Natural gas boiler flue gas de-whitening device and method

Abstract

This invention discloses a device and method for eliminating white smoke from natural gas boiler flue gas. The inlet of a primary heat pump evaporator is adapted to be connected to the boiler's exhaust port. The first flue gas discharged from the boiler can exchange heat with the refrigerant and be cooled to the second flue gas level within the primary heat pump evaporator. The inlet of the primary heat pump condenser is adapted to be connected to the system's return water pipe, and the outlet of the primary heat pump condenser is adapted to be connected to the boiler. The inlet of a secondary heat pump evaporator is connected to the outlet of the primary heat pump evaporator. The second flue gas discharged from the primary heat pump evaporator can exchange heat with the refrigerant and be cooled to the third flue gas level within the secondary heat pump evaporator. The third flue gas discharged from the secondary heat pump evaporator can exchange heat with the refrigerant in the flue gas reheater and be heated to the fourth flue gas level, which is not lower than the outdoor temperature, before being discharged. The device and method for eliminating white smoke from natural gas boiler flue gas of this invention can prevent the generation of white smoke during flue gas discharge and can effectively utilize the heat in the flue gas.

Description

Technical Field

[0001] This invention relates to the field of flue gas whitening technology, specifically to a flue gas whitening device for a natural gas boiler and a whitening method using the device. Background Technology

[0002] Because the volumetric water vapor content in the flue gas of natural gas boilers is generally 15% to 19%, while that of gas-fired boilers is very low due to the high water vapor content, white smoke will be produced if no whitening treatment is performed during flue gas emission. The white smoke is mainly caused by the emission of saturated water vapor from the wet flue gas, which contains a large amount of waste heat energy, resulting in energy waste. Furthermore, the white smoke can adsorb harmful substances from the surrounding environment, forming a "moist plume," and the high humidity can affect the safety of electrical equipment.

[0003] Patent CN216203467U discloses a flue gas whitening device for a natural gas boiler using heat pump technology. The device includes a base, a tower body, a condensate pan, a flue gas heat exchanger, a flue gas reheat heat exchanger, and a heat pump unit. The base is used to mount the tower body onto the chimney of the natural gas boiler. A flue gas inlet is located at the bottom of the tower body and connects to the chimney; a flue gas outlet is located at the top of the tower body. The flue gas heat exchanger and the flue gas reheat heat exchanger are arranged inside the tower body from bottom to top. The condensate pan is located below the flue gas heat exchanger, and a condensate outlet is located on the side of the condensate pan. The heat pump unit includes an evaporator and a condenser. The evaporator is connected to the flue gas heat exchanger and cools the medium inside the flue gas heat exchanger. The condenser is connected to the flue gas reheat heat exchanger and heats the medium inside the flue gas reheat heat exchanger. Since the energy required for flue gas whitening is less than the energy of waste heat in the flue gas, although flue gas whitening is achieved in this patent, the waste heat in the flue gas is not fully utilized, resulting in energy waste. Summary of the Invention

[0004] Therefore, this invention proposes a natural gas boiler flue gas whitening device to solve the problems of white smoke generated during boiler flue gas emission and low waste heat utilization efficiency in the flue gas.

[0005] This invention also proposes a method for eliminating whitening using the above-mentioned flue gas whitening device.

[0006] The flue gas whitening device for a natural gas boiler according to an embodiment of the present invention includes a primary whitening unit and a secondary whitening unit. The primary whitening unit includes a primary heat pump evaporator, a primary compressor, and a primary heat pump condenser. The inlet of the primary heat pump evaporator is adapted to be connected to the boiler's exhaust port. The first flue gas discharged from the boiler can exchange heat with the refrigerant and be cooled to the second flue gas in the primary heat pump evaporator. The refrigerant outlet of the primary heat pump evaporator is connected to the refrigerant inlet of the primary compressor. The refrigerant outlet of the primary compressor is connected to the refrigerant inlet of the primary heat pump condenser. The refrigerant outlet of the primary heat pump condenser is connected to the refrigerant inlet of the primary heat pump evaporator. The water inlet of the primary heat pump condenser is adapted to be connected to the system return water pipe. The water outlet of the primary heat pump condenser is adapted to be connected to the boiler. The return water in the system return water pipe can exchange heat with the refrigerant in the primary heat pump condenser and then be introduced into the boiler.

