TECHNICAL FIELD

The invention concerns in general the structural solutions of sea-going vessels that use gaseous fuel in at least one of their own engines. Especially the invention concerns the structural solutions with which the proper division into hazard zones of different classification is ensured.

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 -162 degrees centigrade (-260 degrees Fahrenheit). Natural gas can be also stored for use as fuel by keeping it compressed to a sufficiently high pressure, in which case the acronym CNG (Compressed Natural Gas) is used. This description refers mainly to LNG because liquefying is considered more economical than com- pressing at the time of writing this text.

Classification societies maintain and publish regulations and guidelines that place certain requirements to the structure and operation of gas-fuelled vessels. As a prominent example the classification regulations of Germanischer Lloyd Aktiengesellschaft comprises a volume VI, Part 3 (Machinery Installa- tions), Chapter 1 : Guidelines for the Use of Gas as Fuel for Ships, published in 2010. Among others, it defines three classes of hazardous areas in the following way:

- zone 0: an area in which an explosive gas atmosphere or a flammable gas with a flash point below 60 °C is present continuously or is present for long periods

- zone 1 : an area in which an explosive gas atmosphere or a flammable gas with a flash point below 60 °C is likely to occur in normal operation - zone 2: an area in which an explosive gas atmosphere or a flammable gas with a flash point below 60 °C is not likely to occur in normal operation and, if it does occur, is likely to do so only infrequently and will exist for a short period only. Anything beyond zone 2 is considered a safe zone from the viewpoint of gas- originated hazards (fire, explosion, poisoning, suffocation). The regulations mentioned above are referred to in the following as the Lloyd regulations.

Fig. 1 is a simplified illustration of the storage and use of gas as fuel onboard a sea-going vessel. LNG is stored in a double-walled tank 101 , which is located in a tank hold 102. An evaporator 103 is used to vaporize the gas, after which it is delivered to the engine 104 through a gas pipeline 105. The evaporator 103 and other process equipment are located inside an enclosure known as the tank room 106, which in this case directly adjoins the tank 101 so that the outer wall of the tank 101 and the walls of the tank room 106 constitute a sin- gle, integral, gastight entity. From the tank room 106 to the engine 104 the gas pipeline 105 goes inside an outer shell 107, the inside of which is constantly ventilated to open air (not shown). One or more bulkheads 108 separate the tank hold 102 from the engine room 109, in which the engine 104 is located. The tank 101 and the tank room 106 with all the equipment inside it can be de- livered to a shipyard as an integral, separately assembled package such as the solutions marketed under the trade mark LNGpac by Wartsila Corporation, Helsinki, Finland.

Figs. 2a and 2b show schematically how some of the spaces illustrated in fig. 1 belong to the zones defined by the Lloyd regulations. The inside of the tank 101 belongs undoubtedly to zone 0. The inside of the tank room 106 belongs to zone 1 . However, whether or not the tank hold 102 belongs to zone 2 depends on whether the access hatch or door 201 to the tank room 106 is open. In fig. 2a it is closed, so the tank hold 102 counts as a safe zone. However, if the access hatch or door 201 to the tank room 106 is open, as in fig. 2b, the tank hold 102 belongs to zone 2.

The tank room needs to be accessed every now and then, so the shipbuilder must prepare for the situation of 2b, and build the tank hold 102 so that it conforms with zone 2 regulations. This means, among others, choosing only ATEX-certified electrical devices for installation and use in the tank hold 102. ATEX means the directive 94/9/EC for apparatus intended for use in explosive environments, and is an example of an applicable safety regulation. Other corresponding regulations exist outside Europe. Another consequence of the tank hold belonging to zone 2 is the mandatory use of an airlock 202 at its entrance. Classification requirements could also require that all electric equipment in the tank hold must be de-energized in the case of a ventilation failure, but that will lead to a contradiction with other regulations; for example (electric) emergency lighting must be available for operation at any times.

The tank hold may be large, and it may comprise a large number of electric in- stallations. Electric apparatus certified for explosive environments are expensive, which may mean a significant additional cost to the shipbuilder. If a previously oil-fuelled ship is converted to use gaseous fuel, and some existing space onboard is rebuilt as a tank hold, the requirement for conformity with ATEX and Lloyd regulations may necessitate scrapping large numbers of oth- erwise completely usable previous installations.

