Quantity-optimised production of methanol and therefrom formaldehyde urea in a combined ammonia-urea system

Abstract

The present invention relates to a method for producing ammonia, for further reacting the ammonia to form urea, and for subsequently granulating the urea, wherein additionally methanol is produced, wherein the methanol is reacted to form formaldehyde and the formaldehyde is reacted to form a formaldehyde-urea mixture, wherein the formaldehyde-urea mixture is added to the urea prior to granulation, characterised in that, for methanol synthesis, three gas streams are combined, wherein a first processing gas stream (24) after the processing of an amine solution of an amine-carbon dioxide scrubber (20) is selected as the first gas stream, wherein the first processing gas stream (24) has, above all, carbon dioxide, hydrogen and nitrogen, wherein a first inert gas evacuation stream (36) from the converter circuit of the ammonia synthesis is selected as the second gas stream, wherein the first inert gas evacuation stream (36) is removed after an aqueous ammonia scrubber (33), wherein the first inert gas evacuation stream (36) has, above all, hydrogen and methane, wherein a second inert gas evacuation stream is selected as the third gas stream, wherein the second inert gas evacuation stream (37) is removed after a hydrogen recovery (34), wherein the second inert gas evacuation stream (37) has, above all, methane, nitrogen and some hydrogen.

Description

[0001] Quantitatively optimized production of methanol and formaldehyde-urea in a combined ammonia-urea plant

[0002] The invention relates to an optimized plant combination for the production of ammonia and urea from ammonia and for the subsequent granulation of the urea. To optimize the urea granules, a formaldehyde-urea mixture is added to the urea in small quantities as a standard additive. Therefore, methanol is typically produced separately in dedicated methanol production plants, and from this, formaldehyde. Urea is then transported to the formaldehyde synthesis plant, where the formaldehyde-urea mixture is produced, and then repurchased by the urea manufacturer and transported back. This represents a significant cost factor, where dependence on raw materials could also influence production. Therefore, there is interest in producing methanol, and from the methanol, formaldehyde, and thus the formaldehyde-urea mixture, at the site of ammonia and urea synthesis.However, it is currently not possible to produce the methanol and thus also the formaldehyde-urea mixture in sufficient quantities and in an economically viable manner while avoiding a reduction in the economic efficiency of the plant network.

[0003] It is known that methanol can be produced from certain gas streams in an ammonia plant and urea formaldehyde can be produced from it.

[0004] WO2019122809A1 describes a process for the co-production of methanol and ammonia, comprising the steps of: (a) forming a first synthesis gas stream by reacting a first portion of a hydrocarbon feedstock and steam in a steam reformer, (b) forming a second synthesis gas stream in parallel to the first synthesis gas stream by reacting a second portion of the hydrocarbon feedstock with an oxygen-containing gas and steam in an autothermal reformer, (c) synthesizing methanol from a first process gas comprising the first synthesis gas stream, and (d) synthesizing ammonia from a second process gas produced from the second synthesis gas stream, wherein a hydrogen-containing purge stream is obtained from the methanol synthesis step (c) and a portion of the purge gas stream is fed to the autothermal reformer and / or the second synthesis gas in step (b).

