EP2379970A1

EP2379970A1 - Co2 recovery method using cryo-condensation

Info

Publication number: EP2379970A1
Application number: EP09803850A
Authority: EP
Inventors: Frédérick LOCKWOOD; Alain Ravex; Jean-Pierre Tranier; Claire Weber
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2008-12-19
Filing date: 2009-12-14
Publication date: 2011-10-26
Also published as: CN102317726A; FR2940413B1; EP2379199A1; EP2379971A1; CN102317207A; US20110252827A1; CN102326044B; FR2940413A1; EP2379971B1; WO2010070226A1; WO2010076467A1; US20110296868A1; WO2010076466A1; US20110302955A1; CN102326044A

Abstract

Disclosed is a method for producing at least one gas having a low CO₂ concentration and one or more primary fluids having a high CO₂ concentration from a fluid which is to be treated and contains CO₂ and at least one compound that is more volatile than CO₂. Said method comprises the following steps: a) the fluid to be treated is subjected to a first cooling process using heat exchange without the fluid undergoing a change of state; b) at least some of the fluid to be treated and cooled in step a) is cooled a second time such that a solid is obtained which contains mainly CO₂ and at least the gas having a low CO₂ concentration; and c) a step in which at least some of said solid is liquefied and/or sublimed such that the one or more primary fluids having a high CO₂ concentration are obtained. The disclosed method is characterized in that at least some of the cold required for the first cooling process and/or the second cooling process is supplied by one or more refrigeration cycles, each of which includes at least one quasi isentropic expansion of a gas.

Description

Process for capturing CO2 by cryo-condensation

The present invention relates to a process for capturing carbon dioxide in a fluid comprising at least one more volatile compound than CO2 carbon dioxide, for example methane CH4, oxygen O2, argon Ar, nitrogen N2, carbon monoxide CO, helium He and / or hydrogen H2.

The invention can be applied in particular to electricity production units and / or steam from carbonaceous fuels such as coal, hydrocarbons (natural gas, fuel, petroleum residues ...), household waste, biomass but also to gases from refineries, chemical factories, steel factories or cement factories, to the processing of natural gas at the output of production wells. It could also apply to the fumes of boilers used for heating buildings or even the exhaust of transport vehicles, more generally to any industrial process generating fumes including CO2.

Carbon dioxide is a greenhouse gas. For environmental and / or economic reasons, it is increasingly desirable to reduce or even eliminate CO ₂ emissions into the atmosphere, by capturing it and then, for example, storing it in appropriate geological layers or enhancing it. as a product.

A number of techniques are known for capturing carbon dioxide, for example processes based on washing fluids with solutions of compounds that separate the CO2 by chemical reaction, for example washing with MEA. These methods typically have the following disadvantages:

high energy consumption (related to the regeneration of the compound that reacts with CO2), degradation of the compound reacting with carbon dioxide, corrosion due to the carbon dioxide-reactive compound.

In the field of cryo-condensation, ie cooling until the appearance of solid CO2, let us mention the document FR-A-2820052 which discloses a process for extracting CO2 by anti-sublimation, c ie solidification from a gas without passage through the liquid state. The necessary cold is provided by means of fractional distillation of refrigerants. This process is very energy intensive.

The document FR-A-2894838 discloses the same type of process, with a recycling of a portion of the liquid CO2 produced. Cold can be provided by spraying LNG (natural gas liquefied). This synergy reduces the specific energy consumption of the process, which nevertheless remains high, and requires an LNG terminal.

US-A-3614872 discloses a separation process wherein the adiabatic and isentropic expansion of carbon dioxide provides a coolant.

An object of the present invention is to provide an improved method of capturing carbon dioxide from a fluid comprising CO2 and at least one more volatile compound than this.

The invention firstly relates to a process for producing at least one CO2-poor gas and one or more CO2-rich primary fluids from a fluid to be treated comprising CO2 and at least one more volatile compound than CO2, implementing: a) a first cooling of said fluid to be treated by heat exchange without change of state; b) a second cooling of at least a portion of said fluid to be treated cooled in step a) so as to obtain at least one solid comprising mainly CO2 and at least said CO2-poor gas; and c) a step comprising liquefying and / or sublimating at least a portion of said solid and making it possible to obtain said one or more primary fluids rich in CO2; said method being characterized in that at least a portion of the cold necessary to effect said first cooling and / or said second cooling is provided by one or more refrigerating cycles each comprising at least one substantially isentropic expansion of a gas.

The fluid to be treated generally comes from a boiler or any installation producing smoke. These fumes may have undergone several pre-treatments, in particular to remove NOx (nitrogen oxides), dust, SOx (sulfur oxides) and / or water.

Before separation, the fluid to be treated is either monophasic, in gaseous or liquid form, or multiphase. By "gaseous" form is meant "essentially gaseous", that is to say it may contain especially dust, solid particles such as soot and / or droplets of liquid.

The fluid to be treated contains CO2 which it is desired to separate by cryo-condensation from the other constituents of said fluid. These other constituents comprise at least one or more compounds which are more volatile than carbon dioxide in the sense of condensation, for example methane CH4, oxygen O2, argon Ar, nitrogen N2, carbon monoxide CO, Helium He and / or H2 hydrogen. The fluids to be treated generally comprise mainly nitrogen, or mainly CO or predominantly hydrogen.

In step a) the fluid to be treated is first cooled without changing state. This cooling can advantageously be done at least partly by heat exchange with fluids rich in CO2 from the separation process. Complementarily or alternatively, it can advantageously be done at least partly by heat exchange with the CO2-poor gas from the separation process. These cold fluids from the separation are heated, while the fluid to be treated is cooled. This reduces the amount of energy required for the cooling operation.

Step b) consists in solidifying initially gaseous CO2 by bringing the fluid to be treated to a temperature below the triple point of CO2, whereas the partial pressure of the CO2 in the fluid to be treated is lower than that of the triple point of CO2. . For example, the total pressure of the fluid to be treated is close to atmospheric pressure. This solidification operation is sometimes called

"Cryo-condensation" or "anti-sublimation" of CO2 and by extension of the fluid to be treated.

According to a particular embodiment, all the components of the fluid to be treated which do not solidify in step a), or are not solidified with solid CO2, remain in the gaseous state. They constitute the gas that is low in CO2.

Some compounds more volatile than CO2 do not solidify and remain in a gaseous state. With non-solidified CO2, they will constitute said CO2-poor gas, that is to say comprising less than 50% of CO2 by volume and preferably less than 10% CO2 by volume. According to one particular embodiment, said CO2-poor gas comprises more than 1% of CO2 by volume. According to another particular mode, it comprises more than 2%. According to another particular mode, it comprises more than 5%. A solid is formed comprising predominantly CO2, ie at least 90% by volume brought back to the gaseous state, preferably at least 95% by volume and even more preferably at least 99% of CO2 by volume.

