Thermal energy storage systems and carbon dioxide capture systems

Abstract

To provide a heat storage system that can acquire a liquid gas utilizing surplus power and is reduced in limitation of installation site, and to provide a carbon dioxide recovery system.SOLUTION: A heat storage system includes: an air compressor 6 for compressing air; cooling means for expanding the air compressed by the air compressor 6 to cool the air and acquire cooled air; a rectifying tower 10 for refining a liquid gas from the cooled air; and storage means for storing the liquid gas that is refined by the rectifying tower, where the air compressor is driven by surplus power.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a heat storage system that produces and stores liquefied gas using surplus power, and to a carbon dioxide recovery system that recovers carbon dioxide using liquefied gas purified by the system. Background Art

[0002] To achieve carbon neutrality, recovering and storing all carbon dioxide generated at thermal power plants, factories, and the like has become an important issue (see, for example, Patent Document 1).

[0003] There are a plurality of methods for recovering and storing carbon dioxide generated at thermal power plants, but any of these methods requires large power for carbon dioxide recovery. When power is consumed for carbon dioxide recovery, the amount of power that can be transmitted decreases, transmission end efficiency decreases, and power generation cost rises; this is the problem.

[0004] To solve these problems, an exhaust gas cooling type carbon dioxide recovery system called the TSS method has been proposed, which assumes a gas turbine thermal power plant using liquefied natural gas (LNG) (see Non-Patent Document 1). Unlike conventional carbon dioxide recovery technologies, this system does not use a carbon dioxide absorbent, and thus significant cost reduction can be expected, but it has not yet been put to practical use. Additionally, it has a problem that it is difficult to apply to thermal power plants and factories that are not located near an LNG terminal.

[0005] On the other hand, similar exhaust gas cooling type carbon dioxide recovery systems have recently been developed (see Non-Patent Documents 2 and 3). This system is a system that cools exhaust gas with electricity: it compresses exhaust gas with an electric compressor, then depressurizes it at a stroke with an expansion turbine to cool the exhaust gas, and can be installed even in locations not near an LNG terminal. On the other hand, these technologies have the problem that power is required for exhaust gas cooling.

[0006] On the other hand, in industrial complexes including steel mills, air separation units (ASUs) have been used to extract oxygen from the air. An air separation unit is equipment that compresses air with an electric compressor, cools the liquefied air with an expansion turbine, and then purifies liquefied gases such as liquefied oxygen and liquefied nitrogen in a rectification column based on the difference in their boiling points (see, for example, Patent Document 2).

[0007] In recent years, with the expansion of solar power generation facilities, the amount of electricity generated by variable renewable energy (VRE) during the day has increased, and the exploration of demand for such renewable energy (upward demand response, upward DR) is being considered. However, in reality, large-scale applications have not been found, so the amount of solar power generation that can be installed is limited based on the maximum generation capacity, and the introduction of renewable energy has plateaued.

[0008] If a need is found for storing excess renewable energy during the day as some form of energy and shifting its use to times when energy is needed (upward demand response), it is expected that the amount of renewable energy introduced, such as solar power, can be further expanded. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2013-174182 [Patent Document 2] Japanese Patent Publication No. 2007-255802 [Non-patent literature]

[0010] [Non-Patent Document 1] Chugoku Electric Power Co., Inc., 2001 Environmental Report, p. 51, [online], Internet<URL:https: / / www.energia.co.jp / energy / energia / kankyou / pdf / 2001 / 01kan1-14.pdf> [Non-Patent Document 2] Cryogenic Carbon Capture, [Accessed August 17, 2022], Internet<URL:https: / / www.chartindustries.com / Products / Carbon-Capture> [Non-Patent Document 3] Cryocap (registered trademark) H2 - Cryogenic CO2 Separation, [Accessed August 17, 2022], Internet<URL:https: / / www.engineering-airliquide.com / cryocap-h2-cryogenic-co2-separation> [Overview of the project] [Problems that the invention aims to solve]

[0011] To achieve carbon neutrality, carbon dioxide capture systems for exhaust gas cooling systems, designed for thermal power plants and factories, are attracting attention. However, widespread adoption requires a reduction in exhaust gas cooling power, and the use of LNG cold energy, which is considered promising, is limited to only a very small number of locations, making it unlikely to be a method for capturing all carbon dioxide generated domestically.

