Comparing the Safety of Bunkering LNG, LH2 AND NH3 Using Quantitative Risk Assessment- A PhD Thesis Summary

Kurzfassung

The shipping industry, responsible for approximately 3% of global greenhouse gas emissions, is under increasing pressure to transition to low-carbon fuel sources. Hydrogen, along with methanol and ammonia, has emerged as a promising alternative to conventional fossil fuels. While liquified hydrogen (LH2) boasts superior gravimetric storage densities, its extremely low temperature of 20 K presents significant technical challenges. In comparison, liquified natural gas (LNG), already widely adopted for maritime use, operates at a significantly higher temperature, approximately 90 K above LH2. Even higher temperatures of 240 K or a pressure of approx. 10 bar at ambient temperature are employed for the storage of ammonia (NH3). Besides the ignition hazards present between all three fuels, ammonia is toxic as well. A critical aspect of implementing hydrogen-based fuels involves the safe and efficient bunkering process, which includes transferring LH2 via flexible pipelines or loading arms, necessitating rigorous safety protocols to mitigate associated risks. The thesis employed a quantitative risk assessment to compare the safety of bunkering LNG, as a state-of-the-art benchmark to the safety of bunkering LH2 and NH3. Initially, the frequencies of the hazardous events “pool fire”, “flash fire”, “vapor cloud explosion” and “toxicity/asphyxiation” are obtained by means of an event tree. Subsequently, the consequences of each event are modeled and translated into a required safety distance. A comparison is made between the frequencies and safety distances of two distinct systems. The initial system exhibits uniform pipe diameter for all three fuels, consequently yielding substantially divergent bunkering durations for each fuel type. In the second system, the pipe diameter is adapted in a manner that yields the same bunkering duration for all three fuels. The findings indicate, that the pipe diameter of the system and the duration of bunkering have a substantial influence on the frequencies of the hazardous events. Conversely, the pipe diameter has no influence on the consequences for a leak of the same size. An observable influence is only evident in the context of a full rupture. The dispersion cases, flash fire and toxicity/asphyxiation, require for all fuels the largest safety distances, thereby dictating the overall safety distance.