Energy storage system

Abstract

To provide an energy storage system that liquefies air and storing it as energy capable of being converted into electricity, efficiently improves power generation efficiency, and easily recovers carbon dioxide from exhaust gas.SOLUTION: An energy storage system according to the present invention comprises: an LNG storage tank 10; an LNG pump 20; a power generation unit 120 that generates power using vaporized LNG gas and / or evaporated LNG gas as fuel; a cryogenic separation unit 50 that separates and extracts nitrogen and oxygen as liquid; a cryogenic separation heat exchanger 60 that supplies cold heat of the LNG to the cryogenic separation unit 50; a high-temperature oxygen heat exchanger 100; an oxygen expansion turbine 110 that expands the evaporated oxygen to generate power; an exhaust gas circulation line 187 that circulates exhaust gas of the power generation unit 120 to the intake air of the power generation unit 120, and supplies exhaust heat to the high-temperature oxygen heat exchanger 100; and an oxygen gas confluence line 188 that confluences a portion of the oxygen gas at an outlet of the oxygen expansion turbine 110 with the exhaust gas circulation line 187.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an energy storage system that liquefies air and stores it as energy that can be converted into electric power.

Background Art

[0002] With the spread of renewable energy, the need for energy storage systems has been increasing, and energy storage using liquid air has also been proposed as one of the methods. However, there has been a demerit that the charging and 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 low pressure by cooling it stepwise with LNG and liquid hydrogen (LH2), using the cold heat of the LNG and LH2 that has been used as fuel for power generation equipment, and supplying the liquefied air as an oxidant to the power generation equipment.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, since the technique of Patent Document 1 assumes LH2, which is difficult to obtain, the feasibility of the equipment is poor. Even if it could be obtained, the high cost of LH2 would be reflected in the equipment operation cost, so there is a high possibility of impairing the business viability. In addition, although there is a description that the liquefied air is vaporized with water or air before expanding it with an air turbine for power generation, water and air can only reach a temperature of about normal temperature, and the power generation efficiency by the expansion turbine becomes low.

[0006] Furthermore, even if LH2 is co-fired with LNG, carbon dioxide in the exhaust gas will be dissipated into the atmosphere. Even when separation and recovery are performed, recovering low-concentration carbon dioxide in the exhaust gas requires a huge amount of energy, so there is a high possibility of impairing business profitability.

[0007] The present invention has been made to solve such problems, and in a system for liquefying air and storing it as energy convertible into electricity, it is an object of the present invention to efficiently increase the power generation efficiency with the energy within the system and to facilitate the recovery of carbon dioxide from the exhaust gas.

Means for Solving the Problems

[0008] (1) The energy storage system according to the present invention includes an LNG storage tank for storing LNG, an LNG pump for boosting the pressure of the LNG stored in the LNG storage tank and discharging it, a power generation device that generates electricity using the vaporized gas obtained by vaporizing the LNG discharged from the LNG pump and / or the evaporation gas generated in the LNG storage tank as fuel, a cryogenic separation device that separates and extracts nitrogen and oxygen as liquids from a gas mainly composed of nitrogen and oxygen, a cryogenic separation heat exchanger that supplies the cold heat of the LNG discharged from the LNG pump to the cryogenic separation device, a liquid oxygen tank for storing the liquid oxygen generated by the cryogenic separation device, a liquid oxygen pump for boosting the pressure of the liquid oxygen stored in the liquid oxygen tank and discharging it, an oxygen high-temperature heat exchanger that heats the liquid oxygen discharged from the liquid oxygen pump using the exhaust heat of the power generation device, an oxygen expansion turbine that expands the oxygen evaporated by the oxygen high-temperature heat exchanger and generates electricity, an exhaust gas circulation line that circulates the exhaust gas of the power generation device to the intake air of the power generation device and supplies exhaust heat to the oxygen high-temperature heat exchanger, An oxygen gas confluence line that merges a part of the oxygen gas at the outlet of the oxygen expansion turbine into the exhaust gas circulation line.

[0009] (2) Further, in the invention according to (1) above, in the upstream of the high-temperature heat exchanger for oxygen, it is characterized by having a low-temperature heat exchanger for oxygen that heats the liquid oxygen with normal-temperature water.

[0010] (3) Further, in the invention according to (1) or (2) above, a cryogenic circulation LNG return line that returns LNG from the LNG line downstream of the LNG pump to the LNG storage tank, A cryogenic circulation LNG cooling heat exchanger that cools the LNG flowing through the cryogenic circulation LNG return line by utilizing the cold heat of the liquid oxygen discharged by the liquid oxygen pump.

