Green urea manufacturing system and manufacturing 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 present invention relates to an apparatus for synthesizing urea having the features of claim 1.

Background Art

[0002] The production of green chemicals is becoming increasingly important. The term "green" refers to chemicals produced sustainably (and thus in a climate-neutral and environmentally friendly manner), such that, in particular for their production, no additional carbon dioxide is released into the atmosphere. These can be chemicals produced in processes where, for example, the production energy requirements are met by renewable energy sources (e.g., by electrical energy obtained from renewable energy sources, such as in a photovoltaic power plant, a wind turbine, a geothermal power plant or a tidal power plant), and the reactants used in the production are not obtained from fossil raw materials. One area that is clearly of interest here is the production of green ammonia, since the production of ammonia currently almost exclusively uses natural gas. In said production, 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 utilize this carbon dioxide together with ammonia, mainly for the conversion to urea used as a fertilizer. The use of both production streams from an ammonia plant in a urea plant is one reason why these two plants are often fixedly integrated with each other. This integrated plant setup has the further advantage, for example, that steam can be exchanged between the two plants as an energy carrier. The carbon dioxide bound during urea production is ultimately released again if used on-site. Since this carbon dioxide is derived from the natural gas used in ammonia production, the urea thus produced is not green.

[0003] The production of urea from ammonia and CO2 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] European Patent Application Publication No. 3725401 discloses the use of renewable energy for the manufacture of chemicals, with the increased use being primarily done with electricity instead of steam produced from fossil fuel sources.

[0005] Chinese Patent Application Publication No. 111378980 discloses an energy storage system for generating hydrogen and urea.

[0006] U.S. Patent Application Publication No. 2019 / 0152901 discloses a method for producing ammonia and urea from a conventional gas turbine that uses natural gas as fuel.

[0007] The production of ammonia and its further conversion to urea has, until now, generally required integrated manufacturing 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 thermal energy is also typically generated using natural gas. This hydrogen then reacts with nitrogen from the air to form ammonia. The Haber-Bosch process generates steam as waste heat, which can be very easily utilized not only for ammonia production itself but also for other processes, such as the downstream urea process. The high steam requirements for the urea process arise from the steam turbines commonly 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 alters its process characteristics. The first step in green synthesis is typically the production of hydrogen by electrolysis using renewablely generated energy. Alternatively, direct electrochemical production of ammonia is also possible. As a result, CO2 is no longer formed as a byproduct but is required as a raw material for urea synthesis. Being independent of the natural gas raw material previously used makes it possible to move ammonia synthesis to areas where renewable energy is readily available (e.g., sunny desert regions). A further point of discussion in this context is that the ammonia thus produced is an easily transportable storage medium for renewable energy and can be used over relatively long distances. This takes advantage of the fact that ammonia is relatively easy to liquefy (unlike hydrogen, for example) to obtain a liquid energy carrier with high energy density.

[0009] Unlike ammonia, CO2 is not easily transported over relatively long distances. Therefore, it is realistic to assume that new urea synthesis sites will be located in the future near CO2 sources that have been little or nowhere used, such as waste incineration plants or cement manufacturing plants. However, these sites may be located far from ammonia synthesis sites. In that case, a challenge arises: the steam (energy) normally supplied 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 ammonia synthesis is no longer sufficient to meet the energy demands of urea synthesis. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] U.S. Patent Application Publication No. 2018 / 0208551 [Patent Document 2] European Patent Application Publication No. 3725401 [Patent Document 3] Chinese Patent Application Publication No. 111378980 Specification [Patent Document 4] U.S. Patent Application Publication No. 2019 / 0152901 [Overview of the project] [Problems that the invention aims to solve]

[0012] The object of the present invention is to provide a plant for producing green urea from green ammonia, wherein urea synthesis is separated from an integrated plant that has previously been used for gray ammonia synthesis (for example, ammonia synthesis in which the reactants therefor are provided using carbon-based fuels, more specifically using fossil fuels such as petroleum, natural gas, coal or the above components, and the reactants are obtained, for example, in steam reforming or in electrolysis using electricity generated using the fuels). [Means for solving the problem]

[0013] This objective is achieved by an apparatus having the features described in claim 1. Advantageous developments will become apparent from the dependent claims, the following description, and the drawings.

[0014] The apparatus according to the present invention is used for the synthesis of urea. The apparatus 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 consists of several process steps and apparatus, in particular a urea reactor. The object of the present invention is not, in particular, to modify the actual process (and therefore the plant) for the synthesis of urea, but rather to design the connection to the environment so that the production process operates according to the current state of the art, even if it is not connected to an ammonia synthesis apparatus, particularly one operating on natural gas. The ammonia source should be understood in a broad sense for the purposes of the present invention. The ammonia source can be an ammonia synthesis apparatus. However, the ammonia source may be, for example, a storage tank or a connection to an ammonia pipeline. Importantly, the ammonia source does not supply steam to the urea synthesis unit, or supplies only insufficient steam, and no longer supplies CO2. The ammonia source is connected to the urea synthesis unit, more specifically to one or more apparatuses of the urea synthesis unit, via a reactant conduit. According to the present invention, the apparatus includes an ammonia gas turbine. The ammonia source is connected to the ammonia gas turbine via a fuel conduit. The ammonia gas turbine is connected to the urea synthesis unit via a steam conduit.

