Process and system for obtaining a hydrogen-containing product using ammonia

Abstract

The invention relates to a process and a device (100) for producing a hydrogen-containing product, in which an ammonia feedstock (1) is introduced into a burner-fired ammonia cracker (10) in order to be reacted, with catalytic assistance, to form a cracked gas (2) containing hydrogen, nitrogen and ammonia, the cracked gas subsequently being subjected to a pressure-swing adsorption (20) to obtain a product fraction (3), enriched with hydrogen and depleted in ammonia compared to the cracked gas (2), and a residual gas (4), depleted in hydrogen and enriched in ammonia compared to the cracked gas (2). The invention is characterized in that the residual gas (4) is compressed in a gas ejector (30), in which a fuel gas insert (5) acts as a propellant, and is combined with the fuel gas insert (5) to form a fuel gas (6), at least part of which is burned in order to fire the ammonia cracker (10).

Description

[0001] Description

[0002] Process and plant for producing a hydrogen-containing product using ammonia

[0003] The invention relates to a process and a plant for obtaining a hydrogen-containing product using ammonia.

[0004] Background of the invention

[0005] Ammonia (NH3) can be catalytically cracked into nitrogen (N2) and hydrogen (H2) according to the reaction 2 NH3 — ► N2 + 3 H2. The reaction is endothermic and favored by low pressure and high temperature. However, higher cracking pressures are desirable to avoid hydrogen compression.

[0006] The main reaction products, hydrogen and nitrogen, can be provided as a mixture, or the hydrogen can be purified. A hydrogen-nitrogen mixture is also referred to as forming gas. Further use of the hydrogen or hydrogen-nitrogen mixture, for example in a gas turbine coupled to a generator, is also possible. In all cases, which may correspond to embodiments of the invention, hydrogen is thus obtained from ammonia. The "obtaining of a hydrogen-containing product" in the sense understood here does not exclude the obtaining of a hydrogen-containing gas mixture, other products such as nitrogen, and / or subsequent use.

[0007] Various process concepts and reactors for the decomposition of ammonia into hydrogen and nitrogen have been described in the patent and non-patent literature. Further details are provided in the relevant literature, for example, D. Sima et al., Int. J. Hydrogen Energy 45 (2020) 9342-9352.

[0008] Corresponding process concepts can include a reaction unit (also known as an ammonia cracker) similar to a steam reformer, which is associated with a pressure swing adsorption (PSA) process for hydrogen purification. For example, see EP 4 112 539 A1 and EP 4 112 540 A1.

[0009] In corresponding concepts, the hydrogen can be separated from a residual gas using pressure swing adsorption, whereby the residual gas can be used to fire the ammonia cracker. Additional combustion capacity can be provided by the combustion of pure ammonia. The mass flow-based ratio of fuel to combustion air in ammonia cracking is approximately 1:2 compared to 1:4 in conventional steam methane reforming. The higher the ratio, the more beneficial it is to preheat the fuel gas, which, however, requires an additional fuel gas preheater. This additional equipment requires a higher pressure of the residual gas generated by pressure swing adsorption. However, increasing the residual gas pressure reduces the hydrogen yield of the PSA system, so the PSA system must be upgraded.

[0010] The present invention aims to improve heat generation in corresponding processes and plants for producing a hydrogen product.

[0011] Disclosure of the invention

[0012] Against this background, a process and a plant for producing a hydrogen-containing product with the features of the independent patent claims are proposed. Further embodiments are the subject of the dependent patent claims and the following description.

[0013] When we refer to a "portion" or a "part" of a gas in the following, this can refer to a partial stream formed (merely) by splitting the gas, i.e., a subset with the same component contents as the gas itself. However, a "portion" can also be a fraction formed in a subsequent separation process such as pressure swing adsorption. Combinations can also be considered.

[0014] A process for producing a hydrogen-containing product is proposed, in which at least a portion of an ammonia feed is introduced into a burner-fired ammonia cracker to be converted with catalytic assistance to a cracked gas containing hydrogen, nitrogen, and ammonia. The cracked gas is subsequently subjected to pressure swing adsorption to obtain a product fraction that is enriched in hydrogen and depleted in ammonia compared to the cracked gas and a residual gas that is depleted in hydrogen and enriched in ammonia compared to the cracked gas. The residual gas is present, in particular, at an absolute pressure of at most 1.9 bar, at most 1.5 bar, or at most 1.1 bar.

