Views: 5 Author: Site Editor Publish Time: 2021-12-20 Origin: Site
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, and the difference in liquid density is the stratification of LNG in the storage tank. Generally, when the temperature difference in the vertical direction of the liquid in the tank is greater than 0.2°C 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 generally filled.
When filling heavy weight into a light weight storage tank, it is better to fill at the top; when filling light weight into a heavy weight storage tank, it is better to fill it at the bottom. Using mixing nozzles and perforated pipes for filling can fully mix the charged new LNG with the original LNG, thereby avoiding stratification.
If the liquid in the storage tank has stratified, part of the heat absorbed by the upper liquid will be consumed by the latent heat required for the evaporation of the liquid on the liquid surface, and the remaining heat will increase 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.