Effect of HCl and CO on nitrogen oxide formation mechanisms within the temperature window of SNCR

Selective non-catalytic reduction (SNCR) is an effective way to limit NO emissions in power plants. However, the concentration of HCl in the flue gas may be relatively high for some chloride-containing solid fuels combustion. HCl may play an important role in adjusting NO formation within the temperature window of SNCR. In addition, the various combustion atmospheres (from oxidizing to reducing) can influence pollutant formation. To reveal the effect mechanism of HCl and CO on NO emission, the reaction system is simplified as a CO/NH3/O-2/H2O/HCl system with N-2 as the balance gas. The experiments are investigated in a tube flow reactor for CO/NH3 combustion under the temperature window of SNCR (from 1173 to 1423 K). Different inlet concentrations of HCl, CO, NH3, O-2, and H2O with N-2 as the balance gas are used to simulate the process of fuel combustion. The results obtained from the experiments show that HCl addition can decrease the temperature window. HCl can inhibit NH3 oxidation to NO at 1173 K and exhibits promotion at higher temperatures (> 1173 K). The concentration of NO tends to increase with a slight fluctuation when the concentration of CO increases from 1% to 6% under an oxidizing atmosphere. However, CO inhibits NO emission under lean oxidation conditions. The modeling predictions are in good agreement with the experimental results. The calculated results demonstrate that HCl and CO addition can affect NO formation by the recombination of H, O and OH radicals. The competitive relationships among various elementary reactions determine the final results.