JPH0231331B2 - NIJUKAKUTEIONTANKUNOGASUROEIKENCHISOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an apparatus for sampling gas from between the inner and outer tanks of a double-shell cryogenic tank, performing gas detection, and detecting leakage of stored low-temperature liquefied gas from the inner tank. .

Conventional technology Double-shell cryogenic tanks that store low-temperature liquefied gases such as LPG and LNG have a storage capacity of tens of thousands of tons in large-scale tanks, and contain an extremely large amount of energy, making safety management extremely important. be. Therefore, in order to prevent disasters due to tank destruction, it is important to detect cracks in the inner tank wall at an early stage. The occurrence of cracks is generally detected by sampling the seal gas between the inner and outer tanks, which serve as a cold insulation layer, and detecting the gas.

By the way, it is an important matter in the operation of the tank which part of the tank the leakage point is. for example,
The degree of potential danger differs greatly depending on whether the leak point is the inner tank roof or the side plate.
Furthermore, the degree of danger is different depending on whether the leakage point is located in a relatively upper portion of the inner tank side plate or in a lower portion. For this reason, the countermeasure method and level of urgency will differ depending on the location of the leak.

Therefore, it is very important to detect where leakage has occurred in the height direction of the side panels and roof of the inner tank.

Now, if the low-temperature liquefied gas stored in the double-shell low-temperature tank leaks from the inner tank into the cold insulation layer and vaporizes, its specific gravity will be higher than the specific gravity of the nitrogen gas used as the seal gas in the cold insulation layer. If the leaked gas contains small amounts of methane or the like as a component, the leaked gas will rise through the ventilation gap of the cold insulation material of the cold insulation layer along the outer surface of the inner tank.

Purpose: In view of the above-mentioned requirements for leakage detection in a double-shell cryogenic tank, the present invention provides an inner tank of a double-shell cryogenic tank that stores a low-temperature liquefied gas whose specific gravity when vaporized is smaller than the specific gravity of the seal gas in the cold insulation layer. An object of the present invention is to provide a gas leakage detection device capable of early detecting gas leakage by appropriately sectioning side plates and a roof.

Configuration The gas leak detection device according to the present invention that achieves this object has ring-shaped weirs for the flow from below, which are placed on the outer surface of the inner tank side plate at a plurality of positions in the height direction.
For example, a ring with an L-shaped cross section with the flange facing downward is provided, and a plurality of ring-shaped weirs with different radii are provided concentrically on the lower surface of the outer tank roof, and the upper corner of the side dammed by these weirs and the roof are cooled. A gas sampling means is provided at the top of the layer, and gas detection instrumentation is provided to separately detect the sample gas corresponding to each weir.

Hereinafter, the present invention will be explained in detail based on embodiments shown in the drawings.

The attached drawing shows an embodiment in which the present invention is applied to an LNG tank with a double shell flat bottom structure, and shows a space 3 between an inner tank side plate 1 and an outer tank side plate 2, an inner tank roof 4 and an outer tank roof 5. The space 6 between the two serves as a cold insulation layer, and the inside of the inner tank serves as an LNG storage space 7. The cold insulation layers 3 and 6 are filled with a cold insulation material 8 and nitrogen gas as a seal gas. Note that a bottom cold insulation 11 is formed between the inner tank bottom plate 9 and the outer tank bottom plate 10 using a relatively hard cold insulation material.

Ring-shaped members 12 having an L-shaped cross section with flanges facing downward are attached to the inner tank side plate 1 at a plurality of positions in the height direction by welding with the toe on the opposite side of the flange abutting against the outer surface of the inner tank 1. It forms a dam. Further, a plurality of ring-shaped weirs 13 having different radii are provided concentrically on the lower surface of the outer tank roof. The weir 12 can also use an inner tank stiffener, and the weir 13 can also use the roof bones of the outer tank roof.

