Thermoelectric decoupling system coupled with fused salt energy storage and method for improving efficiency of thermoelectric decoupling system

Abstract

The invention relates to a thermoelectric decoupling system coupled with fused salt energy storage and a method for improving the efficiency of the thermoelectric decoupling system. 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 fused salt tank, a high-temperature fused salt tank, a buffer tank, a steam-fused salt heat exchanger, a main steam-fused salt heat exchanger, a reheated steam-fused salt heat exchanger, a steam ejector, a heat exchanger, a steam superheater and a saline water double-medium heat storage tank. A heat exchanger 15 is arranged between the low-pressure cylinder and the steam boiler, and a steam outlet of the salt-water double-medium heat storage tank is connected with a steam superheater to exchange heat with high-temperature molten salt. The unit extracts part of main steam and reheated steam under the stable combustion load working condition of the boiler to store energy in a heat-heat conversion mode, and under the heat release working condition, the boiler operates under the stable load, heat in the high-temperature fused salt and saline water double-medium heat storage tank is released, boiler feed water is heated, and the power capability of the unit is improved.

Description

Technical Field

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

[0002] At present, the implementation of clean substitution of renewable energy has become the main route for green and low-carbon transformation in the energy field. However, since renewable energy such as wind and solar energy are greatly affected by natural environmental factors, their obvious volatility, intermittency and other natural properties have created 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 "light 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 flexible operation capabilities of coal-fired units such as load response speed and peak-shaving depth, while taking into account the problems of increased coal consumption and wear of units caused by frequent peak-shaving.

[0003] The coupled energy storage system of coal-fired units can achieve "furnace-machine decoupling", which is an important way to improve the flexible operation capacity of coal-fired units. Molten salt energy storage is the only energy storage method that is not restricted by geographical factors and can achieve long-term, large-scale and low-cost. At present, there are two mainstream molten salt energy storage methods used in thermal power units: one is steam extraction energy storage, which extracts high-temperature steam from the steam turbine system and exchanges heat with low-temperature molten salt to transfer heat to high-temperature molten salt; the other is electric-to-heat energy storage, which uses the electricity at the generator outlet to heat the low-temperature molten salt through an electric heater, and converts electrical energy into heat energy and stores it in high-temperature molten salt. Both energy storage methods can effectively reduce the output load of the unit.

[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 a 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 in 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: 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, 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; 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 heat 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 medium-pressure cylinder 3 on the one hand, and to the steam inlet of the brine dual-medium heat 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; The steam outlet of the intermediate pressure cylinder 3 is connected to the steam inlet of the low pressure cylinder 4, and 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, and the outlet of the condenser 6 is connected to the inlet of the condensate pump 7 on one hand, and the outlet of the condensate pump 7 is connected to the feed water inlet of the steam boiler 1 on the other hand. 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. 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; 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; The steam outlet of the brine dual-medium heat 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.

[0008] Furthermore, the brine dual-medium heat storage tank comprises a steam collecting pipe, a surrounding pipe, and a serpentine pipe. Steam is introduced 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.

[0009] Furthermore, the steam collecting pipe comprises multiple layers of horizontally arranged annular pipes, a horizontal guide pipe arranged on the diameter of the annular pipe, and a vertical guide pipe connected to the horizontal guide pipe and the inlet of the heat storage tank. The surrounding pipe is evenly surrounded by the steam collecting pipe, and the serpentine pipe is on the central axis plane of the heat storage tank. The steam collecting pipe, the surrounding pipe and the serpentine pipe do not interfere with each other. Nozzles are evenly arranged on the steam collecting pipe, and the nozzles and the surrounding pipe do not interfere with each other.

[0010] Furthermore, molten salt can be selected as energy storage medium from ternary molten salt widely used in solar thermal power stations. The ternary molten salt has the advantages of wide operating temperature range, high thermal stability and low price. KNO3-NaNO2-NaNO3 (53%-4096-796) ternary molten salt is preferred. The ternary molten salt will decompose slightly above 427 °C, and the molten salt will solidify and block the channel at too low a temperature. Therefore, the working temperature of the high-temperature molten salt tank is designed to be 425 °C, and the working 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 demand for molten salt in the low-temperature heat exchange interval will be slightly greater than that in the high-temperature interval. A buffer tank is set to store excess medium-temperature molten salt, and its working temperature is 305 °C.

