Carnot battery system based on shunt expansion heat pump and operation method of Carnot battery system

Abstract

The invention belongs to the technical field of coal-fired power generation, and particularly relates to a Carnot battery system based on a shunt expansion heat pump and an operation method of the Carnot battery system. The Carnot cell system comprises a heat pump system taking carbon dioxide as a working medium, a heat storage system and a coal-fired power generation system; the heat pump system comprises a compressor, a heat regenerator, a first turbine and a second turbine; the heat storage system comprises a hot tank and a cold tank; the coal-fired power generation system comprises a coal-fired boiler, a high-pressure cylinder, an intermediate-pressure cylinder, a low-pressure cylinder, a power 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. According to the invention, the shunt expansion process is utilized and is matched with the heat regenerator and the molten salt heater, so that the energy efficiency coefficient of the Carnot battery in the electricity-to-heat conversion process is improved, and the round-trip efficiency of the Carnot battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal-fired power generation, and in particular relates to a Carnot battery system based on a split-flow expansion heat pump and an operation method thereof. Background Art

[0002] As the proportion of renewable energy (such as wind and solar energy) in the power system increases, the stability of the power grid faces challenges. The Carnot battery is a new type of energy storage technology whose working principle is based on the Carnot cycle. It realizes the electric-heat-electric cycle process by converting electrical energy into thermal energy for storage and then converting thermal energy back into electrical energy. Specifically, the Carnot battery includes the following steps: (1) Conversion of electrical energy into thermal energy: When there is excess electricity, the Carnot battery converts electrical energy into high-temperature thermal energy through an electric heater and stores it in a high-temperature heat storage medium. (2) Thermal energy storage: High-temperature thermal energy is stored in a dedicated heat storage device, usually using molten salt or other high-efficiency heat storage materials. (3) Conversion of thermal energy into electrical energy: When electricity demand peaks, the stored thermal energy is converted into electrical energy through a heat engine (such as a steam turbine or Brayton cycle) and resupplied to the power grid. The power generation of renewable energy is volatile and intermittent. When there is excess power generation, the excess electricity can be converted into heat energy and stored in the Carnot battery. When there is insufficient power generation, the Carnot battery can convert the stored heat energy into electricity, helping to stabilize the output of the power grid and reduce dependence on fossil fuel power plants.

[0003] Traditional coal-fired power plants have a slow start and stop speed and cannot respond quickly to changes in grid load. Carnot batteries can be integrated with coal-fired power plants, allowing power plants to convert excess electricity into thermal energy storage when the load is low, and then convert it into electrical energy output when the power demand peaks. This method improves the flexibility of coal-fired units, reduces the idle time of power plants when the load is low, and improves overall operating efficiency. At the same time, it is a general trend to gradually reduce dependence on coal-fired power generation worldwide. However, many existing coal-fired power plants still have a long service life. By introducing Carnot battery technology, the economy and competitiveness of coal-fired power plants can be extended, the economic losses caused by large-scale elimination can be avoided, and more stringent environmental protection requirements can be met. Therefore, in the process of energy structure transformation, Carnot batteries provide an important technical support for the cleanliness and efficiency of coal-fired power plants.

[0004] However, the current electric-to-heat conversion efficiency is still low (the coefficient of efficiency COP is about 1.3), which is much lower than the theoretical Carnot efficiency. Improving the actual efficiency of electric-to-heat conversion is the bottleneck that Carnot batteries need to break through in practical applications, especially in the environment of coal-fired power plants, where high-efficiency electric-to-heat conversion is crucial. Improving thermoelectric materials, technologies and processes is the key to improving overall system efficiency. Summary of the invention

[0005] In view of the shortcomings of the existing methods, the present invention proposes a Carnot battery system based on a split expansion heat pump and an operation method thereof. By innovatively transforming the electric-to-heat process of the Carnot battery, the electric-to-heat process has a higher energy efficiency coefficient, thereby improving the round-trip efficiency of the Carnot battery.

