DE102014209635A1 - Synthesis of synthesis gas with two autothermal reformers - Google Patents

Abstract

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

Description

The invention relates to an apparatus and a process 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 the 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, the dimensions of the apparatuses and pipelines can generally 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 increasing the pressure are not always economically viable to increase capacity.

As far as the two-stage reforming process is concerned, the steam reformer has a comparatively large share of the total construction costs due to its complexity and the great demands placed on it. In principle, a steam reformer can be considered as a parallel connection of a large number of individual tubular reactors whose individual capacity can not be significantly increased. 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 two-stage reforming is the purely autothermal reforming of natural gas with the help of cheaper autothermal reformers (ATR). In order to provide the additional 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, systems based on purely autothermal reforming have, in principle, a considerably 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, increasing the partial pressure of the carbon monoxide formed in the reforming by 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 addition of water vapor, ie the lowest possible water vapor / carbon ratio is sought for the reforming, as this allows the oxygen demand can be minimized. A smaller one Water vapor quantity 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 2004/083114 A2 discloses a method of producing 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, inter alia 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 Pat. No. 6,444,712 B1 discloses a process for producing 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.

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.

• (a) Bereitstellen eines Gasgemischs umfassend Kohlenwasserstoffe, vorzugsweise Methan oder Erdgas; Wasserdampf; und ein Oxidationsmittel, vorzugsweise Sauerstoff oder mit Sauerstoff angereicherte Luft;
• (b) Reformieren des in Schritt (a) bereitgestellten Gasgemischs in einem ersten autothermen Reformer, wodurch ein erstes Synthesegas umfassend Wasserstoff, Kohlenstoffmonoxid, Kohlenstoffdioxid und Methan erhalten wird;
• (c) Erhöhen des Gehalts an Wasserstoff des in Schritt (b) erhaltenen ersten Synthesegases durch Abtrennen eines Gasgemischs umfassend Kohlenstoffmonoxid, Kohlenstoffdioxid und Methan;
• (d) Bereitstellen eines Gasgemischs umfassend das in Schritt (c) abgetrennte Gasgemisch;
• (e) Reformieren des in Schritt (d) bereitgestellten Gasgemischs in einem zweiten autothermen Reformer, wodurch ein zweites Synthesegas umfassend Wasserstoff, Kohlenstoffmonoxid und Kohlenstoffdioxid erhalten wird;

wobei der erste autotherme Reformer in Schritt (b) bei einem Druck betrieben wird, der höher ist als der Druck, bei dem der zweite autotherme Reformer in Schritt (e) betrieben wird.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, CO 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, CO 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 fed to a second autothermal reforming and reformed here with air, possibly moderately oxygen-enriched air to a second synthesis gas. The subsequent purification of this second synthesis gas from the second autothermal reformer is then preferably carried out 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, if necessary with the amount still required to achieve the desired stoichiometry Nitrogen enriched 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-stranded process management 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 less water vapor is added, the smaller the oxygen requirement for synthesis gas production becomes. the lower the water vapor / carbon ratio is. However, it was surprisingly found in this connection that the residual content of methane in the synthesis gas after reforming in the autothermal reformer increases with lower addition of steam and at elevated pressure to values that are no longer acceptable for the overall process.

In a purely single-stranded production of synthesis gas based on a single autothermal reformer would therefore increase the capacity to increase the pressure, the steam addition can also be increased accordingly to keep the residual content of methane after reforming at the level of the conventional system and the synthesis gas compressor relieve. 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 utilized 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 takes place autothermally. 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.

• – der erste autotherme Reformer in Schritt (b) bei einem Druck betrieben, der mindestens um 5 bar, bevorzugter mindestens um 10 bar, noch bevorzugter mindestens um 15 bar, am bevorzugtesten mindestens um 20 bar und insbesondere mindestens um 25 bar höher ist als der Druck, bei dem der zweite autotherme Reformer in Schritt (e) betrieben wird; und/oder
• – der erste autotherme Reformer in Schritt (b) bei einem Druck von mindestens 30 bar betrieben, bevorzugt mindestens 35 bar oder mindestens 40 bar, bevorzugter mindestens 45 bar oder mindestens 50 bar, noch bevorzugter mindestens 55 bar oder mindestens 60 bar, am bevorzugtesten mindestens 65 bar oder mindestens 70 bar, und insbesondere mindestens 75 bar oder mindestens 80 bar; und/oder
• – der zweite autotherme Reformer in Schritt (e) bei einem Druck von höchstens 60 bar betrieben, bevorzugt höchstens 55 bar oder höchstens 50 bar, bevorzugter höchstens 45 bar oder höchstens 40 bar, noch bevorzugter höchstens 38 bar oder höchstens 36 bar, am bevorzugtesten höchstens 34 bar oder höchstens 32 bar, und insbesondere höchstens 30 bar, höchstens 28 bar, höchstens 26 bar, höchstens 24 bar, höchstens 22 bar oder höchstens 20 bar.

