LU103095B1 - Quantitatively optimized production of methanol and formaldehyde-urea in a combined ammonia-urea plant - Google Patents

Abstract

The present invention relates to a process for producing ammonia, further converting the ammonia to urea and subsequently granulating 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 methanol synthesis, wherein a first processing gas stream 24 is selected as the first gas stream after processing an amine solution of an amine-carbon dioxide scrubber 20, wherein the first processing gas stream 24 comprises in particular carbon dioxide, hydrogen and nitrogen, wherein a first inert gas discharge stream 36 is selected as the second gas stream from the converter circuit of the ammonia synthesis, wherein the first inert gas discharge stream 36 is removed after an aqueous ammonia scrubber 33, wherein the first inert gas discharge stream 36 in particular comprises 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 in particular comprises methane, nitrogen and some hydrogen.

Description

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Quantitatively optimized production of methanol and formaldehyde

Urea in a combined ammonia-urea plant

The invention relates to an optimized plant network for the production of ammonia and urea from the ammonia and subsequent granulation of the urea, whereby a formaldehyde-urea mixture is added to the urea in small quantities as a usual additive to optimize the urea granulate. Therefore, nowadays methanol is usually produced in dedicated methanol production plants and formaldehyde is produced from it in separate locations, urea is then used for formaldehyde

synthesis plant, where the formaldehyde-urea mixture is produced and then bought back by the urea manufacturer and transported back.

This is a significant cost factor, where dependence on raw materials also

production. Therefore, there is interest in methanol and from the

Methanol then formaldehyde and thus the formaldehyde-urea mixture at the site of

ammonia and urea synthesis. However, it is currently not possible to

Methanol and thus also the formaldehyde-urea mixture in sufficient quantities and economically viable while avoiding the reduction of the economic efficiency in

to manufacture the system network itself.

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

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 part of a

hydrocarbon feedstock and steam in a steam reformer, (b) forming a second synthesis gas stream 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 coming from the second

Synthesis gas stream was produced, whereby a hydrogen-containing purge stream from the 1

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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).

WO2018185459A1 describes a process for producing formaldehyde-stabilized urea, comprising the steps of: (a) producing a

synthesis gas; (b) subjecting the synthesis gas to one or more stages of

Water-gas conversion in one or more water-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

to form carbon dioxide-depleted synthesis gas; (e) synthesis of 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 in order to

to form formaldehyde in a stabilizer production unit; (g) subjecting the

methanol synthesis offgas from a 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) converting a part 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. 2

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WO2017103564A1 describes a process for producing formaldehyde-stabilized urea, comprising the steps of: (a) producing a

hydrogen, nitrogen, carbon monoxide, carbon dioxide and steam

synthesis gas in a synthesis gas generation unit, (b) subjecting the

synthesis gas one or more water-gas shift stages in one or more

water-gas shift reactors to form a shifted gas; (c) recovering carbon dioxide 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

Recovery of methanol and a methanol synthesis exhaust gas containing nitrogen,

hydrogen and residual carbon monoxide; (e) subjecting at least one

Part of the recovered methanol is oxidized 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 produce a

to form ammonia synthesis gas; (g) synthesizing ammonia from the ammonia

synthesis gas in an ammonia production unit and recovering the ammonia; (h)

Converting 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, with part of the formaldehyde recovered from the synthesis gas

synthesis gas produced by the production unit, either the one or more

Water-gas shift bypasses reactors; the carbon dioxide removal unit; or the one or more water-gas shift reactors and the carbon dioxide

unit of distance.

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) dividing 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

Gas conversion in one or more water-gas conversion reactors to 3

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carbon dioxide removal unit to form a carbon dioxide depleted synthesis gas; (f) subjecting the carbon dioxide depleted synthesis gas to a

Methanization stage in one or more methanation reactors to produce a

to form 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 produce a

urea stream; and (i) stabilizing the urea by mixing the

urea stream and one produced using formaldehyde

stabilizer to form a stabilized urea, whereby the formaldehyde is

steps comprising; (1) passing the second portion of the synthesis gas through a scrubber to remove impurities therefrom and produce a scrubbed

synthesis gas; (2) synthesis of methanol from the washed synthesis gas in a methanol synthesis unit and recovery of 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 is oxidized with air in a formaldehyde stabilizer production unit to produce formaldehyde.

WO2016132091A1 describes a process for producing formaldehyde, comprising (a) subjecting methanol to oxidation with air in a

Formaldehyde production unit, whereby a formaldehyde-containing stream is produced; (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 is carried out.