[0006] To achieve the above object, the present invention adopts the following technical solution: A Carnot battery system based on a split expansion heat pump includes a heat pump system using carbon dioxide as a working fluid, a heat storage system and a coal-fired power generation system; The heat pump system comprises a regenerator, the cold end outlet of the regenerator is connected to the inlet of the compressor, the outlet of the compressor is connected to the hot end inlet of the molten salt heater, the hot end outlet of the molten salt heater is respectively connected to the inlet of the first turbine and the hot end inlet of the regenerator; the outlet of the first turbine is connected to the cold end inlet of the regenerator, the hot end outlet of the 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, and the cold end outlet of the working fluid heater is connected to the cold end inlet of the regenerator; The heat storage system comprises a hot tank and a cold tank, the outlet of the cold tank is connected to the first molten salt pump, the molten salt heater and the inlet of the hot tank in sequence, 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 inlet of the evaporator, and the hot end outlet of the evaporator is connected to the preheater, the second molten salt pump and the inlet of the cold tank in sequence; The coal-fired power generation system includes a coal-fired boiler, the main steam of the coal-fired boiler is connected to the high-pressure cylinder inlet, the high-pressure cylinder outlet is connected to the coal-fired boiler reheater inlet and the reheater cold end inlet, the reheater cold end outlet and the coal-fired boiler reheater outlet are both connected to the medium-pressure cylinder inlet, the medium-pressure cylinder outlet is connected to the low-pressure cylinder and the condenser inlet, the condensate at the condenser outlet is sequentially connected to the feed water inlet of the first high-pressure heater after passing through a condensate pump, an eighth low-pressure heater, a seventh low-pressure heater, a sixth low-pressure heater, a fifth low-pressure heater, a deaerator, a feed water pump, a third high-pressure heater, and a second high-pressure heater, the feed water 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, and the cold end outlet of the preheater is connected to the evaporator, the superheater and the high-pressure cylinder inlet.

[0007] Preferably, the compressor, the first turbine, and the second turbine are coaxially connected, and the high-pressure cylinder, the medium-pressure cylinder, the low-pressure cylinder, and the generator are coaxially connected.

[0008] 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 drain of the outlet of the seventh low-pressure heater.

[0009] Preferably, the extraction steam of the first high-pressure heater and the second high-pressure heater comes from the high-pressure cylinder, the extraction steam of the third high-pressure heater and the deaerator comes from the medium-pressure cylinder, and the extraction steam of the eighth low-pressure heater, the seventh low-pressure heater, the sixth low-pressure heater and the fifth low-pressure heater comes from the low-pressure cylinder.

[0010] The operation method of the Carnot battery system based on the split expansion heat pump 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 generator system needs to be lower than its minimum power generation, the energy storage process is entered. At this time, the external abandoned power or the excess power generated by the coal-fired unit and the first turbine and the second turbine jointly drive the compressor, and the first molten salt pump is operated to drive the molten salt from the cold tank to the hot tank after being heated by the molten salt heater, thereby completing the energy storage process of the Carnot battery; When there is no abandoned electricity to be absorbed and the required electricity 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 respectively to heat the reheated steam and main steam. After the molten salt releases heat, it converges and is driven by the second molten salt pump. After releasing heat to the feed water through the evaporator and preheater, it enters the cold tank, completing the energy release process of the Carnot battery.

[0011] Preferably, in the energy release process, the steam mass flow rates heated by the reheater and the superheater are the same.

[0012] Preferably, in the energy release process, when the power generation load is low or the coal-fired boiler is shut down due to a fault, all the feed water at the outlet of the first high-pressure heater enters the preheater.