A gas sampling device 14 for gas detection is provided at the upper corner of the side where gas having a specific gravity lower than the sealing gas is dammed by these dams 12 and 13 and at the top of the roof cold insulation layer. If the gas sampling device is a dot-like suction port, it is necessary to provide a plurality of them along a ring-shaped weir in one weir. As the gas sampling device 14, a ring-shaped pipe having a large number of small holes in the pipe wall may be provided along the weir. Gas detection instrumentation is provided that can individually detect the gas sampled by the sampling device corresponding to each weir and the top of the cold storage layer. To do this, for example, the instrumentation piping from the gas sampling device installed at each weir can be connected to individual gas detection instrumentation, or it can be switched at a predetermined timing with a switching valve to one gas detection instrumentation. This is achieved by connecting.

Since this device is configured as described above, for example, if a crack occurs somewhere in the inner tank roof and the gas in the inner tank leaks into the cold insulation layer 6, the leaked gas will be affected by the difference in specific gravity from the seal gas. As a result, it reaches the lower surface of the outer tank roof through the ventilation interval of the roof cold insulation layer 6, moves toward the center along the lower surface of the outer tank roof, and reaches the first dam 13.
It is dammed up and accumulates above the outside of the dam, or it accumulates below the top of the dome-shaped roof. In addition, the stored gas that leaked from a crack that occurred somewhere on the side plate 1 vaporizes within the cold insulation layer 3, and due to the difference in specific gravity with the nitrogen gas, which is the sealing gas, rises along the outer surface of the inner tank side plate 1, and initially is stopped by weir 12, which meets weir 1.
It accumulates at the bottom of the space surrounded by the flange 2, the horizontal part, and the inner tank side plate 1.

Therefore, by continuously sampling the seal gas from the gas sampling device 14 corresponding to each weir 12, 13 and the top of the roof cold insulation layer and detecting the gas, the gas drawn from the gas sampling device corresponding to a certain weir can be detected. If a stored gas component is detected in the stored gas, the location of the leak is within the range between the weir and the weir adjacent to the upstream side (i.e., the periphery of the weir for the roof 4, and the lower part of the weir for the side plate 1). It is determined that something is true.

In order to facilitate the movement of leaked gas within the cold insulation layer, it is effective to use glass wool with good air permeability in an appropriate thickness range on the side of the side cold insulation that is in contact with the inner tank side plate. In that case, it is more effective to limit the movement range of the leaked gas by covering the outer surface of the glass wool layer with a suitable film such as polyethylene film, polyester film, vinyl chloride film, etc.

Effects As described above, according to the present invention, leakage from the inner tank of a double-shell cryogenic tank can be detected early along with the range of the leakage point, so appropriate measures can be taken to ensure safety. Significant management effects can be obtained.

[Brief explanation of drawings]

The attached drawings are cross-sectional views showing embodiments of the present invention. 1... Inner tank side plate, 2... Outer tank side plate, 3... Side cold insulation layer, 4... Inner tank roof, 5... Outer tank roof, 6...
...Roof cold insulation layer, 7...Stored low-temperature liquefied gas, 8...
Cold insulation material, 12, 13... weir, 14... gas sampling device.

Claims (1)

[Claims] 1 Gas is detected by sampling gas from between the inner and outer tanks of a double-shelled flat-bottomed cryogenic tank, which stores low-temperature liquefied gas in the inner tank and fills cold insulation material and seal gas between the inner and outer tanks to form a cold insulation layer. In a device for detecting gas leakage from an inner tank, in which the specific gravity of the low-temperature liquefied gas when vaporized is smaller than the specific gravity of the seal gas, there is a mark on the outer surface of the inner tank side plate in the height direction. Ring-shaped weirs for the flow from below are provided at multiple locations, and multiple ring-shaped weirs with different radii are provided concentrically on the lower surface of the outer tank roof, and the upper corner and roof of the side that is dammed by these weirs is A gas leak detection device characterized in that a gas sampling means is provided at the top of a cold insulation layer, and a gas detection instrumentation is provided for separately detecting sample gas corresponding to each weir.