Carbon benefit assessment and path optimization of scrap steel utilization based on multi-standard comparison

As a key area of global carbon emissions, the steel industry's low-carbon transformation is of vital importance, and increasing the proportion of scrap steel usage is a crucial measure for steel enterprises to achieve carbon reduction. However, at present, there are two core problems in the carbon accounting of scrap steel, inconsistent standards and difficulty in coordinating technology and economy, which urgently need to be solved. This article aims to explore the optimized path for scrap steel utilization through multi-standard comparison and modeling, helping enterprises balance carbon reduction and benefits. The research systematically compared four major standards, the LCI methodology of the World Steel Association, the "Evaluation Method for Low-Carbon Emission Steel" of the China Iron and Steel Association, the Responsible Steel (RS) standard, and the German LESS, and analyzed the differences in the definition, classification, and accounting boundaries of scrap steel. In light of the production characteristics dominated by converters in China, a collaborative optimization model for thermal balance, material balance, and carbon emission-cost was constructed. The effects of carbon-based/silicon-based heat supplements and preheating of scrap steel on the scrap steel ratio were quantified, and the roles of scrap steel yield and the price difference between molten iron and scrap steel were explored. The results show that the "Evaluation Method for Low-Carbon Emission Steel" is more in line with the national conditions of China's steel production due to the introduction of localized parameters and is suitable to be used as a unified benchmark for domestic carbon accounting. Among the supplementary heating measures, preheating scrap steel is the optimal carbon reduction technical path, which can increase the scrap steel ratio by approximately 9% and has the least impact on the quality of molten steel. Coke supplementary heating can increase the scrap steel ratio by approximately 7%, while ferrosilicon supplementary heating only raises it by about 1%. In terms of the coordinated optimization of the economy and the environment, when the price difference between molten iron and scrap steel exceeds 300 RMB/t (LCI methodology) or 100 RMB/t (evaluation method for low-carbon emission steel), increasing the scrap steel ratio can achieve a win-win situation of carbon reduction and cost. In addition, the scrap steel harvest rate has a significant impact on the stability of material balance and economic and environmental benefits. Improving the quality of scrap steel is the core guarantee for high-proportion scrap steel smelting.