Method for separating co 2 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. A mixture of heating medium (3) and expelled CO2 is formed and then the adsorbent (1) is acted upon by a cooling medium (5) which differs from the heating medium (3) and is prepared for a new adsorption step (A). The cooling medium (5) is brought into heat exchange with a refrigerant (M) circulating in a closed circuit and is thus cooled, wherein first of all the refrigerant (M) is provided at an initial pressure (pA) and is heated to an initial temperature (TA) in the heat exchange, wherein the refrigerant (M) is then compressed to a final pressure (pE), and wherein useful heat is transferred from the refrigerant (M) to the heating medium (3) and cooled refrigerant (M) is returned and again brought into a heat exchange with the cooling medium (5). The invention further relates to a separation device (9) for separating CO2 from the atmosphere.

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 designed specifically for carrying out the method.

[0004] The combustion of fossil fuels currently meets approximately 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 production, 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 CO2 recycling.

[0005] An important application is the capture of carbon dioxide (CO2) from gas streams, e.g., flue gases, exhaust gases, industrial waste gases, or atmospheric air. The capture of CO2 directly from the atmosphere, known as direct air capture (DAC), is one of several means to mitigate 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 on, for example, 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 for the extraction of carbon dioxide from the atmospheric ambient air. Furthermore,

[0007] WO 2019 / 092127 A1 describes another class of sorption materials based on potassium carbonate functionalization. This material class is also suitable for cyclic CO2 adsorption and desorption processes.

[0008] The adsorption process typically takes place under atmospheric conditions. Air flows through a bed of sorbent material or a carrier material coated with a sorbent. A portion of the CO2 contained in the air is chemically and / or physically bound or adsorbed on the surface or in the adsorbents.

[0009] During the subsequent CO2 desorption, the adsorption material is typically heated, and the partial pressure of carbon dioxide above the sorbent is often reduced by applying a vacuum and / or expelling CO2 from the sorbent with a so-called stripping gas, e.g., steam. It is important that the stripping gas can be easily separated from the desorbed CO2, particularly by condensation, so that the latter can be recovered in concentrated form.

[0010] One of the greatest challenges for the energy- and cost-efficient implementation of direct air capture arises from the comparatively low CO2 concentration in atmospheric air, which is nominally approximately 400 ppm as of 2019. This results in very high separation effort, and correspondingly large quantities, i.e., volume flows, of atmospheric air must be processed in suitable gas separation processes. In the course of the desired industrial application, from an economic perspective, in addition to a particularly efficient cyclic process control of the adsorption and desorption process, the service life and long-term stability of the adsorbent material - also called adsorbent - for the adsorption and desorption of atmospheric CO2 for the highest possible number of cycles are increasingly being considered.

[0011] Against this background, the object of the invention is to provide an improved process for separating CO2 from the atmosphere, which enables a particularly energy- and cost-efficient cyclic process, while at the same time being as gentle as possible on the adsorbent. A further object of the invention is to provide a correspondingly upgraded separation device for separating CO2 from the atmosphere.

[0012] The object directed to a method is achieved according to the invention by a method for separating CO2 from the atmosphere, in which an adsorption step and a desorption step following the adsorption step are carried out, wherein in the adsorption step an adsorbent is exposed to air, wherein a portion 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, wherein adsorbed CO2 is thermally expelled, wherein a mixture of heating medium and expelled CO2 is formed, and wherein the adsorbent is subsequently exposed to a cooling medium different from the heating medium and prepared for a new adsorption step, wherein the cooling medium is brought into heat exchange with a coolant circulating in a closed circuit and is cooled in the process,wherein the refrigerant is initially provided at an initial pressure and heated to an initial temperature in the heat exchanger, wherein the refrigerant is subsequently compressed to a final pressure, and wherein useful heat is transferred from the refrigerant to the heating medium, and cooled refrigerant is returned and again brought into heat exchange with the cooling medium. The invention is based on the recognition that DAC (Direct Air Capture) is a new technology,which 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 in this area is based on processes for the selective adsorption 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 of ambient air by evacuating it in a closed system. In a second step, the adsorbent is heated to approximately 100°C, thereby providing the required desorption heat. The CO2 is desorbed at a pressure reduced compared to the ambient pressure and can be extracted from a sorption device.

[0013] The heat required for desorption in known systems is usually generated outside the process in the form of low-pressure steam and provided externally, e.g. taken from a steam generator, and fed from outside to the sorption apparatus. The hot adsorbent must then be cooled - particularly to limit its rapid degradation - in order to prepare the material for the absorption of CO2 from the ambient air in the next step, i.e. to regenerate it. The overall process thus comprises at least four repeatedly repeating sub-steps: adsorption - evacuation - desorption - cooling. To ensure continuous operation from the overall system perspective, these steps are carried out at staggered times in parallel in a large number of appropriately interconnected modules of the DAC system as a batch process.

[0014] These previously used plant and operating concepts require comparatively high energy expenditure and are associated with correspondingly high operating costs for the supply and removal of heat from the modules of a DAC plant. This is accompanied by an undesirably rapid degradation of the adsorbent, which is either not addressed or not adequately addressed.

[0015] In contrast, the present invention has now identified further potential for improvement in the overall process control for DAC and the underlying DAC plant concept compared to previously known concepts, and specifically focuses on heat management and heat flows. On the one hand, the problem of designing heat supply and heat removal in the DAC process control with the lowest possible energy expenditure and, above all, sustainability is addressed. Here, it is proposed to efficiently use the smallest possible quantities of renewable energy, e.g. electrical power generated from renewable sources, to provide and couple in the required desorption heat and heat supply. On the other hand, the necessary heat removal from the DAC process for cooling the adsorbent and its regeneration is improved.This allows for particularly long-life and low-cost, i.e. energetically efficient, regeneration and use of the adsorbent over many DAC process cycles.

[0016] In the improved overall DAC process, heat is still added or removed. However, this can advantageously be achieved with as little effort as possible and using renewable energy. The use of renewable energy is particularly preferred because otherwise the actual purpose—reducing the CO2 content in the Earth's atmosphere—cannot be achieved. The majority of renewable energy is generated by hydropower plants, wind turbines, and photovoltaic systems and is available for further use almost exclusively as renewable electricity.

