Apparatus for separating carbon dioxide from ambient air, method, and control device for operating such an apparatus

Abstract

The invention relates to an apparatus (100) for separating carbon dioxide (C) from ambient air (A). The apparatus (100) comprises a sorption chamber (110) having a sealable air inlet (112) for admitting ambient air (A), a sealable air outlet (114) for releasing carbon dioxide-reduced outlet air (B), and a sealable carbon dioxide outlet (116) for releasing carbon dioxide (C). The apparatus (100) also comprises a sorption means (120) which is arranged in the sorption chamber (110) and is designed to cause reversible adsorption of carbon dioxide (C) from the ambient air (A) on the sorption means (120). The apparatus (100) also comprises at least one conveying device (130) which is designed to convey the ambient air (A) into the sorption chamber (110), to convey the outlet air (B) out of the sorption chamber (110), to evacuate the sorption chamber (110), and to convey carbon dioxide (C) out of the sorption chamber (110). The apparatus (100) also comprises a temperature-control device (140) which is designed to control the temperature of the sorption means (120) in order to desorb carbon dioxide (C) sorbed on the sorption means (120). The apparatus (100) also comprises at least one electrochemical gas sensor (150) which is designed to detect at least one oxygen-dependent measurement variable in the sorption chamber (110).

Description

[0001] Description

[0002] title

[0003] Device for separating carbon dioxide from ambient air, method and control device for operating such a device

[0004] State of the art

[0005] The invention relates to a device for separating carbon dioxide from ambient air, and to a method and a control device for operating such a device according to the preamble of the independent claims. The present invention also relates to a computer program.

[0006] The process known as Direct Air Capture (DAC) describes the removal of carbon dioxide from the atmosphere. DAC processes are typically time-controlled, with sufficient process time being allowed until each sub-process is safely completed, which can represent a certain inefficiency in plant utilization.

[0007] Disclosure of the invention

[0008] Against this background, the approach presented here presents a device for separating carbon dioxide from ambient air, a method for operating such a device, a corresponding control unit, and finally a corresponding computer program according to the main claims. The measures listed in the dependent claims enable advantageous refinements and improvements of the device specified in the independent claim. According to embodiments, suitable gas sensors, for example automotive gas sensors, can be used in DAC systems to detect and control oxygen-based state variables and process times. In other words, the use of gas sensors, for example automotive exhaust gas sensors, is proposed in particular to detect relevant switching conditions in the DAC system instead of a time control.In particular, the integration of an electrochemical gas sensor, such as an automotive exhaust gas sensor or automotive electrochemical exhaust gas sensor, can be provided for measuring the oxygen excess or deficiency in the form of atmospheric oxygen or carbon dioxide directly in the process fluid in a DAC system to enable targeted system control. For example, sensors similar to or equivalent to known broadband lambda sensors, step-type lambda sensors, or nitrogen oxide sensors (NOx sensors) can be used.

[0009] The integration of at least one gas sensor, for example an automotive exhaust gas sensor or an automotive electrochemical exhaust gas sensor, enables cost-effective system control and performance optimization of a DAC system compared to systems without direct determination or measurement of the oxygen or carbon dioxide content as characteristic system parameters, or compared to determination using complex measurement methods. Only sophisticated broadband lambda sensors, step-type lambda sensors, or NOx sensors can be used as the basis for such a sensor. By using a suitable gas sensor in a DAC system, the following advantages can be achieved, among others: simplification of the sensor technology in a DAC system; detection of and compliance with specified limit values ​​for a process step;direct recording of key, particularly oxygen-based, system state points, upon reaching which a subsequent process step is to be triggered, enabling an improvement in the dynamic behavior and more effective utilization of the plant, whereby investment costs can be spread over more operating hours;and optimized operational management, whereby an increase in efficiency and a reduction in degradation can be achieved. A device for separating carbon dioxide from ambient air is presented, the device having the following features: a sorption chamber for accommodating a sorbent, with a closable air inlet for admitting (carbon dioxide-rich) ambient air into the sorption chamber, a closable air outlet for discharging carbon dioxide-reduced (carbon dioxide-poor) outlet air from the sorption chamber, and a closable carbon dioxide outlet for discharging carbon dioxide from the sorption chamber; at least one conveying device configured to convey the ambient air into the sorption chamber, the outlet air out of the sorption chamber, evacuate the sorption chamber, and convey carbon dioxide out of the sorption chamber;a temperature control device configured to control the temperature of the sorbent to effect desorption of carbon dioxide sorbed on the sorbent from the sorbent; and at least one electrochemical gas sensor configured to detect at least one oxygen-dependent measured variable in the sorption chamber.

[0010] The device can also be referred to as a CO2 separation device, DAC device, DAC plant or DAC system, where DAC stands for Direct Air Capture. The at least one oxygen-dependent measured variable can be an oxygen partial pressure. The at least one oxygen-dependent measured variable can be related to carbon dioxide and correlated with an oxygen partial pressure, an oxygen molar amount or another oxygen-dependent sensor signal. Using the at least one oxygen-dependent measured variable, oxygen can be detected directly and optionally also carbon dioxide can be detected indirectly. Preferably, the sorbent is arranged between the air inlet and the air outlet in the sorption space, wherein the sorbent is designed to bring about a reversible adsorption of carbon dioxide from the ambient air on the sorbent. The sorbent or sorbent is preferably an adsorbent oran adsorbent.

