Combined system for producing steel, and method for operating the combined system

Abstract

The invention relates to a combined system (1) for producing steel, said combined system comprising: a blast furnace (2) for producing pig iron; a converter steel mill (3) for producing crude steel; a blast furnace gas line system (4) for gases generated during the pig iron production; a composite line system (5) for gases generated during the pig iron production and / or crude steel production; a plant (6) for producing hydrogen or hydrogen-containing synthesis gas; a hydrogen line (8) for hydrogen-containing gases generated during the production of hydrogen or hydrogen-containing synthesis gas, the blast furnace gas line system (4) being connected to the plant (6) for producing hydrogen or hydrogen-containing synthesis gas as an input line into the plant (6) for producing hydrogen or hydrogen-containing synthesis gas, and the hydrogen line (8) being connected to the plant (6) for producing hydrogen or hydrogen-containing synthesis gas as an output line from the plant (6) for producing hydrogen or hydrogen-containing synthesis gas.

Description

[0001] Plant network for steel production and a method for operating the plant network

[0002] The invention relates to a plant network for steel production and a method for operating the plant network.

[0003] The steel production plant complex comprises a blast furnace for pig iron production, a converter steelworks for crude steel production, and a combined pipeline system for gases generated during pig iron production and / or crude steel production. Pig iron is extracted in the blast furnace from iron ores, additives, coke, and other reducing agents such as coal, oil, gas, biomass, recycled plastics, or other carbon and / or hydrogen-containing materials. CO, CO2, and in particular hydrogen and water vapor are inevitably produced as products of the reduction reactions. Blast furnace top gas, also known as blast furnace top gas, often contains high levels of nitrogen in addition to the aforementioned components and may also contain impurities. The gas quantity and composition of the blast furnace top gas depend on the feedstock and operating mode and are subject to fluctuations.Typically, however, blast furnace top gas contains 35 to 60 vol.% N2, 20 to 30 vol.% CO2, 20 to 30 vol.% CO2, and 2 to 15 vol.% H2. Around 30 to 40% of the blast furnace top gas generated during pig iron production is typically used to heat the hot blast for the blast furnace process in hot blast stoves; the remaining blast gas can also be used externally, for example, in other plant areas for heating purposes or to generate electricity.

[0004] In the converter steelworks, which follows the blast furnace process, pig iron is converted into crude steel. By blowing oxygen onto the liquid pig iron, disruptive impurities such as carbon, silicon, sulfur, and phosphorus are removed. Since the oxidation processes cause significant heat generation, scrap is often added as a coolant in quantities of up to 25% of the pig iron. Lime is also added for slag formation and alloying agents. A converter gas is withdrawn from the steel converter. This gas has a high CO content and also contains nitrogen, hydrogen, and CO2. A typical converter gas composition comprises 50 to 70 vol.% CO, 10 to 20 vol.% N2, approximately 15 vol.% CO2, and approximately 2 vol.% H2. The converter gas is

[0005] REPLACEMENT SHEET (RULE 26) either flared or captured in modern steelworks and used for energy recovery.

[0006] In an integrated steelworks operated in conjunction with a coking plant, approximately 40 to 50% of the raw gases generated as blast furnace top gas, converter gas, and coke oven gas are used for process engineering. Approximately 50 to 60% of the resulting gases are fed to the power plant and used to generate electricity. The electricity generated in the power plant covers the electricity demand for pig iron and crude steel production. Ideally, the energy balance is closed, so that apart from iron ore and carbon in the form of coal and coke as energy sources, no further energy input is required, and no product leaves the plant complex other than crude steel and slag.

[0007] The current state of the art is problematic due to high CO2 emissions, particularly a large CO2 footprint.

[0008] The invention is therefore based on the object of improving the sustainability of the overall process and the CO2 balance, in particular CO2 emissions, and reducing the CO2 footprint while at the same time enabling stable, continuous and sustainable operation of plants.

