WO2015177051A1

WO2015177051A1 - Production of syngas using two autothermal reformers

Info

Publication number: WO2015177051A1
Application number: PCT/EP2015/060749
Authority: WO
Inventors: Joachim Johanning; Evgeni Gorval; Bernd Keil; Katja POSCHLAD; Christiane Potthoff
Original assignee: Thyssenkrupp Industrial Solutions Ag; Thyssenkrupp Ag
Priority date: 2014-05-21
Filing date: 2015-05-15
Publication date: 2015-11-26
Also published as: DE102014209635A1

Abstract

The invention relates to a device and a method for producing syngas using two autothermal reformers (1, 2), followed by synthesis of ammonia from the syngas.

Description

Synthesis of synthesis gas with two autothermal reformers

The invention relates to an apparatus and a method for the production of synthesis gas with the aid of two autothermal reformers and the subsequent synthesis of ammonia from the synthesis gas thus produced.

The large-scale production of synthesis gas from natural gas for ammonia synthesis is based today largely on a two-stage reforming with an externally heated steam reformer as a primary reformer and operated with compressed air as an oxidant secondary reformer. With capacities of up to 3,300 tpd of ammonia, this two-stage reforming is technically feasible with great reliability and economically unsurpassed compared to alternatives for the production of syngas.

In order to increase the capacity of an ammonia plant to more than 3,300 tpd ammonia, in principle, the dimensions of the apparatus and pipelines can be increased accordingly. Alternatively or additionally, to increase the capacity and the operating pressure in the production of synthesis gas can be increased. The increase in pressure in the reformer reduces the volume flow in the entire process path and thus allows larger capacities even without increasing the components of the system. In addition, a higher operating pressure for a discharge of the syngas compressor, which is required for the subsequent ammonia synthesis at significantly higher pressure. This is of particular importance because the available syngas compressors are already limiting components for plant capacities of 3300 tpd of ammonia. The reasons are u.a. For technical reasons and in particular concern the drive turbine.

However, increasing the components of the system and pressure increase are not always economically useful to increase capacity.

As regards the two-stage reforming, the steam reformer has a comparatively large proportion of the total construction costs because of its complexity and the great stress. In principle, a steam reformer can be considered as a parallel connection of a large number of individual tubular reactors, their individual capacity can not be increased significantly. The capacity of a steam reformer is therefore closely related to the number of tubular reactors and an increase is essentially only possible by increasing the number of tubular reactors. Almost all components required for the realization of a steam reformer are coupled to the number of tube reactors. The construction costs of a steam reformer are therefore largely proportional to the capacity of the entire system. Increasing the steam reformer to increase capacity is not economically viable. Also, an increase in the operating pressure are set relatively narrow limits in the two-stage reforming, because the pipes already work in the steam reformer anyway at the load limit defined by pressure and temperature.

An alternative to the two-stage reforming is the purely autothermal reforming of natural gas using cheaper autothermal reformer (ATR). In order to provide the extra amount of oxygen required for this purpose, either oxygen from an air separation plant or a correspondingly larger amount of air is required. However, the cost of air separation or the provision of additional air and the removal of excess nitrogen are significant and, with plant capacities of up to 3,300 tpd of ammonia, compensate for the savings achieved by eliminating the steam reformer. However, devices for the separation of air and the separation of the excess nitrogen show a significant degression of the additional costs when increasing their capacity by increasing the components. With increasing capacity above 3300 tpd of ammonia, the increase in the components of plants based on purely autothermal reformers brings cost advantages compared to the two-stage reforming.

Furthermore, plants based on purely autothermal reforming in principle have a much greater potential for increasing the operating pressure in the production of synthesis gas. An increase in the operating pressure in the production of synthesis gas is not arbitrarily possible or useful even with purely autothermal reforming. The pressure dependence of the equilibrium position of the reforming reaction means that the methane conversion decreases with increasing pressure and the residual content of methane in the synthesis gas produced increases. In the synthesis gas treatment then an increasing proportion of the cycle stream must be removed from the synthesis (purge), whereby the plant economy is adversely affected. Furthermore, the partial pressure of the carbon monoxide formed in the reforming, which increases as a result of the pressure increase, leads to additional stress in the subsequent treatment steps, in particular in the conversion of carbon monoxide. This partial pressure of carbon monoxide is already in conventional systems at the limit of technical feasibility. The conditions are exacerbated by the fact that the lowest possible water vapor addition, ie the lowest possible water vapor / carbon ratio is sought for the reforming, as this the oxygen demand can be minimized. A smaller amount of water vapor causes larger partial pressures of the other gases in the mixture and thus has in principle the same effects as an increase in the total pressure, ie higher residual content of methane and greater partial pressure of carbon monoxide in the product gas.

WO 2004/0831 14 A2 discloses a process for the production of hydrogen in which a heat exchanger reformer and an autothermal reformer are connected in parallel.

EP 0 999 178 A1 relates to a process for the production of synthesis gas, i.a. for the subsequent ammonia synthesis, in which a conventional steam reformer and an autothermal reformer are arranged in parallel. The product streams from both reformers are then combined with each other and further processed together.

US 6,444,712 B1 discloses a process for the production of methanol from natural gas. Preferably, about half of the natural gas flow is directed to a steam reformer to produce reformed gas therein. The thus reformed gas is then mixed with the other half of the natural gas stream and sent to an autothermal reformer.

[001 1] US 2013 312384 A1 relates to a process for the production of H ₂ and CO from hydrocarbons and biofuel. For safety reasons, several smaller parallel autothermal reformers are preferably used.

These conventional processes for the production of synthesis gas are not satisfactory in every respect, especially with regard to an increase in capacity.

The invention has for its object to provide an advantageous method and apparatus for the production of synthesis gas for the subsequent ammonia synthesis. The process and apparatus should enable significant increases in capacity above the level of 3300 tpd of ammonia to be achieved without exceeding the technical and economical limits. This object is solved by the subject matter of the claims.

One aspect of the invention relates to a process for the production of synthesis gas comprising the steps

(A) providing a gas mixture comprising hydrocarbons, preferably methane or natural gas; Steam; and an oxidizing agent, preferably oxygen or oxygen-enriched air;

(b) reforming the gas mixture provided in step (a) in a first autothermal reformer, thereby obtaining a first synthesis gas comprising hydrogen, carbon monoxide, carbon dioxide and methane;

(c) increasing the content of hydrogen of the first synthesis gas obtained in step (b) by separating a mixed gas comprising carbon monoxide, carbon dioxide and methane;

(d) providing a gas mixture comprising the gas mixture separated in step (c);

(e) reforming the gas mixture provided in step (d) in a second autothermal reformer, thereby obtaining a second synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide;

wherein the first autothermal reformer in step (b) is operated at a pressure higher than the pressure at which the second autothermal reformer is operated in step (e).

