GB2591487A - An instrument air supply system for an offshore plant and a method for supplying instrument air to an offshore plant - Google Patents
An instrument air supply system for an offshore plant and a method for supplying instrument air to an offshore plant Download PDFInfo
- Publication number
- GB2591487A GB2591487A GB2001270.4A GB202001270A GB2591487A GB 2591487 A GB2591487 A GB 2591487A GB 202001270 A GB202001270 A GB 202001270A GB 2591487 A GB2591487 A GB 2591487A
- Authority
- GB
- United Kingdom
- Prior art keywords
- air
- instrument
- offshore plant
- air supply
- instrument air
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/0072—Electrical cables comprising fluid supply conductors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/14—Submarine cables
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- Laying Of Electric Cables Or Lines Outside (AREA)
Abstract
An instrument air supply system (1) for supplying instrument air to an offshore platform, comprising an onshore air supply station (2) adapted to supply dry, compressed instrument air, an offshore plant (3) adapted to receive the instrument air, and a submarine cable (4) connecting the onshore air supply station (2) to the offshore plant (3), where the submarine cable comprises a plurality of electrical conductors (10, Fig 2) and an air conduit (14, Fig 2). In this way, instrument air can be supplied to an offshore plant through the umbilical for an extended period during a gas leakage at the offshore plant. The instrument air may be for pressurised explosion protection (Ex-p rated). The air pressure may be between 8 and 18 bar, and the air flow may be 4-8kg/h. The cable may be at least 100km long, and the air conduit may have a diameter of at least 25mm. The offshore plant may be an offshore platform for oil or gas extraction.
Description
AN INSTRUMENT AIR SUPPLY SYSTEM FOR AN OFFSHORE PLANT AND A METHOD FOR SUPPLYING INSTRUMENT AIR TO AN OFFSHORE PLANT
TECHNICAL FIELD
The present invention relates to a system for supplying instrument air to an offshore plant from an onshore plant. The system is adapted to ensure that instrument air is available at the offshore plant for an extended period during a gas leakage. The present invention further relates to a method for supplying instrument air to an offshore plant from an onshore air supply station.
BACKGROUND ART
On remote locations or offshore installations, there might be a need for clean instrument air to maintain an Ex-p type (pressurized) explosion protection. Normally, instrument air is produced locally at the offshore platform using air compressors, air filters and air dryers. However, if the main part of the power system (e.g. high voltage transformers for power import) need to be explosion protected (e.g. Ex-p rated), and there is a risk for natural gas in the air-intake to the local air compressors, sustained production of the necessary compressed air quantities to maintain the Ex-p rating of the high voltage transformers (Un > 15kV) will not be possible.
Typically firewater pump-drive solutions based on electric power from an onshore power station will for a "gas in the air-intake" scenario soon lose the Ex-p protection on their high voltage transformer terminals if they are only supplied with "Ex-p air" from local compressed air accumulators, which are typically sized for 30 or 60 minutes consumption. Hence, a typical required supply of firewater for 18 hours will not be possible if the air accumulators are dimensioned such that the Ex-p protection is lost after 30 or 60 minutes.
Normally, this problem is solved through accumulator tanks for compressed air dimensioned for the required time duration. However, this may require very large accumulator tanks. There is thus room for an improved instrument air supply system for an offshore platform.
DISCLOSURE OF INVENTION
An object of the present invention is therefore to provide an improved instrument air supply for an offshore platform. A further object of the invention is to provide a method for supplying instrument air to an offshore platform.
The solution to the problem according to the invention is described in the characterizing part of claim 1 with regard to the instrument air supply system and in claim 12 with regard to the method. The other claims contain advantageous embodiments and further developments of the instrument air supply system and the method.
In an instrument air supply system for supplying instrument air to an offshore plant, comprising an onshore air supply station adapted to supply compressed instrument air, an offshore plant adapted to receive the instrument air, a submarine cable connecting the onshore air supply station to the offshore plant, the object of the invention is achieved in that the submarine cable comprises a plurality of electrical conductors and an air conduit.