This solid may comprise other compounds than CO2. There may be mentioned, for example, other compounds which would also have solidified, or else bubbles and / or drops of fluid taken in mass in said solid. This explains why the solid may not be purely constituted of solid CO2. This "solid" may comprise non-solid parts such as fluid inclusions (drops, bubbles, etc.). This solid is then isolated from the non-solidified compounds after the cryo-condensation and recovered. Then, in step c), it is brought back to conditions of temperature and pressure such that it changes to a fluid, liquid and / or gaseous state. It can therefore occur liquefaction of at least a portion of said solid. This gives rise to one or more primary fluids rich in CO2. These fluids are said to be "primary" to distinguish them from process fluids that are called "secondary" fluids. By "rich in CO2" is meant "comprising predominantly CO2" in the sense defined above.

The inventors have shown that it is particularly advantageous to carry out the first and / or the second cooling of the fluid to be treated by means of one or more refrigerating cycles each comprising at least one almost isentropic expansion of a gas. These refrigerating cycles consist of several steps that pass a fluid called "working" by several physical states characterized by given conditions of composition, temperature, pressure ... The presence, among the stages of the cycle, of at least one almost isentropic expansion, ie increasing the entropy of the fluid expanded by less than 25%, preferentially less than 15% and even more preferably less than 10%, makes it possible to improve the energy consumption of the separation process . By convention, the entropy is taken zero at a temperature of zero K (kelvin).

Depending on the case, the method according to the invention may comprise one or more of the following characteristics:

said refrigerating cycles each comprising at least one quasi-isentropic expansion using working fluids chosen from the following:

an auxiliary fluid comprising nitrogen and / or argon and / or a mixture of gases of the air;

a fluid comprising all or part of said CO2-poor gas or derived from all or part of said CO2-poor gas; and or

a fluid comprising all or part of said fluid to be treated or derived from all or part of said fluid to be treated.

at least part of the cold necessary to carry out said second cooling is provided by exchange with:

the working fluid of one of said refrigerating cycles each comprising at least one quasi-isentropic expansion; an auxiliary fluid comprising nitrogen and / or argon and / or a mixture of gases of the air;

a fluid comprising all or part of said CO2-poor gas or derived from all or part of said CO2-poor gas; and or a fluid comprising all or part of said fluid to be treated or derived from all or part of said fluid to be treated.

at least part of the cold necessary to carry out said second cooling is provided by direct exchange.

at least one of said refrigerating cycles each comprising at least one quasi-isentropic expansion uses all or part of said fluid to be treated as working fluid.

at least one of said refrigerating cycles each comprising at least one quasi-isentropic expansion comprises at least one quasi-isentropic expansion providing external work.

the method further comprises a step d) of heating at least one of said CO2-rich primary fluids and / or of said CO2-poor gas by cold compression and / or by heat exchange with an auxiliary fluid. This auxiliary fluid may be the fluid to be treated.

said virtually isentropic expansion of at least one of said refrigerating cycles each comprising at least one quasi-isentropic expansion comprises one or more of the following steps:

- Rotating the fluid to be treated about an axis substantially parallel to the flow direction of said fluid to be treated;

- Speeding the fluid to be treated;

- Separation of solid CO2 from the fluid to be treated by centrifugal effect;

- Deceleration of the gas depleted in CO2.

in step b), cooling of at least a portion of said treated fluid cooled in step a) is carried out so as to obtain moreover a liquid mainly comprising CO 2.

said fluid to be treated comes from industrial fumes.

said fluid to be treated comes from a steel plant.

said fluid to be treated comes at least partially from a blast furnace.

said CO2-poor gas is recycled at least partially in said blast furnace.

said fluid to be treated comes at least partially from a refinery and / or a chemical plant. said fluid to be treated comes at least partially from the gasification and / or partial oxidation and / or oxygen reforming of a given carbon fuel.

said fluid to be treated comes from an installation comprising an air separation unit.

said quasi-isentropic expansion of at least one of said refrigerating cycles each comprising at least one quasi-isentropic expansion of a gas is carried out in said air separation unit.

a part of the cold necessary to carry out said first cooling and / or said second cooling is provided by at least one refrigeration cycle comprising a non-quasi-isentropic expansion of a fluid.

said at least one quasi-isentropic expansion providing external work provides a work at least partially used to compress a fluid of said production process.

To provide another part of the cold necessary to achieve the first and / or second cooling, one can use one or more cycles comprising a non-isentropic expansion of a fluid, for example inverted Rankine cycles. They are said to be inverted because used in refrigerating cycles. Their interest, as a complement to refrigeration cycles with almost isentropic expansion, is not to require a large amount of working fluid. On the other hand, they are less energy efficient.

According to one embodiment, some of the quasi-isentropic detents of the refrigerating cycle or cycles provide work. They are for example made by introducing the working fluid into a turbine.

Working fluids can be of different natures. According to different embodiments, these fluids may comprise nitrogen and / or argon. They may also include all or part of the CO2-poor gas obtained or the fluid to be treated. These fluids can be mixed with other fluids or have undergone intermediate stages of compression, relaxation, etc.

When the working fluid of the refrigerating cycle comprises all or part of the fluid to be treated, the almost isentropic expansion (s) without providing external work can give rise to a cooling of the working fluid such that solid CO2 appears. This may constitute all or part of the second cooling of the fluid to be treated. According to a particular embodiment, these quasi-isentropic detents are performed through a Venturi (a Venturi effect collar). The rotation of the fluid of which it question above can be obtained by any conventional means, for example by appropriately oriented fins. Speeding is done by the Venturi effect. The temperature of the working fluid drops. Solid particles of CO2 appear. The fluid has a rotational movement about an axis substantially parallel to the direction of flow, such as a spin. This creates a centrifugal effect making it possible to recover these solid particles at the periphery of the flow.

According to a preferred embodiment, the work possibly produced by the quasi-isentropic expansion (s) serves in part to compress fluids in other steps of the process.

The invention also relates to the process applied to industrial fumes for the purpose of capturing CO2.

According to one particular mode, these fumes come from a production plant

(steam, electricity) and may have undergone pre-treatments.

