改性桑树枝焦对模拟烟气中汞的吸附性能

采用固定床热解、蒸汽活化和改性剂(H₂O₂、ZnCl₂和NaCl)浸渍等方法制得不同的桑树枝焦。在固定床吸附实验台上,研究了蒸汽活化、改性剂、吸附温度和烟气组分等对改性桑树枝焦汞吸附性能的影响。结果表明:蒸汽活化显著提高了桑树枝热解焦的比表面积,H₂O₂改性可进一步提高桑树枝蒸汽活化焦比表面积并改善其孔隙结构参数,ZnCl₂和NaCl改性则降低了桑树枝蒸汽活化焦的比表面积、D-R微孔容积和总孔容。10%H₂O₂和30%H₂O₂浸渍改性桑树枝焦的单位汞吸附量分别是蒸汽活化焦的2.02倍和1.77倍;相同改性剂浓度下,ZnCl₂改性焦的单位汞吸附量比NaCl改性焦稍好;随着ZnCl₂浓度增大,改性桑树枝焦的汞吸附性能增强,MT600-A-ZnCl₂(5%)桑树枝焦的单位汞吸附量达到29.55 μg·g^-1,是蒸汽活化焦的3.37倍。在吸附温度为60～120℃范围内,H₂O₂改性焦的汞吸附效率及单位汞吸附量随着吸附温度的升高而下降,而ZnCl₂改性焦的单位汞吸附量则随着吸附温度提高呈现先增大后减小的趋势,最佳吸附温度为90℃。烟气中SO₂和NO组分对汞吸附性能有一定的抑制作用,随着SO₂和NO浓度的增加,汞吸附效率和单位汞吸附量均稍有下降。

Mercury adsorption performance by modified mulberry twig chars

Several mulberry twig (MT) chars were prepared by conventional pyrolysis, steam activation, and impregnation with H₂O₂, ZnCl₂ and NaCl.Adsorption performance of mercury in a simulated flue gas by MT chars were studied in a bench-scale fixed bed absorber, and the effects of steam activation, impregnation agent, adsorption temperature, and the composition of simulated flue gas, etc.on mercury adsorption performance were analyzed.The results indicated that steam activation could significantly increase surface areas of MT pyrolysis chars.Impregnation with H₂O₂ can further improve surface areas of steam activated MT chars and its pore structure. However, impregnation with ZnCl₂ and NaCl led to decrease of surface areas, D-R micro-pore and total pore volume of MT chars in some extent.The mercury adsorption capacities of MT chars impregnated with 10% and 30% H₂O₂ were 2.02 and 1.77 times of that for steam activated MT char, respectively, and that of MT char impregnated with ZnCl₂ was a little better than that impregnated with NaCl at the same impregnation concentration.The performance of mercury adsorption enhanced with increase of ZnCl₂ concentration for modified MT char.The mercury adsorption for MT600-A-ZnCl₂(5%) was 29.55 μg·g^-1, 3.37 times of that for steam activated MT char.At temperature of 60—120℃, the mercury adsorption efficiency and capacity of MT chars impregnated with H₂O₂ decreased with increase of adsorption temperature. However, the capacity of MT chars impregnated with ZnCl₂ showed an increase trend at first and then decrease, and its optimum adsorption temperature was 90℃.SO₂ and NO in the simulated flue gas showed adverse effect on mercury adsorption.Both mercury adsorption efficiency and capacity decreased slightly with increase of SO₂ and NO concentration.