Normal temperature liquid compressed carbon dioxide mixed working medium energy storage system and method

Abstract

The application provides a normal-temperature liquid compressed carbon dioxide mixed working medium energy storage system and method, which comprises that one outlet of a compressor is connected with a hot side inlet of an energy storage heat exchanger in sequence, and another outlet of the compressor is connected with a hot side inlet of a regenerator; a hot side outlet of the energy storage heat exchanger is connected with a high-pressure storage tank, an energy release heat exchanger and a hot side inlet of a cooler in sequence, and a cold side outlet of the regenerator is connected with an inlet of the compressor; an outlet of a cold storage device is connected with an inlet of the energy storage heat exchanger, a heat storage device, a heat pump and the cold storage device in sequence, and the heat pump is connected with the cooler and the energy release heat exchanger respectively. The energy storage system can increase the compression work of unit working medium, reduce the working medium flow and the storage amount of the working medium, and further reduce the volume of the storage tank and improve the energy storage density by throttling and depressurizing the liquid low-pressure mixed working medium, heating and gasifying the working medium and driving the compressor to compress the gaseous working medium by using the surplus power.

Description

Technical Field

[0001] This invention belongs to the field of energy storage technology and relates to an energy storage system and method using a mixed working fluid of room temperature liquid compressed carbon dioxide. Background Technology

[0002] To reduce pollutant and carbon dioxide emissions, my country has rapidly developed renewable energy, with the installed capacity of new energy sources such as photovoltaic power generation and wind power growing rapidly. However, new energy sources are greatly affected by weather, resulting in intermittent and unstable power output, which can affect the safe and stable operation of the power grid when connected to the grid. Therefore, it is necessary to combine new energy with energy storage technology to store unstable and surplus renewable energy power and output it stably when needed, thereby solving the problem of large-scale renewable energy consumption.

[0003] Carbon dioxide is non-toxic, pollution-free, physically stable, abundant, and readily available. Its critical point is moderate at 31.1℃ and 7.38MPa, and it is easily compressible. Furthermore, supercritical carbon dioxide has a high density, which can significantly reduce equipment volume, making the system more compact. Therefore, mechanical energy storage systems using carbon dioxide as the working medium have been proposed for large-scale energy storage. However, for existing compressed transcritical carbon dioxide energy storage systems, the low critical temperature of the working medium makes it difficult to condense in a room-temperature cooling medium, requiring additional energy for cooling, thus reducing energy storage efficiency. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a room-temperature liquid compressed carbon dioxide mixed working fluid energy storage system and method. By mixing other substances into carbon dioxide, the critical temperature of the mixed working fluid is increased, so that the mixed working fluid can be condensed by a room-temperature cooling medium and stored in liquid state, effectively solving the problem of low energy storage density.

[0005] This invention is achieved through the following technical solution:

[0006] A room-temperature liquid compressed carbon dioxide mixed working fluid energy storage system includes,

[0007] Compressors, energy storage heat exchangers, high-pressure storage tanks, energy release heat exchangers, turbines, coolers, low-pressure storage tanks, regenerators, thermal storage tanks, cold storage tanks, and heat pumps;

[0008] The compressor has two outlets. One outlet is connected to the hot-side inlet of the energy storage heat exchanger, and the other outlet is connected to the hot-side inlet of the regenerator. The hot-side outlet of the energy storage heat exchanger is connected to the inlets of the high-pressure storage tank, the energy release heat exchanger, and the turbine. The turbine outlet is connected to the hot-side inlet of the cooler. The hot-side outlet of the cooler is connected to the cold-side inlets of the low-pressure storage tank and the regenerator. The cold-side outlet of the regenerator is connected to the inlet of the compressor. The outlet of the cold storage unit is connected to the cold-side inlet of the energy storage heat exchanger. The cold-side outlet of the energy storage heat exchanger is connected to the inlet of the heat storage unit. The outlet of the heat storage unit is connected to the inlets of the heat pump and the cold storage unit. The heat pump is connected to both the cooler and the energy release heat exchanger.

[0009] Preferably, the heat pump has two heat absorption ends, wherein the inlet of one heat absorption end of the heat pump is connected to the outlet of the heat storage device, and the outlet of the other heat absorption end of the heat pump is connected to the inlet of the cold storage device; the inlet of the other heat absorption end of the heat pump is connected to the cold side outlet of the cooler, and the outlet of the other heat absorption end of the heat pump is connected to the cold side inlet of the cooler.

[0010] Preferably, the heat pump's heat release end inlet is connected to the heat side outlet of the energy release heat exchanger, and the heat pump's heat release end outlet is connected to the heat side inlet of the energy release heat exchanger.

