Offloading liquid carbon dioxide into a subsea co2 storage tank

Abstract

The disclosure notably relates to a method for offloading liquid carbon dioxide (CO2) stored in a carrier into a subsea CO2 storage tank. The method comprises flowing the liquid CO2 from the carrier into the subsea CO2 storage tank. The method also comprises obtaining vaporized CO2 from CO2 fluid contained in the subsea CO2 storage tank. The method also comprises flowing the obtained vaporized CO2 into the carrier.

Description

[0001] OFFLOADING LIQUID CARBON DIOXIDE INTO A SUBSEA CO2STORAGE TANK

[0002] TECHNICAL FIELD

[0003] The disclosure relates to the field of carbon capture storage technology, and more specifically to a method for offloading liquid carbon dioxide (CO2) stored in a carrier into a subsea CO2 storage tank.

[0004] BACKGROUND

[0005] Carbon capture storage (CCS) technology projects rely on transport and storage of CO2 from their emitters to the final CO2 subsurface or subterranean storage reservoir. The transport may be performed by ships having thereon carriers that store the CO2 from a location of the emitter and offload it to a temporary storage (also called buffer) connected to an offshore pipeline which transports the CO2 to the final CO2 subsurface or subterranean storage reservoir.

[0006] However, offloading the CCh from the carrier to the subsea CO2 storage tank involves several challenges. The offloading of CO2 leads to a decrease in pressure and thereby an undesired increase of temperature. Existing solutions to address this issue include installing additional equipment on ships to stabilize the pressure and thus the temperature. Such equipment is costly and complex to install. The operation of the equipment leads to increased fuel consumption, thus increased CO2 emissions, and it may also involve increased safety risks for the operators.

[0007] Within this context, there is still a need for an improved method for offloading liquid carbon dioxide (CO2) stored in a carrier into a subsea CO2 storage tank.

[0008] SUMMARY

[0009] It is therefore provided a method for offloading liquid carbon dioxide (CO2) stored in a carrier into a subsea CO2 storage tank. The method comprises flowing the liquid CO2 from the carrier into the subsea CO2 storage tank. The method also comprises obtaining vaporized CO2 from CO2 fluid contained in the subsea CO2 storage tank. The method also comprises flowing the obtained vaporized CO2 into the carrier.

[0010] The method may comprise one or more of the following: the flowing of the obtained vaporized CO2 into the carrier is performed to maintain pressure inside the carrier, as liquid CO2 is flowed from the carrier into the subsea CO2 storage tank; the flowing of the obtained vaporized CO2 into the carrier is performed via pressure differential; the CO2 fluid contained in the subsea CO2 storage tank is a mixture of stored liquid CO2 and stored vaporized CO2, the obtained vaporized CO2 being obtained from the stored vaporized CO2; the mixture of stored liquid CO2 and stored vaporized CO2 is formed from the liquid CO2 flowed from the carrier into the subsea CO2 storage tank; the stored vaporized CO2 is located at an upper portion of the subsea CO2 storage tank, said upper portion comprising an outlet, the method comprising establishing a fluid communication from the outlet to the carrier; the liquid CO2 is flowed from the carrier into an inlet of the subsea CO2 storage tank located at a distance from the outlet higher than 5 meters, and / or at a depth relative to the outlet higher than 10 meters; the method comprises generating vaporized CO2 inside the subsea CO2 storage tank by heating the liquid CO2 with seawater; the carrier is one of a tank mounted on a ship, a tank mounted on an offloading tower, and a tank mounted on a near shore jetty; the subsea CO2 storage tank lies at the bottom of the sea; the subsea CO2 storage tank further comprises at least one outlet connected to an offshore pipeline; offloading a volume of the CO2 fluid contained in the subsea CO2 storage tank to the offshore pipeline, thereby using the subsea CO2 storage tank as a buffer tank; the offshore pipeline is further connected to an injection well; the subsea CO2 storage tank has a storage volume between 5% to 25% larger than a storage volume of the carrier; the subsea CO2 storage tank comprises at least one of a pipe rack, a bundled pipeline, and a single pipeline; the vaporized CO2 flowed into the carrier is between 5% and 15% of the liquid CO2 flowed into the subsea CO2 storage tank; wherein the liquid CO2 stored in the carrier has a density between 700 and 1100kg / m3.

