초록 ▼

Disclosed are a method and system for sweetening a raw natural gas feed stream using a multi-stage membrane separation process, and in embodiments a two-stage membrane separation process. The method and system also include use of a gas turbine which operates with an impure fuel gas stream (such as i

Disclosed are a method and system for sweetening a raw natural gas feed stream using a multi-stage membrane separation process, and in embodiments a two-stage membrane separation process. The method and system also include use of a gas turbine which operates with an impure fuel gas stream (such as in the sense of having a relatively high CO2 and H2S acid gas contaminant content) as derived from a permeate gas stream obtained in at least the second stage of a membrane separation process, or later stages if more than two stages are employed. In embodiments, the gas turbine is coupled with an electrical generator, which generates electrical power that drives a compressor for the second stage (or higher) of the membrane separation process, as well as other process equipment associated therewith, such as air coolers and process pumps. Alternatively, the gas turbine can be coupled mechanically to the compressor employed. In other embodiments, the power generated by the turbine generator combination can be exported to a local power grid. In other embodiments, the turbine generator is a micro-turbine generator (MTG) which can advantageously be used in applications where space is limited, such as an offshore platform or other oil/gas production facility or on board a floating vessel.

대표청구항 ▼

What is claimed is: 1. A method for sweetening a raw natural gas feed stream by removing undesired contaminants selected from acid gases, non-combustibles, or mixtures thereof to produce a sweetened natural gas stream, the method comprising: (a) contacting the raw natural gas feed stream with a fir

What is claimed is: 1. A method for sweetening a raw natural gas feed stream by removing undesired contaminants selected from acid gases, non-combustibles, or mixtures thereof to produce a sweetened natural gas stream, the method comprising: (a) contacting the raw natural gas feed stream with a first stage separation membrane to obtain a sweetened natural gas product stream rich in methane and reduced in contaminant content relative to the raw natural gas stream, and a first stage permeate gas stream comprised of methane and having a contaminant content which is greater than that of the raw natural gas stream; (b) compressing the first stage permeate gas stream to provide a compressed first stage permeate gas stream; (c) contacting the compressed first stage permeate gas stream with a second stage separation membrane to obtain a recycle gas stream and a second stage permeate gas stream; (d) directing the recycle gas stream to be combined with the raw natural gas feed stream at any point prior to being contacted with the first stage separation membrane; and (e) directing the second stage permeate gas stream to be used as a fuel gas for a gas turbine that combusts the second stage permeate gas stream and thereby generates mechanical work. 2. The method of claim 1 wherein steps (b) and (c) are repeated at least once. 3. The method of claim 1 wherein the separation membranes employed are selectively permeable for acid gases selected from CO2, H2S, and mixtures thereof. 4. The method of claim 1 wherein the gas turbine is coupled to an electrical generator to produce electrical power. 5. The method of claim 4 wherein at least a portion of the electrical power is used to drive a compressor for step (b). 6. The method of claim 4 wherein at least a portion of the electrical power is used to drive other process equipment. 7. The method of claim 4 wherein at least a portion of the electrical power is exported for sale to a local power grid. 8. The method of claim 1 wherein the separation membranes employed are selectively permeable for nitrogen. 9. The method of claim 1 wherein the method is conducted offshore on a production platform or vessel. 10. A method for sweetening a raw natural gas feed stream by removing undesired acid gases selected from CO2 and H2S to produce a sweetened natural gas stream having reduced levels of such acid gases therein, the method comprising: (a) contacting the raw natural gas feed stream with a first stage separation membrane selectively permeable to acid gas contaminants so as to obtain a sweetened natural gas product stream rich in methane and reduced in acid gas contaminant content relative to the raw natural gas stream, and a first stage permeate gas stream comprised of methane and having an acid gas contaminant content which is greater than that of the raw natural gas stream; (b) compressing the first stage permeate gas to provide a compressed first stage permeate gas stream; (c) contacting the compressed first stage permeate gas stream with a second stage separation membrane selectively permeable to acid gas contaminants so as to obtain a recycle gas stream and a second stage permeate gas stream; (d) directing the recycle gas stream to be combined with the raw natural gas feed stream at any point prior to being contacted with the first stage separation membrane; and (e) directing the second stage permeate gas stream to be used as a fuel gas for a gas turbine that combusts the second stage permeate gas stream and thereby generates mechanical work. 11. The method of claim 10 wherein steps (b) and (c) are repeated at least once. 12. The method of claim 10 wherein the gas turbine is coupled to an electrical generator to produce electrical power. 13. The method of claim 12 wherein at least a portion of the electrical power is used to drive a compressor for step (b). 14. The method of claim 12 wherein at least a portion of the electrical power is used to drive other process equipment. 15. The method of claim 12 wherein at least a portion of the electrical power is exported for sale to a local power grid. 16. The method of claim 10 wherein the method is conducted offshore on a production platform or vessel. 17. A system for sweetening a raw natural gas feed stream by removing undesired contaminants therein selected from acid gases, non-combustibles, or mixtures thereof to produce a sweetened natural gas product stream, the system comprising: (a) a first stage separation membrane unit having a raw gas feed inlet, a feed gas side of the unit fluidly connected to the raw feed gas inlet, a sweetened natural gas product outlet fluidly connected to the feed gas side, a permeate gas side of the unit, a first separation membrane dividing the raw feed gas side from the permeate gas side, and a permeate gas outlet fluidly connected to the permeate gas side of the unit; (b) a permeate gas compressor which is fluidly connected with the permeate gas outlet of the first separation membrane unit and having a compressed permeate gas outlet; (c) a second stage separation membrane unit having a compressed permeate gas inlet fluidly connected to the compressed permeate gas outlet of the permeate gas compressor, a compressed permeate gas side of the unit, a recycle gas outlet fluidly connected to the compressed permeate gas side and fluidly connected to the raw gas feed inlet of the first stage membrane separation unit, a second permeate gas side of the unit, a second separation membrane dividing the compressed permeate gas side from the second permeate gas side, and a second permeate gas outlet fluidly connected to the second permeate gas side; and (d) a gas turbine unit comprised of a combustion chamber fluidly connected with the second permeate gas outlet of the second stage membrane separation unit and said combustion chamber also fluidly connected to a source of an oxidant for corn busting a fuel gas stream conveyed from the second permeate gas outlet, the gas turbine unit also comprising a shaft coupled to the turbine unit for purposes of generating mechanical work. 18. The system of claim 17 wherein the shaft of the gas turbine unit is coupled to an electric generator. 19. The system of claim 18 wherein the gas turbine and electric generator comprise a micro-turbine generator unit (MTG). 20. The system of claim 18 or 19 wherein an electrical line is connected from the electric generator to the permeate gas compressor so that electrical power from the electrical generator is used to power the permeate gas compressor. 21. The system of claim 17 wherein the shaft of the gas turbine unit is coupled to a drive shaft for the permeate gas compressor such that mechanical work from the gas turbine unit is used to drive the permeate gas compressor.