Flue gas waste heat recovery system

Abstract

The invention relates to the technical field of flue gas waste heat recovery, in particular to a flue gas waste heat recovery system. Comprising a heating furnace, the top of the heating furnace is connected with a flue gas inlet of a high-temperature air preheater through a first flue gas pipeline, a flue gas outlet of the high-temperature air preheater is connected with a flue gas inlet of a low-temperature air preheater through a second flue gas pipeline, and a flue gas outlet of the low-temperature air preheater is connected with a chimney through a third flue gas pipeline. The bottom of the heating furnace is connected with an air outlet of the high-temperature air preheater through a first air pipeline, and an air inlet of the high-temperature air preheater is connected with an air outlet of the low-temperature air preheater through a second air pipeline; corrugated plate bundles are arranged in the air preheaters, so that the heat exchange efficiency of flue gas waste heat is improved; a bypass air duct is arranged on one side of the high-temperature air preheater and used for adjusting the temperature of a smoke outlet of the high-temperature air preheater, and dew point corrosion is avoided. A bypass flue is arranged on one side of the low-temperature air preheater and used for releasing flue gas in the flue when a fault occurs.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas waste heat recovery, and more particularly to a flue gas waste heat recovery system. Background Art

[0002] Energy conservation and emission reduction are the needs of transforming the production mode and also a long-term goal for the sustainable development of the refining, chemical and even the entire industry. In a refining unit, the heating furnace is the main heat supply equipment, and its fuel consumption accounts for a relatively large proportion of the total energy consumption of the refining unit. Among various ways of energy conservation in heating furnaces, using flue gas to preheat air is a commonly adopted method to recover the waste heat of the heating furnace flue gas and improve the thermal efficiency.

[0003] In the existing flue gas waste heat recovery system, since a flue gas recovery system is arranged on one side of the heating furnace, the structure is relatively complex, and there are strict requirements for the temperatures of the flue gas and air. Once a failure occurs, it is difficult for the existing flue gas waste heat recovery system to be effectively controlled. In addition, currently, various heating furnaces generally use air preheaters to recover the waste heat in the flue gas to achieve the purpose of improving the thermal efficiency of the heating furnace and saving fuel. There are many types of air preheaters, and there are mainly three types widely used for recovering high- and low-temperature flue gases: one is the traditional smooth tube bundle type, which uses smooth tubes as heat transfer elements; another is the enhanced tube type, which takes various enhancement measures on the basis of smooth tubes to improve the heat transfer effect, such as the finned tube type air preheater with fins outside the tube and turbulators as flow disturbing elements inside the tube; and there is also the heat pipe type, which converts the heat transfer between the traditional inner and outer surfaces into the heat transfer between the outer surfaces of the two tube ends by means of the evaporation and condensation of the intermediate working fluid, so that both the cold and hot ends can be enhanced by adding fins. These three types of air preheaters all belong to tube type air preheaters, and there are more or less some limitations or deficiencies in terms of structure and use. For example, the tube bundle type has a large structure and low heat transfer efficiency; the heat pipe type is prone to failure and ash accumulation, etc. Therefore, the present application provides a flue gas waste heat recovery system to solve the problems raised in the above background art. Summary of the Invention

[0004] The purpose of the present invention is to provide a flue gas waste heat recovery system to solve the problems that the existing flue gas waste heat recovery system is not easy to control when a failure occurs, and the heat transfer efficiency of the air preheater in the system is low, resulting in waste of flue gas waste heat.

[0005] To solve the above technical problems, the present invention provides a flue gas waste heat recovery system, which includes a heating furnace. The top of the heating furnace is connected to the flue gas inlet of a high-temperature air preheater through a first flue gas pipeline. The flue gas outlet of the high-temperature air preheater is connected to the flue gas inlet of a low-temperature air preheater through a second flue gas pipeline. The flue gas outlet of the low-temperature air preheater is connected to a chimney through a third flue gas pipeline. The bottom of the heating furnace is connected to the air outlet of the high-temperature air preheater through a first air pipeline. The air inlet of the high-temperature air preheater is connected to the air outlet of the low-temperature air preheater through a second air pipeline. The air inlet of the low-temperature air preheater is connected to a blower through a third air pipeline.

[0006] Corrugated plate bundles are arranged in both the high-temperature air preheater and the low-temperature air preheater to improve the heat exchange efficiency of the flue gas waste heat.