[0011] BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Non-limiting examples will now be described in reference to the accompanying drawings, where:

[0013] FIG. 1 shows a flowchart of the method;

[0014] FIG.s 2A to 17 illustrate examples of the method.

[0015] DETAILED DESCRIPTION

[0016] With reference to the flowchart of FIG. 1, it is proposed a method for offloading liquid carbon dioxide (CO2) stored in a carrier into a subsea CO2 storage tank. The method comprises flowing S10 the liquid CO2 from the carrier into the subsea CO2 storage tank. The method also comprises obtaining S20 vaporized CO2 from CO2 fluid contained in the subsea CO2 storage tank. The method also comprises flowing S30 the obtained vaporized CO2 into the carrier.

[0017] Such a method improves the offloading of the liquid CO2 stored in the carrier. Indeed, on the one hand the method takes out the excess vaporized CO2 from the CO2 fluid contained in the subsea CO2 storage tank, for example formed after some exchange of heat has occurred due to the subsea CO2 storage tank being in contact with the sea. On the other hand, as vaporized CO2 is flowed into the carrier, the method ensures that the pressure inside the carrier is maintained, e.g., stable when performing the offloading. Thereby, the method allows an energetically efficient offloading of the liquid CO2 stored in the carrier, as the method reduces (e.g., even eliminates) the use of external equipment. In particular, the method reduces or eliminates the need for additional ship equipment to produce, on ship, vaporized CO2 or vaporized water, for example to replace the offloaded liquid CO2 by the produced vapor so as to maintain pressure. The method may indeed perform S30 so as to maintain pressure inside the carrier, as liquid CO2 is flowed at S10 from the carrier into the subsea CO2 storage tank (such flowing S10 tending otherwise to naturally decrease pressure). In other words, the quantity, rate, and timing at which vaporized CO2 is flowed at S30 into the carrier may be such that the pressure inside the carrier is maintained, , for example, the pressure stays within a range + / - 20% of its initial value (the pressure value before starting S10). If the pressure is low, the range may be high, e.g., higher than 20%.

[0018] The method thereby allows using vaporized CO2 already present in the subsea CO2 storage tank as replacement vapor. The method thereby reduces fuel consumption, CO2 emissions, and safety risks such as for example exposure to CO2 of operators (for example relative to producing vaporized CO2 on ship), in contexts such as CCS projects.

[0019] The method is for offloading liquid CO2 stored in the carrier into the subsea CO2 storage tank. In other words, the method performs a transfer of the liquid CO2 stored in the carrier into the subsea CO2 storage tank.

[0020] The carrier may be a storage used for picking up the liquid CO2 at an emitter's location. The carrier may be one of a tank mounted on a ship, a tank mounted on an offloading tower, and a tank mounted on a near shore jetty.

[0021] The method may be integrated into a process comprising:

[0022] - docking the carrier at a proximity of the subsea CO2 storage tank, for example at an onshore terminal or jetty;

[0023] - connecting (e.g., fluidically) the carrier to the subsea CO2 storage tank, e.g. using one or more conduits;

[0024] - performing the method; and

[0025] - disconnecting and undocking the carrier from the subsea CO2 storage tank, the carrier thereby leaving without (at least substantially) the liquid CO2.

[0026] The whole process, from the carrier docking at a proximity of the subsea CO2 storage tank to the undocking, may take a time less than a predetermined duration, e.g., less than three days or less than two days.

