Abstract

Climate change requires transforming the production processes of high-emission industries toward low-carbon technologies. One of the main emitters of greenhouse gases is the steel industry. Therefore, steel manufacturers are planning to substitute the blast furnace-basic oxygen furnace route with hydrogen-based direct reduction and electric arc furnaces. Thus, direct greenhouse gas emissions can be avoided almost entirely. This involves changes in the materials and energies used. Besides hydrogen, natural gas is becoming more important for the direct reduction of iron ores. Therefore, future greenhouse gas emissions associated with low-carbon steelmaking are deeply intertwined with the developments of the system environment. Upon potential transformation pathways of the system environment, future greenhouse gas emissions from natural gas and hydrogen-based direct reduction coupled with electric arc furnaces are investigated. To this end, a prospective cradle-to-gate life cycle assessment approach is used. The results indicate that greenhouse gas emissions highly depend on the electricity mix if hydrogen is produced by electrolysis. Using natural gas for direct reduction is a viable short-term option until the decarbonization of the energy sector is further advanced.

Introduction

Due to climate change, it is required to decarbonize highemission industries such as the steel industry. Approximately 7% of global greenhouse gas (GHG) emissions result from steelmaking processes, especially from primary steelmaking [1]. In most cases, the coal-based blast furnace-basic oxygen furnace (BF-BOF) route is used for the primary production of crude steel [2]. However, alternative technologies for reducing direct GHG emissions of steelmaking already exist. As of today, most steel manufacturers are planning to substitute BFBOF production facilities with direct reduction plants (DRP) and electric arc furnaces (EAF) from 2025 onwards [3–۵]. In this process design, sponge iron is produced within the DRP. Afterward, the sponge iron is further processed within the EAF for crude steel production. Existing DRPs are currently solely operated with natural gas (NG/DR) for direct reduction [1]. The NG/DR-EAF process serves as a transitional technology in the transformation process of integrated steel mills toward lowcarbon steelmaking. In the long term, NG/DR can be substituted by hydrogen-based direct reduction (H/DR) of iron ore. If hydrogen is used, direct GHG emissions can be reduced by up to 97% [6]. A framework for designing economically advantageous transformation pathways is developed within [7].

Conclusion

Most European steel manufacturers are planning to transform their integrated steel mills’ production infrastructure toward DR-EAF production to significantly reduce GHG emissions from primary steelmaking. This article consists of a prospective cradle-to-gate LCA approach for DR-EAF steelmaking. For environmental impact assessment, it is differentiated between NG/DR, H/DR with hydrogen from electrolysis using the German electricity mix, and H/DR with hydrogen from electrolysis using electricity from onshore wind turbines. The developed assessment provides an understanding of the environmental impacts of the DR-EAF route considering different future developments of the system environment.

This study finds that direct GHG emissions can be reduced by around 96% if H/DR-EAF production is applied to substitute the BF-BOF route. However, indirect GHG emissions are highly intertwined with future developments of the system environment. Thus, fast decarbonization of the energy sector is highly important to heavily reduce overall GHG emissions. Also, GHG emissions from raw material extraction, processing, and transportation need to be reduced to aim for a low GHG emission steel industry. Process-related, direct GHG emissions are higher when NG/DR is applied. Indirect emissions, however, are less affected by system environment developments. Thus, natural gas provides a viable short-term option for the DR process. Besides decarbonization of the system environment which needs to be driven by policymakers, steel manufacturers need to focus on measures to increase their shares of low-carbon hydrogen in the early phase of the transformation process. To this end, electrolysis capacities need to be installed if sufficient external hydrogen sources for H/DR are not available. Also, increasing the share of low-carbon electricity to operate electrolysis facilities is of high importance.