Boiler flue gas heat recovery system and recovery method

Abstract

The invention relates to a boiler flue gas heat recovery system which comprises a heat supply device, the heat supply device comprises a boiler and a heat supply pipeline, the heat supply pipeline comprises a boiler water inlet pipe and a boiler water outlet pipe which communicate with the boiler, a flue is formed in a smoke exhaust device, and a first heat exchanger and a second heat exchanger are sequentially arranged in the flue in the flue gas flowing direction; the first waste heat recovery device comprises a first waste heat recovery flow path and a heat pump, the first waste heat recovery flow path is connected with the first heat exchanger and a boiler water inlet pipe, the heat pump is arranged on the first waste heat recovery flow path, the second waste heat recovery device comprises a second waste heat recovery flow path, and the second waste heat recovery flow path communicates with external air and a boiler. By arranging the heat pump, on one hand, the heat transfer temperature difference can be increased, smoke sensible heat and even part of latent heat can be efficiently recycled, on the other hand, the recycled heat can be flexibly adjusted according to changes of boiler loads, and therefore the system can adapt to changes of loads output by the system under different conditions.

Description

Technical Field

[0001] This application relates to the field of energy recovery technology, and in particular to a boiler flue gas heat recovery system and recovery method. Background Technology

[0002] With increasing global demands for energy efficiency and environmental protection, energy conservation and emission reduction in industrial boilers have become crucial issues. While boilers burn fuels such as coal, oil, and natural gas to provide heat for production and daily life, they also generate large amounts of high-temperature flue gas. This flue gas contains considerable heat; direct emission would not only result in significant energy waste but also increase thermal pollution. Therefore, waste heat recovery from boiler flue gas is an effective way to improve the overall thermal efficiency of boilers and reduce fuel consumption and operating costs.

[0003] Currently, mainstream boiler flue gas waste heat recovery systems primarily employ a single heat exchange mode. One common technology uses an "economizer" or "flue gas condenser," which is essentially a gas-water heat exchanger. This type of system introduces the boiler's heating return water or softened makeup water into the heat exchanger coils, where it indirectly exchanges heat with the high-temperature flue gas. It preheats the boiler feedwater by absorbing the sensible heat of the flue gas, thus achieving energy savings. Another technical solution is direct contact heat exchange, which uses equipment such as spray towers to allow circulating water to directly contact the flue gas, utilizing the evaporation and condensation processes of water to transfer heat. This method, due to its high heat transfer coefficient, can lower the flue gas temperature further, thereby recovering the latent heat of condensation of water vapor in the flue gas, resulting in relatively high recovery efficiency.

[0004] However, all of the above-mentioned technical solutions have significant drawbacks. For indirect gas-water heat exchange systems, the heat exchange efficiency is severely limited by the temperature of the heat exchange medium (water). Since the water entering the heat exchanger is typically at a high temperature, the temperature difference between the water and the flue gas is small, which not only limits the overall heat exchange but also makes it difficult to further reduce the flue gas temperature below the dew point. This hinders the effective recovery of the large proportion of latent heat, resulting in low overall recovery efficiency. While direct contact heat exchange systems offer higher recovery efficiency, acidic gases such as sulfur oxides and nitrogen oxides in the flue gas dissolve in the circulating water, forming a highly corrosive acidic liquid that severely corrodes subsequent pipes, pumps, and equipment, leading to high system maintenance costs and a short lifespan. Summary of the Invention

[0005] To address the problem that existing heat recovery systems cannot simultaneously recover energy from both high-temperature and low-temperature sections of flue gas while ensuring system safety, resulting in poor heat recovery efficiency, this application provides a boiler flue gas heat recovery system and method.

