Step heat storage system of steam supply backpressure unit and operation method

Abstract

The invention discloses a cascade heat storage system of a steam supply backpressure unit and an operation method, and belongs to the technical field of industrial steam supply. In particular to steam-fused salt / heat conduction oil collaborative heat storage and an industrial steam supply backpressure unit flexible optimization and peak regulation technology, and aims at achieving flexible regulation of thermoelectric decoupling and loads through collaborative heat storage of steam and fused salt / heat conduction oil, so that the energy utilization efficiency and the power grid peak regulation capacity of the unit are improved. According to the system, through cooperative operation of the power generation and steam supply subsystem, the steam heat storage subsystem and the high-temperature heat storage subsystem, thermoelectric decoupling, flexible load adjustment, energy time shifting and system energy efficiency improvement are achieved.

Description

Technical Field

[0001] This invention relates to a cascade thermal storage system and operation method for a steam-supplying back-pressure unit, belonging to the field of industrial steam supply technology. Background Technology

[0002] Traditional industrial back-pressure turbine unit technology: This technology system mainly consists of a boiler, a back-pressure steam turbine, a generator, a feedwater heating device, and steam supply pipelines. Its core workflow is as follows: High-temperature, high-pressure steam generated by the boiler enters the back-pressure steam turbine, expands, and performs work, driving the generator to produce electricity. The steam, after performing work, still maintains a certain pressure and temperature. This portion of the turbine's exhaust steam (back-pressure steam) is directly or after desuperheating and pressure reduction, and then transported to industrial users through pipelines as process steam. The unit operates according to the principle of "heat-driven power generation," with power generation highly coupled to the steam supply load. This system achieves cascaded energy utilization, using high-grade heat energy for power generation and low-grade heat energy for steam supply, resulting in high overall energy efficiency.

[0003] Steam thermal energy storage technology: This technology typically uses a large, pressure-bearing steel container as the thermal storage body, filled with water. Its core technology lies in utilizing the sensible heat and latent heat of vaporization of water to store energy. During the thermal storage process, high-temperature, high-pressure steam extracted from a boiler or turbine is directly injected into the water through an internal injection device. The steam condenses, releasing its latent heat of vaporization, heating the water and increasing the pressure inside the container. The energy is stored in the form of high-temperature saturated water. When heat release is needed, the container pressure is reduced, and some of the saturated water undergoes superheating and vaporization (flash evaporation), producing saturated steam at the required pressure for output. This technology achieves the storage and re-release of steam thermal energy, can smooth out steam load fluctuations, and is suitable for buffering load fluctuations in steam or hot water systems, such as assisting in stabilizing heating output during short-term peak demand periods in urban centralized heating systems.

[0004] Molten salt thermal energy storage technology: This technology typically uses a mixture of nitrates and other substances as the heat storage medium. The system mainly consists of molten salt storage tanks (cold tanks and hot tanks), molten salt pumps, molten salt-working fluid heat exchangers (such as molten salt heaters and steam generators), and an electric heat tracing system. During the heat storage process, cold molten salt is heated to a high temperature using electrical energy or high-temperature extracted steam through the heat exchanger and stored in the hot tank. During the heat release process, the high-temperature molten salt is pumped out of the hot tank and flows through the steam generator, transferring the heat it carries to the feedwater, thereby generating superheated steam. This technology utilizes the sensible heat of molten salt in its liquid state for heat storage, featuring high operating temperature, large heat capacity, and the ability to achieve high-temperature and high-pressure steam output. It can achieve long-term, large-capacity thermal energy storage and is commonly used in scenarios such as solar thermal power generation and long-term storage of industrial waste heat, playing a regulatory role in the time mismatch between heat energy supply and demand.

[0005] Thermal oil heat storage technology: This technology typically uses thermal oil (such as mineral oil or synthetic oil) as the heat storage medium. The system mainly consists of a thermal oil heater, thermal oil storage tanks (hot and cold tanks), a thermal oil pump, an oil-working fluid heat exchanger (such as an oil-water heat exchanger), and a temperature control system. During the heat storage process, electrical energy, high-temperature flue gas, or waste heat from the process are used to heat the thermal oil to a high temperature (usually above 300°C) via the heater, and it is stored in the hot tank. During the heat release process, the high-temperature thermal oil is pumped out from the hot tank and flows through the oil-working fluid heat exchanger, transferring the heat it carries to water or other working fluids, thereby generating steam or hot water. This technology utilizes the sensible heat of the thermal oil for heat storage and features high operating temperature, low system pressure (atmospheric or low-pressure operation), good thermal stability, and safe operation. It is suitable for industrial applications requiring a stable high-temperature heat source, such as chemical, textile, and food processing industries, and can achieve heat energy storage and on-demand supply. However, the heat capacity of the thermal oil is relatively low, and there are risks of aging, leakage, and environmental pollution.

[0006] Limited operational flexibility and energy waste coexist: Existing industrial steam supply systems, especially traditional back-pressure units, operate on a "heat-driven power generation" model, resulting in rigid coupling between power generation and steam load, making independent adjustment impossible. When grid electricity consumption fluctuates between peak and off-peak times or user steam demand changes, the units struggle to flexibly adjust power output to respond to grid demands. Furthermore, they cannot effectively reduce operating costs while ensuring stable steam supply, leading to uneconomical energy use and insufficient operational flexibility.