Other particularities and advantages will appear on reading the following description, made with reference to the figures in which:

FIG. 1 diagrammatically represents an installation implementing a method for purifying CO2 according to the invention, with a refrigerating cycle implementing an auxiliary fluid as a working fluid,

FIG. 2 diagrammatically represents a part of an installation implementing a variant of this process, with a refrigeration cycle using the CO2-poor gas as working fluid and comprising an almost isentropic expansion with production of work,

FIG. 3 diagrammatically represents a part of an installation implementing another variant of this process, with a refrigerating cycle using the CO2-poor gas as working fluid and comprising a quasi-isentropic expansion with production of work, FIG. 4 schematically represents a part of an installation implementing a variant of the process with a refrigerating cycle using the fluid to be treated as a working fluid and comprising a quasi isentropic expansion with production of work, during which there is no cryo -condensation of CO2,

FIG. 5 diagrammatically represents a part of an installation implementing a variant of the process with a refrigerating cycle using the fluid to be treated as working fluid and comprising a quasi-isentropic expansion with production of work, during which there is cryogenic CO2 condensation, FIG. 6 schematically represents a part of an installation implementing a variant of the process with a refrigerating cycle using the fluid to be treated as a working fluid and comprising a virtually isentropic expansion without production of work, during which there is cryogenic condensation of CO2, - Figure 7 schematically represents a part of an installation implementing a variant of the process, wherein the second cooling also comprises liquefaction, and further comprising a refrigerant cycle using the fluid to be treated as a working fluid and comprising quasi-isentropic relaxation without production during which there is cryo-condensation of CO2. - Figure 8 shows schematically the use of a method according to the invention in a coal-based power generation plant with combustion in air.

- Figure 9 schematically shows the use of a method according to the invention in a coal-based power generation plant with mixed combustion or oxygen.

FIG. 10 schematically represents the use of a method according to the invention in a steel plant.

FIG. 11 schematically represents the use of a method according to the invention in an installation for the production of synthesis gas operating with oxygen;

FIG. 12 schematically represents the use of a process according to the invention in an installation for producing carbon monoxide from a synthesis gas originating from a steam reforming of a synthesis gas.

FIG. 13 schematically represents the use of a process according to the invention with, on the one hand, a cycle of production of energy using the cold of the melting of solid CO2 and, on the other hand, additional purifications by distillation of the less volatile compounds than CO2, then more volatile compounds than CO2 - Figures 14 and 15 show a turbine for achieving a virtually isentropic expansion of the fluid to be treated with production of external work according to the invention.

The installation illustrated in FIG. 1 implements the steps described below.

The fluid 24 consisting of fumes is compressed in a compressor 101, in particular to compensate for the pressure losses in the various equipment of the installation. Note that this compression can also be combined with the so-called draw compression of the boiler giving rise to smoke. It can also be carried out between other stages of the process, or downstream of the CO2 separation process;

The compressed fluid 30 is injected into a filter 103 to remove the particles to a concentration level of less than 1 mg / m ³ , preferably less than 100 μg / m ³ .

Then, the dust-free fluid 32 is cooled to a temperature close to 0 ^° C., generally between 0 ^° C. and 10 ^° C., so as to condense the water vapor that it contains. This cooling is carried out in a tower 105, with two-level water injection, cold water 36 and water at temperature close to ambient 34. Indirect contact can also be considered. Tower 105 may or may not have packings.

The fluid 38 is sent to a residual water vapor removal unit 107, using, for example, one and / or the other of the following methods: adsorption on fixed beds, fluidized beds and / or rotary drier, the adsorbent may be activated alumina, silica gel or a molecular sieve (3A, 4A, 5A, 13X, ...); Condensation in a direct or indirect contact exchanger.

The dried fluid 40 is then introduced into the exchanger 109 where the fluid is cooled to a close temperature, but in any case, greater than the solidification temperature of the CO2. This can be determined by those skilled in the art knowing the pressure and the composition of the fluid 40 to be treated. The latter is located at about -100 ⁰ C if the CO2 content of the fluid to be treated is of the order of 15% by volume and a near atmospheric pressure.

The fluid 42 having undergone a first cooling 109 is then introduced into a chamber 111 to continue cooling to the temperature which provides the desired CO2 capture rate. A cryo-condensation of at least a portion of the CO2 contained in the fluid 42 occurs, so as to produce on the one hand a gas 44 depleted of CO2 and on the other hand a solid 62 comprising mainly CO2. The gas 44 leaves the enclosure 111 at a temperature of the order of -12O ⁰ C. This temperature is chosen according to the target CO2 capture rate. With this temperature, the CO2 content in the gas 44 is of the order of 1.5% by volume, ie a capture rate of 90% starting from a fluid to be treated comprising 15% CO 2.

Several technologies can be envisaged for this enclosure 111:

- Continuous solid cryo-condensation exchanger in which solid CO2 is produced in the form of dry ice, which is extracted for example by a screw and is pressurized to introduce it into a liquid CO2 bath 121, where there is a pressure greater than that of the triple point of CO2. This pressurization can also be performed in batches in a silo system. Continuous solid cryo-condensation can itself be carried out in several ways:

- Exchanger with scraped surface, the scrapers being for example in the form of screws so as to promote the extraction of the solid;

- Exchanger fluidized bed so as to cause dry ice and clean the tubes by particles for example of higher density than that of dry ice;

- Exchanger with extraction of solid by vibrations, ultrasound, pneumatic or thermal effect (intermittent heating so as to fall the dry ice); - Accumulation on a smooth surface, with a periodic "natural" drop in a tray;

Solid batch cryo-condensation (or "batch" in English): in this case, several exchangers in parallel can be used alternately. Then they are isolated, pressurized to a higher pressure than the triple point of CO2, so as to liquefy the solid CO2 and possibly partially vaporize it.

The fluid 46 is then reheated in the exchanger 109. At the outlet, the fluid 48 may also be used in particular to regenerate the residual vapor removal unit 107 and / or to produce cold water 36 by evaporation in a tower with direct contact 1 15 where a dry fluid is introduced

50 which will saturate with water by vaporizing a part. Optionally, the cold water may be further cooled in a refrigeration unit 119.

The solid 62 comprising predominantly CO2 is transferred to a liquid CO2 bath 121. This bath 121 must be heated to remain liquid, to compensate for the cold input by the solid 62 (latent heat of fusion and sensible heat). This can be done in different ways:

- By heat exchange with a fluid 72 hotter. The frigories of the fluid 74 can be used elsewhere in the process by direct exchange, for example by taking a fluid 80 from the bath 121, by heating it in the exchanger 109 and re-injecting it into the bath 121.

Liquid 64 comprising mainly CO2 is taken from the bath 121. This liquid is divided into three streams. In the example, the first is obtained by an expansion 65 to 5.5 bar absolute producing a two-phase fluid, gas-liquid, 66. The second, 68, is obtained by compression 67, for example at 10 bar. The third, 70, is compressed for example at 55 bar. The 5.5 bar level brings cold to a temperature close to that of the triple point of CO2. The level at 10 bar allows the transfer of the latent heat of vaporization of the fluid 68 at about -40 ^° C. Finally, at 55 bar, the fluid 70 does not vaporize during the exchange 109. This allows a good valuation of the frigories contained in the fluid 64 during the exchange 109 while limiting the energy required to produce a stream of purified and compressed CO2 5.

