Heat exchange system

Abstract

To suppress solidification due to excessive cooling of carbon dioxide and liquefaction failure due to insufficient cooling, in a heat exchange system for liquefying carbon dioxide by using cold of low-temperature liquefied gas.SOLUTION: The heat exchange system 1 is disposed across the low-temperature flow path 2 and the liquefaction target flow path 3, and performs heat exchange between the low-temperature liquefied gas flowing through the low-temperature flow path 2 and the carbon dioxide flowing through the liquefaction target flow path 3 via the intermediate medium M. A first heat exchanger 6 that vaporizes the low-temperature liquefied gas and liquefies the carbon dioxide, a temperature detection unit 15 that detects a temperature of the intermediate medium M or a temperature correlated with the temperature, a flow rate adjustment unit 11,12 capable of adjusting a flow rate of at least one of the low-temperature liquefied gas and the carbon dioxide supplied to the first heat exchanger 6, and a control unit 10 that controls the flow rate adjustment unit 11,12 such that a temperature detected by the temperature detection unit 15 becomes a predetermined target temperature. The predetermined target temperature is a temperature at which carbon dioxide does not solidify.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[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 equipped with an intermediate medium type heat exchanger (see, for example, Patent Document 1). This heat exchanger has a shell in which a liquid intermediate medium is stored, 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 inside the heat source pipe, and the evaporated intermediate medium is condensed by heat exchange between the evaporated intermediate medium and the liquefied gas inside the heat transfer pipe, and the low-temperature liquefied gas is vaporized using the heat of condensation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5409440 Summary of the Invention [Problem to be solved by the invention]

[0005] 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 is becoming increasingly important in recent years as it is also used for liquefying and capturing carbon dioxide amid growing demand for carbon neutrality.

[0006] 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.

[0007] Furthermore, in the conventional intermediate-medium heat exchanger, the heated medium is often LNG and the heated 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.

[0008] The present invention has been made to solve the above-mentioned problems, and 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. [Means for solving the problem]

[0009] 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 liquefaction target flow path through which gaseous carbon dioxide is introduced and flows; a first heat exchanger that is disposed across the low-temperature flow path and the liquefaction target flow path 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 liquefaction target flow path 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.

[0010] 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.

[0011] 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 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.

[0012] 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.

[0013] 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 the liquefied carbon dioxide 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.

[0014] In the third invention, it is preferable that the second invention further includes 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 liquefaction target flow path, thereby heating the vaporized gas to a predetermined required temperature while pre-cooling the carbon dioxide.

[0015] 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. Therefore, the usability of the heat exchange system as a vaporized gas generation system can be improved. In this specification, the predetermined required temperature is, for example, an arbitrary temperature required (set) by the user depending on the application.

[0016] 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.

[0017] 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.

[0018] In a fifth invention, in any one of the first to fourth inventions, it is preferable that the intermediate medium consists of any one of a mixture of difluoromethane and pentafluoroethane, difluoromethane, and propane.

[0019] According to this configuration, the intermediate medium can be constructed inexpensively and with high thermal conductivity. [Effects of the Invention]

[0020] According to the present invention, in a heat exchange system that liquefies carbon dioxide by utilizing the cold of a low-temperature liquefied gas, it is possible to prevent the carbon dioxide from being solidified due to excessive cooling. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a system diagram showing a schematic configuration of a heat exchange system according to a first embodiment. [Figure 2] FIG. 1 is a perspective view showing a stacked heat exchanger provided in a CO2 liquefier. [Figure 3] FIG. 3 is a perspective view of the laminated heat exchanger of FIG. 2 taken along line III-III. [Figure 4] This is a TQ diagram showing the temperature change of the working fluid in a heat exchange system, with heat quantity (enthalpy) on the horizontal axis and temperature on the vertical axis. [Figure 5] 10 is a flowchart illustrating an example of temperature control of an intermediate medium executed by a controller. [Figure 6] FIG. 6 is a view corresponding to FIG. 5 and showing a modified example of the first embodiment. [Figure 7] FIG. 6 is a view corresponding to FIG. 5 and shows the second embodiment. [Figure 8] FIG. 1 is a view equivalent to FIG. 1 and showing another embodiment. [Figure 9] FIG. 1 is a view equivalent to FIG. 1 and showing another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0023] (Embodiment 1) 1 is a system diagram showing a schematic configuration of a heat exchange system 1 in embodiment 1. This 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).

