Liquefied carbon dioxide purification process

Abstract

Process for Purifying Liquefied Carbon Dioxide. The invention relates to a process for purifying liquefied carbon dioxide from a liquefied gas containing more than 70% carbon dioxide by volume, comprising the following successive steps: a step of vaporizing the liquefied gas using a vapor condenser, then a step of compressing the gas leading to an increase in the pressure of said gas from the previous step of 3 to 5 bar, then at least one step of filtering the gas, then a step of self-liquefaction of the gas in the vapor condenser, then a step of depressurizing the liquefied gas via a pressure-reducing valve, then a step of distilling the fluid so as to separate the pure liquefied carbon dioxide from the other components of the gas, and then a step of recovering the carbon dioxide in liquid form. The invention also relates to the installation implementing this process. FIGURE 5

Description

Title of the invention: Process for purifying liquefied carbon dioxide. Technical field

[0001] The present invention relates to a method for purifying carbon dioxide in liquid form containing more than 70% carbon dioxide by volume. The invention also relates to a device for purifying carbon dioxide in liquid form and its use. Technical background

[0002] Currently, processes for valorizing waste, and in particular waste from biomass, are being sought. To this end, methanization processes are being developed.

[0003] Methanization is a process of decomposition of organic matter. It consists of fermenting livestock effluents or by-products from the agri-food industry. The principle is as follows: organic effluents are stored in a sealed tank called a "digester," where they are subjected to the action of microorganisms (bacteria) in the absence of oxygen (anaerobic fermentation) for a specific period (generally around 60 days). This process generates biogas, which contains, among other things, methane (CH4, in proportions of 50% to 70%), carbon dioxide (CO2), and an organic residue (called "digestate," used as fertilizer). The biogas can be converted into electricity or into gas and fuel for vehicles.

[0004] Methanization represents a substantial economic interest; the biogas produced can replace natural gas in all its current uses: heat production, electricity production and fuel for vehicles, and the digestate is fully utilized, notably in the form of fertilizer whose composition is much more complete than that of a chemical fertilizer.

[0005] Anaerobic digestion also presents an environmental benefit, as biogas is a renewable energy source. While its production and use do generate polluting emissions into the atmosphere, such as carbon dioxide, these emissions remain lower than those of fossil fuels. During biogas purification, a gas consisting mainly of carbon dioxide, called "lean gas," is produced. The present invention relates to the valorization of this "lean gas," rich in carbon dioxide, from these digesters. However, the carbon dioxide generated during this process is only of interest if it is purified and reaches a very high purity level while recovering the residual methane remaining in the lean gas. This This would allow for the recovery of all the methane and carbon dioxide produced by methanization. Therefore, it is necessary to develop a carbon dioxide purification process that aims for a high level of purity and is not excessively energy-intensive. Technical problem to solve

[0006] There is therefore a real need to provide an efficient and energy-saving carbon dioxide purification process that yields very high-purity carbon dioxide. In other words, the process according to the invention aims to valorize a by-product of methanation, namely a "lean gas," by isolating and purifying the carbon dioxide to obtain very high-purity carbon dioxide. The process according to the invention aims to treat a carbon dioxide-rich gas in liquid form and purify it to achieve food-grade quality, in particular by complying with EIGA Doc 126-11 (Appendix 1, page 6). The carbon dioxide produced can be used, for example, in the production of sparkling water.

[0007] The process according to the invention also aims to obtain liquid carbon dioxide of pharmaceutical grade, in compliance with the European Pharmacopoeia and GMP. It can, for example, be used for cryogenics.

[0008] 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.

[0009] It is also possible to utilize carbon dioxide-rich gases produced by cement plants, or by steam reforming or oxy-combustion processes. Indeed, the process according to the invention is not limited to carbon dioxide-rich gases from methanizers but to carbon dioxide-rich gases in general.

[0010] In general, the process according to the invention aims to valorize carbon dioxide-rich gases, which are reaction by-products, and which are generally sent to the atmosphere.

[0011] This process has the advantage of being energy-efficient, leading to good yield and providing carbon dioxide of very high purity.

[0012] This process may also have the advantage of recycling all or part of other components of the gas, such as methane, oxygen or nitrogen.

