Combined cycle unit waste heat boiler low-temperature flue gas latent heat recovery heating system

Abstract

The invention discloses a low-temperature flue gas latent heat recovery heating system for a combined cycle unit waste heat boiler, and aims to improve the energy utilization efficiency. The system is mainly composed of a gas turbine, a steam turbine, a generator, a waste heat boiler and a heat supply pipe network, and heat in flue gas is gradually recovered through a three-stage flue gas heat exchanger. Heat supply network return water is divided into two paths: one path directly enters the flue gas primary heat exchanger to recover sensible heat; and the other path recovers sensible heat and latent heat at deeper levels through the absorption heat pump I and the absorption heat pump II. In order to further improve the heat energy recovery effect, an absorption heat pump III is further added in the system, a third intermediate medium circulation loop is arranged between the absorption heat pump III and the flue gas third-stage heat exchanger, and branches of the first path of outlet water and the outlet water of the first medium circulation loop can be retreated. The system is coupled with a combined cycle unit, a new flue gas waste heat recovery heating technological process is constructed, the waste heat grade is improved, better economic benefits can be obtained, and better environmental benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of waste heat recovery and utilization, and in particular to a heating system for recovering latent heat of low-temperature flue gas from a waste heat boiler of a combined cycle unit. Background Art

[0002] Gas-steam combined cycle heating units generally have the problem of high exhaust temperature. The amount of low-temperature waste heat (below 100°C) in the flue gas is huge. Lowering the exhaust temperature and improving the efficiency of natural gas utilization are effective means to promote energy conservation and emission reduction and increase heating capacity.

[0003] At present, flue gas waste heat recovery generally adopts direct heat exchange between heat network return water (which is the cold source) and flue gas (which is the heat source) for heating, such as patent application number: CN201010141597.3. An energy supply system based on gas-steam combined cycle cogeneration belongs to the field of energy technology. The system adopts a flue gas condensation heat exchanger, a condenser, a steam-type absorption heat pump, a high-temperature flue gas heat exchanger, and a steam-water heat exchanger for combined heating on the heat source side; the heat network return water directly recovers the low-temperature flue gas condensation waste heat, the high-temperature flue gas waste heat or the condensation waste heat, and the steam-driven steam absorption heat pump is used to recover the condensation exhaust heat or part of the flue gas waste heat. In winter, the user end uses the supplementary hot water absorption heat pump and the water-water heat exchanger to heat the secondary heat network water for heating, and at the same time extracts low-grade heat from the shallow soil source, groundwater source or geothermal water resources for heating; in summer, the hot water of the heat network is cooled by the hot water absorption heat pump, dehumidified by the liquid dehumidification air conditioner, and preheated by the domestic hot water at the user end. Its defect is that the high-temperature flue gas of the waste heat boiler only exchanges heat with the return water of the heat network through two sets of heat exchangers: high-temperature flue gas heat exchanger 9 and flue gas condensing heat exchanger 10. The heat exchange equipment used in the high-temperature flue gas heat exchanger 9 and flue gas condensing heat exchanger 10 is a plate or shell and tube heat exchanger. Limited by the 45-60℃ heating return water temperature and the step difference of the heat exchanger, the flue gas temperature can only be reduced from 100℃ to about 50℃, and the sensible heat is recovered, and the recovered flue gas waste heat is limited. After the flue gas temperature drops below 50 degrees, the waste heat of the flue gas latent heat is not recovered, the heat recovery is unreasonable, the energy cascade utilization is poor, and the flue gas below 50 degrees is released into the atmosphere. This part of heat accounts for about 10% of the input of the low calorific value calculation of natural gas.

[0004] In view of the above, how to further improve the heating capacity of the unit, it is necessary to propose a combined cycle unit waste heat boiler low-temperature flue gas latent heat recovery heating system to solve the above problems. Summary of the invention

[0005] The object of the present invention is to overcome the defects in the prior art and provide a heating system for recovering latent heat of low-temperature flue gas from a waste heat boiler of a combined cycle unit.

