Co 2 battery reservoir network

Abstract

The disclosure provides an energy storage system and a method of storing and releasing energy. The system comprises a first vessel (1), a second vessel (6) and a decompression apparatus (3). The first vessel comprises a rigid housing defining a first volume therein. The first vessel is configured to store or transport a fluid comprising carbon dioxide at a first pressure in the first volume. The second vessel comprises a rigid housing defining a second volume therein. The second vessel is configured to store or transport the fluid comprising carbon dioxide at a second pressure in the second volume. The second pressure is lower than the first pressure. The decompression apparatus is configured to transport the fluid comprising carbon dioxide from the first vessel to the second vessel, to reduce the pressure of the fluid comprising carbon dioxide from the first pressure to the second pressure and to capture energy released from the fluid comprising carbon dioxide as it depressurises.

Description

[0001] CO2BATTERY RESERVOIR NETWORK

[0002] The present invention relates to an energy storage system and methods of storing energy.

[0003] If the world is to successfully transition from fossil fuels then storing the energy generated from renewable sources is a crucial step on this journey. There are many options for energy storage, including traditional batteries such as Li-ion, pumped hydro, gas compression and a host of other options. However, there are challenges associated with these known energy storage systems, limiting the amount they can be used.

[0004] For instance, energy storage in conventional batteries is utilised across the world. The biggest facility using battery storage is currently the Moss Landing Energy Storage Facility in California which uses lithium ion batteries, namely 256 Tesla Megapacks, each weighing 38 tonnes. The facility has a 750MW output and 3,000 MWh capacity. Based on a continuous 12-hour discharge this equates to 25.7 kWh per tonne of battery. The round-trip efficiencies of the charge I discharge phases are claimed to be as high 92 - 94% in these systems. The biggest disadvantage of these systems is that they are sensitive to temperature, with heat causing degradation of the cells, they are susceptible to cold reducing their capacity, and are inherently flammable releasing toxic vapours upon thermal runaway with great difficulties encountered in extinguishing any fires. Additionally, it is reported that a looming shortage of lithium could limit the ability to provide such facilities.

[0005] Hydroelectric plants can be used to store energy. A hydroelectric plant generally comprises an upper body of water and a lower body of water. The difference in height between the upper and lower bodies of water is called a head. When power generation is required, water is fed from the upper body of water, through turbines, to the lower body of water. During off-peak times, water can be pumped from the second body of water to the first body of water. For instance, the Dinorwig Power Station is the UK's largest hydroelectric power station. Water is stored in Marchlyn Mawr reservoir, which is at a height of about 636 meters above sea level. When the station is required to generate power, the water is sent through turbines to Llyn Peris, a lake at a height of about 100 meters above sea level. The system holds a total of approximately 6.7 million m3of water (6.7 million tonnes), with a head between the upper and lower storage lakes of 494 - 542 metres. This equates to a total power storage of 9.1 GWh and an efficiency of approximately 75%. The station is set up to deliver 1,728 MWh to the UK's power grid for approximately 51 / 4 hours before it has exhausted its water capacity. If the water was discharged over a 12-hour period, this would equate to 0.758 kWh power per tonne of water moved. Other pumped hydroelectric power systems have efficiencies between 70 - 87%. The single biggest drawback of such systems is the limited number of suitable geographical locations where two large volume water bodies are separated by a suitable head.

[0006] There are currently only two commercial compressed air energy storage plants in the world, the Huntorf plant in Germany and the McIntosh plant in the USA. Both plants comprise large underground salt caverns where compressed air is stored. It is vital that the caverns are gas impermeable. Air is compressed and stored in the caverns during off-peak times. When power generation is required, the gas is expanded and used to drive a turbine to generate electricity. For instance, the Huntorf plant comprises a cavern with a volume of 310,000 m3and a pressure tolerance of 46 - 72 Bar. This plant has a 290 MW capacity, which is discharged over 2 hours. If the gas is released over a 12-hour period, this equates to 0.7 - 1 kWh of power released per tonne of compressed air stored. The efficiency of this system is claimed to be around 42%. In other, smaller capacity systems, efficiencies of 42 - 70% are claimed. The main challenge limiting the ability to build more of these systems is the need to find suitably located large gas impermeable caverns which can be filled with compressed air and the low energy storage density of compressed air.

[0007] Liquid air energy storage is a similar concept to air energy storage. In this system, during off-peak times air is liquified. This liquid air is stored in an insulated tank. When power generation is required, liquid air is drawn from the tank and allowed to evaporate. This air can then be used to drive a turbine or piston. For instance, Highview Power utilises liquefied air for storage and is currently building a 50MW I 300 MWh plant in the UK. Air is compressed and liquefied reducing its volume by around 700 times, giving slightly higher power densities than that seen in liquid CO2 storage. However, to achieve this larger volumes of air must be cooled and maintained at - 196 °C in the compressed state which incurs significant costs in refrigeration & insulation to store the fluid. Typical efficiencies of 45 - 70% are claimed.

[0008] Energy Dome have developed a system utilising carbon dioxide as a battery. In this system CO2 is stored in a dome / flexible bag. During off-peak times the system is charged by drawing the CO2 from the dome, pressurising it and storing it under pressure. At times power generation is required, the CO2 is depressurised and can be used to power a turbine or piston, similarly to a compressed air energy storage plant or a liquid air energy storage plant. The decompressed air is fed back into the dome. The biggest drawback of this system is the need to provide the massive flexible bag I dome to store the decompressed carbon dioxide. A 200 MWh system is reported to require around 5 hectares I 12 acres I 48,562 m2of flat land the majority of which is required for the dome. Furthermore, a major drawback of such a system is that should the dome be damaged in such a way as to cause a leak, there would be an immediate threat to life in the vicinity of the plant due to carbon dioxides asphyxiation. Furthermore, it is reported that during storage conditions the working fluid should be typically between 10 and 150 Bar (for instance, see EP 3927949) and that the fluid should be discharged to atmospheric pressure. The volume required to contain CO2 at 1 Bar is typically >400 - 500 times the volume required of the carbon dioxide in the stored dense phase, making the process very space inefficient occupying large areas of land which may be better utilised for other purposes.

[0009] Additionally, for all of compressed air energy storage, liquid air energy storage and compressed carbon dioxide energy storage it is also necessary to deal with efficiency issues upon compression (gas heats up) and release (gas cools down).

[0010] Additionally, it is widely acknowledged that to meet the targets required to reduce global heating to a manageable level then it will be necessary to capture emissions produced from fossil fuels during the transition period. It will likely also be necessary to remove vast quantities of CO2 from the atmosphere. Again, at this stage, the infravessel required is not advanced enough to do this in a practical and cost-effective manner. Even if the technology existed that made these carbon capture processes efficient enough to employ, questions would remain regarding what to do with the vast quantities of CO2 that would be captured.

[0011] The present work arises from the inventors attempting to develop new energy storage systems.

[0012] In accordance with a first aspect of the disclosure, there is provided an energy storage system, the system comprising: a first vessel comprising a rigid housing defining a first volume therein, wherein the first vessel is configured to store or transport a fluid comprising carbon dioxide at a first pressure in the first volume; a second vessel comprising a rigid housing defining a second volume therein, wherein the second vessel is configured to store or transport the fluid comprising carbon dioxide at a second pressure in the second volume, wherein the second pressure is lower than the first pressure; and a decompression apparatus configured to transport the fluid comprising carbon dioxide from the first vessel to the second vessel, to reduce the pressure of the fluid comprising carbon dioxide from the first pressure to the second pressure and to capture energy released from the fluid comprising carbon dioxide as it depressurises.

[0013] Advantageously, the system of the first aspect can be used to release energy.

[0014] The fluid comprising carbon dioxide preferably comprises a high concentration of carbon dioxide. Preferably, the fluid comprising carbon dioxide comprises at least 5 vol%, at least 10 vol%, at least 20 vol%, at least 30 vol%, at least 40 vol%, at least 50 vol%, at least 60 vol%, at least 70 vol%, at least 80 vol% or at least 90 vol% carbon dioxide. The fluid comprising carbon dioxide may comprise at least 95 vol%, at least 99 vol% or at least 99.9 vol% carbon dioxide.

[0015] The fluid comprising carbon dioxide may further comprise other chemicals. These may be known to a person skilled in the art, and may be considered to be impurities.

[0016] Typical impurities may include, but are not limited to, water, hydrogen sulphide, total sulphur, methane, hydrocarbons, carbon monoxide, nitrogen, oxygen, glycol, argon, hydrogen, oxides of sulphur, oxides of nitrogen, total non-condensables, particulates, ammonia, mercury and / or hydrogen cyanide.

[0017] The decompression apparatus may be configured to convert the energy released from the fluid comprising carbon dioxide to mechanical energy, heat energy, cooling energy, electrical energy and / or hydraulic pressure. In some embodiments, the decompression apparatus is configured to convert the energy released from the fluid comprising carbon dioxide to electrical energy.

[0018] The decompression apparatus may comprise a decompressor or expander, configured to reduce the pressure of the carbon dioxide from the first pressure to the second pressure and to capture energy released from the fluid comprising carbon dioxide as it depressurises. The decompressor or expander may comprise one or more pressure reduction nozzles and / or one or more pressure reduction valves, the pressure reduction nozzles and / or pressure reduction valves being configured to reduce the pressure of the carbon dioxide from the first pressure to the second pressure. The decompressor or expander may comprise an expander wheel, a piston, a turbine and / or a shaft comprising one or more blades, the expander wheel, the piston, turbine and / or shaft being configured to be driven by the fluid comprising carbon dioxide as it depressurises. The expander may be or comprise a hot gas expander.

[0019] The decompression apparatus may further comprise a generator configured to generate electrical energy. The generator may be connected to the decompressor or expander, such that as the fluid comprising carbon dioxide depressurises it drives the generator. In some embodiments, the expander wheel, the piston, turbine or shaft in the decompressor or expander drives the generator and thereby generates electrical energy.

[0020] The decompression apparatus may comprise a first decompression conduit extending between the first vessel and the decompressor or expander, and being configured to transport the fluid comprising carbon dioxide from the first vessel to the decompressor or expander. It may be appreciated that the first decompression conduit may be configured to transport the fluid comprising carbon dioxide at the first pressure. The decompression apparatus may comprise one or more valves disposed in the first decompression conduit. The one or more valves may be configured to selectively stop and start the flow of the fluid comprising carbon dioxide from the first vessel to the decompressor or expander and / or to control the rate of flow of the fluid comprising carbon dioxide from the first vessel to the decompressor or expander. The one or more valves may be or comprise a solenoid valve, a flow control valve and / or a one way valve.

