Heat storage system for hierarchically storing sensible heat and latent heat of steam and operation method of heat storage system

Abstract

The invention discloses a heat storage system for hierarchically storing sensible heat and latent heat of steam and an operation mode of the heat storage system. The system comprises a steam heat accumulator, a main steam bypass valve, a water supply bypass valve, a steam valve, a fused salt cold tank, a fused salt hot tank, a 1 # fused salt-steam heat exchanger, a 2 # fused salt-steam heat exchanger, a 1 # fused salt pump and a 2 # fused salt pump. In the heat storage process, sensible heat and latent heat of high-temperature and high-pressure steam of the coal-fired unit are stored in a classified mode through fused salt and the steam heat accumulator, saturated steam released by the steam heat accumulator is heated into reheated steam through the stored sensible heat in the heat release process, and the reheated steam returns to a steam turbine for power generation, so that efficient utilization of energy is achieved. The system can quickly assist the coal-fired unit in peak and frequency regulation, ensures high operation efficiency, is easy to control, has the advantage of economy, is a novel heat energy storage technology, and can provide powerful support for stabilizing power grid and user load fluctuation, promoting new energy consumption and constructing a novel power system.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal energy storage, and in particular to a heat storage system for storing sensible and latent heat of steam in stages and an operating method thereof. Background Art

[0002] Renewable energy generation such as wind and solar power has a strong time-varying characteristic, which significantly affects the stability and reliability of the power grid. How to achieve efficient and flexible coordination in the process of variable load is a key core issue that needs to be urgently addressed in the development of my country's power industry. The application of thermal energy storage technology can solve this core problem. Storing the heat of steam in coal-fired power plants is an effective means to assist coal-fired units in peak load regulation and frequency regulation, and to improve the flexibility of coal-fired units. However, the storage and release of steam heat is often accompanied by phase change, which makes it difficult to match the heat exchange temperature and heat in the heat storage and release process with steam as the heat source, resulting in large losses and low energy utilization efficiency. Summary of the Invention

[0003] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a heat storage system for hierarchical storage of sensible heat and latent heat of steam and its operation method. The hierarchical storage method is adopted, molten salt is used to store the sensible heat of high-temperature and high-pressure steam, and a steam accumulator is used to store the latent heat of steam. During the heat release process, the stored heat is used to generate high-temperature and high-pressure superheated steam. The heat exchange temperature matching degree of the heat storage and release process is high, and a higher energy utilization efficiency can be achieved.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A heat storage system for hierarchical storage of sensible and latent heat of steam, the heat storage system comprising a steam accumulator 2, a main steam bypass valve 3, a feedwater bypass valve 15, a steam valve 16, a molten salt cold tank 17, a molten salt hot tank 18, a 1# molten salt-steam heat exchanger 19, a 2# molten salt-steam heat exchanger 20, a 1# molten salt pump 21 and a 2# molten salt pump 22; the main steam outlet of the boiler 1 of the coal-fired unit is respectively connected to the inlet of the high-pressure cylinder 4 and the steam inlet of the 1# molten salt-steam heat exchanger 19 through the main steam bypass valve 3, the steam outlet of the 1# molten salt-steam heat exchanger 19 is connected to the steam inlet of the steam accumulator 2, and the steam outlet of the steam accumulator 2 is connected to the steam inlet of the 2# molten salt-steam heat exchanger 20 through the 1# steam valve 16. The inlet of the medium-pressure cylinder 5 and the inlet of the low-pressure cylinder 6, the steam at the outlet of the high-pressure cylinder 4 is heated by the boiler 1 to obtain reheated steam, the steam outlet of the 2# molten salt-steam heat exchanger 20 and the reheated steam hot outlet of the boiler 1 are connected to the steam inlet of the medium-pressure cylinder 5, and the outlet of the feed water pump 13 of the coal-fired unit is connected to the hot water inlet of the steam accumulator 2 through the feed water bypass valve 15; the outlet of the molten salt cold tank 17 is connected to the molten salt inlet of the 1# molten salt-steam heat exchanger 19 through the 1# molten salt pump 21, the molten salt outlet of the 1# molten salt-steam heat exchanger 19 is connected to the inlet of the molten salt hot tank 18, the outlet of the molten salt hot tank 18 is connected to the molten salt inlet of the 2# molten salt-steam heat exchanger 20 through the 2# molten salt pump 22, and the molten salt outlet of the 2# molten salt-steam heat exchanger 20 is connected to the inlet of the molten salt cold tank 17.

