Study On Reaction Mechanism Of Activated Carbon For Removing Pollutants From Flue Gas

At present,the situation of air pollution in China is still serious,especially in Beijing,Tianjin,Hebei and its surrounding areas.To improve the atmosphere quality has become a key and difficult problem to resolve.The flue gas purification technology using activated carbons can simultaneously remove multi-pollutant,such as SO₂,NOx and H₂S.Activated carbon technology consumes no water,produces no secondary pollution.It has been used in the flue gas purification of coal-fired power plants and sintering machines.Although activated carbon technology has many advantages,the denitrification efficiency needs to be improved.In the coking industry,for the coke oven flue gas with the emission characteristics of low sulfur,high nitrogen and multi-pollutant coexisting,the activated carbon technology demands a higher denitrification efficiency and effectively capturing multiple pollutants.This work explores the effect of modification on the denitrification efficiency over activated carbon,investigates physical and chemical properties of activated carbon affecting the denitrification efficiency,and further describes the SCR reaction mechanism of activated carbon.Meanwhile,for the H₂S in the coke oven flue gas,the removal mechanism and oxidation products of H₂S are investigated,and the interaction mechanism between pollutants and functional groups of activated carbon is clarified.The activated carbon was modified with four kinds of nitrogen containing additives.The results showed that the specific surface area and total pore volume of activated carbon were reduced,and the denitrification efficiency of activated carbon was obviously improved.The main reason is that the disorder of graphite microcrystalline structure of activated carbon increases the adsorption site,and pyridine,pyrrole,quaternary amine and other nitrogen containing officials are increased.The functional groups of activated carbon were characterized before and after the denitrification reaction.It was found that the content of phenol hydroxyl was reduced and the content of quinone carbonyl increased,and pyridine,pyrrole and quaternary amine functional groups decreased and the pyridine-N-oxide content of pyridine increased significantly after NO and NH₃ had SCR reaction on activated carbon.According to the transient response test,the reaction follows the Langmuir-Hinshelwood mechanism at 110℃,and there are two routes at 1150℃.The adsorbed NH₃ react with the adsorbed NO,following Langmuir-Hinshelwood mechanism,or the NO of the gas state directly involved in the reaction,following Eley-Rideal mechanism.Pyridine,pyrrole and quaternary amine groups can adsorb gaseous NO,while phenolic hydroxyl groups can be used as the adsorption sites of NH₃ to produce quinones and N₂,thus completing the SCR reaction.The characteristics of the pore structure and the functional groups of activated carbon after H₂S adsorbed under different atmospheres have been investigated.It is found that in a single oxidizing gas atmosphere,oxidation is strongly related to the order of SO₂>O₂>NO.When the reducing gas NH₃ is present,the removal efficiency of H₂S decreases significantly.Compared with anaerobic atmospheres,the oxidation of H₂S is more prone to occur in aerobic atmospheres and the removal efficiency is higher.In the absence of O₂,H₂S adsorbed on the surface of activated carbon oxidized by oxygen-containing functional groups,and then formed solid elemental sulfur and sulfate on the activated carbon.In the presence of O₂,the H₂S and the gaseous O₂ adsorbed the active sites on the surface of the activated carbon,and the oxidation reaction produces the elemental sulfur.The elemental sulfur further reacts with the O₂ in the atmosphere to produce SO₂,resulting in the SO₂ spillover of the gaseous state.