Cold energy power generation system

Abstract

To provide a cold heat power generation system capable of utilizing cold heat of LNG to the maximum by using carbon dioxide as a medium.SOLUTION: A cold energy power generation system 1 according to the present invention includes a liquefied carbon dioxide storage tank 21, a liquefied carbon dioxide pump 30 that pressurizes liquefied carbon dioxide, a liquefied carbon dioxide heater 40, a carbon dioxide expansion turbine 50, a carbon dioxide gas solidification device 10 that solidifies carbon dioxide gas to generate dry ice, a carbon dioxide gas supply line 171 that supplies carbon dioxide gas to the carbon dioxide gas solidification device 10, a dry ice supply line 172 that supplies dry ice generated by the carbon dioxide gas solidification device 10 to the liquefied carbon dioxide storage tank 21, and a dry ice melting device 22 that melts dry ice by heat exchange with a fluid having a temperature higher than a melting point of dry ice to generate liquefied carbon dioxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cold energy power generation system that utilizes the cold energy of a cryogenic fluid, and more particularly to a cold energy power generation system that uses carbon dioxide as a medium. [Background technology]

[0002] Generally, the cold energy from liquefied natural gas (hereinafter referred to as "LNG") is disposed of in the environment, such as in seawater, but with the recent trend toward energy conservation, development of technologies to effectively utilize the cold energy from LNG is progressing.

[0003] In this regard, Patent Document 1 discloses a cold energy power generation technology that uses propane as the working fluid. In this cold energy power generation technology, propane is condensed using the cold energy of LNG, then pressurized with a pump, and evaporated using seawater or hot water (hot water produced using waste heat from a nearby factory), which then turns a turbine to generate electricity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5885114 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the technology described in Patent Document 1, the condensation temperature of propane (at least about -42°C at atmospheric pressure) differs from the evaporation temperature of LNG (about -160°C at atmospheric pressure for 100% methane, and about -83°C at critical pressures of 4 MPaG or higher), resulting in insufficient exchange of latent heat and ineffective use of heat. Furthermore, the use of propane, a flammable gas, as the working fluid is highly dangerous, and the maintenance and management costs of the equipment are also high.

[0006] The present invention has been made to solve such problems, and aims to provide a cold energy power generation system that can make maximum use of the cold energy of LNG by using carbon dioxide as a medium. [Means for solving the problem]

[0007] (1) The cold energy power generation system according to the present invention comprises: a liquefied carbon dioxide storage tank for storing liquefied carbon dioxide; a liquefied carbon dioxide pump that pressurizes the liquefied carbon dioxide stored in the liquefied carbon dioxide storage tank; a liquefied carbon dioxide heater for heating the liquefied carbon dioxide pressurized by the liquefied carbon dioxide pump through heat exchange with a heat medium to convert it into a gas phase or a supercritical phase; a carbon dioxide expansion turbine that expands the carbon dioxide that has been converted into a gas phase or supercritical phase by the liquefied carbon dioxide heater to recover energy; a carbon dioxide gas solidification device that solidifies the low-pressure carbon dioxide gas expanded by the carbon dioxide expansion turbine through heat exchange with liquefied natural gas as a refrigerant to produce dry ice; a carbon dioxide gas supply line for supplying the carbon dioxide gas solidification device with low-pressure carbon dioxide gas expanded by the carbon dioxide expansion turbine; a dry ice supply line that supplies the dry ice generated by the carbon dioxide gas solidification device to the liquefied carbon dioxide storage tank; and a dry ice melting device that melts the dry ice supplied to the liquefied carbon dioxide storage tank by heat exchange with a fluid having a temperature higher than the melting point of the dry ice to produce liquefied carbon dioxide.

[0008] (2) In addition, in the above (1), a carbon dioxide gas cooler is provided to cool the carbon dioxide gas supplied from the carbon dioxide expansion turbine to the carbon dioxide gas solidification device, The heat obtained from the carbon dioxide gas in the carbon dioxide gas cooler is supplied to the dry ice melting device.

[0009] (3) Furthermore, in the above (2), a carbon dioxide-containing gas cooler is provided between the carbon dioxide gas cooler and the carbon dioxide gas solidification device, and cools the carbon dioxide gas to be supplied to the carbon dioxide gas solidification device using liquefied natural gas after the cold energy has been utilized in the carbon dioxide gas solidification device.

