Low-temperature fluid transfer system

Abstract

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

Description

Cryogenic fluid transfer systems

[0001] SUMMARY The present disclosure relates to a system for transporting a cryogenic fluid to a destination.

[0002] One example of a cryogenic fluid transfer system is disclosed in Patent Document 1. Specifically, Patent Document 1 discloses a system for transferring boil-off gas generated in an LNG ship to a propulsion engine as fuel. This transfer system includes a compressor for drawing boil-off gas from an LNG tank, a high-temperature, high-pressure pipe through which the boil-off gas, whose temperature has been increased by compression in the compressor, flows, a heat exchanger connected to the high-temperature, high-pressure pipe, and a low-temperature, high-pressure pipe for directing the boil-off gas cooled by the heat exchanger to the propulsion engine.

[0003] According to the transfer system of Patent Document 1, a heat exchanger is provided between the compressor and the engine, so that the boil-off gas pumped from the compressor can be cooled to a temperature suitable for the engine by the heat exchanger before being supplied to the engine. However, in Patent Document 1, a heat medium needs to be supplied to the heat exchanger from outside the system to cool the boil-off gas. In this case, depending on the temperature range and flow rate of the boil-off gas, a large amount of heat medium needs to be prepared, leaving room for improvement in terms of effective use of resources.

[0004] JP 2017-194038 A

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide a cryogenic fluid transfer system that is capable of adjusting the temperature of the cryogenic fluid supplied to the destination while reducing the amount of heat medium used that is supplied from the outside.

[0006] In order to solve the above problem, one aspect of the present disclosure provides a low-temperature fluid transfer system that includes a compressor that compresses low-temperature boil-off gas produced by vaporizing liquefied gas to a destination, a first line that connects a source of the boil-off gas to the compressor, a second line that connects the compressor to the destination, a heat exchanger provided in the second line, a bypass line that branches off from a branch on the first line and leads to the heat exchanger, and a return line that connects the heat exchanger to a position downstream of the branch on the first line.

[0007] According to the cryogenic fluid transfer system of the present disclosure, it is possible to adjust the temperature of the cryogenic fluid supplied to the transfer destination while reducing the amount of heat medium used that is supplied from the outside.

[0008] It is a side view showing the schematic configuration of a cryogenic fluid transfer system according to an embodiment of the present disclosure. It is a diagram showing the relationship between the temperature and pressure of each part of the transfer system. It is a functional block diagram showing the control system of the transfer system. It is a schematic diagram for explaining a mechanism for controlling the opening degree of each valve provided in the transfer system.

[0009] Hereinafter, an embodiment of a cryogenic fluid transfer system according to the present disclosure will be described in detail with reference to the drawings. The transfer system according to the present disclosure is a system including a pipe through which a cryogenic fluid flows. The cryogenic fluid is a low-temperature boil-off gas produced by vaporizing a liquefied gas. The liquefied gas may be, for example, liquefied hydrogen, liquid helium, or LNG.

[0010] [Configuration of Transfer System] FIG. 1 is a side view schematically illustrating the configuration of a cryogenic fluid transfer system 1 according to an embodiment of the present disclosure. The transfer system 1 of this embodiment is a system applied to a liquefied hydrogen facility that handles liquefied hydrogen and is configured to transfer low-temperature boil-off gas (BOG) generated by the vaporization of liquefied hydrogen. The liquefied hydrogen facility may be of any type as long as it handles liquefied hydrogen. In this embodiment, however, a facility that generates and stores liquefied hydrogen is exemplified as the liquefied hydrogen facility. Therefore, the liquefied hydrogen facility includes a liquefier 100 that liquefies hydrogen gas as a raw material. The liquefier 100 may be of any type as long as it can cool and liquefy hydrogen gas. For example, the liquefier 100 may include a cooler that cools hydrogen gas to a state just before liquefaction by heat exchange using a refrigeration cycle, and a Joule-Thomson valve that liquefies the hydrogen gas cooled by the cooler by Joule-Thomson expansion (isenthalpic expansion).

