Method and system for purification of natural gas using membranes

Patent metadata

Field	Value
Publication number	US-2017157557-A1
Application number	US-201615367582-A
Country	US
Kind code	A1
Filing date	Dec 2, 2016
Priority date	Dec 3, 2015
Publication date	Jun 8, 2017
Grant date	—

Abstract

Natural gas may be purified by removing C 3+ hydrocarbons and CO 2 in respective one or more separation units to yield conditioned gas lower in C 3+ hydrocarbons and CO 2 in comparison to the un-conditioned natural gas. Notably, the feed gas need not be subjected to joule-thomson expansion and molecular sieve dehydration performed by conventional processes. Rather, any water-rich reject stream from the separation unit(s) is dried downstream with a smaller compressor and smaller molecular sieve or gas separation membrane dehydration unit before it may be re-injected deep underground or deep under the sea bed.

First claim

What is claimed is:

1 . A method for purification of natural gas including methane, CO 2 , water, and C 3+ hydrocarbons, comprising the steps of:
feeding a feed gas consisting of the natural gas to at least one separation unit;
withdrawing a dry conditioned natural gas from the at least one separation unit that is enriched in methane in comparison to the feed gas and deficient in C 3+ hydrocarbons, CO 2 , and water in comparison to the feed gas;
withdrawing one or more gaseous reject streams from the at least one separation unit, a totality of the one or more gaseous reject streams being enriched in deficient in C 3+ hydrocarbons, water, and CO 2 in comparison to the feed gas and deficient in methane in comparison to the feed gas;
compressing one of the gaseous reject streams so as to cause condensation of least some of the water contained therein produce a biphasic stream having liquid and gaseous phases; and
feeding the gaseous phase to a dehydration apparatus so as to remove at least some of the water contained therein and produce a stream of the dried gaseous phase.

2 . The method of claim 1 , wherein the feed gas is extracted from a subsea or subterranean oil or gas field and has not been dehydrated after extraction therefrom.

3 . The method of claim 2 , further comprising a step of injecting the stream of the dried gaseous phase into a subsea or subterranean oil or gas field.

4 . The method of claim 1 , wherein the dry conditioned natural gas meets pipeline specifications for natural gas or fuel specifications for natural gas-powered heavy equipment.

5 . The method of claim 1 , wherein the dry conditioned natural gas has a carbon dioxide concentration below 3% (vol/vol) and a C 3+ hydrocarbon dewpoint of no more than −20° C.

6 . The method of claim 1 , wherein the dried gaseous phase has a water content of no more than 2 ppm.

7 . The method of claim 1 , wherein the separation unit comprises first and second separation units and said method further comprises the steps of:
removing at least some water and C 3+ hydrocarbons from the feed gas at the first separation unit to provide a water-enriched and C 3+ hydrocarbons-enriched stream and a water-deficient and C 3+ hydrocarbons-deficient stream, wherein the one or more gaseous reject streams comprises first and second gaseous reject streams, the first gaseous reject stream being the water-enriched and C 3+ hydrocarbons-enriched stream; and removing at least some CO 2 from the water-deficient and C 3+ hydrocarbons-deficient stream at the second separation unit to provide the dry conditioned natural gas and the second gaseous reject stream.

8 . The method of claim 7 , wherein each of the first and second separation units comprises an adsorbent bed, at least one of the adsorbent beds exhibits adsorptive affinity for C 3+ hydrocarbons over methane, at least one of the adsorbent beds exhibits adsorptive affinity for water over methane, and at least one of the adsorbent beds exhibits adsorptive affinity for CO 2 over methane.

9 . The method of claim 7 , wherein the first and second separation units comprise first and second gas separation membrane units, respectively, the first gas separation membrane unit comprises one or more membranes in parallel or in series each of which has a selective layer that is selective for C 3+ hydrocarbons over methane and water over methane, and the second gas separation unit comprises one or more membranes in parallel or in series each of which has a selective layer that is selective for CO 2 over methane.