[0012] Furthermore, pumped-storage hydroelectric power, which utilizes surplus electricity, is also generally known, but it has the problem of having significant limitations on installation locations.

[0013] In view of these circumstances, the present invention aims to provide a heat storage system and a carbon dioxide capture system that can obtain liquefied gas by utilizing surplus electricity and that also reduces restrictions on installation location. [Means for solving the problem]

[0014] An aspect of the present invention that solves the above problems is a heat storage system comprising: an air compressor for compressing air; a cooling means for obtaining cooled air by expanding the air compressed by the air compressor; a rectification column for purifying liquefied gas from the cooled air; and a storage means for storing the liquefied gas purified in the rectification column, wherein the air compressor is operated by surplus electricity.

[0015] In this configuration, by converting surplus electricity into liquefied gas and storing it, there is no need to restrict the introduction of renewable energy at peak power generation levels, thus contributing to further decarbonization. Furthermore, the thermal storage system can effectively utilize surplus electricity without being limited by installation location, unlike pumped-storage hydroelectric power plants that use surplus electricity.

[0016] In this case, it is preferable to have a pre-cooling means that cools at least the rectification column using the liquefied gas stored in the storage means when the air compressor is not operating due to surplus power. This allows the rectification column to be cooled and kept at a low temperature by the liquefied gas storage means while the air compressor is not operating.

[0017] Furthermore, it is preferable that the rectification column purifies liquid oxygen and liquid nitrogen as the liquefied gas, and that the pre-cooling means preferentially uses liquid nitrogen. This allows liquid oxygen to be used for other purposes and enables effective utilization of liquid oxygen.

[0018] Furthermore, it is preferable that the pre-cooling means and the rectification column are enclosed in a cold box having an insulating structure, and that the pre-cooling means cools the inside of the cold box. In this case, if equipment other than the rectification column, such as a main heat exchanger or expansion turbine, is installed in the cold box, these pieces of equipment can be cooled together with the rectification column while the air compressor is not operating.

[0019] It is also preferable to further comprise control means for adjusting the purification amount of the liquefied gas according to a change in the surplus power. According to this configuration, by adjusting the purification amount of the liquefied gas according to a change in the surplus power, the surplus power can be efficiently converted into liquefied gas and stored.

[0020] Another aspect of the present invention provides a carbon dioxide recovery system comprising: the heat storage system according to the above aspect; and carbon dioxide recovery means for recovering carbon dioxide using cold energy of the liquefied gas stored in the storage means.

[0021] In this aspect, carbon dioxide can be recovered using the liquefied gas purified and stored by the heat storage system using surplus power, and both effective utilization of surplus power and reduction of environmental load through suppression of carbon dioxide emission can be achieved.

[0022] Here, it is preferable that the carbon dioxide recovery means solidifies and recovers carbon dioxide contained in exhaust gas. According to this configuration, by solidifying carbon dioxide contained in exhaust gas, carbon dioxide can be efficiently recovered.

[0023] It is also preferable to comprise discharge equipment that discharges the exhaust gas. According to this configuration, carbon dioxide can be efficiently recovered from the exhaust gas discharged from the discharge equipment. Effects of the Invention

[0024] According to the present invention, by purifying and storing liquefied gas using surplus power, the surplus power can be converted into liquefied gas and stored. The cold energy stored from surplus power during peak demand can be shifted to a required time, or transported to a required location, and used for applications such as carbon dioxide recovery, thereby enabling stable power grid operation. Furthermore, unlike pumped-storage power generation that uses surplus power, the heat storage system of the present invention is not limited in installation location, and thus can effectively utilize surplus power in a wide range of applications. Brief Description of the Drawings

[0025] [Figure 1] This is a schematic diagram of the heat storage system according to Embodiment 1. [Figure 2] This graph illustrates the amount of electricity generated and the operating status of the air compressor. [Figure 3] This is a schematic diagram of the carbon dioxide capture system according to Embodiment 1. [Figure 4] This graph shows power generation based on weather conditions. [Figure 5] This graph illustrates the amount of electricity generated and the operating status of the air compressor. [Modes for carrying out the invention]

[0026] The present invention will be described in detail below based on embodiments. (Embodiment 1) Figure 1 is a schematic diagram of the heat storage system 1 according to Embodiment 1 of the present invention.

