System and method for compressing carbon dioxide with multi-stage compression and supercritical pump

Abstract

The invention relates to a method for compressing carbon dioxide, comprising at least the following steps: a) compressing (Comp) a fluid to a pressure (P1) greater than 8 bar and strictly less than 50 bar, b) cooling (Ref1) the compressed fluid to a temperature (T1 ') of between-50 DEG C and 15 DEG C in order to partially liquefy the fluid, the gas volume fraction of the fluid being in the range of between 1% and 99%, c) carrying out multiphase compression (PP) of the cooled compressed fluid to a pressure (P3) strictly below the critical pressure of the fluid, d) preferably cooling (Ref2) the fluid from the multiphase compression (PP), and d) preferably cooling (Ref3) the fluid from the multiphase compression (PP) to a temperature (T1') of between-50 DEG C and 15 DEG C in order to partially liquefy the fluid. E) compressing (PSP) the fluid such that the fluid pressure (P4) exceeds the critical point of the fluid. The invention also relates to a method for transporting and storing carbon dioxide and to a compression system.

Description

Technical Field

[0001] The present invention relates to the field of compression of carbon dioxide for its transport and sequestration (storage).

[0002] In the context of combating global warming, huge efforts are needed to reduce the amount of carbon dioxide (CO2) released into the atmosphere. The development of CO2 capture and storage facilities is one of the most promising ways to significantly reduce emissions from the most polluting industries and achieve a soft energy transition. These systems are designed to capture and process the CO2 emitted by these industries and store it underground, in suitable geological formations or in artificial reservoirs. Background Art

[0003] A known technology for storing captured carbon dioxide consists in compressing the carbon dioxide in gaseous form and then cooling it in order to convert it into a liquid or supercritical phase for its transport and storage.

[0004] Patent application WO-2011 / 101,296 relates to a method for compressing carbon dioxide by maintaining it in the gas phase. The gas pressure is increased in successive compression stages until a critical pressure is exceeded. The stream is then cooled to the desired temperature for transport.

[0005] Patent application JP-2010 / 266,154 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. Subsequently, it is compressed in the liquid state until the critical pressure is reached.

[0006] For these methods, very high purity levels of CO2 are required: impurities may on the one hand produce yield losses and / or degradation of single-phase compression systems (liquid or gas) and on the other hand modify the phase change properties of the fluid (in particular the critical point towards the supercritical state).

[0007] Also known is patent application FR-2,891,609 (US-2009 / 075,219) filed by the applicant, which includes a method for carbon dioxide capture and compression using a multiphase pump.

[0008] However, in this method, the transition to the supercritical state takes place within the multiphase pump, which is not optimal for the operation of the pump and the method. Summary of the invention

[0009] It is an object of the present invention to provide a method and system for compressing a fluid comprising carbon dioxide and likely to contain a high content of impurities (preferably at least 5% impurities), including non-condensable gases, with improved energy efficiency.

[0010] The present invention therefore relates to a method for compressing a fluid comprising at least 80% carbon dioxide, the method comprising at least the following steps:

[0011] a) compressing the fluid in one or more compression stages to a pressure greater than 8 bar and strictly less than 50 bar,

[0012] b) cooling the compressed fluid to a temperature between -50°C and 15°C, the fluid pressure being maintained at a level greater than 8 bar and strictly less than 50 bar, so as to partially liquefy the carbon dioxide of the fluid, the gas volume fraction of the fluid ranging between 1% and 99%,

[0013] c) performing multiphase compression of the cooled compressed fluid to a pressure strictly below the critical pressure of the fluid, the multiphase compression being performed in one or more multiphase compression stages,

[0014] d) preferably cooling the fluid resulting from the multiphase compression so as to completely liquefy at least the carbon dioxide of the fluid,

[0015] e) compressing the fluid so that the fluid pressure exceeds the critical point of the fluid, preferably reaching a temperature below 60°C.

[0016] Advantageously, a single integrally geared compressor is used to compress the fluid in step a).

[0017] Preferably, between at least two compression stages in step a), the fluid is cooled so as to maintain a temperature between 10°C and 100°C.

