Flue gas deep waste heat recovery system capable of simultaneously heating boiler inlet air and heat supply network water

Abstract

The utility model discloses a flue gas deep waste heat recovery system capable of simultaneously heating boiler inlet air and heat supply network water, and belongs to the technical field of coal-fired boiler waste heat supply. The system is composed of an original boiler, a flue gas treatment subsystem and a flue gas waste heat recycling subsystem, and the flue gas waste heat recycling subsystem comprises a flue gas spraying heat exchange module (6), a boiler air inlet low-temperature air heater (15), a low-temperature process water heater (18) and matched parts and connecting pipelines of the low-temperature process water heater (18). And a flue gas inlet device (5) is arranged at a water tank at the lower part of the flue gas spraying heat exchange module (6). The flue gas high-temperature section waste heat is used for heating heat supply network return water, the flue gas low-temperature section waste heat is used for low-temperature heating of in-plant process water and boiler inlet air, and the boiler inlet air and the process water are heated in a flue gas waste heat spraying mode, so that the flue gas outlet temperature is remarkably reduced, and the waste heat recovery rate and the energy-saving benefit are remarkably improved.

Description

Technical Field

[0001] This utility model relates to a deep waste heat recovery system for flue gas that simultaneously heats boiler intake air and hot water in the heating network, belonging to the field of waste heat supply technology for coal-fired boilers. Background Technology

[0002] During the heat production process, boilers emit a large amount of high-temperature flue gas. Waste heat recovery from flue gas can not only reduce boiler heat loss, but also reduce fuel consumption and emissions of pollutants such as greenhouse gases, and improve boiler thermal efficiency. Existing flue gas waste heat recovery systems mainly include three types: (1) The first type is to use indirect heat exchangers to realize flue gas waste heat recovery, that is, to use low-temperature economizers or energy savers. Heat exchangers with shell and tube structures are installed on the boiler outlet flue to recover the waste heat of flue gas and heat the boiler feedwater or heating return water. This method is simple and the total cost is relatively low. The disadvantage is that the waste heat recovery rate is low. It is affected by changes in the inlet temperature of the heated water and the flue gas temperature. Usually, the actual temperature difference is only about 20 to 30°C, which is equivalent to about 1% to 2% of the boiler heat production. It is impossible to recover the latent heat of vaporization of water vapor contained in the flue gas, so deep heat recovery cannot be achieved. (2) The second type is to use absorption heat pump flue gas deep recovery technology. By using an absorption heat pump to recover waste heat from flue gas and heat the return water of the heating network, the flue gas temperature can be significantly reduced to about 30°C. The amount of waste heat recovered is equivalent to 8% to 15% of the boiler's heat output, thus achieving deep heat recovery. However, the absorption heat pump requires high-temperature heat sources such as steam for operation, and the flue gas will produce a large amount of acidic condensate, requiring the use of corrosion-resistant heat exchangers, resulting in relatively high equipment investment. (3) The third type is the total heat exchange recovery technology based on air-flue gas. By humidifying the air, the dew point temperature of the flue gas is increased, and the condensation heat of the flue gas is recovered in the tail flue. This method has a simple system structure, requires no additional driving heat source, and has low investment costs. In recent years, the series of patented technologies for "water-steam heat-carrying boiler flue gas waste heat recovery" (patent numbers CN104110675B, CN107166420A, CN206929794U, etc.) jointly developed by Tsinghua University and Beijing Tsinghua Tiangong Energy Technology Research Institute have been widely promoted and applied and have good application prospects. However, the flue gas waste heat spray tower usually extracts heat from the flue gas by using intermediate water. The size of the flue gas waste heat spray tower is very large, and the flue gas side will increase a certain resistance. If the original induced draft fan has insufficient pressure margin, the fan needs to be replaced or a booster induced draft fan needs to be installed. All of the above situations will increase the cost, and sometimes the site does not have the conditions for implementation.