[0009] This problem is initially solved by the features of patent claim 1. The steel production plant network comprises a blast furnace for pig iron production, a converter steelworks for crude steel production, a blast furnace gas pipeline system for gases generated during pig iron production, a combined pipeline system for gases generated during pig iron production and / or crude steel production, and a plant for the production of hydrogen or hydrogen-containing synthesis gas.Furthermore, the plant network comprises a hydrogen pipeline for hydrogen-containing gases which arise during the production of hydrogen or hydrogen-containing synthesis gas, wherein the blast furnace gas pipeline system is connected to the plant for the production of hydrogen or hydrogen-containing synthesis gas as an input line into the plant for the production of hydrogen or hydrogen-containing synthesis gas and the hydrogen pipeline is connected to the plant for the production of hydrogen or hydrogen-containing synthesis gas as an output line from the plant for the production of hydrogen or hydrogen-containing synthesis gas.In the context of the present invention, a plant for producing hydrogen is understood to mean a plant for producing hydrogen, in particular a plant which provides hydrogen, for example a water-gas shift reaction plant, in particular by converting the CO content by a water-gas shift reaction (CO + H2O <=> CO2 + H2), a plant for separating hydrogen, in particular a hydrogen separation membrane plant or a combination thereof.

[0010] With the help of the hydrogen production plant, hydrogen-containing gases with different hydrogen concentrations can be provided, which can be used for a wide variety of synthesis reactions in possible chemical plants, whereby the chemical plant can be installed downstream of the hydrogen production plant.

[0011] In a first embodiment of the plant network according to the invention, it is provided that the plant for producing hydrogen or hydrogen-containing synthesis gas comprises a water-gas shift reaction plant and / or a hydrogen separation membrane plant, in particular the hydrogen separation membrane plant is connected downstream of the water-gas shift reaction plant in the flow direction.

[0012] In a further embodiment of the plant network according to the invention, it can be provided that the plant for producing hydrogen or hydrogen-containing synthesis gas additionally comprises a first CO2 separation plant, wherein the first CO2 separation plant is arranged upstream of the hydrogen separation membrane plant in the flow direction. The first CO2 separation plant can, in particular, be connected to the network pipeline system via a first CO2 line.

[0013] In a further advantageous embodiment of the plant network according to the invention, it is provided that the plant network additionally comprises a first CO2 switch for CO2 that is produced in the first plant for CO2 separation, wherein the first CO2 switch is connected to the first CO2 line.

[0014] In preferred embodiments, the hydrogen separation membrane plant can be configured to set a stoichiometric mixing ratio in the hydrogen-rich synthesis gas of a dividend with the molar amount of hydrogen and a divisor with the molar amount of nitrogen in the range from 1 to 4.0, particularly preferably in the range from 2.0 to 3.8, most preferably in the range from 2.5 to 3.5.

[0015] In alternative embodiments, the hydrogen separation membrane plant can be configured to set a stoichiometric mixing ratio in the hydrogen-rich synthesis gas consisting of a dividend with the molar amount of hydrogen and a divisor with the molar amount of nitrogen in the range of greater than 4, preferably greater than 7, particularly preferably greater than 9.

[0016] In a particularly preferred embodiment of the plant network according to the invention, an ammonia plant for producing ammonia from hydrogen-containing synthesis gas is provided in the plant for producing hydrogen or hydrogen-containing synthesis gas. The ammonia plant can, for example, be connected to the integrated control system, with the hydrogen line being connected to the integrated control system upstream of the ammonia plant in the flow direction.

[0017] Ammonia is the world's second most produced synthetic chemical. Ammonia is produced primarily from the elements hydrogen and nitrogen in the presence of an iron catalyst. Temperatures often range between 400 °C and 500 °C and pressures exceeding 100 bar. The key factor in the process costs is the supply of hydrogen and nitrogen. Accordingly, ammonia production is preferably based on the "Haber-Bosch process" from the elements according to equation [1]:

[0018] 3 H2 + N2 ^ 2 NH3 + 92.28 kJ [1]

[0019] By using a plant to produce hydrogen or hydrogen-containing synthesis gas, primarily hydrogen and nitrogen, the complex process of steam reforming can be eliminated. Likewise, it is not necessary to obtain nitrogen from air separation if nitrogen is already produced during the hydrogen production process in the plant for producing hydrogen or hydrogen-containing synthesis gas.

[0020] To remove small residual amounts of CO and CO2, which act as catalyst poisons, a further embodiment of the plant network according to the invention provides for a methanation plant to be arranged upstream of the ammonia plant in the direction of flow. The energy released during methanation can also be used to activate the reaction in the ammonia plant, ensuring the plant operates as energy-efficiently as possible.