[0017] The invention combines effective process control with gentle regeneration of the adsorbent with the recovery of process heat generated within the system and its targeted recirculation. This achieves internal heating of the heating medium and significantly reduces the need for external heat input. In particular, the principle of a heat pump is applied accordingly and specifically integrated into the DAC process. After regeneration and cooling of the adsorbent, the heated cooling medium, for example, nitrogen, is brought into heat exchange with a refrigerant circulating in a closed circuit. This refrigerant provides a heat source or heat transport medium for the operation of the heat pump process.On the other hand, the refrigerant, due to its thermal circuit coupling, forms a heat sink for the heat released from the cooling medium to the refrigerant during the regeneration process, thus forming the cold side of the heat pump process. Heat is extracted from the cooling medium and transferred to the refrigerant. The refrigerant is provided at an initial pressure and heated to an initial temperature by heat exchange or heat transfer. Depending on the choice of refrigerant and the thermodynamic process control in the refrigerant circuit, this can advantageously cause the refrigerant to evaporate, i.e. undergo a phase transition from liquid to gas. The refrigerant is then compressed to a final pressure. Useful heat is then transferred from the refrigerant to the heating medium, which heats up.The useful heat can be advantageously obtained by utilising the condensation enthalpy of the refrigerant during the phase transition from the gaseous to the liquid phase, i.e. from a condensation process. The condensation enthalpy released corresponds to the evaporation enthalpy of the refrigerant during evaporation by absorbing heat. The refrigerant cools down. This represents the hot side in the heat pump process, from which useful heat can be released. From the point of view of the heat pump process, this is a heat sink, and from the point of view of the absorbing heating medium, the hot side forms a heat source. Cooled, especially condensed, refrigerant is returned and once again put into heat exchange with the cooling medium. An analysis of the heat added and removed or removed in the desorption step.The heat flows dissipated in the cooling step show that they are present on a scale that allows for thermally favorable combination with an appropriately adapted heat pump process. The heating medium, in particular pressurized and superheated heating steam, is cooled in the desorption step by expelling the CO2 from the loaded adsorbent from a high temperature of greater than 100°C to a lower temperature of approximately 50°C to 70°C, in particular 65°C. The energy for desorbing the CO2 is provided by the heating medium. The cooling medium for regenerating the adsorbent is heated from a low, cool temperature to a higher temperature of approximately 25°C - 40°C, in particular 30°C.

[0018] In a particularly preferred embodiment of the method, in the heat exchange the refrigerant is first evaporated at the initial pressure with the addition of heat, then compressed and cooled at a final pressure with the release of useful heat, whereby useful heat is transferred to the heating medium and this is heated, and whereby the refrigerant is then expanded.

[0019] It can be advantageous to deliberately expand the refrigerant after compression, thereby condensing it. In addition to the condensation heat, the refrigerant's evaporation enthalpy also generates compression heat, which is utilized as useful heat. The useful heat thus obtained is transferred to the heating medium, heating the latter.

[0020] The refrigerant is cyclically fed into a closed refrigerant circuit in a thermodynamic cycle, the heat pump process. Evaporation represents the heat source for the refrigerant, as the heat is absorbed from the outside by the cooling medium. Condensation represents the heat sink, as condensation enthalpy is captured, released as useful heat, and transferred to the heating medium. Water is preferably selected as the heating medium, which is heated to a working temperature typically higher than the normal boiling point of water of 100°C at atmospheric pressure for the desorption task. Typically, superheated steam is provided at a pressure of 1.2 bar and a temperature of 107°C.

[0021] In a particularly preferred embodiment of the method, an indirect or indirect heat exchange is carried out, wherein thermal energy is transferred from the cooling medium to the refrigerant via an intermediate circuit in which a heat transfer medium, in particular water, is circulated.

[0022] This implements a very advantageous decoupling of the heat pump process, which operates continuously as a thermodynamic cycle, from the cyclic operation of a DAC adsorption module, which comprises an adsorption step and a desorption step. The heat sources are therefore not integrated into the heat pump process directly, e.g., from the water vapor-saturated nitrogen as the cooling medium or the water vapor-CCy mixture, but preferably via an intermediate closed water circuit.

[0023] This is very practical and advantageous, as it creates the possibility of operating a large number of DAC adsorption modules, possibly hundreds of DAC modules, in parallel. This also allows for the implementation of quite long pipelines from the individual heat sources to a jointly usable heat pump arrangement. Given the large volume flows of the gases or vapors serving as heat sources, it is not expedient to route these over long distances and to implement correspondingly large pipe diameters, etc. A "one-to-one" connection and assignment of individual, small-sized heat pump arrangements to individual or a few DAC modules, however, would be disadvantageous, as CCy production should be as continuous as possible, meaning that the serial steps in different DAC modules must always run in parallel with a time delay.The use of an intermediate water circuit has the further advantage of providing a buffer during the switchover processes that are inevitable in a batch process. Depending on the size, wiring type, operating mode, etc. of the DAC system, it may be necessary to provide special buffer devices, such as storage tanks.

[0024] In a preferred embodiment of the method, in a first step, refrigerant is compressed from the initial pressure to a first intermediate pressure, wherein the mixture of heating medium and expelled CO2 is brought into heat exchange with recirculated refrigerant, wherein heat is transferred to recirculated refrigerant, wherein thus heated recirculated refrigerant is admixed with the compressed refrigerant at the first intermediate pressure, so that a combined stream of refrigerant at the first pressure is provided.

[0025] The recirculated refrigerant heated in this way can also be at least partially or completely evaporated, i.e. returned in the vapor phase and mixed with the first intermediate pressure.

[0026] It has proven very useful to carry out a multi-stage compression of the refrigerant so that an intermediate pressure is created that allows the admixture of a partial flow of refrigerant recirculated from the source to the sink of the heat pump at a first pressure stage at the first intermediate pressure. In this way, refrigerant returned from thermal engineering at a defined first pressure level above the initial pressure can be brought into heat exchange with the mixture of heating medium and CO2. This is preferably carried out indirectly via an intermediate circuit, as described above. Heat is thus transferred from the mixture to the refrigerant and utilized as useful heat. The heat pump process is therefore characterized by the multi-stage compression of the refrigerant, in particular n-butane.In the first compression stage, the refrigerant vapor supplied at initial pressure via heat source A – the cooling medium – is brought to an intermediate pressure. At this pressure level, additional refrigerant vapor supplied via heat source B – the water vapor-CCp mixture – is added.

