LU103255B1 - Process and plant for producing a synthesis gas for the production of ammonia - Google Patents

Abstract

The invention relates to a method 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 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 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. In a method for producing a synthesis gas for producing ammonia, in which CO2 emissions can be reduced, it is provided that the regeneration cycle of the pressure swing adsorption (7) is adjusted in terms of its duration such that the hydrogen content of the exhaust gas stream is adjusted, preferably increased, and the exhaust gas stream is at least partially provided as fuel gas for a process step of the method.

Description

221671P00LU

Process and plant for producing a synthesis gas for the production 1041053255 of ammonia

The invention relates to methods for providing a synthesis gas for the production of

Ammonia, wherein desulfurized natural gas is reformed with steam and oxygen-enriched air or with oxygen in a reforming step to form a synthesis gas comprising hydrogen,

CO and CO, whereby CO, from the synthesis gas in a

separation step, whereby in a pressure swing adsorption a

Hydrogen stream and a hydrogen-rich exhaust stream are formed, whereby the

Pressure swing adsorption in an adsorption cycle to provide the

hydrogen stream, and a regeneration cycle to provide the hydrogen-rich exhaust gas stream, with nitrogen being added to the synthesis gas in a

enrichment step is added.

In addition, the invention relates to a plant for producing a synthesis gas for

Production of ammonia, comprising at least: a reformer; a carbon monoxide (CO) converter; a carbon dioxide (CO) scrubber unit with regeneration; a

Pressure swing adsorption to provide hydrogen and a hydrogen-rich

Exhaust gas stream, whereby the pressure swing adsorption in an adsorption cycle, for

Provision of the hydrogen stream, and a regeneration cycle to provide the hydrogen-rich exhaust gas stream.

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. However, ammonia is now also used to transport hydrogen, as it has a higher volumetric energy density than liquid hydrogen.

This means that more energy can be transported via ammonia in the same volume than in the form of liquid hydrogen. It is therefore foreseeable that ammonia will continue to

will gain importance.

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 pressures exceeding 100 bar.

The factor for the process costs lies in the provision of hydrogen from the synthesis gas production (Ullmann’s, page 139). 1

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Accordingly, ammonia production is preferably carried out in principle as described in LU103255, 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 method” from the elements according to equation [1]: 3 Hz + N; = 2 NH; + 92.28 kJ [1]

The reactant nitrogen (Na) can be obtained, for example, by low-temperature air separation. Hydrogen is preferably produced via the steam reforming process (e.g. as 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]:

CnHom + N'H,0 = (n+m) H, + n CO [2]

In the subsequent “carbon monoxide conversion” a further conversion takes place according to

Equation (3):

CO + H;O = CO; + H, [3]

Due to the exothermic nature of the ammonia formation reaction,

Relatively large amounts of heat are required during the process. For a good specific

Energy consumption of the entire process must be used as efficiently as possible.

In general, the use of waste heat is associated with thermodynamically unavoidable losses. Therefore, there has been no lack of attempts to develop alternatives to the Haber-Bosch

To develop processes that work 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.

According to equation [3], a comparatively large amount of carbon dioxide is released, particularly during the production of hydrogen.

ammonia plant, there are various approaches, such as the aforementioned waste heat recovery to reduce heating sources, especially fuels, where

To avoid CO emissions during combustion. 2

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However, since these lead to thermodynamic losses, the present invention is based on the LU103255

The task is to develop an alternative process and a plant for the production of a

synthesis gas for the production of ammonia, where CO emissions can be reduced.

This object is firstly achieved by patent claim 1 in that during the operation of the pressure swing adsorption a recovery rate is set, wherein the

Recovery rate from the ratio between the amount of hydrogen in the

Hydrogen flow from pressure swing adsorption and the amount of hydrogen in the

Synthesis gas is introduced into the pressure swing adsorption, whereby the

The recovery rate is influenced by the duration of the regeneration cycle and 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, through which heat is transferred to at least one process step of the

The fuel gas can be used in various burners and/or furnaces, which are used to heat various

Flows or substances occur or are used within the process.

