Liquid carbon dioxide energy storage system and method coupled with LNG cold energy gradient utilization

Abstract

The invention discloses a liquid carbon dioxide energy storage system and method coupled with LNG cold energy gradient utilization. The liquid carbon dioxide energy storage system coupled with LNG cold energy gradient utilization comprises an energy storage unit and a power generation unit. The energy storage unit comprises an LNG heat exchanger, a low-pressure liquid storage tank, a low-pressure compressor, a first-stage cooler, a high-pressure liquid storage tank, a first-stage heater and a high-pressure expansion machine. The first input end of the LNG heat exchanger is connected with the output end of the power generation unit, and the first output end of the LNG heat exchanger is connected with the input end of the low-pressure liquid storage tank; the output end of the low-pressure liquid storage tank is connected with the input end of the low-pressure compressor, and the output end of the low-pressure compressor is connected with the first input end of the first-stage cooler. The technical problems that in the compressed carbon dioxide energy storage technology in the prior art, gas at the low-pressure end is difficult to liquefy, and LNG cold energy is seriously wasted are solved, efficient conversion and multi-scene application of the LNG cold energy are achieved, and the economical efficiency, flexibility and environment friendliness of an energy storage system are remarkably improved.

Description

Technical Field

[0001] This application relates to the technical field of integrated utilization of physical energy storage and cold energy, and particularly relates to a liquid carbon dioxide energy storage system and method coupled with cascaded utilization of LNG cold energy. Background Art

[0002] Compressed gas energy storage has become one of the most promising solutions due to its advantages of large scale and low cost. However, the theoretical efficiency and energy storage density of traditional air energy storage are limited by the physical properties of air and rely on cave gas storage. The critical temperature of carbon dioxide (31.1°C) is close to normal temperature, and the liquefaction pressure is significantly lower than that of air, making it a more suitable working medium for energy storage systems with higher energy storage density. Liquefied storage can get rid of the limitation of geographical space. In liquid carbon dioxide energy storage, a large amount of cold energy is required for the liquefaction of carbon dioxide under low-pressure conditions. Some scholars use devices such as vortex tubes, ejectors, and cold storage packed beds to achieve this, but these increase the complexity and investment cost of the system and also cause losses to the system efficiency. LNG (liquefied natural gas) is obtained by treating natural gas through acid removal and dehydration and then freezing it through a low-temperature process. The temperature is about -162°C, and it consumes 850 kWh of electricity to liquefy one ton of natural gas. According to different user requirements, after being pressurized and heated at the LNG receiving station, it is transported to users, releasing about 830 kJ / kg of cold energy, equivalent to about 240 kWh of power generation.

[0003] Currently, the liquid carbon dioxide energy storage system faces the problem of difficult gas liquefaction at the low-pressure end, which requires additional consumption of a large amount of cold energy. Traditional solutions such as vortex tubes and cold storage packed beds are complex and inefficient. On the other hand, a large amount of cold energy (about 830 kJ / kg) released during the gasification process of LNG is wasted. Existing cold energy utilization technologies are mostly single-temperature zone applications (such as air separation or single-stage Rankine cycle), with problems such as large heat transfer temperature difference, serious losses, and low cold energy utilization rate (only 10%-25%). Especially in the utilization of high-grade cold energy (-160°C to -100°C), traditional methods have insufficient efficiency (such as the direct expansion method with an efficiency of 24% and the Rankine cycle method with an efficiency of 18%) and cannot be dynamically matched with the cold energy demand of the energy storage system. Therefore, there is an urgent need for an integrated solution that can achieve cascaded utilization of LNG cold energy, improve the efficiency of the energy storage system, and realize multi-energy combined supply. Summary of the Invention

[0004] By providing a liquid carbon dioxide energy storage system and method coupled with cascaded utilization of LNG cold energy in the embodiments of this application, the technical problems of difficult gas liquefaction at the low-pressure end in the existing compressed carbon dioxide energy storage technology and serious waste of LNG cold energy are solved. The efficient conversion and multi-scenario application of LNG cold energy are realized, and the economy, flexibility, and environmental friendliness of the energy storage system are significantly improved, providing an innovative solution for the consumption of renewable energy and the construction of integrated energy systems.

[0005] In a first aspect, an embodiment of the present invention provides a liquid carbon dioxide energy storage system coupled with cascaded utilization of LNG cold energy, including an energy storage unit and a power generation unit; the energy storage unit includes an LNG heat exchanger, a low-pressure liquid storage tank, a low-pressure compressor, a first cooler, a high-pressure liquid storage tank, a first heater, and a high-pressure expander; a first input end of the LNG heat exchanger is connected to an output end of the power generation unit, and a first output end of the LNG heat exchanger is connected to an input end of the low-pressure liquid storage tank; an output end of the low-pressure liquid storage tank is connected to an input end of the low-pressure compressor, and an output end of the low-pressure compressor is connected to a first input end of the first cooler; a first output end of the first cooler is connected to an input end of the high-pressure liquid storage tank, and an output end of the high-pressure liquid storage tank is connected to a first input end of the first heater; a first output end of the first heater is connected to a first input end of the high-pressure expander, and a first output end of the high-pressure expander is connected to a second input end of the LNG heat exchanger.

