Carbon Dioxide Compression System and Method Using Multiphase Compression and Supercritical Pumps

Abstract

The present invention relates to a method for compressing carbon dioxide, comprising at least the following steps: a) a step (Comp) of compressing a fluid to a pressure (P1) above 8 bar and strictly below 50 bar; b) a step of cooling the compressed fluid to a temperature (T1') between -50 °C and 15 °C to partially liquefy the fluid; the gas fraction of the fluid is between 1% and 99% by volume; c) a step (PP) of compressing the cooled and compressed fluid to a pressure (P3) strictly lower than the critical pressure of the fluid by multistage compression; d) preferably, a step (Ref2) of cooling the fluid produced by the multistage compression step (PP); at least carbon dioxide is completely liquefied; e) a step (PSP) of compressing the fluid such that the pressure (P4) of the fluid exceeds the critical point of the fluid. The present invention also relates to a transportation and storage method, as well as a system for compressing carbon dioxide.

Description

【Technical Field】 【0001】 The present invention relates to the field of compression of carbon dioxide for the transport and isolation (storage) of carbon dioxide. 【0002】 In the context of the fight against global warming, significant efforts are required to reduce the amount of carbon dioxide (CO2) released into the atmosphere. Developing carbon dioxide capture and storage facilities is one of the most promising ways to dramatically reduce emissions from the most polluting industries and enable a soft energy transition. These systems aim to capture and process the CO2 emitted by these industries and to isolate it underground, in suitable geological formations or in artificial reservoirs. 【Background Art】 【0003】 Known techniques for storing captured carbon dioxide consist of compressing the carbon dioxide in gaseous form and then cooling it to convert it into a liquid or supercritical phase for its transport and storage. 【0004】 A patent application (Patent Document 1) relates to a method of compressing carbon dioxide by maintaining it in the gas phase. The pressure of the gas is increased in successive compression stages until it exceeds the critical pressure. The stream is then cooled to the desired temperature for transport. 【0005】 A patent application (Patent Document 2) relates to a method of compressing carbon dioxide in a gaseous state to a pressure strictly below the critical pressure. The carbon dioxide is then cooled to a completely liquid state. It is then compressed in the liquid state until it reaches the critical pressure. 【0006】 In the case of these methods, carbon dioxide requires a very high level of purity: impurities can, on the one hand, cause yield losses and / or degradation of single-phase compression systems (liquid or gas) and, on the other hand, modify the phase change characteristics of the fluid (in particular, the critical point of the transition to the supercritical state). 【0007】 Patent Document 3 (Patent Document 4), which is a patent application filed by the present applicant, includes a method for the capture and compression of carbon dioxide using a multiphase pump, and this is also known. 【0008】 However, in this method, a transition to the supercritical state occurs within the multiphase pump, which is not optimal for the operation of the pump and the method. 【Prior Art Documents】 【Patent Documents】 【0009】 【Patent Document 1】 International Publication No. 2011 / 101296 【Patent Document 2】 Published Application No. 2010 / 266154 【Patent Document 3】 Specification of French Patent Application Publication No. 2891609 【Patent Document 4】 Specification of US Patent Application Publication No. 2009 / 075219 【Summary of the Invention】 【Means for Solving the Problems】 【0010】 (Summary of the Invention) An object of the present invention is to provide a method and a system for compressing a fluid containing carbon dioxide and likely to contain a high level of impurities (preferably at least 5% impurities), including non-condensable gases, with improved energy efficiency. 【0011】 The present invention thus relates to a method for compressing a fluid containing at least 80% carbon dioxide, the method comprising at least the following steps: a) Compressing the fluid in one or more compression stages to a pressure of more than 8 bar and strictly less than 50 bar. b) Step of cooling the compressed fluid to a temperature between -50°C and 15°C; the fluid pressure is maintained above 8 bar and strictly below 50 bar, and partially liquefies the carbon dioxide in the fluid; the gas volume fraction of the fluid ranges from 1% to 99%, c) Step of performing multiphase compression of the cooled and compressed fluid to a pressure strictly below the critical pressure of the fluid; the multiphase compression is performed in one or more multiphase compression stages, d) Preferably, step of cooling the fluid from multiphase compression to completely liquefy at least the carbon dioxide in the fluid; e) Step of compressing the fluid so that the fluid pressure exceeds the critical point of the fluid, preferably to a temperature below 60°C. 【0012】 Advantageously, in step a), the fluid is compressed using a single integrated gear compressor. 【0013】 Preferably, between at least two compression stages in step a), the fluid is cooled to be maintained at a temperature between 10°C and 100°C. 