【作者】 兰天；

【导师】 雷乐成；

【作者基本信息】 浙江大学 ， 环境科学， 2013， 博士

【摘要】 S(Ⅳ)的快速氧化是海水法燃煤烟气脱硫工艺中需要重点解决的问题。本文通过系统研究脱硫海水的水质特性及S(Ⅳ)在海水中的氧化规律,发现微量Fe、Mn等可变价态过渡金属离子对氧化过程起到非常重要的催化作用,由此提出SO2在脱硫填料塔中的吸收-催化氧化一体化海水脱硫工艺,用于解决传统海水脱硫水质恢复工艺中的不足。有望实现海水脱硫工艺的简化,节省火电厂海水脱硫系统的基建投资与能耗。本论文首先通过半间歇的吸收实验研究脱硫海水的水质特性,分析海水对SO2的吸收容量。根据水质特性研究发现,在天然海水中S(Ⅳ)的氧化过程受pH值和有催化作用的过渡金属离子的重要影响。建立了描述脱硫海水中HCO3-、S(Ⅳ)、S(Ⅵ)与pH值之间联系的离子平衡模型,较好地预测了出水pH与S(Ⅳ)浓度的相互关系。其次重点研究S(Ⅳ)在海水中的氧化规律。采用乙酸根作为pH缓冲剂,分别研究了S(Ⅳ)的无催化自氧化动力学、Fe2+催化氧化动力学以及Mn2+催化氧化动力学,并通过Fe离子的价态分析及添加甲醇作为自由基清除剂等方法,对S(Ⅳ)的氧化机理进行研究。结果表明：在所研究的溶解氧浓度范围内,无论是S(Ⅳ)的自氧化,还是Fe2+、Mn2+作用下的催化氧化,溶解氧的反应级数都是零级。无催化下的S(Ⅳ)自氧化反应涉及自由基链反应,反应对S(Ⅳ)的反应级数为二级。在过渡金属离子作用下的催化氧化中,S(IV)的反应级数是可变的,对Fe2+催化氧化而言,pH值在2.5～3.5的范围呈现一级反应；对Mn2+催化氧化而言,pH值在4.0～5.0的范围内呈一级反应,而在pH为5.0～5.9的范围内则呈二级反应。实验证明,Fe、Mn等过渡金属离子极大促进了S(Ⅳ)在海水中的氧化。最后对吸收-催化氧化一体化工艺进行了深入研究。分别考察向海水中人工添加微量Fe2+、Mn2+,以及将Fe2O3、MnO2作为催化剂负载在人造沸石填料上的均相和非均相吸收-催化氧化一体化工艺。结果表明,这两种方法都成功实现了S02的吸收与氧化过程的一体化耦合。进一步研究表明,负载型Mn02催化剂在S02吸收-催化氧化一体化工艺中能实现S02的快速氧化转化,且出水极少残留Mn离子,对色度无影响,该技术为海水法燃煤脱硫工艺提供了新思路和新方法。更多还原

【Abstract】 S(IV) oxidation process is a very important issue in seawater desulfurization process (SFGD). This paper systematically studied the desulfurization effluent in SFGD process and S(IV) oxidation mechanism in seawater. Experiment results found that trace amount of transition metal ions have variable valence states can greatly catalyze S(IV) oxidation. According to the results, an one-step SFGD technology combine absorption and catalyzed oxidation process had been raised. This technology could simplify traditional SFGD process, save capital cost and energy consumption.Firstly, characteristic of desulfurization effluent had been investigated through semi-batch adsorption experiments. Experiment results indicated that S(IV) oxidation in natural seawater is greatly influenced by pH and transition metal ions which have catalytic effects. The seawater absorption capacity of SO2was studied and an ion equilibrium model which describe the relationship between HCO3-, S(IV), S(VI) and pH value was established to forecast the effluent seawater quality.Secondly, kinetics of uncatalyzed, Fe2+catalyzed, and Mn2+catalyzed oxidation of S(IV) in seawater were studied separately using acetic buffer. Reaction path was discussed through analyzing the valence states of Fe ion and using methanol as radical scavenger. Results indicated that the reaction order with respect to dissolved oxygen is zero. Non-radical oxidation pathway does not exist in both catalyzed and uncatalyzed conditions. Reaction order with respect to S(Ⅳ) is variable:second-order under uncatalyzed condition(4.0≤pH≤7.0); first-order under Fe2+-catalyzed oxidation (2.5≤pH≤3.5); first-order (4.0≤pH≤5.0and second-order (5.5≤pH≤5.9) under Mn2+-catalyzed oxidation. Kinetic experiments found that Fe and Mn ion greatly accelerate S(IV) oxidation, this catalytic effect can be utilized to design one-step SFGD process combine the absorption and oxidation.Finally, technical studies of one-step SFGD process was carried out. Two kind of method: adding Fe2+or Mn2+to seawater, and prepare Fe2O3and MnO2supported artificial zeolite packing, all achieved combination of high absorption and oxidation efficiency. Furthermore, MnO2immobilized catalyst has no shortage which cause chroma increase in seawater. This study offered new ideas for the design of SFGD process.更多还原