Systems and methods for capture, storage and / or purification of carbon species in heat transfer processes

Abstract

A method and system for heat transfer is proposed wherein a liquid water stream in a (heat transfer) process discharged from a condenser or flash evaporator is loaded with CO2 from a flue gas stream thereof to thereby convert both streams to a less harmful and potentially more useful form, wherein the carbon fraction is respectively increased and reduced. The invention furthermore proposes CO2-purification by means of the CO2-loading.

Description

[0001] Title: SYSTEMS AND METHODS FOR CAPTURE, STORAGE AND / OR PURIFICATION OF CARBON SPECIES IN HEAT TRANSFER PROCESSES

[0002] The present invention relates to the field of heat transfer between streams in heat transfer processes, in particular in systems for thermal energy conversion.

[0003] In the field of heat transfer, condensers are commonly used components. A condenser is configured to effectuate the exchange of heat between a coolant stream, having a low temperature and being supplied through a coolant inlet port of the condenser, and a gas stream, having a higher temperature and being supplied through a gas inlet port of the condenser, in such a manner that a condensable part of the gas stream is condensed and subsequently discharged as a condensate stream through the liquid outlet port. The coolant stream is after the heat exchange discharged through a coolant outlet port, and any noncondensable part of the gas stream through a gas outlet port. The condensate stream forms the product stream, and the stream of non-condensable gases is a waste stream. In some common practical thermal energy conversion systems, these non-condensable gases contain CO2, the supplied gas stream often being formed by a discharge stream from a turbine, e.g. a discharge stream of steam of a steam turbine. In a closed cycle condenser, the coolant is recirculated to the coolant inlet port after a processing step involving a temperature decrease, usually accomplished be means of expansion, in order to lose the heat gained in the heat exchange with the gas in the condenser again and be restored to the conditions at the coolant inlet port. In an open cycle condenser, the discharged coolant stream is instead of being recirculated, released as a waste stream.

[0004] The discharge of waste streams from condensers into the environment is undesired in multiple ways. For example the release of the waste gases containing CO2 is harmful to the environment for contributing to global warming, a decrease of the pH of oceans through the uptake of CO2 thereby in upper ocean layers, and so on. The release of coolant streams at a higher temperature than at the intake may result in undesired temperature increases at the sink of the coolant stream at the long term.

[0005] The present invention in particular relates to the field of heat transfer in systems for ocean thermal energy conversion (OTEC), more in particular in open-cycle OTEC. OTEC harnesses the temperature differences of the ocean between the deep ocean and the upper ocean, i.e. water in an upper layer directly under the surface, to run a heat engine and produce work which usually is in the form of electricity. The warm ocean surface water of the ocean, which is heated up by the sun, delivers the heat for the evaporation of a refrigerant into steam in an evaporator, after which the vapor drives a low pressure turbine for generating e.g. electricity. This vapor is subsequently condensed in a condenser wherein the coolant is the colder sea water from the deep ocean.

[0006] In open-cycle OTEC, the sea water itself is used as a refrigerant (R718), and the turbine is a steam turbine which works at sub-atmospheric pressures in view of the temperature of the sea water in an upper ocean layer of around 20-30 °C, e.g. around 25°C, e.g. typically 26°C. The evaporation into steam happens at sudden depressurization in a vessel to the vapor pressure of seawater at its intake temperature of around 26 °C. In the vacuum vessel, also called flash vessel, water instantly boils. The heat of vaporization is coming from the sensible heat present in seawater which will cool down when it delivers energy for the vaporization. The vapor pressure in the condenser is even lower in order to have a pressure difference over the steam turbine, wherein the steam discharged from the turbine is condensed under the production of desalinated water and non-condensable gases. These non-condensable gases include CO2, N2 and O2 and are mixed with the coolant stream of sea water discharged from the condenser, which is released into the upper ocean layer in a mixed waste stream together with the discharge stream of not-evaporated sea water from the evaporator. In the open-cycle OTEC system, the release of the carbon species by the not-evaporated sea water discharged from the evaporator in the upper ocean layer does, contrary to other heat transfer processes, not lead to a net increase of carbon species there, since it originates from the very same upper ocean layer. However, a net increase of carbon species is involved with the coolant stream discharged from the condenser, since this originates from the deep ocean layer where the content of carbon species is already higher.

[0007] An upper ocean layer is considered to have a depth of 250 m or less from the water surface. The upper ocean layers are in communication with the air above it, exchanging carbon species. Pollution of the air leads to an increased uptake thereof in the upper ocean layer below it, increasing the carbon content thereof and therefore decreasing acidity. Release of further CO2 in this layer worsens this problem - and furthermore leads to a decreased uptake of CO2 from the air so that pollution has more effect there.

[0008] A deep ocean layer is considered to have a depth of 500 m or more from the water surface, e.g. 750 m or more, e.g. around 900 m, 1000 m, or 1100 m depth, or even more, e.g. up to 2000 m depth. Sea water at a depth of around 1000 m depth from sea level has a temperature of around 4 °C.

[0009] It is an object of the present invention to reduce the release of waste streams from condensers in heat transfer processes into the environment. It is a further object of the present invention to reduce the harmful effect of these waste streams on the environment in terms of changes caused thereby in e.g. temperature and pH. It is an even further object of the present invention to make condenser waste streams provide a net positive effect on the environment.

[0010] The present invention proposes to load at least a part of the liquid water coolant discharged from the condenser with at least a part of the CCh-rich gas stream of non-condensable gases including CO2 discharged by the condenser in a way that the relative content - i.e., the molar fraction - thereof is decreased in the gas stream whilst the carbon species are increased in the liquid water. When introduced into liquid water, the CO2 may be present as different carbon species. This includes CO2, which forms gas bubbles in the water, bicarbonate ions (HCOa'), carbonate ions (CCh2'), and carbonic acid (H2CO3).

[0011] The invention proposes a method according to claim 1 , and a system according to claim 25. Embodiments are described in subclaims 2-24 and 26-34, respectively, which are elucidated and complemented hereinafter.

[0012] The idea of the CC>2-loading of the liquid water coolant discharged by the condenser with the CO2 from the discharged gas stream of non-condensable components is firstly based on the insight that a discharged waste stream of non-condensable gases including CO2 from the condenser, and a discharged stream of liquid water as a coolant from this same condenser, may by means of a subsequent process be made to interact with each other to provide discharge streams having different constitutions and / or conditions, due to which the streams discharged after the subsequent process may be in a more favorable form in the sense that these are, and / or can more conveniently be treated in a way that is, less harmful to the environment when released therein. Such treatment may include further refinement, for which the stream may now thus be regarded a product stream instead of a waste stream, or storage, e.g. long term storage, e.g. subterranean storage, e.g. long term storage in a deep ocean layer. Underground storage is also envisaged, e.g. where no ocean, in particular deep ocean, is available, e.g. by sea water injection. This may also be done where the invention is applied with the OTEC-system. The idea is furthermore based on the further insight that the streams discharged after the subsequent process may in particular be made more favorable by loading the liquid coolant water with the CO2 from at least a part of the non-condensable gas stream in a way that the molar content of the gas stream is reduced, since this would yield a remaining gas stream which is less harmful to the environment, while at the same time, the CO2 is in more suitable form for subsequent sequestration thereof when loaded into liquid water.

[0013] The present invention proposes a particularly preferred embodiment, wherein this CO2- loading of the discharged liquid water is in the form of dissolving of the CO2. Such dissolving involves that the CO2 takes the form of (bi)carbonate ions in the water and possibly also carbonic acid. The dissolving can in particular be established by means of an absorption process, wherein the liquid water coolant acts as the solvent and the CO2 from the non- condensable gases is at least partly dissolved in the liquid water. Therein, as a skilled person will acknowledge from general knowledge for absorption processes, the gas stream of non- condensable gases should be such that the solubility of the CO2 in the water is higher than that of the (total of the) other non-condensable gases in the stream, in order to achieve a net reduction of the molar fraction of the CO2 in the gas stream and a net increase of the molar fraction of the carbon species in the liquid water. In a particular example wherein this is the case, the non-condensable gases other than CO2 in the discharged gas stream consist of nitrogen, N2, and oxygen, O2. Said CC>2-loading then results in a relative increase of the molar fraction of N2 and O2 in the gas stream. Where steam of water from an open water, e.g. sea water, e.g. from an upper ocean layer, is condensed in the condenser, for example where the condenser is a condenser of an open-cycle OTEC-system, the CC>2-rich stream of non- condensable gases discharged therefrom substantially consists of N2, O2 besides the CO2.

[0014] In a practical embodiment of the inventive method, the absorption process involves:

[0015] - supplying at least a part of the discharged CC>2-rich gas stream to a gas inlet of an absorber,

[0016] - supplying at least a part of the discharged coolant stream of the liquid water to a solvent inlet of the absorber,

[0017] - dissolving at least a part, e.g. a majority, of the CO2 of the CC>2-rich gas stream in the liquid water of the supplied coolant stream by means of an absorber, the CO2 therein forming the (bi)carbonate ions in the liquid water, the liquid water acting as a solvent,

[0018] - discharging as a loaded solvent stream of from a solvent outlet of the absorber the liquid water loaded with the dissolved CO2 in the form of bicarbonate ions and potentially carbonic acid, and

[0019] - discharging as a lean gas stream from a gas outlet of the absorber non-condensable gases of the gas stream not dissolved into the liquid water solvent. This particularly preferred embodiment is based on the further insight by the inventors that the CO2 loaded into water is in a more suitable form for subsequent sequestration thereof into open waters when loaded into liquid water by being dissolved therein, that is, in the form of (bi)carbonate ions, avoiding migration of any CO2, which would without the dissolving still be in gas form, towards the water surface. In particular the dissolved form of the CO2 makes it suitable for being sequestered underground, or in deep ocean layers where the pH is already considerably lower than at the ocean surface so that any pH change due to the discharge of the CO2-loaded water is minimized or absent, and the residence time of these ions - and therefore the prevention of any harmful effect of the contained CO2 on the environment - is relatively long.

