A Carnot battery system based on a coal-fired power generator and its operation method

Abstract

This invention belongs to the field of coal-fired power generation technology, specifically relating to a Carnot battery system based on a coal-fired power generator set and its operation method. The Carnot battery system includes a heat pump system using supercritical carbon dioxide as the working fluid, a thermal storage system, and a coal-fired power generation system. The heat pump system includes a first compressor, a second compressor, a first regenerator, a second regenerator, a third regenerator, a first turbine, and a second turbine. The thermal storage system includes a hot tank and a cold tank. The coal-fired power generation system includes a coal-fired boiler, a high-pressure cylinder, a medium-pressure cylinder, a low-pressure cylinder, a generator, a condenser, an eighth low-pressure heater, a seventh low-pressure heater, a sixth low-pressure heater, a fifth low-pressure heater, a deaerator, a first high-pressure heater, a second high-pressure heater, and a third high-pressure heater. This invention utilizes the split compression and split expansion processes, combined with multi-stage regenerators and multi-stage molten salt heaters, to improve the energy efficiency coefficient of the Carnot battery's electrothermal conversion process, thereby increasing the Carnot battery's round-trip efficiency.

Description

Technical Field

[0001] This invention belongs to the field of coal-fired power generation technology, specifically relating to a Carnot battery system based on a coal-fired power generator set and its operation method. Background Technology

[0002] As the proportion of renewable energy (such as wind and solar power) in the power system increases, the stability of the power grid faces challenges. Carnot batteries are a new type of energy storage technology that works based on the Carnot cycle. It realizes an electric-heat-electricity cycle by converting electrical energy into heat energy for storage and then converting the heat energy back into electrical energy. Specifically, Carnot batteries include the following steps: (1) Electric energy to heat energy conversion: When there is a power surplus, the Carnot battery converts electrical energy into high-temperature heat energy through an electric heater and stores it in a high-temperature heat storage medium. (2) Heat energy storage: The high-temperature heat energy is stored in a special heat storage device, usually using molten salt or other high-efficiency heat storage materials. (3) Heat energy to electricity energy conversion: During peak electricity demand, the stored heat energy is converted into electricity through a heat engine (such as a steam turbine or Brayton cycle) and resupplyed to the power grid. The generation of renewable energy is volatile and intermittent. When there is a surplus of electricity, the excess electricity can be converted into heat and stored in a Carnot battery. When there is a shortage of electricity, the Carnot battery can convert the stored heat into electricity, helping to stabilize the grid output and reduce dependence on fossil fuel power plants.

[0003] Traditional coal-fired power plants have slow start-up and shutdown speeds, making them unable to quickly respond to changes in grid load. Carnot batteries, however, can be integrated with coal-fired power plants, allowing them to convert excess electrical energy into thermal energy for storage during low-load periods and then convert it back into electricity output during peak demand. This approach improves the flexibility of coal-fired units, reduces idle time during low-load periods, and enhances overall operating efficiency. Meanwhile, globally, the trend towards reducing reliance on coal-fired power generation is inevitable. However, many existing coal-fired power plants still have long service lives. Introducing Carnot battery technology can extend the economic viability and competitiveness of coal-fired power plants, avoiding economic losses from large-scale phase-out, while also meeting stricter environmental requirements. Therefore, in the process of energy structure transformation, Carnot batteries provide crucial technological support for the cleaner and more efficient operation of coal-fired power plants.

[0004] However, current electro-thermal conversion efficiency remains low (COP of approximately 1.3), far below the theoretical Carnot efficiency. Improving the actual efficiency of electro-thermal conversion is a bottleneck that Carnot batteries need to overcome in practical applications, especially in the environment of coal-fired power plants, where high-efficiency electro-thermal conversion is crucial. Improving thermoelectric materials, technologies, and processes is key to improving overall system efficiency. Summary of the Invention

[0005] To address the shortcomings of existing methods, this invention proposes a Carnot battery system and its operation method based on a coal-fired power generation unit. By innovatively modifying the electro-thermal conversion process of the Carnot battery, the electro-thermal conversion process achieves a higher energy efficiency coefficient, thereby improving the round-trip efficiency of the Carnot battery.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A Carnot battery system based on a coal-fired power generation unit includes a heat pump system using supercritical carbon dioxide as the working fluid, a thermal storage system, and a coal-fired power generation system;

