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

ABSTRACT

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.

KEYWORDS:

• NOx reduction
• air staging
• reagent injection
• stoichiometric ratio
• temperature

Additional information

Funding

This work was supported by the National Key R&D Program of China [grant number 2018YFB0604202].