Thermal-electric decoupling system coupled with molten salt energy storage and method for improving its efficiency

Abstract

The present invention provides a thermoelectric decoupling system coupled with molten salt energy storage and a method for improving its efficiency. The system includes a steam boiler, a high-pressure cylinder, an intermediate-pressure cylinder, a low-pressure cylinder, a generator, a condenser, a condensate pump, a low-temperature molten salt tank, a high-temperature molten salt tank, a buffer tank, a steam-molten salt heat exchanger, a main steam-molten salt heat exchanger, a reheat steam-molten salt heat exchanger, a steam ejector, a heat exchanger, a steam superheater, and a brine dual-medium thermal storage tank. A heat exchanger 15 is provided between the low-pressure cylinder and the steam boiler, and a steam superheater is connected to the steam outlet of the brine dual-medium thermal storage tank to exchange heat with the high-temperature molten salt. Under steady-state boiler load conditions, the unit extracts a portion of the main steam and reheat steam to store energy in the form of heat-to-heat conversion. Under heat release conditions, the boiler operates at a steady load, releasing heat from the high-temperature molten salt and brine dual-medium thermal storage tanks to heat the boiler feed water, thereby improving the unit's work capacity.

Description

Technical Field

[0001] The present invention belongs to the field of heat storage peak-shaving power generation, and specifically relates to a thermoelectric decoupling system coupled with molten salt energy storage and a method for improving the efficiency thereof. Background Art

[0002] At this stage, the implementation of clean renewable energy substitution has become the main route for the green and low-carbon transformation of the energy sector. However, because renewable energy such as wind and solar energy are greatly affected by natural environmental factors, their obvious volatility and intermittent nature create inherent power generation properties with poor output stability and regulation. At the same time, due to the mismatch between "source-load" in time and space, a large number of "wind abandonment" and "solar abandonment" phenomena have occurred, resulting in a huge waste of resources. Therefore, in order to improve the absorption capacity of new energy power generation systems and stabilize grid fluctuations, it is necessary to improve the load response speed and peak-shaving depth of coal-fired units, and other flexible operating capabilities. At the same time, it is necessary to take into account the problems of increased coal consumption and wear of units caused by frequent peak-shaving.

[0003] Coal-fired units coupled with energy storage systems can achieve "boiler-generator decoupling," a key approach to improving the operational flexibility of coal-fired units. Molten salt energy storage is the only energy storage method that is not restricted by geographical factors and can be implemented over a long period of time, on a large scale, and at a low cost. Currently, there are two mainstream molten salt energy storage methods used in thermal power units: extraction steam energy storage, which extracts high-temperature steam from the steam turbine system and exchanges heat with low-temperature molten salt, transferring the heat to the high-temperature molten salt; and power-to-heat energy storage, which uses electricity from the generator output to heat the low-temperature molten salt via an electric heater, converting the electrical energy into heat energy that is stored in the high-temperature molten salt. Both energy storage methods can effectively reduce the unit's output load.

[0004] However, most molten salt energy storage systems use a small amount of extracted main steam or a larger amount of extracted reheated steam as the heat source for heat storage, and the condensate is returned to the turbine system after cooling and pressure reduction after heat exchange. In this way, the steam condenses into water after heat exchange, which will cause a large amount of condensation heat loss, resulting in a decrease in the economy of the entire system. At the same time, there is the problem of overheating of the reheater pipeline, and the peak regulation depth is limited.

[0005] In view of the above factors, the present invention proposes a thermoelectric decoupling system coupled with molten salt energy storage and a method for improving its efficiency. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a thermoelectric decoupling system coupled with molten salt energy storage and a method for improving its efficiency.

[0007] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0008] In the first aspect, the present invention provides a thermoelectric decoupling system coupled with molten salt energy storage, comprising a steam boiler, a high-pressure cylinder, an intermediate-pressure cylinder, a low-pressure cylinder, a generator, a condenser, a condensate pump, a low-temperature molten salt tank and a high-temperature molten salt tank; the system also includes a buffer tank, a steam-molten salt heat exchanger, a main steam-molten salt heat exchanger, a reheated steam-molten salt heat exchanger, a steam ejector, a heat exchanger, a steam superheater and a brine dual-medium thermal storage tank, the steam outlet of the steam boiler 1 is connected to the steam inlet of the high-pressure cylinder 2 on the one hand, and to the steam end inlet of the main steam-molten salt heat exchanger 12 on the other hand, the steam outlet of the high-pressure cylinder 2 is connected to the reheater inlet of the steam boiler 1, the reheater outlet of the steam boiler 1 is connected to the steam inlet of the intermediate-pressure cylinder 3 on the one hand, and to the steam inlet of the brine dual-medium thermal storage tank 16 on the other hand, and to the steam end inlet of the reheated steam-molten salt heat exchanger 13 on the other hand;

[0009] The steam outlet of the intermediate pressure cylinder 3 is connected to the steam inlet of the low pressure cylinder 4. The steam outlet of the low pressure cylinder 4 is connected to the inlet of the condenser 6 on one hand and to the generator 5 on the other hand. The outlet of the condenser 6 is connected to the inlet of the condensate pump 7 on one hand. The outlet of the condensate pump 7 is connected to the feed water inlet of the steam boiler 1 on one hand and to the feed water inlet of the heat exchanger 15 on the other hand.

