Experimental Investigation on Pulverized Coal Reburning Crucially Related with Its Ignition Mode

• Published in: Energy & fuels Vol. 23; no. 2; pp. 657 - 664
• Main Authors: Qi, Yong-Feng, Zhang, Ming-Chuan, Xiao, Jia-Yuan, Lin, Yu-Yu, Zhang, Jian
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 19.02.2009
• Subjects: 01 COAL, LIGNITE, AND PEAT; AIR POLLUTION ABATEMENT; BITUMINOUS COAL; Combustion; IGNITION; NITRIC OXIDE; PULVERIZED FUELS; STAGED COMBUSTION; STOICHIOMETRY
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/ef800610j

Experimental investigation on reburning by a pulverized bituminous coal was performed in a one-dimensional flow reactor, in which the ignition statuses of the coal were monitored by on-line gas analysis, solid sampling, and direct image acquisition. The experimental results indicate that NO reduction efficiency (RE) varies nonmonotonically with stoichiometric ratio of oxygen to coal (SR) entering the reburning zone: the lower SR does not necessarily result in the higher RE, mainly due to the great influence of ignition modes of the coal. Before ignition, RE increases with increasing SR, since a little oxygen is in favor of homogeneous NO reduction. Then, RE decreases greatly after homogeneous ignition with increase of SR, due to the rapid consumption of NO-reducing species by the volatile flame in the boundary layer of the particle, before going to the flue gas for NO reduction. When the joint heterohomogeneous ignition happens with further increase of SR, the char temperature increases violently, the heterogeneous NO reduction rate rises obviously with increasing temperature, then the whole RE begins to increase again. As a result of even higher SR, the char combustion is controlled by diffusion, and it is difficult for the oxygen necessary for heterogeneous NO reduction reactions to reach the surface, then the RE decreases again. The promotion effects of char ignition on RE are more obvious at lower temperature in the reburning zone, and the SR values at which the above relevant phenomena appear are lower for coarser coal particles.