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Chemical kinetics simulation of semi-dry dechlorination in coal-fired flue gas

燃煤烟气半干法脱氯的化学动力学模拟

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Abstract

HCl in coal-fired flue gas has adverse impact on the environment, equipment, and the flue gas desulfurization (FGD) system. The existence of HCl also increases the difficulty of the treatment of desulfurization waste water. Semi-dry dechlorination technology is put forward to attach chlorine to fly ash by spraying in alkaline solution. Simultaneously, desulphurization waste water is used as the solvent of alkali, and this could help realize the target of near-zero emission of desulfurization waste water. CHEMKIN is used to build a chemical kinetics model, which is based on the measured components of flue gas in a coal-fired power plant. NaOH is set as the alkali absorbent in the model. Both the competitive relationship of SO2 and HCl and the effects of different factors on HCl reaction efficiency are analyzed. SO2 with high concentration would compete for more NaOH, but when Na/Cl (ratio in mole) is 1, the reaction efficiency of HCl achieves 22.28%, and it is positively correlated with Na/Cl. When Na/Cl surpasses 5, the reaction efficiency of HCl increases to beyond 70%. As Na/Cl continues to increase, there is a slower growth of HCl reaction efficiency and it finally achieves 100% when Na/Cl reaches 12. With a fixed value of Na/Cl, a change of 1000 mg/m3 in SO2 concentration would change the reaction efficiency of HCl about 13%. The effect of flue temperature on HCl reaction efficiency is not significant. Acid gases in flue gas react with NaOH completely in 0.1 s and come to equilibrium after about 1 s.

概要

目的

燃煤锅炉烟气中的HCl 对环境、设备及脱硫系统有不利的影响,也是脱硫废水处理的难点。本文提出半干法脱氯技术,探讨其技术合理性,并研究不同因素对反应效率的影响,为进一步工程应用提供理论依据,实现燃煤烟气中HCl 的脱除及脱硫废水零排放。

创新点

1. 提出半干法脱氯技术,将氯离子固化到飞灰中;2. 脱氯后脱硫废水大幅减少,将脱硫废水作为碱基溶剂回喷到烟道中,实现脱硫废水零排放;3.建立良搅拌反应器(PSR)模型,探讨半干法脱氯过程的化学动力学反应机理与关键参数。

方法

1. 通过CHEMKIN 构建PSR 模型,模拟实际燃煤烟气组分下的半干法脱氯过程;2. 通过敏感性分析,探讨SO2 与HCl 之间的竞争关系(图8~10);3. 通过单变量模拟,研究不同因素对反应效率的影响(图13~16)

结论

1. 烟气中的SO2 对HCl 的脱除存在较大竞争关系,但即使Na/Cl(摩尔比)为1 时,HCl 的反应效率依然可观。2. HCl 的反应效率与Na/Cl 呈正相关;综合考虑反应效率和运行成本,设置Na/Cl为5 较为合理。3. SO2 浓度的小范围变化不会对HCl 的反应效率造成显著影响。4. 仅通过化学动力学模拟,烟气温度对HCl 的反应效率影响不明显。5. 烟气中酸性气体与NaOH 在0.1 s 内即可完成反应,在1 s 左右达到平衡。

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Authors and Affiliations

  1. The State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou, 310027, China

    Chang Liu, Hong Zhao, Wei-ying Yang, Kun-zan Qiu, Jian-guo Yang & Zi-wen Geng

  2. Zhejiang Provincial Energy Group Co., Ltd., Hangzhou, 310007, China

    Wei-ming Teng

  3. Zhejiang Energy Changxing Power Generation Co., Ltd., Huzhou, 313100, China

    Wei-zhong Yuan & Xi-jiong Chen

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  1. Chang Liu
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  2. Hong Zhao
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Correspondence to Jian-guo Yang.

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Project supported by the Zhejiang Provincial Natural Science Foundation of China (No. LY15E060002)

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Liu, C., Zhao, H., Yang, Wy. et al. Chemical kinetics simulation of semi-dry dechlorination in coal-fired flue gas. J. Zhejiang Univ. Sci. A 19, 148–157 (2018). https://doi.org/10.1631/jzus.A1600653

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  • DOI: https://doi.org/10.1631/jzus.A1600653

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