Ultralow-temperature flue gas waste heat deep recovery heat supply system of gas turbine circulating backpressure heat supply unit

Abstract

The invention provides a gas turbine circulating backpressure heat supply unit ultralow temperature flue gas waste heat deep recovery heat supply system which comprises a dividing wall type heat exchanger and an absorption heat pump unit, in the heat supply season, a first inlet of the dividing wall type heat exchanger is connected with ultralow temperature flue gas discharged by a waste heat boiler, and a second inlet of the dividing wall type heat exchanger is connected with a water outlet of an evaporator in the absorption heat pump unit; the first outlet is connected to a chimney, the second outlet is connected with a water inlet of an evaporator in the absorption heat pump unit, a heat source inlet of a generator in the absorption heat pump unit is connected with a steam turbine circulating device through a driving steam inlet pipeline, and a water inlet of an absorber in the absorption heat pump unit is connected with a heat supply network water inlet pipeline provided with a booster pump. And the water outlet returns to a heat user through the condenser and a heat supply network water outlet pipeline. Smoke waste heat discharged by the circulating back pressure heat supply unit of the gas turbine is efficiently recycled and converted into low-carbon and efficient heat supply energy, sustainable utilization of the energy is achieved, the utilization rate of natural gas is increased, and the purposes of energy conservation and emission reduction are achieved.

Description

Technical Field

[0001] This invention relates to the fields of energy utilization, combined heat and power, and low-carbon environmental protection, specifically to a deep recovery heating system for waste heat from ultra-low temperature flue gas in a gas turbine circulating back pressure heating unit. Background Technology

[0002] Combined cycle power units, with their high efficiency and good peak-shaving capabilities, and following the principle of "temperature matching and energy cascade utilization," have become the mainstay units for centralized heating in combined heat and power (CHP) systems. Currently, increased heating pressure and insufficient heating capacity are the main constraints on the widespread application of combined cycle power units. Therefore, improving the heating efficiency of these units is key to solving this problem.

[0003] "Ultra-low temperature flue gas waste heat" refers to the waste heat energy from flue gas that is currently not recovered and utilized, is above ambient temperature, and still has further recovery value. In back-pressure unit heating processes, the exhaust gas temperature at the tail end of the waste heat boiler is generally 70-90℃, with a water vapor content of approximately 7%-15%. The waste heat from the flue gas accounts for 10%-20% of the input fuel heat. If this heat can be effectively recovered, it will significantly improve the overall energy efficiency of the unit. With the severe challenges of global climate change, low-carbon heating technology has become crucial for reducing carbon emissions and achieving energy transition.

[0004] Currently, most flue gas waste heat recovery systems employ a combination of spray heat exchange and absorption heat pumps, primarily for preheating steam turbines or boilers, and are largely unsuitable for heating systems recovering waste heat from gas turbine cycles. A utility model patent with authorization announcement number CN210424998U discloses a device for cascaded recovery of waste heat from power plant flue gas, comprising a medium-temperature flue gas waste heat recovery unit, a low-temperature flue gas waste heat recovery unit, and a low-temperature flue gas grade enhancement unit. Specifically: the medium-temperature flue gas waste heat recovery unit recovers waste heat from the power plant's medium-temperature flue gas and discharges low-temperature flue gas; the low-temperature flue gas waste heat recovery unit recovers waste heat from the low-temperature flue gas and discharges low-temperature circulating water; and the low-temperature flue gas grade enhancement unit recovers waste heat from the low-temperature circulating water and supplies heat externally. The inventors of this application discovered through research that the device mainly uses a heat exchanger to recover the waste heat of medium-temperature flue gas for steam turbines, and a spray heat exchanger to recover the latent heat of low-temperature flue gas for heating, and uses condensate as a refrigerant. If this device is used in a gas turbine cycle back pressure heating unit, it will cause the exhaust gas temperature on the waste heat boiler side to rise, which will be counterproductive. During the non-heating season, the resistance of the demister at the spray tower end and the resistance on the flue side are relatively large, which will have adverse effects on the combined cycle power, efficiency, and overall plant thermal efficiency.