[0007] Limitations of Energy Storage and Release: Existing thermal storage technologies, whether steam accumulators or molten salt / thermal oil thermal storage systems, often have limited functionality in application, making it difficult to simultaneously achieve rapid response and high-parameter output. While steam accumulators offer rapid response, the stored and released steam parameters (pressure, temperature) are mutually constrained, making it difficult to directly meet the high-grade industrial steam supply demands. Molten salt / thermal oil thermal storage systems, although capable of providing high-parameter steam, suffer from high system inertia, relatively slow response, and high initial investment and operating / maintenance costs. Simply placing these two technologies side-by-side, without deep integration and tiered coordination, fails to achieve the optimal configuration of "graded storage and on-demand release" of energy based on its grade.

[0008] Insufficient system synergy and the need to improve overall energy efficiency: In existing technical solutions, core components such as power generation, steam supply, thermal storage, and water replenishment are usually designed independently or simply superimposed, lacking organic synergy and integration. The energy and information flows between subsystems are fragmented, making it impossible to perform unified, efficient, and intelligent scheduling and optimization of the entire system based on real-time energy prices, grid commands, and user loads. This results in suboptimal overall system energy efficiency and makes it difficult to unify the unit's flexible peak-shaving capabilities, stable steam supply, and economic operation goals, thus failing to meet the comprehensive optimization needs of complex energy scenarios. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a cascade thermal storage system and operation method for a steam-supplying back-pressure unit. Through the synergistic thermal storage of steam and molten salt / heat transfer oil, thermoelectric decoupling and flexible load adjustment are achieved, thereby improving energy utilization efficiency and the unit's grid peak-shaving capability. To achieve the above objectives / to solve the above technical problems, the present invention is implemented using the following technical solution: First aspect: A cascade thermal storage system for a steam-supplying back-pressure turbine unit, comprising: The power generation and steam supply subsystem includes a boiler, one of which is connected to the first generator set via valve one, and the other is connected to the second generator set via valve two; one of the first generator sets is connected to the high-temperature heat storage subsystem, and the other is used for industrial steam extraction one; one of the other lines of the first generator set is equipped with a second high-pressure heater and a deaerator in parallel, and the other line is used for industrial steam extraction three, and the other is connected to the steam heat storage subsystem; the second generator set is connected to a water supply pipeline; A steam heat storage subsystem includes a heat storage spherical tank, which is used to store high-temperature heat during peak electricity demand and to generate steam during off-peak electricity demand to supplement industrial steam extraction. The high-temperature thermal storage subsystem includes a high-temperature tank and a low-temperature tank. One end of the high-temperature tank is connected to a high-temperature fluid heater via valve ten, and the other end is connected to a steam generator via high-temperature fluid pump two. One end of the low-temperature tank is connected to a high-temperature fluid heater via high-temperature fluid pump one, and the other end is connected to a steam generator via valve thirteen. The output end of the thermal storage spherical tank is connected to pump three, the steam generator, and industrial steam extraction three. Valves eight and six are provided on this pipeline. The high-temperature fluid heater is connected to the first generator set, and the high-temperature fluid heater is connected to the thermal storage spherical tank via valve twelve.

[0010] Optionally, the second generator set includes a medium-pressure cylinder two and a low-pressure cylinder. One of the medium-pressure cylinder two is connected to industrial steam extraction three through valve four. Valve four is connected to the thermal storage tank in sequence through valve five and valve eleven. The other of the medium-pressure cylinder two is connected to the No. 1 high-pressure heater. One of the low-pressure cylinders is used for heating steam extraction, and the other is connected to the water supply pipeline through valve seven.

[0011] Optionally, the water supply pipeline includes a water supply heater, and the water supply heater, deaerator, second high-pressure heater, and first high-pressure heater are connected in sequence. One branch of the first high-pressure heater is connected to the boiler, and the other branch is connected to the second high-pressure heater. The second high-pressure heater is connected to the deaerator, and the other branch of the deaerator is connected to the steam heat storage subsystem. A second pump is provided between the water supply heater and the deaerator, and a first pump is provided between the second high-pressure heater and the deaerator.

[0012] Optionally, the first generator set includes a high-pressure cylinder and an intermediate-pressure cylinder. The high-pressure cylinder is connected to a high-temperature fluid heater via a valve, and the intermediate-pressure cylinder is connected to a second high-pressure heater.

[0013] Optionally, the thermal storage sphere is connected to another line of the first generator set, and valves five and eleven are sequentially installed on this pipeline; valves nine and fifteen are sequentially installed on the pipeline connecting the thermal storage sphere to the deaerator; the thermal storage sphere is connected to the high-temperature thermal storage subsystem.

