EP4790307A1

EP4790307A1 - Low-temperature fluid transfer system

Info

Publication number: EP4790307A1
Application number: EP24885433.3A
Authority: EP
Inventors: Taizou KOBAYASHI; Yoshia KOSHI; Kazuki KITADA; Ryo ISHIGURO
Original assignee: Kawasaki Heavy Industries Ltd; Kawasaki Jukogyo KK
Current assignee: Kawasaki Heavy Industries Ltd; Kawasaki Motors Ltd
Priority date: 2023-10-31
Filing date: 2024-10-15
Publication date: 2026-08-12
Also published as: JP2025075552A; KR20260100355A; WO2025094659A1; TW202519758A; AU2024369659A1

Abstract

A low-temperature fluid transfer system (1) includes: a compressor (11) that pressure-feeds a low-temperature boil-off gas (BOG) resulting from vaporization of a liquefied gas to a transfer destination; a first line (2) linking a supply source of the boil-off gas and the compressor (11); a second line (3) linking the compressor (11) and the transfer destination; a heat exchanger (12) provided in the second line (3); a bypass line (4) that branches from a branch part (J1) on the first line (2) and reaches the heat exchanger (12); and a return line (5) linking a position downstream of the branch part (J1) in the first line (2) and the heat exchanger (12).

Description

Technical Field

The present disclosure relates to a system for transferring a low-temperature fluid to a predetermined transfer destination.

Background Art

As an example of a low-temperature fluid transfer system, one disclosed in Patent Literature 1 is known. Specifically, Patent Literature 1 discloses a system that transfers boil-off gas generated in an LNG carrier to a propulsion engine as fuel. The transfer system includes a compressor that sucks out a boil-off gas from an LNG tank, a high-temperature and high-pressure pipe through which a boil-off gas temperature-raised by compression by the compressor flows, a heat exchanger connected to the high-temperature and high-pressure pipe, and a low-temperature and high-pressure pipe for leading a boil-off gas cooled by the heat exchanger to the propulsion engine.
According to the transfer system of Patent Literature 1, since the heat exchanger is provided between the compressor and the engine, a boil-off gas pressure-fed from the compressor can be supplied to the engine after being cooled to a temperature suitable for the engine by the heat exchanger. However, in Patent Literature 1, in order to cool the boil-off gas, it is necessary to supply a heat medium from the outside of the system to the heat exchanger. In this case, depending on a temperature zone or a flow rate of the boil-off gas, an amount of the heat medium to be prepared increases, and there is room for improvement in terms of effective use of resources.

Citation List

Patent Literature

Patent Literature 1: JP 2017-194038 A

Summary of Invention

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a low-temperature fluid transfer system capable of regulating a temperature of a low-temperature fluid supplied to a transfer destination while reducing an amount of use of a heat medium supplied from the outside.
In order to solve the above problem, a low-temperature fluid transfer system according to an aspect of the present disclosure includes: a compressor that pressure-feeds a low-temperature boil-off gas resulting from vaporization of a liquefied gas to a transfer destination; a first line linking a supply source of the boil-off gas and the compressor; a second line linking the compressor and the transfer destination; a heat exchanger provided in the second line; a bypass line that branches from a branch part on the first line and reaches the heat exchanger; and a return line linking a position downstream of the branch part in the first line and the heat exchanger.
According to the low-temperature fluid transfer system of the present disclosure, it is possible to regulate a temperature of a low-temperature fluid supplied to a transfer destination while reducing an amount of use of a heat medium supplied from the outside.

Brief Description of Drawings

FIG. 1 is a side diagram schematically illustrating a configuration of a low-temperature fluid transfer system according to an embodiment of the present disclosure.
FIG. 2 is a diagram illustrating a relationship between a temperature and a pressure of each part of the transfer system.
FIG. 3 is a functional block diagram illustrating a control system of the transfer system.
FIG. 4 is a schematic diagram for explaining a mechanism for controlling an opening of each valve provided in the transfer system.