[0027] The subsea CO2 storage tank may be a storage for gathering (e.g., temporarily)

[0028] CO2 underwater (for example, prior to transmitting the CO2 to an offshore pipeline for its subsequent injection on an injection well). The subsea CO2 storage tank may thus be f luidica lly connected to one or more injection wells. The subsea CO2 storage tank may have walls each having a wall thickness between 30 and 70mm, for example 50mm. The walls may be made of steel. The subsea CO2 storage tank may have a cross-sectional dimension (e.g., width, for example a diameter in the case that the subsea CO2 storage tank is a tube) between 100 and 15000 millimeters, for example 711.2 millimeters (or approximately 28 inches). The subsea CO2 storage tank may have a length, for example, of 100 meters or more, for example 1000 meters or more such as 40 km. The subsea CO2 storage tank may be lying at the bottom of the sea, for example on a seabed. For example, the subsea CO2 storage tank may lie along a sloped surface of the seabed. The subsea CO2 storage tank may have a storage volume between 5% to 25% larger than a storage volume of the carrier. The subsea CO2 storage tank may, for example, have a storage volume of 16 500 m3, with the subsea CO2 storage tank having a cross-sectional dimension of 711.2 millimeters (28 inches) and a length of 40km. The subsea CO2 storage tank may comprise at least one of a pipe rack, a bundled pipeline, and a single pipeline.

[0029] The method flows S10 the liquid CO2 from the carrier into the subsea CO2 storage tank. The liquid CO2 contained in the carrier may have a temperature lower than 0°C, for example -26°C, e.g. when S10 is started (and the temperature may be maintained, stay within + / -20% of its initial value, as the method is performed since the pressure is maintained). The carrier may have a low pressure, for example 30 bar or less, e.g., 20 bar. The liquid CO2 stored in the carrier may have a density between 700 and 1100 kg / m3. The carrier may comprise at least one (e.g., a plurality of) outlet(s). The subsea CO2 storage tank may comprise at least one inlet. Flowing S10 the liquid CO2 may comprise coupling the carrier to the subsea CO2 storage tank before hand so that the liquid CO2 flows from the outlet of the carrier to the inlet of the subsea CO2 storage tank. The coupling may also comprise passing the liquid CO2 from the outlet of the carrier through offloading equipment. The offloading equipment may be as known per se in the field of carbon capture storage technology, for example the offloading equipment may comprise at least one pump, a flowmeter, and pressure and / or temperature sensors. The offloading equipment may be is thereby configured for performing the offloading. The pumps may be for example

[0030] 500 KW pumps.

[0031] The method obtains S20 vaporized CO2 from CO2 fluid contained in the subsea CO2 storage tank. By CO2 "fluid" (contained in the subsea CO2 storage tank), it is meant CO2 in any flowable state, such as liquid or gas, or more commonly a mixture of stored liquid CO2 and stored vaporized CO2.

[0032] The obtained vaporized CO2 may be obtained from the stored vaporized CO2. By "vaporized" it is meant that the CO2 is in a gas state. The mixture of stored liquid CO2 and stored vaporized CO2 may be formed from the liquid CO2 flowed from the carrier into the subsea CO2 storage tank. In other words, the stored vaporized CO2 may result from the flowing of the liquid CO2 from the carrier into the CO2 storage tank. For example, the stored vaporized CO2 may be the result of the liquid CO2 being heated inside the CO2 storage tank due to the seawater being in thermodynamic exchange with the CO2 storage tank. In other words, the seawater may condition the temperature of the liquid CO2 to go up (e.g., above 0°C), due to the thermodynamic exchange performed between the seawater and the CO2 storage tank, thereby creating vaporized CO2. The CO2 storage tank may have walls of a predetermined material and / or of a predetermined thickness so as to allow thermodynamic exchange. In examples, the CO2 storage tank may also be heated due to contact with the seabed. The seabed may be at a temperature ranging from 0 °C to 5 °C.

[0033] Additionally or alternatively, the obtained vaporized CO2 may be obtained by using an evaporation unit. The evaporation unit may comprise one or more pipes configured to exchange heat with the seawater, for example by being in contact with the seawater. The evaporation unit may be placed next to the CO2 storage tank. The method may obtain the vaporized CO2 resulting concomitantly from the flowing and the evaporation unit. For example, the method may obtain the vaporized CO2 resulting from the evaporation unit when detecting that the vaporized CO2 resulting from the flowing is not sufficient to maintain the pressure of the carrier. The detection may be performed automatically or semi-automatically, e.g., at predetermined time intervals. The method may alternate between obtaining the vaporized CO2 resulting from the flowing and the evaporation unit according to the pressure needs of the carrier resulting from the detection.

