Green urea production system and production method

Abstract

The present invention relates to an apparatus for synthesizing urea, comprising an ammonia source 10 and a urea synthesis unit 20, wherein the ammonia source 10 is connected to the urea synthesis unit 20 via a reactant line 30, and wherein the apparatus comprises an ammonia gas turbine 40, wherein the ammonia source 10 is connected to the ammonia gas turbine 40 via a fuel line 50, and wherein the ammonia gas turbine 40 is connected to the urea synthesis unit 20 via a steam line 60.

Description

[Technical Field]

[0001] The present invention relates to the production of green urea. More particularly, the invention relates to an apparatus for synthesizing urea having the features of claim 1. [Background technology]

[0002] The production of green chemicals is becoming increasingly important. The term "green" refers to chemicals that are produced sustainably (and therefore climate-neutral and environmentally friendly), so that, in particular, no additional carbon dioxide is released into the atmosphere due to their production. These can be, for example, chemicals produced in processes in which the production energy requirements are met by renewable (renewable) energy sources (e.g., by electrical energy obtained from renewable energy sources, e.g., in photovoltaic plants, wind turbines, geothermal power plants, or tidal power plants) and the reactants used in production are not obtained from fossil feedstocks. One area of ​​obvious interest here is the production of green ammonia, since ammonia production currently uses almost exclusively natural gas. In said production, carbon dioxide (CO2) is generated as a by-product. If this carbon dioxide is not reused, it will be released into the environment. However, urea plants can utilize this carbon dioxide along with ammonia for conversion to urea, which is primarily used as a fertilizer. The use of both product streams from ammonia plants in urea plants is one reason why these two plants are often permanently integrated with each other. This integrated plant setup has the added advantage that steam can be exchanged between the two plants, for example, as an energy carrier. The carbon dioxide bound during urea production is eventually released again once it is used on-site. Because this carbon dioxide comes from the natural gas used in ammonia production, urea produced in this way is not green.

[0003] The production of urea from ammonia and CO is carried out on a large scale worldwide and is known to those skilled in the art. One process is described in U.S. Patent Application Publication No. 2018 / 0208551.

[0004] EP 3725401 A1 discloses the use of renewable energy for the production of chemicals, with increasing use being primarily with electricity instead of steam generated from fossil energy sources.

[0005] CN111378980 discloses an energy storage system for producing hydrogen and urea.

[0006] US Patent Application Publication No. 2019 / 0152901 discloses a method for producing ammonia and urea therefrom in which a conventional gas turbine based on natural gas is used as fuel.

[0007] Until now, the production of ammonia and its further conversion to urea has generally required integrated production facilities. Ammonia is currently produced almost exclusively by the Haber-Bosch process. In this process, hydrogen and CO2 are first produced from natural gas, and the necessary heat energy is also typically generated using natural gas. This hydrogen then reacts with nitrogen from the air to form ammonia. The Haber-Bosch process produces steam as process waste heat, which can be very easily utilized not only for ammonia production itself but also for other processes, such as downstream urea processes. The high steam requirements for the urea process arise from the steam turbines typically used for the required CO2 compressors and from the need to perform multiple thermal separation processes in the synthesis.

[0008] Switching 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 using renewable energy. Alternatively, direct electrochemical production of ammonia is also possible. As a result, CO2 is no longer formed as a by-product but is required as a feedstock for urea synthesis. Independence from the natural gas feedstock previously used also makes it possible to move ammonia synthesis to areas where renewable energy is readily available (e.g., sunny desert regions). A further discussion point in this context is that the ammonia produced in this way is an easily transportable storage medium for renewable energy and can also be utilized over relatively long distances. This takes advantage of the fact that ammonia (unlike, for example, hydrogen) is relatively easy to liquefy to obtain a liquid energy carrier with high energy density.

[0009] Unlike ammonia, CO2 is not very easy to transport over relatively long distances. Therefore, it is realistic to assume that new urea syntheses will be located in the future near previously little-used or completely unused CO2 sources, such as waste incineration plants or cement manufacturing plants. However, these sites may be located far from ammonia synthesis. In this case, the challenge arises: the steam (energy) normally provided by ammonia synthesis is no longer available for urea production.

