FR3090395A1 - PROCESS FOR TREATING A GAS STREAM IN DEEP WATER - Google Patents

Abstract

The present invention relates to a method for treating a gas flow in deep water, as well as a device for treating a gas flow in deep water.

Description

Description

Title of the invention: PROCESS FOR TREATING A GAS STREAM IN DEEP WATER

The present invention relates to a method for treating a gas flow in deep water, especially in deep sea water, as well as a device for the treatment of a gas flow in deep water, especially in water from deep sea.

Natural gas is today the third most used source of thermal energy in the world, accounting for around 22% of global energy consumption, after petroleum and coal. Its share in the energy mix is growing rapidly (it was only 16% in 1973), as is its world production.

Indeed, each year, new resources are brought to light, in particular because technological innovation makes it possible to push exploration further. Thus, almost two thirds of the natural gas newly discovered in recent years is buried in offshore reserves, which were previously unusable.

In this context, the natural gas deposits on the shelf and on the continental slope of the oceans are becoming increasingly important for the supply of energy.

Natural gas includes, in addition to methane, carbon dioxide, other heavier hydrocarbons at a variable rate, possibly hydrogen sulfide, and other contaminants that may require purification.

Carbon dioxide, without energy value, reduces the calorific value of natural gas, increases the compression and transport costs, and limits the economic benefit of its recovery to local use.

Hydrogen sulfide is toxic and bothersome.

[0008] Off-shore (deep ocean) natural gas processing technologies therefore constitute an important challenge for optimizing the exploitation of fossil resources.

The techniques conventionally used to remove CO ₂ from natural gas call for selective absorption in a chemical solvent (amine most often), associated with a regeneration step by steam stripping. The offshore gas treatment and / or CO ₂ capture units by washing, in particular with amines, include columns for absorption and regeneration of fluids, liquid or gaseous. The latter operate in counter-current or co-current gas / liquid flow and are installed on boats, floating barges or offshore platforms, for example of the FPSO type (from Floating Production, Storage and Offloading which means storage and unloading production platform), or of the FLNG type (from the English Floating Liquefied Natural Gas which means liquefied natural gas platform). However, these technologies cannot be used in the deep ocean. In addition, they require a regeneration step and consume energy.

A process has now been developed, in deep water, in particular in deep sea water, for a gas stream comprising at least methane and carbon dioxide, advantageously making it possible to remedy the aforementioned drawbacks.

This method also offers several advantages.

Firstly, the fact of carrying out a pre-treatment of the gas flow (raw natural gas) directly at the well outlet makes it possible to reduce the gas flow to be treated on the platform and to limit the operations to be carried out on it .

In addition, this pretreatment is done without rotating parts, without energy supply, without use or generation of chemicals (especially volatile, such as organic solvents), and without regeneration step. It is therefore economical, reliable, requires minimal maintenance due to its passive operation, and respects the environment. The corresponding device is compact, and therefore easily transportable.

The treatment method according to the invention can be carried out in steady state (continuous operation). It can be implemented at room temperature (that is to say about 4 ° C. at the bottom of the ocean), and under these conditions allows CO _{2 to be} eliminated, in particular, without prohibitive loss of methane.

The treatment method according to the invention allows an elimination of CO _{2 in} particular, by dissolution in water, so as to control the gas evolution eliminated in water, for example the turbulence generated in water, in particular sea water, around the pretreatment process.

Thus, according to a first aspect, the invention relates to a process for treating in deep water, in particular in deep sea water, a gas stream comprising at least methane, carbon dioxide and optionally hydrogen. sulfide, in which the gas flow is brought into contact, within a membrane module immersed in deep water, in particular in deep sea water, with at least one membrane separating the gas flow from water, said at least one membrane being impermeable to water while being more permeable to carbon dioxide and, where appropriate, to hydrogen sulphide than to methane, and in which the gas flow leaving the module is depleted in carbon dioxide and, where appropriate where appropriate, hydrogen sulfide.

According to a particular embodiment, the invention relates to a process for treating in deep water, in particular in deep sea water, a gas stream comprising at least methane and carbon dioxide, in which the gas stream is brought into contact, within a membrane module immersed in deep water, in particular in deep sea water, with at least one membrane separating the gas flow from water, said at least one membrane being impermeable to water while by being more permeable to carbon dioxide than to methane, and in which the gas flow leaving the module is depleted in carbon dioxide.