【0014】 Advantageously, after cooling the fluid after at least one compression stage in step a), the fluid in the liquid state is separated from the fluid in the gaseous state. 【0015】 According to the configuration of the present invention, the multiphase compression is performed using a helicoaxial type multiphase pump. 【0016】 Preferably, the multiphase compression is performed in several multiphase compression stages, and the fluid is preferably cooled by a cooler, preferably a water cooler, between at least two multiphase compression stages. 【0017】 According to one embodiment of the present invention, the fluid is carbon dioxide containing 0% to 20% impurities. 【0018】 According to a variant of the invention, after step d) of cooling the fluid from the multiphase compression stage, if the impurities contain non-condensable gas, the fluid is preferably treated by gas / liquid separation to reduce the gas volume fraction to a value of less than 5%. 【0019】 The invention also relates to a method for the transport and storage of a fluid containing at least 80% carbon dioxide, the fluid being compressed according to the compression method described above and then transported to a storage location where it is stored in a storage reservoir of the storage location. 【0020】 The invention also relates to a system for compressing a fluid containing at least 80% carbon dioxide, the compression system continuously comprising at least one compression means, a first cooling means for partially liquefying the fluid, a multiphase pump, a second cooling means for completely liquefying the fluid, and a supercritical pump, the compression means preferably consisting of a single integrated compressor with gears, and this system is suitable for implementing the method described above. 【0021】 Advantageously, the system comprises several compression means and a third cooling means and may further comprise a gas / liquid separator, which is preferably arranged between the compression means. 【0022】 Preferably, the system comprises at least one gas / liquid separation means, which is preferably located between the second cooling means and the supercritical pump. 【Embodiments for Carrying Out the Invention】 【0023】 (Brief Description of the Drawings) Other features and advantages of the method and / or system according to the invention will become apparent from the following description of embodiments given by way of non-limiting example with reference to the following attached drawings: - Figure 1 shows a fluid compression system according to the invention, - Figure 2 illustrates a fluid compression method according to the invention. - Figure 3 compares the thermodynamic path of the compression method according to the present invention (path c)) with the thermodynamic paths of the compression methods of the prior art (paths (a) and (b)), and - Figure 4 illustrates various gas / liquid saturation curves for various fluids containing carbon dioxide. 【0024】 (Detailed Description of Embodiments) The present invention is part of the chain of carbon dioxide capture and storage, called "conditioning" or "compression". Its purpose is to transfer the captured CO2 from its capture conditions (for example, the pressure ranges from 1 to 3 bar (0.1 to 0.3 MPa), preferably from 1 to 1.5 bar (0.1 to 0.15 MPa), and the temperature ranges from 10 °C to 50 °C, preferably from 10 °C to 35 °C, while the carbon dioxide may contain various types and levels of impurities depending on where it is captured) to supercritical conditions (the pressure exceeds the supercritical pressure, for example, 74 bar, i.e., 7.4 MPa for pure or nearly pure carbon dioxide, and the temperature ranges from 0 °C to 60 °C) for its transportation and isolation. 【0025】 To achieve this ultimate goal, the present invention relates to a novel method and system for CO2 compression, and in particular, it is equipped with a multiphase pump. According to the present invention, it is possible to compress CO2 regardless of the presence of a high level of impurities (more than 5% by volume). This method is also optimized in terms of energy efficiency for the flow resulting from capture. 【0026】 Impurities are understood to be any molecules different from CO2 molecules. Impurities can be solid, liquid or gaseous particles: they may be related, in particular, to non-condensable gases, for example, dinitrogen or dihydrogen. 【0027】 What is understood by "pure or nearly pure carbon dioxide" is less than 1% impurities in carbon dioxide. 【0028】 The level of impurities is understood to be the volume fraction of impurities in the fluid. 【0029】 The non-condensable gas is understood to be a gas whose liquefaction temperature is extremely low, for example, less than -150°C. 【0030】 The critical point is the point corresponding to the pressure and temperature when the fluid transitions to the supercritical state; the critical temperature is the lowest temperature at which the fluid can start to transition to the supercritical state. 