Doctoral Network on the adoption of Hydrogen mEtalLurgy In the climate-neutral production Of Steel - HELIOS

WP1: Hydrogen-based primary steelmaking through the H-DR route

WP1 targets research objective RO1 by developing novel methods, advanced models and key datasets indispensable for efficient and flexible H-DR based primary steelmaking processes. This objective is driven by 3 technical challenges related to full scale and full potential hydrogen-based steelmaking: (1) optimize the DR shaft process operating with hydrogen as main reductant; (2) Create a flexible and efficient carburization and melting process of H2-Direct Reduced Iron (H-DRI) accommodating low-grade pellets; and (3) ensure the same steel quality as the BF-BOF produced steel. For each of these challenges, we defined innovative research topics for which the findings will excel the current knowhow, methods and process tools.

For the first challenge, although a shaft furnace operating with hydrogen as main reductant is based on the same process technology as well-established shaft furnaces operating with natural gas blended with hydrogen (Midrex or Energiron Shaft Furnace), it leads to two important differences: (1) the heat balance is different, because of the stronger endothermic nature of the H2 reduction reactions compared to the reactions in CO/H2 mixtures from natural gas; and (2) carbon needs to be introduced to the H-DRI to facilitate its subsequent melting and to obtain steel with the required carbon content. In addition, the current commercial natural gas-based DR process can handle only high-grade iron ore as DR grade pellets, which accounts for only 20% of the total iron ore resources. Creating appropriate working conditions for the H-DR process for the remaining 80% of the iron ore resources (normal or BF pellets) is essential for the major transition from carbon-based BF ironmaking to the H-DR process. This requires a profound study to elucidate the optimal way to achieve for different pellet grades both high reduction degrees and ideal carbon contents, preferably from renewable resources. For this, DC1 at TU Delft will determine the complex reduction and in-situ carburisation phenomena in the reduction, transition and cooling zone of a direct reduction shaft furnace. DC1 will design lab-scale tests to investigate the effect of varying reducing-gas compositions (H2, CO, CO2, CH4, H2O, N2) and temperatures (up to 1050 °C) on the reduction and degradation behaviour of different BF and DR grade pellets and sinter. Through a sensitivity analysis, the effect of the process conditions and pellet grade on the final product quality will be assessed. DC1 will also study the in-situ reforming of methane/hydrocarbons, used as carburisation agent for the DRI, and determine the gas utilisation efficiency through advanced gas property analysis.

The second challenge is related to the melting of the H-DRI pellets to make liquid steel directly or to prepare a hot metal for making steel in the existing BOF process. This can be done in either an existing Electric Arc Furnace (EAF) or in an electric smelter, such as an Open Slag Bath Furnace (OSBF). Although it is possible to create zero carbon DRI using hydrogen-based reduction, an appropriate amount of carbon is overall beneficial to the melting process and is anyway needed to meet the minimum requirement to make steel: Carbon not only reduces iron oxides in the burden and the slag, it lowers the melting point of the liquid steel and it provides chemical energy in the EAF/OSBF through its oxidation, thereby contributing to the decrease of needed electrical power. A crucial aspect is therefore the optimal introduction and nature of carbon in H-DRI pellets to facilitate melting, preferentially using biomass as an alternative C source for carbon neutral steelmaking. Besides carbon, another important aspect for the melting is the pellet grade. The production of fossil-free steel has been proven (cf example by the Associated Partner SSAB in the HYBRIT project), although only from DR grade pellets which is based on iron ore with a higher quality than the iron ore currently processed in the BF-BOF route. In view that a tenfold rise in DR-grade iron ore supply in the coming decades may be hard to realize, we consider in HELIOS the way forward is to perfect the smelting of low-grade DRI[1]. In brief, to meet the carbon content in the steel product and to improve the yield and productivity of the melting, including lower energy consumption and time-to-tap, there needs to be a.o. efficient C sourcing, optimized raw material mixtures and the right foamy slag practice. The Beneficiaries TU Delft and University of Oulu will tackle this by two strategies: (1) DC2 at TU Delft will adopt an experimental approach, developing novel carburisation methods and designing pellets with improved melting characteristics; and (2) DC3 at the University of Oulu will develop a dynamic process model to assess the use of different pellet grades and foaming agents on the melting rate. DC2 will develop novel carburization methods, using in-situ carburisation and reduction processes in connection with DC1 and applying biomass as C-source, to create carburized pellets in a specially designed high-temperature furnace leading to the desired melting characteristics. DC3 will develop an advanced dynamic model for the EAF furnace based on mass and energy balances, and including modules for scrap melting, gas phase reactions, metal-slag reactions and slag foaming. The model will use the Channel Arc Model (CAM) approach to provide a physically relevant description of the plasma and its effect on the radiative heat transfer. DC3 will also apply machine-learning algorithms on offline information to tune the model parameters and use online measurements by offgas, vibration or Optical Emission Spectroscopy to validate the predicted melting rate.

Finally, to ensure a steel quality with at least the same quality as obtained in the BF-BOF route, DC4 at TU Delft will investigate in a thermodynamic and kinetic study the influence of H-DRI hot metal on the converter process practices and develop new strategies to control and optimize the process through the metal-slag equilibrium. This project is connected to DC2 through the carburization degree of the H-DRI, as the C concentration plays a critical role on the refining process.