[0010] (4) In addition, in the device described in any one of (1) to (3) above, the liquefied carbon dioxide heater is characterized by having a plurality of heaters with different heating temperature ranges.

[0011] (5) In addition, in the device described in any one of (1) to (4) above, an additive gas addition line that adds an additive gas having a lower solidification temperature than the carbon dioxide gas to the carbon dioxide gas flowing through the carbon dioxide gas supply line; The carbon dioxide gas solidification device is characterized by having an added gas circulation line that connects the outlet of the carbon dioxide gas solidification device to the carbon dioxide gas supply line and circulates the added gas that has not solidified in the carbon dioxide gas solidification device between the inlet side and the outlet side of the carbon dioxide gas solidification device.

[0012] (6) In the device described in any one of (1) to (5) above, the heat source of the heat medium used in the liquefied carbon dioxide heater is waste heat from the plant. [Effects of the Invention]

[0013] According to the present invention, a cold energy power generation system that can make maximum use of the cold energy of LNG can be realized. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing a cold energy power generation system according to a first embodiment of the present invention. [Figure 2] FIG. 5 is a schematic diagram showing a cold energy power generation system according to a second embodiment of the present invention. [Figure 3] FIG. 10 is a schematic diagram showing a cold energy power generation system according to a third embodiment of the present invention. [Figure 4] FIG. 10 is a schematic diagram showing a cold energy power generation system according to a fourth embodiment of the present invention. [Figure 5] FIG. 10 is a schematic diagram showing a cryogenic power generation system according to a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Embodiment 1] First, the configuration and functions of the first embodiment of the present invention will be described with reference to FIG. The cold energy power generation system 1 according to embodiment 1 includes a liquefied carbon dioxide storage tank 21, a liquefied carbon dioxide pump 30, a liquefied carbon dioxide heater 40, a carbon dioxide expansion turbine 50, a carbon dioxide gas solidification device 10, and a dry ice melting device 22.

[0016] <Liquefied carbon dioxide storage tank> The liquefied carbon dioxide storage tank 21 is a metal container, and uses the heat of a melting heat medium supplied from the outside by the dry ice melting device 22 to melt the dry ice supplied from the dry ice supply line 172 and discharge it to the liquefied carbon dioxide discharge line 181.

[0017] <Liquefied carbon dioxide pump> The liquefied carbon dioxide pump 30 is a centrifugal pump, which pressurizes the liquefied carbon dioxide supplied from the liquefied carbon dioxide discharge line 181 and discharges it to the liquefied carbon dioxide pump outlet line 182 .

[0018] <Liquefied carbon dioxide heater> The liquefied carbon dioxide heater 40 is a shell-and-tube type heat exchanger that uses the heat of a heat medium supplied from outside to heat the liquefied carbon dioxide supplied from a liquefied carbon dioxide pump outlet line 182 by heat exchange with the heat medium, converting it to a gas phase or supercritical phase, and discharges it to a carbon dioxide gas expansion turbine inlet line 185. The heat medium is supplied from an evaporation heat medium inlet line 183, and after its heat has been used, it is discharged to an evaporation heat medium outlet line 184.

[0019] <Carbon dioxide expansion turbine> The carbon dioxide gas expansion turbine 50 is a centrifugal turbine that recovers energy by expanding the gaseous or supercritical carbon dioxide supplied from the carbon dioxide gas expansion turbine inlet line 185, converting it into turbine rotational energy to generate electricity, and then discharging the low-pressure carbon dioxide gas to the carbon dioxide gas supply line 171.

[0020] <Carbon dioxide gas solidification equipment> The carbon dioxide gas solidification device 10 is composed of a scraped surface heat exchanger, and solidifies the carbon dioxide gas by heat exchange between the carbon dioxide gas and LNG to produce dry ice. The carbon dioxide gas solidification device 10 solidifies the carbon dioxide gas supplied from the carbon dioxide gas supply line 171 using the cold energy of the LNG, scrapes it off, and discharges it to the dry ice supply line 172. The LNG is supplied from the refrigerant inlet line 175, and is discharged from the refrigerant outlet line 176 after the cold energy has been utilized.

