DE102011016759A1 - Preparing ammonia comprises conducting alkane dehydrogenation to produce hydrogen-rich stream, purifying the stream, optionally mixing purified nitrogen with hydrogen-rich stream, compressing the stream, preparing ammonia and liquefying - Google Patents

Abstract

Preparing ammonia comprises: (a) conducting an alkane dehydrogenation, in which the alkane is catalytically dehydrogenated using hydrogen to alkene, to produce a hydrogen-rich stream; (b) purifying the hydrogen-rich stream from step (a) to produce a purified hydrogen-rich stream; (c) optionally mixing purified nitrogen with the hydrogen-rich stream from step (b); (d) compressing the stream of step (c) on a synthesis pressure to produce a ammonia synthesis gas; (e) preparing ammonia in one or more reactors, to produce an ammonia-rich gas; and (f) liquefying the ammonia-rich gas.

Description

The invention relates to an integrated process for the preparation of NH ₃ , wherein by-products which are generated in an alkane dehydrogenation, such as H ₂ and N ₂ , are used in the production of NH ₃ . This method is used to increase the efficiency of a dehydrogenation process.

The dehydrogenation of alkanes according to the following formula C _n H _{2n + 2} ↔ C _n H _2n + H ₂ (1) is an endothermic reaction which normally proceeds between 400 ° C and 800 ° C, preferably between 500 ° C and 650 ° C. In this case, the heat required in the steam reformer is supplied by the external heating of the reactor, and in the oxidative dehydrogenation reactor, part of the heat required is obtained by selective hydrogen combustion by adding oxygen. For this purpose, an air separation plant is used, which supplies the necessary oxygen. In order to achieve a high conversion in the dehydrogenation, a catalyst which accelerates the reaction is usually used.

For example, in the propane dehydrogenation (PDH) process, propylene is produced from propane via the following reaction route: C ₃ H ₈ → C ₃ H ₆ + H ₂ (2)

In this case, propane is dehydrogenated with the release of one equivalent of hydrogen to give propylene and it is still obtained as a by-product of hydrogen, which contains a concentration of> 70% H ₂ . From the prior art it is known to use this by-product for the firing of the steam reformer used in propane dehydrogenation.

For other industrial purposes, hydrogen is the starting material and must be produced from resources such as natural gas in a complex process. In this case, hydrocarbon-containing starting materials are reacted with steam according to the steam reforming method known in the literature or by partial oxidation to hydrogen-containing synthesis gas in accordance with reaction equations (3) or (4). CH ₄ + H ₂ O → CO + 3 H ₂ (steam reforming) (3) 2 CH ₄ + O ₂ → 2 CO + 4 H ₂ (partial oxidation) (4)

In a final step, the carbon monoxide is then oxidized to carbon dioxide.

The synthesis gas thus obtained can then be used as a substrate for the methanol, ammonia, oxo and Fischer-Tropsch synthesis.

For the production of ammonia, the synthesis gas of CO _{2 is} purified in a gas scrubber, enriched with N ₂ from an air separation plant compressed to a synthesis pressure and converted into NH ₃ in one or more reactors according to reaction equation (4). N ₂ + 3 H ₂ ↔ 2 NH ₃ (4)

This is usually carried out by the Haber-Bosch process, in which the gas mixture of hydrogen and nitrogen is reacted on an iron oxide mixed catalyst to form ammonia.

In most cases, a circuit synthesis system according to the conventional state of the art follows, wherein the generated ammonia is withdrawn as liquid ammonia. This circulatory system is necessary because ammonia production is an equilibrium reaction and ammonia must be separated from the remainder of the gas, which consists of inert and unreacted synthesis gas due to the incomplete gas phase reaction. This separation is carried out by condensation. The remaining gas is introduced as recycle gas after the reactor for NH ₃ generation back into the process, which closes the circuit.