[0015] An ammonia gas turbine is a gas turbine that operates using ammonia as its fuel gas. In an ammonia gas turbine, ammonia is burned to form nitrogen and water, which are released into the environment. Such an ammonia gas turbine 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 as gas turbines from turbines where an already existing high-temperature gas flow is used to drive further units such as compressors (such turbines are known, for example, from the International Publication No. 2020 / 212926 brochure, where urea synthesis uses a turbocharger to supply carbamates, enabling the combined supply of ammonia and carbamates driven by liquid ammonia). More specifically, an ammonia gas turbine can be used to generate a high-temperature gas flow, and its kinetic energy can be utilized, for example, to compress process gases or to drive compressors and / or generators to generate electrical energy. Thus, industrial ammonia gas turbines are currently being built to enable the conversion of ammonia, a green energy carrier, into electricity. For example, International Publication No. 2015 / 192877 discloses the use of an ammonia gas turbine for power generation, in which green ammonia is used as the fuel gas. Thus, the ammonia gas turbine provides the energy required for the urea process, which is therefore no longer derived from gray ammonia synthesis.

[0016] In this case, ammonia is used as the fuel gas in the ammonia gas turbine. Therefore, the ammonia source is connected not only 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 achieved, in particular, by utilizing the waste heat generated in the ammonia gas turbine to produce steam in a downstream heat exchanger (the steam can also come from a downstream heat exchanger in the actual combustion process), which is then supplied to the urea synthesis unit via a steam conduit, allowing the thermal energy of the steam in the urea synthesis unit to be utilized, for example, to heat the reaction mixture to the required temperature.

[0017] Using green ammonia as an energy supplier has the advantage of not requiring renewable energy production to be provided on-site at the facility, or ensuring that renewable energy production is present there. Since the combustion of green ammonia generates CO2 free energy, this allows for the provision of green energy for urea synthesis in a simple manner. This combustion of gaseous ammonia can be carried out efficiently within a gas turbine, and the space required for this is far less than that of other renewable energy suppliers such as wind and / or solar power plants.

[0018] Using green ammonia as both a feedstock for urea synthesis and a feedstock for generating green energy, such as electricity or steam, in combination with the use of carbon dioxide from other sources, means that the urea thus produced can be described as green in a CO2-neutral sense.

[0019] In a further embodiment of the invention, the ammonia gas turbine is connected via a further steam conduit to a Haber - Bosch reactor for ammonia synthesis. More specifically, the steam generated by the Haber - Bosch process is supplied to the urea reactor after being superheated in the ammonia gas turbine. For this purpose, the ammonia gas turbine preferably has a heat exchanger in which the steam is further heated by combustion off - gases, more specifically the off - gases from ammonia combustion. The steam can be used as a heat transfer medium within the urea synthesis unit, i.e., for example, in only one or more of the heat exchangers of the urea reactor. Thus, the steam functions only 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. In an off - gas scrubbing or biogas plant, for example, CO2 is generated at approximately ambient pressure. For urea synthesis, the CO2 has to be compressed to, for example, 150 bar. The direct coupling achieves a dual use of the ammonia gas turbine. That is, the waste heat is directly utilized in the process and the mechanical power is utilized to compress CO2.

[0021] In a further embodiment of the invention, the ammonia gas turbine is press - fit connected to a generator. Thus, the ammonia gas turbine can drive the generator and thereby generate electricity by the combustion of ammonia. The generator is electrically connected to the urea synthesis unit. This combination has the advantage of constituting a reliable power source for the remaining infrastructure. This is particularly applicable when green ammonia is used to generate green electricity, since other renewable energy sources such as sunlight and electricity can be subject to fluctuations.

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

[0023] When the speeds of the gas turbine / compressor and the generator are different, the power transmission between the two machines can be carried out via a gearbox.

[0024] Depending on the operating conditions, the combustion of ammonia may result in the formation of nitrogen oxides in the gas turbine, which must then be removed in subsequent off-gas treatment. A person 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 press-connected to a CO2 compressor. More specifically, the ammonia gas turbine and the CO2 compressor can be arranged on the same shaft which may optionally include a gearbox. In this embodiment, the ammonia gas turbine mechanically directly drives the CO2 compressor, and as a result, for example, energy losses during power generation and electrical operation of the CO2 compressor can be avoided.

[0026] A further embodiment of the present invention includes a thermal splitting device (thermal decomposition device). The thermal splitting device is designed to split ammonia into hydrogen and nitrogen. The thermal splitting device is connected to an ammonia source. Thereby, ammonia is supplied to the splitting device. The thermal splitting device is connected to an ammonia gas turbine. Since the ammonia combustion process itself can be subject to fluctuations, in some variants of the ammonia gas turbine, hydrogen is mixed for more stable combustion. For said splitting, it is useful for nitrogen and hydrogen to be in equilibrium with ammonia which can be advantageously shifted to the elements at low pressure.

