Heat storage device and heat storage method

Abstract

To provide a heat accumulation device capable of accumulating cold heat so as to enable effective utilization of variable renewable energy.SOLUTION: A heat accumulation device 1 has: a refrigerator 10 operable by variable renewable energy; a brine storage tank 20 connected to the refrigerator, and capable of storing brine; a first circulation line 30 through which the brine stored in the brine storage tank circulates; and a first heat exchange unit 40 that exchanges heat between the brine circulating in the first circulation line and LPG.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heat storage device and a heat storage method for storing cold energy generated by a refrigerator that can be operated using variable renewable energy. [Background technology]

[0002] When low-temperature liquefied gases (hereinafter referred to as liquefied gases) such as liquefied natural gas and liquefied hydrogen are heated by heat input from outside the storage tank, boil-off gas (BOG) is generated, which causes an increase in pressure inside the storage tank.

[0003] In this regard, a treatment method for re-liquefying the generated BOG has been known (for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-19199 Summary of the Invention [Problem to be solved by the invention]

[0005] Generally, reliquefaction systems for reliquefying BOG use a compressor to increase pressure, then cool and liquefy it using a heat exchanger, or inject BOG into the liquefied gas being sent out to liquefy it, and then pump it out. However, this system is complicated, and it poses issues such as reduced reliability and increased equipment size.

[0006] At the same time, there is a need to make effective use of variable renewable energy sources such as solar, wind, and solar thermal. Variable renewable energy sources do not emit greenhouse gases and can be produced domestically, making them promising, diverse, and important low-carbon domestic energy sources that can also contribute to energy security.

[0007] The present invention has been invented to solve the above-mentioned problems, and aims to provide a heat storage device and a heat storage method that can store cold heat generated by a refrigerator that can operate with variable renewable energy. [Means for solving the problem]

[0008] A heat storage device according to the present invention that achieves the above object is a heat storage device that stores cold energy for cooling liquefied gas and suppresses the generation of BOG from a storage tank for the liquefied gas. The heat storage device includes a brine storage tank capable of storing brine for cooling the liquefied gas, a refrigerator that is operated by variable renewable energy and cools the brine in the brine storage tank when the variable renewable energy is present and stores the cold energy in the brine, a first circulation line through which the brine stored in the brine storage tank circulates, and a first heat exchange unit that exchanges heat between the brine circulating through the first circulation line and the liquefied gas in a liquid state delivered from the storage tank, thereby cooling the liquefied gas. The first heat exchange unit exchanges heat between the brine in the liquid state and the liquefied gas in a liquid state. transformation The subcooling heat exchanger is characterized in that it cools gas to a subcooled state using the brine, the liquefied gas being LPG or liquefied ammonia, and the subcooled liquefied gas is returned to the storage tank.

[0009] Furthermore, a heat storage method according to the present invention that achieves the above-mentioned object is a heat storage method that stores cold heat using the above-mentioned heat storage device, in which the brine is cooled by operating the refrigerator using the variable renewable energy, cold heat is stored in the brine, the brine with the cold heat stored therein is circulated through the first circulation line, and heat is exchanged with the liquefied gas in the first heat exchange section. [Effects of the Invention]

[0010] According to the heat storage device and heat storage method described above, the brine can be cooled and cold energy can be stored in the brine by operating a refrigerator using variable renewable energy. Then, at a predetermined timing, the brine with the cold energy stored therein can be circulated through the first circulation line and heat exchanged with liquefied gas in the first heat exchanger. Therefore, cold energy generated by a refrigerator that can be operated using variable renewable energy can be suitably stored. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic view showing a heat storage device according to a first embodiment of the present invention. [Figure 2] FIG. 1 is a diagram illustrating a subcooled state, showing a phase diagram. [Figure 3] FIG. 4 is a schematic view showing a modified example of the heat storage device according to the first embodiment. [Figure 4] FIG. 4 is a schematic view showing a heat storage device according to a second embodiment of the present invention. [Figure 5] FIG. 10 is a schematic view showing a modified example of the heat storage device according to the second embodiment. [Figure 6] FIG. 10 is a schematic diagram showing a heat storage device according to a first modified example. DETAILED DESCRIPTION OF THE INVENTION

[0012] First Embodiment A first embodiment of the present invention will be described with reference to Figures 1 and 2. In the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted. The dimensional proportions in the drawings have been exaggerated for the sake of explanation, and may differ from the actual proportions.

