JP6700892B2 - Low temperature liquefied gas storage facility - Google Patents

Description

  The present invention relates to a low temperature liquefied gas storage facility for storing low temperature liquefied gas such as liquefied natural gas and liquefied petroleum gas.

  In the low-temperature liquefied gas storage facility, a gas compressor (compressor in the publication) is connected to the tank as shown in Patent Document 1, for example. That is, when a large amount of boil-off gas is generated in the tank due to heat input when supplying liquefied gas to the tank, the boil-off gas is taken out to the compressor and compressed for combustion, etc., and the internal pressure of the tank is prevented from rising too much. To be prevented.

JP, 2005-175488, A

For example, when adding a new tank to a base that already has a tank, the design pressure of the new tank should be the same as the design pressure of the existing tank, taking into consideration that the receiving method and receiving amount of liquefied gas will be changed in the future. May be set higher than. In recent years, in tanks that store liquefied natural gas, the design pressure of the tank is on an upward trend compared to the conventional one because the tank pressure for operation is raised and boil-off gas generation is suppressed, and when changing the design pressure, it is higher than before. Tends to set.
In addition, when the conditions that affect the increase/decrease in the amount of boil-off gas generated, such as the amount of new tanks received, are changed, it may be necessary to set a high operating tank pressure only for new tanks depending on the equipment conditions of the existing base.
If the design pressure is made higher than that of the existing tank, it will increase the thickness of the roof plate, etc., and the facility cost will be incurred, but there has been no method to recover this facility cost.
Also, in a low-temperature liquefied gas storage facility equipped with tanks with different operating tank pressures, if dedicated gas compressors for tanks with low operating tank pressure and tanks with high operating tank pressure are installed, a gas compressor will be installed. High equipment cost is required. In addition to this, many gas compressors must be driven and controlled, which increases operating costs.

  The present invention provides a low-temperature liquefied gas storage facility that is inexpensive even though it has tanks with different operating tank pressures or design pressures.

The low temperature liquefied gas storage facility according to the present invention comprises:
A first tank for storing low temperature liquefied gas;
A second tank which is operated at an operation tank pressure higher than the operation tank pressure of the first tank and stores low temperature liquefied gas;
A gas compressor connected to the first tank via a first boil-off gas passage, for extracting boil-off gas from the first tank and performing compression processing;
A second boil-off gas passage that is provided between the first boil-off gas passage and the second tank and that allows boil-off gas generated in the second tank to flow into the first boil-off gas passage;
A pressure adjusting valve which is provided in the second boil-off gas passage and adjusts the pressure of boil-off gas flowing to the first boil-off gas passage;
A pressure control means for controlling the pressure regulating valve,
The pressure control means measures a differential pressure value between the internal pressure of the second tank and the internal pressure of the first tank, the internal pressure of the second tank is higher than the internal pressure of the first tank, and the differential pressure value is When it is measured that it is equal to or more than the set value, the pressure adjusting valve is adjusted and controlled to the open side, and the differential pressure value is set to the set value even if the internal pressure of the second tank is higher than the internal pressure of the first tank. When it is measured that the pressure is less than the value, the pressure control valve is controlled to be closed .

  According to the above configuration, the boil-off gas generated in the second tank is decompressed to the gas compressor so as not to affect the operating tank pressure of the first tank by appropriately manipulating the pressure regulating valve or automatically controlling it. Can be supplied. Further, by appropriately operating the pressure adjusting valve, it is possible to prevent the boil-off gas of the second tank from flowing out too much, and to accumulate the pressure of the boil-off gas in the second tank.

  That is, the required number of gas compressors can be reduced by sharing the gas compressor that compresses the boil-off gas generated in the first tank and the gas compressor that compresses the boil-off gas generated in the second tank. Although the gas compressor for the first tank and the gas compressor for the second tank, which has a higher operating tank pressure than the first tank, are used in common, the second tank is set to the operating tank pressure accumulation state. As a result, the generation of boil-off gas in the second tank can be suppressed, and the time for driving the gas compressor and the amount of compressed gas for compression processing of the boil-off gas generated in the second tank can be reduced.

