WO2018069173A1

WO2018069173A1 - Process for producing ammonia from a nitrogen- and hydrogen-containing process gas mixture

Info

Publication number: WO2018069173A1
Application number: PCT/EP2017/075456
Authority: WO
Inventors: Joachim Johanning; Evgeni Gorval; Christiane Potthoff
Original assignee: Thyssenkrupp Industrial Solutions Ag; Thyssenkrupp Ag
Priority date: 2016-10-12
Filing date: 2017-10-06
Publication date: 2018-04-19
Also published as: DE102016219850A1; EP3526166A1

Abstract

The present invention relates to a process for removing nitrogen and optionally further gas components having a relatively high molecular weight from an essentially nitrogen- and hydrogen-containing process gas mixture for ammonia synthesis, wherein according to the invention the removal of nitrogen and optionally further gas components of relatively high molecular weight is effected by means of at least one centrifugal separator (23). While the previously employed large industrial scale processes for removing nitrogen from air for producing pure oxygen or from synthesis gas for establishing a suitable hydrogen-nitrogen ratio for ammonia synthesis are based predominantly on the principle of low-temperature distillation, the concept proposed with the present invention is based on utilizing the markedly different molecular weights of the components of the synthesis gas in ammonia plants to separate them in a centrifugal field. Since in this way an excess of nitrogen may be removed from the process gas mixture in cost-effective fashion a secondary reformer (13) may be operated with an excess of air and the overall process optimized.

Description

Process for producing ammonia from a nitrogen and hydrogen-containing process gas mixture

The present invention relates to a process for the production of ammonia from a nitrogen and hydrogen-containing process gas mixture which contains at least one further gas component having a higher molecular weight than hydrogen, which is separated from the process gas mixture in at least one separation step.

It is known from US Pat. No. 3,643,452 A to obtain a lighter gas such as hydrogen or helium in greater purity from a gas mixture with other gases containing this light gas, passing the gas mixture through a rotating gas centrifuge. When a gas mixture of hydrogen and nitrogen is introduced into the central region of a centrifuge, the heavier nitrogen accumulates in the peripheral region of the centrifuge, whereas the hydrogen content in the edge region is only relatively small. The separation process is carried out at low temperature and elevated pressure so that the gas mixture is initially above its dew point, but passes through the dew point as it flows through the centrifugal force to the peripheral wall of the centrifuge. Gaseous impurities are condensed and the light gas is recovered in increased purity. The known method is used for industrial processes in which hydrogen is needed in high purity, for example for the hydrogenation of fats and oils.

For the production of synthesis gas for the production of ammonia, the steam reforming of natural gas is mainly used today because of their economic advantages. The conversion of hydrocarbons in natural gas with steam to carbon monoxide and hydrogen is a highly endothermic process, which in addition only at high temperatures of approx. 800 ° C to approx. 1000 ° C and relatively high pressures of over 30 bar economically usable conversion rates or yields.

In order to meet the energy needs of the process, a portion of the natural gas must be completely oxidized, i. converted to carbon dioxide and water. In today's dominant ammonia process with two-stage steam reforming, most of the full oxidation takes place under atmospheric conditions with ambient air. The resulting heat must be transferred by convection and conduction over metallic pipe walls to the usually high-pressure process gas, the natural gas / steam mixture. The primary reformer contained in the ammonia plant works at the limit of material-technical possibilities and is a correspondingly expensive and sensitive component. With the heat supplied, the primary reformer converts about two-thirds of the hydrocarbons fed with the natural gas / vapor mixture to crude synthesis gas.

The remaining part of the natural gas is converted into a downstream secondary reformer. The heat required for this purpose is provided in-process (autotherm) by partial oxidation of the process gas itself. Here one uses the nitrogen requirement of the ammonia production and leads the Process gas to a corresponding amount of air. Due to the given oxygen content of the air, the ratio of the gap performance of the two reformers is fixed.

The secondary reformer is much simpler in terms of its design than the primary reformer and its procurement costs are considerably less expensive. It has therefore been lacking in the past approaches to increase the cleavage performance of the secondary reformer at the expense of the primary reformer to eliminate the primary reformer in the extreme case and ideally provide a purely autothermal reforming. However, this requires a correspondingly greater oxygen addition to the secondary reformer or autothermal reformer. This can be realized only by a larger amount of air or a larger Sa uergstoffg content in the supplied oxygen / nitrogen mixture.