[0011] Preferably, a throttling valve is provided between the low-pressure storage tank and the regenerator.

[0012] Preferably, the carbon dioxide mixed working medium includes carbon dioxide and a doped working medium; the doped working medium includes at least one of SF6, R161 and R32.

[0013] Preferably, the doped working fluid accounts for 10%-40% of the mass of the carbon dioxide mixed working fluid.

[0014] Preferably, the carbon dioxide mixture stored in both the high-pressure and low-pressure storage tanks is in liquid form.

[0015] Preferably, the high-pressure storage tank has a working pressure of 15-30 MPa and a working temperature of 25-40°C.

[0016] Preferably, the low-pressure storage tank has an operating pressure of 6-8 MPa and an operating temperature of 25℃-40℃.

[0017] A method for energy storage using a mixture of compressed liquid carbon dioxide and ambient temperature working fluid, comprising:

[0018] During energy storage, the low-pressure carbon dioxide mixture in the low-pressure storage tank is heated by the high temperature at the inlet of the regenerator and compressor, becoming a gaseous carbon dioxide mixture. It then enters the compressor for compression, pressure increase, and temperature rise, before being divided into two paths. The gaseous mixture is condensed and liquefied in the regenerator and the energy storage heat exchanger, respectively, and then stored in the high-pressure storage tank. The cold storage medium in the cold accumulator absorbs heat in the energy storage heat exchanger and then enters the heat accumulator to store heat.

[0019] During energy release, the high-pressure carbon dioxide mixture in the high-pressure storage tank is first heated in the energy release heat exchanger, then enters the turbine to do work and generate electricity to release energy; the carbon dioxide mixture gas discharged from the turbine is cooled into liquid in the cooler and stored in the low-pressure storage tank; the heat pump extracts heat from the heat storage medium in the heat accumulator and the gaseous carbon dioxide mixture discharged from the cooler, and converts it into high-temperature heat, which is used to heat the carbon dioxide mixture in the energy release heat exchanger.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] This invention provides a room-temperature liquid compressed carbon dioxide mixed working fluid energy storage system and method. The carbon dioxide mixed working fluid energy storage method increases the critical temperature of the mixed working fluid by mixing other substances into the carbon dioxide, allowing the mixed working fluid to be condensed by a room-temperature cooling medium and stored in a liquid state, effectively solving the problem of low energy storage density. Simultaneously, the energy storage system of this invention increases the compression work per unit working fluid and reduces the working fluid flow rate by throttling and depressurizing the low-pressure liquid mixed working fluid and heating it to vaporize. The surplus electricity then drives a compressor to compress the gaseous working fluid, increasing the compression work per unit working fluid, reducing the working fluid flow rate, and thus reducing the amount of working fluid stored, thereby reducing the tank volume and increasing the energy storage density. Furthermore, the heat pump of this invention absorbs low-temperature heat from turbine exhaust and the heat storage medium, converting it into high-temperature heat to heat the working fluid at the turbine inlet, increasing the turbine inlet temperature, reducing system energy loss, and improving system energy storage efficiency.

[0022] Furthermore, the present invention uses a mixed working fluid with a high critical temperature, which can be cooled into a liquid state at room temperature for storage, thereby increasing the energy storage density.

[0023] Furthermore, the system of the present invention has the advantages of small device size, simple and compact system, and high flexibility. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a room-temperature liquid compressed carbon dioxide mixed working fluid energy storage system according to the present invention.

[0025] In the diagram: 1. Compressor; 2. Energy storage heat exchanger; 3. High-pressure storage tank; 4. Energy release heat exchanger; 5. Turbine; 6. Cooler; 7. Low-pressure storage tank; 8. Throttling valve; 9. Regenerator; 10. Heat storage tank; 11. Cold storage tank; 12. Heat pump. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0027] A room-temperature liquid compressed carbon dioxide mixed working fluid energy storage system includes,

[0028] Compressor 1, energy storage heat exchanger 2, high pressure storage tank 3, energy release heat exchanger 4, turbine 5, cooler 6, low pressure storage tank 7, regenerator 9, heat storage tank 10, cold storage tank 11, and heat pump 12;

[0029] The compressor 1 has two outlets. One outlet of the compressor 1 is connected to the hot side inlet of the energy storage heat exchanger 2, and the other outlet of the compressor 1 is connected to the hot side inlet of the regenerator 9. The hot side outlet of the energy storage heat exchanger 2 is connected to the inlets of the high-pressure storage tank 3, the energy release heat exchanger 4, and the turbine 5. The outlet of the turbine 5 is connected to the hot side inlet of the cooler 6. The hot side outlet of the cooler 6 is connected to the cold side inlet of the low-pressure storage tank 7 and the regenerator 9. The cold side outlet of the regenerator 9 is connected to the inlet of the compressor 1.

