Device and method for drying air or a sorbent in a system for separating carbon dioxide from the ambient air

Abstract

The invention relates to a drying unit (20) for drying air (58) or a sorbent (70) in a system (10) for separating carbon dioxide from the ambient air, wherein the drying unit (20) is located upstream or downstream of a process chamber (12) of the system (10) for separating the carbon dioxide from the ambient air, wherein the drying unit (20) has a main channel (22), wherein the dehumidifying unit (36) has at least one heating element (42) by means of which a sorbent (70) of the dehumidifying unit (36) can be heated substantially independently of the air flow through the drying unit (20). The invention furthermore relates to a system (10) for separating carbon dioxide from the ambient air, and to a method for drying air (58) or a sorbent (70) using such a drying unit (20).

Description

[0001] Description

[0002] Apparatus and method for drying air or a sorbent in a plant for separating carbon dioxide from the ambient air

[0003] The invention relates to a method for drying air and / or a sorbent in a plant for separating carbon dioxide from the ambient air and to a device for carrying out such a method for drying air and / or a sorbent in a plant for separating carbon dioxide from the ambient air according to the preamble of the independent patent claims.

[0004] To reduce the carbon dioxide content in the ambient air and achieve climate neutrality, not only must carbon dioxide emissions be reduced, but unavoidable carbon dioxide emissions must also be compensated accordingly. One option for compensating these carbon dioxide emissions is to capture carbon dioxide from the ambient air. This process is also known as a "direct air capture process," in which the carbon dioxide is captured directly from the ambient air and fed into a further process. Alternatively or additionally, carbon dioxide emissions can be compensated by permanently storing carbon dioxide in a reservoir, particularly in a rock layer, thus preventing it from entering the atmosphere.

[0005] Most known processes for separating carbon dioxide from ambient air employ a combination of pressure and temperature swing processes. Depending on the choice of negative pressure during desorption, the temperature ranges between adsorption and desorption, and the properties of the sorbent material, a carbon dioxide purity of more than 70% can be achieved in the product stream. Very high purity of more than 95% is usually only possible with a very strong vacuum during desorption.

[0006] Particularly with so-called physisorbents, which bind carbon dioxide from the ambient air primarily through physical binding mechanisms, the ambient air must be dried as completely as possible before the carbon dioxide is separated. This is because the absorption capacity of the physisorbents for water molecules is generally higher than for carbon dioxide, and in humid ambient air, the absorption capacity of the sorbent material for water vapor competes with the absorption capacity for carbon dioxide. Such drying of the ambient air can be achieved, for example, using silica gels, zeolites, or other hydroscopic materials, or a combination of several moisture-binding materials.

[0007] Regeneration of the hydroscopic substances can be achieved, in particular, by convective heat supply from a heated carrier gas, especially from heated ambient air. However, the amount of heat required for this is considerable due to the desorption enthalpy required and is higher than the pure evaporation enthalpy and the necessary heating of the hydroscopic substances and their carrier systems.

[0008] In the physisorbent group of sorbents, the most complete possible steam drying using hydroscopic sorbents is required prior to CO2 adsorption. Examples of these hydroscopic sorbents include silica gels, molecular sieves, zeolites, graphite, and other, sometimes organic, desiccants. They are used, for example, for air drying in industrial compressed air systems. To regenerate the desiccants used, manufacturers often recommend drying by heating for a certain period of time. These parameters depend on the desiccant used. However, the energy required for this is considerable and significantly exceeds the enthalpy input actually required to evaporate the water from the respective desiccant.

[0009] Furthermore, the use of sorbents for air drying is known, among other things, from the generation of instrument air with high requirements for low residual moisture, critical processes using process air, such as the filling and packaging of powdered hydrophilic active ingredients in medical technology, breathing air treatment in space travel or sorption drying in dishwashers.

[0010] In addition, other drying processes for temperature-sensitive materials, such as vacuum drying or freeze-drying, are known, particularly in the food and pharmaceutical industries. In vacuum drying, the applied negative pressure creates the desired partial pressure difference and, together with an energy input, expels the bound water vapor from the desiccant. However, this process requires considerable structural complexity, particularly for the large drying sizes and volumes typical of direct air capture systems. Freeze-drying is a drying process that utilizes the sublimation properties of water, allowing the necessary enthalpy to be added at low temperatures. A continuous stream of cold, dry air is used to remove the escaping water vapor.Here, too, the structural effort required to create the cold environment, including the cold chamber and freeze generation unit, is particularly significant. Drying using a vacuum or freeze-drying process requires significantly greater structural effort, which leads to correspondingly high costs for systems that capture carbon dioxide from the ambient air and the typical volume flows involved.

[0011] US 6610 122 B1 discloses a process for removing water vapor from a mixture of air, metabolic carbon dioxide (CO2), and water vapor, wherein the water vapor is removed from the mixture before the carbon dioxide is separated. The water vapor-containing mixture is passed through a membrane module that separates the water vapor from the air and carbon oxide mixture. The water vapor in the incoming mixture flows in one direction through the membrane in the module, from an inlet side of the membrane to an outlet side of the membrane. The membrane divides the module into two chambers, one of which receives the water vapor-containing mixture, and the other of which receives carbon dioxide-free air from a carbon oxide adsorbent station.