[0015] The product fraction can, in particular, consist of more than 75%, 80%, 90%, 95%, 98%, 99%, 99.5%, 99.9%, or 99.99% hydrogen and, accordingly, contain 0.01 to 25% of other gas components. In particular, the product fraction can also be a so-called forming gas, which, for example, consists of 75% hydrogen and 25% nitrogen. The residual gas can, in particular, contain 0 to 10% ammonia and otherwise contain nitrogen and hydrogen, and possibly also water if technical ammonia is used as the ammonia feed.

[0016] The residual gas is compressed in a gas ejector, in which a fuel gas feed serves as the propellant, and combined with the fuel gas feed to form a fuel gas. The fuel gas is then combusted to provide all or part of the heat supplied to the ammonia cracker. The fuel gas feed is typically an ammonia mixture, such as technical ammonia, or pure ammonia. Preferably, the fuel gas feed is a portion of the ammonia feed. The use of a hydrocarbon-containing gas, such as natural gas, or a portion of the cracked gas produced in the ammonia cracker is also possible.

[0017] By using the gas ejector, on the one hand, the PWA residual gas is effectively mixed with a fuel gas feed to form a fuel gas and, at the same time, the pressure of the residual gas at the pressure swing adsorber can be kept low, thereby increasing the efficiency of pressure swing adsorption and thus the overall efficiency of hydrogen production.

[0018] Unlike the prior art, where the fuel gas feed, which is present at a pressure of up to 40 bar, is depressurized to the pressure of the residual gas from the PWA to generate the fuel gas, the process according to the invention makes it possible to obtain a fuel gas at a significantly higher pressure and to burn it, for example, via a cost-effective lance-type burner. At the same time, the increased pressure improves the flame pattern, as well as the burnout and part-load behavior of the burner.

[0019] In one embodiment, the fuel gas feed is generated, for example, from an ammonia-containing liquid phase by increasing the pressure and subsequent evaporation and / or superheating. The ammonia-containing liquid phase can be part of the ammonia feed.

[0020] In another embodiment, the fuel gas feed, or a portion thereof, or the fuel gas itself is preheated prior to combustion. In particular, only the fuel gas feed can be preheated. In this case, the fuel gas feed is preheated to a temperature higher than the optimum temperature for combustion, since the temperature drops again during the subsequent mixing of the fuel gas feed with the residual gas from the PWA.

[0021] An increased temperature of the fuel gas also leads to an improvement in the flame pattern as well as the burnout and part-load behavior of the burner.

[0022] In a further embodiment, an electric heater is used to preheat the fuel gas insert or the fuel gas.

[0023] In a further embodiment, the cracked gas is subjected to heat integration before being subjected to pressure swing adsorption to obtain a cooled cracked gas. Heat extracted from the cracked gas can be used, in particular via a heat exchanger, to preheat the fuel gas feed, a portion thereof, or the fuel gas. Furthermore, heat from the cracked gas can be used to vaporize and / or superheat the ammonia feed before it is fed to the ammonia cracker. This can improve the overall efficiency of the process with regard to the heat generated in the process. To preheat fuel gas or fuel gas feed, in addition to heat lost in the process itself (heat integration), heat generated in an electric preheater, regardless of the operating conditions, can also be used.This can increase the load flexibility of the process, since the fuel gas or the fuel gas feed can be preheated to a sufficient level even if no or only small amounts of heat are lost in the process, as can be the case, for example, during start-up operation.

[0024] In one embodiment, heat of the flue gas formed during combustion of the fuel gas or a portion thereof is used to preheat combustion air supplied to the combustion and / or to preheat the fuel gas used to generate the heat supplied to the ammonia cracker and / or the fuel gas feed.

[0025] The heat from the hot cracked gas can therefore be recovered, particularly using a suitable heat exchanger, to heat the fuel gas and / or the fuel gas feed. Especially when preheating the combustion air with hot flue gas, the flue gas outlet temperature is reduced to 50 to 150°C. Condensation of the flue gas should be avoided, as this can lead to corrosion in the corresponding heat exchanger.

[0026] In one embodiment, the ammonia cracking process comprises a pre- and main cracking stage. An adiabatic pre-cracker can be used for the pre-cracking process, i.e., the ammonia feedstock is partially converted in the pre-cracker without the addition of heat. This lowers the temperature of the gas mixture. In contrast, heat is supplied to the main cracker, into which the ammonia feedstock partially converted in the adiabatic pre-cracker is introduced for the main cracking process.