[0013] Furthermore, according to one embodiment, the liquefied gas can originate from one or more collection sites. It is then possible to recover the liquefied gas from each site and process it at a single, so-called central site, according to the purification process of the invention. The centralized site is thus shared. This allows for savings in energy, infrastructure, and money. Indeed, it is no longer necessary to install a separate site. purification for each collection site. This process therefore has the advantage of being able to recover gas from very small-scale collection sites, whose production volumes do not justify the installation of a purification site. Brief description of the invention

[0014] Thus, the invention relates to a process for purifying liquefied carbon dioxide from a liquefied gas comprising more than 70% by volume of carbon dioxide, comprising the following successive steps:

[0015] a) a step of vaporizing the liquefied gas using a vapor condenser, the temperature of the gas at the outlet of this step being between -10°C and 10°C and the pressure of the gas at the outlet of this step being between 15 and 25 bar, then

[0016] b) a gas compression step leading to an increase in the pressure of said gas from 3 to 5 bars; at the outlet of this step, the gas is at a pressure between 20 and 25 bars and then

[0017] c) at least one gas filtration step, then

[0018] d) a self-liquefaction step of the gas in the vapor-condenser of step a), the temperature of the gas at the outlet of this step being between -15°C and -30°C and the pressure of the gas at the outlet of this step being between 20 and 25 bar, then

[0019] e) a step of reducing the liquefied gas via a pressure-reducing valve, the pressure of the liquefied gas at the outlet of this valve being between 15 and 20 bar, then

[0020] f) a step of distilling the fluid so as to separate the pure liquefied carbon dioxide from the other components of the gas,

[0021] g) a step of recovering carbon dioxide in liquid form from step f).

[0022] The invention also relates to a device for purifying liquefied carbon dioxide from a liquefied gas comprising more than 70% by volume of carbon dioxide, comprising the following elements fluidly connected to each other in this order:

[0023] - a vapor-condenser (E101), allowing the vaporization of the fluid then

[0024] - a compressor (CP), then

[0025] - at least one filtration unit (F101), the filtration unit being connected to said vaporizer condenser, allowing the gas to liquefy, then

[0026] - a pressure relief valve (V101), then

[0027] - a distillation column (DC), allowing the gas to be purified, then

[0028] - a storage tank (STK101) connected to the base of the distillation column, allowing the recovery of purified liquefied carbon dioxide.

[0029] The invention finally relates to the use of the purification device to purify liquefied carbon dioxide.

[0030] Other advantageous features of the process according to the invention are specified below.

[0031] The process comprises the following successive steps:

[0032] h) a step of liquefying the gas recovered at the top of the distillation column in step f), the gas exiting this step being at a temperature between -55 and -30°C and at a pressure between 15 and 20 bar, then

[0033] i) a step of separating the liquid phase from the gaseous phase of the fluid resulting from the liquefaction step h), then

[0034] j) a step of recycling the liquid phase from the separation step i) to the distillation step f).

[0035] The process comprises the following successive steps:

[0036] - a step of heating the gaseous phase from step i),

[0037] - a membrane filtration step of the heated gas phase,

[0038] - a step for recycling the gas from the previous filtration step, before the step c) compression.

[0039] According to one embodiment, the process includes, upstream of step a), a step of collecting liquefied gas from one or more satellite production sites. Advantageously, the gas from the satellite production sites undergoes pretreatment comprising the following successive steps:

[0040] 1) a step of supplying a raw gas comprising more than 70% carbon dioxide carbon,

[0041] 2) a possible gas compression step, the gas pressure at the outlet of this the step being between 15 and 20 bars.

[0042] 3) a possible step of drying the liquefied gas and then,

[0043] 4) a liquefaction step, the liquefied gas exiting this step being at a temperature between -50 and -25°C and a pressure between 15 bars and 20 bars.

[0044] The process includes, upstream of step a), a step of storing the liquefied gas to be purified.

[0045] Other advantageous features of the device according to the invention are specified below.

[0046] The device comprises:

[0047] - a liquefier (E302) connected to the head of the distillation column (DC), then

[0048] - a separator (Sep) separating the liquid phase from the gaseous phase,

[0049] - a conduit (C310) connecting the separator area recovering the liquid phase to the distillation column (DC),

[0050] - a membrane filter (F304) connected to the area of ​​the separator recovering the phase gaseous, the membrane filter separating a gas consisting mainly of carbon dioxide from a gas consisting mainly of carbon dioxide,

[0051] the membrane filter (F304) is equipped

[0052] of a pipe (C312), discharging the gas comprising a minority of carbon dioxide, and

[0053] of a pipe (C313) connecting the filter area (F304) recovering the gas consisting mainly of carbon dioxide to the compressor (CP). Brief description of the figures

[0054] Non-limiting examples will now be discussed with reference to the figures.

[0055] Fig. 1 is a diagram of an installation implementing the process according to the invention.

[0056] Fig. 2 is a diagram of a second embodiment of an installation implementing the process according to the invention.

[0057] Fig. 3 is a diagram of a third embodiment of an installation implementing the process according to the invention.

[0058] Fig. 4 is a diagram of the installation implementing a pretreatment process at a satellite site.

