Method for high-pressure liquefaction and purification of carbon dioxide

Abstract

The invention relates to a method for liquefying and purifying carbon dioxide from a gas comprising more than 70% by volume of carbon dioxide, the method comprising the following consecutive steps: a step of filtering the gas, then a step of compressing the gas at a pressure of between 60 bar and 80 bar, then a step of drying the gas, then a step of liquefying the gas, then a step of subcooling the liquefied gas, a step of expanding the liquefied gas, then a step of distilling the fluid so as to isolate the carbon dioxide, then a step of recovering the carbon dioxide in liquid form. The invention also relates to the device implementing the method and to the use thereof.

Description

[0001] High-pressure liquefaction and purification process for carbon dioxide

[0002] technical field

[0003] The present invention relates to a high-pressure liquefaction and purification process for a gas comprising more than 70% carbon dioxide by volume. The invention also relates to a device for liquefying and purifying carbon dioxide and its use.

[0004] Technical background

[0005] In light of current environmental challenges, solutions for waste recovery and recycling are being sought.

[0006] In the field of gases, and particularly carbon dioxide, the industrial applications are especially promising. Indeed, the gases emitted by numerous industrial processes are often rich in carbon dioxide. For example, biomass energy plants, cement plants, steam reforming processes, oxy-combustion processes, and others generate carbon dioxide-rich fumes as byproducts. Similarly, all internal combustion engines running on gasoline or diesel fuel generate this type of fume.

[0007] Thus, recycling these fumes addresses two needs. The first is to limit, or even prevent, their release into the atmosphere. The second is to recover value from these fumes for reuse, transforming them into a directly reusable raw material.

[0008] Therefore, research is underway to find ways to utilize these carbon dioxide-rich gases. However, the carbon dioxide generated during these processes is only useful if it is purified. It can also be used for cryogenics, particularly for cryogenic cleaning, for the production of dry ice, or as a precursor to biofuel. In agriculture, it can also be used to enrich the atmosphere of agricultural greenhouses with carbon dioxide, increasing the concentration from 350 ppm to 1200 ppm.

[0009] If it reaches a very high purity level, carbon dioxide can achieve food-grade quality, particularly by complying with EIGA Doc 126-11 (Annex 1, page 6) and ISBT quality guidelines. The carbon dioxide produced can be used, for example, in the manufacture of sparkling water.

[0010] Technical problem to solve

[0011] Current methods for purifying carbon dioxide are very energy-intensive. Specifically, the carbon dioxide is liquefied and then distilled. This liquefaction step is extremely energy-intensive.

[0012] The invention aims to solve this technical problem by proposing a process for liquefying and purifying carbon dioxide-rich gas, which is energy-efficient, has good efficiency and allows a very high level of purity to be achieved.

[0013] The invention thus relates to a process which allows liquefaction at a temperature close to ambient temperature, followed by distillation.

[0014] This liquefaction step at room temperature is possible by compressing the gas to be purified at high pressure beforehand, then carrying out a subcooling step before the liquefaction step.

[0015] This liquefaction at a temperature close to ambient temperature represents a significant energy saving. Furthermore, the process according to the invention and the device implementing it are relatively compact, meaning they comprise few components. They can be easily installed, particularly at the industrial site that produces the gas to be treated.

[0016] This sequence of specific steps makes it possible to answer the problem posed.

[0017] Brief description of the invention: The invention relates to a process for liquefying and purifying carbon dioxide from a gas comprising more than 70% by volume of carbon dioxide, comprising the following successive steps: a) at least one gas filtration step, then b) a gas compression step to a pressure between 60 and 80 bar, then c) a gas drying step, then d) a liquefaction step, the temperature of the liquefied gas at the outlet of this step being between 10°C and 30°C and the pressure of the liquefied gas at the outlet of this step being between 60 and 80 bar, then e) a subcooling step of the liquefied gas, f) an expansion step, the temperature of the fluid at the outlet of this step being between -30°C and -22°C and the pressure of the fluid at the outlet of this step being between 15 and 20 bar, then g) a distillation step of the fluid so as to isolate carbon dioxide,then h) a step of recovering the carbon dioxide in liquid form from step g) at the bottom of the distillation column.

[0018] Other advantageous features of the process according to the invention are detailed below.

[0019] -The process includes the following successive additional steps, after step h): i) a liquefaction step by cooling the gas recovered at the top of the distillation column in step g), the temperature of the liquefied gas at the outlet of this step being between -40 °C and -25 °C, then j) a step of separating the liquid phase from the gaseous phase of the fluid from the liquefaction step i), the liquid phase from the separation step j) is directed to the distillation step g).

[0020] -The process includes the following successive steps, after step j): k) a membrane filtration step of the gas phase from the separation step k), then l) a gas recycling step, which is composed of more than 50% by volume of carbon dioxide relative to the total volume of gas, from the previous filtration step k), before step b) of compression.

[0021] -The liquefaction step i) is carried out using a heat exchanger, which uses as a refrigerant part of the subcooled gas from step e).

[0022] - Step b) of compression is carried out using a compression system (CP102) bringing the gas to a pressure between 60 and 80 bar, chosen from:

[0023] -a set of at least three compressors mounted in series (CP301, CP302, CP303), equipped with at least three heat exchangers (E301, E302, E303), the heat exchangers being connected to a cooling device (CL301);

[0024] -a single multi-stage compressor equipped with at least two heat exchangers;

[0025] -a liquid piston compressor (CPL401),

[0026] -a screw compressor, and

[0027] -an axial compressor.

[0028] The invention also relates to a device for liquefying and purifying carbon dioxide (1), from a gas comprising more than 70% by volume of carbon dioxide, comprising the following elements, fluidly connected to each other and in this order:

[0029] - at least one filtration unit (F101),

[0030] - a compression system (CP101) bringing the gas to a pressure between 60 and 80 bar,

[0031] - a drying device (D 101),

[0032] - a heat exchanger (E101), enabling the liquefaction of the gas,

[0033] - a heat exchanger (E102), connected to a cooling system (CL101), allowing the subcooling of the gas,

[0034] - a pressure relief valve (V101),

[0035] - a distillation column (DC) for purifying the gas. Other advantageous features of the device according to the invention are detailed below.

[0036] -The system includes:

[0037] -a heat exchanger (E203) connected to the head of the distillation column (DC),

[0038] -a separator (Sep), which recovers the liquefied gas from the heat exchanger (E203), the separator (Sep) reintroduces the liquid phase into the distillation column

[0039] (DC) and evacuates the gaseous phase via a pipe (C219).

