Method for preparing a gas mixture

Abstract

The present invention relates to a method for preparing a gas mixture which contains hydrogen and impurities, in which method - the gas mixture is subjected to a purification process in which pure hydrogen is separated from the gas mixture, and - the residual gas remaining after the separation of the pure hydrogen from the gas mixture and containing residual hydrogen and impurities concentrated therein is subjected to a thermal utilisation process in which the residual gas is oxidised with the addition of an oxidising agent, in particular air, to form an exhaust gas and with the release of heat.

Description

[0001] DESCRIPTION

[0002] Method for processing a gas mixture

[0003] The present invention relates to a method for processing a gas mixture containing hydrogen and impurities, and in particular a method for efficiently purifying hydrogen that is contaminated by impurities.

[0004] Hydrogen obtained from reforming, cracking, or dehydrogenation processes typically contains impurities. The same applies to so-called white hydrogen, which is of natural origin and is obtained, for example, from the Earth's crust.

[0005] Purifying contaminated hydrogen is crucial to ensure that it can be used as a clean and efficient energy carrier.

[0006] Impurities can occur in various forms. For example, hydrogen can contain solid particles that can usually be filtered out. However, hydrogen can also contain hazardous gaseous impurities such as benzene, carbon monoxide, or nitrogen oxides, which can be harmful to humans upon contact. Furthermore, such impurities in hydrogen can impair the performance and durability of equipment in which it is used. This is particularly true for fuel cells, which are used in various power generation applications. Hydrogen purification helps ensure the safe and reliable operation of fuel cells and other hydrogen-based systems. Similarly, impurities in hydrogen can impair the performance of devices and processes that rely on clean hydrogen.For example, impurities can clog or damage pipes, valves, seals, and other components, leading to reduced efficiency or higher maintenance costs. Hydrogen purification helps maintain the desired performance level and extend the service life of the equipment used.

[0007] A commonly used method for purifying hydrogen is pressure swing adsorption (PSA). In this process, special porous materials are used as adsorbents in an adsorber bed, which can selectively absorb desired impurities. During pressure swing adsorption, higher and lower pressures are applied alternately. At high pressure, one or more components of the supplied gas mixture are adsorbed into the adsorber bed, while at low pressure, the adsorbed gas is desorbed to remove the adsorbed impurities from the adsorber bed and thus regenerate it. This enables the efficient removal of impurities such as water, carbon monoxide, or hydrocarbons from the hydrogen gas.

[0008] Pressure swing adsorption (PSA) is particularly useful when the contaminated hydrogen is already present at a high pressure, for example in pressure cylinders or caverns. In this case, PSA is often the most cost-effective way to purify hydrogen.

[0009] In addition to pressure swing adsorption (PSA), temperature swing adsorption (TSA) is also used. TSA does not require an elevated pressure level. It utilizes the temperature dependence of adsorption. Here, the adsorbent is loaded with the components to be removed and, in a subsequent step, largely freed from these components by the introduction of thermal energy (desorption or regeneration step). Therefore, if contaminated hydrogen is present at low pressure and the heat required for the elevated temperatures in desorption is available, TSA represents a cost-effective method for purifying hydrogen.

[0010] Both pressure swing adsorption (PSA) and temperature swing adsorption (TSA) require multiple adsorber beds in which adsorption and desorption alternate to ensure continuous operation. It is also possible to combine pressure swing adsorption with temperature swing adsorption in a PSA / TSA hybrid system. Using PSA / TSA hybrids can reduce hydrogen purification costs while increasing H₂ efficiency and lowering acquisition costs. Here, too, at least one adsorber and one desorber are required for continuous operation, alternating their operating modes. For stable, continuous operation, multiple adsorber / desorber units are common, for example, four.

[0011] The PSA / TSA hybrid technology leverages the advantages of both approaches to achieve efficient removal of impurities from hydrogen. While PSA uses pressure to control adsorption, TSA enables temperature regulation for the regeneration of the adsorption material. The PSA / TSA hybrid technology thus offers high flexibility and adaptability to different hydrogen flows and impurity profiles. The integration of the two adsorption mechanisms allows for effective and economical hydrogen purification, which is particularly advantageous in large industrial hydrogen production plants. Membrane filtration is also used for hydrogen purification. This process employs membranes that selectively allow some molecules to pass through while retaining others. This technology is particularly effective at removing gaseous impurities because it operates at the molecular level.By selecting specific membrane materials, various impurities can be filtered out in a targeted manner.

