LNG production in cryogenic natural gas processing plants
First Claim
1. A method for liquifying a natural gas stream, comprising the step ofa) cooling and condensing the natural gas stream in a heat exchanger to produce a condensed natural gas stream;
- wherein said natural gas stream is in gaseous form and comprises compressed residue gas from a cryogenic plant;
wherein said cryogenic plant utilizes a separation means to separate methane gas from liquified heavier hydrocarbons; and
wherein cooling is provided in said heat exchanger by a slipstream of said separated methane gas taken as overhead from said separation means.
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Accused Products
Abstract
A method and system for liquifying natural gas using a cryogenic process is described. The method is well suited for producing high methane purity natural gas which can be used as a vehicle fuel. The invention utilizes residue gas from a cryogenic plant as a natural gas feedstock. The natural gas feedstock is condensed by heat exchange with overhead gas from the demethanizer of the cryogenic plant. In the preferred embodiment of the invention the pressure of the condensed natural gas is reduced to a level at which it can be readily stored and transported by expansion through one or more Joule-Thomson valves.
188 Citations
59 Claims
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1. A method for liquifying a natural gas stream, comprising the step of
a) cooling and condensing the natural gas stream in a heat exchanger to produce a condensed natural gas stream; wherein said natural gas stream is in gaseous form and comprises compressed residue gas from a cryogenic plant;
wherein said cryogenic plant utilizes a separation means to separate methane gas from liquified heavier hydrocarbons; and
wherein cooling is provided in said heat exchanger by a slipstream of said separated methane gas taken as overhead from said separation means.- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A process for producing liquid natural gas comprising the steps of:
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a) cooling a natural gas feedstock with a cooling means to obtain a cooled liquid/gas mixture; b) separating said cooled liquid/gas mixture in a separation means to obtain a gas fraction comprising primarily methane and a liquid fraction comprising primarily ethane and heavier hydrocarbons; c) compressing said gas fraction to obtain a compressed gas fraction; and d) condensing at least a part of said compressed gas fraction via heat exchange with at least a portion of the gas fraction taken from said separation means, to obtain a liquified natural gas fraction; wherein said natural gas feedstock consists primarily of natural gas in gaseous form. - View Dependent Claims (13, 14, 15, 16)
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17. A process for producing liquid natural gas comprising the steps of:
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a) cooling a natural gas feedstock with a cooling means to obtain a cooled liquid/gas mixture; b) separating said cooled liquid/gas mixture in a separation means to obtain a gas fraction comprising primarily methane and a liquid fraction comprising primarily ethane and heavier hydrocarbons and a small amount of methane; c) recovering methane from said liquid fraction with a fractionation means; d) combining said gas fraction and said methane recovered from said liquid fraction to form a residue gas; e) compressing said residue gas to obtain a compressed gas fraction; f) cooling at least a part of said compressed gas fraction via heat exchange with at least a portion of said residue gas to obtain a liquified natural gas/fraction; and g) expanding said liquified natural gas fraction to reduce the temperature and pressure of said liquified natural gas fraction to produce a liquid natural gas product. - View Dependent Claims (18, 19, 20, 21)
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22. A process for producing liquid natural gas comprising the steps of:
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a) cooling a natural gas feedstock with a cooling means to obtain a cooled liquid/gas stream; b) separating said cooled liquid/gas stream into a gaseous fraction and a liquid fraction in an expander inlet separator; c) performing a first expansion of said gaseous fraction to obtain an expanded gaseous/fraction; d) introducing said expanded gaseous fraction to a demethanizer; e) introducing said liquid fraction to said demethanizer; f) dividing the overhead gasses from said demethanizer into a slipstream and a mainstream; g) routing said slipstream through a residue gas condenser as a cooling medium; h) recombining said slipstream and said mainstream to form a residue gas stream; i) compressing said residue gas stream to obtain a compressed residue gas stream; j) cooling said compressed residue gas stream to obtain a cooled, compressed gas stream; k) further cooling at least a part of said cooled, compressed residue gas stream in said residue gas condenser to obtain a condensed residue gas stream; and l) performing a second expansion of said condensed residue gas stream to obtain a liquid natural gas product and a flash vapor fraction. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37)
