Fate of heavy metals in CaO-conditioned sludge gasification

doi:10.11949/j.issn.0438-1157.20161018

Abstract

Abstract:

Lime, which is mainly presented as CaO, is often used in sludge conditioning and stabilization.To study the effects of CaO on the fate of heavy metals in pyrolysis and sludge gasification process, the sludge pyrolysis and gasification experiments were conducted with a drop-tube furnace and a fixed-bed system.The content and speciation of typical heavy metals(Mn, Zn, Cu, Cr, Ni) were also analyzed.Samples included different sludges(raw sludge, CaO conditioned sludge), their corresponding pyrolysis chars and gasification ashes.The results indicated that after CaO conditioning, the content of heavy metals reduced due to the dilution effect.Mn, Zn, Cr transformed to stable state.Some heavy metals ions reacted with OH-to form precipitate which then decomposed to produce oxide during sludge gasification process.In addition, CaO can increase the residual rate of heavy metals in solids, and also absorb HCl, SO₂ and other acid gases from decomposition of chloride or sulfate to promote the formation of oxides at high temperatures.Subsequently, eutectic was generated in the reactions between these oxides and compounds such as Al₃O₂, SiO₂, Fe₂O₃ and CaO, thus suppressing the release of heavy metals.

Key words: sludge, gasification, conditioner CaO, biological energy, heavy metals

摘要：

以CaO为主要成分的石灰常用于污泥的调理和稳定。为探究其对污泥气化过程中重金属迁移转化规律的影响，在沉降炉-固定床反应器和固定床上于600、800、1000℃进行了污泥的热解及气化实验，并分析了不同污泥样品、热解焦和气化灰中典型重金属（Mn、Zn、Cu、Cr、Ni）的含量及形态分布。结果表明，CaO的加入将稀释调理污泥中的重金属，并使Mn、Zn、Cr向稳定态转化；CaO会使重金属离子与OH-结合生成沉淀，继而在气化反应中分解成氧化物。在气化过程中，CaO会提高重金属的残留率，也会吸收其氯化物、硫酸盐等在高温下分解生成的HCl、SO₂等酸性气体，促使氧化物的生成和抑制重金属的释放。

关键词: 污泥, 气化, 调理剂CaO, 生物能源, 重金属

CLC Number:

TK16

LU Geng, LIU Huan, HU Hongyun, ZHANG Qiang, YI Linlin, YAO Hong. Fate of heavy metals in CaO-conditioned sludge gasification[J]. CIESC Journal, 2017, 68(1): 272-280.

卢更, 刘欢, 胡红云, 张强, 易琳琳, 姚洪. 氧化钙调理污泥气化过程中重金属的迁移转化规律[J]. 化工学报, 2017, 68(1): 272-280.

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