Energy storage system

Abstract

To provide an energy storage system capable of storing energy using liquefied air as a medium and of reducing operational costs by preventing the generation of BOG through the utilization of cold energy in a cryogenic region.SOLUTION: An energy storage system 1 comprises: a LNG storage tank 10; a cold circulation LNG return line 181 which returns a portion of LNG flowing through a LNG delivery line to the LNG storage tank 10; an air liquefaction device 50 which liquefies air using cold energy of LNG; a liquified air storage tank 70; a liquefied air delivery line; a cold circulation LNG cooling heat exchanger 90 which cools the LNG flowing through the cold circulation LNG return line 181 using the cold energy of the liquefied air flowing through the liquefied air delivery line; a liquefied air heating heat exchanger 100; and an air expansion turbine 110 which is arranged downstream of the liquefied air heating heat exchanger 100 in the liquefied air delivery line and generates power by expanding gaseous air flowing through the liquefied air delivery line to drive the turbine.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an energy storage system that stores energy as energy that can be converted into electric power using liquefied air as a medium.

Background Art

[0002] With the spread of renewable energy, the need for energy storage systems has been increasing, and storing energy using liquid air has been proposed as one of the methods. However, there has been a demerit that the charging / discharging efficiency is low because the compression power when liquefying air is extremely large.

[0003] In this regard, Patent Document 1 discloses a technique of liquefying air at a low pressure by gradually cooling air with liquefied natural gas (LNG) and liquid hydrogen (LH2), using the cold heat of the used LNG and LH2 as fuel for a power generation facility, and supplying liquefied air as an oxidant to the power generation facility.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1, although nothing is described about the source of the LNG used for cooling air, a general source of LNG is an LNG storage tank. In the LNG storage tank, the internal LNG evaporates due to natural heat input from the atmosphere, work heat input from a pump, etc., and boil-off gas (hereinafter referred to as "BOG") is generated. If BOG is left untreated, it will exceed the design pressure of the LNG storage tank. Therefore, it is necessary to process BOG. Generally, BOG is extracted from the LNG storage tank, compressed, and then merged into the gas supply pipeline for treatment. However, since the pressure of BOG is almost atmospheric pressure, a large amount of power is required to compress it to a high pressure, which increases the operating cost.

[0006] The present invention is made to solve such problems, and an object thereof is to provide an energy storage system capable of achieving both energy storage using liquefied air as a medium and reduction of operating costs by preventing the generation of BOG using the cold heat in the cryogenic region.

Means for Solving the Problems

[0007] (1) The energy storage system according to the present invention includes an LNG storage tank for storing LNG, an LNG pump for boosting and discharging the LNG stored in the LNG storage tank, an LNG discharge line through which the LNG discharged by the LNG pump flows, a cold-insulated circulating LNG return line for refluxing a part of the LNG flowing through the LNG discharge line to the LNG storage tank, an air liquefaction device for liquefying air by using the cold heat of the LNG discharged by the LNG pump, a liquefied air storage tank for storing the air liquefied by the air liquefaction device, a liquefied air pump for boosting and discharging the liquefied air stored in the liquefied air storage tank, a liquefied air discharge line through which the liquefied air discharged by the liquefied air pump flows, a cold-insulated circulating LNG cooling heat exchanger for cooling the LNG flowing through the cold-insulated circulating LNG return line by using the cold heat of the liquefied air flowing through the liquefied air discharge line, a liquefied air heating heat exchanger disposed downstream of the cold-insulated circulating LNG cooling heat exchanger in the liquefied air discharge line and heating the liquefied air flowing through the liquefied air discharge line, An air expansion turbine that is disposed downstream of the liquefied air heating heat exchanger in the liquefied air discharge line and expands the air in the liquefied air discharge line to generate electricity by the rotational force of the turbine.

