Estimation of LNG evaporation rate due to the fluctuation of atmosphere temperature and pressure (1)

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  • 外気温度及び大気圧力変化によるLNG蒸発量の変動予測(その1)
  • 外気温度及び大気圧力変化によるLNG蒸発量の変動予測-1-
  • ガイキ オンド オヨビ タイキ アツリョク ヘンカ ニ ヨル LNG ジョウハ

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For the LNG carrier, the rate of LNG evaporation (hereinafter boil off rate, BOR) is settled under certain design conditions of temperature, pressure, cargo component, etc., for instance 0.25%/day, and the particulars of LNG handling equipments and the properties of tank insulation are decided accordingly. During the actual sea voyage, however, the temperature of atmosphere and sea water and the atmosphere pressure are not constant and vary with time. Thermal variation results in the change of heat gain to the tank and the pressure variation results in the distortion of equilibrium state of LNG which was stable at a saturated state, because the vapor pressure in the tank is controlled in close connection with the atmosphere pressure. These two influential factors lead to the change of LNG BOR in a short term. According to this change of BOR adjustment of LNG, gas handling machinery and the pre-estimated consumption of LNG should be modified. In this paper authors stated the theory of estimation method of LNG BOR necessary for a satisfactory operation of machinery and a more accurate estimation of LNG consumption during voyage. As a result, authors indicated that daily or hourly variation of BOR could be calculated with the knowledge of temperature and pressure in advance, and the control of BOR could be possible within a certain range. Numerical studies should be further done analyzing the empirical or actual ship data for the confirmation of the theory and the establishment of correlation coefficient.

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