Experimental study on NOx emission characteristics of Zhundong coal in cyclone furnace

Abstract

Slag tapping cyclone furnace has drawn increasing attention due to its promising advantage in burning Zhundong coal safely, but is accompanied by high NOx emission. To develop low NOx combustion technology for cyclone furnace, the NOx formation characteristics of Zhundong coal in cyclone furnace were experimentally investigated in this study with a 100 kW cyclone combustion test bench. Results show that the key point of NOx reduction in cyclone furnace is to create a strong reducing atmosphere, which can be available in the central zone and lower part of cyclone barrel when the cyclone stoichiometric ratio (SR) is not greater than 0.8. When the cyclone SR drops from 1.1 to 0.8 and 0.7, NOx formations at the outlet of burnout furnace decrease by 41.8% and 54.9%, respectively. In addition, lowering primary air rate can remarkably reduce the initial formation of NOx because of an additional strong reducing atmosphere region created in the primary-air-controlled zone, where the volatile NOx can be remarkably inhibited. In cyclone barrel, the NOx formation is higher in the near-wall zone, which hinders the further NOx reduction. It is mainly attributed to the elevated O2 concentration in this region. To reduce NOx formation, the centralized air supply should be avoided to narrow the area with high concentration O2. The staging secondary air arranged in separating way is recommended.