湿法脱硫及其副产品加工过程中汞再释放及迁移的研究

发布时间：2018-01-31 01:23

  本文关键词： 湿法脱硫 汞 石膏 pH 值 金属离子　出处：《华中科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：燃煤过程汞排放是主要的大气汞排放来源,对人类健康和环境存在潜在的风险。难捕捉的元素态汞(Hg0)的脱除成为燃煤电站汞减排的瓶颈问题,湿法脱硫系统虽然可以高效脱除燃煤烟气中SO2和氧化态汞(Hg2+),但又存在Hg2+被还原成Hg0的再释放现象,增加燃煤电站汞减排的难度。为提高燃煤电站和湿法脱硫系统的脱汞效率,本文实验研究了湿法脱硫及其副产品加工过程汞再释放及迁移规律。首先采用单因素分析方法研究了pH对Hg0再释放的作用机理。脱硫清液p H值在3.0-8.0时,pH越高Hg0再释放越难发生。pH值低于4.0时,亚硫酸氢根与氧化态汞生成的亚硫酸汞和亚硫酸氢汞易分解,造成Hg0大量释放。pH值上升使亚硫酸根增加,其会与亚硫酸汞生成更稳定的Hg(SO3)22-,减少Hg0再释放。采用数学拟合方法得到的亚硫酸盐浓度、pH、时间与Hg0释放率的定量关系式能初步预测Hg0再释放。为了深入研究金属离子对Hg0再释放的作用,结合热力学理论探讨了金属离子及其与亚硫酸盐协同对Hg0再释放的作用。碱性环境时Fe2+、Mn2+和Co2+能使Hg0再释放,酸性环境时Fe2+能使Hg0再释放。碱性环境和酸性环境时Mn2+、Co2+、Ni2+与亚硫酸盐的协同作用显著促进了Hg0再释放。本文通过实验探究了湿法脱硫系统三相汞迁移特性和煅烧过程中石膏汞释放规律。二氧化碳、氧气和硝酸根增加气相汞比例,减少固相和液相汞比例。亚硫酸钙和氯离子抑制汞向气相迁移,氯离子大幅增加液相汞比例。添加剂TMT、DTCR和Na HS明显减少气相和液相的汞比例,增加固相汞比例,其富集汞到石膏的能力依次减弱,使煅烧后的石膏剩余汞含量升高。Na HS、TMT和DTCR添加后石膏汞热稳定性依次减小,分别使石膏中形成HgS、Hg3(TMT)2和Hg(DTCR)2。程序升温实验中,Hg3(TMT)2和Hg(DTCR)2的分解温度为170℃-290℃和110℃-270℃,峰值温度为235℃和198℃。
[Abstract]:Mercury emission from coal combustion process is the main source of mercury emission in the atmosphere, which has potential risks to human health and environment. The removal of elemental mercury (Hg0) from coal-fired power plants has become the bottleneck of mercury emission reduction in coal-fired power plants. Although the wet desulfurization system can efficiently remove SO2 and Hg2 (oxidized mercury) from coal-fired flue gas, there is a rerelease phenomenon in which Hg2 is reduced to Hg0. In order to improve the efficiency of mercury removal in coal-fired power plants and wet desulfurization systems, it is difficult to reduce mercury emissions in coal-fired power stations. In this paper, the rerelease and migration of mercury in wet desulfurization and by-product process were studied experimentally. Firstly, the mechanism of pH on Hg0 rerelease was studied by single factor analysis. H values ranged from 3.0 to 8.0. The higher the pH is, the more difficult the rerelease of Hg0 is. When the pH value is lower than 4. 0, the mercurous sulfite and mercurous hydrogen sulfate produced by H2SO4 and mercuric oxide are easily decomposed. The increase of pH value of Hg0 resulted in the increase of sulfite radical, which together with mercurous sulfate produced a more stable HgCSO3 (22-). To reduce the rerelease of Hg0, the concentration of sulfite and pH were obtained by mathematical fitting method. The quantitative relationship between time and Hg0 release rate can predict the rerelease of Hg0. In order to study the effect of metal ions on the rerelease of Hg0. Combined with thermodynamic theory, the effect of metal ions and their coordination with sulfite on the rerelease of Hg0 was discussed. In alkaline environment, Hg0 can be rereleased by Fe2 limn 2 and Co2. Fe2 can rerelease Hg0 in acidic environment and Mn2 CO2 in alkaline environment and acidic environment. The synergistic effect of Ni2 and sulfite significantly promoted the rerelease of Hg0. In this paper, the characteristics of three-phase mercury migration in wet desulphurization system and the rules of mercury release from gypsum during calcination were investigated. Oxygen and nitrate increase the proportion of mercury in gas phase and decrease the ratio of mercury in solid phase and liquid phase. Calcium sulfite and chloride ions inhibit the migration of mercury to gas phase, and chlorine ion significantly increases the proportion of mercury in liquid phase. Additive TMT. DTCR and NaHS obviously reduced the proportion of mercury in gas phase and liquid phase, increased the proportion of mercury in solid phase, its ability to enrich mercury to gypsum decreased in turn, and the residual mercury content of calcined gypsum increased .NaHS. After the addition of TMT and DTCR, the thermal stability of gypsum mercury decreased in turn, which resulted in the formation of HgSN Hg3 TMT2 and HgGN DTCR2 in gypsum, respectively. The decomposition temperatures of Hg3(TMT)2 and Hg(DTCR)2 are 170 鈩，

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