脱硝催化剂及运行参数对燃煤电厂SO3生成的影响

Influence of SCR catalysts and operating parameters on SO generation in coal-fired power plants

为实现燃煤电厂尾部烟气中SO3的有效控制,实现燃煤电厂安全经济运行与污染物超低排放,选取不同燃煤电厂的商业V/W/Ti系脱硝催化剂研究SO3的生成特性,系统地探讨了不同催化剂及运行参数(温度、空速、O2、SO2和NH3:NO比)对燃煤电厂尾部烟气中SO3生成的影响,以期为燃煤电厂SO3治理提供指导。结果表明:催化剂化学组成显著影响SO3的生成,催化剂中V负载量是决定SO3生成的重要参数;V负载量为1%~3%时,负载量的增加可对SO3的生成起促进作用,而Si对SO3的生成起显著抑制作用。对于催化剂样品A,当空速达到10 000 h-1时,SO3生成将不再随空速的增加而变化。随着反应温度的升高,催化剂表面SO3生成率逐渐增加。温度的升高有利于催化剂中活性组分V5+和V4+之间的转化,从而提高催化剂的氧化活性。即使燃煤电厂负荷降低,当烟气温度低至280℃时,催化剂表面仍然有SO3生成。此外,烟气中不同组分也会影响SO3的生成。随SO2浓度的增加,生成的SO3通过竞争吸附抑制SO2的氧化,导致SO3的生成率降低。而O2、NH3和NO的存在将促进SO2的转化,且浓度越高,其促进作用越大。综合上述结果可以看出,催化剂表面SO3的生成受催化剂组成、温度、空速、O2、SO2和NH3∶NO比值等多种因素影响,在实际工程中应综合考虑各因素的影响以实现对燃煤烟气SO3的有效控制。

In order to achieve the effective control of SO3 in flue gas of coal-fired power plants, the safe and economic operation of coal-fired power plants and the ultra-low emissions of pollutants, commercial V/W/Ti SCR catalysts used in different power plants were selected to study the characteristics of SO3 generation. The effects of different catalysts and the operating parameters(temperature, space velocity, contents of O2 and SO2,ratio of NH3∶NO) on SO3 generation in flue gas were systematically explored, which could provide guidance for SO3 control in coal-fired power plants. The results indicated that the chemical composition of catalyst significantly affected the generation of SO3. The amount of V supported in the catalyst was an important parameter that determined the generation of SO3. Within loading ratios of 1%~3%, the increase of V loading promoted the formation of SO3, while the existence of Si significantly inhibited the formation of SO3. For catalyst A, SO3 generation rate no longer changed with the increase of space velocity when space velocity reached 10 000 h-1. With the increase of reaction temperature, the SO3 generation rate on catalyst surface gradually increased. The increase of temperature was beneficial to the conversion reaction between V5+ and V4+,thus increasing the oxidation activity of the catalyst. Even the loading of coal-fired power plants was reduced,SO3 would be generated on the catalyst surface at the reaction temperature as low as 280 ℃. In addition, the different components in flus gas also affected the generation of SO3. With the increase of SO2 concentration, the generated SO3 inhibited the oxidation of SO2 through competitive adsorption, resulting in the reduction of SO3 generation rate. The presence of O2, NH3 and NO could promote the transformation of SO2, the higher the concentration, the greater the promoting effect. The above results showed that the characteristics of SO3 generation on the catalyst surface were affected by various factors such as catalyst composition, temperature,space velocity, O2, SO2 and NH3∶NO ratio, etc. In order to achieve effective control of SO3 in coal flue gas, the influences of various factors should be comprehensively considered in actual projects.