Heat exchange system

Abstract

A heat exchange system (1) comprises: a first heat exchanger (6) that is disposed astride a low-temperature flow path (2) and a liquefaction target flow path (3), and that performs heat exchange, through an intermediate medium (M), between a low-temperature liquefied gas flowing through the low-temperature flow path (2) and carbon dioxide flowing through the liquefaction target flow path (3), thereby vaporizing the low-temperature liquefied gas and liquefying the carbon dioxide; a temperature detection unit (15) that detects the temperature of the intermediate medium (M) or a temperature correlated with this temperature; flow rate adjustment units (11, 12) capable of adjusting the flow rate of the low-temperature liquefied gas and / or the carbon dioxide supplied to the first heat exchanger (6); and a control unit (10) that controls the flow rate adjustment units (11, 12) so that the temperature detected by the temperature detection unit (15) reaches a predetermined target temperature. The predetermined target temperature is a temperature at which carbon dioxide is not solidified on the inner surface of the liquefaction target flow path (3).

Description

Heat Exchange System

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

[0002] BACKGROUND ART Conventionally, a heat exchange system is known that liquefies carbon dioxide by utilizing the cold energy of a low-temperature liquefied gas such as liquefied natural gas (hereinafter referred to as LNG) or liquefied hydrogen.

[0003] One known example of this type of heat exchange system is one that includes an intermediate medium-type heat exchanger (see, for example, Patent Document 1). This heat exchanger includes a shell that stores a liquid intermediate medium, a heat source pipe through which a heating medium flows, and a heat transfer pipe through which a low-temperature liquefied gas, the medium to be heated, flows. The heat source pipe is immersed in the intermediate medium in the shell. In the heat exchanger, the intermediate medium is evaporated using the heat retained in the heating medium flowing through the heat source pipe, and the evaporated intermediate medium is condensed by heat exchange with the liquefied gas in the heat transfer pipe. The condensation heat (heat generated by the condensation of the intermediate medium) is used to vaporize the low-temperature liquefied gas.

[0004] Incidentally, in the heat exchange system shown in Patent Document 1, it is conceivable to use gaseous carbon dioxide as the heating medium. In this case, the low-temperature liquefied gas is vaporized via the intermediate medium by the heat contained in the carbon dioxide, and the carbon dioxide is liquefied by the cold heat of the intermediate medium. Carbon dioxide liquefaction technology has become increasingly important in recent years as it is also used for liquefying and recovering carbon dioxide amid growing demand for carbon neutrality.

[0005] However, in conventional intermediate medium heat exchangers, the temperature of the intermediate medium is determined by the balance between the vaporization capacity (evaporation capacity) of the intermediate medium due to the carbon dioxide flowing through the heat source pipe and the condensation capacity of the intermediate medium due to the low-temperature liquefied gas flowing through the heat transfer pipe. Therefore, if the temperature of the intermediate medium determined by this process is lower than the solidification temperature of carbon dioxide (-56°C under typical storage and transportation pressures), there is a risk that the carbon dioxide will solidify due to the cold heat of the intermediate medium.

[0006] Furthermore, in the conventional intermediate medium-type heat exchanger, the heated medium is often LNG and the heating medium (heat source medium) is water. In such cases, the water heating medium only needs to be at a temperature where it will not freeze. In other words, it is only necessary to note that the lower limit of the temperature range of the water after heat exchange is a temperature where it will not freeze, and the upper limit does not need to be considered. However, as described above, when vaporizing the heated medium LNG and simultaneously liquefying the heated medium carbon dioxide, carbon dioxide has a narrower temperature range in which it can exist as a liquid than water. Therefore, it is necessary to provide sufficient cold to liquefy the gaseous carbon dioxide while ensuring that not only the lower limit but also the upper limit of the temperature range of the carbon dioxide after heat exchange is below a predetermined temperature. Therefore, if the temperature of the intermediate medium is too high, the temperature of the carbon dioxide will exceed the predetermined temperature at which it can exist as a liquid, resulting in poor liquefaction of the carbon dioxide.

[0007] Patent No. 5409440

[0008] The present invention aims to suppress solidification of carbon dioxide due to excessive cooling and poor liquefaction due to insufficient cooling of carbon dioxide in a heat exchange system that liquefies carbon dioxide using the cold energy of a low-temperature liquefied gas.

[0009] a first heat exchanger arranged across the low-temperature flow path and the flow path to be liquefied, and performing heat exchange via an intermediate medium between the low-temperature liquefied gas flowing through the low-temperature flow path and the carbon dioxide flowing through the flow path to be liquefied, thereby vaporizing the low-temperature liquefied gas and liquefying the carbon dioxide; a temperature detection unit that detects the temperature of the intermediate medium or a temperature correlated to that temperature; a flow rate adjustment unit that can adjust the flow rate of at least one of the low-temperature liquefied gas supplied to the low-temperature flow path of the first heat exchanger and the carbon dioxide supplied to the flow path to be liquefied of the first heat exchanger; and a control unit that controls the flow rate adjustment unit so that the temperature detected by the temperature detection unit becomes a predetermined target temperature, wherein the predetermined target temperature is set so that the temperature of the liquefied carbon dioxide discharged from the first heat exchanger becomes a predetermined required temperature and so that the carbon dioxide does not solidify on the inner surface of the flow path to be liquefied of the first heat exchanger.

[0010] FIG. 1 is a system diagram showing a schematic configuration of a heat exchange system according to the first embodiment. ２ FIG. 3 is a perspective view showing a stacked heat exchanger provided in a liquefier. FIG. 3 is a cutaway perspective view of the stacked heat exchanger of FIG. 2 taken along line III-III. 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. 5 is a flowchart showing an example of temperature control of the intermediate medium executed by a controller. FIG. 6 is a diagram equivalent to FIG. 5, showing a modification of the first embodiment. FIG. 7 is a diagram equivalent to FIG. 5, showing the second embodiment. FIG. 8 is a diagram equivalent to FIG. 1, showing another embodiment. FIG. 9 is a diagram equivalent to FIG. 1, showing another embodiment.

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0012] 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).

[0013] [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 carbon dioxide gas to be liquefied is introduced and flows, an LNG bypass flow path 4 and a CO ２ By performing heat exchange between the bypass flow path 5, the LNG flowing through the low-temperature flow path 2, and the carbon dioxide flowing through the liquefaction target flow path 3, the LNG is vaporized and the carbon dioxide is liquefied. ２ liquefier 6 (corresponding to the first heat exchanger), and ２ The system is equipped with an NG heater 7 (corresponding to a second heat exchanger) that heats the NG vaporized from LNG in the liquefier 6 to a predetermined required temperature by heat exchange between the NG and the carbon dioxide flowing through the liquefaction target flow path 3, an intermediate medium temperature sensor 15 as a temperature detection unit, and a controller 10 as a control unit. ２ The liquefier 6 corresponds to the first heat exchanger, and the NG heater 7 corresponds to the second heat exchanger. The predetermined required temperature is an arbitrary temperature required (set) by the user depending on the application.

