Additive Injection for NOx Control

Injecting aqueous solutions of nitrogen-based additives into the furnace for reducing NOx emissions from coal-fired utility boilers has been studied at Ontario Hydro's 640 MJ/h Combustion Research Facility under conditions simulating full scale operation. Three additives were tested: urea, ammonia and ammonium carbonate. NOx reduction was found to be a function of injection temperature and mode of injection, additive stoichiometry, additive concentration and initial NOx concentration. Under optimized operating conditions while burning a 1.7% S eastern US bituminous coal and injecting urea cocurrently with the flue gas at a temperature of 1100°C, up to 90% NOx reduction can be achieved at an additive/NOx stoichiometry of 1.7. Under similar operating conditions, 84% removal was achieved with ammonia and 80% with ammonium carbonate. Ash resistivities and the performance of the electrostatic precipitator are not affected by in-furnace injection of these sorbents.