Apparatus and method for producing ammonia

Abstract

The invention relates to a device and a method for producing ammonia, comprising an ammonia reactor (2) for producing ammonia (NH3) from syngas, where the syngas comprises hydrogen (H2) and nitrogen (N2), further comprising an electrolyser (3) for producing hydrogen and oxygen from water, where the electrolyser (3) is operated with renewable energy, where the electrolyser (3) is connected to the ammonia reactor (2). The device further comprises a gas turbine (7) operated with hydrogen, the exhaust gas of the gas turbine (7) containing nitrogen (N2) being used to produce the synthesis gas.

Description

Technical Field

[0001] The invention relates to a device and a method for producing ammonia, wherein ammonia (NH3) is produced from synthesis gas in an ammonia reactor, wherein the synthesis gas contains hydrogen (H2) and nitrogen (N2). Background Art

[0002] The production of ammonia is based on a known process that generally requires a lot of energy. According to initial estimates, the production of ammonia currently requires about 1% of the energy produced worldwide.

[0003] Ammonia produced from renewable energy sources is called green ammonia. Green ammonia is considered a rapidly growing energy carrier for hydrogen. In addition, ammonia is used in many industrial processes, especially in fertilizers. It is estimated that about 50% of the green hydrogen produced in the next few years will be directly processed into liquid ammonia for long-distance transportation of hydrogen, because the liquefaction of pure hydrogen is very energy-intensive.

[0004] In addition to hydrogen production by electrolysis and nitrogen production by air separation units, the largest energy consumption and compression costs are syngas compression and cold boxes The synthesis gas compression compresses the nitrogen-hydrogen mixture to the pressure of 150-200 bar required for the synthesis process, and the cold box provides the refrigeration energy for liquefying and cooling ammonia to about -33°C at atmospheric pressure.

[0005] A preheating unit is usually required for heating the synthesis gas to the reaction temperature.

[0006] Currently, the nitrogen and hydrogen required to produce ammonia are usually compressed to the required synthesis pressure in a syngas compressor. The inlet pressure of this compressor is usually determined by the hydrogen pressure, which in green ammonia applications where electrolysis is performed on site is limited to the maximum outlet pressure of the electrolysis system (maximum 30-40bar).

[0007] The shaft power for the compressor is provided by a steam turbine, while the required steam is generated from the heat released during the ammonia synthesis. Preheating of the synthesis gas must be achieved by fuel-driven or electrically driven heaters or by utilizing waste heat from the ammonia process, thereby reducing the amount of steam that can be generated for the steam turbine.

[0008] Liquefaction is achieved through the refrigerant cycle.

[0009] Ammonia is produced worldwide in large quantities as a fertilizer for agriculture, however, natural gas or other fossil fuels are used in this process to provide hydrogen as a raw material and energy for the synthesis process. As a result, the production of ammonia by these methods causes almost 1.5% of CO2 emissions worldwide.

[0010] Given the responsibility to achieve net-zero emissions targets, new carbon-free fuels such as green ammonia and green hydrogen are needed to decarbonize energy generation, heat, transport and industry.

[0011] It is estimated that around 50% of the green hydrogen produced in the next few years will be converted into green ammonia.

[0012] Ammonia can be used as a practical hydrogen energy carrier, and existing industry produces, stores and trades millions of tonnes of ammonia per year, meaning the infrastructure and technology to kick-start a hydrogen economy already exist.

[0013] In addition to the production of hydrogen by electrolysis and nitrogen by air separation units, the most important energy consumption and compression costs are synthesis gas compression and cold boxes. Synthesis gas compression compresses the nitrogen-hydrogen mixture to the pressure of 150-200 bar required for the synthesis process, and the cold box provides refrigeration energy for liquefying and cooling ammonia to about -33°C at atmospheric pressure.

[0014] In conventional ammonia production, hydrogen (H2) is obtained from steam methane reforming (SMR), the most widely used process for producing hydrogen, and nitrogen (N2) is obtained from air or from an air separation unit.

[0015] N2 and H2 are mixed in a stoichiometric ratio (1:3), compressed with a syngas compressor, and introduced into an ammonia synthesis reactor at a pressure of 150 to 220 bar. The ammonia synthesis gas reactor operates at an operating temperature of about 500°C. The process is exothermic, releasing a large amount of heat of 46 kJ per mol of ammonia, and this heat is used to generate steam. After the reaction, about 25% of the ammonia is obtained as a product, and the rest of the ammonia is returned via a circulating compressor. The produced ammonia is then liquefied by cryogenic distillation. Summary of the invention

[0016] It is an object of the present invention to provide an improved device and an improved process for producing ammonia, in particular with regard to the use of energy required for producing the ammonia.