[0007] A bypass air duct is arranged on one side of the high-temperature air preheater to adjust the flue gas outlet temperature of the high-temperature air preheater and avoid dew point corrosion.

[0008] A bypass flue is arranged on one side of the low-temperature air preheater to release the flue gas in the flue when a failure occurs.

[0009] A further improvement of the technical solution of the present invention is that the high-temperature air preheater and the low-temperature air preheater have the same structure. Both include a box body. The top of the box body is provided with adjacent flue gas inlet and air outlet, and the flue gas inlet and air outlet are respectively communicated with the inside of the box body. The bottom of the box body is provided with adjacent air inlet and flue gas outlet, and the flue gas inlet and air outlet are respectively communicated with the inside of the box body. A plurality of juxtaposed corrugated plate bundles are filled and arranged inside the box body, and a limit frame is arranged at the top and bottom of each corrugated plate bundle.

[0010] A further improvement of the technical solution of the present invention is that the cross-section of the corrugated plate bundle is formed by connecting the heads and tails of multiple opposite trapezoidal surfaces in a staggered manner and arranged linearly, and a channel is arranged between adjacent corrugated plate bundles.

[0011] A further improvement of the technical solution of the present invention is that the corrugated plate bundle of the high-temperature air preheater is made of stainless steel, and the corrugated plate bundle of the low-temperature air preheater is made of Corten steel.

[0012] A further improvement of the technical solution of the present invention is that the bypass air duct includes a first air branch pipe tapped from the third air pipeline. The first air branch pipe is connected to a T-shaped joint. One side of the T-shaped joint is branched to a second air branch pipe, and the second air branch pipe is connected to the first air pipeline. The other side of the T-shaped joint is branched to a third air branch pipe, and the third air branch pipe is connected to the second air pipeline.

[0013] A further improvement of the technical solution of the present invention is that a first regulating butterfly valve is arranged on the first air branch pipe, and a second regulating butterfly valve is arranged on the second air branch pipe.

[0014] A further improvement of the technical solution of the present invention lies in that a flue gas branch pipe is tapped from the third flue gas pipe and connected to the second flue gas pipe.

[0015] A further improvement of the technical solution of the present invention lies in that an induced draft fan is provided on the second flue gas pipe, an induced draft damper is provided at the inlet of the induced draft fan, and a forced draft damper is provided at the inlet of the forced draft fan.

[0016] A further improvement of the technical solution of the present invention lies in that a first sealing damper is provided on the first flue gas pipe, and the top of the heating furnace is connected to the chimney through a second sealing damper.

[0017] A further improvement of the technical solution of the present invention lies in that a furnace bottom air duct is provided at the bottom of the heating furnace, and a pneumatic air door is provided in the furnace bottom air duct.

[0018] Adopting the above technical solution, the present invention has the following beneficial effects:

[0019] 1. A flue gas waste heat recovery system provided by the present invention is beneficial to enabling the combustion air to absorb the flue gas waste heat, reducing the flue gas discharge temperature, and improving the thermal efficiency of the heating furnace. The waste heat recovery system adopts a two-stage air preheating system. Its process feature is that the flue gas temperature of 160 °C is used as the boundary. Above 160 °C is high temperature, and below 160 °C is low temperature. The flue gas-air preheater is divided into two independent devices, namely a high-temperature section and a low-temperature section. The hot flue gas of the heating furnace enters the high-temperature air preheater through the first flue gas pipe. After heat exchange with the air, the flue gas enters the low-temperature air preheater through the second flue gas pipe. The flue gas temperature is reduced to about 100 °C and then discharged into the chimney. The two-stage air preheating system improves the thermal efficiency by 3% - 4% compared with the one-stage air preheating system.

[0020] 2. A flue gas waste heat recovery system provided by the present invention is easy to control when a failure occurs. When the flue gas waste heat recovery system is operating normally, the first sealing damper is in a fully open state, while the second sealing damper is in a closed state. When a failure occurs in the waste heat recovery system, the first sealing damper is interlocked and closed. At the same time, the second sealing damper and the pneumatic air door provided on the furnace bottom air duct of the heating furnace are opened, and the air supply fan and the flue gas induced draft fan are stopped, and the system is changed to natural ventilation operation to prevent the pressure in the heating furnace from being too high and causing danger;

