JP2005195110A - Underground low-temperature tank facility and ground freezing preventing method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent approach of freezing area to be formed around a reservoir nearly close to a surface of the ground. <P>SOLUTION: This underground low-temperature tank facility has a structure that a cavity excavated underground is used as the reservoir 1 to store a low-temperature fluid and that air-tightness and liquid-tightness of the reservoir are secured by the freezing area formed around the reservoir. A water-sealing boring 4 is provided underground over the reservoir, and water is circulated inside the water-sealing boring to maintain temperature of the peripheral ground at the freezing temperature or more to hinder enlargement of the freezing area at that position. In the case of storing liquefied gas as a low-temperature fluid in the reservoir, warm wasted heat generated when liquefying the evaporated gas from the liquefied gas again in a ground surface part to heat the water circulating inside the water sealing boring. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an underground cryogenic tank facility having a structure in which a cryogenic fluid is stored in a cavity excavated in an underground ground, and a ground freeze prevention method for preventing freezing of the surrounding ground of the facility.

  This type of underground cryogenic tank facility excavates a large-scale cavity in a stable underground rock, and uses the cavity as a storage tank (tank) for low-temperature liquefied gas such as LPG, LNG, DME (dimethyl ether), or other It is a facility for storing cryogenic liquids and cryogenic gases. In such an underground cryogenic tank facility, the stored water is extremely cold, so the groundwater existing around the storage tank naturally freezes to form a stable freezing area around the storage tank.Therefore, there are cracks and gaps in the bedrock. Even in such cases, since the airtightness and liquid tightness of the storage tank are naturally secured, it is sufficient to install a support like a sprayed concrete on the inner surface of the cavity for the construction of the storage tank. Therefore, there is an advantage that the structure is simple and the construction cost can be suppressed.

  By the way, in this kind of underground cryogenic tank facility, not only the freezing area is formed around the storage tank, but also after the operation of the facility, the freezing area gradually expands over a wide area around the storage tank, so the depth of the storage tank is compared. In such a case, it is assumed that the frozen region will reach the surface near the surface in the future, and in such a case, there is a concern that the structure on the surface and the natural ecosystem may be adversely affected. .

  Therefore, when planning this type of facility, it is said that the depth of the storage tank must be sufficiently large so that the frozen region will not reach near the surface in the future. Since it requires a large-scale excavation work to install it in the construction site, it requires a great deal of cost for the construction, and also increases the equipment cost, operation cost, maintenance cost, etc. for receiving and receiving the storage after operation. Therefore, there is a demand not to increase the depth of the storage tank so much in terms of economy and profitability.

Conventionally, low temperature liquefied fuel storage tanks such as LNG and LPG have been widely embedded in the vicinity of the surface, and Patent Document 1 discloses a measure for preventing freezing of the surrounding ground of such a buried tank. Discloses a method of forming a heat fence by providing pipes through which a heat medium such as hot water is passed at the bottom or side of an embedded tank. In addition, Patent Document 2 discloses that the same buried type tank is applied, and the cover surface on the roof surface is prevented from freezing by keeping the roof surface at a constant temperature by spraying a heat medium such as hot water on the roof surface. The technique of doing is disclosed.
JP-A-6-278791 Japanese Patent Laid-Open No. 7-48952

  Although it is not necessary to increase the depth of the storage tank as long as the antifreezing method as shown in Patent Document 1 and Patent Document 2 described above can be applied as it is even in a large-scale facility that is the subject of the present invention, Applying the anti-freezing method for small-scale buried tanks buried in a shallow position on the surface of the earth to a underground cryogenic tank facility that uses a large cavity in the underground ground as a storage tank It was not realistic, and it was urgent to develop a more effective anti-freezing method in order to spread this kind of underground cryogenic tank facility.

  In view of the above circumstances, the underground cryogenic tank facility of the present invention stores a cryogenic fluid using a cavity excavated in the underground ground as a storage tank, and ensures the airtightness and liquid tightness of the storage tank by a freezing area formed around the storage tank. A water-sealed boring for maintaining the surrounding ground at a freezing temperature or more by circulating water inside the storage tank while keeping the ground saturated and forming a freezing region around the storage tank, It is provided in the ground above the storage tank.

  The ground freeze prevention method of the present invention is applied to the underground cryogenic tank facility having the above structure to prevent freezing of the surrounding ground, and water is circulated in the above water-sealed boring to circulate the surrounding ground. By maintaining the freezing temperature or higher, expansion of the freezing region formed around the storage tank is prevented at the position of the water-sealed boring. When the low-temperature fluid stored in the storage tank is a liquefied gas, the waste heat generated when the vaporized gas from the liquefied gas is taken out and re-liquefied at the surface and returned to the storage tank is used. It is conceivable to heat the water circulating in the water-sealed boring.