[0040] -The device includes a membrane filtration system (M201), which recovers the gaseous phase at the outlet of the separator (Sep), the membrane filtration system (M201) comprising:

[0041] -a pipe (C220), which recovers the carbon dioxide and recycles it upstream of the compression system (CP101), bringing the gas to a pressure between 60 and 80 bar, and

[0042] -a pipe (C221), which recovers the other gases.

[0043] -The compression system (CP101) bringing the gas to a pressure between 60 and 80 bar is chosen from:

[0044] -a set of at least three compressors mounted in series (CPS 301; CP301, CP302, CP303), equipped with at least three heat exchangers (E301, E302, E303), the heat exchangers being connected to a cooling device (CL301);

[0045] -a single multi-stage compressor equipped with at least two heat exchangers;

[0046] -a liquid piston compressor (CPL401),

[0047] -a screw compressor, and

[0048] -an axial compressor.

[0049] The compression system (CP102) is a liquid piston compressor (CPL401) comprising:

[0050] - a rotary multi-way distribution valve (V401) or several distribution valves, allowing the gas to be directed to the liquid-gas pressure exchanger,

[0051] - a liquid-gas pressure exchanger comprising at least two columns

[0052] (CN), - a distribution valve (V402) allowing the high-pressure liquid to be distributed to a cooling circuit,

[0053] - a tank for storing high-pressure liquid (STK401),

[0054] -a pump and

[0055] -a heat exchanger (E401), itself connected to a cooling system (CL401), allowing the high-pressure liquid to be cooled

[0056] The invention also relates to the use of the device as defined above to liquefy and purify a gas comprising more than 70% by volume of carbon dioxide.

[0057] Brief description of the figures

[0058] Non-exhaustive examples will now be discussed with reference to the figures.

[0059] Figure 1 is a diagram of a device implementing the method according to the invention.

[0060] Figure 2 is a diagram of a second embodiment of a device implementing the process according to the invention.

[0061] Figure 3 is a diagram of a set of compressors that can be used to carry out step c) of the process according to the invention.

[0062] Figure 4 is a diagram of a liquid piston compressor that can be used to carry out step c) of the process according to the invention.

[0063] Figure 5 is a diagram of another embodiment of an installation implementing the process according to the invention.

[0064] Detailed description

[0065] Other features, aspects, objects and advantages of the present invention will become even clearer upon reading the description that follows.

[0066] It is specified that the expressions "from ... to ..." and "between ... and ..." used in this description should be understood as including each of the limits mentioned. Unless otherwise indicated, all temperatures given below are in degrees Celsius and all pressures are in bar and are absolute pressures. The notation "bar" in this disclosure is therefore equivalent to the notation "bar a" or "bara" (denoting absolute pressure).

[0067] The liquefaction and purification process

[0068] The raw material for the process is a gas comprising more than 70% by volume of carbon dioxide relative to the total gas volume, preferably more than 80% by volume. This gas is referred to interchangeably as the initial gas or the gas to be purified.

[0069] The process according to the invention can also be implemented on carbon dioxide gases that have already been treated by one or more purification processes. The aim of the process is then to increase the purity level of this gas.

[0070] As mentioned above, the initial gas can come from various sources. For example, it can originate from a cement plant, a methanizer, steam reforming processes, oxy-combustion processes, or be recovered from combustion fumes.

[0071] Its composition is therefore diverse and depends on the process from which it originates. The other components of the liquefied gas can thus be methane, oxygen, nitrogen, hydrogen, carbon monoxide, hydrogen sulfide, water vapor, volatile organic compounds referred to below as VOCs or others.

[0072] At the process inlet, the gas temperature is preferably at ambient temperature, i.e., between 15°C and 45°C, and preferably between 20°C and 40°C. The gas temperature also depends on the process from which it originates. Thus, the gas entering the process may have a temperature up to 5°C higher or lower than ambient temperature.

[0073] At the process inlet, the gas is at atmospheric pressure.

[0074] The process according to the invention comprises at least the following 8 consecutive steps: steps a) to h). Step a) Gas filtration

[0075] The process includes at least one filtration step to remove impurities present in the initial gas and increase the purity level of the carbon dioxide.

[0076] The process according to the invention may include different types of filtration, each filtration step allowing the removal of a specific type of impurity.

[0077] Filtration can be activated carbon filtration, particle filtration, adsorption filtration, or bacterial filtration.

[0078] The process according to the invention can comprise from one to twenty filtration stages. It is possible to use a single device comprising several layers of filter materials, or several devices each comprising a single type of filter material, or several devices each comprising several types of filter materials.

[0079] The number of filtration stages and the type of filtration required depend on the quality of the gas to be purified, in other words, its initial carbon dioxide content, i.e., its purity level, and also its source. These successive filtrations aim to remove fine particles and dust, bacteria, volatile sulfur compounds, volatile hydrocarbon compounds, water molecules, and NVORs (Non-Volatile Organic Residues), such as traces of grease, sulfur and sulfur derivatives, oil, and other organic compounds.

[0080] Preferably, the process according to the invention comprises two filtration steps: a1) at least one or more filtration steps on an activated carbon filter, and a2) one or more filtration steps on a particle filter.

[0081] The process according to the invention may also include one or more steps a3) of filtration on an adsorption filter and / or one or more steps a4) of bacterial filtration.

[0082] Activated carbon filtration aims to remove volatile organic compounds (VOCs) from the gas. Particulate filtration aims to remove solid particles and dust from the gas. When performed after activated carbon filtration, this filtration stage removes any remaining activated carbon residue from the previous filtration, whether in powder or dust form. The particle filter can be, for example, a molecular sieve. Preferably, the process comprises between one and five particle filtration stages, and more specifically between two and three.

[0083] Step b) Compression of the gas, known as "high pressure"

[0084] The filtered gas then undergoes a high-pressure compression stage.

[0085] This second compression stage is a high-pressure compression. At the compressor inlet, the gas pressure can be between 1 and 2 bar, and the gas temperature can be between 25°C and 45°C, preferably between 30°C and 40°C. Generally, the filtration stage(s) can reduce the pressure and increase the gas temperature. At the outlet of this second compression stage, the gas pressure is between 45 and 80 bar, preferably between 60 and 70 bar, and even more preferably between 63 and 70 bar.

[0086] The compression stage can be implemented using various types of compressors. Preferably, the compression system used is chosen from among a multi-stage piston compressor, several piston compressors connected in series, a liquid piston compressor, screw compressors, or axial compressors. Preferably, the compressors are screw or piston compressors.

