Method for separating co2 from the atmosphere, and separation device, in particular for carrying out the method
Patent Information
- Application Number
- AE202602922
- Authority / Receiving Office
- AE · AE
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-03-04
- Filing Date
- 2025-02-07
Smart Images
Figure ABST_ABST
Abstract
Description
Method for separating CO2 from the atmosphere, and separation device, in particular for carrying out the methodThe invention relates to a method for separating CO2 from the atmosphere. The invention further relates to a separation apparatus that has been designed in particular to perform the method.The combustion of fossil fuels currently covers about 80% of the global energy demand. As a result of these combustion processes and other industrial production processes, around 38 017 million tonnes of carbon dioxide (CO2) was emitted into the atmosphere globally in 2019. In addition to fossil energy generation, the production and transformation of industrial raw materials with a share of 9.2% of total emissions makes a significant contribution to the continuous rise in the concentration of CO2 in the atmosphere. The discussion relating to the adverse effects of the greenhouse gas CO2 on the climate has led to considering re-utilizing CO2.An important application is the separation of carbon dioxide (CO2) from gas streams, for example from flue gases, exhaust gases, industrial offgases or atmospheric air. The capture of CO2 directly from the atmosphere, the so-called Direct Air Capture (DAC), is one of several ways of reducing anthropogenic greenhouse gas emissions, and as a non-fossil, location-independent CO2 source offers attractive economic perspectives for the raw materials market and for the production of synthetic fuels.A particular approach to direct air capture is based on a cyclical adsorption and desorption process on solid, chemically functionalized sorption materials, for example. For instance, WO 2016 / 005226 A1 and WO 2017 / 009241 A1 thus disclose processes based on cyclic adsorption and desorption with the aid of steam or a suitable amine-functionalized sorption material for extracting carbon dioxide from the atmospheric ambient air. In addition, WO 2019 / 092127 A1 discloses a further class of sorption materials based on a potassium carbonate functionalization. This class of materials is also suitable for cyclical CO2 adsorption and desorption processes.The adsorption process generally takes place under atmospheric ambient conditions. This involves a flow of air through a bed comprising sorbent material or a carrier material populated by a sorbent. A portion of the CO2 present in the air is chemically and / or physically bound or adsorbed on the surface or in the adsorbents.In the subsequent CO2 desorption, the adsorption material is generally heated, and in addition the partial pressure of the carbon dioxide above the sorbent is frequently reduced by applying reduced pressure and / or driving CO2 out of the sorbent with a so-called stripping gas, for example with steam. It is important here that the stripping gas can be easily separated from the desorbed CO2, in particular by condensation, in order that the latter is obtained in concentrated form.One of the greatest challenges for energy-efficient and cost-efficient realization of direct air capture arises from the comparatively low CO2 concentration in the atmospheric air, which is nominally about 400 ppm from 2019. This results in very high separation complexity, and correspondingly large volumes, i.e. volume flow rates, of atmospheric air have to be processed in suitable gas separation processes. Because the aim is industrial use, from an economic point of view, there is a focus not only on a particularly efficient cyclical process regime of the adsorption and desorption process but increasingly also on the service lives or the long-term stability of the adsorbent material - also called adsorbent - for the adsorption and desorption of atmospheric CO2 for a maximum number of cycles.Against this background, it is the object of the invention to specify an improved method for separating CO2 from the atmosphere, by means of which a particularly energy-efficient and cost-efficient cyclic process regime is possible, and which at the same time is also as gentle as possible in respect of the adsorbent. It is a further object of the invention to specify a separation apparatus equipped in a corresponding manner for separating CO2 from the atmosphere.The object directed to a method is achieved in accordance with the invention by a method for separating CO2 from the atmosphere, in which an adsorption step and a desorption step that follows the adsorption step are conducted, wherein, in the adsorption step, an adsorbent is contacted with air, wherein a portion of the CO2 present in the air is adsorbed by the adsorbent, and wherein, in the desorption step, the CO2-laden adsorbent is contacted with a heating medium and heated, wherein adsorbed CO2 is driven out thermally, forming a mixture of heating medium and driven-out CO2, and wherein the adsorbent is then contacted with a cooling medium other than the heating medium and is prepared for a new adsorption step, wherein the cooling medium is subjected to a heat exchange with a coolant circulating in a closed circuit and cooled, wherein the coolant is first provided at a starting pressure and heated to a starting temperature in the heat exchange, wherein the coolant is then compressed to a final pressure, and wherein useful heat is transferred from the coolant to the heating medium, and cooled coolant is recycled and subjected to a heat exchange again with the cooling medium.The invention already proceeds from the knowledge that DAC (direct air capture) is a new technology that enables the removal of CO2 from the atmosphere. However, technology is currently still in an intensifying development and industrialization phase. The most developed technology here is based on methods of selective adsorption of CO2 on adsorbents specially developed for this purpose. The recovery and removal of the pure CO2 takes place in the subsequent desorption process. The adsorbent here is first freed of ambient air in a closed system by evacuating. In a second step, the adsorbent is heated to about 100°C, and this provides the required heat of desorption. The CO2 is desorbed under reduced pressure compared to the environment and can be sucked out of a sorption apparatus.The heat needed for the desorption is generated outside the process in the known plants, generally in the form of low-pressure steam, and provided externally, for example taken from a steam generator, and fed to the sorption apparatus from the outside. The hot adsorbent should subsequently be cooled — in particular in order to limit rapid degradation thereof — in order to prepare, i.e. regenerate, the material again for the absorption of the CO2 from the ambient air that follows in the next step. The overall process thus comprises at least four constantly repeating component steps: adsorbing - evacuating - desorbing - cooling. In order to ensure continuous operation from the point of view of the overall plant, these steps are conducted as a batch process in parallel with a time delay in a multitude of correspondingly interconnected modules of the DAC plant.These plant concepts and operating concepts that have been used to date entail comparatively high energy expenditure and are associated with correspondingly high operating costs for the supply and removal of the heat from the modules of a DAC plant.This is accompanied by an undesirably rapid degradation of the adsorbent, which is not counteracted sufficiently, if at all.By contrast, the present invention has now recognized further potential for improvement in the overall process regime for DAC and the underlying DAC plant concept with respect to the concepts known to date, and in so doing focuses specifically on the heat management and the heat flows. One problem addressed here is that of designing the heat input and the heat output in the DAC process regime so as to minimize energy expenditure and in particular maximize sustainability. What is proposed here is to employ, in an efficient manner, the use of minimum amounts of renewable energy generated, for example electrical power generated from renewable sources, for the provision and coupling-in of the required heat of desorption and heat input. At the same time, on the other hand, the necessary heat output from the DAC process for the cooling of the adsorbent and regeneration thereof is improved. As a result, in respect of the adsorbent, it is possible to achieve regeneration and utilization of the adsorbent over many DAC process cycles in a manner that particularly preserves its service life and is undemanding, i.e. energy-efficient.In the improved overall DAC process, heat is still supplied and removed. However, this can advantageously be effected with minimum expenditure and via renewable energies. The use of renewable energies is particularly preferable because otherwise the actual purpose — the reduction of the CO2 content in the Earth's atmosphere — cannot be achieved. The majority of renewable energies are generated by hydroelectric power plants, wind turbines and photovoltaic systems and are available for further use almost exclusively as renewable power.The invention combines an effective process regime with gentle regeneration of the adsorbent with recovery of process heat