Thermal power plant heating system and operation method based on two-phase flow ejector and molten salt heat storage

Abstract

The present invention discloses a thermal power plant heating system and operating method based on a two-phase flow ejector and molten salt heat storage, belonging to the field of thermal power plant heating technology. The system includes a thermal power unit body, a heat recovery steam extraction system, an electrically heated molten salt heat storage system, and a two-phase flow ejector heating system. The abandoned electricity of the thermal power plant is stored in molten salt using an electrically heated heat storage technology. When there is a demand for heating, the heat storage of the molten salt is used to increase the temperature of the deaerator bypass feed water, and the new steam produced by the boiler is used to inject the high-temperature feed water for heating to meet the needs of heat users. The present invention also improves the deep peak regulation capability and heating level of the thermal power unit, and has many advantages such as achieving furnace-machine decoupling of the thermal power unit, improving the energy utilization efficiency and heating capacity of the unit.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal power plant heating, and in particular relates to a thermal power plant heating system based on a two-phase flow ejector and molten salt heat storage and an operating method thereof. Background Art

[0002] With the implementation of the carbon peak and carbon neutrality strategies, the proportion of wind power and solar power generation will increase significantly in the next decade. In order to eliminate the impact of the temporal and spatial instability brought by wind and solar power generation on the security of the power grid, deep peak regulation of thermal power units has become an inevitable choice.

[0003] Molten salt heat storage technology is a potential path for improving the flexibility of coal-fired power plants, enhancing their operational flexibility and renewable energy consumption. Using electric heating technology, surplus electricity can be converted into high-quality heat, stored in molten salt. This heat can then be released during peak hours for power generation. This allows for deep peak shaving and zero grid access, effectively absorbing renewable energy from the grid. Furthermore, the system's simplicity and ease of frequency regulation make it a promising approach for future applications.

[0004] Ejector heating technology has the advantages of flexible steam source selection, good heat load regulation performance, efficient operation under variable working conditions, and flexible allocation of thermal and electric loads. It does not require turbine center door modification and has no moving parts. It has broad application prospects in the field of industrial heating.

[0005] For thermal power units, the problem of continued rapid growth in heat load demand and relatively slow growth in electricity load is becoming increasingly prominent. Therefore, there is an urgent need to carry out flexibility transformation and develop efficient, flexible and safe heating technologies. Summary of the Invention

[0006] In response to the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a thermal power plant heating system and operation method based on two-phase flow ejectors and molten salt heat storage, which utilizes the abandoned electricity of the power plant that cannot be connected to the grid to heat molten salt for heat storage. When supplying heat, the superheated steam generated by the boiler is used to inject the feed water heated by the molten salt, and the mixed water is heated and pressurized before being supplied to heat users, thereby improving the heating level of the unit to meet user needs.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A thermal power plant heating system based on a two-phase flow ejector and molten salt heat storage, comprising a thermal power unit body, a heat recovery steam extraction system, an electrically heated molten salt heat storage system, and a two-phase flow ejector heating system;

[0009] The thermal power unit body includes a boiler 1, a steam turbine high-pressure cylinder 2, a steam turbine intermediate-pressure cylinder 3, a steam turbine low-pressure cylinder 4 and a generator 5 which are connected in sequence;

[0010] The regenerative steam extraction system includes a condenser 9, a condensate pump 18, a low-pressure regenerative heater 8, a deaerator 6, a first feedwater pump 17 and a high-pressure regenerative heater 7;