According to a particular embodiment, the invention relates to a process for the treatment in deep water, in particular in deep sea water, of a gas stream comprising at least methane, carbon dioxide and hydrogen sulfide, in which the gas flow is brought into contact, within a membrane module immersed in deep water, in particular in deep sea water, with at least one membrane separating the gas flow from water, said at least one membrane being impermeable to water while being more permeable to carbon dioxide and to hydrogen sulfide than to methane, and in which the gas flow leaving the module is depleted in carbon dioxide and in hydrogen sulfide.

According to a particular embodiment, the deep water is deep sea water.

According to a particular embodiment, the treated gas stream is a stream of natural gas.

According to a particular embodiment, the gas flow is devoid of oxygen.

The contact between the at least one membrane of the membrane module can for example be ensured within a membrane module of the commercial type, in which is made direct contact with water, in particular sea water , exterior. By “direct contact”, it is meant in particular that the water, in particular sea water, outside, is in contact with the at least one membrane by the fact of the immersion of the module in water, without it is necessary to circulate the water, for example using a pump, so that this water is in contact with the membrane.

This direct contact can in particular be provided within a module whose housing is pierced with a plurality of holes. Drilling holes in the protective casing of a commercial type membrane module allows contacting as defined above.

In particular, seawater in contact with the at least one circulating membrane does not circulate by means of a pump, in particular thermal or electric.

According to a particular embodiment, the water in contact with the at least one membrane circulates by natural convection.

According to a particular embodiment, the membrane module further comprises one or more means of evacuation of part of the gas flow, this evacuation taking place in the membrane module itself or at the entrance of said module.

According to a particular embodiment, the at least one membrane being in the form of a plurality of hollow fibers and the or the discharge means are one or more porous fibers, in particular closed at their upper end.

In this case, these porous fibers can in particular allow bubbling in seawater in contact with said hollow fibers of a fraction of the gas flow. The gas bubbles thus formed circulate outside the bundle of hollow fibers, in seawater in contact with said hollow fibers. This allows convection on the surface of the membrane, and can therefore promote the dissolution of carbon dioxide, and where appropriate hydrogen sulfide, in water.

In particular, and in particular in the context defined in the two preceding paragraphs, a fraction of the gas flow, in particular from 0.01 to 1% by volume of the gas flow, in particular approximately 0.1% by volume , is released into water on contact with at least one membrane.

According to a particular embodiment, the selectivity of the at least one membrane with respect to carbon dioxide with respect to methane is from 15 to 200, in particular from 30 to 100, this selectivity being in particular d 'around 60.

According to a particular embodiment, the selectivity of the at least one membrane with respect to hydrogen sulfide with respect to methane is from 15 to 200, in particular from 30 to 100, this selectivity being in particular approximately 6O. In particular, the membrane has a carbon dioxide permeability greater than 10, in particular between 50 and 500 GPU (Gas Permeance Unit).

In particular, the membrane has a permeability to hydrogen sulfide greater than 10, in particular between 50 and 500 GPU.

In addition, the membrane has a methane permeability less than or equal to 10 GPU, in particular between 0.1 and 10 GPU, in particular from 0.1 to 1 GPU.

According to a particular embodiment, the at least one membrane is in one of the following forms: planar, tubular, hollow fiber, in the form of a spiral.

According to a particular embodiment, the at least one membrane is a dense membrane.

According to a particular embodiment, the material of the at least one membrane is chosen from: cellulosic polymers, polyamides, polyimides, polydimethylsiloxanes (PDMS), polymethylpentenes (PMP), fluorinated polymers including Teflon -AF, polysulfones.

According to a particular embodiment, the membrane module is chosen from gas permeation modules, reverse osmosis modules and gas-liquid membrane contactors, in particular with dense skin, in particular contactors of which the at least one membrane is of the composite or self-supporting type with dense skin.

According to a particular advantageous embodiment, the membrane module is a gas permeation module, the at least one membrane being in the form of a plurality of hollow fibers, the material of which is chosen from losu cellu5 polymers, polyamides and polyimides.

