Heat exchange system

Abstract

A heat exchange system (1) comprises: a low-temperature flow path (2) through which low-temperature liquefied gas is introduced and flows; a liquefaction object flow path (3) through which gaseous carbon dioxide to be liquefied is introduced and flows; a heat source medium flow path through which water serving as a heat source medium is introduced and flows; a first heat exchanger (10) which vaporizes the low-temperature liquefied gas by performing heat exchange between the low-temperature liquefied gas flowing through the low-temperature flow path (2) and the water flowing through the heat source medium flow path (3); and a second heat exchanger (20) which is provided downstream of the first heat exchanger (10) in the flow direction of the low-temperature liquefied gas and which causes the carbon dioxide to be liquefied by performing heat exchange between the vaporized gas that has been vaporized from the low-temperature liquefied gas in the first heat exchanger (10) and the gaseous carbon dioxide flowing through the liquefaction object flow path (3).

Description

Heat Exchange System

[0001] The present invention relates to a heat exchange system.

[0002] Conventionally, a heat exchange system has been known that liquefies a target gas by utilizing the cold energy of a low-temperature liquefied gas such as liquefied natural gas (hereinafter referred to as LNG) or liquefied hydrogen (see, for example, Patent Document 1). This heat exchange system includes a low-temperature flow path through which LNG (an example of a low-temperature liquefied gas) flows, a target gas flow path through which nitrogen, the target gas, flows, and a heat exchanger disposed across both flow paths to exchange heat between the LNG and the nitrogen. The LNG is heated and vaporized by heat exchange with the nitrogen in the heat exchanger. Meanwhile, the nitrogen, the target gas, is cooled and liquefied by heat exchange with the LNG in the heat exchanger.

[0003] In the heat exchange system shown in Patent Document 1, it is possible to use carbon dioxide instead of nitrogen as the gas to be liquefied. Carbon dioxide liquefaction technology has become increasingly important in recent years as it is also used for liquefying and capturing carbon dioxide amid growing demand for carbon neutrality.

[0004] However, the temperature of the low-temperature liquefied gas used to cool carbon dioxide in the heat exchanger is, for example, -150°C to -160°C, which is significantly lower than the solidification temperature (approximately -56°C) of carbon dioxide at typical pressures (0.52 MPa to 3 MPa) during storage and transportation. Therefore, there is a risk that the carbon dioxide flowing through the gas flow path to be liquefied in the heat exchanger will solidify due to the cold heat of the low-temperature liquefied gas, causing blockage of the flow path.

[0005] Japanese Patent Application Laid-Open No. 2019-168207

[0006] An object of the present invention is to suppress solidification of carbon dioxide due to the cold energy of low-temperature liquefied gas in a heat exchange system that liquefies carbon dioxide using the cold energy of low-temperature liquefied gas.

[0007] A heat exchange system according to one aspect of the present invention is a heat exchange system that liquefies gaseous carbon dioxide by utilizing the cold energy of a low-temperature liquefied gas, and includes a low-temperature flow path through which the low-temperature liquefied gas is introduced and flows, a liquefaction target flow path through which the gaseous carbon dioxide to be liquefied is introduced and flows, a heat source medium flow path through which water is introduced and flows as a heat source medium, a first heat exchanger that vaporizes the low-temperature liquefied gas by performing heat exchange between the low-temperature liquefied gas flowing through the low-temperature flow path and the water flowing through the heat source medium flow path, and a second heat exchanger that is provided downstream of the first heat exchanger in the flow direction of the low-temperature liquefied gas and liquefies the carbon dioxide by performing heat exchange between the vaporized gas vaporized from the low-temperature liquefied gas in the first heat exchanger and the gaseous carbon dioxide flowing through the liquefaction target flow path.

[0008] FIG. 1 is a system diagram showing a schematic configuration of a heat exchange system according to a first embodiment of the present invention. ２ FIG. 2B is a diagram showing a schematic configuration of a liquefier. FIG. 2B is a view taken in the direction of arrow IIB in FIG. 2A. FIG. 3 is a partial cross-sectional view showing a portion of the cross section taken along line III-III in FIG. 2A. FIG. 4 is a TQ diagram showing temperature changes of the working fluid of the heat exchange system, with heat quantity (enthalpy) on the horizontal axis and temperature on the vertical axis. FIG. 5A is a diagram corresponding to FIG. 2A showing Modification 1 of Embodiment 1. FIG. 5B is a diagram taken in the direction of arrow VB in FIG. 5A. FIG. 6 is a diagram corresponding to FIG. 5B showing Modification 2. FIG. 7 is a diagram corresponding to FIG. 1 showing Embodiment 2. FIG. 8 is a diagram corresponding to FIG. 4 showing Embodiment 2. FIG. 9 is a diagram corresponding to FIG. 1 showing another embodiment, showing an example in which the LNG vaporizer is configured as a shell-and-tube heat exchanger. FIG. 10 is a diagram corresponding to FIG. 1 showing another embodiment, showing an example in which the LNG vaporizer is configured as an open rack heat exchanger.

[0009] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0010] 1 is a system diagram that schematically illustrates the configuration of a heat exchange system 1 according to Embodiment 1. The heat exchange system 1 has the function of liquefying gaseous carbon dioxide by utilizing the cold energy of liquefied natural gas (hereinafter referred to as LNG), which is an example of a low-temperature liquefied gas, and vaporizing the LNG to produce natural gas (hereinafter referred to as NG).

[0011] [Overall Configuration of Heat Exchange System] Specifically, the heat exchange system 1 includes a low-temperature flow path 2 through which LNG is introduced and flows, a liquefaction target flow path 3 through which gaseous carbon dioxide to be liquefied is introduced and flows, a heat source medium flow path 4 through which seawater (an example of water) as a heat source medium is introduced and flows, a bypass flow path 5 (described later), an LNG vaporizer 10 that vaporizes the LNG into NG (vaporized gas) by performing heat exchange between the LNG flowing through the low-temperature flow path 2 and the seawater, and a CO liquefaction system that liquefies the carbon dioxide by performing heat exchange between the NG vaporized from the LNG in the LNG vaporizer 10 and the gaseous carbon dioxide flowing through the liquefaction target flow path 3. ２ liquefier 20 and CO ２ The system includes a NG heater 30 that heats the NG discharged from the liquefier 20 to a predetermined required temperature by heat exchange between the NG and seawater flowing through the heat source medium flow path 4, and a controller 100 as a control unit. The LNG vaporizer 10 corresponds to a first heat exchanger, and the CO ２ The liquefier 20 corresponds to the second heat exchanger, and the NG heater 30 corresponds to the third heat exchanger.

[0012] In the flow direction of the LNG in the low-temperature flow path 2, the LNG vaporizer 10 and the CO ２ The liquefier 20 and the NG heater 30 are arranged in this order from the upstream side to the downstream side.

[0013] In the direction of seawater flow in the heat source medium flow path 4, the NG heater 30 and the LNG vaporizer 10 are arranged in this order from the upstream side to the downstream side.

[0014] The bypass flow path 5 is arranged to branch off from the low-temperature flow path 2 and bypass the LNG vaporizer 10. That is, the bypass flow path 5 has an upstream end connected to a portion of the low-temperature flow path 2 upstream of the LNG vaporizer 10, and a downstream end connected to a portion of the low-temperature flow path 2 upstream of the LNG vaporizer 10. ２ and a downstream end connected to the portion between the liquefier 20 and the downstream end.

[0015] The heat exchange system 1 further includes a bypass valve 8 disposed in the bypass flow path 5, a first main valve 6 disposed at the upstream end of the low-temperature flow path 2, and a second main valve 7 (corresponding to a liquefaction target flow rate control valve) disposed at the upstream end of the liquefaction target flow path 3. The first main valve 6, the second main valve 7, and the bypass valve 8 are controlled by a controller 100.