Since the ammonia synthesis requires a largely stoichiometric hydrogen / nitrogen ratio of about 3: 1, when operating with excess air, the unneeded nitrogen must be removed from the process gas again. According to the prior art, both cryogenic processes, which condense the nitrogen at low temperatures of about -180 ° C., and pressure swing adsorptions, in which the nitrogen is retained in suitable adsorbents, are available for this purpose.

The apparatus implementation of these methods is very complex and correspondingly expensive. In addition, there are moderate additional costs for the larger equipment, due to the somewhat larger amount of process gas in all apparatuses of synthesis gas production. The ammonia synthesis plants built according to this process concept have not proven to be significantly less expensive than the plants that use stoichiometric air addition in the secondary reformer.

A greater oxygen content in the supplied oxygen / nitrogen mixture requires air separation. This is also a very expensive unit. In addition, the air separation has a significant power requirement, which has no counterpart in the conventional ammonia plant. In principle, an ammonia plant with integrated air separation has a slightly higher specific energy consumption than a plant based on conventional two-stage reforming.

The investigations carried out so far show that such plants will only become economically competitive at capacities above 4,000 tpd (tonnes per day) of ammonia. In principle, cryogenic distillation and pressure swing adsorption are also used for air separation. However, at the levels of oxygen required for today's ammonia production plants, cryogenic distillation is the more economically advantageous process.

There is thus a need for a more cost effective method of separating the excess nitrogen from the process gas for ammonia synthesis. The object of the present invention is to provide a more effective and less expensive process for the separation of nitrogen and optionally further gas components with a higher molecular weight from a process gas mixture for ammonia synthesis available.

The solution to this problem provides a process according to the invention for the production of ammonia from a nitrogen and hydrogen-containing process gas mixture, in which a separation of nitrogen and optionally further gas components with a higher molecular weight from the process gas mixture is provided with the features of claim 1.

According to the invention it is provided that the separation of nitrogen and optionally further gas components with higher molecular weight by means of at least one centrifugal separator takes place.

Preferably, only an excess of nitrogen is removed from the process gas mixture, which goes beyond the necessary for the ammonia synthesis stoichiometric ratio of 3: 1 (hydrogen to nitrogen).

While the hitherto used large-scale processes for the separation of nitrogen from air to produce pure oxygen or synthesis gas to set the correct hydrogen-nitrogen ratio for the ammonia synthesis mainly based on the principle of cryogenic distillation, by taking advantage of the differences in the evaporation temperatures To bring the species involved in different phases and thus easier to separate, the concept proposed by the present invention is based on exploiting the significantly different molecular weights of the components of the synthesis gas in ammonia plants in order to separate them in a centrifugal force field. Synthesis gas for ammonia production from the steam reforming of natural gas consists of the main components hydrogen and nitrogen, the educts of the ammonia formation reaction, a significant proportion of carbon dioxide and residual contents of methane, carbon monoxide and argon.

Hydrogen has a very low molecular weight of only about 2 kg / kmol, while nitrogen has a ca. 28 kg / kmol. In the gas phase, all molecules occupy the same space, ie. Due to the low molecular weight, hydrogen has a correspondingly low density and experiences significant buoyancy in a heavy gas environment. In a force field of relatively high acceleration, as can be realized, for example, in a cyclone or in a rotating centrifuge, the heavy gas components preferably accumulate in the outer region, since they displace the lighter hydrogen molecules toward the inner radius. By controlled discharge of a portion of the gas flow from the outside area can be removed with this concept, the excess nitrogen - together with at least a portion of the other gas components - from the process gas. The other gas components are invariably undesirable in the ammonia synthesis, since they at least deteriorate the conditions of synthesis, in the case of the oxygen-carrying species even act as catalyst poisons. These components are therefore limited in the synthesis gas production of ammonia plants usually technically / economically acceptable residual levels, optionally removed. Since these components invariably have larger molecular weights than hydrogen (carbon dioxide about 44 kg / kmol, carbon monoxide about 28 kg / kmol, methane about 16 kg / kmol, argon about 44 kg / kmol) they are used in the centrifugal separation method according to the invention also separated with the nitrogen stream.

