A split-flow liquid co2 mixture energy storage system and method

Abstract

The application discloses a shunt type liquid CO2 mixture energy storage system and method, which comprises a low-temperature liquid mixture storage tank, an evaporator, a compressor, a mixer, a high-temperature mixture storage tank and a turbine which are sequentially communicated. The system divides the liquid at the outlet of the low-temperature liquid mixture storage tank into two parts, and a part of the low-temperature liquid is directly pressurized to high pressure by a liquid pump without passing through the evaporator and the compressor, and then is mixed with high-pressure high-temperature gas pressurized and heated by the compressor, so that the density of the high-pressure high-temperature gas is further increased. The system is a high-efficiency energy storage system, which can solve the problem of large occupied space of compressed air energy storage, does not introduce low-temperature cooling, and expands the application range of the compressed air energy storage, is helpful for the development and utilization of new energy, and relieves the impact of unstable power supply on the power grid.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy storage systems, and particularly relates to a shunt type liquid CO2 mixture energy storage system and method. BACKGROUND

[0002] With the increase of new energy, especially wind power and solar photovoltaic power generation, the impact of new energy power generation on the power grid is becoming greater and greater. In order to solve this problem, the state encourages the research in the direction of photovoltaic energy storage, wind power energy storage, energy storage peak shaving power station and the like. Although there are many forms of energy storage, such as pumped storage, battery energy storage, compressed air energy storage, heat storage, flywheel energy storage and the like. However, at present, only compressed air energy storage, heat storage and pumped storage are suitable for large-scale energy storage. Although battery energy storage has the highest efficiency, the cost is too high, and it is suitable for small and compact applications such as new energy vehicles, but it is not suitable for large-scale energy storage of power station level. Flywheel energy storage is suitable for frequency modulation which requires fast response, and is also not suitable for large-scale energy storage of power station level. Compared with compressed air energy storage, pumped storage and heat storage, pumped storage has the lowest cost and relatively high efficiency, but the disadvantage is that it needs to build a reservoir, and is only suitable for construction in areas rich in water resources such as rivers and lakes. Heat storage is a rising energy storage method in recent years, and is widely used in the field of solar thermal power generation. However, heat storage cannot be used alone, but is used as a supporting system for solar power generation system. If used as a separate energy storage power station, the cost is relatively high at present. Compressed air energy storage is another energy storage method comparable to pumped storage.

[0003] Compressed air energy storage has successively experienced the development process of supplemental combustion compressed air energy storage power station and heat storage compressed air energy storage power station, and is currently developing towards liquefied compressed air energy storage power station and supercritical compressed air energy storage power station. The traditional supplemental combustion compressed air energy storage power station and heat storage compressed air energy storage power station need to store a large amount of compressed air, and generally choose special topography such as natural caves, abandoned mines, underground caves and aquifers to store compressed air. The newly built heat storage compressed air energy storage power stations in China mostly store compressed air in the form of ground storage tanks and pipeline gas storage. There are also designs of underwater airbags for storing compressed air abroad. However, these storage methods all have the problems of large occupation of land and high investment. The storage space of the most advanced liquefied compressed air energy storage and supercritical compressed air energy storage can theoretically be reduced to one twentieth of the original, but these two technologies involve low-temperature cooling technology, which needs to cool the air to below -200℃ and -196℃. The deep cooling technology is difficult and has high investment. That is, these two new technologies introduce new technical difficulties while solving the problem of compressed air storage space. SUMMARY

[0004] The present application aims at overcoming the above-mentioned defects of the prior art, and provides a shunt type liquid CO2 mixture energy storage system and method to solve the problem of large occupation of space by compressed air energy storage in the prior art, and to introduce the problem of low-temperature cooling.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A shunt type liquid CO2 mixture energy storage system comprises a low-temperature liquid mixture storage tank, a mixer and an evaporator, wherein the low-temperature liquid mixture storage tank stores a compressed liquid CO2 mixture.

[0007] The outlet of the low-temperature liquid mixture storage tank is divided into two branches, i.e., a first branch and a second branch, the two ends of the first branch are connected to the bottom of the low-temperature liquid mixture storage tank and the mixer respectively, and the two ends of the second branch are connected to the top of the low-temperature liquid mixture storage tank and the cold side inlet of the evaporator respectively, the cold side outlet of the evaporator is connected to a compressor, and the outlet of the compressor is connected to the inlet of the mixer.

