A hierarchical heat storage type flue gas waste heat heating system and method

Abstract

This invention belongs to the field of combined cycle gas turbine and steam turbine technology, and discloses a staged waste heat recovery system and method for flue gas. The system includes a gas turbine, a waste heat boiler, a steam turbine, and a plate heat exchanger. Exhaust steam from the steam turbine is connected to the generator of an absorption heat pump unit. An electric heat pump and an absorption heat pump are connected in series to raise the temperature. A high-temperature water storage device is used for peak shaving, and heat is supplied to users. Low-temperature and medium-temperature intermediate water storage devices are connected in series and respectively connected to the evaporator side of the electric heat pump and the absorption heat pump, forming a closed loop to achieve staged recovery of waste heat from flue gas. This invention is not only applicable to combined cycle gas turbines but can also be extended to coal-fired units and various low-grade waste heat recovery scenarios, significantly improving energy utilization efficiency and possessing extremely high engineering application and promotion value.

Description

Technical Field

[0001] This invention belongs to the field of combined cycle gas and steam technology, and particularly relates to a staged heat storage type flue gas waste heat heating system and method. Background Technology

[0002] Gas-steam combined cycle (GSCB) units, with their high efficiency, low emissions, and excellent regulation performance, have become an important component of the power and cogeneration sector. However, existing technologies still face significant bottlenecks in practical applications. First, these units generally employ back-pressure or extraction-condensing heating, heavily relying on high-grade steam, leading to a rigid "heat-driven power generation" operating mode that severely restricts peak-shaving capacity and operational flexibility. Second, the exhaust gas from the gas turbine, after heat exchange in a waste heat boiler, still maintains a high temperature of 80-100°C, containing a large amount of sensible heat and latent heat of steam condensation. However, due to the high temperature requirements of the heating network supply water (≥80°C), this low-grade waste heat is difficult to utilize directly and is usually directly discharged, resulting in energy waste. Furthermore, existing waste heat recovery methods have limitations: single absorption heat pumps are limited by the grade of the driving heat source, making it difficult to achieve large temperature rises; single electric-driven heat pumps operate under large temperature difference conditions with large pressure differentials, resulting in a significant decrease in the coefficient of performance (COP) and a surge in power consumption. Simultaneously, existing systems lack effective thermal energy storage units, failing to achieve peak shaving and valley filling, and smooth regulation of heat output.

[0003] Therefore, a graded heat storage flue gas waste heat heating system and method are needed to solve the problems of high thermoelectric coupling, low flue gas waste heat utilization, limited energy efficiency of single heat pumps, and lack of energy storage and regulation means. Summary of the Invention

[0004] The purpose of this invention is to provide a graded thermal storage type flue gas waste heat heating system and method to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides a staged thermal storage type flue gas waste heat heating system, comprising: gas turbine; Waste heat boiler, whose flue gas inlet is connected to the exhaust port of gas turbine; A steam turbine, the steam inlet of which is connected to the steam outlet of a waste heat boiler; The plate heat exchanger has its flue gas inlet connected to the tail flue gas outlet of the waste heat boiler; the flue gas outlet of the plate heat exchanger is connected to the chimney. Electric heat pump unit; The generator inlet of the absorption heat pump unit is connected to the exhaust steam outlet of the steam turbine; the condenser inlet of the absorption heat pump unit is connected to the condenser outlet of the electric heat pump unit; the condenser outlet of the absorption heat pump unit is connected to the inlet of the high-temperature water energy storage device and the inlet of the heat user respectively. The device includes a low-temperature intermediate water thermal storage device and a medium-temperature intermediate water thermal storage device. The low-temperature intermediate water thermal storage device is connected to the intermediate water side of a plate heat exchanger to store waste heat from flue gas. The low-temperature intermediate water thermal storage device is connected to the evaporator side of an electric heat pump unit through a pipeline to form a closed loop. The low-temperature intermediate water thermal storage device is connected in series with the medium-temperature intermediate water thermal storage device, and the medium-temperature intermediate water thermal storage device is connected to the evaporator side of an absorption heat pump unit to form a closed loop.

