Variable load type efficient heat exchanger

Abstract

The utility model relates to a variable load type efficient heat exchanger which comprises a plurality of heat exchanger modules which are arranged side by side front and back, the air side and the smoke side of each heat exchanger module are respectively connected through an air duct system and a flue system, and the air duct system is provided with an air inlet, two air outlets and a plurality of air duct baffle valves. The flue system is provided with a flue gas inlet, two flue gas outlets and a plurality of flue baffle valves. According to the utility model, the circulation of flue gas and air in each heat exchanger module is controlled through the opening and closing of the plurality of baffle valves, so that parameters such as net circulation sectional area, tube pass number, heat exchange area and the like in the heat exchanger are changed, and finally, the purpose of changing the load of the heat exchanger is achieved.

Description

Technical Field

[0001] This utility model relates to the fields of petroleum refining, petrochemical and coal chemical technology, and specifically to a variable load high-efficiency heat exchanger applied to waste heat recovery systems of heating furnaces in the petroleum refining, petrochemical and coal chemical industries. Background Technology

[0002] Heat exchangers are widely used in the petroleum refining, petrochemical, and coal chemical industries. An air preheater is a type of heat exchanger that uses the heat from the exhaust gas of heating furnaces and other equipment to preheat air. Its function is to reduce the exhaust gas temperature of heating furnaces and other equipment, improve thermal efficiency, make fuel easier to ignite, ensure stable combustion, and enhance combustion efficiency.

[0003] However, the air preheaters used in waste heat recovery systems of heating furnaces in the petroleum refining, petrochemical, and coal chemical industries both domestically and internationally are all fixed-load heat exchangers, meaning that the net flow cross-sectional area and heat exchange area inside the heat exchanger remain constant. Sometimes, the actual operating conditions of the heating furnace differ significantly from the original design conditions. In such cases, it is difficult for these fixed-load heat exchangers to meet the requirements of different operating conditions. This phenomenon is the main reason for the frequent modifications to waste heat recovery systems and the frequent replacement of air preheaters in the industry. Utility Model Content

[0004] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a variable load high-efficiency heat exchanger. By opening and closing multiple baffle valves, the flow of flue gas and air within each heat exchanger module is controlled, thereby changing parameters such as the net flow cross-sectional area, number of tube passes, and heat exchange area inside the heat exchanger, and ultimately changing the load of the heat exchanger.

[0005] The purpose of this utility model is achieved as follows:

[0006] A variable load high-efficiency heat exchanger includes multiple heat exchanger modules arranged side-by-side. The air side and flue gas side of each heat exchanger module are connected by a duct system and a flue system, respectively. The duct system has one air inlet, two air outlets, and multiple duct damper valves. The flue system has one flue gas inlet, two flue gas outlets, and multiple flue gas damper valves. Each heat exchanger module has air branch pipes at both ends on the air side. The air branch pipes on the air inlet side converge at the air inlet, and the air branch pipes on the air outlet side converge at the first air outlet. Each air branch pipe and each air outlet is equipped with a duct damper valve. Similarly, each heat exchanger module has flue gas branch pipes at both ends on the flue gas side. The flue gas branch pipes on the flue gas inlet side converge at the flue gas inlet, and the flue gas branch pipes on the flue gas outlet side converge at the first flue gas outlet. Each flue gas branch pipe and each flue gas outlet is equipped with a flue gas damper valve.

[0007] Preferably, the second air outlet of the air duct system is located on the air branch pipe corresponding to the first or last heat exchanger module, and the second flue gas outlet of the flue system is located on the flue gas branch pipe of the first or last heat exchanger module.

[0008] Preferably, it includes two heat exchanger modules, namely a first heat exchanger module and a second heat exchanger module from front to back. A first air duct baffle valve and a second air duct baffle valve are respectively installed in the air branch pipes on the air inlet side of the first heat exchanger module and the air outlet side of the second heat exchanger module. A third air duct baffle valve and a fourth air duct baffle valve are respectively installed in the air branch pipes on the air outlet side of the first heat exchanger module and the second heat exchanger module. The air branch pipes on the air inlet side of the first heat exchanger module and the second heat exchanger module converge at the air inlet. The air branch pipes on the air outlet side of the first heat exchanger module and the second heat exchanger module converge at the first air outlet. A fifth air duct baffle valve is installed at the first air outlet.

