To explore the combustion flow rules in boiler

numerical simulation was performed to analyze the combustion in the boiler and NO_x emissions under conditions with different excess air coefficients

different ratios of separated over-fire air(SOFA)

different air distribution modes and different swing angles. The results show that

at the furnace height of 10～30 m

the synergy angle quickly decreases from 82° to 70°

and then fluctuates violently. At the furnace height above 30 m

the synergy angle shows a parabolic shape. The synergy angle decreases as the excess air coefficient and the ratio of SOFA increase

and it reaches the smallest under the equal air distribution mode. The combination of air staged combustion and rich-lean separation burner can effectively inhibit NO_x formation in the main combustion zone. The larger the excess air coefficient is

the higher the NO_x emission is. The NO_x mass concentration firstly decreases and then increases as the ratio of SOFA increases

and the optimal ratio of SOFA is 15%～25%. The outlet NO_x mass concentration reaches the smallest in the equal air distribution mode

the outlet oxygen volume fraction is the smallest in the girdled air distribution mode

and the reduction of NO_x formation in the main combustion zone can be promoted in the inverted-tower air distribution mode. The downward swing angle of the burner and the upward swing angle of SOFA can also reduce the NO_x emission.