Flue gas bypass system for reducing exhaust gas temperature under deep peak regulation condition

Abstract

According to the technical scheme, an inlet of a bypass flue is connected with a tail steering chamber, an outlet of the bypass flue is connected with a denitration inlet flue, a newly-added heat exchanger is arranged in a denitration outlet flue in front of an air pre-heater, and the newly-added heat exchanger is connected with the tail steering chamber. An inlet of the newly-added heat exchanger inlet air duct is connected with an air pre-heater outlet hot primary air mother pipe, an outlet of the newly-added heat exchanger inlet air duct is connected with an inlet of the newly-added heat exchanger, and an inlet of the newly-added heat exchanger outlet air duct is connected with an outlet of the newly-added heat exchanger. An outlet of the newly-added heat exchanger outlet air pipeline is connected with the air pre-heater outlet hot primary air mother pipe. The utility model has the beneficial effects that the bypass flue outlet is arranged on the horizontal flue, and high-temperature flue gas is extracted into the main flue behind the economizer, so that the load reduction of a boiler and the uniformity of flue gas temperature distribution during peak regulation are ensured, the catalyst activity temperature of a denitration system is kept stable, and continuous and stable commissioning is realized.

Description

Technical Field

[0001] This utility model relates to the field of power plant boiler technology, and in particular to a flue gas bypass system for reducing flue gas temperature under deep peak shaving conditions. Background Technology

[0002] In oilfield production, self-owned power plants play a crucial role in ensuring production. These power plants are typically thermal power plants. Currently, with thermal power units participating in deep peak shaving, long-term low-load operation has become the norm. Ensuring the normal operation of the denitrification system under peak load is a fundamental requirement for boiler operation. Flue gas bypass systems, as a solution with a large temperature adjustment range and relatively low modification costs, have gained widespread application. However, a disadvantage of flue gas bypass systems is that they lead to increased exhaust gas temperature during operation, affecting the unit's economic efficiency. Under long-term low-load conditions, the impact of higher exhaust gas temperature on boiler operating economics becomes even more pronounced.

[0003] Chinese patent application number 202111066086.4, entitled "A Deep Peak-Shaving System for Combined Thermal Storage of Flue Gas and Steam in a Coal-Fired Boiler and its Operation Method," describes a system comprising a thermal system of a coal-fired power generation unit and a coupled thermal storage system including a cold and hot thermal storage medium tank, a cold thermal storage medium tank outlet regulating valve, a cold thermal storage medium pump, a thermal storage medium heater, and a feedwater preheater. Thermal storage medium heaters are arranged both inside the boiler flue and on the turbine side. The flow rate of the thermal storage medium entering the heaters is regulated by the thermal storage medium pump, simultaneously absorbing heat from the boiler flue gas and turbine steam. This allows the unit to operate stably under extremely low loads while reducing boiler exhaust temperature and improving unit economy. The flow rates of feedwater and thermal storage medium entering the heat exchangers are regulated by the high-pressure and low-pressure heater bypass regulating valve groups and the inlet regulating valves of the thermal storage medium and feedwater heat exchangers, respectively, ensuring the system meets the unit's rapid load change rate requirements. This invention can expand the unit's operating load range and improve flexibility and economy.

[0004] Chinese patent application number 202220914973.6, entitled "A Deep Peak Shaving System for Circulating Fluidized Bed Units," modifies the material circulation system, working fluid, and heat recovery system of circulating fluidized bed units, and incorporates a water bypass for the economizer. The material circulation system, through the installation of a circulating ash removal system combined with flue gas recirculation, ensures bed temperature at low loads, addressing the issues of stable combustion at low boiler loads and low in-furnace desulfurization efficiency. The working fluid and heat recovery system, through the implementation of condensate recirculation, addresses the issues of condensate working fluid and heat recovery during low-load transition to a wet state in supercritical units. The economizer water bypass lowers the inlet temperature of the water-cooled walls, reducing evaporation and helping to maintain steam temperatures close to the rated value. This helps prevent excessively low exhaust gas temperatures from both the working fluid and flue gas sides, thus preventing low-temperature corrosion.