[0009] The flue gas branch pipes on the flue gas inlet side of the first heat exchanger module and the second heat exchanger module are respectively equipped with a first flue gas damper valve and a second flue gas damper valve. The flue gas branch pipes on the flue gas outlet side of the first heat exchanger module and the second heat exchanger module are respectively equipped with a third flue gas damper valve and a fourth flue gas damper valve. The flue gas branch pipes on the flue gas inlet side of the first heat exchanger module and the second heat exchanger module converge at the flue gas inlet. The flue gas branch pipes on the flue gas outlet side of the first heat exchanger module and the second heat exchanger module converge at the first flue gas outlet. A fifth flue gas damper valve is provided at the first flue gas outlet.

[0010] Preferably, the branch pipe where the second air outlet is located is connected to the air inlet side air branch pipe of the first heat exchanger module, and the branch pipe where the second air outlet is located is located after the first air duct baffle valve, and a sixth air duct baffle valve is provided at the second air outlet.

[0011] The branch pipe where the second flue gas outlet is located is connected to the flue gas branch pipe on the flue gas inlet side of the second heat exchanger module, and the branch pipe where the second flue gas outlet is located is set after the second flue damper valve. A sixth flue damper valve is provided at the second flue gas outlet.

[0012] Preferably, it includes three heat exchanger modules, namely, a second heat exchanger module, a first heat exchanger module, and a third heat exchanger module, arranged from front to back. A first air duct baffle valve, a second air duct baffle valve, and a seventh air duct baffle valve are correspondingly installed in the air branch pipes on the air inlet side of the first, second, and third heat exchanger modules. A third air duct baffle valve, a fourth air duct baffle valve, and an eighth air duct baffle valve are correspondingly installed in the air branch pipes on the air outlet side of the first, second, and third heat exchanger modules. The air branch pipes on the air inlet side of the first, second, and third heat exchanger modules converge at the air inlet, and the air branch pipes on the air outlet side of the first, second, and third heat exchanger modules converge at the first air outlet. The air outlets converge at the first air outlet, where a fifth duct damper valve is installed. The flue gas branch pipes on the flue gas inlet side of the first, second, and third heat exchanger modules are equipped with corresponding first, second, and seventh flue gas damper valves. The flue gas branch pipes on the flue gas outlet side of the first, second, and third heat exchanger modules are equipped with corresponding third, fourth, and eighth flue gas damper valves. The flue gas branch pipes on the flue gas inlet side of the first, second, and third heat exchanger modules converge at the flue gas inlet, and the flue gas branch pipes on the flue gas outlet side of the first, second, and third heat exchanger modules converge at the first flue gas outlet, where a fifth flue gas damper valve is installed.

[0013] Preferably, the branch pipe where the second air outlet is located is connected to the air outlet side air branch pipe of the third heat exchanger module, and the branch pipe where the second air outlet is located is set before the eighth air duct baffle valve, and the sixth air duct baffle valve is provided at the second air outlet.

[0014] The branch pipe where the second flue gas outlet is located is connected to the flue gas branch pipe on the flue gas outlet side of the second heat exchanger module, and the branch pipe where the second flue gas outlet is located is set before the fourth flue damper valve. The sixth flue damper valve is provided at the second flue gas outlet.

[0015] Preferably, the air inlet side air branch pipes of the first heat exchanger module and the third heat exchanger module are connected by an air bypass pipe. The air bypass pipe is located after the first air duct baffle valve and the seventh air duct baffle valve, and a ninth air duct baffle valve is provided on the air bypass pipe.

[0016] The flue gas branch pipes on the flue gas inlet side of the first heat exchanger module and the second heat exchanger module are connected by a flue gas bypass pipe. The flue gas bypass pipe is located after the first flue damper valve and the second air duct damper valve, and a ninth flue damper valve is provided on the air bypass pipe.