The inventive method is based on the reforming in two autothermal reformers at different pressures. The first autothermal reforming is operated at such a high pressure that the hydrogen-rich first synthesis gas formed after separation of CO, C0 ₂ and possibly residues of unreacted CH ₄ can be passed directly before the second stage of the synthesis gas compressor, which is upstream of the ammonia reactor , This synthesis gas compressor is preferably multi-stage, wherein a first compressor stage preferably compresses the gas mixture to a first pressure in the range of 50 to 150 bar, more preferably 60 to 140 bar, and wherein a downstream second compressor stage the (pre-compressed) gas mixture to a second pressure in the range of preferably at least 150 bar, more preferably compressed at least 170, as required for the subsequent ammonia synthesis. The separation of CO, C0 ₂ and optionally CH ₄ is preferably carried out by pressure swing adsorption (PSA, Pressure Swing Absorption) or with the aid of membranes. The separated gas mixture is optionally (preferably) compressed and a second autothermal reforming and reformed here with air, optionally moderately oxygen-enriched air, to a second synthesis gas. The subsequent purification of this second synthesis gas from the second autothermal reformer is then carried out preferably by (i) one or two-stage conversion of CO, (ii) separation of CO ₂ and / or (iii) final purification, for example by methanation, pressure swing adsorption or nitrogen wash. The first synthesis gas and the second synthesis gas are then optionally combined after separate (pre-) compression, optionally enriched with the still required to achieve the desired stoichiometry amount of nitrogen and fed to the ammonia synthesis in an ammonia reactor. In this case, the first synthesis gas is preferably compressed only in the second compressor stage of the synthesis gas compressor, while the second synthesis gas is preferred both in the first compressor stage and - after being combined with the first synthesis gas - in the second compressor stage.

The inventive method requires additional and / or other apparatus in comparison with a conventional single-strand process control with only a single autothermal reformer. For example, a second autothermal reformer (preferably together with cooling section) for the synthesis gas, a device for separating off the remaining constituents of the synthesis gas (preferably by pressure swing adsorption) and an additional compressor are required for the process according to the invention. However, the method according to the invention makes it possible to operate the first autothermal reformer with a very low steam / carbon ratio and thus to minimize the oxygen requirement, ie also the size of the expensive air separation. The sizes of the devices for the subsequent purification of the synthesis gas from the second autothermal reformer are significantly reduced by the compared to the conventional single-strand process control smaller volume flows. Overall, therefore, there are cost advantages for the inventive method over a conventional single-strand system of the same capacity, which could not be realized single-stranded according to the current state of the art.

Autothermal reformers have an increased oxygen demand compared to conventional steam reformers. It has surprisingly been found that the oxygen demand for the production of synthesis gas becomes smaller the less water vapor is added, ie the lower the water vapor / carbon ratio. However, it was surprisingly found in this context that the residual content of methane in the synthesis gas after reforming in the autothermal reformer at lower Water vapor addition and increases at elevated pressure on for the overall process is no longer acceptable values.

In a purely single-stranded synthesis gas production based on a single autothermal reformer would therefore increase the capacity to increase the pressure, the steam addition is also increased accordingly to keep the residual content of methane after reforming at the level of conventional plant and to relieve the syngas compressor. As the addition of water vapor increases, however, the need for expensive oxygen also increases, so that a reduction in the oxygen requirement and corresponding operating and investment costs in the case of a pure single-strand synthesis gas based on a single autothermal reformer would not be feasible. Because of the high proportion of air separation in the total cost of an ammonia plant based on autothermal reforming, this has a significant impact on economy, i. on the cost relations compared to conventional systems. Ultimately, this results in a larger limit capacity, from which an ammonia plant based on autothermal reforming has cost advantages over a conventional system.

It has surprisingly been found that all the advantages of the autothermal reforming can be used if the reforming is carried out in two steps at different pressure levels. The first step preferably uses both the advantage of a small amount of steam in the process gas to minimize the required amount of oxygen as well as an increased pressure to relieve the synthesis gas compressor.

An autothermal reformer in the context of the invention is a reformer in which the heat produced during the reforming by exothermic reactions is used for endothermic reactions, so that the reforming process is autothermal. In this case, the autothermal reformer preferably has a catalyst and a burner. Reactors for the autothermal partial catalytic oxidation of noble metal catalysts which have no burner are preferably not autothermal reformers in the sense of the invention.

In the method according to the invention is preferred

the first autothermal reformer in step (b) is operated at a pressure which is at least 5 bar, more preferably at least 10 bar, even more preferably at least 15 bar, most preferably at least 20 bar and in particular at least 25 bar is higher than the pressure at which the second autothermal reformer is operated in step (e); and or

the first autothermal reformer in step (b) is operated at a pressure of at least 30 bar, preferably at least 35 bar or at least 40 bar, more preferably at least 45 bar or at least 50 bar, even more preferably at least 55 bar or at least 60 bar, most preferably at least 65 bar or at least 70 bar, and in particular at least 75 bar or at least 80 bar; and or

the second autothermal reformer in step (e) is operated at a pressure of at most 60 bar, preferably at most 55 bar or at most 50 bar, more preferably at most 45 bar or at most 40 bar, even more preferably at most 38 bar or at most 36 bar, most preferably at most 34 bar or not more than 32 bar, and in particular not more than 30 bar, not more than 28 bar, not more than 26 bar, not more than 24 bar, not more than 22 bar or not more than 20 bar.

Preferably, the first autothermal reformer is operated in step (b) at a pressure which is higher by 20 to 45 bar than the pressure at which the second autothermal reformer in step (e) is operated. In this case, the first autothermal reformer in step (b) is preferably operated at such a high pressure that after deduction of all further pressure losses downstream of the first autothermal reformer, the resulting gas mixture can safely be fed to the subsequent stage of a multi-stage synthesis gas compressor subsequent ammonia synthesis, said Compression ratio, for example, preferably 2.5.

The pressure at which the first autothermal reformer is operated is preferably in the range of 30 to 80 bar. A pressure below 30 bar is not preferred because this would adversely affect the dimensioning of the second autothermal reformer upstream compressor. A pressure above 80 bar is not preferred since this would adversely affect the equilibrium position of the reaction taking place in the first autothermal reformer (steam reforming).

The pressure at which the second autothermal reformer is operated is preferably in the range of 30 to 60 bar. A pressure below 30 bar is basically possible, but has an unfavorable effect on the dimensioning of the second autothermal reformer. A pressure above 60 bar is not preferred because then, for a given compression ratio, the first autothermal reformer would have to be operated at such high pressures, in which the equilibrium position of the reaction taking place in the first autothermal reformer (steam reforming) would be on the side of the educts.