[0034] The method flows S30 the obtained vaporized CO2 into the carrier. In other words, the method may perform a transfer of the vaporized CO2 back to the carrier. The CO2 storage tank may comprise an outlet configured for outputting the vaporized CO2. The carrier may comprise an inlet configured for receiving the vaporized CO2.

[0035] The flowing S30 of the obtained vaporized CO2 into the carrier may be performed via pressure differential. In other words, the flow may be performed due to the difference in pressure of the subsea CO2 storage tank with respect to the pressure of the carrier. The difference in pressure may be due the pressure inside the carrier decreasing as S10 is performed, and also to the subsea CO2 storage tank being located below sea level (for example, at the bottom of the sea) and the carrier being located at or above sea level, for example when the carrier is one of the tank mounted on a ship, the tank mounted on an offloading tower, and the tank mounted on a near shore jetty. The vaporized CO2 flowing into the carrier at S30 may have a pressure between 10 to 100 bar, for example 50 bar if the subsea CO2 storage tank is placed in warm sea water.

[0036] The liquid CO2 may be flowed from the carrier into an inlet of the subsea CO2 storage tank. The inlet may be located at a distance from the outlet. The subsea CO2 storage tank may also be connected to a NPSH (Net Positive Suction Head) to ensure liquid flow into the pump or to a multiphase pump. The distance from the outlet may be higher than a first predetermined distance. Additionally or alternatively, the inlet may be located at a depth relative to the outlet higher than a second predetermined distance. The first predetermined distance and second predetermined distance may be set in any manner (e.g., independently of each other or alternatively the first predetermined distance may be dependent of the second predetermined distance or vice versa), for example so as to allow that there is a minimal distance between the inlet and the outlet from which the obtained vaporized CO2 is flowed from the outlet into the carrier, thereby avoiding to mix the vaporized CCh with the liquid CO2. For example, the inlet may be located deeper than the outlet, so that the liquid CO2 is injected at a location of the subsea CO2 storage tank deeper than the outlet. This facilitates the flow of the vaporized CO2, moreover it facilitates the formation of the vaporized CCh due to thermodynamic exchange inside the subsea CO2 storage tank. For example, the inlet may be located at a distance of 10km of the subsea CO2 storage tank when the subsea CO2 storage tank comprises a single pipe. The inlet may be located at a distance between 10 to 20 meters when the subsea CO2 storage tank comprises a pipe rack.

[0037] The vaporized CO2 flowed into the carrier (resulting from the flowing of the liquid CO2 from the carrier into the CO2 storage tank and / or the evaporation unit) may be between 5% and 15% in weight of the liquid CO2 flowed into the subsea CO2 storage tank.

[0038] The stored vaporized CO2 may be located at an upper portion of the subsea CO2 storage tank. The upper portion may comprise an outlet. In examples, the subsea CO2 storage tank may lie along the sloped surface of the seabed and the upper portion may be located on a side of the subsea CO2 storage tank which is positioned closest to sea level. The method may comprise establishing a fluid communication from the outlet to the carrier. For example, the method may pump the stored vaporized CO2 from the outlet to the carrier.

[0039] The method may comprise generating vaporized CO2 inside the subsea CO2 storage tank by heating the liquid CO2 with seawater. For example, the method may convert the liquid CO2 through the evaporation unit described above. The output of the evaporation unit may be flowed into the carrier.

[0040] The subsea CO2 storage tank may further comprise at least one outlet connected to an offshore pipeline. In other words, the subsea CO2 storage tank is configured for outputting a volume of the CO2 fluid into the offshore pipeline. The offshore pipeline may have walls each having a wall thickness between 10 and 40mm, for example 20mm. The walls may be made of carbon steel.