[0059] Fig. 5 is a diagram of the installation illustrating pretreatment at a satellite site and purification at the central site. Detailed description

[0060] Other features, aspects, objects and advantages of the present invention will become even clearer upon reading the following description.

[0061] 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.

[0062] 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 purification process

[0063] The raw material of the process is a liquefied gas comprising more than 70% by volume of carbon dioxide relative to the total volume of the liquefied gas, preferably more than 80% by volume.

[0064] The process according to the invention can also be carried out on pure liquefied carbon dioxide gases. The aim of the process is then to increase the purity level of this gas.

[0065] 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 or oxy-combustion processes.

[0066] 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 and volatile organic compounds referred to below as VOCs.

[0067] At the process inlet, the temperature of the liquefied gas is preferably between -40 °C and -15 °C, preferably between -20 °C and -15 °C. The temperature of the liquefied gas depends on its chemical composition. Indeed, this directly influences its liquefaction temperature.

[0068] At the process inlet, the pressure of the liquefied gas is preferably between 15 bar and 25 bar. Generally, the initial liquefied gas is transported in tanks at a pressure of 16 to 17 bar.

[0069] The method according to the invention comprises at least the following 7 consecutive steps: steps a) to g). Step a) Vaporization of the liquefied gas

[0070] The liquefied gas is conveyed to a vapor-condenser. A pump can be used to regulate the flow rate at the inlet of the device.

[0071] Vaporization is carried out via a vapor-condenser, which transforms a liquid into a gas in step a) of the process according to the invention and a gas into a liquid in step d) of the process according to the invention. Thus, the energy produced for the liquid / gas phase change is used for the gas / liquid phase change.

[0072] The vapor-condenser is a heat exchanger equipped with two inlets and two outlets, one for each fluid. The liquefied gas, comprising more than 70% carbon dioxide by volume relative to the total volume of the liquefied gas, enters through the first inlet of the vapor-condenser. The vapor-condenser allows the liquefied gas to be vaporized.

[0073] The vaporized gas at the outlet of the vaporizer has a temperature between -10 °C and 10 °C and a pressure between 15 and 25 bars. Step b) Gas compression

[0074] The gas from the vapor-condenser is then compressed using a compressor. The purpose of this step is to impose a pressure differential when the gas re-enters the vapor-condenser in step d), this time to be liquefied. The pressure differential between the two inlets of the vapor-condenser allows for a greater temperature difference between the inlet fluids and the saturation temperature of carbon dioxide. This pressure differential allows the use of a single fluid to carry out both changes of state within the vapor-condenser.

[0075] Increasing the gas pressure reduces the power required to liquefy carbon dioxide and improves the energy efficiency of the process. This compression step eliminates the need for a thermodynamic cycle to liquefy the gas. The gas compression step results in an increase in the initial gas pressure of 3 to 5 bar.

[0076] At the compressor outlet, the gas pressure is between 20 and 25 bar and the gas temperature generally corresponds to ambient temperature + 5 °C. Step c) Filtration

[0077] 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.

[0078] The process according to the invention may include different types of filtration, each filtration step allowing the removal of a specific type of impurity.

[0079] Filtration can be activated carbon filtration, particle filtration, adsorption filtration or bacterial filtration.

[0080] The process according to the invention can comprise a single filtration step up to twenty steps. 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.

[0081] The number of filtration stages and the type of filtration to be carried out depend on the quality of the initial gas, 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.

[0082] Preferably, the process according to the invention comprises three filtration steps:

[0083] Cl) at least one or more filtration steps on an activated carbon filter, then

[0084] C2) one or more filtration stages on a particle filter,

[0085] C3) one or more filtration stages on an adsorption filter.

[0086] Activated carbon filtration aims to remove volatile organic compounds present in the gas. Particle 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 carried over from the previous filtration, whether in powder or dust form. The particle filter can, for example, be a molecular sieve.

[0087] Preferably, the process comprises between one and five particle filtration stages, and more particularly between two and three particle filtration stages. Step d) Self-liquefaction

[0088] The filtered gas then undergoes an auto-liquefaction step. The gas enters the vapor-condenser of step a) through the second inlet, preferably at a pressure between 20 and 25 bar and at a temperature between 0 and 40 °C.

[0089] For the purposes of this invention, self-liquefaction means liquefaction independent of any external energy input. In the present case, as indicated above, the energy generated by the condensation in step a) is used to carry out this self-liquefaction.

[0090] The pressure difference between the carbon dioxide in liquid form at the first inlet of the vaporizer and the carbon dioxide in gaseous form at the second inlet of the vaporizer allows both the vaporization of the liquid at the first inlet of the vaporizer, which is relatively cold (Temperature below -20 °C) and the liquefaction of the gas at the second inlet of the vaporizer liquefier, which is relatively hot (temperature close to 20°C, without additional external energy input).

