钙基湿法烟气脱硫浆液中二价汞的还原影响因素研究

发布时间：2018-06-14 11:34

本文选题：汞 + 还原　；参考：《湘潭大学》2015年硕士论文

【摘要】：汞对环境的污染引起了国内外广泛关注,而燃煤烟气排放的汞是最主要的大气汞污染源之一。钙基湿法烟气脱硫系统(Wet Flue Gas Desulfurization,WFGD)具有能协同脱除燃煤烟气中50-95%的Hg2+的潜力,但是在一定条件下,被WFGD系统捕获的Hg2+又会被还原为Hg0,导致WFGD脱汞效率降低,造成二次污染。这一现象成为当前利用已有烟气净化装置协同净化汞污染控制的突出难点问题。本文针对钙基湿法脱硫系统中Hg2+易被还原为Hg0再释放的现象,在实验室模拟条件下对影响汞还原的主要因素进行研究,探讨各因素对汞还原的影响效果,初步探索了Hg2+在湿法脱硫系统中的还原机制,以期对钙基湿法脱硫装置协同控制汞污染的工艺和操作优化提供有价值的参考。在实验室模拟湿法烟气脱硫浆液环境中,考察了pH值、温度、Cl-、SO32-、Ca2+等因素对Hg2+还原的影响。结果表明,升高温度、降低pH促进了汞还原;而过量SO32-会与Hg2+形成比HgSO3稳定的络合物Hg(SO3)22-,从而难以释放出Hg0;加入Cl-会明显抑制Hg2+还原,Ca2+与SO32-形成难溶的CaSO3,消耗过量的SO32-,一定程度上促进汞还原。基于单因素影响的实验研究,采用Box-Behnken响应曲面法和Design Expert 8.0.6软件设计4因素3水平实验方案,获得不同条件下湿法脱硫系统中二价汞的还原率。对实验数据进行多元化拟合,得到脱硫浆液中Hg2+还原率对温度(A)、pH(B)、Cl-(C)、SO32-(D)的多元回归预测模型。二因素交互作用对汞还原率影响的响应面分析表明,温度的升高使得Hg2+→Hg0反应加快,促进Hg2+还原;而Cl-与SO32-浓度交互作用较为显著,随着Cl-与SO32-浓度的增加,Hg2+的还原率减小。通过考察接触时间、pH、反应温度、初始汞浓度和石膏含量等对溶液中汞浓度的影响,分析对比石膏对汞的摄入能力,并结合模拟吸附等温线、动力学进一步探讨石膏与汞的亲和性。结果表明:石膏结晶过程中本身对汞有一定吸附、沉积包裹作用;石膏对汞的摄取量随时间的增长而增加并于18h趋于平缓,基本符合二级反应动力学模型;在碱性条件下,石膏对汞有较高的摄取量,pH=13时,摄取量最大为8.72ug/g,且随石膏含量的增大而减小;pH=6时,石膏与汞的亲和性在一定范围内(Hg2+浓度为60-1000ug/L)与Langmuir EXT1模型有良好的一致性。结合XPS分析,揭示同时含有石膏与亚硫酸根的浆液中汞的还原机理主要是Hg2+与SO32-形成汞-硫络合物,最终释放出Hg0。对湿法脱硫系统中二价汞还原过程的基本反应式进行了热力学计算,判断还原反应可以进行,且反应限度很深。
[Abstract]:The pollution of mercury to the environment has aroused widespread concern at home and abroad, and mercury emitted from coal-fired flue gas is one of the most important sources of atmospheric mercury pollution. Wet Flue Gas Desulfuration WFGDhas the potential of synergistic removal of 50-95% Hg2 from coal-fired flue gas, but under certain conditions, Hg2 captured by WFGD system will be reduced to Hg0, resulting in lower removal efficiency and secondary pollution of WFGD. This phenomenon has become an outstanding and difficult problem of mercury pollution control by using existing flue gas purifying devices. In view of the phenomenon that Hg _ 2 is easily reduced to Hg _ 0 rerelease in calcium based wet desulfurization system, the main factors affecting mercury reduction are studied in laboratory simulation, and the effects of various factors on mercury reduction are discussed. The reduction mechanism of Hg _ 2 in wet desulfurization system was preliminarily explored in order to provide a valuable reference for the process and operation optimization of calcium based wet desulfurization plant for mercury pollution control. In the laboratory simulation of wet flue gas desulphurization slurry environment, the effects of pH value and temperature of Cl-so _ 2-O _ 2 Ca _ 2 on Hg _ 2 reduction were investigated. The results showed that increasing temperature and decreasing pH promoted mercury reduction. However, excess SO32- can form a stable complex of Hg2 with HgSO3, which is difficult to release from Hg0.The addition of Cl- can obviously inhibit the formation of insoluble CaSO3 from Hg2 reduction Ca 2 and SO32-, consume excess SO32-and promote mercury reduction to a certain extent. Based on the experimental study of single factor effect, a four-factor and three-level experimental scheme was designed by using Box-Behnken response surface method and Design expert 8.0.6 software. The reduction rate of mercury in wet desulfurization system was obtained under different conditions. The multivariate regression prediction model of Hg2 reduction rate in desulphurized slurry was obtained by multivariate fitting of experimental data. The response surface analysis of the effect of two-factor interaction on mercury reduction rate shows that the increase of temperature accelerates the Hg _ 2 reduction and accelerates the reduction of Hg _ 2, while the interaction between Cl- and SO32- concentration is significant, and the reduction rate of Hg _ 2 decreases with the increase of Cl- and SO32- concentration. The effects of contact time pH, reaction temperature, initial mercury concentration and gypsum content on mercury concentration in solution were investigated, and the absorption capacity of gypsum to mercury was analyzed and compared with simulated adsorption isotherm. The affinity of gypsum to mercury was further investigated by kinetics. The results show that the gypsum itself adsorbs and deposits mercury in the crystallization process, and the amount of mercury absorbed by gypsum increases with time and tends to be gentle at 18 h, which basically accords with the kinetic model of second-order reaction. Gypsum has a high mercury uptake pH = 13:00, and the maximum uptake is 8.72ugr / g, and decreases with the increase of gypsum content (pH = 6). The affinity of gypsum to mercury is 60-1000ugr / L in a certain range, which is in good agreement with Langmuir EXT1 model. Combined with XPS analysis, it was revealed that the reduction mechanism of mercury in the slurry containing gypsum and sulfite is that Hg _ 2 and so _ (32)-form mercury-sulfur complex, and finally release Hg _ (0). The thermodynamic calculation of the basic reaction formula of the divalent mercury reduction process in the wet desulfurization system is carried out, and it is judged that the reduction reaction can be carried out and the reaction limit is very deep.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X701

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