| 摘要 |
A method for the combined reduction of sulfur dioxide, SO2, and nitrogen oxides, NOx, in the gas stream of a furnace from the combustion of fossil fuels is disclosed. In a narrow gas temperature zone in a furnace, NOx is converted to nitrogen by reaction with a reducing agent such as urea or ammonia with negligible residual ammonia and other reaction pollutants. In about this same temperature zone, SO2 will react with calcium oxide particles, derived from the calcination of lime, Ca(OH)2, or limestone, CaCO3, to form CaSO4 particles. A wide size distribution of aqueous droplets, containing dispersed lime or very fine limestone particles and dissolved urea or ammonia, is injected at the outer edge of the furnace gas zone at which the SO2 and NOx reduction reaction are effective. The key element in this invention is that the aqueous droplet size distribution is optimized for the specific furnace dimension while the concentration of the reactants, urea or ammonia and lime or very fine limestone, is optimized for optimum reaction rates. Special injectors produce the different size droplets that vaporize throughout said gas zone, thereby distributing said lime or limestone particles and urea or ammonia gas molecules exclusively throughout the combustion gas zone being treated. Also disclosed is a system to produce said aqueous mixture and effectively accomplish this injection. This method can be combined with other NOx and SO2 reduction processes to sharply reduce overall NOx and SO2 emissions from the combustion gas effluent.
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