汞在燃煤固态产物中的富集规律及其影响因素

Enrichment Characteristics of Mercury in Solid Products of Coal-Fired Power Plants and Influencing Factors

选取6个燃煤电厂对燃煤固态产物进行取样.使用DMA80全自动测汞仪分析固态产物的汞含量,并进一步得到了汞在燃煤固态产物中的富集因子.实验还对固态产物的未燃尽碳含量进行了测定.结果表明,汞在煤粉炉固态产物中有亏损的趋势,而流化床锅炉属低温燃烧,飞灰具有高含碳量和发达的孔隙结构,所以汞在灰中有富集的趋势.随着取样点接近烟道下游,温度降低,汞的富集因子增大,明显带有物理吸附的特征.烟气中汞在尾部烟道内的转化过程受动力学因素的限制.飞灰残碳的含量和反应活性是汞吸附的最主要影响因素,静电除尘器中第三电场灰的汞富集因子最高,具有高含碳量的一电场灰由于残碳反应活性的降低而未表现出更强的汞吸附能力.随着锅炉容量和机组负荷的增大,飞灰中汞的富集因子减小.

The solid products of six coal-fired power plants in China were taken.The mercury contents in the solid products were obtained based on the analyzing instrument DMA80,and the mercury enrichment coefficients were then calculated.By analyzing the mercury enrichment coefficients combined with the unburned carbon content（UBC）in fly ash,combustion manners,boiler capacity and unit output,the enrichment characteristics of mercury in solid products and the influencing factors were obtained.The mercury enrichment coefficients in solid products from pulverized coal boilers are less than 1,which means mercury in them is deficient.In circulated fluidized combustion boiler,the fly ash has higher UBC and is porous because of low combustion temperature,and the mercury enrichment coefficients in solid products are greater than 1,which means mercury in them is enriched.The results show that when the sampling point approaches the backward position,the temperature of flue gas drops gradually,and the enrichment coefficient of mercury in fly ash increases,which indicates the characteristic of physical adsorption.The content and reactivity of unburned carbon in fly ash are the main factors influencing mercury enrichment coefficient.The mercury enrichment coefficient at the ash of the third ESP stage is the highest,and the first stage doesn’t show higher adsorption activity although the UBC is the highest in some cases because of low reactivity of carbon in the ash.The mercury enrichment coefficient decreases with the increase of boiler capacity and unit output.