Method and plant for producing hydrogen

Abstract

The invention relates to a method and a device (100) for producing hydrogen, wherein ammonia (3) is provided in liquid form and is subjected to feed evaporation (110) in order to obtain an ammonia feed gas (5), the ammonia feed gas (5) or a portion thereof is subjected to ammonia cracking (130) in order to obtain a hydrogen- and nitrogen-containing cracked ammonia gas (7), and the cracked ammonia gas (7) is subjected to a cracked gas cooling process (140) in order to obtain a cooled cracked ammonia gas (8), wherein, in the cracked gas cooling process (140), heat removed from the cracked ammonia gas (7) is at least partially used in the feed evaporation (110). The invention is characterised in that the feed evaporation (110) and the cracked gas cooling process (140) are carried out using a shared heat transfer unit (200, 300) having an evaporator vessel (210) and a tube bundle (220) which is arranged in the evaporator vessel (210) and which comprises a plurality of tubes (221, 222).

Description

[0001] Description

[0002] Process and plant for the production of hydrogen

[0003] The invention relates to a process and a plant for producing hydrogen by converting ammonia.

[0004] background

[0005] Hydrogen production on an industrial scale is currently still predominantly based on hydrocarbons. Several processes are known and described in common reference works, for example, in the article "Hydrogen" in Ullmann's Encyclopedia of Industrial Chemistry, June 15, 2000, DOI: 10.1002 / 14356007. a13_297, Section 4, "Production."

[0006] Alternatively, hydrogen can also be obtained by decomposition (cracking, splitting, reforming, etc.) of ammonia, whereby the ammonia can be used as a hydrogen storage form. Two molecules of ammonia are converted into one molecule of nitrogen and three molecules of hydrogen. The reaction is endothermic and is favored by low pressure and high temperature. However, higher pressures are desirable to avoid the need for a hydrogen compressor. An overview of corresponding processes can be found, for example, in an article by I. Lucentini et al., "Review of the Decomposition of Ammonia to Generate Hydrogen," Ind. Eng. Chem. Res. 2021, 60, 51, 18560-18611.

[0007] In general, “ammonia” should be understood here as meaning so-called technical ammonia with a commercially available content of foreign components, in particular water.

[0008] EP 4 112 539 A1 discloses a process and apparatus for producing a hydrogen product from ammonia. A burner-fired cracking furnace with catalytic support converts an ammonia-containing feedstock into a cracked gas containing hydrogen and nitrogen. The hydrogen product is separated from the cracked gas to obtain a nitrogen-rich residual gas comprising combustible substances. At least a portion of the residual gas is combusted to fuel the cracking furnace. An oxygen-rich stream is supplied from an oxygen source and used as an oxidizing agent, either directly or after admixture with air, in the combustion of the residual gas.

[0009] EP 4 112 540 A1 discloses a method and apparatus for producing a hydrogen product from ammonia. A first ammonia-containing feedstock is fed to a first fission reactor heated by an imported energy source to split ammonia into hydrogen and nitrogen with catalytic assistance, yielding a hot first fission gas containing hydrogen and nitrogen. A second ammonia-containing feedstock is converted in a second fission reactor to a second fission gas containing hydrogen and nitrogen, the hot first fission gas being used to heat the second fission reactor and being cooled in the process.

[0010] The present invention particularly addresses problems that may arise during heat integration in corresponding processes.

[0011] Overview

[0012] Against this background, a process and a plant for producing hydrogen by reacting ammonia are proposed, having the features of the independent patent claims. Further embodiments are the subject of the dependent patent claims and the following description.

[0013] The proposed process for producing hydrogen comprises providing ammonia in liquid form and subjecting it to feed evaporation to obtain an ammonia feed gas, subjecting the ammonia feed gas, or a portion thereof, to ammonia cracking in an ammonia cracking reactor to obtain an ammonia cracking gas containing hydrogen and nitrogen, and subjecting the ammonia cracking gas to cracking gas cooling to obtain a cooled ammonia cracking gas, wherein heat extracted from the ammonia cracking gas during the cracking gas cooling is at least partially used in the feed evaporation. The proposed process and its embodiments overcome specific disadvantages of ammonia cracking processes of the type explained above. The high outlet temperature of the ammonia cracking reactor, which can reach up to 900°C, leads to challenges in heat integration.Using a feed-effluent heat exchanger, the liquid ammonia could be vaporized against the hot ammonia cracking gas. However, since a suitable feed-effluent heat exchanger must be designed with a tube sheet that is permanently stable at temperatures up to 900°C and resistant to nitration, this heat exchanger can only be implemented at high cost. Another option is the use of a process gas cooler, similar to those used to generate steam in steam reforming plants. However, this solution is unfavorable because steam is generally not required for ammonia cracking. Another possibility for harnessing the heat from the hot ammonia cracking gas would be to use it as a heating medium in a second ammonia cracking reactor, although its temperature may not be high enough for efficient ammonia cracking.

