The Behavior Of Hg、As、Pb In Xiangyuan Coal During The Thermal Processing

China is a big country of coal production and coal combustion,due to oil and gas resources are relatively poor,therefore the dominant position of coal in energy structure will not change for a long time in the future.According to statistics that the use of coal accounts for 60 percent of primary energy in China.In recent years,the research about the release and the transformation behavior of trace metals in the process of coal utilization has become a hot topic,especially some of the volatile elements which cannot be effectively collected and finally released into the atmosphere,which has become an important man made source of air pollution.There are many factors affect the release of trace elements in coal,includes the types of coal,temperature,atmosphere and the forms of elements.In this paper,we choose Xiangyuan coal which contains higher content of arsenic and mercury as the research object,investigating the release rules of harmful trace elements in the process of pyrolysis and gasification in a fixed bed;exploring the forms of mercury,arsenic,and lead in Xiangyuan coal and the thermal stability of different forms of elements.At last this paper explore the influence of mineral to the release efficiency of Hg.The main contents and conclusions are as follows:1.This paper researches the release behavior of Hg,As and Pb during the process of pyrolysis and gasification.(1)The influence of temperature: With the gradual increase of temperature,the release of Hg,As,Pb presents phasic characteristics.The major release temperature of Hg,As,Pb are 150~450oC、400~800oC and 500~900oC respectively;And one element has different release intensities,this phenomenon depends on their own binding forms.(2)The influence of atmosphere: During the utilize of coal,different atmospheres(N2、CO2、 N2+O2,4%)will influence their release efficiency: N2+O2,4% will promote the release efficiency of these elements compared to N2 because of gasification and disintegrate of coal.And we can also find that the release ration of these elements is relatively low during 400-600 oC in CO2 atmosphere;but when temperature continues to rise,we find out that CO2 promote the release efficiency of Hg,As,Pb significantly.2.By using the method of sequential chemical extraction,this paper researches the modes of Hg,As,Pb and analysis the thermal stability of different modes.At the same time,influence of minerals on the release of trace elements were also investigated.(1)Hg in Xiangyuan coal about 51% is present in pyrite,14% is the organic combination state,only a small amount of Hg is present in other forms;And about 49% of As associated with pyrite,33% is present in the form of carbonate,sulfate,phosphate,ect.Only a small amount of As exists in the organic bound state;But the Pb in Xiangyuan coal is distributed in all kinds of minerals and is mainly associated with sulfate,sulfide and pyrite.(2)The thermal stability of trace element organic combination state is the worst.The decomposition of the binding form and the release and transformation of trace elements can be observed at 300oC;Aluminosilicate has a strong thermal stability,and the thermal stability of the other bonded forms depends on the specific physical and chemical properties of the existing form.(3)During the pyrolysis of Xiangyuan coal which has been demineralized,we find that aluminosilicates inhibit the release of Hg.And different atmospheres(N2、CO2、N2+O2,4%)will influence the process of inhibit.