[0011] The electrically heated molten salt thermal storage system comprises a low-temperature molten salt tank 12, an electric heater 10, a high-temperature molten salt tank 11 and a salt / water heat exchanger 13 which are connected in sequence; the electric heater 10 is connected to a generator 5; the outlet of the low-temperature molten salt tank 12 is connected to the inlet of the high-temperature molten salt tank 11 via a low-temperature molten salt pump 20, a first regulating valve 24, the electric heater 10, a second regulating valve 25 and a high-temperature molten salt pump 19; the outlet of the high-temperature molten salt tank 11 is connected to the inlet of the low-temperature molten salt tank 12 via a third regulating valve 26, a salt / water heat exchanger 13 and a second circulating pump 22; the outlet bypass of the high-temperature molten salt tank 11 is connected to the inlet bypass of the low-temperature molten salt tank 12 via a fourth regulating valve 27 and the first circulating pump 21; The water side inlet of the salt / water heat exchanger 13 is connected to the feed water outlet bypass pipe of the deaerator 6 through the second feed water pump 23 and the fifth regulating valve 29; the two-phase flow ejector heating system includes a two-phase flow ejector 14, a heat user 15 and a return water tank 16 that are connected in sequence; the high-pressure inlet of the two-phase flow ejector 14 is connected to the main steam pipe of the boiler 1 through the main steam regulating valve 28; the low-pressure inlet of the two-phase flow ejector 14 is connected to the water side outlet of the salt / water heat exchanger 13 through the sixth regulating valve 30; the outlet of the two-phase flow ejector 14 is connected to the inlet pipe of the deaerator 6 through the seventh regulating valve 31, the heat user 15, the eighth regulating valve 32, the return water tank 16, the ninth regulating valve 33 and the check valve 34;

[0012] The electric heater 10 utilizes the abandoned electricity of the thermal power unit that cannot be connected to the grid to heat the molten salt for energy storage, so that the thermal power unit achieves near-zero output at the minimum power load. When there is a demand for heating, the stored heat of the molten salt is used to release heat to the water bypass at the outlet of the deaerator 6, and the water flow entering the salt / water heat exchanger 13 is regulated by the fifth regulating valve 29.

[0013] The two-phase flow ejector 14 is a gas-liquid two-phase flow ejector with central steam inlet and circumferential water inlet. The high-pressure inlet superheated steam flow is regulated by the main steam regulating valve 28, and the low-pressure inlet feed water flow is regulated by the sixth regulating valve 30; according to the needs of the heat user 15, the flow of the mixed fluid is regulated by the seventh regulating valve 31.

[0014] The return water tank 16 controls the water recovered from the heat user 15 through the eighth regulating valve 32, and after treatment, it is returned to the water tank of the deaerator 6 through the ninth regulating valve 33 and the check valve 34 to maintain the steam-water balance of the steam turbine; in addition, the return water tank 16 has the function of receiving external supplementary water, which can maintain the steam-water balance of the steam turbine when the heating medium is lost.

[0015] The molten salt in the electrically heated molten salt thermal storage system is a binary molten salt of 60% sodium nitrate and 40% potassium nitrate, and its operating temperature range is 220-600°C. Due to its high melting point, there is a risk of "frozen pipes". Therefore, the molten salt temperature is adjusted by the fourth regulating valve 27 and the first circulating pump 21 to prevent the molten salt from deviating from the operating temperature range and to keep the molten salt within the operating temperature range.

[0016] The operating method of the thermal power plant heating system based on the two-phase flow ejector and molten salt heat storage is as follows: in the heat storage mode, the first regulating valve 24 and the second regulating valve 25 are opened, the cold molten salt in the low-temperature molten salt tank 12 enters the electric heater 10 through the low-temperature molten salt pump 20 to absorb heat, and the hot molten salt enters the high-temperature molten salt tank 11 through the high-temperature molten salt pump 19 for storage, completing the heat storage process;

[0017] In the heat release mode, the high-temperature molten salt releases heat in the salt / water heat exchanger 13 and then enters the low-temperature molten salt tank 12 through the second circulation pump 22;