Part of the cold required for the first cooling 109 and the second cooling 11 1 is provided by a refrigerating cycle 200 implementing a working fluid

51 which is argon. It comprises successively: a compression 129, possibly two compressions 56 and 57, a cooling by indirect exchange 109, a quasi isentropic relaxation

131 which induces a cooling, a heating in the enclosure 111, a warming 109. During the cooling 109, a portion of the working fluid is removed, then undergoes a near isentropic expansion 130, then an indirect exchange 109 and finally a compression 128 to join the compression 129. The quasi-isentropic relaxers 130 and 131 provide a work of which a part serves for the compressions 56 and 57.

This cycle 200 produces cold between about -100 and -12O ⁰ C for cryo-condensation 111 and between about 5 ⁰ C and -100 ⁰ C to overcome the deficit of cold during the exchange 109. Another part of the cold required for the first cooling 109 is provided by an additional refrigerant cycle 181, 183, for example of the inverted Rankine type.

Another part of the cold necessary for the second cooling 111 is provided by an additional refrigerant cycle 191, 193 for example of the inverted Rankine type. After the indirect exchange 109, the CO2-rich primary fluids 66, 68, 70 are stagedly compressed 141, 142, 143. For example, the first stages compress gas streams. If necessary, the compressed CO2 75 is cooled by an indirect contact exchanger to be liquid. Then it is mixed with the stream 73. This liquid mixture is pumped to the transport pressure (fluid 5). Since the transport pressure is generally supercritical, supercritical fluids are considered to be supercritical fluids at a temperature lower than that of the critical point of CO2.

In FIGS. 2 to 7, which represent examples in accordance with particular embodiments of the invention, the steps relating to the fluid to be treated before its first cooling 109 and the compression of the primary fluids are not shown. After the heat exchange, the CO2 content is high. 109. Only that which is different from FIG. 1 is shown, and which essentially concerns the refrigerating cycles bringing cold to the exchanges 109 and 111.

FIG. 2 illustrates a variant of the quasi-isentropic expansion with production of work, where the working fluid is the CO2-poor gas 44. The cryo-condensation process is the same as in FIG. 1. Only the modifications are detailed herein. -Dessous.

The CO2-poor gas 44 is compressed for example by a stage compressor 315. At the outlet, the fluid 303 is cooled, if necessary, to the inlet temperature of the exchanger 109 via the exchanger 316. It may be in direct contact with or indirect.

The compressed CO2-poor gas 304 is cooled in the exchanger 109 to be able to be expanded in the turbine 312 (virtually isentropic expansion), in order to supply a part of the cold necessary for the exchange 111. The fluid 307 leaving the exchanger 1 11 is relaxed again

(Nearly isentropic expansion) to provide work and cold for the exchanger 111 via the fluid 308. This expansion loop of the CO2-poor gas can be repeated as many times as necessary.

After the exchanger 11, the CO2-poor gas 46 is heated in the exchanger 109. The outgoing fluid 48 is treated as the fluid 48 of FIG.

Part of the cold necessary for the exchanger 11 may be provided by a Rankine-type refrigerant cycle 191, 193.

Figure 3 illustrates another variant of the quasi-isentropic expansion with work output. The CO2-poor gas 44 gives up these frigories in the exchangers 111 and 109. It is then compressed by the compressor 415 stage. Then it is cooled if necessary to the inlet temperature of the exchanger 109 in the exchanger 416. This may be direct or indirect contact. The CO2-poor gas 404 is again cooled in the exchanger 109 before being expanded by the turbine 412. This quasi-isentropic turbine produces the cold necessary to compensate for part of the deficiency of frigories of the exchanger 111.

Then, the fluid 407 is again expanded by the quasi-isentropic turbine 414. The fluid 408 gives up its frigories to compensate for a part of the deficit of frigories of the exchanger 111. This expansion loop of the CO2-poor gas can be repeated as many times as before. times as necessary.

After the exchanger 11, the CO2-poor gas 46 is heated in the exchanger 109. Finally, the outgoing fluid 48 is treated as the fluid 48 of FIG.

FIG. 4 illustrates another variant of the quasi-isentropic expansion with production of work.

The fluid to be treated 40 is compressed by the compressor 512 which can be floor. The CO2-poor gas is expanded in a near isentropic turbine 514. The temperature of the fluid 503 must remain above the cryo-condensation temperature of the CO2.

A portion of the CO2 contained in the fluid 503 then condenses in the enclosure 111. The solid CO2 62 is poured into the liquid bath 121 and the following steps are the same as those described in FIG. 1 (from the bath 121 and stream 64). The CO2-poor gas 44 transmits its frigories to exchangers 111 and 109. Outgoing fluid 48 is treated as fluid 48 of FIG.

FIG. 5 illustrates another variant of the quasi-isentropic relaxation with production of work, in which the working fluid is the fluid to be treated.

An almost isentropic expansion is achieved with the production of fluid 42 working in the turbine 612 in order to cool the fluid to a temperature below the cryocondensation temperature of CO 2 and thus produce solid CO 2, in the form of dry ice, and a gas depleted in CO2 602.

This 612 expansion turbine must be designed with great care. It must be adapted to large flows such as those of fumes 40 of an industrial plant, have a very good isentropic efficiency, and resist the possible additional erosion due to the presence of solid CO2. To do this, the presence of dry ice in the rotor part of the turbine (zone between the leading edge 951 and the trailing edge 954 in FIGS. 14 and 15 is forbidden, or prohibited, or in the stator part 960 upstream of the rotor part (zone upstream of the trailing edge of the stator vanes 950), it must be minimized so as not to erode the leading edge of the vanes 952 of the rotor part. In other words, it is preferably that the CO2 is in the vapor or supersaturated vapor state in the stator part, or that it has carbon dioxide nuclei sufficiently small to prevent erosion of the rotor part (less than 10 μm, preferably 1 μm of hydraulic diameter).

The turbine may be radial (centripetal or centrifugal). It can be supersonic shock wave. It can be axial.

This last technology is best suited to large flows, but it requires many successive stator and rotor stages. To avoid erosion, it will be preferable to separate the dry ice downstream of each rotor stage, before the entry of the fluid into the next stator stage. The first two technologies have the advantage of remaining effective for high relaxation rates (greater than 10), so they avoid having to perform multiple separations.

