Power station boiler flue gas waste heat regenerative system

Abstract

The utility model belongs to the technical field of boiler flue gas waste heat recovery, and particularly relates to a power station boiler flue gas waste heat regenerative system which comprises an air preheater, an electric dust remover and an induced draft fan which are arranged on a main flue. A heating medium water heat exchanger is arranged between the air preheater and the electric dust remover, a first heating medium water loop is connected to the heating medium water heat exchanger, and heating medium water of the first heating medium water loop is connected into a steam turbine heat regeneration system; one part of outlet water of the first heating medium water loop returns to a steam turbine regenerative system, and the other part of outlet water of the first heating medium water loop is connected with the primary air heater and the secondary air heater through the second heating medium water loop; and outlet water of the second heating medium water loop and inlet water of the first heating medium water loop are mixed and then enter the heating medium water heat exchanger. By arranging the heating medium water heat exchange system and the air preheater system, the temperature of flue gas at an outlet of an air preheater is increased to 135-185 DEG C, the temperature of hot air of secondary air is increased by 3-15 K compared with the conventional temperature, the flue gas waste heat recovery effect is effectively improved, and the power supply coal consumption of the unit is reduced by 3-4 g / kWh.

Description

Technical Field

[0001] The utility model belongs to the technical field of boiler flue gas waste heat recovery, and particularly relates to a power station boiler flue gas waste heat regeneration system. Background Technique

[0002] The efficient recovery of flue gas waste heat from coal-fired power generation boilers is an important research direction for improving the power generation efficiency of coal-fired power generation units. The most direct way to recover flue gas waste heat is to use a low-low temperature economizer (see Figure 1 ), using condensate to reduce the boiler flue gas temperature from about 130°C to 85 - 90°C. The heated condensate returns to the low-pressure heating system, thereby reducing the extraction steam volume of the steam turbine, increasing the work done by the steam turbine, and thus improving the cycle efficiency of the unit. This method has a simple system, but the waste heat recovery efficiency is relatively low. Usually, it can only reduce the power supply coal consumption by about 2 g / kWh, of which 0.5 g / kWh is due to the reduction of flue gas resistance after the flue gas temperature decreases, etc. As a result, the coal consumption directly reduced due to waste heat recovery usually does not exceed 1.5 g / kWh.

[0003] To improve the effect of flue gas waste heat recovery, a boiler flue gas waste heat recovery system with partial flue gas bypass has been introduced in China in recent years (see Figure 2 ), and it has been widely applied to newly built large coal-fired power generation units. This system can recover flue gas waste heat more efficiently. Usually, it can reduce the power supply coal consumption by about 3 g / kWh. At the same time, due to the use of technologies such as bypass flue ducts, the operating flexibility of the unit has also been improved. However, this system has the following problems:

[0004] (1) The primary air does not participate in the recovery of low-temperature flue gas waste heat. The set forced circulation heat pipe system only heats the secondary air, and the primary air directly enters the air preheater. The primary air accounts for about 25% of the total air volume and is not used for low-temperature flue gas cooling and low-temperature zone flue gas waste heat recovery, which will reduce the effect of flue gas waste heat recovery.

[0005] (2) The outlet air temperature of the air preheater is lower than the working condition without flue gas waste heat recovery, that is, after about 15% of the flue gas bypass, the air temperature for combustion is lower than the original design value, which will lead to a decrease in boiler efficiency and thus an increase in coal consumption. Although this scheme improves the effect of flue gas waste heat recovery by setting a forced circulation heat pipe system to preheat the secondary air and by setting technical means such as flue gas bypass, due to the decrease in the outlet air temperature of the air preheater, part of the waste heat recovery effect is offset, thus affecting the overall efficiency of flue gas waste heat recovery, and the actual operation effect often fails to reach the design value.

[0006] (3) This scheme usually cannot be used for the transformation of existing boilers because there is not enough space in the original air preheater area to arrange the bypass flue duct.

[0007] Based on the above problems, how to construct a flue gas waste heat recovery system to achieve coal saving and improve the cycle efficiency of the unit is an urgent problem to be solved. Summary of the Invention

[0008] To solve the problems in the above background technology, the present utility model provides a flue gas waste heat recovery system for a power station boiler. Through this system, the waste heat of low-temperature flue gas is efficiently recovered and utilized, and the power supply coal consumption of the unit can be reduced by 3 - 4 g / kWh.

