Liquefied carbon dioxide and hydrate energy storage combined system utilizing LNG (Liquefied Natural Gas) cold energy

Abstract

The utility model provides a liquefied carbon dioxide and hydrate energy storage combined system utilizing LNG cold energy. The liquefied carbon dioxide and hydrate energy storage combined system comprises a liquefied carbon dioxide energy storage subsystem, a hydrate energy storage subsystem and an LNG heat exchange unit. The liquefied CO2 energy storage subsystem comprises an energy storage stage and an energy release stage, CO2 is liquefied and stored in the energy storage stage, and liquid CO2 is gasified and expanded to do work in the energy release stage; the hydrate energy storage subsystem comprises an energy storage stage and an energy release stage, in the energy storage stage, raw material gas and water react to generate hydrate and store the hydrate, and in the energy release stage, the hydrate is decomposed, gasified and expanded to do work; the LNG heat exchange unit provides cold energy for the gaseous CO2 after expansion acting by using LNG in the cryogenic area, so that the gaseous CO2 is liquefied; lNG in an intercooling area is used as raw material gas, and cold energy is provided for hydration reaction. The performance of a conventional liquid CO2 energy storage system can be improved, the flexibility of an energy storage peak regulation system is enhanced, and the LNG cold energy utilization rate is increased.

Description

Technical Field

[0001] The utility model relates to a combined system for liquefying carbon dioxide and hydrate energy storage by utilizing LNG cold energy, belonging to the technical field of renewable energy. Background Technique

[0002] The "dual carbon" goal promotes the large-scale grid-connected utilization of renewable energy. However, new energy power generation methods such as wind energy and solar energy have obvious randomness and volatility, bringing many challenges to the operation quality and safety of the power grid. At present, energy storage technology plays an important role in improving the consumption ratio of renewable energy and ensuring the safe and stable operation of the power system, and is a key technology to ensure China's energy security and support the development of new energy. The existing large-scale energy storage technologies mainly include pumped storage and compressed air energy storage, and these two technologies have relatively strict requirements for the geological conditions of the energy storage location. At present, the installed capacity of pumped storage in China is 39.8GW, accounting for 86% of the total energy storage installed capacity, while the installed capacity of compressed air energy storage is small, accounting for less than 0.4%. It is reported that the development potential of pumped storage is limited by the lack of suitable locations and the difficulty of eliminating the negative impacts on the ecological environment. Although there are more locations where compressed air energy storage can be built, the actual cycle efficiency is low, and the process technology needs to be improved and optimized before realizing economic operation. In addition, although liquefied air energy storage can improve the energy storage density, the critical conditions of air (-141°C, 3.77MPa) require extremely low temperature operating conditions, which pose great requirements for the safety of equipment.

[0003] In recent years, carbon dioxide (CO2) energy storage technology, as a new energy storage solution, has received key attention at home and abroad. On the one hand, due to the advantages of simple process, high energy density, relatively high cycle efficiency, etc. of the system, and CO2 has suitable critical physical properties (31.3°C, 7.38MPa), is easier to liquefy than air, non-toxic and safe, etc. On the other hand, with the commercial application of carbon capture technology, effectively utilizing the large amount of captured CO2 has become one of the current focus issues. Among them, the low-temperature liquid CO2 energy storage system effectively solves the problem of large storage space of the gas energy storage system, improves the energy storage density, enhances the safety and feasibility of the CO2 energy storage system, and outputs liquid CO2 products during both the energy storage and release stages. Low-temperature liquid CO2 can also supply cold externally. Therefore, how to introduce a suitable cold source and combine it with the liquefied CO2 energy storage system so that CO2 in the energy storage and release stages is stored in a liquid form is one of the key issues of this technology.

[0004] Liquefied Natural Gas (LNG) is to condense natural gas into a cryogenic liquid at about -162°C under normal pressure. As a clean fossil energy source, it is imported and applied in large quantities. Considering the huge cold energy of LNG and the large temperature range available for utilization, in recent years, researchers have tried various cold energy utilization methods, such as cold energy power generation, cold energy air separation, and cryogenic liquid air energy storage. When a liquid CO2 energy storage system operates, there is a problem that the performance of the expander is limited in a low-temperature environment, resulting in relatively low charge-discharge efficiency.

[0005] Currently, CO2 hydrate is considered to be one of the most promising phase change cold storage materials, with advantages such as high dissociation enthalpy, low phase change temperature, and high cold storage density. CO2 hydrate is a crystal structure formed by the contact of CO2 and water molecules under certain conditions. The hydrate reaction conditions are mild, and the gas and water released after dissociation can be recycled.

[0006] In summary, in view of the urgent need for a suitable low-temperature cold source for the liquid CO2 energy storage system, the receiving station contains a large amount of LNG cold energy, and the advantages of CO2 hydrate in improving energy storage performance, a combined energy storage system of liquefied carbon dioxide and hydrate using LNG cold energy is established. It has important practical significance for improving the performance of the conventional liquid CO2 energy storage system, enhancing the flexibility of the energy storage peak shaving system, simultaneously realizing the efficient recovery and utilization of the captured CO2, improving the utilization rate of LNG cold energy in the receiving station, as well as the system resource utilization rate and technical and economic matching. Summary of the Invention

[0007] In view of the above technical problems existing in the prior art, an embodiment of the present invention provides a combined energy storage system of liquefied carbon dioxide and hydrate using LNG cold energy.

[0008] The technical solution adopted in the embodiment of the present invention is: a combined energy storage system of liquefied carbon dioxide and hydrate using LNG cold energy, including a liquefied CO2 energy storage subsystem, a hydrate energy storage subsystem, and an LNG heat exchange unit;

[0009] The liquefied CO2 energy storage subsystem includes an energy storage stage and an energy release stage. The liquefied CO2 energy storage subsystem is used to liquefy and store CO2 in the energy storage stage, and to gasify and expand the liquid CO2 stored in the energy storage stage to do work in the energy release stage;

[0010] The hydrate energy storage subsystem includes an energy storage stage and an energy release stage. The hydrate energy storage subsystem is used to react the raw material gas with water to form hydrate and store it in the energy storage stage, and to decompose and gasify the stored hydrate and expand it to do work in the energy release stage;

[0011] The LNG heat exchange unit includes a first-stage cold release unit and a second-stage cold release unit connected in series. The first-stage cold release unit is connected to the liquefied CO2 energy storage subsystem. The LNG in the cryogenic zone of the first-stage cold release unit provides cold energy for the expanded and work-done gaseous CO2 to liquefy the gaseous CO2. The second-stage cold release unit is connected to the hydrate energy storage subsystem, so that the LNG in the medium-temperature cooling zone of the second-stage cold release unit provides cold energy for the raw material gas of the hydrate energy storage subsystem and the hydration reaction.