[0006] In combination with the first aspect, in a possible implementation, the power generation unit includes a first condenser, a regenerator, a first evaporator, and a first Rankine cycle expander; a first input end of the first condenser inputs LNG cold energy, and a first output end of the first condenser is connected to a first input end of the regenerator; a first output end of the regenerator is connected to an input end of the first evaporator, an output end of the first evaporator is connected to an input end of the first Rankine cycle expander, an output end of the first Rankine cycle expander is connected to a second input end of the first condenser; a second output end of the first condenser is connected to a first input end of the LNG heat exchanger.

[0007] In combination with the first aspect, in a possible implementation, the power generation unit further includes a second condenser, a second evaporator, and a second Rankine cycle expander; a first input end of the second condenser is connected to a second output end of the first condenser, and a first output end of the second condenser is connected to an input end of the second evaporator; an output end of the second evaporator is connected to an input end of the second Rankine cycle expander, a first output end of the second Rankine cycle expander is connected to a second input end of the second condenser, and a second output end of the second Rankine cycle expander is connected to a second input end of the regenerator; a second output end of the regenerator is connected between the second condenser and the second evaporator; a second output end of the second condenser is connected to a first input end of the LNG heat exchanger.

[0008] In combination with the first aspect, in a possible implementation, the energy storage unit further includes a high-pressure compressor, a secondary cooler, a secondary heater, and a low-pressure expander; the input end of the high-pressure compressor is connected to the first output end of the primary cooler, and the output end of the high-pressure compressor is connected to the first input end of the secondary cooler; the first output end of the secondary cooler is connected to the input end of the high-pressure liquid storage tank; the output end of the high-pressure expander is connected to the first input end of the secondary heater, and the first output end of the secondary heater is connected to the input end of the low-pressure expander; the output end of the low-pressure expander is connected to the second input end of the LNG heat exchanger.

[0009] In combination with the first aspect, in a possible implementation, the energy storage unit further includes a first cold storage device; the input end of the first cold storage device is connected to the output end of the low-pressure liquid storage tank, and the output end of the first cold storage device is connected to the input end of the low-pressure compressor.

[0010] In combination with the first aspect, in a possible implementation, the energy storage unit further includes a first hot water tank, a second hot water tank, and a cold water tank; the input ends of the cold water tank are respectively connected to the second output end of the primary heater and the second output end of the secondary heater, and the output ends of the cold water tank are respectively connected to the second input end of the primary cooler and the second input end of the secondary cooler; the input end of the first hot water tank is connected to the second output end of the primary cooler, and the output end of the first hot water tank is connected to the second input end of the secondary heater; the input end of the second hot water tank is connected to the second output end of the secondary cooler, and the output end of the second hot water tank is connected to the second input end of the primary heater.

[0011] In combination with the first aspect, in a possible implementation, the power generation unit further includes an LNG pump, a first Rankine cycle pump, a second Rankine cycle pump, a first valve, and a second valve; the LNG cold energy is input to the first input end of the first condenser through the LNG pump; a first Rankine cycle pump is connected between the first condenser and the regenerator; the first input end of the first valve is connected to the first output end of the second condenser, the second input end of the first valve is connected to the second output end of the regenerator, and the output end of the first valve is connected to the second evaporator; a second Rankine cycle pump is connected between the second valve and the second evaporator.

[0012] In combination with the first aspect, in a possible implementation, it further includes a second cold storage device and an LNG expander; the input end of the second cold storage device is connected to the second output end of the LNG heat exchanger, and the output end of the second cold storage device is connected to the LNG expander.

[0013] Second aspect, an embodiment of the present invention provides a method for liquid carbon dioxide energy storage coupled with cascaded utilization of LNG cold energy, using the liquid carbon dioxide energy storage system coupled with cascaded utilization of LNG cold energy in the first aspect or any possible implementation manner combined with the first aspect, including the following steps: The input end of the first cold storage device is connected to the output end of the low-pressure liquid storage tank, and the output end of the first cold storage device is connected to the input end of the low-pressure compressor; When the energy storage unit is in the energy storage stage, the working medium in the low-pressure liquid storage tank is transported to the first cold storage device, evaporated into a gaseous state, compressed by the low-pressure compressor, cooled by the first-stage cooler, and then stored in the high-pressure liquid storage tank; When the energy storage unit is in the energy release stage, the high-pressure liquid carbon dioxide flows out of the high-pressure liquid storage tank, is heated by the first-stage heater, evaporated into a gaseous state, then enters the high-pressure expander to do work, absorbs the low-grade cold energy of LNG through the LNG heat exchanger, condenses into a liquid state, and is stored in the low-pressure liquid storage tank.