[0011] The liquefied hydrogen produced by the liquefier 100 is stored in a storage tank (not shown). The liquefied hydrogen stored in the storage tank gradually evaporates (gasifies) due to heat input from the outside. The hydrogen gas produced by this evaporation, i.e., boil-off gas (BOG), is returned to the liquefier 100 via the transfer system 1. That is, the transfer system 1 of this embodiment constitutes a part of a boil-off gas return system for returning the boil-off gas to the liquefier 100 and liquefying it again. The boil-off gas returned by the transfer system 1 is mixed with the raw material hydrogen gas in the raw material tank 17 and then supplied to the liquefier 100.

[0012] 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 the "first line" in this disclosure, and the downstream line 3 corresponds to the "second line" in this disclosure.

[0013] The upstream line 2 is a piping line connecting a boil-off gas (BOG) supply source to the compressor 11. The boil-off gas is supplied, for example, from the gas phase of the storage tank. In this case, the gas phase of the storage tank functions as the boil-off gas supply source.

[0014] A tank 15 is provided in the upstream line 2. The tank 15 is a container with an expanded volume so as to have a larger cross-sectional area than the upstream line 2, and is provided to allow the boil-off gas from the return line 5 to merge with the upstream line 2 and promote gas mixing.

[0015] The downstream line 3 is a piping line connecting the compressor 11 and the liquefaction machine 100. The heat exchanger 12 and the raw material tank 17 are arranged on the downstream line 3 in this order from the upstream side (the left side in FIG. 1 ).

[0016] The bypass line 4 is a piping line that branches off from the upstream line 2 and leads to the heat exchanger 12. Specifically, the bypass line 4 branches off from a first branch point J1 on the upstream line 2 upstream of the tank 15 (on the left side in FIG. 1 ), extends in parallel with the upstream line 2, and is disposed so as to bypass the tank 15 and the compressor 11 and lead to the heat exchanger 12. The first branch point J1 corresponds to the "branch point" in this disclosure.

[0017] The return line 5 is a piping line that connects the heat exchanger 12 and the tank 15. The small-sized compressor 13 is provided midway along the return line 5. The return line 5 is provided with an inner reflux line 7 that connects two points on the return line 5 that sandwich the small-sized compressor 13.

[0018] The reflux line 6 is a piping line that connects the downstream line 3 and the upstream line 2 outside the bypass line 4. Specifically, the reflux line 6 connects the second branch point J2, which is located between the heat exchanger 12 and the raw material tank 17 in the downstream line 3, to the third branch point J3, which is located upstream of the branch point (first branch point J1) from the upstream line 2 to the bypass line 4.

[0019] The compressor 11 is a device for compressing and feeding the boil-off gas, and is disposed between the upstream line 2 and the downstream line 3. The compressor 11 sucks in the boil-off gas from the upstream line 2, compresses it, and discharges it into the downstream line 3.

[0020] The heat exchanger 12 is a device that cools the boil-off gas flowing through the downstream line 3 by heat exchange with the boil-off gas extracted from the upstream line 2 via the bypass line 4. That is, the heat exchanger 12 cools the boil-off gas flowing through the downstream line 3, i.e., the boil-off gas that has been compressed and heated by the compressor 11, by heat exchange using the low-temperature boil-off gas extracted from the upstream line 2 as a heat medium.

[0021] The small-sized compressor 13 has a smaller compression ratio than the compressor 11. The small-sized compressor 13 sucks in boil-off gas from the heat exchanger 12, pressurizes it, and discharges it into the tank 15. Specifically, the small-sized compressor 13 sucks in the boil-off gas, which serves as a heat medium and is introduced into the heat exchanger 12 via the bypass line 4, through the upstream part of the return line 5, and pressure-feeds the sucked boil-off gas to the tank 15 through the downstream part of the return line 5. Note that the upstream and downstream parts of the return line 5 refer to the side closer to the heat exchanger 12 as the upstream side and the side closer to the tank 15 as the downstream side.