[0027] In a further preferred embodiment of the method, in a second step, the combined stream of refrigerant is further compressed to a second intermediate pressure, wherein refrigerant returned to the refrigerant is supplied at the second intermediate pressure, so that a combined stream of refrigerant is provided at the second intermediate pressure.

[0028] It is expedient that returned gaseous refrigerant is metered into the refrigerant at the second intermediate pressure, so that the returned refrigerant is supplied in a gas phase at the second intermediate pressure. A second pressure stage creates the possibility of improving the heat pump process and feeding expanded or evaporated refrigerant back into the compression process in an adapted manner. This increases the mass flow of refrigerant after the second compression stage. The combined flow of refrigerant can thus advantageously be further compressed after the first compression stage up to a defined second intermediate pressure. At this pressure level, further refrigerant vapor can then be metered into the combined and partially compressed refrigerant flow, in particular provided via a flash box, for example. The total flow of working medium vapor is then compressed to the final pressure.The working fluid vapor is then condensed in the condenser of the heat pump process, and the condensation heat is available for steam generation. The resulting working fluid condensate is then gradually expanded via several throttle valves and is available for evaporation at the various pressure levels mentioned above.

[0029] In a preferred embodiment of the process, the combined refrigerant stream is compressed from the second intermediate pressure to the final pressure and liquefied. This achieves multi-stage compression and a particularly advantageous and efficient process control and integration of the heat pump process, utilizing the heat sources. The resulting refrigerant condensate is then gradually expanded via several throttle valves and is available for evaporation at the aforementioned various pressure levels. The combined refrigerant stream is compressed to the final pressure and liquefied, transferring heat to the heating medium. The heat transfer to the heating medium can expediently take place indirectly via heat exchange using a heat exchanger.

[0030] This process allows the advantages of the heat pump process to be exploited in a special way. On the one hand, the cold provided by the heat pump process at a favorable temperature level is used to cool the adsorbent or to pre-cool the water vapor / CC>2 mixture. On the other hand, the useful heat provided at a temperature level high enough for heat pumps is used to heat and evaporate the heating medium, particularly to generate steam as the heating medium.

[0031] In a particularly preferred embodiment of the process, water in the form of low-pressure steam is used as the heating medium, whereby useful heat is supplied to the water and water is evaporated.

[0032] For the thermal removal of CO2 adsorbed on the loaded adsorbent, low-pressure steam is advantageously used as a heating medium. This is obtained from cold feed water, which is superheated. The water is therefore initially supplied as cold feed water or added later and heated to the desired steam state for the desorption step. The heat pump process integrated into the process at least supports any additional heating that may still be required.

[0033] In this way, hot steam is ultimately provided as the heating medium, which expels the CO2 from the loaded adsorbent. Additionally or alternatively, low-pressure steam can be generated as needed in an electrically or solar-thermally powered steam generator, for example, and extracted as needed, or from a specially provided steam reservoir (steam vessel). The recovered useful heat is used to generate steam, so that any additional electrical or solar-thermal heating or storage system that might still be required can be significantly reduced in size.

[0034] 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 offers 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 recognized in the state of the art, can be addressed very effectively and simply, as cooling efficiency is increased and oxygen exposure at excessively high adsorbent temperatures is prevented.

[0035] For example, the approaches known to date include a cooling step in the desorption step. This cooling step takes advantage of the fact that low-pressure steam is used to heat the adsorbent. This creates condensate, which also precipitates on the surface of the adsorbent. A further significant reduction in pressure in the desorption chamber causes this condensate to evaporate, thereby cooling the adsorbent. A disadvantage of this approach, however, is that in the event of even minor leaks, ambient air flows into the desorption chamber and again supplies damaging oxygen. Furthermore, there is no guarantee that the wetting of the adsorbent material with condensate is uniform and sufficient for the necessary adsorbent cooling.Degradation of the adsorbent by oxygen is therefore not sufficiently prevented in the known approaches.

[0036] If cooling is carried out using, for example, nitrogen as a cooling medium, the water adhering to the adsorbent also evaporates and thus also contributes to the cooling effect.

[0037] In a particularly preferred embodiment of the process, water is condensed out of the CO2 expelled with the low-pressure steam, and desorbed CO2 is obtained in concentrated form.

[0038] The phase mixture of gaseous CO2, CO2 dissolved in water, and water vapor is subjected to phase separation, and in the process CO2 is separated from the mixture. The phase separation of CO2 dissolved in water and gaseous CO2 in the mixture achieves further efficient and particularly economical water use in a cycle, with a simultaneous high separation rate of pure and concentrated CO2. By cooling, for example, the water can be condensed out of the low-pressure steam and made available again as a heating medium. Separation of the mixture of water and desorbed and at least partially dissolved CO2 is achieved, as well as particularly economical further use of the water. In addition, the CO2 can be further processed, in particular dried and stored or transported away.

[0039] This process offers significant advantages, particularly compared to 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 capacity of these DAC systems depends solely on how much and where the condensate deposits on the surface of the adsorbent. These disadvantages are overcome by the cooling principle of the invention.

[0040] 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 viable recycling. In contrast, with the known cooling principles, the residual condensate remaining on the adsorbent after vacuum flash evaporation was evaporated by the ambient air flow during the subsequent adsorption step and released into the atmosphere. 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. With the invention, a DAC system can also be operated in water-scarce areas where inexpensive renewable energy in the form of solar energy is often available for operating 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 solely with 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.

[0041] Preferably, the process uses a refrigerant (M), in particular n-butane, which circulates in a closed circuit, whereby a phase transition is brought about, whereby useful heat is obtained from the enthalpy of vaporization.

[0042] In this way, the process of a condensation heat pump is implemented. This utilizes the physical effect of evaporation enthalpy. The refrigerant circulates in a closed circuit, driven by a compressor, alternating between liquid and gaseous states. The refrigerant absorbs the evaporation enthalpy through evaporation at low pressure and low temperature.