[0009] The present utility model adopts the following technical solutions:

[0010] A flue gas waste heat recovery system for a power station boiler includes a main flue, and an air preheater, an electrostatic precipitator, and an induced draft fan that are sequentially arranged on the main flue;

[0011] A heat medium water heat exchanger is arranged on the main flue between the air preheater and the electrostatic precipitator. A first heat medium water circuit is connected to the heat medium water heat exchanger, and the heat medium water in the first heat medium water circuit is accessed from the steam turbine regenerative system;

[0012] A part of the water outlet of the first heat medium water circuit returns to the steam turbine regenerative system, and the other part of the water outlet is connected to the primary air air heater and the secondary air air heater respectively through a second heat medium water circuit. The primary air air heater is arranged on the inlet air duct of the primary air, and the secondary air air heater is arranged on the inlet air duct of the secondary air. Both the primary air air heater and the secondary air air heater are arranged before the air preheater. The primary air air heater is used to heat the primary air, and the secondary air air heater is used to heat the secondary air; the water outlet of the second heat medium water circuit is mixed with the water inlet of the first heat medium water circuit and then enters the heat medium water heat exchanger;

[0013] A heat medium water heat exchanger is set and the flow rates of each circuit are adjusted so that the outlet flue gas temperature of the air preheater is 135 - 185 °C.

[0014] Further, the air preheater includes a primary air preheater and a secondary air preheater arranged on the main flue. Part of the heating surface of the primary air preheater is changed to be used for preheating the secondary air to form an additional secondary air preheater;

[0015] A primary air fan is arranged on the inlet air duct of the primary air air heater, and a secondary air fan is arranged on the inlet air duct of the secondary air air heater. The primary air fan is connected to the primary air preheater through the primary air air heater, and the secondary air fan is connected to the additional secondary air preheater and the secondary air preheater respectively through the secondary air air heater.

[0016] Further, the second heat medium water circuit includes a primary air heat medium water branch and a secondary air heat medium water branch. The primary air air heater is connected to the primary air heat medium water branch, and the secondary air air heater is connected to the secondary air heat medium water branch; the water outlets of the primary air heat medium water branch and the secondary air heat medium water branch are both connected to the water inlet pipe of the first heat medium water circuit.

[0017] Further, a primary air preheater inlet water regulating valve is provided on the inlet pipeline of the primary air hot medium water branch, and a hot medium water return regulating valve is provided on the main return pipeline of the first hot medium water circuit.

[0018] Further, a secondary air preheater inlet water regulating valve is provided on the inlet pipeline of the secondary air hot medium water branch, and a hot medium water return regulating valve is provided on the main return pipeline of the first hot medium water circuit.

[0019] Further, a primary air preheater inlet water regulating valve is provided on the inlet pipeline of the primary air hot medium water branch, a secondary air preheater inlet water regulating valve is provided on the inlet pipeline of the secondary air hot medium water branch, and a hot medium water return regulating valve is provided on the main return pipeline of the first hot medium water circuit.

[0020] Further, a hot medium water pump is provided on the inlet pipeline of the first hot medium water circuit, and the hot medium water pump is provided on the inlet pipeline after the water outlet of the second hot medium water circuit is mixed with the water inlet of the first hot medium water circuit.

[0021] Further, the system is applied to the retrofit of existing units or the application to new units.

[0022] Compared with the prior art, the beneficial effects of the present utility model are as follows:

[0023] For the power station boiler flue gas waste heat recovery system provided by the present application, a hot medium water heat exchanger is provided on the main flue between the air preheater and the electrostatic precipitator. The cooling water of the hot medium water heat exchanger is connected from the steam turbine regenerative system. After passing through the hot medium water heat exchanger, the flue gas temperature is reduced to 85-90 °C. After the hot medium water absorbs the waste heat of the flue gas, a part of it returns to the steam turbine regenerative system, thereby reducing the extraction steam of the steam turbine regenerative system. This part of the extraction steam continues to do work in the steam turbine, reducing the coal consumption; the remaining hot medium water enters the primary air preheater and the secondary air preheater respectively to heat the primary air and the secondary air, increasing the temperatures of the primary air and the secondary air. Then the primary air and the secondary air continue to enter the air preheater for heating, realizing that both the primary air and the secondary air effectively participate in the waste heat recovery of the flue gas, especially the waste heat recovery of the low-temperature part. After the waste heat recovery, it enters the furnace of the boiler along with the air, which can directly reduce the input heat brought by the coal, thereby improving the boiler efficiency.