[0007] The secondary flue gas elimination unit includes a secondary heat pump evaporator, a secondary compressor, and a flue gas reheater. The inlet of the secondary heat pump evaporator is connected to the outlet of the primary heat pump evaporator. The second flue gas discharged from the primary heat pump evaporator can exchange heat with the refrigerant and be cooled to the third flue gas temperature in the secondary heat pump evaporator. The refrigerant outlet of the secondary heat pump evaporator is connected to the refrigerant inlet of the secondary compressor. The refrigerant outlet of the secondary compressor is connected to the refrigerant inlet of the flue gas reheater. The refrigerant outlet of the flue gas reheater is connected to the refrigerant inlet of the secondary heat pump evaporator. The third flue gas discharged from the secondary heat pump evaporator can exchange heat with the refrigerant and be heated to the fourth flue gas temperature (not lower than the outdoor temperature) in the flue gas reheater before being discharged.

[0008] In some embodiments, the temperature of the third flue gas is not greater than the outdoor temperature.

[0009] In some embodiments, the temperature difference between the fourth flue gas and the outdoor temperature is N, and 0° < N ≤ 5°.

[0010] In some embodiments, the primary whitening unit further includes a primary electronic expansion valve, which is located between the refrigerant outlet of the primary heat pump condenser and the refrigerant inlet of the primary heat pump evaporator.

[0011] In some embodiments, the secondary whitening unit further includes a secondary electronic expansion valve, which is located between the refrigerant outlet of the flue gas reheater and the refrigerant inlet of the secondary heat pump evaporator.

[0012] In some embodiments, the flue gas whitening device further includes an electrically controlled regulating valve, which is adapted to be installed between the system return water pipe and the boiler.

[0013] The flue gas whitening method based on any of the above embodiments of the natural gas boiler flue gas whitening device includes the following steps:

[0014] The temperature T1, relative humidity φ1, and mass flow rate Qm of the first flue gas emitted from the boiler are detected and obtained. The enthalpy H1 of the first flue gas can be obtained through sensor data and automatic calculation program.

[0015] The outdoor air temperature T2 and relative humidity φ2 are detected and acquired. The enthalpy H2 of the outdoor air can be obtained through sensor data and automatic calculation program.

[0016] The first flue gas is controlled to pass through the first-stage heat pump evaporator. The first-stage heat pump evaporator can cool the first flue gas to the second flue gas at a temperature of T3. The enthalpy value H3 of the second flue gas can be obtained through sensor data and automatic calculation program. The cooling capacity Q1 = (H1-H3)*Qm in the first-stage heat pump evaporator per unit time can be obtained.

[0017] The second flue gas is controlled to pass through a secondary heat pump evaporator. The secondary heat pump evaporator can cool the second flue gas to a third flue gas with a temperature of T4. At this time, the moisture content of the third flue gas is d. The enthalpy value H4 of the third flue gas can be obtained through sensor data and automatic calculation program. The cooling capacity Q2 = (H3-H4)*Qm in the secondary heat pump evaporator per unit time can be obtained, where temperature T4 ≤ temperature T2.

[0018] The third flue gas is controlled to pass through the flue gas reheater. The flue gas reheater can heat the third flue gas to the fourth flue gas at a temperature of T5 and discharge it. The temperature T5 is greater than the temperature T2. At this time, the moisture content in the fourth flue gas is still d. The enthalpy value H5 of the fourth flue gas can be obtained through sensor data and automatic calculation program. The amount of flue gas reheating heat per unit time in the flue gas reheater can be obtained as Q3 = (H5-H4)*Qm.

[0019] The control system's return water pipe supplies water to the first-stage heat pump condenser, and the return water is heated by the first-stage heat pump condenser before being fed into the boiler.

[0020] Here, the sum of the power of the first-stage compressor and the second-stage compressor is defined as Q4, and the heat obtained by the return water in the first-stage heat pump condenser per unit time is defined as Q5. According to Q1+Q2+Q4=Q3+Q5, the water supply from the system return water pipe to the heat pump condenser per unit time can be obtained.