[0027] Since the main cracking can take place at a low temperature and due to the lower ammonia content of the ammonia feed, nitriding is reduced or completely prevented, thereby reducing the design costs of the reactors used to convert the ammonia feed, as these do not need to be protected from nitriding, or only to a lesser extent. In one embodiment, the burner-fired ammonia cracker is operated with flue gas recirculation. In particular, as already explained at the beginning, it can be designed like a fired reforming reactor and have a furnace chamber within which the flue gas recirculation or flue gas recirculation takes place. In this way, the temperature of the flue gas upon exiting the radiation zone can be reduced to a value of approx.150 to 200 K above the reactor outlet temperature. This also allows other advantages, such as a reduction in the formation of nitrogen oxides, to be realized in corresponding embodiments of the present invention.

[0028] Embodiments of the present invention may also include burning the product obtained or a portion thereof in a gas turbine coupled to a generator to generate electrical energy.

[0029] The invention further relates to a plant for producing a hydrogen-containing product, comprising a burner-fired ammonia cracker in which an ammonia feed is catalytically converted to obtain a cracked gas containing hydrogen, nitrogen and ammonia, and a pressure swing adsorber with which a hydrogen-enriched and ammonia-depleted product fraction and a hydrogen-depleted and ammonia-enriched residual gas can be obtained from the cracked gas.

[0030] According to the invention, the plant comprises a gas ejector in which a fuel gas feed can be used as a propellant, and which is connected to the burner-fired ammonia cracker and the pressure swing adsorber in such a way that the residual gas can be compressed in the gas ejector and combined with the fuel gas feed to form a fuel gas, at least a portion of which can subsequently be combusted to provide heat to be supplied to the ammonia cracker. In particular, the plant is designed to carry out the process configurations described above.

[0031] Brief description of the drawing Embodiments of the invention are described below purely by way of example with reference to the attached drawing and explanation of the technical background.

[0032] Figure 1 illustrates a method or a system according to an embodiment of the present invention,

[0033] Figure 2 illustrates a method or a system according to a further embodiment of the present invention,

[0034] Figure 3 illustrates a method or a system according to a further embodiment of the present invention,

[0035] Figure 4 illustrates a method or a system according to a further embodiment of the present invention, and

[0036] Figure 5 illustrates a method and a system according to another embodiment of the present invention.

[0037] Embodiments of the invention

[0038] The embodiments described below are provided solely for the purpose of assisting the reader in understanding the claimed and previously discussed features. They are merely representative examples and are not intended to be exhaustive and / or limiting of the features of the invention. It is to be understood that the advantages, embodiments, examples, functions, features, structures, and / or other aspects described above and below are not to be considered limitations on the scope of the invention as defined in the claims or limitations on equivalents to the claims, and that other embodiments may be utilized and changes may be made without departing from the scope of the claimed invention. Different embodiments of the invention may include other useful combinations of the described elements, components, features, parts, steps, means, etc.comprise, consist of, or consist essentially of, even if such combinations are not specifically described herein.

[0039] Explanations relating to devices, apparatus, arrangements, systems, etc. according to embodiments of the present invention may also apply to methods, processes, methods, etc. according to the embodiments of the present invention, and vice versa. Elements, method steps, etc. that are identical, have the same effect, are functionally equivalent, are structurally identical, or are comparable may be identified by identical reference numerals.

[0040] Figure 1 illustrates a method and a system according to one embodiment of the present invention. The method and the system are designated overall by 100.

[0041] An ammonia feed 1, for example from a tank, is pressurized, if necessary, by means of a pump and subjected to pretreatment. The pretreatment comprises, in particular, evaporation and superheating of the ammonia feed 1. The ammonia feed 1, or the evaporated and superheated ammonia feed 1, is fed to the ammonia cracker 10 and catalytically converted therein to obtain an unreacted ammonia as well as a cracked gas 2 containing hydrogen and nitrogen.