[0005] WO2018185459A1 describes a process for producing formaldehyde-stabilized urea, comprising the steps of: (a) generating a synthesis gas; (b) subjecting the synthesis gas to one or more stages of water-to-gas conversion in one or more water-to-gas conversion reactors to form a converted gas; (c) cooling the converted gas below the dew point and recovering condensate to form a dried converted gas; (d) recovering carbon dioxide from the dried converted gas in a carbon dioxide removal unit to form a carbon dioxide-depleted synthesis gas; (e) synthesizing methanol from the carbon dioxide-depleted synthesis gas in a methanol synthesis unit and recovering the methanol and a methanol synthesis off-gas; (f) subjecting at least a portion of the recovered methanol to oxidation with air,to form formaldehyde in a stabilizer production unit; (g) subjecting the methanol synthesis off-gas to methanation in a methanation reactor containing a methanation catalyst to form an ammonia synthesis gas; (h) synthesizing ammonia from the ammonia synthesis gas in an ammonia production unit and recovering the ammonia; (i) reacting a portion of the ammonia and at least a portion of the recovered carbon dioxide stream in a urea production unit to form a urea stream; and (j) stabilizing the urea by mixing the urea stream and a stabilizer produced using the formaldehyde produced in the stabilizer production unit,wherein the carbon dioxide removal unit operates by absorption using a liquid absorbent and comprises an absorbent regeneration unit. The process comprises recovering a carbon dioxide-containing gas stream from the absorbent regeneration unit, compressing at least a portion of the recovered carbon dioxide-containing gas stream to form a compressed carbon dioxide-containing gas stream, and passing the compressed carbon dioxide-containing gas stream to the methanol synthesis plant. WO2017103564A1 describes a process for producing formaldehyde-stabilized urea, comprising the steps of: (a) generating a synthesis gas containing hydrogen, nitrogen, carbon monoxide, carbon dioxide, and steam in a synthesis gas generation unit; (b) subjecting the synthesis gas to one or more water-gas shift stages in one or more water-gas shift reactors,to form a shifted gas; (c) carbon dioxide is recovered from the shifted gas in a carbon dioxide removal unit to form a carbon dioxide-depleted synthesis gas; (d) synthesizing methanol from the carbon dioxide-depleted synthesis gas in a methanol synthesis unit and recovering the methanol and a methanol synthesis off-gas comprising nitrogen, hydrogen and residual carbon monoxide; (e) subjecting at least a portion of the recovered methanol to oxidation with air in a formaldehyde production unit; (f) subjecting the methanol synthesis off-gas to methanation in a methanation reactor containing a methanation catalyst,to form an ammonia synthesis gas; (g) synthesizing ammonia from the ammonia synthesis gas in an ammonia production unit and recovering the ammonia; (h) reacting a portion of the ammonia and at least a portion of the recovered carbon dioxide stream in a urea production unit to form a urea stream; and (i) stabilizing the urea by mixing the urea stream and a stabilizer produced using formaldehyde recovered from the formaldehyde production unit, wherein a portion of the synthesis gas produced by the synthesis gas generation unit bypasses either the one or more water-gas shift reactors, the carbon dioxide removal unit, or the one or more water-gas shift reactors and the carbon dioxide removal unit.

[0006] WO2018078318A1 describes an integrated process for producing a formaldehyde-stabilized urea, comprising the steps of: (a) generating a synthesis gas comprising hydrogen, nitrogen, carbon monoxide, carbon dioxide, and steam in a synthesis gas generation unit; (b) splitting the synthesis gas into a first synthesis gas stream and a smaller second synthesis gas stream; (c) subjecting the first synthesis gas stream to one or more stages of water-to-gas conversion in one or more water-to-gas conversion reactors to form a converted gas; (d) cooling the converted gas below the dew point and recovering condensate to form a dried converted gas; (e) recovering carbon dioxide from the dried converted gas in a carbon dioxide removal unit to form a carbon dioxide-depleted synthesis gas;(f) subjecting the carbon dioxide-depleted synthesis gas to a methanation step in one or more methanation reactors to form an ammonia synthesis gas; (g) synthesizing ammonia from the ammonia synthesis gas in an ammonia production unit and recovering the ammonia; (h) reacting a portion of the ammonia and at least a portion of the recovered carbon dioxide stream in a urea production unit to form a urea stream; and (i) stabilizing the urea by mixing the urea stream and a stabilizer prepared using formaldehyde to form a stabilized urea, wherein formaldehyde is produced by steps comprising: (1) passing the second portion of the synthesis gas through a scrubber to remove impurities therefrom and form a scrubbed synthesis gas;(2) synthesizing methanol from the scrubbed synthesis gas in a methanol synthesis unit and recovering the methanol and a methanol synthesis off-gas; (3) combining the methanol synthesis off-gas with the converted gas; and (4) subjecting at least a portion of the recovered methanol to oxidation with air in a formaldehyde stabilizer production unit to produce formaldehyde.

