Research On Life Cycle Multi-Objective Integrated Evaluation Of Sintering Flue Gas Treatment Process In The Iron And Steel Industry

The demand for iron and steel has been increasing with the rapid industrialization and urbanization.As the world's largest steel producer,China's steel output accounted for 56.5%of the world's total steel output in 2020.As an economic pillar industry,the rapid development of iron and steel industry(IS I)has brought a heavy pressure to the ecological environment.In 201 7,the emissions of SO2,NOx,and particulate matter in China's ISI reached 1.06 million tons,1.72 million tons,and 2.81 million tons,accounting for 7%,10%and 20%of the total national emissions,respectively.ISI has surpassed the power sector and has become the largest pollutants emitter in the industrial sector.As an important part of steel production,sintering process has large emissions of flue gas,various pollutants,high concentration and complex composition,which is a difficult and key point for the flue gas treatment.In April 2019,China issued an ultra-low emission policy for the ISI,stipulating that the emission concentration limits for particulate matter,sulfur dioxide and nitrogen oxides in the flue gas from sintering machine head are 10,35 and 50 mg/m3,respectively.Since then,the sintering flue gas ultra-low emission transformation in China's ISI has officially kicked off,which is not only an important measure to win the battle against the blue sky,but a major thrust for the high-quality development and green development of ISI.In this context,China's ISI is facing new challenges in the management of air pollutants.How to implement pollutant treatment technology with good environmental benefit,low economic cost and good technical performance to achieve ultra-low emission standards has become a issue that needs to be solved in ISI.This paper selects three typical sintering flue gas ultra-low emission treatment technologies as research objects(S1 Technology:semi-dry flue gas desulfurization+semi-dry flue gas denitration with O3+bag filter;S2 Technology:wet flue gas desulfurization+wet electrostatic precipitator+selective catalytic reduction denitration;S3 Technology:semi-dry flue gas desulfurization+bag filter+selective catalytic reduction denitration),constructs a life-cycle multi-objective decision model,and performs an integrated evaluation study of the three technologies from three dimensions of environmental pollution,economic cost,and technical performance.The ReCiPe2008 model is selected to quantify the 18 midpoint environmental impact categories in the environmental dimension.The economic dimension is measured by two indicators:investment and renovation costs and operational costs.The indicators of technological dimension consist of technology maturity,environmental risk,safety risk,potential of waste comprehensive utilization,and difficulty of system operation and maintenance.In this paper,the environmental impacts of three technologies are assessed by life cycle assessment(LCA),based on the production of 1 ton of sinter as a functional unit and "cradle to gate" as the system boundary.According to the standardization results,the S1,S2 and S3 technologies have produced a total environmental impact of 0.1822,0.1298 and 0.1170 per functional unit,respectively.The economic costs of the three technologies are evaluated using life cycle costing(LCC),which are 11.622RMB,10.353RMB,and 10.435RMB per functional unit,respectively.The performance of the three technologies in the technological dimension is evaluated using TOPSIS combined with TFAHP method.The relative closeness of S1,S2 and S3 to the optimal solution is 0.5710,0.4219 and 0.4248,respectively.The TOPSIS method is applied for the integrated evaluation of the three technologies in environmental,economic,and technological dimensions.When the decision-makers have no decision preference and the three indicators are given the same weights,the relative closeness of the three technologies is 0.4142,0.5572 and 0.5822,respectively.Therefore,S3 is the optimal choice,followed by S2 and finally S1.When the weights of environment,economy and technology change,S3 is still the first choice in the optimal scheme.Among all the weight combinations,the probability of S3 becoming the optimal option accounts for 48%.After the identification of environmental and economic key processes,key factors and sensitivity analysis for each of the three technologies,the optimization sequence and optimization scheme are determined.The first is the optimization of electric power structure.Driven by the goals of "Carbon Peaking" and "Carbon Neutrality",the construction of a new power structure based on new energy will become a huge revolution in China's energy sector,which will not only reduce carbon emissions,but reduce pollutant emissions from the source.The second is optimizations for other key factors including the use of catalysts to reduce the demand for ozone,the addition of antioxidant inhibitors to the sodium sulfite absorber,improving the absorption efficiency of calcium-based absorbers for NOx,and replacing lime with calcium carbide slag in the semi-dry desulfurization process.Third,at the technological level,some optimization measures are proposed,such as using the sintering waste heat,residual gas or residual pressure of steel production process to generate electricity,adopting high efficiency equipment and improving equipment operation to reduce the impact of electric power consumption.This study provides a reference for the selection of ultra-low emission technology in the future for the ISI,and offers technological support and theoretical guidance for the government's decision-making and deployment of ultra-low emission transformation in the future.