By this first embodiment of the instrument air supply system according to the invention, clean instrument air can be supplied to an offshore plant in a continuous manner, regardless of the air quality on the offshore plant. By supplying instrument air from an onshore instrument air supply, the Ex-p explosion protection of crucial equipment at the offshore plant can be ensured. One such critical equipment is e.g. a high voltage transformer, having a voltage rating above 15 kV, for a firewater pump, which may lose its Ex-p rating if it is not supplied with instrument air.
In a conventional instrument air supply system at an offshore plant, a compressor at the offshore plant supplies compressed air to the instrument air system through air filters and air dryers. In normal conditions, this type of instrument air supply is sufficient, but if there would be a gas leakage, the air intake to the compressor would be contaminated, and the supplied compressed air would not be clean enough to meet the required Ex-p rating. Pollutions and particles etc. may be removed with the air filter, but gas may not.
A conventional instrument air supply will comprise compressed air accumulator tanks dimensioned for 30 or 60 minutes air supply to the Ex-p rated equipment. However, it is stipulated that e.g. a firewater supply should be available for 18 hours. Such a conventional system will thus not meet the requirements if the air intake to the compressor is not clean enough.
In the inventive instrument air supply system, instrument air is supplied from an onshore air supply station through an air conduit integrated in a high power electric submarine cable. The cable may e.g. be adapted to transmit power at a voltage of over 76 kV, and the cable may be at least 100 km long. In one example, the submarine cable is a 3-phase cable having a 300 mm2 core of cupper and having an air conduit with a diameter of e.g. 25-30 The supplied instrument air pressure arriving at the offshore plant should preferably correspond to the air system of the regular air system at the offshore plant, which is 6-8 bar(a). Due to the long distance of the submarine cable, the pressure drop through the submarine cable will be significant, and will greatly depend on the air flow. The instrument air supply system will thus only be suitable for low air flows in the range between 4-8 kg/h. The air compressor at the onshore air supply station will have a nominal rating between 8-18 bar(a). For an air conduit having a class AC rating, the maximum operating air pressure is 18 bar(a). The submarine cable is manufactured in a conventional way, where the air conduit is embedded in the internal isolation material.
In a method for supplying instrument air from an onshore air supply station to an offshore plant through a submarine cable, the steps of; compressing air with an air compressor at the onshore air supply station, transferring the instrument air through a submarine electrical cable comprising an air conduit, receiving the instrument air at the offshore plant, and supplying the received instrument air to an Ex-p rated component are disclosed.
By this method, a reliable supply of instrument air to equipment at an offshore plant can be ensured. Further, with the inventive method, compressed air accumulator tanks at the offshore plant are not required, which saves space, weight and cost.
The compressed air is compressed at an onshore air supply station, where clean ambient air is used, and where it is ensured that no pollution gas is present in the air. The compressed air is still fed through an air filter and an air dryer to ensure that particles and humidity is removed from the compressed air. The compressed air is then fed through an air conduit integrated in a high voltage electric submarine cable to the offshore plant.
The air flow through the air conduit is held at a low flow rate, preferably between 4-8 kg/h, in order to reduce the internal friction in the air conduit and thus the pressure drop. At the offshore plant, the instrument air is forwarded to the Ex-p rated equipment.
BRIEF DESCRIPTION OF DRAWINGS
The invention will be described in greater detail in the following, with reference to the embodiments that are shown in the attached drawings, in which Fig. 1 shows a schematic view of an instrument air supply system according to the invention, Fig. 2 shows a schematic cut view of a submarine cable to be used in an instrument air supply system according to the invention, and Fig. 3 shows a flow chart of the method to prevent overvoltage according to the invention.
MODES FOR CARRYING OUT THE INVENTION
The embodiments of the invention with further developments described in the following are to be regarded only as examples and are in no way to limit the scope of the protection provided by the patent claims.
Fig. 1 shows a schematic view of an instrument air supply system according to the invention. The instrument air supply system 1 comprises an onshore air supply station 2 that is adapted to supply an offshore plant 3 with instrument air. The offshore plant is a plant arranged offshore that requires a certain amount of instrument air, which is an extremely clean supply of compressed air that is free from contaminates such as moisture and particulates. The instrument air is e.g. used in high voltage transformers to ensure a sufficiently high isolation and to reduce the explosion risk.