[0014] A solution to overcome these difficulties is proposed here. This solution involves using the high-temperature heat of the ammonia cracking gas at the outlet of the ammonia cracking reactor to vaporize the ammonia, i.e., to provide the ammonia feed gas. This concept enables the integration of heat into the ammonia cracking process in combination with a suitable and technically feasible heat exchanger design. Due to the good heat transfer to a boiling liquid, the metal temperatures in the heat exchanger can be limited, enabling a cost-effective material selection.

[0015] In the embodiments proposed here, the feed evaporation and the cracked gas cooling can be carried out using a common heat transfer device comprising an evaporator vessel and a tube bundle with multiple tubes arranged in the evaporator vessel. Known, proven concepts for heat transfer devices can be used here.

[0016] In the embodiments proposed here, at least part of the

[0017] The feed evaporation takes place in the evaporator vessel, and at least part of the cracked gas cooling takes place in the tube bundle. As mentioned, the presence of liquid on the outer surfaces of the tubes in the tube bundle can prevent adverse effects such as nitriding of the tube material.

[0018] In the embodiments proposed here, the ammonia cracked gas, or a portion thereof, can be fed into the heat transfer device in a feed zone and distributed among the tubes of the tube bundle in the feed zone. The feed zone is lined with a heat-resistant lining. Conventional linings can be used to ensure that a corresponding zone can withstand the resulting temperatures.

[0019] In the embodiments proposed here, a space occupied by the tube bundle in the evaporator vessel can have an elongated shape with a horizontally extending tube bundle longitudinal axis. The evaporator vessel can also have an elongated shape with an evaporator vessel longitudinal axis. The tube bundle longitudinal axis and the evaporator vessel longitudinal axis can be arranged parallel to one another and spaced apart from one another. This allows sufficient space to be created, particularly in a region above the tube bundle, for separating liquid and gas, for example, when foam formation is expected. The tube bundle can be operated completely submerged, thus utilizing the aforementioned good heat transfer properties of the liquid.

[0020] In the embodiments proposed here, the tubes of the tube bundle can comprise several tubes with a first cross-section and one or more tubes with a second cross-section, wherein the second cross-section is larger than the first cross-section. This makes it possible to specifically adapt the heat exchange surface of the respective tubes to the respective requirements.

[0021] In the embodiments proposed here, the flow through the one or more second tubes can be adjusted according to the amount of heat to be transferred. This allows for a targeted bypass of the actual heat exchanger tubes, as also explained below. In the embodiments proposed here, the heat transfer device can comprise a separator vessel connected to the evaporator vessel via a downcomer and a riser line. In this way, improved separation of gas and liquid can be achieved.

[0022] In the embodiments proposed here, the heat transfer device can be operated such that liquid ammonia flows into the evaporator vessel via the downcomer line, and ammonia vaporized in the evaporator vessel enters the separator vessel via the riser line. In this way, the aforementioned improved evaporation can be achieved.

[0023] The proposed plant for producing hydrogen is designed to subject liquid ammonia to feed evaporation to obtain an ammonia feed gas, to subject the ammonia feed gas or a portion thereof to ammonia cracking to obtain an ammonia cracking gas containing hydrogen and nitrogen, and to subject the ammonia cracking gas to cracking gas cooling to obtain a cooled ammonia cracking gas, wherein the plant is further designed to use heat extracted from the ammonia cracking gas in the cracking gas cooling at least in part in the feed evaporation.

[0024] For further features and advantages of a corresponding system and its configurations, reference is expressly made to the above explanations concerning the proposed method and its configurations, since these apply equally to this.

[0025] The same applies to a system designed to carry out a process according to any configuration.

[0026] Drawings

[0027] Embodiments of the invention are described below purely by way of example with reference to the accompanying drawings, in which

[0028] Figure 1 shows a heat integration in block diagram form; Figures 2A and 2B show a heat transfer device;

[0029] Figure 3 shows another heat transfer device; and

[0030] Figures 4A and 4B show details of another heat transfer device.