[0021] The decompression apparatus may comprise a second decompression conduit extending between the decompressor or expander and the second vessel, and being configured to transport the fluid comprising carbon dioxide from the decompressor or expander to the second vessel. It may be appreciated that the second decompression conduit may be configured to transport the fluid comprising carbon dioxide at the second pressure. The decompression apparatus may comprise one or more valves disposed in the second decompression conduit. The one or more valves may be configured to selectively stop and start the flow of the fluid comprising carbon dioxide from the decompressor or expander to the second vessel and / or to control the rate of flow of the fluid comprising carbon dioxide from the decompressor or expander to the second vessel. The one or more second decompression valves may be or comprise a solenoid valve, a flow control valve and / or a one way valve.

[0022] The system may be connected to an energy network, and the system may be configured to supply electrical energy generated by the decompression apparatus to the energy network. In some embodiments, the generator is connected to the energy network. Accordingly, electrical energy generated by the generator may be supplied to the energy network. The energy network may be an existing energy network, e.g. an energy network which predates the energy storage system of the first aspect. In an alternative embodiment, the energy network may have been purpose built to receive power from the system of the first aspect.

[0023] For instance, the existing energy network may be a local, regional or national power grid. Alternatively, the existing energy network may be the energy network of an offshore vessel or structure, such as an oil and gas platform. In a further alternative, the existing energy network may be the energy network of an onshore vessel or structure. The energy network may be an individual site and / or a small cluster of sites. The energy network may be configured to provide energy for industrial, commercial and / or domestic use. The energy network may not be connected to a national power grid, i.e. the network may be referred to as "off-grid". The energy network may be configured to provide energy for a transport network. For instance, the energy network may be configured to provide energy to transport and / or transport infrastructure associated with a road, a railway, a tramline, a canal, a river, or a combination or network thereof. Accordingly, the system may be used to power the energy network.

[0024] In some embodiments, the system may be configured to provide the majority or all of the energy used by the energy network.

[0025] In alternative embodiments, the energy network may receive energy from an alternative source and the system may be configured to provide additional energy to the energy network. The alternative source may provide the majority of the energy used by the energy network. The system may be configured to provide energy at times when the alternative source cannot meet the required energy demand. For instance, the system may be configured to provide energy to the energy network at times of high energy usage and / or peak demand.

[0026] The decompression apparatus may be disposed adjacent, substantially adjacent or near to the energy network. In some embodiments the decompression apparatus may be a significant distance from the energy network. A person skilled in the arts would be able to determine the best placement of the decompression apparatus with respect to the energy network. The determination may be made based upon a combination of technical and commercial reasoning. The system may comprise a compression apparatus configured to increase the pressure of the fluid comprising carbon dioxide in the second vessel from the second pressure to the first pressure. The compression apparatus may be configured to transport the fluid comprising carbon dioxide from the second vessel to the first vessel.

[0027] The compression apparatus may comprise a compressor, configured to increase the pressure of the carbon dioxide from the second pressure to the first pressure. The compressor may be a single-stage compressor or a multi-stage compressor. In some embodiments, the compressor is a multi-stage compressor. The compressor may be a single-vane compressor or a multi-vane compressor.

[0028] The compressor may be or comprise a dynamic compressor and / or a positive displacement compressor. It may be appreciated that a dynamic compressor is configured to continuously increase the momentum of a gas as it flows therethrough. It may be appreciated that a positive displacement compressor is configured to draw in and capture a volume of gas in a chamber, and to then reduce the volume of the chamber to compress the gas. The compressor may be or comprise a centrifugal compressor, a reciprocating piston compressor, a screw compressor, a rotary screw compressor, a rotary vane compressor, a scroll compressor, a fluid ejector compressor, a liquid rung pump, an ejector compressor, a mixed flow compressor, a scroll compressor, a diaphragm compressor and / or a piston compressor. The fluid ejector compressor may be a liquid ejector compressor or a gas ejector compressor. It may be appreciated that a scroll compressor may also be known as a spiral compressor.

[0029] The compression apparatus may comprise a motor configured to drive the compressor. The motor may be connected to the compressor.

[0030] The compression apparatus may comprise a first compression conduit extending between the second vessel and the compressor, and being configured to transport the fluid comprising carbon dioxide from the second vessel to the compressor. It may be appreciated that the first compression conduit may be configured to transport the fluid comprising carbon dioxide at the second pressure. The compression apparatus may comprise one or more valves disposed in the first compression conduit. The one or more valves may be configured to selectively stop and start the flow of the fluid comprising carbon dioxide from the second vessel to the compressor and / or to control the rate of flow of the fluid comprising carbon dioxide from the second vessel to the compressor. The one or more valves may be or comprise a solenoid valve, a flow control valve and / or a one way valve.

[0031] The compression apparatus may comprise a second compression conduit extending between the compressor and the first vessel, and being configured to transport the fluid comprising carbon dioxide from the compressor to the first vessel. It may be appreciated that the second compression conduit may be configured to transport the fluid comprising carbon dioxide at the first pressure. The compression apparatus may comprise one or more valves disposed in the second compression conduit. The one or more valves may be configured to selectively stop and start the flow of the fluid comprising carbon dioxide from the compressor to the second vessel and / or to control the rate of flow of the fluid comprising carbon dioxide from the compressor to the second vessel. The one or more second compression valves may be or comprise a solenoid valve, a flow control valve and / or a one way valve.

[0032] The compression apparatus may be connected to a power source, such that the power source powers the compression apparatus. The power source may power the motor. The power source may be an energy network or a renewable energy source. For instance, the renewable energy source may be a wind farm or a solar farm. The energy network may be as defined above. The system may be configured to compress the fluid comprising carbon dioxide at times of surplus supply and / or low demand. Accordingly, the system can thereby store energy at times of energy surplus / low energy demand and release it at times of high energy demand.

[0033] The compression apparatus may be disposed adjacent, substantially adjacent or near to the power source. In some embodiments, the compression apparatus may be a significant distance from the power source. A person skilled in the arts would be able to determine the best placement of the compression apparatus with respect to the power source. The determination may be made based upon a combination of technical and commercial reasoning.

[0034] The system may compromise a turboexpander. In particular, the turboexpander may comprise the decompression apparatus and the compression apparatus. The decompression apparatus and the compression apparatus may be as defined above and the turboexpander may be configured to capture energy released from the fluid comprising carbon dioxide as it depressurises and use the energy to at least partially power the compression apparatus. In some embodiments, the decompression apparatus comprises an expander wheel or turbine, the compression apparatus comprises a compression wheel, and the turboexpander comprises a shaft which extends between and mechanically connects the expander wheel or turbine and the compression wheel. Accordingly, it may be understood that rotating the expander wheel or turbine will cause the compression wheel to rotate. The shaft may also extend between and mechanically connect the expander wheel or turbine, the compression wheel and the generator and / or the motor. Accordingly, it may be understood that rotating the expander wheel or turbine may drive the generator, and driving the motor may drive the compression wheel. Alternatively, the turboexpander may comprise a motor-generator and the shaft may also extend between and mechanically connect the expander wheel or turbine, the compression wheel and the motor-generator.

[0035] It may be appreciated that as the fluid comprising carbon dioxide expands it will cool. The system may comprise a decompression heat exchanger. The decompression heat exchanger may be configured to transfer heat into the decompression apparatus. The decompression heat exchanger may be configured to transfer heat into the decompressor or expander. The system may comprise a cold store, a refrigerator, a freezer or an air-conditioning system and the decompression heat exchanger may be configured to transfer heat from the cold store, the refrigerator, the freezer or the air- conditioning system to the cold store. The decompression heat exchanger may comprise a heat exchanger conduit extending between the decompression apparatus and the cold store, the refrigerator, the freezer or the air-conditioning system and configured to transport a fluid therebetween and thereby transfer heat from the cold store, the refrigerator, the freezer or the air-conditioning system to the cold store. The decompression heat exchanger conduit may comprise a closed loop, and be configured to circulate fluid between the decompression apparatus and the cold store, the refrigerator, the freezer or the air-conditioning system. The cold store may comprise a cold storage medium configured to allow heat to be transferred therefrom. Accordingly, the cold storage medium may effectively store the cold caused by expansion of the fluid in the decompressor or expander. The cold storage medium may be a gas, a liquid or a solid (e.g. a thermal brick). The cold storage medium may be transported and / or used elsewhere as required.

[0036] It may be appreciated that as the fluid comprising carbon dioxide is compressed it will heat up. The system may comprise a compression heat exchanger. The compression heat exchanger may be configured to transfer heat out of the compression apparatus. The compression heat exchanger may be configured to transfer heat out of the compressor. The system may comprise a hot store or a location to be heated and the decompression heat exchanger may be configured to transfer heat from the compression apparatus to the hot store or the location to be heated. The compression heat exchanger may comprise a heat exchanger conduit extending between the compression apparatus and the hot store or the location to be heated and configured to transport a fluid therebetween and thereby transfer heat from the compression apparatus to the hot store or the location to be heated. The compression heat exchanger conduit may comprise a closed loop, and be configured to circulate fluid between the compression apparatus and the hot store or the location to be heated. The hot store may comprise a hot storage medium configured to allow heat to be transferred thereto. Accordingly, the hot storage medium may effectively store the heat generated upon compression of the fluid in the compressor. The hot storage medium may be a gas, a liquid or a solid (e.g. a thermal brick). The hot storage medium may be transported and / or used elsewhere as required. The location to be heated may be a domestic, commercial or industrial location, such as a house, a commercial unit or an industrial unit.

[0037] In some embodiments, the system may comprise a heat exchanger configured to transfer heat between the decompression apparatus and the compression apparatus. The heat exchanger may be configured to transfer heat from the compressor into the decompressor or expander. The heat exchanger may comprise a heat exchanger conduit extending between the compression apparatus and the decompression apparatus and configured to transport a fluid therebetween and thereby transfer heat from the compression apparatus to the decompression apparatus. The n heat exchanger conduit may comprise a closed loop, and be configured to circulate fluid between the compression apparatus and the decompression apparatus.

