implement may be a solid, hollow, rigid or semi-rigid rod carrying at its end a device that scrapes the inner surface of the cooling tube to dislodge any deposit. If a heavy build up of deposit has taken place, it may be difficult to clean the cooling tubes using a rod and it may be necessary to resort to high pressure jetting.

Because cleaning of such a heat exchanger requires the heat exchanger to be taken off line, a plant operator will normally tolerate a gradual reduction in performance over a period of typically one year before the thermal efficiency drops to such an extent that servicing of the heat exchanger becomes unavoidable.

Object of the invention The present invention is concerned with the cleaning of the interior of the cooling tubes of a heat exchanger and aims to permit such cleaning to be performed while the heat exchanger is still in use, thereby avoiding down time and enabling the heat exchanger to operate at all times near its peak efficiency.

Summary of the invention

According to the present invention, there is provided a heat exchanger having a stack of cooling tubes extending between two headers and holes in at least one of the headers aligned with the inner bores of the cooling tube to allow a cleaning implement to be inserted into each cooling tube through the header, characterised in that each hole is plugged by means of a valve which in its open position has a through passage of sufficiently large diameter to permit a cleaning implement to be introduced through the valve into the bore of the aligned cooling tube without allowing the fluid within the header to escape.

Currently headers with plugged holes aligned with the individual cooling tubes are only used on air cooled heat exchangers but the manner in which heat is rejected from the cooling tubes is not of fundamental importance to the present invention. Thus, the invention can equally be applied to heat exchangers in which the sections of the cooling tubes extending between the headers are encased in a shell through which a second fluid flows.

Preferably, each valve comprises a valve body screwed at one end into a respective hole in the header, the valve body having a straight through passage communicating with the interior of the header and at least one valve element for selective shutting off the through passage, the valve body also having a coupling thread to permit the through passage to be capped.

The valve element may be a ball or cylinder rotatable about an axis perpendicular to that of the through passage.

Alternatively, the valve element may be pivotable flap or a slidable gate. The design of the valve element is not of fundamental importance provided only that it allows a cleaning implement to be passed via the through passage in the valve body into the cooling tube when the valve is open.

The valve internals and the space either side of the valves may have a high temperature seal encompassed so as to assist in sealing the cleaning rod as it travels into the tube.

The coupling thread can receive a cap to close off the through passage when cleaning is not taking place. The cap offers additional security in that even if the valve is opened in error, no escape of fluid from the header will take place if the cap is in place.

The coupling thread may also be used to secure a collar at the end of the cleaning implement to the valve body. To commence a cleaning operation, the cap on the end of the valve body is removed while the valve is still closed. The end of the cleaning implement is then inserted into the end of the through passage uncovered by the removal of the cap and the collar on the end of the implement is screwed to the valve body to seal the through passage once again. The valve is now opened to allow the cleaning implement to be advanced through it into the header and then into the aligned cooling tube.

After the cap has been removed and before the cleaning implement has been connected up to the valve body, the valve element is the sole obstacle to an escape of liquid from the header. To safeguard against a defect in the valve element, it is preferable to provide two or more valve elements in line with one another and staggered along the length of the through passage in the valve body.

Each valve element is preferably operated by inserting and turning a key into a proprietary recess in an operating shaft of the valve element that does not project beyond the valve body. The need for a proprietary key and the fact that the operating does not project from the housing together ensure that the valves can only be opened by authorised personnel.

If the valve elements have shafts that do not project beyond the valve body, it is possible for the cap used to blank off the through passage to fit over the valves and form a sealed enclosure encasing the operating shafts of the valve elements. In this case, the valve operating shafts are safeguarded from the elements, additional safety is provided in the event of failure of the valve seals and accidental opening of a valve is prevented by the fact that the operating shafts are inaccessible until the cap has been removed.

Because the invention allows frequent cleaning of the cooling tubes, the cleaning of the cooling tubes is simplified and will only require a light scraping of inner surface of cooling tube to dislodge the molecular bonding layer that allows a deposit to build up on the inner walls.

