System and integrated process for liquid natural gas production

Abstract

A system and method for producing liquid natural gas (LNG) from a natural gas stream is presented. The system includes a moisture removal device and compressor for removing moisture from and compressing the natural gas stream. The low moisture compressed natural gas stream is cooled in a heat exchanger to discharge a cooled compressed discharge stream. A multi-phase turbo expander provides for further cooling and expansion of the cooled compressed discharge stream, generating an expanded exhaust stream comprising a mixture of a vapor comprised substantially of CH 4 and a LNG/ice/solid CO 2 slurry. The expanded exhaust stream is separated to generate a vapor stream comprised substantially of CH 4 and a liquid natural gas/ice/solid CO 2 slurry stream. Further separation of the liquid natural gas/ice/solid CO 2 slurry stream generates a liquid natural gas output stream and an output stream comprised substantially of ice/solid CO 2 .

What is claimed is: 
     
         1 . A system for producing liquid natural gas (LNG) from a natural gas stream, comprising:
 a moisture removal device and a compressor for removing moisture from and compressing the natural gas stream and generating a low moisture compressed natural gas stream;   a heat exchanger for cooling the low moisture compressed natural gas stream and generating a cooled compressed discharge stream;   a multi-phase turbo expander for expanding the cooled compressed discharge stream and generating an expanded exhaust stream comprised of a mixture of a vapor comprised substantially of CH 4  and a liquid natural gas/ice/solid CO 2  slurry;   a separator for separating the expanded exhaust stream and generating a vapor stream comprised substantially of CH 4  and a liquid natural gas/ice/solid CO 2  slurry stream; and   at least one additional separator for separating the liquid natural gas/ice/solid CO 2  slurry stream and generating a liquid natural gas output stream and an output stream comprised substantially of ice/solid CO 2 .   
     
     
         2 . The system of  claim 1 , wherein the moisture removal device comprises molecular sieves beds. 
     
     
         3 . The system of  claim 1 , wherein the low moisture compressed natural gas stream comprises a natural gas stream having a moisture content of less than 180 ppm. 
     
     
         4 . The system of  claim 1 , wherein the multi-phase turbo expander is configured to further cool the cooled compressed discharge stream from the heat exchanger such that primarily formed is the liquid natural gas/ice/solid CO 2  slurry. 
     
     
         5 . The system of  claim 1 , further comprising a recirculation path configured to recirculate the vapor stream comprised substantially of CH 4  into the natural gas stream. 
     
     
         6 . The system of  claim 5 , wherein the recirculation path further comprises a compressor for compressing the vapor stream comprised substantially of CH 4  and generating a compressed vapor stream comprised substantially of CH 4 . 
     
     
         7 . The system of  claim 1 , wherein the at least one additional separator is one of a filter, a cyclone or a gravity separator. 
     
     
         8 . The system of  claim 1 , wherein the multi-phase turbo expander comprises:
 a housing;   at least one rotating component disposed within the housing;   at least one inlet disposed in the housing, wherein the inlet is configured to receive the cooled compressed discharge stream; and   at least one outlet disposed in the housing, wherein the outlet is configured to discharge the expanded exhaust stream comprised of a mixture of a vapor comprised substantially of CH 4  and a liquid natural gas/ice/solid CO 2  slurry,   wherein the multi-phase turbo expander is configured to further cool the cooled compressed discharge stream from the heat exchanger such that the vapor comprised substantially of CH 4  is formed, a liquid natural gas is formed and at least a portion of CO 2  in the cooled discharge natural gas stream forms a solid CO 2 .   
     
     
         9 . The system of  claim 8 , wherein the multi-phase turbo expander is further configured to separate the vapor comprised substantially of CH 4  and the liquid natural gas/ice/solid CO 2  slurry to discharge a vapor stream comprised substantially of CH 4  and a slurry stream comprised substantially of a liquid natural gas/ice/solid CO 2 . 
     
     
         10 . The system of  claim 1 , further comprising an external refrigeration system in fluidic communication with the heat exchanger to provide further cooling to the low moisture compressed natural gas stream. 
     