[0014] The NG heater 7 is configured to heat the CO ２ It is arranged downstream of the liquefier 6.

[0015] The LNG bypass flow path 4 branches off from the low-temperature flow path 2 and ２ The LNG bypass flow path 4 is arranged to bypass the liquefier 6. That is, the LNG bypass flow path 4 is arranged to bypass the CO ２ an upstream end connected to a portion upstream of the liquefier 6; and a CO ２The low-temperature flow path 2 has a downstream end connected to a portion downstream of the liquefier 6 and upstream of the NG heater 7. A first NG temperature sensor 16 is connected between the NG heater 7 and the connection position of the low-temperature flow path 2 with the downstream end of the LNG bypass flow path 4. In addition, a second NG temperature sensor 18 is connected to the low-temperature flow path 2 downstream of the heater 7.

[0016] The CO ２ The bypass flow path 5 is arranged to branch off from the liquefaction target flow path 3 and bypass the NG heater 7. ２ The bypass flow path 5 has an upstream end connected to a portion of the liquefaction target flow path 3 upstream of the NG heater 7, and a downstream end connected to a portion of the liquefaction target flow path 3 downstream of the NG heater 7 and downstream of the CO ２ The CO liquefaction target flow path 3 has a downstream end connected to a portion upstream of the liquefier 6. ２ Downstream of the liquefier 6, CO ２ A temperature sensor 17 is connected.

[0017] The heat exchange system 1 includes an LNG bypass valve 13 disposed in the LNG bypass flow path 4, and a CO ２ CO disposed in the bypass flow path 5 ２ a bypass valve 14, an LNG main valve 11 disposed at the upstream end of the low-temperature flow path 2, and a CO 2 main valve 12 disposed at the upstream end of the liquefaction target flow path 3; ２ a main valve 12, an LNG pump 8 disposed upstream of the LNG main valve 11, and a CO ２ A CO ２ The LNG pump 8 and the CO ２ Compressor 9, LNG main valve 11, CO ２ Main valve 12, LNG bypass valve 13 and CO ２ The bypass valve 14 is configured to be controllable by the controller 10 .

[0018] During operation of the heat exchange system 1, the controller 10 controls the LNG main valve 11 and the CO ２ The opening of the main valve 12 is controlled to ２ The temperature of the intermediate medium M in the liquefier 6 is controlled. ２If it is not permitted to change the flow rate of the LNG main valve 11 and the CO ２ While the main valve 12 is maintained at a predetermined opening, the LNG bypass valve 13 and the CO ２ The opening of the bypass valve 14 is controlled to ２ The temperature of the intermediate medium M in the liquefier 6 is controlled.

[0019] [Configuration of liquefier] CO ２ In this example, the liquefier 6 is configured as an intermediate medium type heat exchanger. ２ The liquefier 6 has a shell 61, a stacked heat exchanger 62, and a number of heat transfer tubes 63. In Fig. 1, for ease of viewing, the number of heat transfer tubes 63 is shown as a single flow path line.

[0020] The shell 61 is a horizontally long, sealed hollow tank. A liquid intermediate medium M (propane in this example) is stored in the lower part of the shell 61. The lower part of the shell 61 functions as a liquid reservoir 61e.

[0021] An LNG supply port 61a for supplying LNG to the heat transfer tubes 63 in the shell 61 and an NG discharge port 61b for discharging NG vaporized in the heat transfer tubes 63 are formed on the upper wall of the shell 61. The heat transfer tubes 63 constitute a part of the low-temperature flow path 2.

[0022] In addition, a CO 2 supply pipe for supplying carbon dioxide to the stacked heat exchanger 62 in the shell 61 is provided on the lower wall of the shell 61. ２ supply port 61c and a CO 2 supply port 61d for discharging the carbon dioxide liquefied in the stacked heat exchanger 62. ２ An outlet 61d is formed. ２ The supply port 61c and the stacked heat exchanger 62 are connected to a CO ２ It is connected via an inlet pipe 64. ２ The outlet 61d and the stacked heat exchanger 62 are connected to the CO ２ It is connected via an outlet pipe 65. ２ Inlet pipe 64 and CO ２ The outlet pipe 65 is immersed in the intermediate medium M. ２ Inlet pipe 64 and CO２ The outlet pipe 65 does not necessarily need to be immersed in the intermediate medium M, but may be arranged so as to pass above the liquid surface of the intermediate medium M.

[0023] The stacked heat exchanger 62 is entirely immersed in the intermediate medium M. The stacked heat exchanger 62 ２ By performing heat exchange between the gaseous carbon dioxide supplied from the inlet pipe 64 and the intermediate medium M, a part of the intermediate medium M is vaporized and the carbon dioxide is liquefied to produce CO ２ The heat exchanger 62 is discharged into the outlet pipe 65. The entire stacked heat exchanger 62 does not necessarily need to be immersed in the intermediate medium M, and only a portion of the stacked heat exchanger 62 may be immersed in the intermediate medium M. Details of the stacked heat exchanger 62 will be described later.

[0024] The large number of heat transfer tubes 63 are arranged above the liquid level of the intermediate medium M stored in the shell 61. Each heat transfer tube 63 is curved in a U-shape and arranged horizontally within the shell 61. One end of each heat transfer tube 63 is connected to the LNG supply port 61a of the shell 61 via a collecting pipe (not shown), and the other end of each heat transfer tube 63 is connected to the LNG discharge port 61b of the shell 61 via a collecting pipe (not shown). Note that it is not necessary to provide multiple heat transfer tubes 63, and only one may be provided. Furthermore, the shape of the heat transfer tube 63 does not necessarily have to be U-shaped, and may be any shape, such as a straight shape.

