Utilizing the Mehra process for processing and BTU upgrading of nitrogen-rich natural gas streams

Claim 2

A process for separating C 1 + hydrocarbons and nitrogen from a nitrogen-rich natural gas stream which contains more than 3 mol % of said nitrogen, comprising the following steps: A. extracting said natural gas stream with a physical solvent to produce a nitrogen stream and a methane-rich solvent stream; B. flashing said solvent stream at a flashing pressure which is selected to be in between 1300 psia and 2 psia and is sufficiently low that substantially all said C 1 + hydrocarbons are separated from a stripped solvent stream and are produced as a stream of flashed-off gases; and C. recycling said stripped solvent stream to said extracting of said Step A.

Claim 3

The process of claim 1, wherein said nitrogen stream is passed through a power recovery turbine.

Claim 4

The process of claim 1, wherein said flashing utilizes up to eight flashing stages, having a ratio of absolute pressures between successive said flashing stages of at least 2.0.

Claim 5

The process of claim 1, wherein said flashed-off gases are compressed and cooled to form a C 1 -rich gas product.

Claim 6

The process of claim 4, wherein: A. said nitrogen-rich natural gas stream contains C 2 + hydrocarbons and is lean with respect to C 5 + hydrocarbons; and B. said nitrogen-rich natural gas stream is extracted in one stage with said physical solvent to remove said C 2 + hydrocarbons and produce a residue natural gas stream primarily comprising nitrogen and methane for further extracting in said Step A of claim 1.

Claim 7

The process of claim 4, wherein said nitrogen-rich natural gas stream contains more than 2 mol percent of C 5 + hydrocarbons and is extracted in two stages with said physical solvent to remove C 2 + hydrocarbons and produce a residue natural gas stream primarily comprising nitrogen and methane for further extracting in said Step A of claim 1.

Claim 8

The process of claim 6, wherein: A. said nitrogen-rich natural gas stream contains said C 2 + hydrocarbons and acidic compounds which are extracted by said physical solvent and are present with said C 2 + hydrocarbons; B. said C 2 + hydrocarbons are compressed, cooled, condensed, and stripped to produce a sour natural gas liquid product containing said acidic compounds; and C. said sour natural gas liquid product is contacted with an aqueous amine solution to remove said acidic compounds and produce a sweet natural gas liquid product.

Claim 9

The process of claim 6, wherein said nitrogen-rich natural gas stream is extracted in the first stage of said two stages with a main solvent stream containing less than 15 mol % of C 5 + hydrocarbons to produce a partially stripped natural gas stream and a rich solvent stream containing said C 2 + hydrocarbons.

Claim 10

The process of claim 8, wherein said partially stripped natural gas stream is extracted in the second stage of said two stages with a lean-and-dry solvent stream, which is lean with respect to C 1 + hydrocarbons and dry with respect to water, to produce said residue natural gas stream, primarily comprising said nitrogen and said methane, and an enriched solvent stream.

Claim 11

The process of claim 9, wherein said enriched solvent stream is added to said main solvent stream in said first stage of said two stages for extracting said nitrogen-rich natural gas stream containing more than 2 mol percent of C 5 + hydrocarbons, whereby said rich solvent stream is produced.

Claim 12

The process of claim 1, wherein: A. said nitrogen-rich natural gas stream contains acidic compounds which are extracted by said physical solvent and are present with said C 1 + hydrocarbons; B. said C 1 + hydrocarbons are compressed and cooled to form a sour C 1 -rich gas product comprising said acidic compounds; and C. said sour C 1 -rich gas product is contacted with an aqueous amine solution to remove said acidic compounds and produce a sweet C 1 -rich gas product.

Claim 13

In a continuous process for producing a natural gas liquid hydrocarbon product having a selected composition, that is selectively adjustable to substantially any selected degree in accordance with market conditions, and a residue natural gas stream of pipeline quality, that selectively includes ethane (C 2 ), propane (C 3 ), and butane (C 4 ), by extraction of a natural gas stream, containing from 3 to 75 mol percent of nitrogen-rich, with a stream of a physical solvent to produce a rich solvent stream in addition to said residue natural gas stream, said rich solvent stream being flashed to at least atmospheric pressure to produce: (a) a stream of C 1 -rich flashed gases which are recycled for extraction with said physical solvent stream, (b) a stream of C 1 -lean flashed gases which are compressed, cooled, and condensed for demethanizing to produce a selected stream of C 1 -C 4 rejected gases and said natural gas liquid product, and (c) a recycle solvent stream that is split into a major solvent stream and a solvent slipstream which is regenerated to form a lean-and-dry solvent stream for recycling to said extraction, wherein there exists a need for reducing the content of said nitrogen in said residue natural gas stream to less than 3 mol percent in order to obtain said pipeline quality, an improvement which enables minor components of said nitrogen-rich natural gas stream to be removed in at least one extracting stage to produce a nitrogen-rich residue natural gas stream, consisting essentially of methane and said nitrogen, before isolating said nitrogen, said process comprising the following steps: A. extracting said nitrogen natural gas stream with a stream of said physical solvent that selectively comprises said lean-and-dry solvent stream to produce said rich solvent stream and said residue natural gas stream; B. extracting said residue natural gas stream with a sufficient quantity of said lean-and-dry solvent stream to extract said methane and to produce a C 1 -rich solvent stream and a stream of said nitrogen; and C. flashing said C 1 -rich solvent stream to produce a C 1 -rich gas product and a dry stripped solvent stream.