Furthermore, other precautions should preferably be taken to achieve such a turbine: to minimize heterogeneous nucleation (on the stator and rotor surfaces), for example by heating some of these surfaces or by applying special coatings; delay nucleation by removing less volatile compounds than CO2 (including solid particles) before entering the turbine, so that they are not nuclei that promote solid CO2 nucleation; increase the erosion resistance of surfaces by the use of stronger metals, such as titanium or a special coating or surface treatment; in the case of the centripetal radial turbine, it is preferable to circulate a flushing gas in the back of the wheel 953. This gas mixes with the expanded gas at the interface between the stator part (blades) and the rotor part ( wheel). Thus, it avoids the formation and accumulation of solid back wheel. Then this carbon dioxide snow is separated from the CO2-depleted gas in a separator

612 to obtain a solid comprising mainly CO2 62 and a gas low in CO2 44.

This separation can be done downstream of the rotor part by using the rotation of the fluid in the rotor part as well as the centrifugal effect to separate a fraction rich in CO2 at the periphery of a fraction depleted of CO2 in the center. It may also be interesting to realize a setting speed and thus additional relaxation of the fluid in a convergent 956 (so-called Laval turbine). By decreasing the pressure before deceleration of the gas, this makes it possible to increase the amount of solidified CO2. Most of the CO2-poor gas is recovered at the center of the 959 flow and the bulk of the solid CO2 at the periphery 958 is mixed with a gas fraction. The interest of a turbine to achieve solid cryo-condensation is to generate a lot of solid CO2 in a very small volume compared to indirect exchange systems.

If necessary, an additional refrigerant cycle 191, 193 of the Rankine type or comprising a quasi isentropic expansion of a working fluid with or without production of work brings cold to the separator 612. The solid comprising predominantly CO2 62 is poured into the liquid bath 121 and the following steps are the same as those shown in Figure 1.

The CO2-poor gas 44 is heated by heat exchange with the fluid to be treated in the exchanger 109. The fluid 605 is then compressed at a pressure greater than or equal to atmospheric pressure. Finally, the outgoing fluid 48 is treated as in FIG.

FIG. 6 illustrates an embodiment with almost isentropic expansion without production of work. The fluid to be treated 42 is still cooled below the cryocondensation temperature of the CO2 in the enclosure 111 to produce a CO2-depleted gas 701 and cooled. It is also possible to place this chamber after the "relaxation / Venturi" portion 702 of the process, which will now be described.

Part of the CO2 to be captured has solidified in the form of a solid containing mainly CO2 62 and is extracted from the chamber 1 11. To improve the capture of CO2, the fluid 701 is rotated around a axis substantially parallel to the direction of its flow by a system of fixed vanes 717.

The fluid 703 is expanded at the outlet of the fins and cools below the cryo-condensation temperature of the CO2 without producing work. The expansion can be effected by the Venturi effect by passing the fluid into a restriction 718. Solid particles comprising predominantly CO2 are formed and are recovered at the periphery of the flow due to the centrifugal effect induced by the rotation of the fluid.

A 705 mixture of solid comprising mainly CO2 and gas is recovered. The incondensables 44, 46 outgoing yield their frigories in the heat exchangers 111 and 109. The stream 705 is composed mainly of solid, however it may be necessary to separate the residual gas from the solid in a separator pot 731. The incondensable part then yields its frigories in the exchangers 11 1 and 109.

The solid comprising predominantly CO2 62 is poured into the liquid bath 121 and undergoes the same steps as those described in Figure 1. The flows 48 are used to cool the water, in the same way as the stream 50 of Figure 1 .

FIG. 7 illustrates another embodiment with almost isentropic expansion without production of work. The fluid to be treated 40 is under pressure, for example up to 60 bar (compression performed by the compressor 101 or by an additional compressor). It is possibly more concentrated in CO2 than in the other examples, typically between 50 and 90% by volume. The exchange 809 has the same characteristics as the exchange 109 of Figure 1. The exchanger 811 cools the fluid to be treated 42 at a temperature below the liquefaction temperature of CO2. A cooled process fluid 801 is outputted to a separator pot 812. A CO2-rich liquid 816 is extracted by the separator 812. The residual fluid 802 is rotated about an axis substantially parallel to the direction of its flow. flow through a system of fixed fins 817. It is relaxed output 803 fins after its rotation and cools below the cryo-condensation temperature of CO2 without producing work. The expansion can be effected by Venturi effect by passing the fluid in a restriction 818.

Solid particles comprising predominantly CO2 are formed and are recovered at the periphery of the flow due to the centrifugal effect induced by the rotation of the fluid. The stream 805 is composed mainly of solid, however it may be necessary to separate the residual gas from the solid in a separator pot 841. The incondensables 44 yield their frigories in the exchangers 811 and 809.

To improve the CO2 capture rate, it is possible to add a second (or even a third or more) almost isentropic expansion stage of the fluid 806 with Venturi effect. This step is identical to the previous one: the fluid 806 is rotated about an axis substantially parallel to the flow direction by a fixed fin system 807; after being set in rotation, the fluid at the outlet of the fins 808 is expanded to cool it below the cryo-condensation temperature of the CO 2 without production of work. The expansion can be effected by the Venturi effect by passing the fluid in a restriction 822.

The solid 62 comprising mainly CO2 recovered at the outlet of separator pots 841 and possibly 851 is poured into the liquid bath 121 and treated as in FIG. 1. Fluxes 48 are used to cool the water, in the same manner as the flow. 50 of Figure 1.

FIG. 8 represents a coal-based electricity generation installation, implementing various purification units 4, 5, 6 and 7 of the fumes 19. A primary air flow 15 passes through the unit 3 where the coal 15 is sprayed and driven to the burners of the boiler 1. A secondary air flow 16 is provided directly to the burners to provide additional oxygen necessary for near-complete combustion of the coal. Supply water 17 is sent to the boiler 1 to produce steam 18 which is expanded in a turbine 8. The fumes 19 from the combustion, comprising nitrogen, CO2, steam water and other impurities, undergo several treatments to remove some of said impurities. Unit 4 removes NOx for example by catalysis in the presence of ammonia. The unit 5 removes the dust for example by electrostatic filter and the unit 6 is a system of desulfurization to remove SO2 and / or SO3. Units 4 and 6 may be redundant depending on the composition of the required product. The purified flow 24 from unit 6 (or 5 if 6 is not present) is sent to a low temperature purification unit 7 by cryo-condensation to produce a relatively pure CO2 flow rate 26 and a residual flow rate. enriched in nitrogen. This unit 7 is also called a CO2 capture unit and implements the method that is the subject of the invention, as illustrated, for example, by FIGS. 1 to 7.

