Study On Mercury Removal From Flue Gas By Fenton-like Reagent/activated?NH₄?₂S₂O₈/K₂FeO₄

Mercury in the flue gas from coal combustion,due to its strong toxicity,caused great harm to both human living environment and heath,which has attracted worldwide attention.The methods for mercury removal from flue gas by using existing wet flue gas desulfurization?WFGD?devices and activated carbon injection?ACI?technology were considered to be the most promising and effective ones.In this paper,three kinds of green environmental oxidants including Fenton-like reagent,?NH_-4?₂S₂O₈ and K₂FeO₄ were proposed and the capacity of these three oxidants for mercury removal from flue gas was investigated in spray and fixed-bed reactors respectively.The main contents and results are as follows:A novel process on oxidation removal of elemental mercury from flue gas using Fenton-like reagents in a spray reactor was developed.The effects of several process parameters such as solution pH,reaction temperature,liquid-gas ratio,H₂O₂ concentration,Fe³⁺ concentration,Cu²⁺ concentration,Hg^o inlet concentration,NO concentration and SO₂ concentration on Hg^o removal were investigated.The liquid reaction products and free radicals were also determined by using ion chromatography,liquid fluorescence mercury analyzer and electron spin resonance spectrometer.On the basis of liquid reaction products and free radicals,the mercury removal paths were also proposed.The results show that increasing H₂O₂ concentration,Fe³⁺ concentration,Cu²⁺ concentration or liquid-gas ratio significantly promotes Hg^o removal.However,increasing solution pH,NO concentration and SO₂ concentration significantly inhibits Hg^o removal.Changing Hg^o inlet concentration and reaction temperature has a small impact on Hg^o removal.Oxidation of Hg^o by ·OH plays a major role for Hg^o removal and Hg^o removal by H₂O₂ oxidation only plays a secondary role.The enhancement of the mercury removal from flues gas in a urea-WFGD system using high temperature-activated?NH₄?₂S₂O₈ was investigated in a spray reactor.The effects of several process parameters such as?NH₄?₂S₂O₈ concentration,liquid-gas ratio,Hg^o inlet concentration,solution pH,urea concentration and SO₂ concentration on Hg^o removal were investigated.The liquid reaction products and free radicals were also determined by using ion chromatography,UV spectrophotometry,liquid fluorescence mercury analyzer and electron spin resonance spectrometer.On the basis of liquid reaction products and free radicals,the mercury removal paths were also proposed.The results show that increasing?NH₄?₂S₂O₈ concentration and liquid-gas ratio significantly increases the Hg^o removal efficiency.However,increasing solution pH and urea concentration significantly decreases the Hg^o removal efficiency.Changing Hg^o inlet concentration and SO₂ concentration only has a small impact on Hg^o removal.S₂O₈2-/·OH/ SO₄^- oxidations play important roles in the removal of Hg^o and Hg2+ was the final reaction product.Wheat straw?WS?char prepared by pyrolysis and chemical modification was developed and the effects of K₂FeO₄ loading,reaction temperature,Hg^o inlet concentration and concentrations of gas mixtures O₂,NO and SO₂ in flue gas on Hg^o removal were investigated in a fixed-bed reactor.The results show that K₂FeO₄-impregnation can improve pore structure of WS char and produce new active sites,Fe₂O₃ and K₂FeO₄,which significantly enhance Hg^o removal.Increasing O₂ concentration increases Hg^o removal efficiency.However,increasing Hg^o inlet concentration significantly decreases Hg^o removal efficiency.The presence of NO obviously promotes Hg^o removal.However,SO₂ in flue gas decreases Hg^o removal efficiency.The increase in reaction temperature has a dual impact on Hg^o removal.