High temperature and high pressure steam heating molten salt energy storage system for thermal power plants

Abstract

The present invention relates to a high-temperature and high-pressure steam-heated molten salt energy storage system for a thermal power plant. The energy storage system includes a conventional thermal power generation system, a steam-heated molten salt system and a molten salt heat storage system. The conventional thermal power generation system is a reheat steam unit; the steam-heated molten salt system is composed of five heat exchangers, which are respectively connected to the thermal power generation system and the molten salt heat storage system to realize the heat exchange function between the high-temperature and high-pressure steam of the thermal power generation system and the molten salt heat storage system. The present invention heats the molten salt energy storage system through a high-temperature and high-pressure steam to store the high-quality steam of the thermal power generation system, and can also bypass the steam at the turbine inlet to achieve complete thermoelectric decoupling, which is beneficial to the flexible operation and deep peak regulation of the thermal power generation system, while ensuring the safe operation of the boiler and steam turbine generator set.

Description

Technical Field

[0001] The present invention relates to the field of energy storage technology, and in particular to a high-temperature and high-pressure steam-heated molten salt energy storage system for a thermal power plant. Background Art

[0002] In order to practice the concept of green development, China's energy structure has rapidly transformed to new energy in recent years. The rapid growth of new energy such as wind energy and solar energy has greatly increased the number of times thermal power units participate in peak regulation and the requirements for their quality. On the other hand, due to economic development, the peak-to-valley difference in electricity consumption is increasing, and cogeneration units are mostly used in northern China to ensure winter heating. The peak-to-valley difference in electricity consumption and the contradiction between heat and power in the heating season have deteriorated sharply. Since thermal power units are still the most important basic power generation method in China, the power grid has continuously improved its standards and required thermal power units to respond quickly to load changes. The development of thermal-electric decoupling technology is conducive to the flexible peak regulation and wide load operation of thermal power generation systems, ensuring the safe operation of the power grid.

[0003] Because molten salt energy storage systems have been widely used in solar thermal power generation systems and have the ability to be applied on a large scale in commercial applications, domestic scholars have proposed molten salt heat storage technology for thermal power plants. Chinese patents CN 107401430 A and CN108534576 A respectively disclose "Thermal Storage System for Electric Power and Thermal Power Peak Regulation in Thermal Power Plants" and "A Molten Salt Energy Storage System for Electric Power Peak Regulation of Thermal Power Units". During the day, steam turbines are used to extract steam to heat molten salt and store heat energy. Chinese patents CN 108316980 A, CN 110206603 A, and CN 110207092 A respectively disclose "A thermal power unit molten salt heat storage and heat release peak-shaving system", "A thermal power unit thermoelectric decoupling system and method based on steam-heated molten salt heat storage", and "A thermal power unit power generation peak-shaving system and method based on steam-heated molten salt heat storage". Part of the high-temperature reheated steam is extracted from the boiler reheat outlet, and heat is exchanged with the molten salt in the molten salt heat storage system to complete the molten salt heat storage. Chinese patent "CN 106885232A" discloses "A liquid energy storage system suitable for deep peak-shaving of thermal power units", which uses one of the high-pressure main steam or high-temperature reheated steam to heat the molten salt system to achieve heat storage, and the steam after heat release continues to return to the steam turbine to do work or to the boiler reheat system. Chinese patents "CN 108426238 A" and "CN 108548168 A" respectively disclose "A molten salt heat storage heating system for thermal power plants using main steam heating" and "A molten salt heat storage peak-shaving system for thermal power plants using main steam heating", extracting a part of the main steam to exchange heat with molten salt to achieve heat storage. (Only a small part of the main steam can be extracted because the reheat steam becomes less). Chinese patent "CN 208418894 U" discloses "A molten salt energy storage heating system for deep peak-shaving and flexibility transformation of power plants", extracting a part of the high-pressure main steam and a part of the reheat steam to exchange heat with molten salt respectively, and the high-pressure main steam becomes low-temperature high-pressure main steam after heat exchange, and enters the reheater after mixing with the second-stage exhaust of the steam turbine. After heat exchange, the reheat steam becomes low-temperature reheat steam for heating. (Only a small amount of main steam can be extracted, otherwise the low-temperature and high-pressure main steam will cause overpressure in the reheater; there must be a heating load to achieve heat storage; high-temperature steam phase change heating cannot be used, and most of the heat energy is wasted for heating or condensation). The Chinese patent "CN 110006026 A" discloses "A deep peak regulation system for thermal power plants", which extracts a portion of high-pressure main steam and a portion of reheated steam for heat exchange with molten salt respectively. The high-pressure main steam is depressurized and then heat exchanged, and then enters the reheater. After heat exchange, the reheated steam becomes low-temperature steam and enters the low-pressure heater of the steam turbine. (The high-pressure main steam is greatly depressurized, resulting in energy loss; the high-temperature steam phase change cannot be used for heating, and most of the heat energy is wasted for heating or condensation)