[0087] A very slight negative pressure can be applied at the compressor inlet in order to draw in the filtered gas.

[0088] For example, gas compression can be achieved in stages using a multi-stage compressor. The pressure applied by each compressor in each stage is calculated to reach the required pressure at the outlet of the last compressor. The compression ratio is calculated based on the number of stages. The compression ratio is the square root of the number of stages of the final pressure. In other words, the compression ratio is the nth root of the desired final pressure, where n represents the number of stages in the multi-stage compressor. Therefore, the compression ratio is the ratio of the pressure at the outlet of a stage to the pressure at the inlet of that stage.

[0089] For example, if the process inlet gas pressure is 1 bar and the desired pressure is 80 bars, the process using a three-stage compressor, the compression ratio is the cube root of 80, or about 4.3. Thus, the outlet pressure of the first-stage compressor is about 4.3 bars (P = 1*4.3), the outlet pressure of the second compressor at the second stage is about 18.5 bars (P = 4.3*4.3), the outlet pressure of the third compressor at the third stage is 80 bars (P = 18.5*4.3).

[0090] Preferably, the gas can be compressed to a pressure within the ranges as previously mentioned at a temperature compatible with maintaining said gas in the physical gaseous state.

[0091] Since this high compression generates a significant increase in gas temperature, the gas can be cooled. Preferably, the gas is cooled during this "high-pressure" compression stage.

[0092] Preferably, at the outlet of this "high pressure" compression stage, the gas temperature is between 100°C and 200°C. When present, cooling systems allow the gas temperature to be lowered, preferably to a temperature between 40°C and 45°C.

[0093] High-pressure gas compression increases the gas's liquefaction temperature. This allows gas liquefaction to be carried out at temperatures close to ambient. Increasing the gas pressure reduces the energy required for liquefaction, thus lowering the energy cost of the process. This increased pressure also improves process efficiency. High-pressure gas compression enables the use of simpler and more efficient equipment for subsequent gas liquefaction at higher temperatures, specifically above 10°C, bringing it closer to ambient temperature.

[0094] The energy generated by this compressor (or these compressors) can be released into the atmosphere or recovered for reuse. It also improves the efficiency of subsequent purification stages, such as drying and filtration.

[0095] Step c) Gas drying

[0096] The gas is then dried to eliminate traces of water and reach a dew point temperature at the outlet of the drying device of between -65 °C and -45 °C or a water content of less than 20 ppm.

[0097] Preferably, a device incorporating a zeolite that selectively adsorbs water is used. The device used to perform this drying step can be equipped with two columns: one adsorbing traces of moisture from the gas and the other enabling water desorption, i.e., column regeneration. Continuous, cyclic operation of the two columns is preferred.

[0098] This drying step is essential, both to meet food grade specifications and to avoid frost formation in subsequent heat exchangers.

[0099] Possible filtration step(s)

[0100] The dried gas may still undergo one or more additional filtration stages in order to remove any traces of impurities.

[0101] The filtration(s) can be carried out using molecular sieves and / or activated carbon.

[0102] The purpose of this or these potential filtrations is to ensure that the gas is as pure as possible before the liquefaction stage.

[0103] Step d) Liquefaction step

[0104] Liquefaction, in the context of the present invention, refers to the process by which a gas passes from a gaseous physical state to a liquid physical state by cooling.

[0105] The high-pressure gas is cooled using a heat exchanger to liquefy it. At the exchanger inlet, the gas pressure is between 60 and 80 bar. The gas's liquefaction temperature depends primarily on its composition. Depending on the gas's composition and purity level, the liquefaction temperature can range from 5°C to 30°C. The pressure is maintained during the liquefaction process.

[0106] The heat exchanger can be connected to a cooling system, which is adjusted to the desired gas liquefaction temperature. For example, to liquefy a gas at 19°C, the cooling system temperature can be set to 15°C.

[0107] Step e) Subcooling stage of the liquefied gas

[0108] For the purposes of this invention, subcooling refers to a reduction in the liquid's temperature below its saturation temperature (or boiling point), without it changing state. This subcooling step is particularly advantageous during the subsequent expansion stage, where a minimal volume of liquefied gas transitions to a gaseous state under ideal pressure and temperature conditions before purification in the distillation column.

[0109] Preferably, the temperature between 10 and -10°C is targeted for this subcooling stage, advantageously between 5 and -5°C, preferably at 0°C.

[0110] In other words, if the liquefied gas is at 30°C, a subcooling of 30°C is carried out to reach 0°C.

[0111] In other words, if the liquefied gas is at 20°C, a subcooling of 20°C is carried out to reach 0°C.

[0112] The heat exchanger is connected to a cooling system adjusted to the desired gas temperature. For example, to subcool the liquefied gas to 0 °C, the temperature of the cooling system can be set to -3 °C.

[0113] Step f) Relaxation stage

[0114] For the purposes of this invention, expansion refers to a thermodynamic process in which a gas changes from a high pressure to a lower pressure after passing through a valve, orifice, or turbine. This process may also be accompanied by a decrease in the temperature of the liquefied gas due to the Joule-Thomson effect.

[0115] The liquefied gas then passes through a pressure-reducing valve. This reduction lowers the initial pressure, which is between 60 and 80 bar, to between 10 and 30 bar, preferably between 15 and 20 bar.

[0116] The gas pressure is thus adjusted to the pressure required for the subsequent distillation stage. The liquefied gas exiting the pressure-reducing valve preferably has a temperature between -45°C and -20°C and a pressure between 15 and 20 bar. This pressure range is particularly suitable for transport. An additional pressure-reducing stage can be added to adapt the pressure of the purified carbon dioxide to the pressure required by the end user.

[0117] Step g) Distillation step of the liquefied gas

[0118] The liquefied gas from the previous step undergoes distillation to isolate the carbon dioxide from other potentially present gases and impurities.

[0119] Thus, liquefied carbon dioxide is collected at the bottom of the column, while gaseous impurities are collected at the top. The temperature within the column is preferably between -45°C and -20°C, at a pressure generally between 15 and 20 bar.

[0120] Step h) Liquefied carbon dioxide recovery step

[0121] The liquefied and purified carbon dioxide is recovered. It can be sent to a tank for storage. It can also be used directly for a subsequent application. It can be vaporized for use in vapor form.

[0122] The liquefied carbon dioxide is then at a temperature between -20 °C and -30 °C and at a pressure between 15 and 20 bars.

