High-pressure liquefaction and purification process for carbon dioxide

Abstract

Process for purifying liquefied carbon dioxide. 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: at least one gas filtration step, then a gas compression step to a pressure between 60 and 80 bar, then a gas drying step, then 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 a subcooling step of the liquefied gas, 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 a distillation step of the fluid so as to isolate the carbon dioxide.then a step of recovering the carbon dioxide in liquid form at the bottom of the distillation column. The invention also relates to the device implementing this process and its use. Figure 1,

Description

Title of the invention: High-pressure liquefaction and purification process for carbon dioxide technical field

[0001] The present invention relates to a high-pressure liquefaction and purification process for a gas comprising more than 70% by volume of carbon dioxide. The invention also relates to a device for liquefying and purifying carbon dioxide and its use. Technical background

[0002] In view of current environmental challenges, solutions for the recovery and recycling of waste are being sought.

[0003] 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 by-products. Similarly, all internal combustion engines operating on the combustion of gasoline or diesel generate this type of fume.

[0004] Thus, recycling these fumes meets two expectations. The first is to limit, or even avoid, the release of these fumes into the atmosphere. The second is to recover value from these fumes for reuse and to make them a directly reusable raw material.

[0005] Processes for utilizing these carbon dioxide-rich gases are therefore being sought. However, the carbon dioxide generated during these processes is only of interest 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.

[0006] In the agricultural field, it can also be used to enrich the atmosphere of agricultural greenhouses with carbon dioxide by increasing the carbon dioxide level from 350 ppm to 1200 ppm.

[0007] If it reaches a very high level of purity, carbon dioxide can achieve food-grade quality, in particular 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. Technical problem to solve

[0008] Known processes for purifying carbon dioxide use very energy-intensive methods. In particular, the carbon dioxide is liquefied and then distilled. This liquefaction step is very energy-intensive.

[0009] 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.

[0010] The invention thus relates to a process which allows liquefaction at a temperature close to ambient temperature, then distillation.

[0011] 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.

[0012] This liquefaction at a temperature close to ambient temperature represents a real 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.

[0013] This sequence of specific steps makes it possible to answer the problem posed. Brief description of the invention

[0014] Thus, 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:

[0015] a) at least one gas filtration step, then

[0016] b) a step of compressing the gas to a pressure between 60 and 80 bar, then

[0017] c) a gas drying step, then

[0018] 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 stage being between 60 and 80 bar, then

[0019] e) a subcooling step of the liquefied gas,

[0020] f) a pressure-reducing 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

[0021] g) a step of distilling the fluid so as to isolate the carbon dioxide, then

[0022] h) a step of recovering carbon dioxide in liquid form from step g) at the bottom of the distillation column.

[0023] Other advantageous features of the process according to the invention are specified below.

[0024] -The process comprises the following successive additional steps, after step h):

[0025] 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

[0026] j) a step of separating the liquid phase from the gaseous phase of the fluid resulting from the liquefaction step i),

[0027] the liquid phase from the separation step j) is directed to the distillation step g).

[0028] -The process comprises the following successive steps, after step j):

[0029] k) a membrane filtration step of the gas phase from the separation step k), then

[0030] 1) 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).

[0031] -The liquefaction step i) is carried out using a heat exchanger, which uses as a refrigerant part of the subcooled gas from step e).

[0032] - Step b) of compression is carried out using a compression system (CP 102) bringing the gas to a pressure between 60 and 80 bar is chosen from:

[0033] -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);

[0034] -a single multi-stage compressor equipped with at least two heat exchangers;

[0035] -a liquid piston compressor (CPL401),

[0036] -a screw compressor, and

[0037] -an axial compressor.

[0038] 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:

[0039] - at least one filtration unit (Fl01),

[0040] - a compression system (CP101) bringing the gas to a pressure between 60 and 80 bars,

[0041] - a drying device (D101),

[0042] - a heat exchanger (E101), enabling the liquefaction of the gas,

[0043] - a heat exchanger (E102), connected to a cooling system (CL101), allowing the subcooling of the gas,

[0044] - a pressure relief valve (V101),

[0045] - a distillation column (DC) for purifying the gas.

[0046] Other advantageous features of the device according to the invention are specified below.

[0047] -The device comprises:

[0048] -a heat exchanger (E203) connected to the head of the distillation column (DC),

[0049] -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 removes the gaseous phase via a pipe (C219).

