Air preheater system for boiler and method for reducing exhaust gas temperature of air preheater system

Abstract

The invention provides an air preheater system for a boiler and a method for reducing the exhaust gas temperature of the air preheater system, and belongs to the technical field of boilers of heat energy engineering. The problem that the boiler efficiency is reduced due to the fact that the smoke exhaust temperature is reduced through a smoke waste heat utilization device but absorbed heat cannot return to a boiler system is solved. The device comprises a main flue, a bypass flue, a high-pressure fluidizing air heater and a rotary air preheater, an inlet of the main flue is connected with the tail of the boiler, a main flue gas adjusting baffle and the rotary air preheater are sequentially arranged in the main flue in the circulation direction, the bypass flue is arranged on the main flue, and the high-pressure fluidizing air heater is arranged on the bypass flue. An inlet of the bypass flue is arranged above the main flue gas adjusting baffle, a high-pressure fluidized air heater is arranged in the bypass flue, and a bypass flue gas adjusting baffle is arranged above the high-pressure fluidized air heater. The boiler efficiency is improved mainly by reducing the exhaust gas temperature.

Description

Technical Field

[0001] The invention belongs to the technical field of boilers in thermal energy engineering, and in particular relates to an air preheater system for a boiler and a method for reducing exhaust gas temperature thereof. Background Art

[0002] Circulating fluidized bed boiler (CFB boiler for short), boiler thermal efficiency is a key indicator for evaluating boiler operating conditions and an important basis for guiding boiler efficient operation. The factors affecting boiler thermal efficiency have potential application value in improving boiler operating efficiency. The high-pressure fluidizing air of CFB boilers generally uses cold air, resulting in a high boiler cold air rate, which limits further reduction of boiler exhaust temperature and is not conducive to improving boiler efficiency. There is often a certain amount of energy loss during operation, which is not conducive to achieving energy-saving goals and obtaining economic benefits.

[0003] At present, the existing coal-fired power generation unit boiler rotary preheater bypass flue is generally equipped with a flue gas waste heat utilization device, which is used to heat part of the condensate, improve the thermal efficiency of the unit, and heat the circulating water of the heat network for heating. The flue gas waste heat utilization device is used to reduce the exhaust gas temperature of the boiler, but the reduced heat cannot be returned to the boiler system, which not only does not contribute to the improvement of boiler efficiency, but also reduces the boiler efficiency, and as the boiler body is adjusted in operation, it will affect the entire steam turbine system. Summary of the invention

[0004] In view of this, the present invention aims to propose an air preheater system for a boiler and a method for reducing the exhaust temperature through the air preheater system of the boiler, so as to solve the problem that the exhaust temperature is reduced by the flue gas waste heat utilization device, but the absorbed heat cannot be returned to the boiler system, resulting in a decrease in boiler efficiency.

[0005] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: an air preheater system for a boiler, which includes a main flue, a bypass flue, a high-pressure fluidized air heater, and a rotary air preheater, wherein the main flue inlet is connected to the tail of the boiler, and a main flue gas regulating baffle and a rotary air preheater are sequentially arranged in the main flue along the flow direction, a bypass flue is opened on the main flue, and the bypass flue inlet is arranged above the main flue gas regulating baffle, a high-pressure fluidized air heater is arranged in the bypass flue, and a bypass flue gas regulating baffle is arranged above the high-pressure fluidized air heater, the outlet of the bypass flue is connected to the outlet of the main flue, and the high-pressure fluidized air inlet and outlet are arranged on the high-pressure fluidized air heater, and the outlet of the high-pressure fluidized air is connected to the boiler.

[0006] Furthermore, the rotary air preheater is connected to the cold air duct and the hot air duct respectively.

[0007] Furthermore, an economizer is arranged in the main flue, and the economizer is arranged above the inlet of the bypass flue.

[0008] Furthermore, the high-pressure fluidized air heater includes a heating shell, a heat exchange serpentine, an inlet wind box and an outlet wind box. The heat exchange serpentine is arranged in the heating shell, the inlet wind box is arranged on the lower side wall of the heating shell, and the outlet wind box is arranged on the upper side wall. The inlet wind box is the inlet of the high-pressure fluidized air, and the outlet wind box is the outlet of the high-pressure fluidized air. The inlet wind box is connected to the inlet of the heat exchange serpentine, and the outlet wind box is connected to the outlet of the heat exchange serpentine.

[0009] Furthermore, there are a plurality of heat exchange serpentine tubes, and the plurality of heat exchange serpentine tubes are arranged side by side.

[0010] Furthermore, the inlet wind box and the outlet wind box are connected to the inlet and the outlet of the heat exchange serpentine tube respectively through the tube sheet.