[0010] However, even if green ammonia synthesis is operated directly in parallel with urea synthesis, the lower steam output of said ammonia synthesis is no longer sufficient to meet the energy demand of urea synthesis. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] US Patent Application Publication No. 2018 / 0208551 [Patent Document 2] European Patent Application Publication No. 3725401 [Patent Document 3] Chinese Patent Application Publication No. 111378980 [Patent Document 4] US Patent Application Publication No. 2019 / 0152901 Summary of the Invention [Problem to be solved by the invention]

[0012] The object of the present invention is to provide a plant for producing green urea from green ammonia, in which the urea synthesis is decoupled from the integrated plants hitherto used by gray ammonia synthesis (for example ammonia synthesis for which reactants are provided using carbon-based fuels, more particularly fossil fuels such as oil, natural gas, coal or the components mentioned above, and the reactants are obtained, for example, in steam reforming or in electrolysis using electricity generated using said fuel). [Means for solving the problem]

[0013] This object is achieved by a device having the features of claim 1. Advantageous developments will become apparent from the dependent claims, the following description and the drawings.

[0014] The device according to the present invention is used for the synthesis of urea. The device comprises an ammonia source and a urea synthesis unit. The urea synthesis unit is a conventional urea synthesis unit known to those skilled in the art for the production of urea. The urea synthesis unit typically comprises several process steps and devices, in particular a urea reactor. The objective of the present invention is not to modify the actual process (and thus the plant) for the synthesis of urea, but rather to design an environmental connection so that the production process operates according to the current state of the art, even if it is not connected to an ammonia synthesis unit, particularly one that operates on natural gas. The ammonia source, for the purposes of the present invention, should be understood in broad terms. The ammonia source can be an ammonia synthesis unit. However, the ammonia source can also be, for example, a connection to a storage tank or an ammonia pipeline. What is important is that the ammonia source does not supply steam to the urea synthesis unit, or supplies insufficient steam, and no longer supplies CO2. The ammonia source is connected to the urea synthesis unit, more specifically to one or more devices of the urea synthesis unit, via a reactant conduit. According to the present invention, the device includes an ammonia gas turbine. The ammonia source is connected via a fuel conduit to the ammonia gas turbine, which is connected via a steam conduit to the urea synthesis unit.

[0015] An ammonia gas turbine is a gas turbine that operates on ammonia as a fuel gas (fuel). In an ammonia gas turbine, ammonia is burned to form nitrogen and water, which are released into the environment. Such ammonia gas turbines can provide both thermal and mechanical energy, which can be utilized in different ways for urea synthesis units. Ammonia gas turbines differ in structure and function from turbines in which an existing hot gas stream is used to drive additional units, such as a compressor (such turbines are known, for example, from WO 2020 / 212926, where urea synthesis uses a turbocharger to supply carbamate, enabling the combined supply of ammonia and carbamate driven by liquid ammonia). More specifically, ammonia gas turbines can be used to generate a hot gas stream, the kinetic energy of which can be utilized as a drive for a compressor and / or a generator, for example, to compress process gases or to generate electrical energy. Therefore, industrial ammonia gas turbines are currently being built to enable the conversion of the green energy carrier ammonia into electricity. For example, WO 2015 / 192877 discloses the use of an ammonia gas turbine for power generation, in which green ammonia is used as fuel gas. The ammonia gas turbine therefore provides the energy required for the urea process, which therefore no longer comes from grey ammonia synthesis.

[0016] In this case, the ammonia gas turbine uses ammonia as fuel gas. Therefore, the ammonia source is not only connected to the urea synthesis unit via a reactant conduit, but also to the ammonia gas turbine via a fuel conduit. The ammonia gas turbine is also connected to the urea synthesis unit via a steam conduit. This can be realized in particular by using waste heat generated in the ammonia gas turbine to generate steam in a downstream heat exchanger (the steam can also come from a downstream heat exchanger of the actual combustion process) and supplying this to the urea synthesis unit via the steam conduit, so that the thermal energy of the steam in the urea synthesis unit can be used to heat, for example, a reaction mixture to a required temperature.

[0017] The use of green ammonia as an energy supplier has the advantage that renewable energy production does not need to be provided or ensured on-site. Combustion of green ammonia produces CO2-free energy, providing green energy for urea synthesis in a simple manner. This combustion of gaseous ammonia can be efficiently carried out in a gas turbine, requiring much less space than other renewable energy suppliers, such as wind and / or solar power plants.

[0018] The use of green ammonia as both a feedstock for urea synthesis and for the generation of green energy, e.g. electricity or steam, in combination with the use of carbon dioxide derived from other sources means that the urea produced in this way can be described as green in the sense of being CO2-neutral.