[0050] -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:

[0051] -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

[0052] -a pipe (C221), which recovers the other gases.

[0053] -The compression system (CP101) bringing the gas to a pressure between 60 and 80 bar is chosen from:

[0054] -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);

[0055] -a single multi-stage compressor equipped with at least two heat exchangers;

[0056] -a liquid piston compressor (CPL401),

[0057] -a screw compressor, and

[0058] -an axial compressor.

[0059] The compression system (CP102) is a liquid piston compressor (CPL401) comprising:

[0060] - a rotary multi-way distribution valve (V401) or several valves of distribution, allowing the gas to be directed to the liquid-gas pressure exchanger,

[0061] - a liquid-gas pressure exchanger comprising at least two columns (CN),

[0062] - a distribution valve (V402) for distributing the high-pressure liquid towards a cooling circuit,

[0063] - a reservoir for storing the liquid at high pressure (STK401),

[0064] -a pump and

[0065] - a heat exchanger (E401), itself connected to a cooling system (CL401), allowing the high-pressure liquid to be cooled

[0066] The invention finally relates to a use of the device as defined above to liquefy and purify a gas comprising more than 70% by volume of carbon dioxide. Brief description of the figures

[0067] Non-limiting examples will now be discussed with reference to the figures.

[0068] Figure 1 is a diagram of a device implementing the method according to the invention.

[0069] Figure 2 is a diagram of a second embodiment of a device putting implement the process according to the invention.

[0070] Fig. 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.

[0071] 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.

[0072] Fig. 5 is a diagram of another embodiment of an installation implementing the process according to the invention. Detailed description

[0073] Other features, aspects, objects and advantages of the present invention will become even clearer upon reading the following description.

[0074] 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.

[0075] 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). The liquefaction and purification process

[0076] The raw material for the process is a gas comprising more than 70% by volume of carbon dioxide relative to the total volume of the gas, preferably more than 80% by volume. This gas is referred to interchangeably as the initial gas or the gas to be purified.

[0077] 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.

[0078] As indicated above, the initial gas can come from various sources. For example, it can come from a cement plant, a methanizer, steam reforming processes, oxy-combustion processes or be recovered from combustion fumes.

[0079] 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.

[0080] At the process inlet, the gas temperature is preferably at ambient temperature, i.e., between 15°C and 45°C, preferably between 20°C and 40°C. The gas temperature also depends on the process from which it originates. Thus, the gas at the process inlet may have a temperature up to 5°C higher or lower than ambient temperature.

[0081] At the process inlet, the gas is at atmospheric pressure.

[0082] The method according to the invention comprises at least the following 8 consecutive steps: steps a) to h). Step a) Gas filtration

[0083] 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.

[0084] The process according to the invention may include different types of filtration, each filtration step allowing the removal of a specific type of impurity.

[0085] Filtration can be activated carbon filtration, particle filtration, adsorption filtration or bacterial filtration.

[0086] 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.

[0087] The number of filtration stages and the type of filtration to be carried out depend on the quality of the gas to be purified, in other words, its initial carbon dioxide content, i.e., its level of purity, and also its origin. These successive filtrations aim to remove fine particles and dust, bacteria, volatile sulfur compounds, volatile hydrocarbon compounds, water molecules, NVORs (Non-Volatile Organic Residues), such as traces of grease, sulfur and sulfur derivatives, oil, and other organic compounds.

[0088] Preferably, the process according to the invention comprises two filtration steps:

[0089] a) at least one or more filtration steps on an activated carbon filter, and

[0090] a2) one or more filtration stages on a particle filter.

[0091] 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.

[0092] Activated carbon filtration aims to remove volatile organic compounds present in the gas. Particulate filtration aims to remove solid particles and dust present in the gas. When positioned after activated carbon filtration, this filtration allows for the removal of any activated carbon residues potentially carried over from the previous filtration, whether in powder form or not. or dust. The particle filter can, for example, be a molecular sieve. Preferably, the process comprises between one and five particle filtration stages, and more particularly between two and three particle filtration stages.

[0093] Step b ]_ Gas compression _ called “high pressure”

[0094] The filtered gas then undergoes a high-pressure compression step.

[0095] 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.

[0096] The compression stage can be implemented using different types of compressors. Preferably, the compression system used is chosen from among a multi-stage piston compressor, several piston compressors mounted in series, a liquid piston compressor, screw compressors, and axial compressors. Preferably, the compressors are screw or piston compressors.