In step (a) of the method according to the invention

Preferably, the oxidizing agent is in the form of pure oxygen or in the form of oxygen-enriched air containing at least 90% by volume of oxygen, more preferably at least 92% by volume, even more preferably at least 94% by volume, most preferably at least 96 vol .-% and in particular at least 98 vol .-% provided, wherein the required oxygen preferably originates from an air separation plant; and or

the hydrocarbons in the form of methane or natural gas are preferably added to the gas mixture, the natural gas optionally having been preferably desulfurized beforehand; and / or preferably the gas mixture provided has a molar steam / carbon ratio of not more than 3.6, not more than 3.4 or not more than 3.2, preferably not more than 3.0, not more than 2.8 or not more than 2.6; more preferably at most 2.4, at most 2.2 or at most 2.0; even more preferably not more than 1, 8, and possibly even not more than 1, 6, not more than 1, 4, not more than 1, 2, not more than 1, 0, not more than 0.8, not more than 0.6, not more than 0.4 or not more than 0, 2; and or

For example, the gas mixture provided preferably has a nitrogen content of at most 10% by volume, more preferably at most 8% by volume, even more preferably at most 6% by volume, most preferably at most 4% by volume, and most preferably at most 2% by volume. -%.

The molar water vapor / carbon ratio in the context of the invention is the molar ratio of molecules of water vapor to atoms carbon in the gas mixture, but only those carbon atoms of compounds are included, which are pure hydrocarbons, i. are free of oxygen. Carbon atoms of alcohols, aldehydes, etc. are not included accordingly.

Although a molar water vapor / carbon ratio of greater than 3.2 is technically possible, it is not preferred because it would result in more oxygen being consumed than is necessary and the yield of hydrogen would decrease. According to the invention, therefore, a molar water vapor / carbon ratio of 3.2 preferably represents the economic upper limit. A molar water vapor / carbon Ratio of less than 0.3 is not preferred, otherwise there would be soot that would deactivate the catalyst.

Preferably, the first synthesis gas obtained in step (b) of the process according to the invention

a molar hydrogen / carbon monoxide ratio of at most 4.5, preferably at most 4.2, at most 3.9 or at most 3.6; more preferably at most 3.3, at most 3.0 or at most 2.7; even more preferably at most 2.4, at most 2.1 or at most 1, 8; most preferably at most 1, 5, at most 1, 2 or at most 1, 0; and in particular not more than 0.8, not more than 0.6 or not more than 0.4; and / or a content of methane of at least 0.3 vol .-%, preferably at least 0.6 vol .-%, at least 0.9 vol .-% or at least 1, 2 vol .-%; more preferably at least 1, 5 vol.%, at least 1, 8 vol.% or at least 2.1 vol.%; even more preferably at least 2.4 vol%, at least 2.7 vol%, or at least 3.0 vol%; most preferably at least 3.3 vol%, at least 3.6 vol%, or at least 3.9 vol%; and in particular at least 4.2% by volume, at least 4.5% by volume or at least 4.8% by volume; and or

a content of hydrogen of at least 30% by volume, preferably at least 32% by volume, at least 34% by volume or at least 36% by volume; more preferably at least 38% by volume, at least 40% by volume or at least 42% by volume; even more preferably at least 44% by volume, at least 46% by volume or at least 48% by volume; most preferably at least 50% by volume, at least 52% by volume or at least 54% by volume; and in particular at least 56% by volume, at least 58% by volume or at least 60% by volume; and or

a content of carbon monoxide in the range of 20 ± 19% by volume, more preferably 20 ± 16% by volume, more preferably 20 ± 13% by volume, most preferably 20 ± 9% by volume, and especially 20 ± 5 vol .-%; and or

a content of carbon dioxide in the range of 12 ± 1 1% by volume, more preferably 12 ± 10% by volume, more preferably 12 ± 8% by volume, most preferably 12 ± 6% by volume, and especially 12 ± 4% by volume; and or

a content of nitrogen of at most 10% by volume, more preferably at most 8% by volume, even more preferably at most 6% by volume, most preferably at most 4% by volume, and most preferably at most 2% by volume; and or a water vapor content of 30 ± 29% by volume, more preferably 30 ± 25% by volume, more preferably 30 ± 20% by volume, most preferably 30 ± 15% by volume, and especially 30 ± 10% by volume. -%; wherein the contents are each moist concentrations.

Unless otherwise expressly stated, all percentages in relation to gas mixtures containing water vapor are to be construed as wet concentrations.

Calculated dry, the first synthesis gas obtained in step (b) of the process according to the invention is preferred

a content of hydrogen in the range of 38 to 69 vol .-%; and or

a content of carbon monoxide in the range of 7 to 31% by volume; and / or a content of carbon dioxide in the range of 3 to 19 vol .-%.

The content of methane in the first synthesis gas can in principle also be more than 4.8% by volume, in particular if a low molar steam / carbon ratio is set and the first autothermal reformer is supplied with a comparatively small amount of oxygen, so that the temperature in the POX zone of the reactor is comparatively low. However, methane contents of more than 4.8% by volume are not preferred since they have to be separated off in step (c) of the process according to the invention, so that subsequently a larger amount of gas must be recompressed to the pressure of the second autothermal reformer. This increases the operating costs.

Suitable measures to adjust the relative content of the individual gas components in autothermally produced first and second synthesis gas are known in the art, in particular oxygen, steam, hydrocarbon, temperature and pressure. If necessary, the influence of these parameters on the composition of the synthesis gas can be verified by suitable routine tests.

The first synthesis gas produced in the first autothermal reformer is poor or even unsuitable for a subsequent CO conversion because of its comparatively high CO partial pressure and the comparatively low content of water vapor. However, with the help of a pressure swing adsorption (PSA), the hydrogen at high pressure level and fed directly to the synthesis gas compressor. The pressure in the first autothermal reforming is therefore preferably selected so that the hydrogen can be fed directly to the synthesis gas compressor, preferably the second stage of a multistage synthesis gas compressor.

Preferably, in step (c) of the process according to the invention, the separation of the gas mixture comprising CO, C0 ₂ and CH ₄ from the first synthesis gas (i) by pressure swing adsorption (PSA) or (ii) by selective membrane Permeation and subsequent pressure swing adsorption.