The procedural implementation of the concept proposed here envisages integrating a separation stage based on the centrifugal force principle into the process gas path of the ammonia plant in the manner illustrated in the appended FIGS. 1 and 2 and removing the nitrogen from the process gas path which has been added more than stoichiometrically in the secondary reformer with the process air , In Figures 1 and 2, the basic arrangement possibilities of such a separation stage are shown, both of which each have specific advantages.

According to a preferred development of the present invention, a circular or spiral tube, a cyclone separator or a centrifuge is provided as centrifugal separator, in which the process gas mixture to be separated is exposed to a high acceleration, so that the heavy gas components accumulate in a radially outer region and are separated there can be. Centrifuges are dynamic devices with rotating components, said spiral tube and the cyclone separator, however, are static separation devices without rotational drive and therefore operate at a particularly low cost.

Preferably, according to the present invention, the centrifugal separator, the process gas mixture is supplied via an infeed pipe and preferably via an inlet nozzle.

Preferably, the process gas mixture is accelerated in the centrifugal separator to a defined speed and then guided on a circular path or spiral path, the radius of the circular path or spiral path and the gas velocity in the main flow direction are dimensioned so that the required for the separation centrifugal acceleration.

Furthermore, according to a preferred variant of the method, the process gas mixture is separated in the centrifugal separator by baffles, partitions and / or channels in different gas components.

According to a preferred embodiment of the method, at least excess nitrogen and carbon dioxide are separated in the centrifugal separator. According to a preferred development of the process according to the invention, carbon dioxide which is obtained, which has been enriched in nitrogen and carbon dioxide, is then separated off, preferably in a CGy absorber. The gas mixture obtained after the separation of carbon dioxide, which contains nitrogen and hydrogen radicals, can then be returned, for example via a residual gas line to the primary reformer and used there for heating, ie for providing the heat of reaction.

An alternative variant of the invention provides that at least excess nitrogen is separated off in the centrifugal separator. Before introducing the gas mixture into the centrifugal separator or after flowing through the centrifugal separator, at least partially carbon dioxide can be separated from the gas mixture in at least one further separating device in this variant.

In all process variants, in addition to nitrogen and carbon dioxide in the centrifugal separator, other heavy gases contained in the gas mixture, such as argon or carbon monoxide can be separated with. The separation of carbon monoxide is particularly advantageous because less methane is then formed during the methanation. Likewise, the separation of argon is advantageous. Upon separation of these two gas components in the centrifugal separator may later turn out the purge lower. This can increase the ammonia capacity of the plant and / or reduce their energy requirements.

A preferred development of the method according to the invention provides that the gas stream depleted of nitrogen and carbon dioxide after separation in the centrifugal separator flows through at least one further separation device and / or conversion device in which further separation of carbon dioxide or separation of carbon monoxide occurs before this gas flow the ammonia synthesis is supplied. As at least one further separation device, for example, a CGyAbsorber into consideration, by means of which C0 ₂ can be separated from the process gas mixture. Furthermore, alternatively or additionally, a methanation stage can be provided, by means of which it is possible in particular to separate off carbon monoxide which is a catalyst poison in the subsequent ammonia synthesis and which is converted to methane in the methanation by reaction with hydrogen.

According to a preferred embodiment of the method according to the invention, an H ₂ recovery takes place from a purge gas stream derived from the ammonia synthesis, wherein preferably a recycling of the recovered hydrogen to the input-side process gas mixture is provided for the production of ammonia.

Preferably, in the process according to the invention, the process gas mixture flows through at least one primary reformer and at least one secondary reformer before the separation step in the centrifugal separator, optionally only an autothermal reformer and / or at least one CO converter and / or at least one water separator. Come as a CO converter For example, high-temperature CO converter and / or low-temperature CO converter or optionally medium temperature CO converter into consideration. The separation device according to the invention for the separation of gases of higher molecular weight such as nitrogen, carbon monoxide and carbon dioxide by centrifugal separation is thus preferably incorporated into a process by means of which natural gas by reforming with steam, a suitable for ammonia synthesis Rohsynthesegas is obtained, which then in the further process in can advantageously be separated by centrifugal separation of excess nitrogen and other components of higher molecular weight.

