Experimental Study On Hg⁰ Oxidization By NaClO₂ In Coal-fired Flue Gas

Mercury pollution from coal combustion is another atmospheric pollution which attracts much attention after dust,nitrogen oxides and sulfur dioxide.Among various mercury pollution control technologies for coal-fired flue gas,it is a practical and feasible method to use the existing air pollution control devices to remove mercury.Elemental mercury（Hg⁰）in coal-fired flue gas is volatile and insoluble in water,which is difficult to be removed by existing air pollution control devices.Therefore,NaClO₂ solution was used in this paper to reduce the content of Hg⁰ in flue gas,so that Hg⁰ in flue gas could be oxidized into water-soluble mercury oxide(Hg²⁺),and mercury could be removed by existing pollution control devices.In this paper,a self-built experimental system was used to investigate the oxidation performance of NaClO₂ solution in flue gas through two ways of gas phase oxidation and liquid phase oxidation.The gas phase oxidation experiment mainly investigated the influence of reaction temperature,composition and proportion of single coal-fired gas and mixed coal-fired gas,entrance of Hg⁰,reaction residence time on the oxidation performance of Hg⁰ NaClO₂ solution vaporization.Liquid phase oxidation experiment mainly investigated the influence of coal-fired gas composition,slurry characteristics,reaction temperature and other factors on the performance of NaClO₂ solution for Hg⁰ oxidation.The experimental results show that there is a positive correlation between reaction efficiency and temperature.When the temperature of vaporizing chamber and reaction chamber are 230℃and 250℃,oxidation efficiency can be 87.2%;The reaction residence time was not significant for Hg⁰ oxidation efficiency.The multi-flue gas components including SO₂ and NO promoted the oxidation efficiency of Hg⁰.In the liquid phase oxidation reaction,both SO₂ and NO have significant effects on the oxidation efficiency of Hg⁰.With the increase of SO₂ concentration in flue gas,the Hg⁰ oxidation efficiency decreases.There is no obvious influence when NO is contained in flue gas.NaClO₂concentration increased and the oxidation efficiency increased.The oxidation efficiency of Hg⁰ in NaClO₂ solution was greatly affected by pH value.With the increase of the pH,the oxidation efficiency of Hg⁰ decrease significantly.When the pH value is greater than 7,the oxidation efficiency of Hg0 is almost to 0.The influence on NaClO₂ oxidation of Hg⁰ caused by slurry temperature and content of Cl^-is not significant.The research results provide a theoretical basis for the simultaneous removal of mercury by existing air pollution control devices in coal-fired power plants and preparation for the continuous improvement of Hg⁰ oxidation technology.