According to another particular advantageous embodiment, the membrane module is a reverse osmosis module, the at least one membrane being in the form of a spiral, the material of which is chosen from cellulosic polymers, polyamides and polyimides

According to a particular advantageous embodiment, the membrane module is a gas-liquid membrane contactor with dense skin, the at least one membrane being in the form of a plurality of hollow fibers formed by or comprising dense skin, possibly in contact with a material chosen from polydimethylsiloxanes (PDMS), polymethylpentenes (PMP), Teflon-AF, fluorinated polymers.

This dense skin can be of the same nature as said material in contact (support). This is called an asymmetric membrane.

Alternatively, this dense skin can be of a different nature from said material in contact (support). This is called a composite membrane.

According to a particular embodiment, the membrane module has an interfacial area of between 500 and 10,000 m ² / m ³ .

According to a particular embodiment, the flow rate of the gas flow is from 0.1 to 10 Nm ³ .s ¹ .

According to a particular embodiment the speed of the gas flow is between approximately 0.01m.s ¹ to approximately 5 ms', in particular approximately 0.05m.s ¹ to approximately 1 ms -1

According to a particular embodiment, the pressure of the gas flow is from 1 to 150 Bar, in particular from 10 to 100 Bar, the pressure being in particular around 50 Bar.

According to another aspect, the invention also relates to a device for the treatment in deep water, in particular in deep sea water, of a gas stream comprising at least methane, carbon dioxide and optionally hydrogen sulfurized, said device comprising a membrane module immersed in deep water, in particular in deep sea water, said module comprising at least one membrane separating the gas flow from water, said at least one membrane being impermeable to water while being more permeable to carbon dioxide and, where appropriate, to hydrogen sulfide than to methane.

It should be noted that all of the embodiments defined above with regard to the method can be applied to the device, alone or in combination.

In particular, seawater in contact with the at least one membrane does not circulate by means of a pump, in particular a thermal or electric pump.

Definitions

As used in the present description, the term "approximately" refers to a range of values of ± 10% of a specific value. By way of example, the expression “approximately 120 mg” includes the values of 120 mg ± 10%, that is to say the values of 108 mg to 132 mg.

Within the meaning of the present description, the percentages refer to percentages by volume relative to the total volume of the gas flow, unless otherwise indicated.

As understood here, the value ranges in the form of "xy" or "from x to y" or "between x and y" include the terminals x and y as well as the integers between these terminals . By way of example, “1-5”, or “from 1 to 5” or “between 1 and 5” denote the integers 1, 2, 3, 4 and 5. The preferred embodiments include each integer taken individually in the value range, as well as any sub-combination of these integers. For example, preferred values for "1-5" may include the integers 1, 2, 3, 4, 5, 1-2, 1-3, 1-4, 1-5, 2-3, 2 -4, 2-5, etc.

By "deep water" is meant in particular the water of the seas, oceans and lakes situated at a depth greater than or equal to 200 m, in particular greater than or equal to 300 m, for example at a greater depth. or equal to 500 m from sea level (or ocean, or lake).

By “deep sea water” is meant in particular the water of the seas and oceans lying at a depth greater than or equal to 200 m, in particular greater than or equal to 300 m, for example at a depth greater than or equal to 500 m from sea level (or ocean level), in particular in contact with the continental shelf or slope.

The deep sea water is located in particular at a depth relative to sea level (or the ocean) of between 200, 300 or 500 m to 5000 m, in particular from 200, 300 or 500 m to 4000 m , in particular from 200, 300 or 500 m to 3000 m.

The pressure (total) at such depths can be calculated as follows: [Math.l]

Ptot. = p · g h + Psurface

With: the height (or depth) h, the density of the sea water p, the acceleration of gravity g, the atmospheric pressure at the surface Psurface.

Thus, every 10 meters deep, the water pressure increases by one atmosphere (1 atm ~ 1 bar). In deep sea water as defined above, at a depth relative to sea level (or the ocean) of 200, 300 or 500 m to 5000 m, the pressure range is comprised of 21, 31 or 51 to 501 atm.