[0025] The CO ２ In the liquefier 6, the CO is liquefied in a stacked heat exchanger 62 immersed in an intermediate medium M. ２When gaseous carbon dioxide is supplied through the inlet pipe 64, heat exchange occurs between the liquid intermediate medium M and the carbon dioxide. As a result, at least a portion of the liquid intermediate medium M evaporates to become an intermediate medium gas, which exchanges heat with the LNG in the heat transfer tube 63. The intermediate medium gas is cooled and condensed by the LNG in the heat transfer tube 63, while the LNG in the heat transfer tube 63 is heated by the heat of condensation of the intermediate medium gas to become NG (an example of a vaporized gas), which is supplied to the NG heater 7 described below. The condensed intermediate medium gas becomes liquid intermediate medium M and falls to the bottom of the shell 61. The intermediate medium M circulates within the shell 61, alternately liquefying and gasifying it. The stacked heat exchanger 62 and the shell 61 function as an intermediate medium evaporator E1 that evaporates the intermediate medium M. The heat transfer tube 63 and the shell 61 function as a liquefied gas vaporizer E2 that vaporizes the LNG.

[0026] Next, the above-mentioned stacked heat exchanger 62 will be described in detail with reference to Figures 2 and 3. Figure 2 is a perspective view showing the stacked heat exchanger 62, and Figure 3 is a cutaway perspective view of the stacked heat exchanger 62 of Figure 2 taken along line III-III. In the following, the description will be based on the definitions of front, back, left, and right indicated by the directional axes in each figure, but these definitions do not limit the configuration of the present invention.

[0027] The stacked heat exchanger 62 includes a stacked body 620 that is substantially rectangular parallelepiped and is elongated in the left-right direction, and a CO ２ A supply header 625 and a CO ２ and a discharge header 626.

[0028] The laminate 620 has a pair of end plates 623 located at both ends in the front-rear direction, and first flow path layers 621 and second flow path layers 622 sandwiched between the pair of end plates 623 and stacked alternately in the front-rear direction. The first flow path layer 621 is recessed with a number of first flow path sections 621a (corresponding to intermediate medium flow path sections) into which the intermediate medium M stored in the lower part (liquid reservoir section 61e) of the shell 61 penetrates. The second flow path layer 622 is recessed with a number of first flow path sections 621a (corresponding to intermediate medium flow path sections) into which the intermediate medium M stored in the lower part (liquid reservoir section 61e) of the shell 61 penetrates. ２A large number of second flow path sections 622a (corresponding to carbon dioxide flow path sections; see FIG. 3 ) are formed through which carbon dioxide supplied from the inlet pipe 64 flows. Heat exchange occurs between the intermediate medium M that has entered the first flow path sections 621a of the first flow path layer 621 and the carbon dioxide flowing through the second flow path sections 622a of the second flow path layer 622, whereby the intermediate medium M is heated and vaporized, and the carbon dioxide is cooled and liquefied. The second flow path sections 622a constitute a part of the flow path 3 to be liquefied.

[0029] The first flow path layer 621 and the second flow path layer 622 are each made of a single metal plate and are bonded to each other by diffusion bonding. Note that the first flow path layer 621 and the second flow path layer 622 do not necessarily have to be made of a single metal plate, but may be made by stacking multiple metal plates. That is, for example, the first flow path layer 621 may be made of two metal plates, and the second flow path layer 622 may be made of three metal plates.

[0030] The first flow path layer 621 is disposed vertically so that the first flow path portion 621a extends in the up-down direction. The second flow path layer 622 is disposed horizontally so that the second flow path portion 622a extends in the left-right direction. Note that the flow path layers 621, 622 do not necessarily have to be disposed entirely horizontally or vertically; for example, some may be disposed vertically, some horizontally, or they may be disposed at an angle.

[0031] The CO ２ The supply header 625 ２ It is connected to the inlet pipe 64. ２ The supply header 625 ２ The gaseous carbon dioxide introduced from the introduction pipe 64 is received and supplied to each second flow path portion 622 a of the stack 20 .

[0032] CO ２ The discharge header 626 ２ It is connected to the outlet pipe 65. ２ The discharge header 626 collects the carbon dioxide that has been liquefied by flowing through each second flow path portion 622a in the stack 620 and discharges it into the CO ２ It is discharged into the outlet pipe 65.

[0033] In the examples of Figures 2 and 3, the stacked heat exchanger 62 has a microchannel structure, but this is not limited to this. For example, the stacked heat exchanger 62 may have a brazed plate fin structure in which a large number of corrugated metal plates and metal plates separating them are alternately stacked, and the spaces between adjacent metal plates are formed as first and second flow path sections.

[0034] [Configuration of NG Heater] Returning to FIG. 1, the configuration of the NG heater 7 will be described. ２ The NG heater 7 is configured by a microchannel laminated heat exchanger similar to the liquefier 6. The NG heater 7 is not limited to the microchannel type, and may be a brazed plate fin type or a multi-tube type.

[0035] Specifically, the NG heater 7 is configured by alternately stacking a flow path layer (not shown) having a first flow path section 71 (corresponding to a vaporized gas flow path section) through which the NG flows, and a flow path layer (not shown) having a second flow path section 72 (carbon dioxide flow path section) through which gaseous carbon dioxide flows. The NG flowing through the first flow path section 71 is heated to a predetermined required temperature (5°C, for example, in this example) by heat exchange with the gaseous carbon dioxide flowing through the second flow path section 72, and at the same time, the gaseous carbon dioxide is pre-cooled. The first flow path section 71 constitutes a part of the low-temperature flow path 2, and the second flow path section 72 constitutes a part of the flow path to be liquefied 3.

[0036] [Explanation of Basic Operation] Next, the basic operation of the heat exchange system 1 will be described with reference to Fig. 1 and Fig. 4. Fig. 4 is a TQ diagram showing the temperature change of each working fluid (LNG, carbon dioxide, and propane constituting the intermediate medium M) 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. Note that in Fig. 4, the flow rate of LNG flowing through the LNG bypass passage 4 and the CO ２ The following description will be given on the assumption that the flow rate of carbon dioxide flowing through the bypass flow path 5 is zero.

[0037] LNG is supplied from an LNG supply source provided outside the heat exchange system 1 at −150° C.２ It is supplied to the liquefier 6 (see FIG. 1). ２ The LNG supplied to the liquefier 6 increases in heat quantity by heat exchange with the propane constituting the intermediate medium M (see FIG. 4). As a result, the LNG is heated from −150° C. to −48° C. and vaporized to become NG.

[0038] The vaporized NG flows into the first flow path section 71 of the NG heater 7 (see Figure 1) at -48°C, and its heat content increases as it exchanges heat with the carbon dioxide flowing through the second flow path section 72. At the outlet of the NG heater 7, the NG is heated to 5°C (an example of a predetermined required temperature) and is then discharged (see Figure 4).