[0013] Fig. 1 is a schematic diagram showing a heat storage device 1 according to a first embodiment of the present invention, and Fig. 2 is a diagram showing a phase diagram for explaining a subcooled state.

[0014] The heat storage device 1 according to the first embodiment is a device that appropriately stores cold energy generated by a chiller 10 that can be operated using variable renewable energy, and uses the stored cold energy to suppress the generation of BOG (boil-off gas) from liquefied gas. The liquefied gas is not particularly limited, but examples include LNG (liquefied natural gas), LPG (liquefied petroleum gas), liquefied hydrogen, liquefied nitrogen, and liquefied ammonia. By employing LPG or liquefied ammonia, the coefficient of performance of the chiller 10 can be increased, and variable renewable energy can be efficiently converted into cold energy. The following description will be given taking the case where LPG is used as the liquefied gas as an example.

[0015] As shown in FIG. 1, the heat storage device 1 includes a refrigerator 10, a brine storage tank 20 in which brine cooled by the refrigerator 10 is stored, a first circulation line 30 through which the brine circulates, a first heat exchange unit 40 that exchanges heat between the brine and liquid LPG, a second circulation line 50 through which the brine circulates, a second heat exchange unit 60 that exchanges heat between the liquid LPG flowing out of the storage tank T and the brine circulating through the second circulation line 50, a pump 70 provided within the storage tank T, an LPG circulation line 80 that connects the pump 70 and the first heat exchange unit 40 and through which LPG flows, a branch line 90 that branches off from the LPG circulation line 80 and sends the LPG in the storage tank T to the outside, and a control unit (not shown) that controls the movement of the brine in the refrigerator 10 and the brine storage tank 20.

[0016] As shown in FIG. 1, LPG is delivered to a storage tank T from a cargo S of a ship via a receiving pipe L at a predetermined timing.

[0017] When solar power generation is used as the variable renewable energy source, the refrigerator 10 is turned on using surplus electricity that is likely to be generated during the daytime to cool the brine in the brine storage tank 20. When there is no surplus electricity, the refrigerator 10 is turned off. The on / off control of the refrigerator 10 is performed by a control unit. In this way, by performing intermittent operation using surplus electricity from the variable renewable energy, the refrigerator 10 can make effective use of the variable renewable energy and store heat from the variable renewable energy, thereby achieving carbon neutrality.

[0018] The refrigerator 10 is not particularly limited as long as it can suitably cool the brine in the brine storage tank 20, but from the viewpoint of the coefficient of performance, for example, a vapor compression cycle refrigerator can be used.

[0019] Brine is stored in the brine storage tank 20. The brine is not particularly limited, but for example, antifreeze can be used. By using brine in this way, the LPG and the refrigerator 10 can be separated, which simplifies the equipment and regulations. Specifically, the brine storage tank 20 and the refrigerator 10 can be made non-explosion-proof. In particular, there is a great advantage to making the refrigerator 10 non-explosion-proof. Furthermore, expansion is easy, so it can also be easily added to existing equipment.

[0020] 1, the brine storage tank 20 is connected to a first circulation line 30 and a second circulation line 50. The brine in the brine storage tank 20 is switched between circulating through the first circulation line 30 or the second circulation line 50 by a control unit.

[0021] The first circulation line 30 circulates the brine stored in the brine storage tank 20. The first circulation line 30 is connected to the brine storage tank 20.

