Device and method for processing boil-off gas in liquefied gas regasification system

Abstract

A device for processing boil-off gas in a liquefied gas regasification system includes a fuel compressor for compressing boil-off gas at a pressured required by a fuel consumer; a high-pressure compressor installed at the rear end of the fuel compressor in series with the fuel compressor so as to compress the low-pressure boil-off gas, which has been compressed by the fuel compressor, at a pressure required by a regasified gas consumer; a low-temperature heat exchanger for cooling the high-pressure boil-off gas compressed by the high-pressure compressor; a pressure-reducing device for reducing the pressure of the high-pressure boil-off gas, which has been cooled by the low-temperature heat exchanger, to the inner pressure of a liquefied gas storage tank for storing the liquefied gas; and a liquefied gas drum for separating flash gas generated by the pressure-reducing device in the pressure-reducing process.

1 . A device for processing boil-off gas in a liquefied gas regasification system, the device comprising:
 a fuel compressor compressing boil-off gas to a pressure required for a fuel demand site;   a high-pressure compressor disposed in series with the fuel compressor downstream of the fuel compressor and compressing the low-pressure boil-off gas compressed by the fuel compressor to a pressure required for a regasified gas demand site;   a low-temperature heat exchanger cooling the high-pressure boil-off gas compressed by the high-pressure compressor;   a decompression unit decompressing the high-pressure boil-off gas cooled by the low-temperature heat exchanger to an internal pressure of a liquefied gas storage tank; and   a liquefied gas drum separating flash gas generated during decompression by the decompression unit,   wherein reliquefied boil-off gas separated by the liquefied gas drum is returned to the liquefied gas storage tank.   
     
     
         2 . The device according to  claim 1 , further comprising:
 an expander expanding and cooling some of the high-pressure boil-off gas to be supplied to the low-temperature heat exchanger,   wherein the low-temperature heat exchanger cools the high-pressure boil-off gas through heat exchange with the boil-off gas expanded and cooled by the expander.   
     
     
         3 . The device according to  claim 2 , further comprising:
 a high-temperature heat exchanger precooling the high-pressure boil-off gas to be supplied to the low-temperature heat exchanger to an inlet temperature of the expander,   wherein some of the high-pressure boil-off gas to be supplied to the low-temperature heat exchanger from the high-temperature heat exchanger is sent to the expander.   
     
     
         4 . The device according to  claim 3 , wherein the high-temperature heat exchanger cools the high-pressure boil-off gas to be supplied to the low-temperature heat exchanger and the expander through heat exchange with the expanded boil-off gas heated through heat exchange in the low-temperature heat exchanger and discharged from the low-temperature heat exchanger. 
     
     
         5 . The device according to  claim 3 , further comprising:
 a gas compressor compressing the expanded boil-off gas subjected to heat exchange in the low-temperature heat exchanger and discharged from the low-temperature heat exchanger to a pressure of a flow of the boil-off gas compressed by the fuel compressor,   wherein the boil-off gas compressed by the gas compressor is joined with the flow of the boil-off gas compressed by the fuel compressor.   
     
     
         6 . The device according to  claim 5 , wherein the gas compressor is connected to the expander via a common shaft. 
     
     
         7 . The device according to  claim 5 , further comprising:
 a gas cooler regulating a temperature of the boil-off gas compressed and heated by the gas compressor.   
     
     
         8 . The device according to  claim 3 , wherein the flash gas separated by the liquefied gas drum is joined with a flow of the expanded boil-off gas to be supplied to the low-temperature heat exchanger. 
     
     
         9 . A method for processing boil-off gas in a liquefied gas regasification system, comprising:
 compressing boil-off gas to a low pressure required for a fuel demand site,   compressing the low-pressure boil-off gas to a high pressure required for a regasified gas demand site,   cooling the high-pressure boil-off gas,   decompressing the cooled high-pressure boil-off gas to an internal pressure of a liquefied gas storage tank; and   separating flash gas generated during decompression of the cooled high-pressure boil-off gas and returning reliquefied boil-off gas to the liquefied gas storage tank.   
     
     
         10 . The method according to  claim 9 , wherein cooling the high-pressure boil-off gas comprises:
 expanding and cooling some of the high-pressure boil-off gas before cooling the high-pressure boil-off gas; and   liquefying at least part of the high-pressure boil-off gas through heat exchange between the expanded and cooled boil-off gas and the high-pressure boil-off gas.   
     
     
         11 . The method according to  claim 10 , further comprising:
 precooling the high-pressure boil-off gas through heat exchange with the expanded boil-off gas heated while cooling the high-pressure boil-off gas, before performing heat exchange between the expanded and cooled boil-off gas and the high-pressure boil-off gas.   
     
     
         12 . The method according to  claim 11 , wherein precooling the high-pressure boil-off gas comprises:
 cooling the high-pressure boil-off gas to an inlet temperature of an expander expanding the high-pressure boil-off gas.   
     
     
         13 . The method according to  claim 11 , wherein the expanded boil-off gas heated while cooling the high-pressure boil-off gas is compressed to a pressure of a flow of boil-off gas to be compressed by a fuel compressor before being joined with the flow of the boil-off gas. 
     
     
         14 . The method according to  claim 13 , wherein expansion work in expanding the high-pressure boil-off gas is recovered as compression work in compressing the expanded boil-off gas. 
     
     
         15 . The method according to  claim 11 , wherein the separated flash gas is joined with a flow of the expanded boil-off gas exchanging heat with the high-pressure boil-off gas.