Heat exchanger and heat exchanging system

Abstract

To provide a heat exchanger for liquefying a carbon dioxide by a cooing heat of a low-temperature liquefied gas, in which solidification of the carbon dioxide is suppressed.SOLUTION: A heat exchanger 2 includes; a low-temperature passage 21 in which a low-temperature liquefaction gas is introduced; and a liquefaction target passage 22 in which a gaseous carbon dioxide is introduced. The low-temperature passage 21 includes a low-temperature fluid inlet 21a at a position corresponding to an intermediate position between a CO2 inlet 22a and a CO2 outlet 22b of the liquefaction target passage 22, and includes a low-temperature fluid outlet 21b at a position corresponding to the CO2 inlet 22a of the liquefaction target passage 22. The low-temperature passage 21 heats the low-temperature liquefaction gas received from the low-temperature fluid inlet 21a by exchanging heat between the carbon dioxide flowing through a first predefined region of the liquefaction target passage 22, to make it a gasified gas. The heated gasified gas passes through a CO2 outlet opening 21c provided at a position corresponding to the CO2 outlet 22b of the liquefaction target passage 22, and a heat is exchanged with respect to the carbon dioxide flowing through a second predefined region of the liquefaction target passage 22.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-168207 Summary of the Invention [Problem to be solved by the invention]

[0004] It is possible to use carbon dioxide instead of nitrogen as the gas to be liquefied in the heat exchanger and heat exchange system shown in Patent Document 1. Carbon dioxide liquefaction technology has become increasingly important in recent years as the demand for carbon neutrality has increased and it is also used for liquefying and capturing carbon dioxide.

[0005] However, the temperature of the low-temperature liquefied gas used to cool carbon dioxide in the heat exchanger is, for example, -150°C to -160°C, which is significantly lower than the solidification temperature (approximately -56°C) of carbon dioxide at typical pressures (0.52 MPa to 3 MPa) during storage and transportation. Therefore, there is a risk that the carbon dioxide flowing through the gas flow path to be liquefied in the heat exchanger will solidify due to the cold heat of the low-temperature liquefied gas, causing blockage of the flow path.

[0006] The present invention has been made to solve the above-mentioned problems, and aims to suppress solidification of carbon dioxide due to the cold energy of low-temperature liquefied gas in a heat exchanger and heat exchange system that liquefies carbon dioxide using the cold energy of low-temperature liquefied gas. [Means for solving the problem]

[0007] a low-temperature flow path having a low-temperature fluid inlet into which the low-temperature liquefied gas is introduced and a low-temperature fluid outlet from which vaporized gas obtained after vaporization of the low-temperature liquefied gas is discharged; and a flow path to be liquefied having a CO2 inlet into which the gaseous carbon dioxide to be liquefied is introduced and a CO2 outlet from which the liquefied carbon dioxide is discharged. The low-temperature flow path has the low-temperature fluid inlet at a position corresponding to an intermediate position between the CO2 inlet and the CO2 outlet in the flow path to be liquefied, and has the low-temperature fluid outlet at a position corresponding to the CO2 inlet in the flow path to be liquefied. The low-temperature liquefied gas received from the low-temperature fluid inlet is heated and converted into vaporized gas by circulating the low-temperature liquefied gas while exchanging heat with carbon dioxide flowing through a first predetermined region of the flow path to be liquefied. The heated vaporized gas is then heat exchanged with carbon dioxide flowing through a second predetermined region of the flow path to be liquefied via a CO2 outlet-corresponding position corresponding to the CO2 outlet of the flow path to be liquefied, and is then discharged from the low-temperature fluid outlet.

[0008] According to this configuration, the low-temperature fluid inlet is located at a position corresponding to the midpoint between the CO2 inlet and the CO2 outlet in the liquefaction target flow path. The low-temperature liquefied gas flowing through the low-temperature fluid inlet is heated and then passed through the CO2 outlet-corresponding position corresponding to the CO2 outlet. This suppresses the solidification of carbon dioxide due to the cold energy of the low-temperature liquefied gas. Specifically, the low-temperature liquefied gas temperature is lowest at the low-temperature fluid inlet in the low-temperature flow path. However, if the low-temperature fluid inlet is located at a position corresponding to the CO2 outlet, the inner surface of the CO2 outlet is cooled by the lowest-temperature low-temperature liquefied gas. As a result, the wall temperature around the CO2 outlet may fall below the solidification temperature of carbon dioxide. Here, if the temperature of the carbon dioxide discharged from the CO2 outlet is high, the carbon dioxide will not solidify even if the temperature of the inner surface of the CO2 outlet falls below the solidification temperature. However, if the temperature of the carbon dioxide discharged is low (e.g., between −40°C and −50°C), the carbon dioxide may solidify on the inner surface of the CO2 outlet.

[0009] This problem can be avoided by setting the temperature of the carbon dioxide discharged from the CO2 outlet, i.e., the temperature of the liquefied carbon dioxide required by the user, higher, but doing so limits the temperature range of the liquefied carbon dioxide obtained through the heat exchanger, reducing the useful value of the heat exchanger. Therefore, it is possible to use a high-temperature refrigerant other than the low-temperature liquefied gas only near the CO2 outlet, thereby controlling the inner surface temperature of the CO2 outlet to a temperature at which the carbon dioxide does not solidify (for example, a temperature higher than -56°C, but this is not limited to this). However, in this case, additional equipment is required to store and circulate the high-temperature refrigerant, which increases costs.

[0010] In contrast, with the above-described configuration, the cryogenic fluid inlet, where the low-temperature liquefied gas is at its lowest, is located at a position corresponding to the midpoint between the CO2 inlet and the CO2 outlet in the liquefaction-target flow path. This distance from the cryogenic fluid inlet minimizes the temperature drop on the inner surface of the CO2 outlet. This ultimately suppresses the solidification of carbon dioxide. Meanwhile, at the midpoint of the liquefaction-target flow path, carbon dioxide is cooled by the lowest-temperature cryogenic liquefied gas flowing into the cryogenic fluid inlet. However, carbon dioxide is in a gaseous state near the CO2 inlet, a condensed state in the center, and a liquid state near the CO2 outlet. Therefore, the heat transfer coefficient of the condensed state at the midpoint of the liquefaction-target flow path is typically higher than the heat transfer coefficient of the liquid state near the CO2 outlet. Therefore, the cooling effect of the cryogenic liquefied gas on the flow path wall is reduced at the midpoint of the liquefaction-target flow path compared to near the CO2 outlet. Therefore, as in the above configuration, arranging the low-temperature fluid inlet at an intermediate position of the flow path to be liquefied can suppress solidification of carbon dioxide more effectively than arranging it near the CO2 outlet.

[0011] The low-temperature liquefied gas flowing in from the low-temperature fluid inlet is heated as it passes through the first predetermined area to become a vaporized gas, and the heated vaporized gas is passed through the CO2 outlet corresponding position, thereby reliably suppressing a decrease in the temperature of the inner surface of the CO2 outlet. Therefore, solidification of carbon dioxide on the inner surface of the CO2 outlet can be suppressed as much as possible.

[0012] A second invention is related to the first invention, wherein the low-temperature flow path comprises a first flow path section that heats the low-temperature liquefied gas received from the low-temperature fluid inlet by performing counterflow or crossflow heat exchange with carbon dioxide flowing in an intermediate region in the flow path length direction of the flow path to be liquefied, and discharges the heated vaporized gas, and a second flow path section that receives the heated vaporized gas discharged from the first flow path section from the CO2 outlet corresponding position, and performs counterflow heat exchange between the received vaporized gas and carbon dioxide flowing in a downstream region downstream of the intermediate region in the flow path to be liquefied. the third flow path section that receives the vaporized gas after passing through the second flow path section and performs countercurrent heat exchange with carbon dioxide flowing in an upstream region upstream of the intermediate region in the flow path to be liquefied; a first connecting flow path section that connects the downstream end of the first flow path section to the upstream end of the second flow path section; and a second connecting flow path section that connects the downstream end of the second flow path section to the upstream end of the third flow path section, and it is preferable that the first predetermined region is the intermediate region of the flow path to be liquefied and the second predetermined region is composed of the downstream region and the upstream region of the flow path to be liquefied.

[0013] According to this configuration, the vaporized gas heated in the first flow path section can be passed through the CO2 outlet-corresponding position in the low-temperature flow path that corresponds to the CO2 outlet and then flow into the second flow path section. Therefore, the same effects as those of the first invention can be obtained. Furthermore, according to this configuration, the heat exchange method between the low-temperature liquefied gas introduced into the low-temperature flow path and the carbon dioxide introduced into the liquefaction target flow path can be realized by a counterflow method or a combination of a counterflow method and a crossflow method. Therefore, the temperature of the evaporated low-temperature liquefied gas discharged from the heat exchanger can be made higher than when a parallel flow method is used. Therefore, a wide temperature range of the evaporated low-temperature liquefied gas desired by users can be accommodated.