WO2016132092A1 describes a process for producing formaldehyde-stabilized urea, comprising the steps of: (a) producing a 4

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synthesis gas comprising hydrogen, nitrogen, carbon monoxide, carbon dioxide and

Steam in a synthesis gas generation unit; (b) carbon dioxide is recovered from the synthesis gas to form a carbon dioxide-depleted synthesis gas; (c)

Synthesis of methanol from the carbon dioxide-depleted synthesis gas in a

Methanol synthesis unit and recovery of 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 offgas from a 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) converting a part 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 obtained using formaldehyde from the formaldehyde production unit.

Formaldehyde was produced by compressing an air source and dividing it into a first and a second part, the first part of the formaldehyde

production unit for the oxidation of methanol and the second part is further compressed and fed to the synthesis gas production unit.

A catalysis 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

Process. More specifically, a catalyst or a catalyst substrate according to the invention comprises at least one metal and/or

Alloy body produced by a melt spinning or melt extraction process.

WO2022064214A1 discloses a method for installing catalyst supports in a first selected reactor tube of a tubular reactor. The method comprises

Steps: i) providing an installation tool, the installation tool comprising: a) an installation frame; b) a movable plunger attached to the

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Installation frame mounted and configured to accommodate one or more

catalyst support into the first selected reactor tube; and c) one or more anchors for releasably securing the installation frame to the tubular reactor; il) 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.

WO2022064211A1 discloses a reactor tube for a tubular reactor and a

A holding device associated with a reactor tube is known, wherein the reactor tube comprises an elongated tube having a bore for receiving a catalyst in the

Use defined and an outlet at one end of the bore for discharging the

catalyst from the bore; wherein the retaining 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 to the

Retention of the catalyst inside the bore blocked; and in the second

Position the outlet is sufficiently unobstructed to allow the catalyst to drain from the outlet.

The aim is to find sources for methanol and subsequent formaldehyde production that do not come 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.

The object of the invention is therefore to provide an economical and sufficient production of methanol and subsequently of urea-formaldehyde in an ammonia

urea plant.

This object is achieved by the method with the features specified in claim 1

Features and by the system combination with the 6 specified in claim 5

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Features. Advantageous further developments emerge from the subclaims, the following description and the drawing.

The process according to the invention is used for the production of ammonia, the further

Conversion of ammonia to urea and subsequent granulation of the

Urea. Such plant systems for carrying out such a process are well known and are used worldwide. The granulation aid used so far is

Formaldehyde-urea mixture is purchased and introduced into the process. In order to build up a certain level of self-sufficiency, the added value within the

In addition, methanol is produced. The methanol is then further converted to formaldehyde and the formaldehyde is then further converted to a

Formaldehyde-urea mixture is converted. The formaldehyde-urea mixture is then added to the urea before granulation.

According to the invention, three gas streams are combined for methanol synthesis.

Gas streams are not fed from the main gas stream, i.e. the generation of

Hydrogen or the hydrogen-nitrogen mixture, the

Converter circuit for the production of ammonia or the ammonia gas stream for

Urea synthesis. Only gas streams are used which arise in cleaning or separation processes and usually only undergo thermal

This means that the additional formaldehyde produced has no influence on the amount of ammonia or urea produced.

At the same time, it is possible to produce sufficient formaldehyde by combining the selected gas streams. The first gas stream is a “first

Work-up gas stream after work-up of an amine solution of an amine

The first processing gas stream comprises in particular carbon dioxide, hydrogen and nitrogen. In particular,

In connection with the composition of gas streams, it is understood that the

Gas stream usually contains at least 90 vol.% of the corresponding components. Other components, for example argon or

Carbon monoxide, are present in some gas streams. These other components are less than 10 vol.% in the sum of the other components. The second gas stream is a first inert gas discharge stream from the converter circuit of the 7

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ammonia synthesis. The first inert gas discharge stream is taken after an aqueous ammonia scrubber. The first

Inert gas discharge stream contains hydrogen and methane in particular. A second inert gas discharge stream is selected as the third gas stream. The second

Inert gas discharge stream is removed after hydrogen recovery.

The second inert gas discharge stream contains mainly methane, nitrogen and some hydrogen. These three gas streams are usually used for thermal

Utilization, either in the burner of the primary reformer or used for electricity generation.