[0020] The particular embodiment is based on the even further insight that the discharged gas stream and the discharged stream of liquid water may be made to interact in particular in an absorption process, in order to have the CO2 loaded into the water in a dissolved manner, that is, in the form of (bi)carbonate ions and optionally carbonic acid.

[0021] In a practical embodiment, only a part of the coolant stream discharged by the condenser is loaded with said at least part of the CO2 from the gas stream discharged by the condenser, in order to attune the flow rate of the solvent stream in the absorption process to that of the condensable gas stream e.g. for the sake of efficiency and effectiveness of the absorption process. Therein, the method may further comprise rejoining the loaded solvent stream with a remaining part of the condenser outlet stream of the coolant to form a single CC>2-loaded liquid water stream. The handling of a single liquid water stream loaded with CO2 discharged from the total process, instead of handling both a CC>2-loaded stream discharged from the absorption process and a remaining coolant stream discharged from the condenser may yield advantages in terms of convenience in handling thereof in particular where the condenser is an open-cycle condenser. Therein the single stream may at once be transported to its destination, e.g. for sequestration, e.g. in a deep ocean layer, instead of separate transportation of the CC>2-loaded stream discharged from the absorption process, e.g. for sequestration, e.g. a deep ocean layer, and transporting the remaining coolant stream discharged from the condenser to its destination, e.g. for disposal thereof. In particular, the single stream may be transported to a deep ocean layer for sequestration. For example where the CO2-loaded stream is to be sequestered into a deep ocean layer and the remaining coolant stream would otherwise be released into an upper ocean layer, the transportation of this remaining coolant in the single stream along with the CO2 loaded liquid water provides a particularly efficient handling wherein temperature changes in the upper ocean layer are avoided.

[0022] In an embodiment the coolant used in the condenser is sea water, e.g. sea water from a deep or intermediate ocean layer. This may provide additional advantages for sequestration of the CO2 loaded coolant resulting from the absorption process in terms of required pumping power and similarity in constitution and conditions between the CC>2-loaded coolant and the seawater already present in the deep or intermediate ocean layer.

[0023] In an example embodiment wherein the absorption process is applied, the pH of the solvent liquid water inlet stream is artificially increased, e.g. by means of an electrochemical device or by dissolving materials therein. The effect is that the reduction of the pH involved with the loading of CO2 in the solvent water stream is at least partly compensated. Therewith, in case of sequestration, e.g. in an intermediate or deep ocean layer, said pH reduction is at least partly avoided. In an embodiment the pH reduction is completely compensated, e.g. accompanied by an even further increase in the pH to even overcompensate said pH reduction, e.g. where the pH of the solvent stream is already below neutral prior to the CO2- loading, e.g. such as to increase the pH to neutral or even to above neutral, with the purpose of being ahead of expected future reduction thereof and / or to effect a pH increase as well in the sink of the CCh-loaded solvent.

[0024] In an example embodiment, ultrasounds or any other support technique, e.g. mixing, is used in the evaporator to enhance the dissolution of bicarbonate.

[0025] In an example embodiment, the coolant stream extracted from the cold water reservoir is heated up by providing cooling to an external process, for example an industrial process or a datacenter. This additional cooling service can take place before, after, or in conjunction with the condenser of the main process.

[0026] The inventors have realized that the present invention may in some applications enable to utilize the non-condensable gas stream in which the CO2 fraction has been reduced in the absorber to restore the ratio between other non-condensable gases therein and the CO2 in environments where this is ratio is unfavorable, by discharge of at least a part of this stream. Suitable applications and environments would be those in which the non-condensable gases are already naturally present in the environment along with CO2 in an unfavorable ratio, where an increase of the other non-condensable gases and a reduction of the CO2 would improve this ratio. Such an environment could for example be the air, where discharge of a stream of non-condensable N2and / or O2-gases with a reduced or eliminated CO2 content would lead to an increase of the mentioned N2and / or O2content relative to the CO2 content of this air so as to reduce the harmful effects thereof on climate change. Or, the environment could be an open water, e.g. upper ocean layer, which has become acidified due to uptake of CO2 from the air above it, where such discharge may result in an increase of the pH. and / or an increased uptake from the air above it to reduce the CO2 content in the air where it contributes to climate change. Another example may be (subterranean) zones where the soil has been affected by CO2-induced acidification. In this context, an embodiment of the invention is configured for increasing the ratio between the (molar) content of carbon species and that of other non-condensable components in such environments, and thereto provides that said CCh-loading is followed by transporting at least a part of the gas stream with the reduced CC>2-fraction - and therefore, the increased N2- and Ch-fraction - now forming a CO2- lean gas stream to such an environment and releasing said CCh-lean stream into this environment. An example embodiment, which would in particular be suitable for use with an OTEC-system, is configured for increasing the ratio between the molar carbon species content and the molar O2- and / or N2-content of an open water, e.g. of sea water, at a depth of 250 m or less from sea level, e.g. sea water of an upper ocean layer, the CCh-loading being followed by transporting at least a part of the gas stream with the reduced CCh-fraction - and therefore, the increased N2- and O2-fraction - now forming a CC>2-lean gas stream to said open water and subsequently releasing said CC>2-lean stream into this open water.

[0027] In an embodiment, the CC>2-loading is followed by transporting at least a part, e.g. all, of the CC>2-loaded liquid water to a sequestration location, e.g. by pumping, and subsequently released therein. In a particular example embodiment the transportation is done to an intermediate ocean layer, i.e. an ocean layer below the upper ocean layer to at most 500m depth from the water surface, followed by release of the transported CC>2-loaded liquid water into said intermediate ocean layer, for sequestration of CO2 for a relatively short residence time. Therein it is envisaged that the CC>2-loaded water is more accessible to be retrieved at a relatively short term for other uses. In another particular example embodiment, the transportation is done to a deep ocean layer, e.g. a deep ocean layer at at least 500 m depth, e.g. at least 750 m depth, e.g. at approximately 900 m, 1000 m or 1100 m depth, from the water surface, followed by release of the transported CO2-loaded liquid water into said deep ocean layer. By sequestration in a deep ocean layer, the sequestration can be long-term, e.g. around 500 years or more at 500 m depth or deeper, e.g. around 1000 years or more at a depth of 1000 m or more, e.g. around 1.5-2 millenniums at 1500 m depth or deeper. This particular embodiment provides additional advantages when the coolant of the condenser is sea water from a deep or intermediate ocean layer. Firstly in terms of the location of the condenser then only having to be attuned to that of the deep or intermediate ocean layer, since it at this location both the source of the coolant and the sink of the carbon-loaded discharged coolant water are present. Secondly in particular in case of sequestration in the deep ocean layer, when the sea water discharged from the condenser after the condensation process would be transported back to the intermediate or deep ocean layer to be released there, the sequestration does not even require an extra transportation duct and would bring along a minimal change in the conditions - for example temperature and pH - there. Where only a part of the coolant discharged from the condenser is loaded with the CO2 in the absorber, the CC>2-loaded stream discharged thereby can be sequestered in the intermediate or deep ocean layer simply by rejoining the stream with the other part of the coolant stream discharged by the condenser to be transported along therewith to the deep ocean layer. Obviously, similar advantages can be achieved in embodiments with other sources for the coolant and / or sinks for the CO2-loaded water stream, by letting these sources and sinks correspond with each other. In the examples of the sequestration in the intermediate or deep ocean layer, where sea water, in particular from an upper ocean layer, is also used as a source of the steam which e.g. after producing work is condensed in the condenser, e g. as is the case in the open-cycle OTEC system, there is an even additional efficiency since also the location of the steam source may correspond to that of the coolant source and sink.

[0028] As shortly mentioned above already, the discharged CC>2-rich gas stream of non-condensable gases from the condenser may have been formed during condensation in the condenser by a non-condensable part of a supply stream of steam to the condenser, for example from a steam turbine to the condenser. This is generally also the case in an open-cycle OTEC- system, wherein the steam is steam formed out of water from an open water, e.g. sea, e.g. upper ocean layer by evaporation thereof, but embodiments are also envisaged wherein steam from another source is fed to the condenser. This may also be steam formed from water out of an open water. The steam may be at a sub-atmospheric pressure, e.g. far below atmospheric pressure, e.g. at a pressure near vacuum, which is commonly encountered when the water source has a relatively low temperature, e.g. around 20-30 °C, e.g. around 25 °C, which is also the case when an upper ocean layer is the source of the condensed steam. The CC>2-rich gas stream may downstream of the condenser and prior to said CC>2-loading be compressed by a compressor, e.g. to approximately atmospheric pressure. In an embodiment, the absorption is in the form of pressure swing absorption.