[0021] <Dry ice melting device> The dry ice melting device 22 melts the dry ice produced by the carbon dioxide gas solidification device 10 through heat exchange with a fluid having a temperature higher than the melting point of the dry ice to produce liquefied carbon dioxide. The dry ice melting device 22 supplies a melting heat medium to the liquefied carbon dioxide storage tank 21 from a melting heat medium inlet line 177 and discharges the melting heat medium that has used its heat from a melting heat medium outlet line 178.

[0022] Next, the operation of the cold energy power generation system 1 according to this embodiment will be described. The carbon dioxide gas supplied to the carbon dioxide gas solidification device 10 is cooled by high-pressure LNG (for example, 5 MPaG, -150°C), causing it to precipitate as dry ice on the surface of a heat transfer tube (not shown). The precipitated dry ice is scraped off by a mechanical mechanism (not shown), drops, and is discharged to the dry ice supply line 172. The temperature of the dry ice is low, for example, at or below -79°C, the solidification temperature of carbon dioxide under atmospheric pressure.

[0023] In the carbon dioxide gas solidification apparatus 10, if the composition of LNG is 100% methane, its boiling point is approximately -83°C, and the solidification temperature of carbon dioxide gas is approximately -79°C, so these temperatures are close. Therefore, in the carbon dioxide gas solidification apparatus 10, the latent heat of vaporization of LNG is efficiently used to solidify the carbon dioxide gas.

[0024] The dry ice dispensed into the dry ice supply line 172 is dispensed into the liquefied carbon dioxide storage tank 21 by alternately opening and closing the first dry ice dispensing valve 173 and the second dry ice dispensing valve 174.

[0025] The dry ice discharged to the liquefied carbon dioxide storage tank 21 is melted by being heated to, for example, −50° C. by a melting heat transfer medium. The liquefied carbon dioxide produced by the melting of the dry ice is supplied to the liquefied carbon dioxide pump 30 via the liquefied carbon dioxide discharge line 181.

[0026] The liquefied carbon dioxide supplied to the liquefied carbon dioxide pump 30 is pressurized to a high pressure (for example, 10 MPaG) and discharged to the liquefied carbon dioxide pump outlet line 182.

[0027] The high-pressure liquefied carbon dioxide is evaporated in the liquefied carbon dioxide heater 40 by an evaporation heat medium (for example, silicone oil) that uses, for example, factory waste heat, and is heated to, for example, 100° C. This causes the carbon dioxide to enter a supercritical state.

[0028] The supercritical carbon dioxide drives the turbine in the carbon dioxide gas expansion turbine 50 to generate electricity.

[0029] The carbon dioxide gas that has driven the carbon dioxide gas expansion turbine 50 is discharged to the carbon dioxide gas supply line 171 and solidified again in the carbon dioxide gas solidification device 10.

[0030] According to the cold energy power generation system 1 of this embodiment, the cold energy of LNG can be effectively used to solidify carbon dioxide gas, thereby reducing the amount of cold energy of LNG that has previously been discarded into the environment. For example, LNG vaporizers that use seawater as a heating medium discard LNG cold energy into the ocean, but this can reduce the amount of cold energy discarded into the ocean, thereby reducing the impact on the ocean.

[0031] Furthermore, according to the cold energy power generation system 1 of this embodiment, the latent heat of vaporization of LNG can be exchanged with the latent heat of solidification of carbon dioxide in the carbon dioxide gas solidification device 10, thereby maximizing the amount of carbon dioxide solidified per unit flow rate of LNG and maximizing the amount of power generation utilizing the cold energy of LNG.

[0032] Furthermore, according to the cold energy power generation system 1 of this embodiment, non-flammable carbon dioxide is used as the medium for the cold energy power generation cycle, which eliminates the risk of the medium catching fire or exploding, thereby improving the safety of the equipment.

[0033] Furthermore, according to the cold energy power generation system 1 of this embodiment, carbon dioxide, which has a high density in gas and liquid form, is used as the medium for the cold energy power generation cycle, so the size of the piping and equipment can be halved compared to when propane is used, thereby reducing the installation space and reducing the costs of the foundation and building.

[0034] Furthermore, in this embodiment, the carbon dioxide gas expansion turbine 50 has been described as a single unit configuration, but it may also be configured as a series multi-stage configuration with a heater installed between the stages. This makes it possible to prevent carbon dioxide from solidifying due to temperature and pressure, while further improving the power generation efficiency of the carbon dioxide gas expansion turbine 50.

