Green Steel World June 2025 | Page 35

� GREEN DRI �

The energy system for green hydrogen production

Hölling et al.¹ calculated the hydrogen requirement for hot briquetted iron( HBI) production using the direct reduction process based on the production at ArcelorMittal’ s Hamburg plant. With an annual production of 1 Mt HBI and a specific hydrogen demand of 528 Nm ³/ t HBI, plus a purging rate of 10 %, a demand of 635 Nm ³/ t HBI is needed. These values are confirmed by other authors.², ³ This study uses the value of 635 Nm ³/ t HBI, resulting in an annual hydrogen demand of 53,404 t H 2 for a 1 Mt DRI process plant – or about 6.1 t H 2

/ h. To keep the reduction process efficient, this level of hydrogen must be supplied continuously over the years.

According to M. El-Shafie 4, modern electrolyzers can produce hydrogen at up to 19 kg H 2

/ MWh. Considering a 1 % annual degradation rate, an average constant production rate of 18 kg H 2

/ MWh over 10 years is assumed for both baseload and cyclic operation. This requires electrolyzers with a capacity of about 338 MW and a power purchase agreement( PPA) of at least 2.967 TWh for hydrogen production. To meet the steel industry’ s decarbonization targets, the power demand should be generated with as high a share of renewable energy as possible.

As stated above, the main challenge for a reliable green hydrogen supply arises when intermittent RES like wind and PV are used. To evaluate green hydrogen production, different boundary conditions based on hourly generation profiles in various countries are considered. These profiles – sourced from renewables. ninja 5 and based on 2019 weather data – are analyzed throughout the whole year( see details in Table 1). For onshore wind, the hub height has been adjusted according to assumptions by the National Renewable Energy Laboratory( NREL) of the U. S.

Department of Energy, to align with their published installation costs.

The RES profiles for Spain and Oman assume grid connection, allowing the use of non-RES power. In a second stage, a BESS is added to further reduce the carbon footprint of hydrogen production – up to producing it completely green.

Australian profiles are assumed to be off-grid, prioritizing power for a 24 / 7 mining operation as the primary consumer. Remaining RES generation can be used for hydrogen production, either for export to the steel industry offshore( for the 1 Mt DRI plant) or for producing green pig iron locally.

The energy system was optimized for the lowest investment costs, with accuracies of ± 50 MW for RES generation, ± 10 MW for electrolyzer installation, and BESS ratings of 200 MW, 400 MW, 600 MW, and 800 MW – with capacities of 2 h, 4 h, 6 h,

Country Latitude Longitude PV Configuration a Wind Onshore b

a

PV configuration: Tilt = 35 °, Azimuth = 180 °, Tracking = No b

Wind onshore: Hub height 98 m Table 1. Data selected for RES power generation. 5 For the wind profiles, a Vestas V90-2000 was se lected with adjusted hub heights.

Green Steel World | Issue 18 | June 2025 35