[0005] Therefore, developing a new and efficient gas turbine cycle ultra-low temperature flue gas waste heat deep recovery and low-carbon heating system is of great significance for improving the natural gas utilization rate of the unit, increasing the heating rate, and achieving energy conservation and emission reduction. Summary of the Invention

[0006] To address the technical problems existing in the prior art, this invention provides an ultra-low temperature flue gas waste heat deep recovery heating system for gas turbine circulating back pressure heating units. This system aims to efficiently recover the waste heat emitted by the flue gas from the gas turbine circulating back pressure heating units and convert it into low-carbon, high-efficiency heating energy, thereby achieving sustainable energy utilization, realizing "temperature matching and energy quality improvement utilization", improving natural gas utilization rate, and achieving the goal of energy conservation and emission reduction.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A gas turbine circulating back-pressure heating unit ultra-low temperature flue gas waste heat deep recovery heating system includes a partition wall heat exchanger and an absorption heat pump unit. The absorption heat pump unit includes a generator, condenser, evaporator, and absorber connected in sequence via refrigerant piping. During the heating season, the first inlet of the partition wall heat exchanger is connected to 70-90℃ low-temperature flue gas discharged from the waste heat boiler via a flue gas inlet pipe. The flue gas inlet of the waste heat boiler is connected to the exhaust outlet pipe of the gas turbine circulating unit. The second inlet of the partition wall heat exchanger is connected to the outlet of the evaporator in the absorption heat pump unit via a low-temperature intermediate water outlet pipe. An intermediate water outlet switching valve is connected to the low-temperature intermediate water outlet pipe. The first outlet of the partition wall heat exchanger is connected to... The flue gas outlet pipe is connected to the chimney. The second outlet of the indirect heat exchanger is connected to the inlet of the evaporator in the absorption heat pump unit via a low-temperature intermediate water inlet pipe. An intermediate water inlet switching valve is connected to the low-temperature intermediate water inlet pipe. The heat source inlet of the generator in the absorption heat pump unit is connected to the low-pressure steam line in the steam turbine circulation device via a drive steam inlet pipe. After the generator releases heat, the condensate is recovered via a condensate recovery pipe. The inlet of the absorber is connected to the heating network water inlet pipe. A booster pump is installed on the heating network water inlet pipe. The outlet of the absorber is connected to the inlet of the condenser via a heating network water supply pipe. The outlet of the condenser is returned to the heat user via a heating network water outlet pipe.

[0009] Furthermore, during the non-heating season, a condensate inlet pipe is connected to the low-temperature intermediate water outlet pipe between the second inlet of the partition wall heat exchanger and the intermediate water outlet switching valve. A condensate inlet switching valve is connected to the condensate inlet pipe. A condensate pump is installed on the low-temperature intermediate water outlet pipe between the second inlet of the partition wall heat exchanger and the condensate inlet switching valve. A condensate outlet pipe is connected to the low-temperature intermediate water inlet pipe between the second outlet of the partition wall heat exchanger and the intermediate water inlet switching valve. A condensate outlet switching valve is sequentially connected to the condensate outlet pipe. The end of the condensate outlet pipe is connected to the condensate heater in the waste heat boiler.

[0010] Furthermore, during the heating season, the waste heat from the low-temperature flue gas at 70-90℃ is absorbed by the low-temperature intermediate water in the evaporator of the absorption heat pump unit, reducing the temperature to 30-37℃. The total heat recovered from the flue gas is no less than 30MW, with a latent heat ratio of 37.6%~56.3%. The recovered condensate is 17t / h~38t / h. After conditioning, the flue gas condensate enters the water tank as supplementary water for the heating network, achieving improved utilization of waste heat and increasing the overall thermal efficiency by 4%. During the non-heating season, the indirect heat exchanger acts as a low-temperature economizer, becoming the final heating surface of the waste heat boiler. The condensate at 30℃ is heated to 50℃ by the recovered flue gas waste heat before entering the waste heat boiler, reducing the flue gas temperature to 50℃. At this point, the recovered flue gas waste heat is 15MW.