[0014] Combined with the second aspect, in a possible implementation manner, the input end of the high-pressure compressor is connected to the first output end of the first-stage cooler, and the output end of the high-pressure compressor is connected to the first input end of the second-stage cooler; The first output end of the second-stage cooler is connected to the input end of the high-pressure liquid storage tank; The output end of the high-pressure expander is connected to the first input end of the second-stage heater, and the first output end of the second-stage heater is connected to the input end of the low-pressure expander; The output end of the low-pressure expander is connected to the second input end of the LNG heat exchanger; When the energy storage unit is in the energy storage stage, the medium-pressure low-temperature gas cooled by the first-stage cooler is compressed into a supercritical state by the high-pressure compressor, cooled to a liquid state by the cooling water in the second-stage cooler, and then stored in the high-pressure liquid storage tank; When the energy storage unit is in the energy release stage, the gas that has done work after entering the high-pressure expander is heated by the second-stage heater and then enters the low-pressure expander to do work, absorbs the low-grade cold energy of LNG through the LNG heat exchanger, condenses into a liquid state, and is stored in the low-pressure liquid storage tank.

[0015] One or more technical solutions provided by this application have at least the following technical effects:

[0016] The embodiment of the present invention adopts a liquid carbon dioxide energy storage system and method coupled with cascaded utilization of LNG cold energy, and constructs a cascaded utilization system of "high-grade power generation - low-grade liquefaction" of LNG cold energy through an energy storage unit and a power generation unit. Among them, the high-grade cold energy of LNG is used for multi-stage Rankine cycle power generation, the low-grade cold energy is used for liquefying low-pressure carbon dioxide in the energy storage system and storing it in the cold storage device, and the pressure energy is used for direct expansion cycle power generation. At the same time, due to the large heat transfer temperature difference of the working fluid in the organic Rankine cycle in the evaporator, serious cold energy loss occurs. Therefore, a regenerator is added in the organic Rankine cycle and the transcritical carbon dioxide cycle to use the lower-temperature organic working fluid to condense part of the working fluid in the transcritical carbon dioxide cycle, realizing the targeted utilization of cold energy temperature. This application solves the technical problems of difficult liquefaction of low-pressure end gas in the compressed carbon dioxide energy storage technology and serious waste of LNG cold energy in the prior art, realizes the efficient conversion and multi-scenario application of LNG cold energy, significantly improves the economy, flexibility and environmental friendliness of the energy storage system, and provides an innovative solution for the consumption of renewable energy and the construction of integrated energy systems. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments of the present application. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 It is a schematic diagram of a liquid carbon dioxide energy storage system coupled with cascaded utilization of LNG cold energy provided by the embodiment of the present application;

[0019] Reference numerals: 1 - energy storage unit; 11 - LNG heat exchanger; 12 - low-pressure liquid storage tank; 13 - low-pressure compressor; 14 - primary cooler; 15 - high-pressure liquid storage tank; 16 - primary heater; 17 - high-pressure expander; 18 - high-pressure compressor; 19 - secondary cooler; 191 - secondary heater; 192 - low-pressure expander; 193 - first cold storage device; 194 - first hot water tank; 195 - second hot water tank; 196 - cold water tank; 197 - carbon dioxide pump; 2 - power generation unit; 21 - first condenser; 22 - regenerator; 23 - first evaporator; 24 - first Rankine cycle expander; 25 - second condenser; 26 - second evaporator; 27 - second Rankine cycle expander; 28 - LNG pump; 29 - first Rankine cycle pump; 30 - second Rankine cycle pump; 31 - first valve; 32 - second valve; 33 - second cold storage device; 34 - LNG expander. Detailed Embodiments

[0020] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0021] In the description of the embodiments of the present application, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limitations on the present application. The terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance. In addition, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0022] The traditional heating method is to directly use seawater vaporizer or gas heater for heating, which leads to waste of cold energy and even has adverse effects on the environment. LNG cold energy has great potential for utilization. The value of cold energy at different temperatures is different. For example, in building air conditioning, the COP power consumption efficiency of 7-12℃ cold energy production must be above 5, while the COP of -160℃ low-temperature cold energy only needs 0.156. When the low-temperature cold energy is below -100℃, its economic value is relatively high, which can save a lot of low-temperature cold energy electricity. At present, the utilization projects of LNG cold energy are all single users, and there are relatively few multi-user integrated projects. In the existing cold energy utilization technology, except for air separation utilization between -150℃ and -70℃, the demand temperature zone of many users does not match the distribution of LNG gasification cold energy temperature, and its utilization rate is relatively low. LNG cold energy power generation is a form of efficient use of LNG cold energy. Common cold energy power generation processes include direct expansion, Rankine cycle, combined method, Brayton cycle and gas turbine utilization. Currently, the technologies in global commercial operation include Rankine cycle, natural gas direct expansion method and combined system. Direct expansion method only uses pressure The efficiency is low, only 24%. The Rankine cycle is generally a single-stage cycle, and the circulating working fluid is mostly propane. The equipment is simple and the reliability is high, but the heat exchange temperature difference is large. The losses are severe and the efficiency is only 18%. The overall utilization rate of LNG cold energy in China is only 10%-25%, the proportion of power generation projects is insufficient, and most of the cold energy is still wasted.

