System and method for improving primary and secondary air temperature at the inlet of an air preheater during start-up of a thermal power unit

Abstract

This invention discloses a system and method for increasing the primary and secondary air temperatures at the inlet of an air preheater during the startup of a thermal power unit. The system includes a boiler furnace, with an air preheater connected downstream of the furnace. Above the furnace are main steam and reheat steam pipelines. The main steam enters the high-pressure cylinder and the reheat steam cold section pipeline via the high-pressure main valve and high-pressure bypass valve, respectively. The high-pressure cylinder exhaust steam passes through the high-pressure cylinder exhaust valve before the high-pressure exhaust check valve and then undergoes desuperheating and pressure reduction before entering the condensate expansion tank. The reheat steam enters the intermediate-pressure cylinder and the condensate expansion tank via the intermediate regulating valve and intermediate bypass valve, respectively. Primary and secondary air enter the air preheater after passing through a heat exchanger and an air heater, respectively. The heat source for the heat exchanger is from the high-pressure bypass valve, and after heat exchange, it enters the reheat steam pipeline via desuperheating and pressure reduction. This invention offers flexible switching, increases the temperature of the primary and secondary air entering the air preheater, prevents acid dew point corrosion of the air preheater, extends the lifespan of the air preheater, reduces the energy consumed by the air heater, recovers some high-pressure bypass energy, and improves the unit's economic efficiency.

Description

Technical Field

[0001] This invention belongs to the field of boiler technology for thermal power units, specifically relating to a system and operating method for increasing the primary and secondary air temperatures at the inlet of an air preheater during the startup process of a thermal power unit. Background Technology

[0002] With the continuous increase in the installed capacity of new energy power sources such as wind power and photovoltaics, the stability of the power grid has been affected to a certain extent. As a result, the power grid has placed higher demands on the peak-shaving capacity of coal-fired power plants, leading to a significant increase in the number of start-ups and shutdowns of units throughout the year.

[0003] During the start-up process, the air heaters require auxiliary steam. Since there are many users of auxiliary steam during the start-up process, including steam for heating the deaerator, steam for the turbine shaft seal, steam for continuous soot blowing of the boiler air preheater, and steam for the plasma ignition air heaters, especially when using the steam-driven feedwater pump start-up method, the steam source of the feedwater pump turbine is also auxiliary steam, which results in a relatively limited amount of auxiliary steam for heating the air heaters.

[0004] If the inlet primary and secondary air temperatures of the air preheater are too low, when they fall below the dew point of the flue gas, the SO2 in the flue gas reacts with water to form sulfuric acid, which corrodes the tail heating surfaces. Therefore, it is essential to raise the inlet primary and secondary air temperatures of the air preheater to above the dew point of the flue gas. During boiler startup, the flue gas temperature is relatively low, making it crucial to increase the inlet primary and secondary air temperatures of the air preheater during startup.

[0005] During the startup process of thermal power units, in order to automatically control the feedwater, main steam pressure, reheat steam pressure, flow rate, and temperature during boiler combustion, and to ensure that these parameters can be steadily and quickly raised to the values ​​required for turbine startup, and to guarantee the steam parameters at the boiler outlet, a large portion of the steam does not pass through the turbine but is instead de-heated and depressurized through the bypass system before being fed into the reheat steam cold section pipeline or discharged into the condenser, resulting in a significant waste of energy.

[0006] To address the above issues, patent CN 115289458A discloses an auxiliary heating system and operating method for the feed air during the startup process of a coal-fired power plant. This invention utilizes the heat from flue gas and steam to heat the primary air, which then preheats the coal mill. The heat from the flue gas is then used to heat the secondary air before it is introduced into the boiler body. This reduces the consumption of auxiliary fuel oil during system startup and shortens the time required for the system to reach normal operation, thereby reducing the startup cost and energy consumption of coal-fired power plants. However, in this invention, the primary and secondary air heating channels share the same channel in the feed air heater. While this reduces the number of pipes in the system, it may lead to uneven heat exchange in the heat exchanger, resulting in a more complex heat exchanger design and higher investment costs for large heat exchangers. Furthermore, placing the heat exchanger after the air preheater prevents the increase of the primary and secondary air inlet temperatures from the air preheater, meaning the operation of the warm air heater still requires significant energy consumption.