[0031] Embodiments

[0032] The embodiments described below are described 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 with regard to 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 as limitations on the scope of the invention as defined in the claims or as 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.

[0033] Different embodiments of the invention may include, have, consist of, or consist essentially of other useful combinations of the described elements, components, features, parts, steps, means, etc., even if such combinations are not specifically described herein.

[0034] Furthermore, the disclosure may cover other inventions which are not currently claimed but which may be claimed in the future, particularly if they are included within the scope of the independent claims.

[0035] 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. Identical, similarly acting, functionally corresponding, structurally identical, or comparably constructed elements, method steps, etc. may be identified by identical reference numerals. The following explanations and definitions relating to some of the principles of the invention may apply to all or part of the embodiments presented here, and the explanation of certain aspects in connection with only part or one of the embodiments should not be understood to mean that these aspects cannot also be implemented with other or all embodiments, as far as technically possible and reasonable.

[0036] All percentages used here may refer to molar, quantitative, or volume fractions. Pressures in bar are to be understood as absolute pressures, unless otherwise stated.

[0037] The conjunction "and / or," when used before the last term in a list, should be understood to mean that all terms mentioned above in the list can be combined in any way. In other words, "A, B, and / or C" means "A and / or B and / or C" or "at least one of the elements A, B, and C in any combination."

[0038] If reference is made here to a "portion" of a material stream, this can be a proportion with the same composition that has simply been diverted from an initial stream, but also a portion of a different composition and possibly only a component of the initial stream that is formed by a process such as condensation, evaporation, boiling, distillation, rectification, absorption, adsorption, flashing, membrane separation, deposition, or the like, or that remains as a residue in a corresponding step. A "portion" can also be present after a combination of any of the aforementioned steps, for example, after the diverted portion has been subjected to separation processing.

[0039] The following describes specific types of heat transfer equipment. For expert understanding, reference is expressly made to relevant literature, such as R.L. Shilling et al., "Heat-Transfer Equipment," Section 11 in D.W. Green (ed.), "Perry's Chemical Engineers' Handbook," 7th Edition 1997, McGraw-Hill. Of particular relevance is Section 11-33, "TEMA-Style Shell-and-Tube Heat Exchangers," and Figure 11-35, which illustrates different types of heat exchangers according to the "Standards of the Tubular Exchanger Manufacturers Association," 6th Edition 1978. Figure 1 illustrates heat integration in a process 100 for producing hydrogen 2 by converting ammonia 1 in a block diagram.In the process, a feed evaporation 110, a fuel evaporation 120, an ammonia cracking 130, a cracked gas heat recovery 140, a pressure swing adsorption 150 and a flue gas heat recovery 160 are carried out or used.

[0040] The ammonia is divided into partial streams 3 and 4 to the feed evaporator 110 and the fuel evaporator 120, where it is evaporated to yield an ammonia feed gas 5 and an ammonia fuel gas 6, respectively. The ammonia feed gas 5 is fed to the ammonia cracking reactor 130 to yield an ammonia cracking gas 7. The ammonia cracking gas 7 is subjected to cracking gas heat recovery 140 to yield a cooled ammonia cracking gas, now designated 8.

[0041] The cooled ammonia cracking gas 8 is subjected to pressure swing adsorption 150 to obtain essentially pure hydrogen 2 and a pressure swing adsorption residual gas 9, which may contain, in particular, hydrogen, unreacted ammonia, and nitrogen. The pressure swing adsorption residual gas 9 is combined with the ammonia fuel gas 6 to form a collective stream 10 and combusted to heat the ammonia cracking reactor 130. Combustion air 11 can be used for this purpose, which can be heated in the flue gas heat recovery 160 to obtain heated combustion air 13. Flue gas 12 formed during combustion is passed through the flue gas heat recovery 160 and cooled there to obtain cooled flue gas 14.

[0042] In the embodiments of the process 100 proposed here, as illustrated by a dotted arrow, heat W extracted from the ammonia cracking gas 7 in the cracking gas heat recovery 140 is used in the feed evaporator 110 to evaporate the partial stream 3. The use of the heat W is not limited to this, but can also be used for other purposes, such as the evaporation of portion 4 to provide the ammonia fuel gas 6, particularly taking into account the problems mentioned above. The hot ammonia cracking gas 7 leaving the ammonia cracking reactor 130 (temperature approximately 900 °C) is therefore used in the embodiments of the process 100 proposed here to evaporate portion 3, and thus to provide the ammonia feed 5. Evaporation of portion 4 to form the ammonia fuel gas 6 can also be carried out accordingly, so that separate apparatus for this purpose can be dispensed with.A combination of the feed and fuel evaporation 110, 120 in a common apparatus can also be provided according to embodiments.