[0006] Optionally, the exhaust steam outlet of the steam turbine is connected to the inlet of the condenser and the generator inlet of the absorption heat pump unit via a first three-way valve; the feedwater outlet of the waste heat boiler is connected to the outlet of the condenser and the generator outlet of the absorption heat pump unit via a second three-way valve.

[0007] Optionally, the condenser outlet of the absorption heat pump unit is also connected to a third three-way valve, the two outlets of which are connected to the inlet of the high-temperature water energy storage device and the inlet of the heat user, respectively.

[0008] Optionally, the high-temperature water storage device is also equipped with an emergency heat replenishment outlet, which is used to directly replenish high-temperature hot water to heat users when there is a heating load gap.

[0009] Optionally, a low-temperature intermediate water thermal storage device is used to store intermediate water at 25~35℃; a medium-temperature intermediate water thermal storage device is used to store intermediate water at 35~45℃.

[0010] Optionally, a control unit may also be included, which monitors the real-time load of heat users and dynamically adjusts the output and heat extraction of the electric heat pump unit and the absorption heat pump unit accordingly.

[0011] Optionally, the electric heat pump unit is configured to extract heat from a low-temperature intermediate water storage device to preheat the return water of the heating network from 50°C to 55~65°C; the absorption heat pump unit is configured to extract heat from a medium-temperature intermediate water storage device to raise the temperature of the heating network water from 55~65°C to 85°C.

[0012] This invention provides a staged heat storage method for flue gas waste heat supply, comprising the following steps: S1. The high-temperature flue gas generated by the gas turbine is passed through a waste heat boiler for heat exchange and then passed through a plate heat exchanger to exchange heat with intermediate water. The flue gas temperature is reduced to 30~40℃ before being discharged to the chimney. S2. The intermediate water after heat exchange is stored according to temperature grade; intermediate water with a temperature of 25~35℃ is stored in a low temperature intermediate water heat storage device, and intermediate water with a temperature of 35~45℃ is stored in a medium temperature intermediate water heat storage device. S3. The return water from the heating network flows sequentially through the electric heat pump unit and the absorption heat pump unit for tiered temperature increase. The electric heat pump unit uses the heat from the low-temperature intermediate water heat storage device for preheating, while the absorption heat pump unit uses the heat from the medium-temperature intermediate water heat storage device and the exhaust steam from the steam turbine for secondary temperature increase. S4. The heated high-temperature water is delivered to the heat users, and the excess heat is stored in the high-temperature water energy storage device.

[0013] Optionally, in step S3: When heat users are in low load demand, the output of electric heat pump units and absorption heat pump units is reduced, so that the temperature of the intermediate water at the outlet of the plate heat exchanger is increased and stored in the medium-temperature intermediate water heat storage device to achieve energy storage. When heat users are under high load demand, the output of electric heat pump units and absorption heat pump units is increased to fully extract and store heat, and the high-temperature water energy storage device is activated to supplement heat.

[0014] Optionally, after the intermediate water completes the heat exchange, its temperature decreases and it returns sequentially to the medium-temperature intermediate water heat storage device and the low-temperature intermediate water heat storage device, and then re-enters the plate heat exchanger to absorb the waste heat of the flue gas, forming a closed loop.

[0015] Compared with the prior art, the present invention has the following advantages and technical effects: This invention divides the intermediate water into two temperature zones: low and medium. By utilizing an electric heat pump to extract heat from the low-temperature zone (25-35°C), the temperature of the intermediate water returning to the plate heat exchanger is maintained at an extremely low level. This successfully reduces the exhaust gas temperature from 80-100°C to 30-40°C, breaking through the water vapor dew point barrier and achieving large-scale, deep recovery of the latent heat of water vapor from natural gas combustion, thus greatly improving the overall thermal efficiency of the combined cycle unit.

