Liquefaction system

Abstract

This liquefaction system is provided with a liquefier (2) for liquefying a gas, a regulating valve (13) provided in a discharge path (4) for discharging the liquefied gas liquefied in the liquefier (2), a control unit (14) for controlling opening / closing operations of the regulating valve (13), and a temperature sensor (15) for detecting the temperature of the liquefied gas in the liquefier (2) and / or the temperature of the liquefied gas in the discharge path (4). The control unit (14) opens the regulating valve (13), when it is determined that the temperature of the liquefied gas is lower than a predetermined value on the basis of a result of the detection by the temperature sensor (15).

Description

Liquefaction system

[0001] This disclosure relates to a liquefaction system.

[0002] Conventionally, in order to reduce the volume of gas for easy storage and transportation, a liquefaction system for liquefying gas is known. The liquefaction system includes a liquefier for liquefying gas and a cooling device for supplying refrigerant to the liquefier. The gas supplied to the liquefier is cooled and condensed by exchanging heat with the refrigerant in the liquefier. As a result, the gas becomes a saturated liquid (condensed fluid) state. Then, the liquid component with a large specific gravity moves to the lower part of the liquefier, and the gas component with a small specific gravity moves to the upper part as gas. Thereby, liquefied gas is generated.

[0003] When transporting the gas liquefied in this way, if the gas is heated up and vaporized again, the total amount of available liquid will decrease. For this reason, in order to supercool the gas liquefied by the heat exchanger, a technique of providing a subcooling exchanger on the outlet side of the heat exchanger has been proposed (see, for example, Patent Document 1). Thereby, when transporting the liquefied gas, it is possible to suppress the gas from being heated up to the vaporization temperature.

[0004] Japanese Patent Application Laid-Open No. 2013-242138

[0005] However, in the above-mentioned conventional technology, there is a problem that the liquefaction system becomes complicated and large-sized because a subcooler is required to supercool the gas.

[0006] Therefore, the present disclosure provides a liquefaction system that can supercool liquefied gas while simplifying and miniaturizing the equipment.

[0007] In order to solve the above problems, the liquefaction system according to the present disclosure includes a liquefier for liquefying gas, a regulating valve provided in a discharge path for discharging the liquefied gas liquefied in the liquefier, a control unit for controlling the opening and closing operation of the regulating valve, and a temperature sensor for detecting at least one of the temperature of the liquefied gas in the liquefier and the temperature of the liquefied gas in the discharge path. When the control unit determines that the temperature of the liquefied gas is lower than a predetermined value based on the detection result of the temperature sensor, the control unit opens the regulating valve.

[0008] According to this disclosure, the liquefaction system can be simplified and miniaturized while also enabling supercooling of the liquefied gas.

[0009] This is a schematic diagram of the liquefaction system in an embodiment of the disclosure.

[0010] Next, embodiments of the present disclosure will be described with reference to the drawings.

[0011] <Liquefaction System> Figure 1 is a schematic diagram of the liquefaction system 1. As shown in Figure 1, the liquefaction system 1 mainly consists of a liquefier 2, a cooling device 3 attached to the liquefier 2, a tank 5 connected to the liquefier 2 via a discharge passage 4, and a control valve 13 provided in the discharge passage 4.

[0012] Liquefitter 2 is a heat exchanger for generating liquefied gas (hereinafter referred to as liquefied gas) by exchanging heat between vaporized gas (hereinafter referred to as vaporized gas) and a refrigerant liquefied by the cooling device 3 described later. Examples of substances to be liquefied in liquefitter 2 include carbon dioxide (CO2), natural gas, nitrogen (N2), ammonia (NH3), fluorocarbon gases, and hydrogen (H2). The substances to be liquefied are not limited to these, and various other substances can be used in the liquefaction system 1.