[0014] Second aspect: A method for operating a cascade thermal storage system based on the steam-supplying back-pressure turbine unit described in the first aspect, the method comprising: When operating at low power levels, the power generation and steam supply subsystem is activated, while the steam storage subsystem and high-temperature storage subsystem are shut down. The operating mode is as follows: The high-temperature, high-pressure superheated steam generated by the boiler enters the two generator sets through valves 1 and 2 to generate electricity. The steam at the outlet of the high-pressure cylinder is discharged as industrial extraction steam 1. The steam at the outlet of the intermediate-pressure cylinder 1 is divided into three paths: one path is discharged as industrial extraction steam 3, and the other two paths enter the No. 2 high-pressure heater and the deaerator respectively to heat and make-up water. The steam at the outlet of the intermediate-pressure cylinder 2 is divided into three paths: one path merges with the steam at the outlet of the intermediate-pressure cylinder 1 through valve 4, one path enters the No. 1 high-pressure heater to heat and make-up water, and one path is discharged as industrial extraction steam 2. The steam at the outlet of the low-pressure cylinder is divided into two paths: one path is discharged as heating extraction steam, and the other path enters the makeup water heater to heat and make-up water. After makeup water, it passes through the makeup water heater, pump 2, deaerator, pump 1, the No. 2 high-pressure heater, and the No. 1 high-pressure heater in sequence before returning to the boiler for recycling.

[0015] Optionally, the method includes: During peak electricity consumption, the boiler evaporation rate increases, the power generation and steam supply subsystem increases, the cylinder exhaust rate increases, and the steam storage subsystem and high-temperature storage subsystem start to store heat. In the first stage of heat storage, the operation mode is as follows: the makeup water from the deaerator outlet passes through valve nine and valve fifteen in sequence to enter the heat storage sphere tank and is stored. The steam from the high-pressure cylinder outlet is divided into one path and enters the high-temperature fluid heater through valve three to release heat and cool it. Then, it passes through valve twelve and valve fourteen in sequence to enter the heat storage sphere tank and is stored. When the water level in the thermal storage sphere tank reaches the preset value, the thermal storage enters the second stage. The system operates as follows: maintaining the operation mode of the first stage of thermal storage, the exhaust steam from the intermediate pressure cylinder one is split into one channel and passes through valve five and valve eleven in sequence to enter the thermal storage sphere tank. The water inside is further heated and pressurized by higher-grade steam to complete the final thermal storage.

[0016] Optionally, during the operation of the power level segment, valves 1, 2, 4, 7, pumps 1 and 2 are open, while valves 3, 5, 6, 8, 9, 10, 11, 12, 13, 14, 15, high-temperature fluid pump 1, high-temperature fluid pump 2 and pump 3 are closed. During peak electricity consumption and the first stage of heat storage, valves 1, 2, 3, 4, 7, 9, 10, 12, 14, 15, pumps 1, 2, and high-temperature fluid pump 1 are opened, while valves 5, 6, 8, 11, 13, high-temperature fluid pumps 2 and 3 are closed.

[0017] Optionally, the method further includes: During periods of low electricity demand, the power generation and steam supply subsystem generates less electricity, the cylinder exhaust volume decreases, and the steam heat storage subsystem and high-temperature heat storage subsystem activate to release heat. The system operates as follows: The hot water in the thermal storage tank passes through valves 15 and 9 in sequence, merging with the makeup water to reduce the steam consumption of the deaerator and makeup water heater. The other path passes through valve 14, enters pump 3 for pressurization, and then enters the steam generator to absorb heat and become superheated steam. After passing through valves 8 and 6 in sequence, it is discharged as industrial extraction steam, thereby reducing the steam discharge of the steam turbine, reducing the boiler evaporation and back pressure steam, and reducing power generation.

[0018] Optionally, during off-peak electricity usage, valves 1, 2, 4, 6, 7, 8, 9, 13, 14, 15, pumps 1, 2, high-temperature fluid pump 2, and pump 3 are opened, while valves 3, 5, 10, 11, 12, and high-temperature fluid pump 1 are closed.

[0019] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: Significantly enhanced operational flexibility and peak-shaving capacity: By adjusting the makeup water flow rate and coordinating the steam-molten salt / thermal oil thermal storage system, the traditional back-pressure unit's "heat-driven power generation" operational constraint is broken. The unit's power generation is no longer rigidly tied to the steam supply load, allowing it to proactively increase power generation for grid connection during peak electricity demand and reduce power generation during off-peak demand by utilizing stored thermal energy to stabilize steam supply, thereby significantly improving the unit's grid peak-shaving flexibility and market competitiveness.

[0020] Achieving tiered energy storage and efficient utilization: This invention achieves graded storage of thermal energy by storing high-grade steam heat in a high-temperature thermal storage subsystem and medium- and low-grade thermal energy in a steam thermal storage subsystem. During heat release, high-parameter superheated steam or preheated water can be generated or provided as needed, realizing on-demand energy release and tiered utilization, effectively improving the overall system efficiency and comprehensive energy utilization rate.

[0021] Enhancing steam supply reliability and reducing operating costs: The thermal storage subsystem (steam thermal storage and molten salt / thermal oil thermal storage) acts as a significant "heat buffer," smoothing out fluctuations in boiler load and user steam consumption. When the unit operates at reduced load, the heat release system can supplement steam supply, ensuring the continuity and stability of steam supply for industrial users. Simultaneously, the system utilizes peak-valley electricity price differences, storing heat during off-peak hours and releasing heat for power generation / steam supply during peak hours, effectively reducing the unit's average operating cost.

[0022] High system integration and optimized collaborative control: This invention highly integrates three subsystems—power generation and steam supply, steam thermal storage, and high-temperature thermal storage—through optimized pipelines and valves, and designs adaptive operation strategies for different electricity price periods. This integrated design enables tight coupling of energy flow and information flow between the subsystems, allowing for rapid and unified collaborative control based on changes in external conditions, thereby maximizing the overall energy efficiency and economic benefits of the system. Attached Figure Description

[0023] Figure 1 The diagram shown is a schematic representation of an embodiment of the system provided by the present invention.