[0004] The current molten salt heat storage systems are highly coupled with thermal power generation systems and have small heat storage capacity. They cannot achieve molten salt energy storage alone when the steam turbine is shut down. The heat storage capacity of some molten salt heat storage systems is limited by the heating capacity, and some molten salt heat storage systems cannot store steam phase change heat, resulting in heat waste. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a high-temperature and high-pressure steam-heated molten salt energy storage system for a thermal power plant. By heating the molten salt system with steam, partial peak-shaving of the turbine load can be achieved, and full peak-shaving of the turbine load can be achieved without being restricted by heat supply. At the same time, it ensures that almost all high-grade steam thermal energy is stored, further improving the deep peak-shaving capability of the thermal power plant.

[0006] The technical solution adopted by the present invention is: a high-temperature and high-pressure steam-heated molten salt energy storage system for a thermal power plant, comprising a thermal power generation system, a steam-heated molten salt system and a molten salt heat storage system, characterized in that: the thermal power generation system, the steam-heated molten salt system and the molten salt heat storage system are connected in sequence to realize the heat exchange function between the high-temperature and high-pressure steam of the thermal power generation system and the molten salt heat storage system.

[0007] Preferably, the steam-heated molten salt system comprises a superheater, an evaporator heater, a preheater A, a high-pressure water feed pump and a high-pressure feed temperature mixing device. The high-pressure main steam of the thermal power generation system enters the superheater through the steam inlet pipe of the hot heater, exchanges heat with the molten salt in the superheater, and then enters the evaporator heater through the steam outlet pipe of the hot heater, exchanges heat with the molten salt in the evaporator heater, condenses into high-pressure water, and then enters the preheater A through the high-pressure water inlet pipe of the preheater A, becomes high-pressure supercooled water, and is finally pressurized by the high-pressure water feed pump and sent to the water supply system to realize the high-pressure steam-water circulation.

[0008] Furthermore, the steam-heated molten salt system also includes a reheat heater, a preheat heater B, a high-temperature and high-pressure steam connecting pipe and a low-temperature reheat steam exhaust to auxiliary steam header pipe. The high-temperature reheat steam of the thermal power generation system is first mixed with part of the high-pressure main steam from the high-temperature and high-pressure steam connecting pipe, and after the pressure is increased, it enters the reheat heater through the reheat heater steam inlet pipe, exchanges heat with the molten salt in the reheat heater, and then enters the preheat heater B through the reheat heater steam outlet pipe. After becoming low-temperature reheat steam, it returns to the low-temperature reheat system, and the incremental steam brought by the high-pressure main steam enters the auxiliary steam header through the low-temperature reheat steam exhaust to auxiliary steam header pipe, thereby realizing the high-temperature reheat steam-water cycle.

[0009] Furthermore, the low-temperature molten salt in the low-temperature molten salt heat storage tank of the molten salt heat storage system is pressurized by a low-temperature molten salt pump and then divided into two molten salt paths, one path enters the preheating heater A to be heated, and the other path enters the preheating heater B to be heated. The two molten salt paths are mixed and then enter the evaporation heater. After heating, they are divided into two molten salt paths again, one path enters the superheating heater to be heated, and the other path enters the reheating heater to be heated. The two molten salt paths are mixed and then enter the high-temperature molten salt heat storage tank, thereby realizing the flow and heat storage of the molten salt circuit.

[0010] Furthermore, the operating temperature of the high-temperature molten salt heat storage tank is 400°C to 565°C.

[0011] Furthermore, the operating temperature of the low-temperature molten salt heat storage tank is 290°C to 310°C.

[0012] The beneficial effects achieved by the present invention are: the high-temperature and high-pressure steam of the thermal power plant is used to heat the molten salt, and the high-pressure main steam and the high-temperature reheat steam heat the molten salt at the same time, and the low-temperature molten salt is heated into high-temperature molten salt. After the high-pressure main steam is cooled by the molten salt, it becomes high-pressure condensate, which is pressurized and returned to the boiler feed water system to complete the cycle heating. After being cooled by the molten salt, the high-temperature reheat steam becomes low-temperature reheat steam, which returns to the boiler reheater to complete the cycle heating. In this way, the steam turbine can be flexibly variable in load, while ensuring the stable load operation of the boiler, and it can also be shut down without stopping the boiler.

