Influence of steam on chromium retention by minerals under oxy-fuel combustion

doi:10.11949/j.issn.0438-1157.20171460

Abstract

Abstract:

Coal combustion experiments and kinetic simulations were conducted to investigate the effect of H₂O on chromium behaviors and the influence of H₂O on the ability of absorbents in terms of capturing chromium vapors. It was found that, both in air and oxy-fuel combustion, CaO and Fe₂O₃ showed high reactivity with chromium vapor. Limestone exhibited lower Cr solidification effect compared to CaO and Fe₂O₃. Kaolin had little effect on Cr retention in solid ash both in air and oxy-fuel combustion. H₂O promoted the oxidation of trivalent Cr(Ⅲ) to high valance Cr vapors such as CrO(OH)₂, CrO₂(OH) and CrO₂(OH)₂ in a short second time scale. The capability of Fe₂O₃ was enhanced, while the capability of CaO was inhibited by steam on capturing Cr during oxy-fuel combustion. CaO, particularly in the coexistence of H₂O, remarkably enhanced the formation of toxic Cr(VI) in solid ash, up to 43% of the total Cr. The presence of H₂O in flue gas promoted the retention of Cr in solid ash, which decreased again with the increase of H₂O from 8% to 20% during oxy-fuel combustion, attributing to the inhibition of CaO by steam in terms of capturing Cr vapors.

Key words: chromium, adsorbents, steam, coal combustion, kinetics

摘要：

通过沉降炉煤燃烧实验及动力学模拟研究了水蒸气对Cr转化行为的作用及水蒸气对矿物吸附剂捕集Cr的影响。研究表明，CaO及Fe₂O₃在空气及富氧燃烧下均能较好地捕获Cr蒸气，石灰石的作用远差于CaO及Fe₂O₃，高岭土无论空气还是富氧燃烧下对捕集Cr均无效果。动力学模拟表明H₂O促进Cr（Ⅲ）快速转化为高价Cr蒸气CrO（OH）₂、CrO₂（OH）及CrO₂（OH）₂。富氧燃烧下H₂O抑制了CaO与Cr的反应，但燃烧灰中六价铬化合物大量增加，特别是当H₂O与CaO同时存在时，灰中43%的铬为六价铬。水蒸气促进了Fe₂O₃捕集铬化合物使其固定在灰中。富氧燃烧下水蒸气促进Cr在煤灰中富集，随着H₂O浓度由8%升高至20%，灰中铬的富集率又下降，主要由于水蒸气对CaO捕集Cr的抑制作用。

关键词: 铬, 吸附剂, 水蒸气, 煤燃烧, 动力学

CLC Number:

TK16

LI Xiaoyu, DONG Hui, ZHAO Xiaoping, CHEN Juan, LU Chunmei, YAO Hong. Influence of steam on chromium retention by minerals under oxy-fuel combustion[J]. CIESC Journal, 2018, 69(6): 2714-2721.

李箫玉, 董卉, 赵小平, 陈娟, 路春美, 姚洪. 富氧燃烧下水蒸气对矿物捕集铬的影响[J]. 化工学报, 2018, 69(6): 2714-2721.

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