[0038] In some embodiments, the first vessel is configured to store or transport the fluid comprising carbon dioxide in a liquid, supercritical fluid and / or a dense phase state. In some embodiments, the first pressure is a pressure at which the fluid comprising the carbon dioxide is a liquid, a supercritical fluid and / or a dense phase fluid.

[0039] It may be appreciated that whether the fluid comprising carbon dioxide is in a liquid, supercritical fluid and / or dense phase or in a gaseous phase will depend upon a number of factors. These include the chemical composition of the fluid, the temperature of the fluid and the pressure. The skilled person could, for instance, readily determine the chemical composition of a fluid. The skilled person could also determine the temperature in the first vessel. The skilled person could then select a suitable first pressure to ensure that the fluid comprising carbon dioxide is in a liquid, supercritical fluid and / or a dense phase state in the first vessel. Furthermore, a skilled person would know that the pressure is related to the flow rate of a fluid and would be able to identify the effect of changing the flow rate on the pressure and its subsequent effects. A skilled person would also understand the effect of changes described above would have on pressure and the subsequent changes would have on the flow rate. For the avoidance of doubt, the chemical composition may be understood to relate to the amount of carbon dioxide and the presence and amounts of any impurities, as defined above.

[0040] The first pressure may be a pressure of at least 2 bar, at least 5 bar, at least 10 bar, at least 20 bar, at least 30 bar, at least 40 bar, at least 50 bar, at least 55 bar, at least 57 bar, at least 57.5 bar, at least 58 bar, at least 60 bar, at least 70 bar, at least 80 bar, at least 90 bar or at least 95 bar. The first pressure may be a pressure of at least 100 bar, at least 250 bar, at least 500 bar, at least 750 bar, at least 1,000 bar, at least 2,000 bar, at least 3,000 bar, at least 4,000 bar or at least 5,000 bar.

[0041] The first pressure may be a pressure of between 5 and 500 bar, between 10 and 400 bar, between 20 and 300 bar, between 30 and 250 bar, between 40 and 200 bar or between 50 and 180 bar. In some embodiments, the first pressure may be between 60 and 160 bar, between 70 and 140 bar, between 80 and 120 bar, between 90 and 110 bar or between 95 and 105 bar. In some embodiments, the first pressure may be between 100 and 200 bar, between 110 and 190 bar, between 120 and 180 bar, between 130 and 170 bar, between 140 and 160 bar or between 145 and 155 bar.

[0042] The first pressure may be a pressure of less than 100 bar, less than 80 bar, less than 60 bar, less than 40 bar, less than 20 bar or less than 10 bar above the pressure at which the fluid comprising carbon dioxide is converted from a gas to a liquid, a supercritical fluid and / or a dense phase fluid. The first pressure may be a pressure of at least 1 bar, at least 2 bar, at least 5 bar, at least 10 bar, at least 20 bar or at least 50 bar above the pressure at which the fluid comprising carbon dioxide is converted from a gas to a liquid, a supercritical fluid and / or a dense phase fluid. The first pressure may be a pressure between 0.01 and 100 bar, between 0.05 and 50 bar, between 0.1 and 10 bar, between 0.5 and 5 bar or between 1 and 3 bar above the pressure at which the fluid comprising carbon dioxide is converted from a gas to a liquid, a supercritical fluid and / or a dense phase fluid. In some embodiments, the first pressure may be between 40 and 90 bar, between 45 and 80 bar, between 50 and 70 bar, between 55 and 65 bar, between 56 and 60 bar, between 57 and 59 bar or between 57.5 and 58.5 bar. It may be appreciated that at 20°C then a pressure of 58 bar is above the pressure at which pure CO2 is converted from a gas to a liquid.

[0043] Preferably, the second vessel is configured to store or transport the fluid comprising carbon dioxide in a gaseous state. In some embodiments, the second pressure is a pressure at which the fluid comprising the carbon dioxide is a gas.

[0044] As noted above, whether the fluid would be in a gaseous state or a liquid, dense phase or supercritical fluid state would depend upon a number of factors. If the skilled person knew the chemical composition of the fluid and the temperature of the second vessel, they could select a suitable second pressure.

[0045] The second pressure may be a pressure of less than 250 bar, less than 240 bar, less than 230 bar, less than 220 bar, less than 210 bar less than 200 bar, less than 190 bar, less than 180 bar, less than 170 bar, less than 160 bar, less than 150 bar, less than 140 bar, less than 130 bar, less than 120 bar, less than 110 bar, less than 100 bar, less than 90 bar, less than 80 bar, less than 70 bar or less than 60 bar. In some embodiments, the second pressure is less than 58 bar, less than 58.5 bar, less than 57 bar, less than 56.5 bar, less than 56 bar or less than 55 bar. In some embodiments, the second pressure is less than 50 bar, less than 40 bar, less than 30 bar, less than 20 bar, less than 10 bar, less than 5 bar or less than 2 bar. In some embodiments, the second pressure is at least 2 bar, at least 5 bar, at least 10 bar, at least 20 bar, at least 30 bar, at least 40 bar or at least 50 bar.

[0046] The second pressure may be a pressure of less than 100 bar, less than 80 bar, less than 60 bar, less than 40 bar, less than 20 bar, less than 10 bar, less than 5 bar, less than 3 bar or less than 1 bar below the pressure at which the fluid comprising carbon dioxide is converted from a gas to a liquid, dense phase and / or a supercritical fluid. The second pressure may be a pressure between 0.01 and 100 bar, between 0.05 and 50 bar, between 0.1 and 10 bar, between 0.5 and 5 bar or between 1 and 3 bar below the pressure at which the fluid comprising carbon dioxide is converted from a gas to a liquid, dense phase and / or a supercritical fluid. Advantageously, it the second pressure is below, but close to the pressure at which the fluid comprising carbon dioxide is converted from a gas to a liquid, a supercritical fluid and / or a dense phase fluid then the gas will have a relatively small volume. In some embodiments, the second pressure is between 1 and 100 bar, between 10 and 90 bar, between 20 and 80 bar, between 30 and 75 bar, between 40 and 70 bar, between 50 and 65 bar, between 52.5 and 60 bar, between 55 and 57 bar or between 55.5 and 56.5 bar. It may be appreciated that at 20°C then a pressure of 56 bar is below the pressure at which pure carbon dioxide is converted from a liquid, supercritical fluid and / or dense phase to gaseous carbon dioxide.

[0047] In some embodiments, the difference between the first pressure and the second pressure may be a the minimum required to change the fluid comprising carbon dioxide from a liquid, supercritical fluid and / or a dense phase to a gas. The difference between the first pressure and the second pressure may be less than 100 bar, less than 90 bar, less than 80 bar, less than 70 bar, less than 60 bar, less than 50 bar, less than 40 bar, less than 30 bar, less than 20 bar, less than 10 bar or less than 5 bar.

[0048] The decompression apparatus may be configured to transport a first portion of the fluid comprising carbon dioxide disposed in the first vessel from the first vessel to the second vessel. Accordingly, the system may be configured to leave a second portion of the fluid comprising carbon dioxide in the first vessel, and not remove it therefrom. The relative size of the first portion of CO2 and the second portion of the fluid comprising carbon dioxide may vary. In some embodiments, the size of the second portion of the fluid comprising carbon dioxide is sufficient such that after removal of the first portion of the fluid comprising carbon dioxide from the first vessel, the second portion of the fluid comprising carbon dioxide has a third pressure, wherein the third pressure is greater than the second pressure. In some embodiments, the third pressure is sufficient to maintain the second portion of the fluid comprising carbon dioxide in a liquid phase, a dense phase and / or a supercritical fluid phase. As noted above, the skilled person could readily identify a suitable pressure if they knew the temperature which the first vessel will be subjected to and the chemical composition of the fluid comprising carbon dioxide.

[0049] In some embodiments, the first pressure may be chosen to be above a predetermined minimum, such that the third pressure is sufficient to maintain the second portion of the fluid comprising carbon dioxide in a liquid phase, a dense phase and / or a supercritical fluid phase. The third pressure may be a pressure of at least 2 bar, at least 5 bar, at least 10 bar, at least 20 bar, at least 30 bar, at least 40 bar, at least 50 bar, at least 55 bar, at least 57 bar, at least 57.5 bar, at least 58 bar, at least 60 bar, at least 70 bar, at least 80 bar, at least 90 bar or at least 95 bar. The third pressure may be a pressure of at least 100 bar, at least 250 bar, at least 500 bar, at least 750 bar, at least 1,000 bar, at least 2,000 bar, at least 3,000 bar, at least 4,000 bar or at least 5,000 bar.

[0050] The third pressure may be a pressure of between 5 and 500 bar, between 10 and 400 bar, between 20 and 300 bar, between 30 and 250 bar, between 40 and 200 bar or between 50 and 180 bar. In some embodiments, the third pressure may be between 60 and 160 bar, between 70 and 140 bar, between 80 and 120 bar, between 90 and 110 bar or between 95 and 105 bar. In some embodiments, the third pressure may be between 100 and 200 bar, between 110 and 190 bar, between 120 and 180 bar, between 130 and 170 bar, between 140 and 160 bar or between 145 and 155 bar.

[0051] The third pressure may be a pressure of less than 100 bar, less than 80 bar, less than 60 bar, less than 40 bar, less than 20 bar, less than 10 bar, less than 5 bar, less than 3 bar or less than 1 bar above the pressure at which the fluid comprising carbon dioxide is converted from a gas to a liquid, a supercritical fluid and / or a dense phase state. The third pressure may be a pressure between 0.01 and 100 bar, between 0.05 and 50 bar, between 0.1 and 10 bar, between 0.5 and 5 bar or between 1 and 3 bar above the pressure at which the fluid comprising carbon dioxide is converted from a gas to a liquid, a supercritical fluid and / or a dense phase state.

[0052] In some embodiments, the system may comprise a plurality of decompression apparatuses. Each decompression apparatus may be as defined above.

[0053] In some embodiments, the system may comprise a plurality of compressors. Each compressor may be as defined above.