[0097] A very slight negative pressure can be applied at the inlet of the compressor so as to draw in the filtered gas.

[0098] By way of example, gas compression can be carried out in several stages using a multi-stage compressor. The pressure applied by each compressor in each stage is calculated so as to reach the required pressure at the outlet of the last compressor. The compression ratio is calculated as a function of 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 corresponds to the nth root of the desired final pressure, where n corresponds to the number of stages in the multi-stage compressor. Therefore, the compression ratio is the ratio between the pressure at the outlet of a stage and the pressure at the inlet of the stage.

[0099] For example, if the process inlet gas pressure is 1 bar and the desired pressure is 80 bar, 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 compressor at the first stage is about 4.3 bar (P = 1*4.3), the outlet pressure of the second compressor at the second stage is about 18.5 bar (P = 4.3*4.3), the outlet pressure of the third compressor at the third stage is 80 bar (P = 18.5*4.3).

[0100] 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.

[0101] Since this high compression generates a significant increase in the gas temperature, the gas can be cooled. Preferably, the gas is cooled during this "high pressure" compression step.

[0102] 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.

[0103] Compressing gas at high pressure increases its liquefaction temperature. This allows gas liquefaction to be carried out at a temperature close to ambient temperature. Increasing the gas pressure reduces the energy required for liquefaction, thus lowering the energy cost of the process. This increase in gas pressure also improves process efficiency. High-pressure gas compression enables the use of simpler and more efficient equipment for subsequent gas liquefaction, which takes place at a higher temperature, particularly above 10°C, and thus closer to ambient temperature.

[0104] The energy generated by this or these compressors can be released into the atmosphere or recovered for reuse.

[0105] It also makes it possible to improve the efficiency of subsequent purification steps, for example drying and filtration(s). Step c) Gas drying

[0106] The gas is then dried in such a way as 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.

[0107] Preferably, a device comprising a zeolite that selectively adsorbs water is used. The device used to perform this drying step may be equipped with two columns, one adsorbing traces of moisture from the gas and the second enabling water desorption, i.e., column regeneration. Continuous, cyclic operation of the two columns is preferred.

[0108] This drying step is essential, both to meet food grade specifications and to avoid frosting phenomena in subsequent exchangers. Possible filtration step(s)

[0109] The dried gas can still undergo one or more additional filtration steps in order to remove any traces of impurities.

[0110] The filtration(s) can be carried out on molecular sieves and / or activated carbon.

[0111] The purpose of this or these possible filtrations is to ensure that the gas is as pure as possible before the liquefaction step. Step d) Liquefaction step

[0112] Liquefaction, in the context of the present invention, means the process by which the gas passes from a gaseous physical state to a liquid physical state by cooling.

[0113] The high-pressure gas is cooled using a heat exchanger in order to be liquefied. At the inlet of the exchanger, the gas is at a pressure of between 60 and 80 bar. The liquefaction temperature of the gas depends primarily on its composition. Depending on the gas composition and its purity level, the liquefaction temperature can range from 5 °C to 30 °C. The pressure is maintained during the liquefaction stage.

[0114] 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 temperature of the cooling system can be set to 15 °C.

[0115] Step e) Subcooling step of the liquefied gas

[0116] For the purposes of this invention, subcooling means lowering the temperature of the liquid to a level below its saturation temperature (or boiling point), without it changing state. This subcooling step is particularly advantageous during the subsequent expansion step, where a minimal volume of liquefied gas transitions to a gaseous state under ideal pressure and temperature conditions before purification in the distillation column.

[0117] Preferably, the temperature between 10 and -10°C is targeted for this subcooling step, advantageously between 5 and -5°C, preferably to 0°C.

[0118] In other words, if the liquefied gas is at 30°C, a subcooling of 30°C is carried out to reach 0°C.

[0119] In other words, if the liquefied gas is at 20°C, a subcooling of 20°C is carried out to reach 0°C.

[0120] 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. Step f) Relaxation stage

[0121] 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.

[0122] The liquefied gas then passes through a pressure-reducing valve. This pressure reduction allows the initial pressure, between 60 and 80 bar, to be reduced to a pressure between 10 and 30 bar, preferably between 15 and 20 bar.

[0123] The gas pressure is thus adjusted to the pressure required for the subsequent distillation step. 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 step can be added to adapt the pressure of the purified carbon dioxide to the pressure required by the end user. Step g) Distillation step of the liquefied gas

[0124] The liquefied gas from the previous step undergoes distillation in order to isolate the carbon dioxide from other potentially present gases and impurities.