[0011] Furthermore, the intermediate water temperature at the outlet of the evaporator in the absorption heat pump unit is 20-30℃, and the intermediate water temperature at the inlet of the evaporator in the absorption heat pump unit is 30-37℃.

[0012] Furthermore, the inlet water temperature of the absorber is 40-50℃, and the outlet water temperature of the condenser is 60-80℃.

[0013] Furthermore, the condensate recovered by the indirect heat exchanger is connected to a water tank via a condensate connecting pipe for pH adjustment, and then enters the heating network water replenishment device through the condensate outlet pipe as heating network replenishment water.

[0014] Compared with existing technologies, the ultra-low temperature flue gas waste heat deep recovery heating system for gas turbine cycle back-pressure heating units provided by this invention has the following advantages: 1) By efficiently and deeply recovering the waste heat from the flue gas emitted by the gas turbine cycle back-pressure heating unit, especially the latent heat portion, and converting it into low-carbon, high-efficiency heating energy, sustainable energy utilization is achieved: During the heating season, the 70-90℃ low-temperature flue gas waste heat is absorbed by the low-temperature intermediate water in the evaporator of the absorption heat pump unit, and the temperature drops to 30-37℃. The total heat recovery from the flue gas is not less than 30MW, and the latent heat... The proportion of waste heat is 37.6%~56.3%; during the non-heating season, the indirect heat exchanger acts as a low-temperature economizer, and the flue gas temperature drops to about 50℃. At this time, the waste heat recovered from the flue gas is about 15MW; the natural gas utilization rate is increased by 8%, and the overall thermal efficiency is increased by 4%; 2) Low-carbon heating is achieved, temperature is matched, and energy is utilized in a higher quality way; 3) Condensate in the flue gas is recovered and treated with pH value adjustment before being recovered. It can be used as supplementary water for the heating network: 17t / h~38t / h of condensate is recovered, and low-grade heat quality is recovered, realizing the utilization of waste heat in a higher quality way. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the ultra-low temperature flue gas waste heat deep recovery heating system for a gas turbine circulating back pressure heating unit provided by the present invention.

[0016] In the diagram, 1. Indirect heat exchanger; 2. Absorption heat pump unit; 201. Generator; 202. Condenser; 203. Evaporator; 204. Absorber; 3. Flue gas inlet pipe; 4. Waste heat boiler; 5. Gas turbine cycle unit; 6. Low-temperature intermediate water outlet pipe; 7. Intermediate water outlet switching valve; 8. Flue gas outlet pipe; 9. Low-temperature intermediate water inlet pipe; 10. Intermediate water inlet switching valve; 11. Drive steam inlet. Piping; 12. Steam turbine circulation system; 13. Condensate recovery pipeline; 14. Heating network water inlet pipeline; 15. Heating network water supply pipeline; 16. Heating network water outlet pipeline; 17. Booster pump; 18. Condensate inlet pipeline; 19. Condensate inlet switching valve; 20. Condensate outlet pipeline; 21. Condensate outlet switching valve; 22. Condensate pump; 23. Condensate connecting pipe; 24. Water tank; 25. Condensate outlet pipeline. Detailed Implementation

[0017] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific illustrations.

