燃煤烟气SCR脱硝对细颗粒物排放特性影响的试验研究

发布时间：2018-10-18 16:12

【摘要】：当前我国正面临严重的细颗粒物(PM2.5)污染,其中燃煤电厂是我国PM25的主要排放源。SCR脱硝对于PM25的生成和脱除以及化学组成都有可能产生影响,并引起燃煤电厂排放特征的改变,在我国燃煤电厂大规模安装SCR脱硝装置的背景下,研究脱硝对燃煤电厂PM2.5排放的影响具有重要意义。本文利用自主设计搭建的SCR脱硝模拟试验装置,基于V2O5-WO3/TiO2商用催化剂,采用电称低压冲击器(ELPI)、PM10/PM2.5采样器、X射线衍射(XRD)、场发射扫描电镜-能谱分析(FSEM-EDX)等分析测试仪器,首先考察了SCR脱硝系统对细颗粒排放浓度及粒度分布的影响,并对SCR烟气脱硝中形成的细颗粒形貌、元素及物相组成进行了测试分析。结果表明,SCR脱硝过程中会形成大量颗粒物,其数量浓度约1x106个/cm3,质量浓度约数十mg/m3,从数浓度角度,形成的颗粒物主要属于亚微米级微粒,但从质量浓度角度,则以微米级及大于10微米的颗粒物为主。颗粒物的主要成分为硫酸氢铵以及少量硫酸铵。在此基础上,通过调节脱硝操作参数和模拟烟气中气体组分含量,试验考察了SCR脱硝工艺参数和烟气组分对SCR脱硝过程中细颗粒形成的影响,分析了细颗粒物形成与SCR脱硝中SO2氧化的关系。结果表明,细颗粒生成量随反应温度的升高和NH3/NO摩尔比的增加而增加,在脱硝效率较高时,颗粒物形成量也趋于增多；烟气中H20和Oz浓度的增加均会导致细颗粒物形成量的增加；细颗粒物数浓度的变化趋势与SO2氧化为SO3的变化趋势呈现出良好的相关一致性。细颗粒物产生及物性发生变化的主要原因可归结于：一是在SCR脱硝反应器中S03与NH3、H20反应生成硫酸铵、硫酸氢铵细颗粒,该反应为与SCR脱硝同时进行的可逆过程,一部分以可凝结细颗粒形式带出SCR脱硝系统,其余在催化剂表面沉积,导致催化剂失活；二是SO3与逃逸的NH3、H20在SCR脱硝装置后续系统(如空预器)等装置时发生反应形成硫酸铵、硫酸氢铵细颗粒；三是烟气中游离碱土金属氧化物(如CaO等)通过与SO3的反应改变颗粒物的物性。最后,在自行设计搭建的燃煤热态SCR脱硝试验装置中,利用商用蜂窝状钒钨钛催化剂,试验考察了SCR脱硝反应前后细颗粒物的物性变化。结果表明：在实际燃煤烟气环境下,SCR脱硝反应同样会加重细颗粒物的排放,细颗粒物的生成量随着氨氮摩尔比和SO2浓度的增加而提高；同时研究还发现,SCR脱硝过程中形成的亚微米级细颗粒难以被后续电除尘及湿法脱硫工艺有效捕集,从而导致WFGD系统出口细颗粒物浓度的增加。
[Abstract]:At present, China is facing serious fine particulate matter (PM2.5) pollution, of which coal-fired power plant is the main emission source of PM25 in China. SCR denitrification may have an impact on the formation and removal of PM25 and chemical composition, and cause the change of emission characteristics of coal-fired power plant. Under the background of large-scale installation of SCR denitrification unit in coal-fired power plants in China, it is of great significance to study the effect of denitrification on PM2.5 emissions from coal-fired power plants. In this paper, the SCR denitrification simulation test device is designed and built. Based on the commercial catalyst of V2O5-WO3/TiO2, the (ELPI), PM10/PM2.5 sampler of low pressure impactor, the scanning electron microscopy (FSEM-EDX) of X-ray diffraction (XRD), field emission and energy dispersive analysis (FSEM-EDX) are used in this paper. The effects of SCR denitrification system on the concentration and particle size distribution of fine particles were investigated, and the morphology, element and phase composition of fine particles formed in SCR flue gas denitrification were analyzed. The results showed that a large number of particles were formed in the process of denitrification with SCR. The mass concentration of 1x106 / cm3, was about tens of mg/m3,. From the angle of number and concentration, the particles formed mainly belonged to submicron particles, but from the angle of mass concentration. Micron and more than 10 micron particles are the main. The main components of particulate matter are ammonium hydrogen sulfate and a small amount of ammonium sulfate. On this basis, the effects of SCR denitrification process parameters and flue gas components on the formation of fine particles in the denitrification process of SCR were investigated by adjusting the operation parameters of denitrification and simulating the gas component content in flue gas. The relationship between the formation of fine particles and SO2 oxidation in SCR denitrification was analyzed. The results showed that the yield of fine particles increased with the increase of reaction temperature and the molar ratio of NH3/NO. When the denitrification efficiency was high, the amount of particles formed tended to increase. The increase of H20 and Oz concentration in flue gas would lead to the increase of fine particulate matter formation, and there was a good correlation between the change trend of fine particle number concentration and the trend of SO2 oxidation to SO3. The main reasons for the formation of fine particles and the change of physical properties can be attributed to the following: first, in SCR denitrification reactor, S03 reacts with NH3,H20 to form ammonium sulfate and ammonium hydrogen sulfate fine particles, which is a reversible process in parallel with SCR denitrification. A portion of the SCR denitrification system was carried out in the form of condensable fine particles, while the rest was deposited on the surface of the catalyst, which resulted in the deactivation of the catalyst. Second, the SO3 reacted with the escaping NH3,H20 in the SCR denitration unit follow-up system (such as an air preheater) to form ammonium sulfate. Third, free alkaline earth metal oxides (such as CaO) in flue gas changed the physical properties of particles by reacting with SO3. Finally, the physical properties of fine particles before and after SCR denitrification were investigated using commercial honeycomb vanadium tungsten titanium catalyst in a self-designed SCR denitrification test facility. The results showed that the denitrification reaction of SCR would also increase the emission of fine particles in the actual coal-fired flue gas environment, and the amount of fine particles would increase with the increase of the molar ratio of ammonia to nitrogen and the concentration of SO2. At the same time, it is found that the submicron fine particles formed in the process of SCR denitrification are difficult to be effectively captured by the subsequent electrodedusting and wet desulphurization process, resulting in the increase of the concentration of fine particles at the outlet of the WFGD system.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X773

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