Method for separating co2 from the atmosphere, and separation device, in particular for carrying out the method

Abstract

The invention relates to a method for separating CO2 from the atmosphere, in which an adsorption step (A) and a desorption step (D) following the adsorption step are carried out, wherein in the adsorption step air is applied to an adsorbent (1), wherein a portion of the CO2 contained in the air is adsorbed by the adsorbent (1), and wherein in the desorption step (D) the adsorbent (1) loaded with CO2 is acted upon by a heating medium (3) and heated, wherein adsorbed CO2 is thermally expelled, and wherein thereafter the adsorbent (1) is acted upon by a cooling medium (5) and prepared for a repeated adsorption step (A). The invention further relates to a separation device (9) for separating CO2 from the atmosphere, comprising a desorption chamber (11) through which a working medium can flow and also a DAC system comprising a separation device (9).

Description

[0001] Description

[0002] Process for separating CO2 from the atmosphere and separation device, in particular for carrying out the process

[0003] The invention relates to a method for separating CO2 from the atmosphere. The invention further relates to a separation device which is particularly designed to carry out the method.

[0004] The combustion of fossil fuels currently meets around 80% of global energy needs. These combustion and other industrial production processes emitted approximately 38,017 million tons of carbon dioxide (CO2) into the atmosphere worldwide in 2019. In addition to fossil energy generation, the production and conversion of industrial raw materials, accounting for 9.2% of total emissions, makes a significant contribution to the continuous rise in CO2 concentrations in the atmosphere. The debate about the negative impacts of the greenhouse gas CO2 on the climate has led to consideration of recycling CO2. From a thermodynamic perspective, CO2 is very low and therefore difficult to reduce to usable products.

[0005] One important application is the capture of carbon dioxide (CO2) from gas streams, e.g., flue gases, exhaust gases, industrial waste gases, or atmospheric air. Direct air capture (DAC) is one of several means of mitigating anthropogenic greenhouse gas emissions and, as a non-fossil, location-independent source of CO2, offers attractive economic prospects for the raw materials market and for the production of synthetic fuels.

[0006] A special approach for direct air capture is based on a cyclic adsorption and desorption process, for example, on solid, chemically functionalized sorption materials. For example, WO 2016 / 005226 A1 and WO 2017 / 009241 A1 disclose processes based on cyclic adsorption and desorption using steam or a suitable amine-functionalized sorption material to extract carbon dioxide from the ambient atmospheric air. Furthermore, WO 2019 / 092127 A1 describes another class of sorption materials based on potassium carbonate functionalization. This class of materials is also suitable for cyclic CO2 adsorption and desorption processes.

[0007] The adsorption process normally takes place under atmospheric ambient conditions, where air flows through the sorbent material and a portion of the CO2 contained in the air is chemically and / or physically bound or adsorbed on the surface or in the adsorbents. During the subsequent CO2 desorption, the adsorption material is normally heated, and optionally the partial pressure of carbon dioxide surrounding the sorbent can be reduced by additionally applying a vacuum or by expelling the sorbent from the structure in a purge gas stream, e.g. including steam. In this process, the previously separated carbon dioxide is removed from the sorbent and can be recovered in concentrated form.

[0008] One of the greatest challenges for the energy- and cost-efficient implementation of direct air capture arises from the low CO2 concentration in atmospheric air, which is nominally approximately 400 ppm as of 2019, and the transfer of the correspondingly large quantities of atmospheric air to a suitable gas separation structure, as well as efficient cyclic adsorption and desorption processes. In the course of the desired industrial application, the service life and long-term stability of the adsorbent material for the adsorption and desorption of atmospheric CO2 for the highest possible number of cycles are increasingly being considered, also from an economic perspective.

[0009] Against this background, the object of the invention is to provide an improved process for separating CO2 from the atmosphere, with which increased stability of the adsorbent can be achieved. A further object of the invention is to provide a correspondingly improved separation device for separating CO2 from the atmosphere.

[0010] The object directed to a process is achieved according to the invention by a process for separating CO2 from the atmosphere, in which an adsorption step and a two-stage desorption step following the adsorption step are carried out, wherein in the adsorption step an adsorbent is exposed to air, wherein a part of the CO2 contained in the air is adsorbed by the adsorbent, and wherein in the desorption step the adsorbent loaded with CO2 is exposed to a heating medium and heated in a first desorption step, wherein adsorbed CO2 is thermally expelled, and wherein thereafter in a second desorption step the adsorbent is exposed to a cooling medium different from the heating medium and is prepared for a new adsorption step.

[0011] The invention is based on the knowledge that DAC (Direct Air Capture) is a new technology that enables the removal of CO2 from the atmosphere. However, the technology is currently still in a phase of increasing development and industrialization. The most advanced technology is based on processes for the selective absorption of CO2 on specially developed adsorbents. The extraction and separation of pure CO2 takes place in the subsequent desorption process. In this process, the adsorbent is first freed from ambient air by evacuation in a closed system. In a second step, the adsorbent is heated to approx. 100 °C and under reduced pressure CO2 is released and can be sucked off from a sorption apparatus.A significant disadvantage of the processes known to date is that the adsorbent, which is usually chemically pretreated with an amine-based component, is sensitive to oxygen at elevated temperatures and thus a rapid degradation of the adsorbent is observed when the adsorbent is exposed again uncooled to the air stream for the next adsorption step after the desorption step.