[0018] Advantageously, after cooling the fluid after at least one compression stage in step a), the fluid in liquid state is separated from the fluid in gaseous state.

[0019] According to the configuration of the present invention, a helical coaxial type multiphase pump is used to implement multiphase compression.

[0020] Preferably, the multiphase compression is carried out 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.

[0021] According to one embodiment of the invention, the fluid is carbon dioxide comprising between 0% and 20% impurities.

[0022] According to a variant of the invention, after step d) of cooling the fluid coming from the multiphase compression stage, when the impurities contain non-condensable gases, the fluid is treated to reduce the gas volume fraction to a value lower than 5%, preferably by gas / liquid separation.

[0023] The invention also relates to a method for transporting and storing a fluid comprising at least 80% carbon dioxide, wherein the fluid is compressed according to the compression method as described above and then transported to a storage point and stored in a storage tank at the storage point.

[0024] The present invention also relates to a system for compressing a fluid comprising at least 80% carbon dioxide, the compression system comprising successively at least one compression device, a first cooling device for partially liquefying the fluid, a multiphase pump, a second cooling device for completely liquefying the fluid, and a supercritical pump, the compression device preferably consisting of a single integrally geared compressor, the system being suitable for implementing the method as described above.

[0025] Advantageously, the system comprises several compression means, and a third cooling means, possibly followed by a gas / liquid separator, is preferably arranged between the compression means.

[0026] Preferably, the system comprises at least one gas / liquid separation device, preferably positioned between the second cooling device and the supercritical pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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 examples with reference to the accompanying drawings, in which:

[0028] - Figure 1 A fluid compression system according to the present invention is shown,

[0029] - Figure 2 The fluid compression method according to the present invention is illustrated.

[0030] - Figure 3 Comparing 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

[0031] - Figure 4 Various gas / liquid saturation curves for various fluids containing carbon dioxide are shown. DETAILED DESCRIPTION

[0032] The present invention is a link in the CO2 capture and storage chain (called "conditioning" or "compression"). The purpose is to bring the captured CO2 from its capture conditions (e.g., pressures ranging between 1 and 3 bar (0.1 and 0.3 MPa), preferably between 1 and 1.5 bar (0.1 to 0.15 MPa), and temperatures ranging between 10°C and 50°C, preferably between 10°C and 35°C, while the carbon dioxide may contain various types and amounts of impurities, depending on where it is captured) to supercritical conditions (pressures above the supercritical pressure, e.g., for pure or nearly pure carbon dioxide, the supercritical pressure is 74 bar (i.e., 7.4 MPa), and temperatures ranging between 0°C and 60°C) in order to transport and store it.

[0033] To achieve this objective, the present invention relates to a novel CO2 compression method and system, which in particular comprises a multiphase pump. It allows the compression of CO2 despite the presence of high levels of impurities (greater than 5% by volume). The method is also optimized in terms of energy efficiency according to the flow generated by the capture.

[0034] Impurities are understood to be any molecules other than CO 2 molecules. Impurities may be solid, liquid or gaseous particles: they may in particular be non-condensable gases such as, for example, nitrogen or hydrogen.

[0035] "Pure or nearly pure carbon dioxide" is understood to mean carbon dioxide containing less than 1% impurities.

[0036] The impurity content is understood as the volume fraction of the impurity in the fluid.

[0037] A non-condensable gas is understood to be a gas whose liquefaction temperature is cryogenic (eg below -150° C.).

[0038] The critical point is the point corresponding to the pressure and temperature at which the fluid changes into the supercritical state; the critical temperature is the lowest temperature from which the fluid can change into the supercritical state.

[0039] A multiphase pump is understood to be a device for compressing a fluid flowing into a compression device in a multiphase form having at least one gas phase and at least one liquid phase. A multiphase pump may correspond in particular to the helical coaxial multiphase pumps 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 may then comprise one or more multiphase compression stages. The multiphase pump may comprise at least one movable wheel rotating about an axis and mounted in a casing, and at least one fixed wheel fixed to the casing, the movable wheel comprising a hub provided with at least two blades so as to form at least two channels defined by two of the hub, the casing and the blades, and the channels having a centrifugal portion. The multiphase pump may also correspond to a gear pump or any other type of multiphase pumping technology.