[0029] A particular embodiment of the present invention provides application thereof with, or in, the open-cycle OTEC system wherein as explained before an open-cycle evaporator and opencycle condenser is employed. In the open-cycle OTEC-system, the coolant sea water discharged from the condenser is conventionally mixed with the sea water discharged from the evaporator and released into the upper ocean layer along with the CC>2-rich gas stream in a mixed discharge. Even though there is thus no net CO2 discharge involved with the system, because CO2 is discharged in the upper ocean layer downstream of the condenser in the same amount as it is taken up therefrom upstream of the evaporator, the inventors have realized that the system provides an opportunity for providing a net uptake of the CO2 from the upper ocean layer if the discharge after the condenser is intercepted and subsequently processed for handling in a more favorable form. In particular it is realized that favorable use can be made of the fact that the CO2 is - along with the other gases, in particular N2and O2 - in this process extracted from the seawater by the vacuum degassing in the evaporator, due to which at least a part of the CO2 has effectively migrated to the steam phase, which may not only enable a subsequent separation from the other gases for purification and processing of the CO2 to a more favorable form in the sense of an opportunity to discharge it in a less harmful way, in particular not in the upper ocean layer, but also enables to utilize the stream of the other gases in the stream from which the CO2 has been removed to restore the ratio between these other gases and the CO2 by discharge in environments where this is fruitful - as precedingly discussed. In particular, advantageously, such an environment would be the upper ocean layer which, efficiently, also forms the very source of the evaporator. In the open-cycle OTEC, the CC>2-rich gas stream substantially consists of nitrogen and oxygen apart from the CO2, with the evaporated sea water downstream of the steam turbine being fed to the condenser. In the condenser, condensation of this steam at far sub-atmospheric pressure by deep ocean layer sea water of an even lower temperature takes place under the production of condensate water which is in practice employed as a product stream of desalinated water.

[0030] This particular embodiment of the invention is furthermore based on the recognition that an open-cycle OTEC-system involves flash evaporation to produce the steam to be fed to the steam turbine, which leads to a net migration of carbon species from the source water to the gas phase. Because there is in the flash vessel no atmospheric counterweight to the vapor pressure of the seawater, it causes nearly all present molecular dissolved CO2, via carbonic acid as interstage, to flash out of the boiling water, along with the other dissolved gasses, which are as mentioned mostly N2(nitrogen) and O2 (oxygen). This effect provides a further potential for separating off the CO2 in the taken up sea water and preventing it from ending up therein again after the process by being discharged within a waste stream.

[0031] An even further insight on which this embodiment of the invention is based, is the potential for (further) reduction of the carbon species content in the upper ocean layer by reducing or eliminating release of the coolant stream discharged by the condenser, which has a higher content of these carbon species. Such reduction or elimination can in embodiments be facilitated by the invention.

[0032] The invention proposes a method according to dependent claim 19, an embodiment being defined in claim 20, and a system according to claim 31. Embodiments are elucidated and complemented hereinafter.

[0033] According to the invention, the discharged sea water coolant is loaded with the CO2 from the CC>2-rich gas stream, wherein the molar fraction of the CO2 is reduced in the gas stream and the molar fraction of the carbon species is increased in at least a part of the coolant sea water. The carbon-loaded coolant sea water may be transported for further refinement or storage. Thereby, the release in the upper ocean layer of at least a part, e g. a majority, of the CO2 which has been taken up therefrom for evaporation in the evaporator, can advantageously be prevented.

[0034] The inventors have furthermore recognized the advantageous possibility with the OTEC- system for sequestration in an intermediate or deep sea layer in an efficient manner, as this may be achieved at a corresponding location and the fact that the same deep sea layer also forms the coolant source for the evaporator. Practically, the sequestration can thus efficiently be achieved by some additional pumping power and tubing. The inventors thus propose to in an embodiment discharge the carbon-loaded coolant sea water in the intermediate or deep ocean layer for long-term sequestration thereof - where in particular the CC>2-loading by dissolving, e.g. in an absorption process as described before, is suitable. Therein the CO2 is present in the form of (bi)carbonate ions, whereas a gaseous form could lead to migration towards the surface again. The deep sea layer already having a lower pH, makes that the sequestration of the carbon species does not involve significant changes in the acidity of the sea water in this layer and yields a long residence time. The extra pumping power involved can advantageously be provided in an efficient manner, without external energy supply, by utilizing a small amount of the energy produced in the steam turbine - which amount is by the present inventors calculated as only 2% or less of the total energy production. Alternatively the pump may e.g. be powered by photovoltaic panels. Where only part of the coolant stream discharged by the condenser is split off to be loaded with CO2, this part can after the CO2- loading be rejoined with the remaining part of the discharged cooling stream so that the entire discharged cooling stream can be released into the intermediate or deep ocean layer. The invention furthermore envisages that instead of, or in addition to at least a part of the discharged sea water coolant, a stream of sea water from the upper ocean layer is loaded with the CO2 from the COz-rich gas stream, wherein the molar fraction of the CO2 is reduced in the gas stream and the molar fraction of the carbon species is increased in at least a part of the coolant sea water. In one example, only a stream of sea water from the upper ocean layer is fed to the absorber. In another example, a stream of sea water from the upper ocean layer is mixed with a split off part of the coolant stream discharged by the condenser. In these embodiments, a net transfer of CO2 from the upper ocean layer to the intermediate or deep ocean layer is advantageously achieved.

[0035] The inventors have furthermore realized, that the advantageous technical effects achieved by the invention may be amplified by a further feature which may enhance the CCh-loading. The invention namely proposes further purification of the carbon species in the CCh-loaded stream of liquid water by,

[0036] - flash evaporation of the CO2-loaded liquid water wherein depressurization flashes noncondensable gases including CO2 out of the CCh-loaded liquid water under production of a gas stream of the flashed out non-condensable gases and reduction of the molar fraction of the non-condensable components in the liquid water, and

[0037] - optionally, downstream of the flash evaporation, further CC>2-loading of the liquid water by dissolving at least a part, e.g. a majority of, of the CO2 in the flashed out gas stream of non- condensable gases in the liquid water by means of an absorption process wherein the liquid water is the solvent, the CO2 therein forming (bi)carbonate ions and possibly also carbonic acid in the liquid water solvent, such as to reduce the molar CC>2-fraction in the flashed out gas stream while further increasing the CC>2-fraction in the liquid water.

[0038] The effect of the flash evaporation is that the CO2 that has upstream thereof been loaded into the liquid water, is now again flashed out of the water together with other non-condensable components present in the water. The subsequent loading of the CO2 into the water relative to these non-condensable components by absorption, establishes an enhancement of the ratio between the carbon species in the water and the other non-condensable components therein, i.e., a further increase in the fraction of the carbon species in the water. The flashed out non-condensable gases form a CC -lean gas stream which can, e.g. together with the CC>2-lean gas stream produced during the original CC>2-loading, be used for further refinement or storage, e.g. for enhancing the fraction of the non-condensable components other than carbon species in environments where this would be fruitful. In an embodiment, the step of flash evaporation may be performed without the subsequent step of CC>2-loading, for the purpose of obtaining gas stream as an output from the system with higher CO2 purity, i.e. a higher fraction thereof amongst other non-condensable components, than would be obtained without the CC>2-loading and subsequent flashing. For example, a purity of at least 75%, 80%, 85% or higher may be obtained, which may be further increased by one or more further subsequent purification steps of CO2-loading and flashing. A gas stream with high-purity CO2 may, in contrast to the non-condensable gas stream obtained in prior art systems, be considered a product stream in some applications since a constitution with high-purity may enable e.g. further refinement thereof, production out of the stream of synthetic fuels, further use of the CO2 in unrefined form for greenhouse fertilization, or sequestration in gas form. With regard to the latter, it is for example known that the fraction of O2 in the gas stream should be kept below 3% in order for it to be injected in depleted natural gas fields.

[0039] The inventors have found that by repeating the flash evaporation and absorption steps, e.g. in an open-cycle OTEC-system, one or more times in series, a purity of water dissolved carbon species of at least 85%, e.g. at least 90%, e.g. at least 95% can be achieved.

[0040] The absorption process may in an embodiment be in the form of vacuum absorption. This would in some applications obviate the use of an expander relative to the employment of pressure swing absorption.

[0041] The CC>2-loading according to the inventive concept may also be applied downstream of the flash evaporator in processes wherein these are used, and one or both of the thereby discharged outlet streams are otherwise treated as a waste stream. The CC>2-loading may be applied to at least a part of the flash evaporator outlet streams to achieve the technical effects and possibilities discussed before in relation to its application to the outlet streams of a condenser, the outlet streams thereof being in a more favorable form in terms of the distribution of carbon species fractions being mixed with other gases and being loaded into liquid water. In this context, the invention furthermore relates to methods according to claims 30 and 31 , embodiments being defined in claims 32 and 33, and a system according to claim 34 with embodiments defined in claims 35-37.

[0042] It is envisaged, that an advantageous application thereof may be achieved when water from an open water, e.g. sea water, e.g. sea water from an upper ocean layer is fed to the flash evaporator, wherein the CO2-loading - as discussed before - both leads to an advantageous higher fraction of the carbon species therein for further refinement or storage as discussed before, e.g. in a deep ocean layer, whereby a net uptake of the loaded CO2 from the open water is achieved, and to an advantageous CC>2-lean gas stream with a lower CC>2-fraction, providing the possibility of feeding this CC>2-lean gas stream to an environment affected by a too high carbon content for lowering in that environment its content relative to that of the other non-condensable components, i.e. to restore the ratio between CO2 and the other components, in particular being nitrogen and oxygen. Also here, the flash evaporation and subsequent absorption may be applied multiple times in series to achieve higher CC>2-purities.

[0043] In an example embodiment wherein the absorption process is applied, the pH of the solvent liquid water inlet stream is artificially increased, e.g. by means of an electrochemical device or by dissolving materials therein. The effect is that the reduction of the pH involved with the loading of CO2 in the solvent water stream is at least partly compensated. Therewith, in case of sequestration, e.g. in an intermediate or deep ocean layer, said pH reduction is at least partly avoided. In an embodiment the pH reduction is completely compensated, e.g. accompanied by an even further increase in the pH to even overcompensate said pH reduction, e.g. where the pH of the solvent stream is already below neutral prior to the CO2- loading, e.g. such as to increase the pH to neutral or even to above neutral, with the purpose of being ahead of expected future reduction thereof and / or to effect a pH increase as well in the sink of the CCh-loaded solvent.

