JPH06322781A - Two-stage construction method for large scale lng underground tank and composite underground tank structure - Google Patents

Abstract

PURPOSE:To construct a large scale LNG underground tank safely at a low cost by a method having the same content as that of a freezing method through utilization of freezing of a ground by means of the cold heat of LNG stored in a small scale LNG underground tank. CONSTITUTION:An underground tunnel in an annular shape in a horizontal direction is excavated in a plurality of rings in the outer periphery of the construction position of a large scale LNG underground tank 2 and a heat insulating material 6 and a membrane 7 are arranged as a lining on the inner surface of a structural body. Airtightness is ensured by using the membrane 7 to build a first stage small scale LNG underground tank 1. LNG is stored for a feed in the small scale LNG underground tank 1. After it is confirmed that the freeze region 8 of a ground occurring owing to a feed is developed to a degree at which no problem arises, the inner ground of the ring is excavated to build a non-freezing type large scale LNG underground tank 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is divided into two stages, a large-scale LNG underground tank that is implemented by utilizing the freezing phenomenon of the ground due to underground storage of liquefied natural gas (LNG) at extremely low temperatures. And a composite tank structure constructed by the above method.

[0002]

2. Description of the Related Art In recent years, as a clean energy source for thermal power generation, there is a growing interest in the active use of LNG, which is rich in reserves and is free from fear of air pollution due to NO _X , SO _X, etc. after combustion. As part of this, active discussions are underway toward the construction of a domestic natural gas pipeline network. Therefore, it has a larger capacity than before, for example, a capacity of 20 to
The need to build 300,000 KL of LNG storage tanks has been recognized.

Large-scale L having a conventional capacity of 100,000 to 200,000 KL
The construction of the NG underground storage tank was generally carried out by implementing a large-scale earth retaining excavation method corresponding to the ground conditions of the construction site. In this case, the earth retaining excavation work usually involves large-scale continuous underground walls for earth retaining work, ground improvement work, and large-scale underground work including water stoppage work. It requires huge construction costs.

[0004]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to positively utilize the freezing of the ground generated by storing cryogenic LNG underground, so to speak, at present, ground reinforcement and stoppage. A method of constructing a large-scale LNG underground storage tank at a low cost and safely by a two-step construction method with the same content as the freezing method, which is the most reliable (but said to be the most expensive) water method. Providing a composite tank structure constructed by the method.

[0005]

As a means for solving the above-mentioned conventional problems, a large-scale LNG according to the present invention is used.
The two-stage construction method of the underground tank is a large-scale L to be constructed later.
In the outer peripheral portion of the construction position of the NG underground tank 2, the ring diameter is slightly larger than the outer diameter of the tank 2, and the appropriateness of the ground freezing area 8 that will occur later to a portion equal to or slightly deeper than the underground depth of the tank. A plurality of underground underground tunnels that are ring-shaped in the horizontal direction are excavated at a pitch effective for effective formation, and the lining of the tunnel is provided with a heat insulating material 6 on the inner surface of the structural body, and a membrane 7 is further provided on the inner surface thereof. Deploy. The membrane 7 is air-tightly secured by welding or adhesive-type bonding to ensure the small-scale L of the first stage.
Building the NG underground tank 1, small-scale LNG as described above
After confirming that LNG is stored and used in the underground tank 1, and that the frozen area 8 of the ground caused by the use of the small-scale LNG underground tank 1 has progressed to the extent that there is no problem in the next second stage construction , A large-scale non-frozen LNG by excavating the ground inside the ring which is the small-scale LNG tank 1
Each is characterized by constructing an underground tank 2.

The present invention also relates to the first stage small scale LN.
At the time of construction of the G underground tank 1, the temperature sensors 10 are installed in a radial arrangement outside the tunnel.
During the service period of the G underground tank 1, the progress of the frozen area 8 of the ground is monitored through the temperature sensor 10 to confirm whether or not there is a problem in the second stage construction.

Next, the composite tank structure according to the present invention is
The small-scale underground tank 1 having a circular multi-ring structure is constructed on the outer peripheral portion by the two-step construction method described above, and the large-scale underground tank 2 is independently constructed inside the small-scale underground tank 1.