[0016] The controller 100 is configured to be able to switch the operation mode of the heat exchange system 1 between a normal operation mode and a vaporization operation mode by controlling the first main valve 6 and the second main valve 7. In the normal operation mode, both the carbon dioxide liquefaction function and the LNG vaporization function of the heat exchange system 1 are enabled, while in the vaporization operation mode, the carbon dioxide liquefaction function of the heat exchange system 1 is disabled and only the LNG vaporization function is enabled. In the following description, unless otherwise specified, it is assumed that the heat exchange system 1 is in the normal operation mode.

[0017] The controller 100 is also configured to be able to execute bypass control for controlling the opening degree of the bypass valve 8. The operation mode switching control and bypass control executed by the controller 100 will be described in detail later.

[0018] [LNG Vaporizer] In this example, the LNG vaporizer 10 is configured as an intermediate medium type heat exchanger. Specifically, the LNG vaporizer 10 has a shell 11, a number of heat source pipes 12 provided in the shell 11 and into which seawater is introduced, and a number of heat transfer pipes 13 provided in the shell 11 and into which LNG is introduced. A liquid intermediate medium M (propane, in this example, as an example) having a boiling point lower than that of the seawater introduced into the heat source pipes 12 is stored in the lower part of the shell 11. Each of the heat source pipes 12 is disposed so as to be immersed in this liquid intermediate medium M.

[0019] The heat source pipe 12 constitutes a part of the heat source medium flow path 4, and the heat transfer pipe 13 constitutes a part of the low-temperature flow path 2. For simplification, Fig. 1 shows only one heat source pipe 12 and one heat transfer pipe 13. Furthermore, the number of heat source pipes 12 and heat transfer pipes 13 does not necessarily have to be multiple, and they may be one, and their shape may be any shape, such as linear or U-shaped.

[0020] When seawater is introduced into each heat source tube 12 immersed in the intermediate medium M, heat exchange occurs between the liquid intermediate medium M and the seawater. As a result, at least a part of the liquid intermediate medium M evaporates to become intermediate medium gas, which heats the heat transfer tube 13. As a result, the LNG in the heat transfer tube 13 is vaporized to become NG (an example of vaporized gas), and the CO ２ The intermediate medium M is supplied to the liquefier 20. Meanwhile, the intermediate medium gas obtained by heating the LNG is condensed by recovering the cold energy of the LNG, becoming a liquid intermediate medium M, which falls to the bottom of the shell 11. The intermediate medium M circulates within the shell 11, alternately liquefying and gasifying. Thus, the heat source pipe 12 and the shell 11 function as an intermediate medium evaporator E1 that evaporates the intermediate medium M. Furthermore, the heat transfer pipe 13 and the shell 11 function as a liquefied gas vaporizer E2 that vaporizes the LNG.

[0021] The intermediate medium M used in the LNG vaporizer 10 is not limited to propane, but may be, for example, an HFC-based mixed refrigerant.

[0022] [CO ２ Next, referring to FIGS. 2A, 2B, and 3, ２ The details of the liquefier 20 will now be described. ２ Fig. 2B is a view taken along the line IIB in Fig. 2A, showing a schematic configuration of liquefier 20. Fig. 3 is a partial cross-sectional view showing a part of the cross section taken along line III-III in Fig. 2A.

[0023] As shown in FIG. ２The liquefier 20 is configured as a counterflow type heat exchanger that performs heat exchange by circulating carbon dioxide, which is a high-temperature fluid, and NG, which is a low-temperature fluid, in opposite directions. ２ The liquefier 20 is, for example, configured by a microchannel laminated heat exchanger 20L. ２ The liquefier 20 is configured by alternately stacking a number of first metal layers 21 (corresponding to first flow path forming layers) and a number of second metal layers 22 (corresponding to second flow path forming layers). The first metal layer 21 has a number of first flow path sections 21a recessed therein through which non-burning gas flows. These first flow path sections 21a constitute a part of the low-temperature flow path 2. The second metal layer 22 has a number of second flow path sections 22a recessed therein through which carbon dioxide flows. These second flow path sections 22a constitute a part of the liquefaction target flow path 3. The first metal layer 21 and the second metal layer 22 are each configured of a metal plate with excellent heat transfer properties. Heat exchange occurs between the non-burning gas flowing through each first flow path section 21a formed in the first metal layer 21 and the carbon dioxide flowing through each second flow path section 22a formed in the second metal layer 22, thereby heating the non-burning gas and cooling the carbon dioxide. The carbon dioxide is liquefied by being cooled and discharged to the outside of the heat exchange system 1. 3 shows an example of a lamination pattern in which one first metal layer 21 and one second metal layer 22 are alternately laminated, but the present invention is not limited to this. For example, two first metal layers 21 and one second metal layer 22 may be alternately laminated, three first metal layers 21 and one second metal layer 22 may be alternately laminated, or three first metal layers 21 and two second metal layers 22 may be alternately laminated. In other words, the lamination pattern of the first metal layers 21 and the second metal layers 22 may be any pattern. In addition, in the example of FIG. 3, ２ The liquefier 20 is shown as a microchannel type stacked heat exchanger 20L, but is not limited to this and may be configured as, for example, a plate-fin type stacked heat exchanger or the like.

[0024] 2A and 2B , a first inflow header 23 having an inlet 23a and a first outflow header 24 having an outlet 24a are connected to the first flow path portion 21a formed in the first metal layer 21. Furthermore, a second inflow header 25 having an inlet 25a and a second outflow header 26 having an outlet 26a are connected to the second flow path portion 22a formed in the second metal layer 22. NG (strictly speaking, a mixed fluid of NG and LNG passing through a bypass flow path 5 described later) supplied from the LNG vaporizer 10 is distributed to each first flow path portion 21a through the first inflow header 23 (corresponding to the gas inlet portion), flows through each first flow path portion 21a, and then gathers in the first outflow header 24 to form CO ２ On the other hand, the second inlet header 25 is supplied with CO 2 (not shown) from outside the heat exchange system 1. ２ Gaseous carbon dioxide is supplied from a supply source. The supplied gaseous carbon dioxide is distributed to each second flow path section 22a through the second inlet header 25, and after flowing through each second flow path section 22a, is collected in the second outlet header 26 and discharged as a CO ２ It is discharged from the liquefier 20.

[0025] [Configuration of NG Heater] Returning to Fig. 1, the configuration of the NG heater 30 will be described. The NG heater 30 is disposed to the side of the intermediate medium type LNG vaporizer 10 (intermediate medium evaporation section E1 and liquefied gas vaporization section E2). In the example of Fig. 1, the location of the NG heater 30 is to the side of the LNG vaporizer 10, but this is not limited thereto. For example, the NG heater 30 may be disposed above the LNG vaporizer 10 or at a position away from the LNG vaporizer 10. In this example, the NG heater 30 is a shell-and-tube type heat exchanger, and includes a shell 31 and a plurality of heat transfer tubes 32 through which seawater, which is a heat source fluid, flows. ２ The NG discharged from the liquefier 20 flows into the shell 31, and then passes between the plurality of heat transfer tubes 32, where it exchanges heat with the seawater flowing in each of the heat transfer tubes 32, whereby it is heated to a predetermined required temperature (5° C. in this example, for example), and is then discharged outside the shell 31. The plurality of heat transfer tubes 32 (only one is shown in FIG. 1 ) form part of the heat source medium flow path 4, and the space within the shell 31 forms part of the low-temperature flow path 2.