[0003] In recent years, a novel flue gas waste heat recovery technology based on desulfurization slurry flash evaporation has emerged. This technology abandons conventional flue gas waste heat exchangers and instead employs a combination of desulfurization slurry flash evaporation and an absorption heat pump. Heat is extracted from the flue gas through a flash tank from the desulfurization slurry, and the flash vapor is sent to the heat pump for waste heat recovery, heating the return water of the heating network or other process water. The concentrated liquid is returned to the desulfurization circulating water. Its advantages include: no need to modify the flue gas system, reducing on-site implementation difficulty; and better condensate quality, facilitating recycling. However, its disadvantages are also significant: the flue gas temperature can typically only be reduced to 42-45℃, recovering only about half of the waste heat. This is not considered deep heat recovery and can only be considered a partial project, with a large amount of waste heat still escaping from the flue gas. Further modifications are needed to achieve deep heat recovery. The cost per unit of waste heat recovered is relatively high, and the investment payback period is long. The fundamental reasons why it cannot reduce the flue gas temperature to 30°C and achieve deep heat recovery are as follows: First, the desulfurization slurry flash evaporation equipment is a vacuum system, which is complex to integrate and has high requirements for protection. The lower the flash steam temperature, the larger the specific volume, and the larger the equipment volume, the higher the cost. Second, a large amount of non-condensable gases such as SO2 will escape during the flash evaporation of the desulfurization slurry. The flash steam is sent to the absorption heat pump, but it is difficult to create a vacuum during the condensation and heat release process in the horizontal evaporator of the heat pump. The absolute pressure during actual operation can only be maintained at about 7-8 kPa. It is difficult to further increase the vacuum degree with existing equipment and conditions, and it is impossible to further increase the vacuum degree like a conventional condenser. Therefore, the saturation temperature of the flash steam can only be reduced to 38-40°C, resulting in the flue gas temperature being reduced to 40-45°C. Third, this technology is essentially still a heat pump method, only the heat extraction device is different. It still requires a large amount of driving steam, resulting in high operating costs, which worsens the flexibility adjustment problem of thermal power plants, and sometimes even seriously affects the technical and economic benefits of power plants. Utility Model Content

[0004] The purpose and objective of this utility model is to address the inherent technical limitations of the aforementioned flue gas waste heat recovery systems and their impact on the economic efficiency of power plants, and to achieve deep waste heat recovery by utilizing flue gas waste heat in stages without adopting a heat pump method that consumes excessive operating energy. This waste heat can be used to heat the return water of the heating network and the intake air of the low-temperature boiler.

[0005] The specific description of this utility model is as follows: A deep waste heat recovery system for flue gas that simultaneously heats boiler inlet air and hot water network, comprising an original boiler and flue gas treatment subsystem and a flue gas waste heat recovery and utilization subsystem. The original boiler and flue gas treatment subsystem includes an original desulfurization tower 1, an original flue gas inlet pipe 2, an original slurry pump 3, a boiler body 8, an air preheater 9, a high-temperature warm air blower 10, a forced draft fan 11, a dust collector 12, an induced draft fan 13, and their connecting pipes. The key feature is that the flue gas waste heat recovery and utilization subsystem includes a flue gas spray heat exchange module 6 and a low-temperature warm air blower for boiler inlet air 15. The low-temperature process water heater 18 and its supporting components and connecting pipes include a flue gas inlet device 5 located in the lower water tank of the flue gas spray heat exchange module 6. The flue gas inlet of the flue gas inlet device 5 is connected to the outlet section of the clean flue gas Y2 above the desulfurization spray layer 7 inside the original desulfurization tower 1. The upper part of the flue gas inlet device 5 and the lower part of the waste heat spray layer 4 form the spray heat exchange zone. The upper part of the waste heat spray layer 4 is the outlet section of the low-temperature clean flue gas Y3. The outlet of the lower water tank of the flue gas spray heat exchange module 6 is connected to the inlet of the waste hot water circulation pump 16. The outlet of the waste hot water circulation pump 16 is supplied with warm air. The bypass valve 17 is connected to the high-temperature inlet of the boiler inlet low-temperature warm air heater 15. The outlet of the waste hot water circulation pump 16 is also connected to the high-temperature inlet of the low-temperature process water heater 18 via the process water bypass valve 19. The high-temperature outlet of the low-temperature process water heater 18 is connected to the high-temperature outlet of the boiler inlet low-temperature warm air heater 15 and to the spray water inlet of the waste heat spray layer 4. The low-temperature inlet of the low-temperature process water heater 18 is connected to the inlet pipe of the heated low-temperature process water C1, and the low-temperature outlet of the low-temperature process water heater 18 is connected to the outlet pipe of the heated low-temperature process return water C2. Water pipes are connected; the low-temperature side inlet of the boiler air inlet low-temperature warm air blower 15 is connected to the ambient air A0, the low-temperature side outlet of the boiler air inlet low-temperature warm air blower 15 is connected to the air inlet of the high-temperature warm air blower 10 through the connecting pipe of the preheated air A1, the air outlet of the high-temperature warm air blower 10 is connected to the air inlet of the air preheater 9 of the boiler body 8 through the blower 11, and the exhaust port of the air preheater 9 is connected to the original flue gas inlet pipe 2 of the original flue gas Y1 through the dust collector 12 and the induced draft fan 13; the spray inlet of the desulfurization spray layer 7 inside the original desulfurization tower 1 is connected to the slurry outlet of the bottom desulfurization slurry pool through the original slurry pump 3.