[0011] Furthermore, the working temperature of the high temperature molten salt tank 9 is not higher than the decomposition temperature of the ternary molten salt, the working 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.

[0012] In the 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 arranged between a high-temperature molten salt tank and a low-temperature molten salt tank, a steam-molten salt heat exchanger 11 is arranged between the buffer tank and the low-temperature molten salt tank, a reheat steam-molten salt heat exchanger 13 is arranged between the buffer tank and the high-temperature molten salt tank, and a main steam-molten salt heat exchanger 12 is arranged between the buffer tank and the steam boiler 1, and 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 pressurized by a steam ejector and the flow rate is increased before entering the reheater pipeline of the steam boiler 1; A temperature detection point is set on the reheater pipe, and the steam pressure, temperature and flow parameters output by the steam ejector can match the steam parameters required in the reheater pipe, so that over-temperature will not occur under energy storage conditions; The reheated steam outputted by the reheater is first supplied to the intermediate pressure cylinder steam according to the load, and 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; 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; Heat release condition: Under the stable load condition of the steam boiler 1, the high-pressure feed water of the feed water part of the steam boiler 1 is extracted and heated to high temperature in the heat exchanger with the high-temperature molten salt in the high-temperature molten salt tank 9 and the buffer tank 10 as the heat source, and then sent to the steam boiler. The steam expansion work efficiency in each stage of the high, medium and low pressure cylinders decreases successively, and 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 through the generator 5 of the steam turbine system; The high-temperature and high-pressure water medium in the brine dual-medium heat storage tank 16 flashes through the steam outlet in the brine dual-medium heat storage tank 16, and is adjusted to medium-temperature steam with suitable parameters through the pressure regulating valve. The high-temperature molten salt turns the steam passing through the steam superheater 17 into superheated steam with suitable superheat, and then enters the low-pressure cylinder 4 to perform work, thereby ensuring the safety of the steam turbine operation; the high-temperature molten salt after heat exchange returns to the buffer tank 10; in the heat release project of the brine dual-medium heat storage tank 16, the water medium is continuously cooled down, and the high-temperature molten salt in the surrounding pipe 1602 and the serpentine pipe 1603 continuously transfers heat to the water medium through the pipe wall heat exchange, thereby reducing the cooling rate of the water medium and timely regulating the load and power fluctuations; Energy storage condition: Under the steady combustion load 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. A part of the main steam cooled after the heat exchange 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 and stored in the buffer tank 10. The steam after the heat exchange becomes high-pressure condensed water and enters the water supply part of the steam boiler 1. 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°C. 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.

[0013] Compared with the prior art, the present invention has the following beneficial effects: Under the boiler steady combustion load condition, the unit extracts part of the main steam and reheat 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 peak regulation through high, medium and low molten salts, and brine dual-medium heat storage tanks, which can efficiently realize the "boiler-machine decoupling" of thermal power units. Boiler-machine decoupling means that the boiler and the generator set can be operated separately, and steam is provided by the energy storage system to supply the generator set for power generation without relying on the boiler, thereby improving its flexible operation capability. At the same time, it broadens the range of upward and downward peak regulation of the unit, providing a wider space for absorbing new energy electricity. In the system of the present invention, the high-pressure main steam after heat storage and heat exchange is used to eject the reheated steam after heat exchange, and new steam with matching parameters is obtained to compensate the steam flow at the reheater inlet. The compensation flow maintains the reheater temperature in a range, which solves the problem of overheating of the reheater pipeline caused by large-scale extraction of main steam for heat storage when the unit is running at low load. At the same time, the low-pressure reheated steam is ejected by the steam ejector to avoid condensing the steam after heat exchange into water and returning to the steam turbine system by reducing temperature and pressure, which causes a large amount of condensation heat loss, and effectively reduces the condensation heat loss caused by steam extraction and heat storage under deep peak regulation conditions. The steam extraction energy storage method in the present invention is superior to the electric heating energy storage method under the same conditions in terms of energy storage capacity, the whole process of heat storage-release, 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 medium, high, and low pressure cylinders and generators) will be directly increased, or the heat recovery extraction steam will be reduced to indirectly increase the steam flow in the steam turbine cylinder. From the perspective of energy, the work efficiency of high and medium pressure cylinders is higher than that of low pressure cylinders, and the work efficiency of steam expansion in each stage of the cylinder decreases successively. When directly heating the boiler feed water, the heat carried by the molten salt heats the high pressure feed water to increase the thermal efficiency obtained by the steam flow of the high and medium pressure cylinders, which is significantly better than the thermal efficiency obtained by increasing the steam flow of the low pressure cylinder. The efficiency is higher. The present invention adopts ternary molten salt coupled thermoelectric decoupling. The ternary molten salt will decompose slightly above 427 ° C. At the same time, the molten salt will solidify and block the channel at too low a temperature. Therefore, the working temperature of the high temperature molten salt tank is set to 425 ° C, and the working 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 interval will be slightly greater than that in the high temperature interval. A buffer tank is set to store excess medium temperature molten salt, and its working temperature is 305 ° C. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 2It is a schematic diagram of the local pipeline arrangement of the brine dual-medium heat storage tank of the present invention; 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 heat storage tank; 1601. steam collecting pipe; 1602. surrounding pipe; 1603. serpentine pipe; 17. steam superheater. DETAILED DESCRIPTION