[0011] Understandably, the ambient air is richer in carbon dioxide than the carbon dioxide-reduced outlet air.

[0012] According to one embodiment, the at least one electrochemical gas sensor can be configured to detect at least one oxide-dependent measured variable in the sorption chamber. Such an embodiment offers the advantage that oxygen bound in oxygen compounds, and thus also carbon dioxide, can be directly detected.

[0013] The at least one electrochemical gas sensor can also have a potentiometric and, additionally or alternatively, an amperometric detection principle. Such an embodiment offers the advantage that common, accurate, and inexpensive sensor types can be used.

[0014] Furthermore, the at least one electrochemical gas sensor can comprise an exhaust gas sensor, an exhaust gas sensor for motor vehicles, a nitrogen oxide sensor, a lambda sensor, a broadband lambda sensor, and additionally or alternatively, a step-type lambda sensor. In other words, the at least one electrochemical gas sensor can comprise an exhaust gas sensor, wherein the exhaust gas sensor can be a sensor suitable for motor vehicles or a sensor commonly used in motor vehicles, for example, a nitrogen oxide sensor, a lambda sensor, a broadband lambda sensor, and additionally or alternatively, a step-type lambda sensor. Such an embodiment offers the advantage that reliable, proven, and readily available sensor types can be used.

[0015] Furthermore, the device can comprise a plurality of electrochemical gas sensors. At least one first gas sensor can be arranged in the inlet region, and at least one second gas sensor can be arranged in the outlet region. Such an embodiment offers the advantage of achieving particularly fast and precise detection of the at least one measured variable.

[0016] According to one embodiment, at least a subset of the gas sensors can be of the same sensor type. Additionally or alternatively, at least a subset of the gas sensors can have different sensor types. Such an embodiment offers the advantage that different sensor configurations can be selected depending on the specific application.

[0017] In particular, at least one of the electrochemical gas sensors can be a nitrogen oxide sensor. Such an embodiment offers the advantage that an oxygen-dependent measured variable and an additional oxide-dependent measured variable can be measured easily, reliably, and accurately.

[0018] Furthermore, the at least one electrochemical gas sensor can be configured to detect a carbon dioxide partial pressure at the inlet and a carbon dioxide partial pressure at the outlet as measured variables, the relationship between which represents a switching condition for controlling the air inlet, the air outlet, and the at least one conveying device when the sorbent is saturated with carbon dioxide. Such a switching condition can also be referred to as a first switching condition. Such an embodiment offers the advantage that saturation of the sorbent with carbon dioxide can be reliably and precisely detected, and subsequently, a suitable response can be made with regard to controlling or regulating the device.

[0019] The at least one electrochemical gas sensor can also be configured to detect an oxygen partial pressure in the sorption chamber as a measured variable, the relationship of which to a predefined limit value represents a switching condition for controlling the at least one conveying device and the temperature control device when the sorption chamber is evacuated. Such a switching condition can also be referred to as a second switching condition. Such an embodiment offers the advantage that it is possible to quickly and reliably determine when the sorption chamber is sufficient, and to react accordingly and appropriately with regard to the control or regulation of the device.

[0020] Furthermore, the at least one electrochemical gas sensor can be designed to detect an oxygen partial pressure and additionally or alternatively a carbon dioxide partial pressure at the carbon dioxide outlet as a measured variable, the relationship of which to a predefined threshold value represents a switching condition for controlling the temperature control device, the at least one conveying device, the air inlet, the air outlet and the carbon dioxide outlet when desorption is complete. Such a switching condition can also be referred to as a third switching condition. Such an embodiment offers the advantage that it can be reliably and precisely determined at what point the desorption and thus the extraction of carbon dioxide is complete and the adsorption of carbon dioxide can be started again, and thus a suitable response can be made to this with regard to the control or regulation of the device.

[0021] A method for operating an embodiment of a device mentioned herein is also presented, the method comprising the following steps:

[0022] Reading in a sensor signal from the at least one electrochemical gas sensor, wherein the sensor signal represents at least one oxygen-dependent measured variable in the sorption space detected by the at least one electrochemical gas sensor; and

[0023] Controlling the air inlet, the air outlet, the carbon dioxide outlet, the at least one conveying device and / or the tempering device depending on the sensor signal read in the reading step.

[0024] Thus, in particular, the detection of oxygen-based operating cycle points in a DAC system can be implemented using suitable gas sensors, for example, automotive sensors or exhaust gas sensors, to optimize system operation and increase system efficiency. According to one embodiment, a machine learning algorithm can be applied to the measured variable in the reading step, using a multivariate linear regression, a neural network, and additionally or alternatively a Gaussian process. The algorithm can be trained with training data for estimating a measurement error of the at least one electrochemical gas sensor at various operating points of the device. Such an embodiment offers the advantage that the accuracy of the detected measured variable can be further increased for subsequent use in control.

