Boil-off gas recovery system

Abstract

A boil-off gas recovery system 1 includes a tank 2 storing liquefied gas, an oil supply type compressor 3 b for compressing boil-off gas generated by partial evaporation of the liquefied gas in the tank 2 , and a reliquefying system 9 for liquefying the boil-off gas compressed by the oil supply type compressor 3 b and returning the liquefied gas that has been liquefied to the tank 2 . The reliquefying system 9 includes a heat exchanger for oil constituent condensation 11 for cooling down the boil-off gas to a temperature equal to or lower than a condensation temperature of an oil constituent contained in the boil-off gas, a separator 14 for separating the oil constituent condensed by the heat exchanger for oil constituent condensation 11 from the boil-off gas, and a reliquefying portion for liquefying the boil-off gas from which the oil constituent is separated.

What is claimed is: 
     
         1 . A boil-off gas recovery system comprising:
 a tank storing liquefied gas;   an oil supply type compressor for compressing boil-off gas generated by partial evaporation of the liquefied gas in the tank; and   a reliquefying system for liquefying the boil-off gas compressed by the oil supply type compressor and returning the liquefied gas that has been liquefied to the tank,   wherein the reliquefying system includes a heat exchanger for oil constituent condensation for cooling down the boil-off gas to a temperature equal to or lower than a condensation temperature of an oil constituent contained in the boil-off gas, a separator for separating the oil constituent condensed by the heat exchanger for oil constituent condensation from the boil-off gas, and a reliquefying portion for liquefying the boil-off gas from which the oil constituent is separated.   
     
     
         2 . The boil-off gas recovery system according to  claim 1 , wherein the reliquefying portion includes a heat exchanger for gas liquefaction for cooling down the boil-off gas, from which the oil constituent has been separated by the separator, to a liquefiable temperature, an expansion valve for liquefying the boil-off gas by reducing a pressure of the boil-off gas that has been cooled down by the heat exchanger for gas liquefaction, and a gas-liquid separator for separating the boil-off gas, which has been liquefied at least in part by the expansion valve, into a liquid component and a gas component. 
     
     
         3 . The boil-off gas recovery system according to  claim 2 , wherein the heat exchanger for oil constituent condensation exchanges heat between the boil-off gas sent from the tank to the oil supply type compressor and the boil-off gas that has been compressed by the oil supply type compressor. 
     
     
         4 . The boil-off gas recovery system according to  claim 2 , wherein:
 the reliquefying system includes a refrigerating system of a refrigerator;   the heat exchanger for oil constituent condensation is an evaporator arranged at a circulation passage through which a cooling medium circulates in the refrigerating system of the refrigerator; and   the evaporator evaporates the cooling medium in the refrigerating system and cools down the boil-off gas to the temperature equal to or lower than the condensation temperature by exchanging heat between the cooling medium and the boil-off gas that has been compressed by the oil supply type compressor.   
     
     
         5 . The boil-off gas recovery system according to  claim 3 , wherein the reliquefying system includes a temperature control means for adjusting a temperature of the boil-off gas after being cooled down by the heat exchanger for oil constituent condensation, but before the oil constituent is separated from the boil-off gas by the separator. 
     
     
         6 . The boil-off gas recovery system according to  claim 5 , wherein the temperature control means increases the temperature of the boil-off gas after being cooled down by the heat exchanger for oil constituent condensation by merging the boil-off gas before being cooled down by the heat exchanger for oil constituent condensation to the boil-off gas after being cooled down by the heat exchanger for oil constituent condensation. 
     
     
         7 . The boil-off gas recovery system according to  claim 6 , wherein the temperature control means includes a bypass pipe in which a bypass passage is formed for merging the boil-off gas before being cooled down by the heat exchanger for oil constituent condensation to the boil-off gas after being cooled down by the heat exchanger for oil constituent condensation, a valve arranged at the bypass pipe for adjusting an opening of the bypass passage, and an opening control portion for controlling the opening of the bypass passage. 
     
     
         8 . The boil-off gas recovery system according to  claim 1 , wherein the reliquefying system includes an oil filter for removing the oil constituent contained in the boil-off gas before being cooled down by the heat exchanger for oil constituent condensation. 
     
     
         9 . The boil-off gas recovery system according to  claim 4 , wherein the reliquefying system includes a temperature control means for adjusting a temperature of the boil-off gas after being cooled down by the heat exchanger for oil constituent condensation, but before the oil constituent is separated from the boil-off gas by the separator.