[0007] Patent CN 211011462U discloses a system for regulating the temperature of primary and secondary air using condensate to improve the air heater. This system utilizes gas-water heat exchange, which is more efficient than traditional steam-gas heat exchange, avoids corrosion from the acid dew point of the air preheater, extends the lifespan of the air preheater, and reduces power plant operating costs. While this system uses the heat from the condensate to heat the primary and secondary air, increasing the temperature of the air entering the air preheater, it cannot recover energy from the turbine bypass. Summary of the Invention

[0008] In order to overcome the problems existing in the prior art, the purpose of this invention is to propose a system and operation method for increasing the primary and secondary air temperatures at the inlet of the air preheater during the startup process of a thermal power unit, so as to solve the problem of low primary and secondary air temperatures at the inlet of the air preheater of a thermal power unit and to recover some of the energy in the turbine bypass.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A system for increasing the primary and secondary air temperatures at the inlet of an air preheater during the startup of a thermal power unit includes a boiler furnace 1, with an air preheater 8 connected to the boiler furnace 1. Above the boiler furnace 1 are a main steam pipeline 2 and a reheat steam pipeline 3. The main steam enters the high-pressure cylinder 25 and the reheat steam cold section pipeline 13 through the high-pressure main valve 21 and the high-pressure bypass valve 31, respectively. The high-pressure cylinder exhaust passes through the high-pressure cylinder exhaust valve 24 before the high-pressure exhaust check valve 22 and then enters the condensate expansion tank 28 through the fifth desuperheating and pressure reducing device 20. The reheat steam enters the intermediate-pressure cylinder 26 and the condensate expansion tank 28 through the intermediate regulating valve 23 and the intermediate bypass valve 17, respectively.

[0011] Primary air 11 enters air preheater 8 after passing through primary air heat exchanger 9 and air heater 32; secondary air 12 enters air preheater 8 after passing through secondary air heat exchanger 10 and air heater 32; the heat source pipeline 33 of the primary air heat exchanger is connected to the high-pressure bypass 31, and the hot steam is transferred to the reheat steam cold section pipeline 13 after heat exchange in the primary air heat exchanger 9 and then through the fourth desuperheating and pressure reducing device 19; the heat source pipeline 34 of the secondary air heat exchanger is connected to the high-pressure bypass 31, and the hot steam is transferred to the reheat steam cold section pipeline 13 after heat exchange in the secondary air heat exchanger 10 and then through the third desuperheating and pressure reducing device 18.

[0012] Primary air 11 and secondary air 12 pass through the heater and then through temperature measuring point 36.

[0013] A first control valve 14 is installed on the heat source pipeline 33 of the primary air heat exchanger; a second control valve 15 is installed on the heat source pipeline 34 of the secondary air heat exchanger.

[0014] Steam in high-pressure bypass 31 flows into reheat steam cold section pipeline 13 after passing through the first desuperheating and pressure reducing device 16, and steam in medium-pressure bypass 35 enters condensate expansion tank 28 after passing through the second desuperheating and pressure reducing device 17.

[0015] After the air preheater 8, an electrostatic precipitator 7, an induced draft fan 6, a desulfurization tower 5, and a chimney 4 are connected in sequence.

[0016] The intermediate pressure cylinder 26 is connected to the low pressure cylinder 27 via a pipeline, and the low pressure cylinder 27 is connected to the condensate expansion tank 28 and the condenser 29.

[0017] High-pressure cylinder 25, medium-pressure cylinder 26 and low-pressure cylinder 27 are connected to generator 30 via shafts.

[0018] The operating method of the system for increasing the primary and secondary air temperatures at the inlet of the air preheater during the start-up of a thermal power unit is as follows: during the start-up of the thermal power unit, part of the main steam generated in the boiler furnace 1 enters the high-pressure cylinder 25 of the steam turbine, and another part enters the high-pressure bypass 31. Part of the main steam in the high-pressure bypass 31 is de-heated and de-pressurized by the first de-heating and de-pressurization device 16 and then flows into the reheat steam cold section pipeline 13. Another portion of the main steam is introduced into the primary air heat exchanger 9 and the secondary air heat exchanger 10 through the primary air heat exchanger heat source pipeline 33 and the secondary air heat exchanger heat source pipeline 34, respectively, to heat the air. After heat exchange, the steam passes through the fourth desuperheating and pressure reducing device 19 and the third desuperheating and pressure reducing device 18, respectively, and then flows into the reheat steam cold section pipeline 13. In order to achieve temperature control and flexible switching, a first control valve 14 is installed on the primary air heat exchanger heat source pipeline 33, and a second control valve 15 is installed on the secondary air heat exchanger heat source pipeline 34. The steam flow entering the primary air heat exchanger 9 and the secondary air heat exchanger 10 is controlled by the opening of the first control valve 14 and the second control valve 15. Temperature measurement point 36 is installed after air preheater 8. The temperature of primary air and secondary air is monitored through temperature measurement point 36. When the unit is in the start-up process, the exhaust gas temperature is low. If the temperature of primary and secondary air entering the air preheater is too low, it will cause adverse consequences. Some steam is introduced into primary air heat exchanger 9 and secondary air heat exchanger 10 through primary air heat exchanger heat source pipeline 33 and secondary air heat exchanger heat source pipeline 34 to heat the air temperature. The flow rate of high temperature steam is controlled by first control valve 14 and second control valve 15 to accurately control the temperature of primary and secondary air within the specified range, thereby achieving the effect of controlling the temperature of primary and secondary air and recovering some energy at the same time.

