JP2000179798A - Method for preventing roll-over from being generated inside low-temperature liquefied gas storage tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing generation of roll-over without using a jet-mixing method, inexpensive in an equipment cost and free from sudden BOG generation at the time of stratification elimination. SOLUTION: A delivery line 13 of a delivery pump 11 to a vaporizer is branched in an outside of an LNG storage tank 10, a tip 14b of a branched over-roll preventing line 14 is introduced again into a canopy 10a of the storage tank 10, the delivery pump 11 is driven to make delivered LNG fall down naturally from a top inside the storage tank 10 into a liquid, stratification of the liquid is thereby eliminated by cutting of a lower layer and mixing of an upper layer and the lower layer so as to prevent the generation of roll-over and so as to suppress also BOG generation generated inside the storage tank 10 in the stratification elimination.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a tank for storing a low-temperature liquefied gas such as liquefied natural gas or liquefied petroleum gas. The present invention relates to a method for preventing occurrence of a liquid layer inversion phenomenon called over.

[0002]

2. Description of the Related Art Liquefied natural gas (hereinafter referred to as "LNG")
When a liquid having a specific gravity different from that of the stored liquid stored in the tank is received in a tank storing an ultra-low temperature liquefied gas, an upper layer having a lower specific gravity and a lower layer having a higher specific gravity are formed in the tank. May occur. If this state is left, only the lower layer will have a lower specific gravity due to temperature rise (heat storage) due to natural heat input, and the difference in specific gravity between the upper layer and the lower layer will eventually reverse, causing a so-called rollover phenomenon in which the upper layer and the lower layer are reversed at once. , There is a risk of accident.
For this reason, in tanks for storing LNG, measures to prevent rollover have conventionally been taken.

[0003] A conventional rollover prevention method will be described with reference to FIG. In this conventional method, a discharge line 3 extending from a discharge pump 2 inserted into a lower portion of a storage tank 1 to a vaporizer (not shown) is branched outside the tank 1 and a tip of the branched line 4 is connected. The LNG is introduced into the lower part of the tank 1 and the LNG introduced from the jet mixing nozzle 5 is jetted into the liquid in the lower part, and the LNG in the tank is mixed by this energy to eliminate stratification.

[0004]

However, the jet mixing method shown in FIG. 4 has the following disadvantages.
1. It is necessary to install the jet mixing nozzle 5 in the tank 1, which requires equipment costs. Furthermore, when installing the tank 1 in operation, the tank 1 needs to be emptied and the air atmosphere needs to be performed before the construction, which requires considerable construction time and cost. 2. When the jet mixing method is adopted, BOG is rapidly generated when the stratification is eliminated, and the processing becomes a problem.

An object of the present invention is to provide a method for preventing the occurrence of rollover in which it is not necessary to install a jet mixing nozzle in a tank and BOG does not suddenly occur during a stratification preventing operation.

[0006]

In order to achieve the above object, according to the first aspect of the present invention, in a method for preventing rollover in a low-temperature liquefied gas storage tank, LNG stored in the storage tank is temporarily removed. By discharging the discharged LNG to the top of the tank and letting it naturally fall into the liquid in the tank from here, the liquid in the tank is mixed and agitated by the natural falling energy to form a layer. It is characterized by being eliminated.

Further, in the invention according to claim 2,
According to the first aspect of the present invention, the LNG discharged to the outside of the tank is all or a part of LNG delivered to the carburetor using a discharge pump in the tank.

Further, in the invention according to claim 3,
In the invention according to claim 1, LNG discharged out of the tank refers to LNG for cooling or after cooling, which is pumped up to keep the inside of the receiving pipe cool using a discharge pump in the tank.
Characterized in that it is all or part of

Further, in the invention according to claim 4,
In the invention according to claim 1, the LNG paid out of the tank is all or a part of the minimum flow of the minimum flow line.

[0010]

The LNG discharged out of the tank is again introduced into the top of the tank and falls naturally into the liquid from there, and a downward flow is generated from the upper layer to the lower layer in the tank by the natural falling energy, This downward flow scrapes the lower layer while entraining the surrounding liquid and simultaneously stirs the liquid. As a result, the liquids of the upper layer and the lower layer are mixed, and stratification is eliminated.