[0123] The purified carbon dioxide, collected at the bottom of the column, can be analyzed. Depending on the purity of the liquid obtained, the circuit may include a bypass valve.

[0124] The liquid can be sent directly to a storage tank or used directly for a subsequent application. A preliminary step of gas compression may be required.

[0125] The process according to the invention may include a preliminary step to step a) of filtration. The gas to be purified may be conveyed to a first compressor. The gas can thus undergo a first compression step.

[0126] At the compressor outlet, the gas pressure can be between 1 and 2 bars, preferably between 1 and 1.3 bars.

[0127] Preferably, an oil-free, dry compressor is used. This prevents contamination of the gas with oil residue.

[0128] Increasing the gas pressure at this stage improves the efficiency of subsequent stages, particularly the filtration stage(s).

[0129] Step i) Possible liquefaction step by cooling the gas at the top of the column

[0130] The gas recovered at the top of the distillation column in step g) is a gas with a low carbon dioxide content, that is, a content necessarily lower than that of the gas entering the process according to the invention. This gas may optionally include oxygen, nitrogen, methane, hydrogen, carbon monoxide, or other impurities depending on the origin of the initial gas.

[0131] This gas can undergo a liquefaction step. It is then cooled to a temperature between -45 °C and -35 °C and to a pressure between 15 and 20 bars.

[0132] This step liquefies the carbon dioxide, which is not yet liquefied and isolated at this stage of the process. At the end of this step, a two-phase fluid comprising a liquid phase and a gaseous phase is obtained.

[0133] Step j) Possible phase separation step

[0134] The two-phase fluid from the previous step (i) is conveyed to a separator, which separates the liquid phase from the gaseous phase. The liquid phase from step (i), including the liquefied carbon dioxide, can then be reintroduced to the distillation step (g).

[0135] This second liquefaction stage, the separation stage, and the recovery of the liquid phase increase the process yield.

[0136] Step k) Optional membrane filtration of the gaseous phase from separation step j)

[0137] The gas can be filtered through a membrane in order to separate a gas rich in carbon dioxide from a gas poor in carbon dioxide.

[0138] The membrane filtration system separates a gas consisting mainly of carbon dioxide from a gas consisting mainly of carbon dioxide.

[0139] A gas composed primarily of carbon dioxide is defined as a gas containing more than 50% carbon dioxide by volume. A gas composed primarily of carbon dioxide is defined as a gas containing less than 50% carbon dioxide by volume.

[0140] Step I) Possible step of recycling the majority of the gas into carbon dioxide

[0141] The gas, which is composed of more than 50% by volume of carbon dioxide relative to the total volume of gas, from the previous filtration step k) can be recycled before the compression step b).

[0142] The gas with a lower carbon dioxide content can be recycled, for example, back to a unit producing the original gas, or used on-site. If it is a gas rich in methane, it can, for example, be injected into the city gas network. If the original gas comes from a methanization unit, it can be recycled back to another methanization unit or to a wastewater treatment plant. In the case of gas from an oxy-combustion process, if the gas is predominantly oxygen, it can be recycled back to a combustion unit. In the case of gas from steam reforming, if the gas is predominantly hydrogen, it can be recycled back to a steam reforming unit.

[0143] Therefore, depending on the gas being treated, it is possible to recycle, and thus recover, the gases recovered following the liquefaction of carbon dioxide.

[0144] Purification device

[0145] The invention also relates to the device, which enables the implementation of the process according to the invention.

[0146] The liquid carbon dioxide liquefaction and purification device, also called a gas liquefaction and purification plant, can be located, for example, at the outlet of a biogas purification unit, at the outlet of a unit recovering gases produced by a cement plant, at the outlet of a steam reforming unit or at the outlet of an oxy-combustion unit.

[0147] The carbon dioxide purification device according to the invention comprises the following elements fluidly connected to each other in this order:

[0148] - at least one filtration unit,

[0149] - a compression system bringing the gas to a pressure between 60 and 80 bar, known as "high pressure"

[0150] - a drying device,

[0151] - a heat exchanger, enabling the liquefaction of the gas,

[0152] - a heat exchanger, connected to a cooling system, allowing the subcooling of the gas,

[0153] - a pressure relief valve,

[0154] - a distillation column to purify the gas.

[0155] Preferably, the first compressor is a dry, oil-free compressor.

[0156] As described above, the installation may include a succession of filtration units, with different specifications depending on the quality of the fluid to be purified.

[0157] According to a particular embodiment, the device comprises 2 filtration units mounted in series and arranged in this order: an activated carbon filtration unit and a particle filtration unit.

[0158] According to a particular embodiment, the device comprises 2 filtration units mounted in series and arranged in this order: a particle filtration unit and an activated carbon filtration unit.

[0159] According to a particular embodiment, the device comprises 2 filtration units mounted in series and arranged in this order: an activated carbon filtration unit and an adsorption filtration unit.

[0160] According to a particular embodiment, the device comprises 3 filtration units mounted in series and arranged in this order:

[0161] - an activated carbon filtration unit,

[0162] - a particle filtration unit and

[0163] - an adsorption filtration unit.

[0164] According to a particular embodiment, the device comprises 3 filtration units mounted in series and arranged in this order:

[0165] - an activated carbon filtration unit,

[0166] - a particle filtration unit, and

[0167] - a bacterial filtration unit.

[0168] According to a particular embodiment, the device comprises 4 filtration units mounted in series and arranged in this order:

[0169] - an activated carbon filtration unit,

[0170] - a particle filtration unit,

[0171] - an adsorption filtration unit, and

[0172] - a bacterial filtration unit.

[0173] The system can be implemented in several stages, for example using multiple compressors connected in series. Preferably, two, three, or four compressors are used in series. The so-called "high-pressure" compression system, which brings the gas to a pressure between 60 and 80 bar, can be chosen from the following systems:

[0174] -a set of at least three compressors mounted in series, equipped with at least three heat exchangers, the heat exchangers being connected to a cooling device;

[0175] -a single multi-stage compressor equipped with a heat exchanger;

[0176] -a liquid piston compressor.

[0177] According to a first embodiment, the device comprises 3 to 20 compressors connected in series, preferably 3 to 15 compressors connected in series, and preferably 3 to 10 compressors connected in series. According to another embodiment, the compressor may be a multistage radial compressor with 3 to 20 cells connected in series, preferably 3 to 15, and more particularly 3 to 10 cells connected in series.

[0178] According to a second embodiment, the compression system can be a multi-stage compressor. Each stage of the multi-stage compressor is connected to a heat exchanger after each compression stage.