[0027] The heat storage system 1 comprises an air separation unit (ASU) 2, a liquefied gas storage tank 3, a liquefied gas return line 4, and a control unit 5.

[0028] The air separation apparatus 2 comprises an air compressor 6, adsorbents 7a and 7b, a main heat exchanger 8, an expansion turbine 9, a rectification column 10, and a cold box 11.

[0029] The air compressor 6 operates using surplus power derived from the VRE. The air compressor 6 can also operate using other power sources, such as the power plant's internal electricity.

[0030] The air compressed by the air compressor 6 has carbon dioxide, moisture, etc. removed in the adsorbents 7a and 7b. Adsorbents 7a and 7b consist of two identical towers arranged in parallel. One tower removes moisture and carbon dioxide from the air, while the other regenerates the adsorbent, which has absorbed moisture and carbon dioxide, by passing high-temperature impure nitrogen (excess gas from the rectification column 10) through it, thereby removing moisture and carbon dioxide. In other words, adsorbents 7a and 7b continuously purify the air by alternately switching between the two towers for adsorption and regeneration. Figure 1 shows adsorbent 7a removing moisture and carbon dioxide from the air and sending it to the main heat exchanger 8, and adsorbent 7b being regenerated by being supplied with impure nitrogen from the rectification column 10.

[0031] The air purified in adsorbents 7a and 7b is supplied to the main heat exchanger 8, where it is pre-cooled. The air pre-cooled in the main heat exchanger 8 is then supplied to the rectification column 10 and the expansion turbine 9.

[0032] The expansion turbine 9 is the cooling means in this embodiment, and it cools the air compressed by the air compressor 6 by expanding it. The cooled air cooled by the expansion turbine 9 is supplied to the rectification column 10.

[0033] The rectification column 10 separates various gases such as nitrogen and oxygen contained in the air from the pre-cooled air supplied from the main heat exchanger 8 and the cooling air supplied from the expansion turbine 9, according to their boiling points, and purifies the separated gases together with liquefied gases such as liquid oxygen and liquid nitrogen.

[0034] These main heat exchangers 8, expansion turbines 9, and rectification columns 10 are installed inside a cold box 11.

[0035] The cold box 11 contains the main heat exchanger 8, the expansion turbine 9, and the rectification column 10, and has an insulating structure insulated with obsidian perlite or a vacuum wall to keep them at a low temperature.

[0036] The liquefied gas purified in the rectification column 10 of such an air separation device 2 is stored in a liquefied gas storage tank 3, which is an example of a storage means. In this embodiment, the rectification column 10 purifies liquid oxygen and liquid nitrogen as liquefied gas. Therefore, the liquefied gas storage tank 3 in this embodiment has a liquefied gas storage tank 3a for storing liquid oxygen and a liquefied gas storage tank 3b for storing liquid nitrogen. Hereafter, when the liquefied gas storage tank 3a for storing liquid oxygen and the liquefied gas storage tank 3b for storing liquid nitrogen are not distinguished, they will be referred to as the liquefied gas storage tank 3.

