JP7323990B2 - Dew point temperature adjustment device and dew point temperature adjustment method - Google Patents

Description

The present invention relates to an apparatus and method for adjusting the dew point temperature of the inner space of a container that stores cryogenic liquefied gas.

The dew point temperature of the inner space of the container storing the low temperature liquefied gas must be lowered in advance before the low temperature liquefied gas is filled. This is because if the low-temperature liquefied gas is filled without lowering the dew point temperature, the moisture in the container may freeze and damage the equipment.

Patent Document 1 discloses a so-called "nitrogen swing method" as an example of a method for adjusting the dew point temperature of the loading arm. The “nitrogen swing method” means (1) filling the target space (inside the loading arm pipe in the example of Patent Document 1) with high-purity nitrogen gas, (2) holding pressure of the filled nitrogen gas, and (3) ) Emission of gas from the target space, by repeating the work consisting of these steps (1) to (3), gradually lowering the moisture content (that is, the dew point temperature) of the gas in the target space. .

JP 2012-229039 A

Using the nitrogen swing method, the adjustment of the dew point temperature is costly, including the cost of the high-purity nitrogen gas itself, the time and personnel costs for its preparation, and the personnel costs for performing repetitive operations.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an apparatus and method capable of adjusting the dew point temperature of the inner space of a container storing low-temperature liquefied gas at low cost.

A dew point temperature adjusting device according to one aspect of the present invention is a device for adjusting the dew point temperature of an inner space of a container that stores a low-temperature liquefied gas, comprising: an internal pressure gauge that detects an internal pressure that is the pressure of the inner space; a decompression pump for decompressing the internal space; and a control configured to operate the decompression pump to decompress the internal space until the internal pressure detected by the internal pressure gauge becomes equal to or less than an internal pressure threshold. Equipped with a vessel and

Hereinafter, the partial pressure of water when the internal pressure as the total pressure of the internal space is the internal pressure threshold may be referred to as the "partial pressure threshold". According to the above configuration, by decompressing the inner space with the decompression pump, the saturated water vapor pressure in the inner space is lowered and the dew point temperature of the inner space is lowered. As the internal pressure drops to or below the internal pressure threshold, the dew point temperature is adjusted below the temperature at which the saturated vapor pressure of water is at the partial pressure threshold. This dew point temperature adjustment is realized by controlling the operation of the decompression pump, and does not require preparation of nitrogen gas or repetitive work. Therefore, the dew point temperature can be adjusted at low cost.

a dew point meter for detecting a dew point temperature of the inner space, wherein the controller starts monitoring the dew point temperature detected by the dew point meter when the internal pressure is at or below the internal pressure threshold; The operation of the decompression pump may be stopped when the dew point temperature becomes a predetermined temperature or less.

According to this configuration, if the dew point temperature exceeds the predetermined temperature when the internal pressure becomes equal to or less than the internal pressure threshold value, the pressure reduction of the internal space is continued. Even if the internal space is hot and humid at the start of decompression of the internal space, the dew point temperature can be reliably adjusted to a predetermined temperature or less.

The container has an outer tank and an inner tank that is accommodated in the outer tank to form the inner space, and the device is the pressure in the inter-tank space between the outer tank and the inner tank. The controller further comprises an inter-tank pressure gauge for detecting an inter-tank pressure, wherein the controller detects in advance that the inter-tank pressure detected by the inter-tank pressure gauge is equal to or less than an inter-tank pressure threshold value before depressurization of the inner space. The inter-tank space may be decompressed until the decompression pump is operated.

According to this configuration, the inter-tank space is depressurized before depressurizing the inner space formed by the inner tanks. Therefore, it is possible to prevent the inner tank from being damaged when the inner space is depressurized without particularly increasing the pressure resistance performance of the inner tank.

A dew point temperature adjustment method according to one aspect of the present invention is a method for adjusting the dew point temperature of an inner space of a container that stores a low-temperature liquefied gas, wherein the internal pressure, which is the pressure of the inner space, is detected and detected. The internal pressure is reduced until the internal pressure is at or below an internal pressure threshold.

ADVANTAGE OF THE INVENTION According to this invention, the apparatus and method which can adjust the dew point temperature of the inner space of the container which stores low-temperature liquefied gas at low cost can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the dew point temperature adjustment apparatus which concerns on embodiment. 4 is a flow chart showing a dew point adjustment method used in a dew point adjustment device; 3A and 3B are explanatory diagrams of the dew point temperature adjustment method.

Hereinafter, embodiments will be described with reference to the drawings. The same or corresponding elements are denoted by the same reference numerals throughout all the drawings, and overlapping detailed descriptions are omitted.