The instrument air is produced at the onshore air supply station by an air compressor. The air compressor has a rated maximum pressure of e.g. 18 bar(a). The air supply to the air compressor is drawn from the ambient air and the compressed air is cleaned through an air filter and is dried by an air dryer in order to remove most of the contaminations and humidity, such that an Ex-p rating can be achieved with the instrument air.
The instrument air is fed through a high voltage electric submarine cable comprising an air conduit. An example of such a submarine cable is shown in Fig. 2. The cable comprises in the shown example three electrical conductors 10 having a cupper core 11 and insulation 12. Each conductor is provided with a conventional protective layer. Around the conductors, there are fillers 13 filling the voids and holding the conductors in place. The air conduit 14 is arranged in one of the fillers. The complete cable comprises a conventional outer protective layer. The diameter of the air conduit is preferably in the range between 25-30 mm.
The air flow from the onshore air supply station is held at a low flow rate, in the range between 4-8 kg/h. This low air flow will ensure a high enough pressure at the receiving end at the offshore plant. With this solution, instrument air can be fed through submarine cables having a length of more than 100 km, and up to 200 km. This air flow is enough to supply the most important Ex-p rated equipment of the offshore plant, such as high voltage transformers. This will e.g. ensure that firewater can be supplied even if a gas leakage occurs at the offshore plant, when the ambient air can not be used to produce instrument air at the offshore plant.
The submarine cable will of course also supply electric energy to the offshore platform, which may be adapted to drill for oil and/or gas, but other offshore plants such as a desalination plant, a fish farm, a subsea factory, etc. may also be supplies with instrument air by the inventive system. The offshore plant is connected to an onshore power station (not shown) through the submarine cable 4, which is adapted to transmit the required energy. In one example, the submarine cable is e.g. arranged to transmit power at a high voltage of e.g. 76 kV or more, and the length of the submarine cable may e.g. be a 3-phase cable having a 300 mm2 core of cupper and having a length of e.g. 162 km. The offshore plant may also be a small island supplied with electricity from the mainland.
The onshore power station is mainly adapted to supply electric energy to the offshore plant, but may also receive electric energy from the offshore plant, e.g. if the offshore plant at some times produces more energy than it consumes, or if the submarine cable is also connected to a wind power plant or a solar panel array.
The offshore plant, in the shown example an offshore drill platform, comprises several different machinery that consumes electric energy. Some of the electrical equipment at the offshore platform are Ex-p rated, in order to minimize the risk of explosions when there is a gas leakage.
With the inventive instrument air supply system, clean instrument air can be supplied to the required EX-p rated electrical equipment at the offshore plant during a gas leakage. Even though the air flow of the instrument air is relatively low, it is sufficient to supply instrument air to the electrical equipment that are required during a gas leakage. When there is no gas leakage, instrument air can be supplied by the air compressor of the offshore platform.
In the method for supplying instrument air to an offshore plant 3 from an onshore air supply station 2 through a submarine cable 4, the following steps are comprised.
In step 100, compressed air is produced by an air compressor at an onshore air supply station. The air is cleaned and dehumified at the onshore air supply station.
In step 110, the compressed air is supplied through an submarine cable comprising a plurality of electric conductors and an air conduit. In this way, the offshore plant can be supplied with both electric power and instrument air.
In step 120, the instrument air is received at the offshore plant.
In step 130, the instrument air is distributed to the electrical equipment that is required during a gas leakage. This may e.g. be a high voltage transformer supplying electric energy to a firewater pump.
The invention is not to be regarded as being limited to the embodiments described above, a number of additional variants and modifications being possible within the scope of the subsequent patent claims. The instrument air supply system may have any size and configuration.
REFERENCE SIGNS
1: Air supply system 2: Onshore air supply station 3: Offshore plant 4: Submarine cable 10: Electric conductor 11: Cupper core 12: Insulation 13: Filler 14: Air conduit 15: Protective outer layer
Claims (10)
- CLAIMS1 An instrument air supply system (1) for supplying instrument air to an offshore plant, comprising an onshore air supply station (2) adapted to supply compressed instrument air, an offshore plant (3) adapted to receive the instrument air, a submarine cable (4) connecting the onshore air supply station (2) to the offshore plant (3), characterized in that the submarine cable comprises a plurality of electrical conductors (10) and an air conduit (14).
