Knowledge Management System Of Institute of process engineering,CAS
随着燃煤电力行业超低排放改造的实施，截至2019年底，燃煤机组的SCR脱硝装置安装率接近100%。SCR脱硝装置的大量加装，导致燃煤烟气中SO3浓度显著增加，引起有色烟羽，产生不良环境问题，腐蚀设备、堵塞空气预热器，对设备的运行产生不利影响，因此控制烟气中SO3排放具有非常重要的意义。准确检测SO3是控制SO3的前提，然而SO3性质活泼，比SO2浓度低约两个数量级，导致准确测量很困难，因此亟需探索SO3检测的影响因素，探寻降低测试误差的方法。目前，SO3的生成机制尚不明确，需要深入探索以期为源头削减SO3提供理论依据。另外，在SO3脱除工艺中碱性吸收剂的利用率较低，亟待探究工艺过程影响因素。论文主要研究内容和结论如下。（1）探究了异丙醇吸收法在线监测SO3的影响因素，发现SO3的测量误差主要来源于两方面。一方面来自仪器，包括蠕动泵管变形、气泡和氯冉酸钡泄露，这些误差可以通过调整优化仪器来消除；另一方面来自组分性质，包括采样气体流量的测量误差、IPA溶液的挥发损失、SO3的副反应和SO2氧化应，针对这四个误差来源分别提出了修正系数，建立了修正公式，用于修正SO3浓度。另外NH3对SO3检测的干扰很大，尽量选择在不含NH3的位点进行测试。测试仪器优化结合修正公式显著降低了SO3测量误差，在考查的10 ~ 40 ppm范围内将测量误差从25 ~ 54%减小到小于25%以内，在20 ppm以上时，误差降低到了5%以内。（2）探究了SO3在V2O5/TiO2催化剂表面生成的影响因素。获得了SO3生成的动力学参数，O2、SO2和SO3的表观反应级数分别为0、0.77和-0.19，表观活化能为74.3 kJ/mol。通过测试不同温度下的SO2转化量，SO3生成量和沉积硫酸盐量，阐明了不同温度下SO2氧化产物的赋存状态。270 oC以上氧化产物以气态SO3为主，270 oC以下氧化产物以沉积的NH4HSO4为主。随着温度升高，气态SO3和NH4HSO4的总平均反应速率先下降然后上升，最低点出现在250 ~ 270 °C附近。（3）揭示了V2O5/TiO2催化剂表面SO2氧化生成SO3的机理。气态SO2先通过载体表面的羟基化学吸附在载体表面，同时释放H2O，化学吸附态的SO2被V5+氧化三齿硫酸盐，同时V5+被还原成V3+，三齿硫酸盐分解脱附生成气态SO3，V3+在O2作用下转化为V5+。三齿硫酸盐是关键中间产物，在150 oC以上开始生成，在270 oC以上开始分解脱附生成气态SO3。探明了烟气复杂气氛对SO3生成的影响，NOx有明显的促进作用，源于NO2将V3+氧化为V5+；H2O有轻微抑制作用，NH3有强烈的抑制作用，源于它们与三齿硫酸盐结合生成了更稳定的二齿硫酸盐和硫铵盐。明确了低温下硫酸氢铵的形成有两条路径，先氧化后铵化和先铵化后氧化。（4）探索了Ca(OH)2、MgO和NaHCO3三种碱性吸收剂吸收SO3的影响因素。提出了不同吸收剂的使用温度窗口，Ca(OH)2在500 oC及以上的高温区使用，MgO在320 oC及以下的低温区使用，NaHCO3应避免在180 ~ 260 oC范围内使用。NaHCO3吸收SO3的过程符合缩核模型，而Ca(OH)2和MgO吸收SO3的过程符合颗粒模型。发现了Ca(OH)2和MgO的利用率较低的原因是致密的产物层阻碍了SO3向未反应核心的扩散。;With the implementation of ultra-low emission retrofits in the coal-fired power industry, as of the end of 2019, the installation rate of SCR denitration devices for coal-fired units was close to 100%. The large-scale installation of SCR denitration devices has resulted in a significant increase in the concentration of SO3 in coal-fired flue gas. It causes adverse environmental problems, such as colored plumes. In addition, it adversely affect the operation of the equipment, such as corrosion of the equipment and blockage of the air preheater. Therefore, the control of SO3 in flue gas is very important. The accurate detection of SO3 is the premise of SO3 control. However, SO3 has a lively nature and about two orders of magnitude lower than the SO2 concentration, making accurate measurement difficult. Therefore, it is necessary to explore the influencing factors of SO3 detection and find ways to reduce test errors. At present, the generation mechanism of SO3 is not clear, and in-depth exploration is needed to provide a theoretical basis for reducing SO3 at the source. In addition, due to the low utilization rate of alkaline absorbents in the SO3 removal process, it is urgent to explore the influencing factors of the alkaline absorbents' absorption of SO3 in order to guide the process optimization. The main research contents and conclusions of the paper are as follows.(1) The influencing factors of the online monitoring of SO3 by the isopropanol absorption method were investigated. The measurement error of SO3 mainly comes from two aspects. On the one hand, several measurement errors of SO3 come from the instrument, including the deformation of the peristaltic pump tube, bubbles and leakage of BaC6O4Cl2, which can be eliminated by adjusting and optimizing the instrument. On the other hand, several measurement errors of SO3 come from the nature of the components, including sampling gas flow error, IPA solution volatility loss, SO3 side reaction and SO2 oxidation. Correction coefficients were proposed for these four sources of error, and a correction formula was established to correct the SO3 concentration. In addition, NH3 interferes greatly with the detection of SO3, so try to choose the location without NH3 for testing. Test instrument optimization combined with correction formula significantly reduces SO3 measurement error. The measurement error is reduced from 25 to 54% to less than 25% within the range of 10 to 40 ppm, and the error is reduced to less than 5% when it exceeds 20 ppm.