Experimental Study On Mercury Removal By Injection Of Halogen Modified Rice Husk Coke Into Flue Gas

Mercury,as the fourth major pollutant produced by coal combustion,has attracted worldwide attention.However,the energy consumption structure of coal-based energy in China will not be changed in a relatively long period of time.China is facing a more severe mercury pollution situation than other countries.At present,the commercialized and effective technology for mercury emission control in coal-fired power plants is activated carbon injection technology?ACI?,but the cost is high and the regeneration performance is poor.Biomass coke has a developed pore structure similar to that of activated carbon,and thus has a certain physical adsorption capacity.By chemical modification of halogen,it can form active functional groups on the surface of biomass coke,which is conducive to mercury adsorption.It is possible to obtain cost-effective mercury removal sorbents by using halogen modified biomass coke instead of traditional coal activated carbon to reduce process cost of the ACI system,save high carbon energy,and realize industrialization promotion and application.Rice husk coke?RHC?,NH₄Br modified rice husk coke?RHC-Br?,NH₄Br modified coconut husk activated carbon?CNAC-Br?and NH₄Br modified coal-based activated carbon?CAC-Br?were prepared.Physicochemical characterization was carried out.The effects of initial Hg⁰ concentration,flue gas temperature and flue gas composition on mercury adsorption of RHC-Br were investigated under condition of simulated flue gas on a fixed bed reactor.The mercury adsorption performance of RHC-Br,RHC-Br,CNAC-Br and CAC-Br sorbents were compared.The results show that the mercury adsorption performance of the sorbent is CAC-Br>CNAC-Br>RHC-Br>RHC;increasing the initial Hg⁰ concentration can improve the mercury adsorption capacity of RHC-Br.The mercury adsorption capacity of RHC-Br increases with the increase of temperature in the range of 80¹20? and decreases with the increase of temperature in the range of 120¹60?,respectively.The presence of SO₂ in the flue gas inhibits the adsorption of Hg⁰ by RHC-Br,while NO promotes the adsorption of Hg⁰ by RHC-Br.The performance of sorbents injection into a simulated flue gas for mercury removal was verified on an entrainment flow reactor.The characteristics of mercury removal by injection of RHC,RHC-Br,CNAC-Br and CAC-Br were compared in the entrainment flow reactor.The effects of initial Hg⁰ concentration,residence time,flue gas temperature,injection amount and flue gas component on mercury removal by injection were investigated.The mercury species on the surface was studied by temperature programmed desorption?TPD?method.The results show that increasing the initial mercury concentration of flue gas and the residence time of sorbent improves the injection mercury removal efficiency and mercury adsorption capacity of RHC-Br,while increasing the injection amount of sorbent can improve the injection mercury removal efficiency of RHC-Br,but reduce the mercury adsorption capacity.In the range of80¹20?,the mercury removal efficiency and mercury adsorption capacity of RHC-Br increase with the increase of flue gas temperature,while the mercury removal efficiency and mercury adsorption capacity of RHC-Br decrease with the increase of flue gas temperature from120? to 160?.Similar to the fixed bed results,the presence of SO₂ in the flue gas component inhibites the adsorption of Hg⁰ by RHC-Br,while NO promotes the adsorption of Hg⁰ by RHC-Br.Due to the influence of pore structure and halogen modification,the sorbent injection mercury removal performance and mercury adsorption capacity of sorbent are CAC-Br>CNAC-Br>RHC-Br>RHC;the adsorption of Hg⁰ on RHC is mainly physical adsorption,with a small amount of chemical adsorption,the product is HgO;the adsorption of Hg⁰ on RHC-Br is mainly chemical adsorption,and the product is HgBr₂;The mercury emission characteristics of Guizhou anthracite combustion was studied in a0.3MW pilot scale coal-fired circulating fluidized bed combustor system.The effects of ACI temperature,sorbent injection amount,NO concentration,SO₂ concentration and ammonia-nitrogen ratio on mercury removal by RHC-Br sorbent injection were investigated in actual coal-fired flue gas.The mercury removal performances of RHC-Br,CAC-Br and CNAC-Br sorbents were compared.The results show that the conbination of ACI mercury removal device with the presence of pollutant control devices?SCR+FF?can effectively remove mercury from coal-fired flue gas.The synergetic mercury removal efficiency can reach 97.73%.In real coal-fired flue gas,the injection removal efficiency of CAC-Br is the best,reaching 80.01%,followed by RHC-Br with a mercury removal efficiency of 73.40%,and the CANC-Br has mercury removal efficiency of 69.03%.Increasing ACI temperature and injection amount of sorbent can improve the mercury removal efficiency of RHC-Br.Considering the cost,it can be concluded that the optimum C/Hg ratio of RHC-Br sorbent is 16000.Among the flue gas components,NO and ammonia-nitrogen ratio have an obvious positive effect on the mercury removal efficiency of RHC-Br injection,while SO₂ inhibites the mercury removal efficiency by injection of RHC-Br sorbent.