Description of Embodiment

Hereinafter, an embodiment of a low-temperature fluid transfer system of the present disclosure will be described in detail with reference to the drawings. The transfer system of the present disclosure is a system including a pipe through which a low-temperature fluid flows. The low-temperature fluid is a low-temperature boil-off gas resulting from vaporization of a liquefied gas. The liquefied gas is, for example, liquefied hydrogen, liquid helium, LNG, or the like.

[Configuration of Transfer System]

FIG. 1 is a side diagram schematically illustrating a configuration of a low-temperature fluid transfer system 1 according to an embodiment of the present disclosure. The transfer system 1 of the present embodiment is a system applied to a liquefied hydrogen facility for handling liquefied hydrogen, and is configured to transfer a low-temperature boil-off gas (BOG) resulting from vaporization of the liquefied hydrogen. Although the liquefied hydrogen facility may be of any type as long as it is a facility that handles liquefied hydrogen, in the present embodiment, a facility that generates and stores liquefied hydrogen is exemplified as a liquefied hydrogen facility. Therefore, the liquefied hydrogen facility includes a liquefier 100 that liquefies a hydrogen gas as a raw material. Although the liquefier 100 may be of any type as long as it can liquefy a hydrogen gas by cooling the hydrogen gas, it may, for example, include a cooler that cools the hydrogen gas to a state immediately before liquefaction by heat exchange using a refrigeration cycle, and a Joule-Thomson valve that subjects the hydrogen gas cooled by the cooler to Joule-Thomson expansion (isenthalpic expansion) to liquefy the hydrogen gas.
The liquefied hydrogen generated by the liquefier 100 is stored in a storage tank not shown. The liquefied hydrogen stored in the storage tank is evaporated (vaporized) little by little upon receiving heat input from the outside. A hydrogen gas resulting from the evaporation, i.e., a boil-off gas (BOG) is refluxed to the liquefier 100 through the transfer system 1. In other words, the transfer system 1 of the present embodiment constitutes a part of a reflux system of a boil-off gas for returning the boil-off gas to the liquefier 100 and liquefying the boil-off gas again. The boil-off gas refluxed by the transfer system 1 is mixed with a raw material hydrogen gas in a raw material tank 17 and then supplied to the liquefier 100.
The transfer system 1 includes an upstream line 2, a downstream line 3, a bypass line 4, a return line 5, a reflux line 6, a compressor 11, a heat exchanger 12, and a small compressor 13. The upstream line 2 corresponds to a "first line" in the present disclosure, and the downstream line 3 corresponds to a "second line" in the present disclosure.
The upstream line 2 is a piping line linking a supply source of a boil-off gas (BOG) and the compressor 11. The boil-off gas is supplied from, for example, a gas phase part of the storage tank described above. In this case, the gas phase part of the storage tank functions as the supply source of the boil-off gas.
A tank 15 is provided in the upstream line 2. The tank 15 is a container whose volume is increased so as to have a cross-sectional area larger than that of the upstream line 2, and is provided to merge the boil-off gas from the return line 5 into the upstream line 2 to promote gas mixing.
The downstream line 3 is a piping line that links the compressor 11 and the liquefier 100. The heat exchanger 12 and the raw material tank 17 are arranged in this order from the upstream side (left side in FIG. 1) on the downstream line 3.
The bypass line 4 is a piping line branching from the upstream line 2 and reaching the heat exchanger 12. Specifically, the bypass line 4 is disposed to branch from a first branch part J1 on the upstream side (left side in FIG. 1) of the tank 15 in the upstream line 2, extend in parallel with the upstream line 2, and bypass the tank 15 and the compressor 11 to reach the heat exchanger 12. The first branch part J1 corresponds to a "branch part" in the present disclosure.
The return line 5 is a piping line that links the heat exchanger 12 and the tank 15. The small compressor 13 is provided in the return line 5. The return line 5 is provided with an inner reflux line 7 that connects two portions of the return line 5 across the small compressor 13.
