Ammonia Systems for Power Generation
Anhydrous ammonia (NH3​) is used in power plants for two main purposes: pollution control (the current dominant use) and increasingly as a zero-carbon fuel (an emerging application).
Anhydrous ammonia (NH3​) is used in power plants for two main purposes: pollution control (the current dominant use) and increasingly as a zero-carbon fuel (an emerging application).
The vast majority of anhydrous ammonia in power plants is used to reduce harmful nitrogen oxide (NOx​) emissions, which contribute to smog and acid rain. This is achieved through a technology called Selective Catalytic Reduction (SCR).
Selective Catalytic Reduction (SCR)
In fossil-fuel power plants (coal, gas, oil), combustion creates NOx​. The SCR system injects anhydrous ammonia into the hot exhaust gas (flue gas) before it passes through a specialized catalyst.
The Process:
Anhydrous ammonia is stored, often as a compressed liquid, and then vaporized into a gas.
The ammonia gas is injected into the stream of hot flue gas.
The mixture passes over a catalyst (typically made of vanadium, titanium, or tungsten).
The catalyst causes the ammonia to selectively reduce the NOx​ molecules.
The Reaction: The NOx​ is converted into harmless, naturally occurring substances:
4NO+4NH3​+O2​ Catalyst→ ​4N2​+6H2​O
(Nitric Oxide + Ammonia + Oxygen → Nitrogen + Water)
6NO2​+8NH3​ Catalyst → ​7N2​+12H2​O
(Nitrogen Dioxide + Ammonia → Nitrogen + Water)
Result: SCR systems using ammonia are highly effective, often removing over 90% of the NOx​ emissions.
Alternative Reductants
While anhydrous ammonia is the most effective and often preferred reagent for large utility boilers, some plants use:
Aqueous Ammonia (NH4​OH): Ammonia dissolved in water; safer to handle but less concentrated.
Urea (CO(NH2​)2​): A less hazardous solid that must be thermally converted to ammonia before injection.
As the world transitions to lower-carbon energy, anhydrous ammonia is gaining significant interest as a potential zero-carbon fuel or a hydrogen carrier in power generation.
The Advantage: Ammonia (NH3​) contains no carbon, meaning its combustion does not produce CO2​. It is also much easier to store and transport as a liquid than hydrogen (H2​).
The Application:Â Power plant operators are exploring two primary methods for utilizing ammonia as a fuel:
Co-Firing:Â Blending ammonia with traditional fuels (like coal or natural gas) in existing boilers or turbines. This allows for a gradual reduction in carbon emissions.
Dedicated Ammonia Turbines: Developing gas turbines capable of burning 100% ammonia. The main challenge here is managing the nitrogen oxides (NOx​) that are produced when the fuel's nitrogen atoms (from the NH3​) react with oxygen during combustion.
The Future Vision:Â Green ammonia (produced using renewable electricity) is seen as a way to store and transport clean energy globally, which could then be burned in power plants to generate carbon-free electricity.