- 2 The air supply system according to claim 1, characterized in that the maximum air pressure at the onshore air supply station is below 18 bar(a).
- 3. The air supply system according to claim 1 or 2, characterized in that the minimum air pressure at the offshore plant is at least 8 bar(a).
- 4 The air supply system according to any of the preceding claims, characterized in that the air flow through the air conduit is between 4-8 kg/h.
- 5. The air supply system according to any of the preceding claims, characterized in that the submarine cable (4) is at least 100 km long.
- 6. The air supply system according to any of the preceding claims, characterized in that the diameter of the air conduit is at least 25 mm.
- 7. The air supply system according to any of the preceding claims, characterized in that the offshore plant (3) is an offshore platform for oil/gas extraction.
- 8 A method for supplying instrument air to an offshore plant (3) from an onshore air supply station (2) through a submarine cable (4), comprising the following steps: compressing air at the onshore air supply station, transferring the instrument air through a submarine electrical cable comprising an air conduit, receiving the instrument air at the offshore plant, supplying the received instrument air to an Ex-p rated component.
- 9 The method according to claim 8, characterized in that the air pressure of the compressed air at the onshore air supply station is at least 8 bar(a).
- 10.The method according to claim 8 or 9, characterized in that the air flow through the submarine cable is between 4-8 kg/h.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB2001270.4A GB2591487B (en) | 2020-01-30 | 2020-01-30 | An instrument air supply system for an offshore plant and a method for supplying instrument air to an offshore plant |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB2001270.4A GB2591487B (en) | 2020-01-30 | 2020-01-30 | An instrument air supply system for an offshore plant and a method for supplying instrument air to an offshore plant |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB202001270D0 GB202001270D0 (en) | 2020-03-18 |
| GB2591487A true GB2591487A (en) | 2021-08-04 |
| GB2591487B GB2591487B (en) | 2022-07-06 |
Family
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB2001270.4A Active GB2591487B (en) | 2020-01-30 | 2020-01-30 | An instrument air supply system for an offshore plant and a method for supplying instrument air to an offshore plant |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2591487B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN118059663A (en) * | 2024-03-22 | 2024-05-24 | 江苏润扬船业有限公司 | Compressed air system for double-body ocean wind power transportation ship |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4698456A (en) * | 1984-10-20 | 1987-10-06 | Martin Hamacher | Electrical device for use in an explosive environment |
| WO1988006835A1 (en) * | 1987-03-02 | 1988-09-07 | Jan Grosch | Means in connection with an enclosed electrical apparatus |
| DE102005040804A1 (en) * | 2005-08-29 | 2007-03-22 | Schopf, Walter, Dipl.-Ing. | Current cable and end connection for transporting air especially for maritime and wind energy uses has integrated air leads with cable cover or a separately connected lead |
| WO2007074416A2 (en) * | 2005-12-28 | 2007-07-05 | Abb As | Integrated explosion protection apparatus for supervision and control of advanced electrical apparatuses |
-
2020
- 2020-01-30 GB GB2001270.4A patent/GB2591487B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4698456A (en) * | 1984-10-20 | 1987-10-06 | Martin Hamacher | Electrical device for use in an explosive environment |
| WO1988006835A1 (en) * | 1987-03-02 | 1988-09-07 | Jan Grosch | Means in connection with an enclosed electrical apparatus |
| DE102005040804A1 (en) * | 2005-08-29 | 2007-03-22 | Schopf, Walter, Dipl.-Ing. | Current cable and end connection for transporting air especially for maritime and wind energy uses has integrated air leads with cable cover or a separately connected lead |
| WO2007074416A2 (en) * | 2005-12-28 | 2007-07-05 | Abb As | Integrated explosion protection apparatus for supervision and control of advanced electrical apparatuses |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2591487B (en) | 2022-07-06 |
| GB202001270D0 (en) | 2020-03-18 |
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