[0040] A supercritical pump is understood to be a device for compressing a fluid that flows into the pump and leaves the pump in a supercritical state or flows into the pump in the liquid phase and leaves the supercritical pump in a supercritical state. Without being limited to these examples, the technology used may be the following: diaphragm pump, gear pump, canned pump, peristaltic pump.

[0041] A multiphase pump may consist of one or more multiphase stages followed by one or more non-helical coaxial stages in order to allow the fluid to be in a supercritical state at the outlet of the multiphase pump. Therefore, a multiphase pump is also a supercritical pump.

[0042] The invention relates to a method for compressing a fluid comprising at least 80% carbon dioxide. In other words, the fluid may be carbon dioxide with impurities between 0% and 20%.

[0043] Advantageously, the fluid may comprise between 5% and 20% impurities.

[0044] When the fluid enters the compression process, the fluid can have a pressure between 1 and 3 bar (0.1 to 0.3 MPa), preferably between 1 and 1.5 bar (0.1 to 0.15 MPa) (i.e., a pressure close to atmospheric pressure), and a temperature between 10°C and 50°C, preferably between 10°C and 35°C.

[0045] According to the present invention, the method comprises at least the following steps:

[0046] a) compressing the fluid to a pressure greater than 8 bar (0.8 MPa) and strictly less than 50 bar (5 MPa) in one or more compression stages. This pressure range is important for improving the energy efficiency of the process. In fact, at pressures below 8 bar (0.8 MPa), the liquefaction temperature of carbon dioxide is less than -50°C. Therefore, for partial carbon dioxide liquefaction, cooling requires a lot of energy consumption. In addition, above 50 bar (5 MPa), the use of multiphase compression loses its interest, because the pressure will then be too close to the critical pressure (74 bar, i.e. 7.4 MPa, for pure or nearly pure carbon dioxide).

[0047] Using several compression stages allows improving the overall compression efficiency.

[0048] Preferably, the fluid may be compressed to a pressure ranging between 10 and 30 bar (1 to 3 MPa), and more preferably between 12 and 20 bar (1.2 to 2 MPa), these value ranges providing a better reduction in the energy consumption of the process.

[0049] At the outlet of the last compression stage the temperature of the fluid may range, for example, between 10°C and 100°C.

[0050] b) cooling the compressed fluid to a temperature between -50°C and 15°C, during which the pressure of the fluid is substantially maintained at the pressure of step a), or slightly varied, but kept greater than 8 bar (0.8 MPa) and strictly less than 50 bar (5 MPa), so as to partially liquefy the carbon dioxide of the fluid, the gas volume fraction of the fluid at the cooling outlet ranging between 1% and 99%. Preferably, the compressed fluid can be cooled to a temperature greater than -50°C and strictly less than 0°C, which allows to further reduce the energy consumption of the method.

[0051] Partial liquefaction is understood to mean that the fluid is multiphase and that it comprises a portion in gaseous form and another portion in liquid form, i.e. the fluid is not completely liquefied, a portion of the fluid is still in gaseous form (e.g. at least 1%). The gas volume fraction of the fluid may advantageously range between 50% and 95%, more preferably between 60% and 90%, these proportions allowing to improve the energy performance of the method.

[0052] c) Implementing a multiphase compression of the cooled compressed fluid to a pressure strictly below the critical pressure of the fluid, for example using a multiphase pump. The fluid is thus kept in a multiphase state with a gaseous part and a liquid part, which allows improving the efficiency of the multiphase pump. The multiphase compression can be implemented in one or more multiphase compression stages, depending in particular on the inlet pressure and the outlet pressure of the multiphase pump. At the multiphase compression outlet, the temperature of the fluid can range between 0°C and 60°C. The use of multiphase compression allows accepting carbon dioxide with a high content of impurities: for example, the fluid can include at least 5% of impurities, which is not the case with the systems and methods of the prior art, in which the compression is only single-phase. Therefore, the method of the present invention can accept the gas as captured without pre-treating the fluid to remove impurities. This allows simplifying the global method and reducing the overall carbon dioxide storage costs.

