A coupled material-energy‑carbon flow method for quantifying changes in energy consumption and CO2 emissions of iron and steel sites

The iron and steel sites, being a quintessential energy-intensive and emission-heavy sector, urgently requires precise accounting methodologies to quantify the systemic impacts of material and energy flow variations on energy consumption and CO2 emissions. Current approaches predominantly focus on analyzing localized effects of individual material or energy flows, with synergistic interactions between different flows being oversimplified as linear superimpositions of their respective impacts. This simplification neglects the consequential effects that alterations in material or energy flows exert on associated units' energy consumption and CO2 emissions. To address these limitations, this study decouples the material-energy‑carbon flow models, establishing a relational model that links input material or energy flows to the energy consumption and CO2 emissions of upstream, current, and downstream units. Our investigation systematically examines how modifications in material or energy flows affect energy consumption and CO2 emissions throughout the entire production process. Results demonstrate that increasing scrap ratio, ratio of pellet to sinter, grade of sinter, oxygen enrichment rate, and imported coke can effectively reduce energy consumption and CO2 emissions across the entire production process. Notably, enhancing the scrap ratio yields the most significant improvement - increasing this ratio from 0.14 to 0.30 reduces energy consumption by 93.75 kgce (kilogram of coal equivalent) /tcs (ton of crude steel) and CO2 emissions by 269.76 kg/tcs. Furthermore, when the material and energy flows change simultaneously, the energy conservation and CO2 emissions reduction are not simply the linear sum of the changes caused by each flow. When the aforementioned factors increase together, the energy consumption and CO2 emissions of the on-site power plant decreased by 21.24 kgce/tcs and 7.64 kg/tcs, respectively. In contrast, when the changes induced by these five factors are summed linearly, energy consumption decreases by 70.25 kgce/tcs and CO2 emissions increase by 37.61 kg/tcs.