Steam and electric heat storage coupled heat storage system and method

Abstract

The invention relates to the field of thermal power, in particular to a steam and electric heat storage coupled heat storage system and method.The steam and electric heat storage coupled heat storage system comprises a low-temperature molten salt tank, a high-temperature molten salt tank, a molten salt electric heater, a main steam heat storage heat exchanger, a reheated steam heat storage heat exchanger, a steam generator and a high-pressure heater; the fused salt heat storage can be carried out in an electric heat storage mode under the extreme condition that steam cannot be extracted, and heat storage can be carried out through pure steam under the condition that the steam flow is sufficient. Meanwhile, the fused salt heat storage process can be achieved through coupling of steam and electric heat storage under the condition that the steam extraction amount is limited, and therefore efficient storage of energy is achieved under the condition that the unit operation safety is guaranteed, flexibility is good, and the problem that when the unit operation load is low, energy consumption is low is solved. And a pure steam heat storage mode cannot meet the molten salt heat storage requirement, and the cold source loss of pure electric heat storage is large.

Description

Technical Field

[0001] The present invention relates to the field of thermal power generation, and specifically to a steam and electricity heat storage coupled heat storage system and method, in particular to a steam and electricity heat storage coupled heat storage system for peak power generation and coal saving by coupling steam and electricity heat storage and utilizing high-temperature molten salt to release heat, and a control method thereof. Background Art

[0002] The rapid development of new energy sources such as wind power and solar power with strong time-varying characteristics has brought severe challenges to the safe and stable operation of the power grid. As the main peak-shaving power source, coal-fired power units can effectively store and release thermal energy by configuring large-capacity heat storage devices, which is an effective technical approach to improve peak-shaving capacity. Among the many heat storage technologies, molten salt heat storage is considered to be one of the best choices for large-scale, low-cost energy storage technology due to its high operating temperature, high thermal stability, high specific heat capacity, and low viscosity.

[0003] After deep adjustment, the pure condensing unit can reduce the load to about 15-20%, which is the limit of deep adjustment. In order to further improve the deep adjustment capability of the unit, the pure condensing thermal power unit coupled with molten salt heat storage technology is the best technical solution currently available. Since there is no external heat supply for the pure condensing unit, there is no problem of heat-to-electricity, and the unit operating load can be reduced to a lower load during deep adjustment. However, during the deep adjustment, the parameters such as steam pressure and flow are low. For the pure molten salt steam heat storage process, a large amount of main steam or reheat steam needs to be extracted to heat the low-temperature molten salt to a specified high temperature (generally 380℃~400℃). If pure electric heat storage is used, a large amount of cold source loss will be generated in the power generation process before heat storage, reducing the energy utilization efficiency of the entire process. In addition, since there is no external heat or steam supply for the pure condensing unit, the steam generated by the molten salt heat release process is difficult to be directly provided to external users. Therefore, the molten salt heat release process needs to be coupled with the unit, and the heat needs to be returned to the thermal system.

[0004] It can be seen that the disadvantage of the current pure molten salt steam heat storage system is that in order to meet the requirements of heating the low-temperature molten salt to the high-temperature molten salt of the specified temperature, the flow rate of the main steam or reheated steam extracted by the unit is relatively large under low load. In order to ensure the safety of unit operation under low load, the steam extraction capacity of the unit is often limited. Therefore, the heat storage capacity of the pure steam molten salt heat storage process is often limited, making the heat storage process lack flexibility. The electricity used in the pure electric heat storage route has already generated a large amount of cold source loss in the process of generating electricity before heat storage. For pure condensing units without industrial steam supply and heating, pure electric heat storage has low energy utilization efficiency in the entire large cycle process. Summary of the invention

[0005] In view of the problems in the prior art that when the unit operating load is low, the pure steam heat storage method cannot meet the molten salt heat storage demand and the cold source loss of pure electric heat storage is large, the present invention provides a steam and electric heat storage coupled heat storage system and method.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides a steam and electric heat storage coupled heat storage system, comprising a low-temperature molten salt tank, a high-temperature molten salt tank, a molten salt electric heater, a main steam heat storage heat exchanger, a reheat steam heat storage heat exchanger, a steam generator and a high-pressure heater; The main high-pressure steam extraction outlet of the high-pressure cylinder of the unit is connected to the high-pressure heater and the unit deaerator in sequence; the outlet of the unit deaerator is connected to the water inlet of the high-pressure heater, the water outlet of the high-pressure heater is connected to the steam generator, the outlet of the steam generator is respectively connected to the main steam heat storage heat exchanger and the high-pressure cylinder inlet, and the steam output end of the main steam heat storage heat exchanger is connected to the steam generator and the medium-pressure cylinder inlet; The high-pressure exhaust steam outlet of the high-pressure cylinder is connected to the evaporator; the outlet of the steam generator is respectively connected to the reheat steam heat storage heat exchanger and the inlet of the medium-pressure cylinder, and the outlet of the reheat steam heat storage heat exchanger is connected to the inlet of the low-pressure cylinder; The low-temperature molten salt outlet of the low-temperature molten salt tank is respectively connected to the molten salt electric heater and the reheat steam heat storage heat exchanger, the outlet of the molten salt electric heater is connected to the inlet of the high-temperature molten salt tank, and the molten salt outlet of the reheat steam heat storage heat exchanger is sequentially connected to the main steam heat storage heat exchanger, the molten salt electric heater and the high-temperature molten salt tank.

[0007] Optionally, it also includes a heat exchanger for heating water and releasing heat, and a heat exchanger for releasing heat and producing steam; The medium-pressure steam extraction outlet of the medium-pressure cylinder is connected to the unit deaerator, and the output of the unit deaerator is respectively connected to the heat-releasing steam production heat exchanger and the feedwater heating heat-releasing heat exchanger; The steam outlet of the heat-releasing steam-generating heat exchanger is connected to the inlet of the low-pressure cylinder; the water outlet of the water-heating heat-releasing heat exchanger is connected to the high-pressure heater and the steam generator in sequence; the steam outlet of the steam generator is respectively connected to the main steam heat storage heat exchanger and the inlet of the high-pressure cylinder; the steam output end of the main steam heat storage heat exchanger is connected to the inlet of the medium-pressure cylinder; The high-temperature molten salt outlets of the high-temperature molten salt tank are respectively connected to the water heating heat release heat exchanger and the heat release steam production heat exchanger; the molten salt outlets of the water heating heat release heat exchanger and the heat release steam production heat exchanger are both connected to the low-temperature molten salt tank inlet.