[0006] The steam accumulator 2 contains a certain amount of saturated water and steam before heat storage. During the heat storage process, steam and hot water are injected to increase the pressure in the steam accumulator. During the heat release process, the 1# steam valve 16 is opened to cause flash evaporation inside the steam accumulator and release saturated steam.

[0007] The main steam bypass valve 3 arranged between the 1# molten salt-steam heat exchanger 19 and the boiler 1, and the feed water bypass valve 15 arranged between the steam accumulator 2 and the feed water pump 13 respectively control the steam and hot water flow rates entering the steam accumulator 2, and the steam valve 16 arranged at the steam outlet of the steam accumulator 2 controls the steam flow rate and pressure at the steam outlet.

[0008] The working pressure range of the steam accumulator 2 before heat storage is 2.0-4.0 MPa, and the working pressure range after heat storage is 4.0-6.0 MPa.

[0009] The molten salt cold tank 17 and the molten salt hot tank 18 use solar salt, i.e. 60% by mass of NaNO3 and 40% by mass of KNO3, as heat storage medium, and the working range is 220-600°C.

[0010] The 1# molten salt-steam heat exchanger 19 and the 2# molten salt-steam heat exchanger 20 are plate heat exchangers, shell and tube heat exchangers or coil heat exchangers.

[0011] The total mass of steam and hot water charged into the steam accumulator 2 during the heat storage process should be equal to the steam flow rate released during the heat release process to ensure that the water level of the steam accumulator remains unchanged before and after heat storage.

[0012] The volume content of liquid water in the steam accumulator 2 before heat storage is between 40-60%, and the maximum volume content of liquid water after heat storage does not exceed 90%.

[0013] The 1# molten salt pump 21 and the 2# molten salt pump 22 are vertical cantilever pumps, vertical pumps, vertical submerged pumps or axial flow pumps.

[0014] The operating method of the heat storage system for storing sensible and latent heat of steam in a staged manner, the heat storage process of the system is as follows: open the main steam bypass valve 3 and the feed water bypass valve 15, so that the main steam of the coal-fired unit first enters the 1# molten salt-steam heat exchanger 19, heats the molten salt in the molten salt cold tank 17 through the 1# molten salt pump 21 and enters the molten salt in the 1# molten salt-steam heat exchanger 19, the heated molten salt is stored in the molten salt hot tank 18, the cooled high-pressure steam and the hot water from the heat recovery system of the coal-fired unit enter the steam accumulator 2, the pressure of the steam accumulator 2 increases, the output power of the coal-fired unit decreases, and when the stored steam flow increases, the outlet of the 1# molten salt steam heat exchanger 19 enters the steam accumulator 2. The steam temperature in the steam accumulator increases, and the final pressure of the steam accumulator increases. When the stored steam flow rate decreases, the steam temperature entering the steam accumulator decreases, and the final pressure of the steam accumulator decreases. The system heat release process is as follows: the hot molten salt in the molten salt hot tank 18 enters the 2# molten salt-steam heat exchanger 20 through the 2# molten salt pump 22, and at the same time, the steam valve 16 is opened. Part of the saturated steam released by the steam accumulator 2 enters the 2# molten salt-steam heat exchanger 20 to fully exchange heat with the molten salt, becoming high-temperature superheated steam. After merging with the reheated steam at the outlet of the boiler 1, it enters the intermediate pressure cylinder 5, and the other part of the steam directly enters the low pressure cylinder 6, thereby increasing the power generation of the coal-fired unit.

[0015] Advantages of the present invention

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] (1) The present invention utilizes molten salt and steam accumulators to store steam sensible heat and latent heat in stages, resulting in high energy utilization efficiency;

[0018] (2) The present invention utilizes a steam accumulator to directly store the turbine working fluid, which has a rapid response and auxiliary peak and frequency regulation functions, and the working fluid is inexpensive, thus having an economic advantage;