[0013] The liquefier 2 comprises a storage section 2d, a vaporized gas supply port 2a for supplying vaporized gas to the storage section 2d from the outside, a vaporized gas outlet 2b for discharging vaporized gas existing as a gas in the storage section 2d, and a liquefied gas outlet 2c for discharging liquefied gas existing as a liquid in the storage section 2d. The vaporized gas supply port 2a and the vaporized gas outlet 2b are located on the upper surface of the liquefier 2 in the direction of gravity. The liquefied gas outlet 2c is located on the lower surface of the liquefier 2 in the direction of gravity. Hereinafter, the upper (upper) and lower (lower) surfaces in the direction of gravity will be simply referred to as the upper (upper) and lower (lower) surfaces, respectively.

[0014] The cooling device 3 comprises a refrigerant flow path 6, a compressor 7 connected to the refrigerant flow path 6, an oil separator 8, a condenser 9, and an expansion valve 10. The compressor 7 comprises a compressor 11 and a motor 12 that serves as the drive source for the compressor 11. The drive source is not limited to the motor 12; any device that drives the compressor 11 is acceptable. For example, an engine or the like may be used as the drive source.

[0015] The compressor 7 circulates the refrigerant through the refrigerant flow path 6. Hereinafter, these may be referred to as the upstream side, downstream side, etc., with respect to the direction of refrigerant flow. In the direction of refrigerant flow, the compressor 7, oil separator 8, condenser 9, and expansion valve 10 are connected to the refrigerant flow path 6 in this order. The liquefaction unit 2 is connected downstream of the expansion valve 10 in the refrigerant flow path 6. This constitutes a so-called refrigeration cycle, and the refrigerant liquefied by the cooling device 3 is supplied to the liquefaction unit 2.

[0016] The discharge passage 4 connects the liquefied gas outlet 2c and the tank 5. Therefore, the liquefied gas produced in the liquefier 2 flows through the liquefied gas outlet 2c to the discharge passage 4, and then to the tank 5. Hereinafter, the flow direction of the liquefied gas in the discharge passage 4 may be referred to as the upstream side, the downstream side, etc. A control valve 13 is provided in the discharge passage 4. The control valve 13 opens and closes the discharge passage 4. A temperature sensor 15 is provided between the control valve 13 in the discharge passage 4 and the liquefier 2. The temperature sensor 15 detects the temperature of the liquefied gas inside the discharge passage 4, particularly between the control valve 13 and the liquefier 2.

[0017] These control valves 13 and temperature sensors 15 are communicated to the control unit 14. The detection result from the temperature sensor 15 is output as a signal to the control unit 14. Based on the detection result detected by the temperature sensor 15, the control unit 14 controls the opening and closing of the control valve 13 (details will be described later). In addition, the discharge passage 4 is provided with a bypass passage 21 that connects the upstream and downstream sides of the control valve 13. In other words, the bypass passage 21 connects the control valve 13 to the liquefier 2 and the control valve 13 to the tank 5 within the discharge passage 4.

[0018] Tank 5 is positioned below liquefier 2 in the direction of gravity and stores liquefied gas. Liquefied gas is supplied from Tank 5 to, for example, a transport vehicle (not shown), and transported to the desired location. A supply passage 16 for supplying liquefied gas to external devices such as transport vehicles is connected to Tank 5. A first pressure equalization passage 17a is connected to the upper surface of Tank 5 in the direction of gravity. The first pressure equalization passage 17a connects Tank 5 to the vaporized gas outlet 2b of liquefier 2. Furthermore, a second pressure equalization passage 17b is provided that connects a bypass passage 21 to the vaporized gas outlet 2b of liquefier 2.

[0019] The tank 5 and the liquefier 2 are connected via the first pressure equalization path 17a, and the pressure inside the tank 5 and the pressure inside the liquefier 2 are maintained uniformly. The bypass path 21 and the liquefier 2 are connected via the second pressure equalization path 17b, and the pressure in the bypass path 21 and the pressure inside the liquefier 2 are maintained uniformly. The first pressure equalization path 17a and the second pressure equalization path 17b are also connected to each other. As a result, the pressure inside the tank 5, the pressure inside the liquefier 2, and the pressure inside the bypass path 21 are maintained uniformly. A pressure sensor 18 is provided in the first pressure equalization path 17a. The pressure sensor 18 detects the pressure of the vaporized gas in the first pressure equalization path 17a and the second pressure equalization path 17b.