Brief description of the drawings

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a plan view from above of a conventional air cooled heat exchanger as used in an oil refiner, Fig. 2 is a side view of a header of the heat exchanger in Fig. 1, Fig. 3 is a section in the section plane designated A-A in Fig. 2, and Fig. 4 a similar section to that of Fig. 3 through an embodiment of the invention in which three of the bolts plugging screw threaded holes in the header have been replaced with valves that allow the cooling tubes to be cleaned without taking the heat exchanger off line.

Detailed description of the preferred embodiment

Fig. 1 shows a conventional air cooled heat exchanger having headers 12 and 14 and cooling tubes 16 extending between the headers 12, 14. Inlet and outlet connectors 18 and 20 are provided for the fluid to be cooled, which in the case of an oil refinery may be hot crude oil. The connectors 18 and 20 are shown as beinq on different headers but they may be mounted on the same header. This will depend on the manner in which the headers are partitioned and the number of passes that the fluid makes through different cooling tubes of the heat exchanger. The invention is not restricted to any particular design of fluid flow path.

The sections of the cooling tubes 16 between the headers 12, 14 have fins 22 to increase the surface area over which heat transfer can occur. In the illustrated embodiment, the fins 22 are shown as circular discs fitted to individual cooling tubes. Touching hexagonal spacers 26 are also fitted to the cooling tubes 16 along their length so that they support one another.

To allow the cooling tubes 16 to be cleaned, threaded holes normally plugged by means of bolts 24 are formed in at least one of the headers 12, 14. The bolts 24 are shown in Fig. 2 which is an end view of the header 12 and in Fig. 3 which is a section through the header in the section plane A-A in Fig. 2.

In heat exchanger shown in Fig. 2, the cooling tubes 16 are arranged in a hexagonal matrix (in each group of three adjacent cooling tubes 16 the centres of the tubes lie at the apices of an equilateral triangle) but the cooling tubes may be in a square array. As a further possibility, instead of being finned and air cooled, the cooling tubes 16 may be encased on a shell and cooled by another liquid, for example water.

Conventionally, each cooling tube 16 is cleaned by feeding a cleaning implement, such as a rod or a lance, through the aligned hole in one of the headers 12, 14. For this to be done, the bolt 24 plugged the hole must first be removed and this cannot of course be done while hot crude oil is flowing through the heat exchanger. Consequently, the tubes 16 can only be cleaned after the heat exchanger has been taken off line.

To allow the interior of the cooling tubes 16 to be cleaned while the heat exchanger is in operation, the preferred embodiment of the invention, shown in section of Fig. 4, replaces each of the bolts 24 by a valve assembly generally designated 30. Six such valve assemblies 30 are shown in Fig. 4, three in section and three in side view.

Each valve assembly comprises a valve body 32 fitted with a cap 40. In the case of the uppermost valve assembly, shown in side view in Fig. 4, the cap 40 has been removed but the cap is shown in place on the other two valve assemblies seen in side view and the cap 40 is shown in section in second valve assembly from the top in Fig. 4.

The valve body 32 is formed with a screw at one end to engage in the hole in the header and is traversed by a through passage 38. Two ball valves 34 and 36 are arranged one after the other to intersect the through passage. The uppermost valve assembly 30 shows the operating shafts of the two ball valves 34 and 36. These shafts do not protrude from the valve body and have a blind recess for receiving a proprietary seven sided key. By inserting a key into the recess and rotating it through 9Q0 the relevant valve is opened and closed.

The valve elements need not necessarily be balls. They may be any form of element which, when the valve is opened, leaves the through passage 32 unobstructed to that a cleaning implement may be inserted into the aligned cooling tube 16.

The lowermost valve assembly in Fig. 4 shows how once the two valves 34 and 36 have been opened, it is possible to pass a cleaning implement, in this case a rod 52, through the two valves and the header, into the cooling tube 16.

The rod 52 is inserted into the valve assembly 30 through a collar 50, relative to which it is sealed by 0-rings 54 or a packing. The collar 50 is screwed onto the coupling thread 42 on the valve body 32 in place of the cap 40.

