Technical field of the invention

The present invention relates to a sea-going vessel in accordance with the preamble of claim 1 .

Background of the invention

Natural gas, or in general mixtures of hydrocarbons that are volatile enough to make the mixture appear in gaseous form in room temperature, constitutes an advantageous alternative to fuel oil as the fuel of internal combustion engines. In sea-going vessels that use natural gas as fuel, the natural gas is typically stored onboard in liquid form, giving rise to the commonly used acronym LNG (Liquefied Natural Gas). Natural gas can be kept in liquid form by maintaining its temperature below a boiling point, which is approximately -1 62 degrees centigrade. Natural gas can be also stored for use as fuel by keeping it com- pressed to a sufficiently high pressure, in which case the acronym CNG (Compressed Natural Gas) is used.

Since natural gas has a low boiling point and it is highly flammable, strict regulations govern its use in sea-going vessels. To allow good ventilation in case of leaking natural gas, the equipment for handling the gas usually needs to be placed on an open deck of the vessel. A conventional solution has been to provide a so called evaporation skid, which comprises different gas handling equipment and which has been arranged on an open deck of the ship. This solution is often problematic, since the equipment may take space that could otherwise be used for cargo or for other purposes. In addition, long pipes are needed for supplying gas to the engines of the vessel.

Summary of the invention

The object of the present invention is to provide an improved sea-going vessel, which is provided with at least one engine that can be operated using fuel that is introduced into the engine in gaseous state or as a supercritical fluid, the vessel comprising gas handling equipment for handling the fuel. The characterizing features of the vessel according to the present invention are given in the characterizing part of claim 1 .

According to the invention, the vessel comprises a gas-tight gas handling room for accommodating at least part of the gas handling equipment, the gas handling room being enclosed entirely by the hull of the vessel and separated from the engine room(s) of the vessel by a double bulkhead.

Because of the gas-tight gas handling room and the double bulkhead between the gas handling room and the engine room, gaseous fuel can be effectively prevented from entering other parts of the vessel. Consequently, the equipment can be placed more freely in the vessel. By arranging the gas handling room within the hull, i.e. below the main deck, open deck space can be saved for cargo, such as containers, or for other purposes. The arrangement also protects the gas handling equipment from impacts from cargo handling opera- tions. In addition, the length of the piping that is needed for transferring the gas can be reduced.

According to an embodiment of the invention, the gas handling room is accessible from an upper deck via a vertical shaft. Preferably, the gas handling room is accessible only via the shaft. This guarantees that the gas handling room remains gas-tight in other directions. An air lock can be arranged between the gas handling room and the shaft to provide safe access into the gas handling room.

According to an embodiment of the invention, the gas handling room is located adjacent to an engine room. The length of the piping between the gas handling equipment and the engines can thus be minimized.

According to an embodiment of the invention, the gas handling equipment comprises a pump for pressurizing the fuel and the pump is arranged in the gas handling room.

According to an embodiment of the invention, the gas handling room is divided at least into a first gas-tight compartment and a second gas-tight compartment. By dividing the gas handling room into two or more compartments, different parts of the gas handling equipment can be separated from each other to better control possible fuel leakages. For instance, the pump for pressurizing the fuel can be arranged in the first compartment and the drive of the pump in the second compartment. Preferably, the second compartment of the gas handling room does not contain any gas handling equipment where the fuel is stored or circulated. A pump for pressurizing fuel is a possible leaking component, and by arranging the pump and similar components in the first compartment, the risk level of the second compartment can be lowered.

According to an embodiment of the invention, the first gas-tight compartment is accessible only via the second gas-tight compartment. The compartment containing the more hazardous components is thus better separated from the rest of the vessel.

The fuel used in the engines can be liquefied natural gas.

Preferably, the gas handling room is located such that no space accessible by the vessel crew is located directly beneath it.

The gas handling room can be arranged in the vessel such that at least one deck is located between the gas handling room and the main deck of the vessel. Alternatively, the gas handling room can be delimited by the main deck.

