JP2012092895A - Method for manufacturing double shell tank, and double shell tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the work period and reduce the construction cost, in manufacturing a double shell tank.SOLUTION: In a method for manufacturing a double shell tank, a spacing S formed between an inner tank and an outer tank, is fed with dry air that has higher dryness than that of the air previously existing in the spacing during the period of time after starting the storage of a test fluid to the inner tank 2, and then a blanket is installed in the spacing S.

Description

  The present invention relates to a method for manufacturing a double shell tank and a double shell tank.

Conventionally, liquefied gases such as LNG (liquefied natural gas), LPG (liquefied petroleum gas), and LEG (liquefied ethylene gas) are stored and stored in a double shell tank including an inner tank and an outer tank.
In such a double shell tank, an outer tank is disposed so as to surround the inner tank, a cold insulating material or the like is filled in a gap between the inner tank and the outer tank, and the liquefied gas is stored in the inner tank.

By the way, if a cold insulator or the like placed in the gap between the inner tank and the outer tank absorbs water, the water is condensed or frozen when the double shell tank is used, and the equipment is installed along with the double shell tank. There is a risk of causing defects such as. In addition, heat insulation performance decreases due to moisture condensation or freezing, and the amount of BOG (boil-off gas) generated increases, and the increase in BOG increases the burden on the processing equipment.
Furthermore, since the stored liquefied gas is flammable, it is preferable that oxygen is not present in the double shell tank.
Therefore, in the conventional method for manufacturing a double shell tank, dry nitrogen gas is supplied between the inner tank and the outer tank, and the air existing in advance between the inner tank and the outer tank is purged.

On the other hand, when manufacturing such a double shell tank, a pressure resistance test for confirming the airtightness of the inner tank and the outer tank is performed. In the pressure test, in order to confirm the airtightness of the inner tank, a water filling test is performed in which a test liquid such as water or seawater is stored in the inner tank.
During the water filling test, since the test liquid is stored in the inner tank, the humidity in the double shell tank is maintained extremely high. Furthermore, since the inner tank is cooled by the test liquid, a large amount of dew condensation water adheres to the outer wall surface of the inner tank (that is, between the inner tank and the outer tank). Thus, for example, a blanket placed with a cold insulation material is highly hygroscopic and cannot be installed during a water filling test.
Therefore, in the conventional double shell tank manufacturing method, the water filling test is completed, the test liquid is drained from the inner tank, the condensed water on the outer wall surface of the inner tank is wiped off, and then a cold insulation material such as a blanket is installed. Further, purging with the above-described nitrogen gas is performed thereafter (see Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 58-196397 JP 58-196398 A

However, even if the outer wall surface of the inner tank is wiped after the water filling test, the air containing a large amount of water is filled between the inner tank and the outer tank. For this reason, a blanket etc. absorbs a lot of moisture.
As a result, the above-described purging with nitrogen gas is required for a very long time, leading to a prolonged construction period and an increase in construction cost.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to shorten the construction period and reduce the construction cost when manufacturing a double shell tank.

  In order to achieve the above object, in the present invention, as a first solution, a method for producing a double shell tank comprising an inner tank for storing liquefied gas and an outer tank for enclosing the inner tank, Supplying a dry air that has been dried from the air previously present in the gap to the gap between the inner tank and the outer tank in a period after the start of storage of the test liquid in the inner tank; And a step of installing a blanket in the supplied gap.

  As the second solving means, in the first solving means, a means is adopted in which the dry air is supplied upward from the bottom of the gap between the inner tank and the outer tank.

  As a third solving means, in the first or second solving means, after the discharge of the test liquid from the inner tank is completed, the dry air is supplied into the inner tank. adopt.

  As a fourth solution, in the first to third solutions, a method is adopted in which the dry air has a lower temperature than the outside air outside the outer tub.

  As a fifth solving means, a double-shell tank comprising an inner tank for storing liquefied gas and an outer tank surrounding the inner tank, the gap between the inner tank and the outer tank being set in advance in the gap A means of providing dry air supply means for supplying dry air that is dryer than the existing air is adopted.