[0006] Firstly, the boiler flue gas heat recovery system provided in this application adopts the following technical solution: A boiler flue gas heat recovery system includes: A heating device includes a boiler and a boiler inlet pipe and a boiler outlet pipe connecting the boiler. The boiler inlet pipe is used to inject water into the boiler, and the boiler outlet pipe is used to discharge water from the boiler. The exhaust device has a flue, and a first heat exchanger and a second heat exchanger are sequentially arranged in the flue along the flue gas flow direction. A first waste heat recovery device includes a first waste heat recovery flow path and a heat pump. The first waste heat recovery flow path connects a first heat exchanger and a boiler inlet pipe. The heat pump is located in the first waste heat recovery flow path. The second waste heat recovery device includes a second waste heat recovery flow path, the inlet of which is connected to the outside air and the outlet of which is connected to the boiler, and the second heat exchanger is located in the second waste heat recovery flow path.

[0007] By adopting the above technical solution, and by setting up a first heat exchanger and a second heat exchanger, along with corresponding first and second waste heat recovery structures, the flue gas is continuously cooled through staged heat exchange. This method fully considers the heat transfer characteristics between the flue gas and the heat exchange fluid at different temperature states. At high temperatures, it utilizes the excellent heat transfer performance between the high-temperature flue gas and the heat exchange fluid; at low temperatures, it utilizes low-temperature fluids (such as cold air) to ensure the heat transfer effect of the flue gas after temperature reduction, greatly improving the waste heat utilization rate. At the same time, the warm air after heat exchange is introduced into the boiler, reducing the fuel consumption for heating the cold air. In addition, the first and second heat exchangers adopt indirect heat exchange and are connected to the heat exchangers through the first and second waste heat recovery flow paths, which can avoid the acidic corrosion problem caused by the precipitation of condensate in the flue gas and its mixing with intermediate water. Meanwhile, by installing a heat pump in the first waste heat recovery flow path, the water temperature entering the heat exchanger can be actively reduced, thereby increasing the heat transfer temperature difference and enhancing heat exchange efficiency when the flue gas temperature is high. This enables efficient recovery of sensible heat and even some latent heat from the flue gas. On the other hand, the recovered heat can be flexibly adjusted according to changes in boiler load, avoiding the "small load, large power" operation problem caused by load changes. As a result, the boiler flue gas heat recovery system can adapt to changes in system output load under different conditions, improving the economy and stability of system operation.

[0008] Preferably, the heat pump includes an evaporator and a condenser; The first waste heat recovery flow path includes a waste heat inlet water pipe and a waste heat return water pipe. The evaporator is located in the waste heat inlet water pipe to cool the waste heat inlet water pipe, and the condenser is located in the waste heat return water pipe to heat the waste heat return water pipe.

[0009] By adopting the above technical solution, a waste heat inlet water pipeline and a waste heat return water pipeline are set up to form a circulation loop. The return water from the boiler inlet water pipeline is introduced into the first heat exchanger to exchange heat with the flue gas, and the water after heat exchange is introduced back into the boiler return water pipeline. An evaporator is set up to cool the water in the waste heat inlet water pipeline, and a condenser is set up to heat the water in the waste heat return water pipeline, thereby significantly improving the overall waste heat recovery efficiency.

[0010] Preferably, the first waste heat recovery device further includes a waste heat recovery pump disposed in the first waste heat recovery flow path.

[0011] By adopting the above technical solution and setting up a waste heat recovery pump, the circulation flow rate in the first waste heat recovery flow path can be independently controlled. This allows for flexible adjustment of the flow rate based on the flue gas temperature and waste heat recovery requirements. When the flue gas temperature is high, the flow rate can be increased to improve the heat exchange capacity. When the flue gas temperature is low, the flow rate can be reduced to ensure the heat exchange temperature difference. Furthermore, by precisely controlling the flow rate, the flow velocity of the water in the first heat exchanger can be optimized to keep it within the optimal heat exchange efficiency range. This avoids the problems of increased pressure loss due to excessive flow velocity or decreased heat exchange coefficient due to excessively low flow velocity.

[0012] Preferably, the first waste heat recovery device further includes a first calorimeter disposed in the waste heat inlet water pipeline, the first calorimeter being located between the heat pump and the first heat exchanger; and / or, The first waste heat recovery device further includes a second calorimeter installed in the waste heat return water pipeline; the second calorimeter is located between the heat pump and the boiler inlet pipe.