[0007] WO2016132091 A1 describes a process for producing formaldehyde, comprising (a) subjecting methanol to oxidation with air in a formaldehyde production unit, thereby producing a formaldehyde-containing stream; (b) separating the formaldehyde-containing stream into a formaldehyde product stream and a formaldehyde off-gas stream, wherein the off-gas stream, optionally after treatment in an off-gas treatment unit, is passed to one or more stages of: (i) synthesis gas production, (ii) carbon dioxide removal, (iii) methanol synthesis, or (iv) urea synthesis.

[0008] WO2016132092A1 describes a process for producing formaldehyde-stabilized urea, comprising the steps of: (a) generating a synthesis gas comprising hydrogen, nitrogen, carbon monoxide, carbon dioxide, and steam in a synthesis gas generation unit; (b) recovering carbon dioxide from the synthesis gas to form a carbon dioxide-depleted synthesis gas; (c) synthesizing methanol from the carbon dioxide-depleted synthesis gas in a methanol synthesis unit and recovering the methanol and a methanol synthesis off-gas comprising nitrogen, hydrogen, and residual carbon monoxide; (d) subjecting at least a portion of the recovered methanol to oxidation with air in a formaldehyde production unit; (e) subjecting the methanol synthesis off-gas to methanation in a methanation reactor containing a methanation catalyst to form an ammonia synthesis gas;(f) synthesizing ammonia from the ammonia synthesis gas in an ammonia production unit and recovering the ammonia; (g) reacting a portion of the ammonia and at least a portion of the recovered carbon dioxide stream in a urea production unit to form a urea stream; and (h) stabilizing the urea by mixing the urea stream and a stabilizer produced using formaldehyde recovered from the formaldehyde production unit, wherein an air source is compressed and divided into a first and a second portion, the first portion being fed to the formaldehyde production unit for the oxidation of methanol and the second portion being further compressed and fed to the synthesis gas generation unit.

[0009] A catalytic process is known from US4362655A. In particular, US4362655A relates to a catalytic metal or a catalytic alloy, or both, in a form with improved catalytic properties and their use in catalytic processes. More specifically, the catalyst or catalyst substrate described therein comprises at least one metal and / or alloy body produced by a melt spinning or melt extraction process.

[0010] From WO2022064214A1 a method for installing catalyst supports in a first selected reactor tube of a tubular reactor is known.The method comprises the steps of: i) providing an installation tool, the installation tool comprising: a) an installation frame; b) a movable ram mounted to the installation frame and configured to push one or more catalyst supports into the first selected reactor tube; and c) one or more anchors for releasably securing the installation frame to the tubular reactor; ii) attaching the installation tool to the tubular reactor by engaging the one or more anchors with one or more reactor tubes disposed adjacent to the first selected reactor tube to align the movable ram with the first selected reactor tube; and iii) actuating the movable ram to push the one or more catalyst supports into the first selected reactor tube.

[0011] From WO2022064211A1, a reactor tube for a tubular reactor and a holding device associated with the reactor tube are known, wherein the reactor tube comprises an elongated tube defining a bore for receiving a catalyst in use and having an outlet at one end of the bore for discharging the catalyst from the bore, wherein the holding device is configured to be rotatable between a first position and a second position, wherein in the first position the retaining device at least partially blocks the outlet for retaining the catalyst within the bore, and in the second position the outlet is sufficiently unobstructed to allow the catalyst to be discharged from the outlet.

[0012] The aim is to find sources for methanol and subsequent formaldehyde production that do not originate predominantly or entirely from the primary product flow and thus come at the expense of the actual production, but at the same time to provide methanol in sufficient quantities.

