A dust removal and smoke exhaust system for a regenerative aluminum double-chamber furnace and its temperature control method

Abstract

The invention discloses a dust removal and smoke exhaust system for a regenerative aluminum double-chamber furnace and a temperature control method thereof; belonging to the technical field of metal casting processing auxiliary devices; it includes a front furnace and a rear furnace equipped with a low-temperature flue and a high-temperature flue; the tail end of the low-temperature flue passes through a low-temperature heat exchanger and is then connected to a bag filter; the tail end of the high-temperature flue passes through a high-temperature heat exchanger and is then connected to a desulfurization and denitration tower; both the low-temperature heat exchanger and the high-temperature heat exchanger are supplied with coolant by a coolant supply device; before the high-temperature flue is connected to the high-temperature heat exchanger, it is also connected to an intermediate heat exchanger through a branch pipe with a first electric control valve; the discharge end of the intermediate heat exchanger is communicated with the discharge end of the high-temperature heat exchanger, and the coolant of the intermediate heat exchanger is provided by the coolant that has undergone heat exchange in the low-temperature heat exchanger; the invention effectively solves the problems that there is currently a lack of a reliable flue gas emission system for the regenerative aluminum double-chamber furnace and it is difficult to effectively control the flue gas temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of metal casting processing auxiliary devices, and particularly relates to a dust removal and smoke exhaust system for a regenerative aluminum double-chamber furnace and a temperature control method therefor. Background Art

[0002] In the production process of regenerative aluminum, since the raw materials of regenerative aluminum are roughly divided into two categories, one is the processing waste generated by aluminum plants in other production processes, and the other is the waste aluminum materials recycled from society; for these two types of raw materials, there is currently a double-chamber melting furnace to meet the different melting and casting requirements between the two; generally, the furnace body is divided into two ends, the front furnace and the rear furnace, by a partition wall, and different types of raw materials are added to the front furnace and the rear furnace respectively during operation; in the front furnace, the processing waste with a higher aluminum content (purity) requires a relatively lower temperature to reach the melting and casting temperature, and at the same time, the waste pollution generated by combustion heating in the furnace chamber is relatively small; while the waste aluminum materials with a lower aluminum content (purity) require a higher heating temperature, and at the same time, due to more impurities contained, more polluted flue gas containing elements such as sulfur and nitrate will be generated during combustion heating, and in addition, components such as dioxins and dust particles will also be generated; and currently, the treatment method for the flue gas discharged from the double-chamber furnace is still a mode of uniformly collecting the flue gas generated in the front furnace and the rear furnace and then treating it, but as mentioned above, there are significant differences in the composition and temperature of the two types of flue gas. Since there are requirements for the reaction temperature with the flue gas during desulfurization and denitrification, and when the flue gas temperature is too high, the filter bags in a conventional bag filter are likely to be ignited; therefore, it is necessary to design a green, efficient and low-energy consumption smoke exhaust system in cooperation with the regenerative aluminum double-chamber furnace. Summary of the Invention

[0003] The technical problem to be solved by the present invention is: to provide a dust removal and smoke exhaust system for a regenerative aluminum double-chamber furnace and a temperature control method therefor, so as to solve the problem that there is currently no reliable flue gas emission system for the regenerative aluminum double-chamber furnace and the flue gas temperature is difficult to be effectively controlled.

[0004] To solve the above problems, the present invention provides the following technical solutions:

[0005] A dust removal and smoke exhaust system for a regenerative aluminum double-chamber furnace; it includes a front furnace and a rear furnace; a low-temperature flue and a high-temperature flue are respectively installed through gas collection hoods on the upper tops of the front furnace and the rear furnace; blowers for providing pressure to the flue gas are arranged in both the low-temperature flue and the high-temperature flue; the tail end of the low-temperature flue is connected to a bag filter after passing through a low-temperature heat exchanger; the tail end of the high-temperature flue is connected to a desulfurization and denitrification tower after passing through a high-temperature heat exchanger; both the low-temperature heat exchanger and the high-temperature heat exchanger are tubular heat exchangers, and both are supplied with coolant by a coolant supply device; before the high-temperature flue is connected to the high-temperature heat exchanger, it is also connected to an intermediate heat exchanger through a branch pipe with a first electric control valve; the discharge end of the intermediate heat exchanger is communicated with the discharge end of the high-temperature heat exchanger, and the coolant of the intermediate heat exchanger is provided by the coolant that has undergone heat exchange in the low-temperature heat exchanger.