[0125] Thus, the liquefied carbon dioxide is recovered at the bottom of the column, while the impurities in gaseous form are recovered at the top of the column. The temperature within the column is preferably between -45 °C and -20 °C, at a pressure generally between 15 and 20 bar.

[0126] Step h) Liquefied carbon dioxide recovery step

[0127] The liquefied and purified carbon dioxide is recovered. It can be sent into It has a reservoir for storage. It can also be used directly for later application. It can be vaporized for use in vapor form.

[0128] The liquefied carbon dioxide is then at a temperature between -20 °C and -30 °C and at a pressure between 15 and 20 bars.

[0129] The purified carbon dioxide, recovered at the bottom of the column, can be analyzed. Depending on the purity of the liquid obtained, the circuit may include a bypass valve.

[0130] The liquid can be sent directly to a storage tank or used directly for a later application. Possible preliminary step of gas compression

[0131] 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 may thus undergo a first compression step.

[0132] At the compressor outlet, the gas pressure can be between 1 and 2 bars, preferably between 1 and 1.3 bars.

[0133] Preferably, an oil-free dry compressor is used. This prevents contamination of the gas with oil residues.

[0134] Increasing the gas pressure at this stage improves the efficiency of the following stages, in particular the filtration stage(s).

[0135] Step i)_ Optional step 1 of liquefaction by cooling of the gas at the top of the column

[0136] The gas recovered at the top of the distillation column in step g) is a gas comprising a low carbon dioxide content, that is to say, a content necessarily lower than that of the gas entering the process according to the invention. This gas may optionally comprise oxygen, nitrogen, methane, hydrogen, carbon monoxide, or other impurities depending on the origin of the initial gas.

[0137] 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 bar.

[0138] 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.

[0139] Step j)_ Possible step of _ s separation of s phases s

[0140] The two-phase fluid from the previous step i) is brought to a separator, which allows the liquid phase to be separated from the gaseous phase.

[0141] The liquid phase from step i), comprising the liquefied carbon dioxide, can be reintroduced to step g) of distillation.

[0142] This second liquefaction step, the separation step and the recovery of the liquid phase make it possible to increase the yield of the process

[0143] Step k) Optional membrane filtration of the gaseous phase from the separation step j)

[0144] The gas can be filtered through a membrane so as to separate a gas rich in carbon dioxide from a gas poor in carbon dioxide.

[0145] The membrane filtration system separates a gas consisting mainly of carbon dioxide from a gas consisting mainly of carbon dioxide.

[0146] A gas consisting mainly of carbon dioxide is understood to be a gas that contains more than 50% carbon dioxide by volume. A gas consisting mainly of carbon dioxide is understood to be a gas that contains less than 50% carbon dioxide by volume.

[0147] Step 1) Possible step of recycling the major gas into carbon dioxide

[0148] The gas, which is composed of more than 50% by volume of carbon dioxide per relative to the total volume of gas, from the previous filtration step k) can be recycled before the compression step b).

[0149] The gas with a low carbon dioxide content can be recycled, for example, back to a unit producing the initial gas, or used on-site. If it is a gas rich in methane, it can, for example, be injected into the town gas network. If the initial gas comes from a methanization unit, it can be recycled to a a methanization unit or a wastewater treatment unit. In the case of gas treatment from an oxy-combustion process, if the gas is predominantly oxygen, it can be recycled to a combustion unit. In the case of gas treatment from steam reforming, if the gas is predominantly hydrogen, it can be recycled to a steam reforming unit.

[0150] Therefore, depending on the gas treated, it is possible to recycle, and thus recover, the gases recovered following the liquefaction of carbon dioxide. Purification device

[0151] The invention also relates to the device, which enables the implementation of the process according to the invention.

[0152] The liquid carbon dioxide liquefaction and purification device, also called a gas liquefaction and purification plant, can be arranged, for example, at the outlet of a biogas purification unit, at the outlet of a unit for recovering gases produced by a cement plant, at the outlet of a steam reforming unit or at the outlet of an oxy-combustion unit.

