Investigating The Environmental Sustainability Of Flue Gas Denitration Systems Based On Emergy Analysis

Nitrogen Oxides,as one of main air pollutants,can cause photochemical smog,acid rain,ozone hole and other environmental problems when being discharged into the atmosphere.According to Chinese official statistic data,thermal power industry is the main source of total NOx emissions in China,and the flue gas denitration system plays an irreplaceable role in reducing NOx emissions from this industry.Therefore,the evaluation of resource efficiency,environmental impact and economic benefit of the flue gas denitrification system from the pros and cons can reflect its environmental sustainable level more completely.Compared to other environmental impact assessment methods,emergy analysis considers the quality differences of diverse categories of energy,material and money and the environmental contribution to economic activity,so it can be used to quantify the negative impact of the pollution emissions and the environmental benefit of this system,so as to give a comprehensive evaluation of a flue gas denitration system.This dissertation took two typical flue gas denitration systems as cases studied(one is a Selective Catalytic Reduction(SCR)denitration system,and the other is a Selective Non-Catalytic Reduction(SNCR)denitration system).It adopted an emergy method,which was combined with Ecological Dilution Method,Disability Adjusted Life Years(DALY)Method and Land Occupation Method to quantify pollution emissions’ impacts,and then the corresponding indicator system characterizing the flue gas denitration system was set up to evaluate this system’ s performance.The study results were summarized as follows:(1)For the SCR flue gas denitrification system,the total emergy input is 3.55E+19 sej,of which 98.60%comes from non-renewable resources and 99.97%comes from purchased resources(especially purchased non-renewable resources account for the largest proportion).For the SNCR flue gas denitration system,the total emergy input is 3.76E+18 sej,of which74.50%comes from non-renewable resources and 75.04%comes from purchased resources.Similarly,purchased resources,especially purchased non-renewable resources,account for the largest proportion.(2)The direct emissions’ impact of the SCR gas denitrification system is 3.82E+18 sej while the indirect impact is 1.16E+20 sej.The direct emissions’ impact of the SNCR gas denitrification system is 3.76E+18 sej while the indirect impact is 7.35E+17 sej.(3)As for direct emissions’ impact of the SCR denitrification system,the main contributor of ecological services is NO_x(54.93%),and the main contributor of emergy loss is dust(55.96%).For indirect emissions’ impact,the main contributor of ecological services is ammonium ion(52.35%),the main contributor of emergy loss is SO_x(82.57%),and the production process of titanium dioxide and vanadium pentoxide is the main pollution source.(4)For direct emissions’ impact of the SNCR denitrification system,the main contributor of ecological services is SO_x(92.46%),and the main contributor of emergy loss is SO_x(95.17%).For indirect emissions’ impact,the main contributor of ecological services is dust(36.88%),and the main contributor of emergy loss is also dust(88.3%).(5)According to the classic emergy index system,the values of PESI of the SCR and the SNCR flue gas denitrification systems are 0.00027 and 0.44186,respectively.When the impact of emissions being considered,the former is improved to 0.00327 and the latter is reduced to 0.05802.Generally these two systems are unsustainable in the long term.Finally,this dissertation puts forward the following suggestions for improving the comprehensive performance of flue gas denitrification systems,including(1)implementing clean production;(2)researching and developing or introducing regeneration technologies of denitrification catalyst;(3)optimizing the resource structure of the flue gas denitration systems,and(4)improving the pollutant control measures.