[0008] Optionally, a booster water pump is provided between the unit deaerator and the feed water heating and heat release heat exchanger.

[0009] Optionally, a feed water pump is provided between the feed water heating and heat release heat exchanger and the high pressure heater.

[0010] Optionally, the main high-pressure steam extraction outlet of the high-pressure cylinder is also connected to a high-pressure heater and a unit deaerator in sequence.

[0011] Optionally, a low-pressure heater, a condenser and a condensate pump are also included; The low-pressure extraction steam outlet of the low-pressure cylinder is connected to the low-pressure heater, condenser, condensate pump and unit deaerator in sequence; the low-pressure exhaust steam of the low-pressure cylinder is connected to the condenser, condensate pump and unit deaerator in sequence.

[0012] Optionally, a low-temperature molten salt pump is provided at the molten salt outlet of the low-temperature molten salt tank.

[0013] Optionally, a high-temperature molten salt pump is provided at the molten salt outlet of the high-temperature molten salt tank.

[0014] Optionally, the extraction steam flow entering the main steam heat storage heat exchanger is equal to the steam flow entering the reheat steam heat storage heat exchanger.

[0015] The present invention provides a heat storage method using the above system, comprising: When the unit cannot extract steam: the low-temperature molten salt in the low-temperature molten salt tank is heated by the molten salt electric heater and then enters the high-temperature molten salt tank for heat storage; When the unit is running at a high load and the unit has sufficient steam extraction capacity: the low-temperature molten salt in the low-temperature molten salt tank is sequentially entered into the reheat steam heat storage heat exchanger and the main steam heat storage heat exchanger for heating, and then enters the high-temperature molten salt tank for heat storage; the exhaust steam of the unit's high-pressure cylinder is divided into two paths, one path is directly reheated through the steam generator and then enters the medium-pressure cylinder, and the other path enters the reheat steam heat storage heat exchanger for heat exchange with the low-temperature molten salt and then enters the low-pressure cylinder; the main high-pressure extraction steam extracted from the high-pressure cylinder of the unit enters the unit's deaerator through the high-pressure heater, and the outlet water of the unit's deaerator enters the main steam heat storage heat exchanger through the steam generator for heat exchange with the low-temperature molten salt, and then merges with the high-pressure cylinder exhaust steam, and then enters the steam generator again for reheating, and the steam after reheating enters the medium-pressure cylinder; When the unit is running at a low load and the unit's steam extraction capacity is limited: a part of the low-temperature molten salt in the low-temperature molten salt tank enters the reheat steam heat storage heat exchanger and the main steam heat storage heat exchanger in turn to be heated, and then enters the high-temperature molten salt tank for heat storage after being heated by the molten salt electric heater, and the other part of the low-temperature molten salt enters the high-temperature molten salt tank for heat storage after being heated by the molten salt electric heater; the exhaust steam of the unit's high-pressure cylinder is divided into two paths, one path directly enters the medium-pressure cylinder after being reheated by the steam generator, and the other path enters the reheat steam heat storage heat exchanger after heat exchange with the low-temperature molten salt and enters the low-pressure cylinder; the main high-pressure extraction steam extracted from the high-pressure cylinder of the unit enters the unit's deaerator through the high-pressure heater, and the outlet water of the unit's deaerator enters the main steam heat storage heat exchanger through the steam generator to exchange heat with the low-temperature molten salt, and then merges with the high-pressure cylinder exhaust steam, and then enters the steam generator again for reheating, and the steam after reheating enters the medium-pressure cylinder.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a steam and electric heat storage coupled heat storage system, comprising a low-temperature molten salt tank, a high-temperature molten salt tank, a molten salt electric heater, a main steam heat storage heat exchanger, a reheat steam heat storage heat exchanger, a steam generator and a high-pressure heater; when the unit cannot extract steam, the low-temperature molten salt is heated by the molten salt electric heater to be converted into high-temperature molten salt for heat storage; when the unit is running at a high load and the unit has sufficient steam extraction capacity, the low-temperature molten salt in the low-temperature molten salt tank can be sequentially passed through the reheat steam heat storage heat exchanger and the main steam heat storage heat exchanger for heat exchange with the high-temperature extraction steam from the high-pressure cylinder, and then heated and enter the high-temperature molten salt tank. Heat storage; when the steam extraction capacity of the unit is limited, part of the low-temperature molten salt can be sent to the high-temperature molten salt heat storage after being heated by the high-temperature steam extraction heat exchange of the high-pressure cylinder and the molten salt electric heater, and the other part of the low-temperature molten salt can be directly heated by the molten salt electric heater and then enter the high-temperature molten salt tank for heat storage; that is, during the deep peak regulation period of the pure condensing unit, when the unit boiler and steam turbine body reach the deep regulation limit, the 200℃ low-temperature molten salt can be heated to 380℃~400℃ high-temperature molten salt heat storage through three methods: steam and low-temperature molten salt heat exchange, molten salt and electric heat storage, and steam coupled with electric heat storage molten salt heat storage. This heat storage method cleverly combines steam heat storage and electric heat storage, and realizes molten salt heat storage under the condition of ensuring the safe operation of the unit at low load. The heat storage flexibility is better, further increasing the peak regulation, peak and coal saving capabilities of the pure condensing unit, realizing the storage and utilization of energy across time and space, and high energy utilization rate.

[0017] It also includes a feedwater heating heat exchanger, a unit deaerator, and a heat-releasing steam heat exchanger. Through the heat-releasing steam heat exchanger, the heat stored in the high-temperature molten salt tank can be re-entered into the low-pressure cylinder in the form of heat exchange for power generation; through the feedwater heat exchanger, the heat stored in the high-temperature molten salt tank can be sent back to the thermal system in the form of heat exchange for water supply and coal saving. In the end, the heat released by the system can be used to heat the feedwater to save coal for the unit, and can also generate steam to be sent to the unit's low-pressure cylinder for peak power generation. It has good applicability for pure condensing conditions in both peak and non-peak conditions.