[0019] When the high-pressure cylinder 25, intermediate-pressure cylinder 26, and low-pressure cylinder 27 of the steam turbine are not started, all the steam generated in the boiler furnace 1 passes through the high-pressure bypass 31 and the first desuperheating and pressure reducing device 16 before entering the reheat steam cold section pipeline 13. At this time, the primary air heat exchanger 9 and the secondary air heat exchanger 10 are started to recover the heat of the bypass steam. The steam flow rate entering the heat source pipeline 33 of the primary air heat exchanger and the heat source pipeline 34 of the secondary air heat exchanger is controlled by adjusting the first control valve 14 and the second control valve 15. The primary and secondary air temperatures are monitored through the temperature measuring point 36 to ensure that the primary and secondary air temperatures at the outlets of the primary air heat exchanger 9 and the secondary air heat exchanger 10 are within the specified range.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention proposes a system and operating method for increasing the primary and secondary air temperatures at the inlet of an air preheater during the startup process of a thermal power unit. This system can increase the temperature of the primary and secondary air at the air preheater inlet during startup, preventing acid dew point corrosion of the air preheater and extending its lifespan. Simultaneously, by increasing the temperature of the primary and secondary air at the air preheater inlet, the amount of auxiliary steam used by the air heater can be reduced, using bypass steam instead of auxiliary steam, thus saving auxiliary steam during the power plant startup process and reducing startup costs.

[0022] This invention is easy to put into operation or shut down, highly flexible, and will not affect the normal operation of the unit.

[0023] The system proposed in this invention utilizes the steam in the bypass during the startup of thermal power units, thereby recovering and utilizing some of the wasted energy, improving the energy utilization efficiency and economy of the startup process. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a system for increasing the primary and secondary air temperatures at the inlet of an air preheater during the startup process of a thermal power unit, according to the present invention. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1 As shown, this invention proposes a system for regulating the primary and secondary air temperatures during the startup of a thermal power unit, including a boiler furnace 1, an air preheater 8 connected to the boiler furnace 1, and an electrostatic precipitator 7, an induced draft fan 6, a desulfurization tower 5, and a chimney 4 connected sequentially after the air preheater 8; above the boiler furnace 1 are a main steam pipeline 2 and a reheat steam pipeline 3. The main steam enters the high-pressure cylinder 25 and the reheat steam cold section pipeline 13 through the high-pressure main valve 21 and the high-pressure bypass valve 31, respectively. The high-pressure cylinder exhaust passes through the high-pressure cylinder exhaust valve 24 before the high-pressure exhaust check valve 22 and then enters the condensate expansion tank 28 through the fifth desuperheating and pressure reducing device 20. The reheat steam enters the intermediate-pressure cylinder 26 and the condensate expansion tank 28 through the intermediate regulating valve 23 and the intermediate bypass valve 17, respectively. The intermediate-pressure cylinder 26 is connected to the low-pressure cylinder 27 through a pipeline. The low-pressure cylinder 27 is connected to the hot well 28 and the condenser 29.

[0027] Primary air 11 enters air preheater 8 after passing through primary air heat exchanger 9 and air heater 32; secondary air 12 enters air preheater 8 after passing through secondary air heat exchanger 10 and air heater 32; the heat source pipeline 33 of the primary air heat exchanger is connected to the high-pressure bypass 31, and the hot steam is transferred to the reheat steam cold section pipeline 13 after heat exchange in the primary air heat exchanger 9 and then through the fourth desuperheating and pressure reducing device 19; the heat source pipeline 34 of the secondary air heat exchanger is connected to the high-pressure bypass 31, and the hot steam is transferred to the reheat steam cold section pipeline 13 after heat exchange in the secondary air heat exchanger 10 and then through the third desuperheating and pressure reducing device 18.