Claim 14

In a continuous process for producing a natural gas liquid hydrocarbon product having a selected composition, that is selectively adjustable to substantially any selected degree in accordance with market conditions, and a residue natural gas stream of pipeline quality, that selectively includes ethane (C 2 ), propane (C 3 ), and butane (C 4 ), by extraction of a natural gas stream, containing from 3 to 75 mol percent of nitrogen-rich, with a stream of a physical solvent to produce a rich solvent stream in addition to said residue natural gas stream, said rich solvent stream being flashed to at least atmospheric pressure to produce: (a) a stream of C 1 -rich flashed gases which are recycled for extraction with said physical solvent stream, (b) a stream of C 1 -lean flashed gases which are compressed, cooled, and condensed for demethanizing to produce a selected stream of C 1 -C 4 rejected gases and said natural gas liquid product, and (c) a recycle solvent stream that is split into a major solvent stream and a solvent slipstream which is regenerated to form a lean-and-dry solvent stream for recycling to said extraction, wherein there exists a need for reducing the content of said nitrogen in said residue natural gas stream to less than 3 mol percent in order to obtain said pipeline quality, an improvement which enables minor components of said nitrogen-rich natural gas stream to be removed in at least one extracting stage to produce a nitrogen-rich residue natural gas stream, consisting essentially of methane and said nitrogen, before isolating said nitrogen, said process comprising the following steps: A. extracting said nitrogen natural gas stream with a stream of said physical solvent that selectively comprises said lean-and-dry solvent stream to produce said rich solvent stream and said residue natural gas stream; B. extracting said residue natural gas stream with a sufficient quantity of said lean-and-dry solvent stream to extract said methane and to produce a C 1 -rich solvent stream and a stream of said nitrogen; and C. flashing said C 1 -rich solvent stream to produce a C 1 -rich gas product and a dry stripped solvent stream.

Claim 15

The improved process of claim 9, wherein said lean-and-dry solvent stream contains less than 1 wgt. % of water and less than 1 volume % of C 5 + hydrocarbons.

Claim 16

The improved process of claim 13, wherein said nitrogen-rich natural gas stream contains water and more than 2 mol percent of C 5 + hydrocarbons and is extracted in two stages to remove said water and said C 2 + hydrocarbons, producing said residue natural gas stream.

Claim 17

The improved process of claim 14, wherein said nitrogen-rich natural gas stream is extracted with a main solvent stream containing less than 15 mol % of C 5 + hydrocarbons to produce a partially stripped natural gas stream and a rich solvent stream containing said water and said C 2 + hydrocarbons.

Claim 18

The improved process of claim 15, wherein said partially stripped natural gas stream is extracted with a lean-and-dry solvent stream, which is lean with respect to C 1 + hydrocarbons and dry with respect to water, to produce said residue natural gas stream and an enriched solvent stream.

Claim 19

The improved process of claim 16, wherein said enriched solvent stream is added to said main solvent stream for extracting said nitrogen-rich natural gas stream containing more than 2 mol percent of C 5 + hydrocarbons, whereby said rich solvent stream is produced.

Claim 20

The improved process of claim 17, wherein said rich solvent stream is flashed to produce said stream of C 1 -rich flashed gases, said stream of C 1 -lean flashed gases, and a wet stripped solvent stream.

Claim 21

The improved process of claim 16, wherein said enriched solvent stream is flashed to produce said stream of C 1 -rich flashed gases, said stream of C 1 -lean flashed gases, and a wet stripped solvent stream.

Claim 22

The improved process of claims 18 or 19, wherein said wet solvent stream is split to form said main solvent stream and said solvent slipstream which is regenerated to form said lean-and-dry solvent stream.

Claim 23

The process of claim 20, wherein said regenerating is done by distillation.

Claim 24

The improved process of claim 20, wherein said dry stripped solvent stream from said Step C contains less than 1 mol percent of C 5 + hydrocarbons and is split into a second solvent slipstream which is regenerated to form a part of said lean-and-dry solvent stream, the remaining portion of said stripped solvent stream being selectively combined with said lean-and-dry solvent stream from said regenerating.