[0044] According to the results of a simulation of an example embodiment of the invention with the OTEC-system in Aspen Plus, wherein 1 MW of net electric output is generated by means of the steam turbine, more than 0.3 tonnes / hour of CO2 can be sequestered in a deep ocean layer. The electricity used to overcome the pressure drop in the transportation to the deep ocean layer is calculated to be 24 kW, which boils down to a specific energy (electricity) use of 0.28 MJ per kg of CO2 for both the capture and sequestration thereof. This is significantly lower than regular processes for direct CO2 capture from air (DAC), which require an exergy input of around 1.4 - 3.7 GJ / ton of CO2 (Sabatino et.al. 2021). The dissolving of CO2 in the ocean water in the absorber involves, according to the simulation, a change in the pH from 7.2 to 5.6. Albeit subject to design and circumstances, this is an indication that the majority of the CO2-content being released from the upper layer ocean water is absorbed in the water flow that passes the absorber. The absorber is therein dimensioned as having a diameter of 0.6 meters and a height of 4 meters, and is packed with Raschig-rings, so that the volume of the absorber is such as to absorb a majority of the CO2 with a small water flow, i.e. practically close to minimal, and to eject the remaining inert gases N2and O2. The invention furthermore relates to a method for capture and long-term sequestration of CO2, comprising:

[0045] - evaporating water from a warm water source, thereby producing a CO2-rich stream of steam containing CO2 and other non-condensable gases,

[0046] - convert part of the enthalpy of the steam into work, e.g. by means of a steam turbine,

[0047] - downstream thereof, supply a CO2-rich gas stream of the steam now having lower enthalpy to a condenser,

[0048] - supply a liquid water stream to the condenser, for use as a coolant,

[0049] - condense in the condenser the CC>2-rich gas stream of the steam to condensate by transferring heat therefrom to the supplied liquid water stream coolant,

[0050] - downstream of the heat transfer, discharge from the condenser a stream of the thereby heated liquid water coolant stream, discharge a stream of the condensate, and discharge a not condensed part of the CO2-rich gas stream,

[0051] - loading at least a part of the discharged water coolant stream and at least a part of a water stream from the warm water source with at least a part of the CO2 from the discharged gas stream such as to reduce the molar CCh-fraction in the gas stream while increasing the fraction of carbon species in said coolant water and / or water from the warm water source. The loading of the water coolant stream may partially or completely be done by combination with the CC>2-loaded warm water source stream.

[0052] The invention furthermore relates to a system for capture and long-term sequestration of CO2, comprising:

[0053] - an evaporator for evaporating water from a warm water source, thereby producing a CO2- rich stream of steam containing CO2 and other non-condensable gases,

[0054] - downstream thereof, a heat engine, e.g. a steam turbine, configured for, and connected at a steam inlet port thereof with a steam outlet port of the evaporator for, converting part of the energy content of the steam into work,

[0055] - downstream thereof, a condenser having a coolant inlet port for receiving a stream of water, a gas inlet port, a coolant outlet port, a condensate outlet port, and a gas outlet port, the condenser being configured to, and fluidly connected at the steam inlet port thereof to a steam outlet port of the heat engine to:

[0056] - transfer heat from the steam supplied through the gas inlet port to the liquid water coolant stream supplied through the coolant inlet port such as to condense a part of the CO2-rich gas stream to condensate, downstream of the heat transfer, discharging a stream of the thereby heated liquid sea water through the coolant outlet port, and downstream of the heat transfer, discharge a stream of the condensate through the condensate outlet port, downstream of the heat transfer, discharge a stream of the not condensed part of the CO2-rich gas stream from the gas outlet port,

[0057] - downstream of the condenser, an absorber having a solvent inlet port, a gas inlet port, a liquid outlet port, and a gas outlet port, the absorber being configured to, and fluidly connected at the solvent inlet port thereof to the warm water source and optionally also to the coolant outlet port of the condenser, and fluidly connected at the gas inlet port thereof to the gas outlet port of the condenser, to: dissolve a part, e.g. a majority, of gaseous CO2 present in the non-condensable gas stream in the liquid water of the liquid water stream, the CO2 therein forming carbonate ions in the liquid water, discharge out of the solvent outlet port a liquid outlet stream of the liquid water with the dissolved CO2, and discharge out of the gas outlet port a gas outlet stream of non-condensable gases from the CO2-rich gas stream which have not been dissolved into the liquid water solvent in the absorber.

[0058] Therein the condenser-discharged coolant may, in particular when not led through the absorber, be combined with the absorber-discharged CC>2-loaded stream, in order to be loaded with the CO2. For example a mixture of a part of the condenser-discharged coolant stream and the stream of liquid water from the warm water source may be led through the absorber and optionally combined with the remainder of the condenser-discharged coolant stream.

[0059] In the method and system, the heat for said evaporation of the water may in particular be at least partly provided by a (part of a) waste heat stream. Examples are cooling mediums released by industrial processes and / or by a water electrolyzer. The water to be evaporated may also be at least partly heated by a renewable source, for example a solar pond or a geothermal reservoir. In examples, shallow ocean water may be used as a sink for the heat still remaining in said evaporation heat source after providing the evaporation heat and / or for the outlet stream of the evaporator.

[0060] In embodiments wherein coolant water from the condenser is used as solvent in the absorber, a particularly efficient and convenient process is achieved. In embodiments wherein (additionally) water from the warm water source is used as solvent, a net transfer of CO2 from the warm water source, e.g. an upper ocean layer, to a sink for the liquid outlet stream of the absorber, e.g. an intermediate or deep ocean layer, may advantageously be achieved. It will be apparent to the skilled person, that certain features explained herein in relation to the different methods and systems may be readily combined to provide the same or similar advantages. In particular where the same or similar method steps and materials, including system parts, sinks and sources, are involved.

[0061] The invention will hereinafter be described in relation to the appended figures. Therein:

[0062] Figure 1 illustrates a prior art condenser,

[0063] Figures 2-3 illustrate a method and system according to an embodiment of the invention,

[0064] Figure 4 illustrates another method and system according to an embodiment of the invention,

[0065] Figure 5 illustrates another method and system according to an embodiment of the invention,

[0066] Figure 6 illustrates a prior art open-cycle OTEC-system,

[0067] Figures 7-9 illustrate a method and system according to embodiments of the invention with an open-cycle OTEC-system.

[0068] Figure 1 illustrates the use of a condenser N in a heat transfer process, according to the prior art. The condenser N condenses within the condenser N a gas stream by means of heat transfer from this gas stream to a stream of liquid water with a lower temperature. This stream of liquid water forms the coolant of the condenser as refrigerant R718.

[0069] The gas stream enters the condenser as gas inlet stream Gi which comes from a gas source SCG. The condensation within the condenser N creates out of the gas stream Gi a stream D of condensate, which is discharged by the condenser and led to condensate sink SND, and a stream G2 of non-condensable components still in gaseous state, which is discharged by the condenser and led to gas sink SNG.

[0070] The liquid water stream enters the condenser N as inlet liquid water coolant stream CW1 which is pumped by pump P from a liquid water source SCcw to the condenser N. The condensation within the condenser N leads to a temperature increase of the liquid water, which is subsequently discharged by the condenser N as outlet liquid water coolant stream CW2at a higher temperature.

[0071] In common heat transfer processes the gas inlet stream Gi consists of steam. Its source SCG may be a steam turbine, in which part of the enthalpy of the steam has been converted into work, e.g. electricity. The steam inlet stream Gi is then transported from the turbine to the condenser N to be condensed, so that the condensate D is produced as a product for further use and the gas stream G2 is disposed of as a waste stream. The condensate D substantially contains, e.g. essentially entirely consists of, purified water, i.e. H2O, whereas the discharged gas stream G2substantially contains the non-condensable components N2(nitrogen), O2(oxygen), and CO2. In practice the fraction of CO2in the outlet gas stream G2is often higher than that of atmospheric air. For example in the case of steam which originates from a relatively cold water source, e.g. open water, e.g. an upper ocean layer as in the open-cycle OTEC system, the steam is produced by flash evaporation upstream of the turbine which involves a net migration of CO2from the water in the liquid state to the water in the gas state. A source affected by acidification through CO2pollution, may lead to even higher CO2levels of the stream G2.

[0072] The liquid water source SCcw may in an example, alike in an open-cycle OTEC-system, be a deep layer from the ocean. The outlet coolant stream CW2is disposed of as a waste stream.

[0073] Thus, in the prior art use of the open-cycle condenser N, the CO2-rich gas stream G2of non- condensable gases including CO2is discharged from the condenser N, and the coolant stream CW2of liquid water is discharged from said condenser N.