[0012] In an alternative embodiment, the liquefied CO2 energy storage subsystem includes a compression unit, an energy storage unit, an energy release unit, and a heating unit connected in series through a CO2 closed-loop pipeline. The CO2 gas flowing in the CO2 closed-loop pipeline is compressed and cooled into a liquid state by the compression unit and then stored in the energy storage unit. The liquid CO2 in the energy storage unit can enter the energy release unit for gasification and expansion power generation. The gasified CO2 exchanges heat with the LNG in the LNG heat exchange unit for the first time, absorbs the cold energy of the LNG and liquefies. The liquefied CO2 is heated and exchanged heat in the heating unit to be heated into a gaseous state and then returned to the compression unit.

[0013] In an alternative embodiment, the hydrate energy storage subsystem includes a hydrate synthesis unit, a hydrate decomposition unit, and an expansion power generation unit. The hydrate synthesis unit is used to carry out a hydration reaction between a gas and water to generate a hydrate. The LNG heat exchange unit is connected to the hydrate synthesis unit, so that the LNG in the medium-high temperature zone of the LNG heat exchange unit provides cold energy for the gas of the hydrate synthesis unit and the hydration reaction. The hydrate decomposition unit is connected to the hydrate synthesis unit and is used to decompose the hydrate generated by the hydrate synthesis unit to release gas. The expansion power generation unit is connected to the hydrate decomposition unit and is used to generate power by expanding the gas decomposed by the hydrate decomposition unit.

[0014] In an alternative embodiment, the compression unit includes a cold box and at least one set of first compressor units. The cold box is connected to the first compressor unit located at the most downstream, so that the CO2 in the CO2 closed-loop pipeline is compressed and cooled by multiple sets of the first compressor units and then enters the cold box for further cooling; and / or

[0015] The energy storage unit includes a high-pressure CO2 storage tank connected to the cold box. The high-pressure CO2 storage tank is used to store the liquid CO2 compressed and cooled by the compression unit; and / or

[0016] The energy release unit includes a cryogenic pump and at least one set of first expansion units. The inlet of the cryogenic pump is connected to the high-pressure CO2 storage tank, and the outlet of the cryogenic pump is connected to the first expansion unit located at the most upstream, so that the liquid CO2 in the high-pressure CO2 storage tank is pressurized by the cryogenic pump and converted into gas, and then enters the first expansion unit for power generation by expansion; and / or

[0017] The heating unit includes a low-pressure CO2 storage tank, a booster pump and a heater. The inlet of the low-pressure CO2 storage tank is connected to the LNG heat exchange unit. The low-pressure CO2 storage tank is used to store the low-temperature liquid CO2 after heat exchange with the LNG in the LNG heat exchange unit. The outlet of the low-pressure CO2 storage tank is connected to the inlet of the booster pump, the outlet of the booster pump is connected to the inlet of the heater, and the outlet of the heater is connected to the inlet of the first compressor of the first compression unit located at the most upstream.

[0018] In an alternative embodiment, the LNG heat exchange unit includes a primary LNG heat exchanger and a secondary LNG heat exchanger. The inlet of the cold fluid side of the primary LNG heat exchanger is connected to the LNG input pipeline, the outlet of the cold fluid side of the primary LNG heat exchanger is connected to the inlet of the cold fluid side of the secondary LNG heat exchanger, and the outlet of the cold fluid side of the secondary LNG heat exchanger is connected to the NG output pipeline; the inlet of the hot fluid side of the primary LNG heat exchanger is connected to the outlet of the expander of the first expansion unit located at the most downstream, and the outlet of the hot fluid side of the primary LNG heat exchanger is connected to the low-pressure CO2 storage tank; the hot fluid side of the secondary LNG heat exchanger is connected to the hydrate synthesis unit, and the cold energy of the LNG absorbed by the heat exchange medium flowing in the hot fluid side of the secondary LNG heat exchanger is used for cooling the raw material gas for the hydration reaction and the cooling during the hydrate synthesis reaction process.

[0019] In an alternative embodiment, the liquefied CO2 energy storage subsystem further includes an energy storage unit. The energy storage unit includes a cold water pump, a cold water tank, a hot water pump and a hot water tank. The inlet of the cold water pump is connected to the outlet of the cold water tank, and the outlet of the cold water pump is connected to the inlet of the cold fluid side of the cooler of the first compression unit located at the most downstream, so as to send the low-temperature circulating medium in the cold water tank into the cold fluid side of the cooler of the first compression unit through the cold water pump to absorb the compression heat generated by the compression of CO2 in the first compression unit;

[0020] The inlet of the hot water tank is connected to the cold fluid side outlet of the cooler of the first compressor unit located at the most upstream, so that the circulating medium that has absorbed the compression heat of CO2 is stored in the hot water tank; the outlet of the hot water tank is connected to the inlet of the hot water pump, and the outlet of the hot water pump is connected to the hot fluid side outlet of the heating heat exchanger of the first expansion unit located at the most downstream, so that the high-temperature circulating medium in the hot water tank exchanges heat with the CO2 on the cold fluid side of the heating heat exchanger of the first expansion unit to cool down; the hot fluid side outlet of the heating heat exchanger of the first expansion unit located at the most upstream is connected to the inlet of the cold water tank, so that the circulating medium that has exchanged heat with CO2 and cooled down is stored in the cold water tank.

[0021] In an alternative embodiment, the high-pressure CO2 storage tank and the low-pressure CO2 storage tank include, but are not limited to, Dewar flasks or cryogenic storage tanks, and are equipped with a pressure stabilizing device; the storage pressure of the high-pressure CO2 storage tank is 20 MPa, and the storage pressure of the low-pressure CO2 storage tank is 610 kPa.

[0022] In an alternative embodiment, the hydrate synthesis unit includes a hydrate synthesis reactor, a hydrate storage tank, a feed water pump, a refrigeration unit, and a plurality of second compressor units connected in series in sequence. The cold fluid side of the refrigeration unit is connected to the hot fluid side outlet of the secondary LNG heat exchanger of the LNG heat exchange unit through a heat exchange pipeline. The hot fluid side of the refrigeration unit is respectively connected to the cold fluid side of the gas heat exchanger of the second compressor unit and the hydrate synthesis reactor to transfer the cold energy of LNG to the gas heat exchanger and the hydrate synthesis reactor; the inlet of the second compressor of the second compressor unit located at the most upstream is connected to the raw gas input pipeline, and the raw gas input pipeline is connected to a CO2 gas source or the NG output pipeline of the LNG heat exchange unit; the hot fluid side outlet of the gas heat exchanger of the second compressor unit located at the most downstream is connected to the gas inlet of the hydrate synthesis reactor, the outlet of the feed water pump is connected to the liquid inlet of the hydrate synthesis reactor, and the hydrate outlet of the hydrate synthesis reactor is connected to the hydrate storage tank.

[0023] In an alternative embodiment, the hydrate decomposition unit includes a hydrate slurry pump and a hydrate decomposer. The inlet of the hydrate slurry pump is connected to the hydrate outlet of the hydrate storage tank, and the outlet of the hydrate slurry pump is connected to the inlet of the hydrate decomposer, which is used to send the hydrate in the hydrate storage tank into the hydrate decomposer. The gas outlet of the hydrate decomposer is connected to the inlet of the expander of the expansion power generation unit, which is used to send the decomposed gas into the expansion power generation unit for expansion power generation.