[0014] In a third invention, in the first invention, the low-temperature flow path has a first flow path section configured to heat the low-temperature liquefied gas received from the low-temperature fluid inlet by performing counterflow or crossflow heat exchange with carbon dioxide flowing in an intermediate region in the flow path length direction of the flow path to be liquefied, thereby converting it into a vaporized gas; a second flow path section that receives the heated vaporized gas from the CO2 outlet corresponding position and performs counterflow heat exchange between the received vaporized gas and carbon dioxide flowing in the entire region in the flow path length direction of the flow path to be liquefied; and a connecting flow path section that connects the downstream end of the first flow path section and the upstream end of the second flow path section, and it is preferable that the first predetermined region consists of the intermediate region of the flow path to be liquefied and the second predetermined region consists of the entire region of the flow path to be liquefied.

[0015] According to this configuration, the vaporized gas heated in the first flow path section can flow into the second flow path section via the CO2 outlet-corresponding position in the low-temperature flow path. Therefore, the same effects as those of the first aspect of the present invention can be achieved. Furthermore, according to this configuration, the heat exchange between the low-temperature liquefied gas introduced into the low-temperature flow path and the carbon dioxide introduced into the liquefaction-target flow path can be achieved using a counterflow method or a combination of a counterflow and a crossflow method. This allows the temperature of the evaporated low-temperature liquefied gas discharged from the heat exchanger to be higher than when a parallel flow method is used. This allows for a wider temperature range of the evaporated low-temperature liquefied gas desired by users. Furthermore, according to this configuration, heat exchange occurs between the vaporized gas flowing through the second flow path section and the carbon dioxide flowing throughout the entire length of the liquefaction-target flow path. This eliminates the need to extend the second flow path section to the outside of the heat exchanger. Therefore, the heat exchange flow paths can be concentrated as much as possible within the heat exchanger, reducing the number of connecting pipes.

[0016] A fourth invention is the first invention, which comprises a first flow path section that heats the low-temperature liquefied gas received from the low-temperature fluid inlet by performing parallel flow heat exchange with carbon dioxide flowing through an outlet side region from the intermediate position in the liquefaction target flow path to the CO2 outlet, and discharges the heated gas as the vaporized gas; a second flow path section that receives the vaporized gas discharged from the first flow path section and performs counter flow heat exchange with carbon dioxide flowing through an inlet side region upstream of the outlet side region in the liquefaction target flow path; and a connecting flow path section that connects the downstream end of the first flow path section and the upstream end of the second flow path section, and it is preferable that the first predetermined region consists of the outlet side region of the liquefaction target flow path and the second predetermined region consists of the inlet side region of the liquefaction target flow path.

[0017] According to this configuration, the vaporized gas heated in the first flow path section can be introduced into the second flow path section via the CO2 outlet-corresponding position in the low-temperature flow path that corresponds to the CO2 outlet. Therefore, the same effects as those of the first invention can be achieved. Furthermore, according to the configuration, the heat exchange between the low-temperature liquefied gas introduced into the low-temperature flow path and the carbon dioxide introduced into the liquefaction target flow path can be achieved by combining parallel flow and counterflow flow. This allows the temperature of the evaporated low-temperature liquefied gas discharged from the heat exchanger to be higher than when a parallel flow system is used throughout the flow path. This allows for a wider temperature range of the evaporated low-temperature liquefied gas desired by users. Furthermore, by using a parallel flow system for the first flow path section, the flow path configuration from the low-temperature fluid inlet of the first flow path section to the CO2 outlet-corresponding position can be simplified. This avoids the problems of increased costs and increased assembly man-hours due to a complex flow path configuration.

[0018] In a fifth aspect of the present invention, in the first aspect, the low-temperature flow path has a first flow path section that performs heat exchange in a parallel flow manner between the low-temperature liquefied gas received from the low-temperature fluid inlet and carbon dioxide flowing in an outlet-side region from the intermediate position of the flow path to the CO2 outlet, and discharges the low-temperature liquefied gas as the vaporized gas, a second flow path section that receives the vaporized gas discharged from the first flow path section, performs heat exchange in a counterflow manner between the low-temperature liquefied gas and carbon dioxide flowing in the entire region of the flow path to be liquefied from the CO2 outlet to the CO2 inlet, and discharges the vaporized gas, and a connecting flow path section that connects the downstream end of the first flow path section and the upstream end of the second flow path section, and it is preferable that the first predetermined region consists of the outlet-side region of the flow path to be liquefied and the second predetermined region consists of the entire region of the flow path to be liquefied.

[0019] According to this configuration, the vaporized gas heated in the first flow path section can be introduced into the second flow path section via the CO2 outlet-corresponding position in the low-temperature flow path that corresponds to the CO2 outlet. Therefore, the same effects as those of the first invention can be achieved. Furthermore, according to the configuration, the heat exchange method between the low-temperature liquefied gas introduced into the low-temperature flow path and the carbon dioxide introduced into the liquefaction target flow path can be achieved by combining parallel flow and counterflow methods. This allows the temperature of the evaporated low-temperature liquefied gas discharged from the heat exchanger to be higher than when a parallel flow method is used throughout the flow path. Therefore, it is possible to accommodate a wide temperature range of the evaporated low-temperature liquefied gas desired by users. Furthermore, by using a parallel flow method for the first flow path section, the flow path configuration from the low-temperature fluid inlet of the first flow path section to the CO2 outlet-corresponding position can be simplified.

[0020] Furthermore, with this configuration, heat exchange occurs between the heated vaporized gas that has flowed into the second flow path section and the carbon dioxide that flows through the entire length of the flow path to be liquefied, so there is no need to extend the second flow path section to the outside of the heat exchanger along the way.This makes it possible to concentrate the flow paths for heat exchange within the heat exchanger as much as possible and reduce the number of connecting pipes.

[0021] A sixth invention is a heat exchange system including a heat exchanger according to the second, third or fifth invention, comprising: a supply flow path connected to the low-temperature fluid inlet and guiding low-temperature liquefied gas supplied from outside to the low-temperature fluid inlet; a bypass flow path branching from the supply flow path, bypassing the first flow path section of the low-temperature flow path and connected to a predetermined portion of the low-temperature flow path upstream of the CO2 outlet corresponding position; and a bypass valve provided in the bypass flow path.

[0022] According to this configuration, the low-temperature liquefied gas that has passed through the bypass flow path and the vaporized gas discharged from the first flow path unit join together and are supplied to the CO2 liquefaction position at a lower temperature than the vaporized gas discharged from the first flow path unit. Here, since the bypass flow path is provided with a bypass valve, by controlling the opening degree of the bypass valve, the flow rate ratio between the low-temperature liquefied gas that has passed through the bypass flow path and the vaporized gas discharged from the first flow path unit can be adjusted, making it possible to easily control the temperature of the mixed fluid (low-temperature fluid that cools carbon dioxide) supplied to the CO2 liquefaction position. As a result, it is possible to easily control the temperature of the liquefied carbon dioxide discharged from the heat exchanger.

[0023] A seventh invention is the sixth invention, further comprising a temperature detection unit that detects the temperature of a mixed fluid of the vaporized gas vaporized in the first flow path section and the low-temperature liquefied gas that has passed through the bypass flow path, or a temperature correlated to that temperature, and a control unit that controls the bypass valve based on the temperature detected by the temperature detection unit, and the control unit is preferably configured to perform bypass valve control that controls the bypass valve so that the temperature detected by the temperature detection unit becomes a predetermined target temperature.

[0024] According to this configuration, the bypass valve is automatically controlled by the control unit, so that the temperature of the mixed fluid can be more easily controlled than when the bypass valve is opened and closed manually.

[0025] The eighth invention is, in the seventh invention, preferably, the predetermined target temperature is a temperature that is set in advance so that the temperature of the liquefied carbon dioxide discharged from the heat exchanger becomes a predetermined required temperature and so that the carbon dioxide does not solidify on the inner surface of the liquefaction target flow path.

[0026] According to this configuration, the temperature of the liquefied carbon dioxide discharged from the liquefaction target flow path can be controlled to a predetermined required temperature, while solidification of the carbon dioxide within the liquefaction target flow path can be reliably prevented.

[0027] A ninth invention is a heat exchange system equipped with the heat exchanger according to the fourth invention, comprising: a supply flow path connected to the low-temperature fluid inlet and guiding low-temperature liquefied gas supplied from outside to the low-temperature fluid inlet; a bypass flow path branching from the supply flow path, bypassing the first flow path section of the low-temperature flow path and connected to a predetermined portion of the low-temperature flow path downstream of the CO2 outlet corresponding position; and a bypass valve provided in the bypass flow path.

