A ship

Abstract

A ship (1) comprises a walkable deck (2), a superstructure (3) above the deck (2), an opening or a closable opening in the deck (2) or the superstructure (3) such as a door or ventilation opening, an internal combustion engine (6), a closed tank (7) for containing a low flashpoint liquid fuel (8), a fuel supply system (11) for supplying fuel (8) from the tank (7) to the internal combustion engine (6), an inert gas supply system (12) for supplying inert gas to the tank (7), a tank venting pipe (14) extending from the tank (7) to a vent outlet (15) of the tank venting pipe (14) and a pressure relief system (16) for allowing gas to flow from the tank (7) through the tank venting pipe (14) to the vent outlet (15) when pressure in the tank (7) exceeds a predetermined pressure level. The tank (7) has a fire retardant wall (10) and a storage volume which is larger than 1.5 m3. The vent outlet (15) is located within 3 m from the deck (2) and / or within 10 m from the opening or the closable opening and / or within 10 m from a potential ignition source.

Description

[0001] A ship

[0002] The present invention relates to a ship comprising a walkable deck, a superstructure above the deck, an opening or a closable opening in the deck or the superstructure such as a door or ventilation opening, an internal combustion engine, a closed tank for containing a low flashpoint liquid fuel, a fuel supply system for supplying fuel from the tank to the internal combustion engine, an inert gas supply system for supplying inert gas to the tank, a tank venting pipe extending from the tank to a vent outlet of the tank venting pipe, a pressure relief system for allowing gas to flow from the tank through the tank venting pipe to the vent outlet when pressure in the tank exceeds a predetermined pressure level, wherein the tank has a fire retardant wall and a storage volume which is larger than 1.5 m3.

[0003] Such a ship is known in the art. The vent outlet of the known ship is located remote from locations where personnel is often present or where possible ignition sources are located in order to avoid hazardous conditions in the event that the pressure relief system opens, for example caused by fire nearby the tank. Such a location of the vent outlet can be selected relatively easy in case of a relatively large ship, but becomes more difficult in case of relatively small ships.

[0004] The present invention aims to provide a ship which minimizes the mentioned difficulty.

[0005] For this purpose, in the ship according to the invention the vent outlet is located within 3 m from the deck and / or within 10 m from the opening or the closable opening and / or within 10 m from a potential ignition source.

[0006] The applicant has found that a combination of the fire retardant wall of the tank, the storage volume of the tank and the predetermined pressure level provides sufficient delay before the pressure relief system opens and venting from the vent outlet starts in case of a fire next to the tank. The combination of these parameters may be selected such that the delay time is about an hour or more, for example. The general opinion is that the vent outlet must be located remote from a potential ignition source or a workplace on the deck, for example in a tall mast above the deck, but this appears to be unnecessary .

[0007] The vent outlet may even be located within 2 m from the deck and / or within 5 m from the opening or the closable opening and / or within 5 m from a potential ignition source.

[0008] The ship may be a pilot boat, a tug, a crew transfer vessel, a patrol vessel, or the like.

[0009] A low flashpoint liquid fuel means that the liquid fuel is easily ignited by a spark or open flame. More specifically, the flash point is the lowest temperature at which there will be enough flammable vapor to support combustion when an ignition source is applied. For that reason the ship is provided with the closed tank, the inert gas supply, the tank venting and the pressure relief system. The tank is inerted to supress oxygen content in the tank. A small overpressure may be used to supress fuel vapour in the tank and to ensure adequate inert gas pressure .

[0010] The liquid fuel may comprise methanol. This is advantageous in terms of environmental impact. Methanol may me produced from natural gas, i.e. from a fossil fuel, but it may also be produced fossil-free from many renewable feedstocks, for example pulp mill black liquor which is a by-product of the process at mills to turn wood into pulp for making paper.

[0011] In an embodiment the tank contains the low flashpoint liquid fuel .

[0012] The inert gas may comprise nitrogen.

[0013] Preferably, the wall of the tank has a welding seam where adjacent parts of the wall are welded along the entire thickness of the adjacent parts of the wall. This may be called full penetration welding. Preferably, all welding seams of the wall of the tank are formed by full penetration welding. This may be achieved by welding the adjacent parts from opposite sides thereof. The adjacent parts of the wall may be steel, aluminium or the like.

[0014] The tank may form a structural part of the ship. This means that it is not a separate unit which is placed in the ship .

[0015] The potential ignition source comprises at least one of sparking equipment, lighting, a switch, electrical equipment, a hot surface, a winch and any moving part not certified for use in hazardous zones.

[0016] The opening may comprise a ventilation opening.

[0017] The low flashpoint liquid fuel may have a flashpoint below 30°C, preferably below 15°C.

[0018] The ship may have a length larger than 16m and a width larger than 5m.

[0019] The ship may have a length larger than 19m.

[0020] The storage volume of the tank may be larger than 3 or 4 m3.

[0021] The fire retardant wall of the tank may comprise a metal sheet surrounded by a non-flammable insulation layer onto the metal sheet. The applicant has found that when welding seams of the wall of the tank are formed by full penetration welding, thus forming the metal sheet as described above, and applying the insulation layer provides the opportunity to omit a secondary safety barrier around the tank. Preferably, the insulation layer has an A60 fire class rating.

[0022] The invention will hereafter be elucidated with reference to the schematic drawings showing an embodiment of the invention by way of example.

[0023] Fig. 1 is a top view of an embodiment of a ship according to the invention.

