Method and plant for producing a synthesis gas for production of ammonia

Abstract

The invention relates to a method of providing a synthesis gas for production of ammonia, wherein desulfurized natural gas is converted with steam and oxygen-enriched air or with oxygen in a reforming step to form a synthesis gas comprising hydrogen, CO and CO2, wherein CO2 is separated from the synthesis gas in a separation step, wherein a hydrogen stream and a hydrogen-rich offgas stream are formed in a pressure swing adsorption (7), the pressure swing adsorption being operated in an adsorption cycle for providing the hydrogen stream and in a regeneration cycle for providing the hydrogen-rich offgas stream, wherein nitrogen is added to the synthesis gas in an enrichment step. In a method of producing a synthesis gas for production of ammonia in which the CO2 output can be reduced, the duration of the regeneration cycle of the pressure swing adsorption (7) is adjusted such that the hydrogen content of the offgas stream is adjusted, preferably increased, and the offgas stream is at least partly provided as fuel gas for a method step of the method.

Description

[0001] Process and plant for producing a synthesis gas for the production of ammonia

[0002] The invention relates to processes for providing a synthesis gas for producing ammonia, wherein desulfurized natural gas is converted with steam and oxygen-enriched air or with oxygen in a reforming step to a synthesis gas comprising hydrogen, CO and CO2, wherein CO2 is separated from the synthesis gas in a separation step, wherein a hydrogen stream and a hydrogen-rich exhaust gas stream are formed in a pressure swing adsorption, wherein the pressure swing adsorption is operated in an adsorption cycle to provide the hydrogen stream and a regeneration cycle to provide the hydrogen-rich exhaust gas stream, wherein nitrogen is added to the synthesis gas in an enrichment step.

[0003] In addition, the invention relates to a plant for producing a synthesis gas for producing ammonia, comprising at least: a reformer; a carbon monoxide (CO) converter; a carbon dioxide (CO2) scrubber unit with regeneration; a pressure swing adsorption unit for providing hydrogen and a hydrogen-rich exhaust gas stream, wherein the pressure swing adsorption unit is operable in an adsorption cycle for providing the hydrogen stream and a regeneration cycle for providing the hydrogen-rich exhaust gas stream.

[0004] Ammonia is one of the most important raw materials. Global annual production currently amounts to approximately 170 million tons. Most of this ammonia is used to produce fertilizers. Ammonia is now also used to transport hydrogen, as it has a higher volumetric energy density than liquid hydrogen. This allows ammonia to transport more energy for the same volume than liquid hydrogen. It is therefore foreseeable that ammonia will continue to gain in importance.

[0005] Ammonia is produced primarily from the elements hydrogen and nitrogen in the presence of an iron catalyst. Temperatures often range between 400 °C and 500 °C and at a pressure above 100 bar. The main factor in the process costs lies in the provision of hydrogen from synthesis gas production (Ullmann's, page 139). Ammonia is therefore preferably produced in accordance with the principle described, for example, in Holleman, Wiberg, Textbook of Inorganic Chemistry, 102nd edition, 2007, pages 662-665 (ISBN 978-3-11-017770-1), based on the "Haber-Bosch process" from the elements according to equation [1]:

[0006] 3 H2+ N22 NH3+ 92.28 kJ [1]

[0007] The reactant nitrogen (N2) can be obtained, for example, by low-temperature air separation. Hydrogen is preferably obtained via the steam reforming process (e.g., as described in Andreas Jess, Peter Wasserscheid, Chemical Technology, An Integrated Textbook, Wiley-VCH, 2013, pages 536 to 539, ISBN 978-3-527-30446-2) according to equation [2]:

[0008] C n H 2m + n H2O (n+m) H2+ n CO [2]

[0009] In the subsequent “carbon monoxide conversion” a further conversion takes place according to equation (3):

[0010] CO + H2O CO2 + H2[3]

[0011] Due to the exothermic nature of the ammonia formation reaction, relatively large amounts of heat are generated during the process. To ensure a good specific energy consumption of the overall process, this heat must be utilized as efficiently as possible. In general, waste heat utilization is associated with thermodynamically unavoidable losses. Therefore, there has been no shortage of attempts to develop alternatives to the Haber-Bosch process that operate without the high temperatures and pressures. In the Haber-Bosch process, the fundamental difficulty of activating the very inert nitrogen molecule is overcome by the use of specifically very active catalysts in combination with relatively high temperatures.