[0053] d) preferably cools the fluid from the multiphase compression so as to at least completely liquefy the carbon dioxide of the fluid. In other words, step d) is optional. By implementing step d) at the cooling outlet, the carbon dioxide of the fluid is completely in the liquid state and the impurities can be liquid or gaseous. The transition to the liquid state of carbon dioxide promotes the next step, which consists in bringing the fluid to a supercritical state. Therefore, as the next step is promoted, the energy performance of the method is also improved.

[0054] e) compressing the fluid so that the fluid pressure exceeds the critical point (critical pressure) of the fluid, preferably using a supercritical pump. The transition to the supercritical state in the supercritical pump is facilitated when the carbon dioxide has previously been completely liquefied. Preferably, at the outlet of the supercritical pump, the temperature of the fluid is below 60° C. in order to limit heat losses for subsequent transportation and / or storage of the fluid.

[0055] Advantageously, in step a), an integrally geared compressor may be used to compress the fluid, this type of compressor being suitable for compressing gaseous fluids.

[0056] According to a variant of the invention, between at least two compression stages of step a), cooling means, such as heat exchangers, may be used to cool the fluid so as to maintain it at a temperature between 10° C. and 100° C. The cooling may be performed, for example, by direct or indirect heat exchangers. Cooling the fluid before the next compression stage prevents the fluid from reaching too high a temperature, which limits the cooling of the fluid later and causes the various compression means of each stage, in particular the compressor, to operate at a temperature close to the operating temperature and therefore close to its nominal efficiency.

[0057] In this variant, the gaseous and liquid parts of the fluid may preferably be separated after cooling the fluid after at least one compression stage of step a).

[0058] Thus, when cooling the fluid after a compression stage, it may be advantageous to separate the liquid contained in the fluid after this cooling step. In fact, when cooling the fluid, the amount of liquid increases due to condensation, so a separation step after cooling may be useful in order to eliminate as much liquid as possible before the next compression stage and thus to best protect the next compression means. For example, the liquid contained in the fluid may be separated after each cooling performed after each compression stage in order to avoid damaging the compression means of the next stage.

[0059] Advantageously, the multiphase compression of step c) can be carried out using a multiphase pump of the helical coaxial type. This type of pump provides good compression efficiency in situations where the gas fraction in the fluid may vary greatly.

[0060] 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, which allows avoiding excessive temperatures and associated heat losses. This also allows increasing the fluid content at the outlet of the following multiphase compression stage.

[0061] Advantageously, the fluid may be carbon dioxide comprising between 0% and 20% impurities, preferably between 5% and 20%. It is thus possible to use compression methods directly after capture, without having to pre-treat the fluid to limit the content of impurities to a very small fraction (less than 5%).

[0062] Preferably, after step d) of cooling the fluid from the multiphase compression, when the impurities contain non-condensable gases (in particular non-condensable gases with a volume fraction higher than 5%), the fluid can be treated to reduce the gas volume fraction to a value lower than 5%, preferably by gas / liquid separation.

[0063] For example, in order to implement such a treatment aimed at reducing the gas volume fraction to a value below 5%, the fluid in the gaseous state can be separated from the fluid in the liquid state after the cooling step in step d): the gases contained in the fluid, in particular the non-condensable gases, can be separated in order to limit the proportion of gas in the fluid and thus optimize the operation of the supercritical pump.

[0064] The invention also relates to a method for transporting and storing a fluid comprising at least 80% carbon dioxide (preferably, the fluid is carbon dioxide with 5% to 20% impurities), wherein the fluid is compressed according to the compression method as described above, then transported to a storage point and stored in a storage reservoir at the storage point. The storage reservoir may be an artificial reservoir or a natural reservoir, such as a geological reservoir, for example a reservoir containing oil or natural gas. By means of the compression method of the invention, the fluid can be pretreated only by a gas / liquid separator, which simplifies the pretreatment, allows reducing the transportation and storage costs, and limits the energy consumption.

[0065] The invention further relates to a system for compressing a fluid comprising at least 80% carbon dioxide (preferably the fluid is carbon dioxide with 5% to 20% impurities). The compression system comprises successively at least one compression device (in particular a compressor) for compressing the fluid according to step a), a first cooling device (such as a heat exchanger) for partially liquefying the fluid according to step b), a multiphase pump for step c), a second cooling device (such as a second heat exchanger) for completely liquefying the fluid in order to implement step d), and a supercritical pump for implementing step e).