generated in the system and controlled recycling thereof. This achieves internal heating of heating medium within the system and considerably reduces the need for external heat input. In this case, in particular, the principle of a heat pump is employed in a corresponding manner and incorporated in the DAC process in a strategic manner. This involves subjecting the heated cooling medium, for example nitrogen, to a heat exchange with a coolant circulating in a closed circuit after the regeneration and cooling of the adsorbent. This coolant firstly forms a heat source or the heat transfer medium for the operation of the heat pump process. The coolant secondly forms, by virtue of its coupling to the heat circuit, a heat sink for the heat released from the cooling medium to the coolant from the regeneration process, i.e. thus the cold side of the heat pump process. Heat is removed here from the cooling medium and transferred to the coolant. The coolant is provided at a starting pressure and is heated to a starting temperature by the heat exchange or the heat transfer; depending on the choice of the coolant and the thermodynamic process regime in the coolant circuit, evaporation of the coolant is advantageously brought about, i.e. a phase transition from liquid to gaseous. The coolant is then compressed to a final pressure. Useful heat is then transferred from the coolant to the heating medium, and the latter heats up. The useful heat can advantageously be obtained, for instance, with exploitation of the enthalpy of condensation of the coolant in the phase transition from the gaseous phase to the liquid phase, i.e. from a condensation process. The enthalpy of condensation released corresponds to the enthalpy of evaporation of the coolant in the case of evaporation by absorption of heat. The coolant 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, in particular condensed, coolant is recycled and subjected again to a heat exchange with the cooling medium.Considering the heat flows supplied and removed in the desorption step or removed in the cooling step shows that they are of an order of magnitude which enables a thermally favorable linkage with a correspondingly adapted heat pump process. The heating medium, in particular pressurized and superheated heating steam, is cooled in the desorption step from a high temperature of greater than 100°C to a lower temperature of about 50°C to 70°C, in particular 65°C, as a result of the driving of the CO2 out of the laden adsorbent. The energy for desorption of 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 to about 25°C-40°C, in particular 30°C.In a particularly preferred embodiment of the method, in the heat exchange, the coolant at the starting pressure is first evaporated with supply of heat, then compressed and cooled at a final pressure with release of useful heat, wherein useful heat is transferred to the heating medium and the latter is heated, and wherein the coolant is then expanded.It may advantageously be the case here that, after the compression, the coolant is expanded and condenses out in a controlled manner. In addition to the heat of condensation, the enthalpy of evaporation of the coolant additionally provides heat of compression and renders it usable as useful heat. The useful heat obtained in this way is transferred to the heating medium, wherein the heating medium is heated.The coolant is conducted cyclically here in a closed coolant circuit in a thermodynamic cycle process, the heat pump process. The evaporation constitutes the heat source with respect to the coolant, since the heat is absorbed by the cooling medium from the outside. The condensation constitutes the heat sink, since enthalpy of condensation is obtained, released as useful heat and transferred to the heating medium. The heating medium chosen may preferably be water, which, for the desorption task, is brought to an operating temperature typically greater than the normal boiling temperature of the water of 100°C at atmospheric pressure. Typically, superheated steam is provided at a pressure of 1.2 bar at a temperature of 107°C.In a particularly preferred configuration of the method, an indirect heat exchange is conducted, in that heat energy is transferred from the cooling medium to the coolant via an interposed circuit in which a heat transfer medium, in particular a water, is circulated.This implements very advantageous decoupling of the heat pump process, which is operated continuously and as a thermodynamic cycle process, from the timed mode of operation, having an adsorption step and a desorption step, of the adsorption, desorption and regeneration of a DAC adsorption module. The heat sources are therefore not incorporated directly into the heat pump process, for example from the water vapor-saturated nitrogen as cooling medium or the water vapor / CO2 mixture, but preferably via an interposed closed water circuit. This is very appropriate and advantageous, since the possibility of operating very many DAC adsorption modules, possibly hundreds of DAC modules, in parallel is created. It is thus also possible to convert quite long conduit paths of the individual heat sources to a jointly usable heat pump arrangement. With regard to the large volume flows of the gases or vapors that serve as heat sources, it is not productive to run them over long distances and to achieve correspondingly large tube diameters, etc. By contrast, a "one-to-one" interconnection and assignment of individual small-size heat pump arrangements to individual or a few DAC modules would be disadvantageous since the production of CO2 is to be very substantially continuous, such that the serial steps in different DAC modules must then always take place in parallel with a time delay. The use of an intermediate water circuit has the further advantage that a buffer is made available during the changeover operations that are unavoidable in a batch process. Depending on the size, type of interconnection, mode of operation, etc. of the DAC system, it may also be necessary as required to provide specific buffer devices, for example storage tanks.In a preferred configuration of the method, in a first step, coolant is compressed from the starting pressure to a first intermediate pressure, wherein the mixture of heating medium and driven-out CO2 is subjected to a heat exchange with recycled coolant, wherein heat is transferred to recycled coolant, wherein recycled coolant heated in this way is added to the compressed coolant at the first intermediate pressure, such that a combined stream of coolant is provided at the first pressure.The recycled coolant heated in this way may also be at least partly or fully evaporated here, i.e. recycled in its vapor phase and added at the first intermediate pressure.It has been found to be very appropriate to implement a multistage compression of the coolant, such that an intermediate pressure is provided that permits adding of a partial flow of coolant recirculated from the source to the sink of the heat pump at a first pressure level at the first intermediate pressure. It is thus possible in terms of heat to subject coolant recirculated at a defined first pressure level above the starting pressure to a heat exchange with the mixture of heating medium and CO2. This is preferably effected indirectly via an intermediate circuit, as described above. Heat is thus transferred from the mixture to the coolant and rendered usable as useful heat. The heat pump process is therefore notable in that multistage compression of the coolant, in particular n-butane, is conducted. In the first compression stage, the coolant vapor provided at starting pressure via the heat source A — the cooling medium — is brought to an intermediate pressure. At this pressure level, further coolant vapor provided via the heat source B - the water vapor / CO2 mixture - is added.In a further preferred configuration of the method, in a second step, the combined stream of coolant is compressed further to a second intermediate pressure, wherein coolant recycled to the coolant is fed in at the second intermediate pressure, such that a combined stream of coolant is provided at the second intermediate pressure.It is appropriate here that gaseous coolant recycled to the coolant is metered in at the second intermediate pressure, such that the recycled coolant in the present case is supplied in a gas phase at the second intermediate pressure. A second pressure level creates the possibility of improving the heat pump process and recycling expanded or evaporated coolant into the compression process in an appropriate manner. This increases the mass flow rate of coolant after the second compression stage. The combined stream of the coolant can thus advantageously first be compressed further after the first compression stage up to a defined second intermediate pressure. At this pressure level, it is then possible to meter further coolant vapor into the combined and partly compressed coolant stream, in particular provided by means of a flash box for example. Thereafter, the overall stream of the working medium vapor is compressed to the final pressure. Subsequently, the working medium vapor is condensed in the condenser of the heat pump process, and the heat of condensation is available for steam generation. The resulting working medium condensate is then expanded in stages via a plurality of flow control valves and is available for evaporation at the various pressure levels mentioned above.In a