【0031】 The multiphase pump is understood to be a device for compressing a fluid that flows into a compression device in a multiphase form having at least one gas phase and at least one liquid phase. The multiphase pump may correspond, inter alia, to the helical shaft multiphase pump described in patent applications FR-2,665,224 (US-5,375,976), FR-2,899,944 (US-2009 / 311,094) or FR-3,010,463 (US-2016 / 222,977). The multiphase pump can then include one or more multiphase compression stages. The multiphase pump can comprise at least one movable wheel that rotates about an axis and is mounted within a casing, and at least one fixed wheel fixed to the casing, the movable wheel comprising a hub that comprises at least two blades, the hub, casing and two of the blades defining at least two channels having a centrifugal portion. The multiphase pump can also correspond to a gear pump or any other type of multiphase pump technology. 【0032】 The supercritical pump is understood to be a device for compressing a fluid that flows in and out in a supercritical state, or a fluid that flows into the pump in a liquid phase and flows out of the supercritical pump in a supercritical state. Without being limited to these examples, the technology used can be as follows: diaphragm pump, gear pump, canned motor pump, peristaltic pump. 【0033】 The multiphase pump can consist of one or more multiphase stages, and one or more non-helical shaft stages are further provided to bring the fluid to a supercritical state at the multiphase pump outlet. The multiphase pump is, therefore, also a supercritical pump. 【0034】 The present invention relates to a method for compressing a fluid containing at least 80% carbon dioxide. In other words, the fluid can be carbon dioxide containing 0% to 20% impurities. 【0035】 Advantageously, the fluid can contain 5% to 20% impurities. 【0036】 When the fluid enters the compression method, the pressure of the fluid can be 1 to 3 bar (0.1 to 0.3 MPa), preferably 1 to 1.5 bar (0.1 to 0.15 MPa), that is, a pressure close to atmospheric pressure, and the temperature is 10°C to 50°C, preferably 10°C to 35°C. 【0037】 According to the present invention, the method includes at least the following steps: a) Compressing the fluid in one or more compression stages to a pressure above 8 bar (0.8 MPa) and strictly below 50 bar (5 MPa). This pressure range is important for improving the energy efficiency of the method. In fact, below a pressure of 8 bar (0.8 MPa), the liquefaction temperature of carbon dioxide is below -50°C. Therefore, cooling for partial liquefaction of carbon dioxide requires a significant amount of energy consumption. Furthermore, when exceeding 50 bar (5 MPa), using multiphase compression loses its significance. This is because the pressure is considered to be too close to the critical pressure (74 bar, i.e., 7.4 MPa in the case of pure or nearly pure carbon dioxide). 【0038】 By using several compression stages, it becomes possible to improve the overall compression efficiency. 【0039】 Preferably, the fluid can be compressed to a pressure ranging from 10 to 30 bar (1 to 3 MPa), more preferably from 12 to 20 bar (1.2 to 2 MPa), and these ranges of values result in a better reduction in the energy consumption of the method. 【0040】 At the outlet of the last compression stage, the temperature of the fluid can range, for example, from 10 °C to 100 °C. b) cooling the compressed fluid to a temperature between - 50 °C and 15 °C; the fluid pressure is maintained by varying slightly while remaining substantially at the pressure of step a) or above 8 bar (0.8 MPa) and strictly below 50 bar (5 MPa) during cooling, partially liquefying the carbon dioxide of the fluid, and the gas volume fraction of the fluid ranges from 1% to 99% at the cooling outlet. Preferably, the compressed fluid can be cooled to a temperature above - 50 °C and strictly below 0 °C, thereby further reducing the energy consumption of the method. 【0041】 What is understood by partial liquefaction is that the fluid is multiphase and contains a part in gaseous form and another part in liquid form, i.e., the fluid is not completely liquefied and a part of the fluid remains in gaseous form (e.g., at least 1%). The gas volume fraction of the fluid can advantageously range from 50% to 95%, more preferably from 60% to 90%, and these ratios make it possible to improve the energy performance of the method. c) A step of performing multiphase compression of the compressed and cooled fluid to a pressure strictly below the critical pressure of the fluid, for example using a multiphase pump. The fluid thus remains in a multiphase state consisting of a gaseous part and a liquid part, which makes it possible to improve the multiphase pump efficiency. The multiphase compression can be carried out in one or more multiphase compression stages, especially according to the pressures at the inlet and outlet of the multiphase pump. At the multiphase compression outlet, the temperature of the fluid can range from 0 °C to 60 °C. By using multiphase compression, it becomes possible to accept carbon dioxide with a high level of impurities: for example, the fluid can contain at least 5% impurities, which does not apply to cases where the prior art is such that the compression is only single-phase. Therefore, the method of the present invention can accept the gas as it is captured and does not require pretreatment of the fluid to remove impurities. This simplifies the overall method and makes it possible to reduce the overall carbon dioxide storage cost. d) Preferably, a step of cooling the fluid from the multiphase compression to completely liquefy at least the carbon dioxide of the fluid. In other words, step d) is optional. By performing step d) at