[0039] On the other hand, the carbon dioxide to be liquefied is supplied to the NG heater 7 as a gas at 30°C from a supply source provided outside the heat exchange system 1. The gaseous carbon dioxide supplied to the NG heater 7 gradually loses heat by exchanging heat with the NG flowing in the first flow path section 71 of the NG heater 7 (see FIG. 4). Accordingly, the temperature of the carbon dioxide gradually drops from 30°C and eventually reaches the liquefaction temperature of -17.2°C (under the condition of 2.1 MPa in this example). Then, the carbon dioxide is converted into CO at -17.2°C. ２ The CO is supplied to the liquefier 6. ２ The amount of heat is reduced by heat exchange with LNG in the liquefier 6. When the carbon dioxide reaches the liquefaction temperature, it starts to condense from gas to liquid, and in this condensation section, the carbon dioxide is in a state where gas and liquid coexist, and the temperature remains constant regardless of the reduction in the amount of heat. When the amount of heat of the carbon dioxide further decreases and the condensation 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 6.

[0040] The propane constituting the intermediate medium M is CO ２ The LNG is stored at −45° C. in the shell 61 of the liquefier 6 and repeatedly undergoes evaporation due to heat exchange with carbon dioxide and condensation due to the cold heat of the LNG.

[0041] [Temperature Control of Intermediate Medium] Next, the configuration of a control system related to the temperature control of the intermediate medium M by the controller 10 will be described with reference to FIG.

[0042] The controller 10 controls the LNG pump 8, the CO ２ Compressor 9, LNG main valve 11, CO ２ Main valve 12, LNG bypass valve 13, CO ２ A bypass valve 14, an intermediate medium temperature sensor 15, a first NG temperature sensor 16, a second NG temperature sensor 18, and a CO ２ The controller 10 is connected so as to be able to send and receive signals to and from the temperature sensor 17. The controller 10 is configured by a computer having a CPU, ROM, and RAM, and executes various processes which will be explained later with reference to the flowchart of FIG.

[0043] The intermediate medium temperature sensor 15 detects the CO ２ The temperature (liquid temperature) of the intermediate medium M stored in the shell 61 of the liquefier 6 is detected, and the detected temperature information is transmitted to the controller 10. The first NG temperature sensor 16 detects the temperature of the NG supplied to the NG heater 7, and transmits the detected temperature information to the controller 10. The second NG temperature sensor 18 detects the temperature of the NG discharged from the NG heater 7, and transmits the detected temperature information to the controller 10. ２ The temperature sensor 17 detects CO ２ The temperature of the liquefied carbon dioxide discharged from the liquefier 6 is detected, and the detected temperature information is sent to the controller 10 .

[0044] The controller 10 controls the LNG main valve 11 and the CO ２ The temperature of the intermediate medium M is controlled to a predetermined target temperature by controlling the opening degree of the main valve 12. ２ The temperature of the liquefied carbon dioxide discharged from the liquefier 6 is set to a predetermined required temperature (-42°C in this example) and the CO ２ This temperature is set in advance so that carbon dioxide does not solidify on the inner surface of the second flow path portion 622a (part of the liquefaction target flow path 3) in the stack 620 in the liquefier 6. In the following description, the controller 10 controls the LNG main valve 11 and the CO２ An example of controlling the main valve 12 will be described, but the present invention is not limited to this. As will be described later, the LNG bypass valve 13 and the CO ２ It may be configured to control the bypass valve 14 .

[0045] FIG. 5 is a flowchart showing an example of the temperature control of the intermediate medium M executed by the controller 10.

[0046] In step SA1, the temperature detected by the intermediate medium temperature sensor 15 is acquired.

[0047] In step SA2, it is determined whether the detected temperature acquired in step SA1 is equal to the predetermined target temperature, and if the determination is YES, the process returns to step SA1, whereas if the determination is NO, the process proceeds to step SA3.

[0048] In step SA3, it is determined whether the detected temperature acquired in step SA1 is lower than the target temperature. If the determination is NO, the process proceeds to step SA5, whereas if the determination is YES, the process proceeds to step SA4.

[0049] In step SA4, the opening of the LNG main valve 11 is decreased by a predetermined amount and the CO ２ In order to increase the opening of the main valve 12 by a predetermined amount, the LNG main valve 11 and the CO ２ A control signal is sent to the main valve 12. ２ Since the supply amount of carbon dioxide, which is the high-temperature fluid supplied to the liquefier 6, increases and the supply amount of LNG, which is the low-temperature fluid, decreases, the temperature of the intermediate medium M increases and the detected temperature approaches the predetermined target temperature. After the processing of step SA4, the process returns to step SA1. The predetermined amount may be a predetermined constant or may be set according to the acquired detected temperature.

[0050] In step SA5, which is reached when the determination in step SA3 is NO, the opening degree of the LNG main valve 11 is increased by a predetermined amount and the CO ２ In order to reduce the opening of the main valve 12 by a predetermined amount, the LNG main valve 11 and the CO ２ A control signal is sent to the main valve 12. ２Since the supply amount of carbon dioxide, which is the high-temperature fluid supplied to the liquefier 6, decreases and the supply amount of LNG, which is the low-temperature fluid, increases, the temperature of the intermediate medium M decreases and the detected temperature approaches the predetermined target temperature. After the processing of step SA5, the process returns to step SA1. The predetermined amount may be a predetermined constant or may be set according to the acquired detected temperature.

[0051] In steps SA4 and S5, the predetermined amount may be set based on PID control, PI control, PD control, or the like.

[0052] [Operation and Effect] As described above, the heat exchange system 1 of this embodiment ２ The intermediate medium temperature sensor 15 detects the temperature of the intermediate medium M stored in the lower part (liquid reservoir 61e) of the shell 61 of the liquefier 6, and the controller 10 controls the LNG main valve 11 and the CO 2 so that the temperature detected by the intermediate medium temperature sensor 15 becomes the predetermined target temperature. ２ Adjust the opening of the main valve 12 to ２ The flow rate of LNG and the flow rate of carbon dioxide supplied to the liquefier 6 are adjusted. ２ The temperature of the liquefied carbon dioxide discharged from the liquefier 6 is set to a predetermined required temperature, and the CO ２ This temperature is set so that carbon dioxide does not solidify on the inner surface of the second flow path portion 622 a (part of the liquefaction target flow path 3 ) provided in the stack 620 of the liquefier 6 .

