Research On The Content,Occurrence And Emission Control Of Heavy Metals In Fuel Coals From Some Coal-rich Regions In China

The emission of heavy metals,during coal combustion,not only pollute the ecological environment but also threaten human health.The concentration,occurrence and the ways of emission determine the size of its harm,at the same time,it also determines the mechanism of transformation in combustion process.Facing these problem,the relationship between content of metals bounded to organic and coal rank,total content and control of emission were studied.Details are as follows:(1)Basic characteristics of heavy metals in coal were studied.The content of Cu, Zn, Pb, Cr, Cd in coal coming from 15 coal mines were determined.The result showed that:the range of concentration was wide according to different coal mines in northern China;In northwest China, Zn 、 Pb content are below 10 μ g/g and 7 μ g/g respectively,meanwhile,they are less than other coal samples from coal-rich regions in north and northeast China.(2)The relationship between the content of Cu、Zn bounded to organic matter and coal rank were studied,using volatile size as the index of coal rank.Sequential chemical extraction method were used to extract the heavy metal bounded to organic matter.The content were determined by AAS.The results showed that:the content of Zn、Cu bounded to organic matter decreased with the increasing of coal rank.(3)Experiments with the addition of adsorbent limestone and the change of ashing temperature were carried out to control the heavy metal pollutants,and the control mechanism was infered and verified.It was observed that the used limestone could increase the fixed rate of Cu、Zn、Cd、Cr and Pb.The size of variation:Cd>Pb>Cr>Zn>Cu.With the increasing of temperature from 800℃ to 900℃,the fixed rates of Zn、Cu and Cd rise in the first then fall in the presence of limestone(8%).Ashing temperature 900℃ gave a better result than 800℃、1000℃ for the deposit of Zn 、 Cu 、 Cd.The mechanism : Zn 、 Cu and Cd were sulphophile elements.When heated,limestone occur desulfurization with sulfuret at 800℃ and indirect desulfurization at 900℃.In the process of indirect desulfurization at 800℃,the CO2 generated would escape from limestone inside, which could increase poriness,but not 800℃.So the fixed rate of Cu、Zn、Cd、Cr and Pb at 900℃ higher than 800℃.