[0153] The carbon dioxide purification device according to the invention comprises the following elements fluidly connected to each other in this order:

[0154] - at least one filtration unit,

[0155] - a compression system bringing the gas to a pressure between 60 and 80 bars, also known as "high pressure"

[0156] - a drying device,

[0157] - a heat exchanger, enabling the liquefaction of the gas,

[0158] - a heat exchanger, connected to a cooling system, allowing the sub- gas cooling,

[0159] - a pressure relief valve,

[0160] - a distillation column for purifying the gas.

[0161] Preferably, the first compressor is a dry, oil-free compressor.

[0162] As described above, the installation may include a succession of filtration units, with different specificities depending on the quality of the fluid to be purified.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] According to a particular embodiment, the device comprises 3 filtration units mounted in series and arranged in this order:

[0167] - an activated carbon filtration unit,

[0168] - a particle filtration unit and

[0169] - an adsorption filtration unit.

[0170] According to a particular embodiment, the device comprises 3 filtration units connected in series and arranged in this order:

[0171] - an activated carbon filtration unit,

[0172] - a particle filtration unit, and

[0173] - a bacterial filtration unit.

[0174] According to a particular embodiment, the device comprises 4 filtration units connected in series and arranged in this order:

[0175] - an activated carbon filtration unit,

[0176] - a particle filtration unit,

[0177] - an adsorption filtration unit, and

[0178] - a bacterial filtration unit.

[0179] The device can be made in several stages, for example using several compressors positioned in series. Preferably, two, three or four compressors are used in series.

[0180] The so-called "high pressure" compression system bringing the gas to a pressure between 60 and 80 bar can be chosen from the following systems:

[0181] -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;

[0182] -a single multi-stage compressor equipped with a heat exchanger;

[0183] -a liquid piston compressor.

[0184] According to a first embodiment, the device comprises 3 to 20 compressors connected in series, preferably 3 to 15 compressors connected in series, and more 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.

[0185] 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.

[0186] According to another embodiment, the compression system may 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:

[0187] - the gas to be compressed fills the pressure exchange column, then

[0188] - 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 latter to be compressed, while regulating its temperature, and

[0189] - the high-pressure liquid is evacuated from the pressure exchange column to be cooled via a cooling system.

[0190] The compression cycle is repeated by this back-and-forth process. The compressor preferably includes at least two pressure exchange columns, which allows for continuous operation, i.e., continuous compression. The compressor may include at least two pressure exchange columns; this set of columns defines a gas-liquid pressure exchanger. Preferably, the compressor includes between two and ten pressure exchange columns. The plurality of columns allows for continuous operation of the compressor. The cooled high-pressure liquid may 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.

[0191] This compression of the gas by a high-pressure liquid which is sprayed into the gas makes it possible to reduce electrical consumption by at least 20% compared to a conventional compressor.

[0192] 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 quasi-isothermal compression.

[0193] These cooling systems can use fluids selected from water, glycol water, ambient air, coolants such as CFCs, HCFCs, hydrofluorocarbons (HFCs) or hydrofluoroolefins (HFOs) or natural fluids.

[0194] It is also possible to use the gas treated by the process according to the invention.

[0195] The device then includes a drying device. Preferably, a device comprising a zeolite that selectively adsorbs water is used.

[0196] The device then includes a heat exchanger used for liquefying the gas. As indicated above, the heat exchanger can be connected to a cooling system, which is adjusted to the desired gas liquefaction temperature.

[0197] Depending on the environment and the season, the ambient air, for example in winter, may be sufficient to cool the gas and liquefy it.

[0198] According to another embodiment, the heat exchanger can be connected to a cooling system, which uses water to liquefy the gas.

[0199] The heat exchanger used for subcooling the liquefied gas is connected to a cooling system.

[0200] 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 the gas temperature and reduces energy consumption, compared to the case where only one heat exchanger had been used.

[0201] The device then includes a pressure relief valve for depressurizing the subcooled liquefied gas.

[0202] The distillation column purifies carbon dioxide. Like all distillation columns, it provides a temperature gradient. At the bottom of the column, the pure carbon dioxide is collected at a temperature of -22°C in liquid form.

[0203] 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.

[0204] 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 constant.

[0205] The device may include a set of elements for treating the fluids recovered at the top of the distillation column.

[0206] Thus, the device according to the invention can be supplemented by the following elements and in this order:

[0207] - a liquefier connected to the head of the distillation column, then

[0208] -a separator separating the liquid phase from the gaseous phase.

[0209] According to one embodiment, the liquefier can be a heat exchanger connected to a cooling system using coolant. This embodiment is described in [Fig.2].