[0022] The first heat exchange unit 40 exchanges heat between the brine circulating through the first circulation line 30 and the liquid LPG circulating through the LPG circulation line 80. In the LPG circulation line 80, the liquid LPG that has passed through the first heat exchange unit 40 receives cold heat from the brine and becomes subcooled. In other words, the first heat exchange unit 40 is a subcooling heat exchanger that cools the liquid LPG to a subcooled state using the brine. Meanwhile, in the first circulation line 30, the brine that has passed through the first heat exchange unit 40 receives hot heat from the LPG and its temperature rises.

[0023] The subcooled state will be explained below with reference to the phase diagram in Figure 2. LPG is normally in a saturated state at the boundary between the liquid and gas phases, indicated by the black circle in Figure 2. By cooling this saturated LPG with the cold energy of brine, it moves from the black circle to the white circle on the left, and enters a subcooled state. Since LPG in a subcooled state is completely liquid, the generation of BOG can be suppressed.

[0024] The second circulation line 50 circulates the brine stored in the brine storage tank 20. The second circulation line 50 is connected to the brine storage tank 20. A second heat exchange unit 60 is disposed on the second circulation line 50.

[0025] The second heat exchange unit 60 exchanges heat between the brine circulating through the second circulation line 50 and the liquid LPG passing through the branch line 90. In the branch line 90, the liquid LPG that has passed through the second heat exchange unit 60 is heated by the brine circulating through the second circulation line 50 and is transferred to a downstream spherical tank or pillow-shaped tank in a room-temperature, high-pressure liquid state. Meanwhile, in the second circulation line 50, the brine that has passed through the second heat exchange unit 60 receives cold energy from the LPG and is cooled.

[0026] As shown in Fig. 1, the pump 70 is provided near the bottom of the storage tank T. The pump 70 is provided to send the LPG in the storage tank T to the first heat exchange section 40 via the LPG circulation line 80. The pump 70 is also provided to send the LPG in the storage tank T to a spherical tank or a pillow-shaped tank via the LPG circulation line 80 and a branch line 90. A known pump can be used as the pump 70.

[0027] The LPG circulation line 80 has a first line 81 leading from the pump 70 to the first heat exchange unit 40 and a second line 82 leading from the first heat exchange unit 40 to the storage tank T.

[0028] A branch line 90 branches off from the first line 81. The LPG flowing through the second line 82 is in a subcooled state.

[0029] The second heat exchange section 60 is disposed in the branch line 90. The branch line 90 is connected to a spherical tank or a pillow-shaped tank.

[0030] The control unit controls the on / off of the refrigerator 10. The control unit also controls switching of the circulation of the brine stored in the brine storage tank 20 to the first circulation line 30 or the second circulation line 50. The control unit also controls the driving of the pump 70. The control unit is, for example, a PLC.

[0031] Next, a method will be described in which the cold energy generated by the chiller 10 that can be operated using variable renewable energy is stored in brine using the heat storage device 1 according to the first embodiment, and the cold energy stored in the brine is used to suppress the generation of BOG from LPG.

[0032] First, the control unit circulates the brine stored in the brine storage tank 20 through the second circulation line 50. The brine circulating through the second circulation line 50 receives cold heat from the LPG in the second heat exchange unit 60 and is pre-cooled.

[0033] Next, the control unit uses the surplus power to operate the refrigerator 10 to cool the brine in the brine storage tank 20. As a result, the cold energy generated by the refrigerator 10 can be stored in the brine storage tank 20.

[0034] Next, the control unit circulates the brine stored in the brine storage tank 20 through the first circulation line 30. The brine circulating through the first circulation line 30 cools the LPG circulating through the LPG circulation line 80 to a subcooled state in the first heat exchange unit 40. The LPG cooled to a subcooled state in the first heat exchange unit 40 then returns to the storage tank T via the second line 82. This makes it possible to suppress the generation of BOG in the storage tank T.

