Effects of secondary air velocity on NO emission with coal preheating technology

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This study investigated experimentally the effects of the injection velocity of the secondary air on combustion and NO emissions of Shenmu semi-coke in a 30 kW coal preheating combustion test rig. Results showed that the self-preheating burner could provide with the high temperature preheated fuel (coal gas and coal char) stably and continuously without extra heat input. Most of volatile-N was released following with the release of volatiles during the preheating process, which was conductive to inhibit NO formation. The combustion temperatures were uniform in the down-fire-combustor and flame images were all dark red with no obvious flame fronts. The coal gas was rapidly consumed in the upper part while the coal char was burnt out in the lower part of the down-fire-chamber. The presence of two combustion zones would contribute to leading to more uniform temperatures. Char-N was the main source of NO in the research, and NO was reduced by the coal gas (CO, CHi, NHi and other species) and char simultaneously above 1000 mm. While below 1000 mm, char was dominating for NO reduction. In the paper, the relationship of injection velocity of secondary air and exit NOx emissions was not clearly revealed. It was believed that the effects of secondary air velocity were multifactorial. Mean temperature and root mean square temperature were associated with the exit NOx emissions. When mean temperature and root mean square temperature are low, the exit NOx emissions are low correspondingly.