Experimental study on influencing factors of NOx reduction by combining air staging and reagent injection

This work indicates the functionality of injection reagent combined with air staging, which achieves a better NOx reduction than bare air staging in coal combustion. The key influencing factors of NOx reduction were investigated by experiments on a bench-scale combustion test system. The results showed that the NOx reduction efficiency could be increased by 22.2% compared to bare air staging. The primary stoichiometric ratio SR1 was the key parameter, and the optimum SR1 for NOx reduction by injection was 0.85. There was no benefit for NOx reduction by injection urea in the very fuel-rich zone, but when SR≥1, the injected urea solution at the higher temperature leads to more NOx formation. A higher temperature greatly improved NOx reduction by injection when SR1 was less than 1. It is because that high temperatures were the necessary condition for a greater generation of OH free-radicals, which promoted NOx reduction with NH3 in the absence of oxygen. Therefore, this technology broken through the limitation of narrow temperature window in the traditional technologies with NO reduction by NH3 reagent. Moreover, deeper NOx reduction can be achieved by this technology combined with the existing low NOx combustion technologies.