Method and plant for producing a hydrogen stream

Abstract

The invention relates to a method for producing a hydrogen stream (1), wherein a carbon-containing energy carrier stream (3) and an oxygen stream (4) from an oxygen generation arrangement (5) of a plant (2) are supplied to an ATR reactor arrangement (6) of the plant (2) in order to produce a synthesis gas stream (7) comprising hydrogen and carbon oxides, wherein the ATR reactor arrangement (6) produces the synthesis gas stream (7) from the energy carrier stream (3) by autothermal reforming with the oxygen stream (4), such that a partial oxidation, in particular a catalytic partial oxidation, provides the heat required for the endothermic reforming reactions, wherein the synthesis gas stream (7) is at least in part supplied to an adsorption device (8) of the plant (2) in order to separate the synthesis gas stream (7) into the hydrogen-containing hydrogen stream (1) and into a first purge stream (10a) and a second purge stream (10b), each comprising carbon oxides. The method is characterised in that: the first purge stream (10a) is supplied to a recovery adsorption device (11) of the plant (2) in order to separate hydrogen from the first purge stream (10); the recovery adsorption device (11) provides a recovery stream (12), that comprises the separated hydrogen, and a remaining recycle stream (13); the recycle stream (13) is supplied substantially completely to the energy carrier stream (3); and the second purge stream (10b) is supplied for combustion to at least one feedstock heater (15a) of a plurality of feedstock heaters (15a-e) of the plant (2). The invention also relates to a corresponding plant for producing a hydrogen stream and to a method for preparing methanol.

Description

[0001] Process and plant for generating hydrogen flow

[0002] The invention relates to a method for obtaining a hydrogen stream with the features of the preamble of claim 1, a method for producing ammonia with the features of the preamble of claim 14, and a plant for obtaining a hydrogen stream with the features of the preamble of claim 15.

[0003] The economic importance of hydrogen is increasing, particularly because it can be used as an energy carrier without CO2 emissions. Hydrogen can also serve as a feedstock for the production of other substances such as ammonia, which in turn can be used to transport hydrogen.

[0004] In this context, there is increased interest in producing hydrogen, and potentially ammonia or other substances from it, in a way that has a very small carbon footprint. In the case of a so-called "low-low carbon footprint," the term "blue" hydrogen or "blue" ammonia is used when the hydrogen or ammonia is produced from natural gas.

[0005] One fundamental way to produce hydrogen is to start with synthesis gas. This synthesis gas can be obtained from a carbon-based energy carrier stream such as natural gas.

[0006] However, producing synthesis gas from natural gas requires energy, and when using a steam reformer for this purpose, up to 30% of the natural gas used is needed for its underfiring. The CO2 contained in the flue gas is released into the atmosphere. CO2 produced during the process can be separated by scrubbing and used or sequestered without being released into the atmosphere.

[0007] A reduction in the amount of CO2 emitted in the flue gas, corresponding to approximately 10% of the natural gas used, can be achieved by exclusively using autothermal reforming (ATR) for synthesis gas production instead of steam reforming. In autothermal reforming, where the required temperature is generated by catalytic partial oxidation with oxygen, no external heat input is needed for synthesis gas production. At most, the energy carrier stream needs to be preheated by gas-fired feedstock heaters before being fed into the autothermal reforming process. Furthermore, the air separation process used for autothermal reforming can also simultaneously provide the nitrogen for any subsequent ammonia synthesis.

[0008] Very low emission levels are already achieved by using the off-gas from the PSA (which can also be described as exhaust gas) for the necessary preheating of the synthesis gas before the ATR (Automated Thermal Transfer). The remaining energy difference is compensated for with desulfurized natural gas.

[0009] Similarly, decarbonized synthesis gas can be used in gas-fired feedstock heaters to reduce CO2 emissions. However, this requires the use of a very effective CO2 scrubber, as otherwise the remaining CO2 in the synthesis gas will increase residual emissions.

[0010] Furthermore, the decarbonized synthesis gas often requires further processing, as methane from the methane slip of the ATR (ammonia-releasing reactor) accounts for the majority of CO2 emissions after combustion in the gas-fired feedstock heaters. However, even such processing cannot prevent the methane from entering the off-gas in one way or another. Therefore, reducing residual emissions below the target value of 0.2 t CO2 per t ammonia is not possible.

