Natural gas liquefaction process

Abstract

A natural gas liquefaction process according to the present invention uses a single closed-loop refrigeration cycle employing a mixed refrigerant, thereby having a simple structure for the liquefaction process and allowing the liquefaction process to be easily operated. Furthermore, the present invention cools natural gas after one stream is separated into two streams, thereby having an excellent efficiency of the liquefaction process.

1 . A natural gas liquefaction process in which natural gas is primarily cooled in a first heat exchange part and secondarily cooled in a second heat exchange part distinguished from the first heat exchange part by using a single closed-loop refrigeration cycle using a mixed refrigerant, the closed-loop refrigeration cycle comprising:
 a condensation step of partially condensing the mixed refrigerant;   a first separation step of separating the mixed refrigerant into a first stream having a liquid phase and a second stream having a gas phase after the condensation step;   a first introduction step of introducing the first stream into the first heat exchange part after the first separation step;   a first expansion step of expanding the first stream discharged from the first heat exchange part after the first introduction step;   a first cooling step of introducing the first stream again into the first heat exchange part to cool the natural gas in the first heat exchange part through the first stream after the first expansion step;   a first recovery step of recovering the first stream from the first heat exchange part after the first cooling step;   a second introduction step of introducing the second stream into the first heat exchange part after the first separation step;   a third introduction step of introducing the second stream discharged from the first heat exchange part into the second heat exchange part after the second introduction step;   a second expansion step of expanding the second stream discharged from the second heat exchange part after the third introduction step;   a second cooling step of introducing the second stream again into the second heat exchange part to cool the natural gas in the second heat exchange part through the second stream after the second expansion step; and   a second recovery step of recovering the second stream from the second heat exchange part after the second cooling step;   wherein the first stream is transferred for the condensation step after the first recovery step, and the second stream is transferred for the condensation step after the second recovery step.   
     
     
         2 . The natural gas liquefaction process of  claim 1 , wherein the condensation step comprises:
 a first compression step of compressing the second stream;   a first mixing step of mixing the first stream with the second stream to form a main stream after the first compression step; and   a second compression step of compressing the main stream after the first mixing step.   
     
     
         3 . The natural gas liquefaction process of  claim 1 , wherein the condensation step comprises:
 a first compression step of compressing the second stream;   a first mixing step of mixing the first stream with the second stream to form a main stream after the first compression step;   a second separation step of separating the main stream into a third stream having a liquid phase and a fourth stream having a gas phase after the first mixing step;   a second compression step of compressing the fourth stream after the second separation step; and   a second mixing step of transferring the third stream by using a pump to mix the third stream with the fourth stream, which is formed after the second compression step, after the second separation step ;      wherein the third stream and the fourth stream are transferred together for the first separation step after the second mixing step.   
     
     
         4 . The natural gas liquefaction process of  claim 1 , wherein the condensation step comprises:
 a first compression step of compressing the second stream;   a second compression step of compressing the first stream;   a first mixing step of mixing the first stream with the second stream to form a main stream after the first and second compression steps; and   a third compression step of compressing the main stream after the first mixing step.   
     
     
         5 . The natural gas liquefaction process of  claim 1 , wherein the condensation step comprises:
 a first compression step of compressing the second stream;   a second compression step of compressing the first stream;   a third compression step of compressing the second stream after the first compression step;   a first mixing step of mixing the first stream with the second stream to form a main stream after the second and third compression steps;   a second separation step of separating the main stream into a third stream having a liquid phase and a fourth stream having a gas phase after the first mixing step;   a second mixing step of mixing the third stream with the second stream after the second separation step; and   a fourth compression step of compressing the fourth stream after the second separation step,   wherein the third stream is transferred for the third compression step together with the second stream after the second mixing step, and the fourth stream is transferred for the first separation step after the fourth compression step.   
     
     
         6 . The natural gas liquefaction process of  claim 1 , wherein
 a first compression step of compressing the second stream;   a second compression step of compressing the first stream;   a first mixing step of mixing the first stream with the second stream to form a main stream after the first and second compression steps;   a second separation step of separating the main stream into a third stream having a liquid phase and a fourth stream having a gas phase after the first mixing step;   a third compression step of compressing the fourth stream after the second separation step; and   a second mixing step of transferring the third stream by using a pump to mix the third stream with the fourth stream, which is formed after the third compression step, after the second separation step,   wherein the third and fourth streams are transferred together for the first separation step after the second mixing step.   
     
     
         7 . The natural gas liquefaction process of any one of  claims 1  to  6 , wherein each of the first and second heat exchange parts comprises a spiral wound heat exchanger (SWHE)-type heat exchanger. 
     
