A method and a device for capturing carbon dioxide and / or methane from sea water

Abstract

The invention relates to a method for capturing carbon dioxide and / or methane from sea water. The invented method includes the steps of providing a heat transfer system having a first heat exchanger (2) in the sea, a second heat exchanger (3) and piping (1) connecting the first and second heat exchangers in a closed circuit, which first heat exchanger (2) is arranged to heat the surrounding sea water, whereby an upstream (A) of sea water is created and which second heat exchanger (2) is arranged to be heated directly or indirectly by the surrounding sea water, - providing a first pipe (7) around at least a central portion of the upstream (A), - connecting the upstream (A) to a gas separator (11) arranged to separate gas from the upstream, - ducting away the separated gas to a gas storage device (13). The invention also relates to a device for performing the method.

Description

[0001] A METHOD AND A DEVICE FOR CAPTURING CARBON DIOXIDE AND / OR METHANE FROM SEA WATER

[0002] DESCRIPTION

[0003] Field of the invention

[0004] The present invention in a first aspect relates to a method for capturing carbon dioxide and / or methane from an upstream of sea water. In a second aspect the invention relates to a device for capturing carbon dioxide and methane from an upstream of seawater which device is provided with positioning means for arranging the device in the sea, such as floating means and / or anchoring means.

[0005] It is to be understood that the term sea in the context of the present application also includes large lakes and the like. Although the invention is focused on the greenhouse gases carbon dioxide and methane it is to be understood that it applies also to other gases dissolved in the sea.

[0006] Background of the invention

[0007] The increasingly growing concern of the future of our planet due to the temperature rise caused by the greenhouse effect has encouraged intense efforts to cope with the underlying problems. The greenhouse effect is created by the rapidly increasing content of in the first place carbon dioxide but also methane in the atmosphere. Although this problem has to be addressed by changing the way of our living behaviour and a rapid and drastic decrease in using fossil energy in particular in the short run, it is also necessary to find ways to reduce the content of the greenhouse gases in the air and in the sea.

[0008] A variety of ideas and suggestions for processes and devices that can capture carbon dioxide from the air thus has been presented. Less efforts have been made to reduce the carbon dioxide, mainly in aqueous state, that is contained in seawater and is increasing. Reducing the content of greenhouse gases dissolved in the sea will increase the ability to absorb such gases from the atmosphere. The present invention thus is focused on reducing the amount of greenhouse gases dissolved in the sea.

[0009] WO 2010 / 142943 discloses an example of trying to obtain such reduction of the content of dissolved carbon dioxide in the sea. The disclosure describes how the carbon dioxide is released by heating the seawater with the aid of a heat transfer system having a working fluid such as water. The working fluid is heated in a first heat exchanger having a solar energy collector and then pumped to a second heat exchanger in which the working fluid heats sea water that has been pumped up from the depth. The system thus has the limitation that a pump is required for distributing cold water to the system and the system requires an external heat source for heating the working fluid.

[0010] In US 2016 / 0257577 is disclosed how carbon dioxide and methane can be removed from an upstream in lake Kivu. The conditions in that lake, being a volcanic lake are very specific. The disclosed process therefore is specifically adapted to the very specific conditions in that lake.

[0011] Further, there are disclosures relating to how natural or artificial upwelling can be used for other purposes than the separation of carbon dioxide, e.g. increasing the nutrition or decreasing the salinity of the sea surface water or providing turbines in the upflowing water to generate electrical energy. In some disclosures the temperature difference in temperature of the sea surface water and the deep water is used as a driving force. Thereby various heat exchanging systems are employed, including those having a two-phase working fluid. Representative examples of such disclosures are WO 2014060783, W0 2011021992, EP 2903425, EP 2435633, EP 0045789, US 20060006657, US 9394771, US8602682, US 8353162, US 4597360, US 4311012, CA 2958456, FR 2887935, CN 103858811, CN 114793999, CN 204718769, CN 104026046, KR10-2016-0005511 and KR10-1390190.

[0012] The present invention has the object to overcome the drawbacks and limitation entailing previous attempts in this field and provide a simple, efficient and energy effective way to capture gaseous carbon dioxide and / or methane from the sea.