By combusting the hydrogen-rich exhaust stream from pressure swing adsorption, CO emissions are significantly reduced, since no CO is produced when hydrogen is burned. It is also conceivable to split the exhaust stream, for example, so that the hydrogen-rich exhaust stream can be used as fuel gas at various stages of the process.

It can be provided that the hydrogen content in the exhaust gas stream of the

Pressure swing adsorption is deliberately increased, relatively or absolutely, by

Extension of the regeneration cycle. It is not absolutely necessary to

Pressure swing adsorption to change its dimensions. However, it is also conceivable that the

The dimension of pressure swing adsorption is intentionally smaller than would be chosen for efficient hydrogen yield.

Pressure swing adsorption can include further process steps, such as LT

Shift conversion, one that replaces methanation and even a secondary reformer.

Molecular sieves are used as adsorbents in a series of containers operated in a staggered cyclic mode and switched between a

Adsorption phase and various regeneration stages. The regeneration of the loaded adsorbent is achieved by gradual pressure relief and by the

Use of the resulting gas to flush other adsorbers on another 3

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pressure level in the regeneration cycle. The hydrogen recovery in LU103255

Normally about 90%, depending on the number of adsorbers in a line. Very high purity can be achieved, with about 50 ppm argon and less than 10 ppm at other

Contamination.

The recovery rate is defined by the amount of hydrogen in the

Product flow of pressure swing adsorption, i.e. the hydrogen flow, in relation to the

Amount of hydrogen in the inlet stream into the pressure swing adsorption, that is, the

Synthesis gas fed into the pressure swing adsorption.

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 gas flow, which allows it to provide greater heat output.

The hydrogen-rich exhaust stream, at a high recovery rate, delivers too little

Heat output to fire a conventional front end. Conventionally, this is compensated by the addition of natural gas. The burning of natural gas in the

Combustion gas mixture with the hydrogen-rich exhaust stream provides further CO,-

Emissions. To reduce these, natural gas is replaced by hydrogen by

Recovery rate is reduced compared to the conventional process.

The PSA recovery rate is reduced by extending the regeneration cycle, i.e., extending the backwash time. This not only increases the

amount of hydrogen in the hydrogen-rich exhaust stream, but also the purity of

Hydrogen. By burning the hydrogen-rich exhaust gas stream in the fired burner or furnace, reactants are preheated and missing power for the

Steam generation is replaced. The term oven is used in the application as a synonym for

burner. The steam generated in this way is used in a variety of ways in the plant.

The majority is used to drive the compressors. If these compressors are

Powered by electricity, the steam requirement of the plant can be reduced and thus the

The question at this point is the CO,-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).

If all compressor (and pump) drives are steam-powered, the lowest practical recovery rate is achieved. This ranges from approximately 70% to 80%, preferably around 75%. 4

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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, a synthesis gas compressor is located downstream of the pressure swing adsorption. High pressure also saves energy for this. Therefore, the

Pressure swing adsorption can be operated at the highest pressure the process can provide.

The high pressure of pressure swing adsorption results from the process. The low pressure must be somewhat higher than in a “standard pressure swing adsorption”, i.e.

Pressure swing adsorption with optimal recovery rate, without taking into account the CO,-

Emissions in the process, which are compensated accordingly by higher pressure.

In a first embodiment of the method according to the invention, it is provided that 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 stream is sufficient to fuel the front-end of an ammonia plant without the need for additional natural gas blending.

In a further preferred embodiment of the process according to the invention, it is provided that the amount of gas in the synthesis gas stream obtained in the reforming step is changed 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. Such a change is preferably achieved by changing the capacity or the dimensions of the front

Ends can be changed. 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 considering CO; emissions. Otherwise, the amount of product at

hydrogen is reduced. To compensate for this loss, the front end (the part of the

plant that supplies the hydrogen). This will lead to additional

Equipment costs. However, this investment can reduce the CO2 emissions of the entire plant.