[0019] In a further embodiment of the invention, the ammonia gas turbine is connected via an additional steam conduit to a Haber-Bosch reactor for ammonia synthesis. More specifically, the steam generated in the Haber-Bosch process is superheated in the ammonia gas turbine and then supplied to the urea reactor. For this purpose, the ammonia gas turbine preferably has a heat exchanger in which the steam is further heated with combustion off-gas, more specifically, off-gas from ammonia combustion. The steam can be used only as a heat transfer medium within the urea synthesis unit, i.e., in one or more of the heat exchangers of the urea reactor, for example. Thus, the steam functions solely as a heat transfer medium.

[0020] In a further embodiment of the invention, the ammonia gas turbine is designed to directly drive a CO2 compressor. For example, in an off-gas scrubbing or biogas plant, CO2 is produced at near-ambient pressure. For urea synthesis, the CO2 must be compressed, for example, to 150 bar. This direct coupling achieves dual use of the ammonia gas turbine: waste heat is utilized directly in the process, and mechanical power is used to compress the CO2.

[0021] In a further embodiment of the present invention, the ammonia gas turbine is connected to a generator in a pressurized manner. The ammonia gas turbine can thus drive the generator, thereby generating electricity by burning the ammonia. The generator is electrically connected to the urea synthesis unit. This combination has the advantage of providing a reliable power source for the rest of the infrastructure. This is especially true when green ammonia is used to generate green electricity, since other renewable energy sources, such as solar and electricity, can be subject to fluctuations.

[0022] In a further embodiment of the present invention, the generator is electrically connected to the CO2 compressor.

[0023] If the speed of the gas turbine / compressor and the speed of the generator are different, the power transmission between the two machines can be done through a gearbox.

[0024] Depending on operating conditions, the combustion of ammonia can result in the formation of nitrogen oxides within the gas turbine, which must be removed in subsequent off-gas treatment. Those skilled in the art will be familiar with common methods for this, such as selective catalytic reduction.

[0025] In a further embodiment of the present invention, the ammonia gas turbine is connected to the CO2 compressor in a pressurized manner. More specifically, the ammonia gas turbine and the CO2 compressor may be arranged on the same shaft, which may optionally include a gearbox. In this embodiment, the ammonia gas turbine directly drives the CO2 compressor mechanically, thereby avoiding energy losses during, for example, the power generation and electrical operation of the CO2 compressor.

[0026] A further embodiment of the present invention includes a thermal splitter (pyrolysis device). The thermal splitter is designed to split ammonia into hydrogen and nitrogen. The thermal splitter is connected to an ammonia source, which supplies the ammonia to a splitter. The thermal splitter is connected to an ammonia gas turbine. Because the ammonia combustion process itself can be subject to fluctuations, some variations of the ammonia gas turbine incorporate hydrogen for more stable combustion. For the splitting, it is useful for the nitrogen and hydrogen to be in equilibrium with the ammonia, which can be favorably shifted to elements at low pressure.

[0027] In a further embodiment of the invention, the apparatus includes a hydrogen source. For purposes of the present invention, the hydrogen source may be, for example, a hydrogen electrolyzer, a hydrogen tank, or a connection to a piped hydrogen source. The hydrogen source is connected to the ammonia gas turbine via a hydrogen conduit. This allows a constant amount of hydrogen to be metered into the ammonia, allowing for more stable combustion.

[0028] In a further embodiment of the invention, the ammonia gas turbine is connected to a heat splitter via a heat conduit, such that waste heat from the ammonia gas turbine is utilized to at least partially decompose the ammonia back into hydrogen and nitrogen.

[0029] The device according to the invention is explained in more detail below with reference to exemplary embodiments shown in the drawings. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 illustrates a first embodiment. [Figure 2] FIG. 10 is a diagram illustrating a second embodiment. [Figure 3] FIG. 10 is a diagram illustrating a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0031] FIG. 1 illustrates a first embodiment of the apparatus according to the present invention. The apparatus is preferably located near a suitable CO₂ source 80. This CO₂ source 80 can be, for example, a waste incineration plant, a biogas plant, or a direct air capture process. Because the ammonia produced for green urea production is not specifically produced from natural gas, the CO₂ source is not an ammonia synthesizer, as in the previous case. The apparatus further includes an ammonia source 10. Theoretically, the ammonia source 10 could be an ammonia synthesizer. However, this only makes sense if there is sufficient renewable energy available for the local production of green ammonia, as well as a suitable CO₂ source 80 for urea production. However, this cannot be assumed in all cases. In fact, it is expected that this will not be the case. Consequently, the ammonia is transported from the ammonia synthesizer to a user, such as the apparatus according to the present invention. Therefore, the ammonia source 10 can be a storage tank or a connection to an ammonia pipeline.

