赤泥催化剂的制备及其对模拟烟气中微量氨的脱除性能

Preparation of red mud-based catalyst and performance for trace ammonia in simulative tail gas

以赤泥固废为原料,采用酸解-碱沉淀法制备了赤泥粉体催化剂,并提出一种将催化剂直接喷入SNCR尾气中的除氨工艺,考察了催化剂加入点温度、空速、NH_3浓度及水蒸气对氨去除能力的影响。研究发现,该催化过程具有很高的活性和N_2的选择性,450℃以上NH_3的转化率可达100%,同时在400～500℃间,N2的选择性高于80%,达到了很好的除氨效果;在500℃,空速为3×10~6～6×10~6h^(-1)之间时,出口NH_3浓度均为0;此工艺对于逃逸NH_3浓度的适用性较强,入口[NH_3]=50×10^(-6)～1000×10^(-6)mol/L范围内均可完全脱除,且具有一定的抗水能力。通过一系列表征发现,该种方法制备的赤泥催化剂不仅消除了原始固废的强碱性,还提高了其表面酸性,具有较高的比表面积、孔容和丰富的表面微观结构,使NH_3的吸附及活化反应能力大大增加;该催化剂过程遵循iSCR机理,在400～500℃温度区间主要发生NH_3-SCO反应,低于400℃主要发生NH_3-SCR反应,粉体催化剂通过NH_3-SCR和NH_3-SCO协同反应达到了去除尾气中微量氨的目的。

A Fe-based powder catalyst was prepared from red mud (RM) solid waste with acid base neutralization method, which was used to eliminate the trace ammonia thought the proposed process of directly spraying the catalyst into SNCR tail gas. The effects of temperature, space velocity, NH3 concentration and water vapor on ammonia removal capacity of the catalyst were investigated in details, and excellent removal efficiency could be achieved with 100% NH3 conversion above 450℃ as well as > 80% selectivity of N 2 between 400-500℃. Especially, the trace ammonia in the tail gas can completely be cleared with 0 left between the space velocity of 3× 10^6-6 × 10^6 h^-1 at 500℃. Meanwhile, the catalytic process is also effective for the removal of NH3 with wide concentration of (40 × 10^-6 ~800 × 10^-6 mol / L) even in the presence of water. The multiple characterizations further revealed that the strong alkalinity of the original solid waste was removed together with the increase of surface acidity as well as large specific surface area and rich surface microstructure for the obtained red mud catalyst, which accounts for its significant increase of adsorption and activation of NH3. Moreover, it was found the removal process of NH3 follows the internal selective catalytic reduction (iSCR) mechanism, and the NH3 was eliminated through both the NH3-SCR and NH3-SCO reactions, which mainly function below 400℃ and between 400-500℃, respectively.