Study on NO emissions during the coupling process of preheating-combustion of pulverized coal with multi-air staging

Abstract

Controlling the NOx formation during the combustion process is the most direct and efficient way to minimize NOx emissions, so low NOx combustion technology is essential. In this work, in order to develop multi-air staging pulverized coal (PC) preheating-combustion technology and further optimize the preheating-combustion burner, a 35 kW PC preheating-combustion test system was built, and three types of burners with different outer secondary air (OSA) injection structures were designed. Using Huangling bituminous coal (HL coal) and Wuhai bituminous coal (WH coal), the coupling process of PC preheating-combustion with multi-air staging on NOx emissions was studied systematically. The results showed that the depth furnace air staging could further reduce NOx emissions. When close-coupled over-fire air (CCOFA) and separated over-fire air (SOFA) were applied simultaneously, a significant NOx reduction of 70.2% could be reached 217 mg m−3. Compared with the NOx emissions, the unburned carbon in fly ash presented opposite tendency. Compared to burner II (high-speed swirl jet) and III (low-speed axial jet), burner I (high-speed axial jet) showed the lowest NOx emissions under the multi-air staging preheating-combustion conditions. Furthermore, the depth furnace air staging had greater denitrification potential for high-quality bituminous coal.