[0025] This method can be implemented, for example, in software or hardware or in a mixed form of software and hardware, for example in a control unit or device.

[0026] The approach presented here further provides a control unit configured to perform, control, or implement the steps of a variant of a method presented here in corresponding devices. This embodiment of the invention in the form of a control unit also allows the problem underlying the invention to be solved quickly and efficiently. The control unit can be part of a system that also includes the device.

[0027] For this purpose, the control unit can have at least one computing unit for processing signals or data, at least one memory unit for storing signals or data, at least one interface to a sensor or an actuator for reading sensor signals from the sensor or for outputting control signals to the actuator, and / or at least one communication interface for reading or outputting data embedded in a communication protocol. The computing unit can be, for example, a signal processor, a microcontroller, or the like, wherein the memory unit can be a flash memory or a magnetic storage unit.The communication interface can be designed to read in or output data wirelessly and / or wired, wherein a communication interface that can read in or output wired data can read this data, for example, electrically or optically from a corresponding data transmission line or output it to a corresponding data transmission line.

[0028] In this case, a control unit can be understood as an electrical device that processes sensor signals and outputs control and / or data signals depending on them. The control unit can have an interface that can be implemented in hardware and / or software. In a hardware implementation, the interfaces can, for example, be part of a so-called system ASIC, which contains a wide variety of functions of the control unit. However, it is also possible for the interfaces to be separate integrated circuits or to consist at least partially of discrete components. In a software implementation, the interfaces can be software modules that are present, for example, on a microcontroller alongside other software modules.

[0029] Also advantageous is a computer program product or computer program with program code that can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out, implement and / or control the steps of the method according to one of the embodiments described above, in particular when the program product or program is executed on a computer or a device.

[0030] Examples of the approach presented here are shown in the drawings and explained in more detail in the following description. It shows:

[0031] Fig. 1 is a schematic representation of an embodiment of a device for separating carbon dioxide from ambient air;

[0032] Fig. 2 is a schematic representation of an embodiment of a gas sensor of the device from Fig. 1;

[0033] Fig. 3 is a schematic representation of an embodiment of a gas sensor of the device from Fig. 1; Fig. 4 is a schematic representation of an embodiment of a gas sensor of the device from Fig. 1;

[0034] Fig. 5 is a flowchart of an embodiment of a method for operating a device for separating carbon dioxide from ambient air;

[0035] Fig. 6 is a schematic representation of an embodiment of a control device; and

[0036] Fig. 7 is a flowchart of an operating process in connection with the method of Fig. 5.

[0037] In the following description of advantageous embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and having a similar effect, whereby a repeated description of these elements is omitted.

[0038] Fig. 1 shows a schematic representation of an embodiment of a device 100 for separating carbon dioxide C from ambient air A. The device 100 can also be referred to as a system or device for so-called direct air capture. The device 100 is designed to perform a direct air capture process. Such a process is explained in more detail below.

[0039] In the illustration of Fig. 1, only a sorption chamber 110, an air inlet 112, an air outlet 114, a carbon dioxide outlet 116, a sorption agent 120, at least one conveying device 130, a temperature control device 140 and at least one gas sensor 150 are shown of the device 100 by way of example.

[0040] The sorption chamber 110, which can also be referred to as a sorption chamber or the like, comprises the air inlet 112, the air outlet 114, and the carbon dioxide outlet 116. The air inlet 112, the air outlet 114, and the carbon dioxide outlet 116 are each designed to be closable or independently closable. The sorption chamber 110 is sealed off from the environment when the air inlet 112, the air outlet 114, and the carbon dioxide outlet 116 are all closed. The air inlet 112 is designed to admit carbon dioxide-rich ambient air A into the sorption chamber 110. The air outlet 114 is designed to discharge carbon dioxide-reduced or low-carbon dioxide outlet air B from the sorption chamber 110. The carbon dioxide outlet 116 is designed to discharge carbon dioxide (CO2 or CO2) C from the sorption chamber.If water is co-sorbed due to the properties of the sorbent, water is also directed through this outlet. Alternatively, the air outlet 114 and the carbon dioxide outlet 116 could also be physically identical.

[0041] A sorption agent 120 is arranged in the sorption chamber 110 between the air inlet 112 and the air outlet 114. The sorption agent 120 is designed to effect a reversible adsorption of carbon dioxide C from the ambient air A onto the sorption agent 120.

[0042] The device 100 further comprises at least one conveying device 130. The conveying device 130 is designed to convey the ambient air A into the sorption chamber 110, to convey the outlet air B out of the sorption chamber 110, to evacuate the sorption chamber 110, and optionally to additionally convey carbon dioxide C out of the sorption chamber 110. The at least one conveying device 130 comprises, for example, at least one fan and / or at least one pump.

[0043] The temperature control device 140 is designed to control the temperature of the sorbent 120, in particular to heat it, for example to 100°C, in order to desorb carbon dioxide C sorbed on the sorbent 120 from the sorbent 120. Desorbed carbon dioxide C can then be removed via the carbon dioxide outlet 116.