the cooling outlet, the carbon dioxide of the fluid is in a completely liquid state, and the impurities can be in a liquid or gaseous state. The transition of the carbon dioxide to the liquid state facilitates the next step of bringing the fluid to a supercritical state. Thus, since the next step is facilitated, the energy performance of the method is also improved. e) A step of compressing the fluid, preferably using a supercritical pump, such that the fluid pressure exceeds the critical point (critical pressure) of the fluid. The transition to the supercritical state inside the supercritical pump is promoted when the carbon dioxide is completely liquefied in advance. Preferably, at the supercritical pump outlet, the temperature of the fluid is less than 60 °C to limit the heat loss for subsequent fluid transport and / or storage. 【0042】 Advantageously, in step a), the fluid can be compressed using an integrally geared compressor, and this type of compressor is suitable for compressing gaseous fluids. 【0043】 According to a variant of the invention, between at least two compression stages of step a), the fluid can be cooled using cooling means, such as a heat exchanger, and maintained at a temperature between 10°C and 100°C. The cooling can be carried out, for example, by a direct or indirect heat exchanger. By cooling the fluid before the next compression stage, it is prevented from reaching an excessive temperature, thereby limiting its subsequent cooling and enabling the various compression means (especially compressors) at each stage to operate at a temperature close to the operating temperature, and thus at a temperature close to their nominal efficiency. 【0044】 In this variant, the gaseous and liquid parts of the fluid can preferably be separated after cooling the fluid after at least one compression stage of step a). 【0045】 Therefore, when the fluid is cooled after a compression stage, the liquid contained in the fluid can advantageously be separated after this cooling step. In fact, while cooling the fluid, the amount of liquid increases by condensation, and the separation step can therefore be useful after cooling, removing the liquid as much as possible before the next compression stage and thus best protecting the next compression means. For example, the liquid contained in the fluid can be separated after each cooling carried out after each compression stage, avoiding damage to the compression means of the next stage. 【0046】 Advantageously, the multiphase compression of step c) can be carried out by a helical shaft type multiphase pump. This type of pump provides good compression efficiency but may be accompanied by high fluctuations in the gas fraction in the fluid. 【0047】 According to an embodiment of the invention, during the multiphase compression of step c), the fluid can be cooled by a cooler, preferably a water cooler, between at least two multiphase compression stages. The temperature rise is thus limited, making it possible to avoid excessive high temperatures and associated heat losses. This also makes it possible to increase the fluid level at the inlet of the next multiphase compression stage. 【0048】 Advantageously, the fluid can be carbon dioxide containing 0% to 20% impurities, preferably 5% to 20% impurities. Thus, it is possible to use a compression method immediately after capture, and there is no need to pretreat the fluid to limit the impurity level to a very small proportion (less than 5%). 【0049】 Preferably, after step d) of cooling the fluid from multiphase compression, if the impurities contain non-condensable gas (especially with a volume fraction of non-condensable gas exceeding 5%), the fluid can preferably be treated by gas / liquid separation to reduce the gas volume fraction to a value less than 5%. 【0050】 For example, in order to perform this treatment intended to reduce the gas volume fraction to a value less than 5%, after the cooling step of step d), the fluid in the gaseous state can be separated from the fluid in the liquid state: the gas contained in the fluid, especially the non-condensable gas, can be separated, limiting the proportion of gas in the fluid and thereby optimizing the operation of the supercritical pump. 【0051】 The present invention also relates to a method for the transport and storage of a fluid containing at least 80% carbon dioxide (preferably the fluid is carbon dioxide having 5% to 20% impurities), wherein the fluid is compressed according to the above compression method and then the fluid is transported to a storage location, which is stored in a storage reservoir of the storage location. The storage reservoir can be an artificial reservoir or a natural reservoir, such as a geological reservoir, such as a reservoir containing oil or natural gas. By the compression method of the present invention, the fluid can only be pretreated by a gas / liquid separator, thereby simplifying the pretreatment, reducing the transportation and storage note costs, and limiting the energy consumption. 【0052】 The present invention further relates to a system for compressing a fluid containing at least 80% carbon dioxide (preferably, the fluid is carbon dioxide containing 5% - 20% impurities). This compression system includes at least one compression means (especially a compressor) for compressing the fluid according to step a), a first cooling means, such as a heat exchanger, for partially liquefying the fluid according to step b), a multiphase pump for step c), a second cooling means, such as a second heat exchanger, for completely liquefying the fluid to perform step d), and a supercritical pump for performing step e), and is continuously provided with them. 