[0010] The steam end outlet of the main steam-molten salt heat exchanger 12 is connected to the steam end inlet of the steam-molten salt heat exchanger 11 on the one hand, and is connected to the inlet of the steam ejector 14 on the other hand. The steam end outlet of the steam-molten salt heat exchanger 11 is connected to the feed water inlet of the steam boiler 1. The steam end outlet of the reheated steam-molten salt heat exchanger 13 is connected to the inlet of the steam ejector 14 on the one hand, and is connected to the steam inlet of the low-pressure cylinder 4 on the other hand. The outlet of the steam ejector 14 is connected to the reheater inlet of the steam boiler 1;

[0011] The outlet of the low-temperature molten salt tank 8 is connected to the molten salt end inlet of the steam-molten salt heat exchanger 11, and the molten salt end outlet of the steam-molten salt heat exchanger 11 is connected to the inlet of the buffer tank 10. The outlet of the buffer tank 10 is connected to the molten salt end inlet of the main steam-molten salt heat exchanger 12 on the one hand, and to the molten salt end inlet of the reheat steam-molten salt heat exchanger 13 on the other hand;

[0012] The molten salt end outlet of the main steam-molten salt heat exchanger 12 is connected to the inlet of the high-temperature molten salt tank 9, the molten salt end outlet of the reheated steam-molten salt heat exchanger 13 is connected to the inlet of the high-temperature molten salt tank 9, the outlet of the high-temperature molten salt tank 9 is connected to the molten salt end inlet of the heat exchanger 15, the molten salt end outlet of the heat exchanger 15 is connected to the inlet of the low-temperature molten salt tank 8, and the feed water end outlet of the heat exchanger 15 is connected to the feed water inlet of the steam boiler;

[0013] The steam outlet of the brine dual-medium thermal storage tank 16 is connected to the steam end inlet of the steam superheater 17, the steam end outlet of the steam superheater 17 is connected to the steam inlet of the low-pressure cylinder 4, the outlet of the high-temperature molten salt tank 9 is connected to the molten salt end inlet of the steam superheater 17, and the molten salt end outlet of the steam superheater 17 is connected to the inlet of the buffer tank 10.

[0014] Furthermore, the brine dual-medium heat storage tank includes a steam collecting pipe, a surrounding pipe, and a serpentine pipe. Steam is passed into the steam collecting pipe, the surrounding pipe and the serpentine pipe are filled with phase change salt, and the heat storage tank is filled with water medium, which occupies no more than 80% of the inner cavity space.

[0015] Furthermore, the steam collecting pipe includes multiple layers of horizontally arranged annular pipes, horizontal guide pipes arranged on the diameter of the annular pipes, and vertical guide pipes connected to the horizontal guide pipes and the inlet of the heat storage tank. The surrounding pipes are evenly arranged around the steam collecting pipes, and the serpentine pipes are on the central axis plane of the heat storage tank. The steam collecting pipes, surrounding pipes, and serpentine pipes do not interfere with each other; nozzles are evenly arranged on the steam collecting pipes, and the nozzles and the surrounding pipes do not interfere with each other.

[0016] Furthermore, ternary molten salts, widely used in solar thermal power plants, can be used as energy storage media. These ternary molten salts have the advantages of a wide operating temperature range, high thermal stability, and low price. KNO3-NaNO2-NaNO3 (53%-4096-796) ternary molten salt is preferred. This ternary molten salt will undergo trace decomposition above 427°C. At the same time, at temperatures too low, the molten salt will solidify and block the channel. Therefore, the operating temperature of the high-temperature molten salt tank is designed to be 425°C, and the operating temperature of the low-temperature molten salt tank is 190°C. During energy storage, due to the inconsistent heat in the two-stage heat exchange process, the molten salt demand in the low-temperature heat exchange zone will be slightly greater than that in the high-temperature zone. A buffer tank is set to store excess medium-temperature molten salt, and its operating temperature is 305°C.

[0017] Furthermore, the operating temperature of the high-temperature molten salt tank 9 is not higher than the decomposition temperature of the ternary molten salt, the operating temperature of the low-temperature molten salt tank 8 is 185-200°C, and the temperature of the medium-temperature molten salt in the buffer tank is 300-320°C.