[0041] The method may further comprise offloading a volume of the CO2 fluid contained in the subsea CO2 storage tank to the offshore pipeline. The method may also comprise (continuously or at predetermined time intervals), flowing S10 the liquid CO2 from the carrier into the subsea CO2 storage tank while offloading the volume of CO2. The method may for example flow S10 the liquid CO2 from the carrier into the subsea CO2 storage tank so as to fill a first predetermined volume of the subsea CO2 storage tank. The method thereby uses the subsea CO2 storage tank as a buffer tank. The method may wait a predetermined period of time before performing the offloading. The method thereby provides a sufficient amount of time for performing the flowing S30 of the obtained vaporized CO2 into the carrier and thus allows to maintain the pressure of the carrier.

[0042] The offshore pipeline may be further connected to an injection well.

[0043] In examples, the method may perform the flowing S10 the liquid CO2 from the carrier into the subsea CO2 storage tank continuously (for example at the first predetermined rate) wile offloading (also continuously) the volume of CO2 (for example at the second predetermined rate), all while performing the flowing S30 of the obtained vaporized CO2 into the carrier. The first predetermined rate may be faster than the second predetermined rate, e.g., two times faster or more, for example, the carrier may be emptied at the first rate in ten hours while the subsea CO2 storage tank may be emptied at the second rate in three days. The method thereby offloads the carrier faster than what the offshore pipeline can take, which in turn allows to have a continuous injection from the offshore pipeline to the injection well.

[0044] Examples of the method are now discussed with reference to FIG.s 2A to 18.

[0045] FIG. 2A shows an example of the carrier as a tank mounted on a ship 200. The carrier may transport liquid CO2 , for example cryogenic CO2. The carrier may have a volume between 5 and 50 000 cubic meters. FIG. 2B shows an example of a system 210 for flowing the liquid CO2 from the carrier into the subsea CO2 storage tank.

[0046] The system 210 comprises an onshore or subsea offloading system 211 configured for flowing the liquid CO2 from the carrier 200 into the subsea CO2 storage tank 214 and for flowing the obtained vaporized CO2 into the carrier 200. The onshore or subsea offloading system 211 may comprise equipment for performing the flowing from or to the carrier, for example a transfer pump (configured to transfer the obtained vaporized CO2 into the carrier 200 with pressure between 20 to 40 bar) and / or offloading pumps, e.g., 500kw pumps. The onshore or subsea offloading system 211 is fluidically connected to an onshore or subsea Pipe Line End Manifold (PLEM) 212 that is configured to transfer the liquid CO2 to the subsea CO2 storage tank 214. The onshore or subsea PLEM 212 may also be connected to a temporary pig launcher / receiver 213. The subsea CO2 storage tank 214 may be arranged in a sloped position, for example by lying on the bottom of the sea (not shown). The subsea CO2 storage tank 214 may be configured to operate with a pressure between 50 to 250 bar. The subsea CO2 storage tank 214 is connected to a pump 215. The subsea CO2 storage tank 214 is also connected to a dH 216 (also called NPSH or Net Positive Suction Head) to ensure liquid flow into the pump, that is, liquid at low injection PLEM. The pump 216 is connected to an (optional) temporary pig launcher / receiver 216. The pump 216 may be connected to an onshore or offshore pipeline (not shown).

[0047] The subsea CO2 storage tank 214 is used as a buffer tank for the pipeline 217. The liquid CO2 entering the subsea CO2 storage tank 214 may be at a temperature ranging from -10 °C to -50 °C, for example from -20 °C to -30 °C. The seawater (not shown) may heat the CO2 inside the CO2 storage tank 214 to a temperature above 0 °C, thereby generating vaporized CO2 inside the subsea CO2 storage tank 214. For example, the seawater may heat the CO2 inside the CO2 storage tank 214 to a temperature ranging between 1 °C and 30 °C, i.e. to a condition suitable for generating the vaporized CO2 (e.g., located at an upper portion 214.1 of the subsea CO2 storage tank 214) and flowing the obtained vaporized CO2 into the carrier 200. Concomitantly to the foregoing, the method offloads continuously a volume of the CO2 fluid contained in the subsea CO2 storage tank 214 (e.g., a volume of the CO2 fluid located at a lower portion 214.2 of the CO2 storage tank 214, the volume for example comprising, e.g., essentially, stored liquid CO2) to the pipeline.