【0053】 Therefore, this system is suitable for implementing a compression method and a method of transportation and storage according to any one or a combination of the above-described modifications. 【0054】 Preferably, the various compression phases of step a) can be performed using a single integrated geared compressor. In other words, this system can be provided with a single integrated geared compressor for compressing the fluid according to step a), regardless of whether it includes one or more compression phases. 【0055】 Advantageously, this system can be provided with several compression means to optimize the compression energy efficiency, thereby performing several compression stages in step a). 【0056】 Preferably, a third cooling means can be arranged (in the direction of the fluid flow) between the compression means to cool the fluid to an appropriate temperature (for example, 10°C - 100°C) before the next compression means, so as to cool the fluid to an appropriate temperature (for example, 10°C - 100°C) and improve the efficiency of the compression means. 【0057】 More preferably, at least one of the third cooling means, preferably behind each of the third cooling means, a gas / liquid separator can follow (in the direction of the fluid flow) to remove the liquid contained in the fluid. Therefore, the gas / liquid separator is placed between the third cooling means and the compression means to remove the liquid that may have condensed in the third cooling means before the fluid reaches the next compression means. By removing the liquid, damage to the next compression means is thus prevented and its service life is improved. 【0058】 According to a modification of the invention, the system can comprise at least one gas / liquid separation means (a second gas / liquid separator) for removing the gas contained in the fluid, and the gas / liquid separation means is preferably located between the second cooling means and the supercritical pump (in the direction of fluid flow). By removing the gas contained in the fluid, which may originate from gases other than carbon dioxide, especially non-condensable gases, it becomes possible to improve the operation of the supercritical pump. The gas / liquid separation means is preferably designed such that the gas volume fraction of the fluid is less than 5% at the outlet of the gas / liquid separation means, thereby making it possible to improve the performance of the supercritical pump. 【0059】 FIG. 1 schematically illustrates a compression system according to one embodiment of the invention, by way of non-limiting example. 【0060】 The system comprises several compressors C1, C2, C3 and C4 in series (here there are four compressors, but the system can have a different number of compressors). 【0061】 Compressors C1, C2, C3 and C4 make it possible to gradually increase the pressure of a fluid stream (10) containing at least 80% carbon dioxide. This fluid may originate, inter alia, from the gas outlet of a combustion chamber or from any other industrial installation that generates carbon dioxide potentially containing up to 20% impurities. Thus, from upstream in the direction of fluid flow, the fluid is first compressed in compressor C1, then in compressors C2 and C3, and finally in compressor C4. At the outlet of the last compressor C4 through which the fluid stream passes, the fluid reaches a desired pressure of between 8 and 50 bar, i.e. 0.8 to 5 MPa (50 bar, i.e. 5 MPa not included). 【0062】 Compressors C1, C2, C3 and C4 are separated by coolers, which here are in the form of first heat exchangers R1, R2 and R3 without direct contact (which do not modify the fluid composition). A gas / liquid separator (not shown) may be provided immediately after each cooler R1, R2 and R3 to remove the condensed fluid in liquid state before reaching the next compressor C2, C3 or C4. 【0063】 What is meant by a heat exchanger without direct contact or with indirect contact is that the fluid exchanges heat with the heat transfer fluid without direct contact between the fluid and the heat transfer fluid: for example, this heat exchange without direct contact can occur through a wall, with the fluid on one side of the wall and the heat transfer fluid on the other side. This may apply, inter alia, to tube or plate exchangers. 【0064】 Coolers R1, R2 and R3 make it possible to maintain the fluid temperature at a predetermined value, for example between 10°C and 100°C. 【0065】 The assembly consisting of compressors C1, C2, C3 and C4 and first heat exchangers R1, R2 and R3 without direct contact forms a compression device (15). 【0066】 At the outlet of the compression device (15) (and thus of the last compressor C4), the fluid enters the first cooling means (20) and is partially liquefied. This cooling means can be a heat exchanger and is preferably one without direct contact. 