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

doi:10.11949/j.issn.0438-1157.20181051

Abstract

Abstract:

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 N₂ between 400—500℃. Especially, the trace ammonia in the tail gas can completely be cleared with 0 left between the space velocity of 3×10⁶—6×10⁶ 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.

Key words: ammonia slip, waste treatment, red med, catalyst, simulation, iSCR

摘要：

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、NH₃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N₂的选择性，450℃以上NH₃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3×10⁶~6×10⁶ h^-1之间时，出口NH₃浓度均为0；此工艺对于逃逸NH₃浓度的适用性较强，入口[NH₃] = 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NH₃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NH₃-SCO反应，低于400℃主要发生NH₃-SCR反应，粉体催化剂通过NH₃-SCR和NH₃-SCO协同反应达到了去除尾气中微量氨的目的。

关键词: 氨逃逸, 废物处理, 赤泥, 催化剂, 模拟, 内部催化氧化

CLC Number:

TQ 426.6

Chao WANG, Changming LI, Lin HUANGFU, Ping LI, Yunquan YANG, Shiqiu GAO, Jian YU, Guangwen XU. Preparation of red mud-based catalyst and performance for trace ammonia in simulative tail gas[J]. CIESC Journal, 2019, 70(3): 1056-1064.

王超, 李长明, 皇甫林, 李萍, 杨运泉, 高士秋, 余剑, 许光文. 赤泥催化剂的制备及其对模拟烟气中微量氨的脱除性能[J]. 化工学报, 2019, 70(3): 1056-1064.

Figures/Tables 8

Fig.1 Schematic diagram of municipal solid waste incineration power generation process together with removal process of ammonia slip

Fig.2 XRD patterns (a), TG analysis (b), nitrogen adsorption isotherms (c) and pore size distributions（d）of RM and MRM

Table 1 Main chemical composition of RM and MRM

样品	主要组成/%(mass)
样品	Na₂O	MgO	Al₂O₃	CaO	SO₃	Fe₂O₃	TiO₂	SiO₂	Others
RM	10.97	0.23	19.92	1.29	0.64	44.18	8.01	13.43	1.33
MRM	0.00	0.00	19.12	0.75	4.58	53.78	8.81	11.83	0.26

Fig.3 SEM images of RM and MRM

Table 2 Specific surface area and pore volumes of RM and MRM

样品

比表面积/(m²/g）

孔体积/

(cm³/g)

Fig.4 NH3-TPD spectra of RM and MRM

Fig.5 Effect of space velocity，NH3 concentration and water on SCO activity over dust catalysts

Fig.6 NH3-SCO (a) and NH3-SCR (b) performance and yield proportions of reaction products over MRM at different temperatures[reaction conditions: 1.5 g of catalyst, [NH3]=500×10-6 mol/L, [NO]=500×10-6 mol/L(only for SCR process), [O2]=5%(vol), balance gas: N2, total flow rate 1500 ml/min, GHSV=10000 h-1]

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