[0048] FIG. 2C shows an example of the pipeline, e.g., an onshore or (preferably) offshore pipeline 217. The pipeline 217 may be fluidically connected for offloading the CO2 fluid to an injection facility 218 (e.g. an injection well).

[0049] FIG. 3 shows (e.g., alternative) examples of the subsea CO2 storage tank 214. The subsea CO2 storage tank 214. may be a pipe rack such as a CSSU pipe rack 301, a bundled pipeline 302 and / or a single pipeline 303. FIG. 4 illustrates an example of a functional block diagram 400 of a theoretic system, showing offloading equipment that could be naively used for offloading CO2 liquid in a manner different from the method. The functional block diagram 400 shows the carrier 410 (e.g., at sea level). The functional block diagram 400 also shows, at quay level 420, tanker offloading equipment 420.1, offloading pumps 420.2 (for example 500 kw offloading pumps). The functional block diagram 400 of the system also shows, onshore 430, the subsea CO2 storage tank 430.1. The functional block diagram 400 of the system also shows a vaporizer heater 430.2. The vaporizer heater

[0050] 430.2 may be of a power of 2000kw or more (for example comprising two or more heaters of 2000kw). The subsea CO2 storage tank 430.1 is connected to booster pumps 430.3. The booster pumps flow CO2 fluid to the fluid (to recirculate vaporized CO2 to the carrier 410) and export pumps 430.4. The export pumps 430.4 offload a volume of the CO2 fluid contained in the subsea CO2 storage tank 430.1 to a pipeline 440 via another heater 430.5 (for example a 12000kw heater) and metering equipment 430.6. The pipeline 440 comprises the offshore pipeline 440.7 and a pig launcher tie-in point 440.8.

[0051] Contrary to the foregoing figure, FIG. 5 illustrates an example of a functional block diagram 500 of the offloading equipment for offloading CO2 liquid according to the method. The blocks are substantially identical to those of the functional block diagram 400, although the diagram does not include the vaporizer heater 430.2, the booster pumps 430.3 and the heater 430.5, which are shown crossed out. This is due to the flowing of the obtained vaporized CO2 into the carrier 400 according to the method, which eliminates the need of the vaporizer heater 430.2, the booster pumps

[0052] 430.3 and the heater 430.5.

[0053] FIG. 6 illustrates examples for obtaining vaporized CO2 from CO2 fluid contained in the subsea CO2 storage tank 214. A first example 601 shows using an internal system for ensuring that vapor comes out from the subsea CO2 storage tank 214. The subsea CO2 storage tank 214 comprises an inlet 601.1 configured for flowing the liquid CO2 from the carrier into the subsea CO2 storage tank to a downdip portion of the subsea CO2 storage tank 214. The subsea CO2 storage tank 214 comprises an output port 601.2 located at an upper portion of the subsea CO2 storage tank 214. The inlet 601.1 is located at a distance from the outlet 601.2 higher than a predetermined number of meters and at a depth from the outlet 601.2. The method may hence flow vaporized CO2 to the carrier due to the heating of the subsea CO2 storage tank 214. A second example 602 shows using a system on a subsea CO2 storage tank 214 which is a pipeline. The second example 602 comprises an inlet 602.1 and taps off vapor from an outlet placed at a high point 602.2 (with respect to a position at the bottom of the sea) of the pipeline 214. The third example 603 comprises a separate evaporator unit configured for generating vaporized CO2 taken from the carrier by heating the liquid CO2 with seawater. The subsea CO2 storage tank 214 comprises a dedicated inlet 603.1 for receiving a portion of the liquid from the carrier, e.g., through a subsea PLM. The subsea PLM may be configured for inputting a volume of the liquid CO2 to the separate evaporator unit through an outlet 603.2. The separate evaporator unit is configured to flow the obtained vaporized CO2 into the carrier.