[0013] The positive beneficial effects of the present invention are: The present invention discloses a Carnot battery system based on a split expansion heat pump and an operation method thereof. Compared with the heat pump cycle with heat recovery in the traditional Carnot battery, the present invention has two improvements: (1) The split expansion of the first turbine and the second turbine expanders increases the work done by the turbines, and the characteristic of supercritical carbon dioxide that the work done at the critical point is utilized. Part of the working fluid directly expands and works without passing through the second regenerator, away from the critical point. Although this process reduces the heat absorption of carbon dioxide in the working fluid heater, it increases the work done by the working fluid per unit mass flow rate. (2) The extraction steam of the low-pressure cylinder is used as a heat source to increase the average heat absorption temperature of the heat pump cycle, thereby increasing the cycle COP. At the same time, the increased extraction steam can reduce the power generation of the coal-fired unit, which is beneficial to its deeper peak regulation. The present invention improves the energy efficiency coefficient of the Carnot battery's electric-to-heat process by innovatively transforming the Carnot battery's electric-to-heat process, utilizing the split expansion process, cooperating with the regenerator and the molten salt heater, and improving the energy efficiency coefficient of the Carnot battery's electric-to-heat process by at least 10%, thereby improving the round-trip efficiency of the Carnot battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1A schematic diagram of a Carnot battery system based on a split expansion heat pump according to the present invention; Figure 2 A schematic diagram of a Carnot battery system (energy storage process) based on a split expansion heat pump according to the present invention; Figure 3 A schematic diagram of a Carnot battery system (energy release process) based on a split expansion heat pump according to the present invention; In the figure: 1-compressor, 2-regenerator, 3-first turbine, 4-second turbine, 5-working fluid heater, 6-molten salt heater, 7-hot tank, 8-cold tank, 9-first molten salt pump, 10-reheater, 11-superheater, 12-evaporator, 13-preheater, 14-second molten salt pump, 15-coal-fired boiler, 16-high-pressure cylinder, 17-medium-pressure cylinder, 18-low-pressure cylinder, 19-generator, 20-condenser, 21-condensate pump, 22-eighth low-pressure heater, 23-seventh low-pressure heater, 24-sixth low-pressure heater, 25-fifth low-pressure heater, 26-deaerator, 27-feedwater pump, 28-third high-pressure heater, 29-second high-pressure heater, 30-first high-pressure heater. DETAILED DESCRIPTION

[0015] The present invention is further described below in conjunction with some specific embodiments.

[0016] See also Figure 1-3 , a Carnot battery system based on a split expansion heat pump, comprising a heat pump system using supercritical carbon dioxide as a working fluid, a heat storage system and a coal-fired power generation system; The heat pump system includes a regenerator 2, the cold end outlet of the regenerator 2 is connected to the inlet of the compressor 1, the outlet of the compressor 1 is connected to the hot end inlet of the molten salt heater 6, the hot end outlet of the molten salt heater 6 is respectively connected to the inlet of the first turbine 3 and the hot end inlet of the regenerator 2; the outlet of the first turbine 3 is connected to the cold end inlet of the regenerator 2, the hot end outlet of the regenerator 2 is connected to the inlet of the second turbine 4, the outlet of the second turbine 4 is connected to the cold end inlet of the working fluid heater 5, and the cold end outlet of the working fluid heater 5 is connected to the cold end inlet of the regenerator 2; The heat storage system includes a hot tank 7 and a cold tank 8, the outlet of the cold tank 8 is connected to the first molten salt pump 14, the molten salt heater 6 and the inlet of the hot tank 7 in sequence, the outlet of the hot tank 7 is connected to the hot end inlet of the reheater 9 and the superheater 10 respectively, the hot end outlets of the reheater 9 and the superheater 10 are both connected to the hot end inlet of the evaporator 11, and the hot end outlet of the evaporator 11 is connected to the preheater 12, the second molten salt pump 13 and the inlet of the cold tank 8 in sequence; The coal-fired power generation system includes a coal-fired boiler 15, the main steam of the coal-fired boiler 15 is connected to the inlet of the high-pressure cylinder 16, the outlet of the high-pressure cylinder 16 is connected to the inlet of the reheater of the coal-fired boiler 15 and the inlet of the cold end of the reheater 9, the outlet of the cold end of the reheater 9 and the outlet of the reheater of the coal-fired boiler 15 are both connected to the inlet of the medium-pressure cylinder 17, the outlet of the medium-pressure cylinder 17 is connected to the inlet of the low-pressure cylinder 18 and the condenser 20, the condensate at the outlet of the condenser 20 is connected to the feed water inlet of the first high-pressure heater 30 after passing through the condensate pump 21, the eighth low-pressure heater 22, the seventh low-pressure heater 23, the sixth low-pressure heater 24, the fifth low-pressure heater 25, the deaerator 26, the feed water pump 27, the third high-pressure heater 28, and the second high-pressure heater 29 in sequence, the feed water outlet of the first high-pressure heater 30 is connected to the cold end inlet of the economizer and the preheater 12 of the coal-fired boiler 15, and the cold end outlet of the preheater 12 is connected to the evaporator 11, the superheater 10 and the inlet of the high-pressure cylinder 16.

