Coal-fired unit flexible peak regulation system using steam and flue gas to heat fused salt for heat storage

Abstract

The invention discloses a coal-fired unit flexible peak shaving system for heating fused salt for heat storage by using steam and flue gas. The coal-fired unit flexible peak shaving system comprises a coal-fired unit, a fused salt heat storage system and a fused salt heat release system. Steam and flue gas are used as heat sources to heat fused salt, conversion to electric energy is avoided in the process, cold source loss is reduced, and more energy is saved; the flue gas is used for further heating the fused salt, so that the final temperature of the fused salt can be increased; fused salt is directly heated through flue gas, the heat exchange process is reduced, and the energy utilization efficiency is higher. The condensation water preheater is arranged, so that the cold salt temperature can be effectively controlled; according to the method, deep peak regulation and peak regulation of the unit can be considered, and energy transfer in time and space is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of peak regulation of coal-fired power plants, and in particular to a flexible peak regulation system for coal-fired units that utilizes steam and flue gas to heat molten salt for heat storage. Background Art

[0002] Renewable energy generation boasts the advantages of being low-carbon, clean, and environmentally friendly, and is the future direction of energy development. However, renewable energy sources such as solar and wind power suffer from intermittent and unstable power generation. As renewable energy installed capacity continues to increase and its share in the energy mix continues to rise, these shortcomings are increasingly impacting the security and stability of the power grid.

[0003] To mitigate the impact of power generation fluctuations on the grid after renewable energy sources such as solar and wind power are integrated, and to protect the grid's security and stability, coal-fired power plants typically undertake peak load regulation and peak load peaking tasks. When renewable energy generation is high, coal-fired units reduce their power output and generate less; when renewable energy generation is low, coal-fired units increase their power output and generate more. This places high demands on the operational flexibility of coal-fired units. However, due to unit aging or equipment issues, the peak load regulation capabilities of some coal-fired units are limited. To improve the deep regulation capabilities of these units, integrating coal-fired units with energy storage systems is an effective way to improve their deep regulation capabilities.

[0004] Using molten salt as a heat storage medium and heating it with steam or electricity for peak-shaving is a common method for thermal energy storage. However, due to the heat transfer temperature difference between steam and molten salt, the temperature of the molten salt must be lower than that of the steam, limited by the steam temperature. Therefore, during the heat release process, the molten salt cannot heat water to produce high-parameter steam such as main steam or reheat steam. Using electricity as a heat source to heat the molten salt can raise the temperature of the molten salt to a level higher than that of steam. However, electricity is the primary energy source of coal-fired power plants, and due to cooling losses, over 50% of the energy is wasted during the power generation process, a well-known fact in the power industry. Therefore, using electricity to heat molten salt for peak-shaving is uneconomical and environmentally unfriendly.

[0005] Therefore, research and development of a flexible peak-shaving system for coal-fired units that uses steam and flue gas to heat molten salt for heat storage is of great significance for flexible peak-shaving of coal-fired power plants, ensuring the stability and safety of the power grid, and accommodating new energy power generation. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention designs a flexible peak-shaving system for coal-fired units that uses steam and flue gas to heat molten salt for heat storage. The present invention uses wide-temperature molten salt as a heat storage medium. When the unit needs to peak, the main steam and reheated steam are extracted to heat the molten salt for energy storage, and the thermal energy of the steam is transferred to the molten salt, thereby reducing the amount of steam entering the steam turbine and achieving unit peak regulation. The molten salt initially heated by steam is further heated into high-temperature molten salt in the bypass flue gas duct. When the unit needs to peak, the feed water from the deaerator outlet is extracted and heated in the heat exchanger to generate main steam, and enters the steam turbine, thereby achieving unit peak.