[0035] The type of heat transfer medium, pump, valve, heat exchanger, and container described in this embodiment may be selected appropriately within the scope of design.

[0036] [Embodiment 2] Next, the configuration and functions of the second embodiment will be described with reference to FIG. The same numbers are used for components having the same configurations and functions as those in the first embodiment. In a cold energy power generation system 200 according to the second embodiment, a dry ice melting device 22 includes a carbon dioxide gas cooler 210 and a melting heat medium circulation pump 220 .

[0037] The carbon dioxide gas cooler 210 is a shell-and-tube type heat exchanger that uses the heat medium used for heat exchange with dry ice in the liquefied carbon dioxide storage tank 21 to cool the carbon dioxide gas supplied to the carbon dioxide gas solidification device 10.

[0038] The heat melting medium circulation pump 220 is a centrifugal pump, and circulates the heat melting medium between the carbon dioxide gas cooler 210 and the liquefied carbon dioxide storage tank 21 .

[0039] Next, the operation of the energy storage system 200 according to this embodiment will be described. The explanation of the same functions as those in the first embodiment will be omitted. The melting heat transfer medium circulated in the melting heat transfer medium inlet line 177 and the melting heat transfer medium outlet line 178 by the melting heat transfer medium circulation pump 220 supplies the heat of melting of the dry ice in the liquefied carbon dioxide storage tank 21 and is itself cooled to a temperature close to that of the liquefied carbon dioxide (e.g., -50°C).

[0040] The molten heat transfer medium cooled in the liquefied carbon dioxide storage tank 21 is supplied to the carbon dioxide gas cooler 210, where it cools the room temperature carbon dioxide gas and is heated to a temperature close to that of the carbon dioxide gas.Then, it is supplied to the liquefied carbon dioxide storage tank 21 again.

[0041] According to the cold energy power generation system 200 of this embodiment, the molten heat transfer medium cooled in the liquefied carbon dioxide storage tank 21 is used to cool the carbon dioxide gas in the carbon dioxide gas cooler 210, thereby making it possible to efficiently utilize the thermal energy within the system.

[0042] Furthermore, according to the cold-heat power generation system 200 of this embodiment, the carbon dioxide gas supplied to the carbon dioxide gas solidification device 10 can be cooled, so that the heat transfer area for cooling the carbon dioxide gas in the carbon dioxide gas solidification device 10 can be reduced, and the size of the carbon dioxide gas solidification device 10 can be reduced.

[0043] [Embodiment 3] Next, the configuration and functions of the third embodiment will be described with reference to FIG. Components having the same configurations and functions as those in the first and second embodiments are given the same numbers. The cold energy power generation system 300 according to the third embodiment includes a carbon dioxide gas additional cooler 310 .

[0044] The carbon dioxide gas cooler 310 is a shell-and-tube type heat exchanger that uses the cold heat of the LNG from which the latent heat of vaporization has been removed in the carbon dioxide gas solidification device 10 to further cool the carbon dioxide gas supplied to the carbon dioxide gas solidification device 10.

[0045] Next, the operation of the cold energy power generation system 300 according to this embodiment will be described. Explanation of the same functions as those in the first and second embodiments will be omitted. The carbon dioxide gas cooled in the carbon dioxide gas cooler 210 is supplied to a carbon dioxide gas additional cooler 310 .

[0046] The carbon dioxide gas supplied to the carbon dioxide gas cooler 310 is cooled to a low temperature (e.g., -70°C) that is lower than the temperature after cooling by the carbon dioxide gas cooler 210 (e.g., -50°C) but does not reach the solidification temperature, by heat exchange with LNG (in a supercritical state of about -80°C) from which the latent heat of vaporization has been removed in the carbon dioxide gas solidification device 10.

[0047] According to the cold energy power generation system 300 of this embodiment, the carbon dioxide gas additional cooler 310 utilizes the cold energy of the LNG (in a supercritical state of about -80°C) from which the latent heat of vaporization has been removed in the carbon dioxide gas solidification device 10, thereby enabling more efficient utilization of the thermal energy within the system.

[0048] Furthermore, according to the cold-heat power generation system 300 of this embodiment, the carbon dioxide gas is cooled to a low temperature (e.g., -70°C) that is lower than the temperature (e.g., -50°C) after cooling by the carbon dioxide gas cooler 210 and does not reach the solidification temperature, so that the carbon dioxide gas supplied to the carbon dioxide gas solidification device 10 can be further cooled. This allows the heat transfer area for cooling the carbon dioxide gas in the carbon dioxide gas solidification device 10 to be further reduced, and the size of the carbon dioxide gas solidification device 10 to be further reduced.