[0013] The object of the invention is therefore to enable an economical and sufficient production of methanol and subsequently of urea-formaldehyde in an ammonia-urea plant.

[0014] This object is achieved by the method having the features specified in claim 1 and by the plant network having the features specified in claim 5. Advantageous further developments emerge from the subclaims, the following description and the drawing. The method according to the invention is used for the production of ammonia, the further conversion of the ammonia to urea and subsequent granulation of the urea. Plant networks of this type for carrying out such a process are well known and in use worldwide. As a granulation aid, a formaldehyde-urea mixture has previously been purchased and introduced into the process. In order to establish a certain degree of self-sufficiency here, the added value within the plant network is being expanded. For this purpose, methanol is also produced. The methanol is then further converted to formaldehyde and the formaldehyde is again converted to a formaldehyde-urea mixture.The formaldehyde-urea mixture is then added to the urea before granulation.

[0015] According to the invention, three gas streams are combined for methanol synthesis. These gas streams are fed, at least to a considerable extent, not at all or not at all from the main gas stream, i.e., the production of hydrogen or the hydrogen-nitrogen mixture, the converter circuit for ammonia production, or the ammonia gas stream for urea synthesis. Only gas streams that arise in purification or separation processes and are usually only subjected to thermal utilization are used. As a result, the additionally produced formaldehyde has no influence on the amount of ammonia or urea produced. At the same time, the combination of the selected gas streams makes it possible to produce sufficient formaldehyde. The first gas stream selected is a first workover gas stream following the workup of an amine solution from an amine-carbon dioxide scrubber.The first reprocessing gas stream primarily comprises carbon dioxide, hydrogen, and nitrogen. The second gas stream is a first inert gas ejection stream from the ammonia synthesis converter circuit. The first inert gas ejection stream is removed after an aqueous ammonia scrubber. The first inert gas ejection stream primarily comprises hydrogen and methane. The third gas stream is a second inert gas ejection stream. The second inert gas ejection stream is removed after hydrogen recovery. The second inert gas ejection stream primarily comprises methane, nitrogen, and some hydrogen. These three gas streams are typically used for thermal recovery, either in the primary reformer burner or for power generation. Therefore, the use of these gas streams has no impact on the actual production of ammonia and urea, but rather does not affect this main gas stream.At the same time, the use of these gas streams allows a significantly higher amount of methanol to be produced compared to the state of the art, thus covering significantly more than the plant's own demand for methanol and thus for urea-formaldehyde.

[0016] In the context of the composition of gas streams, “primarily” is understood to mean that the gas stream predominantly comprises the corresponding constituents: This means that the first processing gas stream can comprise the constituents carbon dioxide, hydrogen and nitrogen, usually to at least 90 vol.%, in particular to a total of at least 95 vol.%, wherein other components can occur in the first processing gas stream, for example argon, carbon monoxide, methane or individual components of the amine solution, wherein the total proportion of these other components in the first processing gas stream is then at most 10 vol.% and is preferably less than 10 vol.% in the sum of the other components, in particular at most 5 vol.%; the sum of the constituents and the other components can in particular add up to 100 vol.% in the first processing gas stream.This also means that the first inert gas discharge stream can typically comprise the components hydrogen and methane in a total of at least 60 vol.%, in particular in a total of at least 90 vol.%, wherein other components can correspondingly occur in the first inert gas discharge stream, for example nitrogen, argon or water, wherein the total proportion of these other components in the first inert gas discharge stream is then at most 40 vol.%, in particular less than 10 vol.% in the sum of the other components; the sum of the components and the other components can in particular add up to 100 vol.% in the first inert gas discharge stream. This also means that the second inert gas discharge stream can typically comprise the components methane, nitrogen and hydrogen in a total of at least 85 vol.%, in particular in a total of at least 90 vol.-%, whereby other components may be present in the second inert gas discharge stream, for example argon, whereby the total proportion of these other components in the second inert gas discharge stream amounts to a maximum of 15 vol.%, in particular less than 10 vol.% in the sum of the other components; the sum of the constituents and the other components may in particular add up to 100 vol.% in the second inert gas discharge stream.