In this technique, it is disadvantageous that there is an enrichment of inert gases in the recycle gas, which are introduced via the hydrogen, which has been generated by steam reforming or partial oxidation of hydrocarbon-containing starting materials. For this reason, a partial flow of the recycle gas must be discharged in order to avoid a negative influence on the conversion of hydrogen and nitrogen into ammonia.

It is an object of the present invention to provide an integrated process for the production of NH ₃ which is more economical than the methods known in the prior art and in which the discharge of the recycle gas in the ammonia synthesis can be minimized or completely dispensed with.

• (a) Durchführung einer Alkandehydrierung, bei der Alkane durch Abgabe von H₂ zu Alkenen katalytisch dehydriert werden, wobei ein H₂-reicher Strom generiert wird,
• (b) Reinigung des H₂-reichen Stroms aus Schritt (a), wodurch ein gereinigter H₂-reicher Strom generiert wird,
• (c) gegebenenfalls Zumischung von N₂ zu dem gereinigten H₂-reichen Strom aus Schritt (b),
• (d) Komprimierung des Stroms aus Schritt (c) auf einen Synthesedruck, wodurch ein NH₃-Synthesegas generiert wird,
• (e) Herstellung von NH₃ in einem oder mehreren Reaktoren, wobei ein NH₃-reiches Gas generiert wird,
• (f) Verflüssigung des NH₃-reichen Gases aus Schritt (e).

The object is achieved by a method for producing NH ₃ , comprising the following steps,

• (a) performing an alkane dehydrogenation in which alkanes are catalytically dehydrogenated by the release of H ₂ to alkenes, generating a H ₂ -rich stream,
• (b) purifying the H ₂ -rich stream from step (a), thereby generating a purified H ₂ -rich stream,
• (c) optionally admixing N ₂ to the purified H ₂ -rich stream from step (b),
• (d) compressing the stream of step (c) to a synthesis pressure, thereby generating an NH ₃ synthesis gas,
• (e) producing NH ₃ in one or more reactors, generating an NH ₃ -rich gas,
• (f) liquefying the NH ₃ -rich gas from step (e).

In a preferred embodiment of the invention, the alkane dehydrogenation from step (a) is carried out in two or more strands in a parallel connection. This has the advantage that one plant strand can be regenerated, while another is used for alkane dehydrogenation, and thus the productivity of the plant is always maintained.

In the alkane dehydrogenation of step (a), the prior art employs a reformer consisting of many tubes filled with a catalyst material. Usually, the catalyst consists of small pellets whose active surface is accomplished by impregnation with Pt. An alkane gas / steam mixture is passed as an input stream at about 550 ° C through the reformer containing the catalyst pellets. In the reformer, an endothermic dehydrogenation reaction takes place, whereby the temperature in the reactor drops sharply and consequently the reaction is slowed down. In order to be able to lead the reaction close to equilibrium, therefore, sufficient heat must be introduced from the outside into the reformer tubes. The reformer is operated so that the process gas has just reached equilibrium in the exit of the reformer. In the other case, the by-products are favored. Thus, in a reformer about 30% of the alkanes contained in the input stream are converted.

The equilibrium reaction is shown in equation (5): C ₃ H ₈ ↔ C ₃ H ₆ + H ₂ + by-products (CH ₄ , CO ₂ , C ₂ H ₆ , etc ...) (endothermic) (5)

To further advance the reaction, some of these reformers are operated in series in series, which series can be implemented in multiple parallel strands.

Preferably, the alkane dehydrogenation of step (a) is carried out in a two-stage process comprising a reformer in which an alkane gas / steam mixture is introduced, which is passed over a catalyst as described above and the product gas from the reformer together with O _{2 is passed} into an oxyreactor where it is passed over a catalyst to generate an H ₂ -rich stream and alkenes.

