A peak shaving device for coupling a coal power unit with a supercritical carbon dioxide energy storage system

Abstract

The present application belongs to the field of coal-fired power generation and energy storage technology, and particularly relates to a peak shaving device coupled with a supercritical carbon dioxide energy storage system of a coal-fired power unit. The present application uses supercritical carbon dioxide (sCO2) as an energy carrier to build a closed Brayton cycle comprising a compressor, a turbine, a heat exchanger and a storage tank, thereby improving the cycle thermal efficiency of the energy storage medium, avoiding the risks of solidification, leakage and corrosion of the working medium, and improving the safety of system operation. The device directly communicates the hot side inlet of the first heat exchanger with the inlet of the high-pressure cylinder of the coal-fired power unit, directly heats the sCO2 compressed by the compressor with high-temperature and high-pressure steam at the highest parameter of the boiler outlet, and does not need to be supplemented with heating. The waste heat of the sCO2 turbine exhaust is used to heat the feed water at the outlet of the deaerator and the condensate water at the outlet of the condensate water pump in sequence through the designed second and third heat exchangers, thereby reducing the amount of steam originally required to be extracted by the steam turbine and greatly increasing the power generation.

Description

Technical Field

[0001] This invention belongs to the field of coal-fired power generation and energy storage technology, specifically relating to a peak-shaving device that couples a coal-fired power unit with a supercritical carbon dioxide energy storage system. Background Technology

[0002] With the construction of new power systems, the installed capacity of new energy sources such as wind power and photovoltaics continues to increase. However, wind and solar energy are intermittent and fluctuating, and large-scale grid connection can have a significant impact on grid stability. To improve grid stability, it is necessary to configure energy storage systems on the generation side. However, building completely independent energy storage power stations (such as independent battery stations or independent compressed air energy storage) not only requires a large land area and high initial investment, but also fails to effectively utilize the existing thermal infrastructure of thermal power plants, resulting in resource waste. Therefore, to achieve deep peak shaving during off-peak periods and flexible capacity expansion during peak periods, while avoiding the construction of large independent energy storage islands, exploring peak shaving and capacity expansion technologies that can couple with existing coal-fired power unit thermal systems (such as feedwater and steam circuits) has received increasing attention.

[0003] Chinese patent CN223062505U discloses a peak-shaving and capacity-enhancing system suitable for supercritical power units. During off-peak hours, it organically integrates steam-molten salt energy storage technology and electrothermal molten salt energy storage technology to store excess heat and electricity in molten salt, reducing the power output of the thermal power unit. During peak hours, the stored high-temperature molten salt is used to generate supercritical steam, which, along with steam from the boiler, enters the turbine to expand and perform work, thereby increasing the unit's power output. This achieves bidirectional load regulation for supercritical thermal power generating units, significantly improving the unit's flexibility. However, this existing technology has the following two drawbacks: (1) This scheme relies on huge molten salt cold / hot storage tanks to store sensible heat. Molten salt working medium is prone to solidification at high temperature, resulting in a high risk of pipeline blockage and safety hazards of leakage and corrosion of equipment. In addition, its energy release process is essentially to use the heat of molten salt to generate steam to drive the steam turbine, which is still a traditional steam Rankine cycle. It is limited by the thermodynamic Carnot cycle and has a low energy conversion efficiency.

[0004] (2) During the energy storage phase, the scheme mainly relies on extracting boiler steam to heat molten salt. However, in order to reach the required energy release temperature, it is often necessary to configure a high-power electric heater for supplementary heating, resulting in a low overall round-trip efficiency of the system and increased operating costs. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a peak-shaving device that couples a coal-fired power unit with a supercritical carbon dioxide energy storage system, using supercritical carbon dioxide as the circulating working fluid to construct a closed energy storage / release cycle, thereby achieving safety, high efficiency and low cost of the peak-shaving device.