[0005] Under long-term low-load operation of boiler units, the flue gas temperature is too high and the denitrification inlet flue gas temperature is too low under the existing technical solutions, which cannot meet the requirements for safe and reliable operation of the unit under deep peak shaving, and the boiler operation economy is poor. The existing technologies mentioned above cannot solve the above problems. Utility Model Content

[0006] The purpose of this invention is to address the aforementioned deficiencies in the existing technology by providing a flue gas bypass system that reduces exhaust gas temperature under deep peak shaving conditions. When this system is put into operation under deep peak shaving load, it can effectively increase the inlet flue gas temperature of the denitrification system while reducing the exhaust gas temperature, thereby improving the economic efficiency of boiler operation.

[0007] The present invention discloses a flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions. The technical solution includes a furnace (1), a tail-end turning chamber (2), a low-temperature superheater (3), an economizer (4), and a denitrification outlet flue (10). It also includes a denitrification inlet flue (6), a bypass flue (7), an air preheater (11), a new heat exchanger (12), a new heat exchanger inlet air duct (13), a new heat exchanger outlet air duct (15), and an air preheater outlet hot primary air header (16). The inlet of the bypass flue (7) is connected to the tail-end turning chamber (2). The outlet of the bypass flue (7) is connected to the denitrification inlet flue (6). The new heat exchanger (12) is arranged in the denitrification outlet flue (10) before the air preheater (11). The inlet of the new heat exchanger inlet duct (13) is connected to the air preheater outlet hot primary air header (16). The outlet of the new heat exchanger inlet duct (13) is connected to the inlet of the new heat exchanger (12). The inlet of the new heat exchanger outlet duct (15) is connected to the outlet of the new heat exchanger (12). The outlet of the new heat exchanger outlet duct (15) is connected to the air preheater outlet hot primary air header (16).

[0008] Preferably, an air preheater outlet hot primary air main pipe regulating valve (14) is arranged on the air preheater outlet hot primary air main pipe (16) between the junction of the newly added heat exchanger outlet air duct (15) and the air preheater outlet hot primary air main pipe (16) and the branch port between the newly added heat exchanger inlet air duct (13) and the air preheater outlet hot primary air main pipe (16).

[0009] Preferably, the bypass flue (7) is provided with a bypass flue shut-off door (8) and a bypass flue regulating door (9).

[0010] Preferably, an economizer outlet main flue regulating valve (5) is installed in the above-mentioned denitrification inlet flue (6).

[0011] Preferably, the economizer outlet main flue regulating valve (5) is located upstream of the main flue at the junction of the bypass flue (7) and the denitrification inlet flue (6).

[0012] Preferably, the newly added heat exchanger (12) is a tubular or plate air preheater.

[0013] Preferably, the furnace (1) is provided with a tail turning chamber (2) on the upper side, and a low temperature superheater (3) and an economizer (4) are provided in the tail turning chamber (2), and the denitrification inlet flue (6) is connected to the lower end of the tail turning chamber (2).

[0014] Preferably, the above-mentioned denitrification inlet flue (6) is provided with multiple layers of denitrification catalyst (6.1).

[0015] Preferably, the lower part of the above-mentioned denitrification inlet flue (6) is connected to the denitrification outlet flue (10), and a new heat exchanger (12) is installed at the lower part of the denitrification outlet flue (10). The lower part of the new heat exchanger (12) is an air preheater (11).

[0016] Preferably, the above-mentioned new heat exchanger (12) is provided with one or more sets.

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

[0018] This invention proposes setting a bypass flue outlet in the horizontal flue to extract high-temperature flue gas into the main flue after the economizer, ensuring the uniformity of flue gas temperature distribution when the boiler reduces load and participates in peak shaving, keeping the catalyst activity temperature of the denitrification system stable, and achieving continuous and stable operation.

[0019] A regulating valve is installed in the economizer outlet flue, and a regulating valve is also installed in the flue gas bypass system. When the flue gas bypass regulating valve is opened to its maximum but still does not meet the denitrification inlet flue gas temperature requirement, the economizer outlet main flue gas regulating valve can be closed to allow more high-temperature flue gas to enter the economizer downstream main flue gas through the flue gas bypass. This ensures both low-load operation and that the denitrification inlet flue gas temperature is continuously maintained above the lower limit of the catalyst's active temperature, adapting to various load conditions.

[0020] While increasing the inlet flue gas temperature of the denitrification system by bypassing the flue gas, the inlet flue gas temperature of the denitrification system, the outlet flue gas temperature of the denitrification system, and the exhaust gas temperature of the air preheater outlet will all rise simultaneously, resulting in a decrease in boiler efficiency. At this time, a feedback function to reduce the inlet flue gas temperature of the denitrification system can be achieved by adding a heat exchanger, thereby reducing the exhaust gas temperature and improving boiler efficiency.