[0049] [Embodiment 4] Next, the configuration and functions of the fourth embodiment will be described with reference to FIG. The same numbers are used for components having the same configurations and functions as those in the first to third embodiments. The cold energy power generation system 400 according to the fourth embodiment includes a liquefied carbon dioxide additional heat generator 410 .

[0050] The liquefied carbon dioxide additional heater 410 is a shell-and-tube type heat exchanger, which uses the heat of a high-temperature heat medium supplied from the outside to further raise the temperature of the liquefied carbon dioxide evaporated in the liquefied carbon dioxide heater 40 and discharges it to a high-temperature carbon dioxide discharge line 472. The high-temperature heat medium is supplied from a high-temperature heat medium inlet line 473, and after its heat has been utilized, is discharged to a high-temperature heat medium outlet line 474.

[0051] Next, the operation of the cold energy power generation system 400 according to this embodiment will be described. The explanation of the same functions as those in the first to third embodiments will be omitted.

[0052] In this embodiment, the heat medium supplied to the liquefied carbon dioxide heater 40 is a low-temperature heat medium, such as low-temperature waste heat from a plant (for example, waste heat below 100°C), which is discarded in relatively large quantities as low-quality waste heat. Therefore, the latent heat of evaporation required for evaporating the liquefied carbon dioxide is supplied by the low-temperature heat medium. In the liquefied carbon dioxide heater 40, the latent heat of evaporation is imparted to the liquefied carbon dioxide, and the temperature is raised to, for example, 50°C, thereby becoming a supercritical state.

[0053] The high-temperature heat medium supplied to the liquefied carbon dioxide additional heater 410 has as its heat source, for example, high-temperature exhaust gas (e.g., 350°C) from a gas engine fueled by boil-off gas from an LNG storage tank at an LNG terminal. Therefore, the carbon dioxide that has become supercritical in the liquefied carbon dioxide heater 40 is further heated in the liquefied carbon dioxide additional heater 410, and becomes supercritical carbon dioxide at, for example, 200°C.

[0054] According to the cold energy power generation system 400 of this embodiment, the liquefied carbon dioxide heater 40 uses low-quality, low-temperature waste heat that is discarded in relatively large quantities to provide the latent heat of evaporation of liquefied carbon dioxide, and the liquefied carbon dioxide additional heater 410 uses high-temperature waste heat that is not present in large quantities to provide sensible heat to the carbon dioxide to further raise its temperature, thereby enabling efficient use of both low-temperature and high-temperature waste heat.

[0055] Furthermore, according to the cold energy power generation system 400 of this embodiment, the carbon dioxide can be heated to a high temperature in the liquefied carbon dioxide additional heat generator 410, and therefore the power generation efficiency of the carbon dioxide gas expansion turbine 50 can be improved.

[0056] [Embodiment 5] Next, the configuration and functions of the fifth embodiment will be described with reference to FIG. The same numbers are used for components having the same configurations and functions as those in the first to fourth embodiments. In this fifth embodiment, by lowering the partial pressure of carbon dioxide gas, the solidification temperature of carbon dioxide is brought closer to the critical temperature of the refrigerant LNG, thereby improving the efficiency of heat exchange between the latent heat of solidification of carbon dioxide and the latent heat of vaporization of the refrigerant LNG, thereby enabling more carbon dioxide to be solidified with a smaller LNG flow rate.

[0057] The cold-thermal power generation system 500 according to the fifth embodiment includes an added gas circulation line 570 and an added gas addition line 574 that adds to the added gas circulation line 570 an added gas having a lower solidification temperature than carbon dioxide gas. The added gas circulation line 570 connects the outlet of the carbon dioxide gas solidification device 10 to the carbon dioxide gas supply line 171, and circulates the added gas that has not solidified in the carbon dioxide gas solidification device 10 between the inlet and outlet sides of the carbon dioxide gas solidification device 10. The additive gas circulation line 570 is provided with an additive gas circulation blower 510 for circulating the additive gas that has not solidified.