10 . The method of claim 9 , wherein the selective layer of each of the gas separation membranes of the first gas separation membrane unit comprises a polymer or copolymer including repeating units of a monomer selected from the group consisting of tetramethylene oxide, propylene oxide, and ethylene oxide.

11 . The method of claim 10 , wherein the polymer or copolymer comprises repeating units according to formula (I):

wherein:
PA is an aliphatic polyamide according to formula (II) or formula (III):

and
PE is selected from the group consisting of poly(ethylene oxide) and poly(tetramethylene oxide).

12 . The method of claim 10 , wherein the polymer or copolymer comprises copolymers obtained by copolymerization of acrylated monomers containing oligomeric propylene oxide, ethylene oxide, or tetramethyelene oxide.

13 . The method of claim 10 , wherein the polymer or copolymer comprises a copolymer copolymerized from the monomers according to formulae (IV) and (V):

where x+y=1.

14 . The method of claim 10 , wherein each of the gas separation membranes of the first gas separation membrane unit has a membrane productivity for methane of below 68 GPU (22.4 mol/m 2 ·sec·Pa). Often, it is below 34 GPU or even below 20 GPU.

15 . The method of claim 9 , wherein a pressure drop between the feed gas and the water-deficient and C 3+ hydrocarbons-deficient stream of the first gas separation membrane unit is less than 50 psi (3.45 bar).

16 . The method of claim 9 , wherein the selective layer is supported by a support layer comprising poly(ether ether ketone).

17 . The method of claim 1 , wherein the dehydration apparatus comprises a molecular sieve.

18 . The method of claim 1 , wherein the dehydration apparatus comprises a gas separation unit comprising one or more gas separation membranes that are selective for water over CO 2 and selective for water over C 3+ hydrocarbons.

19 . The method of claim 9 , wherein the selective layer of each of the gas separation membranes of the second gas separation membrane unit comprises a polymer or copolymer selected from the group consisting of polyimides, cellulose acetate and polysulfone.

20 . A system for purification of natural gas including methane, CO 2 , water, and C 3+ hydrocarbons, comprising:
a first gas separation unit comprising one or more gas separation membranes in parallel or in series each of which has a selective layer that is selective for C 3+ hydrocarbons over methane and water over methane, the first gas separation unit being adapted and configured to receive the natural gas and separate the natural gas into a water-enriched and C 3+ hydrocarbons-enriched stream and a water-deficient and C 3+ hydrocarbons-deficient stream;
a second gas separation unit comprising one or more gas separation membranes in parallel or in series each of which has a selective layer that is selective for CO 2 over methane, the second gas separation unit in downstream flow communication with the first gas separation unit and being adapted and configured to receive the water-deficient and C 3+ hydrocarbons-deficient stream and separate the water-deficient and C 3+ hydrocarbons-deficient stream into a dry conditioned natural gas and a dry CO 2 -enriched gaseous reject stream;
a compressor in downstream flow communication with the first gas separation unit, the compressor being adapted and configured to receive and compress the water-enriched and C 3+ hydrocarbons-enriched stream from the first gas separation unit and produce a biphasic water-enriched and C 3+ hydrocarbons-enriched stream;
a phase separator in downstream flo

Assignees

• Air Liquide Advanced Tech Us Llc

Inventors

• Ding Yong
• Karode Sandeep K

Classifications

• B01D2259/414

  using different types of adsorbents · CPC title

• B01D2256/24

  Hydrocarbons · CPC title

• B01D2257/80

  Water · CPC title

• B01D2257/7027

  Aromatic hydrocarbons · CPC title

• B01D53/22

  by diffusion (manufacturing semi-permeable membranes B01D67/00; form, structure or properties of semi-permeable membranes B01D69/00; material for semi-permeable membranes B01D71/00) · CPC title