[0026] [Explanation of Basic Operation] Next, the basic operation of the heat exchange system 1 will be described with reference to Figures 1 and 4. Figure 4 is a TQ diagram showing the temperature changes of the working fluids (LNG, carbon dioxide, propane as an intermediate medium, and seawater as a heat source medium) of the heat exchange system 1, with the heat quantity (enthalpy) on the horizontal axis and the temperature on the vertical axis. In this TQ diagram, the heat quantity (enthalpy) increases toward the left side of the horizontal axis, and the temperature increases toward the upper side of the vertical axis. In Figure 4, for simplicity of explanation, the bypass flow rate of LNG flowing through the bypass flow path 5 is assumed to be 0.

[0027] LNG is supplied to the LNG vaporizer 10 (see FIG. 1) at a temperature of −150°C from an LNG supply source provided outside the heat exchange system 1. The LNG supplied to the LNG vaporizer 10 exchanges heat with seawater via propane, which serves as an intermediate medium, thereby increasing its heat content (see FIG. 4). As a result, the LNG is heated from −150°C to −56°C and vaporized to become NG.

[0028] The NG vaporized in the LNG vaporizer 10 is ２ The carbon dioxide flows into the first flow path 21a of the liquefier 20 (see FIG. 1) at −56° C., and exchanges heat with the carbon dioxide flowing through the second flow path 22a, increasing the amount of heat. ２ At the outlet of the liquefier 20, the NG is heated to -15°C (see FIG. 4). The heated NG flows into the shell 31 of the NG heater 30, and heat exchanges with the seawater flowing in the heat transfer tube 32, thereby further increasing the amount of heat and heating the NG. The NG is then finally heated to 5°C (an example of a predetermined required temperature) and is then discharged from the NG heater 30.

[0029] On the other hand, the carbon dioxide to be liquefied is liquefied in a CO ２ CO as a gas at 30°C from a supply source ２ It is supplied to the liquefier 20. ２ The gaseous carbon dioxide supplied to the liquefier 20 is ２The amount of heat gradually decreases by heat exchange with the NG flowing in the first flow path portion 21a of the liquefier 20 (see FIG. 4). Accordingly, the temperature of the carbon dioxide gradually decreases from 30°C and eventually reaches the liquefaction temperature of -17.2°C (under the condition of 2.1 MPa in this example). When the carbon dioxide reaches the liquefaction temperature, it starts to transition from gas to liquid. In this transition section, the carbon dioxide is in a state where gas and liquid coexist, and the temperature remains constant regardless of the decrease in the amount of heat. When the amount of heat of the carbon dioxide further decreases and the transition section ends, all of the carbon dioxide is liquefied, and thereafter the temperature decreases as the amount of heat decreases, and finally the carbon dioxide becomes liquid carbon dioxide at -42°C (an example of a predetermined required temperature) and is released as CO ２ It is discharged from the liquefier 20.

[0030] Seawater, which is the heat source medium, is supplied to the NG heater 30 (see FIG. 1) as seawater at 10°C from a seawater supply source provided outside the heat exchange system 1. The seawater supplied to the NG heater 30 is cooled by the NG flowing inside the shell 31 of the NG heater 30 while flowing inside the heat transfer tube 32, and its temperature is reduced. Thereafter, the seawater flows into the heat source tube 12 of the LNG vaporizer 10, where it receives the cold energy of the intermediate medium M, and its temperature is further reduced, and it is discharged as seawater at 5°C (see FIG. 4).

[0031] Propane is stored at 0° C. in the shell 11 of the LNG vaporizer 10 and repeatedly evaporates due to heat exchange with seawater and condenses due to the cold heat of the NG.

[0032] [Regarding Bypass Control] Incidentally, if the heating capacity of the LNG vaporizer 10 is too high, the temperature of the NG discharged from the LNG vaporizer 10 becomes excessively high. ２ In the liquefier 20, the low-temperature fluid, NG, cannot sufficiently cool the high-temperature fluid, carbon dioxide, and the CO ２ The cooling capacity (i.e., liquefaction capacity) of the carbon dioxide in the liquefier 20 decreases.

[0033] To avoid this problem, in this embodiment, bypass control is executed by the controller 100. In this bypass control, the opening of the bypass valve 8 is controlled to mix the excessively heated NG in the LNG vaporizer 10 with the extremely low-temperature LNG that has passed through the bypass flow path 5, and the mixed fluid is controlled to a predetermined target temperature.

[0034] Specifically, the heat exchange system 1 includes a temperature sensor 9 (corresponding to a temperature detection unit) that detects the temperature of the mixed fluid (hereinafter referred to as mixed NG). In this example, the temperature sensor 9 is connected to the low-temperature flow path 2 at a connection position P1 with the downstream end of the bypass flow path 5, and ２ The temperature sensor 9 is connected between the liquefier 20 and the mixed NG to detect the temperature of the mixed NG. The temperature sensor 9 may be a sensor that detects a temperature correlated with the temperature of the mixed NG (for example, the temperature of the pipe wall through which the mixed NG flows).

[0035] The controller 100 is configured by a computer having a CPU, ROM, and RAM, and is connected to the temperature sensor 9 and the bypass valve 8 via signal lines.

[0036] The controller 100 acquires the temperature detected by the temperature sensor 9 and controls the opening of the bypass valve 8 so that the acquired detected temperature becomes a predetermined target temperature.

[0037] This predetermined target temperature is ２ The target temperature is set in advance so that the temperature of the liquefied carbon dioxide discharged from the second flow path section 22a of the liquefier 20 reaches a predetermined required temperature and so that the carbon dioxide does not solidify on the inner surface of the outlet section (downstream end) of the second flow path section 22a. ２ The temperature of the mixed NG, which is the low-temperature fluid flowing into the liquefier 20, also increases, reducing the cooling capacity of the mixed NG for the carbon dioxide, resulting in problems such as a partial or complete failure to liquefy the carbon dioxide or a temperature of the liquefied carbon dioxide being higher than the required temperature. ２The temperature of the mixed NG, which is the low-temperature fluid flowing into the liquefier 20, also decreases, so the cooling capacity of the mixed NG for the carbon dioxide increases, causing the problem that the temperature of the liquefied carbon dioxide becomes lower than the predetermined required temperature. ２ The inner surface temperature of the outlet of the second flow path section 22a of the liquefier 20 falls below the solidification temperature of carbon dioxide (−56°C in this example), causing a problem of carbon dioxide solidifying at the outlet of the second flow path section 22a. Therefore, in this example, the predetermined target temperature is set in advance to a temperature at which all of the gaseous carbon dioxide is liquefied, the temperature of the liquefied carbon dioxide reaches a predetermined required temperature, and the carbon dioxide does not solidify at the outlet (downstream end) of the second flow path section 22a. The reason why the target temperature is specified as a temperature at which carbon dioxide does not solidify at the outlet of the second flow path section 22a is because the temperature of carbon dioxide is lowest at this outlet in the heat exchange system 1 of this example, making solidification more likely. Note that, in this example, the target temperature is set to −56°C as an example, but is not limited thereto and may be, for example, −50°C to −60°C. That is, the target temperature may be any temperature at which all of the carbon dioxide can be liquefied, the temperature of the liquefied carbon dioxide reaches a predetermined required temperature, and the carbon dioxide does not solidify on the inner surface of the second flow path portion 22 a. In this example, the predetermined target temperature is set to a temperature at which all of the gaseous carbon dioxide is liquefied, but this is not limited thereto, and the predetermined target temperature may be set to a temperature at which only a portion of the gaseous carbon dioxide is liquefied.

[0038] [Regarding Operation Mode Switching Control] Next, the switching control between the normal operation mode and the vaporization operation mode by the controller 100 will be described.

[0039] The controller 100 is connected to an operation panel (not shown) via a signal line. An operator can set the operation mode of the heat exchange system 1 to either a normal operation mode or an evaporation operation mode via the operation panel.