A further advantage of the present invention is that more methane is burned from the process gas during operation of the secondary reformer with excess air. This increases the CGy component compared to the N ₂ component. In the hitherto customary, stoichiometric operation of the secondary reformer is obtained for the downstream urea plant always less C0 ₂ than would be required for the complete conversion of the entire ammonia to urea. When operating the secondary reformer with excess air, not only can the primary reformer be relieved, but the system network can also be optimized towards a so-called "balanced plant".

The present invention further relates to a plant for the treatment of a process gas mixture for ammonia synthesis comprising at least one ammonia synthesis reactor in which the synthesis of ammonia from a nitrogen and hydrogen-containing process gas, and at least one ammonia synthesis reactor upstream in the flow path separating device for separating at least one gas component from the Process gas, wherein at least one centrifugal separator is provided as a separator for the separation of excess nitrogen and optionally other gas components with higher molecular weight.

Preferably, according to a further development of the invention, this system further comprises at least one primary reformer connected upstream of the centrifugal separator in the flow path and at least one secondary reformer connected downstream of the primary reformer and upstream of the centrifugal separator. In the two reformers, the natural gas is first split with steam (steam reforming). In a further preferred embodiment of the method according to the invention can be dispensed with the primary reformer with external heating entirely and the entire reforming be made by an autothermal reformer.

The system according to the invention further comprises, according to a preferred development, at least one high-temperature CO converter upstream of the centrifugal separator in the flow path and at least one low-temperature CO converter upstream of the centrifugal separator in the flow path, optionally alternatively a medium-temperature CO converter. The CO conversion step uses a portion of the unwanted CO in the cleavage gas to produce H ₂ product. In the flow path after the CO conversion, for example, a separation device can follow, in which water is separated from the process gas stream. Following this separation device, for example, the centrifugal separator according to the invention may be provided to separate nitrogen and other components with a higher molecular weight compared to hydrogen.

Before the separation of nitrogen by centrifugal separation but according to a variant of the invention, a separate separate separation device for a separation of C0 ₂ may be provided, for example, a CGyAbsorber.

Alternatively, however, at least one further separating device or conversion device for separating off or converting carbon dioxide or carbon monoxide in the flow path behind the nitrogen separation by centrifugal separation can also be located, for example. These may be, for example, a CGy absorber for the C0 ₂ separation and a methanation stage for a conversion of CO into methane.

With regard to the lower investment costs and the greater reliability in operation, the apparatus realization of the concept according to the invention primarily provides for the centrifugal force separation to be carried out in a static separation apparatus. The flow of the process gas is accelerated, for example, from the supplying pipe by means of an inlet nozzle and a corresponding static pressure difference to the required speed and then guided on a circular path. The radius of the circular path is dimensioned such that the centrifugal acceleration required for the separation occurs.

Of course, one can use as an alternative to such a static separation device, a rotating device such as a centrifuge. Experience has shown that such a device is more expensive and has a higher energy requirement than a static device. The latter can be structurally relatively simple.

According to such a structurally simple embodiment of the present invention, therefore, the centrifugal separator comprises a static, non-rotating device with at least one circular or approximately spirally guided pipe through which the process gas mixture to be separated is passed.

After a structurally predetermined circulation angle of the circular or spirally guided pipe, the gas stream is then divided by suitable separating means such as partitions, baffles, channels or the like and subsequent lines. The partial stream drawn off at the periphery contains predominantly the heavy gas components. The circulation angle of the gas flow in the apparatus is in principle a design parameter and determines, in cooperation with the gas velocity and the channel width in the radial direction, the selectivity of the arrangement.

Preferably, according to an embodiment of the invention, the circular or spirally guided tube in its output-side end region at least one partition or subdivision through which at least two channels are formed, via the process gas components with different molecular weights separately flow out of the tube. In these separate areas (channels) you can then connect each lines, through which the previously separated gas components drain separately.