The reflux line 6 is a piping line that links the downstream line 3 and the upstream line 2 outside the bypass line 4. Specifically, the reflux line 6 connects a second branch part J2 between the heat exchanger 12 and the raw material tank 17 in the downstream line 3 and a third branch part J3 on the upstream side of the branch part (first branch part J1) from the upstream line 2 to the bypass line 4 to each other.
The compressor 11 is a device that pressure-feeds a boil-off gas, and is arranged between the upstream line 2 and the downstream line 3. The compressor 11 sucks a boil-off gas from the upstream line 2, pressurizes the boil-off gas, and discharges the boil-off gas to the downstream line 3.
The heat exchanger 12 is a device that cools a boil-off gas flowing through the downstream line 3 by heat exchange with a boil-off gas extracted from the upstream line 2 via the bypass line 4. In other words, the heat exchanger 12 cools the boil-off gas flowing through the downstream line 3, i.e., the boil-off gas compressed and temperature-raised by the compressor 11 by heat exchange using the low-temperature boil-off gas extracted from the upstream line 2 as a heat medium.
The small compressor 13 is a compressor having a compression ratio smaller than that of the compressor 11 described above. The small compressor 13 sucks a boil-off gas from the heat exchanger 12, pressurizes the boil-off gas, and discharges the boil-off gas to the tank 15. In detail, via an upstream portion of the return line 5, the small compressor 13 sucks the boil-off gas introduced as the heat medium into the heat exchanger 12 via the bypass line 4 and pressure-feeds the sucked boil-off gas to the tank 15 via a downstream portion of the return line 5. Here, the upstream portion and the downstream portion of the return line 5 are used in a case where a side close to the heat exchanger 12 is defined as an upstream side and a side close to the tank 15 is defined as a downstream side.
FIG. 2 is a diagram illustrating a relationship between temperature and pressure of each part of the transfer system 1. As illustrated in the drawing, temperatures and pressures of the boil-off gas flowing through the respective parts of the transfer system 1 are defined as first to sixth temperatures T1 to T6 and first to sixth pressures P1 to P6, respectively. The first temperature T1 and the first pressure P1 are a temperature and a pressure of a boil-off gas flowing upstream of the tank 15 in the upstream line 2. The second temperature T2 and the second pressure P2 are a temperature and a pressure of a boil-off gas flowing from the tank 15 toward the compressor 11, in other words, an inlet temperature and an inlet pressure of the compressor 11. The third temperature T3 and the third pressure P3 are a temperature and a pressure of a boil-off gas flowing from the compressor 11 toward the heat exchanger 12, in other words, an inlet temperature and an inlet pressure of the heat exchanger 12. The fourth temperature T4 and the fourth pressure P4 are a temperature and a pressure of a boil-off gas flowing from the heat exchanger 12 toward the raw material tank 17, in other words, an outlet temperature and an outlet pressure of the heat exchanger 12. The fifth temperature T5 and the fifth pressure P5 are a temperature and a pressure of a boil-off gas flowing through the upstream portion of the return line 5, i.e., a temperature and a pressure of a boil-off gas flowing from the heat exchanger 12 toward the small compressor 13 after being used as the heat medium in the heat exchanger 12. The sixth temperature T6 and the sixth pressure P6 are a temperature and a pressure of a boil-off gas flowing from the small compressor 13 toward the tank 15, i.e., a boil-off gas returned to the tank 15 through the return line 5.
From temperature increase and pressure increase actions in the compressor 11 and the small compressor 13, a heat balance in the heat exchanger 12, and the like, the above temperatures and pressures respectively satisfy the relationships as shown in Expression (1) in FIG. 2. In other words, the second temperature T2 is higher than the first temperature T1 and lower than the sixth temperature T6. The third temperature T3 is higher than both the second temperature T2 and the fourth temperature T4. The fifth temperature T5 is higher than the first temperature T1 and lower than the sixth temperature T6.
In addition, the third pressure P3 is higher than the second pressure P2. The sixth pressure P6 is higher than the fifth pressure P5 and equivalent to the first pressure P1.