(2) The factors influencing the generation of SO3 on the surface of V2O5/TiO2 catalyst were investigated, and the kinetic parameters of SO3 generation were obtained. The apparent reaction order of O2, SO2 and SO3 are 0, 0.77 and -0.19, respectively. And the apparent activation energy is 74.3 kJ/mol. By testing the amount of SO2 conversion, the amount of SO3 produced and the amount of sulfate deposited at different temperatures, the existential forms of SO2 oxidation products at different temperatures was clarified. Above 270 oC, the main product is gaseous SO3; below 270 oC, the main product is deposited NH4HSO4. As the temperature rises, the total reaction rate of gaseous SO3 and NH4HSO4 first decreases and then increases, and the lowest point occurs near 250 ~ 270 °C.(3) The mechanism of SO2 oxidation to SO3 over the surface of V2O5/TiO2 catalyst is revealed. Firstly, gaseous SO2 is chemically adsorbed on the surface of the carrier through the hydroxyl groups, and H2O is released at the same time. Secondly, the chemically adsorbed SO2 is oxidized by V5+ to tridentate sulfate, while V5+ is reduced to V3+. Finally, the tridentate sulfate decomposes to form gaseous SO3, and the l V3+ is converted into V5+ under the action of O2. Tridentate sulfate is a key intermediate product, which begins to form above 150 oC and begins to decompose and desorb to form gaseous SO3 above 270 oC. NOx obviously promotes the generation of SO3, which originates from the oxidation of V3+ to V5+ by NO2. H2O has a slight inhibition effect, and NH3 has a strong inhibition effect. The promotion effect of NOx comes from the oxidation of low-valent vanadium to high-valent vanadium by NO2. H2O slightly inhibits the generation of SO3, and NH3 strongly inhibits the generation of SO3. The inhibitory effect comes from their combination with tridentate sulfate to form more stable bidentate sulfate and ammonium sulfate. It is proved that there are two paths for the formation of ammonium bisulfate at low temperature. Oxidation followed by ammonification and oxidation followed by ammonification.(4) Finally, the factors affecting the absorption of SO3 by three basic absorbents Ca(OH)2, MgO and NaHCO3 were investigated. The temperature windows for different absorbents is proposed. Ca(OH)2 should be used in the high temperature region of 500 oC and above. MgO should be used in the low temperature region of 320 oC and below. And avoid using NaHCO3 in the range of 180 ~ 260 oC. The process of NaHCO3 absorbing SO3 conforms to the shrinking core model, while the process of Ca(OH)2 and MgO absorbing SO3 conforms to the grain model. It was found that the reason for the low utilization rate of Ca(OH)2 and MgO is that the diffusion of SO3 to the unreacted core is hinded by their dense product layers.
|熊劲. 燃煤电厂SCR脱硝过程中SO3的生成、检测及控制基础研究[D]. 中国科学院大学,2020.|
|Files in This Item:|
|燃煤电厂SCR脱硝过程中SO3的生成、检（4076KB）||学位论文||限制开放||CC BY-NC-SA||Application Full Text|
|Recommend this item|
|Export to Endnote|
|Similar articles in Google Scholar|
|Similar articles in Baidu academic|
|Similar articles in Bing Scholar|
Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.