[0043] Electrically driven heat pumps operate with a closed refrigerant circuit. The refrigerant evaporates at low pressure, absorbing heat. After compression, the refrigerant condenses, releasing useful heat. In a throttle, the liquid refrigerant expands from high pressure to low pressure. This causes most of the refrigerant to evaporate, and the temperature drops. In small systems, the throttle consists of a capillary; in larger systems, thermostatically controlled valves are used to adjust the pressure in the evaporator so that the corresponding saturated vapor temperature is slightly lower than the temperature of the heat source, causing the refrigerant to evaporate as it absorbs heat.

[0044] As a refrigerant in the working area of ​​the separation device, n-butane, for example, is particularly suitable and can be used advantageously. N-butane is gaseous at room temperature and atmospheric pressure and has a melting point of -138 °C and a boiling point of -0.5 °C. However, other refrigerants are also possible with appropriately adapted process control of the heat pump process, such as tetrafluoroethane for the time being. In the future, refrigerants with no or less climate-effective impact, such as carbon dioxide, ammonia, propane, or 2,3,3,3-tetrafluoropropene, are to be used instead of tetrafluoroethane, and these are then to be preferred. 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 supply 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 supply 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 adsorbent with a heating medium to supplying the adsorbent with a cooling medium as the working medium, wherein a heating line and a cooling line are connected to the second switching device on the outlet side, wherein a first cooling unit is connected to the heating line and a second cooling unit is connected to the cooling line, wherein at least one of the cooling units is configured as a heat reservoir and is thermally coupled to the cold side of a heat pump arrangement, wherein the heat pump arrangement is operable and configured to provide useful heat on its hot side,which is transferable to the heating medium.

[0045] With the separation device designed and upgraded in this way, a particularly good energy balance and efficiency can be achieved. A heat pump arrangement is integrated into the separation device. This is achieved by thermal wiring and coupling to locally available heat sources on the output side in the heating line and the cooling line. Heat can be dissipated and transferred to the cold side of the heat pump arrangement either via the first and / or the second cooling unit. The thermal coupling to the heat pump arrangement can advantageously be effected indirectly via an intermediate circuit, whereby a cooling unit absorbs heat from the fluid in the heating line or the cooling line and initially transfers it to an intermediate circuit as a heat reservoir. The heat can then be transferred to the circulating refrigerant on the cold side of the heat pump arrangement.This heat can be tapped via the heat pump arrangement, e.g. after compression with the addition of technical work, as useful heat on the hot side of the heat pump arrangement at a high temperature level. The use and transfer of the useful heat thus obtained is intended in particular to a heating device arranged upstream of the supply line to the desorption chamber. This allows the heating medium to be heated with the useful heat thus obtained and, if water is used as the heating medium, to be evaporated. A lower supply of externally provided energy is achieved through the integrated heat pump arrangement. This external heating element, for example a steam generator operated with an electric heating element, can then be dimensioned smaller.

[0046] At the same time, the proposed integration of a heat pump arrangement fully retains the remaining elements and functions of the separation device with regard to adsorption and desorption, significantly improving the overall energy efficiency of a DAC system equipped in this way. At the same time, cyclic operation with efficient regeneration of the adsorbent is ensured, which has a positive effect on the adsorbent's service life.

[0047] The separation device of the invention therefore proposes an improved device for a DAC system that is particularly upgraded and suitable for carrying out the inventive method 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 containing the adsorbent 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 is achievable during operation, with degradation of the adsorbent due to oxygen exposure being avoided by the particularly effective cooling. Furthermore, the switching devices make the separation device particularly advantageously configured and usable for cyclic operation. The first and second cooling units provide for thermal coupling and dissipation of heat, which is fed to the cold side of the integrated heat pump arrangement.

[0048] 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 flexibly operated 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, allowing the respective working medium to be selectively supplied with the adsorbent to the desorption chamber.

[0049] In a particularly preferred embodiment of the separation device, a steam vessel is provided which is designed to receive useful heat from the heat pump arrangement and transfer it to water as a heating medium, such that water in the form of low-pressure steam can be fed into the desorption chamber via the supply line. The heat transfer of the useful heat obtained from the heat pump process, for example also through indirect heat transfer or coupling of useful heat into a steam vessel, is energetically particularly advantageous for steam generation and steam provision in addition to a correspondingly smaller-sized electrical heating device. Here, heating steam can be provided for the heating steam in the steam vessel at a high temperature of more than 100 °C and above and at a pressure of greater than 1 bar, in particular at around 2 to 5 bar.

[0050] It is also possible for the steam vessel, in a preferred embodiment, to be realized as a flash tank or for the steam vessel to have a flash tank as an integral functional component. The flash tank is a functional component designed to receive useful heat from the heat pump arrangement in the form of pressurized hot water, so that steam is formed in the flash tank through a targeted pressure reduction and expansion, thus making low-pressure steam available as needed and supplying it to the desorption chamber via the supply line.

[0051] Preferably, a gas container for an inert purge gas is provided in the separation device, so that an inert purge gas is provided as a cooling medium, with which the desorption chamber with the adsorbent can be purged and cooled.

[0052] The inert purge gas can be fed in at such a pressure that an overpressure is created in the separation device compared to the ambient pressure. It is advantageous to store the inert purge gas, for example, in 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 extracted and removed as the inert purge gas. A metering device with a pressure regulator can be provided to provide the desired purge pressure of the inert purge gas at the desired overpressure.

[0053] In a particularly preferred embodiment of the separation device, the heat pump arrangement comprises a compression heat pump operable with a refrigerant, which comprises an evaporator, a compressor and a condenser connected downstream of the compressor.

[0054] An expansion device or throttle can advantageously be integrated into the heat pump arrangement in order to specifically effect expansion cooling of the compressed refrigerant and to bring about or support the expansion and condensation of the refrigerant.

[0055] The integration of a compression heat pump into the separation device is particularly efficient and advantageous for recovering useful heat from the desorption process. A compression heat pump utilizes the physical effect of evaporation enthalpy. In the compression heat pump, a refrigerant circulates in a circuit. Driven by a compressor, the refrigerant alternates between liquid and gaseous states, providing a heat source on the hot side and a heat sink on the cold side of the compression heat pump, thus creating a temperature difference.