[0024] In the diagram: 1. Boiler; 2. Valve 1; 3. High-pressure cylinder; 4. Medium-pressure cylinder 1; 5. Valve 2; 6. Medium-pressure cylinder 2; 7. Low-pressure cylinder; 8. Valve 3; 9. Valve 4; 10. Valve 5; 11. Valve 6; 12. Valve 7; 13. High-pressure heater No. 1; 14. High-pressure heater No. 2; 15. Pump 1; 16. Deaerator; 17. Pump 2; 18. Makeup water heater; 19. Valve 8; 20. Valve 9; 21. High-temperature fluid heater; 22. Valve 10; 23. High-temperature fluid pump 1; 24. Valve 11; 25. High-temperature tank; 26. Low-temperature tank; 27. Valve 12; 28. Thermal storage sphere tank; 29. ​​High-temperature fluid pump 2; 30. Steam generator; 31. Valve 13; 32. Pump 3; 33. Valve 14; 34. Valve 15. Detailed Implementation

[0025] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0026] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0027] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] Example 1

[0029] like Figure 1 As shown, a cascade thermal storage system for a steam-supplying back-pressure turbine unit is disclosed, comprising three subsystems: a power generation and steam supply subsystem, a steam thermal storage subsystem, and a high-temperature thermal storage subsystem. The system can flexibly adjust the electrical load, cope with electricity price fluctuations through thermal storage and release, improve the unit's operating economy and reliability, increase power generation and store thermal energy during peak electricity demand, and reduce power generation and release thermal energy during off-peak electricity demand, thereby optimizing energy use and reducing operating costs.

[0030] The power generation and steam supply subsystem comprises a boiler 1, valve 1 2, high-pressure cylinder 3, intermediate-pressure cylinder 1 4, valve 2 5, intermediate-pressure cylinder 2 6, low-pressure cylinder 7, valve 3 8, valve 4 9, valve 6 11, valve 7 12, high-pressure heater 13, high-pressure heater 2 14, pump 1 15, deaerator 16, pump 2 17, and makeup water heater 18, and is used for power generation and supplying industrial steam extraction and heating steam extraction. Boiler 1 has one branch connected to the first generator set via valve 2 and the other branch connected to the second generator set via valve 5. One branch of the first generator set is connected to the high-temperature heat storage subsystem, and the other branch is used for industrial steam extraction. One branch of the first generator set is equipped with a second high-pressure heater 14 and a deaerator 16 in parallel, and the other branch is used for industrial steam extraction and connected to the steam heat storage subsystem. The second generator set is connected to a makeup water heater 18. The makeup water heater 18, deaerator 16, second high-pressure heater 14, and first high-pressure heater 13 are connected in sequence. The first high-pressure heater 13 is connected in sequence to the boiler 1 via one branch and to the second high-pressure heater 14 via another branch. The second high-pressure heater 14 is connected to the deaerator 16, and the deaerator 16 is connected to the steam heat storage subsystem via another branch. A second pump 17 is installed between the makeup water heater 18 and the deaerator 16, and a first pump 15 is installed between the second high-pressure heater 14 and the deaerator 16.

[0031] The first generator set includes a high-pressure cylinder 3 and a medium-pressure cylinder 4. The high-pressure cylinder 3 is connected to a high-temperature fluid heater 21 via a valve 3 8, and the medium-pressure cylinder 4 is connected to a second high-pressure heater 14.

[0032] The second generator set includes a medium-pressure cylinder 6 and a low-pressure cylinder 7. One of the medium-pressure cylinders 6 is connected to the industrial steam extraction unit 3 via valve 4 9. Valve 4 9 is connected to the thermal storage tank 28 via valve 5 10 and valve 11 24 in sequence. The other of the medium-pressure cylinders 6 is connected to the first high-pressure heater 13. One of the low-pressure cylinders 7 is used for heating steam extraction, and the other is connected to the water supply heater 18 via valve 7 12.

[0033] In this embodiment, by adjusting the water supply flow rate and coordinating the steam-molten salt / thermal oil co-storage system, the traditional back-pressure unit's "heat-driven power generation" operational constraint is broken. The unit's power generation is no longer rigidly tied to the steam supply load, allowing it to proactively increase power generation for grid connection during peak electricity demand and reduce power generation during off-peak demand by utilizing stored heat energy to stabilize steam supply. This significantly improves the unit's grid peak-shaving flexibility and market competitiveness.

[0034] The steam thermal storage subsystem consists of valve 510, valve 920, valve 11224, valve 1227, thermal storage spherical tank 28, pump 32, valve 1433, and valve 1534. It is used to store the heat of steam and hot water during peak electricity demand and release the stored hot water during off-peak electricity demand to reduce boiler evaporation and power generation, balance supply and demand, and help maintain the stability of steam supply.

[0035] The thermal storage spherical tank 28 is connected to another line of the first generator set, and valve 10 and valve 24 are installed in sequence on the pipeline; valve 20 and valve 34 are installed in sequence on the pipeline connecting the thermal storage spherical tank 28 to the deaerator 16; the thermal storage spherical tank 28 is connected to the high-temperature thermal storage subsystem.

