燃煤电厂烟气中SO3协同控制情况及排放现状

燃煤电厂锅炉燃烧中SO2/SO3的转化率为0.5%~5%;超低排放条件下,SCR脱硝中SO2/SO3的转化率控制在1%以内。运行中为控制SO3在脱硝催化剂下层和空预器中的消耗,应尽量减少H2SO4和NH4HSO4的冷凝吸附,保证催化剂的活性及空预器的安全运行。理论上低低温电除尘器(LL-ESP)对SO3脱除效果显著,但不同工程实测表明,LL-ESP对SO3的脱除效率差别较大,介于1.8%~96.6%之间。此外,研究认为,电袋复合除尘器对SO3脱除效率为74.3%~85.9%。超低排放工况下,除空塔脱硫和海水脱硫技术外,大部分湿法脱硫技术对SO3的脱除效率高于50%;SO3在湿式电除尘器中的脱除效率也大于50%,但整体上与国外成熟案例相比稍有差距。总体而言,超低排放条件下,燃煤硫分低于1.5%时,燃煤电厂全流程环保净化设备对SO3的综合脱除效率高于90%,大部分机组的SO3排放浓度低于5 mg/m^3。

SO3 Cooperative Control and Emission Situation in the Flue Gas of Coal-Fired Power Plant

The conversion rate of SO₂/SO₃ is 0.5%~5% in boiler combustion, but it can be controlled within 1% in SCR DeNO_x in coal-fired power plant. In operation, to control the consumption of SO₃ in the sub-layer of SCR catalyst and air pre-heater in operation, the condensation adsorption quantity of H₂SO₄ and NH₄HSO₄ should be reduced as much as possible, which is aimed at protecting the catalyst activity and ensuring the safety of air pre-heater operation. Theoretically, the low-low temperature electrostatic precipitator has the excellent removal efficiency for SO₃. However, the efficiency may changes from 1.8% to 96.6% in different projects. Study shows that the electrostatic-bag filter has removal efficiency about 74.3%~85.9% for SO₃. Most technologies of wet flue gas desulfurization have removal efficiency of above 50% for SO₃ except the empty absorption tower desulfurization and seawater desulfurization under ultra-low emission condition. Besides, the removal efficiency of wet electrostatic precipitator for SO₃ can be above 50% as well, although there is still a slight gap compared with the mature cases abroad. Overall, the comprehensive removal efficiency for SO₃ of the whole process environmental protection purification equipment of ultra-low emission coal-fired power plants is over 90% and the SO₃ emission concentration of most units are less than 5 mg/m³, when the sulfur content of coal is under 1.5%.