[0035] As described above, the heat storage device according to this embodiment is a heat storage device 1 that stores cold energy. The heat storage device 1 includes a chiller 10 that can be operated using variable renewable energy, a brine storage tank 20 that is connected to the chiller 10 and can store brine, a first circulation line 30 through which the brine stored in the brine storage tank 20 circulates, and a first heat exchange unit 40 that exchanges heat between the brine circulating through the first circulation line 30 and LPG. With the heat storage device 1 configured in this manner, the brine can be cooled and cold energy can be stored in the brine by operating the chiller 10 using variable renewable energy. Then, at a predetermined timing, the brine with the cold energy stored therein can be circulated through the first circulation line 30 and heat exchanged with LPG in the first heat exchange unit 40. Therefore, cold energy generated by the chiller 10 that can be operated using variable renewable energy can be suitably stored.

[0036] The first heat exchange section 40 is a subcooling heat exchanger that cools liquid LPG to a subcooled state using brine. According to the heat storage device 1 configured in this manner, the generation of BOG can be more suitably suppressed.

[0037] The heat storage device 1 also includes a second circulation line 50 connected to the brine storage tank 20 and through which the brine in the brine storage tank 20 circulates, and a second heat exchange unit 60 that cools the brine by exchanging heat between the liquid LPG and the brine circulating through the second circulation line 50. According to the heat storage device 1 configured in this manner, the brine stored in the brine storage tank 20 can be pre-cooled in the second heat exchange unit 60 by circulating it through the second circulation line 50. Therefore, the cooling efficiency of the brine stored in the brine storage tank 20 can be improved.

[0038] As described above, the heat storage method according to this embodiment is a heat storage method for storing cold energy using the heat storage device 1 described above, and involves operating the refrigerator 10 using variable renewable energy to cool the brine, storing cold energy in the brine, circulating the brine with the stored cold energy through the first circulation line 30, and exchanging heat with LPG in the first heat exchange section 40. According to this heat storage method, cold energy can be stored so that variable renewable energy can be effectively utilized to suppress the generation of BOG.

[0039] <Modification of the first embodiment> Next, the configuration of a heat storage device 2 according to a modified example of the first embodiment will be described with reference to Fig. 3. Fig. 3 is a schematic diagram showing a heat storage device 2 according to a modified example of the first embodiment.

[0040] The heat storage device 2 according to the modified example of the first embodiment is not provided with the second circulation line 50 and the second heat exchange section 60, as compared with the heat storage device 1 according to the first embodiment. The other configurations of the heat storage device 2 are the same as those of the heat storage device 1 according to the first embodiment. According to the heat storage device 2 configured in this way, the structure of the heat storage device 2 can be simplified, and the cold energy generated by the refrigerator 10 can be stored in the brine.

[0041] Second Embodiment Next, the configuration of a heat storage device 3 according to a second embodiment will be described with reference to Fig. 4. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted. Fig. 4 is a schematic diagram showing a heat storage device 3 according to a second embodiment of the present invention. The heat storage device 2 according to the second embodiment differs from the heat storage device 1 according to the first embodiment in the target that exchanges heat with brine in the first heat exchange section 140.

[0042] As shown in FIG. 4, the heat storage device 3 according to the second embodiment includes a refrigerator 10, a brine storage tank 20 in which brine cooled by the refrigerator 10 is stored, a first circulation line 30 through which the brine circulates, a first heat exchange unit 140 that exchanges heat between the brine and gaseous LPG (BOG), a second circulation line 50 through which the brine circulates, a second heat exchange unit 60 that exchanges heat between liquid LPG flowing out of the storage tank T and the brine circulating through the second circulation line 50, a pump 70 provided in the storage tank T, a first LPG line 180 that sends the LPG in the storage tank T from the pump 70 to a spherical tank or a pillow-shaped tank, a second LPG line 190 that sends the BOG in the storage tank T to the first heat exchange unit 140 and returns the condensed LPG to the storage tank T, and a control unit (not shown) that controls the operation of the refrigerator 10 and the brine in the brine storage tank 20. The configurations of the refrigerator 10, brine storage tank 20, first circulation line 30, second circulation line 50, second heat exchange section 60, pump 70, and control section are the same as those of the heat storage device 1 according to the first embodiment, and therefore will not be described again.

