To solve high nitrogen oxide(NOx)emission problem occurred in Foster Wheeler down-fired boilers

the combustion characteristics and NOxformation properties in the furnace were analyzed.The low NOxcombustion control mechanism applying the "injection-reflux and multipoint-multistage"mechanism was developed.On the basis of this mechanism

the low NOxcombustion retrofitting was carried out on a660 MW unit boiler applying the Foster Wheeler technique.The experimental results after retrofitting indicate that the NOxemissions can not be reduced significantly by simply adding OFA system in down-fired boilers.The secondary air should be shifted from the rear and front wall to the right place of arches to realize the "injection-reflux and multipoint-multistage" mechanism in the whole furnace.Thus the ideal NOxemissions level(≤800mg/m3)can be reached.