[0012] US 2018 / 0214 822 A1 discloses a system and method for removing carbon dioxide from ambient air using a sorbent to obtain relatively pure carbon dioxide. The carbon dioxide is removed from the sorbent using process heat, preferably in the form of steam, at a temperature in the range of no more than about 130°C to capture the relatively pure carbon dioxide and regenerate the sorbent for repeated use. Increased efficiency can be achieved by adding a smaller amount of a preferably pretreated exhaust gas containing a higher carbon dioxide concentration to the ambient air before contacting the sorbent. The captured carbon dioxide can be stored for further use or permanently sequestered.The above process provides purified carbon dioxide for further use in agriculture and chemical processes or for permanent sequestration. WO 2022 / 109746 A1 discloses an apparatus and method for separating carbon dioxide from air, in particular from air having a temperature of 0°C or less and / or a humidity of less than 5 grams of water per kilogram of air, using adsorbents. The apparatus comprises a housing having an internal volume containing a carbon dioxide absorbent bed, as well as a vacuum source, an inlet air source, and a heater connected to the housing so that the contents, pressure, and temperature of the internal volume of the housing can be controlled.

[0013] The prior art method of heating the desiccant by convective heating via a hot air stream until the sorbent material is dried fulfills the drying purpose, but has low energy efficiency because very large volumes of air must be heated, which are then passed through the desiccant. However, depending on the degree of dryness of the desiccant, only a portion of the introduced heat is actually used to evaporate the water and dry the desiccant. This results in the hot, humid exhaust air leaving the system essentially unused. While some of this waste heat can be recovered via heat exchangers, energy efficiency remains low even then. Furthermore, the utilization of waste heat via heat exchangers is complex and leads to increased design effort.Drying by vacuum drying or freeze drying also results in high construction costs for the system and is difficult to implement given the volume flows that occur in carbon dioxide separation systems.

[0014] The invention is based on the object of improving the drying of the air before it enters the process chamber for separating the carbon dioxide in a plant for separating carbon dioxide from the ambient air, in particular a device known as a direct air capture plant for separating carbon dioxide from the ambient air, and in particular of reducing the energy consumption of the plant.

[0015] According to the invention, this object is achieved by a drying unit for drying air or a sorbent in a system for separating carbon dioxide from the ambient air. The drying unit is arranged upstream or downstream of a process chamber of the system for separating the carbon dioxide from the ambient air. The drying unit has a main flow path in which a dehumidification unit for reducing the humidity of the ambient air is arranged before it flows into the process chamber, wherein the dehumidification unit has at least one heating element with which a sorbent of the dehumidification unit can be heated essentially independently of an air flow through the drying unit. A drying unit according to the invention enables particularly efficient drying of a sorbent for drying air in a system for separating carbon dioxide from the ambient air.In particular, this can prevent the heat from flowing out of the system essentially unused, thus wasting energy that cannot be used to dry the sorbent.

[0016] The additional features listed in the dependent claims enable advantageous further developments and improvements of the drying unit described in the independent claim.

[0017] In a preferred embodiment of the invention, the drying unit has a bypass with which the dehumidification unit can be bypassed. The drying unit further has a control element, in particular a control flap, with which an air flow can be directed selectively through the main flow path, through the bypass, or partially through both the main flow path and the bypass.

[0018] In a preferred embodiment of the drying unit, the dehumidification unit comprises at least one heating element, with which a sorbent of the dehumidification unit can be heated independently of the air flow. This enables particularly efficient heat transfer for drying the sorbent.

[0019] It is particularly preferred if the heating element is configured to transfer its heat to the sorbent of the dehumidification unit essentially by conduction. Heat transfer by conduction is a particularly efficient method of heat transfer, allowing for selective heat introduction into the sorbent and thus achieving particularly efficient drying of the sorbent.

[0020] Alternatively, it is advantageously provided that the heating element is designed to transfer its heat to the sorbent of the dehumidification unit essentially by thermal radiation. Heat transfer by thermal radiation is a further possibility for specifically introducing heat into the dehumidification unit of the drying unit to dry the sorbent. In a further improvement of the drying unit, a heat exchanger for heating the gas stream is arranged upstream of the dehumidification unit in the flow direction of a gas stream from the process chamber of the system through the drying unit. This allows additional energy to be introduced into the gas stream so that the moisture can be more easily evaporated from the sorbent and the sorbent can be regenerated. In addition, energy efficiency can be further increased if an already existing heat source is utilized via a heat exchanger to heat the gas stream.

[0021] A further improvement to the drying unit provides for a heat exchanger for heat recovery to be installed downstream of the dehumidification unit in the direction of flow of a gas stream from the plant's process chamber through the drying unit. A downstream heat exchanger for heat recovery can further increase the efficiency of the drying unit. In particular, the recovered heat can be fed into the plant's process chamber as process heat for separating carbon dioxide from the ambient air.