[0024] In an alternative embodiment, the hydrate synthesis reactor adopts a spiral groove tube - type hydrate rapid generation reactor. The hydrate reaction temperature is 2 - 5 °C, the operating pressure is 5 - 7 MPa, the induction time is less than 8 min, and the gas storage capacity is higher than 150 v / v.

[0025] Compared with the prior art, the beneficial effects of the embodiments of the present utility model are as follows: The present utility model has important practical significance for improving the performance of the conventional liquid CO2 energy storage system, enhancing the flexibility of the energy storage peak - shaving system, simultaneously realizing the efficient recycling of the captured CO2, improving the utilization rate of the cold energy of LNG at the receiving station, as well as the system resource utilization rate and the technical - economic matching.

[0026] It should be understood that the foregoing general description and the following detailed description are merely exemplary and explanatory, and are not used to limit the present utility model.

[0027] The overview of various implementations or examples of the technologies described in the present utility model is not a full disclosure of the entire scope or all features of the disclosed technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In the drawings, which are not necessarily drawn to scale, the same reference numerals may describe similar components in different views. The drawings generally illustrate various embodiments by way of example rather than limitation, and are used together with the description of the specification and the claims to explain the disclosed embodiments. Where appropriate, the same reference numerals are used throughout all the drawings to refer to the same or similar parts. Such embodiments are illustrative and are not intended to be an exhaustive or exclusive embodiment of the device or method.

[0029] Figure 1 It is a flowchart of the liquefied carbon dioxide and hydrate energy storage combined system using the cold energy of LNG according to the embodiment of the present utility model.

[0030] Figure 2 It is a schematic flow diagram of the liquefied carbon dioxide and hydrate energy storage combined system using the cold energy of LNG according to the embodiment of the present utility model.

[0031] Reference Numerals:

[0032] 1 - Compression unit; 11 - Cold box; 12 - First compressor unit; 121 - First compressor; 122 - Cooler; 13 - CO2 closed - loop pipeline;

[0033] 2 - Energy storage unit; 21 - High - pressure CO2 storage tank;

[0034] 3 - Energy release unit; 31 - Cryogenic pump; 32 - First expansion unit; 321 - First expander; 322 - Heating heat exchanger;

[0035] 4 - LNG heat exchange unit; 41 - primary LNG heat exchanger; 42 - secondary LNG heat exchanger; 43 - LNG input pipeline; 44 - NG output pipeline;

[0036] 5 - heating unit; 51 - low - pressure CO2 storage tank; 52 - booster pump; 53 - heater;

[0037] 61 - cold water pump; 62 - cold water tank; 63 - hot water pump; 64 - hot water tank; 65 - circulation pipeline;

[0038] 7 - hydrate synthesis unit; 71 - hydrate synthesis reactor; 72 - hydrate storage tank; 73 - feed water pump; 74 - refrigeration unit; 75 - second compression unit; 751 - second compressor; 752 - gas heat exchanger; 76 - heat exchange pipeline; 77 - raw gas input pipeline;

[0039] 8 - hydrate decomposition unit; 81 - hydrate slurry pump; 82 - hydrate decomposer;

[0040] 9 - expansion power generation unit; 91 - second expansion unit; 911 - second expander; 912 - inter - stage heater. Detailed implementation manners

[0041] In order to make the objectives, technical solutions and advantages of the embodiments of the present utility model clearer, the technical solutions of the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present utility model. Obviously, the described embodiments are some, but not all, of the embodiments of the present utility model. Based on the described embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present utility model.

[0042] Unless otherwise defined, the technical terms or scientific terms used in the present utility model shall have the ordinary meanings understood by those of ordinary skill in the art to which the present utility model belongs. The "first", "second" and similar terms used in the present utility model do not denote any order, quantity or importance, but are only used to distinguish different components. The terms such as "including" or "comprising" mean that the elements or objects appearing before this term cover the elements or objects listed after this term and their equivalents, without excluding other elements or objects. The terms such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms such as "upper", "lower", "left", "right" are only used to represent relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0043] To keep the following description of the embodiments of the present utility model clear and concise, the detailed descriptions of known functions and known components are omitted in the present utility model.

[0044] An embodiment of the present utility model provides a combined system for liquefying carbon dioxide and hydrate energy storage using LNG cold energy, which includes a liquefied CO2 energy storage subsystem, a hydrate energy storage subsystem, and an LNG heat exchange unit 4.

[0045] The liquefied CO2 energy storage subsystem includes an energy storage stage and an energy release stage. In the energy storage stage, the liquefied CO2 energy storage subsystem is used to liquefy and store CO2, and in the energy release stage, it is used to gasify the liquid CO2 stored in the energy storage stage and expand to do work.

[0046] The hydrate energy storage subsystem includes an energy storage stage and an energy release stage. In the energy storage stage, the hydrate energy storage subsystem is used to react raw gas with water to generate hydrates and store them, and in the energy release stage, it is used to decompose and gasify the stored hydrates and expand to do work.

[0047] The LNG heat exchange unit 4 includes a series-connected primary cold release unit and a secondary cold release unit. The primary cold release unit is connected to the liquefied CO2 energy storage subsystem. The LNG flowing through the cryogenic zone of the primary cold release unit provides cold energy for the expanded and working gaseous CO2 to liquefy the gaseous CO2. The secondary cold release unit is connected to the hydrate energy storage subsystem. The LNG in the medium-temperature cold zone of the secondary cold release unit provides cold energy for the raw gas of the hydrate energy storage subsystem and the hydrate reaction, so as to cool down the raw gas and absorb the reaction heat in the process of hydrate synthesis reaction, so that the hydrate synthesis reaction can be maintained at an appropriate temperature.

[0048] The embodiment of the present utility model introduces the hydrate energy storage of CO2 into the liquefied CO2 energy storage, which can improve the problem of limited low-temperature expansion discharge of the conventional liquefied CO2 energy storage system, improve the charge and discharge performance of the system, realize flexible energy storage and release, and increase the flexibility of power grid peak shaving. Moreover, this combined system couples the high-grade LNG cold energy (LNG cold energy in the cryogenic zone, the temperature and pressure of LNG are -160°C to -100°C, 9.97 MPa) with the liquefied CO2 energy storage subsystem, and further introduces the medium- and low-grade LNG cold energy (LNG cold energy in the medium-temperature cold zone, the temperature of LNG is higher than -100°C to -50°C) into the hydrate energy storage subsystem, realizing the efficient cascade utilization of LNG cold energy. At the same time, this combined system has a wide applicable temperature range for the LNG supplied by the receiving station, enhancing the operation flexibility and adaptability of the combined system, and can be applied to the current LNG receiving station cold energy recovery and utilization projects.