[0054] The first vessel may comprise or be a first vessel conduit. The first vessel conduit may extend between a first location and a second location. The first vessel conduit may comprise or be one or more pipes. The first vessel conduit may be partially, substantially or completely disposed below ground. In alternative embodiments, the first vessel conduit may be partially, substantially or completely disposed above ground. The first vessel conduit may comprise a conduit used in a carbon capture, utilisation and storage (CCUS) application or may be a conduit originally provided for fossil fuel infravessel. Alternatively, the first vessel conduit may be purpose built. Alternatively, or additionally, the first vessel may comprise or be a store configured to store the fluid comprising carbon dioxide. The store may be natural or manmade. The carbon dioxide store may be an underground store. The store may be a salt cavern, a gas impermeable fissure, a void, a subsea well, an oil and natural gas reservoir, an unmineable coal seam, a basalt formation, an organic rich shale, another suitable geological storage site and / or a storage facility previously used for storing methane, hydrogen and / or any other gas.

[0055] The second vessel may be configured such that the pressure in the second volume is not in equilibrium with the pressure of the atmosphere.

[0056] The second vessel may comprise or be a second vessel conduit. The second vessel conduit may comprise or be one or more pipes. The second vessel conduit may be partially, substantially or completely disposed below ground. The second vessel conduit may be partially, substantially or completely disposed above ground, The second vessel conduit may comprise a conduit used in a carbon capture, utilisation and storage (CCUS) application or may be a conduit originally provided for fossil fuel infravessel. Alternatively, the second vessel conduit may be purpose built.

[0057] Alternatively, or additionally, the second vessel may comprise or be a store configured to store the fluid comprising carbon dioxide. The store may be as defined above.

[0058] The decompression apparatus may be disposed at a decompression point, the decompression point being adjacent to the first location, adjacent to the second location or between the first and second locations. In embodiments where the system comprises a plurality of decompression apparatuses, the plurality of decompression apparatuses may be disposed at a plurality of decompression points. Each decompression point may independent be adjacent to the first location, adjacent to the second location or between the first and second locations.

[0059] The compression apparatus may be disposed at the decompression point. Alternatively, the compression apparatus may be disposed at a compression point, spaced apart from the decompression point. The compression point may be adjacent to the first location, adjacent to the second location or between the first and second locations. In some embodiments, the compression point may be between the decompression point and the second location. In embodiments where the system comprises a plurality of compression apparatuses, the plurality of compression apparatuses may be disposed at a plurality of compression points. Each compression point may independently be adjacent to the first location, adjacent to the second location or between the first and second locations.

[0060] The second vessel conduit may be disposed alongside and / or substantially adjacent to the first vessel conduit. The second vessel conduit may define a length which is substantially the same as the length of the first vessel conduit. Accordingly, the second vessel conduit may be disposed alongside and / or substantially adjacent to the first vessel conduit for substantially the entire length of the first vessel conduit. The second vessel conduit may extend between the first location and the second location. Alternatively, the second vessel conduit may define a length which is less than the length of the first vessel conduit. The second vessel conduit may extend between the decompression point and the compression point. In embodiments where the system comprises a plurality of compression and / or decompression points, the system may comprise a plurality of second vessel conduits, where each conduit extends between a decompression point and a compression point. Accordingly, the second vessel conduit may be disposed alongside and / or substantially adjacent to a portion of the first vessel conduit.

[0061] The system may be configured to hold the fluid comprising carbon dioxide permanently or semi-permanently therein. For instance, the first vessel, the second vessel the decompression apparatus and the compression apparatus may form part of a closed system. Accordingly, the fluid comprising carbon dioxide could pass between the first and second vessels but may not leave the closed system.

[0062] Alternatively, the first vessel conduit may be configured to transport the fluid comprising carbon dioxide from the first location to the second location. The second vessel conduit may also be configured to transport the fluid comprising carbon dioxide from the first location to the second location.

[0063] The first location may comprise a source of the fluid comprising carbon dioxide. For instance, the first location may be or comprise an industrial site or area which generates and captures carbon dioxide. The first location may be onshore. The fluid comprising carbon dioxide may have been obtained using any method known to a person skilled in the art for processing and / or capturing carbon dioxide. For instance, the fluid comprising carbon dioxide may have been obtained using the methods described in international patent application no. PCT / GB2023 / 051887 or PCT / GB2023 / 052810. The second location may comprise a store or processing plant configured to store or process the gas comprising the carbon dioxide. The second location may be onshore or offshore.

[0064] The store may be natural or manmade. The store may be an underground store. The store may be a salt cavern, a gas impermeable fissure, a void, a subsea well, an oil and natural gas reservoir, an unmineable coal seam, a basalt formation, an organic rich shale, another suitable geological storage site and / or a storage facility previously used for storing methane, hydrogen and / or any other gas.

[0065] The first vessel conduit may be configured to feed the fluid comprising carbon dioxide into the store at the first pressure.

[0066] The second vessel conduit may be configured to feed the fluid comprising carbon dioxide into the store at the second pressure. Alternatively, the system may comprise a further compression apparatus, the further compression apparatus may be configured to compress the fluid comprising carbon dioxide to a fourth pressure prior to it being fed into the store. The fourth pressure may be greater than the second pressure. The fourth pressure may the same, more or less than the first pressure. The fourth pressure may the same, more or less than the third pressure. The fourth pressure may be a pressure at which the fluid comprising carbon dioxide is a liquid, in a dense state or is a supercritical fluid.

[0067] The further compression apparatus may be disposed between the second vessel conduit and the store. The further compression apparatus may substantially be as defined above in relation to the compression apparatus. The only difference may be that the compression apparatus may comprise a second compression conduit extending between the compressor and the store, and being configured to transport the fluid comprising carbon dioxide from the compressor to the store.

[0068] The store may be configured to store the fluid comprising carbon dioxide at a fifth pressure. The fifth pressure may be greater than the second pressure. The fifth pressure may be the same, more or less than the first pressure. The fifth pressure may be the same, more or less than the third pressure. The fifth pressure may be the same, more or less than the fourth pressure. The fifth pressure may be a pressure at which the fluid comprising carbon dioxide is a liquid, in a dense state or is a supercritical fluid. The system may comprise a further decompression apparatus disposed between the store and either the second vessel or a third vessel, the further decompression apparatus being configured to transport the fluid comprising carbon dioxide from the store to the second vessel or the third vessel, to reduce the pressure of the fluid comprising carbon dioxide being transported from the fifth pressure to the second pressure and to capture energy released from the fluid comprising carbon dioxide as it depressurises. Advantageously, the fluid comprising carbon dioxide held within the store may be used to store and release energy.

[0069] The further decompression apparatus may be a decompression apparatus substantially as defined above. The only difference may be that in the further decompression apparatus the first decompression conduit may extending between the store and the decompressor or expander, and be configured to transport the fluid comprising carbon dioxide from the store to the decompressor or expander. It may be appreciated that the first decompression conduit may be configured to transport the fluid comprising carbon dioxide at the fifth pressure. Additionally, the second decompression conduit may extend between the decompressor or expander and the second vessel or the third vessel, and be configured to transport the fluid comprising carbon dioxide from the decompressor or expander to the second vessel or the third vessel.

[0070] The third vessel may comprise a rigid housing defining a third volume therein. The third vessel may be configured to store or transport the fluid comprising carbon dioxide at the second pressure in the third volume. The third vessel may be or comprise a third vessel conduit. The third vessel conduit may be as defined above in relation to the second vessel conduit. Alternatively, or additionally, the third vessel may comprise or be a store configured to store the fluid comprising carbon dioxide. The store may be as described above in relation to the second vessel.

[0071] The system may comprise a fourth vessel comprising a rigid housing defining a fourth volume therein. The fourth vessel may be configured to store or transport the fluid comprising carbon dioxide at a sixth pressure in the fourth volume. The sixth pressure may be greater than the second pressure. The sixth pressure may be greater than the third pressure. The sixth pressure may be more, less or substantially the same as the first pressure. The sixth pressure may be as defined above in relation to the first pressure. The fourth vessel may be or comprise a fourth vessel conduit. The fourth vessel conduit may be as defined above in relation to the first vessel conduit. Alternatively, or additionally, the fourth vessel may comprise or be a store configured to store the fluid comprising carbon dioxide. The store may be as described above in relation to the first vessel.

[0072] The system may comprise a repressurisation conduit extending between the first and fourth vessels and configured to transport the fluid comprising carbon dioxide from the fourth vessel to the first vessel. The system may comprise one or more valves disposed in the repressurisation conduit. The one or more valves may be configured to selectively stop and start the flow of the fluid comprising carbon dioxide from the fourth vessel to the first vessel and / or to control the rate of flow of the fluid comprising carbon dioxide from the fourth vessel to the first vessel. The one or more valves may be or comprise a solenoid valve, a flow control valve and / or a one way valve.

[0073] The system may comprise a pressure sensor in the first vessel.

[0074] The system may comprise a controller. The controller may be configured to cause the fluid comprising carbon dioxide to flow from the fourth vessel to the first vessel if the pressure in the first vessel falls below a predetermined minimum pressure. The predetermined minimum pressure may be less than 20 bar, less than 10 bar, less than 5 bar, less than 2 bar or less than 1 bar above the pressure at which the fluid comprising carbon dioxide is converted from a liquid, a supercritical fluid and / or a dense phase fluid to a gas. Advantageously, the system can prevent the fluid comprising carbon dioxide from evaporating within the first vessel.

[0075] The processing plant may be configured to convert carbon dioxide into a chemical feedstock. Examples of a commercially usable product include a carbonate, syngas, a fuel, a chemical feedstock, an aliphatic polycarbonate, monoethylene glycol, a polyether-polycarbonate polyol, a thermoplastic and a polyhydroxyalkanoate. The carbon dioxide may be reacted by the catalytic conversion of urea, methanol, salicylic acid, cyclic carbonates, dimethyl carbonate, alcohols, olefins, methane, gasoline or another fuel. The carbon dioxide may be reacted with a metal hydroxide to produce a carbonate. The carbonate can then be utilized in the production of cement, as a limestone aggregate for road building, use in the production of iron from iron ore, used in neutralizing acidic soil for agricultural purposes, or used in paper, adhesive, sealants, plastics, rubbers, ceramic tiles and paints as a filler or pigment. The carbon dioxide may be reacted by electrochemical conversion to produce syngas. The syngas may be used as a building block for a synthetic fuel and / or a chemical feedstock. The carbon dioxide may be reacted by photocata lytic and photothermal catalytic conversion to a fuel and / or a chemical feedstock. The carbon dioxide may be reacted by copolymerization of carbon dioxide with another feedstock. The copolymerization may produce an aliphatic polycarbonate, monoethylene glycol, a polyetherpolycarbonate polyol, a thermoplastic and / or a polyhydroxyalkanoate.