[0011] Furthermore, a fixing device is arranged inside the heating shell, and the heat exchange serpentine tube is fixed in the heating shell by the fixing device.

[0012] Furthermore, the fixing device includes a support and a hook, the support is fixed on the inner wall of the heating shell, one end of the hook is connected to the support, and the other end is connected to the heat exchange serpentine tube.

[0013] Furthermore, a plurality of individual manhole doors and a plurality of steam soot blowers are also arranged on the side wall of the heating shell, and the plurality of individual manhole doors and the plurality of steam soot blowers are arranged at equal intervals.

[0014] A method for reducing exhaust gas temperature, the method is implemented based on an air preheating system for a boiler, and the method comprises the following steps:

[0015] S1: The flue gas generated by the boiler enters the main flue and is divided into two paths before entering the air preheater. One part enters the rotary air preheater and the other part enters the bypass flue. The main flue gas regulating damper is adjusted to control the flue gas volume entering the rotary air preheater from the main flue, and the bypass flue gas regulating damper is adjusted to control the flue gas volume entering the high-pressure fluidized air heater from the bypass flue.

[0016] S2: The flue gas in the main flue enters the rotary air preheater for heat exchange, and the flue gas in the bypass flue enters the high-pressure fluidized air heater for heat exchange, thereby reducing the exhaust gas temperature of the two routes;

[0017] S3: The flue gases in the main flue and the bypass flue are cooled and then discharged.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention arranges the high-pressure fluidized air heater and the rotary air preheater in parallel to increase the temperature difference at the hot end of the rotary air preheater, thereby making the exhaust temperature of the main flue lower than the exhaust temperature of the high-pressure fluidized air heater and the rotary air preheater arranged in series;

[0020] 2. The present invention divides the flue gas into two paths before the flue gas enters the rotary air preheater. When the amount of cold air entering the rotary air preheater from the cold air duct remains unchanged, the amount of flue gas entering the rotary air preheater is reduced, thereby improving the efficiency of the rotary air preheater and reducing the exhaust temperature of the main flue gas.

[0021] 3. The present invention sets a high-pressure fluidized air heater in the bypass flue, and uses high-pressure fluidized air to cool the flue gas in the bypass flue, thereby reducing the exhaust temperature of the bypass flue, making the flue gas temperature drop to a lower level, and finally making the boiler exhaust temperature lower and the boiler operation efficiency higher;

[0022] 4. The high-pressure fluidized air heater of the present invention adopts a heat exchange serpentine tube form and is connected by a tube sheet, which effectively reduces the air leakage rate of the high-pressure fluidized air heater and also effectively reduces the resistance loss along the way, thereby improving reliability and economy;

[0023] 5. The present invention arranges flue gas regulating dampers in the main flue and the bypass flue, and realizes the adjustment of boiler exhaust temperature through coordinated adjustment of the flue gas regulating dampers in the main flue and the bypass flue. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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:

[0025] Figure 1 This is a structural schematic diagram of an air preheater system for a boiler according to the present invention;

[0026] Figure 2 It is a structural schematic diagram of a high-pressure fluidized air heater for an air preheater system of a boiler according to the present invention;

[0027] Figure 3 This is a schematic structural diagram of a fixing device for a high-pressure fluidized air heater of an air preheater system of a boiler according to the present invention.

[0028] In the figure:

[0029] 1. Main flue; 2. Bypass flue; 3. Main flue gas regulating damper; 4. Bypass flue gas regulating damper; 5. High-pressure fluidized air heater; 6. Rotary air preheater; 7. Cold air duct; 8. Hot air duct; 9. Heater shell; 10. Heat exchange serpentine tube; 11. Inlet bellows; 12. Outlet bellows; 13. Tube sheet; 14. Manhole door; 15. Steam soot blower; 16. Fixing device; 17. Economizer; 18. Support; 19. Hook. DETAILED DESCRIPTION

[0030] 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.

