Fuel supply system for marine structure having reliquefaction apparatus and high-pressure natural gas injection engine

Abstract

Provided is a fuel supply system for a marine structure. The fuel supply system includes a BOG compression unit configured to receive and compress BOG generated in a storage tank, a reliquefaction apparatus configured to receive and liquefy the BOG compressed by the BOG compression unit, a high-pressure pump configured to compress the liquefied BOG generated by the reliquefaction apparatus, and a high-pressure gasifier configured to gasify the liquefied BOG compressed by the high-pressure pump. The fuel supply system includes a recondenser installed at an upstream side of the high-pressure pump and configured to recondense a portion or all of the generated BOG by using liquefied gas received from the storage tank. The BOG compression unit compresses BOG to a pressure of about 12 to 45 bara such that the BOG is liquefied under the compression pressure of the BOG compression unit.

Description

TECHNICAL FIELD[0001]The present invention relates to a fuel supply system for a high-pressure natural gas injection engine, and more particularly, to a fuel supply system for a marine structure such as a liquefied natural gas (LNG) carrier having a boil-off gas (BOG) reliquefaction apparatus and a high-pressure natural gas injection engine (e.g., a MAN Electronic-Gas Injection (ME-GI) engine), which can efficiently supply fuel to the high-pressure natural gas injection engine and minimize energy consumption in the BOG reliquefaction apparatus.BACKGROUND ART[0002]Recently, the consumption of natural gas, such as liquefied natural gas (LNG) or liquefied petroleum gas (LPG), has been rapidly increasing throughout the world. Liquefied gas is transported in a gaseous state through onshore or offshore gas pipelines, or transported to a remote consumption place while being stored in a liquefied state inside a liquefied gas carrier. Liquefied gas, such as LNG or LPG, is obtained by cooling...

AI Technical Summary

Benefits of technology

The present invention provides a fuel supply system for a high-pressure natural gas injection engine. The system uses the excess gas (BOG) generated in a liquefied gas storage tank as fuel for the engine. The BOG is compressed to a medium pressure and then liquefied using a reliquefaction apparatus. The liquefied BOG is then sent to the engine. This system has several technical benefits: efficient fuel supply, minimized energy consumption, reduced load on the reliquefaction apparatus, reduced thermal stress, reduced size of the apparatus, and reduced power requirements. The system also uses a nonflammable mixed refrigerant for safer and more efficient reliquefaction of the BOG.

Problems solved by technology

The generated natural gas may increase the internal pressure of the storage tank and accelerate the flow of the natural gas due to the rocking of the vessel, causing structural problems.

However, the LNG stored in the storage tank is maintained at an ambient pressure state, and therefore, if a pressure of the liquefied BOG is excessively high, flash gas may be generated when the BOG is returned to the storage tank.

Consequently, the BOG needs to be compressed to the above-mentioned low pressure of about 4 to 8 bara, in spite of low reliquefaction efficiency.

Also, it is well known in the art that it is technically inappropriate to compress BOG to a pressure higher than the above-mentioned pressure.

Meanwhile, since the nitrogen refrigeration cycle uses nitrogen gas (N2) as a refrigerant, the liquefaction efficiency is low.

Also, the mixed refrigerant cycle uses a refrigerant mixed with nitrogen and hydrocarbon gases as a refrigerant, the stability is low.

The nitrogen reverse Brayton cycle used for the offshore LNG liquefaction apparatus is relatively simple in the configuration of the apparatus and thus is advantageous to a limited vessel or offshore plant, but has low efficiency.

The mixed-refrigerant Joule-Thomson refrigeration cycle used for the onshore LNG liquefaction plant has relatively high efficiency but is complicated in the configuration of the apparatus because a separator needs to be used for separating a mixed refrigerant when a gaseous state and a liquid state coexist due to the feature of the mixed refrigerant.

Images