In the method according to the invention is preferred

• - The first autothermal reformer in step (b) operated at a pressure which is at least 5 bar, more preferably at least 10 bar, more preferably at least 15 bar, most preferably at least 20 bar and in particular at least 25 bar higher than that Pressure at which the second autothermal reformer is operated in step (e); and or
• - The first autothermal reformer in step (b) 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, 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) 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, more preferably at most 38 bar or at most 36 bar, most preferably at most 34 bar or at most 32 bar, and in particular at most 30 bar, at most 28 bar, at most 26 bar, at most 24 bar, at most 22 bar or at most 20 bar.

Preferably, the first autothermal reformer in step (b) is operated at a pressure which is 20 to 45 bar higher than the pressure at which the second autothermal reformer is operated in step (e). 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 of the first autothermal reformer would have to be operated at such high pressures at which the equilibrium position of taking place in the first autothermal reformer reaction (steam reforming) would be on the side of the reactants.

• – wird bevorzugt das Oxidationsmittel in Form von reinem Sauerstoff oder in Form von mit Sauerstoff angereicherter Luft mit einem Gehalt an Sauerstoff von mindestens 90 Vol.-%, bevorzugter mindestens 92 Vol.-%, noch bevorzugter mindestens 94 Vol.-%, am bevorzugtesten mindestens 96 Vol.-% und insbesondere mindestens 98 Vol.-% bereitgestellt, wobei der benötigte Sauerstoff vorzugsweise aus einer Luftzerlegungsanlage stammt; und/oder
• – werden bevorzugt dem Gasgemisch die Kohlenwasserstoffe in Form von Methan oder Erdgas zugesetzt, wobei das Erdgas ggf. bevorzugt zuvor entschwefelt wurde; und/oder
• – weist bevorzugt das bereitgestellte Gasgemisch ein molares Wasserdampf/Kohlenstoff-Verhältnis von höchstens 3,6, höchstens 3,4 oder höchstens 3,2 auf, bevorzugt höchstens 3,0, höchstens 2,8 oder höchstens 2,6; bevorzugter höchstens 2,4, höchstens 2,2 oder höchstens 2,0; noch bevorzugter höchstens 1,8, unter Umständen ggf. auch höchstens 1,6, höchstens 1,4, höchstens 1,2, höchstens 1,0, höchstens 0,8, höchstens 0,6, höchstens 0,4 oder höchstens 0,2; und/oder
• – weist bevorzugt das bereitgestellte Gasgemisch einen Gehalt an Stickstoff von höchstens 10 Vol.-% auf, bevorzugter höchstens 8 Vol.-%, noch bevorzugter höchstens 6 Vol.-%, am bevorzugtesten höchstens 4 Vol.-%, und insbesondere höchstens 2 Vol.-%.

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

• It is preferred that the oxidizing agent be 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 provided at least 96 vol .-% and in particular at least 98 vol .-%, wherein the required oxygen preferably originates from an air separation plant; and or
• - Are preferably added to the gas mixture, the hydrocarbons in the form of methane or natural gas, wherein the natural gas, if appropriate, preferably previously desulfurized; and or
• The gas mixture provided preferably 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; more preferably at most 1.8, possibly even at most 1.6, at most 1.4, at most 1.2, at most 1.0, at most 0.8, at most 0.6, at most 0.4 or at most 0, 2; and or
• The gas mixture provided preferably has a content of nitrogen of not more than 10% by volume, more preferably not more than 8% by volume, even more preferably not more than 6% by volume, most preferably not more than 4% by volume and in particular not more than 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 which 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. Therefore, according to the invention, a molar steam / carbon ratio of 3.2 preferably represents the upper limit of the economy. A molar steam / carbon ratio of less than 0.3 is not preferred, since otherwise carbon black would form, which would deactivate the catalyst.