[0012] The invention has recognized that efficient, effective, and controllable cooling is required here, which also reliably avoids or reduces damaging oxygen exposure of the adsorbent. The proposed method of the invention is therefore particularly suitable for the selective separation or capture of CO2 from the ambient air under atmospheric pressure conditions, wherein the adsorbent is successively exposed to two media in the desorption step. This type of treatment of the adsorbent advantageously leads to a service life-extending treatment and promotes multiple cyclical use of the adsorbent for the adsorption of CO2 in a DAC system.The proposed process of desorption and treatment in at least two successive partial steps with a respective heating medium and a respective cooling medium achieves a significantly longer stability and thus a longer usability (service life) for the adsorbent, which is particularly sensitive to oxygen input.

[0013] The process is carried out in two stages in the desorption step, with a discharge phase using the heating medium and a subsequent regeneration phase using the cooling medium. In the first desorption step, the CO2 is largely – although generally only almost completely – expelled from the adsorbent by the heating medium, and the adsorbent is heated to, for example, 100 °C. The subsequent application of the cooling medium in the second desorption step brings about a further advantage in the desorption step, in addition to the advantageous cooling effect for the sensitive adsorbent. In particular, any residues of condensed heating medium still adhering to the surface of the adsorbent as a result of the first desorption step are efficiently and completely expelled from the structure by the application of the cooling medium.The disadvantageous and therefore sometimes incomplete removal of CO2 from the adsorbent is improved by the two-stage desorption step. This type of processing and surface preparation also results in increased separation rates (coating) and cleaning of the adsorbent and more effective use of the available adsorbent surface. In addition to the cooling effect and the regeneration of the adsorbent by flushing with the cooling medium, any heating medium condensed on surface areas of the adsorbent is also effectively expelled and removed. Thus, not only is the CO2 discharged from the adsorbent, but the adsorbent is also processed and prepared for the next adsorption step. The flow of the cooling medium through the adsorbent in the second desorption step, for example cooled nitrogen, leads to a particularly uniform and extensive cooling of the adsorbent.A cooling medium different from the heating medium and not saturated with water is used. Because the cooling medium flow is not saturated with water, the water that has not evaporated during the previous application of the heating medium can be completely removed from the desorption chamber and reused.

[0014] This reduces adsorbent degradation compared to conventional processes, and a significantly higher number of cycles is achieved with virtually unchanged storage efficiency. Thus, cyclic adsorption and desorption processes with a large number of cycles are possible, regardless of the technical design and handling of a chamber or module containing the adsorbent. The process can be flexibly applied to various designs of cyclic adsorption and desorption devices and state-of-the-art DAC container solutions.

[0015] In a preferred embodiment of the process, the supply of heating medium is interrupted in the desorption step and switched to the supply of the cooling medium.

[0016] By switching from the heating medium to the cooling medium, the two sub-steps in the desorption process are carried out as separate sub-steps. This is achieved by converting or switching from the heating medium to the cooling medium when applying the adsorbent. The change of medium during adsorbent flushing results in the desorption step being divided into independent sub-steps. This process leads to advantages in the degradation behavior of the adsorbent.

[0017] In a preferred embodiment of the process, the adsorbent is exposed to the cooling medium so that the adsorbent is cooled and dried.

[0018] Thus, in addition to cooling and corresponding inerting against harmful oxygen exposure at high temperatures, the cooling medium also dries the adsorbent, making effective use of the surface for adsorption possible. Furthermore, the service life of the adsorbent is extended. It has been found that the use of the cooling medium results in effective evaporation of residues of condensed heating medium on the surface of the adsorbent. This maintains the capacity of the adsorbent, and it is regenerated with almost no loss in each cycle. This makes it possible to achieve particularly advantageous and sustainable processing of the adsorbent in each cycle from both a technical and economic perspective. In a particularly preferred embodiment of the process, the cooling medium is extracted from the adsorbent and cooled to a cooling temperature.

[0019] The adsorbent is exposed to the cooling medium by flushing the adsorbent, whereby the cooling medium is passed over the adsorbing surfaces of the adsorbent and through channel structures of the adsorbent and extracted by suction. A pressure difference is set as the suction pressure across the adsorbent from the inlet line to an outlet line on the outlet side and is maintained for the purification process. For example, a pump or compressor can be used on the outlet side and the coolant can be sucked in to carry out the flushing process with the cooling medium. The cooling medium absorbs the heat of the adsorbent and heats up. After the flushing process, the cooling medium is cooled to a cooling temperature of, for example, 10 °C - 20 °C.

[0020] Preferably, the cooling medium is guided in a cooling circuit, with fresh cooling medium being supplied to the cooling circuit as required.