In the pressure swing adsorption, the gas mixture comprising H ₂ , CO, C0 ₂ and CH _{4 is} physically separated from each other under pressure by means of adsorption. Preferably, porous materials (eg zeolites, activated carbon) are used as adsorbent. According to the invention, the release effect can be based on two different principles: equilibrium adsorption or molecular sieve action. The gas mixture is preferably introduced under elevated pressure into a fixed bed reactor, which is filled with the adsorbent, so that it is flowed through. CO, C0 ₂ and CH ₄ from the gas mixture are now adsorbed and at the outlet of the bed H ₂ can be removed. After a while, the adsorber bed is saturated and the process is switched by valves so that the outlet for H _{2 is} closed and an outlet for CO, C0 ₂ and CH _{4 is} opened. This is accompanied by a pressure reduction. At the lower pressure, the adsorbed CO, C0 ₂ and CH _{4 are} desorbed again and can be recovered at the outlet. Two or more adsorbers alternately loaded and unloaded preferably allow continuous operation.

In a preferred variant of the method according to the invention, in step (c), the first synthesis gas is first fed to a membrane separation plant for separating carbon monoxide and carbon dioxide by selective membrane permeation. The membrane has the property of permeating carbon monoxide and carbon dioxide much faster than hydrogen. The driving force for this separation process is the difference in the partial pressures of the component to be separated on the high and low pressure side of the membrane. Here, the pressure on the low pressure side of the membrane is set so that it is only slightly higher than the pressure of the hydrocarbons (natural gas) at the plant boundary. In the membrane separation plant, the first synthesis gas is separated into a hydrogen and methane-enriched retentate stream and a carbon monoxide and carbon dioxide-enriched permeate stream. Of the Retentate stream is only then supplied to the separation of carbon monoxide, carbon dioxide and methane according to step (c), wherein the separation of carbon monoxide, carbon dioxide and methane then preferably also takes place by pressure swing adsorption. The resulting exhaust gas contains predominantly methane, previously not deposited carbon monoxide and carbon dioxide and in small quantities also hydrogen. It can be used as fuel gas, for example, in an auxiliary boiler for steam generation.

After separating the gas mixture comprising carbon monoxide, carbon dioxide and methane in step (c), the first synthesis gas has been preferred

a content of hydrogen of at least 90% by volume, more preferably at least 92% by volume, even more preferably at least 94% by volume, most preferably at least 96% by volume, and especially at least 98% by volume; and or

a content of nitrogen of at most 10% by volume, more preferably at most 8% by volume, even more preferably at most 6% by volume, most preferably at most 4% by volume, and most preferably at most 2% by volume.

The main part of the hydrogen is contained after the separation of the gas mixture in the first synthesis gas. For its part, the separated gas mixture comprises, for the most part, CO formed in the reforming, unreacted CH ₄ and further comparatively small amounts of CO ₂ and H ₂ . It has surprisingly been found that the further implementation of this stream is most advantageously carried out in a second autothermal reforming step in order to react both the residual methane and to avoid problems with the CO conversion due to the large partial pressure of the carbon monoxide. Possibly. after addition of further hydrocarbons, preferably methane or natural gas, the separated gas mixture, which preferably originates from the pressure swing adsorption, fed to a second autothermal reformer and here also autothermally reformed with compressed air, possibly also moderately oxygen-enriched air as the oxidation medium. Due to the lower pressure in this reforming and a specifically greater addition of steam to the process gas results in this second autothermal reformer, a residual content of methane, which is comparable to that of a conventional plant.

The inventive method thus uses the advantages of a higher pressure levels in the first autothermal reforming, but avoids a larger methane entry in the preferred subsequent ammonia synthesis and a larger Stressing the subsequent process stages for the purification of the synthesis gas and also allows a significant relief of the syngas compressor.

In step (d) of the method according to the invention

is preferably the gas mixture air or oxygen-enriched air containing at most 90 vol .-% of oxygen, more preferably at most 80 vol .-%, more preferably 70 vol .-%, most preferably at most 60 vol .-% and in particular at most 50% by volume added; and or

Hydrocarbons in the form of methane or natural gas are preferably added to the gas mixture, the natural gas possibly being desulphurized beforehand; and / or preferably the gas mixture provided has a molar steam / carbon ratio of at least 3.2, preferably at least 3.4, at least 3.6 or at least 3.8; more preferably at least 4.0, at least 4.2, or at least 4.4; more preferably at least 4.6, at least 4.8, or at least 5.0; most preferably at least 5.2, at least 5.4, or at least 5.6; and in particular at least 5.8, at least 6.0 or at least 6.2; and or

For example, the gas mixture provided preferably has a nitrogen content of at most 70% by volume, more preferably at most 60% by volume, even more preferably at most 50% by volume, most preferably at most 40% by volume, and most preferably at most 30% by volume. -%; and or

For example, the gas mixture provided preferably has a nitrogen content of at least 10% by volume, more preferably at least 20% by volume, even more preferably at least 30% by volume, most preferably at least 40% by volume, and most preferably at least 50% by volume. -%.

After the reaction in the second autothermal reformer is carried out according to the invention preferably a high-temperature conversion of carbon monoxide with steam to carbon dioxide and hydrogen. Therefore, the second autothermal reformer is preferably operated so that after steam reforming there is still enough water vapor in the second synthesis gas to enable the high temperature conversion of carbon monoxide to be efficiently carried out.

The molar water vapor / carbon ratio in the autothermal reforming in the second autothermal reformer in step (e) of the method according to the invention is preferably greater than the molar water vapor / carbon ratio in the autothermal Reforming in the first autothermal reformer in step (b). Preferably, the relative difference in the molar steam / carbon ratio in step (e) to the molar steam / carbon ratio in step (b) is at least 0.1 or at least 0.2, more preferably at least 0.3 or at least 0.4 , more preferably at least 0.5 or at least 0.6, most preferably at least 0.7 or at least 0.8 and in particular at least 0.9 or at least 1.0.

Preferably, the second synthesis gas obtained in step (e) of the process according to the invention

a molar hydrogen / carbon monoxide ratio of at most 4.5, preferably at most 4.2, at most 3.9 or at most 3.6; more preferably at most 3.3, at most 3.0 or at most 2.7; even more preferably at most 2.4, at most 2.1 or at most 1, 8; possibly also not more than 1, 5, not more than 1, 2, not more than 1, 0, not more than 0.8, not more than 0.6 or not more than 0.4; and or

a content of methane of not more than 10% by volume, not more than 7,5% by volume, not more than 5,0% by volume or not more than 4,8% by volume, preferably not more than 4,5% by volume, not more than 4.2% by volume or not more than 3.9% by volume; more preferably at most 3.6% by volume, at most 3.3% by volume or at most 3.0% by volume; even more preferably at most 2.7% by volume, at most 2.4% by volume or at most 2.1% by volume; most preferably at most 1. 8% by volume, at most 1.5% by volume or at most 1.2% by volume; and in particular at most 0.9% by volume, at most 0.6% by volume or at most 0.3% by volume; and or