[0179] In another embodiment, the compression system can be a liquid-cooled piston compressor comprising the use of a high-pressure liquid cooled in pressure-exchange columns or cylinders. Compression takes place in a pressure-exchange column according to the following sequence:

[0180] - the gas to be compressed fills the pressure exchange column, then

[0181] - The cooled, high-pressure liquid is pumped into the pressure exchange column where it is sprayed against the gas to be compressed; this pressure of the liquid directly on the gas causes the gas to be compressed, while also regulating its temperature, and

[0182] - the high-pressure liquid is evacuated from the pressure exchange column to be cooled via a cooling system.

[0183] The compression cycle is repeated by this back-and-forth process. The compressor preferably includes at least two pressure exchange columns, which ensures continuous operation, i.e., continuous compression. The compressor can include at least two pressure exchange columns; this set of columns defines a gas-liquid pressure exchanger. Preferably, the compressor includes between 2 and 10 pressure exchange columns. The plurality of columns allows for continuous compressor operation. The cooled high-pressure liquid can be water or any other liquid suitable for this function. Preferably, the cooled high-pressure liquid is water. The temperature of the high-pressure liquid is regulated by means of a heat exchanger located next to the liquid storage tank.

[0184] This compression of the gas by a high-pressure liquid which is sprayed into the gas reduces electrical consumption by at least 20% compared to a conventional compressor.

[0185] Compressors can be connected to one or more heat exchangers, which are themselves connected to one or more cooling systems. Similarly, each stage of a multi-stage compressor is connected to a heat exchanger, which is itself connected to a cooling system. In the case of a liquid-cooled piston compressor, it is the cooled high-pressure liquid that regulates the temperature during compression. Thus, through these cooling mechanisms, it is possible to achieve near-isothermal compression.

[0186] These cooling systems can use fluids chosen from water, glycol water, ambient air, coolants such as CFCs, HCFCs, hydrofluorocarbons (HFCs) or hydrofluoroolefins (HFOs) or natural fluids.

[0187] It is also possible to use the gas treated by the process according to the invention.

[0188] The device then includes a drying device. Preferably, a device comprising a zeolite that selectively adsorbs water is used.

[0189] The device then includes a heat exchanger used for gas liquefaction. As mentioned above, the heat exchanger can be connected to a cooling system, which is adjusted to the desired gas liquefaction temperature. Depending on the environment and season, ambient air, for example in winter, may be sufficient to cool and liquefy the gas.

[0190] According to another embodiment, the heat exchanger can be connected to a cooling system, which uses water to liquefy the gas.

[0191] The heat exchanger used for subcooling the liquefied gas is connected to a cooling system.

[0192] For example, the liquefaction stage can use water as the refrigerant, and the subcooling stage can use glycol water as the refrigerant. Using different refrigerants in this order allows for a gradual decrease in gas temperature and reduces energy consumption, compared to using only one heat exchanger.

[0193] The device then includes a pressure relief valve designed to depressurize the subcooled liquefied gas.

[0194] The distillation column purifies carbon dioxide. Like all distillation columns, it creates a temperature gradient. At the bottom of the column, pure carbon dioxide is collected in liquid form at a temperature of -22°C.

[0195] At the top of the column, depending on the components of the liquefied gas to be purified, the temperature is generally between -30 and -45°C.

[0196] The device can be equipped with a storage tank for the purified carbon dioxide. This storage tank can be equipped with a cooling system to maintain its temperature and pressure at a constant level.

[0197] The device may include a set of elements to treat the fluids recovered at the top of the distillation column.

[0198] Thus, the device according to the invention can be completed by the following elements, in this order: - a liquefier connected to the head of the distillation column, then

[0199] -a separator separating the liquid phase from the gaseous phase.

[0200] In one embodiment, the liquefier can be a heat exchanger connected to a cooling system using coolant. This embodiment is described in Figure 2.

[0201] In another embodiment, the liquefier can be a heat exchanger connected to a cooling system, which uses the subcooled liquefied gas as the refrigerant. The subcooled liquefied gas undergoes an expansion step so that its pressure and temperature are adjusted to the desired temperature for the second liquefaction. This embodiment is shown in Figure 5. This cooling method is particularly advantageous because it avoids the use of an additional refrigerant and simplifies the device.

[0202] Preferably, the separator is positioned above the distillation column, allowing the liquid phase to fall by gravity into the distillation column, so as to undergo a further purification step.

[0203] This second liquefaction stage increases the yield of the process.

[0204] The device may also include a membrane filtration system connected to the separator area that recovers the gas phase. The membrane filtration system comprises a pipe that recovers carbon dioxide and recycles it upstream of the high-pressure compression system, and a pipe that recovers the other gases.

[0205] The invention finally aims at using the device described above to liquefy and purify a gas comprising more than 70% by volume of carbon dioxide relative to the total volume of the gas.

[0206] The method according to the invention and the device are described in more detail with reference to Figures 1 to 5. Description of Figure 1

[0207] Figure 1 is a diagram of an embodiment of the device implementing the process according to the invention. The solid white arrows indicate the direction of the gas and the solid black arrows indicate the direction of the different refrigerants.

[0208] The gas to be treated is fed via line C101 into the filtration unit F101. The filtered gas is then conveyed via line C102 to the high-pressure compression system CP101 to undergo compression between 60 and 80 bar. From the CP101 compression system, the gas is conveyed via line C103 to the drying unit D101. The gas is then directed via line C104 to the heat exchanger E101. The gas is then liquefied. The heat exchanger E101 is fluidically connected to the cooling system CL101 via lines C106 and C107. Line C106 carries a refrigerant at a temperature between 5°C and 20°C from the cooling system CL101 to the heat exchanger E101. Pipe C107 carries the refrigerant, at a temperature between 10°C and 40°C, from the heat exchanger E101 to the cooling system CL101.The liquefied gas is then conveyed to heat exchanger E102 via line C105 for subcooling. Heat exchanger E102 is fluidically connected to cooling system CL102 via lines C108 and C109. Line C108 carries a refrigerant, at a temperature between -10°C and 5°C, from cooling system CL102 to heat exchanger E102. Line C109 carries the refrigerant, at a temperature between -3°C and 10°C, from heat exchanger E102 to cooling system CL102. The subcooled gas is directed, via line C110, to the expansion valve V101. Line C11 carries the liquefied gas to distillation column DC. The liquefied and purified carbon dioxide is recovered at the bottom of the DC distillation column and conveyed into the STK101 storage tank via the C112 line.

[0209] The gas is vented at the top of the DC distillation column via line C113.