[0008] (2) Further, in the above (1), the air expansion turbine is an air expansion turbine for oxygen enrichment that generates electricity by reducing the pressure of the outlet air to the pressure required for the operation of the oxygen enrichment device. A power generation device that generates electricity using the evaporation gas of LNG generated in the LNG storage tank as fuel, and / or a power generation device that generates electricity using the vaporization gas of LNG discharged by the LNG pump as fuel. An oxygen enrichment device that is disposed at the outlet of the air expansion turbine for oxygen enrichment and extracts high-concentration oxygen air with a concentrated oxygen concentration by permeating the air at the outlet of the air expansion turbine for oxygen enrichment. A high-concentration oxygen air supply line that supplies the high-concentration oxygen air discharged from the permeation side of the oxygen enrichment device to the inlet of the power generation device. An exhaust gas discharge line that discharges the exhaust gas of the power generation device. An exhaust gas circulation line that diverts a part of the exhaust gas flowing through the exhaust gas discharge line and returns it to the inlet of the power generation device. An exhaust gas cooler that is disposed downstream of the liquefied air heating heat exchanger in the liquefied air discharge line and cools the exhaust gas returned to the inlet of the power generation device using the air flowing through the liquefied air discharge line.

[0009] (3) Further, in the above (2), a power generation air expansion turbine that is disposed downstream of the liquefied air heating heat exchanger in the liquefied air discharge line, expands the gaseous air flowing through the liquefied air discharge line to rotate the turbine, and generates electricity by reducing the pressure of the outlet air to atmospheric pressure.

[0010] (4) Further, in any one of the above (1) to (3), it has a cold storage material, and has a cold storage tank that stores the cold of the liquefied air flowing through the liquefied air discharge line in the cold storage circulation LNG cooler in the cold storage material, and uses the cold of the cold storage tank to cool the LNG flowing through the cold storage circulation LNG return line. It is characterized by being able to do so.

Effect of the Invention

[0011] According to the present invention, in a system for liquefying air and storing it as energy convertible into electric power, it is possible to achieve both energy storage using liquefied air as a medium and reduction of operating costs by preventing BOG generation using the cold heat in the cryogenic region.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0013] [Embodiment 1] First, with reference to FIG. 1, the configuration and function of Embodiment 1 of the present invention will be described. The energy storage system 1 according to the first embodiment of the present invention includes an LNG storage tank 10, an LNG pump 20, an LNG vaporizer 30, an air liquefaction device 50, an air liquefaction heat exchanger 60, a liquid air tank 70, a liquid air pump 80, a cold-insulated circulation LNG return line 181, a cold-insulated circulation LNG cooling heat exchanger 90, a liquid air heating heat exchanger 100, and an air expansion turbine 110.

[0014] The LNG storage tank 10 is a ground-mounted PC (Pre-stressed Concrete) storage tank, which has a steel inner tank and an outer tank, and is circumferentially surrounded by a PC wall. The space between the inner tank and the outer tank is filled with particles called perlite to form a nitrogen atmosphere, which exhibits a high heat insulation effect. As a result, the LNG storage tank 10 stores a large amount of LNG at an extremely low temperature (about -160°C) while suppressing heat input from the outside.

[0015] The LNG pump 20 is, for example, a vertical centrifugal submerged pump disposed on the downstream side of the LNG storage tank 10, with the pump body immersed inside the pot. The LNG pump 20 boosts the pressure of the LNG supplied from the LNG storage tank 10 through the LNG pump inlet line 171 and discharges it.

[0016] The LNG vaporizer 30 is an ORV (Open Rack Vaporizer) type vaporizer. LNG flows from the bottom to the top inside a vertically arranged heat transfer tube group, and seawater flows from the top to the bottom outside. This completely evaporates the LNG supplied from the LNG pump outlet line 172 and supplies it to the gas supply line 173.

[0017] The air liquefaction device 50 is a refrigerator that uses a general nitrogen refrigerant to cool the atmosphere taken in from the air inlet line 174 and produce liquid air.