[0028] According to this configuration, the bypass flow path branches off from the supply flow path, bypasses the first flow path section, and is then connected to a predetermined location downstream of the CO2 outlet-corresponding position. Therefore, for example, by increasing the flow rate of the low-temperature liquefied gas flowing through the bypass flow path, the flow rate of the low-temperature liquefied gas flowing from the supply flow path into the first flow path section decreases, thereby increasing the temperature of the vaporized gas at the CO2 outlet-corresponding position (the downstream end of the first flow path section). Conversely, for example, by decreasing the flow rate of the low-temperature liquefied gas flowing through the bypass flow path, the flow rate of the low-temperature liquefied gas flowing from the supply flow path into the first flow path section increases, thereby decreasing the temperature of the vaporized gas at the CO2 outlet-corresponding position (the downstream end of the first flow path section). Thus, by controlling the aperture of the bypass valve provided in the bypass flow path, the temperature of the vaporized gas at the CO2 outlet-corresponding position can be easily controlled. Consequently, the temperature of the liquefied carbon dioxide discharged from the heat exchanger can be easily controlled.

[0029] The tenth invention is the ninth invention, further comprising a temperature detection unit that detects the temperature of the vaporized gas after being vaporized in the first flow path section and before being merged with the low-temperature liquefied gas that has passed through the bypass flow path, or a temperature correlated to that temperature, and a control unit that controls the bypass valve based on the temperature detected by the temperature detection unit, and the control unit is configured to perform bypass valve control that controls the bypass valve so that the temperature detected by the temperature detection unit becomes a predetermined target temperature.

[0030] According to this configuration, the bypass valve is automatically controlled by the control unit, so that the temperature of the mixed fluid can be more easily controlled than when the bypass valve is opened and closed manually.

[0031] In the 11th invention, in the invention of claim 10, the predetermined target temperature is a temperature that is set in advance so that the temperature of the liquefied carbon dioxide discharged from the heat exchanger becomes a predetermined required temperature and so that the carbon dioxide does not solidify on the inner surface of the liquefaction target flow path.

[0032] According to this configuration, the temperature of the liquefied carbon dioxide discharged from the liquefaction target flow path can be controlled to a predetermined required temperature, while solidification of the carbon dioxide within the liquefaction target flow path can be reliably prevented. [Effects of the Invention]

[0033] According to the present invention, in a heat exchanger and a heat exchange system that liquefies carbon dioxide by utilizing the cold of a low-temperature liquefied gas, it is possible to suppress solidification of carbon dioxide due to the cold of the low-temperature liquefied gas. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a system diagram showing a schematic configuration of a heat exchange system including a heat exchanger according to a first embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of a heat exchanger body. [Figure 3]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 4] FIG. 1 is a view corresponding to FIG. 1 and showing a modification of the first embodiment. [Figure 5] FIG. 10 is a system diagram illustrating a schematic configuration of a heat exchange system including a heat exchanger according to a second embodiment. [Figure 6] FIG. 6 is a view corresponding to FIG. 5 and showing a modified example of the second embodiment. [Figure 7] FIG. 10 is a system diagram illustrating a schematic configuration of a heat exchange system including a heat exchanger according to a third embodiment. [Figure 8] FIG. 10 is a view corresponding to FIG. 3 and showing a third embodiment. [Figure 9] FIG. 10 is a view corresponding to FIG. 7 and showing a modified example of the third embodiment. [Figure 10] FIG. 4 is a view equivalent to FIG. 3 and showing another embodiment. [Figure 11] FIG. 4 is a view equivalent to FIG. 3 and showing another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0035] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0036] (Embodiment 1) 1 is a system diagram showing a schematic configuration of a heat exchange system 1 including a heat exchanger 2 in embodiment 1. This heat exchange system 1 is a system that liquefies gaseous carbon dioxide using the cold energy of liquefied natural gas (hereinafter referred to as LNG), which is an example of a low-temperature liquefied gas, and vaporizes the LNG to produce natural gas (an example of a vaporized gas, hereinafter referred to as NG).

[0037] Specifically, the heat exchange system 1 has a heat exchanger 2 that performs heat exchange between LNG and carbon dioxide, an LNG supply flow path 3 that guides LNG supplied from an LNG supply source provided outside the heat exchange system 1 to the heat exchanger 2, an NG discharge flow path 4 that discharges NG vaporized in the heat exchanger 2 to the outside of the heat exchange system 1, a liquefaction target supply flow path 5 that supplies gaseous carbon dioxide to be liquefied to the heat exchanger 2, a CO2 discharge flow path 6 that discharges carbon dioxide liquefied in the heat exchanger 2, a bypass flow path 7 branching off from the LNG supply flow path 3, a bypass valve 8 provided in the bypass flow path 7, a temperature sensor 9 as a temperature detection unit, and a controller 100 as a control unit.

[0038] [Heat exchanger configuration] The heat exchanger 2 has a liquefaction target flow path 22 through which carbon dioxide to be liquefied is introduced and flows, a low-temperature flow path 21 through which LNG is introduced and flows, and a heat exchanger body 20 that has a part of the low-temperature flow path 21 and the entire liquefaction target flow path 22 inside. The low-temperature flow path 21 is formed so that a part of it is exposed to the outside of the heat exchanger body 20. The liquefaction target flow path 22 is formed entirely inside the heat exchanger body 20. The heat exchanger 2 is configured to perform heat exchange between the carbon dioxide flowing through the liquefaction target flow path 22 and the LNG introduced into the low-temperature flow path 21.

[0039] 1, the heat exchange areas in this heat exchanger 2 are roughly divided into an upper heat exchange area A1 located in the upper section of the heat exchanger body 20, a middle heat exchange area A2 located in the middle section, and a lower heat exchange area A3 located in the lower section. In the following description, unless otherwise specified, the terms "upper section," "middle section," and "lower section" refer to the sections corresponding to the upper heat exchange area A1, the middle heat exchange area A2, and the lower heat exchange area A3, respectively.

[0040] The heat exchanger body 20 is configured as a stacked heat exchanger, as will be described later. The heat exchanger body 20 is disposed vertically so that the carbon dioxide flowing through the liquefaction target flow path 22 flows from the top to the bottom.

[0041] The liquefaction target flow path 22 has a CO2 inlet 22a located at its upstream end in the carbon dioxide flow direction, and a CO2 outlet 22b located at its downstream end. The liquefaction target supply flow path 5 is connected to the CO2 inlet 22a, and the CO2 outlet 22b is connected to the CO2 discharge flow path 6. The CO2 inlet 22a receives gaseous carbon dioxide supplied from the liquefaction target supply flow path 5. The CO2 outlet 22b discharges carbon dioxide liquefied in the liquefaction target flow path 22 toward the CO2 discharge flow path 6. The CO2 inlet 22a opens at the outer surface of the upper end of the heat exchanger body 20, and the CO2 outlet 22b opens at the outer surface of the lower end of the heat exchanger body 20.

[0042] In this example, the liquefaction target flow path 22 extends linearly in the vertical direction. The liquefaction target flow path 22 has an upper flow path section 22c, a middle flow path section 22d, and a lower flow path section 22e, which correspond to the upper, middle, and lower sections, respectively, of the heat exchanger 2. Note that the liquefaction target flow path 22 does not necessarily have to be linear, and may be formed in a spiral or zigzag shape, for example.

[0043] The low-temperature flow path 21 has an LNG inlet 21a (corresponding to a low-temperature fluid inlet) located at its upstream end in the LNG flow direction, and an NG outlet 21b (corresponding to a low-temperature fluid outlet) located at its downstream end. The LNG inlet 21a is disposed at a predetermined position in an intermediate region between the upper heat exchange region A1 including the CO2 inlet 22a and the lower heat exchange region A3 including the CO2 outlet 22b. The LNG inlet 21a is connected to the LNG supply flow path 3. The NG outlet 21b is provided in the upper heat exchange region A1 including the CO2 inlet 22a. The NG outlet 21b is connected to the NG discharge flow path 4. The LNG inlet 21a receives LNG supplied from the LNG supply flow path 3. The NG outlet 21b discharges NG vaporized in the low-temperature flow path 21 toward the NG discharge flow path 4.

[0044] The LNG inlet 21a opens to the outer surface of the middle part in the vertical direction of the heat exchanger body 20. The NG outlet 21b and the CO2 inlet 22a are arranged on the same surface (the upper end surface in this example) at the upper end of the heat exchanger body 20, with a gap between them.

[0045] Furthermore, a CO2 outlet-corresponding opening 21c is formed at the lower end of the heat exchanger body 20. The CO2 outlet-corresponding opening 21c is located midway along the low-temperature flow path 21 and is arranged at a CO2 outlet-corresponding position corresponding to the CO2 outlet 22b. The CO2 outlet-corresponding opening 21c is arranged so that NG vaporized by passing through a middle flow path section 21e of the low-temperature flow path 21, which will be described later, passes through it. The CO2 outlet-corresponding opening 21c and the CO2 outlet 22b are arranged at an interval on the same surface (the lower end surface in this example) at the lower end of the heat exchanger body 20.