[0013] Summary of the invention

[0014] This object has according to the first aspect of the invention been achieved in that a method of the kind specified in the preamble of claim 1 includes the specific measure specified in the characterizing portion of claim 1. The invented method thus includes the measures of providing a heat transfer system having a first heat exchanger in the sea, a second heat exchanger and piping connecting the heat exchangers, which first heat exchanger is arranged to heat the surrounding sea water, whereby an upstream of sea water is created and which second heat exchanger is arranged to be heated directly or indirectly by the sea water, providing a first pipe around at least a central portion of the upstream, connecting the upstream to a gas separator arranged to separate gas from the upstream and ducting away the separated gas to a storage device.

[0015] The invention thereby does not rely on external heating sources such as solar panels since the heat necessary to create the upstream is taken from the surrounding water. This makes it possible to perform the method in a simple and cost-efficient way allowing a large scale extraction of greenhouse gases from the sea. And by providing a pipe for the water flowing due to the heat from first heat exchanger, the water stream will be concentrated with the result that the gas separation can be effectively performed.

[0016] A reduction of the content of greenhouse gases dissolved in the sea water will increase the ability of the sea water to absorb greenhouse gases from the air at the location where the method is performed

[0017] According to a preferred embodiment of the invented method, the heat transfer system includes at least one two-phase heat transfer circuit with a phase-changing fluid such as ammonia as working fluid.

[0018] Thanks to using a heat transferring system operating with a phase-changing working medium a particularly effective heating of the sea water will be obtained and the method does not require a temperature difference between the sea water that heats the second heat exchanger and the sea water being heated by the first heat exchanger. This embodiment also provides a better possibility to control and govern the process. The two- phase heat transfer circuit may constitute the heat transferring system or form a part of it.

[0019] According to a further preferred embodiment, the two-phase heat transfer circuit has a condenser acting as the first heat exchanger and an evaporator in heat exchanging relation with the sea water.

[0020] In this embodiment the two-phase heat transfer circuit thus constitutes the heat transferring system. The benefits of using phase-shifting working fluid thereby directly and efficiently increase the temperature of the sea water creating a strong upstream that enhances the forming of bubbles.

[0021] According to a further preferred embodiment, the evaporator is located in the sea close to the sea surface.

[0022] An advantage of this embodiment is that the difference in temperature between the sea water that heats the working medium and the sea water that is heated by the working fluid is as high as possible which leads to an optimal performance of the two-phase heat circuit. And an advantageous downwelling is achieved for the sea water that has been cooled by the second heat exchanger.

[0023] According to a further preferred embodiment the length of the first pipe is at least 20 meters.

[0024] With a long pipe the temperature of the sea water that enter through its lower end opening will be correspondingly low and the pressure high, and therewith its content of dissolved greenhouse gases. The longer the pipe is, the more accentuated is this effect. Therefor the pipe preferably may be more than 100 meters long or even more than 500 meters long. According to a further preferred embodiment a second pipe is arranged around the downstream of sea water that is created by the evaporator, which second pipe has an upper open end.

[0025] This second pipe contributes to concentrate and enhance the downflow of the surface water cooled by the evaporator so that new relatively warm surface water will flow into contact with the evaporator, whereby the efficiency of the heat transfer system will be increased.

[0026] According to a further preferred embodiment the gas separator has an outlet conduit for sea water, from which the gases has been separated, which outlet conduit ends close to the second heat exchanger.

[0027] The degassed sea water will due to the heating from the first heat exchanger be relatively warm. It is therefore advantageous to make use of this water for heating the second heat exchanger.

[0028] According to a further preferred embodiment a turbine is provided in the first pipe, which turbine is connected to an electric generator.

[0029] Thereby the method not only provides the capturing of the greenhouse gases but also generates electrical energy. The electrical energy generation offers the possibility to obtain a more cost-effective operation. Advantageously a turbine is also provided in the second pipe so that also the kinetic energy in the downflow is made use of.

[0030] According to the second aspect of the invention the object is achieved in that a device of the kind specified in the preamble of claim 9 includes the specific features specified in the characterizing portion of the claim. The device thus includes a heat transfer system having a heat exchanger in the sea, which heat exchanger is arranged to heat the surrounding sea water, whereby an upstream of sea water is created, a first pipe arranged around at least a central part of the upstream of sea water, a gas separator connected to the upstream, which gas separator is arranged to separate gas from the upstream of sea water, and a conduit arranged to duct away the separated gas to a storage device.

