System for preventing low-temperature corrosion of boiler air preheater and using method thereof

Abstract

The invention provides a system for preventing low-temperature corrosion of a boiler air preheater and a using method of the system, and belongs to the technical field of boiler equipment. The problem of low-temperature corrosion of the boiler air preheater is solved. The device comprises a cold air duct, an air preheater, an air preheater flue inlet, a hot air duct and a bypass flue, the inlet of the cold air duct is connected with a fan, the outlet of the cold air duct is connected with the inlet of the air preheater, the air preheater is connected with the inlet of the air preheater flue, and a second smoke temperature measuring device is arranged on the inlet of the air preheater flue. An outlet of the air preheater is connected with the hot air duct, one end of the bypass flue is arranged on the cold air duct, the other end of the bypass flue is arranged on the hot air duct, a third air door is arranged on the hot air duct, a first air door is arranged on the cold air duct, and a second air door is arranged on the bypass flue. The device is mainly used for preventing low-temperature corrosion of the boiler air preheater.

Description

Technical Field

[0001] The invention belongs to the technical field of boiler equipment, and in particular relates to a system for preventing low-temperature corrosion of a boiler air preheater. Background Art

[0002] The tubular air preheater is an important heat exchange device at the tail of the boiler. Its main function is to use the waste heat of the flue gas to preheat the air entering the boiler, thereby improving the thermal efficiency of the boiler. However, since it is located in the area with the lowest flue temperature in the flue at the tail of the boiler, especially the last tube box, the flue gas and air temperatures are low, and the wall temperature is also low, so it is prone to low-temperature corrosion.

[0003] Low temperature corrosion is mainly caused by sulfur dioxide SO and sulfur trioxide SO generated during the combustion of sulfur in the fuel. Among them, sulfur trioxide SO reacts with water vapor in the flue gas to generate sulfuric acid vapor HSO. When the exhaust temperature is close to the acid dew point temperature, sulfuric acid vapor will condense on the outer wall of the tube, causing acid corrosion on the metal wall. The acid dew point temperature is usually in the range of 105℃-130℃, depending on the sulfur content of the fuel. The higher the sulfur content in the fuel, the more sulfur trioxide SO is generated, and the more serious the corrosion. The presence of catalysts (such as denitrification catalysts) will accelerate the oxidation of sulfur dioxide SO to sulfur trioxide SO, thereby increasing the risk of corrosion, and solid particles in the flue gas will form ash accumulation in the air preheater tube bundle, reducing heat exchange efficiency and aggravating corrosion. Low temperature corrosion will affect the combustion efficiency of the boiler, and easily increase the power consumption of the induced draft fan, reduce the thermal efficiency of the boiler, and increase the equipment maintenance cost and replacement frequency. Summary of the invention

[0004] In view of this, the present invention aims to provide a system for preventing low-temperature corrosion of a boiler air preheater and a method of using the system to solve the problem of low-temperature corrosion of the boiler air preheater.

[0005] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a system for preventing low-temperature corrosion of a boiler air preheater, which includes a cold air duct, an air preheater, an air preheater flue inlet, a hot air duct and a bypass air duct, wherein the cold air duct inlet is connected to a fan, and the outlet is connected to the air preheater inlet, the air preheater is connected to the air preheater flue inlet, a second flue gas temperature measuring device is arranged on the air preheater flue inlet, the air preheater outlet is connected to the hot air duct, one end of the bypass air duct is arranged on the cold air duct, and the other end is arranged on the hot air duct, a third air gate is arranged on the hot air duct, a first air gate is arranged on the cold air duct, and a second air gate is arranged on the bypass air duct.

[0006] Furthermore, there are two cold air ducts and two fans, one fan is provided at the entrance of each cold air duct, and the first smoke temperature measuring device is provided at the outlet ends of the two cold air ducts and is connected to the air preheater.

[0007] Furthermore, a first air volume measuring device is provided on each of the two cold air ducts, and the first air volume measuring device is provided in front of the first air door.

[0008] Furthermore, there are two bypass air ducts, each of which is connected to a cold air duct, and the inlets of the two bypass air ducts are arranged between the first air gate and the first air volume measuring device, and the second air volume measuring device and the second air gate are arranged on the two bypass air ducts.

[0009] Furthermore, there are two hot air ducts, and the third air door is arranged on each of the two hot air ducts, and each of the two hot air ducts is connected to a bypass air duct.

[0010] Furthermore, there are two air preheater flue inlets, which are arranged in parallel.

[0011] Furthermore, pressure measuring devices are provided on the bypass air duct, the hot air duct and the cold air duct.

[0012] Furthermore, air duct balancing pipes are provided on both cold air ducts.