Therefore, the use of these gas streams has no influence on the actual

Production of ammonia and urea, but does not affect this main gas flow. At the same time, the use of these gas flows can produce a significantly higher amount of methanol than with the state of the art, and thus significantly more than the company's own demand for methanol, and thus for urea-formaldehyde, can be covered.

An important point here is that, as before, a gas stream is not selected, for example the main gas stream instead of a methanizer, in order to

To produce methanol, three gas streams are used, the

The composition alone is not useful for the synthesis of methanol. Rather, it is the mixture that makes it possible to create a suitable

gas mixture, whereas each gas stream on its own appears to be unsuitable.

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 is mixed according to the chemical composition. The composition of the mixed gas stream is adjusted to a value

Composition suitable for methanol synthesis. The composition not suitable for

The portions of the three gas streams used in the mixed gas stream can be used for thermal recycling, for example. Continuous

Analysis of the composition of the three gas streams 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 8

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The ratio of carbon dioxide to hydrogen in particular for methanol synthesis can be adjusted.

In a further embodiment of the invention, no gas stream is taken directly from the

Main gas stream of methanol synthesis.

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 unreacted hydrogen in particular to be fed back into the ammonia synthesis, which further increases overall efficiency.

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 combinations are well known and are in use in large numbers. The plant for the production of ammonia has a reformer and a converter circuit with a converter. Between the

An amine-carbon dioxide scrubber is arranged between the reformer and the converter circuit.

This removes the carbon dioxide from the gas stream, so that behind the scrubber the

Gas stream contains practically only hydrogen and nitrogen and is therefore suitable for conversion to

ammonia in the converter. At the same time, the scrubber supplies the

Urea synthesis required carbon dioxide as a second reactant besides ammonia.

Converter circuit has an inert gas discharge. This is necessary, otherwise, for example, argon would continue to accumulate in the converter circuit over time, the

Partial pressures of hydrogen and nitrogen and thus the yield would decrease.

It is therefore necessary and usual to carry out an appropriate inert gas discharge, which allows the greatest possible, but never complete, recovery of the

useful gases, especially hydrogen and ammonia.

Inert gas discharge therefore has an aqueous ammonia scrubber and a

Hydrogen recovery. These components are found in virtually every plant for producing ammonia and urea today.

In order to be able to produce at least part of the required formaldehyde-urea mixture in-house, it is known that the plant network can be expanded. The 9

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The plant network comprises a methanol synthesis device. The plant network further comprises a formaldehyde synthesis device in order to produce formaldehyde from the methanol. The plant network further comprises a device for producing a

Formaldehyde-urea mixture. The methanol synthesis device is used for

Transfer of methanol connected to the formaldehyde synthesis device. The

Formaldehyde synthesis device is designed to convert formaldehyde with the

Device for producing a formaldehyde-urea mixture. The

Device for producing a formaldehyde-urea mixture is connected to the urea granulation plant for transferring formaldehyde-urea mixture.

What is important now is which gas streams are used to produce the methanol, i.e. which parts of the plant network are used to transfer gas streams with the

methanol synthesis device. The used

Gas flows do not reduce the production of ammonia or urea and thus reduce the actual product quantity and thus the

Instead, other gas streams should be used to maintain the economic efficiency of the plant network and to

No purchase of the formaldehyde-urea mixture

According to the invention, the amine carbon dioxide scrubber is provided with the

Methanol synthesis device, so that the amine

Carbon dioxide, methane and hydrogen-containing solutions

Reprocessing gas stream is transferred to the methanol synthesis device. Secondly, the inert gas discharge is connected to the methanol synthesis device in such a way that, on the one hand, the inert gas discharge behind the aqueous ammonia scrubber is connected to the methanol synthesis device so that the first

Inert gas discharge stream, which in particular comprises 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 after hydrogen recovery with the

methanol synthesis device, so that the second

Inert gas discharge stream, which mainly contains methane, nitrogen and some

hydrogen, is transferred to the methanol synthesis device.

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These three gas streams have different gas compositions and would normally be fed to thermal utilization. By feeding them to the methanol synthesis device via the above-mentioned connections, and only by combining all three connections to the methanol synthesis device, a gas composition is achieved there that is suitable for methanol synthesis.

In a further embodiment of the invention, the system network has a

Mixing device. The mixing device is arranged in front of the methanol synthesis device and is connected to it for transferring a mixed gas stream. The

Mixing device, the processing gas stream, the first

Inert gas discharge stream and the second inert gas discharge stream.