[0017] For example, in the first processing gas stream, the proportion of carbon dioxide can be in a range of 30-95 vol.%, in particular 60-80 vol.%, the proportion of hydrogen in a range of 4-45 vol.%, in particular 15-35 vol.%, and the proportion of nitrogen in a range of 1-15 vol.%, in particular 1-10 vol.% (where the three proportions add up to a total proportion of at least 90 vol.%, in particular at least 95 vol.%), in the first inert gas discharge stream, for example, the proportion of hydrogen can be in a range of 30-90 vol.%, in particular 30-50 vol.%, and the proportion of methane in a range of 10-70 vol.%, in particular 10-30 vol.% (where the two proportions add up to a total proportion of at least 60 vol.%, preferably at least 70 vol.%, in particular at least 90 vol.%), and in the second Inert gas discharge stream, for example, the proportion of methane can be in a range of 10-40 vol.-%, in particular from 15-30 vol. -%, the proportion of nitrogen in a range of 10-40 vol. -%, in particular from 15-30 vol. -%, and the proportion of hydrogen in a range of 20-60 vol. -%, in particular from 40-60 vol. -% (wherein the three proportions add up to a total proportion of at least 85 vol. -%, in particular of at least 90 vol. -%).

[0018] A key point here is that, unlike previously, a single gas stream is not selected to produce methanol, for example, the main gas stream instead of a methanator. Instead, three gas streams are used, each of whose compositions, taken individually, is not useful. Rather, it is the mixing that results in a gas mixture suitable for methanol synthesis, whereas each gas stream appears unsuitable on its own (both in terms of the total amount and the respective molar ratio of carbon, hydrogen, and oxygen). In a further embodiment of the invention, the first reprocessing gas stream, the first inert gas discharge stream, and the second inert gas discharge stream are mixed according to their chemical composition. The composition of the mixed gas stream is adjusted to a composition suitable for methanol synthesis.The portions of the three gas streams not used for the mixed gas stream can, for example, be fed into thermal energy recovery. Therefore, continuous analysis of the composition of the three gas streams is preferred in order to be able to adapt the proportions of the three gas streams to the current composition of the three gas streams. Since each of the streams has a different composition, an optimal ratio, particularly of carbon dioxide to hydrogen, can be set for methanol synthesis.

[0019] In a further embodiment of the invention, no gas stream is fed directly from the main gas stream to the methanol synthesis. The main gas stream can, in particular, comprise the gas stream in which the end products of this plant and their intermediates are produced, i.e., in particular, the gas stream in the production of hydrogen or the hydrogen-nitrogen mixture, the gas stream in the converter circuit for the production of ammonia, or the ammonia gas stream for urea synthesis. Accordingly, according to this embodiment, only gas streams that are directly branched off from gas streams other than the main gas stream are fed to the methanol synthesis.

[0020] In a further embodiment of the invention, the residual gas not converted in the methanol synthesis is fed to the amine carbon dioxide scrubber. This allows, in particular, unconverted hydrogen to be recycled to the ammonia synthesis, further increasing overall efficiency.

[0021] In a further aspect, the invention relates to a plant network comprising a plant for producing ammonia, a plant for producing urea from ammonia, and a urea granulation plant. Such plant networks are known and in use in large numbers. The plant for producing ammonia has a reformer and a converter circuit with a converter. An amine-carbon dioxide scrubber is arranged between the reformer and the converter circuit. This scrubber removes the carbon dioxide from the gas stream, so that downstream of the scrubber, the gas stream contains practically only hydrogen and nitrogen and is thus suitable for conversion to ammonia in the converter. At the same time, the scrubber supplies the carbon dioxide required for urea synthesis as a second reactant alongside the ammonia. The converter circuit has an inert gas discharge.This is necessary; otherwise, for example, argon would continue to accumulate in the converter circuit over time, reducing the partial pressures of hydrogen and nitrogen, and thus the yield. Therefore, it is necessary and common practice to implement an appropriate inert gas removal system, which enables the most extensive, but never complete, recovery of the useful gases, especially hydrogen and ammonia. The inert gas removal system therefore includes an aqueous ammonia scrubber and a hydrogen recovery system. These components are found in virtually every modern ammonia and urea production plant.