[0019] (3) The present invention can control the initial and final pressures of the steam accumulator by the steam flow rate, and the heat storage and release process is easy to control. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the system structure of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0022] As attached Figure 1 As shown, a heat storage system for storing sensible and latent heat of steam in stages includes a steam accumulator 2, a main steam bypass valve 3, a steam valve 16, a feed water bypass valve 15, a molten salt cold tank 17, a molten salt hot tank 18, a 1# molten salt-steam heat exchanger 19, a 2# molten salt-steam heat exchanger 20, a 1# molten salt pump 21 and a 2# molten salt pump 22; the main steam outlet of the boiler 1 of the coal-fired unit is respectively connected to the inlet of the high-pressure cylinder 4 and the inlet of the 1# molten salt-steam heat exchanger 19 through the main steam bypass valve 3. The steam inlet of the 1# molten salt-steam heat exchanger 19 is connected to the steam inlet of the steam accumulator 2. The steam outlet of the steam accumulator 2 is connected to the steam inlet of the 2# molten salt-steam heat exchanger 20 and the inlet of the low-pressure cylinder 6 through the 1# steam valve 16. The steam at the outlet of the high-pressure cylinder 4 is heated by the boiler 1 to obtain reheated steam. The steam outlet of the 2# molten salt-steam heat exchanger 20 is connected to the steam outlet of the high-pressure cylinder 4 heated by the boiler 1 and connected to the steam inlet of the medium-pressure cylinder 5. The outlet of the medium-pressure cylinder 5 is connected The inlet and outlet of the low-pressure cylinder 6 are connected to the condenser 11, condensate pump 12, low-pressure heater group 8, deaerator 9, feed water pump 13 and high-pressure heater group 10 in sequence, and the outlet of the high-pressure heater group 10 is connected to the feed water inlet of the boiler 1; the high-pressure cylinder 4, the medium-pressure cylinder 5 and the low-pressure cylinder 6 are coaxially connected to drive the generator 7 to rotate, and the steam extraction outlets of the high-pressure cylinder 4, the medium-pressure cylinder 5 and the low-pressure cylinder 6 are respectively connected to the steam inlets of the high-pressure heater group 10, the deaerator 9 and the low-pressure heater group 8; the coal-fired unit The outlet of the water supply pump 13 is connected to the hot water inlet of the steam accumulator 2 through the water supply bypass valve 15; the outlet of the molten salt cold tank 17 is connected to the molten salt inlet of the 1# molten salt-steam heat exchanger 19 through the 1# molten salt pump 21, the molten salt outlet of the 1# molten salt-steam heat exchanger 19 is connected to the inlet of the molten salt hot tank 18, the outlet of the molten salt hot tank 18 is connected to the molten salt inlet of the 2# molten salt-steam heat exchanger 20 through the 2# molten salt pump 22, and the molten salt outlet of the 2# molten salt-steam heat exchanger 20 is connected to the inlet of the molten salt cold tank 17.

[0023] As a preferred embodiment of the present invention, the steam accumulator 2 contains a certain amount of saturated water and steam before heat storage. During the heat storage process, steam and hot water are injected to increase the pressure in the steam accumulator. During the heat release process, the steam valve of the steam accumulator is opened to cause flash evaporation inside the steam accumulator, releasing saturated steam. The rapid nature of the flash evaporation process allows for rapid heat release and adaptability to load changes.

[0024] As a preferred embodiment of the present invention, a main steam bypass valve 3, located between the No. 1 molten salt-steam heat exchanger 19 and boiler 1, and a feedwater bypass valve 15, located between the steam accumulator 2 and the feedwater pump 13, respectively control the steam and hot water flows entering the steam accumulator 2. A steam valve 16, located at the steam outlet of the steam accumulator 2, controls the steam flow and pressure at the outlet. Coordinated valve control improves system flexibility and optimizes the coordinated operating efficiency of the boiler and steam accumulator.

[0025] As a preferred embodiment of the present invention, the operating pressure range of the steam accumulator 2 before heat storage is 2.0-4.0 MPa, and the operating range after heat storage is 4.0-6.0 MPa. This allows the steam pressure at the steam accumulator outlet to reach the operating pressure of the intermediate pressure cylinder, which is beneficial to the stability of the system components.

[0026] As a preferred embodiment of the present invention, the hot molten salt storage tank 4 and the cold molten salt storage tank 5 use solar salt, including but not limited to 60% NaNO3 and 40% KNO3 by mass, as the heat storage medium, with an operating temperature range of 220-600°C. This ensures that the steam can be heated to the required operating temperature range in the second molten salt-steam heat exchanger 20.

[0027] As a preferred embodiment of the present invention, the types of the 1# molten salt-steam heat exchanger 19 and the 2# molten salt-steam heat exchanger 20 include but are not limited to plate heat exchangers, shell and tube heat exchangers and coil heat exchangers. All three types of heat exchangers have the characteristics of efficient heat transfer, flexible structure and strong medium adaptability.

[0028] As a preferred embodiment of the present invention, the total mass of steam and hot water charged into the steam accumulator 2 during the heat storage process should be equal to the steam flow rate released during the heat release process, so as to ensure that the water level of the steam accumulator remains unchanged before and after heat storage, thereby ensuring the stability of equipment operation.