[0023] Based on the above background, the present invention proposes a power generation and liquid carbon dioxide energy storage system and an operation method using LNG cold energy, realizing the cascaded utilization of LNG cold energy, simultaneously solving the problem of low-pressure carbon dioxide liquefaction in the energy storage system, improving the charge-discharge efficiency and energy storage density of the system, and realizing the combined supply of cold, heat, and electricity. When in the valley electricity period, the liquid carbon dioxide in the low-pressure tank of the system compresses carbon dioxide using renewable energy and liquefies it through cooling water to be stored as high-pressure liquid carbon dioxide at room temperature. At this time, the electric energy generated by LNG cold energy power generation can be used to supply the system pumps and compressors. When in the peak electricity period, the liquid carbon dioxide uses compression heat to preheat and enter the turbine for expansion power generation. The low-pressure carbon dioxide at the turbine outlet exchanges heat with the low-temperature section of LNG that has experienced two-stage Rankine cycle power generation and liquefies, storing in the low-pressure storage tank. This system improves the utilization rate of LNG cold energy and the charge-discharge efficiency of the energy storage system, and can also provide hot water, cold energy, and electric energy for users.

[0024] An embodiment of the present invention provides a liquid carbon dioxide energy storage system coupled with cascaded utilization of LNG cold energy, including an energy storage unit 1 and a power generation unit 2; the energy storage unit 1 includes an LNG heat exchanger 11, a low-pressure liquid storage tank 12, a low-pressure compressor 13, a first-stage cooler 14, a high-pressure liquid storage tank 15, a first-stage heater 16, and a high-pressure expander 17; the first input end of the LNG heat exchanger 11 is connected to the output end of the power generation unit 2, and the first output end of the LNG heat exchanger 11 is connected to the input end of the low-pressure liquid storage tank 12; the output end of the low-pressure liquid storage tank 12 is connected to the input end of the low-pressure compressor 13, and the output end of the low-pressure compressor 13 is connected to the first input end of the first-stage cooler 14; the first output end of the first-stage cooler 14 is connected to the input end of the high-pressure liquid storage tank 15, and the output end of the high-pressure liquid storage tank 15 is connected to the first input end of the first-stage heater 16; the first output end of the first-stage heater 16 is connected to the first input end of the high-pressure expander 17, and the first output end of the high-pressure expander 17 is connected to the second input end of the LNG heat exchanger 11.

[0025] Exemplarily, a carbon dioxide pump 197 is also connected between the first cold storage device 193 and the low-pressure liquid storage tank 12.

[0026] Exemplarily, if there is an excess of external load, the energy storage section of the energy storage system starts to operate. Carbon dioxide flows out of the low-pressure liquid storage tank 12, first exchanges heat with the cold storage medium, evaporates, and then enters the low-pressure and high-pressure compressors 18 respectively to be compressed into a high-pressure state. The compression heat of the two stages is stored by the heat storage medium respectively. After condensation, the carbon dioxide is stored in the high-pressure liquid storage tank 15. If the external load is insufficient, the energy release section of the energy storage system starts to operate. The circulating working medium flows out of the high-pressure liquid storage tank 15, passes through the first heater 16 and the second heater 191 to absorb the compression heat stored during the energy storage process, and then enters the high-pressure and low-pressure turbines. The low-pressure gas at the outlet is cooled to a liquid state through the LNG cold energy heat exchanger and enters the low-pressure liquid storage tank 12 for storage.

[0027] Exemplarily, during energy storage, the working medium in the low-pressure liquid storage tank 12 is transported to the first cold storage device 193 by the carbon dioxide pump 197, evaporates into a gas state, is compressed by the low-pressure compressor 13, cooled by the first cooler 14, and the medium-pressure low-temperature gas is compressed into a supercritical state by the high-pressure compressor 18 and cooled to a liquid state by the cooling water in the second cooler 19 and stored in the high-pressure liquid storage tank 15. During energy release, the high-pressure liquid carbon dioxide flows out of the high-pressure liquid storage tank 15, is heated by the first heater 16, evaporates into a gas state, then enters the high-pressure expander 17 to do work, is heated by the second heater 191, enters the low-pressure expander 192 to do work, and absorbs the low-grade cold energy of LNG through the LNG heat exchanger 11 to be condensed into a liquid state and stored in the low-pressure liquid storage tank 12.

[0028] Exemplarily, the present application constructs a cascade utilization system for high-grade power generation and low-grade liquefaction of LNG cold energy. The high-grade cold energy of LNG is used for multi-stage Rankine cycle power generation, the low-grade cold energy is used for liquefying the low-pressure carbon dioxide in the energy storage system and storing it in the cold storage device, and the pressure energy is used for direct expansion cycle power generation.