[0046] The low-temperature flow path 21 includes a middle-stage flow path section 21e (corresponding to the first flow path section) located in the middle stage of the heat exchanger body 20, a lower-stage flow path section 21g (corresponding to the second flow path section) located in the lower stage section, an upper-stage flow path section 21i (corresponding to the third flow path section) located in the upper stage section, an internal supply flow path 21d connecting the LNG inlet 21a and the upstream end of the middle-stage flow path section 21e, a first connection flow path section 21f connecting the downstream end of the middle-stage flow path section 21e and the upstream end of the lower-stage flow path section 21g, and a second connection flow path section 21h connecting the downstream end of the lower-stage flow path section 21g and the upstream end of the upper-stage flow path section 21i. The middle-stage flow path section 21e, the lower-stage flow path section 21g, and the upper-stage flow path section 21i all extend in the vertical direction parallel to the liquefaction target flow path 22 and are configured to allow NG to flow from the bottom to the top.

[0047] More specifically, the middle flow path section 21e heats and vaporizes the LNG received from the LNG inlet 21a by performing countercurrent heat exchange between the LNG and carbon dioxide flowing through the middle flow path section 22d (corresponding to the intermediate region of the liquefaction target flow path) of the liquefaction target flow path 22, and discharges the LNG as NG.

[0048] The first connecting flow path section 21f first guides the NG that has reached the downstream end of the middle flow path section 21e outward from the side of the heat exchanger main body 20, and then supplies it to the above-mentioned CO2 outlet corresponding opening 21c formed at the lower end of the heat exchanger main body 20.

[0049] The lower flow path section 21g receives NG supplied to the CO2 outlet corresponding opening 21c (CO2 outlet corresponding position) from the first connection flow path section 21f, and performs countercurrent heat exchange between the received NG and the carbon dioxide flowing in the lower flow path section 22e (corresponding to the downstream region downstream of the intermediate region in the liquefaction target flow path) of the liquefaction target flow path 22.

[0050] The second connecting flow path section 21h temporarily guides the NG that has reached the downstream end of the lower flow path section 21g to the outside of the heat exchanger body 20 (to the right in the example of FIG. 1), and then supplies it to the upper flow path section 21i.

[0051] The upper flow path section 21i receives NG supplied from the second connection flow path section 21h, performs countercurrent heat exchange with the carbon dioxide flowing in the upper flow path section 22c (corresponding to the upstream region upstream of the intermediate region in the liquefaction target flow path) of the liquefaction target flow path 22, and then discharges the NG from the NG outlet 21b into the NG discharge flow path 4.

[0052] FIG. 2 is a schematic cross-sectional view of the heat exchanger body 20. As shown in this figure, the heat exchanger body 20 is configured, for example, as a microchannel-type laminated heat exchanger. That is, the heat exchanger body 20 is configured by alternately laminating a large number of first metal layers 201 and a large number of second metal layers 202. The first metal layer 201 is recessed to form a large number of NG flow path portions 201a through which NG flows. These NG flow path portions 201a constitute part of the low-temperature flow path 21. The second metal layer 202 is recessed to form a large number of CO2 flow path portions 202a through which carbon dioxide flows. These CO2 flow path portions 202a constitute part of the liquefaction target flow path 22. The first metal layer 201 and the second metal layer 202 are each configured from a metal plate with excellent heat transfer properties. Heat exchange occurs between the NG flowing through each NG flow path portion 201a formed in the first metal layer 201 and the carbon dioxide flowing through each CO2 flow path portion 202a formed in the second metal layer 202, whereby the NG is heated and the carbon dioxide is cooled. The carbon dioxide is liquefied by being cooled and is discharged to the outside of the heat exchanger body 20.

[0053] 2 shows an example of a stacking pattern in which one first metal layer 201 and one second metal layer 202 are alternately stacked, but this is not limiting. For example, two first metal layers 201 and one second metal layer 202 may be alternately stacked, three first metal layers 201 and one second metal layer 202 may be alternately stacked, or three first metal layers 201 and two second metal layers 202 may be alternately stacked. In other words, the stacking pattern of the first metal layers 201 and the second metal layers 202 may be any pattern. Furthermore, in the example of FIG. 2, the heat exchanger body 20 is shown as a microchannel-type stacked heat exchanger, but this is not limiting. For example, the heat exchanger body 20 may be configured as a plate-fin-type stacked heat exchanger, etc.

[0054] However, if the heating capacity of LNG in the middle-stage flow path section 21e is too high, the temperature of the NG discharged from the middle-stage flow path section 21e becomes excessively high. As a result, the carbon dioxide, which is a high-temperature fluid, cannot be sufficiently cooled by the NG, which is a low-temperature fluid flowing through the lower-stage flow path section 21g and the upper-stage flow path section 21i, which are arranged downstream of the middle-stage flow path section 21e, resulting in a problem of a decrease in the cooling capacity (i.e., liquefaction capacity) of carbon dioxide in the heat exchanger 2.

[0055] To avoid this problem, in this embodiment, bypass valve control is executed by the controller 100. Details of the bypass valve control will be described below along with the configurations of the bypass flow path 7 and the bypass valve 8.

[0056] The bypass flow path 7 branches off from the LNG supply flow path 3 and is connected to the first connecting flow path section 21f, bypassing the middle-stage flow path section 21e. In other words, the bypass flow path 7 has an upstream end connected to the LNG supply flow path 3 and a downstream end connected to the first connecting flow path section 21f. By employing such a bypass structure, the heated NG that has passed through the middle-stage flow path section 21e and the LNG that has passed through the bypass flow path 7 are mixed at a connection site P1 (a predetermined site) of the first connecting flow path section 21f with the bypass flow path 7, and this mixed fluid (hereinafter referred to as mixed NG) flows into the lower-stage flow path section 21g through the CO2 outlet corresponding opening 21c.

[0057] The bypass valve 8 is disposed in the bypass flow path 7. The bypass valve 8 is configured to be able to adjust the flow rate of LNG flowing through the bypass flow path 7 by changing the opening degree thereof. The bypass valve 8 is controlled by a controller 100.

[0058] The temperature sensor 9 (an example of a temperature detection unit) is connected to a portion of the low-temperature flow path 21 (more specifically, the first connection flow path section 21f) between a connection portion P1 with the downstream end of the bypass flow path 7 and the CO2 outlet corresponding opening 21c. The temperature sensor 9 detects the temperature of the mixed NG between this connection portion P1 and the CO2 outlet corresponding opening 21c, and transmits the detected temperature information to the controller 100. The temperature sensor 9 may also be a sensor that detects a temperature correlated with the temperature of the mixed NG (for example, the temperature of a pipe wall through which the mixed NG flows).

[0059] The controller 100 is configured by a computer having a CPU, ROM, and RAM, and is connected to the temperature sensor 9 and the bypass valve 8 via signal lines.

[0060] The controller 100 then acquires the temperature detected by the temperature sensor 9 and controls the opening of the bypass valve 8 so that the acquired detected temperature becomes a predetermined target temperature.

[0061] This predetermined target temperature is set in advance so that the temperature of the liquefied carbon dioxide discharged from the CO2 outlet 22b reaches the predetermined required temperature and so that the carbon dioxide does not solidify on the inner surface of the CO2 outlet 22b. That is, if this target temperature is too high, the temperature of the mixed NG, which is the low-temperature fluid flowing into the heat exchanger 2 from the CO2 outlet-corresponding opening 21c, also rises, reducing the cooling capacity of the mixed NG for the carbon dioxide. This results in a problem that some or all of the carbon dioxide does not liquefy, or the temperature of the liquefied carbon dioxide is higher than the predetermined required temperature. On the other hand, if this target temperature is too low, the temperature of the mixed NG, which is the low-temperature fluid flowing into the heat exchanger 2, also falls, increasing the cooling capacity of the mixed NG for the carbon dioxide, resulting in a problem that the temperature of the liquefied carbon dioxide is lower than the predetermined required temperature. Furthermore, if this target temperature is too low, the cold energy of the mixed NG causes the inner surface temperature of the CO2 outlet 22b of the liquefaction target flow path 22 to fall below the solidification temperature of carbon dioxide (−56°C in this example), which could lead to the carbon dioxide solidifying on the inner surface of the CO2 outlet 22b. Therefore, in this example, the predetermined target temperature is set in advance to a temperature at which the temperature of the liquefied carbon dioxide reaches a predetermined required temperature and at which the carbon dioxide does not solidify at the CO2 outlet 22b. The reason why the target temperature is specified as a temperature at which the carbon dioxide does not solidify at the CO2 outlet 22b is because, in the heat exchange system 1 of this example, the temperature of the carbon dioxide at the CO2 outlet 22b is lowest, making solidification more likely to occur. Note that, in this embodiment, the target temperature is set to -56°C as an example, but is not limited to this and may be, for example, -50°C to -60°C. In other words, the target temperature may be any temperature at which all of the carbon dioxide can be liquefied, at which the temperature of the liquefied carbon dioxide reaches the predetermined required temperature, and at which the carbon dioxide does not solidify on the inner surface of the CO2 outlet 22b.