Therefore, even in a low-temperature liquefied gas storage facility including a first tank and a second tank having different operation tank pressures, a few gas compressors may be installed, and the driving time of the gas compressor and the amount of compressed gas are reduced. Therefore, it can be installed at low cost and can be operated at low cost.
Even if the design pressures of the tanks are different, it is possible to contribute to the suppression of boil-off gas by efficiently setting the pressure corresponding to the difference in the design pressures as the difference between the tank operating pressures, and to efficiently recover the equipment cost. Further, the amount of boil-off gas generated when the low-temperature liquefied gas is received in the tank can be significantly reduced by increasing the tank pressure, and the power cost of the gas compressor can be reduced. When the boil-off gas generation amount increases and the processing capacity of the existing gas compressor at the base is exceeded, it is necessary to increase the boil-off gas processing amount, and in some cases, it is necessary to add a gas compressor or increase the processing capacity.

In addition, according to this configuration, since the pressure adjusting valve is automatically adjusted to an operating state that appropriately corresponds to the pressure of the boil-off gas of the second tank, the boil-off gas of the second tank is discharged and the boil-off of the second tank is boiled off. Accumulation of pressure by gas can be made appropriate, and the drive time of the gas compressor and the amount of compressed gas can be adjusted appropriately.

In order to make the present invention more suitable, the following configuration is provided.
A bypass passage for introducing boil-off gas generated in the second tank into the first boil-off gas passage by bypassing the pressure control valve; and a bypass valve provided in the bypass passage. It was

  By opening the bypass valve at the time of cool down or the like, a large amount of boil-off gas in the second tank can be smoothly discharged to the gas compressor by bypassing the pressure control valve through the bypass passage. Further, the boil-off gas of the second tank can be discharged to the gas compressor through the bypass passage when the pressure regulating valve is maintained.

In order to make the present invention more suitable, the following configuration is provided.
A first pressure sensor for detecting an internal pressure of the first tank or an inlet pressure of the gas compressor;
A second pressure sensor provided in a portion of the second boil-off gas passage between the pressure regulating valve and the second tank,
The pressure control means measures a differential pressure value between the internal pressure of the second tank and the internal pressure of the first tank based on the pressure detected by the first pressure sensor and the pressure detected by the second pressure sensor. It was equipped with the configuration.

Since the fluctuation of the internal pressure of the first tank is large due to the influence of the performance of the gas compressor, when the method of controlling the internal pressure of the second tank to a predetermined value, the fluctuation of the flow rate occurs and the control range of the pressure regulating valve is changed. Highly likely to deviate.
According to this configuration, since the control is performed based on the pressure difference between the pressure in the first tank and the pressure in the second tank, fluctuations in the flow rate can be suppressed and the influence on downstream equipment such as a gas compressor can be suppressed. Can be avoided.

In order to make the present invention more suitable, the following configuration is provided.
The gas compressor is controlled based on the internal pressure of the first tank.

  According to this configuration, the boil-off gas of the first tank can be discharged to the gas compressor while maintaining the operating tank pressure of the first tank appropriately.

In order to make the present invention more suitable, the following configuration is provided.
When the internal pressure of the second tank exceeds the set high pressure, the pressure adjusting valve is adjusted and controlled to open.

  According to this configuration, when a large amount of boil-off gas is generated in the second tank and the internal pressure of the second tank exceeds the set high pressure, the boil-off gas of the second tank can be flown out to the second boil-off gas passage. The second tank can be protected so that the internal pressure of the tank does not rise excessively.

It is a block diagram which shows low temperature liquefied gas storage equipment. It is a flow chart of compression control. It is a flow chart of pressure control.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a configuration diagram showing a low temperature liquefied gas storage facility according to an embodiment of the present invention. As shown in FIG. 1, the low temperature liquefied gas storage facility includes two first tanks 1 and one second tank 2.

  A gas supply path 3 and a gas shipping path 4 are connected to the two first tanks 1. In each of the first tanks 1, liquefied natural gas (hereinafter referred to as LNG) is supplied to the first tank 1 via the gas supply passage 3 and stored therein. The LNG stored in the first tank 1 is taken out via the gas shipping path 4 and shipped to a supply destination such as a user.

