Fused salt-water coupled cascade heat storage system

Abstract

The invention relates to a fused salt-water coupled cascade heat storage system, which relates to the technical field of heat storage and comprises a steam heat accumulator, a fused salt single tank, a fused salt electric heater, a superheater and a buffer tank. The water heat storage technology and the fused salt single-tank heat storage technology are coupled, saturated steam is overheated through fused salt, the problem that the water heat storage technology can only supply saturated steam externally can be solved, and the requirement for externally supplying overheated steam all day long is met. Energy needed in the water phase change vaporization process is stored through the water heat storage technology, the steam supply cost can be greatly reduced, and the problems that a traditional fused salt double-tank heat storage system is large in heat storage material consumption, high in cost, large in occupied area and complex in control system are solved; due to the design of high-position arrangement of the fused salt heater and the superheater, rapid salt dredging in the start-stop process is facilitated, the system is simplified, and the system is suitable for frequent start-stop of steam supply systems in the industrial and commercial fields.

Description

Technical Field

[0001] The present invention relates to the technical field of water thermal energy storage, and particularly relates to a cascaded thermal energy storage system coupling molten salt and water. Background Art

[0002] Industrial steam, as an important raw material for industrial production, has a large market demand. Currently, the technical routes for thermal energy storage and steam supply mainly include solid thermal energy storage technology, phase change thermal energy storage technology, molten salt thermal energy storage technology, water thermal energy storage technology, etc. Among them, the molten salt thermal energy storage technology is limited by the problem of molten salt solidification, with a complex system and relatively high investment cost. While the water thermal energy storage technology uses water as the thermal energy storage medium, and can meet the demand for external supply of saturated steam through pressure reduction and flashing. The system is simple, has high thermal efficiency and low cost. However, due to the diversity of user needs, only supplying saturated steam cannot meet the demand for superheated steam from users, which is also an important factor restricting the commercial application of water thermal energy storage technology. Therefore, it is urgent to design a cascaded thermal energy storage system coupling molten salt and water, which couples the water thermal energy storage technology with the molten salt thermal energy storage technology, uses the saturated steam generated by the water thermal energy storage system, and the molten salt thermal energy storage system superheats it to meet the demand for low-cost external supply of superheated steam, which helps to promote the large-scale application of thermal energy storage technology. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a cascaded thermal energy storage system coupling molten salt and water, which utilizes the technical advantages of molten salt thermal energy storage technology and water thermal energy storage technology to make up for the deficiency that the water thermal energy storage technology can only supply saturated steam externally, and realizes the demand for low-cost and all-weather external supply of superheated steam.

[0004] To achieve the above object, the technical solution of the present invention provides a cascaded thermal energy storage system coupling molten salt and water, including a steam accumulator, a single molten salt tank, a molten salt electric heater, a superheater, and a buffer tank; the inlet of the steam accumulator is connected to an external steam pipeline, and the outlet is connected to the inlet of the buffer tank; the outlet of the buffer tank is connected to the steam inlet of the superheater; the inlet of the single molten salt tank is connected to the molten salt outlet of the superheater, and the outlet is connected to the inlet of the molten salt electric heater; the system can operate in a thermal energy storage mode, a heat release mode, and a mode of storing and releasing heat simultaneously.

[0005] Preferably, the specific operation process of the present invention is as follows:

[0006] a. In the thermal energy storage mode, the superheater does not work, and the external steam enters the steam accumulator to heat the internal low-pressure saturated water. The steam cools and condenses into water and is stored in the steam accumulator; the molten salt in the single molten salt tank flows into the molten salt electric heater, and after the temperature rises, it flows through the superheater and then into the single molten salt tank, realizing the molten salt thermal energy storage and temperature rise cycle;

[0007] b. Under the heat release condition, the molten salt electric heater does not work, and the steam accumulator releases heat to generate saturated steam. After the saturated steam flows through the buffer tank, it enters the superheater and is heated by the hot molten salt into superheated steam for external supply. The molten salt in the single molten salt tank flows through the molten salt heater, then flows into the superheater, releases heat and cools down, and then flows back into the single molten salt tank, realizing the molten salt heat release and cooling cycle.

[0008] c. Under the condition of storing and releasing heat simultaneously, the external steam enters the steam accumulator to heat the internal low-pressure saturated water. At the same time, the steam accumulator releases heat to generate saturated steam. After the saturated steam flows through the buffer tank, it enters the superheater and is heated by the hot molten salt into superheated steam for external supply. The molten salt in the single molten salt tank flows into the molten salt heater, its temperature rises and then flows into the superheater, releases heat and cools down, and then flows back into the single molten salt tank. The molten salt is first heated and then cooled in one cycle.

[0009] Preferably, the external steam is sourced from the extraction steam of the unit, the electrode boiler or the exhaust steam of the back pressure machine.

[0010] Preferably, a pressure reducing valve and a flow regulating valve are provided at the outlet of the steam accumulator to control the pressure and flow rate of the saturated steam at the outlet of the accumulator.

[0011] Preferably, a water replenishing port is provided at the lower part of the steam accumulator to adjust the water level in the accumulator; a steam-water separator is provided at the upper part of the steam accumulator to ensure the dryness of the saturated steam.