[0018] The air liquefaction heat exchanger 60 is a general shell & tube type heat exchanger, and as will be described later, supplies the cold heat of LNG to the nitrogen refrigerant in the air liquefaction device 50.

[0019] FIG. 2 is a schematic diagram showing the details of the air liquefaction apparatus 50 and the relationship between the air liquefaction apparatus 50 and the heat exchanger 60 for air liquefaction. As shown in FIG. 2, the air liquefaction apparatus 50 includes a raw material air compressor 51, an adsorber 53, a raw material air cooler 54, and a nitrogen compressor 55. The raw material air compressor 51 is a centrifugal compressor that compresses the air introduced from the air inlet line 174 and supplies it to the compressed air line 52.

[0020] The adsorber 53 is an adsorption tower filled with a zeolite-based adsorbent, which adsorbs moisture and carbon dioxide from the compressed air flowing through the compressed air line 52. The raw material air cooler 54 is a plate heat exchanger that uses the cold heat of liquid nitrogen described later to cool and liquefy the compressed air flowing through the compressed air line 52.

[0021] The nitrogen compressor 55 is a centrifugal compressor that compresses the nitrogen gas flowing through the nitrogen circulation line 56. The nitrogen expansion valve 57 is a remotely operated globe valve that rapidly decompresses the nitrogen gas cooled by LNG in the heat exchanger 60 for air liquefaction to generate liquid nitrogen. The generated liquid nitrogen cools the air in the raw material air cooler 54 and evaporates itself.

[0022] Returning to FIG. 1, the liquid air tank 70 is a vertical cylindrical steel tank that temporarily stores the liquid air supplied from the liquid air supply line 175. The liquid air pump 80 is a centrifugal pump that boosts the liquid air supplied from the liquid air pump suction line 176 and supplies it to the liquid air pump discharge line 177.

[0023] The cold insulation circulation LNG return line 181 is a pipe with one end connected to the LNG pump outlet line 172 and the other end connected to the LNG storage tank 10. The cold insulation circulation LNG that constantly flows through the LNG pump outlet line 172 to maintain a cooled state is refluxed from the vicinity of the end of the LNG pump outlet line 172 to the LNG storage tank 10.

[0024] The cold-insulated circulation LNG return flow control valve 182 is a remotely operated globe valve that regulates the flow rate of the cold-insulated circulation LNG flowing through the cold-insulated circulation LNG return line 181 and returning to the LNG storage tank 10.

[0025] The heat exchanger 90 for cooling the cold-insulated circulation LNG is a shell & tube heat exchanger that uses liquid air as a refrigerant to cool the cold-insulated circulation LNG flowing through the cold-insulated circulation LNG return line 181. The heat exchanger 100 for heating the liquefied air is an open rack type heat exchanger that uses normal temperature water such as seawater or warm water as a heating medium to heat the liquid or gaseous air after passing through the heat exchanger 90 for cooling the cold-insulated circulation LNG.

[0026] The air expansion turbine 110 is a centrifugal expansion turbine that reduces high-pressure air to the equivalent of atmospheric pressure, converts its pressure energy into rotational motion of the turbine, and generates electricity by means of a generator.

[0027] Next, the operation of the energy storage system 1 according to this embodiment will be described. The energy storage system 1 operates the air liquefaction device 50, liquefies air by utilizing the cold heat of LNG, and stores it in the liquid air tank 70. Thereby, the energy storage system 1 accumulates energy convertible into electric power in the form of liquefied air.

[0028] The energy storage system 1 operates the liquid air pump 80 to boost the cryogenic (e.g., -190°C) liquid air stored in the liquid air tank 70 and discharge it as high-pressure liquid air (e.g., 10 MPaG) into the liquid air pump discharge line 177.

[0029] The high-pressure liquid air discharged into the liquid air pump discharge line 177 is heated by the cold-insulated circulation LNG flowing through the cold-insulated circulation LNG return line 181 in the heat exchanger 90 for cooling the cold-insulated circulation LNG. In other words, the cold-insulated circulation LNG is cooled in the heat exchanger 90 for cooling the cold-insulated circulation LNG.

