The problem of high air leakage rate existing on rotary air preheater of boielr for 300 MW unit in Xutang Power Generation Co Ltd has been analysed.It is believed that the main causes leading to high air leakage are as follows:the radial expansion of rotor in operation is larger than the cold end expansion;the axial expansion of rotor centre makes the rotor to produce mushroom-shaped deformation;the sealed gap between segment plate and the end-face of rotor being increased.The rotary air preheater has been retrofitted to adopt contacting type flexible seal.After retrofitting

the air leakage rate has reduced from 12% to 5%

having remarkable effectiveness

reaching the expected purpose of retrofit.