[0018] A booster water pump is provided between the unit deaerator and the feed water heating and heat release heat exchanger, and the booster water pump is used to initially boost the incoming water in the unit deaerator. Since the boost to the feed water is relatively small, compared with the method of heating part of the feed water by bypassing all high-pressure heaters, while heating the feed water, the phenomenon of leakage of the working fluid caused by excessive feed water pressure in the feed water heating and heat release heat exchanger can be effectively avoided. As a result, the newly added design pressure parameter of the feed water heating and heat release heat exchanger is relatively low, which can effectively save manufacturing costs.

[0019] A feed water pump is arranged between the feed water heating and heat release heat exchanger and the high-pressure heater, and is used to pump the water after heat exchange in the feed water heating and heat release heat exchanger to the high-pressure heater and the evaporator to generate main steam and reheat steam with specified parameters.

[0020] The molten salt outlet of the low-temperature molten salt tank is provided with a low-temperature molten salt pump for pumping out the low-temperature molten salt for heating and heat storage.

[0021] The molten salt outlet of the high-temperature molten salt tank is provided with a high-temperature molten salt pump for pumping out the high-temperature molten salt for releasing heat and doing work.

[0022] The extraction steam flow entering the main steam heat storage heat exchanger is equal to the steam flow entering the reheat steam heat storage heat exchanger, so as to avoid serious imbalance in the axial thrust of the high-pressure and intermediate-pressure cylinders caused by the large difference in the extraction steam flow, thereby effectively ensuring the safety of the steam turbine and saving the cost of the steam turbine axial thrust modification.

[0023] The present invention also provides a heat storage method using the above system, which combines the advantages and disadvantages of steam heat storage and electric heat storage. It can store heat in molten salt by electric heat storage in extreme cases where steam cannot be extracted, and can store heat by pure steam when the steam flow is sufficient. At the same time, the coupling of steam and electric heat storage can be used to realize the molten salt heat storage process when the steam extraction amount is limited, thereby realizing efficient energy storage under the condition of ensuring the safety of unit operation, solving the problem that the pure steam heat storage method cannot meet the molten salt heat storage demand and the large cold source loss of pure electric heat storage when the unit operation load is low. The method is simple and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of a steam and electricity heat storage coupled heat storage system of the present invention.

[0025] Figure 2 This is a control flow chart of the heat storage process in Example 2 of the present invention.

[0026] Figure 3 This is a flow chart of the heat release process control in Example 2 of the present invention.

[0027] Among them, 1- low-temperature molten salt tank, 2- high-temperature molten salt tank, 3- molten salt electric heater, 4- main steam heat storage heat exchanger, 5- reheat steam heat storage heat exchanger, 6- steam generator, 7- high-pressure heater, 8- feed water heating heat exchanger, 9- feed water pump, 10- unit deaerator, 11- booster pump, 12- heat release steam heat exchanger, 13- low-pressure heater, 14- condenser, 15- condensate pump, 16- high-pressure cylinder, 17- medium-pressure cylinder , 18-low-pressure cylinder, 19-high-temperature molten salt pump, 20-low-temperature molten salt pump, 21-first valve, 22-second valve, 23-third valve, 24-fourth valve, 25-fifth valve, 26-sixth valve, 27-seventh valve, 28-eighth valve, 29-ninth valve, 30-tenth valve, 31-eleventh valve, 32-twelfth valve, 33-thirteenth valve, 34-fourteenth valve, 35-generator. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0031] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0032] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0033] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0035] The present invention discloses a steam and electric heat storage coupled heat storage system, referring to Figure 1 , including a low-temperature molten salt tank 1, a high-temperature molten salt tank 2, a molten salt electric heater 3, a main steam heat storage heat exchanger 4, a reheat steam heat storage heat exchanger 5, a steam generator 6 and a high-pressure heater 7; The main high-pressure steam extraction outlet of the high-pressure cylinder 16 of the unit is connected to the high-pressure heater 7 and the unit deaerator 10 in sequence; the outlet of the unit deaerator 10 is connected to the water inlet of the high-pressure heater 7, the water outlet of the high-pressure heater 7 is connected to the steam generator 6, the outlet of the steam generator 6 is respectively connected to the main steam heat storage heat exchanger 4 and the inlet of the high-pressure cylinder 16, and the steam output end of the main steam heat storage heat exchanger 4 is connected to the steam generator 6 and the inlet of the medium-pressure cylinder 17; The high-pressure exhaust steam outlet of the high-pressure cylinder 16 is connected to the evaporator 6; the outlet of the steam generator 6 is respectively connected to the reheat steam heat storage heat exchanger 5 and the inlet of the medium-pressure cylinder 17, and the outlet of the reheat steam heat storage heat exchanger 5 is connected to the inlet of the low-pressure cylinder 18; The low-temperature molten salt outlet of the low-temperature molten salt tank 1 is respectively connected to the molten salt electric heater 3 and the reheat steam heat storage heat exchanger 5, the outlet of the molten salt electric heater 3 is connected to the inlet of the high-temperature molten salt tank 2, and the molten salt outlet of the reheat steam heat storage heat exchanger 5 is sequentially connected to the main steam heat storage heat exchanger 4, the molten salt electric heater 3 and the high-temperature molten salt tank 2.

