Effect of flue gas and fly ash components on mercury removal by bromine modified fly ash

doi:10.16085/j.issn.1000-6613.2017-1357

Abstract

Abstract: Unburned carbon(UBC) and metal oxides have a certain adsorption and oxidation abilities of mercury. Fly ash has been considered as a cheap and potential mercury removal adsorbent in coal-fired power plant,but the efficiency is to be improved. In this paper,two kinds of fly ash with different contents of UBC were chosen and modified by 1%NH₄ Br solution. Effect of flue gas components(O₂,SO₂ and NO) and metal oxides on mercury removal by the modified fly ash was investigated in fixed-bed reactor,in order to obtain high efficiency mercury removal adsorbent and adsorption mechanism. The results showed that O₂ has a little positive effect on the mercury oxidation. SO₂ has a certain inhibitory effect. NO promotes the oxidation of Hg⁰ obviously. Fe₂O₃ and TiO₂ in bromine modified fly ash played a major role in the oxidation of Hg⁰. The reason was that bromine modification increases the lattice oxygen content of Fe₂O₃ and TiO₂ which promotes the catalytic oxidation of Hg⁰,and mainly follows the Mars-Maessen mechanism. UBC content of fly ash has a great impact on the removal of Hg⁰. When the bromide was embedded in the UBC of the fly ash surface,the activity of the neighborhood was enhanced. As a result,the adsorption capacity of the carbonaceous surface to Hg⁰ was enhanced,and the subsequent reaction was promoted.

Key words: leaching, adsorbents, mercury, fixed-bed, metal oxide

摘要： 燃煤飞灰中的未燃碳（unburned carbon，UBC）和金属氧化物因对汞有一定的吸附和氧化作用而被认为是燃煤电厂廉价的潜在脱汞吸附剂，但效率有待提高。文章选取两种UBC含量不同的飞灰，采用质量分数1%的NH₄Br溶液对其浸渍改性，利用固定床汞吸附实验台探究了烟气组分（O₂、SO₂和NO）以及飞灰中无机金属氧化物对汞吸附和氧化的影响，以期获得高效脱汞吸附剂吸附机理。结果表明，O₂对于溴素改性飞灰氧化汞有较小的促进效果，SO₂具有一定的抑制作用，NO促进Hg⁰的氧化效果明显；溴素改性飞灰中的Fe₂O₃和TiO₂对Hg⁰的氧化起着主要作用，原因在于溴素改性增加了金属氧化物Fe₂O₃和TiO₂中的晶格氧含量，促进了Hg⁰的催化氧化，主要遵循Mars-Maessen机理。另外，UBC含量对飞灰脱除Hg⁰的影响很大，溴素嵌入飞灰表面的UBC时，会使其邻域的活性加强，从而增强碳质表面对Hg⁰的吸附能力，促进了后续反应的进行。

关键词: 浸取, 吸附剂, 汞, 固定床, 金属氧化物

CLC Number:

X511

LIU Shuai, DUAN Yufeng, CHEN Mingming, ZHAO Shilin, ZHENG Yiwu, LIU Meng. Effect of flue gas and fly ash components on mercury removal by bromine modified fly ash[J]. Chemical Industry and Engineering Progress, 2018, 37(04): 1599-1607.

柳帅, 段钰锋, 陈明明, 赵士林, 郑逸武, 刘猛. 烟气及飞灰组分对溴改性飞灰脱汞特性的影响[J]. 化工进展, 2018, 37(04): 1599-1607.

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