[0006] To achieve the above-mentioned purpose, the technical solution of the present invention is as follows: a combined cycle unit waste heat boiler low-temperature flue gas latent heat recovery heating system, comprising a gas turbine, a steam turbine, a generator, a waste heat boiler, and a heating pipe network; a flue gas primary heat exchanger, a flue gas secondary heat exchanger, and a flue gas tertiary heat exchanger are sequentially arranged on the flue gas discharge pipe of the waste heat boiler; The return water from the heat network is divided into two routes. The first route enters the primary flue gas heat exchanger to directly recover the sensible heat in the flue gas. In addition, the second route recovers the sensible heat and latent heat in the flue gas through the absorption heat pump II and the absorption heat pump I, and then merges with the water output of the first route and sends it to the heat network for water supply; a second intermediate medium circulation loop is provided between the absorption heat pump II and the secondary flue gas heat exchanger; a first intermediate medium circulation loop is provided between the absorption heat pump I and the primary flue gas heat exchanger; It also includes an absorption heat pump III, and a third medium circulation loop is arranged between the absorption heat pump III and the flue gas tertiary heat exchanger. Branch pipes are arranged on the first outlet water on the flue gas primary heat exchanger and the outlet water of the first medium circulation loop to merge and be connected to the absorption heat pump III, and the outlet water flows back to the heat network return water.

[0007] The absorption heat pump I, absorption heat pump II and absorption heat pump III are all driven by steam turbine exhaust to provide heat sources.

[0008] Furthermore, the absorption heat pump II includes a generator II, a condenser II, an evaporator II, and an absorber II. A second intermediate medium circulation loop is formed between the evaporator II and the secondary flue gas heat exchanger; the steam turbine is provided with an exhaust connection to the generator II.

[0009] Furthermore, the secondary flue gas heat exchanger is a low-resistance partition-wall flue gas / water heat exchanger, which reduces the flue gas temperature to below the dew point and deeply recovers the sensible heat and latent heat in the flue gas; the medium circulating in the second intermediate medium circulation loop is intermediate water, and the second intermediate medium circulation loop is provided with an intermediate water circulation pump II.

[0010] Furthermore, the second path passes through absorber II and condenser II in absorption heat pump II in sequence; a bypass regulating pipe is arranged at the point where the second path passes through absorption heat pump II.

[0011] Furthermore, the heat source end of the flue gas primary heat exchanger is the high-temperature flue gas of the waste heat boiler, and the cold source end is divided into two paths, one of which comes directly from the return water of the heating network to increase the water temperature of the heating network, and the other comes from the first intermediate medium circulation loop; the absorption heat pump I includes a generator I, a condenser I, an evaporator I, and an absorber I; the first intermediate medium circulation loop is connected to the evaporator I, and a circulation pump I is provided on the first intermediate medium circulation loop; the second path enters the absorption heat pump I after passing through the absorption heat pump II and / or the bypass regulating pipe and flows out through the absorber I and the condenser I in turn and is sent to the heating network for water supply.

[0012] Furthermore, the absorption heat pump III includes a generator III, a condenser III, an evaporator III, and an absorber III. The third intermediate medium circulation loop passes through the absorber III and the condenser III in the absorption heat pump III in sequence; the branch pipes of the first water outlet on the primary flue gas heat exchanger and the first medium circulation loop water outlet are connected to the evaporator III, and the branch pipes are provided with a circulation pump III.

