System and method for liquefying natural gas

Abstract

Provided is a system for liquefying natural gas including: a pre-cooling means; a gas-liquid separating means; a first heat exchanging means; a second heat exchanging means; a first expanding means; a second expanding means; a first mixed refrigerant converting means; a pre-cooled refrigerant supplying means; a natural gas supplying means; and a mixer. Provided is also a method for liquefying natural gas including: a first pre-cooling operation (S 01 ); a first mixed refrigerant separating operation (S 02 ); a first introducing operation (S 03 ); a first expanded refrigerant forming operation (S 04 ); a second introducing operation (S 05 ); a second expanded refrigerant forming operation (S 06 ); and a second cooling operation (S 07 ).

1 . A system for liquefying natural gas, comprising:
 a pre-cooling means;   a gas-liquid separating means connected to the pre-cooling means;   a first heat exchanging means connected to the pre-cooling means and the gas-liquid separating means, respectively;   a second heat exchanging means connected to the first heat exchanging means;   a first expanding means having one end which is connected to the first heat exchanging means;   a second expanding means having both ends which are each connected to the second heat exchanging means;   a first mixed refrigerant converting means connected to the pre-cooling means and the first heat exchanging means, respectively;   a pre-cooled refrigerant supplying means connected to the pre-cooling means;   a natural gas supplying means connected to the pre-cooling means; and   a mixing means connecting the other end of the first expanding means and the first heat exchanging means to each other and connected to the second heat exchanging means.   
     
     
         2 . The system for liquefying natural gas of  claim 1 , wherein the first heat exchanging means is a first heat exchanger connected to the pre-cooling means and the gas-liquid separating means, and
 the second heat exchanging means is a third heat exchanger connected to the first heat exchanger.   
     
     
         3 . The system for liquefying natural gas of  claim 1 , wherein the first heat exchanging means is a first heat exchanger connected to the pre-cooling means and the gas-liquid separating means, and a second heat exchanger connected to the first heat exchanger, and
 the second heat exchanging means is a third heat exchanger connected to the second heat exchanger, and a fourth heat exchanger connected to the third heat exchanger.   
     
     
         4 . The system for liquefying natural gas of  claim 3 , wherein the first expanding means has one end connected to the first heat exchanger and the other end connected to the second heat exchanger, and
 the second expanding means has one end connected to the third heat exchanger and the other end connected to the fourth heat exchanger.   
     
     
         5 . The system for liquefying natural gas of  claim 1 , wherein the first mixed refrigerant converting means supplies a first mixed refrigerant to the pre-cooling means,
 the pre-cooled refrigerant supplying means supplies a pre-cooled refrigerant to the pre-cooling means,   the natural gas supplying means supplies natural gas to the pre-cooling means,   the pre-cooling means pre-cools the first mixed refrigerant and the natural gas which are each supplied from the pre-cooling means and the natural gas supplying means using the pre-cooled refrigerant supplied from the first mixed refrigerant converting means,   the gas-liquid separating means separates the first mixed refrigerant introduced from the pre-cooling means into a first separated refrigerant of a liquid state and a second separated refrigerant of a gas state,   the first heat exchanging means introduces the natural gas, the first separated refrigerant, and the second separated refrigerant from the pre-cooling means, cools the natural gas, the first separated refrigerant, and the second refrigerant using a mixed refrigerant, and forms the first separated refrigerant at high temperature by cooling less the first separated refrigerant than the natural gas and the second separated refrigerant,   the first expanding means forms a first expanded refrigerant by expanding the first separated refrigerant introduced from the first heat exchanging means,   the second heat exchanging means introduces the natural gas and the second separated refrigerant from the first heat exchanging means, cools the natural gas and the second separated refrigerant using a second expanded refrigerant, forms the second separated refrigerant at high temperature by cooling less the second separating refrigerant than the natural gas, and forms liquefied natural gas by over-cooling the natural gas,   the second expanding means supplies the second expanded refrigerant formed by expanding the second separated refrigerant introduced from the second heat exchanging means to the second heat exchanging means, and   the mixing means supplies the mixed refrigerant formed by mixing a portion of the first expanded refrigerant introduced from the first expanding means and the second expanded refrigerant introduced from the second heat exchanging means to the first heat exchanging means.   
     
     
         6 . The system for liquefying natural gas of  claim 5 , wherein the pre-cooled refrigerant is a single refrigerant or a second mixed refrigerant. 
     
     
         7 . The system for liquefying natural gas of  claim 5 , wherein the first mixed refrigerant converting means converts a mixed refrigerant introduced from the first heat exchanging means into a first mixed refrigerant by sequentially compressing and cooling the mixed refrigerant introduced from the first heat exchanging means and supplies the first mixed refrigerant to the pre-cooling means. 
     
     
         8 . A method for liquefying natural gas, comprising:
 a first pre-cooling operation pre-cooling a first mixed refrigerant and natural gas;   a first mixed refrigerant separating operation separating the first mixed refrigerant into a first separated refrigerant of a liquid state and a second separated refrigerant of a gas state, respectively;   a first introducing operation introducing the natural gas, the first separated refrigerant, and the second separated refrigerant into a first heat exchanging region without being mixed;   a first expanded refrigerant forming operation forming a first expanded refrigerant by introducing the first separated refrigerant into a first expanding region and expanding the first separated refrigerant which is introduced into the first expanding region;   a second introducing operation introducing the natural gas and the second separated refrigerant into a second heat exchanging region without being mixed;   a second expanded refrigerant forming operation forming a second expanded refrigerant by introducing the second separated refrigerant into a second expanding region and expanding the second separated refrigerant which is introduced into the second expanding region;   an over-cooling operation cooling the natural gas and the second separated refrigerant which were introduced into the second heat exchanging region by supplying the second expanded refrigerant to the second heat exchanging region, forming the second separated refrigerant at high temperature by cooling less the second separated refrigerant than the natural gas, and forming liquefied natural gas by over-cooling the natural gas;   a mixed refrigerant forming operation forming a mixed refrigerant by mixing the second expanded refrigerant and the first expanded refrigerant; and   a cooling operation cooling the natural gas, the first separated refrigerant, and the second separated refrigerant which were introduced into the first heat exchanging region by supplying the mixed refrigerant to the first heat exchanging region, and forming the first separated refrigerant at high temperature by cooling less the first separated refrigerant than the natural gas and the second separated refrigerant.   
     
     
         9 . The method for liquefying natural gas of  claim 8 , wherein in the first pre-cooling operation, the first mixed refrigerant and the natural gas are pre-cooled using a single refrigerant or a second mixed refrigerant. 
     
     
         10 . The method for liquefying natural gas of  claim 8 , further comprising:
 a converting operation converting the mixed refrigerant into the first mixed refrigerant by sequentially compressing and cooling the mixed refrigerant;   a second pre-cooling operation pre-cooling the first mixed refrigerant and the natural gas; and   a repetition cycle operation repeating the first mixed refrigerant separating operation to the second pre-cooling operation as one period one or more times.   
     
     
         11 . The method for liquefying natural gas of  claim 10 , wherein in the second pre-cooling operation, the first mixed refrigerant and the natural gas are pre-cooled using a single refrigerant or a second mixed refrigerant.