[0066] The system is therefore suitable for implementing a compression method as well as a transport and storage method according to any of the variants or combinations of variants described above.

[0067] Preferably, a single integrally geared compressor may be used to implement each compression stage of step a). In other words, the system may comprise a single integrally geared compressor for compressing the fluid according to step a), whether or not it comprises one or more compression stages.

[0068] Advantageously, the system may comprise several compression means in order to optimize the compression energy efficiency and thus to perform several compression stages in step a).

[0069] Preferably, a third cooling device may be arranged between the compression devices (in the flow direction of the fluid) to cool the fluid to a suitable temperature (eg 10°C to 100°C) before the next compression device, so as to improve the efficiency of each compression device.

[0070] Still more preferably, at least one of the third cooling devices and preferably each third cooling device may be followed by a gas / liquid separator to eliminate liquid contained in the fluid (in the flow direction of the fluid). Thus, the gas / liquid separator is positioned between the third cooling device and the compression device in order to eliminate liquid that may condense in the third cooling device before the fluid reaches the next compression device. Thus, eliminating liquid prevents damage to the next compression device and improves its service life.

[0071] According to a variant of the present invention, the system may include at least one gas / liquid separation device (second gas / liquid separator) for eliminating the gas contained in the fluid, and the gas / liquid separation device is preferably positioned between the second cooling device and the supercritical pump (along the flow direction of the fluid). Eliminating the gas contained in the fluid (the gas may come from a gas other than carbon dioxide, and in particular a non-condensable gas) allows the operation of the supercritical pump to be improved. The gas / liquid separation device is preferably designed in such a way that at the outlet of the gas / liquid separation device, the gas volume fraction of the fluid is less than 5%, which allows the performance of the supercritical pump to be improved.

[0072] Figure 1 By way of non-limiting example, a compression system according to one embodiment of the invention is schematically illustrated.

[0073] The system comprises several compressors C1 , C2, C3, C4 connected in series (here four compressors, but the system may have a different number of compressors).

[0074] Compressors C1, C2, C3 and C4 carry out a stepwise rise in the pressure of a fluid stream 10 comprising at least 80% carbon dioxide. This fluid may in particular come from the gas exhaust of a combustion chamber or from any other industrial device producing carbon dioxide with potentially up to 20% impurities. Thus, starting from upstream in the direction of flow of the fluid, the fluid is first compressed in compressor C1, then in compressor C2 and compressor C3, and finally in compressor C4. At the outlet of the last compressor C4 through which the fluid stream passes, the fluid reaches the desired pressure, which is between 8 and 50 bar, i.e. between 0.8 and 5 MPa (50 bar, i.e. 5 MPa (exclusive)).

[0075] The compressors C1, C2, C3 and C4 are separated by a cooler (here in the form of a first heat exchanger) without directly contacting R1, R2 and R3 (so as not to modify the fluid composition). A gas / liquid separator (not shown) may also be provided just after each cooler R1, R2 and R3 to eliminate the condensed fluid in liquid state before reaching the next compressor C2, C3 or C4.

[0076] A heat exchanger without direct contact or with indirect contact means that heat is exchanged between a fluid and a heat transfer fluid without direct contact between the fluid and the heat transfer fluid: for example, such heat exchange without direct contact may take place through a wall, with the fluid on one side of the wall and the heat transfer fluid on the other side of the wall. This may in particular be the case with tube or plate heat exchangers.

[0077] Coolers R1 , R2 and R3 allow the temperature of the fluid to be maintained at a predetermined value, for example between 10°C and 100°C.

[0078] The assembly consisting of the compressors C1 , C2 , C3 and C4 and the first heat exchanger not in direct contact with R1 , R2 and R3 forms the compression device 15 .

[0079] At the outlet of the compression device 15 (and therefore the last compressor C4), the fluid enters a first cooling means 20 for partially liquefying the fluid. This cooling means may be a heat exchanger, preferably without direct contact.