[0091] The liquefied gas at the second outlet of the vapor-condenser has a temperature between -15°C and -30°C and a pressure between 20 and 25 bars. Step e) Expansion of the liquefied gas

[0092] Upon exiting the vapor-condenser, the liquefied gas undergoes expansion using an expansion valve. This step reduces the gas pressure after the autoliquefaction stage. The gas pressure is thus adjusted to the pressure required for the subsequent distillation stage. Preferably, the pressure after this expansion stage is between 15 and 20 bar.

[0093] The liquefied gas at the outlet of the expansion valve preferably has a temperature between -45 °C and -20 °C and a pressure between 15 and 20 bars. Step f) Distillation

[0094] The liquefied gas from the previous step undergoes distillation in order to isolate the carbon dioxide from other potentially present gases and impurities.

[0095] 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 -18 °C, at a pressure generally between 15 and 20 bar.

[0096] Step g) Recovery of liquefied carbon dioxide

[0097] 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. The liquefied carbon dioxide is then at a temperature between -20 and -30°C and at a pressure between 15 and 20 bar.

[0098] 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.

[0099] If the purity of the recovered liquid is insufficient, the liquid can be returned to the circuit to undergo the purification process according to the invention again. In one embodiment, the liquid can be sent back to the initial storage tank.

[0100] If the purity of the recovered liquid is satisfactory, the liquid can be sent directly to a storage tank or used directly for a subsequent application. Step h) Possible liquefaction of the gas

[0101] The gas recovered at the top of the distillation column in step f) 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 contain oxygen, nitrogen, methane, hydrogen, carbon monoxide, or other impurities depending on the origin of the initial gas.

[0102] This gas can undergo a liquefaction step to be cooled to a temperature between -55 °C and -35 °C and to a pressure between 15 and 20 bar. A liquefier using glycol water as a coolant can be used.

[0103] This step allows the carbon dioxide, which is not yet liquefied and isolated at this stage of the process, to be liquefied. At the end of this step, a two-phase fluid is obtained. Step i) Phase separation

[0104] The two-phase fluid from the previous step h) is brought to a separator, which allows the liquid phase to be separated from the gaseous phase.

[0105] Step j)_ Possible recycling of the liquid phase towards distillation

[0106] The liquid phase from the previous step i), comprising the liquefied carbon dioxide, can be recycled to the distillation step f). Step k) Possible recycling of the gaseous phase

[0107] The gaseous phase from the separation step i) can be heated using an exchanger.

[0108] The heated gas can be filtered through a membrane so as to separate a gas rich in carbon dioxide from a gas poor in carbon dioxide.

[0109] By gas rich in carbon dioxide is meant a gas composed of more than 50% by volume relative to the total volume of carbon dioxide gas.

[0110] By gas low in carbon dioxide, we mean a gas composed of less than 50% by volume relative to the total volume of carbon dioxide gas.

[0111] The carbon dioxide-rich gas can be recycled and returned to the circuit, before step c) of gas compression.

[0112] Low-carbon gas can be recycled, for example, to a unit producing the initial gas, or used on-site. If it is high-methane gas, 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 the methanization unit or to the wastewater treatment unit. In the case of processing gas from an oxy-combustion process, if the gas consists mainly of oxygen, it can be recycled to the combustion unit. In the case of processing gas from steam reforming, if the gas consists mainly of hydrogen, it can be recycled to the steam reforming unit.

[0113] Therefore, depending on the gas treated, it is possible to recycle, and thus recover, the gases recovered following the liquefaction of carbon dioxide. Step 1) Possible collection step

[0114] Prior to step a), a liquefied gas collection step containing carbon dioxide may take place. The liquefied gas may originate from one or more so-called "satellite" production sites. This gas may be conveyed to a central site.

[0115] By "central site" is meant the site on which the process described above is carried out.

[0116] By "satellite sites" we mean sites of initial gas production. The site A satellite site can be a methanization unit, a biogas purification unit, a steam reforming unit, an oxy-combustion unit, or even a unit for recovering gases produced by a cement plant and their mixtures. Satellite sites may have identical or different production volumes, with identical or different gas purities.

[0117] Satellite sites enable the production of raw gas. This raw gas is a mixture of gases consisting mainly of carbon dioxide. The composition of the gas mixture consisting mainly of carbon dioxide can vary from one satellite site to another. The composition of the gas mixture consisting mainly of carbon dioxide can vary even at the same satellite site. The raw gas produced at a satellite site is in gaseous form and contains more than 70% carbon dioxide by volume.

[0118] The gas produced by the satellite sites must undergo pretreatment before being transported to the central site for further purification. Indeed, the gas produced must to arrive at the central site in liquefied form. In other words, the purpose of pretreatment is the liquefaction of raw gas from one or more satellite sites.

