JP3404783B2 - Dispensing method of low-temperature liquefied gas - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for discharging a low-temperature liquefied gas from a low-temperature tank, and more particularly to a method for discharging a low-temperature liquefied gas which does not generate gas even when the liquid level is low. It is related to the payout method. 2. Description of the Related Art A low-temperature tank for storing a low-temperature liquefied gas such as LNG and LPG is provided with a drain nozzle for discharging the stored liquid as a low-temperature liquefied gas. The low-temperature tank is a tank having a closed structure, and the upper side of the liquid level of the stored liquid is filled with a low-temperature gaseous liquefied gas. Since the drain nozzle discharges the low-temperature liquefied gas in the liquid phase, the drain nozzle is provided near the bottom of the low-temperature tank. FIG. 2 is a cross-sectional view of a low-temperature tank showing the structure of a conventional drain nozzle. The drain nozzle 20 is inserted through the low-temperature tank 21 substantially horizontally at a predetermined height.
The drain nozzle 20 is bent downward in the low-temperature tank 21. The suction port 22 of the drain nozzle 20 has a tip near the bottom 23 of the low-temperature tank 21 and
3 is provided. Outside the low-temperature tank 21, an on-off valve 24 is connected to the drain nozzle 20, and a pipe 25 connected to a payout destination is connected to the on-off valve 24. Although not shown, a payout pump is provided on the payout side, and payout is performed by suction with this pump. The height of the drain nozzle 20 from the bottom 23 is, for example, 350 mm, which is considerably lower than the height of the low-temperature tank 21. Further, the height of the suction port 22 is 50
mm and almost touches the bottom 23. Since the suction port 22 of the drain nozzle 20 is provided near the bottom 23 of the low-temperature tank 21 as described above, the suction port 22 is immersed in the liquid storage L even when the liquid level is low. further,
Since the suction port 22 faces the bottom 23, the gas G is prevented from being entrained from the gas phase portion in the low-temperature tank until the liquid level is just below its height. [0005] The low-temperature tank 21 is entirely composed of
6 and is well kept at low temperatures. Normally, the temperature of the storage liquid L is kept exactly at the boiling point.
For example, in the case of LNG, the boiling point is −162 ° C. under the pressure of 1000 mmAq, so in the low-temperature tank 21 storing LNG, the pressure in the gas phase is 1000 mmAq, and the temperature in the liquid phase is −162 ° C. ing. This is true whether the liquid level is high or low. [0006] However, it has been found that the fact that the temperature of the storage liquid L is at the boiling point poses a problem when dispensing by the drain nozzle 20. That is, when the liquid level is lower than the height of the drain nozzle 20, the following problem occurs. Here, FIG. 3 shows a state in which the horizontal portion 30 of the drain nozzle 20 is located above the liquid level S because the liquid level has become low. [0007] When the internal pressure of the portion of the gas phase at this time as P _1, the pressure on the liquid surface S is P _1. On the other hand, the horizontal portion 30 of the drain nozzle 20 at a height h from the liquid level S
Static pressure P _{2 of, P 2 = P 1 -hρ (} ρ is the specific gravity of the liquid reservoir), and a lower pressure than P _1. When P ₁ = 1000 mmAq, the boiling point is lower than −162 ° C. in the horizontal portion 30 of the drain nozzle 20 because the pressure is lower than P ₁ . On the other hand, since the temperature of the storage liquid L is -162 ° C., the storage liquid La (hereinafter referred to as “transfer liquid”) sucked into the drain nozzle 20 from the suction port 22 and sent to the payout destination is also −162.
° C. Then, in the horizontal portion 30 of the drain nozzle 20, the temperature of the transfer liquid La exceeds the boiling point. For this reason, the transfer liquid La boils violently in the drain nozzle 20 and becomes a gas. This gas, together with the transfer liquid La, passes through a pipe 25 connected to the drain nozzle 20, reaches a pump for dispensing, and is mixed into the pump. For this reason, the pump is in a state in which gas cannot be dispensed due to the ingestion of gas. As described above, the conventional dispensing method has a disadvantage that if the liquid level is low, gas is generated and dispensing cannot be performed. However, since the drain nozzle 20 is provided near the bottom of the low-temperature tank, It did not hinder normal use. However, it is necessary to pay out all the stored liquid L in the low-temperature tank 21 at the time of periodic inspection or the like. Conventionally, in order to dispense the entire storage L, the dispense is normally performed until the liquid level approaches the height of the drain nozzle 20, and then the dispense in the liquid phase is abandoned. All were vaporized and the gas was discharged. The vaporization of the stored liquid is forcibly performed by heating. The gas is discharged by suction or by introducing a purge gas.