In the present embodiment, since the compression ratio of the compressor 11 is larger than that of the small compressor 13, a temperature difference and a pressure difference before and after the compressor 11 are larger than a temperature difference and a pressure difference before and after the small compressor 13. In other words, a difference between the third temperature T3 and the second temperature T2 is larger than a difference between the sixth temperature T6 and the fifth temperature T5, and a difference between the third pressure P3 and the second pressure P2 is larger than a difference between the sixth pressure P6 and the fifth pressure P5.
As illustrated in FIG. 1, the bypass line 4 is provided with a flow control valve 21. The flow control valve 21 is a valve that regulates a flow rate of a boil-off gas flowing through the bypass line 4. As an opening of the flow control valve 21 increases, a proportion of a boil-off gas introduced as the heat medium into the heat exchanger 12 through the bypass line 4 increases. When the flow rate of the bypass line 4, i.e., a flow rate of the heat medium increases, an amount of heat exchange between a boil-off gas flowing through the downstream line 3 and the heat medium increases, so that the temperature of the boil-off gas flowing from the heat exchanger 12 toward the raw material tank 17 easily decreases.
The inner reflux line 7 is provided with a first spillback valve 22. The first spillback valve 22 is a valve that regulates the pressure of the boil-off gas returned to the tank 15 through the return line 5, i.e., a return pressure to the tank 15. For example, as an opening of the first spillback valve 22 increases, a proportion of a boil-off gas refluxed from the downstream side to the upstream side of the small compressor 13 through the inner reflux line 7 increases, so that the return pressure to the tank 15 decreases.
The reflux line 6 is provided with a second spillback valve 23. The second spillback valve 23 is a valve that controls an inlet pressure of the liquefier 100 by regulating a proportion of a boil-off gas that is refluxed from the downstream side to the upstream side of the compressor 11 through the reflux line 6. For example, as an opening of the second spillback valve 23 increases, the proportion of the boil-off gas that is refluxed from the downstream side to the upstream side of the compressor 11 through the reflux line 6 increases, so that a pressure of a boil-off gas introduced from the downstream line 3 into the raw material tank 17 decreases. This can reduce the inlet pressure of the liquefier 100.
Although the flow control valve 21, the first spillback valve 22, and the second spillback valve 23 may be manual valves, in the present embodiment, each of the valves 21 to 23 is an automatic valve. In other words, the openings of the flow control valve 21, the first spillback valve 22, and the second spillback valve 23 are automatically controlled by a controller 30 to be described later.
The transfer system 1 is provided with a plurality of sensors that detect a state quantity of a boil-off gas flowing through each line. Specifically, in the present embodiment, the plurality of sensors include a first flow rate sensor SN1 provided in the upstream line 2, a second flow rate sensor SN2 provided in the bypass line 4, a temperature sensor SN3 and a first pressure sensor SN4 that are provided in the downstream line 3, and a second pressure sensor SN5 provided in the return line 5.
The first flow rate sensor SN1 detects a flow rate of the upstream line 2, in detail, a flow rate of a boil-off gas flowing through a portion of the upstream line 2 between the first branch part J1 and the tank 15. The second flow rate sensor SN2 detects the flow rate of the boil-off gas flowing through the bypass line 4. The temperature sensor SN3 and the first pressure sensor SN4 detect a temperature and a pressure of a boil-off gas flowing through a portion of the downstream line 3 between the heat exchanger 12 and the raw material tank 17. The second pressure sensor SN5 detects a pressure of a boil-off gas flowing through a portion of the return line 5 downstream of the small compressor 13. The temperature detected by the temperature sensor SN3 corresponds to the fourth temperature T4 illustrated in FIG. 2, the pressure detected by the first pressure sensor SN4 corresponds to the fourth pressure P4 illustrated in FIG. 2, and the pressure detected by the second pressure sensor SN5 corresponds to the sixth pressure P6 illustrated in FIG. 2.

