Study On Removal Of Hg~0 From Flue Gas By MnO_x/PG

The element mercury（Hg⁰）has gradually become the focus of attention due to its high toxicity,volatility and bioaccumulation.Mercury can be absorbed by the human body through diet and skin contact,and it can Serious damage to the system and central nervous system.Coal-fired power plants have been supposed to be one of the major reasons of anthropogenic emission of mercury due to mercury enrichment in coal.Coal is China’s main energy source,and the large amount of coal combustion causes the mercury emissions from flue gas to account about 30%of total mercury emissions.The“Emission Standard of Air Pollutants for Thermal Power Plants”（GB13223-2011）,which was issued in 2011,clearly puts out mercury emission control limits.Thus,it is imperative for the coal-fired power plant to remove mercury from flue gas.Mercury in flue gas mainly exists in three forms:elemental mercury（Hg⁰）,oxidized mercury(Hg²⁺),and particulate mercury（Hg_P）.Among them,oxidized mercury and particulate mercury are easily removed by existing pollutant control devices（APCD）,in power plant.However,elemental mercury is difficult to capture due to its stability,volatility,and low solubility in water.Therefore,how to remove elemental mercury from flue gas has become a research focus and difficulty in mercury pollution control in coal-fired power plants.The goal of this study is to develop a catalyst with low temperature activity to remove Hg⁰ from coal-fired flue gas.In this paper,natural attapulgite（PG）is used as a catalyst carrier after pretreatment,and a impregnation method is used to support the transition metal Mn oxide to prepare a mercury removal catalyst（MnO_x/PG catalyst）.Hg⁰ removal experiments were carried out in a quartz-tube fixed bed reactor.The catalysts were characterized by SEM,BET,XRD,TPD and other technologies.It was found that the MnO_x/PG catalyst had a good Hg⁰ removal activity.The regeneration experiments were also performed for the used catalyst.It was found that the regenerated catalyst still had a high Hg⁰ removal activity.By optimizing the operating conditions of the MnO_x/PG catalyst for Hg⁰ removal,it was found that the MnO_x/PG catalyst with a MnO_x loading of 8%has the highest Hg⁰ removal performance.Under the reaction conditions of reaction temperature210°C,space velocity 6000 h^-1.Hg⁰ concentration 80μg/m³,the Hg⁰ removal efficiency by MnO_x/PG can reach 95.9%.In addition,the effects of flue gas components on Hg⁰ removal by MnO_x/PG catalysts we also examined.The results showed that:O₂ had a promoting effect on Hg⁰ removal,and the addition of SO₂ and H₂O caused a decrease in Hg⁰ removal.O₂ promotion effect may be due to the supplementary of active O over MnO_x/PG catalysts bt gaseous O₂,Which was consumed in Hg⁰ removal by MnO_x/PG.SO₂ and H₂O can cause competitive adsorption with Hg⁰ on the surface of MnO_x/PG catalysts,leading to the decrease of Hg⁰ removal efficiency by MnO_x/PG.