[0008] The heat pump system includes a second regenerator. The cold end outlet of the second regenerator is connected to the inlet of the first compressor and the cold end inlet of the first regenerator, respectively. The outlet of the first compressor is connected to the hot end inlet of the first molten salt heater, and the hot end outlet of the first molten salt heater is connected to the hot end inlet of the second regenerator. The cold end outlet of the first regenerator is connected to the inlet of the second compressor, the outlet of the second compressor is connected to the hot end inlet of the second molten salt heater, the hot end outlet of the second molten salt heater is connected to the hot end inlet of the first regenerator, and the hot end outlet of the first regenerator is connected to the hot end inlet of the second regenerator. The hot end outlet of the second regenerator is connected to the inlet of the first turbine and the hot end inlet of the third regenerator, respectively. The outlet of the first turbine is connected to the cold end inlet of the third regenerator, the hot end outlet of the third regenerator is connected to the inlet of the second turbine, the outlet of the second turbine is connected to the cold end inlet of the working fluid heater, the cold end outlet of the working fluid heater is connected to the cold end inlet of the third regenerator, and the cold end outlet of the third regenerator is connected to the cold end inlet of the second regenerator.

[0009] The thermal storage system includes a hot tank and a cold tank. The outlet of the cold tank is connected in sequence to the first molten salt pump, the first molten salt heater, the second molten salt heater, and the inlet of the hot tank. The outlet of the hot tank is connected to the hot end inlets of the reheater and the superheater, respectively. The hot end outlets of the reheater and the superheater are both connected to the hot end inlets of the evaporator. The hot end outlet of the evaporator is connected in sequence to the inlet of the preheater, the second molten salt pump, and the cold tank.

[0010] The coal-fired power generation system includes a coal-fired boiler. The main steam of the coal-fired boiler is connected to the inlet of the high-pressure cylinder. The outlet of the high-pressure cylinder is connected to the inlet of the reheater and the cold end inlet of the reheater. The cold end outlet of the reheater and the outlet of the reheater are both connected to the inlet of the intermediate-pressure cylinder. The outlet of the intermediate-pressure cylinder is connected to the inlet of the low-pressure cylinder and the condenser. The condensate from the condenser outlet passes sequentially through the condensate pump, the eighth low-pressure heater, the seventh low-pressure heater, the sixth low-pressure heater, the fifth low-pressure heater, the deaerator, the feedwater pump, the third high-pressure heater, and the second high-pressure heater before being connected to the feedwater inlet of the first high-pressure heater. The feedwater outlet of the first high-pressure heater is connected to the economizer and the cold end inlet of the preheater of the coal-fired boiler. The cold end outlet of the preheater is connected to the evaporator, the superheater, and the inlet of the high-pressure cylinder.

[0011] Preferably, the first compressor, the second compressor, the first turbine, and the second turbine are coaxially connected, and the high-pressure cylinder, the medium-pressure cylinder, and the low-pressure cylinder are coaxially connected to the generator.

[0012] Preferably, the hot end inlet of the working fluid heater is connected to the steam extraction port of the low-pressure cylinder, and the hot end outlet of the working fluid heater merges with the condensate outlet of the seventh low-pressure heater.

[0013] Preferably, the steam extraction from the first and second high-pressure heaters comes from the high-pressure cylinder, the steam extraction from the third high-pressure heater and the deaerator comes from the intermediate-pressure cylinder, and the steam extraction from the eighth, seventh, sixth, and fifth low-pressure heaters comes from the low-pressure cylinder.

[0014] The above-mentioned operation method of the Carnot battery system based on coal-fired power generation units includes an energy storage process and an energy release process: when there is abandoned power that needs to be absorbed and the load of the coal-fired boiler cannot be further reduced, or when there is no abandoned power to be absorbed but the power generation load of the coal-fired power generation unit system needs to be lower than its minimum power generation, the energy storage process is entered. At this time, the abandoned power from the outside or the extra power generated by the coal-fired unit, together with the first turbine and the second turbine, drive the first compressor and the second compressor. The first molten salt pump runs, driving the molten salt from the cold tank through the first molten salt heater and the second molten salt heater in sequence to enter the hot tank, thus completing the energy storage process of the Carnot battery.