  According to the present invention, by circulating water at a temperature of about room temperature in the water-sealed boring, the ground around the water-sealed boring is maintained at a freezing temperature or higher, and therefore the freezing area formed around the storage tank is expanded. It is possible to prevent the freezing area from reaching the vicinity of the ground surface by itself being blocked at that position and various adverse effects. In addition, even when there is not enough groundwater at the depth to provide a cavity as a storage tank, water is naturally injected around the storage tank from the above-mentioned water-sealed boring provided in the ground above it and penetrated. As a result, the ground is always kept in a saturated state, a freezing region is surely formed around the storage tank, and the airtightness and liquid tightness required for the cavity as the storage tank can be ensured without any trouble.

  In addition, as a heat source for heating the water circulating in the water-sealed boring, it is possible to use the waste heat generated when re-liquefying the vaporized gas from the liquefied gas as a stored product. As a result, the operating cost can be reduced.

  An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a conceptual diagram of an underground cryogenic tank facility according to an embodiment of the present invention, in which a plurality of cavities (three tunnel-shaped cavities in the illustrated example) are excavated in an underground ground that is a stable rock, These cavities are used as storage tanks 1 for storing low-temperature fluids such as low-temperature liquefied gases such as LPG, LNG, and DME. Reference numeral 2 is a vertical shaft for accessing the storage tank 1 from the ground, and 3 is a horizontal shaft for connecting the storage tanks 1 to each other.

  As already described, since the low-temperature liquefied gas stored in such a storage tank 1 is extremely low temperature, the groundwater existing in the ground around the storage tank 1 is naturally frozen after the start of operation, and the storage tank 1 A stable freezing region is formed around the storage tank 1, so that the airtightness and liquid tightness necessary for the storage tank 1 can be secured by itself. In this embodiment, such a freezing area is reliably provided around the storage tank 1. In order to prevent the freezing area from expanding to the vicinity of the surface part, a plurality of water-sealed borings 4 are formed on the upper ground so as to cover the entire storage tank 1. The water is circulated in the water-sealed boring 4.

  That is, in this embodiment, as shown in FIG. 1, the horizontal shaft 5 is excavated above the storage tank 1 located at the center, and as shown in FIG. The water-sealed boring 4 is formed in a slightly lowered state at a predetermined interval. In addition, pipes 6 and 7 for forming a circulation path are laid in the horizontal shaft 5 and each water-sealed boring 4, and the same pipe is also installed in the vertical shaft 8 that connects the surface portion and the horizontal shaft 5. By providing a passage 9 (see FIG. 1) and supplying water to the shaft 8 by a circulation pump 10 connected to the conduit 9, each shaft 8 passes through the side shaft 5 as shown by arrows in FIG. The inside of the water-sealed boring 4 is in a water-sealed state, and is forcedly circulated so that the water-sealed boring 4 is returned to the ground surface through the pipes 7, 6, 9 from the tip of each water-sealed boring 4.

  In this way, by circulating water in the water-sealed boring 4 provided above the storage tank 1, a part of the water is naturally injected into the ground through cracks and gaps, and thus the natural groundwater level. Is lower than the formation position of the storage tank 1, that is, even if a frozen region cannot be effectively generated around the storage tank 1 as it is, the ground is always kept in a saturated state and the surroundings of the storage tank 1 Therefore, it is possible to maintain a groundwater always present, so that a frozen region can be surely formed around the storage tank 1 at the start of operation, and the airtightness and liquid tightness can be sufficiently secured.

  In addition, even after such a frozen region is formed, the ground temperature around each water-sealed boring 4 is naturally circulated by forcedly circulating water in the water-sealed boring 4 as described above. The temperature is maintained at a temperature level and does not drop below the freezing temperature. Therefore, the expansion of the freezing area formed around the storage tank 1 is prevented at that position, and the freezing area extends beyond the water-sealed boring 4 and above it. Enlarging and reaching the vicinity of the surface can be reliably prevented.

  The temperature of the circulating water does not have to be high as long as the ground around the water-sealed boring 4 does not reach the freezing temperature. If the temperature is too high, there is a concern that the freezing area to be formed around the storage tank 1 may be adversely affected. Therefore, it is sufficient that the water temperature is about room temperature (for example, about 15 to 20 ° C.), and if possible, natural water such as river water and lake water can be circulated as it is (but desired throughout the year). The condition is that sufficient water temperature can be secured and there is no adverse impact on the ecosystem). Of course, if necessary, the circulating water may be heated by an appropriate heat source 11 and circulated while controlling the temperature to a predetermined temperature. In this case, it is preferable to effectively use various types of waste heat. In particular, when the stored material in this facility is a liquefied gas such as DME or LPG, the vaporized gas (BOG) that accumulates in the upper part of the storage tank 1 is taken out to the surface and re-liquefied by a refrigerator and returned to the storage tank. It is normal to perform the operation, and warm waste heat from the refrigerator is generated during the re-liquefaction. Therefore, it is conceivable to heat the circulating water using the warm waste heat as the heat source 11. By doing so, it is possible to effectively utilize the heat and waste heat that has been simply dissipated to the atmosphere in the past, and is extremely rational.