[0011] EP 4 269 332 A1, from which the present invention is considered the closest related, discloses a process and a plant for producing ammonia, wherein the hydrogen required for this purpose is obtained from natural gas. However, even the firing of the gas-fired feedstock heaters with already produced, high-purity hydrogen, as disclosed here, does not prevent the occurrence of methane in the off-gas. And it is, of course, inefficient to design a PSA (Production Supply System) for the highest purity only to then combust the produced, high-purity hydrogen again.

[0012] Based on the prior art, the object of the invention is therefore to provide an improved approach for obtaining a hydrogen stream which can further reduce the CO2 footprint during its production.

[0013] With regard to a process for producing hydrogen according to the preamble of claim 1, this problem is solved by the features of the characterizing part of claim 1. With regard to a process for producing ammonia according to the preamble of claim 14, this problem is solved by the features of the characterizing part of claim 14. With regard to a plant for producing hydrogen according to the preamble of claim 15, this problem is solved by the features of the characterizing part of claim 15.

[0014] The invention is based on the finding that the total amount of CO2 emitted in a hydrogen production plant using autothermal reforming can be surprisingly reduced even further by operating the plant's feedstock heaters largely electrically and using only a small portion of them with off-gas to prevent enrichment processes. Such electrically operated feedstock heaters are also known as electric heating devices. It has been found that this minimizes CO2 emissions and simultaneously increases the overall process efficiency, as electricity can be used instead of hydrogen to power the feedstock heaters.

[0015] Subclaims 9 and 11 describe a particularly advantageous selection of a special feedstock heater for feeding by the exhaust gas.

[0016] Further details, features, embodiments, objectives, and advantages of the present invention are explained below with reference to the drawing, which merely illustrates exemplary embodiments. In the drawing, Fig. 1 schematically shows the flow diagram of a proposed system for carrying out the proposed method according to a first exemplary embodiment and

[0017] Fig. 2 schematically shows the flow diagram of a proposed plant for carrying out the proposed method according to a second embodiment.

[0018] The proposed method serves to obtain a hydrogen stream 1, wherein a carbon-containing energy carrier stream 3 and an oxygen stream 4 from an oxygen recovery arrangement 5 of plant 2 are fed to an ATR reactor arrangement 6 of plant 2 to obtain a synthesis gas stream 7 containing hydrogen and carbon oxides. The method is first described with reference to the embodiment shown in Fig. 1. Unless otherwise described, the embodiment shown in Fig. 2 corresponds to the embodiment shown in Fig. 1. Preferably, the oxygen stream 4 consists essentially of oxygen.

[0019] In the proposed process, the ATR reactor arrangement 6 obtains the synthesis gas stream 7 from the energy carrier stream 3 by means of an autothermal reforming with the oxygen stream 4, so that a particularly catalytic partial oxidation provides the heat required for the endothermic reforming reactions.

[0020] In the proposed process, the synthesis gas stream 7 is further fed, at least partially, to an adsorption device 8 of plant 2 for the separation of the synthesis gas stream 7 into the hydrogen-containing hydrogen stream 1 and into a first purge stream 10a and a second purge stream 10b, each containing carbon oxides. The first purge stream 10a and the second purge stream 10b also contain methane and hydrogen.

[0021] The proposed method is characterized in that the first purge stream 10a is fed to a recovery adsorption device 11 of plant 2 for separating hydrogen from the first purge stream 10a. The proposed method is further characterized in that the recovery adsorption device 11 provides a recovery stream 12 containing the separated hydrogen and a remaining recycling stream 13, that the recycling stream 13 is substantially entirely fed to the energy carrier stream 3, and that the second purge stream 10b is fed to at least one feedstock heater 15a of a plurality of feedstock heaters 15a-e of plant 2 for combustion. In other words, the second purge stream 10b is fed to this at least one feedstock heater 15a for heating by combustion. Such a feedstock heater 15a is evidently a gas-fired feedstock heater.The system 2 of the first embodiment of Fig. 1 has a total of five feedstock heaters 15a-e, whereas the system 2 of the second embodiment of Fig. 2 has a total of four feedstock heaters 15a-d.