FIG. 9 represents a coal-based electricity generation installation, implementing different purification units 5 and 7 of the fumes 19. A primary air flow 15 passes through the unit 3, where the coal 15 is sprayed. and fed to the burners of the boiler 1. A secondary oxidant flow 16 is provided directly to the burners to provide additional oxygen necessary for near-complete combustion of the coal. This secondary oxidant results from the mixture of recirculated fumes 94 using a fan 91 and oxygen 90 produced by an air gas separation unit 10. Feed water 17 is sent to the boiler 1 for producing steam 18, which is expanded in a turbine 8.

The fumes 19 from the combustion of coal, including nitrogen, CO2, water vapor and other impurities, undergo several treatments to remove some of said impurities. Unit 5 (ESP) removes dust, for example by means of an electrostatic filter. The de-dusted flow 24 from the unit 5 is sent to a low temperature purification unit 7, by cryo-condensation, to produce a relatively pure CO2 flow rate and a nitrogen-enriched residual flow rate. This unit 7 is also called a CO2 capture unit and implements the method that is the subject of the invention, as illustrated, for example, by FIGS. 1 to 7. In this case, the presence of a unit is used. separating the gases from the air to provide low level refrigeration for the solid cryo-condensation of the CO 2 in the unit 7 and carry out a cryocondensation, preferably by direct exchange with the gas to be treated. The fluid 93 may be in liquid, gaseous or two-phase form and consists of a mixture of cooled air gases. For example, it may be air or cold nitrogen gas (between -56 ⁰ C and -196 ⁰ C), or air or liquid nitrogen. It is intended to be introduced into the enclosure referenced 1 11 in FIGS. 1 to 4 and in FIG. 6, 612 in FIG. 5, 731 in FIG. 6 and finally 841, 851 in FIG.

The unit 7 can also produce a fluid 92 that will be used in the air separation unit. It may for example be a fraction of the lean gas leaving the enclosure 11 1 of FIGS. 1 to 4 and 6, 612 of FIG. 5, 731 of FIG. 7 and 841, 851 of FIG. This lean gas, in a way, returns cold to the unit 10 at a higher temperature level than that brought from the unit 10 by the fluid 93.

It is advantageous to vary the flow rate of this fluid injection 93 over time. For example, liquid nitrogen can be produced and stored at night, when the energy is available and inexpensive, and inject the liquid nitrogen during the day so as to reduce the energy consumed. The moment when the cold is produced by the unit 10 (for example liquid nitrogen) and when it is used in the unit 7 is dissociated. In this case, the quasi-isentropic expansion of a gas can be carried out in the unit 10 rather than in unit 7. This scheme may be well suited to cases of modification of existing plants, where the replacement of the primary air sent to the carbon sprays by a mixture of recycled fumes plus oxygen may be revealed complex, on the one hand because of the increase in water content, fumes containing much more than moist air, on the other hand for security reasons, although this should not be overestimated. Moreover, it may be advantageous to combine the units 7 and 10 into one, in particular by performing one (or more) exchange (s) of heat between fluids of the two units.

Figure 10 shows schematically the use of a method according to the invention in a steel plant. An air separation unit 10 supplies oxygen 90 to a blast furnace 900 into which iron ore 901 and carbon products 902 (coal and coke) are additionally introduced. The blast furnace works in this case in the presence of very little nitrogen.

The blast furnace gases 903 composed for example of 47% CO, 36% CO 2, 8% N 2 and 9% other compounds such as H 2 and H 2 O can be divided in half. Most of the 905 goes to the CO2 capture unit, another part 904 serves to deconcentrate the nitrogen content in the loop. The fluid 905 is previously cooled in a direct contact heat exchanger 906, dedusted in the filter 103, then compressed by a compressor 901, cooled in a heat exchanger 105 and dried in a dryer 107, before entering the heat exchanger at low temperature 109, where it will be cooled and then partially liquefied at a temperature close to the triple point of CO2 without solid formation. The two-phase gas-liquid fluid 912 obtained is separated into a gaseous fraction 502 and a liquid fraction 920 in the separator 928. The gaseous fraction 502 is then cooled by a quasi-isentropic expansion, for example in a turbine 514, so as to obtain a two-phase gas-solid fluid 503. This is separated in the chamber 111 into a gas fraction 44 and a solid fraction 62 rich in CO2. The solid fraction 62 is compressed for example by a worm and mixed with the liquid 920 in the bath 121, which is heated by gas 72 produced by the vaporization of the liquid 74 in the exchanger 109. The liquid CO2 64 is compressed by a pump 69 so as to obtain a pressurized liquid 70 and heated in the exchanger 109 without undergoing vaporization, or pseudo-vaporization if the pressure is greater than the supercritical pressure. The lean gas is successively heated by a compressor 315 and the exchanger 109. The invention can also be adapted for blast furnace types operating with enriched air, for example by adding a CO / N2 separation by cryogenic distillation. by cooling the gas 44 to the necessary temperature. FIG. 11 schematically represents the use of a process according to the invention in an installation for the production of synthesis gas from an oxygen process

(partial oxidation, gasification, auto-thermal reformer, etc.). An air gas separation unit 10 supplies oxygen 90 to a reactor 900 into which a carbon product 902 (coal, natural gas, biomass, household waste, etc.) is introduced.

The synthesis gas 903 mainly comprises the compounds CO, CO2, H2 and H2O. CO can be converted (so-called shift reaction) into CO2 and H2 in the presence of water vapor: CO + H2O <-> CO2 + H2. The fluid 905 may optionally be dedusted in a filter 103, then compressed by a compressor 101, cooled in an exchanger 105 and dried in a dryer 107, before entering the low temperature heat exchanger 109, where it may be partially liquefied at a temperature close to that of the triple point of CO2. This two-phase gas-liquid fluid 912 is separated into a gaseous fraction 502 and a liquid fraction 920 in the separator 928. The gaseous fraction 502 is then cooled by a quasi-isentropic expansion, for example in a turbine 514, so as to obtain a gas-solid two-phase flow 503. This is separated into a gaseous fraction 44 and a CO2-rich solid fraction 62 in the enclosure 111. The solid fraction 62 is mixed with the liquid 920 in the bath 121, which is heated with water. gas 74 produced by the vaporization of the liquid 72 in the exchanger 109. The liquid CO2 64 is compressed by a pump and heated in the exchanger 109 without undergoing vaporization, or pseudo-vaporization if the pressure is greater than the supercritical pressure . The lean gas 44 is successively heated by a compressor 924 and the exchanger 109. This lean gas consists essentially of hydrogen can be sent to a gas turbine to achieve combustion without CO2 emissions. The unit 10 can supply hot nitrogen 90a, which will be introduced downstream of the dryers 910, and / or cold nitrogen 90b introduced directly into the chamber 111 to increase the amount of CO2 captured. In the first case, the expansion in the turbine 514 of the hot nitrogen present in the flow 502 provides additional cooling for the solid cryo-condensation of the CO2 in the turbine 514; in the second case, the cold nitrogen 90b, by heating in contact with the fluid 503, generates the solid cryo-condensation of CO2. The other advantage of the hot nitrogen 90a is to increase the molecular weight of the gas 502, which may be advantageous for reducing the cost of the expansion 514 and / or the compression 924. Indeed, when these gases are very rich in hydrogen, it is not easy to compress / relax these gases with the most suitable technologies for large flows namely axial type technologies, radial or supersonic shock wave. It is then necessary to use volumetric type technologies such as piston or screw very expensive to implement.