In a further advantageous embodiment of the method according to the invention, it is provided that a chimney temperature and/or a temperature of the heated media is measured and that an adjustment of the recovery rate takes place when the

Temperature exceeds or falls below a specified temperature. From the 5

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Measured variables are then checked for missing or oversized H, in the hydrogen-rich LU103255

Exhaust gas flow is inferred. 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.

In a further embodiment of the invention it is provided that in the

Reforming step a reformer comprising a steam reformer with or without

secondary reformer and/or an autothermal reformer are used and that the hydrogen-rich exhaust gas stream is used at least partly as fuel gas for the provision of the

Heat is used for the reforming step. The reformer or the reactants of the

Reformers can be heated by combusting the hydrogen-rich exhaust stream. This significantly reduces the CO emissions typically generated during reforming by external heat input from natural gas combustion.

In a further embodiment of the method according to the invention, it is provided that

Hydrogen from an external source to the hydrogen-rich exhaust stream of the

Pressure swing adsorption is added. An external source can provide

This refers to hydrogen that is not directly present in the process 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 present in the process as a result of reforming. In this way, the

The dimensioning of the pressure swing adsorption must 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.

Alternatively, in a further embodiment of the method according to the invention, it can be provided that the mixed flow is fed into the exhaust gas stream in a ratio of 1 to 0.2 of the

pressure swing adsorption and the hydrogen from the external source. If the combustion power of the exhaust stream of the pressure swing adsorption is not sufficient to

To realize firing in a further stage of the process, just enough external hydrogen is added to enable complete combustion of the hydrogen in the hydrogen-rich exhaust gas stream.

The above-mentioned object is also achieved by a plant for producing a

Synthesis gas for the production of ammonia, comprising at least: a reformer; a carbon monoxide (CO) converter; a carbon dioxide (CO) scrubber unit with 6

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Regeneration; a pressure swing adsorption for providing hydrogen and a LU103255 hydrogen-rich exhaust gas stream, wherein the pressure swing adsorption is carried out in a

Adsorption cycle, to provide the hydrogen stream, and a

Regeneration cycle to provide the hydrogen-rich exhaust gas stream.

At least one line is provided through which the hydrogen-rich exhaust gas stream of the

Pressure swing adsorption as fuel gas for a burner or furnace in a

section of the plant. Furthermore, it is planned that during operation of the

Pressure swing adsorption has an adjustable recovery rate, whereby the

Recovery rate from the ratio between the amount of hydrogen in the

Hydrogen flow from pressure swing adsorption and the amount of hydrogen in the

Synthesis gas, which is introduced into the pressure swing adsorption, is formed, whereby the

The recovery rate can be influenced by the duration of the regeneration cycle, and the recovery rate can be adjusted such that the energy content of the hydrogen-rich exhaust gas stream can be adjusted, preferably increased.

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 function and design 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 includes units known to the person skilled in the art for the stated purpose.

Devices and apparatus, in this case typically/for example an absorber, a desorber, one or more circulation pumps and heat exchangers for

Heating/cooling of the solvent. A carbon dioxide (CO,) scrubber unit with

Regeneration can, for example, be carried out as a known device/arrangement in which carbon dioxide is dissolved in an absorber under pressure in a suitable solvent - for example potassium carbonate or amines - and then separated from the remaining synthesis gas (which is in the carbon dioxide (CO,) scrubber unit with regeneration on

The solvent can then be reheated and regenerated in a stripping column (desorber). A detailed description can be found, for example, at

Ullmann’s, Chapter 6.1.3, pages 182 to 184.

In a first embodiment of the system according to the invention, it is provided 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%. At 7

221671P00LU a recovery rate in this range, the energy content of the hydrogen-rich LU103255

exhaust gas flow to fire the front end of an ammonia plant without

Adding natural gas would also be necessary.