[0013] A heating method for a combined cycle unit waste heat boiler low-temperature flue gas latent heat recovery heating system includes flue gas sensible heat and latent heat recovery. High-temperature flue gas generated by a gas turbine enters the waste heat boiler and passes through a primary flue gas heat exchanger, a secondary flue gas heat exchanger and a tertiary flue gas heat exchanger in sequence on a flue gas discharge pipeline. The primary flue gas heat exchanger directly recovers sensible heat from the high-temperature flue gas. The secondary flue gas heat exchanger is a low-resistance partition-type heat exchanger, which reduces the flue gas temperature to below the dew point and deeply recovers the sensible heat and latent heat in the flue gas. The tertiary flue gas heat exchanger further reduces the flue gas temperature and continues to recover the remaining heat. Two-way treatment of heat network return water: The first route: the return water from the heating network directly enters the primary flue gas heat exchanger to recover the sensible heat in the flue gas, and then the water temperature is increased before being sent to the heating network for water supply; Second route: The return water from the heat network passes through absorption heat pump II and absorption heat pump I to recover the sensible heat and latent heat in the flue gas. This water flow first passes through absorber II and condenser II in absorption heat pump II, and then merges with the first water flow and is sent to the heat network for water supply;

[0014] Applications of absorption heat pumps: Absorption heat pumps I, II, and III all use steam turbine exhaust as the driving heat source; Absorption heat pump I: A first intermediate medium circulation loop is provided between the first flue gas heat exchanger to further increase the hot water temperature; Absorption heat pump II: A second intermediate medium circulation loop is provided between the secondary flue gas heat exchanger, and heat is exchanged through evaporator II to recover the heat in the flue gas; Absorption heat pump III: A third intermediate medium circulation loop is provided between the flue gas three-stage heat exchanger, which is used to assist in regulating the energy distribution in the system and return part of the water flow to the heat network to optimize the overall thermal efficiency; Regulation of bypass regulating tube: A bypass regulating pipe is provided at the absorption heat pump II, which can be used to adjust the flow rate and temperature of the second water flow to ensure stable operation of the system and efficient heat recovery.

[0015] The advantages and beneficial effects of the present invention are as follows: a combined cycle unit waste heat boiler low-temperature flue gas latent heat recovery heating system of the present invention effectively recovers the waste heat of the flue gas by setting a multi-stage flue gas heat exchanger at the tail of the waste heat boiler, reduces the flue gas temperature to below the dew point, effectively utilizes the flue gas waste heat in a cascade manner, improves the utilization efficiency of the waste heat, deeply recovers the sensible heat and latent heat in the flue gas, and improves the thermal efficiency of the combined cycle unit. When there are multi-stage flue gas heat exchangers, condensed water absorbs acidic gases such as SO2 and NOX in the flue gas at the same time, which can improve the local environmental quality. Coupled with the combined cycle unit, a new flue gas waste heat recovery heating process is constructed. The ultra-low temperature flue gas waste heat recovery heating system of the combined cycle unit waste heat boiler based on the absorption heat pump technology improves the quality of waste heat, which can obtain better economic benefits and better environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is one of the schematic diagrams of the process of a heating system for recovering latent heat of low-temperature flue gas from a waste heat boiler of a combined cycle unit according to the present invention; Figure 2 This is the second schematic diagram of the process of a combined cycle unit waste heat boiler low-temperature flue gas latent heat recovery heating system of the present invention; Figure 3 It is a schematic diagram of the process of the absorption heat pump II in the present invention; In the figure: 1. gas turbine; 2. steam turbine; 3. generator; 4. waste heat boiler; 5. heating network; 6. primary flue gas heat exchanger; 7. secondary flue gas heat exchanger; 8. tertiary flue gas heat exchanger; 9. first route; 10. second route; 11. absorption heat pump I; 12. absorption heat pump II; 13. first intermediate medium circulation loop; 14. second intermediate medium circulation loop; 15. absorption heat pump III; 16. third medium circulation loop; 17. intermediate water circulation pump II; 18. bypass regulating pipe; 19. circulation pump III; 20. circulation pump I; 21. low resistance partition type flue gas / water heat exchanger; 22. main chimney; 23. generator II; 24. condenser II; 25. evaporator II; 26. absorber II; 27. circulation pump IV. DETAILED DESCRIPTION

