Slag tapping cyclone furnace is suitable and promising for the utilization of low-ash-melting-point coals without worrying about the fouling and slagging problems, but its high NO x emission has limited its application. In this study, the temperature profiles, species concentration distributions, and slag tapping behavior of the cyclone barrel were explored on a self-built 100 kW cyclone furnace system. A reasonable slag capture ratio of 0.70 can be achieved for the cyclone barrel even under air-staged conditions. The coincidence of high temperature and high O2 concentration in the annular near-wall area of the cyclone barrel can lead to a large amount of NO x formation, while a NO x reduction area with high CO concentration is formed in the central and lower zones of the cyclone barrel due to strong swirling effect. The NO x emission of cyclone staged combustion is lower than that of laminar drop-tube staged combustion in either air-staged or nonstaged cases, which could be attributed to the swirling effect. The NO x reduction area can be expanded by decreasing the cyclone stoichiometric ratio (SR) or reducing the primary air rate (PAR). Compared with the limit effects on the reduction of NO x emission by overall-SR, NO x formation can be greatly dropped by 56% when the cyclone-SR decreases from 1.1 to 0.7. The swirling intensity in cyclone barrel increases from 1.23 to 12.81 as PAR reduces from 0.4 to 0.2, which results in a reduction of NO x formation at the outlet of the cyclone barrel by half. Besides, the O2 concentration in the annular near-wall region can be remarkably reduced by the decentralized secondary air supply, resulting in a 23% reduction in NO x formation in the cyclone barrel.
© 2022 The Authors. Published by American Chemical Society.