Direct air capture apparatuses and methods of operating direct air capture apparatuses

Abstract

The present invention relates to a method of operating a CO2 separation device (100; 200), particularly a direct air capture device (100; 200), comprising a desorption step of desorbing CO2 from an adsorbent (2) present in an adsorption or desorption chamber (1), wherein the desorption step comprises: applying a negative pressure to the adsorption or desorption chamber (1), and changing the atmosphere containing CO2 and H2O in the adsorption or desorption chamber (1) such that the molar ratio of CO2 to H2O is greater than 50%.

Description

[0001] This invention relates to a method of operating a CO2 separation device, particularly a direct air capture device, and a CO2 separation device with low energy consumption, particularly a direct air capture device. Existing technology

[0002] Carbon dioxide (CO2) is a greenhouse gas that contributes to global warming. Therefore, efforts are underway worldwide to separate CO2 from the air and then convert it, for example, through synthesis into other products for other uses (such as greenhouses, CO2-containing beverages), or permanently store it in liquid or solid form, such as in underground storage facilities. Currently, there are devices capable of removing and separating CO2 from the air on an industrial scale. These devices are called direct air capture (DAC) devices and include an adsorption or desorption chamber (ADK) into which ambient air is introduced, and CO2 is selectively bound to a liquid or solid adsorbent (also called an adsorbent) through chemical or physical means, thereby removing it from the air. If the adsorbed CO2 is needed, it is desorbed from the adsorbent by heating and optionally applying negative pressure, and can then be stored or further utilized. Desorption of CO2 from the adsorbent requires high energy consumption, especially high temperatures.

[0003] Invention disclosure In contrast, the method of operating the CO2 separation device, particularly the DAC device, of the present invention and the CO2 separation device, particularly the DAC device, of the present invention are characterized by lower energy consumption, because the temperature at which CO2 is desorbed from the adsorbent can be significantly reduced by about 10 to 50 Kelvin compared to the previously disclosed temperature (100°C).

[0004] Therefore, the method of operating the CO2 separation device of the present invention includes a desorption step of desorbing CO2 from the adsorbent present in the adsorption or desorption chamber (hereinafter referred to as: ADK) of the CO2 separation device, wherein a negative pressure is applied to the ADK and the atmosphere containing CO2 and H2O in the ADK is changed so that the molar ratio of CO2 and H2O is greater than 50%.

[0005] Without adhering strictly to theory, it is assumed that CO2 binds to the adsorbent in the form of hydrated hydrogen ion carbamate (containing one molecule of CO2 and one molecule of H2O at each adsorption site). Therefore, the atmosphere composition during CO2 desorption is set at 50 mol% H2O and 50 mol% CO2. If the atmosphere composition during CO2 desorption in ADK is now changed to favor CO2 and therefore disfavor H2O, such that the molar ratio of CO2 to H2O is greater than 50 mol%, then according to the principle of least constraint, the system will deviate, causing the hydrated hydrogen ion carbamate to convert to ammonium carbamate, which contains one molecule of CO2 and no water molecules at each of two adsorption sites. Therefore, despite supplying CO2 to the system, each of the two binding sites on the adsorbent releases two molecules of water and one molecule of CO2. This process occurs solely due to the change in the partial pressure of CO2, without the need for high temperatures. Therefore, the temperature required for desorption can be significantly reduced, particularly to below 90°C, preferably only 20 to 80°C, and especially 20 to 60°C, which is about 10 to 50 Kelvin lower than the otherwise common desorption temperature of 100°C. The achieved temperature reduction depends on the negative pressure applied during desorption, which refers to the absolute pressure in the system, advantageously 50 to 200 mbar according to the invention. Further required temperatures can be achieved by introducing heat into the ADK during desorption, for example, through a heating element. Various heating devices are suitable for this purpose.

