Filling method when LNG encounters stratification and rollover

Layering

LNG is a multi-component mixture, and changes in temperature and composition will cause density changes. The difference in liquid density is the stratification of LNG in the storage tank. Generally, when the vertical upward temperature difference of the liquid in the tank is greater than 0.2℃ and the density difference is greater than 0.5kg/m³, it is considered that the liquid in the tank has stratified.

The liquid stratification in the LNG storage tank is often caused by the different density of the filled LNG or the high nitrogen content of the LNG. Choosing the correct filling method can effectively prevent delamination. When the density is similar, the bottom is usually filled.

When filling the heavy weight into the light weight storage tank, the top is filled; when filling the light weight into the heavy weight storage tank, the bottom is filled. Using mixing nozzles and perforated pipes for filling can fully mix the charged new LNG with the original LNG, thereby avoiding stratification.

Roll

If the liquid in the storage tank has been stratified, part of the heat absorbed by the upper liquid is consumed and the latent heat required for the evaporation of the liquid on the liquid surface, and the remaining heat increases the temperature of the upper liquid.

As the evaporation continues, the density of the upper liquid increases, and the density of the lower liquid decreases. When the density of the upper and lower liquids is close, the boundary layer disappears, the liquid layers are mixed quickly and accompanied by a large amount of liquid evaporation, the evaporation rate at this time is much higher than Normal evaporation rate, tumbling occurs.

With the appearance of the tumbling phenomenon, a large amount of gas is emitted from the storage tank in a short period of time. If no measures are taken, unnecessary waste and loss will be caused.