[0022] According to an advantageous embodiment of the drying unit, the bypass comprises a nozzle with which the flow conditions, in particular the pressure conditions, in the drying unit can be manipulated. This allows pressure equalization between the main duct and the bypass, so that the flow conditions, in particular the partial air flows through the main duct and the bypass, can be adjusted accordingly.

[0023] In a further preferred embodiment of the invention, the drying unit comprises a first drying stage with a first drying material and a second drying stage, arranged upstream or downstream of the first drying stage, with a second drying material different from the first drying material. This enables particularly efficient drying of the ambient air supplied to the process chamber of the carbon dioxide separation system.

[0024] According to a particularly advantageous embodiment of the drying unit, the first drying material is a silica gel or comprises a silica gel. Silica gel enables incomplete pre-drying of the ambient air in a simple and cost-effective manner. Furthermore, it is advantageously provided that the second drying material is a zeolite or comprises a zeolite. A zeolite can separate the remaining moisture from the ambient air, so that essentially completely dry air can be supplied to the process chamber of the system for separating carbon dioxide from the ambient air. This enables particularly efficient separation of carbon dioxide, particularly when using a physisorbent.

[0025] A further improvement to the drying unit provides for the dehumidification unit to be separated from the main duct in a substantially gas-tight manner by additional separation elements and then evacuated. For this purpose, a suppression or vacuum pump can be installed on the dehumidification unit. This can further promote the drying of the sorbent and further reduce the energy required for drying.

[0026] According to a further advantageous embodiment of the drying unit, the drying unit comprises a compressor directly connected to the dehumidification unit via an air line. The air line comprises air injection tubes configured to inject hot, dry air into the sorbent. The compressor can provide a dry, hot air stream, which can be introduced into the sorbent to remove the water evaporated by the heating element and thus reduce the partial pressure. This can promote the evaporation of further water bound in the sorbent and reduce energy consumption.

[0027] It is preferred if the air line has a branch and branches into a first branch and a second branch, with a heating device arranged in the first branch and a cooling device arranged in the second branch. The heating device allows particularly hot, dry air to be introduced into the sorbent to promote the evaporation of water and the removal of water vapor. The cooling unit allows the sorbent to be cooled again after complete regeneration with low energy consumption in order to condition the sorbent for the dehumidification of air in a subsequent operating cycle.

[0028] It is particularly preferred if the two branches reunite to form a common air line downstream of the heating device or downstream of the cooling device. This minimizes the design effort and only requires one air line to distribute the air, which is to be introduced into the sorbent via the air injection tubes. In an advantageous embodiment of the drying unit, air ducts are integrated into the sorbent or a sorbent holder in order to introduce the air flow from the compressor into the sorbent and to distribute it from the air ducts into the air injection tubes. This enables particularly efficient removal of water vapor escaping from the sorbent material, so that the partial pressure during regeneration can be kept low and essentially complete regeneration of the sorbent can be achieved.

[0029] In a further advantageous embodiment of the invention, the dehumidification unit comprises a heating element, in particular a heat exchanger, for heating the sorbent. The heating element has at least one inlet line for introducing hot steam into the heating element and one outlet line for removing condensate from the heating element. This enables particularly energy-efficient heating of the dehumidification unit. Energy can be saved, particularly compared to a method known from the prior art, in which the dehumidification unit is regenerated convectively by a heated gas stream.

[0030] In a further advantageous embodiment of the drying unit, the heating element comprises several heating plates, each with at least one condensation loop. The heating plates are integrated into a sorbent holder for the sorbent or form this sorbent holder. This enables particularly uniform and efficient heating of the sorbent.

[0031] In an advantageous embodiment of the heating plates, the heating plates are additionally provided with air injection tubes, through which hot, dry air can be injected into the sorbent material. This simplifies the design of the sorbent holder and eliminates the need for additional air ducts for supplying dry, hot air to the sorbent material.

[0032] A further aspect of the invention relates to a system for separating carbon dioxide from the ambient air, which comprises a drying unit as described in the preceding paragraphs. Such a system enables particularly efficient drying of the air stream supplied to the process chamber of the system.

[0033] It is particularly preferred if the system comprises a process chamber and a sorption material arranged in the process chamber for absorbing carbon dioxide, wherein the sorption material is a physisorbent or comprises a physisorbent. Since physisorbents in particular have a high binding affinity for atmospheric humidity, this humidity can limit the absorption of carbon dioxide. Therefore, especially when using a physisorbent, it is particularly important to achieve efficient drying of the ambient air by the proposed drying unit.

[0034] A further aspect of the invention relates to a method for drying air and / or a sorbent in a plant for separating carbon dioxide from the ambient air with such a drying unit, which comprises the following steps:

[0035] Drying an air stream supplied to a process room of the plant for separating carbon dioxide from the ambient air by a sorbent of a dehumidification unit,

[0036] Regenerating the sorbent, whereby hot, dry air from the process chamber is introduced into the drying unit and fed to the dehumidification unit, reducing the cross-section of the main duct by a control element, whereby a first partial air flow is passed through a bypass and a second partial air flow is passed through the narrowed main duct,

[0037] Heating the sorbent of the dehumidification unit by a first heating element, wherein the heat of the heating element is transferred to the sorbent substantially independently of an air flow through the drying unit, in particular by heat conduction.