[0006] Preferably, first temperature sensors are respectively arranged at positions of the low-temperature flue and the high-temperature flue close to the gas collection hood; between the two first temperature sensors and the low-temperature heat exchanger and the high-temperature heat exchanger, branch pipes corresponding to the tails of the low-temperature flue and the high-temperature flue are respectively installed through a second electric control valve and a third electric control valve.

[0007] Preferably, a second temperature sensor for monitoring the temperature of the flue gas discharged from the high-temperature heat exchanger is also arranged on the high-temperature flue at the discharge end of the high-temperature heat exchanger.

[0008] Preferably, a coolant return pipe is arranged between the low-temperature heat exchanger, the high-temperature heat exchanger and the intermediate heat exchanger and the coolant supply device, and a branch pipe for connecting to the coolant inlet of the intermediate heat exchanger is arranged on the coolant return pipe of the low-temperature heat exchanger through a fourth electric control valve.

[0009] Preferably, it further includes a controller; the controller is respectively connected by signals to the low-temperature heat exchanger, the high-temperature heat exchanger, the coolant supply device, the intermediate heat exchanger, the first electric control valve, the first temperature sensor, the second electric control valve, the third electric control valve, the fourth electric control valve and the second temperature sensor.

[0010] Preferably, a buffer empty bin is also arranged before the high-temperature flue is connected to the desulfurization and denitrification tower.

[0011] Preferably, when the first electric control valve is opened, the flow rate of the high-temperature flue gas entering the intermediate heat exchanger from the branch pipe through the first electric control valve is less than the flow rate of the high-temperature flue gas entering the high-temperature heat exchanger.

[0012] The present invention also provides a temperature control method for a dust removal and smoke exhaust system of a regenerative aluminum double-chamber furnace; the corresponding measures for the following different working conditions are as follows:

[0013] S1. The heat exchanger does not work:

[0014] When the controller receives signals from the two first temperature sensors and respectively shows that the temperature of the flue gas in the low-temperature flue does not exceed 125°C and the temperature of the flue gas in the high-temperature flue does not exceed 250°C, the controller controls the second and third electronically controlled valves on the low-temperature flue and the high-temperature flue to respectively introduce the flue gas into the bag filter and the desulfurization and denitrification tower through the branch pipes. In this state, the low-temperature heat exchanger, the high-temperature heat exchanger, and the intermediate heat exchanger do not work;

[0015] S2. Only the low-temperature heat exchanger works:

[0016] When the signals from the two first temperature sensors show that the temperature of the flue gas in the low-temperature flue exceeds 125°C and the temperature of the flue gas in the high-temperature flue does not exceed 250°C, the controller controls the third electronically controlled valve on the high-temperature flue to introduce the flue gas into the desulfurization and denitrification tower through the branch pipe, and controls the second electronically controlled valve on the low-temperature flue to introduce the flue gas into the low-temperature heat exchanger. At the same time, the controller controls the coolant supply device to supply coolant to the low-temperature heat exchanger. The low-temperature heat exchanger works and inputs the flue gas cooled to not more than 125°C into the bag filter; in this process, the coolant in the low-temperature heat exchanger directly returns to the coolant supply device along the recovery pipeline for circulation;

[0017] S3. Only the high-temperature heat exchanger works:

[0018] When the signals from the two first temperature sensors show that the temperature of the flue gas in the low-temperature flue does not exceed 125°C and the temperature of the flue gas in the high-temperature flue exceeds 250°C; the controller controls the second electronically controlled valve on the low-temperature flue to introduce the flue gas into the bag filter, and controls the third electronically controlled valve on the high-temperature flue to introduce the flue gas into the high-temperature heat exchanger. At the same time, the controller controls the coolant supply device to supply coolant to the high-temperature heat exchanger. The high-temperature heat exchanger works and inputs the flue gas cooled to a temperature between 180°C and 250°C into the desulfurization and denitrification tower; in this process, the coolant in the high-temperature heat exchanger directly returns to the coolant supply device along the recovery pipeline for circulation;