[0022] In order to be able to additionally produce at least a portion of the required formaldehyde-urea mixture in-house, it is known to expand the plant network. The plant network has a methanol synthesis device. The plant network also has a formaldehyde synthesis device for producing formaldehyde from the methanol. The plant network also has a device for producing a formaldehyde-urea mixture. The methanol synthesis device is connected to the formaldehyde synthesis device for transferring methanol. The formaldehyde synthesis device is connected to the device for producing a formaldehyde-urea mixture for transferring formaldehyde. The device for producing a formaldehyde-urea mixture is connected to the urea granulation plant for transferring the formaldehyde-urea mixture.

[0023] What is crucial now is which gas streams are used to produce the methanol, i.e., which parts of the plant network for transferring gas streams are connected to the methanol synthesis device. The gas streams used should not reduce the production of ammonia or urea, thereby reducing the actual product quantity and thus lowering the economic efficiency. Rather, other gas streams should be used to maintain the economic efficiency of the plant network and, by avoiding the purchase of the formaldehyde-urea mixture,

[0024] According to the invention, the amine-carbon dioxide scrubber is connected to the methanol synthesis device in such a way that the carbon dioxide-, methane-, and hydrogen-containing workup gas stream produced during the workup of the amine solution is transferred to the methanol synthesis device. Second, the inert gas discharge is connected to the methanol synthesis device in such a way that, firstly, the inert gas discharge downstream of the aqueous ammonia scrubber is connected to the methanol synthesis device, so that the first inert gas discharge stream, which primarily contains hydrogen and methane, is transferred to the methanol synthesis device.Furthermore, the inert gas discharge is connected to the methanol synthesis device in such a way that, on the other hand, the inert gas discharge is connected to the methanol synthesis device after a hydrogen recovery, so that the second inert gas discharge stream, which mainly comprises methane, nitrogen and some hydrogen, is transferred to the methanol synthesis device.

[0025] These three gas streams have different gas compositions and would normally be fed for thermal utilization. By feeding them to the methanol synthesis device via the aforementioned connections, and only by combining all three connections in the methanol synthesis device, a gas composition suitable for methanol synthesis is achieved.

[0026] In a further embodiment of the invention, the plant complex comprises a mixing device. The mixing device is arranged upstream of the methanol synthesis device and connected to it for transferring a mixed gas stream. The processing gas stream, the first inert gas discharge stream, and the second inert gas discharge stream are fed to the mixing device. The mixing device is designed for the quantitatively variable mixing of the three gas streams. This allows the mixing device to react to a changing composition of the three gas streams and create a gas mixture suitable for methanol synthesis. Therefore, the mixing device can be connected to a device for thermal utilization in order to be able to feed the unused gas stream portion for thermal utilization there, for example, in a burner of a primary reformer.

[0027] In a further embodiment of the invention, there is no connection between the main gas stream and the methanol synthesis device, in particular, there is no direct connection between a line of the main gas stream and the feed line of the methanol synthesis device. This means, in particular, that the supply of the gas streams to the methanol synthesis device is directly connected to a line other than the lines of the gas stream in which the end products of this plant and their intermediate products are conducted, i.e., in particular, the line of the gas stream in the production of hydrogen or the hydrogen-nitrogen mixture, the gas stream in the converter circuit for the production of ammonia, or the ammonia gas stream for urea synthesis.

[0028] The system combination according to the invention is explained in more detail below using an embodiment shown in the drawing.