Figure 12 shows schematically the use of a process according to the invention in a synthesis gas production facility from a steam reforming. Carbonaceous product 902 (natural gas, methanol, naphtha, etc.) is introduced into a reactor 900. The synthesis gas 903 produced in the reactor 900 mainly comprises the compounds CO, CO2, H2 and H2O. The fluid 905 can optionally be compressed by a compressor 101, cooled in an exchanger 105 and dried in a dryer 107, before entering a low temperature heat exchanger 109, where it can be partially liquefied at a temperature close to that of the point. triple CO2. The two-phase gas-liquid fluid 912 obtained is separated into a gaseous fraction 502 and a liquid fraction 920 in the separator 928. The gaseous fraction 502 is then cooled by a quasi-isentropic expansion, for example in a turbine 514, so as to obtain a gas-solid two-phase 503. This is separated into a gaseous fraction 44 and a CO2-rich solid fraction 62 in the chamber 111. The solid fraction 62 is mixed with the liquid 920 in the bath 121, which is heated with water. gas 74 produced by the vaporization of the liquid 72 in the exchanger 109. The liquid CO2 64 is compressed by a pump and heated in the exchanger 109 without undergoing vaporization, or pseudo-vaporization if the pressure is greater than the supercritical pressure . The lean gas 44 can then be purified to CO2 at low temperature for example by adsorption with a 13X molecular sieve before being introduced into a cryogenic unit 924 for the production of CO. This works for example by washing with methane or partial condensation of CO. This unit 924 produces a hydrogen enriched gas 929 and a CO 925 enriched gas. One or more fluids of this unit can be compressed at low temperature and then reintroduced into the heat exchanger 926.

In this case, the solid cryo-condensation replaces an elimination of CO2 by absorption with amines (MDEA or MEA). If it is desired to produce pure hydrogen, it is possible to add a PSA H2 in this scheme either upstream of this purification by solid cryo- condensation that is to say at the outlet of the reformer 900 after cooling of the synthesis gas, or on the gas rich in H2 929.

One might think that these processes of solid cryo-condensation are in deficit of cold. In fact, it is not so. On the contrary, these solid cryo-condensation processes with almost isentropic expansion of the gas to be treated produce too much cold, especially if the process also provides external work. The problem is that the CO2-rich fluids and the CO2-poor gas come out at low temperatures, which is a significant energy loss. To minimize the energy consumption of this process, one or more of the following operations can be carried out: internally: o cold compression of one of the fluids of the cryo-condensation process:

- gas to be treated that is cooled at low temperature before compression; • CO2-poor gas that is compressed at low temperature (see Figure 2). It can either be relaxed again or compressed under vacuum to bring it back to atmospheric pressure, or relax after heating in the hot part of the process that produced the gas to be treated; o indirect solid cryo-condensation in an exchanger; externally: o cold compression of any fluid of the installation; o production of liquid nitrogen and / or liquid air; o transcritical Rankine cycle on CO2

FIG. 13 schematically represents the use of a process according to the invention implementing a transcritical Rankine cycle on CO2. It also includes the characteristics of a process in which a liquid cryo-condensation is successively carried out, then a solid cryo- condensation and where the purity of the CO2 produced by two distillation columns is improved, one to eliminate the components less volatile than CO2 (NO2 or N2O4, SO2, ...) and another to eliminate the more volatile components.

The fluid 24 consists of fumes and may be at a temperature of the order of 150 ^° C. It is injected into a filter 103 to remove the particles to a concentration level of less than 1 mg / m ³ , preferably less than 1 mg / m ^3. 100 μg / m ³ . The dust-free fluid 30 is cooled to a temperature close to 0 ^° C., generally between 0 ^° C. and 100 ^° C., so as to condense the water vapor that it contains. This cooling is performed in a tower 105b, with two-level water injection, cold water 36b and water at a temperature close to the humid temperature of the ambient air 34b. One can also consider an indirect contact. Tower 105 may or may not have packings. This tower can also serve as a SO2 scrubber. At the outlet of this first tower, the optionally desaturated fluid is compressed at a pressure between 5 and 50 bar abs in the compressor 101. The fluid 32 is cooled to a temperature close to 0 ^° C., generally between 0 ^° C. and 10 ^° C. ⁰ C, so as to condense the water vapor that it contains. This cooling is performed in a tower 105, with two-level water injection, cold water 36 and water at a temperature close to the humid temperature of the ambient air 34. It is also possible to envisage indirect contact. Tower 105 may or may not have packings.

The fluid 38 is sent to a residual water vapor removal unit 107, using, for example, one and / or the other of the following methods:

Adsorption on fixed beds, fluidized beds and / or rotary dryer, the adsorbent may be activated alumina, silica gel or a molecular sieve (3A, 4A, 5A, 13X, ...); - Condensation in a heat exchanger with direct or indirect contact.

The fluid to be treated 40 is cooled and then contacted in a distillation column 79 with pure CO2, so as to recover the less volatile compounds that the CO2 in the form of a liquid containing CO2 and for example NO2 ( or its dimer N2O4). This liquid can be pumped and vaporized in the unit 78, then sent either into a combustion chamber to reduce the NO 2, or into the purification unit of the flow by low pressure washing of the SO 2, to serve as reagent either directly as NO2 or as nitric acid after reaction with water. The fluid to be treated 74a is then cooled and partially condensed in liquid form and sent to the separator 76. The liquid fraction 76a is sent to the bath 121. The gaseous fraction 76b is sent to an expansion turbine so as to produce a two-phase flow therein. gas-solid 42 which is sent into the chamber 111 to be separated between a CO2-poor gas 44 and solid CO2 62. An auxiliary fluid 93 for example from an air separation unit can possibly provide additional cooling for solid cryo-condensation. In this case, it may be advantageous to take from the CO2-poor gas 44 a fluid 92 which returns to the unit which supplied the fluid 93. The solid 62 is compressed for example by a worm and injected into the bath liquid CO2 121, from which a liquid 64 is taken. This liquid can optionally be pumped and introduced into a distillation column 75 to remove more volatile compounds than CO2. The pure liquid 68 is heated without vaporization, or pseudo-vaporization if it is supercritical. It can be pumped again to obtain the fluid ready for transport. Part of the fluid 5 can be removed for vaporization, or pseudo-vaporization, in a unit 72. This unit 72 is for example any source of heat from the plant producing the fluid to be treated. This portion of the fluid 80 is then expanded in a turbine 73 used to produce electricity or mechanical power, then cooled in the exchanger 109 and condensed by direct exchange in the bath 121, while carrying out the melting of the solid CO2 .