【0067】 Consequently, the fluid is cooled and partially liquefied. When leaving the first cooling means, the fluid contains a gaseous part and a liquid part. It is therefore a multiphase fluid and can enter a multiphase pump (30) which allows a pressure increase to a predetermined value below the critical pressure of the fluid. When using a multiphase pump (30), the inlet fluid can be carbon dioxide with a high level of impurities (for example, 5% - 20% impurities), which makes it possible to avoid a fluid pretreatment device at the inlet. Furthermore, these impurities can be, among other things, non-condensable gases. This is because the multiphase pump is designed to receive a high proportion of gas (ranging from at least 50%, preferably 75% - 95%). 【0068】 The compressed multiphase fluid is then cooled in a second cooling means (40), for example a heat exchanger, preferably to a predetermined temperature ranging from 0 °C to 60 °C, to completely liquefy the carbon dioxide of the fluid. This second cooling means (40) is, however, optional. At the outlet of the second cooling means (40), the fluid contains only carbon dioxide in liquid form. It is then sent into a supercritical pump (60) to reach the critical pressure and thus change to a supercritical state (10'), after which it can be transported, for example, through a transport pipe and stored in a geological or artificial reservoir. 【0069】 Optionally, a gas / liquid separation means (for example, a gas / liquid separator) can be located between the second cooling means (40) and the supercritical pump (60) to remove the gas or reduce the amount of gas contained in the fluid to a volume fraction of less than 5% to facilitate the operation of the supercritical pump (60) and improve its performance. 【0070】 FIG. 2 schematically illustrates, by way of non-limiting example, a compression method according to the present invention. 【0071】 A fluid containing at least 80% carbon dioxide flows into a compression device at a pressure P0 (e.g., 1 to 3 bar) and a temperature T0 (e.g., 10° C. to 50° C.), which includes one or more compression stages. The fluid is then compressed (Comp) to a pressure P1 (greater than 8 bar and strictly less than 50 bar) at a temperature T1 (e.g., 10° C. to 100° C.). The fluid is then cooled and undergoes partial liquefaction (Ref1). After step Ref1, the fluid is a multiphase fluid containing both a gaseous part and a liquid part, which is at a temperature T1' (e.g., -50° C. to 15° C.) below the pressure P1 and T1. 【0072】 The fluid is multiphase and can be compressed in a multiphase pump PP and exits at a pressure P3 (e.g., 65 to 100 bar, i.e., 6.5 to 10 MPa) and a temperature T3 (e.g., 0° C. to 60° C.). The pressure P3 is strictly less than the critical pressure of the fluid to avoid a transition to a supercritical state within the multiphase pump. 【0073】 At the outlet of the multiphase compression PP, the fluid is optionally cooled (Ref2) to completely liquefy at least the carbon dioxide contained in the fluid. It then flows therefrom at a pressure P3 and a temperature T3' below T3. 【0074】 If necessary, the fluid can be separated in gas / liquid separation means to reduce the gas fraction to a value less than 5%. This step is particularly advantageous when the fluid contains more than 5% non-condensable gas. 【0075】 The fluid flows either directly from the cooling step Ref2 or from the gas / liquid separation step as shown, and this fluid is then compressed in a supercritical pump PSP where it changes to a supercritical state. It exits in the supercritical state at a pressure P4 (e.g., 74 to 200 bar, i.e., 7.4 to 20 MPa) and a temperature T4 higher than the critical pressure of the fluid. 【0076】 It can then be transported and stored, for example, in an artificial or geological reservoir. 【0077】 FIG. 3 schematically illustrates a comparison between the thermodynamic paths (a) and (b) of two prior art carbon dioxide compression methods and the thermodynamic path (c) of a compression method for a fluid containing at least 80% carbon dioxide according to the present invention. 【0078】 The thermodynamic path (a) is indicated by a solid arrow, the thermodynamic path (b) is indicated by a dashed arrow, and the thermodynamic path (c) is indicated by a dash-dotted arrow. 【0079】 For the thermodynamic paths (b) and (c), the first part of the path is the same as the thermodynamic path (a), and only the part of the path deviating from the thermodynamic path (a) is indicated by a dashed arrow or a dash-dotted arrow. 【0080】 The thermodynamic path (a) corresponds to the thermodynamic path of the prior art patent application WO-2011 / 101,296, while the thermodynamic path (b) corresponds to the thermodynamic path of the prior art patent application JP-2010 / 266,154. 【0081】 The thermodynamic path (a) is characterized by a series of compressions followed by cooling, and the fluid is maintained in a gaseous state (to the right and outside of the envelope characterized by the fluid saturation curve (50)). 【0082】 When a fluid in a gaseous form (without a liquid portion) reaches a pressure higher than the critical point (52) pressure (point (54)), the fluid is cooled to point (57). It is then compressed to the desired transport pressure P4 (point (58)). 【0083】 The thermodynamic path (b) is characterized by a series of compressions followed by cooling, and the fluid is maintained in a gaseous state (to the right and outside of the envelope characterized by the fluid saturation curve (50)) to a pressure P2 (point (53)) below the pressure of the critical point (52). In this portion, the thermodynamic path (b) is substantially the same as the thermodynamic path (a). 