Modified Claude Process for Producing Liquefied Gas

Abstract

A system and method for liquefying gas are provided. The method includes combining an input gas and a first recycle stream to form a first blended stream, and producing a cooled first blended stream and a heated second blended stream by passing the first blended stream and a second blended stream through a heat exchanger. The method also includes producing a mixture of gas and liquefied gas from the cooled first blended stream using a first expander, and producing the liquefied gas at an outlet. The method further includes producing a second recycle stream from the gas from the output of the first expander using a first compressor, and combining the second recycle stream and a third recycle stream to form the second blended stream. The method still further includes producing the first recycle stream from the heated second blended stream using a second compressor, and producing the third recycle stream from the first recycle stream using a second expander.

What is claimed is: 
     
         1 . A gas liquefying system, comprising:
 a first combiner adapted to form a first blended stream from a combination of an input gas and a first portion of a first recycle stream;   a heat exchanger adapted to receive the first blended stream and a second blended stream, transferring heat from the first blended stream to the second blended stream, producing a cooled first blended stream and a heated second blended stream;   a first expander adapted to receive the cooled first blended stream and to produce a mixture of gas and liquefied gas;   an outlet adapted to produce the liquefied gas;   a first compressor adapted to receive the gas from the mixture of gas and liquefied gas and to produce a second recycle stream;   a second combiner adapted to form the second blended stream from the second recycle stream and a third recycle stream and to provide the second blended stream to the heat exchanger;   a second compressor adapted to receive the heated second blended stream from the heat exchanger and produce the first recycle stream and to provide the first portion of the first recycle stream to the first combiner;   a second expander adapted to receive a second portion of the first recycle stream and to produce the third recycle stream and to provide the third recycle stream to the second combiner.   
     
     
         2 . The gas liquefying system of  claim 1 , wherein one or more of the expanders and compressors are gerotors. 
     
     
         3 . The gas liquefying system of  claim 1 , wherein the second compressor comprises a series of compressors with inter-stage cooling. 
     
     
         4 . The gas liquefying system of  claim 1 , wherein the heat exchanger is adapted to maintain a substantially constant temperature differential between the first blended stream and the second blended stream along its full length. 
     
     
         5 . The gas liquefying system of  claim 1 , wherein the second compressor is adapted to produce the first recycle stream with an entropy that is substantially the same as an entropy of the gas from the mixture of gas and liquefied gas produced by the first expander. 
     
     
         6 . The gas liquefying system of  claim 1 , wherein the temperature and pressure of the input gas substantially match the temperature and pressure of the gas exiting the second compressor. 
     
     
         7 . The gas liquefying system of  claim 1 , wherein the first expander, the first compressor, the second compressor, and the second expander are coupled to a common shaft. 
     
     
         8 . The gas liquefying system of  claim 7 , further comprising a motor coupled to the common shaft and adapted to provide power to compensate for inefficiencies in components of the gas liquefying system and work done by the gas liquefying system in producing the liquefied gas. 
     
     
         9 . The gas liquefying system of  claim 2 , wherein the one or more of the expanders and compressors operate in a range of 80 to 90% efficiency. 
     
     
         10 . A method of liquefying gas, the method comprising:
 combining an input gas and a first portion of a first recycle stream to form a first blended stream;   producing a cooled first blended stream and a heated second blended stream by passing the first blended stream and a second blended stream through a heat exchanger adapted to transfer heat from the first blended stream to the second blended stream;   producing a mixture of gas and liquefied gas from the cooled first blended stream using a first expander;   producing the liquefied gas at an outlet;   producing a second recycle stream from the gas from the mixture of gas and liquefied gas using a first compressor;   combining the second recycle stream and a third recycle stream to form the second blended stream;   producing the first portion and a second portion of the first recycle stream from the heated second blended stream using a second compressor;   producing the third recycle stream from the second portion of the first recycle stream using a second expander.   
     
     
         11 . The method of  claim 10 , wherein one or more of the expanders and compressors are gerotors. 
     
     
         12 . The method of  claim 10 , wherein the second compressor comprises a series of compressors with inter-stage cooling. 
     
     
         13 . The method of  claim 10 , further comprising maintaining a substantially constant temperature differential between the first blended stream and the second blended stream along the full length of the heat exchanger. 
     
     
         14 . The method of  claim 10 , further comprising producing the first recycle stream with an entropy that is substantially the same as an entropy of the gas from the mixture of gas and liquefied gas produced by the first expander. 
     
     
         15 . The method of  claim 10 , wherein the temperature and pressure of the input gas substantially match the temperature and pressure of the gas exiting the second compressor. 
     
     
         16 . The method of  claim 10 , wherein the first expander, the first compressor, the second compressor, and the second expander are coupled to a common shaft. 
     
     
         17 . The method of  claim 16 , further comprising providing power to the common shaft using a motor, wherein the power compensates for inefficiencies in components performing the method of liquefying gas and work done in performing the method of liquefying gas. 
     
     
         18 . The method of  claim 11 , wherein the one or more of the expanders and compressors operate in a range of 80% to 90% efficiency. 
     
     
         19 . A gas liquefying system, comprising:
 a heat exchanger adapted to receive an input gas and produce a cooled gas; and   a gerotor expander adapted to receive the cooled gas and to produce a mixture of gas and liquefied gas.   
     
     
         20 . The gas liquefying system of  claim 19 , wherein the heat exchanger is further adapted to receive a working fluid and to transfer heat from the input gas to the working fluid, the gas liquefying system further comprising:
 a system adapted to cool the working fluid to a temperature below a temperature of the input gas prior to the working fluid entering the heat exchanger.