[0080] Therefore, the fluid is cooled and partially liquefied. When leaving the first cooling device, the fluid includes a part of gas and a part of liquid. Therefore, the fluid is a multiphase fluid, and it can be transferred into the multiphase pump 30, which will allow the pressure to increase to a predetermined value below the critical pressure of the fluid. When using the multiphase pump 30, the inlet fluid can be a carbon dioxide with a high content of impurities (for example, impurities between 5% and 20%), which makes it possible to avoid the need for a fluid pretreatment device at the inlet. In addition, these impurities can be particularly non-condensable gases, because the multiphase pump is designed to accept a high proportion of gas (at least 50%, preferably ranging between 75% and 95%).

[0081] Then, the compressed multiphase fluid is cooled to a predetermined temperature in a second cooling device 40 (such as a heat exchanger), and the predetermined temperature preferably ranges between 0°C and 60°C so as to completely liquefy the carbon dioxide of the fluid. However, the second cooling device 40 is optional. At the outlet of the second cooling device 40, the fluid only includes carbon dioxide in liquid form. Then, the fluid is sent to a supercritical pump 60 to reach a critical pressure and thus become a supercritical state 10', in which the fluid can then be transported by, for example, a transport pipeline and stored in a geological reservoir or an artificial reservoir.

[0082] Optionally, a gas / liquid separation device (e.g., a gas / liquid separator) can be positioned between the second cooling device 40 and the supercritical pump 60 to eliminate gas or reduce the amount of gas contained in the fluid to a volume fraction of less than 5%, thereby facilitating the operation of the supercritical pump 60 and improving its performance.

[0083] Figure 2 The compression method according to the invention is schematically illustrated by way of non-limiting example.

[0084] A fluid comprising at least 80% of carbon dioxide flows at a pressure P0 (for example, between 1 and 3 bars) and a temperature T0 (for example, between 10°C and 50°C) into a compression device comprising one or more compression stages. The fluid is then compressed Comp to a pressure P1 (greater than 8 bars and strictly less than 50 bars) and a temperature T1 (for example, between 10°C and 100°C). The fluid is then cooled Ref1 so that it undergoes partial liquefaction. After step Ref1, the fluid is a multiphase fluid comprising both a gaseous portion and a liquid portion, and it is at a pressure P1 and a temperature T1' (for example, between -50°C and 15°C) lower than T1.

[0085] In the case where the fluid is then multiphase, it can be compressed in a multiphase pump PP, from which the fluid leaves at a pressure P3 (e.g. between 65 and 100 bar, i.e. between 6.5 and 10 MPa) and a temperature T3 (e.g. between 0° C. and 60° C.). The pressure P3 is strictly less than the critical pressure of the fluid in order to avoid transitions to a supercritical state in the multiphase pump.

[0086] At the outlet of the multiphase compressor PP, the fluid is optionally cooled Ref2 in order to completely liquefy at least the carbon dioxide contained in the fluid. The fluid thus flows out of the outlet at a pressure P3 and a temperature T3' lower than T3.

[0087] If necessary, the fluid can then be separated in a gas / liquid separation device in order to reduce the gas fraction to a value below 5%. This step is particularly advantageous when the fluid comprises more than 5% of non-condensable gases.

[0088] Then, the fluid (either directly flowing out of the cooling step Ref2 as shown, or flowing out of the optional gas / liquid separation step) is compressed in a supercritical pump PSP, where the fluid becomes supercritical. The fluid flows out in the supercritical state at a pressure P4 (e.g., between 74 and 200 bar, i.e., between 7.4 and 20 MPa) greater than the critical pressure of the fluid and at a temperature T4.

[0089] The fluid can then be transported and stored in artificial reservoirs or geological reservoirs.

[0090] Figure 3 A comparison between thermodynamic paths (a) and (b) of two carbon dioxide compression methods according to the prior art and a thermodynamic path (c) of a compression method for a fluid comprising at least 80% carbon dioxide according to the present invention is schematically illustrated by way of non-limiting example.

[0091] The thermodynamic path (a) is shown by a solid arrow, the thermodynamic path (b) is shown by a dashed arrow, and the thermodynamic path (c) is shown by a dash-dot arrow.