[0018] In the heating mode, the third regulating valve 26 and the fifth regulating valve 29 are opened, and the molten salt flow entering the salt / water heat exchanger 13 is adjusted according to the water consumption demand of the heat user 15 to match the heat load. The feed water absorbs heat and heats up in the salt / water heat exchanger 13 to meet the basic heating requirements. Then, the main steam regulating valve 28 and the sixth regulating valve 30, the seventh regulating valve 31, the eighth regulating valve 32, and the ninth regulating valve 33 are opened. The superheated steam flow entering the high-pressure inlet of the two-phase flow ejector 14 is adjusted according to the injection ratio parameter of the two-phase flow ejector 14. The working fluid and the injection fluid are fully mixed in the mixing chamber of the two-phase flow ejector 14. The mixed fluid is heated and pressurized at the outlet of the diffusion chamber. The flow rate of the mixed fluid is adjusted according to the heat demand and sent to the heat user 15 for heating. The return water after heating enters the return water tank through the eighth regulating valve 32 for water quality treatment and storage. Finally, the flow rate and pressure are adjusted by the ninth regulating valve 33 and the check valve 34, and then it is sent back to the deaerator 6, completing the heating process.

[0019] Compared with existing technologies, the present invention offers the following advantages: Based on two-phase flow ejectors and molten salt thermal storage technology, it proposes a novel thermal power plant heating system. This system stores the power plant's abandoned electricity in molten salt via electric heating and thermal storage. When heating is needed, the molten salt's thermal storage is used to raise the temperature of the deaerator bypass feedwater. Fresh steam from the boiler is then used to inject the high-temperature feedwater for heating, meeting the needs of heat users. The proposed system simultaneously improves the deep peak-shaving capability and heating level of thermal power units, offering numerous advantages, such as achieving boiler-generator decoupling, enhancing the unit's energy efficiency, and improving its heating capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of a thermal power plant heating system based on two-phase flow ejector and molten salt heat storage proposed by the present invention.

[0021] The numbers in the figure correspond to: 1. Boiler; 2. Steam turbine high-pressure cylinder; 3. Steam turbine intermediate-pressure cylinder; 4. Steam turbine low-pressure cylinder; 5. Generator; 6. Deaerator; 7. High-pressure regenerative heater; 8. Low-pressure regenerative heater; 9. Condenser; 10. Electric heater; 11. High-temperature molten salt tank; 12. Low-temperature molten salt tank; 13. Salt / water heat exchanger; 14. Two-phase flow ejector; 15. Heat user; 16. Return water tank; 17. First feed water pump; 18 , condensate pump; 19. High-temperature molten salt pump; 20. Low-temperature molten salt pump; 21. First circulation pump; 22. Second circulation pump; 23. Second feed water pump; 24. First regulating valve; 25. Second regulating valve; 26. Third regulating valve; 27. Fourth regulating valve; 28. Main steam regulating valve; 29. ​​Fifth regulating valve; 30. Sixth regulating valve; 31. Seventh regulating valve; 32. Eighth regulating valve; 33. Ninth regulating valve; 34. Check valve. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to the accompanying drawings.

[0023] like Figure 1 The figure shows a schematic diagram of a thermal power plant heating system based on a two-phase flow ejector and molten salt heat storage, including the thermal power unit body, a heat recovery steam extraction system, an electrically heated molten salt heat storage system, and a two-phase flow ejector heating system, wherein:

[0024] The thermal power unit body includes a boiler 1, a steam turbine high-pressure cylinder 2, a steam turbine intermediate-pressure cylinder 3, a steam turbine low-pressure cylinder 4, and a generator 5, which are connected in sequence. The fresh steam pipe of the boiler 1 connects to the high-pressure cylinder 2 and the high-pressure inlet of the two-phase flow ejector 14, respectively. The reheat steam pipe of the boiler 1 connects to the steam inlet of the intermediate-pressure cylinder 3. The exhaust pipes of the high-pressure cylinder 2 and the intermediate-pressure cylinder 3 connect to the reheater inlet of the boiler 1 and the steam inlet of the low-pressure cylinder 4, respectively. The exhaust pipe of the low-pressure cylinder 4 connects to the condenser 9.