[0210] Description of Figure 2: Figure 2 is a diagram of a second embodiment of the device implementing the process according to the invention. This diagram describes the recycling of the gases from the distillation step. The solid white arrows indicate the direction of gas flow, and the solid black arrows indicate the direction of the various refrigerants.

[0211] The gas to be treated is brought into the device according to the invention via the inlet pipe C201 in the filtration device F201.

[0212] The filtered gas is then conveyed via line C202 to the high-pressure compression system CP201 ​​to undergo compression between 60 and 80 bar. From the outlet of the high-pressure compression system CP201, the gas is conveyed via line C203 to the drying unit D201.

[0213] The gas is then directed via line C204 to heat exchanger E201, where it undergoes liquefaction. Heat exchanger E201 is fluidically connected to cooling system CL201 via lines C206 and C207. Line C206 carries a refrigerant, at a temperature between 5°C and 20°C, from cooling system CL201 to heat exchanger E201. Line C207 carries the refrigerant, at a temperature between 10°C and 40°C, from heat exchanger E201 to cooling system CL201. The liquefied gas is then directed to heat exchanger E202 via line C205 for subcooling. Heat exchanger E202 is fluidically connected to cooling system CL203 via lines C208 and C209. Pipe C208 carries a refrigerant fluid at a temperature between -15°C and 5°C, from the CL202 cooling system, to the E202 exchanger.Pipe C209 carries the refrigerant, at a temperature between 3°C and 10°C, from the heat exchanger E202 to the cooling system CL202. The subcooled liquid is then directed via pipe C210 to the expansion valve V201.

[0214] Line C211 carries the liquefied and depressurized gas to the DC distillation column. The liquefied and purified carbon dioxide is collected at the bottom of the DC distillation column and directed to the STK201 storage tank via line C212. The storage tank is fluidically connected to the CL203 cooling system via lines C213 and C214. Line C213 carries the refrigerant at a temperature between -40°C and -20°C from the CL203 cooling system to the STK201 storage tank. Line C214 carries the refrigerant, at a temperature between -45°C and -20°C, from the STK201 storage tank to the CL203 cooling system.

[0215] The gas is discharged from the top of the DC distillation column via line C215, which is connected to heat exchanger E203, for a second liquefaction. The gas discharged from the top of the DC distillation column is at a pressure between 10 and 20 bar and a temperature between -45°C and -25°C. Heat exchanger E203 is fluidically connected to cooling system CL204 via lines C217 and C218. Line C217 carries the refrigerant, at a temperature between -55°C and -35°C, from cooling system CL203 to heat exchanger E203. Line C218 carries the refrigerant, at a temperature between -45°C and -25°C, from heat exchanger E203 to cooling system CL204. Pipeline C216 transports the liquefied gas at a pressure between 10 and 20 bar and at a temperature between -45°C and -25°C from exchanger E203 to separator Sep.In the Sep separator, the liquid phase is separated from the gaseous phase. The liquid phase is directed to the DC distillation column. The gaseous phase is discharged via line C219 to the membrane filtration unit M201. Gases other than carbon dioxide are recovered via line C221. The gaseous carbon dioxide is recycled via line C220 upstream of the high-pressure compression system CP201.

[0216] Description of Figure 3

[0217] Figure 3 is a diagram of a "high pressure" compression system. This diagram describes a device that allows the gas pressure to increase.

[0218] Solid white arrows indicate the direction of the gas and solid black arrows indicate the direction of the different refrigerants.

[0219] The filtered gas is conveyed, via the C301 line, to the CPS301 high-pressure compression system consisting of 3 compressors mounted in series: CP301, CP302 and CP303.

[0220] Each compressor increases the pressure to achieve a pressure between 60 and 80 bar at the outlet of compressor CP303. Each compressor is connected to a heat exchanger, which is itself connected to the CL3O1 cooling system. Compressors CP301, CP302, and CP303 are connected to heat exchangers E301, E302, and E303, respectively.

[0221] Compressor CP301 is connected to heat exchanger E301 via line C302. Line C302 carries the compressed gas to heat exchanger E301, thus limiting the temperature increase caused by the compression performed by compressor CP301. Heat exchanger E301 is fluidically connected to cooling system CL3O1 via lines C308 and C309. Line C308 carries refrigerant from cooling system CL3O1 at a temperature between 30°C and 50°C. Line C309 carries refrigerant at a temperature between 55°C and 75°C from heat exchanger E301 to cooling system CL301.

[0222] Pipe C303 transports the gas compressed for the first time to the compressor CP302 in order to undergo a second compression.

[0223] The CP302 compressor performs a second compression. It is fluidically connected to the E302 heat exchanger via line C304. Line C304 carries the compressed gas to the E302 heat exchanger, thus limiting the temperature increase associated with the compression performed by the CP302 compressor. The E302 heat exchanger is fluidically connected to the CL301 cooling system via lines C310 and C311. Line C310, connected to line C308, carries the refrigerant from the CL301 cooling system at a temperature between 30°C and 50°C. Line C311, connected to line C309, carries the refrigerant at a temperature between 55°C and 75°C from the E302 heat exchanger to the CL301 cooling system.

[0224] Line C305 carries the compressed gas a second time to compressor CP303. Compressor CP303 performs a third compression to a pressure that brings the final pressure to the desired level. Compressor CP303 is fluidically connected to heat exchanger E303 via line C306. Line C306 carries the compressed gas to heat exchanger E303, thus limiting the temperature increase associated with the compression performed by compressor CP303. Heat exchanger E303 is fluidically connected to cooling system CL3O1 via lines C312 and C313. Line C312, connected to line C308, carries the refrigerant from cooling system CL3O1 at a temperature between 30°C and 50°C. Pipe C313, connected to pipe C309, transports the refrigerant at a temperature between 55°C and 75°C from the heat exchanger E303 to the cooling system CL301.

[0225] The CL301 cooling unit is connected to lines C308 and C309 to form a loop. The unit includes line C308, which carries the refrigerant at a temperature between 30°C and 50°C. This line is interrupted by a pump P301, which propels the refrigerant through the loop. Lines C310 and C312 are branches of line C308 and are therefore connected to it. Lines C308, C310, and C312 supply heat exchangers E301, E302, and E303, respectively. As shown in Figure 3, the cooling system initially supplies heat exchanger E303, then E302, and finally E301. However, the CL301 cooling unit could be configured differently, for example, to supply heat exchanger E301 first.

[0226] Pipe C309 is connected to the E301 exchanger and is connected by pipes C311 and C313 which come from the E302 and E303 exchangers respectively.