By "waterproof membrane" is meant a membrane whose permeability to water, in particular to sea water, is less than 500 Barrer.

The gas flow being generally saturated with water, the driving force leading to the passage of water, in particular sea water, in the gas compartment may be low in the context of the invention.

By “depleted in carbon dioxide” is meant in particular that the molar fraction of carbon dioxide in the gas flow at the outlet of the membrane module is lower than that at the inlet of the membrane module, the volume content of dioxide carbon of the gas flow at the outlet of the membrane module being notably less than or equal to 20%, more particularly comprised from 2 to 20%, or less than or equal to 2%.

By "natural convection" is meant in particular all the movements (vertical and / or horizontal) which animate the sea water in contact with the at least one membrane. This convection is notably linked to the heat exchange between the at least one membrane and the seawater in contact with it. Indeed, the membrane is generally at a temperature higher than that of sea water in contact with it, because this membrane is itself in contact with the gas flow whose temperature is higher than that of sea water.

In particular, the term "natural convection" excludes causes independent of temperature differences and of the gas flow itself, in particular the use of means operating with energy not related to temperature differences and to the gas flow itself, such as for example pumps, in particular thermal or electric.

Thus, in particular, the sea water in contact with the at least one membrane does not circulate by means of a pump, in particular thermal or electric.

In contrast, according to one embodiment, a fraction of the gas flow is released into seawater on contact with the at least one membrane. In this case, to the natural convection linked to the heat exchange between the at least one membrane and the seawater in contact with it, is added all the movements created by the displacement of the gas bubbles in the sea water from said fraction of the gas stream.

By "released into seawater in contact with the at least one membrane" is meant in particular that the fraction of the gas flow allows all or part of the seawater to be put into motion in contact with the at least one membrane.

By "cellulosic polymers" is meant in particular cellulose esters, in particular cellulose acetates, and cellulose ethers,

By "fluoropolymers", or fluoropolymers, is meant polymers in which the or one of the repeating units is a fluorocarbon. This or these repeating units include in particular one or more strong carbon-fluorine bonds.

The fluoropolymer is in particular a polytetrafluoroethylene (known in particular under the brand Teflon from DuPont), in particular an amorphous polytetrafluoroethylene (known in particular under the name Teflon-AF from DuPont).

By "dense membrane" is meant in particular membranes which no longer have any free porosity.

By "dense skin" means a physical barrier included in or constituting the at least one membrane. In particular, dense skin limits the flow of water, especially seawater, in the membrane. The thin thickness of the dense skin (in particular from about 1 pm to about 2 pm) makes it possible to limit the resistance to material transfer.

In particular, the dense skin is a dense skin of poly [1- (trimethylsilyl) -l-propyne] (PTMSP), of Teflon-AE, in particular of Teflon AE2400, or of poly (phenylene oxide) (PPO) .

By "oxygen-free" is meant that the gas stream comprises less than 1% by volume of oxygen, in particular less than 0.1% by volume of oxygen, in particular less than 0.01% by volume of dioxygen.

Brief description of the drawings

[Fig.l]

Ligure 1 relates to a particular embodiment in which the gas flow to be treated (11) circulates through a contactor, inside a plurality of dense fibers (13) to come out treated (12). The contactor further comprises one or more porous fibers (14), closed at their upper end for diffusion / bubbling in seawater in contact with the fibers (13) of a fraction of the gas flow (11). [Fig.2]

Ligure 2 relates to a particular embodiment in which the gas flow to be treated circulates through a contactor, inside a plurality of dense gas permeation fibers (23) to come out treated (22). The dense fibers (23) leave a dissolving flux (25) of carbon dioxide, and possibly hydrogen sulfide, as well as trace methane. The contactor further comprises one or more porous fibers (24), closed at their upper end for diffusion / bubbling in seawater in contact with the fibers (23) of a fraction of the incoming gas flow The gas bubbles thus formed (26) circulate outside the bundle of permeation fibers, in seawater.

[Fig.3]

Ligure 3 illustrates the evolution of the composition of the gas phase in a selective dense membrane contactor (polyimide, selectivity CO2 / CH4 = 60) for dissolution of CO2 in seawater in the deep ocean. The curves indicate the content (% vol) of CO2 and CH4 for different gas speeds in the module, from left to right 0.05; 0.1; 0.2; 0.5; 1.0 m. s-1.

