(398c) Optimization of Steel Decarbonization Strategies in the United States

Hard-to-abate sectors, such as iron and steel, have fossil fuel intensive processes that have been used to materials for centuries¹. Given the US climate goals for 2030 and beyond, the iron and steel sector will require decarbonization strategies to reduce CO₂ emissions². Currently, majority of the world produces primary (non-recycled) steel with coal-based production methods. Within the US, primary steel is often produced from iron using the blast furnace (BF) In the ironmaking process, coal is used as a reducing agent to transform raw ore (iron oxide) into hot iron metal. Then, the hot metal becomes the desirable steel in the basic oxygen furnace (BOF) where composition of carbon is controlled¹. Raw material preparation, such as coking, sintering, and pelletization, is also required. The emissions for this process is over 2 tonnes of CO₂ per tonne of crude steel (tCO₂/t steel)³. There is also direct reduced iron (DRI) process, which is occurs in three US plants, where iron pellets are reduced in a shaft furnace by natural gas⁴. Afterwards, steel can be produced using an electric arc furnace (EAF). This process generates about 1-1.4 tCO₂/t steel^1,5. Both of these processes rely on fossil fuels, which is not suitable for US climate goals: 50-52% GHG reduction compared to 2005 levels by 2030 and net zero emission by 2050². As the fourth largest steel producer, the US has to transition its steel sector to more environmentally friendly manufacturing³.

The cost and emission analysis are developed and evaluated using the Sustainable Energy Systems Analysis Modelling Environment (SESAME). SESAME is a software tool that conducts life cycle, techno-economic, and systems-level analysis for power, transportation, and industrial sectors^6,7. Specifically, the SESAME Industry Model calculates cradle-to-gate CO2 emissions for the raw material preparation, ironmaking, and steelmaking steps. A combination of literature and industry sources provide material and energy inputs for the plant-level carbon balance. SESAME currently includes the following steel production routes: BF-BOF (and with CCS), HIsarna-BOF (and with CCS), COREX-BOF (and with CCS), DRI-EAF (Coal, Natural Gas, Natural Gas with CCS, Electrolytic Hydrogen), and scrap-based EAF. Molten oxide electrolysis (MOE) and DRI-EAF natural gas with CCS is also to be incorporated. Costs are based on capital and operational expenditures sourced from literature and industry reports and scaled accordingly. Overall, the SESAME Industry Model is a user-facing tool that assists in estimating emissions & costs for decarbonization for the iron and steel industry within the US and beyond. For optimizing the steel sector production routes, a linear program in Python, using Pyomo, is applied to provide greenfield analysis. Constraints are based on Ryan et al, which limits the percentage of primary production routes and restricts the scrap-based production based on available scrap⁸.

Current preliminary results indicate (with 2040 electricity grid intensity) a large difference in cost and emissions depending on the objective function. For minimization of gate-to-gate emissions, the cost is about $70.8 billion and 69.5 Mt of CO₂ with a mix of NG-DRI, H2-DRI, EAF, BFBOF with CCS, and COREX with CCS. Meanwhile, the minimization of cost leads to $61.6 Billion and 158 Mt of CO₂ with a mix of BFBOF, COREX, NGDRI, and H2DRI_. Comparing the two scenarios yields a nearly $104 cost of CO_2. In addition, there is nearly 20 MT more scrap consumed in the emission minimization case. Further analysis will evaluate the optimum mix to reach US climate goals and consider brownfield (current infrastructure) scenarios.

Sources

(1) IEA. Iron and Steel Technology Roadmap - Towards More Sustainable Steelmaking. 2020, 190.

(2) National Climate Task Force. The White House. https://www.whitehouse.gov/climate/ (accessed 2023-02-26).

(3) Christopher D. Watson. Domestic Steel Manufacturing: Overview and Prospects; Summary; Congressional Research Service, 2022. https://crsreports.congress.gov/product/pdf/R/R47107 (accessed 2023-02-21).

(4) Global Energy Monitor. Global Steel Plant Tracker. https://globalenergymonitor.org/projects/global-steel-plant-tracker/ (accessed 2022-05-16).

(5) Sarkar, S.; Bhattacharya, R.; Roy, G. G.; Sen, P. K. Modeling MIDREX Based Process Configurations for Energy and Emission Analysis. Steel Res. Int. 2018, 89 (2), 1700248. https://doi.org/10.1002/srin.201700248.

(6) Gençer, E.; Torkamani, S.; Miller, I.; Wu, T. W.; O’Sullivan, F. Sustainable Energy System Analysis Modeling Environment: Analyzing Life Cycle Emissions of the Energy Transition. Appl. Energy 2020, 277, 115550. https://doi.org/10.1016/j.apenergy.2020.115550.

(7) Gençer, E. SESAME. https://sesame.mit.edu/ (accessed 2022-04-11).

(8) Ryan, N. A.; Miller, S. A.; Skerlos, S. J.; Cooper, D. R. Reducing CO2 Emissions from U.S. Steel Consumption by 70% by 2050. Environ. Sci. Technol. 2020, 54 (22), 14598–14608. https://doi.org/10.1021/acs.est.0c04321.