[0038] Such a process enables particularly energy-efficient regeneration of the sorbent used to dry the air stream supplied to the plant's process chamber. This can reduce the plant's energy requirements.

[0039] Alternatively, a method for drying air or a sorbent in a plant for separating carbon dioxide from the ambient air with a drying unit is proposed, which comprises the following steps:

[0040] Drying an air stream supplied to a process chamber of the carbon dioxide separation system by means of a sorbent in a dehumidification unit, heating the sorbent by means of a heating element. The heating element is designed as a heat exchanger, and hot steam is introduced into the heating element and condensate is removed from the heating element. The sorbent is regenerated by introducing hot, dry air from the process chamber or heated fresh air into the sorbent. This process also enables particularly energy-efficient regeneration of the sorbent, since heating is primarily achieved through heat conduction and heat radiation from the energy supplied to the sorbent via the heating element. The hot, dry air merely supports the regeneration of the sorbent by removing the water vapor from the sorbent and thus reducing the partial pressure. This can accelerate the drying of the sorbent.

[0041] In an advantageous embodiment of the method, it is provided that a humidity and / or a temperature of the second partial air flow, in particular a humidity and a temperature, are determined downstream of the dehumidification unit, and the heating power of the first heating element and / or the air volume of the second partial air flow is controlled as a function of the determined humidity and / or temperature of the second partial air flow. By controlling or regulating the heating power and / or the second partial air flow, the energy efficiency of the drying unit and thus of the system for separating carbon dioxide from the ambient air can be further improved.

[0042] In a further improvement of the method, it is provided that at least a portion of the heat introduced into the drying unit by the heating element is recovered by a heat recovery unit and fed to the process chamber of the plant for separating carbon dioxide from the ambient air.

[0043] This will further improve the energy efficiency of the system for separating carbon dioxide from the ambient air.

[0044] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case.

[0045] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. They show:

[0046] Figure 1 is a schematic representation of a system according to the invention for

[0047] Separation of carbon dioxide with a drying unit according to the invention; Figure 2 shows a drying unit according to the invention in a first operating state, in which a sorbent in the dehumidification unit dries the ambient air supplied to the process chamber;

[0048] Figure 3 shows a drying unit according to the invention in a second operating state in which the sorbent of the dehumidification unit is regenerated;

[0049] Figure 4 shows a flow chart for carrying out a method according to the invention;

[0050] Figure 5 shows a further embodiment of an inventive

[0051] Drying unit for a plant for separating carbon dioxide from the ambient air;

[0052] Figure 6 shows a drying unit with a plurality of sorbent beds for such a

[0053] drying unit;

[0054] Figure 7 shows a housing for such a drying unit; and

[0055] Figure 8 shows a further embodiment of an inventive

[0056] Drying unit for a plant for separating carbon dioxide from the ambient air.

[0057] Figure 1 shows a schematic representation of a system 10 for separating carbon dioxide from the ambient air. The system 10 comprises a process chamber 12 in which a sorbent holder 14 is arranged, which supports a sorbent 16. The sorbent 16 is a physisorbent 80, which binds carbon dioxide from the ambient air essentially through physical binding mechanisms and thus separates it from the ambient air. Such physisorbents 80 generally have a higher absorption capacity for water vapor or atmospheric humidity than for carbon dioxide. Therefore, with physisorbents, it is particularly important that the air 58 supplied to the process chamber 10 is essentially free of atmospheric humidity. The system 10 further comprises a conveying element 82, in particular a fan 84, for generating an air flow and conveying the ambient air into the process chamber 12 or expelling the air 58 from the process chamber.Furthermore, an evacuation unit 86 is provided on the process chamber 12, with which a negative pressure can be generated in the process chamber 12, as well as a heating device 88, with which the process chamber 12 can be heated to a process temperature for separating the carbon dioxide, which process temperature is above the ambient temperature, in particular in a temperature range of 90°C to 200°C, preferably in the range of 120°C to 150°C.

[0058] The process chamber 12 is connected via an inlet 18 to a drying unit 20, via which dried ambient air is supplied to the process chamber 12. For this purpose, the ambient air is introduced into the drying unit 20 through an inlet 54 or sucked into the drying unit 20 by the conveying element 82. The drying unit 20 comprises a main duct 22, in which a dehumidification unit 36 ​​is arranged, and a bypass 24, via which the dehumidification unit 36 ​​can be bypassed. For this purpose, the bypass 24 branches off from the main duct 22 at a branch 28 downstream of the inlet 54 and upstream of the dehumidification unit 36 ​​and flows back into the main duct 22 at an inlet 26 downstream of the dehumidification unit 36 ​​and upstream of the inlet 18 into the process chamber 12.At the inlet 26, a control element 30 in the form of a control flap 32 is arranged, with which the air flow through the main duct 22 and / or through the bypass 24 can be controlled. To manipulate the flow conditions in the drying unit 20, a nozzle 34 can be arranged in the bypass 24, with which the flow can be accelerated and the pressure reduced accordingly. A drive unit 52 for adjusting the control flap 32 is arranged on the control flap 32.