[0019] S4. The low-temperature heat exchanger and the high-temperature heat exchanger work simultaneously;

[0020] When the signals of the two first temperature sensors indicate that the temperature of the flue gas in the low-temperature flue exceeds 125°C and the temperature of the flue gas in the high-temperature flue exceeds 250°C; the controller controls the second and third electronically controlled valves on the low-temperature flue and the high-temperature flue to introduce the flue gas into the low-temperature heat exchanger and the high-temperature heat exchanger respectively, and at the same time controls the coolant supply device to supply coolant to the low-temperature heat exchanger and the high-temperature heat exchanger; the low-temperature heat exchanger operates and inputs the flue gas cooled to no more than 125°C into the bag filter; the high-temperature heat exchanger operates and inputs the flue gas that has been cooled and has a temperature between 180°C and 250°C into the desulfurization and denitrification tower; in this process, the coolant in the low-temperature heat exchanger and the high-temperature heat exchanger directly returns to the coolant supply device along the recovery pipeline for circulation;

[0021] S5. All heat exchangers operate simultaneously:

[0022] In the S4 state, when the temperature of the flue gas in the high-temperature flue is still greater than 250°C after passing through the high-temperature heat exchanger; the controller further opens the first electronically controlled valve to introduce a part of the high-temperature flue gas into the intermediate heat exchanger, and at the same time controls the fourth electronically controlled valve to introduce the coolant discharged from the low-temperature heat exchanger into the intermediate heat exchanger to cool and dissipate the heat of this part of the high-temperature flue gas. The flue gas output by the intermediate heat exchanger will be mixed with the flue gas discharged from the high-temperature heat exchanger in the buffer bin, and its temperature is controlled to be between 180°C and 250°C and then enters the desulfurization and denitrification tower.

[0023] Advantages of the present invention:

[0024] The present invention provides a dust removal and smoke exhaust system for a regenerative aluminum double-chamber furnace. By analyzing the characteristics of the low-temperature flue gas and high-temperature flue gas generated in the corresponding flues of the front furnace and the rear furnace, a smoke exhaust pipeline system equipped with three heat exchangers, corresponding control valves and temperature sensors is further designed, so as to effectively control the flue temperature, and at the same time realize the full recycling of the coolant, making it have the effects of green energy conservation and reducing production costs. Description of the drawings

[0025] Figure 1 is a schematic structural diagram of the invention device in Embodiment 1;

[0026] Figure 2 is a schematic diagram of the pipeline layout of the flue in Embodiment 1;

[0027] Figure 3 is a schematic diagram of the pipeline layout of the heat exchanger and the coolant system in Embodiment 1;

[0028] Figure 4 is a schematic diagram of the flue gas flow direction in Embodiment 2;

[0029] Figure 5 is a schematic diagram of the flue gas flow direction in Embodiment 3;

[0030] Figure 6 It is a schematic diagram of the flue gas flow direction in Embodiment 4;

[0031] Figure 7 It is a schematic diagram of the flue gas flow direction in Embodiment 5;

[0032] Figure 8 It is a schematic diagram of the flue gas flow direction in Embodiment 6;

[0033] Explanation of reference numerals: 1. Front furnace, 2. Rear furnace, 3. Low-temperature flue, 4. High-temperature flue, 5. Second temperature sensor, 6. Low-temperature heat exchanger, 7. Bag filter, 8. High-temperature heat exchanger, 9. Desulfurization and denitrification tower, 10. Coolant supply device, 11. Intermediate heat exchanger, 12. First electric control valve, 13. First temperature sensor, 14. Second electric control valve, 15. Third electric control valve, 16. Fourth electric control valve. Detailed implementation manners

[0034] The present invention will be further introduced below in conjunction with the accompanying drawings and specific embodiments:

[0035] Embodiment 1:

