Abstract: The experimental study is conducted on the problems of instable combustion and high combustibles in fly ash which exist in two 600-MW down-shot firing boilers of a power plant equipped with swirl burners. Based on the analysis of the experiment phenomena, the ignition and combustion stabilization mechanisms are discovered, The experimental and theoretical analysis show that: first, it is not the inner gas recirculation of the high temperature flue gas in the swirl burners but the radiation heat absorption plays the important role in the ignition process of the primary air jet, which happens far from the burner nozzle; second, the combustion stability is enhanced and the economics of the combustion is improved with the lower swirl intensity setting and deeper penetration into the lower furnace.

Key words: down-shot firing boiler, swirl burner, ignition, flame stabilization, combustibles in fly ash, primary air