[0007] The present invention adopts the following technical solutions: A flexible peak-shaving system for coal-fired units that utilizes steam and flue gas to heat molten salt for heat storage, comprising a coal-fired unit, a molten salt heat storage system, and a molten salt heat release system; The coal-fired unit includes a boiler and a steam turbine. The boiler superheater is connected to the high-pressure cylinder of the steam turbine through the main steam pipe. The outlet of the high-pressure cylinder of the steam turbine is connected to the boiler reheater through the cold reheat steam pipe. The boiler reheater is connected to the intermediate-pressure cylinder of the steam turbine through the reheat steam pipe. The outlet of the intermediate-pressure cylinder of the steam turbine is connected to the low-pressure cylinder of the steam turbine. The outlet of the low-pressure cylinder of the steam turbine is connected to the condenser, the condenser is connected to the low-pressure heater, and then to the deaerator, the deaerator is connected to the high-pressure heater, and the high-pressure heater is connected to the boiler superheater through a pipeline. The molten salt heat storage system includes a cold salt tank, a cold salt pump, a main steam heat exchanger, a reheat steam heat exchanger, a flue gas heat exchanger and a hot salt tank. The cold salt tank, the cold salt pump, the main steam heat exchanger, the reheat steam heat exchanger, the flue gas heat exchanger and the hot salt tank are connected in sequence through pipelines; the high-pressure cylinder of the steam turbine is connected to the main steam heat exchanger through a pipeline, and finally connected to the cold reheat steam pipeline, the medium-pressure cylinder of the steam turbine is connected to the reheat steam heat exchanger through a pipeline, and finally connected to the low-pressure cylinder of the steam turbine. A bypass flue gas pipeline is provided in the boiler, and a flue gas heat exchanger is provided in the bypass flue gas pipeline; The molten salt heat release system includes a hot salt tank, a hot salt pump, a superheater, an evaporator, a feed water preheater, a condensate preheater and a cold salt tank. The hot salt tank, the hot salt pump, the superheater, the evaporator, the feed water preheater, the condensate preheater and the cold salt tank are connected in sequence through pipelines; the deaerator is connected to the feed water preheater, the evaporator, the superheater in sequence through feed water pump 2, and finally connected to the high-pressure cylinder of the steam turbine. The low-pressure heater is connected to the condensate preheater through condensate pump 2, and finally connected to the deaerator.

[0008] Preferably, the condenser and the low-pressure heater are connected via a condensate pump.

[0009] Preferably, the deaerator is connected to the high-pressure heater via a feed water pump.

[0010] Preferably, the steam extraction port of the intermediate pressure cylinder of the steam turbine is connected to the deaerator through a pipeline.

[0011] Preferably, the steam turbine is coaxially connected to the generator. Steam expands in the steam turbine to do work, driving the generator to rotate and generate electricity.

[0012] Preferably, a smoke damper is provided at the inlet of the bypass smoke duct, and the opening and closing size of the smoke damper controls the amount of smoke entering the bypass smoke duct.

[0013] Preferably, a regulating valve 1 is installed between the main steam heat exchanger and the cold reheat steam pipeline. The regulating valve 1 regulates the amount of extracted main steam.

[0014] Preferably, a second regulating valve is installed between the reheat steam heat exchanger and the low-pressure cylinder of the steam turbine. The second regulating valve regulates the amount of extracted reheat steam.

[0015] The beneficial effects of the present invention are as follows: (1) the present invention utilizes steam and flue gas as heat sources to heat molten salt without undergoing conversion to electrical energy in the middle, thereby reducing cold source loss and being more energy-efficient; (2) the present invention utilizes flue gas to further heat the molten salt, thereby increasing the final temperature of the molten salt; (3) the present invention utilizes flue gas to directly heat the molten salt, thereby reducing the heat exchange process and achieving higher energy utilization efficiency; (4) the present invention is provided with a condensate preheater, thereby effectively controlling the cold salt temperature; (5) the present invention can take into account both deep peak regulation and peak load regulation of the unit, thereby realizing energy transfer in time and space. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 and Figure 2 Schematic diagrams of the heat storage and heat release structures of the present invention, respectively, wherein steam and water are represented by solid lines, and molten salt is represented by dotted lines; Figure: 1. Boiler; 1a. Boiler superheater; 1b. Boiler reheater; 1c. Main steam pipe; 1d. Reheat steam pipe; 2. Steam turbine high-pressure cylinder; 2a. Cold reheat steam pipe; 3. Steam turbine intermediate-pressure cylinder; 4. Steam turbine low-pressure cylinder; 5. Generator; 6. Condenser; 7. Condensate pump (1); 8. Low-pressure heater; 9. Deaerator; 10. Feedwater pump (1); 11. High-pressure heater; 12. Bypass flue gas Gas pipeline; 13. Flue gas damper; 14. Cold salt tank; 14a. Cold salt pump; 15. Hot salt tank; 15a. Hot salt pump; 16. Main steam heat exchanger; 16a. Control valve 1; 17. Reheat steam heat exchanger; 17a. Control valve 2; 18. Flue gas heat exchanger; 19. Condensate pump 2; 20. Feed water pump 2; 21. Condensate preheater; 22. Feed water preheater; 23. Evaporator; 24. Superheater. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is further described in detail below through specific embodiments and in conjunction with the accompanying drawings: Example: Figure 1 and Figure 2 As shown, a flexible peak-shaving system for coal-fired units using steam and flue gas to heat molten salt for heat storage includes a coal-fired unit, a molten salt heat storage system, and a molten salt heat release system; The coal-fired unit includes a boiler 1 and a steam turbine. The boiler superheater 1a is connected to the turbine's high-pressure cylinder 2 via a main steam pipe 1c. The outlet of the turbine's high-pressure cylinder 2 is connected to the boiler's reheater 1b via a cold reheat steam pipe 2a. The boiler's reheater 1b is connected to the turbine's intermediate-pressure cylinder 3 via a reheat steam pipe 1d. The outlet of the turbine's intermediate-pressure cylinder 3 is connected to the turbine's low-pressure cylinder 4. The steam turbine is coaxially connected to a generator 5. Steam expands in the turbine, generating work and driving the generator to generate electricity.