Advantages of the Invention

[0011] According to the present invention, in a system that liquefies air and stores it as energy convertible into electric power, it is possible to efficiently increase the power generation efficiency with the energy within the system and facilitate the recovery of carbon dioxide from the exhaust gas.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode 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. An energy storage system 1 according to Embodiment 1 of the present invention includes an LNG storage tank 10, an LNG pump 20, an LNG vaporizer 30, a first power generation device 40, a cryogenic separation device 50, a liquid oxygen tank 70, a liquid nitrogen tank 71, a liquid oxygen pump 80, a liquid nitrogen pump 81, an oxygen expansion turbine 110, a nitrogen expansion turbine 111, and a second power generation device 120.

[0014] The energy storage system 1 also includes a cryogenic separation heat exchanger 60, a low-temperature heat exchanger 90 for oxygen, a low-temperature heat exchanger 91 for nitrogen, a high-temperature heat exchanger 100 for oxygen, a high-temperature heat exchanger 101 for nitrogen, an exhaust gas circulation line 187, an oxygen gas confluence line 188, an oxygen gas diffusion flow rate control valve 112, and an oxygen gas branch flow rate control valve 113.

[0015] The LNG storage tank 10 is an above-ground 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.

[0016] The LNG pump 20 is, for example, a vertical centrifugal submerged pump disposed on the downstream side of the LNG storage tank 10, and the pump body is 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.

[0017] The LNG vaporizer 30 is an ORV (Open Rack Vaporizer) type vaporizer. LNG flows from the bottom to the top inside the vertically arranged heat transfer tube group, and seawater flows from the top to the bottom outside. By doing so, the LNG supplied from the LNG pump outlet line 172 is completely vaporized and supplied as vapor gas to the gas supply line 173.

[0018] The first power generation device 40 is a natural gas power generation device adopting a gas turbine combined cycle (GTCC; Gas-Turbine-Combined-Cycle). It uses natural gas, which is the vapor gas vaporized from the LNG supplied from the gas supply line 173, as fuel to drive the gas turbine 42, and efficiently generates electricity by a combination of a steam turbine 46 driven by the steam generated by the exhaust gas of the gas turbine 42. Generators (not shown) are provided for the gas turbine 42 and the steam turbine 46.

[0019] The first power generation device 40 is equipped with a boiler 44 that generates steam to be supplied to the steam turbine 46 using the exhaust heat of the gas turbine 42, a condenser 47 that condenses the exhaust steam of the steam turbine 46, and a condensate pump 49 that sends the condensate condensed by the condenser 47 to the boiler 44. The exhaust gas of the gas turbine 42 is supplied to the boiler 44 via the exhaust gas line 43. The steam generated by the boiler 44 is supplied to the steam turbine 46 via the steam line 45. The condensate condensed by the condenser 47 is supplied to the boiler 44 via the condensate line 48. A large amount of seawater is supplied to the condenser 47 via the seawater supply line 192. This seawater is cooled by an oxygen cryogenic heat exchanger 90 and a nitrogen cryogenic heat exchanger 91 before being supplied to the condenser 47. Then, the steam is condensed in the condenser 47 by the cooled seawater, and thereafter, the seawater is discharged into the ocean. That is, the low-temperature exhaust heat of the first power generation device 40 is transferred to the seawater and discarded into the ocean.

[0020] The cryogenic separation device 50 is a general double-column type air cryogenic separation device that produces liquid oxygen (LO2) and liquid nitrogen (LN2) from the atmospheric air taken in from the air inlet line 174. The cryogenic separation device 50 can also produce argon, but the explanation regarding argon is omitted.

[0021] The cryogenic separation heat exchanger 60 is a general shell & tube type heat exchanger that supplies the cold heat of LNG to the nitrogen for refrigerant within the cryogenic separation device 50 as described later.

[0022] Figure 2 is a schematic diagram showing the details of the cryogenic separation device 50 and the relationship between the cryogenic separation device 50 and the cryogenic separation heat exchanger 60. As shown in Figure 2, the cryogenic separation device 50 includes a raw material air compressor 51, an adsorber 53, a raw material air cooler 54, a nitrogen compressor 55, and a rectification column 58. 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.

[0023] The adsorber 53 is an adsorption tower filled with a zeolite-based adsorbent that 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 type heat exchanger that cools the compressed air flowing through the compressed air line 52 using the cold heat of nitrogen described later.