The subject matter of the present invention is furthermore a separating device comprising a centrifugal separator for separating gases of higher molecular weight than hydrogen from a hydrogen-containing process gas mixture, in particular for use in a plant of the type described above, wherein the centrifugal separator is a static, non-rotating device with at least one approximately spiral comprises guided tube through which the process gas mixture to be separated is passed.

The present invention furthermore relates to the use of a plant or a separation device with the features described above in a process for the production of ammonia from a process gas mixture containing nitrogen and hydrogen.

Hereinafter, the present invention will be explained in more detail by means of embodiments with reference to the accompanying drawings. Showing:

Figure 1 is a schematic flow diagram of a first exemplary system according to the invention for the treatment of a process gas mixture for the production of ammonia;

FIG. 2 shows a further schematic flow diagram of a second alternative system according to the invention for treating a process gas mixture for the production of ammonia;

Figure 3 is a simplified schematic diagram of an exemplary centrifugal separator, which is used in the method according to the invention.

Hereinafter, a possible first embodiment of the present invention will be explained in more detail with reference to FIG. The illustration shows a schematic flow diagram in which the various parts of the system are each represented by blocks. In the drawing on the left an input line 10 is shown, through which natural gas is fed into a primary reformer 11, 12 steam is added via the branch line, so that in the primary reformer from the hydrocarbons of the natural gas by a reforming reaction with steam, a synthesis gas mixture is generated among others Contains carbon monoxide and hydrogen. Subsequently, the primary reformer 11 leaving the gas mixture is fed to a secondary reformer 13, which is also supplied from the outside via a line 14 and a compressor 15 air, so that takes place in the secondary reformer further oxidation of the synthesis gas mixture to carbon dioxide and water.

The gas mixture leaving the secondary reformer 13 flows through a heat exchanger 16 and is then fed to a high-temperature CO converter 17. Through the step of CO conversion a portion of the unwanted CO in the cleavage gas to produce H ₂ product is used according to the reaction equation: CO + H ₂ 0 - »C0 ₂ + H ₂

The CO conversion reaction is exothermic and, with decreasing temperature, increasingly shifts its equilibrium to the right side of the reaction equation, i. to carbon dioxide and hydrogen. The high-temperature CO conversion usually takes place at temperatures of approx. 300 ° C to 450 ° C instead and allows a reduction in the CO content, for example, up to approx. 2.5%. In CO conversion, a specific catalyst is usually used in a fixed bed, so that the exiting gas mixture is largely in chemical equilibrium.

The gas mixture leaving the high-temperature converter 17 passes through a further heat exchanger 18 and is then fed to a low-temperature converter 19 in order to further reduce the CO content. This low-temperature converter 19 also operates using a catalyst usually at temperatures in the range of about 180 ° C to about. 250 ° C and usually allows a further reduction of the CO content to about 0.2%.

The gas mixture leaving the low-temperature converter 19 passes through a further heat exchanger 20 and then passes into a water separator 21, in which water is separated off. The thus purified process gas mixture is then fed via the line 22 to a separation device 23, in which a separation of high-molecular weight gas is carried out, namely on the one hand from excess amounts of nitrogen and on the other carbon dioxide. The process gas mixture leaving the separating device 23 is then fed to a C0 ₂ absorber 24, in which a further separation of C0 ₂ takes place. After leaving the C0 ₂ absorber 24, the process gas mixture passes into a methanation stage 25, in which a methanation for the separation of carbon monoxide and optionally C0 ₂ takes place, since in particular small amounts of carbon monoxide in the subsequent ammonia synthesis act as a catalyst poison. The methanation follows the following reaction equation:

CO + 3 H ₂ -> CH ₄ + H ₂ O

After the methanation, the process gas mixture flows through a compressor 26 and then enters the ammonia synthesis reactor 27. In the ammonia synthesis gaseous ammonia is generated, which is supplied to a refrigeration system 28. In this refrigeration system 28 liquid ammonia is generated, which is then discharged via the output line 29 as a product and stored for example in tanks. If additional ammonia is required in the ammonia synthesis, liquid ammonia from the refrigeration system 28 can also be recycled to the ammonia synthesis 27.