[0036] The high-temperature thermal storage subsystem includes a high-temperature tank 25 and a low-temperature tank 26. One end of the high-temperature tank 25 is connected to a high-temperature fluid heater 21 via valve 10 22, and the other end is connected to a steam generator 30 via a high-temperature fluid pump 29. One end of the low-temperature tank 26 is connected to the high-temperature fluid heater 21 via a high-temperature fluid pump 1 23, and the other end is connected to the steam generator 30 via valve 13 31. The output end of the thermal storage spherical tank 28 is connected to pump 3 32, the steam generator 30, and industrial steam extraction 3. Valves 8 19 and 6 11 are installed on this pipeline. The high-temperature fluid heater 21 is connected to the first generator set and is connected to the thermal storage spherical tank 28 via valve 12 27. This subsystem can use molten salt or thermal oil as the thermal storage medium to store high-temperature heat during peak electricity demand and generate steam during off-peak electricity demand to supplement industrial steam extraction, reduce the generator load of the unit, and improve system flexibility.

[0037] Example 2

[0038] Based on Example 1, the thermal storage medium and subsystem can be replaced as follows: In scenarios with limited investment or space, a simplified single thermal storage system can omit the high-temperature thermal storage subsystem, retaining only the steam thermal storage subsystem. The high-grade extracted steam originally entering the high-temperature fluid heater 21 is directly or after adjustment and incorporated into the steam thermal storage subsystem for thermal storage. While this simplified solution sacrifices some high-grade thermal energy storage and the independent generation capacity of high-temperature steam, it significantly simplifies the system structure, reduces initial investment and maintenance costs, and still achieves basic peak shaving and valley filling functions as well as thermoelectric decoupling.

[0039] Alternative heat storage medium: In the steam heat storage subsystem, other solid fillers (such as ceramic balls, crushed stone, etc.) can be used to partially or completely replace the water in the heat storage spherical tank 28 to form a sensible heat storage bed. This solution utilizes the stable physicochemical properties and wide operating temperature range of solid materials, avoids the complexity of pressure control caused by phase change, and enhances the seismic performance and extends the service life of the system. Example

[0040] Based on Example 1, in the high-temperature thermal storage subsystem, the high-temperature fluid heater 21 can be replaced or an electric heating device can be added in parallel. During off-peak hours at night, when electricity prices are extremely low, or when there is a surplus of renewable energy, electrical energy can be used to directly heat the molten salt / thermal oil for thermal storage. This scheme converts electrical energy into high-grade thermal energy storage, achieving deeper peak shaving and valley filling, and improving the system's ability to absorb fluctuating renewable energy.

[0041] The high-temperature heat storage subsystem or steam heat storage subsystem can utilize heat sources beyond just steam extracted from steam turbines. Waste heat resources such as high-temperature exhaust gases and molten slag generated during industrial processes in industries like petrochemicals, steel, and cement can be connected to the system via additional heat exchangers as supplementary or alternative heat sources for heat storage. This expanded application transforms the system into a comprehensive energy hub for industrial parks, enabling broader industrial waste heat recovery and utilization.

[0042] In this embodiment, the thermal storage spherical tank is structurally designed as follows: the thermal storage spherical tank 28 adopts a double-layer pressure-resistant steel shell. The inner shell, which is in contact with the medium, is made of corrosion-resistant stainless steel. An air insulation layer is set between the outer shell and the insulation layer, and the insulation layer is made of aluminum silicate fiber composite insulation material. This structure can withstand the long-term effects of high-pressure steam / hot water, improves corrosion resistance, and reduces heat loss from the tank. Compared with traditional cylindrical thermal storage tanks, the spherical structure has more uniform stress distribution, occupies less space, and is suitable for compact plant layouts.

[0043] Selection and adaptation of high-temperature heat storage medium: The high-temperature heat storage subsystem can flexibly select molten salt or heat transfer oil as the heat storage medium according to the specific needs of the project, so as to achieve the optimal configuration in terms of technical and economic efficiency.

[0044] Molten salt solution: A sodium nitrate-potassium nitrate mixed molten salt (mass ratio 60:40) is preferred as the heat storage medium. This mixed molten salt has a melting point of approximately 220℃, a wide operating temperature range covering 250℃ to 550℃, and exhibits excellent thermal stability within this range with no significant decomposition. Compared to single-component nitrate molten salt, its specific heat capacity is increased by approximately 12%, resulting in a higher heat storage density. This mixed molten salt shows good compatibility with the carbon steel heat exchanger tube bundles of the high-temperature fluid heater 21 and the steam generator 30, exhibiting a low corrosion rate and significantly extending the service life of critical equipment.

[0045] Thermal oil options: Synthetic thermal oils such as biphenyl-biphenyl ether mixtures or hydrogenated terphenyl can be used as the heat storage medium. Their operating temperature range covers 250℃ to 400℃, offering significant advantages in liquid atmospheric or low-pressure operation within this temperature range. The system boasts high safety and ease of operation. Compared to molten salt, thermal oil does not require heat tracing or anti-condensation, reducing the complexity of system maintenance. However, its disadvantages include a generally lower upper operating temperature and volumetric heat storage density compared to molten salt, and the risk of aging and cracking during long-term operation, necessitating regular monitoring and replacement.