[0017] The beneficial effects of this utility model are:

[0018] 1. Under the high flow rate condition of the heating furnace, by adjusting the opening and closing of each baffle valve on the flue system and air duct system, the heat exchanger modules can be put into operation in parallel, so that the heat exchangers can meet the requirements of this condition.

[0019] 2. Under low flow conditions of the heating furnace, by adjusting the opening and closing of various baffle valves on the flue system and air duct system, each heat exchanger module can be partially put into operation, so that the heat exchanger can meet the requirements of this operating condition.

[0020] 3. Under high thermal efficiency conditions of the heating furnace, by adjusting the opening and closing of various baffle valves on the flue system and air duct system, the heat exchanger modules can be connected in series and put into operation, so that the heat exchangers can meet the requirements of this operating condition. Attached Figure Description

[0021] Figure 1 This is a front view of Embodiment 1 of the Variable Load High-Efficiency Heat Exchanger of this utility model.

[0022] Figure 2 This is a top view of Embodiment 1 of the Variable Load High-Efficiency Heat Exchanger of this utility model.

[0023] Figure 3 This is a left view of Embodiment 1 of the Variable Load High-Efficiency Heat Exchanger of this utility model.

[0024] Figure 4 This is a front view of Embodiment 2 of the Variable Load High-Efficiency Heat Exchanger of this utility model.

[0025] Figure 5 This is a top view of Embodiment 2 of the Variable Load High-Efficiency Heat Exchanger of this utility model.

[0026] Figure 6 This is a left view of Embodiment 2 of the Variable Load High-Efficiency Heat Exchanger of this utility model.

[0027] in:

[0028] First heat exchanger module 1; Second heat exchanger module 2; Duct system 3; First duct damper valve 4; Second duct damper valve 5; Third duct damper valve 6; Fourth duct damper valve 7; Fifth duct damper valve 8; Sixth duct damper valve 9; Flue system 10; First flue damper valve 11; Second flue damper valve 12; Third flue damper valve 13; Fourth flue damper valve 14; Fifth flue damper valve 15; Sixth flue damper valve 16; Third heat exchanger module 17; Seventh duct damper valve 18; Eighth duct damper valve 19; Ninth duct damper valve 20; Seventh flue damper valve 21; Eighth flue damper valve 22; Ninth flue damper valve 23. Detailed Implementation

[0029] See Figure 1-6This utility model relates to a variable load high-efficiency heat exchanger, which includes multiple heat exchanger modules arranged side by side. The air side and flue gas side of each heat exchanger module are connected through a duct system and a flue system, respectively. The duct system has one air inlet, two air outlets and multiple duct damper valves. The flue system has one flue gas inlet, two flue gas outlets and multiple flue damper valves. The duct damper valves and flue damper valves enable one or more heat exchanger modules to operate in series, parallel or series-parallel.

[0030] Each heat exchanger module has air branch pipes at both ends of the air side. The air branch pipes on the air inlet side merge at the air inlet, and the air branch pipes on the air outlet side merge at the first air outlet. Each air branch pipe and each air outlet is equipped with a duct damper valve.

[0031] Each heat exchanger module has flue gas branch pipes at both ends on the flue gas side. The flue gas branch pipes on the flue gas inlet side converge at the flue gas inlet, and the flue gas branch pipes on the flue gas outlet side converge at the first flue gas outlet. Each flue gas branch pipe and each flue gas outlet is equipped with a flue damper valve. Example 1

[0032] See Figure 1-3 This utility model relates to a variable load high-efficiency heat exchanger, including a first heat exchanger module 1 and a second heat exchanger module 2 arranged side by side. The first heat exchanger module 1 is located behind the second heat exchanger module 2. The air side and flue gas side of the first heat exchanger module 1 and the second heat exchanger module 2 are connected by a duct system 3 and a flue system 10, respectively. The duct system 3 and the flue system 10 connect the first heat exchanger module 1 and the second heat exchanger module 2 into a complete heat exchanger. The duct system 3 has one air inlet, two air outlets and six duct damper valves. The flue system 10 has one flue gas inlet, two flue gas outlets and six flue damper valves.

