Power-to-ammonia

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The aim of the power-to- ammonia process is to make energy from renewable energy sources transportable and storable by storing energy chemically in the form of ammonia .

Ammonia can be used as a carbon-free fuel u. a. be used in internal combustion engines or in fuel cells .

Ammonia is a climate-neutral (fuel) substance if conventional natural gas is not used for the production of the required hydrogen . B. is produced by electrolysis using green electricity and only renewable energies are used in the further process. Renewable energy is already available in many parts of the world. Converted into the energy carrier ammonia, this energy can be transported to the major consumption centers via pipelines and ships. There it can be consumed as required and does not have to be geared to the fluctuating generation of renewable energies.

If, on the other hand, ammonia is produced conventionally from natural gas without the use of renewable energies, around 1.5 tons of the greenhouse gas carbon dioxide are produced per ton of ammonia produced .

The production of ammonia is widespread, currently around 2% of the total commercial energy requirement worldwide is expected to be used for this.

Storage and transportation

Ammonia becomes liquid at −33 ° C. At 20 ° C the evaporation pressure is approx. 9 bar. Large tanks, for example in ships, can transport the ammonia without pressure by cooling it to −33 ° C. Pressure tanks are suitable for smaller tanks (similar to propane / butane ). The energy density of liquid ammonia is 4.25 kWh / l or 6.25 kWh / kg (for comparison: gasoline has an energy density of 9.7 kWh / l or 12.7 kWh / kg).

Ammonia can also be stored bound as a solid. The following salts, for example, come into consideration: ammonium carbamate , ammonium carbonate and ammonium hydrogen carbonate . These decompose below 60 ° C and release the bound ammonia again.

Manufacturing

In the conventional process, hydrogen is first obtained from natural gas. Together with nitrogen from the air, ammonia is then produced in a high-pressure reactor over a catalyst using the Haber-Bosch process.

Hydrogen can also be produced in a climate-neutral way via electrolysis using renewable energies. The Haber-Bosch process should also be climate-neutral with renewable energies.

In the Solid State Ammonia Synthesis process (SSAS process), ammonia is electrolytically produced directly from water , nitrogen (from air) and electricity. This method is still under research. With this method, only 8.3 kilowatt hours of electricity should be required per kilogram of ammonia.

use

Ammonia can be used in modified conventional power plants and engines: gas and steam turbines, modified internal combustion engines. Ammonia can be converted back into electricity directly in special fuel cells, the ammonia fuel cells . In addition, hydrogen can be recovered from ammonia.

Ammonia is used in large quantities in the fertilizer industry.

Advantages and disadvantages

advantages

  • Easily transportable by ship and pipeline .
  • Flammability lower than heating oil , low risk of explosion .
  • Since ammonia very often z. B. is used as a fertilizer or environmentally friendly refrigerant , the production and handling is practiced.
  • The advantage over hydrogen is the better storage and transportability due to the higher energy density .
  • The advantage over methane is that ammonia is not a greenhouse gas , while methane often escapes into the environment, where it is around 20 to 25 times more harmful than CO 2 .
  • Another advantage over methane is that nitrogen can be separated from the air easily and inexpensively. In contrast, methane synthesis would require a source of carbon dioxide. A separation of carbon dioxide from the ambient air for the climate-neutral production of other, carbon-containing fuels is currently not possible at low cost because of the low concentration of carbon dioxide in the air.

disadvantage

  • Hazardous substance , poisonous and corrosive gas. However, poisoning is rare, as people flee from the danger zone because of the pungent odor even at low concentrations.
  • Lower energy density than gasoline.
  • Gaseous at normal pressure.
  • When used as fuel, there should be a certain amount of ammonia slip, i.e. small amounts degenerate unused in the exhaust gas, which, however , should be able to be oxidized to harmless products nitrogen (N 2 ) and water (H 2 O) with the help of an ammonia slip catalyst.
  • When it is converted into usable energy through combustion, harmful nitrogen oxides are produced .

Similar procedures

The articles describe further processes for obtaining alternative fuels

literature

  • Ioannis Garagounis, Vasileios Kyriakou, Aglaia Skodra, Eirini Vasileiou, Michael Stoukides: Electrochemical synthesis of ammonia in solid electrolyte cells . In: Fuel Cells . tape 2 , 2014, p. 1 , doi : 10.3389 / fenrg.2014.00001 .

Web links

Individual evidence

  1. ↑ a b Peter H. Pfromm: Towards sustainable agriculture: Fossil-free ammonia. In: Journal of Renewable and Sustainable Energy. 9, 2017, p. 034702, doi : 10.1063 / 1.4985090 .
  2. ↑ Carreon Moises A: Membranes For gas separation. World Scientific, 2017, ISBN 978-9-813-20772-1 , p. 330 ( limited preview in Google Book Search).
  3. ↑ Interkat: AMMONIA SLIP CATALYST (ASC)
  4. ↑ Hideaki Kobayashi, Akihiro Hayakawa, KD Kunkuma A. Somarathne, Ekenechukwu C. Okafor: Science and technology of ammonia combustion . In: Proceedings of the Combustion Institute . tape 37 , no. 1 , 2019, p. 109-133 , doi : 10.1016 / j.proci.2018.09.029 .