[0030] For example, in the heat exchanger 90 for cooling LNG in the cold insulation circulation, assuming that the temperature of the liquid air is -190°C, the pressure is 10 MPaG, the flow rate is 10 ton / h, the temperature of the LNG in the cold insulation circulation is -150°C, the pressure is 5 MPaG, and the flow rate is 5 ton / h, at the outlet of the heat exchanger 90 for cooling LNG in the cold insulation circulation, the temperature of the liquid air is -171°C and the temperature of the LNG in the cold insulation circulation is -170°C. Assuming that the LNG is 100% methane, since it is in a supercooled state lower than the boiling point of -160°C at the internal pressure of 10 kPaG in the LNG storage tank 10, there is an effect of cooling the LNG storage tank 10.

[0031] The air heated in the heat exchanger 90 for cooling LNG in the cold insulation circulation is further heated and evaporated in the heat exchanger 100 for heating liquefied air, and becomes high-pressure air (supercritical state) at normal temperature (for example, 20°C).

[0032] The high-pressure air generated in the heat exchanger 100 for heating liquefied air is introduced into the air expansion turbine 110, drives the air expansion turbine 110 with pressure reduction and temperature reduction, and generates electricity. The low-pressure air at the outlet of the air expansion turbine 110 is discharged to the atmosphere through the air discharge line 178.

[0033] According to the energy storage system 1 according to the present embodiment, in order to effectively utilize the cold heat of the LNG in the heat exchanger 60 for liquefying air, the compression power in the air liquefaction device 50 can be reduced and the operation can be energy-saving.

[0034] Further, according to the energy storage system 1 according to the present embodiment, since the LNG in the cold insulation circulation can be cooled by using the cryogenic cold heat (about -190°C) of the liquid air, the LNG storage tank 10 can be cooled. As a result, the boil-off gas (BOG) generated from the LNG storage tank 10 can be reduced, and thus the power of the BOG compressor required for the treatment of the BOG can be significantly reduced.

[0035] Moreover, according to the energy storage system 1 according to the present embodiment, since the cold heat of LNG can be effectively utilized for air liquefaction, the cold heat of LNG that has been discarded into the environment can be reduced. For example, an LNG vaporizer using seawater as a heating medium has discarded the cold heat of LNG into the ocean, but since the amount can be reduced, the impact on the ocean can be reduced.

[0036] In addition, in the present embodiment, the form of the heat exchanger including the air liquefaction heat exchanger 60 has been described as a shell & tube type or an open rack type, but it is not limited to this, and the form is appropriately selected within the scope of design. The same applies to pumps and valves.

[0037] Also, in the present embodiment, it has been described that the cryogenic circulation LNG flowing through the cryogenic circulation LNG return line 181 near the end of the discharge line of the LNG pump 20 is cooled, but it is not limited to the cryogenic circulation LNG return line 181 as long as it is a line that returns to the LNG storage tank 10. For example, there may be a case where the LNG receiving line for receiving LNG from the LNG tanker into the LNG storage tank 10 is cryogenically circulated, and the cryogenic circulation LNG flowing through such an LNG receiving line may be cooled.

[0038] Also, in the present embodiment, it has been described that the total amount of liquid air is introduced into the cryogenic circulation LNG cooler 90, but there may be a line that bypasses the cryogenic circulation LNG cooler 90 with respect to the liquid air pump discharge line 177. If the cryogenic circulation LNG is excessively cooled, there may be effects such as the cryogenic circulation LNG solidifying or the internal pressure of the LNG storage tank 10 decreasing too much. Therefore, the flow rate of the bypass line and the flow rate to the cryogenic circulation LNG cooler 90 may be adjusted.