[0074] Figure 2 illustrates the same open-cycle condenser N with the same inlet streams G1 and CW1, and the same outlet streams G2and CW2. Other than in the prior art, in the use in the arrangement shown in figure 2, a part CW31 of the discharged liquid water coolant stream CW2is loaded with CO2from the discharged gas stream G2. This is done by absorber A, to which the part of the coolant stream CW3.1 is thereto fed at one end thereof and the gas stream G2is fed at the opposite end thereof. In the absorber A, the majority of the CO2present in the CO2-rich gas stream G2is dissolved in the liquid water by means of an absorption process wherein the liquid water is the solvent. The CO2therein forming (bi)carbonate ions in the liquid water solvent. Thereby, the molar Contraction in the gas stream G2is reduced, and the fraction of carbon species, including mainly bicarbonate and carbonate ions, in the liquid water is increased. There is thus a net migration of carbon species accomplished from the gas stream G2to the liquid water of the partial coolant stream CW3.1, so that the absorber discharges a carbon-lean gas stream GL and a carbon-rich liquid water stream CW4. The carbon-rich liquid water stream CW4is rejoined with the remaining part CW32of the coolant stream CW2discharged by the condenser to a carbon-rich water stream CWR. The elimination of the CC>2-rich gas stream G2 as a discharge stream and the discharge of the carbon-lean gas stream GL instead, makes that as discussed before in the general description, sink SNGfor the gas stream may now be more environmentally friendly and even useful for improving environmental conditions in some applications. Furthermore the form of the gas stream may render it (more) suitable for further refinement or use in further processes, so that the gas stream may be considered a product stream instead of a waste stream. For example, the gas stream now being carbon-lean makes that release into an environment involves less, no, or even a negative, effect on the carbon-content of that environment.

[0075] The CO2 now being captured in the carbon-rich liquid water stream CWR makes, as discussed before in the general description, further use thereof, or storage, e g. in a deep ocean layer, more convenient and favorable than in the prior art situation with the CO2 in the gas stream G2 along with other non-condensable gases.

[0076] The compressor M, present in the illustrated embodiment but in fact optional, is provided for compressing the gas stream upstream of the absorber, i.e. in embodiments wherein this is needed. This is e.g. the case when the pressure of the gas stream G2 discharged by the condenser N is below atmospheric and the absorber needs (near) atmospheric pressure of the gas.

[0077] Figure 3 illustrates the difference between the prior art arrangement with the condenser N of figure 1 and the arrangement according to the invention of figure 2. Therein, the dashed lines indicate what has been removed in the prior art arrangement, and the double lines what has been added in figure 2. Furthermore, figure 3 indicates the relevant components, in particular the non-condensable components N2and O2 and, in boldface, the carbon species in the streams, which are mainly present in the streams for the case that SCG is steam, in particular evaporated from an open water, e.g. sea water. This comparison makes it even more clear, how CO2 which would in the prior art situation end up in the gas sink SNGnow advantageously ends up in a more suitable form in the liquid water sink SNCW, and leads to a more favorable gas constitution for the gas sink SNG.

[0078] Figure 4 illustrates in the same way how a flash evaporator V may according to an embodiment of the invention be used in combination with absorber A to achieve similar effects. The flash evaporator does not process a gas stream G1 from a gas source SCGnor produces a condensate stream D. Instead, by flash evaporation of liquid water stream CW1 wherein the non-condensable components are flashed out of the liquid water, it produces a non-condensable gas stream G2 and a liquid water stream CW2from which the noncondensable components of gas stream G2have been removed. By means of the absorber A, by means of which may in particular vacuum absorption may be established, at least part of the CO2in the gas stream G2which would conventionally otherwise end up in the gas sink SNGis advantageously dissolved in the part CW3.1 of the discharged liquid water stream CW2.

[0079] In figure 5, it is in the same way illustrated how purification components may in a particularly favorably way be used in combination with a flash evaporator V for purification of CO2and discharge in gaseous form for further use. The addition and removal of streams and sinks relative to a prior art process with the flash evaporator V is indicated by respectively the double and dashed lines. The source SCvw for the evaporator V is in particular upper ocean layer OUL. In the prior art - see the dashed lines - the CO2-rich flashed out gases are, unfavorably, discharged in sink SNG, for example the CO2-fraction being 10-20%, e.g. around 15%. By the addition of the absorber A, the gas stream GL is discharged in the sink SNG which is advantageously CO2-lean. The CO2-loaded sea water stream VW4 is led to a further flash evaporator Vp with the purpose of flashing the non-condensable components thereof which now have an increased Contraction, e g. around 75-85%, out of the sea water, which is discharged from the further flash evaporator VP as a purified gas stream GP. This purified gas stream is as described in the general description, suitable for further use in a sink SNGP, e.g. after compression. In addition, the further flash evaporator VP discharges sea water stream VWs from which the carbon species have substantially been flashed out. This makes it, advantageously, particularly suitable for being discharged into the upper ocean layer OUL as well without increasing carbon species content, e.g. therein even enhancing the fraction of O2and N2relative to the carbon species therein. Thus, a method and system is illustrated which accomplishes to instead of discharging a polluting CO2-rich waste gas stream G2, a useable purified CO2product gas stream GP, and a CO2-lean, even restoring, gas and sea water stream GL and VW5. The embodiment is shown utilizing sea water from an upper ocean layer OUL, but is envisaged to utilize water from other, e.g. shallow, open waters as well as source SCvw and sinks SNvwi, SN 2 for providing similar advantages, e.g. water of seas such as the North Sea, or e.g. river water, or e.g. waste water, e.g. from a cooling tower or waste gas scrubber. As described herein, it is also envisaged to connect downstream of the further evaporator VPa further absorber, e.g. for producing CO2-loaded water with an enhanced purity and a CO2-lean gas stream with even further reduced Contraction, or an absorber connected downstream thereof with an even further flash evaporator for producing a further purified gas stream GP and further CO2-reduced sea water stream. Figure 6 illustrates an open-cycle OTEC-system as is known in the art. A flash evaporator degasses in a vacuum vessel water from water stream VWi taken from an upper layer OUL of the ocean O, producing a stream of stream of CO2-rich steam VWSand CO2-lean water stream VW2. The steam is utilized in steam turbine T to produce electricity E for use in a sink SNEwherein this renewable electricity is stored or used. The - still CO2-rich - steam discharged from the turbine after electricity production forms the source SCG for the gas stream Gi to the condenser N which has been discussed before in relation to figures 1-3. The source SCcw for the liquid coolant water is a deep layer ODL of the ocean O, from which the stream CWi is pumped up by pump P. After condensation, the discharged heated up liquid water coolant stream CW2and gas stream G2 of non-condensable components is combined after compression of the latter by compressor M, and discharged in a mixed discharge to the upper ocean layer OUL. The upper ocean layer thus forms the sink SNw and SNcw for both of the water streams VW2 and CW2 discharged by the evaporator V and the condenser N, respectively, and furthermore the sink SNG for the stream of non-condensable gases G2 discharged by the condenser N.

[0080] Figure 7 illustrates the same open-cycle OTEC-system wherein, in the same way as discussed in relation to figure 2, a part CW3.1 of the liquid water coolant stream CW2 discharged by the condenser N is loaded with CO2 from the gas stream G2. This is done by absorber A, to which the part of the coolant stream CW31 is thereto fed at one end thereof and the gas stream G2 is fed at the opposite end thereof. In the absorber A, the majority of the CO2 present in the CO2-rich gas stream G2 is dissolved in the liquid water by means of an absorption process wherein the liquid water is the solvent. The CO2 therein forming (bi)carbonate ions in the liquid water solvent. Thereby, the molar CO2-fraction in the gas stream G2 is reduced, and the fraction of carbon species, including mainly bicarbonate and carbonate ions, in the liquid water is increased. There is thus a net migration of carbon species accomplished from the gas stream G2 to the liquid water of the partial coolant stream CW3.1, so that the absorber discharges a carbon-lean gas stream GL and a carbon-rich liquid water stream CW4. The carbon-rich liquid water stream CW4is rejoined with the remaining part CW3.2 of the coolant stream CW2discharged by the condenser to a carbon-rich water stream CWR.

[0081] Other than in the prior art open-cycle OTEC-system, the carbon-rich water stream CWRis transported to the deep ocean layer ODL now forming the sink SNcw for the coolant water, for long-term sequestration of the carbon-species advantageously dissolved therein in the form of (bi)carbonate ions. Preferably the stream CWRis released at a depth of around 1000 m below the ocean surface Os, where the residence time is around a millennium. The upper ocean layer OUL still forms the sink SNGfor the gas, however, the gas is now fed thereto in a CC>2-lean form.

[0082] In figure 8, the changes between the arrangement of figure 7 and that according to the prior art in figure 6 have been indicated in the same manner as in figures 3 and 4. Dashed lines indicate removals relative to the prior art and double lines additions. Furthermore, the noncondensable components mainly present in relevant streams have been indicated for comparison. It may therefrom be verified that the arrangement achieves an uptake of carbon species from the upper ocean layer OUL, and a long term sequestration thereof in the deep ocean layer ODL.

[0083] It is noted, that figures 7 and 8 are also illustrative for the methods and systems of claims 21- 24 and 32-34. Therein, instead of the open cycle use of the upper ocean layer as both a source of the evaporation heat and the source of water to be evaporated is optionally envisaged to be replaced by another source, e.g. the use of a waste stream or a source of renewable heat and a separate stream of water to be evaporated in a closed cycle evaporation process.

[0084] In figure 9, an envisaged system according to the invention is shown wherein water AWi from the upper ocean layer OUL is used as a source SCAW for the absorber as a solvent AW2 for the absorber A. As indicated by the dotted arrow between the discharge coolant stream CW2 from the condenser N, at least a part CW22 of this discharge coolant stream CW2 may optionally join the stream AW2to together form the solvent stream. In other cases it may be removed. The difference with the system of figure 7, the relative thereto added stream AWI,2, is indicated by a double line and the optionally relative thereto removed stream CW2.2 is dotted.

[0085] In the embodiment of figure 9, the CC>2-loading of the coolant stream CW2discharged from the condenser N takes place by the joining of the stream AW3to the coolant stream CW2to form CWR.