[0017] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0018] A combined cycle unit waste heat boiler low temperature flue gas latent heat recovery heating system, such as Figure 1-3As shown, it includes a gas turbine 1, a steam turbine 2, a generator 3, a waste heat boiler 4, and a heating network 5; a flue gas primary heat exchanger 6, a flue gas secondary heat exchanger 7, and a flue gas tertiary heat exchanger 8 are sequentially arranged on the flue gas discharge pipe of the waste heat boiler 4; the flue gas primary heat exchanger 6 directly exchanges heat with the return water of the heating network 5 at a temperature of about 500 degrees Celsius from the high-level exhaust gas of the waste heat boiler 4, so that the sensible heat in the exhaust gas is directly transferred to the heating network, and the flue gas temperature after the primary heat exchange is reduced, which can be rationally It should be noted that the figure only schematically shows one primary flue gas heat exchanger 6. In actual use, multiple primary flue gas heat exchangers 6 can be arranged and connected in parallel or in series to form step-by-step heat exchange and cooling. From the perspective of waste heat utilization of the flue gas, the flue gas temperature is reduced to about 50 degrees Celsius after passing through the primary flue gas heat exchanger 6. At this time, limited by the 45-60°C heating return water temperature and the step difference of the heat exchanger, the flue gas temperature can only be reduced to about 50°C, and the sensible heat in the flue gas is recovered in the primary flue gas heat exchanger 6. After the flue gas temperature drops below 50 degrees, its latent heat still needs to be utilized. Specifically, a flue gas secondary heat exchanger 7 is set, and the second intermediate medium circulation loop 14 is connected to the absorption heat pump II 12. In this embodiment, the absorption heat pump II 12 is mainly used to absorb and utilize the latent heat below 50 degrees Celsius in the flue gas. After passing through the flue gas secondary heat exchanger 7, the flue gas temperature is reduced to about 30 degrees Celsius. Since the flue gas contains about 15% moisture, if it is directly discharged, the wet saturated flue gas in the exhaust gas after being discharged into the atmosphere will be rapidly cooled during the diffusion process after being discharged through the main chimney 22, and condensed droplets will be precipitated to form white plumes. In order to avoid visual pollution, this embodiment is provided with a flue gas tertiary heat exchanger 8, and the flue gas is slightly heated by the absorption heat pump III 15. Specifically, an absorption heat pump III 15 is provided. Pump III15, a third medium circulation loop 16 is provided between the absorption heat pump III15 and the flue gas tertiary heat exchanger 8, a branch pipe is set at the first outlet water 9 on the flue gas primary heat exchanger 6 and the first medium circulation loop outlet water, and the branch pipe is connected to the absorption heat pump III15; the absorption heat pump III15 includes a generator III, a condenser III, an evaporator III, and an absorber III, and the third intermediate medium circulation loop passes through the absorber III and the condenser III in the absorption heat pump III15 in sequence; the branch pipes of the first outlet water 9 on the flue gas primary heat exchanger 6 and the first medium circulation loop outlet water are connected to the evaporator III, and a circulation pump III19 is provided on the branch pipe, and the heat of the flue gas primary heat exchanger 6 is transferred to the evaporator III through forced reflux by the circulation pump III19, and then sent back to the heat network return water for another heating cycle.

[0019] The energy of the absorption heat pump III 15 comes from part of the hot water in the hot water network after being heated by the flue gas primary heat exchanger 6 and the exhaust gas of the steam turbine 2 to drive the absorption heat pump III 15; thus, the "whitening" problem of flue gas can be solved with less energy input.