[0022] It has been found that in this way the requirement to remove methane and inert gases from the cycle to prevent their accumulation can be reconciled with the energy demand of a gas-fired feedstock heater 15a. The recirculated gas quantity thus fulfills a dual function: providing energy for the gas-fired feedstock heater 15a and removing methane and inert gases from the cycle.

[0023] The methane present in the exhaust gas stream 13 is fed back to the ATR reactor arrangement 6 via the feed of the recycled stream 13 to the energy carrier stream 3, where at least some of the methane can be split. This allows the carbon, or the carbon oxide obtained from the methane, to be sequestered and neither pollute the hydrogen stream 1 nor be released into the atmosphere as CO2.

[0024] In principle, the mass flow rate of the first purge stream 10a can be in any ratio to the mass flow rate of the second purge stream 10b. Preferably, the second purge stream 10b has a mass flow rate of less than 30%, and in particular less than 25%, of the combined mass flow rate of the first purge stream 10a and the second purge stream 10b. Alternatively or additionally, the second purge stream 10b can have a mass flow rate of at least 5%, preferably at least 10%, and in particular at least 15%, of the combined mass flow rate of the first purge stream 10a and the second purge stream 10b. Likewise, the second purge stream 10b can have a mass flow rate of substantially 20% of the combined mass flow rate of the first purge stream 10a and the second purge stream 10b.

[0025] A preferred embodiment of the proposed method is characterized in that the additional feedstock heaters 15b-e of Annex 2 are electrically operated. They are therefore electric heating devices. This eliminates the need for either hydrogen combustion or exhaust gas combustion, which would result in CO2 emissions. The additional feedstock heaters 15b-e are those feedstock heaters 15b-e of the plurality of feedstock heaters 15a-e of Annex 2 that are not supplied by the second purge stream 10b.

[0026] Another preferred embodiment of the proposed method is characterized in that the adsorption device 8 is configured for pressure swing adsorption and / or temperature swing adsorption.

[0027] It is also preferred that the recovery adsorption device 11 is configured for pressure swing adsorption and / or temperature swing adsorption.

[0028] According to a preferred embodiment of the proposed method, it is provided that the system 2 has a recovery compressor 19 which increases the pressure of the first purge stream 10a before it is fed to the recovery adsorption device 11.

[0029] According to a further preferred embodiment of the proposed method, the synthesis gas stream 7 is fed to a carbon dioxide scrubber 20 of plant 2 for the removal of at least a portion of the carbon dioxide from the synthesis gas stream 7. The carbon dioxide removed in this way is preferably sequestered. It is further preferred that the carbon dioxide is removed in the carbon dioxide scrubber 20 by means of a scrubbing medium containing methanol. It is also preferred that the carbon dioxide is removed from the synthesis gas stream 7 in the carbon dioxide scrubber 20 in multiple stages. The carbon dioxide removed in this way reduces the carbon dioxide content of the recycle stream 13 and can be sequestered.

[0030] A preferred embodiment of the proposed method is characterized in that the synthesis gas stream 7 is fed to a shift device 21 of the plant 2, that the synthesis gas stream 7 fed to the shift device 21 contains water, and that a water-gas shift reaction takes place in the shift device 21 to convert at least a predominant part of the carbon monoxide in the synthesis gas stream 7 with the water into carbon dioxide and hydrogen. Preferably, the shift device 21 is located upstream of the carbon dioxide scrubber 20. The carbon dioxide thus produced can then be scrubbed out in the subsequent carbon dioxide scrubber 20.

[0031] Another preferred embodiment of the proposed method is characterized in that the second purge stream 10b is fed to exactly one feedstock heater 15a of the plant 2 for combustion. It has been found that in this way the correct balance between the combustion of the purged gas and the electrical operation of the other feedstock heaters 15b-e is achieved.