[0043] The first heat exchange unit 140 exchanges heat between the brine circulating through the first circulation line 30 and the BOG passing through the second LPG line 190. In the second LPG line 190, the BOG that has passed through the first heat exchange unit 140 receives cold heat from the brine and is condensed. That is, the first heat exchange unit 140 is used as a BOG condenser. The condensed LPG then returns to the storage tank T via the second LPG line 190. This makes it possible to suppress the generation of BOG from the storage tank T. Meanwhile, in the first circulation line 30, the brine that has passed through the first heat exchange unit 140 receives hot heat from the BOG and its temperature rises.

[0044] The first LPG line 180 connects the pump 70 and the spherical tank. The first LPG line 180 has a second heat exchange unit 60 disposed therein.

[0045] The second LPG line 190 has a first line 191 leading from the storage tank T to the first heat exchange unit 140, and a second line 192 leading from the first heat exchange unit 140 to the storage tank T. BOG flows through the first line 191, and condensed LPG flows through the second line 192.

[0046] Next, a method will be described in which the heat storage device 3 according to the second embodiment is used to suitably store the cold energy generated by the chiller 10 that can be operated using variable renewable energy, and the stored cold energy is used to suppress the generation of BOG from LPG.

[0047] First, the control unit circulates the brine stored in the brine storage tank 20 through the second circulation line 50. The brine circulating through the second circulation line 50 receives cold heat from the LPG in the second heat exchange unit 60 and is pre-cooled.

[0048] Next, the control unit uses the surplus power to operate the refrigerator 10 to cool the brine in the brine storage tank 20. As a result, the cold energy generated by the refrigerator 10 can be stored in the brine storage tank 20.

[0049] Next, the control unit circulates the brine stored in the brine storage tank 20 through the first circulation line 30. The brine circulating through the first circulation line 30 cools and condenses the BOG passing through the second LPG line 190 in the first heat exchange unit 140. The LPG condensed in the first heat exchange unit 140 is then returned to the storage tank T. This makes it possible to suppress the generation of BOG in the storage tank T.

[0050] In the heat storage device 3 according to the second embodiment, the first heat exchange section 140 is a BOG condenser that cools and condenses BOG with brine. According to the heat storage device 3 configured in this manner, the BOG generated in the storage tank T can be condensed and returned to the storage tank T. Therefore, the generation of BOG can be suppressed.

[0051] <Modification of the second embodiment> Next, the configuration of a heat storage device 4 according to a modified example of the second embodiment will be described with reference to Fig. 5. Fig. 5 is a schematic diagram showing a heat storage device 4 according to a modified example of the second embodiment.

[0052] Compared to the heat storage device 3 according to the second embodiment, the heat storage device 4 does not include the second circulation line 50 and the second heat exchange section 60. The other configurations of the heat storage device 4 are the same as those of the heat storage device 3 according to the second embodiment. According to the heat storage device 2 configured in this way, it is possible to store the cold energy generated by the refrigerator 10 in the brine while simplifying the structure of the heat storage device 4.

[0053] Although the present invention has been described above through the embodiments and modifications, the present invention is not limited to the above-described embodiments and modifications, and various modifications can be made within the scope of the claims.