[0062] [Explanation of TQ curve] Next, the basic operation of the heat exchanger 2 will be described with reference to FIGS. 1 and 3. FIG. 3 is a TQ diagram showing the temperature changes of the working fluids (LNG and carbon dioxide) of the heat exchanger 2, with the heat exchange amount on the horizontal axis and temperature on the vertical axis. The arrows on the temperature lines in this TQ diagram are illustrated to allow intuitive understanding of the flow direction of the working fluid. The dashed-dotted line in the diagram indicates the temperature change of CO2, and the thick solid line indicates the temperature change of LNG. The thin dashed-two-dot line in the diagram indicates the temperature change of LNG in a conventional example. Note that in FIG. 3, for simplicity of explanation, the bypass flow rate of LNG flowing through the bypass flow path 7 is assumed to be zero. Furthermore, the temperature values ​​described below are merely examples and are not limited to these.

[0063] 3, in the heat exchanger 2 of this embodiment, LNG is supplied from an LNG supply source provided outside the system 1 via the LNG supply flow path 3 and the internal supply flow path 21d to the middle flow path section 21e of the middle heat exchange area A2 at a temperature of −150° C. Then, the LNG supplied to the middle flow path section 21e is heated to −50° C. (see FIG. 3) by heat exchange with carbon dioxide flowing through the middle flow path section 22d of the liquefaction target flow path 22, and vaporizes to become NG.

[0064] The NG vaporized in the middle flow path section 21e passes through the first connecting flow path section 21f (see FIG. 1), and then flows from the CO2 outlet corresponding opening 21c into the lower flow path section 21g at −50° C. Then, in the lower flow path section 21g, heat exchange occurs with the carbon dioxide flowing in the lower flow path section 22e of the liquefaction target flow path 22, increasing the amount of heat and warming the NG to −30° C. (see FIG. 3).

[0065] The heated NG passes through the second connection flow path portion 21h (see FIG. 1) and then flows into the upper flow path portion 21i of the low-temperature flow path 21. Then, in the upper flow path portion 21i, heat is exchanged with the carbon dioxide flowing in the upper flow path portion 22c of the liquefaction target flow path 22, increasing the amount of heat, and the NG is heated to 5°C (an example of a predetermined required temperature), and is then discharged from the NG outlet 21b to the NG discharge flow path 4.

[0066] Meanwhile, carbon dioxide to be liquefied is supplied to the liquefaction-target flow path 22 as a gas at 30°C from a CO2 supply source provided outside the heat exchange system 1. The gaseous carbon dioxide supplied to the liquefaction-target flow path 22 gradually loses heat as it exchanges heat with NG flowing through the upper flow path section 21i of the low-temperature flow path 21. 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). Upon reaching the liquefaction temperature, the carbon dioxide begins to condense from a gas to a liquid. During this condensation section, the carbon dioxide coexists as a gas and a liquid, and its temperature remains constant regardless of the decrease in heat content. When the heat content of the carbon dioxide further decreases and the condensation section ends, all of the carbon dioxide is liquefied. Thereafter, the temperature decreases as the heat content decreases, and the carbon dioxide is finally discharged from the liquefaction-target flow path 22 as liquid carbon dioxide at −42°C (an example of a predetermined required temperature). The predetermined required temperature can be set arbitrarily by the user and may be, for example, −42°C or lower.

[0067] (Action and effect) As described above, in this embodiment, the low-temperature flow path 21 has an LNG inlet 21a at a location corresponding to the middle section (an example of an intermediate position) of the liquefaction-target flow path 22, and an NG outlet 21b at a location corresponding to the CO2 inlet 22a of the liquefaction-target flow path 22. The low-temperature flow path 21 is configured to heat LNG received from the LNG inlet 21a by circulating the LNG while exchanging heat with carbon dioxide flowing through a middle flow path section 22d (an example of a first predetermined region) of the liquefaction-target flow path 22, to produce NG, and to exchange heat with carbon dioxide flowing through a lower flow path section 22e and an upper flow path section 22c (an example of a second predetermined region) of the liquefaction-target flow path 22 via the CO2 outlet-corresponding opening 21c located at a position corresponding to the CO2 outlet 22b of the liquefaction-target flow path 22, and then discharge the heated NG from the NG outlet 21b.

[0068] This configuration can suppress solidification of carbon dioxide due to the cold energy of LNG. Specifically, with this configuration, the LNG inlet 21a, where the LNG is at its lowest temperature, is positioned at a location corresponding to the middle section (an example of an intermediate position) of the liquefaction-targeted flow path 22. This distance between the LNG inlet 21a and the CO2 outlet 22b minimizes a decrease in the temperature of the inner surface of the CO2 outlet 22b. Consequently, solidification of carbon dioxide can be suppressed. Meanwhile, the middle section (an example of an intermediate position) of the liquefaction-targeted flow path 22 is cooled by the coldest LNG flowing into the LNG inlet 21a. However, carbon dioxide is in a gaseous state near the CO2 inlet 22a of the liquefaction-targeted flow path 22, a condensed state in the central section, and a liquid state near the CO2 outlet 22b. Therefore, the heat transfer coefficient of the condensed state at the intermediate position of the liquefaction-targeted flow path 22 is typically higher than the heat transfer coefficient of the liquid state near the CO2 outlet 22b. Therefore, the cooling effect of LNG on the channel wall surface is lower at the intermediate position of the liquefaction target channel 22 than near the CO2 outlet 22b. Therefore, as in the above configuration, locating the LNG inlet 21a at the intermediate position of the liquefaction target channel 22 can suppress the solidification of carbon dioxide more effectively than locating the LNG inlet 21a near the CO2 outlet 22b.

[0069] In this embodiment, the upper flow path section 21i, the middle flow path section 21e, and the lower flow path section 21g of the low-temperature flow path 21 are configured to perform heat exchange by a counterflow method between the LNG introduced into the low-temperature flow path 21 and the carbon dioxide introduced into the liquefaction target flow path 22. Therefore, the temperature of the NG discharged from the heat exchanger 2 can be made higher than when a parallel flow method is adopted. Therefore, it is possible to widely accommodate the temperature range of the NG after evaporation desired by the user.

[0070] (Modification of the first embodiment) Fig. 4 is a view corresponding to Fig. 1, showing a modification of the first embodiment. This modification differs from the first embodiment in that the heat exchange method in the middle flow path section 21e of the low-temperature flow path 21 is a cross-flow method. In Fig. 4, the same components as those in Fig. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0071] That is, in this modification, the middle flow path section 21e of the low-temperature flow path 21 is disposed so as to horizontally cross the heat exchanger body 20 from the LNG inlet 21a and is disposed so as to be perpendicular to the liquefaction target flow path 22 when viewed from the side. The LNG that flows into the middle flow path section 21e of the low-temperature flow path 21 from the LNG inlet 21a is heated and becomes NG by cross-flow heat exchange with the carbon dioxide flowing in the liquefaction target supply flow path 5. The heat exchange process after the LNG becomes NG is the same as in the first embodiment, and therefore a description thereof will be omitted.

[0072] The heat exchanger 2 according to this modification has the same configuration as that of the first embodiment, except that the heat exchange method in the middle flow path section 21e of the low-temperature flow path 21 is a cross-flow method. Therefore, the same effects as those of the first embodiment can be obtained.

[0073] (Embodiment 2) Fig. 5 is a system diagram showing a schematic configuration of a heat exchange system 1 including a heat exchanger 2 in embodiment 2. This embodiment differs from embodiment 1 in that the low-temperature flow path 21 includes a middle-stage flow path section 21q and a full-stage flow path section 21s arranged in parallel with each other. In Fig. 5, the same components as those in embodiment 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0074] That is, in this embodiment, the heat exchanger 2 has a middle-stage flow path section 21q (corresponding to the first flow path section) extending parallel to the liquefaction-target flow path 22 in the middle section in the vertical direction of the heat exchanger main body 20, an all-stage circulation flow path section 21s (corresponding to the second flow path section) arranged throughout the entire vertical direction of the heat exchanger main body 20 and extending parallel to the liquefaction-target flow path 22, an internal supply flow path section 21p connecting the upstream end of the middle-stage flow path section 21q to the LNG inlet 21a, and a connection flow path section 21r connecting the downstream end of the middle-stage flow path section 21q to the upstream end of the all-stage circulation flow path section 21s.

[0075] The internal supply passage section 21p supplies LNG received from the LNG inlet 21a to the middle passage section 21q.

[0076] The middle flow path section 21q heats and vaporizes the LNG supplied from the internal supply flow path section 21p by performing countercurrent heat exchange with the carbon dioxide flowing through the middle flow path section 22d (corresponding to the intermediate region) of the liquefaction target flow path 22, and discharges it as NG.

[0077] The connecting flow path section 21r first guides the NG that has reached the downstream end of the middle flow path section 21q outward from the side of the heat exchanger main body 20, and then supplies it to the CO2 outlet corresponding opening 21c formed at the lower end of the heat exchanger main body 20.

[0078] The all-stage flow path section 21s receives NG supplied to the CO2 outlet corresponding opening 21c (CO2 outlet corresponding position) via the connection path section 21r, and performs counterflow heat exchange between the received NG and the carbon dioxide flowing through the liquefaction target path 22 over the entire vertical area, and then discharges it from the NG outlet 21b into the NG discharge path 4.