preferred embodiment of the method, the combined stream of coolant is compressed from the second intermediate pressure to the final pressure and liquefied. This achieves multistage compression, and a particularly advantageous and efficient process regime and integration of the heat pump process with exploitation of the heat sources. The resulting coolant condensate is then expanded in stages via a plurality of flow control valves and is available for evaporation at the various pressure stages mentioned above. The combined stream of coolant is compressed to final pressure and liquefied with heat transfer to the heating medium. The heat transfer to the heating medium can appropriately be effected indirectly via a heat exchange by means of a heat exchanger.This process regime makes it possible to exploit the advantages in the heat pump process in an exceptional manner. Firstly, utilizing the refrigeration provided by the heat pump process at a favorable temperature level for cooling the adsorbent or for precooling the water vapor / CO2 mixture, and secondly exploiting the useful heat provided at a high temperature level for heat pumps for heating and evaporating the heating medium, in particular for generating steam as heating medium.In a particularly preferred configuration of the method, the heating medium used is water in the form of low-pressure steam, with supply of useful heat to the water and evaporation of water.The heating medium used to thermally drive out CO2 adsorbed on the laden adsorbent is advantageously low-pressure steam. This is obtained from cold feedwater, with superheating of the water. The water is therefore first provided or replenished as cold feedwater and brought to the desired vapor state for the desorption step. The heat pump process integrated into the method acts here at least in support of an additional heater that may still be required.In this way, hot steam is ultimately made available as heating medium, with which the CO2 is driven out of the laden adsorbent. Supplementarily or alternatively, low-pressure steam can be generated if necessary in a steam generator operated electrically or solar-thermally, for example, and removed if necessary or removed from a separately provided steam reservoir (steam vessel). The useful heat obtained is used for steam generation, such that any additional electrical or solar-thermal heater or storage device still required can be distinctly smaller in size.The use of low-pressure steam as heating medium and pure low-temperature nitrogen as cooling medium in two-stage and separately executed component steps in the desorption process results in numerous advantages over the known solutions. In this way, the DAC process can be conducted in a particularly advantageous and simple manner. The problem of oxidative adsorbent degradation, which has long been known in the prior art, can thus be countered very effectively and in a simple manner since the cooling efficiency is increased and an oxygen exposure at excessively high temperatures of the adsorbent is prevented.For example, in the approaches known to date, a cooling step in the desorption step is provided. This cooling step makes use of the fact that a direct introduction of low-pressure steam into the desorption space with the laden adsorbent is utilized for heating the adsorbent. This gives rise to condensate, which also precipitates on the surface of the adsorbent. Another significant lowering of the pressure in the desorption space brings about an evaporation of this condensate, as a result of which the adsorbent is cooled.However, a disadvantage of this procedure is that, in the event even of small leaks, ambient air flows into the desorption space and replenishes harmful oxygen. Moreover, it is not reliably assured that the wetting of the adsorbent material with condensate is uniform and adequate for the necessary adsorbent cooling. Degradation of the adsorbent by oxygen is therefore insufficiently prevented in the known approaches.If the cooling is effected with nitrogen, for example, as the cooling medium, the water adhering to the adsorbent also evaporates and thus likewise contributes to the cooling effect.In a particularly preferred embodiment of the method, water is condensed out of the CO2 driven out with the low-pressure steam, and desorbed CO2 is obtained in concentrated form.The phase mixture of gaseous CO2 and CO2 dissolved in water and water vapor is subjected to a phase separation and CO2 is separated from the mixture. The phase separation of CO2 dissolved in water and gaseous CO2 in the mixture achieves an efficient further particularly economical use of water in a circuit, with a simultaneously high separation rate of pure and concentrated CO2. By cooling, for example, the water can be condensed out of the low-pressure steam and provided again as heating medium. Separation of the mixture of water and desorbed and at least partly dissolved CO2 is achieved, as is particularly economical further utilization of the water. In addition, the CO2 can be processed further, in particular dried and stored or transported away.This method regime has considerable advantages over the known solutions in particular. In these solutions, the amount of condensed water that can be evaporated as condensate on the surface of the adsorbent, and hence the actual cooling performance, is limited and also cannot be influenced or controlled. In these DAC plants, the cooling performance depends solely on how much and where the condensate precipitates on the surface of the adsorbent. These disadvantages are overcome by the cooling principle of the invention.This is because 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 to send it, for example, to a recycling operation of economic interest. In contrast, in the known cooling principles, the residual condensate remaining on the adsorbent after the vacuum flash evaporation was evaporated by the air stream of the ambient air in the subsequent adsorption step and released to the atmosphere. It follows that this technology results in a considerable consumption of water and is therefore found to be very disadvantageous for use in arid regions or employment there is virtually ruled out. With the invention, a DAC plant can be operated even in arid regions, exactly where cheap renewable energy in the form of solar energy is frequently available for the plant operation of a DAC plant. Moreover, in known methods, an evacuation step following the desorption is additionally proposed in order thereby to initiate evaporation of the condensate and to cool the adsorbent as far as possible before it is exposed again to the ambient air. If the evaporation and cooling were to be conducted solely with air, the adsorbent at 100°C would come into contact with oxygen from the ambient air in a correspondingly high concentration, which would lead to rapid degradation of the adsorbent.Preferably, a coolant (M) is employed in the method, in particular n-butane, which circulates in a closed circuit, wherein a phase transition is brought about, wherein useful heat is obtained from the enthalpy of evaporation.In this way, the process of a condensation heat pump is implemented in the method. The physical effect of the enthalpy of evaporation is exploited here. This involves circulating the coolant in a closed circuit, and the coolant, driven by a compressor, alternately assumes the liquid and gaseous states of matter. In the case of the coolant, the enthalpy of evaporation is absorbed by evaporation at low pressure and low temperature.Electrically driven heat pumps are operated with a closed coolant circuit. The coolant evaporates at low pressure with supply of heat and, after compression, the coolant condenses with release of the useful heat. In a flow control valve, the liquid coolant is expanded from the high pressure to the low pressure. This evaporates the majority of the coolant, and the temperature drops. In the case of small plants, the flow control valve consists of capillaries; in the case of larger plants, thermostatically controlled valves are used, which adjust the pressure in the evaporator such that the corresponding saturated steam temperature is somewhat lower than the temperature of the heat source, such that the coolant evaporates through the absorptions of heat.An example of a particularly suitable and advantageously usable coolant in the working region of the separation apparatus is n-butane. n-Butane is gaseous at room temperature and standard pressure and has a melting point of -138°C and a boiling point of -0.5°C. However, other coolants are also possible with a correspondingly adapted process regime of the heat pump process, for instance still tetrafluoroethane for the moment. The intention is that, in the future, non-climate-active or less climate-active coolants will be used, for example carbon dioxide, ammonia, propane or 2,3,3,3-tetrafluoropropene, which will then be preferable, instead of tetrafluoroethane.The object directed to a separation apparatus is achieved in accordance with the invention by a separation apparatus 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 an inlet is connected to the desorption chamber on the inlet side and an outlet for the working medium on the outlet side, wherein a first changeover apparatus is connected upstream of the inlet and a second changeover apparatus is connected downstream of the outlet, such that, in desorption operation in a desorption step, it is possible to switch from