[0086] It can readily be seen that, evenas figures 7 and 8, figure 9 is also illustrative for the methods and systems of claims 21-24 and 32-34. Therein, instead of the open cycle use of the upper ocean layer as both a source of the evaporation heat and the source of water to be evaporated may be replaced by another source, e.g. the use of a waste stream or a source of renewable heat and a separate stream of water to be evaporated in a closed cycle evaporation process.

Claims

C L A I M S1. Method of handling streams discharged from a condenser (N) in a heat transfer process, wherein a CO2-rich gas stream (G2) of non-condensable gases including CO2 is discharged from the condenser (N), and a coolant stream (CW2) of liquid water is discharged from said condenser (N), the method comprising loading at least a part of the discharged liquid water with at least a part of the CO2 from the discharged gas stream (G2) such as to reduce the molar CCh-fraction in the gas stream while increasing the fraction of carbon species in the liquid water.

2. Method according to claim 1 , wherein the CO2-loading comprises dissolving at least a part, e.g. a majority of, of the CO2 in the CO2-rich gas stream (G2) in the liquid water by means of an absorption process wherein the liquid water is the solvent, the CO2 therein forming (bi)carbonate ions in the liquid water solvent.

3. Method according to claim 2, wherein said absorption process involves:- supplying at least a part of the discharged CC>2-rich gas stream (G2) to a gas inlet of an absorber (A),- supplying at least a part (CW31) of the discharged coolant stream (CW2) of the liquid water to a solvent inlet of the absorber (A),- dissolving at least a part, e.g. a majority of, of the CO2 from the CO2-rich gas stream (G2) in the liquid water of the supplied coolant stream (CW3.1) by means of the absorber, the CO2 therein forming the (bi)carbonate ions in the liquid water as the solvent,- discharging as a loaded solvent stream (CW4) from a solvent outlet of the absorber (A) the liquid water loaded with the dissolved CO2, and- discharging as a lean gas stream (GL) from a gas outlet of the absorber (A) non- condensable gases from the CC>2-rich gas stream (G2) which have not been dissolved into the liquid water solvent in the absorber.

4. Method according to any one or more of the preceding claims, wherein only a part (CW3.1) of the coolant stream (CW2) discharged by the condenser (N) is loaded with said at least part of the CO2 from the CO2-rich gas stream (G2) discharged by the condenser (N), the method further comprising rejoining the loaded solvent stream (CW4) with a remaining part(CW3.2) of the coolant stream (CW2) discharged by the condenser (N) but not C02-loaded to together form a single carbon-rich liquid water stream (WR).

5. Method according to any one or more of the preceding claims, wherein the CO2- loading is followed by transporting at least a part, e.g. all, of the CO2-loaded liquid water to an underground storage location or a deep ocean layer (ODL), e.g. by pumping, e.g. to a deep ocean layer at at least 500 m depth, e.g. at least 750 m depth, e.g. at approximately 900 m, 1000 m or 1100 m depth, from the water surface (Os), and releasing the transported CO2- loaded liquid water into said underground storage location or deep ocean layer.

6. Method according to any one or more of the preceding claims, wherein the liquid water coolant of the condenser (N) is water from an open water, e.g. sea water, e.g. sea water from an ocean (O), e.g. from a deep layer (ODL) of the ocean (O).

7. Method according to any one or more of the preceding claims, wherein the CO2-rich gas stream (G2) of non-condensable gases discharged from the condenser (N), further to CO2, substantially consists of N2and O2, so that said CO2-loading results in a relative increase of the molar fraction of N2and O2in the gas stream.

8. Method according to any one or more of the claims 2-7, wherein said dissolving is performed in the form of pressure swing absorption.

9. Method according to any one or more of claims 2-8, wherein the majority of the CO2of the CO2-rich gas stream is dissolved in the liquid water solvent by means of the absorption process, e.g. wherein said majority of the CO2is at least 75% of all of the CO2in the CO2-rich gas stream (G2), e.g. at least 80%.

10. Method according to any one or more of the preceding claims, wherein the liquid water of the coolant stream (CW2) is seawater from a sea or ocean (O), e.g. from a deep layer (ODL) of the ocean (O) at at least 500 m depth, e.g. at least 750 m depth, e.g. at approximately 900 m, 1000 m or 1100 m depth, from sea level (Os).11 . Method according to any one or more of the preceding claims, preferably according to claim 2, more preferably according to claims 2 and 10, wherein the method is configured for long term carbon sequestration in a deep ocean layer (ODL), and the CO2-loading is followed by transporting at least a part of the CO2-loaded liquid water to the deep ocean layer (ODL), e.g. by pumping, e.g. a deep ocean layer at at least 500 m depth, e.g. at least 750 m depth,e.g. at approximately 900 m, 1000 m or 1100 m depth, from sea level (Os), and releasing said CO2-loaded liquid water into the deep ocean layer.

12. Method according to claim 7, wherein the method is configured for increasing the ratio between the molar content of carbon species and the molar O2- and / or N2-content of an open water, e.g. of sea water, at a depth of 250 m or less from sea level, e.g. sea water of an upper ocean layer (OUL), and said CO2-loading is followed by transporting at least a part of the gas stream with the reduced CC>2-fraction - and therefore, the increased N2- and 02-fraction - now forming a CC>2-lean gas stream to said open water and releasing said CC>2-lean stream into said open water.

13. Method according to any one or more of the preceding claims, wherein the discharged CC>2-rich gas stream (G2) of non-condensable gases from the condenser has been formed during condensation in the condenser (N) by a non-condensable part of a supply stream (G1) of steam to the condenser (N), e.g. from a steam turbine (T) to the condenser, e.g. at a sub- atmospheric pressure, e.g. far below atmospheric pressure, e.g. at a pressure near vacuum.

14. Method according to claims 7 and 13, wherein at least the majority, e.g. all, of the steam has been formed by evaporating water from an open water in an evaporator (V) upstream of the condenser (N), e.g. upstream of the steam turbine (T), if present, e.g. water from a sea or an upper ocean layer (OUL) at a depth of 250 m or less from sea level (Os).

15. Method according to claim 13 or 14, wherein the steam is at a sub-atmospheric pressure, e.g. far below atmospheric pressure, e.g. at a pressure near vacuum, and the CO2- rich gas stream (G2) has downstream of the condenser (N) and prior to said CO2-loading been compressed by a compressor (R), e.g. to approximately atmospheric pressure.

16. Method according to claim 15, wherein the condenser (N) is the condenser of an Ocean Thermal Energy Conversion (OTEC-) system, e.g. a method according to claim 14 and 15 wherein the condenser is the condenser of an open-cycle OTEC-system.

17. Method according to claims 12 and 16, wherein the method further comprises rejoining the CO2-lean stream with a water stream (VW2) discharged from the evaporator (V) of the OTEC-system, e.g. open-cycle OTEC-system, which is downstream from its discharge released into said open water.

18. Method according to claims 2 and 10, further comprising, downstream of the CO2- loading by dissolving, one or more COz-purification steps comprising:- flash evaporation of the CO2-loaded liquid water wherein depressurization flashes noncondensable gases including CO2 out of the CC>2-loaded liquid water under production of a gas stream of the flashed out non-condensable gases and reduction of the molar fraction of the non-condensable components in the liquid water, and- optionally downstream of the flash evaporation, further CC>2-loading of the liquid water by dissolving at least a part, e.g. a majority, of the CO2 in the flashed out gas stream of non- condensable gases in the liquid water by means of an absorption process wherein the liquid water is the solvent, the CO2 therein forming (bi)carbonate ions in the liquid water solvent, such as to reduce the molar CC>2-fraction in the flashed out gas stream while further increasing the CC>2-fraction in the liquid water, e.g. wherein the absorption is in the form of vacuum absorption, e.g. wherein after performing both steps these are repeated one or more times, e.g. followed by a repetition of only the flash evaporation step one more time.

19. Method according to any one or more of the preceding claims, the method furthermore being suitable for capture and long-term sequestration of CO2, comprising providing an open-cycle OTEC-system, and operating the OTEC-system such as to:- evaporate sea water (VW1) from an upper layer (OUL) of an ocean (O), thereby producing a CC>2-rich stream of steam (VWS) containing CO2 and other non-condensable gases,- convert part of the enthalpy of the steam (VWS) into work, e.g. by means of a steam turbine (T),- downstream thereof, supply a CO2-rich gas stream (G1) of the steam now having lower enthalpy to a condenser (N),- supply a liquid water stream (CW1) of sea water from a deep layer (ODL) of the ocean (O) to the condenser (N), for use as a coolant,- condense in the condenser (N) the CC>2-rich gas stream (G1) of the steam to condensate by transferring heat therefrom to the supplied liquid sea water stream coolant (CW1),- downstream of the heat transfer, discharge from the condenser the thereby heated liquid sea water as said coolant stream (CW2), discharge a stream (D) of the condensate, and discharge a not condensed part of the CO2-rich gas stream (G1) as said CO2-rich gas stream (G2),- performing said loading of at least a part of the discharged liquid water of the sea water coolant stream (CW2) with at least a part of the CO2 from the discharged gas stream (G2) such as to reduce the molar Contraction in the gas stream (G2) while increasing the fraction of carbon species in the coolant sea water20. Method according to claim 19, wherein the method further comprises:- transporting the CO2-loaded sea water coolant to the deep ocean layer (ODL) or an underground storage location, and releasing it into the deep ocean layer or underground storage location, and / or- transporting the CO2-reduced gas to the upper ocean layer (OUL) and releasing it into the upper ocean layer.21 . Method according to any one or more of claims 1-20, wherein the method is suitable for capture and long-term sequestration of CO2, and comprises:- evaporating water (VW1) from a water source (SCvw), e.g. an upper ocean layer, thereby producing a CO2-rich stream of steam (VWS) containing CO2and other non-condensable gases,- convert part of the enthalpy of the steam (VWS) into work, e.g. by means of a steam turbine (T),- downstream thereof, supply a CO2-rich gas stream (G1) of the steam now having lower enthalpy to a condenser (N),- supply a liquid water stream (CW1) to the condenser (N), for use as a coolant,- condense in the condenser (N) the CO2-rich gas stream (G1) of the steam to condensate by transferring heat therefrom to the supplied liquid water stream coolant (CW1),- downstream of the heat transfer, discharge from the condenser a stream (CW2) of the thereby heated liquid water coolant stream (CW2), discharge a stream (D) of the condensate, and discharge a not condensed part (G2) of the CO2-rich gas stream (G1) , wherein besides said loading of at least a part of the discharged water coolant stream (CW2), the method further comprises loading at least a part of a stream from the water source (SCvw) with at least a part of the CO2from the discharged gas stream (G2) such as to reduce the molar CO2-fraction in the gas stream (G2) while increasing the fraction of carbon species in the coolant water.