[0012] Finally, electrochemical processes are employed. For example, electrolysis cells can be used to remove impurities through electrochemical reactions. This method offers the advantage of continuous and efficient impurity removal, but often requires specialized electrode materials and precise control of the respective process parameters.

[0013] All processes share the common feature that a hydrogen stream enriched with impurities is produced as residual gas, also known as off-gas or regeneration gas. For PSA (Permanent Hydrogen Recovery), the H2 efficiency – also called the recovery rate – is typically in the range of 80 to 90%. This means that approximately 10 to 20% of the hydrogen flowing through the system is lost as regeneration gas. Similar conditions apply to the other processes.

[0014] Against this background, it is an object of the invention to provide a method for processing a gas mixture containing hydrogen and impurities, and in particular a method for efficiently processing hydrogen contaminated by impurities, which has a high efficiency and operates cost-effectively. This object is achieved according to the invention by a method for processing a gas mixture containing hydrogen and impurities, in which

[0015] - the gas mixture is subjected to a purification process in which pure hydrogen is separated from the gas mixture, and

[0016] - the residual gas remaining after the separation of pure hydrogen from the gas mixture, containing concentrated impurities, is subjected to a thermal utilization process in which the residual gas is oxidized by adding an oxidizing agent, in particular air, forming an exhaust gas and releasing heat.

[0017] The invention is therefore based on the idea of ​​processing a gas mixture in two stages. In the first stage, the gas mixture is subjected to a purification process in which pure hydrogen is separated from the gas mixture. After the purification process, the gas mixture is thus separated into pure hydrogen and a residual gas / off-gas, which contains hydrogen and concentrated impurities.

[0018] In the second stage, the residual gas undergoes a thermal recovery process in which it is oxidized with the addition of an oxidizing agent, specifically air, producing exhaust gas and releasing heat. In other words, the residual gas is combusted in an exothermic reaction. The resulting exhaust gas complies with the German Technical Instructions on Air Quality Control (TA-Luft) and provides usable heat at a high temperature level (T > 300°C). For example, the heat from the exhaust gas can be used to preheat the gas mixture before it undergoes the cleaning process, particularly by transferring heat from the exhaust gas to the gas mixture in a heat exchanger.

[0019] It is also possible to use the heat from the exhaust gas to preheat the oxidizing agent before it is fed into the thermal recovery process, in particular by transferring heat from the exhaust gas of an oxidizing agent in a heat exchanger. Preferably, the oxidizing agent is compressed before it is used to carry out the thermal recovery process.

[0020] Finally, according to one embodiment of the invention, it is provided that at least a part of the exhaust gas is mixed with the oxidizing agent before the latter is oxidized in the thermal recovery process, wherein, in particular, the mixing of the exhaust gas with the oxidizing agent takes place after its compression and / or preheating by the exhaust gas.

[0021] In other words, the heat from the exhaust gas can be used to preheat the gas mixture and / or the oxidizer. It can also be added to the oxidizer or the residual gas to adjust the gas mixture to be combusted in the thermal recovery process. If several of these options are to be implemented, the exhaust gas stream is divided accordingly.

[0022] According to a further embodiment of the invention, the heat released in the thermal recovery process is transferred to a heat transfer medium and dissipated via this medium, whereby, in particular, the thermal energy is used for the purification process. In a further embodiment of the invention, it is provided that during the oxidation of the residual gas, the oxygen concentration of the mixture of residual gas and oxidizing agent is adjusted or maintained below the limiting oxygen concentration.

[0023] The limiting oxygen concentration indicates the oxygen content below which a gas mixture is no longer explosive. At this concentration, there is insufficient oxygen to allow an explosion. Therefore, a flame independent of an ignition source can no longer propagate on its own. In particular, no explosive mixture is present anywhere. This significantly reduces the technical complexity.