In a further embodiment of the system according to the invention, it is provided that the

Reformer a steam reformer with or without secondary reformer and/or an autothermal

Reformer. Especially with a high daily ammonia production, the

Reformers can also consist of one or more autothermal reformers.

In a further advantageous embodiment of the plant according to the invention, it is provided 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 about 10% larger. If the front end, i.e. the

If 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 CO2 emissions. Otherwise, the amount of hydrogen produced is reduced. To compensate for this loss, the front end (the part of the plant that supplies the hydrogen) must be enlarged. This results in additional equipment costs. However, this investment can reduce the CO2 emissions of the entire plant.

In a further preferred embodiment of the invention it is provided that a

A temperature measuring device is provided for measuring the stack temperature and/or the temperature of the heated media. From the measured values, it can then be concluded that there is a lack of or excessive H in the hydrogen-rich exhaust gas stream. This can then lead to an adjustment of the regeneration cycle. In the optimal case, the

Regeneration cycle is set at the beginning of the operating time and remains constant during (somewhat) stationary operation.

In a further advantageous embodiment of the system according to the invention, it is provided that an external hydrogen source is included and that a line is provided, the external hydrogen of the external hydrogen source can be provided

Hydrogen that is not directly produced by the aforementioned process in the

process, for example hydrogen produced by electrolysis. The additional

Hydrogen can also be obtained from a hydrogen-rich stream that is already in the process through reforming. In this way, the dimensioning of the

Pressure swing adsorption can be adapted to the existing conditions so that the 8

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Exhaust gas stream can be used entirely as fuel gas without the LU103255

Pressure swing adsorption must be adapted in its dimensions.

Furthermore, in a further embodiment of the system according to the invention, a

A mixing device must be provided to achieve 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.

Furthermore, a further embodiment provides that the system can be used to implement 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.

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:

Fig. 1 is a schematic representation of a method or a

Plant for the production of synthesis gas for ammonia synthesis,

Fig. 2 shows a further schematic representation of a process or a plant for the production of synthesis gas with an additional external

Hydrogen source and

Fig. 3 shows a comparison of CO2 emissions between a conventional

Ammonia plant and a plant according to the invention.

Figure 1 shows a schematic flow diagram of a plant 1 for the production of hydrogen-containing synthesis gas. A reformer 2, preferably a primary and a secondary reformer and/or an autothermal reformer, serves to provide hydrogen. The heat required for the reformer 2 is supplied via reformer burners. The plant also includes a carbon monoxide (CO) converter 3. In this converter, the carbon monoxide (CO) formed and not required in the actual ammonia synthesis is further

Hydrogen formation is converted into carbon dioxide. 9

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This is followed by a carbon dioxide (CO2) scrubber unit 4 with regeneration. The LU103255

Carbon dioxide (CO2) scrubber unit 4 can be designed, for example, as a known device or arrangement in which carbon dioxide is absorbed in an absorber under

pressure in a suitable solvent, such as potassium carbonate or amines, and then released again separately from the synthesis gas (“flash”).

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.

Furthermore, a pressure swing adsorption 7 is provided, through which a hydrogen stream and a hydrogen-rich exhaust gas stream are provided. Advantageously, line 8 is provided, through which the hydrogen-rich exhaust gas stream of the pressure swing adsorption 7 is fed as

Fuel gas can be fed into a section of plant 1. It is intended that the hydrogen-rich exhaust gas stream is used as fuel gas for reformer 2. Reformer 2 can be heated by combustion of the hydrogen-rich exhaust gas stream.

In this way, the CO emissions typically caused by reforming can be significantly reduced. Furthermore, it is not necessary to use natural gas as an additional heating medium.

To use.