[0056] In a particularly preferred embodiment of the separation device, the compressor in the heat pump arrangement has at least two compression stages connected in series, wherein a supply line opens between two successive compression stages at an intermediate pressure, so that returned refrigerant can be mixed with the refrigerant.

[0057] The multi-stage design of the compressor allows for stage- and pressure-adjusted metering of returned expanded and gaseous refrigerant at selected pressure levels. In particular, by admixing partial refrigerant flows, the mass flow of refrigerant can be specifically increased as it flows through the compression stages and during compression. By selecting the pressure stage of the respective intermediate pressure, pressure- and temperature-adjusted metering of refrigerant is also easily achieved. The overall process of the heat pump arrangement and heat recovery is thus improved.

[0058] In a particularly preferred embodiment of the separation device, a cooling unit is thermally coupled via an intermediate circuit to an evaporator arranged on the cold side of the heat pump arrangement, so that an indirect heat transfer is provided.

[0059] This creates a decoupling of the time-synchronized switching processes from the adsorption step to the desorption step. The intermediate circuit provides buffering or inertia to the system, preventing the switching processes from disrupting the system and allowing the heat pump arrangement to operate continuously. The use of water as a circulating heat transfer fluid in the intermediate circuit is particularly advantageous here. A water intermediate circuit offers the simple advantage of providing a buffer during the switching processes unavoidable in a batch process. It is possible for a large number of DAC modules to be thermally coupled to an appropriately dimensioned central intermediate circuit via a respective cooling unit, feeding heat into the intermediate circuit. The intermediate circuit can contain storage tanks to provide additional buffering and to maintain additional thermal storage capacity.

[0060] Thus, thermal energy from the heating medium or the cooling medium can initially be transferred to the intermediate circuit via the first or second cooling unit. A thermal coupling is implemented from the intermediate circuit to the heat pump assembly, allowing heat to be introduced to the cold side of the heat pump assembly.

[0061] Therefore, it is particularly preferred that a plurality of desorption chambers and a central intermediate circuit are provided in the separation device, so that a plurality of desorption chambers are thermally coupled to the central intermediate circuit via the cooling unit.

[0062] This makes it possible to implement a complex DAC system designed to separate CO2 from the atmosphere on a large scale. Such a DAC system can also comprise multiple separation devices.

[0063] 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 specified combination, but also in other combinations or on their own, without departing from the scope of the invention.

[0064] Embodiments of the invention are explained in more detail with reference to the accompanying drawings, which show schematically and in a highly simplified manner the

[0065] FIG 1 shows a DAC system with a separation device according to the invention;

[0066] FIG. 2 shows the heat pump arrangement integrated into the separation device with its essential functional elements; FIG. 3 shows a block diagram of a simplified process sequence for the separation of CO2 from the atmosphere.

[0067] 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 inserted. 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 adsorption or absorption of CO2. It is also possible for the adsorbent 1 to be 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, in the case of an adsorbent 1 loaded with CO2, the desorption process can be carried out in the desorption chamber 11 under conditions hermetically sealed and separated from the ambient air.

[0068] 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 by connecting a heating line 19a to the inlet of the first switching device 17a, via which heating line a heating medium 3 can be delivered 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-specific and specific treatment of the heating medium 3 and the cooling medium 5, a heating line 19b and a cooling line 21b branch off 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 first cooling unit 37, and a separating tank 27. The first cooling unit 37 is designed as a cooler or condenser and can be flowed through by a heat exchange medium. As a result, thermal energy Qi can be removed from the heating medium 3 via the first cooling unit and recovered, so that useful heat Q. Ncan be provided. The heating medium 3 is cooled, whereas the heat exchange medium is heated, and the absorbed heat energy Qi is transported. The heat energy Qi thus obtained is utilized in a heat pump arrangement 101 by thermally coupling heat energy Qi to the cold side of a heat pump arrangement 101 and transferring it, in particular via a heat reservoir, or can also advantageously be introduced specifically within the heat pump process.

[0069] The separating device 25 on the cooling line 21b has a compressor 35 or blower, to which a second cooling unit 39 and a separator vessel 27 are connected in the flow direction of the cooling medium 5. The second cooling unit 39 is designed as a gas cooler and can also be flowed through by a heat exchange medium. As a result, thermal energy Q2 can be removed from the cooling medium 5 via the second cooling unit 39 and recovered, so that useful heat QN can be provided. In this case, the cooling medium 5 is cooled, whereas the heat exchanger medium is heated and the absorbed heat energy Q2 is transported. The use of the heat energy Q2 thus obtained also takes place in the heat pump arrangement 101, in that heat energy Qi is thermally coupled to the cold side of a heat pump arrangement 101, in particular via a heat reservoir not shown in detail in FIG. 1. The useful heat QN obtained in the heat pump arrangement 101 can be transferred or coupled to the heating medium 3 on the inlet side of the desorption chamber 11. It is possible that useful heat Q Nis at least partially introduced into the steam tank 29 in order to generate or provide low-pressure steam S as heating medium 3. Due to this efficient use of heat, an external electrical heating device for obtaining heating medium 3 can be dimensioned smaller and is operated in particular only as needed, for example in the event of a failure of the heat pump as a backup heating device.

[0070] The compressor 35 is connected to the cooling line 21b such that its suction side connects to the outlet of the second switching device 17b. The vacuum pump 33 is connected with its suction side to the heating line 19b and connects accordingly to the second switching valve 17b.

[0071] 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, it is possible to switch specifically and selectively to a respective working medium which is applied to the adsorbent 1.

[0072] For desorption operation, low-pressure steam S is provided as heating medium 3 from a steam vessel 29. 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 to compensate for any operational loss of cooling medium 5. The cooling medium 5 is fed into a cooling circuit 7, wherein nitrogen N2 can be supplied to the cooling circuit 7 as fresh cooling medium 5a only as needed. When acted upon by the coolant 5, the coolant 5 is guided in a closed cooling circuit 7. For phase separation of liquid and gaseous components in the flow media, a separating vessel 27 is provided in each of the separating devices 23, 25, which is connected to the heating line 19b or to the cooling line 21b, respectively.