[0037] The liquefied gas return line 4 uses the liquefied gas from the liquefied gas storage tank 3 to cool at least the rectification column 10. The liquefied gas return line 4 comprises a liquefied gas return line 4a through which liquid oxygen passes, connecting the liquefied gas storage tank 3a and the rectification column 10, and a liquefied gas return line 4b through which liquid nitrogen passes, connecting the liquefied gas storage tank 3b and the rectification column 10. Hereafter, when the liquefied gas return line 4a through which liquid oxygen passes and the liquefied gas return line 4b through which liquid nitrogen passes are not distinguished, they will be referred to as the liquefied gas return line 4. A valve 12 for opening and closing the liquefied gas return line 4 is provided in the middle of the liquefied gas return line 4. In this embodiment, a valve 12a is provided in the liquefied gas return line 4a, and a valve 12b is provided in the liquefied gas return line 4b, and the liquefied gas return lines 4a and 4b can be opened and closed independently by valves 12a and 12b, respectively.

[0038] The liquefied gas stored in the liquefied gas storage tanks 3a and 3b is sent to the rectification column 10 via the liquefied gas return lines 4a and 4b by opening the valves 12a and 12b. This allows the rectification column 10 to be pre-cooled by the liquefied gas when the air compressor 6 is not operating. In other words, in this embodiment, the liquefied gas return lines 4 are provided as a pre-cooling means for pre-cooling the rectification column 10 when the air compressor 6 is not operating. Furthermore, while the air compressor 6 is operating due to surplus power, the valves 12a and 12b are closed, and the liquefied gas remains stored in the liquefied gas storage tank 3.

[0039] By using the liquefied gas stored in the liquefied gas storage tank 3 to cool the rectification column 10 at least while the air compressor 6 is not operating, the purification of the liquefied gas can begin from a low temperature when the air compressor 6 starts operating. Therefore, compared to when the rectification column 10 returns to room temperature while the air compressor 6 is not operating, unnecessary energy consumption can be suppressed and the waiting time until the liquefied gas is purified can be shortened.

[0040] In this embodiment, the liquefied gas return line 4 returns the liquefied gas stored in the liquefied gas storage tank 3 to the rectification column 10, but it is not limited to this. For example, the liquefied gas return line 4 may also cool the inside of the cold box 11 by sending the liquefied gas from the liquefied gas storage tank 3 into the cold box 11. In other words, by cooling the inside of the cold box 11 with the liquefied gas stored in the liquefied gas storage tank 3, the main heat exchanger 8 and the expansion turbine 9 may be cooled simultaneously in addition to the rectification column 10. This makes it possible to cool not only the rectification column 10 but also the main heat exchanger 8 and the expansion turbine 9 while the air compressor 6 is not operating, further reducing the waiting time from when the air compressor 6 starts operating until the liquefied gas is purified.

[0041] Furthermore, the opening and closing of the valve 12 provided in the liquefied gas return line 4 is performed by the control unit 5, which is a control means. The control unit 5 controls the opening and closing of valves 12a and 12b, as well as the overall control of the heat storage system 1. In other words, the control unit 5 controls the supply and stopping of surplus power to the air compressor 6. Such a control unit 5 is composed of a central processing unit (CPU), a read-and-write memory (RAM) which is an example of a storage means, a read-only memory (ROM) for storing various programs, and an interface unit that interfaces with peripheral circuits, etc.

[0042] Furthermore, it is preferable to use liquid nitrogen preferentially for pre-cooling. In other words, the control unit 5 controls valves 12a and 12b to preferentially use liquid nitrogen for pre-cooling. This is because the nitrogen content in the air is higher than that of oxygen, more liquid nitrogen is purified from the rectification column 10 than liquid oxygen, and liquid oxygen can be used for a wider variety of applications than liquid nitrogen. Therefore, by preferentially using liquid nitrogen for pre-cooling, liquid oxygen can be used for other purposes, such as recovering carbon dioxide from exhaust gas, which will be described in more detail later, thus making effective use of liquid oxygen.

[0043] In this thermal energy storage system 1, surplus electricity is used to operate the air separation device 2 and purify liquefied gas. Therefore, when surplus electricity is generated, it is temporarily stored as cold energy and used at night, thereby enabling stable operation of the power grid and optimal production of liquefied gas using surplus electricity. Furthermore, the thermal energy storage system 1 of this embodiment can be easily installed in any location where surplus electricity can be received. Consequently, the thermal energy storage system 1 of this embodiment is less limited in terms of installation location compared to pumped-storage hydropower and the like that which use surplus electricity.