[0015] The specific embodiments are given below in combination with the embodiments and drawings. The specific embodiments are only used to further illustrate the technical solution of the present invention in detail, and do not limit the protection scope of the present application.

[0016] Example 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, a medium-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 heat storage tank 16, and a steam superheater 17; 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 medium-pressure cylinder 3 on the one hand, and to the steam inlet of the brine dual-medium heat 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; The steam outlet of the intermediate pressure cylinder 3 is connected to the steam inlet of the low pressure cylinder 4, and 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, and the outlet of the condenser 6 is connected to the inlet of the condensate pump 7 on one hand, and the outlet of the condensate pump 7 is connected to the feed water inlet of the steam boiler 1 on the other hand. 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. 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; 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; The steam outlet of the brine dual-medium heat 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.

[0017] Furthermore, the brine dual-medium heat 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, a horizontal guide pipe arranged on the diameter of the annular pipe, and a vertical guide pipe connected to the horizontal guide pipe and the inlet of the brine dual-medium heat 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 heat storage tank 16. The steam collecting pipe 1601, the surrounding pipe 1602, and the serpentine pipe 1603 do not interfere with each other.

[0018] 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 heat storage tank 16 is filled with water medium, and the space occupied does not exceed 80% of the inner cavity space.

[0019] Furthermore, molten salt can be selected as energy storage medium using ternary molten salt widely used in solar thermal power stations. The ternary molten salt has the advantages of wide operating temperature range, high thermal stability and low price. In this embodiment, KNO3-NaNO2-NaNO3 (53%-4096-796) ternary molten salt is used. The ternary molten salt will decompose slightly above 427 °C. At the same time, the molten salt will solidify and block the channel at too low a temperature. Therefore, the working 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 working 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 working temperature is 305 °C. The specific attribute parameters of the ternary molten salt are as follows:

[0020] The working principle and workflow of this embodiment are: Energy storage condition: Under the steady combustion load condition of the steam boiler 1, the main steam (10MPa, 560℃) 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 molten salt in the buffer tank 10 is heated to 305℃ and 425℃, and enters the high-temperature molten salt tank 9 for storage. A part of the main steam (10MPa, 315℃) cooled after the heat exchange is 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 and stored in the buffer tank 10. The steam after heat exchange becomes high-pressure condensed water and enters the water supply part of the steam boiler 1.

[0021] 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: 1.7 MPa, 560°C). A part of the reheated steam is heat-exchanged with the molten salt from the buffer tank 10 through the reheated steam-molten salt heat exchanger 13 (the steam pressure and temperature after heat exchange are 1.55 MPa, 315°C), and the medium-temperature molten salt in the buffer tank 10 at 305°C is heated to a high-temperature molten salt temperature of 425°C and enters the high-temperature molten salt tank 9 for storage again. Secondly, the other part of the reheated steam is heat-exchanged with the main steam-molten salt heat exchanger 12. The main steam (10MPa, 315℃) and the reheated steam (1.55MPa, 315℃) after heat exchange in the reheated steam-molten salt heat exchanger 13 are ejected through the steam ejector 14 to obtain mixed steam with a steam pressure of 1.6MPa and a temperature of 301℃. 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 salt water dual-medium heat storage tank 16 for energy storage. Finally, the reheated steam that has not been heat exchanged by the steam ejector 14 is depressurized and returned to the low-pressure cylinder 4 to perform work.