[0036] The heat storage process is as follows: when the unit cannot extract steam: the low-temperature molten salt in the low-temperature molten salt tank 1 is heated by the molten salt electric heater 3 and then enters the high-temperature molten salt tank 2 for heat storage; when the unit is running at a high load and the unit has sufficient steam extraction capacity: the low-temperature molten salt in the low-temperature molten salt tank 1 enters the reheat steam heat storage heat exchanger 5 and the main steam heat storage heat exchanger 4 in turn for heating and then enters the high-temperature molten salt tank 2 for heat storage; the exhaust steam of the high-pressure cylinder 16 of the unit is divided into two paths, one of which is directly reheated by the steam generator 6 and then enters the medium-pressure cylinder 17, and the other enters the reheat steam heat storage heat exchanger 5 and then exchanges heat with the low-temperature molten salt and then enters the low-pressure cylinder 18; the main high-pressure extraction steam extracted from the high-pressure cylinder 16 of the unit enters the deaerator 10 of the unit through the high-pressure heater 7, and the outlet water of the deaerator 10 of the unit enters the main steam heat storage heat exchanger 4 through the steam generator 6 and exchanges heat with the low-temperature molten salt, and then merges with the exhaust steam of the high-pressure cylinder 16, and then enters the steam generator 6 again for reheating, and the steam after reheating enters the medium The exhaust steam of the high-pressure cylinder 16 of the unit is divided into two paths, one of which is directly reheated by the steam generator 6 and then enters the medium-pressure cylinder 17, and the other enters the reheat steam heat storage heat exchanger 5 and the low-temperature molten salt and then enters the low-pressure cylinder 18; the main high-pressure extraction steam extracted from the high-pressure cylinder 16 of the unit enters the deaerator 10 of the unit through the high-pressure heater 7, and the outlet water of the deaerator 10 of the unit enters the main steam heat storage heat exchanger 4 through the steam generator 6 and exchanges heat with the low-temperature molten salt, and then merges with the exhaust steam of the high-pressure cylinder 16, and then enters the steam generator 6 for reheating, and the steam after reheating enters the medium-pressure cylinder 17.

[0037] Example 2 See also Figure 1 The present invention discloses a molten salt heat storage and release system of a pure condensing unit, comprising a low-temperature molten salt tank 1, a high-temperature molten salt tank 2, a molten salt electric heater 3, a main steam heat storage heat exchanger 4, a reheat steam heat storage heat exchanger 5, a steam generator 6, a high-pressure heater 7, a feed water heating and heat release heat exchanger 8, a feed water pump 9, a booster water pump 11, a heat release steam production heat exchanger 12, a low-pressure heater 13, a condenser 14, a condensate pump 15, a high-temperature molten salt pump 19 and a low-temperature molten salt pump 20; and also comprising a first valve 21, a second valve 22, a third valve 23, a fourth valve 24, a fifth valve 25, a sixth valve 26, a seventh valve 27, an eighth valve 28, a ninth valve 29, a tenth valve 30, an eleventh valve 31, a twelfth valve 32, a thirteenth valve 33 and a fourteenth valve 34.

[0038] The high-pressure steam extraction outlet of the high-pressure cylinder 16 of the unit is connected to the high-pressure heater 7, and the steam outlet of the high-pressure heater 7 is connected to the unit deaerator 10, the booster water pump 11 and the feed water pump 9 in sequence, and the outlet of the feed water pump 9 is connected to the water inlet of the high-pressure heater 7 and the steam generator 6 in sequence; the outlet of the steam generator 6 is connected to the first valve 21 and the inlet of the high-pressure cylinder 16 respectively; the first valve 21 is connected to the main steam heat storage heat exchanger 4, the second valve 22, the steam generator 6 and the intermediate pressure cylinder 17 in sequence; The exhaust steam outlet of the high-pressure cylinder 16 is connected to the steam generator 6, and the outlet of the steam generator 6 is respectively connected to the third valve 23 and the inlet of the medium-pressure cylinder 17, and the third valve 23 is sequentially connected to the reheat steam heat storage heat exchanger 5, the fourth valve 24 and the inlet of the low-pressure cylinder 18; The low-temperature molten salt outlet of the low-temperature molten salt tank 1 is connected to the low-temperature molten salt pump 20, and the outlet of the low-temperature molten salt pump 20 is respectively connected to the fifth valve 25 and the eighth valve 28, and the eighth valve 28 is sequentially connected to the molten salt electric heater 3, the seventh valve 27 and the high-temperature molten salt tank 2, and the fifth valve 25 is sequentially connected to the reheat steam heat storage heat exchanger 5, the main steam heat storage heat exchanger 4, the sixth valve 25, the molten salt electric heater 3, the seventh valve 27 and the high-temperature molten salt tank 2; The high-temperature molten salt outlet of the high-temperature molten salt storage tank 2 is connected to the thirteenth valve 33 and the eleventh valve 31 respectively; the thirteenth valve 33 is connected to the water heating heat exchanger 8, the fourth valve 34 and the inlet of the low-temperature molten salt storage tank 1 in sequence; the eleventh valve 31 is connected to the heat release steam heat exchanger 12, the twelfth valve 32 and the inlet of the low-temperature molten salt storage tank 1 in sequence; The medium-pressure steam extraction outlet of the medium-pressure cylinder 17 is connected to the unit deaerator 10, and the output end of the unit deaerator 10 is respectively connected to the ninth valve 29 and the booster water pump 11, and the ninth valve 29 is sequentially connected to the heat release steam production heat exchanger 12, the tenth valve 30 and the inlet of the low-pressure cylinder 18; the booster water pump 11 is sequentially connected to the feed water heating heat release heat exchanger 8, the feed water pump 9 and the high-pressure heater 7; The output end of the low-pressure cylinder 18 is connected to the generator 35, the low-pressure extraction steam outlet of the low-pressure cylinder 18 is connected to the low-pressure heater 13 and the condenser 14 in sequence, and the low-pressure exhaust steam outlet of the low-pressure heater 13 is connected to the condenser 14, the condensate pump 15, the low-pressure heater 13 and the unit deaerator 10 in sequence.

[0039] When the unit cannot extract steam: the low-temperature molten salt in the low-temperature molten salt tank 1 is heated by the molten salt electric heater 3 and then enters the high-temperature molten salt tank 2 for heat storage; When the unit is under high operating load and has sufficient steam extraction capacity, the low-temperature molten salt in the low-temperature molten salt tank 1 enters the reheat steam heat storage heat exchanger 5 and the main steam heat storage heat exchanger 4 in turn to heat up and then enters the high-temperature molten salt tank 2 for heat storage. The exhaust steam of the high-pressure cylinder 16 of the unit is divided into two paths, one of which is directly reheated by the steam generator 6 and then enters the medium-pressure cylinder 17, and the other enters the reheat steam heat storage heat exchanger 5 and then exchanges heat with the low-temperature molten salt and then enters the low-pressure cylinder 18. The main high-pressure extraction steam extracted from the high-pressure cylinder 16 of the unit enters the deaerator 10 of the unit through the high-pressure heater 7, and the outlet water of the deaerator 10 of the unit enters the main steam heat storage heat exchanger 4 through the steam generator 6 and exchanges heat with the low-temperature molten salt and then merges with the exhaust steam of the high-pressure cylinder 16, and then enters the steam generator 6 again for reheating, and the steam after reheating enters the medium-pressure cylinder 17. When the unit cannot extract steam, only the low-temperature molten salt pump 20, the seventh valve 27, the eighth valve 28 and the molten salt electric heater 3 are opened, so that the 200°C low-temperature molten salt is pumped to the molten salt electric heater 3 through the low-temperature molten salt pump 20 and the eighth valve, and is heated to 380°C~400°C, and then enters the high-temperature molten salt tank 2 through the seventh valve 27 for heat storage.