[0076] Alternatively, or additionally, processing the output gas may comprise utilizing the carbon dioxide in a biological process. The biological process may be a process where an enzyme or an organism utilizes the carbon dioxide as a food source. The organism may be a microbe, such as bacteria. The organism may convert the carbon dioxide into an alcohol, syngas, a hydrocarbon or an acid. The alcohol may be ethanol. The acid may be formic acid.

[0077] In some embodiments, the first vessel may comprise a plurality or network of first vessel conduits. The network of first vessel conduits may be configured to transport the fluid comprising carbon dioxide from multiple first locations to multiple second locations, wherein the first and second locations are as defined above.

[0078] The second vessel may also comprise a plurality or network of second vessel conduits. The network of second vessel conduits may also be configured to transport the fluid comprising carbon dioxide from multiple first locations to multiple second locations, wherein the first and second locations are as defined above.

[0079] The network of first and / or second vessel conduits may be regional, national and / or international.

[0080] In accordance with a second aspect, there is provided a method of storing and releasing energy, the method comprising: providing a first vessel comprising a rigid housing defining a first volume therein, wherein a fluid comprising carbon dioxide at a first pressure is disposed in the first volume; providing a second vessel comprising a rigid housing defining a second volume therein; and feeding at least a portion of the fluid comprising carbon dioxide from the first volume into the second volume, wherein feeding the at least a portion of the fluid comprising carbon dioxide into the second volume comprises reducing the pressure of the at least a portion of the fluid comprising carbon dioxide from the first pressure to a second pressure, wherein the second pressure is lower than the first pressure, and capturing energy released from the at least a portion of the fluid comprising carbon dioxide as it depressurises.

[0081] The first and second vessels and the first and second pressures may be as defined in relation to the first aspect.

[0082] The method of the second aspect may be conducted using the apparatus of the first aspect.

[0083] The fluid comprising carbon dioxide disposed in the first volume at the first pressure may be in a liquid, supercritical or dense phase state.

[0084] Subsequent to feeding it into the second volume and reducing the pressure to the second pressure, the at least a portion of the fluid comprising carbon dioxide may be in a gaseous state.

[0085] The at least a portion of the fluid comprising carbon dioxide which is fed from the first volume into the second volume may be a first portion of the fluid comprising carbon dioxide. The method may comprise leaving a second portion of the gas comprising the fluid comprising carbon dioxide in the first volume. The size of the second portion may be such that the pressure in the first volume has a third pressure, wherein the third pressure is greater than the second pressure. The third pressure may be as defined in relation to the first aspect. Accordingly, the second portion of carbon dioxide may be in a gaseous state after removal of the first portion of the fluid comprising carbon dioxide from the first volume.

[0086] Reducing the pressure of the at least a portion of the fluid comprising carbon dioxide from the first pressure to the second pressure may comprise feeding the at least a portion of the fluid comprising carbon dioxide through a decompressor or expander. The decompressor or expander may be as defined in relation to the first aspect.

[0087] The energy released due to the at least a portion of the fluid comprising carbon dioxide depressurising may be understood to be in the form of kinetic energy. The energy may be captured by converting the energy released into mechanical energy, heat energy, cooling energy, electrical energy and / or hydraulic pressure. Accordingly, the method may comprise causing the depressurised fluid comprising carbon dioxide to drive an expander wheel, a turbine or a piston. Driving the expander wheel, turbine or piston may generate electrical energy.

[0088] The method may comprise feeding the electrical energy into an energy network. The energy network may be as defined in relation to the first aspect.

[0089] Subsequent to feeding the at least a portion of the fluid comprising carbon dioxide from the first volume into the second volume, the method may further comprise: feeding the at least a portion of the fluid comprising carbon dioxide from the second volume into the first volume, wherein feeding the at least a portion of the fluid comprising carbon dioxide into the first volume comprises increasing the pressure of the at least a portion of the fluid comprising carbon dioxide from the second pressure to the first pressure.

[0090] Increasing the pressure of the at least a portion of the fluid comprising carbon dioxide from the second pressure to the first pressure may comprise feeding the at least a portion of the fluid comprising carbon dioxide through a compressor. The compressor may be as defined in relation to the first aspect.

[0091] The method may comprise powering the compressor from a power source. The power source may be as defined in relation to the first aspect.

[0092] In some embodiments, the method may comprise simultaneously: feeding at least a portion of the fluid comprising carbon dioxide from the first volume into the second volume, wherein feeding the at least a portion of the fluid comprising carbon dioxide into the second volume comprises reducing the pressure of the at least a portion of the fluid comprising carbon dioxide from the first pressure to a second pressure, wherein the second pressure is lower than the first pressure, and capturing energy released from the at least a portion of the fluid comprising carbon dioxide as it depressurises; and feeding a portion of the fluid comprising carbon dioxide from the second volume into the first volume, wherein feeding the portion of the fluid comprising carbon dioxide into the first volume comprises increasing the pressure of the portion of the fluid comprising carbon dioxide from the second pressure to the first pressure.

[0093] It may be appreciated that as the fluid comprising carbon dioxide depressurises it will cool. The method may comprise utilising this cooling effect to cool a body. The body may be or comprise a refrigerator, a freezer, an air-conditioning system or a cold store. The method may comprise reducing the pressure of the at least a portion of the fluid comprising carbon dioxide inside or adjacent to the body, and thereby cooling the body. Alternatively, the method may comprise reducing the pressure of the at least a portion of the fluid comprising carbon dioxide in a depressurisation location and using a heat exchanger to transfer heat from the body to the depressurisation location.

[0094] The method may comprise transferring heat out of the compressor as the at least a portion of the fluid comprising carbon dioxide is repressurised. The method may comprise transferring heat out of the compressor to another location. The other location may be a domestic, commercial or industrial location. Additionally the system may be configured to utilise the heat for any purpose within the proposed energy system itself.

[0095] Alternatively, or additionally, the method may comprise transferring heat from the compressor to the depressurisation location.

[0096] The method may comprise holding the fluid comprising carbon dioxide permanently or semi-permanently within the first and second vessels, and optionally also the compression apparatus and decompression apparatus.

[0097] The first vessel may comprise or be a first vessel conduit. The first vessel conduit may extend between a first location and a second location.

[0098] The second vessel may comprise or be a second vessel conduit.

[0099] The method may comprise transporting the fluid comprising carbon dioxide inside the first vessel from the first location towards the second location. The method may comprise feeding the at least a portion of the fluid comprising carbon dioxide from the first volume into the second volume, as defined above, at a depressurisation point between the first and second locations.

[0100] The method may comprise feeding the at least a portion of the fluid comprising carbon dioxide from the second volume into the first volume, as defined above, at the depressurisation point.

[0101] Alternatively, the method may comprise transporting the fluid comprising carbon dioxide inside the second vessel from the depressurisation point to a compression point, wherein the compression point is spaced apart from the depressurisation point. The method may comprise feeding the at least a portion of the fluid comprising carbon dioxide from the second volume into the first volume, as defined above, at the compression point.

[0102] The method may comprise feeding the fluid comprising carbon dioxide at the first pressure into the first vessel. The method may comprise feeding the fluid comprising carbon dioxide from a source into the first vessel. The method may comprise feeding the fluid comprising carbon dioxide into the first vessel at the first location.

[0103] The method may comprise feeding the fluid comprising carbon dioxide from the first and / or second vessel into a store or processing plant. The method may comprise feeding the fluid comprising carbon dioxide from the first and / or second vessel into the store or processing plant at the second location.

[0104] In embodiments where the method comprises feeding the fluid comprising carbon dioxide from the second vessel into the store, the method may comprise feeding the fluid comprising carbon dioxide from the second vessel into the store at the second pressure. Alternatively, the method may comprise compressing the fluid comprising carbon dioxide from the second vessel to a fourth pressure, which is greater than the second pressure, and then feeding it into the store. The fourth pressure may be as defined in relation to the first aspect. Compressing the fluid comprising carbon dioxide may comprise feeding it through a compressor.

[0105] The method may comprise feeding at least a portion of the fluid comprising carbon dioxide from the store into the second volume or a third volume, wherein feeding the at least a portion of the fluid comprising carbon dioxide into the second or third volume comprises reducing the pressure of the at least a portion of the fluid comprising carbon dioxide from the fifth pressure to the second pressure, wherein the second pressure is lower than the fifth pressure, and the method comprises capturing energy released from the at least a portion of the fluid comprising carbon dioxide as it depressurises. The method may comprise feeding the at least a portion of the fluid comprising carbon dioxide through a decompressor or expander.

[0106] The method may subsequently comprise feeding the at least a portion of the fluid comprising carbon dioxide from the second or third volume into the store, wherein feeding the at least a portion of the fluid comprising carbon dioxide into the store comprises increasing the pressure of the at least a portion of the fluid comprising carbon dioxide from the second pressure to the first, third, fourth or fifth pressure. The method may comprise maintaining the pressure in the first volume above a predetermined minimum pressure. The predetermined minimum pressure may be as defined above in relation to the first aspect.

[0107] The method may comprise feed the fluid comprising carbon dioxide at a sixth pressure from a fourth volume to the first volume to maintain the pressure in the first volume above the predetermined minimum pressure. The sixth pressure may be as defined above in relation to the first aspect. The method may comprise feeding a sufficient volume of fluid comprising carbon dioxide from the fourth volume to the first volume to maintain the pressure in the first volume above the predetermined minimum pressure.

[0108] In embodiments where, the method comprises feeding the fluid comprising carbon dioxide from the first and / or second vessel into the processing plant, the method may comprise converting the fluid comprising carbon dioxide into a chemical feedstock.

[0109] In some embodiments, the method of the second aspect may be considered to be a batch process.

[0110] For instance, the step of feeding at least a portion of the fluid comprising carbon dioxide from the first volume into the second volume may be a discrete step. This step may be conducted until a predetermined amount of energy has been released and / or a predetermined amount of the fluid comprising carbon dioxide has been fed from the first volume into the second volume. This step may be conducted at times of high power demand.

[0111] Similarly, in embodiments where it is present, the step of feeding the at least a portion of the fluid comprising carbon dioxide from the second volume into the first volume may be a discrete step. This step may be conducted at times of low power demand or when power would otherwise be idled / curtailed due to grid capacity saturation.