[0022] FIG. 2 is a diagram showing the relationship between the temperatures and pressures of the various components of the transfer system 1. As shown in this figure, the temperatures and pressures of the boil-off gas flowing through the various components 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 first pressure P1 are the temperature and pressure of the boil-off gas flowing upstream of the tank 15 in the upstream line 2. The second temperature T2 and second pressure P2 are the temperature and pressure of the boil-off gas flowing from the tank 15 to the compressor 11, in other words, the inlet temperature and inlet pressure of the compressor 11. The third temperature T3 and third pressure P3 are the temperature and pressure of the boil-off gas flowing from the compressor 11 to the heat exchanger 12, in other words, the inlet temperature and inlet pressure of the heat exchanger 12. The fourth temperature T4 and fourth pressure P4 are the temperature and pressure of the boil-off gas flowing from the heat exchanger 12 to the raw material tank 17, in other words, the outlet temperature and outlet pressure of the heat exchanger 12. The fifth temperature T5 and the fifth pressure P5 are the temperature and pressure of the boil-off gas flowing upstream of the return line 5, that is, the boil-off gas that flows toward the small-sized compressor 13 after being used as a heat transfer medium in the heat exchanger 12. The sixth temperature T6 and the sixth pressure P6 are the temperature and pressure of the boil-off gas that flows from the small-sized compressor 13 toward the tank 15, that is, the boil-off gas that is returned to the tank 15 through the return line 5.

[0023] Due to the temperature and pressure increasing actions of the compressor 11 and the small compressor 13, and the heat balance in the heat exchanger 12, the above temperatures and pressures each satisfy the relationship shown in formula (1) in Fig. 2. That is, 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.

[0024] The third pressure P3 is higher than the second pressure P2. The sixth pressure P6 is higher than the fifth pressure P5 and equal to the first pressure P1.

[0025] In this embodiment, the compression ratio of the compressor 11 is greater than that of the small-sized compressor 13, and therefore the temperature difference and pressure difference before and after the compressor 11 are greater than the temperature difference and pressure difference before and after the small-sized compressor 13. That is, the difference between the third temperature T3 and the second temperature T2 is greater than the difference between the sixth temperature T6 and the fifth temperature T5, and the difference between the third pressure P3 and the second pressure P2 is greater than the difference between the sixth pressure P6 and the fifth pressure P5.

[0026] As shown in Fig. 1, the bypass line 4 is provided with a flow control valve 21. The flow control valve 21 is a valve that adjusts the flow rate of the boil-off gas flowing through the bypass line 4. The larger the opening of the flow control valve 21, the greater the proportion of the boil-off gas that passes through the bypass line 4 and is introduced as a heat transfer medium into the heat exchanger 12. When the flow rate in the bypass line 4, i.e., the flow rate of the heat transfer medium, increases, the amount of heat exchanged between the boil-off gas flowing through the downstream line 3 and the heat transfer medium increases, and the temperature of the boil-off gas flowing from the heat exchanger 12 to the raw material tank 17 tends to decrease.

[0027] A first spillback valve 22 is provided in the inner return line 7. The first spillback valve 22 is a valve that adjusts the pressure of the boil-off gas returned to the tank 15 through the return line 5, i.e., the return pressure to the tank 15. For example, as the opening of the first spillback valve 22 increases, the proportion of boil-off gas that is returned from the downstream side to the upstream side of the small compressor 13 through the inner return line 7 increases, and the return pressure to the tank 15 decreases.

[0028] A second spillback valve 23 is provided in the reflux line 6. The second spillback valve 23 is a valve that controls the inlet pressure of the liquefier 100 by adjusting the proportion of 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 the opening of the second spillback valve 23 increases, the proportion of boil-off gas that is refluxed from the downstream side to the upstream side of the compressor 11 through the reflux line 6 increases, and the pressure of the boil-off gas introduced from the downstream line 3 into the raw material tank 17 decreases. This allows the inlet pressure of the liquefier 100 to be reduced.