[Valve Control]

FIG. 3 is a functional block diagram illustrating a control system of the transfer system 1. The controller 30 illustrated in this drawing is a control device having, as a main part, a microcomputer including a processor (CPU) that performs calculation, memories such as a ROM and a RAM, and various input/output buses. The controller 30 receives information detected by the above sensors SN1 to SN5, and controls the openings of the flow control valve 21, the first spillback valve 22, and the second spillback valve 23 on the basis of the received information.
FIG. 4 is a schematic diagram for explaining a mechanism for controlling the opening of each valve. As illustrated in this drawing, the opening of the flow control valve 21 is controlled on the basis of each input information from the first flow rate sensor SN1, the second flow rate sensor SN2, and the temperature sensor SN3. Specifically, the controller 30 controls the opening of the flow control valve 21 on the basis of the input information from each of the sensors SN1 to SN3 so that a temperature of a hydrogen gas introduced into the liquefier 100, in other words, an inlet temperature of the liquefier 100 falls within a predetermined target temperature range.
For example, as the opening of the flow control valve 21 increases, a flow rate proportion of the boil-off gas flowing through the bypass line 4 bypassing the compressor 11, in other words, the boil-off gas introduced into the heat exchanger 12 as a cooling heat medium increases, and a flow rate proportion of the boil-off gas whose temperature rises with the compression in the compressor 11 decreases. Therefore, as the opening of the flow control valve 21 increases, the temperature of the boil-off gas introduced from the heat exchanger 12 into the raw material tank 17 decreases, and the inlet temperature of the liquefier 100 decreases. Meanwhile, due to properties of the liquefier 100, it is necessary to keep the inlet temperature of the liquefier 100 within the predetermined target temperature range in order to appropriately perform liquefaction treatment of the hydrogen gas including the boil-off gas in the liquefier 100. Therefore, the controller 30 regulates the temperature of the boil-off gas introduced into the raw material tank 17 through opening control of the flow control valve 21 so that the inlet temperature of the liquefier 100 falls within the target temperature range.
Specifically, a ratio of the flow rate of the bypass line 4 detected by the second flow rate sensor SN2 to the flow rate of the upstream line 2 detected by the first flow rate sensor SN1 is defined as a bypass flow rate ratio. The controller 30 stores in advance, as a target flow rate ratio, a value of the bypass flow rate ratio such that the inlet temperature of the liquefier 100 falls within the target temperature range under assumed typical operating conditions. Then, the controller 30 controls the opening of the flow control valve 21 so that the bypass flow rate ratio becomes the target flow rate ratio on the basis of each of the detected flow rates by the first and second flow rate sensors SN1 and SN2. However, even when the bypass flow rate ratio is regulated to be the target flow rate ratio, an expected temperature may not be obtained depending on conditions. Therefore, the controller 30 checks a temperature detected by the temperature sensor SN3, and when the checked temperature deviates from the assumed temperature, corrects the opening of the flow control valve 21 toward a direction in which the deviation is settled.
The opening of the first spillback valve 22 is controlled on the basis of the input information from the second pressure sensor SN5. Specifically, the controller 30 controls the opening of the first spillback valve 22 so that the pressure detected by the second pressure sensor SN5, i.e., the pressure of the boil-off gas returned to the tank 15 through the return line 5 becomes a predetermined target pressure. For example, when the detected pressure exceeds the target pressure, the opening of the first spillback valve 22 is increased to decrease the pressure. The target pressure in this case is set to a value equivalent to a pressure in the upstream line 2 so that the boil-off gas can be introduced from the return line 5 to the tank 15 without any trouble.
The opening of the second spillback valve 23 is controlled on the basis of the input information from the first pressure sensor SN4. Specifically, the controller 30 controls the opening of the second spillback valve 23 so that the pressure detected by the first pressure sensor SN4, i.e., the pressure of the boil-off gas introduced to the raw material tank 17 becomes a predetermined target pressure. For example, when the detected pressure exceeds the target pressure, the opening of the second spillback valve 23 is increased to decrease the pressure. The target pressure in this case is set to a value equivalent to a pressure of the raw material hydrogen gas introduced into the raw material tank 17.
The opening control of each valve described above is basically performed in a steady state in which temperature and pressure conditions are stable. In an unsteady state such as at the time of activation of the transfer system 1, the opening of each valve may be controlled according to a predetermined program, or switching to manual operation may be performed.

