基于火电烟尘控制的除汞技术研究

发布时间：2018-06-28 23:54

本文选题：燃煤电厂 + 汞排放　；参考：《南京师范大学》2014年硕士论文

【摘要】：汞污染控制是继燃煤电厂控制烟尘、SO2和NOX排放之后一个亟待解决的问题,本文依托环保部公益项目和国电集团重点科技项目,对火电厂烟尘颗粒对汞的吸附与氧化机理,除尘器对烟气中汞的脱除效果以及影响除尘器除汞的主要因素进行了相关研究,为燃煤汞控制技术的进一步发展打下基础。对15家燃煤电厂采集的煤、飞灰、炉渣及除尘器出口处烟气中汞浓度进行测试,并对电站各部分燃烧产物中汞分布情况及排放特性进行分析,结果表明：测试电站的燃煤平均汞含量为0.171mg/kg,炉渣中平均汞量为0.0538mg/kg,飞灰中平均汞含量为0.223mg/kg。汞的质量平衡在47.3%-106%之间,基本符合一般接受的70%-130%范围。燃煤电厂汞的各排放环节中底渣中汞含量很低,基本可以忽略；飞灰中汞含量约占汞排放的13%；除尘器出口烟气中HgP含量很低,可以忽略,除尘器出口烟气中汞仍占很大比例。基于固定床汞吸附机理实验系统,研究了燃煤电厂飞灰与汞的相互作用机理,从吸附动力学角度分析了汞在飞灰上的吸附过程,考察了烟气中O2、HCl对飞灰氧化烟气汞的影响,结果表明：1)飞灰吸附烟气中Hg0在初始阶段,呈现较快的吸附速率,该阶段Hg0吸附速率与表面吸附有关；随着吸附的进行,表面活性位逐渐被占据,Hg0需要扩散到飞灰内部孔隙中的活性位上发生吸附,吸附速率急剧下降,直至达到汞吸附平衡；2)吸附动力学研究表明,准二阶吸附动力学模型可以较好的预测Hg0在飞灰上的动态吸附过程,说明化学吸附是Hg0在飞灰上吸附过程的速率控制步骤；3)在N2气氛下,飞灰对汞有微弱的氧化作用,与飞灰表面存在大量氧化性官能团有关。O2对飞灰氧化汞有微弱的促进作用,HC1对飞灰氧化汞的促进作用明显。基于燃煤电厂实测数据研究了燃煤电厂除尘器除汞效果,考察了燃烧方式(煤粉炉、循环流化床锅炉)、除尘器的类型(静电除尘器、布袋除尘器)、飞灰中的残炭、选择性催化还原(SCR)脱硝装置对除尘器协同除汞效果的影响,结果表明：1)静电除尘器除汞效率平均为37.4%,与烟气中颗粒态汞含量关系明显；CFB+ESP机组的协同脱汞效率高于PC+ESP机组的除汞效率；袋式除尘器的协同除汞效率平均为50%,优于静电除尘器的协同除汞效率；2)飞灰残炭量对飞灰汞含量影响较为明显,煤中氯含量和硫含量与除尘器的协同除汞效率关系不明显；3)SCR反应器后烟气中飞灰汞含量有明显提高,SCR通过氧化烟气中Hg0为Hg2+,提高了飞灰对汞的吸附能力,提高了除尘器协同除汞的效果。
[Abstract]:Mercury pollution control is an urgent problem to be solved after coal-fired power plants control the emission of so _ 2 and no _ X. Based on the public welfare project of Ministry of Environmental Protection and the key scientific and technological projects of Guodian Group, the mechanism of adsorption and oxidation of mercury to dust particles in thermal power plants is discussed in this paper. The removal effect of mercury in flue gas and the main factors affecting the removal of mercury from flue gas were studied in order to lay a foundation for the further development of mercury control technology in coal combustion. The mercury concentration in the flue gas of coal, fly ash, slag and dust collector at the outlet of 15 coal-fired power plants was measured, and the distribution and emission characteristics of mercury in the combustion products of each part of the power plant were analyzed. The results show that the average mercury content in coal combustion is 0.171 mg / kg, the average mercury content in slag is 0.0538 mg / kg, and the average mercury content in fly ash is 0.223 mg / kg. The mass balance of mercury is between 47.3% and 106%, which basically conforms to the generally accepted range of 70%-130%. The mercury content in bottom slag of coal-fired power plant is very low, which can be neglected basically; the mercury content in fly ash accounts for about 13% of mercury emission; the HGP content in outlet flue gas of dust collector is very low, which can be ignored, and the mercury content in flue gas of dust collector outlet still accounts for a large proportion. Based on the experimental system of fixed-bed mercury adsorption mechanism, the interaction mechanism between fly ash and mercury in coal-fired power plants was studied. The adsorption process of mercury on fly ash was analyzed from the point of view of adsorption kinetics, and the effect of O _ 2H _ 2HCl in flue gas on the oxidation of mercury in fly ash was investigated. The results showed that the adsorption rate of Hg _ 0 in flue gas was faster at the initial stage, and the adsorption rate of Hg _ 0 was related to the surface adsorption. The surface active sites gradually occupied by Hg0 need to diffuse to the active sites in the pores of fly ash, and the adsorption rate decreases sharply until the mercury adsorption equilibrium is reached. The quasi-second-order adsorption kinetic model can predict the dynamic adsorption process of Hg _ 0 on fly ash, which indicates that chemical adsorption is the rate control step of Hg _ 0 adsorption on fly ash. (3) in N2 atmosphere, fly ash has weak oxidation of mercury. There are a lot of oxidizing functional groups on the surface of fly ash. O2 has a weak promoting effect on mercury oxide in fly ash. HC1 can promote mercury oxide in fly ash obviously. Based on the measured data of coal-fired power plant, the mercury removal effect of dust remover in coal-fired power plant was studied. The combustion mode (pulverized coal boiler, circulating fluidized bed boiler), the type of dust collector (electrostatic precipitator, bag dust collector), and the residual carbon in fly ash were investigated. The effect of selective catalytic reduction (SCR) denitrification device on the synergistic mercury removal efficiency of dust precipitator was investigated. The results showed that the average removal efficiency of mercury in electrostatic precipitator was 37.4, which was obviously related to the content of mercury particles in flue gas. The synergistic mercury removal efficiency of CFB ESP is higher than that of PC ESP, and the average efficiency of bag dust collector is 50, which is better than that of electrostatic precipitator. There is no obvious relationship between chlorine content and sulfur content in coal and synergistic mercury removal efficiency of precipitator. 3) Mercury content in fly ash in SCR reactor can obviously increase Hg content in flue gas by oxidation of Hg _ 0 to Hg _ 2, which improves the adsorption ability of fly ash to mercury. The synergistic mercury removal effect of dust collector is improved.
【学位授予单位】：南京师范大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：X773

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