• – ein molares Wasserstoff/Kohlenstoffmonoxid-Verhältnis von höchstens 4,5 auf, bevorzugt höchstens 4,2, höchstens 3,9 oder höchstens 3,6; bevorzugter höchstens 3,3, höchstens 3,0 oder höchstens 2,7; noch bevorzugter höchstens 2,4, höchstens 2,1 oder höchstens 1,8; am bevorzugtesten höchstens 1,5, höchstens 1,2 oder höchstens 1,0; und insbesondere höchstens 0,8, höchstens 0,6 oder höchstens 0,4; und/oder
• – einen Gehalt an Methan von mindestens 0,3 Vol.-% auf, bevorzugt mindestens 0,6 Vol.-%, mindestens 0,9 Vol.-% oder mindestens 1,2 Vol.-%; bevorzugter mindestens 1,5 Vol.-%, mindestens 1,8 Vol.-% oder mindestens 2,1 Vol.-%; noch bevorzugter mindestens 2,4 Vol.-%, mindestens 2,7 Vol.-% oder mindestens 3,0 Vol.-%; am bevorzugtesten mindestens 3,3 Vol.-%, mindestens 3,6 Vol.-% oder mindestens 3,9 Vol.-%; und insbesondere mindestens 4,2 Vol.-%, mindestens 4,5 Vol.-% oder mindestens 4,8 Vol.-%; und/oder
• – einen Gehalt an Wasserstoff von mindestens 30 Vol.-% auf, bevorzugt mindestens 32 Vol.-%, mindestens 34 Vol.-% oder mindestens 36 Vol.-%; bevorzugter mindestens 38 Vol.-%, mindestens 40 Vol.-% oder mindestens 42 Vol.-%; noch bevorzugter mindestens 44 Vol.-%, mindestens 46 Vol.-% oder mindestens 48 Vol.-%; am bevorzugtesten mindestens 50 Vol.-%, mindestens 52 Vol.-% oder mindestens 54 Vol.-%; und insbesondere mindestens 56 Vol.-%, mindestens 58 Vol.-% oder mindestens 60 Vol.-%; und/oder
• – einen Gehalt an Kohlenstoffmonoxid im Bereich von 20 ± 19 Vol.-% auf, bevorzugter 20 ± 16 Vol.-%, noch bevorzugter 20 ± 13 Vol.-%, am bevorzugtesten 20 ± 9 Vol.-%, und insbesondere 20 ± 5 Vol.-%; und/oder
• – einen Gehalt an Kohlenstoffdioxid im Bereich von 12 ± 11 Vol.-% auf, bevorzugter 12 ± 10 Vol.-%, noch bevorzugter 12 ± 8 Vol.-%, am bevorzugtesten 12 ± 6 Vol.-%, und insbesondere 12 ± 4 Vol.-%; und/oder
• – einen Gehalt an Stickstoff von höchstens 10 Vol.-% auf, bevorzugter höchstens 8 Vol.-%, noch bevorzugter höchstens 6 Vol.-%, am bevorzugtesten höchstens 4 Vol.-%, und insbesondere höchstens 2 Vol.-%; und/oder
• – einen Gehalt an Wasserdampf von 30 ± 29 Vol.-% auf, bevorzugter 30 ± 25 Vol.-%, noch bevorzugter 30 ± 20 Vol.-%, am bevorzugtesten 30 ± 15 Vol.-%, und insbesondere 30 ± 10 Vol.-%;

wobei die Gehaltsangaben jeweils Feuchtkonzentrationen sind.The first synthesis gas obtained in step (b) of the process according to the invention preferably has

• 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% by volume, preferably at least 0.6% by volume, at least 0.9% by volume or at least 1.2% by volume; 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%; at the 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 hydrogen content 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% by volume; and or
• A content of carbon dioxide in the range of 12 ± 11% 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 especially 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 expressly stated otherwise, all percentages in relation to gas mixtures containing water vapor are to be construed as wet concentrations.

• – einen Gehalt an Wasserstoff im Bereich von 38 bis 69 Vol.-% auf; und/oder
• – einen Gehalt an Kohlenstoffmonoxid im Bereich von 7 bis 31 Vol.-% auf; und/oder
• – einen Gehalt an Kohlenstoffdioxid im Bereich von 3 bis 19 Vol.-% auf.

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 from 38 to 69% by volume; 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% by volume.

The content of methane in the first synthesis gas can basically also be more than 4.8% by volume, in particular if a low molar steam / carbon ratio is set and a comparatively small amount of oxygen is fed to the first autothermal reformer, 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. With the help of a pressure swing adsorption (PSA) but the hydrogen can be separated at a 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, CO ₂ and CH ₄ from the first synthesis gas (i) by pressure swing adsorption (PSA - Pressure Swing Adsorption) or (ii) by selective membrane permeation and subsequent pressure swing adsorption.

In pressure swing adsorption, the gas mixture comprising H ₂ , CO, CO ₂ and CH _{4 is} physically separated from each other under pressure by 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, CO 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, CO ₂ and CH _{4 is} opened. This is accompanied by a pressure reduction. At the lower pressure, the adsorbed CO, CO ₂ and CH _{4 are} now 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 that it lets carbon monoxide and carbon dioxide through 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. The retentate stream is then fed 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 further used as fuel gas, e.g. in an auxiliary boiler for steam generation.

• – einen Gehalt an Wasserstoff von mindestens 90 Vol.-%, bevorzugter mindestens 92 Vol.-%, noch bevorzugter mindestens 94 Vol.-%, am bevorzugtesten mindestens 96 Vol.-%, und insbesondere mindestens 98 Vol.-%; und/oder
• – einen Gehalt an Stickstoff von höchstens 10 Vol.-% auf, bevorzugter höchstens 8 Vol.-%, noch bevorzugter höchstens 6 Vol.-%, am bevorzugtesten höchstens 4 Vol.-%, und insbesondere höchstens 2 Vol.-%.