[0031] Specific implementation method: see Figure 1 The present embodiment is described, an air preheater system for a boiler, comprising a main flue 1, a bypass flue 2, a high-pressure fluidized air heater 5, and a rotary air preheater 6. The inlet of the main flue 1 is connected to the tail of the boiler. The main flue 1 is used to recover the flue gas generated by the boiler. A main flue gas regulating baffle 3 and a rotary air preheater 6 are sequentially arranged in the main flue 1 along the flow direction. The main flue gas regulating baffle 3 is used to regulate the amount of flue gas entering the rotary air preheater 3. The rotary air preheater 6 is used to perform heat exchange on the flue gas entering the main flue 1. A bypass flue 2 is opened on the main flue 1. The bypass flue 2 is used to disperse the amount of flue gas entering the main flue 1. The inlet of the bypass flue 2 is arranged above the main flue gas regulating baffle 3. Before the flue gas enters the air rotary preheater 6, a portion of the flue gas is separated and enters the bypass flue 2. A high-pressure fluidized air heater 5 is arranged in the bypass flue 2. The high-pressure fluidized air heater 5 is used to exchange heat with the flue gas entering the bypass flue 2. A bypass flue gas regulating baffle 4 is arranged above the high-pressure fluidized air heater 5. The bypass flue gas regulating baffle 4 is used to control the amount of flue gas entering the high-pressure fluidized air heater 5. The outlet of the bypass flue 2 is connected to the outlet of the main flue 1. The flue gas is collected at the outlet of the main flue 1 after heat exchange through the air rotary preheater 6 and the high-pressure fluidized air heater 5. The high-pressure fluidized air inlet and outlet are arranged on the high-pressure fluidized air heater 5. The outlet of the high-pressure fluidized air is connected to the boiler, and the heat generated by the flue gas is recovered to the boiler through the high-pressure fluidized air outlet.

[0032] The working principle of the present invention is as follows:

[0033] The flue gas generated by the boiler is divided into two paths before entering the rotary air preheater 6. One part enters the main flue 1 and is heat exchanged through the rotary air preheater 6, and the other part enters the bypass flue 2 and is heat exchanged through the high-pressure fluidized air heater 5 in the bypass flue 2. By setting the main flue 1 and the bypass flue 2, the flue gas entering the rotary air preheater 6 is reduced, and the heat exchange efficiency of the rotary air preheater 6 is made higher, thereby reducing the exhaust temperature of the main flue 1. The bypass flue 2 exchanges heat with the flue gas through the high-pressure fluidized air heater 5. After the flue gas temperature is reduced by the rotary air preheater 6 and the high-pressure fluidized air heater 5, it is gathered at the outlet of the main flue 1 and discharged. The heat absorbed by the rotary air preheater 6 and the high-pressure fluidized air heater 5 is recovered into the boiler through the corresponding outlet.

[0034] The rotary air preheater 6 is connected to the cold air duct 7 and the hot air duct 8 respectively. The cold air duct 7 is connected to the pipeline of the boiler air inlet for conveying unheated cold air to the rotary air preheater 6. The hot air duct 8 is connected to the pipeline of the boiler air outlet for conveying heated hot air to the boiler for combustion.

[0035] An economizer 17 is arranged in the main flue 1. The economizer 17 is used to improve the thermal efficiency of the boiler and reduce the coal consumption by recovering the heat in the flue gas, so as to achieve the purpose of energy saving and emission reduction. The economizer 17 is arranged above the entrance of the bypass flue 2. After the flue gas generated by the boiler passes through the economizer 17, part of the flue gas enters the main flue 1, and part enters the bypass flue 2.

[0036] See also Figure 2 In this embodiment, the high-pressure fluidized air heater 5 includes a heating shell 9, a heat exchange coil 10, an inlet wind box 11 and an outlet wind box 12. The heat exchange coil 10 is arranged in the heating shell 9. The heating shell 9 is used to accommodate other components and provide necessary space for heat exchange. The heat exchange coil 10 is used to increase the heat exchange area. The heat exchange coil 10 is usually made of high temperature resistant and corrosion resistant materials to withstand the high temperature flue gas environment. The inlet wind box 11 is arranged on the lower side wall of the heating shell 9, and the outlet wind box 12 is arranged on the upper side wall. 2. The inlet wind box 11 is the inlet of the high-pressure fluidizing air, and the outlet wind box 12 is the outlet of the high-pressure fluidizing air. The inlet wind box 11 is connected to the inlet of the heat exchange coiled tube 10, and the outlet wind box 12 is connected to the outlet of the heat exchange coiled tube 10. The inlet wind box 11 is used to introduce the high-pressure fluidizing air that needs to be heated. The high-pressure fluidizing air enters the heat exchange coiled tube 10 through the inlet wind box 11, and the outlet wind box 12 is used to collect the high-pressure fluidizing air heated by the heat exchange coiled tube 10. The heated high-pressure fluidizing air is discharged from the outlet wind box 12 and is ready to enter the boiler.

[0037] There are a plurality of heat exchange serpentine tubes 10, which are arranged side by side, thereby increasing the heat exchange surface area and achieving a better heat exchange effect.