[0024] [Overall configuration of heat exchange system] Specifically, this heat exchange system 1 includes a low-temperature flow path 2 through which LNG flows, a liquefaction-target flow path 3 through which carbon dioxide gas to be liquefied flows, an LNG bypass flow path 4 and a CO2 bypass flow path 5 (described later), a CO2 liquefier 6 (corresponding to a first heat exchanger) that vaporizes LNG and liquefies carbon dioxide by performing heat exchange between the LNG flowing through the low-temperature flow path 2 and the carbon dioxide flowing through the liquefaction-target flow path 3, a NG heater 7 (corresponding to a second heat exchanger) that heats the NG vaporized from LNG in the CO2 liquefier 6 to a predetermined required temperature by performing 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. The CO2 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 a user depending on the application.

[0025] The NG heater 7 is disposed downstream of the CO2 liquefier 6 in the direction of flow of LNG in the low-temperature flow path 2.

[0026] The LNG bypass flow path 4 branches off from the low-temperature flow path 2 and is arranged to bypass the CO2 liquefier 6. That is, the LNG bypass flow path 4 has an upstream end connected to a portion of the low-temperature flow path 2 upstream of the CO2 liquefier 6, and a downstream end connected to a portion of the low-temperature flow path 2 downstream of the CO2 liquefier 6 and upstream of the NG warmer 7. A first NG temperature sensor 16 is connected between the NG warmer 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.

[0027] The CO2 bypass flow path 5 branches off from the liquefaction target flow path 3 and is arranged to bypass the NG heater 7. That is, the CO2 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 upstream of the CO2 liquefier 6. A CO2 temperature sensor 17 is connected to the liquefaction target flow path 3 downstream of the CO2 liquefier 6.

[0028] The heat exchange system 1 further includes an LNG bypass valve 13 arranged in the LNG bypass flow path 4, a CO2 bypass valve 14 arranged in the CO2 bypass flow path 5, an LNG main valve 11 arranged at the upstream end of the low-temperature flow path 2, a CO2 main valve 12 arranged at the upstream end of the liquefaction target flow path 3, an LNG pump 8 arranged upstream of the LNG main valve 11, and a CO2 compressor 9 arranged upstream of the CO2 main valve 12. The LNG pump 8, the CO2 compressor 9, the LNG main valve 11, the CO2 main valve 12, the LNG bypass valve 13, and the CO2 bypass valve 14 are configured to be controllable by a controller 10.

[0029] During operation of the heat exchange system 1, the controller 10 controls the apertures of the LNG main valve 11 and the CO2 main valve 12 to control the temperature of the intermediate medium M in the CO2 liquefier 6. However, if it is not permissible to change the flow rates of LNG and CO2, the controller 10 controls the temperature of the intermediate medium M in the CO2 liquefier 6 by controlling the apertures of the LNG bypass valve 13 and the CO2 bypass valve 14 while maintaining the LNG main valve 11 and the CO2 main valve 12 at predetermined apertures, respectively.

[0030] [Liquidizer configuration] In this example, the CO2 liquefier 6 is configured as an intermediate medium type heat exchanger. Specifically, the CO2 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 multiple heat transfer tubes 63 are shown as a single flow path line.

[0031] The shell 61 is made of a horizontally long, sealed hollow tank. A liquid intermediate medium M (in this example, propane) is stored in the lower part of the shell 61. Thus, the lower part of the shell 61 functions as a liquid reservoir 61e.

[0032] 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 form a part of the low-temperature flow path 2.