[0040] When the controller 100 receives a setting signal for the normal operation mode from the operation panel, it opens both the first main valve 6 and the second main valve 7 at a predetermined opening degree (an opening degree corresponding to the required flow rate). This allows the heat exchange system 1 to function both as a carbon dioxide liquefaction system and as an LNG vaporization system. On the other hand, when the controller 100 receives a setting signal for the vaporization operation mode from the operation panel, it opens the first main valve 6 at a predetermined opening degree and closes the second main valve 7 fully. This allows the heat exchange system 1 to function both as a carbon dioxide liquefaction system and as an LNG vaporization system. ２ Since gaseous carbon dioxide is no longer supplied to the liquefier 20, the CO ２ The carbon dioxide liquefaction function of the liquefier is disabled, and the heat exchange system 1 functions only as an LNG vaporization system.

[0041] In the normal operation mode, when the bypass control is executed, the controller 100 controls the opening degree of the bypass valve 8 while keeping the bypass valve 8 open. Under predetermined conditions (for example, under conditions where the flow rate of the supplied LNG is constant), the controller 100 controls the opening degree of the second main valve 7 (in other words, the amount of CO2 to be liquefied) to a smaller value. ２ The opening degree of the bypass valve 8 is increased as the flow rate of the gaseous carbon dioxide supplied to the liquefier 20 increases.

[0042] The controller 100 executes bypass control in the vaporization operation mode as well as in the normal operation mode. ２ Since the liquefier 20 is disabled, the problem arises as to how to set the target temperature detected by the temperature sensor 9, which is the control target value. In this example, this target temperature is set to the same temperature as the target temperature in normal operation mode.

[0043] Here, in the vaporization operation mode, CO ２The NG heating capacity of the liquefier 20 is disabled. Therefore, if the target temperature is set to the same temperature as in the normal operation mode, and assuming that the flow rate of LNG is the same, for example, it is necessary to increase the amount of heating by the NG heater 30 in order to raise the temperature of the NG discharged from the NG heater 30 to a predetermined required temperature (5° C. in the example of FIG. 4 ). Therefore, in this embodiment, the maximum heat exchange capacity (maximum heating capacity) of the NG heater 30 is set in advance to be higher than the heat exchange capacity (heating capacity) required in the normal operation mode.

[0044] [Operation and Effect] As described above, the heat exchange system 1 of this embodiment includes the low-temperature flow path 2 through which LNG is introduced and flows, the liquefaction-target flow path 3 through which the gaseous carbon dioxide to be liquefied is introduced and flows, the heat source medium flow path 4 through which seawater as a heat source medium is introduced and flows, the LNG vaporizer 10 that vaporizes the LNG by performing heat exchange between the LNG flowing through the low-temperature flow path 2 and the seawater flowing through the heat source medium flow path 4, and the CO2 vaporizer 10 that is provided downstream of the LNG vaporizer 10 in the flow direction of the LNG and liquefies the carbon dioxide by performing heat exchange between the LNG vaporized from the LNG in the LNG vaporizer 10 and the gaseous carbon dioxide flowing through the liquefaction-target flow path 3. ２ and a liquefier 20.

[0045] According to this configuration, CO ２ The carbon dioxide liquefied in the liquefier 20 is ２ This can prevent solidification in the liquefaction target flow path 3 of the liquefier 20. That is, according to the above configuration, in the LNG vaporizer 10, LNG is heated and vaporized by heat exchange with seawater, which is a heat source medium, to generate NG, and CO ２ In the liquefier 20, the carbon dioxide is liquefied by heat exchange between the heated NG and the carbon dioxide. Therefore, the CO ２ The temperature of the low-temperature fluid (fluid that cools carbon dioxide) flowing into the liquefier 20 can be increased. ２This can prevent the carbon dioxide from solidifying in the liquefaction target flow path 3 of the liquefier 20. As a result, it can prevent the liquefaction target flow path 3 from being blocked by the solidified carbon dioxide.

[0046] Furthermore, with the above configuration, there is no need to prepare a high-temperature refrigerant separate from LNG to directly exchange heat with the carbon dioxide so as not to cool the carbon dioxide excessively, which prevents the configuration of the heat exchange system 1 from becoming complicated and allows the entire system to be constructed inexpensively.

[0047] Furthermore, according to the above configuration, by using seawater instead of carbon dioxide as the heat source medium for the LNG vaporizer 10, it is possible to sufficiently ensure the LNG heating capacity (vaporization capacity) of the LNG vaporizer 10 even if the flow rate of the carbon dioxide to be liquefied is changed.

[0048] In this embodiment, the heat exchange system 1 branches off from the low-temperature flow path 2, bypasses the LNG vaporizer 10, and ２ The system is provided with a bypass flow path 5 capable of supplying the LNG to a location upstream of the liquefier 20, and a bypass valve 8 capable of adjusting the flow rate of the LNG flowing from the low-temperature flow path 2 into the bypass flow path 5.

[0049] According to this configuration, the mixed NG obtained by mixing the low-temperature LNG passing through the bypass flow path 5 and the NG discharged from the LNG vaporizer 10 is CO ２ The bypass flow path 5 is provided with a bypass valve 8, and by controlling the opening degree of the bypass valve 8, the mixing ratio of the LNG that has passed through the bypass flow path 5 and the LNG that has passed through the LNG vaporizer 10 can be adjusted to reduce the CO ２ The temperature of the mixed NG (low-temperature fluid that cools the carbon dioxide) supplied to the liquefier 20 can be easily controlled. ２ The temperature of the liquefied carbon dioxide discharged from the liquefier 20 can be easily controlled.

[0050] In this embodiment, the heat exchange system 1 further includes a controller 100 that controls the bypass valve 8 and a temperature sensor 9 that detects the temperature of the mixed NG, and the controller 100 is configured to execute bypass valve 8 control that controls the bypass valve 8 so that the temperature detected by the temperature sensor 9 becomes a predetermined target temperature.

[0051] According to this configuration, the bypass valve 8 is automatically controlled by the controller 100, so that the temperature of the mixed NG can be controlled to the target temperature with higher precision and the burden on the operator can be reduced compared to when the bypass valve 8 is opened and closed manually.

[0052] In this embodiment, the predetermined target temperature is ２ The temperature of the liquefied carbon dioxide discharged from the liquefier 20 is set to a predetermined required temperature and the CO ２ This temperature is set in advance so that the carbon dioxide does not solidify in the second flow path portion 22 a of the liquefier 20 .

[0053] According to this configuration, CO ２ The temperature of the liquefied carbon dioxide discharged from the liquefier 20 is controlled to a predetermined required temperature. ２ This makes it possible to reliably prevent carbon dioxide from solidifying in the second flow path portion 22a of the liquefier 20.

[0054] In this embodiment, the LNG vaporizer 10 is an intermediate medium type heat exchanger that performs heat exchange between the LNG and the seawater via an intermediate medium.

[0055] According to this configuration, by configuring the LNG vaporizer 10 as an intermediate medium-type heat exchanger, it is possible to vaporize the LNG by utilizing the condensation heat of the intermediate medium. Furthermore, by indirectly exchanging heat via an intermediate medium rather than directly exchanging heat between the LNG and the heat source medium, which have a large temperature difference, it is possible to reduce thermal stress occurring in the heat exchange portion of the LNG vaporizer 10. Therefore, even if the LNG vaporizer 10 vaporizes LNG that is significantly below the solidification temperature of carbon dioxide (e.g., −56°C), the thermal stress resistance performance of the LNG vaporizer 10 can be sufficiently ensured. Furthermore, because there is no direct heat exchange between the LNG, which has a large temperature difference, and the heat source medium, seawater (an example of water), it is possible to prevent freezing of the seawater due to the cold heat of the LNG.

[0056] In this embodiment, CO ２ The liquefier 20 is a stacked heat exchanger 20L that includes a first metal layer 21 having a first flow path portion 21a into which the NG is introduced, and a second metal layer 22 that is stacked on the first metal layer 21 and has a second flow path portion 22a into which the gaseous carbon dioxide is introduced.