[0031] According to preferred embodiments of the invented device, it includes means arranged for performing the method according to any of the preferred embodiments thereof, and which means are inherently defined by the wording of the corresponding claims.

[0032] The invented device and the preferred embodiments thereof have the corresponding advantages as the invented method and the preferred embodiments thereof, and which have been described above.

[0033] The above mentioned preferred embodiments are set out in the dependent claims. Further preferred embodiments may include features derived from the description of examples in combination with the above mentioned preferred embodiments. Brief Description of the Drawings

[0034] Fig. 1 is a schematic illustration of a first and second example of the device according to the present invention.

[0035] Fig. 2 is a schematic illustration of a third example of the device according to the present invention.

[0036] Fig. 3 is a schematic illustration of a fourth and a fifth example of a device according to the invention.

[0037] Fig. 4 is a schematic illustration of a sixth example of a device according to the invention.

[0038] Fig. 5 is a schematic illustration of a seventh example of a device according to the invention.

[0039] Fig. 6 illustrates an eight example of the invention.

[0040] Fig. 7 illustrates a ninth example of the invention.

[0041] Fig. 8 illustrates a tenth example of the invention.

[0042] All the figures are seen in a vertical plane taken through the sea.

[0043] Description of illustrative Examples of the Invention

[0044] Fig. 1 schematically illustrates an example of a device arranged for performing the method according to the invention. A two-phase heat transfer circuit having a piping 1 formed as a closed loop operating with e.g. ammonia as the working fluid is arranged in the sea. The flow direction of the working fluid is counter-clockwise as seen in the figure. It has the evaporator 3 located close to the sea surface S and the condenser 2 deep in the sea, in this example not far from the sea bottom SB. A compressor 4 is arranged between the evaporator 3 and the condenser and a throttle 5 is arranged between the condenser 2 and the evaporator 3 in the other section of the piping 1. The heat transfer system thus is of a conventional kind operating with a two-phase working fluid. Preferably, the piping 1 is provided with thermal insulation (not shown) at least along parts of its extension.

[0045] A pipe 7 is vertically arranged with an open lower end 9 adjacent the condenser 2 and a closed upper end 8 close to the sea surface S. At its upper end, the pipe 7 is connected to a gas separator 11, which by a conduit 12 is connected to a gas storage device 13. The gas separator is provided with an outlet 23 through which the degassed water is returned to the sea. The pipe 7 in this example has circular cross section and the diameter thereof is larger than the diametric extension of the condenser 2. However, another cross section of the pipe 7 than circular is within the scope of the invention. And the pipe does not necessarily have a uniform cross section area. It might for example be tapering in the upward direction. The pipe 7 at its lower end has a funnel shaped section 10, the purpose of which is to enhance the flow of deep sea water towards the condenser 2. Preferably, the pipe 7 is thermally insulated.

[0046] The device is held in a working position by positioning means 14, 15, 16, 17. The positioning means may be a float 14 connected to the pipe 7 by a wire 16 or a rigid rod. The float may be a boat or a platform. The positioning means may alternatively or additionally be one or more anchoring devices 15 at the sea bottom SB and connected to the pipe 7 by a respective wire 17 or a rigid rod. The working position as illustrated is substantially vertical. This is normally optimal, but it is included in the invention that the direction may deviate from the strict vertical orientation so that the pipe is leaning. The piping 1 of the heat transfer system may either be held in place by being mechanically secured to the pipe 7 or by separate connection to the float or the bottom.

[0047] Since the figure primarily has the aim to illustrate the principle of the invention, it is to be understood that the various components in the first place are depicted as symbols, and not reflect the size of the component in relation to the size of other components. For example are the relative dimensions of the gas separator 11 normally much larger than shown, e.g. its diameter may exceed the diameter of the first pipe 7.