[0018] In a second aspect, the present invention provides a method for improving the efficiency of a thermoelectric decoupling system coupled with molten salt energy storage, wherein a buffer tank is provided between a high-temperature molten salt tank and a low-temperature molten salt tank, a steam-molten salt heat exchanger 11 is provided between the buffer tank and the low-temperature molten salt tank, a reheat steam-molten salt heat exchanger 13 is provided between the buffer tank and the high-temperature molten salt tank, and a main steam-molten salt heat exchanger 12 is provided between the buffer tank and the steam boiler 1. The steam after heat exchange in the reheat steam-molten salt heat exchanger and the main steam after heat exchange in the main steam-molten salt heat exchanger are both pressurized and flow-increased by a steam ejector before entering the reheater pipe of the steam boiler 1;

[0019] A temperature detection point is set on the reheater pipe. The steam pressure, temperature and flow parameters output by the steam ejector can match the steam parameters required in the reheater pipe, so that overheating will not occur under energy storage conditions.

[0020] The reheated steam output from the reheater is first supplied to the intermediate pressure cylinder steam according to the load, then enters the reheated steam-molten salt heat exchanger 13 to provide heat for molten salt heat exchange, and finally is stored in the reheated steam-molten salt heat exchanger 13;

[0021] A heat exchanger 15 is provided between the low-pressure cylinder and the steam boiler, and a steam superheater is connected to the steam outlet of the brine dual-medium heat storage tank to exchange heat with the high-temperature molten salt;

[0022] Heat release operating condition: Under the stable load condition of the steam boiler 1, high-pressure feed water is extracted from the feed water part of the steam boiler 1 and heated to a high temperature in the heat exchanger using the high-temperature molten salt in the high-temperature molten salt tank 9 and the buffer tank 10 as a heat source. The high-pressure feed water is then fed into the steam boiler. The steam expansion work efficiency in each stage of the high-, medium-, and low-pressure cylinders decreases in sequence. The work efficiency of the high- and medium-pressure cylinders is higher than that of the low-pressure cylinder. The heat carried by the medium- and high-temperature molten salt heats the high-pressure feed water to about 275-285°C, thereby increasing the thermal efficiency obtained by the steam flow of the high- and medium-pressure cylinders, and improving the efficiency of power generation by the generator 5 of the steam turbine system.

[0023] The high-temperature and high-pressure water medium in the brine dual-medium thermal storage tank 16 flashes through the steam outlet of the brine dual-medium thermal storage tank 16, and is adjusted to medium-temperature steam with suitable parameters by the pressure regulating valve. The high-temperature molten salt converts the steam passing through the steam superheater 17 into superheated steam with an appropriate superheat degree, and then enters the low-pressure cylinder 4 to perform work, ensuring the safe operation of the steam turbine; the high-temperature molten salt after heat exchange returns to the buffer tank 10; during the heat release process of the brine dual-medium thermal storage tank 16, the water medium is continuously cooled, and the high-temperature molten salt in the surrounding pipe 1602 and the serpentine pipe 1603 continuously transfers heat to the water medium through pipe wall heat exchange, reducing the cooling rate of the water medium and timely regulating the load and power fluctuations;

[0024] Energy storage operating condition: Under the steady-fire load operating condition of the steam boiler 1, the main steam generated by the steam boiler 1 exchanges heat with the molten salt from the buffer tank 10 through the main steam-molten salt heat exchanger 12, and the medium-temperature molten salt in the buffer tank 10 is heated to the temperature of the high-temperature molten salt and enters the high-temperature molten salt tank 9 for storage. After the heat exchange, a portion of the main steam that has cooled down exchanges heat with the low-temperature molten salt from the low-temperature molten salt tank 8 through the steam-molten salt heat exchanger 11. The low-temperature molten salt in the low-temperature molten salt tank 8 is heated by heat exchange and stored in the buffer tank 10. The steam after heat exchange becomes high-pressure condensate and enters the water supply part of the steam boiler 1;