[0043] The basic design features of the process gas cooler (PGC) in a steam reforming (SMR) plant can be considered. Aspects illustrated and explained below include a refractory-lined tube-side inlet area, optionally ferrules to protect the front tubesheet from hot ammonia cracking gas 7, and a central bypass tube for power regulation, control, and mixing of the streams in a tube-side outlet area. Since the tubes and tubesheets, as mentioned, are always in contact with boiling ammonia, which has a high heat transfer coefficient, it is possible to limit the operating temperatures of the metals, thus enabling cost-effective material selection and a reliable mechanical design.

[0044] In embodiments of the process 100 proposed here, as mentioned several times, the feed evaporation 110 and the cracked gas cooling 140 are carried out using a common heat transfer device 200. An example is shown in Figures 2A and 2B, where Figure 2A is an external longitudinal view and Figure 2B is a cross-sectional view.

[0045] The heat transfer device 200 comprises an evaporator vessel 210 and a tube bundle 220 arranged in the evaporator vessel 210 with a plurality of tubes 221, 222. Feed and withdrawal headers for ammonia cracked gas 7, 8 are designated 211 and 212, respectively. These serve, as known, for example, from the specialist literature cited above, to distribute gas to the tubes 221, 222 and to collect gas from the tubes 221, 222 of the tube bundle 220. The feed and withdrawal of the ammonia cracked gas 7, 8 is evident from the corresponding designation. Feed and withdrawal nozzles are not separately designated. The feed of ammonia 3 or a corresponding partial stream, as illustrated in Figure 1, in liquid form and the removal of the ammonia feed gas 5 are also indicated by the corresponding reference numerals. Again, the feed and removal nozzles are not shown for the sake of clarity.

[0046] From Figures 2A and 2B it follows that at least part of the feed evaporation 110 is carried out in the evaporator vessel 210 and at least part of the cracked gas cooling 140 is carried out in the tube bundle 220.

[0047] As can be seen from the cross-sectional view of Figure 2B, the space occupied by the tube bundle 220 in the evaporator vessel 210 has an elongated shape with a tube bundle longitudinal axis. The evaporator vessel 210 also has an elongated shape with an evaporator vessel longitudinal axis. The tube bundle longitudinal axis and the evaporator vessel longitudinal axis are arranged parallel to one another and spaced apart from one another, resulting in a larger space above the tube bundle 220 than below it. In the view of Figure 2B, these axes run perpendicular to the plane of the paper. This allows the ammonia s in the evaporator vessel 210 to accumulate up to an ammonia level 213, and foam up to a foam height of 214 can be permitted.

[0048] As can also be seen from Figure 2B, the tubes 221, 222 of the tube bundle 220 have a plurality of tubes 221 with a first tube cross-section and one or more tubes 222 with a second tube cross-section, wherein the second tube cross-section is larger than the first tube cross-section. In Figure 2B, only one of the tubes 221 is designated with the first tube cross-section. A flow through the one or more second tubes 222 can be adjusted to adjust the amount of heat to be transferred, since a heat exchange surface of the one or more tubes 222 with the second tube cross-section is smaller than a heat exchange surface of the tubes 221 with the first tube cross-section. This makes it possible to bypass the heat exchange in the tubes 221 with the first tube cross-section in a simple and effective manner. An alternative embodiment of a heat transfer device is shown in Figure 3 and is designated overall by 300.This may include components that are partially or completely identical to those of the heat transfer device 200 or that fulfill an identical, comparable, or similar function and are therefore designated accordingly. The heat transfer device 300 has a separator tank 310, which is connected to the evaporator tank 210 via downcomer lines 311 (fall lines for liquid) and via riser lines 312 (riser lines for gas or gas / liquid mixtures), whereby only one downcomer and riser line 311, 312 is designated in each case.

[0049] The ammonia 3 fed into the separator tank 310 forms a liquid level in the separator tank 310, the height of which can be adjusted accordingly. Liquid is discharged into the evaporator tank 210 via the downcomer lines 311, and gas rises from there via the riser lines 312 into the separator tank 310, from where it can be withdrawn in the form of the ammonia feed gas 5. In particular, the heat transfer device 300 can be operated such that ammonia evaporating in the evaporator tank 210 enters the separator tank 310 via the riser lines 312 below an ammonia level.