[0012] Preferably, the positions of the molten salt heater and the superheater can be interchanged according to the actual situation.

[0013] Preferably, the superheater is a hairpin heat exchanger, with steam flowing through the shell side and molten salt flowing through the tube side.

[0014] Preferably, the single molten salt tank is a horizontal storage tank arranged at a low position, and the molten salt electric heater and the superheater are arranged at a high position, adopting a high-low layout; the power supply of the molten salt electric heater is grid power, new energy power or plant power.

[0015] Preferably, the heat storage medium in the single molten salt tank is a single molten salt or a multi-component mixed molten salt. Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] (1) The present invention couples the water heat storage technology with the single molten salt tank heat storage technology, and uses molten salt to superheat the saturated steam, which can solve the problem that the water heat storage technology can only supply saturated steam externally and meet the demand for all-weather external supply of superheated steam.

[0017] (2) The present invention utilizes water heat storage technology to store the energy required during the phase change vaporization of water, which can significantly reduce the steam supply cost and solve the problems of large amount of heat storage material, high cost, large floor area, and complex control system in the traditional molten salt double-tank heat storage system.

[0018] (3) The present invention adopts the design of arranging the molten salt single tank at a low position and the molten salt heater and superheater at a high position, which is convenient for rapid salt drainage during start-up and shutdown, simplifies the system, and is suitable for the characteristics of frequent start-up and shutdown of the steam supply system in the industrial and commercial fields. Brief Description of the Drawings

[0019] Figure 1 It is a schematic diagram of a molten salt-water coupled cascade heat storage system.

[0020] Reference Numerals: 1, steam accumulator; 2, molten salt single tank; 3, molten salt heater; 4, superheater; 5, buffer tank. Detailed Embodiments

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] The present invention is a molten salt-water coupled cascade heat storage system, as Figure 1 shown, including a steam accumulator 1, a molten salt single tank 2, a molten salt electric heater 3, a superheater 4, and a buffer tank 5; the inlet of the steam accumulator 1 is connected to the external steam pipeline, and the outlet is connected to the inlet of the buffer tank 5; the outlet of the buffer tank 5 is connected to the steam inlet of the superheater 4; the inlet of the molten salt single tank 2 is connected to the molten salt outlet of the superheater 4, and the outlet is connected to the inlet of the molten salt electric heater 3. A pressure reducing valve and a flow regulating valve are provided at the outlet of the steam accumulator 1 to control the pressure and flow rate of the saturated steam at the outlet of the accumulator. A water replenishing port is provided at the lower part of the steam accumulator 1 to adjust the water level in the accumulator; a steam-water separator is provided at the upper part of the steam accumulator 1 to ensure the dryness of the saturated steam. The superheater 4 is a hairpin heat exchanger, with steam flowing through the shell side and molten salt flowing through the tube side. The molten salt single tank 2 is a horizontal storage tank, which can be arranged at a low position, and the molten salt electric heater 3 and the superheater 4 are arranged at a high position, adopting a high-low position arrangement.

[0023] As an optional embodiment, the external steam can be sourced from unit extraction steam, electrode boilers, or exhaust steam from a back pressure turbine; the positions of the molten salt electric heater 3 and the superheater 4 can be interchanged according to actual conditions; the heat storage medium in the molten salt single tank 2 is a single molten salt or a multi-component mixed molten salt; the power supply of the molten salt electric heater 3 is grid power, new energy power, or plant power.

[0024] In this embodiment, the molten salt selected is Hitec ternary salt (53% KNO3 + 40% NaNO2 + 7% NaNO3), with an operating temperature range of 230 - 360°C. The source of external steam is the extraction steam of the unit at 3.8 Mpa and 400°C, and the power source is the valley electricity of the power grid. It can supply industrial steam at 0.8 Mpa and 220°C. The system for externally supplying superheated steam based on water thermal energy storage can flexibly switch between the thermal energy storage mode, heat release mode, and combined thermal energy storage and release mode according to different power grid load conditions to achieve efficient energy management and supply. The following is the specific operation process of the system:

[0025] Thermal energy storage mode: The superheater 4 is in a non-operating state. The extraction steam of the unit at 3.8 Mpa and 400°C flows into the steam accumulator 1, heating the low-pressure saturated water inside, and the steam cools and condenses into water and is stored in the steam accumulator 1. Start the molten salt electric heater 3. The molten salt in the single molten salt tank 2 is pumped out by the molten salt pump, flows to the molten salt electric heater 3, and after the temperature rises, it flows through the superheater 4 and then into the single molten salt tank 2; the molten salt is continuously circulated and heated. After being heated to 360°C, the thermal energy storage mode ends;

[0026] Heat release mode: The molten salt electric heater 3 is in a non-operating state. The steam accumulator 1 releases heat to generate saturated steam at 0.8 Mpa. After the saturated steam flows through the buffer tank 5, it is heated into superheated steam at 0.8 Mpa and 220°C by the hot molten salt in the superheater 4 and is directly supplied externally. The molten salt in the single molten salt tank 2 is pumped out by the molten salt pump, flows through the molten salt heater 3, and then flows to the superheater 4. After the temperature drops, it flows into the single molten salt tank 2; the molten salt is continuously circulated and cooled. After being cooled to 230°C, the heat release mode ends.