  A gas supply path 5 and a gas shipping path 6 are connected to the second tank 2. LNG is supplied to and stored in the second tank 2 via the gas supply path 5. The LNG stored in the second tank 2 is taken out through the gas shipping path 6 and shipped to a supply destination such as a user.

  The operating tank pressures [T1] of the two first tanks 1 are set to the same operating tank pressure. The operating tank pressure [T2] of the second tank 2 is set to a higher operating tank pressure than the operating tank pressure [T1] of the first tank 1. The two first tanks 1 are operated such that the internal pressures of the two first tanks 1 become the operating tank pressure [T1] regardless of the generation of boil-off gas in the first tank 1, and the boil-off of the second tank 2 is performed. An operation device 7 that operates the second tank 2 is configured as shown in FIG. 1 so that the internal pressure of the second tank 2 becomes the operation tank pressure [T2] regardless of the generation of gas.

  As shown in FIG. 1, the operation device 7 includes a gas compressor 8 and compression control means 9.

  The gas compressor 8 is connected to the two first tanks 1 via the first boil-off gas passage 10. The first boil-off gas passage 10 includes a compressor-side passage portion 10b extending from the gas compressor 8 to a branch point 10a, and two tank-side passage portions 10c that extend separately from the branch point 10a into two first tanks 1. I have it. A pressure sensor 11 is provided in the compressor-side passage portion 10b of the first boil-off gas passage 10. The compressor-side passage portion 10b in which the pressure sensor 11 is located communicates with the first tank 1, so the pressure sensor 11 detects the internal pressure of the compressor-side passage portion 10b as the internal pressure of the first tank 1.

  The compression control means 9 is composed of a control device 12 using a microcomputer. The compression control means 9 is linked to the gas compressor 8 and the pressure sensor 11, and the pressure [P1] (see FIG. 2) of the first tank 1 detected by the pressure sensor 11 and the compression control shown in FIG. It operates based on the flow and.

  As shown in FIG. 2, the compression control means 9 compares the pressure [P1] of the first tank 1 detected by the pressure sensor 11 with the operating tank pressure [T1], and the detected pressure [P1] is It is determined whether the operating tank pressure [T1] is exceeded. When the compression control unit 9 determines that the detected pressure [P1] exceeds the operating tank pressure [T1], the compression control unit 9 issues a command to drive the gas compressor 8 to a drive unit (not shown) of the gas compressor 8. ) To drive the gas compressor 8. When the compression control means 9 determines that the detected pressure [P1] does not exceed the operating tank pressure [T1], it outputs a command to stop the gas compressor 8 to the drive unit of the gas compressor 8. The gas compressor 8 is stopped by.

  Even if boil-off gas is generated in the first tank 1, the gas compressor 8 is stopped while the internal pressure of the first tank 1 does not exceed the operating tank pressure [T1], so that the boil-off gas in the first tank 1 flows out. It is prevented and the first tank 1 is put into a pressure accumulation state. Generation of boil-off gas in the first tank 1 can be suppressed by accumulating pressure. When the internal pressure of the first tank 1 exceeds the operating tank pressure [T1], the gas compressor 8 is driven and the boil-off gas of the first tank 1 is taken out by the gas compressor 8 and compressed. The boil-off gas compressed by the gas compressor 8 is supplied to the user via the supply path 8a. Although the boil-off gas compressed by the gas compressor 8 is supplied to the user in the present embodiment, it is returned to the first tank 1 or supplied to equipment other than the first tank in the base. It may be configured as follows. The supply destination of the boil-off gas compressed by the gas compressor 8 is not limited to the user, and various supply destinations may be set.

  The operation device 7 includes a second boil-off gas passage 20, a pressure adjusting valve 21, and a pressure control means 22.

  The second boil-off gas passage 20 is provided across the first boil-off gas passage 10 and the second tank 2. Specifically, the second boil-off gas passage 20 is provided across the compressor-side passage portion 10 b of the first boil-off gas passage 10 and the second tank 2. The pressure adjusting valve 21 is provided in the second boil-off gas passage 20. Specifically, the pressure regulating valve 21 is provided between the portion of the second boil-off gas passage 20 that is connected to the compressor-side passage portion 10b and the portion that is connected to the second tank 2. ing. The second boil-off gas passage 20 allows the boil-off gas generated in the second tank 2 to flow into the compressor-side passage portion 10b of the first boil-off gas passage 10 when the pressure adjustment valve 21 is adjusted and controlled.