According to the present invention, dry air that is dryer than the air existing in the gap between the inner tank and the outer tank is supplied to the gap in a period after the start of storage of the test liquid in the inner tank. .
For this reason, while dry air is supplied to the gap between the inner tank and the outer tank, the amount of moisture absorbed by the cold insulator or the like can be reduced by installing the cold insulator or the like in the gap.
Therefore, after the pressure resistance test including the water filling test, the time for purging with nitrogen gas can be shortened, and the construction period can be shortened and the construction cost can be reduced.
Furthermore, even while the test liquid is stored in the inner tank, dew condensation on the outer wall surface of the inner tank can be prevented by supplying dry air between the inner tank and the outer tank. For this reason, according to this invention, even if it is during the liquid for a test being stored in the inner tank, installation work, such as a cold insulating material, can be performed in the clearance gap between an inner tank and an outer tank. Therefore, according to the present invention, the construction period can be further shortened.

It is sectional drawing which shows typically schematic structure of the LNG tank in one Embodiment of this invention. It is a flowchart explaining the manufacturing process of the LNG tank in one Embodiment of this invention. It is a schematic diagram for demonstrating the flow of the dry air in the manufacturing process of the LNG tank in one Embodiment of this invention. It is a schematic diagram for demonstrating the flow of the dry nitrogen gas in the manufacturing process of the LNG tank in one Embodiment of this invention.

  Hereinafter, with reference to drawings, one embodiment of a manufacturing method of a double shell tank and a double shell tank concerning the present invention is described. In the following drawings, the scale of each member is appropriately changed in order to make each member a recognizable size.

  FIG. 1 is a cross-sectional view schematically showing a schematic configuration of an LNG tank (double shell tank) 1 in the present embodiment. As shown in this figure, the LNG tank 1 of this embodiment includes an inner tank 2, an outer tank 3, a blanket 4, a cold insulating material 5, a suspended deck 6, a purge pipe 7, and a dry air pressure feeding unit 8. And a dry air generating unit 9.

The inner tank 2 is a container formed of a metal material such as nickel steel or aluminum, and is a container for directly storing LNG inside.
The upper part of the inner tank 2 is an open end and is closed by the suspended deck 6.
However, as shown in FIG. 1, a pipe 2a communicating with the outside is connected to the inner tub 2, and the pipe 2a is configured to be opened and closed by a valve 2b.

The outer tub 3 is a container disposed around the inner tub 2, and is formed of, for example, carbon steel. The outer tub 3 has a ceiling portion 3a. And the ceiling part 3a is provided with a manhole 3b serving as an entrance for the worker. The manhole 3b is used for inspection and the like, and is closed when the LNG tank 1 is normally used.
A plurality of through holes (not shown) for supplying pearlite used as the cold insulating material 5 to the inside of the outer tub 3 are provided in the upper part of the peripheral surface of the outer tub 3.

  The blanket 4 is a sheet member excellent in heat insulation, and is formed of, for example, glass wool. And this blanket 4 is affixed with respect to the outer wall surface of the inner tank 2, and is arrange | positioned in the annular space S which is the clearance gap between the inner tank 2 and the outer tank 3. FIG.

  The cold insulating material 5 is a heat insulating material that blocks heat radiation from the inner tub 2 to the outside together with the blanket 4, and is filled between the outer tub 3. As this cold insulating material 5, for example, powdery pearlite can be used.

The suspended deck 6 closes the upper part of the inner tank 2 as described above, and is made of, for example, aluminum.
The suspended deck 6 is supported by being suspended from the ceiling portion 3a of the outer tub 3. In the suspended deck 6, a through hole 6a provided for insertion of a purge pipe 7 or ventilation is provided in the vertical direction. It is provided through (see FIG. 3).