[0036] Refer to Figures 1 to 3 This embodiment provides a dust removal and smoke exhaust system for a regenerative aluminum double-chamber furnace; it includes a front furnace 1 and a rear furnace 2; a low-temperature flue 3 and a high-temperature flue 4 are respectively installed on the upper tops of the front furnace 1 and the rear furnace 2 through gas collection hoods; fans for providing pressure to the flue gas are provided in both the low-temperature flue 3 and the high-temperature flue 4; the tail end of the low-temperature flue 3 passes through the low-temperature heat exchanger 6 and is then connected to the bag filter 7 for installation; the tail end of the high-temperature flue 4 passes through the high-temperature heat exchanger 8 and is then connected to the desulfurization and denitrification tower 9 for installation; both the low-temperature heat exchanger 6 and the high-temperature heat exchanger 8 are tubular heat exchangers, and both are supplied with coolant by the coolant supply device 10; before the high-temperature flue 4 is connected to the high-temperature heat exchanger 8, it is also connected to the intermediate heat exchanger 11 through a branch pipe with a first electric control valve 12; the discharge end of the intermediate heat exchanger 11 is communicated with the discharge end of the high-temperature heat exchanger 8, and the coolant of the intermediate heat exchanger 11 is provided by the coolant that has undergone heat exchange in the low-temperature heat exchanger 6.

[0037] First temperature sensors 13 are respectively provided at positions of the low-temperature flue 3 and the high-temperature flue 4 close to the gas collection hoods; branch pipes corresponding to the low-temperature flue 3 and the tail end of the high-temperature flue 4 are respectively installed between the two first temperature sensors 13 and the low-temperature heat exchanger 6 and the high-temperature heat exchanger 8 through second electric control valves 14 and third electric control valves 15.

[0038] A second temperature sensor 5 for monitoring the temperature of the flue gas discharged from the high-temperature heat exchanger 8 is also provided on the high-temperature flue 4 at the discharge end of the high-temperature heat exchanger 8.

[0039] A coolant return pipe is provided between the low-temperature heat exchanger 6, the high-temperature heat exchanger 8, the intermediate heat exchanger 11 and the coolant supply device 10, and a branch pipe for connecting to the coolant inlet of the intermediate heat exchanger 11 is provided on the coolant return pipe of the low-temperature heat exchanger 6 through a fourth electric control valve 16.

[0040] It further includes a controller; the controller is respectively connected by signals to the low-temperature heat exchanger 6, the high-temperature heat exchanger 8, the coolant supply device 10, the intermediate heat exchanger 11, the first electric control valve 12, the first temperature sensor 13, the second electric control valve 14, the third electric control valve 15, the fourth electric control valve 16 and the second temperature sensor 5.

[0041] A buffer empty bin 17 is further provided before the high-temperature flue 4 is connected to the desulfurization and denitration tower 9. The buffer empty bin 17 is provided to mix the two streams of high-temperature flue gas that are shunted and pass through the high-temperature heat exchanger and the intermediate heat exchanger respectively. Because the temperature reduction effect of passing through the intermediate heat exchanger is relatively weaker than that of the high-temperature heat exchanger, it is beneficial to balance the temperature of the flue gas after sufficient mixing.

[0042] When the first electric control valve is opened, the flow rate of the high-temperature flue gas entering the intermediate heat exchanger 11 from the branch pipe through the first electric control valve 12 is smaller than the flow rate of the high-temperature flue gas entering the high-temperature heat exchanger 8.

[0043] Figure 3 The arrow in [[ ]] indicates the flow direction of the coolant.

[0044] Embodiment 2:

[0045] Referring to [[ ]] Figure 4 This embodiment provides the working state of the dust removal and smoke exhaust system when the heat exchanger is not working; mainly when the system is just started, the air discharged from both the high-temperature flue and the low-temperature flue is low in dust, sulfur, nitrate compounds and dioxins;

[0046] When the signals transmitted by the two first temperature sensors 13 to the controller respectively show that the temperature of the flue gas in the low-temperature flue 3 does not exceed 125°C and the temperature of the flue gas in the high-temperature flue 4 does not exceed 250°C under this working condition, the controller controls the second electric control valve 14 and the third electric control valve 15 on the low-temperature flue 3 and the high-temperature flue 4 to respectively introduce the flue gas into the bag filter 7 and the desulfurization and denitration tower 9 through the branch pipe. In this state, the low-temperature heat exchanger 6, the high-temperature heat exchanger 8 and the intermediate heat exchanger 11 do not work.