[0016] This invention breaks through the performance bottleneck of traditional single heat pumps under high temperature rise conditions. The electric heat pump is specifically designed to extract heat from the low-temperature layer of the graded heat storage system, responsible for the basic temperature rise of the heating network water in the low-temperature range of 50°C to 55~65°C; while the absorption heat pump extracts heat from the medium-temperature layer, responsible for the quality improvement in the high-temperature range of 55~65°C to 85°C. This matching method of utilizing heat according to grade results in a very small operating pressure difference for the electric heat pump, significantly improving the coefficient of performance (COP) and greatly reducing power consumption; at the same time, it avoids the irreversible heat exchange losses caused by the temperature mismatch of the heat source in the absorption heat pump.

[0017] A "staged thermal storage system using intermediate water" was installed on the source side, while a "high-temperature water energy storage system" was installed on the load side. The staged thermal storage system using intermediate water effectively mitigated the instability of waste heat sources caused by fluctuations in gas turbine load; the high-temperature water energy storage system directly compensated for the heating gap when the unit participated in grid peak shaving through "heat storage during off-peak hours and heat release during peak hours." This dual energy storage mechanism completely broke the traditional "heat-driven power generation" model's absolute dependence on high-grade steam extraction, ensuring the continuity and stability of heating supply.

[0018] The graded recycling concept provided by this invention is not only applicable to gas-steam combined cycle, but can also be seamlessly transferred to coal-fired units or various industrial scenarios with low-grade waste heat recovery needs, and has extremely high engineering application and promotion value. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is an overall schematic diagram of a graded thermal storage type flue gas waste heat heating system proposed in this invention; Among them: 1. Gas turbine; 2. Waste heat boiler; 3. Steam turbine; 4. First three-way valve; 5. Condenser; 6. Second three-way valve; 7. Plate heat exchanger; 8. Absorption heat pump unit; 9. Electric heat pump unit; 10. High temperature water energy storage device; 11. Heat user; 12. Chimney; 13. Third three-way valve; 14. Low temperature intermediate water heat storage device; 15. Medium temperature intermediate water heat storage device. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] Reference Figure 1 As shown, the present invention provides a staged thermal storage type flue gas waste heat heating system, including: a gas turbine 1; Waste heat boiler 2, whose flue gas inlet is connected to the exhaust port of gas turbine 1; Steam turbine 3, whose steam inlet is connected to the steam outlet of waste heat boiler 2; The plate heat exchanger 7 has its flue gas inlet connected to the tail flue gas outlet of the waste heat boiler 2; the flue gas outlet of the plate heat exchanger 7 is connected to the chimney 12. Electric heat pump unit 9; The absorption heat pump unit 8 has its generator inlet connected to the exhaust steam outlet of the steam turbine 3; the condenser inlet of the absorption heat pump unit 8 is connected to the condenser outlet of the electric heat pump unit 9; the condenser outlet of the absorption heat pump unit 8 is connected to the inlet of the high-temperature water energy storage device 10 and the inlet of the heat user 11 respectively. The system includes a low-temperature intermediate water heat storage device 14 and a medium-temperature intermediate water heat storage device 15. The low-temperature intermediate water heat storage device 14 is connected to the intermediate water side of the plate heat exchanger 7 and is used to store waste heat from the flue gas. The low-temperature intermediate water heat storage device 14 is connected to the evaporator side of the electric heat pump unit 9 through a pipeline to form a closed loop. The low-temperature intermediate water heat storage device 14 and the medium-temperature intermediate water heat storage device 15 are connected in series, and the medium-temperature intermediate water heat storage device 15 is connected to the evaporator side of the absorption heat pump unit 8 to form a closed loop.

[0023] Furthermore, the exhaust steam outlet of the steam turbine 3 is connected to the inlet of the condenser 5 and the generator inlet of the absorption heat pump unit 8 via the first three-way valve 4; the feedwater outlet of the waste heat boiler 2 is connected to the outlet of the condenser 5 and the generator outlet of the absorption heat pump unit 8 via the second three-way valve 6.