[0033] The air inlet side air branch pipes of the first heat exchanger module 1 and the second heat exchanger module 2 are respectively equipped with a first air duct baffle valve 4 and a second air duct baffle valve 5. The air outlet side air branch pipes of the first heat exchanger module 1 and the second heat exchanger module 2 are respectively equipped with a third air duct baffle valve 6 and a fourth air duct baffle valve 7. The air inlet side air branch pipes of the first heat exchanger module 1 and the second heat exchanger module 2 converge at the air inlet. The air outlet side air branch pipes of the first heat exchanger module 1 and the second heat exchanger module 2 converge at the first air outlet. The first air outlet is equipped with a fifth air duct baffle valve 8. The branch pipe where the second air outlet is located is connected to the air inlet side air branch pipe of the first heat exchanger module 1, and the branch pipe where the second air outlet is located is located after the first air duct baffle valve 4. The second air outlet is equipped with a sixth air duct baffle valve 9.

[0034] The flue gas branch pipes on the flue gas inlet side of the first heat exchanger module 1 and the second heat exchanger module 2 are respectively equipped with a first flue gas damper valve 11 and a second flue gas damper valve 12. The flue gas branch pipes on the flue gas outlet side of the first heat exchanger module 1 and the second heat exchanger module 2 are respectively equipped with a third flue gas damper valve 13 and a fourth flue gas damper valve 14. The flue gas branch pipes on the flue gas inlet side of the first heat exchanger module 1 and the second heat exchanger module 2 converge at the flue gas inlet. The flue gas branch pipes on the flue gas outlet side of the first heat exchanger module 1 and the second heat exchanger module 2 converge at the first flue gas outlet. The first flue gas outlet is equipped with a fifth flue gas damper valve 15. The branch pipe where the second flue gas outlet is located is connected to the flue gas branch pipe on the flue gas inlet side of the second heat exchanger module 2, and the branch pipe where the second flue gas outlet is located is located after the second flue gas damper valve 12. The second flue gas outlet is equipped with a sixth flue gas damper valve 16.

[0035] Each duct damper valve and flue damper valve is equipped with a pneumatic actuator, which can be remotely operated to open and close each damper valve.

[0036] The variable load method for this high-efficiency heat exchanger is as follows:

[0037] Under high flow rate conditions of the heating furnace, the sixth air duct damper valve 9 at the second air outlet and the sixth flue gas duct damper valve 16 at the second flue gas outlet are closed, while all other damper valves are opened, allowing the first heat exchanger module 1 and the second heat exchanger module 2 to operate in parallel. In this operating mode, the heat exchangers can achieve the maximum net flow cross-sectional area on both the flue gas and air sides, and the internal resistance reduction requirements of the heat exchangers can be met even under high flow rate conditions of the heating furnace.

[0038] Under low-flow conditions of the heating furnace, the first air duct damper valve 4, the third air duct damper valve 6, and the sixth air duct damper valve 9 at the second air outlet are closed. The first flue damper valve 11, the third flue damper valve 13, and the sixth flue damper valve 16 at the second flue gas outlet are also closed. All other damper valves are opened, thus disabling the first heat exchanger module 1 and putting the second heat exchanger module 2 into operation. In this operating mode, the heat exchanger modules are partially operational, achieving high flow rates inside the heat exchangers even under low-flow conditions of the heating furnace, thereby achieving effective heat exchange.

[0039] Under high thermal efficiency conditions of the heating furnace, the first air duct damper valve 4 and the fifth air duct damper valve 8 at the first air outlet are closed, the second flue damper valve 12 and the fifth flue damper valve 15 at the first flue gas outlet are closed, and all other damper valves are opened, allowing the first heat exchanger module 1 and the second heat exchanger module 2 to operate in series. In this operating mode, the heat exchangers can achieve the maximum flue gas side flow length and air side flow length, resulting in the highest heat exchange efficiency and thus the highest thermal efficiency of the heating furnace.

