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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:
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:
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