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

• A hydrogen content 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, 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 CO formed for the most part 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 avoid problems with the CO conversion by the large partial pressure of the carbon monoxide. Possibly. after addition of further hydrocarbons, preferably of 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 process according to the invention thus utilizes the advantages of a higher pressure level in the first autothermal reforming, but avoids a larger methane input into the preferably subsequent ammonia synthesis and greater stress on the subsequent process stages for the purification of the synthesis gas and also allows a significant relief of the synthesis gas compressor.

• – wird bevorzugt dem Gasgemisch Luft oder mit durch Sauerstoff angereicherte Luft mit einem Gehalt an Sauerstoff von höchstens 90 Vol.-%, bevorzugter höchstens 80 Vol.-%, noch bevorzugter 70 Vol.-%, am bevorzugtesten höchstens 60 Vol.-% und insbesondere höchstens 50 Vol.-% zugesetzt; und/oder
• – werden bevorzugt dem Gasgemisch Kohlenwasserstoffe in Form von Methan oder Erdgas zugesetzt, wobei das Erdgas ggf. bevorzugt zuvor entschwefelt wurde; und/oder
• – weist bevorzugt das bereitgestellte Gasgemisch ein molares Wasserdampf/Kohlenstoff-Verhältnis von mindestens 3,2 auf, bevorzugt mindestens 3,4, mindestens 3,6 oder mindestens 3,8; bevorzugter mindestens 4,0, mindestens 4,2 oder mindestens 4,4; noch bevorzugter mindestens 4,6, mindestens 4,8 oder mindestens 5,0; am bevorzugtesten mindestens 5,2, mindestens 5,4 oder mindestens 5,6; und insbesondere mindestens 5,8, mindestens 6,0 oder mindestens 6,2; und/oder
• – weist bevorzugt das bereitgestellte Gasgemisch einen Gehalt an Stickstoff von höchstens 70 Vol.-% auf, bevorzugter höchstens 60 Vol.-%, noch bevorzugter höchstens 50 Vol.-%, am bevorzugtesten höchstens 40 Vol.-%, und insbesondere höchstens 30 Vol.-%; und/oder
• – weist bevorzugt das bereitgestellte Gasgemisch einen Gehalt an Stickstoff von mindestens 10 Vol.-% auf, bevorzugter mindestens 20 Vol.-%, noch bevorzugter mindestens 30 Vol.-%, am bevorzugtesten mindestens 40 Vol.-%, und insbesondere mindestens 50 Vol.-%.

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

• Is preferably the gas mixture air or oxygen-enriched air with an oxygen content of at most 90 vol .-%, 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 having been previously desulphurized; and or
• The gas mixture provided preferably 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
• 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 in particular not more than 30% by volume .-%; and or
• The gas mixture provided preferably has a nitrogen content of at least 10 vol. %, 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 steam / carbon ratio in the autothermal reforming in the second autothermal reformer in step (e) of the process according to the invention is preferably greater than the molar steam / carbon ratio in the autothermal reforming in the first autothermal reformer in step (b). Preferably, the relative difference of 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.