[0040] By changing parameters such as the net flow cross-sectional area, number of tube passes, and heat exchange area inside the heat exchanger, the load on the heat exchanger can be changed, thereby enabling the heat exchanger to meet the requirements of different operating conditions of the heating furnace. Example 2

[0041] See Figure 4-6 This utility model relates to a variable load high-efficiency heat exchanger, including a first heat exchanger module 1, a second heat exchanger module 2, and a third heat exchanger module 17 arranged side by side. The first heat exchanger module 1 is located between the second heat exchanger module 2 and the third heat exchanger module 17, and the third heat exchanger module 17 is located behind the first heat exchanger module 1. The air side and flue gas side of the first heat exchanger module 1, the second heat exchanger module 2, and the third heat exchanger module 17 are connected by a duct system 3 and a flue system 10, respectively. The duct system 3 and the flue system 10 connect the first heat exchanger module 1, the second heat exchanger module 2, and the third heat exchanger module 17 into a complete heat exchanger. The duct system 3 has one air inlet, two air outlets, and nine duct damper valves. The flue system 10 has one flue gas inlet, two flue gas outlets, and nine flue damper valves.

[0042] The air inlet side air branch pipes of the first heat exchanger module 1, the second heat exchanger module 2, and the third heat exchanger module 17 are equipped with a first duct baffle valve 4, a second duct baffle valve 5, and a seventh duct baffle valve 18, respectively. The air outlet side air branch pipes of the first heat exchanger module 1, the second heat exchanger module 2, and the third heat exchanger module 17 are equipped with a third duct baffle valve 6, a fourth duct baffle valve 7, and an eighth duct baffle valve 19, respectively. The air branch pipes on the air inlet side of 7 converge at the air inlet. The air branch pipes on the air outlet side of the first heat exchanger module 1, the second heat exchanger module 2, and the third heat exchanger module 17 converge at the first air outlet. The first air outlet is equipped with a fifth air duct baffle valve 8. The branch pipe where the second air outlet is located is connected to the air branch pipe on the air outlet side of the third heat exchanger module 17, and the branch pipe where the second air outlet is located is located before the eighth air duct baffle valve 19. The second air outlet is equipped with a sixth air duct baffle valve 9.

[0043] The air inlet side air branch pipes of the first heat exchanger module 1 and the third heat exchanger module 17 are connected by an air bypass pipe. The air bypass pipe is located after the first air duct baffle valve 4 and the seventh air duct baffle valve 18, and the ninth air duct baffle valve 20 is provided on the air bypass pipe.

[0044] The first heat exchanger module 1, the second heat exchanger module 2, and the third heat exchanger module 17 are equipped with a first flue damper valve 11, a second flue damper valve 12, and a seventh flue damper valve 21 in the flue gas branch pipes on the flue gas inlet side. The first heat exchanger module 1, the second heat exchanger module 2, and the third heat exchanger module 17 are equipped with a third flue damper valve 13, a fourth flue damper valve 14, and an eighth flue damper valve 22 in the flue gas branch pipes on the flue gas outlet side. The flue gas branch pipes on the flue gas inlet side of 17 converge at the flue gas inlet. The flue gas branch pipes on the flue gas outlet side of the first heat exchanger module 1, the second heat exchanger module 2, and the third heat exchanger module 17 converge at the first flue gas outlet. A fifth flue gas damper valve 15 is provided at the first flue gas outlet. The branch pipe where the second flue gas outlet is located is connected to the flue gas branch pipe on the flue gas outlet side of the second heat exchanger module 2. The branch pipe where the second flue gas outlet is located is located before the fourth flue gas damper valve 14. A sixth flue gas damper valve 16 is provided at the second flue gas outlet.

[0045] The flue gas branch pipes on the flue gas inlet side of the first heat exchanger module 1 and the second heat exchanger module 2 are connected by a flue gas bypass pipe. The flue gas bypass pipe is located after the first flue damper valve 11 and the second air duct damper valve 12. A ninth flue damper valve 23 is provided on the air bypass pipe.

[0046] Each duct damper valve and flue damper valve is equipped with a pneumatic actuator, which can be remotely operated to open and close each damper valve.

