Application conditions and kinetics simulation over SCR catalyst for flue gas denitrification under low temperature

doi:10.11949/j.issn.0438-1157.20181438

Abstract

Abstract:

With the more stringent requirements of atmospheric pollutant emission standards, medium and low temperature catalyst would have larger market and greater challenge. In order to further clarify the application characteristics of the low temperature denitration catalyst, the denitration activity of the industrialized honeycomb catalyst was systematically investigated under different temperatures, flue gas flow rate, catalyst length and water vapor content. The applicable temperature range and kinetic parameters of the catalyst under low temperature window were also determined. These results showed that theoretical denitrification rate of NH₃/NO can be achieved above 160℃ by adjustments of gas velocity and length of honeycomb catalyst. Moreover, it was found that NO conversion gradually decreased with the increase of steam content, and the negative impact become more severely below 180℃ with less than 70% DeNO _x efficiency at 160℃ and 35% steam content in flue gas. According to the relationship between denitrification rate and residence time (at 2－4 m/s gas velocity), the reaction activation energy was calculated to be 22.7 kJ/mol, suggesting that the reaction is limited by the external diffusion. The industrial DeNO _x demonstration of flue gas with 180000 m³/h over this catalyst exhibits more than 90% DeNO _x efficiency at 180℃ and promising industrialization prospect.

Key words: SCR, low temperature catalyst, operating range, industrial application, kinetic parameters

摘要：

随着国家对大气污染物排放要求的进一步提高，中低温脱硝催化剂也将迎来更大的市场和挑战。为进一步明确低温脱硝催化剂的应用特性，在不同温度、烟气流速、催化剂长度和水蒸气含量下对已产业化的蜂窝催化剂的脱硝活性进行了系统考察，获得该中低温脱硝催化剂的适用区间与动力学参数。实验表明，在温度高于160℃条件下，通过调变气速与催化剂长度可以实现理论氨氮比的脱硝率；且在考察水蒸气对脱硝活性的影响时，发现脱硝率随着水蒸气含量的增加而逐步降低，在低温条件下降低更加显著，最大降幅达30%；依据2 ~ 4 m/s气速下的脱硝率与停留时间的关系，拟合脱硝反应活化能为22.7 kJ/mol，属于典型的气体外表面扩散控制，可为低温脱硝催化剂选型提供重要参考；180000 m³/h烟气量的脱硝示范验证了该催化剂在180℃下脱硝率超过90%，显示了优良的工业应用和推广前景。

关键词: 选择性催化还原, 低温催化剂, 操作范围, 工业示范, 动力学参数

CLC Number:

TQ 028.8

Ping LI, Changming LI, Zhengkang DUAN, Shiqiu GAO, Guangwen XU, Jian YU. Application conditions and kinetics simulation over SCR catalyst for flue gas denitrification under low temperature[J]. CIESC Journal, 2019, 70(8): 2981-2990.

李萍, 李长明, 段正康, 高士秋, 许光文, 余剑. 低温烟气脱硝催化剂适用条件与动力学[J]. 化工学报, 2019, 70(8): 2981-2990.

Figures/Tables 11

Fig.1 Schematic diagram for evaluation of catalytic activity

Fig.2 Characterization results of honeycomb catalyst

Table 1 NO conversions over honeycomb catalyst under different reaction conditions

催化剂长度/cm	气速/(m/s)	NO转化率/%
催化剂长度/cm	气速/(m/s)	120℃	160℃	200℃	240℃
20	1	7.5	45.9	71.3	85.4
	2	6.7	27.5	51.3	70
	3	2.8	18.9	39.4	50.3
	4	2.8	18.7	38.5	50.7
40	1	23.9	78	95.6	100
	2	20.4	59	83.8	99.7
	3	10.3	43.7	76.9	91.3
	4	3.5	35.4	69.8	86.5
60	1	56.1	99.9	100	100
	2	31.5	85.6	98.5	100
	3	12	55.6	84.8	96.8
	4	7.9	23.7	70	92.8
80	1	60	100	100	100
	2	45.1	96.9	100	100
	3	16.5	70	96.6	100
	4	9.2	48.1	90.3	100

Fig.3 NO conversion vs gas velocity under different catalyst length

Fig.4 Three-dimensional diagrams for gas velocity， temperature and NO conversion from Table 1

Fig.5 Inhibition of steam content on catalytic activity and stability test in presence of SO2 and H2O

Fig.6 NO conversion vs gas velocity at the same residence time

Fig.7 NO conversion vs residence time under different temperatures

Fig.8 Fitting of rate constant linear

Fig.9 Linear fitting for lnK-1/T on Arrhenius equation

Fig.10 Process flow of industrial demonstration

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