[0021] The beneficial effects of this invention are as follows: After the first flue gas emitted from the boiler undergoes heat recovery in the primary heat pump evaporator, the refrigerant that gains heat can be used to heat the system return water after being heated and pressurized by the primary compressor, thus making full and effective use of the flue gas waste heat. In addition, the second flue gas, after being cooled and dehumidified, can undergo further de-whitening treatment in the secondary heat pump evaporator to reduce the water content in the flue gas. Furthermore, during this de-whitening treatment, the refrigerant that gains heat, after being heated and pressurized by the secondary compressor, enters the flue gas reheater, which can heat the third flue gas into a fourth flue gas with a temperature slightly higher than the outdoor temperature. Since the water content in the fourth flue gas at this time is not greater than the outdoor saturated water vapor partial pressure, the generation of white smoke can be avoided when the fourth flue gas is discharged outdoors.

[0022] In addition, the present invention can precisely reheat the second flue gas to a third flue gas with a temperature slightly higher than the outdoor temperature that does not produce white smoke when discharged, based on changes in outdoor temperature, thereby achieving precise heat control and maximizing the utilization of waste heat in the flue gas. Attached Figure Description

[0023] Figure 1 This is a structural schematic diagram of an embodiment of the present invention.

[0024] Figure label:

[0025] 1. Boiler; 2. System return water pipe; 3. Primary heat pump evaporator; 4. Primary heat pump condenser; 5. Primary compressor; 6. Primary electronic expansion valve; 7. Secondary heat pump evaporator; 8. Secondary compressor; 9. Flue gas reheater; 10. Secondary electronic expansion valve; 11. Electric regulating valve. Detailed Implementation

[0026] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0027] like Figure 1 As shown, the natural gas boiler flue gas whitening device of this embodiment includes a primary whitening unit and a secondary whitening unit. The primary whitening unit includes a primary heat pump evaporator 3, a primary compressor 5, and a primary heat pump condenser 4. The inlet end of the primary heat pump evaporator 3 is adapted to communicate with the exhaust port of the boiler 1. The first flue gas discharged from the boiler 1 can exchange heat with the refrigerant and be cooled to the second flue gas in the primary heat pump evaporator 3. Specifically, the first flue gas discharged from the boiler 1 can be introduced into the primary heat pump evaporator 3 through the inlet end of the primary heat pump evaporator 3. The first flue gas contains a certain amount of water vapor. The primary heat pump evaporator 3 can use the high latent heat characteristic of the first flue gas to make the refrigerant evaporate. At the same time, the first flue gas can be cooled and dehumidified after passing through the primary heat pump evaporator 3 to become the second flue gas. Some of the water vapor in it can be liquefied into liquid water and discharged from the primary heat pump evaporator 3.

[0028] The refrigerant outlet of the first-stage heat pump evaporator 3 is connected to the refrigerant inlet of the first-stage compressor 5 so that the refrigerant after being heated and evaporated in the first-stage heat pump evaporator 3 can be introduced into the first-stage compressor 5 for heating and pressurization.

[0029] The refrigerant outlet of the first-stage compressor 5 is connected to the refrigerant inlet of the first-stage heat pump condenser 4, the refrigerant outlet of the first-stage heat pump condenser 4 is connected to the refrigerant inlet of the first-stage heat pump evaporator 3, and the water inlet of the first-stage heat pump condenser 4 is adapted to be connected to the system return water pipe 2, and the water outlet of the first-stage heat pump condenser 4 is adapted to be connected to the boiler 1. The return water in the system return water pipe 2 can exchange heat with the refrigerant in the first-stage heat pump condenser 4 and then be introduced into the boiler 1.

[0030] Specifically, the refrigerant after being heated and pressurized by the first-stage compressor 5 can be introduced into the first-stage heat pump condenser 4. At the same time, the system return water pipe 2 can supply water to the first-stage heat pump condenser 4. In the first-stage heat pump condenser 4, the high-temperature and high-pressure refrigerant can heat the water. The heated water can be introduced into the boiler 1 for use. After the refrigerant has finished heating the water, it can be circulated back into the first-stage heat pump evaporator 3.