[0057] According to this configuration, CO ２ The liquefier 20 can be constructed compactly and robustly.

[0058] In this embodiment, the CO ２ The CO ２ The system further includes a NG heater 30 that heats the NG discharged from the liquefier 20 to a predetermined required temperature by performing heat exchange between the NG and seawater flowing through the heat source medium flow path 4.

[0059] According to this configuration, CO ２ The NG discharged from the liquefier 20 can be heated to a predetermined required temperature by the NG heater 30. This improves the usability of the heat exchange system 1 as an LNG vaporization system. Furthermore, because the heat source of the NG heater 30 is seawater, the heating capacity of the NG heater 30 can be sufficiently ensured even if the flow rate of carbon dioxide to be liquefied changes.

[0060] In addition, this embodiment further includes a second main valve 7 that can adjust the flow rate of the gaseous carbon dioxide introduced into the liquefaction target flow path 3, and the controller 100 is configured to be able to control the second main valve 7 to switch the operating mode of the heat exchange system 1 between a normal operating mode in which the flow rate of carbon dioxide introduced into the liquefaction target flow path 3 is greater than 0, and a vaporization operating mode in which the flow rate of carbon dioxide is 0 and the system only performs the function of vaporizing the LNG.

[0061] According to this configuration, under the control of the controller 100, the operating state of the heat exchange system 1 can be switched between a normal operation mode and a vaporization operation mode. In the normal operation mode, both the carbon dioxide liquefaction function and the LNG vaporization function are performed, and in the vaporization operation mode, the carbon dioxide flow rate is zero, so the carbon dioxide liquefaction function is disabled and only the LNG vaporization function is performed. Therefore, the operating mode of the heat exchange system 1 can be flexibly switched between when there is a request for carbon dioxide liquefaction and when there is no request for carbon dioxide liquefaction. This improves the usability of the heat exchange system 1 depending on whether there is a request for carbon dioxide liquefaction.

[0062] The predetermined target temperature when the bypass valve 8 control is executed in the normal operation mode and the vaporization operation mode is set to the same temperature.

[0063] With this configuration, even if the operation mode is frequently switched between the vaporization operation mode and the normal operation mode, the target temperature when controlling the bypass valve is the same in each operation mode, making control easier and reducing the calculation load on the controller 100.

[0064] In this embodiment, CO ２ The liquefier 20 is composed of a counterflow heat exchanger.

[0065] According to this configuration, CO ２ By configuring the liquefier 20 as a counterflow heat exchanger, CO ２The discharge temperature of the carbon dioxide cooled and liquefied in the liquefier 20 can be set as low as possible. Here, if the discharge temperature of the carbon dioxide after liquefaction is set low, the problem of the carbon dioxide solidifying described above is likely to occur. Therefore, as described above, the LNG is heated and vaporized in advance by the LNG vaporizer 10, and then the CO ２ The configuration of the present disclosure feeding the liquefier 20 is particularly useful.

[0066] (Modification 1) Fig. 5A is a view corresponding to Fig. 2A showing Modification 1, and Fig. 5B is a view taken in the direction of arrow VB in Fig. 5A. In this modification, ２ The difference from the first embodiment is that the liquefier 20 is configured from a plurality of stacked heat exchangers 20L. In Figures 5A and 5B, the same components as those in Figures 2A and 2B are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0067] Specifically, in this modification, CO ２ The liquefier 20 is configured by arranging four stacked heat exchangers 20L in parallel. However, the number of stacked heat exchangers 20L is not limited to four.

[0068] The gaseous carbon dioxide inlet ports 25a of the four stacked heat exchangers 20L are each connected to one inlet-side collecting pipe 203 via four inlet-side branch pipes (not shown). The liquefied carbon dioxide outlet ports 26a of the four stacked heat exchangers 20L are each connected to one outlet-side collecting pipe 204 via four outlet-side branch pipes (not shown). The inlet-side collecting pipe 203 and the outlet-side collecting pipe 204 form part of the liquefaction target flow path 3. The gaseous carbon dioxide that flows into the inlet-side collecting pipe 203 is distributed to the four stacked heat exchangers 20L via each inlet-side branch pipe. After being liquefied in each stacked heat exchanger 20L, the distributed gaseous carbon dioxide passes through four outlet-side branch pipes (not shown) to join in the outlet-side collecting pipe 204 and further flow downstream.

[0069] 5B , the mixed NG inlets 23 a of the four stacked heat exchangers 20L are each connected to one inlet-side collecting pipe section 201 via four inlet-side branch pipes (not shown). The NG outlets 24 a of the four stacked heat exchangers 20L are each connected to one outlet-side collecting pipe section 202 via four outlet-side branch pipes (not shown). The inlet-side collecting pipe section 201 and the outlet-side collecting pipe section 202 constitute a part of the low-temperature flow path 2.

[0070] The downstream end of the bypass flow path 5 is connected to the upstream side of the inlet collecting pipe 201 in the low-temperature flow path 2. Therefore, the LNG flowing through the bypass flow path 5 is merged with NG upstream of the inlet collecting pipe 201 and mixed, and the mixed NG after merging flows into the inlet collecting pipe 201.

[0071] 5B, the mixed NG that has flowed into the inlet-side collecting pipe section 201 is distributed to the four stacked heat exchangers 20L via the inlet-side branch pipes. The distributed mixed NG is heated in each stacked heat exchanger 20L and becomes NG, and then passes through four outlet-side connecting pipes (not shown) to join in the outlet-side collecting pipe section 202 and flow further downstream.

[0072] As described above, in this modification 1, CO ２ The liquefier 20 is configured by a plurality of stacked heat exchangers 20L, so that the CO ２ The cooling capacity of the carbon dioxide in the liquefier 20 can be increased as much as possible.

[0073] Furthermore, the heat exchange system 1 of the first modification is ２ Except for the fact that the liquefier 20 is configured by four stacked heat exchangers 20L, the configuration is the same as that of the first embodiment. Therefore, the same effects as those of the first embodiment can be obtained.

[0074] (Modification 2) Fig. 6 is a view equivalent to Fig. 5B showing Modification 2. Modification 2 differs from Modification 1 in that the bypass flow path 5 is directly connected to each of the stacked heat exchangers 20L. In Fig. 6, the same components as those in Fig. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

[0075] That is, in the heat exchange system 1 of this modified example, the downstream end of the bypass flow path 5 branches into four paths that are connected to each of the stack-type heat exchangers 20L. Specifically, the bypass flow path 5 has one main flow path portion 5a and four branch flow path portions 5b that branch from the main flow path portion 5a and are connected to each of the stack-type heat exchangers 20L. The downstream end of each of the branch flow path portions 5b is connected to the first inlet header 23 of each of the stack-type heat exchangers 20L so that LNG can be supplied to the space within the first inlet header 23.

[0076] Although not shown, in this example, the temperature sensor 9 is disposed so as to be able to measure the temperature of the first inflow header 23, which is the mixing point of NG and LNG.

[0077] According to the heat exchange system 1 of the present modified example 2 configured as above, the mixed NG can be supplied evenly to each of the stacked heat exchangers 20L, compared to the above-described modified example 1.

[0078] That is, in the heat exchange system 1 of the above-described first modification, the mixing position (confluence position) of the NG flowing through the low-temperature flow path 2 and the LNG that has passed through the bypass flow path 5 is set upstream of the inlet-side collecting pipe section 201. Therefore, if the mixed NG becomes a gas-liquid two-phase flow after mixing at the mixing position, there is a risk that the flow rate of the mixed NG distributed to each stacked-type heat exchanger 20L will be uneven.

