Plant and method for producing ammonia

Abstract

The present invention relates to a plant and a method for producing ammonia. The plant includes an ammonia reactor (2) formed to produce ammonia (NH3) from synthesis gas containing hydrogen (H2) and nitrogen (N2), and further includes an electrolyzer (3) formed to produce hydrogen and oxygen from water. The electrolyzer (3) is operated with renewable energy and further includes a gas turbine (7) operated with hydrogen. In this case, the exhaust gas of the gas turbine (7) containing nitrogen (N2) is used for the production of synthesis gas.

Description

Technical Field

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

[0002] The production of ammonia dates back to known processes that usually require very large amounts of energy. According to initial estimates, about 1% of the energy generated worldwide today is required for ammonia production.

[0003] Ammonia produced from renewable energy is called green ammonia. Green ammonia is considered to be a rapidly growing energy carrier for hydrogen. Furthermore, it is used in many industrial processes, especially for fertilizers. It is estimated that about 50% of the green hydrogen produced in the coming years will be directly converted to liquid ammonia for the long-distance transport of hydrogen, because the liquefaction of pure hydrogen is very energy-intensive.

[0004] The largest energy costs and compression costs, along with hydrogen production by electrolysis and nitrogen production by an air separation plant, are synthesis gas compression and a cold box. 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 supplies refrigeration energy for the liquefaction and cooling of ammonia at about -33 °C under atmospheric pressure.

[0005] Normally, a preheating unit is required to heat the synthesis gas to the reaction temperature.

[0006] Currently, the nitrogen and hydrogen required for ammonia production are usually compressed to the required synthesis pressure in a synthesis gas compressor. The intake pressure of this compressor is generally determined by the hydrogen pressure, which is limited to the maximum outlet pressure of the electrolysis system (up to 30 - 40 bar maximum) in the case of green ammonia utilization where electrolysis is carried out on-site.

[0007] The shaft power for the compressor is supplied by a steam turbine, while the required steam is generated by the heat released during ammonia synthesis. The preheating of the synthesis gas must be carried out by a fuel-driven or electric-driven heater, or by waste heat recovery from the ammonia process, which reduces the amount of steam that can be generated for the steam turbine.

[0008] Liquefaction is carried out by a refrigerant circulation circuit.

[0009] Ammonia is produced in large quantities as an agricultural fertilizer worldwide, but natural gas or other fossil fuels are used to provide both hydrogen as a raw material and energy for the synthesis process. As a result, ammonia production causes approximately 1.5% of global CO2 emissions in these ways.

[0010] In view of the commitment to achieve pure zero emissions, new zero-carbon fuels such as green ammonia and green hydrogen are needed to decarbonize energy generation, heat supply, transportation, and industry.

[0011] It is estimated that approximately 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, meaning that the existing industries that produce, store, and trade millions of tons of ammonia per year already have the infrastructure and technology to drive the hydrogen economy.

[0013] Along with hydrogen production by an electrolysis device and nitrogen production by an air separation system, the most important energy costs and compression costs are the synthesis gas compression for compressing the nitrogen-hydrogen mixture to the pressure of 150 - 200 bar required for the synthesis process, and the cold box for supplying the cooling energy to cool and liquefy ammonia to approximately -33°C at atmospheric pressure.

[0014] In conventional ammonia production, hydrogen gas (H2) is obtained from steam methane reforming (SMR), the most common method for hydrogen production, and nitrogen gas (N2) is obtained from air or an air separation system.

[0015] N2 and H2 are stoichiometrically mixed (1:3), compressed by a synthesis gas compressor, and led to an ammonia synthesis reactor at a pressure of 150 - 220 bar. The ammonia synthesis gas reactor operates at an operating temperature of approximately 500°C. This process is an exothermic process, and a large amount of heat of 46 kJ / mol ammonia is released and utilized for steam generation. After this reaction, approximately 25% of the ammonia is obtained as a product, and the rest is returned via a recycle compressor. The produced ammonia is then liquefied by low-temperature distillation.

Summary of the Invention

Problems to be Solved by the Invention

[0016] The problem of the present invention is to provide an improved plant and an improved method for manufacturing ammonia, particularly considering the energy use required for ammonia production.

Means for Solving the Problems

[0017] This problem is solved by the plant according to claim 1 and the method according to claim 11.

[0018] The present invention proposes an innovative concept for an environmentally friendly ammonia plant by combining an electrolysis device with renewable energy.

[0019] Advantageous development forms are described in the dependent claims.