contacting the adsorbent with a heating medium to contacting the adsorbent with a cooling medium as working medium, wherein a heating conduit and a cooling conduit are connected to the second changeover apparatus on the outlet side, wherein a first cooling unit is connected into the heating conduit and a second cooling unit into the cooling conduit, wherein at least one of the cooling units is set up 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 set up to provide useful heat on its hot side, which is transferable to the heating medium.The separation device that has been configured and equipped in this way is capable of achieving a particularly good energy balance and efficiency. A heat pump arrangement is integrated here into the separation apparatus. This is achieved by thermal interconnection and coupling to locally available heat sources on the output side in the heating conduit and the cooling conduit. Optionally, heat can be discharged via the first and / or the second cooling unit and heat can be transferred to the cold side of the heat pump arrangement. The thermal coupling to the heat pump arrangement may advantageously be indirect via an intermediate circuit, in which case a cooling unit absorbs heat from the fluid in the heating conduit or the cooling conduit and first transfers it to an intermediate circuit as heat reservoir. Subsequently, the heat can be transferred to the circulating coolant to the cold side of the heat pump arrangement. This heat can be tapped off as useful heat on the hot side of the heat pump arrangement at a high temperature level via the heat pump arrangement, for example after a compression with performance of technical work. Utilization and transfer of the useful heat thus obtained is provided in particular to a heating device upstream in the inlet in the inflow to the desorption chamber. The heating medium can thus be heated with the useful heat thus obtained and, if appropriate, also evaporated in the case of water as the heating medium. A lower supply of energy to be provided externally should be recorded by the integrated heat pump arrangement. This external heating element, for instance a steam generator operated with an electric heating bar, may then be smaller in size.At the same time, by means of the proposed integration of a heat pump arrangement, the remaining elements and functions of the separation apparatus with regard to adsorption and desorption are fully conserved, with considerable improvement in the overall energy efficiency of a DAC plant thus equipped. At the same time, a cyclical mode of operation with efficient regeneration of the adsorbent is ensured, which has a favorable effect on the lifetime of the adsorbent.With the separation apparatus of the invention, what is therefore proposed is an improved device for a DAC plant which is equipped and suitable in an exceptional manner in order to perform the method according to the invention for separating CO2 from the atmosphere. This is enabled by an advantageous combination of a first changeover apparatus and a second changeover apparatus. A first changeover apparatus is connected upstream of the desorption chamber, and a second changeover apparatus downstream of the desorption chamber. Thus, depending on the switching state, the desorption chamber with the adsorbent can be charged with or subjected to a flow of either a heating medium or a cooling medium. In this case, separate flow paths for the heating medium and the cooling medium open on the inlet side into those of the first changeover apparatus. Accordingly, separate flow paths for the heating medium and the cooling medium branch off from the second changeover apparatus on the outlet side. In this way, the separation apparatus is configured in such a way that the desorption step of a CO2-laden adsorbent is performable in the desorption chamber in two stages or in two component steps, wherein different working media are suppliable separately. Thus, an efficient and almost complete desorption of CO2 can be achieved in operation, with avoidance of the degradation of the adsorbent owing to oxygen exposure through the particularly effective cooling. By means of the changeover apparatuses, the separation apparatus, moreover, is configured and usable particularly advantageously for cyclical operation. The first and the second cooling unit provide thermal coupling and dissipation of heat, which is fed to the cold side of the integrated heat pump arrangement.The separation apparatus is usable in and connectable or integratable into a DAC plant irrespective of the specific structural design and the handling of the adsorbent, for example an adsorbent module. Thus, the separation apparatus is operable flexibly both in a DAC plant with movable and with fixedly mounted adsorbent modules with corresponding movable flaps for the supply air. It is merely necessary to provide an inlet and an outlet as connection to the desorption chamber, such that the respective working medium is optionally feedable to the desorption chamber with the adsorbent.In a particularly preferred embodiment of the separation apparatus, a steam vessel is provided and is set up to receive useful heat from the heat pump arrangement and to transfer it to water as heating medium, such that water in the form of low-pressure steam can be fed into the desorption chamber via the inlet.The heat transfer of the useful heat obtained from the heat pump process, for example even by indirect heat transfer or coupling useful heat into a steam vessel, is particularly advantageous in terms of energy for steam production and steam provision, in addition to an electrical heating device of correspondingly smaller size. Here, heating steam is providable for the heating steam in the steam vessel at a high temperature of more than 100°C and beyond and at a pressure greater than 1 bar, in particular at about 2 to 5 bar.It is also possible here for the steam vessel, in a preferred configuration, to be implemented by 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 which is set up to receive useful heat from the heat pump arrangement in the form of pressurized hot water, such that steam is formed in the flash tank by a controlled pressure reduction and expansion, such that low-pressure steam is thereby providable as required and suppliable to the desorption chamber via the inlet.Preferably, a gas vessel for an inert purge gas is provided in the separation apparatus, such that the cooling medium provided is an inert purge gas, by means of which the desorption chamber with the adsorbent is flushable and coolable.The inert purge gas can be fed in under pressure in such a way that a positive pressure compared to the environment is provided in the separation apparatus. An advantageous option is to keep a reservoir of the inert purge gas, in which case, for example, a gas vessel for nitrogen is provided. It is also possible to simply provide a vessel of gas bottles or to keep a reservoir vessel containing liquid nitrogen from a coupled air fractionation plant, from which gaseous nitrogen is obtained and removed as inert purge gas. A metering device with a pressure regulator may be provided in order to provide the desired purge pressure of the inert purge gas at the desired positive pressure.In the separation apparatus, in a particularly preferred configuration, the heat pump arrangement has a compression heat pump which is operable with a coolant and which has an evaporator, a compressor, and a condenser downstream of the compressor.An expansion device or flow control valve can advantageously be integrated in the heat pump arrangement in order to achieve expansion cooling of the compressed coolant in a controlled manner and to bring about or assist the expansion and condensation of the coolant.The integration of a compression heat pump into the separation apparatus is particularly efficient and advantageous for the recovery of useful heat from the desorption process. A compression heat pump utilizes the physical effect of the enthalpy of evaporation. In the compression heat pump, a coolant circulates in a circuit which, driven by a compressor, alternately assumes the liquid and gaseous states of matter, such that a heat source is provided on the hot side and a heat sink on the cold side of the compression heat pump, i.e. a temperature differential.In a particularly preferred configuration of the separation apparatus, in the heat pump arrangement, the compressor has at least two compression stages connected in series, wherein a feed conduit merges in between two successive compression stages at an intermediate pressure, such that recirculated coolant can be mixed into the coolant.The multistage design of the compressor enables metered addition, adapted to the stage or pressure, of recirculated expanded and gaseous coolant at selected pressure levels. In particular, the addition of substreams of coolant allows a controlled increase in the mass flow rate of coolant as it flows through the compression stages and the compression. Through the choice of the pressure level of the respective intermediate pressure, pressure- and temperature-adapted metered addition of coolant can additionally be brought about in a simple manner. The overall process of the heat pump arrangement and the heat recovery is improved as a result.In a particularly preferred configuration of the separation apparatus, a cooling unit is thermally coupled via an intermediate circuit to an evaporator arranged on the