Field test of SO₃ removal in ultra-low emission coal-fired power plants

Under the extensive implementation of ultra-low emission (ULE) facilities in coal-fired power plants of China, sulfur trioxide (SO₃) has received increasing attention due to its impact on human health and operation safety of power plants. However, systematic research and evaluation for controlling SO₃ emission in various ULE facilities are still lacking. Here, a systematic study was conducted based on 378 in situ performance evaluation tests carried out in 148 coal-fired power plants. The results illustrate that the SO₂/SO₃ conversion rate of the selective catalytic reduction devices can be controlled within 1% before and after ULE retrofit. Also, the synergistic removal efficiency of SO₃ in the low-low-temperature electrostatic precipitator and the wet electrostatic precipitator can be higher than 70%. The removal efficiency of SO₃ in the wet limestone-gypsum flue gas desulfurization scrubber is 33-64% before ULE and 31-81% after, and the average efficiency of the double scrubbers is 8.7% higher than that of the single scrubber. Due to the different SO₃ removing abilities of various technologies, the overall efficiency of SO₃ removal is in the range between 27 and 95% adopting different ULE technical routes. Average concentration of SO₃ emission can be decreased by 51.8% after ULE application.