[0021] The cooling medium is advantageously almost never consumed thanks to cyclical reuse and treatment. Nevertheless, it is advisable to maintain a reservoir or storage facility with a cooling medium so that, if necessary, any loss of cooling medium during repeated cyclical execution of the process can be withdrawn and fed back into the cooling circuit, thus refreshing it. This also ensures the long-term quality of the cooling medium. In the event of maintenance, a complete change and thus replacement of the cooling medium can be carried out.

[0022] In a particularly preferred embodiment of the process, a cooling medium different from the heating medium is used in the desorption step. This facilitates the implementation of the switching process from the heating medium to the cooling medium and leads to greater efficiency in the purification of the adsorbent. Thus, a respective adapted medium can be used as the heating medium and as the cooling medium in the sub-steps. Furthermore, the adapted selection of two media in the desorption step facilitates the cyclical operation of the adsorption step and the multi-stage desorption step. In principle, it is also conceivable to carry out the additional cooling step under vacuum using "cold" steam as the cooling medium, so that a cooling medium different from the heating medium is also provided for carrying out the desorption step.

[0023] In a further preferred embodiment of the method, in the desorption step, before the adsorbent loaded with CO2 is exposed to the heating medium, the adsorbent is subjected to a negative pressure, wherein the air surrounding the adsorbent is pumped out.

[0024] The environment of the CO2-laden adsorbent is thus advantageously first freed of as much oxygen as possible before the actual desorption begins. Pumping out the ambient air around the adsorbent prepares for the actual desorption and prevents exposure of the adsorbent to damaging oxygen during heating with the heating medium. It is important and advantageous to avoid oxidative degradation of the adsorbent, especially in this preparatory step. At the same time, a high CCU purity of the CO2 thermally expelled together with the heating medium is achieved.

[0025] In the process, an inert purge gas, in particular pure nitrogen, is preferably used as the cooling medium, wherein the inert purge gas is brought to the cooling temperature and fed to the adsorbent. Nitrogen is readily available as an inert gas and can be used particularly advantageously for purging the adsorbent. The nitrogen can be provided in a nitrogen tank or in gas cylinders. Alternatively, the nitrogen can also be obtained "in situ" from an air separation process, if required, and used as the cooling medium for the process.

[0026] In the process, water in the form of low-pressure steam is preferably fed to the adsorbent as the heating medium.

[0027] The low-pressure steam can be extracted from a steam generator or a steam reservoir. This provides hot steam as a heating medium, which is used to expel the CO2 from the loaded adsorbent.

[0028] The use of low-pressure steam as the heating medium and pure cool nitrogen as the cooling medium in a two-stage, separate desorption process results in numerous advantages over conventional solutions. This allows the DAC process to be carried out in a particularly advantageous and simple manner. The problem of oxidative adsorbent degradation, which has long been known in the state of the art, can be countered very effectively and simply, as the cooling efficiency is increased and oxygen exposure at excessively high adsorbent temperatures is prevented.

[0029] For example, the approaches known to date include a cooling step in the desorption step. This cooling step takes advantage of the fact that, in order to heat the adsorbent, low-pressure steam is introduced directly into the desorption chamber containing the loaded adsorbent. This creates condensate, which also precipitates on the surface of the adsorbent. A further significant reduction in the pressure in the desorption chamber causes this condensate to evaporate, thereby cooling the adsorbent. A disadvantage of this procedure, however, is that in the event of even minor leaks, ambient air flows into the desorption chamber and again supplies damaging oxygen. This does not, however, adequately prevent degradation of the adsorbent by oxygen.

[0030] In a particularly preferred embodiment of the process, water is condensed out of the CO2 expelled with the low-pressure steam, whereby desorbed CO2 is obtained in concentrated form.

[0031] The phase separation of CO2 dissolved in water enables further efficient and particularly economical water use in a cycle, while at the same time achieving a high separation rate of pure and concentrated CO2. By cooling, for example, the water can be condensed out of the low-pressure steam used as a heating medium, thus separating the mixture of water and desorbed and at least partially dissolved CO2. In addition, the CO2 can be further processed, in particular dried and stored or transported away. This process has considerable advantages, particularly over known solutions. In these cases, the amount of condensed water that can evaporate as condensate on the surface of the adsorbent, and thus the actual cooling capacity, is limited and cannot be influenced or controlled.The cooling performance of these DAC systems depends solely on the amount and location of the condensate on the surface of the absorbent. These disadvantages are overcome by the cooling principle of the invention.

[0032] The cooling principle of the invention with the two-stage desorption step makes it possible to almost completely evaporate condensate adhering to the adsorbent and thus, for example, to subject it to economically interesting recycling. In contrast, with the known cooling principles with residual condensate wetted adsorbent was only dried by the ambient air stream in the subsequent adsorption step. This means that this technology results in considerable water consumption and is therefore very disadvantageous for use in water-scarce regions or rather, its use there is practically impossible. The invention also enables a DAC system to be operated in water-scarce regions where cheap renewable energy in the form of solar energy is often available for the operation of a DAC system.In addition, known processes propose an additional evacuation step following desorption to initiate evaporation of the condensate and cool the adsorbent as much as possible before it is re-exposed to the ambient air. If evaporation and cooling were carried out using only air, the 100 °C hot adsorbent would come into contact with oxygen from the ambient air in a correspondingly high concentration, which would lead to rapid degradation of the adsorbent.