[0044] Furthermore, the heat storage system 1 of this embodiment can purify liquefied gas using surplus electricity and store the resulting cold energy. Therefore, it can be used in other facilities that use liquefied gas or the cold energy of liquefied gas, such as integrated gasification combined cycle (IGCC) power plants, thermal power plants, industrial complexes including steel mills, and carbon dioxide recovery facilities. In this case, by supplying liquefied gas from the heat storage system 1 of this embodiment to other facilities, there is no need for the other facilities to purify the liquefied gas independently, thus reducing the power consumption required for purifying the liquefied gas in those facilities.

[0045] Here, the operation of the heat storage system 1 will be explained with reference to Figure 2. Figure 2 is a graph showing the amount of electricity generated by solar power generation and the operating status of the air compressor as a function of time.

[0046] As shown in Figure 2, the amount of electricity generated by solar power generation fluctuates mainly depending on the amount of sunlight. In other words, the amount of electricity generated by solar power generation gradually increases from just after 6:00 AM, which is the boundary between time period A1 (sunrise) and time period A2, and gradually decreases towards 6:00 PM, which is the boundary between time period A2 (sunset) and time period A3. For this reason, surplus electricity is thought to be mainly generated during time period A2, when solar power generation takes place. Therefore, the air separation device 2 operates during time period A2, when surplus electricity is generated, and converts the surplus electricity into liquefied gas for storage.

[0047] Furthermore, during time periods A1 and A3 when no surplus power is generated, the liquefied gas stored in the liquefied gas storage tank 3 is returned to the rectification column 10 via the liquefied gas return line 4, thereby pre-cooling the rectification column 10. As a result, when the air separation device 2 is operated using surplus power during time period A2, the rectification column 10 is pre-cooled, which shortens the time required to cool the rectification column 10 to the temperature at which the liquefied gas is purified, thus shortening the time required to purify the liquefied gas.

[0048] Such a heat storage system 1 is used in a carbon dioxide capture system 100. The carbon dioxide capture system 100 of this embodiment will now be described with reference to Figure 3. Figure 3 is a block diagram illustrating the carbon dioxide capture system.

[0049] As shown in Figure 3, the carbon dioxide recovery system 100 of this embodiment comprises the heat storage system 1 described above, an exhaust equipment 20 that discharges exhaust gas, and a carbon dioxide recovery means 30 that recovers carbon dioxide from the exhaust gas of the exhaust equipment 20.

[0050] The emission facility 20 is a facility that emits exhaust gas containing carbon dioxide, and examples include thermal power plants such as integrated gasification combined cycle (IGCC) plants, industrial complexes including steel mills, collection hubs for recovering exhaust gas containing carbon dioxide, and collection hubs for storing exhaust gas containing carbon dioxide. The exhaust gas from the emission facility 20 is sent to the carbon dioxide recovery means 30 via a pipeline.

[0051] The carbon dioxide recovery means 30 recovers carbon dioxide from exhaust gas by utilizing the phenomenon in which carbon dioxide in exhaust gas solidifies (also known as dry ice formation) when the exhaust gas is cooled to below the sublimation temperature of carbon dioxide, and comprises a dryer 31, a sublimator 32, a dry ice collection device 33, and a melting machine 34.

[0052] The dryer 31 is a device that removes moisture contained in the exhaust gas. The dryer 31 may also remove other impurities contained in the exhaust gas, such as nitrogen oxides, along with the moisture. As such a dryer 31, a so-called bubbling type dryer can be used, in which the exhaust gas is supplied into a dehumidifying refrigerant such as silicone oil to cool and solidify the moisture contained in the exhaust gas, and the solidified moisture is collected in the dehumidifying refrigerant. In addition, it is preferable to use liquefied gas that has been purified and stored in the heat storage system 1 as the cold energy for the dryer 31.