[0048] In operation the evaporator 3, located close to the sea surface S, will be exposed to sea water that is relatively warm, typically 20 to 25 degrees C. The working fluid thereby will be heated, and flows to the compressor 4 where its pressure is increased before entering the condenser 2. The condenser is exposed to sea water that is relatively cold, typically about 4 degrees C. The condensed working fluid then returns to the evaporator 3 via the throttle 5.

[0049] The deep see water thereby receives the condensation heat and will be heated. Its density thereby will decrease and the water by buoyancy will flow upward inside the pipe 7 as indicated by the arrows A. The seawater contains carbon dioxide and methane dissolved therein. The solubility of the gases is a function of pressure and temperature. The higher the pressure is, the higher is the solubility, and the higher the temperature is, the lower is the solubility. Since the condenser 2 is located at a substantial depth, the pressure can be in the order of 50 bars or more.

[0050] When the water thus has been heated by the condenser 2 it will decrease its ability to maintain the gases dissolved so that they will form bubbles C that flow up inside the pipe 7. When the water rises within the pipe 7 its pressure will gradually decrease which further will enhance the formation of gas bubbles C.

[0051] The gas bubbles C will be captured by the gas separator 11, which can be of any conventional kind. The captured gas is ducted through a conduit 12 to storage 13. The sea water from which the gas has been separated is led back to the sea through a conduit 23. It will have lower content of dissolved greenhouse gases than the prevailing water close to the sea surface S. When they mix, the mixture will therefore have a reduced content of dissolved greenhouse gases in compared to the content normally prevailing at the location. This surface water therefore will be able to absorb and dissolve greenhouse gases from the atmosphere, so that the content of greenhouse gases in the atmosphere becomes locally reduced.

[0052] The water close to the sea surface S cooled by the evaporator 3 will due to the increase of its density flow downwards towards the sea bottom SB. The water close to the sea surface S has a relatively small content of dissolved greenhouse gases. After being cooled its ability to contain dissolved greenhouse gases increases, and as it flows downwards the ability to contain dissolved greenhouse gases will increase further, due to the increased pressure. The water existing at large depth D has a higher content of dissolved greenhouse gases. When it mixes with the down flowing water, the content in the mixture will have a lower content of dissolved greenhouse gases than the content normally prevailing at this depth. It will thereby have a potential to absorb and dissolve more greenhouse gases migrating from above. This will further contribute to the ability of the surface water to absorb and dissolve greenhouse gases from the atmosphere.

[0053] Close to the sea surface S, the water that flows down will continuously be replaced by new surface water flowing substantially horizontally from the surroundings of the evaporator 3.

[0054] In the figure the pipe 7 is depicted as having a length that substantially equals the distance between the first heat exchanger 2 and the sea surface S. Within the limits of the invention the pipe 7, however may be much shorter that distance as well as much longer. The piping of the heat transfer system is in the figure located outside the first pipe. However, the piping may alternatively be located inside the first pipe. In that case thermal insulation of the piping may not be present in the downflowing part of the piping. It might even be advantageous without thermal insulation so that also the piping contributes to heat the upflowing sea water.

[0055] Fig. 1 also illustrates an alternative example with regard to the location of the compressor, which alternative is represented by broken lines. In this example the compressor 4a is located above the sea e.g. on the boat / platform 14, and the piping has a portion la that connects the compressor 4a to the submerged part of the piping 1.

[0056] Fig. 2 illustrates a further example of a device according to the invention. The heat transfer system with the piping 1 and the other components of the system is similar to that described in connection with fig. 1. As in fig.l also the device of fig.2 is provided with a gas separator 11, a conduit 12 for the separated gases, a gas storage device 13 and an outlet for degassed water 23. Also the device of the second example is provided with means for positioning the device in a proper orientation, such as floating means and / or anchoring means and connections to these. These means are omitted from fig. 2 for better clarity.

[0057] The main difference is that the device in fig. 2 is provided with a second substantially vertical pipe 18. The second pipe 18 has an open upper end 19 beneath and close to the sea surface S and an open lower end 20 at large depth D. The second pipe 18 has the function to lead down and concentrate the downstream B of water from the sea surface S. Also the second pipe 18 may be thermally insulated.

[0058] The first pipe 7 has a funnel shaped lower end 10 similar to that in fig. 1. And the second pipe 18 may have a funnel shaped upper end 21 for directing the surface water towards the evaporator 3.