[0006] The method according to the invention offers several advantages, namely, due to the significantly reduced temperature during the desorption process: - Energy costs for operating DAC devices can be effectively reduced. - The lower temperature in ADK prevents the CO2 adsorbent from aging, especially when using amine-containing or polymer-based adsorbents. - By using a lower temperature, the required heating power can be provided from sources other than direct heating. - Heat pumps can also be used as heating elements; the smaller the temperature difference between the heat pump and the ambient temperature, the higher its efficiency.

[0007] The dependent claims illustrate preferred extensions of the invention.

[0008] The higher the molar ratio of CO2 to water, the lower the temperature that can be set in the ADK during the desorption phase. According to an advantageous extension, the atmosphere in the ADK is thus modified so that the molar ratio of CO2 to H2O is at least 80%, and more particularly at least 90%.

[0009] In order to set a favorable atmosphere during the desorption phase, the negative pressure in the preferred ADK is adjusted to be greater than or equal to 50 mbar and less than or equal to 200 mbar.

[0010] There are multiple possible methods to change the atmosphere to the desired range, which favors CO2, and these methods can all be used interchangeably or in combination.

[0011] According to a favorable extension scheme, the atmosphere is altered by supplying CO2 to ADK. As described above, this changes the molar ratio of CO2 to water in favor of CO2, thereby releasing more CO2.

[0012] When CO2 is obtained, for example, from a storage facility, it is preferable that the CO2 be supplied from outside, i.e. from outside the CO2 separation unit.

[0013] Alternatively or additionally, CO2 can also be returned from the outlet of ADK to the inlet of ADK via a gas return line. However, since the gas leaving ADK initially contains approximately equal proportions of CO2 and water, at least a portion of the water must be separated from the exhaust gas from ADK in the gas return line to change the molar ratio in favor of CO2.

[0014] According to another favorable extension scheme, the atmosphere can be changed to favor CO2 by reducing the water content in ADK.

[0015] Reducing the water content in an ADK can be advantageously achieved by contacting a gas mixture from the ADK with a second chamber comprising a dry adsorbent (e.g., an adsorbent that adsorbs moisture), a cold trap, and / or a water separator. Two or more such water-reducing devices can also be used in combination.

[0016] Furthermore, a first CO2 separation device or DAC according to the invention is described, comprising an ADK having an air inlet and an air outlet, and an exhaust gas outlet located at the ADK outlet. The CO2 separation device or DAC according to the invention also includes a supply line for supplying CO2 to the ADK and / or a return line (also called a circulation line) for returning exhaust gas from the ADK to the ADK inlet, wherein the return line includes a water separator, a cold trap, and / or a drying adsorbent to separate water from the exhaust gas. To supply external CO2 to the ADK, a CO2 storage tank can be provided, connected to the air inlet of the ADK or directly to a separate inlet of the ADK, and can be selectively opened, for example, by an actuating valve, so that CO2 can flow from the CO2 storage tank into the ADK.

[0017] In the return line, water is separated from the ADK exhaust gas through at least one of the aforementioned devices, thereby obtaining a high proportion of CO2, which can be used at least in part to change the atmosphere in the ADK to one that favors CO2.

[0018] Furthermore, a second CO2 separation device or DAC according to the invention is described, which also includes an ADK having an air inlet, an air outlet, and an exhaust gas outlet located at the ADK outlet. The second CO2 separation device or DAC according to the invention also includes a second chamber having a water separator, a cold trap, and / or a drying adsorbent, such as, in particular, an adsorbent for adsorbing moisture, which can be connected to the ADK for gas exchange during the desorption process of the DAC, for example, by opening the corresponding supply line via a valve, etc.