[0020] Specifically, from the perspective of the heating network 5, Figure 1 , 2 As shown, the return water from the heat network is divided into two routes, the first route 9 enters the flue gas primary heat exchanger 6 to directly recover the sensible heat in the flue gas; the second route 10 recovers the sensible heat and latent heat in the flue gas through the absorption heat pump II 12 and the absorption heat pump I 11, and is sent to the heat network water supply after merging with the water outlet of the first route 9; a second intermediate medium circulation loop 14 is provided between the absorption heat pump II 12 and the flue gas secondary heat exchanger 7; a first intermediate medium circulation loop 13 is provided between the absorption heat pump I 11 and the flue gas primary heat exchanger 6; it can be understood that in the first route 9, the return water from the heat network directly divides part of the flow to directly exchange heat with the high-temperature flue gas, and the return water from the heat network directly heats up using the sensible heat in the flue gas, and is sent to the heat network water supply for heating. It can be understood that the route can be used in conjunction with flow regulation and other methods to control the flow entering the heat network water supply The temperature meets the demand; in addition, in the second path 10, part of the flow of the heat network return water is heated from the second path 10, and the working temperature of the flue gas primary heat exchanger 6 is higher than the working temperature of the flue gas secondary heat exchanger 7. The absorption heat pump II 12 is driven by the latent heat below 50 degrees Celsius in the recovered flue gas and the energy of the steam turbine 2 exhaust, so that the absorption heat pump II 12 performs preliminary heating of the heat network return water. After flowing out of the absorption heat pump II 12, it immediately enters the absorption heat pump I 11. The absorption heat pump I 11 uses the first intermediate medium circulation loop 13 and the steam turbine 2 exhaust as a drive, and can perform secondary heating on the heat network return water, thereby realizing the effective utilization of the flue gas waste heat in stages. After two-stage heating, the hot network water of the second path 10 merges with the hot network water of the first path 9 to provide heating to the heating users.

[0021] like Figure 1 , 2 As shown, the absorption heat pump I 11, absorption heat pump II 12, and absorption heat pump III 15 are all driven by steam turbine 2. When in use, each steam pipeline is provided with a regulating valve to supply steam according to the amount of steam used by each absorption heat pump.

[0022] The absorption heat pump II 12 includes a generator II 23, a condenser II 24, an evaporator II 25, and an absorber II 26. Figure 2 , 3As shown, a second intermediate medium circulation loop 14 is formed between the evaporator II 25 and the secondary flue gas heat exchanger 7; the steam turbine 2 is provided with an exhaust connection to the generator II 23. The secondary flue gas heat exchanger 7 is a low-resistance partition-type flue gas / water heat exchanger 21, which reduces the flue gas temperature to below the dew point and deeply recovers the sensible heat and latent heat in the flue gas; the medium circulating in the second intermediate medium circulation loop 14 is intermediate water, and the second intermediate medium circulation loop 14 is provided with an intermediate water circulation pump II 17. The return water of the heating network enters the absorber II 26 and the condenser II 24 in turn, and is merged into the heating network after being heated. The steam is driven into the generator II 23 to release heat, and the condensed water returns to the condensate recovery system of the power plant.

[0023] Arrange a partition-type flue gas / water heat exchanger in the flue. Preferably, a low-resistance new partition-type flue gas / water heat exchanger is selected. The intermediate water circulation pump Ⅱ17 is arranged on the return water pipeline of the partition-type flue gas / water heat exchanger. The flue gas is cooled to below the dew point by the low-resistance new partition-type flue gas / water heat exchanger, and the sensible heat and latent heat in the flue gas are deeply recovered. After the steam from the power plant, which serves as the heat source driving the absorption heat pump Ⅱ12 unit, releases heat, the condensate enters the condensate recovery system of the power plant. The absorption heat pump group heats up the return water of the heating network, and the heated return water of the heating network enters the absorption heat pump Ⅰ11 to continue to heat up, or it can be directly supplied as the heating network water supply through the heating network circulation pump.

[0024] The heat source end of the flue gas primary heat exchanger 6 is the high-temperature flue gas of the waste heat boiler 4, and the cold source end is divided into two paths, one of which comes directly from the return water of the heat network to increase the water temperature of the heat network, and the other comes from the first intermediate medium circulation loop 13; the absorption heat pump I11 includes a generator I, a condenser I, an evaporator I, and an absorber I; the first intermediate medium circulation loop 13 is connected to the evaporator I, and a circulation pump I20 is provided on the first intermediate medium circulation loop 13; the second path 10 enters the absorption heat pump I11 after passing through the absorption heat pump II12 and / or the bypass regulating pipe 18, and flows out through the absorber I and the condenser I in turn, and then is sent to the heat network water supply. Thus, the second path 10 heats the water of the heat network at the second path 10 at a secondary temperature increase.