[0029] Although the flow rate adjustment valve 21, the first spillback valve 22, and the second spillback valve 23 may each be a manual valve, in this embodiment, each of the valves 21 to 23 is an automatic valve. That is, the opening degree of each of the flow rate adjustment valve 21, the first spillback valve 22, and the second spillback valve 23 is automatically controlled by a controller 30 (control unit) described later.

[0030] The transfer system 1 is provided with a plurality of sensors for detecting state quantities of the boil-off gas flowing through each line. Specifically, in this embodiment, the plurality of sensors includes 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 provided in the downstream line 3, and a second pressure sensor SN5 provided in the return line 5.

[0031] The first flow rate sensor SN1 detects the flow rate of the upstream line 2, specifically, the flow rate of the boil-off gas flowing through a portion of the upstream line 2 between the first branch 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 the temperature and pressure of the 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 the pressure of the boil-off gas flowing through a portion of the return line 5 downstream of the small-sized compressor 13. The temperature detected by the temperature sensor SN3 corresponds to the fourth temperature T4 shown in FIG. 2, the pressure detected by the first pressure sensor SN4 corresponds to the fourth pressure P4 shown in FIG. 2, and the pressure detected by the second pressure sensor SN5 corresponds to the sixth pressure P6 shown in FIG. 2.

[0032] [Valve Control] Figure 3 is a functional block diagram showing the control system of the transfer system 1. The controller 30 shown in this figure is a control device whose main component is a microcomputer including a processor (CPU) that performs calculations, memories such as ROM and RAM, and various input / output buses. The controller 30 receives information detected by the sensors SN1 to SN5 and controls the opening degrees of the flow rate adjustment valve 21, the first spillback valve 22, and the second spillback valve 23 based on the received information.

[0033] 4 is a schematic diagram illustrating a mechanism for controlling the aperture of each valve. As shown in the figure, the aperture of the flow rate adjustment valve 21 is controlled based on 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 aperture of the flow rate adjustment valve 21 based on the input information from the sensors SN1 to SN3 so that the temperature of the hydrogen gas introduced into the liquefier 100, in other words, the inlet temperature of the liquefier 100, falls within a predetermined target temperature range.

[0034] For example, the larger the aperture of the flow control valve 21, the greater the flow rate 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 heat medium for cooling, and the smaller the flow rate of the boil-off gas whose temperature increases as it is compressed in the compressor 11. Therefore, the larger the aperture of the flow control valve 21, the lower the temperature of the boil-off gas introduced from the heat exchanger 12 into the raw material tank 17, and the lower the inlet temperature of the liquefier 100. Meanwhile, due to the characteristics of the liquefier 100, in order to properly liquefy hydrogen gas containing boil-off gas in the liquefier 100, it is necessary to keep the inlet temperature of the liquefier 100 within a predetermined target temperature range. Therefore, the controller 30 adjusts the temperature of the boil-off gas introduced into the raw material tank 17 by controlling the aperture of the flow control valve 21, thereby keeping the inlet temperature of the liquefier 100 within the target temperature range.

[0035] Specifically, the bypass flow rate ratio is the ratio of the flow rate in the bypass line 4 detected by the second flow rate sensor SN2 to the flow rate in the upstream line 2 detected by the first flow rate sensor SN1. The controller 30 pre-stores, as a target flow rate ratio, a value of the bypass flow rate ratio that ensures that the inlet temperature of the liquefier 100 falls within the target temperature range under expected typical operating conditions. The controller 30 then controls the aperture of the flow rate control valve 21 based on the flow rates detected by the first and second flow rate sensors SN1 and SN2 so that the bypass flow rate ratio becomes the target flow rate ratio. However, even if the bypass flow rate ratio is adjusted to the target flow rate ratio, the expected temperature may not be obtained depending on the conditions. Therefore, the controller 30 checks the temperature detected by the temperature sensor SN3, and if the confirmed temperature deviates from the expected temperature, corrects the aperture of the flow rate control valve 21 to reduce the deviation.