[0025] The heat recovery steam extraction system includes a condenser 9 , a condensate pump 18 , a low-pressure heat recovery heater 8 , a deaerator 6 , a first feedwater pump 17 and a high-pressure heat recovery heater 7 . The inlet of the condenser 9 is connected to the exhaust pipe of the low-pressure cylinder 4 of the turbine and the drain pipe of the low-pressure regenerative heater 8; the outlet of the condenser 9 is connected to the inlet of the deaerator 6 via the condensate pump 18 and the low-pressure regenerative heater 8; the inlet of the deaerator 6 is connected to the extraction pipe of the intermediate-pressure cylinder 3 of the turbine, the drain pipe of the high-pressure regenerative heater 7, the outlet feed water pipe of the low-pressure regenerative heater 8 and the heat return water pipe at the outlet of the return water tank 16; the outlet feed water pipe of the deaerator 6 is connected to the feed water inlet pipe of the boiler 1 via the first feed water pump 17 and the high-pressure regenerative heater 7; the extraction steam inlet of the low-pressure regenerative heater 8 is connected to the extraction steam pipe of the low-pressure cylinder 4 of the turbine; the extraction steam inlet of the high-pressure regenerative heater 7 is connected to the extraction steam pipes of the high-pressure cylinder 2 of the turbine and the intermediate-pressure cylinder 3 of the turbine.

[0026] The electrically heated molten salt thermal storage system includes an electric heater 10, a high-temperature molten salt tank 11, a low-temperature molten salt tank 12, a salt / water heat exchanger 13, a high-temperature molten salt pump 19, a low-temperature molten salt pump 20, a first circulation pump 21, a second circulation pump 22, a second water supply pump 23, first to fourth regulating valves 24-27, and fifth to sixth regulating valves 29-30. The electric heater 10 is connected to the generator 5; the outlet of the low-temperature molten salt tank 12 is connected to the inlet of the high-temperature molten salt tank 11 via the low-temperature molten salt pump 20, the first regulating valve 24, the electric heater 10, the second regulating valve 25 and the high-temperature molten salt pump 19; the outlet of the high-temperature molten salt tank 11 is connected to the inlet of the low-temperature molten salt tank 12 via the third regulating valve 26, the salt / water heat exchanger 13 and the second circulating pump 22; the outlet bypass of the high-temperature molten salt tank 11 is connected to the inlet bypass of the low-temperature molten salt tank 12 via the fourth regulating valve 27 and the first circulating pump 21; the water side inlet of the salt / water heat exchanger 13 is connected to the water feed outlet bypass pipe of the deaerator 6 through the second water feed pump 23 and the fifth regulating valve 29.

[0027] The two-phase flow ejector heating system includes a two-phase flow ejector 14, a heat user 15, a return water tank 16, a main steam regulating valve 28, a seventh regulating valve 31, an eighth regulating valve 32, a ninth regulating valve 33, and a check valve 34. The high-pressure inlet of the two-phase flow ejector 14 is connected to the main steam pipeline of the boiler 1 via the main steam regulating valve 28; the low-pressure inlet of the two-phase flow ejector 14 is connected to the water-side outlet of the brine / water heat exchanger 13 via the sixth regulating valve 30; and the outlet of the two-phase flow ejector 14 is connected to the inlet pipeline of the deaerator 6 via the seventh regulating valve 31, the heat user 15, the eighth regulating valve 32, the return water tank 16, the ninth regulating valve 33, and the check valve 34.

[0028] In the heat storage mode, the first regulating valve 24 and the second regulating valve 25 are opened, and the cold molten salt in the low-temperature molten salt tank 12 enters the electric heater 10 through the low-temperature molten salt pump 20 to absorb heat, and the hot molten salt enters the high-temperature molten salt tank 11 for storage via the high-temperature molten salt pump 19, completing the heat storage process.

