SCR催化剂催化氧化单质汞实验研究

发布时间：2018-05-10 10:37

本文选题：燃煤 + 脱汞　；参考：《华北电力大学》2015年硕士论文

【摘要】：燃煤汞污染是继粉尘、NO_x和SO_2后又一备受关注的大气污染物。目前并没有一种应用成熟的燃煤烟气脱汞技术,在各种燃煤烟气汞污染控制技术中,利用现有空气污染物控制装置实现汞的联合脱除是一种经济有效的方法。汞在烟气有3种不同形态(Hg~0、Hg~(2+)、Hg~P),现有空气污染物控制装置脱汞效率受烟气中汞的形态影响很大。大多数的Hg~P能随着飞灰被电除尘器(ESP)和布袋除尘器捕获;二价汞离子具有较好的水溶性,能够被湿法脱硫装置捕集;Hg~0由于其在低温下的弱氧化活性以及在高温下较高的热力学稳定性,Hg~0很难被现有的空气污染控制装置去除。因此降低其单质汞的比例,使烟气中的单质汞尽可能的氧化成易溶于水的二价汞离子,是利用现有污染物控制装置脱汞技术的关键所在。SCR催化剂具有将单质汞氧化成二价汞离子的能力,但受烟气成分等因素的影响,传统SCR催化剂氧化单质汞的效率不高。研究SCR催化剂对单质汞的催化氧化特性,强化其对单质汞的催化氧化效率,将很好的解决燃煤电厂汞污染控制问题。本文首先在自建的SCR催化剂催化氧化单质汞实验台上,对传统SCR催化剂催化氧化单质汞的特性进行了实验研究,研究了反应温度、氨氮比和SO_2含量等因素对传统SCR催化剂对单质汞催化氧化的影响。实验结果表明,在一定程度上升高温度能够促进单质汞的氧化,但是温度过高会降低单质汞的转化率;喷氨量的增加会明显抑制单质汞的氧化,在氨氮比为1.5时,反应装置出口Hg~(2+）浓度几乎为零;较高浓度的SO_2条件下,单质汞的氧化效率略有提高,但是效果并不明显。在上述实验的基础上,本文采用浸渍法对传统SCR催化剂进行改性,并对改性SCR催化剂对单质汞的催化氧化效果进行了实验研究,研究了改性SCR催化剂在不同温度,不同SO_2、NH_3等气体含量的条件下对单质汞的催化氧化规律,并与传统SCR催化剂进行了对比。实验结果表明,在不同温度条件下两种改性SCR催化剂比传统SCR催化剂对单质汞的氧化效率均有明显的提升,氧化效率均在90%以上,温度窗口较宽;改性SCR催化剂对单质汞的氧化效率受喷氨量的影响不大,较传统SCR催化剂有明显的提升,氧化效率均在90%以上;在不同浓度的SO_2条件下,改性SCR催化剂氧化单质汞的效率均能保持在90%左右,研究结果为燃煤电厂利用现有空气污染控制装置同时脱汞提供了理论基础。
[Abstract]:Mercury pollution from coal combustion is one of the most concerned air pollutants after dust nox and SO_2. At present, there is no mature technology for mercury removal from coal-fired flue gas. Among all kinds of mercury pollution control technologies in coal-fired flue gas, it is an economical and effective method to realize mercury removal by using existing air pollutant control devices. There are three different forms of mercury in the flue gas. The mercury removal efficiency of the existing air pollutant control devices is greatly affected by the mercury species in the flue gas. Most of the Hg~P can be captured with the fly ash by the ESP) and the bag dust collector, and the divalent mercury ions have good water solubility. Because of its weak oxidation activity at low temperature and high thermodynamic stability at high temperature, it is difficult to remove HgC0 from the existing air pollution control devices. Thus reducing the proportion of its elemental mercury, so that the elemental mercury in the flue gas is oxidized as much as possible into water-soluble divalent mercury ions, SCR catalyst has the ability to oxidize elemental mercury to divalent mercury ion, but the traditional SCR catalyst is not efficient in the oxidation of elemental mercury due to the influence of flue gas composition and other factors. The study on the catalytic oxidation characteristics of SCR catalyst for elemental mercury and the enhancement of its catalytic oxidation efficiency will solve the problem of mercury pollution control in coal-fired power plants. In this paper, the catalytic oxidation of elemental mercury with SCR catalyst was studied on a self-built experimental bench, and the reaction temperature was studied. Effects of NH _ 3-N ratio and SO_2 content on the Catalytic Oxidation of Mercury over conventional SCR Catalysts. The experimental results show that increasing temperature can promote the oxidation of elemental mercury to some extent, but too high temperature will reduce the conversion rate of elemental mercury, and the increase of ammonia injection will obviously inhibit the oxidation of elemental mercury, when the ratio of ammonia to nitrogen is 1.5, The concentration of Hg~(2 at the outlet of the reactor was almost zero, and the oxidation efficiency of elemental mercury was slightly improved under the condition of higher SO_2 concentration, but the effect was not obvious. On the basis of the above experiments, the traditional SCR catalyst was modified by impregnation method, and the catalytic oxidation effect of modified SCR catalyst on elemental mercury was studied experimentally, and the modified SCR catalyst at different temperatures was studied. The catalytic oxidation of mercury was studied under the conditions of different contents of so _ 2H _ 3 and NH _ 3, and the results were compared with those of traditional SCR catalysts. The experimental results show that the oxidation efficiency of the two modified SCR catalysts is obviously higher than that of the traditional SCR catalyst at different temperature, the oxidation efficiency is above 90%, and the temperature window is wide. The modified SCR catalyst has little effect on the oxidation efficiency of elemental mercury by ammonia injection, and the oxidation efficiency of the modified SCR catalyst is above 90% compared with that of the traditional SCR catalyst, and the oxidation efficiency of the modified SCR catalyst is above 90% under the conditions of different concentration of SO_2. The efficiency of oxidation of elemental mercury by modified SCR catalyst is about 90%. The results provide a theoretical basis for simultaneous mercury removal by using existing air pollution control devices in coal-fired power plants.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X701;X773

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