[0079] According to the heat exchanger 2 and heat exchange system 1 configured as described above, the all-stage flow passage section 21s of the low-temperature flow passage 21 is configured to exchange heat with the carbon dioxide flowing through the liquefaction-target flow passage 22 over the entire region in the flow path length direction of the liquefaction-target flow passage 22. Therefore, since there is no need to extend the all-stage flow passage section 21s to the outside of the heat exchanger 2 along the way, the flow passages for heat exchange can be concentrated within the heat exchanger 2 as much as possible, and the number of connecting pipes can be reduced.

[0080] (Modification of the second embodiment) Fig. 6 is a view equivalent to Fig. 5, showing a modification of the second embodiment. This modification differs from the second embodiment in that the heat exchange method in the middle flow path section 21q of the low-temperature flow path 21 is a cross-flow method. In Fig. 6, the same components as those in Fig. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0081] That is, in this modification, the middle flow path section 21q of the low-temperature flow path 21 is disposed so as to horizontally cross the heat exchanger body 20 from the LNG inlet 21a and is disposed so as to be perpendicular to the liquefaction target flow path 22 when viewed from the side. The LNG that flows into the middle flow path section 21q of the low-temperature flow path 21 from the LNG inlet 21a is heated and becomes NG by cross-flow heat exchange with the carbon dioxide flowing in the liquefaction target supply flow path 5. The heat exchange process after the LNG becomes NG is the same as in the second embodiment, and therefore a description thereof will be omitted.

[0082] The heat exchanger 2 of this modified example has the same configuration as that of the second embodiment, except that the heat exchange method in the middle flow path section 21q of the low-temperature flow path 21 is a cross-flow method. Therefore, the same effects as those of the second embodiment can be obtained.

[0083] (Embodiment 3) Fig. 7 is a system diagram that schematically shows the configuration of a heat exchange system 1 including a heat exchanger 2 in embodiment 3, and Fig. 8 is a diagram corresponding to Fig. 3 that shows embodiment 3. This embodiment differs from embodiment 1 in that the low-temperature flow path 21 includes a lower flow path section 21u that is a heat exchange flow path section that uses a parallel flow system. In Fig. 7, the same components as those in embodiment 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0084] Specifically, in this embodiment, the heat exchange area of ​​the heat exchanger 2 is broadly divided into an upper heat exchange area B1 and a lower heat exchange area B2, and the upper heat exchange area B1 performs counterflow heat exchange, while the lower heat exchange area B2 performs parallel flow heat exchange.

[0085] The liquefaction target flow path 22 is a linear flow path that extends over the entire heat exchanger 2 in the vertical direction.

[0086] The low-temperature flow path 21 has a lower flow path section 21u (corresponding to the first flow path section) located in the lower section of the heat exchanger main body 20, an upper flow path section 21w (corresponding to the second flow path section) located in the upper section, an internal supply flow path section 21t connecting the LNG inlet 21a and the upstream end of the lower flow path section 21u, and a connection flow path section 21v connecting the downstream end of the lower flow path section 21u and the upstream end of the upper flow path section 21w.

[0087] The lower flow path section 21u and the upper flow path section 21w both extend in the vertical direction parallel to the liquefaction target flow path 22. The lower flow path section 21u is configured to allow NG to flow from the upper side to the lower side, while the upper flow path section 21w is configured to allow NG to flow from the lower side to the upper side.

[0088] The lower flow path section 21u heats and vaporizes LNG received from the LNG inlet 21a via the internal supply flow path section 21t by performing parallel flow heat exchange with the carbon dioxide flowing through the lower flow path section 22g of the liquefaction target flow path 22. The lower flow path section 21u then discharges the heated and vaporized NG from the CO2 outlet-corresponding opening 21c to the connection flow path section 21v.

[0089] The connecting flow path section 21v first guides the NG that has reached the downstream end of the lower flow path section 21u to the outside from the lower end of the heat exchanger main body 20, and then supplies it into the upper flow path section 21w from the lower end of the upper flow path section 21w.

[0090] The upper flow path section 21w receives NG supplied from the connection flow path section 21v and heats the received NG to a predetermined required temperature by countercurrent heat exchange between the received NG and the carbon dioxide flowing in the upper flow path section 22f of the liquefaction target flow path 22. The upper flow path section 21w discharges the heated NG from the NG outlet 21b to the NG discharge flow path 4.

[0091] Furthermore, the heat exchanger 2 of this embodiment has a bypass flow path 7 and a bypass valve 8, similar to the first embodiment. The bypass flow path 7 branches off from the LNG supply flow path 3, bypasses the lower flow path section 21u, and is connected to the connection flow path section 21v. In other words, the bypass flow path 7 has an upstream end connected to the LNG supply flow path 3 and a downstream end connected to the connection flow path section 21v.

[0092] By employing such a bypass structure, the heated NG that has passed through the lower flow path section 21u and the LNG that has passed through the bypass flow path 7 are mixed at a connection site P1 of the connecting flow path section 21v with the bypass flow path 7, and this mixed NG flows into the upper flow path section 21w through the connecting flow path section 21v. While flowing through the upper flow path section 21w, the mixed NG is heated by the carbon dioxide flowing through the upper flow path section 22f of the liquefaction target flow path 22, and becomes NG, which is discharged from the NG outlet 21b to the NG discharge flow path 4.

[0093] The temperature sensor 9 is connected between the connection site P1 in the connection flow path section 21v and the CO2 outlet corresponding opening 21c, which is the downstream end of the lower flow path section 21u. The temperature sensor 9 detects the temperature of the vaporized gas NG after being vaporized in the lower flow path section 21u and before being merged with the LNG that has passed through the bypass flow path 7. The temperature sensor 9 may also be a sensor that detects a temperature correlated with the detected temperature (for example, the temperature of a pipe wall through which the NG flows). The controller 100 controls the aperture of the bypass valve 8 provided in the bypass flow path 7 so that the temperature detected by the temperature sensor 9 becomes a predetermined target temperature. This target temperature is set in advance to a temperature at which the temperature of the carbon dioxide discharged from the CO2 outlet 22b becomes a predetermined required temperature and at which the carbon dioxide does not solidify at the CO2 outlet 22b.

[0094] [Explanation of TQ curve] Next, the basic operation of the heat exchanger 2 in the third embodiment will be described with reference to Figures 7 and 8. Figure 8 is a diagram equivalent to Figure 3, illustrating the third embodiment. The dashed-dotted line in the figure indicates the temperature change of CO2, and the thick solid line indicates the temperature change of LNG. The thin dashed-two-dot line in the figure indicates the temperature change of LNG in a conventional example. Note that, in Figure 8, for simplicity of explanation, the explanation will be given assuming that the bypass flow rate of LNG flowing through the bypass flow path 7 is 0. Furthermore, the temperature values ​​described below are merely examples and are not limited to these.

[0095] In the heat exchanger 2 of this embodiment, LNG is supplied from an LNG supply source provided outside the system 1 via the internal supply passage section 21t to the upper end of the lower passage section 21u at a temperature of −150° C. Then, while flowing from top to bottom within the lower passage section 21u, the LNG supplied to the upper end of the lower passage section 21u is heated to −50° C. (see FIG. 8 ) by heat exchange with carbon dioxide flowing within the lower passage section 22g of the liquefaction-target passage 22. The lower passage section 22g of the liquefaction-target passage 22 corresponds to the outlet region.

[0096] The heated NG passes through the CO2 outlet-corresponding opening 21c, which is the downstream end of the lower-stage flow path section 21u, and is then supplied to the lower end of the upper-stage flow path section 21w via the connecting flow path section 21v. As the NG flows from the bottom to the top of the upper-stage flow path section 21w, it exchanges heat with the carbon dioxide in the upper-stage flow path section 22f of the liquefaction-target flow path 22, whereby it is heated to 5°C (an example of a predetermined required temperature), and is finally discharged from the NG outlet 21b. The upper-stage flow path section 22f of the liquefaction-target flow path 22 corresponds to the inlet-side region.

[0097] On the other hand, carbon dioxide to be liquefied is supplied as a gas at 30°C from a CO2 supply source provided outside the heat exchange system 1 to the liquefaction target flow path 22, cooled to the liquefaction temperature of -17.2°C while flowing through the upper flow path section 22f, and then cooled to -42°C (an example of a predetermined required temperature) while flowing through the lower flow path section 22g, and is discharged as liquid carbon dioxide from the CO2 outlet 22b of the liquefaction target flow path 22. The predetermined required temperature can be set arbitrarily by the user and may be, for example, -42°C or lower.

[0098] As described above, in the third embodiment, the heat exchange method between the LNG introduced into the low-temperature flow path 21 and the carbon dioxide introduced into the liquefaction target flow path 22 can be achieved by combining the parallel flow method and the counterflow method. This makes it possible to increase the temperature of the NG discharged from the heat exchanger 2 compared to when the parallel flow method is adopted throughout the entire flow path. This makes it possible to accommodate a wide range of NG temperatures desired by users. Furthermore, by adopting the parallel flow method for the lower flow path section 21u, it is possible to simplify the flow path configuration from the LNG inlet 21a to the CO2 outlet-corresponding opening 21c in the lower flow path section 21u. This makes it possible to avoid problems such as increased costs and increased assembly man-hours due to a complicated flow path configuration.

