Vessel

Patent metadata

Field	Value
Publication number	US-10858077-B2
Application number	US-201615776032-A
Country	US
Kind code	B2
Filing date	Oct 24, 2016
Priority date	Nov 12, 2015
Publication date	Dec 8, 2020
Grant date	Dec 8, 2020

Abstract

A vessel includes a heat exchanger for heat-exchanging compressed boil-off gas (hereinafter, referred to as “first fluid”) by using, as a refrigerant, the boil-off gas discharged from a storage tank, to cool the same; a main compression part for compressing a part of the boil-off gas discharged from the storage tank; a rest compression part provided in parallel to the main compression part so as to compress the other part of the boil-off gas discharged from the storage tank; and a decompression device for expanding the first fluid having been cooled by exchanging heat with the boil-off gas, which is discharged from the storage tank, in the heat exchanger. The first fluid is a flow in which the boil-off gas compressed by the main compression part and the boil-off gas compressed by the rest compression part join; or the boil-off gas compressed by the main compression part.

First claim

The invention claimed is:

1. A method of operating a vessel, the method comprising:
providing the vessel comprising: an engine,
an LNG tank containing LNG and boil-off gas (BOG) of the LNG,
a BOG processing system comprising a first gas-to-gas pathway, a gas-to-liquid pathway and a second gas-to-gas pathway,
the first gas-to-gas pathway configured to generate a pressurized gas composition for sending to the engine, wherein the first gas-to-gas pathway comprises a heat exchanger and a bypass line bypassing the heat exchanger,
the gas-to-liquid pathway configured to liquefy a portion of the pressurized gas composition for returning to the LNG tank,
the second gas-to-gas pathway connecting between the gas-to-liquid pathway and the first gas-to-gas pathway;
 running the first gas-to-gas pathway which comprises:
discharging BOG from the LNG tank,
pressurizing, at a first multi-stage compressor, a gas composition comprising BOG discharged from the LNG tank to generate the pressurized gas composition, and
supplying part of the pressurized gas composition to the engine;
 running the gas-to-liquid pathway which comprises:
branching off a stream of the pressurized gas composition between the first multi-stage compressor and the engine,
heat-exchanging, at the heat exchanger, the stream of the pressurized gas composition with the gas composition of the first gas-to-gas pathway to generate a cooled composition,
depressurizing the cooled composition at a depressurizer to generate a depressurized composition that comprises a liquid-gas mixture,
generating a liquid phase and a gas phase from the liquid-gas mixture at a liquid-gas separator, and
returning the liquid phase to the LNG tank; and
 running the second gas-to-gas pathway which comprises:
sending the gas phase from the liquid-gas separator to the first gas-to-gas pathway for adding to the discharged BOG thus making the gas composition in the first gas-to-gas pathway at a point between the LNG tank and the heat exchanger;
 wherein, in a first operation mode, the method runs the first gas-to-gas pathway with the bypass line, in which the gas composition comprising BOG discharged from the LNG tank bypasses the heat exchanger via the bypass line and is pressurized at the first multi-stage compressor to generate the pressurized gas composition,
 wherein, in a second operation mode, the method runs the first gas-to-gas pathway with the heat exchanger, in which the gas composition comprising BOG discharged from the LNG tank is transmitted to the heat exchanger and heated at the heat exchanger before being pressurized at the first multi-stage compressor,
 wherein, in a first operation stage of the BOG processing system, the method runs the first gas-to-gas pathway in the first operation mode to bypass the heat exchanger,
 whereas, in a second operation stage subsequent to the first operation stage of the BOG processing system, the method runs the gas-to-liquid pathway to supply the pressurized gas composition to the heat exchanger, and the method runs the first gas-to-gas pathway to transmit the gas composition comprising BOG discharged from the LNG tank to the heat exchanger for heat exchange of the pressurized gas composition with the gas composition comprising BOG discharged from the LNG tank,
 wherein the first gas-to-gas pathway further comprises a second multi-stage compressor that is located between the heat exchanger and the engine and the first and second multi-stage compressors are arranged in a fluidly parallel relationship with each other,
 wherein, when an amount of the BOG discharged from the tank is greater than a predetermined amount, the vessel runs the first gas-to-gas pathway such that the gas composition is divided in two streams at a point upstream of the first and second multi-stage compressors, each of the two streams of the gas composition is supplied to and pressurized in one of the first and second multi-stage compressors, and the pressurized gas composition from the first multi-stage compressor and the pressurized gas composition from the second multi-stage compressor are mixed at a point downstream of the first and second multi-stage compressors for supplying the pressurized gas composition to the engine or the gas-to-liquid pathway,
 wherein, when an amount of the BOG discharged from the tank is smaller than the predetermined amount, the vessel runs the first gas-to-gas pathway such that the entire amount of the gas composition is supplied to and pressurized in the first multi-stage compressor for supplying the pressurized gas composition to the engine or the gas-to-liquid pathway.

2. The method according to claim 1 , compressor is referred to as a first multi stage compressor, and the first gas to gas pathway further comprises a second multi stage compressor arranged in a parallel relationship with the first multi stage compressor between the heat exchanger and the engine,
wherein, during anchoring of the vessel or during transportation of liquefied gas supplied to the vessel at a production site, both of the first and second multi-stage compressors are operated, wherein, during navigation of the vessel or after unloading of the liquefied gas at a demand site, the second multi-stage compressor is not operated while the first multi-stage compressor is operated, wherein during navigation of the vessel or after unloading of the liquefied gas at a demand site and when determined that the first multi-stage compressor fails, the second multi-stage compressor is operated.

3. The method of claim 1 ,
wherein, when the vessel departs from a port, the vessel runs the first gas-to-gas pathway such that the gas composition is divided in two streams at a point upstream of the first and second multi-stage compressors, each of the two streams of the gas composition is supplied to and pressurized in one of the first and second multi-stage compressors, and the pressurized gas composition from the first multi-stage compressor and the pressurized gas composition from the second multi-stage compressor are mixed at a point downstream of the first and second multi-stage compressors for supplying the pressurized gas composition to the engine or the gas-to-liquid pathway.

4. The method of claim 1 , wherein the first gas-to-gas pathway further comprises an oil separator disposed downstream of the multi-stage compressors, wherein running the first gas-to-gas pathway comprising separating oil from the pressurized gas composition at the oil separator.

Assignees

• Daewoo Shipbuilding & Marine

Inventors

• Lee Joon Chae
• Kim Nam Soo

Classifications

• F17C7/04 Primary

  with change of state, e.g. vaporisation · CPC title

• F17C2227/0358

  by expansion · CPC title

• F17C2265/034

  with condensing the gas phase · CPC title

• F17C2201/052

  large (>1000 m3) · CPC title

• F17C9/02

  with change of state, e.g. vaporisation · CPC title