Abstract: In order to explore the influence of mixing mode and air distribution mode on burnout rate and NO_xemission of blended coal,a660 MW tangential fired boiler was taken as the research object,numerical simulations were carried out to study the synergistic optimization of un-burned carbon and NO_xformation in the combustion process of blended coal.The results show that under the condition of deep air staging,the un-burned carbon is mainly affected by many factors such as coal particle residence time,coal blending methodand air distribution method and other factors.Synergistic optimization of un-burned carbon and NO_xemissions can be achieved by a combination of reasonable blending method and air distribution method.Compared with the blending method outside the furnace,the in-furnace blending method is more flexible,and the low-volatile coal combustion can be optimized and adjusted to lower the un-burned carbon level of blended coal.Under the in-furnace blending method,the low volatile coal is placed near the upper burner under uniform air distribution or the low volatile coal is placed in the lower burner near the lower burner under"Zhengbaota"air distribution,which are both conducive to the burnout of low volatile coal,while setting high-volatile coal near the upper burner is more conducive to the reduction of NO_xemission.Considering the characteristics of the unburned carbon and NO_xemission of blended coal,the burnout level of the low-volatile coal is increased and the un-burned carbon level of blended coal is decreased by setting high-volatile coal near the upper burner and adopting the"Zhengbaota"air distribution which can provide relatively sufficient oxygen for the combustion of low volatile coal in the lower part.Meanwhile,the volatile from the high-volatile coal near the upper burner contains a large amount of intermediate HCN,which can restore the generated NO_xand is benefit to reduce NO_xformation of blended coal in the furnace.