a content of hydrogen of at least 50% by volume, preferably at least 52% by volume, at least 54% by volume or at least 56% by volume; more preferably at least 58% by volume, at least 60% by volume or at least 62% by volume; even more preferably at least 64% by volume, at least 66% by volume or at least 68% by volume; most preferably at least 70% by volume, at least 72% by volume or at least 74% by volume; and in particular at least 76% by volume, at least 78% by volume or at least 80% by volume; and or

a content of carbon dioxide in the range of 12 ± 1 1% by volume, more preferably 12 ± 10% by volume, more preferably 12 ± 8% by volume, most preferably 12 ± 6% by volume, and especially 12 ± 4% by volume; and or a content of nitrogen of at most 10% by volume, more preferably at most 8% by volume, even more preferably at most 6% by volume, most preferably at most 4% by volume, and most preferably at most 2% by volume; and or

a content of water vapor of 40 ± 30% by volume, more preferably 40 ± 25% by volume, more preferably 40 ± 20% by volume, most preferably 40 ± 15% by volume, and especially 40 ± 10% by volume. -%; wherein the contents are each moist concentrations.

Dry calculated, the second synthesis gas obtained in step (e) of the process according to the invention preferably

a content of hydrogen in the range of 38 to 69 vol .-%; and or

In particular, if the subsequent purification of the second synthesis gas is not carried out by C0 ₂ scrubbing and methanation, but by pressure swing adsorption or N ₂ - scrubbing, thereby the residual methane can be separated from the second synthesis gas with. The separated methane can then be used together with the also separated carbon monoxide, carbon dioxide and excess nitrogen as fuel gas. In this variant of the method according to the invention, it is perfectly tolerable if the content of methane in the second synthesis gas is more than 5% by volume. If, however, the subsequent purification of the second synthesis gas is carried out by C0 ₂ scrubbing and methanation, the content of methane in the second synthesis gas is preferably below 5% by volume.

A comparatively high content of water vapor in the second synthesis gas is preferred, so that sufficient steam is available for the high-temperature conversion of carbon monoxide, which is preferably carried out subsequently. A content of water vapor before high-temperature conversion of, for example, 35 to 40% by volume is preferred. A content of water vapor of more than 40% by volume may also be relevant, but is not preferred. For a correspondingly high relative molar water vapor / carbon ratio at the entrance of the second autothermal reformer and thus a high content of water vapor in the second synthesis gas at the outlet of the second autothermal reformer would namely more oxygen required, which would adversely affect the yield of hydrogen.

The residual content of methane in the first synthesis gas, which is obtained in the autothermal reforming in the first autothermal reformer in step (b), is preferably greater than the residual content of methane in the second synthesis gas, which in the autothermal reforming in the second autothermal reformer in Step (e) is obtained. Preferably, the relative difference of the residual content of methane of the first synthesis gas obtained in step (b) and the residual content of methane of the second synthesis gas obtained in step (e) is at least 0.4 vol% or at least 0.8 vol% more preferably at least 1.2 vol.% or at least 1.6 vol.%, more preferably at least 2.0 vol.% or at least 2.4 vol.%, most preferably at least 2.8 vol at least 3.2% by volume and in particular at least 3.6% by volume or at least 4.0% by volume.

The content of carbon monoxide in the first synthesis gas, which is obtained in the autothermal reforming in the first autothermal reformer in step (b) is preferably greater than the content of carbon monoxide in the second synthesis gas, which in the autothermal reforming in the second autothermal reformer in Step (e) is obtained. Preferably, the relative difference in the content of carbon monoxide of the first synthesis gas obtained in step (b) and the content of carbon monoxide of the second synthesis gas obtained in step (e) is at least 0.4% by volume or at least 0.8% by volume. more preferably at least 1.2% by volume or at least 1.6% by volume, more preferably at least 2.0% by volume or at least 2.4% by volume, most preferably at least 2.8% by volume or at least 3.2% by volume and in particular at least 3.6% by volume or at least 4.0% by volume.

The content of water vapor in the first synthesis gas, which is obtained in the autothermal reforming in the first autothermal reformer in step (b) is preferably smaller than the content of water vapor in the second synthesis gas, which in the autothermal reforming in the second autothermal reformer in Step (e) is obtained. Preferably, the relative difference in the content of water vapor of the second synthesis gas obtained in step (e) and the content of water vapor of the first synthesis gas obtained in step (b) is at least 5 vol.% Or at least 6 vol.%, More preferably at least 7 vol % or at least 8% by volume, more preferably at least 9% by volume or at least 10% by volume, most preferably at least 1% by volume or at least 12% by volume and in particular at least 13% by volume % or at least 14% by volume. Preferably, the inventive method comprises the additional steps

(f) converting one or two stages of carbon monoxide contained in the second synthesis gas obtained in step (e) into carbon dioxide;

(g) separating carbon dioxide contained in the second synthesis gas obtained in step (f); and

(h) finally purifying the second synthesis gas obtained in step (g), preferably by methanation or nitrogen scrubbing.

Alternatively, the method according to the invention comprises the additional steps

(f) converting one or two stages of carbon monoxide contained in the second synthesis gas obtained in step (e) into carbon dioxide; and

(g ') separating a gas mixture comprising carbon monoxide, carbon dioxide and methane from the second synthesis gas by pressure swing adsorption.

If the process according to the invention comprises the pressure swing adsorption according to step (g '), carbon monoxide, carbon dioxide and methane are completely separated off from the second synthesis gas by the pressure swing adsorption. Nitrogen is only partially removed, so that sufficient nitrogen remains in the second synthesis gas in order to adjust the required H ₂ / N ₂ ratio for the ammonia synthesis can. Hydrogen is practically not separated by the pressure swing adsorption. The exhaust stream of the pressure swing adsorption can be burned for example as a fuel gas in an auxiliary boiler. If the process according to the invention also comprises separation by pressure swing adsorption in step (c), the process according to the invention comprises a total of two pressure swing adsorptions.

The measures necessary for carrying out these steps are known to the person skilled in the art. For example, reference may be made to A. Nielsen, I. Dybkjaer, Ammonia-Catalysis and Manufacture, Springer Berlin 1995, Chapter 6, pages 202-326.

The steps (a) to (h) of the process according to the invention are preferably carried out successively in time, although the provision in step (a) at least partially coincides with the first autothermal reforming in step (b). and / or according to which the provision in step (d) can be carried out at least partially simultaneously with the first autothermal reforming in step (e).

