【作者】 江举辉；

【导师】 蔡伟民；

【作者基本信息】 上海交通大学 ， 环境工程， 2008， 博士

【摘要】 传统石灰石膏法烟气脱硫工艺产生大量的固体废弃物和二次废水污染。利用过渡金属Fe（III）溶液吸收烟气中SO₂,S（Ⅳ）在溶液中被氧化为S（Ⅵ）,既达到脱除SO₂的目的,又可利用产生的稀硫酸制取不同的副产物,是回收法脱硫的一种重要研究方向。以千代田法为代表的Fe（III）溶液烟气脱硫工艺,在酸性操作条件下,高液气比增加了运行费用,利用副产物稀硫酸制备石膏也限制了其发展。因此,降低运行成本,实现副产物的资源化是Fe（III）脱硫今后的重点研究的问题。此外,在以往的研究中,对于Fe（III）溶液吸收SO₂,尚缺少设备放大的动力学数据报导。综合以上的考虑,本文在系统地对Fe（III）溶液吸收SO₂工艺参数进行实验研究的基础上,提出以铸铁屑作为填料协同Fe（III）溶液吸收SO₂,通过控制吸收液的pH值,提高SO₂吸收效率,得到副产物铁盐溶液;在此基础上,进一步使用直流磁场强化铸铁填料吸收SO₂;在副产物综合利用上,采用Fe₂（SO₄）₃-Urea体系均相水解制备高附加值的纳米氧化铁红,并且得到硫酸铵化肥。本研究的Fe（III）/铸铁屑工艺实现了烟气脱硫的绿色化。具体内容如下:1.在Fe（III）-S（IV）反应机理分析的基础上,系统研究了0.001-0.12M浓度范围内Fe（III）溶液对SO₂的吸收,并对溶液pH值,温度,液气比,SO₂浓度等工艺参数进行优化。表明:填料塔体积质量传质系数为0.0025s-1,pH≥2.0,[Fe（III）]≥0.05M,温度控制在40℃左右,液气比保持在10L/m3,SO₂吸收效率可大于75%。计算了不同pH值条件下Fe（III）和SO₂水解过程中反应活性物种浓度分布,对不同实验条件下影响Fe（III）溶液吸收SO₂的影响进行了探讨。根据动力学反应方程r=k[FeOH2+][HSO3-],可以判据Fe（III）-S（IV）催化氧化反应为二级反应。在双膜理论和气液流体传质理论分析的基础上,计算出不同实验条件下宏观反应动力学因子-增强因子E,可解释不同条件下SO₂吸收效率的变化。验证了动力学反应方程r=k[FeOH2+][HSO3-]的正确性,为反应器的设计和放大提供理论依据。研究表明,在pH<2.0的条件下利用Fe（III）溶液吸收SO₂,具有较低催化氧化反应速率和增强因子,为保证一定的脱硫效率,需要较大的气液接触表面积和较高的能耗,从成本上考虑需要采用其他方法协同进行烟气脱硫。2.提出了利用铸铁屑填料协同Fe（III）溶液吸收烟气中SO₂的方法。对溶液pH,不同电解质溶液,SO₂浓度,温度,填料层高度等单因素,以及吸收液循环喷淋进行了研究。表明铸铁屑的腐蚀过程能够提高SO₂的吸收,所产生的Fe（III）催化氧化液相中的S（IV）,并且得到了具有一定经济价值的硫酸铁盐副产物。化学分析,XRD,和FIIR等研究手段表明,腐蚀过程中沉积的铁锈累积抑制腐蚀,从而降低SO₂的吸收效率。吸收液中溶解氧不足会影响到Fe（II）氧化并导致Fe（III）浓度降,也阻碍了SO₂的吸收。SO₂在腐蚀过程中的增强吸收和腐蚀途径为:当SO₂进入溶液,就导致一序列电化学腐蚀反应;腐蚀初阶段的水合亚铁氧化物很容易氧化为三价铁氧化物;部分铁氧化物溶解进入溶液,从而控制吸收液的pH值并催化氧化S（IV）;部分铁氧化物也反应生成难溶的羟基硫酸或亚硫酸铁盐,从而对SO₂的吸收过程产生抑制作用。3.提出利用直流磁场强化Fe（III）/铸铁屑填料吸收SO₂,改善了填料层的板结状况,减轻填料层的重量,提高了脱硫效率。结果表明,直流磁场强化方法适用于低浓度烟气（700ppm < Cso2in < 1350ppm）处理;随着磁场强度增加,脱硫效率也逐步增加,超过20mT的磁场强度对脱硫效率并无显著性增加;温度过高吸收将由SO₂物理吸收控制;直流磁场能够明显降低填料层高度,通过调节填料层高度,可以适应不同脱硫工况的变化。SO₂去除效率的增强主要由腐蚀过程控制,直流磁场的作用在于改变铸铁屑表面的铁锈沉积形态,改善了填料层的板结问题。磁流体（MHD）力和磁场梯度力两种磁场作用力都能作用于铸铁屑表面的电化学腐蚀过程,铸铁屑表面产生的离子进入溶液后,不同离子在磁场力作用下产生定向迁移和运动,从而促使沉积的铁锈结构发生变化,使其更加疏松,有利于腐蚀进行和SO₂吸收。4.在副产物资源化方面,探索了纳米级铁红的Fe₂（SO₄）₃-Urea体系均相水解制备,通过反应时间,铁离子浓度,尿素浓度,水解温度,煅烧温度等参数影响铁红颗粒形状和尺寸。在Urea/Fe=1.7,T=95℃,[Fe（III）]=0.125M的条件下,8hr反应时间,可以控制溶液pH低于5, 85%以上的Fe（III）形成了铁红,水解产物经过800℃高温煅烧,获得50nm左右均一的球形赤铁矿晶形的铁红。Fe₂（SO₄）₃-Urea体系水解和热处理过程为:Fe₂（SO₄）₃-Urea体系水解形成各种碱式硫酸铁盐,进一步水解生成铵化黄钾铁钒和水合氢化黄钾铁钒,并形成少量的水铁矿晶,黄钾铁钒和水铁矿经过200-800热处理,得到产生均一的赤铁矿晶形铁红。更多还原