[0030] The outlet of the cold storage 11 is connected to the cold side inlet of the energy storage heat exchanger 2, the cold side outlet of the energy storage heat exchanger 2 is connected to the inlet of the heat storage 10, the outlet of the heat storage 10 is connected in sequence to the inlet of the heat pump 12 and the cold storage 11, and the heat pump 12 is connected to the cooler 6 and the energy release heat exchanger 4 respectively.

[0031] A heat pump is a device that transfers heat energy from a low-temperature heat source to a high-temperature heat source to achieve cooling and heating. When a heat pump is working, it consumes a portion of its own energy, extracting energy stored in the ambient medium and utilizing it by raising the temperature through a heat transfer fluid circulation system. The work consumed by the entire heat pump device is only a small fraction of the output work; therefore, using heat pump technology can save a significant amount of high-grade energy. The heat pump 12 has two heat absorption ends. One heat absorption end inlet is connected to the outlet of the heat accumulator 10, and the other heat absorption end outlet is connected to the inlet of the cold accumulator 11. The other heat absorption end inlet is connected to the cold-side outlet of the cooler 6, and the other heat absorption end outlet is connected to the cold-side inlet of the cooler 6.

[0032] The heat pump 12's heat release end inlet is connected to the heat side outlet of the energy release heat exchanger 4, and the heat pump 12's heat release end outlet is connected to the heat side inlet of the energy release heat exchanger 4.

[0033] In a preferred embodiment of the present invention, the carbon dioxide mixed working fluid stored in the high-pressure storage tank 3 and the low-pressure storage tank 7 is in liquid state. The liquid working fluid has a high density, which can reduce the volume of the high-pressure storage tank 3 and the low-pressure storage tank 7 and increase the energy storage density.

[0034] In a preferred embodiment of the present invention, a throttling valve 8 is provided between the low-pressure storage tank 7 and the regenerator 9. The throttling valve 8 reduces the pressure of the working fluid, and a portion of the working fluid is diverted from the outlet of the compressor 1 into the regenerator 9 to heat the throttled working fluid. The gaseous working fluid has a large unit compression work, which can reduce the working fluid flow rate, thereby reducing the volume of the stored working fluid and increasing the energy storage density.

[0035] In a preferred embodiment of the present invention, the heat pump 12 extracts heat from the medium in the heat storage tank 10 and the exhaust gas from the turbine 5, and then releases heat in the energy release heat exchanger 4 to heat the working fluid, which can reduce energy loss and increase the inlet temperature of the turbine 5, thereby effectively improving the energy storage efficiency.

[0036] In a preferred embodiment of the present invention, the high-pressure storage tank 3 has an operating pressure of 15–30 MPa and an operating temperature of 25–40°C. The low-pressure storage tank 7 has an operating pressure of 6–8 MPa and an operating temperature of 25–40°C.

[0037] In a preferred embodiment of the present invention, the carbon dioxide mixed working fluid comprises carbon dioxide and a dopant; the dopant includes at least one of SF6 (sulfur hexafluoride), R161 (fluoroethane), and R32 (difluoromethane). The dopant accounts for 10%-40% of the mass of the carbon dioxide mixed working fluid. R32, with the molecular formula CH2F2, is a non-explosive, non-toxic, flammable, and safe refrigerant. R32's energy-saving, environmentally friendly, and ozone-depleting properties have made it a rising star among modern refrigerants. SF6 (sulfur hexafluoride), used as a refrigerant in the refrigeration industry, has a cooling range of -45°C to 0°C.

[0038] A method for energy storage using a mixture of compressed liquid carbon dioxide and ambient temperature working fluid, comprising:

[0039] During energy storage, the low-pressure carbon dioxide mixture in the low-pressure storage tank 7 is heated by the high temperature at the inlet of the regenerator 9 and the compressor 1, becoming a gaseous carbon dioxide mixture. It then enters the compressor 1 for compression, pressure increase, and temperature increase, and is divided into two paths. It is condensed and liquefied in the regenerator 9 and the energy storage heat exchanger 2 respectively, and then stored in the high-pressure storage tank 3. The cold storage medium in the cold accumulator 11 absorbs heat in the energy storage heat exchanger 2 and then enters the heat accumulator 10 to store heat.