[0012] According to equation [3], a comparatively large amount of carbon dioxide is released, particularly during the production of hydrogen. Various approaches exist to reduce the carbon footprint of an ammonia plant, such as the aforementioned waste heat utilization, to avoid heat sources, particularly fuels whose combustion results in CO2-free combustion. However, since these lead to thermodynamic losses, the present invention is based on the object of providing an alternative process and a plant for producing a synthesis gas for ammonia production, in which CO2 emissions can be reduced.

[0013] This object is initially achieved by patent claim 1 in that a recovery rate is set during the operation of the pressure swing adsorption, wherein the recovery rate is formed from the ratio between the amount of hydrogen in the hydrogen stream from the pressure swing adsorption and the amount of hydrogen in the synthesis gas that is introduced into the pressure swing adsorption, wherein the recovery rate is influenced by the duration of the regeneration cycle and wherein the recovery rate is set such that the energy content of the hydrogen-rich exhaust gas stream is sufficient for the hydrogen-rich exhaust gas stream to be used as fuel gas in a burner, by means of which heat can be introduced into at least one process step of the method.The fuel gas can be used in various burners and / or furnaces that occur or are used to heat various streams or materials within the process. Combusting the hydrogen-rich exhaust gas stream from pressure swing adsorption significantly reduces CO2 emissions, since no CO2 is produced when hydrogen is burned. It is also conceivable to split the exhaust gas stream, for example, so that the hydrogen-rich exhaust gas stream can be used as fuel gas at different stages of the process.

[0014] It can be planned that the hydrogen content in the exhaust stream of the pressure swing adsorption process is deliberately increased, either relatively or absolutely, by extending the regeneration cycle. It is not absolutely necessary to change the dimensions of the pressure swing adsorption process. However, it is also conceivable that the dimensions of the pressure swing adsorption process are deliberately lower than those that would be selected for efficient hydrogen yield.

[0015] Pressure swing adsorption can replace additional process steps, such as LT shift conversion, methanation, and even a secondary reformer. Molecular sieves are used as adsorbents in a series of vessels operating in a staggered cyclic mode, alternating between an adsorption phase and various regeneration stages. Regeneration of the loaded adsorbent is achieved by gradually depressurizing the adsorbent and using the resulting gas to purge other adsorbers at a different pressure level in the regeneration cycle. Hydrogen recovery is typically around 90%, depending on the number of adsorbers in a line. Very high purity can be achieved, with approximately 50 ppm argon and less than 10 ppm of other impurities.

[0016] The recovery rate is defined by the amount of hydrogen in the product stream of pressure swing adsorption, i.e. the hydrogen stream, in relation to the amount of hydrogen in the inlet stream to pressure swing adsorption, i.e. the synthesis gas introduced into pressure swing adsorption.

[0017] The lower the recovery rate, the less product (hydrogen) is in the product stream. This increases the amount of hydrogen in the hydrogen-rich exhaust stream, allowing it to provide greater heat output.

[0018] The hydrogen-rich exhaust stream, at a high recovery rate, provides insufficient heat output to fuel a conventional front-end. Conventionally, this is compensated for by blending with natural gas. Combusting natural gas in the fuel gas mixture with the hydrogen-rich exhaust stream generates additional CO2 emissions. To reduce these emissions, the natural gas is replaced with hydrogen by reducing the recovery rate compared to the conventional process.

[0019] The PSA recovery rate is reduced by extending the regeneration cycle, i.e., extending the backflushing time. This not only increases the amount of hydrogen in the hydrogen-rich exhaust stream, but also the purity of the hydrogen. By burning the hydrogen-rich exhaust stream in the fired burner or furnace, reactants are preheated and the missing power for steam generation is replaced. The term furnace is used synonymously with burner in the application. The steam generated in this way has a variety of uses within the plant. A large portion is used to drive the compressors. If these compressors are powered by electricity, the plant's steam requirement can be reduced, thus maintaining a higher recovery rate. The question at this point is the CO2 assessment of the electricity: Is this considered CO2-neutral (e.g.,Electricity from wind power) or does a CO2 equivalent also have to be taken into account here (electricity generated from fossil fuels).

