【作者】 沈桂芬；

【导师】 王祖武；

【作者基本信息】 武汉大学 ， 环境工程， 2021， 博士

【摘要】 SO₂和NO是燃煤电厂产生的主要气态污染物,目前普遍采用湿法烟气脱硫（WFGD）和选择性催化还原法脱硝（SCR）两种相互独立的工艺分别对其脱除净化,这种工艺组合存在投资费用高、占地面积大等缺点;而研究中的吸附再生、液相吸收等SO₂/NO联合脱除技术存在系统复杂、二次污染和运行成本偏高等不足,限制了其规模化的应用。本文针对SO₂/NO含有强电负性元素S和O可结合电子生成负离子或负离子簇的特点,提出了一种SO₂/NO静电增强膜吸收去除的方法。这种方法将电迁移和膜吸收结合起来,以膜介质为分离界面,避免气液两相直接接触产生的相变和腐蚀等问题;通过电晕放电产生低能电子与SO₂/NO结合生成负离子（簇）,以电场力作为带电粒子迁移的推动力,提高SO₂/NO膜吸收去除的效率。因电场力直接作用于荷电后的负离子,可在较低的气体阻力和较小的膜面积上达到较高的吸收去除效率。本文在自制膜反应器中采用针板电极进行了静电增强膜吸收SO₂/NO的特性和机理的研究,膜另侧吸收液采用循环流动的方式不断进行表面更新,减少液相阻力,并在此基础上进行了一系列的实验和研究,得出如下结论:（1）通过静电增强方式可显著提高膜吸收去除SO₂/NO的效率和总传质系数。与电压为0时相比,放电电压为18 k V时,通过静电增强的方式可使SO₂的吸收去除效率从58.78%提高至95.53%,总传质系数从38.5×10^-3m/min增加至135.2×10^-3m/min;NO的吸收去除效率从6.93%提高至51.20%,总传质系数从3.1×10^-3m/min增加至31.2×10^-3m/min。（2）SO₂和NO在结合电子生成负离子（簇）上存在竞争关系,SO₂的电子亲和能大,与NO的竞争中更易结合电子生成负离子（簇）,吸收去除效率在放电初期随电压升高上升明显;静电增强时入口浓度、烟气流量等增加对SO₂吸收去除效率的影响更小。放电电压由0升高至12 k V时,SO₂的吸收去除效率从58.78%增加至91.42%,NO的吸收去除效率增加不明显;电压由12 k V升高至18 k V时,NO的吸收去除效率从12.25%增加至51.20%,而SO₂的吸收去除效率增幅不足5%。静电增强电压为18 k V时,烟气流量从0.5 L/min上升至0.9 L/min,SO₂的吸收去除效率下降5.11%,而NO的吸收去除效率下降值达13.52%。（3）入口浓度、放电电压和烟气流量对吸收去除效率的影响中,放电电压的影响最显著,其次是入口浓度;放电电压和烟气流量以及放电电压和入口浓度之间的交互作用在电压较高时影响更显著;实测NO吸收去除效率和传质系数分别为53.07%和0.043 m/min,与响应曲面法预测值基本吻合。（4）静电增强时O₂对SO₂/NO的吸收去除有一定的协同促进作用,对NO的协同促进作用较SO₂更明显。放电电压为18 k V时,烟气中的O₂从0升高至4.9%,SO₂的吸收去除效率提高了2.57%,而NO吸收去除效率的增加达8.13%。（5）SO₂/NO可结合电子生成带一个负电荷的离子簇并在浓度梯度和电场力的作用下透过微孔膜,负离子簇生成反应的级数近似1级;常温下负离子在气相中的电迁移率约为扩散系数的39倍,吸收去除的推动力以电场力为主,吸收去除总传质系数的数学模型为K_G=-Q/Aln（1-η）。（6）SO₂/NO与KMnO₄/NaCl O₂可发生快速化学反应,Na Cl O₂与SO₂/NO以及SO₂与KMn O₄/Na Cl O₂的反应更彻底,吸收去除效率更高;吸收产物中SO₄^2-、NO₃^-离子浓度的占比随放电电压的升高呈上升趋势。更多还原