[0024] 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 cryogenic separation heat exchanger 60 to generate liquid nitrogen.

[0025] The air cooled by liquid nitrogen in the raw material air cooler 54 is separated into liquid oxygen and liquid nitrogen in the rectification column 58. The liquid oxygen is supplied from the rectification column 58 to the liquid oxygen supply line 175, and the liquid nitrogen is supplied from the rectification column 58 to the liquid nitrogen supply line 176.

[0026] Returning to FIG. 1, the liquid oxygen tank 70 is a vertical cylindrical steel tank that temporarily stores the liquid oxygen supplied from the liquid oxygen supply line 175. The liquid nitrogen tank 71 is a vertical cylindrical steel tank that temporarily stores the liquid nitrogen supplied from the liquid nitrogen supply line 176.

[0027] The liquid oxygen pump 80 is a centrifugal pump that boosts the pressure of the liquid oxygen supplied from the liquid oxygen pump suction line 177 and supplies it to the liquid oxygen pump discharge line 181. The liquid nitrogen pump 81 is a centrifugal pump that boosts the pressure of the liquid nitrogen supplied from the liquid nitrogen pump suction line 178 and supplies it to the liquid nitrogen pump discharge line 182.

[0028] The cryogenic heat exchanger 90 for oxygen is an open rack type heat exchanger that heats and evaporates the liquid oxygen flowing through the liquid oxygen pump discharge line 181 using the seawater at the inlet of the condenser 47 of the first power generation device 40 as a heating medium. The cryogenic heat exchanger 91 for nitrogen is an open rack type heat exchanger that heats and evaporates the liquid nitrogen flowing through the liquid nitrogen pump discharge line 182 using the seawater at the inlet of the condenser 47 of the first power generation device 40 as a heating medium.

[0029] The high-temperature heat exchanger 100 for oxygen is a shell & tube type heat exchanger that warms the oxygen gas flowing through the liquid oxygen pump discharge line 181 using the exhaust gas flowing through the exhaust gas discharge line 186 described later as a heating medium. The high-temperature heat exchanger 101 for nitrogen is a shell & tube type heat exchanger that warms the nitrogen gas flowing through the liquid nitrogen pump discharge line 182 using the exhaust gas flowing through the exhaust gas discharge line 186 described later as a heating medium.

[0030] The oxygen expansion turbine 110 is a centrifugal expansion turbine that converts the pressure energy into rotational motion of the turbine by reducing the pressure of the high-pressure oxygen gas to atmospheric pressure equivalent and generates electricity by a generator. The nitrogen expansion turbine 111 is a centrifugal expansion turbine that converts the pressure energy into rotational motion of the turbine by reducing the pressure of the high-pressure nitrogen gas to atmospheric pressure equivalent and generates electricity by a generator. The low-pressure oxygen gas released from the oxygen expansion turbine 110 is dissipated to the outside through the oxygen gas dissipation line 183.

[0031] The oxygen gas dissipation line 183 is provided with an oxygen gas dissipation flow control valve 112 which is a remotely operated butterfly valve, and it adjusts the flow rate of the oxygen gas flowing through the oxygen gas dissipation line 183.

[0032] The second power generation device 120 is a power generation device using a reciprocating gas engine. It generates electricity using BOG (Boil-Off-Gas) supplied from the LNG storage tank 10 through the BOG supply line 185 as fuel, and supplies the generated exhaust gas to the exhaust gas discharge line 186.

[0033] The exhaust gas circulation line 187 has a starting end branched from the downstream of the high-temperature heat exchanger 100 for oxygen and the high-temperature heat exchanger 101 for nitrogen in the exhaust gas discharge line 186, and a terminal end connected to the intake port of the second power generation device 120. It diverts a part of the exhaust gas flowing through the exhaust gas discharge line 186 and circulates it to the intake port of the second power generation device 120.

[0034] The oxygen gas confluence line 188 has a starting end branched from the oxygen gas dissipation line 183 and a terminal end connected to the exhaust gas circulation line 187. The oxygen gas confluence line 188 is provided with an oxygen gas branch flow control valve 113 which is a remotely operated butterfly valve, and it adjusts the flow rate of the oxygen gas flowing through the oxygen gas confluence line 188.