[0054] FIG. 7 describes examples of the carrier 200. The carrier 200 may be a tank mounted on a ship 701. In this example, the carrier may be connected to an arm system configured for flowing the obtained vaporized CO2 into the carrier. Alternatively, the carrier 200 may be a tank mounted on an offloading tower 702. The carrier may be connected to a SAL / Buoy / Harbor for offloading the liquid CO2. The method may be performed fully automatically, that is, no manning is required. Alternatively, the carrier 200 may be a tank mounted on a near shore jetty 703. The near shore jetty may accept any standard ship.

[0055] FIG. 8 shows an example of the subsea CO2 storage tank connected to an onshore terminal and connected to an offshore pipeline.

[0056] The onshore terminal is connected to a carrier mounted on a ship and is configured for flowing the liquid CO2 from the carrier into the subsea CO2 storage tank. The subsea CO2 storage tank is connected to the offshore pipeline via a subsea lift pump. The method offloads a volume of the CO2 fluid contained in the subsea CO2 storage tank to the offshore pipeline while the method flows the obtained vaporized CO2 into the carrier. The subsea CO2 storage tank is thus a buffer volume for offloading CO2 from the carrier to the offshore pipeline, as the rate in which the volume of the CO2 fluid contained in the subsea CO2 storage tank to the offshore pipeline is slower than the rate by which the liquid CO2 is offloaded from the carrier into the subsea CO2 storage tank. Moreover, the subsea CO2 storage tank conditions the liquid CO2 (which is cryogenic) to seawater temperature, so that the vaporized CO2 is generated inside the subsea CO2 storage tank. This simplifies overall the onshore terminal due to the reduction of equipment. Indeed, there is an 80% removal of equipment.

[0057] FIG. 9 shows an example of the subsea CO2 storage tank connected to a near shore jetty and connected to an offshore pipeline (not shown) through a bottom PLEM. The near shore jetty is an onshore terminal substitute. There is no qualification needed. Moreover, the near shore jetty accepts a standard ship that contains the carrier. The system of FIG. 9 requires no personnel, that is, no manning.

[0058] FIG. 10 shows an example of a system for using the method for flowing the liquid CO2 from the carrier into the subsea CO2 storage tank. The subsea CO2 storage tank is a tube having a diameter of 28" (approximately 711.2mm) and a length of 40km. The subsea CO2 storage tank has a volume of 16.500m3. The subsea CO2 storage tank has a design pressure between 50 to 150 bar. The subsea CO2 storage tank may operate between 30 to 60 bar, and may operate at temperatures between -26 to 30°C. The liquid CO2 may be at a pressure of approximately 40 bar. The subsea CO2 storage tank may be connected to a subsea lift pump and to a tube of 10km with a width of 24" (609.6mm) to offload a volume of the CO2 fluid contained in the CO2 storage tank to the offshore pipeline via a subsea lift pump. A loading tower may be configured for flowing the liquid CO2 from the carrier into the subsea CO2 storage tank.

[0059] FIG. 11 shows another example of a system for using the method for flowing the liquid CO2 from the carrier into the subsea CO2 storage tank. The subsea CO2 storage tank is used as a buffer tank linked to an onshore terminal. The main function of the buffer tank is to be used as a buffer volume for offloading a volume of the CO2 fluid contained in the subsea CO2 storage tank to the offshore pipeline, thereby using the subsea CO2 storage tank as a buffer tank, for example the method flows the liquid C02from the carrier into the subsea CO2storage tank and while the method flows the obtained vaporized CO2into the carrier.

[0060] FIG. 12 shows another example of a system for using the method for flowing the liquid CO2from the carrier into the subsea CO2storage tank. The subsea CO2storage tank is a pipeline of a large diameter, for example between 30" to 72" (approximately between 76.2 cm and 182.88 cm). The internal volume may be large enough to hold the volume of liquid CO2contained in the carrier and flowed into the subsea CO2storage tank.

[0061] FIG. 13 shows an example of an implementation of the method in the context of a carbon capture storage project. The CO2may be captured from industrial plants and compressed and stored in a carrier in the form of CO2liquid. The carrier may be transported by ship to a facility so as to perform the method.

[0062] FIG. 14 shows another example of an implementation of the method in the context of a carbon capture storage project.