[container]
As shown in FIG. 1, the dew point temperature adjusting device 100 is a device that adjusts the dew point temperature Td of the inner space 13 of the container 1 that stores the low temperature liquefied gas. Low-temperature liquefied gas may be defined as a gas having a boiling point of −160° C. or less under normal pressure, and specific examples of low-temperature liquefied gas include liquid helium, liquid hydrogen, liquid oxygen, liquid nitrogen, and liquefied natural gas. The dew point temperature adjusting device 100 is a device that adjusts the dew point temperature Td before filling the inner space 13 with the low temperature liquefied gas. Typically, the manufacturer of the container 1 adjusts the dew point temperature Td using the dew point temperature adjusting device 100 as a final stage of production before shipping the container 1 .

The container 1 is used for land transportation of cryogenic liquefied gas. The container 1 has a double-shell structure for better heat insulation. The container 1 has an outer tub 11 and an inner tub 12 that is housed in the outer tub 11 and forms an inner space 13 . As an example, the container 1 (outer tank 11) is formed in a cylindrical shape, and the inner tank 12 is also formed in a cylindrical shape. An inter-tank space 14 is formed between the inner surface of the outer tank 11 and the outer surface of the inner tank 12 .

The container 1 is provided with a filling port 15 and a suction port 16 . The filling port 15 communicates the exterior of the container 1 with the inner space 13 . The filling port 15 is originally used for filling cryogenic liquefied gas. In this embodiment, it is used for depressurizing the inner space 13 as described later. The suction port 16 communicates the outside of the container 1 with the inter-tank space 14 . The suction port 16 is used for evacuating the inter-tank space 14 . By increasing the degree of vacuum in the inter-tank space 14, the inner space 13 can be provided with high heat insulation.

The outer tank 11 is composed of a pressure-resistant wall having sufficient pressure resistance to withstand the differential pressure between the atmospheric pressure and the pressure in the inter-tank space 14 . On the other hand, the inner tank 12 is composed of a non-pressure resistant wall having lower pressure resistance than the pressure resistant wall of the outer tank 11 . A plurality of rods (not shown) bridging between the inner surface of the outer tank 11 and the outer surface of the inner tank 12 may be provided in the inter-tank space 14 .

[Adjuster]
As shown in FIG. 1, the dew point temperature adjusting device 100 includes a decompression pump 2, a first decompression line 3, a second decompression line 4, an internal pressure gauge 5, a dew point gauge 6, an inter-tank pressure gauge 7, and a controller 9. .

The vacuum pump 2 is connectable to the filling port 15 via the first vacuum line 3 . Also, the decompression pump 2 can be connected to the suction port 16 via the second decompression line 4 . The first decompression line 3 connects the suction port of the decompression pump 2 to the filling port 15 . The second decompression line 4 connects the suction port of the decompression pump 2 to the suction port 16 .

The internal pressure gauge 5 detects an internal pressure Pi, which is the pressure in the internal space 13 (more specifically, the total pressure). A dew point meter 6 detects the dew point temperature Td of the inner space 13 . The inter-tank pressure gauge 7 detects an inter-tank pressure Pa, which is the pressure in the inter-tank space 14 (more specifically, the total pressure). Note that the internal pressure gauge 5 may not necessarily be arranged in the internal space 13 and the inter-tank pressure gauge 7 may not necessarily be arranged in the inter-tank space 14 . The internal pressure gauge 5 may detect the pressure in the first decompression line 3 that is substantially the same as the internal pressure Pi when the decompression pump 2 is connected to the filling port 15 and operated. The inter-tank pressure gauge 7 detects the pressure in the second decompression line 4 which becomes substantially the same as the inter-tank pressure Pa when the decompression pump 2 is connected to the suction port 16 and operates. good too.

Controller 9 is connected to internal pressure gauge 5 , dew point gauge 6 , inter-tank pressure gauge 7 , and decompression pump 2 . The controller 9 controls the operation of the decompression pump 2 based on the signals output from these instruments 5-7. The controller 9 has a memory for storing a program for adjusting the dew point temperature Td, a CPU for executing the program stored in the memory, and an input/output interface connected to the gauge 5-7 and the decompression pump 2. .

[Adjustment method]
FIG. 2 is a flow chart showing a dew point adjustment method executed by the controller 9 of the dew point adjustment device 100. As shown in FIG. At the beginning of the implementation of the method, the dew point temperature Td of the inner space 13 is approximately equal to that of the outside air. The internal pressure Pi and inter-tank pressure Pa are also approximately equal to the outside air pressure (atmospheric pressure).