[0035] Next, the operation of the energy storage system 1 according to the present embodiment will be described. The energy storage system 1 operates the cryogenic separation device 50, generates liquid oxygen and liquid nitrogen using air as a raw material while utilizing the cold heat of LNG, and stores them in the liquid oxygen tank 70 and the liquid nitrogen tank 71 from the liquid oxygen supply line 175 and the liquid nitrogen supply line 176 respectively. Thereby, the energy storage system 1 accumulates energy convertible into electric power in the form of liquid oxygen and liquid nitrogen.

[0036] The energy storage system 1 operates the liquid oxygen pump 80 to boost the pressure of the cryogenic (e.g., -183°C) liquid oxygen stored in the liquid oxygen tank 70 and discharge it as high-pressure liquid oxygen (e.g., 10 MPaG) into the liquid oxygen pump discharge line 181. Also, the energy storage system 1 operates the liquid nitrogen pump 81 to boost the pressure of the cryogenic (e.g., -196°C) liquid nitrogen stored in the liquid nitrogen tank 71 and discharge it as high-pressure liquid nitrogen (e.g., 10 MPaG) into the liquid nitrogen pump discharge line 182.

[0037] The high-pressure liquid oxygen discharged into the liquid oxygen pump discharge line 181 is heated by a large amount of seawater in the cryogenic heat exchanger 90 for oxygen and evaporated to become high-pressure oxygen gas at room temperature (e.g., 20°C). Also, the high-pressure liquid nitrogen discharged into the liquid nitrogen pump discharge line 182 is heated by a large amount of seawater in the cryogenic heat exchanger 91 for nitrogen and evaporated to become high-pressure nitrogen gas at room temperature (e.g., 20°C).

[0038] The high-pressure oxygen gas generated in the cryogenic heat exchanger 90 for oxygen is heated by the high-temperature (e.g., 350°C) exhaust gas of the second power generation device 120 in the high-temperature heat exchanger 100 for oxygen and becomes high-pressure oxygen gas at high temperature (e.g., 200°C). Also, the high-pressure nitrogen gas generated in the cryogenic heat exchanger 91 for nitrogen is heated by the high-temperature (e.g., 350°C) exhaust gas of the second power generation device 120 in the high-temperature heat exchanger 101 for nitrogen and becomes high-pressure nitrogen gas at high temperature (e.g., 200°C).

[0039] The oxygen gas that has become high temperature and high pressure in the high-temperature heat exchanger 100 for oxygen is introduced into the oxygen expansion turbine 110, driving the oxygen expansion turbine 110 with decompression and temperature reduction and generating electricity. Also, the nitrogen gas that has become high temperature and high pressure in the high-temperature heat exchanger 101 for nitrogen is introduced into the nitrogen expansion turbine 111, driving the nitrogen expansion turbine 111 with decompression and temperature reduction and generating electricity.

[0040] The oxygen gas that has been depressurized and cooled in the oxygen expansion turbine 110 is supplied to the oxygen gas diffusion line 183. The oxygen gas supplied to the oxygen gas diffusion line 183 has its flow rate adjusted by passing through the oxygen gas diffusion flow rate control valve 112, the oxygen gas branch flow rate control valve 113, or both.

[0041] The oxygen gas that has passed through the oxygen gas diffusion flow rate control valve 112 is diffused into the atmosphere. The oxygen gas that has passed through the oxygen gas branch flow rate control valve 113 merges with the exhaust gas flowing through the exhaust gas circulation line 187 and is supplied to the intake port of the second power generation device 120.

[0042] The nitrogen gas that has been depressurized and cooled in the nitrogen expansion turbine 111 is supplied to the nitrogen gas diffusion line 184. The nitrogen gas supplied to the nitrogen gas diffusion line 184 is diffused into the atmosphere.

[0043] The evaporated gas (BOG; Boil-Off-Gas) of LNG generated in the LNG storage tank 10 flows through the BOG line 185 and is supplied to the second power generation device 120, where it is used as fuel for the second power generation device 120 and converted into electricity.

[0044] In the second power generation device 120, methane gas is supplied from the BOG line 185, and a mixed gas of the recycled portion of its own exhaust gas and the oxygen gas at the outlet of the oxygen expansion turbine 110 is supplied from the exhaust gas circulation line 187. By using oxygen as an oxidant instead of air, since the nitrogen content, which accounts for about 80% of the air, is reduced, mainly carbon dioxide and water are discharged as exhaust gas from the second power generation device 120 to the exhaust gas discharge line 186. Also, in a situation where nitrogen is completely exhausted, nitrogen oxides (NOx) are not generated.