SUMMARY OF THE INVENTION

The following presents a simplified summary in order to provide a basic understanding of some aspects of various invention embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention.

According to an aspect of the invention there is provided a fuel storage and de- livery system for a gas-fuelled sea-going vessel, which fuel storage and delivery system enables using cost-effective solutions in the construction of the vessel. According to another aspect of the invention there is provided a fuel storage and delivery system of the described kind that can be easily used in retrofitting projects. According to an additional aspect of the invention there is provided a fuel storage and delivery system that can be separately assembled and delivered to a shipyard to that its inclusion to a ship under construction is fast and easy.

Advantageous objectives of the invention are achieved by placing an airlock at the access hatch or door of the tank room. A fuel storage and delivery system for a gas-fuelled sea-going vessel according to the invention is characterized by the features recited in the characterising part of the independent claim directed to a fuel storage and delivery system. An airlock at the entrance to the tank room, together with the proper ventilation of the tank room, ensures that not even the characteristics of zone 2 need to be fulfilled by the tank hold. This means that the tank hold can be equipped with electric devices that do not need to be certified for explosive environments. It also makes it simpler for members of the crew to access other places in the tank hold than the tank room, because they do not need to go through an airlock every time. An integrated fuel storage and delivery system with an airlock at the entrance to the tank room is very advantageous in retrofit projects where a space that was previously used for something else is converted into a tank hold as a part of making a previously oil-fuelled vessel utilize gase- ous fuel, because it places very few additional requirements to such a space.

The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 illustrates a prior art fuel storage and delivery system,

fig. 2a illustrates a division into zones of a prior art fuel storage and delivery system,

fig. 2b illustrates a different division into zones of the system of fig. 2a, fig. 3 illustrates a division into zones of a fuel storage and delivery system according to an embodiment of the invention, fig. 4 illustrates a division into zones of a fuel storage and delivery system according to another embodiment of the invention,

fig. 5 illustrates a division into zones of a fuel storage and delivery system according to another embodiment of the invention, and

fig. 6 illustrates a division into zones of a fuel storage and delivery system according to another embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

According to the Lloyd regulations a tank room means a gas-tight space surrounding the parts of the bunker tank containing all tank connections and all tank valves. For the purposes of the present invention we may present a slightly different definition, according to which the tank room is the gastight enclosure in which there is located the evaporator that is used to vaporize liquid gas for delivery to at least one gas-fuelled engine of a sea-going vessel. If compressed gas is used instead of liquefied gas, the role of an evaporator is taken by a pressure reducing valve. As a consequence of the definition the inside of a tank room belongs to zone 1 in the classification of gas-hazardous zones.

Fig. 3 is a schematic illustration from above of parts of a fuel storage and delivery system for a gas-fuelled sea-going vessel. It comprises a tank room 106, so - although not separately shown - in accordance with the definition above there is an evaporator for vaporizing liquid gas or pressure reducing valve for reducing the pressure of compressed gas located in the tank room 106. The gas to be evaporated or the pressure of which is to be reduced comes from a gas tank 101 . An airlock 301 constitutes the sole access to the tank room 106. As a consequence the tank hold 102, which is the at least mostly closed space in which the tank 101 and the tank room 106 are located, does not become a zone 2 gas-hazardous area at any times, so it can be constructed and equipped following normal standards instead of those that concern explosive areas.