[0024] Using the system of the present application to efficiently recover the low-temperature flue gas waste heat can reduce the unit power supply coal consumption by 3-4 g / kWh and improve the low-load operation performance of the unit at the same time. Description of the Drawings

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0026] Figure 1 It is a structural diagram of a low-low temperature economizer flue gas waste heat recovery system in the prior art;

[0027] Figure 2 It is a structural diagram of a boiler flue gas waste heat recovery system with a flue gas bypass in the prior art;

[0028] Figure 3 It is a structural diagram of a power station boiler flue gas waste heat regeneration system provided by an embodiment of the present application;

[0029] Wherein: 1 - main flue, 2 - air preheater, 21 - primary air preheater, 22 - additional secondary air preheater, 23 - secondary air preheater, 3 - electrostatic precipitator, 4 - induced draft fan, 5 - heat medium water heat exchanger, 6 - first heat medium water circuit, 7 - primary air air heater, 8 - secondary air air heater, 9 - primary air fan, 10 - secondary air fan, 11 - primary air heat medium water branch, 12 - secondary air heat medium water branch, 13 - primary air air heater inlet regulating valve, 14 - secondary air air heater inlet regulating valve, 15 - heat medium water return regulating valve, 16 - heat medium water pump. Detailed implementation manners

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0031] The following combines the attached Figure 3 And specific embodiments to elaborate on the present invention in detail.

[0032] A coal-fired power generation unit has two regenerative systems, namely the boiler flue gas-air regenerative system and the steam turbine extraction steam regenerative system. The functions of both regenerative systems are to recover the waste heat to be discharged into the environment and improve the energy quality through a high-temperature heat source (furnace) for continued work, so it is called regeneration. When constructing a deep regeneration system for the waste heat of a power station boiler flue gas, the two regenerative systems must be optimized overall to achieve the highest cycle efficiency of the unit. The waste heat of the flue gas is used to heat the combustion air and returns to the furnace with the combustion air, which is defined as airborne regeneration; the waste heat of the flue gas is used to heat the working medium water and then returns to the steam turbine regenerative system with the working medium water, which is defined as waterborne regeneration. The utilization efficiency is higher when the waste heat of the flue gas is carried by the combustion air, while the utilization efficiency is lower when the waste heat of the flue gas is carried by the working medium water, that is, the efficiency of airborne regeneration is always higher than that of waterborne regeneration. During the design, the two regenerative systems need to be reasonably coordinated overall to maximize the regeneration effect of the waste heat of the flue gas, improve the cycle efficiency of the unit, and reduce the coal consumption for power supply.

[0033] The utility model provides a waste heat regeneration system for a power station boiler flue gas, which includes a main flue 1 and an air preheater 2, an electrostatic precipitator 3, and an induced draft fan 4 that are sequentially arranged on the main flue 1;

[0034] A heat medium water heat exchanger 5 is arranged on the main flue 1 between the air preheater 2 and the electrostatic precipitator 3. A first heat medium water circuit 6 is connected to the heat medium water heat exchanger 5, and the heat medium water of the first heat medium water circuit 6 is connected from the steam turbine regenerative system;

[0035] A part of the water outlet of the first heat medium water circuit 6 returns to the steam turbine regenerative system, and the other part of the water outlet is connected to a primary air air heater 7 and a secondary air air heater 8 respectively through a second heat medium water circuit. The primary air air heater 7 is arranged on the inlet air pipe of the primary air, and the secondary air air heater 8 is arranged on the inlet air pipe of the secondary air. Both the primary air air heater 7 and the secondary air air heater 8 are arranged in front of the air preheater 2. The primary air air heater 7 is used to heat the primary air, and the secondary air air heater 8 is used to heat the secondary air; the water outlet of the second heat medium water circuit is mixed with the water inlet of the first heat medium water circuit and then enters the heat medium water heat exchanger 5 to adjust the flow rates of the first heat medium water circuit 6 and the second heat medium water circuit so that the outlet flue gas temperature of the air preheater 2 is 135 - 185 °C.

