WO2018004348A1

WO2018004348A1 - Improvements relating to the maintenance of heat exchangers

Info

Publication number: WO2018004348A1
Application number: PCT/NO2016/050145
Authority: WO
Inventors: Erling LUNDE; Anders RØYRØY
Original assignee: Statoil Petroleum As
Priority date: 2016-06-28
Filing date: 2016-06-28
Publication date: 2018-01-04
Also published as: WO2018004350A1

Abstract

A maintenance apparatus for use with a heat exchanger for cooling or heating a fluid, said heat exchanger comprising a plurality of heat exchanger tubes each arranged to carry a heat exchanger fluid, comprises: a rotatably mounted beam; a tool carriage movable mounted on said beam so as to be movable along said beam; and a tool insertion device mounted on said tool carriage, said tool insertion device being arranged to carry a maintenance tool for insertion into one of said heat exchanger tubes, wherein rotation of said beam and movement of said tool carriage allow said tool to be positioned adjacent the end of a selected cooling tube, and wherein said tool insertion device is arranged to move said tool into said selected cooling tube.

Description

Improvements relating to the maintenance of heat exchangers

FIELD OF THE INVENTION

The invention relates to improvements relating to the maintenance of heat exchangers.

The invention is particularly applicable to internal cleaning, inspection, repair and sealing of shell and tube heat exchangers, of the type used for example in the oil and gas industry, or in any process industry, to improve their efficiency and detect faults, such as leaks, at an early stage. Embodiments of the invention allow maintenance of the tubes of a heat exchanger during regular operation.

The invention is applicable to heat exchangers for both cooling and heating.

BACKGROUND OF THE INVENTION

The following methods for cleaning heat exchangers are known:

1 . Hydraulic cleaning by means of high pressure water manually administered through a "lance tube cleaner".

2. Mechanical cleaning by means of rotating brushes etc. that travel through the tube.

3. Chemical cleaning by means of adding strong chemicals to the fluid flow through the tubes.

A borescope/endoscope video camera may be used to manually inspect the inside of the tube of a heat exchanger. Several sensing technologies may be applied to inspect the pipe wall for erosion, cracks, pits, etc. These include ultrasound, eddy current, and others.

The following links describe some existing technology in this field: Examples of equipment suppliers are:

http://www.peinemannequipment.com/products/bundle_cleaning/single_lance_tube_cle aner, and

http: ww¥.CQncosystems.Gom

tecnnoioqies p:-G5e ies¾£2¾84%Ag-;ube cleaning Tube inspection by ultrasonic, eddy current sensors, is offered by Innospection http://www.innospection.com/pdfs/Tube%20lnspection%20Datasheet.pdf

as well as Olympus:

http://www.olympus-ims.com/sv/ms-5800-tube-inspection/ The above-mentioned technologies have several drawbacks, as follows:

1 . The lance tube cleaner is effective for cleaning tubes, but cleaning a whole heat exchanger with several thousand tubes is a very time consuming process. This usually means taking the heat exchanger out of production and the cleaning operations are to a large extent manual.

2. The rotating brushes are normally free-running (water powered) so that they have to be picked up at the tube outlet. That is, it is necessary to provide an additional system for inserting "brushes" and retrieving them at the outlet.

3. Chemical cleaning is not always effective, and may have serious environmental downsides. For large heat exchangers, large amounts of chemicals are needed. Most probably, the heat exchanger needs to be taken out of production and chemicals injected in a closed loop system.

4. Inspection technologies generally require offline operations.

5. The heat exchanger is opened up, and a potential for leakage after the operation is introduced.

A drawback with all these technologies is that the heat exchanger has to be taken out of production (offline), which leads to considerable production losses. None of these technologies have been demonstrated inline. SUMMARY OF THE INVENTION

The invention provides a maintenance apparatus, heat exchanger and method as set out in the accompanying claims.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a schematic cross-section of the main components of a shell and tube heat exchanger; Figure 2 is a top view of a manipulator mechanism in accordance with an embodiment of the invention;

Figure 3 is a more detailed view of part of the manipulator mechanism ; Figure 4 shows the interfaces and drives of a control system; Figure 5 shows a lance tube hydraulic cleaner; and

Figure 6 is a cross-sectional view of a tube sheet indicating entry holes for each cooling tube.

