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Ammonia and Dual FGC Systems

Unlike sulfur trioxide flue gas conditioning which only reduces ash resistivity, ammonia conditioning is used for a variety of reasons:

  • Improve fly ash absorption of sulfur trioxide for low alkali ash
  • Agglomerate fly ash and reduce rapper re-entrainment
  • Increase space charge effect to optimize collection efficiency
  • Improve high carbon fly ash collection
  • Lower acid dew point when high sulfur coal is burned, minimizing precipitator corrosion
  • Reduce SO3 slip and resulting SO3 plume

Dual conditioning involves the injection of both sulfur trioxide and ammonia to achieve many of the benefits of both. Specifically better control of resistivety and ash cohesivity. Dual conditioning also has been shown to improve collection of high silica/alumina ash.

Ammonia is vaporized, metered (using a boiler load signal) and mixed with process air. The ammonia/air mixture is injected into the flue gas ahead of the precipitator. Typical injection rates are usually about 4 to 8 ppm in the flue gas which is about 20 to 40lb./hr. of ammonia for a 600 MW unit. Anhydrous ammonia, aqueous ammonia, or urea can be used. Capital and operating costs are usually the lowest for anhydrous ammonia.

Chemithon Ammonia Systems for NOx Reduction

Chemithon supplies anhydrous, aqueous, or urea based systems for Selective Catalytic Reduction (SCR) and for Selective Non-Catalytic Reduction (SNCR) for NOx reduction.

In the selective catalytic reduction process (SCR) dilute ammonia gas is injected into the hot side of the flue gas duct upstream of the catalyst bed where it oxidizes the NOx in the flue gas stream to form nitrogen (N2) and water vapor.

In the selective non-catalytic reduction process (SNCR), dilute ammonia gas is injected into the flue gas exiting the boiler where it thermally oxidizes the NOx in the flue gas stream to form nitrogen (N2) and water vapor.

Flue Gas Conditioning Equipment Retrofits

Modern FGC systems are far more reliable, more efficient and offer lower operating costs than older systems. Retrofitting the equipment to modern designs can often dramatically improve precipitator performance, reduce the potential for plant derates, and often recover the cost in weeks or months of operation. The most common retrofits are:

  • Replacement of outdated control systems with new PLC designs
  • Retrofitting in-tank sulfur pumping systems to existing sulfur tank to eliminate inaccurate and messy external sulfur pumping systems
  • Conversion of ‘granular sulfur feed’ to molten sulfur feed
  • Injection probes that properly distribute sulfur trioxide
  • Replacement sulfur burners or converters

For More Information:

Hal Busick
Manager of Sales



Flue Gas Conditioning

Ammonia Systems (anhydrous and aqueous)

SafeDeNOx Urea to Ammonia


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