[0032] Ammonia from an ammonia source 10 is supplied to the urea synthesis unit 20 via a reactant conduit 30. Similarly, carbon dioxide from a CO source 80 is supplied to the urea synthesis unit 20 via a CO compressor 70 at the necessary pressure for urea synthesis. In the urea synthesis unit 20, the carbon dioxide and ammonia react to form urea. The urea exits the urea synthesis unit 20 as a product and is supplied to a granulator, for example, optionally after first being mixed with other ingredients.

[0033] To provide the required energy, the apparatus includes an ammonia gas turbine 40, which is connected to an ammonia source 10 via a fuel conduit 50. If it is green ammonia produced in the ammonia gas turbine 40 that is reacting, the energy thus produced is likewise without CO2 emissions. When ammonia is burned, only nitrogen and water are formed and released into the environment.

[0034] The ammonia gas turbine 40 is connected to the CO2 compressor 70 in a pressure-fit manner; more specifically, they are both arranged on the same shaft, which can optionally include a gearbox. The ammonia gas turbine 40 thereby directly drives the CO2 compressor 70. At the same time, the waste heat produced in the ammonia gas turbine 40 is utilized to produce steam in a downstream heat exchanger, which is supplied to the urea synthesis unit 20 via a steam conduit 60. In this case, the steam can also come from a heat exchanger downstream of the actual combustion process.

[0035] As shown here, the ammonia gas turbine 40 may also be optionally connected in a pressurized manner to a generator 90. Electrical energy generated therein may be supplied to the urea synthesis unit 20 via an electrical connection 100.

[0036] 2 shows a second embodiment that includes a heat splitting device 110 in addition to the first embodiment. The heat splitting device 110 is supplied with waste heat from the ammonia gas turbine 40 via a heat conduit 120. A portion of the ammonia from the ammonia source 10 is supplied to the heat splitting device 110, and the resulting mixture of ammonia, hydrogen, and nitrogen is supplied to the ammonia gas turbine 40. The additional hydrogen provides more stable combustion in the ammonia gas turbine 40.

[0037] Figure 3 shows a third embodiment, which differs from the first embodiment shown in Figure 1 in that the ammonia gas turbine 40 is only connected in a pressure-fit manner to the generator 90, more specifically, arranged on the same shaft. The generator 90 is connected to the CO2 compressor 70 via an electrical connection and therefore operates purely electrically. The advantage of this embodiment is the optimal operating mode of the ammonia gas turbine 40 for the generator 90, which makes it easier to respond to fluctuating electrical demands, for example in the urea synthesis unit 20, and independently of the CO2 gas flow being compressed. [Explanation of symbols]

[0038] 10. Ammonia Source 20 Urea synthesis unit 30 Reactant conduit 40 Ammonia Gas Turbine 50 Fuel conduit 60 Steam Pipe 70 CO2 compressor 80 CO2 source 90 Generator 100 Electrical connection 110 Heat splitting device 120 Heat Conduction 130 Product outlet 140 Offgas

Claims

1. 1. An apparatus for synthesizing urea, comprising an ammonia source (10) and a urea synthesis unit (20), wherein the ammonia source (10) is connected to the urea synthesis unit (20) through a reactant conduit (30), the apparatus comprising an ammonia gas turbine (40), the ammonia source (10) is connected to the ammonia gas turbine (40) through a fuel conduit (50), and the ammonia gas turbine (40) is connected to the urea synthesis unit (20) through a steam conduit (60).

2. The ammonia gas turbine (40) ２ 2. Device according to claim 1, characterized in that it is designed to drive a compressor (70).

3. 3. The apparatus according to claim 1 or 2, characterized in that the ammonia gas turbine (40) is connected in a press-fit manner to a generator (90), and the generator (90) is electrically connected to the urea synthesis unit (20).

4. The generator (90) ２ 4. The device according to claim 3, characterized in that it is electrically connected to a compressor (70).

5. The ammonia gas turbine (40) ２ 5. The device according to claim 1, wherein the compressor (70) is connected in a press-fit manner.

6. 6. The apparatus according to claim 1, further comprising a thermal splitter (110) designed to convert ammonia into hydrogen and nitrogen, the thermal splitter (110) being connected to the ammonia source (10), and the thermal splitter (110) being connected to the ammonia gas turbine (40).

7. 7. The apparatus of claim 6, wherein the ammonia gas turbine (40) is connected to the heat dividing device (110) via a heat conduit (120).

Images