[0024] According to a further embodiment of the invention, it is provided that the oxidation of the residual gas takes place at least substantially stoichiometrically, so that a substantially inert exhaust gas is produced, wherein, in particular, the inert exhaust gas is used to carry out regeneration steps within the cleaning process.

[0025] It is also possible to extract heat from the exhaust gas, especially via a recuperator, which can then be used for regeneration in a TSA used in the cleaning process.

[0026] During the oxidation process, a catalytic oxidation of the hydrogen contained in the residual gas and a catalytic oxidation of the impurities preferably take place. Suitable catalysts, in particular precious metal catalysts and preferably platinum and palladium catalysts, can be used for the catalytic oxidation of hydrogen and hydrocarbons contained as impurities in the residual gas. For the selective catalytic reduction of reducible impurities and nitrogen oxides contained in the residual gas, suitable catalysts, in particular precious metal catalysts and preferably platinum and palladium catalysts, are advantageously used. In other words, a total oxidation of the impurities to harmless substances takes place. For example, benzene is converted to CO₂ and H₂O, and sulfur compounds are converted to SO₂ and H₂O. Due to the catalytic reaction at low temperatures, NOₓ can be reduced. XEmissions can be avoided. Nitrogen oxides present in the residual gas can be reduced to N2 and H2O during catalytic conversion with hydrogen as a reducing agent, also known as selective catalytic reduction (H2-SCR).

[0027] Since the catalytic conversion takes place at low concentrations, even regeneration or residual gas mixtures with low H2 concentrations and high inert gas content (N2, H2O, CO2) can be thermally utilized. Furthermore, recirculating the inert exhaust gases to the residual gas / oxidizing agent stream allows for adjustments to changing compositions of the residual / regeneration gas due to heating, pressure build-up, cooling, and pressure drop phases, enabling optimal control of the residual gas composition at the catalyst.

[0028] In the purification process, the gas mixture can be subjected to a pressure swing adsorption (PSA) process to remove impurities. Alternatively / additionally, the gas mixture can also be subjected to a temperature swing adsorption (TSA) process. If the gas mixture is subjected to a pressure and / or temperature swing adsorption process in this way, the resulting pure hydrogen can be used to regenerate the TSA or PSA equipment. In this case, the regeneration gas is preferably subjected to the thermal recovery process.

[0029] According to one embodiment of the invention, the gas mixture is subjected to a hybrid pressure and temperature swing adsorption (PSA) process during the purification process. This involves the use of a PSA / TSA hybrid process. This process is preferably characterized in that, during the purification process, the gas mixture is subjected to a pressure swing adsorption process in one purification step (a) or to a temperature swing adsorption process in one purification step (b), with the two purification steps (a) and (b) being repeated alternately. Pure hydrogen obtained in step (a) can be used to regenerate a TSA unit used in step (b), and vice versa.The regeneration gases from steps a) and b) are then subjected to the thermal utilization process.

[0030] Alternatively / additionally, hydrogen can be separated from the gas mixture using a membrane, particularly a low-temperature membrane, preferably a polymer-based membrane, or a palladium membrane. The membrane process is preferred when a pressure difference exists between the contaminated and purified hydrogen due to the intended use. In this case, the pressure difference in the H₂ partial pressure can be optimally utilized by the membrane separation process. Palladium membranes are primarily used for this purpose. The hydrogen dissociates at the palladium on the membrane, migrates through the membrane, and re-associates on the other side. Palladium is highly hydrogen-selective, thus retaining impurities. The operating temperature is approximately 300°C to 400°C.When using the membrane process, the waste heat from the thermal recycling process can be used to carry out the membrane process, thereby saving on heating costs.

[0031] It is also possible to separate hydrogen from the gas mixture in the cleaning process by using an electrochemical compressor (EHC).

[0032] The use of an electrochemical hydrogen compressor is advantageous when the impure hydrogen is present at a pressure level lower than the pressure required for the utilization of the purified hydrogen. An electric hydrogen compressor combines pressure increase and purification in a single process. A potential difference is applied across the diaphragm, which induces the dissociation and association of hydrogen molecules. Elevated temperatures, as required in pressure-driven purification, are not necessary. Alternatively, other purification methods can also be combined with a downstream pressure boosting unit.