Claim 25

The process of claim 1 or 12, wherein said inlet natural gas stream is selected from the group consisting of: A. natural gas saturated with water; B. natural gas at less than saturation with water; C. sour natural gas; D. sour natural gas which is pre-sweetened in gas phase with an aqueous amine solution; E. sweet natural gas; and F. dry natural gas.

Claim 26

The process of claim 23, wherein the volumes of said physical solvent streams for said extracting are determined by respective quantities of water, methane, nitrogen, C 2 -C 4 hydrocarbons, and C 5 + hydrocarbons, loading capacities of said physical solvent for the hydrocarbons to be extracted, and relative solubilities in said physical solvent of the C 1 + hydrocarbons with respect to nitrogen.

Claim 27

The process of claim 23, wherein said physical solvent is selective toward ethane and heavier hydrocarbon components of said inlet natural gas stream over methane, such that the relative volatility of methane over ethane is at least 5.0 and the hydrocarbon loading capacity, defined as solubility of ethane in solvent, is at least 0.25 standard cubic feet of ethane per gallon of solvent.

Claim 28

The process of claim 25, wherein said physical solvent is selected from the group consisting of dialkyl ethers of polyalkylene glycol, N-methyl pyrrolidone, dimethyl formamide, propylene carbonate, sulfolane, and glycol triacetate.

Claim 29

The process of claim 26, wherein said solvent is selected from the group consisting of dimethyl ether of polyethylene glycol, dimethyl ether of polypropylene glycol, dimethyl ether of tetramethylene glycol, and mixture thereof.

Claim 30

The process of claim 27, wherein said solvent is dimethyl ether of polyethylene glycol containing 3-10 ethylene units and having a molecular weight of 146 to 476.

Claim 31

The process of claim 12, wherein said selected flashing pressures of said successive flashing stages vary between 1300 psia and 2 psia.

Claim 32

The process of claim 12, wherein said bottoms temperature of said demethanizing is varied between 0° F. and 300° F.

Claim 33

In a process for treating a nitrogen-rich hydrocarbon gas stream containing more than 3 mol % nitrogen, the improvement which comprises contacting said gas stream with a physical solvent, which is selective toward ethane and heavier hydrocarbon components of said hydrocarbon gas stream over methane,such that the relative volatility of methane over ethane is at least 5.0 and the hydrocarbon loading capacity of said solvent, defined as solubility of ethane in solvent, is at least 0.25 standard cubic feet of ethane per gallon of solvent, said contacting being at solvent flow rates selectively varying between 0.001 and 0.5 gallon/SCF of solvent of said hydrocarbon gas stream, to produce a hydrocarbon gas product meeting desired nitrogen specifications.

Claim 34

In a process for treating a nitrogen-rich hydrocarbon gas stream containing more than 3 mol % nitrogen, the improvement which comprises contacting said gas stream with a physical solvent, which is selective toward ethane and heavier hydrocarbon components of said hydrocarbon gas stream over methane,such that the relative volatility of methane over ethane is at least 5.0 and the hydrocarbon loading capacity of said solvent, defined as solubility of ethane in solvent, is at least 0.25 standard cubic feet of ethane per gallon of solvent, said contacting being at solvent flow rates selectively varying between 0.001 and 0.5 gallon/SCF of solvent of said hydrocarbon gas stream, to produce a hydrocarbon gas product meeting desired nitrogen specifications.

Claim 35

The improved process of claim 31, wherein said contacting comprises: (1) contacting said hydrocarbon gas stream with a first stream of said physical solvent to extract substantailly all C 2 + hydrocarbons in a rich solvent stream and to produce a methane-rich residue gas stream and (2) contacting said methane-rich gas stream with a second stream of said physical solvent to extract substantially all of said methane in a methane-rich solvent stream and to produce a nitrogen stream.

Claim 36

The improved process of claim 32, wherein said hydrocarbon gas stream is a wellhead natural gas stream and said improved process is operable at the wellhead, whereby said hydrocarbon gas product is suitable for pipeline shipment.

Claim 37

The process of claim 31, wherein said physical solvent is selected from the group consisting of dialkyl ethers of polyalkylene glycol, N-methyl pyrrolidone, dimethyl formamide, propylene carbonate, sulfolane, and glycol triacetate.

Claim 38

The process of claim 34, wherein said physical solvent is selected from the group consisting of dimethyl ether of polyethylene glycol, dimethyl ether of polypropylene glycol, dimethyl ether of tetramethylene glycol, and mixtures thereof.

Claim 39

The process of claim 35, wherein said physical solvent is dimethyl ether of polyethylene glycol containing 3-10 ethylene units and having a molecualr weight of 146 to 476.