The oxyreactor consists of a vessel which usually contains the same catalyst as the reformer. The product gas from the reformer is introduced into the oxyreactor. Before entering the catalyst, a defined amount of O _{2 is} added to the gas. The O ₂ reacts with the H _{2 of} the product gas from the reformer. Between O ₂ and H ₂ , an exothermic reaction proceeds to form water, see equation (6). 2H ₂ + O ₂ → 2 H ₂ O (exothermic) (6)

Reaction (6) proceeds as long as the supplied O _{2 is present} in the gas mixture. This is usually already completed in the upper part of the oxy reactor and provides the gas with the necessary heat for the simultaneous endothermic catalytic dehydrogenation reaction in the oxy reactor after reaction (7), C ₃ H ₈ ↔ C ₃ H ₆ + H ₂ (endothermic) (7)

Advantageously, the product gas from the reformer is admixed with so much O ₂ that the temperature in the oxyreactor is between 500 ° C. and 650 ° C., preferably 600 ° C. The required O ₂ originates from an air separation plant in which N ₂ is obtained as a by-product.

By using a combination of reformer and oxyreactor, an optimum yield of alkenes can thus be achieved. Here, too, it is possible to provide the series connection of reformer and oxyreactor in two or more phases in a parallel connection.

Preferably, the catalyst of step (a) comprises a porous support and at least one active surface element, wherein the support comprises elements of the main groups or subgroups II to IV of the Periodic Table, and one or more active surface elements is from main group IV of the Periodic Table. Advantageously, the catalyst comprises a zinc aluminate or calcium aluminate carrier with platinum and / or tin impregnation.

In a preferred embodiment of the invention, the catalysts of the reformer and the oxyreactor are of the same material.

Preferably, in step (a) an H ₂ -rich stream is generated which has an H ₂ concentration of> 70% H ₂ , preferably of> 86% H ₂ . The higher the alkane dehydrogenation achieved purity of the by-product stream H ₂ , the lower a discharge flow in the liquefaction of NH ₃ -rich gases in step (f) can be designed. Step (f) is usually carried out in a circuit according to the prior art. Outlet streams are necessary to keep the concentration of inert in the circulation as low as possible. Under standard conditions, however, pure H _{2 is} generated in the alkane dehydrogenation in such a way that discharge of the recycle gas can be completely dispensed with. If a minimum discharge is nevertheless necessary, then this stream is provided as purge gas as fuel for the alkane dehydrogenation in step (a).

The H ₂ -rich by-product stream generated in step (a) is subsequently subjected to purification. There are essentially two options for purifying this H ₂ -rich current, which are briefly described below.

A variant of the process according to the invention provides for purifying the H ₂ -rich stream from step (a) by means of pressure swing adsorption. The pressure swing adsorption process is a widely used purification process. In this case, an H ₂ yield of 86 to 90% can be achieved. The resulting PSA exhaust gas can be further burned as fuel gas in the reformer furnace.

In an alternative embodiment of the process according to the invention, the purification of the H ₂ -rich stream from step (a) is carried out by means of liquid N ₂ scrubbing. Liquid N ₂ scrubbing utilizes the solubility of hydrocarbons in liquid nitrogen. If a suitable design is provided, the synthesis gas ratio in this step is already set to a H ₂ : N ₂ ratio of 3: 1.

If the latter is not the case or if a pressure swing adsorption is provided, then in step (c) N _{2 is added} to the purified H ₂ -rich stream from step (b). This happens to an extent that sets the above-mentioned H ₂ : N ₂ ratio of 3: 1. Ie. an admixture of N ₂ in step (c) takes place only if the N ₂ concentration by the previous steps, such. B. the purification in step (b), not enough N ₂ is already present.

In a further embodiment, the waste gases resulting from the purification by pressure swing adsorption or liquid N ₂ scrubbing are returned to the alkane dehydrogenation.

After purification by one or both of these purification stages, the generated H ₂ -rich stream is present in a purity of> 99.9 vol%. Thus, there is a H ₂ -rich current that is almost completely free of inert.