[0044] The device 100 also includes at least one gas sensor 150, which is embodied as an electrochemical gas sensor. The at least one gas sensor 150 is designed to detect at least one oxygen-dependent measured variable in the sorption chamber 110. The at least one gas sensor 150 is arranged, for example, in the sorption chamber 110. Alternatively, the at least one gas sensor 150 is fluidically connected to the sorption chamber 110.

[0045] In particular, the at least one electrochemical gas sensor 150 is also configured to detect at least one oxide-dependent measured variable in the sorption chamber 110. The at least one electrochemical gas sensor 150 employs, for example, a potentiometric and / or amperometric detection principle. The at least one electrochemical gas sensor 150 comprises, for example, an exhaust gas sensor, an exhaust gas sensor for motor vehicles, a nitrogen oxide sensor, a lambda sensor, a broadband lambda sensor, and / or a step-type lambda sensor, or is designed as such.

[0046] According to one embodiment, the device 100 comprises a plurality of electrochemical gas sensors 150. At least a first gas sensor 150 of the plurality of gas sensors 150 is arranged in the region of the inlet 112. At least a second gas sensor 150 of the plurality of gas sensors 150 is arranged in the region of the outlet 114. Furthermore, according to one embodiment, at least a subset of the gas sensors 150 is of the same sensor type. Additionally or alternatively, at least a subset of the gas sensors 150 has different sensor types. In particular, according to one embodiment, at least one of the electrochemical gas sensors 150 is or comprises a nitrogen oxide sensor.

[0047] DAC, or Direct Air Capture, refers to the removal of CO2 from the atmosphere, in this case, ambient air A. The ambient air A is drawn through a collector or sorption chamber 110 by a fan or conveyor 130, and the CO2 is captured on the surface of a highly selective filter material or sorbent 120 located inside the collector. Once the filter material is filled with CO2, the collector, more specifically the air inlet 112 and the air outlet 114, closes. The collector is first evacuated and then heated to approximately 100°C.The CO2 bound in the sorbent 120 is desorbed again under these conditions and pumped out of the collector via the carbon dioxide outlet 116. It can then be reused externally by the DAC system, for example, by mixing it with a carrier medium such as H2O and pumping it deep underground for storage, or by using it in another process that requires CO2, e.g., in Power-to-X technology for the production of e-fuels. Unlike conventional processes, the DAC process is not time-controlled but rather controlled or regulated by sensor signals from at least one gas sensor 150, which increases efficiency in system utilization.

[0048] Since adsorption and desorption occur separately in time, suitable sampling and piping allow gas flows from both processes to be analyzed with at least one measuring unit or at least one gas sensor 150. For example, the CO2 inlet and outlet concentration during adsorption can also be measured with at least one gas sensor 150 by alternately feeding gas samples from the supply air and exhaust air paths to the at least one gas sensor 150. Since the adsorption process proceeds slowly and the inlet concentration is almost constant over time, even this procedure would be relatively error-prone.

[0049] A report by the IPCC (International Panel on Climate Change) shows that urgent climate action is needed to halve emissions by 2030. To achieve this, emissions must be drastically reduced and old CO2 emissions must be removed from the air. To permanently remove the captured CO2, DAC technologies must be combined with CO2 storage technologies, for example, to safely sequester it underground. The advantages of direct air capture are listed below. DAC is location-independent: CO2 is present in the air at the same concentration everywhere in the world. This means that DAC systems can be set up anywhere, as they do not need to be connected to an emissions source. They should simply be located near a renewable energy source and in a location where CO2 can be stored.DAC is highly scalable and measurable: The systems are based on a modular technology concept, making them highly scalable. Furthermore, the amount of CO2 captured by the systems can be precisely measured. DAC enables efficient land use: The systems require less land than other technologies. For example, an area of ​​0.42 hectares can remove 4,000 tons of CO2 from the air per year, which is almost 1,000 times more effective than trees. The same area would support approximately 220 trees with an estimated capacity of 22 kg each, meaning only 4.62 tons of CO2 per year.

[0050] Fig. 2 shows a schematic representation of an embodiment of a gas sensor 150 of the device from Fig. 1. The gas sensor 150 is designed as a nitrogen oxide sensor or NOx sensor, as is known, for example, from automotive technology or is similarly known. This type of gas sensor 150 can be used for one, several, or all of the gas sensors of the device.

[0051] Of the gas sensor 150 designed as a nitrogen oxide sensor, a first pumping chamber 251, a second pumping chamber 252, a reference oxygen chamber 253, diffusion barriers 254, electrodes 255, a ceramic electrolyte 256, heating elements 257 and an electrical insulation 258 are shown in the illustration in Fig. 2.

