Taking the secondary-air-box of a 300 MW unit boiler with front and rear wall opposed firing as the example

numerical simulation method was employed to investigate the effects of closing-to-wall air on air distribution and flow characteristics inside the secondary-air-box. The results show that

the flow rates of the side burners were lower than that of the middle ones before the transformation. Once the closing-to-wall air jet was added

the flow rates of the side burners increased and became higher than that of the middle ones

and the uniformity of the air distribution turned better. The flue gas velocity at the burner exit section changed in the same rule. The closing-to-wall air rate was stable at about 6.57% in each case. Under rated load condition

the deviation of the burner flow rate was within 3% when adding 4% secondary air rate

which could still ensure the furnace stability.