Abstract: In the boiler No.3 of the Huadian International Bainian Electric Power Development Corporation Limited, due to the blockage of the tubular air preheater and the corrosion and scaling of the heat exchanging surface, the temperature of the hot air was lower, the air leakage was serious, and the temperature of the flue gas was higher. The boiler efficiency in summer was less than the designed value, and the gross coal consumption rate was exceeded the standard seriously. After the air preheater was replaced by rotary airpreheater, the heatexchange efficiency was increased in large amplitude. The primary air temperature was increased by 50℃ above the designed value, the temperature of the mixture of air and coal powder was increased by 30℃, the consumption speed was increased, the air flow into the air preheater was increased, the temperature of the flue gas was decreased, the carbon content in combustible matter in flyash was reduced, and the boiler efficiency was increased.

Key words: primary air temperature, flue gas temperature, boiler efficiency, energy-saving and consumption-reducing