Modelling of Accident Scenarios from Liquid Hydrogen Transport and Use

Abstract

Hydrogen is one of the most suitable candidates to replace hydrocarbons and reduce the environmental pollution and CO2 emissions. Hydrogen is valuable energy carrier, potentially clean and renewable thanks to its peculiar properties. However, hydrogen has a few characteristics, such as high flammability and low density that must be taken into account when stored or handled, especially in relation to the associated safety. For this reason, this PhD study aims to increase the knowledge on safety of hydrogen technologies. Hydrogen safety is a broad topic which involves several disciplines. This PhD focusses on the modelling of atypical accident scenarios of liquid hydrogen (LH2) technologies by adopting a multidisciplinary approach. This type of accident scenarios is called atypical because they have low probability to happen but high consequences. A few times, the neglection of these scenarios by conventional risk assessment techniques led to major accidents. For this reason, the atypical accident scenario cannot be omitted during a risk assessment and must be further analysed. Firstly, through a comprehensive literature review, this PhD study investigates the causes of loss of integrity (LOI) and loss of containment (LOC) of hydrogen equipment since the atypical accident scenarios always occurred after these critical events. The consequences of an LH2 release are then analysed. The focus is placed on the boiling liquid expanding vapour explosion (BLEVE) and the rapid phase transition (RPT) explosions for liquid hydrogen technologies because a significant dearth of knowledge is still present. Secondly, the possibility for the BLEVE to occur after the catastrophic rupture of an LH2 vessel is theoretically assessed by gathering information on previous accident and applying accepted thermodynamic theories for this event. The consequences of a potential BLEVE for LH2 (pressure wave, missiles and fireball) are evaluated. Unique experimental series on LH2 bursting tank scenario and fire tests are simulated. Different approaches are employed for the BLEVE event: analytical models, empirical correlations and CFD analysis. Finally, the time to failure of an LH2 tank exposed to a fire is estimated with a thermal node model. Thirdly, the RPT event is analysed from a more theoretical approach since no records of LH2 RPT are found in literature. The knowledge gained for other substances such as liquefied natural gas (LNG) and liquid nitrogen (LIN) is applied to LH2. The consequences of a hypothetical LH2 RPT are evaluated by means of an analytical model and compared to the LNG RPT aftermath. The main contributions of this PhD study are the following: • investigation on the causes of LOI of hydrogen technology; • identification of the LH2 release consequences; • understanding of the BLEVE feasibility for LH2 storage systems; • determination of the LH2 BLEVE consequences; • estimation of the time to failure of LH2 tanks exposed to a fire; • analysis of the theories and mechanisms of RPT explosions; • determination of the LH2 RPT consequences. This PhD study provides relevant safety indications on the causes of LOI of hydrogen technologies as well as on the BLEVE and RPT phenomena for LH2 technologies. The knowledge gap in these topics is highlighted and partially fulfilled. The limitations of existing models for the simulation of these explosions are emphasised. The results of this thesis serve as a starting point for future studies.