Basic Characteristics Study On NO_x Deep Removal In The Flue Gas By Active Molecules (Ozone)-catalytic Method

China’s economic and social development is in a rapid speed,with the improvement of people’s life,which also gave rise to the serious environment pollution.People want bule sky and white clouds more than ever before.It’s our duty to deal with the pollution emission during energy utilization process.Our country’s energy structure is changing with the development-of new energy.But coal is still the dominant energy,which can not be replaced in a short time.Certainly,the increasing serious national emission standard of thermal power plants enhanced its combustor improvement and flue gas treatment effectively.However,due to small capacity and wide distribution,the pollution of industrial boiler or furnace are facing severe challenges.The ultra-low emission standard will bring higher requirement in the future.In present,nitrogen oxides(NOx)is one of the key target pollutants in the emission treatment of industrial boiler or furnace.Based on the low temperature oxidation by ozone for simultaneous removel of SO2 and NOx,this paper proposes a new tehnicial pathway for simultaneous removal of SO2 and NOx by NO deep oxidation into N2O5 by ozone combined with Wet Flue Gas Desulfuration(WFGD),which breaks through the NO primary oxidation into NO2.The kinetics modelling is combined with experimental testing to investigate the N2O5 formation mechanism during NO deep oxidation by ozone.This paper proposes a 24-step NO deep oxidation reaction mechanism,and the crucial elementary reactions are found.The effect of temperature and residence time on N2O5 formaiton is obtained,which can provide a theoretical foundation for industrital application.Hereafter,catalysts are introduced to solve the problems in NO deep oxidation,including high ozone consumpation,long reaction time,and high ozone leakage.Firstly,catalytic NO oxidation into NO2 by O2 is investigated to reduce ozone usage primarily.Secondly,catalytic NO deep oxidation into N2O5 by O3 is investigated to further recduce ozone usage,shorten required time for N2O5 formation,and reduce ozone leakage.The catalytic activity,stability,and resistance to SO2 and H2O are studied in detail.Finally,catalyst charactization measurements are used to help uncover the reaction process and deactivation mechanis.Ozone based low temperature oxidation deNOx process was investigated especially the N2O5 formation mechanism.In this paper,Fourier Transform Infrared Spectroscopy(FTIR)is used to measure N2O5 semi-quantitatively.Temperature and residence time are crucial factors during N2Os formation process.Temperature has no effect on oxidation process when O3/NO<1.0.While O3/NO>1.0,NO2 concentration increases continuously,but N2O5 and O3 outlet concentration decreases along with temperature under same O3/NO.Almost 90%NO can be oxidized into N2O5 with O3/NO = 2.0 under the temperature range of 60-80 ℃,which is regarded as the optical temperature window.N2O5 formation is so slow that it can be formed with 3~5 s when O3/NO>1.0 at temperature 60-80 ℃.The crucial elementary reactions of N2O5 foramtion include O3+NO=O2+NO2,NO+N O3=2N 2NO2 NO2+NPO3=N2O5,O3+NO2=NO3+O2,and NO2+NO3=O2+NO+NO2.The slow formation rate of NO3,key intermediate for N2O5 formation,resulting in long residence time of N2O5 formation.The decomposition of NO3 and N2O5 acelerates along with temperature,and results in no N2O5 can be detected when temperature was higher than 130 ℃.Finally,the N2O5 formation pathway is put forward:NO oxidized by O3 into NO2,NO2 oxidized by O3 into NO3,finally NO2 combining with NO3 to generate N2O5.The decomposition of NO3(NO and NO2),N2O5(NO2 and NO3),and O3(O2)is always accompanied.The denitration project of ultra-low emission treatement engineering in Longyou Hengsheng Thermal Co.Ltd.is designed by ozone deep oxidation.The field debugging results demonstrate that NOx emission concentration can meet with the ultra-low emission standard(<50 mg/Nm3).There is residual O2 in the flue gas,which can be used to catalytic NO oxidation into NO2.Ce-Mn bimetallic catalysts are prepared by sol-gel method.The highest NO conversion efficiency reaches 96%at 238 ℃ when the molar ratio of Mn/Ce is 0.4.Due to thermodynamic limitation,NO conversion efficiency declines when the temperature further increases.Two main reduction peaks are detected between 200~342 ℃ in TPR profiles for Ce-Mn catalysts,indicating strong low temperature redox ability.When SO2 is introduced into the system,NO conversion efficiency declines significantly.After 400 min,it declines from 92%to 22,indicating catalytst deactivation.The catalyst displays excellent SO2 adsorption ability with long break-through time.The catalytst deactivation by SO2 is irreversible that can not be recovered by removing SO2.Large amounts of sulfates are formed on catalyst surface during catalyst sulfation,which almost completely replace the nitrogen species,nitrates and nitrites.Hereafter,surface area is declined,low temperature redox ability is disappeared,NO adsorption ability is weakened,and surface metal ions are reduced.Finally,the active sites for NO oxidation can not be recovered,and reaction intermediates disappear,resulting in reaction cycle termination.The catalytic NO deep oxidation into N2O5 by ozone is investigated in this paper.The catalytsts of monmetallic oxides and spherical alumina supported manganese-based oxides are prepared to evaluate catalytic activity.Manganese oxides exhibit the highest catalytic activity among all these monmetallic oxides,which can reach the deep oxidation efficiency of 80%at O3/NO = 2.0.Next,the spherical alumina(SA)is slected as the support for manganses oxides(Mn/SA),which can provide higher surface area.Meanwhile,the spherical arrangement is favorable for reducing gas flow resistance,extanding resistance time,and promoting surface heat transfer.Finally,desirable catalytic behavior is obtained:83%deep oxidation efficiency can be reached at O3/NO = 1.5 when the temperature is 100 ℃ and resistance time is 0.12 s,and ozone leakage is lower than 20 ppm.Ce,Fe,Cr,Cu,and Co oxides are doped into Mn/SA to get manganese based bimetallic oxides catalytsts.Ce-Mn/SA and Fe-Mn/SA exhibit best catalytic performance:the outlet concentration of NO+NO2 is lower than 50 mg/Nm3(88%)and 25 mg/Nm3(94%),respectively,at O3/NO =1.5,which all can meet with ultra-low emission standard.The dominant reaction pathway for catalytic NO deep oxidation into N2O5 by ozone is uncovered.The manganese(Ⅲ)is oxidized into manganese(Ⅳ)and manganese(Ⅶ)by ozone;in turn,the oxidized manganese ions oxidize NO2;N2O5 is formed by combination;a reaction cycle finishes after desorption of N2O5.Catalytst resistance to SO2 and H2O is studied in detail during catalytic NO deep oxidation process.Mn/SA exhibits good stability and resistance to SO2,while with weak decline in efficiency while later with.Ce-Mn/SA exhibits almost no decline in the test of stability and resistance to SO2.TPD and TGA results demonstrate that the NOx and O2 adosrption ability can be enhanced significantly in the presence of ozone,which can also be maintained under SO2 atmosphere.However,the introduction of H2O results in 50%drop in efficiency.Fe-Mn/SA exhibits excellent stability,but worse resistance to SO2 and H2O,with 50%drop in efficiency.