  FIG. 3 shows the result of predicting the situation after 50 years of the frozen region formed around the storage tank 1 provided at a depth of 50 m by heat conduction analysis. (A) shows a case where water-sealed boring is not provided, (b) shows a case where water-sealed boring is provided at a position of a depth of 30 m and water at 15 ° C. is circulated. In (b), the frozen area remains at about 35 m below the ground surface (about 5 m below the water ring boring), and the expansion of the frozen area is effective by water ring boring. You can see that it is blocked.

  FIG. 4 shows the temperature distribution of the ground surface in the above case. When there is no water-sealed boring, a maximum 2 deg. In this case, it is understood that not only the temperature decrease is about 0.3 deg at the maximum, but also the range where the temperature decrease occurs is small.

  As described above, according to the underground cryogenic tank facility and the freeze prevention method of the present embodiment, it is possible to effectively prevent the frozen region formed around the storage tank 1 from reaching the vicinity of the ground surface. Thus, it is not necessary to provide the storage tank 1 at a large depth, and it is possible to provide the storage tank 1 at a relatively shallow position, thereby significantly reducing the construction cost of the entire facility and sufficiently reducing the operating cost after operation. It becomes possible. In addition, when constructing this type of facility, in any case, it is usual to provide a water-sealed boring 4 in order to secure the groundwater level around the storage tank 1, and thus providing such a water-sealed boring 4 itself. The cost does not increase, and it is only necessary to add a function for circulating water, so the overall cost increase is negligible.

  In the above embodiment, the circulation paths are formed by laying the pipelines 9, 6, and 7 in the vertical shaft 8, the horizontal shaft 5, and the water-sealed boring 4, respectively. Instead, what is necessary is to configure the water-sealed boring 4 so that water can circulate. For example, the water-sealed boring 4 is divided into an outward path and a return path, or a circulation path is formed. The boring 4 itself may be provided so as to form a series of circulation paths.

  Further, as in the above embodiment, it is realistic that the circulation of water in the water-sealed boring 4 is always forced circulation by the circulation pump 10, but various natural energy can be used as power for that purpose. Depending on the situation, it may be possible to perform intermittent or intermittent circulation, and further, it may be possible to form a circulation path in which natural circulation occurs by utilizing the water temperature difference. Of course, it goes without saying that the shape and scale of the cavity as the storage tank 1 can be arbitrarily changed, and the water ring boring 4 may be provided in an appropriate form at an appropriate position accordingly.

It is a conceptual diagram of the underground type cryogenic tank facility which is embodiment of this invention. It is a figure which shows a water seal boring same as the above. It is a figure which shows an analysis result similarly. It is a figure which shows an analysis result similarly.

Explanation of symbols

1 Storage tank (hollow)
2 Vertical shaft 3 Horizontal shaft 4 Water-sealed boring 5 Horizontal shaft 6, 7 Pipe 8 Vertical shaft 9 Pipe 10 Circulation pump 11 Heat source

Claims (3)

It is an underground cryogenic tank facility with a structure in which a cryogenic fluid is stored using a cavity excavated in the underground ground as a storage tank, and the airtightness and liquid tightness of the storage tank are secured by a freezing area formed around the storage tank,
A water-sealed boring is provided in the ground above the storage tank to keep the ground saturated and to form a freezing area around the storage tank and to circulate water inside the storage tank to maintain the surrounding ground above the freezing temperature. An underground cryogenic tank facility. A ground freeze prevention method applied to the underground cryogenic tank facility according to claim 1,
Underground low temperature characterized by preventing the expansion of the freezing area formed around the storage tank at the position of the water-sealed boring by circulating water in the water-sealed boring and maintaining the surrounding ground above the freezing temperature Ground freeze prevention method in tank facility. The ground freeze prevention method according to claim 2,
Take out the vaporized gas from the liquefied gas as the low-temperature fluid stored in the storage tank, re-liquefy it at the surface, return it to the storage tank, and use the heat and waste heat generated during the re-liquefaction in the water-sealed boring A method for preventing ground freezing in an underground cryogenic tank facility, characterized by heating the water circulating in the ground.

Images