Experimental and kinetic studies of NO reduction by ammonia injection into high-temperature reducing atmosphere

Abstract

Experiments were conducted to investigate the NOx reduction performance by ammonia injection into a high-temperature reducing atmosphere and the integrated effects of temperature and oxygen concentration were discussed in detail. Ammonia oxidation was trivial at lower temperatures and the presence of oxygen facilitated the replenishment of OH radicals, enhancing the NOx reduction efficiency. The replenishment of OH radicals and ammonia oxidation were simultaneously promoted at higher temperatures. Therefore, trace amount of oxygen was preferred for higher temperatures to suppress the NOx formation from ammonia oxidation. A maximum NOx reduction efficiency of over 95 % was achieved at 1573 K and 0.0 vol% O2 with normalized stoichiometric ratio of 1.5 and residence time of 0.71 s. Furthermore, rate-of-production analysis was performed to provide insights into NH3/NO reaction pathways in the absence of oxygen. Results showed that the NOx reduction process was initiated by thermal decomposition of NH3 and CO2 acted the role of O2 when oxygen is absent, which could provide O atoms to react with H for the replenishment of OH radicals. The relatively high activation energy of NH3 decomposition accounted for the shift of the temperature window towards higher temperatures in the absence of oxygen.