[0045] The exhaust gas discharged to the exhaust gas discharge line 186 is cooled to room temperature (for example, 20 °C) by the high-pressure oxygen gas flowing through the liquid oxygen pump discharge line 181 and the high-pressure nitrogen gas flowing through the liquid nitrogen pump discharge line 182 in the high-temperature heat exchanger 100 for oxygen and the high-temperature heat exchanger 101 for nitrogen, respectively.

[0046] A part of the exhaust gas cooled to room temperature diverges into the exhaust gas circulation line 187, and the remainder is discharged to the outside. Since the main components of the exhaust gas are carbon dioxide and water as described above, it is easy to separate and recover carbon dioxide from the exhaust gas discharged to the outside.

[0047] The vaporized gas vaporized by the LNG vaporizer 30 is supplied to the first power generation device 40 via the gas supply line 173 and used as fuel for the gas turbine 42. In the first power generation device 40, power generation is efficiently performed by combining the gas turbine 42 and the steam turbine 46.

[0048] According to the energy storage system 1 according to the present embodiment, since the cold heat of LNG is effectively utilized in the cryogenic separation heat exchanger 60, the cryogenic separation device 50 can be operated in an energy-saving manner. In addition, by effectively utilizing the cold heat of LNG for cryogenic separation, the cold heat of LNG that has been discarded into the environment can be reduced. For example, although the LNG vaporizer using seawater as a heating medium has discarded the cold heat of LNG into the ocean, the amount can be reduced, so the impact on the ocean can be reduced.

[0049] In addition, the energy storage system 1 according to the present embodiment cools the seawater introduced into the condenser 47 by the low-temperature heat exchanger 90 for oxygen and the low-temperature heat exchanger 91 for nitrogen, and condenses the steam with the cooled seawater. Therefore, the steam pressure in the condenser can be reduced and the efficiency of the steam turbine can be improved. As a result, the power generation amount of the first power generation device 40 can be increased. In addition, the cooled seawater is heated by the steam and discharged into the sea via the seawater discharge line 193, but the temperature is lower than when normal temperature seawater is heated by the steam. Therefore, the energy storage system 1 according to the present embodiment can reduce the waste heat discharged into the ocean, so the impact on the ocean environment can be reduced.

[0050] Further, according to the energy storage system 1 according to the present embodiment, in the oxygen high-temperature heat exchanger 100 and the nitrogen high-temperature heat exchanger 101, the high-temperature circulating exhaust gas of the second power generation device 120 is used to further heat the oxygen and nitrogen in the front flow of the expansion turbine, so that the power generation efficiency in the oxygen expansion turbine 110 and the nitrogen expansion turbine 111 can be increased.

[0051] Further, according to the energy storage system 1 according to the present embodiment, when storing energy, instead of simply liquefying and storing air, it is stored in the form of liquefied nitrogen and liquefied oxygen by cryogenic separation. When releasing energy, the low-pressure oxygen gas after driving the oxygen expansion turbine 110 can be effectively utilized as an oxidant for the second power generation device 120. As a result, the carbon dioxide concentration in the exhaust gas of the second power generation device 120 increases, so that the recovery energy of carbon dioxide from the exhaust gas can be reduced.

[0052] Further, according to the energy storage system 1 according to the present embodiment, the exhaust gas of the second power generation device 120 is cooled by the second oxygen heat exchanger 100 and the second nitrogen heat exchanger 101 and then circulated to the intake port of the second power generation device 120. Therefore, in the case where the temperature of the combustion chamber becomes too high due to the combustion of only BOG and oxygen, excessive temperature rise is prevented by mixing the exhaust gas, which is an inert gas.

[0053] In the present embodiment, the type of the heat exchanger including the cryogenic separation heat exchanger 60 has been described as a shell & tube type or an open rack type, but it is not limited thereto, and the type is appropriately selected within the design range. The same applies to pumps and valves.

[0054] In the present embodiment, the second nitrogen heat exchanger 101 is disposed in the exhaust gas discharge line 186 downstream of the second oxygen heat exchanger 100, but it may be installed in the exhaust gas circulation line 187. In that case, since the exhaust gas that does not flow into the exhaust gas circulation line 187 and is discharged to the outside remains at a high temperature, high-temperature exhaust heat can be supplied to other facilities.

[0055] Also, in this embodiment, the oxygen gas confluence line 188 is confluent with the exhaust gas circulation line 187, but these lines do not necessarily have to be confluent. Any mode is acceptable as long as the oxygen gas at the outlet of the oxygen expansion turbine 110 is supplied to the intake air of the second power generation device 120.