[0032] According to a first preferred embodiment, the single feedstock heater 15a is the one in plant 2 with the highest energy demand. In other words, it is the feedstock heater 15a that requires the greatest heating power. This embodiment corresponds to the embodiment shown in Fig. 1. In this way, the overall energy requirement for the multiple feedstock heaters 15a-e is minimized. If, for example, the other feedstock heaters 15a-e are fueled with hydrogen, and this hydrogen is scarce in plant 2 or only available with a comparatively unfavorable CO2 balance, then, according to this embodiment, less hydrogen is required overall for the operation of the feedstock heaters 15a-e.In this variant, it is also highly likely that sufficient gas is removed from the cycle to prevent an accumulation of methane and inert substances. According to a second preferred variant, the single feedstock heater 15a is the one in plant 2 with the lowest energy requirement. This corresponds to the embodiment shown in Fig. 2, which is otherwise identical to the embodiment shown in Fig. 1 except for the aforementioned difference in the total number of feedstock heaters 15a-e. In other words, it is the feedstock heater 15a that requires the least heating power. Therefore, very little gas needs to be circulated to operate this feedstock heater 15a, which is why the associated CO2 emissions are also particularly low.It is possible that the feedstock heater 15a with the lowest energy requirement is the one that is arranged first in the process among the multitude of feedstock heaters 15a. In other words, it is the first feedstock heater 15a to which the energy carrier flow 3 is supplied. It is possible that this feedstock heater 15a has less than 50% of the energy requirement of the feedstock heater 15a-e with the next highest energy requirement among the multitude of feedstock heaters 15a-e.

[0033] It is further preferred that the recovery stream 12 is at least partially fed into the hydrogen stream 1. In particular, it is possible that the recovery stream is fed essentially entirely into the hydrogen stream 1.

[0034] According to a preferred embodiment of the proposed method, the plant 2 comprises a pre-reformer 22 for splitting hydrocarbons with at least two carbon atoms into methane, to which the energy carrier stream 3 is fed before being supplied to the ATR reactor arrangement 6. It is further preferred that the second purge stream 10b is supplied to an ATR feedstock heater 23 of the plurality of feedstock heaters 15a-e for combustion, which ATR feedstock heater 23 is arranged process-wise between the pre-reformer 22 and the ATR reactor arrangement 6. This variant corresponds to the embodiment shown in Fig. 1. Preferably, this ATR feedstock heater 23 is exactly one of the plurality of feedstock heaters 15a-e to which the second purge stream 10b is supplied for combustion.It has turned out that the energy demand of this feedstock heater 15a is particularly high. It is therefore possible that this ATR feedstock heater 23 is the feedstock heater 15a with the highest energy demand. Therefore, it may be advantageous to operate precisely this feedstock heater 15a with the exhaust gas from the synthesis gas cycle instead of, for example, electrically.

[0035] In this variant, as also shown in Fig. 1, it is preferred that an electrically operated feed heater 15e of the system 2 is arranged upstream of the single feed heater 15a, to which the second purge stream 10b is fed for combustion. As shown, and preferably, the feed heater 15a, to which the second purge stream 10b is fed for combustion, is the ATR feed heater 23. In particular, the electrically operated feed heater 15e can be located directly upstream of the single feed heater 15a. This electrically operated feed heater 15e can also be referred to as an electric preheater 28. In other words, this electric preheater 28 and the ATR feed heater 23 together provide the heating power required for the ATR reactor arrangement 6.

[0036] In addition to the pre-reformer 22, the system 2 can include further devices to which the energy carrier flow 3 is supplied process-wise upstream of the ATR reactor arrangement 6. Preferably, the system 2 includes a saturation stage 25 to which the energy carrier flow 3 is supplied before being supplied to the ATR reactor arrangement 6.

[0037] Alternatively or additionally, the system 2 can include a desulfurization stage 26 for desulfurizing the energy carrier stream 3 before it is fed to the ATR reactor arrangement 6. This desulfurization stage 26 is preferably located upstream of the pre-reformer 22. Likewise, the system 2 can include a natural gas compressor 27 for increasing the pressure of the energy carrier stream 3, which is preferably located upstream of the desulfurization stage 26.

[0038] According to a further preferred embodiment of the proposed method, the energy carrier stream 3 comprises natural gas. It is also possible that the energy carrier stream 3 consists essentially of natural gas. Preferably, the hydrogen stream 1 consists essentially of hydrogen. Likewise, it is preferred that the recovery stream 12 consists essentially of hydrogen.