[0015] When there is no waste power to be consumed and the required power load is higher than the minimum load of the coal-fired boiler, the energy release process begins. At this time, the molten salt in the hot tank enters the reheater and superheater to heat the reheat steam and main steam respectively. After the molten salt releases heat, it is combined and driven by the second molten salt pump. After releasing heat to the feedwater through the evaporator and preheater, it enters the cold tank, completing the energy release process of the Carnot cell.

[0016] Preferably, in the energy release process, the steam mass flow rates heated by the reheater and the superheater are the same.

[0017] Preferably, in the energy release process, when the power generation load is low or the coal-fired boiler fails and shuts down, all the feedwater from the outlet of the first high-pressure heater enters the preheater.

[0018] The positive and beneficial effects of this invention are as follows:

[0019] This invention discloses a Carnot battery system based on a coal-fired power generation unit and its operation method. Compared with the heat pump cycle with regeneration in the traditional Carnot battery, the improvements of this invention are threefold: (1) By splitting the compression of the first compressor and the second compressor, different working fluid temperatures are obtained. Combined with the staged heating of molten salt by the first molten salt heater and the second molten salt heater, the first compressor produces carbon dioxide at a lower temperature, which is used to heat the molten salt by the first molten salt heater. The second compressor produces carbon dioxide at a higher temperature, which is used to heat the molten salt by the second molten salt heater. Compared with the traditional Carnot battery system that only produces carbon dioxide at a higher temperature and only includes a first-stage molten salt heater, the average heat release temperature of the heat pump cycle is reduced, thereby improving the COP of the system. (2) By splitting the expansion of the first turbine and the second turbine expanders, the work done by the turbine is increased. Taking advantage of the characteristic that supercritical carbon dioxide does less work when expanding at the critical point, some working fluids expand directly without passing through the third regenerator, far from the critical point. Although this process reduces the heat absorption of carbon dioxide in the working fluid heater, it increases the work done per unit mass flow rate of the working fluid. (3) By using the extracted steam from the low-pressure cylinder as a heat source, the average heat absorption temperature of the heat pump cycle is increased, thereby improving the cycle COP. At the same time, the increased steam extraction volume can reduce the power generation of the coal-fired unit, which is conducive to its deeper peak regulation. This invention improves the energy efficiency coefficient of the Carnot battery's electro-thermal conversion process by using the split compression and split expansion processes in conjunction with a multi-stage regenerator and a multi-stage molten salt heater, thereby increasing the Carnot battery's round-trip efficiency by at least 10%. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the Carnot battery system based on a coal-fired power generator set according to the present invention;

[0021] Figure 2 This is a schematic diagram of the Carnot battery system (energy storage process) based on a coal-fired power generation unit according to the present invention;

[0022] Figure 3 This is a schematic diagram of the Carnot battery system (energy release process) based on a coal-fired power generation unit according to the present invention;

[0023] In the diagram: 1-First compressor, 2-Second compressor, 3-First regenerator, 4-Second regenerator, 5-Third regenerator, 6-First turbine, 7-Second turbine, 8-Working fluid heater, 9-Second molten salt heater, 10-First molten salt heater, 11-Hot tank, 12-Cold tank, 13-First molten salt pump, 14-Reheater, 15-Superheater, 16-Evaporator, 17-Preheater, 18-Second molten salt pump, 19-Coal-fired boiler, 20-High-pressure cylinder, 21-Medium-pressure cylinder, 22-Low-pressure cylinder, 23-Generator, 24-Condenser, 25-Condensate pump, 26-Eighth low-pressure heater, 27-Seventh low-pressure heater, 28-Sixth low-pressure heater, 29-Fifth low-pressure heater, 30-Deaerator, 31-Feed water pump, 32-Third high-pressure heater, 33-Second high-pressure heater, 34-First high-pressure heater. Detailed Implementation

[0024] The present invention will be further described below with reference to some specific embodiments.