[0006] The technical solution adopted in this invention is as follows: A peak-shaving device coupled with a coal-fired power unit and a supercritical carbon dioxide energy storage system includes a coal-fired power unit, a carbon dioxide energy storage system, and a carbon dioxide energy release system. The coal-fired power unit includes a boiler, and a high-pressure cylinder, an intermediate-pressure cylinder, and a low-pressure cylinder connected coaxially; the coal-fired power unit is used to drive a first generator to generate electricity; the exhaust steam from the low-pressure cylinder passes sequentially through a condenser, a low-pressure heater assembly, and a high-pressure heater assembly before entering the boiler; a deaerator is provided between the low-pressure heater assembly and the high-pressure heater assembly; The carbon dioxide energy storage system includes a supercritical low-pressure carbon dioxide storage tank, a compressor, a first heat exchanger, and a supercritical high-pressure carbon dioxide storage tank connected in sequence; the hot-side inlet of the first heat exchanger is connected to the inlet of the high-pressure cylinder; the compressor is powered by an electric motor. The carbon dioxide energy release system includes a supercritical carbon dioxide high-pressure storage tank, a turbine, a second heat exchanger, a third heat exchanger, a cooler, and a supercritical carbon dioxide low-pressure storage tank connected in sequence. The cold side of the second heat exchanger is connected to the high-pressure heater assembly; the cold side of the third heat exchanger is connected to the low-pressure heater assembly; the turbine is used to drive a second generator to generate electricity; the cooler is located between the third heat exchanger and the supercritical carbon dioxide low-pressure storage tank and is used to further cool the carbon dioxide after heat exchange by the third heat exchanger.

[0007] Preferably, the low-pressure heater assembly includes a first low-pressure heater, a second low-pressure heater, a third low-pressure heater, and a fourth low-pressure heater connected in sequence.

[0008] Preferably, a condensate pump is installed on the cold-side inlet connecting pipe between the condenser and the first low-pressure heater.

[0009] Preferably, the high-pressure heater assembly includes a first high-pressure heater, a second high-pressure heater, and a third high-pressure heater connected in sequence.

[0010] Preferably, a water pump is provided in the pipeline connecting the deaerator and the cold-side inlet of the first high-pressure heater.

[0011] Preferably, the hot-side inlet of the first heat exchanger is connected to the inlet of the high-pressure cylinder, and the hot-side outlet of the first heat exchanger is connected to the cold-side outlet of the third high-pressure heater.

[0012] Preferably, the cold-side inlet of the second heat exchanger is connected to the outlet of the feed water pump, and the cold-side outlet of the second heat exchanger is connected to the cold-side outlet of the third high-pressure heater; the cold-side inlet of the third heat exchanger is connected to the outlet of the condensate pump, and the cold-side outlet of the third heat exchanger is connected to the cold-side outlet of the fourth low-pressure heater. The working principle of the above peak-shaving device is as follows: In normal operation, the steam from the boiler is sequentially output to the high-pressure cylinder, the medium-pressure cylinder, and the low-pressure cylinder, which together drive the first generator to generate electricity. The exhaust steam from the low-pressure cylinder is cooled into condensate by the condenser and then flows into the boiler through the low-pressure heater assembly and the high-pressure heater assembly. When the generator output is reduced, the carbon dioxide in the supercritical carbon dioxide low-pressure storage tank is transferred to the compressor. The electricity generated by the first generator drives the compressor to do work. After the compressor compresses the carbon dioxide to a preset pressure, it flows into the cold side of the first heat exchanger and exchanges heat with the high-temperature and high-pressure steam from the steam turbine. The heated carbon dioxide flows into the supercritical carbon dioxide high-pressure storage tank. When increasing generator output, carbon dioxide from the supercritical carbon dioxide high-pressure storage tank is fed into the turbine to perform work. After performing work, the carbon dioxide passes through the second and third heat exchangers, where it exchanges heat with the coal-fired power unit's feedwater and condensate to recover waste heat. It then enters the cooler for further cooling and is finally stored in the supercritical carbon dioxide low-pressure storage tank. The cold source for the second heat exchanger comes from the deaerator's outlet feedwater, and the cold source for the third heat exchanger comes from the condensate pump's outlet feedwater.