[0056] Also, in this embodiment, nothing is installed in the BOG supply line 185, but the cold heat of BOG may be used for cooling the circulated exhaust gas supplied to the intake port of the second power generation device 120, or the cold heat of BOG may be used for cooling the air in the cryogenic separation device 50.

[0057] Also, in this embodiment, it was explained that among the oxygen gas at the outlet of the oxygen expansion turbine 110, those that do not merge with the circulated exhaust gas are dissipated into the atmosphere, and the nitrogen gas at the outlet of the nitrogen expansion turbine 111 is also dissipated into the atmosphere. However, since it can be said that dissipating the nitrogen and oxygen separated by applying energy to air into the atmosphere is a loss of resources, they may be supplied to another oxygen user or nitrogen user. Thereby, resources and energy can be utilized more effectively.

[0058] Also, in this embodiment, there are a figure and an explanation such that only the BOG from the BOG supply line 185 and the exhaust gas from the exhaust gas circulation line 187 are supplied to the second power generation device 120, but it does not prevent the mixing of air into the second power generation device 120.

[0059] In this embodiment, there are two power generation devices: the first power generation device 40 using BOG as fuel and the second power generation device 120 using the vaporized gas of LNG as fuel. Among these two power generation devices, the second power generation device 120 has the exhaust gas circulation line which is a constituent element of the present invention. Therefore, the power generation device corresponding to the present invention is the second power generation device 120. However, it is also possible to provide an exhaust gas circulation line to the first power generation device 40 using vaporized gas as fuel to make it the power generation device of the present invention.

[0060] FIG. 3 is a diagram showing an embodiment in which only the first power generation device 40 is provided without providing the second power generation device 120, an exhaust gas circulation line 43a is provided in the first power generation device 40, and an oxygen gas merging line 188 is connected to the exhaust gas circulation line 43a. When only the first power generation device 40 is provided, liquid oxygen and liquid nitrogen are respectively evaporated by the low-temperature heat exchanger 90A for oxygen and the low-temperature heat exchanger 91A for nitrogen and heated to room temperature (for example, 20°C), and oxygen and nitrogen are further heated by the high-temperature heat exchanger 100A for oxygen and the high-temperature heat exchanger 101A for nitrogen, and power is generated by the oxygen expansion turbine 110 and the nitrogen expansion turbine 111. Note that the exhaust gas from the exhaust gas circulation line 43a, the mixed gas of oxygen at the outlet of the oxygen expansion turbine 110, and air are sucked into the gas turbine in the first power generation device 40, but the intake of air can also be completely eliminated. In that case, it is possible to prevent the generation of NOx. This embodiment is effective when the LNG base and the first power generation device 40 are close to each other and the second power generation device 120 is not installed at the LNG base.

[0061] Also, in the embodiment shown in FIG. 1, it is also possible to provide only the second power generation device 120 without providing the first power generation device 40. When only the second power generation device 120 is provided, as shown in FIG. 4, liquid oxygen and liquid nitrogen are respectively evaporated by seawater or warm water in the low-temperature heat exchanger 90B for oxygen and the low-temperature heat exchanger 91B for nitrogen, and liquid oxygen and liquid nitrogen are respectively evaporated by the high-temperature heat exchanger 100B for oxygen and the high-temperature heat exchanger 101B for nitrogen and heated to a high temperature (for example, 200°C), and power is generated by the oxygen expansion turbine 110 and the nitrogen expansion turbine 111. This embodiment is effective when the LNG base and the first power generation device 40 are at a considerable distance from each other and the first power generation device 40 is installed at the LNG base.

[0062] Also, as shown in FIG. 5, a liquid nitrogen-oxygen connection line 212 may be provided, and the branch flow rate from the liquid nitrogen pump discharge line 182 to the liquid oxygen pump discharge line 181 may be adjusted by a liquid nitrogen flow rate control valve 211 and a liquid nitrogen branch flow rate control valve 213. This makes it possible to mix liquid nitrogen with liquid oxygen, which has extremely high oxidizing properties and combustion-supporting properties, and can reduce the risk of oxidation and heat generation of the piping and heat insulation material. That is, according to the above aspect, while eliminating the difficulties of handling pure liquid oxygen, it is possible to increase the carbon dioxide concentration in the exhaust gas as much as possible and facilitate the separation and recovery of carbon dioxide.