[0018] In the description of this invention, it should be understood that the terms "longitudinal," "radial," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are 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. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0019] 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 can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0020] Please refer to Figure 1As shown, taking a 9F-class gas turbine combined cycle back-pressure heating unit as an example, this invention provides an ultra-low temperature flue gas waste heat deep recovery heating system for a gas turbine combined cycle back-pressure heating unit, including a partition heat exchanger 1 and an absorption heat pump unit 2. The partition heat exchanger 1 can be implemented using a novel plate heat exchanger with high-efficiency heat transfer and low resistance. The absorption heat pump unit 2 includes a generator 201, a condenser 202, an evaporator 203, and an absorber 204 connected in sequence through refrigerant pipelines. The absorption heat pump unit 2 can be implemented using a steam-type lithium bromide unit, the specific structure of which is well known to those skilled in the art. During the heating season, the first inlet of the partition heat exchanger 1 is connected to the flue gas discharged from the waste heat boiler 4 through a flue gas inlet pipeline 3. Low-temperature flue gas at 70-90℃ enters the indirect heat exchanger 1 through the flue gas inlet pipe 3. The flue gas inlet of the waste heat boiler 4 is connected to the exhaust outlet pipe of the gas turbine circulation device 5. The second inlet of the indirect heat exchanger 1 is connected to the outlet of the evaporator 203 in the absorption heat pump unit 2 through the low-temperature intermediate water outlet pipe 6. An intermediate water outlet switching valve 7 is connected to the low-temperature intermediate water outlet pipe 6, so the low-temperature heat source of the evaporator 203 is the intermediate water after absorbing the waste heat of the flue gas. The first outlet of the indirect heat exchanger 1 is connected to the chimney through the flue gas outlet pipe 8. At this time, the flue gas at the first outlet of the indirect heat exchanger 1 has been cooled to 30-40℃. The second outlet of the wall-mounted heat exchanger 1 is connected to the inlet of the evaporator 203 in the absorption heat pump unit 2 via a low-temperature intermediate water inlet pipe 9. An intermediate water inlet switching valve 10 is connected to the low-temperature intermediate water inlet pipe 9. The heat source inlet of the generator 201 in the absorption heat pump unit 2 is connected to the low-pressure steam line in the steam turbine circulation device 12 via a drive steam inlet pipe 11. Specifically, the driving heat source for the generator 201 comes from the extraction of low-pressure steam. The driving heat source provided by the low-pressure steam line is 0.4 MPa, 140°C heating extraction steam. The driving heat source heats the dilute lithium bromide solution from the absorber 204 within the generator 201, and then recovers it as 90°C condensate through the condensate recovery pipe 13. The inlet of the absorber 204 is connected to the heating network water inlet pipe 14, and a booster pump 17 is installed on the heating network water inlet pipe 14. The outlet of the absorber 204 is connected to the inlet of the condenser 202 through the heating network water supply pipe 15. The outlet of the condenser 202 is returned to the heat user through the heating network water outlet pipe 16. Thus, the heating network water absorbs heat from the absorber 204 and condenser 202 through the heating network water supply pipe 15 and then returns to the heat user through the heating network water outlet pipe 16. This deeply recovers the latent heat of the flue gas and the condensate, while also reducing the possibility of white smoke. It truly achieves low-carbon heating and zero-energy recovery of flue gas waste heat, solving the problem of insufficient back pressure heating capacity of large gas turbines.

[0021] For a specific embodiment, please refer to Figure 1 As shown, during the non-heating season, a condensate inlet pipe 18 is connected to the low-temperature intermediate water outlet pipe 6 between the second inlet of the indirect heat exchanger 1 and the intermediate water outlet switching valve 7. A condensate inlet switching valve 19 is connected to the condensate inlet pipe 18. A condensate pump 22 is installed on the low-temperature intermediate water outlet pipe 6 between the second inlet of the indirect heat exchanger 1 and the condensate inlet switching valve 19. A condensate outlet pipe 20 is connected to the low-temperature intermediate water inlet pipe 9 between the second outlet of the indirect heat exchanger 1 and the intermediate water inlet switching valve 10. A condensate outlet switching valve 21 is connected to the condensate outlet pipe 20 in sequence. The end of the condensate outlet pipe 20 is connected to the condensate heater in the waste heat boiler 4. Therefore, during the non-heating season, in order to avoid the dry burning of the indirect heat exchanger 1 and the adverse effects of flue gas side resistance on the non-heating operation of the combined cycle unit, a valve group is used to switch the water circulation of the indirect heat exchanger 1. Specifically, the condensate inlet switching valve 19 and the condensate outlet switching valve 21 are opened, while the intermediate water outlet switching valve 7 and the intermediate water inlet switching valve 10 are closed. As a result, the condensate entering from the condensate inlet pipe 18 is heated and continues to enter the tail heat exchange surface of the waste heat boiler 4 for heat exchange, and part of the flue gas waste heat is also recovered. During the non-heating season, the indirect heat exchanger 1 acts as a low-temperature economizer. By switching valves, 30°C condensate first enters the indirect heat exchanger 1, making it a preheating device for the condensate, which then enters the condensate heater in the existing waste heat boiler 4 for heating. As the final stage heating surface, the heat exchanger fully utilizes the corrosion resistance of 316L steel to increase the heat absorption of the waste heat boiler 4, thereby improving the waste heat utilization efficiency, reducing low-temperature corrosion of the existing heating surface, and reducing the power consumption of the condensate circulation pump.

