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The Selective Non-Catalytic Reduction is a post-combustion process involving the injection of a nitrogen based reagent (Urea or Ammonia) into the furnace at elevated temperature in order to reduce the concentration of Nitrogen Oxides.
Under certain conditions of temperature (850 °C - 1100 °C) and residence time, reduction efficiencies up to 50% can be achieved; higher performances are limited by the presence of un-reacted Ammonia (NH3 slip).
SNCR is considered a proven technology and has been extensively utilised on Utility and Industrial Boilers, Waste Incinerators, Process Heaters and other combustion sources.
Although the mechanism of SNCR reactions is rather complex and involves, dozens of reversible reactions, the overall reduction can be summarised as follows:
Typically the plant is composed of a reagent storage section, a reagent circulation and metering system and the injection zones.
The design of the system depends on several parameters like temperature and velocity fields, stoichiometry of the process (NOx baseline and reagent injection ratios), presence of CO, excess O2 levels, geometrical configuration of boiler.
SNCR technology is a cost effective way to obtain relatively low reduction efficiencies on stable load combustion sources.
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