[0021] This invention has greater application value for boilers that have wide-load denitrification and still require increased primary air temperature and improved drying output of the pulverizing system under low load. Attached Figure Description

[0022] Figure 1 This is a structural schematic diagram of Embodiment 1 of this utility model;

[0023] Figure 2 This is a structural schematic diagram of Embodiment 2 of this utility model;

[0024] Figure 3 This is a structural schematic diagram of Embodiment 5 of this utility model;

[0025] In the diagram above: Furnace 1, Tail Turning Chamber 2, Low-Temperature Superheater 3, Economizer 4, Economizer Outlet Main Flue Regulating Valve 5, Denitrification Inlet Flue 6, Bypass Flue 7, Bypass Flue Shut-off Valve 8, Bypass Flue Regulating Valve 9, Denitrification Outlet Flue 10, Air Preheater 11, New Heat Exchanger 12, New Heat Exchanger Inlet Air Duct 13, Air Preheater Outlet Hot Primary Air Main Pipe Regulating Valve 14, New Heat Exchanger Outlet Air Duct 15, Air Preheater Outlet Hot Primary Air Main Pipe 16, Denitrification Catalyst 6.1. Detailed Implementation

[0026] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0027] Example 1, referring to Figure 1 This utility model discloses a flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions, comprising a furnace 1, a tail-end turning chamber 2, a low-temperature superheater 3, an economizer 4, and a denitrification outlet flue 10. It also includes a denitrification inlet flue 6, a bypass flue 7, an air preheater 11, a new heat exchanger 12, a new heat exchanger inlet air duct 13, a new heat exchanger outlet air duct 15, and an air preheater outlet hot primary air header 16. The inlet of the bypass flue 7 is connected to the tail-end turning chamber 2. The outlet of duct 7 is connected to the denitrification inlet flue 6. The newly added heat exchanger 12 is arranged in the denitrification outlet flue 10 before the air preheater 11. The inlet of the newly added heat exchanger inlet duct 13 is connected to the air preheater outlet hot primary air header 16. The outlet of the newly added heat exchanger inlet duct 13 is connected to the inlet of the newly added heat exchanger 12. The inlet of the newly added heat exchanger outlet duct 15 is connected to the outlet of the newly added heat exchanger 12. The outlet of the newly added heat exchanger outlet duct 15 is connected to the air preheater outlet hot primary air header 16.

[0028] An air preheater outlet hot primary air main pipe regulating valve 14 is arranged on the air preheater outlet hot primary air main pipe 16 between the junction of the newly added heat exchanger outlet air duct 15 and the air preheater outlet hot primary air main pipe 16, and between the branching port of the newly added heat exchanger inlet air duct 13 and the air preheater outlet hot primary air main pipe 16.

[0029] An economizer outlet main flue regulating valve 5 is installed in the denitrification inlet flue 6, and a bypass flue shut-off valve 8 is installed on the bypass flue 7.

[0030] The economizer outlet main flue regulating valve 5 mentioned above is located upstream of the main flue at the junction of the bypass flue 7 and the denitrification inlet flue 6.

[0031] The newly added heat exchanger 12 mentioned above is a tubular air preheater.

[0032] The furnace 1 is provided with a tail turning chamber 2 on the upper side. A low temperature superheater 3 and an economizer 4 are provided in the tail turning chamber 2. The denitrification inlet flue 6 is connected to the lower end of the tail turning chamber 2.

[0033] The lower part of the aforementioned denitrification inlet flue 6 is connected to the denitrification outlet flue 10. A new heat exchanger 12 is installed at the lower part of the denitrification outlet flue 10, and the lower part of the new heat exchanger 12 is the air preheater 11.

[0034] The typical working process of this invention is as follows:

[0035] When the boiler denitrification inlet flue gas temperature is normal, the bypass flue shut-off valve 8 and the air preheater outlet hot primary air main pipe regulating valve 14 remain closed. When the unit participates in peak shaving and load reduction until the denitrification inlet flue gas temperature tends to be lower than the lower limit of the catalyst activity temperature, the bypass flue shut-off valve 8 is opened, and the high-temperature flue gas from the tail diversion chamber 2 enters the denitrification inlet flue 6 through the bypass flue 7 to mix with the low-temperature flue gas in the main flue, thereby increasing the denitrification inlet flue gas temperature.