[0013] Furthermore, a filtering device is provided at the outlet end of the fan.

[0014] A method for using a system for preventing low temperature corrosion of a boiler air preheater comprises the following steps:

[0015] S1: When the boiler is running at high load, when the second flue gas temperature detection device on the air preheater inlet flue detects that the flue gas temperature is higher than the acid dew point temperature, the second damper on the bypass air duct is closed, the first damper on the cold air duct and the third damper on the hot air duct are both opened, and the air is sent into the cold air duct through the fan and enters the air preheater. After being heated by the flue gas, it is led out through the hot air duct and enters the various air points of the boiler;

[0016] S2: When the boiler is running at low load, the second flue gas temperature detection device on the air preheater inlet flue detects that the flue gas temperature is lower than the acid dew point temperature, the first damper on the cold air duct and the third damper on the hot air duct are closed, the second damper on the bypass air duct is opened, and the air is sent into the cold air duct through the fan, then enters the bypass air duct, and finally enters the boiler's air use point.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The present invention establishes a bypass air duct. When the flue gas temperature is close to the acid dew point temperature, the cold air generated by the fan directly enters the hot air duct through the bypass air duct, and no longer passes through the air preheater to cool the flue gas, thereby avoiding low-temperature corrosion of the air preheater;

[0019] 2. The present invention is provided with temperature measuring devices and dampers on the hot air duct, the cold air duct and the bypass air duct. The temperature measuring devices and dampers on the hot air duct, the cold air duct and the bypass air duct are linked to realize automatic switching of working conditions without manual intervention, thus reducing the amount of manual work;

[0020] 3. The present invention can automatically adjust the operation mode according to the changes in boiler load and flue gas temperature, adapt to different working conditions, and ensure the stable operation of the boiler under different load conditions. Under high load conditions, the air preheater works normally, which can make full use of the waste heat of the flue gas and improve the thermal efficiency of the boiler;

[0021] 4. The bypass design of the present invention effectively avoids the corrosion problem of the air preheater under low temperature conditions, reduces the cost of equipment maintenance and replacement, and extends the service life of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0023] Figure 1 The present invention is a schematic structural diagram of a system for preventing low-temperature corrosion of a boiler air preheater.

[0024] In the figure:

[0025] 1. First air volume detection device; 2. First air door; 3. First smoke temperature measuring device; 4. Second air volume measuring device; 5. Second air door; 6. Third air door; 7. Bypass air duct; 8. Hot air duct; 9. Cold air duct; 10. Air preheater; 11. Air preheater smoke duct inlet; 12. Second smoke temperature measuring device; 13. Fan. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely explain the technical solutions in the embodiments of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict, and the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0027] Specific implementation method: see Figure 1The present embodiment is described as a system for preventing low-temperature corrosion of a boiler air preheater, comprising a cold air duct 9, an air preheater 10, an air preheater flue inlet 11, a hot air duct 8 and a bypass air duct 7. The inlet of the cold air duct 9 is connected to a fan 13, and the outlet is connected to the inlet of the air preheater 10. The cold air duct 9 is used to transport air from the fan 13 to the air preheater 10. The air preheater 10 is connected to the air preheater flue inlet 11. The air preheater 10 uses the waste heat of the flue gas at the tail end of the boiler to heat the cold air entering the boiler, thereby improving the thermal efficiency of the boiler. A second flue gas temperature measuring device 12 is provided on the air preheater flue inlet 11. The second flue gas temperature measuring device 12 is used to monitor the temperature of the flue gas in real time. The outlet of the device 10 is connected to the hot air duct 8, and the hot air duct 8 is used to transport the cooled flue gas to various air-using points of the boiler. One end of the bypass air duct 7 is arranged on the cold air duct 9, and the other end is arranged on the hot air duct 8. The bypass air duct 7 is used to bypass the air preheater 10, so that the cold air generated by the fan 13 no longer enters the air preheater 10, thereby no longer cooling the air in the air preheater 10, preventing the cold end of the air preheater 10 from generating a lower temperature and causing corrosion to the pipeline. A third damper 6 is arranged on the hot air duct 8, a first damper 2 is arranged on the cold air duct 9, and a second damper 5 is arranged on the bypass air duct 7. The first damper 2, the second damper 5 and the third damper 6 respectively control the opening and closing of the cold air duct 9, the bypass air duct 7 and the hot air duct 8.

