Life Cycle Theory Based Research On Environmental And Economic Impact Assessment Of Ultra-low Emission Treatment Technology Of Sintering Flue Gas In Steel Industry

Steel is the main industrial product widely used in the world,and China's steel output has remained the world's first since 1996.In 2018,China's total crude steel output reached 928 million tons,accounting for 51.3%of the world's total output.However,the steel industry has always been a typical resource and energy-intensive industry and it is also an industry with a large amount of pollutants.Among them,the major air pollutants emitted by the steel industry account for about 7.35%of the national total industrial emissions.In the steel production process,the sintering process is the process with the largest emissions of particulate matter,SO2,NOx and other air pollutants in the steel industry.The implementation of ultra-low emission treatment of steel sintering flue gas will help reduce the total amount of regional pollutant emissions and improve environmental quality.In order to control the emissions of particulate matter,SO2,and NOx,the ultra-low emission policy of the iron and steel industry promulgated by the Chinese government requires that the concentration of particulate matter,SO2,and NOx emissions must not exceed 10,35,and 50 mg/m3,respectively.The transformation of ultra-low emission treatment technology in the steel industry is being rolled out across the country,which poses a serious challenge to the pollutant emission control technology in the steel industry.In this study,a combination of a life cycle assessment method and a life cycle costing analysis method was used to study the ultra-low emission treatment technology of sintered flue gas from a steel company in China.After the transformation of ultra-low emissions,the emission concentrations of particulate matter,SO2,NOx,PCDDs and other pollutants were reduced by 96.55%,99.2%,91.2%,and 96.6%,respectively,and the pollutant concentrations reached the emission standards.With 1 ton of sinter as the functional unit and "cradle to gate" as the system boundary,the environmental impact and economic cost analysis of electrostatic precipitation process,ozone oxidation process,lime-gypsum wet desulfurization process,wet denitration process,condensation dehumidification process,wet electrostatic precipitation process and the discharge of residual pollutants were carried out.The results show that the total environmental impact caused by this technology is 0.1811,and the main environmental impact categories are freshwater eutrophication,human toxicity,freshwater ecotoxicity and marine ecotoxicity.The main environmental load is concentrated in the wet denitration and ozone oxidation processes,sodium sulfite in the wet denitration process,electricity and liquid oxygen in the ozone oxidation process are the key materials that cause environmental impact The total economic cost of ultra-low emission treatment per functional unit is 172.79 RMB,of which internal cost is 34.64 RMB and external environmental cost is 138.15 RMB.Of the total cost,the ozone oxidation process contributed 70.44 RMB,followed by the wet denitration process contributed 63.12 RMB;but ozone oxidation contributed the largest internal cost,and wet denitration contributed the largest external cost.Combining environmental impact and economic cost analysis,the key process optimization order was determined as wet denitration process and ozone oxidation process;the key materials optimization order was sodium sulfite in wet denitration process,liquid oxygen and electricity in ozone oxidation process.Based on the "3R"principle of circular economy,optimization measures based on sintered flue gas emission technology were proposed.For example,controlling the generation of NO from the source,pre-granulating or modifying the coke during sintering,and rationally controlling the oxidation degree of NO in flue gas can reduce the consumption of sodium sulfite.According to the real-time pollutant concentration change of the sintering flue gas to reasonably control the production input of ozone,the consumption of liquid oxygen can be adjusted.Adopting a cleaner gas phase ClO2 oxidant method or emulsifying yellow phosphorus method for denitrification can replace the ozone oxidation process to reduce environmental impact and economic cost.In terms of electricity use,the choice of clean energy alternatives such as steel waste heat utilization may reduce the environmental impact caused by electricity.In addition,the localized life cycle inventory and environmental impact and cost analysis results established in this study also provide a theoretical basis and reference for China's steel sintering flue gas ultra-low emission retrofit project.