[0210] According to 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 to allow the second liquefaction. This embodiment is described in [Fig. 5]. This embodiment of Cooling is particularly advantageous because it avoids the use of an additional refrigerant and simplifies the device.

[0211] Preferably, the separator is arranged above the distillation column, allowing the liquid phase to fall by gravity into the distillation column, so as to undergo a further purification step.

[0212] This second liquefaction step makes it possible to increase the yield of the process.

[0213] The device may also include a membrane filtration system connected to the separator area that recovers the gas phase. The membrane filtration system includes a pipe that recovers carbon dioxide and recycles it upstream of the "high-pressure" compression system, and a pipe that recovers the other gases.

[0214] 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.

[0215] 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

[0216] 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.

[0217] The gas to be treated is conveyed via line C101 to the filtration device 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 device 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. The Cl07 line carries the refrigerant, at a temperature between 10°C and 40°C, from the E101 exchanger to the CL101 cooling system.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... Line Cl 10 leads to the pressure-reducing valve V101. Line Cl 11 carries the liquefied 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 STK101 storage tank via line Cl 12.

[0218] The gas is vented at the top of the DC distillation column via line Cl 13. See Figure 2 for details.

[0219] 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 different refrigerants.

[0220] The gas to be treated is brought into the device according to the invention via the inlet pipe C201 in the filtration device F201.

[0221] 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 device D201.

[0222] The gas is then directed via line C204 to heat exchanger E201. There, 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 to undergo 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.

[0223] Line C211 carries the liquefied and depressurized gas to the DC distillation column. The liquefied and purified carbon dioxide is recovered 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 a 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 transports the refrigerant, at a temperature between -45 °C and -20 °C, from the STK201 storage tank to the CL203 cooling system.

[0224] The gas is discharged from the top of the DC distillation column via line C215, which is connected to the 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. The heat exchanger E203 is fluidically connected to the cooling system CL204 via lines C217 and C218. Line C217 carries the refrigerant, at a temperature between -55 °C and -35 °C, from the cooling system CL203 to the heat exchanger E203. Line C218 carries the refrigerant, at a temperature between -45 °C and -25 °C, from the heat exchanger E203 to the 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 device 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. Description of Figure 3

[0225] Figure 3 is a diagram of a "high pressure" compression system. This diagram describes a device for increasing the pressure of the gas.

[0226] Solid white arrows indicate the direction of the gas and solid black arrows indicate the direction of the different refrigerants.

[0227] 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.

[0228] Each compressor allows an increase in pressure so as to obtain a pressure between 60 and 80 bar at the outlet of the CP303 compressor.

[0229] Each compressor is connected to a heat exchanger, which is itself connected to the CL301 cooling system. Compressors CP301, CP302 and CP303 are connected respectively to heat exchangers E301, E302 and E303.

[0230] 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 associated with the compression performed by compressor CP301. Heat exchanger E301 is fluidically connected to cooling system CL301 via lines C308 and C309. Line C308 carries a refrigerant from cooling system CL301 to a temperature between 30 °C and 50 °C. The C309 line transports the refrigerant at a temperature between 55 °C and 75 °C from the E301 heat exchanger to the CL301 cooling system.

[0231] The C303 line transports the gas compressed for the first time to the CP302 compressor so as to undergo a second compression.

[0232] The CP302 compressor enables a second compression. The CP302 compressor is fluidically connected to a heat exchanger E302 via line C304. Line C304 carries the compressed gas to the heat exchanger E302, thus limiting the temperature increase associated with the compression performed by the CP302 compressor. The heat exchanger E302 is fluidically connected to the cooling system CL301 via lines C310 and C311. Line C310, connected to line C308, carries the refrigerant from the cooling system CL301 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 heat exchanger E302 to the cooling system CL301.

[0233] Line C305 carries the compressed gas a second time to compressor CP303. Compressor CP303 performs a third compression to a pressure that leads to the desired final pressure. 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 CL301 via lines C312 and C313. Line C312, connected to line C308, carries the refrigerant from cooling system CL301 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.

[0234] The cooling device CL301 is connected to lines C308 and C309 to form a loop. The device includes a 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 into 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 [Fig. 3], the cooling system first supplies heat exchanger E303 and then heat exchanger E302. and the E301 exchanger. However, the CL301 cooling system could be placed differently, for example, to supply the E301 exchanger first.