[0227] At the outlet of the E303 exchanger, the gas is brought via the C307 line to the drying device not shown in Figure 3.

[0228] Description of Figure 4

[0229] Figure 4 is a diagram of another "high-pressure" compression system. This diagram depicts a device for increasing gas pressure. The solid white arrows indicate the direction of gas flow, and the solid black arrows indicate the direction of the various refrigerants.

[0230] The filtered gas is conveyed, via the C401 line, to the "high pressure" compression system consisting of a CPL401 liquid piston compressor. The V401 multi-way distribution valve allows the gas to be directed to the CPL401 liquid piston compressor or to be released to subsequent stages of the process; in other words, the gas entering the CPL401 liquid piston compressor and the gas exiting said compressor.

[0231] Line C402 connects the multi-way distribution valve V401 and the pressure exchange columns CN401, CN402, CN403 and CN404, respectively via lines C402-1, C402-2, C402-3 and C402-4. Lines C402-1, C402-2, C402-3 and C402-4 allow the transport of the gas to be compressed from valve V401 to columns CN401, CN402, CN403 and CN404 and the transport of the compressed gas from columns CN401, CN402, CN403 and CN404 back to valve V401.

[0232] The gas is compressed via gas-liquid pressure exchange columns. Figure 4 illustrates four columns: CN401, CN402, CN403, and CN404.

[0233] Pipe C403 connects the multi-way distribution valve V402 and the pressure exchange columns CN401, CN402, CN403 and CN404, respectively via pipes C403-1, C403-2, C403-3 and C403-4. Pipes C403-1, C403-2, C403-3 and C403-4 allow the transport of cooled high-pressure liquid, particularly water, from valve V402 to columns CN401, CN402, CN403 and CN404 and the transport of heated high-pressure liquid, particularly water, from columns CN401, CN402, CN403 and CN404 to valve V402.

[0234] The V402 multi-way distribution valve allows for the optional distribution of cooled and heated high-pressure fluid. Line C404 provides the fluid connection between the V402 multi-way distribution valve and the E401 heat exchanger. Line C405 provides the fluid connection between the E401 heat exchanger and the STK401 high-pressure fluid reservoir. Line C406 provides the fluid connection between the V402 multi-way distribution valve and the STK401 high-pressure fluid reservoir. Line C406 includes the P401 pump.

[0235] Heat exchanger E401 is fluidically connected to cooling system CL401 via lines C407 and C408. Line C407 carries a refrigerant at a temperature between 30°C and 50°C from heat exchanger E401 to cooling system CL401. Line C408 carries the first refrigerant at a temperature between 60°C and 80°C from cooling system CL401 to heat exchanger E401. Line C408 includes pump P402.

[0236] The function of pump P401 is to pump the cooled, high-pressure liquid to valve V402, which directs the liquid to the pressure exchange columns CN401, CN402, CN403, and CN404. The high-pressure liquid, cooled by the pump pressure, is sprayed against the gas to be compressed. The gas is thus directly subjected to the liquid's pressure. Compression causes a temperature increase, which heats the high-pressure liquid. The heated high-pressure liquid is then returned to valve V402 and directed via line C404 to heat exchanger E401 for cooling. The cooled high-pressure liquid is then directed via line C405 to reservoir STK401.

[0237] The compressed gas exits the pressure exchange columns CN401, CN402, CN403 and CN404 and is conveyed via line C402 and valve V401 to line C409. The compressed gas is then at a pressure between 60 and 80 bar and at a temperature between 40 °C and 50 °C.

[0238] At the outlet of the CPL401 liquid piston compressor, the gas is brought via the C409 line to a drying device not shown in Figure 4.

[0239] Description of Figure 5

[0240] Figure 5 is a diagram of a fifth embodiment of the device implementing the process according to the invention. This diagram describes a device implementing an alternative cooling system for the second liquefaction step (i). The solid white arrows indicate the direction of gas flow, and the solid black arrows indicate the direction of the different refrigerants.

[0241] The gas to be treated is brought via the C501 line into the F501 filtration device.

[0242] The filtered gas is then conveyed to the CP501 compression system for compression to between 60 and 80 bar. From the CP501 compression system, the gas is conveyed via line C503 to the D501 drying unit. The gas is then directed via line C504 to the E501 heat exchanger, where it undergoes liquefaction. The E501 heat exchanger is fluidically connected to the CL501 cooling system via lines C506 and C507. Line C506 carries a refrigerant, at a temperature between 5°C and 20°C, from the CL501 cooling system to the E501 heat exchanger. Line C507 carries the refrigerant, at a temperature between 10°C and 40°C, from the E501 heat exchanger to the CL501 cooling system.

[0243] The liquefied gas is then conveyed to heat exchanger E502 via line C505 for subcooling. Heat exchanger E502 is fluidically connected to cooling system CL502 via lines C508 and C509. Line C508 carries a refrigerant at a temperature between -15°C and 5°C from cooling system CL502 to heat exchanger E502. Line C509 carries the refrigerant, at a temperature between 3°C and 10°C, from heat exchanger E502 to cooling system CL502.

[0244] The subcooled liquid is directed via line C510, which splits into 2 lines C510A and C510B respectively, to expansion valves V501 and V502. These valves allow the liquefied gas to be depressurized.

[0245] Line C511 carries the liquefied and depressurized gas to the DC distillation column. The liquefied and purified carbon dioxide is collected at the bottom of the DC distillation column and conveyed to the STK501 storage tank via line C519.

[0246] The gas is discharged from the top of the DC distillation column via line C513, which is connected to heat exchanger E503, for a second liquefaction. The gas discharged from the top of the DC distillation column is at a pressure between 10 and 30 bar and a temperature between -25 °C and -20 °C. Line C514 carries the liquefied gas, at a pressure between 10 and 20 bar and a temperature between -40 °C and -20 °C, from heat exchanger E503 to separator Sep.

[0247] In the Sep separator, the liquid phase is separated from the gaseous phase. The liquid phase is directed to the DC distillation column. The gaseous phase is discharged via line C515 to the membrane filtration unit M501. Gases other than carbon dioxide are recovered via line C520. The gaseous carbon dioxide is recycled via line C516, then via line C519 upstream of the CP501 compression system.

