A secondary air declivitous angle regulating device installed at F layer wind box of a FW(Foster Wheeler) down-fired boiler was designed

to realize freedom regulation of the secondary air declivitous angle

and to adapt to the change of operation conditions

thus to improve the combustion performance and increase the boiler efficiency.The experimental results showed that

the down flow depth of the primary air increased with the declivitous angle.The best flow field was achieved when the declivitous angle was set at 45°.After the improvement

the fly ash carbon content decreased from 10% to 4.4%(by more than 5%);the desuperheater spray quantity fell from up to 100 t/h to 65 t/h;the boiler efficiency increased from 86.95% to 90.11%.