The mixing device is designed for the variable-quantity mixing of the three gas streams. This allows the mixing device to react to a changing composition of the three gas streams and to produce a mixture suitable for methanol synthesis.

create a gas mixture. Therefore, the mixing device can be connected to a device for thermal utilization in order to be able to supply the unused gas stream portion there for thermal utilization, for example in a burner of a primary reformer.

In a further embodiment of the invention, there is no connection between the main gas stream and the methanol synthesis device.

The system network according to the invention is explained in more detail below using an embodiment shown in the drawing.

Fig. 1 Flow diagram

In Fig. 1, an exemplary system is shown schematically and in a highly simplified manner. In particular, compressors and heat exchangers are 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 a 11

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Steam reforming. The gas mixture leaving the primary reformer 11 is supplied with air through an air supply in order to provide oxygen for combustion and

Nitrogen for ammonia synthesis. In the secondary reformer, autothermal reforming takes place, so that the gas mixture ideally consists of hydrogen, nitrogen and carbon dioxide in particular. 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. In the converter circuit, the converter 30, in which the

Conversion of hydrogen and nitrogen to ammonia takes place on a catalyst, whereby this is an equilibrium reaction and complete conversion is not achieved. Therefore, ammonia is separated in the ammonia separator 31. The separated ammonia is fed to the plant for the production of urea 40 and the urea produced there is fed to the urea granulation plant 41.

The amine carbon dioxide scrubber 20 is connected via an amine circuit with a

Carbon dioxide separation 21, in which the bound carbon dioxide is released again and used as carbon dioxide stream 23 for the urea synthesis of the plant for

The amine cycle also has a

Amine preparation 22. The amine preparation 22 and the carbon dioxide separation 21 can also be combined in a common device. The

Processing 22 Processing gas stream 24 is referred to as a gas stream of

methanol synthesis device 50.

The converter circuit also has an inert gas discharge 32. This can also be formed in a common device with the ammonia separator 31. The inert gas discharge 32 has an aqueous

Ammonia scrubber 33, from which a first inert gas discharge stream 36 is generated and fed to the methanol synthesis device 50. Furthermore, the

Inert gas discharge 32 a \hydrogen recovery 34. In the

Hydrogen recovery 34 generates the second inert gas discharge stream 37 and is fed as a third gas stream to the methanol synthesis device 50. 12

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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. The device for producing a

Formaldehyde-urea mixture 52 also contains urea from the plant for

Production of urea 40. The product in the device for producing a

The formaldehyde-urea mixture produced from the formaldehyde-urea mixture 52 is mixed with the main stream of urea and fed to the urea granulation plant 41.

reference sign

Natural gas-water supply 11 Primary reformer 12 Air supply 13 Secondary reformer

Amine-carbon dioxide scrubber 21 Carbon dioxide separation 22 Amine processing 23 Carbon dioxide stream 24 Processing gas stream

methanizer

Converter 31 Ammonia separator 32 Inert gas discharge 33 Aqueous ammonia scrubber 34 Hydrogen recovery

Inert gas stream 36 first inert gas discharge stream 37 second inert gas discharge stream

Plant for the production of urea 41 Urea granulation plant

Methanol synthesis device 51 Formaldehyde synthesis device 52 Device for producing a formaldehyde-urea mixture 13

Claims (7)

221152P00LU LU103095 patent claims 1. Process for the production of ammonia, further conversion of the ammonia to urea and 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 a first processing gas stream (24) is selected as the first gas stream after processing an amine solution of an amine-carbon dioxide scrubber (20), wherein the first processing gas stream (24) comprises in particular carbon dioxide, hydrogen and nitrogen, wherein a first inert gas discharge stream (36) is selected as the second gas stream from the converter circuit of the ammonia synthesis, wherein the first inert gas discharge stream (36) is taken after an aqueous ammonia scrubber (33), wherein the first Inert gas discharge stream (36) in particular comprises 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) in particular comprises 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. 1 221152P00LU LU103095 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 network 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 network has a methanol synthesis device (50), wherein the plant network has a formaldehyde synthesis device (51), wherein the plant network 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, 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) arising 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) behind the aqueous ammonia scrubber (33), so that the first Inert gas discharge stream (36), which in particular 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) 2 221152P00LU LU103095, so that on the other hand the inert gas discharge (32) is connected to the methanol synthesis device (50) after a hydrogen recovery (34), so that the second inert gas discharge stream (37), which in particular comprises methane, nitrogen and some hydrogen, is transferred to the methanol synthesis device (50). 6. Plant network according to claim 5, characterized in that the plant network 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 flow and the methanol synthesis device (50). 3