[0050] Due to the hot ammonia cracking gas 7, additional measures may be necessary to protect the heat transfer device 200 or 300. This is illustrated in Figures 4A and 4B in a cross-sectional and a longitudinal sectional view through an end section of a corresponding heat transfer device 200, 300, wherein the previously used reference numerals continue to apply. The cracking gas 7, or a portion thereof, is fed into the heat transfer device 200, 300 in the feed region 211 and distributed in the feed region 211 to the tubes 221, 222 of the tube bundle 220. The feed region is provided with a heat-resistant lining 231, and the tube sheet is protected from the direct influence of the hot ammonia cracking gas 7 by ferrules 232 (shown only in Figure 4B and as an example).

[0051] Although some features have been illustrated and explained above in specific combinations, any other combinations are possible provided they are technically reasonable and feasible. The invention is not limited to the embodiments described above.

Claims

Patent claims 1. A process (100) for producing hydrogen, comprising providing ammonia (3) in liquid form and subjecting it to a feed evaporation (110) to obtain an ammonia feed gas (5), subjecting the ammonia feed gas (5) or a portion thereof to an ammonia cracking (130) to obtain an ammonia cracking gas (7) containing hydrogen and nitrogen, and subjecting the ammonia cracking gas (7) to a cracking gas cooling (140) to obtain a cooled ammonia cracking gas (8), wherein heat extracted from the ammonia cracking gas (7) in the cracking gas cooling (140) is used at least in part in the feed evaporation (110), characterized in that the feed evaporation (110) and the cracking gas cooling (140) are carried out using a common heat transfer device (200, 300) having an evaporator vessel (210) and a the evaporator vessel (210) arranged tube bundle (220) with several tubes (221, 222).

2. The method (100) according to claim 1, which comprises providing further ammonia (4) in liquid form and subjecting it to a fuel gas evaporation (120) to obtain an ammonia fuel gas (6) which is used for heating in the ammonia cracking (130), wherein the feed evaporation (110) and the fuel gas evaporation (120) are carried out using the common heat transfer device (200, 300) or a separate heat transfer device.

3. Method (100) according to claim 1 or 2, wherein the cracked gas (7) or a part thereof is fed into the heat transfer device (200, 300) in a feed region (211) and is distributed in the feed region (211) to the tubes (221, 222) of the tube bundle (220), wherein the feed region is lined with a heat-resistant lining (231) and / or an inlet region into the tubes (221, 222) is each provided with heat-resistant ferrules (232).

4. The method (100) according to any one of claims 1 to 3, wherein a space occupied by the tube bundle (220) in the evaporator vessel (210) has an elongated shape with a tube bundle longitudinal axis, the Evaporator vessel (210) has an elongated shape with an evaporator vessel longitudinal axis, and the tube bundle longitudinal axis and the evaporator vessel longitudinal axis are arranged parallel to one another and spaced apart from one another.

5. The method (100) according to any one of claims 1 to 4, wherein the tubes (221, 222) of the tube bundle (220) comprise a plurality of tubes (221) having a first tube cross-section and one or more tubes (222) having a second tube cross-section, wherein the second tube cross-section is larger than the first tube cross-section.

6. The method (100) according to claim 5, wherein a flow through the one or more second tubes (222) is adjusted to adjust an amount of heat to be transferred.

7. The method according to any one of claims 1 to 6, wherein the heat transfer device (300) comprises a separator tank (310) which is connected to the evaporator tank (210) via downcomer lines (311) and riser lines (312).

8. Plant (100) for producing hydrogen, comprising a feed evaporator (110) configured to subject liquid ammonia (3) to feed evaporation to obtain an ammonia feed gas (5), an ammonia cracking reactor (130) configured to subject the ammonia feed gas (5) or a portion thereof to ammonia cracking to obtain an ammonia cracking gas (7) containing hydrogen and nitrogen, and a cracked gas heat recovery unit (140) with which the ammonia cracking gas (7) can be subjected to cracked gas cooling to obtain a cooled ammonia cracking gas (8), wherein heat extracted from the ammonia cracking gas (7) in the cracked gas heat recovery unit (140) can be used at least in part in the feed evaporator (110), characterized in that the feed evaporator (110) and the cracked gas heat recovery unit (140) are arranged in a common heat transfer device (200, 300),which has an evaporator tank (210) and a tube bundle (220) arranged in the evaporator tank (210) with a plurality of tubes (221, 222).

9. Plant (100) according to claim 8, which is arranged to carry out a method according to one of claims 1 to 7.

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