Study Of Waste Energy Recovery And Energy Efficiency Improvement In China's Iron And Steel Industry

As main energy-intensive manufacturing industries,China's iron and steel industry(CISI)consumes tremendous primary energy,most of which lost as metallurgical associated gas and waste energy.Literature review shows that waste energy recovery and utilization presents a crucial opportunity in primary energy reduction and energy efficiency improvement for the global manufacturing industry.However,lack of systematic and practical methodology,the exact quantity of waste energy is often poorly quantified.In addition,the present studies focus on energy-saving potential from the thermodynamic theoretical perspective;insufficient understanding of the benefits and cost effectiveness of technology has created barriers to the wide promotion of energy—saving technology.Taking tremendous potential waste energy of CISI as main research object,this thesis applying the first law and second law of thermodynamics,thermo-economic theory and other related ones to fill the research gaps,aims to identifying practical waste energy recovery and utilization potential in CISI,and to provide scientific and reliable theoretical basis for maximizing the energy efficiency of steel production systems and minimizing the corresponding energy costs.Firstly,the theory and evaluation methods of waste energy are reviewed,and the drawbacks and limitation of traditional research methods are pointed out.The main research method of exergetic analysis,thermo-economic matrix method,and energy conservation supply curve(ECSC)are established.And then,this thesis presents a set of novel evaluation index,from the perspectives of reasonable energy utilization,technical feasibility,and investment efficiency,to evaluate waste energy potential and energy efficiency improvement comprehensively.Based on the actual production data,this thesis develops the energy and exergy flow metabolism model at process level to analyze the quantity,quality,main recycling technology,and potential associated with waste energy resources.Finally,a typical benchmarking flow is constructed,and the energy and exergy flow diagram of the system are mapped with e!Sankey software.The results show that the exergy efficiency of the sintering process is only 18.76%.However,the largest loss of the system is the blast furnace process,the total exergy loss coefficient of which is 17.59%.The energy efficiency and exergy efficiency of the system under present technology recovery level are 40.15%and 24.92%,respectively;and the highest recovery rate located in coking process.The utilization of 13 recycling technologies improves the systematic exergy efficiency by 2%.Based on the model of thermodynamic analysis and the structural theory of thermo-economic,a set of generalized thermo-economic modeling method and malfunction diagnosis platform for "multi—stream coupling" complex production system are constructed.This thesis develops a thermo-economic model,the physical structure model is included,to calculate unit exergy cost of 64 flows by application of thermo-economic analysis of energy systems software(TEASS),and analyze the thermodynamic process of cost formation and the distribution of the resources throughout the main product.The reason for malfunction cost and increase of the irreversible loss from each processes are quantified and diagnosed.The results show that the unit exergy cost of the sintering process is the highest,and the malfunction cost of which accounts for 51.4%of the total system malfunction cost.Compared with the reference state,the operation state with waste energy recovery system reduces extra exergy consumption of the system of 347.0 MJ.An ECSC model is developed to analyze benefits and cost effectiveness of thirty-five energy—saving technologies.The results show that the cumulative energy savings of all technologies is 3.08 GJ/t steel,the energy savings of the nineteen cost-effective technologies of which account for 62.67%,and pulverized coal injection has the lowest cost of conserved energy.Scenario analysis shows that technology implementation is the main driver for energy consumption reduction.Sensitivity analysis indicates that energy price and discount rate have greater significant influences on the cost effectiveness of energy saving technologies.