[0020] If all compressor (and pump) drives are steam-powered, the lowest practical recovery rate is achieved. This lies in a range of approximately 70% to 80%, preferably around 75%. Pressure swing adsorption works effectively when the pressure difference between the feed, i.e. the synthesis gas, and the hydrogen-rich exhaust stream is large. In the product flow direction downstream of the pressure swing adsorption, a synthesis gas compressor is arranged in the conventional system. High pressure also saves energy for this. Therefore, pressure swing adsorption should be operated at the highest pressure available in the process. The high pressure of pressure swing adsorption results from the process. The low pressure must be somewhat higher than that required for "standard pressure swing adsorption", i.e. pressure swing adsorption with an optimal recovery rate, without taking into account the CO2 emissions in the process, which is compensated for accordingly by a higher pressure.

[0021] In a first embodiment of the process according to the invention, a recovery rate is set in the range between 70% and 85%, preferably between 76% and 82%, particularly preferably between 79.0% and 80.5%. With a recovery rate in this range, the energy content of the hydrogen-rich exhaust gas stream is sufficient to fuel the front end of an ammonia plant without the need for additional admixture of natural gas.

[0022] In a further preferred embodiment of the process according to the invention, the amount of gas in the synthesis gas stream obtained in the reforming step is varied as a function of the recovery rate, in particular the amount of gas in the synthesis gas stream obtained in the reforming step is increased when the recovery rate is reduced. Such a change is preferably achieved by changing the capacity or dimensions of the front end. If the front end is enlarged, the same amount of product can be obtained that a plant with an optimal recovery rate for the process can achieve without regard to CO2 emissions. Otherwise, the amount of hydrogen product is reduced. To compensate for this loss, the front end (the part of the plant that supplies the hydrogen) must be enlarged. This leads to additional equipment costs.However, this investment can reduce the CO2 emissions of the entire plant.

[0023] In a further advantageous embodiment of the method according to the invention, a stack temperature and / or a temperature of the heated media is measured, and the recovery rate is adjusted if the temperature exceeds or falls below a predetermined temperature. The measured values ​​are then used to determine whether there is a lack of or excess H2 in the hydrogen-rich exhaust gas stream. This can then lead to an adjustment of the regeneration cycle. Ideally, the regeneration cycle is set at the beginning of the operating period and remains constant during (somewhat) steady-state operation.

[0024] In a further embodiment of the invention, a reformer comprising a steam reformer with or without a secondary reformer and / or an autothermal reformer is used in the reforming step, and the hydrogen-rich exhaust gas stream is used at least partially as fuel gas to provide the heat for the reforming step. The reformer or the reactants of the reformer can be heated by combustion of the hydrogen-rich exhaust gas stream. In this way, the CO2 emission, which is typically caused during reforming by external heat supply via natural gas firing, can be significantly reduced.

[0025] In a further embodiment of the process according to the invention, hydrogen from an external source is admixed to the hydrogen-rich exhaust gas stream from the pressure swing adsorption. An external source can mean hydrogen that is not already in the process directly as a result of the aforementioned process, for example, hydrogen produced by electrolysis. However, the additional hydrogen can also be used from a hydrogen-rich stream that is already in the process as a result of reforming. In this way, the dimensioning of the pressure swing adsorption can be adapted to the existing conditions, so that the fuel gas consists entirely of exhaust gases from the pressure swing adsorption and admixed hydrogen-rich streams.

[0026] Alternatively, in a further embodiment of the process according to the invention, the mixed stream can be set at a ratio of 1 to 0.2 of the exhaust gas stream from the pressure swing adsorption and the hydrogen from the external source. If the combustion power of the exhaust gas stream from the pressure swing adsorption is insufficient to realize firing in a subsequent stage of the process, just enough external hydrogen is added to enable complete combustion of the hydrogen in the hydrogen-rich exhaust gas stream.