[0047] Embodiment 3:

[0048] Referring to [[ ]] Figure 5, this embodiment provides the operating state of the dust removal and smoke exhaust system when only the low-temperature heat exchanger is working; this stage is because after the double-chamber furnace is started, low-temperature flue gas exceeding the limit temperature requirement of 125 °C will be generated at the front furnace first and needs to be cooled down.

[0049] Under this working condition, the signals of the two first temperature sensors 13 show that the temperature of the flue gas in the low-temperature flue 3 exceeds 125 °C, and the temperature of the flue gas in the high-temperature flue does not exceed 250 °C. The controller controls the third electric control valve 15 on the high-temperature flue 4 to introduce the flue gas into the desulfurization and denitrification tower 9 through the branch pipe, and controls the second electric control valve 14 on the low-temperature flue 3 to introduce the flue gas into the low-temperature heat exchanger 6. At the same time, the controller controls the coolant supply device 10 to supply coolant to the low-temperature heat exchanger 6. The low-temperature heat exchanger 6 works and inputs the flue gas cooled down to not exceeding 125 °C into the bag filter; during this process, the coolant in the low-temperature heat exchanger 6 directly returns to the coolant supply device 10 along the recovery pipeline for circulation;

[0050] Embodiment 4:

[0051] Refer to Figure 6 , this embodiment provides the operating state of the dust removal and smoke exhaust system when only the high-temperature heat exchanger is working; this stage is because the temperature of the low-temperature flue gas generated at the front furnace is stable below 125 °C; and the high-temperature flue gas generated at the rear furnace is greater than 250 °C and needs to be cooled down.

[0052] Under this working condition, the signals of the two first temperature sensors 13 show that the temperature of the flue gas in the low-temperature flue 3 does not exceed 125 °C, and the temperature of the flue gas in the high-temperature flue exceeds 250 °C; the controller controls the second electric control valve 14 on the low-temperature flue 3 to introduce the flue gas into the bag filter 7 through the branch pipe, and controls the third electric control valve 15 on the high-temperature flue 4 to introduce the flue gas into the high-temperature heat exchanger 8. At the same time, the controller controls the coolant supply device 10 to supply coolant to the high-temperature heat exchanger 8. The high-temperature heat exchanger 8 works and inputs the flue gas that has been cooled and has a temperature in the range of 180 °C to 250 °C into the desulfurization and denitrification tower 9; during this process, the coolant in the high-temperature heat exchanger 8 directly returns to the coolant supply device 10 along the recovery pipeline for circulation;

[0053] Embodiment 5:

[0054] Refer to Figure 7 , this embodiment provides the operating state of the dust removal and smoke exhaust system when the high- and low-temperature heat exchangers work simultaneously; this stage is because the low-temperature flue gas and high-temperature flue gas generated corresponding to the front furnace and the rear furnace have temperatures above 125 °C and above 250 °C respectively.

[0055] Under this operating condition, the signals of the two first temperature sensors 13 indicate that the temperature of the flue gas in the low-temperature flue 3 exceeds 125 °C, and the temperature of the flue gas in the high-temperature flue exceeds 250 °C; the controller controls the second electric control valve 14 and the third electric control valve 15 on the low-temperature flue 3 and the high-temperature flue 4 to introduce the flue gas into the low-temperature heat exchanger 6 and the high-temperature heat exchanger 8 respectively, and at the same time controls the coolant supply device 10 to supply coolant to the low-temperature heat exchanger 6 and the high-temperature heat exchanger 8; the low-temperature heat exchanger 6 operates and inputs the flue gas cooled to no more than 125 °C into the bag filter; the high-temperature heat exchanger 8 operates and inputs the flue gas that has been cooled and has a temperature in the range of 180 °C to 250 °C into the desulfurization and denitrification tower 9; during this process, the coolant in the low-temperature heat exchanger 6 and the high-temperature heat exchanger 8 directly returns to the coolant supply device 10 along the recovery pipeline for circulation;

[0056] Embodiment 6:

[0057] Referring to Figure 8 , this embodiment provides the operating state of the dust removal and smoke exhaust system when all heat exchangers work simultaneously; at this stage, the high-temperature flue gas is fed back by the second temperature sensor after passing through step S4, and its temperature is still greater than 250 degrees Celsius.