[0099] In addition, the heat exchange system 1 of this embodiment is equipped with a bypass flow path 7 that branches off from the LNG supply flow path 3, bypasses the lower flow path section 21u, and is connected to a connection site P1 (predetermined site) downstream of the CO2 outlet corresponding opening 21c in the low-temperature flow path 21, and a bypass valve 8 provided in the bypass flow path 7.

[0100] According to this configuration, the bypass flow path 7 branches off from the LNG supply flow path 3, bypasses the first flow path section, and is then connected downstream of the CO2 outlet opening 21c. Therefore, by adjusting the aperture of the bypass valve 8 to adjust the flow rate of LNG flowing into the lower flow path section 21u, the temperature of LNG at the CO2 outlet opening 21c, which is the downstream end of the lower flow path section 21u, can be easily adjusted. Consequently, the temperature of the liquefied carbon dioxide discharged from the heat exchanger 2 can be easily controlled. The aperture of the bypass valve 8 is controlled by the controller 100 so that the temperature detected by the temperature sensor 9 becomes a predetermined target temperature. This makes adjustment easier than manually controlling the bypass valve 8. The predetermined target temperature is preset to a temperature such that the temperature of the carbon dioxide discharged from the CO2 outlet 22b becomes a predetermined required temperature and does not solidify at the CO2 outlet 22b. Therefore, solidification of carbon dioxide due to the cold energy of the LNG can be suppressed.

[0101] (Modification of the third embodiment) Fig. 9 is a view corresponding to Fig. 7 showing a modification of embodiment 3. This modification differs from embodiment 3 in that the low-temperature flow path 21 includes an all-stage flow path section 21y in addition to a lower-stage flow path section 21u. In Fig. 9, the same components as those in Fig. 7 are designated by the same reference numerals, and detailed description thereof will be omitted.

[0102] That is, in this modified example, the low-temperature flow path 21 has a lower-stage flow path section 21u (corresponding to the first flow path section) extending parallel to the liquefaction-target flow path 22 in the lower stage section of the heat exchanger main body 20, an all-stage circulation flow path section 21y (corresponding to the second flow path section) arranged throughout the entire vertical direction of the heat exchanger main body 20 and extending parallel to the liquefaction-target flow path 22, an internal supply flow path section 21t connecting the upstream end of the lower-stage flow path section 21u to the LNG inlet 21a, and a connection flow path section 21x connecting the downstream end of the lower-stage flow path section 21u to the upstream end of the all-stage circulation flow path section 21s.

[0103] The internal supply passage section 21t supplies LNG received from the LNG inlet 21a to the lower passage section 21u.

[0104] The lower flow path section 21u circulates the LNG supplied from the internal supply flow path section 21t from the top to the bottom, thereby performing parallel flow heat exchange with the carbon dioxide flowing in the lower flow path section 22g of the liquefaction target flow path 22. The lower flow path section 21u then heats and vaporizes the LNG through heat exchange with the carbon dioxide, and discharges it as NG to the connection flow path section 21x.

[0105] The connecting flow path section 21x first guides the NG that has reached the downstream end of the lower flow path section 21u to the outside from the lower end of the heat exchanger main body 20, and then supplies it to the CO2 outlet corresponding opening 21c formed at the lower end of the heat exchanger main body 20.

[0106] The all-stage circulation flow path section 21y circulates the NG supplied from the connection flow path section 21x to the CO2 outlet-corresponding opening 21c from the lower side to the upper side, thereby performing counterflow heat exchange across all stages in the vertical direction with the carbon dioxide flowing through the liquefaction target flow path 22. The all-stage circulation flow path section 21y then heats the LNG to a predetermined required temperature through heat exchange with the carbon dioxide, and discharges the LNG from the NG outlet 21b to the NG discharge flow path 4.

[0107] Next, the bypass flow path structure in this modification will be described. The bypass flow path 7 branches off from the LNG supply flow path 3, bypasses the lower flow path section 21u, and is connected to the connection flow path section 21x. In other words, the bypass flow path 7 has an upstream end connected to the LNG supply flow path 3 and a downstream end connected to the connection flow path section 21x.

[0108] According to this bypass structure, the heated NG that has passed through the lower-stage flow path section 21u and the LNG that has passed through the bypass flow path 7 are mixed at a connection site P1 of the connection flow path section 21x with the bypass flow path 7, and this mixed NG flows into the all-stage circulation flow path section 21y through the connection flow path section 21v. As the mixed NG flows through the all-stage circulation flow path section 21y, it exchanges heat with the carbon dioxide in the liquefaction target flow path 22 and is heated to a predetermined required temperature. The heated NG is discharged from the NG outlet 21b.

[0109] The temperature sensor 9 is connected between the connection site P1 in the connection flow path section 21x and the CO2 outlet corresponding opening 21c. The controller 100 controls the aperture of the bypass valve 8 provided in the bypass flow path 7 so that the temperature detected by the temperature sensor 9 becomes a predetermined target temperature. This target temperature is set in advance to a temperature at which the temperature of the carbon dioxide discharged from the CO2 outlet 22b becomes a predetermined required temperature and at which the carbon dioxide does not solidify at the CO2 outlet 22b.

[0110] As described above, in this modification, heat exchange is performed by a parallel flow method in the lower-stage flow path section 21u of the low-temperature flow path 21, thereby achieving the same effects as those of the third embodiment. Moreover, in this modification, the all-stage flow path section 21y is configured to perform heat exchange with the carbon dioxide flowing through the entire region in the flow path length direction of the liquefaction target flow path 22, so it is necessary to extend the all-stage flow path section 21y to the outside of the heat exchanger 2 from a certain point. Therefore, the flow paths for heat exchange can be concentrated as much as possible within the heat exchanger 2, thereby reducing the number of connecting pipes.

[0111] (Other embodiments) Although the heat exchanger 2 and the heat exchange system 1 according to the embodiment of the present invention have been described above, the present invention is not limited to this.

[0112] (1) In each of the above-described embodiments and variations, the liquefaction target flow path 22 of the heat exchanger 2 and the low-temperature flow path 21 excluding the middle flow path section 21e in FIG. 4 and the middle flow path section 21q in FIG. 6 are extended in the vertical direction, but this is not limited to this and they may be arranged, for example, in a zigzag or serpentine pattern.

[0113] (2) In the above-described embodiments and modifications, the heat exchanger 2 is configured as a single unit, but this is not limitative and the heat exchanger 2 may be divided into, for example, two or three parts.

[0114] (3) In each of the above embodiments and variants, the CO2 inlet 22a and NG outlet 21b of the heat exchanger 2 are arranged on the upper surface of the upper end of the heat exchanger 2, and the CO2 outlet 22b and CO2 outlet corresponding opening 21c are arranged on the lower surface of the lower end of the heat exchanger 2, but this is not limited to this. For example, both or one of the CO2 inlet 22a and NG outlet 21b may be arranged on the side surface of the upper end, or both or one of the CO2 outlet 22b and CO2 outlet corresponding opening 21c may be arranged on the side surface of the lower end.

[0115] (4) In each of the above embodiments and variants, the heat exchange system 1 has a bypass flow path 7 and a bypass valve 8, but this is not limited to this and the heat exchange system 1 may be configured without the bypass flow path 7 and the bypass valve 8.

[0116] (5) In each of the above-described embodiments and modifications, the heat exchanger 2 is configured as a stacked heat exchanger. However, the present invention is not limited to this and may be configured as, for example, an aluminum plate fin heat exchanger.

[0117] (6) In the above-described embodiments and modifications, LNG (liquefied natural gas) has been described as an example of a liquefied gas. However, the present invention is not limited to this, and LH2 (liquefied hydrogen) may also be used, for example. Fig. 10 shows, as an example, a TQ curve obtained when LH2 is used instead of LNG in the heat exchanger 2 of the first embodiment. Fig. 11 shows, as an example, a TQ curve obtained when LH2 is used instead of LNG in the heat exchanger 2 of the third embodiment. The contents of Figs. 10 and 11 are substantially the same as those of the first and third embodiments, except that the temperature of the LH2 flowing into the heat exchanger 2 is −250°C, and therefore detailed description thereof will be omitted.

[0118] (7) In each of the above embodiments and modifications, the gaseous carbon dioxide supplied to the liquefaction target flow path 22 does not need to be 100% 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 22 may be any fluid containing carbon dioxide.

