SCR脱硝过程中细颗粒物排放特性

Characteristics of fine particulates emission from SCR reactor

为了减少选择性催化还原(SCR)脱硝过程中细颗粒物的形成,针对商用V_2O_5-WO_3/TiO_2脱硝催化剂,采用电称低压冲击器(ELPI)、PM_(10)/PM_(2.5)采样器、X线衍射(XRD)、高分辨率扫描电镜和能谱仪的联用技术(HRSEM/EDX)等对SCR脱硝反应器出口烟气中细颗粒粒径分布、形貌、元素及物相组成等进行测试分析。研究结果表明:SCR脱硝系统出口细颗粒物主要为亚微米级(dp<1μm)硫酸铵、硫酸氢铵,同时存在少量硅铝质颗粒;反应温度、NH_3与NO的摩尔比(n(NH_3)/n(NO))、SO_2质量浓度、水蒸气体积分数增加时,细颗粒形成量与SO_2氧化率之间存在显著的关联性,主要因为SO_2氧化成SO_3后,继而与NH_3和H_2O生成硫酸铵、硫酸氢铵细颗粒;O_2体积分数增加促使硅铝质颗粒的形成,但这些硅铝质颗粒物的生成与SO_2氧化量无关,因此O_2体积分数增加时,细颗粒形成量与SO_2氧化率之间相关性略差。降低SO_2的氧化率有助于降低亚微米级硫酸铵、硫酸氢铵细颗粒;控制O_2体积分数有助于减少硅铝质颗粒。

In order to reduce the fine particulates emission from SCR reactor, a study was carried out to characterize the particle size, distribution, morphology, element compositions and chemical compositions of aerosols in the exhaust of a SCR-De NOx system with commercial WO3-V2O5/TiO2 catalysts using electrical low pressure impactor（ELPI）, PM（10）/PM（2.5） samplers, X-ray diffraction, and high resolution scanning electron microscopy/energy dispersive analysis system of X-ray（HRSEM/EDX）. The results show that the majority of fine particles（dp1 μm） are ammonium sulfate/bisulfate. The small amounts of alumino-silicate particles are detected at the same time. With the increase of temperature, molar ratio of NH3 to NO, and the volume fraction of H2 O and mass concentration of SO2, particle count all significantly contribute to the conversion between SO2 and SO3. The main reason might be the oxidation of SO2 to SO3 with NH3 which generated ammonium sulfate/bisulfate. Alumino-silicate particles yield is promoted by the increase of oxygen volume fraction, although they exerte no impact on SO2-SO3-conversion. So the concentration of particle count poorly correlates with SO2-SO3-conversion. The reduction of SO2 oxidation rate can help decrease the production of ammonium sulfate/bisulfate while less O2 can help decrease the production of alumino-silicate particles.