cold side of the heat pump arrangement, such that indirect heat transfer is provided.As a result, decoupling of the timed switching operations from the adsorption step into the desorption step is set up. The intermediate circuit brings about buffering or inertia in the system, such that the switching operations do not cross over and the heat pump arrangement is operable continuously. The utilization of water as circulating heat transfer fluid in the intermediate circuit is particularly favorable here. An intermediate water circuit achieves the advantage in a simple manner that a buffer is available during the changeover operations that are unavoidable in a batch process. It is possible here for very many DAC modules to be thermally coupled to a correspondingly dimensioned central intermediate circuit via a respective cooling unit, and for heat to be fed into the intermediate circuit. The intermediate circuit may contain storage tanks in order to provide additional buffering and in order to retain additional thermal storage capacity.Thus, thermal energy is transferable from the heating medium or the cooling medium via the first or the second cooling unit initially to the intermediate circuit. Thermal coupling to the heat pump arrangement is achieved by the intermediate circuit, such that heat can be introduced on the cold side of the heat pump arrangement.It is therefore particularly preferable that a plurality of desorption chambers and a central intermediate circuit are provided in the separation apparatus, such that a plurality of desorption chambers is thermally coupled to the central intermediate circuit via the cooling unit.Thus, a complex DAC system is also implementable, which is set up to separate CO2 from the atmosphere on a large scale. Such a DAC system may also include a plurality of separation apparatuses.Further advantages, features and details of the invention will be apparent from the description of preferred working examples that follows, and also from the drawing. The features and combinations of features cited above in the description and the features and combinations of features cited below in the description of the figures and / or shown on their own in the sole figures are usable not just in the respectively specified combination but also in other combinations or on their own, without departing from the scope of the invention.Working examples of the invention are elucidated in detail by a drawing. These show, in schematic and highly simplified form:FIG 1a DAC plant having a separation apparatus according to the invention;FIG 2the heat pump arrangement integrated into the separation apparatus with its essential functional elements;FIG 3a simplified method sequence for separating CO2 from the atmosphere in a block diagram.FIG 1 shows, in a simplified diagram, a detail of a direct air capture plant, "DAC plant" for short, for selectively separating carbon dioxide CO2 from the ambient air. For this purpose, the DAC plant has a separation apparatus 9. The separation apparatus 9 comprises a desorption chamber 11 into which an adsorbent module 41 has been 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 may be introduced into the adsorbent module 41 as a finely granular bed or in some other structure, such that a maximum effective adsorbent surface area is provided for adsorption or absorption of CO2. For instance, it is also possible that the adsorbent 1 is in the form of channel structures, honeycomb structures or other porous structures. The desorption chamber 11 has closure elements 45 and a sealing system 43, such that, in the case of a CO2-laden adsorbent 1, the desorption process can be performed in the desorption chamber 11 under conditions that are hermetically sealed and isolated from the ambient air.Connected to the desorption chamber 11 on the inlet side is an inlet 13, and on the outlet side an outlet 15, for a respective working medium with which the adsorbent 1 can be contacted. For this purpose, a respective working medium flows through the desorption chamber 11 with the adsorbent module 41. A first changeover apparatus 17a is connected into the inlet 13 and a second changeover apparatus 17b into the outlet 15, such that changeover operation and hence contacting of the adsorbent 1 with different working media becomes possible. This is achieved in that a heating conduit 19a, via which a heating medium 3 can be fed to the desorption chamber 11, is connected to the first changeover apparatus 17a on the inlet side. In addition, a cooling conduit 21a is connected to the first changeover apparatus 17a. A cooling medium 5 is suppliable as required to the desorption chamber 11 via the cooling conduit 21a. For separating the conduit paths and for a further method-related and specific treatment of the heating medium 3 and the cooling medium 5, a heating conduit 19b and a cooling conduit 21b branch off correspondingly on the outlet side at the second changeover apparatus 17b. The heating conduit 19b is connected here to a separating device 23, and the cooling conduit to a separating device 25. The separating device 23 on the heating conduit 19b has a vacuum pump 33, a first cooling unit 37 and a separating vessel 27. The first cooling unit 37 is configured as a cooler or condenser, through which a heat exchange medium can flow. As a result, thermal energy Q1 is removable from the heating medium 3 via the first cooling unit and can be recovered, such that useful heat QN can be provided. The heating medium 3 is cooled here, whereas the heat exchange medium is heated and the thermal energy Q1 absorbed is transported. The thermal energy Q1 thus obtained is used in a heat pump arrangement 101 in that thermal energy Q1 is thermally coupled and transferred to the cold side of a heat pump arrangement 101, in particular via a heat reservoir, or else can advantageously be introduced in a controlled manner even within the heat pump process.The separating device 25 on the cooling conduit 21b has a compressor 35 or blower which is adjoined, in flow direction of the cooling medium 5, by a second cooling unit 39 and a separation vessel 27. The second cooling unit 39 is designed as a gas cooler, through which a heat exchange medium can likewise flow. As a result, thermal energy Q2 is removable from the cooling medium 5 via the second cooling unit 39 and can be recovered, such that useful heat QN can be provided. The cooling medium 5 is cooled here, whereas the heat exchange medium is heated and the thermal energy Q2 absorbed is transported. The thermal energy Q2 thus obtained is likewise utilized in the heat pump arrangement 101 in that thermal energy Q1 is thermally coupled to the cold side of a heat pump arrangement 101, in particular via a heat reservoir (not shown in any detail in FIG 1). The useful heat QN obtained in the heat pump arrangement 101 is transferable or couplable to the heating medium 3 on the inlet side of the desorption chamber 11. It is possible here that useful heat QN is introduced at least partly into the steam vessel 29 in order to generate or provide low-pressure steam S as heating medium 3. As a result of this efficient use of heat, an external electrical heating device for obtaining heating medium 3 may be smaller in size and is operated in particular only as required, for example in the event of failure of the heat pump, as a backup heater.The compressor 35 is connected into the cooling conduit 21b in such a way that the suction side thereof adjoins the exit from the second changeover apparatus 17b. The vacuum pump 33 is connected by its suction side into the heating conduit 19b and correspondingly adjoins the second changeover valve 17b. The first changeover apparatus 17a and the second changeover apparatus 17b each have a controllable 3-way fitting, such that, when a desorption process is being performed in the desorption chamber 11, it is possible to switch in a controlled and selective manner to a respective working medium with which the adsorbent 1 is contacted.For desorption operation, the heating medium 3 provided is a low-pressure steam S from a steam vessel 29. The cooling medium 5 provided is an inert gas, in the present context cooled gaseous nitrogen N2. The nitrogen N2 can be stored in a gas vessel 31 and taken therefrom as required. Nitrogen N2 can thus be replenished as fresh cooling medium 5a in order to compensate for any operational loss of cooling medium 5. The cooling medium 5 is conducted into a cooling circuit 7, in which case nitrogen N2 can be fed to the cooling circuit 7 merely as required as fresh cooling medium 5a. On charging with the coolant 5, the coolant 5 is guided in a closed cooling circuit 7. For phase separation of liquid and gaseous constituents in the flow media, a separation vessel 27 is provided in each of the separation apparatuses 23, 25 and is connected in each case to the heating conduit 19b and to the cooling conduit 21b.FIG 2 shows and gives a detailed elucidation of the heat pump arrangement 101 integrated into the separation apparatus 9 and with its essential functional elements. The heat pump arrangement 101 is based on the principle of a compression heat pump and is configured accordingly. The compression heat pump uses the physical effect of the enthalpy of evaporation. In the compression heat pump, a coolant M circulates in a circuit which, driven by a compressor, alternately assumes the liquid and gaseous states of matter. For this purpose, the heat pump arrangement 101 has an evaporator 