Influence mechanism of oxygen volume fraction on NO formation characteristics in ammonia-coal co-combustion
Ammonia is an ideal carbon-free fuel,and co-firing ammonia with coal in coal-fired power generation is an effective measure to achieve carbon reduction.However,the co-combustion of ammonia and coal has the risk of high NOx emission,in which the oxygen volume frac-tion has a significant effect on the formation of NO during co-combustion.The impact of oxygen volume fraction on NO formation characteristics during ammonia-coal co-combustion at different tem-peratures(1 000℃-1 500℃)and ammonia co-firing ratio(0％-20％)was investigated using a high-temperature tubular furnace.The results show that when the excess air coefficient(α)increases from 1.1 to 1.2,the increase in oxygen volume fraction promotes the conversion of fuel-N to NO for pure coal combustion condition;however,at temperatures of 1 100℃ and 1 300℃,the increase in oxygen volume fraction inhibits the conversion of fuel-N to NO during ammonia-coal co-combustion;at 1 500℃,the conversion rate of fuel-N to NO increases with the increase of oxygen volume fraction,the ammonia co-firing ratio and temperature are important factors influencing the variation of fuel-N conversion rate with increasing oxygen volume fraction.The increase in oxygen volume fraction facilitates the formation of oxidative free radicals,promoting the oxidation processes NH2→HNO→NO,NH2→H2NO→HNO→NO,as well as the oxidation of NCO byfree radicals like O and O2,thereby enhancing the generation of NO during the co-firing process.
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