[Fig.4]

Ligure 4 illustrates the evolution of the composition of the gas phase in a selective dense membrane contactor (polyimide, selectivity CO2 / CH4 = 60) for dissolution of CO2 in seawater in the deep ocean. The curves show the losses (in%) of CO2 and CH4 for different gas speeds in the module, from left to right 0.05; 0.1; 0.2; 0.5; 1.0 m. s-1.

EXAMPLE

Natural gas processing

Natural gas, of the deep ocean offshore type, and with the following properties:

- pressure: P = 50 Bar;

- temperature: T = 60 ° C;

- composition (by volume): CO ₂ , 30%; CH ₄ , 70%;

Is treated as follows.

Equipment and dissolution medium

The equipment used is a dense membrane contactor, with the following characteristics:

- length: 3m;

- polyimide type membrane, with CO ₂ / CH ₄ selectivity = 60, in particular the commercial Evonik membrane, devoid of casing;

- fibers with an internal diameter of 100 µm, and a thickness of 10 µm;

- material transfer coefficient: 10 ⁵ ms'.

The dissolution medium is as follows:

- seawater, with low turbulence and bubbling application, for example using porous fibers as described above;

- temperature: T = 5 ° C;

- material transfer coefficient: 10 ⁴ ms'.

Procedure

[0085] The evolution of the treated gas stream composition (content of residual CH ₄ and loss of CH ₄₎ is reported for different speeds of the inlet gas of the contactor.

Results

The results obtained are as follows:

- selective purification (progressive drop in the CO ₂ content in the mixture) is observed (Figure 3);

- excellent purification of natural gas (CH ₄ > 98% at the output of the contactor) is obtained, associated with a CH ₄ loss rate of less than 5% (Figure 4).

Claims (1)

Claims [Claim 1] Process for deep water treatment of a gas stream comprising at least methane, carbon dioxide and optionally hydrogen sulfide, in which the gas stream is brought into contact, within a membrane module immersed in deep water , with at least one membrane separating the gas flow from the water, said at least one membrane being impermeable to water while being more permeable to carbon dioxide than to methane and, where appropriate, more permeable to hydrogen sulfide than methane, and in which the gas stream leaving the module is depleted in carbon dioxide and, where appropriate, in hydrogen sulfide. [Claim 2] The method of claim 1, wherein the water in contact with the at least one membrane circulates by natural convection. [Claim 3] Method according to any one of the preceding claims, in which the membrane module further comprises means for evacuating part of the gas flow, this evacuation taking place in the membrane module itself or at the inlet of said module. [Claim 4] Method according to any one of the preceding claims, in which a fraction of the gas flow, in particular from 0.01 to 1% by volume of the gas flow, is released into water in contact with the at least one membrane. [Claim 5] Process according to any one of the preceding claims, in which the selectivity of the at least one membrane with respect to carbon dioxide with respect to methane is from 15 to 200, in particular from 30 to 100, this selectivity being especially around 60. [Claim 6] Method according to any one of the preceding claims, in which the at least one membrane is in one of the following forms: planar, tubular, hollow fiber, in the form of a spiral. [Claim 7] Method according to any one of the preceding claims, in which the material of the at least one membrane is chosen from: cellulosic polymers, polyamides, polyimides, polydimethylsiloxanes (PDMS), polymethylpentenes (PMP), Teflon-AF , fluorinated polymers, polysulfones. [Claim 8] Method according to any one of the preceding claims, in which the membrane module is chosen from gas permeation modules, reverse osmosis modules and gas-liquid membrane contactors, in particular with dense skin. [Claim 9] Method according to any one of the preceding claims, in which the membrane module has an interfacial area of between 500 and 10,000 m ² / m ³ . [Claim 10] Device for deep water treatment of a gas stream comprising at least methane, carbon dioxide and optionally hydrogen sulfide, said device comprising a membrane module immersed in deep water, said module comprising at least one membrane separating the gas flow of water, said at least one membrane being impermeable to water while being more permeable to carbon dioxide and, where appropriate, to hydrogen sulphide than to methane. 1/3