System and method for producing green urea
Patent Information
- Application Number
- EP2023776059
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-09-23
- Filing Date
- 2023-09-21
- Publication Date
- 2025-07-30
AI Technical Summary
The production of traditional urea is not green due to its reliance on fossil fuels for energy and raw materials, and the Haber-Bosch process for ammonia synthesis generates significant steam requirements that are not met by green ammonia synthesis alone, making it challenging to produce urea independently from natural gas.
A device that incorporates an ammonia gas turbine to generate thermal and mechanical energy for urea synthesis using green ammonia, which is connected to the urea synthesis unit via a steam line, allowing for the use of waste heat and mechanical power to drive a compressor or generator, and optionally connects to a Haber-Bosch reactor for superheating steam or directly drives a CO2 compressor, ensuring energy independence from fossil fuels.
This solution enables the production of green urea by utilizing green ammonia as both a feedstock and energy source, reducing carbon emissions and allowing for CO2-neutral urea production, even in locations without reliable renewable energy, by providing the necessary steam and energy for the urea synthesis process.
Smart Images
Figure 1.1
Abstract
Description
[0001] Plant and process for the production of green urea
[0002] The invention relates to the production of green urea. In particular, the invention relates to a device for synthesizing urea having the features of claim 1.
[0003] The production of green chemicals is becoming increasingly important. "Green" refers to chemicals that are produced sustainably (and therefore climate-neutral and environmentally friendly), meaning that no additional carbon dioxide is released into the atmosphere during their production. For example, these chemicals can be manufactured using processes whose energy requirements for production are met by renewable / regenerative energies (e.g., using electrical energy generated from renewable energies, such as in a photovoltaic system, a wind turbine, a geothermal power plant, or a tidal power plant), and in which the reactants used in production are not obtained from fossil fuels. The production of green ammonia is a clear focus here, as natural gas is currently used almost exclusively for ammonia production.During this production process, carbon dioxide (CO2) is produced as a by-product. If this carbon dioxide is not reused, it is released into the environment. However, urea plants can use this carbon dioxide together with the ammonia to convert it into urea, which is mainly used as a fertilizer. The use of both product streams from the ammonia plant in the urea plant is one reason why these two plants are often firmly linked. This plant network has the further advantage that steam, for example, can be exchanged between the two plants as an energy source. The carbon dioxide bound during urea production is ultimately released again when it is used in the field. Since this carbon dioxide comes from the natural gas used in ammonia production, the urea produced in this way is not green.
[0004] The production of urea from ammonia and CO2 takes place worldwide on a large scale and is well known to those skilled in the art. One process is described in US 2018 / 0208551 A1. EP 3 725 401 A1 describes the use of renewable energy for the production of chemicals, with electricity increasingly being used instead of steam, which is usually generated using fossil fuels.
[0005] An energy storage system for the production of hydrogen and urea is known from CN 111378980 A.
[0006] US 2019 / 0152901 A1 discloses a process for producing ammonia and urea from it, using a conventional gas turbine based on natural gas as fuel.
[0007] Until now, the production of ammonia and its further conversion to urea usually required a combined plant. Nowadays, ammonia is produced almost exclusively using the Haber-Bosch process. This process involves first producing hydrogen and CO2 from natural gas, with the required heat energy usually also being generated using natural gas. This hydrogen is then converted into ammonia with nitrogen from the air. In the Haber-Bosch process, steam is produced as process waste heat, which can be used both for ammonia production itself and for other processes, such as a downstream urea process. The high steam requirement for the urea process results, on the one hand, from the frequently used steam turbine of the required CCh compressor and, on the other hand, from the need to carry out several thermal separation processes during the synthesis.
[0008] Converting ammonia synthesis to a green synthesis route fundamentally changes its process characteristics. The first step in green synthesis is usually the production of hydrogen by electrolysis from renewable energy. Alternatively, ammonia can also be produced directly electrochemically. This eliminates CO2 as a byproduct, which is required as a feedstock for urea synthesis. Independence from natural gas as a traditional raw material also makes it possible to relocate ammonia synthesis preferentially to regions where renewable energies are readily available (e.g., sunny desert regions). In this context, the use of the ammonia produced in this way as an easily transportable storage medium for renewable energies, even over long distances, is also being discussed.This takes advantage of the fact that ammonia is comparatively easy to liquefy (unlike hydrogen, for example) in order to obtain a liquid energy carrier with a high energy density.
