JPS6330559B2 - - Google Patents

Description

[Detailed description of the invention] In a storage tank for low-temperature liquefied gas such as LNG,
When the specific gravities of the remaining liquid and the received liquid are different, the tank 1 shown in FIG. 1A may be stratified into two layers: a lower liquid 2 with a higher specific gravity d and an upper liquid 3 with a lower specific gravity d'.

At this time, the temperature of the upper layer liquid 3 is kept almost constant due to evaporation from the surface, but the lower layer liquid 2 accumulates heat and rises in temperature due to heat input from the bottom and side walls of the tank 1, and the specific gravity d gradually decreases. When the specific gravity difference between the upper layer liquid 3 and the lower layer liquid 2 disappears, rapid mixing and evaporation called a rollover phenomenon occur. Figures 1A to 1C are explanatory diagrams showing the process from stratification of the liquid stored in the tank to the occurrence of rollover, and Figure 2 is an explanatory diagram showing the process from stratification of the liquid stored in the tank to the occurrence of rollover. It is a chart showing changes in quantity and liquid specific gravity.

When the rollover phenomenon occurs, the amount of evaporated gas increases rapidly, and in the worst case, the tank may be destroyed.

The present invention was proposed in order to prevent rollover of such low-temperature liquefied gas storage tanks. The present invention relates to a rollover prevention method characterized in that, after cooling, the cooled storage liquid is returned to the lower layer of the tank.

In the present invention, as described above, in a tank in which the cooled storage liquid is layered in advance,
By pumping out the stored liquid from the lower part of the tank, cooling it outside the tank, and returning the cooled stored liquid, which has lowered its temperature and increased its specific gravity, to the lower part of the tank, the cooled stored liquid can be reused. Can be layered on the tank bottom. This layer is heated by heat input from the bottom of the tank, but by cooling and removing the amount of heat as described above, the heat input from the bottom to the lower liquid in the tank can be almost eliminated. Rather, the lower liquid is cooled on the upper surface of the cooled storage liquid.

Therefore, the heat input to the lower layer liquid in the tank is only from the side wall, the heat storage temperature increase rate of the lower layer liquid decreases, and the time until rollover occurs becomes longer, during which time the stored liquid in the tank is consumed or the lower layer liquid is transferred. By doing so, rollover can be prevented from occurring.

The present invention will be described below with reference to the illustrated embodiments.

11 is a storage tank for low-temperature liquefied gas such as LNG,
A stored liquid dispensing pipe 13 connected to a dispensing pump 12 disposed at the bottom of the tank 11 passes through a cooler 14 disposed outside the tank 11 and configured to be cooled with a coolant such as liquid nitrogen. Thereafter, it is inserted into the tank 11 again and is connected to a bottom feed pipe 15 that opens at the bottom of the tank.

Then, the pump 12 is driven to pump up the lower liquid 16 in the tank 11 through the discharge pipe 13 and cooled by the cooler 14 disposed outside the tank 11. The coolant 16', whose temperature has decreased and its specific gravity has increased, is transferred from the bottom feed pipe 15 to the tank 1.
The cooling liquid 16' is layered on the bottom of the tank 11 by supplying the cooling liquid 16' to the bottom of the tank 11. Coolant 1
The layer 6' is heated by heat input from the bottom of the tank 11, but by pumping out the cooling liquid 16' with the pump 12 and cooling it with the cooler 14, the cooling liquid 16' is heated. Remove the amount of heating,
In this way, heat input from the bottom of the tank 11 to the lower liquid 16 is almost eliminated, or rather, the heat input from the bottom of the tank 11 to the lower liquid 16 is reduced.
6' It is cooled on the upper surface.

By removing the heat input from the bottom of the tank 11 with the cooling liquid 16', the heat input to the lower layer liquid 16 is only from the side wall of the tank 11, and the heat storage temperature increase rate of the lower layer liquid 16 is reduced. , the time until rollover occurs becomes longer, and during that time tank 11
By consuming the internally stored liquid or transferring the lower layer liquid 16, rollover can be prevented from occurring.

As described above, when the stored liquid in the tank 11 is heated only from the side wall, as is well known, the natural convection boundary layer 17 on the tank side wall breaks through the lower surface of the upper layer liquid 18 in the tank and reaches the liquid level in the tank. Therefore, most of the heat input from the side wall is released through evaporation. At the same time, the lower layer liquid 16 is gradually taken to the upper layer and the amount of the lower layer liquid decreases, so that the interface 19 between the upper layer liquid 18 and the lower layer liquid 16 gradually descends as shown by the arrow in FIG. parts disappear.
In this manner, the amount of evaporation remains approximately constant while the boundary surface is lowered, and rollover with a sudden peak in evaporation amount is prevented from occurring. In addition, FIG. 5 is a chart showing changes in the height of the boundary surface and the amount of evaporation over time.

According to the rollover prevention method, there is no need to make any improvements to the tank itself, and it is only necessary to provide a cooler outside the tank, resulting in a significant reduction in equipment costs.

Although the present invention has been described above with reference to embodiments, the present invention is, of course, not limited to such embodiments, and can be modified in various ways without departing from the spirit of the present invention. .

[Brief explanation of the drawing]

Figures 1A to 1C are explanatory diagrams showing the process leading to the occurrence of a rollover phenomenon in the tank, Figure 2 is a chart showing changes over time in the amount of evaporation and the specific gravity of the upper and lower liquids in the tank, and Figure 3 is a diagram of the book. FIG. 4 is a vertical cross-sectional view of a tank to which the rollover prevention method according to the invention is applied, FIG. 4 is a vertical cross-sectional view showing its operating status, and FIG. This is a chart showing the changes. 11...tank, 12...dispensing pump, 13
...Stored liquid discharge pipe, 14...Cooler, 15...
Bottom feed pipe, 16... lower layer liquid, 16'...
Coolant, 18... Upper layer liquid.

Claims (1)

[Claims] 1. A rollover prevention method characterized by pumping out the stored liquid from the lower layer of the tank, cooling it, and then returning the cooled stored liquid to the lower layer of the tank in a tank in which the cooled stored liquid is layered in advance.