[0047] The variable load method for this high-efficiency heat exchanger is as follows:

[0048] Under high flow rate conditions of the heating furnace, the sixth duct damper valve 9 and the ninth duct damper valve 20 at the second air outlet are closed, while the sixth flue gas damper valve 16 and the ninth flue gas damper valve 23 at the second flue gas outlet are closed. All other damper valves are opened, allowing the first heat exchanger module 1, the second heat exchanger module 2, and the third heat exchanger module 17 to operate in parallel. In this operating mode, the heat exchangers can achieve the maximum net flow cross-sectional area on both the flue gas and air sides, and the internal resistance reduction requirements of the heat exchangers can be met even under high flow rate conditions of the heating furnace.

[0049] Under low-flow conditions of the heating furnace, the second air duct damper valve 5, the fourth air duct damper valve 7, and the fifth air duct damper valve 8 are opened, while the second flue damper valve 12, the fourth flue damper valve 14, and the fifth flue damper valve 15 are also opened. All other damper valves are closed, thus disabling the first heat exchanger module 1 and the third heat exchanger module 17, and activating the second heat exchanger module 2. In this operating mode, with only some heat exchanger modules in use, high flow rates can be achieved within the heat exchangers even under low-flow conditions, thereby enabling effective heat exchange.

[0050] Under high thermal efficiency conditions of the heating furnace, the first air duct damper valve 4, the fifth air duct damper valve 8, the seventh air duct damper valve 18, and the eighth air duct damper valve 19 are closed, while the first flue damper valve 11, the second flue damper valve 12, the fourth flue damper valve 14, and the fifth flue damper valve 15 are closed. All other damper valves are opened, allowing the first heat exchanger module 1, the second heat exchanger module 2, and the third heat exchanger module 17 to operate in series. In this operating mode, the heat exchangers can achieve the maximum flue gas side flow length and the air side flow length, resulting in the highest heat exchange efficiency and thus the highest thermal efficiency of the heating furnace.

[0051] By changing parameters such as the net flow cross-sectional area, number of tube passes, and heat exchange area inside the heat exchanger, the load on the heat exchanger can be changed, thereby enabling the heat exchanger to meet the requirements of different operating conditions of the heating furnace.

[0052] In addition to the above embodiments, this utility model also includes other implementation methods. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of this utility model.

Claims

1. A variable load high-efficiency heat exchanger, characterized in that: It comprises multiple heat exchanger modules arranged side-by-side. The air side and flue gas side of each heat exchanger module are connected by a duct system and a flue system, respectively. The duct system has one air inlet, two air outlets, and multiple duct damper valves. The flue system has one flue gas inlet, two flue gas outlets, and multiple flue gas damper valves. Each heat exchanger module has air branch pipes at both ends of its air side. The air branch pipes on the air inlet side converge at the air inlet, and the air branch pipes on the air outlet side converge at the first air outlet. Each air branch pipe and each air outlet is equipped with a duct damper valve. Similarly, each heat exchanger module has flue gas branch pipes at both ends of its flue gas side. The flue gas branch pipes on the flue gas inlet side converge at the flue gas inlet, and the flue gas branch pipes on the flue gas outlet side converge at the first flue gas outlet. Each flue gas branch pipe and each flue gas outlet is equipped with a flue gas damper valve.

2. The variable load high-efficiency heat exchanger according to claim 1, characterized in that: The second air outlet of the air duct system is located on the air branch pipe corresponding to the first or last heat exchanger module, and the second flue gas outlet of the flue system is located on the flue gas branch pipe of the first or last heat exchanger module.