[0036] As the load continues to decrease, the inlet flue gas temperature for denitrification is maintained above the lower limit of the catalyst's active temperature. If the denitrification inlet flue gas temperature requirement is not met, the regulating valve 5 at the economizer outlet main flue can be closed to allow more high-temperature flue gas to pass through the bypass flue 7, thereby increasing the denitrification inlet flue gas temperature.

[0037] During the process of closing the bypass flue shut-off valve 8 and the economizer outlet main flue regulating valve 5, the flue gas temperature at the denitrification inlet, the flue gas temperature at the denitrification outlet, and the exhaust gas temperature at the air preheater outlet will all rise simultaneously, resulting in a decrease in boiler efficiency. At this time, the regulating valve 14 of the hot primary air header at the air preheater outlet can be gradually closed, allowing part of the hot primary air at the air preheater outlet to be further heated through the new heat exchanger 12 and then sent back to the hot primary air header 16 at the air preheater outlet. By further closing the opening of the regulating valve 14 of the hot primary air header at the air preheater outlet, the amount of primary air entering the new heat exchanger 12 can be increased, thereby reducing the flue gas temperature at the outlet of the new heat exchanger 12, which is the original inlet of the air preheater 11, and thus reducing the exhaust gas temperature and improving boiler efficiency.

[0038] Example 2,

[0039] This utility model discloses a flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions. It includes a furnace 1, a tail-end turning chamber 2, a low-temperature superheater 3, an economizer 4, and a denitrification outlet flue 10. It also includes a denitrification inlet flue 6, a bypass flue 7, an air preheater 11, a new heat exchanger 12, a new heat exchanger inlet air duct 13, a new heat exchanger outlet air duct 15, and an air preheater outlet hot primary air header 16. The inlet of the bypass flue 7 is connected to the tail-end turning chamber 2. The outlet of 7 is connected to the denitrification inlet flue 6. The newly added heat exchanger 12 is arranged in the denitrification outlet flue 10 before the air preheater 11. The inlet of the newly added heat exchanger inlet duct 13 is connected to the air preheater outlet hot primary air header 16. The outlet of the newly added heat exchanger inlet duct 13 is connected to the inlet of the newly added heat exchanger 12. The inlet of the newly added heat exchanger outlet duct 15 is connected to the outlet of the newly added heat exchanger 12. The outlet of the newly added heat exchanger outlet duct 15 is connected to the air preheater outlet hot primary air header 16.

[0040] The difference from Example 1 is:

[0041] Reference Figure 2 In this embodiment, the newly added heat exchanger 12 is provided in more than one set, thereby achieving a better heat exchange effect.

[0042] This invention has greater application value for boilers that have wide-load denitrification and still require increased primary air temperature and improved drying output of the pulverizing system under low load.

[0043] Example 3,

[0044] This utility model discloses a flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions. It includes a furnace 1, a tail-end turning chamber 2, a low-temperature superheater 3, an economizer 4, and a denitrification outlet flue 10. It also includes a denitrification inlet flue 6, a bypass flue 7, an air preheater 11, a new heat exchanger 12, a new heat exchanger inlet air duct 13, a new heat exchanger outlet air duct 15, and an air preheater outlet hot primary air header 16. The inlet of the bypass flue 7 is connected to the tail-end turning chamber 2. The outlet of 7 is connected to the denitrification inlet flue 6. The newly added heat exchanger 12 is arranged in the denitrification outlet flue 10 before the air preheater 11. The inlet of the newly added heat exchanger inlet duct 13 is connected to the air preheater outlet hot primary air header 16. The outlet of the newly added heat exchanger inlet duct 13 is connected to the inlet of the newly added heat exchanger 12. The inlet of the newly added heat exchanger outlet duct 15 is connected to the outlet of the newly added heat exchanger 12. The outlet of the newly added heat exchanger outlet duct 15 is connected to the air preheater outlet hot primary air header 16.

[0045] The difference from Example 1 or 2 is:

[0046] The newly added heat exchanger 12 mentioned in this embodiment is a plate air preheater. As a result, the lower exhaust gas temperature and the denitrification inlet gas temperature are both lower in this embodiment, which can meet the requirements for safe and reliable operation of the unit under deep peak shaving and the boiler has good operating economy.