[0059] The dehumidification unit 36 ​​comprises a first dehumidification stage 38 and a second dehumidification stage 40 arranged downstream of the first dehumidification stage 38 in the flow direction, each of which is provided with a sorbent 70 for absorbing atmospheric moisture. The first dehumidification stage 38 comprises a first drying material 76, in particular a silica gel 72, with which a cost-effective, but generally incomplete, drying of the air can be achieved. The second dehumidification stage 40 comprises a second drying material 78, in particular a zeolite 74, with which a substantially complete drying of the air flow supplied to the process chamber 12 is achieved. The dehumidification unit 36 ​​can be heated via a first heating element 42.The first heating element 42 can be designed, in particular, as an electrical heating element or a heat exchanger, wherein the heat from the first heating element is transferred, in particular, by thermal conduction to the sorbents 70 of the first dehumidification stage 38 and / or the second dehumidification stage 40. Alternatively, the first heating element 42 can also be designed as a heating element that transfers its heat primarily by thermal radiation to the sorbents 70 of the dehumidification unit 36. Furthermore, a temperature sensor 48 and a humidity sensor 50 are arranged in the main channel 22 of the drying unit 20.

[0060] Downstream of the dehumidification unit 36 ​​and upstream of the inlet 18 into the process chamber 12, a second heating element 44, in particular a heat exchanger, can be arranged, with which the dehumidified air can be further heated before entering the process chamber 12. Furthermore, a heat recovery unit 46 can be arranged upstream of the dehumidification unit 36.

[0061] The system 10 for separating carbon dioxide from the ambient air or the drying unit 20 is assigned a control unit 60, with which the process for drying the air and / or separating the carbon dioxide can be controlled. The control unit 60 comprises a memory unit 62 and a computing unit 64. Computer program code 66 is stored in the memory unit 62, which executes a method according to the invention for drying air and / or a sorbent when the computer program code 66 is executed by the computing unit 64 of the control unit 60.

[0062] Figure 2 shows the drying unit 20 in a first operating state, in which ambient air is supplied to the process chamber 12 of the system 10 for separating carbon dioxide, and this ambient air 58 is dried by the drying unit 20. The bypass 24 is closed by the control flap 32, so that the air flow is guided completely through the main duct 22 of the drying unit 20. The air flow is first pre-dried by the first dehumidification stage 38, in particular by a silica gel 72, of the dehumidification unit 36. The air flow is then essentially completely dried by the second dehumidification stage 40 of the dehumidification unit 36, in particular by a zeolite 74, and then fed to the process chamber 12 of the system for separating carbon dioxide, in which the carbon dioxide is bound by a physisorbent and separated from the dried ambient air.In addition, the dried ambient air can be heated by the first heating element 42 in the dehumidification unit 36 ​​and / or by the second heating element 44, which is arranged downstream of the dehumidification unit 36 ​​and upstream of the process chamber 12.

[0063] Figure 3 shows the drying unit 20 in a second operating state, in which the sorbents 70 of the dehumidification unit 36 ​​are regenerated in order to be able to dry this ambient air again when the process chamber 12 of the system is subsequently refilled with ambient air. In this second operating state, the flow is guided essentially opposite to the flow direction in the first operating state. In a desorption phase of the system 10 for flushing out the carbon dioxide bound in the physisorbent 82, dry, hot air initially flows from the process chamber 12 into the drying unit 20. This dry, hot air is initially passed completely through the main duct 22 of the drying unit 20 and thus through the dehumidification unit 36.However, the volume of this heated air is limited and thus the temperature decreases rapidly, so that with decreasing warming effects the control flap 32 is closed and only a portion of the air flow is passed through the dehumidification unit 36 ​​and another, preferably significantly larger portion, is passed through the bypass 24, so that only a gap 56 at the branch 26 remains as an inlet into the main duct 22.

[0064] The bypass 24 can contain a contour adjustment, in particular a nozzle 34 or other flow components that generate a certain air pressure buildup, leading to a certain pressure equalization between the bypass 24 and the main channel 22. Alternatively, the amount of purge air through the dehumidification unit 36 ​​can also be controlled via two or more control elements 30, which are preferably designed as louvers, flaps, or slides, with one control element 30 being arranged upstream of the inlet 18 into the drying unit 20 and another control element 30 being arranged at the junction 26 between the main channel 22 and the bypass 24. The amount of purge air for drying the sorbent 70 in the dehumidification unit 36 ​​can be regulated over the drying process according to the required amount.