[0033] Furthermore, a CO2 supply port 61c for supplying carbon dioxide to the stacked heat exchanger 62 in the shell 61 and a CO2 outlet 61d for discharging carbon dioxide liquefied in the stacked heat exchanger 62 are formed on the lower wall of the shell 61. The CO2 supply port 61c and the stacked heat exchanger 62 are connected via a CO2 inlet pipe 64 arranged in the shell 61. The CO2 outlet 61d and the stacked heat exchanger 62 are connected via a CO2 outlet pipe 65 arranged in the shell 61. Both the CO2 inlet pipe 64 and the CO2 outlet pipe 65 are immersed in the intermediate medium M. The CO2 inlet pipe 64 and the CO2 outlet pipe 65 do not necessarily need to be immersed in the intermediate medium M, and may be arranged to pass above the liquid level of the intermediate medium M.

[0034] The stacked heat exchanger 62 is entirely immersed in the intermediate medium M. The stacked heat exchanger 62 performs heat exchange between gaseous carbon dioxide supplied from a CO2 inlet pipe 64 and the intermediate medium M, thereby vaporizing a portion of the intermediate medium M and liquefying the carbon dioxide, which is then discharged into a CO2 outlet pipe 65. Furthermore, the stacked heat exchanger 62 does not necessarily have to be entirely 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.

[0035] 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 an 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 an LNG discharge port 61b of the shell 61 via a collecting pipe (not shown). It is not necessary to provide multiple heat transfer tubes 63, and only one heat transfer tube 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 line.

[0036] In the CO2 liquefier 6 configured as described above, when gaseous carbon dioxide is supplied to the stacked heat exchanger 62 immersed in the intermediate medium M through the CO2 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 tubes 63. The intermediate medium gas is cooled and condensed by the LNG in the heat transfer tubes 63, while the LNG in the heat transfer tubes 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 warmer 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 vaporizing section E2 that vaporizes LNG.

[0037] 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.

[0038] The stacked heat exchanger 62 comprises a stack 620 that is approximately rectangular and elongated in the left-right direction, a CO2 supply header 625 that covers the left side of the stack 620, and a CO2 discharge header 626 that covers the right side of the stack 620.

[0039] The laminate 620 includes a pair of end plates 623 located at both ends in the front-rear direction, and first and second flow path layers 621 and 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 permeates. The second flow path layer 622 is formed with a number of second flow path sections 622a (corresponding to carbon dioxide flow path sections) through which carbon dioxide supplied from the CO2 inlet pipe 64 flows. Heat exchange occurs between the intermediate medium M permeating 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 liquefaction target flow path 3.

[0040] 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, and 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.

[0041] 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 all need to be disposed horizontally or vertically; for example, some may be disposed vertically, some horizontally, or they may be disposed at an angle.

[0042] The CO2 supply header 625 is connected to the CO2 introduction pipe 64. The CO2 supply header 625 receives gaseous carbon dioxide introduced from the CO2 introduction pipe 64 and supplies it to each second flow path portion 622a of the stack 20.

[0043] The CO2 discharge header 626 is connected to the CO2 outlet pipe 65. The CO2 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 to the CO2 outlet pipe 65.

[0044] 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 heat exchanger 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.

[0045] [NG heater configuration] Returning to Figure 1, the configuration of the NG heater 7 will be described. The NG heater 7 is configured as a microchannel stacked heat exchanger, similar to the CO2 liquefier 6. Note that the NG heater 7 is not limited to the microchannel type, and may be a brazed plate fin type or a multi-tube type.

[0046] 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 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 3 to be liquefied.

[0047] [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, 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 on the horizontal axis, and the temperature increases toward the upper side of the vertical axis. Note that, for simplicity of explanation, in Figure 4, the flow rate of LNG flowing through the LNG bypass flow path 4 and the flow rate of carbon dioxide flowing through the CO2 bypass flow path 5 will be described as zero.

[0048] LNG is supplied from an LNG supply source located outside the heat exchange system 1 at a temperature of -150°C. The LNG is supplied to the CO2 liquefier 6 (see Figure 1). The LNG supplied to the CO2 liquefier 6 exchanges heat with the propane that constitutes the intermediate medium M, increasing its heat content (see Figure 4). As a result, the LNG is heated from -150°C to -48°C and vaporizes to become NG.

[0049] 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).

