Selective Non-Catalytic Reduction for Nitrogen Dioxides Reduction in Preheater Lime Kilns
Gideon M. Siringi

Abstract
Nitrogen dioxide emissions commonly referred to as NOx from industrial plants is becoming a worldwide issue due to the impact on the environment and as governmental regulations become more stringent, it has become necessary to apply known emission mitigation technologies from one industry to another. One such technology which has been widely successful in coal-fired boilers for power plants is Selective Non-Catalytic Reduction (SNCR).In this paper, findings on the application of SNCR in preheater lime kilns are discussed. The main challenge for preheater lime kilns is finding a suitable location for injection of the reagent for the SNCR reaction. An SNCR trial in two preheater lime kilns sought to find out if SNCR technology can be applicable in the lime industry, how much NOx reduction can be achieved, which of the two reagents, urea and ammonia, would give better NOx reduction efficiency, the ideal location for injection and the best nozzle configuration. A reduction of 50-60% in NOx was achieved making SNCR technology an economically viable alternative for NOx reduction. Both urea and ammonia were found to be effective reagents for SNCR, but urea was more effective and therefore recommended for use. The ideal location was identified as the preheater cone with four nozzle configuration. No side effects like ammonia slip and loss of production was noted. Increase in specific heat consumption was negligible. Presence of carbon monoxide above 5000 ppm was found to reduce SNCR effectiveness by about 10% and therefore running SNCR in oxidized conditions is recommended.

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