Safety studies for clean energy applications: pressure-liquefied ammonia release and hydrogen risk analysis

Abstract

This doctoral research explores critical knowledge gaps in the safe use of ammonia both as a hydrogen carrier and a marine fuel. Employing advanced Computational Fluid Dynamics (CFD) techniques, the study provides significant insights into key safety challenges related to ammonia storage and handling. Three comprehensive CFD models were developed to simulate ammonia behaviour across various scenarios. The first model investigated flash boiling and the subsequent pressure recovery phenomenon during ammonia venting from a tank’s ullage space. The simulation captured the characteristic delay in vapor bubble formation and the progressive release of evaporated ammonia, revealing the mechanisms driving pressure recovery. The second model focused on large-scale ammonia gas dispersion, integrating real-time meteorological data to simulate wind fields with high accuracy. By capturing atmospheric turbulence and wind meandering, the model was validated against experimental data, successfully replicating transient concentration fluctuations and decay up to 800 meters from the release point. This confirms its predictive capability for estimating hazard distances related to ammonia’s toxicity and flammability. The third model introduced a novel numerical approach to simulate dynamic flash boiling during releases from the bulk liquid phase. A modified phase change mechanism was developed to handle varying mass transfer rates based on phasic volume fractions, addressing complexities linked to interfacial area densities. The model accurately reproduced the experimental pressure and temperature data, including the observed cooling effects at the nozzle. Beyond CFD modelling, the thesis presents a novel quantitative risk assessment (QRA) framework tailored for emerging energy infrastructures. This framework was demonstrated through a case study on hydrogen tank rupture incidents in road tunnels, integrating inherently safer design principles. The scalable approach enables application to other alternative fuels and scenarios. Overall, this research advances CFD modelling and QRA methodologies, offering valuable contributions to safety engineering and risk management for ammonia and hydrogen-based energy systems.

Date of Award	Oct 2025
Original language	English
Supervisor	Vladimir Molkov (Supervisor), Dmitriy Makarov (Supervisor) & Donatella Cirrone (Supervisor)