[0049] In some embodiments, such as Figure 1As shown, the liquefied CO2 energy storage subsystem includes a compression unit 1, an energy storage unit 2, an energy release unit 3, and a heating unit 5 connected in series in sequence through a CO2 closed-loop pipeline 13. The CO2 gas flowing in the CO2 closed-loop pipeline 13 is compressed and cooled into a liquid state by the compression unit 1 and then stored in the energy storage unit 2. The liquid CO2 in the energy storage unit 2 can enter the energy release unit 3 for gasification and expansion power generation. The gasified CO2 exchanges heat with the LNG in the LNG heat exchange unit 4 for the first time, absorbs the cold energy of the LNG and liquefies. The liquefied CO2 is heated and warmed into a gaseous state in the heating unit 5 and then returns to the compression unit 1.

[0050] Continuing to combine Figure 1 , the hydrate energy storage subsystem includes a hydrate synthesis unit 7, a hydrate decomposition unit 8, and an expansion power generation unit 9. The hydrate synthesis unit 7 is used to carry out a hydration reaction between a raw material gas and water to generate a hydrate. The LNG heat exchange unit 4 is connected to the hydrate synthesis unit 7 so that the LNG in the medium-high temperature area of the LNG heat exchange unit 4 provides cold energy for the raw material gas of the hydrate synthesis unit 7 and the hydration reaction process, to cool a raw material gas such as CO2 or NG and absorb the reaction heat of the hydration reaction, so that the hydration reaction proceeds continuously. The hydrate decomposition unit 8 is connected to the hydrate synthesis unit 7 and is used to decompose the hydrate generated by the hydrate synthesis unit 7 to release gas; the expansion power generation unit 9 is connected to the hydrate decomposition unit 8 and is used to generate power by expanding the gas decomposed by the hydrate decomposition unit 8.

[0051] In some embodiments, as Figure 2 shown, the compression unit 1 includes a cold box 11 and at least one set of first compressor units 12. When there are multiple sets of first compressor units 12, the multiple sets of first compressor units 12 are connected in series in sequence. The cold box 11 is connected to the first compressor unit 12 located at the most downstream, so that the CO2 in the CO2 closed-loop pipeline 13 is compressed and cooled by multiple sets of first compressor units 12 in sequence and then enters the cold box 11 for further cooling.

[0052] The number of the first compressor units 12 is not limited and can be one set or multiple sets, and can be specifically determined according to actual needs. For example, three sets of first compressor units 12 connected in series are set. The first compressor unit 12 includes a first compressor 121 and a cooler 122. The outlet of the first compressor 121 is connected to the inlet of the hot fluid side of the cooler 122. The CO2 gas is compressed by the first compressor 121 and then enters the hot fluid side of the cooler 122, exchanges heat with the heat exchange medium (i.e., the circulating medium in the following text) flowing through the cold fluid side of the cooler 122 to lower the temperature, and then enters the energy storage unit 2 for energy recovery.

[0053] In the above embodiments, the first compressor 121 can adopt a centrifugal compressor. Under normal operating conditions, the temperature of the gas at the outlet of the compression unit 1 is 20 °C and the pressure is 20 MPa.

[0054] As shown Figure 2 in the figure, the energy storage unit 2 includes a high-pressure CO2 storage tank 21 connected to the cold box 11. The high-pressure CO2 storage tank 21 is used to store the liquefied CO2 compressed and cooled by the compression unit 1. During the energy storage stage, the low-temperature CO2 at the outlet of the compression unit 1 enters the high-pressure CO2 storage tank 21 for storage. During the energy release stage, the CO2 in the high-pressure CO2 storage tank 21 is introduced into the cryogenic pump 31 (to be introduced below) of the energy release unit 3 for energy release power generation.

[0055] Continuing to combine Figure 2 with the figure, the energy release unit 3 includes a cryogenic pump 31 and at least one set of first expansion units 32. When there are multiple sets of first expansion units 32, the multiple sets of first expansion units 32 are connected in series in sequence. The inlet of the cryogenic pump 31 is connected to the high-pressure CO2 storage tank 21, and the outlet of the cryogenic pump 31 is connected to the first expansion unit 32 located at the most upstream, so that the liquefied CO2 in the high-pressure CO2 storage tank 21 is pressurized by the cryogenic pump 31 and converted into a gaseous state and then enters the first expansion unit 32 for expansion power generation.

[0056] The number of the first expansion units 32 is not limited, and can be one set or multiple sets, which can be specifically determined according to actual needs. For example, three sets of first expansion units 32 connected in series are set. The first expansion unit 32 includes a first expander 321 and a heating heat exchanger 322. The outlet of the cryogenic pump 31 is connected to the inlet of the cold fluid side of the heating heat exchanger 322, the outlet of the cold fluid side of the heating heat exchanger 322 is connected to the inlet of the first expander 321, the outlet of the first expander 321 is connected to the inlet of the cold fluid side of the heating heat exchanger 322 in a set of first expansion units 32 located downstream thereof, and the outlet of the first expander 321 in the last set of first expansion units 32 is connected to the LNG heat exchange unit 4.

[0057] As shown Figure 2 in the figure, the heating unit 5 includes a low-pressure CO2 storage tank 51, a booster pump 52 and a heater 53. The inlet of the low-pressure CO2 storage tank 51 is connected to the LNG heat exchange unit 4, so that the CO2 gas after expansion power generation in the first expansion unit 32 exchanges heat with the LNG in the LNG heat exchange unit 4, absorbs the cold energy of the LNG and liquefies into liquid CO2 and enters the low-pressure CO2 storage tank 51 for storage. That is, the low-pressure CO2 storage tank 51 is used to store the low-temperature liquid CO2 after heat exchange with the LNG in the LNG heat exchange unit 4. The outlet of the low-pressure CO2 storage tank 51 is connected to the inlet of the booster pump 52, the outlet of the booster pump 52 is connected to the inlet of the heater 53, and the outlet of the heater 53 is connected to the inlet of the first compressor 121 of the first compression unit 12 located at the most upstream. The cold energy of the LNG is used to cool and liquefy the low-pressure gaseous CO2 after performing work in the energy release unit 3, and store it back into the low-pressure CO2 storage tank 51 to wait for the next cycle, improving the energy storage density of the system, reducing the storage volume, and enhancing the safety of the operation of the energy storage system.

[0058] Exemplarily, the high-pressure CO2 storage tank 21 and the low-pressure CO2 storage tank 51 include, but are not limited to, Dewar flasks or cryogenic storage tanks, and are equipped with a pressure stabilizing device; under normal operating conditions, the storage pressure of the high-pressure CO2 storage tank 21 is 20-23 Mpa, and the storage pressure of the low-pressure CO2 storage tank 51 is 610-700 kPa.