     
         11 . A system for producing liquid natural gas (LNG) from a natural gas stream, comprising:
 at least one compression stage and at least one cooling stage configured to compress and cool a natural gas stream and generate a cooled compressed discharge stream; and   at least one expansion stage configured to expand the cooled compressed discharge stream and generate an expanded exhaust stream, the at least one expansion stage comprising at least one multi-phase turbo expander in fluid communication with the compression stage and the cooling stage, the multi-phase turbo expander comprising:
 a housing; 
 at least one rotating component disposed within the housing; 
 at least one inlet disposed in the housing, wherein the inlet is configured to receive the cooled compressed discharge stream; and 
 at least one outlet disposed in the housing, wherein the outlet is configured to discharge an expanded exhaust stream comprising a mixture of a vapor comprised substantially of CH 4  and a liquid natural gas/ice/solid CO 2  slurry. 
   
     
     
         12 . The system of  claim 11 , further comprising a separation stage configured to separate the mixture of a vapor comprised substantially of CH 4  and a liquid natural gas/ice/solid CO 2  slurry into a vapor stream comprised substantially of CH 4  and an output stream comprised substantially of liquid natural gas/ice/solid CO 2  slurry. 
     
     
         13 . The system of  claim 12 , further comprising a recirculation stage configured to recirculate the vapor stream comprised substantially of CH 4  into the natural gas stream. 
     
     
         14 . The system of  claim 13 , wherein the recirculation stage comprises a compressor for compressing the vapor stream comprised substantially of CH 4  and generating a compressed vapor stream comprised substantially of CH 4 . 
     
     
         15 . The system of  claim 11 , wherein the multi-phase turbo expander is configured to further cool the cooled compressed discharge stream such that a liquid natural gas is formed and at least a portion of CO 2  in the cooled discharge natural gas stream forms a solid CO 2 . 
     
     
         16 . The system of  claim 11 , at least one cooling stage further comprises an external refrigeration system configured to provide further cooling to the low moisture compressed natural gas stream. 
     
     
         17 . A method for producing liquid natural gas (LNG) from a natural gas stream, comprising:
 providing an input natural gas stream;   removing moisture, compressing and cooling the natural gas stream and generating a cooled compressed discharge stream;   expanding the cooled compressed discharge stream in a multi-phase turbo expander and generating an expanded exhaust stream comprising a mixture of a vapor comprised substantially of CH 4  and a liquid natural gas/ice/solid CO 2  slurry;   separating the expanded exhaust stream in at least one separator and generating a vapor stream comprised substantially of CH 4  and a liquid natural gas/ice/solid CO 2  slurry stream; and   separating the liquid natural gas/ice/solid CO 2  slurry stream in at least one additional separator and generating an output stream comprised substantially of ice/solid CO 2  and a liquid natural gas (LNG) output stream.   
     
     
         18 . The method of  claim 17 , further comprising recirculating the vapor stream comprised substantially of CH 4  to the input natural gas stream in a recirculation path. 
     
     
         19 . The method of  claim 17 , further comprising separating at least portion of ice/solid CO 2  from the cooled compressed natural gas stream in the multi-phase turbo expander. 
     
     
         20 . The method of  claim 17 , wherein the multi-phase turbo expander comprises:
 a housing;   at least one rotating component disposed within the housing;   at least one inlet disposed in the housing, wherein the inlet is configured to receive the cooled compressed discharge stream; and   at least one outlet disposed in the housing, wherein the outlet is configured to discharge the expanded exhaust stream comprising a mixture of a vapor comprised substantially of CH 4  and a liquid natural gas/ice/solid CO 2  slurry;   wherein the multi-phase turbo expander is configured to further cool the cooled compressed discharge stream such that the vapor comprised substantially of CH 4  is formed, a liquid natural gas is formed and at least a portion of CO 2  in the cooled discharge natural gas stream forms a solid CO 2 .   
     
     
         21 . The method of  claim 17 , further comprising further cooling the natural gas stream in an external refrigeration system in fluidic communication with the cooled compressed discharge stream. 
     
     
         22 . The method of  claim 17 , further comprising separating at least portion of the vapor stream comprised substantially of CH 4  and a slurry stream comprised substantially of a liquid natural gas/ice/solid CO 2  within the multi-phase turbo expander.