[0027] The above-mentioned object is also achieved by a plant for producing a synthesis gas for producing ammonia, comprising at least: a reformer; a carbon monoxide (CO) converter; a carbon dioxide (CO2) scrubber unit with regeneration; a pressure swing adsorption for providing hydrogen and a hydrogen-rich exhaust gas stream, wherein the pressure swing adsorption is carried out in a

[0028] Adsorption cycle, to provide the hydrogen stream, and a

[0029] Regeneration cycle, for providing the hydrogen-rich exhaust gas stream, is operable. At least one line is provided through which the hydrogen-rich exhaust gas stream from the pressure swing adsorption can be conducted into a section of the plant as fuel gas for a burner or furnace. Furthermore, it is provided that a recovery rate can be adjusted during operation of the pressure swing adsorption, wherein the recovery rate is formed from the ratio between the amount of hydrogen in the hydrogen stream from the pressure swing adsorption and the amount of hydrogen in the synthesis gas that is introduced into the pressure swing adsorption, wherein the recovery rate can be influenced by the duration of the regeneration cycle and wherein the recovery rate can be adjusted such that the energy content of the hydrogen-rich exhaust gas stream can be adjusted, preferably increased.

[0030] A description of the functioning of a reformer can be found in Ullmann's, Chapter 6.1.1, pages 174 to 179. Furthermore, the system according to the invention comprises a carbon monoxide (CO) converter. A description of the functioning and structure of possible carbon monoxide (CO) converters ("Carbon Monoxide Shift Conversion") can be found in Ullmann's, Chapter 6.1.2, pages 179 to 182. The carbon monoxide (CO) converter is followed by a carbon dioxide (CO2) scrubber unit with regeneration. The term "unit" in the sense of the invention encompasses devices and apparatus known to the person skilled in the art for the stated purpose, in this case typically / for example an absorber, a desorber, one or more circulation pumps, and heat exchangers for heating / cooling the solvent.A carbon dioxide (CO2) scrubber unit with regeneration can, for example, be designed as a known device / arrangement in which carbon dioxide is dissolved in a suitable solvent—for example, potassium carbonate or amines—under pressure in an absorber and then flashed separately from the remaining synthesis gas (the synthesis gas depleted of carbon dioxide or freed of carbon dioxide in the carbon dioxide (CO2) scrubber unit with regeneration). The solvent can then be reheated and regenerated in a stripping column (desorber). A detailed description can be found, for example, in Ullmann's, Chapter 6.1.3, pages 182 to 184.

[0031] In a first embodiment of the system according to the invention, a recovery rate is set in the range between 75% and 85%, preferably between 78% and 82%, particularly preferably between 79.5% and 80.5%. With a recovery rate in this range, the energy content of the hydrogen-rich exhaust gas stream is sufficient to fuel the front end of an ammonia plant without the need for additional admixture of natural gas.

[0032] In a further embodiment of the plant according to the invention, the reformer comprises a steam reformer with or without a secondary reformer and / or an autothermal reformer. Particularly with a high daily ammonia production, the reformer can also consist of only one or more autothermal reformers.

[0033] In a further advantageous embodiment of the plant according to the invention, the reformer is dimensioned larger than is necessary for producing a given production quantity of ammonia at a recovery rate in the range of 85% to 95%, preferably approximately 10% larger. If the front end, i.e. the reformer, is enlarged, the same amount of product can be obtained that a plant with an optimal recovery rate for the process can achieve without considering CCh emissions. Otherwise, the product quantity of hydrogen is reduced. To compensate for this loss, the front end (the part of the plant that supplies the hydrogen) must be enlarged. This leads to additional equipment costs. However, this investment can reduce the CCh emissions of the entire plant.

[0034] In a further preferred embodiment of the invention, a temperature measuring device is provided for measuring a stack temperature and / or a temperature of the heated media. From the measured values, conclusions can then be drawn about missing or oversized H2 in the hydrogen-rich exhaust gas stream. This can then lead to an adjustment of the regeneration cycle. Ideally, the regeneration cycle is set at the beginning of the operating period and remains constant during (somewhat) steady-state operation.