  The pressure regulating valve 21 is regulated to regulate the pressure of the boil-off gas flowing through the second boil-off gas passage 20. That is, by controlling the pressure adjusting valve 21 to open, the flow resistance applied to the boil-off gas by the pressure adjusting valve 21 becomes small, and the pressure adjusting valve 21 controls the boil-off gas in the second tank 2 to the compressor side. It facilitates the flow into the passage portion 10b. The larger the opening of the pressure adjusting valve 21, the easier the boil-off gas of the second tank 2 will flow into the compressor-side passage portion 10b. By controlling the pressure adjusting valve 21 to be closed, the flow resistance applied to the boil-off gas by the pressure adjusting valve 21 becomes large, and the pressure adjusting valve 21 moves from the second tank 2 to the compressor side passage portion 10b. Stops or suppresses the flow of boil-off gas. The smaller the opening of the pressure adjusting valve 21, the more difficult it is for the boil-off gas of the second tank 2 to flow into the compressor-side passage portion 10b.

  The first pressure sensor 23 is provided in a portion of the second boil-off gas passage 20 between the portion connected to the compressor-side passage portion 10b and the pressure regulating valve 21. A portion of the second boil-off gas passage 20 where the first pressure sensor 23 is located, that is, a portion of the second boil-off gas passage 20 downstream of the pressure adjusting valve 21 is connected via the first boil-off gas passage 10. Since the first pressure sensor 23 communicates with the first tank 1, the first pressure sensor 23 determines the pressure of the portion of the second boil-off gas passage 20 where the first pressure sensor 23 is located as the internal pressure [P1] of the first tank 1 (see FIG. 3). ). In the present embodiment, the first pressure sensor 23 that detects the pressure of the second boil-off gas passage 20 as the internal pressure of the first tank 1 is adopted, but instead of the first pressure sensor 23, the inlet of the gas compressor 8 is used. A pressure sensor that detects the pressure as the internal pressure of the first tank 1 may be adopted.

  A second pressure sensor 24 is provided in a portion of the second boil-off gas passage 20 between the portion where the pressure regulating valve 21 is provided and the second tank 2. A portion of the second boil-off gas passage 20 where the second pressure sensor 24 is located, that is, a portion of the second boil-off gas passage 20 upstream of the pressure adjusting valve 21 communicates with the second tank 2. Therefore, the second pressure sensor 24 detects the pressure of the portion of the second boil-off gas passage 20 where the second pressure sensor 24 is located as the internal pressure [P2] (see FIG. 3) of the second tank 2.

  The pressure control means 22 is constituted by the control device 12. The pressure control means 22 is linked to the pressure regulating valve 21, the first pressure sensor 23, and the second pressure sensor 24, and the detection result by the first pressure sensor 23, the detection result by the second pressure sensor 24, and The pressure control flow shown in FIG.

  As shown in FIG. 3, the pressure control means 22 includes an internal pressure [P1] of the first tank 1 detected by the first pressure sensor 23 and an internal pressure [P2] of the second tank 2 detected by the second pressure sensor 24. ] To determine whether or not the internal pressure [P2] of the second tank 2 is higher than the internal pressure [P1] of the first tank 1.

  When the pressure control unit 22 determines that the internal pressure [P2] of the second tank 2 is higher than the internal pressure [P1] of the first tank 1, the internal pressure [P2] of the second tank 2 and the first tank 1 The differential pressure value [PS] with respect to the internal pressure [P1] is measured (calculated). The pressure control means 22 compares the measured differential pressure value [PS] with a preset set value [PA], and determines whether the differential pressure value [PS] is equal to or greater than the set value [PA] or the differential pressure value. It is determined whether [PS] is less than the set value [PA]. When the pressure control means 22 determines that the differential pressure value [PS] is greater than or equal to the set value [PA], it outputs a signal for controlling the pressure adjustment valve 21 to the open side to the drive portion 21a of the pressure adjustment valve 21. By doing so, the pressure adjusting valve 21 is adjusted and controlled to the open side.