[0021] In a further particularly preferred embodiment of the plant network according to the invention, a urea plant is provided for producing urea, with the ammonia plant being arranged upstream of the urea plant in the direction of flow. In the large-scale production of urea, the high-pressure synthesis of ammonia (NH3) and carbon dioxide (CO2) at approximately 150 bar and approximately 180 degrees Celsius is used almost exclusively. The two feedstocks are often obtained from a neighboring ammonia plant. In conjunction with the ammonia plant, ammonia would already be available as a reactant. In addition, CO2 can be obtained by means of the aforementioned CO2 separation plant and fed directly to the urea plant via the aforementioned CO2 switch.

[0022] Various processes are known in the art for the production of particulate, urea-containing compositions. In the past, urea particles were typically produced by spray crystallization, in which a substantially anhydrous urea melt (water content of 0.1 to 0.3 wt. %) is sprayed from the top of a spray crystallization tower into an ascending stream of air at ambient temperature, and the droplets solidify into crystals (prills). The resulting prills have relatively small diameters and low mechanical strength.

[0023] The above-mentioned object is also achieved by a method for operating a steel production plant network comprising a blast furnace for pig iron production, a converter steelworks for crude steel production, a blast furnace gas pipeline system for gases arising from pig iron production, a pipeline system for gases arising from pig iron production and / or crude steel production, a plant for producing hydrogen or hydrogen-containing synthesis gas, a hydrogen pipeline for hydrogen-containing gases arising from the production of hydrogen or hydrogen-containing synthesis gas,wherein the blast furnace gas piping system is connected to the plant for producing hydrogen or hydrogen-containing synthesis gas as an input line into the plant for producing hydrogen or hydrogen-containing synthesis gas, and the hydrogen line is connected to the plant for producing hydrogen or hydrogen-containing synthesis gas as an output line from the plant for producing hydrogen or hydrogen-containing synthesis gas, wherein in the plant for producing hydrogen or hydrogen-rich synthesis gas, a mixed gas is adjusted with a stoichiometric mixing ratio consisting of a dividend with the molar amount of hydrogen and a divisor with the molar amount of nitrogen. The above statements regarding the plant network according to the invention also apply accordingly to the process according to the invention.

[0024] In a first embodiment of the process according to the invention, the plant network additionally comprises an ammonia plant for producing ammonia from the hydrogen-containing synthesis gas of the plant for producing hydrogen or hydrogen-containing synthesis gas. The ammonia plant can, for example, be connected to the integrated control system, and the hydrogen line can be connected to the integrated control system upstream of the ammonia plant in the direction of flow. The plant for producing hydrogen or hydrogen-rich synthesis gas sets a mixed gas for ammonia synthesis, with a stoichiometric mixing ratio of a dividend with the molar amount of hydrogen and a divisor with the molar amount of nitrogen in the range from 1 to 4.0, particularly preferably in the range from 2.0 to 3.8, most preferably in the range from 2.5 to 3.5.In this way, a favorable stoichiometric ratio of hydrogen to nitrogen is obtained for ammonia synthesis.

[0025] In a further embodiment of the process according to the invention, it is provided that in the plant for producing hydrogen or hydrogen-rich synthesis gas, a hydrogen-rich gas is produced with a stoichiometric mixing ratio of a dividend with the molar amount of hydrogen and a divisor with the molar amount of nitrogen in the range of greater than 4, preferably greater than 7, particularly preferably greater than 9. In this way, a hydrogen-rich gas can be adjusted to, for example, 90 mol% hydrogen at a ratio of 9:1. Due to the high purity of the hydrogen produced in this way, it can be used for a variety of different technical applications without synthesizing ammonia from it. Other chemical plants that use hydrogen as a reactant are conceivable. Part of the hydrogen produced could also be used as an energy source for other applications in a plant complex.Preferably, the plant for producing hydrogen or hydrogen-rich synthesis gas can comprise a water-gas shift reaction plant, a first plant for CO2 separation and a hydrogen separation membrane plant arranged downstream of one another in the flow direction, wherein the hydrogen separation membrane plant sets the stoichiometric mixing ratio.