• – ein molares Wasserstoff/Kohlenstoffmonoxid-Verhältnis von höchstens 4,5 auf, bevorzugt höchstens 4,2, höchstens 3,9 oder höchstens 3,6; bevorzugter höchstens 3,3, höchstens 3,0 oder höchstens 2,7; noch bevorzugter höchstens 2,4, höchstens 2,1 oder höchstens 1,8; unter Umständen ggf. auch höchstens 1,5, höchstens 1,2, höchstens 1,0, höchstens 0,8, höchstens 0,6 oder höchstens 0,4; und/oder
• – einen Gehalt an Methan von höchstens 10 Vol.-%, höchstens 7,5 Vol.-%, höchstens 5,0 Vol.-% oder höchstens 4,8 Vol.-% auf, bevorzugt höchstens 4,5 Vol.-%, höchstens 4,2 Vol.-% oder höchstens 3,9 Vol.-%; bevorzugter höchstens 3,6 Vol.-%, höchstens 3,3 Vol.-% oder höchstens 3,0 Vol.-%; noch bevorzugter höchstens 2,7 Vol.-%, höchstens 2,4 Vol.-% oder höchstens 2,1 Vol.-%; am bevorzugtesten höchstens 1,8 Vol.-%, höchstens 1,5 Vol.-% oder höchstens 1,2 Vol.-%; und insbesondere höchstens 0,9 Vol.-%, höchstens 0,6 Vol.-% oder höchstens 0,3 Vol.-%; und/oder
• – einen Gehalt an Wasserstoff von mindestens 50 Vol.-% auf, bevorzugt mindestens 52 Vol.-%, mindestens 54 Vol.-% oder mindestens 56 Vol.-%; bevorzugter mindestens 58 Vol.-%, mindestens 60 Vol.-% oder mindestens 62 Vol.-%; noch bevorzugter mindestens 64 Vol.-%, mindestens 66 Vol.-% oder mindestens 68 Vol.-%; am bevorzugtesten mindestens 70 Vol.-%, mindestens 72 Vol.-% oder mindestens 74 Vol.-%; und insbesondere mindestens 76 Vol.-%, mindestens 78 Vol.-% oder mindestens 80 Vol.-%; und/oder
• – einen Gehalt an Kohlenstoffmonoxid im Bereich von 20 ± 19 Vol.-% auf, bevorzugter 20 ± 16 Vol.-%, noch bevorzugter 20 ± 13 Vol.-%, am bevorzugtesten 20 ± 9 Vol.-%, und insbesondere 20 ± 5 Vol.-%; und/oder
• – einen Gehalt an Kohlenstoffdioxid im Bereich von 12 ± 11 Vol.-% auf, bevorzugter 12 ± 10 Vol.-%, noch bevorzugter 12 ± 8 Vol.-%, am bevorzugtesten 12 ± 6 Vol.-%, und insbesondere 12 ± 4 Vol.-%; und/oder
• – einen Gehalt an Stickstoff von höchstens 10 Vol.-% auf, bevorzugter höchstens 8 Vol.-%, noch bevorzugter höchstens 6 Vol.-%, am bevorzugtesten höchstens 4 Vol.-%, und insbesondere höchstens 2 Vol.-%; und/oder
• – einen Gehalt an Wasserdampf von 40 ± 30 Vol.-% auf, bevorzugter 40 ± 25 Vol.-%, noch bevorzugter 40 ± 20 Vol.-%, am bevorzugtesten 40 ± 15 Vol.-%, und insbesondere 40 ± 10 Vol.-%;

wobei die Gehaltsangaben jeweils Feuchtkonzentrationen sind.The second synthesis gas obtained in step (e) of the process according to the invention preferably has

• 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 at most 4.2% by volume or at most 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 vol%, at most 1.5 vol% or at most 1.2 vol%; and in particular at most 0.9 vol.%, at most 0.6 vol.% or at most 0.3 vol.%; 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 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% by volume; and or
• A content of carbon dioxide in the range of 12 ± 11% 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 especially 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.

• – einen Gehalt an Wasserstoff im Bereich von 38 bis 69 Vol.-% auf; und/oder
• – einen Gehalt an Kohlenstoffmonoxid im Bereich von 7 bis 31 Vol.-% auf; und/oder
• – einen Gehalt an Kohlenstoffdioxid im Bereich von 3 bis 19 Vol.-% auf.

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

• A content of hydrogen in the range from 38 to 69% by volume; 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% by volume.

In particular, if the subsequent purification of the second synthesis gas is not carried out by CO ₂ scrubbing and methanation, but by pressure swing adsorption or N ₂ scrubbing, thereby the residual methane can be separated from the second syngas with synonymous. 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 the subsequent purification of the second synthesis gas, however, by CO ₂ scrubbing and methanation, so the content of methane in the second synthesis gas is preferably below 5 vol .-%.

A comparatively high content of water vapor in the second synthesis gas is preferred so that sufficient steam is available for the preferably subsequent high-temperature conversion of carbon monoxide. 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 more oxygen would be required, which would adversely affect the yield of hydrogen ,

The residual content of methane in the first synthesis gas, which is obtained during 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 ). 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.% 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 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 ). 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 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.% 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 steam 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 ). 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 11% by volume or at least 12% by volume and in particular at least 13% by volume or at least 14% by volume.

• (f) ein- oder zweistufiges Konvertieren von Kohlenstoffmonoxid, welches in dem in Schritt
• (e) erhaltenen zweiten Synthesegas enthalten ist, zu Kohlenstoffdioxid;
• (g) Abtrennen von Kohlenstoffdioxid, welches in dem in Schritt (f) erhaltenen zweiten Synthesegas enthalten ist; und
• (h) abschließendes Reinigen des in Schritt (g) erhaltenen zweiten Synthesegases vorzugsweise durch Methanisierung oder Stickstoffwäsche.

The method according to the invention preferably comprises the additional steps

• (f) one or two step conversion of carbon monoxide, which is in the step
• (e) obtained second synthesis gas is included, to 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.

• (f) ein- oder zweistufiges Konvertieren von Kohlenstoffmonoxid, welches in dem in Schritt
• (e) erhaltenen zweiten Synthesegas enthalten ist, zu Kohlenstoffdioxid; und
• (g') Abtrennen eines Gasgemischs umfassend Kohlenstoffmonoxid, Kohlenstoffdioxid und Methan vom zweiten Synthesegas durch Druckwechsel-Adsorption.