[0059] The device of fig. 2 has a turbine 22 arranged in the water flowing up through the pipe 7. The turbine 22 is connected to a generator (not shown) for delivering electric energy to a storage or to a grid. A part of the produced electric energy may be used for running the compressor 4 in the heat transfer system. A turbine (not shown) for generating electrical energy may also be provided in the downwards directed water flow B in the second pipe 18. It is to be understood that the example of the device shown in fig. 1 also may be provided with a corresponding turbine in the upwards water flow A in the pipe 7.

[0060] In the figure the second pipe is shown as outside and parallel to the first pipe. It is, however, to be understood that the second pipe can be arranged concentric, e.g. outside the first pipe.

[0061] In both examples the vertical sections of the piping 1 alternatively may be located in the interior of pipe7, and in the second example also in pipe 18.

[0062] Fig. 3 illustrates an example having a two-phase heat transfer system in which the condenser 2 and the evaporator 3 are located at substantially the same depth in the sea. The condenser 2 and the evaporator 3 thus are exposed to sea water of substantially the same temperature, which may be as low as about 4 degrees C depending on how large the depth of their positions is. The heat transfer thus solely is achieved from the phase transformation of the working fluid, in this example ammonia. The low pressure liquid ammonia flowing from the expansion valve 5 to the evaporator 3 will have a temperature that is lower than the temperature of the surrounding sea water, i.e. less than 4 degrees C. The surrounding sea water therefore will heat the liquid ammonia in the evaporator 3, and the ammonia turns into gaseous stage with a relatively low pressure. The pressure and temperature is increased by the compressor 4. When the gaseous ammonia condenses in the condenser 2 the surrounding sea water will be heated and flow up through the pipe 7. The pressure of the liquid ammonia is then reduced when passing through the expansion valve 5 towards the evaporator 3. Since the heat transfer system in this example is located at a substantial depth it might in some cases be appropriate to locate the compressor higher up in the sea or even above the sea surface. This alternative is illustrated by broken lines in fig. 3, where the compressor 4a is located e.g. on a floating platform. A part la of the piping 1 connects the compressor 4a to the other components of the system. Having the compressor 4a above the sea surface or at a moderate depth allows the compressor to be less robust than is required at large depths which reduces the costs. Also maintenance and power supply will be facilitated.

[0063] In fig. 3 only those details that elucidate the particulars of this example are shown. It is to be understood that in all other respects corresponding parts of the system depicted in fig. 1 and 2 may be present also in a device according to the example in fig. 3. This applies also to the examples illustrated in figures 4-8.

[0064] In the example illustrated in fig. 4 the heat transfer system is operating with a working fluid that does not change phase during the heat transfer, e.g. water. This heat transfer system thus relies on a temperature difference between the two heat exchangers. The first heat exchanger 2 in this example is located at a substantial depth, where the temperature may be as low as 4 degrees C. The second heat exchanger 3 is located close to the sea surface S, where the temperature might be in the order of 25 degrees C. The water in the piping 1 is heated by the warm sea water surrounding the second heat exchanger 3 and flows to the second heat exchanger 2, where it is cooled by the surrounding sea water and then flows up to the second heat exchanger 3 to enter the next cycle. The sea water surrounding the first heat exchanger 2 thereby will be heated so that it flows up through the pipe 7, forming gas bubbles that then are separated from the sea water in a way similar to that described in connection with figures 1 and 2. A pump (not shown) advantageously may be mounted in the piping 1 in order to initiate and enhance the circulation of the water in the piping 1.

[0065] In the example illustrated in fig. 5 a one phase heat transfer system is combined with a two phase heat transfer system. A first heat exchanger 2 located aligned with the pipe 7 is by the piping 1 connected to a second heat exchanger 3 located close to the sea surface S and forms a one phase heat transfer system having e.g. water as working fluid. The working fluid is heated in the second heat exchanger 3 and flows down to the first heat exchanger 2 located at a substantial depth where it heats the surrounding sea water. This sea water flows up through the pipe 7, forming gas bubbles that then are separated from the sea water in a way similar to that described in connection with figures 1 and 2.