[0013] By adopting the above technical solution, a first calorimeter is installed on the waste heat inlet water pipe so that the first calorimeter can measure the heat of the water entering the first heat exchanger after being cooled by the heat pump, thereby facilitating real-time monitoring of the heat recovery status of the first waste heat recovery device. A second calorimeter is installed on the waste heat return water pipe so that the second calorimeter can measure the heat of the water after being heated by the heat exchanger and the heat pump, thereby facilitating real-time monitoring of the heat recovery status of the first waste heat recovery device.

[0014] Preferably, the heat pump includes an evaporator and a condenser; The first waste heat recovery flow path includes a first waste heat circulation pipeline and a second waste heat circulation pipeline. The condenser is located in the first waste heat circulation pipeline to heat the first waste heat circulation pipeline, and the evaporator is located in the second waste heat circulation pipeline to cool the second waste heat circulation pipeline.

[0015] By adopting the above technical solution, and by setting up a first waste heat circulation pipeline and a second waste heat circulation pipeline, the heat source side and the cold source side are completely isolated. The first waste heat circulation pipeline directly heats the boiler feed water through the condenser, avoiding the influence of the water quality of the first waste heat recovery device on the boiler system. The second waste heat circulation pipeline forms an independent closed loop, which can use special antifreeze or treated water, improving the system's adaptability to low-temperature environments. At the same time, this design allows the two circulation systems to use different operating pressures and flow rates, making the system design more flexible. In particular, the second circulation pipeline can use a lower operating pressure, reducing the strength requirements of the heat exchanger and pipeline, reducing equipment investment, and the independent circulation systems facilitate separate water treatment and maintenance, improving the system's maintainability.

[0016] Preferably, the first waste heat circulation pipeline is equipped with a first waste heat circulation pump; and / or, The second waste heat circulation pipeline is equipped with a second waste heat circulation pump.

[0017] By adopting the above technical solution, a first waste heat circulation pump is installed to provide power to the first waste heat circulation pipeline. This allows the first waste heat circulation pipeline to adjust the water flow rate according to its own heat exchange, which is beneficial for accurately controlling the heat exchange process of the condenser and thus ensuring effective preheating of the boiler feed water. Furthermore, a second waste heat circulation pump is installed to provide power to the second waste heat circulation pipeline. This allows the second waste heat circulation pipeline to adjust the water flow rate according to its own heat exchange, which is beneficial for accurately controlling the heat exchange process of the evaporator. This approach not only fully absorbs the heat from the flue gas but also avoids corrosion problems caused by direct contact between acidic gases and circulating water, thus helping to extend the service life of the equipment.

[0018] Preferably, the smoke exhaust device includes a chimney, the chimney forming a smoke exhaust channel, the flue including the smoke exhaust channel, and both the first heat exchanger and the second heat exchanger are disposed in the smoke exhaust channel; and / or, The second waste heat recovery path is equipped with a fan.

[0019] By adopting the above technical solution, both the first and second heat exchangers are located in the flue gas duct, making full use of the vertical space of the chimney, reducing the additional floor space and pipe connections, and lowering the system investment cost. At the same time, the natural upward flow of flue gas in the chimney helps to enhance heat exchange, and the draft effect generated by the height difference of the chimney can reduce the power consumption of the fan. By setting up the fan, the air flow can be actively controlled to ensure the heat exchange effect of the second heat exchanger. Especially when natural ventilation is insufficient, the fan can provide a stable air flow to ensure the stable operation of the system. This active control can also adjust the amount of preheated air according to seasonal changes. In winter, the air volume is increased to raise the temperature of the preheated air for heating, and in summer, the air volume is reduced to reduce system resistance.

[0020] Preferably, a first flue gas temperature sensor is provided inside the flue, and the first flue gas temperature sensor is located on the front side of the first heat exchanger; and / or, A second flue gas temperature sensor is installed inside the flue, and the second flue gas temperature sensor is located between the first heat exchanger and the second heat exchanger; and / or, A third flue temperature sensor is installed inside the flue, and the third flue temperature sensor is located on the rear side of the second heat exchanger.