[0035] In a further advantageous embodiment of the plant according to the invention, it is provided that an external hydrogen source is included and that a line is provided. External hydrogen from the external hydrogen source can be hydrogen that is not already in the process directly as a result of the aforementioned process, for example hydrogen produced by electrolysis. However, the additional hydrogen can also consist of a hydrogen-rich stream that is already in the process as a result of reforming. In this way, the dimensioning of the pressure swing adsorption can be adapted to the existing conditions, so that the exhaust gas stream can be used entirely as fuel gas without the pressure swing adsorption having to be adapted in its dimensions.

[0036] Furthermore, in a further embodiment of the plant according to the invention, a mixing device can be provided by which a molar ratio of 1 to 0.2 of the exhaust gas flow of the pressure swing adsorption and the hydrogen from the external source can be set.

[0037] Furthermore, a further embodiment provides that the system can be used to carry out a method according to the invention. The above statements regarding the method according to the invention also apply accordingly to the system according to the invention.

[0038] In detail, there are numerous possibilities for designing and developing the method and system according to the invention. Reference is made to the claims subordinate to claims 1 and 10, as well as to the following description of preferred embodiments in conjunction with the drawings. The drawings show:

[0039] Fig. 1 is a schematic representation of a process or a plant for producing synthesis gas for ammonia synthesis,

[0040] Fig. 2 shows a further schematic representation of a process or a plant for producing synthesis gas with an additional external hydrogen source and

[0041] Fig. 3 shows a comparison of CO2 emissions between a conventional ammonia plant and a plant according to the invention.

[0042] Figure 1 shows a schematic flow diagram of a plant 1 for producing hydrogen-containing synthesis gas. Hydrogen is provided by a reformer 2, preferably a primary and a secondary reformer and / or an autothermal reformer. The heat required for the reformer 2 is supplied by reformer burners. The plant also includes a carbon monoxide (CO) converter 3. In this converter, the carbon monoxide (CO) formed and not required for the actual ammonia synthesis is converted into carbon dioxide, producing further hydrogen. This is followed by a carbon dioxide (CO2) scrubber unit 4 with regeneration. The carbon dioxide (CO2) scrubber unit 4 can, for example, be designed as a known device or arrangement in which carbon dioxide is dissolved in a suitable solvent—for example, potassium carbonate or amines—under pressure in an absorber and then expanded (“flashed”) separately from the synthesis gas.The solvent can then be reheated and regenerated in a stripping column (desorber). The synthesis gas is then converted to ammonia in an ammonia synthesis unit 6.

[0043] Furthermore, a pressure swing adsorption system 7 is provided, which provides a hydrogen stream and a hydrogen-rich exhaust stream. Conduit 8 is advantageously provided, through which the hydrogen-rich exhaust stream from pressure swing adsorption 7 can be conducted as fuel gas into a section of plant 1. It is intended that the hydrogen-rich exhaust stream be used as fuel gas for reformer 2. Reformer 2 can be heated by combustion of the hydrogen-rich exhaust stream. In this way, the CCh release, which is typically caused during reforming, can be significantly reduced. Furthermore, it is not necessary to use natural gas as an additional heating medium.

[0044] Figure 2 shows a system according to Figure 1, wherein an external hydrogen source 9 is additionally provided in this exemplary embodiment. The hydrogen from the external hydrogen source 9 is admixed with the hydrogen-rich exhaust gas stream of the pressure swing adsorption 7. In this exemplary embodiment, the external hydrogen source 9 is hydrogen produced by electrolysis. In this way, the dimensioning of the pressure swing adsorption 7 can be adapted to the existing conditions, so that the exhaust gas stream can be fully utilized as fuel gas without the pressure swing adsorption having to be dimensioned larger.