[0119] (8) In the above-described embodiments and modifications, the temperature of NG at the CO2 outlet-corresponding opening 21c is set to −50°C. However, this is not limited to this and may be, for example, −50°C to −60°C. That is, the solidification temperature of carbon dioxide is −56°C under typical storage and transportation pressures (0.52 MPa to 3 MPa). Therefore, if the temperature of NG at the CO2 outlet-corresponding opening 21c is higher than −56°C, the problem of carbon dioxide solidification will not occur. Therefore, in the above-described embodiments, the temperature of NG at the CO2 outlet-corresponding opening 21c is set to −50°C, which is higher than −56°C. However, it does not necessarily have to be higher than −56°C. As an example, the temperature of NG at the CO2 outlet-corresponding opening 21c may be approximately −60°C. That is, the temperature of NG at the CO2 outlet-corresponding opening 21c may be any temperature as long as the temperature of carbon dioxide discharged from the CO2 outlet 22b reaches a predetermined required temperature and the carbon dioxide does not solidify. [Explanation of symbols]

[0120] 1: Heat exchange system 2: Heat exchanger 7: Bypass flow path 8: Bypass valve 9: Temperature sensor (temperature detection part) 21: Low temperature flow path 21a:LNG inlet (low temperature fluid inlet) 21b:NG outlet (low temperature fluid outlet) 21c: CO2 outlet opening 21d: Internal supply channel 21e: Middle flow path section (first flow path section) 21f: First connecting flow path section 21g: Lower flow path section (second flow path section) 21h: Second connecting flow path 21i: Upper flow path section (third flow path section) 21p: Internal supply flow path 21q: Middle flow path section (first flow path section) 21r: Connection flow path section 21s: All-stage flow passage section (second flow passage section) 21t: Internal supply passage 21u: Lower flow path section (first flow path section) 21v: Connection flow path 21w: Upper flow path section 21x: Connection flow path 21y: All-stage flow passage section (second flow passage section) 22: Flow path for liquefaction 22a :CO2 inlet 22b :CO2 outlet 100: Controller (control unit) P1: Connection site

Claims

1. A heat exchanger that liquefies gaseous carbon dioxide by utilizing the cold heat of a low-temperature liquefied gas, a low-temperature flow path having a low-temperature fluid inlet into which the low-temperature liquefied gas is introduced and a low-temperature fluid outlet from which the vaporized gas of the low-temperature liquefied gas is discharged; CO into which the gaseous carbon dioxide to be liquefied is introduced ２ Inlet and outlet CO2 after liquefaction ２ a flow path to be liquefied having an outlet; The low-temperature flow path includes: The CO in the liquefaction target flow path ２ Inlet and CO ２ The low-temperature fluid inlet is located at a position corresponding to an intermediate position between the low-temperature fluid inlet and the CO ２ a cryogenic fluid outlet at a location corresponding to the inlet, The low-temperature liquefied gas received from the low-temperature fluid inlet is heated and vaporized by circulating the low-temperature liquefied gas while exchanging heat with the carbon dioxide flowing through the first predetermined region of the liquefaction target flow path, and the heated vaporized gas is then vaporized by circulating the low-temperature liquefied gas through the first predetermined region of the liquefaction target flow path. ２ CO corresponding to the exit ２ a heat exchanger configured to exchange heat with carbon dioxide flowing through a second predetermined region of the liquefaction target flow path via an outlet corresponding position, and then discharge the low-temperature fluid from the low-temperature fluid outlet.

2. 2. The heat exchanger according to claim 1, The low-temperature flow path includes: a first flow path section that heats the low-temperature liquefied gas received from the low-temperature fluid inlet by performing heat exchange between the low-temperature liquefied gas and carbon dioxide flowing in an intermediate region of the flow path to be liquefied in a longitudinal direction thereof by a counterflow method or a crossflow method, and discharges the heated gas as a vaporized gas; The heated vaporized gas discharged from the first flow path portion is ２ a second flow path section that receives the vaporized gas from the outlet corresponding position and performs counterflow heat exchange between the received vaporized gas and carbon dioxide flowing in a downstream region downstream of the intermediate region in the liquefaction target flow path; a third flow path section that receives the vaporized gas after passing through the second flow path section and performs countercurrent heat exchange with carbon dioxide flowing in an upstream region upstream of the intermediate region in the liquefaction target flow path; a first connecting flow path portion that connects a downstream end of the first flow path portion and an upstream end of the second flow path portion; a second connecting flow path portion that connects a downstream end of the second flow path portion and an upstream end of the third flow path portion; It has the first predetermined region is the intermediate region of the liquefaction target flow path, A heat exchanger, wherein the second predetermined region is constituted by the downstream region and the upstream region of the liquefaction target flow path.

3. 2. The heat exchanger according to claim 1, The low-temperature flow path includes: a first flow path section configured to heat the low-temperature liquefied gas received from the low-temperature fluid inlet by performing heat exchange between the low-temperature liquefied gas and carbon dioxide flowing in an intermediate region in the flow path length direction of the liquefaction target flow path in a counterflow or crossflow manner, thereby converting the low-temperature liquefied gas into a vaporized gas; The heated vaporized gas is ２ a second flow path section that receives the vaporized gas from the outlet corresponding position and performs countercurrent heat exchange between the received vaporized gas and the carbon dioxide flowing through the liquefaction target flow path over the entire region of the liquefaction target flow path in the flow path length direction; a connecting flow path portion connecting a downstream end of the first flow path portion and an upstream end of the second flow path portion, the first predetermined region is the intermediate region of the liquefaction target flow path, A heat exchanger, wherein the second predetermined area comprises the entire area of ​​the liquefaction target flow path.

4. 2. The heat exchanger according to claim 1, The low-temperature flow path includes: The low-temperature liquefied gas received from the low-temperature fluid inlet is liquefied from the intermediate position in the liquefaction target flow path to the CO ２ a first flow path portion that performs heat exchange in a parallel flow manner with carbon dioxide flowing through an outlet-side region leading to an outlet, thereby heating the gas and discharging it as the vaporized gas; a second flow path section that receives the vaporized gas discharged from the first flow path section and performs countercurrent heat exchange with carbon dioxide flowing through an inlet side region upstream of the outlet side region in the liquefaction target flow path; a connecting flow path portion connecting a downstream end of the first flow path portion and an upstream end of the second flow path portion; It has the first predetermined region is the outlet side region of the liquefaction target flow path, The second predetermined region is the inlet region of the flow path to be liquefied.

5. 2. The heat exchanger according to claim 1, The low-temperature flow path guides the low-temperature liquefied gas received from the low-temperature fluid inlet from the intermediate position of the flow path to be liquefied to CO ２ a first flow path portion that performs heat exchange in a parallel flow manner with carbon dioxide flowing through an outlet-side region leading to an outlet, and discharges the vaporized gas; The vaporized gas discharged from the first flow path portion is received, and the CO ２ The CO ２ a second flow path portion that performs countercurrent heat exchange with carbon dioxide flowing through the entire region up to the inlet and then discharges the carbon dioxide; a connecting flow path portion that connects a downstream end of the first flow path portion and an upstream end of the second flow path portion; It has the first predetermined region is the outlet side region of the liquefaction target flow path, A heat exchanger, wherein the second predetermined area comprises the entire area of ​​the liquefaction target flow path.

6. A heat exchange system comprising the heat exchanger according to claim 2, 3 or 5, a supply flow path connected to the low-temperature fluid inlet, for guiding a low-temperature liquefied gas supplied from an external source to the low-temperature fluid inlet; The CO ２ a bypass flow path connected to a predetermined portion upstream of the outlet corresponding position; a bypass valve provided in the bypass flow path.

7. 7. The heat exchange system according to claim 6, a temperature detection unit that detects a temperature of a mixed fluid of the vaporized gas vaporized in the first flow path unit and the low-temperature liquefied gas that has passed through the bypass flow path, or a temperature that is correlated with the temperature; a control unit that controls the bypass valve based on the temperature detected by the temperature detection unit, The control unit is configured to execute bypass valve control to control the bypass valve so that the temperature detected by the temperature detection unit becomes a predetermined target temperature.

8. 8. The heat exchange system according to claim 7, A heat exchange system in which the specified target temperature is a temperature that is set in advance so that the temperature of the liquefied carbon dioxide discharged from the 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.

9. A heat exchange system comprising the heat exchanger according to claim 4, a supply flow path connected to the low-temperature fluid inlet, for guiding a low-temperature liquefied gas supplied from an external source to the low-temperature fluid inlet; The CO ２ a bypass flow path connected to a predetermined portion downstream of the outlet corresponding position; a bypass valve provided in the bypass flow path.

10. 10. The heat exchange system of claim 9, a temperature detection unit that detects the temperature of the vaporized gas after being vaporized in the first flow path unit and before being merged with the low-temperature liquefied gas that has passed through the bypass flow path, or a temperature that is correlated with the temperature; a control unit that controls the bypass valve based on the temperature detected by the temperature detection unit, The control unit is configured to execute bypass valve control to control the bypass valve so that the temperature detected by the temperature detection unit becomes a predetermined target temperature.

11. 11. The heat exchange system of claim 10, A heat exchange system in which the specified target temperature is a temperature that is set in advance so that the temperature of the liquefied carbon dioxide discharged from the 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.

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