[0029] In a preferred embodiment of the present invention, the liquid water volume content of steam accumulator 2 before heat storage is between 40% and 60%, leaving a sufficient steam space. This allows steam to condense and release heat upon injection, simultaneously increasing pressure. The maximum liquid water volume content after heat storage is no more than 90%, preventing excessive liquid water from reducing flash evaporation efficiency during heat release and avoiding safety issues caused by excessive pressure.

[0030] As a preferred embodiment of the present invention, the types of the 1# molten salt pump 21 and the 2# molten salt pump 22 include but are not limited to vertical cantilever pumps, vertical pumps, vertical submerged pumps and axial flow pumps.

[0031] The operation mode of the heat storage system for storing sensible and latent heat of steam in a staged manner, the heat storage process of the system is as follows: open the main steam bypass valve 3 and the feed water bypass valve 15, so that the main steam of the coal-fired unit first enters the 1# molten salt steam heat exchanger 19, heats the molten salt in the molten salt cold tank 17 through the 1# molten salt pump 21 and enters the molten salt in the 1# molten salt-steam heat exchanger 19, the heated molten salt is stored in the molten salt hot tank 18, the cooled high-pressure steam and the hot water from the heat recovery system of the coal-fired unit enter the steam accumulator 2, the pressure of the steam accumulator 2 increases, the output power of the coal-fired unit decreases, and when the stored steam flow increases, the outlet of the 1# molten salt steam heat exchanger 19 enters the steam accumulator 2. The steam temperature in the accumulator increases, and the final pressure of the steam accumulator increases. When the stored steam flow rate decreases, the steam temperature entering the steam accumulator decreases, and the final pressure of the steam accumulator decreases. The system heat release process is as follows: the hot molten salt in the molten salt hot tank 18 enters the 2# molten salt-steam heat exchanger 20 through the 2# molten salt pump 22, and at the same time, the 1# steam valve 16 is opened. A part of the saturated steam released by the steam accumulator 2 enters the 2# molten salt-steam heat exchanger 20 to fully exchange heat with the molten salt, becoming high-temperature superheated steam. After merging with the reheated steam at the outlet of the boiler 1, it enters the intermediate pressure cylinder 5, and the other part of the steam directly enters the low pressure cylinder 6, thereby increasing the power generation of the coal-fired unit.

[0032] This invention achieves efficient energy utilization by utilizing molten salt and steam accumulators to stage the sensible and latent heat of high-temperature, high-pressure steam from coal-fired units during the heat storage process. During the heat release process, the stored sensible heat is used to heat the saturated steam released from the steam accumulators into reheated steam, which is then returned to the steam turbine for power generation. This system can rapidly assist coal-fired units in peak and frequency regulation while ensuring high operational efficiency. It is also easy to control and offers economic advantages. This innovative thermal energy storage technology can help smooth grid and user load fluctuations, promote the integration of new energy sources, and provide strong support for the construction of new power systems.

Claims

1. A heat storage system for storing sensible and latent heat of steam in stages, characterized in that: The heat storage system comprises a steam accumulator (2), a main steam bypass valve (3), a feed water bypass valve (15), a steam valve (16), a molten salt cold tank (17), a molten salt hot tank (18), a 1# molten salt-steam heat exchanger (19), a 2# molten salt-steam heat exchanger (20), a 1# molten salt pump (21), a 2# molten salt pump (22) and a coal-fired unit; the main steam outlet of the boiler (1) of the coal-fired unit is respectively connected to the inlet of the high-pressure cylinder (4) and the steam inlet of the 1# molten salt-steam heat exchanger (19) through the main steam bypass valve (3), the steam outlet of the 1# molten salt-steam heat exchanger (19) is connected to the steam inlet of the steam accumulator (2), and the steam outlet of the steam accumulator (2) is connected to the steam inlet of the 2# molten salt-steam heat exchanger (20) and the low-pressure cylinder ( 6) inlet, the outlet steam of the high-pressure cylinder (4) is heated by the boiler (1) to obtain reheated steam, the steam outlet of the 2# molten salt-steam heat exchanger (20) and the reheated steam hot outlet of the boiler (1) are connected to the steam inlet of the medium-pressure cylinder (5), the outlet of the feed water pump (13) of the coal-fired unit is connected to the hot water inlet of the steam accumulator (2) through the feed water bypass valve (15); the outlet of the molten salt cold tank (17) is connected to the molten salt inlet of the 1# molten salt-steam heat exchanger (19) through the 1# molten salt pump (21), the molten salt outlet of the 1# molten salt-steam heat exchanger (19) is connected to the inlet of the molten salt hot tank (18), the outlet of the molten salt hot tank (18) is connected to the molten salt inlet of the 2# molten salt-steam heat exchanger (20) through the 2# molten salt pump (22), and the molten salt outlet of the 2# molten salt-steam heat exchanger (20) is connected to the inlet of the molten salt cold tank (17).