The purge pipe 7 is a pipe provided with a plurality of nozzles for injecting dry air into the annular space S and the inside of the inner tank 2.
In the LNG tank 1 of the present embodiment, as the purge pipe 7, an annular shape annular ring pipe 7 a laid at the bottom of the annular space S and a straight pipe 7 b arranged at the bottom of the inner tank 2 are provided. Is provided.
Each purge pipe 7 is connected to a supply pipe 10 connected to the dry air pressure feeding unit 8. The annular ring pipe 7a is divided into a plurality of parts in plan view, and a supply pipe 10 is connected to each divided area (see FIG. 3).

  The dry air pressure feeding unit 8 is for feeding dry air to each purge pipe 7 via the supply pipe 10.

The dry air generation unit 9 generates dry air to be supplied to the annular space S and the inner tank 2 and, for example, condenses and removes moisture contained in the external air by taking in the external air and cooling it. To produce dry air.
As will be described in detail later, in the present embodiment, dry air is supplied to the annular space S for the main purpose of drying the annular space S when the LNG tank 1 is manufactured. For this reason, the dry air produced | generated in the dry air production | generation part 9 needs to be dried rather than the air previously existing in the annular space S at the time of manufacture.
In the present embodiment, it is assumed that an operator works in the annular space S while supplying dry air to the annular space S when the LNG tank 1 is manufactured. For this reason, it is preferable that the dry air produced | generated in the dry air production | generation part 9 shall be the temperature suitable for an operator's work. However, in order to efficiently reduce moisture in the annular space S and prevent condensation, the dry air is preferably at a lower temperature than the outside air outside the outer tub 3.
For example, when the outside air is 30 ° C., the dry air generation unit 9 condenses and removes moisture by cooling the outside air to 0 ° C., and then generates dry air by heating to about 20 ° C.

  In addition, when the plant in which the LNG tank 1 is installed includes an existing dry air generation unit, the dry air is acquired from the dry air generation unit, and the installation of the dry air generation unit 9 in the present embodiment is performed. It can be omitted. Furthermore, when the existing dry air generating unit can pump dry air with sufficient pressure, the installation of the dry air pressure feeding unit 8 can be omitted.

  The purge pipe 7, the dry air pressure feeding unit 8 and the dry air generating unit 9 shown in FIG. 1 constitute the dry air supply means in the present invention, and are used only in the manufacturing stage of the LNG tank 1, and the LNG tank Not used after completion of 1.

  Below, the manufacturing method of the LNG tank in this embodiment using the purge pipe | tube 7, the dry air pressure sending part 8, and the dry air production | generation part 9 is demonstrated, referring the flowchart of FIG.

  As shown in FIG. 2, the manufacturing method of the LNG tank includes a construction process S1 for constructing the inner tank 2 and the outer tank 3, a pressure test process S2 for testing the pressure resistance of the inner tank 2 and the outer tank 3, A blanket placement step S3 for placing the blanket 4 in the annular space S. In the blanket arrangement step S3, the cold insulation material 5 is filled in addition to the blanket 4 as necessary.

  The pressure resistance test step S2 is a step of performing a pressure resistance test for confirming the pressure resistance of the inner tank 2 and the outer tank 3 after the inner tank 2 and the outer tank 3 are completed. As shown in FIG. 2, the pressure test step S <b> 2 includes a water filling test step S <b> 21 in which a test liquid such as water or seawater is stored in the inner tank 2 to check the pressure resistance of the inner tank 2, and the inside of the outer tank 3. The pressurization test process S22 which pressurizes and confirms the pressure | voltage resistance of the outer tank 3 is performed in order. In the present embodiment, the pressure test is performed in a state where the test liquid is stored in the inner tank 2.

In the method for manufacturing the LNG tank 1 of the present embodiment, the annular space is compared with the annular space S in a period after the start of storage of the test liquid in the inner tank 2 (that is, after the start of the pressure test). The blanket arrangement process S3 is performed while the dry air dried from the air previously existing in S is supplied and the dry air is supplied to the annular space S.
Specifically, as a period for supplying dry air to the annular space S, as shown in FIG. 2, the period during the water filling test and after the pressurization test (pattern 1), only during the water filling test (pattern 2), Only the period after the end of the pressure test (pattern 3) can be considered.
And when the pattern 1 and the pattern 2 are selected, it becomes possible to perform the blanket arrangement | positioning process 3 from the middle of the pressure | voltage resistant test process S2.