[0052] At least one such electrochemical gas sensor 150 is configured to detect, as measured variables, a carbon dioxide partial pressure at the inlet and a carbon dioxide partial pressure at the outlet of the sorption chamber of the device, the relationship between which represents a switching condition for controlling the air inlet, the air outlet, and the at least one conveying device when the sorbent is saturated with carbon dioxide. This switching condition is also referred to as the first switching condition for the operation of the device, in which a carbon dioxide partial pressure at the air inlet is equal to or approximately equal to a carbon dioxide partial pressure at the air outlet of the sorption chamber of the device, i.e., p(CO2,in) = p(CO2,out). The first switching condition is precisely detected using the gas sensor 150, here the NOx sensor and its dual pumping chamber system.In the first pumping chamber 251, the readily available pure O2 molecules are pumped out of the measuring chamber by an appropriately applied and suitable pumping voltage and thus a correlating pumping current l_O,Pump1. The more difficult-to-separate CO2 molecule remains untouched and diffuses into the second measuring chamber or pumping chamber 252. There, a higher pumping voltage is applied to the pumping electrodes 255, whereby O is removed from the CO2. The then measurable pumping current l_O,Pump2 is a clearly correlating indicator of the CO2 content present in the measured gas. The relationship x_CO2 = f(l_O,Pump2) therefore applies. For use in the device, at least one NOx sensor is placed as a gas sensor 150 at the sorber inlet or air inlet and at the sorber outlet or air outlet of the device. If both sensors measure the same CO2 value, the point has been reached where the sorbent is saturated with CO2 and can no longer absorb any more CO2.

[0053] NOx sensors are used in automotive technology to reduce nitrogen oxide emissions. They measure the oxygen and nitrogen oxide concentrations in the exhaust gas, allowing appropriate urea to be added to reduce nitrogen oxide emissions and the NOx-storage catalyst to be regenerated through a short rich phase. Generally, a NOx sensor comprises a Nernst cell and two modified oxygen pump cells (oxygen pump cell, NOx cell). These consist of electrodes 255 and oxygen-ion-conducting ceramic solid electrolyte layers 256. Additionally, a heater element 257 is integrated into the sensor, which heats the sensor to a constant operating temperature between 500 and 800 °C.

[0054] In the oxygen pump cell, the outer pump electrode is located in the exhaust gas, and the inner pump electrode is located in the first cavity, the first chamber 251. The cavity is separated from the exhaust gas by a diffusion barrier 254. Additionally, the first cavity also contains the Nernst cell, which measures the Nernst potential between the electrode 255 in the first cavity and the reference electrode 255 in the reference gas chamber or in the reference oxygen chamber 253 with a defined and known oxygen concentration. These two components are identical to the functional principle of a broadband lambda sensor.

[0055] Following a further diffusion barrier 254, the modified oxygen pump cell is located as a NOx cell in the second hollow chamber or pump chamber 252, in which an electrode 255 is located in the second hollow chamber and the counter electrode 255 is in turn located in the reference gas space or in the reference oxygen chamber 253.

[0056] The inner pump electrode 255 of the first oxygen pump cell in the first cavity or first pump chamber 251 is made of platinum and gold, for example, which means it has lower activity than a broadband lambda sensor. This means that the applied pump voltage is only sufficient to split simple oxygen-containing molecules, e.g. NO2 NO + O. Any NO present passes through this electrode 255 virtually unchanged. In the second cavity or second pump chamber 252, however, a higher pump voltage is applied to the pump electrode 255, as a result of which the NO is completely split at the pump electrode 255 and the oxygen is transported away. The pump electrode 255 also has a higher catalytic activity due to the addition of rhodium, for example. Similar to NO, the gas CO or CO2 is also a molecule that is difficult to split and thus cannot be broken down at the inner pump electrode 255 in the first cavity orPump chamber 251 is not split. The effect of a non-splitting of CO or CO2 at a pump electrode 255 is known from the application of broadband lambda sensors in CO2-bearing gases.

[0057] The temporal progression of the loading state during adsorption is qualitatively as follows: At some point, the loading reaches saturation. When saturation is reached, the CO2 concentration at the inlet is equal to the CO2 concentration at the outlet. However, there is no need to wait that long in order to avoid wasting too much time for a low CO2 yield. If the sorbent is not yet fully loaded, the CO2 outlet concentration is lower than at the inlet. In order to draw direct quantitative conclusions about the loading, it can be taken into account that the concentration difference depends, for example, on the volume flow rate at which the air is conveyed through it, and also on other environmental factors such as temperature and humidity. The relationship between volume flow, concentration difference, and loading state can be modeled.

[0058] Fig. 3 shows a schematic representation of an embodiment of a gas sensor 150 of the device from Fig. 1. The gas sensor 150 is designed as a broadband lambda probe, such as is known, for example, from automotive technology or is similarly known. This type of gas sensor 150 can be used for at least one gas sensor of the device.

[0059] Of the gas sensor 150, which is designed merely as an example as a broadband lambda probe, a first pump chamber 251, a reference oxygen chamber 253, diffusion barriers 254, electrodes 255, a ceramic electrolyte 256, heating elements 257 and an electrical insulation 258 are shown in the illustration in Fig. 3.

[0060] At least one such electrochemical gas sensor 150 is configured to detect, as a measured variable, an oxygen partial pressure in the sorption chamber, the relationship of which to a predefined limit value represents a switching condition for controlling the at least one conveying device and the temperature control device when the sorption chamber is evacuated. This switching condition is also referred to as the second switching condition for the operation of the device, in which the oxygen partial pressure is equal to or nearly zero or less than or equal to a predefined limit value, i.e., p(O2) = 0 OR p(O2) <= limit value.

