Carbon footprint of scenarios towards climate-neutral steel according to ISO 14067

Abstract

Within this paper, new findings of the potential of four considered intermediate solutions towards a primary climate-neutral steel production are reported. (1) Injection of natural gas into a blast furnace, (2) injection of hydrogen into a blast furnace, (3) natural gas-based direct reduction with subsequent input of the hot briquetted iron (HBI) in a blast furnace, and (4) hydrogen-based direct reduction with subsequent input of the hot briquetted iron in a blast furnace.The current study is a carbon footprint assessment applied to the product hot-rolled coil (HRC) according to the ISO norm 14067:2019. A cradle to gate approach is used including the production of raw materials to the production of hot-rolled coil. To define a reference point, a carbon footprint of hot-rolled coil produced via a typical blast furnace – basic oxygen furnace (BF-BOF) route is presented. The basic data set is based on primary data from the integrated site of thyssenkrupp Steel Europe AG (tkSE), year 2018. Within a novel approach, this base line is enhanced by integrating metallurgical models from the literature. Thereby all changes of the complex material and energy supply chain of an integrated site and of the upstream chain are reported. The carbon footprint of each process unit is presented in detail so that optimization potentials are identified, which impacts are analysed within a sensitivity analysis. A holistic comparison of using hydrogen in a blast furnace to using hydrogen in a direct reduction plant is presented and delivers important findings. This can help steel producers to maximize the efficiency of hydrogen use.Since the focus of this paper lies on the comparison of steel production routes and the assessments for all considered scenarios are based on the same methodologies and databases the sensitivity of made assumptions on the deltas between these scenarios is much weakened than the sensitivity of absolute values. That's one of the reasons why, the conclusions of this paper, which are referred to the plant of tkSE, can be transferred to other production sites, as well. The presented results can help decision-makers to know the potentials of possible intermediate solutions towards a climate-neutral steel production and how the potentials can be maximized.The carbon footprint of the product hot-rolled coil is 2.1 t CO2eq/tHRC following the recycled content approach and 0.82 t CO2eq/tHRC following the end-of-life recycling approach. The reduction potential for the carbon footprint is about 4 % for injecting natural gas into a blast furnace and about 9 % for injecting hydrogen into a blast furnace. The hydrogen is produced via electrolysis driven by a renewable German energy mix, year 2018. Using hot briquetted iron (HBI) within a blast furnace leads to a reduction potential between 5 % and 12 % for natural gas based-HBI and between 10 % and 17 % for H2-based HBI. The reduction potential strongly depends on the iron feedstock, which is replaced by the hot briquetted iron. Between 4.5 and 7.0 kg CO2eq/kg H2 are avoided by injecting hydrogen into a blast furnace, and about 5.4 kg CO2eq/kg H2 are prevented if the hydrogen is injected into a direct reduction plant.