Effect of SCR on particulate matter emissions from a coal-fired boiler

doi:10.11949/j.issn.0438-1157.20180303

Abstract

Abstract:

Selective catalytic reduction (SCR) technology is usually used in coal combustion power plant to reduce NO_x emission. The effects of SCR DeNO_x on PM emission are still unclear. In this work, PM and fly ash before and after SCR was sampled. Particle size distribution (PSD) and chemical composition of PM was analyzed. Computer-controlled scanning electron microscope (CCSEM) was used to analyze the fly ash and obtain the composition distribution property of individual PM particles. The effect of SCR DeNO_x on PM emission characteristic and its mechanism was investigated. The results show that PM is bimodal distribution before and after SCR. After the flue gas flows through the SCR, PM_0.21 decreases 62%(mass) and PM_0.21-1 increases 19%(mass). The relative amount of SO₂ in PM₁ increases 6%(mass) and SiO₂ and Al₂O₃ decrease, while the variation of CaO is insignificant after SCR. The amount of PM_1-10 decreases 17%(mass) after SCR. Insignificant change of its chemical composition is observed after SCR. However, the chemical composition distribution of individual PM_1-10 particle becomes more homogeneous after SCR. It suggests that significant interaction between PM₁₀ has happened in or after SCR. Therefore, decrease of PM_1-10 after SCR is not only because of PM₁₀ deposition in the SCR, but also because of particle interaction.

Key words: coal combustion, particulate matter, particle size distribution, SCR, emission, CCSEM

摘要：

我国电厂多数采用选择性催化还原（SCR）脱硝技术降低电厂NO_x排放，目前关于电厂中SCR对颗粒物排放特性的影响研究十分匮乏。本研究对一热电联产锅炉SCR前后颗粒物和飞灰进行取样，分析颗粒物质量粒径分布以及化学成分。采用计算机控制扫描电镜（CCSEM）对飞灰进行分析，获得颗粒物单颗粒成分。结果表明SCR前后PM₁₀均呈双峰分布。经过SCR后，PM_0.21浓度降低约62%（质量），而PM_0.21-1浓度升高19%（质量）；PM₁中SO₂相对含量增加约6%（质量），SiO₂和Al₂O₃相对含量降低，而CaO相对含量没有明显变化；经过SCR后，PM_1-10浓度降低约17%（质量），成分基本没有变化，但是颗粒成分变得更均一，说明经过SCR后，PM_1-10发生交互作用。因此经过SCR后PM_1-10浓度降低不仅由于颗粒物在SCR中发生沉积，更有可能是颗粒物之间交互作用导致。

关键词: 煤燃烧, 颗粒物, 粒度分布, 选择催化还原, 排放特性, CCSEM

CLC Number:

X513

LIU Fangqi, YU Dunxi, WU Jianqun, LEI Yu, WEN Chang, XU Minghou. Effect of SCR on particulate matter emissions from a coal-fired boiler[J]. CIESC Journal, 2018, 69(9): 4051-4057.

刘芳琪, 于敦喜, 吴建群, 雷煜, 温昶, 徐明厚. 燃煤锅炉SCR对颗粒物排放特性影响[J]. 化工学报, 2018, 69(9): 4051-4057.

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