[0025] The exhaust steam generated by the high-pressure cylinder 2 enters the reheater of the steam boiler 1 and becomes reheated steam. A part of the reheated steam exchanges heat with the molten salt from the buffer tank 10 through the reheated steam-molten salt heat exchanger 13, and the medium-temperature molten salt in the buffer tank 10 is heated to the high-temperature molten salt temperature and enters the high-temperature molten salt tank 9 for storage again. Secondly, another part of the main steam after heat exchange through the main steam-molten salt heat exchanger 12 and the reheated steam after heat exchange through the reheated steam-molten salt heat exchanger 13 are ejected through the steam ejector 14 to obtain a mixed steam with a steam pressure of 1.6-1.7MPa and a temperature of 300-310℃. The mixed steam is adapted to the steam temperature and pressure parameters required by the reheater. After entering the reheater of the steam boiler 1, the steam flow of the reheater is compensated to ensure that the reheater pipeline will not overheat under the energy storage condition; part of the reheated steam enters the brine dual-medium heat storage tank 16 for energy storage.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] Under the boiler steady-combustion load condition, the unit extracts part of the main steam and reheated steam to store energy in the form of heat-to-heat conversion, ensuring the safe and stable operation of the boiler at low load and the power generation load of the unit. Under the heat release condition, the boiler operates at a stable load, releasing the heat in the high-temperature molten salt and brine dual-medium heat storage tank, heating the boiler feed water, increasing the steam inlet flow of the turbine, improving the work capacity of the unit, and obtaining additional output power. The thermoelectric decoupling system of the present invention uses molten salt heat storage and peak regulation through high, medium and low molten salts, and brine dual-medium heat storage tanks, which can efficiently achieve "boiler-machine decoupling" of thermal power units. Boiler-machine decoupling means that the boiler and the generator set can operate separately, and steam is provided to the generator set for power generation through the energy storage system, without relying on the boiler, thereby improving its flexible operation capability. At the same time, it widens the range of upward and downward peak regulation of the unit, providing a wider space for absorbing new energy electricity. The system of the present invention uses high-pressure main steam after heat storage and heat exchange to eject reheated steam after heat exchange, obtaining new steam with matching parameters to compensate for the steam flow at the reheater inlet. The compensation flow maintains the reheater temperature within a certain range, solving the problem of overheating of the reheater pipes caused by large-scale extraction of main steam for heat storage during low-load operation of the unit. At the same time, the low-pressure reheated steam is ejected through the steam ejector, avoiding the condensation of the heat exchanged steam into water and returning it to the steam turbine system through the method of temperature reduction and pressure reduction, resulting in a large amount of condensation heat loss. This effectively reduces the condensation heat loss caused by steam extraction heat storage under deep peak regulation conditions. The steam extraction energy storage method of the present invention is superior to the electric heating energy storage method under the same conditions in terms of energy storage capacity, the entire storage-heat release process, and thermal efficiency. During the heat release process of the molten salt system (9, 10, 8, 16), the steam flow required by the steam turbine system (including the medium, high, and low pressure cylinders and the generator) will be directly increased, or the steam flow in the turbine cylinder will be indirectly increased by reducing the heat recovery extraction steam. From an energy perspective, the high- and medium-pressure cylinders have higher work efficiency than the low-pressure cylinder, and the steam expansion work efficiency decreases with each stage within the cylinder. When directly heating the boiler feedwater, the heat carried by the molten salt heats the high-pressure feedwater, increasing the thermal efficiency achieved by increasing the steam flow rate of the high- and medium-pressure cylinders. This is significantly better than the thermal efficiency achieved by increasing the steam flow rate of the low-pressure cylinder, resulting in higher efficiency. The present invention utilizes a ternary molten salt coupled thermoelectric decoupling. This ternary molten salt undergoes trace decomposition above 427°C, and at temperatures too low, the molten salt solidifies and blocks the channel. Therefore, the operating temperature of the high-temperature molten salt tank is set to 425°C, and the operating temperature of the low-temperature molten salt tank is set to 190°C. During energy storage, due to the inconsistent heat exchange between the two stages, the molten salt demand in the low-temperature heat exchange zone is slightly greater than that in the high-temperature zone. Therefore, a buffer tank is provided to store excess medium-temperature molten salt, with an operating temperature of 305°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0029] Figure 2This is a schematic diagram of the local piping arrangement of the brine dual-medium thermal storage tank of the present invention;

[0030] In the figure, 1. steam boiler; 2. high-pressure cylinder; 3. medium-pressure cylinder; 4. low-pressure cylinder; 5. generator; 6. condenser; 7. condensate pump; 8. low-temperature molten salt tank; 9. high-temperature molten salt tank; 10. buffer tank; 11. steam-molten salt heat exchanger; 12. main steam-molten salt heat exchanger; 13. reheat steam-molten salt heat exchanger; 14. steam ejector; 15. heat exchanger; 16. brine dual-medium thermal storage tank; 1601. steam collecting pipe; 1602. surrounding pipe; 1603. serpentine pipe; 17. steam superheater. DETAILED DESCRIPTION

[0031] The specific embodiments are given below in conjunction with the embodiments and drawings. The specific embodiments are only used to further illustrate the technical solutions of the present invention and do not limit the scope of protection of this application.

[0032] Example

[0033] Reference Figure 1 The present invention is a thermoelectric decoupling system coupled with molten salt energy storage, comprising a steam boiler 1, a high-pressure cylinder 2, an intermediate-pressure cylinder 3, a low-pressure cylinder 4, a generator 5, a condenser 6, a condensate pump 7, a low-temperature molten salt tank 8, a high-temperature molten salt tank 9, a buffer tank 10, a steam-molten salt heat exchanger 11, a main steam-molten salt heat exchanger 12, a reheated steam-molten salt heat exchanger 13, a steam ejector 14, a heat exchanger 15, a brine dual-medium thermal storage tank 16, and a steam superheater 17;

[0034] The steam outlet of the steam boiler 1 is connected to the steam inlet of the high-pressure cylinder 2 on one hand, and to the steam end inlet of the main steam-molten salt heat exchanger 12 on the other hand. The steam outlet of the high-pressure cylinder 2 is connected to the reheater inlet of the steam boiler 1. The reheater outlet of the steam boiler 1 is connected to the steam inlet of the intermediate-pressure cylinder 3 on one hand, and to the steam inlet of the brine dual-medium thermal storage tank 16 on the other hand, and to the steam end inlet of the reheat steam-molten salt heat exchanger 13 on the other hand.