[0017] Furthermore, the compressor 1 , the first turbine 3 , and the second turbine 4 are coaxially connected, and the high-pressure cylinder 16 , the medium-pressure cylinder 17 , the low-pressure cylinder 18 and the generator 19 are coaxially connected.

[0018] Furthermore, in the heat pump system using carbon dioxide as the working fluid, the hot end inlet of the working fluid heater 5 is connected to the steam extraction port of the low-pressure cylinder 18, and the hot end outlet of the working fluid heater 5 merges with the drain at the outlet of the seventh low-pressure heater 23.

[0019] Furthermore, in the coal-fired power generation system, the extraction steam of the first high-pressure heater 30 and the second high-pressure heater 29 comes from the high-pressure cylinder 16, the extraction steam of the third high-pressure heater 28 and the deaerator 26 comes from the medium-pressure cylinder 17, and the extraction steam of the eighth low-pressure heater 22, the seventh low-pressure heater 23, the sixth low-pressure heater 24 and the fifth low-pressure heater 25 comes from the low-pressure cylinder 18.

[0020] The operation method of the Carnot battery system based on the shunt expansion heat pump 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 15 cannot be further reduced, or when there is no abandoned power to be absorbed but the power generation load of the coal-fired generator system needs to be lower than its minimum power generation, the energy storage process is entered. At this time, the external abandoned power or the excess power generated by the coal-fired unit and the first turbine 3 and the second turbine 4 jointly drive the compressor 1, and the first molten salt pump 14 is running to drive the molten salt from the cold tank 8 to the hot tank 7 after being heated by the molten salt heater 6, thereby completing the energy storage process of the Carnot battery; When there is no abandoned electricity to be consumed and the required electricity load is higher than the minimum load of the coal-fired boiler 15, the energy release process begins. At this time, the molten salt in the hot tank 7 enters the reheater 9 and the superheater 10 respectively to heat the reheated steam and the main steam. After the molten salt releases heat, it converges and is driven by the second molten salt pump 13. After releasing heat to the feed water through the evaporator 11 and the preheater 12, it enters the cold tank 8, completing the energy release process of the Carnot battery.

[0021] Furthermore, in the energy release process, the mass flow rates of steam heated by the reheater 9 and the superheater 10 are the same.

[0022] Furthermore, in the energy release process, when the power generation load is low or the coal-fired boiler 15 stops working due to a fault, all the feed water at the outlet of the first high-pressure heater 30 enters the preheater 12 .