In an advantageous embodiment of the invention, the N ₂ is generated for addition to the purified H ₂ -rich stream from step (b) in an air separation plant. This also preferably applies to the O ₂ which is fed into the oxyreactor. In a particularly advantageous embodiment, the N ₂ for mixing to the purified H ₂ -rich stream from step (b) and the O ₂ , which is guided into the oxy reactor, generated in the same air separation plant. As a result, only one air separation plant is necessary, which provides for the supply of oxygen in the alkane dehydrogenation and for the supply of nitrogen in the NH ₃ synthesis. This makes the process very economical, since in this embodiment all incidental by-product streams, ie H ₂ , N ₂ and O ₂ , are further used in the process.

In the further process sequence, the stream from step (c) is then compressed in step (d), whereby an NH ₃ synthesis gas is generated. Advantageously, in step (d) an NH ₃ synthesis gas of a synthesis pressure of up to 400 bar is generated by means of piston compressors. The choice of the compressor depends essentially on the synthesis capacity. If smaller turbo-boost engines are not available, reciprocating compressors must be used. Then the synthesis pressure can be set up to 400 bar. Thus, advantageously, the cooling energy for the NH ₃ liquefaction can be saved in step (f).

In an alternative approach, in step (d) an NH ₃ synthesis gas of a synthesis pressure of 180 to 200 bar is generated by means of gear turbo machines. This embodiment is preferably used for larger capacities. The type of compressor used here is robust and reliable, so that can be dispensed with standby machines.

In an advantageous embodiment of the present invention, the NH ₃ synthesis gas generated in step (d) is temporarily stored in a gas pressure accumulator. The thus buffered NH ₃ synthesis gas is removed from the gas pressure accumulator as soon as one of the two or more times provided in a parallel connection Alkandehydrierungsstränge is regenerated. Advantage of such an embodiment is to supply the NH ₃ synthesis at relatively constant load with fresh synthesis gas.

In process step (e), an NH ₃ -rich gas is then subsequently generated in one or more reactors. It is advantageously a heat recovery over the Steam generation provided. This recovery of NH ₃ -rich gas is carried out according to the prior art. Examples of corresponding embodiments provide the writings DD 225029 A3 . EP 1339641 B1 and DE 10057863 ,

In ammonia production usually cycle processes are used. In this case, the resulting ammonia must be separated from the remaining gas, which consists of inert and unreacted synthesis gas, after the gas phase reaction, which is always incomplete for reasons of chemical equilibrium, for example by continuous condensation. This condensation is favored by high synthesis pressure, high ammonia concentration and low temperature. Thus, step (f) of the method according to the invention is described, which comprises the liquefaction of the NH ₃ -rich gas from step (e).

In the method according to the invention a discharge of the cycle gas is reduced to a minimum, or it can be completely dispensed with a discharge. The reason for this is that the H ₂ -rich gas from the alkane dehydrogenation after the purification in step (b) can be generated in such a pure form that inert enrichment in the NH ₃ synthesis loop is not to be expected.

Optionally, the liquid NH ₃ from step (f) is stored in a tank farm. This tank farm is advantageously equipped with loading facilities to ensure transport to other facilities that ensure the further processing of the generated NH ₃ .

In a further advantageous embodiment of the method, the liquid NH ₃ from step (f) is fed to a urea synthesis. Urea is industrially produced in large quantities and is used, for example, as a nitrogen fertilizer. Ie. Here, hydrogen production would first be carried out by alkane dehydrogenation with subsequent ammonia production and subsequent urea production. In this case, ammonia and carbon dioxide react to ammonium carbamate in an exothermic reaction according to equation (8). Ammonium carbamate then reacts in the endothermic reaction to urea and water according to equation (9). 2 NH ₃ + CO ₂ → [H ₂ N-CO-O] NH ₄ (8) [H ₂ N-CO-O] NH ₄ → H ₂ N-CO-NH ₂ + H ₂ O (9)

In the reactor, only a portion of the reaction components is converted into urea. This is obtained in a solution containing, besides the carbamate, free ammonia and water. For this reason, it is necessary to purify the urea solution.