[0058] The additive gas addition line 574 is provided with an additive gas introduction amount adjustment valve 573 for adjusting the amount of additive gas to be introduced. In addition, an additive gas discharge line 575 is provided that branches off from the additive gas circulation line 570 and discharges unsolidified additive gas to the outside, and an additive gas discharge amount control valve 576 is provided in the additive gas discharge line 575. In the added gas circulation line 570, the line from the carbon dioxide gas solidification device 10 to the added gas circulation blower 510 is called the added gas circulation blower inlet line 571, and the line from the added gas circulation blower 510 to the carbon dioxide gas supply line 171 is called the added gas circulation blower outlet line 572.

[0059] The additive gas circulation blower 510 is a centrifugal blower, which pressurizes the additive gas supplied from an additive gas circulation blower inlet line 571 and discharges it to an additive gas circulation blower outlet line 572 .

[0060] The additive gas may be any gas having a lower solidification temperature than carbon dioxide gas, such as nitrogen gas, oxygen gas, or argon gas.

[0061] Next, the operation of the cold energy power generation system 500 according to this embodiment will be described. Explanation of the same functions as those in the first to fourth embodiments will be omitted.

[0062] When nitrogen gas, for example, is added as an additive gas, the partial pressure of the carbon dioxide gas decreases due to the addition of nitrogen gas in the carbon dioxide gas solidification device 10, and the solidification temperature of the carbon dioxide decreases. For example, the solidification temperature of carbon dioxide is approximately -79°C when the partial pressure is atmospheric pressure, but it decreases further as the partial pressure decreases. In other words, the solidification temperature of carbon dioxide can be changed by adjusting the partial pressure of the carbon dioxide gas.

[0063] On the other hand, when considering methane as an example of the composition of LNG, which is a refrigerant, its critical temperature is approximately -83°C and its critical pressure is approximately 4.6 MPaG. As the pressure of a high-pressure LNG line at a typical LNG terminal is approximately 5 MPaG, this exceeds the critical pressure, and it is thought that as it is heated, it will release the latent heat of vaporization near the critical temperature.

[0064] Since the solidification of carbon dioxide requires latent heat several times greater than sensible heat, by adding an additive gas to bring the solidification temperature of carbon dioxide closer to the critical temperature of LNG, the refrigerant LNG also releases a large amount of latent heat of vaporization near the solidification temperature of carbon dioxide. As a result, a large amount of carbon dioxide is solidified with a small flow rate of LNG through the heat exchange between latent heats.

[0065] The nitrogen gas that has not been solidified in the carbon dioxide gas solidification device 10 is circulated by the added gas circulation blower 510 and joins the carbon dioxide gas cooler 210 and the carbon dioxide gas additional cooler 310 .

[0066] According to the cold energy power generation system 500 of this embodiment, the efficiency of heat exchange between the latent heat of solidification of carbon dioxide and the latent heat of vaporization of the LNG refrigerant is further improved in the carbon dioxide gas solidification device 10, so that more carbon dioxide can be solidified with less refrigerant. As a result, the scale of the device can be easily expanded.

[0067] Since the composition of LNG varies depending on its origin, it is desirable to adjust the partial pressure of carbon dioxide gas according to the composition. Therefore, when it is desired to lower the partial pressure of carbon dioxide gas, the additive gas introduction amount adjustment valve 573 can be opened to increase the amount of additive gas introduced. Conversely, when it is desired to increase the partial pressure of carbon dioxide gas, the additive gas discharge amount adjustment valve 576 can be opened to discharge the additive gas. To further increase the partial pressure of carbon dioxide, it is possible to maintain the outlet pressure of the carbon dioxide expansion turbine 50 high and increase the pressure of the carbon dioxide gas supplied to the carbon dioxide gas solidification device 10. This makes it possible to deal with cases where the boiling point of LNG is higher than the solidification temperature (approximately -79°C) of carbon dioxide gas under atmospheric pressure.

