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At least 24 liquefied natural gas (LNG) rollover incidents have been reported since 1960. During rollover, because of the heat ingress through the tank walls, a stratified LNG may be suddenly homogenized while releasing massive amounts of vapor. It can result in an overpressure in the tank and significant amounts of potentially explosive LNG vapor being vented out. Both of these factors represent considerable hazards. Rollover is a physical mixing process in a single tank with two or more different cells of LNG of different compositions, temperatures, and densities that can manifest in large boil-off rates. It can exceed venting equipment capacities, and vapor pressure in tank increases rapidly and in extreme cases can lead to tank damage. This paper presents numerical approach for determination of time of rollover occurrence in storage tank. The presented model is based on the energy balance of the stratified cryogenic liquid and the gas phase as separate three thermodynamic systems in the storage tank. As a result of proposed model, for the adopted assumptions and cylindrical tank volume of 78,500 m3, the approximate time of the rollover occurrence was determined for two cases. In the first case, for heavier LNG, the rollover phenomenon will occur 193.25 h after the start of the calculations from the assumed initial conditions. In the second case, for light LNG with a higher initial liquid level in the tank, the rollover will occur after 150.25 h. [ABSTRACT FROM AUTHOR]

Over the last decade, developments could be observed in the structure of primary energy consumption in EU countries. In order to achieve the goals, energy carriers with minimum impact on the natural environment are used, and natural gas is considered to be such a fuel. The share of natural gas in the EU’s energy balance in the analysed period, from 2000 to 2016, remained at a relatively stable level. However, in the case of individual countries, its share in the energy balance depends on specific characteristics of a country. Regardless of the share of natural gas in the energy consumption structure of individual countries, they strive to diversify the supply of natural gas. One of the main constituents of natural gas supply diversification is the construction of LNG import terminals. Access to this infrastructure enhances energy security and offers better opportunities when negotiating long-term contracts for the supply of natural gas. The EU possesses significant possibilities of importing natural gas through LNG terminals, but until now they have been used to a limited extent, it may indicate that in addition todiversification tasks, terminals are a guarantee in the event ofinterruptions in gas supplies using gas pipelines.

Natural gas transmission is strongly connected with fire and explosion safety. Generally, explosion hazard occurs, when at least 5% of natural gas is present in the atmospheric air. As high-pressure gas transmission infrastructure includes many potential sources of gas releases, both operational and accidental, many different cases should be considered. To properly face the potential hazard of explosive atmosphere formation, the hazardous zone should be estimated. There are some guidelines, describing the process of hazardous zones calculating. This paper compares calculations of such hazardous based on Polish and European standards which are also valid in Poland. Calculations are focused on releases that may occur on the safety block and relief valve systems.