[0029] In the embodiment of the present application, as Figure 1 shown, the power generation unit 2 includes a first condenser 21, a regenerator 22, a first evaporator 23, and a first Rankine cycle expander 24. The first input end of the first condenser 21 inputs the LNG cold energy, and the first output end of the first condenser 21 is connected to the first input end of the regenerator 22. The first output end of the regenerator 22 is connected to the input end of the first evaporator 23, the output end of the first evaporator 23 is connected to the input end of the first Rankine cycle expander 24, the output end of the first Rankine cycle expander 24 is connected to the second input end of the first condenser 21. The second output end of the first condenser 21 is connected to the first input end of the LNG heat exchanger 11.

[0030] Exemplarily, the cold energy of LNG gasification is available throughout the day, while the cold energy required by the carbon dioxide energy storage system is relatively large during the peak electricity load period. Therefore, the LNG cold energy power generation system has different operation strategies according to different stages of the energy storage system. In the organic Rankine cycle, the organic working fluid is pressurized by the first Rankine cycle pump 29. After being preheated by the recuperator 22, the pressurized high-pressure working fluid enters the first evaporator 23, and the gas after heat exchange with seawater or geothermal water enters the first Rankine cycle expander 24 to do work. The discharged low-temperature gas enters the first condenser 21 and is condensed into a liquid and then enters the first Rankine cycle pump 29 to form a cycle.

[0031] Exemplarily, due to the large heat exchange temperature difference of the working fluid in the organic Rankine cycle in the evaporator, the cold energy loss is serious. Therefore, a recuperator 22 is added in the organic Rankine cycle and the transcritical carbon dioxide cycle to use the colder organic working fluid to condense part of the working fluid in the transcritical carbon dioxide cycle, so as to realize the targeted utilization of cold energy temperature.

[0032] In the embodiment of the present application, as Figure 1 shown, the power generation unit 2 further includes a second condenser 25, a second evaporator 26 and a second Rankine cycle expander 27; the first input end of the second condenser 25 is connected to the second output end of the first condenser 21, and the first output end of the second condenser 25 is connected to the input end of the second evaporator 26; the output end of the second evaporator 26 is connected to the input end of the second Rankine cycle expander 27, the first output end of the second Rankine cycle expander 27 is connected to the second input end of the second condenser 25, and the second output end of the second Rankine cycle expander 27 is connected to the second input end of the recuperator 22; the second output end of the recuperator 22 is connected between the second condenser 25 and the second evaporator 26; the second output end of the second condenser 25 is connected to the first input end of the LNG heat exchanger 11.

[0033] Exemplarily, in the transcritical carbon dioxide Rankine cycle, the working fluid carbon dioxide is pressurized by the second Rankine cycle pump 30, enters the second evaporator 26 and evaporates into a gas, then enters the second Rankine cycle expander 27 to do work. The outlet gas is split by the second valve 32, part of it enters the second condenser 25 and is condensed into a liquid, and part of it enters the recuperator 22 and is condensed into a liquid. After mixing in the first valve 31, it enters the second Rankine cycle pump 30 to form a cycle. When the energy storage system is in the energy storage stage, the low-grade cold energy of LNG is used for power generation in the transcritical carbon dioxide Rankine cycle. When in the energy release stage, the condensation pressure is controlled to adjust the outlet temperature of the LNG after passing through the second condenser 25, so that part of the low-grade cold energy is used to condense the low-pressure carbon dioxide in the energy storage system.

[0034] In the embodiment of the present application, as Figure 1As shown, the energy storage unit 1 further includes a high-pressure compressor 18, a secondary cooler 19, a secondary heater 191, and a low-pressure expander 192; the input end of the high-pressure compressor 18 is connected to the first output end of the primary cooler 14, and the output end of the high-pressure compressor 18 is connected to the first input end of the secondary cooler 19; the first output end of the secondary cooler 19 is connected to the input end of the high-pressure liquid storage tank 15; the output end of the high-pressure expander 17 is connected to the first input end of the secondary heater 191, and the first output end of the secondary heater 191 is connected to the input end of the low-pressure expander 192; the output end of the low-pressure expander 192 is connected to the second input end of the LNG heat exchanger 11.

[0035] In the embodiment of the present application, as Figure 1 shown, the energy storage unit 1 further includes a first cold storage device 193; the input end of the first cold storage device 193 is connected to the output end of the low-pressure liquid storage tank 12, and the output end of the first cold storage device 193 is connected to the input end of the low-pressure compressor 13.