[0013] The beneficial effects obtained by adopting the above technical solution are as follows: (1) This invention uses supercritical carbon dioxide (sCO2) as an energy carrier to construct a closed Brayton cycle including a compressor, turbine, heat exchanger and storage tank, which improves the cycle thermal efficiency of the energy storage medium. At the same time, since sCO2 is gaseous at normal temperature and pressure, the risk of working fluid solidification blocking the pipeline, leakage and corrosion is avoided, which improves the safety of system operation.

[0014] (2) In the energy storage stage, the hot side inlet of the first heat exchanger is directly connected to the inlet of the high-pressure cylinder of the coal-fired power unit. The high-temperature and high-pressure steam with the highest parameters at the boiler outlet is used to directly heat the sCO2 after compression by the compressor, making full use of the high-quality heat source without the need for an additional electric heater to supplement the temperature. In the energy release stage, through the designed second and third heat exchangers, the waste heat of the exhaust gas discharged from the sCO2 turbine is used to heat the feedwater at the deaerator outlet and the condensate at the condensate pump outlet in sequence. This can reduce the amount of steam that the turbine originally needs to extract, so that this part of the steam can continue to expand and do work in the turbine to the low-pressure cylinder, thereby significantly increasing the power generation without increasing the boiler fuel consumption and improving the overall round-trip efficiency of the system "electricity-heat-electricity". Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of a peak-shaving device that couples a coal-fired power unit with a supercritical carbon dioxide energy storage system according to the present invention.

[0016] Explanation of reference numerals in the attached figures: 1. Boiler; 2. High-pressure cylinder; 3. Intermediate-pressure cylinder; 4. Low-pressure cylinder; 5. First generator; 6. Condenser; 7. Condensate pump; 8. First low-pressure heater; 9. Second low-pressure heater; 10. Third low-pressure heater; 11. Fourth low-pressure heater; 12. Deaerator; 13. Feed water pump; 14. First high-pressure heater; 15. Second high-pressure heater; 16. Third high-pressure heater; 17. Electric motor; 18. Compressor; 19. First heat exchanger; 20. First electric shut-off valve; 21. Supercritical carbon dioxide high-pressure storage tank; 22. Throttling valve; 23. Turbine; 24. Second generator; 25. Second heat exchanger; 26. Third heat exchanger; 27. Cooler; 28. Second electric shut-off valve; 29. ​​Supercritical carbon dioxide low-pressure storage tank; 30. Third electric shut-off valve. Detailed Implementation

[0017] The technical solution of the present invention will now be described more clearly and completely with reference to the accompanying drawings.

[0018] This invention provides a peak-shaving device coupled with a coal-fired power unit and a supercritical carbon dioxide energy storage system, comprising: a coal-fired power unit, a carbon dioxide energy storage system, and a carbon dioxide energy release system; The coal-fired power unit includes a boiler 1 and a high-pressure cylinder 2, an intermediate-pressure cylinder 3, and a low-pressure cylinder 4 connected coaxially; the coal-fired power unit is used to drive a first generator 5 to generate electricity; the exhaust steam from the low-pressure cylinder 4 passes sequentially through a condenser 6, a low-pressure heater assembly, and a high-pressure heater assembly before entering the boiler 1; The carbon dioxide energy storage system includes a supercritical low-pressure carbon dioxide storage tank 29, a compressor 18, a first heat exchanger 19, and a supercritical high-pressure carbon dioxide storage tank 21 connected in sequence; the hot side inlet of the first heat exchanger 19 is connected to the inlet of the high-pressure cylinder 2; the compressor 18 is powered by an electric motor 17. The carbon dioxide energy release system includes a supercritical carbon dioxide high-pressure storage tank 21, a turbine 23, a second heat exchanger 25, a third heat exchanger 26, a cooler 27, and a supercritical carbon dioxide low-pressure storage tank 29 connected in sequence. The cold side of the second heat exchanger 25 is connected to the high-pressure heater assembly. The cold side of the third heat exchanger 26 is connected to the low-pressure heater assembly. The cooler 27 is located between the third heat exchanger 26 and the supercritical carbon dioxide low-pressure storage tank 29. The turbine 23 is used to drive a second generator 24 to generate electricity.

