Abstract: In coal-fired power plants, the normal operation state of SCR flue gas denitration system is of great significance to environmental protection. In several SCR denitration equipments of a coal-fired power plant, the ammonia control valves are blocked in the winter, and the equipment has to be shutdown to carry out manual cleaning, which will severely interrupt the normal operation of the SCR system and affect NO_x emissions specified by national standards. Through the analysis on the liquid ammonia quality, ambient temperature, equipment structure and materials, and the ingredients of the blockade, it is found out that the blockage is caused by the mixture of carbon steel rusting on the inner wall of ammonia supply tube and the oily volatile matter in the ammonia Based on the actual situation of the equipment, the problem is entirely solved by virtue of a series of countermeasures such as adjusting the operation mode of the ammonia evaporator, pipeline purging, the structure retrofitting of the ammonia injection valve, and replacing the pipe with the stainless steel material, etc.

Key words: coal-fired power plant, ammonia injection valve structure, ammonia evaporator, blocking, scale sample analysis