Liquefied gas treatment system for vessel

Abstract

A liquefied gas treatment system includes: a first stream of boil-off gas, which is generated from the liquefied natural gas in the cargo tank and is discharged from the cargo tank; a second stream of the boil-off gas, which is supplied as fuel to the engine in the first stream; and a third stream of the boil-off gas, which is not supplied to the engine in the first stream. The first stream is compressed in a compressor and is then branched into the second stream and the third stream. The third stream is liquefied by exchanging heat with the first stream in a heat exchanger, so that the boil-off gas is treated without employing a reliquefaction apparatus using a separate refrigerant.

Description

TECHNICAL FIELD[0001]The present invention relates to a liquefied gas treatment system for a vessel.BACKGROUND ART[0002]Recently, the consumption of liquefied 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 gas state through onshore or offshore gas pipelines, or is 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 natural gas or petroleum gas to a cryogenic temperature (in the case of LNG, about −163° C.). Since the volume of liquefied gas is considerably reduced as compared to a gas state, liquefied gas is very suitable for a long-distance marine transportation.[0003]A liquefied gas carrier such as an LNG carrier is designed to load liquefied gas, sail across the sea, and unload the liquefied gas at an onshore consumption place. To this end, the liquefi...

AI Technical Summary

Benefits of technology

The present invention provides a liquefied gas treatment system for a vessel that can reuse the energy of BOG (which is generated during the transportation of LNG cargo) as the fuel of a high pressure gas injection engine, without the need for a separate reliquefaction apparatus. The system compresses a part of the BOG discharged from the cargo tank and returns it to the tank by liquefying it with cold energy. This avoids wasted energy and reduces the amount of BOG consumed in the process. The system can also generate energy during expansion, further reducing energy waste. Overall, the system saves energy and reduces installation and operation costs.

Problems solved by technology

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

Therefore, when an amount of fuel necessary for an engine is smaller than a generation amount of BOG, there is a problem that BOG is burnt in a gas combustion unit (GCU) or is vented to atmosphere.

Even though a conventional LNG carrier equipped with a reliquefaction facility and a low-speed diesel engine can treat BOG through the reliquefaction facility, the control of the entire system is complicated due to the operation complexity of the reliquefaction facility using nitrogen gas, and a considerable amount of power is consumed.

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