Preparation Of Mn-Ce Modified Semi-Coke Sorbent And Simultaneous Removal Of S0₂ And Hg⁰ From Flue Gas

Coal is the main energy source of China,and it is cleaner way that is used to generate electricity.Coal contains a small amount of nitrogen,sulfur and traces of heavy metals.Nitrogen and sulfur are converted into nitrogen oxides and sulfur dioxide after combustion.Heavy metals are present in their own stable state in ash or in flue gas.Mercury of flue gas exists mainly in elemental mercury?Hg⁰?.Both SO₂ and Hg⁰ vapor are atmospheric pollutants,which pose the great threat to humans,animals and plants.At present,the most mature flue gas desulfurization technology is wet desulfurization with better efficiency.However,the by-product is a large amount of gypsum and it is difficult to treat.Meanwhile,the cost of desulfurization wastewater treatment and the equipment investment are very expensive,which is not suitable for middle and small-sized enterprises.Activated carbon,activated coke and other sorbents can remove Hg⁰ by physical adsorption.These adsorbed mercury is unstable and d easily cause secondary pollution.Therefore,it is necessary to develop a kind of sorbent for the oxidative adsorption of SO₂ and Hg⁰.Based on the pre-laboratory work,Mn-Ce/SC bimetallic sorbents were prepared by ultrasound-assisted high-pressure impregnation,with active components of Mn and Ce and semi-coke carrier.Then,sorbents were used to remove SO₂ and Hg⁰ on the fixed-bed evaluation device.The physical and chemical properties of the sorbent were characterized by BET,XRD,XPS and FTIR.The characterization results were correlated with the evaluation results of the removal activity to obtain the mechanism of combined desulfurization and mercury removal.At the same time,the preparation conditions of the sorbent and its adaptability to the use environment were investigated.The main findings are as follows:?1?Mn-Ce/SC bimetallic sorbents have high SO₂ and Hg⁰ removal activity.The removal efficiency of SO₂ and Hg⁰ in simulated flue gas?15%CO₂,3%O₂,3000 mg/m³ SO₂,100?g/m³ Hg,N₂ as the balance?reached 100%and 95%,respectively.It fully satisfied the requirements of national emission standards of flue gas.?2?The desulfurization and mercury removal activity of the Mn-Ce/SC sorbent is provided by the two metal components of Mn and Ce,and the activity of the bimetallic sorbents prepared is more outstanding.The adsorption of SO₂ is completely chemical adsorption,and the SO₂ is oxidized by MnO_x and CeO_y on the surface of the sorbent.The adsorption of Hg⁰ has both oxidative and physical adsorption,and the chemical adsorption is that MnO_x and CeO_y on the sorbent surface oxidize Hg⁰ to HgO.Mn is favorable for desulfurization and Ce is beneficial for mercury removal.There is competitive adsorption between SO₂ and Hg⁰.When SO₂ and Hg⁰ are simultaneously removed,the Hg⁰ removal ability is affected by the SO₂ removal ability.?3?The desulfurization and mercury removal activity of Mn-Ce/SC sorbents is greatly affected by the temperature and composition of the flue gas.The desulfurization capacity of the sorbents increases with increasing temperature,but the mercury removal capacity decreases.The increase of oxygen concentration is beneficial to the removal of SO₂ and Hg⁰,but it is easy to cause loss of the sorbent.CO₂ and H₂O have little effect on desulfurization and mercury removal of the sorbents.NO_x inhibits the removal of SO₂ and Hg⁰,thereby reducing the adsorption capacity of the Mn-Ce/SC.