[Operation and Effects]

As described in the foregoing, the boil-off gas transfer system 1 according to the present embodiment includes the upstream line 2 and the downstream line 3, the compressor 11 provided between the lines 2 and 3, the heat exchanger 12 provided on the downstream line 3, the bypass line 4 branching from the first branch part J1 on the upstream line 2 and reaching the heat exchanger 12, and the return line 5 linking the position (tank 15) downstream of the first branch part J1 on the upstream line 2 and the heat exchanger 12. According to such a configuration, there is an advantage that the inlet temperature of the liquefier 100 can be appropriately regulated while reducing an amount of use of a heat medium supplied from the outside.
In other words, in the present embodiment, since a low-temperature boil-off gas before being compressed by the compressor 11 is extracted through the bypass line 4, and the extracted low-temperature boil-off gas is introduced into the heat exchanger 12 as a heat medium, it is possible to cool, by using the heat exchanger 12, the boil-off gas flowing through the downstream line 3, i.e., the boil-off gas temperature-raised by the compression by the compressor 11 (T4<T3). Such cooling by the heat exchanger 12 leads to suppression of the temperature of the boil-off gas introduced into the raw material tank 17 through the downstream line 3. As a result, the temperature of the hydrogen gas introduced into the liquefier 100, i.e., the inlet temperature of the liquefier 100 can be kept within a relatively low temperature range suitable for the liquefaction treatment.
The boil-off gas used as the heat medium, i.e., the boil-off gas introduced into the heat exchanger 12 from the bypass line 4 is returned to the position (tank 15) downstream of the first branch part J1 in the upstream line 2 through the return line 5. As a result, the temperature of the boil-off gas introduced into the compressor 11 can be increased, and temperature performance required for the compressor 11 can be relaxed. In other words, the boil-off gas introduced from the bypass line 4 into the heat exchanger 12 is temperature-raised by heat exchange with the boil-off gas flowing through the downstream line 3 after being compressed by the compressor 11. Then, the temperature-raised boil-off gas is returned to the upstream line 2 through the return line 5, whereby the temperature of the boil-off gas introduced into the compressor 11 can be increased (T1<T2), resulting in preventing an extremely low temperature boil-off gas close to a temperature zone of the liquefied hydrogen from being introduced into the compressor 11. As a result, a general-purpose compressor for use in, for example, LNG facilities or the like can be used as the compressor 11, and it becomes unnecessary to prepare a special compressor having excellent temperature performance (low temperature resistance).
Moreover, in the present embodiment, since the low-temperature boil-off gas separated from the upstream line 2 is used as the heat medium for cooling the downstream line 3, it is not necessary to separately supply the heat medium from the outside, and resources can be effectively utilized. Although the heat medium may be separately supplied from the outside depending on a cooling capacity and the like required for the heat exchanger 12, even in that case, according to the present embodiment in which the boil-off gas separated from the upstream line 2 is used as the heat medium, the amount of use of the heat medium supplied from the outside can be reduced, so that resource consumption in the transfer system 1 can be suppressed.
In the present embodiment, since the flow control valve 21 is provided in the bypass line 4, the flow rate of the boil-off gas introduced as the heat medium from the bypass line 4 to the heat exchanger 12 can be regulated using the flow control valve 21. As a result, an amount of heat exchange in the heat exchanger 12 can be regulated, and a temperature of the boil-off gas flowing from the heat exchanger 12 toward the liquefier 100 can be regulated to a temperature suitable for the liquefaction treatment in the liquefier 100.
More specifically, in the present embodiment, the flow rates of the upstream line 2 and the bypass line 4 are detected by the first and second flow rate sensors SN1 and SN2, respectively, and the opening of the flow control valve 21 is controlled on the basis of each of the detected flow rates. In this way, in a case where the opening of the flow control valve 21 is controlled on the basis of the detected flow rates of the lines 2 and 4, the opening of the flow control valve 21 can be automatically regulated so that the bypass flow rate ratio, which is the ratio of the flow rate of the bypass line 4 to the flow rate of the upstream line 2, becomes an appropriate value, and the amount of heat exchange in the heat exchanger 12 can be regulated through the opening regulation. As a result, the temperature of the hydrogen gas containing the boil-off gas flowing from the heat exchanger 12 toward the liquefier 100, i.e., the inlet temperature of the liquefier 100 can be kept within an appropriate temperature range.
In the present embodiment, since the small compressor 13 having the compression ratio smaller than that of the compressor 11 is provided in the return line 5, the pressure of the boil-off gas returned to the upstream line 2 through the return line 5 can be increased. For example, the pressure of the boil-off gas can be increased to the extent that a pressure loss resulting from passing through the bypass line 4 and the heat exchanger 12 is recovered. As a result, the boil-off gas can be returned to the upstream line 2 through the return line 5 without any trouble. In addition, since the boil-off gas temperature-raised by the compression in the small compressor 13 is returned to the upstream line 2, the temperature of the boil-off gas introduced into the compressor 11 can be sufficiently increased, so that the temperature performance (low temperature resistance) required for the compressor 11 can be relaxed.
In the present embodiment, since the tank 15 is provided at a merging part of the upstream line 2 and the return line 5, a low-temperature boil-off gas introduced from the upstream line 2 into the tank 15 and a relatively high-temperature boil-off gas introduced from the return line 5 into the tank 15 can be uniformly mixed in the tank 15, and the boil-off gas uniformly temperature-raised by the mixing can be introduced into the compressor 11.