[0235] Pipe C309 is connected to the exchanger E301 and is connected by pipes C311 and C313 which come from the exchangers E302 and E303 respectively.

[0236] At the outlet of the exchanger E303, the gas is brought via the pipe C307 to the drying device not shown in [Fig.3]. Description of Figure 4

[0237] Fig. 4 is a diagram of another "high pressure" compression system. This diagram describes 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 different refrigerants.

[0238] The filtered gas is conveyed, via the C401 line, to the "high pressure" compression system consisting of a CPL401 liquid piston compressor.

[0239] The multi-way distribution valve V401 allows the gas to be directed to the liquid piston compressor CPL401 to be either directed to the subsequent stages of the process; in other words, the gas entering the liquid piston compressor CPL401 and the gas exiting said compressor.

[0240] The C402 line connects the multi-way distribution valve V401 and the pressure exchange columns CN401, CN402, CN403 and CN404, respectively via the C402-1, C402-2, C402-3 and C402-4 lines. The C402-1, C402-2, C402-3 and C402-4 lines allow the transport of the gas to be compressed from the valve V401 to the columns CN401, CN402, CN403 and CN404 and the transport of the compressed gas from the columns CN401, CN402, CN403 and CN404 back to the valve V401.

[0241] Gas compression is carried out via gas-liquid pressure exchange columns. [Fig.4] illustrates 4 columns: CN401, CN402, CN403 and CN404.

[0242] The C403 line connects the multi-way distribution valve V402 and the pressure exchange columns CN401, CN402, CN403 and CN404, respectively via the lines C403-1, C403-2, C403-3 and C403-4. The lines C403-1, C403-2, C403-3 and C403-4 allow the transport of the liquid, in particular water, at high pressure cooled from the valve V402 to the columns CN401, CN402, CN403 and CN404 and the transport of the liquid, in particular water, at high pressure heated from the columns CN401, CN402, CN403 and CN404 to the valve V402.

[0243] The multi-way distribution valve V402 allows the high-pressure cooled and heated liquid to be directed as needed. Line C404 provides the fluid connection between the multi-way distribution valve V402 and the heat exchanger E401. Line C405 provides the fluid connection between the heat exchanger E401 and the high-pressure liquid reservoir STK401. Line C406 provides the fluid connection between the multi-way distribution valve V402 and the high-pressure fluid reservoir STK401. The C406 line includes the P401 pump.

[0244] The heat exchanger E401 is fluidically connected to the cooling system CL401 via lines C407 and C408. Line C407 carries a refrigerant at a temperature between 30 °C and 50 °C from the heat exchanger E401 to the cooling system CL401. Line C408 carries the first refrigerant at a temperature between 60 °C and 80 °C from the cooling system CL401 to the heat exchanger E401. Line C408 includes the pump P402.

[0245] The pump P401 pumps the cooled high-pressure liquid to the 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 pressure. Compression causes a temperature increase, which heats the high-pressure liquid. The heated high-pressure liquid is then returned to the valve V402 and directed via the line C404 to the heat exchanger E401 for cooling. The cooled high-pressure liquid is then directed via the line C405 to the tank STK401.

[0246] 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.

[0247] At the outlet of the liquid piston compressor CPL401, the gas is brought via the line C409 to a drying device not shown in [Fig.4]. Description of Figure 5

[0248] 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 the gas and the solid black arrows indicate the direction of the different refrigerants.

[0249] The gas to be treated is brought via the C501 line into the F501 filtration device.

[0250] The filtered gas is then conveyed to the CP501 compression system in such a way to undergo compression between 60 and 80 bars. At the outlet of the CP501 compression system, the gas is conveyed via the C503 line to the D501 drying device.

[0251] The gas is then directed via line C504 to heat exchanger E501. There, it undergoes liquefaction. Heat exchanger E501 is fluidically connected to cooling system CL501 via lines C506 and C507. Line C506 carries a refrigerant, at a temperature between 5°C and 20°C, from the system CL501 cooling to the E501 exchanger. The C507 line transports the refrigerant, at a temperature between 10°C and 40°C, from the E501 exchanger to the CL501 cooling system.

[0252] The liquefied gas is then conveyed to the heat exchanger E502 via line C505 for subcooling. The heat exchanger E502 is fluidically connected to the cooling system CL502 via lines C508 and C509. Line C508 carries a refrigerant at a temperature between -15°C and 5°C from the cooling system CL502 to the heat exchanger E502. Line C509 carries the refrigerant, at a temperature between 3°C and 10°C, from the heat exchanger E502 to the cooling system CL502.