3. A variable load high-efficiency heat exchanger according to claim 1 or 2, characterized in that: It includes two heat exchanger modules, namely the first heat exchanger module and the second heat exchanger module from front to back. The air inlet side air branch pipes of the first heat exchanger module and the second heat exchanger module are equipped with a first air duct baffle valve and a second air duct baffle valve respectively. The air outlet side air branch pipes of the first heat exchanger module and the second heat exchanger module are equipped with a third air duct baffle valve and a fourth air duct baffle valve respectively. The air inlet side air branch pipes of the first heat exchanger module and the second heat exchanger module converge at the air inlet. The air outlet side air branch pipes of the first heat exchanger module and the second heat exchanger module converge at the first air outlet. The first air outlet is equipped with a fifth air duct baffle valve. The flue gas branch pipes on the flue gas inlet side of the first heat exchanger module and the second heat exchanger module are respectively equipped with a first flue gas damper valve and a second flue gas damper valve. The flue gas branch pipes on the flue gas outlet side of the first heat exchanger module and the second heat exchanger module are respectively equipped with a third flue gas damper valve and a fourth flue gas damper valve. The flue gas branch pipes on the flue gas inlet side of the first heat exchanger module and the second heat exchanger module converge at the flue gas inlet. The flue gas branch pipes on the flue gas outlet side of the first heat exchanger module and the second heat exchanger module converge at the first flue gas outlet. A fifth flue gas damper valve is provided at the first flue gas outlet.

4. A variable load high-efficiency heat exchanger according to claim 3, characterized in that: The branch pipe where the second air outlet is located is connected to the air inlet side air branch pipe of the first heat exchanger module, and the branch pipe where the second air outlet is located is located after the first air duct baffle valve. A sixth air duct baffle valve is provided at the second air outlet. The branch pipe where the second flue gas outlet is located is connected to the flue gas branch pipe on the flue gas inlet side of the second heat exchanger module, and the branch pipe where the second flue gas outlet is located is set after the second flue damper valve. A sixth flue damper valve is provided at the second flue gas outlet.

5. A variable load high-efficiency heat exchanger according to claim 1 or 2, characterized in that: It comprises three heat exchanger modules, from front to back: the second heat exchanger module, the first heat exchanger module, and the third heat exchanger module. The air inlet side air branch pipes of the first, second, and third heat exchanger modules are equipped with a first air duct baffle valve, a second air duct baffle valve, and a seventh air duct baffle valve, respectively. The air outlet side air branch pipes of the first, second, and third heat exchanger modules are equipped with a third air duct baffle valve, a fourth air duct baffle valve, and an eighth air duct baffle valve, respectively. The air inlet side air branch pipes of the first, second, and third heat exchanger modules converge at the air inlet, and the air outlet side air branch pipes of the first, second, and third heat exchanger modules converge at the first air outlet. The first air outlet is equipped with a fifth duct damper valve; the flue gas branch pipes on the flue gas inlet side of the first, second, and third heat exchanger modules are equipped with a first flue gas damper valve, a second flue gas damper valve, and a seventh flue gas damper valve, respectively; the flue gas branch pipes on the flue gas outlet side of the first, second, and third heat exchanger modules are equipped with a third flue gas damper valve, a fourth flue gas damper valve, and an eighth flue gas damper valve, respectively; the flue gas branch pipes on the flue gas inlet side of the first, second, and third heat exchanger modules converge at the flue gas inlet; the flue gas branch pipes on the flue gas outlet side of the first, second, and third heat exchanger modules converge at the first flue gas outlet, where a fifth flue gas damper valve is located.

6. A variable load high-efficiency heat exchanger according to claim 5, characterized in that: The branch pipe where the second air outlet is located is connected to the air outlet side air branch pipe of the third heat exchanger module, and the branch pipe where the second air outlet is located is set before the eighth air duct baffle valve. The sixth air duct baffle valve is provided at the second air outlet. The branch pipe where the second flue gas outlet is located is connected to the flue gas branch pipe on the flue gas outlet side of the second heat exchanger module, and the branch pipe where the second flue gas outlet is located is set before the fourth flue gas damper valve. The sixth flue gas damper valve is provided at the second flue gas outlet.

7. A variable load high-efficiency heat exchanger according to claim 6, characterized in that: The air inlet side air branch pipes of the first heat exchanger module and the third heat exchanger module are connected by an air bypass pipe. The air bypass pipe is located after the first air duct baffle valve and the seventh air duct baffle valve, and the air bypass pipe is equipped with a ninth air duct baffle valve. The flue gas branch pipes on the flue gas inlet side of the first heat exchanger module and the second heat exchanger module are connected by a flue gas bypass pipe. The flue gas bypass pipe is located after the first flue damper valve and the second air duct damper valve, and a ninth flue damper valve is provided on the air bypass pipe.

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