[0033] The object directed to a separation device is achieved according to the invention by a separation device for separating CO2 from the atmosphere, comprising a desorption chamber through which a working medium can flow and into which an adsorbent can be introduced, wherein a feed line for the working medium is connected to the desorption chamber on the inlet side and a discharge line on the outlet side, wherein a first switching device is connected upstream of the feed line and a second switching device is connected downstream of the discharge line, so that during desorption operation in a desorption step it is possible to switch from supplying the absorbent with a heating medium to supplying the absorbent with a cooling medium as the working medium.

[0034] The separation device of the invention proposes a device for a DAC plant which is particularly upgraded and suitable for carrying out the method according to the invention for separating CO2 from the atmosphere. This is made possible by an advantageous combination of a first switching device and a second switching device. A first switching device is connected upstream of the desorption chamber and a second switching device is connected downstream of the desorption chamber. Thus, depending on the switching state, the desorption chamber with the absorbent can be supplied with and flowed through either a heating medium or a cooling medium. Separate flow paths for the heating medium and the cooling medium open into the first switching device on the inlet side. Accordingly, separate flow paths for the heating medium and the cooling medium branch off from the second switching device on the outlet side.In this way, the separation device is designed such that the desorption step of a CO2-laden adsorbent in the desorption chamber can be carried out in two stages or in two partial steps, with different working media being able to be supplied separately. Thus, efficient and almost complete desorption of CO2 can be achieved during operation, with degradation of the adsorbent due to oxygen exposure being avoided by the particularly effective cooling. Furthermore, thanks to the switching devices, the separation device is particularly advantageously configured and usable for cyclic operation.

[0035] The separation device can be used in a DAC system, and can be connected or integrated into it, regardless of the specific design and handling of the adsorbent, e.g., an adsorbent module. The separation device can thus be operated flexibly in a DAC system with both movable and fixed adsorbent modules with corresponding movable flaps for the supply air. Only one supply line and one outlet line are required to connect to the desorption chamber, so that the respective working medium can be optionally supplied to the desorption chamber with the adsorbent.

[0036] In a preferred embodiment, a heating line for the heating medium and a cooling line for the cooling medium are connected to the first switching device on the inlet side of the separation device. Separate feed connections for the working media are thus provided in the first switching device, so that the heating medium and the cooling medium can be fed separately, i.e. via a respective line, on the inlet side of the first switching device. At the same time, in a switching state when one of the working media is fed in, the same feed line and the same discharge line of the desorption chamber can be used. This makes the separation device particularly cost-effective.

[0037] In a further preferred embodiment of the separation device, a heating line is connected to the output side of the second switching device, into which a separating device is connected, which is designed such that a mixture of heating medium and desorbed CO2 can be extracted from the desorption chamber and the CO2 can be separated from the heating medium.

[0038] Depending on the properties of the mixture, the separation device can be functionally designed as a phase separation device or as a substance separation device.

[0039] In this way, during heating operation, the mixture can be expelled from the desorption chamber and removed by flowing through the adsorption chamber via the heating line. At the same time, a substance or phase separation can be achieved in the mixture by spatially separating the heating medium and the expelled CO2. This enables the recovery and further use of the separated CO2 in a very pure form, as well as the reuse of the heating medium.

[0040] In a particularly preferred embodiment of the separation device, a cooling line is connected to the output side of the second switching device, into which cooling line a separating device is connected which is designed such that a mixture comprising the cooling medium and heating medium can be extracted from the desorption chamber and the heating medium can be separated from the cooling medium. This advantageously allows residues of condensed heating medium to be expelled from the desorption chamber when the absorbent is exposed to the cooling medium, so that the condensate can be completely removed and particularly effective cooling can be achieved by additional evaporative cooling of the absorbent. In addition, any residual amounts of CO2 can be expelled with the cooling medium, so that complete CCt discharge and very effective cooling of the adsorbent can be achieved.Through this treatment in the desorption chamber, the adsorbent is reprocessed to a high quality for further loading, i.e., it is freed of CO2 and cooled. A multitude of adsorption and desorption cycles with minimal degradation due to damaging oxygen exposure are possible with this separation device.

[0041] This design further ensures that both a cooling line and a heating line branch off and can be switched to at the second switching device. This implements separate line paths on the output side of the switching device, and a specifically different process-engineered treatment of the respective working medium is provided depending on the switching state of the switching device. The heating medium and the cooling medium can be guided in a targeted manner via separate line paths, each of which has a separating device designed specifically for the respective medium.

[0042] In a particularly preferred embodiment of the separation device, the respective separation device has a separating container in the cooling line and in the heating line, so that a phase separation of the liquid phase and the gaseous phase can be brought about.