[0045] For this purpose, a further line 10 is provided through which, via a mixing device 11, a mixed flow can be set in which the exhaust gas flow from the pressure swing adsorption 7 and the hydrogen from the external source have a ratio of 1 to 0.2. If the combustion power of the exhaust gas flow from the pressure swing adsorption 7 is not sufficient to fire a further section of the process, just enough external hydrogen is added to enable complete combustion of the hydrogen in the hydrogen-rich exhaust gas flow. The upper section of Figure 3 shows a plant for producing ammonia. A front end 12 is provided for producing synthesis gas. The synthesis gas is then fed into a pressure swing adsorption 7 and then into an ammonia synthesis unit 6. A balance chamber 13 is arranged around the schematic representation.Heat is required to operate the plant, for example, to produce steam as a heating medium and to generate sufficient reaction heat. This heat is obtained, among other things, through the use of fuels, the combustion of which often also leads to CCH emissions.

[0046] The upper part of Figure 3 shows a conventional plant for producing ammonia. Natural gas 14 is fed to the front-end 12 and converted to produce a synthesis gas. The synthesis gas is passed into the pressure swing adsorption unit 7, producing a hydrogen stream 15 that is used for the synthesis of ammonia in the ammonia synthesis unit 6. In addition, a hydrogen-rich exhaust gas stream 16 is obtained, which is suitable for use as fuel gas in the front-end 12. Since the energy content of the hydrogen-rich exhaust gas stream 16 is not sufficient to operate the front-end or to supply it with sufficient heat, additional natural gas is burned. The combustion of natural gas produces CO2, which is released into the environment via the balance space. Figure 3 only shows the portion of the CO2 that is actually released into the environment via the balance boundary. Overall, more CO2 is produced than is emitted.The CO2 separated or washed out in the CCH scrubbing process can be compressed. It is then not part of the emissions.

[0047] The lower part of Figure 3 shows a plant with an inventive concept for providing synthesis gas. Pressure swing adsorption 7 is deliberately operated at a lower recovery rate than in a conventional plant for producing ammonia. This increases the energy content of the hydrogen-rich exhaust gas stream 16, as more hydrogen is contained in the hydrogen-rich exhaust gas stream 16. In this exemplary embodiment, the energy content is sufficient to operate the front end 12 or to supply the front end 12 with heat. It is not necessary to additionally burn natural gas. This way, since primarily hydrogen is burned, CO2 emissions are significantly reduced.

[0048] To compensate for the lower recovery rate of pressure swing adsorption 7, the front end in this embodiment is approximately 10% larger. This allows the same amount of product, i.e., ammonia, to be obtained as in the conventional system, while simultaneously significantly reducing CO2 emissions.

[0049] 1. Appendix

[0050] 2. Reformers

[0051] 3. Carbon monoxide (CO) converter

[0052] 4. Carbon dioxide (CO2) scrubber unit

[0053] 6. Ammonia synthesis unit

[0054] 7. Pressure swing adsorption

[0055] 8. Management

[0056] 9. External hydrogen source

[0057] 10. Further management

[0058] 11. Mixing device

[0059] 12. Front End

[0060] 13. Balance sheet area

[0061] 14. Natural gas

[0062] 15. Hydrogen stream

[0063] 16. Hydrogen-rich exhaust stream

Claims

Patent claims 1. A process for providing a synthesis gas for producing ammonia, wherein desulfurized natural gas is converted with steam and oxygen-enriched air or with oxygen in a reforming step to a synthesis gas comprising hydrogen, CO, and CO2, wherein CO2 is separated from the synthesis gas in a separation step, wherein a hydrogen stream and a hydrogen-rich exhaust gas stream are formed in a pressure swing adsorption (7), wherein the pressure swing adsorption is operated in an adsorption cycle to provide the hydrogen stream and a regeneration cycle to provide the hydrogen-rich exhaust gas stream, wherein nitrogen is added to the synthesis gas in an enrichment step, characterized in that a recovery rate is set during the operation of the pressure swing adsorption (7),wherein the recovery rate is formed from the ratio between the amount of hydrogen in the hydrogen stream from the pressure swing adsorption (7) and the amount of hydrogen in the synthesis gas introduced into the pressure swing adsorption (7), wherein the recovery rate is influenced by the duration of the regeneration cycle and wherein the recovery rate is adjusted such that the energy content of the hydrogen-rich exhaust gas stream is sufficient for the hydrogen-rich exhaust gas stream to be used as fuel gas in a burner by means of which heat can be introduced into a process step of the method.

