Systems and methods for producing cng and ngls from raw natural gas, flare gas, stranded gas, and/or associated gas

Abstract

The present invention is a field-deployable system for producing compressed natural gas (CNG) and natural gas liquids (NGLs) from a raw gas stream comprising a compressor; a dehydrator; a refrigerator having one or more stages; and a separation subsystem adapted to separate the raw gas stream into three useable product streams: a methane stream that is at least 70% methane, an ethane-rich stream, and a NGLs stream having a vapor pressure of no more than 17 bar (250 psi) at 38° C. (100° F.). The methane stream is sufficiently lean to be useable in existing natural gas engines without modification, and is compressed to produce CNG. The system can be utilized to capture and provide value to stranded or flared gas from liquids-rich gas production sites, by producing natural gas liquids for transport, and CNG which can be transported and is suitable for use in existing gas generators, vehicles, and/or trucks.

What is claimed is: 
     
         1 . A system for converting a raw natural gas stream into three useable streams, including compressed natural gas (CNG), natural gas liquids (NGLs), and a stream to power the system itself, the system comprising:
 one or more compressors adapted to compress the raw natural gas stream;   a dehydration subsystem adapted to remove trace humidity from the compressed natural gas stream;   a refrigeration subsystem adapted to lower a temperature of the dehydrated, compressed natural gas stream to a low temperature, the refrigeration subsystem comprising a high-stage cascade refrigeration loop and a low-stage autocascade refrigeration loop having mixed hydrocarbon refrigerants;   a separation subsystem adapted to separate the dehydrated, compressed, and refrigerated natural gas stream into three product streams consisting essentially of a methane stream that is at least 70% methane, an ethane-rich stream that is high in ethane content, and a natural gas liquids (NGLs) stream having a vapor pressure of no more than 17 bar at 38° C.;   a CNG compressor for compressing the methane stream into compressed natural gas (CNG) having at least 70% methane at a pressure of at least 105 bar (1500 psig);   a NGLs storage tank for storing the natural gas liquids stream having a Y-grade specification of no more than 17 bar at 38° C.; and   a power generation subsystem tuned to run on the ethane-rich stream adapted to provide electricity to run the system.   
     
     
         2 . The system of  claim 1 , wherein the natural gas liquids stream has a vapor pressure of no more than 14 bar at 38° C. 
     
     
         3 . The system of  claim 1 , further comprising a chassis for holding the system for field deployment, said chassis mountable to a trailer, a truck, a train, a boat, a floating platform, or an airplane. 
     
     
         4 . The system of  claim 1 , wherein the dehydration subsystem employs two desiccant beds in alternation, wherein heat required to dry the two desiccant beds is derived from waste heat from the power generation subsystem. 
     
     
         5 . The system of  claim 1 , wherein the refrigeration subsystem further comprises:
 a high-stage refrigeration loop for lowering a temperature of the dehydrated, compressed natural gas stream; and   a low-stage refrigeration loop for further lowering the temperature of the dehydrated, compressed natural gas stream, wherein the low-stage refrigeration loop is an autocascade loop having mixed refrigerants.   
     
     
         6 . The system of  claim 1 , wherein the refrigeration subsystem cools the dehydrated, compressed natural gas stream to a temperature range of −40° C. to −80° C., sufficient to achieve NGLs separation in a separation column. 
     
     
         7 . The system of  claim 1 , further comprising:
 a sulfur removal module adapted to reduce a sulfur content of the raw natural gas stream entering the system positioned upstream of the one or more compressors.   
     
     
         8 . An apparatus for producing compressed natural gas (CNG) and natural gas liquids (NGLs) from a raw natural gas stream, comprising:
 at least one chassis adapted to hold the apparatus for field deployment;   one or more compressors adapted to compress the raw natural gas stream;   one or more dehydrators adapted to remove water from the compressed natural gas stream;   a refrigerator having one or more stages adapted to lower a temperature of the dehydrated, compressed natural gas stream;   a separator adapted to separate the dehydrated, compressed, and refrigerated natural gas stream into three product streams consisting essentially of a methane stream that is at least 70% methane, an ethane-rich stream that is high in ethane content, and a natural gas liquids stream having a vapor pressure of no more than 17 bar at 38° C.; and   a CNG compressor for compressing the methane stream to compressed natural gas (CNG) having at least 70% methane at a pressure of at least 105 bar (1500 psig).   
     
     
         9 . The apparatus of  claim 8 , further comprising:
 a power generator tuned to run on the ethane-rich stream adapted to provide electricity to run the one or more compressors, the refrigerator, the CNG compressor, and other system components.   
     
     
         10 . The apparatus of  claim 8 , wherein the methane stream is at least 75% methane. 
     
     
         11 . The apparatus of  claim 8 , wherein the natural gas liquids stream has a vapor pressure of no more than 14 bar at 38° C. 
     
     
         12 . The apparatus of  claim 8 , wherein the one or more compressors compress the raw natural gas stream to a pressure range of 6 to 35 bar. 
     
     
         13 . The apparatus of  claim 8 , wherein the refrigerator further comprises:
 a high-temperature refrigeration loop for lowering a temperature of the dehydrated, compressed natural gas stream; and   a low-temperature refrigeration loop for further lowering the temperature of the dehydrated, compressed natural gas stream, wherein the low-temperature refrigeration loop is an autocascade loop having mixed refrigerants.   
     
     
         14 . The apparatus of  claim 8 , wherein the refrigerator cools the dehydrated, compressed natural gas stream to a temperature range of −40° C. to −80° C., sufficient to achieve NGLs separation in a separation column. 
     
     
         15 . The apparatus of  claim 8 , wherein the dehydrators comprise two desiccant beds employed in alternation, and wherein heat required to dry the two desiccant beds is derived from waste heat from a power generator. 
     
     
         16 . A method for producing useable streams including compressed natural gas (CNG) and natural gas liquids (NGLs) from a raw natural gas stream, comprising:
 a compression step for compressing the raw natural gas stream to a pressure range of 6 to 35 bar;   a dehydration step for removing trace moisture from the compressed natural gas stream;   a refrigeration step for reducing a temperature of the dehydrated, compressed natural gas stream to a temperature range of −40° C. to −80° C.;   a separation step for separating the dehydrated, compressed, and refrigerated natural gas stream into three product streams consisting essentially of a methane stream of at least 70% methane, an ethane-rich stream that is high in ethane content, and a natural gas liquids stream having a vapor pressure of no more than 17 bar at 38° C.; and   an additional compression step for compressing the methane stream to compressed natural gas (CNG) having at least 70% methane at a pressure of at least 105 bar (1500 psig).   
     
     
         17 . The method of  claim 16 , further comprising:
 a generation step for generating power utilizing the ethane-rich stream to provide electricity to the compression steps and the refrigeration step.   
     
     
         18 . The method of  claim 16 , wherein the dehydration step employs two desiccant beds in alternation, wherein heat required to dry the two desiccant beds is derived from waste heat from power generation. 
     
     
         19 . The method of  claim 16 , wherein the refrigeration step cools the dehydrated, compressed natural gas stream to a temperature range of −50° C. to −60° C. 
     
     
         20 . The method of  claim 16 , further comprising:
 removing trace humidity from the natural gas stream to achieve an aqueous dew point below at least −40° C. to −80° C.