  Even if the pressure control means 22 determines that the internal pressure [P2] of the second tank 2 is higher than the internal pressure [P1] of the first tank 1, the differential pressure value [PS] is less than the set value [PA]. When it is determined that the pressure adjustment valve 21 is closed, the pressure adjustment valve 21 is adjusted and closed by outputting a signal to the drive unit 21a.

  For example, when the operating tank pressure [T1] of the first tank 1 is 4 to 8 kPa and the operating tank pressure [T2] of the second tank 2 is 9 to 13 kPa, set [5 kPa] as the set value [PA]. To do. In this way, the set value [PA] is appropriately set based on the operating tank pressure [T1] of the first tank 1 and the operating tank pressure [T2] of the second tank 2.

  In that case, even if boil-off gas is generated in the second tank 2, the differential pressure value [PS] becomes less than the set value [PA] as long as the internal pressure of the second tank 2 does not exceed the operating tank pressure [T2]. Since the pressure adjusting valve 21 is adjusted and controlled to the closing side, the outflow of the boil-off gas from the second tank 2 to the first boil-off gas passage 10 is stopped or suppressed, and the second tank 2 is in a pressure accumulation state. To be Generation of boil-off gas in the second tank 2 can be suppressed by accumulating pressure. When the internal pressure of the second tank 2 exceeds the operating tank pressure [T1], the differential pressure value [PS] becomes equal to or greater than the set value [PA] and the pressure adjustment valve 21 is adjusted to the open side. The boil-off gas in the tank 2 flows into the second boil-off gas passage 20 and then flows from the second boil-off gas passage 20 into the first boil-off gas passage 10.

  At this time, the drive of the gas compressor 8 is controlled based on the internal pressure of the first tank 1. That is, the pressure of the boil-off gas flowing out from the first tank 1 acts on the pressure sensor 11, and the compression control means 9 drives the gas compressor 8 based on the detection result of the pressure sensor 11. Further, not only the boil-off gas flowing out from the first tank 1 but also the boil-off gas flowing out from the second tank whose pressure is reduced by the pressure adjusting valve 21 is simultaneously compressed by the gas compressor 8. The boil-off gas compressed by the gas compressor 8 is supplied to the user via the supply path 8a. Although the boil-off gas compressed by the gas compressor 8 is supplied to the user in this embodiment, it is returned to the second tank 2 or supplied to equipment other than the second tank in the base. It may be configured as follows. The supply destination of the boil-off gas compressed by the gas compressor 8 is not limited to the user, and various supply destinations may be set.

  The pressure control means 22 compares the internal pressure [P2] of the second tank detected by the second pressure sensor 24 with a preset high pressure [PH], and the detected internal pressure [P2] is the preset high pressure. It is determined whether [PH] is exceeded. When the pressure control means 22 determines that the detected internal pressure [P2] exceeds the set high pressure [PH], the pressure control means 22 adjusts and controls the pressure adjustment valve 21 to the open side. As the set high pressure [PH], a design pressure (for example, 18 kPa) larger than the operating tank pressure of the second tank 2 or a pressure close to the design pressure is set.

  That is, when the internal pressure of the second tank 2 exceeds the set high pressure [PH], the pressure adjusting valve 21 is adjusted to the open side by the pressure control means 22, and the boil-off gas of the second tank 2 is adjusted to the second boil-off gas passage 20. It is possible to avoid an abnormal increase in the internal pressure of the second tank 2 by flowing out to the first boil-off gas passage 10 via the. In this case also, the gas compressor 8 is driven by the compression control means 9 that operates based on the detection result of the pressure sensor 11.