[0017] This object is achieved by a device according to claim 1 and a method according to claim 11 .

[0018] The present invention proposes an innovative concept of realizing an environmentally friendly ammonia plant by combining an electrolyzer with renewable energy.

[0019] The dependent claims specify advantageous developments.

[0020] The advantages of the device according to the invention and the method according to the invention are:

[0021] - Processes for green hydrogen and green ammonia are more efficient, environmentally friendly and economical;

[0022] - Incorporation of H2-operated gas turbine exhaust gases enables the production of N2 and green electrical / mechanical drive energy as well as water for electrolysis;

[0023] - Compared with long-distance transport of lean H2, transporting N2-H2 mixtures by pipeline consumes less current and is safer, more flexible and has a longer pipeline life;

[0024] - Uses pressurized O2 to convert into electrical current, increasing overall efficiency and enabling the device to operate from fluctuating renewable energy sources;

[0025] -The processes for green hydrogen and green ammonia are more efficient, environmentally friendly and economical. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above-mentioned characteristics, features and advantages of the present invention and the manner of achieving them are more clearly explained in conjunction with the following description of the embodiments, and the embodiments are explained in more detail in conjunction with the accompanying drawings.

[0027] In this case, identical components or components having the same function are provided with the same reference numerals.

[0028] Embodiments of the present invention are described below with reference to the accompanying drawings. These drawings are not intended to show the embodiments to scale, but are schematic diagrams and / or slightly deformed diagrams for explanation. For supplements to the teachings apparent in the drawings, please refer to the relevant prior art. Among them:

[0029] Figure 1 A schematic diagram of an apparatus for producing ammonia is shown. DETAILED DESCRIPTION

[0030] like Figure 1 As shown, the electrolyzer takes electricity from renewable energy sources, such as wind or photovoltaics, and produces H2 and O2 (about 8 times the mass of H2). These gases are produced under pressure (1-30 bar). Usually, O2 is not used, but discharged.

[0031] According to the present invention, pressurized O2 is heated in a waste heat boiler with exhaust gas from a gas turbine and then expanded in a hot gas expander to generate mechanical or electrical energy. This energy can be utilized in some supply equipment or auxiliary equipment.

[0032] For the ammonia process, N2 and H2 are required as raw materials, which are mixed in a stoichiometric ratio of 1:3. In conventional devices, N2 is supplied from an air separation unit or from air, while H2 mainly comes from methane steam reforming.

[0033] According to the invention, N2 is separated from the exhaust gas of a gas turbine operated with hydrogen (by means of an absorber / PSA unit), so that no air separation unit is required. The water vapor from the gas turbine exhaust gas is condensed and can be used as water feedstock for the electrolysis unit (up to 15% of the required water).

[0034] The N2 separated from the gas turbine exhaust gas is mixed stoichiometrically with the H2 from the electrolysis unit to produce the synthesis gas mixture required for the synthesis of ammonia.

[0035] The syngas mixture (molar mass 8 g / mol) is then compressed to pipeline pressure and transported to the location of the ammonia plant with the ammonia reactor 2. This syngas transport requires less energy than pure H2 transport and enables safer pipeline operation compared to H2-lean transport.

[0036] To support ammonia production (at reduced capacity), hydrogen and oxygen buffers are integrated to supply the ammonia plant with reduced hydrogen and the expander with gas turbine fuel and oxygen during times when renewable energy sources are not available. The size of the buffer depends on the length of time without continuous power supply and the minimum capacity of the ammonia synthesis.

[0037] Synthesis gas is supplied to the ammonia reactor 2. The synthesis gas contains hydrogen (H2) and nitrogen (N2). Hydrogen (H2) and nitrogen (N2) react in the ammonia reactor 2 according to the following chemical reaction formula:

[0038] N2+3H2→2NH3+92kJ / mol.

[0039] This chemical reaction is a highly exothermic reaction, ie the ammonia NH 3 produced in the ammonia reactor has a relatively high temperature, wherein, according to the invention, this high temperature is used to preheat the nitrogen N 2 .

[0040] A detailed illustration of the ammonia reactor 2 is omitted here.

[0041] The device 1 comprises an electrolyser 3 which is supplied with water 4 and which decomposes the water into hydrogen and oxygen by means of a renewable energy source 5 .

[0042] The oxygen is supplied to a first buffer store 6. The hydrogen is partly used as fuel for a gas turbine 7. The line for the hydrogen as fuel for the gas turbine 7 is symbolically indicated by the reference numeral 8.

[0043] In order to operate the gas turbine 7 , air 9 is required in addition to the hydrogen, with ambient air usually being used.