[0053] The sublimator 32 cools the exhaust gas to below the sublimation temperature of carbon dioxide, solidifying the carbon dioxide. The liquefied gas used as the cooling catalyst for the sublimator 32 is purified in the heat storage system 1 and stored in the liquefied gas storage tank 3, namely liquid nitrogen (-196°C) and liquid oxygen (-183°C). The sublimator 32 is equipped with heat transfer tubes through which the liquefied gas passes, and the exhaust gas introduced into the sublimator 32 is cooled by the liquefied gas and solidifies (turns into dry ice) on the surface of the heat transfer tubes.

[0054] The dry ice collection device 33 collects carbon dioxide (dry ice) that has been solidified in the sublimator 32. The dry ice collected by the dry ice collection device 33 is liquefied by pressurization in the melting machine 34, and the liquefied carbon dioxide (liquid carbon dioxide) is stored in a liquid carbon dioxide storage tank (not shown) or directly supplied to other facilities via a pipeline for effective use. When storing dry ice in a liquid carbon dioxide storage tank, the carbon dioxide recovery system 100 includes a liquid carbon dioxide storage tank as a component.

[0055] Furthermore, the decarbonated gas from the dryer 31 and sublimator 32 is discharged into the atmosphere through the chimney.

[0056] When liquid nitrogen is used as the cooling medium in the sub-meter 32, the nitrogen gas used in the sub-meter 32 is discharged from the chimney. When liquid oxygen is used as the cooling medium in the sub-meter 32, the liquid oxygen and oxygen gas used in the sub-meter 32 can be stored or sent to nearby factories via pipelines for effective use in various industrial applications. For example, the oxygen gas can be sent to steel mills for use in steelmaking, reducing the power required for oxygen production and lowering steelmaking costs. Furthermore, when the introduction of carbon dioxide capture type thermal power plants using oxygen combustion boilers is considered in the future, the power required for oxygen production can be significantly reduced. Alternatively, the liquid oxygen and oxygen gas used in the sub-meter 32 can be used to generate coal gasification gas by oxygen blowing in integrated gasification combined cycle (IGCC) power plants. Furthermore, the liquid nitrogen and nitrogen gas used in the sub-meter 32 can not only be discharged from the chimney, but can also be used as nitrogen gas for sealing various parts of an integrated gasification combined cycle (IGCC) power plant, stored and transported for use as liquid nitrogen, or sent to nearby factories via pipelines, allowing for effective use in a variety of industrial applications.

[0057] In this embodiment, the carbon dioxide recovery system 100 is equipped with an exhaust facility 20 that discharges exhaust gas. However, for example, without providing an exhaust facility 20, the exhaust gas from the exhaust facility 20 may be stored in a tank or the like and transported, and the carbon dioxide recovery means 30 may recover carbon dioxide from the exhaust gas stored in the transported tank.

[0058] Furthermore, in this embodiment, the carbon dioxide recovery means 30 recovers carbon dioxide contained in the exhaust gas by utilizing the cold energy of the liquefied gas purified in the heat storage system 1, but it is not limited to this. The carbon dioxide recovery means 30 may also be a so-called DAC (Direct Air Capture) that directly recovers carbon dioxide contained in the air by utilizing the cold energy of the liquefied gas purified in the heat storage system 1.

[0059] As described above, the heat storage system 1 according to Embodiment 1 of the present invention comprises an air compressor 6 that compresses air using surplus electricity, an expansion turbine 9 which is a cooling means that expands the air compressed by the air compressor 6 to obtain cooled air, a rectification column 10 that purifies liquefied gas from the cooled air, and a liquefied gas storage tank 3 which is a storage means that stores the liquefied gas purified in the rectification column 10.

[0060] By using surplus electricity to operate the air compressor 6 and purify and store liquefied gas, it is possible to purify liquefied gas in a more environmentally friendly way without using fossil fuels. Furthermore, since the air compressor 6 in this embodiment operates on surplus electricity, when surplus electricity is generated, it can be converted into liquid gas and stored, and then effectively utilized by shifting the time and location, thus eliminating the need to limit the amount of renewable energy introduced by the maximum power of renewable energy. In addition, the thermal storage system 1 in this embodiment can be easily installed wherever needed, without being restricted in terms of installation location, unlike pumped-storage hydropower.