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

• (f) one or two step conversion of carbon monoxide, which is in the step
• (e) obtained second synthesis gas is included, to 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. In this regard, 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 method according to the invention are preferably carried out in succession, although the provision in step (a) at least partially coincides with the first autothermal reforming in step (b) and / or according to the provision in step (a). d) at least partially simultaneously with the first autothermal reforming in step (e) can be performed.

• – einen Gehalt an Wasserstoff im Bereich von 40 ± 35 Vol.-% auf, bevorzugter 40 ± 30 Vol.-%, noch bevorzugter 40 ± 25 Vol.-%, am bevorzugtesten 40 ± 20 Vol.-%, und insbesondere 40 ± 15 Vol.-%; und/oder
• – einen Gehalt an Stickstoff im Bereich von 60 ± 55 Vol.-% auf, bevorzugter 60 ± 50 Vol.-%, noch bevorzugter 60 ± 45 Vol.-%, am bevorzugtesten 60 ± 40 Vol.-%, und insbesondere 60 ± 35 Vol.-%.

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

• A content of hydrogen in the range of 40 ± 35% by volume, more preferably 40 ± 30% by volume, more preferably 40 ± 25% by volume, most preferably 40 ± 20% by volume, and especially 40 ± 15% by volume; and or
• A content of nitrogen in the range of 60 ± 55% by volume, more preferably 60 ± 50% by volume, more preferably 60 ± 45% by volume, most preferably 60 ± 40% by volume, and especially 60 ± 35% by volume.

The process according to the invention is preferably operated continuously. The process of the present invention preferably provides a total production of more than 3300 tpd of synthesis gas (total 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 synthesis gas 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, more preferably at least 2000 tpd, most preferably at least 2500 tpd, and especially At least 3000 tpd of syngas.

The second autothermal reformer preferably has a capacity of at least 1000 tpd of syngas based on the instant, unpurified reaction product of the second autothermal reforming in step (e), more preferably at least 1500 tpd, even more preferably at least 2000 tpd, most preferably at least 2500 tpd, and especially At least 3000 tpd of syngas.

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 optionally 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.

A further 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.

Preferably, the first synthesis gas obtained in step (c) is compacted without further purification with the aid of 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 at a pressure in the range using a syngas compressor precompressed from 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 tpc of ammonia, more preferably at least 3500 tpd, even more preferably at least 3700 tpd, most preferably at least 3900 tpd and especially at least 4000 tpd of ammonia.

• – einen ersten autothermen Reformer zum Herstellen eines ersten Synthesegases umfassend Wasserstoff, Kohlenstoffmonoxid, Kohlenstoffdioxid und Methan aus einem Gasgemisch umfassend Kohlenwasserstoffe, Wasserdampf und ein Oxidationsmittel, vorzugsweise Sauerstoff oder mit Sauerstoff angereicherte Luft;
• – eine Anlage zum Abtrennen eines Gasgemischs umfassend Kohlenstoffmonoxid, Kohlenstoffdioxid und Methan von dem ersten Synthesegas;
• – einen zweiten autothermen Reformer zum Herstellen eines zweiten Synthesegases umfassend Wasserstoff, Kohlenstoffmonoxid und Kohlenstoffdioxid aus einem Gasgemisch umfassend Kohlenstoffmonoxid, Kohlenstoffdioxid und Methan;
• – Mittel zum Überführen des von dem ersten Synthesegas abtrennten Gasgemischs umfassend Kohlenstoffmonoxid, Kohlenstoffdioxid und Methan zu dem zweiten autothermen Reformer;

wobei der erste autotherme Reformer für einen Druck ausgelegt ist, der höher ist als der Druck, für den der zweite autotherme Reformer ausgelegt ist.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 separated from the first synthesis gas gas mixture 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 were 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 respect.

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.

• – eine Entschwefelungsanlage zum Entfernen von Schwefelverbindungen aus Kohlenwasserstoffen und Mittel zum Überführen der entschwefelten Kohlenwasserstoffe zum ersten autothermen Reformer oder einer dem autothermen Reformer vorgeschalteten Mischanlage; und/oder
• – eine Luftzerlegungsanlage und Mittel zum Überführen von reinem Sauerstoff oder von mit Sauerstoff angereicherter Luft mit einem Gehalt an Sauerstoff von mindestens 90 Vol.-% zum ersten autothermen Reformer oder einer dem autothermen Reformer vorgeschalteten Mischanlage; und/oder
• – eine ein- oder zweistufige Konvertierungsanlage zur Konvertierung von Kohlenstoffmonoxid, welches in dem zweiten Synthesegas enthalten ist, zu Kohlenstoffdioxid; und/oder
• – eine Anlage zur Abtrennung von Kohlenstoffdioxid, welches in dem zweiten Synthesegas enthalten ist; und/oder
• – eine Anlage zum Abtrennen eines Gasgemischs umfassend Kohlenstoffmonoxid, Kohlenstoffdioxid und Methan von dem zweiten Synthesegas, vorzugsweise durch Druckwechsel-Adsorption; und/oder
• – eine Anlage zur abschließenden Reinigung des zweiten Synthesegases, vorzugsweise durch Methanisierung oder Stickstoffwäsche.