DESCRIPTION OF PREFERRED EMBODIMENTS

Heat exchangers used in oil and gas production facilities, for the cooling of oil, gas, coolants and other fluids found in an oil and gas facility, are prone to fouling and scaling, which leads to reduced through-flow as well as reduced heat exchange efficiency and capacity.

In the following description the example used is a heat exchanger where the fluid flow through the tubes is used to cool down the fluid on the shell side, hence the heat exchanger is denoted a cooler. The invention is equally relevant for cases where the heat flow goes in the opposite direction, where the purpose is to heat up one fluid, and for cases where the fluids may be liquids or gases. Figure 1 shows a shell and tube cooler (ie heat exchanger) 2, in which cooling fluid (such as sea water) flows through a large number of small diameter cooling tubes 4 (only four of which are shown in Figure 1 , for simplicity) that periodically need to be cleaned to restore their cooling efficiency. The cooling fluid enters the cooler 2 through an inlet plenum 6, passes through the tubes 4, and exits the cooler 2 through an outlet plenum 8. The production fluid to be cooled enters the cooler 2 through an inlet 10, passes around the cooling tubes 4, which cool the production fluid, and exits the cooler 2 through an outlet 12.

An inlet tube sheet 14 is provided adjacent the inlet plenum 6, and an outlet tube sheet 16 is placed adjacent the outlet plenum 8. Figure 5 shows a portion of the inlet tube sheet 14 or the outlet tube sheet 16, both of which contain many holes 18 to which the cooling tubes 4 are connected. Each cooling tube 4 thus runs from inlet tube sheet 14 to the outlet tube sheet 16, and each cooling tube 4 transfers cooling fluid from the inlet plenum 6 to the outlet plenum 8.

Periodically, the cooling tubes 4 need to be inspected for defects, weak spots and leaks to maintain the integrity of the cooler 2. We describe an embodiment which allows accessing of these tubes 4 while the heat exchanger 2 runs in regular operation. The number of tubes 4 may be several thousand, all of which may require cleaning and inspection.

Bulk cleaning of the tubes 4 may be approached by adding strong chemicals to the cooling fluid flow. However, the effect of this has not been convincing and the negative environmental issues are considerable. Here we propose an approach that cleans one tube at the time, primarily by the use of hydraulic cleaning, ie cleaning using pressurized water, but also with the option of targeted chemical cleaning.

Inspection of the cooling tubes 4 is known, but requires that the cooler 2 is taken out of production and the inspection operation is mainly manual. As shown in Figure 2, the proposed system comprises a manipulator system 18 to position an access tool onto a desired tube inlet. Each tube 4 is welded onto a circular baffle plate (ie tube sheet) 14, 16, with each plate 14, 16 having one hole 18 per cooling tube 4. The manipulator 18 is to be permanently stationed inside the cooler's inlet plenum 6 or outlet plenum 8, but may be operated from the outside. A new plenum may be designed and manufactured to host the manipulator 18, if necessary.

The manipulator system 18 comprises a tool insertion device 20 (shown in Figure 3), which is carried on a tool carriage or carrier 22 which can be positioned in polar coordinates at any position within the circular cross section of the cooler 2.

A beam 24 spans the diameter of the cooler 2. The beam 24 can be rotated by moving the outer ring 30 around a track 34 at the circumference of the cooler 2, and can thereby be oriented at any angle.

The tool carriage 22 is slidably mounted on the beam 24, and can be positioned at any position along the beam 24.

By a combination of the orientation of the beam 24 and the position of the tool carriage 22, the tool insertion device 20 can reach any location on one of the circular tube sheets 14 or 16.

A tool 42, or a component thereof, can extend from the tool carrier 22 onto the tube sheet 14 or 16, and through a hole 18 to the inside of a cooling tube 4, by means of a linear actuator, which may be a tool piston 28 as shown in Figure 3.

The tool 42 may be a cleaning, inspection, repair or sealing tool, and may for example be a lance cleaner. The tool 42 may be a cleaning tool which arranged to clean the heat exchanger tubes 4, or an inspection tool arranged to allow inspection of the heat exchanger tubes 4.