At the start of the method, the vacuum pump 2 is connected via the second vacuum line 4 to the suction port 16 . Under this connection state, the decompression pump 2 is operated to decompress the inter-tank space 14 (S1). This depressurization process S1 may be started by giving a command to the controller 9 from the operator after the connection state is obtained. The controller 9 monitors the inter-tank pressure Pa detected by the inter-tank pressure gauge 7, and compares the detected inter-tank pressure Pa with the inter-tank pressure threshold value P2 (S2). If the inter-tank pressure Pa exceeds the inter-tank pressure threshold value P2 (S2: NO), the operation of the decompression pump 2 and the pressure reduction of the inter-tank space 14 are continued (S1). When the inter-tank pressure Pa becomes equal to or less than the inter-tank pressure threshold value P2 (S2: YES), the operation of the decompression pump 2 and thus the reduction of the inter-tank pressure Pa are stopped (S3). As a result, the inter-tank space 14 is held at the inter-tank pressure threshold value P2 or a pressure slightly lower than it.

Next, the vacuum pump 2 is connected to the filling port 15 via the first vacuum line 3 . Under this connection state, the decompression pump 2 is operated to decompress the inner space 13 (S4). This decompression process S4 may be started by giving a command to the controller 9 from the operator after the connection state is obtained. The controller 9 monitors the internal pressure Pi detected by the internal pressure gauge 5 and compares the detected internal pressure Pi with the internal pressure threshold value P1 (S5). If the internal pressure Pi exceeds the internal pressure threshold value P1 (S2: NO), the operation of the decompression pump 2 and the decompression of the internal space 13 are continued (S4). If the internal pressure Pi is equal to or less than the internal pressure threshold value P1 (S5: YES), the controller 9 starts monitoring the dew point temperature Td detected by the dew point meter 6 (S6). is compared with a predetermined temperature Td1 (S7). Nitrogen gas is filled in the inner space 3 when starting the measurement of the dew point temperature Td. If the detected dew point temperature Td is higher than the predetermined temperature Td1 (S7: NO), the operation of the decompression pump 2 and thus the pressure reduction of the inner space 13 are continued (S4), and the monitoring of the dew point temperature Td is continued (S6). . When the detected dew-point temperature Td becomes the predetermined temperature Td1 or less (S7: YES), the operation of the decompression pump 2 and thus the decompression of the inner space 13 are stopped (S9). This completes the dew point temperature adjustment method.

3A and 3B are explanatory diagrams of the dew point temperature adjustment method. In both FIGS. 3A and 3B, the horizontal axis indicates temperature, the left vertical axis indicates saturated water vapor pressure, and the right vertical axis indicates water vapor content (g/m ³ ). As shown in FIG. 3A, if the ambient air temperature (dry bulb) at the start of the method is t, then the temperature (dry bulb) of the inner space 13 is also t. The amount of water vapor contained in the air in the inner space 13 is a value (RHa(t)) obtained by multiplying the saturated water vapor amount a(t) corresponding to the temperature t by the relative humidity RH of the ambient air. When the internal pressure Pi decreases to the internal pressure threshold value P1 by executing step S4, the partial pressure of water in the internal space 13 becomes the partial pressure threshold value P1(H ₂ O). The internal pressure threshold P1 is a fixed value pre-stored in the controller 9, while the partial pressure threshold P1(H ₂ O) is influenced by the water vapor mole fraction of the surrounding atmosphere (i.e. temperature and relative humidity of the surrounding atmosphere). Takes different values depending on the situation. When the determination in step S5 is YES, the dew point temperature Td is the temperature at which the saturated water vapor pressure reaches the partial pressure threshold value P1( _H2O ).

In the situation illustrated in FIG. 3A, the dew-point temperature Td is lower than the predetermined temperature Td1 at the first YES determination in step S5. Therefore, the dew point temperature adjustment method ends there. In the situation illustrated in FIG. 3B, the temperature of the ambient air is the same as in the situation illustrated in FIG. 3A, but the relative humidity RH of the ambient air is higher (RH=100%). The dew point temperature Td exceeds the predetermined temperature Td1 when a YES determination is made for the first time in step S5. Therefore, the process returns to step S4 and pressure reduction continues until the dew point temperature Td reaches the predetermined temperature Td1 and a YES determination is made in step S7. It should be noted that the loop of steps S7->S4->S6->S7 is automatically started and ended by the controller 9 after proceeding from step S5 to step S7 for the first time. There is no need for manual work such as a worker giving a command to the controller 9 to start or end the continuation of pressure reduction again.