[0054] For example, in the second embodiment described above, one storage tank T, one first circulation line 30, one first heat exchanger 140, one pump 70, and one second LPG line 190 are provided. However, as shown in FIG. 6, two storage tanks T, two first circulation lines 30, two first heat exchangers 140, two pumps 70, and two second LPG lines 190 may be provided. Note that the pump 70 and the first LPG line 180 are omitted from FIG. 6. Furthermore, three or more storage tanks T, two first circulation lines 30, two first heat exchangers 140, two pumps 70, and three or more second LPG lines 190 may be provided. This configuration enables condensation of BOG generated in multiple storage tanks T. Furthermore, by storing LPG in one of the two storage tanks T and liquid ammonia in the other, it is possible to suppress the generation of BOG of different liquefied gases. Furthermore, the configuration using two storage tanks T described above can also be applied to the heat storage device 1 according to the first embodiment. The same system can also be used if an LPG tank is converted into an ammonia tank.

[0055] Furthermore, in the above-described embodiment and modified examples, LPG has been used as an example of liquefied gas, but liquid ammonia can also be used as the liquefied gas.

[0056] In the above-described embodiment and modified example, the cold energy stored in the thermal storage device is used to suppress the generation of BOG. ​​However, the cold energy stored in the thermal storage device can also be used for cooling offices and control rooms within the base, as well as for a data center in an adjacent location, a plant factory, an aquaculture business, a food cold chain, and the like. [Explanation of symbols]

[0057] 1, 2, 3, 4 Heat storage device, 10 refrigeration units, 20 brine storage tanks, 30 First circulation line, 40, 140 first heat exchange section, 50 Second circulation line, 60 second heat exchange section, 70 pumps, 80 LPG circulation line, 90 Branch Line, 180 First LPG Line, 190 Second LPG Line, T storage tank.

Claims

1. A heat storage device that stores cold heat for cooling liquefied gas and suppresses generation of BOG from a storage tank of the liquefied gas, a brine storage tank capable of storing brine for cooling the liquefied gas; a refrigerator operated by variable renewable energy, cooling the brine in the brine storage tank when the variable renewable energy is present, and storing the cold energy in the brine; a first circulation line through which the brine stored in the brine storage tank circulates; a first heat exchange unit that exchanges heat between the brine circulating through the first circulation line and the liquefied gas in a liquid state sent from the storage tank, and cools the liquefied gas; The first heat exchange unit is a subcooling heat exchanger that cools the liquefied gas in a liquid state to a subcooled state by the brine, the liquefied gas is LPG or liquefied ammonia, The heat storage device is characterized in that the liquefied gas in the subcooled state is returned to the storage tank.

2. A heat storage device that stores cold heat for cooling BOG from a storage tank of liquefied gas and suppresses generation of the BOG from the storage tank, a brine storage tank capable of storing brine for cooling the BOG; a refrigerator operated by variable renewable energy, cooling the brine in the brine storage tank when the variable renewable energy is present, and storing the cold energy in the brine; a first circulation line through which the brine stored in the brine storage tank circulates; a first heat exchange unit that exchanges heat between the brine circulating through the first circulation line and the BOG to cool the BOG; a first line connecting the storage tank and the first heat exchange unit and supplying the BOG to the first heat exchange unit; a second line connecting the first heat exchange unit and the storage tank and returning the BOG cooled and condensed in the first heat exchange unit to the storage tank; and the first heat exchange unit is a BOG condenser that cools and condenses the BOG with the brine, the liquefied gas is LPG or liquefied ammonia, the second line is configured to return the condensed BOG to the storage tank; A heat storage device, characterized in that no booster device is installed on the first line and the second line.

3. a second circulation line connected to the brine storage tank through which the brine in the brine storage tank circulates; The heat storage device according to claim 1 or 2, further comprising a second heat exchange section that exchanges heat between the liquefied gas in a liquid state and the brine circulating through the second circulation line to cool the brine.

4. The heat storage device according to any one of claims 1 to 3, wherein a plurality of storage tanks for storing the liquefied gas are provided.

5. A heat storage method for storing cold heat using the heat storage device according to any one of claims 1 to 4, The refrigerator is operated using the variable renewable energy to cool the brine and store cold energy in the brine; The brine in which the cold heat has been stored is circulated through the first circulation line, and heat is exchanged with the liquefied gas in the first heat exchange section.

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