The device according to the invention preferably comprises

• - A desulfurization plant for removing sulfur compounds from hydrocarbons and means for transferring the desulfurized hydrocarbons to the first autothermal reformer or upstream of the autothermal reformer mixing plant; and or
• - An air separation plant and means for transferring pure oxygen or oxygen-enriched air containing at least 90 vol .-% of oxygen to the first autothermal reformer or upstream of the autothermal reformer mixing plant; and or
• A one- or two-stage conversion plant for converting carbon monoxide contained in the second synthesis gas into carbon dioxide; and or
• - An apparatus for the separation of carbon dioxide, which is contained in the second synthesis gas; and or
• A system for separating a gas mixture comprising carbon monoxide, carbon dioxide and methane from the second synthesis gas, preferably by pressure swing adsorption; and or
• - An installation 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 method according to the invention. For example, the production of synthesis gas for an ammonia plant with a capacity of 3600 tpd requires 73 t / h of pure oxygen.

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

• – einen mehrstufigen Verdichter umfassend eine erste Verdichtungsstufe und eine nachgeschaltete zweite Verdichtungsstufe;
• – Mittel zum Überführen des ersten Synthesegases aus der Anlage zum Abtrennen des Gasgemischs umfassend Kohlenstoffmonoxid, Kohlenstoffdioxid und Methan von dem ersten Synthesegas zur zweiten Verdichtungsstufe; und
• – eine Anlage zur abschließenden Reinigung des zweiten Synthesegases, vorzugsweise durch Methanisierung, Druckwechsel-Adsorption oder Stickstoffwäsche, und Mittel zum Überführen des abschließend gereinigten zweiten Synthesegases zur ersten Verdichtungsstufe.

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 is based on the 1 exemplified. 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.

1 schematically illustrates 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 optionally in a desulfurization plant ( 5 ) desulfurizes. Subsequently, a first natural gas flow via line (a) to a compressor ( 12 ), wherein the natural gas to the operating pressure of the first autothermal reformer ( 1 ) is compressed. Behind the compressor ( 12 ) the natural gas stream is preferably mixed with water vapor and the mixture comprising natural gas and water vapor is the first autothermal reformer ( 1 ). An air separation plant ( 6 ) preferably provides pure oxygen or oxygen-enriched air, which is also the first autothermal reformer ( 1 ) is supplied. The mixing of natural gas and water vapor can alternatively in the first autothermal reformer ( 1 ) or outside the first autothermal reformer ( 1 ) in line (c) or in a first autothermal reformer ( 1 ) upstream mixing plant done. According to 1 First, the mixing of the first natural gas stream with water vapor in line (c) and then the addition of oxygen in the first autothermal reformer ( 1 ).

The autothermal reforming in the first autothermal reformer ( 1 ) provides a first synthesis gas, which is preferably in the heat exchanger ( 13 ) and then via line (d) of a plant ( 4 ) is supplied to separate CO, CO ₂ and CH ₄ , wherein the separation of CO, CO 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 for the ammonia synthesis amount of compressed nitrogen, direct compression stage ( 11 ), 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 ( 11 ). From the second compression level ( 11 ), the first synthesis gas is added to the ammonia reactor ( 3 ).

The Annex to 4 ) separated gas mixture comprising CO, CO ₂ and CH ₄ is via lines (f) and (g) the compressor ( 14 ), which is the second autothermal reformer ( 2 ) is connected upstream. 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, CO ₂ and CH ₄ is then in the compressor ( 14 ) to the operating pressure of the second autothermal reformer ( 2 ) compacted. Subsequently, water vapor is added to the mixture. From the compressor ( 14 ), the gas mixture, possibly after preheating, the second autothermal reformer ( 2 ). Air or oxygen enriched air is injected into the compressor ( 15 ) to the operating pressure of the second autothermal reformer ( 2 ) and also the second autothermal reformer ( 2 ). Pure oxygen from the air separation plant ( 6 ) via line (s) directly to the second autothermal reformer ( 2 ) and / or the air in front of the compressor ( 15 ). The mixing of natural gas, gas mixture comprising CO, CO 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 1 First, the mixing of the second natural gas stream, gas mixture comprising CO, CO ₂ and CH ₄ , and Steam in line (g) and then the addition of air into the second autothermal reformer ( 2 ). If the separation is in Annex ( 4 ) by pressure swing adsorption, this is in Appendix ( 4 ) separated gas mixture comprising CO, CO ₂ and CH ₄ at a pressure which is usually insufficient to bring it to the suction side of the compressor ( 14 ). In this case, an additional cycle compressor is preferably installed (in 1 not shown), which compresses the separated gas mixture back 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 in the heat exchanger ( 16 ) and then via line (h) of a one- or two-stage conversion plant ( 7 ) is supplied for the conversion of CO. The CO is converted to CO ₂ and H ₂ with the addition of H ₂ O and in this way the content of H ₂ and CO ₂ in the second synthesis gas is further increased and the CO content is reduced. After preferential cooling in the heat exchanger ( 17 ), the converted second synthesis gas is passed via line (i) of an installation ( 8th ) for the removal of CO 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 in an over line (k) plant ( 9 ) subjected to a final purification, preferably by methanation, pressure swing adsorption or N ₂ scrubbing. Subsequently, the finally purified second synthesis gas of the first compression stage ( 10 ) in which it is precompressed before it is combined with the first synthesis gas stream and the second compression stage ( 11 ) is supplied from which it after compression to the ammonia reactor ( 3 ) is supplied.

