Experimental Investigation on Combustion and NO(x) Formation Characteristics of Low-Ash-Melting-Point Coal in Cyclone Furnace

[Image: see text] 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 O(2) 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 O(2) 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.