Liquefaction system

Abstract

The aim is to provide a liquefaction system that simplifies and miniaturizes equipment while also enabling supercooling of liquefied gas. [Solution] The system comprises a liquefier 2 for liquefying gas, a control valve 13 provided in a discharge passage 4 for discharging the liquefied gas liquefied in the liquefier 2, a control unit 14 for controlling the opening and closing operation of the control valve 13, and a temperature sensor 15 for detecting at least one of the temperature of the liquefied gas in the liquefier 2 and the temperature of the liquefied gas in the discharge passage 4. The control unit 14 opens the control valve 13 when it determines, based on the detection result of the temperature sensor 15, that the temperature of the liquefied gas is lower than a predetermined value.

Description

Technical Field

[0001] The present invention relates to a liquefaction system.

Background Art

[0002] Conventionally, in order to reduce the volume of gas for easy storage and transportation, a liquefaction system for liquefying vaporized gas is known. This system includes a liquefier for liquefying gas and a cooling device for supplying the liquefied refrigerant to the liquefier. The gas supplied to the liquefier is cooled and condensed by heat exchange 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 a 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.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[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 invention provides a liquefaction system that can supercool liquefied gas while simplifying and miniaturizing the equipment. [Means for solving the problem]

[0007] To solve the above problems, the liquefaction system according to the present invention comprises 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. 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.

[0008] By configuring the system in this way, the liquefied gas can be retained in the liquefier by controlling the opening and closing of the control valve. Therefore, the liquefier can also perform the function of a conventional supercooler. Consequently, the installation of a separate supercooler, which was previously required, can be eliminated, simplifying and miniaturizing the liquefaction system while still allowing for supercooling of the liquefied gas.

[0009] In the above configuration, the discharge passage is provided with a tank located downstream of the control valve in the flow direction of the liquefied gas, and a pressure equalization passage connecting the tank and the liquefier.

[0010] This configuration allows for uniform pressure between the tank and the liquefier. This enables efficient storage of supercooled liquefied gas in the tank. It also suppresses pulsation of the liquefied gas caused by the pressure difference between the tank and the liquefier during the flow of liquefied gas between the tank and the liquefier.

[0011] In the above configuration, the discharge passage is provided with a bypass passage that connects the upstream and downstream sides of the control valve in the flow direction of the liquefied gas.

[0012] This configuration allows for the forced flow of liquefied gas through the discharge passage even if, for example, a malfunction occurs in the control valve. Therefore, it provides a fail-safe function that prevents failure of the entire liquefaction system.

[0013] In the above configuration, a pressure equalization path is provided that connects the bypass path and the liquefaction device.

[0014] This configuration allows for uniform pressure between the bypass and the inside of the liquefier. This enables smooth flow of liquefied gas through the bypass. When flowing liquefied gas through the bypass, pulsation of the liquefied gas caused by the pressure difference between the bypass and the inside of the liquefier can be suppressed.

[0015] In the above configuration, the system includes 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 liquefier 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.

[0016] This configuration prevents the pressure values ​​inside the liquefier, tank, and pressure equalization path from exceeding predetermined values. Therefore, the gas saturation pressure can be maintained. [Effects of the Invention]

[0017] According to the present invention, the liquefaction system can be simplified and miniaturized while the liquefied gas can be supercooled. [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic diagram of the liquefaction system in an embodiment of the present invention. [Modes for carrying out the invention]

[0019] Next, embodiments of the present invention will be described with reference to the drawings.

[0020] <Liquefaction System> Figure 1 is a schematic configuration 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 path 4, and a regulating valve 13 provided in the discharge path 4.

[0021] The liquefier 2 is a heat exchanger for generating liquefied gas (hereinafter referred to as liquefied gas) by exchanging heat between the vaporized gas (hereinafter referred to as vaporized gas) and the refrigerant liquefied by the cooling device 3 described later. Examples of the gas include carbon dioxide (CO2), natural gas, nitrogen (N2), ammonia (NH3), fluorocarbon gas, hydrogen (H2), etc. The gas is not limited to these, and various other gases can be used in the liquefaction system 1.