[Modification]

Although the preferred embodiment of the present disclosure has been described in the foregoing, the present disclosure is not limited to the above embodiment, and various modifications can be made without departing from the gist of the present disclosure.
For example, although in the above embodiment, the description has been made of the example in which the present disclosure is applied to the transfer system 1 that supplies a boil-off gas to the liquefier 100, the transfer destination of the transfer system 1 is not limited to the liquefier 100. For example, the transfer system of the present disclosure may be a system that transfers a boil-off gas to a generator including a gas turbine or the like that burns hydrogen gas to generate power.
In the above embodiment, the description has been made of the example in which the present disclosure is applied to the transfer system 1 that transfers a low-temperature boil-off gas (hydrogen gas) resulting from vaporization of liquefied hydrogen. However, the present disclosure is widely applicable to a system that transfers a low-temperature gas, and the present disclosure is also applicable to a system that transfers a low-temperature boil-off gas resulting from vaporization of a liquefied gas other than liquefied hydrogen.

[Conclusion]

The above embodiment and modifications thereof include the following disclosure.
A low-temperature fluid transfer system according to a first aspect of the present disclosure includes: a compressor that pressure-feeds a low-temperature boil-off gas resulting from vaporization of a liquefied gas to a transfer destination; a first line linking a supply source of the boil-off gas and the compressor; a second line linking the compressor and the transfer destination; a heat exchanger provided in the second line; a bypass line that branches from a branch part on the first line and reaches the heat exchanger; and a return line linking a position downstream of the branch part in the first line and the heat exchanger.
According to the first aspect, since a low-temperature boil-off gas before being compressed by the compressor is extracted through the bypass line, and the extracted low-temperature boil-off gas is introduced as a heat medium into the heat exchanger, it is possible to cool, by using the heat exchanger, a boil-off gas flowing through the second line, i.e., a boil-off gas temperature-raised by compression by the compressor. Therefore, even when a temperature condition of the boil-off gas required by the transfer destination is low, a boil-off gas having an appropriate temperature matching this temperature condition can be supplied to the transfer destination.
In addition, since the boil-off gas used as the heat medium, i.e., the boil-off gas introduced into the heat exchanger from the bypass line is returned to the position downstream of the branch part in the first line through the return line, the temperature of the boil-off gas introduced into the compressor can be increased, so that the temperature performance (low temperature resistance) required for the compressor can be relaxed.
Moreover, in the first aspect, since the low-temperature boil-off gas separated from the first line is used as the heat medium for cooling the second line, an amount of use of the heat medium supplied from the outside can be reduced, so that resources can be effectively utilized.
A transfer system according to a second aspect further includes, in the first aspect, a flow control valve that regulates a flow rate of a boil-off gas flowing through the bypass line.
According to the second aspect, the flow rate of the boil-off gas introduced as the heat medium from the bypass line to the heat exchanger can be regulated using the flow control valve. As a result, an amount of heat exchange in the heat exchanger can be regulated, so that a temperature of a boil-off gas directed from the heat exchanger to the transfer destination can be regulated to an appropriate temperature.
A transfer system according to a third aspect further includes, in the second aspect, a first flow rate sensor that detects a flow rate of the first line; a second flow rate sensor that detects a flow rate of the bypass line; and a controller that controls an opening of the flow control valve on the basis of the flow rates detected by the first flow rate sensor and the second flow rate sensor.