[0039] Further, as a means for preventing excessive cooling of the cold-insulated circulating LNG, a cold-insulated circulating LNG cooler bypass line 371 that bypasses the cold-insulated circulating LNG cooler 90 may be provided in the cold-insulated circulating LNG return line 181, as in the energy storage system 300 shown in FIG. 3, and a cold-insulated circulating LNG cooler bypass flow control valve 372 may be provided in the cold-insulated circulating LNG cooler bypass line 371.

[0040] The cold-insulated circulating LNG cooler bypass flow control valve 372 is a general remote-operated globe valve and adjusts the flow rate of the cold-insulated circulating LNG that bypasses the cold-insulated circulating LNG cooler 90.

[0041] The total flow rate of the cold-insulated circulating LNG and the flow rate of the cold-insulated circulating LNG supplied to the cold-insulated circulating LNG cooler 90 are adjusted by the cold-insulated circulating LNG return flow control valve 182 and the cold-insulated circulating LNG cooler bypass flow control valve 372.

[0042] According to the energy storage system 300, the cold-insulated circulating LNG can be cooled according to the required cooling heat quantity of the LNG storage tank 10 without affecting the total amount of the cold-insulated circulation amount of the LNG piping system, so that the internal pressure management of the LNG storage tank 10 can be performed more flexibly.

[0043] Also, in the present embodiment, although the low-pressure air at the outlet of the air expansion turbine 110 has been described as being discharged to the atmosphere, it may be supplied to the intake of a power generation device (not shown). Since the temperature of the air has decreased in the air expansion turbine 110, the density has increased, and as a result, more oxygen will be supplied to the power generation device, so that the power generation efficiency of the power generation device can be improved.

[0044] [Embodiment 2] Next, with reference to FIG. 4, the configuration and functions of Embodiment 2 will be described. Components having the same configuration and functions as those in Embodiment 1 are assigned the same numbers. The energy storage system 200 according to Embodiment 2 includes an exhaust gas cooler 210, an oxygen-enriched air expansion turbine 221, a power generation air expansion turbine 222, an oxygen enrichment device 230 having an oxygen enrichment membrane, a power generation device 240, an air pressure control valve 272, and an air flow control valve 275.

[0045] The exhaust gas cooler 210 is a shell & tube type heat exchanger, and cools the exhaust gas of the power generation device 240 using the air at the outlet of the liquefied air heater 100 as a cold heat source.

[0046] The oxygen-enriched air expansion turbine 221 is a centrifugal expansion turbine. By reducing the pressure of high-pressure air to the pressure required for the operation of the oxygen enrichment device 230, its pressure energy is converted into the rotational motion of the turbine, and electricity is generated by a generator. The power generation air expansion turbine 222 is a centrifugal expansion turbine. By reducing the pressure of high-pressure air to the equivalent of atmospheric pressure, its pressure energy is converted into the rotational motion of the turbine, and electricity is generated by a generator.

[0047] The oxygen enrichment device 230 is provided with an oxygen enrichment membrane based on a polymer material, and utilizes the fact that the permeation rate of oxygen molecules is greater than the dropping rate of nitrogen molecules to allow air with high-concentration oxygen to permeate to the downstream.

[0048] The power generation device 240 is a power generation device using a reciprocating gas engine. It generates electricity using the BOG supplied from the LNG storage tank 10 via the BOG supply line 279 as fuel, and supplies the generated exhaust gas to the exhaust gas discharge line 276.

[0049] The air pressure control valve 272 is a general remote-operated butterfly valve, and adjusts the flow rate of the oxygen-enriched air expansion turbine outlet line 271 so that the inlet pressure of the oxygen enrichment device 230 becomes a predetermined value. The air flow control valve 275 is a general remote-operated butterfly valve, and adjusts the flow rate of the power generation air expansion turbine outlet line 274.

[0050] Next, the operation of the energy storage system 200 according to the present embodiment will be described. In the heat exchanger 100 for heating liquefied air, the high-pressure air heated and evaporated is used to cool the high-temperature (e.g., 350°C) exhaust gas of the power generation device 240 in the exhaust gas cooler 210. At the same time, the high-pressure air itself is further heated and becomes high-pressure air at a high temperature (e.g., 200°C).