[0073] FIG. 2 shows and explains in more detail the heat pump arrangement 101 integrated into the separation device 9, along with its essential functional elements. The heat pump arrangement 101 is based on the principle of a compression heat pump and is designed accordingly. The compression heat pump utilizes the physical effect of evaporation enthalpy. In the compression heat pump, a refrigerant M circulates in a circuit which, driven by a compressor, alternates between the liquid and gaseous states. For this purpose, the heat pump arrangement 101 has an evaporator 103, which is arranged on the heat-absorbing cold side 115 of the heat pump arrangement 101. A condenser 111 for the refrigerant M is arranged on the heat-emitting hot side 117.Furthermore, a compressor 105 is provided, which comprises a plurality of compression stages 105a, 105b, 105c connected in series, which are connected to a flow line 123, which opens into the condenser 111. Thus, the compression heat pump is configured such that a first intermediate pressure p2 and a second intermediate pressure p2 are provided along the compression section in the flow line 123. In the subsequent third compression stage 105c, the refrigerant M is compressed to the final pressure p. EA return line 125 leads from the condenser 111 with the throttle device back to the evaporator 103, thus creating a closed circuit for the refrigerant M. A first bypass line 107 and a second bypass line 109 are connected in parallel and connect the return line 125 to the flow line 123 and open into the respective compression stage at the selected intermediate pressure p2, p2. As a result, refrigerant Mi, M2 returned via the return line 125 can be mixed with the refrigerant M. An evaporator 119, which can be subjected to a heat flow Qi, is connected to the first bypass line 107. The evaporator 103 is thermally coupled to the incoming heat flow Q2, so that during operation the refrigerant M is evaporated while absorbing the heat Q2. The second bypass line 109 is connected to the return line 125 via a flash box 121.Thus, at the second pressure stage p2, a partial flow of refrigerant M2 returned from the condenser 117 via the return line 125 can be fed into the compressor 105. The multi-stage compressor 105 is operated by an electric motor 113 powered by renewable energy. Typical operating data of the heat pump arrangement 101 is a volume flow of 245 m³ on the cold side 103. 3 / h for the heat exchanger medium. The heat exchanger medium, in this case water H2O, has, for example, a pressure of approximately 4 bar at a temperature of 30 °C when it flows into the heat sink of the evaporator 103. The specific heat content in the inflow is 126 kJ / kg, with a mass flow of 68 kg / s being recorded. After heat Q2 has been transferred to the refrigerant M in the evaporator 103, the water H2O has cooled to a temperature of 12 °C at the outlet of the evaporator 103. The specific heat content has been reduced and is now only 51 kJ / kg. In addition, a quantity of heat Q2 can be transferred to the returned refrigerant M1 in the superheater 119. The coolant M1 is heated to a temperature of approx. Refrigerant Ml, which has already been preheated and evaporated to 65 °C, is mixed into the compressor 105 via the first bypass line 107 at the first intermediate pressure p2.

[0074] Typical operating data of the heat pump arrangement 101 on the hot side 117 are such that the heat exchange medium, also water H2O, initially has a pressure of approximately 6 bar at a temperature of 20 °C when flowing into the heat source of the condenser 111. The specific heat content in the inflow is approximately 85 kJ / kg, with a mass flow of 3.8 kg / s being set. After the release of useful heat Q NIn condenser 111, the pressure at the outlet of condenser 111 has been reduced to 1.2 bar by the refrigerant M and transferred to the water H2O, and the heat exchange medium has been heated to a temperature of 108 °C through a phase change (evaporation) and superheating. The specific heat content has increased significantly to 2690 kJ / kg. The ratio of heat output delivered to the heating circuit to the electrical compression power supplied is referred to as the coefficient of performance (COP) and is, for example, 2.5. The thermal circuit integration of the heat pump arrangement 101 into the separation device 9 is advantageously designed such that a cooling unit 37, 39 is coupled to the evaporator 103 or the evaporator 119 arranged on the cold side 115 of the heat pump arrangement 101 via an intermediate circuit (not shown in detail in FIGS. 1 and 2).This can be a common central intermediate circuit operated with a suitable circulating heat exchange medium, such as water (H2O). This enables indirect heat transfer of the respective heat flows Q1 and Q2 to the compression heat pump. This enables a very advantageous decoupling of the separation device 9 from the cyclic, discontinuous, and regular switching from adsorption mode to desorption mode.

[0075] In the condensation heat pump, the compressor 105 is electrically driven by the motor 113 and the refrigerant M is operated in a closed circuit. The refrigerant M evaporates at low pressure p A with heat supply Q2 and after compression the refrigerant M condenses with release of useful heat Q N. In the throttle or expansion valve behind the condenser 117, the liquid refrigerant M is expanded from high pressure to low pressure. In the process, a portion of the refrigerant M evaporates and the temperature drops. The throttle or expansion valve consists of a capillary in small systems; in larger systems, thermostatically controlled valves are used. The pressure in the evaporator 117 is set so that the corresponding saturated steam temperature is slightly lower than the temperature of the heat source, so that the refrigerant M evaporates due to the heat absorption. The compressor 105 is operated so that the pressure at the final compression pressure p EThe corresponding saturated steam temperature is slightly above the heat sink temperature. The refrigerant M is selected in relation to the process so that the phase transition temperatures are sufficiently far from the temperatures of the heat source and heat sink for heat transfer. Where possible, a refrigerant M is used whose evaporation pressure at the lowest operating temperature is above ambient pressure to prevent air from entering the refrigerant circuit.