[0024] Furthermore, the condenser outlet of the absorption heat pump unit 8 is also connected to a third three-way valve 13, and the two outlets of the third three-way valve 13 are respectively connected to the inlet of the high-temperature water energy storage device 10 and the inlet of the heat user 11.

[0025] Furthermore, the high-temperature water storage device 10 is also equipped with an emergency heat replenishment outlet, which is used to directly replenish high-temperature hot water to the heat user 11 when there is a heating load gap.

[0026] Furthermore, the low-temperature intermediate water thermal storage device 14 is used to store intermediate water at 25~35℃; the medium-temperature intermediate water thermal storage device 15 is used to store intermediate water at 35~45℃.

[0027] Furthermore, it also includes a control unit, which monitors the real-time load of the heat user 11 and dynamically adjusts the output and heat extraction of the electric heat pump unit 9 and the absorption heat pump unit 8 accordingly.

[0028] Furthermore, the electric heat pump unit 9 is configured to extract heat from the low-temperature intermediate water heat storage device 14 to preheat the return water of the heating network from 50°C to 55~65°C; the absorption heat pump unit 8 is configured to extract heat from the medium-temperature intermediate water heat storage device 15 to raise the temperature of the heating network water from 55~65°C to 85°C.

[0029] This invention provides a staged heat storage method for flue gas waste heat supply, comprising the following steps: S1. The high-temperature flue gas generated by the gas turbine 1 is passed through the waste heat boiler 2 for heat exchange and then passed through the plate heat exchanger 7 to exchange heat with the intermediate water. The flue gas temperature is reduced to 30~40℃ and then discharged to the chimney 12. S2. The heat exchanged intermediate water is stored according to temperature grade; intermediate water with a temperature of 25~35℃ is stored in low temperature intermediate water heat storage device 14, and intermediate water with a temperature of 35~45℃ is stored in medium temperature intermediate water heat storage device 15. S3. The return water of the heating network flows through the electric heat pump unit 9 and the absorption heat pump unit 8 in sequence to raise the temperature in stages. The electric heat pump unit 9 uses the heat of the low temperature intermediate water heat storage device 14 for preheating, and the absorption heat pump unit 8 uses the heat of the medium temperature intermediate water heat storage device 15 and the exhaust steam of the steam turbine 3 for secondary temperature raising. S4. The heated high-temperature water is delivered to the heat user 11, and the excess heat is stored in the high-temperature water energy storage device 10.

[0030] Furthermore, in step S3: When the heat user 11 is in a low load demand, the output of the electric heat pump unit 9 and the absorption heat pump unit 8 is reduced, so that the temperature of the intermediate water at the outlet of the plate heat exchanger 7 is increased and stored in the medium temperature intermediate water heat storage device 15 to achieve energy storage. When the heat user 11 is under high load demand, the output of the electric heat pump unit 9 and the absorption heat pump unit 8 is increased to fully extract and store heat, and the high-temperature water energy storage device 10 is started to supplement heat.

[0031] Furthermore, after completing the heat exchange, the temperature of the intermediate water decreases, and it returns sequentially to the medium-temperature intermediate water heat storage device 15 and the low-temperature intermediate water heat storage device 14, and then re-enters the plate heat exchanger 7 to absorb the waste heat of the flue gas, forming a closed loop.

[0032] The working principle of the staged heat storage type flue gas waste heat heating system and method provided by this invention is as follows: After the gas turbine 1 burns natural gas, it produces high-temperature flue gas. This high-temperature flue gas first enters the waste heat boiler 2, where the high-grade heat energy in the flue gas is used to generate steam. The generated steam then enters the steam turbine 3 to expand and generate electricity. The exhaust steam discharged from the steam turbine 3 is split through the first three-way valve 4. One path enters the condenser 5 for heat exchange and provides heat to the outside. The condensate formed is then returned to the waste heat boiler 2 after being combined through the second three-way valve 6, forming a closed-loop steam-condensate circulation loop. The other path serves as the driving steam to enter the generator of the absorption heat pump unit 8, providing the driving heat source for the absorption heat pump unit 8.