[0036] In the embodiment of the present application, as Figure 1 shown, the energy storage unit 1 further includes a first hot water tank 194, a second hot water tank 195, and a cold water tank 196; the input ends of the cold water tank 196 are respectively connected to the second output end of the primary heater 16 and the second output end of the secondary heater 191, and the output ends of the cold water tank 196 are respectively connected to the second input end of the primary cooler 14 and the second input end of the secondary cooler 19; the input end of the first hot water tank 194 is connected to the second output end of the primary cooler 14, and the output end of the first hot water tank 194 is connected to the second input end of the secondary heater 191; the input end of the second hot water tank 195 is connected to the second output end of the secondary cooler 19, and the output end of the second hot water tank 195 is connected to the second input end of the primary heater 16.

[0037] Exemplarily, the low-grade cold energy in the working medium is stored by the cold storage device and can be used for cold storage in cold storages or industrial and domestic refrigeration. The cold water in the cold water tank 196 is heated after passing through the primary cooler 14, and the heated hot water is stored in the first hot water tank 194. The cold water in the cold water tank 196 is heated after passing through the secondary cooler 19, and the heated hot water is stored in the second hot water tank 195.

[0038] Exemplarily, adiabatic and heat-insulating materials are provided outside the first hot water tank 194 and the second hot water tank 195; the pressure after LNG pressurization and the pressure after expansion power generation are adjusted according to the requirements of the user terminal.

[0039] In the embodiment of the present application, as Figure 1As shown, the power generation unit 2 further includes an LNG pump 28, a first Rankine cycle pump 29, a second Rankine cycle pump 30, a first valve 31, and a second valve 32; the LNG cold energy is input to the first input end of the first condenser 21 through the LNG pump 28; a first Rankine cycle pump 29 is connected between the first condenser 21 and the regenerator 22; the first input end of the first valve 31 is connected to the first output end of the second condenser 25, the second input end of the first valve 31 is connected to the second output end of the regenerator 22, and the output end of the first valve 31 is connected to the second evaporator 26; a second Rankine cycle pump 30 is connected between the second valve 32 and the second evaporator 26.

[0040] In the embodiment of the present application, as Figure 1 shown, it further includes a second cold energy storage device 33 and an LNG expander 34; the input end of the second cold energy storage device 33 is connected to the second output end of the LNG heat exchanger 11, and the output end of the second cold energy storage device 33 is connected to the LNG expander 34.

[0041] Exemplarily, in direct expansion, after the high-pressure LNG pressurized by the LNG pump 28 releases cold energy through the first condenser 21, the second condenser 25, the LNG heat exchanger 11, and the cold energy storage unit, it enters the LNG expander 34 to do work, making full use of the pressure energy of the high-pressure LNG.

[0042] The embodiment of the present invention provides a method for liquid carbon dioxide energy storage coupling with cascaded utilization of LNG cold energy, as Figure 1 shown, using a liquid carbon dioxide energy storage system coupling with cascaded utilization of LNG cold energy, including the following steps:

[0043] When the energy storage unit 1 is in the energy storage stage, the working medium in the low-pressure liquid storage tank 12 is transported to the first cold energy storage device 193, evaporated into a gas state, compressed by the low-pressure compressor 13, cooled by the primary cooler 14, and then stored in the high-pressure liquid storage tank 15; when the energy storage unit 1 is in the energy release stage, the high-pressure liquid carbon dioxide flows out of the high-pressure liquid storage tank 15, is heated by the primary heater 16, evaporated into a gas state, and then enters the high-pressure expander 17 to do work, and is condensed into a liquid state by absorbing the low-grade cold energy of LNG through the LNG heat exchanger 11 and stored in the low-pressure liquid storage tank 12.

[0044] In the embodiment of the present application, as Figure 1As shown, when the energy storage unit 1 is in the energy storage stage, the medium-pressure low-temperature gas cooled by the primary cooler 14 is compressed into a supercritical state by the high-pressure compressor 18, cooled to a liquid state by the cooling water in the secondary cooler 19, and then stored in the high-pressure liquid storage tank 15; when the energy storage unit 1 is in the energy release stage, the gas that has done work in the high-pressure expander 17 is heated by the secondary heater 191 and then enters the low-pressure expander 192 to do work, and condenses to a liquid state by absorbing the low-grade cold energy of LNG through the LNG heat exchanger 11 and is stored in the low-pressure liquid storage tank 12.

[0045] Exemplarily, when the energy storage unit 1 is in the energy storage stage, the low-grade cold energy of LNG is used for transcritical carbon dioxide Rankine cycle power generation; when the energy storage unit 1 is in the energy release stage, the condensation pressure is controlled to adjust the outlet temperature of the LNG after passing through the second condenser 25, so that a part of the low-grade cold energy is used to condense the low-pressure carbon dioxide in the energy storage system.

