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Computer program for simulating the rollover phenomenon during the storage of the stratified layers of liquefied natural gas.

Number: pap. n. 091

Author(s) : BELGACEM A., REBIAI R., BELMEDANI M.

Summary

The rollover phenomenon occurs when two stratified layers of liquefied natural gas (LNG) with different temperatures and/or densities are stored for a long period in the same tank. The stratification will appear when the light layer is stored above the heavier one, or when the cold layer is stored on the warm one. The incoming of heat from the surroundings and from the bottom of the tank is the source of the evaporation of both layers. As the upper layer in contact with the free surface of the tank, the evaporation of its components (the light hydrocarbons and the nitrogen) causes an increase in its density. However, this heat will be trapped in the lower layer which can’t evaporate, so the density will stay slightly constant. After a period of storage the two densities will equalize, this result in a rollover and a sudden mixing, followed by an important evaporation called « boil off ». In fact, this study is based essentially on the comprehension and interpretation of the phenomenon of rollover and its evolution in the time. It allowed the authors to develop a mathematical model leading to a computer program whose purpose is to predict in advance the time of the mixing and the intensity of evaporation rates. The program can also be performed to evaluate the variation of the properties (temperature, density, compositions) of each layer before, during and after the rollover. For validation of the model they compared their results with two existing theoretical models (HMS, Sugawara) and the practical results of the best documented incident occurred in the complex of La Spezia (Italy). From the results of the simulation, solutions can be proposed in order to predict and possibly prevent the development of rollover due to the change of the temperature and/or density in storage conditions.

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Pages: 427-434

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Details

  • Original title: Computer program for simulating the rollover phenomenon during the storage of the stratified layers of liquefied natural gas.
  • Record ID : 30007014
  • Languages: English
  • Source: Cryogenics 2012. Proceedings of the 12th IIR International Conference: Dresden, Germany, September 11-14, 2012.
  • Publication date: 2012/09/11

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