Design of Clean Steel Production with Hydrogen: Impact of Electricity System Composition

In Europe, electrification is considered a key option to obtain a cleaner production of steel at the same time as the electricity system production portfolio is expected to consist of an increasing share of varying renewable electricity (VRE) generation, mainly in the form of solar PV and wind power. We investigate cost-efficient designs of hydrogen-based steelmaking in electricity systems dominated by VRE. We develop and apply a linear cost-minimization model with an hourly time resolution, which determines cost-optimal operation and sizing of the units in hydrogen-based steelmaking including an electrolyser, direct reduction shaft, electric arc furnace, as well as storage for hydrogen and hot-briquetted iron pellets. We show that the electricity price following steelmaking leads to savings in running costs but to increased capital cost due to investments in the overcapacity of steel production units and storage units for hydrogen and hot-briquetted iron pellets. For two VRE-dominated regions, we show that the electricity price following steel production reduces the total steel production cost by 23% and 17%, respectively, as compared to continuous steel production at a constant level. We also show that the cost-optimal design of the steelmaking process is dependent upon the electricity system mix.

Development of a Mass and Energy Balance Model and Its Application for HBI Charged EAFs

A static mass and energy balance model combined with a MgO saturation slag model is developed for electric arc furnaces. The model parameters including distribution ratios and dust factors are calibrated for a specific furnace using experimental data. Afterward, the model is applied to study the effect of charging different amounts of hot briquetted iron (HBI) on energy consumption, charged slag former amount, and slag composition. The following results were obtained per each 1% increase of HBI additions: (i) a 0.16 Nm3/t decrease in the amount of injected oxygen for metal oxidation, (ii) a 1.29 kWh/t increase in the electricity consumption, and (iii) a 34 kg increase in the amount of the slag.

Study of hot briquetted iron secondary oxidation speed aimed at forecasting of its metallurgical value retention duration

Hot briquetted iron (HBI), as also metallized pellets, undergo oxidation during transportation and storing. To forecast acceptable duration of HBI storing with metallurgical value retention it is important to have scientifically based data on the briquettes secondary oxidation speed. Methods of determining metallized pellets secondary oxidation speed are presented in domestic and foreign practice, but the matter of HBI secondary oxidation in scientific and technicalliterature practically is not covered. To determine HBI secondary oxidation speed two methods elaborated and tested at the Department of metallurgy and metal science of Stary Oskol Technological Institute after A.A. Ugarov (branch of National Research Technological University “MISiS”). The first– weighting method – based on determining of metal iron content change in HBI during a long term storing. During the experiment the mass of each briquette was weighted every 12 h within a month. The result of metal iron content determining by the experiment and by a chemical analysis had a difference of less than 1%. The weighting method enables to obtain the HBI reaction ability values without particular expenses, but requires carrying out long term enough experiments untilcomplete moisture removal out of the studied samples. The other method – determination of oxygen absorption speed bybriquettes in a closed vessel. It enables determining the reaction ability of the reduced iron within a comparatively short period, enables sufficient reliability duringthe briquettes testing. Based on it a methodology elaborated for determining of HBI secondary oxidation speed, meeting the requirements of real production. During loading-unloading operations, briquettes can partially go to ruin. The forming fragments of different sizes undergo a higher degree of oxidation that decreases the HBI metallurgical value. In view of this, studies of HBI oxidation speed continue depending on different sizes content and finalization of the methodology of determination of HBI secondary oxidation speed.