Brief description of the drawings

Embodiments of the invention are described below in more detail with refer- ence to the accompanying drawings, in which

Fig. 1 shows schematically a top view of a deck of a sea-going vessel,

Fig. 2 shows a cross-sectional view of the vessel of Fig. 1 taken along line A- A,

Fig. 3 shows an enlarged view of part of the deck shown in Fig. 1 , and Fig. 4 shows a gas handling room of a vessel according to one embodiment of the invention. Description of embodiments of the invention

In figure 1 is shown a deck of a sea-going vessel according to an embodiment of the invention. The vessel of the figures is a cargo ship that is configured to carry containers. However, the invention is not limited to container ships or even cargo ships, but the invention can be applied to many kinds of sea-going vessels, such as cruisers, off-shore ships or RoRo ships.

The ship is provided with a main engine 4, which produces propulsion for the ship, and with several auxiliary engines 5a, 5b, 5c for producing electricity and/or for driving different equipment of the ship. All the engines 4, 5a, 5b, 5c are piston engines. The main engine 4 is connected to the propeller 16 of the ship via a propeller shaft 17. However, the main engine 4 could also be used for producing electricity for an electric motor driving the propeller 16. The ship could also be provided with more than one main engines 4. In the embodiment of the figures, the main engine 4 is a two-stroke dual-fuel engine that can be operated using either gaseous or liquid fuel. The operation with gaseous fuel can be combined with liquid pilot fuel injection. Also the auxiliary engines 5a, 5b, 5c can be dual-fuel engines, which operate mainly by gas that is ignited by a pilot fuel injection. At least one of the auxiliary engines 5a, 5b, 5c could also be a gas-engine, which is always operated on gaseous fuel that is spark ignit- ed. It is also possible that the main engine 4 is configured only for operation on liquid fuel. In any case, at least one of the engines 4, 5a, 5b, 5c of the ship is operable on gaseous fuel. The fuel does not necessarily need to be gaseous when it is injected into the engine, but the fuel can also be injected into the engine as a supercritical fluid, which is at a pressure and temperature above its critical point. Such fluid is quickly changed into gas in the cylinders of the engine.

The main engine 4 and the auxiliary engines 5a, 5b, 5c are arranged in an engine room 3. The main engine 4 and the auxiliary engines 5a, 5b, 5c could also be arranged in different engine rooms. The ship is provided with a main deck 103 and with several decks 100, 101 , 102 that are arranged below the main deck 103 and with several decks 104, 105, 106, 107 that are arranged above the main deck 103. The term 'main deck' refers here to the uppermost complete deck extending from bow to stern. The decks 104 to 107 above the main deck 103 form the superstructure of the ship. The engine room 3 is arranged inside the hull of the ship below the main deck 103. Due to the height of the main engine 4, the engine room 3 extends from a lower deck 100 to an upper deck 101 . The engine room may extend over even more decks. For gas-fuelled operation of the main engine 4 and/ or the auxiliary engines 5a, 5b, 5c, the ship is provided with one or more tanks (not shown) for storing liquefied natural gas (LNG). The engines 4, 5a, 5b, 5c could also use compressed natural gas or some other fuel that can be injected into the engine in gaseous state or as a supercritical fluid. According to an embodiment of the invention, the fuel is injected into the cylinders of the main engine 4 at high pressure, for instance at pressure in the range of 200 to 400 bar. For handling the fuel, the ship is provided with gas handling equipment. The gas handling equipment refers here to equipment that is used for handling the fuel, irrespective of whether the fuel is in liquid, gaseous or supercritical form. In the embodiment of figure 3, the gas handling equipment comprises a pump 6a for pressurizing the fuel, a feed pump 8a, an LNG vaporizer 7, and optionally a boil-off gas (BOG) compressor 9. The BOG compressor 9 forms part of a BOG reliquefaction system that condenses excess gas boiling in the tanks, which can then be returned to the tanks in liquid state or used in the main engine 4 as fuel. The gas handling equipment can also comprise further devices 10. In the embodiment of figure 3, the pump 6a is a high pressure pump. The feed pump 8a supplies the fuel in liquid state to the high-pressure pump 6a, which raises the pressure of the fuel to the required level. The fuel is then vaporized in the LNG vaporizer 7 and heated to suitable injection temperature. The fuel can be taken directly from the LNG tank, or it can be condensate from the BOG reliquefaction system. The fuel could also be injected into the engines at a lower pressure, in which case pump 6a would not be a high-pressure pump, but one or more low-pressure pumps would be used for introducing the fuel into the engines. The gas handling equipment is arranged in a gas handling room 1 . The gas handling room 1 is a gas-tight space that is arranged completely within the hull of the ship. In the embodiment of the figures, the gas handling room 1 is arranged on the same deck 101 with the engine room 3. The gas handling room 1 is thus below the main deck 103 of the ship. In the embodiment of the fig- ures, there is one deck 102 between the gas handling room 1 and the main deck 103, but the gas handling room 1 could also be delimited by the main deck 103, or there could be several decks between the gas handling room 1 and the main deck 103. Not all the gas handling equipment needs to be located in the gas handling room 1 . For example, the ship can be provided with tank connection rooms that are arranged in connection with the LNG tanks and part of the gas handling equipment, such as low-pressure pumps, can be arranged in the tank connection rooms.