In the third aspect, since the opening of the flow control valve is controlled on the basis of the detected flow rates of the first line and the bypass line, the opening of the flow control valve can be automatically regulated so that the bypass flow rate ratio, which is the ratio of the flow rate of the bypass line to the flow rate of the first line, becomes an appropriate value, and the amount of heat exchange in the heat exchanger can be regulated through the opening regulation. As a result, the temperature of the boil-off gas directed from the heat exchanger to the transfer destination can be regulated to an appropriate temperature.
In a transfer system according to a fourth aspect, a small compressor having a compression ratio smaller than a compression ratio of the compressor is provided in the return line in the first to third aspects.
According to the fourth aspect, a pressure of a boil-off gas returned to the first line through the return line can be increased by the small compressor, and the boil-off gas can be returned to the first line through the return line without any trouble. In addition, since the boil-off gas temperature-raised by the compression in the small compressor is returned to the first line, the temperature of the boil-off gas introduced into the compressor can be sufficiently increased, so that the temperature performance required for the compressor can be relaxed.
In a transfer system according to a fifth aspect, a tank is provided at the position downstream of the branch part in the first line, and a downstream end of the return line is connected to the tank in the first to fourth aspects.
According to the fifth aspect, the low-temperature boil-off gas introduced into the tank from the first line and the relatively high temperature boil-off gas introduced into the tank from the return line can be uniformly mixed in the tank, so that the boil-off gas uniformly temperature-raised by the mixing can be introduced into the compressor.
In a transfer system according to a sixth aspect, the transfer destination is a liquefier that re-liquefies the boil-off gas in the first to fifth aspects.
According to the sixth aspect, a temperature of a boil-off gas introduced into the liquefier as the transfer destination, i.e., an inlet temperature of the liquefier can be kept within a relatively low temperature range suitable for the liquefaction treatment, and generation of a liquefied gas can be promoted.

Description for reference signs

1: transfer system
2: upstream line (first line)
3: downstream line (second line)
4: bypass line
5: return line
11: compressor
12: heat exchanger
13: small compressor
15: tank
21: flow control valve
30: controller
100: liquefier
SN1: first flow rate sensor
SN2: second flow rate sensor

Claims

A low-temperature fluid transfer system comprising:
a compressor that pressure-feeds a low-temperature boil-off gas resulting from vaporization of a liquefied gas to a transfer destination;

a first line linking a supply source of the boil-off gas and the compressor;

a second line linking the compressor and the transfer destination;

a heat exchanger provided in the second line;

a bypass line that branches from a branch part on the first line and reaches the heat exchanger; and

a return line linking a position downstream of the branch part in the first line and the heat exchanger.
The low-temperature fluid transfer system according to claim 1, further comprising a flow control valve that regulates a flow rate of a boil-off gas flowing through the bypass line.
The low-temperature fluid transfer system according to claim 2, further comprising:
a first flow rate sensor that detects a flow rate of the first line;

a second flow rate sensor that detects a flow rate of the bypass line; and

a controller that controls an opening of the flow control valve on the basis of the flow rates detected by the first flow rate sensor and the second flow rate sensor.
The low-temperature fluid transfer system according to claim 1, wherein a small compressor having a compression ratio smaller than a compression ratio of the compressor is provided in the return line.
The low-temperature fluid transfer system according to claim 1, wherein a tank is provided at the position downstream of the branch part in the first line, and a downstream end of the return line is connected to the tank.
The low-temperature fluid transfer system according to any one of claims 1 to 5, wherein the transfer destination is a liquefier that re-liquefies the boil-off gas.