[0021] 3. A flue gas waste heat recovery system provided by the present invention uses a corrugated plate bundle for heat exchange, with high heat exchange efficiency. Since the cross-sectional shape of the flow channel of the corrugated plate bundle continuously changes along the flue gas flow direction, the disturbance of the flue gas is greatly enhanced, so that turbulence can be formed at a very low Reynolds number. In addition, a pure countercurrent plate type is adopted in the structure, that is, the flue gas and air flow in opposite directions, avoiding temperature crossover and having a small end temperature difference, thus significantly improving the heat transfer performance of the corrugated plate bundle; both the high-temperature air preheater and the low-temperature air preheater adopt unequal flow channel plate types, which not only helps to improve the heat transfer efficiency but also can well match the pressure drops at the hot end and the cold end. In addition, the characteristics such as a large flow area, a smooth straight channel, a short flow path, and high compactness between adjacent corrugated plate bundles make the flue gas flow in the corrugated plate bundle have a small resistance.

[0022] 4. A flue gas waste heat recovery system provided by the present invention uses a corrugated plate bundle for heat exchange, with excellent long-term heat transfer performance. The corrugated plate bundle of the high-temperature air preheater is made of stainless steel, with a smooth surface. Due to the relatively high internal temperature, it is not easy to accumulate ash, or there is a small amount of dry ash, which is easy to remove during the reverse convection of air. The fouling resistance is small and the heat transfer performance is stable. The heat transfer surfaces of the corrugated plate bundle are all primary heat transfer surfaces, with good long-term performance; since the temperature of the low-temperature air preheater is relatively low, even reaching the dew point corrosion temperature, the corrugated plate bundle of the low-temperature air preheater is made of Corten steel, which is beneficial to resisting low-temperature sulfuric acid corrosion.

[0023] 5. The bypass duct of the flue gas waste heat recovery system provided by the present invention is beneficial to adjusting the flue gas outlet temperature of the high-temperature air preheater and avoiding dew point corrosion. When the heating furnace operates at low load, the opening degrees of the first regulating butterfly valve and the second regulating butterfly valve can be appropriately adjusted to increase the inflow of air, promote combustion, and control the temperature of the flue gas leaving the low-temperature air preheater from being too low to avoid the occurrence of dew point corrosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 It is an overall schematic diagram of a flue gas waste heat recovery system;

[0026] Figure 2 It is a structural schematic diagram of a high-temperature air preheater;

[0027] Figure 3 It is a cross-sectional view of a high-temperature air preheater;

[0028] Figure 4 Schematic diagram of the structure of multiple corrugated plate bundles arranged side by side;

[0029] Figure 5 Schematic diagram of the structure of the corrugated plate bundle.

[0030] Reference numerals: 1, heating furnace; 2, high-temperature air preheater; 21, flue gas inlet; 22, flue gas outlet; 23, air outlet; 24, air inlet; 25, corrugated plate bundle; 26, box body; 27, limit frame; 3, low-temperature air preheater; 41, T-joint; 42, first air branch pipe; 43, second air branch pipe; 44, third air branch pipe; 45, first regulating butterfly valve; 46, second regulating butterfly valve; 5, bypass flue; 51, flue gas branch pipe; 6, first flue gas pipeline; 7, second flue gas pipeline; 8, third flue gas pipeline; 9, chimney; 10, first air pipeline; 11, second air pipeline; 12, third air pipeline; 13, air blower; 14, air supply baffle; 15, induced draft fan; 16, induced draft baffle; 17, first sealing baffle; 18, second sealing baffle; 19, furnace bottom air duct. Detailed implementation manners

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0033] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0034] The present invention will be further explained and illustrated below in conjunction with specific embodiments.