[0039] In the proposed process for producing ammonia 18, a hydrogen stream 1, obtained according to the proposed process for generating a hydrogen stream 1, and a nitrogen stream 16 are supplied to an ammonia reactor arrangement 17 of the system 2. The hydrogen contained in the hydrogen stream 1 and the nitrogen contained in the nitrogen stream 16 are converted into ammonia in the ammonia reactor arrangement 17. This utilizes the proposed advantage of obtaining the hydrogen stream for the production of ammonia 18. Preferably, the system 2 includes an ammonia synthesis compressor 24, which increases the pressure of the hydrogen stream 1 and the nitrogen stream 16 before they are supplied to the ammonia reactor arrangement 17.

[0040] The proposed system 2 serves to generate a hydrogen stream 1 and comprises an oxygen recovery arrangement 5 for generating an oxygen stream 4 and an ATR reactor arrangement 6 for generating a synthesis gas stream 7 containing hydrogen and carbon oxides, to which a carbon-containing energy carrier stream 3 and the oxygen stream 4 are supplied. The oxygen recovery arrangement 5 is preferably an air separation unit that separates the ambient air 9 and thereby also provides the nitrogen stream 16.

[0041] In the proposed system 2, the ATR reactor arrangement 6 is designed to obtain the synthesis gas stream 7 from the energy carrier stream 3 by means of autothermal reforming with the oxygen stream 4, so that a particularly catalytic partial oxidation provides the heat required for the endothermic reforming reactions.

[0042] The proposed system 2 further comprises an adsorption device 8 for separating at least a part of the synthesis gas stream 7 into the hydrogen-containing hydrogen stream 1 and into a first purge stream 10a and a second purge stream 10b, each containing carbon oxides, as well as a plurality of feedstock heaters 15a-e.

[0043] The proposed Annex 2 is characterized in that the Annex 2 has a recovery adsorption device 11 for separating hydrogen from the first purge stream 10a, that the recovery adsorption device 11 provides a recovery stream 12 containing the separated hydrogen and a remaining recycling stream 13, that the recycling stream 13 is substantially completely fed to the energy carrier stream 3, and that the second purge stream 10b is fed to at least one feedstock heater 15a-e of the plurality of feedstock heaters 15a-e for combustion.

[0044] The preferred configurations, features and properties of the proposed method described above correspond to preferred configurations, features and properties of the proposed plant and vice versa.

Claims

Patent claims 1. A method for obtaining a hydrogen stream (1), wherein a carbon-containing energy carrier stream (3) and an oxygen stream (4) from an oxygen recovery arrangement (5) of a plant (2) are fed to an ATR reactor arrangement (6) of the plant (2) for obtaining a synthesis gas stream (7) containing hydrogen and carbon oxides, wherein the ATR reactor arrangement (6) obtains the synthesis gas stream (7) from the energy carrier stream (3) by autothermal reforming with the oxygen stream (4), such that a particularly catalytic partial oxidation provides the heat required for the endothermic reforming reactions, wherein the synthesis gas stream (7) is fed at least partially to an adsorption device (8) of the plant (2) for separating the synthesis gas stream (7) into the hydrogen-containing hydrogen stream (1) and into a first purge stream (10a) and second purge stream (10b), respectively containing carbon oxides, characterized in thatthat the first purge stream (10a) is fed to a recovery adsorption device (11) of the plant (2) for separating hydrogen from the first purge stream (10), that the recovery adsorption device (11) provides a recovery stream (12) containing the separated hydrogen and a remaining recycling stream (13), that the recycling stream (13) is substantially all fed to the energy carrier stream (3), that the second purge stream (10b) is fed to at least one feedstock heater (15a) or a plurality of feedstock heaters (15a-e) of the plant (2) for combustion, 2. Method according to claim 1, characterized in that the further feedstock heaters (15b-e) of the system (2) are electrically operated.

3. Method according to claim 1 or 2, characterized in that the adsorption device (8) is configured for pressure swing adsorption and / or temperature swing adsorption, preferably that the recovery adsorption device (11) is configured for pressure swing adsorption and / or temperature swing adsorption.