[0068] In the above example, the additive gas addition line 574 is connected to the additive gas circulation line 570, but the additive gas only needs to be able to be added to the carbon dioxide gas flowing through the carbon dioxide gas supply line 171, and the additive gas addition line 574 may also be connected to the carbon dioxide gas supply line 171. [Industrial Applicability]

[0069] The present invention can be used as a cold energy power generation system that can make maximum use of the cold energy of LNG. [Explanation of symbols]

[0070] 1. Cold energy power generation system (embodiment 1) 10 Carbon dioxide gas solidification device 21 Carbon dioxide storage tank 22 Dry ice melting device 30 Liquefied carbon dioxide pump 40 Liquefied carbon dioxide heater 50 Carbon dioxide expansion turbine 171 Carbon dioxide gas supply line 172 Dry Ice Supply Line 173 First dry ice dispensing valve 174 Second dry ice dispensing valve 175 Refrigerant inlet line 176 Refrigerant outlet line 177 Melting heat transfer medium inlet line 178 Melting heat transfer medium outlet line 181 Liquefied carbon dioxide discharge line 182 Liquefied carbon dioxide pump outlet line 183 Evaporation heat medium inlet line 184 Evaporation heat transfer medium outlet line 185 Carbon dioxide gas expansion turbine inlet line 200 Cold energy power generation system (embodiment 2) 210 Carbon dioxide gas cooler 220 Melting heat transfer medium circulation pump 300 Cold energy power generation system (embodiment 3) 310 Carbon dioxide gas cooler 400 Cold energy power generation system (embodiment 4) 410 Liquid carbon dioxide additional heater 472 High-temperature carbon dioxide discharge line 473 High temperature heat medium inlet line 474 High temperature heat transfer medium outlet line 500 Cold energy power generation system (embodiment 5) 510 Additive gas circulation blower 570 Additive gas circulation line 571 Additive gas circulation blower inlet line 572 Additive gas circulation blower outlet line 573 Additive gas introduction amount control valve 574 Additive gas addition line 575 Additive gas discharge line 576 Additive gas discharge control valve

Claims

1. a liquefied carbon dioxide storage tank for storing liquefied carbon dioxide; a liquefied carbon dioxide pump that pressurizes the liquefied carbon dioxide stored in the liquefied carbon dioxide storage tank; a liquefied carbon dioxide heater for heating the liquefied carbon dioxide pressurized by the liquefied carbon dioxide pump through heat exchange with a heat medium to convert the liquefied carbon dioxide into a gas phase or a supercritical phase; a carbon dioxide expansion turbine that expands the carbon dioxide that has been converted into a gas phase or supercritical phase by the liquefied carbon dioxide heater to recover energy; a carbon dioxide gas solidification device that solidifies the low-pressure carbon dioxide gas expanded by the carbon dioxide expansion turbine through heat exchange with liquefied natural gas as a refrigerant to produce dry ice; a carbon dioxide gas supply line for supplying the carbon dioxide gas solidification device with low-pressure carbon dioxide gas expanded by the carbon dioxide expansion turbine; a dry ice supply line that supplies the dry ice generated by the carbon dioxide gas solidification device to the liquefied carbon dioxide storage tank; A cold energy power generation system characterized by having a dry ice melting device that melts the dry ice supplied to the liquefied carbon dioxide storage tank by heat exchange with a fluid having a temperature higher than the melting point of the dry ice to produce liquefied carbon dioxide.

2. a carbon dioxide gas cooler that cools the carbon dioxide gas supplied from the carbon dioxide expansion turbine to the carbon dioxide gas solidification device, 2. The cold energy power generation system according to claim 1, wherein heat obtained from the carbon dioxide gas in the carbon dioxide gas cooler is supplied to the dry ice melting device.

3. The cold energy power generation system of claim 2, further comprising a carbon dioxide-containing gas cooler disposed between the carbon dioxide gas cooler and the carbon dioxide gas solidification device, which cools the carbon dioxide gas supplied to the carbon dioxide gas solidification device using liquefied natural gas after the cold energy has been utilized in the carbon dioxide gas solidification device.

4. 2. The cold energy power generation system according to claim 1, wherein the liquefied carbon dioxide heater has a plurality of heaters that heat in different temperature ranges.

5. an additive gas addition line that adds an additive gas having a lower solidification temperature than the carbon dioxide gas to the carbon dioxide gas flowing through the carbon dioxide gas supply line; 2. The cold-energy power generation system of claim 1, further comprising an added gas circulation line that connects the outlet of the carbon dioxide gas solidification device to the carbon dioxide gas supply line and circulates the added gas that has not solidified in the carbon dioxide gas solidification device between the inlet and outlet sides of the carbon dioxide gas solidification device.

6. 6. The cold energy power generation system according to claim 1, wherein a heat source of the heat medium used in the liquefied carbon dioxide heater is waste heat from a plant.

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