[0063] Although not shown in the drawings, it goes without saying that it is also possible to adopt an aspect in which both the first power generation device 40 and the second power generation device 120 are power generation devices of the present invention. In this case, the second power generation device 120 shown in FIG. 1 may be combined with the first power generation device 40 shown in FIG. 3.

[0064] In the above embodiment, an example in which seawater is used as the heat source for the cryogenic heat exchangers 90 and 90A for oxygen and the cryogenic heat exchangers 91 and 91A for nitrogen is shown, but the heat source is not limited to seawater and may be water at normal temperature. Water at normal temperature is water having a temperature of about 0°C to 40°C. Examples other than seawater include water after heating LNG in the vaporizer 30, but the present invention is not limited thereto.

[0065] [Embodiment 2] Next, with reference to FIG. 6, the configuration and function of Embodiment 2 will be described. Components having the same configuration and function as those in Embodiment 1 are given the same reference numerals. The energy storage system 300 according to Embodiment 2 includes a first cold-insulated circulation LNG cooling heat exchanger 310, a second cold-insulated circulation LNG cooling heat exchanger 311, a cold-insulated circulation return line 371, and a cold-insulated circulation flow rate control valve 372.

[0066] The first cryogenic circulation LNG cooling heat exchanger 310 is a shell & tube heat exchanger, which uses the liquid oxygen discharged from the liquid oxygen pump 80 as a cold heat source to cool the cryogenic circulation LNG flowing through the cryogenic circulation return line 371. The second cryogenic circulation LNG cooling heat exchanger 311 is a shell & tube heat exchanger, which uses the liquid nitrogen discharged from the liquid nitrogen pump 81 as a cold heat source to cool the cryogenic circulation LNG flowing through the cryogenic circulation return line 371.

[0067] The cryogenic circulation return line 371 is a pipe, one end of which is connected to the upstream of the LNG vaporizer 30, and the other end of which is connected to the LNG storage tank 10. The cryogenic circulation flow control valve 372 is a general remote-operated globe valve, which adjusts the flow rate of the cryogenic circulation LNG returning to the LNG storage tank 10.

[0068] Next, the operation of the energy storage system 300 according to the present embodiment will be described. The LNG flowing through the cryogenic circulation return line 371 (hereinafter referred to as "cryogenic circulation LNG") is constantly flowing to keep the pipes and equipment in the LNG system cold. Therefore, in order to transport the heat received from the pipes and equipment into the LNG storage tank, the cryogenic circulation LNG will become a heat input means to the LNG storage tank if the heat is not taken away by cooling or the like, and the amount of BOG generated in the LNG storage tank will increase by the amount of heat transported by the cryogenic circulation LNG.

[0069] Therefore, in the present embodiment, as means for taking away the heat, a first cryogenic circulation LNG cooling heat exchanger 310 and a second cryogenic circulation LNG cooling heat exchanger 311 are provided. The temperature of the cryogenic circulation LNG supplied to the first cryogenic circulation LNG cooling heat exchanger 310 is, for example, -130°C, but it is cooled to, for example, -140°C by heat exchange with liquid oxygen (for example, -183°C). Further, in the second cryogenic circulation LNG cooling heat exchanger 311, it is cooled to, for example, -170°C by heat exchange with liquid nitrogen (for example, -196°C).

[0070] Since the temperature of the LNG in the LNG storage tank 10 is approximately -160°C, the cooled cold-insulation circulating LNG becomes a heat source for the LNG storage tank 10, and part or all of the other heat input to the LNG storage tank 10 (such as heat input from the atmosphere to the main body of the LNG storage tank 10) will be canceled out.

[0071] According to the energy storage system 300 according to this embodiment, in the first cold-insulation circulating LNG cooling heat exchanger 310 and the second cold-insulation circulating LNG cooling heat exchanger 311, since the cold-insulation circulating LNG can be cooled, the effect of cooling the LNG storage tank 10 can be obtained. As a result, it leads to a reduction in the generation amount of BOG from the LNG storage tank 10, reduces the energy required for BOG treatment, and realizes energy savings.

[0072] In addition, in this embodiment, although it has been described that the cold-insulation circulating LNG is cooled in the first cold-insulation circulating LNG cooling heat exchanger 310 and the second cold-insulation circulating LNG cooling heat exchanger 311, only one of these heat exchangers may be used. Also, a bypass line and a flow rate control valve for bypassing these heat exchangers may be provided, and the amount of cold-insulation circulating LNG flowing through the bypass line and the amount of cold-insulation circulating LNG to be cooled may be adjusted so that the cold-insulation circulating LNG is not overcooled.