[0029] Fig. 1 : Flow chart

[0030] Fig. 1 shows an exemplary plant combination schematically and in a highly simplified manner. In particular, compressors and heat exchangers have been omitted for simplicity. Hydrocarbons and water are fed to the primary reformer 11 via a natural gas-water supply 10. The primary reformer is heated, and steam reforming takes place. The gas mixture emerging from the primary reformer 11 is supplied with air via an air supply to provide oxygen for combustion and nitrogen for ammonia synthesis. Autothermal reforming takes place in the secondary reformer, so that the final gas mixture ideally consists primarily of hydrogen, nitrogen, and carbon dioxide. The gas mixture passes through an amine-carbon dioxide scrubber 20 to separate the carbon dioxide and then a methanizer 25, in which any remaining carbon monoxide (catalyst poison) is converted with hydrogen to methane. The gas mixture is then introduced into the converter circuit.The converter circuit includes converter 30, where the conversion of hydrogen and nitrogen to ammonia takes place over a catalyst. This is an equilibrium reaction, and complete conversion is not achieved. Therefore, ammonia is separated in ammonia separator 31. The separated ammonia is fed to the urea production plant 40, and the urea produced there is fed to the urea granulation plant 41.

[0031] The amine carbon dioxide scrubber 20 is connected via an amine circuit to a carbon dioxide separation unit 21, in which the bound carbon dioxide is released again and fed as a carbon dioxide stream 23 for urea synthesis to the urea production plant 40. The amine circuit also has an amine treatment unit 22. The amine treatment unit 22 and the carbon dioxide separation unit 21 can also be combined in a common device. The treatment gas stream 24 in the amine treatment unit 22 is fed as a gas stream to the methanol synthesis device 50, the composition of which lies within the described range.

[0032] The converter circuit further comprises an inert gas discharge 32. This can also be implemented in a common device with the ammonia separator 31. The inert gas discharge 32 comprises an aqueous ammonia scrubber 33, from which a first inert gas discharge stream 36 is generated and fed to the methanol synthesis device 50, the composition of which lies within the described range. Furthermore, the inert gas discharge 32 comprises a hydrogen recovery 34. In the hydrogen recovery 34, the second inert gas discharge stream 37 is generated and fed as a third gas stream to the methanol synthesis device 50, the composition of which lies within the described range.

[0033] The methanol synthesis device 50 is fed to the formaldehyde synthesis device 51, and the formaldehyde produced there is fed to the device for producing a formaldehyde-urea mixture 52. Urea from the urea production plant 40 is also fed to the device for producing a formaldehyde-urea mixture 52. The formaldehyde-urea mixture produced in the device for producing a formaldehyde-urea mixture 52 is mixed with the main urea stream and fed to the urea granulation plant 41.

