System and method for producing ammonia
Patent Information
- Application Number
- EP2023734607
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-07-01
- Filing Date
- 2023-06-21
- Publication Date
- 2025-02-26
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] Plant and process for the production of ammonia
[0003] The invention relates to a plant and a method for producing ammonia, wherein ammonia (NH3) is produced from a synthesis gas in an ammonia reactor, wherein the synthesis gas comprises hydrogen (H2) and nitrogen (N2).
[0004] Ammonia production is based on a well-known process that typically requires a great deal of energy. According to initial estimates, around 1% of the world's energy production is currently used for ammonia production.
[0005] Ammonia produced from renewable energy sources is called green ammonia. Green ammonia is considered a rapidly growing energy carrier for hydrogen. It is also used in many industrial processes, especially fertilizers. It is estimated that approximately 50% of the green hydrogen produced in the coming years will be processed directly into liquid ammonia for long-distance hydrogen transport, as the liquefaction of pure hydrogen is highly energy-intensive.
[0006] The greatest energy and compression expenditure, apart from hydrogen production through electrolysis and nitrogen production through air separation plants, is the synthesis gas compression, which compresses the nitrogen-hydrogen mixture to the pressure of 150-200 bar required for the synthesis process, and the cold box, which provides the cooling energy for the liquefaction and cooling of the ammonia to approximately -33°C at atmospheric pressure.
[0007] Typically, a preheating unit is required to heat the synthesis gas to the reaction temperature. Currently, the nitrogen and hydrogen required for ammonia production are typically compressed to the required synthesis pressure in a synthesis gas compressor. The intake pressure for this compressor is typically determined by the hydrogen pressure, which, in green ammonia applications where electrolysis is operated on-site, is limited to the maximum outlet pressure of an electrolysis system (max. 30-40 bar).
[0008] The shaft power for the compressor is supplied by a steam turbine, while the required steam is generated from the heat released during ammonia synthesis. Preheating of the synthesis gas must be achieved either by a fuel- or electricity-fired heater or by utilizing waste heat from the ammonia process, which reduces the amount of steam that can be generated for the steam turbine.
[0009] Condensation occurs through a refrigerant circuit.
[0010] Ammonia is produced in large quantities worldwide as an agricultural fertilizer, but natural gas or other fossil fuels are used to provide both the hydrogen feedstock and the energy for the synthesis process. As a result, ammonia production using these methods accounts for nearly 1.5% of global CO2 emissions.
[0011] Given commitments to achieve net-zero emissions targets, new carbon-free fuels such as green ammonia and green hydrogen are needed to decarbonise power generation, heat supply, transport and industry.
[0012] It is estimated that approximately 50% of the green hydrogen produced in the coming years will be converted into green ammonia. Ammonia can be used as a practical hydrogen energy carrier, and the existing industry that produces, stores, and trades millions of tons of ammonia each year means that the infrastructure and technology are already in place to kick-start the hydrogen economy.
[0013] The most important energy and compression inputs, in addition to hydrogen production through electrolysis and nitrogen production through air separation plants, are the synthesis gas compression, which compresses the nitrogen-hydrogen mixture to the pressure of 150-200 bar required for the synthesis process, and the cold box, which supplies the cooling energy for the liquefaction and cooling of the 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 widely used method for hydrogen production, and nitrogen gas (N2) is obtained either from air or from an air separation plant.
[0015] N2 and H2 are mixed stoichiometrically (1:3) and compressed using a syngas compressor. The gas is fed into an ammonia synthesis reactor at a pressure of 150 to 220 bar. The ammonia synthesis reactor operates at an operating temperature of approximately 500°C. The process is exothermic; the large amount of heat (46 kJ / mol) of ammonia is released and used to generate steam. After the reaction, approximately 25% of the ammonia is recovered as a product, and the remainder is recycled via a recirculation compressor. The produced ammonia is then liquefied by cryogenic distillation.
[0016] The invention aims to provide an improved plant and an improved process for producing ammonia, particularly with regard to the use of the energy required for the production of the ammonia. This object is achieved by a plant according to claim 1 and a process according to claim 11.
[0017] The invention proposes an innovative concept for an environmentally friendly ammonia plant by integrating an electroli zer with renewable energy.