This is usually done by a CO ₂ -Strippung to remove unreacted ammonia. This is usually followed by recirculation and evaporation steps, followed by desorption and hydrolysis.

The thus obtained urea is then worked up according to the invention in a prilling or granulation. Embodiments of such equipment parts are, for example, in EP 2119489 A1 and EP 2192099 A1 described.

According to the invention, a CO ₂ stream which is branched off from the alkane dehydrogenation from step (a) is integrated into the urea synthesis and / or into the prilling or granulation. This integration can be provided in any arbitrary process step, which requires CO ₂ . Again, this step helps to provide an integrated process in which all product bypasses are advantageously reused.

The invention will be exemplified below 1 explained in more detail.

1 : Schematic representation of the integrated process according to the invention for the preparation of NH ₃ , wherein by-products which are generated in an alkane dehydrogenation, such as H ₂ and N ₂ , are used in the NH ₃ production.

In 1 will be in the unit 1 carried out an alkane dehydrogenation. There is the unit 1 preferably from a reformer and a downstream oxy reactor, which together form a plant strand. To ensure regeneration of this plant strand without having to shut down the alkane dehydrogenation, another plant strand is provided, which then ensures the alkane dehydrogenation. For alkane dehydrogenation of the unit 1 for example propane 2 and water vapor 3 fed. In an air separation plant 5 becomes the fed air 6 in oxygen 7 and nitrogen 8th disassembled. The oxygen thus generated 7 gets into the oxyreactor of the unit 1 to react with hydrogen from the upstream reformer to water. As a result of this exothermic reaction, so much heat is supplied that a further supply of heat from the outside into the oxyreactor for the endothermic dehydrogenation reaction can be omitted. That in the reaction in unit 1 resulting main product propylene 4 is discharged and further processed as known from the prior art.

The by-product is a H ₂ -rich stream 9 according to the invention in the unit 10 is further processed. For the purpose of this further processing is unity 10 from a purification step, which takes place by way of example in a pressure swing adsorption. This achieves an H ₂ yield of 86 to 90%. The resulting exhaust gases 11 be back in the reformer of unity 1 recycled. The purified hydrogen coming out of the purification stage is subsequently treated with nitrogen 8th Enriched, from the air separation plant 5 comes. This mixture 12 is then compressed and brought to the necessary pressure up to 400 bar for ammonia production. This compression takes place via piston compressors 13 , This produces an NH ₃ synthesis gas 14 , which is stored in a gas pressure accumulator (not shown). Once a plant strand of the exemplary double-stranded alkane dehydrogenation unit 1 is shut down for regeneration, the thus cached NH ₃ synthesis gas 14 be reused without the operation of the ammonia reactors from unit 15 is impaired. For the generation of ammonia-rich gas one or more reactors are used, which are in unit 15 are integrated.

The ammonia production takes place by means of a circulation synthesis system. This is successively NH ₃ synthesis gas 14 via a cycle compressor 17 in an ammonia reactor, which usually consists of several sections with intermediate cooling, passed over a cooling and condensation section in an ammonia separation, in the liquid ammonia 16 is won. The rest of the cycle gas 18 becomes the NH ₃ synthesis gas 14 added, which closes the cycle. An evacuation of recycle gas 18 can be dispensed with due to the purity of the hydrogen generated in this way of producing ammonia, since an inerting in the cycle gas is thus reduced to a minimum. This is an absolute advantage of the present invention, which is solved in the prior art by laborious recycling of discharged cycle gas and other structural measures.