[0061] Whether the predefined limit has been reached during evacuation (an absolute vacuum is technically impossible) can also be detected using a NOx sensor using the first pumping chamber 251. Accordingly, this is equivalent to a broadband lambda sensor, since the first pumping chamber 251 is also implemented in such a sensor. Alternatively, this can also be achieved via the jump in the Nernst voltage of a jump-type lambda sensor when the oxygen partial pressure drops. In this case, the relationship p(O2) = f(l_O,Pump1) OR p(O2) = f(U_Nernst) applies.

[0062] Lambda sensors measure the oxygen excess or deficiency in relation to the stoichiometric composition in a gas, particularly in combustion exhaust gas. The typical measuring range is 0.65 to 1.3. For X < 1, the following relationship applies in incompletely reformed, partially oxidized CHO gas or gas mixtures, whose molecules consist exclusively of C, H, and O atoms: 1 = (xCO + xH2O + xCO2) / ( xCO + xH2O + xth + xCC + xCt ). This is especially true for broadband lambda sensors, where the oxygen excess or deficiency in relation to the stoichiometric composition in a gas or combustion exhaust gas is measured using a linear signal. Jump lambda sensors, on the other hand, have a jumpy signal behavior around X = 1, which makes them particularly suitable for diagnosing a change from oxygen-containing, lean gas to oxygen-poor, rich exhaust gas.

[0063] A broadband lambda sensor represents a combination of potentiometric and amperometric measuring methods. A Nernst cell and a pump cell are connected in series, with a measuring gap or chamber for the measuring gas provided between the two cell variants. A ceramic diffusion barrier 254 with defined, known properties or diffusion properties is located between the measuring chamber 251 and the exhaust gas. A heating element 257 keeps the sensor at a constant temperature, thereby eliminating any influence of temperature on the sensor signal or the pump current. Furthermore, the broadband lambda sensor exhibits high signal dynamics with response times of less than 100 ms. Due to the different oxygen partial pressures in the chamber and the ambient air as a reference gas, the voltage signal of the Nernst cell should have a constant value of 450 mV, thus X = 1 in the measuring chamber 251.For this purpose, in automotive applications, oxygen is to be pumped into or out of the measuring chamber 251 depending on the air-fuel mixture. The pumping current required for this is proportional to the mass flow of oxygen. When the exhaust gas is rich, oxygen is pumped from the exhaust electrode of the pump cell into the measuring chamber 251. For this purpose, oxygen is generated by the reduction of H2O and CO2 at the exhaust electrode 255. The electrolyte in the measuring chamber 251 causes the oxygen to then react with diffused exhaust gas components, and the reaction products (H2O and CO2) diffuse back out through the diffusion barrier 254. When the exhaust gas or ambient air is lean, oxygen is pumped from the inner pump electrode in the measuring chamber 251 of the pump cell to the outer pump electrode.

[0064] A step-through sensor, also known as a two-point lambda sensor, represents an application of the Nernst cell and is used in automotive engineering to control a stoichiometric air-fuel mixture for optimal exhaust gas treatment. It measures the Nernst potential between the gas at gas electrode 255 and the known oxygen at reference electrode 255 in reference chamber 253.

[0065] Fig. 4 shows a schematic representation of an embodiment of a gas sensor 150 of the device from Fig. 1. The gas sensor 150 is designed as a broadband lambda probe, such as is known, for example, from automotive technology or is similarly known. This type of gas sensor 150 can be used for at least one gas sensor of the device.

[0066] Of the gas sensor 150, which is designed merely as an example as a broadband lambda probe, a first pump chamber 251, a reference oxygen chamber 253, diffusion barriers 254, electrodes 255, a ceramic electrolyte 256, heating elements 257 and an electrical insulation 258 are shown in the illustration in Fig. 4.

[0067] At least one such electrochemical gas sensor 150 is configured to detect, as a measured variable, an oxygen partial pressure and / or a carbon dioxide partial pressure at the carbon dioxide outlet, the relationship of which to a predefined threshold value represents a switching condition for controlling the temperature control device, the at least one conveying device, the air inlet, the air outlet, and the carbon dioxide outlet upon completion of desorption. This switching condition is also referred to as the third switching condition for the operation of the device, in which the partial pressure of oxygen, carbon dioxide, and water is less than or equal to the predefined threshold value, i.e., p(O2, CO2, H2O) <= threshold value

[0068] Equivalent behavior to the second switching condition in Fig. 3 also applies here. In the case of prior mixed adsorption of CO2 and parts of O2 and H2O, these are essentially also detected as the total O equivalent. Ultimately, a lambda sensor detects the O partial pressure and does not distinguish between the origins of the detected O atoms. The relationship p(O2) = f(l_O,Pump1) OR p(O2) = f(U_Nernst) applies. Alternatively, a step-type lambda sensor can be used, with evaluation similar to that for lean exhaust gas.

[0069] To determine the CO2 concentration, a NOx sensor designed specifically for CO2 is used. This allows CO2 to be measured separately from H2O and atmospheric oxygen. This allows the desorption process to determine when CO2 is of sufficient quality.