[0061] Furthermore, in the heat storage system 1 of this embodiment, it is preferable to include a liquefied gas return line 4, which is a pre-cooling means that cools at least the rectification column 10 using liquefied gas stored in the liquefied gas storage tank 3, which is a storage means, when the air compressor 6 is not operating due to surplus power. In this way, by cooling the rectification column 10 with the liquefied gas return line 4 when the air compressor 6 is not operating, it is possible to suppress the rectification column 10 from returning to room temperature when the air compressor 6 is restarted, and to start the purification of liquefied gas immediately.

[0062] Furthermore, in the heat storage system 1 of this embodiment, the rectification column 10 purifies liquid oxygen and liquid nitrogen as liquefied gases, and it is preferable that the pre-cooling means preferentially uses liquid nitrogen. This allows liquid oxygen to be effectively utilized for other purposes.

[0063] Furthermore, in this embodiment of the heat storage system 1, the pre-cooling means and the rectification column 10 are enclosed in a cold box 11 having an insulating structure, and it is preferable that the pre-cooling means cools the inside of the cold box 11. This allows the main heat exchanger 8, expansion turbine 9, and rectification column 10 inside the cold box 11 to be cooled, so that when the air compressor 6 is restarted, the rectification column 10 does not return to room temperature and the purification of liquefied gas can be started immediately.

[0064] Furthermore, the carbon dioxide recovery system 100 according to Embodiment 1 of the present invention comprises the heat storage system 1 described above and a carbon dioxide recovery means 30 that recovers carbon dioxide using the cold energy of liquefied gas stored in a liquefied gas storage tank 3, which is a storage means. In this way, the carbon dioxide recovery system 100 recovers carbon dioxide using liquefied gas that has been purified and stored by the heat storage system 1 using surplus electricity. In other words, it is possible to achieve both the effective use of surplus electricity and the reduction of environmental burden due to carbon dioxide emissions.

[0065] Furthermore, in the carbon dioxide recovery system 100 of this embodiment, it is preferable that the carbon dioxide recovery means 30 recovers the carbon dioxide contained in the exhaust gas by solidifying it. This allows the carbon dioxide recovery means 30 to efficiently recover the carbon dioxide contained in the exhaust gas.

[0066] Furthermore, the carbon dioxide recovery system 100 of this embodiment preferably includes an exhaust equipment 20 that discharges exhaust gas. Carbon dioxide contained in the exhaust gas discharged from the exhaust equipment 20 can be recovered.

[0067] Furthermore, the control unit 5 may adjust the amount of liquefied gas purified in accordance with changes in surplus power. Now, the amount of solar power generated based on weather conditions will be explained with reference to Figure 4. Figure 4 is a graph showing the amount of solar power generated based on weather conditions.

[0068] As shown in Figure 4, solar power generation fluctuates depending on the amount of sunlight. Therefore, the amount of power generated is higher on sunny days, lower on cloudy days, and lowest on rainy days. The surplus power also fluctuates based on this solar power generation. For this reason, the control unit 5 adjusts the amount of liquefied gas purified based on the change in surplus power. In other words, the control unit 5 adjusts the amount of liquefied gas purified to increase when there is a large surplus power, and to decrease when there is a small surplus power. For example, if the amount of liquefied gas purified on a sunny day—in other words, the load on the air separation device 2—is 100%, then the load on the air separation device 2 on a cloudy day is set to 50%, and the load on the air separation device 2 on a rainy day is set to 0%. This allows surplus power to be efficiently converted into liquefied gas and stored.

[0069] Furthermore, the adjustment of the amount of liquefied gas purified by the control unit 5 in response to changes in surplus power may be controlled based on weather forecasts, or it may be controlled based on real-time information on surplus power.