[0035] The steam outlet of the intermediate pressure cylinder 3 is connected to the steam inlet of the low pressure cylinder 4. The steam outlet of the low pressure cylinder 4 is connected to the inlet of the condenser 6 on one hand and to the generator 5 on the other hand. The outlet of the condenser 6 is connected to the inlet of the condensate pump 7 on one hand. The outlet of the condensate pump 7 is connected to the feed water inlet of the steam boiler 1 on one hand and to the feed water inlet of the heat exchanger 15 on the other hand.

[0036] The steam end outlet of the main steam-molten salt heat exchanger 12 is connected to the steam end inlet of the steam-molten salt heat exchanger 11 on one hand, and is connected to the inlet of the steam ejector 14 on the other hand. The steam end outlet of the steam-molten salt heat exchanger 11 is connected to the feed water inlet of the steam boiler 1. The steam end outlet of the reheated steam-molten salt heat exchanger 13 is connected to the inlet of the steam ejector 14 on one hand, and is connected to the steam inlet of the low-pressure cylinder 4 on the other hand. The outlet of the steam ejector 14 is connected to the reheater inlet of the steam boiler 1;

[0037] The outlet of the low-temperature molten salt tank 8 is connected to the molten salt end inlet of the steam-molten salt heat exchanger 11, and the molten salt end outlet of the steam-molten salt heat exchanger 11 is connected to the inlet of the buffer tank 10. The outlet of the buffer tank 10 is connected to the molten salt end inlet of the main steam-molten salt heat exchanger 12 on the one hand, and to the molten salt end inlet of the reheat steam-molten salt heat exchanger 13 on the other hand;

[0038] The molten salt end outlet of the main steam-molten salt heat exchanger 12 is connected to the inlet of the high-temperature molten salt tank 9, the molten salt end outlet of the reheated steam-molten salt heat exchanger 13 is connected to the inlet of the high-temperature molten salt tank 9, the outlet of the high-temperature molten salt tank 9 is connected to the molten salt end inlet of the heat exchanger 15, the molten salt end outlet of the heat exchanger 15 is connected to the inlet of the low-temperature molten salt tank 8, and the feed water end outlet of the heat exchanger 15 is connected to the feed water inlet of the steam boiler;

[0039] The steam outlet of the brine dual-medium thermal storage tank 16 is connected to the steam end inlet of the steam superheater 17, the steam end outlet of the steam superheater 17 is connected to the steam inlet of the low-pressure cylinder 4, the outlet of the high-temperature molten salt tank 9 is connected to the molten salt end inlet of the steam superheater 17, and the molten salt end outlet of the steam superheater 17 is connected to the inlet of the buffer tank 10.

[0040] Furthermore, the brine dual-medium thermal storage tank 16 includes a steam collecting pipe 1601, a surrounding pipe 1602, and a serpentine pipe 1603. The steam collecting pipe 1601 includes multiple layers of horizontally arranged annular pipes, horizontal guide pipes arranged on the diameter of the annular pipes, and vertical guide pipes connected to the horizontal guide pipes and the inlet of the brine dual-medium thermal storage tank 16. The surrounding pipe 1602 is evenly surrounded by the steam collecting pipe 1601, and the serpentine pipe 1603 is on the central axis plane of the brine dual-medium thermal storage tank 16. The steam collecting pipe 1601, the surrounding pipe 1602, and the serpentine pipe 1603 do not interfere with each other.

[0041] Furthermore, steam is introduced into the steam collecting pipe 1601, and phase change salt is filled in the surrounding pipe 1602 and the serpentine pipe 1603. Nozzles are evenly arranged on the steam collecting pipe 1601, and the nozzles and the surrounding pipe 1602 do not interfere with each other. The brine dual-medium thermal storage tank 16 is filled with water medium, and the space occupied does not exceed 80% of the inner cavity space.