[0025] Furthermore, the second path 10 passes through the absorber II 26 and the condenser II 24 in the absorption heat pump II 12 in sequence; the second path 10 is provided with a bypass regulating pipe 18 at the point where it passes through the absorption heat pump II 12. By controlling the opening of the bypass regulating pipe 18 and the opening of the pipeline passing through the absorption heat pump II 12, the heating ratio of the hot water in the second path 10 is controlled, thereby achieving more accurate temperature control.

[0026] This system recovers the waste heat of low-grade flue gas for heating, reducing heating operating costs and increasing heating revenue; it reduces the flue gas temperature to below the dew point, deeply recovers the sensible heat and latent heat in the flue gas, and the condensed water absorbs acidic gases such as SO2 and NOX in the flue gas at the same time, which can improve the local environmental quality.

[0027] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A combined cycle unit waste heat boiler low-temperature flue gas latent heat recovery heating system, comprising a gas turbine (1), a steam turbine (2), a generator (3), a waste heat boiler (4), and a heating pipe network (5); characterized in that: A primary flue gas heat exchanger (6), a secondary flue gas heat exchanger (7), and a tertiary flue gas heat exchanger (8) are sequentially arranged on the flue gas discharge pipe of the waste heat boiler (4); The return water from the heat network is divided into two routes, the first route (9) enters the primary flue gas heat exchanger (6) to directly recover the sensible heat in the flue gas; In addition, the second path (10) recovers sensible heat and latent heat in the flue gas through the absorption heat pump II (12) and the absorption heat pump I (11), and then merges with the water output from the first path (9) and is sent to the heat network for water supply; a second intermediate medium circulation loop (14) is provided between the absorption heat pump II (12) and the secondary flue gas heat exchanger (7); a first intermediate medium circulation loop (13) is provided between the absorption heat pump I (11) and the primary flue gas heat exchanger (6); It also includes an absorption heat pump III (15), wherein a third medium circulation loop (16) is provided between the absorption heat pump III (15) and the flue gas tertiary heat exchanger (8), and a branch pipe is provided at the outlet water of the first path (9) on the flue gas primary heat exchanger (6) and the outlet water of the first medium circulation loop to be connected to the absorption heat pump III (15), and the outlet water of this path flows back to the heat network return water; The absorption heat pump I (11), absorption heat pump II (12), and absorption heat pump III (15) are all driven by exhaust gas from the steam turbine (2) to provide a heat source.

2. A combined cycle unit waste heat boiler low-temperature flue gas latent heat recovery heating system according to claim 1, characterized in that: The absorption heat pump II (12) comprises a generator II (23), a condenser II (24), an evaporator II (25), and an absorber II (26); a second intermediate medium circulation loop (14) is formed between the evaporator II (25) and the secondary flue gas heat exchanger (7); and the steam turbine (2) is provided with an exhaust gas connection to the generator II (23).

3. A combined cycle unit waste heat boiler low-temperature flue gas latent heat recovery heating system according to claim 2, characterized in that: The flue gas secondary heat exchanger (7) is a low-resistance partition-type flue gas / water heat exchanger (21), which reduces the flue gas temperature to below the dew point and deeply recovers the sensible heat and latent heat in the flue gas; the medium circulating in the second intermediate medium circulation loop (14) is intermediate water, and the second intermediate medium circulation loop (14) is provided with an intermediate water circulation pump II (17).

4. A combined cycle unit waste heat boiler low-temperature flue gas latent heat recovery heating system according to claim 2, characterized in that: The second path (10) passes through the absorber II (26) and the condenser II (24) in the absorption heat pump II (12) in sequence; a bypass regulating pipe (18) is provided at the point where the second path (10) passes through the absorption heat pump II (12).