[0031] The secondary flue gas elimination unit includes a secondary heat pump evaporator 7, a secondary compressor 8, and a flue gas reheater 9. The inlet of the secondary heat pump evaporator 7 is connected to the outlet of the primary heat pump evaporator 3. The second flue gas discharged from the primary heat pump evaporator 3 can exchange heat with the refrigerant in the secondary heat pump evaporator 7 and be cooled to the third flue gas. Specifically, the second flue gas cooled by the primary heat pump evaporator 3 can be introduced into the secondary heat pump evaporator 7 through the inlet of the secondary heat pump evaporator 7 and exchange heat with the refrigerant in the secondary heat pump evaporator 7 for further cooling and dehumidification, finally generating the third flue gas with a temperature not higher than the outdoor temperature. As the second flue gas cools to the third flue gas, the liquefied liquid water in the flue gas can be discharged from the secondary heat pump evaporator 7.

[0032] The refrigerant outlet of the secondary heat pump evaporator 7 is connected to the refrigerant inlet of the secondary compressor 8 so that the refrigerant after being heated and evaporated in the secondary heat pump evaporator 7 can be introduced into the secondary compressor 8 for heating and pressurization.

[0033] The refrigerant outlet of the secondary compressor 8 is connected to the refrigerant inlet of the flue gas reheater 9, and the refrigerant outlet of the flue gas reheater 9 is connected to the refrigerant inlet of the secondary heat pump evaporator 7. The third flue gas discharged from the secondary heat pump evaporator 7 can exchange heat with the refrigerant in the flue gas reheater 9 and be heated to a fourth flue gas temperature not lower than the outdoor temperature before being discharged.

[0034] Specifically, the refrigerant heated and pressurized in the secondary compressor 8 can be introduced into the flue gas reheater 9. The refrigerant heated and pressurized in the flue gas reheater 9 can exchange heat with the third flue gas to heat the third flue gas to a fourth flue gas temperature not lower than the outdoor temperature. During the process of heating from the third flue gas to the fourth flue gas, the water vapor content in the flue gas remains unchanged, so that the generation of white smoke can be avoided when the fourth flue gas is discharged outdoors.

[0035] The temperature of the third flue gas is not higher than the outdoor temperature, which ensures that the water vapor content in the third flue gas is not higher than the saturated water vapor partial pressure of the outdoor environment. This prevents the generation of white smoke when the third flue gas is heated and discharged through the flue gas reheater 9. Preferably, the temperature of the third flue gas is equal to the outdoor temperature, which allows the white smoke elimination device to achieve the purpose of white smoke elimination while consuming less energy and being more economical.

[0036] In some embodiments, the temperature difference between the fourth flue gas and the outdoor temperature is N, and 0° < N ≤ 5°. Specifically, the temperature difference between the fourth flue gas and the outdoor temperature after treatment by the flue gas reheater 9 can be 1°, 2°, 3°, 4°, 5°, etc. Preferably, in this embodiment, the temperature difference between the fourth flue gas and the outdoor temperature can be 5°, which better ensures that white smoke is avoided due to sudden changes in the outside temperature.

[0037] In some embodiments, the primary whitening unit further includes a primary electronic expansion valve 6, which is located between the refrigerant outlet of the primary heat pump condenser 4 and the refrigerant inlet of the primary heat pump evaporator 3. The secondary whitening unit further includes a secondary electronic expansion valve 10, which is located between the refrigerant outlet of the flue gas reheater 9 and the refrigerant inlet of the secondary heat pump evaporator 7. The primary electronic expansion valve 6 and the secondary electronic expansion valve 10 can be used to control the flow rate of refrigerant in the primary whitening unit and the secondary whitening unit, as well as the opening and closing of refrigerant flow.

[0038] In some embodiments, the flue gas whitening device further includes an electric regulating valve 11, which is adapted to be installed between the system return water pipe 2 and the boiler 1. The electric regulating valve 11 can be used to control and regulate the flow rate of return water in the system return water pipe 2 leading to the primary heat pump condenser 4 and the boiler 1.

[0039] In some embodiments, sensors are provided at the air inlet of the primary heat pump evaporator 3, the air outlet of the primary heat pump evaporator 3, the air outlet of the secondary heat pump evaporator 7, and outdoors to detect the relative humidity, temperature, etc. of the flue gas or outdoor air.

