燃煤锅炉SCR脱硝过程对颗粒物和痕量元素的影响

Effects of SCR De NO_x on the PM and trace elements

选择性催化还原(SCR)技术广泛被应用于燃煤电厂NOx减排,而SCR脱硝技术对颗粒物(PM)的影响尚不清楚。在两台300 MW煤粉锅炉机组SCR反应器的入口和出口进行了颗粒物现场采样,分析了SCR脱硝过程对PM的质量粒径分布和痕量元素含量的影响。研究结果显示,SCR脱硝过程产生NH+4,SO2+4等组分并部分转化为颗粒物,促使0.1μm以下颗粒物团聚、长大,导致0.3μm以下颗粒物的峰值粒径由0.1μm增大到0.3μm,同时使S含量显著升高,最终导致0.3μm以下颗粒物浓度升高约30.67%。烟气中部分0.3μm以上颗粒物在SCR反应器中受惯性碰撞作用而分离,使其浓度降低0.06%~33.11%,但峰值粒径和组成成分不变。SCR反应器入口烟气中的气态痕量元素在脱硝过程中向颗粒物转移,引起PM中痕量元素含量变化。实验条件下,经过SCR反应器后,0.3μm以下颗粒物中Cd,As,Pb含量分别升高104.15%,12.26%和12.18%,而Cr含量降低23.38%;0.3μm以上颗粒物中各痕量元素含量均略有升高。

Selective Catalytic Reduction (SCR) technology has been widely used in coal-fired power plants to control the NOxemission. However, its effects on the PMs are not clear yet. In this study, the sampling of the PMs at the inlet and outlet of SCR DeNOxreactors installed at two 300 MW pulverized coal-fired boiler units was conducted to analyze the effects of the NH3-sprayed SCR DeNOxon the PM and trace element characteristics. The results show that the species like NH4+and SO42+form during the SCR process migrate into the PMs and enhance the coagulation and growth of PMs less than 0.1 μm. This progress increases the yield of fine PM by 30.67% and shifts the modal peak size from 0.1 μm to 0.3 μm. The size of PMs larger than 0.3 μm is not changed significantly, but its yield is reduced by 0.06%-33.11% due to the impaction and separation in the SCR reactor. Parts of the gaseous trace elements entering the SCR are migrated into the PMs, which causes the content variation of the trace elements in the PMs combining with the yield variation of the PMs. In the study, the contents of As, Cd, Pb in the PMs less than 0.3 μm after the SCR reactor are increased by 104.15%, 12.26% and 12.18% respectively while the content of Cr is reduced by 23.38%. Additionally, the contents of the above trace elements in the PMs larger than 0.3 μm are increased slightly after the SCR process as well. © 2015, China Coal Society. All right reserved.