103 arranged on the heat-absorbing cold side 115 of the heat pump arrangement 101. A condenser 111 for the coolant M is arranged on the hot side 117 that releases the heat. Also provided is a compressor 105 comprising a plurality of series-connected compression stages 105a, 105b, 105c that are connected into a feed conduit 123 that opens into the condenser 111. The compression heat pump is thus set up such that a first intermediate pressure p1 and a second intermediate pressure p2 are provided along the compression zone in the feed conduit 123. In the subsequent third compression stage 105c, a compression of the coolant M to the final pressure pE is performed. A return conduit 125 leads from the condenser 111 with the flow control valve device back to the evaporator 103, so as to achieve a closed circuit for the coolant M. A first bypass conduit 107 and a second bypass conduit 109 are connected in parallel with one another and connect the return conduit 125 to the feed conduit 123 and open into the respective compression stage at the selected intermediate pressure p1, p2. As a result, coolant M1, M2 returned via the return conduit 125 can be added to the coolant M. Connected into the first bypass conduit 107 is an evaporator 119 that can be supplied with a heat flow Q1. The evaporator 103 is thermally coupled to the incoming heat flow Q2, such that, in operation, the coolant M is evaporated to absorb the heat Q2. The second bypass conduit 109 is connected to the return conduit 125 via a flash box 121. At the second pressure level p2, a substream of coolant M2 recycled from the condenser 117 via the return conduit 125 can thus be fed into the compressor 105. The multistage compressor 105 is operated via an electric motor 113 which is fed with renewable energies. Typical operating data of the heat pump arrangement 101 are a volume flow rate of 245 m3 / h for the heat exchange medium on the cold side 103. The heat exchange medium, in the present context water H2O, for example at the inlet when it flows into the heat sink of the evaporator 103, is at a pressure of about 4 bar at a temperature of 30°C. The specific heat content in the feed stream is 126 kJ / kg, with a mass flow rate of 68 kg / s. After a heat Q2 has been released in the evaporator 103 to the coolant M, the water H2O has cooled down to a temperature of 12°C at the outlet of the evaporator 103. The specific heat content has been reduced and is only 51 kJ / kg. In addition, an amount of heat Q2 can be transferred in the superheater 119 to recirculated coolant M1. The coolant M1 that has already been preheated to a temperature of about 65°C and evaporated in this way is mixed into the compressor 105 via the first bypass conduit 107 at the first intermediate pressure p1.Typical operating data of the heat pump arrangement 101 on the hot side 117 are such that the heat exchange medium, likewise water H2O, is at a pressure of about 6 bar at a temperature of 20°C, for example at the inlet when flowing into the heat source of the condenser 111. The specific heat content in the feed stream is about 85 kJ / kg, with a mass flow rate of 3.8 kg / s being established. After useful heat Qn has been released in the condenser 111 by the coolant M and transferred to the water H2O, the pressure at the outlet of the condenser 111 has been reduced to 1.2 bar and the heat exchange medium has been heated via a phase change (evaporation) and superheating to a temperature of 108°C. The specific heat content has increased significantly to 2690 kJ / kg. The ratio of heat output released into the heating circuit to electrical compression output supplied is referred to as the coefficient of performance (COP for short) and is, for example, 2.5. In an advantageous embodiment, the thermal integration of the heat pump arrangement 101 into the separation apparatus 9 is designed in such a way that a cooling unit 37, 39 is coupled to the evaporator 103 arranged on the cold side 115 of the heat pump arrangement 101 or to the evaporator 119 via an intermediate circuit - not shown in any detail in FIG 1 and FIG 2. This may be a common central intermediate circuit operated with a suitable circulating heat exchange medium, for instance water H2O. As a result, indirect heat transfer of the respective heat flows Q1 and Q2 into the compression heat pump is achieved. This enables, in the separation apparatus 9, very advantageous decoupling from the timed, discontinuous and regular switching from adsorption operation to desorption operation.In the condensation heat pump, the compressor 105 is electrically driven via the motor 113 and the coolant M is operated in a closed circuit. The coolant M evaporates at low pressure pA with supply of the heat Q1 and, after compression, the coolant M condenses with the release of the useful heat QN. In the flow control valve or the expansion valve downstream of the condenser 117, the liquid coolant M is expanded from the high pressure to the low pressure. At the same time, a proportion of the coolant M evaporates and the temperature drops. The flow control valve or the expansion valve consists of a capillary in the case of small plants; in the case of larger plants, thermostatically controlled valves are used. The pressure in the evaporator 117 is adjusted such that the corresponding saturated steam temperature is somewhat lower than the temperature of the heat source, such that the coolant M evaporates as a result of the absorptions of heat. The compressor 105 is run in such a way that the saturated steam temperature associated with the final compression pressure pE is slightly above the temperature of the heat sink. The coolant M is chosen in relation to the process such that the temperatures of the phase transition have a margin from the temperatures of heat source and heat sink which is sufficient for transfer of heat. As far as possible, a coolant M is used that has an evaporation pressure at the lowest working temperature that is above the ambient pressure, in order to prevent air from penetrating into the coolant circuit.The method for separating CO2 from the ambient air is illustrated in a highly simplified manner in FIG 3 in a schematic block diagram. This involves conducting 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 contacted with ambient air, which flows through the adsorption chamber 11. A portion of the CO2 present in the air is adsorbed here by the adsorbent 1 and intercalated into the surface-rich structure of the adsorbent 1, and a CO2-laden adsorbent 1 is formed. On attainment of a saturation value and a sufficient loading of the adsorbent 1 with CO2, the adsorption step A is ended and the exposure to ambient air is adjusted. This is done, for example, in that the adsorption chamber 11 is closed using movable closure elements 45 and sealed off in an airtight manner using the sealing system 43. It is also possible that the adsorbent module 41 with the laden adsorbent 1 is moved from an exposure position in the ambient air into a position in the desorption chamber 11 and the desorption chamber 11 with the adsorbent module 41 is then sealed off. This airtight closure of the desorption chamber 11 is illustrated in FIG 3 by a closing step A1, which can also be regarded as a final step and a component step of the adsorption step A.A desorption can then be performed. In the desorption step D initiated for this purpose, the adsorptiοn / desorptiοn space is first evacuated in order to remove air present as completely as possible. Thus, the achievable CO2 purity is increased and the presence of sorbent-damaging oxygen in the course of desorption is avoided. The CO2-laden adsorbent 1 is then contacted with the heating medium 3 and heated in a first desorption step D1. The heating medium 3 used is low-pressure steam S, which is fed to the desorption chamber 11. Adsorbed CO2 here is thermally driven out of the adsorbent 1 and treated further. The mixture of heating medium 3 and CO2 flows here through the first cooling unit 37. The first cooling unit 37 is configured as a cooler or condenser, through which a heat exchange medium can flow. As a result, surplus thermal energy Q1 is removable from the heating medium 3 via the first cooling unit 37 and can be utilized energetically. The thermal energy Q1 is supplied to the heat pump arrangement 101 (FIG 2), such that useful heat QN can be obtained and provided from the heat pump process. The useful heat QN is utilized energetically and used to generate low-pressure steam S.In a second desorption step D2, the adsorbent 1 is then contacted with the cooling medium 5 and processed for a new adsorption step A, the so-called regeneration phase. The desorption is effected here as a two-stage process, wherein the cooling medium 5 used is cooled nitrogen N2, for example. First of all, in the desorption step D1, the supply of heating medium 3 is interrupted and operation is switched over to contacting with the cooling medium 5 - for example nitrogen N2. The adsorbent 1 is contacted here with the cooling medium 5 and flows through it circumferentially, also with cooling of the adsorbent 1 and drying to free it of a residual coating with condensed water H2O from the first desorption step D1. The cooling efficiency is distinctly improved thereby through additional utilization of the evaporative cooling of the evaporating water H2O. The cooling medium 5 is continuously drawn off from the adsorbent 1 and cooled again. The cooling medium 5 is conducted in a cooling circuit 