[0006] A heat network return water heater 14 is installed on the outlet pipe of the waste hot water circulation pump 16. The high-temperature side inlet of the heat network return water heater 14 is connected to the outlet of the waste hot water circulation pump 16. The high-temperature side outlet of the heat network return water heater 14 is connected to the inlet of the heater bypass valve 17 and the process water bypass valve 19. The low-temperature side inlet of the heat network return water heater 14 is connected to the inlet pipe of the heat network return water supply H1. The low-temperature side outlet of the heat network return water heater 14 is connected to the outlet pipe of the heat network return water return H2.

[0007] The outlet pipe of the waste heat circulation pump 16 is directly connected to the inlet of the heater bypass valve 17 and the process water bypass valve 19. At this time, the flue gas waste heat recovery subsystem also includes a desulfurization slurry flash heat recovery module 28, which includes a flash tank 21, a flash heater 26, and their supporting components and connecting pipes. The slurry inlet of the flash tank 21 is connected to the waste heat slurry outlet of the bottom desulfurization slurry pool of the original desulfurization tower 1 via a waste heat slurry pump 20. The concentrated slurry outlet of the flash tank 21 is connected to the inlet of the original slurry pump 3. A flash steam demister 22 and a washing spray layer 23 are installed in the upper part of the flash tank 21. Its flash steam outlet is connected to the steam inlet of the flash heater 26 via a flash steam connecting pipe 25. The condensate outlet of 6 is connected to the inlet of condensate pump 27, and the outlet of condensate pump 27 is connected to the inlet of washing spray layer 23 and the outlet pipe of external condensate W respectively; the low temperature water inlet of flash heater 26 is connected to the inlet pipe of heat network return water H1, and the low temperature water outlet of flash heater 26 is connected to the outlet pipe of heat network return water H2; the outlet of non-condensable gas S of flash heater 26 is connected to the inlet of vacuum pump 24, and the exhaust port of vacuum pump 24 is connected to the original flue gas inlet pipe 2 of the original desulfurization tower 1; the circulating liquid outlet of the bottom desulfurization slurry tank of the original desulfurization tower 1 is connected to the inlet of original slurry pump 3, the inlet pipe of desulfurization makeup water B and the concentrated slurry outlet of flash tank 21 respectively, and the sewage outlet of the bottom desulfurization slurry tank of the original desulfurization tower 1 is connected to the drainage pipe of desulfurization wastewater P.

[0008] The flue gas spray heat exchange module 6 and the original desulfurization tower 1 are configured as an integrated structure, or as a separate structure.

[0009] The beneficial effects of this utility model are as follows.