[0019] The inlet of the supercritical carbon dioxide high-pressure storage tank 21 is connected to the cold side outlet of the first heat exchanger 19 through a pipeline, and a first electric shut-off valve 20 is installed on the pipeline; the inlet of the supercritical carbon dioxide high-pressure storage tank 21 is connected to the inlet of the turbine 23 through a pipeline, and a throttle valve 22 is installed on the pipeline. The inlet of the supercritical carbon dioxide low-pressure storage tank 29 is connected to the hot-side outlet of the third heat exchanger 26 via a pipeline, and a second electric shut-off valve 27 is installed on the pipeline; the hot-side outlet of the third heat exchanger 26 is connected to the inlet of the cooler 27 via a pipeline, and the outlet of the cooler 27 is connected to the inlet of the supercritical carbon dioxide low-pressure storage tank 29 via a pipeline, and a second electric shut-off valve 28 is installed on the pipeline.

[0020] Working principle of the invention: The outlet of the boiler 1 in the coal-fired power unit's steam power generation cycle is connected to the inlet of both the high-pressure cylinder 2 and the intermediate-pressure cylinder 3. The outlet of the intermediate-pressure cylinder 3 is connected to the low-pressure cylinder 4. The superheated steam from the boiler 1 outlet enters the high-pressure cylinder 2 to do work, then returns to the boiler 1 reheater for a second temperature increase, and then enters the intermediate-pressure cylinder 3 and the low-pressure cylinder 4 to do work, driving the first generator 5 to generate electricity. The exhaust steam from the low-pressure cylinder 4 enters the condenser 6 and condenses into condensate. The condensate flows sequentially through the condensate pump 7, the first low-pressure heater 8, the second low-pressure heater 9, the third low-pressure heater 10, and the fourth low-pressure heater 11, then through the deaerator 12 and the feedwater pump 13, and then sequentially through the first high-pressure heater 14, the second high-pressure heater 15, and the third high-pressure heater 16 before entering the boiler 1 to absorb heat, thus completing the steam power generation cycle of the coal-fired power unit.

[0021] The outlet pipe of boiler 1 is connected to the hot side inlet of the first heat exchanger 19, and the outlet of compressor 18 in the carbon dioxide energy storage system is connected to the cold side inlet of the first heat exchanger 19.

[0022] The outlet pipe of condensate pump 7 is connected to the inlet of the third heat exchanger 26, and the outlet pipe of feed water pump 13 is connected to the side inlet of the second heat exchanger 25.

[0023] In the energy storage stage of the carbon dioxide energy storage system, carbon dioxide from the supercritical low-pressure carbon dioxide storage tank 29 enters the compressor 18 and is compressed. The compressed carbon dioxide then enters the cold side of the first heat exchanger 19 and is heated. The heated carbon dioxide passes through the first electric shut-off valve 20 and is stored in the supercritical high-pressure carbon dioxide storage tank 21. In the energy release stage, the high-temperature and high-pressure carbon dioxide from the supercritical high-pressure carbon dioxide storage tank 21 enters the turbine 23 after passing through the throttle valve 22 to do work, driving the second generator 24 to generate electricity. After doing work, the carbon dioxide passes through the second heat exchanger 25, the third heat exchanger 26 and the cooler 27 in sequence before entering the supercritical low-pressure carbon dioxide storage tank 29.

[0024] Under normal circumstances, the first electric shut-off valve 20, the second electric shut-off valve 28, the third electric shut-off valve 30, and the throttle valve 22 are closed to keep the carbon dioxide energy storage and release system in a closed state, thus maintaining the normal operation of the steam power generation cycle of the coal-fired power unit.

[0025] When it is necessary to reduce the power output of the first generator, the first electric shut-off valve 20 and the third electric shut-off valve 30 are opened, while the remaining valves remain closed. The steam power generation cycle of the coal-fired power unit operates normally, and the excess electrical energy drives the compressor 18 through the motor 17. The compressor 18 compresses the carbon dioxide in the supercritical carbon dioxide low-pressure storage tank 29 to a preset pressure and then flows into the cold side of the first heat exchanger 19 to exchange heat with the high-temperature and high-pressure steam from the high-pressure cylinder 2. The heated carbon dioxide flows into the supercritical carbon dioxide high-pressure storage tank 21. After the energy storage is completed, the third electric shut-off valve 30 is closed first, and then the first electric shut-off valve 20 is closed.