7, where nitrogen N2 can be fed to the cooling circuit 7 as fresh cooling medium 5a merely as required — for example in order to replace residues of cooling medium 5 that remained in the desorption chamber 11 (sorption space) for operational reasons after the cooling process. The desorption step D is performed in two stages - with regard to the actual desorption of the CO2. Therefore, a heating medium 3 is used in the first desorption step D1 and a cooling medium 5 in the second desorption step D2, wherein the heating medium 3 and the cooling medium 3 are different media or fluids, in order to achieve a particularly advantageous desorption by means of the combination of first desorption step D1 and second desorption or regeneration step D2 and, in particular, a distinctly improved cooling effect in the second desorption step D2. Degradation of the adsorbent 1 can be prevented or at least distinctly reduced by the extensive cooling and a low temperature. Oxygen exposure at a lower working temperature in the adsorption step A is less harmful to the adsorbent 1, and so longer service lives for the adsorbent 1 are achieved and hence a multitude of successive cycles of an adsorption step A and a desorption step D with component steps D1, D2 can be performed.In the desorption step D, after the closing step A1, an evacuation step E is first conducted. The evacuation step E serves to prepare the desorption chamber 11 with the laden adsorbent 1 for the actual desorption process. In the evacuation step E, before the contacting of the CO2-laden adsorbent 1 with the heating medium 3, the adsorbent 1 is first subjected to a subatmospheric pressure. This is done by pumping out the air around the adsorbent 1 in the desorption chamber 11. This is effected by activating the vacuum pump 33 for removing the air. This is followed by the desorption step D1 in which the heating medium 3 supplied to the adsorbent 1 is water H2O in the form of low-pressure steam S, which correspondingly flows through the desorption chamber 11. The water H2O from the mixture of low-pressure steam S and driven-out CO2 is condensed out in the separation vessel 27, and desorbed CO2 in concentrated form is obtained and separated off at the top of the separation vessel 27. The changeover is followed by the second desorption step D2, in which the cooling medium 5 used is the inert purge gas, in particular pure nitrogen N2. The nitrogen N2 is conducted in heat exchange with a heat exchange medium in the second cooling unit 39, cooled down to a predetermined cooling temperature and fed to the adsorbent 1 via the cooling conduit 21a through the first changeover apparatus 17a. The flow passes here through the adsorbent 1 and is cooled and processed for a further adsorption step A. Via the outlet 15, the nitrogen N2 is conducted to the separating device 25 through the second changeover apparatus 17b via the cooling conduit 21b. A cooling circuit 7 is achieved here. The heat Q2 obtained from the nitrogen N2 via the heat exchange medium in the second cooling unit 39 is fed to the heat pump arrangement 101. Useful heat QN can be obtained therefrom in the heat pump process, which is used to heat the heating medium 3. In the present context, energetic utilization is envisaged within the separation apparatus in that the useful heat QN is used to generate low-pressure steam S.The invention proposes a two-stage desorption process, with distinctly improved heat utilization by integration of a heat pump process for obtaining useful heat QN that arises inherently and utilization thereof for heating the heating medium 5. By means of a cheap external cooling medium 5 in the second desorption step D2, the cooling of the adsorbent 1 becomes much more efficient, more effective and, moreover, better controllable and reproducible. For this purpose, a dedicated cooling medium 5 is introduced into the desorption chamber 11 for the cooling step in the second desorption step D2. One particularly advantageous option here is, for example, nitrogen N2 as gaseous inert heat transfer medium. In order to minimize the nitrogen consumption, the heated nitrogen N2 is cooled again in a second cooling unit 39, a gas cooler, and can be recycled many times. The flooding and purging of the desorption chamber 11 with pure nitrogen N2 in the second desorption step D2 makes it possible that CO2 which has not been fully desorbed beforehand from the laden adsorbent 1 in the first desorption step D1 is now additionally driven out of the adsorbent 1 in the desorption chamber 11 together with the inert purge medium nitrogen N2. However, this is unproblematic in that the CO2 content in the circulation stream will accumulate only up to a partial pressure corresponding to the residual loading of the adsorbent 1 after the desorption D1, the effect of which is that the desorption of residual CO2 from the adsorbent 1 no longer experiences any driving force. After startup, for example with pure nitrogen, the cooling medium 5 experiences the described accumulation and CO2 saturation with a constantly low CO2 concentration in a cooling circuit 7 and can thus be further utilized efficiently continuously as cooling medium 5.At the same time, the contacting with nitrogen N2 as cooling medium 5 also results in controlled evaporation of the condensate of water H2O remaining on the adsorbent 1 and hence in an additional contribution to the cooling effect by evaporative cooling. Since the temperature of the nitrogen N2 can be controlled for this type of cooling and the duration of the desorption step D2 can also be chosen freely with the cooling step, it is possible to control a desired target temperature of the adsorbent for operation in the adsorption step A and also the degree of drying of the adsorbent. In the second cooling unit 39 (gas cooler), the water H2O evaporated by evaporative cooling is first separated again as condensate, i.e. liquid water H2O, and can thus advantageously be reused. The adhering water H2O is not emitted and consumed with the treated air flow.The cooling process in the second desorption step D2 is conducted at a slight positive pressure relative to the atmospheric pressure of the environment. Thus, there is no risk that oxygen from the ambient air can flow 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 gas volume of nitrogen N2 is released to the atmosphere when the adsorbent module 41 is again contacted and laden with ambient air. It is therefore advantageous and appropriate to replenish at least this gas volume of nitrogen N2 into the cooling circuit 7, for example by removal from the gas vessel 31. This can be effected, for example, in that a chosen working pressure is re-established as target pressure in the cooling circuit 7 by feeding nitrogen N2 from the gas vessel 31 into the cooling circuit 7 in a correspondingly controlled manner. Continuous supply of an inert purge gas, for example nitrogen N2, allows the cooling to be regulated and controlled in accordance with the requirements. As a result, cooling to a necessary surface temperature of the adsorbent 1 can be established reliably, 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 uniformly distributed manner via gas distributors (not shown in any detail in FIG 1), which avoids very disadvantageous temperature gradients or uneven temperature distributions. This is very advantageous compared to cooling by flash evaporation under reduced pressure according to the concepts known to date. This is because, in the case of the known flash evaporation, it is dependent on where and in what amount condensate has precipitated. Depending on the geometry of the adsorbent module 41, the precipitate of the condensate will not be distributed uniformly over the surface of the adsorbent 1. With the aid of flash evaporation, the evaporation thus only removes energy locally from the adsorbent material where water H2O is also present. Regions in the adsorbent module 41 where more water H2O is precipitated than is required for cooling cannot make any further contribution to cooling since no further energy flow is possible owing to the prevailing temperatures.A significant economic benefit results from the integration of the heat pump arrangement 101 into the separation apparatus 9. The main benefit of the approach described lies in the simultaneous use of the refrigeration provided at a favorable temperature level by the heat pump arrangement 101 for cooling the adsorbent 1. At the same time, preliminary cooling of the water vapor / CO2 mixture is brought about. At a high temperature level for heat pumps, useful heat QN can be provided for steam generation. This ensures a highly efficient process that, compared to the use of the renewable power in a solely electrically heated steam generator and a separate cooling system, lowers the power demand to < 40% relative to conventional DAC systems.Moreover, the proposed separation apparatus and the process regime bring about distinctly reduced degradation of the adsorbent 1 by oxygen exposure. As a result of degradation, the adsorbent gradually loses storage capacity for the binding of CO2, and so it either has to be replaced or regenerated in a complex manner. An extension of the lifetime of the adsorbent 1 by the cooling concept of the invention and the separation apparatus 9 proposed for this purpose and the advantageous method regime for the desorption step D additionally reduces maintenance expenditure and increases the plant availability of a DAC plant.
