Abstract: The blockage of SCR system caused by large particles ash, especially by the popcorn ash, is one of main reasons making the SCR system to be failure and influences on safe and stable operation of the boiler seriously. The countermeasures and advanced technologies of developed countries and regions were introduced, and several domestic and oversea successful engineering projects were enumerated, which can be used as reference for preventing the blockage fault by large particles ash and for fast and healthy development of domestic denitration career.

Key words: coal-fired power plant, selective catalytic reduction (SCR), deNOx, large particles ash, blockage