[0112] In alternative embodiments, the method of the second aspect may be considered to be a continuous process.

[0113] For instance, the step of feeding at least a portion of the fluid comprising carbon dioxide from the first volume into the second volume may be a continuous step. The at least a portion of the fluid comprising carbon dioxide may be fed from the first volume into the second volume at the depressurisation point.

[0114] Similarly, in embodiments where it is present, the step of feeding the at least a portion of the fluid comprising carbon dioxide from the second volume into the first volume may also be a continuous step. The at least a portion of the fluid comprising carbon dioxide may be fed from the second volume into the first volume at the compression point. The compression point may be spaced apart from the depressurisation point. Accordingly, in this embodiment, the method transfers power between locations.

[0115] In a further alternative embodiment, the method may be a combination of the batch and continuous methods described above. Accordingly, the step of feeding at least a portion of the fluid comprising carbon dioxide from the first volume into the second volume may be a discrete step and the step of feeding the at least a portion of the fluid comprising carbon dioxide from the second volume into the first volume may also be a continuous step. Alternatively, the step of feeding at least a portion of the fluid comprising carbon dioxide from the first volume into the second volume may be a continuous step and the step of feeding the at least a portion of the fluid comprising carbon dioxide from the second volume into the first volume may also be a discrete step.

[0116] All features described herein (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined with any of the above aspects in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0117] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying Figures, in which:-

[0118] Figure 1 is a schematic diagram of a decompression point in a system in accordance with the claimed invention;

[0119] Figure 2 is a schematic diagram of a compression point in a system in accordance with the claimed invention;

[0120] Figure 3 is a schematic diagram of a turboexpander in a system in accordance with the claimed invention;

[0121] Figure 4 is a schematic diagram of a turboexpander and heat exchanger in a system in accordance with the claimed invention; and Figure 5 is a phase diagram from pure carbon dioxide.

[0122] EXAMPLES

[0123] Example 1 - Energy Storage System Comprising Decompression and Recompression Points

[0124] The present invention relates to a system which stores energy using a fluid comprising carbon dioxide.

[0125] In its simplest form, the system comprises a high-pressure vessel or pipeline 1 which is configured to hold liquid, dense phase or supercritical CO2 at a first pressure. The system further comprises a low pressure vessel or pipeline 6, which is configured to hold gaseous carbon dioxide at a second pressure, which is lower than the first pressure. The low-pressure pipeline may have a similar or larger diameter to the high-pressure pipeline.

[0126] It may be appreciated that in some embodiments, the system may comprise a plurality of high-pressure vessels and / or pipelines. Alternatively, or additionally, the system may comprise a plurality of low-pressure vessels and / or pipelines.

[0127] The system comprises one or more decompression points connecting the high- pressure vessel or pipeline and the low-pressure vessel or pipeline. The decompression point in its simplest form is shown in figure 1. As shown in Figure 1, a decompression point valve 2a allows the liquid, dense phase or supercritical CO2 to flow from the high-pressure pipeline 1 into a decompressor / expander 3 where it expands to provide gas at the second pressure. The expanded gas drives a turbine wheel 4, which drives a generator 5. Meanwhile, the gas produced in the decompressor / expander 3 flows into the low-pressure pipeline 6, which is lower than the first pressure. The generator 5 produces electricity which powers an energy network 7a.

[0128] At times of peak demand, the system could partially (or fully) depressurise sections of the high-pressure pipeline at the decompression point to generate electricity. The depressurised gas would be discharged into the low-pressure pipeline.

[0129] The system may further comprise one or more recompression points. The recompression point in its simplest form is shown in figure 2. As can be seen in Figure 2, the recompression point comprises a first recompression point valve 2b, which allows gaseous carbon dioxide at the second pressure to flow from the low-pressure pipeline 6 into a compressor 8. An energy network 7b provides energy to a motor 15, which drives a compressor wheel 11, which compresses the gas to the first pressure such that it reverts to a liquid, dense phase or supercritical state. The liquid, dense phase or supercritical CO2 then passes through a second recompression point valve 2c into the high pressure pipeline 1.

[0130] It is noted that the energy network 7b, shown in Figure 2, which powers the motor 15 in the recompression point may be the same or different to the energy network 7a, shown in Figure 1, which received electrical energy from generator 5 in the decompression point.

[0131] For instance, the system could provide energy to an energy network, by decompressing gas, at times of high demand. The system could also receive energy from the same energy network, and use it to compress gas, at times of low demand / energy surplus.

[0132] Alternatively, the system could provide energy to a first energy network in a first location, by decompressing gas at a decompression point located adjacent or near the first location. The system could then transport the decompressed gas along the second pipeline 6 to a compression point located near or adjacent to a second energy network in a second location. The compression point could then receive energy from the second energy network to compress the gas. Accordingly, this would allow the system to effectively transfer energy between different energy networks.

[0133] The energy storage capacity of each charge I discharge cycle would vary depending upon a number of factors. These include, the pressure at which the carbon dioxide is compressed to upon storage, the pressure to which the carbon dioxide is decompressed to upon discharge, the amount of carbon dioxide stored in the pipeline, the temperature of the stored carbon dioxide, the temperature of the discharged carbon dioxide, the chemical composition of the carbon dioxide (i.e. whether it is pure or if any impurities are present), the flow rate of the high-pressure carbon dioxide, the flow rate of the low-pressure carbon dioxide, and the efficiency of system during the charge / discharge cycle as described above.

[0134] If there was a likelihood that an energy generation hub might reduce the pressure of the high-pressure CO2 pipeline 1 to such an extent that the gas remaining therein would no longer be in a liquid, dense or super critical phase and / or would reduce the operational efficiency of the system then additional high pressure parallel pipelines could be laid alongside the existing network capable of holding the amount of pressurised CO2 needed to maintain the pressure in the main high-pressure pipeline 1 above a minimum pressure. The additionally high pressure parallel pipelines could be depressurised completely (if necessary) without effecting the operational efficiency of the main system.

[0135] Example 2 - Energy Storage System Comprising a Turboexoander

[0136] The decompression and compression points could be provided at any point(s) along the high-pressure and low-pressure pipelines. In some embodiments, the decompression and compression points could be provided close together, such that a turboexpander system could be employed, as shown in figure 3.

[0137] The turboexpander system comprises a decompressor / expander 3, comprising an expander wheel 9, and a compressor 8, comprising a compressor wheel 11. The turboexpander further comprises a motor-generator 16. The expander wheel 9, compressor wheel 11 and motor-generator 16 are connected by a shaft 10.

[0138] A first turboexpander valve 2d allows liquid, dense phase or supercritical CO2 to flow from the high-pressure pipeline 1 into the decompressor / expander 3. In the expander, the CO2 expands to form a gas, and drives the expander wheel 9. The gas produced flows through a second turboexpander valve 2e into the into a first low- pressure pipeline 6A.

[0139] The first low-pressure pipeline is connected to a second low-pressure pipeline 6B via a third turboexpander valve 2f. The gas in the first low-pressure pipeline 6A is at the second pressure and the gas in the second low-pressure pipeline may be at the second pressure, or a third pressure which is lower than the second pressure.

[0140] Gas can flow from the second low-pressure pipeline 6B through a fourth turboexpander valve 2g to the compressor 8. The compressor wheel 11 can then compress it to convert it into liquid, dense phase or supercritical CO2. The liquid, dense phase or supercritical CO2 can then flow through a fifth turboexpander valve 2h into the high-pressure pipeline 1.

[0141] One advantage of the turbo expander is that the expander wheel 9 can drive the compressor wheel 11 to recompress gas from the low-pressure pipelines 6A, 6B. This would reduce or negate the amount of input energy which would be required to be drawn from the energy network 7 to drive the motor-generator 16 to compress the gas for recharging the system. Depending on the flow through the decompressor / expander 3 and compressor 11, the system can either (a) produce excess energy to drive a generator 16 to produce electricity which powers the energy network 7 or (b) the energy network 7 can be drawn upon to drive the motor 16 to compress CO2.

[0142] The turboexpander may also have a heat exchange system, as shown in Figure 4. The heat exchange system recovers and utilises the heat released upon compression and cooling effect on expansion for greater efficiency.

[0143] In particular, upon compression of the gas, heat is generated. A fluid may flow between the compressor 8 and a first heat exchanger 12a to extract the heat from the compressor 8. In the first heat exchanger 12a, the heat could then be transferred to another medium (e.g. a liquid, a thermal brick, etc.). The heat which is extracted could be used to heat a domestic, commercial or industrial location 13.

[0144] Similarly, as the CO2 expands in the expander 3 a cooling effect would be observed. A fluid may flow between the expander 3 and a second heat exchanger 12b to transfer heat into the expander 3. In the second heat exchanger 12b, the heat could be transferred from another medium (e.g. a liquid, a thermal brick, etc.). The cooled medium could be used to cool another location 14 (e.g. a refrigerator).

[0145] Alternatively, heat generated in the compressor 8 could be transferred to the expander 3. This would reduce the temperature change experienced in both the compressor 8 and the expander 3. This could ensure that CO2 leaving the expander 3 is in a gaseous state and CO2 leaving the compressor 8 is in a liquid, dense phase or supercritical phase.

[0146] It may be appreciated that heat generated in the compressor 8 could be stored until required. Similarly, heat could be transferred into the expander 3, to generate a cooled medium. This could be stored until a cooling effect was required.

[0147] Example 3 - Pressure of the carbon dioxide

[0148] As noted above, it is envisaged that systems of the present invention use a decompressor or expander to convert a fluid comprising carbon dioxide from a liquid, dense or supercritical phase to a gaseous phase, and extract energy therefore. It is also envisaged that systems of the present invention can store energy in the form or pressurised carbon dioxide by using a compressor to convert carbon dioxide gas to a liquid, dense or supercritical phase.

[0149] It may be appreciated that the pressure at which a fluid comprising carbon dioxide changes from a gas to a liquid, dense or supercritical phase will vary depending upon a number of factors including the temperature. A phase diagram for pure CO2 is provided in Figure 5.