[0033] On the flue gas waste heat recovery side, the low-temperature flue gas at the tail end, after heat exchange in the waste heat boiler 2, enters the plate heat exchanger 7 at approximately 85-95°C, where it exchanges heat with the closed-loop circulating intermediate water. The intermediate water absorbs the sensible heat and some of the latent heat of condensation from the flue gas in the plate heat exchanger 7, raising its temperature. The flue gas temperature is further cooled to 30-40°C before being discharged through the chimney 12, thus achieving deep recovery of the flue gas waste heat.

[0034] After absorbing waste heat from the flue gas, the intermediate water is classified and stored in two independent intermediate water storage devices according to the heating load required by the system and its own temperature grade. The system achieves physical isolation of intermediate water in different temperature zones by setting up independent low-temperature intermediate water storage device 14 and medium-temperature intermediate water storage device 15.

[0035] Under normal operation or high heating load conditions, intermediate water with a temperature in the range of 25~35℃ enters the low-temperature intermediate water thermal storage device 14, and intermediate water with a temperature in the range of 35~45℃ enters the medium-temperature intermediate water thermal storage device 15. This configuration of independent dual-group thermal storage enables heat sources of different grades to supply heat to different heat pump units as needed, realizing the cascade matching and utilization of heat sources and heat loads.

[0036] During heating operation, the control unit monitors the actual heating load required by heat user 11 in real time, and accordingly makes adaptive dynamic adjustments to the operating status, output, and heat extraction of electric heat pump unit 9 and absorption heat pump unit 8. When heat user 11 requires little heat, i.e., is under low heating load demand, the electric heat pump unit 9 and the absorption heat pump unit 8 reduce their output accordingly. At this time, the heat pump unit 8 extracts less heat from the variable-temperature intermediate water closed loop, causing the overall temperature of the intermediate water after circulating and absorbing heat in the plate heat exchanger 7 to rise to the range of 35~45℃. Driven by the control unit, it switches to the medium-temperature intermediate water heat storage device 15 for storage, realizing the quality improvement and accumulation of surplus low-grade heat and energy buffering. The low-temperature heat network return water from heat user 11 first enters the electric heat pump unit 9 for preheating. The electric heat pump unit 9 extracts low-grade heat of 25~35℃ from the low-temperature intermediate water heat storage device 14, and improves the heat quality through the work of the compressor, raising the heat network return water from about 50℃ to the corresponding preheating temperature, completing the basic temperature rise process of heating.

[0037] Subsequently, the preheated hot water from the heating network, after being heated by the electric heat pump unit 9, further enters the absorption heat pump unit 8 for secondary temperature increase. The absorption heat pump unit 8 extracts medium-temperature heat (35-45°C) from the medium-temperature intermediate water storage device 15, and simultaneously uses the driving steam provided by the steam turbine 3 as the driving heat source. Through the coordinated operation of the generator, evaporator, absorber, and condenser, the hot water from the heating network is further heated to 85°C, forming a high-temperature water supply that meets the heating demand.

[0038] High-temperature water supply reaching 85℃ is distributed through the third three-way valve 13. When the real-time heat supply of the system exceeds the actual heat load demand of the heat user 11, some of the high-temperature hot water enters the high-temperature water energy storage device 10 for heat storage, storing heat energy in the form of sensible heat of hot water, realizing heat transfer across time. At the same time, the temperature of the intermediate water after heat exchange on the evaporator side of the electric heat pump unit 9 and the absorption heat pump unit 8 decreases, and it returns to the corresponding low-temperature intermediate water heat storage device 14 and medium-temperature intermediate water heat storage device 15, and then re-enters the plate heat exchanger 7 to absorb the waste heat of flue gas, forming a closed-loop circulation loop of intermediate water.