[0044] The hot exhaust gas 10 from the gas turbine 7 is fed to a heat exchanger 11. The oxygen located in the buffer store 6 is fed into the heat exchanger 11, wherein the temperature of the oxygen is increased by the hot exhaust gas 10 from the gas turbine 7.

[0045] The heated oxygen is supplied to the expander 13 via the pipeline 12 .

[0046] In the expander 13 , the thermal energy of the oxygen is converted into mechanical energy. The mechanical energy is used to drive the generator 14 .

[0047] The exhaust gas from the expander 13 is then supplied to further components: a second expander 15 , a heat exchanger 16 .

[0048] Another part of the hydrogen from the electrolyser 3 is supplied to a further buffer store 17 , wherein the buffer store 17 is used to provide energy when energy from renewable energy sources is not available.

[0049] The exhaust gas 10 from the gas turbine 7 cooled after the heat exchanger 11 is supplied to a further heat exchanger 19 and then led to a separation unit 20. In the separation unit 20, the exhaust gas is separated into water 21 and nitrogen 22. The water 21 is supplied to the electrolyser.

[0050] Another part of the hydrogen from the electrolyser 3 is supplied to a synthesis gas compressor 18. The synthesis gas compressor 18 is likewise supplied with nitrogen 22 from a separation unit 20. The synthesis gas thus produced is compressed in the synthesis gas compressor 18 and conveyed (partially over a longer distance) in a line 24 to the ammonia reactor 2.

[0051] The compressor 23 required for producing ammonia is driven via the gas turbine 7 .

Claims

1. A device for producing ammonia (1), The device comprises an ammonia reactor (2) for producing ammonia (NH3) from synthesis gas, wherein: The synthesis gas comprises hydrogen (H2) and nitrogen (N2), The device also includes an electrolyzer (3) for producing hydrogen and oxygen from water. wherein the electrolyzer (3) is operated using renewable energy, The device also comprises a gas turbine (7) operated with hydrogen, It is characterized in that The exhaust gas from the gas turbine (7) containing nitrogen (N2) is used to generate the synthesis gas.

2. The device (1) according to claim 1, in, The hydrogen (H2) produced by the electrolyzer (3) is mixed with the nitrogen (N2) produced from the exhaust gas of the gas turbine (7) to produce the synthesis gas.

3. The device (1) according to claim 2, The apparatus also comprises a first compressor (18) for compressing the synthesis gas.

4. The device (1) according to claim 3, The device comprises a separation unit (20) for separating the exhaust gas from the gas turbine (7) into nitrogen and water, wherein: The nitrogen is used for the synthesis gas, wherein the water is supplied to the electrolyser (3).

5. The device (1) according to any one of the preceding claims, The device has a first buffer store (6) for the oxygen obtained from the electrolyser (3).

6. The device (1) according to claim 5, The device has a heat exchanger (11) which allows hot exhaust gases (10) from the gas turbine (7) to heat oxygen flowing out of the first buffer store (6).

7. The device (1) according to claim 6, The device has an expander (13) which converts the thermal energy of the oxygen from the first buffer store (6) into mechanical energy.

8. The device (1) according to claim 7, The device has a generator (15) which is used to generate electrical energy and is driven by the expansion machine (13).

9. The device (1) according to any one of the preceding claims, in, The synthesis gas compressed in the first compressor (18) is passed to a second synthesis gas compressor (23), wherein the second synthesis gas compressor (23) is driven by the gas turbine (7).

10. The device (1) according to claim 9, in, The synthesis gas flowing out from the second synthesis gas compressor (23) is supplied to the ammonia reactor (2).

11. A process for producing ammonia, in, Ammonia (NH3) is produced in an ammonia reactor (2) from synthesis gas, wherein the synthesis gas contains hydrogen (H2) and nitrogen (N2), Therein, hydrogen and oxygen are produced in an electrolyser (3) using renewable energy, and the hydrogen is used to operate a gas turbine (7) which drives a synthesis gas compressor (23).

12. The method according to claim 11, in, A heat exchanger (11) is used which allows the exhaust gases (10) from the gas turbine to heat the oxygen originating from the electrolyser (3).

13. The method according to claim 12, in, An expander (13) is used, which is operated using the heated oxygen from the heat exchanger (11).

14. The method according to claim 13, in, A generator (15) is used, which is operated by means of the expansion machine (13), wherein the generator (15) is used to generate electrical energy.

15. The method according to any one of the preceding claims, in, A separation unit (20) is used, with which the exhaust gas (10) from the gas turbine (7) is separated into hydrogen and water.

16. The method according to claim 15, in, The water is directed to the electrolyser (3).

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