Reactions of sodium species in the promoted SNCR process

Selective Non-Catalytic Reduction (SNCR) is a well-known commercial NO, control process based on injecting a nitrogen agent into combustion products containing NO at temperatures near 1250 K. A serious limitation of the SNCR processes is that the temperature range over which nitrogen agents are effective is relatively narrow. In this work, we show that adding small amounts of sodium salts significantly improves the performance of the SNCR process. Parts per million levels of sodium compounds enhance NO removal and extend the effective SNCR temperature range in comparison with use of a nitrogen agent alone. When added in the same sodium atom amounts, the efficiencies of different sodium compounds are similar. Kinetic modeling suggests that the performance improvement can be explained as a homogeneous chain reaction ensuing after the sodium compounds are converted into NaOH. The overall result of introducing sodium compounds is conversion of H2O and inactive HO2 radicals into reactive OH radicals, with the effective stoichiometry H2O + HO2 --> 3 OH, which enhances the SNCR performance of nitrogen agents by increasing the production rate of NH, radicals. (C) 1999 by The Combustion Institute.