[0050] Meanwhile, 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 exchanges heat with NG flowing through the first flow path section 71 of the NG heater 7, gradually reducing its heat content (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 a pressure of 2.1 MPa in this example). The carbon dioxide is then supplied to the CO2 liquefier 6 at −17.2°C, where it exchanges heat with LNG and reduces its heat content. Having reached the liquefaction temperature, the carbon dioxide begins to condense from a gas to a liquid. During this condensation period, the carbon dioxide coexists as a gas and a liquid, and its temperature remains constant regardless of the reduction in heat content. When the calorific value of the carbon dioxide further decreases and the condensation section ends, all of the carbon dioxide is liquefied, and then the temperature drops as the calorific value decreases, and the carbon dioxide is finally discharged from the CO2 liquefier 6 as liquid carbon dioxide at -42°C (an example of a predetermined required temperature).

[0051] The propane constituting the intermediate medium M is stored at −45° C. in the shell 61 of the CO2 liquefier 6, and repeatedly evaporates due to heat exchange with carbon dioxide and condenses due to the cold heat of the LNG.

[0052] [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.

[0053] The controller 10 is connected to be able to send and receive signals to the LNG pump 8, CO2 compressor 9, LNG main valve 11, CO2 main valve 12, LNG bypass valve 13, CO2 bypass valve 14, intermediate medium temperature sensor 15, first NG temperature sensor 16, second NG temperature sensor 18, and CO2 temperature sensor 17. The controller 10 is configured by a computer having a CPU, ROM, and RAM, and executes various processes that will be explained in the flowchart of Figure 5, which will be described later.

[0054] The intermediate medium temperature sensor 15 detects the temperature (liquid temperature) of the intermediate medium M stored in the shell 61 of the CO2 liquefier 6 and transmits the detected temperature information to the controller 10. Furthermore, the first NG temperature sensor 16 detects the temperature of 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 NG discharged from the NG heater 7 and transmits the detected temperature information to the controller 10. The CO2 temperature sensor 17 detects the temperature of liquefied carbon dioxide discharged from the CO2 liquefier 6 and transmits the detected temperature information to the controller 10.

[0055] The controller 10 controls the temperature of the intermediate medium M to a predetermined target temperature by controlling the apertures of the LNG main valve 11 and the CO2 main valve 12 based on the temperature detected by the intermediate medium temperature sensor 15. This predetermined target temperature is a temperature that is set in advance so that the temperature of the liquefied carbon dioxide discharged from the CO2 liquefier 6 becomes a predetermined required temperature (-42°C in this example) and so that the 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 CO2 liquefier 6. Note that, below, an example will be described in which the controller 10 controls the LNG main valve 11 and the CO2 main valve 12 when controlling the temperature of the intermediate medium M, but this is not limiting, and the controller 10 may be configured to control the LNG bypass valve 13 and the CO2 bypass valve 14 as described below.

[0056] FIG. 5 is a flowchart showing an example of the temperature control of the intermediate medium M executed by the controller 10.

[0057] In step SA1, the temperature detected by the intermediate medium temperature sensor 15 is acquired.

[0058] In step SA2, it is determined whether the detected temperature acquired in step SA1 is equal to the predetermined target temperature. If the determination is YES, the process returns to step SA1, whereas if the determination is NO, the process proceeds to step SA3.

[0059] 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.

[0060] In step SA4, control signals are sent to the LNG main valve 11 and the CO2 main valve 12 to decrease the aperture of the LNG main valve 11 by a predetermined amount and increase the aperture of the CO2 main valve 12 by a predetermined amount. As a result, the supply amount of carbon dioxide, which is the high-temperature fluid supplied to the CO2 liquefier 6, increases and the supply amount of LNG, which is the low-temperature fluid, decreases, so that the temperature of the intermediate medium M increases and the detected temperature approaches the predetermined target temperature. After processing 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.

[0061] In step SA5, which is reached when the determination in step SA3 is NO, control signals are sent to the LNG main valve 11 and the CO2 main valve 12 to increase the opening of the LNG main valve 11 by a predetermined amount and decrease the opening of the CO2 main valve 12 by a predetermined amount. As a result, the supply amount of carbon dioxide, which is the high-temperature fluid supplied to the CO2 liquefier 6, decreases and the supply amount of LNG, which is the low-temperature fluid, increases, so that the temperature of the intermediate medium M decreases and the detected temperature approaches the predetermined target temperature. After processing 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.