[0042] Furthermore, ternary molten salts widely used in solar thermal power stations can be used as energy storage media for molten salts. These ternary molten salts have the advantages of a wide operating temperature range, high thermal stability, and low price. In this embodiment, KNO3-NaNO2-NaNO3 (53%-4096-796) ternary molten salt is used. This ternary molten salt will decompose slightly above 427°C. At the same time, if the temperature is too low, the molten salt will solidify and block the channel. Therefore, the operating temperature of the high-temperature molten salt tank 9 is set to 425°C (slightly lower than the decomposition temperature of the ternary molten salt), and the operating temperature of the low-temperature molten salt tank 8 is 190°C. During energy storage, due to the inconsistent heat in the two-stage heat exchange process, the molten salt demand in the low-temperature heat exchange interval will be slightly greater than that in the high-temperature interval. A buffer tank 10 is set to store excess medium-temperature molten salt, and its operating temperature is 305°C. The specific attribute parameters of the ternary molten salt are as follows:

[0043]

[0044] The working principle and workflow of this embodiment are:

[0045] Energy storage operating condition: Under the steady combustion load condition of the steam boiler 1, the main steam (10MPa, 560℃) generated by the steam boiler 1 is heat exchanged with the molten salt from the buffer tank 10 through the main steam-molten salt heat exchanger 12, and the molten salt in the buffer tank 10 is heated to 425℃ high-temperature molten salt, which enters the high-temperature molten salt tank 9 for storage. After the heat exchange, a part of the main steam (10MPa, 315℃) that has been cooled is heat exchanged with the low-temperature molten salt from the low-temperature molten salt tank 8 through the steam-molten salt heat exchanger 11. The low-temperature molten salt of 190℃ in the low-temperature molten salt tank 8 is heated by heat exchange and stored in the buffer tank 10. The steam after heat exchange becomes high-pressure condensate and enters the water feed part of the steam boiler 1.

[0046] The exhaust steam generated by the high-pressure cylinder 2 enters the reheater of the steam boiler 1 and becomes reheated steam (the pressure and temperature of the reheated steam are: 1.7MPa, 560℃). A part of the reheated steam passes through the reheated steam-molten salt heat exchanger 13 to exchange heat with the molten salt from the buffer tank 10 (the steam pressure and temperature after heat exchange are 1.55MPa, 315℃), and the medium-temperature molten salt in the buffer tank 10 at 305℃ is heated to a high-temperature molten salt temperature of 425℃ and enters the high-temperature molten salt tank 9 for further storage. Secondly, the other part of the reheated steam after heat exchange through the main steam-molten salt heat exchanger 12 is used. Main steam (10 MPa, 315°C) and reheated steam (1.55 MPa, 315°C) after heat exchange in the reheat steam-molten salt heat exchanger 13 are ejected through the steam ejector 14 to produce a mixed steam with a steam pressure of 1.6 MPa and a temperature of 301°C. This mixed steam meets the steam temperature and pressure parameters required by the reheater. After entering the reheater of the steam boiler 1, it compensates for the reheater steam flow to prevent overheating of the reheater piping during energy storage. A portion of the reheated steam also enters the brine dual-medium thermal storage tank 16 for energy storage. Finally, the reheated steam that has not passed through the steam ejector 14 is depressurized and returned to the low-pressure cylinder 4 to perform work.

[0047] The steam ejector's main operating principle is to use high-pressure steam to eject low-pressure steam to be pressurized at high speed, creating medium-pressure steam that meets the required pressure after energy exchange. The high-pressure steam (working medium) is also called working steam, the ejected low-pressure steam is also called ejected steam, and the mixed medium-pressure steam is called mixed steam.

[0048] The reheated steam enters the steam collecting pipe 1601 of the brine dual-medium thermal storage tank 16, and the reheated steam in the steam collecting pipe 1601 exchanges heat with the molten salt in the surrounding pipe 1602 surrounding the steam collecting pipe 1601 through the pipe wall, thereby increasing the temperature of the molten salt in the surrounding pipe 1602. The reheated steam in the steam collecting pipe 1601 enters the brine dual-medium thermal storage tank 16 through the nozzle on the steam collecting pipe 1601, thereby increasing the temperature of the water medium in the brine dual-medium thermal storage tank 16. The heated water medium exchanges heat with the molten salt in the serpentine pipe 1603, thereby increasing the temperature of the molten salt in the serpentine pipe 1603.

[0049] Heat release working condition: Under the stable load condition of the steam boiler 1, the high-pressure feed water of the water supply part of the steam boiler 1 is extracted and enters the heat exchanger 15. The temperature of the high-pressure feed water is about 190°C. The high-temperature molten salt in the high-temperature molten salt tank 9 and the buffer tank 10 is used as a heat source to heat the high-pressure feed water to a high temperature of about 280°C and send it to the steam boiler. The low-temperature molten salt after cooling is returned to the low-temperature molten salt tank 8 for storage.