[0008] The outlet of the compressor is connected to a high-temperature mixture storage tank, the outlet of the high-temperature mixture storage tank is connected to a turbine, and the outlet of the turbine is connected to the inlet of the low-temperature liquid mixture storage tank.

[0009] Further improvements of the present application are as follows:

[0010] Preferably, the first branch is provided with a liquid pump before the mixer.

[0011] Preferably, a condenser is arranged between the turbine and the low-temperature liquid mixture storage tank.

[0012] Preferably, the compressed liquid CO2 mixture is a mixture of CO2-dimethyl carbonate, CO2-toluene or CO2-benzene.

[0013] Preferably, the density of the compressed liquid CO2 mixture stored in the low-temperature liquid mixture storage tank is greater than the density of the high-temperature and high-pressure mixture stored in the high-temperature mixture storage tank.

[0014] A kind of energy storage method of the above-mentioned shunt type liquid CO2 Mixture energy storage system, during energy storage process, the compressed liquid CO2 Mixture is heated after passing through evaporator and becomes gaseous, gaseous enters compressor and is pressurized into high-temperature high-pressure mixed gas;Mixed gas and compressed liquid CO2 Mixture are mixed in mixer to form high-temperature high-pressure mixture, and high-temperature high-pressure mixture is stored in high-temperature mixture storage tank;The temperature and density of high-temperature high-pressure mixture are controlled by two fluid flow, when the temperature of high-temperature high-pressure mixture is higher than the set value, increase the flow of liquid pump, reduce temperature, while density increases;When the temperature of high-temperature high-pressure mixture is lower than the set value, reduce the flow of liquid pump, increase temperature, while density decreases.

[0015] Preferably, during energy release process, high-temperature high-pressure mixture in high-temperature mixture storage tank enters turbine, turbine drives generator to generate electricity, and outputs electric energy;High-temperature high-pressure mixture after work is stored in low-temperature liquid mixture storage tank.

[0016] Preferably, high-temperature high-pressure mixture after work is cooled in condenser, and high-temperature high-pressure mixture becomes liquid, and the liquid is stored in low-temperature liquid mixture storage tank.

[0017] Compared with prior art, the present application has the following beneficial effects:

[0018] The application discloses a shunt type liquid CO2 Mixture energy storage system, which comprises a low-temperature liquid mixture storage tank, an evaporator, a compressor, a mixer, a high-temperature mixture storage tank and a turbine which are sequentially connected. The system divides the liquid at the outlet of the low-temperature liquid mixture storage tank into two parts, pressurizes a part of the low-temperature liquid to high pressure through a liquid pump without passing through the evaporator and the compressor, and then mixes the high-pressure low-temperature liquid with high-temperature high-pressure gas pressurized and heated by the compressor, so that the density of the high-temperature high-pressure gas is further increased. The system is a high-efficiency energy storage system, which can solve the problem of large occupation space of compressed air energy storage, does not introduce low-temperature cooling, expands the application range of compressed air energy storage, helps the development and utilization of new energy, and relieves the impact of unstable power supply on the power grid.

[0019] Further, a liquid pump is arranged in front of the mixer, so that the low-temperature liquid can be pressurized to high pressure by the liquid pump.

[0020] Further, the condenser between the turbine and the low-temperature liquid mixture storage tank can further release the heat in the high-temperature high-pressure mixture after work.

[0021] The application also discloses a method for storing energy of the shunt type liquid CO2 mixture energy storage system, which adopts a shunt mixing design. In the energy storage process, the low-temperature liquid mixture is divided into two parts. One part passes through an evaporator and a compressor to form a high-temperature and high-pressure gas. The high-temperature and high-pressure gas is mixed with the low-temperature liquid to form a high-temperature and high-pressure mixture. Compared with the compressed single-phase gaseous working medium (for example, compressed air) energy storage, the method solves the defect of the traditional compressed gas working medium energy storage system which needs a large amount of storage space. Compared with the compressed liquid working medium (for example, liquefied compressed air or liquefied compressed pure CO2), since the condensation temperature of the CO2 mixture is relatively high, the technical difficulty of low-temperature cooling of the new generation of liquefied compressed air energy storage system is avoided. At the same time, since there are two paths for pressure increase in the energy storage process, one path is evaporated into a gaseous state through the evaporator, which can ensure that there is no liquefaction in the compressor, and the other path directly increases the pressure of the liquid, which can effectively solve the phase separation of the low-temperature liquid mixture in the storage process. Even if phase separation occurs, the liquid working medium is pressurized by a liquid pump, and the gaseous working medium is pressurized by a compressor, which will not damage the rotating machinery. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 An example 1 of the system of the application is shown in the schematic diagram.