[0010] (1) To address the inherent problem of low efficiency in flue gas waste heat recovery systems without heat pumps, such as the scale of waste heat recovery and the extent of flue gas temperature reduction being affected by the return water temperature of the heating network, a tiered utilization of flue gas waste heat is achieved. Specifically, the high-temperature flue gas waste heat is used to heat the return water of the heating network, while the low-temperature flue gas waste heat is used to preheat boiler intake air and other low-temperature process water in winter, including preheating boiler feedwater and demineralized water makeup water. This allows for a greater reduction in exhaust gas temperature and a significant increase in the scale of waste heat recovery, thus enabling deep heat recovery from the flue gas.

[0011] (2) For the recovery of waste heat in the high-temperature section of flue gas and the heating of the heat network return water, a flue gas spray heat exchange module can be used to heat the heat network return water from the high-temperature section of the waste heat circulating water; or a desulfurization slurry flash evaporation method can be used to heat the heat network return water from the flash steam, which is more suitable for scenarios where there is no way to set up a flue gas waste heat spray heat exchange module on site.

[0012] (3) The matching vacuum pump can be a high vacuum model, which can significantly improve the working vacuum of the final stage flash tank and flash steam heat exchanger, which is more conducive to reducing the exhaust temperature and improving the waste heat recovery rate.

[0013] (4) Using the condensate from flash steam to wash the demister in the flash tank can maintain a higher demisting effect and replenish the desulfurization slurry to replace part or all of the original desulfurization replenishment water B. The latter replenishment water source is often wastewater with a high chloride content. After replacing it with the condensate from flash steam, it can help to significantly reduce the discharge flow of desulfurization wastewater P and greatly reduce the secondary pollution and operation and maintenance costs caused by it, and improve the operation effect of the desulfurization system.

[0014] (5) The condensate from the flash steam can also be used as makeup water for the heat network return water, which helps to significantly reduce the amount of softened water produced and its cost; at the same time, the full recycling and utilization of condensate also significantly reduces the consumption of water resources.

[0015] (6) It can preheat the low-temperature process water and boiler air in the plant, effectively saving energy and reducing emissions, and reducing coal consumption and costs.

[0016] (7) The flue gas spray heat exchange module 6 and the original desulfurization tower 1 can be set as an integrated structure according to the on-site installation conditions, which can greatly save the floor space and cost; or they can be set as a separate structure. Attached Figure Description

[0017] Figure 1 , 2 This is a system schematic diagram of this utility model.

[0018] Figure 1 , 2 The component numbers and names are as follows.

[0019] 1. Original desulfurization tower; 2. Original flue gas inlet pipe; 3. Original slurry pump; 4. Waste heat spray layer; 5. Flue gas inlet device; 6. Flue gas spray heat exchange module; 7. Desulfurization spray layer; 8. Boiler body; 9. Air preheater; 10. High-temperature warm air heater; 11. Forced draft fan; 12. Dust collector; 13. Exhaust fan; 14. Heat network return water heater; 15. Boiler inlet low-temperature warm air heater; 16. Waste hot water circulation pump; 17. Warm air heater bypass valve; 18. Low-temperature process water heater; 19. Process water bypass valve; 20. Waste heat slurry pump; 21. Flash tank. 22. Flash steam demister, 23. Washing spray layer, 24. Vacuum pump, 25. Flash steam connecting pipe, 26. Flash steam heater, 27. Condensation pump, 28. Desulfurization slurry flash steam heat recovery module, 29. Ambient air A0, Preheated air A1, Desulfurization makeup water B, Heated low-temperature process water C1, Heated low-temperature process return water C2, Heat network return water H1, Heat network return water H2, Desulfurization wastewater P, Non-condensable gas S, Discharged condensate W, Raw flue gas Y1, Clean flue gas Y2, Low-temperature clean flue gas Y3. Detailed Implementation

[0020] Figure 1 , 2 This is a system schematic diagram and embodiment of the present invention.

[0021] The specific embodiments of this utility model are as follows.

