Severe corrosion and high air leakage occurred on the tubular air preheater

condensation and the subsequent adhering of sulphocompound caused by SO3 appearing in flue gas and the low wall temperature of heating surface which is below the flue gas dew point was considered as the major reason.To solve the problems

several measurements were proposed:blocking the leaked tube;enhancing both frequency and quality of soot blowing;adopting proper excess air coefficient;strictly controlling hot air temperature in the earlier stage of boiler start;maintaining the air preheater after the unit shutdown;changing the entire tube box when the number of invalid tubes occupied more than 10% of the total.After these improvements

the average air leakage rate of the retrofitted boiler decreased to about 3%.