[0026] Advantageously, in a further embodiment of the method according to the invention, it can be provided that the plant network additionally comprises: a first plant for CO2 separation and a urea plant, wherein the first plant for CO2 separation is connected upstream of the hydrogen separation membrane plant in the direction of flow, wherein the first plant for CO2 separation is connected to the network line system with a first CO2 line, in particular the first CO2 line is connected to the network line system upstream of the urea plant in the direction of flow to the network line system and a first CO2 switch for CO2 that arises in the first plant for CO2 separation, wherein the first CO2 switch is connected to the first CO2 line.It is intended that the first CO2 diverter will provide CO2 for the urea plant, and the stoichiometric ratio of the CO2 provided to the urea plant will be in the range 0.2-0.7, based on a stoichiometric quotient of a dividend representing the molar amount of CO2 and a divisor representing the molar amount of ammonia. In this way, a CO2 to NH3 ratio can be set that is required for subsequent urea synthesis in the urea plant.

[0027] Overall, the plant can be used flexibly to produce hydrogen or a hydrogen-containing synthesis gas in order to provide the optimal stoichiometric ratios for various synthesis reactions.

[0028] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case.

[0029] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. They show:

[0030] Figure 1 is a simplified schematic representation of a plant network for steel production with a downstream ammonia plant and Figure 2 is the block diagram according to Figure 1 with an additional urea plant.

[0031] Figure 1 shows, according to one embodiment of the invention, a steelmaking plant complex 1 comprising a blast furnace 2 for pig iron production and a converter steelworks 3 for crude steel production. The plant complex comprises a blast furnace gas piping system 4 for gases generated during pig iron production, a composite piping system 5 for gases generated during pig iron production and / or crude steel production, a plant 6 for producing hydrogen or hydrogen-containing synthesis gas, and an ammonia plant 7. The ammonia plant 7 is connected downstream of the plant 6 for producing hydrogen or hydrogen-containing synthesis gas.

[0032] The blast furnace gas pipeline system 4 is connected to the hydrogen or hydrogen-containing synthesis gas production plant 6 as an input line into the hydrogen or hydrogen-containing synthesis gas production plant 6, and the hydrogen pipeline 8 is connected to the hydrogen or hydrogen-containing synthesis gas production plant 6 as an output line from the hydrogen or hydrogen-containing synthesis gas production plant 6. The hydrogen or hydrogen-containing synthesis gas production plant 6 is represented as a water-gas shift reaction plant 9 and a hydrogen separation membrane plant 10, 10'.

[0033] The plant 6 for producing hydrogen or hydrogen-containing synthesis gas can provide a gas mixture that largely contains hydrogen and nitrogen. A first CO2 separation plant 11 is arranged upstream of the hydrogen separation membrane plant 10, 10' in the flow direction. The first CO2 separation plant 11 has a first CO2 line 12, with which it can be connected to the interconnected pipeline system 5. A first CO2 diverter 13 for CO2 produced during the CO2 separation 11 is connected to the first CO2 line 12.

[0034] If CO2 is separated from the gas mixture, it is possible to produce synthesis gas that can be used to synthesize ammonia. For this purpose, the ammonia plant 7 is connected downstream of the plant 6 for producing hydrogen or hydrogen-containing synthesis gas. In the ammonia plant 7, ammonia is synthesized from a gas mixture with a stoichiometric ratio of hydrogen to nitrogen of 3 to 1. A methanation plant 14 is connected upstream of the ammonia plant 7. The energy released by the methanation plant 14 can be used for the ammonia plant 7.

[0035] The hydrogen separation membrane system 10, 10' can be configured to adjust a stoichiometric mixing ratio in the hydrogen-rich synthesis gas, consisting of a dividend with the molar amount of hydrogen and a divisor with the molar amount of nitrogen, in the range of 1 to 4.0, particularly preferably in the range of 2.0 to 3.8, most preferably in the range of 2.5 to 3.5. This is preferably intended for use of the synthesis gas for ammonia production.

[0036] In particular for other purposes, the hydrogen separation membrane system 10, 10' can also be configured to set a stoichiometric mixing ratio in the hydrogen-rich synthesis gas from a dividend with the molar amount of hydrogen and from a divisor with the molar amount of nitrogen in the range of greater than 4, preferably greater than 7, particularly preferably greater than 9.

[0037] The configuration of the hydrogen separation membrane system 10, 10' to set the desired stoichiometric mixing ratio can be achieved, for example, by selecting the type and number of separation membranes used and their interconnection. This selection is preferably made depending on the composition of the gas in the input line of system 6 for producing hydrogen or hydrogen-containing synthesis gas. Connecting several membranes in series can, for example, lead to increased nitrogen removal and thus increase the hydrogen content in the hydrogen-containing synthesis gas passing through. Furthermore, the stoichiometric mixing ratio can be influenced by adjusting the pressure ratio of the gas pressure in the flow direction upstream and downstream of the hydrogen separation membrane system 10, 10'.