[0043] A separation tank can be designed as a condensate separator which has a connection for the working medium on the inlet side. The heating line or the cooling line is connected to the inlet side connection. The phase separation takes place through gravity and the density differences of the mixtures, so that the liquid phase accumulates at the bottom and the gaseous phase at the top of the separation tank and can be tapped off for further use. This ensures that gaseous CO2 desorbed in the heating line by the separation tank is separated from the heating medium, for example water. A cooler or condenser can be connected beforehand in the heating line so that the phase mixture of heating medium and CO2 is first cooled before phase separation.Furthermore, the separator vessel in the cooling line separates the cooling medium from the heating medium, for example water. When an inert gas is used as the cooling medium, for example pure nitrogen, a gas-liquid phase separation is also provided in the condensate separator. When an inert gas is used, a gas cooler can also be installed upstream of the separator vessel in the cooling line so that the phase mixture of cooling medium, for example nitrogen, and the heating medium is first cooled before phase separation. Residues of desorbed gaseous CO2 can also be expelled via the cooling line, resulting in a gas mixture of the gaseous inert cooling medium and portions of CO2.The CCp content in the cooling medium will, during cyclic operation in a circuit of the cooling medium, adjust itself to a constant low value corresponding to the partial pressure in an almost stationary manner.

[0044] In a particularly preferred embodiment of the separation device, upon activation of the first switching device and the second switching device for supplying the desorption chamber with the cooling medium as a working medium, a cooling circuit for the cooling medium is formed.

[0045] It is practical and particularly economically advantageous to conduct the cooling medium flow in a closed cooling circuit during its activation. Thus, when nitrogen is used as the inert gas and cooling medium, a closed nitrogen circuit can be provided. A cooling medium supply via a connection in the cooling circuit is advantageously provided as needed.

[0046] In the separation device, the first switching device and the second switching device each have a controllable 3-way valve.

[0047] Switchable and electrically controlled 3-way valves allow the desired flow paths to be automatically opened during a switching process for the heating medium and the cooling medium. This allows for reliable cyclical application of an adsorption step followed by a two-stage desorption step, with the heating medium being applied to the desorption chamber and the cooling medium being applied thereafter.

[0048] The separation device preferably has a steam container so that water in the form of low-pressure steam can be fed into the desorption chamber via the feed line as the heating medium.

[0049] The low-pressure steam can be provided as needed in the steam tank itself by heating water. The heating can be achieved electrically, for example, via a heating element. It is also possible to generate and provide low-pressure steam from solar thermal heating, for example, in conjunction with a DAC system and a CSP (Concentrated Solar Power) system, and store it in the steam tank or extract it from the solar thermal system in a controlled manner as needed.

[0050] The separation device preferably includes a gas container for an inert purge gas, so that an inert purge gas is provided as the cooling medium, with which the desorption chamber containing the absorbent can be purged and cooled. It is advisable to store the inert purge gas, for example, by providing a gas container for nitrogen. It is also possible to simply provide a container of gas cylinders or to keep a container with liquid nitrogen from a connected air separation plant, from which gaseous nitrogen is obtained and removed as inert purge gas.

[0051] In a particularly preferred embodiment, the separation device can be used in a system for separating CO2 from the atmosphere. Such a system can be designed as a DAC system and has a separation device.

[0052] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the single figures can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0053] Examples of the invention are explained in more detail with reference to the accompanying drawings. These show schematically and in a highly simplified manner the

[0054] FIG 1 shows a DAC system with a separation device according to the invention;

[0055] FIG 2 shows a block diagram of a simplified process sequence for the separation of CO2 from the atmosphere with a two-stage desorption step according to the invention.

[0056] FIG 1 shows a simplified representation of a section of a direct air capture system, or “DAC system” for short, for the selective separation of carbon dioxide CO2 from the ambient air. For this purpose, the DAC system has a separation device 9. The separation device 9 comprises a desorption chamber 11 into which an adsorbent module 41 is introduced. The adsorbent module 41 has an adsorbent 1. The adsorbent 1 is a material that can selectively adsorb CO2 from the ambient air. The adsorbent 1 can be introduced into the adsorbent module 41 as a fine-granular bed or in another structure, so that the largest possible effective adsorbent surface is provided for the adsorption or absorption of CO2. It is also possible that the adsorbent 1 is designed in channel structures, honeycomb structures or other porous structures.The desorption chamber 11 has closure elements 45 and a sealing system 43 so that an adsorbent 1 loaded with CO2 can be carried out in the desorption process under conditions hermetically sealed and separated from the ambient air in the desorption chamber 11.