     
         8 . A natural gas liquefaction process in which natural gas is primarily cooled in a first heat exchange part and secondarily cooled in a second heat exchange part distinguished from the first heat exchange part by using a single closed-loop refrigeration cycle using a mixed refrigerant, the closed-loop refrigeration cycle comprising:
 a condensation step of partially condensing the mixed refrigerant,   a first separation step of separating the mixed refrigerant into a first stream having a liquid phase and a second stream having a gas phase after the condensation step;   a first introduction step of introducing the first stream into the first heat exchange part after the first separation step;   a first expansion step of expanding the first stream discharged from the first heat exchange part after the first introduction step;   a first cooling step of introducing the first stream again into the first heat exchange part to cool the natural gas in the first heat exchange part through the first stream after the first expansion step;   a first recovery step of recovering the first stream from the first heat exchange part after the first cooling step;   a second introduction step of introducing the second stream into a third heat exchange part which is distinguished from the first heat exchange part after the first separation step;   a third introduction step of introducing the second stream discharged from the third heat exchange part into the second heat exchange part after the second introduction step;   a second expansion step of expanding the second stream discharged from the second heat exchange part after the third introduction step;   a second cooling step of introducing the second stream again into the second heat exchange part to cool the natural gas in the second heat exchange part through the second stream after the second expansion step; and   a fourth introduction step of recovering the second stream from the second heat exchange part to introduce the recovered second stream again into the third heat exchange part after the second cooling step; and   a second recovery step of recovering the second stream from the third heat exchange part after the fourth introduction step;   wherein the first stream is transferred for the condensation step after the first recovery step, and the second stream is transferred for the condensation step after the second recovery step.   
     
     
         9 . The natural gas liquefaction process of  claim 8 , further comprising:
 a third separation step of separating the second stream into a first portion and a second portion after the first separation step; and   a fifth introduction step of introducing the second portion into the first heat exchange part,   wherein the second introduction step comprises introducing the first portion into the third heat exchange part, and   the third introduction step comprises introducing the first and second portions together into the second heat exchange part after the second and fifth introduction steps,   
     
     
         10 . A natural gas liquefaction process in which natural gas is liquefied by using a single closed-loop refrigeration cycle using a mixed refrigerant, the closed-loop refrigeration cycle comprising:
 a condensation step of partially condensing the mixed refrigerant;   a first separation step of separating the mixed refrigerant into a first stream having a liquid phase and a second stream having a gas phase after the condensation step;   a first introduction step of introducing the first stream into the first heat exchange part after the first separation step;   a second introduction step of introducing the second stream into the first heat exchange part after the first separation step;   a first expansion step of expanding the first stream discharged from the first heat exchange part after the first introduction step;   a first cooling step of introducing the first stream again into the first heat exchange part to cool the second stream in the first heat exchange part through the first stream after the first expansion step;   a first recovery step of recovering the first stream from the first heat exchange part after the first cooling step;   a third introduction step of introducing the second stream discharged from the first heat exchange part into a second heat exchange part which is distinguished from the first heat exchange part after the first cooling step;   a second expansion step of expanding the second stream discharged from the second heat exchange part after the third introduction step;   a second cooling step of introducing the second stream again into the second heat exchange part to cool the natural gas in the second heat exchange part through the second stream after the second expansion step;   a third cooling step of recovering the second stream from the second heat exchange part to introduce the recovered second stream into a third heat exchange part which is distinguished from the first heat exchange part, thereby cooling the natural gas in the third heat exchange part through the second stream after the second cooling step; and   a second recovery step of recovering the second stream from the third heat exchange after the third cooling step,   wherein the first stream is transferred for the condensation step after the first recovery step, and the second stream is transferred for the condensation step after the second recovery step, and   the natural gas is primarily cooled in the third heat exchange part and secondarily cooled in the second heat exchange part, thereby being liquefied.   
     
     
         11 . The natural gas liquefaction process of  claim 10 , further comprising:
 a step of separating the natural gas into a first portion and a second portion;   a first natural gas introduction step of introducing the first portion into the third heat exchange part;   a second natural gas introduction step of introducing the second portion into the first heat exchange part;   a natural gas mixing step of mixing the first portion with the second portion after the first and second natural gas introduction steps; and   a third natural gas introduction step of introducing the first portion together with the second portion into the second heat exchange part after the natural gas mixing step.   
     
     
         12 . The natural gas liquefaction process of any one of  claims 8  to  11 , wherein the condensation step comprises:
 a first compression step of compressing the second stream; 
 a second compression step of compressing the first stream; 
 a third compression step of compressing the second stream after the first compression step; 
 a first mixing step of mixing the first stream with the second stream to form a main stream after the second and third compression steps; 
 a second separation step of separating the main stream into a third stream having a liquid phase and a fourth stream having a gas phase after the first mixing step; 
 a second mixing step of mixing the third stream with the second stream after the second separation step; and 
 a fourth compression step of compressing the fourth stream after the second separation step, 
 wherein the third stream is transferred for the third compression step together with the second stream after the second mixing step, and 
 the fourth stream is transferred for the first separation step after the fourth compression step. 
 
     
     
         13 . The natural gas liquefaction process of any one of  claims 8  to  11 , wherein each of the first and second heat exchange parts comprises a spiral wound heat exchanger (SWHE)-type heat exchanger.