Figure 2 shows a system according to Figure 1, wherein in this embodiment an external hydrogen source 9 is additionally provided. The hydrogen from the external

Hydrogen source 9 is added to the hydrogen-rich exhaust gas stream of pressure swing adsorption 7. The external hydrogen source 9 in this case is

This embodiment involves hydrogen produced by electrolysis. In this way, the dimensions of pressure swing adsorption 7 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 dimensioned larger.

For this purpose, a further line 10 is provided through which a mixing device 11, a

Mixed flow can be set, in 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 source. If the

Combustion power of the exhaust gas stream of pressure swing adsorption 7 is not sufficient to

To realize firing in a further stage of the process, just enough external hydrogen is added to enable complete combustion of the hydrogen in the hydrogen-rich exhaust stream. 10

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Figure 3 shows the upper section of a plant for the production of ammonia. A LU103255

Front-end 12 is provided for the production of synthesis gas. Furthermore, the synthesis gas is fed into a pressure swing adsorption unit 7 and then into an ammonia synthesis unit 6. A balance chamber 13 is arranged around the schematic diagram. 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 provided, among other things, by the

Use of fuels, the combustion of which often also leads to CO2 emissions.

The upper part of Figure 3 shows a conventional plant for the production of ammonia. Natural gas 14 is fed to the front-end 12 and converted to obtain a synthesis gas. The synthesis gas is fed into the pressure swing adsorption 7, where a

Hydrogen stream 15 is obtained, which 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 flow 16 is not sufficient to

End or to provide sufficient heat, additionally

Natural gas is burned. The combustion of natural gas produces CO,, which is released into the environment via the balance space. Figure 3 shows only the part of the CO, that is actually released into the environment via the balance boundary. Overall, more

CO2 than is emitted. The CO2 that is separated or scrubbed in the CO2 scrubbing process can be compressed. It is then not part of the emissions.

In the lower part of Figure 3, a system with a concept according to the invention for

The pressure swing adsorption 7 is operated with a lower recovery rate than in the conventional

Plant for the production of ammonia. In this way, the energy content of the hydrogen-rich exhaust stream 16 increases, since more hydrogen is contained in the hydrogen-rich exhaust stream 16. The energy content is sufficient in this embodiment to

End 12, or to supply heat to Front-End 12. It is not necessary to burn additional natural gas. In this way, since primarily

When hydrogen is burned, CO2 emissions drop sharply.

To compensate for the lower recovery rate of pressure swing adsorption 7, the

In this example, the front end is approximately 10% larger. This allows the same amount of product, i.e., ammonia, to be obtained as in the conventional plant, while simultaneously significantly reducing CO2 emissions. 11

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List of reference symbols 1. Plant 2 reformer 3. Carbon monoxide (CO) converter 4. Carbon dioxide (CO) scrubber unit 6. Ammonia synthesis unit 7. Pressure swing adsorption 8. Line 9. External hydrogen source 10. Additional line 11. Mixing device 12. Front-end 13. Balance chamber 14. Natural gas 15. Hydrogen stream 16. Hydrogen-rich exhaust stream 12

Claims (16)

221671P00LU Patent claims LU103255 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 for providing the hydrogen stream and a regeneration cycle for providing the hydrogen-rich exhaust gas stream, wherein nitrogen is added to the synthesis gas in an enrichment step, characterized in that during the operation of the pressure swing adsorption (7) a recovery rate is set, 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 that is introduced into the pressure swing adsorption (7), wherein the recovery rate is determined by the duration of the Regeneration cycle is influenced 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 through which heat can be introduced into a process step of the process. 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 1 221671P00LU that the recovery rate is adjusted when the temperature exceeds or falls below a LU103255 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 the production of 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 (CO,) 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 is operable 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 during operation of the pressure swing adsorption a recovery rate is adjustable, 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 2 221671P00LU of hydrogen in the synthesis gas which is introduced into the pressure swing adsorption (7), LU103255, wherein the recovery rate can be influenced by the duration of the regeneration cycle and wherein the recovery rate is adjustable 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). 3