Title of Invention

A PROCESS FOR PURIFYING A PRESSURIZED NATURAL GAS

Abstract

A process is described for purifying a pressurized natural gas which is saturated with water and contains hydrocarbons and hydrogen sulphide (H2S) from a producing well. At least a portion of the natural gas is brought into contact with at least a portion of recycled liquid condensate in a cyclone. The vapour phase containing H2S and hydrocarbons, is cooled in a zone, condensed and separated in a separator. A gas which is enriched in methane and depleted in H2S is recovered while the condensate is recycled to the cyclone after preheating if necessary. A water-containing liquid effluent which is enriched in H2S and depleted in hydrocarbons is recovered from' the bottom of the cyclone. This is reintroduced into the well.

Full Text

The invention concerns a process for the pretreatment of a very acidic natural gas containing a substantial quantity of hydrogen sulphide (H2S) which may be combined with carbon dioxide {CO2). Our European patent EP-B-0 362 023 describes this type of natural gas. A gas producer is faced with a dilemma when confronted with the need to treat a very acidic natural gas containing, for example, more than 20 mole % of hydrogen sulphide, especially as it is known that the gas production rate is over 2 million cubic meters per day and that production of sulphur cannot be justified economically. It is a question of how to eliminate a large quantity of hydrogen sulphide while complying with safety and environmental standards, and how to reduce the energy consumption involved in separating and eliminating hydrogen sulphide. Occasionally, hydrogen sulphide and carbon dioxide from a natural gas can be eliminated by reinvesting the recovered mixture into a reservoir which is partially exhausted, thus avoiding the need for a downstream sulphur recovery unit to be installed which is expensive and consumes a large amount of energy. In order to be able to sell a gas containing less than 3 ppm by volume of hydrogen sulphide, separation A second problem with the membrane permeation process derives from the fact that the membrane is not perfectly selective towards acidic gases and allows considerable diffusion of methane into the permeate. The loss of marketable methane can be as high as 10 % to 15 % of the feed introduced. One of the objects of the invention is thus to overcome the problems mentioned above. A further object is to preterit a natural gas which is very rich in H2S and CO2 to render it exploitable and marketable without damaging the environment. A further object of the invention is to dehydrate the gas and eliminate the majority of the acidic constituents in liquid form, into a partially exhausted reservoir. In general, the invention concerns a process for the pretreatment of a pressurized natural gas which is saturated with water and contains mainly hydrocarbons and a substantial quantity of hydrogen sulphide, from at least one producing well, characterized in that: a) at least a portion of the natural gas is brought into contact with at least a portion of a recycled liquid condensate from step d) below in a contact and vaporizing zone (5) under appropriate contact conditions, and a vapour phase containing hydrogen sulphide and hydrocarbons is recovered overhead and a liquid effluent containing a major portion of the hydrogen sulphide, water and a minor portion of hydrocarbons is recovered from the bottom; b) at least a portion of the vapour phase is cooled and condensed in a cooling or depressurising step under suitable cooling or depressurising conditions; c) the condensate obtained is separated in a separation zone and a gas which is enriched in hydrocarbons and depleted in hydrogen sulphide is recovered along with a liquid condensate which is enriched in hydrogen sulphide and contains hydrocarbons; d) said condensate is recycled to the contact zone, and e) the liquid effluent is reintroduced into said producing well or into a different well. The term hydrocarbons means mainly methane and small percentages of ethane, propane and butane. The acidic natural gas may have a partial pressure of hydrogen sulphide of at least 5 bar, preferably at least 10 bar (1 bar = 10^ Pa). It may also contain carbon dioxide. In order to achieve an effective flash in the contact zone (stripper) between the liquid condensate and the very acidic natural gas leaving the well, the condensate can be at least partially preheated by a heat exchanger to vaporize at least a portion of the 0We Claim: 1. A process for the pretreatment of a pressurized natural gas which is saturated with water and contains mainly hydrocarbons and a substantial quantity of hydrogen sulphide, from at least one producing well, characterised in that: a) at least a portion of the natural gas (1) is brought into contact with at least a portion of a recycled liquid condensate (2) from step d) below in a contact and vaporizing zone (5) under appropriate contact conditions, a vapour phase (6) containing hydrogen sulphide and hydrocarbons is recovered overhead and a liquid effluent (7) containing a major portion of the hydrogen sulphide, water and a minor portion of hydrocarbons is recovered from the bottom; b) at least a portion of the vapour phase is cooled and condensed in a cooling or depressurising step under suitable cooling or depressurising conditions; c) the condensate obtained is separated in a separation zone (3) and a gas (30) which is enriched in hydrocarbons and depleted in hydrogen sulphide is recovered along with a liquid condensate (2) which is enriched in hydrogen sulphide and contains hydrocarbons; d) said condensate is recycled to the contact zone (5), and e) the liquid effluent is reintroduced into said producing well or into a different well. 2. A process according to claim 1, wherein the condensate (2) is preheated at least in part by an external heat exchanger (2a). 3. A process according to claim 1 or claim 2, wherein the condensate is preheated by at least a portion of the vapour phase in a heat exchange zone (15). 4. A process according to any one of claims 1 to 3, wherein the condensate is recycled upstream of the contact zone (5). 5. A process according to any one of claims 1 to 4, wherein the vapour phase contains a substantial quantity of water and in which an appropriate quantity of methanol (11) is introduced upstream of the cooling zone. 6. A process according to claim 5, wherein the water and the methanol are separated from the condensate after condensing and recycled with the condensate (2). '. A process according to claim 5, wherein the water and the methanol are separated from the condensate after condensing and sent to a multi-stage stripping zone (22) using at least a portion of the vapour phase (23), and a methanol enriched effluent vapour (24) is recovered overhead which is recycled upstream of the cooling zone, water (25) being recovered from the bottom. !. A process according to any one of claims 1 to 7, wherein the operating conditions are as follows: a) Contact zone: T° = 0 to 100°C, preferably 20°C to 60*0, P > 10 bars absolute, preferably 40 to 100 bar; b) Zone for separation after cooling: T°C = -80°C to +30°C, preferably -40°C to 0°C, P > 10 bars, preferably 40 to 100 bar; c) Preheating temperature: -10°C to 90°C, preferably 10°C to 50°C. 9. A process according to any one of claims 1 to 8, wherein the contact zone is constituted by a cyclone separator. 10. A process according to any one of claims 1 to 9, wherein the pressurized natural gas has a partial pressure of hydrogen sulphide of at least 5 bar, preferably at least 10 bar.

Documents:

106-mas-95 abstract.pdf

106-mas-95 claims.pdf

106-mas-95 correspondence-others.pdf

106-mas-95 correspondence-po.pdf

106-mas-95 description (complete).pdf

106-mas-95 drawings.pdf

106-mas-95 form-1.pdf

106-mas-95 form-26.pdf

106-mas-95 form-4.pdf

106-mas-95 others document.pdf

106-mas-95 others.pdf