[0119] This pretreatment comprises the following successive steps:

[0120] Step 1) supply of a raw gas

[0121] As indicated above, the raw gas may originate from one or more methanation units, one or more biogas purification units, one or more steam reforming units, one or more oxy-combustion units, or one or more units for recovering gases produced by a cement plant and their mixtures. The raw gas contains more than 70% carbon dioxide by volume relative to the total gas volume.

[0122] Step 2) Possible compression of the raw gas

[0123] The raw gas can undergo a compression step.

[0124] At the compressor inlet, the gas pressure can be between 1.05 and 1.40 bar. At the compressor outlet, the gas pressure is between 15 and 20 bar.

[0125] Increasing the gas pressure reduces the power required to liquefy carbon dioxide and improves the efficiency of the process.

[0126] During this compression step, the gas must be compressed at least to a pressure greater than the triple point pressure of carbon dioxide, i.e. 5.18 bars, in order to avoid icing.

[0127] Preferably, the compression is carried out in at least two stages, using a multi-stage compressor. At each stage, at the compressor outlet, at least two heat exchangers connected in series are used to recover the energy generated by the gas compression at different temperature levels. In addition, cooling the gas protects the compressor from potential overheating.

[0128] Preferably, an oil-free dry compressor is used. This prevents contamination of the gas with oil residues.

[0129] Preferably, the process uses a two-stage compressor. At the outlet of the first compressor, the gas temperature is between 110 and 210 °C, preferably between 110 and 190 °C. At the outlet of the second compressor, the gas temperature is between 150 and 220 °C. The at least two heat exchangers connected in series reduce this temperature range to between 25 and 50 °C, preferably to ambient temperature.

[0130] At the compressor outlet, the gas is preferably between 15 and 20 bar.

[0131] The gas can then pass through a buffer tank, which serves to stabilize the gas pressure within the process. In other words, the buffer tank aims to dampen fluctuations in the gas flow rate, which depend on the gas production process. This tank is positioned downstream of the compressor and upstream of the drying unit so that the pressure at the inlet of the drying unit remains constant.

[0132] Step 3) Possible drying of the gas

[0133] The gas can then be dried so as to eliminate the remaining traces of water and reach a dew point temperature at the outlet of the drying device of between -65 and -45 °C at 20 bars or a water content of less than 20 ppm.

[0134] Preferably, a zeolite that selectively adsorbs water is used. The apparatus used to perform this drying step can be equipped with two columns, one adsorbing traces of moisture from the gas and the second allowing the desorption of water, i.e., the regeneration of the column. Continuous, cyclic operation of the two columns is preferred.

[0135] This drying step is essential if a food grade of the final liquefied carbon dioxide is targeted.

[0136] Step 4) Gas liquefaction

[0137] The gas, possibly compressed and dried, then undergoes a liquefaction step. The gas passes through a liquefier, which allows the carbon dioxide to change state from gas to liquid. The liquefier is a heat exchanger that uses a refrigerant. At the outlet of the liquefier, a two-phase fluid containing liquefied carbon dioxide is obtained. It is at a temperature between -50 and -25°C and a pressure between 15 and 20 bar.

[0138] The liquefied gas is directed to a tank where it is stored. Preferably, the stored gas has a temperature between -50 and -25 °C and a pressure between 15 and 20 bar.

[0139] The gas thus liquefied can be transported to the central site where it will be purified.

[0140] The process according to the invention includes, upstream of step a), a storage step liquefied gas to be purified.

[0141] This embodiment of the process, which combines satellite sites and a central site, has the advantage of pooling equipment where possible, in order to reduce the costs associated with the production and purification of liquefied carbon dioxide. This can be achieved by collecting raw gas containing carbon dioxide from multiple production sites. The liquefaction of the raw gas can be carried out at the satellite sites. The gas thus obtained can be transported to a central site, where it can then be stored. The central site has the necessary equipment for its purification. Thus, a single distillation column can be used to purify liquefied carbon dioxide from multiple independent production sites. Purification device

[0142] The invention also relates to the device, which enables the implementation of the process according to the invention.

[0143] The carbon dioxide purification device according to the invention comprises the following elements fluidly connected to each other in this order: 1. A vapor-condenser, 2. A compressor, 3. At least one filter unit, said filter being connected to the vaporizer-condenser, 4. A pressure relief valve, 5. A distillation column and 6. A storage tank.

[0144] As described above, the vaporizer, compressor and filter(s) form a loop, allowing the vaporizer to operate with only one fluid, which is the carbon dioxide-rich fluid to be purified.

[0145] Preferably, the compressor is a dry, oil-free compressor.

