Cost-Efficient Nitrogen Oxides Control by a Hybrid Selective Noncatalytic Reduction and Selective Catalytic Reduction System on a Utility Boiler

Abstract

Abstract The hybrid process of selective noncatalytic reduction (SNCR) followed by selective catalytic reduction (SCR) is an up-to-date nitrogen oxides control technique and can achieve a high efficiency (60%–95%) with moderate cost. The SNCR/SCR hybridization was investigated through experimentation on a 100 MW, coal-fired utility boiler in China. The baseline nitrogen oxides emission of the hybrid urea-based SNCR/SCR system was 170 ppm at 6% O2 controlled by coal reburning technology. The hybrid SNCR/SCR system including only 89 m3 catalysts could control NO emission under 25 ppm with ammonia slip <4 ppm at 300–430 tons/h of boiler load. Total NO reduction efficiency was generally about 85% and could be beyond 90%, in which SCR's efficiency was 50%–70% individually and SNCRs was about 60%–75%. NO emission decreased from about 65 to 15 ppm when the flow rate of 35% urea solution increased from 0.15 to 0.47 tons/h. At higher boiler load, more urea solution had to be injected and higher layer of the agent ...