[0053] According to this configuration, CO ２ By using an intermediate medium type heat exchanger as the liquefier 6, direct heat exchange between LNG and carbon dioxide, which has a large temperature difference, is avoided, and the occurrence of thermal stress is minimized. ２ The temperature of the intermediate medium M is controlled to the predetermined target temperature by controlling the main valve 12 (an example of a flow rate adjusting unit). ２This can prevent carbon dioxide from solidifying on the inner surface of the second flow path portion 622a of the liquefier 6 and suppress poor liquefaction due to insufficient cooling of the carbon dioxide. That is, in a conventional intermediate medium type heat exchanger, the temperature of the intermediate medium M is determined by the natural course of events, and there are cases where the temperature of the intermediate medium M becomes lower than the solidification temperature of carbon dioxide. In contrast, in this embodiment, the temperature of the intermediate medium M is detected by the intermediate medium temperature sensor 15, and the LNG main valve 11 and the CO refrigerant flow control valve 12 are controlled so that the temperature detected by the intermediate medium temperature sensor 15 becomes a temperature at which carbon dioxide does not solidify (the predetermined target temperature). ２ The opening of the main valve 12 is controlled by the controller 10. Therefore, unlike the conventional method, the temperature of the intermediate medium M is not excessively reduced, and CO ２ Solidification of carbon dioxide in the liquefier 6 can be suppressed.

[0054] In this embodiment, CO ２ The liquefier 6 includes a laminate 620 in which a first flow path layer 621 having a first flow path portion 621a into which the intermediate medium M penetrates and a second flow path layer 622 having a second flow path portion 622a that serves as a flow path for carbon dioxide are laminated, and a heat transfer tube 63 that is disposed above the liquid surface of the liquid intermediate medium M and through which LNG is introduced and flows. ２ The liquefier 6 is configured to vaporize a portion of the intermediate medium M by performing heat exchange between the intermediate medium M in the first flow path section 621a and the carbon dioxide in the second flow path section 622a in the stacked heat exchanger 62, and to perform heat exchange between the vaporized intermediate medium M and the LNG flowing in the heat transfer tube 63.

[0055] According to this configuration, CO ２ The part of the liquefier 6 that evaporates the intermediate medium M is configured as a stacked heat exchanger 62, so that CO ２ The CO ２ This makes it possible to more reliably prevent the carbon dioxide from solidifying in the liquefier 6 .

[0056] That is, compared with a shell-and-tube heat exchanger, the stacked heat exchanger 62 usually has a heat transfer section made of a thinner material and has a larger heat transfer area per unit volume, so that it is possible to minimize the temperature difference between the intermediate medium M, which is the low-temperature fluid in the stacked heat exchanger 62, and carbon dioxide, which is the high-temperature fluid. In other words, it is possible to set the target temperature of the intermediate medium as high as possible. Therefore, the CO ２ Even if the required temperature of the liquefied carbon dioxide discharged from the liquefier 6 is close to its solidification temperature (for example, −56° C.), it is possible to prevent the temperature of the intermediate medium M from falling below the solidification temperature of the carbon dioxide as much as possible. ２ Compared with the case where the liquefier 6 is configured as a multi-tube heat exchanger, ２ Solidification of carbon dioxide in the liquefier 6 can be suppressed as much as possible.

[0057] In this embodiment, the heat exchange system 1 is configured such that the CO ２ The NG heater 7 is provided downstream of the liquefier 6. The NG heater 7 ２ By performing heat exchange between the NG vaporized from LNG in the liquefier 6 and the carbon dioxide gas in the flow path 3 to be liquefied, the NG is heated to a predetermined required temperature while pre-cooling the carbon dioxide gas.

[0058] According to this configuration, CO ２ The NG discharged from the liquefier 6 can be heated to a predetermined required temperature by the NG heater 7. This improves the usability of the heat exchange system 1 as a vaporized gas generation system.

[0059] In addition, in this embodiment, the NG heater 7 is composed of a stacked heat exchanger in which a flow path layer (not shown) having a first flow path section 71 (corresponding to a vaporized gas flow path section) which serves as a flow path for NG and a flow path layer (not shown) having a second flow path section 72 (corresponding to a carbon dioxide flow path section) which serves as a flow path for carbon dioxide are stacked, and is configured to perform heat exchange between the carbon dioxide flowing through the second flow path section 72 and the NG flowing through the first flow path section 71.

[0060] According to this configuration, CO ２By configuring not only the liquefier 6 but also the NG heater 7 as stacked heat exchangers, the entire heat exchange system 1 can be configured compactly.

[0061] (Modification of the First Embodiment) Fig. 6 is a diagram corresponding to Fig. 5 showing a modification of the first embodiment. In this modification, when controlling the temperature of the intermediate medium M, the LNG pump 8 and the CO ２ This embodiment differs from the previous embodiment in that it controls the compressor 9. In the following description, the same processes as those in the first embodiment will be omitted as appropriate.

[0062] In steps SB1 to SB3, the same processes as in steps SA1 to SA4 in the first embodiment are executed.

[0063] In step SB4, which is reached when the determination in step SB3 is YES, the discharge flow rate of the LNG pump 8 is reduced by a predetermined amount and the CO ２ The LNG pump 8 and the CO ２ A control signal is sent to the compressor. ２ Since the supply amount of carbon dioxide, which is the high-temperature fluid supplied to the liquefier 6, increases and the supply amount of LNG, which is the low-temperature fluid, decreases, the temperature of the intermediate medium M increases and the detected temperature approaches the predetermined target temperature. After the processing of step SB4, the process returns to step SB1. The predetermined amount may be a predetermined constant or may be set according to the acquired detected temperature.

[0064] In step SB5, which is reached when the determination in step SB3 is NO, the discharge flow rate of the LNG pump 8 is increased by a predetermined amount and the CO ２ The LNG pump 8 and the CO ２ A control signal is sent to the compressor. ２Since the supply amount of carbon dioxide, which is the high-temperature fluid supplied to the liquefier 6, decreases and the supply amount of LNG, which is the low-temperature fluid, increases, the temperature of the intermediate medium M decreases and the detected temperature approaches the predetermined target temperature. After the processing of step SB5, the process returns to step SB1. The predetermined amount may be a predetermined constant or may be set according to the acquired detected temperature.

[0065] In steps SB4 and SB5, the predetermined amount may be set based on PID control, PI control, PD control, or the like.

[0066] As described above, according to this modification, the LNG pump 8 and the CO ２ The temperature of the intermediate medium M can be controlled to the target temperature by controlling the compressor 9 (an example of a flow rate adjusting unit). Therefore, the same effects as those of the first embodiment can be obtained.

[0067] 7 is a view corresponding to FIG. 5 showing a second embodiment. In this embodiment, when controlling the temperature of the intermediate medium M, the LNG bypass valve 13 and the CO ２ This embodiment differs from the previous embodiment in that it controls the opening degree of the bypass valve 14. In the following description, the same processes as those in the first embodiment will be omitted as appropriate.

[0068] In steps SC1 to SC3, the same processes as in steps SA1 to SA3 in the first embodiment are executed.