[0029] In the heat release mode, the high-temperature molten salt releases heat in the salt / water heat exchanger 13 and then enters the low-temperature molten salt tank 12 through the second circulation pump 22 .

[0030] In the heating mode, the third regulating valve 26 and the fifth regulating valve 29 are opened, and the molten salt flow entering the salt / water heat exchanger 13 is adjusted according to the water demand of the heat user 15 to match the heat load. The feed water absorbs heat and heats up in the salt / water heat exchanger 13 to meet the basic heating requirements. Then, the main steam regulating valve 28 and the sixth regulating valve 30, the seventh regulating valve 31, the eighth regulating valve 32, and the ninth regulating valve 33 are opened. The superheated steam flow entering the high-pressure inlet of the two-phase flow ejector 14 is adjusted according to parameters such as the injection ratio of the two-phase flow ejector 14. The working fluid and the injection fluid are fully mixed in the mixing chamber of the two-phase flow ejector 14. The mixed fluid is heated and pressurized at the outlet of the diffusion chamber. The flow rate of the mixed fluid is adjusted according to the heat demand and sent to the heat user 15 for heating. The return water after heating enters the return water tank through the eighth regulating valve 32 for water quality treatment and storage. Finally, the ninth regulating valve 33 and the check valve 34 are used to adjust the flow rate and reduce the pressure before returning to the deaerator 6, thus completing the heating process.

[0031] The first circulation pump 21 and the fourth regulating valve 27 are used to adjust the temperature of the molten salt to prevent the molten salt from deviating from the operating temperature range.

[0032] When the heating medium is lost, the return water tank receives external supplementary water to maintain the steam-water balance.

Claims

1. A thermal power plant heating system based on two-phase flow ejector and molten salt heat storage, characterized in that: It includes the thermal power unit body, heat recovery steam extraction system, electric heating molten salt heat storage system and two-phase flow ejector heating system; The thermal power unit body comprises a boiler (1), a steam turbine high-pressure cylinder (2), a steam turbine intermediate-pressure cylinder (3), a steam turbine low-pressure cylinder (4) and a generator (5) which are connected in sequence; The heat recovery steam extraction system includes a condenser (9), a condensate pump (18), a low-pressure heat recovery heater (8), a deaerator (6), a first feedwater pump (17) and a high-pressure heat recovery heater (7); The electric heating molten salt heat storage system comprises a low-temperature molten salt tank (12), an electric heater (10), a high-temperature molten salt tank (11) and a salt / water heat exchanger (13) which are connected in sequence; the electric heater (10) is connected to a generator (5); the outlet of the low-temperature molten salt tank (12) is connected to the inlet of the high-temperature molten salt tank (11) via a low-temperature molten salt pump (20), a first regulating valve (24), an electric heater (10), a second regulating valve (25) and a high-temperature molten salt pump (19); the high-temperature molten salt tank (1 The outlet of the high-temperature molten salt tank (11) is connected to the inlet of the low-temperature molten salt tank (12) through the third regulating valve (26), the salt / water heat exchanger (13) and the second circulating pump (22); the outlet bypass of the high-temperature molten salt tank (11) is connected to the inlet bypass of the low-temperature molten salt tank (12) through the fourth regulating valve (27) and the first circulating pump (21); the water side inlet of the salt / water heat exchanger (13) is connected to the water outlet bypass pipeline of the deaerator (6) through the second water supply pump (23) and the fifth regulating valve (29); The two-phase flow ejector heating system comprises a two-phase flow ejector (14), a heat user (15) and a return water tank (16) which are connected in sequence; the high-pressure inlet of the two-phase flow ejector (14) is connected to the main steam pipeline of the boiler (1) via a main steam regulating valve (28); the low-pressure inlet of the two-phase flow ejector (14) is connected to the water side outlet of the salt / water heat exchanger (13) via a sixth regulating valve (30); the outlet of the two-phase flow ejector (14) is connected to the inlet pipeline of the deaerator (6) via a seventh regulating valve (31), the heat user (15), the eighth regulating valve (32), the return water tank (16), the ninth regulating valve (33) and the check valve (34); The electric heater (10) utilizes the abandoned electricity of the thermal power unit that cannot be connected to the grid to heat the molten salt for energy storage, and the minimum power load of the thermal power unit achieves near-zero output. When there is a demand for heat supply, the stored heat of the molten salt is used to release heat to the water bypass of the deaerator (6) outlet, and the water flow entering the salt / water heat exchanger (13) is regulated by the fifth regulating valve (29).