[0033] Preferably, naturally obtained hydrogen, also called white hydrogen, is purified, and / or the contaminated hydrogen is obtained from a hydrogen release reaction from a hydrogen storage molecule, which is obtained in particular by methane reforming, methanol reforming, dimethyl ether reforming or ammonia cracking.

[0034] The following describes embodiments of the inventive process for treating gas mixtures containing hydrogen and impurities, with reference to the accompanying drawing. The drawing shows

[0035] Figure 1 schematically shows a plant for carrying out a process for processing a gas mixture containing hydrogen and impurities, according to a first embodiment of the present invention and

[0036] Figure 2 shows a schematic representation of a plant for carrying out a process for the preparation of a gas mixture containing hydrogen and impurities, according to a second embodiment of the present invention.

[0037] Figure 1 schematically depicts a circuit diagram of a system for carrying out a process for treating a gas mixture containing hydrogen and impurities, in particular for purifying hydrogen contaminated by impurities, according to a first embodiment of the invention. The system comprises a purification device 1. This device is configured to subject a supplied gas mixture A, containing hydrogen and impurities, to a purification process in which pure hydrogen is separated from the supplied gas mixture A.

[0038] In the purification process, the gas mixture can be subjected to a pressure swing adsorption (PSA) process to remove impurities. Alternatively, the gas mixture can also be subjected to a temperature swing adsorption (TSA) process. Preferably, a PSA / TSA hybrid process is used. This is characterized by the fact that, during the purification process, the gas mixture is subjected to a pressure swing adsorption process in one step and to a temperature swing adsorption process in another, with the two purification steps being repeated alternately. Thus, a PSA unit and a TSA unit are available, connected in parallel and alternately subjected to the flow of the gas mixture to remove impurities.Pure hydrogen obtained in step a) is then used to regenerate a TSA unit used in step b), and pure hydrogen obtained in step b) is used to regenerate a TSA unit used in step a), the regeneration gases from steps a) and b) being subjected to the thermal recovery process.

[0039] Alternatively / additionally, hydrogen can be separated from the gas mixture using a membrane, particularly a low-temperature membrane, preferably a polymer-based membrane, or a palladium membrane. The membrane process is preferred when a pressure difference exists between the contaminated and purified hydrogen due to the intended use. In this case, the pressure difference in the H₂ partial pressure can be optimally utilized by the membrane separation process. Palladium membranes are primarily used for this purpose. The hydrogen dissociates at the palladium on the membrane, migrates through the membrane, and re-associates on the other side. Palladium is highly hydrogen-selective, thus retaining impurities. The operating temperature is approximately 300°C to 400°C.When using the membrane process, the waste heat from the thermal recovery process can be used to carry out the membrane process, thus saving on heating costs. It is also possible to separate hydrogen from the gas mixture in the purification process using an electrochemical compressor (EHC).

[0040] The use of an electrochemical hydrogen compressor is advantageous when the impure hydrogen is present at a pressure level lower than the pressure required for the utilization of the purified hydrogen. An electric hydrogen compressor combines pressure increase and purification in a single process. A potential difference is applied across the diaphragm, which induces the dissociation and association of hydrogen molecules. Elevated temperatures, as required in pressure-driven purification, are not necessary. Alternatively, other purification methods can also be combined with a downstream pressure boosting unit.

[0041] The pure hydrogen can be used freely and is discharged from purification unit 1 as hydrogen stream B. The residual gas remaining after the hydrogen has been separated from the gas mixture contains hydrogen and concentrated impurities such as hydrocarbons, CO2, benzene, etc. This residual gas / off-gas is discharged from purification unit 1 as residual gas stream C and fed to a thermal recovery unit 2 of the plant, which is designed to subject the residual gas to a thermal recovery process. In this process, the residual gas is oxidized with the addition of an oxidizing agent—in this case, air—forming an exhaust gas and releasing heat. The air is mixed with residual gas stream C before it enters thermal recovery unit 2.