[0008]

The small-scale LNG underground tank 1 constructed by the first-stage construction can be used for LNG underground storage with a capacity of, for example, about 50 to 100,000 KL. Access to the ground is made using shafts 3 and 4. When the small-scale LNG underground tank 1 is used for underground storage of the LNG, L
The cold heat of NG promotes freezing of the surrounding ground. The formation of the frozen region 8 is controlled by the placement of insulation 6 and 9 in the tunnel lining. Since the small-scale LNG underground tank 1 is configured to actively use the freezing of the ground, after a certain period of service,
Along the ring-shaped underground tank 1, a cylindrical frozen region 8 is generated in the vertical direction from near the ground to a deep underground position.
It is possible to form a frozen mountain retainer as if the frozen construction method was implemented.

Therefore, in the second stage construction, the frozen mountain retaining structure can be used as it is as a highly reliable ground reinforcement and water stopping method, and the ground inside the frozen mountain retaining structure can be excavated safely and efficiently. A large-scale non-frozen LNG underground tank 2 can be constructed. The large-scale LNG underground tank 2 thus constructed can, of course, store a large amount of LNG and supply it to applications such as thermal power generation. On the other hand, a small LN on the periphery
The G underground tank 1 can of course also be used for storage of LNG, but in some cases storage of other liquids, eg large scale LN.
G Use the cold heat leaked from the underground tank 2 to effectively store the liquid that needs to be kept cool, or circulate the liquid that efficiently absorbs the cold heat of the LNG and use it for wide-area cooling on the ground, etc. It is also possible.

[0010]

EXAMPLE An example of the present invention shown in the drawings will be described below.
1A and 1B are a small-scale LNG underground tank 1 having a circular multiple ring structure of the outer peripheral portion constructed in the first stage construction,
Large-scale LN constructed inside the circular multi-ring structure
The conceptual diagram of the compound tank structure which consists of G underground tank 2 is simplified and shown. The two tanks 1 and 2 are completely independent structures. Therefore, each application can be made independent. The large-scale LNG storage tank 2 has a capacity of 20.
~ 300,000 KL in size, so its diameter is 50
The depth of the underground is about 50m to about 60m. The small-scale LNG underground tank 1 in the outer peripheral portion is not only constructed as a structure completely independent of the large-scale LNG underground tank 2 but also the small-scale LNG underground tank 1
It is important to store LNG inside and use the cold heat of LNG to freeze the surrounding ground, and to intentionally form a controlled frozen cliff retaining necessary for the construction of a large-scale LNG tank by the second stage construction. It Therefore, the diameter of the ring of the small-scale LNG underground tank 1 is much larger than the diameter of the large-scale LNG underground tank 2 described above, and the number of rings is equal to or more than the underground depth of the large-scale LNG underground tank 2 described above. From the deep portion to near the ground, the required number of pitches will be constructed in the vertical direction effective for proper formation (control) of the frozen region 8. Therefore, the present invention is particularly effective for implementation in alluvial ground, diluvial ground, or soft rock ground where the influence of groundwater is large.

In the case of the present invention, the small-scale LNG underground tank 1 having a multiple circular ring structure is constructed in the first stage construction.
When considering the above-mentioned role and conditions of the small-scale LNG underground tank 1, its layout diagram is as shown in FIG.
They are classified as ~ (d). In (a) and (b), the horizontal rings 1 are vertically and independently arranged side by side, and (c),
In (d), the ring 1 is formed in a series of spirals. Both layouts are based on the excavation of an underground tunnel by adopting the shield construction method that can cope with the above-mentioned offshore, diluvial ground or soft rock, and the vertical shaft 3 for shield starting and the vertical shaft 4 for shield arrival as required. It will be constructed. However, when the influence of groundwater is small, it is effective to adopt the NATM (NATM) method, which is much cheaper than the shield method. When the small scale LNG underground tank 1 is used for underground storage of LNG, the shield starting shaft 3 and the shield reaching shaft 4 are also used for access to the ground. Techniques for constructing vertical shafts up to about 100 m underground have already been developed (for example, Japanese Patent Application Nos. 4-186860, 4-188088, 4-210258, and 4-2).
99716 and 4-338590).

