Research On Mercury Emission During Heat Treatment Of Coal Gangue And Coal Slime

In recent years,large amount of coal gangue and coal slime produced in the process of coal mining and coal washing have been produce,which occupied lands and caused environmental pollution.Therefore,the comprehensive utilization of coal gangue and coal slime is attracting more and more attention.Because coal gangue and coal slime have some extent calorific value,they are often used as fuel of low calorific value coal power plant to generate electricity,so as to achieve the purpose of comprehensive utilization.However,the mercury of coal gangue and coal slime will be released into the atmosphere during the comprehensive utilization process,causing the mercury pollution of atmosphere.The temperature-programmed decomposition?TPD?coupled with an atomic fluorescence spectroscopy?TPD-AFS?was adopted to determine the real-time dynamic behavior of gas mercury from the coal gangue and slime samples during the process of heating treatment.The Ontario Hydro method was also used to determine the Hg⁰ and Hg²⁺from the reactor,which could reflect the effects of atmosphere on the release of Hg.The kinetic release of mercury was investigated by measuring the release rate of mercury.Through the mixed heat treatment experiment of raw coal and coal gangue,the effects of atmosphere and mixing ratio on mercury release were investigated.The main conclusions of this paper are as follow:1.Hg⁰ is the main form of mercury release from coal gangue and coal slime during fixed bed heat treatment.Hg⁰ release profile is different under different heat treatment atmospheres.For the coal gangues,the release profile of Hg⁰presented two main peaks under N₂ atmosphere,located at about 200-500? and 500-650?,while it presented one main peak located at about 300-500? in air.For the coal slimes,it presented three main peaks located at about200-500?,500-650?,and 950-1100? under N₂ atmosphere,while it presented three main peaks located at about 200-400?,400-550?,and700-850? in air.The release rate of Hg⁰ in coal gangue and coal slime under nitrogen atmosphere is higher than that of Hg⁰ in air.At the same time,the volatilization rates of coal gangue and slime in the nitrogen atmosphere are lower than those in the air atmosphere.2.The mercury release rate of coal gangue increases with the increase of the combustion temperature during the laboratory scale fluidized bed combustion process and it is more than 90%.Meanwhile,the Hg⁰ release rate and Hg²⁺release rate vary with the coal gangue samples and temperature,and Hg⁰ is the main form of gaseous mercury.It is also found that the release rate of Hg⁰ was positively correlated with temperature.Through the linear relationship between ln(r_max)and 1/T,the activation energy of Hg⁰ release from two gangues used in this study can be obtained,which are 18.20 KJ/mol and 17.14 KJ/mol,respectively.And the pre-exponential factors are 4.49 and 5.49,respectively.Furthermore,the kinetic equations of Hg⁰ release are r?x?=4.49en-18.20/RT?-1.62x⁴+4.09x³-2.08x²-1.69x+1.31?,r?x?=5.49e-17.14/RT?1.74x⁴-2.95x³+2.21x²-2.34x+1.34?,respectively.3.In the mixed heat treatment experiment of raw coal and coal gangue,mixed pyrolysis under nitrogen atmosphere mainly affects the temperature range of mercury release and has little effect on mercury release.Under air atmosphere,the mixed combustion is not only affects the temperature release range of mercury,but also affects the amount of mercury released.The mixed ratio of coal and coal gangue has some effect on the mercury release behavior to somme extent.