[0040] In this embodiment, after the first flue gas emitted from the boiler undergoes heat recovery in the primary heat pump evaporator 3, the refrigerant that gains heat can be used to heat the system return water after being heated and pressurized by the primary compressor 5, thus making full and effective use of the flue gas waste heat. In addition, the second flue gas, after being cooled and dehumidified, can undergo further de-whitening treatment in the secondary heat pump evaporator 7 to reduce the water content in the flue gas. During this de-whitening treatment, the refrigerant that gains heat gains heats and pressurizes after being heated and pressurized by the secondary compressor 8, and then enters the flue gas reheater 9 to heat the third flue gas into a fourth flue gas with a temperature slightly higher than the outdoor temperature. Since the water content in the fourth flue gas is not greater than the outdoor saturated water vapor partial pressure, the generation of white smoke can be avoided when the fourth flue gas is discharged outdoors.

[0041] The following describes a method for eliminating white smoke according to an embodiment of the present invention.

[0042] The flue gas whitening method based on the natural gas boiler flue gas whitening device in the above embodiments includes the following steps:

[0043] The temperature T1, relative humidity φ1, and mass flow rate Qm of the first flue gas emitted from boiler 1 are detected and obtained. The enthalpy H1, relative humidity RH1, and absolute humidity AH1 of the first flue gas can be obtained through sensor data and automatic calculation program.

[0044] The outdoor air temperature T2 and relative humidity φ2 are detected and obtained. The enthalpy H2 and other physical properties of the outdoor air can be obtained through sensor data and automatic calculation program.

[0045] The first flue gas is controlled to pass through the first-stage heat pump evaporator 3. The first-stage heat pump evaporator 3 can cool the first flue gas to the second flue gas at a temperature of T3. Through sensor data and automatic calculation program, the physical property parameters of the second flue gas, such as enthalpy H3, relative humidity RH3, and absolute humidity AH3, can be obtained. The cooling capacity Q1 = (H1-H3)*Qm in the first-stage heat pump evaporator 3 per unit time can be obtained.

[0046] The second flue gas is controlled to pass through the secondary heat pump evaporator 7. The secondary heat pump evaporator 7 can cool the second flue gas to the third flue gas at a temperature of T4. At this time, the moisture content of the third flue gas is d. Through sensor data and automatic calculation program, the physical property parameters of the third flue gas, such as enthalpy H4, relative humidity RH4, and absolute humidity AH4, can be obtained. The cooling capacity per unit time in the secondary heat pump evaporator 7 can be calculated as Q2 = (H3-H4)*Qm, where temperature T4 ≤ temperature T2.

[0047] The third flue gas is controlled to pass through the flue gas reheater 9. The flue gas reheater 9 can heat the third flue gas to the fourth flue gas at a temperature of T5 and discharge it. The temperature T5 is greater than the temperature T2. At this time, the moisture content in the fourth flue gas is still d. The enthalpy value H5 of the fourth flue gas can be obtained through sensor data and automatic calculation program. The amount of flue gas reheating heat per unit time in the flue gas reheater 9 can be obtained as Q3 = (H5-H4)*Qm.

[0048] The control system's return water pipe 2 supplies water to the primary heat pump condenser 4, and the return water is heated by the primary heat pump condenser 4 before being introduced into the boiler 1.

[0049] Here, the sum of the power of the first-stage compressor 5 and the second-stage compressor 8 is defined as Q4, and the heat obtained by the return water in the first-stage heat pump condenser 4 per unit time is defined as Q5. According to Q1+Q2+Q4=Q3+Q5, the water supply from the system return water pipe 2 to the heat pump condenser per unit time can be obtained.

[0050] Specifically, the calculation methods for the relevant physical property parameters in this invention are shown in Table 1:

[0051]