[0036] In this application, a heat medium water heat exchanger 5 is provided to absorb the waste heat of low-temperature flue gas. The cooling water of the heat medium water heat exchanger 5 comes from the turbine regenerative system. After the cooling water passes through the heat medium water heat exchanger 5, the flue gas temperature is reduced to T3 (generally 85 - 90 °C). After the heat medium water absorbs the waste heat of the flue gas, a part of it returns to the turbine regenerative system, reducing the extraction steam of the turbine regenerative system, enabling this part of the extraction steam to continue to do work in the turbine and reducing the coal consumption. The remaining heat medium water enters the primary air preheater 7 and the secondary air preheater 8 through the second heat medium water circuit, heating the primary air and the secondary air, thereby increasing the temperatures of the primary air and the secondary air. Then, the primary air and the secondary air continue to enter the air preheater 2. Through the indirect heating method, both the primary air and the secondary air effectively participate in the recovery of waste heat from the flue gas, especially the recovery of waste heat from the low-temperature part of the flue gas, rather than only the secondary air participating in the recovery of waste heat from the low-temperature part of the flue gas. After the secondary air recovers the waste heat of the flue gas, it then enters the boiler furnace, which can directly reduce the input heat brought in by the fuel, thereby improving the boiler efficiency. Using the system of this application can achieve efficient recovery and utilization of the waste heat of low-temperature flue gas, and the comprehensive power supply coal consumption of the unit can be reduced by 3 - 4 g / kWh.

[0037] It should be noted that the increase in the return water temperature of the first heat medium water circuit 6 returning to the turbine regenerative system helps to reduce the heat consumption.

[0038] In a specific embodiment, by providing the primary air preheater 7 and the secondary air preheater 8, the flue gas temperature T2 at the inlet of the heat medium water heat exchanger 5 can be increased. T2 is also the flue gas temperature at the outlet of the air preheater 2. T2 is an important parameter in the system design of this application. Using the system of this application and by adjusting the flow rates of the first heat medium water circuit 6 and the second heat medium water circuit, T2 is increased to 135 - 185 °C. The increase in T2 will increase the outlet water temperature ts2 of the heat medium water heat exchanger 5. The increase in ts2 indicates an increase in the return water temperature to the turbine regenerative system, which is beneficial to reducing the turbine heat consumption and thus reducing the coal consumption. At the same time, the increase in T2 also creates conditions for increasing the outlet air temperature of the air preheater 2. The increase in the temperature of the air preheater 2 will increase the hot air outlet temperature t23 of the secondary air. Usually, t23 can be increased by 3 - 15 K compared with the conventional situation. After calculation, when the hot air temperature ts23 of the secondary air is increased by 10 K, the power generation coal consumption of the unit can be reduced by about 1 g / kWh. Through this system, efficient recovery and utilization of the waste heat of low-temperature flue gas can be achieved, and the comprehensive power supply coal consumption of the unit can be reduced by about 3 - 4 g / kWh. It should be noted that after the temperature t23 of the secondary air is increased, the boiler needs to make adaptive combustion adjustments. On the one hand, it is necessary to try to improve the boiler combustion efficiency and the boiler thermal efficiency. On the other hand, through deep staged combustion, the generation of NOx is reduced. How to specifically carry out the combustion adjustment is not specifically limited in this application.

[0039] The flue gas flow of the embodiment of this application is as follows: The flue gas (T1 = 360 - 370 °C) from the outlet of the boiler economizer, after passing through the air preheater, the flue gas temperature drops to T2 = 135 - 185 °C; after passing through the heat medium water heat exchanger 5, the flue gas temperature drops to T3 = 85 - 90 °C, and then enters the electrostatic precipitator.

