It is necessary to study the formation,concentration,emission level and influencing factors of the sulfur trioxide in the control process of flue gas pollutants in thermal power plants because the sulfur trioxide in the flue gas is one of the precursors of smog.Based on the onsite measurements of ultra-low emission facilities of 300～1 000 MW coal-fired units and the whole process test of a 1 000 MW unit,the comparison with the conventional pollutant control process shows that the ultra-low emission facilities have a better control effect on SO3 with SO3 comprehensive removal efficiency reaching 90％.The SO3 removal mechanism and effect of each equipment in flue gas flow process were also analyzed.The results show that:(1) SCR denitrification device has a catalytic oxidation effect on SO2 converted to SO3.(2) The air preheater consumes SO3 indirectly during the process of the flue gas temperature drop.The low-low temperature electrostatic precipitator,the wet desulfurization absorber and the wet electrostatic precipitator all contribute to the SO3 reduction,accounting for 30％,40％,15％ and 5％ of total reduction respectively.(3) The air preheater,electrostatic precipitator operating temperature has great impacts on SO3 removal rate.(4) The high-efficiency desulfurization synergistic dust removing integrated absorption tower has a better effect of SO3 removal.%烟气三氧化硫(SO3)是形成雾霾的前驱体之一,研究火电厂烟气污染物控制流程中sO3的形态、浓度、排放水平以及影响因素很有必要.对容量300～1 000 MW的燃煤机组超低排放设施进行实测,并对1 000 MW机组开展了全流程测试,同时与常规污染物控制流程进行比较,表明超低排放设施对SO3具有更好的控制效果,SO3综合脱除效率可达到90％.对烟气流程各设备脱除SO3机理与减排效果进行分析,结果表明:(1) SCR脱硝装置具有将SO2催化氧化成SO3的作用.(2)空气预热器烟温降低过程间接消耗SO3,低低温电除尘器、湿法脱硫吸收塔与湿式电除尘器对SO3有削减作用,各设备对SO3的削减份额分别占SO3总量的30％、40％、15％、5％.(3)空气预热器、电除尘器运行温度对SO3脱除率有较大影响.(4)高效脱硫协同除尘一体化吸收塔具有更好的脱除SO3效果.
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