[0028] The working principle of the present invention is as follows:

[0029] When the boiler is operated under high load conditions, that is, ≥40% BMCR conditions, and the flue gas temperature detected by the second flue gas temperature detection device 12 on the air preheater inlet flue 11 is higher than the acid dew point, the first damper 2 and the third damper 6 are opened to allow cold air to enter the air preheater 10 through the cold air duct 9. After the cold air is heated in the air preheater 10, it is transported to various air use points of the boiler through the hot air duct 8. At this time, the second damper 5 is in a closed state, and the bypass air duct 7 does not work. When the boiler is under low load, the second damper 5 is in a closed state, and the bypass air duct 7 does not work. When the air preheater is under low load conditions, that is, when the BMCR condition is ≤40%, and the flue gas temperature detected by the second flue gas temperature detection device 12 on the air preheater inlet flue 11 is close to the acid dew point, the first damper 2 and the third damper 6 are closed to prevent cold air from entering the air preheater 10, and the second damper 5 is opened, and the cold air directly enters the hot air duct 8 through the bypass air duct 7, bypassing the air preheater 10. The air in the hot air duct 8 is directly transported to various air consumption points of the boiler to avoid damage to the air preheater 10 due to low-temperature corrosion.

[0030] There are two cold air ducts 9 and two fans 13. A fan 13 is set at the entrance of each cold air duct 9. The first smoke temperature measuring device 3 is set at the outlet end of the two cold air ducts 9 and is connected to the air preheater 10. The stability of air supply and the reliability of the system are ensured by setting two cold air ducts 9 and two fans 13. The fan 13 is used to provide power for the cold air ducts 9 to send cold air into the air preheater 10. The first smoke temperature measuring device 3 is used to ensure that the air temperature entering the air preheater meets the design requirements.

[0031] A first air volume measuring device 1 is provided on both cold air ducts 9. The first air volume measuring device 1 is used to measure the cold air volume entering the air preheater 10. The first air volume measuring device 1 is arranged in front of the first damper 2 to ensure that the air volume is accurately measured before the first damper 2 adjusts the air volume.

[0032] There are two bypass air ducts 7, each of which is connected to a cold air duct 9. The entrances of the two bypass air ducts 7 are arranged between the first air gate 2 and the first air volume measuring device 1 to ensure that the air volume measuring device can accurately measure the bypass air volume when the bypass is in operation. The two bypass air ducts 7 are used to bypass the air preheater 10 when the boiler is in a low-load condition to prevent low-temperature corrosion. The second air volume measuring device 4 and the second air gate 5 are arranged on the two bypass air ducts 7. The design of double cold air ducts 9 and double bypass air ducts 7 improves the redundancy and reliability of the system. Even if some equipment fails, the system can still operate normally.

[0033] There are two hot air ducts 8, each of which is provided with a third air door 6, and each of the two hot air ducts 8 is connected to a bypass air duct 7. The hot air duct 8 is used to transport the hot air heated by the air preheater 10 to the combustion system of the boiler or other air use points.

[0034] There are two air preheater flue inlets 11, which are arranged in parallel. The air preheater flue inlets 11 are used to introduce the flue gas in the tail flue of the boiler into the air preheater for heat exchange.

[0035] The bypass air duct 7, the hot air duct 8 and the cold air duct 9 are all provided with pressure measuring devices, which can monitor the pressure changes in the air duct and the flue in real time, and help the operator to adjust the system operating parameters in time to avoid equipment damage or efficiency reduction due to abnormal pressure.

[0036] The two cold air ducts 9 are both provided with an air duct balance pipe, and the main function of the air duct balance pipe is to balance the air volume distribution in the two cold air ducts. By adjusting the pressure in the balance pipe, the air volume of the two cold air ducts can be ensured to be uniform, avoiding uneven air volume distribution caused by differences in air duct resistance.

[0037] The outlet end of the fan 13 is provided with a filter device, which is mainly used to filter dust and impurities in the air to protect the normal operation of subsequent equipment and improve combustion efficiency.

[0038] A method for using a system for preventing low temperature corrosion of a boiler air preheater comprises the following steps:

[0039] S1: When the boiler is running at high load, when the second smoke temperature detection device 12 on the air preheater inlet flue 11 detects that the smoke temperature is higher than the acid dew point temperature, the second damper 5 on the bypass air duct 7 is closed, and the bypass air duct 7 does not work at this time, ensuring that the air is heated by the air preheater 10. The first damper 2 on the cold air duct 9 and the third damper 6 on the hot air duct 8 are both opened, and the air is sent into the cold air duct 9 and enters the air preheater 10 through the fan 13. After being heated by the smoke, the air is led out through the hot air duct 8 and enters each wind point of the boiler, thereby making full use of the waste heat of the smoke, improving the thermal efficiency of the boiler, and avoiding the problem of low-temperature corrosion of the air preheater 10 caused by low-temperature smoke;

[0040] S2: When the boiler is running at low load, when the second smoke temperature detection device 12 on the air preheater inlet flue 11 detects that the smoke temperature is lower than the acid dew point temperature, the first damper 2 on the cold air duct 9 and the third damper 6 on the hot air duct 8 are both closed to prevent cold air from entering the air preheater 10, and the second damper 5 on the bypass air duct 7 is opened to allow cold air to bypass the air preheater 10. The air is sent into the cold air duct 9 through the fan 13 and then enters the bypass air duct 7, and finally enters the boiler's air use points.