The capacity of this small-scale LNG underground tank 1 is about 25,000 KL. Therefore, the shield diameter is 5
The size is about 10m. As for the underground tunnel excavated in the horizontal ring shape, the structural frame with segments is of course completed, but the lining construction for the LNG tank is also performed. Specifically, as shown in FIG. 3, the segment 5
The structural body is assembled, the heat insulating material 6 is installed on the inner surface thereof as required, and the membrane 7 made of, for example, a stainless steel plate is arranged on the inner surface. The seam of the membrane 7 is LN to ensure airtightness by welding all around through a corrugation capable of expansion and contraction or by bonding with an adhesive type.
The tank for G is completed. In this case, the heat insulating material 6 is appropriately designed and installed in order to intentionally control the size and freezing speed of the freezing area 8 of the ground.

As described above, the construction work is temporarily suspended when the small-scale LNG underground tank 1 is completed, and LNG is stored in the tank 1 for actual service. As a result, the cold heat emitted by LNG at an extremely low temperature of −162 ° C. propagates to the surrounding ground, and the ground freezes. The freezing of the ground proceeds along the ring-shaped tunnel forming the small-scale LNG underground tank 1 in a state where the size of the freezing region 8 and the freezing speed are controlled by the arrangement of the heat insulating material 6 as described above, It is also formed radially around the cross section of the tunnel, as shown schematically in FIG. When viewed comprehensively, the frozen region 8 of the ground formed as described above with each ring 1 as the center is wrapped in the up-down direction to be connected in a series, and in the end, the geometrical figure is exaggeratedly expressed in FIG. As described above, the frozen region 8 having a cylindrical shape in the vertical direction is formed in a layer thickness necessary for the frozen mountain retaining.

Therefore, after the freezing debris has been sufficiently developed, as a second stage construction, the inner ground of the cylindrical freezing area 8 is excavated as an open cut construction method to construct a large-scale LNG underground tank 2. Is advanced. Considering the easiness of excavation of the ground in the second stage construction, the frozen area 8 of the ground is exaggerated in FIG. 4 or FIG. 6B as long as the layer thickness necessary and sufficient for the function (function) as the frozen mountain retaining can be obtained. As described above, it is advantageous that the outer peripheral side of the ring is thickened in the cross section of the tunnel, and it is desirable to control the freezing of the ground in this way. As a control means, FIGS. 6A and 6B show a configuration in which the heat insulating material 9 is attached to the inner peripheral side of the ring over a predetermined arc angle in the cross section of the tunnel.

By the way, in the above-mentioned second stage construction, since the above-mentioned freezing area 8 is used as a frozen mountain retaining work for ground excavation work and the like, when starting the second stage construction work, It is important to confirm whether or not the area 8 has been developed to the situation where construction safety can be secured. As a means thereof, as illustrated in FIGS. 7A and 7B, at the stage of the tunnel construction of the small-scale LNG underground tank 1 in the first stage, the temperature sensor 10 such as a thermocouple is radially arranged in the outer ground of the tunnel. Place many in a wide area. And L by the small-scale LNG underground tank 1
From the time point when the underground storage of NG is started, the temperature sensor 10 monitors the temperature from above the ground, and the development status of the frozen region 8 is specifically confirmed by the change of the temperature distribution. After the confirmation is done, the second stage construction is started.

When starting the construction of the second stage, it is preferable to switch the LNG stored in the small-scale LNG underground tank 1 to a non-combustible storage of, for example, liquefied nitrogen gas (-192 ° C). This is to ensure the safety of the second stage construction. Further, from the stage of completing the construction of the large-scale LNG underground tank 2 and using it for underground storage of LNG, the small-scale LNG underground tank 1 can of course be used for storage of LNG. It is also effective to use it for underground storage of various liquids or gases that require cold storage. In particular, by circulating a liquid or gas useful as a cooling / heating medium in the small-scale LNG underground tank 1, the cold heat released by the LNG stored in the large-scale LNG underground tank 2 can be efficiently absorbed and used for ground-based wide-area cooling or the like. Then,
At the same time, it is effective in preventing the freezing of the surrounding ground. That is, the small-scale LNG underground tank 1 can be used as an antifreezing system for the surrounding ground, and at the same time, the cold heat of the LNG stored in the large-scale LNG underground tank 2 can be effectively used.