[0022] Embodiment 1 of this utility model, see system schematic diagram. Figure 1 As shown, its specific description is: a deep waste heat recovery system for flue gas that simultaneously heats boiler inlet air and hot water, comprising an original boiler and flue gas treatment subsystem and a flue gas waste heat recovery and utilization subsystem. The original boiler and flue gas treatment subsystem includes an original desulfurization tower 1, an original flue gas inlet pipe 2, an original slurry pump 3, a boiler body 8, an air preheater 9, a high-temperature warm air blower 10, a forced draft fan 11, a dust collector 12, an induced draft fan 13, and their connecting pipes. The characteristic feature is that the flue gas waste heat recovery and utilization subsystem includes a flue gas spray heat exchange module 6, a boiler inlet low-temperature warm air blower 15, and a low-temperature... The process water heater 18 and its supporting components and connecting pipes include a flue gas inlet device 5 located in the lower water tank of the flue gas spray heat exchange module 6. The flue gas inlet of the flue gas inlet device 5 is connected to the outlet section of the clean flue gas Y2 above the desulfurization spray layer 7 inside the original desulfurization tower 1. The upper part of the flue gas inlet device 5 and the lower part of the waste heat spray layer 4 form the spray heat exchange zone. The upper part of the waste heat spray layer 4 is the outlet section of the low-temperature clean flue gas Y3. The outlet of the lower water tank of the flue gas spray heat exchange module 6 is connected to the inlet of the waste hot water circulation pump 16. The outlet of the waste hot water circulation pump 16 passes through a heater. Bypass valve 17 is connected to the high-temperature inlet of boiler inlet low-temperature warm air blower 15. The outlet of waste hot water circulation pump 16 is also connected to the high-temperature inlet of low-temperature process water heater 18 via process water bypass valve 19. The high-temperature outlet of low-temperature process water heater 18 is connected to the high-temperature outlet of boiler inlet low-temperature warm air blower 15 and to the spray water inlet of waste heat spray layer 4. The low-temperature inlet of low-temperature process water heater 18 is connected to the inlet pipe of heated low-temperature process water C1. The low-temperature outlet of low-temperature process water heater 18 is connected to the outlet pipe of heated low-temperature process return water C2. The pipes are connected; the low-temperature side inlet of the boiler air inlet low-temperature warm air blower 15 is connected to the ambient air A0, the low-temperature side outlet of the boiler air inlet low-temperature warm air blower 15 is connected to the air inlet of the high-temperature warm air blower 10 through the connecting pipe of the preheated air A1, the air outlet of the high-temperature warm air blower 10 is connected to the air inlet of the air preheater 9 of the boiler body 8 through the blower 11, and the exhaust port of the air preheater 9 is connected to the original flue gas inlet pipe 2 of the original flue gas Y1 through the dust collector 12 and the induced draft fan 13; the spray inlet of the desulfurization spray layer 7 inside the original desulfurization tower 1 is connected to the slurry outlet of the bottom desulfurization slurry pool through the original slurry pump 3.

[0023] A heat network return water heater 14 is installed on the outlet pipe of the waste hot water circulation pump 16. The high-temperature side inlet of the heat network return water heater 14 is connected to the outlet of the waste hot water circulation pump 16. The high-temperature side outlet of the heat network return water heater 14 is connected to the inlet of the heater bypass valve 17 and the process water bypass valve 19. The low-temperature side inlet of the heat network return water heater 14 is connected to the inlet pipe of the heat network return water supply H1. The low-temperature side outlet of the heat network return water heater 14 is connected to the outlet pipe of the heat network return water return H2.

[0024] The flue gas spray heat exchange module 6 and the original desulfurization tower 1 are designed as separate structures.