[0035] As Figures 1-5 shown, a flue gas waste heat recovery system provided in this embodiment is characterized in that it includes a heating furnace 1. The top of the heating furnace 1 is connected to the flue gas inlet 21 of a high-temperature air preheater 2 through a first flue gas pipeline 6. The flue gas outlet 22 of the high-temperature air preheater 2 is connected to the flue gas inlet 21 of a low-temperature air preheater 3 through a second flue gas pipeline 7. The flue gas outlet 22 of the low-temperature air preheater 3 is connected to a chimney 9 through a third flue gas pipeline 8. The bottom of the heating furnace 1 is connected to the air outlet 23 of the high-temperature air preheater 2 through a first air pipeline 10. The air inlet 24 of the high-temperature air preheater 2 is connected to the air outlet 23 of the low-temperature air preheater 3 through a second air pipeline 11; the air inlet 24 of the low-temperature air preheater 3 is connected to a blower 13 through a third air pipeline 12; corrugated plate bundles 25 are arranged in both the high-temperature air preheater 2 and the low-temperature air preheater 3 to improve the heat exchange efficiency of the flue gas waste heat; a bypass air duct is arranged on one side of the high-temperature air preheater 2 to adjust the temperature of the flue gas outlet 22 of the high-temperature air preheater 2 and avoid dew point corrosion; a bypass flue 5 is arranged on one side of the low-temperature air preheater 3 to release the flue gas in the flue when a failure occurs. This system is beneficial to enabling the combustion air to absorb the flue gas waste heat, reducing the flue gas discharge temperature, and improving the thermal efficiency of the heating furnace 1. The waste heat recovery system adopts a two-stage air preheating system, and its process feature is that with 160 °C of the flue gas temperature as the boundary, above 160 °C is high temperature and below 160 °C is low temperature. The flue gas-air preheater is divided into two independent devices, namely a high-temperature section and a low-temperature section. The hot flue gas of the heating furnace 1 enters the high-temperature air preheater 2 through the first flue gas pipeline 6. After heat exchange with the air, the flue gas enters the low-temperature air preheater 3 through the second flue gas pipeline 7, and the flue gas temperature drops to about 100 °C and then is discharged into the chimney 9. The two-stage air preheating system improves the thermal efficiency by 3% - 4% compared with the one-stage air preheating system.

[0036] As Figures 2-5As shown, in this embodiment, the high-temperature air preheater 2 and the low-temperature air preheater 3 have the same structure, and both include a box body 26. At the top of the box body 26, an adjacent flue gas inlet 21 and an air outlet 23 are provided. The flue gas inlet 21 and the air outlet 23 are respectively communicated with the inside of the box body 26. At the bottom of the box body 26, an adjacent air inlet 24 and a flue gas outlet 22 are provided. The flue gas inlet 21 and the air outlet 23 are respectively communicated with the inside of the box body 26. A plurality of corrugated plate bundles 25 arranged side by side are filled and provided inside the box body 26. Limit frames 27 are provided at the top and bottom ends of each corrugated plate bundle 25. The cross-section of the corrugated plate bundle 25 is formed by connecting the tops and tails of a plurality of opposite trapezoidal surfaces in a staggered manner and arranged linearly. Channels are provided between adjacent corrugated plate bundles 25. This system uses the corrugated plate bundle 25 for heat exchange, and the heat exchange efficiency is high. Since the cross-sectional shape of the flow channel of the corrugated plate bundle 25 in the flue gas flow direction continuously changes, the disturbance of the flue gas is greatly enhanced, so that turbulence can be formed at a very low Reynolds number (Re>100), while under the same conditions, the Reynolds number of the tubular heat exchange element (Re>4000) is required to form turbulence; secondly, compared with the tubular type, since the heat exchange areas on both sides of the plate heat transfer element are completely equal, there is only a very small film thermal resistance, and there is no amplification effect of the internal film thermal resistance of the tube. In terms of structure, the corrugated plate bundle 25 adopts a pure countercurrent plate type, that is, the flue gas and air flow in opposite directions, avoiding temperature crossover and having a small end temperature difference, thus significantly improving the heat transfer performance of the corrugated plate bundle 25; both the high-temperature air preheater 2 and the low-temperature air preheater 3 adopt an unequal flow channel plate type, which is not only beneficial to improving the heat transfer efficiency but also can well match the pressure drops at the hot end and the cold end. In addition, there are characteristics such as a large flow area, a smooth straight channel, a short flow path, and a high compactness between adjacent corrugated plate bundles 25, making the flue gas flow in the corrugated plate bundle 25 have a small resistance. Further, using the corrugated plate bundle 25 for heat exchange has excellent heat transfer long-term performance. The corrugated plate bundle 25 of the high-temperature air preheater 2 is made of stainless steel, with a smooth surface. Since the internal temperature is relatively high, it is not easy to accumulate ash, or there is a small amount of dry ash, which is easy to remove during the reverse convection of air. The fouling resistance is small and the heat transfer performance is stable. The heat transfer surfaces of the corrugated plate bundle 25 are all primary heat transfer surfaces, and the long-term performance is good; since the temperature of the low-temperature air preheater 3 is relatively low, even reaching the dew point corrosion temperature, the corrugated plate bundle 25 of the low-temperature air preheater 3 is made of Corten steel, which is beneficial to resisting low-temperature sulfuric acid corrosion.

