Cradle-to-gate life cycle assessment of hydrogen delivery using an iron-based redox carrier

Abstract

Hydrogen could contribute to low-carbon energy systems; however, its environmental performance does not merely depend on production technology, but also on transport, delivery pathways and storage. This research study assesses an iron-based redox carrier route for hydrogen delivery, where hydrogen is released in Finland via Wet oxidation of powdered iron and the resulting iron oxides are returned to Spain for regeneration and reuse.

The aim of the study was to quantify the climate impacts of delivering 1 kg of hydrogen at the system gate in Finland using an iron-based carrier loop, within a cradle-to-gate system boundary. Sphera LCA for Experts was used to conduct this process-based, attributional life cycle assessment. Two foreground configurations were modelled in the study: a virgin carrier reference configuration and a regenerated-carrier configuration with virgin make-up iron. Both configurations were evaluated under grid-mix and renewable electricity supply scenarios, while the climate impacts were assessed using Global Warming Potential 100 (GWP)100 and GWP20 indicators.

Key findings demonstrate that carrier regeneration lowers the climate impact of the entire system under both electricity supply scenarios. Considering GWP100, the highest impact was reported by the virgin-carrier reference configuration under grid-mix electricity, accounting for an impact of around 32 kilogram carbon dioxide equivalent per functional unit (kg CO2-eq/FU), whereas the lowest impact of around 11 kg CO2-eq/FU was reported by the regenerated-carrier configuration under renewable electricity. Regeneration has reduced GWP100 climate impact by about 54% under grid-mix electricity and around 24% under renewable electricity. In all modelled scenarios, GWP20 values were higher than GWP100 values, however the ranking of the scenarios remained consistent.

Accordingly, the contribution analysis reveals that electricity-intensive virgin-carrier production is a major hotspot in virgin-carrier reference configuration under grid-mix electricity. Once regeneration and renewable electricity is applied to the system, transport driven climate impacts become the prominent remaining contribution. Results show that the climate performance of the iron-based carrier loop is dependent on the combined effects of carrier regeneration, electricity supply, carrier loss compensation and logistics. Findings of the study are specific to the cradle-to-gate system boundary modelled between Spain and Finland. Future studies could investigate carrier losses, regeneration efficiency, logistics and comparisons with established hydrogen delivery routes using consistent system boundaries.