[0062] In steps SA4 and S5, the predetermined amount may be set based on PID control, PI control, PD control, or the like.

[0063] [Action and effect] As described above, the heat exchange system 1 of this embodiment includes the intermediate medium temperature sensor 15 that detects the temperature of the intermediate medium M stored in the lower part (liquid reservoir section 61e) of the shell 61 of the CO2 liquefier 6, and the controller 10. The controller 10 is configured to adjust the apertures of the LNG main valve 11 and the CO2 main valve 12 to adjust the flow rates of LNG and carbon dioxide supplied to the CO2 liquefier 6 so that the temperature detected by the intermediate medium temperature sensor 15 becomes the predetermined target temperature. The target temperature is set so that the temperature of the liquefied carbon dioxide discharged from the CO2 liquefier 6 becomes the predetermined required temperature and so that the carbon dioxide does not solidify on the inner surface of the second flow path section 622a (part of the liquefaction target flow path 3) provided in the stack 620 of the CO2 liquefier 6.

[0064] According to this configuration, by using an intermediate medium-type heat exchanger as the CO2 liquefier 6, direct heat exchange between LNG and carbon dioxide, which have a large temperature difference, is avoided, thereby minimizing the occurrence of thermal stress. Furthermore, by controlling the LNG main valve 11 and the CO2 main valve 12 (an example of a flow rate adjusting unit) by the controller 10 to control the temperature of the intermediate medium M to the predetermined target temperature, it is possible to prevent carbon dioxide from solidifying on the inner surface of the second flow path section 622a of the CO2 liquefier 6 and suppress poor liquefaction due to insufficient cooling of carbon dioxide. That is, in conventional intermediate medium-type heat exchangers, the temperature of the intermediate medium M is determined by chance, and therefore the temperature of the intermediate medium M may fall below 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 apertures of the LNG main valve 11 and the CO2 main valve 12 are controlled by the controller 10 so that the temperature detected by the intermediate medium temperature sensor 15 is a temperature at which carbon dioxide does not solidify (the predetermined target temperature). Therefore, it is possible to prevent the temperature of the intermediate medium M from dropping excessively, which occurs in the conventional case, and to prevent the carbon dioxide from solidifying in the CO2 liquefier 6.

[0065] In this embodiment, the CO2 liquefier 6 includes a laminate 620 including a first flow path layer 621 immersed in the intermediate medium M in the liquid reservoir 61e and 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 serving as a flow path for carbon dioxide, and a heat transfer tube 63 disposed above the liquid level of the liquid intermediate medium M and through which LNG flows. The CO2 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 portion 621a and the carbon dioxide in the second flow path portion 622a in the laminated heat exchanger 62, and to perform heat exchange between the vaporized intermediate medium M and the LNG flowing through the heat transfer tube 63.

[0066] According to this configuration, the part of the CO2 liquefier 6 that evaporates the intermediate medium M is constructed using a stacked heat exchanger 62, which makes it possible to more reliably suppress the solidification of carbon dioxide in the CO2 liquefier 6 while reducing the overall size of the CO2 liquefier 6.

[0067] That is, compared to a multi-tubular heat exchanger, the stacked heat exchanger 62 typically has a heat transfer section made of thinner materials and a larger heat transfer area per unit volume. This allows the temperature difference between the intermediate medium M, which is the low-temperature fluid in the stacked heat exchanger 62, and the carbon dioxide, which is the high-temperature fluid, to be minimized. In other words, the target temperature of the intermediate medium can be set as high as possible. Therefore, even if the required temperature of the liquefied carbon dioxide discharged from the CO2 liquefier 6 is close to its solidification temperature (e.g., −56°C), it is possible to minimize the temperature of the intermediate medium M falling below the solidification temperature of the carbon dioxide. Therefore, compared to a multi-tubular heat exchanger, the solidification of carbon dioxide in the CO2 liquefier 6 can be minimized.