[0047] Example 4,

[0048] This utility model discloses a flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions. It includes a furnace 1, a tail-end turning chamber 2, a low-temperature superheater 3, an economizer 4, and a denitrification outlet flue 10. It also includes a denitrification inlet flue 6, a bypass flue 7, an air preheater 11, a new heat exchanger 12, a new heat exchanger inlet air duct 13, a new heat exchanger outlet air duct 15, and an air preheater outlet hot primary air header 16. The inlet of the bypass flue 7 is connected to the tail-end turning chamber 2. The outlet of 7 is connected to the denitrification inlet flue 6. The newly added heat exchanger 12 is arranged in the denitrification outlet flue 10 before the air preheater 11. The inlet of the newly added heat exchanger inlet duct 13 is connected to the air preheater outlet hot primary air header 16. The outlet of the newly added heat exchanger inlet duct 13 is connected to the inlet of the newly added heat exchanger 12. The inlet of the newly added heat exchanger outlet duct 15 is connected to the outlet of the newly added heat exchanger 12. The outlet of the newly added heat exchanger outlet duct 15 is connected to the air preheater outlet hot primary air header 16.

[0049] The difference from Example 1 or 2 is:

[0050] In this embodiment, the denitrification inlet flue 6 is equipped with a multi-layer denitrification catalyst 6.1, which can achieve better denitrification effect and reduce air pollution.

[0051] Example 5,

[0052] This utility model discloses a flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions. It includes a furnace 1, a tail-end turning chamber 2, a low-temperature superheater 3, an economizer 4, and a denitrification outlet flue 10. It also includes a denitrification inlet flue 6, a bypass flue 7, an air preheater 11, a new heat exchanger 12, a new heat exchanger inlet air duct 13, a new heat exchanger outlet air duct 15, and an air preheater outlet hot primary air header 16. The inlet of the bypass flue 7 is connected to the tail-end turning chamber 2. The outlet of 7 is connected to the denitrification inlet flue 6. The newly added heat exchanger 12 is arranged in the denitrification outlet flue 10 before the air preheater 11. The inlet of the newly added heat exchanger inlet duct 13 is connected to the air preheater outlet hot primary air header 16. The outlet of the newly added heat exchanger inlet duct 13 is connected to the inlet of the newly added heat exchanger 12. The inlet of the newly added heat exchanger outlet duct 15 is connected to the outlet of the newly added heat exchanger 12. The outlet of the newly added heat exchanger outlet duct 15 is connected to the air preheater outlet hot primary air header 16.

[0053] The difference from Example 1 or 2 is:

[0054] Reference Figure 3 In this embodiment, a bypass flue shut-off valve 8 and a bypass flue regulating valve 9 are provided on the bypass flue 7 to draw high-temperature flue gas into the main flue after the economizer, ensuring the uniformity of flue gas temperature distribution when the boiler reduces load and participates in peak shaving, so as to keep the catalyst activity temperature of the denitrification system stable and achieve continuous and stable operation.

[0055] The typical working process of this invention is as follows:

[0056] When the boiler denitrification inlet flue gas temperature is normal, the bypass flue shut-off valve 8, the bypass flue regulating valve 9, and the air preheater outlet hot primary air main pipe regulating valve 14 remain closed. When the unit participates in peak shaving and load reduction until the denitrification inlet flue gas temperature tends to be lower than the lower limit of the catalyst activity temperature, the bypass flue shut-off valve 8 is opened, and the bypass flue regulating valve 9 is gradually opened. The high-temperature flue gas from the tail turning chamber 2 enters the denitrification inlet flue 6 through the bypass flue 7 and mixes with the low-temperature flue gas from the main flue, thereby increasing the denitrification inlet flue gas temperature.

[0057] As the load continues to decrease, the opening of the bypass flue regulating valve 9 increases until it is fully open, so that the inlet flue gas temperature of the denitrification system remains above the lower limit of the catalyst's active temperature. If the denitrification inlet flue gas temperature requirement is still not met even when the bypass flue regulating valve 9 is opened to its maximum, the economizer outlet main flue regulating valve 5 can be closed to allow more high-temperature flue gas to pass through the bypass flue 7, thereby increasing the denitrification inlet flue gas temperature.