[0022] As a specific embodiment, during the heating season, the low-temperature flue gas waste heat at 70-90℃ is absorbed by the low-temperature intermediate water in the evaporator 203 of the absorption heat pump unit 2, and the temperature drops to 30-37℃. The total heat recovered from the flue gas is not less than 30MW, the latent heat accounts for 37.6%~56.3%, and the condensate is recovered at 17t / h~38t / h. After conditioning, the flue gas condensate enters the water tank 24 as supplementary water for the heating network, realizing the improved utilization of waste heat and increasing the overall thermal efficiency by 4%. During the non-heating season, the indirect heat exchanger 1 serves as a low-temperature economizer and becomes the final heating surface of the waste heat boiler 4. The condensate at 30℃ is heated to 50℃ by the recovered flue gas waste heat and enters the waste heat boiler 4. The flue gas temperature drops to 50℃, and at this time, the recovered flue gas waste heat is 15MW.

[0023] In a specific embodiment, the intermediate water temperature at the outlet of the evaporator 203 in the absorption heat pump unit 2 is 20-30℃, and the intermediate water temperature at the inlet of the evaporator 203 in the absorption heat pump unit 2 is 30-37℃. This allows the intermediate water at 20-30℃ in the evaporator 203 to absorb waste heat from the flue gas in the partition heat exchanger 1 and then be heated to 30-37℃. The flue gas is then cooled to 30-37℃ and enters the chimney. The low-temperature heat source of the evaporator 203 is the intermediate water after absorbing waste heat from the flue gas.

[0024] In a specific embodiment, the inlet water temperature of the heat network water in the absorber 204 is 40-50℃, and the outlet water temperature of the heat network water in the condenser 202 is 60-80℃. That is, after the heat network water gradually absorbs the heat released by the absorber 204 and the condenser 202, the temperature gradually rises to 60-80℃, and then returns to the heat user through the heat network water outlet pipe 16.

[0025] For a specific embodiment, please refer to Figure 1 As shown, the indirect heat exchanger 1 recovers the total heat (sensible heat and latent heat) of the ultra-low temperature flue gas and the condensate. The condensate recovered by the indirect heat exchanger 1 is connected to the water tank 24 through the condensate connecting pipe 23 for pH adjustment, and then enters the heating network water replenishment device through the condensate outlet pipe 25 as heating network replenishment water, thereby completing the recycling and utilization of water resources.

[0026] To better understand the ultra-low temperature flue gas waste heat deep recovery heating system for gas turbine circulating back pressure heating units provided by this invention, the working process of the system will be described below:

[0027] The indirect heat exchanger 1 is installed at the tail end of the waste heat boiler 4. Low-temperature flue gas of 70-90℃ is discharged from the waste heat boiler 4 and enters the indirect heat exchanger 1 through the flue gas inlet pipe 3. After heat exchange and cooling to 30-37℃, it enters the chimney. During the heating season, the first inlet and outlet pipelines of the cold fluid in the indirect heat exchanger 1 are connected to the evaporator 203 in the absorption heat pump unit 2 by controlling the opening of the intermediate water outlet switching valve 7 and the intermediate water inlet switching valve 10 (at this time, the condensate inlet switching valve 19 and the condensate outlet switching valve 21 are closed). The low-temperature heat source at the evaporator 203, the intermediate water at 20-30℃, exchanges heat in the indirect heat exchanger 1, and rises to 30-37℃ after absorbing the waste heat of the flue gas. The low-temperature waste heat of the flue gas at 70-90℃ is absorbed by the low-temperature intermediate water in the evaporator 203 in the absorption heat pump unit 2, and the temperature drops to 30-37℃. The total heat recovered from the flue gas is not less than 30MW, the latent heat accounts for 37.6%~56.3%, and the condensate water is recovered at 17t / h~38t / h. After conditioning, the flue gas condensate enters the water tank 24 as supplementary water for the heating network, realizing the improved utilization of waste heat and increasing the overall thermal efficiency by 4%. The low-temperature heat source of the evaporator 203 is the intermediate water after absorbing the waste heat of the flue gas. After absorbing the heat from the absorber 204 and the condenser 202, the heating network water is returned to the heat user through the heating network water outlet pipe 16 via the heating network water supply pipeline 15.