[0011]

Embodiment 1 An embodiment corresponding to the first and second aspects of the present invention will be described with reference to FIG. In FIG. 1, 1
0 is an LNG storage tank, 11 is a dispensing pump, 13 is a dispensing line leading to a vaporizer (not shown), and LNG dispensed from the dispensing pump 11 via the dispensing line 13.
Is vaporized by the vaporizer and sent to the consumer side. Reference numeral 14 denotes a rollover prevention line in which the payout line 13 is branched outside the storage tank 10 and the tip 14b is introduced into the canopy 10a of the storage tank 10.

In this embodiment, when the rollover prevention operation is performed, when the payout is performed from the payout line 13, when the valve 14 a of the rollover prevention line 14 is opened, the payout from the payout line 13 is performed. A part of the LNG that has been removed from the rollover prevention line 14 via the canopy 10a of the storage tank 10
At the top, falls naturally from the tip 14b to the liquid surface,
As shown in FIG. 3, the dropped LNG descends while rolling the surrounding LNG from the upper layer to the lower layer, scrapes the lower layer, and mixes the liquids of the upper layer and the lower layer. As a result,
Layering is eliminated and rollover is prevented from occurring.

When the minimum flow described in claim 4 is used, a minimum flow line is introduced into the top of the storage tank 10 in the same manner as in the first embodiment, and all or a part of the minimum flow is supplied therefrom. Let fall naturally to eliminate stratification.

[0014]

Embodiment 2 An embodiment corresponding to the third aspect of the present invention will be described with reference to FIG. In this embodiment, the storage tank 10
LNG transported by tanker into the receiving line 15
When the receiving device is not performing the receiving, the cooling line LNG is received in the receiving line 15.
Is circulating. Then, the tip 16a of the LNG for cooling is introduced into the canopy 10a of the storage tank 10 via the top feed line 16 and is allowed to fall naturally into the liquid. In addition, rollover is prevented from occurring. In the present embodiment, all of the LNG for keeping cold is supplied to the top feed line 1.
6 or may be introduced into the tank 10 or a part thereof.

[0015]

As described above, according to the present invention, the discharged LNG dispensed using the dispensing pump or the LNG pumped out for cooling the receiving line is allowed to fall naturally from the top of the tank into the liquid in the tank, thereby forming the upper layer in the tank. By mixing the liquid of the lower layer and the lower layer, stratification is eliminated and the occurrence of rollover is prevented, so that the following effects are obtained.

1. Equipment cost for installing a jet mixing nozzle in the tank to prevent rollover can be reduced. Furthermore, when a rollover prevention device is installed in an operating tank, it can be handled without emptying the tank. 2. In order to eliminate stratification, a liquid was introduced into the top of the tank, and the naturally falling LNG flow scraped off the lower layer that had accumulated heat, and the upper layer grew along with this, and the stratification was eliminated. Is achieved. Therefore, unlike the case where the jet mixing method is performed, the BOG does not increase sharply when the stratification is eliminated.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention in which stratification is eliminated using a payout LNG or a minimum flow.

FIG. 2 is an explanatory view of an embodiment of the present invention in which layering is eliminated by using LNG for cooling.

FIG. 3 is an explanatory diagram of a stratification eliminating mechanism.

FIG. 4 is an explanatory view of a conventional rollover prevention device employing a jet mixing method.

[Explanation of symbols]

 Reference Signs List 10 LNG storage tank 10a Canopy 11 Discharge pump 13 Discharge line 14 Rollover prevention line 14a Valve 14b Tip 15 Receiving line 16 Top feed line 16a Tip

Claims (4)

[Claims] The LNG stored in the storage tank is once discharged to the outside of the tank, and the discharged LNG is introduced again into the top of the tank, and is naturally dropped from the LNG into the liquid in the tank. A method in which the liquid in the tank is mixed and agitated by natural fall energy to eliminate stratification and prevent rollover. 2. The rollover according to claim 1, wherein the LNG discharged to the outside of the tank is all or a part of LNG delivered to the carburetor using a discharge pump in the tank. How to prevent. 3. The LNG discharged from the tank according to claim 1, wherein the LNG discharged from the tank is a LN pumped or cooled after cooling for cooling the inside of the receiving pipe using a discharge pump in the tank.
A method for preventing the occurrence of rollover, wherein the method is all or part of G. 4. The method according to claim 1, wherein the LNG paid out of the tank is all or a part of the minimum flow of the minimum flow line.