[0059] In some embodiments, as Figure 2 shown, the LNG heat exchange unit 4 includes a primary LNG heat exchanger 41 and a secondary LNG heat exchanger 42. The inlet of the cold fluid side of the primary LNG heat exchanger 41 is connected to the LNG input pipeline 43, the outlet of the cold fluid side of the primary LNG heat exchanger 41 is connected to the inlet of the cold fluid side of the secondary LNG heat exchanger 42, and the outlet of the cold fluid side of the secondary LNG heat exchanger 42 is connected to the NG output pipeline 44. The inlet of the hot fluid side of the primary LNG heat exchanger 41 is connected to the outlet of the first expander 321 of the most downstream first expansion unit 32, and the outlet of the hot fluid side of the primary LNG heat exchanger 41 is connected to the low-pressure CO2 storage tank 51. The CO2 gas after expansion power generation by the first expansion unit 32 exchanges heat with LNG in the primary LNG heat exchanger 41, absorbs the cold energy of LNG and liquefies, and the liquefied CO2 is stored in the low-pressure CO2 storage tank 51. The hot fluid side of the secondary LNG heat exchanger 42 is connected to the hydrate synthesis unit 7, so that the heat exchange medium flowing in the hot fluid side of the secondary LNG heat exchanger 42 uses the cold energy of LNG it absorbs for cooling the raw material gas for the hydrate reaction and the cooling process of the hydrate synthesis reaction.

[0060] The LNG from the receiving terminal first enters the primary LNG heat exchanger 41 through the LNG input pipeline 43, and uses the cold energy of the LNG deep cooling zone (-160°C to -100°C) to liquefy CO2, that is, provides high-grade LNG cold energy for the CO2 gas after expansion power generation in the liquefied CO2 energy storage subsystem, so that the CO2 gas liquefies. The liquefied CO2 is stored in the low-pressure CO2 storage tank 51. The medium-cooling zone (-100°C to -50°C) LNG coming out of the primary LNG heat exchanger 41 is further reheated and vaporized into natural gas (NG) above 0°C in the secondary LNG heat exchanger 42, and is incorporated into the natural gas pipeline through the NG output pipeline 44 and transported to the receiving terminal pipe network. At the same time, the secondary LNG heat exchanger 42 provides the cold energy of the medium-cooling zone LNG to the hydrate synthesis unit 7 for hydrate synthesis, realizing the efficient cascade utilization of LNG cold energy. This system has a relatively wide applicable temperature range for the LNG supplied by the receiving terminal, enhances the operation flexibility and adaptability of the energy storage system, and can be applied to the current LNG receiving terminal cold energy recovery and utilization projects.

[0061] In the above embodiments, the LNG comes from the external transmission pipeline of the receiving terminal, and the adaptable temperature fluctuation range of the LNG external transmission is -160°C to -100°C, and the flow rate fluctuation is 91 - 171 t / h. Under normal conditions, the temperature of the LNG transported to the liquefied CO2 energy storage subsystem is about -140°C, and the pressure is 1 - 10 MPa.

[0062] In the above embodiments, the natural gas transportation can be quickly cut off from the LNG receiving terminal through a valve, and multiple manual valves are provided for truncation to ensure the safety of the LNG receiving terminal.

[0063] In some embodiments, as Figure 2 shown, the liquefied CO2 energy storage subsystem further includes an energy storage unit, and the energy storage unit includes a cold water pump 61, a cold water tank 62, a hot water pump 63, and a hot water tank 64.

[0064] The inlet of the cold water pump 61 is connected to the outlet of the cold water tank 62, and the outlet of the cold water pump 61 is connected to the inlet of the cold fluid side of the cooler 122 of the first compressor unit 12 located at the most downstream. The cold water pump 61 sends the low-temperature circulating medium in the cold water tank 62 into the cold fluid side of the cooler 122 of the first compressor unit 12 to absorb the compression heat generated by the compression of CO2 in the first compressor unit 12.

[0065] The inlet of the hot water tank 64 is connected to the outlet of the cold fluid side of the cooler 122 of the first compressor unit 12 located at the most upstream, so that the circulating medium that has absorbed the compression heat of CO2 is stored in the hot water tank 64. The outlet of the hot water tank 64 is connected to the inlet of the hot water pump 63, and the outlet of the hot water pump 63 is connected to the outlet of the hot fluid side of the heating heat exchanger 322 of the first expansion unit 32 located at the most downstream, so that the high-temperature circulating medium in the hot water tank 64 exchanges heat with the CO2 on the cold fluid side of the heating heat exchanger 322 of the first expansion unit 32 to cool down, and the CO2 is heated up to facilitate entering the first expander 321 to do work. The outlet of the hot fluid side of the heating heat exchanger 322 of the first expansion unit 32 located at the most upstream is connected to the inlet of the cold water tank 62, so that the circulating medium that has exchanged heat and cooled down with CO2 is stored in the cold water tank 62.

[0066] The energy storage unit supplies the inter-stage waste heat of the compressor recovered in the hot water tank 64 to the heating heat exchanger 322 of the energy release unit 3 through the circulating pipeline 65, and at the same time uses the cooling water in the cold water tank 62 to complete the inter-stage cooling of the first compressor 121, forming a closed cycle.

[0067] The circulating medium of the energy storage unit can be selected according to the actual situation, and this embodiment does not limit it. For example, cold and hot water at 40°C to 129°C can be used as the circulating medium.

[0068] The cold fluid side (refrigerant heat exchange side) of the cooler 122 of the compression unit 1 in the embodiment of the present utility model is connected to the energy storage unit through a circulation pipeline 65, and the inter-stage cooling is completed by means of the low-temperature circulating medium stored in the cold water tank 62. At the same time, the compression heat is stored in the hot water tank 64 for the expansion power generation of the energy release unit 3.

[0069] In some embodiments, as Figure 2 shown, the hydrate synthesis unit 7 includes a hydrate synthesis reactor 71, a hydrate storage tank 72, a feed water pump 73, a refrigeration unit 74, and at least one set of second compression units 75. The cold fluid side of the refrigeration unit 74 is connected to the hot fluid side outlet of the secondary LNG heat exchanger 42 of the LNG heat exchange unit 4 through a heat exchange pipeline 76. The hot fluid side of the refrigeration unit 74 is respectively connected to the cold fluid side of the gas heat exchanger 752 of the second compression unit 75 and the hydrate synthesis reactor 71, so as to transfer the cold energy of the LNG to the gas heat exchanger 752 and the hydrate synthesis reactor 71, enabling the raw material gas flowing through the hot fluid side of the gas heat exchanger 752 to release the compression heat to the LNG. At the same time, the LNG absorbs the reaction heat generated during the reaction in the hydrate synthesis reactor 71, keeping the hydrate synthesis reactor 71 at an appropriate temperature. The inlet of the second compressor 751 of the second compression unit 75 located at the most upstream is connected to the raw material gas input pipeline 77. The hot fluid side outlet of the gas heat exchanger 752 of the second compression unit 75 located at the most downstream is connected to the gas inlet of the hydrate synthesis reactor 71, for feeding the compressed and cooled raw material gas into the hydrate synthesis reactor 71. The inlet of the feed water pump 73 is connected to a water inlet tank (not shown in the figure), and the water inlet tank stores low-temperature cold water. The outlet of the feed water pump 73 is connected to the liquid inlet of the hydrate synthesis reactor 71, for feeding the low-temperature cold water in the water inlet tank into the hydrate synthesis reactor 71 to carry out a hydration reaction with the raw material gas. The hydrate outlet of the hydrate synthesis reactor 71 is connected to the hydrate storage tank 72, for feeding the hydrate generated by the hydration reaction into the hydrate storage tank 72 for storage.

