JPH05223200A - Semi-underground storage facilities for liquefied natural gas - Google Patents

Abstract

PURPOSE:To provide safe semi-underground storage facilities for liquefied natural gas for preventing generation of fire and explosion by quickly and positively diffusing LNG gas flowed out on an earth surface due to cracks on the tank cover of an LNG tank in earthquake down to flash concentration. CONSTITUTION:In liquefied gas storage facilities formed by burying a liquefied gas tank in underground, there are provided a ring groove 4 formed on the upper end earth surface of the liquefied gas tank 1 and surrounding the upper end part of the liquefied gas tank 1 and circumferentially partitioned by a plurality of partitions 4a, a rigid and cylindrical common exhaust gas duct 10 in which its lower end is connected to each partition 4a through an exhaust gas inlet valve respectively, and a means for automatically opening and closing the exhaust gas inlet valve corresponding to wind direction.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a semi-underground storage of liquefied natural gas.

[0002]

2. Description of the Related Art LNG (Liquified Nature)
ral Gas) is liquefied by cooling natural gas containing methane as a main component. At the time of liquefaction, all impurities such as sulfur and carbon dioxide in the gas are removed, and it is used for electricity, city gas, etc. Is expanding. By the way, almost all of LNG depends on imports, and landing storages are also constructed in various parts of the country. LNG has a higher ignition temperature (540 ° C.) than other liquid fuels and gas fuels, and has a high mixing ratio (5.0 to 15.0%) with air for combustion, and can be said to be a relatively safe gas. However, various measures are taken in the storage to prevent fires caused by gas leaks due to earthquakes and the like.

That is, as shown in the whole perspective view of FIG. 4, the LNG tank 01 is connected with the LNG in / out pipe 02 for unloading from a tanker and supplying to a consumer.
Considering the disaster caused by the earthquake, the risk of liquid (gas) leakage due to the damage of the pipe joint 03 is greatest. Therefore, pipe fitting 03
A collecting pit 04 is provided under the tank, and a liquid dam 05 is set around the premises including the LNG tank 01.
Even if all the NG leaks out, it is possible to prevent it from leaking outside the storage premises. In addition, as a fire extinguishing facility in the event of a fire, a powder fire extinguishing facility 07, a foaming agent discharging facility 06, and the like are provided to ensure a complete disaster prevention system on the premises of the storage facility.

However, the L leaked during the earthquake
When NG is liquid, it accumulates at the bottom of the liquid collection pit 04 or dike 05, and the LNG that has been exposed to the outside air and has risen in temperature and gasified is lighter than air and drifts out of the storage. It is quite dangerous when the mixing ratio with the air is about 5%.

Therefore, in the conventional storage, as shown in the vertical sectional view of FIG. 5, a large number of water curtain nozzles 0 are provided around the liquid barrier 05.
The water supply pipe 08 equipped with 9 is installed so as to diffuse the mixture ratio of LNG to 5% or less. That is, the exhaust gas 011 of the LNG trying to cross the liquid barrier 05 is diffused in the sky by passing over the upper end of the water curtain 010 formed by the fountain from the water curtain nozzle 09.

However, although the diffusion of exhaust gas by the water curtain shown in FIG. 5 has been confirmed in a model test, formation of a perfect water curtain by jetting from all water curtain nozzles, securing of water pressure and height of water curtain and There is a problem such as the relationship between the wind speed and the water curtain, and in the event of an LNG gas leakage disaster that rarely occurs, it is necessary to determine whether or not the water curtain system's exhaust gas diffusion means operates reliably and achieves its intended effect. I am worried about its certainty.

[0007] Therefore, the applicant of the present invention has previously filed Japanese Patent Application No. 3-3.
As No. 26517, as shown in FIG. 6, in a liquefied fuel gas storage in which a liquefied gas tank for storing liquefied fuel gas is surrounded by a levee, it stands on the site between the liquefied gas tank and the levee. Installed, motor driven exhaust gas fan 0
14 and an exhaust gas temperature raising device 016, 018 are provided, and a vertical exhaust gas duct 013 having a liquefied gas inlet 015 at the lower end and a liquefied gas outlet 024 at the upper end is proposed. ..

According to such a device, the LNG suction port 015 at the lower end of the exhaust gas duct is provided at a position slightly higher than the expected maximum liquid level of the leaked LNG in the liquid barrier, and the LNG at the upper end is formed.
The NG discharge port 024 is provided at a position slightly higher than the LNG tank, and the built-in exhaust gas fan 014 positively gasifies the LNG from a high place to the sky. that time,
The built-in exhaust gas temperature raising device 016,018 raises the temperature of exhaust gas so that it has a specific gravity at least equal to that of the atmosphere, and discharges the exhaust gas. However, the structure is complicated and the cost is high.

By the way, as a result of a study on the disaster prevention of the liquefied fuel storage, the present inventor believes that if the LNG tank is buried underground, the leakage of LNG to the ground can be almost prevented, and a large earthquake that causes a ground crack will occur. Even if a crack occurs in the LNG tank and liquid leakage occurs, it is considered that LNG will not flow out to the ground. However, it is not unlikely that the LNG liquid level will move violently and the tank cover of the LNG tank will be destroyed by the earthquake, and at that time, there is a risk prevention measure against gasified LNG leaking to the ground. It is important to take it.

[0010]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above circumstances, and it is possible to quickly and reliably reduce the LNG gas overflowing to the ground surface due to a crack in the tank cover of an LNG tank to a level below the ignition concentration during an earthquake. The purpose is to provide a safe, semi-underground storage place for liquefied natural gas that can be diffused in and prevent fires and explosions.