The thus obtained liquid ammonia 16 is then in a tank farm 19 stored between, to be supplied for further uses. In 1 is exemplified, the intermediate liquid ammonia 20 in unit 21 in a urea synthesis plant with subsequent prilling or granulation to nitrogen fertilizer 22 continue to process. This is a CO ₂ stream 23 who is in unity 1 the alkane dehydrogenation is generated in unit 21 integrated.

Thus, in this embodiment, advantageously, all by-product streams continue to be used in an integrated process cycle, thereby increasing the economics of the individual processes. These by-product streams are on the one hand in the unit 1 generated H ₂ , which is further processed to NH ₃ . Another by-product stream from the alkane dehydrogenation is nitrogen 8th from the air separation plant 5 , This is also used in ammonia production in the generation of NH ₃ synthesis gas. If, in addition, a urea synthesis plant is used, so will the unit 1 resulting CO ₂ stream is advantageously used and reused.

The increased cost-effectiveness of this integrated production cycle is to be shown in detail in an embodiment below.

Based on a production capacity of 450,000 t / a of propylene in an alkane dehydrogenation plant consisting of reformer and oxy-reformer, about 1,384 kmol / h of H _{2 are} released. The demand for O ₂ in the oxyreactor is thus about 161 kmol / h. This O ₂ is produced in an air separation plant. In this case, N ₂ is released as by-product stream in an amount of 600 kmol / h. If the hydrogen is further processed into ammonia in its total amount generated, then the stoichiometric demand for N ₂ according to equation (4) is 461 kmol / h. The theoretical NH ₃ production would thus be 922 kmol / h or 376 t / d. As can be seen from this observation, the resulting N ₂ from the air separation plant, which is used for the alkane dehydrogenation, far from sufficient to ensure the need for N ₂ in the subsequent production of ammonia. In the production of, for example, propylene, the two substances H ₂ and N _{2 are present} in large quantities and can be used with minimal effort for the production of ammonia. It is estimated that in addition to propylene sales of ammonia in the amount of $ 50 to 60 million / year can be achieved.

• – anfallende Nebenproduktströme aus der Alkandehydrierung werden vorteilhaft weiterverarbeitet ökonomisch und ökologisch vorteilhaftes Verfahren
• – die Reinheit des H₂ aus der Alkandehydrierung ist so hoch, dass eine Ausschleusung des Kreislaufgases bei der NH₃-Synthese minimiert werden kann und evtl. ganz darauf verzichtet werden kann
• – bei kleinen Kapazitäten kann durch Erzielung eines hohen Synthesedruckes bei der NH₃-Generierung Kälteenergie für die NH₃-Verflüssigung im Kreislaufsynthesesystem eingespart werden

Advantages resulting from the invention:

• - Obtaining by-product streams from the alkane dehydrogenation are advantageously further processed economically and ecologically advantageous method
• - The purity of the H ₂ from the alkane dehydrogenation is so high that a discharge of the recycle gas in the NH ₃ synthesis can be minimized and possibly can be completely dispensed with
• - At low capacities can be saved by achieving a high synthesis pressure in the NH ₃ generation cooling energy for the NH ₃ liquefaction in the circulation synthesis system

LIST OF REFERENCE NUMBERS

1

unit

2

propane

3

Steam

4

propylene

5

Air separation plant

6

air

7

oxygen

8th

nitrogen

9

H ₂ -rich current

10

unit

11

exhaust

12

mixture

13

reciprocating compressors

14

NH ₃ synthesis gas

15

unit

16

liquid ammonia

17

Cycle compressor

18

Recycle gas

19

tank farm

20

intermediate liquid ammonia

21

unit

22

nitrogen fertilizer

23

CO ₂ stream

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DD 1339641 B1 [0036]
• EP 1339641 B1 [0036]
• DE 10057863 [0036]
• EP 2119489 A1 [0043]
• EP 2192099 A1 [0043]

Claims (22)