[0026] When increased power generation is required, the second electrically operated shut-off valve 28 and the throttle valve 22 are opened, while the remaining valves remain closed. Carbon dioxide from the supercritical high-pressure carbon dioxide storage tank 21 is throttled by the throttle valve 22 and then enters the turbine 23 to drive the second generator 24, increasing power generation. The carbon dioxide from the turbine 23 undergoes heat exchange in the second heat exchanger 25 and the third heat exchanger 26 before entering the cooler 27 for further cooling, and is subsequently stored in the supercritical low-pressure carbon dioxide storage tank 29. After energy release is complete, the throttle valve 22 is closed first, followed by the second electrically operated shut-off valve 28.

Claims

1. A peak-shaving device coupling a coal-fired power unit with a supercritical carbon dioxide energy storage system, characterized in that, This includes coal-fired power units, carbon dioxide energy storage systems, and carbon dioxide energy release systems; The coal-fired power unit includes a boiler (1) and a high-pressure cylinder (2), a medium-pressure cylinder (3) and a low-pressure cylinder (4) connected coaxially. The exhaust steam from the low-pressure cylinder (4) passes through a condenser (6), a low-pressure heater assembly and a high-pressure heater assembly in sequence before entering the boiler (1). A deaerator (12) is provided between the low-pressure heater assembly and the high-pressure heater assembly. The carbon dioxide energy storage system includes a supercritical low-pressure carbon dioxide storage tank (29), a compressor (18), a first heat exchanger (19), and a supercritical high-pressure carbon dioxide storage tank (21) connected in sequence; the hot side inlet of the first heat exchanger (19) is connected to the inlet of the high-pressure cylinder (2); The carbon dioxide energy release system includes a supercritical carbon dioxide high-pressure storage tank (21), a turbine (23), a second heat exchanger (25), a third heat exchanger (26), a cooler (27), and a supercritical carbon dioxide low-pressure storage tank (29) connected in sequence. The cold side of the second heat exchanger (25) is connected to the high-pressure heater assembly. The cold side of the third heat exchanger (26) is connected to the low-pressure heater assembly. The cooler (27) is located between the third heat exchanger (26) and the supercritical carbon dioxide low-pressure storage tank (29) and is used to further cool the carbon dioxide after heat exchange by the third heat exchanger (26).

2. The peak-shaving device according to claim 1, characterized in that, The low-pressure heater assembly includes a first low-pressure heater (8), a second low-pressure heater (9), a third low-pressure heater (10), and a fourth low-pressure heater (11) connected in sequence.

3. The peak-shaving device according to claim 2, characterized in that, A condensate pump (7) is installed on the cold side inlet connecting pipe between the condenser (6) and the first low-pressure heater (8).

4. The peak-shaving device according to claim 3, characterized in that, The high-pressure heater assembly includes a first high-pressure heater (14), a second high-pressure heater (15), and a third high-pressure heater (16) connected in sequence.

5. The peak-shaving device according to claim 4, characterized in that, A water pump (13) is installed on the cold side inlet connection pipeline between the deaerator (12) and the first high-pressure heater (14).

6. The peak-shaving device according to claim 4, characterized in that, The hot side inlet of the first heat exchanger (19) is connected to the inlet of the high-pressure cylinder (2), and the hot side outlet of the first heat exchanger (19) is connected to the cold side outlet of the third high-pressure heater (16).

7. The peak-shaving device according to claim 5, characterized in that, The cold-side inlet of the second heat exchanger (25) is connected to the outlet of the feed water pump (13), and the cold-side outlet of the second heat exchanger (25) is connected to the cold-side outlet of the third high-pressure heater (16); the cold-side inlet of the third heat exchanger (26) is connected to the outlet of the condensate pump (7), and the cold-side outlet of the third heat exchanger (26) is connected to the cold-side outlet of the fourth low-pressure heater (11).

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