In the separation device 23 are mainly N ₂ and C0 _{2 separated} as components of higher molecular weight, depending on the selectivity and lower amounts of hydrogen may be contained in the separated there gas mixture. This separated, nitrogen and Enriched carbon dioxide, gas mixture is then fed via line 30 to a second CCyAbsorber 31, in which C0 _{2 is} separated. This second CGy absorber is in communication with a regeneration device 32, from which via the output line 33 C0 ₂ can be removed from the system.

From the second C0 ₂ absorber 31 performs an output-side line 34, via the after the separation of C0 _2, a gas mixture which contains substantially N ₂ and H ₂ , can be recycled via a residual gas line 35 to the primary reformer 11. This residual gas line 35 can be supplied with gas streams of separated gases. For example, a purge gas stream from the ammonia synthesis reactor 27 is supplied via line 36 to an H ₂ recovery device 37. The hydrogen thus obtained is recycled via the line 38 into the line which leads from the methanation stage 25 to the ammonia synthesis reactor 27, wherein the hydrogen is preferably fed before the compressor 26. In this way, the recovered hydrogen can be recycled and used again in the ammonia synthesis. On the other hand, the remaining gases separated off in the device 37 during the H ₂ recovery can be supplied via the line 39 to the residual gas line 35. Since the residual gas line 35 leads back to the reformer, these gas shares can be recycled at least energetically.

A further alternative embodiment of the present invention will be explained below with reference to FIG. In this variant, some components of the system and their interconnection in the region upstream of the ammonia synthesis reactor 27 are identical to the variant described above with reference to FIG. 1, so that reference is made to the above description at this point. These are the primary reformer 11, the secondary reformer 13, the high-temperature CO converter 17, the low-temperature CO converter 19 and the water separator 21 as well as the heat exchangers 16, 18 and 20 and the compressor 15 also used in the variant of FIG ,

In the variant of Figure 2, however, the process gas mixture first flows to the water separator 21 via conduit 22 into a first CGyAbsorber 24, in which a separation of C0 ₂ is carried out before then passing to C0 ₂ depleted process gas mixture into the inventive separation device 23, the is designed as a centrifugal separator. Thus, predominantly excess nitrogen is separated off in the centrifugal separator 23, since a proportion of CO ₂ in the CCy absorber 24 has already been separated beforehand. The nitrogen-depleted gas mixture then flows from the separator 23 to a methanation stage 25 in which a conversion of carbon monoxide occurs according to the reaction equation given above. The process gas mixture thus treated then finally passes into the ammonia synthesis reactor 27, where the synthesis of ammonia from nitrogen and hydrogen takes place (usually according to the Haber-Bosch process).

In the variant according to FIG. 2 too, hydrogen in the device 37 can be obtained from the purge gas stream flowing out of the ammonia synthesis reactor via the line 36 be recovered, which is then recycled via line 38 in the region upstream of the ammonia synthesis reactor. The residual gas mixture obtained after separation of the hydrogen can also be supplied in this variant via the line 39 of the residual gas line 35, from where the residual gas is recycled to the primary reformer eleventh

Also in the variant according to FIG. 2, the carbon dioxide-laden solvent flowing out of the CO ₂ absorber 24 passes into a regeneration device 32. This regeneration device 32 has the task of regenerating the solvent used for CO ₂ absorption. From the regeneration device 32, the solvent flows back into the C0 ₂ absorber 24 after regeneration. The separated in the regeneration device 32 C0 ₂ can be discharged via the output line 33 from the system. The depleted at C0 ₂ residual gas stream can be passed from the regeneration device 32 directly into the residual gas line 35 and back to the reformer. In the separating device 23 separated excess nitrogen, which may also contain small amounts of hydrogen, CO and argon, can also be supplied via the line 34 of the residual gas line 35 and thus be led back to the reformer 11.

Although the process control according to the variant of FIG. 1 may require an additional C0 ₂ absorber 31 and thus potentially the somewhat larger investment costs. Due to the division of the process stream and the conditions which are more favorable in the individual absorbers 24, 31, the apparatuses in this variant are, however, distinctly smaller than the individual C0 ₂ absorber 24 in the variant of FIG. 2. The variant according to FIG. 1 is suitable thus better for very large plant capacities, where the size of the absorber column is a criterion.