[0057] A supply line 13 is connected to the inlet side of the desorption chamber 11, and a discharge line 15 for a respective working medium with which the adsorbent 1 can be charged is connected to the outlet side. For this purpose, a respective working medium flows through the desorption chamber 11 with the adsorbent module 41. A first switching device 17a is connected to the supply line 13, and a second switching device 17b is connected to the discharge line 15, so that switching operation and thus charging of the adsorbent 1 with different working media is possible. This is achieved in that a heating line 19a is connected to the inlet side of the first switching device 17a, via which heating line a heating medium 3 can be supplied to the desorption chamber 11. Furthermore, a cooling line 21a is connected to the first switching device 17a. If required, a cooling medium 5 can be supplied to the desorption chamber 11 via the cooling line 21a.To separate the line paths and for further process-related and specific treatment of the heating medium 3 and the cooling medium 5, corresponding heating lines 19b and a cooling line 21b branch off at the output side of the second switching device 17b. The heating line 19b connects to a separating device 23 and the cooling line to a separating device 25. The separating device 23 on the heating line 19b has a vacuum pump 33, a cooler or condenser 37 and a separating tank 27. The separating device 25 on the cooling line 21b has a blower or compressor 45, to which a gas cooler 39 and a separating tank 27 are connected in the flow direction of the cooling medium 5. The compressor 35 is connected in the cooling line 21b in such a way that its suction side is connected to the outlet of the second switching device 17b.The vacuum pump 33 is connected with its suction side into the heating line 19b and connects accordingly to the second switching valve 17b. The first switching device 17a and the second switching device 17b each have a controllable 3-way valve, so that when carrying out a desorption process in the desorption chamber 11, a targeted and selective switching can be carried out to a respective working medium that is applied to the adsorbent 1.

[0058] For desorption operation, low-pressure steam S is provided as heating medium 3 from a steam vessel 19. An inert gas, in this case cooled gaseous nitrogen N2, is provided as cooling medium 5. The nitrogen N2 can be stored in a gas vessel 31 and withdrawn therefrom as needed. Thus, nitrogen N2 can be replenished as fresh cooling medium 5a in order to compensate for any operational loss of cooling medium 5. When acted upon by the coolant 5, the coolant 5 is guided in a closed cooling circuit 7.

[0059] The process for separating CO2 from the ambient air is illustrated in FIG 2 in a highly simplified schematic block diagram. This involves an adsorption step A and a desorption step D following the adsorption step. In the adsorption step A, the adsorption chamber 11 is opened and the discharged adsorbent 1 is exposed to ambient air which flows through the adsorption chamber 11. Part of the CO2 contained in the air is adsorbed by the adsorbent 1, incorporated in the surface-rich structure of the adsorbent 1 and an adsorbent 1 loaded with CO2 is formed. After a saturation value has been reached and the adsorbent 1 is sufficiently loaded with CO2, the adsorption step A is ended and the exposure to ambient air is discontinued. This is done, for example, by closing the adsorption chamber 11 via movable closure elements 45 and sealing it airtight via the sealing system 43.It is also possible for the adsorbent module 41 with the loaded absorbent 1 to be moved from an exposure position to the ambient air into a position within the desorption chamber 11, and for the desorption chamber 11 to be subsequently sealed with the adsorbent module 41. This airtight closure of the desorption chamber 11 is illustrated in FIG. 2 with a closing step A1, which can also be regarded as a final step and sub-step of the adsorption step A.

[0060] Desorption can now be carried out. In the desorption step D initiated for this purpose, the adsorbent 1 laden with CO2 is first exposed to the heating medium 3 and heated in a first desorption step D1. Low-pressure steam S is used as the heating medium 3 and is fed to the desorption chamber 11. Adsorbed CO2 is thermally expelled from the adsorbent 1. In a second desorption step D2, the adsorbent 1 is then exposed to the cooling medium 5 and prepared for a new adsorption step A. Desorption takes place as a two-stage process, with pure and cooled nitrogen N2 being used as the cooling medium 5. First, in the desorption step D1, the supply of heating medium 3 is interrupted and the system switches to exposure to the cooling medium 5 - for example nitrogen N2.The adsorbent 1 is subjected to the cooling medium 5 and flowed through circumferentially, wherein the adsorbent 1 is also cooled and dried to remove any residual condensed water H2O from the first desorption step D1. The cooling efficiency is thereby significantly improved by additional utilization of the evaporative cooling of the evaporating water H2O. The cooling medium 5 is extracted from the adsorbent 1 and the adsorbent is cooled to a cooling temperature. The cooling medium 5 is fed into a cooling circuit 7, wherein nitrogen N2 can be fed to the cooling circuit 7 as fresh cooling medium 5a only when required. The desorption step D is carried out in two stages as far as the actual desorption of the CO2 is concerned. Thus, in the first desorption step D1, a heating medium 3 is used and in the second desorption step D2, a cooling medium 5 is used, wherein the heating medium 3 and the cooling medium 3 are different media.Fluids are used to achieve particularly advantageous desorption through the combination of the first desorption step D1 and the second desorption step D2 and, above all, a significantly improved cooling effect in the second desorption step D2. Degradation of the adsorbent 1 can be prevented or at least significantly reduced by comprehensive cooling and a low temperature. Oxygen exposure at a lower operating temperature in the adsorption step A is less damaging to the adsorbent 1, so that longer service lives are achieved for the adsorbent 1 and thus a large number of successive cycles consisting of an adsorption step A and a desorption step D with the sub-steps D1, D2 can be carried out.

