Natural gas liquefaction process

Abstract

Disclosed herein is a natural gas liquefaction process of pre-cooling natural gas using a closed loop pre-cooling cycle and liquefying the pre-cooled natural gas using a closed loop liquefying cycle, wherein the closed loop pre-cooling cycle includes first and second pre-cooling cycles in parallel for pre-cooling supplied natural gases together in the same first heat exchange region through the respective pure refrigerants, and the closed loop liquefying cycle includes at least one liquefying cycle for liquefying the pre-cooled natural gas through a mixed refrigerant, the first and second pre-cooling cycles being a closed circuit cooling cycle.

1 . A natural gas liquefaction process of pre-cooling natural gas using a closed loop pre-cooling cycle and liquefying the pre-cooled natural gas using a closed loop liquefying cycle, wherein the closed loop pre-cooling cycle includes first and second pre-cooling cycles for pre-cooling supplied natural gases together in the same first heat exchange region through the respective pure refrigerants, and the closed loop liquefying cycle includes at least one liquefying cycle for liquefying the pre-cooled natural gas through a mixed refrigerant, the first and second pre-cooling cycles being a closed circuit cooling cycle. 
     
     
         2 . The natural gas liquefaction process according to  claim 1 , wherein the pure refrigerant of the first pre-cooling cycle is ethane (C2), and the pure refrigerant of the second pre-cooling cycle is butane (C4). 
     
     
         3 . The natural gas liquefaction process according to  claim 1 , wherein the first and second pre-cooling cycles include a step of compressing the pure refrigerant, a step of cooling the compressed refrigerant, a step of additionally cooling the cooled refrigerant in the first heat exchange region, and a step of expanding the additionally cooled refrigerant. 
     
     
         4 . The natural gas liquefaction process according to  claim 1 , wherein the closed loop liquefying cycle includes a step of compressing the mixed refrigerant, a step of after-cooling the compressed refrigerant, a step of additionally cooling the cooled refrigerant in the first heat exchange region to partially condense the cooled refrigerant, a step of separating the partially condensed refrigerant into a liquid-phase refrigerant portion and a gas-phase refrigerant portion according to a difference in boiling points, a step of primarily cooling the pre-cooled natural gas in a second heat exchange region using the liquid-phase refrigerant portion, and a step of secondarily cooling the primarily cooled natural gas in a third heat-exchange region using the gas-phase refrigerant portion. 
     
     
         5 . The natural gas liquefaction process according to  claim 4 , wherein the step of primarily cooling the pre-cooled natural gas includes a first step of cooling the liquid-phase refrigerant portion through heat exchange in the second heat exchange region, a second step of expanding the refrigerant portion cooled in the first step, and a third step of heat-exchanging the refrigerant portion expanded in the second step and the natural gas in with each other the second heat exchange region to cool the natural gas. 
     
     
         6 . The natural gas liquefaction process according to  claim 4 , wherein the step of secondarily cooling the primarily cooled natural gas includes a cooling step of cooling the gas-phase refrigerant portion through heat exchange in the second heat exchange region, a condensing step of condensing the refrigerant portion cooled in the cooling step through heat exchange in the third heat exchange region, an expanding step of expanding the refrigerant portion condensed in the condensing step, and a step of heat-exchanging the refrigerant portion expanded in the expanding step and the natural gas with each other in the third heat exchange region to cool the natural gas.