[0009] Unlike ammonia, CO2 is not as easily transported over long distances. Therefore, it is realistic to assume that new urea synthesis plants will be located near previously underutilized or unused CO2 sources, such as waste incineration plants or cement production facilities. However, these sites may be geographically distant from ammonia synthesis plants. This presents the challenge that the steam (energy) typically provided by ammonia synthesis is not available for urea production.
[0010] But even if a green ammonia synthesis is operated in direct conjunction with a urea synthesis, the lower steam production of this ammonia synthesis is no longer sufficient to cover the energy requirements of the urea synthesis.
[0011] The object of the invention is to provide a plant for producing green urea from green ammonia, in which the urea synthesis is decoupled from the previous plant network with a grey ammonia synthesis (i.e. an ammonia synthesis whose reactants are provided using carbon-based fuels, in particular using fossil fuels such as crude oil, natural gas, coal or components of the aforementioned, wherein the reactants are obtained, for example, in a steam reforming or in an electrolysis with electricity which is generated using these fuels).
[0012] This object is achieved by a device having the features specified in claim 1. Advantageous further developments emerge from the subclaims, the following description and the drawings. The device according to the invention is used for the synthesis of urea. The device has an ammonia source and a urea synthesis unit. The urea synthesis unit is a conventional urea synthesis unit for the production of urea, known to those skilled in the art. The urea synthesis unit usually consists of several process steps and apparatus, including a urea reactor. The aim of the invention is precisely not to intervene in the actual process (and thus the plant) for the synthesis of urea, but to design the connection to the environment in such a way that the production process functions according to the current state of the art even without connection to an ammonia synthesis device, in particular one powered by natural gas.Ammonia source is to be understood broadly within the meaning of the invention. The ammonia source can be an ammonia synthesis device. However, the ammonia source can also be, for example, a storage tank or a connection to an ammonia pipeline. The only essential factor is that the ammonia source no longer provides any or only insufficient steam and no CO2 for the urea synthesis unit. The ammonia source is connected to the urea synthesis unit, in particular to one or more devices of the urea synthesis unit, via a reactant line. According to the invention, the device comprises an ammonia gas turbine. The ammonia source is connected to the ammonia gas turbine via a fuel line. The ammonia gas turbine is connected to the urea synthesis unit via a steam line.
[0013] An ammonia gas turbine is a gas turbine that uses ammonia as fuel. In the ammonia gas turbine, ammonia is burned, producing nitrogen and water, which are released into the environment. Such an ammonia gas turbine can provide both thermal energy and mechanical energy, which can be used in various ways for the urea synthesis unit. As a gas turbine, the ammonia gas turbine differs structurally and functionally from turbines in which an existing hot gas flow is used to drive additional units such as compressors (such a turbine is known, for example, from WO 2020 / 212926 A1, where a turbocharger is used to feed carbamate in a urea synthesis process. This turbocharger, driven by liquid ammonia, enables a coupled feed of ammonia and carbamate).In particular, the ammonia gas turbine can be used to generate a hot gas flow whose kinetic energy can be used to drive a compressor and / or a generator, for example, to compress a process gas or to generate electrical energy. Therefore, ammonia gas turbines are currently being built for industrial use to enable the conversion of green ammonia into electricity. For example, WO 2015 / 192877 A1 discloses the use of an ammonia gas turbine for electricity generation, in which green ammonia is used as the fuel gas. The ammonia gas turbine thus provides the energy required for the urea process, which no longer comes from gray ammonia synthesis.
[0014] In this case, ammonia is used as fuel gas in the ammonia gas turbine. Therefore, the ammonia source is connected not only to the urea synthesis unit via a reactant line, but also to the ammonia gas turbine via a fuel line. The ammonia gas turbine is further connected to the urea synthesis unit via a steam line. This can be implemented in particular by using the waste heat generated in the ammonia gas turbine to produce steam in a downstream heat exchanger (the steam can, of course, also originate from a heat exchanger downstream of the actual combustion process). This steam can be fed to the urea synthesis unit via a steam line to utilize the thermal energy of the steam in the urea synthesis unit, for example, to heat the reaction mixture to the required temperature.
[0015] The use of green ammonia as an energy source has the advantage that renewable energy production does not need to be available or reliably available at the location of the device. Since the combustion of green ammonia generates CCh-free energy, green energy supply for urea synthesis can be achieved easily. This combustion of gaseous ammonia can be carried out efficiently in gas turbines, whereby the space required is much smaller than for other renewable energy sources such as a wind farm and / or a photovoltaic system. Due to the use of green-produced ammonia both as a feedstock for urea synthesis and for the production of green energy, for example, electricity or steam, in combination with the use of carbon dioxide from other sources, the urea produced in this way can be described as green in the sense of CO2-neutral.