[0025] See Figure 1-3 A Carnot battery system based on a coal-fired power generation unit includes a heat pump system using supercritical carbon dioxide as the working fluid, a thermal storage system, and a coal-fired power generation system;

[0026] The heat pump system includes a second regenerator 4. The cold end outlet of the second regenerator 4 is connected to the inlet of the first compressor 1 and the cold end inlet of the first regenerator 3, respectively. The outlet of the first compressor 1 is connected to the hot end inlet of the first molten salt heater 10, and the hot end outlet of the first molten salt heater 10 is connected to the hot end inlet of the second regenerator 4. The cold end outlet of the first regenerator 3 is connected to the inlet of the second compressor 2, and the outlet of the second compressor 2 is connected to the hot end inlet of the second molten salt heater 9. The hot end outlet of the second molten salt heater 9 is connected to the hot end inlet of the first regenerator 3. The hot end outlet of the first regenerator 3 is connected to the hot end inlet of the second regenerator 4; the hot end outlet of the second regenerator 4 is connected to the inlet of the first turbine 6 and the hot end inlet of the third regenerator 5 respectively; the outlet of the first turbine 6 is connected to the cold end inlet of the third regenerator 5; the hot end outlet of the third regenerator 5 is connected to the inlet of the second turbine 7; the outlet of the second turbine 7 is connected to the cold end inlet of the working fluid heater 8; the cold end outlet of the working fluid heater 8 is connected to the cold end inlet of the third regenerator 5; and the cold end outlet of the third regenerator 5 is connected to the cold end inlet of the second regenerator 4.

[0027] The thermal storage system includes a hot tank 11 and a cold tank 12. The outlet of the cold tank 12 is connected in sequence to the first molten salt pump 13, the first molten salt heater 10, the second molten salt heater 9 and the inlet of the hot tank 11. The outlet of the hot tank 11 is connected to the hot end inlets of the reheater 14 and the superheater 15 respectively. The hot end outlets of the reheater 14 and the superheater 15 are both connected to the hot end inlet of the evaporator 16. The hot end outlet of the evaporator 16 is connected in sequence to the preheater 17, the second molten salt pump 18 and the inlet of the cold tank 12.

[0028] The coal-fired power generation system includes a coal-fired boiler 19. The main steam of the coal-fired boiler 19 is connected to the inlet of the high-pressure cylinder 20. The outlet of the high-pressure cylinder 20 is connected to the inlet of the reheater and the cold end inlet of the reheater 14 of the coal-fired boiler 19. The cold end outlet of the reheater 14 and the reheater outlet of the coal-fired boiler 19 are both connected to the inlet of the intermediate-pressure cylinder 21. The outlet of the intermediate-pressure cylinder 21 is connected to the inlet of the low-pressure cylinder 22 and the condenser 24. The condensate from the outlet of the condenser 24 passes sequentially through the condensate pump 25, the eighth low-pressure heater 26, the seventh low-pressure heater 27, the sixth low-pressure heater 28, the fifth low-pressure heater 29, the deaerator 30, the feedwater pump 31, the third high-pressure heater 32, and the second high-pressure heater 33 before being connected to the feedwater inlet of the first high-pressure heater 34. The feedwater outlet of the first high-pressure heater 34 is connected to the economizer and the cold end inlet of the preheater 17 of the coal-fired boiler 19. The cold end outlet of the preheater 17 is connected to the evaporator 16, the superheater 15, and the inlet of the high-pressure cylinder 20.

[0029] Furthermore, in the heat pump system using carbon dioxide as the working fluid, the first compressor 1, the second compressor 2, the first turbine 6, and the second turbine 7 are coaxially connected, and the high-pressure cylinder 20, the medium-pressure cylinder 21, the low-pressure cylinder 22, and the generator 23 are coaxially connected.

[0030] Furthermore, in the heat pump system using carbon dioxide as the working fluid, the hot end inlet of the working fluid heater 8 is connected to the steam extraction port of the low-pressure cylinder 22, and the hot end outlet of the working fluid heater 8 merges with the condensate outlet of the seventh regenerator 27.