[0020] An exhaust passage 19 is connected to the first pressure equalization passage 17a. An exhaust valve 20 is provided in the exhaust passage 19. The exhaust valve 20 opens and closes the exhaust passage 19. The exhaust valve 20 and the pressure sensor 18 are communicated to the control unit 14. The detection result from the pressure sensor 18 is output as a signal to the control unit 14. The control unit 14 controls the opening and closing of the regulating valve 13 based on the detection result detected by the pressure sensor 18 (details will be described later).

[0021] <Operation of Liquefaction System 1> Next, the operation of liquefaction system 1 will be explained. The liquefier 2 is supplied with refrigerant liquefied by the cooling device 3. As a result, the vaporized gas supplied into the liquefier 2 via the vaporized gas supply port 2a is cooled and condensed by heat exchange with the refrigerant. When the vaporized gas condenses, it becomes a saturated liquid (condensable fluid) state, that is, a state in which it is easily separated into gas and liquid. The heavier liquid portion is stored as liquefied gas at the bottom of the liquefier 2 (see the shaded area in Figure 1). The lighter gas portion moves to the top as vaporized gas.

[0022] The liquefied gas flows from the liquefied gas 2 through the liquefied gas outlet 2c to the discharge channel 4. When the control unit 14 determines that the temperature sensor 15 detects a value above a predetermined value, it drives the control valve 13 to close the discharge channel 4. The predetermined value here is an arbitrary supercooling temperature of the liquefied gas. For example, if the gas is carbon dioxide (CO2) and its saturation temperature is -20°C, the predetermined value is approximately -25°C (supercooling of 5°C). The liquefied gas that flows into the discharge channel 4 is blocked by the control valve 13, and liquefied gas continues to be stored in the liquefied gas 2. As a result, the liquefied gas in the liquefied gas 2 becomes supercooled, and the liquefied gas in the discharge channel 4 also becomes supercooled.

[0023] The control unit 14 opens the control valve 13 and opens the discharge passage 4 when the liquefied gas in the discharge passage 4 becomes supercooled and the temperature sensor 15 detects a value below a predetermined value. As a result, the supercooled liquefied gas flows through the discharge passage 4 into the tank 5. In other words, the predetermined value of the liquefied gas temperature that serves as the threshold for opening and closing the control valve 13 is determined based on an arbitrary supercooling temperature corresponding to the type of gas.

[0024] The supercooled liquefied gas stored in tank 5 is supplied via supply passage 16 to external devices such as transport vehicles (not shown). When the supercooled liquefied gas in discharge passage 4 has finished flowing, the liquefied gas that has not been sufficiently cooled flows out into discharge passage 4, causing the temperature of the liquefied gas in discharge passage 4 to rise above a predetermined value again. In this case, the control valve 13 is closed again, blocking the flow of liquefied gas in discharge passage 4. By repeating this process, only supercooled liquefied gas can be supplied to the user side, such as tank 5 and transport vehicles located downstream of tank 5.

[0025] Conventionally, liquefied gas discharged from a liquefier was either stored directly in a tank or transported by other means. As a result, even though the liquefier was sufficiently cooled to suppress vaporization of components, the temperature could rise after discharge. Alternatively, the liquefied gas might simply be stored in the tank without sufficient cooling by the liquefier. Therefore, the system was configured so that after discharge from the liquefier, the liquefied gas would be supercooled by passing it through a supercooler before being stored in the tank in a sufficiently cooled state.