【Abstract】 Traditional methods employing lime and limestone for gas desulfurization are facing many problems, including producing a large amount of calcium sulfate and huge financial burdens. The process of SO₂ absorption with Fe（III） solution is a fundamental research, in which S（IV） can be catalyzed oxidation to S（VI）, and the valuable product can be obtained with the sulfuric acid. The typical process was the Chiyoda which had high consumed-energy and byproduct of calcium sulfate. In order to solve those problems, the desulfurization of Fe（III） solution need to be improved. On the other hand, there lacked of reports of related kinetic data in those processes. Based on the above consideration, in this study, the systematic research was conducted on SO₂ absorption with the Fe（III） solution. Cast iron scraps were used as packing for SO₂ enhancement absorption with Fe（III） solution, which was helpful for invariability of pH and iron sulfate could be obtained; Also, the magnetic field was used for SO₂ enhanced absorption in cast iron scraps system. At last, nano-hematite was prepared with the Fe₂（SO₄）₃-Urea homogeneous system for the further uilitization of byproducts. Then a a green desulfurization processes is formed.1. The systematic research was conducted on SO₂ absorption with different concentration Fe（III） solution （0.001-0.12M）, including: pH, [Fe（III）], gas-liquid ratio and the inlet concentration of SO₂. The optimization parameters was （kLa=0.0025s-1）: pH≥2.0, [Fe（III）]≥0.05M, T=40℃, the ration of liquid/gas kept at 10L/m3.The distribution of Fe（III） and S（IV） species was calculated, which can be used for explain of the influence of SO₂ absorption efficiency with different [Fe（III）]. According to the kinetic equation r=k[FeOH2+][HSO3-], the reaction of Fe（III）-S（IV） can be considered as a second order, and the SO₂ absorption was controlled by gas film and liquid film.According to the two-film model and gas-liquid transfer theory, the enhancement factor for macro-kinetics can be calculated in different experimental conditions, which can be use for reactor design and verification of kinetic equation.It can be deduced that the lower rate of reaction of Fe（III）-S（IV） and enhancement factors was obtained when pH was kept below 2.0. In order to keep higher desulfurization efficiency, higher engery consumed was need. Then the enhanced way shoud be used for desulfurization with Fe（III） solution for the economic consideration.2. The packing of cast iron scraps was used for SO₂ absorption cooperating with Fe（III） in our research. Single factor experiments including pH, electrolyte, inlet concentration of SO₂, temperature, and height of packing, and spraying solution circularly used were conducted. It can be found that, SO₂ absorption can be effectively enhanced by corrosion processes of cast iron scraps, S（IV） can be oxidation by Fe（III） in solution, and a certain valuable iron sulfate can be obtained as byproducts. The corrosion rate was restrained by deposited corrosion product. Also, [Fe（III）] and the dissolved oxygen in solution were gradually decreased and SO₂ absorption was restrained. The SO₂ absorption and corrosion processes include: as SO₂ enters the solution, a series of electrochemical reactions occur; hydrous ferrous oxides are easily oxidized to ferric hydroxides; some of them are dissolved by proton, while others are transformed to insoluble ferrous/ferric hydroxylsulfate and hydroxylsulfite. Then pH was kept constant and the Fe（III）-S（IV） happened. As the deposited rusts were cumlative, the SO₂ absorption was inhibited. 3. DC magnetic field was used for SO₂ absorption in packing reactor of cast iron scraps, the results showed: The compacted phenonmenon was decreased dramatically. The low concentration SO₂ （700ppm < Cso2in < 1350ppm） can be effectively enhanced by DC magnetic field; With the higher intensity magnetic field, the SO₂ removal efficiency was gradually enhanced and the effect was not obvious when the intensity of magnetic field was more than 20mT; more than 50℃, SO₂ absorption was controlled by physical absorption. SO₂ absorption was enhanced by corrosion processes, and the corrosion processes can be changed by magnetic field. It can be thought that two kinds of magnetic field force （MHD and FGF） exist in electrochemical corrosion processes, and they can cause a transport of all ions because of the difference in the magnetic susceptibility in the solution at the cast iron scraps surface with oriental direction, then the deposited rusts turned to be looser and corrosion rate was increased.4. At last, spherical nano-hematite was prepared by homogeneous hydrolysis of Fe₂（SO₄）₃-Urea system for the uilitization of byroducts. The influence factors for the shape and size of hematite were studies, including: reaction time, [Fe（III）], [Urea], hydrolysis temperature, the calcined temperature. In the condition of Urea/Fe=1.7,T=95℃,[Fe（III）]=0.125M, t= 8h, the pH can be controlled below 5, the deposited ration of Fe（III） is above 85%, and with the thermal treatment in the condition of 800℃, the uniform spherical hematite with the size of 50nm is obtained. The hydrolysis and thermal treatment include the subsequent way: a number of ferric sulfate complex species and its basic complexes were formed at first; then ammonium–hydronium jarosite were the main products with a small amount of ferrihydrite; By the thermal treatment at 200-800℃, the poor crystalline products were gradually transformed to spherical crystalline of nano-hematite.更多还原