Fuel gas supply system and method of an lng carrier

1. Technical Field

The present invention relates to a fuel gas supply system and method of a vessel, such as an LNG carrier, and more particularly, to a fuel gas supply system and method of an LNG carrier for efficiently supplying fuel gas from an LNG storage tank to a high-pressure gas injection engine in the LNG carrier.

2. Description of the Related Art

Generally, natural gas is turned into a liquefied natural gas (hereinafter called “LNG”) at a cryogenic temperature in a liquefaction plant, and then transported over long distances to a destination by an LNG carrier.

As liquefaction of natural gas occurs at a cryogenic temperature of −163 degrees Celsius at ambient pressure, LNG is likely to be vaporized even when the temperature of the LNG is slightly higher than −163 degrees Celsius at ambient pressure. In an LNG carrier having an LNG storage tank which is thermally-insulated, as heat is continually transmitted from the outside to the LNG in the LNG storage tank, the LNG is continually vaporized and boil-off gas is generated in the LNG storage tank during the transportation of LNG by the LNG carrier.

In an LNG carrier, if boil-off gas is accumulated in an LNG storage tank, the pressure in the LNG storage tank excessively increases. Consequently, to treat the boil-off gas generated in the LNG storage tank, the boil-off gas is used as a fuel for a ship propulsion engine or burned in a gas combustor.

In case where a high-pressure gas injection engine, for example, MEGI engine manufactured by MAN B&W Diesel Inc., is used as a ship propulsion engine of an LNG carrier, a multi-stage compressor is used in a conventional fuel gas supply system to compress boil-off gas at a high pressure. This multi-stage compression has problems that the fuel gas supply system becomes very complex, and that an excessive amount of power is required to compress the boil-off gas in a gaseous state at a high pressure.

According to one embodiment, a fuel gas supply system and method of an LNG carrier are provided, which can simplify the configuration, reduce power requirements, and prevent an excessive pressure increase due to accumulation of boil-off gas in an LNG storage tank, in supplying fuel gas to a high-pressure gas injection engine of an LNG carrier.

A fuel gas supply system of a vessel according to one embodiment is characterized in that the fuel gas supply system of a ship comprises an LNG tank; a boil-off gas reliquefaction apparatus to reliquefy boil-off gas generated in the LNG tank; a high-pressure gas injection engine; a high-pressure pump for compressing LNG at a high pressure and supplying the compressed LNG to the high-pressure gas injection engine; and an apparatus to gasify the LNG installed downstream of the high-pressure pump, to gasify the compressed LNG.

A fuel gas supply method of a vessel according to one embodiment, as a method for supplying fuel gas to a high-pressure gas injection engine of the ship in which an LNG tank is provided, is characterized in that the fuel gas supply method of a ship comprises compressing LNG to meet the pressure requirements for the high-pressure gas injection engine; and reliquefying boil-off gas generated in the LNG tank.