These heating and exhaust required a lot of heat energy and a long time. In addition, liquefaction and separation of the exhausted gas are troublesome. [0011] When dispensing all the liquid in this way,
The treatment of the remaining liquid after the liquid level became low took time and cost, and was inconvenient and uneconomical. Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a method for dispensing a low-temperature liquefied gas which does not generate gas even when the liquid level is low. [0013] In order to achieve the above object, the present invention provides a method for dispensing substantially all of a stored liquid from a low-temperature tank for storing a low-temperature liquefied gas such as LNG. A drain nozzle for discharging is inserted substantially horizontally into the low-temperature tank at a predetermined height, the drain nozzle is bent downward in the low-temperature tank, and the suction port of the drain nozzle is provided so as to face the bottom of the low-temperature tank. A cooling nozzle for introducing a cooling liquid from the outside into the suction port is drawn in, and when the liquid level falls to the height of the drain nozzle, the stored liquid is discharged while the cooling liquid is poured from the cooling nozzle. . With the above arrangement, when the liquid level falls to the height of the drain nozzle, the cooling liquid is introduced into the suction port through the cooling nozzle. In the suction port, the liquid stored from the low-temperature tank is cooled, and the temperature is lower than the temperature indicating the boiling point under the internal pressure of the low-temperature tank which is the original temperature. When the liquid in the suction port rises inside the drain nozzle and comes to a position higher than the liquid level, the boiling point there is lower than the original liquid storage temperature, but the temperature of the liquid passing through it is higher than the boiling point. Is even lower. Therefore, it does not boil. This stored liquid is sent to the payout destination without containing gas. In this manner, the dispensing can be continued without any trouble until the liquid level reaches the height of the suction port. Since the suction port is near the bottom, the remaining liquid at that time is small,
Discharge becomes easy. An embodiment of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is an enlarged view of a drain nozzle portion of a low-temperature tank. Other parts of the low-temperature tank have substantially the same configuration as that shown in FIG. That is, the low-temperature tank 21
Is provided with a dome-shaped roof on a bottomed cylindrical tank body, and the entire circumference thereof is covered with a cold insulator layer 26. As shown in FIG. 1, a drain nozzle 20 penetrating the inside and outside of the low-temperature tank 21 is provided near the bottom 23 of the side wall of the low-temperature tank 21. The drain nozzle 20 is inserted substantially horizontally through the low-temperature tank 21 to form a horizontal portion 30. Its position is from the bottom 23 to 350
mm. The drain nozzle 20 is bent downward in the low-temperature tank 21. Drain nozzle 20
Extends downward from the bent position and has its lower end at a height of 50 mm from the bottom 23. A portion facing downward from the drain nozzle 20 is a suction port 22. The suction port 22 faces the bottom 23 of the low-temperature tank 21. The opposite side of the drain nozzle 20 is connected to a payout destination via an on-off valve 24 and a pipe 25 as shown in FIG. Outside the low-temperature tank 21, the cooling nozzle 1 is drawn in from outside the drain nozzle 20.
The cooling nozzle 1 is a tube having a diameter smaller than that of the drain nozzle 20, passes through the axis of the drain nozzle 20, enters the low-temperature tank 21, and is bent at a position where the drain nozzle 20 is bent.
It is folded in the same way and extends downwardly therefrom. The lower end of the cooling nozzle 1 is located above the lower end of the suction port 22. Here, the diameter of the drain nozzle 20 is D
In this case, the lower end of the cooling nozzle 1 is located about 2D from the inlet 22. The opposite end of the cooling nozzle 1 is connected to a supply source (not shown) for supplying the same liquid (the same liquid) as the liquid stored in the low-temperature tank 21. For example, if the liquid stored in the low temperature tank 21 is LNG, the supply source is also LNG.
Supply. As a supply source, another low-temperature tank adjacent to the low-temperature tank 21 may be used. However,
The same liquid supplied by the supply source has a lower temperature than the liquid stored in the low-temperature tank 21, and furthermore, the horizontal portion 3 of the drain nozzle 20.
A temperature below the boiling point at zero. This same liquid acts as a cooling liquid. The supply source and the cooling nozzle 1 are connected via an on-off valve 2, so that the supply can be appropriately controlled. The low-temperature tank 21 may be used for periodic inspection, if necessary.