The gas handling room 1 forms a gas-tight room within the hull of the ship. In the embodiment of figures 1 and 3, the gas handling room 1 is divided into a first compartment 1 a and a second compartment 1 b. However, the gas handling room 1 can also be an undivided space, as shown in figure 4. The first compartment 1 a and the second compartment 1 b are gas-tightly separated from each other. The first compartment 1 a is accessible from the second compartment 1 b via a gas-tight door 14. In the embodiment of figure 3, the feed pump 8a, the high-pressure pump 6a, the BOG compressor 9 and other devices 10 that are in contact with the fuel are arranged in the first compartment 1 a of the gas handling room 1 . The gas handling equipment further comprises a drive 6b for operating the high- pressure pump 6a and a drive 8b for operating the feed pump 8a. All the drives 6b, 8b of the gas handling equipment are located in the second compartment 1 b of the gas handling room 1 . All the gas handling equipment that is in contact with the fuel either in gaseous or in liquid state is located in the first compartment 1 a of the gas handling room 1 . The second compartment 1 b is thus free from any devices that are in contact with the fuel. Conversely, the first compartment 1 a is free from the drives 6a, 8a of the gas handling equipment. The risk of leaking fuel entering the second compartment 1 b as well as the risk of ignition of the fuel in the first compartment 1 a is minimized by the arrangement.

In the embodiment of figure 3, the drives 6b, 8b of the pumps 6a, 8a are hy- draulic drives. Each hydraulic drive comprises an electric motor for driving a hydraulic pump. The pressurized hydraulic fluid is used for driving the high- pressure pump 6a and the feed pump 8a. When the electric motor of the hydraulic drive 6b, 8b is located in a space that is gas-tightly separated from the space where the fuel pumps 6a, 8a are arranged, less expensive electric mo- tors can be used. When placing electric motors in an environment with an ex- plosive atmosphere, ATEX certified motors need to be used. The rooms of a ship are divided into different categories on the basis of the risk that an explosive gas atmosphere is present in the room. Different classification societies have slightly different ways to categorize different areas of the ship, but the higher the explosion risk is, the stricter requirements are set for the electrical equipment. By dividing the gas handling room 1 into gas-tight compartments and placing the electrical components into a space with a lower explosion risk, less expensive equipment can be used. Instead of using hydraulic drives for driving the pumps 6a, 8a, electric motors could be used for directly driving the pumps 6a, 8a. Also in this case, it would be preferable to locate the motors in a compartment that is gas-tightly separated from the compartment in which the pumps 6a, 8a are arranged.

