Abstract: Abstract:There were serious ash deposition and blockage in the rotative air preheater of large thermal power units, and the heat exchange efficiency of the air preheater was reduced, the ventilation resistance was increased. In extreme case, the unit may be compelled to reduce the output. Based on research of the mechanisms of the ash deposition and the blockage of the air preheater, some preventive measures were proposed, which include to optimize the ammonia escape measurement system, to optimize the operation mode of the ammonia injection system, to reform the soot blowing system, to optimize operation mode of the soot blowing system, to optimize operation mode of steam air heater, to adopt corrosionresistant material for the lowtemperature heating surface and so on. The safe and economical operation of the unit was ensured.

Key words: Keywords:air preheater, ash deposition, blockage, denitration, ammonia escape, soot blowing, lowtemperature corrosion