[0036] The aperture of the first spillback valve 22 is controlled based on input information from the second pressure sensor SN5. Specifically, the controller 30 controls the aperture 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, if the detected pressure exceeds the target pressure, the aperture of the first spillback valve 22 is increased to reduce the pressure. In this case, the target pressure is set to a value equivalent to the 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 problems.

[0037] The aperture of the second spillback valve 23 is controlled based on input information from the first pressure sensor SN4. Specifically, the controller 30 controls the aperture 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 into the raw material tank 17, becomes a predetermined target pressure. For example, if the detected pressure exceeds the target pressure, the aperture of the second spillback valve 23 is increased to reduce the pressure. In this case, the target pressure is set to a value equivalent to the pressure of the raw material hydrogen gas introduced into the raw material tank 17.

[0038] The valve opening control described above is basically performed under steady-state conditions where the temperature and pressure conditions are stable. During unusual conditions, such as when the transfer system 1 is started up, the valve opening may be controlled according to a predetermined program, or may be switched to manual operation.

[0039] [Operation and Effect] As described above, the boil-off gas transfer system 1 in this 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 point J1 on the upstream line 2 to reach the heat exchanger 12, and the return line 5 connecting a position (tank 15) downstream of the first branch point J1 on the upstream line 2 to the heat exchanger 12. This configuration has the advantage of being able to appropriately adjust the inlet temperature of the liquefier 100 while reducing the amount of heat medium used that is supplied from the outside.

[0040] That is, in this embodiment, the 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 as a heat medium into the heat exchanger 12. Therefore, the boil-off gas flowing through the downstream line 3, i.e., the boil-off gas whose temperature has been increased by compression in the compressor 11, can be cooled using this heat exchanger 12 (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 liquefaction processing.

[0041] Furthermore, the boil-off gas used as a heat transfer medium, i.e., the boil-off gas introduced into the heat exchanger 12 from the bypass line 4, is returned through the return line 5 to a position (tank 15) downstream of the first branch J1 in the upstream line 2. This allows the temperature of the boil-off gas introduced into the compressor 11 to be increased, thereby alleviating the temperature performance requirements of the compressor 11. That is, the boil-off gas introduced into the heat exchanger 12 from the bypass line 4 is heated by heat exchange with the boil-off gas compressed by the compressor 11 and flowing through the downstream line 3. The heated boil-off gas is then returned to the upstream line 2 through the return line 5, thereby increasing the temperature of the boil-off gas introduced into the compressor 11 (T1<T2), and preventing extremely low-temperature boil-off gas close to the temperature range of liquefied hydrogen from being introduced into the compressor 11. As a result, a general-purpose compressor used in, for example, an LNG facility can be used as the compressor 11, eliminating the need for a special compressor with high temperature performance (low-temperature resistance).

[0042] Furthermore, in this embodiment, the low-temperature boil-off gas diverted from the upstream line 2 is used as the heat medium for cooling the downstream line 3, eliminating the need to separately supply a heat medium from the outside, thereby enabling effective use of resources. Note that, depending on the cooling capacity required of the heat exchanger 12, a heat medium may be separately supplied from the outside. Even in this case, however, according to this embodiment, in which the boil-off gas diverted from the upstream line 2 is used as the heat medium, the amount of heat medium supplied from the outside can be reduced, thereby suppressing resource consumption in the transfer system 1.

[0043] In addition, in this embodiment, the flow rate control valve 21 is provided in the bypass line 4, and this flow rate control valve 21 can be used to adjust the flow rate of the boil-off gas introduced as a heat medium from the bypass line 4 to the heat exchanger 12. This makes it possible to adjust the heat exchange amount in the heat exchanger 12, and to adjust the temperature of the boil-off gas flowing from the heat exchanger 12 to a temperature suitable for the liquefaction process in the liquefaction machine 100.