【0084】 From point (53), the fluid is cooled and completely liquefied, reaching a point (55) on the saturation curve (50), i.e., slightly to the left of the saturation curve (50). 【0085】 Thus, at point (55), the fluid is completely liquid. 【0086】 It is then compressed to a pressure P4 at point (61) where it changes to the supercritical state. 【0087】 The thermodynamic path (c) is characterized by a series of compressions followed by cooling, and the fluid is maintained in a gaseous state (to the right and outside of the envelope characterized by the fluid saturation curve (50)) to a pressure P1 (point (51)) below the pressure of the critical point (52). In this portion, the thermodynamic path (c) is substantially the same as the thermodynamic path (a). 【0088】 From point (51), the fluid is cooled and partially liquefied, reaching a point (62) below the saturation curve (50) (within the envelope defined by the saturation curve (50)). The fluid is located below the saturation curve (50) (within the envelope defined by the saturation curve (50)), and it is a multiphase fluid containing both a gaseous portion and a liquid portion. 【0089】 It is then compressed by a multiphase pump to a pressure P3 (point (63)) below the pressure of the critical point (52), remaining in the multiphase state within the multiphase pump and avoiding changing to the supercritical state within this multiphase pump. 【0090】 It is then cooled to reach complete liquefaction of at least carbon dioxide of the fluid at a point (56) located on or slightly to the left of the saturation curve (50). For this reason, at the point (56), the fluid (at least carbon dioxide of the fluid) is completely liquid. 【0091】 It is then compressed to the pressure P4 at the point (59) using a supercritical pump and it changes to the supercritical state. 【0092】 Figure 4 schematically illustrates, as a non-limiting example, the modifications in the thermodynamic properties of the fluid depending on the level of impurities contained in carbon dioxide. 【0093】 The graph shows the pressure P of the fluid (unit bar, 1 bar is equal to 0.1 MPa) on the y-axis and the enthalpy (kJ / kg) on the x-axis. 【0094】 The various curves F1, F2, F3, F4 are the saturation curves of several fluids: - F1 is the saturation curve of a fluid containing 100% carbon dioxide - F2 is the saturation curve of a fluid containing 95% carbon dioxide and 5% diatomic nitrogen - F3 is the saturation curve of a fluid containing 90% carbon dioxide and 10% diatomic nitrogen - F4 is the saturation curve of a fluid containing 85% carbon dioxide and 15% diatomic nitrogen. 【0095】 It is noted that the higher the proportion of impurities (here diatomic nitrogen), the more the envelope of the saturation curve increases and the critical pressure increases from 74 bar (7.4 MPa) in the case of pure carbon dioxide to above 100 bar (above 10 MPa) in the case of carbon dioxide containing 15% diatomic nitrogen. 【0096】 For the optimization of the method and the system, the actual critical pressure of the fluid can be taken into account to improve the efficiency and performance of the method and the system. 【0097】 (Example) The various compression methods of the present invention were sized for the compression of pure carbon dioxide, and these methods of the present invention were subsequently compared. 【0098】 For sizing these various compression methods of the present invention, the inlet fluid is pure carbon dioxide, the mass flow rate is 156.43 kg / s, the inlet pressure is 0.15 MPa, the inlet temperature is 35 °C, and the outlet pressure is 15.3 MPa. 【0099】 The following table (Table 1) gives the values of the various pressures and temperatures corresponding to the thermodynamic path (c) of FIG. 3, as well as the characteristics of the associated compression system, where 1 bar corresponds to 0.1 MPa. 【0100】 [Table 1] 【0101】 These examples show that the methods and systems according to the present invention enable the compression of fluids containing carbon dioxide with a low total power consumption (less than 100 MW). The most advantageous thermodynamic path corresponds to the row with a larger font size in italics in Table 1 with respect to the total energy consumption. In fact, the total energy consumption power is 68.8 MW, while the other thermodynamic paths consume 70.9 MW to 99.8 MW. This embodiment can, therefore, be considered as one of the preferred embodiments of the present invention. 【0102】 For this preferred compression method (the italicized row in Table 1), the pressure at the outlet of step a) is 15 bar (1.5 MPa), the pressure at the outlet of the multiphase compression step c) is 71 bar, i.e., 7.1 MPa (below the critical pressure of 74 bar, i.e., 7.4 MPa for pure carbon dioxide), and the gas volume fraction of the fluid at the multiphase pump inlet is 78%. [Brief Description of the Drawings] 【0103】 【Figure 1】 Shows a fluid compression system according to the present invention. 【Figure 2】 Illustrates a fluid compression method according to the present invention. 【Figure 3】 Compares the thermodynamic path (path c)) of the compression method according to the present invention with the thermodynamic paths (paths (a) and (b)) of the prior art compression methods. 【Figure 4】 Illustrates various gas / liquid saturation curves for various fluids containing carbon dioxide.