[0018] The outlet of the low-pressure cylinder 4 of the steam turbine is connected to the condenser 6, and the condenser 6 is connected to the low-pressure heater 8 through a condensate pump 7, and then connected to the deaerator 9. The deaerator 9 is connected to the high-pressure heater 11 through a feed water pump 10, and the high-pressure heater 11 is connected to the boiler superheater 1a through a pipeline. The steam extraction port of the intermediate-pressure cylinder 3 of the steam turbine is connected to the deaerator 9 through a pipeline.

[0019] The molten salt heat storage system includes a cold salt tank 14, a cold salt pump 14a, a main steam heat exchanger 16, a reheat steam heat exchanger 17, a flue gas heat exchanger 18 and a hot salt tank 15. The cold salt tank 14, the cold salt pump 14a, the main steam heat exchanger 16, the reheat steam heat exchanger 17, the flue gas heat exchanger 18 and the hot salt tank 15 are connected in sequence through pipelines; the high-pressure cylinder 2 of the steam turbine is connected to the main steam heat exchanger 16 and the regulating valve 1 16a through a pipeline, and finally connected to the cold reheat steam pipe 2a, the intermediate-pressure cylinder 3 of the steam turbine is connected to the reheat steam heat exchanger 17 and the regulating valve 2 17a through a pipeline, and finally connected to the low-pressure cylinder 4 of the steam turbine; a bypass flue gas pipe 12 is provided in the boiler, and a flue gas heat exchanger 18 is provided in the bypass flue gas pipe; a flue gas damper 13 is provided at the inlet of the bypass flue gas pipe, and the opening and closing size of the flue gas damper controls the amount of flue gas entering the bypass flue gas pipe.

[0020] The molten salt heat release system includes a hot salt tank 15, a hot salt pump 15a, a superheater 24, an evaporator 23, a feed water preheater 22, a condensate preheater 21 and a cold salt tank 14. The hot salt tank 15, the hot salt pump 15a, the superheater 24, the evaporator 23, the feed water preheater 22, the condensate preheater 21 and the cold salt tank 14 are connected in sequence through pipelines; the deaerator 9 is connected to the feed water preheater 22, the evaporator 23, the superheater 24 in sequence through the feed water pump 20, and finally connected to the turbine high-pressure cylinder 2, the low-pressure heater 8 is connected to the condensate preheater 21 through the condensate pump 2 19, and finally connected to the deaerator 9.

[0021] System heat storage process, such as Figure 1 As shown: During heat storage and peak shaving, the cold molten salt in cold salt tank 14 is driven by cold salt pump 14a into main steam heat exchanger 16 and reheat steam heat exchanger 17 to absorb heat from the steam. The molten salt at the steam heat exchanger outlet enters flue gas heat exchanger 18 to absorb heat from the flue gas. After the molten salt temperature reaches the hot salt temperature, the hot molten salt enters hot salt tank 15. During the heat storage process, flue gas damper 13 is opened, and the amount of flue gas entering the bypass flue gas duct 12 is controlled by controlling the opening and closing of flue gas damper 13.

[0022] Main steam is extracted along the main steam pipeline 1c and enters the main steam heat exchanger 16 to heat the molten salt. The steam at the heat exchanger's outlet is cooled and decompressed by regulating valve 16a before entering the cold reheat steam pipeline 2a. Reheat steam is extracted along the reheat steam pipeline 1d and enters the reheat steam heat exchanger 17 to heat the molten salt. The steam at the heat exchanger's outlet is cooled and decompressed by regulating valve 27a before entering the low-pressure steam turbine. The extraction of main and reheat steam reduces the amount of steam entering the high-pressure and intermediate-pressure steam turbines 2 and 3, reducing the power generated by generator 5 and achieving peak load regulation for the coal-fired unit.

[0023] System exothermic process, such as Figure 2 As shown: At the peak of heat release, the hot molten salt in the hot salt tank 15 is driven by the hot salt pump 15a into the superheater 24, evaporator 23, feedwater preheater 22, and condensate preheater 21 in sequence, where it heats steam and water. After the molten salt temperature drops to the cold salt temperature, the cold molten salt enters the cold salt tank 14. During the heat release process, the flue gas damper 13 is closed.