[0253] 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.

[0254] Line C511 carries the liquefied and depressurized gas to the distillation column DC. The liquefied and purified carbon dioxide is recovered at the bottom of the DC distillation column and conveyed into the STK501 storage tank via the C519 line.

[0255] The gas is discharged from the top of the DC distillation column via line C513 connected to the heat exchanger E503, in order to undergo a second liquefaction. The gas discharged from the top of the DC distillation column is at a pressure between 10 and 30 bar and at a temperature between -25 °C and -20 °C. Line C514 carries the liquefied gas at a pressure between 10 and 20 bar and at a temperature between -40 °C and -20 °C from the heat exchanger E503 to the separator Sep.

[0256] 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 device 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 compression system CP501.

[0257] The E503 heat exchanger uses the subcooled gas from the circuit as its refrigerant. Line C510B and then line C512 supply the E503 heat exchanger. Line C510B includes valve V502, which allows the pressure and temperature of the subcooled gas to be adjusted for liquefying 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. Examples

[0258] 1. Purity of the liquefied carbon dioxide produced

[0259] A gas from a biogas purification unit produced by a methanizer of the following composition is treated by the process according to the invention: co2 93.7% ch4 6% 02 0.15% n2 0.15%

[0260] Table 1

[0261] At the outlet of the process, the gas has the following composition: unit Specification Analysis co2 % >=99.97 >100 h2o ppm <=20.00 <1 CO ppm <=5.00 =1.05 NOx PPm <=2.00 =0.01 S PPm <=0.10 =0.01 ch3oh PPm <=10.00 =0.00 ch3cho PPm <=0.20 =0.01 THCoCH 4 PPm <=20.00 =0.00 c6h6 PPm <=0.02 =0.00 h2 PPm <=10.00 =0.02 nh3 PPm <=2.50 =0.00 n2 PPm <=60.00 =0.02 02 PPm <=30.00 =0.00

[0262] Table 2

[0263] The carbon dioxide produced complies with the European Pharmacopoeia, the EN936 / EIGA / ISBT standard and Regulation RE 231 / 2012EC. 2. Energy consumption of the process

[0264] 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.

[0265] It has been observed that compressing the gas at "high pressure," i.e., at 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.

[0266] The calculation of energy balances was carried out for the liquefaction and purification of a carbon dioxide gas, comprising 6% methane.

[0267] Three different processes were compared:

[0268] -a comparative process carrying out the first liquefaction at P = 16-20 bars and T = -25 to -30 °C;

[0269] - a process according to the invention carrying out the first liquefaction at P = 72 bars and T = 21 °C using a device as described in [Fig.2] and using a set of three compressors as described in [Fig.3] and

[0270] -a process according to the invention carrying out the first liquefaction at P = 72 bars and T = 21 °C using a liquid piston compressor as described in [Fig.4].

[0271] The results are shown in the table below: First-action liquefaction conditions Energy gain Comparative setup P = 16-20 bar and T = -25 to -30 °C - Setup with 3 compressors in series P = 72 bar and T = 21 °C -23% Setup with the liquid piston compressor P = 72 bar and T = 21 °C -38%

[0272] In conclusion, the process according to the invention allows for a very clear saving of energy.

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. 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. 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 separation step j), then 1) 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. 5. The method according to claim 1, characterized in that the compression step b) 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 (F 101), - a compression system (CP101) bringing the gas to a pressure between 60 and 80 bar, - a drying device (D101), - a heat exchanger (E101), allowing the liquefaction of the gas, - a heat exchanger (E102), connected to a cooling system (CL101), allowing the subcooling of the gas, - a pressure-reducing valve (V101), - a distillation column (DC) allowing the purification of the gas.

7. 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) reintroducing the liquid phase into the distillation column (DC) and evacuates the gaseous phase via a pipe (C219).

8. 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 bars, and -a pipe (C221), which recovers the other gases.

9. 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. 10. A 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, for directing the gas to be compressed to the liquid-gas pressure exchanger, - a liquid-gas pressure exchanger comprising at least two columns (CN), - a distribution valve (V402) for distributing the high-pressure liquid to a cooling circuit, - a reservoir for storing the high-pressure liquid (STK401), - a pump, and - a heat exchanger (E401), itself connected to a cooling system (CL401), for cooling the high-pressure liquid.

11. 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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