[0028] The primary air 11 and secondary air 12 pass through the heater 32 and then through the temperature measuring point 36, which facilitates the monitoring of the temperature of the primary air and secondary air, so as to accurately control the air temperature.

[0029] Furthermore, a first control valve 14 is installed on the heat source pipeline 33 of the primary air heat exchanger; a second control valve 15 is installed on the heat source pipeline 34 of the secondary air heat exchanger. By controlling the opening degree of the first control valve 14 and the second control valve 15, the steam flow rate entering the primary air heat exchanger 9 and the secondary air heat exchanger 10 can be precisely controlled.

[0030] Furthermore, the steam in the high-pressure bypass 31 flows into the reheat steam cold section pipeline 13 after passing through the first desuperheating and pressure-reducing device 16, and the steam in the intermediate-pressure bypass 35 flows into the condensate expansion tank 28 after passing through the second desuperheating and pressure-reducing device 17. During the startup of the thermal power unit, when the parameters of the steam generated in the boiler furnace 1 do not reach the starting parameters of the high-pressure cylinder 25 and the intermediate-pressure cylinder 26, the working fluid can be recovered through the high-pressure bypass 31 and the intermediate-pressure bypass 35 to prevent waste and save makeup water; when starting the high-pressure cylinder 25 and the intermediate-pressure cylinder 26, the pressure can be controlled through the high-pressure bypass 31 and the intermediate-pressure bypass 35 to prevent pressure fluctuations. At the same time, the steam entering the reheat steam cold section pipeline 13 can ensure that all heating surfaces in the boiler furnace 1 have a certain amount of steam passing through, ensuring safe operation; if the thermal power unit is started in a hot state, the steam entering the reheat steam cold section pipeline 13 can quickly warm up the boiler furnace 1, shortening the startup time.

[0031] Furthermore, the high-pressure cylinder 25, the medium-pressure cylinder 26, and the low-pressure cylinder 27 are connected to the generator 30 via shafts.

[0032] During the startup of the thermal power unit, part of the main steam generated in the boiler furnace 1 enters the high-pressure cylinder 25 of the turbine, and the other part enters the high-pressure bypass 31. Part of the main steam in the high-pressure bypass 31 is de-cooled and de-pressurized by the first desuperheating and depressurization device 16 before flowing into the reheat steam cold section pipeline 13. The other part of the main steam is introduced into the primary air heat exchanger 9 and the secondary air heat exchanger 10 through the primary air heat exchanger heat source pipeline 33 and the secondary air heat exchanger heat source pipeline 34 respectively to heat the air. After heat exchange, the steam passes through the fourth desuperheating and depressurization device 19 and the third desuperheating and depressurization device 18 respectively before flowing into the reheat steam cold section pipeline 13. To achieve temperature control and flexible switching, a first control valve 14 is installed on the primary air heat exchanger heat source pipeline 33, and a second control valve 15 is installed on the secondary air heat exchanger heat source pipeline 34. By controlling the opening of the first control valve 14 and the second control valve 15, the steam flow rate entering the primary air heat exchanger 9 and the secondary air heat exchanger 10 is controlled. Temperature measuring point 36 is installed after air preheater 8. The temperatures of primary and secondary air are monitored through temperature measuring point 36. When the unit is in the start-up process, the exhaust gas temperature is low. If the temperature of the primary and secondary air entering the air preheater is too low, it will cause adverse consequences. Some steam is introduced into primary air heat exchanger 9 and secondary air heat exchanger 10 through primary air heat exchanger heat source pipeline 33 and secondary air heat exchanger heat source pipeline 34 to heat the air temperature. The flow rate of high temperature steam is controlled by first control valve 14 and second control valve 15 to accurately control the primary and secondary air temperatures within the specified range, thereby achieving the effect of controlling the primary and secondary air temperatures and recovering some energy.