[0017]

According to the two-stage construction method of the large-scale LNG underground tank according to the present invention, the LNG stored in the small-scale LNG underground tank 1 constructed by the first stage construction
By using the freezing of the ground due to the cold heat of the ground, without any special ground freezing cost and labor, at the present, with the same content as the most reliable freezing method in terms of ground reinforcement and water stopping performance,
The large-scale LNG underground tank 2 can be safely constructed at low cost, which can contribute to the positive use of LNG in recent years. Moreover, a small-scale LN located on the outer circumference
Depending on how the G underground tank 1 is used, it is possible to prevent the freezing of the outer ground.

According to the composite underground tank structure comprising the combination of the large-scale LNG underground tank 2 and the small-scale LNG underground tank 1, the small-scale LNG underground tank 1 is particularly preferable.
There are various uses, and for example, it is possible to effectively store the cold heat released by LNG stored underground, or the underground storage of liquids or gases requiring cold storage.

[Brief description of drawings]

1A and 1B are a vertical sectional view and a plan view conceptually showing the structure of a composite underground tank structure.

2A to 2D are perspective views conceptually showing various layouts of a small-scale LNG underground tank.

FIG. 3 is a perspective view showing a lining structure of an underground tunnel.

FIG. 4 is a schematic diagram conceptually showing freezing of the ground along a small-scale LNG underground tank.

FIG. 5 is a vertical sectional view conceptually showing a frozen state of the ground along a small-scale LNG underground tank.

6A and 6B are a front view and a cross-sectional view taken along the line bb in FIG. 6, showing the arrangement of a heat insulating material that controls a frozen region of the ground.

7A and 7B are an elevation view and a cross-sectional view showing the arrangement of temperature sensors.

[Explanation of symbols]

 2 Large-scale LNG underground tank 5 Segment (structure body) 6 Insulation material 7 Membrane 1 Small-scale LNG underground tank 8 Freezing area 10 Temperature sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takao Ueda 2-5-14 Minamisuna, Koto-ku, Tokyo Inside the Takenaka Corporation Technical Research Institute (72) Inventor Hiroshi Iwamoto 2-5, Minamisuna, Koto-ku, Tokyo No. 14 Incorporated Takenaka Corp. Technical Research Institute (72) Inventor Yuichi Komura 2-5-14 Minamisuna, Koto-ku, Tokyo Incorporated Incorporated Takenaka Corp. Technical Research Institute (72) Yasushi Kanzaki Ginza, Chuo-ku, Tokyo Takenaka Civil Engineering Co., Ltd.

Claims (3)

[Claims] 1. A large-scale LNG underground tank to be constructed later, which has a ring diameter slightly larger than the outer diameter of the tank at the outer peripheral portion of the construction position and has a depth equal to or slightly deeper than the underground depth of the tank. A plurality of underground underground tunnels that are ring-shaped in the horizontal direction are excavated at a pitch that is effective for the proper formation of the frozen region that occurs, and the lining of the tunnels has a heat insulating material arranged on the inner surface of the structural frame and a membrane arranged on the inner surface. However, the membrane is airtight by welding or adhesive-type bonding to ensure the small-scale LN of the first stage.
To construct a G underground tank, to store and use LNG in the small-scale LNG underground tank, to such an extent that the frozen area of the ground generated by the use of the small-scale LNG underground tank does not cause a problem in the second stage construction. After confirming that the large-scale LNG underground tank has been developed, the inner ground of the ring, which is the small-scale LNG tank, is excavated to construct a large-scale non-frozen LNG underground tank. Two-step construction method. 2. When constructing a small-scale LNG underground tank in the first stage, temperature sensors are installed radially outside the tunnel, and the temperature sensor is installed through the temperature sensor while the small-scale LNG underground tank is in service. The two-stage construction method for a large-scale LNG underground tank according to claim 1, wherein the progress of the frozen region of the ground is monitored to confirm whether or not there is a problem in the second-stage construction. 3. A composite underground tank structure, wherein a small-scale underground tank having a circular multiple ring structure is built on the outer peripheral portion, and a large-scale underground tank is independently built inside the tank.