[0070] The raw material gas input pipeline 77 can be connected to the cold fluid side outlet of the secondary LNG heat exchanger 42 of the LNG heat exchange unit 4, that is, connected to the NG output pipeline 44. Using NG as the raw material gas for the hydration reaction to generate natural gas hydrate, the natural gas hydrate can be flexibly transported out by a refrigerated truck to urban and rural areas, distributed energy sources, factories, and other areas without natural gas pipelines laid, and can be decomposed and utilized by a hydrate gasification device. This system adopts a combined storage and transportation technology of LNG and natural gas hydrate at the LNG receiving station, realizing the complementary utilization of various natural gas storage methods and improving the operation flexibility and peak shaving capacity of the system.

[0071] The raw gas input pipeline 77 can also be connected to a CO2 gas source. Using CO2 gas as the raw gas, CO2 hydrate is formed. After the CO2 hydrate is heated and gasified in the hydrate decomposer 82, it enters the expansion unit 91 to release energy for power generation, serving as a power generation supplement for the liquefied CO2 energy storage subsystem and increasing the total power generation of the system.

[0072] In the above embodiments, under normal operating conditions of the hydrate energy storage subsystem, the temperature of the hydrate synthesis reaction in the hydrate synthesis reactor 71 is 2 - 5 °C, and the operating pressure is 5 - 7 MPa.

[0073] The number of the second compression units 75 is not limited and can be one or more groups. Specifically, it can be determined according to actual needs. For example, three serially connected second compression units 75 are set. The second compression unit 75 includes a second compressor 751 and a gas heat exchanger 752. The inlet of the non-uppermost second compressor 751 is connected to the outlet of the hot fluid side of the gas heat exchanger 752 in a group of second compression units 75 that is adjacent to and upstream of it. The outlet of the second compressor 751 of any group of second compression units 75 is connected to the inlet of the hot fluid side of the gas heat exchanger 752 in the same group. In this way, the raw gas enters the hot fluid side of the gas heat exchanger 752 after being compressed by the second compressor 751, exchanges heat with the LNG flowing through the cold fluid side of the gas heat exchanger 752 and cools down, and then enters the hydrate synthesis reactor 71. The cold fluid side of the gas heat exchanger 752 is connected to the refrigeration unit 74, so that the refrigerant of the refrigeration unit 74 flows through the cold fluid side of the gas heat exchanger 752. The refrigerant provides the cold energy of the LNG absorbed by it in the secondary LNG heat exchanger 42 to the gas flowing through the hot fluid side of the gas heat exchanger 752, cooling the gas down.

[0074] In the above embodiments, the second compressor 751 in the hydrate energy storage subsystem can adopt a centrifugal compressor. Under normal operating conditions, the gas pressure after being compressed by the second compression unit 75 is 5 - 7 MPa.

[0075] Continue to combine Figure 2 , the refrigerant of the refrigeration unit 74 also flows through the outer wall of the hydrate synthesis reactor 71, and the refrigerant absorbs the reaction heat of the hydrate synthesis reaction in the hydrate synthesis reactor 71, enabling the hydrate synthesis reaction to proceed smoothly.

[0076] In the above embodiments, for the refrigeration unit 74 in the hydrate energy storage subsystem, preferably, the refrigerant is a 30% - 50% ethylene glycol solution or an environment-friendly refrigerant R134a.

[0077] In some embodiments, such as Figure 2As shown in the figure, the hydrate decomposition unit 8 includes a hydrate slurry pump 81 and a hydrate decomposer 82. The inlet of the hydrate slurry pump 81 is connected to the hydrate outlet of the hydrate storage tank 72, and the outlet of the hydrate slurry pump 81 is connected to the inlet of the hydrate decomposer 82, which is used to send the hydrate in the hydrate storage tank 72 into the hydrate decomposer 82. The gas outlet of the hydrate decomposer 82 is connected to the inlet of the expander of the expansion power generation unit 9, which is used to send the decomposed gas into the expansion power generation unit 9 for expansion power generation.

[0078] In the above embodiment, the water generated by the temperature rise and gasification of the hydrate in the hydrate decomposer 82 can be used as circulating water and returned to the water inlet tank for reuse.

[0079] The expansion power generation unit 9 includes at least one group of second expansion units 91, and the second expansion units 91 include a second expander 911 and an inter-stage heater 912. When there are multiple groups of second expansion units 91, the multiple groups of second expansion units 91 are in series. The inlet of the second expander 911 of the second expansion unit 91 located at the most upstream is connected to the gas outlet of the hydrate decomposer 82. The outlet of the second expander 911 of each second expansion unit 91 is connected to the inlet of the cold fluid side of its same-group inter-stage heater 912. The outlet of the cold fluid side of the inter-stage heater 912 of the second expansion unit 91 located at the most downstream is connected to the inlet of the first compressor 751 located at the most upstream, so that the tail gas after expansion power generation returns to the hydrate synthesis unit 7 for reuse.

[0080] In some embodiments, the hydrate synthesis reactor 71 adopts a spiral groove tube type hydrate rapid generation reactor, the hydrate reaction temperature is -5 to 0 °C, the operating pressure is 7 to 9 MPa, the induction time is 10 to 15 min, and the gas storage capacity is 140 to 160 v / v.

[0081] In the above embodiment, optionally, the structural forms of the cooler 122, the heating heat exchanger 322, the first LNG heat exchanger 41, the second LNG heat exchanger 42, the heater 53, the gas heat exchanger 752 and the inter-stage heater 912 include but are not limited to shell-and-tube type, wound-tube type or plate-shell type, and the minimum heat transfer temperature difference is greater than 3 °C.

[0082] In the above embodiment, optionally, the first expander 321 and the second expander 911 can adopt axial flow type, centrifugal type or screw type expanders.

[0083] In the above embodiment, under normal operating conditions, the maximum power generation of the liquefied CO2 energy storage subsystem is 5890 kW. After combining with the combined hydrate energy storage subsystem, the total power generation of the whole system is 11.9 MW, the maximum cycle efficiency is 88.72%, and the LNG cold energy utilization rate is greater than 95%.