[0025] Embodiment 2 of this utility model, see system schematic diagram. Figure 2 As shown, its specific description is as follows: its basic system flow is the same as that of Embodiment 1, but the outlet pipe of the waste hot water circulation pump 16 is not equipped with a heat network return water heater 14. Instead, the outlet pipe of the waste hot water circulation pump 16 is directly connected to the inlet of the heater bypass valve 17 and the process water bypass valve 19. At this time, the flue gas waste heat recovery and utilization subsystem also includes a desulfurization slurry flash heat recovery module 28, which includes a flash tank 21, a flash heater 26 and its supporting components and connecting pipes. The slurry inlet of the flash tank 21 is connected to the waste heat slurry outlet of the bottom desulfurization slurry pool of the original desulfurization tower 1 via a waste heat slurry pump 20. The concentrated slurry outlet of the flash tank 21 is connected to the inlet of the original slurry pump 3. The upper part of the flash tank 21 is equipped with a flash steam demister 22 and a washing spray layer 23. Its flash steam outlet is connected to the flash steam... Connecting pipe 25 is connected to the steam inlet of flash heater 26, the condensate outlet of flash heater 26 is connected to the inlet of condensate pump 27, and the outlet of condensate pump 27 is connected to the inlet of washing spray layer 23 and the outlet pipe of external condensate W respectively; the low temperature water inlet of flash heater 26 is connected to the inlet pipe of heat network return water H1, and the low temperature water outlet of flash heater 26 is connected to the outlet pipe of heat network return water H2; the outlet of non-condensable gas S of flash heater 26 is connected to the air inlet of vacuum pump 24, and the exhaust port of vacuum pump 24 is connected to the original flue gas inlet pipe 2 of original desulfurization tower 1; the circulating liquid outlet of the bottom desulfurization slurry tank of original desulfurization tower 1 is connected to the inlet of original slurry pump 3, the inlet pipe of desulfurization makeup water B and the concentrated slurry outlet of flash tank 21 respectively, and the sewage outlet of the bottom desulfurization slurry tank of original desulfurization tower 1 is connected to the drainage pipe of desulfurization wastewater P. The flue gas spray heat exchange module 6 and the original desulfurization tower 1 are designed as an integrated structure.

[0026] It should be noted that this utility model proposes a technical solution for graded recovery and utilization of flue gas waste heat, and an integrated system and operation strategy for deep flue gas waste heat recovery without the need for a heat pump. According to this overall solution, there can be different specific implementation measures and different structural implementation devices. The above-mentioned specific implementation methods are only a few of them. Any other similar simple modifications, such as simple modifications to the heat exchanger and simple adjustments to the pipeline, fall within the protection scope of this utility model.

Claims

1. A deep waste heat recovery system for flue gas that simultaneously heats boiler inlet air and hot water network, comprising an original boiler and flue gas treatment subsystem and a flue gas waste heat recovery and utilization subsystem, wherein the original boiler and flue gas treatment subsystem includes an original desulfurization tower (1), an original flue gas inlet pipe (2), an original slurry pump (3), a boiler body (8), an air preheater (9), a high-temperature warm air heater (10), a blower (11), a dust collector (12), an induced draft fan (13), and connecting pipes thereof, characterized in that, The aforementioned flue gas waste heat recovery and utilization subsystem includes a flue gas spray heat exchange module (6), a boiler inlet low-temperature warm air heater (15), a low-temperature process water heater (18), and its supporting components and connecting pipes. A flue gas inlet device (5) is installed at the lower water tank of the flue gas spray heat exchange module (6). The flue gas inlet of the flue gas inlet device (5) is connected to the outlet section of the clean flue gas (Y2) above the desulfurization spray layer (7) inside the original desulfurization tower (1). The upper part of the flue gas inlet device (5) is connected to the lower part of the waste heat spray layer (4). In the spray heat exchange zone, the upper part of the waste heat spray layer (4) is the outlet section of the low-temperature clean flue gas (Y3). The outlet of the lower water tank of the flue gas spray heat exchange module (6) is connected to the inlet of the waste hot water circulation pump (16). The outlet of the waste hot water circulation pump (16) is connected to the high-temperature side inlet of the boiler air intake low-temperature warm air heater (15) through the heater bypass valve (17). The outlet of the waste hot water circulation pump (16) is also connected to the high-temperature side inlet of the low-temperature process water heater (18) through the process water bypass valve (19). The high-temperature side outlet of 18) is connected to the high-temperature side outlet of the boiler inlet low-temperature warm air heater (15) and to the spray water inlet of the waste heat spray layer (4). The low-temperature side inlet of the low-temperature process water heater (18) is connected to the inlet pipe of the heated low-temperature process water (C1). The low-temperature side outlet of the low-temperature process water heater (18) is connected to the outlet pipe of the heated low-temperature process return water (C2). The low-temperature side inlet of the boiler inlet low-temperature warm air heater (15) is connected to the ambient air (A0). The low-temperature side outlet is connected to the air inlet of the high-temperature air heater (10) via the preheated air (A1) connecting pipe. The air outlet of the high-temperature air heater (10) is connected to the air inlet of the air preheater (9) of the boiler body (8) via the blower (11). The exhaust port of the air preheater (9) is connected to the original flue gas inlet pipe (2) of the original flue gas (Y1) via the dust collector (12) and the induced draft fan (13). The spray inlet of the desulfurization spray layer (7) inside the original desulfurization tower (1) is connected to the slurry outlet of the bottom desulfurization slurry pool via the original slurry pump (3).