[0018] Advantageous further developments are specified in the subclaims.
[0019] The advantages of the system and method according to the invention are:
[0020] - More efficient, environmentally friendly and economical processes for green hydrogen and green ammonia
[0021] - The integration of H2-powered GT exhaust gases enables the generation of N2 and green electrical / mechanical drive energy as well as water for electrolysis
[0022] - Lower electricity consumption through pipeline transport of N2-H2 mixtures with higher safety, operational flexibility and longer pipeline lifetime compared to transporting lean H2 over long distances
[0023] - The use of pressurized O2 to convert it into electricity increases the overall efficiency and supports the operation of the plant with fluctuating renewable energy.
[0024] - More efficient, environmentally friendly and economical processes for green hydrogen and green ammonia.
[0025] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.
[0026] Identical components or components with the same function are identified by the same reference symbols. Exemplary embodiments of the invention are described below with reference to the drawings. These are not intended to represent the exemplary embodiments to scale; rather, where useful for explanation, the drawings are presented in a schematic and / or slightly distorted form. For supplements to the teachings immediately apparent in the drawings, reference is made to the relevant prior art.
[0027] They show:
[0028] Figure 1 is a schematic representation of a system for
[0029] Production of ammonia
[0030] As shown in Figure 1, the Electrolizer captures electrical energy from renewable sources, such as wind power or photovoltaics, and produces H2 and O2 (approximately 8 times more than H2 by mass). These gases are generated under pressure (1-30 bar). Normally, O2 is not used but diverted.
[0031] According to the invention, the pressurized O2 is heated with the exhaust gas from a gas turbine in a waste heat boiler and then expanded in a hot gas expander to generate mechanical or electrical energy. This energy can be used in some utility or auxiliary facilities.
[0032] The ammonia process requires N2 and H2 as feedstocks, which are mixed stoichiometrically in a ratio of 1:3. In a conventional plant, the N2 is supplied from an air separation plant or from the air, while the H2 comes primarily from methane steam reforming.
[0033] According to the invention, the N2 is separated from the exhaust gas of a hydrogen-powered gas turbine (using an absorber / PSA unit), eliminating the need for an air separation plant. The water vapor from the gas turbine exhaust is condensed and available as water feedstock for the electrolysis plant (up to 15% of the required water input).
[0034] The separated N2 from the GT exhaust gas is mixed stoichiometrically with H2 from the electrolysis plant to produce the required ammonia synthesis gas mixture.
[0035] The synthesis gas mixture (molecular weight 8 g / mol) is then compressed to pipeline pressure and transported to the ammonia plant site via ammonia reactor 2. This syngas transport requires less energy than pure H2 transport and enables safe pipeline operation compared to lean H2 transport.
[0036] To support ammonia production (at reduced capacity), a hydrogen and oxygen buffer will be integrated to provide reduced hydrogen for the ammonia plant and the GT fuel, as well as oxygen for the expander during periods when renewable energy is unavailable. The capacity of the buffer depends on the duration of the period without a sustainable power supply and the minimum capacity of ammonia synthesis.
[0037] A synthesis gas is fed into ammonia reactor 2. The synthesis gas comprises hydrogen (H2) and nitrogen (N2). The hydrogen (H2) and nitrogen (N2) react in the ammonia reactor 2 according to the chemical reaction
[0038] N2+ 3 H2- 2 NH3+ 92 kJ / mol
[0039] This chemical reaction is a strongly exothermic reaction, ie the ammonia NH3 produced in the ammonia reactor has a comparatively high temperature, and this high temperature is used according to the invention to preheat the nitrogen N2.
[0040] A detailed description of the ammonia reactor 2 will be omitted here. Plant 1 includes an electrolizer 3, which is fed with water 4 and uses renewable energy 5 to separate water into hydrogen and oxygen.
[0041] The oxygen is fed to a first buffer storage 6.
[0042] The hydrogen is provided in part as fuel for a gas turbine 7. The line of hydrogen as fuel for the gas turbine 7 is symbolically identified by reference numeral 8.
[0043] In addition to hydrogen, air 9 is also required to operate the gas turbine 7, 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 contained in the buffer storage 6 is fed into the heat exchanger 11, with the temperature of the oxygen being heated by the hot exhaust gas 10 from the gas turbine 7.