[0040] In a specific embodiment, the air preheater 2 includes a primary air preheater 21 and a secondary air preheater 23 arranged on the main flue 1, and part of the heating surface of the primary air preheater 21 is changed to be used for heating the secondary air, forming an additional secondary air preheater 22; a primary air heater 7 is provided with a primary air fan 9 on its inlet pipeline, and a secondary air heater 8 is provided with a secondary air fan 10 on its inlet pipeline. The primary air fan 9 is connected to the primary air preheater 21 through the primary air heater 7, and the secondary air fan 10 is connected to the additional secondary air preheater 22 and the secondary air preheater 23 respectively through the secondary air heater 8. Since the temperature of the primary air usually does not need to be too high, the required temperature of the primary air mainly depends on the requirements of the coal type for drying. The appropriate primary air temperature can be achieved by adjusting the size of the heating surface area of the primary air preheater 21; while increasing the temperature of the secondary air is of great significance for reducing the coal consumption for power generation of the unit. When the temperature of the secondary air increases, especially during low-load operation, it not only helps to stably burn and completely burn the pulverized coal in the boiler, improving the operation stability and economy, but also is conducive to organizing staged combustion, reducing the generation of NOx, and having good environmental protection performance; in this application, by increasing the heating surface area of the secondary air, the temperature of the secondary air is increased, thereby improving the boiler efficiency. The formation method of the additional secondary air preheater 22 in this application is: changing part of the heating surface area of the primary air preheater 21 to preheat the secondary air, that is, reducing the heating surface area of the primary air preheater 21 while increasing the heating surface area of the secondary air preheater. By reducing the heating surface area of the primary air, it is avoided that the hot air temperature of the primary air is too high. If the temperature of the primary air is higher than the requirement of the coal pulverizing system, cold air must be incorporated, which will cause irreversible losses. Increasing the heating surface area of the secondary air can increase the outlet temperature of the secondary air. The formation of the additional secondary air preheater in this application does not require the introduction of new equipment, and only needs to transform the original primary air preheater to achieve, without being restricted by the space scenario.

[0041] It can be known that the waste heat of the flue gas should be used as much as possible to heat the combustion air, especially to heat the secondary air. It has been verified that the waste heat recovery benefit obtained by increasing the temperature of the secondary air is the largest. Based on the above theory, in this application, the heating surface of the primary air preheater 21 is reduced to avoid the hot air temperature of the primary air being too high; at the same time, the heating surface of the secondary air is increased to increase the hot air temperature of the secondary air, thereby improving the boiler efficiency.

[0042] Specifically, the second hot medium water circuit includes a primary air hot medium water branch 11 and a secondary air hot medium water branch 12. The primary air preheater 7 is connected to the primary air hot medium water branch 11, and the secondary air preheater 8 is connected to the secondary air hot medium water branch 12. The outlet water of the primary air hot medium water branch 11 and the outlet water of the secondary air hot medium water branch 12 are both connected to the inlet pipeline of the first hot medium water circuit 6. After the hot medium water passes through the primary air preheater 7 and the secondary air preheater 8, its temperature decreases. At this time, it is led to the inlet pipeline of the first hot medium water circuit 6 to form a hot medium water circulation.

[0043] In some embodiments, a primary air preheater inlet regulating valve 13 is provided on the inlet pipeline of the primary air hot medium water branch 11, and a hot medium water return regulating valve 15 is provided on the main return line of the first hot medium water circuit 6. By adjusting the primary air preheater inlet regulating valve 13 and / or the hot medium water return regulating valve 15, the temperature of the primary air hot air can be adjusted to cancel or reduce the cold air incorporated into the coal pulverizing system, thereby reducing irreversible losses.

[0044] In some embodiments, a secondary air preheater inlet regulating valve 14 is provided on the inlet pipeline of the secondary air hot medium water branch 12, and a hot medium water return regulating valve 15 is provided on the main return line of the first hot medium water circuit 6. By adjusting the secondary air preheater inlet regulating valve 14 and / or the hot medium water return regulating valve 15, the temperature of the secondary air hot air can be adjusted, which is crucial for improving the boiler efficiency and the unit cycle efficiency during low-load operation.

[0045] In some embodiments, a primary air preheater inlet regulating valve 13 is provided on the inlet pipeline of the primary air hot medium water branch 11, a secondary air preheater inlet regulating valve 14 is provided on the inlet pipeline of the secondary air hot medium water branch 12, and a hot medium water return regulating valve 15 is provided on the main return line of the first hot medium water circuit 6. By adjusting the primary air preheater inlet regulating valve 13 and / or the secondary air preheater inlet regulating valve 14 and / or the hot medium water return regulating valve 15, the temperature of the flue gas at the inlet of the electrostatic precipitator 3 can be adjusted, which is very important for ensuring the safe operation of downstream equipment. At the same time, the return temperature of the hot medium water can be adjusted to increase the return temperature of the hot medium water. An increase in the hot medium water return temperature indicates an improvement in the heat recovery quality of the water carrier, which can reduce the heat consumption of the steam turbine and improve the unit cycle efficiency.

[0046] In this application, the setting of each valve increases the adjustable means of the unit and widens the adjustable range, ensuring greater flexibility in operation.

[0047] Furthermore, a hot medium water pump 16 is provided on the inlet pipeline of the first hot medium water circuit 6. The hot medium water pump 16 is arranged on the inlet pipeline after the outlet water of the second hot medium water circuit is mixed with the inlet water of the first hot medium water circuit 6. The hot medium water pump 16 pumps the hot medium water into the hot medium water heat exchanger 5 at a certain flow rate.