2 schematically illustrates a further preferred variant according to the invention of the device or the method according to the invention for the production of ammonia from natural gas. Unlike the in 1 illustrated embodiment, the converted second synthesis gas after preferential cooling in the heat exchanger ( 17 ) via line (i) of a plant ( 10 ) is supplied to separate CO, CO ₂ and CH ₄ , wherein the separation of CO, CO ₂ and CH _{4 is} preferably carried out by pressure swing adsorption. The second synthesis gas purified in this way is purified via line (j), preferably without further treatment, if appropriate after mixing with the amount of compressed nitrogen required for the ammonia synthesis, directly in the first compression stage ( 10 ).

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

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

• WO 2004/083114 [0008]
• EP 0999178 A1 [0009]
• US 6444712 B1 [0010]
• US 2013312384 A1 [0011]

Cited non-patent literature

• A. Nielsen, I. Dybkjaer, Ammonia Catalysis and Manufacture, Springer Berlin 1995, Chapter 6, pages 202-326 [0054]

Claims (16)

A process for producing synthesis gas comprising the steps of (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 ), whereby a first synthesis gas comprising hydrogen, carbon monoxide, carbon dioxide and methane is obtained; (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 ( 2 ), whereby a second synthesis gas comprising hydrogen, carbon monoxide and carbon dioxide is obtained; the first autothermal reformer ( 1 ) is operated in step (b) at a pressure which is higher than the pressure at which the second autothermal reformer ( 2 ) is operated in step (e). 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. The method of claim 1 or 2, wherein in step (a) - the oxidizing agent 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 - added to the gas mixture, the hydrocarbons in the form of methane or natural gas; 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 vol .-%. 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 vol .-%; and or - Has a content of hydrogen of at least 30 vol .-%; and or - Has a content of carbon monoxide in the range of 20 ± 19 vol .-%; and or - Has a content of carbon dioxide in the range of 12 ± 11 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 vol .-%; wherein the contents are each moist concentrations. The process 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. The method according to any one of the preceding claims, wherein in step (d) - air is added to the gas mixture or 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 vol .-%. The method of any one of the preceding claims comprising 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). The method of any of claims 1 to 6, comprising 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. A process for producing ammonia comprising the process according to any one of claims 1 to 8, wherein the first synthesis gas and the second synthesis gas together an ammonia reactor ( 3 ). 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 additional steps (f), (g) and (h) according to claim 7 or according to the additional steps (f) and (g ') according to Claim 8 is cleaned; is then 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. 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; - an annex ( 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 gas mixture separated from the first synthesis gas comprising carbon monoxide, carbon dioxide and methane to the second autothermal reformer ( 2 ); 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. The device according to claim 12, wherein the system ( 4 ) for separating the gas mixture comprising carbon monoxide, carbon dioxide and methane from the first synthesis gas comprises a pressure swing adsorption plant. The apparatus according to claim 12 or 13, comprising - a desulphurisation plant ( 5 ) for removing sulfur compounds from hydrocarbons and means for transferring the desulfurized hydrocarbons to the first autothermal reformer ( 1 ) or an upstream of the autothermal reformer mixing plant; 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 an upstream of the autothermal reformer mixing plant; and / or a one or two-stage conversion system ( 7 to convert carbon monoxide contained in the second synthesis gas; and / or - an attachment ( 8th ) for separating carbon dioxide contained in the second synthesis gas; and / or - an attachment ( 10 ) for separating a gas mixture comprising carbon monoxide, carbon dioxide and methane from the second synthesis gas; and / or - an attachment ( 9 ) for final purification of the second synthesis gas. The apparatus 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 ( 11 ); - means for transferring the first synthesis gas from the plant ( 4 ) to the second compression stage ( 11 ); and - a facility ( 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 consolidation stage ( 10 ). 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 ).

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