Application of Liquid Hydrogen Carriers in Hydrogen Steelmaking

Steelmaking is responsible for approximately one third of total industrial carbon dioxide (CO₂) emissions. Hydrogen (H₂) direct reduction (H-DR) may be a feasible route towards the decarbonization of primary steelmaking if H₂ is produced via electrolysis using fossil-free electricity. However, electrolysis is an electricity-intensive process. Therefore, it is preferable that H₂ is predominantly produced during times of low electricity prices, which is enabled by the storage of H₂. This work compares the integration of H2 storage in four liquid carriers, methanol (MeOH), formic acid (FA), ammonia (NH₃) and perhydro-dibenzyltoluene (H18-DBT), in H-DR processes. In contrast to conventional H₂ storage methods, these carriers allow for H2 storage in liquid form at moderate overpressures, reducing the storage capacity cost. The main downside to liquid H₂ carriers is that thermochemical processes are necessary for both the storage and release processes, often with significant investment and operational costs. The carriers are compared using thermodynamic and economic data to estimate operational and capital costs in the H-DR context considering process integration options. It is concluded that the use of MeOH is promising compared to the other considered carriers. For large storage volumes, MeOH-based H₂ storage may also be an attractive option to the underground storage of compressed H₂. The other considered liquid H₂ carriers suffer from large thermodynamic barriers for hydrogenation (FA) or dehydrogenation (NH3, H18-DBT) and higher investment costs. However, for the use of MeOH in an H-DR process to be practically feasible, questions regarding process flexibility and the optimal sourcing of CO₂ and heat must be answered