Study On The Adsorption Of Gaseous Elemental Mercury In Simulated Flue Gas By Biomass Reburning Coke

Mercury emission control of coal-fired flue gas has been an important research filed.Activated carbon injection(ACI)is one of the most promising technologies for coal-fired mercury emmission,however,the industry application of this technology is limited due to the high cost of activated carbon.Biomass reburning,as a promising in-furnace NO reduction,not only can achieve high NO removal efficiency,but also can produce highly reactive biochar and form appropriate chlorine-contaied flue gas,which is benefit to promote NO reduction and catalytic oxidation of vapor elemental mercury(Hg0).Finally simultaneous control of NOx,SO2 and mercury in conventional air pollution control devices(APCDs)can be achieved.Therefore,it is very significant to carry out the Hg0 adsorption of biochar in simulated flue gas.Different kinds of biochars were prepared in an entrained flow reactor under reburning conditions,and the modifiers(MnCl2 and CuCl2)were used to modify the biochar.The physicochemical properties of different biochars were characterized by scanning electron microscopy-energy dispersive spectrometer(SEM-EDS),specific surface area and pore size analyzer,X-ray diffraction(XRD)and Fourier transform infra-red(FTIR)spectroscopy,respectively.The results indicated that:(1)The chlorine release fractions of rice husk(RH)and wheat straw(WS)are larger than 89.37%under different reburning temperatures.(2)The parameters of BET specific surface area,micropore volume and total pore volume of biochar increase with increasing reburning temperature,and which increases significantly after impregnation with MnCl2 和 CuCl2.Micropores of impregnated biochar decrease gradually with the increase of mass fraction of the modifier,due to the particle accumulation on micropore surface.(3)The reburning temperature and modifier have little effect on the crystal structure of biochar,and the main crystalline phases in the RH biochar and WS biochar were KCl,SiO2,MgSiO3,CaSiO3,K6Si3O9 and Na2Si2O5.(4)The surface oxygen-containing functional groups of biochar decrease significantly compared with that of raw biomass,and the area and species decrease obviously with the increasing of reburning temperature.Impregnation can enhance the area and species of oxygen-containing functional group of biochar.An sorbent injection in-duct reactor for the mercury removal in simulated flue gas was set up to study the effects of initial mercury concentration,adsorption temperature,adsorption time,biomass species,simulated flue gas composition,chemical modification on mercury removal efficieny.The mechanism of mercury removal was also discussed based on the physicochemical properties of biochar.The results indicated that:(1)Mercury removal efficieny of sorbents mixed with biochar and flyash increase obviously compared with that of fly ash.(2)Mercury removal efficieny of sorbents increase first and then decrease with the increase of initial mercury concentration.(3)The adsorption temperature has great influence on the mercury removal efficieny,and the maximum mercury removal efficieny is obtained at the adsorption temperature of 100℃.(4)Increasing adsorption time can improve the mercury removal efficieny.(5)Mercury removal efficieny of sorbent mixed with RH-biochar is higher than that of WS-biochar.(6)Mercury removal efficieny increases slowly with the increase of O2 concentration,decreases rapidly with the increase of SO2,and increased rapidly with the increase of NO concentration.Mercury removal efficieny increases over 90%quickly while the concentration of HCl is more than 50 μL/L.(7)Mercury removal efficieny of the impregnated biochar shows obvious increase than that of raw biochar,and mercury removal efficieny of the biochar modified by CuCl2 is better than that modified by MnCl2.A simplified mathematical model,which contains the external film mass transfer process and the surface adsorption process was established to predict mercury removal efficieny through sorbent injection.On the basis of the sensitivity analysis,the model has been evaluated combined with the experimental results.The results indicated that the model can predict mercury removal efficieny reasonably and the model can be used to predict the consumption of sorbents for mercury removal.The external film mass transfer coefficient and particle size have little effect on mercury removal efficieny,the equilibrium constant K has signifficient influence on mercury removal efficieny.