[0063] FIG. 15A shows another example of an implementation of the method in the context of a carbon capture storage project. This example is from downstream of a compression facility, to a connection point between the offshore pipeline and the injection facility.

[0064] FIG. 15B shows another example of an implementation of the method in the context of a carbon capture storage project. In this example, the ship transports the carrier, the subsea CO2storage tank may be at a facility (comprising for example loading arms) located anywhere in the world, for example the Dunkirk area.

[0065] FIG. 16 shows another example of an implementation of the method in the context of a carbon capture storage project.

[0066] FIG. 17 shows an example of a workflow of a carbon capture storage project. The workflow may comprise a capture stage, comprising CO2capture from a CO2source. The workflow may also comprise a conditioning stage, comprising a conditioning pipeline transport and compression and / or a conditioning ship transport. The workflow may also comprise a transport stage, comprising a pipeline transport and / or an interim storage for ship transport. The workflow may also comprise a storage stage, using the method of FIG. 1.

Claims

CLAIMS1. A method for offloading liquid carbon dioxide (CO2) stored in a carrier into a subsea CO2 storage tank, the method comprising:- flowing (S10) the liquid CO2 from the carrier into the subsea CO2 storage tank;- obtaining (S20) vaporized CO2 from CO2 fluid contained in the subsea CO2 storage tank; and- flowing (S30) the obtained vaporized CO2 into the carrier.

2. The method of claim 1, wherein the flowing (S30) of the obtained vaporized CO2 into the carrier is performed to maintain pressure inside the carrier, as liquid CO2 is flowed from the carrier into the subsea CO2 storage tank.

3. The method of claim 1 or 2, wherein the flowing (S30) of the obtained vaporized CO2 into the carrier is performed via pressure differential.

4. The method of any one of claims 1 to 3, wherein the CO2 fluid contained in the subsea CO2 storage tank is a mixture of stored liquid CO2 and stored vaporized CO2, the obtained vaporized CO2 being obtained from the stored vaporized CO2.

5. The method of claim 4, wherein the mixture of stored liquid CO2 and stored vaporized CO2 is formed from the liquid CO2 flowed from the carrier into the subsea CO2 storage tank.

6. The method of claim 4 or 5, wherein the stored vaporized CO2 is located at an upper portion of the subsea CO2 storage tank, said upper portion comprising an outlet, the method comprising establishing a fluid communication from the outlet to the carrier.

7. The method of claim 6, wherein the liquid CO2 is flowed from the carrier into an inlet of the subsea CO2 storage tank located at a distance from the outlet higher than 5 meters, and / or at a depth relative to the outlet higher than 10 meters.

8. The method of any one of claims 5 to 7, wherein the method comprises generating vaporized CO2 inside the subsea CO2 storage tank by heating the liquid CO2 with seawater.

9. The method of any one of the preceding claims, wherein the carrier is one of a tank mounted on a ship, a tank mounted on an offloading tower, and a tank mounted on a near shore jetty.

10. The method of any one of the preceding claims, wherein the subsea CO2 storage tank lies at the bottom of the sea.

11. The method of any one of the preceding claims, wherein the subsea CO2 storage tank further comprises at least one outlet connected to an offshore pipeline.

12. The method of claim 11, further comprising offloading a volume of the CO2 fluid contained in the subsea CO2 storage tank to the offshore pipeline, thereby using the subsea CO2 storage tank as a buffer tank.

13. The method of claim 12, wherein the offshore pipeline is further connected to an injection well.

14. The method of any one of claims 1 to 13, wherein the subsea CO2 storage tank has a storage volume between 5% to 25% larger than a storage volume of the carrier.

15. The method of any one of the preceding claims, wherein the subsea CO2 storage tank comprises at least one of a pipe rack, a bundled pipeline, and a single pipeline.

16. The method of any one of the preceding claims, wherein the vaporized CO2 flowed into the carrier is between 5% and 15% of the liquid CO2 flowed into the subsea CO2 storage tank.

17. The method of any one of the preceding claims, wherein the liquid CO2 stored in the carrier has a density between 700 and 1100kg / m3.

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