[0068] In this embodiment, the heat exchange system 1 also includes an NG heater 7 that is provided downstream of the CO2 liquefier 6 in the LNG flow direction. The NG heater 7 is configured to perform heat exchange between NG vaporized from LNG in the CO2 liquefier 6 and gaseous carbon dioxide in the liquefaction target flow path 3, thereby heating the NG to a predetermined required temperature and pre-cooling the gaseous carbon dioxide at the same time.

[0069] According to this configuration, the NG discharged from the CO2 liquefier 6 can be heated to a predetermined required temperature by the NG heater 7. Therefore, the usability of the heat exchange system 1 as a vaporized gas generation system can be improved.

[0070] 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.

[0071] According to this configuration, not only the CO2 liquefier 6 but also the NG heater 7 are configured as stacked heat exchangers, so that the entire heat exchange system 1 can be configured compactly.

[0072] (Modification of the first embodiment) 6 is a diagram equivalent to FIG. 5 showing a modification of the first embodiment. This modification differs from the first embodiment in that the LNG pump 8 and the CO2 compressor 9 are controlled when controlling the temperature of the intermediate medium M. In the following description, the same processes as those in the first embodiment will be omitted as appropriate.

[0073] In steps SB1 to SB3, the same processes as in steps SA1 to SA4 in the first embodiment are executed.

[0074] In step SB4, which is reached when the determination in step SB3 is YES, control signals are sent to the LNG pump 8 and the CO2 compressor to decrease the discharge flow rate of the LNG pump 8 by a predetermined amount and increase the discharge flow rate of the CO2 compressor 9 by a predetermined amount. As a result, the supply amount of carbon dioxide, which is the high-temperature fluid supplied to the CO2 liquefier 6, increases and the supply amount of LNG, which is the low-temperature fluid, decreases, so that the temperature of the intermediate medium M increases and the detected temperature approaches the predetermined target temperature. After processing 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.

[0075] In step SB5, which is reached when the determination in step SB3 is NO, control signals are sent to the LNG pump 8 and the CO2 compressor to increase the discharge flow rate of the LNG pump 8 by a predetermined amount and decrease the discharge flow rate of the CO2 compressor 9 by a predetermined amount. As a result, the supply amount of carbon dioxide, which is the high-temperature fluid supplied to the CO2 liquefier 6, decreases and the supply amount of LNG, which is the low-temperature fluid, increases, so that the temperature of the intermediate medium M decreases and the detected temperature approaches the predetermined target temperature. After processing in 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.

[0076] In steps SB4 and SB5, the predetermined amount may be set based on PID control, PI control, PD control, or the like.

[0077] As described above, according to this modification, the temperature of the intermediate medium M can be controlled to the target temperature by controlling the LNG pump 8 and the CO2 compressor 9 by the controller 10. Therefore, the same effects as those of the first embodiment can be obtained.

[0078] (Embodiment 2) 7 is a view corresponding to FIG. 5 showing a second embodiment. This embodiment differs from the above-described embodiments in that the opening degrees of the LNG bypass valve 13 and the CO2 bypass valve 14 are controlled when controlling the temperature of the intermediate medium M. In the following description, the same processes as those in the first embodiment will be omitted as appropriate.

[0079] In steps SC1 to SC3, the same processes as in steps SA1 to SA3 in the first embodiment are executed.

[0080] In step SC4, control signals are sent to the CO2 bypass valve 14 and the LNG bypass valve 13 to increase the aperture of the CO2 bypass valve 14 by a predetermined amount and to increase the aperture of the LNG bypass valve 13 by a predetermined amount. As a result, 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 carbon dioxide that is the high-temperature side fluid supplied to the CO2 liquefier 6 increases, and the supply amount of LNG that is the low-temperature side fluid supplied to the CO2 liquefier 6 decreases, so that the temperature of the intermediate medium M increases and the detected temperature approaches the predetermined target temperature. After processing 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.