[0079] In contrast, in the heat exchange system 1 of this modified example, the mixing position (confluence position) of the NG flowing through the low-temperature flow path 2 and the LNG passing through the bypass flow path 5 is set at the NG inlet portion of the stacked heat exchanger 20L (the space within the first inlet header 23, as an example in this example). Therefore, the NG and LNG can be individually distributed to each stacked heat exchanger 20L and mixed within each stacked heat exchanger 20L. Therefore, unlike the first modified example, there is no bias in the flow rate of the mixed NG flowing into each stacked heat exchanger 20L. This uniformizes the amount of heat exchanged between the carbon dioxide and the mixed NG in each stacked heat exchanger 20L, thereby suppressing temperature variations in the liquefied carbon dioxide discharged from each stacked heat exchanger 20L. This in turn prevents the risk of the carbon dioxide dropping below its solidification temperature due to temperature variations. Therefore, the problem of flow path blockage caused by the solidification of carbon dioxide can be avoided.

[0080] (Embodiment 2) Fig. 7 is a diagram corresponding to Fig. 1 showing embodiment 2, and Fig. 8 is a diagram corresponding to Fig. 4 showing embodiment 2. This embodiment differs from embodiment 1 in that the liquefaction temperature of carbon dioxide to be liquefied is high, so the NG is heated to a predetermined required temperature without providing an NG heater 30.

[0081] That is, in this embodiment, as shown in FIG. ２ The pressure of the gaseous carbon dioxide supplied to the liquefier 20 is 4 MPa, which is set higher than the 2.1 MPa in the heat exchange system 1 of the first embodiment. As a result, in the heat exchange system 1 of the present embodiment, the liquefaction temperature of carbon dioxide is 5.6°C, which is higher than the liquefaction temperature of carbon dioxide of -17.2°C in the first embodiment. When the liquefaction temperature of carbon dioxide is high like this, the CO ２ In the liquefier 20, the temperature of the NG can be heated to a predetermined required temperature (for example, 5°C).

[0082] As described above, in this embodiment, since there is no need to provide the NG heater 30, the heat exchange system 1 can be configured at low cost.

[0083] The heat exchange system 1 of this embodiment has the same configuration as that of the first embodiment except that it does not have the NG heater 30. Therefore, the same effects as those of the first embodiment can be obtained.

[0084] Other Embodiments Although the heat exchange system 1 according to the embodiment of the present invention has been described above, the present invention is not limited to this.

[0085] (1) In other words, in each of the above-described embodiments and modifications, the bypass control is executed in both the normal operation mode and the vaporization operation mode. However, this is not limited to this. That is, the bypass valve control may be executed with the bypass valve 8 open in the normal operation mode, while the bypass valve 8 may be fully closed in the vaporization operation mode to prevent the bypass valve control from being executed. With this configuration, the bypass valve control is executed by adjusting the opening degree of the bypass valve 8 in the normal operation mode, whereas the bypass valve 8 is controlled to be fully closed in the vaporization operation mode. Therefore, in the vaporization operation mode, the heat of the NG heated by the LNG vaporizer 10 is not wasted by mixing with the LNG that has passed through the bypass flow path 5. Therefore, in the vaporization operation mode, the temperature of the NG flowing into the NG heater 30 as the third heat exchanger can be increased compared to the above-described embodiment, thereby reducing the risk of seawater freezing due to the cold heat of the NG.

[0086] (2) Furthermore, in each of the above-described embodiments and modified examples, a bypass flow path 5 and a bypass valve 8 are provided, but this is not limited to this, and the heat exchange system 1 may be configured without the bypass flow path 5 and the bypass valve 8.

[0087] (3) Furthermore, in each of the above embodiments and variants, the operating mode of the heat exchange system 1 is configured to be switchable between a normal operating mode and an evaporation operating mode, but it is not necessarily required to have two modes, and for example, it may have only a normal operating mode.

[0088] (4) In each of the above embodiments and variant examples, an intermediate medium type heat exchanger has been described as an example of the LNG vaporizer 10 (first heat exchanger), but this is not limited to this. For example, a shell-and-tube type heat exchanger (see, for example, Patent Publication No. 2020-70922) or an open rack type heat exchanger (see, for example, Patent Publication No. 2021-148206) may be adopted.

[0089] FIG. 9 is a diagram equivalent to FIG. 1 , illustrating an example in which a shell-and-tube heat exchanger is used as the LNG vaporizer 10. In this example, the LNG vaporizer 10 includes a shell 14 into which water, a heat source medium, is introduced and a number of heat transfer tubes 15 disposed within the shell 14 and into which LNG is introduced. The space within the shell 14 constitutes a part of the heat source medium flow path 4, and the heat transfer tubes 15 constitute a part of the low-temperature flow path 2. The LNG introduced into the heat transfer tube 15 is heated and vaporized by heat exchange with the water flowing within the shell. The heat transfer tube 15 may be a single tube, and may have any shape, such as a straight or U-shape. The water may be any type of water, such as glycol water, industrial water, or seawater. However, from the viewpoint of improving corrosion resistance, glycol water or industrial water is preferably used.

[0090] 10 is a view equivalent to FIG. 1 showing an example in which an open rack-type heat exchanger is used as the LNG vaporizer 10. In this example, the LNG vaporizer 10 is configured to include a large number of heat transfer tubes 16 extending vertically and adjacent to each other in the horizontal direction, a lower-end manifold 17 connecting the lower ends of the large number of heat transfer tubes 16, and an upper-end manifold 18 connecting the upper ends of the large number of heat transfer tubes 16. After being supplied to the lower-end manifold 17, the LNG is distributed into each heat transfer tube 16 and flows upward, exchanging heat with water to become NG, which then gathers in the upper-end manifold 18 and is released as CO ２The LNG is discharged to the liquefier 20. Meanwhile, water, which is the heat source medium, is supplied to a box-shaped trough (not shown) that is open to the top and provided above the large number of heat transfer tubes 16, overflows from the trough, and flows downward along the surfaces of the large number of heat transfer tubes 16. The LNG receives heat from the water via the large number of heat transfer tubes 16 and is vaporized. Each heat transfer tube 16 functions as a part of the low-temperature flow path 2. If the required outlet temperature of the NG discharged from the LNG vaporizer 10 is low, the NG heater 30 serving as the third heat exchanger does not need to be provided. The water may be any water, such as glycol water, industrial water, or seawater.

[0091] (5) In the above-described embodiments and modifications, LNG (liquefied natural gas) is used as an example of liquefied gas. However, the present invention is not limited to this. For example, LH ２ (liquefied hydrogen) or the like.

[0092] (6) In the above-described embodiments and modifications, seawater has been described as an example of a heat source medium. However, the present invention is not limited to this, and may be, for example, industrial water or glycol water.

[0093] (7) In each of the above embodiments and modifications, CO ２ Although the stacked heat exchanger 20L has been described as an example of the liquefier 20 (second heat exchanger), the liquefier 20 is not limited to this and may be, for example, a shell-and-tube heat exchanger.

[0094] (8) In each of the above embodiments and variants, a shell-and-tube type heat exchanger has been described as an example of the NG heater 30 (third heat exchanger), but this is not limited to this, and any other type, such as a stacked type heat exchanger, may be adopted.

[0095] (9) In the above embodiments and modifications, propane has been described as an example of the intermediate medium. However, the intermediate medium is not limited to this and may be, for example, ammonia or fluorocarbon.

[0096] (10) In each of the above embodiments and modifications, it is not necessary that 100% of the gaseous carbon dioxide supplied to the liquefaction target flow path 3 is supplied as carbon dioxide, and for example, the gaseous carbon dioxide may contain components with low melting points, such as nitrogen, as impurities. In other words, the fluid supplied to the liquefaction target flow path 3 may be any fluid that contains carbon dioxide.