[0045] The heated oxygen is fed to an expander 13 via a line 12.
[0046] In the expander 13, the thermal energy of the oxygen is converted into mechanical energy. The mechanical energy is used to drive an electrical generator 14.
[0047] The exhaust gas from the expander 13 is then fed to further components: second expander 15, heat exchanger 16.
[0048] Another part of the hydrogen from the Electrolizer 3 is fed to another buffer storage 17, which serves to provide energy when the energy from the renewable energies is not available.
[0049] The exhaust gas 10 from the gas turbine 7, cooled after the heat exchanger 11, is fed to another heat exchanger 19 and then into a separation unit 20. In the separation unit 20, the exhaust gas is separated into water 21 and nitrogen 22. The water 21 is fed to the electrolizer.
[0050] Another portion of the hydrogen from the electrolizer 3 is fed to a synthesis gas compressor 18. Nitrogen 22 from the separation unit 20 is also fed to the synthesis gas compressor 18. The resulting synthesis gas is compressed in the synthesis gas compressor 18 and transported to the ammonia reactor 2 (sometimes over a longer distance) via a line 24.
[0051] The compressor 23 required for ammonia production is driven by the gas turbine 7.
Claims
Patent claims 1. Plant (1) for producing ammonia, comprising an ammonia reactor (2) which is designed to produce ammonia (NH3) from a synthesis gas, wherein the synthesis gas comprises hydrogen (H2) and nitrogen (N2), further comprising an electrolizer (3) which is designed to produce hydrogen and oxygen from water, wherein the electrolizer (3) is operated with renewable energies, further comprising a hydrogen-operated gas turbine (7), characterized in that the exhaust gas of the gas turbine (7) containing nitrogen (N2) is used to produce the synthesis gas.
2. Plant (1) according to claim 1, wherein the hydrogen (H2) produced from the electrolizer (3) is mixed with the nitrogen (N2) produced from the exhaust gas of the gas turbine (7) to produce the synthesis gas.
3. Plant (1) according to claim 2, further comprising a first compressor (18) for compressing the synthesis gas.
4. Plant (1) according to claim 3, with a separation unit (20) which is designed to separate the exhaust gas from the gas turbine (7) into nitrogen and water, the nitrogen being used for the synthesis gas, the water being fed to the electrolizer (3).
5. Plant (1) according to one of the preceding claims, with a first buffer storage (6) for oxygen obtained from the electrolizer (3). Plant (1) according to claim 5, with a heat exchanger (11) designed such that the hot exhaust gas (10) from the gas turbine (7) heats the oxygen flowing out of the first buffer storage (6). Plant (1) according to claim 6, with an expander (13) designed such that the thermal energy of the oxygen from the first buffer storage (6) is converted into mechanical energy. Plant (1) according to claim 7, with a generator (15) designed to generate electrical energy and driven by the expander (13). Plant (1) according to one of the preceding claims, wherein the synthesis gas compressed in the first compressor (18) is fed to a second synthesis gas compressor (23), wherein the second synthesis gas compressor (23) is driven by the gas turbine (7).Plant (1) according to claim 9, wherein the gas flowing from the second synthesis gas compressor (23) is fed to the ammonia reactor (2). A method for producing ammonia, wherein ammonia (NH3) is produced in an ammonia reactor (2) from a synthesis gas, wherein the synthesis gas comprises hydrogen (H2) and nitrogen (N2), wherein hydrogen and oxygen are produced in an electrolizer (3) using renewable energy, and the hydrogen is used to operate a gas turbine. (7) is used, which drives a synthesis gas compressor (23). Method according to claim 11, wherein a heat exchanger (11) is used which is designed such that the exhaust gas (10) from the gas turbine heats the oxygen originating from the electrolizer (3). Method according to claim 12, wherein an expander (13) is used which is operated with the heated oxygen from the heat exchanger (11). Method according to claim 13, wherein a generator (15) is used which is operated with the expander (13), wherein the generator (15) is designed to generate electrical energy. Method according to one of the preceding claims, wherein a separation unit (20) is used to separate the exhaust gas (10) from the gas turbine (7) into hydrogen and water. Method according to claim 15, wherein the water is passed to the electrolizer (3).