[0040] When the unit is running at a high load and the unit has sufficient steam extraction capacity, pure steam heat exchange can be used for molten salt heat storage. The low-temperature molten salt pump 20, the first valve 21, the second valve 22, the third valve 23, the fourth valve 24, the fifth valve 25, the sixth valve 26 and the seventh valve 27 are opened to perform pure steam heat exchange. The high-pressure exhaust steam of the high-pressure cylinder 16 is divided into two paths, one of which enters the medium-pressure cylinder 17 through the steam generator 6, and the other enters the reheat steam heat storage heat exchanger 5 through the steam generator 6 and the third valve 23 for heat exchange and then enters the low-pressure cylinder 18. The high-pressure exhaust steam of the high-pressure cylinder 16 is divided into two paths, one of which enters the medium-pressure cylinder 17 through the steam generator 6, and the other enters the reheat steam heat storage heat exchanger 5 through the steam generator 6 and the third valve 23 for heat exchange and then enters the low-pressure cylinder 18. The steam passes through the high-pressure heater 7, the unit deaerator 10, the booster pump 11, the feed water pump 9 and the high-pressure heater 7 in sequence, and then enters the steam generator 6 and is divided into two paths. One path enters the main steam heat storage heat exchanger 4 through the first valve 21, and then merges with the exhaust steam of the high-pressure cylinder 16 through the second valve 22, and then enters the steam generator 6 again for reheating and then enters the medium-pressure cylinder 17; the low-temperature molten salt enters the reheat steam heat storage heat exchanger 5 through the fifth valve 25 and exchanges heat with the reheat steam, then enters the main steam heat storage heat exchanger 4 and exchanges heat with the high-pressure extraction steam, and then enters the high-temperature molten salt storage tank 2 for heat storage through the sixth valve 26 and the seventh valve 27. During the heat storage process, the eighth valve 28 and the molten salt electric heater 3 are not started. It should be noted that during the heat storage process, since the reheat steam parameters are lower than the main high-pressure extraction steam parameters, the low-temperature molten salt is first heated by the reheat steam heat storage heat exchanger 5 and then enters the main steam heat storage heat exchanger 4 for further heat exchange to produce high-temperature molten salt. The low-temperature steam after the reheat steam heat exchange is extracted and sent to the inlet of the low-pressure cylinder 18 to generate power. The high-pressure and low-temperature steam after the main steam heat exchange is extracted is sent to the cold reheat pipeline. In this way, it can be ensured that the steam flow in the boiler reheater before and after heat storage does not change significantly, thereby ensuring the safety of the unit reheat pipeline. In addition, the flow rates of the main high-pressure extraction steam and the reheat steam designed in the present invention are exactly the same, so as to avoid the serious imbalance of the axial thrust of the high and medium pressure cylinders caused by the large difference in the steam extraction flow rate, thereby effectively ensuring the safety of the steam turbine and saving the cost of the axial thrust modification of the steam turbine.

[0041] For the condition where the unit is mostly running at low load, the unit has limited steam extraction capacity. At this time, the low-temperature molten salt pump 20, the first valve 21, the second valve 22, the third valve 23, the fourth valve 24, the fifth valve 25, the sixth valve 26, the seventh valve 27 and the eighth valve 28 are started, the remaining valves are closed, and the molten salt electric heater 3 is started at the same time. At this time, the main steam heat storage heat exchanger 4, the reheat steam heat storage heat exchanger 5 and the molten salt electric heater 3 are all running. The high-pressure exhaust steam of the high-pressure cylinder 16 is divided into two paths, one of which enters the medium-pressure cylinder 17 through the steam generator 6, and the other enters the reheat steam heat storage heat exchanger 5 through the steam generator 6 and the third valve 23 for heat exchange and then enters the low-pressure cylinder 18; the high-pressure extraction steam of the high-pressure cylinder 16 passes through the high-pressure heater 7, the unit deaerator 10, the booster water pump 11, the feed water pump 9 and the high-pressure heater 7 in sequence, enters the steam generator 6 and then divides into two paths, one of which enters the main steam heat storage heat exchanger 4 through the first valve 21, and then merges with the exhaust steam of the high-pressure cylinder 16 through the second valve 22, enters the steam generator 6 again for reheating and then enters the medium-pressure cylinder 17; the low-temperature molten salt tank 1 contains the low-temperature molten salt. The molten salt is divided into two paths through the low-temperature molten salt pump 20. One path enters the reheat steam heat storage heat exchanger 5 and the main steam heat storage heat exchanger 4 in turn through the fifth valve 25 for heat exchange, and then is heated by the molten salt electric heater 3 and then enters the high-temperature molten salt tank 2 for heat storage through the seventh valve 27. The other path directly enters the molten salt electric heater 3 through the eighth valve 28 and enters the high-temperature molten salt tank 2 for heat storage through the seventh valve 27. Due to the operating conditions where the unit is mostly operated at low load, the unit's steam extraction capacity is limited, the steam extraction flow is limited, and the molten salt after steam heat exchange fails to reach the specified temperature. The missing heat is supplemented by the molten salt electric heater 3, and finally the molten salt temperature entering the high-temperature tank is achieved to be the specified temperature.