[0024] The deoxygenated water at the outlet of the deaerator 9 is driven by the feed water pump 20 to enter the feed water preheater 22, and then the feed water enters the evaporator 23, where the feed water absorbs heat and evaporates into steam. The steam enters the superheater 24 and is heated into superheated steam. The parameters of the superheated steam are consistent with those of the main steam. The superheated steam enters the high-pressure cylinder 2 of the steam turbine, the amount of steam in the steam turbine increases, the power generation power of the generator 5 increases, and the coal-fired unit reaches its peak.

[0025] Part of the condensate at the outlet of the low-pressure heater 8 is driven by the condensate pump 2 19 into the condensate preheater 21. The condensate absorbs the heat of the molten salt in the condensate preheater 21, and the temperature of the molten salt is cooled to the cold salt temperature. After the condensate temperature reaches the deoxygenated water temperature, it enters the deaerator 9 for deoxygenation.

[0026] The embodiment described above is only a preferred solution of the present invention and does not limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solution described in the claims.

Claims

1. A flexible peak-shaving system for coal-fired units that utilizes steam and flue gas to heat molten salt for heat storage, comprising a coal-fired unit, a molten salt heat storage system, and a molten salt heat release system; The coal-fired unit includes a boiler and a steam turbine. The boiler superheater is connected to the high-pressure cylinder of the steam turbine through the main steam pipe. The outlet of the high-pressure cylinder of the steam turbine is connected to the boiler reheater through the cold reheat steam pipe. The boiler reheater is connected to the intermediate-pressure cylinder of the steam turbine through the reheat steam pipe. The outlet of the intermediate-pressure cylinder of the steam turbine is connected to the low-pressure cylinder of the steam turbine. The outlet of the low-pressure cylinder of the steam turbine is connected to the condenser, the condenser is connected to the low-pressure heater, and then to the deaerator, the deaerator is connected to the high-pressure heater, and the high-pressure heater is connected to the boiler superheater through a pipeline. The invention is characterized in that: The molten salt heat storage system includes a cold salt tank, a cold salt pump, a main steam heat exchanger, a reheat steam heat exchanger, a flue gas heat exchanger and a hot salt tank. The cold salt tank, the cold salt pump, the main steam heat exchanger, the reheat steam heat exchanger, the flue gas heat exchanger and the hot salt tank are connected in sequence through pipelines; the high-pressure cylinder of the steam turbine is connected to the main steam heat exchanger through a pipeline, and finally connected to the cold reheat steam pipeline; the intermediate-pressure cylinder of the steam turbine is connected to the reheat steam heat exchanger through a pipeline, and finally connected to the low-pressure cylinder of the steam turbine; a bypass flue gas pipeline is provided in the boiler, and a flue gas heat exchanger is provided in the bypass flue gas pipeline; The molten salt heat release system includes a hot salt tank, a hot salt pump, a superheater, an evaporator, a feed water preheater, a condensate preheater and a cold salt tank. The hot salt tank, the hot salt pump, the superheater, the evaporator, the feed water preheater, the condensate preheater and the cold salt tank are connected in sequence through pipelines; the deaerator is connected to the feed water preheater, the evaporator, the superheater in sequence through feed water pump 2, and finally connected to the high-pressure cylinder of the steam turbine. The low-pressure heater is connected to the condensate preheater through condensate pump 2, and finally connected to the deaerator.

2. The flexible peak-shaving system for coal-fired units using steam and flue gas to heat molten salt for heat storage according to claim 1 is characterized in that: The condenser is connected to the low-pressure heater via a condensate pump.

3. The flexible peak-shaving system for coal-fired units using steam and flue gas to heat molten salt for heat storage according to claim 1 is characterized in that: The deaerator is connected to the high-pressure heater through a feed water pump.

4. The coal-fired unit flexible peak-shaving system using steam and flue gas to heat molten salt for heat storage according to claim 1 is characterized in that: The steam extraction port of the intermediate pressure cylinder of the steam turbine is connected to the deaerator through a pipeline.

5. The coal-fired unit flexible peak-shaving system using steam and flue gas to heat molten salt for heat storage according to claim 1 is characterized in that: The steam turbine is coaxially connected to the generator.

6. The coal-fired unit flexible peak-shaving system using steam and flue gas to heat molten salt for heat storage according to claim 1 is characterized in that: A smoke damper is provided at the inlet of the bypass smoke duct, and the opening and closing size of the smoke damper controls the amount of smoke entering the bypass smoke duct.

7. The flexible peak-shaving system for coal-fired units using steam and flue gas to heat molten salt for heat storage according to claim 1 is characterized in that: A regulating valve 1 is installed between the main steam heat exchanger and the cold reheat steam pipeline.

8. The coal-fired unit flexible peak-shaving system utilizing steam and flue gas to heat molten salt for heat storage according to claim 1 is characterized in that: A second regulating valve is installed between the reheat steam heat exchanger and the low-pressure cylinder of the steam turbine.

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