[0026] However, according to the liquefaction system 1 of this disclosure, the control valve 13 is controlled so that the liquefied gas is discharged from the liquefier 2 only when the temperature of the liquefied gas in the liquefier 2 or the discharge passage 4 is lower than a predetermined value (an arbitrary supercooling temperature). As a result, the liquefied gas discharged into the tank 5 is always kept at a temperature lower than the predetermined value. Therefore, as is the case in the conventional system, a supercooler does not need to be installed between the cooler and the tank, and the liquefied gas flowing into the tank 5 can be kept at a temperature lower than the predetermined value, thus eliminating the need for a supercooler.

[0027] More specifically, the vaporized gas is cooled and liquefied in liquefaction unit 2, but at the liquefied stage it is still a saturated liquid. If the saturated liquid is further cooled in liquefaction unit 2 for any length of time, the liquefied gas can be turned into a supercooled liquid. Therefore, if liquefied gas is continuously discharged from liquefaction unit 2, there is a risk that saturated liquid at a temperature higher than that of the supercooled liquid will be discharged instead of a supercooled liquid.

[0028] Therefore, in the liquefaction system 1 of this disclosure, the control valve 13 is controlled so that the liquefied gas inside the liquefied gas 2 is discharged only when the temperature of the liquefied gas inside the liquefied gas 2 is lower than a predetermined value (an arbitrary supercooling temperature). As a result, the control valve 13 is closed as appropriate, the liquefied gas is blocked in the discharge passage 4 and the liquefied gas is sufficiently cooled by the liquefied gas 2. After that, the control valve 13 is opened again, and only the sufficiently cooled supercooled liquid is discharged from the discharge passage 4. By repeating this process, only supercooled liquefied gas can be supplied to the user side, such as the tank 5 or a transport vehicle located downstream of the tank 5.

[0029] The temperature sensor 15 may be configured to detect the temperature of the liquefied gas in the discharge passage 4, as shown in Figure 1. With this configuration, even if the temperature of the liquefied gas in the discharge passage 4 rises above a predetermined value, the control valve 13 will only open after the liquefied gas in the discharge passage 4 has been sufficiently cooled by the liquefier 2, so that sufficiently cooled liquefied gas can always flow into the tank 5.

[0030] Alternatively, the temperature sensor 15 may be configured to detect the temperature of the liquefied gas inside the liquefier 2. In this case, it is preferable to install the sensor on the bottom side of the liquefier 2 so that it can detect the temperature of the liquefied gas stored in the liquefier 2.

[0031] The inside of tank 5 is at the same pressure as the inside of liquefier 2 via the first pressure equalization passage 17a. In other words, there is no pressure difference between the inside of liquefier 2 and the inside of tank 5. Furthermore, tank 5 is positioned below liquefier 2 in the direction of gravity. As a result, the liquefied gas in liquefier 2 flows smoothly into tank 5, preventing unintended pulsation of the liquefied gas flow.

[0032] Here, the control unit 14 drives the exhaust valve 20 to maintain the closed state of the exhaust passage 19 when the detection result from the pressure sensor 18 is below a predetermined value, and to open it when it exceeds the predetermined value. The predetermined value here is the saturation pressure relative to the saturation temperature of the gas. For example, if the gas is carbon dioxide (CO2), it is about 2 MPa. For example, if an unintended non-condensable gas such as nitrogen (N2) flows into the liquefier 2, the non-condensable gas will not liquefy even if cooled, leading to an increase in pressure inside the liquefier 2 and the tank 5. When a non-condensable gas flows into the liquefier 2 and the detection result from the pressure sensor 18 exceeds the predetermined value, the control unit 14 opens the exhaust valve 20 and opens the exhaust passage 19. As a result, the non-condensable gas that has flowed into the liquefier 2, tank 5 and first equalizing passage 17a is exhausted, and the pressure in the liquefier 2, tank 5 and first equalizing passage 17a decreases.