[0020] The advantages of the plant according to the invention and the method according to the invention are as follows: - A more efficient, more environmentally friendly and more economical process for green hydrogen and green ammonia. - The combination of GT exhaust gas driven by H2 enables the production of N2 and green electrical / mechanical drive energy as well as water for the electrolyzer. - Pipeline transportation of the N2-H2 mixture, which has higher safety, operational flexibility and a longer pipeline life compared to the long-distance transportation of lean H2, reduces power consumption. - By using pressurized O2 for power conversion, the overall efficiency is improved and the operation of plants using fluctuating renewable energy is supported. - A more efficient, more environmentally friendly and more economical process for green hydrogen and green ammonia.

[0021] The above-mentioned characteristics, features and advantages of the invention, and the manner in which they are achieved, will be described more clearly and specifically based on the following description of exemplary embodiments, which are described in more detail together with the drawings.

[0022] The same reference numerals are assigned to the same components or components having the same function.

[0023] Hereinafter, exemplary embodiments of the invention will be described with reference to the drawings. These are not scale drawings of the exemplary embodiments, and the drawings are made in a schematic and / or slightly distorted form for the purpose of explanation. For directly apparent teachings in the drawings, reference should be made to the relevant prior art.

Brief Description of the Drawings

[0024]

Figure 1

Mode for carrying out the invention

[0025] The drawings show a schematic diagram of a plant for generating ammonia.

[0026] As shown in FIG. 1, this electrolyzer receives electrical energy from renewable energy such as wind power generation or solar power generation, and generates H2 and O2 (about 8 times the mass of H2). These gases are generated under pressure (1 - 30 bar). Usually, O2 is not used and is discharged.

[0027] According to the present invention, in order to generate mechanical or electrical energy, O2 under pressure is heated in a waste heat boiler using the exhaust gas of a gas turbine, and then expanded in a high-temperature gas expander. This energy can be utilized in some supply facilities or auxiliary facilities.

[0028] For this ammonia production method, N2 and H2 are required as raw materials, and these are mixed in a stoichiometric ratio of 1:3. In a conventional plant, N2 is supplied from an air separation plant or air, while H2 is mainly obtained from steam methane reforming.

[0029] According to the present invention, N2 from the exhaust gas of a gas turbine driven by hydrogen is separated (using an absorber / PSA unit), so an air separation device is not required. The water vapor from the gas turbine exhaust gas is condensed and can be used as a water feedstock for the electrolysis plant (up to 15% of the required water usage).

[0030] The separated N2 from the GT exhaust gas is stoichiometrically mixed with H2 from the electrolyzer to produce the required synthesis gas mixture for ammonia synthesis.

[0031] This syngas mixture (molar weight 8 g / mol) is then compressed to pipeline pressure and transported to the location of an ammonia plant equipped with an ammonia reactor 2. This syngas transport requires less energy than pure H2 transport and enables a safe pipeline operation compared to lean H2 transport.

[0032] To support ammonia production (in case of reduced production capacity), a buffer of hydrogen and oxygen is incorporated, which serves to supply reduced hydrogen to the ammonia plant and for GT fuel during periods when renewable energy is not available, as well as to supply oxygen for the expander. The capacity of this buffer depends on the period without sustainable power supply and the minimum capacity of the ammonia synthesis unit.

[0033] Syngas is supplied to the ammonia reactor 2. The syngas contains hydrogen (H2) and nitrogen (N2). This hydrogen (H2) and nitrogen (N2) react in the ammonia reactor according to the following chemical reaction N2 + 3H2 → 2NH3 + 92 kJ / mol in accordance with.

[0034] This chemical reaction is a strong exothermic reaction, that is, the ammonia NH3 produced in the ammonia reactor has a rather high temperature, and this high temperature is used to preheat nitrogen N2 according to the present invention.

[0035] Here, a detailed description of the ammonia reactor 2 is omitted.

[0036] Plant 1 has an electrolyzer 3, to which water 4 is supplied, and the electrolyzer 3 separates water into hydrogen and oxygen using renewable energy 5.

[0037] Oxygen is supplied to the first buffer reservoir 6. A part of the hydrogen is utilized as fuel for the gas turbine 7. The pipeline for hydrogen as fuel for the gas turbine 7 is symbolically shown together with the reference numeral 8.

[0038] For the operation of the gas turbine 7, in addition to hydrogen, air 9 is also required, and usually ambient air is used.

[0039] The high-temperature exhaust gas 10 from the gas turbine 7 is supplied to the heat exchanger 11. Oxygen in the buffer storage 6 is supplied to this heat exchanger 11, and the temperature of this oxygen is heated by the high-temperature exhaust gas 10 of the gas turbine 7.