[0150] The skilled person could readily ascertain the temperature of the first and second pipelines at the point where the expander and / or decompressor was located, or the temperature range the pipelines would be subjected to. The skilled person could then use the phase diagram in Figure 5 to identify the point at which the carbon dioxide would convert from a gas to a liquid or a supercritical fluid. The first pressure would be one at which the carbon dioxide is a liquid or a supercritical fluid. The second pressure would be one at which the carbon dioxide is a gas. The inventors have found that the system described herein is most efficient if the second pressure is only just below the pressure at which the carbon dioxide would convert from a gas to a liquid or a supercritical fluid.

[0151] It may be appreciated that the phase diagram would vary if the fluid comprised impurities, i.e. if the carbon dioxide was not pure. However, the skilled person could readily determine the composition of a fluid, and could then ascertain the pressure at which it would convert from a gas to a liquid or supercritical fluid for a given temperature.

[0152] Example 4 - Carbon Capture, Utilisation and Storage (CCUS) Infravessel The East Coast Cluster comprises two industrial regions in the UK, Teesside and Humber, and CO2 storage sites in the North Sea. It is reported that the East Coast Cluster could capture and store up to 27 million tonnes of CO2 annually by the mid- 20305.

[0153] The East Coast Cluster will have two high-pressure pipelines configured to transport liquefied CO2 to a saline aquifer called the Endurance Reservoir. The Teesside Pipeline will be 145 km in length and the Humber pipeline will be 103 km in length. In both cases the high-pressure pipeline will have diameter will be 28 inches and be configured to transport the liquefied I dense phase I supercritical CO2 at a pressure of 100 bar. It is envisaged that a low-pressure pipeline, or pipelines, may be provided adjacent to each of these new pipelines. The low-pressure pipeline may have a similar or larger diameter to the high-pressure pipeline.

[0154] The system may comprise one or more decompression points connecting the high- pressure pipeline and the low-pressure pipeline. The decompression points may be as described in example 1. At times of peak demand, the system could partially (or fully) depressurise sections of the high-pressure pipeline at the decompression points to generate electricity. The depressurised gas would be discharged into the low-pressure pipeline.

[0155] The system may further comprise one or more recompression points also contacting the high-pressure pipeline and the low-pressure pipeline. The recompression points may be as described in example 1.

[0156] The decompression and compression points could be provided at any point along the high-pressure and low-pressure pipelines. For instance, the recompression point could be provided at or near a location which is prone to have spare electrical capacity, such as a wind farm or a solar farm. These could be offshore and / or onshore. At times of spare capacity, the gas in the low-pressure pipeline could be repressured to 100 bar and re-introduced back into the main pipeline.

[0157] Alternatively, the decompression and compression points could be provided close together, such that a turboexpander system could be employed, as described in example 2.

[0158] The total volume held by the Teeside and Humber pipelines will be about 98,250 m3, which equates to 84,363 tonnes of CO2 at 100 bar pressure. The total energy stored within this pipeline will be up to 1.99 GWh per compression / decompression cycle amounting to 6.3% of the UK's hourly power requirements.

[0159] Example 4 - Existing Oil and Gas Infravessel

[0160] According to National Gas, the UK alone has some 7,666 km of high-pressure pipe in the UK for natural gas transmission.

[0161] The Langeled pipeline is a gas pipeline running between Norway and the UK to transport natural gas (methane). This pipeline is 1,166 km long, with a diameter of 42" and can operate at 250 bar. The total volume of this pipeline is 1,042,208 m3, which equates to 1,003,751 tonnes of CO2 at 250 Bar pressure.

[0162] The inventors have calculated that one ton of stored liquid / dense phase / super critical CO2 can provide 24.46 kWh based on the CO2 being depressurised from 250 Bar in the charged phase to 56 Bar at 20 °C in the discharged phase.

[0163] The total energy stored within this pipeline would be up to 25.5 GWh per compression I decompression cycle amounting to 81.2% of the UK's hourly power requirements.

[0164] The Nord Stream Pipelines between Russia and Germany consists of 4 pipelines for natural gas each of which is 1,224 km long, and 45.4 inch diameter, with a pressure of 177.5 to 220 Bar. The total volume of each pipe is 1,277,997 m3. Based on the lowest pressure of 177.5 Bar, each pipeline would hold 29.2 GWh per compression I decompression cycle amounting to 92.9% of the UK's hourly power requirement. If all 4 pipelines were discharged as described above this would give a total of 116.8 GWh, sufficient to supply 100% of the UK's power requirements for 3.7 hours.

[0165] It may be appreciated that as Europe transitions away from fossil fuels, the abovementioned pipelines will no longer be required for their original purpose. Instead, these pipelines could be used to transport liquefied I dense phase I super critical CO2. As described above, CO2 could be discharged into a low-pressure pipe to generate power when energy requirements were high.

[0166] For instance, one of the four Nord Stream pipelines could be used as a high-pressure pipeline to transport liquefied I dense phase I super critical CO2. The other three pipelines could be designated low-pressure pipelines, and could receive decompressed CO2 from the high pressure pipeline. Based on the lowest pressure of 177.5 Bar for the charged pipeline this would equate to some 3.35 GWh per compression I decompression cycle.

[0167] Globally there are estimated to be 1,180,000 km of oil and gas pipelines around the world. Accordingly, a proportion of the current global network of oil and gas pipelines may be adapted to hold and / or transport high-pressure CO2. The oil and gas pipelines could also provide the low-pressure pipes configured to receive decompressed CO2 from the high-pressure pipes. Assuming an average 28 inch diameter, this equates to a total volume of over 468 million m3, holding 401 million tonnes of CO2 at 100 Bar pressure. Assuming the maximum pressure is 100 Bar within these pipes, this would equate to 8,118 GWh per compression / decompression cycle which is sufficient to power the entire worlds requirements for 2.79 hours.

[0168] Alternatively, if the global network of oil and gas pipelines held both the high pressure (charged) and the low pressure (discharged) CO2. Then assuming that the maximum pressure is 100 Bar for the charged side, this equates to approximately 1,920 GWh of power per compression I decompression cycle, which is 66% of the world's hourly power requirements.

[0169] Example 5 - Linking to Other Types of Large Capacity Storage Facilities

[0170] Utilising the existing pipeline infravessel, discussed in example 2, and adding additional pipelines as necessary, the network could be expanded to any suitable underground CO2 storage facilities, such as salt caverns. There are currently estimated to be around 2,000 suitable candidates worldwide, ranging in capacity from 100,000 - 1,000,000 m3each. Depending on the depths of these caverns, they can be operated with a pressure up to 200 Bar, generating 23.4 GWh per cavern from a single 1,000,000 m3cavern.

[0171] Assuming the geological conditions allowed for the expansion and contraction of the gas stored therein, without adding significant contamination / hydrates to the CO2, the CCUS reservoirs themselves might also be candidates for battery storage.

[0172] In the UK, the Cheshire Salt Cavern Network is sufficiently close to the East and West Coast Clusters to act as a generation hub for both. The discharge storage capacity is approximately 48.6 million m3(i.e. those whose minimum I maximum pressure requirements meet our discharged pressure as described above), which when utilising the optimum high and low pressures above would yield some 200 GWh of power, which is sufficient to power the UK for approximately 6 hours.

[0173] Further storage capacity can also be added to the Salt Cavern Network by utilising the well-established techniques of solution mining in which water is piped into the salt layer forming large caverns capable of storing CO2. In some embodiments, the close proximity of multiple caverns (both currently and if further caverns are added in future) allows for individual and I or groups of caverns to be utilised as the charged side of the battery which are then linked by a short distance to single and or groups of caverns utilised as the discharged side of the battery. For example in the UK the other main industrial clusters producing CO2 include Humberside, Merseyside, The Black Country, South Wales and Southampton, all of which are also close to known salt Caverns. Only Grangemouth is any significant distance from a known salt cavern area, however this area benefits from an extensive fossil fuel pipe network which can be utilised to link to link it to the caverns.

[0174] Example 6 - Global Battery Storage Capacity

[0175] The total estimated storage capacity for CO2 in pipelines, salt caverns, oil & gas wells, aquifers etc is >10,000 Gigatonnes of CO2. In the first instance, if only 0.1% of that space is suitable for the pressurisation I depressurisation cycles required to conduct the methods of the invention, then based on an expansion ratio of 4.32: 1 when going from 58 - 56 Bar (at 20 °C) some 2.36 Gigatonnes of CO2, would generate 52.4 TWh (52,400 GWh).

[0176] Total electricity usage today is estimated to be some 25,000 TWh per annum, with an expectation that this will grow to a total of 55,000 TWh per annum, equating to 6.28 TWh required every hour in 2050. Accordingly, the systems described herein could provide 8.34 hours of the global requirement with every charge I discharge cycle by utilising only 0.1% of the maximum possible storage available.

[0177] Example 7 - Offshore Oil and Gas Infravessel

[0178] As we transition from fossil fuels, there is a growing focus on the decarbonisation of offshore oil and gas production platforms with the current aim to electrify them with power from onshore. If a CCUS pipeline was routed within a serviceable distance from oil and gas assets on its way to a subsea well for underground storage then it may be feasible to utilise this CO2 power source onboard such offshore assets and depressurise it near to the end of its journey to the well from that in the pipeline to a lower pressure while still leaving it above that of the pressure required for the particular storage reservoir. This would save the cost of running electricity cables from land. It may also provide essentially free power if re-pressurisation of the CO2 is not required and / or if the amount removed from the line can be 'flooded' back in without dropping the pressure below that required for the reservoir. If this is not feasible, the depressurised CO2 could be transported to a renewable energy source along the pipeline route, and repressurised there.

[0179] Example 8 - Entry Network for CO2 Captured

[0180] The system of the present invention could also be designed to allow the transport of low-pressure gas (either exhaust fumes, pure CO2 or any combination thereof) via existing pipelines to processing facilities where the CO2 could be purified, if required, and pressurised. It could then be added to the high-pressure system. A regional or national network could be useful to companies removing CO2 from the atmosphere, as it would provide them with somewhere to offload the low pressure CO2 which they captured.

[0181] Additionally, large mobile fossil fuel emitters (e.g. ships) could off load their pressurised CO2 captured during transit. For instance, once the ship was in port the CO2 could be depressurised and fed into a low pressure pipeline system. The depressurisation process could run a turbine and generate power. The ship could be credited for the power produced, thereby reimbursing the ship for the loss of storage space onboard from carrying the CO2.

