LCA study of an innovative process for the production of green steel

Steel is crucial for modern infrastructure, transportation, and energy sectors, playing an important role in global economic growth. However, the steel industry is a major source of carbon emissions, especially from fossil-based methods such as Blast Furnace + Basic Oxygen Furnace (BF-BOF) and Natural Gas–based Direct Reduction of Iron coupled with Electric Arc Furnace (NG-DRI-EAF). As global steel demand rises, there is a necessity to explore more sustainable methods to reduce this sector’s environmental impacts. This study evaluates the environmental impacts of the H2STEEL process, an innovative approach for producing green hydrogen and bio-based solid carbon from circular biowaste streams, aligned with the EU’s decarbonization targets. The objective is to evaluate the environmental performance of this process, which converts sewage sludge into a waste-derived carbon catalyst that is subsequently employed in biomethane cracking for hydrogen production, and to compare it with a conventional natural gas-based route (NG-DRI-EAF). By providing a sustainable alternative to fossil-based hydrogen and carbon sources, H2STEEL process supports the steel industry’s transition to low-carbon solutions, contributing to a carbon-neutral Europe. To evaluate the environmental impacts, a Life Cycle Assessment (LCA) was conducted following ISO 14040 and ISO 14044 standards. The functional unit for the study is defined as one ton of Hot Rolled Coil (HRC), and the system boundary is set to Cradle to Gate (CTG), covering all processes from raw material extraction to product delivery at the factory gate. The data used in this study is obtained from the Ecoinvent v3.10 database, complemented by data from literature. The impact assessment employs several established methodologies to evaluate the environmental effects. The IPCC 2021 methodology is used to assess Global Warming Potential (GWP100). The EF v3.1 method evaluates human toxicity, freshwater ecotoxicity, Ozon layer depletion, Photochemical Oxidant Formation, resource depletion, and the Cumulative Energy Demand (CED) method measures total energy consumption. The H2STEEL process shows reduced impacts in Global Warming Potential (GWP), Cumulative Energy Demand (CED), Ozone Layer Depletion (OLD), and Photochemical Ozone Formation (POF), indicating its effectiveness in decreasing fossil fuel dependency and associated emissions. However, Resource Depletion (RD) is increased in the H2STEEL process, resulting from the use of nitric acid in the biocoal production stage and infrastructure requirements for biomethane production in DRI and Biomethane cracking stages. The remaining impact categories, including Human Toxicity-Carcinogenic (HTC), and Freshwater Ecotoxicity (FE) show negligible differences between the two processes. Overall, the H2STEEL process offers improvements in carbon emissions and energy efficiency but presents trade-offs related to resource depletion, therefore emphasizing the need to improve upstream stages, such as biocoal production, particularly by replacing nitric acid with more sustainable alternatives to reduce environmental burdens.