[0058] During the opening of the bypass flue shut-off valve 8 and the bypass flue regulating valve 9, and the increasing opening of the bypass flue regulating valve 9 while the economizer outlet main flue regulating valve 5 is closed, the flue gas temperature at the denitrification inlet, the flue gas temperature at the denitrification outlet, and the exhaust gas temperature at the air preheater outlet will all rise simultaneously, leading to a decrease in boiler efficiency. At this time, the regulating valve 14 of the hot primary air header at the air preheater outlet can be gradually closed, allowing some of the hot primary air at the air preheater outlet to be further heated through the new heat exchanger 12 before being returned to the hot primary air header 16 at the air preheater outlet. By further closing the opening of the regulating valve 14 of the hot primary air header at the air preheater outlet, the amount of primary air entering the new heat exchanger 12 can be increased, thereby reducing the flue gas temperature at the outlet of the new heat exchanger 12, which is also the inlet of the original air preheater 11, thus reducing the exhaust gas temperature and improving boiler efficiency.

[0059] The above description is merely a preferred embodiment of this utility model. Any person skilled in the art may modify this utility model or modify it into an equivalent technical solution using the technical solutions described above. Therefore, any simple modifications or equivalent transformations made based on the technical solutions of this utility model are within the scope of protection claimed by this utility model.

Claims

1. A flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions, comprising a furnace (1), a tail-end turning chamber (2), a low-temperature superheater (3), an economizer (4), and a denitrification outlet flue (10), characterized in that: It also includes a denitrification inlet flue (6), a bypass flue (7), an air preheater (11), a new heat exchanger (12), a new heat exchanger inlet air duct (13), a new heat exchanger outlet air duct (15), and an air preheater outlet hot primary air header (16). The inlet of the bypass flue (7) is connected to the tail turning chamber (2), and the outlet of the bypass flue (7) is connected to the denitrification inlet flue (6). The new heat exchanger (12) is arranged in the denitrification outlet flue (10) before the air preheater (11). The inlet of the new heat exchanger inlet air duct (13) is connected to the air preheater outlet hot primary air header (16). The outlet of the new heat exchanger inlet air duct (13) is connected to the inlet of the new heat exchanger (12). The inlet of the new heat exchanger outlet air duct (15) is connected to the outlet of the new heat exchanger (12). The outlet of the new heat exchanger outlet air duct (15) is connected to the air preheater outlet hot primary air header (16).

2. The flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions according to claim 1, characterized in that: An air preheater outlet hot primary air main pipe regulating valve (14) is arranged on the air preheater outlet hot primary air main pipe (16) between the junction of the newly added heat exchanger outlet air duct (15) and the air preheater outlet hot primary air main pipe (16) and the branch port between the newly added heat exchanger inlet air duct (13) and the air preheater outlet hot primary air main pipe (16).

3. A flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions as described in claim 2, characterized in that: The bypass flue (7) is equipped with a bypass flue shut-off valve (8) and a bypass flue regulating valve (9).

4. A flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions as described in claim 1, characterized in that: An economizer outlet main flue regulating valve (5) is installed inside the denitrification inlet flue (6).

5. A flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions according to claim 4, characterized in that: The economizer outlet main flue regulating valve (5) is located upstream of the main flue at the junction of the bypass flue (7) and the denitrification inlet flue (6).

6. A flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions according to claim 1, characterized in that: The newly added heat exchanger (12) is a tubular or plate air preheater.

7. A flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions according to claim 1, characterized in that: The furnace (1) is provided with a tail turning chamber (2) on the upper side. A low temperature superheater (3) and an economizer (4) are provided in the tail turning chamber (2). The denitrification inlet flue (6) is connected to the lower end of the tail turning chamber (2).

8. A flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions according to claim 7, characterized in that: The denitrification inlet flue (6) is equipped with multiple layers of denitrification catalyst (6.1).

9. A flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions as described in claim 8, characterized in that: The lower part of the denitrification inlet flue (6) is connected to the denitrification outlet flue (10), and a new heat exchanger (12) is installed at the lower part of the denitrification outlet flue (10). The lower part of the new heat exchanger (12) is an air preheater (11).

10. A flue gas bypass system for reducing exhaust gas temperature under deep peak shaving conditions according to claim 1, characterized in that: The newly added heat exchanger (12) is provided in one or more sets.

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