[0092] For thermodynamic paths (b) and (c), the first portion of the path is identical to thermodynamic path (a), and only the portion of the path that deviates from thermodynamic path (a) is shown by a dashed or dot-dash arrow.

[0093] Thermodynamic path (a) corresponds to the thermodynamic path of prior art patent application WO-2011 / 101,296, while thermodynamic path (b) corresponds to the thermodynamic path of prior art patent application JP-2010 / 266,154.

[0094] Thermodynamic path (a) is characterized by a series of compressions followed by cooling, wherein the fluid remains in the gaseous state (to the right and outside the envelope represented by the fluid saturation curve 50).

[0095] Once the fluid in gaseous form (without liquid portion) reaches a pressure greater than the pressure of the critical point 52 (point 54), the fluid is cooled to point 57. The fluid is then compressed to the desired transport pressure P4 (point 58).

[0096] Thermodynamic path (b) is characterized by a series of compressions followed by cooling, wherein the fluid is maintained in a gaseous state (to the right and outside the envelope represented by the fluid saturation curve 50), up to a pressure P2 (point 53) below the pressure of the critical point 52. In this section, thermodynamic path (b) is essentially the same as thermodynamic path (a).

[0097] From point 53 , the fluid is cooled so as to completely liquefy and reach point 55 on the saturation curve 50 , or slightly to the left of the saturation curve 50 .

[0098] Thus, at point 55, the fluid is completely liquid.

[0099] The fluid is then compressed to a pressure P4 at point 61 where the fluid becomes supercritical.

[0100] Thermodynamic path (c) is characterized by a series of compressions followed by cooling, wherein the fluid is maintained in a gaseous state (to the right and outside the envelope represented by the fluid saturation curve 50), up to a pressure P1 (point 51) below the pressure of the critical point 52. In this section, thermodynamic path (c) is essentially the same as thermodynamic path (a).

[0101] Starting from point 51, the fluid is cooled so as to partially liquefy and reaches point 62 which is located below the saturation curve 50 (in the envelope defined by the saturation curve 50). When the fluid is located below the saturation curve 50 (in the envelope defined by the saturation curve 50), it is a multiphase fluid including both a gas portion and a liquid portion.

[0102] The fluid is then compressed by the multiphase pump to a pressure P3 (point 63) below the pressure of the critical point 52 in order to remain in a multiphase state in the multiphase pump and avoid becoming supercritical in the multiphase pump.

[0103] The fluid is then cooled to achieve complete liquefaction of at least the carbon dioxide of the fluid at a point 56 located on the saturation curve 50 or slightly to the left of the saturation curve 50 .

[0104] Subsequently, the fluid is compressed to a pressure P4 at point 59 using a supercritical pump, and the fluid becomes a supercritical state.

[0105] Figure 4 The modification of the thermodynamic properties of the fluid according to the impurity content contained in the carbon dioxide is schematically illustrated by way of non-limiting example.

[0106] The diagram shows the pressure P of the fluid on the y-axis (in bar, 1 bar equals 0.1 MPa) and the enthalpy on the x-axis (in kJ / kg).

[0107] The various curves F1, F2, F3, and F4 are saturation curves of several fluids:

[0108] -F1 is the saturation curve for a fluid containing 100% carbon dioxide

[0109] -F2 is the saturation curve for a fluid containing 95% carbon dioxide and 5% nitrogen

[0110] -F3 is the saturation curve for a fluid containing 90% carbon dioxide and 10% nitrogen

[0111] -F4 is the saturation curve for a fluid containing 85% carbon dioxide and 15% nitrogen

[0112] It should be noted that the higher the ratio of impurities (here nitrogen), the more the envelope of the saturation curve increases and the more the critical pressure increases (from 74 bar (7.4 MPa) for pure carbon dioxide to more than 100 bar (more than 10 MPa) for carbon dioxide with 15% nitrogen).

[0113] In order to optimize the method and system, the actual critical pressure of the fluid may therefore be taken into account in order to improve the efficiency and performance of the method and system.

[0114] Example

[0115] Various compression methods of the present invention were dimensioned for compression of pure carbon dioxide and then compared.