[0248] The E503 heat exchanger uses the subcooled gas from the circuit as its refrigerant. Lines C510B and C512 supply the E503 heat exchanger. Line C510B includes valve V502, which adjusts the pressure and temperature of the subcooled gas for liquefaction of the gas from the column. Line C512 carries the subcooled and depressurized liquefied gas, at a temperature between -55°C and -35°C, from the expansion valve V502 to the E503 heat exchanger. Line C518 carries the fluid, at a temperature between -45°C and -25°C, from the E503 heat exchanger upstream of the CP501 compression system.

[0249] Examples

[0250] 1. Purity of the liquefied carbon dioxide produced

[0251] A gas from a biogas purification unit produced by a methanizer of the following composition is treated by the process according to the invention:

[0252] Table 1

[0253] At the end of the process, the gas has the following composition:

[0254] Table 2

[0255] The carbon dioxide produced complies with the European Pharmacopoeia, the EN936 / EIGA / ISBT standard and Regulation RE 231 / 2012EC.

[0256] 2. Energy consumption of the process

[0257] The process according to the invention consumes from 0.12kW / h to 0.18kW / h per kg of liquefied CO2 produced, depending on the composition of the gas treated.

[0258] It has been observed that compressing the gas to "high pressure," that is, to a pressure between 60 and 80 bar, reduces the energy consumed in the liquefaction and purification process. This high pressure of the gas to be purified allows liquefaction at a temperature above 10°C, which represents a significant energy saving.

[0259] The calculation of energy balances was carried out for the liquefaction and purification of a carbon dioxide gas, comprising 6% methane.

[0260] Three different processes were compared:

[0261] -a comparative process carrying out the first liquefaction at P = 16-20 bars and T = -25 to -30 °C;

[0262] - a process according to the invention carrying out the first liquefaction at P = 72 bar and T = 21 °C using a device as described in Figure 2 and using a set of three compressors as described in Figure 3 and - a process according to the invention carrying out the first liquefaction at P = 72 bar and

[0263] T = 21 °C using a liquid piston compressor as described in Figure 4.

[0264] The results are shown in the table below:

[0265] In conclusion, the process according to the invention allows for a very significant energy saving.

Claims

DEMANDS 1. A process for liquefying and purifying carbon dioxide from a gas comprising more than 70% by volume of carbon dioxide, comprising the following successive steps: a) at least one gas filtration step, then b) a gas compression step to a pressure between 60 and 80 bar, then c) a gas drying step, then d) a liquefaction step, the temperature of the liquefied gas at the outlet of this step being between 10 °C and 30 °C and the pressure of the liquefied gas at the outlet of this step being between 60 and 80 bar, then e) a subcooling step of the liquefied gas, f) an expansion step, the temperature of the fluid at the outlet of this step being between -30 °C and -22 °C and the pressure of the fluid at the outlet of this step being between 15 and 20 bar, then g) a distillation step of the fluid so as to isolate the carbon dioxide,then h) a step of recovering the carbon dioxide in liquid form from step g) at the bottom of the distillation column.

2. A process according to claim 1, characterized in that it comprises the following successive additional steps, after step h): i) a liquefaction step by cooling the gas recovered at the top of the distillation column in step g), the temperature of the liquefied gas at the outlet of this step being between -40 °C and -25 °C, then j) a step of separating the liquid phase from the gaseous phase of the fluid from the liquefaction step i), the liquid phase from the separation step j) is directed to the distillation step g).

3. A process according to claim 2, characterized in that it comprises the following successive steps, after step j): k) a membrane filtration step of the gas phase from the separation step j), then l) a gas recycling step, which is composed of more than 50% by volume of carbon dioxide relative to the total volume of gas, from the previous filtration step k), before the compression step b).

4. A process according to claim 2 or 3, characterized in that the liquefaction step i) is carried out using a heat exchanger, which uses as a refrigerant a portion of the subcooled gas from step e).

5. A method according to claim 1, characterized in that step b) of compression is carried out using a compression system (CP101) bringing the gas to a pressure between 60 and 80 bar, is selected from: -a set of at least three compressors mounted in series (CP301, CP302, CP303), equipped with at least three heat exchangers (E301, E302, E303), the heat exchangers being connected to a cooling device (CL301); -a single multi-stage compressor equipped with at least two heat exchangers; -a liquid piston compressor (CPL401), -a screw compressor, and -an axial compressor.

6. Device for liquefying and purifying carbon dioxide (1), from a gas comprising more than 70% by volume of carbon dioxide, comprising the following elements, fluidly connected to each other and in this order: - at least one filtration unit (F101), - a compression system (CP101) bringing the gas to a pressure between 60 and 80 bar, - a drying device (D101), - a heat exchanger (E101), enabling the liquefaction of the gas, - a heat exchanger (E102), connected to a cooling system (CL101), allowing the subcooling of the gas, - a pressure relief valve (V101), - a distillation column (DC) to purify the gas.

7. Device according to claim 6, characterized in that it comprises: -a heat exchanger (E203) connected to the head of the distillation column (DC), -a separator (Sep), which recovers the liquefied gas from the heat exchanger (E203), the separator (Sep) reintroduces the liquid phase into the distillation column (DC) and evacuates the gaseous phase via a pipe (C219).

8. Device according to claim 7, characterized in that it comprises a membrane filtration system (M201), which recovers the gaseous phase at the outlet of the separator (Sep), the membrane filtration system (M201) comprising: -a pipe (C220), which recovers the carbon dioxide and recycles it upstream of the compression system (CP101), bringing the gas to a pressure between 60 and 80 bar, and -a pipe (C221), which recovers the other gases.

9. Device according to claims 6 to 8, wherein the compression system (CP101) bringing the gas to a pressure between 60 and 80 bar is selected from: -a set of at least three compressors mounted in series (CP301, CP302, CP303), equipped with at least three heat exchangers (E301, E302, E303), the heat exchangers being connected to a cooling device (CL301); -a single multi-stage compressor equipped with at least two heat exchangers; -a liquid piston compressor (CPL401), -a screw compressor, and -an axial compressor.

10. Device according to claim 9, wherein the compression system (CP101) is a liquid piston compressor (CPL401) comprising: - a rotary multi-way distribution valve (V401) or several distribution valves, allowing the gas to be directed to the liquid-gas pressure exchanger, - a liquid-gas pressure exchanger comprising at least two columns (CN), - a distribution valve (V402) allowing the high-pressure fluid to be distributed to a cooling circuit, - a tank for storing high-pressure liquid (STK401), -a pump and -a heat exchanger (E401), itself connected to a cooling system (CL401), allowing the high-pressure liquid to be cooled 11. Use of the device as defined in any one of claims 6 to 10 for liquefying and purifying a gas comprising more than 70% by volume of carbon dioxide.

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