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38. A process for producing liquid natural gas comprising the steps of:
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a) cooling a natural gas feedstock with a cooling means to obtain a cooled liquid/gas stream; b) separating said cooled liquid/gas stream into a gaseous fraction and a liquid fraction in an expander inlet separator; c) performing a first expansion of said gaseous fraction to obtain an expanded gaseous fraction; d) introducing said expanded gaseous fraction to a demethanizer; e) introducing said liquid fraction to said demethanizer; f) fractionating said expanded gaseous fraction and said liquid fraction in said demethanizer to obtain an overhead stream comprising primarily methane in gaseous form and a bottoms stream comprising liquid ethane and heavier hydrocarbons; g) dividing said overhead stream into a slipstream and a mainstream; h) routing said slipstream through a residue gas condenser as a cooling medium; i) recombining said slipstream and said mainstream to form a residue gas stream; j) compressing said residue gas stream to obtain a compressed residue gas stream; k) cooling said compressed residue gas stream to obtain a cooled, compressed gas stream; l) cooling at least part of said cooled, compressed residue gas stream in said residue gas condenser to obtain a condensed residue gas stream; and m) performing a second expansion of said condensed residue gas stream to obtain a liquid natural gas product and a flash vapor fraction. - View Dependent Claims (39, 40, 41, 42, 43, 44)
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45. An apparatus for liquifying a natural gas stream, comprising:
a) a heat exchanger;
wherein the natural gas stream comprises compressed residue gas from a cryogenic plant;
wherein said cryogenic plant utilizes a separation means;
wherein cooling is provided in said heat exchanger by a slipstream of gas taken from the overhead of said separation means; and
wherein the cooling provided by said heat exchanger is sufficient to condense said natural gas stream to produce a liquid natural gas stream.- View Dependent Claims (46, 47, 48, 49, 50)
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51. An apparatus for producing liquid natural gas comprising:
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a) a cooling means; b) a separation means; c) a compression means; d) a heat exchanger; and e) an expansion means; wherein a natural gas feedstock is cooled in said cooling means to produce a cooled liquid/gas mixture;
wherein said cooled liquid/gas mixture is separated in said separation means into a gas fraction comprising primarily methane and a liquid fraction comprising primarily ethane and heavier hydrocarbons;
wherein at least a portion of said gas fraction is routed through said heat exchanger where it serves as a cooling medium, and subsequently through said compression means where it is compressed to form a compressed gas fraction;
wherein said compressed gas fraction is cooled in said heat exchanger such that it is condensed to a liquid; and
wherein said liquid is expanded in said expansion means, thereby reducing the temperature and pressure of said liquid, to form a liquid natural gas product. - View Dependent Claims (52, 53, 54)
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55. An apparatus for producing liquid natural gas:
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a) a cooling means; b) a liquid/gas separator; c) a first expansion means; d) a demethanizer; e) a compression means; g) a residue gas condenser; and h) a second expansion means; wherein a natural gas feedstock is cooled in said cooling means to produce a cooled liquid/gas mixture;
wherein said cooled liquid/gas mixture is separated in said liquid/gas separator into a first gas fraction and a first liquid fraction;
wherein said gas fraction is expanded in said first expansion means to form a second liquid/gas mixture;
wherein said first liquid fraction and said liquid/gas mixture are introduced to said demethanizer, in which they are fractionated to obtain an overhead gas comprising primarily methane and a bottoms stream comprising primarily liquid ethane and heavier hydrocarbons;
wherein at least a portion of said overhead gas is routed through said heat exchanger where it serves as a cooling medium, and subsequently through said compression means where it is compressed to form a compressed gas fraction;
wherein said compressed gas fraction is cooled in said heat exchanger such that it is condensed to a liquid; and
wherein said liquid is expanded in said expansion means, thereby reducing the temperature and pressure of said liquid, to form a liquid natural gas product. - View Dependent Claims (56, 57, 58, 59)
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Specification