[0042] This heat storage method can achieve the comprehensive utilization of steam and electric heat storage of pure condensing units through the switching of different valves and the start and stop of the molten salt electric heater 3. Figure 2 , the control method of the heat storage process in practical application is as follows: First, determine the rated flow rate of molten salt according to the designed molten salt heat storage scale and rated heat storage time. M 1 and low temperature molten salt temperature T 1 and high temperature molten salt temperature T 2; Then, the molten salt rated flow M 1. Low temperature molten salt temperature T 1 and high temperature molten salt temperature T 2 is the boundary condition, and the simulation software such as Ebsilon and Thermoflex is used to calculate different steam extraction flow rates. M 2. To ensure that the final molten salt temperature reaches T 2. Thermal balance parameters of each heat exchanger in the heat storage process and operating power of the molten salt electric heater Q e ; byM 2From 0t / h pure electric heat storage to maximum extraction flow M 2max Pure steam thermal storage changes. In which, with 1t / h as an increment, the thermal parameters of the molten salt side and steam and the operating power of the molten salt electric thermal storage at different flow rates are calculated; Plotted as extraction steam flow M 2 is the independent variable, the opening of the first valve 21 to the fourth valve 24 and the electric thermal storage power are the dependent variables, and a corresponding database is generated and imported into the molten salt thermal storage DCS control system; The amount of steam that can be extracted from the main steam and reheat steam of the unit in actual operation M 3 is the input parameter, which is the same as the M 2 to compare and put into operation the automatic control. M 3≥ M 2max , then start the low-temperature molten salt pump 20, the first valve 21, the second valve 22, the third valve 23, the fourth valve 24, the fifth valve 25, the sixth valve 26 and the seventh valve 27, and close the remaining newly added valves to perform pure steam heat exchange. M 3=0, then open the low-temperature molten salt pump 20, the seventh valve 27 and the eighth valve 28 and the molten salt electric heater 2, and close the remaining valves for pure electric heat storage. M 3< M 2max , the low-temperature molten salt pump 20, the molten salt electric heater 3, the first valve 21, the second valve 22, the third valve 23, the fourth valve 24, the fifth valve 25, the sixth valve 26, the seventh valve 27 and the eighth valve 28 are started, and the remaining valves are closed to carry out the steam-coupled electric thermal storage process; After the DCS is automatically put into operation, the operator conducts inspections and manual fine-tuning based on the thermal parameters of each heat storage node to complete the entire heat storage control process.

[0043] The heat release of the molten salt system can be used to heat the feed water in the pure condensing unit, thereby reducing the coal consumption of the boiler and generating coal-saving benefits. At the same time, it can also directly heat the feed water to generate steam for the peak power generation of the unit. The system of this application can realize these two different heat release operation modes, as follows: When there is a gap in power generation in the power grid and the unit needs to generate power at top load, the high-temperature molten salt pump 19 and the ninth valve 29, the tenth valve 30, the eleventh valve 31 and the twelfth valve 32 are started, and the other valves are closed. The outlet water of the unit deaerator 10 is heated by the high-temperature molten salt into steam and then sent to the low-pressure cylinder 18 of the unit to generate power at top load. The incoming water in the unit deaerator 10 enters the heat-releasing steam-generating heat exchanger 12 through the ninth valve 29 for heat exchange and then enters the low-pressure cylinder 18 through the tenth valve 30 to perform work, so that the high-temperature molten salt in the high-temperature molten salt tank 2 enters the heat-releasing steam-generating heat exchanger 12 through the high-temperature molten salt pump 19 and the eleventh valve 31 for heat exchange with the incoming water of the unit deaerator 10, and then is converted into low-temperature molten salt and sent to the low-temperature molten salt tank 1 through the twelfth valve 32 to complete heat release.

[0044] When there is no gap in power generation in the power grid and the next peak load period is approaching, the high-temperature molten salt pump 19, the thirteenth valve 33 and the fourteenth valve 34 are started, and the molten salt releases heat to heat the feed water, which can reduce the boiler output to generate coal-saving benefits and prepare for the next molten salt heat storage process. The water from the deaerator 10 of the unit is boosted by the booster pump 11 and enters the feed water heating and heat release heat exchanger 8 for heat exchange, and then enters the high-pressure cylinder 16 through the feed water pump 9, the high-pressure heater 7 and the steam generator 6 to perform work, saving coal while preparing for the next molten salt heat storage process; the high-temperature molten salt in the high-temperature molten salt tank 2 enters the feed water heating and heat release heat exchanger 8 through the high-temperature molten salt pump 19 and the thirteenth valve 33, and is converted into low-temperature molten salt after heat exchange with the water from the booster pump 11, and enters the low-temperature molten salt tank 1 through the fourteenth valve 34 to complete heat release.

[0045] It should be noted that in the present invention, a booster pump 11 is newly added between the unit deaerator 10 and the feed water pump 9 to initially boost the feed water pressure. The boosted feed water exchanges heat with the molten salt to increase the temperature and then is boosted by the feed water pump 9. This method of heating the feed water has a smaller boost in the feed water pressure. Compared with the method of bypassing all high-pressure heaters to heat part of the feed water, while heating the feed water, it can effectively avoid the leakage of the working fluid caused by excessive feed water pressure in the feed water heating heat release heat exchanger 8. That is, the design pressure parameter of the feed water heating heat release heat exchanger 8 is relatively low, which can effectively save manufacturing costs.

[0046] This heat release process can not only achieve rapid top load of the unit, but also save coal. Figure 3 , the control method of this exothermic process in practical application is as follows: According to the design parameters of the molten salt system, determine the heat release time t, the rated flow rate of molten salt heat release and other parameters; Use software to calculate the maximum peak power generation under the designed heat release parameters of the molten salt heat release system when the boiler output remains unchanged W 1max And the corresponding boiler feed water flow and other parameters, at this time all the heat released is used to generate steam peak power generation. At the same time, the peak power generation power is reduced by 0.25MW.W 1. Under the condition that the heat release flow of molten salt remains unchanged, the thermal parameters such as boiler output, feed water flow, water inlet flow of heat exchanger for heat release and steam production, and temperature rise of heated feed water of the unit where part of the molten salt generates steam and the other part of the molten salt heats the feed water are calculated, and the parameters are plotted into a curve with power generation as the independent variable, and imported into the molten salt DCS control system. Among them, when the peak power is 0, it means that the heat release is all for heating the feed water to save coal; In actual operation, the peak demand of the unit W 2 is the input parameter, which is the same as the W 1 to compare and put into operation the automatic control. W 2≥ W 1max , then start the high temperature molten salt pump 19, the ninth valve 29, the tenth valve 30, the eleventh valve 31 and the twelfth valve 32, close the remaining valves to generate steam and only the low pressure cylinder 18 generates peak power. W 2=0, then open the high temperature molten salt pump 19, the thirteenth valve 33 and the fourteenth valve 34, close the other valves to heat the water. W 2< W 1max , then start the high temperature molten salt pump 19, the ninth valve 29, the tenth valve 30, the eleventh valve 31, the twelfth valve 32, the thirteenth valve 33 and the fourteenth valve 34, and close the other valves, so as to reduce the boiler output and save coal as much as possible at the peak; If there is no peak demand for the rated heat release time of t hours before the next heat storage, the heat released by the molten salt at this moment will be used to heat the feed water and save coal, freeing up heat storage capacity for the next heat storage; While the operation process is automatically controlled according to the database in the DCS, the operator conducts inspections and manual fine-tuning based on the actual heat release situation to complete the entire heat release control process.

