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TransAT-LNG is an analytical model (further improvement of the original approach of Heestand et al. 2004, A predictive model for rollover in stratified LNG tanks, AIChE J., 29-2.) designed for use in risk assessment and safety analysis in conjunction with the rollover phenomenain LNG storage tanks (safety analysis). The model predicts incipient rollover because the long times and multiscale nature of the problem make it expensive to perform 3D CFD. The issues of interest in the incipient rollover phenomena that can be treated by TransAT LNG are:

  • Start time of Rollover phenomenon
  • End time of Rollover phenomenon
  • Calculate flow from heat ingress in tank
  • Production of BOG

If two liquefied natural gas from different sources are brought together in a storage tank, the lighter LNG (red curve ) may lie over the heavier LNG ( blue curve) and could eventually lead to rollover.



Physics and Workflow

TransAT-LNG requires the following input data:

  • Mole fractions
  • Temperature
  • Layer height
  • Heat fluxes through tank walls

TransAT-LNG produces the following outputs:

  • Rollover time
  • Boil off rate

Example: la Spezia accident 1971

La Spezia accident in 1971 was caused by “rollover” where two layers of LNG with different densities and heat content formed. The sudden mixing of these two layers resulted in the release of large volumes of vapor. About 2,000 tons of LNG vapor were discharged from the tank safety valves and vents over a period of a few hours, damaging the roof of the tank.

The input data are reported in the Tables below:

  • Mole fractions
  • Temperature&Layer heights
  • Heat fluxes through tank walls

The results produced by TransAT-LNG for a total time of 31Hare as follows:

  • Rollover time
    The figures below compare TransAT LNG results (density overt time) with those of Desphande et al (2011), showing a good agreement between the two strategies.

  • Preferential boil-off:
    Species evolution in the lower layer (blue), upper layer (red), liquid film (yellow) and vapor film (black)


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