[0081] In step SC5, which is reached when the determination in step SC3 is NO, control signals are sent to the CO2 bypass valve 14 and the LNG bypass valve 13 to decrease the aperture of the CO2 bypass valve 14 by a predetermined amount and decrease the aperture of the LNG bypass valve 13 by a predetermined amount. As a result, the proportion of carbon dioxide that passes through the NG heater 7 (i.e., pre-cooled carbon dioxide) among the carbon dioxide that is the high-temperature side fluid supplied to the CO2 liquefier 6 increases, and the supply amount of LNG that is the low-temperature side fluid supplied to the CO2 liquefier 6 increases. As a result, the temperature of the intermediate medium M decreases, and the detected temperature approaches the predetermined target temperature. After processing 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.

[0082] In steps SC4 and SC5, the predetermined amount may be set based on PID control, PI control, PD control, or the like.

[0083] As described above, according to this embodiment, the temperature of the intermediate medium M can be controlled to the target temperature by controlling the LNG bypass valve 13 and the CO2 bypass valve 14 by the controller 10. Therefore, the same effects as those of the first embodiment can be obtained.

[0084] Furthermore, in the configuration of this embodiment in which the temperature of the intermediate medium M is controlled by controlling the LNG bypass valve 13 and the CO2 bypass valve 14, there is no need to change the flow rates of LNG and carbon dioxide supplied to the heat exchange system 1, as compared to the case in which the main valves 11 and 12 are adjusted as in embodiment 1. Therefore, the configuration of this embodiment is particularly useful in cases where, for example, the flow rate of LNG after vaporization and the flow rate of carbon dioxide after liquefaction in the heat exchange system 1 need to be maintained at predetermined required flow rates (constant values).

[0085] In addition, in this embodiment, the downstream end of the LNG bypass flow path 4 is connected to the upstream side of the NG warmer 7, not the downstream side, thereby making it possible to prevent the bypassed liquid LNG from remaining at the outlet of the heat exchange system 1 (the downstream end of the low-temperature flow path 2). In addition, in this embodiment, the downstream end of the CO2 bypass flow path 5 is connected to the upstream side of the CO2 liquefier 6, not the downstream side, thereby making it possible to prevent the bypassed gaseous CO2 from remaining at the outlet of the heat exchange system 1 (the downstream end of the liquefaction target flow path 3).

[0086] 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 that the carbon dioxide will solidify 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.

[0087] (Other embodiments) The heat exchange system 1 according to the embodiment of the present invention has been described above, but the present invention is not limited to this, and for example, the following modified embodiments can be adopted.

[0088] (1) In the first embodiment, the heat exchange system 1 includes the LNG bypass flow path 4, the CO2 bypass flow path 5, the LNG bypass valve 13, and the CO2 bypass valve 14. However, the present invention is not limited to this. In other words, these are not necessarily required in the first embodiment. For example, as shown in FIG. 8, the heat exchange system 1 may be configured without the bypass flow paths 4 and 5 and the bypass valves 13 and 14.

[0089] (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 the downstream end of the CO2 bypass flow path 5 is connected to the upstream side of the CO2 liquefier 6. However, the present invention is not limited to this. For example, as shown in FIG. 9, the downstream end of the LNG bypass flow path 4 may be connected to the downstream side of the NG heater 7, and the downstream end of the CO2 bypass flow path 5 may be connected to the downstream side of the CO2 liquefier 6. In this case, for example, instead of the processing of step SA4, processing may be performed to decrease the aperture of the CO2 bypass valve 14 by a predetermined amount and increase the aperture of the LNG bypass valve 13 by a predetermined amount, and instead of the processing of step SA5, processing may be performed to increase the aperture of the CO2 bypass valve 14 by a predetermined amount and decrease the aperture of the LNG bypass valve 13 by a predetermined amount, thereby achieving the same effects as those of the second embodiment.

[0090] (3) In the above-described embodiments and modifications, both the flow rate of carbon dioxide and the flow rate of LNG supplied to the CO2 liquefier 6 are adjusted (steps SA4 to SC4 and steps SA5 to SC5), but only one of the flow rates may be adjusted. In other words, the flow rate adjustment unit may have any configuration 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 CO2 liquefier 6.

[0091] (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, and 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 be configured to 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.

[0092] (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.

[0093] (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.

[0094] (7) In the above embodiment, LNG is used as an example of a low-temperature liquefied gas, but the present invention is not limited to this and may be liquefied hydrogen (LH2), for example.

