Reducing refrigeration duty on a refrigeration unit in a gas processing system

Abstract

A liquefaction process configured to facilitate thermal transfer in a heat exchanger during liquefaction of a natural gas feedstock. The liquefaction process can include compressing a process stream to a first pressure, the process stream comprising predominantly methane, cooling the process stream to a first temperature, expanding the process stream from the first pressure to a second pressure that is less than the first pressure, bleeding-off a first product from the process stream at the second pressure, and conditioning the first product for storage as liquid natural gas (LNG).

What is claimed is: 
     
         1 . A liquefaction process, comprising:
 compressing a process stream to a first pressure;   cooling the process stream to a first temperature;   expanding the process stream from the first pressure to a second pressure that is less than the first pressure;   bleeding-off a first product from the process stream at the second pressure; and   conditioning the first product for storage as liquid natural gas (LNG).   
     
     
         2 . The liquefaction process of  claim 1 , further comprising:
 compressing the process stream from the second pressure to an intermediate pressure that is between the first pressure and the second pressure.   
     
     
         3 . The liquefaction process of  claim 1 , wherein the process stream comprises liquid at the first pressure. 
     
     
         4 . The liquefaction process of  claim 3 , wherein the process stream comprises both vapor and liquid at the second pressure. 
     
     
         5 . The liquefaction process of  claim 1 , wherein the first pressure and the second pressure form a ratio of from 3 to 10. 
     
     
         6 . The liquefaction process of  claim 1 , further comprising:
 forming the process stream from a feedstock having a concentration of methane of 84% or greater.   
     
     
         7 . The liquefaction process of  claim 6 , further comprising:
 forming a first stream and a second stream from the feedstock, each comprising predominantly methane vapor, wherein the process stream comprises the first stream and the second stream.   
     
     
         8 . The liquefaction process of  claim 7 , further comprising:
 introducing the first stream into the process stream at the intermediate pressure.   
     
     
         9 . The liquefaction process of  claim 7 , further comprising:
 introducing the second stream into the process stream at the second pressure.   
     
     
         10 . The liquefaction process of  claim 7 ,
 separating the feedstock into the first stream and a first bottom product;   distilling the first bottom product to form the second stream and a second bottom product.   
     
     
         11 . A gas processing system, comprising:
 a heat exchanger;   a fluid circuit coupled with the heat exchanger, the fluid circuit directing a process stream through the heat exchanger,   wherein the fluid circuit is configured to:
 compress the process stream to a first pressure; 
 pass the process stream through the heat exchanger at the first pressure; 
 expand the process stream from the first pressure to a second pressure that is less than the first pressure; 
 bleed-off a first stream from the process stream at the second pressure; and 
 condition the first stream for storage as liquid natural gas (LNG). 
   
     
     
         12 . The gas processing system of  claim 11 , further comprising:
 a refrigeration unit coupled with the heat exchanger,   wherein the refrigeration unit is configured to circulate a refrigerant through the heat exchanger.   
     
     
         13 . The gas processing system of  claim 11 , wherein the fluid circuit is configured to receive a feedstock and to circulate the feedstock as the process stream. 
     
     
         14 . The gas processing system of  claim 13 , further comprising:
 a pre-processing unit coupled with the fluid circuit and with the heat exchanger, the pre-processing unit having:
 a separator unit configured to receive the feedstock downstream of the heat exchanger; and 
 a demethanizer coupled downstream of the separator unit, 
   wherein the separator unit and the demethanizer are configured to form a first stream and a second stream, respectively, each comprising methane vapor, and   wherein the process stream comprises the first stream and the second stream.   
     
     
         15 . A gas processing system, comprising:
 a heat exchanger; and   a fluid circuit coupled with the heat exchanger, the fluid circuit configured to circulate a process stream through the heat exchanger, the fluid circuit comprising:
 a methane compressor coupled to the heat exchanger; 
 a turbo-compressor interposed between the methane compressor and the heat exchanger; 
 a turbo-expander coupled to the compressor and to the heat exchanger; and 
 a first separator unit interposed between the turbo-expander and the heat exchanger. 
   
     
     
         16 . The gas processing system of  claim 15 , wherein the methane compressor is configured to pressurize the process stream to a first pressure and the turbo-expander is configured to expand the process stream to a second pressure that maintains a ratio between the first pressure and the second pressure in a range of from 3 to 10. 
     
     
         17 . The gas processing system of  claim 16 , wherein the turbo-compressor is configured to pressurize the process stream to an intermediate pressure that is between the first pressure and the second pressure. 
     
     
         18 . The gas processing system of  claim 17 , wherein the methane compressor is configured to pressurize the process stream from the intermediate pressure to the first pressure. 
     
     
         19 . The gas processing system of  claim 15 , further comprising:
 a second separator unit coupled to the heat exchanger and to the methane compressor; and   a demethanizer coupled to the second separator and to the first separator unit.   
     
     
         20 . The gas processing system of  claim 15 , further comprising:
 an expansion valve disposed downstream of the first separator unit and the heat exchanger.