[0051] The BOG generated in the LNG storage tank 10 flows through the BOG supply line 279 and is supplied to the power generation device 240, where it is used as fuel for the power generation device 240 and converted into electricity.

[0052] In the power generation device 240, methane gas is supplied from the BOG supply line 279. A mixed gas of the recycled portion of its own exhaust gas and the high-concentration oxygen-enriched air supplied from the permeate side of the oxygen enrichment device 230 via the high-concentration oxygen-enriched air supply line 278 is supplied from the exhaust gas circulation line 277. Therefore, exhaust gas containing high-concentration carbon dioxide is discharged from the power generation device 240 to the exhaust gas discharge line 276.

[0053] The exhaust gas discharged to the exhaust gas discharge line 276 is cooled to room temperature (e.g., 20°C) by high-pressure air in the exhaust gas cooler 210.

[0054] Among the exhaust gas cooled to room temperature, the portion discharged outside the system has its flow rate adjusted by the exhaust gas discharge flow rate control valve 281. Among the exhaust gas cooled to room temperature, the portion not discharged outside the system has its flow rate adjusted by the exhaust gas circulation flow rate control valve 282 and is diverted to the exhaust gas circulation line 277, and circulates to the intake port of the power generation device 240 together with the high-concentration oxygen-enriched air supplied via the high-concentration oxygen-enriched air supply line 278.

[0055] According to the energy storage system 200 according to this embodiment, in the exhaust gas cooler 210, the high-temperature exhaust gas of the power generation device 240 is used to further heat the high-pressure air before the expansion turbine, so that the power generation efficiency in the expansion turbine can be increased.

[0056] Moreover, according to the energy storage system 200 according to the present embodiment, the high-concentration oxygen air generated in the oxygen enrichment device 230 can be effectively utilized as an oxidant for the power generation device 240. By using high-concentration oxygen air as an oxidant, since the nitrogen component that accounts for about 80% of the atmosphere is reduced, the carbon dioxide concentration in the exhaust gas of the power generation device 240 can be increased, so that the energy for recovering carbon dioxide from the exhaust gas can be reduced.

[0057] Moreover, according to the energy storage system 200 according to the present embodiment, after the exhaust gas of the power generation device 240 is cooled by the exhaust gas cooler 210, it is circulated to the intake port of the power generation device 240, so that an excessive increase in the combustion chamber temperature of the power generation device 240 due to mixing high-concentration oxygen air into the circulated exhaust gas can be suppressed.

[0058] Moreover, according to the energy storage system 200 according to the present embodiment, by dividing the oxygen enrichment air expansion turbine 221 into a system that produces high-concentration oxygen air and the power generation air expansion turbine 222 into a system specialized for power generation, high-pressure air can be supplied to the oxygen enrichment air expansion turbine 221 only by the amount required for high-concentration oxygen air, so that the power generation amounts in the oxygen enrichment air expansion turbine 221 and the power generation air expansion turbine 222 can be maximized.

[0059] In the present embodiment, the exhaust gas cooler 210 is disposed in the exhaust gas discharge line 276, but it may be installed in the exhaust gas circulation line 277. In that case, since the exhaust gas that does not flow in the exhaust gas circulation line 277 and is discharged to the outside remains at a high temperature, high-temperature exhaust heat can be supplied to other facilities.

[0060] Moreover, in the present embodiment, the high-concentration oxygen air supply line 278 is merged into the exhaust gas circulation line 277, but it is not necessarily required that these lines be merged, and any mode in which high-concentration oxygen air is supplied to the intake air of the power generation device 240 may be used.

[0061] Also, in this embodiment, although nothing is installed in the BOG supply line 279, the cold heat of BOG may be used for cooling the circulated exhaust gas supplied to the intake port of the power generation device 240, or the cold heat of BOG may be used for cooling the air in the air liquefaction device 50.