[0065] At the same time, after the control flap 32 is closed to reduce the cross-section of the main duct 22, heat is supplied to the first heating element 42 integrated in the dehumidification unit 36. Furthermore, the air flow directed through the reduced main duct can be heated by the second heating element 44 to achieve the most efficient expulsion of moisture from the sorbent 70 of the dehumidification unit 36. As the sorbent 70 heats up, water vapor is expelled from the sorbent 70 and transported away. This removal can be facilitated by the air flow through the bypass. As the sorbent 70 dries out, the amount of water vapor expelled also decreases, thus the outlet air contains less moisture.The temperature sensor 48 and the humidity sensor 50 at the outlet of the dehumidification unit 36 ​​can be used to control the heating output of the first and / or second heating element and the air volume passed through the dehumidification unit 36. Optionally, a heat recovery unit 46 is positioned at the outlet of the dehumidification unit 36, which cools the moist outlet air to an economically reasonable extent and, if possible, also condenses a large portion of the water vapor. The extracted heat can advantageously be fed into the internal heat circuit of the system 10 for separating carbon dioxide from the ambient air. Finally, the thus cooled partial air flow from the main duct merges with the air flow from the bypass and can be directed to an exhaust air fan and / or into the environment.

[0066] The process shown in Figure 3 enables a significantly more energy-efficient drying of the air 58 or the sorbent 70, so that the overall energy efficiency of the system 10 for separating carbon dioxide from the ambient air can be improved.

[0067] Figure 4 shows a flow chart for carrying out a method for drying a sorbent 70. In a first process step <100> Hot dry air is expelled from the process chamber 12 of the system 10 for separating carbon dioxide from the ambient air and introduced into the main duct 22 of the drying unit 20. In one process step <110> the cross section of the main channel 22 is narrowed by the control element 30 to a gap 56. In a process step <120> , which is carried out simultaneously with the process step <110> can be done before the procedural step <110> can be started or after the process step <120> is introduced, the sorption material 70 of the dehumidification unit 36 ​​in the main duct 22 is heated by a first heating element 42 essentially independently of the air flow. Heat is essentially transferred from the first heating element 42 to the sorbent 70 by thermal conduction.In addition, in one process step <130> The air flow introduced through the gap 56 into the main channel 22 is heated by a further heating element 44. In a process step <140> The moisture is removed from the sorbent 70, whereby the humidity and temperature of the air flow passing through the dehumidification unit 36 ​​are measured and used to control the air volume and / or the heating power of the first heating element 42. In an optional process step <150> The air can be cooled downstream of the dehumidification unit 36 ​​in a heat recovery unit 46, allowing the liquid to be condensed and removed. Furthermore, the recovered heat can be fed to the process chamber 12 for separating carbon dioxide from the ambient air.In one process step <160> The air flow from the main duct 22 of the drying unit 20 is mixed with the air flow 24 from the bypass and accordingly discharged from the drying unit 20. Figure 5 shows an alternative embodiment of a drying unit 20 according to the invention for a system 10 for separating carbon dioxide from the ambient air. The drying unit 20 comprises a main duct 22, which connects an inlet 54 and an outlet of a housing 98 of the drying unit 20, shown in Figure 7. The drying unit 20 comprises a dehumidification unit 36 ​​with at least one dehumidification stage 38, preferably, as shown in Figure 6, a plurality of dehumidification stages 38, 40 through which an air flow flows sequentially through the main duct 22.To heat the dehumidification unit 36, a heating element 42 in the form of a heat exchanger is provided, wherein hot steam is introduced into the heat exchanger for heating, and this steam condenses at an outlet. For this purpose, the heating element 42 comprises an inlet line 91 for the hot steam and an outlet line 92 for discharging the condensate. The dehumidification unit 36 ​​comprises one or more sorbents 70, in particular a silica gel 72 and / or a zeolite 74, for drying the fresh air supplied to the process chamber 12 of the system 10 for separating carbon dioxide from the ambient air. The dehumidification unit 36 ​​also has a plurality of air ducts 94 for introducing air into the sorbent 70. Starting from the air ducts 94, air injection tubes 96 are provided, with which hot, dry air can be blown into deeper layers to regenerate the sorbent 70.The air channels 94 can be formed either directly in the sorbent 70 or in a sorbent holder 122.

[0068] The sorbent holder 122 can comprise one or more heating plates 116, with which the sorbent holder 122 can be heated. The heating plates 116 are preferably arranged at defined intervals in the sorbent holder 122 in order to introduce heat into the dehumidification unit 36 ​​as evenly as possible. The heating plates 116 each comprise a steam inlet 91 and a condensate outlet 92, wherein the steam inlet 91 and the condensate outlet 92 are connected to one another by a condensation loop 124, so that the steam introduced into the steam inlet 91 cools as it flows through the condensation loop 124, thereby heating the sorbent holder 122 and the sorbent 70. Condensate forms from the steam, which is then drained out of the heating plate 116 through the condensate outlet 92.

[0069] The drying unit 20 further comprises an air line 114, which connects an outlet 18 of a process chamber 12 of the system 10 for separating carbon dioxide to the dehumidification unit 36. A compressor 90 is arranged in the air line 114 to compress the hot, dry exhaust air from the process chamber 12. The air line 114 branches at a branch 26 into a first branch 118 and a second branch 120. A heating device 100 is arranged in the first branch 118, with which the hot, dry exhaust air from the process chamber 12 can be further heated. A cooling device 104 is arranged in the second branch 120. The first branch 118 and the second branch 120 can each be shut off by a control valve 102, 106 so that the air is selectively guided through the first branch 118 or the second branch 120.Downstream of the heating device 100 in the first branch 118 and downstream of the cooling device 104 in the second branch 120, the two branches 118, 120 reunite at an inlet 28 to form a common air line 114.