[0022] The main working principle of the steam ejector is to use high-pressure steam to eject the low-pressure steam to be pressurized at a high speed, and then form medium-pressure steam that meets the needs after energy exchange. The working medium high-pressure steam can also be called working steam, the ejected low-pressure steam can also be called ejection steam, and the mixed medium-pressure steam can be called mixed steam.

[0023] The reheated steam enters the steam collecting pipe 1601 of the brine dual-medium heat 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, and the reheated steam in the steam collecting pipe 1601 enters the brine dual-medium heat 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 heat storage tank 16, and 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.

[0024] Heat release 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.

[0025] The high-temperature and high-pressure water medium in the brine dual-medium heat storage tank 16 flashes through the steam outlet in the brine dual-medium heat storage tank 16, and is adjusted to medium-temperature steam with suitable parameters through a pressure regulating valve (not shown in the figure). The high-temperature molten salt turns the steam passing through the steam superheater 17 into superheated steam with appropriate superheat, and enters the low-pressure cylinder 4 to perform work, ensuring the safety of the turbine operation. The high-temperature molten salt after heat exchange returns to the buffer tank 10. In the heat release project of the brine dual-medium heat 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 the pipe wall heat exchange, reducing the cooling rate of the water medium, further utilizing the stored heat, and improving the energy utilization rate.

[0026] 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 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 heat storage tank, wherein the steam outlet of the steam boiler is connected to the steam inlet of the high-pressure cylinder on the 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 the one hand, and to the steam inlet of the brine dual-medium heat storage tank on the other hand, and 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 the 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 the 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 to 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 heat 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, characterized in that The brine dual-medium heat storage tank comprises a steam collecting pipe, a surrounding pipe and a serpentine pipe. Steam is introduced 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.

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

4. The system according to claim 1, characterized in that Ternary molten salt is selected as the energy storage medium, preferably KNO3-NaNO2-NaNO3 (53%-4096-796) ternary molten salt.

5. The system according to claim 1, characterized in that 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 performance of a thermoelectric decoupling system coupled with molten salt energy storage, characterized in that: A buffer tank is arranged between the high-temperature molten salt tank and the low-temperature molten salt tank, a steam-molten salt heat exchanger is arranged between the buffer tank and the low-temperature molten salt tank, a reheat steam-molten salt heat exchanger is arranged between the buffer tank and the high-temperature molten salt tank, and a main steam-molten salt heat exchanger is arranged 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 pressurized by a steam ejector and the flow rate is increased before entering the reheater pipeline of the steam boiler. A temperature detection point is set on the reheater pipe, and the steam pressure, temperature and flow parameters output by the steam ejector can match the steam parameters required in the reheater pipe, so that over-temperature 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 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 high temperature in the heat exchanger with the high-temperature molten salt in the high-temperature molten salt tank and the buffer tank as the heat source, and then sent to the steam boiler. The steam expansion work efficiency in each stage of the high, medium and low pressure cylinders decreases in turn, and 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℃, 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 and high-pressure water medium in the brine dual-medium heat storage tank flashes through the steam outlet in the brine dual-medium heat storage tank, and is adjusted to medium-temperature steam with suitable parameters through the pressure regulating valve. The high-temperature molten salt turns the steam passing through the steam superheater into superheated steam with appropriate superheat, and then enters the low-pressure cylinder to perform work, ensuring the safety of turbine operation; the high-temperature molten salt after heat exchange returns to the buffer tank; in the heat release project of the brine dual-medium heat storage tank, the water medium is continuously cooled down, and the high-temperature molten salt in the surrounding pipe and the serpentine pipe continuously transfers heat to the water medium through the pipe wall heat exchange, reducing the cooling rate of the water medium and timely regulating the load and power fluctuations; Energy storage condition: Under the steady combustion 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, and the medium-temperature molten salt in the buffer tank is heated to the temperature of the high-temperature molten salt and enters the high-temperature molten salt tank for storage. After the heat exchange, part of the main steam that has been 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 up by heat exchange and stored in the buffer tank. The steam after heat exchange becomes high-pressure condensed water 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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