The issues of poor combustion stability

high carbon content of fly ash and oxygen content bias in furnace width direction occurred in a Foster Wheeler(FW)down-fired boiler.Thus

numerical simulation was conducted to analyze the combustion characteristics of this boiler.The results showed that

with an increase in F secondary air declination angle

the uplifting of the secondary air to primary air flame was reduced

the undershoot of the primary air flame increased significantly

the recirculation zone of the flue gas at the burner outlet got larger

the return of the flue gas was intensified

which had an obvious effect on combustion stability of the primary air but not on the efficiency enhancement.Due to the flow field characteristics of this down-fired boiler

with the increasing F secondary air declination angle

the mixture of the primary air and secondary air delayed and the intensity weakened

and the oxygen content difference between the intermediate and side location in furnace width direction increased.The non-equalization distribution of the F secondary air along the width direction of the furnace can not alleviate the oxygen bias.The declination of the F secondary air had no obvious effect on position of the flame center.After the four side burners was removed

undershoot of the primary air flame significantly increased

and the flame center position dropped dramatically.