[0046] Steam-molten salt / thermal oil synergistic heat storage and release mechanism: The system, through valve groups and control logic, realizes the coordination and switching between the steam heat storage subsystem and the high-temperature heat storage subsystem during the heat storage and release process. During peak electricity consumption, high-grade steam heat can be stored by molten salt / thermal oil or used to increase the water temperature and pressure of the heat storage tank; during off-peak electricity consumption, the hot water in the heat storage tank and the superheated steam generated by the molten salt system can be supplied to the outside simultaneously or separately, realizing the "graded storage" and "on-demand release" of energy according to grade, which is the core of improving system flexibility and energy efficiency.

[0047] Adaptive operation strategy under peak-valley electricity pricing: The system has preset operating logic for three typical operating conditions: "high-consumption period, peak, and low-consumption period." Through the opening and closing of specific valve combinations and the switching of subsystems, the system automatically adjusts its operating status to maximize economic benefits. This strategy ensures that the system can operate stably, economically, and efficiently under different market environments.

[0048] Example 4 discloses a method for cascade thermal storage operation of a steam-supplying back-pressure turbine unit, as detailed below: The system operates in three main modes based on electricity demand: normal operating hours, peak electricity demand, and off-peak electricity demand. These are detailed below.

[0049] When operating at low power, the power generation and steam supply subsystem operates independently, while the steam thermal storage subsystem and the high-temperature thermal storage subsystem stop operating, and the system generates and supplies steam normally.

[0050] The system operates as follows: Valves 1-2, 2-5, 4-9, 7-12, 1-15 and 2-17 are open; Valves 3-8, 5-10, 6-11, 8-19, 9-20, 10-22, 11-24, 12-27, 13-31, 14-33, 15-34, 1-23, 2-9 and 3-32 are closed.

[0051] The high-temperature, high-pressure superheated steam heated in boiler 1 enters two generator sets to generate electricity through valves 1-2 and 2-5. The steam at the outlet of high-pressure cylinder 3 is discharged as industrial extraction steam. The steam at the outlet of intermediate-pressure cylinder 1-4 is divided into three paths: one path is discharged as industrial extraction steam, and the other two paths enter the No. 2 high-pressure heater 14 and deaerator 16 respectively to heat and make-up water. The steam at the outlet of intermediate-pressure cylinder 2-6 is divided into three paths: one path merges with the steam at the outlet of intermediate-pressure cylinder 1-4 through valve 4-9; another path enters the No. 1 high-pressure heater 13 to heat and make-up water; and the third path is discharged as industrial extraction steam. The steam at the outlet of low-pressure cylinder 7 is divided into two paths: one path is discharged as heating extraction steam, and the other path enters the makeup water heater 18 to heat and make-up water. The makeup water passes through the makeup water heater 18 for heating, pump 2-17 for pressurization, deaerator 16 for heating, pump 1-15 for pressurization, No. 2 high-pressure heater 14 for heating, and No. 1 high-pressure heater 13 for heating before returning to boiler 1 for heating, and so on.

[0052] During peak electricity consumption periods, higher electricity prices lead to increased water supply, increased boiler evaporation, and improved power generation from the power generation and steam supply subsystem. This also increases cylinder exhaust steam, activating the steam storage subsystem and the high-temperature storage subsystem. In the first stage of storage, the system operates as follows: valves 1-2, 2-5, 3-8, 4-9, 7-12, 9-20, 10-22, 12-27, 14-33, 15-34, pumps 1-15, 2-17, and high-temperature fluid pump 1-23 are activated; valves 5-10, 6-11, 8-19, 11-24, 13-31, high-temperature fluid pump 2-29, and pump 3-32 are deactivated. Water from the deaerator 16 outlet passes through valves 9-20 and 15-34 before entering the storage tank 28. Steam from the high-pressure cylinder 3 outlet is split into two streams, passing through valve 3-8 to the high-temperature fluid heater 21 for heat release and cooling, before passing through valves 12-27 and 14-33 before entering the storage tank 28. When the water level in the thermal storage tank 28 is sufficient, the thermal storage enters the second stage. The system operates based on the first stage's operation, with valves 5 (10) and 11 (24) opened, and valves 3 (8), 9 (20), 10 (22), 12 (27), 14 (33), 15 (34), and high-temperature fluid pump 1 (23) closed. The exhaust steam from the intermediate-pressure cylinder 4 is diverted through valves 5 (10) and 11 (24) into the thermal storage tank 28, where higher-grade steam further heats and pressurizes the water, completing the final thermal storage. Through this stage, the system simultaneously meets all steam supply requirements and increases power generation output.

[0053] During off-peak electricity demand, electricity prices are lower, reducing water replenishment flow, decreasing boiler evaporation, reducing power generation from the power generation and steam supply subsystem, decreasing cylinder exhaust, and activating the steam storage subsystem and high-temperature storage subsystem to release heat.

[0054] The system operates as follows: Valves 1-2, 2-5, 4-9, 6-11, 7-12, 8-19, 9-20, 13-31, 14-33, 15-34, 15-1, 2-17, 29-2 and 3-2 of the high-temperature fluid pump are open; Valves 3-8, 5-10, 10-22, 11-24, 12-27 and 23-2 of the high-temperature fluid pump are closed.