[0070] Fig. 5 shows a flowchart of an embodiment of a method 500 for operating a device for separating carbon dioxide from ambient air. The method 500 for operating can be implemented to operate the device of Fig. 1 or a similar device or to control the operation thereof. The method 500 for operating comprises a reading step 502 and a controlling step 504.

[0071] In step 502 of reading, a sensor signal from the at least one electrochemical gas sensor is read in. The sensor signal represents at least one oxygen-dependent measured variable in the sorption chamber detected by the at least one electrochemical gas sensor. In step 504 of controlling, the air inlet, the air outlet, the carbon dioxide outlet, the at least one conveying device and / or the temperature control device is / are controlled depending on the sensor signal read in step 502 of reading. In step 504 of controlling, the air inlet and / or the air outlet and / or the carbon dioxide outlet and / or the at least one conveying device and / or the temperature control device are controlled depending on the current operating state of the device.

[0072] According to one embodiment, in step 502 of detecting the measured variable, a machine learning algorithm is applied to it, using a multivariate linear regression, a neural network, and / or a Gaussian process. The algorithm is or will be trained with training data for estimating a measurement error of the at least one electrochemical gas sensor at various operating points of the device.

[0073] In other words, to improve the method 500 shown with the goal of greater accuracy—particularly in determining CO2 and correlating the measured variables for determining the calorific value—the method 500 can be combined with a machine learning (ML) algorithm in the sense of a hybrid system. The ML algorithm can be used, in particular, to estimate the error between the real value hs and the values ​​hs, sensor measured with the sensor concepts shown, and thus improve the latter values. For this purpose, the ML algorithm only needs to be trained in advance with training data for estimating the error at various operating points. The machine learning methods can be implemented as a function of the measured variables of the gas sensors, for example, the lambda sensors, such as pump current, pump voltage, temperature, and Nernst voltage, as well as other variables such as temperatures, pressures, volume flows, etc.from a DAC system in which the gas sensor, in particular the lambda sensor, is used. The sensor error then represents the output variable. In addition to multivariate linear regression, the application of a neural network and, in particular, the application of a Gaussian process represent suitable approaches. The relationships h then apply. s = h s , sensor + £ and £ML = f(lp, Is, Us).

[0074] Fig. 6 shows a schematic representation of a control unit 600 according to an exemplary embodiment. The control unit 600 is configured to execute and / or control the steps of the operating method from Fig. 5 in corresponding units. Thus, the control unit 600 is designed to operate the device 100 from Fig. 1 or a similar device or to control the operation thereof. The control unit 600 is connected to the device 100 in a signal-transmitting manner or is embodied as part of the device 100. The control unit 600 comprises a read-in device 602 and a control device 604.

[0075] The reading device 602 is configured to read a sensor signal 601 from the at least one electrochemical gas sensor 150. The sensor signal 601 represents at least one oxygen-dependent measured variable in the sorption chamber of the device 100 detected by the at least one electrochemical gas sensor 150. The control device 604 is configured to control the air inlet, the air outlet, the carbon dioxide outlet, the at least one conveying device, and / or the temperature control device depending on the sensor signal 601. For this purpose, the control device 604 is configured to generate a control signal 605 and to output it to the air inlet, the air outlet, the carbon dioxide outlet, the at least one conveying device, and / or the temperature control device.

[0076] Fig. 7 shows a flowchart of an operating process 700 in connection with the method of Fig. 5. The operating process 700 also relates to general operating points of a DAC system or the device from one of the figures described above or a similar device. The operating process 700 can be executed to operate the device from one of the figures described above or a similar device.

[0077] In a block 771 of the operating process 700, the sorption agent or CO2 sorption agent is loaded with CO2 from the ambient air. When the sorption agent is fully loaded, which is queried or checked in a block 772, the loading process is stopped or otherwise continued. As an indicator, the state when the CO2 content or carbon dioxide partial pressure at the inlet and outlet is the same or approximately the same can be used here. This is represented by the first switching condition 770A, i.e., p(CO2,in) = p(CO2,out). Before unloading, the sorption chamber must then be evacuated or vacuumized (see block 773) to remove the air contained therein. The end point of the evacuation is reached when there is generally no more oxygen (O2) in the sorption chamber or when a technically relevant limit is undershot, which is queried or checked in block 774. This is reflected by the second switching condition 770B, iep(O2) = 0 OR p(O2) <= limit value. If the second switching condition 770B is met, the sorbent is heated for desorption in a block 775 and the desorbed CO2 is removed in a controlled manner. The desorption process is complete when no more CO2 is present or can be detected. This is the case when desorbing is carried out with steam, because steam is then constantly added to dilute the CO2. Without steam desorption, the flow becomes increasingly weaker until all of the CO2 has been desorbed. Then, at e.g. 100 mbar_absolute, the atmosphere consists only of CO2, but with no flow. Whether the sorbent is discharged is queried or checked in a block 776. A third switching condition 770C is used for this, i.e. p(O2, CO2, H2O) <= threshold value. In the case of previous mixed adsorption of CO2 and parts of 02 and H2O, these are also detected, but this has no negative effects on the method presented here.If the sorbent is discharged, the operating process 700 jumps back to block 771, otherwise block 775 continues and then block 776 is repeated.