The process of building a ship at a shipyard, or a process of converting a pre- viously oil-fuelled vessel into at least partial operation with gaseous fuel, can be made faster and more straightforward by assembling parts of the fuel storage and delivery system separately and bringing them as a more or less completed structural module into place in the ship to be built or converted. For this purpose the gas tank (or gas tanks, of there are two or more) can be integrat- ed into a common mechanical entity with the tank room. In the embodiment shown in fig. 3 this has been accomplished by welding the edges of walls of the tank room 106 to an outer wall of the tank 101 . In other words, an outer wall of the tank (or tanks) and walls of the tank room together delimit a single, integral, gastight entity. A common support base 302, ends of which are seen to protrude from under the tank 101 and the airlock 301 , is arranged to support the weight of the tank (or tanks) and the tank room and to form the mechanical installation interface of the tank (or tanks) and the tank room to the tank hold 102. Fig. 4 is a schematic illustration from above of an embodiment in which the tank 101 and the tank room 106 do not constitute a single mechanical entity. The tank room 106 and the tank 101 (or tanks, if there are two or more) are delimited as separate entities by walls of the tank room and an outer wall of the tank or tanks. Double-walled piping 401 connects the tank 106 (or tanks) to the tank room 106. The requirement of a second barrier could be fulfilled also by enclosing two or more single-walled pipes inside a common gastight outer cover. The fixed, gastight lead-ins of the double-walled piping 401 to the tank room 106 do not count as accesses, so the sole access to the tank room 106 is again through the airlock 301 . Even if the walls of the tank room 106 and the tank 101 are separate from each other, the tank 101 can be integrated into a common mechanical entity as a whole with the tank room for example by using a common support base 302 that is arranged to support the weight of the tank (or tanks) and the tank room.

Fig. 5 is a schematic illustration from above of an embodiment in which the gas tank 101 (or gas tanks, if there are two or more) is completely enclosed inside the tank room 106. Again the airlock 301 at the access to the tank room 106 ensures that there is no need to classify the surrounding tank hold 102 as a gas-hazardous area. Also in this case the common support base 302, if one is used, can be arranged to support the weight of both the tank (or tanks) and the tank room 106, although it naturally supports the weight of the tank 106 only indirectly through the structures of the tank room 106.

The invention does not require that the airlock at the access to the tank room provides a passage between the tank room and the surrounding tank hold; the access to the tank room can be from some other space. Fig. 6 is a schematic illustration from above of an embodiment in which there is an access to the tank hold 102 through a door 601 , but the passage from the tank room 106 through the airlock 301 leads to some other, at least partly closed space onboard the vessel. This other space is assumedly not the open deck, because if the access to and from the tank room would be directly from open deck, there would be no need for any airlock according to the Lloyd regulations at least in the form they have at the time of writing this description.

According to one embodiment of the invention, not only the tank valves and evaporators but even the engine-specific fuel input subsystem(s) are located inside the tank room. An engine-specific fuel input subsystem of a gas-fuelled diesel engine is sometimes referred to as the GVU, or Gas Valve Unit. It comprises typically at least a manual cutoff valve, a pressure regulation valve, a gas filter, and the block and bleed valves needed to enable safely and reliably isolating and emptying the gas pipelines upstream of the engine for example in the case of maintenance or overhaul of the engine. In conventional configura- tions it has been customary to place the GVU close to the engine in the engine room, which - together with the classification requirements about double barriers around gas piping - has necessitated building a particular, gastight enclosure around each GVU. If, however, the GVU(s) is/are located inside the tank room, which by definition constitutes a gastight enclosure, no separate GVU enclosure(s) is/are needed. This may necessitate making the tank room slightly larger than in prior art solutions, but that in turn may have the advantageous side effect of making it easier to equip the tank room with an airlock-equipped access.

Variations and modifications to the embodiments illustrated above are possible without departing from the scope of protection of the appended claims. For example even if the illustrated embodiments all have only one gas tank for the sake of graphical simplicity, the invention does not in any way limit the number of gas tanks that are included in the system. If there are two or more gas tanks, there can be two or more tank rooms respectively; in that case each tank room should be equipped with an airlock of its own, or there should be an access to a first tank room through an airlock, and access to the other tank rooms only through said first tank room. Although advantageous, the use of a common support base or other means for integrating the tank(s) and the tank room together are no necessary parts of the invention. All parts of the descrip- tion that are related to liquefied gas can be generalized to also cover com- pressed gas, with the natural consequence that evaporators are replaced with pressure reducing valves.

Even if some classification regulations would not allow the airlock at the access to the tank room to lift all binding (and potentially highly cost-incurring) regulations concerning electric equipment in the tank room, the provision of an airlock as explained above will in any case add a buffering step in the chain of decreasingly gas-hazardous spaces including the tank room, the tank hold, and the cargo room. The smaller the space in which strict regulations apply concerning explosion-proof equipment, the less additional costs will be in- curred.