[0062] Also, in this embodiment, the high-concentration oxygen air obtained by the oxygen enrichment device 230 is directly merged into the circulated exhaust gas flowing through the exhaust gas circulation line 277. However, air containing even higher-purity oxygen may be obtained by passing it through an oxygen concentrator such as PSA.

[0063] Also, in this embodiment, one oxygen-enriched air expansion turbine 221 and one power generation air expansion turbine 222 are provided respectively. However, the present invention is not limited to this. Only one or a plurality of oxygen-enriched air expansion turbines 221 may be provided, or only one or a plurality of power generation air expansion turbines 222 may be provided. Further, when both the oxygen-enriched air expansion turbine 221 and the power generation air expansion turbine 222 are provided, cases where one is one and the other is a plurality, or cases where each is a plurality are included.

[0064] Also, in this embodiment, there are a figure and an explanation showing that only BOG from the BOG supply line 279 and circulated gas from the exhaust gas circulation line 277 are supplied to the power generation device 240, but it does not prevent the mixing of air into the second combustion device 240.

[0065] [Embodiment 3] Next, with reference to FIG. 5, the configuration and function of Embodiment 3 will be described. Components having the same configuration and function as those in Embodiment 1 and Embodiment 2 are given the same numbers. The energy storage system 400 according to Embodiment 3 includes a cold-insulated circulation LNG cooling heat storage tank 410.

[0066] The heat storage tank 410 for cold storage cycle LNG cooling is a tank that is heat-transferably connected to the heat exchanger 90 for cold storage cycle LNG cooling, and holds a cold storage material such as propane, for example.

[0067] Next, the operation of the energy storage system 400 according to the present embodiment will be described. When operating the air expansion turbine 110, the cold heat of liquid air is stored in the heat storage tank 410 for cold storage cycle LNG cooling.

[0068] When the air expansion turbine 110 is stopped, the cold storage cycle LNG is cooled by the cold heat stored in the heat storage tank 410 for cold storage cycle LNG cooling.

[0069] According to the energy storage system 400 according to the present embodiment, since the cold heat of liquid air can be stored in the heat storage tank 410 for cold storage cycle LNG cooling, the cold storage cycle LNG can be stably cooled regardless of the operating condition of the air expansion turbine 110.

[0070] In the present embodiment, a low-temperature refrigerant such as propane is exemplified as the cold storage agent of the heat storage tank 410 for cold storage cycle LNG cooling, but a solid cold storage material made of an alloy such as lead, bismuth, copper, nickel, holmium, or cobalt may also be used.

Industrial Applicability

[0071] The present invention can be used as an energy storage system that can liquefy air and store it as energy convertible into electric power, and can prevent the generation of BOG and reduce the operation cost by using the cold heat in the extremely low temperature region in the system.

Explanation of Reference Numerals

[0072] 1, 200, 300, 400 Energy storage system 10 LNG storage tank 20 LNG pump 30 LNG vaporizer 50 Air liquefaction device 51 Raw air compressor 52 Compressed air line 53 Suction device 54 Raw air cooler 55 Nitrogen compressor 56 Nitrogen circulation line 57 Nitrogen expansion valve 60 Heat exchanger for air liquefaction 70 Liquid air tank 80 Liquid air pump 90 Heat exchanger for LNG cooling in cold insulation circulation 100 Heat exchanger for heating liquefied air 110 Air expansion turbine 171 LNG pump inlet line 172 LNG pump outlet line 173 Gas supply line 174 Air inlet line 175 Liquid air supply line 176 Liquid air pump suction line 177 Liquid air pump discharge line 178 Air discharge line 181 LNG return line in cold insulation circulation 182 Flow control valve for LNG return in cold insulation circulation 210 Exhaust gas cooler 221 Air expansion turbine for oxygen enrichment 222 Air expansion turbine for power generation 230 Oxygen enrichment device 240 Power generation device 271 Outlet line of air expansion turbine for oxygen enrichment 272 Air pressure control valve 273 Low-concentration oxygen air discharge line 274 Outlet line of air expansion turbine for power generation 275 Air flow control valve 276 Exhaust gas discharge line 277 Exhaust gas circulation line 278 High-concentration oxygen air supply line 279 BOG supply line 281 Exhaust gas discharge flow control valve 282 Exhaust gas circulation flow control valve 371 Cold-insulated cycle LNG cooler bypass line 372 Cold-insulated cycle LNG cooler bypass flow control valve 410 Cold-insulated cycle LNG cooling heat storage tank