[0046] Exemplarily, the operation process of the LNG cold energy power generation system is as follows: If there is a surplus of external load, the LNG cold energy is mainly used for Rankine cycle power generation. The LNG is compressed by a pump and then passes through the condensers of the organic Rankine cycle and the transcritical carbon dioxide Rankine cycle respectively, exchanges heat with the circulating working medium therein and condenses, then enters the cold storage device to exchange heat, and finally passes through the turbine expansion to generate electricity, and the electricity can be used to drive the pumps and compressors of the entire system. If the external load is insufficient, at this time, in addition to exchanging heat with the condenser in the Rankine cycle, the LNG adjusts the mass flow rate in the transcritical carbon dioxide cycle, and a part of the low-grade cold energy of the LNG enters the cold energy heat exchanger of the energy storage system to liquefy the low-pressure carbon dioxide, and then enters the cold storage device to exchange heat, and finally generates electricity through the turbine expansion and is transmitted to the user.

[0047] Exemplarily, based on the operation modes of the energy storage system and the LNG cold energy power generation system, the design of the system component parameters needs to meet the following requirements: The working medium in the organic Rankine cycle needs to be environmentally friendly and have good thermodynamic performance, and propane can be selected; The heat sources in the evaporators of the organic Rankine cycle and the transcritical carbon dioxide Rankine cycle are low-temperature heat sources available in the outside world, such as seawater or geothermal water, etc.; The cold storage medium in the cold storage device can be environmental water, ensuring that it can fully absorb the cold energy of the cold fluid passing through this device, and can be used for cooling in cold storage or data centers, etc., or can also provide industrial or domestic cooling water; Adjust the condensation pressure and mass flow rate of the transcritical carbon dioxide Rankine cycle to ensure that the cold energy released by the LNG when passing through the LNG heat exchanger 11 is sufficient to liquefy the working medium in the energy storage system.

[0048] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, reference can be made to each other. The key points of each embodiment are the differences from other embodiments.

[0049] The above embodiments are only used to illustrate the technical solutions of the present application, rather than limiting the present application; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the present application.

Claims

1. A liquid carbon dioxide energy storage system coupled with cascaded utilization of LNG cold energy, characterized in that, It includes an energy storage unit (1) and a power generation unit (2); The energy storage unit (1) includes an LNG heat exchanger (11), a low-pressure liquid storage tank (12), a low-pressure compressor (13), a first cooler (14), a high-pressure liquid storage tank (15), a first heater (16), and a high-pressure expander (17); The first input end of the LNG heat exchanger (11) is connected to the output end of the power generation unit (2), and the first output end of the LNG heat exchanger (11) is connected to the input end of the low-pressure liquid storage tank (12); The output end of the low-pressure liquid storage tank (12) is connected to the input end of the low-pressure compressor (13), and the output end of the low-pressure compressor (13) is connected to the first input end of the first cooler (14); The first output end of the first cooler (14) is connected to the input end of the high-pressure liquid storage tank (15), and the output end of the high-pressure liquid storage tank (15) is connected to the first input end of the first heater (16); The first output end of the first heater (16) is connected to the first input end of the high-pressure expander (17), and the first output end of the high-pressure expander (17) is connected to the second input end of the LNG heat exchanger (11).

2. The liquid carbon dioxide energy storage system for cascaded utilization of LNG cold energy according to claim 1, wherein The power generation unit (2) includes a first condenser (21), a regenerator (22), a first evaporator (23), and a first Rankine cycle expander (24); LNG cold energy is input into the first input end of the first condenser (21), and the first output end of the first condenser (21) is connected to the first input end of the regenerator (22); The first output end of the regenerator (22) is connected to the input end of the first evaporator (23), the output end of the first evaporator (23) is connected to the input end of the first Rankine cycle expander (24), and the output end of the first Rankine cycle expander (24) is connected to the second input end of the first condenser (21); The second output end of the first condenser (21) is connected to the first input end of the LNG heat exchanger (11).

3. The liquid carbon dioxide energy storage system coupled with the cascaded utilization of LNG cold energy according to claim 2, wherein The power generation unit (2) further includes a second condenser (25), a second evaporator (26), and a second Rankine cycle expander (27); The first input end of the second condenser (25) is connected to the second output end of the first condenser (21), and the first output end of the second condenser (25) is connected to the input end of the second evaporator (26); The output end of the second evaporator (26) is connected to the input end of the second Rankine cycle expander (27), the first output end of the second Rankine cycle expander (27) is connected to the second input end of the second condenser (25), and the second output end of the second Rankine cycle expander (27) is connected to the second input end of the regenerator (22); The second output end of the regenerator (22) is connected between the second condenser (25) and the second evaporator (26); The second output end of the second condenser (25) is connected to the first input end of the LNG heat exchanger (11).

4. The liquid carbon dioxide energy storage system coupled with cascaded utilization of LNG cold energy according to claim 1, wherein The energy storage unit (1) further includes a high-pressure compressor (18), a secondary cooler (19), a secondary heater (191), and a low-pressure expander (192); The input end of the high-pressure compressor (18) is connected to the first output end of the primary cooler (14), and the output end of the high-pressure compressor (18) is connected to the first input end of the secondary cooler (19); The first output end of the secondary cooler (19) is connected to the input end of the high-pressure liquid storage tank (15); The output end of the high-pressure expander (17) is connected to the first input end of the secondary heater (191), and the first output end of the secondary heater (191) is connected to the input end of the low-pressure expander (192); The output end of the low-pressure expander (192) is connected to the second input end of the LNG heat exchanger (11).