[0040] During energy release, the high-pressure carbon dioxide mixture in the high-pressure storage tank 3 is first heated in the energy release heat exchanger 4, and then enters the turbine 5 to do work and generate electricity to release energy. The carbon dioxide mixture gas discharged from the turbine 5 is cooled into liquid in the cooler 6 and stored in the low-pressure storage tank 7. The heat pump 12 extracts heat from the heat storage medium in the heat accumulator 10 and the carbon dioxide mixture discharged from the cooler 6, and converts it into high-temperature heat, which is then used to heat the carbon dioxide mixture in the energy release heat exchanger 4.

[0041] The specific implementation process is as follows:

[0042] like Figure 1 As shown, an ambient temperature liquid compressed carbon dioxide mixed working fluid energy storage system includes an energy storage system, an energy release system, and an energy storage system.

[0043] The energy storage system includes a low-pressure storage tank 7, a throttle valve 8, a regenerator 9, a compressor 1, an energy storage heat exchanger 2, and a high-pressure storage tank 3. The outlet of the low-pressure storage tank 7 is connected to the inlet of the throttle valve 8, the outlet of the throttle valve 8 is connected to the cold side inlet of the regenerator 9, the cold side outlet of the regenerator 9 is connected to the inlet of the compressor 1, and the outlet of the compressor 1 is divided into two paths: one path is connected to the hot side inlet of the energy storage heat exchanger 2, and the hot side outlet of the energy storage heat exchanger 2 is connected to the inlet of the high-pressure storage tank 3; the other path is connected to the hot side inlet of the regenerator 9, and the hot side outlet of the regenerator 9 is connected to the inlet of the high-pressure storage tank 3.

[0044] The energy release system includes a high-pressure storage tank 3, an energy release heat exchanger 4, a turbine 5, a cooler 6, and a low-pressure storage tank 7; the outlet of the high-pressure storage tank 3 is connected to the inlet of the energy release heat exchanger 4, the outlet of the energy release heat exchanger 4 is connected to the inlet of the turbine 5, the outlet of the turbine 5 is connected to the hot side inlet of the cooler 6, and the hot side outlet of the cooler 6 is connected to the low-pressure storage tank 7.

[0045] The energy storage system includes an energy storage heat exchanger 2, a heat storage tank 10, a cold storage tank 11, a heat pump 12, an energy release heat exchanger 4, and a cooler 6. The outlet of the cold storage tank 11 is connected to the cold side inlet of the energy storage heat exchanger 4, the cold side outlet of the energy storage heat exchanger 4 is connected to the inlet of the heat storage tank 10, the outlet of the heat storage tank 10 and the inlet of the cold storage tank 11 are respectively connected to the heat absorption end of the heat pump 12, the cold side inlet and the cold side outlet of the cooler 6 are respectively connected to the heat absorption end of the heat pump 12, and the heat release end of the heat pump 12 is connected to the hot side inlet and the hot side outlet of the energy release heat exchanger 4.

[0046] like Figure 1As shown, an operation method of a room-temperature liquid compressed carbon dioxide mixed working fluid energy storage system is described. During energy storage, the low-pressure carbon dioxide in the low-pressure storage tank 7 is throttled and depressurized through the throttle valve 8, and part of the working fluid is vaporized. Then, after being heated by the higher-temperature working fluid at the outlet of the compressor 1 through the regenerator 9, it becomes a gaseous working fluid and enters the compressor 1 again. The surplus electricity drives the compressor 1 to compress, pressurize, and heat the working fluid, which is then divided into two paths and condensed and liquefied in the regenerator 9 and the energy storage heat exchanger 2, respectively, and then stored in the high-pressure storage tank 3. The medium in the cold accumulator 11 absorbs heat in the energy storage heat exchanger 2 and then enters the heat accumulator 10.

[0047] During energy release, the high-pressure carbon dioxide in the high-pressure storage tank 2 is first heated in the energy release heat exchanger 4, and then enters the turbine 5 to do work and generate electricity to release energy; the exhaust gas from the turbine 5 is cooled into liquid in the cooler 6 and stored in the low-pressure storage tank 7; the heat pump 12 extracts heat from the heat storage medium in the heat accumulator 10 and the exhaust gas from the cooler 6, and converts it into high-temperature heat, which is used to heat the working medium in the energy release heat exchanger 4.

