Abstract: The flue gas waste heat recovery system is to recover flue gas waste heat, improve the thermal efficiency of heating furnace, and reduce flue gas temperature. Air preheater is one of the important equipment in the waste heat recovery system of heating furnace. When the exhaust gas temperature drops to a certain point, there will be a large amount of condensate at the cold flue gas outlet of the preheater. When the wall temperature of flue gas side of heat exchange plate is lower than the dew point temperature of water, the moisture in flue gas will condense on the wall of heat exchange plate, and the dew will gradually converge into water drops, forming flowing condensate. The lower the wall temperature of flue gas side of heat exchange plate is, the more water drops. This problem can be solved by installing pre-stage preheater, hot air circulation and cold air bypass. Among them, hot air circulation is the most flexible, practical and effective method.

Key words: water dripping of preheater, hot air circulation, pre-stage preheater, cold air bypass