[0182] Access to such a network could be a key growth factor in the capture of CO2 in smaller quantities from the environment by allowing a way for CO2 to be deposited and processed. This is not limited to just the large industrial clusters described previously but also includes smaller CO2 emitters would could have their CO2 emissions captured and piped into the main network, such that ultimately any emitter of CO2 could ultimately feed the main network with CO2.

[0183] Example 9 - Heat Pumps, Houses, Towns, Villages and Farms

[0184] New innovations are required to help decarbonise individual houses, cities and towns and access to a CO2 battery network would aid in that development. Access to such an infravessel may prove useful in applications such as district heat pumps and powering small communities / villages. As the technology develops, everything from entire cities to individual homes, particularly those who are connected to mains gas pipelines that could exploit a CO2 battery as a form of energy to heat / cool and provide energy for their homes.

[0185] In situations where individual homes / farms / small villages, particularly in rural areas are already employing renewables or are capturing CO2 from other one site activities, it may be advantageous to compress CO2 on-site in a suitable sized vessel and then hook into the lower pressure pipe network (or create a node to this pipework) for discharging the gas. Thus CO2 battery storage could be gathered on-site during quite periods with a cheap, easy to install node system linking the discharged gas back to the main network.

[0186] Similarly CO2 is currently undergoing a resurgence as a refrigerant in industrial and commercial settings. The cooling effect is obtained from the decompression of carbon dioxide within for example a refrigerator, freezer, cooling, or air-conditioning system. If power was generated as the CO2 was depressurised then this could reduce the electrical power required per system.

[0187] Example 10 - Versatility of Feeding Renewables into the Grid

[0188] It may be generally understood that any method of energy creation that can be used to compress CO2 could be utilised towards feeding the battery network. It may also be generally understood that the nature of this battery system opens a large scope and choice for where renewables can be placed within the network to provide maximum versatility. For example, renewable energy sources such as wind power, wave power and solar could become part of the network from siting offshore windfarms anywhere close to the existing network to utilising the power from solar panels in the Sahara Desert and sending it across national and international boundaries via the pipeline network.

[0189] Example 11 - Power Generation from Manufacture of Chemical Feedstocks

[0190] The CO2 battery network is also capable of power generation where dense phase CO2 is converted into another chemical feedstock after transport. Some CCUS options incorporate the conversion of CO2 into other chemical feedstocks but are limited by local CO2 source availability.

[0191] Using the network envisaged herein, high-pressure CO2 can be transported to a desired location. It can then be removed from the high-pressure pipeline, generating power, and then converted into a commercially attractive feedstock.

[0192] CONCLUSION

[0193] It may be appreciated that there are many global CCUS projects already underway that pump pressurised CO2 to offshore wells, typically involving pipeline infravessel in excess of 100 km or more. There are also networks of fossil fuel pipelines, many capable of operating at high pressure crisscrossing individual countries and linked to other countries and continents comprising more than 1 million km globally, enough to circumnavigate the earth almost 25 times.

[0194] As we transition from fossil fuels these vast networks could be employed, using the described system and method, towards storing dense phase CO2 either for storage in suitable reservoirs or simply to charge sections of high pressure pipelines. This network could also be extended to link to salt caverns and other suitable geological infravessel capable of holding CO2, thereby expanding the capacity of the system defined herein.

[0195] The global infravessel of existing pipelines could hold gigatons of CO2 in their own right and marrying this infravessel up with suitable geological infravessel could extend this significantly and the vast majority of this stored energy could be used as a giant battery of energy storage that could be employed anywhere along the network.

[0196] This solves a multitude of problems including:

[0197] • providing a large enough storage reservoir that can be employed across existing networks;

[0198] • a massive reduction in CAPEX, as much of the infravessel exists already;

[0199] • a cost offset from reduction in decommissioning costs of current pipelines; and / or

[0200] • a useful application for captured CO2.

[0201] Additionally, the present invention also:

[0202] • provides a storage arena for gigatons of CO2;

[0203] • provides a network to introduce CO2 from smaller scale capture facilities;

[0204] • finds a use for existing oil and gas assets as we decarbonise;

[0205] • allows renewables anywhere near the network to recharge the system during off-peak times; and / or

[0206] • to use power that would otherwise be idled / curtailed due to grid capacity saturation during periods of low demand.

[0207] The envisaged system could be 'charged' anywhere in the network where renewables work most efficiently, and discharged through existing infravessel feeding traditional fossil fuel grid entry nodes and anywhere else that requires power. For instance, even existing gas lines to domestic properties could be utilised, providing centralised heating systems for towns, remote 'off grid' locations and essentially anywhere that power is required.

[0208] As the CCUS infravessel grows, the need for fossil fuels would reduce, making more redundant pipe systems available for CO2 battery use. Once the fossil fuels are phased out the system could still remain as instead of pumping CO2 offshore it could instead be retained within the system. As such, this system could act as the backbone for a new energy grid by utilising the pipe network described herein to transport the required power around the world. This could reduce the need for new electrical cables I power lines / pylons to be installed, which would otherwise blight the landscape.

Claims

Claims1. An energy storage system, the system comprising: a first vessel comprising a rigid housing defining a first volume therein, wherein the first vessel is configured to store or transport a fluid comprising carbon dioxide at a first pressure in the first volume; a second vessel comprising a rigid housing defining a second volume therein, wherein the second vessel is configured to store or transport the fluid comprising carbon dioxide at a second pressure in the second volume, wherein the second pressure is lower than the first pressure; and a decompression apparatus configured to transport the fluid comprising carbon dioxide from the first vessel to the second vessel, to reduce the pressure of the fluid comprising carbon dioxide from the first pressure to the second pressure and to capture energy released from the fluid comprising carbon dioxide as it depressurises.

2. The system of claim 1, wherein the decompression apparatus is configured to convert the energy released from the carbon dioxide to mechanical energy, heat energy, cooling energy, electrical energy and / or hydraulic pressure.

3. The system of claim 2, wherein the decompression apparatus is configured to convert the energy released from the carbon dioxide to electrical energy.

4. The system of any preceding claim, wherein the system is connected to an energy network, and the system is configured to feed electrical energy generated by the decompressor into the energy network.

5. The system of any preceding claim, wherein the first pressure is a pressure at which the fluid comprising the carbon dioxide is a liquid, a supercritical fluid and / or a dense phase fluid.

6. The system of any preceding claim, wherein the second pressure is a pressure at which the fluid comprising the carbon dioxide is a gas.

7. The system of any preceding claim, wherein the decompressor is configured to transport a first portion of the fluid comprising carbon dioxide disposed in the first vessel from the first vessel to the second vessel, and the system is configured to leave a second portion of the fluid comprising carbon dioxide in the first vessel, and not remove it therefrom.

8. The system of claim 7, wherein the size of the second portion of the fluid comprising carbon dioxide is sufficient such that after removal of the first portion of the fluid comprising carbon dioxide from the first vessel, the second portion of the fluid comprising carbon dioxide has a third pressure, wherein the third pressure is greater than the second pressure and is sufficient to maintain the second portion of the fluid comprising carbon dioxide in a liquid, a dense phase state and / or a supercritical phase.

9. The system of any preceding claim, wherein the system comprises a compression apparatus configured to transport carbon dioxide from the second vessel to the first vessel and to increase the pressure of the carbon dioxide from the second pressure to the first pressure.

10. The system of any preceding claim, wherein the first vessel comprises or is a first vessel conduit and the second vessel comprises or is a second vessel conduit.

11. The system of claim 10, wherein the first vessel conduit is configured to transport the carbon dioxide from a first location to a second location.

12. The system of claim 11, wherein the first location comprises a carbon dioxide source.

13. The system of claim 11 or 12, wherein the second location comprises a carbon dioxide store or processing plant.

14. The system of claim 13, wherein the first vessel conduit is configured to feed carbon dioxide into the carbon dioxide store at the first pressure.

15. A method of storing and releasing energy, the method of storing and releasing energy, the method comprising: providing a first vessel comprising a rigid housing defining a first volume therein, wherein a fluid comprising carbon dioxide at a first pressure is disposed in the first volume; providing a second vessel comprising a rigid housing defining a second volume therein; and feeding at least a portion of the fluid comprising carbon dioxide from the first volume into the second volume, wherein feeding the at least a portion of the fluid comprisingcarbon dioxide into the second volume comprises reducing the pressure of the at least a portion of the fluid comprising carbon dioxide from the first pressure to a second pressure, wherein the second pressure is lower than the first pressure, and capturing energy released from the at least a portion of the fluid comprising carbon dioxide as it depressurises.

16. The method of claim 15, wherein the fluid comprising carbon dioxide disposed in the first volume at the first pressure may be in a liquid, supercritical or dense phase state.

17. The method of claim 15 or claim 16, wherein subsequent to feeding it into the second volume and reducing the pressure to the second pressure, the at least a portion of the fluid comprising carbon dioxide is in a gaseous state.

18. The method according to any one of claims 15 to 17, wherein the method comprises transporting the fluid comprising carbon dioxide inside the first vessel from a first location towards a second location, and the method comprises feeding the at least a portion of the fluid comprising carbon dioxide from the first volume into the second volume at a depressurisation point between the first and second locations.

19. The method according to any one of claims 15 to 18, wherein subsequent to feeding the at least a portion of the fluid comprising carbon dioxide from the first volume into the second volume, the method may further comprise: feeding the at least a portion of the fluid comprising carbon dioxide from the second volume into the first volume, wherein feeding the at least a portion of the fluid comprising carbon dioxide into the first volume comprises increasing the pressure of the at least a portion of the fluid comprising carbon dioxide from the second pressure to the first pressure.

20. The method according to claim 19, wherein the method comprises transporting the fluid comprising carbon dioxide inside the second vessel from a depressurisation point to a compression point, wherein the compression point is spaced apart from the depressurisation point and the method comprises feeding the at least a portion of the fluid comprising carbon dioxide from the second volume into the first volume at the compression point.

21. The method according to any one of claims 15 to 20, wherein the method is a batch process.

22. The method according to any one of claims 15 to 20, wherein the method is a continuous process.

23. The method according to any one of claims 15 to 22, wherein the fluid comprising carbon dioxide comprises at least 5 vol%, at least 10 vol%, at least 20 vol%, at least 30 vol%, at least 40 vol%, at least 50 vol%, at least 60 vol%, at least 70 vol%, at least 80 vol% or at least 90 vol% carbon dioxide.

Images