Characteristics Of Speciated Mercury Emissions In Coal-fired Fule Gas Under Oxygen?enriched Environment

Mercury emissions from coal combustion are an important source of atmospheric mercury pollution.How to reduce mercury emissions from coal combustion and control the conversion of mercury forms during coal combustion is of concern to researchers around the world.In recent years,oxy-combustion technology has been widely recognized as a new type of combustion technology,but research on the emission characteristics of pollutants（especial y mercury）under oxy-combustion is still in its infancy.In this paper,nine types of coal washing in the main coal producing areas of China were selected first.The mercury emission in the combustion flue gas was determined by cold atomic fluorescence spectrometry.The mercury residue in the coal ash was determined by aqua-water bath-cold atomic fluorescence spectrometry.Characteristics of mercury emissions from coal combustion.The results of the study showed that most of the mercury in the coal was released when the combustion temperature rose to 900°C.When the combustion temperature rises from 500°C to 900°C,the relative proportions of elemental mercury（Hg⁰）,active mercury(Hg²⁺)and particulate mercury（Hg^p）increase from 46.6%,3.2%,4.6%to 76.0%,6.0%.15.8%.The combustion temperature not only promotes the release of mercury in coal-fired flue gas,but also promotes the oxidation of Hg⁰,resulting in an increase in the ratio of Hg²⁺and Hg^p.Different types of coal samples,the amount of mercury released from coal and the proportion of different forms of mercury are not the same,which is mainly caused by the difference in mercury content and element distribution in coal.The relative proportion of Hg²⁺and Hg^p in lignite flue gas is lower than that of bituminous coal and anthracite.Secondly,explore the temperature under the O₂/CO₂ combustion atmosphere（500°C,700°C and 900°C,1100°C）,oxygen volume fraction（air,30%,40%）,coal type(anthracite,bituminous coal,The effect of lignite on the characteristics of mercury emissions from coal combustion.The results show that increasing the combustion temperature and oxygen volume fraction can not only promote the release of mercury from coal combustion,but also promote the oxidation of Hg⁰ and the formation of Hg²⁺and Hg^p.Compared with the air combustion atmosphere,the mercury release rate in the flue gas is slower in the O₂/CO₂ combustion atmosphere,the mercury release in anthracite and bituminous coal is reduced by 24.74%to 29.4%,and the lignite is reduced by 19.5%to 45.4%.Finally,the characteristics of mercury emissions from coal combustion under O₂/N₂ atmosphere were investigated,compared with O₂/CO₂ atmosphere,and the TG/DTG curves were compared under two atmospheres.The results show that under O₂/N₂atmosphere,when the oxygen volume fraction is greater than 30%,when the combustion temperature is 700°C,the mercury in the coal is basically released completely;when the combustion temperature is 500°C,the oxygen volume fraction increases from 21%to 40%,and the Hg⁰release increases from 11.03 ng/g to 22.06ng/g,the combustion temperature At 1100°C,the release of Hg⁰ decreased from 26.99ng/g to 23.04 ng/g.Compared with O₂/CO₂ atmosphere,the release of Hg²⁺and Hg ^P in anthracite combustion flue gas is higher,bituminous coal and lignite are lower,coal The ignition temperature,the burning temperature are lowered,the burning rate is increased,and the burning time is shortened.