Averting rollover in LNG storage tanks

摘要

Cryogenic materials like LNG often behave strangely, and LNG is no exception. One example in the case of LNG is that when stored in a large tank it can form layers of differing densities that do not mix - a phenomenon described as stratification. The trouble with stratification is that it is an unstable situation. Taking as an example a tank in which two layers have formed (see diagram below), to begin with the layer at the bottom will be denser than the layer at the top. However, over time, the more volatile components will boil off from the upper layer, so that it gets richer and denser. Meanwhile, the lower layer is taking in heat from the ground and the tank walls but is prevented from releasing boil-off gas by the upper layer. As it warms it gets less dense.