2. The method according to claim 1, characterized in that a recovery rate is set in the range between 75% and 85%, preferably between 78% and 82%, particularly preferably between 79.5% and 80.5%.

3. A process according to claim 1 or 2, characterized in that the amount of gas in the synthesis gas stream obtained in the reforming step is varied as a function of the recovery rate, in particular that the amount of gas in the synthesis gas stream obtained in the reforming step is increased when the recovery rate is reduced.

4. Method according to one of claims 1 to 3, characterized in that a chimney temperature and / or a temperature of the heated media is measured and that the recovery rate is adjusted when the temperature exceeds or falls below a specified temperature.

5. Process according to one of claims 1 to 4, characterized in that in the reforming step a reformer (2) comprising a steam reformer with or without a secondary reformer and / or an autothermal reformer is used and that the hydrogen-rich exhaust gas stream is used at least partially as fuel gas for the reforming step.

6. Method according to one of claims 1 to 5, characterized in that hydrogen from an external hydrogen source (9) is added to the hydrogen-rich exhaust gas stream of the pressure swing adsorption (7).

7. The method according to claim 3, characterized in that the mixed stream is set in a ratio of 1 to 0.2 of the exhaust gas stream of the pressure swing adsorption (7) and the hydrogen from the external hydrogen source (9).

8. The method according to any one of claims 1 to 4, characterized in that the hydrogen-rich exhaust gas stream of the pressure swing adsorption (7) is provided entirely as fuel gas for a process step of the method.

9. Plant (1) for producing a synthesis gas for the production of ammonia, comprising at least: a.) a reformer (2); b.) a carbon monoxide (CO) converter (3); c.) a carbon dioxide (CO2) scrubber unit (4) with regeneration; d.) a pressure swing adsorption (7) for providing hydrogen and a hydrogen-rich exhaust gas stream, wherein the pressure swing adsorption can be operated in an adsorption cycle for providing the hydrogen stream and a regeneration cycle for providing the hydrogen-rich exhaust gas stream, wherein at least one line (8) is provided through which the hydrogen-rich exhaust gas stream of the pressure swing adsorption (7) can be conducted as fuel gas for a burner into a section of the plant, characterized in that a recovery rate can be set during operation of the pressure swing adsorption, wherein the recovery rate is determined from the ratio between the amount of hydrogen in the hydrogen stream from the pressure swing adsorption (7) and the amount. of hydrogen in the synthesis gas which is introduced into the pressure swing adsorption (7), wherein the recovery rate can be influenced by the duration of the regeneration cycle and wherein the recovery rate can be adjusted such that the energy content of the hydrogen-rich exhaust gas stream can be adjusted, preferably increased.

10. Plant according to claim 9, characterized in that a recovery rate is set in the range between 75% and 85%, preferably between 78% and 82%, particularly preferably between 79.5% and 80.5%.

11. Plant (1) according to claim 9 or 10, characterized in that the reformer (2) comprises a steam reformer with or without a secondary reformer and / or an autothermal reformer.

12. Plant according to claim 11, characterized in that the reformer is dimensioned larger than is necessary for a recovery rate in the range of 85% to 95% in order to produce a given production quantity of ammonia, preferably dimensioned about 10% larger.

13. System according to one of claims 9 to 12, characterized in that a temperature measuring device is provided for measuring a chimney temperature and / or a temperature of the heated media.

14. Plant (1) according to one of claims 9 to 13, characterized in that an external hydrogen source (9) is included and that a further line (10) is provided through which external hydrogen of the external hydrogen source (9) can be mixed with the exhaust gas stream of the pressure swing adsorption (7).

15. Plant according to claim 14, characterized in that a mixing device (11) is provided by which a ratio of 1 to 0.2 of the exhaust gas flow of the pressure swing adsorption (7) and the hydrogen from the external hydrogen source (9) can be set.

16. Plant (1) according to one of claims 9 to 15, characterized in that a method according to one of claims 1 to 6 can be carried out by the plant (1).

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