5. The liquid carbon dioxide energy storage system for coupling and cascaded utilization of LNG cold energy according to claim 1, wherein, The energy storage unit (1) further includes a first cold storage device (193); The input end of the first cold storage device (193) is connected to the output end of the low-pressure liquid storage tank (12), and the output end of the first cold storage device (193) is connected to the input end of the low-pressure compressor (13).

6. The liquid carbon dioxide energy storage system for cascaded utilization of LNG cold energy according to claim 4, characterized in that The energy storage unit (1) further includes a first hot water tank (194), a second hot water tank (195), and a cold water tank (196); The input ends of the cold water tank (196) are respectively connected to the second output end of the primary heater (16) and the second output end of the secondary heater (191), and the output ends of the cold water tank (196) are respectively connected to the second input end of the primary cooler (14) and the second input end of the secondary cooler (19); The input end of the first hot water tank (194) is connected to the second output end of the primary cooler (14), and the output end of the first hot water tank (194) is connected to the second input end of the secondary heater (191); The input end of the second hot water tank (195) is connected to the second output end of the secondary cooler (19), and the output end of the second hot water tank (195) is connected to the second input end of the primary heater (16).

7. The liquid carbon dioxide energy storage system for cascaded utilization of LNG cold energy according to claim 3, wherein, The power generation unit (2) further includes an LNG pump (28), a first Rankine cycle pump (29), a second Rankine cycle pump (30), a first valve (31), and a second valve (32); The LNG cold energy is input to the first input end of the first condenser (21) through the LNG pump (28); A first Rankine cycle pump (29) is connected between the first condenser (21) and the regenerator (22); The first input end of the first valve (31) is connected to the first output end of the second condenser (25), the second input end of the first valve (31) is connected to the second output end of the regenerator (22), and the output end of the first valve (31) is connected to the second evaporator (26); A second Rankine cycle pump (30) is connected between the second valve (32) and the second evaporator (26).

8. The liquid carbon dioxide energy storage system coupled with cascaded utilization of LNG cold energy according to claim 1, characterized in that, It further includes a second cold storage device (33) and an LNG expander (34); The input end of the second cold energy storage device (33) is connected to the second output end of the LNG heat exchanger (11), and the output end of the second cold energy storage device (33) is connected to the LNG expander (34).

9. A method for storing energy in liquid carbon dioxide by coupling with cascaded utilization of LNG cold energy, characterized in that, Using the liquid carbon dioxide energy storage system for coupled LNG cold energy cascade utilization according to any one of claims 1-8, comprising the following steps: The input end of the first cold energy storage device (193) is connected to the output end of the low-pressure liquid storage tank (12), and the output end of the first cold energy storage device (193) is connected to the input end of the low-pressure compressor (13); When the energy storage unit (1) is in the energy storage stage, the working medium in the low-pressure liquid storage tank (12) is transported to the first cold energy storage device (193), evaporated into a gaseous state, compressed by the low-pressure compressor (13), and then cooled by the primary cooler (14) and stored in the high-pressure liquid storage tank (15). When the energy storage unit (1) is in the energy release stage, the high-pressure liquid carbon dioxide flows out of the high-pressure liquid storage tank (15), is heated by the primary heater (16), evaporated into a gaseous state, and then enters the high-pressure expander (17) to do work, and absorbs the low-grade cold energy of LNG through the LNG heat exchanger (11) and condenses into a liquid state and is stored in the low-pressure liquid storage tank (12).

10. The method for liquid carbon dioxide energy storage with coupled LNG cold energy cascade utilization according to claim 9, characterized in that The input end of the high-pressure compressor (18) is connected to the first output end of the primary cooler (14), and the output end of the high-pressure compressor (18) is connected to the first input end of the secondary cooler (19); The first output end of the secondary cooler (19) is connected to the input end of the high-pressure liquid storage tank (15); The output end of the high-pressure expander (17) is connected to the first input end of the secondary heater (191), and the first output end of the secondary heater (191) is connected to the input end of the low-pressure expander (192); The output end of the low-pressure expander (192) is connected to the second input end of the LNG heat exchanger (11); When the energy storage unit (1) is in the energy storage stage, the medium-pressure low-temperature gas cooled by the primary cooler (14) is compressed into a supercritical state by the high-pressure compressor (18), cooled to a liquid state by the cooling water in the secondary cooler (19), and then stored in the high-pressure liquid storage tank (15). When the energy storage unit (1) is in the energy release stage, the gas that has done work in the high-pressure expander (17) is heated by the secondary heater (191) and then enters the low-pressure expander (192) to do work, and absorbs the low-grade cold energy of LNG through the LNG heat exchanger (11) and condenses into a liquid state and is stored in the low-pressure liquid storage tank (12).

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