Claims
1. A method for separating CO2 from the atmosphere, in which an adsorption step (A) and a desorption step (D) that follows the adsorption step are conducted, wherein, in the adsorption step, an adsorbent (1) is contacted with air, wherein a portion of the CO2 present in the air is adsorbed by the adsorbent (1), and wherein, in the desorption step (D), the CO2-laden adsorbent (1) is contacted with a heating medium (3) and heated, wherein adsorbed CO2 is driven out thermally, forming a mixture of heating medium (3) and driven-out CO2, and wherein the adsorbent (1) is then contacted with a cooling medium (5) other than the heating medium (3) and is prepared for a new adsorption step (A), wherein the cooling medium (5) is subjected to a heat exchange with a coolant (M) circulating in a closed circuit and cooled, wherein the coolant (M) is first provided at a starting pressure (pA) and heated to a starting temperature (TA) in the heat exchange, wherein the coolant (M) is then compressed to a final pressure (pE), and wherein useful heat (QN) is transferred from the coolant (M) to the heating medium (3), and cooled coolant (M) is recycled and subjected to a heat exchange again with the cooling medium (5). 2. The method as claimed in claim 1, in which, in the heat exchange, the coolant (M) at the starting pressure (pA) is first evaporated with supply of heat, then compressed and cooled at a final pressure (pE) with release of useful heat (QN), wherein useful heat (QN) is transferred to the heating medium (3) and the latter is heated, and wherein the coolant (M) is then expanded. 3. The method as claimed in claim 1 or 2, in which an indirect heat exchange is conducted, wherein heat energy is transferred from the cooling medium (5) to the coolant (M) via an interposed circuit in which a heat transfer medium, in particular an interposed water circuit, is circulated. 4. The method as claimed in any of the preceding claims, in which, in a first step, coolant (M) is compressed from the starting pressure (pA) to a first intermediate pressure (p1), and wherein the mixture of heating medium (3) and driven-out CO2 is subjected to a heat exchange with recycled coolant (Μ1), wherein heat is transferred to recycled coolant (Μ1), wherein recycled coolant (Μ1) heated in this way is added to the compressed coolant (M) at the first intermediate pressure (p1), such that a combined stream of coolant (M) is provided at the first pressure (p1). 5. The method as claimed in claim 4, in which, in a second step, the combined stream of coolant (M) is compressed further to a second intermediate pressure (p2), wherein coolant (M2) recycled to the coolant (M) is fed in at the second intermediate pressure (p2), such that a combined stream of coolant (M) is provided at the second intermediate pressure (p2). 6. The method as claimed in claim 5, in which the combined stream of coolant (M) is compressed and liquefied from the second intermediate pressure (p2) to the final pressure (pE). 7. The method as claimed in any of the preceding claims, wherein the heating medium (3) used is water (H2O) in the form of low-pressure steam, wherein useful heat is supplied to the water (H2O) and water (H2O) is evaporated. 8. The method as claimed in claim 7, wherein water (H2O) is condensed out of the CO2 that has been driven out with the low-pressure steam (S), and desorbed CO2 is obtained in concentrated form. 9. The process as claimed in any of the preceding claims, in which a coolant (M) is employed, in particular n-butane, which is circulated in a closed circuit, wherein a phase transition is brought about, wherein useful heat is obtained from the enthalpy of evaporation. 10. A separation apparatus (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 an inlet (13) is connected to the desorption chamber (11) on the inlet side and an outlet (15) for the working medium on the outlet side, wherein a first changeover apparatus (17a) is connected upstream of the inlet (13) and a second changeover apparatus (17b) is connected downstream of the outlet (15), such that, in desorption operation in a desorption step (D), it is possible to switch from contacting of the adsorbent (1) with a heating medium (3) to contacting of the adsorbent (1) with a cooling medium (5) as working medium, wherein a heating conduit (19b) and a cooling conduit (21b) are connected to the second changeover apparatus (17b) on the outlet side, wherein a first cooling unit (37) is connected into the heating conduit (19b) and a second cooling unit (39) into the cooling conduit (21b), wherein at least one of the cooling units (39, 37) is set up 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 set up to provide useful heat (QN) on its hot side (117), which is transferable to the heating medium (3). 11. The separation apparatus (9) as claimed in claim 10, in which a steam vessel (29) is provided and is set up to receive useful heat (QN) from the heat pump arrangement (101) and to transfer it to water (H2O) as heating medium (3), such that water (H2O) in the form of low-pressure steam can be fed into the desorption chamber (11) via the inlet (13). 12. The separation apparatus as claimed in claim 11, in which the steam vessel (29) is implemented by a flash tank that has been set up to receive useful heat (QN) from the heat pump arrangement (101) in the form of pressurized hot water, such that low-pressure steam can be provided by a pressure reduction in the flash tank and can be fed to the desorption chamber (11) via the inlet (13). 13. The separation apparatus (9) as claimed in claim 10, 11 or 12, in which a gas vessel (31) for an inert purge gas is provided, such that the cooling medium (5) provided is an inert purge gas, by means of which the desorption chamber (11) with the adsorbent (1) is flushable and coolable. 14. The separation apparatus (9) as claimed in any of claims 10 to 13, in which the heat pump arrangement (101) has a compression heat pump which is operable with a coolant (M) and which has an evaporator (103), a compressor (105), and a condenser (111) downstream of the compressor (105). 15. The separation apparatus (9) as claimed in any of claims 10 to 14, in which, in the heat pump arrangement (101), the compressor (105) has at least two compression stages (105a, 105b, 105c) connected in series, wherein a feed conduit (107, 109) merges in between two successive compression stages (105a, 105b, 105c) at an intermediate pressure (p1, p2), such that recirculated coolant (M1, M2) can be mixed into the coolant (M). 16. The separation apparatus as claimed in any 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), such that indirect heat transfer is provided. 17. The separation apparatus (9) as claimed in claim 16, in which a plurality of desorption chambers (11) are provided and a central intermediate circuit is formed, such that a plurality of desorption chambers (11) is thermally coupled to the intermediate circuit via the cooling unit (37, 39).