某1000 MW超超临界燃煤机组尾部烟道硫酸铵盐沉积分析

Analysis on Ammonium Sulfate Deposition in Tail Flue of a 1000-MW Ultra-supercritical Coal-Fired Unit

超低排放技术可有效降低燃煤机组污染物排放,改善空气质量。为探究超低排放机组尾部烟道积灰、结垢问题的产生机理,以某1 000 MW超低排放机组引风机与二级低温省煤器的结垢灰样为研究对象,采用元素分析仪、X射线荧光光谱仪、X射线衍射仪和扫描电镜对灰样进行检测,详细分析并讨论了积灰样品中结晶矿物相的形成以及不同位置发生积灰的主要原因。结果表明:引风机与二级低温省煤器颗粒沉积位置的灰样主要由(NH_4)Al(SO_4)_2·12H_2O、(NH_4)_3H(SO_4)_2、CaSO_4、SiO_2等结晶矿物质构成;其中,(NH_4)Al(SO_4)_2覆盖于灰颗粒表面是造成引风机及二级低温省煤器严重结垢积灰的直接原因,而SCR脱硝系统较高浓度氨持续逃逸则是其根本原因。建议应根据煤种硫分、氨逃逸量、灰浓度等合理分配一、二级低温省煤器处的烟气温降,避免静电除尘器脱离低低温状态运行,防止二级低温省煤器处烟温降低幅度过大导致硫酸酸雾快速冷凝。

The ultra-low emission technology can effectively reduce pollutant emissions from coal-fired units and improve the air quality.In order to explore the mechanism of fouling in the tail flue of ultra-low emission units,this paper takes the fouling ash on the induced draft fan and the second stage low temperature economizer(LTE)of a 1000-MW unit with ultra-low emission as the research object.The ash samples are examined by using the elemental analyzer,the X-ray fluorescence spectrometer,the X-ray diffraction and the scanning electron microscopy.Then,the major factors contributing to the formation of the crystalline mineral phase of the ash and the ash deposition occurrence at different locations are analyzed and discussed in details.The results show that the ashes on the blades of the induced draft fan and the second stage LTE are mainly comprised of(NH4)Al(SO4)2·12H2O,(NH4)3H(SO4)2,CaSO4 and SiO2.Among them(NH4)3H(SO4)2 covering on the surface of the ash particles is the immediate cause of the severe ash deposition on the induced draft fan and LTE,while,the root cause is determined as the ammonia escape from the SCR.At last,this paper suggests that the temperature drop of the flue gas at the first and second stage economizers should be properly distributed considering the sulfur contents of the coal,the ammonia emissions and the ash concentrations,so as to prevent the ESP being operated out of low-low temperature conditions and avoid drastic flue gas temperature drop at the second stage LTE which may cause the rapid condensing of sulfuric acid mist.