If the ammonia plant has to provide carbon dioxide for a connected urea plant, the second CO ₂ absorber 31 shown in the process variant according to FIG. 1 is required to recover the carbon dioxide separated off with the nitrogen stream and thus a comparable or better CO ₂ yield to ensure in conventional procedures. Generally, ammonia plants with stoichiometric air addition in the secondary reformer provide too little carbon dioxide to convert all the ammonia produced to urea. Systems with more than stoichiometric air addition in the secondary reformer have significantly more carbon dioxide due to the greater degree of partial oxidation of the process gas and usually allow the complete conversion of the entire ammonia produced in the plant to urea (balanced plant).

Depending on the achievable selectivity of the separation stage, the desired excess air in the process gas and the plant capacity, further process variants are possible, in particular parallel circuits of strands with and without integrated nitrogen separation. Reference will now be made to FIG. 3 and on the basis of which an exemplary embodiment of a centrifugal separator 23 which can be used in the method according to the invention as a separating device for separating heavy gases will be explained. In principle, this comprises a spirally bent tube with a pipe socket 40 at the gas inlet side, through which the process gas mixture, which contains, for example, H ₂ , N ₂ , C0 ₂ , CH ₄ and Ar, enters the spiral pipe, where it experiences an acceleration. The gas mixture passes through a spiral pipe loop 41 and due to the different molecular weight dependent centrifugal force in the separator 23, the heavier gas components accumulate in the radially outer region of the tube, while the lighter hydrogen accumulates in the radially inner region.

In the output side region of the pipe loop 41 at least two channels are formed by a partition 44, one of which is further radially outward and the other further radially inwardly relative to the axis of the pipe loop 41. The radially outer channel opens into an outer pipe socket 42nd , can be derived through the heavier gases and directed, for example, to the reformer. The radially inner channel opens into an inner pipe socket 43 and contains a depleted in the heavy components such as carbon dioxide, nitrogen and argon gas mixture, ideally a gas mixture in about a mixing ratio H ₂ : N ₂ of 3: 1, as it was the ammonia synthesis is needed. The effluent with the inner pipe socket 43 gas stream can thus be passed to the ammonia synthesis device, while the outflowing with the outer pipe socket 42 gas stream can be recycled, for example, to the reformer.

LIST OF REFERENCES

10 input line

11 primary reformer

12 branch line

13 secondary reformers

14 line

15 compressors

16 heat exchangers

17 high temperature CO converter

18 heat exchangers

19 low-temperature CO converter

20 heat exchangers

21 water separators

22 line

23 separating device

24 C0 ₂ absorber

25 methanation stage

26 compressors

27 ammonia synthesis reactor

28 refrigeration system

29 output line

30 line

31 second C0 ₂ absorber

32 regeneration device

33 output line management

Residual gas line

management

H ₂ recovery

management

Pipe socket / gas inlet side pipe loop

Pipe socket / gas outlet side outside Pipe socket / gas outlet side inside Partition wall

Claims

claims

1. A process for the production of ammonia from a nitrogen and hydrogen-containing process gas mixture which contains at least one further gas component having a higher molecular weight than hydrogen, which is separated in at least one separation step from the process gas mixture, characterized in that at least one separation step is provided, in which a separation of nitrogen and optionally further gas components with higher molecular weight by means of at least one centrifugal separator (23) from the process gas mixture is carried out before the process gas stream at least one ammonia synthesis reactor (27) is supplied.

2. The method according to claim 1, characterized in that as centrifugal separator (23) at least one circular or spirally guided pipe (41), a cyclone separator or a centrifuge is provided, in which the process gas mixture to be separated is exposed to a large acceleration, so that the heavy gas components accumulate in a radially outer area and can be separated there.

3. The method according to claim 1 or 2, characterized in that the centrifugal separator (23), the process gas mixture is supplied via an infeed pipe and preferably via an inlet nozzle.

4. The method according to any one of claims 1 to 3, characterized in that the

Process gas mixture in the centrifugal separator (23) accelerated to a defined speed and then passed to a circular path or spiral path, wherein the radius of the circular path or spiral path is dimensioned so that the required for the separation centrifugal acceleration.