[0069] In step SC4, CO ２ In order to increase the opening degree of the bypass valve 14 by a predetermined amount and to increase the opening degree of the LNG bypass valve 13 by a predetermined amount, ２ A control signal is transmitted to the bypass valve 14 and the LNG bypass valve 13. ２ As the proportion of carbon dioxide that does not pass through the NG heater 7 (i.e., carbon dioxide that is not pre-cooled) among the high-temperature side fluid carbon dioxide supplied to the liquefier 6 increases, the CO ２Since the supply amount of LNG, which is the low-temperature fluid supplied to the liquefier 6, decreases, the temperature of the intermediate medium M increases, and the detected temperature approaches the predetermined target temperature. After the processing of step SC4, the process returns to step SC1. The predetermined amount may be a predetermined constant, or may be set according to the acquired detected temperature.

[0070] In step SC5, which is reached when the determination in step SC3 is NO, ２ In order to decrease the opening degree of the bypass valve 14 by a predetermined amount and decrease the opening degree of the LNG bypass valve 13 by a predetermined amount, ２ A control signal is transmitted to the bypass valve 14 and the LNG bypass valve 13. ２ As the proportion of carbon dioxide passing through the NG heater 7 (i.e., pre-cooled carbon dioxide) in the high-temperature fluid carbon dioxide supplied to the liquefier 6 increases, the CO ２ Since the supply amount of LNG, which is the low-temperature fluid supplied to the liquefier 6, increases, the temperature of the intermediate medium M decreases, and the detected temperature approaches the predetermined target temperature. After the processing of step SC5, the process returns to step SC1. The predetermined amount may be a predetermined constant, or may be set according to the acquired detected temperature.

[0071] In steps SC4 and SC5, the predetermined amount may be set based on PID control, PI control, PD control, or the like.

[0072] As described above, according to the present embodiment, the LNG bypass valve 13 and the CO ２ The temperature of the intermediate medium M can be controlled to the target temperature by controlling the bypass valve 14 (an example of a flow rate adjusting unit). Therefore, the same effects as those of the first embodiment can be obtained.

[0073] In addition, as in this embodiment, the LNG bypass valve 13 and the CO ２In the configuration in which the temperature of the intermediate medium M is controlled by controlling the bypass valve 14, there is no need to change the flow rates of the LNG and carbon dioxide supplied to the heat exchange system 1, as compared to the case in which the main valves 11, 12 are adjusted as in the first embodiment. Therefore, the configuration of this embodiment is particularly useful in the case in which, for example, the post-vaporization flow rate of LNG and the post-liquefaction flow rate of carbon dioxide in the heat exchange system 1 need to be maintained at predetermined required flow rates (constant values).

[0074] In addition, in this embodiment, the downstream end of the LNG bypass flow path 4 is connected to the upstream side of the NG heater 7, not the downstream side thereof, so that the bypassed liquid LNG can be prevented from remaining at the outlet of the heat exchange system 1 (the downstream end of the low-temperature flow path 2). ２ The downstream end of the bypass flow path 5 is ２ By connecting the liquefier 6 to the upstream side instead of the downstream side, the CO ２ This can prevent the refrigerant from remaining at the outlet of the heat exchange system 1 (the downstream end of the liquefaction target flow path 3).

[0075] In this embodiment, if the temperature of the NG after merging at the downstream end of the LNG bypass flow path 4 drops too much, there is a risk of carbon dioxide solidifying in the NG heater 7. For this reason, the first NG temperature sensor 16 detects the temperature of the NG flowing into the NG heater 7, and the LNG bypass valve 13 is controlled so that the detected temperature of the NG does not become equal to or lower than a predetermined lower limit temperature (for example, −56° C., the solidification temperature of CO2), thereby preventing the carbon dioxide from solidifying.

[0076] 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, and for example, the following modified embodiments can be adopted.

[0077] (1) In the first embodiment, the heat exchange system 1 includes the LNG bypass passage 4, the CO ２ Bypass flow path 5, LNG bypass valve 13 and CO ２Although an example in which the bypass valve 14 is provided has been described, the present invention is not limited to this. That is, these are not necessarily required in the first embodiment, and for example, as shown in FIG. 8 , the configuration may be such that the bypass flow paths 4 and 5 and the bypass valves 13 and 14 are not provided.

[0078] (2) In the second embodiment, the downstream end of the LNG bypass flow path 4 is connected to the upstream side of the NG heater 7, and ２ The downstream end of the bypass flow path 5 is ２ 9, the downstream end of the LNG bypass flow path 4 is connected to the downstream side of the NG heater 7, and the CO ２ The downstream end of the bypass flow path 5 is ２ It may be connected downstream of the liquefier 6. In this case, for example, instead of the process of step SA4, ２ The opening degree of the bypass valve 14 is decreased by a predetermined amount and the opening degree of the LNG bypass valve 13 is increased by a predetermined amount, and instead of the processing of step SA5, ２ By executing the process of increasing the opening degree of the bypass valve 14 by a predetermined amount and decreasing the opening degree of the LNG bypass valve 13 by a predetermined amount, the same effects as those of the second embodiment can be obtained.

[0079] (3) In each of the above embodiments and modifications, CO ２ Although both the flow rate of carbon dioxide and the flow rate of LNG supplied to the liquefier 6 are adjusted (steps SA4 to SC4 and steps SA5 to SC5), it is also possible to adjust only one of the flow rates. ２ Any configuration may be used as long as it is configured to be able to adjust at least one of the flow rate of the low-temperature liquefied gas (for example, LNG) and the flow rate of carbon dioxide supplied to the liquefier 6 .

[0080] (4) In the above embodiment, the intermediate medium temperature sensor 15 is configured to detect the temperature (liquid temperature) of the intermediate medium M, but this is not limited thereto. The intermediate medium temperature sensor 15 may be configured to detect the temperature of the intermediate medium gas (i.e., the temperature of the gas phase) as a temperature correlated with the temperature of the intermediate medium M, or may detect the wall surface temperature, etc. Also, instead of the intermediate medium temperature sensor 15, a pressure sensor may be provided to detect the pressure of the intermediate medium M, and the controller may detect the saturation temperature of the pressure detected by the pressure sensor as a temperature correlated with the temperature of the intermediate medium M. In this case, the pressure sensor and the controller function as a temperature detection unit.

[0081] (5) In the above embodiment, the heat exchange system 1 includes the NG heater 7 . However, the present invention is not limited to this, and the heat exchange system 1 may be configured without the NG heater 7 .

