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 is simply independent injection of both sulfur dioxide and ammonia to achieve the benefits of both.

Ammonia is vaporized and mixed with process air from a blower. A plant boiler load signal controls ammonia vapor flow rate. 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. Feed stocks for these systems can be anhydrous ammonia, aqueous ammonia, or urea. Capital and operating costs are usually the lowest for anhydrous ammonia although permitting costs and risk management programs may offset the financial benefit. Urea based systems are the safest and have lower operating costs than the aqueous systems.

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• Replacement of outdated control systems with new PLC designs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:

Michael W. Rollock, Chem. E.
Regional Manager - Americas
Chemithon Corporation
5430 West Marginal Way SW
Seattle, WA 98106-1598
Phone: (206) 937-9954 ext. 1108
Fax: (206) 932-3786
mrollock@chemithon.com

© 2007 Chemithon Enterprises, Inc