[0028] During the non-heating season, 30℃ condensate flows through condensate inlet pipe 18 and condensate outlet pipe 20, with condensate inlet switching valve 19 and condensate outlet switching valve 21 opened (intermediate water outlet switching valve 7 and intermediate water inlet switching valve 10 closed at this time). It then enters the second inlet and outlet pipes of the cold fluid in the partition wall heat exchanger 1 via condensate pump 22, absorbs waste heat from the flue gas, and then enters the tail heat exchange surface of the waste heat boiler 4 for heat exchange. The flue gas condensate recovered by the partition wall heat exchanger 1 is connected to the water tank 24 through condensate connecting pipe 23. The pH value is adjusted in the water tank 24, and after conditioning, the condensate enters the heating network water replenishment device through condensate outlet pipe 25 as heating network replenishment water, thus completing the recycling and utilization of water resources. During the non-heating season, the indirect heat exchanger 1 serves as a low-temperature economizer and becomes the final heating surface of the waste heat boiler 4. The condensate at 30°C is heated to 50°C by the waste heat from the recovered flue gas and then enters the waste heat boiler 4. The flue gas temperature drops to 50°C, at which point the recovered flue gas waste heat is 15MW.

[0029] In the absorption heat pump unit 2, the driving heat source of the generator 201 comes from the heating extraction steam at 0.4MPa and 140℃. After releasing heat, the condensate cooled to 90℃ is recovered through the condensate recovery pipeline 13. The intermediate water at a temperature of not less than 20℃ in the evaporator 203 absorbs the waste heat of the flue gas in the partition heat exchanger 1 and is then heated to 30-37℃. The heat network return water at 40-50℃ is pumped by the pressurization pump 17 and passes through the heat network water inlet pipeline 14. After absorbing heat in the absorber 204 and condenser 202 respectively, it is heated to 60-80℃ hot water and then sent to the heat user end through the heat network water outlet pipeline 16.

[0030] Compared with existing technologies, the ultra-low temperature flue gas waste heat deep recovery heating system for gas turbine cycle back-pressure heating units provided by this invention has the following advantages: 1) By efficiently and deeply recovering the waste heat from the flue gas emitted by the gas turbine cycle back-pressure heating unit, especially the latent heat portion, and converting it into low-carbon, high-efficiency heating energy, sustainable energy utilization is achieved: During the heating season, the 70-90℃ low-temperature flue gas waste heat is absorbed by the low-temperature intermediate water in the evaporator of the absorption heat pump unit, and the temperature drops to 30-37℃. The total heat recovery from the flue gas is not less than 30MW, and the latent heat... The proportion of waste heat is 37.6%~56.3%; during the non-heating season, the indirect heat exchanger acts as a low-temperature economizer, and the flue gas temperature drops to about 50℃. At this time, the waste heat recovered from the flue gas is about 15MW; the natural gas utilization rate is increased by 8%, and the overall thermal efficiency is increased by 4%; 2) Low-carbon heating is achieved, temperature is matched, and energy is utilized in a higher quality way; 3) Condensate in the flue gas is recovered and treated with pH value adjustment before being recovered. It can be used as supplementary water for the heating network: 17t / h~38t / h of condensate is recovered, and low-grade heat quality is recovered, realizing the utilization of waste heat in a higher quality way.