[0061] In the desorption step D, after the closing step A1, an evacuation step E is first carried out. The evacuation step E serves to prepare the desorption chamber 11 with the loaded adsorbent 1 for the actual desorption process. In the evacuation step E, before the CO2-loaded adsorbent 1 is subjected to the heating medium 3, the adsorbent 1 is first subjected to a negative pressure. The air surrounding the adsorbent 1 in the desorption chamber 11 is pumped out. This is done by activating the vacuum pump 33 to remove the air. This is followed by the desorption step D1, in which water H2O in the form of low-pressure steam S is supplied to the adsorbent 1 as the heating medium 3, which flows through the desorption chamber 11 accordingly.The water H2O from the mixture of low-pressure steam S and expelled CO2 is condensed in the separation vessel 27, and desorbed CO2 in concentrated form is recovered and separated at the top of the separation vessel 27. After the switchover, the second desorption step D2 follows, in which the inert purge gas, in particular pure nitrogen N2, is used as the cooling medium 5. The nitrogen N2 is brought to a predetermined cooling temperature in the gas cooler 39 and fed to the adsorbent 1 via the cooling line 21a via the first switching device 17a, whereby the adsorbent 1 flows through, is cooled, and prepared for a further adsorption step A. Via the outlet line 15, the nitrogen N2 is fed through the second switching device 17b via the cooling line 21b to the separation device 25. A cooling circuit 7 is realized.

[0062] The invention proposes a two-stage desorption process. By using a suitable external cooling medium 5 in the second desorption step D2, the cooling of the adsorbent 1 becomes significantly more efficient, effective, and moreover, easier to control and reproduce. For this purpose, a separate cooling medium 5 is introduced into the desorption chamber 11 for the cooling step in the second desorption step D2. Nitrogen N2, for example, is particularly advantageous here as a gaseous inert heat transfer medium. In order to minimize nitrogen consumption, the heated nitrogen N2 is cooled again in a gas cooler 39 and can be recycled many times.Flooding and flushing the desorption chamber 11 in the second desorption step D2 with pure nitrogen N2 means that CO2 that was not completely desorbed from the loaded adsorbent 1 in the first desorption step D1 is now additionally desorbed and expelled from the desorption chamber 11 together with the inert flushing medium nitrogen N2. However, this is not problematic in that the CO2 content will only build up to a partial pressure, which means that the desorption of residual CO2 from the adsorbent 1 no longer experiences any driving force. The cooling medium 5 can therefore be guided in a cooling circuit 7 after the described build-up and CO2 saturation with a constantly low CO2 concentration.At the same time, by applying nitrogen N2 as the cooling medium 5, the condensate of water H2O remaining on the adsorbent 1 is also specifically evaporated, thus additionally contributing to the cooling effect through evaporative cooling. Since for this type of cooling the temperature of the nitrogen N2 is regulated and the duration of the desorption step D2 with the cooling step can be freely selected, a desired target temperature of the adsorbent for operation in adsorption step A and also the degree of drying of the adsorbent can be controlled. In the gas cooler 39, the water H2O evaporated by evaporative cooling is first separated again as condensate, i.e. liquid water H2O, and can thus be advantageously reused. The water H2O is not emitted and consumed with the treated media stream.

[0063] The cooling process in the second desorption step D2 is carried out at a slight overpressure compared to the atmospheric pressure of the environment. This means that there is no risk of oxygen from the ambient air flowing into the interior of the desorption chamber 11. If the adsorbent module 41 remains filled with nitrogen N2 at the end of the cooling step, this amount of nitrogen N2 gas is released into the atmosphere when the adsorbent module 41 is again pressurised and charged with ambient air. It is therefore advantageous and expedient to feed at least this amount of nitrogen N2 gas into the cooling circuit 7, for example by taking it from the gas container 31. This can be done, for example, by restoring a selected working pressure as the target pressure in the cooling circuit 7 by feeding nitrogen N2 from the gas container 31 into the cooling circuit 7 in a correspondingly controlled manner. By continuously supplying an inert purge gas, e.g.B. nitrogen N2, the cooling can be regulated and controlled according to requirements. This makes it possible to reliably cool to a necessary surface temperature of the adsorbent 1 and to ensure this surface temperature. The cooling medium 5 provided as cooling gas can be passed through the adsorbent 1 in a very evenly distributed manner via gas distributors (not shown in detail in FIG. 1), thereby avoiding very disadvantageous temperature gradients or temperature uneven distributions. This is very advantageous compared to cooling by flash evaporation in a vacuum according to the concepts known to date. With the known flash evaporation it depends on where and in what quantity condensate has precipitated. Depending on the geometry of the adsorbent module 41, the condensate will not be evenly distributed over the surface of the adsorbent 1.With the help of flash evaporation, energy is extracted from the adsorbent material through evaporation only where water (H2O) is present. Areas in the adsorbent module 41 where more water (H2O) precipitates than is required for cooling cannot contribute further to cooling, since no further energy flow can occur due to the prevailing temperatures.

[0064] The significant economic advantage results from reduced degradation of adsorbent 1 due to oxygen exposure. Due to this degradation, the adsorbent loses its storage capacity for binding CO2, so that it must either be replaced or regenerated at great expense. An extension of the service life of adsorbent 1 through the cooling concept of the invention and the separation device 9 proposed therefor, as well as the advantageous process control for the desorption step D, also reduces maintenance costs and increases the plant availability of a DAC plant.