[0039] When the heating load required by heat user 11 increases, the electric heat pump unit 9 and the absorption heat pump unit 8 increase their output to fully extract the stored heat. The low-temperature return water from heat user 11 first enters the electric heat pump unit 9 for preheating. The electric heat pump unit 9 extracts low-grade heat (25-35°C) from the low-temperature intermediate water storage device 14 and upgrades the heat through the compressor, raising the return water temperature from approximately 50°C to the corresponding preheating temperature, completing the basic temperature rise process for heating. Subsequently, the preheated water from the electric heat pump unit 9 further enters the absorption heat pump unit 8 for secondary temperature increase. The absorption heat pump unit 8 extracts medium-temperature heat (35-45°C) from the medium-temperature intermediate water storage device 15, and simultaneously uses the driving steam provided by the steam turbine 3 as the driving heat source. Through the coordinated operation of the generator, evaporator, absorber, and condenser, the water temperature is further increased to 85°C, forming high-temperature water supply that meets the heating demand. When the heat load increases or the unit participates in grid peak shaving, resulting in insufficient heating capacity, the high-temperature water storage device 10 releases the stored high-temperature hot water and directly supplements the heating network system to make up for the heating gap and ensure the stability and continuity of heating. At the same time, the temperature of the intermediate water after heat exchange on the evaporator side of the electric heat pump unit 9 and the absorption heat pump unit 8 decreases, and it returns to the corresponding low-temperature intermediate water storage device 14 and medium-temperature intermediate water storage device 15, and then re-enters the plate heat exchanger 7 to absorb the waste heat of the flue gas, forming a closed-loop circulation loop for the intermediate water.

[0040] Those skilled in the art should understand that the condenser 5, absorption heat pump unit 8, and electric heat pump unit 9 are all mature standard industrial products, and their specific structural parameters can be calculated by technicians based on the actual heat load, falling within the scope of common knowledge. Similarly, the insulation structure and volume design of the low-temperature intermediate water thermal storage device 14 and the medium-temperature intermediate water thermal storage device 15 are also conventional designs. This invention aims to protect the system operation strategy based on the above-mentioned hardware, rather than the microstructure of the hardware itself.

[0041] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to 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 this invention.

[0042] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A staged heat storage type flue gas waste heat heating system, characterized in that, include: Gas turbine (1); Waste heat boiler (2), whose flue gas inlet is connected to the exhaust port of the gas turbine (1); A steam turbine (3) has its steam inlet connected to the steam outlet of the waste heat boiler (2); The plate heat exchanger (7) has its flue gas inlet connected to the tail flue gas outlet of the waste heat boiler (2); the flue gas outlet of the plate heat exchanger (7) is connected to the chimney (12). Electric heat pump unit (9); An absorption heat pump unit (8) has its generator inlet connected to the exhaust steam outlet of the steam turbine (3); the condenser inlet of the absorption heat pump unit (8) is connected to the condenser outlet of the electric heat pump unit (9); the condenser outlet of the absorption heat pump unit (8) is connected to the inlet of a high-temperature water energy storage device (10) and the inlet of a heat user (11). Low-temperature intermediate water heat storage device (14) and medium-temperature intermediate water heat storage device (15), wherein the low-temperature intermediate water heat storage device (14) is connected to the intermediate water side of the plate heat exchanger (7) for storing waste heat from flue gas; the low-temperature intermediate water heat storage device (14) is connected to the evaporator side of the electric heat pump unit (9) through a pipeline to form a closed loop; and the low-temperature intermediate water heat storage device (14) is connected in series with the medium-temperature intermediate water heat storage device (15), and the medium-temperature intermediate water heat storage device (15) is connected to the evaporator side of the absorption heat pump unit (8) to form a closed loop.

