Influences of Ignition Mode and Ignition Time on NO Reduction during Pulverized Coal Reburning

Experimental investigation on pulverized bituminous coal reburning was performed with a one-dimensional flow reactor, in which the influences of stoichiometric ratio of oxygen to coal (SR) and residence time (RT) in reburning zone on NO-reduction efficiency (RE), and the dependency relationships between those influences were investigated by gas analysis and solid sampling. The RE varies non-monotonically with increasing SR in reburning zone, and the ignition mode and ignition time of coal crucially influence the RE. Before ignition, the RE increases with increasing SR; meanwhile, the optimal RT is related to the consumption rate of hydrocarbon species. At higher SR the homogeneous ignition happens, the RE decreases greatly with increasing SR due to the sharp consumption of hydrocarbon species by volatile flame, and the optimal RT coincides with the ignition time on the whole. When the SR further increases to cause the joint heterohomogeneous ignition, the RE firstly increases due to the fleet rise of char temperature, then decreases again because of the diffusion-controlled combustion of coal char, now the optimal RT should be determined considering together with the reburning coal burnout. Based on these results mentioned above, an ideal scheme of pulverized coal reburning is put forward.