[0034] Reference symbol

[0035] 10 Natural gas water supply

[0036] 11 primary reformers

[0037] 12 Air supply

[0038] 13 secondary reformers

[0039] 20 amine carbon dioxide scrubbers

[0040] 21 Carbon dioxide capture

[0041] 22 Amine processing

[0042] 23 Carbon dioxide electricity

[0043] 24 Reprocessing gas stream

[0044] 25 Methanizer

[0045] 30 converters

[0046] 31 ammonia separators

[0047] 32 Inert gas discharge

[0048] 33 aqueous ammonia scrubber

[0049] 34 Hydrogen recovery

[0050] 35 Inert gas stream

[0051] 36 first inert gas discharge stream

[0052] 37 second inert gas discharge stream

[0053] 40 Urea production plant

[0054] 41 Urea granulation plant

[0055] 50 methanol synthesis device

[0056] 51 Formaldehyde synthesis device

[0057] 52 Device for producing a formaldehyde-urea mixture

Claims

Patent claims 1. A process for the production of ammonia, for the further conversion of the ammonia to urea and for the subsequent granulation of the urea, wherein methanol is additionally produced, wherein the methanol is converted to formaldehyde and the formaldehyde to a formaldehyde-urea mixture, wherein the formaldehyde-urea mixture is added to the urea before granulation, characterized in that three gas streams are combined for the methanol synthesis, wherein the first gas stream is a first processing gas stream (24) after the processing of an amine solution of an amine-carbon dioxide scrubber (20), wherein the first processing gas stream (24) mainly comprises carbon dioxide, hydrogen, and nitrogen, wherein the second gas stream is a first inert gas discharge stream (36) from the converter circuit of the ammonia synthesis, wherein the first inert gas discharge stream (36) is taken off after an aqueous ammonia scrubber (33),wherein the first inert gas discharge stream (36) comprises mainly hydrogen and methane, wherein a second inert gas discharge stream is selected as the third gas stream, wherein the second inert gas discharge stream (37) is removed after a hydrogen recovery (34), wherein the second inert gas discharge stream (37) comprises mainly methane, nitrogen and some hydrogen., 2. Process according to claim 1, characterized in that the first processing gas stream (24), the first inert gas discharge stream (36) and the second inert gas discharge stream (37) are mixed according to the chemical composition, the composition of the mixed gas stream being adjusted to a composition suitable for methanol synthesis.

3. Process according to one of the preceding claims, characterized in that no gas stream is fed directly from the main gas stream to the methanol synthesis.

4. Process according to one of the preceding claims, characterized in that the residual gas not converted in the methanol synthesis is fed to the amine carbon dioxide scrubber (20).

5. Plant combination with a plant for producing ammonia, a plant for producing urea (40) from ammonia and a urea granulation plant (41), wherein the plant for producing ammonia has a reformer and a converter circuit with a converter (30), wherein an amine-carbon dioxide scrubber (20) is arranged between the reformer and the converter circuit, wherein the converter circuit has an inert gas discharge (32), wherein the inert gas discharge (32) has an aqueous ammonia scrubber (33) and a hydrogen recovery (34), wherein the plant combination has a methanol synthesis device (50), wherein the plant combination has a formaldehyde synthesis device (51), wherein the plant combination has a device for producing a formaldehyde-urea mixture (52), wherein the methanol synthesis device (50) is connected to the formaldehyde synthesis device (51) for converting methanol. ) is connected,wherein the formaldehyde synthesis device (51) for transferring formaldehyde is connected to the device for producing a formaldehyde-urea mixture (52), wherein the device for producing a formaldehyde-urea mixture (52) for transferring formaldehyde-urea mixture is connected to the urea granulation plant (41), characterized in that the amine-carbon dioxide scrubber (20) is connected to the methanol synthesis device (50) in such a way that the carbon dioxide-, methane- and hydrogen-containing processing gas stream (24) produced during the processing of the amine solution is transferred to the methanol synthesis device (50), wherein the inert gas discharge (32) is connected to the methanol synthesis device (50) in such a way that, on the one hand, the inert gas discharge (32) is connected to the methanol synthesis device (50) downstream of the aqueous ammonia scrubber (33), so that the first inert gas discharge stream (36), which mainly comprises hydrogen and methane, is transferred to the methanol synthesis device (50), wherein the inert gas discharge (32) is connected to the methanol synthesis device (50) in such a way that, on the other hand, the inert gas discharge (32) is connected to the methanol synthesis device (50) downstream of a hydrogen recovery (34), so that the second inert gas discharge stream (37), which mainly comprises methane, nitrogen and some hydrogen, is transferred to the methanol synthesis device (50).

6. Plant combination according to claim 5, characterized in that the plant combination has a mixing device, wherein the mixing device is arranged upstream of the methanol synthesis device (50), wherein the processing gas stream (24), the first inert gas discharge stream (36) and the second inert gas discharge stream (37) are fed to the mixing device, wherein the mixing device is designed for the quantitatively variable mixing of the three gas streams.

7. Plant combination according to one of claims 5 to 6, characterized in that there is no connection between the main gas stream and the methanol synthesis device (50).

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