5. A combined cycle unit waste heat boiler low-temperature flue gas latent heat recovery heating system according to claim 4, characterized in that: The heat source end of the flue gas primary heat exchanger (6) is the high-temperature flue gas of the waste heat boiler (4), and the cold source end is divided into two paths, one of which is directly from the return water of the heating network for increasing the water temperature of the heating network, and the other is from the first intermediate medium circulation loop (13); the absorption heat pump I (11) comprises a generator I, a condenser I, an evaporator I, and an absorber I; the first intermediate medium circulation loop (13) is connected to the evaporator I, and a circulation pump I (20) is provided on the first intermediate medium circulation loop (13); the second path (10) enters the absorption heat pump I (11) after passing through the absorption heat pump II (12) and / or the bypass regulating pipe (18), and flows out through the absorber I and the condenser I in sequence, and is then sent to the heating network for water supply.

6. The combined cycle unit waste heat boiler low-temperature flue gas latent heat recovery heating system according to claim 1, characterized in that: The absorption heat pump III (15) comprises a generator III, a condenser III, an evaporator III, and an absorber III. The third intermediate medium circulation loop passes through the absorber III and the condenser III in the absorption heat pump III (15) in sequence. The branch pipes of the first water outlet (9) and the first medium circulation loop on the primary flue gas heat exchanger (6) are connected to the evaporator III, and the branch pipes are provided with a circulation pump III (19).

7. A combined cycle unit waste heat boiler low temperature flue gas latent heat recovery heating system according to claim 6, characterized in that: The third medium circulation loop (16) is provided with a circulation pump IV (27).

8. The heating method of a combined cycle unit waste heat boiler (4) low-temperature flue gas latent heat recovery heating system according to claim 1, characterized in that: The invention comprises flue gas sensible heat and latent heat recovery, wherein the high-temperature flue gas generated by the gas turbine (1) enters the waste heat boiler (4), and passes through the primary flue gas heat exchanger (6), the secondary flue gas heat exchanger (7) and the tertiary flue gas heat exchanger (8) in sequence on the flue gas discharge pipeline; the primary flue gas heat exchanger (6) directly recovers sensible heat from the high-temperature flue gas; the secondary flue gas heat exchanger (7) is a low-resistance partition-type heat exchanger, which reduces the flue gas temperature to below the dew point, and deeply recovers the sensible heat and latent heat in the flue gas; the tertiary flue gas heat exchanger (8) further reduces the flue gas temperature and continues to recover the remaining heat; Two-way treatment of heat network return water: First route (9): the return water from the heating network directly enters the primary flue gas heat exchanger (6), recovers the sensible heat in the flue gas, raises the water temperature and then sends it to the heating network for water supply; The second route (10): The return water from the heat network passes through the absorption heat pump II (12) and the absorption heat pump I (11) to recover the sensible heat and latent heat in the flue gas. The water flow in this route first passes through the absorber II (26) and the condenser II (24) in the absorption heat pump II (12), and then merges with the water flow of the first route (9) and is sent to the heat network for water supply; Applications of absorption heat pumps: Absorption heat pumps I (11), II and III all use the exhaust gas from the steam turbine (2) as a driving heat source; Absorption heat pump I (11): a first intermediate medium circulation loop (13) is provided between the absorption heat pump I (11) and the primary flue gas heat exchanger (6) to further increase the temperature of the hot water; Absorption heat pump II (12): a second intermediate medium circulation loop (14) is provided between the second flue gas heat exchanger (7) and the second intermediate medium circulation loop (14) is provided to perform heat exchange through evaporator II (25) to recover heat from the flue gas; Absorption heat pump III (15): a third intermediate medium circulation loop is provided between the third-stage flue gas heat exchanger (8), which is used to assist in regulating the energy distribution in the system and to return part of the water flow to the heat network to optimize the overall thermal efficiency; Regulation of the bypass regulating tube (18): A bypass regulating pipe (18) is provided at the point where the absorption heat pump II (12) passes, and can be used to adjust the flow rate and temperature of the water flow in the second path (10), thereby ensuring stable operation of the system and efficient heat recovery.

Images