[0050] The high-temperature, high-pressure water in the brine dual-medium thermal storage tank 16 flashes through the steam outlet of the tank's brine dual-medium thermal storage tank 16. This is then regulated to medium-temperature steam with appropriate parameters by a pressure regulating valve (not shown). The high-temperature molten salt converts the steam passing through the steam superheater 17 into superheated steam with an appropriate superheat level. This steam then enters the low-pressure cylinder 4 to perform work, ensuring safe operation of the steam turbine. After heat exchange, the high-temperature molten salt returns to the buffer tank 10. During the heat release process in the brine dual-medium thermal storage tank 16, the water medium continuously cools. The high-temperature molten salt in the surrounding pipe 1602 and the serpentine pipe 1603 continuously transfers heat to the water medium through heat exchange with the pipe walls, slowing the water medium's cooling rate and further utilizing the stored heat, thereby improving energy efficiency.

[0051] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A thermoelectric decoupling system coupled with molten salt energy storage, comprising a steam boiler, a high-pressure cylinder, a medium-pressure cylinder, a low-pressure cylinder, a generator, a condenser, a condensate pump, a low-temperature molten salt tank, and a high-temperature molten salt tank; characterized in that: The system further includes a buffer tank, a steam-molten salt heat exchanger, a main steam-molten salt heat exchanger, a reheated steam-molten salt heat exchanger, a steam ejector, a heat exchanger, a steam superheater and a brine dual-medium thermal storage tank, wherein the steam outlet of the steam boiler is connected to the steam inlet of the high-pressure cylinder on one hand and to the steam end inlet of the main steam-molten salt heat exchanger on the other hand, the steam outlet of the high-pressure cylinder is connected to the reheater inlet of the steam boiler, the reheater outlet of the steam boiler is connected to the steam inlet of the medium-pressure cylinder on one hand and to the steam inlet of the brine dual-medium thermal storage tank on the other hand, and further to the steam end inlet of the reheated steam-molten salt heat exchanger on the other hand; The steam outlet of the intermediate pressure cylinder is connected to the steam inlet of the low pressure cylinder, the steam outlet of the low pressure cylinder is connected to the condenser inlet on one hand and to the generator on the other hand, the outlet of the condenser is connected to the inlet of the condensate pump, the outlet of the condensate pump is connected to the feed water inlet of the steam boiler on one hand and to the feed water inlet of the heat exchanger on the other hand; The steam end outlet of the main steam-molten salt heat exchanger is connected to the steam end inlet of the steam-molten salt heat exchanger on one hand, and to the inlet of the steam ejector on the other hand. The steam end outlet of the steam-molten salt heat exchanger is connected to the feed water inlet of the steam boiler. The steam end outlet of the reheated steam-molten salt heat exchanger is connected to the inlet of the steam ejector on one hand, and to the steam inlet of the low-pressure cylinder on the other hand. The outlet of the steam ejector is connected to the reheat inlet of the steam boiler. The outlet of the low-temperature molten salt tank is connected to the molten salt end inlet of the steam-molten salt heat exchanger, the molten salt end outlet of the steam-molten salt heat exchanger is connected to the inlet of the buffer tank, and the outlet of the buffer tank is connected to the molten salt end inlet of the main steam-molten salt heat exchanger on the one hand and the molten salt end inlet of the reheat steam-molten salt heat exchanger on the other hand; The molten salt end outlet of the main steam-molten salt heat exchanger is connected to the inlet of the high-temperature molten salt tank, the molten salt end outlet of the reheated steam-molten salt heat exchanger is connected to the inlet of the high-temperature molten salt tank, the outlet of the high-temperature molten salt tank is connected to the molten salt end inlet of the heat exchanger, the molten salt end outlet of the heat exchanger is connected to the inlet of the low-temperature molten salt tank, and the feed water end outlet of the heat exchanger is connected to the feed water inlet of the steam boiler; The steam outlet of the brine dual-medium thermal storage tank is connected to the steam end inlet of the steam superheater, the steam end outlet of the steam superheater is connected to the steam inlet of the low-pressure cylinder, the outlet of the high-temperature molten salt tank is connected to the molten salt end inlet of the steam superheater, and the molten salt end outlet of the steam superheater is connected to the inlet of the buffer tank.

2. The system according to claim 1, wherein: The brine dual-medium heat storage tank includes a steam collecting pipe, a surrounding pipe, and a serpentine pipe. Steam is passed into the steam collecting pipe, the surrounding pipe and the serpentine pipe are filled with phase change salt, and the heat storage tank is filled with water medium, which accounts for no more than 80% of the inner cavity space.

3. The system according to claim 2, characterized in that The steam collecting pipe includes multiple layers of horizontally arranged annular pipes, horizontal guide pipes arranged on the diameter of the annular pipes, and vertical guide pipes connected to the horizontal guide pipes and the heat storage tank inlet. The surrounding pipes are evenly arranged around the steam collecting pipes, and the serpentine pipes are on the central axis plane of the heat storage tank. The steam collecting pipes, surrounding pipes, and serpentine pipes do not interfere with each other; nozzles are evenly arranged on the steam collecting pipes, and the nozzles and the surrounding pipes do not interfere with each other.