[0033] Incidentally, there is a possibility that the control valve 13 may malfunction and the discharge passage 4 may not open. However, the discharge passage 4 is provided with a bypass passage 21 that connects the upstream and downstream sides of the control valve 13. Therefore, even if the discharge passage 4 remains unintentionally blocked due to a malfunction of the control valve 13, it is possible to forcibly flow the liquefied gas in the discharge passage 4 to the tank 5 via the bypass passage 21.

[0034] It is desirable to install the bypass passage 21 in such a way that liquefied gas does not unintentionally flow out through the bypass passage 21 when the control valve 13 is operating normally. For example, the bypass passage 21 is provided to make a large detour above the control valve 13. The size of this detour is, for example, as follows: That is, the setting position X is 20% above the bottom surface of the liquefier 2 relative to the vertical height of the liquefier 2 (see the dashed line in Figure 1). It is desirable to provide the bypass passage 21 so that its upper end is located above the setting position X. This makes it possible to use the hydrostatic pressure of the liquefied gas to prevent liquefied gas from unnecessarily flowing out through the bypass passage 21. The bypass passage 21 is at equal pressure with the inside of the liquefier 2 via the second pressure equalization passage 17b. Therefore, it is prevented that liquefied gas does not unintentionally flow out through the bypass passage 21, or that the flow of liquefied gas in the bypass passage 21 is unintentionally suppressed.

[0035] As described above, the liquefaction system 1 includes a liquefier 2, a control valve 13 provided in the discharge passage 4, a control unit 14 that controls the opening and closing operation of the control valve 13, and a temperature sensor 15 that detects the temperature of the liquefied gas in the discharge passage 4. When the control unit 14 determines, based on the detection result of the temperature sensor 15, that the temperature of the liquefied gas is lower than a predetermined value, it opens the control valve 13. With this configuration, the liquefied gas can be retained in the liquefier 2 by controlling the opening and closing of the control valve 13. Therefore, the liquefier 2 can also perform the function of a conventional subcooler. Thus, the installation of a subcooler, which was conventionally provided separately from the liquefier 2, can be omitted, making the liquefaction system 1 simpler and more compact while still being able to supercool the liquefied gas.

[0036] The liquefaction system 1 includes a tank 5 and a first pressure equalization passage 17a that connects the inside of the tank 5 and the inside of the liquefier 2. This allows the pressure inside the tank 5 and the inside of the liquefier 2 to be made uniform. As a result, the supercooled liquefied gas can be efficiently stored in the tank 5. In the flow of liquefied gas between the tank 5 and the liquefier 2, pulsation of the liquefied gas caused by the differential pressure inside the tank 5 and the inside of the liquefier 2 can be suppressed.

[0037] The discharge passage 4 is provided with a bypass passage 21 that connects the upstream and downstream sides of the control valve 13. Therefore, even if a malfunction occurs in the control valve 13, for example, the liquefied gas in the discharge passage 4 can be forcibly discharged. Thus, a fail-safe function can be provided to prevent failure of the liquefaction system 1 as a whole.

[0038] The liquefaction system 1 includes a second pressure equalization passage 17b that connects the bypass passage 21 to the vaporized gas outlet 2b of the liquefier 2. This allows the pressure inside the bypass passage 21 and inside the liquefier 2 to be made uniform. As a result, the liquefied gas can flow smoothly through the bypass passage 21. When the liquefied gas flows through the bypass passage 21, pulsation of the liquefied gas caused by the pressure difference between the inside of the bypass passage 21 and inside the liquefier 2 can be suppressed.

[0039] A pressure sensor 18 is provided in the first pressure equalization passage 17a, and an exhaust passage 19 is connected to it. An exhaust valve 20 is provided in the exhaust passage 19. The control unit 14 opens the exhaust valve 20 when the pressure value detected by the pressure sensor exceeds a predetermined value. This prevents the pressure values ​​inside the liquefier 2, inside the tank 5, and in each pressure equalization passage 17a, 17b from exceeding the predetermined value. Thus, the gas saturation pressure can be maintained.