[0058] Under this operating condition, the controller further opens the first electric control valve 12 to introduce a part of the high-temperature flue gas into the intermediate heat exchanger 11, and at the same time controls the fourth electric control valve 16 to introduce the coolant discharged from the low-temperature heat exchanger 6 into the intermediate heat exchanger 11 to cool down this part of the high-temperature flue gas. The flue gas output by the intermediate heat exchanger 11 will be mixed with the flue gas output by the high-temperature heat exchanger 8 in the buffer bin 17, and its temperature will be controlled to be in the range of 180 °C to 250 °C before entering the desulfurization and denitrification tower.

Claims

1. A dust removal and smoke exhaust system for a regenerative aluminum double-chamber furnace, which comprises a front furnace (1) and a rear furnace (2); characterized in that: At the upper tops of the front furnace (1) and the rear furnace (2), a low-temperature flue (3) and a high-temperature flue (4) are respectively installed through gas collection hoods; in both the low-temperature flue (3) and the high-temperature flue (4), a fan for providing pressure to the flue gas is provided; the tail end of the low-temperature flue (3) passes through the low-temperature heat exchanger (6) and is then connected to the bag filter (7); the tail end of the high-temperature flue (4) passes through the high-temperature heat exchanger (8) and is then connected to the desulfurization and denitrification tower (9); both the low-temperature heat exchanger (6) and the high-temperature heat exchanger (8) are tubular heat exchangers, and both are supplied with coolant by the coolant supply device (10); before the high-temperature flue (4) is connected to the high-temperature heat exchanger (8), it is also connected to the intermediate heat exchanger (11) through a branch pipe with a first electric control valve (12); the discharge end of the intermediate heat exchanger (11) is communicated with the discharge end of the high-temperature heat exchanger (8), and the coolant of the intermediate heat exchanger (11) is provided by the coolant that has undergone heat exchange in the low-temperature heat exchanger (6); at positions of the low-temperature flue (3) and the high-temperature flue (4) close to the gas collection hoods, first temperature sensors (13) are respectively provided; between the two first temperature sensors (13) and the low-temperature heat exchanger (6) and the high-temperature heat exchanger (8), branch pipes corresponding to and communicated with the tail ends of the low-temperature flue (3) and the high-temperature flue (4) are respectively installed through a second electric control valve (14) and a third electric control valve (15); on the high-temperature flue (4) at the discharge end of the high-temperature heat exchanger (8), a second temperature sensor (5) for monitoring the temperature of the flue gas discharged from the high-temperature heat exchanger (8) is also provided; between the low-temperature heat exchanger (6), the high-temperature heat exchanger (8), the intermediate heat exchanger (11) and the coolant supply device (10), a coolant return pipe is provided, and on the coolant return pipe of the low-temperature heat exchanger (6), a branch pipe for connecting to the coolant inlet of the intermediate heat exchanger (11) is provided through a fourth electric control valve (16); before the high-temperature flue (4) is connected to the desulfurization and denitrification tower (9), a buffer empty bin (17) is also provided; when the first electric control valve is opened, the flow rate of the high-temperature flue gas entering the intermediate heat exchanger (11) from the branch pipe through the first electric control valve (12) is smaller than the flow rate of the high-temperature flue gas entering the high-temperature heat exchanger (8).

2. The dedusting and smoke exhaust system for a regenerative aluminum double-chamber furnace according to claim 1, wherein: It further includes a controller; the controller is respectively connected by signals to the low-temperature heat exchanger (6), the high-temperature heat exchanger (8), the coolant supply device (10), the intermediate heat exchanger (11), the first electric control valve (12), the first temperature sensor (13), the second electric control valve (14), the third electric control valve (15), the fourth electric control valve (16) and the second temperature sensor (5).