[0040] The heated oxygen is supplied to the expander 13 via the pipeline 12.

[0041] In this expander 13, the thermal energy of oxygen is converted into mechanical energy. This mechanical energy is used to drive the generator 14.

[0042] The exhaust gas from the expander 13 is then supplied to further components, namely, the second expander 15 and the heat exchanger 16.

[0043] Another part of the hydrogen from the electrolyzer 3 is supplied to another buffer storage 17, and this buffer storage 17 is used to supply energy when the energy from renewable energy is not available.

[0044] The exhaust gas 10 from the gas turbine 7 cooled by the heat exchanger 11 is supplied to another heat exchanger 19 and then led to the 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 electrolyzer.

[0045] Another part of the hydrogen from the electrolyzer 3 is supplied to the synthesis gas compressor 18. Nitrogen 22 from the separation unit 20 is also supplied to this synthesis gas compressor 18. The synthesis gas thus produced is compressed in the synthesis gas compressor 18 and transported (partially over a longer distance) to the ammonia reactor 2 via the pipeline 24.

[0046] The compressor 23 required for ammonia production is driven via the gas turbine 7.

Explanation of Reference Numerals

[0047] 1 Plant 2 Ammonia Reactor 3 Electrolyzer 7 Gas Turbine

Claims

1. A plant (1) for producing ammonia, An ammonia reactor (2) formed to produce ammonia (NH 3 ), the synthesis gas including hydrogen (H 2 ) and nitrogen (N 2 ). further comprising an electrolyzer (3) configured to produce hydrogen and oxygen from water, wherein the electrolyzer (3) is operated with renewable energy, further comprising a gas turbine (7) operated with hydrogen, in the plant (1), The exhaust gas containing nitrogen (N 2 ) of the gas turbine (7) is used for the production of the synthesis gas, characterized by a plant (1).

2. The plant (1) according to claim 1, The hydrogen (H 2 ) generated by the electrolyzer (3) is mixed with nitrogen (N 2 ) generated from the exhaust gas of the gas turbine (7) to generate the synthesis gas, in a plant (1).

3. The plant (1) according to claim 2, further comprising a first compressor (18) for compressing the synthesis gas, the plant (1).

4. The plant (1) according to claim 3, comprising a separation unit (20) configured to separate the exhaust gas from the gas turbine (7) into nitrogen and water, wherein the nitrogen is used for the synthesis gas and the water is supplied to the electrolyzer (3), the plant (1).

5. The plant (1) according to any one of claims 1 to 4, comprising a first buffer storage (6) for the oxygen obtained in the electrolyzer (3), the plant (1).

6. The plant (1) according to claim 5, comprising a heat exchanger (11) configured such that the high-temperature exhaust gas (10) from the gas turbine (7) heats the oxygen flowing out of the first buffer storage (6), the plant (1).

7. The plant (1) according to claim 6, comprising an expander (13) configured such that the thermal energy of the oxygen from the first buffer storage (6) is converted into mechanical energy, the plant (1).

8. The plant (1) according to claim 7, comprising a generator (15) configured to generate electrical energy, the generator (15) being driven by the expander (13), the plant (1).

9. The plant (1) according to any one of claims 1 to 8, wherein the synthesis gas compressed by the first compressor (18) is guided to a second synthesis gas compressor (23), and the second synthesis gas compressor (23) is driven by the gas turbine (7), the plant (1).

10. The plant (1) according to claim 9, flowing out of the second synthesis gas compressor (23) and supplied to the ammonia reactor (2), the plant (1).

11. A method for producing ammonia, Ammonia (NH 3 ) is generated from synthesis gas in the ammonia reactor (2), and the synthesis gas contains hydrogen (H ２ ) and nitrogen (N ２ ). A method in which hydrogen and oxygen are generated using renewable energy in an electrolysis device (3), the hydrogen is used to drive a gas turbine (7), and the gas turbine (7) drives a synthesis gas compressor (23).

12. The method according to claim 11, wherein a heat exchanger (11) is used which is configured such that the exhaust gas (10) from the gas turbine heats the oxygen obtained from the electrolysis device (3).

13. The method according to claim 12, wherein an expander (13) driven by the heated oxygen from the heat exchanger (11) is used.

14. The method according to claim 13, wherein a generator (15) driven by the expander (13) is used, and the generator (15) is configured to generate electrical energy.

15. The method according to any one of claims 1 to 14, wherein a separation unit (20) is used, and the exhaust gas (10) from the gas turbine (7) is separated into hydrogen and water using the separation unit.

16. The method according to claim 15, wherein the water is guided to the electrolysis device (3).

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