Currently

most power plants apply the selective catalytic reduction(SCR)technology and low temperature electrostatic precipitator to realize ultra-low emission.However

it will result in a much lower flue gas temperature behind the low temperature economizer and sulfates deposition on the induced draft fan blade

which seriously affects the working output of induced draft fan and boiler load.To solve this problem

ash deposits with thickness of 10 mm were collected from the induced draft fan blade in a coalfired power plant with ultra-low emission.The physical and chemical properties of the ash deposits were analyzed by several techniques

such as the element analysis

the mineral matter composition analysis and microstructure analysis.The results show that

the ash samples consisted of calcium sulfate

calcium sulfate dehydrate

aluminium ammonium sulfate(twelve water ammonium aluminum sulfate)

ammonium sulfate and silicon dioxide

the mass fraction of nitrogen

hydrogen and sulfur in ashes was about 22%

after burning the loss mass of unprocessed ash samples was about 60%.The high ammonia concentration escaping from the SCR reactor and the low flue gas temperature behind the low temperature economizer were the main reason for deposition of sulfates on the induced draft fan.So it was suggested that the design of flue gas temperature at the low temperature economizer outlet need further study considering different kinds of coal

ammonia escape

flue gas humidity and ash content.