[0097] (11) In each of the above embodiments and modifications, CO ２ The temperature of the NG at the inlet of the low-temperature flow path 2 (first flow path section 21a) of the liquefier 20 is set to a temperature at which all of the carbon dioxide in the gas supplied to the liquefaction target flow path 3 can be liquefied, but this is not limited to this and it may be set to a temperature at which only a portion of the carbon dioxide can be liquefied.

[0098] (12) In each of the above embodiments and modifications, CO ２ The temperature of the NG at the inlet of the low-temperature flow path 2 (first flow path section 21a) of the liquefier 20 is set to −56° C., but is not limited to this and may be, for example, −50° C. to −60° C. ２ The temperature of the NG flowing into the liquefier 20 is ２ A temperature at which the liquefaction of carbon dioxide in the liquefier 20 is not hindered (a temperature at which part or all of the carbon dioxide can be liquefied), ２ Any temperature may be used as long as the temperature of the carbon dioxide discharged from the liquefier 20 is the predetermined required temperature and the carbon dioxide does not solidify.

[0099] The above-described specific embodiments mainly include inventions having the following configurations.

[0100] A heat exchange system according to one aspect of the present invention is a heat exchange system that liquefies gaseous carbon dioxide by utilizing the cold energy of a low-temperature liquefied gas, and includes a low-temperature flow path through which the low-temperature liquefied gas is introduced and flows, a liquefaction target flow path through which the gaseous carbon dioxide to be liquefied is introduced and flows, a heat source medium flow path through which water is introduced and flows as a heat source medium, a first heat exchanger that vaporizes the low-temperature liquefied gas by performing heat exchange between the low-temperature liquefied gas flowing through the low-temperature flow path and the water flowing through the heat source medium flow path, and a second heat exchanger that is provided downstream of the first heat exchanger in the flow direction of the low-temperature liquefied gas and liquefies the carbon dioxide by performing heat exchange between the vaporized gas vaporized from the low-temperature liquefied gas in the first heat exchanger and the gaseous carbon dioxide flowing through the liquefaction target flow path.

[0101] This configuration can prevent carbon dioxide liquefied in the second heat exchanger from solidifying in the liquefaction-target flow path of the second heat exchanger. Specifically, the first heat exchanger heats and vaporizes the low-temperature liquefied gas through heat exchange with water, which serves as a heat source medium, to generate a vaporized gas warmer than the low-temperature liquefied gas. In the second heat exchanger, heat exchange occurs between the heated vaporized gas as a low-temperature fluid and carbon dioxide as a high-temperature fluid, thereby liquefying the carbon dioxide. Therefore, the temperature of the low-temperature fluid (fluid that cools the carbon dioxide) flowing into the second heat exchanger can be increased compared to conventional heat exchange systems that do not include a first heat exchanger. This prevents carbon dioxide from solidifying in the liquefaction-target flow path of the second heat exchanger due to the cold energy of the low-temperature fluid. Consequently, the liquefaction-target flow path can be prevented from being blocked by solidified carbon dioxide.

[0102] Furthermore, with the above configuration, there is no need to prepare a high-temperature refrigerant that exchanges heat directly with the carbon dioxide, separate from the low-temperature liquefied gas, in order to prevent excessive cooling of the carbon dioxide. This prevents the configuration of the heat exchange system from becoming complicated, and the entire system can be constructed inexpensively.

[0103] Furthermore, according to the above configuration, by using water instead of carbon dioxide as the heat source medium for the first heat exchanger, it is possible to ensure sufficient heating capacity (vaporization capacity) of the low-temperature liquefied gas in the first heat exchanger even if the flow rate of carbon dioxide, which is the target of liquefaction, is changed.

[0104] In a second invention, in the first invention, it is preferable that the second heat exchanger has a gas inlet portion which serves as an inlet for the vaporized gas, and is equipped with a bypass flow path which branches off from the low-temperature flow path, bypasses the first heat exchanger, and is capable of supplying the low-temperature liquefied gas to the gas inlet portion of the second heat exchanger or a portion in the low-temperature flow path upstream of the second heat exchanger, and a bypass valve which is capable of adjusting the flow rate of the low-temperature liquefied gas flowing from the low-temperature flow path into the bypass flow path.

[0105] According to this configuration, the low-temperature liquefied gas that has passed through the bypass flow path and the vaporized gas discharged from the first heat exchanger are joined together and supplied to the second heat exchanger at a temperature lower than that of the vaporized gas discharged from the first heat exchanger. Here, since the bypass flow path is provided with a bypass valve, by controlling the opening degree of the bypass valve, the flow rate ratio between the low-temperature liquefied gas that has passed through the bypass flow path and the vaporized gas discharged from the first heat exchanger can be adjusted, thereby easily controlling the temperature of the mixed fluid (low-temperature fluid that cools the carbon dioxide) supplied to the second heat exchanger. As a result, the temperature of the liquefied carbon dioxide discharged from the second heat exchanger can be easily controlled.

[0106] In a third invention, in the second invention, it is preferable that the system further includes a control unit that controls the bypass valve and a temperature detection unit that detects the temperature of the mixed fluid of the vaporized gas vaporized in the first heat exchanger and the low-temperature liquefied gas that has passed through the bypass flow path, or a temperature correlated to that temperature, and the control unit is configured to perform bypass valve control that controls the bypass valve so that the temperature detected by the temperature detection unit becomes a predetermined target temperature.

[0107] According to this configuration, the bypass valve is automatically controlled by the control unit, so that the temperature of the mixed fluid can be more easily controlled than when the bypass valve is opened and closed manually.

[0108] In a fourth invention, in the third invention, it is preferable that the predetermined target temperature is a temperature that is set in advance so that the temperature of the liquefied carbon dioxide discharged from the second heat exchanger becomes a predetermined required temperature and so that the carbon dioxide does not solidify on the inner surface of the liquefaction target flow path of the second heat exchanger.

[0109] With this configuration, it is possible to reliably prevent the carbon dioxide from solidifying in the liquefaction target flow path of the second heat exchanger while controlling the temperature of the liquefied carbon dioxide discharged from the second heat exchanger to a predetermined required temperature.

[0110] In a fifth invention, in any one of the first to fourth inventions, it is preferable that the first heat exchanger is an intermediate medium type heat exchanger that performs heat exchange between the low-temperature liquefied gas and the water via an intermediate medium.

[0111] According to this configuration, by configuring the first heat exchanger as an intermediate medium-type heat exchanger, the low-temperature liquefied gas can be vaporized using the condensation heat of the intermediate medium. That is, according to this configuration, heat exchange is not performed directly between the low-temperature liquefied gas and the heat source medium, water, which have a large temperature difference, but rather indirectly via the intermediate medium. This reduces thermal stress occurring in the heat exchange portion of the first heat exchanger. Therefore, even when the first heat exchanger vaporizes a low-temperature liquefied gas (e.g., LNG or liquid hydrogen) that is significantly below the solidification temperature of carbon dioxide (e.g., −56°C), the thermal stress resistance of the first heat exchanger can be sufficiently ensured. Furthermore, because direct heat exchange does not occur between the low-temperature liquefied gas and the heat source medium, water, which have a large temperature difference, freezing of the water due to the cold heat of the low-temperature liquefied gas can be prevented.

[0112] In a sixth invention, in any one of the first to fifth inventions, it is preferable that the second heat exchanger is a stacked heat exchanger having a first flow path forming layer having a flow path portion into which the vaporized gas is introduced, and a second flow path forming layer stacked on the first flow path forming layer and having a flow path portion into which the gaseous carbon dioxide is introduced.

[0113] According to this configuration, the second heat exchanger can be made compact and strong.

