Emission Features of Several Trace Elements in Pulverized Coal Boiler

摘要

The contents of eight trace elements ( Mn, Cr, Pb, As, Se, Zn, Cd, Hg) in raw coal, bottom ash and fly ash were measured quantitatively in a 220t/h pulverized coal boiler. Factors affecting emission features of trace elements were investigated, including fly ash diameter, furnace temperature, oxygen content and trace elements' characteristics. Modified enrichment factors show more directly element enrichment in combustion products. The studied elements may be classified into three groups according to their emission features: Group l:Hg, which is very volatile. Group 2: Pb, Zn, Cd, which are partially volatile. Group 3: Mn, which is hardly volatile. Se may be located between groups 1 and 2. Cr has properties of both Group 1 and 3 depending on how the metal occurs in the coal. The smaller the diameter of fly ash, the higher the relative enrichment of trace elements (except Mn). Fly ash shows different adsorption mechanisms of trace elements and the volatilization of some trace elements rises with furnace temperature. Relative enrichments of trace elements (except Mn and Cr) in fly ash are larger than that in bottom ash. Low oxygen content will not always improve the volatilization of trace elements. Pb forms chloride more easily than Cd during coal combustion.