Claims

1. A room-temperature liquid compressed carbon dioxide mixed working fluid energy storage system, characterized in that, include, Compressor (1), energy storage heat exchanger (2), high pressure tank (3), energy release heat exchanger (4), turbine (5), cooler (6), low pressure tank (7), regenerator (9), heat storage tank (10), cold storage tank (11) and heat pump (12). The compressor (1) has two outlets. One outlet of the compressor (1) is connected to the hot-side inlet of the energy storage heat exchanger (2), and the other outlet of the compressor (1) is connected to the hot-side inlet of the regenerator (9). The hot-side outlet of the energy storage heat exchanger (2) is connected in sequence to the inlets of the high-pressure storage tank (3), the energy release heat exchanger (4), and the turbine (5). The outlet of the turbine (5) is connected to the hot-side inlet of the cooler (6). The hot-side outlet of the cooler (6) is connected in sequence to the inlets of the low-pressure storage tank (7). The cold side inlet of the regenerator (9) is connected to the cold side outlet of the regenerator (9) and the inlet of the compressor (1); the outlet of the cold storage tank (11) is connected to the cold side inlet of the energy storage heat exchanger (2), the cold side outlet of the energy storage heat exchanger (2) is connected to the inlet of the heat storage tank (10), the outlet of the heat storage tank (10) is connected to the inlet of the heat pump (12) and the cold storage tank (11) in sequence, and the heat pump (12) is connected to the cooler (6) and the energy release heat exchanger (4) respectively. The heat pump (12) has two heat absorption ends. The inlet of one heat absorption end of the heat pump (12) is connected to the outlet of the heat storage tank (10), and the outlet of the other heat absorption end of the heat pump (12) is connected to the inlet of the cold storage tank (11). The inlet of the other heat absorption end of the heat pump (12) is connected to the cold side outlet of the cooler (6), and the outlet of the other heat absorption end of the heat pump (12) is connected to the cold side inlet of the cooler (6). The carbon dioxide mixed working medium includes carbon dioxide and a doped working medium; the doped working medium includes at least one of SF6, R161 and R32. The doped working fluid accounts for 10%-40% of the mass of the carbon dioxide mixed working fluid.

2. The ambient temperature liquid compressed carbon dioxide mixed working fluid energy storage system according to claim 1, characterized in that, The heat pump (12) has its heat release end inlet connected to the heat side outlet of the heat exchanger (4), and the heat release end outlet of the heat pump (12) is connected to the heat side inlet of the heat exchanger (4).

3. The ambient temperature liquid compressed carbon dioxide mixed working fluid energy storage system according to claim 1, characterized in that, A throttling valve (8) is provided between the low-pressure storage tank (7) and the regenerator (9).

4. The ambient temperature liquid compressed carbon dioxide mixed working fluid energy storage system according to claim 1, characterized in that, The carbon dioxide mixture stored in the high-pressure tank (3) and the low-pressure tank (7) is in liquid form.

5. The ambient temperature liquid compressed carbon dioxide mixed working fluid energy storage system according to claim 1, characterized in that, The high-pressure storage tank (3) has a working pressure of 15~30MPa and a working temperature of 25℃~40℃.

6. The ambient temperature liquid compressed carbon dioxide mixed working fluid energy storage system according to claim 1, characterized in that, The low-pressure storage tank (7) has a working pressure of 6~8MPa and a working temperature of 25℃~40℃.

7. A method for energy storage using a mixture of compressed carbon dioxide and liquid at room temperature, characterized in that, The carbon dioxide mixed working fluid energy storage system according to any one of claims 1-6 includes, During energy storage, the low-pressure carbon dioxide mixture in the low-pressure storage tank (7) is heated by the high temperature at the inlet of the regenerator (9) and the compressor (1) to become a gaseous carbon dioxide mixture. Then, it enters the compressor (1) for compression, pressure increase and temperature increase. It is then divided into two paths and condensed and liquefied in the regenerator (9) and the energy storage heat exchanger (2) respectively, and then stored in the high-pressure storage tank (3). The cold storage medium in the cold storage tank (11) absorbs heat in the energy storage heat exchanger (2) and then enters the heat storage tank (10) to store heat. During energy release, the high-pressure carbon dioxide mixture in the high-pressure storage tank (3) is first heated in the energy release heat exchanger (4) and then enters the turbine (5) to do work and generate electricity to release energy. The carbon dioxide mixture gas discharged from the turbine (5) is cooled into liquid in the cooler (6) and stored in the low-pressure storage tank (7). The heat pump (12) extracts heat from the heat storage medium in the heat storage tank (10) and the gaseous carbon dioxide mixture discharged from the cooler (6) and converts it into high-temperature heat to heat the carbon dioxide mixture in the energy release heat exchanger (4).

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