A process for producing NH ₃ comprising the steps of (a) performing an alkane dehydrogenation in which alkanes are catalytically dehydrogenated by the release of H ₂ to alkenes, generating a H ₂ -rich stream; (b) purifying the H ₂ -rich stream from step (a), whereby a purified H ₂ -rich stream is generated, (c) optionally admixing N ₂ to the purified H ₂ -rich stream from step (b), (d) compressing the stream from step (c) to a synthesis pressure, thereby NH ₃ is generated -Synthesegas, (e) preparation of NH ₃ in one or more reactors, wherein a NH ₃ -rich gas is generated, (f) liquefying the NH ₃ -rich gas from Steps). A method according to claim 1, characterized in that in step (a) an H ₂ -rich stream is generated which has an H ₂ concentration of> 70% H ₂ , preferably of> 86% H ₂ . Method according to one of claims 1 or 2, characterized in that the alkane dehydrogenation of step (a) is carried out in two or more strands in a parallel connection. A process according to any one of claims 1 to 3, characterized in that the alkane dehydrogenation of step (a) is carried out in a two-stage process comprising a reformer in which an alkane gas / steam mixture is passed which is passed over a catalyst and the product gas from the reformer is fed together with O ₂ into an oxyreactor where it is passed over a catalyst to generate an H ₂ -rich stream and alkenes. Method according to one of claims 1 to 4, characterized in that the catalyst from step (a) contains a porous support and at least one active surface element, wherein the support comprises elements of the main groups or subgroups II to IV of the Periodic Table, and one or more active Surface elements from the main group IV of the Periodic Table is. A method according to claim 5, characterized in that the catalyst comprises a zinc aluminate or calcium aluminate support with platinum and / or tin impregnation. A method according to claim 4, characterized in that the catalyst of the reformer and the oxyreactor are of the same material. Method according to one of claims 4 or 7, characterized in that the product gas from the reformer is so much O ₂ admixed that the temperature in the oxyreactor between 500 ° C and 650 ° C, preferably at 600 ° C. Method according to one of the preceding claims, characterized in that the purification of the H ₂ -rich stream from step (a) is carried out by means of pressure swing adsorption. Method according to one of claims 1 to 8, characterized in that the purification of the H ₂ -rich stream from step (a) by means of liquid N ₂ scrubbing is performed. Method according to one of claims 9 or 10, characterized in that exhaust gases resulting from the pressure swing adsorption or liquid N ₂ scrubbing are recycled to the alkane dehydrogenation. Method according to one of the preceding claims, characterized in that the N _{2 is} generated for addition to the purified H ₂ -rich stream from step (b) in an air separation plant. A method according to claim 4, characterized in that the O ₂ , which is guided into the oxyreactor is generated in an air separation plant. Method according to one of claims 12 or 13, characterized in that the N ₂ for mixing to the purified H ₂ -rich stream from step (b) and the O ₂ , which is fed into the oxy reactor, in the same air separation plant is generated. Method according to one of the preceding claims, characterized in that in step (d) an NH ₃ synthesis gas of a synthesis pressure of up to 400 bar is generated by means of piston compressors. Method according to one of claims 1 to 14, characterized in that in step (d) an NH ₃ synthesis gas of a synthesis pressure of 180 to 200 bar is generated by means of gear turbo-machines. Method according to one of the preceding claims, characterized in that in step (d) generated NH ₃ synthesis gas is temporarily stored in a gas pressure accumulator. Method according to one of the preceding claims, characterized in that in the production of NH ₃ in step (e) a heat recovery via the steam generation is carried out. Method according to one of the preceding claims, characterized in that the liquid NH ₃ from step (f) is stored in a tank farm. Method according to one of the preceding claims, characterized in that the liquid NH ₃ from step (f) is supplied to a urea synthesis. A method according to claim 18, characterized in that the urea synthesis is followed by a prilling or granulation. Method according to one of the preceding claims, characterized in that a CO ₂ stream, which is branched off from the alkane dehydrogenation from step (a) is integrated into the urea synthesis and / or in the prilling or granulation.

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