When dispensing all of the stored liquid, normal dispensing (not using the supply source) is performed until the liquid level drops to the position of the drain nozzle 20. This gradually lowers the liquid level. When the liquid level falls to the level of the drain nozzle 20, the same liquid Lb is supplied from the above-mentioned supply source. At this time, if the temperature of the storage liquid L in the low-temperature tank 21 is -162 ° C, the same liquid Lb has a temperature lower than -162 ° C. The same liquid Lb is supplied through the cooling nozzle 1 and flows into the suction port 22. The lower end of the cooling nozzle 1 is the suction port 22
, The same liquid Lb spreads into the suction port 22. At the same time, the liquid L is being sucked into the suction port 22 because the dispensing is continued. The stored liquid L is cooled by the same liquid Lb or mixed with each other to form a transfer liquid La, which is transferred in the drain nozzle 20. The transfer liquid La has a temperature lower than -162 ° C. When the transfer liquid La rises in the drain nozzle 20 and reaches a position higher than the liquid level, the boiling point there is -1.
Although lower than 62 ° C., the temperature of the transfer liquid La is even lower. Therefore, it does not boil. The transfer liquid La is sent to the payout destination without containing gas. Since the storage liquid L and the same liquid Lb as the cooling liquid are both LNG, the transfer liquid La is composed only of LNG, and can be used at the payout destination without performing a process such as separation. In this manner, since the gas is dispensed while cooling so as not to generate gas, the dispensing can be continued without any trouble until the liquid level reaches the height of the suction port 22. Since the suction port 22 is near the bottom 23, the remaining liquid at that time is small, and the discharge is easy. In this embodiment, the cooling nozzle 1 is passed through the drain nozzle 20 to form a so-called double-pipe structure. The tip of the cooling nozzle 1 as the inner pipe is the end of the drain nozzle 20 as the outer pipe. Although it is about 2D above, any structure that allows the same liquid to be introduced into the suction port from outside may be used. For example, an independent nozzle as a cooling nozzle is inserted into the low-temperature tank, and the tip of the nozzle is extended to the end of the drain nozzle 20 and inserted. In this way, the same liquid can be introduced into the suction port 22 using the nozzle. The present invention exhibits the following excellent effects. (1) Conventionally, if the liquid was dispensed to the height of the drain nozzle, it could not be dispensed any more. However, the liquid can be dispensed to the height of the suction port near the bottom. Almost all can be dispensed, saving time and money for residual liquid treatment. (2) Since only the cooling nozzle is drawn in, the inside of the low-temperature tank does not have to be complicated in order to cool the liquid storage, and the operation is simple. (3) Since it is sufficient to cool the liquid stored in the suction port, the amount of the cooling liquid introduced may be small, and the same liquid as the liquid can be used as the cooling liquid. (4) Even when the low-temperature tank is operating, the lower limit of the capacity is lowered, and the operating efficiency can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged view of a drain nozzle portion of a low-temperature tank showing one embodiment of the present invention. FIG. 2 is a cross-sectional view of a low-temperature tank having a drain nozzle. FIG. 3 is an enlarged view of a drain nozzle portion of a low-temperature tank showing a problem of a conventional drain nozzle. [Description of Signs] 1 Cooling nozzle 1 20 Drain nozzle 21 Low temperature tank 22 Suction port 23 Bottom L Storage liquid Lb Same liquid

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A 54-107214 (JP, U) JP-A 54-34429 (JP, U) JP-A 58-142498 (JP, U) JP-B 47-107 46123 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) F17C 9/00-9/04 F17C 13/00 302

Claims (1)

(57) [Claims] [Claim 1] A drain nozzle for discharging a stored liquid is provided in the low-temperature tank when discharging substantially all of the stored liquid from a low-temperature tank storing low-temperature liquefied gas such as LNG. The drain nozzle is bent downward in the low temperature tank at a predetermined height, and the drain nozzle is bent downward.The suction port of the drain nozzle is provided to face the bottom of the low temperature tank, and the cooling liquid is supplied into the suction port from outside the low temperature tank. A method for dispensing a low-temperature liquefied gas, comprising: drawing in a cooling nozzle for introduction, and when the liquid level has dropped to the height of the drain nozzle, discharging the stored liquid while pouring the cooling liquid from the cooling nozzle.