[0011]

To this end, the present invention, in a liquefied gas storage in which a liquefied gas tank is buried underground, is formed on the upper surface of the liquefied gas tank and surrounds the upper end of the liquefied gas tank. Together with the annular groove partitioned into a plurality of compartments in the circumferential direction, a vertical cylindrical common exhaust gas duct whose lower end is connected to each of the compartments via an exhaust gas intake valve, and the exhaust gas intake valve is opened and closed according to the wind direction. It is characterized by having means.

[0012]

With such a structure, there is a possibility that LNG leaking to the ground due to breakage of the tank cover when an earthquake occurs is gasified by solar heat, overflows from the LNG tank, and flows along the surface of the earth. At that time, LNG with a large specific gravity
The LNG gas concentration is reduced to 5 by collecting the gas in the annular groove, sucking it up with a blower, and discharging it into the air from the exhaust gas duct.
Reduce the risk of fire to less than%. When there is no wind,
Since the LNG gas spreads over the entire annular groove, it is desirable to suck the LNG gas from the entire circumferential direction, but normally the wind in the wind direction at that time blows and the overflowing gas flows to the leeward side of the tank cover. Therefore, the annular groove is divided into a plurality of pieces in the circumferential direction, and a gas suction port is provided for each partition groove, so that the suction valve of the gas suction port can be opened / closed according to the wind direction.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall vertical sectional view thereof, FIG. 2 is a plan view of FIG. 1, and FIG. 3 is an enlarged sectional view of an exhaust gas inlet portion of FIG. ..

In the above figure, the LNG tank 1 is a so-called semi-underground type which is buried underground except for the tank cover 2, and an annular groove 4 surrounding the LNG tank 1 on the surface of the ground,
An outflow prevention bank 5 is provided, and as shown in FIG.
Is divided into a plurality of arc-shaped sections 4a at substantially equal intervals by the partition 7.
Is divided into The exhaust gas intake pipe 6 penetrates the partition 7 in an airtight manner and surrounds the entire inner surface of the annular groove 4, and as shown in FIG. 3, an exhaust gas intake port 8 is provided for each divided arcuate section 4a, and an exhaust gas blower It is connected via 9 to a common vertical exhaust gas duct 10. Here, the exhaust gas intake port 8 is equipped with a butterfly valve 14 driven by a valve opening / closing motor 11 by receiving an opening / closing command by a wind direction detector and controller (not shown), and a butterfly valve with hatching in the figure. 14a shows a fully closed state, and 14b shown with a chain line shows a fully opened state. When the wind direction 12 at the time of gas overflow is in the direction shown by the arrow in FIG. 2, the gas overflowing from the LNG tank 1 is collected in the leeward divided arcuate section 4a.
The butterfly valve 14b of the exhaust gas inlet 8b is fully opened as shown in the figure.

According to such an apparatus, the duct structure is
The structure as shown in FIG. 6 does not have to be complicated, and a blower is simply installed, so that the structure is simple and the cost is low.

[0016]

In summary, according to the present invention, in a liquefied gas storage in which a liquefied gas tank is buried underground, the liquefied gas tank is formed on the upper surface of the liquefied gas tank and surrounds the upper end of the liquefied gas tank as well as in the circumferential direction. An annular groove partitioned into a plurality of compartments, a vertical cylindrical common exhaust gas duct whose lower end is connected to each of the compartments via an exhaust gas intake valve,
By providing a means to open and close the exhaust gas intake valve according to the wind direction, the LNG gas overflowing to the surface due to the crack of the tank cover of the LNG tank during the earthquake quickly and reliably diffuses to below the flammable concentration, causing a fire or explosion. INDUSTRIAL APPLICABILITY The present invention is extremely useful in industry because it provides a safe semi-underground storage of liquefied natural gas that prevents the occurrence of

[Brief description of drawings]

FIG. 1 is an overall vertical sectional view showing an embodiment of the present invention.

FIG. 2 is a plan view of FIG.

FIG. 3 is a sectional view taken along line III-III in FIG.

FIG. 4 is an overall perspective view showing a conventional LNG storage.

5 is a vertical sectional view showing the operation of the water curtain nozzle in FIG.

FIG. 6 is a vertical sectional view showing an exhaust gas tower previously proposed by the applicant.

[Explanation of symbols]

 1 LNG tank 2 Tank cover 3 Liquefied fuel 3a Liquid level 4 Annular groove 4a Section 5 Outflow prevention bank 6 Exhaust gas suction pipe 7 Partition 8 Exhaust gas inlet 8a Windward exhaust gas inlet 8b Downwind exhaust gas inlet 9 Exhaust gas blower 10 Exhaust gas duct 11 Valve opening / closing motor 13 Wind direction 14 Butterfly valve 14a Fully closed butterfly valve 14b Fully open butterfly valve

Claims (1)

[Claims] 1. In a liquefied gas storage in which a liquefied gas tank is buried underground, the liquefied gas tank is formed on the upper surface of the liquefied gas tank and surrounds the upper end of the liquefied gas tank and is partitioned into a plurality of sections in the circumferential direction. Liquefaction characterized by comprising an annular groove, a common vertical exhaust gas duct whose lower end is connected to each of the compartments via an exhaust gas intake valve, and means for opening and closing the exhaust gas intake valve according to the wind direction. Semi-underground storage of natural gas.