[0044] More specifically, in this embodiment, the flow rates of the upstream line 2 and the bypass line 4 are detected by the first and second flow sensors SN1, SN2, and the aperture of the flow control valve 21 is controlled based on the detected flow rates. In this way, when the aperture of the flow control valve 21 is controlled based on the detected flow rates of the lines 2, 4, the aperture of the flow control valve 21 can be automatically adjusted 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 through this adjustment, the heat exchange amount in the heat exchanger 12 can be adjusted. As a result, the temperature of the hydrogen gas including boil-off gas flowing from the heat exchanger 12 to the liquefier 100, i.e., the inlet temperature of the liquefier 100, can be kept within an appropriate temperature range.

[0045] Furthermore, in this embodiment, the small-sized compressor 13, which has a compression ratio smaller than that of the compressor 11, is provided in the return line 5, so that 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 such an extent that the pressure loss caused by passing through the bypass line 4 and the heat exchanger 12 is recovered. This allows the boil-off gas to be returned to the upstream line 2 through the return line 5 without any problems. Furthermore, since the boil-off gas is heated by compression in the small-sized compressor 13 and returned to the upstream line 2, the temperature of the boil-off gas introduced into the compressor 11 can be sufficiently increased, and the temperature performance (low-temperature resistance) required of the compressor 11 can be relaxed.

[0046] In addition, in this embodiment, a tank 15 is provided at the confluence of the upstream line 2 and the return line 5, so that the low-temperature boil-off gas introduced into the tank 15 from the upstream line 2 and the relatively high-temperature boil-off gas introduced into the tank 15 from the return line 5 can be uniformly mixed within the tank 15, and the boil-off gas that has been uniformly heated by this mixing can be introduced into the compressor 11.

[0047] [Modifications] Although preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the present disclosure.

[0048] For example, in the above embodiment, an example has been described in which the present disclosure is applied to the transfer system 1 that supplies boil-off gas to the liquefaction machine 100, but the transfer destination of the transfer system 1 is not limited to the liquefaction machine 100. For example, the transfer system of the present disclosure may be a system that transfers boil-off gas to a power generator including a gas turbine that burns hydrogen gas to generate electricity.

[0049] In the above embodiment, an example has been described in which the present disclosure is applied to a transfer system 1 that transfers low-temperature boil-off gas (hydrogen gas) produced by the evaporation of liquefied hydrogen. However, the present disclosure is broadly applicable to systems that transfer low-temperature gases, and can also be applied to systems that transfer low-temperature boil-off gas produced by the evaporation of liquefied gases other than liquefied hydrogen.

[0050] [Summary] The above-described embodiment and its modifications include the following disclosures.

[0051] A cryogenic fluid transfer system according to a first aspect of the present disclosure includes a compressor that compresses low-temperature boil-off gas, which is vaporized liquefied gas, to a transfer destination, a first line that connects a source of the boil-off gas to the compressor, a second line that connects the compressor to the transfer destination, a heat exchanger provided midway along the second line, a bypass line that branches off from a branch on the first line and leads to the heat exchanger, and a return line that connects the heat exchanger to a position downstream of the branch on the first line.

[0052] According to the first aspect, the low-temperature boil-off gas before being compressed by the compressor is extracted through the bypass line and introduced into the heat exchanger as a heat medium, so that the boil-off gas flowing through the second line, i.e., the boil-off gas whose temperature has been increased by compression in the compressor, can be cooled using this heat exchanger. Therefore, even if the temperature condition of the boil-off gas required by the destination is low, boil-off gas at an appropriate temperature that meets this temperature condition can be supplied to the destination.

[0053] Furthermore, the boil-off gas used as a heat transfer medium, i.e., the boil-off gas introduced into the heat exchanger from the bypass line, is returned through the return line to a position downstream of the branch point in the first line, so that the temperature of the boil-off gas introduced into the compressor can be increased, and the temperature performance (low-temperature resistance) required of the compressor can be relaxed.

[0054] Furthermore, in the first aspect, low-temperature boil-off gas diverted from the first line is used as the heat medium for cooling the second line, so that the amount of heat medium supplied from the outside can be reduced, thereby enabling effective use of resources.