4. The system according to claim 1, wherein: Ternary molten salt is selected as the energy storage medium.

5. The system according to claim 1, wherein: The working temperature of the high-temperature molten salt tank is not higher than the decomposition temperature of the ternary molten salt, the working temperature of the low-temperature molten salt tank is 185-200°C, and the temperature of the medium-temperature molten salt in the buffer tank is 300-320°C.

6. A method for improving the efficiency of a thermoelectric decoupling system coupled with molten salt energy storage, characterized in that: The method adopts the system described in any one of claims 1 to 5, wherein a buffer tank is provided between the high-temperature molten salt tank and the low-temperature molten salt tank, a steam-molten salt heat exchanger is provided between the buffer tank and the low-temperature molten salt tank, a reheat steam-molten salt heat exchanger is provided between the buffer tank and the high-temperature molten salt tank, and a main steam-molten salt heat exchanger is provided between the buffer tank and the steam boiler. The steam after heat exchange in the reheat steam-molten salt heat exchanger and the main steam after heat exchange in the main steam-molten salt heat exchanger are both pressurized and flow-increased by a steam ejector before entering the reheater pipeline of the steam boiler. A temperature detection point is set on the reheater pipe. The steam pressure, temperature and flow parameters output by the steam ejector can match the steam parameters required in the reheater pipe, so that overheating will not occur under energy storage conditions. The reheated steam output from the reheater is first supplied to the intermediate pressure cylinder steam according to the load, then enters the reheated steam-molten salt heat exchanger to provide heat for molten salt heat exchange, and finally is stored in the reheated steam-molten salt heat exchanger; A heat exchanger is set between the low-pressure cylinder and the steam boiler, and a steam superheater is connected to the steam outlet of the brine dual-medium heat storage tank to exchange heat with the high-temperature molten salt; Heat release working condition: Under the stable load condition of the steam boiler, the high-pressure feed water of the steam boiler feed water part is extracted and heated to a high temperature in the heat exchanger using the high-temperature molten salt in the high-temperature molten salt tank and the buffer tank as a heat source. The high-pressure feed water is then fed into the steam boiler. The steam expansion work efficiency in each stage of the high-, medium- and low-pressure cylinders decreases in sequence. The work efficiency of the high- and medium-pressure cylinders is higher than that of the low-pressure cylinder. The heat carried by the medium- and high-temperature molten salt heats the high-pressure feed water to 275-285°C, thereby increasing the thermal efficiency obtained by the steam flow of the high- and medium-pressure cylinders, and improving the efficiency of power generation through the generator of the steam turbine system; The high-temperature, high-pressure water medium in the brine dual-medium thermal storage tank flashes through the steam outlet of the brine dual-medium thermal storage tank, and is adjusted to medium-temperature steam with suitable parameters by a pressure regulating valve. The high-temperature molten salt converts the steam passing through the steam superheater into superheated steam with an appropriate superheat degree, which then enters the low-pressure cylinder to perform work, ensuring the safe operation of the steam turbine. After heat exchange, the high-temperature molten salt returns to the buffer tank. During the heat release process of the brine dual-medium thermal storage tank, the water medium is continuously cooled. The high-temperature molten salt in the surrounding pipes and serpentine pipes continuously transfers heat to the water medium through heat exchange on the pipe walls, reducing the cooling rate of the water medium and timely regulating load and power fluctuations. Energy storage operating conditions: Under the steady-fire load condition of the steam boiler, the main steam generated by the steam boiler exchanges heat with the molten salt from the buffer tank through the main steam-molten salt heat exchanger. The medium-temperature molten salt in the buffer tank is heated to the temperature of the high-temperature molten salt and then enters the high-temperature molten salt tank for storage. After the heat exchange, part of the main steam that has cooled down exchanges heat with the low-temperature molten salt from the low-temperature molten salt tank through the steam-molten salt heat exchanger. The low-temperature molten salt in the low-temperature molten salt tank is heated and stored in the buffer tank. The steam after heat exchange becomes high-pressure condensate and enters the water supply part of the steam boiler. The exhaust steam generated by the high-pressure cylinder enters the reheater of the steam boiler and becomes reheated steam. A part of the reheated steam exchanges heat with the molten salt from the buffer tank through the reheated steam-molten salt heat exchanger, and the medium-temperature molten salt in the buffer tank is heated to the high-temperature molten salt temperature and enters the high-temperature molten salt tank for storage again. Secondly, another part of the main steam after heat exchange through the main steam-molten salt heat exchanger and the reheated steam after heat exchange through the reheated steam-molten salt heat exchanger are ejected through the steam ejector to obtain a mixed steam with a steam pressure of 1.6-1.7MPa and a temperature of 300-310℃. The mixed steam is adapted to the steam temperature and pressure parameters required by the reheater. After entering the reheater of the steam boiler, the steam flow of the reheater is compensated to ensure that the reheater pipeline will not overheat under the energy storage condition; part of the reheated steam enters the brine dual-medium heat storage tank for energy storage.

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