Substituting natural gas with hydrogen: A case study on mass, energy, and emissions in electric arc furnace steelmaking

Abstract

This study sets out to explore the use of hydrogen into steelmaking via the electric arc furnace route, weaving together technoeconomic analysis with a comprehensive carbon footprint assessment. Through a detailed examination, we scrutinize the financial prospects of integrating hydrogen within a scrap-based steel mill, using Liberty GFG's data for a case study. Based on the data, the steel plant's annual consumption is 1.2 million GJ/y of energy, primarily derived from natural gas, to produce 0.75 million tonnes of steel. We explore the potential of replacing this natural gas with 10-kilotonnes of hydrogen per year (1.35 t/h), considering the steel mill's capacity factor of 0.82. By employing sophisticated flowsheet-based calculations, we unravel the environmental implications of integrating hydrogen into the steelmaking process. The investigation reveals that the plant consumes 2.9 GJ per tonne of steel from natural gas, indicating a demand of 23.5 kilograms of hydrogen to completely supplant natural gas. This equates to 2.35 kilograms of hydrogen per tonne of steel for every 10% displacement of natural gas. At present, the comprehensive cost of employing hydrogen stands at US$ 144 per tonne of steel, predicated on a wind electricity price of US$ 38 per MWh. In contrast, utilising natural gas amounts to US$ 58 per tonne of steel. However, the horizon holds promise for a substantial reduction in hydrogen costs over the next decade, heralding a potential paradigm shift in its utilisation. The emission analysis shows that the plant produces greenhouse gas emissions of 735 kgCO2e/t steel, out of which 70% is due to the use of dominant fossil electricity and the rest 30% (223 kgCO2e/t steel) from other carbon sources such as natural gas, lump coke, coke fines, and diesel fuel. Modeling proposes that a complete substitution of grid electricity and natural gas would lead to process emissions totaling 104 kgCO2e/t steel. To achieve a net-zero emission target, a strategic shift is suggested: replacing lump coke and coke fines with biochar. This substitution not only eliminates lifecycle emissions but also paves the path towards realising a sustainable, carbon-neutral future.