Experimental investigation on gas-particle flow and combustion characteristics from a pre-combustion chamber burner coupled with in-furnace radial air staging:optimization of secondary air ratio

Abstract

The pre-combustion chamber burner coupled with radial air staging is a combustion technology that reconciles flame stability with NO_x reduction. For this technology, this paper combines cold-state gas-particle flow experiments with pilot-scale hot-state experiments to comprehensively study the effect of key operating parameters (secondary air ratio, R_SA) on the flow field, combustion behavior and NO_x emission. When R_SA ranges from 0.1 to 0.83, there are central and annular recirculation areas (CRA & ARA) in the pre-combustion chamber (PCC). When R_SA is 0.10, weaker entrainment of primary air by the secondary jets shifts the obvious CRA onset downstream (on the plane of x/d = 1.8), compared with the cases where R_SA ranges from 0.22 to 0.83 (on the plane of x/d = 1.0). R_SA increases from 0.10 to 0.83, which is conducive to the rotation and diffusion of the airflow. When R_SA ranges from 0.11 to 0.67, stable ignition is maintained, with temperatures in the furnace exceeding 1473 K. As R_SA increases from 0.11 to 0.67, the PCC center temperature increases; the CO concentration at furnace center shows a decreasing trend, while the NO_x concentration shows an opposite trend; the pulverized coal burnout climbs from 98.4% to 99.8%, while the NO_x emission concentration rises from 59 mg/m³ to 364 mg/m³. Taking all factors into account, the comprehensive performance is superior when the R_SA is 0.25, with a pulverized coal burnout rate of 99.4% and a NO_x concentration of 209 mg/m³ (O₂ = 9%). These findings provide experimental foundations and engineering suggestions for pulverized coal boilers in terms of stable combustion and pollutant control.