Fuel supply method for high-pressure natural gas injection engine

Abstract

Provided is a fuel supply method for a marine structure using a high-pressure natural gas injection engine. BOG stored in a stored in the storage tank is compressed to a pressure of 12 to 45 bara (absolute pressure) and then reliquefied. A reliquefaction apparatus includes a cold box configured to exchange heat between a refrigerant and the BOG, a compression unit configured to compress the refrigerant heated by the cold box, an expansion unit configured to expand the compressed refrigerant to drop the temperature thereof, and a plurality of gas-liquid refrigerant separators configured to separate the refrigerant into a gaseous refrigerant and a liquid refrigerant. A gaseous refrigerant and a liquid refrigerant separated by the gas-liquid refrigerant separator disposed at an upstream side are again mixed and supplied to the gas-liquid refrigerant separator disposed at the most downstream among the plurality of gas-liquid refrigerant separators.

1 . A fuel supply method of a fuel supply system for a high-pressure natural gas injection engine installed in a marine structure, wherein:
 the fuel supply system for the high-pressure natural gas injection engine comprises:   a boil-off gas (BOG) compression unit configured to receive and compress BOG generated in a storage tank storing a liquefied gas;   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 and supply the gasified BOG to the high-pressure natural gas injection engine;   the BOG generated in the storage tank is discharged from the storage tank and compressed in a medium pressure range;   the compressed BOG is liquefied; and   the liquefied BOG is compressed to a high pressure, gasified and supplied to the high-pressure natural gas injection engine,   wherein the medium pressure range is 12 to 45 bara (absolute pressure), so that BOG liquefaction energy is reduced.   
     
     
         2 . The fuel supply method according to  claim 1 , wherein the fuel supply system further comprises a buffer tank configured to receive the liquefied BOG cooled and reliquefied by the reliquefaction apparatus, separate a gaseous component, and supply a liquid component to the high-pressure pump. 
     
     
         3 . The fuel supply method according to  claim 1 , wherein the BOG compression unit comprises:
 one or more BOG compressors configured to compress the BOG; and   one or more intermediate coolers configured to cool the BOG, a temperature of which increases while being compressed by the BOG compressors.   
     
     
         4 . The fuel supply method according to  claim 1 , wherein a refrigerant of the reliquefaction apparatus is nitrogen gas or a mixed refrigerant. 
     
     
         5 . The fuel supply method according to  claim 1 , wherein a refrigerant of the reliquefaction apparatus is a nonflammable mixed refrigerant. 
     
     
         6 . The fuel supply method according to  claim 1 , wherein the BOG compressed by the BOG compression unit exchanges heat with the liquefied BOG compressed by the high-pressure pump. 
     
     
         7 . The fuel supply method according to  claim 1 , wherein nitrogen gas heated in a nitrogen refrigeration cycle used in the reliquefaction apparatus exchanges heat with the liquefied BOG compressed by the high-pressure pump. 
     
     
         8 . The fuel supply method according to  claim 1 , wherein, before the BOG generated in the storage tank storing the liquefied gas is compressed by the BOG compression unit, the BOG exchanges heat with the BOG compressed and discharged by the BOG compression unit, or exchanges heat with a nitrogen refrigerant heated in a nitrogen refrigeration cycle used in the reliquefaction apparatus. 
     
     
         9 . The fuel supply method according to  claim 1 , wherein the marine structure is any one of a liquefied gas carrier, an LNG Regasification Vessel (LNG RV), an LNG Floating Storage and Regasification Unit (LNG FSRU), and an LNG Floating, Production, Storage and Off-loading (LNG FPSO). 
     
     
         10 . The fuel supply method according to  claim 1 , wherein all or a considerable amount of the liquefied BOG is supplied to the high-pressure natural gas injection engine during the operation of the high-pressure natural gas injection engine. 
     
     
         11 . A fuel supply method of a fuel supply system for a high-pressure natural gas injection engine installed in a marine structure, characterized in that:
 the fuel supply system for the high-pressure natural gas injection engine comprises:   a BOG compression unit configured to receive and compress BOG generated in a storage tank storing a liquefied gas;   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 and supply the gasified BOG to the high-pressure natural gas injection engine;   the BOG generated in the storage tank is discharged from the storage tank and compressed in a medium pressure range;   the compressed BOG is liquefied; and   the liquefied BOG is compressed to a high pressure, gasified and supplied to the high-pressure natural gas injection engine,   wherein the medium pressure range is 12 to 45 bara (absolute pressure); and   all of the liquefied BOG is supplied to the high-pressure natural gas injection engine when an amount of fuel required by the high-pressure natural gas injection engine of the marine structure is larger than an amount of the BOG generated in the storage tank.   
     
     
         12 . The fuel supply method according to  claim 11 , wherein a refrigerant of the reliquefaction apparatus is nitrogen gas or a mixed refrigerant. 
     
     
         13 . The fuel supply method according to  claim 11 , wherein a refrigerant of the reliquefaction apparatus is a nonflammable mixed refrigerant. 
     
     
         14 . The fuel supply method according to  claim 11 , wherein the BOG compressed by the BOG compression unit exchanges heat with the liquefied BOG compressed by the high-pressure pump. 
     
     
         15 . The fuel supply method according to  claim 11 , wherein nitrogen gas heated in a nitrogen refrigeration cycle used in the reliquefaction apparatus exchanges heat with the liquefied BOG compressed by the high-pressure pump. 
     
     
         16 . The fuel supply method according to  claim 11 , wherein, before the BOG generated in the storage tank storing the liquefied gas is compressed by the BOG compression unit, the BOG exchanges heat with the BOG compressed and discharged by the BOG compression unit, or exchanges heat with a nitrogen refrigerant heated in a nitrogen refrigeration cycle used in the reliquefaction apparatus. 
     
     
         17 . The fuel supply method according to  claim 11 , wherein LNG stored in the storage tank is supplied to the high-pressure natural gas injection engine when an amount of fuel required by the high-pressure natural gas injection engine of the marine structure is larger than an amount of the BOG generated in the storage tank.