  As shown in FIG. 1, the second boil-off gas passage 20 is provided with a bypass passage 25 that bypasses the pressure regulating valve 21. A bypass valve 26 is provided in the bypass passage 25. By opening the bypass valve 26 at the time of cool-down or the like, a large amount of boil-off gas in the second tank 2 is diverted to the first boil-off gas passage 10 by bypassing the pressure regulating valve 21 by the bypass passage 25, and then to the gas compressor 8. Can be discharged smoothly. Further, during maintenance of the pressure adjusting valve 21, by opening the bypass valve 26, the boil-off gas of the second tank 2 can be discharged to the first boil-off gas passage 10 by the bypass passage 25 without passing through the pressure adjusting valve 21. It can be discharged to the compressor 8. The bypass valve 26 is closed when the pressure control valve 22 controls the pressure control valve 21.

[Another embodiment]
(1) In the above embodiment, the first pressure sensor 23 and the second pressure sensor 24 are provided in the second boil-off gas passage 20, but the first pressure sensor 23 is provided in the first tank 1. The second pressure sensor 24 may be provided in the second tank 2 for implementation.

(2) In the above-described embodiment, an example in which two first tanks 1 are provided has been shown, but the number is not limited to two, and one or three or more first tanks 1 may be provided.

  Note that the configurations disclosed in the above-described embodiments (including other embodiments, the same applies below) can be applied in combination with the configurations disclosed in other embodiments, as long as no contradiction occurs. The embodiment disclosed in the present specification is an example, and the embodiment of the present invention is not limited to this, and can be appropriately modified within a range not departing from the object of the present invention.

  INDUSTRIAL APPLICABILITY The present invention is not limited to liquefied natural gas, and can be used for low-temperature liquefied gas storage equipment for storing various low-temperature liquefied gases such as liquefied petroleum gas.

1 1st tank 2 2nd tank 8 Gas compressor 10 1st boil-off gas passage 20 2nd boil-off gas passage 21 Pressure regulating valve 23 1st pressure sensor 24 2nd pressure sensor 25 Bypass passage 26 Bypass valve P1 Internal pressure of 1st tank P2 Internal pressure of the second tank PH High pressure PS Differential pressure value T1 Operating tank pressure of the first tank T2 Operating tank pressure of the second tank

Claims (5)

A first tank for storing low temperature liquefied gas;
A second tank which is operated at an operation tank pressure higher than the operation tank pressure of the first tank and stores low temperature liquefied gas;
A gas compressor connected to the first tank via a first boil-off gas passage, for extracting boil-off gas from the first tank and performing compression processing;
A second boil-off gas passage that is provided between the first boil-off gas passage and the second tank and that allows boil-off gas generated in the second tank to flow into the first boil-off gas passage;
A pressure adjusting valve which is provided in the second boil-off gas passage and adjusts the pressure of boil-off gas flowing to the first boil-off gas passage;
A pressure control means for controlling the pressure regulating valve,
The pressure control means measures a differential pressure value between the internal pressure of the second tank and the internal pressure of the first tank, the internal pressure of the second tank is higher than the internal pressure of the first tank, and the differential pressure value is When it is measured that it is equal to or more than the set value, the pressure adjustment valve is adjusted and controlled to the open side, and the differential pressure value is set to the set value even if the internal pressure of the second tank is higher than the internal pressure of the first tank. A low-temperature liquefied gas storage facility that controls the pressure adjustment valve to be closed when it is measured to be less than a value . A bypass passage for introducing boil-off gas generated in the second tank into the first boil-off gas passage by bypassing the pressure control valve;
The low-temperature liquefied gas storage facility according to claim 1, further comprising a bypass valve provided in the bypass passage. A first pressure sensor for detecting an internal pressure of the first tank or an inlet pressure of the gas compressor;
A second pressure sensor provided in a portion of the second boil-off gas passage between the pressure regulating valve and the second tank,
The pressure control means measures a differential pressure value between the internal pressure of the second tank and the internal pressure of the first tank based on the pressure detected by the first pressure sensor and the pressure detected by the second pressure sensor. The low-temperature liquefied gas storage facility according to claim 1. The low temperature liquefied gas storage facility according to any one of claims 1 to 3, wherein the gas compressor is controlled based on an internal pressure of the first tank. The low temperature liquefied gas storage facility according to any one of claims 1 to 4, wherein when the internal pressure of the second tank exceeds a set high pressure, the pressure adjustment valve is adjusted and controlled to open.

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