[0084] The working principles of the two operating modes, namely energy storage and energy release, of the combined system for liquefied carbon dioxide and hydrate energy storage using LNG cold energy in the embodiments of the present utility model will be described below:

[0085] When the energy storage process is in progress, (1) in the liquefied CO2 energy storage subsystem, the CO2 raw material gas first enters the first compressor unit 12 of the compression unit 1, is pressurized by the first compressor 121, cooled by the cooler 122, and then enters the cold box 11 for heat exchange and temperature reduction to form liquid CO2 at 20 MPa and 20 °C, and enters the high-pressure CO2 storage tank 21 of the energy storage unit 2 for storage. Among them, the cooler 122 transfers the cold energy to the CO2 gas through the circulating pipeline 65 to exchange heat and reduce its temperature by pumping the circulating water in the cold water tank 62 of the energy storage unit through the cold water pump 61. (2) In the hydrate energy storage subsystem, the CO2 raw material gas enters the second compressor unit 75 of the hydrate synthesis unit 7, is pressurized by the second compressor 751 and then enters the gas heat exchanger 752, is cooled by the refrigerant from the refrigeration unit 74, and then enters the hydrate synthesis reactor 71. The cooling water from the water inlet tank (not shown in the figure) is pressurized by the water inlet pump 73 and then enters the hydrate synthesis reactor 71, where it reacts with the low-temperature gas at 2 °C and 5 MPa to generate hydrate products, which are stored in the hydrate storage tank 72.

[0086] When the energy release process is in progress, (1) in the liquefied CO2 energy storage subsystem, under normal conditions, the liquefied CO2 in the high-pressure CO2 storage tank 21 of the energy storage unit 2 is pressurized to 22 MPa by the cryogenic pump 31 and sent to the first expansion unit 32 of the energy release unit 3. After being heated and raised in temperature by the heating heat exchanger 322, the energy is released and work is done by the first expander 321. Among them, the circulating water from the hot water tank 64 is pressurized by the hot water pump 63 and exchanges heat with the heating heat exchanger 322 and then stored in the cold water tank 62, that is, the cold energy is carried away by the circulating water and released to the energy storage unit. The gaseous CO2 after energy release and power generation then enters the first-stage LNG heat exchanger 41. Among them, the low-temperature high-pressure LNG (-160 to -100 °C, 9.97 MPa) from the receiving station is recycled in two-stage heat exchangers. First, it flows through the first-stage LNG heat exchanger 41, transfers the cold energy to CO2, liquefies CO2 and stores it in the low-pressure CO2 storage tank 51 (-52 °C, 610 kPa), and further enters the second-stage LNG heat exchanger 42 to provide the cold energy of the LNG (-100 °C to -50 °C) in the intermediate cooling zone to the hydrate synthesis unit 7 for low-temperature synthesis of hydrates. The liquid CO2 in the low-pressure CO2 storage tank 51 is then pressurized by the booster pump 52 and exchanges heat and is heated to a gas by the heater 53, and then returns to the compression unit 1 to participate in the energy storage process again as a gas source. (2) In the hydrate energy storage subsystem, the slurry-like hydrate in the hydrate storage tank 72 is transported by the hydrate slurry pump to the hydrate decomposer 82, gasifies after being heated in a water bath at 30 °C, enters the second expansion unit 91, is heated and raised in temperature by the inter-stage heater 912, and the energy is released and work is done by the second expander 911.

[0087] The combined system for liquefied carbon dioxide and hydrate energy storage using LNG cold energy in the embodiment of the present invention utilizes a large amount of energy stored by CO2 hydrates at low temperatures. After dissociation, the normal-temperature gas expands again for power generation and work. Combined with the hydrate energy storage subsystem, it can enhance the charge and discharge performance and flexibility of the energy storage system, improve the problem of limited low-temperature expansion discharge of the conventional liquefied CO2 energy storage system, and enhance the charge and discharge performance of the energy storage system. At the same time, two-stage utilization of high-grade and medium-low-grade LNG cold energy is provided. That is, the high-grade LNG cold energy is introduced into the liquefied CO2 energy storage subsystem to realize storage and energy release sections both storing in liquid CO2, improve the energy storage density of the system, enhance the operation safety of the energy storage system, and the low-temperature liquid CO2 can be recycled as a refrigerant product to provide cooling inside or outside the system, realizing the efficient recycling of captured CO2 and increasing the economy of the system. Further, the medium-low-grade LNG cold energy is introduced into the hydrate energy storage subsystem for hydrate synthesis, realizing the efficient cascade utilization of LNG cold energy, and can be applied to the current LNG receiving station cold energy recovery and utilization project. In addition, the above embodiments are simple and easy to implement, and the hydrate energy storage subsystem and the liquefied CO2 energy storage subsystem have relative independence, improving the operation flexibility and practicality of the overall project.

[0088] The foregoing description is intended to be illustrative and not restrictive, and those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present disclosure. Moreover, the above examples (or one or more aspects thereof) can be used in combination with each other, and it is contemplated that these embodiments can be combined with each other in various combinations or permutations.

Claims

1. A combined system for liquefying carbon dioxide and storing energy with hydrates using LNG cold energy, characterized in that, It includes a liquefied CO2 energy storage subsystem, a hydrate energy storage subsystem, and an LNG heat exchange unit; The liquefied CO2 energy storage subsystem includes an energy storage stage and an energy release stage. In the energy storage stage, the liquefied CO2 energy storage subsystem is used to liquefy and store CO2, and in the energy release stage, it is used to gasify the liquid CO2 stored in the energy storage stage and expand to do work; The hydrate energy storage subsystem includes an energy storage stage and an energy release stage. In the energy storage stage, the hydrate energy storage subsystem is used to react raw gas with water to generate hydrates and store them, and in the energy release stage, it is used to decompose and gasify the stored hydrates and expand to do work; The LNG heat exchange unit includes a first-stage cold release unit and a second-stage cold release unit connected in series. The first-stage cold release unit is connected to the liquefied CO2 energy storage subsystem. The LNG in the cryogenic zone of the first-stage cold release unit provides cold energy for the expanded and worked gaseous CO2 to liquefy the gaseous CO2; the second-stage cold release unit is connected to the hydrate energy storage subsystem, so that the LNG in the medium-temperature cooling zone of the second-stage cold release unit provides cold energy for the raw gas and the hydration reaction of the hydrate energy storage subsystem.

2. The combined system for liquefying carbon dioxide and storing energy with hydrates using LNG cold energy according to claim 1, wherein The liquefied CO2 energy storage subsystem includes a compression unit, an energy storage unit, an energy release unit, and a heating unit connected in series through a CO2 closed-loop pipeline. The CO2 gas flowing in the CO2 closed-loop pipeline is compressed and cooled into a liquid by the compression unit and then stored in the energy storage unit. The liquid CO2 in the energy storage unit can enter the energy release unit to gasify and expand for power generation. The gasified CO2 exchanges heat with the LNG in the LNG heat exchange unit for the first time, absorbs the cold energy of the LNG and liquefies. The liquefied CO2 is heated and warmed into a gas in the heating unit and then returns to the compression unit.