[0023] In the schematic diagram, 1 is a low-temperature liquid mixture storage tank, 2 is a liquid pump, 3 is an evaporator, 4 is a compressor, 5 is a mixer, 6 is a high-temperature mixture storage tank, 7 is a turbine, 8 is a condenser, 9 is a first branch, and 10 is a second branch. DETAILED DESCRIPTION

[0024] The application will be further described in detail below with reference to the accompanying drawings:

[0025] In the description of the application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the application; the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance; in addition, unless otherwise explicitly specified and limited, the terms "mounting", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, or it can be a detachable connection; it can be directly connected, or indirectly connected through an intermediate medium; it can be the communication between two elements inside. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0026] The application discloses a shunt type liquid CO2 mixture energy storage system, which comprises a low-temperature liquid mixture storage tank 1, a liquid pump 2, an evaporator 3, a compressor 4, a mixer 5, a high-temperature mixture storage tank 6, a turbine 7 and a condenser 8.

[0027] The outlet of the low-temperature liquid mixture storage tank 1 is branched into two paths, namely a first branch 9 connected from the top and a second branch 10 connected from the bottom, the second branch 10 is connected with the inlet of the liquid pump 2, the first branch 9 is connected with the cold side inlet of the evaporator 3, the cold side outlet of the evaporator 3 is connected with the inlet of the compressor 4, the outlet of the compressor 4 is connected with the inlet of the mixer 5, the outlet of the liquid pump 2 is also connected with the inlet of the mixer 5, the outlet of the mixer 5 is connected with the inlet of the high-temperature mixture storage tank 6, the outlet of the high-temperature mixture storage tank 6 is connected with the inlet of the turbine 7, the outlet of the turbine 7 is connected with the hot side inlet of the condenser 8, and the hot side outlet of the condenser 8 is connected with the inlet of the low-temperature liquid mixture storage tank 1.

[0028] After the compressed liquid CO2 mixture energy storage technology is adopted, the mixture can be cooled and condensed into liquid near the ambient temperature without low-temperature cooling. Therefore, the low-temperature and low-pressure CO2 mixture can be stored in the form of liquid with high density, and the storage space is small. Meanwhile, the density of the CO2 mixture is also relatively large under the high-pressure state with 20 MPa as an example, but the density of part of the CO2 mixture is still much smaller than the density of the low-temperature liquid, and the storage space of the high-pressure mixture is much larger than the space required by the compressed air storage of the same scale. Taking the CO2-dimethyl carbonate, CO2-toluene and CO2-benzene mixtures as examples, the density of the high-pressure and high-temperature mixture is about 600 kg / m 3 , which is only about half of the liquid density.

[0029] The system is branched into two paths at the outlet of the low-temperature liquid mixture storage tank 1, one path enters the evaporator 3 to be heated into gaseous state and then enters the compressor 4 to be pressurized to high temperature and high pressure, and the other path enters the liquid pump 2 to be directly pressurized. The mixture pressurized by the liquid pump is still liquid, and the temperature rise is very small, which is within 10 DEG C in the example. After the low-temperature and high-pressure mixture liquid is mixed with the high-temperature and high-pressure gaseous mixture, the pressure is still high, but the temperature is significantly lower than that of the mixture working medium at the outlet of the compressor. Due to the temperature reduction, the density of the high-pressure mixture working medium will be further increased, and the density of the CO2-dimethyl carbonate, CO2-toluene and CO2-benzene mixtures can be increased to about 670 kg / m 3 , so that the mixture can be stored in the high-temperature mixture storage tank 6.