[0116] For sizing of these various compression methods of the present invention, the inlet fluid was pure carbon dioxide (without impurities) at a mass flow rate of 156.43 kg / s, an inlet pressure of 0.15 MPa, an inlet temperature of 35°C and an outlet pressure of 15.3 MPa.

[0117] The following table (Table 1) gives the corresponding Figure 3 Thermodynamic path (c) for various pressure and temperature values ​​and the properties of the associated compression system, where 1 bar is equivalent to 0.1 MPa.

[0118] Table 1

[0119]

[0120] These examples show that the method and system according to the invention allow the compression of a fluid including carbon dioxide with a low total power consumption (less than 100 MW). The most favorable thermodynamic path in terms of total energy consumption is the one corresponding to the italic column and the larger font in Table 1. In fact, the total energy consumption power is 68.8 MW, while the consumption of the other thermodynamic paths is between 70.9 MW and 99.8 MW. This embodiment can therefore be considered as one of the preferred embodiments of the present invention.

[0121] For this preferred compression method (italic columns 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 (lower than 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 inlet of the multiphase pump is 78%.

Claims

1. A method for compressing a fluid comprising at least 80% carbon dioxide, the method comprising at least the following steps: a) compressing (Comp) the fluid in one or more compression stages to a pressure (P1) greater than 8 bar and strictly less than 50 bar, b) cooling (Ref1) the compressed fluid to a temperature (T1') between -50°C and 15°C, the fluid pressure (P1) being maintained greater than 8 bar and strictly less than 50 bar, so as to partially liquefy the carbon dioxide of said fluid, the gas volume fraction of said fluid ranging between 1% and 99%, c) carrying out a multiphase compression (PP) of the cooled compressed fluid to a pressure (P3) strictly below the critical pressure of said fluid, the multiphase compression being carried out in one or more multiphase compression stages, d) preferably cooling (Ref2) the fluid resulting from said multiphase compression in order to completely liquefy at least the carbon dioxide of said fluid, e) compressing (PSP) the fluid such that the pressure (P4) of the fluid exceeds the critical point of the fluid, preferably reaching a temperature below 60°C.

2. The method according to claim 1, wherein: In step a) the fluid is compressed (Comp) using a single integrally geared compressor.

3. A method according to any one of the preceding claims, wherein: Between at least two compression stages in step a), the fluid is cooled so as to maintain a temperature between 10°C and 100°C.

4. The method according to claim 3, wherein: After cooling the fluid after at least one compression stage in step a), the fluid in liquid state is separated from the fluid in gaseous state.

5. A method according to any one of the preceding claims, wherein: Multiphase compression (PP) was performed using a helical coaxial type multiphase pump.

6. A method according to any one of the preceding claims, wherein: The multiphase compression (PP) is carried out 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.

7. A method according to any one of the preceding claims, wherein: The fluid is carbon dioxide comprising between 0% and 20% impurities.

8. The method according to claim 7, wherein: After step d) of cooling (Ref2) said fluid coming from the multiphase compression (PP), when said impurities contain non-condensable gases, said fluid is treated so as to reduce said gas volume fraction to a value lower than 5%, preferably by gas / liquid separation.

9. A method for transporting and storing a fluid comprising at least 80% carbon dioxide, wherein: The fluid is compressed according to a compression method according to any one of the preceding claims and then transported to a storage point and stored in a storage reservoir at the storage point.

10. A system for compressing a fluid, the fluid comprising at least 80% carbon dioxide, the compression system comprising successively at least one compression device (C1, C2, C3, C4), a first cooling device (20) for partially liquefying the fluid, a multiphase pump (30), a second cooling device (40) for completely liquefying the fluid, and a supercritical pump (60), the compression device (C1, C2, C3, C4) preferably consisting of a single integral gear compressor, the system being suitable for implementing the method according to any one of the preceding claims.

11. The compression system according to claim 10, wherein: The system comprises several compression means (C1 , C2, C3, C4) and a third cooling means (R1 , R2, R3), possibly followed by a gas / liquid separator, is preferably arranged between the compression means.

12. A compression system according to any one of claims 10 or 11, wherein: The system comprises at least one gas / liquid separation device preferably positioned between the second cooling device (40) and the supercritical pump (60).

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