[0095] (8) In the above embodiment, 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 as long as it contains carbon dioxide.

[0096] (9) In each of the above-described embodiments and modifications, the temperature of the LNG at the LNG supply port 61a (LNG inlet) of the CO2 liquefier 6 is set to -150°C, but this is not limited thereto. That is, the temperature of the LNG flowing into the CO2 liquefier 6 may be any temperature that does not interfere with the liquefaction of carbon dioxide in the CO2 liquefier 6, that allows the temperature of the carbon dioxide discharged from the CO2 liquefier 6 to reach a predetermined required temperature, and that does not solidify the carbon dioxide in the CO2 liquefier 6. Furthermore, in each of the above-described embodiments and modifications, the temperature of the LNG supplied from the LNG supply port 61a to the CO2 liquefier 6 is set to a temperature that can liquefy all of the gaseous carbon dioxide supplied to the liquefaction target flow path 3, but this is not limited thereto, and the temperature may be set to a temperature that can liquefy only a portion of the carbon dioxide.

[0097] (10) In each of the above-described 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 is the predetermined required temperature required at the discharge position and the carbon dioxide does not solidify in the NG heater 7.

[0098] (11) The present invention includes any combination of the above-described embodiments and modifications. Therefore, for example, the aperture control of the main valves 11 and 12 disclosed in the first embodiment and the aperture 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 aperture of the LNG main valve 11, and the flow rate of carbon dioxide may be adjusted by adjusting the aperture of the CO2 bypass valve 14. Also, for example, the flow rate of LNG may be adjusted by adjusting the aperture of the LNG bypass valve 13, and the flow rate of carbon dioxide may be adjusted by adjusting the aperture of the CO2 main valve 12. [Explanation of symbols]

[0099] E1: Intermediate medium evaporation section E2: Liquefied gas vaporizer M: Intermediate medium 1: Heat exchange system 2: Low temperature flow path 3: Flow path for liquefaction 4: LNG bypass flow path 5: CO2 bypass channel 6:CO2 liquefier (1st heat exchanger) 7:NG warmer (second heat exchanger) 10: Controller (control unit) 11:LNG main valve (flow adjustment part) 12:CO2 main valve (flow rate adjustment part) 13: LNG bypass valve (flow rate control section) 14: CO2 bypass valve (flow rate adjustment part) 15: Intermediate medium temperature sensor (temperature detection part) 61e: Liquid reservoir 62: Stacked heat exchanger 63: Heat transfer tube 71: First flow path section (vaporized gas flow path section) 72: Second flow path section (carbon dioxide flow path section) 620: Laminate 621: First flow path layer (flow path layer) 621a: First flow path section (intermediate medium flow path section) 622: Second flow path layer (flow path layer) 622a: Second flow path section (carbon dioxide flow path section)

Claims

1. A heat exchange system that liquefies carbon dioxide using the cold heat of a low-temperature liquefied gas, a low-temperature flow path through which the low-temperature liquefied gas flows; a flow path to be liquefied into 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 performs 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, 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 with the temperature; a flow rate adjusting unit that adjusts 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 liquefaction target flow path of the first heat exchanger; 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, 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. 2. The heat exchange system of claim 1, The first heat exchanger is a liquid reservoir portion in which the liquid intermediate medium is stored; a stacked heat exchanger including a flow path layer immersed in the intermediate medium stored in the liquid reservoir and having an intermediate medium flow path portion into which the intermediate medium infiltrates, and a flow path layer having a carbon dioxide flow path portion that serves as a flow path for the carbon dioxide; 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 flows, A heat exchange system configured to vaporize at least a portion of the intermediate medium by performing 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, condense the intermediate medium by performing heat exchange between the vaporized intermediate medium and the low-temperature liquefied gas flowing in the heat transfer tube, and vaporize the low-temperature liquefied gas using the condensation heat.

3. 3. The heat exchange system according to claim 2, The heat exchange system further includes 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 liquefaction target flow path, thereby heating the vaporized gas to a predetermined required temperature while pre-cooling the carbon dioxide.

4. 4. The heat exchange system according to claim 3, 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.

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

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