[0066] The second heat exchanger 3 is the condenser of a two phase heat transfer circuit located close to the sea surface S and includes evaporator 25, compressor 26, throttle 27 and piping 28 and operates in a similar way as the heat transfer system described in connection with fig.3. The second heat exchanger 3 therefore will have a temperature that is higher than the sea water at the sea surface so that the heating capacity of the second heat exchanger 3 is correspondingly increased when compared to the example of fig. 4. Fig. 6 illustrates an example of the invention, in which there is provided a plurality of two- phase heat transfer circuits lb-ld for heating the sea water in a common pipe 7. The condenser 2d of the lowermost circuit Id heats the sea water closed to the lower end opening 9 of the pipe 7. The condenser lb of the uppermost circuit heats the sea water closed to the upper end of the pipe 7. At least the lowermost condenser 2d may alternatively be located below the lower end opening 9 of the pipe 7. The compressors 4b- 4d in the circuits may alternatively all be located close to the sea surface S and be connected to the respective circuit lb-ld in a manner similar to that depicted with broken lines in fig. 3

[0067] Fig 7 illustrates an example of the invention, where the first heat exchanger 2 is located in the upper part of the first pipe 7. As the first heat exchanger 2 heats the sea water in the upper part of the first pipe 7 so that it rises, cold sea water from the deep will be sucked up from the lower opening 9.

[0068] Fig. 8 illustrates an example of the invention where the first heat exchanger is vertically arranged and continuously heats the sea water raising up within the first pipe 7.

Claims

CLAIMS1. A method for capturing carbon dioxide and / or methane from an upstream (A) of seawater, characterized by- providing a heat transfer system having a first heat exchanger (2) in the sea, a second heat exchanger (3) and piping (1) connecting the first and second heat exchangers in a closed circuit, which first heat exchanger (2) is arranged to heat the surrounding sea water, whereby an upstream (A) of sea water is created and which second heat exchanger (3) is arranged to be heated directly or indirectly by the surrounding sea water- providing a first pipe (7) around at least a central portion of said upstream (A),- connecting said upstream (A) to a gas separator (11) arranged to separate gas from the upstream (A),- ducting away the separated gas to a storage device (13).

2. A method according to claim 1, wherein the heat transfer system includes at least one two-phase heat transfer circuit with a phase-changing fluid such as ammonia as working fluid.

3. A method according to claim 2, wherein said at least one two-phase heat transfer circuit has a condenser acting as said first heat exchanger (2) and an evaporator in heat exchanging relation with the sea water.

4. A method according to claim 3, wherein said evaporator is located in the sea close to the sea surface (S) and constitutes said second heat exchanger (3).

5. A method according to any one of claims 1-4, wherein the length of said first pipe (7) is at least 20 meters, preferably at least 100 meters, and most preferably at least 500 meters.

6. A method according to claim 4, wherein a second pipe (18) is arranged around a downstream (B) of sea water that is created by said evaporator, which second pipe (18) has an upper open end (19).

7. A method according to claim 6, wherein said gas separator (11) has an outlet conduit (23) for water, from which the gases have been separated, which outlet conduit (23) ends close to the second heat exchanger (3).

8. A method according to any one of claims 1-7, wherein a turbine (22) is provided in said first pipe (7), which turbine (22) is connected to an electric generator.

9. A device for capturing carbon dioxide and / or methane from an upstream (A) of sea water, which device is provided with positioning means (14, 15, 16, 17) for arranging the device atleast partly in the sea, such as floating means and / or anchoring means, characterized in that the device includes- a heat transfer system having a first heat exchanger (2) in the sea, a second heat exchanger (3) and piping (1) connecting the first and second heat exchangers, which first heat exchanger (2) is arranged to heat the surrounding sea water, whereby an upstream (A) of sea water is created and which second heat exchanger (3) is arranged to be heated directly or indirectly by the surrounding sea water,- a first pipe (7) arranged around at least a central part of said upstream (A) of sea water,- a gas separator (11) connected to said upstream (A) of sea water, which gas separator (11) is arranged to separate gas from said upstream (A) of sea water, and- a conduit (12) arranged to duct away the separated gas to a storage device (13).

10. A device according to claim 9, which device further includes means arranged for performing the method according to any one of claims 2-8.

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