[0070] The heat supply in the dehumidification unit is primarily provided by the heating element 42. In addition, a small partial flow of exhaust air from the process chamber 12 supports the drying of the sorbent, as this partial flow of exhaust air is compressed by the compressor 90 and the heating device 100 is further heated. The hot, dry purge air thus generated is then passed through the air injection tubes 112, which are arranged between two heating surfaces of the sorbent holder 122 to inject hot, dry air directly into the sorbent through fine outlet openings. The additional injection of hot, dry air can accelerate the drying process of the sorbent 70.

[0071] As the material temperature of the sorbent 70 increases, the evaporation and binding enthalpy of the water stored in the sorbent material is increasingly exceeded. The water is locally evaporated and released into the ambient air around the sorbent 70 in the drying unit 20. However, the partial pressure near the sorbent 70 increases, inhibiting further desorption of water.

[0072] The hot, dry air injected directly into the sorbent 70 now helps transport the locally desorbed water molecules out of the sorbent 70 in vapor form, thus keeping the partial pressure in the dehumidification unit 36 ​​around the sorbent 70 low so that the desorption process is not disrupted and can proceed almost completely. The air-water vapor mixture is discharged via a purge outlet opening 108, shown in Figure 7, on the dryer housing 98 of the drying unit 20 and can be converted into condensate by an exhaust air cooler 110.

[0073] The amount of air to be introduced into the sorbent 70 is primarily determined by the most uniform air injection into the sorbent material and thus the most uniform partial pressure reduction in the sorbent 70. The amount of air used to expel the water vapor from the sorbent 70 is comparatively small. After the drying of the sorbent material of the sorbent 70 is completed, the steam supply via the heating plates 116 is interrupted, and the air stream injected into the sorbent material through the air injection tubes is no longer heated but cooled via the cooling device 104. This removes the compression heat from the air and creates a cold, dry air stream, which is injected into the sorbent 70 via the air injection tubes 96.The aim of this process step is to cool the sorbent material of the sorbent 70, which has been heated by the desorption of the water, in the shortest possible time in order to prepare the sorbent 70 for further drying of fresh air.

[0074] Compared to known drying processes, in which the sorbent 70 is dehumidified and regenerated by a hot gas stream, the proposed process requires only a comparatively small air mass flow to dry the sorbent 70. The main heat supply is via the heating element 42 in order to achieve the most direct heat transfer possible from the heating element 42 to the sorbent 70. This saves a large amount of heat required to heat the gas stream, making the process significantly more energy-efficient than known drying processes for the sorbent.

[0075] Figure 8 shows a further exemplary embodiment of a drying unit 20 for a system 10 for separating carbon dioxide from the ambient air. While the structure is essentially the same as that shown in Figure 5, only the differences will be discussed below. In contrast to the exemplary embodiment shown in Figure 5, the air injection tubes 112 in this exemplary embodiment are integrated into the heating plates 116 of the heating element 42. This eliminates the need for the air channels 94 in the sorbent 70. In this exemplary embodiment, the heating plates 116 are connected to the air line 114 so that the dry, hot exhaust air compressed by the compressor 90 can be fed to the air injection tubes 112 in the heating plates 116.

[0076] List of reference symbols

[0077] Plant for the separation of carbon dioxide from the ambient air

[0078] Process room

[0079] sorbent holder

[0080] Sorbents

[0081] Outlet / Inlet

[0082] Drying unit

[0083] main channel

[0084] bypass

[0085] Junction / Junction

[0086] Junction / Junction

[0087] Control

[0088] control flap

[0089] nozzle

[0090] Dehumidification unit first dehumidification stage second dehumidification stage first heating element second heating element

[0091] Heat recovery unit

[0092] Temperature sensor

[0093] Humidity sensor

[0094] drive unit

[0095] Outlet / Inlet

[0096] gap

[0097] Air control unit

[0098] Storage unit Computing unit Computer program code

[0099] Sorbent

[0100] Silica gel

[0101] Zeolite first drying material second drying material

[0102] Physisorbent conveying element

[0103] fan

[0104] Evacuation unit

[0105] Heating device

[0106] compressor

[0107] Inlet line / steam line

[0108] Drain line / condensate line

[0109] Air ducts

[0110] Air injection tubes

[0111] Dryer housing

[0112] Heating device

[0113] control valve

[0114] Cooling device

[0115] Control valve flush outlet opening

[0116] Exhaust air cooler

[0117] Air injection tubes

[0118] Air line

[0119] Heating plate first branch second branch

[0120] Sorbent holder

[0121] Condensation loop

Claims

Patent claims 1. A drying unit (20) for drying air (58) or a sorbent (70) in a plant (10) for separating carbon dioxide from the ambient air, wherein the drying unit (20) is arranged upstream or downstream of a process chamber (12) of the plant (10) for separating the carbon dioxide from the ambient air, wherein the drying unit (20) has a main duct (22) in which a dehumidification unit (36) is arranged for reducing the humidity of the ambient air before it flows into the process chamber (12), wherein the dehumidification unit (36) has at least one heating element (42) with which a sorbent (70) of the dehumidification unit (36) can be heated substantially independently of an air flow through the drying unit (20).