[0070] Furthermore, if there is little surplus power due to bad weather and the purification and storage of liquefied gas using the surplus power of the heat storage system 1 is insufficient, the control unit 5 may operate the air compressor 6 using commercial power or the like during periods when there is no surplus power to purify and store liquefied gas. In other words, as shown in Figure 5, if there is little surplus power in time period A2 due to cloudy weather, etc., the control unit 5 drives the air separator 2 at a load of 50% during time period A2. If the liquefied gas purified and stored during time period A2 is insufficient, the air separator 2 is driven by commercial power or the like during time periods A1 and A3. In this case, the load of the air separator 2 during time periods A1 and A3 is set to 25%. This makes it possible to purify and store the same amount of liquefied gas that is purified and stored by the heat storage system 1 throughout the day on a sunny day, even on days with bad weather. The air compressor 6 of the heat storage system 1 includes those that are driven not only by surplus power but also by commercial power or the like.

[0071] (Other embodiments) Although various embodiments of the present invention have been described above, the basic configuration of the present invention is not limited to those described above.

[0072] For example, the air separator 2 of the heat storage system 1 described above may be one that is part of a coal gasification combined cycle power generation system. In other words, when the coal gasification combined cycle power generation system stops generating electricity due to an increase in surplus power, the air separator 2 used in the coal gasification combined cycle power generation system may be operated as the heat storage system 1. This makes it possible to reduce the introduction cost of the heat storage system 1 by using existing idle equipment as the air separator 2 used in the heat storage system 1.

[0073] Furthermore, in the above-described embodiment, the heat storage system 1 is provided with a liquefied gas storage tank 3, which is a storage means for storing liquid oxygen and liquid nitrogen as liquefied gases. However, the heat storage system 1 is not limited to this, and as long as it has a storage means for storing liquid oxygen as a liquefied gas, it may not have means for storing other liquefied gases. [Explanation of Symbols]

[0074] 1…Thermal storage system, 2…Air separation device, 3, 3a, 3b…Liquefied gas storage tank, 4, 4a, 4b…Liquefied gas return line, 5…Control unit, 6…Air compressor, 7a, 7b…Adsorber, 8…Main heat exchanger, 9…Expansion turbine, 10…Rectification column, 11…Cold box, 12, 12a, 12b…Valves, 20…Discharge equipment, 30…Carbon dioxide recovery means, 31…Dryer, 32…Sublimeter, 33…Dry ice collection device, 34…Melting machine, 100…Carbon dioxide recovery system

Claims

1. An air compressor that compresses air, A cooling means for obtaining cooled air by expanding the air compressed by the aforementioned air compressor, A rectification column for purifying liquefied gas from the aforementioned cooled air, The system includes a storage means for storing the liquefied gas purified in the rectification column, The aforementioned air compressor operates using surplus power, The system further comprises control means for adjusting the amount of liquefied gas purified in accordance with changes in the surplus power. A heat storage system characterized by the following features.

2. The heat storage system according to claim 1, further comprising a pre-cooling means for cooling at least the rectification column using the liquefied gas stored in the storage means when the air compressor is not operating with surplus power.

3. The aforementioned rectification column purifies liquid oxygen and liquid nitrogen as the liquefied gas, The heat storage system according to claim 2, characterized in that the pre-cooling means preferentially uses the liquid nitrogen.

4. The aforementioned pre-cooling means and the rectification column are enclosed in a cold box having an insulating structure. The heat storage system according to claim 2, characterized in that the pre-cooling means cools the inside of the cold box.

5. A heat storage system according to any one of claims 1 to 4, A separate exhaust system is provided for discharging exhaust gas containing carbon dioxide, A carbon dioxide recovery means that uses the cold energy of the liquefied gas stored in the storage means to recover carbon dioxide contained in the exhaust gas supplied from the discharge equipment, A carbon dioxide capture system characterized by comprising the following features.

6. The carbon dioxide recovery means is characterized by recovering carbon dioxide contained in exhaust gas by solidifying it. A carbon dioxide recovery system as described in claim 5, characterized by...

7. The emission facility is a thermal power plant, an industrial complex including a steel mill, a collection hub for recovering exhaust gas containing carbon dioxide, and a collection hub for storing exhaust gas containing carbon dioxide. The carbon dioxide capture system described in item 6, as described in the following description.

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