In operation of boilers

the problem of "scrambing for air" is existing between the axial induced draft(I.D.) fans connected in parallel operation.Regarding to this

starting from the performance curve and the angle of working point for said fans

the problem of "scrambling for air" concerning AN type axial I.D.fans with stationary blade adjustment has been analysed.Results show that the resistance curve of the whole pipeline network has changed due to "scrambling for air"

making the working point of said fans to be dropped into ∞-shaped region

the "scrambling for air" can make pressure in the furnace to be in an unstable state

even making the fans to be damaged due to occurrence of large electric current.Based on the living examples

the phenomenon

cause

and disposal of problem "scrambling for air" of axial I.D.fans have been explained

and some preventive measures being put forward.