[0052] Table 1

[0053] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0054] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A natural gas boiler flue gas de-whitening device, characterized by, The application relates to a white smoke elimination system, which comprises the following: a first white smoke elimination unit, which comprises a first heat pump evaporator (3), a first compressor (5) and a first heat pump condenser (4), the air inlet end of the first heat pump evaporator (3) is adapted to communicate with the flue gas outlet of a boiler (1), first flue gas discharged by the boiler (1) can exchange heat with refrigerant in the first heat pump evaporator (3) and is cooled to second flue gas, the refrigerant outlet of the first heat pump evaporator (3) communicates with the refrigerant inlet of the first compressor (5), the refrigerant outlet of the first compressor (5) communicates with the refrigerant inlet of the first heat pump condenser (4), the refrigerant outlet of the first heat pump condenser (4) communicates with the refrigerant inlet of the first heat pump evaporator (3), and the water inlet of the first heat pump condenser (4) is adapted to communicate with a system return water pipeline (2), the water outlet of the first heat pump condenser (4) is adapted to communicate with the boiler (1), and return water in the system return water pipeline (2) can exchange heat with the refrigerant in the first heat pump condenser (4) and then flow into the boiler (1); a second white smoke elimination unit, which comprises a second heat pump evaporator (7), a second compressor (8) and a flue gas reheater (9), the air inlet end of the second heat pump evaporator (7) communicates with the air outlet end of the first heat pump evaporator (3), second flue gas discharged by the first heat pump evaporator (3) can exchange heat with refrigerant in the second heat pump evaporator (7) and is cooled to third flue gas, the refrigerant outlet of the second heat pump evaporator (7) communicates with the refrigerant inlet of the second compressor (8), the refrigerant outlet of the second compressor (8) communicates with the refrigerant inlet of the flue gas reheater (9), the refrigerant outlet of the flue gas reheater (9) communicates with the refrigerant inlet of the second heat pump evaporator (7), and third flue gas discharged by the second heat pump evaporator (7) can exchange heat with refrigerant in the flue gas reheater (9) and is heated to fourth flue gas which is not lower than outdoor temperature and is discharged outside; the first white smoke elimination unit further comprises a first electronic expansion valve (6), which is arranged between the refrigerant outlet of the first heat pump condenser (4) and the refrigerant inlet of the first heat pump evaporator (3); the second white smoke elimination unit further comprises a second electronic expansion valve (10), which is arranged between the refrigerant outlet of the flue gas reheater (9) and the refrigerant inlet of the second heat pump evaporator (7); a motor-driven regulating valve (11) is further arranged between the system return water pipeline (2) and the boiler (1); the temperature of the third flue gas is not higher than the outdoor temperature; the temperature difference between the fourth flue gas and the outdoor temperature is N, and 0 < N <= 5.

2. A flue gas whitening method based on the flue gas whitening device of natural gas boiler of claim 1, characterized in that, The application further relates to a white smoke elimination method, which comprises the following steps: detecting the temperature T1, relative humidity phi1 and mass flow Qm of first flue gas discharged by a boiler (1), and obtaining the enthalpy H1 of the first flue gas through sensor data and automatic calculation program; detecting the temperature T2 and relative humidity phi2 of outdoor air, and obtaining the enthalpy H2 of the outdoor air through sensor data and automatic calculation program; Control the first flue gas through the primary heat pump evaporator (3), the primary heat pump evaporator (3) can cool the first flue gas to the second flue gas with temperature T3, through sensor data and automatic calculation program, the enthalpy H3 of the second flue gas can be obtained, and the refrigerating capacity Q1 of the primary heat pump evaporator (3) per unit time can be obtained, Q1=(H1-H3)*Qm; Control the second flue gas through the secondary heat pump evaporator (7), the secondary heat pump evaporator (7) can cool the second flue gas to the third flue gas with temperature T4, at this time, the third flue gas contains d, through sensor data and automatic calculation program, the enthalpy H4 of the third flue gas can be obtained, and the refrigerating capacity Q2 of the secondary heat pump evaporator (7) per unit time can be obtained, Q2=(H3-H4)*Qm, wherein the temperature T4≤ the temperature T2; Control the third flue gas through the flue gas reheater (9), the flue gas reheater (9) can heat the third flue gas to the fourth flue gas with temperature T5 and discharge, the temperature T5 is greater than the temperature T2, at this time, the fourth flue gas still contains d, through sensor data and automatic calculation program, the enthalpy H5 of the fourth flue gas can be obtained, and the flue gas reheating capacity Q3 of the flue gas reheater (9) per unit time can be obtained, Q3=(H5-H4)*Qm; The system backwater pipeline (2) supplies water to the primary heat pump condenser (4), and the backwater is heated in the primary heat pump condenser (4) and then introduced into the boiler (1); Wherein, the sum of the power of the primary compressor (5) and the secondary compressor (8) is defined as Q4, the heat obtained by the backwater in the primary heat pump condenser (4) per unit time is Q5, according to Q1+Q2+ Q4= Q3+ Q5, the water supply amount of the system backwater pipeline (2) to the heat pump condenser per unit time can be obtained.

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