2. The heat storage system for hierarchically storing sensible and latent heat of steam according to claim 1, characterized in that: The steam accumulator (2) contains a certain amount of saturated water and steam before heat storage. During the heat storage process, steam and hot water are injected to increase the pressure in the steam accumulator. During the heat release process, the No. 1 steam valve (16) is opened to generate flash evaporation inside the steam accumulator and release saturated steam.

3. The heat storage system for hierarchically storing sensible and latent heat of steam according to claim 1, characterized in that: A main steam bypass valve (3) provided between the No. 1 molten salt-steam heat exchanger (19) and the boiler (1), and a feedwater bypass valve (15) provided between the steam accumulator (2) and the feedwater pump (13) respectively control the steam and hot water flows entering the steam accumulator (2). A steam valve (16) provided at the steam outlet of the steam accumulator (2) controls the steam flow and pressure at the steam outlet.

4. The heat storage system for hierarchically storing sensible and latent heat of steam according to claim 1, characterized in that: The working pressure range of the steam accumulator (2) before heat storage is 2.0-4.0 MPa, and the working pressure range after heat storage is 4.0-6.0 MPa.

5. The heat storage system for storing sensible and latent heat of steam in stages according to claim 1, characterized in that: The molten salt cold tank (17) and the molten salt hot tank (18) use solar salt, i.e. 60% by mass of NaNO3 and 40% by mass of KNO3, as heat storage medium, and the working range is 220-600°C.

6. The heat storage system for storing sensible and latent heat of steam in stages according to claim 1, characterized in that: The 1# molten salt-steam heat exchanger (19) and the 2# molten salt-steam heat exchanger (20) are plate heat exchangers, shell and tube heat exchangers or coil heat exchangers.

7. The heat storage system for storing sensible and latent heat of steam in stages according to claim 1, characterized in that: The total mass of steam and hot water charged into the steam accumulator (2) during the heat storage process should be equal to the steam flow rate released during the heat release process to ensure that the water level of the steam accumulator remains unchanged before and after heat storage.

8. The heat storage system for storing sensible and latent heat of steam in stages according to claim 1, characterized in that: The volume content of liquid water in the steam accumulator (2) before heat storage is between 40-60%, and the maximum volume content of liquid water after heat storage does not exceed 90%.

9. The heat storage system for storing sensible and latent heat of steam in stages according to claim 1, characterized in that: The 1# molten salt pump (21) and the 2# molten salt pump (22) are vertical cantilever pumps, vertical pumps, vertical submerged pumps or axial flow pumps.

10. The method for operating a heat storage system for storing sensible and latent heat of steam in stages according to any one of claims 1 to 9, characterized in that: The heat storage process of the system is as follows: the main steam bypass valve (3) and the feed water bypass valve (15) are opened, so that the main steam of the coal-fired unit first enters the 1# molten salt-steam heat exchanger (19), and the molten salt in the molten salt cold tank (17) is heated and enters the 1# molten salt-steam heat exchanger (19) through the 1# molten salt pump (21). The heated molten salt is stored in the molten salt hot tank (18). The cooled high-pressure steam and the hot water from the heat recovery system of the coal-fired unit enter the steam accumulator (2). The pressure of the steam accumulator (2) increases, and the output power of the coal-fired unit decreases. When the stored steam flow increases, the temperature of the steam entering the steam accumulator at the outlet of the 1# molten salt steam heat exchanger (19) increases. The final pressure of the steam accumulator is increased. When the stored steam flow rate decreases, the temperature of the steam entering the steam accumulator decreases, and the final pressure of the steam accumulator decreases. The heat release process of the system is as follows: the hot molten salt in the molten salt hot tank (18) enters the 2# molten salt-steam heat exchanger (20) through the 2# molten salt pump (22), and at the same time, the steam valve (16) is opened. A part of the saturated steam released by the steam accumulator (2) enters the 2# molten salt-steam heat exchanger (20) and fully exchanges heat with the molten salt to become high-temperature superheated steam. After merging with the reheated steam at the outlet of the boiler (1), the steam enters the medium-pressure cylinder (5), and the other part of the steam directly enters the low-pressure cylinder (6), thereby increasing the power generation of the coal-fired unit.

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