[0042] The ammonia cracker 10 comprises an adiabatic pre-cracker 10a and a burner-fired main cracker 10b. In the adiabatic pre-cracker 10a, a portion of the ammonia feed 1 is converted to obtain a partially converted ammonia feed, which is then fed to the fired main cracker 10b, where it is further converted with the addition of heat. Between the pre-cracker 10a and the main cracker 10b, in particular, a heat exchanger is arranged, which is designed to reheat the at least partially converted ammonia feed before it is fed to the main cracker 10b. The main cracker 10b can comprise one or more catalyst beds. A nickel-based catalyst is particularly suitable for the high temperatures prevailing in the fired main cracker 10a. The cracked gas 2 obtained in the main cracker 10b is subjected to pressure swing adsorption 20.Unconverted ammonia is converted into a residual gas 4 by pressure swing adsorption 20, while a product fraction 3 is also obtained, which contains mainly hydrogen but may also contain traces of nitrogen. Water, which may also be present in "anhydrous" technical-grade ammonia, is optionally separated with the ammonia and converted into the residual gas 4.

[0043] The residual gas 4 is then mixed with a fuel gas feed 5 in a gas ejector 30. The fuel gas feed 5 is provided by compression, in particular by a pump, and evaporation and superheating. An ammonia mixture, in particular of pure or technical ammonia or natural gas, can be used as the fuel gas feed 5. The fuel gas feed 5 is used as the propellant in the gas ejector 30. Since the fuel gas feed 5 has a higher pressure than the residual gas 4 obtained by the pressure swing adsorption 20, which in particular has a pressure of at most 1.9 bara or at most 1.5 bara or at most 1.1 bara, the residual gas 4 is mixed with the fuel gas feed 5 and brought to a higher pressure level. The fuel gas 6 thus formed is then combusted in a burner to provide heat for the ammonia cracker 10.

[0044] Figure 2 illustrates a method and a system according to a further embodiment of the present invention. The method and the system are designated overall by 100. The same reference numerals denote the same method steps and system units as in Figure 1. A description of these parts will be omitted below; reference is made to the description of Figure 1.

[0045] In the embodiment of the process or plant 100 illustrated by Figure 2, the cracked gas 2 is subjected to heat integration 50 after the ammonia cracker 10 to obtain cooled cracked gas 7 before being fed to the pressure swing adsorption 20. The heat extracted from the cracked gas 2 can be used, for example, in the pretreatment for evaporating and / or superheating the ammonia feed 1. The fuel gas feed 5 is in turn provided by compressing and evaporating ammonia or natural gas. The fuel gas feed 5 is then fed to an electric heater 40, which raises the fuel gas feed 5 to a predetermined temperature. Subsequently, a portion of the heated fuel gas feed 5a is mixed with the residual gas 4 in the gas ejector 30. The remaining portion is fed to the fuel gas 6 downstream of the gas ejector 30.The fuel gas thus produced is then burned to generate the heat supplied to the ammonia cracker 10 or a portion thereof.

[0046] Figure 3 illustrates a method and a system according to a further embodiment of the present invention. The method and the system are designated overall by 100. The same reference numerals designate the same method steps and system units as in Figures 1 and 2. A description of these parts will be omitted below; reference is made to the description of Figures 1 and 2.

[0047] In contrast to the processes and plant 100 shown in Figures 1 and 2, the fuel gas feed 5 is not provided by compressing and vaporizing ammonia, but rather a portion of the ammonia feed 1 supplied to the ammonia cracker 10 is extracted and used as fuel gas feed 5. As already described with reference to Figure 1, the ammonia feed 1 may have been compressed by a pump and vaporized and superheated by a pretreatment unit (not shown).

[0048] After the fuel gas feed 5 has been mixed with the residual gas 4 in the gas ejector 30, the fuel gas 6 is heated. In contrast to the embodiment described with reference to Figure 2, no electric heater 40 is used for this purpose; instead, the heat extracted from the cracked gas 2 during the heat integration 50 is used to heat the fuel gas 6. For this purpose, for example, a heat exchanger can be used which transfers the heat of the cracked gas 2 directly to the fuel gas 6, which is used as a coolant. The fuel gas 6a heated in this way is then combusted to provide the heat supplied to the ammonia cracker 10, or a portion thereof. It should be noted that individual aspects of the embodiments presented can also be combined with one another. For example, heat from the heat integration 50 can be transferred to the fuel gas feed 5, or the fuel gas 6 can be heated by an electric heater.Furthermore, it is conceivable that the fuel gas insert 5 and / or the fuel gas 6 is heated by the transfer of heat from the cracked gas 2 and by an electric heater 40.

[0049] Figure 4 illustrates a method and a system according to a further embodiment of the present invention. The method and the system are designated overall by 100. The same reference numerals designate the same method steps and system units as in Figures 1 to 3. A description of these parts will be omitted below; reference is made to the description of Figures 1 to 3.