[0037] As Figure 1As shown in the figure, in this embodiment, the bypass air duct includes a first air branch pipe 42 branched from the third air pipe 12. The first air branch pipe 42 is connected to a T-shaped joint 41. One side of the T-shaped joint 41 is branched to connect a second air branch pipe 43, and the second air branch pipe 43 is connected to the first air pipe 10. The other side of the T-shaped joint 41 is branched to connect a third air branch pipe 44, and the third air branch pipe 44 is connected to the second air pipe 11. A first regulating butterfly valve 45 is provided on the first air branch pipe 42, and a second regulating butterfly valve 46 is provided on the second air branch pipe 43. A flue gas branch pipe 51 is branched from the third flue gas pipe 8 and connected to the second flue gas pipe 7. An induced draft fan 15 is provided on the second flue gas pipe 7. An induced draft damper 16 is provided at the inlet of the induced draft fan 15, and a forced draft damper 14 is provided at the inlet of the forced draft fan 13. When the induced draft fan 15 and the forced draft fan 13 are started, the induced draft damper 16 and the forced draft damper 14 should be in the closed state. During normal operation, the damper openings of the induced draft fan 15 and the forced draft fan 13 should be adjusted according to the load of the heating furnace 1. A first sealing damper 17 is provided on the first flue gas pipe, and the top of the heating furnace 1 is connected to the chimney 9 through a second sealing damper 18. A furnace bottom air duct 19 is provided at the bottom of the heating furnace 1, and a pneumatic air door is provided in the furnace bottom air duct 19.

[0038] As Figure 1 shown in the figure, in this embodiment, the flue gas waste heat recovery system is easy to control when a failure occurs. When the flue gas waste heat recovery system is operating normally, the first sealing damper 17 is in the fully open state, while the second sealing damper 18 is in the closed state. When a failure occurs in the waste heat recovery system, the first sealing damper 17 is interlocked and closed, and at the same time, the second sealing damper 18 and the pneumatic air door provided on the furnace bottom air duct 19 of the heating furnace 1 are opened. The air supply fan 13 and the flue gas induced draft fan 15 are stopped, and the system is changed to natural ventilation operation to prevent the pressure in the heating furnace 1 from being too high and causing danger.

[0039] As Figure 1As shown, in this embodiment, when the temperature of the flue gas entering the high-temperature air preheater 2 is greater than 400 °C or the temperature of the flue gas leaving the high-temperature air preheater 2 is greater than 220 °C, an alarm is issued. When the temperature of the flue gas entering the high-temperature air preheater 2 is greater than 420 °C or the temperature of the flue gas leaving the high-temperature air preheater 2 is greater than 240 °C, the system will interlock to stop the flue gas induced draft fan 15; when the pressure of the air leaving the high-temperature air preheater 2 is less than 150 Pa, an alarm is issued, and when it is less than 50 Pa, a strong alarm is issued. The operator should confirm whether there are faults in the air supply fan 13, the high-temperature air preheater 2, and the low-temperature air preheater 3; when the pressure of the flue gas entering the high-temperature air preheater 2 is greater than -200 Pa, an alarm is issued, and when it is greater than -100 Pa, a strong alarm is issued. The operator should confirm whether there are faults in the flue gas induced draft fan 15, the air preheater, and the low-temperature air preheater 3; when the flue gas induced draft fan 15 is stopped, the system will interlock to close the first seal baffle 17 and automatically open the second seal baffle 18 at the same time; when the air supply fan 13 is stopped, the system will interlock to stop the flue gas induced draft fan 15 and automatically open the pneumatic damper provided on the bottom furnace air duct 19 at the same time. The system will change to natural ventilation operation. If it is delayed for 20 seconds and 50% or more of the pneumatic dampers of a single heating furnace 1 have no opening signal, and the oxygen content of the flue gas leaving the heating furnace 1 is equal to or less than 1%, a strong alarm is issued, and the main fuel of the heating furnace 1 that meets the interlock conditions is cut off by interlock.