[0055] The hot water in the thermal storage tank 28 passes through valves 15 (34) and 9 (20) in sequence, merging with the makeup water to reduce the steam consumption of the deaerator 16 and the makeup water heater 18. The other path passes through valve 14 (33), enters pump 3 (32) for pressurization, and then enters steam generator 30 to absorb heat and become superheated steam. After passing through valves 8 (19) and 6 (11) in sequence, it is discharged as industrial extraction steam, thereby reducing the steam discharge of the steam turbine, reducing the boiler evaporation and back pressure steam, and reducing power generation.

[0056] This invention achieves graded storage of thermal energy by storing high-grade steam heat in a high-temperature thermal storage subsystem and medium- and low-grade thermal energy in a steam thermal storage subsystem. During heat release, high-parameter superheated steam or preheated water can be generated or provided as needed, realizing on-demand energy release and tiered utilization, effectively improving the overall system efficiency and comprehensive energy utilization rate.

[0057] The thermal storage subsystem (steam thermal storage and molten salt / thermal oil thermal storage) acts as a significant "heat buffer," effectively mitigating fluctuations in boiler load and user steam consumption. When the unit operates at reduced load, the heat release system can supplement steam supply, ensuring the continuity and stability of steam supply for industrial users. Simultaneously, the system utilizes peak-valley electricity price differences, storing heat during off-peak hours and releasing it for power generation / steam supply during peak hours, effectively reducing the unit's average operating cost.

[0058] This invention highly integrates three subsystems—power generation and steam supply, steam heat storage, and high-temperature heat storage—through optimized piping and valves, and designs adaptive operation strategies for different electricity price periods. This integrated design tightly couples energy and information flows between the subsystems, enabling rapid and unified coordinated control based on changes in external conditions, thereby maximizing the overall energy efficiency and economic benefits of the system.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A cascade thermal storage system for a steam-supplying back-pressure turbine unit, characterized in that, include: The power generation and steam supply subsystem includes a boiler (1), one of which is connected to the first generator set via valve one (2), and the other is connected to the second generator set via valve two (5); one of the first generator sets is connected to the high-temperature heat storage subsystem, and the other is used for industrial steam extraction one; one of the other paths of the first generator set is equipped with a second high-pressure heater (14) and a deaerator (16) in parallel, one of the other paths is used for industrial steam extraction three, and the other is connected to the steam heat storage subsystem; the second generator set is connected to a water supply pipeline; The steam heat storage subsystem includes a heat storage spherical tank (28), which is used to store high-temperature heat during peak electricity demand and to generate steam during off-peak electricity demand to supplement industrial steam extraction. The high-temperature heat storage subsystem includes a high-temperature tank (25) and a low-temperature tank (26). One end of the high-temperature tank (25) is connected to a high-temperature fluid heater (21) via valve 10 (22), and the other end is connected to a steam generator (30) via a high-temperature fluid pump 2 (29). One end of the low-temperature tank (26) is connected to a high-temperature fluid heater (21) via a high-temperature fluid pump 1 (23), and the other end is connected to a steam generator (30) via valve 13 (31). The output end of the heat storage sphere tank (28) is connected to pump 3 (32), steam generator (30), and industrial steam extraction 3. Valves 8 (19) and 6 (11) are provided on this pipeline. The high-temperature fluid heater (21) is connected to the first generator set. The high-temperature fluid heater (21) is connected to the heat storage sphere tank (28) via valve 12 (27).

2. The cascade thermal storage system for a steam-supplying back-pressure turbine unit according to claim 1, characterized in that, The second generator set includes a medium-pressure cylinder two (6) and a low-pressure cylinder (7). One of the medium-pressure cylinder two (6) is connected to the industrial steam extraction three via valve four (9). The valve four (9) is connected to the heat storage spherical tank (28) via valve five (10) and valve eleven (24) in sequence. The other of the medium-pressure cylinder two (6) is connected to the first high-pressure heater (13). One of the low-pressure cylinders (7) is used for heating steam extraction, and the other is connected to the water supply pipeline via valve seven (12).

3. The cascade thermal storage system for a steam-supplying back-pressure turbine unit according to claim 1, characterized in that, The water supply pipeline includes a water supply heater (18), and the water supply heater (18), deaerator (16), second high-pressure heater (14), and first high-pressure heater (13) are connected in sequence. One of the first high-pressure heater (13) is connected to the boiler (1), and the other is connected to the second high-pressure heater (14). The second high-pressure heater (14) is connected to the deaerator (16), and the other is connected to the steam heat storage subsystem. A second pump (17) is provided between the water supply heater (18) and the deaerator (16), and a first pump (15) is provided between the second high-pressure heater (14) and the deaerator (16).

4. The cascade thermal storage system for a steam-supplying back-pressure turbine unit according to claim 1, characterized in that, The first generator set includes a high-pressure cylinder (3) and a medium-pressure cylinder (4). The high-pressure cylinder (3) is connected to a high-temperature fluid heater (21) through a valve (8), and the medium-pressure cylinder (4) is connected to a second high-pressure heater (14).