[0047] The present invention also provides a heat storage method using the above system, comprising: When the unit cannot extract steam: the low-temperature molten salt in the low-temperature molten salt tank 1 is heated by the molten salt electric heater 3 and then enters the high-temperature molten salt tank 2 for heat storage; When the unit is under high operating load and has sufficient steam extraction capacity, the low-temperature molten salt in the low-temperature molten salt tank 1 enters the reheat steam heat storage heat exchanger 5 and the main steam heat storage heat exchanger 4 in turn to heat up and then enters the high-temperature molten salt tank 2 for heat storage. The exhaust steam of the high-pressure cylinder 16 of the unit is divided into two paths, one of which is directly reheated by the steam generator 6 and then enters the medium-pressure cylinder 17, and the other enters the reheat steam heat storage heat exchanger 5 and then exchanges heat with the low-temperature molten salt and then enters the low-pressure cylinder 18. The main high-pressure extraction steam extracted from the high-pressure cylinder 16 of the unit enters the deaerator 10 of the unit through the high-pressure heater 7, and the outlet water of the deaerator 10 of the unit enters the main steam heat storage heat exchanger 4 through the steam generator 6 and exchanges heat with the low-temperature molten salt and then merges with the exhaust steam of the high-pressure cylinder 16, and then enters the steam generator 6 again for reheating, and the steam after reheating enters the medium-pressure cylinder 17. When the unit is running at low load and the extraction capacity of the unit is limited: a part of the low-temperature molten salt in the low-temperature molten salt tank 1 enters the reheat steam heat storage heat exchanger 5 and the main steam heat storage heat exchanger 4 in turn to be heated and then enters the high-temperature molten salt tank 2 for heat storage after being heated by the molten salt electric heater 3, and another part of the low-temperature molten salt enters the high-temperature molten salt tank 2 for heat storage after being heated by the molten salt electric heater 3; the exhaust steam of the high-pressure cylinder 16 of the unit is divided into two paths, one of which is directly reheated by the steam generator 6 and then enters the medium-pressure cylinder 17, and the other enters the reheat steam heat storage heat exchanger 5 and heat-exchanges with the low-temperature molten salt and then enters the low-pressure cylinder 18; the main high-pressure extraction steam extracted from the high-pressure cylinder 16 of the unit enters the deaerator 10 of the unit through the high-pressure heater 7, and the outlet water of the deaerator 10 of the unit enters the main steam heat storage heat exchanger 4 through the steam generator 6 to exchange heat with the low-temperature molten salt and then merges with the exhaust steam of the high-pressure cylinder 16, and then enters the steam generator 6 again for reheating, and the steam after reheating enters the medium-pressure cylinder 17. This method combines the advantages and disadvantages of steam heat storage and electric heat storage. It can store heat in molten salt by electric heat storage in extreme cases where steam cannot be extracted, and can also store heat by pure steam when the steam flow is sufficient. At the same time, it can also realize the molten salt heat storage process by coupling steam and electric heat storage when the steam extraction volume is limited.

[0048] In summary, the present invention provides a heat storage system and method that couples steam and electric heat storage, which comprehensively considers the advantages and disadvantages of steam heat storage and electric heat storage, and adopts a method that can realize electric heat storage in the extreme case where steam cannot be extracted, and can also realize pure steam heat storage when the steam flow is sufficient. At the same time, the molten salt heat storage process can be realized by coupling steam and electric heat storage when the steam extraction amount is limited, so as to achieve efficient energy utilization and ensure the safety of unit operation. During the heat release process, the system can be used to heat feed water to save coal for the unit, and can also generate steam to be sent to the peak power generation of the low-pressure cylinder of the unit. It has good applicability for pure condensing conditions in both peak and non-peak conditions.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to impose any limitation on the technical solution of the present invention. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can also be subjected to several simple modifications and substitutions, and these modifications and substitutions are also within the scope of protection covered by the claims.

Claims

1. A steam and electricity heat storage coupled heat storage system, characterized in that: It comprises a low-temperature molten salt tank (1), a high-temperature molten salt tank (2), a molten salt electric heater (3), a main steam heat storage heat exchanger (4), a reheat steam heat storage heat exchanger (5), a steam generator (6) and a high-pressure heater (7); The main high-pressure steam extraction outlet of the high-pressure cylinder (16) of the unit is connected to the high-pressure heater (7) and the unit deaerator (10) in sequence; the outlet of the unit deaerator (10) is connected to the water inlet of the high-pressure heater (7), the water outlet of the high-pressure heater (7) is connected to the steam generator (6), the outlet of the steam generator (6) is respectively connected to the main steam heat storage heat exchanger (4) and the inlet of the high-pressure cylinder (16), and the steam output end of the main steam heat storage heat exchanger (4) is connected to the steam generator (6) and the inlet of the medium-pressure cylinder (17); The high-pressure exhaust steam outlet of the high-pressure cylinder (16) is connected to the evaporator (6); the outlet of the steam generator (6) is respectively connected to the inlet of the reheat steam heat storage heat exchanger (5) and the medium-pressure cylinder (17); and the outlet of the reheat steam heat storage heat exchanger (5) is connected to the inlet of the low-pressure cylinder (18); The low-temperature molten salt outlet of the low-temperature molten salt tank (1) is respectively connected to the molten salt electric heater (3) and the reheat steam heat storage heat exchanger (5), the outlet of the molten salt electric heater (3) is connected to the inlet of the high-temperature molten salt tank (2), and the molten salt outlet of the reheat steam heat storage heat exchanger (5) is sequentially connected to the main steam heat storage heat exchanger (4), the molten salt electric heater (3) and the high-temperature molten salt tank (2).