[0023] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in the field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A Carnot battery system based on a split expansion heat pump, characterized in that: Including heat pump system, heat storage system and coal-fired power generation system using carbon dioxide as working fluid; The heat pump system comprises a regenerator (2), wherein the cold end outlet of the regenerator (2) is connected to the inlet of the compressor (1), the outlet of the compressor (1) is connected to the hot end inlet of the molten salt heater (6), and the hot end outlet of the molten salt heater (6) is respectively connected to the inlet of the first turbine (3) and the hot end inlet of the regenerator (2); the outlet of the first turbine (3) is connected to the cold end inlet of the regenerator (2), the hot end outlet of the regenerator (2) is connected to the inlet of the second turbine (4), the outlet of the second turbine (4) is connected to the cold end inlet of the working fluid heater (5), and the cold end outlet of the working fluid heater (5) is connected to the cold end inlet of the regenerator (2); The heat storage system comprises a hot tank (7) and a cold tank (8), wherein the outlet of the cold tank (8) is connected to the inlet of the first molten salt pump (14), the molten salt heater (6) and the hot tank (7) in sequence, the outlet of the hot tank (7) is connected to the hot end inlets of the reheater (9) and the superheater (10) respectively, the hot end outlets of the reheater (9) and the superheater (10) are both connected to the hot end inlet of the evaporator (11), and the hot end outlet of the evaporator (11) is connected to the preheater (12), the second molten salt pump (13) and the inlet of the cold tank (8) in sequence; The coal-fired power generation system comprises a coal-fired boiler (15), the main steam of the coal-fired boiler (15) is connected to the inlet of the high-pressure cylinder (16), the outlet of the high-pressure cylinder (16) is connected to the inlet of the reheater of the coal-fired boiler (15) and the inlet of the cold end of the reheater (9), the outlet of the cold end of the reheater (9) and the outlet of the reheater of the coal-fired boiler (15) are both connected to the inlet of the medium-pressure cylinder (17), the outlet of the medium-pressure cylinder (17) is connected to the inlet of the low-pressure cylinder (18) and the condenser (20), and the condensate at the outlet of the condenser (20) is sequentially discharged through a condensate pump (21), an eighth low-pressure heater (22), a seventh low-pressure heater (23), a sixth low-pressure heater (24), a fifth low-pressure heater (25), The deaerator (26), the feed water pump (27), the third high-pressure heater (28), and the second high-pressure heater (29) are connected to the feed water inlet of the first high-pressure heater (30), the feed water outlet of the first high-pressure heater (30) is connected to the economizer of the coal-fired boiler (15) and the cold end inlet of the preheater (12), and the cold end outlet of the preheater (12) is connected to the evaporator (11), the superheater (10), and the inlet of the high-pressure cylinder (16).

2. The Carnot battery system based on the split expansion heat pump according to claim 1, characterized in that: The compressor (1), the first turbine (3), and the second turbine (4) are coaxially connected, and the high-pressure cylinder (16), the medium-pressure cylinder (17), the low-pressure cylinder (18) and the generator (19) are coaxially connected.

3. The Carnot battery system based on the split expansion heat pump according to claim 1, characterized in that: The hot end inlet of the working fluid heater (5) is connected to the steam extraction port of the low-pressure cylinder (18), and the hot end outlet of the working fluid heater (5) merges with the drain at the outlet of the seventh low-pressure heater (23).

4. The Carnot battery system based on the split expansion heat pump according to claim 1, characterized in that: The extraction steam of the first high-pressure heater (30) and the second high-pressure heater (29) comes from the high-pressure cylinder (16), the extraction steam of the third high-pressure heater (28) and the deaerator (26) comes from the medium-pressure cylinder (17), and the extraction steam of the eighth low-pressure heater (22), the seventh low-pressure heater (23), the sixth low-pressure heater (24) and the fifth low-pressure heater (25) comes from the low-pressure cylinder (18).

5. A method for operating a Carnot battery system based on a split expansion heat pump according to any one of claims 1 to 4, characterized in that: It 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 (15) 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 external abandoned power or the excess power generated by the coal-fired unit and the first turbine (3) and the second turbine (4) jointly drive the compressor (1), and the first molten salt pump (14) is operated to drive the molten salt from the cold tank (8) to the hot tank (7) after being heated by the molten salt heater (6), thereby completing the energy storage process of the Carnot battery; When there is no abandoned electricity to be absorbed and the required electricity load is higher than the minimum load of the coal-fired boiler (15), the energy release process begins. At this time, the molten salt in the hot tank (7) enters the reheater (9) and the superheater (10) to heat the reheat steam and the main steam respectively. After the molten salt releases heat, it is combined and driven by the second molten salt pump (13). After the evaporator (11) and the preheater (12) release heat to the feed water, it enters the cold tank (8), completing the energy release process of the Carnot battery.

6. The method for operating a Carnot battery system based on a split expansion heat pump according to claim 5, characterized in that: In the energy release process, the mass flow rates of steam heated by the reheater (9) and the superheater (10) are the same.

7. The method for operating a Carnot battery system based on a split expansion heat pump according to claim 5, characterized in that: In the energy release process, when the power generation load is low or the coal-fired boiler (15) stops working due to a fault, all the feed water at the outlet of the first high-pressure heater (30) enters the preheater (12).

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