[0013] The present invention has the following advantages:

[0014] (1) Realize decoupled operation of boiler and steam turbine and improve the operational flexibility of steam turbine;

[0015] (2) Improve the deep peak-shaving capability of thermal power plants to meet grid dispatching needs;

[0016] (3) Higher heat storage efficiency, directly storing high-quality steam heat, avoiding the low heat storage efficiency of electric heating. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1-2 It is a schematic diagram of the process of the high-temperature and high-pressure steam heating molten salt energy storage system of a thermal power plant of the present invention;

[0018] Figure symbols: conventional thermal power generation system 1, high-pressure main steam pipeline 1.1, high-temperature reheat steam pipeline 1.2, low-temperature reheat steam pipeline 1.3, feed water pipeline 1.4, condensate pipeline 1.5, boiler 1.6, steam turbine generator set 1.7, auxiliary steam header 1.8, steam heating molten salt system 2, superheat heater 2.1, superheat heater steam inlet pipeline 2.11, superheat heater molten salt outlet pipeline 2.12, superheat heater steam outlet pipeline 2.13, superheat heater molten salt inlet pipeline 2.14, reheat heater 2.2, reheat heater steam inlet pipeline 2.21, reheat heater molten salt outlet pipeline 2.22, reheat heater steam outlet pipeline 2.23, reheat heater molten salt inlet pipeline 2.24, evaporation heater 2.3. Preheating heater A2.4. High-pressure water inlet pipe of preheating heater A2.41. Molten salt outlet pipe of preheating heater A2.42. High-pressure water outlet pipe of preheating heater A2.43. Molten salt inlet pipe of preheating heater A2.44. Preheating heater B2.5. Steam outlet pipe of preheating heater B2.51. Molten salt inlet pipe of preheating heater B2.52. Molten salt outlet pipe of preheating heater B2.53. High-temperature and high-pressure steam connecting pipe2.6. Low-temperature reheat steam exhaust to auxiliary steam manifold pipe2.7. High-pressure water feed pump2.8. High-pressure feed water mixing device2.9. High-pressure feed water bypass pipe2.91. Molten salt heat storage system3. High-temperature molten salt heat storage tank3.1. Low-temperature molten salt heat storage tank3.2. Low-temperature molten salt pump3.3. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0020] like Figure 1-2 As shown, Figure 2 The thermal power plant high-temperature and high-pressure steam-heated molten salt energy storage system shown includes 1, a thermal power generation system 1, a steam-heated molten salt system 2 and a molten salt heat storage system 3. The steam-heated molten salt system 2 is connected to the thermal power generation system 1 and the molten salt heat storage system 3 respectively to realize the heat exchange function between the high-temperature and high-pressure steam of the thermal power generation system and the molten salt heat storage system. In this embodiment, the thermal power generation system 1 adopts a conventional thermal power generation system.

[0021] The specific heat storage process is:

[0022] The high-pressure main steam of the conventional thermal power generation system 1 enters the superheat heater 2.1 through the hot heater steam inlet pipe 2.11, exchanges heat with the molten salt in the superheat heater 2.1, and then enters the evaporator heater 2.3 through the hot heater steam outlet pipe 2.13, exchanges heat with the molten salt in the evaporator heater 2.3, condenses into high-pressure water, and then enters the preheat heater A through the preheat heater A high-pressure water inlet pipe 2.41, becomes high-pressure supercooled water, and is finally pressurized by the high-pressure water feed pump 2.8 and sent to the water supply system to realize the high-pressure steam-water cycle.

[0023] The high-temperature reheat steam of the conventional thermal power generation system 1 is first mixed with part of the high-pressure main steam from the high-temperature and high-pressure steam connecting pipe 2.6, and after the pressure is increased, it enters the reheat heater 2.2 through the reheat heater steam inlet pipe 2.21, exchanges heat with the molten salt in the reheat heater 2.2, and then enters the preheat heater B through the reheat heater steam outlet pipe 2.23, and is converted into low-temperature reheat steam and then returned to the low-temperature reheat system. The incremental steam brought by the high-pressure main steam is discharged from the low-temperature reheat steam to the auxiliary steam header pipe 2.7 and enters the auxiliary steam header 1.8, realizing the high-temperature reheat steam water cycle.

[0024] The low-temperature molten salt in the low-temperature molten salt heat storage tank 3.2 of the molten salt heat storage system 3 is pressurized by a low-temperature molten salt pump 3.3, and then divided into two molten salts, one of which enters the preheating heater A2.4 to be heated, and the other enters the preheating heater B2.5 to be heated. The two molten salts are mixed and then enter the evaporation heater 2.3. After heating, they are divided into two molten salts again, one of which enters the superheating heater 2.1 to be heated, and the other enters the reheating heater 2.2 to be heated. The two molten salts are mixed and then enter the high-temperature molten salt heat storage tank 3.1 to realize the flow and heat storage of the molten salt circuit.