[0022] The liquefier 2 includes a vaporized gas supply port 2a for supplying vaporized gas from the outside, a vaporized gas discharge port 2b for discharging the vaporized gas, and a liquefied gas discharge port 2c for discharging the liquefied gas. The vaporized gas supply port 2a and the vaporized gas discharge port 2b are arranged on the upper surface of the liquefier 2 in the direction of gravity. The liquefied gas discharge port 2c is arranged on the lower surface of the liquefier 2 in the direction of gravity. Hereinafter, the upper (upper part) and lower (lower part) in the direction of gravity are simply referred to as the upper (upper part) and lower (lower part).

[0023] The cooling device 3 includes a refrigerant flow path 6, a compression device 7, an oil separator 8, a condenser 9, and an expansion valve 10 connected to the refrigerant flow path 6. The compression device 7 includes a compressor 11 and a motor 12 that serves as a drive source for the compressor 11. The drive source is not limited to the motor 12. Any device that drives the compressor 11 may be used. For example, an engine or the like may be used as the drive source.

[0024] 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.

[0025] The discharge channel 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 channel 4, and then further flows to the tank 5. Hereinafter, the flow direction of the liquefied gas in the discharge channel 4 may be referred to as the upstream side, the downstream side, etc. A control valve 13 located in the discharge passage 4 opens and closes the discharge passage 4. A temperature sensor 15 is located in the discharge passage 4 on the liquefier 2 side of the control valve 13. The temperature sensor 15 detects the temperature of the liquefied gas in the discharge passage 4.

[0026] These control valves 13 and temperature sensors 15 are connected 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 valves 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.

[0027] 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 the liquefied gas is transported to the desired location. A supply line 16 is connected to Tank 5 for supplying liquefied gas to external devices such as transport vehicles. 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, which connects the bypass passage 21 to the vaporized gas outlet 2b of liquefier 2.

[0028] The tank 5 and the liquefier 2 are connected via the first pressure equalization passage 17a, and the pressure inside the tank 5 and the liquefier 2 is maintained uniformly. The pressure inside the bypass passage 21 and the liquefier 2 is maintained uniformly via the second pressure equalization passage 17b. The first pressure equalization passage 17a and the second pressure equalization passage 17b are also connected to each other. 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 each pressure equalization path 17a and 17b.

[0029] The first pressure equalization passage 17a is connected to the exhaust passage 19. The exhaust passage 19 is connected to the exhaust valve. A valve 20 is provided. The exhaust valve 20 opens and closes the exhaust passage 19. The exhaust valve 20 and the pressure sensor 18 are connected to the control unit 14. The detection result from the pressure sensor 18 is output as a signal to the control unit 14. Based on the detection result detected by the pressure sensor 18, the control unit 14 controls the opening and closing of the regulating valve 13 (details will be described later).

[0030] <Operation of the liquefaction system> Next, we will explain how the liquefaction system works. 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.

[0031] The liquefied gas flows from the liquefied gas 2 through the liquefied gas outlet 2c to the discharge passage 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 passage 4. The predetermined value here is the 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 temperature of 5°C). The liquefied gas that flows into the discharge passage 4 is blocked by the control valve 13, and the liquefied gas continues to accumulate in the liquefier 2. As a result, the liquefied gas in the liquefier 2 becomes supercooled, and the liquefied gas in the discharge passage 4 also becomes supercooled.

[0032] 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 the supercooling temperature according to the type of gas.

[0033] The supercooled liquefied gas stored in tank 5 is supplied via supply passage 16 to external devices such as a transport vehicle (not shown). Once the supercooled liquefied gas has finished flowing through the discharge channel 4, the liquefied gas that has not been sufficiently cooled will flow out of the discharge channel 4, causing the temperature of the liquefied gas in the discharge channel 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 the discharge channel 4. By repeating this process, only supercooled liquefied gas can be supplied to the user side, such as the tank 5 and the transport vehicle located downstream of the tank 5.

[0034] 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.