[0019] The two CO2 separation devices or DAC devices according to the invention are configured to alter the atmosphere containing CO2 and H2O in the ADK such that the molar ratio of CO2 to H2O in the atmosphere is greater than 50%. Therefore, in these two DAC devices, the desorption of CO2 from the adsorbent present in the ADK can occur at temperatures below normal (100°C). This also brings the following additional advantages to the DAC devices: - Energy costs for operating DAC devices can be effectively reduced. - The lower temperature in ADK prevents the CO2 adsorbent from aging, especially when using amine-containing or polymer-based adsorbents. - By using a lower temperature, the required heating power can be provided from sources other than direct heating. - Heat pumps can also be used as heating elements, and their advantage is that the smaller the temperature difference with the ambient temperature, the higher their efficiency.

[0020] In order to optionally achieve a temperature above room temperature during the desorption phase, the DAC device according to the invention may include, for example, a heating element, or more generally, various types of heating devices.

[0021] The advantages, beneficial effects, and extensions of the method of this invention are also applicable to the DAC device of this invention. Brief description of the attached diagram The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The drawings show: Figure 1 According to the DAC device of the first embodiment, and Figure 2 The DAC device according to the second implementation scheme.

[0023] Embodiments of the present invention The figures only show the basic elements, components, and parts of the DAC device of the present invention. For clarity, all other elements, components, and parts have been omitted. Preferably, all identical parts, elements, and / or units use the same reference numerals in all figures.

[0024] Figure 1This is a schematic diagram of a DAC device 100 according to a first embodiment. Specifically, the DAC device 100 includes an ADK1 containing an adsorbent 2 configured to reversibly bind (adsorb or absorb) CO2 in the air. The ADK1 includes an air inlet 3, a (residual) air outlet 4, and an exhaust outlet 5. Each inlet and outlet may be equipped with a valve to control the inlet and outlet of each component over time.

[0025] A heat exchanger 7 is present at the exhaust gas outlet, which acts as a water separator to remove water from the exhaust gas, leaving CO2, which can be temporarily stored, for example, in a storage tank 8.

[0026] During the adsorption process, air is pumped by pump 6 and introduced into ADK 1 via air supply line 12 through air inlet 3. Exhaust outlet 5 is closed. In ADK 1, adsorbent 2 removes CO2 and optional water from the air, and the remaining air with reduced or no CO2 content leaves ADK 1 through air outlet 4.

[0027] During desorption, air inlet 3 and air outlet 4 are closed. A negative pressure is applied to ADK 1, and optionally, the temperature is also increased (heating element not shown). The exhaust gas exiting ADK 1 is then supplied to heat exchanger 7 or, alternatively, to water separator after passing through exhaust outlet 5, so that water from the exhaust gas condenses and is discharged from the system. Remaining CO2 can be introduced into ADK 1 directly through another inlet 11 via storage tank 8 and pump 10 via return line 9, or via air supply line 12, where the valve at air inlet 3 is open at this time.

[0028] Alternatively or concurrently, CO2 can also be supplied to ADK 1 from an external source. In this case, the return line 9 can be omitted. In this scenario, another CO2 storage tank 8a is provided, which can be closed by a valve and connected to another inlet 11 or air supply line 12 of ADK 1 via an external CO2 supply line 9a, thereby allowing CO2 to be introduced into the system from an external source.

[0029] The purpose of the two aforementioned alternatives, namely external CO2 supply 9a and CO2 supply via return line 9, is to change the atmosphere inside ADK1 containing CO2 and H2O to one that favors CO2, thereby making the molar ratio of CO2 to H2O greater than 50%.

[0030] Based on the principle of minimum constraint, this ensures that more CO2 is released from the adsorbent than is expected at the set temperature without further increasing the temperature. According to the invention, the temperature required to release a corresponding amount of CO2 from the adsorbent 2 by operating the DAC device 100 of the invention is approximately 10 to 50 Kelvin lower than that of a DAC device operating at a conventional desorption temperature (100°C), resulting in significantly lower energy costs for desorption in the DAC device 100 of the invention, and also reducing wear on the adsorbent 2.