2. Drying unit (20) according to claim 1, wherein the drying unit (20) comprises a bypass (24) with which the dehumidification unit (36) can be bypassed, and wherein the drying unit (20) has a control element (30) with which an air flow can be directed selectively through the main duct (22), through the bypass (24) or proportionally through both the main duct (22) and through the bypass (24).

3. Drying unit (20) according to claim 2, wherein the heating element (42) is configured to transfer its heat to the sorbent (70) of the dehumidification unit (36) substantially by thermal conduction or thermal radiation.

4. Drying unit (20) according to one of claims 1 to 3, wherein a heat exchanger (44) for heating the gas flow is connected upstream of the dehumidification unit (36) in the flow direction of a gas flow from the process space (12) of the system (10) through the drying unit (20) and / or wherein a heat exchanger (46) for heat recovery is connected downstream of the dehumidification unit (36) in the flow direction of a gas flow from the process space (12) of the system (10) through the drying unit (20).

5. Drying unit (20) according to one of claims 1 to 4, wherein the drying unit (20) comprises a compressor (90) which is directly connected to the dehumidification unit (36), wherein the air line (114) comprises air injection tubes (96, 112) for blowing hot, dry air into the sorbent (70) for dehumidification.

6. Drying unit (20) according to claim 5, wherein the air line has a branch (26) and branches into a first branch (118) and a second branch (120), wherein a heating device (100) is arranged in the first branch (118) and a cooling device (104) is arranged in the second branch (120).

7. Drying unit (20) according to claim 5 or 6, wherein air channels (94) are integrated into the sorbent (70) in order to introduce the air flow from the compressor (90) into the sorbent (70) and to distribute it from there to the air injection tubes (96, 112).

8. Drying unit (20) according to one of claims 1 to 7, wherein the dehumidification unit (36) comprises a heating element (42) for heating the sorbent (70), wherein the heating element (42) has at least one inlet line (91) for introducing hot steam into the heating element (42) and a drain line (92) for removing a condensate from the heating element (42).

9. Drying unit (20) according to one of claims 1 to 8, wherein the heating element (42) has a plurality of heating plates (116), each having a condensation loop (124), wherein the heating plates (116) are integrated into a sorbent holder (122) for the sorbent (70) or form this sorbent holder (122).

10. Drying unit (20) according to one of claims 1 to 9, wherein the drying unit (20) comprises a first dehumidification stage (38) with a first drying material (76) and a second dehumidification stage (40) upstream or downstream of the first dehumidification stage (38) with a second drying material (78) different from the first drying material (76).

11. Drying unit (20) according to one of claims 1 to 10, wherein the first drying material (76) comprises a silica gel (72) and / or the second drying material (78) comprises a zeolite (74).

12. A method for drying air or a sorbent (70) in a plant (10) for separating carbon dioxide from the ambient air with a drying unit (20) according to one of claims 1 to 4, comprising the following steps: Drying an air stream supplied to a process chamber (12) of the plant (10) for separating carbon dioxide by a sorbent (70) of a dehumidification unit (36), Regenerating the sorbent (70), whereby hot, dry air from the process chamber (12) is introduced into the drying unit (20) and fed to the dehumidification unit (36), Reducing the cross-section of the main duct (22) by a control element (30), wherein a first partial air flow is passed through a bypass (24) and a second partial air flow is passed through the narrowed main duct (22), Heating the sorbent (70) of the dehumidification unit (36) by a first heating element (42), wherein the heat of the heating element (42) is transferred to the sorbent (70) substantially independently of an air flow through the drying unit (20).

13. A method for drying air or a sorbent (70) in a plant (10) for separating carbon dioxide from the ambient air with a drying unit (20) according to one of claims 5 to 9, comprising the following steps: Drying an air stream supplied to a process chamber (12) of the plant (10) for separating carbon dioxide by a sorbent (70) of a dehumidification unit (36), Heating the sorbent (70) by a heating element (42), wherein the heating element (42) is designed as a heat exchanger and hot steam is introduced into the heating element (42) and condensate is discharged from the heating element (42), wherein the sorbent (70) is regenerated by compressing hot, dry air from the process chamber (12) or heated fresh air and then introducing it into the sorbent (70).

14. Plant (10) for separating carbon dioxide from the ambient air with a drying unit (20) according to one of claims 1 to 11 15. Plant (10) for separating carbon dioxide from the ambient air according to claim 14, wherein the plant (10) comprises a process chamber (12) and a Process chamber (12) has sorption material arranged for absorbing carbon dioxide, wherein the sorption material is a physisorbent (80) or comprises a physisorbent (80).

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