[0038] A coke oven plant 15 is connected to the interconnected pipeline system 5.

[0039] In Figure 2, a urea plant 16 is provided in addition to the ammonia plant 15. In the urea plant 16, the high-pressure synthesis of ammonia (NH3) and carbon dioxide (CO2) is carried out at approximately 150 bar and approximately 180 degrees Celsius. Ammonia can be obtained as a reactant from a neighboring ammonia plant 7. In addition, CO2 can be extracted using the aforementioned CO2 separation plant 11 and fed directly to the urea plant 16 via the aforementioned CO2 diverter 14.

[0040] Various processes are known in the art for the production of particulate, urea-containing compositions. In the past, urea particles were typically produced by spray crystallization, in which a substantially anhydrous urea melt (water content of 0.1 to 0.3 wt. %) is sprayed from the top of a spray crystallization tower into an ascending stream of air at ambient temperature, and the droplets solidify into crystals (prills). The resulting prills have relatively small diameters and low mechanical strength.

[0041] Reference symbol

[0042] 1 plant network

[0043] 2 blast furnaces

[0044] 3 Converter steelworks

[0045] 4 Blast furnace gas pipeline system

[0046] 5 Integrated control system

[0047] 6 Plant for the production of hydrogen or hydrogen-containing synthesis gas

[0048] 7 Ammonia plant

[0049] 8 Hydrogen line

[0050] 9 Water-Gas Shift Reaction Plant

[0051] 10, 10' hydrogen separation membrane plant

[0052] 11 CO2 capture plant

[0053] 12 First CO2 line

[0054] 13 First CO2 switch

[0055] 14 Methanization plant

[0056] 15 coke oven plant

[0057] 16 Urea plant

Claims

Patent claims 1. A plant network (1) for steel production comprising a blast furnace (2) for pig iron production, a converter steelworks (3) for crude steel production, a blast furnace gas pipeline system (4) for gases arising from pig iron production, a network pipeline system (5) for gases arising from pig iron production and / or crude steel production, a plant (6) for the production of hydrogen or hydrogen-containing synthesis gas, a hydrogen pipeline (8) for hydrogen-containing gases arising from the production of hydrogen or hydrogen-containing synthesis gas,wherein the blast furnace gas line system (4) is connected to the plant (6) for producing hydrogen or hydrogen-containing synthesis gas as an input line into the plant (6) for producing hydrogen or hydrogen-containing synthesis gas and the hydrogen line (8) is connected to the plant (6) for producing hydrogen or hydrogen-containing synthesis gas as an output line from the plant (6) for producing hydrogen or hydrogen-containing synthesis gas.

2. Plant network (1) according to claim 1, characterized in that the plant (6) for producing hydrogen or hydrogen-containing synthesis gas comprises a water-gas shift reaction plant (9) and / or a hydrogen separation membrane plant (10, 10'), in particular the hydrogen separation membrane plant (10, 10') is connected downstream of the water-gas shift reaction plant (9) in the flow direction.

3. Plant network (1) according to claim 2, characterized in that the plant for producing (6) hydrogen or hydrogen-containing synthesis gas additionally comprises a first plant for CO2 separation (11), wherein the first plant for CO2 separation (11) is arranged upstream of the hydrogen separation membrane plant (10, 10') in the flow direction.

4. Plant network (1) according to claim 3, characterized in that the first plant for CO2 separation (11) is connected to the network line system (5) by a first CO2 line (12).

5. Plant network (1) according to claim 4, characterized in that the plant network (1) additionally comprises a first CO2 switch (13) for CO2 which is produced in the first plant for CO2 separation (11), wherein the first CO2 switch (13) is connected to the first CO2 line (12).

6. Plant combination (1) according to one of claims 2 to 5, characterized in that the Hydrogen separation membrane system (10, 10') is configured to set a stoichiometric mixing ratio of a dividend with the molar amount of hydrogen and a divisor with the molar amount of nitrogen in the range from 1 to 4.0, particularly preferably in the range from 2.0 to 3.8, most preferably in the range from 2.5 to 3.5, in the hydrogen-rich synthesis gas.