[0042] The air required for thermal utilization is supplied to the thermal utilization unit 2 as an airflow D. The thermal utilization unit 2 comprises a reactor unit 2a, in which the oxidation, i.e., the combustion of the residual gas with the oxidizing agent, takes place, and a heat exchanger unit 2b, through which heat from the exhaust gas generated during the reaction in reactor unit 2a is transferred to a heat transfer medium so that it can be used at any point. In a special embodiment, reactor unit 2a and heat exchanger unit 2b can be connected in a catalytic heat exchanger, in which the reaction takes place on the wall of the heat exchanger. The still-hot exhaust gas is discharged from the thermal utilization unit 2 as an exhaust gas stream E via an exhaust gas line.

[0043] Part of the exhaust gas flow is used to preheat the residual gas flow C via a heat exchanger 5 of the system, and to preheat the air flow D via a heat exchanger 6 of the system.

[0044] A further portion of the exhaust gas stream E is recirculated via a blower unit 4 and mixed with the residual gas and air mixture. In the embodiment shown in Figure 1, the exhaust gas is mixed with the air stream D after the latter has been compressed in a compression unit 3 of the system and preheated in the heat exchanger 6, but before the air stream D and the residual gas stream C are combined.

[0045] The embodiment shown in Figure 2 essentially corresponds to the embodiment shown in Figure 1, with the modification that the residual gas stream C is not preheated by the exhaust gas from the thermal recovery unit 2. Instead, a recuperator 7 is provided in a section of the exhaust gas line, through which heat is extracted from a portion of the exhaust gas stream E. This heat is supplied to the cleaning unit 1. If the cleaning unit 1 operates according to the membrane process, the heat can be used to provide the required operating temperature. If a TSA unit is used, the heat can be supplied for the regeneration of the TSA unit. In the latter case, a portion of the exhaust gas stream can also be fed directly to the TSA unit, or to a PSA unit of the cleaning unit 1 for the respective regeneration process.

[0046] In both embodiments of the method, a gas mixture A, which may contain hydrogen and impurities such as hydrocarbons, benzene, methane, carbon monoxide, nitrogen, or nitrogen oxides, is supplied to the purification unit 1. In the purification unit 1, the hydrogen contained in the gas mixture is removed. The pure hydrogen is discharged as a hydrogen stream B. If a TSA or PSA unit is used to separate the hydrogen in the purification unit 1, a portion of the pure hydrogen can be used for its regeneration.

[0047] The residual gas / regeneration gas, which contains concentrated impurities, is preheated, if necessary, in heat exchanger 5 by the exhaust gas from the thermal recovery unit 2. Subsequently, air is added to the residual gas stream C as an oxidizing agent. This air is compressed in the compression unit 3 and preheated in heat exchanger 5. To adjust the mixture, inert exhaust gas from the thermal recovery unit 2 is added via the blower unit 4. This process results in the complete oxidation of the impurities contained in the residual gas / regeneration gas to harmless gases. The result is exhaust gas compliant with the German Technical Instructions on Air Quality Control (TA-Luft), which typically has a high temperature above 300°C. The thermal energy of the exhaust gas is utilized in various ways. A portion of the heat is transferred via heat exchanger 2b to a heat transfer medium, allowing this portion of the thermal energy to be used freely.In particular, the thermal energy can be used in the cleaning unit 1. The remaining residual heat from the exhaust gas is also used to preheat the airflow D. Another portion of the waste heat is used to preheat the residual gas flow C. Furthermore, additional heat can be extracted from the exhaust gas via the recuperator 7, which can be used to provide the heat required for the regeneration step in a TSA unit of the cleaning unit 1.

Claims

REQUIREMENTS 1. Method for processing a gas mixture containing hydrogen and impurities, wherein - the gas mixture is subjected to a purification process in which pure hydrogen is separated from the gas mixture, and - the residual gas remaining after the separation of pure hydrogen from the gas mixture, containing concentrated impurities, is subjected to a thermal utilization process in which the residual gas is oxidized by adding an oxidizing agent, in particular air, forming an exhaust gas and releasing heat.

2. Method according to claim 1, characterized in that during the oxidation of the residual gas, the oxygen concentration of the mixture of residual gas and oxidizing agent is set or maintained below the limiting oxygen concentration.