2. The steam and electricity thermal storage coupled thermal storage system according to claim 1 is characterized in that: It also includes a feedwater heating heat release heat exchanger (8) and a heat release steam generation heat exchanger (12); The intermediate pressure steam extraction outlet of the intermediate pressure cylinder (17) is connected to the unit deaerator (10), and the output of the unit deaerator (10) is respectively connected to the heat release steam production heat exchanger (12) and the feed water heating heat release heat exchanger (8); The steam outlet of the heat-releasing steam-generating heat exchanger (12) is connected to the inlet of the low-pressure cylinder (18); the feedwater outlet of the feedwater heating heat-releasing heat exchanger (8) is connected to the high-pressure heater (7) and the steam generator (6) in sequence; the steam outlet of the steam generator (6) is respectively connected to the main steam heat storage heat exchanger (4) and the inlet of the high-pressure cylinder (16); the steam output end of the main steam heat storage heat exchanger (4) is connected to the inlet of the medium-pressure cylinder (17); The high-temperature molten salt outlet of the high-temperature molten salt tank (2) is respectively connected to the water heating heat release heat exchanger (8) and the heat release steam production heat exchanger (12); and the molten salt outlets of the water heating heat release heat exchanger (8) and the heat release steam production heat exchanger (12) are both connected to the inlet of the low-temperature molten salt tank (1).

3. The steam and electricity thermal storage coupled thermal storage system according to claim 2 is characterized in that: A booster water pump (11) is provided between the unit deaerator (10) and the feed water heating and heat release heat exchanger (8).

4. The steam and electricity thermal storage coupled thermal storage system according to claim 2, characterized in that: A feed water pump (9) is provided between the feed water heating and heat release heat exchanger (8) and the high-pressure heater (7).

5. The steam and electricity thermal storage coupled thermal storage system according to claim 2, characterized in that: The main high-pressure steam extraction outlet of the high-pressure cylinder (16) is also connected in sequence to the high-pressure heater (7) and the unit deaerator (10).

6. The steam and electricity thermal storage coupled thermal storage system according to claim 2, characterized in that: It also includes a low-pressure heater (13), a condenser (14) and a condensate pump (15); The low-pressure extraction steam outlet of the low-pressure cylinder (18) is connected in sequence to the low-pressure heater (13), the condenser (14), the condensate pump (15) and the unit deaerator (10); the low-pressure exhaust steam of the low-pressure cylinder (18) is connected in sequence to the condenser (14), the condensate pump (15) and the unit deaerator (10).

7. The steam and electricity thermal storage coupled thermal storage system according to claim 1, characterized in that: A low-temperature molten salt pump (20) is provided at the molten salt outlet of the low-temperature molten salt tank (1).

8. The steam and electricity thermal storage coupled thermal storage system according to claim 1, characterized in that: A high-temperature molten salt pump (19) is provided at the molten salt outlet of the high-temperature molten salt tank (2).

9. The steam and electricity thermal storage coupled thermal storage system according to any one of claims 1 to 8, characterized in that: The extraction steam flow rate entering the main steam heat storage heat exchanger (4) is equal to the steam flow rate entering the reheat steam heat storage heat exchanger (5).

10. A heat storage method using the system according to any one of claims 1 to 9, characterized in that: include: When the unit is unable to extract steam: the low-temperature molten salt in the low-temperature molten salt tank (1) is heated by the molten salt electric heater (3) and then enters the high-temperature molten salt tank (2) for heat storage; When the unit is running at a high load and the unit has sufficient steam extraction capacity, the low-temperature molten salt in the low-temperature molten salt tank (1) is sequentially introduced into the reheat steam heat storage heat exchanger (5) and the main steam heat storage heat exchanger (4) to be heated and then introduced into the high-temperature molten salt tank (2) for heat storage; the exhaust steam of the unit's high-pressure cylinder (16) is divided into two paths, one path is directly reheated through the steam generator (6) and then introduced into the medium-pressure cylinder (17), and the other path is introduced into the reheat steam heat storage heat exchanger (5) and then heat-exchanged with the low-temperature molten salt and then introduced into the low-pressure cylinder (18); the main high-pressure extraction steam extracted from the unit's high-pressure cylinder (16) is introduced into the unit's deaerator (10) through the high-pressure heater (7); the outlet water of the unit's deaerator (10) is introduced into the main steam heat storage heat exchanger (4) through the steam generator (6) and then heat-exchanged with the low-temperature molten salt and then merged with the exhaust steam of the high-pressure cylinder (16), and then introduced into the steam generator (6) again for reheating, and the steam after reheating enters the medium-pressure cylinder (17); When the unit is running at low load and the unit's steam extraction capacity is limited: a portion of the low-temperature molten salt in the low-temperature molten salt tank (1) is sequentially entered into the reheat steam heat storage heat exchanger (5) and the main steam heat storage heat exchanger (4) to be heated and then heated by the molten salt electric heater (3) and then enter the high-temperature molten salt tank (2) for heat storage; another portion of the low-temperature molten salt is heated by the molten salt electric heater (3) and then enters the high-temperature molten salt tank (2) for heat storage; the exhaust steam of the unit's high-pressure cylinder (16) is divided into two paths, one path is directly reheated by the steam generator (6) and then enters the medium-pressure cylinder (1 7), and the other enters the reheat steam heat storage heat exchanger (5) to exchange heat with low-temperature molten salt and then enter the low-pressure cylinder (18); the main high-pressure extraction steam extracted from the high-pressure cylinder (16) of the unit enters the deaerator (10) of the unit through the high-pressure heater (7), and the outlet water of the deaerator (10) of the unit enters the main steam heat storage heat exchanger (4) through the steam generator (6) to exchange heat with low-temperature molten salt and then merge with the exhaust steam of the high-pressure cylinder (16), and then enters the steam generator (6) again for reheating, and the steam after reheating enters the medium-pressure cylinder (17).

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