【作者】 任雯；

【导师】 陈昌和；

【作者基本信息】 清华大学 ， 动力工程及工程热物理， 2010， 博士

【摘要】 传统的V₂O₅-WO₃/TiO₂脱硝催化剂存在成本较高、钒毒性大、后处理易二次污染等问题。本工作旨在研究铁基脱硝催化剂,以达到在保证高脱硝率的同时降低成本的目的。在综合分析各种脱硝方法的基础上,提出采用FeSO₄制备脱硝催化剂脱除氮氧化物的思路。本文通过固定床实验系统,测试了模拟烟气工况下FeSO₄催化剂的活性和耐久性。实验表明,使用浸渍法制备的催化剂中FeSO₄-NaY和FeSO₄-ZSM-5的脱硝效果最好,脱硝率相比纯FeSO₄可提高20³5%。使用最优制备方法所制备的催化剂最佳脱硝温度由440°C降至340°C,有效温度窗口更宽,模拟烟气中的SO₂和H2O对催化剂性能无明显影响。本文采用穆斯堡尔谱、XPS、XRD和原位红外等方法研究了FeSO₄催化剂脱硝机理,发现所制备催化剂中主要存在形式为FeSO₄、Fe（OH）SO₄与Fe2O（SO₄）的混合物,其具体比例与担载体和制备条件有关,参加脱硝反应后使得硫酸亚铁和分子筛之间的结合更紧密,但仍然以这三种存在形式为主,同时,Fe离子和载体上的Al产生了键合并存在少量的Fe2O₃,Fe（OH）SO₄的催化效果优于Fe2O（SO₄）。硫酸亚铁及FeSO₄-NaY催化剂仅吸附氨产生了NH4+和NH3的谱峰,推测应该遵循Eley-Rideal机理。FeSO₄-ZSM-5催化剂对氨和NO都产生了较强的吸附作用,且其载体本身也具有催化效果,反应机理可能发生了较大变化。反应气体在硫酸亚铁提供的SO₄2-及分子筛提供的羟基处吸附产生了相应负峰,铁离子为氨和氮氧化物的氧化还原反应提供了活性位。本文使用浸渍法制备了硫酸亚铁堇青石蜂窝体催化剂模块,并研究了该方法的最佳制备工艺。分子筛具有良好的比表面,提高了FeSO₄本身的脱硝催化性能,扩大了其有效温度窗口。分子筛担载物涂覆在堇青石陶瓷蜂窝体上增加了FeSO₄催化剂的物理硬度,使得其工业化应用成为可能。通过小型燃煤锅炉系统,对不同工况下优化工艺制得的催化剂模块的活性及耐久性进行了测试,表明在NH₃/NO_x=1和SV=10000/h的条件下,催化剂模块在280³80°C温度区间内的脱硝效率均在80%以上,在320°C时达到95%左右的最高值,并能适应一定程度的工况波动,200h长期运行后催化效果没有明显下降,为工业应用奠定了坚实基础。经济性分析表明,与现有商用催化剂相比,硫酸亚铁原料的来源广泛、价格低廉且无毒性,在初次安装、设备改造维护、催化剂更换以及乏催化剂后处理等方面均具有明显的优势。本文最后还对做制备催化剂模块的工业化应用做了尝试性实验。更多还原

【Abstract】 The conventional V₂O₅-WO₃/TiO₂ SCR catalyst is expensive, complicated to use and may cause secondary pollution to environment after employment. The aim of this research is to develope Fe-based catalyst to reduce the cost of NOx emission control without compromising NOx removal efficiency. After comparing the existing research, the idea of using FeSO₄ as the SCR catalyst to remove NOx in flue gas has been proposed.The activities and endurances of FeSO₄ under simulated flue gas conditions were first tested in a bench-scale fixed-bed reactor system. The experimental results suggested that FeSO₄-NaY and FeSO₄-ZSM-5 prepared by impregnation method performed well in NOx removal. The NOx removal rates of the prepared catalyst were 20– 35% higher than those of pure FeSO₄, The effective temperature window was largely expanded with the best performance temperature shifted from 440°C to 340°C. SO₂ and H2O in flue gas had no obvious effect on catalyst performance.M?ssbauer spectrometry, XPS and in-situ infrared spectra analysis had been employed to investigate the catalytic mechanism of FeSO₄. It had been found that FeSO₄, Fe（OH）SO₄ and Fe2O（SO₄） were the major components existing in prepared catalyst, with their portions related to carrier type and preparing condition. FeSO₄ combined tighter with the carrier after de-NOx reaction. Fe2O₃ and the chemical bond between Fe and Al had been found. Fe（OH）SO₄ was better than that of Fe2O（SO₄）. NH₃ absorbed on FeSO₄-NaY generated the spectra of NH4+ and NH₃, suggesting the Eley-Rideal mechanism. FeSO₄-ZSM-5 absorbed both NH₃ and NO, and the carrier （ZSM-5） itself demonstrated catalytic effect, indicating a different reaction mechanism. SO₄2- from FeSO₄ and the hydroxy from carrier jointly enhanced reaction gas adsorption. Fe provided the active sites for reaction between NH₃ and NO.The preparation of FeSO₄ catalyst module had been attempted by optimized impregnation method. FeSO₄ had been first impregnated on molecular sieve, and then coated on cordierite honeycomb. The effective surface and physical strength of the catalyst had been significantly improved and therefore the industrial application had been enabled. The prepared catalyst module had been tested in a small-scale coal-firing boiler system to verify its reactivity and endurance. The results revealed that, under the condition of NH₃/NO_x=1 and SV=10000/h, the NOx removal rate was above 80% for the temperature range of 280 - 380°C, in spite of flue gas fluctuation. The best NOx removal rate of 95% was achieved under 320°C. No obvious performance lost had been found after 200h continuous test. This preliminary test had proved catalyst’s potential for industrial application.The techno-economic analysis suggested that, comparing with the existing commercial catalysts, FeSO₄ had distinctive advantage in large resource, low installaltion and operation cost, and little attention in aftertreatment. In the last part of the thesis, the preparation methods for industrial catalyst module was attempted.更多还原