[0082] (6) In the above embodiment, the intermediate medium M is made of propane, but this is not limited thereto. The intermediate medium M may be made of, for example, a mixture of difluoromethane and pentafluoroethane (R410A) or difluoromethane (R32). This allows the intermediate medium M to be made inexpensively and with high thermal conductivity.

[0083] (7) In the above embodiment, LNG is used as an example of low-temperature liquefied gas. However, the present invention is not limited to this. For example, liquid hydrogen (LH ２ ) etc.

[0084] (8) In the above embodiment, it is not necessary for 100% of the gaseous carbon dioxide supplied to the liquefaction target flow path 3 to be 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.

[0085] (9) In each of the above embodiments and modifications, CO ２ The temperature of the LNG at the LNG supply port 61a (LNG inlet) of the liquefier 6 is set to -150°C, but is not limited to this. ２The temperature of the LNG flowing into the liquefier 6 is ２ The temperature is such that the liquefaction of carbon dioxide in the liquefier 6 is not hindered, and the CO ２ When the temperature of the carbon dioxide discharged from the liquefier 6 reaches a predetermined required temperature and the carbon dioxide is ２ The temperature may be any temperature that does not solidify in the liquefier 6. In each of the above-described embodiments and modifications, the CO ２ The temperature of the LNG supplied to the liquefier 6 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 the temperature may be set to a temperature at which only a portion of the carbon dioxide can be liquefied.

[0086] (10) In each of the above embodiments and modifications, the temperature of the NG at the inlet of the low-temperature flow path 2 of the NG heater 7 is −48° C. (see FIG. 4 ), but this is not limited to this and may be, for example, −50° C. to −60° C. In other words, the temperature of the NG flowing into the NG heater 7 may be any temperature as long as the temperature of the carbon dioxide discharged from the NG heater 7 reaches the predetermined required temperature required at the discharge position and the carbon dioxide does not solidify in the NG heater 7.

[0087] (11) The present invention includes any combination of the above-described embodiments and modifications. Therefore, for example, the opening control of the main valves 11 and 12 disclosed in the first embodiment and the opening control of the bypass valves 13 and 14 disclosed in the second embodiment may be used in combination. Also, for example, the flow rate of LNG may be adjusted by adjusting the opening of the LNG main valve 11, and the flow rate of carbon dioxide may be adjusted by adjusting the opening of the CO ２ Alternatively, the flow rate of LNG may be adjusted by adjusting the opening of the bypass valve 14. Alternatively, for example, the flow rate of LNG may be adjusted by adjusting the opening of the LNG bypass valve 13, and the flow rate of carbon dioxide may be adjusted by adjusting the opening of the CO ２ This may be done by adjusting the opening of the main valve 12.

[0088] The above-described specific embodiments mainly include inventions having the following configurations.

[0089] A heat exchange system according to a first aspect of the present invention is a heat exchange system that liquefies 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 flow path to be liquefied through which gaseous carbon dioxide is introduced and flows; a first heat exchanger that is disposed across the low-temperature flow path and the flow path to be liquefied and that vaporizes the low-temperature liquefied gas and liquefies the carbon dioxide by performing heat exchange between the low-temperature liquefied gas flowing through the low-temperature flow path and the carbon dioxide flowing through the flow path to be liquefied via an intermediate medium; and a temperature of the intermediate medium or a temperature correlated with the temperature of the intermediate medium. a flow rate adjusting unit capable of adjusting the flow rate of at least one of the low-temperature liquefied gas supplied to the low-temperature flow path of the first heat exchanger and the carbon dioxide supplied to the flow path to be liquefied of the first heat exchanger; and a control unit that controls the flow rate adjusting unit so that the temperature detected by the temperature detecting unit becomes a predetermined target temperature, wherein the predetermined target temperature is set so that the temperature of the liquefied carbon dioxide discharged from the first heat exchanger becomes a predetermined required temperature and so that the carbon dioxide does not solidify on the inner surface of the flow path to be liquefied of the first heat exchanger.

[0090] According to this configuration, by using an intermediate medium-type heat exchanger as the first heat exchanger, direct heat exchange between the low-temperature liquefied gas and carbon dioxide, which have a large temperature difference, is avoided, thereby minimizing the occurrence of thermal stress. Furthermore, by controlling the flow rate regulator by the control unit to maintain the temperature of the intermediate medium at the predetermined target temperature, solidification of carbon dioxide on the inner surface of the liquefaction-target flow path of the first heat exchanger can be prevented and poor liquefaction due to insufficient cooling of carbon dioxide can be suppressed. For example, if the temperature detected by the temperature detector is lower than the predetermined target temperature, the flow rate regulator can reduce the flow rate of the low-temperature liquefied gas supplied to the low-temperature flow path of the first heat exchanger. This reduces the amount of cooling of the intermediate medium due to the cold energy of the low-temperature liquefied gas, thereby increasing the temperature of the intermediate medium and bringing the temperature detected by the temperature detector closer to the target temperature. Note that instead of reducing the supply flow rate of the low-temperature liquefied gas, the supply flow rate of the high-temperature fluid, carbon dioxide, may be increased, or the flow rates of the low-temperature liquefied gas and carbon dioxide may be controlled in combination. On the other hand, if the temperature detected by the temperature detection unit is higher than the predetermined target temperature, the flow rate of the low-temperature liquefied gas supplied to the low-temperature flow path of the first heat exchanger can be increased by the flow rate adjustment unit. This increases the amount of cooling of the intermediate medium by the cold energy of the low-temperature liquefied gas, thereby lowering the temperature of the intermediate medium and bringing the temperature detected by the temperature detection unit closer to the predetermined target temperature. Note that instead of increasing the flow rate of the low-temperature liquefied gas, the supply flow rate of carbon dioxide, which is a high-temperature fluid, may be reduced, or the flow rates of the low-temperature liquefied gas and carbon dioxide may be controlled in combination. In this way, by controlling the temperature of the intermediate medium that directly exchanges heat with the carbon dioxide, it is possible to prevent the carbon dioxide from solidifying and control the temperature of the liquefied carbon dioxide to the predetermined required temperature.

[0091] In a second invention, in the first invention, the first heat exchanger preferably includes a liquid reservoir section in which the liquid intermediate medium is stored, a stacked heat exchanger formed by stacking a flow path layer immersed in the intermediate medium stored in the liquid reservoir section and having an intermediate medium flow path section into which the intermediate medium infiltrates, and a flow path layer having a carbon dioxide flow path section that serves as a flow path for the carbon dioxide, and a heat transfer tube that is arranged above the liquid level of the intermediate medium stored in the liquid reservoir section and through which the low-temperature liquefied gas is introduced and flows, and is configured so that heat exchange between the intermediate medium in the intermediate medium flow path section and the carbon dioxide in the carbon dioxide flow path section is performed in the stacked heat exchanger to vaporize at least a portion of the intermediate medium, and heat exchange between the vaporized intermediate medium and the low-temperature liquefied gas flowing in the heat transfer tube to condense the intermediate medium, and the low-temperature liquefied gas is vaporized by condensation heat generated by the condensation of the intermediate medium.