[0025] The operating temperature of the high-temperature molten salt heat storage tank 3.1 may be different depending on the unit parameters of the thermal power plant. Under the parameters of conventional subcritical and supercritical units, the operating temperature of the high-temperature molten salt heat storage tank 3.1 is about 400°C, and the operating temperature of the low-temperature molten salt heat storage tank 3.2 is about 290°C.

[0026] The energy storage system of the present invention includes a conventional thermal power generation system, a steam-heated molten salt system and a molten salt heat storage system. The conventional thermal power generation system is a reheat steam unit, and the steam-heated molten salt system is composed of five heat exchangers, which are respectively connected to the thermal power generation system and the molten salt heat storage system to realize the heat exchange function between the high-temperature and high-pressure steam of the thermal power generation system and the molten salt heat storage system. The present invention heats the molten salt energy storage system through high-temperature and high-pressure steam to store the high-quality steam of the thermal power generation system, and can also bypass the steam at the turbine inlet to achieve complete thermoelectric decoupling, which is beneficial to the flexible operation and deep peak regulation of the thermal power generation system, while ensuring the safe operation of the boiler and steam turbine generator set.

[0027] The above shows and describes the basic principles and main structural features of the present invention. The present invention is not limited to the above examples. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A high-temperature and high-pressure steam-heated molten salt energy storage system for a thermal power plant, comprising a thermal power generation system (1), a steam-heated molten salt system (2) and a molten salt heat storage system (3), characterized in that: The thermal power generation system (1), the steam heating molten salt system (2) and the molten salt heat storage system (3) are connected in sequence to realize the heat exchange function between the high-temperature and high-pressure steam of the thermal power generation system and the molten salt heat storage system; The steam-heated molten salt system (2) comprises a superheater (2.1), an evaporator (2.3), a preheater A (2.4), a high-pressure water feed pump (2.8) and a high-pressure feed temperature mixing device (2.9). The high-pressure main steam of the thermal power generation system (1) enters the superheater (2.1) through the steam inlet pipe (2.11) of the superheater, exchanges heat with the molten salt in the superheater (2.1), then enters the evaporator (2.3) through the steam outlet pipe (2.13) of the superheater, exchanges heat with the molten salt in the evaporator (2.3), condenses into high-pressure water, enters the preheater A (2.4) through the high-pressure water inlet pipe (2.41) of the preheater A, becomes high-pressure supercooled water, and is finally pressurized by the high-pressure water feed pump (2.8) and sent to the water supply system to realize the high-pressure steam-water cycle; The steam-heated molten salt system (2) also includes a reheat heater (2.2), a preheat heater B (2.5), a high-temperature and high-pressure steam connecting pipe (2.6), and a low-temperature reheat steam exhaust to auxiliary steam header pipe (2.7). The high-temperature reheat steam of the thermal power generation system (1) is first mixed with a portion of the high-pressure main steam from the high-temperature and high-pressure steam connecting pipe (2.6), and after the pressure is increased, it enters the reheat heater (2.2) through the reheat heater steam inlet pipe (2.21), exchanges heat with the molten salt in the reheat heater (2.2), and then enters the preheat heater B (2.5) through the reheat heater steam outlet pipe (2.23), becomes low-temperature reheat steam and then returns to the low-temperature reheat system. The incremental steam brought by the high-pressure main steam enters the auxiliary steam header (1.8) through the low-temperature reheat steam exhaust to auxiliary steam header pipe (2.7), thereby realizing the high-temperature reheat steam steam-water cycle; The low-temperature molten salt in the low-temperature molten salt heat storage tank (3.2) of the molten salt heat storage system (3) is pressurized by a low-temperature molten salt pump (3.3) and then divided into two molten salts, one of which enters the preheating heater A (2.4) to be heated, and the other enters the preheating heater B (2.5) to be heated. The two molten salts are mixed and then enter the evaporation heater (2.3). After heating, they are divided into two molten salts again, one of which enters the superheating heater (2.1) to be heated, and the other enters the reheating heater (2.2) to be heated. The two molten salts are mixed and then enter the high-temperature molten salt heat storage tank (3.1), thereby realizing the flow and heat storage of the molten salt circuit.

2. The high-temperature and high-pressure steam-heated molten salt energy storage system for a thermal power plant according to claim 1, characterized in that: The operating temperature of the high-temperature molten salt heat storage tank (3.1) is 400°C to 565°C.

3. The high-temperature and high-pressure steam-heated molten salt energy storage system for a thermal power plant according to claim 1, characterized in that: The operating temperature of the low-temperature molten salt heat storage tank (3.2) is 290°C to 310°C.

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