At the outlet of the exchanger 109, the fluid 48 may also serve in particular to regenerate the residual vapor removal unit 107 and / or to produce cold water 36a by evaporation in a direct contact tower 115 where the a dry fluid 50 is introduced which will saturate with water by vaporizing a part. Optionally, the cold water can undergo additional cooling in a refrigeration unit 1 19. Then, this cold water can be used in one and / or the other of the towers 105 and 105b so as to cool the gas to be treated before and / or after compression.

Figures 14 and 15 show a turbine for performing a virtually isentropic expansion of the fluid to be treated with production of external work according to the invention. The upstream stator portion 960 begins with the volute (not shown) and then with vanes 950 which can be fixed or variable. Then returns to the rotor portion 960 which comprises for example fins 952 with a leading edge 951 where begins the rotor portion 960 and a trailing edge 954 where it ends.

Downstream of the rotor part, if it is not desired to use the centrifugal force on the solid parts, the rotor part may consist of a simple deceleration cone. If it is desired to use the downstream stator part 961 to achieve a first separation, it is possible to use the rotation of the fluid in the rotor part as well as the centrifugal effect to separate a fraction rich in CO2 at the periphery of a depleted fraction. CO2 in the center. It may also be interesting to realize a speed setting and therefore an additional relaxation of the fluid in a convergent 956 (turbine called "Laval"). By decreasing the pressure before deceleration of the gas, this makes it possible to increase the amount of solidified CO2. Most of the CO2-poor gas is recovered center of flow 959 and the bulk of solid CO2 at the periphery 958 mixed with a fraction of gas.

Claims

A process for producing at least one CO2-poor gas (44) and one or more CO2-rich primary fluids (66, 68, 70) from a process fluid (40) comprising CO2 and at least one more volatile compound than CO2, implementing: a) a first cooling (109) of said fluid to be treated (40) by heat exchange without change of state; b) a second cooling (111) of at least a portion of said fluid to be treated (42) cooled in step a) so as to obtain at least one solid (62) comprising predominantly CO2 and at least said gas poor in CO2 (44); and c) a step comprising liquefying and / or subliming at least a portion of said solid (62) and obtaining said one or more CO2-rich primary fluids (66, 68, 70); said method being characterized in that at least a portion of the cold required to effect said first cooling (109) and / or said second cooling (11) is provided by one or more refrigerating cycles (200) each comprising at least one expansion isentropic (130, 131, 612) of a gas.

2. Method according to claim 1, characterized in that said refrigerating cycles (200) each comprising at least one quasi-isentropic expansion (130, 131, 312, 314, 412, 414, 514,

612) use working fluids selected from among the following:

an auxiliary fluid (51) comprising nitrogen and / or argon and / or a mixture of gases of air;

a fluid comprising all or part of said CO2-poor gas (44) or derived from all or part of said CO2-poor gas (44); and / or a fluid comprising all or part of said fluid to be treated (40) or derived from all or part of said fluid to be treated (40).

3. Method according to any one of claims 1 or 2, characterized in that at least a portion of the cold necessary to achieve said second cooling (111) is provided by exchange with: the working fluid of one of said refrigerating cycles (200) each comprising at least one substantially isentropic expansion (130, 131, 312, 314, 412, 414, 514, 612); an auxiliary fluid (51) comprising nitrogen and / or argon and / or a mixture of air gases; a fluid comprising all or part of said CO2-poor gas (44) or derived from all or part of said CO2-poor gas (44); and / or a fluid comprising all or part of said fluid to be treated (40) or derived from all or part of said fluid to be treated (40).

4. Method according to claim 3, characterized in that at least a portion of the cold necessary to achieve said second cooling (1 11) is provided by direct exchange.

5. Method according to claim 2, characterized in that at least one of said refrigerating cycles (200) each comprising at least one substantially isentropic expansion (131, 131, 612) implements all or part of said fluid to be treated (40). ) as working fluid.

6. Method according to any one of claims 1 to 5, characterized in that at least one of said refrigerating cycles (200) each comprising at least one quasi-isentropic expansion (130,

131, 312, 314, 412, 414, 514, 612) comprises at least one substantially isentropic expansion (130, 131, 312, 314, 412, 414, 514, 612) providing an external work.

7. Method according to claim 6, characterized in that it further comprises a step d) of heating at least one of said primary fluids rich in CO2 (66, 68, 70) and / or said CO2-poor gas ( 44) by cold compression (315) and / or by heat exchange with an auxiliary fluid (191)

8. The method of claim 5, characterized in that said substantially isentropic expansion (702) of at least one of said refrigerating cycles (200) each comprising at least one substantially isentropic expansion (131, 131, 612) comprises one or more of the following steps:

- Rotating (717) the fluid to be treated (701) about an axis substantially parallel to the direction of flow of said fluid to be treated (701);

- Setting speed (703) of the fluid to be treated (701); - Separation of solid CO2 from the fluid to be treated by centrifugal effect (718);

- Deceleration of the CO2 depleted gas (704).

9. Method according to any one of claims 1 to 8, characterized in that, in step b), is carried out a cooling of at least a portion of said fluid to be treated (42) cooled in step a) in order to obtain in addition a liquid (816) comprising predominantly CO2.

10. Process according to any one of claims 1 to 9, characterized in that said fluid to be treated (905) comes from industrial fumes.

11. Method according to any one of claims 1 to 10, characterized in that said fluid to be treated (905) comes from a steel plant (902a).

12. Method according to claim 1 1, characterized in that: said fluid to be treated (905) comes at least partially from a blast furnace (902a); and

said CO2-poor gas (927) is recycled at least partially into said blast furnace (902a).

13. Method according to any one of claims 1 to 10, characterized in that said fluid to be treated (905) comes at least partially from a refinery and / or a chemical plant (902a).

14. The method of claim 13, characterized in that said fluid to be treated (905) comes at least partially from gasification and / or partial oxidation and / or oxygen reforming (902a) of a given carbon fuel.

15. The method of claim 11, characterized in that: said fluid to be treated (905, 24) comes from an installation comprising an air separation unit (10); and said substantially isentropic expansion (130, 131, 612) of at least one of said refrigerating cycles (200) each comprising at least one substantially isentropic expansion (130, 131, 612) of a gas is carried out in said separation unit of the air (10).