Risk and safety assessment of an alkaline electrolyser system for green hydrogen production

Green hydrogen produced through electrolysis offers a sustainable alternative as a clean fuel, playing a crucial role in the global shift towards decarbonization. As green hydrogen production scales up, safety of hydrogen technologies becomes critical to both public trust and sustainable development. The aim of this study was to perform a risk and safety assessment of an alkaline electrolyser system for a green hydrogen production facility theoretically based in the Western Cape region (South Africa). The green hydrogen facility produced 59 ktpa of hydrogen for use in producing 280 ktpa green ammonia. The facility was powered by a renewable energy plant with an 80 % solar and 20 % wind fraction. A 2.2 MW alkaline water electrolyser, comprising 230 cells with a rated current of 5150 A was employed in the process design. A conservative operating current of 4000 A was assumed for the design basis to account for intermittent supply of renewable energy and stack degradation. At the assumed current, a lye circulation rate of 93 800 kg/h was required, i.e., 25 % potassium hydroxide solution, to produce 33.2 kg/h of hydrogen and 263 kg/h of oxygen. The approach for scaling up production entailed systematically scaling from one 2.2 MW stack to a four-stack module, one module to an eight-module cluster, and from one cluster to a 268 MW eight-cluster facility. Stacks required to produce 59 ktpa hydrogen were 244. These were oversized by 100 % to make 488 stacks, producing excess hydrogen for immediate supply to the ammonia plant during intermittent power supply. A 536 MW renewable energy plant was required to power the 244 electrolysers. This was oversized by 200 % to make 1.61 GW, reducing the electrolyser capacity factor. Hazard identification and risk assessment was used to evaluate high risk scenarios. Risks could be reduced to low risk ranks with reliable instrumentation. The highest hazard identified was the release of hydrogen with a 0.113 per annum release probability. The leading event for hydrogen release was due to improper valve management and flange leaks, more likely in larger plants. The probability of a jet fire, and a flash fire or a vapour cloud explosion were calculated as 0.00910, and 0.00475 respectively. Whereas the probability of hydrogen release with no ignition was 0.0735. Recommendations include establishment of shutdown procedures, LOPA studies, and standardisation of hydrogen specific failure rate data. Gas dispersion modelling was performed using ALOHA software for two locations, i.e., near Moorreesburg and the port of Saldanha. Results showed that hydrogen release from a 250 m3 storage presents the highest risk compared to release from a 200 m pipe in an hour. Threat distances for hydrogen release from a continuously fed pipe decreased by 50 % when the unbroken end of the pipe was immediately closed off upon detection of a leak. Locating the plant near the port of Saldanha was unfavourable since threat zones overlapped with nearby buildings. Modelling with computational fluid dynamics software is recommended for more accurate results. The outcome of this work provides an approach for upscaling and performing risk and safety assessment of hydrogen facilities.

Grantor dc:publisher

Stellenbosch : Stellenbosch University

Year dc:date.issued

2026

Author dc:creator

• Sinyage, Rendani Michelle

Advisors dc:contributor.advisor

• Naidoo, Paramespri
• Courtney, Devine

Language dc:language.iso

en

Repository record dc:identifier.uri

https://scholar.sun.ac.za/handle/10019.1/135843

OAI identifier oai:identifier

oai:scholar.sun.ac.za:10019.1/135843