[0027] A molten salt-water coupled cascade thermal energy storage system provided by the present invention is simple to operate and has high safety. It couples the water thermal energy storage technology with the single molten salt tank thermal energy storage technology, and uses molten salt to superheat saturated steam, which can solve the problem that the water thermal energy storage technology can only supply saturated steam externally and meet the demand for all-weather external supply of superheated steam; the present invention uses the water thermal energy storage technology to store the energy required during the phase change vaporization of water, which can greatly reduce the steam supply cost and solve the problems of large amount of thermal energy storage materials, high cost, large floor area, and complex control system in the traditional double molten salt tank thermal energy storage system; the present invention adopts the design of arranging the single molten salt tank at a low position and the molten salt heater and superheater at a high position, which is convenient for rapid salt drainage during start-up and shutdown, simplifies the system, and is suitable for the characteristics of frequent start-up and shutdown of the steam supply system in the industrial and commercial fields.

[0028] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A molten salt - water coupled cascaded thermal energy storage system, characterized in that, It includes a steam accumulator (1), a molten salt single tank (2), a molten salt electric heater (3), a superheater (4), and a buffer tank (5); the inlet of the steam accumulator (1) is connected to an external steam pipeline, and the outlet is connected to the inlet of the buffer tank (5); the outlet of the buffer tank (5) is connected to the steam inlet of the superheater (4); the inlet of the molten salt single tank (2) is connected to the molten salt outlet of the superheater (4), and the outlet is connected to the inlet of the molten salt electric heater (3); the system can operate in heat storage mode, heat release mode, and heat storage and release mode simultaneously.

2. The cascade thermal energy storage system coupled by molten salt and water according to claim 1, wherein The specific operation processes of the three modes are as follows: a. In the heat storage mode, the superheater (4) does not work. External steam enters the steam accumulator (1), heating the low-pressure saturated water inside. The steam cools and condenses into water and is stored in the steam accumulator (1). The molten salt in the molten salt single tank (2) flows into the molten salt electric heater (3), and after the temperature rises, it flows through the superheater (4), and then flows back into the molten salt single tank (2), realizing the molten salt heat storage and temperature rise cycle. b. In the heat release mode, the molten salt electric heater (3) does not work. The steam accumulator (1) releases heat to generate saturated steam. After the saturated steam flows through the buffer tank (5), it enters the superheater (4) and is heated by the hot molten salt into superheated steam for external supply. The molten salt in the molten salt single tank (2) flows through the molten salt heater (3), then flows into the superheater (4), and after the temperature drops, it flows back into the molten salt single tank (2), realizing the molten salt heat release and temperature drop cycle. c. In the heat storage and release mode simultaneously, external steam enters the steam accumulator (1), heating the low-pressure saturated water inside. At the same time, the steam accumulator (1) releases heat to generate saturated steam. After the saturated steam flows through the buffer tank (5), it enters the superheater (4) and is heated by the hot molten salt into superheated steam for external supply. The molten salt in the molten salt single tank (2) flows into the molten salt heater (3), and after the temperature rises, it flows into the superheater (4), and after releasing heat and cooling down, it flows back into the molten salt single tank (2); the molten salt is first heated and then cooled in one cycle.

3. The cascade thermal energy storage system coupled by molten salt and water according to claim 1, characterized in that , The external steam comes from the extraction steam of the unit, the electrode boiler, or the exhaust steam of the back pressure machine.

4. A cascaded heat storage system coupled by molten salt and water according to claim 1, characterized in that , A pressure reducing valve and a flow regulating valve are provided at the outlet of the steam accumulator (1) to control the pressure and flow of the saturated steam at the outlet of the accumulator.

5. A cascade thermal energy storage system coupled by molten salt and water according to claim 1, characterized in that , A water replenishing port is provided at the lower part of the steam accumulator (1) to adjust the water level in the accumulator; a steam-water separator is provided at the upper part of the steam accumulator (1) to ensure the dryness of the saturated steam.

6. A cascade thermal energy storage system coupling molten salt and water according to claim 1, wherein , The positions of the molten salt heater (3) and the superheater (4) can be interchanged according to the actual situation.

7. A cascade thermal energy storage system with molten salt - water coupling according to claim 1, characterized in that , The superheater (4) is a hairpin heat exchanger, with steam flowing in the shell side and molten salt flowing in the tube side.

8. A cascade thermal energy storage system with molten salt-water coupling according to claim 1 or 6, characterized in that The molten salt single tank (2) is a horizontal storage tank arranged at a low position, and the molten salt electric heater (3) and the superheater (4) are arranged at a high position, adopting a high-low layout; the power supply of the molten salt electric heater (3) is grid power, new energy power, or plant power.

9. The cascade thermal energy storage system coupled by molten salt and water according to claim 1, wherein, The heat storage medium in the molten salt single tank (1) is a single molten salt or a multi-component mixed molten salt.

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