22. Method according to claim 21, wherein said loading comprises:- supplying at least a part of the discharged COz-rich gas stream (G2) to a gas inlet of an absorber (A),- supplying the at least a part of a stream from the water source (SCvw) to the solvent inlet of the absorber (A),- dissolving at least a part, e.g. a majority of, of the CO2 from the CO2-rich gas stream (G2) in the liquid water of the supplied solvent stream (AW2, CW2.2) by means of the absorber, the CO2 therein forming the (bi)carbonate ions in the liquid water as the solvent,- discharging as a loaded solvent stream (CW4) from a solvent outlet of the absorber (A) the liquid water loaded with the dissolved CO2, and- discharging as a lean gas stream (GL) from a gas outlet of the absorber (A) noncondensable gases from the CCh-rich gas stream (G2) which have not been dissolved into the liquid water solvent in the absorber, wherein the loading of at least a part of the discharged water coolant stream (CW2) is done by one or more of:- supplying the at least a part (CW3.1) of the discharged coolant stream (CW2) of the liquid water to a solvent inlet of the absorber (A) to form part of the supplied solvent stream,- combining at least a part of the loaded solvent stream (CW4) with at least a part of the discharged coolant stream (CW2) downstream of the absorber (A).

23. Method according to any one or more of claims 18-22, wherein for said evaporation, required evaporation heat is at least partly provided by a waste heat stream, e.g. a cooling medium released by e.g. industrial processes and / or e.g. by a water electrolyzer, and / or at least partly provided by a renewable source, e.g. a solar pond and / or a geothermal reservoir.

24. Method according to any one or more of claims 18-23, wherein a shallow water, e.g. an upper ocean layer, e.g. a surface layer, is used as a sink (SNGL) for a discharge water stream (VW2) of said evaporation and / or for heat of said heat source remaining after providing said evaporation heat.

25. System for heat transfer, the system comprising: a condenser (N), having a coolant inlet port, a gas inlet port, a coolant outlet port, a gas outlet port, and a condensate outlet port, optionally, a supply duct for accommodating a stream (CWi) of liquid water coolant from a source (SCcw) thereof to the coolant inlet port of the condenser (N), and optionally a pump (P) configured and arranged for pumping the liquid water coolant stream (CWi) through the supply duct from the source (SCcw) to the coolant inlet port of the condenser (N), wherein the condenser (N) is configured to transfer heat from a CCh-rich gas stream (Gi) supplied through the gas inlet port to the liquid water stream (CWi) supplied through the coolant inlet port such as to condense a part of the CCh-rich gas stream (Gi) to condensate, downstream of the heat transfer, discharge a stream (CW2) of the thereby heated liquid water through the coolant outlet port, downstream of the heat transfer, discharge a stream (D) of the condensate through the condensate outlet port, and downstream of the heat transfer, discharge a not condensed part (G2) of the COz-rich gas stream (Gi) from the gas outlet port, the system further comprising, downstream of the condenser (N): an absorber (A), having a solvent inlet port, a gas inlet port, a liquid outlet port, and a gas outlet port, wherein the absorber (A) is configured to, and fluidly connected at the solvent inlet port thereof to the coolant outlet port of the condenser (N), and fluidly connected at the gas inlet port thereof to the gas outlet port of the condenser (N), to: dissolve a part, e.g. a majority, of gaseous CO2 present in at least a part of the non-condensable gas stream (G2) in the liquid water of at least a part of the liquid water stream discharged from the condenser, the CO2 therein forming (bi)carbonate ions in the liquid water, discharge out of the solvent outlet port a liquid outlet stream (CW4) of the liquid water with the dissolved CO2, and discharge out of the gas outlet port a gas outlet stream (GL) of non- condensable gases from the CO2-rich gas stream (G2) which have not been dissolved into the liquid water solvent in the absorber (A),e.g. the system further comprising: an intermediate liquid water duct for accommodating a stream of said at least a part of the liquid water discharged from the condenser (N) from the coolant outlet port thereof to the solvent inlet port of the absorber (A), an intermediate gas duct for accommodating a stream of said at least a part of noncondensable gases discharged by the condenser (N) from the gas outlet port therefrom to the gas inlet port of the absorber (A).

26. System according to claim 25, wherein the condenser is an open-cycle condenser of an open-cycle OTEC-system.

27. System according to claim 26, further comprising, downstream of the absorber (A) thereof, one or more CCh-purification parts comprising:- a flash evaporator (Vp) configured for, and fluidly connected with a liquid water inlet port thereof to the liquid water outlet of the absorber (A) for, depressurizing the CO2-loaded liquid water to flash non-condensable gases including CO2 out of the CCh-loaded liquid water, discharging a gas stream of the flashed out non-condensable gases through a gas outlet port, and discharging a stream of the liquid water in which the molar fraction of the non- condensable components has been reduced by the flashing out through a liquid outlet port, and- optionally, downstream of the flash evaporator, a further absorber configured for, and fluidly connected with a gas inlet port thereof to the gas outlet port of the flash evaporator for, and fluidly connected with a solvent inlet port thereof to the liquid outlet port of the absorber for, further CC>2-loading of the liquid water discharged by the evaporator by dissolving at least a part, e.g. a majority, of the CO2 in the flashed out gas stream of non-condensable gases in the liquid water by means of an absorption process in which the liquid water is the solvent, the CO2 therein forming (bi)carbonate ions in the liquid water solvent, such as to reduce the molar CC>2-fraction in the flashed out gas stream while further increasing the fraction of carbon species in the liquid water, for discharging through a liquid outlet port a stream of the further CC>2-loaded liquid water, and discharging through a gas outlet port a gas stream of the non-condensable gases which have not been absorbed, e.g. wherein the absorber is suitable for vacuum absorption.

28. System according to claim 27, further comprising, downstream of the CO2-purification parts already present, one or more further CC>2-purification parts according to claim 23, ofwhich each flash evaporator is with the liquid water inlet port thereof fluidly connected to the liquid water outlet of the absorber directly upstream thereof.

29. System according to claim 28, the one or more further CC>2-purification parts further comprising a further flash evaporator according to claim 23, or one or more of a further flash evaporator and connected absorber according to claim 23 connected in series, e.g. followed by an even further flash evaporator, wherein each flash evaporator is with the liquid water inlet port thereof fluidly connected to the liquid water outlet of the absorber directly upstream thereof.

30. System according to any one or more of claims 21-25, further comprising, where an absorber is the most downstream purification part:- a liquid water duct connected to the liquid outlet port of the most downstream absorber (A) for transporting the COs-loaded coolant water to a deep ocean layer (ODL) or an underground storage location and releasing it into the deep ocean layer or underground storage location, the system e.g. further comprising a pump (P) for this purpose, and / or- a gas duct connected to the gas outlet port of the most downstream absorber (A) for transporting the CCh-reduced gas to an upper ocean layer (OUL) and releasing it into the upper ocean layer, or, where a flash evaporator is the most downstream purification part:- a liquid water duct connected to the liquid outlet port of the most downstream flash evaporator for transporting the COz-lean sea water to the upper ocean layer (ODL) and releasing it into the upper ocean layer.31 . System according to any one or more of claims 25-30, the system furthermore being suitable for capture and long-term sequestration of CO2, thereto comprising an open-cycle OTEC-system which comprises:- an evaporator (V) for evaporating sea water (VW1) from an upper layer (OUL) of an ocean (O), thereby producing a CO2-rich stream of steam (VWS) containing CO2 and other noncondensable gases,- downstream thereof, a heat engine, e.g. a steam turbine (T), configured for, and connected at a steam inlet port thereof with a steam outlet port of the evaporator (V) for, converting part of the energy content of the steam (VWs) into work,- downstream thereof, the condenser (N), wherein the coolant inlet port is arranged for receiving a stream (CW1) of liquid sea water from a deep ocean layer (ODL), the condenserbeing fluidly connected at the steam inlet port thereof to a steam outlet port of the heat engine (T),- downstream of the condenser, the absorber (A), the absorber being fluidly connected at the solvent inlet port thereof to the coolant outlet port of the condenser (N), and fluidly connected at the gas inlet port thereof to the gas outlet port of the condenser (N).

