Abstract: When the coal-fired power plant operates at low loads, the low temperature of the flue gas entering the denitrification device will result in the formation of ammonium hydrogen sulfate on the catalyst, decreasing its activity and performance. The formation mechanism of ammonium hydrogen sulfate and its effects on the SCR catalyst are analyzed. Following that, this paper suggests that reducing the concentration of SO₃ in flue gas is the key to slow down or even to avoid the poisoning of SCR catalyst by ammonium hydrogen sulfate. The methods to reduce the concentration of SO₃ in denitrification unit and other units are reviewed and analyzed from the aspects of process and catalyst design. And the regeneration methods for the poisoned catalyst and their advantages and disadvantages are also reviewed and discussed. We proposed several important research directions in the future to prolong the working life of the catalyst:①spraying alkaline absorbents to reduce the SO₃ concentration before the flue gas goes into the denitrification unit to contact with NH₃;②making a rational design of the composition and structure of the catalyst, since the SCR catalyst in the denitrification device also oxidize SO₂ into SO₃. However, despite of various methods to avoid catalyst poisoning, it is difficult to remain high activity for the SCR catalyst running under low temperature. To develop the regeneration method and build the device are also of importance. One promising way is to increase the catalyst temperature to decompose the ammonium hydrogen sulfate and regenerate the catalyst in operation.

Key words: flue gas, selective catalytic reduction (SCR), SO₂ oxidation, sulfur trioxide, ammonia sulfate salts, ammonium hydrogen sulfate

摘要： 电厂燃煤锅炉低负荷运行导致脱硝装置烟气温度偏低，硫酸氢铵中毒影响低温脱硝催化剂的长期稳定运行。本文分析了硫酸氢铵的形成机理及其对选择性催化还原（selective catalytic reduction，SCR）催化剂的影响，提出控制烟气中SO₃浓度是减缓甚至避免SCR催化剂中毒的关键。文章从工艺和催化剂设计角度详细总结和分析了脱硝装置前端和脱硝装置中SO₃的控制方法，并总结了硫酸氢铵中毒催化剂的再生方法及其优缺点。分析表明，通过喷入碱性吸收剂降低脱硝装置前端SO₃浓度的工艺和对催化剂组分及结构进行合理设计以减少脱硝装置中SO₃生成的方法具有很强的实用性，是未来研究发展的重要方向。低温条件下长期运行难免导致催化剂失活，而在线升温是恢复中毒催化剂活性的良好方法，在工程设计中应考虑相应工艺。

关键词: 烟道气, 选择性催化还原, 二氧化硫氧化, 三氧化硫, 硫铵盐, 硫酸氢铵