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[Display omitted] • Exergy loss of enterprise is optimized by building mathematical programming model. • Influences of 9 key factors on system's total exergy loss and cost are discussed. • Recovery and utilization of waste heat are optimized by detailed technical models. • Waste heat potential and heating capacity of enterprise are evaluated. • Interface loss between upstream & downstream processes is quantified by exergy. A substantial quantity of waste heat resources generated in iron and steel manufacturing process (ISMP) can fulfill certain demand for urban heating. However, the waste heat utilization level of different iron and steel enterprises varies a lot and few studies have combined the upstream enterprise's production with downstream waste heat utilization for discussion. By establishing an optimization model based on material balance, thermodynamic laws and reaction mechanism of the ISMP, this study firstly obtain the minimum exergy loss and the corresponding production cost ＆ exergy efficiency. The total exergy loss of ISMP is reduced from 8413.19 MJ/t-MS to 7669.27 MJ/t-MS. The exergy efficiency of the whole process is increased from 63.75 % to 65.46 % and the total waste heat potential reaches 1471.25 MJ/t-MS. It is found that coke ratio, air leakage rate, scrap steel ratio, etc. have great impact on exergy loss of ISMP. Then, the optimization and evaluation of the waste heat utilization are carried out by establishing models with taking urban heating into consideration. The available external heat supply is 813.15 to 853.55 MJ/t-MS and the enterprise's heating load can reach 229.23–251.47 MW, which allow to supply heat for an area of 5.46–5.93 million m2. Finally, the problem of waste heat instability in the heating process is briefly discussed and some solution strategies are proposed to overcome this defect. [ABSTRACT FROM AUTHOR]

The traditional iron and steel industry (ISI) began to implement technological innovations aimed at lowering carbon footprint and emissions, resulting in hydrogen metallurgy gradually becoming a new trend of green development in ISI. However, there is a lack of comprehensive and in-depth analysis of energy-exergy based on the second law of thermodynamics in the current research of hydrogen metallurgy. To address these issues, a numerical calculation model of hydrogen metallurgy based on material-energy-exergy is established. Two novel evaluation indexes are introduced to better evaluate the impact of various parameters on hydrogen metallurgy. It was found that the exergy intensity is mainly affected by the amount of reducing gas, and increasing the preheating temperature of the ore cannot always reduce the exergy intensity due to the influence of element conservation. And when the ore preheating temperature is higher than 623 K, the exergy utilization efficiency decreases. After calculation, the lowest exergy intensity is 1.23 × 107 kJ/t-DRI when the H 2 content is 41.37% and the ore temperature is 773 K. Furthermore, a simple process is designed to recover a substantial volume of unreacted gas from the furnace top gas. Overall, this study can serve as a reference for actual hydrogen metallurgy production. [Display omitted] • A material-energy-exergy model based on the second law of thermodynamics is created. • In addition to the traditional evaluation indexes, two novel ones are also introduced. • Preheating ore temperature above 623 K reduces the exergy utilization efficiency. • Rising ore preheating temperature does not decrease exergy intensity continuously. • A simple waste energy recovery process is proposed. [ABSTRACT FROM AUTHOR]

For the objective of carbon neutrality stated by the global climate conference, the iron and steel industry, a major carbon emitter, must transition to green and low-carbon development as quickly as feasible. Hydrogen metallurgy direct reduction technology has attracted much attention because of its low emission. However, the current study on hydrogen metallurgy shaft furnace lacks a comprehensive in-depth analysis of gas consumption, gas utilization, and exergy intensity. To tackle these problems, a material and energy optimization model including intermolecular chemical reaction is established. The original process is optimized by this model, the gas utilization is enhanced by 26.7%, gas consumption is decreased by 906.34 m3/t-DRI, and exergy intensity is reduced by 8.8 GJ/t-DRI. Furthermore, the impacts of gas composition, gas temperature, and ore temperature on gas consumption, gas utilization, exergy structure, and exergy intensity, as well as their interactions, are investigated thoroughly. The analysis highlighted that properly reducing hydrogen content and increasing gas and ore temperature can improve gas utilization and reduce gas consumption. Simultaneously, lowering gas consumption can effectively lower exergy intensity. And furnace top gas exergy is closely related to gas utilization. On the whole, it is advantageous to promote the development of hydrogen metallurgy by conducting in-depth and systematic analyses. [Display omitted] • An NLP model including intermolecular chemical reactions is established. • The accuracy of the model is verified by actual production data. • The material and energy assessments are presented considering the exergy of energy. • Relationships of gas utilization, exergy intensity are thoroughly considered. • Suggestions are proposed to improve the energy utilization in actual production. [ABSTRACT FROM AUTHOR]