[0027] In a further embodiment of the present invention, the device includes a hydrogen source. For the purposes of the present invention, the hydrogen source can be, for example, a hydrogen electrolysis device, a hydrogen tank, or a connection to a piped hydrogen supply source. The hydrogen source is connected to the ammonia gas turbine via a hydrogen conduit. Thereby, a certain amount of hydrogen can be metered into the ammonia, enabling more stable combustion.

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

[0029] The apparatus according to the present invention will be described in more detail below with reference to exemplary embodiments shown in the drawings. [Brief explanation of the drawing]

[0030] [Figure 1] This is a diagram showing the first embodiment. [Figure 2] This figure shows a second embodiment. [Figure 3] This figure shows the third embodiment. [Modes for carrying out the invention]

[0031] Figure 1 shows a first embodiment of the apparatus according to the present invention. The apparatus is preferably located near a suitable CO2 source 80. The CO2 source 80 may be, for example, 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 in particular, the CO2 source is not an ammonia synthesis apparatus, as in the previous case. The apparatus further includes an ammonia source 10. The ammonia source 10 can theoretically be an ammonia synthesis apparatus. However, the latter only makes sense if there is sufficient renewable energy for the production of green ammonia at this location, as well as a CO2 source 80 suitable for urea production. However, this cannot be assumed in all cases. On the contrary, it is expected that this will not be the case. As a result, ammonia is transported from the ammonia synthesis apparatus to the user, for example, the apparatus according to the present invention. Therefore, the ammonia source 10 may be a storage tank or a connection to an ammonia pipeline.

[0032] Ammonia is supplied from the ammonia source 10 to the urea synthesis unit 20 via the reactant conduit 30. Similarly, carbon dioxide from the CO2 source 80 is supplied to the urea synthesis unit 20 via the CO2 compressor 70, which is set to the pressure required for urea synthesis. In the urea synthesis unit 20, carbon dioxide and ammonia react to form urea. The urea leaves the urea synthesis unit 20 as a product and is supplied to a granulator, for example, after being mixed with other components first if necessary.

[0033] To supply the necessary energy, the apparatus includes an ammonia gas turbine 40. The ammonia gas turbine 40 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 also does not involve CO2 emissions. When ammonia burns, only nitrogen and water are formed and released into the environment.

[0034] The ammonia gas turbine 40 is injection-connected to the CO2 compressor 70, and more specifically, they are both located on the same shaft, which optionally includes a gearbox. This allows the ammonia gas turbine 40 to directly drive the CO2 compressor 70. At the same time, the waste heat generated 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 downstream heat exchanger in the actual combustion process.

[0035] As shown here, the ammonia gas turbine 40 can also be further connected to the generator 90 in a pressurized manner if necessary. The electrical energy generated therein can be supplied to the urea synthesis unit 20 via the electrical connection 100.

[0036] Figure 2 shows a second embodiment, which includes a heat splitter 110 in addition to the first embodiment. The heat splitter 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 splitter 110, and the resulting mixture of ammonia, hydrogen, and nitrogen is supplied to the ammonia gas turbine 40. The additional hydrogen results in 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 connected to the generator 90 only in a pressurized manner, and more specifically, is located on the same shaft. The generator 90 is connected to the CO2 compressor 70 via an electrical connection and is therefore operated 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 in, for example, the urea synthesis unit 20, and to respond independently of the compressed CO2 gas flow. [Explanation of Symbols]

[0038] 10 Ammonia sources 20 Urea synthesis unit 30 Reactant conduits 40 Ammonia gas turbine 50 Fuel conduit 60 Steam conduit 70 CO2 compressors 80 CO2 source 90 Generators 100 Electrical connection part 110 Heat splitting device 120 Thermal conductivity 130 Product outlet 140 Off-gas

Claims

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) via a reactant conduit (30), the apparatus includes an ammonia gas turbine (40), the ammonia source (10) is connected to the ammonia gas turbine (40) via a fuel conduit (50), and the ammonia gas turbine (40) is connected to the urea synthesis unit (20) via a steam conduit (60).

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

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

4. The apparatus according to claim 2, characterized in that the ammonia gas turbine (40) is connected to the generator (90) in a pressurized manner, and the generator (90) is electrically connected to the urea synthesis unit (20).

5. The generator (90) is the CO ２ The apparatus according to claim 4, characterized in that it is electrically connected to a compressor (70).

6. The ammonia gas turbine (40) ２ The apparatus according to claim 2, characterized in that it is connected to the compressor (70) in a press-fit manner.

7. The apparatus according to any one of claims 1 to 6, comprising a thermal splitter (110), wherein the thermal splitter (110) is designed to convert ammonia into hydrogen and nitrogen, the thermal splitter (110) is connected to the ammonia source (10), and the thermal splitter (110) is connected to the ammonia gas turbine (40).

8. The apparatus according to claim 7, characterized in that the ammonia gas turbine (40) is connected to the heat splitter (110) via a heat conduit (120).

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