Power Plants

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).

1. Primary Use: NOx Pollution Control

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:

  1. Anhydrous ammonia is stored, often as a compressed liquid, and then vaporized into a gas.

  2. The ammonia gas is injected into the stream of hot flue gas.

  3. The mixture passes over a catalyst (typically made of vanadium, titanium, or tungsten).

  4. 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.

2. Emerging Use: Zero-Carbon Fuel Source

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: Power plant operators are exploring two primary methods for utilizing ammonia as a fuel:

  • Co-Firing: 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: 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.