Experimental Study On Mercury Emission Characteristics And Injection Demercuration Of A 75t/h Cfb Boiler Power Plant

The tests of mercury removal and adsorption of bromine modified rice husk coke,bromine modified coconut husk activated carbon and bromine modified activated carbon were conducted in a 75 t/h circulating fludized bed（CFB）.The mercury concentration in flue gas,solid sample and liquid sample were measured respectively to obtain the mercury concentration and distribution in flue gas before and after each pollutant removal device.The mercury removal efficiency of three adsorbents was compared to obtain the mercury removal efficiency of air pollution control devices.The experimental results showed that fabric filter（FF）almost could remove all the particulate mercury in the flue gas,while wet flue gas desulfurization（WFGD）unit could remove some of the element mercury and divalent mercury.The mercury discharged into the atmosphere was mainly in the form of elemental mercury and a small amount of oxidized mercury.Mercury emission was mainly distributed in FF fly ash,followed by flue gas,WFGD gypsum,waste water,and bottom ash.Although it is efficient for air pollution control devices to remove particulate mercury in the flue gas of a coal-fired power plant,it is poor to remove the element mercury in the flue gas.Under condition of adsorbent injection into flue gas for mercury removal（ACI）,it is beneficial to conversion of Hg⁰ and Hg²⁺to Hg^P in the flue gas.The mercury removal efficiency of ACI increased with the increasing of the amount of the injected adsorbent.However,the high injection quantity will lead to the high cost of adsorbent,which is not economical.When the quantity of injected adsorbent was 20 kg/h,the mercury removal efficiency of activated carbon,rice husk coke and coconut husk activated carbon was 58.73%,57.98%and 40.48%respectively.Better pore structure and more oxygen-containing functional groups of activated carbon provided good conditions of the oxidization and adsorption of element mercury.However,the mercury removal efficiency of rice husk coke was comparable to that of activated carbon in the industrial application,indicating that the rick husk coke has good prospect in the industrial application.When ACI was added into the air pollution control devices,its synergistic co-removal for mercury was considerably enhanced.It was found that the concentration of particulate mercury was decreased to zero in the outlet of FF.Element mercury concentration in the flue gas decreased from 0.76-1.39μg/Nm³at the inlet of WFGD to 0.18-0.9μg/Nm³at the outlet of WFGD.While,oxidized mercury concentration in the flue gas decreased from 0.26-0.31μg/Nm³at the inlet of WFGD to 0.15-0.24μg/Nm³at the outlet of WFGD.This may be due to the oxidizing substance in the WFGD slurry oxidized elemental mercury to divalent mercury,and then adsorbed by WFGD slurry.When rice husk coke was injected,the synergistic mercury removal efficiency of ACI+FF+WFGD could be increased to 96.18%-98.42%,which indicated that the air pollution control devices combined with ACI could effectively remove mercury in the coal-fired power plants,and the injection of modified rice husk coke could achieve the same effect as the injection of activated carbon.