硒元素在低热值电厂燃烧残余物中的分布与环境贡献

Distributions and environmental impacts of selenium on low-heating value power plant combustion residues

对煤泥、煤矸石低热值电厂的不同燃料、除尘器飞灰及渣中痕量元素硒进行研究。化学分析表明,硒在颗粒较粗的除尘器飞灰中亏损,而在细颗粒飞灰中显著富集.粗、细飞灰含硒量的差异与飞灰的颗粒大小和形态有关,细小飞灰中存在较大比例的蜂窝状结构,增加了比表面积,吸附能力显著提高.由于锅炉构造和燃烧特征不同,与煤粉炉相比,循环流化床锅炉底渣中硒的亏损更加强烈.通过物质平衡计算,燃烧后的硒近80%～90%存在于除尘器飞灰当中;6.60%～15.23%的硒随气流和烟气细飞灰直接排放入大气;渣中硒含量较低,对于环境的影响很小.脱硫剂石灰粉的使用,在燃烧过程中产生的CaO不仅吸收了SO2还可与高温产生的SeO2气体进行反应,将大部分硒捕获在除尘器飞灰中,降低了硒的挥发性.然而排放入大气的硒活性最高,随着电厂的运行,排放量亦将非常显著,应进一步加以控制.

Selenium in feed coal, fly ash and slag samples, collected from a low-heating power plant, was studied. Results show that Se tends to be enriched in tiny fly ash samples, but loses in coarse fly ash samples. The different distributions of Se in tiny and coarse fly ash samples are caused by the particle size and shape, the wide existence of honeycomb-like structures. The tiny size of fly ash could increases the adsorptive capacity by enhancing specific surface area of the tiny fly ash particles. Selenium tends to deplete much more intensively in the slag of the recirculating fluidized bed than in the coal-powder boiler slag due to the different constructions and combustion systems of the boiler. Mass balance calculation of feed coal indicates that 80~90~/4o of selenium in coal is distributed in the fly ash which is captured by the electrostatic precipitator, and 6.60% ~ 15.23% of the selenium may be released into the atmosphere directly or with the flue gas. The selenium in bottom ashes may cause little environmental impact because of its small proportion. In order to reduce the volatility of Se, the desulfurizing agent was used to produce the CaO to react with the gaseous SeO2 released by the high temperature and capture most of the Se in the fly ash. The amount of selenium released into the air could be very high over time, so further control is necessary for potential environmental risks.