[0016] In a further embodiment of the invention, the ammonia gas turbine is connected to a Haber-Bosch reactor for ammonia synthesis via an additional steam line. In particular, the steam generated in the Haber-Bosch process is superheated in the ammonia gas turbine and then fed to the urea reactor. For this purpose, the ammonia gas turbine preferably has a heat exchanger in which the steam is further heated with the combustion exhaust gases, in particular from ammonia combustion. The steam can be used as a heat transfer medium in the urea synthesis unit, for example, in just one or more heat exchangers of the urea reactor. The steam thus serves only as a heat transfer medium.
[0017] In a further embodiment of the invention, the ammonia gas turbine is designed to directly drive a CO2 compressor. CO2 is generated, for example, in exhaust gas purification or in biogas plants at approximately ambient pressure. For urea synthesis, the CO2 must be compressed to 150 bar, for example. Direct coupling enables dual use of the ammonia gas turbine: the waste heat is used directly in the process, and the mechanical power is used to compress the CO2.
[0018] In a further embodiment of the invention, the ammonia gas turbine is connected to a generator via a power transmission. The ammonia gas turbine drives the generator, allowing electricity to be generated through the combustion of ammonia. The generator is electrically connected to the urea synthesis unit. This combination has the advantage of providing a power source that is independent of the rest of the infrastructure. This is especially true when using green ammonia to produce green electricity, as other renewable energy sources such as solar and electricity can be subject to fluctuations. In a further embodiment of the invention, the generator is electrically connected to the CCh compressor.
[0019] If the speeds of the gas turbine and the compressor or generator are different, the power can be transmitted between the two machines via a gearbox.
[0020] During the combustion of ammonia, depending on the operating conditions, nitrogen oxides can form in the gas turbine, which must be removed in subsequent exhaust gas treatment. For this purpose, experts are already familiar with processes such as selective catalytic reduction.
[0021] In a further embodiment of the invention, the ammonia gas turbine is frictionally connected to the CO2 compressor. In particular, the ammonia gas turbine and CO2 compressor can be arranged on the same shaft, which may include a gearbox. In this embodiment, the ammonia gas turbine directly mechanically drives the CO2 compressor, thus avoiding energy losses, for example, during power generation and electrical operation of the CO2 compressor.
[0022] A further embodiment of the invention comprises a thermal cracking device. The thermal cracking device is designed to crack ammonia into hydrogen and nitrogen. The thermal cracking device is connected to the ammonia source. This feeds ammonia to the cracking device. The thermal cracking device is connected to the ammonia gas turbine. Since the combustion process of ammonia itself can be subject to fluctuations, in some variants of the ammonia gas turbine, hydrogen is added for more stable combustion. For this cracking, it is helpful that an equilibrium exists between nitrogen and hydrogen as well as ammonia, which can be shifted towards the elements at low pressure. In a further embodiment of the invention, the device comprises a hydrogen source.A hydrogen source within the meaning of the invention can be, for example, a hydrogen electrolysis device, a hydrogen tank, or a connection to a hydrogen network. The hydrogen source is connected to the ammonia gas turbine via a hydrogen line. This allows a certain amount of hydrogen to be added to the ammonia, enabling more stable combustion.
[0023] In a further embodiment of the invention, the ammonia gas turbine is connected to the thermal cracking device via a heat pipe. Thus, the waste heat from the ammonia gas turbine is used to at least partially decompose ammonia back into hydrogen and nitrogen.
[0024] The device according to the invention is explained in more detail below with reference to embodiments shown in the drawings.
[0025] Fig. 1 first embodiment
[0026] Fig. 2 second embodiment
[0027] Fig. 3 third embodiment
[0028] Fig. 1 shows a first embodiment of the device according to the invention. The device is preferably located near a suitable CO2 source 80. The CCh source 80 can, for example, be a waste incineration plant, a biogas plant, or a direct air capture process. Since the ammonia produced for the production of green urea is not produced from natural gas, the CCh source is not, as has previously been the case, an ammonia synthesis device. The device further comprises an ammonia source 10. The ammonia source 10 can theoretically be an ammonia synthesis device. The latter, however, only makes sense if there is both sufficient renewable energy to produce the green ammonia and a suitable CCh source 80 for urea production at this location. However, this cannot be assumed in all cases; rather, it can be expected that this is not the case.This transports ammonia from the ammonia synthesis device to the consumers, for example, the device according to the invention. Therefore, the ammonia source 10 can also be a storage tank or a connection to an ammonia pipeline.
