【作者】 付银成；

【导师】 高翔； 方梦祥；

【作者基本信息】 浙江大学 ， 工程热物理， 2011， 硕士

【摘要】 以NH3为还原剂的选择性催化还原(SCR)烟气脱硝技术是目前应用最广最有效的燃煤烟气脱硝技术。作为SCR烟气脱硝技术的核心,SCR催化剂是影响整个SCR系统脱硝效率和经济性的决定因素。而中毒是SCR催化剂在实际应用过程中不可避免的问题,它与燃料特性密切相关。我国火电厂燃用煤种类复杂、多样,内含多种会导致催化剂中毒失活的组份。因此,研究我国典型燃煤中各种组份对SCR催化剂的中毒规律具有重要的实际意义。本文工作的主要研究思路是以钒钛SCR催化剂为研究对象,研究我国火电厂燃煤中检测出的几种典型毒物单独存在对催化剂的中毒规律以及多种组份同时存在对催化剂的复合中毒规律,并在此基础上对钒钛SCR进行改良,得到一种具有良好抗中毒性能的新型催化剂。研究得到主要结果如下：1.研究了相同含量下K、Na、Ca、Pb的氧化物和盐对钒钛催化剂NO转化率的影响。无论是以氧化物形式还是以盐的形式存在催化剂上,碱金属K对钒钛催化剂的钝化作用都是最强。K2O和Na2O的掺入会抑制钒钛催化剂上V205的还原能力,而CaO和PbO的掺入对钒钛催化剂上V205的还原能力没有影响或影响较小。当K或Na以氯盐的形态存在于催化剂上时,其对钒钛催化剂的钝化作用比以硫酸盐的形态存在于催化剂上时强很多。K2SO4和Na2SO4的掺入造成钒钛催化剂NO转化率下降的程度接近,这是因为SO42-对催化剂的影响占据了主导作用。2.研究了K、Na、Ca、Pb的四种氧化物以及三种氯盐两两同时存在对钒钛催化剂复合中毒规律。在中毒元素总量一定的情况下,K、Na、Ca、Pb四种氧化物两两同时存在时,两种组份之间的相互作用会弱化单组份对催化剂的钝化,其中Ca的氧化物对弱化K、Na、Pb氧化物钝化催化剂的作用最大。Ca、Pb氧化物组合中毒后的催化剂,400℃以上可以达到与新鲜钒钛催化剂相同的活性。与氧化物复合中毒规律不同的是,KCl、NaCl、CaCl2三种氯盐单组份或是两种组份对催化剂的钝化程度取决于KCl掺入的含量,掺入KCl越多,催化剂失活越严重。3.研究了单独添加不同含量的Nb氧化物和单独添加不同含量的Sb氧化物对钒钛催化剂NO转化率和反应中N2O生成量的影响。结果表明添加Nb可有效提高催化剂的活性和高温(350℃以上)选择性,拓宽催化剂温度窗口。Nb/V最佳原子比为6,在此含量以下,催化剂的活性随着Nb含量的增加而提高,超过此含量,催化剂活性开始下降。Sb的添加能有效提高催化剂的低温(350℃以下)活性,拓展催化剂低温窗口。但是随着Sb含量的增加,活性提高不明显,反而会增加高温下(350℃以上)N2O的生成,降低了催化剂的选择性,综合NO转化率和选择性考虑,Sb/V最佳原子比为0.5。4.创新性研究了同时添加Sb和Nb氧化物对钒钛催化剂活性和选择性的影响。结果表明在钒钛催化剂上同时添加Sb和Nb可以大幅度提高催化剂脱硝活性,同时还能保证催化剂在高温下的选择性,通过少量Sb和Nb的同时添加达到大量Nb添加的效果,有利于催化剂的经济性。利用XPS手段分析表明Sb和Nb的添加增加了催化剂表面的化学吸附氧和弱结合的氧物种,这应该是催化剂活性提高的原因之一。5.研究了几种典型中毒物质对改良得到的V-Sb-Nb/TiO2催化剂脱硝活性的影响。比较V2O5/TiO2催化剂和V-Sb-Nb/TiO2催化剂中毒后的脱硝活性发现,V-Sb-Nb/TiO2催化剂中毒后活性下降幅度远低于V2O5/TiO2催化剂中毒后活性下降幅度,且V-Sb-Nb/TiO2催化剂中毒后的脱硝活性仍高于新鲜V2O5/TiO2催化剂脱硝活性,表明V-Sb-Nb/TiO2催化剂具有良好的抗金属氧化物及盐中毒的能力。更多还原