[0050] In the embodiment shown in Figure 4, a portion of the fission gas 2 is used as the fuel gas insert 5. If this embodiment is further combined with a heat integration 50, as shown in Figures 2 and 3, the fuel gas insert 5 can be a portion of the fission gas 2 or the cooled fission gas 7.

[0051] Figure 5 illustrates a method and a system according to a further embodiment of the present invention. The method and the system are designated overall by 100. The same reference numerals designate the same method steps and system units as in Figures 1 to 4. A description of these parts will be omitted below; reference is made to the description of Figures 1 to 4.

[0052] In Figure 5, the fuel gas 6 generated by the gas ejector 30 is in turn fed to a heat exchanger 60, in which the fuel gas 6 is preheated to preheated fuel gas 6a, i.e., heated to a predetermined temperature. To provide the heat in the heat exchanger 60, flue gas 8 generated during the combustion of the fuel gas 6 or the preheated fuel gas 6a is used, which transfers heat to the fuel gas 6 in the heat exchanger and cools down in the process.

Claims

Patent claims 1. A process (100) for producing a hydrogen-containing product, in which an ammonia feed (1) is introduced into a burner-fired ammonia cracker (10) in order to be converted with catalytic assistance to a cracked gas (2) containing hydrogen, nitrogen and ammonia, which is subsequently subjected to pressure swing adsorption (20) to obtain a product fraction (3) which is enriched in hydrogen and depleted in ammonia compared to the cracked gas (2) and a residual gas (4) which is depleted in hydrogen and enriched in ammonia compared to the cracked gas (2), characterized in that the residual gas (4) is compressed in a gas ejector (30), in which a fuel gas feed (5) serves as a propellant, and is combined with the fuel gas feed (5) to form a fuel gas (6), at least a portion of which is combusted to fire the ammonia cracker (10).

2. The method (100) according to claim 1, wherein a part of the ammonia feed (1) and / or a part of the cracked gas (2) is used as fuel gas feed (5).

3. Method (100) according to one of claims 1 to 2, wherein the fuel gas feed (5) or a part thereof or the fuel gas (6) is preheated before combustion.

4. The method (100) according to claim 3, wherein the fuel gas insert (5) or a part thereof or the fuel gas (6) is preheated by an electric heater (40).

5. Process according to one of the preceding claims, wherein the cracked gas (2) is subjected to heat integration (50) before being subjected to pressure swing adsorption (20) to obtain a cooled cracked gas (7).

6. The method according to claim 5, wherein the heat extracted from the cracked gas (2) during the heat integration (50) or a part thereof is used to preheat the fuel gas feed (5) or a part thereof or the fuel gas (6) or a part thereof.

7. Method according to one of the preceding claims, wherein heat of the flue gas produced during the combustion of the fuel gas (6) is used to preheat a combustion air and / or fuel gas (6) supplied to the combustion and / or the fuel gas feed (5).

8. Process according to one of the preceding claims, wherein the ammonia cracker (10) is operated with a flue gas recirculation.

9. Method according to one of the preceding claims, wherein the residual gas (4) has a pressure of at most 1.9 bara or at most 1.5 bara or at most 1.1 bara.

10. The process according to any one of the preceding claims, wherein the ammonia cleavage comprises an adiabatic pre-cleavage (10a) and a main cleavage (10b).

11. Method according to one of the preceding claims, wherein the fuel gas feed (5) is natural gas.

12. Plant (100) for producing a hydrogen-containing product, comprising a burner-fired ammonia cracker (10) in which an ammonia feed (1) is catalytically converted to obtain a cracked gas (2) containing hydrogen, nitrogen, and ammonia, and a pressure swing adsorber (20) with which a hydrogen-enriched and ammonia-depleted product fraction (3) and a hydrogen-depleted and ammonia-enriched residual gas (4) can be obtained from the cracked gas, characterized in that it comprises a gas ejector (30) in which a fuel gas feed (5) can be used as a propellant, and which is connected to the burner-fired ammonia cracker (10) and the pressure swing adsorber (20) in such a way that the residual gas (4) can be compressed in the gas ejector (30) and combined with the fuel gas feed (5) to form a fuel gas (6).of which at least a part can subsequently be burned to provide heat to be supplied to the ammonia cracker (10). 13 System (100) according to claim 12, wherein the system (100) is configured to carry out a method according to one of claims 1 to 11.

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