[0078] If an embodiment includes an “and / or” link between a first feature and a second feature, this should be read as meaning that the embodiment according to one embodiment has both the first feature and the second feature and according to another embodiment has either only the first feature or only the second feature.

Claims

Claims 1. Device (100) for separating carbon dioxide (C) from ambient air (A), the device (100) having the following features: a sorption chamber (110) for receiving a sorbent (120) with a closable air inlet (112) for admitting ambient air (A) into the sorption chamber (110), a closable air outlet (114) for discharging carbon dioxide-reduced outlet air (B) from the sorption chamber (110) and a closable carbon dioxide outlet (116) for discharging carbon dioxide (C) from the sorption chamber (110); at least one conveying device (130) designed to convey the ambient air (A) into the sorption space (110), to convey the outlet air (B) out of the sorption space (110), to evacuate the sorption space (110) and to convey carbon dioxide (C) out of the sorption space (110);a temperature control device (140) configured to temperature-control the sorbent (120) to effect desorption of carbon dioxide (C) sorbed on the sorbent (120) from the sorbent (120); and at least one electrochemical gas sensor (150) configured to detect at least one oxygen-dependent measured variable in the sorption chamber (110); 2. Device (100) according to claim 1, wherein the at least one electrochemical gas sensor (150) is designed to detect at least one oxide-dependent measured variable in the sorption space (110).

3. Device (100) according to one of the preceding claims, wherein the at least one electrochemical gas sensor (150) has a potentiometric and / or amperometric detection principle.

4. Device (100) according to one of the preceding claims, wherein the at least one electrochemical gas sensor (150) comprises an exhaust gas sensor and / or an exhaust gas sensor for motor vehicles and / or a nitrogen oxide sensor and / or a lambda probe and / or a broadband lambda probe and / or a step-type lambda probe.

5. Device (100) according to one of the preceding claims, comprising a plurality of electrochemical gas sensors (150), wherein at least one first gas sensor (150) is arranged in the region of the air inlet (112) and at least one second gas sensor (150) is arranged in the region of the air outlet (150).

6. Device (100) according to claim 5, wherein at least a subset of the gas sensors (150) are of the same sensor type and / or at least a subset of the gas sensors (150) are different sensor types.

7. Device (100) according to one of claims 5 to 6, wherein at least one of the electrochemical gas sensors (150) is a nitrogen oxide sensor.

8. Device (100) according to one of the preceding claims, wherein the at least one electrochemical gas sensor (150) is designed to detect as measured variables a carbon dioxide partial pressure at the air inlet (112) and a carbon dioxide partial pressure at the air outlet (114), the relationship of which to one another defines a switching condition (770A) for controlling the air inlet (112), the Air outlet (114) and the at least one conveying device (130) when the sorbent (120) is saturated with carbon dioxide.

9. Device (100) according to one of the preceding claims, wherein the at least one electrochemical gas sensor (150) is designed to detect an oxygen partial pressure in the sorption chamber (110) as a measured variable, the relationship of which to a predefined limit value represents a switching condition (770B) for controlling the at least one conveying device (130) and the temperature control device (140) when the sorption chamber (110) is evacuated.

10. Device (100) according to one of the preceding claims, wherein the at least one electrochemical gas sensor (150) is designed to detect as a measured variable an oxygen partial pressure and / or a carbon dioxide partial pressure at the carbon dioxide outlet (116), the relationship of which to a predefined threshold value represents a switching condition (770C) for controlling the temperature control device (140), the at least one conveying device (130), the air inlet (112), the air outlet (114) and the carbon dioxide outlet (116) when desorption is completed.

11. Device (100) according to one of the preceding claims, wherein the sorbent (120) is arranged between the air inlet (112) and the air outlet (114) in the sorption space (110), wherein the sorbent (120) is designed to effect a reversible adsorption of carbon dioxide (C) from the ambient air (A) on the sorbent (120).

12. A method (500) for operating a device (100) according to any one of the preceding claims, wherein the method (500) comprises the following steps: Reading (502) a sensor signal (601) from the at least one electrochemical gas sensor (150), wherein the sensor signal (601) at least one by the at least one electrochemical Gas sensor (150) represents the oxygen-dependent measured variable in the sorption chamber (110); and Controlling (504) the air inlet (112) and / or the air outlet (114) and / or the carbon dioxide outlet (116) and / or the at least one conveying device (130) and / or the temperature control device (140) in dependence on the sensor signal (601) read in step (502).

13. The method (500) according to claim 12, wherein in the step (502) of detecting, a machine learning algorithm is applied to the measured variable, using a multivariate linear regression, a neural network and / or a Gaussian process, wherein the algorithm is trained with training data for estimating a measurement error of the at least one electrochemical gas sensor at different operating points of the device (100).

14. Control device (600) which is configured to execute and / or control the steps (502, 504) of the method (500) according to one of claims 12 or 13 in corresponding units (602, 604).

15. Computer program configured to execute and / or control the steps (502, 504) of a method (500) according to one of claims 12 or 13.

16. A machine-readable storage medium on which the computer program according to claim 15 is stored.

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