[0038] The inlet wind box 11 and the outlet wind box 12 are respectively connected to the inlet and outlet of the heat exchange serpentine tube 10 through the tube sheet 13. The tube sheet 13 is used to connect the inlet wind box 11 with the inlet of the heat exchange serpentine tube 10 and the inlet wind box 12 with the outlet of the heat exchange serpentine tube 10. Holes are arranged on the tube sheet 13. The holes on the tube sheet 13 match the holes at both ends of the heat exchange serpentine tube 10 to ensure that the high-pressure fluidizing air can enter the heat exchange serpentine tube 10 from the inlet wind box 11 and can flow out from the heat exchange serpentine tube 10 to the outlet wind box 12.

[0039] See also Figure 2-3 To illustrate this embodiment, a fixing device 16 is provided inside the heating shell 9, and the heat exchange serpentine tube 10 is fixed in the heating shell 9 by the fixing device 16. The fixing device 16 is used to ensure the stability of the position of the heat exchange serpentine tube 10 in the heating shell 9 and prevent the heat exchange serpentine tube 10 from moving or deforming during operation, thereby ensuring the heat exchange efficiency and the reliability of the system.

[0040] The fixing device includes a support 18 and a hook 19. The support 18 is fixed on the inner wall of the heating shell 9. One end of the hook 19 is connected to the support 18, and the other end is connected to the heat exchange serpentine tube 10. The support 18 is welded inside the heating shell 9 and provides a support point for the hook 19. The hook 19 is used to adapt to the bending shape of the heat exchange serpentine tube 10, thereby providing better support for the heat exchange serpentine tube 10.

[0041] A plurality of manhole doors 14 and a plurality of steam soot blowers 15 are also provided on the side wall of the heating shell 9. The manhole doors 14 and the steam soot blowers 15 are arranged at equal intervals. The manhole doors 14 are used for personnel to enter and exit the heating shell 9 for inspection, maintenance and cleaning. The steam soot blowers 15 are used to remove accumulated dust and dirt inside the heating shell 9. The steam soot blowers 15 remove dust and other deposits attached to the surface of the heat exchanger by high-pressure steam jets to maintain the heat exchange efficiency and the cleanliness of the equipment. The plurality of steam soot blowers 15 can cover the entire interior of the heating shell 9.

[0042] See also Figure 1-2 The present embodiment is described as a method for reducing the exhaust gas temperature, the method is implemented based on an air preheating system for a boiler, and the method comprises the following steps:

[0043] S1: The flue gas generated by the boiler enters the main flue 1, and is divided into two paths before entering the air preheater 6, one part enters the rotary air preheater 6, and the other part enters the bypass flue 2. The flue gas volume entering the rotary air preheater 6 from the main flue 1 is controlled by adjusting the main flue gas regulating damper 3, and the flue gas volume entering the high-pressure fluidized air heater 5 from the bypass flue 2 is controlled by adjusting the bypass flue gas regulating damper 4. By controlling the flue gas volume of the two paths, the thermal efficiency of the air preheater 6 is improved, thereby controlling the exhaust gas temperature of the two paths;

[0044] S2: The flue gas temperature generated by the boiler is 345℃~350℃. The flue gas in the main flue 1 enters the rotary air preheater 6 for heat exchange with the cold primary air and cold secondary air of the boiler. The rotary air preheater 6 reduces the exhaust gas temperature in the main flue 1 to 113℃~115℃. The flue gas in the bypass flue 2 enters the high-pressure fluidized air heater 5 for heat exchange. The high-pressure fluidized air heater 5 reduces the exhaust gas temperature in the bypass flue 2 to 145℃~147℃. After the bypass flue 2 is set, the amount of flue gas entering the rotary air preheater 6 is reduced, and the exhaust gas temperature in the main flue 1 will be lower. After the flue gas in the bypass flue 2 is heated by the high-pressure fluidized air, the high-pressure fluidized air changes from cold air to hot air, thereby reducing the exhaust gas temperatures of the two routes. The heat absorbed by the rotary air preheater 6 in the main flue 1 and the high-pressure fluidized air heater 5 in the bypass flue 2 is completely returned to the boiler body, thereby improving the thermal efficiency of the boiler;

[0045] S3: The flue gases in the main flue 1 and the bypass flue 2 are cooled down respectively and then mixed into one flue gas. The mixed flue gas has a temperature of 115°C to 117°C and is discharged from the boiler.