Next, how the dry air is supplied to the annular space S will be described in detail with reference to FIGS.
The air existing in advance in the annular space S contains a large amount of moisture because the test liquid exists in the inner tank 2, and contains more moisture than the outside air outside the outer tank 3.
And when supplying dry air to the annular space S, the dry air production | generation part 9 produces | generates dry air, and the dry air supply part 8 pumps this dry air to the annular ring pipe 7a via the supply piping 10. FIG. Is done by.

3 and 4 are schematic diagrams showing the LNG tank 1 in the process of manufacture, and show the LNG tank 1 that is not completed at the time when the pressure resistance test is performed.
Then, when the dry air is pumped to the annular ring pipe 7a, the dry air is jetted and supplied upward from the bottom of the annular space S, as indicated by the solid line in FIG.
As a result, an upward flow of dry air is formed in the annular space S, so that air containing a large amount of moisture existing in the annular space S in advance is excluded from the annular space S.

Here, in this embodiment, the blanket 4 is installed in the annular space S while the dry air is supplied to the annular space S. For this reason, in order to further reduce the amount of moisture absorbed into the blanket 4, it is preferable to supply dry air to the annular space S at least until the test liquid is completely discharged from the inner tank 2. For this reason, the above-mentioned pattern 1 or pattern 3 in which dry air is supplied to the annular space S during the period after the pressurization test is preferable.
And if the cost concerning dry air is considered, the above-mentioned pattern 3 which requires less amount of dry air is more preferable. However, when the installation work of the blanket 4 in the annular space S is an amount that does not end only in the period after the end of the pressurization test, it is preferable to employ the pattern 1 that supplies dry air during water filling.

Then, after the discharge of the test liquid from the inner tank 2 is completed in the period after the pressurization test, dry air is also supplied into the inner tank 2.
Specifically, the dry air generated in the dry air generating unit 9 is supplied by the dry air pressure feeding unit 8 to the straight pipe 7b via the supply pipe 10 so that the dry air is supplied into the inner tank 2.
Thus, when dry air is pumped to the straight tube 7b, the dry air is jetted upward from the bottom of the inner tank 2 and supplied as indicated by the broken line in FIG.
As a result, an upward flow of dry air is formed inside the inner tub 2, whereby air containing a large amount of moisture in the inner tub 2 is removed from the inner tub 2, and the entire inside of the outer tub 3 becomes dry.

When the installation work of the blanket 4 is completed, the inside of the outer tub 3 is purged with dry nitrogen gas in order to set the dew point inside the LNG tank 1 to a preset temperature.
Specifically, as shown in FIG. 4, the manhole 3b is closed, the valve 2b is opened, and dry nitrogen gas is pumped only to the straight tube 7b.
As a result, the dry nitrogen gas supplied to the inner tank 2 is supplied as an inner tank purge nitrogen gas indicated by a broken arrow in FIG. 4, and is exhausted through the pipe 2a. However, some of the nitrogen gas for purging the inner tank flows out of the inner tank 2 through the through holes provided in the suspended deck 6 and is used as the annular gas for purging the annular space indicated by the solid line arrow in FIG. It is supplied to the space S. Then, the nitrogen gas for annular space purge is exhausted to the outside of the outer tub 3 through a through hole (not shown) of the outer tub 3 and the annular ring pipe 7a.

  Then, before starting the purge with the dry nitrogen gas, the LNG tank 1 is completed by performing the work such as filling the annular space S with the pearlite from the through hole (not shown) of the outer tub 3 and performing the purge with the dry nitrogen gas. To do.