After converting carbon monoxide in step (f), separating carbon dioxide in step (g) and finally cleaning in step (h) or after separating carbon monoxide, carbon dioxide and methane in step (g ') the second synthesis gas is preferred

a content of hydrogen in the range of 40 ± 35% by volume, more preferably 40 ± 30% by volume, even more preferably 40 ± 25% by volume, most preferably 40 ± 20% by volume, and especially 40 ± 15 vol .-%; and or

a content of nitrogen in the range of 60 ± 55% by volume, more preferably 60 ± 50% by volume, even more preferably 60 ± 45% by volume, most preferably 60 ± 40% by volume, and especially 60 ± 35 Vol .-%.

The inventive method is preferably operated continuously.

The process of the present invention preferably provides a total production of more than 3300 tpd of synthesis gas (sum over the first synthesis gas and the second synthesis gas, preferably after separation in step (c) and final purification in step (h)), more preferably at least 3500 tpd Synthesis gas, more preferably at least 3800 t of syngas and in particular at least 4000 t of synthesis gas.

The first autothermal reformer preferably has a capacity of at least 1000 tpd of syngas based on the immediate, unpurified reaction product of the first autothermal reformer of step (b), more preferably at least 1500 tpd, even more preferably at least 2000 tpd, most preferably at least 2500 tato and in particular at least 3000 tpd of synthesis gas.

The second autothermal reformer preferably has a capacity of at least 1000 t of synthesis gas, based on the immediate, unpurified reaction product of the second autothermal reforming in step (e), more preferably at least 1500 t, more preferably at least 2000 t, most preferably at least 2500 tato and in particular at least 3000 tpd of synthesis gas.

Preferably, the capacity of the first autothermal reformer substantially corresponds to the capacity of the second autothermal reformer. The hydrocarbon used in step (a) and optionally additionally in step (d) of the process according to the invention is preferably natural gas, which is possibly first desulfurized. The total consumption of natural gas is preferably provided as a natural gas stream, which is preferably divided into two partial streams: the first natural gas partial stream is added in step (a) to the gas mixture, which is then reformed in step (b) in the first autothermal reformer; and the second partial gas stream is added in step (d) to the gas mixture, which is subsequently reformed in step (e) in the second autothermal reformer. In a preferred embodiment, the relative weight ratio of the first partial gas stream to the second partial gas stream is less than 1: 1, more preferably less than 1: 1.5. In another preferred embodiment, the relative weight ratio of the first partial gas stream to the second partial gas stream is greater than 1: 1, more preferably greater than 1.5: 1. In another preferred embodiment, the relative weight ratio of the first partial gas stream to the second partial gas stream is in the range of 70:30 to 30:70, more preferably 60:40 to 40:60, and most preferably 55:45 to 45:55.

Another aspect of the invention relates to a process for the production of ammonia comprising the above-described process according to the invention for the production of synthesis gas, wherein the first synthesis gas and the second synthesis gas are fed together to an ammonia reactor.

The first synthesis gas obtained in step (c) is preferably compressed without further purification using a synthesis gas compressor to a pressure at which the ammonia reactor is operated. Preferably, the ammonia reactor is operated at a pressure of at least 150 bar, more preferably at least 170 bar, even more preferably at least 190 bar, most preferably at least 210 bar and especially at least 230 bar.

The second synthesis gas obtained in step (e) is preferably purified according to the additional steps (f), (g) and (h) or according to the additional steps (f) and (g '); then precompressed with the aid of a synthesis gas compressor initially to a pressure which is lower than the pressure at which the ammonia reactor is operated; and then compressed by means of another synthesis gas compressor to a pressure at which the ammonia reactor is operated. Preferably, the second synthesis gas is first with the aid of a synthesis gas compressor at a pressure in Precompressed range of 100 ± 50 bar, more preferably 100 ± 40 bar, even more preferably 100 ± 30 bar, most preferably 100 ± 20 bar and especially 100 ± 10 bar; and then compressed using a further synthesis gas compressor to a pressure at which the ammonia reactor is operated, which is preferably at least 150 bar, more preferably at least 170 bar, more preferably at least 190 bar, most preferably at least 210 bar and in particular at least 230 bar.

The process of the present invention preferably provides a total production of more than 3300 tpd of ammonia, more preferably at least 3500 tpd, even more preferably at least 3700 tpd, most preferably at least 3900 tpd, and most preferably at least 4000 tpd of ammonia.

Another aspect of the invention relates to a device for the production of synthesis gas comprising

a first autothermal reformer for producing a first synthesis gas comprising hydrogen, carbon monoxide, carbon dioxide and methane from a gas mixture comprising hydrocarbons, water vapor and an oxidizing agent, preferably oxygen or oxygen-enriched air;

a plant for separating a gas mixture comprising carbon monoxide, carbon dioxide and methane from the first synthesis gas;

a second autothermal reformer for producing a second synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide from a gas mixture comprising carbon monoxide, carbon dioxide and methane;

Means for transferring the gaseous mixture separated from the first synthesis gas comprising carbon monoxide, carbon dioxide and methane to the second autothermal reformer;

wherein the first autothermal reformer is designed for a pressure that is higher than the pressure for which the second autothermal reformer is designed.

The device according to the invention is suitable for carrying out the process according to the invention for the production of synthesis gas. A further aspect of the invention therefore relates to the use of the apparatus according to the invention for the production of synthesis gas in the process according to the invention for the production of synthesis gas. All preferred embodiments which have been described above in connection with the method according to the invention apply analogously also with regard to the design and construction of the device according to the invention and are therefore not repeated in this regard.

Preferably, the plant for separating the gas mixture comprising carbon monoxide, carbon dioxide and methane from the first synthesis gas comprises a pressure swing adsorption plant. In a preferred embodiment, the pressure swing adsorption plant is preceded by a membrane separation plant, in which initially a large part of the carbon monoxide and carbon dioxide contained in the first synthesis gas is separated off as permeate stream. The retentate stream containing hydrogen as well as methane and uncut carbon monoxide and carbon dioxide is then fed to the pressure swing adsorption unit.

The device according to the invention preferably comprises

a desulphurisation plant for removing sulfur compounds from hydrocarbons and means for transferring the desulphurised hydrocarbons to the first autothermal reformer or a mixing plant upstream of the autothermal reformer; and or

an air separation plant and means for transferring pure oxygen or oxygen-enriched air containing at least 90% by volume of oxygen to the first autothermal reformer or a mixing plant upstream of the autothermal reformer; and or

a one or two-stage conversion system for converting carbon monoxide contained in the second synthesis gas into carbon dioxide; and or

an apparatus for separating carbon dioxide contained in the second synthesis gas; and or

a plant for separating a gas mixture comprising carbon monoxide, carbon dioxide and methane from the second synthesis gas, preferably by pressure swing adsorption; and or

a plant for the final purification of the second synthesis gas, preferably by methanation or nitrogen scrubbing. The air separation plant is preferably dimensioned so that it produces enough pure oxygen, as required in the inventive method. For the production of synthesis gas for an ammonia plant with a capacity of 3600 tpd, for example, 73 th of pure oxygen may be needed.