Claims

[Claim 1] A method for compressing a fluid containing at least 80% carbon dioxide, comprising at least the following steps: a) A step (Comp) of compressing the fluid to a pressure (P1) greater than 8 bar and strictly less than 50 bar in one or more compression stages. b) A step (Ref1) to cool the compressed fluid to a temperature of -50°C to 15°C (T1'); maintaining the fluid pressure (P1) above 8 bar and strictly below 50 bar; partially liquefying the carbon dioxide in the fluid; the gaseous volume fraction of the fluid being in the range of 1% to 99%. c) A step (PP) of performing multiphase compression (PP) of a compressed and cooled fluid to a pressure (P3) strictly below the critical pressure of the fluid; the multiphase compression is performed in one or more multiphase compression stages. d) Preferably, a step of cooling the fluid from the multiphase compression to completely liquefy at least the carbon dioxide in the fluid (Ref 2), e) A step (PSP) of compressing the fluid to a temperature preferably below 60°C such that the fluid pressure (P4) exceeds the critical point of the fluid. [Claim 2] The method according to claim 1, wherein the fluid is compressed in step a) (Comp) using a single, integrated geared compressor. [Claim 3] The method according to claim 1, wherein the fluid is cooled between at least two compression stages in step a) to maintain a temperature of 10°C to 100°C. [Claim 4] The method according to claim 3, wherein the fluid is cooled after at least one compression stage in step a), and then the fluid in a liquid state is separated from the fluid in a gaseous state. [Claim 5] The method according to claim 1, wherein multiphase compression (PP) is performed using a helical shaft type multiphase pump. [Claim 6] The method according to claim 1, wherein multiphase compression (PP) is performed in several multiphase compression stages, and the fluid is cooled, preferably by a cooler, preferably a water cooler, between at least two multiphase compression stages. [Claim 7] The method according to claim 1, wherein the fluid is carbon dioxide containing 0% to 20% impurities. [Claim 8] The method according to claim 7, wherein, after step d) (Ref 2) of cooling the fluid from multiphase compression (PP), if the impurities contain non-condensable gases, the fluid is treated, preferably by gas / liquid separation, to reduce the gas volume fraction to less than 5%. [Claim 9] A method for transporting and storing a fluid containing at least 80% carbon dioxide, comprising compressing the fluid according to a compression method described in any one of claims 1 to 8, then transporting the fluid to a storage location, and storing it in a storage reservoir of the storage location. [Claim 10] A system for compressing a fluid containing at least 80% carbon dioxide, wherein the compression system comprises, in sequence, at least one compression means (C1, C2, C3, C4), a first cooling means (20) for partially liquefying the fluid, a multiphase pump (30), a second cooling means (40) for completely liquefying the fluid, and a supercritical pump (60), wherein the compression means (C1, C2, C3, C4) preferably consists of a single integrated geared compressor, and the system is suitable for carrying out the method according to any one of claims 1 to 8. [Claim 11] The compression system according to claim 10, comprising several compression means (C1, C2, C3, C4) and a third cooling means (R1, R2, R3), and optionally further comprising a gas / liquid separator, preferably positioned between the compression means. [Claim 12] The compression system according to claim 10, comprising at least one gas / liquid separation means, preferably located between a second cooling means (40) and a supercritical pump (60).

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