【Abstract】 Sulfur dioxide（SO₂）and nitrogen oxides（NOx）are major harmful air pollutants in the flue gas released from coal-fired power plants.To reduce their emissions,wet flue gas desulfurization（WFGD）and selective catalyst reduction（SCR）are widely used presently.Meanwhile,they are accompanied by some problems such as complex systems,high investment costs,and operating costs,secondary pollution,etc.It is just these reasons limited their large-scale application.In view of SO₂and NO molecules containing the strongish electronegative elements S and O,can attach low-energy electrons to form negative ions or negative ion clusters,this paper proposed an integrated membrane separation method that can remove SO₂/NO simultaneously and combine electromigration,membrane separation,chemical absorption as an integral.The separation process took the membrane fiber medium as the separation interface,which can effectively overcome the disadvantages of flooding,channeling in traditional wet absorption equipment by non-contact between gas and liquid.As for electric field force directly acts on the negative ions collided with low energy electrons generated by corona discharge.It can obtain high removal efficiency under low gas driving force and small unit gas membrane area.The separation mechanism of SO₂/NO was analyzed in a self-made membrane reactor.Discharge needle electrodes placed evenly in the upper wall of the reactor and connected with an external negative high-voltage DC power supply.The aqueous absorbent flowed continuously at constant flux on the other side of the membrane to reduce the liquid phase resistance and series of experiments and studies had been carried out in the reactor,the main conclusions were as follows.（1）The removal efficiency and total mass transfer coefficient of SO₂/NO could be significantly improved by electrostatic enhancement.When the discharge voltage was 18 k V,compared with the membrane absorption without discharge,the removal efficiency and total mass transfer coefficient of SO₂raised from 58.78%to 95.53%and from 38.53×10^-3m/min to 135.2×10^-3m/min,that of NO increased from 6.93%to 51.2%and from 3.1×10^-3m/min to 31.2×10^-3m/min respectively.（2）It is the competitive relationship between NO and SO₂on capturing electrons to form negative ions.As for SO₂has a more strongish ability to capture an electron,the removal efficiency increased more obviously in initial discharge stage,removal efficiency less affected by inlet concentration and flue gas flow rate in discharge condition than that of NO.When discharge voltage increased from 0 to 12 k V,the removal efficiency of SO₂increased rapidly from 58.78%to 91.42%while that of NO increased slowly,when the voltage increased from 12 k V to 18 k V,the removal efficiency of NO increased from 12.25%to 51.20%while that of SO₂increased less than 5.0%.When the discharge voltage was 18 k V,the flue gas flow rate increased from 0.5 L/min to 0.9 L/min,the removal efficiency of SO₂decreased with a declining value of 5.11%,while that of NO decreased with a decline of 13.52%.（3）Among the factors of inlet concentration discharge voltage and flue gas flow rate,discharge voltage had the most significant effect on removal efficiency,followed by inlet concentration.The interaction between discharge voltage and flue gas flow,and the interaction of discharge voltage and inlet concentration,had significant effects on removal efficiency when discharge voltage was high.The experimental values of NO removal efficiency and mass transfer coefficient were 53.07%and 0.043 m/min were consistent with the predicted values by Response Surface Methodology.（4）Oxygen can improve the removal efficiency of NO and SO₂on discharge conditions.To compare with SO₂,O₂promoted the removal efficiency of NO more obviously.When the discharge voltage was 18 k V,the oxygen content in flue gas increased from 0 to 4.9%,the removal efficiency of NO improved by 8.13%,while the removal efficiency of SO₂increased by 2.57%.（5）These negative ions cluster which SO₂/NO capture electrons would move to the liquid interface and dissolve in aqueous solution owing to the synergy effect of diffusion and electric field force.The reaction orders of SO₂/NO forming negative ions cluster were approximately level 1.At room temperature,the migration rate of the negative ions was 39 times that of diffusion,and the driving force of absorption main controlled by electric field force,the total mass transfer coefficient can be expressed as K_G=-Q/Aln（1-η）.（6）SO₂/NO can react with KMnO₄/NaClO₂rapidly under alkali conditions.The absorption reactions of SO₂/NO with Na Cl O₂and SO₂with KMn O₄/Na Cl O₂are more thorough than those with KMn O₄and NO.The proportion of SO₄^2-and NO₃^-in solution raised continuously with the increase of discharge voltage.更多还原