The sulfur compounds can be separated by conventional methods known to those skilled in the art. For example, the sulfur compounds can be separated by adsorption on activated carbon or on molecular sieves or by catalytic hydrogenation of the organic sulfur compounds and subsequent adsorption of the hydrogen sulfide formed on zinc oxide.

The device according to the invention preferably comprises

a multi-stage compressor comprising a first compression stage and a downstream second compression stage;

Means for transferring the first synthesis gas from the plant for separating the gas mixture comprising carbon monoxide, carbon dioxide and methane from the first synthesis gas to the second compression stage; and

a plant for the final purification of the second synthesis gas, preferably by methanation, pressure swing adsorption or nitrogen scrubbing, and means for transferring the finally purified second synthesis gas to the first compression stage.

Another aspect of the invention relates to an apparatus for the production of ammonia from synthesis gas comprising the inventive apparatus described above for the production of synthesis gas and an ammonia reactor.

The device according to the invention is suitable for carrying out the process according to the invention for the production of ammonia. A further aspect of the invention therefore relates to the use of the apparatus according to the invention for the production of ammonia in the process according to the invention for the production of ammonia.

The invention will be illustrated by way of example with reference to FIG. A person skilled in the art will recognize that, in the case of a device according to the invention, it is not absolutely necessary for all the imaged features to be realized simultaneously. Figure 1 illustrates schematically a device according to the invention or the inventive method for the production of ammonia from natural gas (C _n H _{2n + 2} ). The natural gas is preferably first freed from the C ₂₊ fraction and possibly desulfurized in a desulfurization plant (5). Subsequently, a first natural gas flow via line (a) to a compressor (12) is supplied, wherein the natural gas is compressed to the operating pressure of the first autothermal reformer (1). Behind the compressor (12), the natural gas stream is preferably mixed with water vapor and the mixture comprising natural gas and water vapor fed to the first autothermal reformer (1). An air separation plant (6) preferably provides pure oxygen or oxygen-enriched air, which is also supplied to the first autothermal reformer (1). The mixing of natural gas and water vapor can alternatively take place in the first autothermal reformer (1) or also outside the first autothermal reformer (1) in line (c) or in a mixing plant upstream of the first autothermal reformer (1). According to FIG. 1, first the mixing of the first natural gas stream with water vapor in line (c) takes place, followed by the addition of oxygen into the first autothermal reformer (1).

The autothermal reforming in the first autothermal reformer (1) provides a first synthesis gas, which is preferably cooled in the heat exchanger (13) and then via line (d) a system (4) for separating CO, C0 ₂ and CH _{4 is} supplied , wherein the separation of CO, C0 ₂ and CH _{4 is} preferably carried out by pressure swing adsorption. The thus purified first synthesis gas, which has an increased content of hydrogen, via line (e), preferably without further treatment, optionally after mixing with the required amount for the ammonia synthesis of compressed nitrogen, directly compression stage (1 1), which preferably forms the second stage of a multi-stage compressor, which comprises the upstream first compression stage (10) and the downstream second compression stage (1 1). From the second compression stage (11), the first synthesis gas is fed to the ammonia reactor (3).

The in Appendix (4) separated gas mixture comprising CO, C0 ₂ and CH ₄ is fed via lines (f) and (g) to the compressor (14), which is connected upstream of the second autothermal reformer (2). It is preferably first mixed with a second natural gas stream, which is introduced via line (b). The mixture of the second natural gas stream and the gas mixture comprising CO, C0 ₂ and CH ₄ is then compressed in the compressor (14) to the operating pressure of the second autothermal reformer (2). Subsequently, water vapor is added to the mixture. From the compressor (14) is the Gas mixture, possibly after preheating, the second autothermal reformer (2) supplied. Air or oxygen-enriched air is compressed in compressor (15) to the operating pressure of the second autothermal reformer (2) and also supplied to the second autothermal reformer (2). For this purpose, pure oxygen from the air separation plant (6) can be fed via line (s) directly to the second autothermal reformer (2) and / or the air upstream of the compressor (15). The mixing of natural gas, gas mixture comprising CO, C0 ₂ and CH ₄ , and water vapor can alternatively in the second autothermal reformer (2) or outside the second autothermal reformer (2) in line (m) or in a second autothermal reformer (2 ) upstream mixing plant done. According to FIG. 1, the mixing of the second natural gas stream, gas mixture comprising CO, C0 ₂ and CH ₄ , and steam in line (g) takes place first, followed by the addition of air into the second autothermal reformer (2). If the separation in Appendix (4) by pressure swing adsorption, so falls in Appendix (4) separated gas mixture comprising CO, C0 ₂ and CH ₄ at a pressure which is usually insufficient to bring it to the suction side of the compressor (14) due. In this case, an additional cycle compressor is preferably installed (not shown in Figure 1), which compresses the separated gas mixture again to the pressure of the natural gas at the plant boundary.

The autothermal reforming in the second autothermal reformer (2) provides a second synthesis gas, which is preferably cooled in the heat exchanger (16) and then via line (h) of a one- or two-stage conversion system (7) for the conversion of CO is supplied. The CO is converted with the addition of H ₂ 0 to C0 ₂ and H ₂ and in this way the content of H ₂ and C0 ₂ in the second synthesis gas further increased and the content of CO reduced. After preferential cooling in the heat exchanger (17), the converted second synthesis gas is fed via line (i) to a plant (8) for the separation of C0 ₂ , preferably using suitable chemical or physical solvents (carbon dioxide scrubbing). The second synthesis gas, which now contains only residual amounts of CO and other impurities in addition to H ₂ and N ₂ , is subjected to a final purification in a line (k) unit (9), preferably by methanation, pressure swing adsorption or N ₂ - Laundry. Subsequently, the finally purified second synthesis gas of the first compression stage (10) is supplied, in which it is precompressed before being combined with the first synthesis gas stream and the second compression stage (1 1) is supplied, from which it is supplied to the ammonia reactor (3) after compression becomes. FIG. 2 schematically illustrates a further preferred variant according to the invention of the device or of the method according to the invention for the production of ammonia from natural gas. In contrast to the embodiment illustrated in FIG. 1, after preferential cooling in the heat exchanger (17), the converted second synthesis gas is fed via line (i) to a plant (10) for separating off CO, CO ₂ and CH ₄ , the removal of CO , C0 ₂ and CH _{4 are} preferably carried out by pressure swing adsorption. The thus purified second synthesis gas is fed via line (j), preferably without further treatment, optionally after mixing with the amount of compressed nitrogen required for the ammonia synthesis, directly to the first compression stage (10).