Thus, by implementing the above method, the internal pressure Pi (the total pressure of the internal space 13) is reduced to the internal pressure threshold value P1 or less, and the saturated water vapor pressure is reduced to the partial pressure threshold value P1 (H ₂ O) or less. Therefore, the dew point temperature Td of the inner space 13 is adjusted to be lower than the dew point temperature when the saturated water vapor pressure is the partial pressure threshold value P1 (H ₂ O). This dew-point temperature adjustment is realized by controlling the continuous operation of the decompression pump 2, and does not require preparation of nitrogen gas or repetitive work. Therefore, the dew point temperature Td can be adjusted at low cost.

When the internal pressure Pi is lowered to the internal pressure threshold value P1, monitoring of the dew point temperature Td detected by the dew point meter 6 is started, and pressure reduction of the internal space 13 is continued until the dew point temperature Td reaches the predetermined temperature Td1. Therefore, as exemplified in FIG. 3B, even if the ambient atmosphere and the inner space 13 are hot and humid at the start of the method, the dew point temperature Td can be reliably adjusted to the predetermined temperature Td1 or lower.

As an example, the predetermined temperature Td1 varies depending on the type of low-temperature liquefied gas (in other words, the boiling point of the target gas). The pressure is set to a low pressure of 0.4 Pa (set to about -40°C dp for liquefied oxygen). In the present embodiment, prior to such decompression of the inner space 13, the inter-tank space 14 is decompressed, and the inter-tank pressure Pa is maintained at the inter-tank pressure threshold value P2 or less. Therefore, it is possible to prevent the inner tank 12 from being damaged when the inner space 13 is depressurized without particularly increasing the pressure resistance performance of the inner tank 12 . Note that the inter-tank pressure threshold P2 can be set to the same value as the internal pressure threshold P1 or a lower value. As described above, when the container 1 is shipped from the manufacturer, the inter-tank space 14 is evacuated to ensure heat insulation. Work for that purpose may be performed in step S1. That is, the inter-vessel pressure threshold value P2 may be set to a pressure value (for example, 0.01 Pa) corresponding to the degree of vacuum in the inter-vessel space 14 required at the time of shipment.

Although the embodiments have been described so far, the configurations and methods described above are examples, and can be appropriately changed, deleted, and/or added within the scope of the present invention. Although the container 1 has a double shell structure, it may have a single shell structure. In that case, the walls that make up the tank are configured to withstand the differential pressure between the inner space and the outer pressure.

1 Container 2 Decompression pump 5 Internal pressure gauge 6 Dew point gauge 7 Inter-tank pressure gauge 9 Controller 11 Outer tank 12 Inner tank 13 Internal space 14 Inter-tank space 100 Dew point temperature adjustment device Pi Internal pressure Pa Inter-tank pressure P1 Internal pressure threshold value P2 Tank Intermediate pressure threshold Td Dew point temperature Td1 Predetermined temperature

Claims (3)

A device for adjusting the dew point temperature of the inner space of a container that stores low-temperature liquefied gas,
an internal pressure gauge that detects internal pressure, which is the pressure in the internal space;
a decompression pump for decompressing the inner space;
a controller configured to operate the decompression pump to decompress the internal space until the internal pressure detected by the internal pressure gauge becomes equal to or less than an internal pressure threshold;
and a dew point meter that detects the dew point temperature of the inner space,
The controller is
operating the decompression pump to decompress the internal space while monitoring the internal pressure detected by the internal pressure gauge ;
When the internal pressure detected by the internal pressure gauge becomes equal to or less than an internal pressure threshold, monitoring the dew point temperature detected by the dew point gauge is started;
A dew point temperature adjusting device that continues to operate the decompression pump until the dew point temperature reaches or falls below a predetermined temperature while continuing to monitor the dew point temperature. The container has an outer tank and an inner tank accommodated in the outer tank to form the inner space,
The device further comprises an inter-tank pressure gauge that detects an inter-tank pressure, which is the pressure in the inter-tank space between the outer tank and the inner tank,
The controller operates the decompression pump until the inter-tank pressure detected by the inter-tank pressure gauge becomes equal to or less than an inter-tank pressure threshold before depressurizing the inner space. 2. The dew point temperature control device of claim 1, wherein the dew point temperature control device is configured to reduce the pressure of the A method for adjusting the dew point temperature of the inner space of a container storing cryogenic liquefied gas, comprising:
detecting the internal pressure, which is the pressure in the internal space;
decompressing the inner space while monitoring the inner pressure ;
when the detected internal pressure is at or below an internal pressure threshold, start monitoring the dew point temperature of the internal space;
A dew point temperature adjusting method comprising: continuing to monitor the dew point temperature and continuing to reduce the pressure in the inner space until the dew point temperature reaches or falls below a predetermined temperature.

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