A combination effect of reburn, post-flame air and acoustic excitation on NOx reduction

The effect of applying acoustic excitation on generated NOx and CO within a combustion tube burning a premixed propane flame was investigated during reburn with and without post air injection. The laboratory-scale, acoustically-enhanced combustion apparatus consisted of a vertically oriented combustion tube with a horizontally oriented acoustic excitation tube. A propane-air premixed burner was located at the bottom of the combustion tube. In order to study the formation of fuel NOx, the propane fuel line was injected with a small amount of ammonia prior to the mixing with combustion air. Methane and secondary air were injected into the combustion tube for reburn and post air, respectively. Gas sampling was made at 20 cm above the center of the acoustic exciter tube by using a vacuum sampling probe; concentrations of NOx, CO, CO2, O-2 and total hydrocarbons were analyzed by using an on-line gas analyzer. A series of combustion experiments were conducted to investigate the effects of the following three parameters on NOx concentration: (1) frequency of the acoustic wave, (2) methane reburn with post air injection, and (3) the amount of injected post-flame air. The largest reduction in the NOx concentration was 95%, and was achieved by a combination of acoustic wave excitation with reburn and post air injection. The second largest NOx reduction, 90%, was obtained with acoustic wave excitation and post air injection. The third largest NOx concentration reduction, 65%, was achieved by using methane reburn regardless of acoustic wave excitation. The combination of the acoustic excitation with the post-flame air injection was found to produce the best result in this study. (C) 2013 Elsevier Ltd. All rights reserved.