[0040] As Figure 1 shown, in this embodiment, the bypass air duct of the flue gas waste heat recovery system is used to adjust the temperature of the flue gas outlet 22 of the high-temperature air preheater 2 to avoid dew point corrosion. When the heating furnace 1 is operating at low load, the opening degrees of the first regulating butterfly valve 45 and the second regulating butterfly valve 46 can be appropriately adjusted to increase the inflow of air, promote combustion, and control the temperature of the flue gas leaving the low-temperature air preheater 3 from being too low to avoid the occurrence of dew point corrosion.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flue gas waste heat recovery system, characterized in that: The heating furnace (1) comprises a heating furnace (1), wherein the top of the heating furnace (1) is connected to the smoke inlet (21) of a high-temperature air preheater (2) through a first smoke duct (6), the smoke outlet (22) of the high-temperature air preheater (2) is connected to the smoke inlet (21) of a low-temperature air preheater (3) through a second smoke duct (7), the smoke outlet (22) of the low-temperature air preheater (3) is connected to a chimney (9) through a third smoke duct (8), the bottom of the heating furnace (1) is connected to the air outlet (23) of the high-temperature air preheater (2) through a first air duct (10), the air inlet (24) of the high-temperature air preheater (2) is connected to the air outlet (23) of the low-temperature air preheater (3) through a second air duct (11); the air inlet (24) of the low-temperature air preheater (3) is connected to a blower (13) through a third air duct (12); A corrugated plate bundle (25) is provided in both the high-temperature air preheater (2) and the low-temperature air preheater (3) to improve the heat exchange efficiency of flue gas waste heat; A bypass air duct is provided on one side of the high-temperature air preheater (2) for adjusting the temperature of the flue gas outlet (22) of the high-temperature air preheater (2) to avoid dew point corrosion; A bypass flue (5) is provided on one side of the low-temperature air preheater (3) for releasing the flue gas in the flue when a failure occurs.

2. A flue gas waste heat recovery system according to claim 1, characterized in that: The high-temperature air preheater (2) and the low-temperature air preheater (3) have the same structure, and both include a box body (26). The top of the box body (26) is provided with an adjacent smoke inlet (21) and an air outlet (23), and the smoke inlet (21) and the air outlet (23) are respectively connected to the inside of the box body (26). The bottom of the box body (26) is provided with an adjacent air inlet (24) and a smoke outlet (22), and the smoke inlet (21) and the air outlet (23) are respectively connected to the inside of the box body (26). The inside of the box body (26) is filled with a plurality of corrugated plate bundles (25) arranged in parallel, and a limit frame (27) is provided at the top and bottom of each corrugated plate bundle (25).

3. A flue gas waste heat recovery system according to claim 2, characterized in that: The cross section of the corrugated plate bundle (25) is a plurality of opposite trapezoidal surfaces which are connected end to end and arranged in an interlaced manner and in a linear arrangement, and channels are arranged between adjacent corrugated plate bundles (25).

4. The flue gas waste heat recovery system according to claim 2, characterized in that: The corrugated plate bundle (25) of the high-temperature air preheater (2) is made of stainless steel, and the corrugated plate bundle (25) of the low-temperature air preheater (3) is made of Corten steel.

5. The flue gas waste heat recovery system according to claim 1, characterized in that: The bypass air duct comprises a first air branch pipe (42) branched from the third air duct (12), the first air branch pipe (42) being connected to a T-joint (41), one side of the T-joint (41) being branched to a second air branch pipe (43), the second air branch pipe (43) being connected to the first air duct (10), the other side of the T-joint (41) being branched to a third air branch pipe (44), the third air branch pipe (44) being connected to the second air duct (11).

6. A flue gas waste heat recovery system according to claim 5, characterized in that: A first regulating butterfly valve (45) is arranged on the first air branch pipe (42), and a second regulating butterfly valve (46) is arranged on the second air branch pipe (43).

7. The flue gas waste heat recovery system according to claim 1, characterized in that: The third flue gas duct (8) is connected to a branch flue gas pipe (51) which is connected to the second flue gas duct (7).

8. The flue gas waste heat recovery system according to claim 1, characterized in that: An induced draft fan (15) is arranged on the second smoke duct (7), an induced draft baffle (16) is arranged at the inlet of the induced draft fan (15), and an air supply baffle (14) is arranged at the inlet of the air supply fan (13).

9. The flue gas waste heat recovery system according to claim 1, characterized in that: A first sealing baffle (17) is arranged on the first smoke pipe, and the top of the heating furnace (1) is connected to the chimney (9) through a second sealing baffle (18).

10. The flue gas waste heat recovery system according to claim 1, characterized in that: A furnace bottom air duct (19) is arranged at the bottom of the heating furnace (1), and a pneumatic damper is arranged in the furnace bottom air duct (19).

Images