Industrial Applicability

[0073] The present invention can be used as an energy storage system that efficiently increases the power generation efficiency with the energy in the system and facilitates the recovery of carbon dioxide from exhaust gas in a system for storing liquefied air as convertible energy into electricity.

Explanation of Reference Numerals

[0074] 1, 200, 300 Energy storage system 10 LNG storage tank 20 LNG pump 30 LNG vaporizer 40 First power generation device 41 Air supply line 42 Gas turbine 43 Exhaust gas line 43a Exhaust gas circulation line 44 Boiler 45 Steam supply line 46 Steam turbine 47 Condenser 48 Condensate line 49 Condensate pump 50 Cryogenic separation unit 51 Feed air compressor 52 Compressed air line 53 Adsorber 54 Feed air cooler 55 Nitrogen compressor 56 Nitrogen circulation line 57 Nitrogen expansion valve 58 Rectification column 60 Heat exchanger for cryogenic separation 70 Liquid oxygen tank 71 Liquid nitrogen tank 80 Liquid oxygen pump 81 Liquid nitrogen pump 90, 90A Low-temperature heat exchanger for oxygen 91, 91A Low-temperature heat exchanger for nitrogen 100, 100A, 100B High-temperature heat exchanger for oxygen 101, 101A, 101B High-temperature heat exchanger for nitrogen 110 Oxygen expansion turbine 111 Nitrogen expansion turbine 112 Oxygen gas bleed flow control valve 113 Oxygen gas branch flow control valve 120 Second power generation device 130 Seawater pumping pump 171 LNG pump inlet line 172 LNG pump outlet line 173 Feed gas line 174 Air inlet line 175 Liquid oxygen supply line 176 Liquid nitrogen supply line 177 Liquid oxygen pump suction line 178 Liquid nitrogen pump suction line 181 Liquid oxygen pump discharge line 182 Liquid nitrogen pump discharge line 183 Oxygen gas diffusion line 184 Nitrogen gas diffusion line 185 BOG supply line 186 Exhaust gas discharge line 187 Exhaust gas circulation line 188 Oxygen gas confluence line 191 Seawater pumping line 192 Seawater supply line 193 Seawater discharge line 211 Liquid nitrogen flow control valve 212 Liquid nitrogen - oxygen connection line 213 Liquid nitrogen branched flow control valve 310 First cryogenic circulation heat exchanger for LNG cooling 311 Second cryogenic circulation heat exchanger for LNG cooling 371 Cryogenic circulation return line 372 Cryogenic circulation flow control valve

Claims

1. An LNG storage tank for storing LNG; An LNG pump for boosting the pressure of the LNG stored in the LNG storage tank and discharging it; A power generation device that generates electricity using the vaporized gas obtained by vaporizing the LNG discharged from the LNG pump and / or the evaporation gas generated in the LNG storage tank as fuel; A cryogenic separation device that separates and extracts nitrogen and oxygen as liquids from a gas mainly composed of nitrogen and oxygen; A cryogenic separation heat exchanger that supplies the cold heat of the LNG discharged from the LNG pump to the cryogenic separation device; A liquid oxygen tank for storing the liquid oxygen generated by the cryogenic separation device; A liquid oxygen pump for boosting the pressure of the liquid oxygen stored in the liquid oxygen tank and discharging it; A high-temperature heat exchanger for oxygen that uses the exhaust heat of the power generation device to heat the liquid oxygen discharged from the liquid oxygen pump; An oxygen expansion turbine that expands the oxygen evaporated by the high-temperature heat exchanger for oxygen and generates electricity; An exhaust gas circulation line that circulates the exhaust gas of the power generation device to the intake air of the power generation device and supplies exhaust heat to the high-temperature heat exchanger for oxygen; An energy storage system, characterized by comprising an oxygen gas confluence line that merges a part of the oxygen gas at the outlet of the oxygen expansion turbine into the exhaust gas circulation line.

2. The energy storage system according to claim 1, further comprising a low-temperature heat exchanger for oxygen that heats the liquid oxygen with normal-temperature water upstream of the high-temperature heat exchanger for oxygen.

3. A cold-insulation circulation LNG return line that returns LNG from the LNG line downstream of the LNG pump to the LNG storage tank; The energy storage system according to claim 1 or 2, further comprising a cold-insulation circulation LNG cooling heat exchanger that cools the LNG flowing through the cold-insulation circulation LNG return line by using the cold heat of the liquid oxygen discharged by the liquid oxygen pump.

Images