4. Method according to one of claims 1 to 3, characterized in that the system (2) has a recovery compressor (19) which increases the pressure of the first purge stream (9) before it is fed to the recovery adsorption device (11).

5. Method according to one of claims 1 to 4, characterized in that the synthesis gas stream (7) is fed to a carbon dioxide scrubber (20) of the plant (2) for washing out at least a part of the carbon dioxide from the synthesis gas stream (7), and that in the carbon dioxide scrubber (20) the carbon dioxide is washed out by a washing medium comprising methanol.

6. Method according to claim 5, characterized in that the carbon dioxide is washed out of the synthesis gas stream (6) in the carbon dioxide scrubbing (19) in multiple stages.

7. Method according to one of claims 1 to 6, characterized in that the synthesis gas stream (7), preferably upstream of the carbon dioxide scrubbing (20) in the process, is fed to a shift device (21) of the plant (2), that the synthesis gas stream (7) fed to the shift device (21) contains water and that a water-gas shift reaction takes place in the shift device (21) to convert at least a predominant part of the carbon monoxide of the synthesis gas stream (7) with the water into carbon dioxide and hydrogen.

8. Method according to one of claims 1 to 7, characterized in that the second purge stream (10b) is fed to exactly one feedstock heater (15a) of the plant (2) for combustion.

9. Method according to claim 8, characterized in that an electrically operated feedstock heater (15e) of the system (2) is arranged upstream of the exactly one feedstock heater (15a) to which the second purge stream (10b) is supplied for combustion.

10. Method according to one of claims 1 to 9, characterized in that the recovery stream (12) is at least partially fed to the hydrogen stream (1).

11. according to one of claims 1 to 10, characterized in that the plant (2) has a pre-reformer (22) for splitting hydrocarbons with at least two carbon atoms into methane, to which the energy carrier stream (3) is supplied before being fed to the ATR reactor arrangement (6), preferably that the second purge stream (14) is supplied to an ATR feedstock heater (23) of the plurality of feedstock heaters (15a-e) for combustion, which is arranged process-wise between the pre-reformer (22) and the ATR reactor arrangement (6).

12. Method according to one of claims 1 to 11, characterized in that the energy carrier flow (3) comprises natural gas.

13. Method according to one of claims 1 to 12, characterized in that the hydrogen stream (1) consists essentially of hydrogen, preferably that the recovery stream (12) consists essentially of hydrogen.

14. A process for the production of ammonia, characterized in that a hydrogen stream (1) obtained according to a process according to one of claims 1 to 13 and a nitrogen stream (16) are supplied to an ammonia reactor arrangement (17) of the plant (2) and that hydrogen comprising the hydrogen stream (1) and nitrogen comprising the nitrogen stream (16) are converted into ammonia in the ammonia reactor arrangement (17).

15. Plant (2) for obtaining a hydrogen stream (1), the plant (2) comprising an oxygen recovery arrangement (5) for obtaining an oxygen stream (4), comprising an ATR reactor arrangement (6) for obtaining a synthesis gas stream (7) with hydrogen and carbon oxides, to which a carbon-containing energy carrier stream (3) and the oxygen stream (4) are supplied, wherein the ATR reactor arrangement (6) is configured to obtain the synthesis gas stream (7) from the energy carrier stream (3) by autothermal reforming with the oxygen stream (4), such that a particularly catalytic partial oxidation is carried out for the endothermic The plant (2) further comprises an adsorption device (8) for separating at least a part of the synthesis gas stream (7) into the hydrogen-containing hydrogen stream (1) and into a first purge stream (10a) and second purge stream (10b), each containing carbon oxides, and the plant (2) comprises a plurality of feedstock heaters (15a-e), characterized in that the plant (2) has a recovery adsorption device (11) for separating hydrogen from the first purge stream (10), wherein the recovery adsorption device (11) provides a recovery stream (12) containing the separated hydrogen and a remaining recycling stream (13), that the recycling stream (13) is substantially completely fed to the energy carrier stream (3), and that the second purge stream (10b) is fed to at least one feedstock heater (15a-e) of the plurality for combustion.

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