5. The method according to any one of claims 1 to 4, characterized in that the

Process gas mixture in the centrifugal separator (23) is separated by baffles and / or channels in different gas components.

6. The method according to any one of claims 1 to 5, characterized in that in the

Centrifugal separator (23) at least excess nitrogen and carbon dioxide are separated.

7. The method according to claim 6, characterized in that from the resulting gas mixture enriched in nitrogen and carbon dioxide then carbon dioxide is preferably separated in a CGyAbsorber (31).

8. The method according to any one of claims 1 to 5, characterized in that in the

Centrifugal separator (23) at least excess nitrogen is separated.

9. The method according to claim 8, characterized in that prior to the introduction of the gas mixture into the centrifugal separator (23) or after flowing through the centrifugal separator (23) in at least one further separating device (24) at least partially carbon dioxide is separated from the gas mixture.

10. The method according to claim 7 or 9, characterized in that the gas mixture obtained after the separation of carbon dioxide, which contains substantially nitrogen and residues of hydrogen, argon and CO, is recycled via a residual gas line (35) to the primary reformer.

11. The method according to any one of claims 6 to 10, characterized in that the heavy gas components such as nitrogen and carbon dioxide depleted gas stream after separation in the centrifugal separator (23) flows through at least one further separating device (24) and / or conversion device (25), in which a further separation of carbon dioxide or a conversion of carbon monoxide is carried out before this gas stream is fed to the ammonia synthesis reactor (27).

12. The method according to claim 11, characterized in that at least one further separating device, a CGyAbsorber (24) and / or a Methanisierungsstufe (25) is provided.

13. The method according to any one of claims 1 to 12, characterized in that an H ₂ - recovery from a from the ammonia synthesis reactor (27) derived Purgegasstrom is provided, wherein preferably a return of the recovered hydrogen is provided to the input-side process gas mixture for ammonia production.

14. The method according to any one of claims 1 to 13, characterized in that before the step of separation in centrifugal separator (23) the process gas mixture at least one primary reformer (11) and at least one secondary reformer (13) or optionally only a purely autothermal reformer and at least one High-temperature CO converter (17) and optionally a low-temperature CO converter (19) or at least one medium-temperature CO converter and / or at least one water separator (21) flows through.

15. Plant for processing a process gas mixture for ammonia synthesis comprising at least one ammonia synthesis reactor (27) in which the synthesis of ammonia from a nitrogen and hydrogen-containing process gas takes place, and at least one ammonia synthesis this reactor (27) upstream in the flow path separating device for separating at least one gas component the process gas, characterized in that at least one centrifugal separator (23) is provided as a separating device for separating excess nitrogen and optionally further gas components with a higher molecular weight.

16. Plant according to claim 15, characterized in that it further comprises at least one centrifugal separator (23) in the flow path upstream primary reformer and at least one primary reformer (11) downstream and the centrifugal separator upstream secondary reformer (13) or optionally at least one purely autothermal reformer.

17. Installation according to one of claims 15 or 16, characterized in that it comprises at least one centrifugal separator (23) upstream in the flow path CO converter (17, 19).

18. Plant according to one of claims 15 to 17, characterized in that it further comprises at least one further separating device or conversion device for the separation or conversion of carbon dioxide or carbon monoxide.

19. Plant according to claim 18, characterized in that the further separation device comprises at least one CGy absorber (24, 31) and / or the conversion device comprises a methanation stage (25).

20. Separating device comprising a centrifugal separator for the separation of gases of higher molecular weight than hydrogen from a hydrogen-containing process gas mixture, in particular for use in a system according to one of claims 15 to 19, characterized in that the centrifugal separator (23) is a static, non-rotating device comprises at least one approximately spirally guided pipe through which the process gas mixture to be separated is passed.

21. Separating device according to claim 20, characterized in that the spirally guided tube at least in its output-side end region has at least one partition or subdivision, are formed by the at least two channels, separated via the process gas components with different molecular weight separately from the tube.

22. Use of a plant for the treatment of a process gas mixture according to one of claims 15 to 19 or a separation device according to one of claims 20 or 21 in a process for the production of ammonia from a nitrogen and hydrogen-containing process gas mixture according to one of claims 1 to 14.