Influence Of The Ratio Of Inner Secondaryair And Outer Secondaryair On Combustion Characteristics Of A Centrally Fuel Rich Swirl Burner

The swirl burners have been playing much more important part in the utilityboilers. The centrally fuel rich swirl burner (CFR), as a kind of high-efficiency andlow-NOxburner capable of controlling the NOxformation during combustion, hasbeen applied in many power plants. In this study, hot-state experiment wasconducted through a pilot-scale test facility with a CFR burner of0.5MW. Inaddition, the corresponding numerical study was carried out to investigate thecomplex principle of the test facility when burning.First, experiment study was carried out through a hot-state test facility with theCFR burner under different ratios of inner secondary air and outer secondary air(RSA). In order to study the influence of RSAon the combustion characteristics andNO formation, the temperature field of different locations of the furnace wasmeasured with thermal couple, while the gas components the flue gas analyzer.Meanwhile, the char burnout ratios of varied points of the furnace, as well as therelease ratios of elements C, H, N, were analyzed. The impact of RSAon thepulverized coal ignition performance, the furnace flame center, and NO emissionswas studied.The increase of RSAbrings the mixing between the secondary air and primaryair to an earlier stage, making the local stoichiometric ratio larger at the beginningof combustion, which is beneficial to the burnout of char and the elements release.However, the variance of RSAdidn’t significantly affect the ignition point of theCFR burner. In addition, the flame center didn’t move significantly. Along thecross-sections of the near-burner zone, the cases of smaller have a CO reducingatmosphere zone with higher concentration and wider range, lowering the formationof NO. The overall NO emission concentration drops with decreasing RSA. At theexit of the measuring zone, as RSAdeclines from2.33to0.25, the NO emissionconcentration decreases from519.90mg/m3@6%O32to335.18mg/m@6%O2，lowering about35.5%.Second, numerical study of the furnace non-premixed combustion of thehot-state experimental facility was conducted with the aid of FLUENT. It found outthat under different RSA, the results obtained from numerical study can wellcorrespond to that of the experimental study.The numerical study of combustion process showed that the increase of RSAhastwo aspects of influence on the combustion performance. On the one hand, theincrease of RSAmade the attenuation of the primary air faster, while bringing the ignition of pulverized coal to an earlier stage which is conducive to the initialignition and combustion of the pulverized coal. Meanwhile, the high temperaturezone near the furnace central line, the low O2concentration zone as well as the highCO concentration zone appear earlier. Along the furnace central line, the increase ofRSAmade the lengths of high temperature zone and the low O2concentration zoneshorter, the radius of the high CO concentration zone larger but its length along thefurnace central line became shorter. On the other hand, the increase of RSAis notconducive to the formation of NO. The low NO concentration zone turns smallerwith increasing RSA. At the exit of the furnace, NO emission concentration increasesfrom791.4mg/m3@6%O2to960.8mg/m3@6%O2as RSAincreases from0.43to1.5.