3. Method according to claim 2, characterized in that the oxidation of the residual gas is carried out at least substantially stoichiometrically, so that a substantially inert exhaust gas is produced, wherein, in particular, the inert exhaust gas is used to carry out regeneration steps within the cleaning process.

4. Method according to one of the preceding claims, characterized in that during the oxidation a catalytic oxidation of the hydrogen contained in the residual gas as well as a catalytic oxidation of the impurities takes place.

5. Method according to claim 4, characterized in that suitable catalysts, in particular precious metal catalysts and preferably platinum and palladium catalysts, are used for the catalytic oxidation of hydrogen and hydrocarbons contained as impurities in the residual gas.

6. Method according to claim 4 or 5, characterized in that suitable catalysts, in particular precious metal catalysts and preferably platinum and palladium catalysts, are used for the selective catalytic reduction of reducible impurities such as nitrogen oxides contained in the residual gas.

7. Method according to one of the preceding claims, characterized in that the heat of the exhaust gas is used to preheat the gas mixture before it is subjected to the cleaning process, wherein, in particular, heat is transferred from the exhaust gas to the gas mixture in a heat exchanger.

8. Method according to one of the preceding claims, characterized in that the heat of the exhaust gas is used to preheat the oxidizing agent before it is fed into the thermal recovery process, wherein, in particular, heat is transferred from the exhaust gas to the oxidizing agent in a heat exchanger.

9. A method according to any one of the preceding claims, characterized in that the oxidizing agent is compressed before it is used to carry out the thermal recovery process.

10. A method according to any one of the preceding claims, characterized in that at least a portion of the exhaust gas is mixed with the oxidizing agent before the latter is oxidized in the thermal recovery process, wherein, in particular, the mixing of the exhaust gas with the oxidizing agent takes place after its compression and / or preheating by the exhaust gas.

11. Method according to one of the preceding claims, characterized in that the heat released in the thermal recycling process is transferred to a heat transfer medium and dissipated via this medium, wherein, in particular, the thermal energy is used for the cleaning process.

12. Method according to one of the preceding claims, characterized in that the gas mixture is subjected to a pressure swing adsorption (PSA) process in the purification process.

13. Method according to one of the preceding claims, characterized in that the gas mixture is subjected to a temperature swing adsorption (TSA) process in the purification process.

14. Method according to claim 12 or 13, characterized in that the gas mixture is subjected to a pressure and / or temperature swing adsorption process during the purification process, wherein the obtained pure hydrogen is used for regeneration and the regeneration gas is subjected to the thermal utilization process.

15. Method according to one of the preceding claims, characterized in that the gas mixture is subjected to a hybrid pressure and temperature swing adsorption process (PSA and TSA process) in the purification process.

16. Method according to claim 15, characterized in that the gas mixture is subjected during the purification process in a purification step a) to a pressure swing adsorption process or in a purification step b) to a temperature swing adsorption process, wherein the two purification steps a), b) are carried out alternately, and that pure hydrogen obtained in step a) is used to regenerate a TSA device used in step b), and pure hydrogen obtained in step b) is used to regenerate a TSA device used in step a), wherein the regeneration gases from steps a) and b) are subjected to the thermal recovery process.

17. Method according to one of the preceding claims, characterized in that in the purification process hydrogen is separated from the gas mixture at a membrane, in particular at a low-temperature membrane and preferably at a polymer-based membrane, or at a palladium membrane.

18. Method according to one of the preceding claims, characterized in that hydrogen is separated from the gas mixture in the cleaning process by using an electrochemical compressor (EHC).

19. A method according to any of the preceding claims, characterized in that the thermal utilization process takes place outside the explosion range at low hydrogen and oxygen concentrations, without the formation of a flame.

20. A method according to any of the preceding claims, characterized in that naturally obtained hydrogen, also called white hydrogen, is purified, and / or that the contaminated hydrogen originates from a hydrogen release reaction from a hydrogen storage molecule, which is obtained in particular by methane reforming, methanol reforming, dimethyl ether reforming, or ammonia cracking.

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