[0146] 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.

[0147] According to a particular embodiment, the device comprises 3 filtration units mounted in series and arranged in this order:

[0148] -an activated carbon filtration unit,

[0149] -a particle filtration unit and

[0150] -an adsorption filtration unit.

[0151] According to a particular embodiment, the device comprises 3 filtration units mounted in series and arranged in this order:

[0152] - an activated carbon filtration unit,

[0153] - a particle filtration unit, and

[0154] - a bacterial filtration unit.

[0155] According to a particular embodiment, the device comprises 4 filtration units connected in series and arranged in this order:

[0156] - an activated carbon filtration unit,

[0157] - a particle filtration unit,

[0158] - an adsorption filtration unit, and

[0159] - a bacterial filtration unit.

[0160] The device may include pumps upstream and downstream of the device so as to adjust the flow rate of the fluid in the device.

[0161] The device may include, connected to the base of the distillation column, a bypass valve, which directs the purified carbon dioxide according to its degree of purity.

[0162] If the carbon dioxide purity level is satisfactory, it is sent to the storage tank downstream of the device. If the carbon dioxide purity level is not satisfactory, it is sent to a storage tank located upstream of the device, i.e., before the vapor-condenser.

[0163] The device may include a set of elements for treating the fluids recovered at the top of the distillation column.

[0164] Thus, to treat the fluids recovered at the top of the distillation column, the device according to the invention can be supplemented by the following elements and in this order:

[0165] - a liquefier connected to the head of the distillation column, then

[0166] - a separator separating the liquid phase from the gaseous phase,

[0167] - a conduit connecting the separator area recovering the liquid phase to the distillation column,

[0168] - a membrane filter connected to the separator area recovering the gaseous phase, the membrane filter separating a gas consisting mainly of carbon dioxide from a gas consisting mainly of carbon dioxide,

[0169] The membrane filter is equipped with:

[0170] -of a pipe, evacuating the gas comprising a minority of carbon dioxide, and

[0171] -of a pipe connecting the filter area recovering the gas consisting mainly of carbon dioxide to the compressor.

[0172] 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.

[0173] The device as described above is intended to be placed on a central site.

[0174] Satellite sites may, for their part, be equipped with a fluid pretreatment device. This pretreatment device makes it possible to liquefy the raw carbon dioxide gas produced either directly on the satellite site or from another production site.

[0175] This pre-treatment device comprises:

[0176] -a compressor,

[0177] -possibly a buffer tank,

[0178] -a drying device,

[0179] -a liquefier, and

[0180] -a storage tank.

[0181] The invention finally aims at using the device described above to purify liquefied carbon dioxide.

[0182] 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

[0183] Fig. 1 is a diagram of an embodiment of the device implementing the process according to the invention.

[0184] The liquefied gas to be treated is fed into the device according to the invention via the inlet line C101 to the vaporizer-condenser E101 so as to undergo vaporization. The gas is then fed via the line C102 into the oil-free dry compressor CP. At the compressor outlet, the gas is preferably at a maximum temperature of 45 °C and a pressure of 25 bar. The gas is then fed via the line C103 into the filtration unit F101. The filtered gas is then returned to the vaporizer-condenser E101 so as to undergo liquefaction. The liquefied gas exits the vaporizer-condenser E101 via the line C105 and undergoes expansion via the expansion valve VIOL. The gas is preferably at a temperature between -45 and -20 °C and at a pressure between 15 and 20 bar. The decompressed gas is then brought to the DC distillation column via the C106 line.The purified and liquefied carbon dioxide is recovered at the bottom of the DC distillation column and conveyed to the STK101 storage tank via line C107. The gas is discharged at the top of the DC distillation column via line Cl08. Description of Figure 2

[0185] Fig. 2 is a diagram of a second embodiment of the device implementing the process according to the invention.

[0186] The liquefied gas to be treated is fed into the device according to the invention via the inlet line C201 to the pump P201. It is then fed via the line C202 into the vaporizer E201 to undergo vaporization. The gas is then fed via the line C203 into the oil-free dry compressor CP. At the compressor outlet, the gas is preferably at a temperature of 50 °C and a pressure of 25 bar. The gas is then fed via the line C204 to a series of filtration units F201, F202, and F203. Preferably, the filtration unit F201 is an activated carbon filtration unit, the filtration unit F202 is a particle filtration unit, using, for example, a molecular sieve and / or bacterial filtration, and the filtration unit F203 is an adsorption filtration unit. The gas is then returned via the C205 line to the E201 vapor condenser in order to undergo liquefaction.The liquefied gas exits the vapor-condenser E201 via line C206 and undergoes expansion via the expansion valve V201. The gas is preferably at a temperature between -45 and -20 °C and a pressure between 15 and 20 bar. The decompressed gas is then conveyed via line C207 to the DC distillation column. The purified and liquefied carbon dioxide is collected at the bottom of the DC distillation column and conveyed via line C208 to pump 202. The gas is then conveyed to the STK202 storage tank via line C209. The gas is discharged from the top of the DC distillation column via line C210. Description of Figure 3

[0187] Fig. 3 is a diagram of a third embodiment of the device implementing the method according to the invention.