2. The staged thermal storage type flue gas waste heat heating system according to claim 1, characterized in that, The exhaust steam outlet of the steam turbine (3) is connected to the inlet of the condenser (5) and the generator inlet of the absorption heat pump unit (8) via a first three-way valve (4); the feedwater outlet of the waste heat boiler (2) is connected to the outlet of the condenser (5) and the generator outlet of the absorption heat pump unit (8) via a second three-way valve (6).

3. The staged thermal storage type flue gas waste heat heating system according to claim 1, characterized in that, The condenser outlet of the absorption heat pump unit (8) is also connected to a third three-way valve (13), and the two outlets of the third three-way valve (13) are respectively connected to the inlet of the high-temperature water energy storage device (10) and the inlet of the heat user (11).

4. The staged thermal storage type flue gas waste heat heating system according to claim 1, characterized in that, The high-temperature water energy storage device (10) is also equipped with an emergency heat replenishment outlet, which is used to directly replenish high-temperature hot water to heat users (11) when there is a heating load gap.

5. The staged thermal storage type flue gas waste heat heating system according to claim 1, characterized in that, The low-temperature intermediate water thermal storage device (14) is used to store intermediate water at 25~35℃; the medium-temperature intermediate water thermal storage device (15) is used to store intermediate water at 35~45℃.

6. The staged thermal storage type flue gas waste heat heating system according to claim 1, characterized in that, It also includes a control unit, which is used to monitor the real-time load of the heat user (11) and dynamically adjust the output and heat extraction of the electric heat pump unit (9) and the absorption heat pump unit (8) accordingly.

7. The staged thermal storage type flue gas waste heat heating system according to claim 1, characterized in that, The electric heat pump unit (9) is configured to extract heat from the low-temperature intermediate water heat storage device (14) to preheat the return water of the heating network from 50°C to 55~65°C; the absorption heat pump unit (8) is configured to extract heat from the medium-temperature intermediate water heat storage device (15) to raise the temperature of the heating network water from 55~65°C to 85°C.

8. A staged thermal storage type flue gas waste heat heating method, employing the system described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. The high-temperature flue gas generated by the gas turbine (1) is passed through the waste heat boiler (2) for heat exchange, and then passed through the plate heat exchanger (7) to exchange heat with the intermediate water. The flue gas temperature is reduced to 30~40℃ and then discharged to the chimney (12). S2. The heat exchanged intermediate water is stored according to temperature grade; intermediate water with a temperature of 25~35℃ is stored in a low temperature intermediate water heat storage device (14), and intermediate water with a temperature of 35~45℃ is stored in a medium temperature intermediate water heat storage device (15). S3. The return water of the heating network flows through the electric heat pump unit (9) and the absorption heat pump unit (8) in sequence to raise the temperature in stages. The electric heat pump unit (9) uses the heat of the low temperature intermediate water heat storage device (14) for preheating, and the absorption heat pump unit (8) uses the heat of the medium temperature intermediate water heat storage device (15) and the exhaust steam of the steam turbine (3) for secondary temperature raising. S4. The heated high-temperature water is delivered to the heat user (11), and the excess heat is stored in the high-temperature water energy storage device (10).

9. A staged thermal storage type flue gas waste heat heating method according to claim 8, characterized in that, In step S3: When the heat user (11) is in a low load demand, the output of the electric heat pump unit (9) and the absorption heat pump unit (8) is reduced, so that the intermediate water temperature at the outlet of the plate heat exchanger (7) is increased and stored in the medium temperature intermediate water heat storage device (15) to achieve energy storage. When the heat user (11) is under high load demand, the output of the electric heat pump unit (9) and the absorption heat pump unit (8) is increased to fully extract and store heat, and the high temperature water energy storage device (10) is started to supplement heat.

10. A staged thermal storage type flue gas waste heat heating method according to claim 9, characterized in that, After the heat exchange is completed, the temperature of the intermediate water decreases and it returns to the medium-temperature intermediate water heat storage device (15) and the low-temperature intermediate water heat storage device (14) in sequence, and then enters the plate heat exchanger (7) again to absorb the waste heat of the flue gas, forming a closed loop.

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