According to the manufacturing method of the LNG tank 1 of the present embodiment as described above, dry air that is dryer than the air existing in advance in the annular space S causes the test liquid to be supplied to the inner tank 2 to the annular space S. Supplied in the period after the start of storage.
For this reason, by installing the blanket 4 in the annular space S while dry air is supplied to the annular space S, the amount of moisture absorbed by the blanket 4 can be reduced.
Therefore, after the pressure resistance test including the water filling test, the time for purging with nitrogen gas can be shortened, and the construction period can be shortened and the construction cost can be reduced.
Furthermore, even while the test liquid is stored in the inner tank 2, by supplying dry air to the annular space S, condensation on the outer wall surface of the inner tank 2 can be prevented. For this reason, according to the present invention, the blanket 4 can be installed in the annular space S even while the test liquid is stored in the inner tank 2. Therefore, according to the manufacturing method of the LNG tank 1 of this embodiment, a work period can be shortened more.

In the method for manufacturing the LNG tank 1 of the present embodiment, dry air is supplied upward from the bottom of the annular space S.
For this reason, an upward flow can be formed in the annular space S, and air containing a lot of moisture previously present in the annular space S can be surely excluded from the annular space S.

Moreover, in the manufacturing method of the LNG tank 1 of this embodiment, dry air was supplied in the inner tank 2 after discharge | emission of the liquid for a test from the inner tank 2 was completed.
For this reason, in addition to the annular space S, the inside of the inner tank 2 can be dried, the time for purging with nitrogen gas can be further shortened, the construction period can be shortened, and the construction cost can be reduced.

Moreover, in this embodiment, it demonstrated that it was preferable that dry air was made into low temperature rather than the external air of the outer side of the outer tank 3. As shown in FIG.
In this way, by setting the dry air at a lower temperature than the outside air outside the outer tub 3, it is possible to prevent the dry air from being cooled in the annular space S and causing condensation.

  As mentioned above, although preferred embodiment of this invention was described referring drawings, this invention is not limited to the said embodiment. Various shapes, combinations, and the like of the constituent members shown in the above-described embodiments are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

For example, in the said embodiment, the manufacturing method of the LNG tank and LNG tank which use LNG as liquefied gas was demonstrated.
However, the present invention is not limited to this, and can be applied to an LPG tank using LPG as a liquefied gas and a method for manufacturing an LPG tank, and an LEG tank using an LEG as a liquefied gas and a method for manufacturing an LEG tank. It is.

Moreover, in the said embodiment, the example which applied this invention to what is called a ground-type metal double shell tank and its manufacturing method was demonstrated.
However, the present invention is not limited to this, and can be applied to an underground membrane tank and a manufacturing method thereof, a prestressed concrete tank and a manufacturing method thereof.
The present invention can also be applied to a double-shelled tank in which an inner tank and an outer tank are independent, and a manufacturing method thereof.

  DESCRIPTION OF SYMBOLS 1 ... LNG tank (double-shell tank), 2 ... Inner tank, 3 ... Outer tank, 4 ... Blanket, 5 ... Coolant, 7 ... Purge pipe (dry air supply means), 7a ... Annular ring tube, 7b ... straight tube, 8 ... dry air pressure feeding part (dry air supply means), 9 ... dry air generating part (dry air supply means), S ... annular space (inner and outer tanks) Gap)

Claims (5)

A method for producing a double-shell tank comprising an inner tank for storing liquefied gas and an outer tank surrounding the inner tank,
Supplying dry air, which is drier than the air existing in the gap, into the gap between the inner tank and the outer tank in a period after the start of storage of the test liquid in the inner tank; And a step of installing a blanket in the gap to which is supplied a double shell tank manufacturing method.   The method for manufacturing a double-shell tank according to claim 1, wherein the dry air is supplied upward from the bottom of the gap between the inner tank and the outer tank.   The method for manufacturing a double-shell tank according to claim 1 or 2, wherein the dry air is supplied into the inner tank after the discharge of the test liquid from the inner tank is completed.   The method for producing a double-shell tank according to any one of claims 1 to 3, wherein the dry air has a lower temperature than the outside air outside the outer tub. A double shell tank comprising an inner tank for storing liquefied gas, and an outer tank surrounding the inner tank,
A double-shell tank comprising a dry air supply means for supplying dry air, which is drier than air existing in the gap, in a gap between the inner tank and the outer tank.

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