2. A thermal power plant heating system based on two-phase flow ejector and molten salt heat storage according to claim 1, characterized in that: The two-phase flow ejector (14) is a gas-liquid two-phase flow ejector with central steam inlet and circumferential water inlet. The high-pressure inlet superheated steam flow is regulated by a main steam regulating valve (28), and the low-pressure inlet feed water flow is regulated by a sixth regulating valve (30); according to the needs of the heat user (15), the flow of the mixed fluid is regulated by a seventh regulating valve (31).

3. A thermal power plant heating system based on two-phase flow ejector and molten salt heat storage according to claim 1, characterized in that: The return water tank (16) controls the water recovered from the heat user (15) through the eighth regulating valve (32), and returns the water to the water tank of the deaerator (6) through the ninth regulating valve (33) and the check valve (34) after treatment, so as to maintain the steam-water balance of the steam turbine; in addition, the return water tank (16) has the function of receiving external supplementary water, so as to maintain the steam-water balance of the steam turbine when the heating medium is lost.

4. A thermal power plant heating system based on two-phase flow ejector and molten salt heat storage according to claim 1, characterized in that: The molten salt in the electrically heated molten salt thermal storage system is a binary molten salt of 60% sodium nitrate and 40% potassium nitrate. The temperature of the molten salt is adjusted by a fourth regulating valve (27) and a first circulating pump (21) to maintain the molten salt within a use temperature range.

5. The method for operating a thermal power plant heating system based on a two-phase flow ejector and molten salt heat storage according to any one of claims 1 to 4, characterized in that: In the heat storage mode, the first regulating valve (24) and the second regulating valve (25) are opened, and the cold molten salt in the low-temperature molten salt tank (12) enters the electric heater (10) through the low-temperature molten salt pump (20) to absorb heat, and the hot molten salt enters the high-temperature molten salt tank (11) for storage via the high-temperature molten salt pump (19), completing the heat storage process; In the heat release mode, the high-temperature molten salt releases heat in the salt / water heat exchanger (13) and then enters the low-temperature molten salt tank (12) through the second circulation pump (22); In the heating mode, the third regulating valve (26) and the fifth regulating valve (29) are opened, and the molten salt flow entering the salt / water heat exchanger (13) is adjusted according to the water demand of the heat user (15) to match the heat load. The feed water absorbs heat and rises in the salt / water heat exchanger (13) to meet the basic heating requirements. Then, the main steam regulating valve (28) and the sixth regulating valve (30), the seventh regulating valve (31), the eighth regulating valve (32), and the ninth regulating valve (33) are opened, and the flow rate of the molten salt entering the two-phase flow ejector (14) is adjusted according to the injection ratio parameter of the two-phase flow ejector (14). The superheated steam flow at the high-pressure inlet of the two-phase flow ejector (14), the working fluid and the ejection fluid are fully mixed in the mixing chamber of the two-phase flow ejector (14). The mixed fluid at the outlet of the diffusion chamber completes the temperature and pressure increase process. The mixed fluid flow is adjusted according to the heat demand and sent to the heat user (15) for heating. The return water after heating enters the return water tank through the eighth regulating valve (32) for water quality treatment and storage. Finally, it is sent back to the deaerator (6) after the flow and pressure are adjusted by the ninth regulating valve (33) and the check valve (34). At this point, the heating process is completed.

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