[0040] This disclosure is not limited to the embodiments described above, but includes various modifications to the embodiments described above without departing from the spirit of this disclosure. For example, in the embodiments described above, the cooling device 3 was described as comprising a refrigerant flow path 6, a compressor 7 connected to the refrigerant flow path 6, an oil separator 8, a condenser 9, and an expansion valve 10. However, it is not limited to this, and the cooling device 3 may be any device capable of cooling the liquefaction device 2.

[0041] In the above-described embodiment, the case in which the temperature of the liquefied gas in the discharge passage 4 is detected by the temperature sensor 15 was explained. However, the invention is not limited to this, and the temperature of the liquefied gas in the liquefier 2 may also be detected by the temperature sensor 15. It is sufficient that the temperature sensor 15 can detect that the liquefied gas in the liquefier 2 is being supercooled.

[0042] In the above-described embodiment, the case in which a pressure sensor 18 is provided in the first pressure equalization path 17a was explained. However, the invention is not limited to this, and it is sufficient to be able to detect the pressure at any point connected by the pressure equalization paths 17a and 17b. That is, a pressure sensor 18 may also be provided in the second pressure equalization path 17b or in the liquefaction device 2.

[0043] In the above-described embodiment, a case was explained in which an exhaust passage 19 connected to the first pressure equalization passage 17a is provided. However, the invention is not limited to this, and the exhaust passage 19 may not be provided. In the above-described embodiment, a case was explained in which a second pressure equalization passage 17b connecting the bypass passage 21 and the first pressure equalization passage 17a is provided. However, the invention is not limited to this, and the second pressure equalization passage 17b may not be provided.

[0044] In the above-described embodiment, the liquefaction system 1 has been described when it includes the tank 5. However, it is not limited to this, and the liquefaction system 1 may not include the tank 5. In this case, by opening the regulating valve 13, the liquefied gas flowing through the discharge passage 4 may be directly supplied to an external device such as a transport vehicle. When the tank 5 is not provided, since the first pressure equalizing passage 17a cannot be provided, it is desirable to provide the second pressure equalizing passage 17b.

[0045] This application is based on Japanese Patent Application No. 2024-161280 filed on September 18, 2024, the content of which is incorporated herein by reference.

Claims

1. A liquefaction system comprising: a liquefaction unit for liquefying gas; a control valve provided in a discharge passage for discharging the liquefied gas liquefied in the liquefaction unit; a control unit for controlling the opening and closing operation of the control valve; and a temperature sensor for detecting at least one of the temperature of the liquefied gas in the liquefaction unit and the temperature of the liquefied gas in the discharge passage, wherein the control unit opens the control valve when it determines, based on the detection result of the temperature sensor, that the temperature of the liquefied gas is lower than a predetermined value.

2. The liquefaction system according to claim 1, comprising: a tank provided downstream of the control valve in the discharge passage in the flow direction of the liquefied gas; and a pressure equalization passage connecting the tank and the liquefaction device.

3. The liquefaction system according to claim 1, further comprising a bypass passage provided in the discharge passage, which connects the upstream and downstream sides of the control valve in the flow direction of the liquefied gas.

4. The liquefaction system according to claim 3, further comprising a pressure equalization path connecting the bypass path and the liquefaction device.

5. A liquefaction system according to claim 2 or claim 4, comprising: an exhaust valve provided in the pressure equalization path and opened and closed by the control unit; and a pressure sensor that detects at least one of the pressure inside the liquefaction device and the pressure in the pressure equalization path, wherein the control unit opens the exhaust valve when the pressure value detected by the pressure sensor exceeds a predetermined value.

6. The liquefaction system according to claim 1, wherein the predetermined value is the supercooling temperature of the liquefied gas.

7. A liquefaction system comprising: a liquefaction unit for liquefying gas; and a control valve provided in a discharge passage for discharging the liquefied gas liquefied in the liquefaction unit, wherein the control valve is opened when at least one of the temperature of the liquefied gas in the liquefaction unit and the temperature of the liquefied gas in the discharge passage is lower than a predetermined value.

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