Predicting triggering and consequence of delayed LNG RPT

Accidental Combustion Phenomena at Cryogenic Conditions

The presented state of the art can be intended as an overview of the current understandings and the remaining challenges on the phenomenological aspects involving systems operating at ultra-low temperature, which typically characterize the cryogenic fuels, i.e., liquefied natural gas and liquefied hydrogen. To this aim, thermodynamic, kinetic, and technological aspects were included and integrated. Either experimental or numerical techniques currently available for the evaluation of safety parameters and the overall reactivity of systems at cryogenic temperatures were discussed. The main advantages and disadvantages of different alternatives were compared. Theoretical background and suitable models were reported given possible implementation to the analyzed conditions. Attention was paid to models describing peculiar phenomena mainly relevant at cryogenic temperatures (e.g., para-to-ortho transformation and thermal stratification in case of accidental release) as well as critical aspects involving standard phenomena (e.g., ultra-low temperature combustion and evaporation rate).

Liquid Hydrogen Spills on Water—Risk and Consequences of Rapid Phase Transition

Liquid hydrogen (LH2) spills share many of the characteristics of liquefied natural gas (LNG) spills. LNG spills on water sometimes result in localized vapor explosions known as rapid phase transitions (RPTs), and are a concern in the LNG industry. LH2 RPT is not well understood, and its relevance to hydrogen safety is to be determined. Based on established theory from LNG research, we present a theoretical assessment of an accidental spill of a cryogen on water, including models for pool spreading, RPT triggering, and consequence quantification. The triggering model is built upon film-boiling theory, and predicts that the mechanism for RPT is a collapse of the gas film separating the two liquids (cryogen and water). The consequence model is based on thermodynamical analysis of the physical processes following a film-boiling collapse, and is able to predict peak pressure and energy yield. The models are applied both to LNG and LH2, and the results reveal that (i) an LNG pool will be larger than an LH2 pool given similar sized constant rate spills, (ii) triggering of an LH2 RPT event as a consequence of a spill on water is very unlikely or even impossible, and (iii) the consequences of a hypothetical LH2 RPT are small compared to LNG RPT. Hence, we conclude that LH2 RPT seems to be an issue of only minor concern.

Forensic analysis on bursting accident of buffer tank in liquefied natural gas bus

In December 2019, a buffer tank burst accident occurred in the maintenance of liquefied natural gas (LNG) bus in China. Failure analysis revealed the bus-mounted buffer tank had been subjected to an excessive internal pressurization, although the tank material met the specifications for engineering practice. The physical evidence related to the failed tank showed that a chemical explosion was impossible. As water was used to pouring the frozen pipeline prior to the accident, according to the consequences observed, the rapid phase transition (RPT) explosion of the residual LNG due to external heat from water was regarded as the main causation of incident. The explosion energy was inversely estimated by the TNT equivalent method, and the rapid expansion of natural gas produced excessive pressure, thus causing the buffer tank to explode.