[0033] When the high-pressure cylinder 25, intermediate-pressure cylinder 26, and low-pressure cylinder 27 of the steam turbine are not started, all the steam generated in the boiler furnace 1 passes through the high-pressure bypass 31 and the first desuperheating and pressure reducing device 16 before entering the reheat steam cold section pipeline 13. At this time, the primary air heat exchanger 9 and the secondary air heat exchanger 10 can be started to recover the heat of the bypass steam. The steam flow rate entering the heat source pipeline 33 of the primary air heat exchanger and the heat source pipeline 34 of the secondary air heat exchanger is controlled by adjusting the first control valve 14 and the second control valve 15. The primary and secondary air temperatures are monitored through the temperature measuring point 36 to ensure that the primary and secondary air temperatures at the outlets of the primary air heat exchanger 9 and the secondary air heat exchanger 10 are within the specified range.

[0034] Example

[0035] During the startup of a thermal power unit, the heat from the turbine bypass is used to heat the primary and secondary air. During boiler operation, the primary and secondary air temperatures at the air preheater inlet should be between 30 and 55℃. Taking an average value of 42.5℃ for calculation, and the ambient temperature as 20℃, the temperature difference Δt = 22.5℃.

[0036] The example calculation uses a 1000MW boiler as an example. When the boiler load is less than 30% BMCR, the primary and secondary air flow rates at the air preheater inlet can be taken as 345kg / s. Assuming that the mass specific heat capacity of air at constant pressure is a constant value, it is taken as 1.0046kJ / kg / K.

[0037] The available bypass heat per hour is: Heat (q) = Flow rate (D) × Temperature difference (Δt) × Specific heat capacity (Cp), i.e.

[0038] q=345×22.5×1.0046×3600=28073547kJ

[0039] Assuming the auxiliary steam used during unit startup is at a pressure of 1.1 MPa and a temperature of 360℃, after heat exchange it becomes saturated water at a pressure of 1 MPa. By consulting the thermal properties of water, the enthalpy difference Δh = 2414 kJ / kg. Therefore, the amount of auxiliary steam saved per hour is: Steam flow rate (F) = Heat (q) / Enthalpy difference (Δh), i.e.

[0040] F = 28073547 ÷ 2414 ≈ 11629

[0041] Calculations show that by utilizing the heat from bypass steam to raise the average temperature of the primary and secondary air at the air preheater inlet to 30°C, approximately 11,629 kg / h of auxiliary steam can be saved during startup. Converted to standard coal equivalent, this translates to a saving of approximately B = 28,073,547 / 29,270 ≈ 959 kg of coal per hour. Therefore, recovering the heat from bypass steam to heat the primary and secondary air during unit startup can save on auxiliary steam consumption and reduce the startup energy consumption of thermal power units.

Claims

1. A system for increasing the primary and secondary air temperatures at the air preheater inlet during the startup of a thermal power unit, characterized in that: The boiler includes a furnace (1), and an air preheater (8) is connected to the furnace (1). Above the furnace (1) are a main steam pipeline (2) and a reheat steam pipeline (3). The main steam enters the high-pressure cylinder (25) and the reheat steam cold section pipeline (13) through the high main valve (21) and the high bypass valve (31), respectively. The high-pressure cylinder exhaust passes through the high-pressure cylinder exhaust valve (24) before the high exhaust check valve (22) and then enters the condensate expansion tank (28) through the fifth desuperheating and pressure reducing device (20). The reheat steam enters the intermediate pressure cylinder (26) and the condensate expansion tank (28) through the intermediate regulating valve (23) and the intermediate bypass valve (35), respectively. The primary air (11) enters the air preheater (8) after passing through the primary air heat exchanger (9) and the air heater (32); the secondary air (12) enters the air preheater (8) after passing through the secondary air heat exchanger (10) and the air heater (32); the heat source pipeline (33) of the primary air heat exchanger is connected to the high-pressure bypass (31), and the hot steam is transferred to the reheat steam cold section pipeline (13) after heat exchange in the primary air heat exchanger (9) and then through the fourth de-heating and pressure reducing device (19); the heat source pipeline (34) of the secondary air heat exchanger is connected to the high-pressure bypass (31), and the hot steam is transferred to the reheat steam cold section pipeline (13) after heat exchange in the secondary air heat exchanger (10) and then through the third de-heating and pressure reducing device (18).

2. The system for increasing the primary and secondary air temperatures at the air preheater inlet during the startup of a thermal power unit according to claim 1, characterized in that: The primary air (11) and secondary air (12) pass through the heater and then through the temperature measuring point (36).