2. The deep waste heat recovery system for flue gas that simultaneously heats boiler inlet air and heating network water as described in claim 1, characterized in that... A heat network return water heater (14) is installed on the outlet pipe of the waste hot water circulation pump (16). The high-temperature side inlet of the heat network return water heater (14) is connected to the outlet of the waste hot water circulation pump (16). The high-temperature side outlet of the heat network return water heater (14) is connected to the inlet of the heater bypass valve (17) and the process water bypass valve (19). The low-temperature side inlet of the heat network return water heater (14) is connected to the inlet pipe of the heat network return water (H1). The low-temperature side outlet of the heat network return water heater (14) is connected to the outlet pipe of the heat network return water (H2).

3. The deep waste heat recovery system for flue gas that simultaneously heats boiler inlet air and heating network water as described in claim 1, characterized in that... The outlet pipe of the waste heat circulation pump (16) is directly connected to the inlet of the heater bypass valve (17) and the process water bypass valve (19). At this time, the waste heat recovery and utilization subsystem of flue gas also includes a desulfurization slurry flash heat recovery module (28), which includes a flash tank (21), a flash heater (26) and its supporting components and connecting pipes. The slurry inlet of the flash tank (21) is connected to the waste heat slurry outlet of the bottom desulfurization slurry pool of the original desulfurization tower (1) via a waste heat slurry pump (20), and the concentrated slurry outlet of the flash tank (21) is connected to the inlet of the original slurry pump (3). The upper part of the flash tank (21) is equipped with a flash steam demister (22) and a washing spray layer (23). Its flash steam outlet is connected to the steam inlet of the flash heater (26) via a flash steam connecting pipe (25). The condensate outlet is connected to the inlet of the condensate pump (27), and the outlet of the condensate pump (27) is connected to the inlet of the washing spray layer (23) and the outlet pipe of the condensate (W) discharge; the low-temperature water inlet of the flash heater (26) is connected to the inlet pipe of the heat network return water (H1), and the low-temperature water outlet of the flash heater (26) is connected to the outlet pipe of the heat network return water (H2); the outlet of the non-condensable gas (S) of the flash heater (26) is connected to the outlet of the non-condensable gas (S). The outlet is connected to the air inlet of the vacuum pump (24), and the exhaust port of the vacuum pump (24) is connected to the original flue gas inlet pipe (2) of the original desulfurization tower (1); the circulating liquid outlet of the bottom desulfurization slurry pool of the original desulfurization tower (1) is connected to the inlet of the original slurry pump (3), the water inlet pipe of the desulfurization makeup water (B) and the concentrated slurry outlet of the flash tank (21), respectively; the sewage outlet of the bottom desulfurization slurry pool of the original desulfurization tower (1) is connected to the drainage pipe of the desulfurization wastewater (P).

4. The deep waste heat recovery system for flue gas that simultaneously heats boiler inlet air and heating network water as described in claim 1, characterized in that... The flue gas spray heat exchange module (6) and the original desulfurization tower (1) are configured as an integrated structure or as a separate structure.

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