3. The liquefied carbon dioxide and hydrate energy storage combined system using LNG cold energy according to claim 1, characterized in that The hydrate energy storage subsystem includes a hydrate synthesis unit, a hydrate decomposition unit, and an expansion power generation unit. The hydrate synthesis unit is used to carry out a hydration reaction between gas and water to generate hydrates; the LNG heat exchange unit is connected to the hydrate synthesis unit, so that the LNG in the medium-high temperature zone of the LNG heat exchange unit provides cold energy for the gas and the hydration reaction of the hydrate synthesis unit; the hydrate decomposition unit is connected to the hydrate synthesis unit and is used to separate out gas from the hydrates generated by the hydrate synthesis unit; the expansion power generation unit is connected to the hydrate decomposition unit and is used to expand and generate power by using the gas separated out by the hydrate decomposition unit.

4. The liquefied carbon dioxide and hydrate energy storage combined system using LNG cold energy according to claim 2, wherein, The compression unit includes a cold box and at least one set of first compression units. The cold box is connected to the first compression unit located at the most downstream, so that the CO2 in the CO2 closed-loop pipeline is compressed and cooled by multiple sets of the first compression units and then enters the cold box for further cooling; and / or The energy storage unit includes a high-pressure CO2 storage tank connected to the cold box. The high-pressure CO2 storage tank is used to store the liquid CO2 compressed and cooled by the compression unit; and / or The energy release unit includes a cryogenic pump and at least one set of first expansion units. The inlet of the cryogenic pump is connected to the high-pressure CO2 storage tank, and the outlet of the cryogenic pump is connected to the first expansion unit located at the most upstream, so that the liquid CO2 in the high-pressure CO2 storage tank is pressurized by the cryogenic pump and converted into gas, and then enters the first expansion unit for power generation by expansion; and / or The heating unit includes a low-pressure CO2 storage tank, a booster pump and a heater. The inlet of the low-pressure CO2 storage tank is connected to the LNG heat exchange unit. The low-pressure CO2 storage tank is used to store the low-temperature liquid CO2 after heat exchange with the LNG in the LNG heat exchange unit. The outlet of the low-pressure CO2 storage tank is connected to the inlet of the booster pump. The outlet of the booster pump is connected to the inlet of the heater. The outlet of the heater is connected to the inlet of the first compressor of the first compression unit located at the most upstream.

5. The liquefied carbon dioxide and hydrate energy storage combined system using LNG cold energy according to claim 4, characterized in that, The LNG heat exchange unit includes a primary LNG heat exchanger and a secondary LNG heat exchanger. The inlet of the cold fluid side of the primary LNG heat exchanger is connected to the LNG input pipeline. The outlet of the cold fluid side of the primary LNG heat exchanger is connected to the inlet of the cold fluid side of the secondary LNG heat exchanger. The outlet of the cold fluid side of the secondary LNG heat exchanger is connected to the NG output pipeline. The inlet of the hot fluid side of the primary LNG heat exchanger is connected to the outlet of the expander of the first expansion unit located at the most downstream. The outlet of the hot fluid side of the primary LNG heat exchanger is connected to the low-pressure CO2 storage tank. The hot fluid side of the secondary LNG heat exchanger is connected to the hydrate synthesis unit. The cold energy absorbed by the heat exchange medium flowing in the hot fluid side of the secondary LNG heat exchanger is used for cooling the raw material gas for the hydration reaction and the temperature reduction during the hydrate synthesis reaction process.

6. The liquefied carbon dioxide and hydrate energy storage combined system using LNG cold energy according to claim 4, wherein The liquefied CO2 energy storage subsystem further includes an energy storage unit. The energy storage unit includes a cold water pump, a cold water tank, a hot water pump and a hot water tank. The inlet of the cold water pump is connected to the outlet of the cold water tank. The outlet of the cold water pump is connected to the inlet of the cold fluid side of the cooler of the first compression unit located at the most downstream, so as to send the low-temperature circulating medium in the cold water tank into the cold fluid side of the cooler of the first compression unit through the cold water pump to absorb the compression heat generated by the compression of CO2 in the first compression unit; The inlet of the hot water tank is connected to the outlet of the cold fluid side of the cooler of the first compression unit located at the most upstream, so that the circulating medium that has absorbed the compression heat of CO2 is stored in the hot water tank. The outlet of the hot water tank is connected to the inlet of the hot water pump. The outlet of the hot water pump is connected to the outlet of the hot fluid side of the heating heat exchanger of the first expansion unit located at the most downstream, so that the high-temperature circulating medium in the hot water tank exchanges heat with the CO2 on the cold fluid side of the heating heat exchanger of the first expansion unit to reduce the temperature. The outlet of the hot fluid side of the heating heat exchanger of the first expansion unit located at the most upstream is connected to the inlet of the cold water tank, so that the circulating medium whose temperature has been reduced by heat exchange with CO2 is stored in the cold water tank.

7. The liquefied carbon dioxide and hydrate energy storage combined system using LNG cold energy according to claim 4, characterized in that, The high-pressure CO2 storage tank and the low-pressure CO2 storage tank include, but are not limited to, Dewar flasks or cryogenic storage tanks, and are equipped with a pressure stabilizing device.

8. The liquefied carbon dioxide and hydrate energy storage combined system using LNG cold energy according to claim 3, wherein The hydrate synthesis unit includes a hydrate synthesis reactor, a hydrate storage tank, a feed water pump, a refrigeration unit, and a plurality of second compressor units connected in series in sequence. The cold fluid side of the refrigeration unit is connected to the hot fluid side outlet of the secondary LNG heat exchanger of the LNG heat exchange unit through a heat exchange pipeline. The hot fluid side of the refrigeration unit is respectively connected to the cold fluid side of the gas heat exchanger of the second compressor unit and the hydrate synthesis reactor to transfer the cold energy of the LNG to the gas heat exchanger and the hydrate synthesis reactor; the inlet of the second compressor of the second compressor unit located at the most upstream is connected to the raw gas input pipeline, and the raw gas input pipeline is connected to the CO2 gas source or the NG output pipeline of the LNG heat exchange unit; the hot fluid side outlet of the gas heat exchanger of the second compressor unit located at the most downstream is connected to the gas inlet of the hydrate synthesis reactor, the outlet of the feed water pump is connected to the liquid inlet of the hydrate synthesis reactor, and the hydrate outlet of the hydrate synthesis reactor is connected to the hydrate storage tank.

9. The liquefied carbon dioxide and hydrate energy storage combined system using LNG cold energy according to claim 8, wherein, The hydrate decomposition unit includes a hydrate slurry pump and a hydrate decomposer. The inlet of the hydrate slurry pump is connected to the hydrate outlet of the hydrate storage tank, and the outlet of the hydrate slurry pump is connected to the inlet of the hydrate decomposer, for feeding the hydrate in the hydrate storage tank into the hydrate decomposer. The gas outlet of the hydrate decomposer is connected to the inlet of the expander of the expansion power generation unit, for feeding the decomposed gas into the expansion power generation unit for expansion power generation.

10. The liquefied carbon dioxide and hydrate energy storage combined system using LNG cold energy according to claim 8, wherein The hydrate synthesis reactor adopts a spiral groove tube type hydrate rapid generation reactor.

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