[0041] When the boiler is running at low load, the present invention bypasses the air preheater 10 through the bypass air duct 7 to avoid corrosion of the air preheater 10 by low-temperature flue gas, which can effectively protect the air preheater 10 and extend the service life of the air preheater 10.

[0042] The specific embodiments of the present invention disclosed above are only used to help explain the present invention. The specific embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. According to the content of this specification, many modifications and changes can be made. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well.

Claims

1. A system for preventing low temperature corrosion of a boiler air preheater, characterized in that: It comprises a cold air duct (9), an air preheater (10), an air preheater flue inlet (11), a hot air duct (8) and a bypass air duct (7). The cold air duct (9) inlet is connected to a fan (13), and the outlet is connected to the air preheater (10) inlet. The air preheater (10) is connected to the air preheater flue inlet (11). A second flue gas temperature measuring device (12) is arranged on the air preheater flue inlet (11). The air preheater (10) outlet is connected to the hot air duct (8). One end of the bypass air duct (7) is arranged on the cold air duct (9), and the other end is arranged on the hot air duct (8). A third air door (6) is arranged on the hot air duct (8). A first air door (2) is arranged on the cold air duct (9), and a second air door (5) is arranged on the bypass air duct (7).

2. A system for preventing low temperature corrosion of a boiler air preheater according to claim 1, characterized in that: There are two cold air ducts (9) and two fans (13), one fan (13) is provided at the entrance of each cold air duct (9), and a first smoke temperature measuring device (3) is provided at the outlet ends of the two cold air ducts (9) and is connected to the air preheater (10).

3. A system for preventing low temperature corrosion of a boiler air preheater according to claim 2, characterized in that: A first air volume measuring device (1) is provided on each of the two cold air ducts (9), and the first air volume measuring device (1) is provided in front of the first air door (2).

4. A system for preventing low temperature corrosion of a boiler air preheater according to claim 3, characterized in that: There are two bypass air ducts (7), each of which is connected to a cold air duct (9). The inlets of the two bypass air ducts (7) are arranged between the first air door (2) and the first air volume measuring device (1). The second air volume measuring device (4) and the second air door (5) are arranged on the two bypass air ducts (7).

5. A system for preventing low temperature corrosion of a boiler air preheater according to claim 4, characterized in that: There are two hot air ducts (8), each of which is provided with a third air door (6), and each of the two hot air ducts (8) is connected to a bypass air duct (7).

6. A system for preventing low temperature corrosion of a boiler air preheater according to claim 1, characterized in that: There are two air preheater flue inlets (11), and the two air preheater flue inlets (11) are arranged in parallel.

7. A system for preventing low temperature corrosion of a boiler air preheater according to claim 1, characterized in that: Pressure measuring devices are provided on the bypass air duct (7), the hot air duct (8) and the cold air duct (9).

8. A system for preventing low temperature corrosion of a boiler air preheater according to claim 2, characterized in that: Air duct balance pipes are provided on both cold air ducts (9).

9. A system for preventing low temperature corrosion of a boiler air preheater according to claim 1, characterized in that: A filtering device is provided at the outlet end of the fan (13).

10. A method for using the system for preventing low temperature corrosion of a boiler air preheater according to claim 1, characterized in that: The following steps are involved: S1: When the boiler is running at high load, the second smoke temperature detection device (12) on the air preheater inlet smoke duct (11) detects that the smoke temperature is higher than the acid dew point temperature, the second damper (5) on the bypass air duct (7) is closed, the first damper (2) on the cold air duct (9) and the third damper (6) on the hot air duct (8) are both opened, and the air is sent into the cold air duct (9) and enters the air preheater (10) through the fan (13), and after being heated by the smoke, it is led out through the hot air duct (8) and enters the various air points of the boiler; S2: When the boiler is running at low load, the second smoke temperature detection device (12) on the air preheater inlet smoke duct (11) detects that the smoke temperature is lower than the acid dew point temperature, the first damper (2) on the cold air duct (9) and the third damper (6) on the hot air duct (8) are both closed, the second damper (5) on the bypass air duct (7) is opened, and the air is sent into the cold air duct (9) through the fan (13), then enters the bypass air duct (7), and finally enters the boiler's air use point.

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