| Recently,with the development of national economy,people have a higher requirement on environmental quality.Nitric oxides,as one of the main air pollutants,have caused serious environmental problems such as acid rain,haze,ozone.Therefore,Chinese government has issued a serious of regulations to restrict the emission of nitric oxides.In the regulation named emission standard of air pollutants for thermal power plants(GB13223-2011),the nitric oxides emission concentration of newly constructed boilers(including boiler using coal,oil,gas as fuels)need to be reduced to no more than 100mg·m-3.Besides,for emission of industrial boiler,Chinese government has issued the regulation named emission standard of air pollutants for boiler(GB13271-2014)to limit air pollutants' emission concentration,in which the nitric oxides emission limit for newly constructed boiler is more demanding and the emission limit for key region's boiler is 200 mg·m-3.Therefore,how to develop flue gas denitrification technology with high denitrification efficiency,low investment and operation cost,no-secondary pollution is one of the research hotspot in air pollution.Chemical absorption-biological reduction(CABR)approach is a promising technology for NOx removal.Ferrous ethylenediaminetetraacetate(Fe(II)EDTA)is employed to form stable complexes with NO(Fe(II)EDTA-NO),then denitrifying bacteria reduced Fe(II)EDTA-NO to Fe(II)EDTA.Since industrial flue gas contains oxygen,some of Fe(II)EDTA is oxidized to Fe(III)EDTA,which can be reduced to Fe(II)EDTA by iron-reducing bacteria.Based on previous research that illumination has effect on ferric reduction process by iron-reducing bacteria,besides,to better employ CABR approach in practical production,a new CABR two-stage denitrification system has been established,and the bacteria acclimation duration and processing load of this system have been compared with conventional integrated denitrification system.At last,this paper discussed how to reduce operation cost by optimizing operation parameter.This paper's mainly conclusions were listed below:1.Comparing Fe(III)EDTA biological reduction process with light and without light,the process without light exhibit higher reduction efficiency and rate.Do research on the cause of two biological process's difference and find EDTA degradation is not the mainly reason for efficiency difference.Molecular biological technique is used to compare two processes' microbial community structure.The result of HTS showed that microbial community in culture with light and without light has quite a big difference.In culture without light,the dominant bacteria includes three kinds of iron-reducing bacteria(Bacteroides,Klebsiella,Desulfovibrio),the whole three's proportion is 47.09%.In culture without light,the dominant bacteria only contain one iron-reducing bacteria Desulfitobacterium,whose proportion is 12.4%.2.Comparing new CABR two-stage denitrification system,which used mixed bacteria to start up,with conventional CABR integrated system,which used iron-reducing bacteria and denitrification bacteria successively to start up,the former has a shorter start-up period.Moreover,new two-stage denitrification system has a better oxygen-resistance ability and a higher processing load in the same flue gas condition.To analyze the reason for low denitrification efficiency under high inlet gas load,the most possible root cause is the lack of denitrification bacteria and iron-reducing bacteria.3.Optimize the operation parameter in the aspect of reducing operation cost,and find that using continuous adding is better than batch-type adding.The new system's outlet NO concentration can maintain below 40pm when initiate Fe(?)EDTA concentration is higher than 4mM.To reduce initiate Fe(?)EDTA concentration can reduce the loss rate of Na2EDTA which means saving operation cost. |
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