[0092] According to this configuration, the part of the first heat exchanger that evaporates the intermediate medium is constructed using a stacked heat exchanger, which makes it possible to more reliably suppress the solidification of carbon dioxide in the first heat exchanger while reducing the size of the first heat exchanger.

[0093] That is, compared to a multi-tubular heat exchanger, a stacked heat exchanger typically has a heat transfer section made of thinner materials and a larger heat transfer area per unit volume. Therefore, carbon dioxide can be liquefied while minimizing the temperature difference between the intermediate medium, which is the low-temperature fluid in the stacked heat exchanger, and the carbon dioxide, which is the high-temperature fluid. In other words, the target temperature of the intermediate medium can be set as high as possible. Therefore, even if the required temperature of carbon dioxide after liquefaction is close to its solidification temperature (e.g., −56°C), it is possible to minimize the temperature of the intermediate medium falling below the solidification temperature of carbon dioxide. Therefore, compared to a multi-tubular heat exchanger, solidification of carbon dioxide in the first heat exchanger can be minimized.

[0094] In a third invention, in the first or second invention, it is preferable that the system further includes a second heat exchanger that is arranged downstream of the first heat exchanger in the flow direction of the low-temperature liquefied gas and performs heat exchange between the vaporized gas vaporized from the low-temperature liquefied gas in the first heat exchanger and the carbon dioxide flowing through the liquefaction target flow path, thereby heating the vaporized gas to a predetermined required temperature while pre-cooling the carbon dioxide.

[0095] According to this configuration, the vaporized gas discharged from the first heat exchanger can be heated to a predetermined required temperature by the second heat exchanger, and simultaneously the carbon dioxide to be liquefied can be pre-cooled. This improves the usability of the heat exchange system as a vaporized gas generation system. In this specification, the predetermined required temperature refers to, for example, an arbitrary temperature required (set) by a user depending on the application.

[0096] In a fourth invention, in the third invention, it is preferable that the second heat exchanger is a stacked heat exchanger in which a flow path layer having a carbon dioxide flow path section that serves as a flow path for the carbon dioxide and a flow path layer having a vaporized gas flow path section that serves as a flow path for the vaporized gas are stacked, and is configured to perform heat exchange between the carbon dioxide flowing through the carbon dioxide flow path section and the vaporized gas flowing through the vaporized gas flow path section.

[0097] According to this configuration, not only the first heat exchanger but also the second heat exchanger are configured as stacked heat exchangers, so that the entire heat exchange system can be configured compactly.

[0098] In a fifth invention, in any one of the first to fourth inventions, it is preferable that the intermediate medium is any one of a mixture of difluoromethane and pentafluoroethane, difluoromethane, and propane.

[0099] According to this configuration, the intermediate medium can be constructed inexpensively and with high thermal conductivity.

Claims

1. A heat exchange system for liquefying carbon dioxide by utilizing the cold energy of a low-temperature liquefied gas, further comprising: a low-temperature flow path into which the low-temperature liquefied gas is introduced and flows; a flow path to be liquefied into which gaseous carbon dioxide is introduced and flows; a first heat exchanger disposed across the low-temperature flow path and the flow path to be liquefied, and which vaporizes the low-temperature liquefied gas and liquefies the carbon dioxide by performing heat exchange via an intermediate medium between the low-temperature liquefied gas flowing through the low-temperature flow path and the carbon dioxide flowing through the flow path to be liquefied; a temperature detection unit which detects the temperature of the intermediate medium or a temperature correlated to that temperature; a flow rate adjustment unit which can adjust the flow rate of at least one of the low-temperature liquefied gas supplied to the low-temperature flow path of the first heat exchanger and the carbon dioxide supplied to the flow path to be liquefied of the first heat exchanger; and a control unit which controls the flow rate adjustment unit so that the temperature detected by the temperature detection unit becomes a predetermined target temperature. A heat exchange system in which the specified target temperature is set so that the temperature of the liquefied carbon dioxide discharged from the first heat exchanger becomes a specified required temperature and so that the carbon dioxide does not solidify on the inner surface of the liquefaction target flow path of the first heat exchanger.

2. A heat exchange system according to claim 1, wherein the first heat exchanger comprises: a liquid reservoir section in which the liquid intermediate medium is stored; a stacked heat exchanger formed by stacking a flow path layer immersed in the intermediate medium stored in the liquid reservoir section, the flow path layer having an intermediate medium flow path section into which the intermediate medium infiltrates, and a flow path layer having a carbon dioxide flow path section which serves as a flow path for the carbon dioxide; and a heat transfer tube arranged above the liquid level of the intermediate medium stored in the liquid reservoir section, through which the low-temperature liquefied gas is introduced and flows, wherein the heat exchange between the intermediate medium in the intermediate medium flow path section and the carbon dioxide in the carbon dioxide flow path section in the stacked heat exchanger is performed to vaporize at least a portion of the intermediate medium, and heat exchange between the vaporized intermediate medium and the low-temperature liquefied gas flowing in the heat transfer tube is performed to condense the intermediate medium, and the low-temperature liquefied gas is vaporized by the condensation heat generated by the condensation of the intermediate medium.

3. A heat exchange system as described in claim 2, further comprising a second heat exchanger that is provided downstream of the first heat exchanger in the flow direction of the low-temperature liquefied gas and performs heat exchange between the vaporized gas vaporized from the low-temperature liquefied gas in the first heat exchanger and the carbon dioxide flowing through the flow path to be liquefied, thereby heating the vaporized gas to a predetermined required temperature while pre-cooling the carbon dioxide.

4. A heat exchange system as described in claim 3, wherein the second heat exchanger is a stacked heat exchanger in which a flow path layer having a carbon dioxide flow path section that serves as a flow path for the carbon dioxide and a flow path layer having a vaporized gas flow path section that serves as a flow path for the vaporized gas are stacked, and the heat exchange system is configured to perform heat exchange between the carbon dioxide flowing through the carbon dioxide flow path section and the vaporized gas flowing through the vaporized gas flow path section.

5. A heat exchange system according to any one of claims 1 to 4, wherein the intermediate medium is any one of a mixture of difluoromethane and pentafluoroethane, difluoromethane, and propane.

Images