The tool 42 may also be a repair tool arranged to allow repair of the heat exchanger tubes 4, or a sealing tool arranged to allow sealing off (for example plugging) of selected heat exchanger tubes 4. Figure 2 shows an outer ring (slewing bearing or similar) 30 and a pneumatic motor 32 for rotating the ring 30 around a circular track 34. A flexible hose 36 extends between the tool insertion device 20 and a point at the shell of the inlet plenum 6 or outlet plenum 8 (depending on whether the manipulator system 18 is positioned in the inlet plenum 6 or outlet plenum 8).

Figure 2 shows a cross-sectional view of the flexible hose 36, which includes at least one pneumatic or hydraulic supply pipe 38 for driving the tool carriage 22, and at least one pneumatic or hydraulic supply pipe 40 for driving the tool insertion device 20. The flexible hose 36 also contains a maintenance tube 41 for carrying maintenance tools (e.g. a lance cleaner, when the tool 42 is a lance cleaner) to one of the cooling tubes 4 as shown in Figure 3. Figure 3 shows an example of a tool 42 for cleaning the cooling tubes 4. The tool 42 in this example is a lance which is slidably movable within the cooling tubes 4. A pneumatic tool piston 28 and a pneumatic tool cylinder 46 are provided for positioning the tip 29 of piston 28 onto the entrance of one of the cooling tubes 4. A pneumatic carriage motor 48 is connected to pneumatic supply pipes 38 carried within the flexible hose 36, and is used to drive the tool carriage 22 along the beam 24. Additional sensors (not shown) may be provided on the tool carriage 22 for accurate position of the tool carriage 22.

Figure 4 shows a control system 52 for controlling operation of the manipulator system 18.

A lance drive unit 53 is provided for driving the lance (or other maintenance tool 42) through the maintenance tube 41 to the tool carriage 22. A drive system (pneumatic, hydraulic or electric) powers the circular motion motor 32, the carriage motor 48 and the tool piston 28. In Figure 4 this drive system is a pneumatic drive system 54, which is connected to an air compressor 56. A hydraulics compressor 58 is connected to a lance cleaner hose 57, which is carried within the maintenance tube 41 within flexible hose 36, and supplies fresh water to the lance 42. A control system 59 is connected to the air compressor 56, the pneumatic drive system 54 and the hydraulics compressor 58, in order to provide control signals to these units.

The control system 59 may be used to:

a. position the tool insertion device 20 at the desired position;

b. start/stop the actual cleaning operation; and

c. position the manipulator system 18 in a parking location/state where it can reside until its next maintenance task. Figure 5 shows the lance 42 in an extended position within one of the cooling tubes 4. A forwardly directed water jet 60 is used to dislodge debris 62 within the cooling tube 4, and one or more rearwardly directed water jets 64 help to clear debris 62 from the cooling tube 4. Figure 4 shows an interface connection 66 to the cleaning system. The tool 42 can be lead through the flexible hose 36 to the tool carriage 22, via the tool piston 28, and into the cooler tube 4.

The following cleaning strategies may be applied:

a. Hydraulic cleaning with a lance cleaning tool 42, as described above; and/or b. Chemical injection into one tube at the time, by injecting a chemical through the lance cleaner tube 41

The manipulator system 18 may also be used for inline inspection of single tubes 4, for example by inserting an inspection sensor to monitor wall thickness throughout the complete length of a tube 4. In this case the lance 42 may itself form the inspection sensor 42.

The external units 54, 56, 58 and 59 can be placed inside an explosion-proof container 68 which may serve as an interface unit for multiple manipulator systems 18.

Figure 6 shows the holes 18 in a portion of one of the tube sheets 14, 16, and also illustrates a coordinate which may be used by the control system 59 for positioning the tool insertion device 20. All operations described above may be carried out while the cooling fluid (e.g. sea water) is flowing through the cooler 2 and the cooling tubes 4, as described above

The described embodiment allows the maintenance of tube and sheet heat exchangers without production losses. The operations can be condition based rather than scheduled. That is, it is possible to intervene at any time and at any location, as and when needed.