[0031] Furthermore, in the coal-fired power generation system, the steam extraction from the first high-pressure heater 34 and the second high-pressure heater 33 comes from the high-pressure cylinder 20, the steam extraction from the third high-pressure heater 32 and the deaerator 30 comes from the intermediate-pressure cylinder 21, and the steam extraction from the eighth low-pressure heater 26, the seventh low-pressure heater 27, the sixth low-pressure heater 28 and the fifth low-pressure heater 29 comes from the low-pressure cylinder 22.

[0032] The above-mentioned operation method of the Carnot battery system based on coal-fired power generation unit includes an energy storage process and an energy release process: when there is abandoned power that needs to be absorbed and the load of coal-fired boiler 19 cannot be further reduced, or when there is no abandoned power to be absorbed but the power generation load of the coal-fired power generation unit system needs to be lower than its minimum power generation, the energy storage process is entered. At this time, the abandoned power from the outside or the extra power generated by the coal-fired unit, together with the first turbine 6 and the second turbine 7, drive the first compressor 1 and the second compressor 2, and the first molten salt pump 13 runs, driving the molten salt from the cold tank 12 through the first molten salt heater 10 and the second molten salt heater 9 in sequence to enter the hot tank 11, thus completing the energy storage process of the Carnot battery;

[0033] When there is no waste power to be consumed and the required power load is higher than the minimum load of the coal-fired boiler 19, the energy release process begins. At this time, the molten salt in the hot tank 11 enters the reheater 14 and the superheater 15 respectively to heat the reheat steam and the main steam. After the molten salt releases heat, it is driven by the second molten salt pump 18. After releasing heat to the feedwater through the evaporator 16 and the preheater 17, it enters the cold tank 12, completing the energy release process of the Carnot cell.

[0034] Furthermore, in the energy release process, the steam mass flow rates heated by the reheater 14 and the superheater 15 are the same, so as to maintain the heat dissipation safety of the superheater and reheater heating surfaces of the coal-fired boiler 19.

[0035] Furthermore, during the energy release process, when the power generation load is low or the coal-fired boiler 19 fails and shuts down, all the feedwater from the outlet of the first high-pressure heater 34 enters the preheater 17.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A Carnot cell system based on a coal-fired power plant, characterized in that, The application relates to a heat pump system, a heat storage system and a coal-fired power generation system using supercritical carbon dioxide as a working medium. The heat pump system comprises a second regenerator (4), the cold end outlet of the second regenerator (4) is connected with the inlet of a first compressor (1) and the cold end inlet of a first regenerator (3) respectively, the outlet of the first compressor (1) is connected with the hot end inlet of a first molten salt heater (10), the hot end outlet of the first molten salt heater (10) is connected with the hot end inlet of the second regenerator (4), the cold end outlet of the first regenerator (3) is connected with the inlet of a second compressor (2), the outlet of the second compressor (2) is connected with the hot end inlet of a second molten salt heater (9), the hot end outlet of the second molten salt heater (9) is connected with the hot end inlet of the first regenerator (3), the hot end outlet of the first regenerator (3) is connected with the hot end inlet of the second regenerator (4), the hot end outlet of the second regenerator (4) is connected with the inlet of a first turbine (6) and the hot end inlet of a third regenerator (5) respectively, the outlet of the first turbine (6) is connected with the cold end inlet of the third regenerator (5), the hot end outlet of the third regenerator (5) is connected with the inlet of a second turbine (7), the outlet of the second turbine (7) is connected with the cold end inlet of a working medium heater (8), the cold end outlet of the working medium heater (8) is connected with the cold end inlet of the third regenerator (5), and the cold end outlet of the third regenerator (5) is connected with the cold end inlet of the second regenerator (4); The heat storage system comprises a hot tank (11) and a cold tank (12), the outlet of the cold tank (12) is connected with a first molten salt pump (13), a first molten salt heater (10), a second molten salt heater (9) and the inlet of the hot tank (11) in sequence, the outlet of the hot tank (11) is connected with the hot end inlets of a reheater (14) and a superheater (15) respectively, the hot end outlets of the reheater (14) and the superheater (15) are connected with the hot end inlet of an evaporator (16), and the hot end outlet of the evaporator (16) is connected with a preheater (17), a second molten salt pump (18) and the inlet of the cold tank (12) in sequence. The coal-fired power generation system comprises a coal-fired boiler (19), a main steam of the coal-fired boiler (19) is connected with an inlet of a high-pressure cylinder (20), an outlet of the high-pressure cylinder (20) is connected with an inlet of a reheater of the coal-fired boiler (19) and an inlet of a cold end of a reheater (14), a cold end outlet of the reheater (14) and a reheater outlet of the coal-fired boiler (19) are connected with an inlet of a medium-pressure cylinder (21), an outlet of the medium-pressure cylinder (21) is connected with an inlet of a low-pressure cylinder (22) and a condenser (24), and condensate water at an outlet of the condenser (24) is connected with an inlet of a feed water of a first high-pressure heater (34) in sequence through a condensate water pump (25), an eighth low-pressure heater (26), a seventh low-pressure heater (27), a sixth low-pressure heater (28), a fifth low-pressure heater (29), a deaerator (30), a feed water pump (31), a third high-pressure heater (32) and a second high-pressure heater (33), a feed water outlet of the first high-pressure heater (34) is connected with a economizer of the coal-fired boiler (19) and an inlet of a cold end of a preheater (17), and a cold end outlet of the preheater (17) is connected with an evaporator (16), a superheater (15) and the inlet of the high-pressure cylinder (20).