[0188] The liquefied gas to be treated is conveyed to the storage tank STK301 via line C301. It is then conveyed via line C302 to the vaporizer-condenser E301 for vaporization. The gas is then conveyed via line C303 to the oil-free dry compressor CP. At the compressor outlet, the gas is preferably at a temperature of 50 °C and a pressure of 25 bar. The gas is then conveyed via line C304 to the filtration unit F301. The gas is then returned via line C305 to the vaporizer-condenser E301 for further liquefaction. The liquefied gas exits the vaporizer-liquefier E301 via line C306 and undergoes expansion via the expansion valve V301. The gas is preferably at a temperature between -45 and -20 °C and a pressure between 15 and 20 bar. The decompressed gas is then brought via the C307 line to the DC distillation column.The purified and liquefied carbon dioxide is recovered at the bottom of the DC distillation column and conveyed via line C314 to valve V302.

[0189] Depending on the purity level of the gas obtained, the gas is directed either to the STK302 storage tank or to the STK301 initial storage tank. In other words, if the gas has the required purity, it is sent to the STK302 storage tank. If it does not have the required purity, it is sent to the STK301 initial storage tank.

[0190] The gaseous mixture recovered at the top of the DC distillation column is conveyed to the liquefier E302 via the line C308. The liquefier E302 can use a refrigerant. Glycol water is denoted EG in [Fig. 3].

[0191] At the outlet of the liquefier E302, the fluid is two-phase. It is fed to the separator Sep. The liquid phase from the separator Sep, which contains liquefied carbon dioxide, is returned to the distillation column DC via line C310. The gaseous phase from the separator Sep is fed to the membrane filtration unit F304. The filtration unit F304 separates a gas rich in carbon dioxide that was not liquefied during the process from a gas low in carbon dioxide. The gas rich in carbon dioxide is recycled upstream of the compressor CP via line C313. The gas low in carbon dioxide, containing, for example, methane and other gases, is discharged via line C312. Description of Figure 4

[0192] Fig. 4 illustrates an embodiment of a pretreatment device operating on a satellite site.

[0193] The raw gas to be purified arrives via line C401 to feed an oil-free dry compressor CP. At the compressor outlet, the gas is preferably at ambient temperature and a pressure between 15 and 20 bar. The gas is then conveyed via line C402 to a drying device D401 to remove any residual water. From the drying device D401, the gas is conveyed via line C403 to the liquefier E401, which is equipped with a cooling device CR for gas liquefaction. The resulting liquefied gas is conveyed via line C404 to the storage tank STK401. Description of Figure 5

[0194] Figure 5 illustrates an embodiment of the process according to the invention combining a pretreatment device at a satellite site and a purification device at a central site. This diagram illustrates the process of purifying the raw gas into purified gas.

[0195] The raw gas to be purified arrives via line C501 to feed an oil-free dry compressor CP. At the compressor outlet, the gas is preferably at ambient temperature and a pressure between 15 and 20 bar. The gas is then conveyed via line C502 to the drying unit D501 to remove any residual water. From the drying unit D501, the gas is conveyed via line C503 to the liquefier E501, which is equipped with a cooling unit CR for gas liquefaction. The resulting liquefied gas is conveyed via line C504 to the storage tank STK501.

[0196] The liquefied carbon dioxide is then conveyed to the central site for purification. The gas is conveyed via an inlet line C505 to a vaporizer-condenser E502 for vaporization. The gas is then conveyed via line C506 to the oil-free dry compressor CP. At the compressor outlet, the gas is preferably at a maximum temperature of 45 °C and a pressure of 25 bar. The gas is then conveyed via line C507 to the filtration unit F501. The gas is then returned via line C508 to the vaporizer-condenser E502 for liquefaction. The liquefied gas exits the vaporizer-condenser E502 via line C509 and undergoes expansion via the expansion valve V501. The gas is preferably at a temperature between -45 and -20 °C and a pressure between 15 and 20 bar. The decompressed gas is then brought to the DC distillation column via the C510 line.

[0197] The purified and liquefied carbon dioxide is recovered at the bottom of the DC distillation column and conveyed into a storage tank STK502 via line C512.

[0198] The gas is vented at the top of the DC distillation column via the C513 line.