Claims

Patent claims 1. A process for separating CO2 from the atmosphere, in which an adsorption step (A) and a two-stage desorption step (D) following the adsorption step are carried out, wherein in the adsorption step an adsorbent (1) is exposed to air, wherein a part of the CO2 contained in the air is adsorbed by the adsorbent (1), and wherein in the desorption step (D) the adsorbent (1) loaded with CO2 is exposed to a heating medium (3) and heated in a first desorption step (D1), wherein adsorbed CO2 is thermally expelled, and wherein thereafter in a second desorption step (D2) the adsorbent (1) is supplied with a cooling medium (5) different from the heating medium (3) and prepared for a new adsorption step (A).

2. The method according to claim 1, wherein in the desorption step (D) the supply of heating medium (3) is interrupted and switched to application of the cooling medium (5).

3. Method according to one of claim 2, wherein the adsorbent (1) is subjected to the cooling medium (5) so that the adsorbent (1) is cooled and dried.

4. The method according to any one of claims 1, 2 or 3, wherein the cooling medium (5) is extracted from the adsorbent (1) and cooled to a cooling temperature.

5. Method according to one of the preceding claims, in which the cooling medium (5) is guided in a cooling circuit (7), wherein fresh cooling medium (5a) is supplied to the cooling circuit (7) as required.

6. Method according to one of the preceding claims, wherein in the desorption step (D) a cooling medium (5) different from the heating medium (3) is used.

7. Method according to one of the preceding claims, wherein in the desorption step (D) before the adsorbent (1) loaded with CO2 is subjected to a negative pressure, the adsorbent (1) being subjected to a negative pressure, wherein the air surrounding the adsorbent (1) is pumped out.

8. Method according to one of the preceding claims, wherein an inert purge gas, in particular pure nitrogen (N2), is used as the cooling medium (5), wherein the inert purge gas is brought to the cooling temperature and fed to the adsorbent (1).

9. Method according to one of the preceding claims, wherein water (H20) in the form of low-pressure steam (S) is supplied to the adsorbent (1) as the heating medium (3).

10. The process according to claim 9, wherein water (H2O) is condensed from the CO2 expelled with the low-pressure steam (S), and desorbed CO2 is recovered in concentrated form.

11. Separation device (9) for separating CO2 from the atmosphere, comprising a desorption chamber (11) through which a working medium can flow and into which an adsorbent (1) can be introduced, wherein a feed line (13) for the working medium is connected to the desorption chamber (11) on the inlet side and a discharge line (15) for the working medium is connected to the outlet side, wherein a first switching device (17a) is connected upstream of the feed line (13) and a second switching device (17b) is connected downstream of the discharge line (15), so that during desorption operation in a desorption step (D) it is possible to switch from supplying the absorbent (1) with a heating medium (3) to supplying the absorbent (1) with a cooling medium (5) as the working medium.

12. Separation device (9) according to claim 11, in which a heating element is connected to the input side of the first switching device (17a). line (19a) for the heating medium (3) and a cooling line (21a) for the cooling medium (5) is connected.

13. Separation device (9) according to claim 11 or 12, wherein a heating line (19b) is connected to the output side of the second switching device (17b), into which heating line a separating device (23) is connected, which is designed such that a mixture of heating medium (3) and desorbed CO2 can be extracted from the desorption chamber (11) and the CO2 can be separated from the heating medium (5).

14. Separation device (9) according to claim 11, 12 or 13, in which the output side of the second switching device (17b) a cooling line (21b) is connected, into which a separating device (25) is connected, which is designed such that a mixture comprising cooling medium (5) and heating medium (3) can be extracted from the desorption chamber (11) and the heating medium (3) can be separated from the cooling medium (5).

15. Separation device (9) according to one of claims 13 or 14, wherein the respective separation device (23, 25) has a separating container (27) in the cooling line (21b) and in the heating line (19b), so that a phase separation of the liquid phase and the gaseous phase can be brought about.

16. Separation device (9) according to one of claims 11 to 15, wherein upon activation of the first switching device (17a) and the second switching device (17b) for supplying the desorption chamber (11) with the cooling medium (5) as a working medium, a cooling circuit (7) for the cooling medium (5) is formed.

17. Separation device (9) according to one of claims 11 to 16, wherein the first switching device (17a) and the second switching device (17b) each have a controllable 3-way valve.

18. Separation device (9) according to one of claims 11 to 17, in which a steam container (31) is provided, so that water (H20) in the form of low-pressure steam can be fed into the desorption chamber (11) as the heating medium (3) via the feed line (13).

19. Separation device (9) according to one of claims 11 to 18, in which a gas container (31) for an inert purge gas is provided, so that an inert purge gas is provided as the cooling medium (5), with which the desorption chamber (11) with the absorbent (1) can be purged and cooled.

20. Plant for separating CO2 from the atmosphere with a separation device (9) according to one of claims 11 to 19.

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