3. The system for increasing the primary and secondary air temperatures at the air preheater inlet during the startup of a thermal power unit according to claim 1, characterized in that: A first control valve (14) is installed on the heat source pipeline (33) of the primary air heat exchanger; a second control valve (15) is installed on the heat source pipeline (34) of the secondary air heat exchanger.

4. The system for increasing the primary and secondary air temperatures at the air preheater inlet during the startup of a thermal power unit according to claim 1, characterized in that: Steam in the high-pressure side (31) flows into the reheat steam cold section pipeline (13) after passing through the first desuperheating and pressure reducing device (16), and steam in the middle side (35) enters the condensate expansion tank (28) after passing through the second desuperheating and pressure reducing device (17).

5. A system for increasing the primary and secondary air temperatures at the air preheater inlet during the startup of a thermal power unit, as described in claim 1, is characterized in that: An electrostatic precipitator (7), an induced draft fan (6), a desulfurization tower (5), and a chimney (4) are connected in sequence after the air preheater (8).

6. The system for increasing the primary and secondary air temperatures at the inlet of the air preheater during the startup process of a thermal power unit according to claim 1, characterized in that: The intermediate pressure cylinder (26) is connected to the low pressure cylinder (27) through a pipeline. The low pressure cylinder (27) is connected to the condensate expansion tank (28) and the condenser (29).

7. A system for increasing the primary and secondary air temperatures at the air preheater inlet during the startup of a thermal power unit, as described in claim 1, is characterized in that: The high-pressure cylinder (25), the medium-pressure cylinder (26), and the low-pressure cylinder (27) are connected to the generator (30) via shafts.

8. The operating method of the system for increasing the primary and secondary air temperatures at the inlet of the air preheater during the startup of a thermal power unit, as described in any one of claims 1 to 7, is characterized in that: During the startup of the thermal power unit, part of the main steam generated in the boiler furnace (1) enters the high-pressure cylinder (25) of the turbine, and the other part enters the high-pressure bypass (31). Part of the main steam in the high-pressure bypass (31) is de-cooled and de-pressurized by the first de-cooling and de-pressurization device (16) and then flows into the reheat steam cold section pipeline (13). The other part of the main steam is introduced into the primary air heat exchanger (9) and the secondary air heat exchanger (10) through the primary air heat exchanger heat source pipeline (33) and the secondary air heat exchanger heat source pipeline (34) to heat the air temperature. After the heat exchange is completed, the steam flows into the reheat steam cold section pipeline (13) through the fourth de-cooling and de-pressurization device (19) and the third de-cooling and de-pressurization device (18). In order to achieve temperature control and flexible switching, a first control valve (14) is installed on the primary air heat exchanger heat source pipeline (33), and a second control valve (15) is installed on the secondary air heat exchanger heat source pipeline (34). The steam flow rate entering the primary air heat exchanger (9) and secondary air heat exchanger (10) is controlled by controlling the opening of the first control valve (14) and the second control valve (15). A temperature measuring point (36) is installed after the air preheater (8). The temperature of the primary air and secondary air is monitored by the temperature measuring point (36). When the unit is in the start-up process, the exhaust gas temperature is low. If the temperature of the primary and secondary air entering the air preheater is too low, it will cause adverse consequences. Some steam is introduced into the primary air heat exchanger (9) and secondary air heat exchanger (10) through the heat source pipeline (33) of the primary air heat exchanger and the heat source pipeline (34) of the secondary air heat exchanger to heat the air temperature. The flow rate of high temperature steam is controlled by the first control valve (14) and the second control valve (15). The temperature of the primary and secondary air is precisely controlled within the specified range to achieve the effect of controlling the temperature of the primary and secondary air and recovering some energy at the same time. When the high-pressure cylinder (25), intermediate-pressure cylinder (26) and low-pressure cylinder (27) of the steam turbine are not started, the steam generated in the boiler furnace (1) all passes through the high-pressure bypass (31) and the first desuperheating and pressure reducing device (16) and enters the reheat steam cold section pipeline (13). At this time, the primary air heat exchanger (9) and the secondary air heat exchanger (10) are started to recover the heat of the bypass steam. The steam flow rate entering the heat source pipeline (33) of the primary air heat exchanger and the heat source pipeline (34) of the secondary air heat exchanger is controlled by adjusting the first control valve (14) and the second control valve (15). The primary and secondary air temperatures are monitored by the temperature measuring point (36) to ensure that the primary and secondary air temperatures at the outlet of the primary air heat exchanger (9) and the secondary air heat exchanger (10) are within the specified range.

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