[0035] Here, the control unit 14 drives the exhaust valve 20 to close the exhaust passage 19 when the detection result from the pressure sensor 18 falls below a 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 when cooled, leading to an increase in pressure inside the liquefier 2 and the tank 5. If a non-condensable gas flows into the liquefier 2 and the detection result by the pressure sensor 18 exceeds a 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 the first pressure equalization passage 17a is exhausted, and the pressure in the liquefier 2, tank 5, and the first pressure equalization passage 17a decreases.

[0036] 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.

[0037] 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 should be installed to make a large detour above the control valve 13. The size of this detour is, for example, as follows: The setting position P 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 install the bypass passage 21 so that its upper end is located above the setting position P. This allows the hydrostatic pressure of the liquefied gas to be used to prevent liquefied gas from unnecessarily flowing out through the bypass passage 21. The bypass channel 21 is at the same pressure as the inside of the liquefier 2 via the second pressure equalization channel 17b. This prevents liquefied gas from unintentionally flowing out through the bypass channel 21 or from being unintentionally suppressed in the flow of liquefied gas through the bypass channel 21.

[0038] 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 supercooler. Thus, the installation of a separate supercooler, which was conventionally provided separately from the liquefier 2, can be omitted, making the liquefaction system 1 simpler and more compact while still allowing for supercooling of the liquefied gas.

[0039] The liquefaction system 1 comprises a tank 5 and a first pressure equalization passage 17a connecting 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.

[0040] 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 entire liquefaction system 1.

[0041] 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.

[0042] 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.

[0043] The present invention is not limited to the embodiments described above, but includes various modifications to the embodiments described above, without departing from the spirit of the invention. For example, in the above-described embodiment, 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 can be any device capable of cooling the liquefaction device 2.

[0044] 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.

[0045] The above-described embodiment explained the case in which a pressure sensor 18 is provided in the first pressure equalization path 17a. However, it 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.

[0046] In the above-described embodiment, the case in which an exhaust passage 19 connected to the first pressure equalization passage 17a is provided was explained. However, the invention is not limited to this, and an exhaust passage 19 may not be provided. In the above-described embodiment, a case was explained in which a second pressure equalization path 17b is provided to connect the bypass path 21 and the first pressure equalization path 17a. However, the invention is not limited to this, and the second pressure equalization path 17b may not be provided.

[0047] In the above-described embodiment, the liquefaction system 1 was described in a case where it is equipped with a tank 5. However, it is not limited to this, and the liquefaction system 1 does not need to be equipped with a tank 5. In this case, the liquefied gas flowing through the discharge passage 4 can be directly supplied to an external device such as a transport vehicle by opening the control valve 13. If a tank 5 is not provided, it is desirable to provide a second pressure equalization passage 17b. [Explanation of Symbols]

[0048] 1…Liquefaction system 2…Liquifier 3...Cooling device 4…Discharge path 5... Tank 13… Regulating valve 14…Control Unit 15…Temperature sensor 17a...First pressure equalization path (pressure equalization path) 17b…Second pressure equalization path (pressure equalization path) 18…Pressure sensor 19… Exhaust passage 20... Exhaust valve 21…Bypass road

Claims

1. A liquefaction device that liquefies gas, A control valve is provided in the discharge passage for discharging the liquefied gas liquefied in the liquefier, A control unit that controls the opening and closing operation of the aforementioned control valve, A temperature sensor that detects at least one of the temperature of the liquefied gas in the liquefier and the temperature of the liquefied gas in the discharge passage, Equipped with, The control unit opens the regulating 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. A liquefaction system characterized by the following features.

2. A tank provided downstream of the control valve in the discharge passage in the flow direction of the liquefied gas, A pressure equalization passage connecting the tank and the liquefier, Equipped with, The liquefaction system according to claim 1.

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

4. The system includes a pressure equalization path that connects the bypass path and the liquefaction device. The liquefaction system according to claim 3.

5. An exhaust valve provided in the pressure equalization path and opened and closed by the control unit, A pressure sensor that detects at least one of the pressure inside the liquefaction unit and the pressure in the pressure equalization path, Equipped with, The control unit opens the exhaust valve when the pressure value detected by the pressure sensor exceeds a predetermined value. The liquefaction system according to claim 2 or 4, characterized by the features described above.

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