[0030] The working principle of the application is as follows:

[0031] A shunt type liquid CO2 mixture energy storage system, when there is surplus electricity to be stored, the liquid mixture working substance stored in the low temperature liquid mixture storage tank 1 is divided into two paths, one path enters the liquid pump 2 and is directly pressurized, the temperature of the pressurized liquid does not rise much, for example, the temperature rises within 10 DEG C. The other path first enters the evaporator 3 to absorb heat and become gaseous substance, the gaseous substance enters the compressor 4 and is pressurized to high temperature and high pressure. Then the high temperature and high pressure gas and the high pressure and low temperature liquid at the outlet of the liquid pump enter the mixer 5 to mix, forming a high temperature and high pressure mixture, which is in a supercritical state, the temperature of the original main flow of high temperature and high pressure gas is lowered and the density is increased. Then it is stored in the high temperature mixture storage tank 6, completing the energy storage process.

[0032] When the output electric energy is needed, the high temperature and high pressure mixture working substance stored in the high temperature mixture storage tank 6 flows into the turbine 7, the turbine 7 does work to output electric energy, the exhaust gas discharged from the turbine enters the hot side of the condenser 8 to release heat, at this time the mixture working substance has become liquid, and then is stored in the low temperature liquid mixture storage tank 1. The energy release process is completed.

[0033] The above only describes the preferred embodiments of the present application and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A split-flow liquid CO2 mixture energy storage system, characterized in that, include: The cryogenic liquid mixture storage tank (1), mixer (5) and evaporator (3) are provided, wherein the cryogenic liquid mixture storage tank (1) stores a mixture of compressed liquid CO2; The outlet of the cryogenic liquid mixture storage tank (1) is divided into two branches, namely the first branch (9) and the second branch (10). The two ends of the first branch (9) are connected to the bottom of the cryogenic liquid mixture storage tank (1) and the mixer (5), respectively. The two ends of the second branch (10) are connected to the top of the cryogenic liquid mixture storage tank (1) and the cold side inlet of the evaporator (3), respectively. The cold side outlet of the evaporator (3) is connected to the compressor (4), and the outlet of the compressor (4) is connected to the inlet of the mixer (5). The outlet of the compressor (4) is connected to a high-temperature mixture storage tank (6), the outlet of the high-temperature mixture storage tank (6) is connected to a turbine (7), and the outlet of the turbine (7) is connected to the inlet of the low-temperature liquid mixture storage tank (1). The first branch (9) is equipped with a liquid pump (2) in front of the mixer (5); The density of the compressed liquid CO2 mixture stored in the low-temperature liquid mixture storage tank (1) is greater than the density of the high-temperature and high-pressure mixture in the high-temperature mixture storage tank (6).

2. The split-flow liquid CO2 mixture energy storage system according to claim 1, characterized in that, A condenser (8) is provided between the turbine (7) and the cryogenic liquid mixture storage tank (1).

3. The split-flow liquid CO2 mixture energy storage system according to claim 1, characterized in that, The mixture of compressed liquid CO2 is a mixture of CO2-dimethyl carbonate, CO2-toluene, or CO2-benzene.

4. An energy storage method for a split-flow liquid CO2 mixture energy storage system as described in claim 1, characterized in that, During the energy storage process, the mixture of compressed liquid CO2 is heated by the evaporator (3) and becomes gaseous. The gaseous state enters the compressor (4) and is pressurized into a high-temperature and high-pressure mixed gas. The mixture of mixed gas and compressed liquid CO2 is mixed in the mixer (5) to form a high-temperature and high-pressure mixture. The high-temperature and high-pressure mixture is stored in the high-temperature mixture storage tank (6). The temperature and density of the high-temperature and high-pressure mixture are controlled by the flow rates of two fluids. When the temperature of the high-temperature and high-pressure mixture is higher than the set value, the flow rate of the liquid pump (2) is increased to decrease the temperature and increase the density. When the temperature of the high-temperature and high-pressure mixture is lower than the set value, the flow rate of the liquid pump (2) is decreased to increase the temperature and decrease the density.

5. The energy storage method for a split-flow liquid CO2 mixture energy storage system according to claim 4, characterized in that, During the energy release process, the high-temperature and high-pressure mixture in the high-temperature mixture storage tank (6) enters the turbine (7), and the turbine (7) drives the generator to generate electricity and output electrical energy; the high-temperature and high-pressure mixture after doing work is stored in the low-temperature liquid mixture storage tank (1).

6. The energy storage method for a split-flow liquid CO2 mixture energy storage system according to claim 4, characterized in that, After the high-temperature and high-pressure mixture is cooled in the condenser (8), it becomes a liquid and is stored in the low-temperature liquid mixture storage tank (1).

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