[0029] Ammonia is fed from the ammonia source 10 to the urea synthesis unit 20 via a reactant line 30. Likewise, the carbon dioxide from the CO2 source 80 is fed to a device in the urea synthesis unit 20 via a CCH compressor 70, in which the carbon dioxide is brought to the pressure required for urea synthesis. In the urea synthesis unit 20, the conversion of carbon dioxide and ammonia to urea takes place. The urea leaves the urea synthesis unit 20 as a product and is fed, for example, to a granulation device, optionally mixed beforehand with other components.
[0030] To provide the necessary energy, the device includes an ammonia gas turbine 40. The ammonia gas turbine 40 is connected to the ammonia source 10 via a fuel line 50. When green ammonia is converted in the ammonia gas turbine 40, the energy thus generated is also free of CCh emissions. When ammonia is burned, only nitrogen and water are produced and released into the environment.
[0031] The ammonia gas turbine 40 is frictionally connected to the CO2 compressor 70; in particular, both are arranged on the same shaft, which may include a gearbox. As a result, the ammonia gas turbine 40 directly drives the CO2 compressor 70. At the same time, the waste heat generated in the ammonia gas turbine 40 is used to produce steam in a downstream heat exchanger, which is then fed to the urea synthesis unit 20 via a steam line 60. The steam can also originate from a heat exchanger downstream of the actual combustion process.
[0032] Optionally, as shown here, the ammonia gas turbine 40 can also be non-positively connected to a generator 90. The electrical energy generated there can be made available to the urea synthesis unit 20 via an electrical connection 100. Fig. 2 shows a second embodiment which, in addition to the first embodiment, has a thermal cracking device 110. The thermal cracking device 110 is fed with the waste heat from the ammonia gas turbine 40 via a heat line 120. A portion of the ammonia from the ammonia source 10 is fed to the thermal cracking device 110, and the resulting mixture of ammonia, hydrogen, and nitrogen is fed to the ammonia gas turbine 40. The additional hydrogen results in more stable combustion in the ammonia gas turbine 40. Fig. 3 shows a third embodiment which differs from that shown in Fig.1 in that the ammonia gas turbine 40 is only non-positively connected to the generator 90, in particular, it is arranged on the same shaft. The generator 90 is connected via an electrical connection to the CO2 compressor 70, which is accordingly operated purely electrically. The advantage of this embodiment is the optimal operation of the ammonia gas turbine 40 for the generator 90, making it easier to respond to fluctuating power requirements, for example, in the urea synthesis unit 20, and independent of the CO2 gas stream to be compressed.
[0033] Reference symbol
[0034] 10 Ammonia source
[0035] 20 Urea synthesis unit 30 Educt line
[0036] 40 ammonia gas turbine
[0037] 50 fuel line
[0038] 60 steam line
[0039] 70 CCh compressor 80 CCh source
[0040] 90 Generator
[0041] 100 electrical connection
[0042] 110 thermal splitting device
[0043] 120 Heat conduction 130 Product outlet
[0044] 140 exhaust
Claims
Patent claims 1. A device for synthesizing urea, the device comprising an ammonia source (10) and a urea synthesis unit (20), the ammonia source (10) being connected to the urea synthesis unit (20) via a reactant line (30), characterized in that the device comprises an ammonia gas turbine (40), the ammonia source (10) being connected to the ammonia gas turbine (40) via a fuel line (50), the ammonia gas turbine (40) being connected to the urea synthesis unit (20) via a steam line (60).
2. Device according to claim 1, characterized in that the ammonia gas turbine (40) is designed to drive a CCh compressor (70).
3. Device according to one of the preceding claims, characterized in that the ammonia gas turbine (40) is non-positively connected to a generator (90), wherein the generator (90) is electrically connected to the urea synthesis unit (20).
4. Device according to claim 3, characterized in that the generator (90) is electrically connected to the CO2 compressor (70).
5. Device according to one of the preceding claims, characterized in that the ammonia gas turbine (40) is non-positively connected to the CO2 compressor (70).
6. Device according to one of the preceding claims, characterized in that it comprises a thermal cracking device (110), wherein the thermal cracking device (110) is designed to convert ammonia into hydrogen and nitrogen, wherein the thermal cracking device (110) is connected to the ammonia source (10), wherein the thermal cracking device (110) is connected to the ammonia gas turbine (40). Device according to claim 6, characterized in that the ammonia gas turbine (40) is connected to the thermal cracking device (110) via a heat line (120).