低温燃烧下NH_3的氧化特性

Characteristics of ammonia oxidation in low-temperature combustion

NH3的气相氧化是低温燃烧过程中NOx(NO和NO2)与N2O的重要来源,为了深入认识其反应规律,在管式流动反应器系统中进行了实验研究。重点考察了挥发分中的可燃气(CO、CH4或H2)和NO对NH3氧化及氮氧化物排放的影响规律,并根据化学反应机理对实验结果进行了分析。研究结果表明,低温氧化性气氛下微量的可燃气就能够显著促进NH3的氧化,并使NOx和N2O的生成量大幅度升高。当可燃气体浓度相同时,H2对NH3氧化的影响最大,CO的影响最小,CH4对NH3氧化的影响略大于CO。随着可燃气体浓度的升高,其对NH3氧化与氮氧化物生成的影响先逐渐增加,然后趋于稳定。反应初始气体中存在NO时,也会加速NH3的氧化。

Low-temperature combustion, such as combustion of solid fuels （low-rank coals, biomass etc.） in grate furnaces or fluidized bed combustors, can make NH3 （fuel-nitrogen） conversion, which is an important source of NOx and N2O. To understand deeply on NH3 oxidation and production of nitrogen oxides in low-temperature combustion process, the effect of combustible gases （CO, CH4, or H2） and NO on ammonia oxidation reaction was experimentally investigated in a tubular flow reactor at temperature range 600-1000℃, and the concentrations of NO, NO2, NH3, CO, CH4 and O2 were monitored continually with online Fourier-transformed infrared gas analyzer （Gasmet DX-4000）. The results obtained were analyzed to clarify the chemical reaction mechanism. It was found that trace amounts of CO, CH4, or H2 could promote the oxidation of ammonia and enhance the emissions of NOx and N2O significantly under the condition of low temperature and oxidizing atmosphere. At equal concentration, the effect of H2 on ammonia oxidation was the greatest, following was CH4 and CO. As concentration increase of the combustible gas, the ammonia concentrations in combustion product decreased and approached rapidly zero, while the emissions of NOx and N2O increased firstly and then arrived at a stable value. When there was NO in initial gas mixture, oxidation reaction of ammonia could be enhanced too.