[0076] The process for separating CO2 from the ambient air is illustrated in a highly simplified schematic block diagram in FIG 3. An adsorption step A and a desorption step D following the adsorption step are carried out. In the adsorption step A, the adsorption chamber 11 is opened and the discharged adsorbent

[0077] I is supplied with ambient air, which the adsorption chamber

[0078] II. In the process, a portion of the CO2 contained in the air is adsorbed by the adsorbent 1, incorporated into the surface-rich structure of the adsorbent 1, and a CO2-laden adsorbent 1 is formed. After a saturation value is reached and the adsorbent 1 is sufficiently loaded with CO2, the adsorption step A is terminated and the exposure to ambient air is discontinued. This is achieved, for example, by closing the adsorption chamber 11 via movable closure elements 45 and sealing it hermetically via the sealing system 43. It is also possible for the adsorbent module 41 with the loaded adsorbent 1 to be moved from an exposure position in the ambient air to a position in 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 3 with a closing step A1, which can also be regarded as the final step and sub-step of the adsorption step A. Desorption can now be carried out. In the desorption step D initiated for this purpose, the adsorption / desorption chamber is first evacuated in order to remove any existing air as completely as possible. This increases the achievable CCp purity and avoids the presence of sorbent-damaging oxygen during desorption. The CO2-laden adsorbent 1 is then subjected to the heating medium 3 in a first desorption step D1 and heated. Low-pressure steam S is used as the heating medium 3 and is fed to the desorption chamber 11. In this process, adsorbed CO2 is thermally expelled from the adsorbent 1 and further treated. The mixture of heating medium 3 and CO2 flows through the first cooling unit 37. The first cooling unit 37 is designed as a cooler orCondenser and through which a heat exchange medium can flow. As a result, excess heat energy Qi can be removed from the heating medium 3 via the first cooling unit 37 and used for energy generation. The heat energy Q1 is fed to the heat pump arrangement 101 (FIG. 2), so that useful heat Q1 is generated. N can be extracted and provided from the heat pump process. The useful heat Q N is used for energy purposes and to generate low-pressure steam S.

[0079] In a second desorption step D2, the adsorbent 1 is then exposed to the cooling medium 5 and prepared for a further adsorption step A, the so-called regeneration phase. Desorption takes place as a two-stage process, with cooled nitrogen N2, for example, 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 cooling medium 5 is applied to the adsorbent 1 and flows through it circumferentially, whereby the adsorbent 1 is also cooled and dried of 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 continuously withdrawn from the adsorbent 1 and cooled again.The cooling medium 5 is guided in a cooling circuit 7, wherein nitrogen N2 can be supplied to the cooling circuit 7 as fresh cooling medium 5a only as needed - for example, to replace residual cooling medium 5 remaining in the desorption chamber 11 (sorption space) following the cooling process due to operational reasons. The desorption step D is carried out in two stages as far as the actual desorption of the CO2 is concerned. Thus, a heating medium 3 is used in the first desorption step D1, and a cooling medium 5 is used in the second desorption step D2. The heating medium 3 and the cooling medium 3 are different media or fluids in order to achieve particularly advantageous desorption through the combination of the first desorption step D1 and the second desorption or regeneration step D2, and above all, a significantly improved cooling effect in the second desorption step D2.Degradation of 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 adsorption step A is less damaging to adsorbent 1, allowing longer service lives for adsorbent 1 and thus enabling multiple consecutive cycles consisting of an adsorption step A and a desorption step D with substeps D1 and D2.

[0080] 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 exposed 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 passed through the second cooling unit 39 in heat exchange with a heat exchange medium, cooled to a predetermined cooling temperature, and fed to the adsorbent 1 via the cooling line 21a via the first switching device 17a. In this process, the adsorbent 1 flows through, is cooled, and is 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 implemented.The heat Q2 obtained from the nitrogen N2 in the second cooling unit 39 via the heat exchange medium is fed to the heat pump arrangement 101. From this, useful heat Q can be obtained in the heat pump process. N which is used to heat the heating medium 3. In this case, an energetic use within the separation device is provided by the useful heat Q N used to generate low-pressure steam S.

[0081] The invention proposes a two-stage desorption process with a significantly improved heat utilization by integrating a heat pump process to recover inherently occurring useful heat Q Nand their use for heating the heating medium 5. 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 also better controllable and reproducible. 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. To minimize nitrogen consumption, the heated nitrogen N2 is cooled again in a second cooling unit 39, a gas cooler, and can be recycled many times.By flooding and flushing the desorption chamber 11 in the second desorption step D2 with pure nitrogen N2, it is possible that CO2, which was previously not completely desorbed from the loaded adsorbent 1 in the first desorption step D1, is now additionally expelled from the adsorbent 1 in the desorption chamber 11 together with the inert flushing medium nitrogen N2. However, this is unproblematic insofar as the CO2 content in the circuit flow will only increase to a partial pressure corresponding to the residual loading of the adsorbent 1 after desorption D1, which means that the desorption of residual CO2 from the adsorbent 1 no longer experiences any driving force. After starting up, for example with pure nitrogen, the cooling medium 5 undergoes the described leveling and CO2 saturation with a constantly low CO2 concentration in a cooling circuit 7 and can thus continue to be used efficiently as a cooling medium 5.

[0082] At the same time, by applying nitrogen N2 as cooling medium 5, the condensate of water H20 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 second cooling unit 39 (gas cooler), the water H20 evaporated by evaporative cooling is first separated again as condensate, i.e. liquid water H20, and can thus be advantageously reused. The adhering water H20 is not mixed with the treated

[0083] Air flow is emitted and consumed. The cooling process in the second desorption step D2 is carried out at a slight overpressure compared to the ambient atmospheric pressure. Thus, 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 is released into the atmosphere when the adsorbent module 41 is again pressurized and charged with ambient air. It is therefore advantageous and expedient to feed at least this amount of nitrogen N2 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. nitrogen N2, the cooling can be regulated and controlled according to requirements. This allows cooling to be reliably adjusted to a required surface temperature of the adsorbent 1 and this surface temperature can be ensured. 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 previously known concepts. With the known flash evaporation, it depends on where and in what quantity condensate has deposited.Depending on the geometry of the adsorbent module 41, the condensate precipitate will not be evenly distributed across 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.

[0084] A significant economic advantage results from the integration of the heat pump arrangement 101 into the separation device 9. The main advantage of the described approach lies in the simultaneous use of the cold provided by the heat pump arrangement 101 at a favorable temperature level to cool the adsorbent 1. At the same time, a pre-cooling of the water vapor / CC>2 mixture is achieved. At a temperature level that is high for heat pumps, useful heat Q N for steam generation. This ensures a highly efficient process that reduces electricity consumption to <40% compared to conventional DAC systems when compared to the use of renewable electricity in a steam generator heated solely by electricity and a separate recooling system.