When the heat exchanger is in normal operation, all the valves 34 and 36 are closed and all the caps 40 are fitted to the valve bodies 32. As shown in the section of the second valve assembly from the top in Fig. 4, the cap 40 has a cylindrical skirt that fits over the valves 34 and 36 and seals against a conical seat at the base of the valve body 32. This provides triple security against an escape or a leakage of the liquid flowing through the header of the heat exchanger. Even is the liquid gets past two closed valves 34 and 36, it will still be contained by the cap 40. The cap design also ensures that the operating shafts of the valves 34 and 36 cannot be access until the cap has been removed.

It is necessary to ensure when unscrewing the cap 40 that the valve body 32 does not rotate and come away from the header. This can be done in an conventional manner, such as the use of a locknut or by using a left handed thread between the cap and the valve body.

To clean one of the cooling tubes 16, one starts by removing the cap 40 to leave the valves exposed as shown for the uppermost valve assembly in Fig. 4. As there are two valves connected in series, there is adequate protection against leakage while the cleaning implement is being attached.

With the valves 34 and 36 still closed, the collar 50 of a cleaning implement is screwed onto the valve body 32 in place of the cap 40, once again sealing the end of the through passage 38. This is shown in the section of the valve assembly lying fourth from the top in Fig. 4.

The valves 34 and 36 can now be opened safely and the rod 52 fed through them, as shown for the lowermost valve assembly in Fig. 4 to clean the inner surface of the aligned cooling tube 16.

It can this be seen that the cleaning of the cooling tubes 16 can be carried without danger while the heat exchanger is in operation. There is no cost penalty in terms of downtime preventing the cleaning operation from being performed frequently, and therefore no major build up of a deposit will occur between service intervals. A light scraping of the tubes 16 is all that will be necessary to dislodge the layer that forms a molecular bond with the inner wall of the tubes 16.

Claims

-10 -CLAIMS1. A heat exchanger having a stack of cooling tubes extending between two headers and holes in at least one of the headers aligned with the inner bore of each cooling tube to allow a cleaning implement to be inserted into each cooling tube through the header, characterised in that each hole is plugged by means of a valve which in its open position has a through passage of sufficiently large diameter to permit a cleaning implement to be introduced through the valve into the bore of the aligned cooling tube without allowinq the fluid within the header to escape.
2. A heat exchanger as claimed in claim 1, wherein each valve comprises a valve body screwed at one end into a respective hole in the header, the valve body having a straight through passage communicating with the interior of the header and at least one valve element for selective shutting off the through passage, the valve body also having a coupling thread to permit the through passage to be capped.
3. A heat exchanger as claimed in claim 2, wherein the valve element is a ball or cylinder rotatable about an axis perpendicular to that of the through passage.
4. A heat exchanger as claimed in claim 2, wherein is a pivotable flap or a slidable gate.
5. A heat exchanger as claimed in claim 2, 3 or 4, wherein a cap is provide to engage the coupling thread a cap to close off the through passage when cleaning is not taking place.
6. A heat exchanger as claimed in any of claims 2 to 5, wherein two or more valve elements are provided in line -11 -with one another and staggered along the length of the through passage in the valve body.
7. A heat exchanger as claimed in any one of claims 3 to 5, wherein each valve element is operable by inserting and turning a key into a proprietary recess in an operating shaft of the valve element that does not project beyond the valve body.
8. A heat exchanger as claimed in claim 7 when appended to claim 5, wherein the cap covers the operating shafts of the valve elements.
9. A heat exchanger as claimed in claim 9, wherein the cap when closed defines a sealed enclosed space encasing the operating shafts of the valve elements.
10. A heat exchanger as claimed in any preceding claim, wherein heat exchanger is air cooled and has finned cooling tubes.
11. A heat exchanger as claimed in any of claim 1 to 9, wherein the cooling tubes are encased in a shell through which a second fluid flows during operation of the heat exchanger.
12. A heat exchanger constructed arranged and adapted to operate substantially as herein before described with reference to and as illustrated in Fig. 4 of the accompanying drawings.