Claims

1. An LNG storage tank for storing LNG, an LNG pump for boosting and discharging the LNG stored in the LNG storage tank, an LNG discharge line through which the LNG discharged by the LNG pump flows, a cold-insulated circulating LNG return line for refluxing a part of the LNG flowing through the LNG discharge line to the LNG storage tank, an air liquefaction device for liquefying air by utilizing the cold heat of the LNG discharged by the LNG pump, a liquefied air storage tank for storing the air liquefied by the air liquefaction device, a liquefied air pump for boosting and discharging the liquefied air stored in the liquefied air storage tank, a liquefied air discharge line through which the liquefied air discharged by the liquefied air pump flows, a cold-insulated circulating LNG cooling heat exchanger for cooling the LNG flowing through the cold-insulated circulating LNG return line by utilizing the cold heat of the liquefied air flowing through the liquefied air discharge line, a liquefied air heating heat exchanger disposed downstream of the cold-insulated circulating LNG cooling heat exchanger in the liquefied air discharge line and heating the liquefied air flowing through the liquefied air discharge line, An energy storage system, comprising: an air expansion turbine disposed downstream of the liquefied air heating heat exchanger in the liquefied air discharge line and expanding the gaseous air flowing through the liquefied air discharge line to generate electricity by the rotational force of a turbine.

2. The air expansion turbine is an air expansion turbine for oxygen enrichment that generates electricity by reducing the pressure of the outlet air to a pressure required for the operation of an oxygen enrichment device, a power generation device that generates electricity using the evaporation gas of the LNG generated in the LNG storage tank as fuel and / or a power generation device that generates electricity using the vaporization gas of the LNG discharged by the LNG pump as fuel, an oxygen enrichment device disposed at the outlet of the air expansion turbine for oxygen enrichment and extracting high-concentration oxygen air with a concentrated oxygen concentration by permeating the air at the outlet of the air expansion turbine for oxygen enrichment, a high-concentration oxygen air supply line for supplying the high-concentration oxygen air discharged from the permeation side of the oxygen enrichment device to the inlet of the power generation device, an exhaust gas discharge line for discharging the exhaust gas of the power generation device, an exhaust gas circulation line for diverting a part of the exhaust gas flowing through the exhaust gas discharge line and refluxing it to the inlet of the power generation device An exhaust gas cooler disposed downstream of the liquefied air heating heat exchanger in the liquefied air discharge line and cooling the exhaust gas refluxed to the inlet of the power generation device by using the air flowing through the liquefied air discharge line, the energy storage system according to claim 1, characterized by comprising the same.

3. An air expansion turbine for power generation, which is disposed downstream of the liquefied air heating heat exchanger in the liquefied air discharge line, expands the gaseous air flowing through the liquefied air discharge line to rotate the turbine, and reduces the pressure of the outlet air to atmospheric pressure to generate power, and the energy storage system according to claim 2, further comprising the same.

4. A cold storage tank having a cold storage material and storing the cold heat of the liquefied air flowing through the liquefied air discharge line in the cold storage circulation LNG cooling heat exchanger in the cold storage material, and being able to cool the LNG flowing through the cold storage circulation LNG return line by using the cold heat of the cold storage tank, the energy storage system according to any one of claims 1 to 3, characterized by the above.

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