3. The temperature control method of a dust removal and smoke exhaust system for a regenerative aluminum double-chamber furnace according to claim 2, characterized in that: The corresponding measures taken for the following different working conditions are as follows: S1. The heat exchanger does not work: When the controller receives signals from the two first temperature sensors (13) and respectively shows that the temperature of the flue gas in the low-temperature flue (3) does not exceed 125 °C and the temperature of the flue gas in the high-temperature flue (4) does not exceed 250 °C, the controller controls the second electric control valve (14) and the third electric control valve (15) on the low-temperature flue (3) and the high-temperature flue (4) to respectively introduce the flue gas into the bag filter (7) and the desulfurization and denitrification tower (9) through the branch pipes. In this state, the low-temperature heat exchanger (6), the high-temperature heat exchanger (8) and the intermediate heat exchanger (11) do not work; S2. Only the low-temperature heat exchanger works: When the signals from the two first temperature sensors (13) show that the temperature of the flue gas in the low-temperature flue (3) exceeds 125 °C and the temperature of the flue gas in the high-temperature flue does not exceed 250 °C, the controller controls the third electric control valve (15) on the high-temperature flue (4) to introduce the flue gas into the desulfurization and denitrification tower (9) through the branch pipe, and controls the second electric control valve (14) on the low-temperature flue (3) to introduce the flue gas into the low-temperature heat exchanger (6). At the same time, the controller controls the coolant supply device (10) to supply coolant to the low-temperature heat exchanger (6). The low-temperature heat exchanger (6) works and inputs the flue gas cooled to not more than 125 °C into the bag filter. In this process, the coolant in the low-temperature heat exchanger (6) directly returns to the coolant supply device (10) along the recovery pipeline for circulation; S3. Only the high-temperature heat exchanger works: When the signals from the two first temperature sensors (13) show that the temperature of the flue gas in the low-temperature flue (3) does not exceed 125 °C and the temperature of the flue gas in the high-temperature flue exceeds 250 °C; the controller controls the second electric control valve (14) on the low-temperature flue (3) to introduce the flue gas into the bag filter (7) through the branch pipe, and controls the third electric control valve (15) on the high-temperature flue (4) to introduce the flue gas into the high-temperature heat exchanger (8). At the same time, the controller controls the coolant supply device (10) to supply coolant to the high-temperature heat exchanger (8). The high-temperature heat exchanger (8) works and inputs the flue gas cooled to 180 °C - 250 °C into the desulfurization and denitrification tower (9); in this process, the coolant in the high-temperature heat exchanger (8) directly returns to the coolant supply device (10) along the recovery pipeline for circulation; S4. The low-temperature heat exchanger and the high-temperature heat exchanger work simultaneously; When the signals of the two first temperature sensors (13) indicate that the temperature of the flue gas in the low-temperature flue (3) exceeds 125 °C and the temperature of the flue gas in the high-temperature flue exceeds 250 °C; the controller controls the second electric control valve (14) and the third electric control valve (15) on the low-temperature flue (3) and the high-temperature flue (4) respectively to introduce the flue gas into the low-temperature heat exchanger (6) and the high-temperature heat exchanger (8), and at the same time controls the coolant supply device (10) to supply coolant to the low-temperature heat exchanger (6) and the high-temperature heat exchanger (8); the low-temperature heat exchanger (6) operates and inputs the flue gas cooled to no more than 125 °C into the bag filter; the high-temperature heat exchanger (8) operates and inputs the flue gas that has been cooled and has a temperature between 180 °C and 250 °C into the desulfurization and denitration tower (9); during this process, the coolant in the low-temperature heat exchanger (6) and the high-temperature heat exchanger (8) directly returns to the coolant supply device (10) along the recovery pipeline for circulation; S5. All heat exchangers operate simultaneously: In the S4 state, when the temperature of the flue gas in the high-temperature flue (4) is still greater than 250 °C after passing through the high-temperature heat exchanger (8); the controller further opens the first electric control valve (12) to introduce a part of the high-temperature flue gas into the intermediate heat exchanger (11), and at the same time controls the fourth electric control valve (16) to introduce the coolant discharged from the low-temperature heat exchanger (6) into the intermediate heat exchanger (11) to cool and dissipate the heat of this part of the high-temperature flue gas. The flue gas output from the intermediate heat exchanger (11) will be mixed with the flue gas output from the high-temperature heat exchanger (8) in the buffer empty bin (17), and its temperature is controlled to be between 180 °C and 250 °C before entering the desulfurization and denitration tower (9).

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