The gas handling room 1 of figure 3 comprises further gas-tight compartments 1 c, 1 d. A third gas-tight compartment 1 c is arranged within the first compart- ment 1 a of the gas handling room 1 , and the feed pump 8a, the high-pressure pump 6a and the LNG vaporizer 7 are arranged in the third compartment 1 c. Also a fourth gas-tight compartment 1 d is arranged in the first compartment 1 a and the BOG compressor 9 is arranged in the fourth compartment 1 d. The walls of the third and the fourth gas tight compartments 1 c, 1 d are made of stainless steel to withstand and contain cold LNG in case of leakage. Also some other material with similar properties could be used. These additional compartments 1 c, 1 d further increase the safety of the gas handling room 1 . It is not necessary to have the third and the fourth compartment 1 c, 1 d in the gas handling room 1 . However, by providing the gas handling room 1 with the third and fourth compartments 1 c, 1 c, it is easier to protect the hull of the ship from cold LNG, since the whole first compartment 1 a does not need to withstand extremely low temperatures.

Figure 4 shows a gas handling room 1 of a vessel that is provided with engines that can be operated using low-pressure gas. The gas handling room 1 is formed of a single compartment. A fuel supply pump 6a for pressurizing the fuel is arranged in the gas handling room 1 . The pump 6a is configured to raise the pressure of the gaseous fuel to the range of 5 to 15 bar. The gas handling room 1 is also provided with an LNG vaporizer 7 and a drive 6b for the pump 6a. In the embodiment of figure 4, the drive 6b comprises an ATEX certified electric motor, and can thus be arranged in the same space with the pump 6a. Also in a ship having only low-pressure pumps, the gas handling room 1 can be divided into different compartments.

The gas handling room 1 is located adjacent to the engine room 3, i.e. it has at least one wall in common with the engine room 3. The wall 15 between the gas handling room 1 and the engine room 3 is a double bulkhead, i.e. a double- walled structure. If the vessel is provided with several engine rooms, between the gas handling room 1 and each of the engine rooms needs to be a double bulkhead. The double bulkhead effectively protects the engine room 3 from leaking LNG. The double bulkhead also protects the gas handling room 1 from a fire occurring in the engine room 3. By arranging the gas handling room 1 next to the engine room 3, the length of piping can be minimized.

The second compartment 1 b of the gas handling room 1 is in connection with a vertical shaft 12 that opens to open air. In the embodiment of figure 4, the single compartment of the gas handling room is in connection with a shaft 12. The shaft 12 can connect the gas handling room 1 for instance with the main deck 103 of the ship or other deck that opens to air outside the vessel's hull. The gas handling room 1 is connected to the shaft 12 via an air lock 1 1 . The shaft 12 is provided with a stairway 13, which provides access into the gas handling room 1 from an upper deck of the ship. The gas handling room 1 is accessible only via the shaft 12, which ensures that the gas handling room 12 remains gas-tight from other directions.

The shaft 12, leading from a deck opening to air outside the vessel's hull, to the gas handling room 1 , creates a vertical structure through the decks that is gas-tight towards the other internal structure of the hull. The shaft 12 may pen- etrate through several decks of the vessel. The gas handling room 1 is at the bottom of the shaft 12. The stairway 13 leads from the gas handling room 1 upwards, possibly through several decks, up to the deck that opens to open air outside the vessel hull. Gas-tight doors may be arranged in the stairway 13 between some the decks, or between all the decks, depending on the need con- sidered.

The gas handling room 1 is arranged in the ship in such a location that there are no rooms directly beneath the gas handling room 1 that would be accessible by the ship crew. This is preferable to protect the gas handling room 1 from fire. In practice, different tanks, such as oily bilge water tanks or sludge tanks can be arranged below the gas handling room 1 .

It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, but may vary within the scope of the appended claims.