【Abstract】 The selective catalytic reduction of NOx with NH3 as reductant is most efficient and widely technology for abating NOx emitted from stationary power stations at present. As the core of SCR technology, catalysts are the main factor affecting the NOx removal efficiency and economical efficiency of the whole SCR system. Poisoning is inevitable for SCR catalysts in the actual application process and relates with the fuel characteristics intimately. The burning coal in power plant of our country is complex and diverse, containing a variety of components which may lead to poisoning and deactivation of catalysts. Therefore, the study on the poisoning order of components containing in coal for SCR catalysts is important and meaningful.The key research point of the present work is taking V2O5/TiO2 SCR catalyst as research object, studying the single poisoning order as were as the compound poisoning order of some representative components detected in the burning coal of power plant in our country. The SCR catalyst was improved to be a novel catalyst with good resistance to poisoning. The main results are shown as following:1. The effect of K, Na, Ca, Pb oxides and salts on the NO conversion of V2O5/TiO2 catalyst was studied. The results show that potassium has the strongest poisoning effect on the catalysts among all four metals whatever in form of oxides or salts. K2O and Na2O may inhibit the reducing capability of V2O5 on the surface of V2O5/TiO2 catalyst, while CaO and PbO have little effect on the reducing capability of V2O5. The deactivation of V2O5/TiO2 catalyst by KCl and NaCl are much stronger than K2SO4and Na2SO4. The decreases of NO conversion for catalysts doped with K2SO4and Na2SO4 are approximate, which is according to the leading role of the effect of SO42- on catalysts.2. The compound poisoning order of K, Na, Ca, Pb oxides and chlorides on V2O5/TiO2 catalystwas investigated. When two kinds of oxides were doped on the catalysts simultaneously, the interaction between the two components will weaken the role of one component on catalyst deactivation, especially when CaO was doped. PbO has the same. The catalyst doped with CaO and PbO has the same activity as fresh V2O5/TiO2 catalyst above 400℃. Unlike the compound poisoning order of metal oxides, the deactivation level of catalysts by salts depends on the contents of KCl, higher KCl content leads stronger catalyst deactivation.3. The effect of the Sb and Nb additives on the V2O5/TiO2 catalyst for the selective catalytic reduction (SCR) of NO with NH3 was investigated. The experimental results show that Nb can improve the activity of V2O5/TiO2 catalyst. Higher Nb loading led to higher N2 selectivity at high temperature above 350℃. The optimal Nb loading is 6 (atomic ratio to V). Sb can improve the activity of V2O5/TiO2 catalyst at low below 350℃. Higher Sb loading cannot improve the activity but lead to more N2O generated from the reaction at high temperature above 350℃. As both of the catalyst activity and the value of N2 selectivity were considered, the optimal Sb loading is 0.5 (atomic ratio to V).4. The effect of simul-doping of Sb and Nb on the V2O5/TiO2 catalyst for the selective catalytic reduction (SCR) of NO with NH3 was investigated. The experimental results show that simul-doping of Sb and Nb can improve the activity of V2O5/TiO2 catalyst highly, while ensuring the N2 selectivity of the catalyst at high temperature above 350℃. The simul-doping of a bit of Sb and Nb can gain the same effectiveness as a lot of Nb was doped, which is conductive to the economical efficiency of catalyst. According to the means of XPS, the doping of Sb and Nb may increase the chemisorbed oxgen and weakly boned oxygen species on the surface of catalyst, which might be one of the reasons to improve the catalytic activity.5. The effect of some representative poisoning components on catalytic activity of V-Sb-Nb/TiO2 catalyst improved form V2O5/TiO2 catalyst was investigated. According to the comparison of V2O5/TiO2 catalyst and V-Sb-Nb/TiO2 catalyst, it can be seen that the decrease of catalytic activity for V-Sb-Nb/TiO2 catalyst doped with poisoning components is much lower than the decrease of catalytic activity for V2O5/TiO2 catalyst doped with poisoning components. The catalytic activity of V-Sb-Nb/TiO2 catalyst doped with poisoning components is still higher than the fresh V2O5/TiO2 catalyst. This means that the V-Sb-Nb/TiO2 catalyst has good anti-poisoning ability from metal oxides and salts.更多还原