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Process and system for carbon dioxide removal from natural gas

IP.com Disclosure Number: IPCOM000244593D
Publication Date: 2015-Dec-23

Publishing Venue

The IP.com Prior Art Database

Abstract

A process and system for removal of carbon dioxide (CO2) from natural gas using membranes is disclosed. The process comprises providing a separation unit (1) with a membrane (2) selectively permeable to carbon dioxide over methane (CH4), the membrane defining a permeate route (3) and a retentate route (4) through the separation unit (1); feeding a hydro carbonaceous (HC) stream (F) with a CO2 content through the separation unit (1), thereby obtaining a CO2-rich permeate (3a) and a CO2-lean retentate (4a) respectively; splitting the CO2-lean retentate into an export gas stream (4a) and a sweep gas stream (4b), and supplying the sweep gas stream (4b) to the permeate route (3) in the separation unit (1).

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279378A   

Process and system for carbon dioxide removal from natural gas

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a process and a system for reducing the concentration of carbon dioxide (CO2) in natural gas using membranes that are

selectively permeable to CO2 over other components in a hydro carbonaceous stream fed through the membrane.

BACKGROUND AND PRIOR ART

Natural gas fields produce hydro carbonaceous gas, especially methane CH4,

containing varying amounts of acidic contaminants such as carbon dioxide and hydrogen sulphide H2S. In natural gas streams carbon dioxide concentration may amount to levels ranging from a few percent to as much as 80 %. High amount of carbon dioxide in natural gas is unwanted and may lead to problems in subsequent processing and refinement of natural gas. Carbon dioxide is highly corrosive in

combination with water, and reduces the heating value in natural gas, e.g. in LNG (Liquefied Natural Gas) plants carbon dioxide must be removed down to a level of about 50 ppm by volume since higher concentration may cause formation of dry ice during liquefaction.

The overall ambition in processes and systems for CO2 removal is to generate an export stream of natural gas that is free or almost free from carbon dioxide and suited for LNG production or as pipeline gas. The CO2 rich residue from the separation process can be used for injection in an enhanced oil recovery (EOR) process.

Several methods and technologies are available for reducing the concentration of carbon dioxide in natural gas. Some of these methods include absorption processes by which the natural gas is subjected to hot potassium carbonate and amine solutions, cryogenic processes, adsorption processes such as pressure swing

adsorption or temperature swing adsorption.

The prior art also contains examples of carbon dioxide separation from natural gas using membranes, as well as integrated membrane and absorption systems. To illustrate the general state of the art and background to the present invention, a few

membrane based solutions for carbon dioxide separation from natural gas are mentioned below.

   

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US 8,192,524 B2 (Chevron U.S.A. Inc.) discloses a process and apparatus using a plurality of polymer membranes to provide a CO2-depleted product gas stream. A two-stage system is shown in which a hydrocarbon retentate from a downstream located membrane is returned to the hydro carbonaceous gas stream supplied to an upstream located membrane.

US 8,388,732 B2 (UOP LLC) discloses a floating liquefied natural gas (FLNG) system installed on a ship comprising membranes and a temperature swing adsorption unit from where a regenerated gas stream is returned and combined with the natural gas stream supplied to an upstream located membrane.

US 2011/0009684 A1 (Shell Oil Company) discloses a multi-stage membrane separation process wherein a hydrocarbon retentate fro...