[0024] Fig. 2 is a partly cut-away view of the ship as shown in Fig . 1. Fig. 1 shows an embodiment of a ship according to the invention in the form of a tug 1. Fig. 2 illustrates an inner side of the tug 1 in a very schematic way. The tug 1 comprises a walkable deck 2 on which personnel can walk or work and a superstructure 3 above the deck 2. On top of the deck 2 is a towing bitt 4, which means that there is a workplace where personnel may often be present.

[0025] Below the deck 2 is an engine room 5 in which an internal combustion engine 6 for propelling the tug 1 is located. Next to the engine room 5 is a closed methanol tank 7. The tank 7 contains liquid methanol 8 and a mixture of methanol vapour and nitrogen 9 above the liquid methanol 8. Liquid methanol has a relatively low flashpoint, lower than 15°C.

[0026] The tank 7 forms a structural part of the tug 1 and has a storage volume of about 2 m3, but this may be different in an alternative embodiment. The tank 7 comprises a wall which includes welded steel sheets which are surrounded by a nonflammable insulation layer 10 having an A60 fire class rating. All welding seams are full penetration welding seams.

[0027] The tug 1 has a fuel supply system 11 for supplying liquid methanol 8 from the tank 7 to the internal combustion engine 6 and a nitrogen supply system 12 for supplying nitrogen from a nitrogen storage 13 to the tank 7.

[0028] The tug 1 is provided with a tank venting pipe 14 which extends from the tank 7 and ends at a vent outlet 15. Between the tank 7 and the vent outlet 15 is a pressure relief system in the form of a pressure relief valve 16 which allows the mixture of methanol vapour and nitrogen 9 to flow from the tank 7 through the tank venting pipe 14 to the vent outlet 15 when pressure in the tank 7 exceeds a predetermined pressure level.

[0029] Under normal circumstances the pressure relief valve 16 may open shortly due to daily temperature changes. The pressure relief valve 16 may also open under exceptional circumstances. More specifically, when there is a fire nearby the tank 7, for example in the adjacent engine room 5, the content of the tank 7 will be heated. However, due to the insulation layer 10 and the relatively large storage volume of the tank 7 the temperature increase appears to be surprisingly slow such that in practice the pressure relief valve 16 may remain closed for at least 60 minutes. This is sufficient time to extinguish the fire and / or leave the tug 1 in an emergency. This means that a permanent hazardous zone around the vent outlet 15 is not required. Such a hazardous zone is illustrated by a large circle in Fig. 1, showing that personnel would never be allowed to walk on the deck 2 near the towing bitt 4, for example. According to the present invention the vent outlet 15 is located within 3 m from the deck 2. The vent outlet 15 is also located within 10 m from any opening or closable opening in the deck 2 or the superstructure 3 or from a potential ignition source such as lighting, a switch, electrical equipment, a hot surface, a winch, any moving part not certified for use in hazardous zones or the like.

[0030] The invention is not limited to the embodiments shown in the drawings and described hereinbefore, which may be varied in different manners within the scope of the claims and their technical equivalents.

Claims

CLAIMS1. A ship (1) comprising a walkable deck (2) , a superstructure (3) above the deck (2) , an opening or a closable opening in the deck (2) or the superstructure (3) such as a door or ventilation opening, an internal combustion engine (6) , a closed tank (7) for containing a low flashpoint liquid fuel (8) , a fuel supply system (11) for supplying fuel (8) from the tank (7) to the internal combustion engine (6) , an inert gas supply system (12) for supplying inert gas to the tank (7) , a tank venting pipe (14) extending from the tank (7) to a vent outlet (15) of the tank venting pipe (14) , a pressure relief system (16) for allowing gas to flow from the tank (7) through the tank venting pipe (14) to the vent outlet (15) when pressure in the tank (7) exceeds a predetermined pressure level, wherein the tank (7) has a fire retardant wall (10) and a storage volume which is larger than 1.5 m3, characterized in that the vent outlet (15) is located within 3 m from the deck (2) and / or within 10 m from the opening or the closable opening and / or within 10 m from a potential ignition source.

2. A ship (1) according to claim 1, wherein the liquid fuel comprises methanol (8) .

3. A ship (1) according to claim 1 or 2, wherein the tank (7) contains the low flashpoint liquid fuel (8) .

4. A ship (1) according to any one of the preceding claims, wherein the inert gas comprises nitrogen.

5. A ship (1) according to any one of the preceding claims, wherein the wall of the tank (7) has a welding seam where adjacent parts of the wall are welded along the entire thickness of the adjacent parts of the wall (7) .

6. A ship (1) according to any one of the preceding claims, wherein the tank (7) forms a structural part of the ship ( 1 ) .

7. A ship (1) according to any one of the preceding claims, wherein the potential ignition source comprises at least one of sparking equipment, lighting, a switch, electrical equipment, a hot surface, a winch and any moving part not certified for use in hazardous zones.

8. A ship (1) according to any one of the preceding claims, wherein the opening comprises a ventilation opening.

9. A ship (1) according to any one of the preceding claims, wherein the low flashpoint liquid fuel (8) has a flashpoint below 30°C, preferably below 15°C.

10. A ship (1) according to any one of the preceding claims, wherein the ship (1) has a length larger than 16m and a width larger than 5m.

11. A ship (1) according to claim 10, wherein the ship (1) has a length larger than 19m.

12. A ship (1) according to any one of the preceding claims, wherein the storage volume of the tank is larger than 3 or 4 m3.

13. A ship (1) according to any one of the preceding claims, wherein the fire retardant wall of the tank (7) comprises a metal sheet surrounded by a non-flammable insulation layer (10) .

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