Tube and sheet heat exchangers may be used in production facilities both onshore and offshore. The described embodiment has a considerable impact on regularity and efficiency of hydrocarbon production.

The invention may allow inline use of existing technologies. In one embodiment the invention provides a manipulator for online maintenance of shell and tube heat exchangers.

Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

CLAIMS:

1 . A maintenance apparatus for use with a heat exchanger for cooling or heating a fluid, said heat exchanger comprising a plurality of heat exchanger tubes each arranged to carry a heat exchanger fluid, said maintenance apparatus comprising: a rotatably mounted beam;

a tool carriage movable mounted on said beam so as to be movable along said beam ; and

a tool insertion device mounted on said tool carriage, said tool insertion device being arranged to carry a maintenance tool for insertion into one of said heat exchanger tubes,

wherein rotation of said beam and movement of said tool carriage allow said tool to be positioned adjacent the end of a selected heat exchanger tube, and

wherein said tool insertion device is arranged to move said tool into said selected heat exchanger tube.

2. An apparatus as claimed in claim 1 , which further comprises a circular, or substantially circular, track, and wherein said beam is movably mounted on said track.

3. An apparatus as claimed in claim 2, wherein opposite ends of said beam are movably mounted on said track at positions which are substantially opposite each other on said circular track.

4. An apparatus as claimed in claim 2 or 3, wherein said beam is movably mounted on said track by means of a ring which extends around said track and which is rotatable relative to said track.

5. An apparatus as claimed in any preceding claim, wherein said tool carriage is mounted on said beam by means of one or more rollers or wheels.

6. An apparatus as claimed in any preceding claim, wherein said tool insertion device is arranged to move said tool between an extended position and a retracted position.

7. An apparatus as claimed in any preceding claim which further comprises a flexible hose which is connected at one end to said tool insertion device.

8. An apparatus as claimed in claim 7, wherein said flexible hose is arranged to provide power to said tool and/or power for moving said tool carriage along said beam.

9. An apparatus as claimed in claim 7 or 8, wherein said flexible hose is arranged to carry fluid to said tool insertion device.

10. An apparatus as claimed in any preceding claim, which further comprises an electronic control system for controlling movement of said tool and operation of said tool insertion device.

1 1 . An apparatus as claimed in any preceding claim, wherein said tool is a cleaning tool arranged to clean said heat exchanger tubes.

12. An apparatus as claimed in any one of claims 1 to 10, wherein said tool is an inspection tool arranged to allow inspection of said heat exchanger tubes.

13. An apparatus as claimed in any one of claims 1 to 10, wherein said tool is a repair tool arranged to allow repair of said heat exchanger tubes.

14. An apparatus as claimed in any one of claims 1 to 10, wherein said tool is a sealing tool arranged to allow sealing off of said heat exchanger tubes.

15. A heat exchanger for cooling or heating a fluid, said heat exchanger comprising a plurality of heat exchanger tubes each arranged to carry a heat exchanger fluid and a maintenance apparatus as claimed in any preceding claim.

16. A heat exchanger as claimed in claim 15, which further comprises a tube sheet containing a plurality of holes, each hole forming an entrance to one of said heat exchanger tubes, and an inlet or outlet plenum adjacent said tube sheet, and wherein said maintenance apparatus is mounted within said inlet or outlet plenum.

17. A method of maintaining a heat exchanger for cooling or heating a fluid, said heat exchanger comprising a plurality of heat exchanger tubes, said method comprising:

a) passing a heat exchanger fluid through said heat exchanger tubes;

b) passing said fluid to be cooled or heated around said heat exchanger tubes so as to change the temperature of the fluid;

c) providing a maintenance apparatus as claimed in any one of claims 1 to 14; and

whilst continuing to perform steps a) and b), performing the following steps: d) positioning said tool adjacent an end of a selected cooling tube; and e) moving said tool into said selected cooling tube.

18. A method as claimed in claim 17, wherein said step of positioning said tool includes rotating said beam and moving said tool carriage along said beam.

19. A method as claimed in claim 17 or 18, wherein said tool is a cleaning device, and wherein said method further includes discharging a jet of water, or other cleaning fluid, from said tool into said selected cooling tube.