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A system for deep recovery of waste heat from ultra-low-temperature flue gas of a back-pressure heat supply unit of a combustion engine cycle, characterized in that, The system includes a wall-mounted heat exchanger and an absorption heat pump unit. The absorption heat pump unit comprises a generator, a condenser, an evaporator, and an absorber connected sequentially via refrigerant piping. During the heating season, the first inlet of the wall-mounted heat exchanger is connected to 70-90°C low-temperature flue gas discharged from a waste heat boiler via a flue gas inlet pipe. The flue gas inlet of the waste heat boiler is connected to the exhaust outlet pipe of the gas turbine cycle unit. The second inlet of the wall-mounted heat exchanger is connected to the outlet of the evaporator in the absorption heat pump unit via a low-temperature intermediate water outlet pipe. An intermediate water outlet switching valve is connected to the low-temperature intermediate water outlet pipe. The first outlet of the wall-mounted heat exchanger is connected to the chimney via a flue gas outlet pipe. The second outlet of the indirect wall heat exchanger is connected to the inlet of the evaporator in the absorption heat pump unit via a low-temperature intermediate water inlet pipe. An intermediate water inlet switching valve is connected to the low-temperature intermediate water inlet pipe. The heat source inlet of the generator in the absorption heat pump unit is connected to the low-pressure steam line in the steam turbine circulation device via a drive steam inlet pipe. After the generator releases heat, the condensate is recovered through a condensate recovery pipe. The inlet of the absorber is connected to the heating network water inlet pipe. A booster pump is installed on the heating network water inlet pipe. The outlet of the absorber is connected to the inlet of the condenser via a heating network water supply pipe. The outlet of the condenser is returned to the heat user via a heating network water outlet pipe.

2. The system according to claim 1, wherein, During the non-heating season, a condensate inlet pipe is connected to the low-temperature intermediate water outlet pipe between the second inlet of the indirect heat exchanger and the intermediate water outlet switching valve. A condensate inlet switching valve is connected to the condensate inlet pipe. A condensate pump is installed on the low-temperature intermediate water outlet pipe between the second inlet of the indirect heat exchanger and the intermediate water inlet switching valve. A condensate outlet pipe is connected to the low-temperature intermediate water inlet pipe between the second outlet of the indirect heat exchanger and the intermediate water inlet switching valve. A condensate outlet switching valve is connected in sequence to the condensate outlet pipe. The end of the condensate outlet pipe is connected to the condensate heater in the waste heat boiler.

3. The system according to claim 2, wherein, During the heating season, the waste heat from the low-temperature flue gas (70-90℃) is absorbed by the low-temperature intermediate water in the evaporator of the absorption heat pump unit, reducing the temperature to 30-37℃. The total heat recovered from the flue gas is no less than 30MW, with a latent heat ratio of 37.6%~56.3%. The recovered condensate is 17t / h~38t / h. After conditioning, the flue gas condensate enters the water tank as supplementary water for the heating network, achieving improved utilization of waste heat and increasing the overall thermal efficiency by 4%. During the non-heating season, the indirect heat exchanger acts as a low-temperature economizer and becomes the final heating surface of the waste heat boiler. The condensate at 30℃ is heated to 50℃ by the recovered flue gas waste heat before entering the waste heat boiler. The flue gas temperature drops to 50℃, at which point the recovered flue gas waste heat is 15MW.

4. The system according to claim 1, wherein, The intermediate water temperature at the outlet of the evaporator in the absorption heat pump unit is 20-30℃, and the intermediate water temperature at the inlet of the evaporator in the absorption heat pump unit is 30-37℃.

5. The system according to claim 1, wherein, The inlet water temperature of the absorber is 40-50℃, and the outlet water temperature of the condenser is 60-80℃.

6. The system according to claim 1, wherein, The condensate recovered by the indirect heat exchanger is connected to a water tank via a condensate connection pipe for pH adjustment, and then enters the heating network water replenishment device through the condensate outlet pipe as heating network replenishment water.

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