5. The cascade thermal storage system for a steam-supplying back-pressure turbine unit according to claim 1, characterized in that, The thermal storage sphere (28) is connected to another line of the first generator set, and valve five (10) and valve eleven (24) are installed in sequence on the pipeline; valve nine (20) and valve fifteen (34) are installed in sequence on the pipeline connecting the thermal storage sphere (28) to the deaerator (16); the thermal storage sphere (28) is connected to the high temperature thermal storage subsystem.

6. A method for operating a cascade thermal storage system based on a steam-supplying back-pressure turbine unit according to any one of claims 1-5, characterized in that, The method includes: When operating at low power levels, the power generation and steam supply subsystem is activated, while the steam storage subsystem and high-temperature storage subsystem are shut down. The operating mode is as follows: The high-temperature and high-pressure superheated steam generated by the boiler enters the two generator sets through valve 1 (2) and valve 2 (5) to generate electricity. The steam at the outlet of the high-pressure cylinder (3) is discharged as industrial extraction steam 1. The steam at the outlet of the medium-pressure cylinder 1 (4) is divided into three paths. One path is discharged as industrial extraction steam 3. The other two paths enter the No. 2 high-pressure heater (14) and deaerator (16) respectively to heat and replenish water. The steam at the outlet of the medium-pressure cylinder 2 (6) is divided into three paths. One path passes through valve 4 (9) and merges with the steam at the outlet of the medium-pressure cylinder 1 (4). Another path enters the No. 1 high-pressure heater (13) to heat and replenish water. Another path is discharged as industrial extraction steam 2. The steam at the outlet of the low-pressure cylinder (7) is divided into two paths. One path is discharged as heating extraction steam. Another path enters the water replenishment heater (18) to heat and replenish water. After replenishment, the steam passes through the water replenishment heater (18), pump 2 (17), deaerator (16), pump 1 (15), No. 2 high-pressure heater (14), and No. 1 high-pressure heater (13) in sequence before returning to the boiler (1) for recycling.

7. The cascade heat storage method for a steam-supplying back-pressure turbine unit according to claim 6, characterized in that, The method includes: During peak electricity consumption, the boiler evaporation rate increases, the power generation and steam supply subsystem increases, the cylinder exhaust rate increases, and the steam storage subsystem and high temperature storage subsystem start to store heat. In the first stage of heat storage, the system operates as follows: the water from the outlet of the deaerator (16) passes through valve nine (20) and valve fifteen (34) to enter the heat storage sphere tank (28) and is stored. The steam from the outlet of the high pressure cylinder (3) is divided into one path and passes through valve three (8) to enter the high temperature fluid heater (21) for heat release and cooling. Then, it passes through valve twelve (27) and valve fourteen (33) to enter the heat storage sphere tank (28) and is stored. When the water level in the heat storage sphere tank (28) reaches the preset value, the heat storage enters the second stage. The system operation mode is as follows: maintain the operation mode of the first stage of heat storage. The exhaust steam of the medium pressure cylinder one (4) passes through valve five (10) and valve eleven (24) in sequence and enters the heat storage sphere tank (28). The water inside is further heated and pressurized by higher grade steam to complete the final heat storage.

8. The cascade heat storage method for a steam-supplying back-pressure turbine unit according to claim 7, characterized in that, When the operating level is in use, valves 1 (2), 2 (5), 4 (9), 7 (12), pump 1 (15) and pump 2 (17) are open, and valves 3 (8), 5 (10), 6 (11), 8 (19), 9 (20), 10 (22), 11 (24), 12 (27), 13 (31), 14 (33), 15 (34), high-temperature fluid pump 1 (23), high-temperature fluid pump 2 (29) and pump 3 (32) are closed. During peak electricity consumption and the first stage of heat storage, valves 1 (2), 2 (5), 3 (8), 4 (9), 7 (12), 9 (20), 10 (22), 12 (27), 14 (33), 15 (34), 15 (15), 2 (17), and 1 (23) of high-temperature fluid pump are opened, while valves 5 (10), 6 (11), 8 (19), 11 (24), 13 (31), 2 (29), and 3 (32) of high-temperature fluid pump are closed.

9. The cascade thermal storage method for a steam-supplying back-pressure turbine unit according to claim 6, characterized in that, The method further includes: During periods of low electricity demand, the power generation and steam supply subsystem generates less electricity, the cylinder exhaust volume decreases, and the steam heat storage subsystem and high-temperature heat storage subsystem start releasing heat. The operating mode is as follows: The hot water in the thermal storage tank (28) passes through valve 15 (34) and valve 9 (20) in sequence, and is combined with the makeup water to reduce the steam consumption of the deaerator (16) and makeup water heater (18). The other path passes through valve 14 (33), enters pump 3 (32) for pressurization, and then enters steam generator (30) to absorb heat and become superheated steam. After passing through valve 8 (19) and valve 6 (11) in sequence, it is discharged as industrial extraction steam, thereby reducing the steam discharge of the steam turbine, reducing the boiler evaporation and back pressure steam, and reducing power generation.

10. The cascade thermal storage method for a steam-supplying back-pressure turbine unit according to claim 9, characterized in that, During the off-peak electricity usage period, valves 1 (2), 2 (5), 4 (9), 6 (11), 7 (12), 8 (19), 9 (20), 13 (31), 14 (33), 15 (34), 15 (15), 2 (17), 2 (29), and 3 (32) are opened, while valves 3 (8), 5 (10), 10 (22), 11 (24), 12 (27), and 1 (23) are closed.

Images