[0114] In the seventh invention, in any one of the first to sixth inventions, it is preferable that the system further comprises a third heat exchanger that is arranged downstream of the second heat exchanger in the flow direction of the vaporized gas and heats the vaporized gas to a predetermined required temperature by performing heat exchange between the vaporized gas discharged from the second heat exchanger and water flowing through the heat source medium flow path.

[0115] According to this configuration, the vaporized gas discharged from the second heat exchanger can be heated to a predetermined required temperature by the third heat exchanger. This improves the usability of the heat exchange system as a vaporized gas generation system. Furthermore, because the heat source of the third heat exchanger is water, sufficient heating capacity by the third heat exchanger can be ensured even if the flow rate of the carbon dioxide to be liquefied is changed.

[0116] In an eighth invention, in any one of the first to seventh inventions, it is preferable that the system further includes a liquefaction target flow rate adjustment valve that can adjust the flow rate of the gaseous carbon dioxide introduced into the liquefaction target flow path, and that the control unit is configured to be able to control the liquefaction target flow rate adjustment valve to switch the operating mode of the heat exchange system between a normal operating mode in which the flow rate of carbon dioxide introduced into the liquefaction target flow path is greater than 0, and a vaporization operating mode in which the flow rate of carbon dioxide is 0 and the system only performs the function of vaporizing the low-temperature liquefied gas.

[0117] According to this configuration, the control unit can switch the operating state of the heat exchange system between a normal operation mode and a vaporization operation mode. In the normal operation mode, both the carbon dioxide liquefaction function and the low-temperature liquefied gas vaporization function are performed, and in the vaporization operation mode, the carbon dioxide flow rate is zero, so the carbon dioxide liquefaction function is disabled and only the low-temperature liquefied gas vaporization function is performed. Therefore, the operating mode of the heat exchange system can be flexibly switched between when there is a demand for carbon dioxide liquefaction and when there is no demand for carbon dioxide liquefaction. This improves the usability of the heat exchange system depending on whether there is a demand for carbon dioxide liquefaction.

[0118] In a ninth invention, in the eighth invention, it is preferable that the control unit is configured to set the predetermined target temperature when executing the bypass valve control in the normal operation mode and the evaporation operation mode to the same temperature.

[0119] With this configuration, even if the operation mode is frequently switched between the vaporization operation mode and the normal operation mode, the target temperature when controlling the bypass valve is the same in each operation mode, making control easier and reducing the calculation load on the control unit.

[0120] In a tenth invention, in the eighth or ninth invention, it is preferable that the control unit is configured to perform the bypass valve control by adjusting the opening degree of the bypass valve in the normal operation mode, while in the evaporation operation mode, the control unit is configured to fully close the bypass valve and not perform the bypass valve control.

[0121] According to this configuration, in the normal operation mode, the bypass valve control is performed by adjusting the opening degree of the bypass valve, whereas in the vaporization operation mode, the bypass valve is controlled to a fully closed state. Therefore, in the vaporization operation mode, the heat of the vaporized gas heated in the first heat exchanger is not wasted by mixing with the low-temperature liquefied gas via the bypass flow path. Therefore, in the vaporization operation mode, the temperature of the vaporized gas flowing into the third heat exchanger can be made higher than in the ninth invention, thereby reducing the risk of water freezing due to the cold energy of the vaporized gas.

[0122] In an eleventh aspect of the present invention, in any one of the first to tenth aspects of the present invention, the second heat exchanger is preferably a counterflow heat exchanger.

[0123] According to this configuration, by configuring the second heat exchanger as a counterflow heat exchanger, it is possible to lower the temperature of the liquefied carbon dioxide discharged from the second heat exchanger compared to when it is configured as a parallel flow heat exchanger. Here, if the temperature of the liquefied carbon dioxide is set low, the problem of solidification of the carbon dioxide described above is more likely to occur, so the configuration of this invention (first invention) is particularly useful.

Claims

1. A heat exchange system that liquefies gaseous carbon dioxide by utilizing the cold energy of a low-temperature liquefied gas, comprising: a low-temperature flow path into which the low-temperature liquefied gas is introduced and flows; a liquefaction target flow path into which the gaseous carbon dioxide to be liquefied is introduced and flows; a heat source medium flow path into which water is introduced and flows as a heat source medium; a first heat exchanger that vaporizes the low-temperature liquefied gas by exchanging heat between the low-temperature liquefied gas flowing through the low-temperature flow path and the water flowing through the heat source medium flow path; and a second heat exchanger that is provided downstream of the first heat exchanger in the flow direction of the low-temperature liquefied gas and liquefies the carbon dioxide by exchanging heat between the vaporized gas vaporized from the low-temperature liquefied gas in the first heat exchanger and the gaseous carbon dioxide flowing through the liquefaction target flow path.

2. A heat exchange system according to claim 1, wherein the second heat exchanger has a gas inlet portion serving as an inlet for the vaporized gas; a bypass flow path that branches off from the low-temperature flow path and bypasses the first heat exchanger, and is capable of supplying the low-temperature liquefied gas to the gas inlet portion of the second heat exchanger or to a portion of the low-temperature flow path upstream of the second heat exchanger; and a bypass valve that is capable of adjusting the flow rate of the low-temperature liquefied gas flowing from the low-temperature flow path into the bypass flow path.

3. A heat exchange system according to claim 2, further comprising a control unit that controls the bypass valve, and a temperature detection unit that detects the temperature of a mixed fluid of the vaporized gas vaporized in the first heat exchanger and the low-temperature liquefied gas that has passed through the bypass flow path, or a temperature that correlates with that temperature, wherein the control unit is configured to execute bypass valve control that controls the bypass valve so that the temperature detected by the temperature detection unit becomes a predetermined target temperature.

4. A heat exchange system as described in claim 3, wherein the predetermined target temperature is a temperature that is set in advance so that the temperature of the liquefied carbon dioxide discharged from the second heat exchanger becomes a predetermined required temperature and so that the carbon dioxide does not solidify on the inner surface of the liquefaction target flow path of the second heat exchanger.

5. A heat exchange system according to claim 1, wherein the first heat exchanger is an intermediate medium type heat exchanger that exchanges heat between the low-temperature liquefied gas and the water via an intermediate medium.

6. A heat exchange system according to claim 1, wherein the second heat exchanger is a laminated heat exchanger having a first flow path forming layer having a flow path portion into which the vaporized gas is introduced, and a second flow path forming layer laminated on the first flow path forming layer and having a flow path portion into which the gaseous carbon dioxide is introduced.

7. A heat exchange system as described in claim 4, further comprising a third heat exchanger that is provided downstream of the second heat exchanger in the flow direction of the vaporized gas and that heats the vaporized gas to a predetermined required temperature by performing heat exchange between the vaporized gas discharged from the second heat exchanger and water flowing through the heat source medium flow path.

8. A heat exchange system as claimed in claim 7, further comprising a liquefaction target flow rate adjustment valve capable of adjusting the flow rate of the gaseous carbon dioxide introduced into the liquefaction target flow path, and the control unit is configured to be able to control the liquefaction target flow rate adjustment valve to switch the operation mode of the heat exchange system between a normal operation mode in which the flow rate of carbon dioxide introduced into the liquefaction target flow path is greater than 0, and a vaporization operation mode in which the flow rate of carbon dioxide is 0 and the system only functions to vaporize the low-temperature liquefied gas.

9. A heat exchange system according to claim 8, wherein the control unit is configured to set the predetermined target temperature when executing the bypass valve control in the normal operation mode and the evaporation operation mode to the same temperature.

10. A heat exchange system according to claim 8, wherein the control unit is configured to execute the bypass valve control by adjusting the opening degree of the bypass valve in the normal operation mode, and to fully close the bypass valve and not execute the bypass valve control in the evaporation operation mode.

11. A heat exchange system according to any one of claims 1 to 10, wherein the second heat exchanger is a counter-flow heat exchanger.

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