7. Plant network (1) according to one of claims 2 to 5, characterized in that the Hydrogen separation membrane system (10, 10') is configured to set a stoichiometric mixing coefficient in the hydrogen-rich synthesis gas from a dividend with the molar amount of hydrogen and from a divisor with the molar amount of nitrogen in the range of greater than 4, preferably greater than 7, particularly preferably greater than 9.

8. Plant network (1) according to one of claims 1 to 6, characterized in that an ammonia plant (7) for producing ammonia from hydrogen-containing synthesis gas of the plant (6) for producing hydrogen or hydrogen-containing synthesis gas is provided.

9. Plant network (1) according to claim 7, characterized in that a methanation plant (14) is arranged upstream of the ammonia plant (7) in the flow direction.

10. Plant network (1) according to claim 8 or 9, characterized in that a urea plant (16) is provided for producing urea, wherein the ammonia plant (7) is arranged upstream of the urea plant (1) in the flow direction.

11. A method for operating a plant network (1) for steel production, which comprises a blast furnace (2) for pig iron production, a converter steelworks (3) for crude steel production, a blast furnace gas pipeline system (4) for gases arising from pig iron production, a network pipeline system (5) for gases arising from pig iron production and / or crude steel production, a plant (6) for producing hydrogen or hydrogen-containing synthesis gas, a hydrogen pipeline (8) for hydrogen-containing gases arising from the production of hydrogen or hydrogen-containing synthesis gas,wherein the blast furnace gas piping system (4) is connected to the plant for producing hydrogen or hydrogen-containing synthesis gas as an input line into the plant (6) for producing hydrogen or hydrogen-containing synthesis gas, and the hydrogen line (8) is connected to the plant (6) for producing hydrogen or hydrogen-containing synthesis gas as an output line from the plant (6) for producing hydrogen or hydrogen-containing synthesis gas, wherein in the plant (6) for producing hydrogen or hydrogen-containing synthesis gas, a mixed gas is adjusted with a stoichiometric mixing coefficient consisting of a dividend with the molar amount of hydrogen and a divisor with the molar amount of nitrogen.

12. The method according to claim 11, wherein the plant network (1) additionally comprises an ammonia plant (7) for producing ammonia from the hydrogen-containing synthesis gas of the plant (6) for producing hydrogen or hydrogen-containing synthesis gas, characterized in that the plant (6) for producing hydrogen or hydrogen-rich synthesis gas sets a mixed gas for ammonia synthesis with a stoichiometric mixing coefficient of a dividend with the molar amount of hydrogen and of a divisor with the molar amount of nitrogen in the range from 1 to 4.0, particularly preferably in the range from 2.0 to 3.8, most particularly preferably in the range from 2.5 to 3.

5.

13. The method according to claim 11, characterized in that in the plant (6) for producing hydrogen or hydrogen-rich synthesis gas, a hydrogen-rich gas is produced with a stoichiometric mixing ratio of a dividend with the molar amount of hydrogen and a divisor with the molar amount of nitrogen in the range of greater than 4, preferably greater than 7, particularly preferably greater than 9.

14. The method according to claim 12 or 13, characterized in that the plant (6) for obtaining hydrogen or hydrogen-rich synthesis gas comprises, downstream of one another in the flow direction, a water-gas shift reaction plant (9), a first plant for CO2 separation (11) and a hydrogen separation membrane plant (10, 10'), wherein the hydrogen separation membrane plant (10, 10') sets the stoichiometric mixing ratio.

15. A method for operating a plant network (1) according to one of claims 11 or 12, wherein the plant network (1) additionally comprises a first plant for CO2 separation (11) and a urea plant (16), wherein the first plant for CO2 separation (11) is connected upstream of the hydrogen separation membrane plant (10, 10') in the flow direction, wherein the first plant for CO2 separation (11) is connected to the network line system (5) by a first CO2 line (12), in particular the first CO2 line (12) is connected to the network line system (5) upstream of the urea plant (16) in the flow direction, and a first CO2 switch (13) for CO2 that accrues in the first plant for CO2 separation (11), wherein the first CO2 switch (13) is connected to the first CO2 line (12) is characterized bythat with the first CO2 switch (13) CO2 is provided for the urea plant (16) and the stoichiometric ratio of the CO2 provided for the urea plant with a stoichiometric quotient of a dividend with the molar amount of CO2 and a divisor with the molar amount of ammonia is in the range 0.2 - 0.7.

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