2. The Carnot cell system based on a coal-fired power generating unit according to claim 1, characterized in that, The first compressor (1), the second compressor (2), the first turbine (6) and the second turbine (7) are coaxially connected, and the high-pressure cylinder (20), the medium-pressure cylinder (21) and the low-pressure cylinder (22) are coaxially connected with a generator (23).

3. The Carnot cell system based on a coal-fired power generating unit according to claim 1, characterized in that, A hot end inlet of the working medium heater (8) is connected with a steam extraction port of the low-pressure cylinder (22), and a hot end outlet of the working medium heater (8) is connected with a drain of an outlet of the seventh low-pressure heater (27).

4. The Carnot cell system based on a coal-fired power generating unit according to claim 1, characterized in that, Steam extraction of the first high-pressure heater (34) and the second high-pressure heater (33) is from the high-pressure cylinder (20), steam extraction of the third high-pressure heater (32) and the deaerator (30) is from the medium-pressure cylinder (21), and steam extraction of the eighth low-pressure heater (26), the seventh low-pressure heater (27), the sixth low-pressure heater (28) and the fifth low-pressure heater (29) is from the low-pressure cylinder (22).

5. A method of operating a Carnot cell system based on a coal-fired power generating unit as claimed in any one of claims 1 to 4, characterized in that, The energy storage process and the energy release process are included: when there is abandoned electricity to be consumed and the load of the coal-fired boiler (19) cannot continue to be lowered, or when there is no abandoned electricity to be consumed but the power generation load of the coal-fired power generation unit system is lower than the minimum power generation amount, the energy storage process is entered, at this time, the abandoned electricity or the power generated by the coal-fired unit drives the first compressor (1) and the second compressor (2) together with the first turbine (6) and the second turbine (7), the first molten salt pump (13) operates to drive the molten salt to be heated from the cold tank (12) to the hot tank (11) through the first molten salt heater (10) and the second molten salt heater (9) in sequence, and the energy storage process of the Carnot cell is completed; when there is no abandoned electricity to be consumed and the demand power load is higher than the minimum load of the coal-fired boiler (19), the energy release process is entered, at this time, the molten salt in the hot tank (11) heats the reheat steam and the main steam in the reheater (14) and the superheater (15) respectively, the molten salt is driven by the second molten salt pump (18) after heat release, and the feed water is heated by the evaporator (16) and the preheater (17) and then enters the cold tank (12), and the energy release process of the Carnot cell is completed.

6. The method of operating a Carnot cell system based on a coal-fired power generating unit according to claim 5, characterized in that, The energy releasing process, the reheater (14) and superheater (15) heat the same steam mass flow.

7. The method of operating a Carnot cell system based on a coal-fired power generating unit according to claim 5, characterized in that, The energy releasing process, when the power generation load is low or the coal-fired boiler (19) is malfunctioned and stopped, the feed water at the outlet of the first high-pressure heater (34) enters the preheater (17) entirely.

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