[0048] Furthermore, the system is applied to the retrofit of existing units or the construction of new units.

[0049] The system of this application overcomes the defect of poor flue gas regeneration effect in the prior art, realizes the efficient recovery of the waste heat of low-temperature flue gas, reduces the power supply coal consumption of the unit by 3 - 4 g / kWh, and improves the low-load operation performance of the unit at the same time.

[0050] The above further describes the present utility model by means of specific embodiments. However, it should be understood that the specific description here should not be construed as a limitation on the essence and scope of the present utility model. Various modifications made by those of ordinary skill in the art to the above embodiments after reading this specification all fall within the scope protected by the present utility model.

Claims

1. A power station boiler flue gas waste heat recovery system, characterized in that: It includes a main flue and an air preheater, an electric precipitator and an induced draft fan which are sequentially arranged on the main flue; A heat medium water heat exchanger is provided on the main flue between the air preheater and the electrostatic precipitator, and a first heat medium water circuit is connected to the heat medium water heat exchanger, and the heat medium water of the first heat medium water circuit is connected to the steam turbine heat recovery system; A portion of the outlet water of the first heat medium water circuit returns to the steam turbine heat recovery system, and the other portion of the outlet water is connected to the primary air heater and the secondary air heater respectively through the second heat medium water circuit. The primary air heater is arranged on the air inlet pipeline of the primary air, and the secondary air heater is arranged on the air inlet pipeline of the secondary air. Both the primary air heater and the secondary air heater are arranged before the air preheater. The primary air heater is used to heat the primary air, and the secondary air heater is used to heat the secondary air. The outlet water of the second heat medium water circuit is mixed with the inlet water of the first heat medium water circuit and then enters the heat medium water heat exchanger. The outlet flue gas temperature of the air preheater is 135-185°C.

2. The power station boiler flue gas waste heat recovery system according to claim 1, characterized in that: The air preheater comprises a primary air preheater and a secondary air preheater arranged on the main flue, and part of the heating surface of the primary air preheater is used to preheat the secondary air to form an additional secondary air preheater; A primary fan is arranged on the air inlet duct of the primary air heater, a secondary fan is arranged on the air inlet duct of the secondary air heater, the primary fan is connected to the primary air preheater through the primary air heater, and the secondary fan is respectively connected to the additional secondary air preheater and the secondary air preheater through the secondary air heater.

3. The power station boiler flue gas waste heat recovery system according to claim 1, characterized in that: The second heat medium water circuit includes a primary air heat medium water branch and a secondary air heat medium water branch, the primary air heater is connected to the primary air heat medium water branch, and the secondary air heater is connected to the secondary air heat medium water branch; the outlet water of the primary air heat medium water branch and the outlet water of the secondary air heat medium water branch are both connected to the water inlet pipe of the first heat medium water circuit.

4. The power station boiler flue gas waste heat recovery system according to claim 3, characterized in that: A primary air heater water inlet regulating valve is arranged on the water inlet pipeline of the primary air heat medium water branch, and a heat medium water return regulating valve is arranged on the main circuit of the first heat medium water circuit.

5. The power station boiler flue gas waste heat recovery system according to claim 3, characterized in that: A secondary air heater water inlet regulating valve is arranged on the water inlet pipeline of the secondary air heat medium water branch, and a heat medium water return regulating valve is arranged on the main circuit of the first heat medium water circuit.

6. The power station boiler flue gas waste heat recovery system according to claim 3, characterized in that: A primary air heater water inlet regulating valve is arranged on the water inlet pipe of the primary air heat medium water branch, a secondary air heater water inlet regulating valve is arranged on the water inlet pipe of the secondary air heat medium water branch, and a heat medium water return regulating valve is arranged on the main circuit of the first heat medium water circuit.

7. The power station boiler flue gas waste heat recovery system according to claim 1, characterized in that: A heat medium water pump is arranged on the water inlet pipeline of the first heat medium water circuit, and the heat medium water pump is arranged on the water inlet pipeline after the outflow water of the second heat medium water circuit and the inflow water of the first heat medium water circuit are mixed.

8. The power station boiler flue gas waste heat recovery system according to claim 1, characterized in that: The system is applied to the transformation of existing units or to newly built units.

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