Through cold modelling test carried on boiler of a 600 MW unit adopting INCFS-Ⅲ combustion system

the vaiational regularity of the relative tangential circle diameter in the zone of separating over-fired air (SOFA)

(Dxd)SOFA

the flow rate moment of residual rotational momentum at furnace outlet Jout

the velocity deviation E

and the uneven coefficienty of velocity M2 due to effect of horizontal flue duct at furnace outlet along with the variation of reversed tangential angle under condition of SOFA ratio is 0.32

has been obtained.When the reversed tangential angle is in a range of 0°~15°

the rotation direction of main gas flow keeps unchanged;Jout

(Dxd)SOFA

E

and M2 decreases with increasing the revesed tangential angle

and being minimum at θ=15°;under condition of the reversed angle is greater than 15° but less than 20°

the rotation direction of rotational gas flow in upper space of the furnace is unstable;after the reversed tangential angle is equal to or greater than 20°

the rotational gas flow in upper space of the furnace will be stable

but the rotation direction being reversed.