[0055] The transfer system according to a second aspect is the transfer system according to the first aspect, further comprising a flow rate adjustment valve that adjusts the flow rate of the boil-off gas flowing through the bypass line.

[0056] According to the second aspect, the flow rate of the boil-off gas introduced as a heat medium from the bypass line into the heat exchanger can be adjusted using the flow rate control valve, thereby adjusting the heat exchange amount in the heat exchanger and adjusting the temperature of the boil-off gas flowing from the heat exchanger to a suitable temperature.

[0057] The transfer system according to the third aspect is the same as that of the second aspect, and further includes a first flow sensor that detects the flow rate of the first line, a second flow sensor that detects the flow rate of the bypass line, and a control unit that controls the opening degree of the flow rate adjustment valve based on the flow rates detected by the first flow sensor and the second flow sensor.

[0058] In the third aspect, the aperture of the flow control valve is controlled based on the detected flow rates in the first line and the bypass line, so that the aperture of the flow control valve can be automatically adjusted so that the bypass flow rate ratio, which is the ratio of the flow rate in the bypass line to the flow rate in the first line, becomes an appropriate value, and through this adjustment, the heat exchange amount in the heat exchanger can be adjusted, thereby adjusting the temperature of the boil-off gas flowing from the heat exchanger to its destination to an appropriate temperature.

[0059] A transfer system according to a fourth aspect is any one of the first to third aspects, wherein a small compressor having a compression ratio smaller than that of the compressor is provided in the return line.

[0060] According to the fourth aspect, the pressure of the 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 problems. In addition, since the boil-off gas is returned to the first line after being heated by compression in the small compressor, the temperature of the boil-off gas introduced into the compressor can be sufficiently increased, and the temperature performance required of the compressor can be alleviated.

[0061] The transfer system of the fifth aspect is the same as any of the first to fourth aspects, in which a tank is provided at a position downstream of the branching point in the first line, and the downstream end of the return line is connected to the tank.

[0062] According to this 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, and the boil-off gas that has been uniformly heated by this mixing can be introduced into the compressor.

[0063] A sixth aspect of the transfer system is any one of the first to fifth aspects, wherein the transfer destination is a liquefier that reliquefies the boil-off gas.

[0064] According to the sixth aspect, the temperature of the boil-off gas introduced into the liquefier to which it is transferred, i.e., the inlet temperature of the liquefier, can be kept within a relatively low temperature range suitable for liquefaction processing, thereby promoting the production of liquefied gas.

[0065] REFERENCE SIGNS LIST 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 (control part) 100 Liquefaction machine SN1 First flow rate sensor SN2 Second flow rate sensor

Claims

1. A cryogenic fluid transport system comprising: a compressor that compresses low-temperature boil-off gas produced by vaporization of liquefied gas to a destination; a first line that connects a source of the boil-off gas to the compressor; a second line that connects the compressor to the destination; a heat exchanger provided in the middle of the second line; a bypass line that branches off from a branch on the first line and leads to the heat exchanger; and a return line that connects a position on the first line downstream of the branch and the heat exchanger.

2. A cryogenic fluid transfer system according to claim 1, further comprising a flow rate control valve for controlling the flow rate of the boil-off gas flowing through the bypass line.

3. A cryogenic fluid transfer system as described in claim 2, further comprising: a first flow rate sensor that detects the flow rate of the first line; a second flow rate sensor that detects the flow rate of the bypass line; and a control unit that controls the opening degree of the flow rate regulating valve based on the flow rates detected by the first flow rate sensor and the second flow rate sensor.

4. A cryogenic fluid transport system according to claim 1, wherein a small compressor having a compression ratio smaller than that of said compressor is provided in said return line.

5. A cryogenic fluid transfer system as claimed in claim 1, wherein a tank is provided at a position downstream of the branching portion in the first line, and the downstream end of the return line is connected to the tank.

6. A cryogenic fluid transfer system according to any one of claims 1 to 5, wherein the transfer destination is a liquefaction machine that re-liquefies the boil-off gas.

Images