[0199] The following examples are intended to illustrate the present invention, but are in no way limiting. Examples

[0200] 1. Purity of the liquefied carbon dioxide produced

[0201] 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 91.7% ch4 8% 02 0.15% n2 0.15%

[0202] Table 1

[0203] 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

[0204] Table 2

[0205] 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

[0206] The process according to the invention consumes from 0.17kW / h to 0.27kW / h per kg of liquefied CO2 produced, depending on the composition of the gas treated.

[0207] The energy impact of the purification process according to the invention is reduced by the use of the vapor liquefier. The latter makes it possible to conserve and reuse the energy required to carry out the phase changes of the gas to be purified.

[0208] When liquefied gas is recovered from satellite sites and processed at the centralized site, pooling resources for gas purification allows for a reduction in the energy cost of this process.

Claims

Demands

1. A process for purifying liquefied carbon dioxide from a liquefied gas containing more than 70% by volume of carbon dioxide, comprising the following successive steps: a) a step of vaporizing the liquefied gas using a vapor condenser, the temperature of the gas exiting this step being between -10°C and 10°C and the pressure of the gas exiting this step being between 15 and 25 bar; then b) a step of compressing the gas leading to an increase in the pressure of said gas from step a) from 3 to 5 bar, the gas exiting this step being at a pressure between 20 and 25 bar; then c) at least one step of filtering the gas; then d) a step of self-liquefaction of the gas in the vapor condenser of step a), the temperature of the gas exiting this step being between -15°C and -30°C and the gas exiting this step being at a pressure between 15 and 25 bar. of this step d) being between 20 and 25 bars,then e) a step of depressurizing the liquefied gas via a depressurization valve, the pressure of the liquefied gas at the outlet of this valve being between 15 and 20 bar, then f) a step of distilling the fluid so as to separate the pure liquefied carbon dioxide from the other components of the gas, g) a step of recovering the carbon dioxide in liquid form from step f).

2. The process according to claim 1, characterized in that it comprises the following successive steps: h) a liquefaction step of the gas recovered at the top of the distillation column in step f), the gas exiting this step being at a temperature between -55 and -30°C and at a pressure between 15 and 20 bars, then i) a separation step of the liquid phase from the gaseous phase of the fluid from the liquefaction step h), then j) a recycling step of the liquid phase from the separation step i) to the distillation step f).

3. 3. A method according to any one of the preceding claims, characterized in that it comprises the following successive steps: - a step of heating the gaseous phase from step i), - a membrane filtration step of the heated gas phase, - a recycling step of the gas from the previous filtration step, before step c) of compression.

4. 4. A process according to any one of the preceding claims, characterized in that it comprises, upstream of step a), a step of collecting liquefied gas from one or more satellite production sites.

5. 5. A process according to claim 4, characterized in that the gas from the satellite production sites undergoes pretreatment comprising the following successive steps: 1) a step of supplying raw gas containing more than 70% carbon dioxide, 2) an optional gas compression step, the gas pressure at the outlet of this step being between 15 and 20 bar, 3) an optional liquefied gas drying step, and then 4) a liquefaction step, the liquefied gas at the outlet of this step being at a temperature between -50 and -25°C and a pressure between 15 and 20 bar.

6. 6. A method according to any one of the preceding claims, characterized in that it comprises, upstream of step a), a step of storing the liquefied gas to be purified.

7. 7. Device for purifying liquefied carbon dioxide (1), from a liquefied gas comprising more than 70% by volume of carbon dioxide, comprising the following elements fluidly connected to each other and in this order: - a vaporizer-condenser (E101), allowing the vaporization of the fluid then - a compressor (CP), then - at least one filtration unit (F101), the filtration unit being connected to said vaporizer-condenser, allowing the liquefaction of the gas, then - an expansion valve (V101), then - a distillation column (DC), allowing the purification of the gas, then - a storage tank (STK101) connected to the bottom of the distillation column, allowing the recovery of the purified liquefied carbon dioxide.

8. Device according to claim 7, characterized in that it comprises:

9. - a liquefier (E302) connected to the head of the distillation column (DC), then - a separator (Sep) separating the liquid phase from the gaseous phase, - a pipe (C310) connecting the separator area recovering the liquid phase to the distillation column (DC), - a membrane filter (F304) connected to the separator area recovering the gas phase, the membrane filter separating a gas consisting mainly of carbon dioxide from a gas consisting mainly of carbon dioxide, the membrane filter (F304) is equipped of a pipe (C312), discharging the gas comprising a minority of carbon dioxide, and of a pipe (C313) connecting the filter area (F304) recovering the gas consisting mainly of carbon dioxide to the compressor (CP).

9. Use of the device as defined in any one of claims 7 and 8 to purify a liquefied carbon dioxide gas.

Images