32. System according to any one or more of claims 25-31 , the method being suitable for capture and long-term sequestration of CO2, comprising:- an evaporator (V) for evaporating water (VW1) from a water source (SCvw), e.g. an upper ocean layer, thereby producing a CCh-rich stream of steam (VWs) containing CO2 and other non-condensable gases,- downstream thereof, a heat engine, e.g. a steam turbine (T), configured for, and connected at a steam inlet port thereof with a steam outlet port of the evaporator (V) for, converting part of the energy content of the steam (VWs) into work,- downstream thereof, the condenser (N), the coolant inlet port thereof being arranged for receiving a stream (CW1) of water, the condenser being fluidly connected at the steam inlet port thereof to a steam outlet port of the heat engine (T),- downstream of the condenser, the absorber (A), the absorber (A) being fluidly connected at the solvent inlet port thereof to said water source (SCvw) and optionally to the coolant outlet port of the condenser (N), and fluidly connected at the gas inlet port thereof to the gas outlet port of the condenser (N),- at least in case the coolant outlet port of the condenser (N) is not fluidly connected to the solvent inlet port, downstream of the absorber (A), an amalgamation of a duct accommodating the loaded liquid water discharged by the absorber and a duct accommodating at least a part of the coolant stream discharged from the condenser.

33. System according to any one or more of claims 27-32, wherein for said evaporation, required heat is at least partly provided by a waste heat stream, e.g. a cooling medium released by e.g. industrial processes and / or e.g. by a water electrolyzer, and / or at least partly provided by a renewable source, e.g. a solar pond and / or a geothermal reservoir.

34. System according to claim 32 or 33, wherein a shallow water, e.g. an upper ocean layer, e.g. a surface layer, is used as a sink (SNGL) for a discharge water stream (VW2) of said evaporation and / or for heat of said heat source remaining after providing said evaporation heat.

35. Method of handling streams discharged from a flash evaporator (VP), wherein a CC>2-rich gas stream (G2) of non-condensable gases including CO2 is discharged from the flash evaporator (VP), and a stream (CW2) of liquid water is discharged from said flash evaporator (VP), the method comprising loading at least a part of the discharged liquid water with at least a part of the CO2 from the discharged gas stream (G2) such as to reduce the molar CC>2-fraction in the gas stream while increasing the fraction of carbon species in the liquid water, e.g. wherein the CO2-loading of the liquid water is performed by dissolving at least a part, e.g. a majority, of the CO2 in the flashed out gas stream of non-condensable gases in the liquid water by means of an absorption process wherein the liquid water is the solvent, the CO2 therein forming (bi)carbonate ions in the liquid water solvent, e.g. wherein the absorption process is in the form of vacuum absorption, e.g. wherein flash evaporation and subsequent CC>2-loading are alternatingly repeated once or more for further purification of the supplied liquid water, e.g. a purification to at least 80%, e.g. at least 85%, e.g. at least 90%, e.g. at least 95% of the CC>2-content of the supplied liquid water.

36. Method according to claim 35, wherein the method is suitable for purification of CO2 out of liquid water, e.g. sea water, containing non-condensable components including CO2, the method comprising:- supplying the liquid water to be purified to the flash evaporator (VP),- performing flash evaporation by operation of the flash evaporator wherein depressurization flashes non-condensable gases including CO2 out of the CC>2-containing liquid water under production of the CO2-rich gas stream (G2) of the non-condensable gases and reduction of the molar fraction of the non-condensable components in the liquid water, and- downstream of the flash evaporation, perform said loading of the at least a part of the discharged liquid water with the at least a part of the CO2 from the gas stream (G2) of the flashed out non-condensable gases such as to reduce the molar CO2-fraction in said flashed out gas stream while increasing the molar fraction of carbon species in the liquid water,e.g. wherein the CC>2-loading of the liquid water is performed by dissolving at least a part, e.g. a majority of, of the CO2 in the flashed out gas stream of non-condensable gases in the liquid water by means of an absorption process wherein the liquid water is the solvent, the CO2 therein forming (bi)carbonate ions in the liquid water solvent, e.g. wherein the absorption process is in the form of vacuum absorption, e.g. wherein at least the step of performing flash evaporation is repeated after the CO2- loading, e.g. wherein both the steps of performing flash evaporation and subsequent CO2- loading are repeated, once or more, e.g. followed by performing flash evaporation once more, for further purification of the supplied liquid water, e.g. a purification to at least 80%, e.g. at least 85%, e.g. at least 90%, e.g. at least 95% of the CO2-content of the supplied liquid water.

37. Method according to claim 30 or 31 , wherein the liquid water is water from an open water, e.g. sea water, e.g. sea water from an ocean, e.g. from an upper layer (OUL) of the ocean (O).

38. Method according to claim 30 or 31, wherein the method further comprises, where performing CC>2-loading forms the last purification step:- transporting the CC>2-loaded water to a deep ocean layer (ODL) or an underground storage location and releasing it into the deep ocean layer or underground storage location, and / or- transporting the CC>2-reduced gas to an upper ocean layer (OUL) and releasing it into the upper ocean layer, or, where performing flash evaporation forms the last purification step:- transporting the CO2-lean water to an upper ocean layer (OUL) and releasing it into the upper ocean layer.

39. System for flash evaporation, the system comprising: a flash evaporator (V), having a liquid water inlet port, a liquid water outlet port, and a gas outlet port, optionally, a supply duct for accommodating a stream (VW1) of the liquid water from a source (SCvw) thereof to the liquid water inlet port of the evaporator (V), and optionally a pump (P) configured and arranged for pumping the liquid water stream (VW1)through the supply duct from the source (SCvw) to the liquid water inlet port of the evaporator (V), wherein the flash evaporator (V) is configured to: depressurize the stream (VWi) of the carbon-rich liquid water supplied through the liquid water inlet port such as to flash non-condensable gases including CO2 out of the carbon-rich liquid water, and reduce the molar fraction of the non-condensable components in the liquid water, downstream of the depressurization, discharge a stream (VW2) of the liquid water with the reduced molar non-condensable components fraction through the liquid water outlet port, and downstream of the depressurization, discharge a gas stream (G2) of the flashed out non-condensable gases including CO2from the gas outlet port, the system further comprising, downstream of the flash evaporator: an absorber (A), having a solvent inlet port, a gas inlet port, a liquid outlet port, and a gas outlet port, the absorber (A) being configured to, and fluidly connected at the solvent inlet port thereof to the liquid water outlet port of the flash evaporator (V), and fluidly connected at the gas inlet port thereof to the gas outlet port of the flash evaporator (V), to dissolve a part, e.g. a majority, of gaseous CO2present in the non- condensable gas stream (G2) in the liquid water of the liquid water stream, the CO2therein forming (bi)carbonate ions in the liquid water, discharge out of the solvent outlet port a liquid outlet stream (VW4) of the liquid water with the dissolved CO2, and discharge out of the gas outlet port a gas outlet stream (GL) of non- condensable gases from the CO2-rich gas stream (G2) which have not been dissolved into the liquid water solvent in the absorber (A), e.g. the system further comprising: an intermediate liquid water duct for accommodating a stream of at least a part of the liquid water discharged from the liquid water outlet port of the flash evaporator (V) to the solvent inlet port of the absorber (A), an intermediate gas duct for accommodating a stream of at least a part of the non- condensable gases discharged from the gas outlet port of the evaporator (V) to the gas inlet port of the absorber (A),e.g. wherein the absorber is suitable for vacuum absorption.

40. System according to claim 39, further comprising, downstream of the absorber (A) thereof, one or more COz-purification parts comprising:- a further flash evaporator configured for, and fluidly connected with a liquid water inlet port thereof to the liquid water outlet of the absorber (A) for, depressurizing the CO2-loaded liquid water flashing non-condensable gases including CO2 out of the CC>2-loaded liquid water, discharging a gas stream of the flashed out non-condensable gases through a gas outlet port, and discharging the liquid water in which the molar fraction of the non-condensable components in the liquid water has been reduced by the flashing out through a liquid outlet port, and- optionally, downstream of the further flash evaporator, a further absorber configured for, and fluidly connected with a gas inlet port thereof to the gas outlet port of the flash evaporator for, and connected with the liquid outlet port of the absorber for, further CCh-loading of the liquid water discharged by the evaporator by dissolving at least a part, e g. a majority of, of the CO2 in the flashed out gas stream of non-condensable gases in the liquid water by means of an absorption process wherein the liquid water is the solvent, the CO2 therein forming (bi)carbonate ions in the liquid water solvent, such as to reduce the molar CO2-fraction in the flashed out gas stream while further increasing the fraction of carbon species in the liquid water, for discharging through a liquid outlet port a stream of the further CO2-loaded liquid water, and discharging through a gas outlet port a gas stream of the non-condensable gases which have not been absorbed, e.g. wherein the absorber is suitable for vacuum absorption.41 . System according to claim 40, further comprising, downstream of the absorber already present, a further flash evaporator according to claim 35, or one or more of a further flash evaporator and connected absorber according to claim 35 connected in series, e.g. followed by an even further flash evaporator, wherein each flash evaporator is with the liquid water inlet port thereof fluidly connected to the liquid water outlet of the absorber directly upstream thereof.

42. System according to any one or more of claims 39-41 , further comprising, where an absorber is the most downstream purification part:- a liquid water duct connected to the liquid outlet port of the most downstream absorber (A) for transporting the CO2-loaded water to a deep ocean layer (ODL) and releasing it into the deep ocean layer, the system e.g. further comprising a pump (P) for this purpose, and / or- a gas duct connected to the gas outlet port of the most downstream absorber (A) for transporting the CC>2-reduced gas to an upper ocean layer (OUL) and releasing it into the upper ocean layer, or, where a flash evaporator is the most downstream purification part,- a liquid water duct connected to the liquid outlet port of the most downstream flash evaporator (VP) for transporting the CC>2-lean water to an upper ocean layer (ODL) and releasing it into the upper ocean layer.

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