[0031] Figure 2 A schematic diagram of a DAC device 200 according to a second embodiment is shown. In this embodiment, neither the return line 9 nor the external CO2 supply line 9a is provided. However, these lines can be used in combination.

[0032] DAC device 200 includes a second chamber 13 with a water separator, a cold trap, and / or a drying adsorbent, such as adsorbent 14, particularly for adsorbing moisture. During desorption, air inlet 3 and air outlet 4 are closed again by valves. To this end, supply line 15 to the second chamber 13 and discharge line 16 from the second chamber 13 to ADK 1 are opened, thereby creating additional volume through the opening of the second chamber 13 from which moisture is removed. Thus, the atmosphere in ADK 1 and the second chamber 13 of the entire system is changed to favor CO2, resulting in the same advantages as DAC device 100: the temperature required to release a corresponding amount of CO2 from the adsorbent 2 by operating the DAC device 200 of the present invention is about 10 to 50 Kelvin lower than that of DAC devices operating at conventional desorption temperatures (100°C), resulting in significantly lower energy costs for desorption in the DAC device 200 of the present invention, and also reducing wear on the adsorbent 2.

Claims

1. A method for operating a CO2 separation device (100, 200), particularly a direct air capture device (100; 200), comprising a desorption step of desorbing CO2 from an adsorbent (2) present in an adsorption or desorption chamber (1), wherein the desorption step comprises: - Apply negative pressure to the adsorption or desorption chamber (1), - Change the atmosphere containing CO2 and H2O in the adsorption or desorption chamber (1) so that the molar ratio of CO2 and H2O is greater than 50%.

2. The method according to claim 1, wherein the atmosphere in the adsorption or desorption chamber (1) is changed such that the molar ratio of CO2 to H2O is at least 80%, especially at least 90%.

3. The method according to claim 1 or 2, wherein the negative pressure is or is set to be greater than or equal to 50 mbar and less than or equal to 200 mbar.

4. The method according to any one of the preceding claims, wherein the atmosphere is altered by supplying CO2 to the adsorption or desorption chamber (1).

5. The method of claim 4, wherein the CO2 is supplied externally.

6. The method according to claim 4 or 5, wherein CO2 is returned from the exhaust gas outlet (5) of the adsorption or desorption chamber (1) to the inlet (3, 11) of the adsorption or desorption chamber (1) via a return line (9), wherein at least a portion of the water contained in the exhaust gas of the adsorption or desorption chamber (1) is separated from the exhaust gas in the adsorption or desorption chamber (1) in the return line (9).

7. The method according to any one of claims 1 to 3, wherein the atmosphere is altered by reducing the water content in the adsorption or desorption chamber (1).

8. The method of claim 7, wherein the water content is reduced by contacting the gas mixture from the adsorption or desorption chamber (1) with a second chamber (13) comprising a dry adsorbent, a cold trap and / or a water separator (14).

9. A CO2 separation device (100), particularly a direct air capture device (100), comprising an adsorption or desorption chamber (1) having an air inlet (3), an air outlet (4), and an exhaust gas outlet (5) located at the outlet of the adsorption or desorption chamber (1), the CO2 separation device (100) further comprising: - Supply line (11) for supplying CO2 to the adsorption or desorption chamber (1) or - A return line (9) for returning the exhaust gas from the adsorption or desorption chamber (1) to the inlet (11) of the adsorption or desorption chamber (1), wherein the return line (9) includes a water separator, a cold trap and / or a dry adsorbent (7).

10. A CO2 separation device (200), particularly a direct air capture device (200), comprising an adsorption or desorption chamber (1) having an air inlet (3), an air outlet (4), and an exhaust gas outlet (5) located at the outlet of the adsorption or desorption chamber (1), the CO2 separation device (200) further comprising: - A second chamber (13) having a water separator, a cold trap and / or a dry adsorbent (14), which can be connected to the adsorption or desorption chamber (1) for gas exchange during the desorption process of the CO2 separation device (200).

Images