REDUCING NO_X EMSSION WITH PRP BURNER FOR ANTHRACITE FIRED BOILERS

摘要

High NO_x emission is a common drawback for anthracite fired boilers and is difficult to control with the conventional low NO_x burners. In this paper, a novel burner named as PRP Burner is introduced. The burner is featured with a preheat chamber in which highly enriched primary air off-centrally passes through and an opened recirculation zone is formed inside the chamber. The in-chamber flue gas recirculation zone overlays another recirculation zone in the furnace generated by the secondary air. A series of experiments were conducted on an industrial scale test boiler to assess its performance on flame stabilization and NO_x emission control. It was found that hot flue gas recirculation effectively established in the preheat chamber to rapidly heat up the fuel-air mixture to a high temperature that is close to the ignition temperature of the fuel. The rapid heating of the mixture plays an important role to coal pyrolysis to facilitate volatile matter release in speed and amount, suppressing ignition delay and enhancing combustion stability. The experimental results showed that NO_x concentration at the furnace exit was significantly less than that of the conventional low NO_x burner as long as the hot gas recirculation was properly organized. The associated mechanisms for NO_x reduction for anthracite firing are discussed.