[0046] The method for reducing the exhaust temperature of the air preheater system of the boiler of the present invention comprises the following steps: by adding a rotary air preheater 6 and a bypass flue 2, the amount of flue gas entering the rotary air preheater 6 is reduced while the amount of cold air entering the rotary air preheater 6 through the cold air duct 7 remains unchanged, thereby reducing the exhaust temperature of the main flue 1; a high-pressure fluidized air heater 5 is arranged in the bypass flue 2, and the flue gas in the bypass flue 2 is cooled by the high-pressure fluidized air, thereby reducing the exhaust temperature of the bypass flue 2 and lowering the flue gas temperature, thereby finally lowering the exhaust temperature of the boiler and improving the operating efficiency of the boiler.

[0047] 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. An air preheater system for a boiler, characterized in that: It comprises a main flue (1), a bypass flue (2), a high-pressure fluidized air heater (5), and a rotary air preheater (6); the inlet of the main flue (1) is connected to the rear of the boiler; a main flue gas regulating baffle (3) and a rotary air preheater (6) are sequentially arranged in the main flue (1) along the flow direction; a bypass flue (2) is provided on the main flue (1); the inlet of the bypass flue (2) is arranged above the main flue gas regulating baffle (3); a high-pressure fluidized air heater (5) is arranged in the bypass flue (2); a bypass flue gas regulating baffle (4) is arranged above the high-pressure fluidized air heater (5); the outlet of the bypass flue (2) is connected to the outlet of the main flue (1); the high-pressure fluidized air inlet and outlet are arranged on the high-pressure fluidized air heater (5); and the outlet of the high-pressure fluidized air is connected to the boiler.

2. An air preheater system for a boiler according to claim 1, characterized in that: The rotary air preheater (6) is connected to the cold air duct (7) and the hot air duct (8) respectively.

3. The air preheater system for a boiler according to claim 1, characterized in that: An economizer (17) is arranged in the main flue (1), and the economizer (17) is arranged above the entrance of the bypass flue (2).

4. The air preheater system for a boiler according to claim 1, characterized in that: The high-pressure fluidizing air heater (5) comprises a heating shell (9), a heat exchange serpentine tube (10), an inlet wind box (11) and an outlet wind box (12). The heat exchange serpentine tube (10) is arranged in the heating shell (9), the inlet wind box (11) is arranged on the lower side wall of the heating shell (9), and the outlet wind box (12) is arranged on the upper side wall. The inlet wind box (11) is the inlet of the high-pressure fluidizing air, and the outlet wind box (12) is the outlet of the high-pressure fluidizing air. The inlet wind box (11) is connected to the inlet of the heat exchange serpentine tube (10), and the outlet wind box (12) is connected to the outlet of the heat exchange serpentine tube (10).

5. An air preheater system for a boiler according to claim 4, characterized in that: The heat exchange serpentine tubes (10) are multiple in number, and the multiple heat exchange serpentine tubes (10) are arranged side by side.

6. The air preheater system for a boiler according to claim 4, characterized in that: The inlet wind box (11) and the outlet wind box (12) are respectively connected to the inlet and outlet of the heat exchange serpentine tube (10) through the tube sheet (13).

7. An air preheater system for a boiler according to claim 4, characterized in that: A fixing device (16) is arranged inside the heating shell (9), and the heat exchange serpentine tube (10) is fixed inside the heating shell (9) by the fixing device (16).

8. An air preheater system for a boiler according to claim 7, characterized in that: The fixing device (16) comprises a support (18) and a hook (19), wherein the support (18) is fixed on the inner wall of the heating shell (9), and one end of the hook (19) is connected to the support (18) and the other end is connected to the heat exchange serpentine tube (10).

9. The air preheater system for a boiler according to claim 4, characterized in that: A plurality of individual manhole doors (14) and a plurality of steam soot blowers (15) are also provided on the side wall of the heating shell (9), and the plurality of individual manhole doors (14) and the plurality of steam soot blowers (15) are respectively arranged at equal intervals.

10. A method for reducing exhaust gas temperature, characterized in that: The method is implemented based on the air preheating system for a boiler according to claim 1, and the method comprises the following steps: S1: Flue gas generated by the boiler enters the main flue (1), and is divided into two paths before entering the air preheater (6), one part enters the rotary air preheater (6), and the other part enters the bypass flue (2). The main flue gas regulating damper (3) is adjusted to control the amount of flue gas entering the rotary air preheater (6) from the main flue (1), and the bypass flue gas regulating damper (4) is adjusted to control the amount of flue gas entering the high-pressure fluidized air heater (5) from the bypass flue (2); S2: The flue gas in the main flue (1) enters the rotary air preheater (6) for heat exchange, and the flue gas in the bypass flue (2) enters the high-pressure fluidized air heater (5) for heat exchange, thereby reducing the exhaust gas temperatures of the two flue gases; S3: The flue gases in the main flue (1) and the bypass flue (2) are cooled and then discharged.

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