FIG. 3 schematically illustrates a further preferred variant according to the invention of the device or of the method according to the invention for the production of ammonia from natural gas. In contrast to the embodiments illustrated in FIGS. 1 and 2, the first synthesis gas is preferably cooled in the heat exchanger (13) and then fed via line (d) to a membrane separation plant (11) for separating off CO and CO ₂ . In the membrane separation plant (11), the cooled first synthesis gas is separated into a hydrogen and methane-enriched retentate stream and a CO ₂ and C0 _2- enriched permeate stream. The permeate stream is passed via line (f) to the suction side of the compressor (14). The retentate stream is further supplied via line (o) of the plant (4) for separating CO, C0 ₂ and CH ₄ , wherein the separation of CO, C0 ₂ and CH _{4 is} preferably carried out by pressure swing adsorption. The waste gas, which is separated in Anage (4), contains predominantly methane, previously not deposited CO and C0 ₂ and in small quantities also H ₂ .

Claims

claims:

1 . Process for the production of synthesis gas comprising the steps

(a) providing a gas mixture comprising hydrocarbons, water vapor and an oxidizing agent;

(b) reforming the gas mixture provided in step (a) in a first autothermal reformer (1), thereby obtaining a first synthesis gas comprising hydrogen, carbon monoxide, carbon dioxide and methane;

(d) providing a gas mixture comprising the gas mixture separated in step (c);

(e) reforming the gas mixture provided in step (d) in a second autothermal reformer (2), thereby obtaining a second synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide;

wherein the first autothermal reformer (1) is operated in step (b) at a pressure higher than the pressure at which the second autothermal reformer (2) is operated in step (e).

2. The method of claim 1, wherein

the first autothermal reformer (1) is operated in step (b) at a pressure which is at least 10 bar higher than the pressure at which the second autothermal reformer (2) is operated in step (e); and or

the first autothermal reformer (1) is operated in step (b) at a pressure of at least 30 bar; and or

the second autothermal reformer (2) is operated in step (e) at a pressure of at most 60 bar.

3. The method according to claim 1 or 2, wherein in step (a)

the oxidant is added to the gas mixture in the form of pure oxygen or in the form of oxygen-enriched air containing at least 90% by volume of oxygen; and or the hydrocarbons in the form of methane or natural gas are added to the gas mixture; and or

the gas mixture has a molar water vapor / carbon ratio of at most 3.2; and or

the gas mixture has a content of nitrogen of at most 10% by volume.

4. The process according to any one of the preceding claims, wherein the first synthesis gas obtained in step (b)

has a molar hydrogen / carbon monoxide ratio of at most 4.5; and or

has a content of methane of at least 0.3% by volume; and / or has a hydrogen content of at least 30% by volume; and / or has a content of carbon monoxide in the range of 20 ± 19% by volume; and or

has a content of carbon dioxide in the range of 12 ± 1 1 vol .-%; and / or has a content of nitrogen of at most 10% by volume; and / or has a content of water vapor of 30 ± 29% by volume; wherein the contents are each moist concentrations.

5. The method according to any one of the preceding claims, wherein in step (c) the separation of the gas mixture

(i) by pressure swing adsorption or

(ii) by selective membrane permeation followed by pressure swing adsorption.

6. The method according to any one of the preceding claims, wherein in step (d)

is added to the gas mixture air or with oxygen-enriched air containing not more than 90% by volume of oxygen; and / or hydrocarbons are added to the gas mixture; and or

the gas mixture has a molar water vapor / carbon ratio of at least 0.2; and or the gas mixture has a content of nitrogen of at most 70% by volume.

The method of any one of the preceding claims, comprising the additional steps

(h) finally purifying the second synthesis gas obtained in step (g).

8. The method according to any one of claims 1 to 6, comprising the additional steps

9. A process for the production of ammonia comprising the process according to any one of claims 1 to 8, wherein the first synthesis gas and the second synthesis gas are fed together to an ammonia reactor (3).

10. The process according to claim 9, wherein the first synthesis gas obtained in step (c) is compressed without further purification to a pressure at which the ammonia reactor (3) is operated.

The process according to claim 9 or 10, wherein the second synthesis gas obtained in step (e) according to the additional steps (f), (g) and (h) of claim 7 or according to the additional steps (f) and (g ') is cleaned according to claim 8; thereafter first precompressed to a pressure which is lower than the pressure at which the ammonia reactor (3) is operated; and then compressed to a pressure at which the ammonia reactor (3) is operated.

12. Apparatus for producing synthesis gas comprising

a first autothermal reformer (1) for producing a first synthesis gas comprising hydrogen, carbon monoxide, carbon dioxide and methane from a gas mixture comprising hydrocarbons, oxygen and water vapor;

a plant (4) for separating a gas mixture comprising carbon monoxide, carbon dioxide and methane from the first synthesis gas; a second autothermal reformer (2) for producing a second synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide from a gas mixture comprising carbon monoxide, carbon dioxide and methane;

Means for transferring the mixed gas separated from the first synthesis gas comprising carbon monoxide, carbon dioxide and methane to the second autothermal reformer (2);

wherein the first autothermal reformer (1) is designed for a pressure which is higher than the pressure for which the second autothermal reformer (2) is designed.

13. The apparatus of claim 12, wherein the plant (4) for separating the gas mixture comprising carbon monoxide, carbon dioxide and methane from the first synthesis gas comprises a pressure swing adsorption plant.

14. The apparatus of claim 12 or 13, comprising

a desulphurisation plant (5) for removing sulfur compounds from hydrocarbons and means for transferring the desulphurised hydrocarbons to the first autothermal reformer (1) or a mixing plant upstream of the autothermal reformer; and or

an air separation plant (6) and means for transferring pure oxygen or oxygen-enriched air containing at least 90% by volume of oxygen to the first autothermal reformer (1) or a mixing plant upstream of the autothermal reformer; and or

a one or two-stage conversion unit (7) for converting carbon monoxide contained in the second synthesis gas; and or

a plant (8) for separating carbon dioxide contained in the second synthesis gas; and or

a plant (10) for separating a gas mixture comprising carbon monoxide, carbon dioxide and methane from the second synthesis gas; and or a plant (9) for the final purification of the second synthesis gas.

15. The device according to any one of claims 12 to 14, comprising

a multi-stage compressor comprising a first compression stage (10) and a downstream second compression stage (1 1);

Means for transferring the first synthesis gas from the plant (4) to the second compression stage (11); and

a plant (9) for the final purification of the second synthesis gas and means for transferring the second synthesis gas from the plant (9) to the first compression stage (10).

16. An apparatus for the production of ammonia from synthesis gas comprising the apparatus according to any one of claims 12 to 15 and an ammonia reactor (3).