[0085] Furthermore, the proposed separation device and process control significantly reduce degradation of adsorbent 1 due to oxygen exposure. Due to degradation, the adsorbent gradually loses its storage capacity for binding CO2, so 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 for this purpose, as well as the advantageous process control for desorption step D, also reduces maintenance costs and increases the availability of a DAC system.

Claims

Patent claims 1. A process 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 an adsorbent (1) is exposed to air, 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) charged with CO2 is exposed to a heating medium (3) and heated, wherein adsorbed CO2 is thermally expelled, wherein a mixture of heating medium (3) and expelled CO2 is formed, and wherein subsequently the adsorbent (1) is exposed to a cooling medium (5) different from the heating medium (3) and is prepared for a renewed adsorption step (A), wherein the cooling medium (5) is brought into heat exchange with a coolant (M) circulating in a closed circuit and is cooled down,where first the refrigerant (M) is at an initial pressure (p, A ) and heated to an initial temperature (T A ), whereby the refrigerant (M) is then heated to a final pressure (p E ) is compressed, and where useful heat (Q N ) is transferred from the refrigerant (M) to the heating medium (3) and cooled refrigerant (M) is returned and again brought into heat exchange with the cooling medium (5).

2. Method according to claim 1, wherein in the heat exchange the refrigerant (M) is at the initial pressure (p A ) is first evaporated under heat, then compressed and at a final pressure (p E ) releasing useful heat (Q N ) is cooled, whereby useful heat (Q N ) is transferred to the heating medium (3) and this is heated, and the coolant (M) is then expanded.

3. Method according to claim 1 or 2, in which an indirect heat exchange is carried out, wherein heat energy is transferred from the cooling medium (5) to the refrigerant (M) via an intermediate circuit in which a heat transfer carrier medium, in particular a water intermediate circuit, is circulated.

4. Method according to one of the preceding claims, in which in a first step refrigerant (M) is reduced from the initial pressure (p A ) is compressed to a first intermediate pressure (p2), and wherein the mixture of heating medium (3) and expelled CO2 is brought into heat exchange with recirculated refrigerant (Mi), wherein heat is transferred to recirculated refrigerant (Mi), wherein such heated recirculated refrigerant (M2) is admixed with the compressed refrigerant (M) at the first intermediate pressure (p2), so that a combined stream of refrigerant (M) at the first pressure (p2) is provided.

5. The method according to claim 4, wherein in a second step the combined stream of refrigerant (M) is further compressed to a second intermediate pressure (p2), wherein refrigerant (M2) returned to the refrigerant (M) is supplied at the second intermediate pressure (p2) so that a combined stream of refrigerant (M) at the second intermediate pressure (p2) is provided.

6. The method according to claim 5, wherein the combined flow of refrigerant (M) is reduced from the second intermediate pressure (p2) to the final pressure (p E ) is compressed and liquefied.

7. Method according to one of the preceding claims, wherein water (H2O) in the form of low-pressure steam is used as the heating medium (3), wherein useful heat is supplied to the water (H2O) and water (H2O) is evaporated.

8. Process according to claim 7, wherein water (H20) is condensed from the CO2 expelled with the low-pressure steam (S), and desorbed CO2 is recovered in concentrated form.

9. Process according to one of the preceding claims, in which a refrigerant (M) is used, in particular n-butane, which is circulated in a closed circuit, whereby a phase transition is brought about, whereby useful heat is obtained from the enthalpy of vaporization.

10. 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 supply line (13) and a discharge line (15) for the working medium are connected to the desorption chamber (11) on the inlet side, wherein a first switching device (17a) is connected upstream of the supply 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 adsorbent (1) with a heating medium (3) to supplying the adsorbent (1) with a cooling medium (5) as the working medium, wherein a heating line (19b) and a cooling line (21b) are connected to the second switching device (17b) on the outlet side is,wherein a first cooling unit (37) is connected into the heating line (19b) and a second cooling unit (39) is connected into the cooling line (21b), wherein at least one of the cooling units (39, 37) is designed as a heat reservoir and is thermally coupled to the cold side (115) of a heat pump arrangement (101), wherein the heat pump arrangement (101) is operable and is designed to generate useful heat (Q, N ) which can be transferred to the heating medium (3).

11. Separation device (9) according to claim 10, wherein a steam container (29) is provided which is designed to generate useful heat (Q N ) from the heat pump arrangement (101) and to transfer it to water (H2O) as heating medium (3), so that water (H2O) in the form of low-pressure steam can be fed into the desorption chamber (11) via the supply line (13).

12. Separation device according to claim 11, wherein the steam container (29) is realized by a flash tank which is designed to generate useful heat (Q N ) from the heat pump arrangement (101) in the form of pressurised hot water, so that low-pressure steam can be provided by reducing the pressure in the flash tank and can be fed to the desorption chamber (11) via the supply line (13).

13. Separation device (9) according to claim 10, 11 or 12, wherein 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 adsorbent (1) can be purged and cooled.

14. Separation device (9) according to one of claims 10 to 13, wherein the heat pump arrangement (101) comprises a compression heat pump operable with a refrigerant (M), which comprises an evaporator (103), a compressor (105) and a condenser (111) connected downstream of the compressor (105).

15. Separation device (9) according to one of claims 10 to 14, wherein in the heat pump arrangement (101) the compressor (105) has at least two compression stages (105a, 105b, 105c) connected in series, wherein a supply line (107, 109) opens between two successive compression stages (105a, 105b, 105c) at an intermediate pressure (Pi, p2), so that returned refrigerant (M1, M2) can be mixed with the refrigerant (M).

16. Separation device according to one of claims 10 to 15, in which a cooling unit (37, 39) is thermally coupled via an intermediate circuit to an evaporator (103, 119) arranged on the cold side (115) of the heat pump arrangement (101), so that an indirect heat transfer is provided.

17. Separation device (9) according to claim 16, wherein a plurality of desorption chambers (11) are provided and a central intermediate circuit is formed, so that a plurality of desorption chambers (11) are thermally coupled to the intermediate circuit via the cooling unit (37, 39).

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