[0021] By adopting the above technical solution, a first flue gas temperature sensor is installed to detect the flue gas temperature in the flue, thereby providing a basis for system start-up, shutdown, and power adjustment. A second flue gas temperature sensor is installed to detect the flue gas temperature after heat exchange in the first heat exchanger, which can evaluate the working status and efficiency of the first heat exchanger in real time. When the temperature rises abnormally, it may indicate scaling in the heat exchanger or a failure in the circulation system. A third flue gas temperature sensor is installed to detect the flue gas temperature after heat exchange in the second heat exchanger, thereby determining the final emission temperature of the flue gas and ensuring that it meets the requirements.

[0022] Secondly, this application provides a boiler flue gas heat recovery method based on a boiler flue gas heat recovery system, the boiler flue gas heat recovery system comprising: a heating device including a boiler and a boiler inlet pipe and a boiler outlet pipe connecting the boiler, the boiler inlet pipe for injecting water into the boiler, and the boiler outlet pipe for discharging water from the boiler; a flue gas exhaust device forming a flue, the flue having a first heat exchanger and a second heat exchanger sequentially arranged along the flue gas flow direction; a first waste heat recovery device including a first waste heat recovery flow path and a heat pump, the first waste heat recovery flow path connecting the first heat exchanger and the boiler inlet pipe, the heat pump being disposed in the first waste heat recovery flow path; and a second waste heat recovery device including a second waste heat recovery flow path, the inlet of the second waste heat recovery flow path being connected to external air, the outlet being connected to the boiler, and the second heat exchanger being disposed in the second waste heat recovery flow path; The boiler flue gas heat recovery method includes: Obtain the actual inlet flue gas temperature of the first heat exchanger; When the actual inlet flue gas temperature is greater than the preset inlet flue gas temperature, the heat pump and the waste heat drive pump are controlled to work.

[0023] By adopting the above technical solution, when the actual outlet flue gas temperature is greater than the preset inlet flue gas temperature, it indicates that the flue gas temperature is too high. It is difficult to reduce the flue gas temperature below the dew point by relying solely on boiler feed water. At this time, it is necessary to start the heat pump to reduce the water temperature entering the first heat exchanger, so as to increase the heat transfer temperature difference and enhance the heat exchange efficiency. In this way, by monitoring the inlet flue gas temperature of the first heat exchanger in real time, it is determined whether to start the waste heat recovery system, avoiding the energy waste caused by operating the first waste heat recovery device when the flue gas temperature is too low. When the flue gas temperature is too high, the heat pump and waste heat recovery pump are started, so that the boiler flue gas heat recovery system can quickly respond to changes in boiler load and ensure that the system always operates under optimal conditions. At the same time, the preset temperature value can be adjusted according to the season and boiler type, improving the adaptability of the system and minimizing the energy consumption of auxiliary equipment while ensuring the waste heat recovery effect.

[0024] Preferably, the step of controlling the operation of the heat pump and the waste heat recovery pump when the actual inlet flue gas temperature is greater than the preset inlet flue gas temperature includes: Obtain the actual outlet flue gas temperature of the first heat exchanger; Based on the actual outlet flue gas temperature and the preset outlet flue gas temperature, the operating strategy of the heat pump and the waste heat drive pump is determined, and the operation of the heat pump and the waste heat drive pump is controlled according to the operating strategy.

[0025] By adopting the above technical solution, when the actual outlet flue gas temperature is greater than the preset outlet flue gas temperature, it indicates that the heat exchange is insufficient. At this time, it is necessary to adjust the power of the heat pump and the operating frequency of the waste heat drive pump so that the circulating water can remove more heat to form a closed-loop control. This adaptive adjustment can cope with the dynamic changes in flue gas flow and temperature as well as the gradual decline in the performance of the heat exchanger, and ensure the long-term stable and efficient operation of the system.

[0026] Preferably, the step of determining the operating strategy of the heat pump and the waste heat driven pump based on the actual outlet flue gas temperature and the preset outlet flue gas temperature, and controlling the operation of the heat pump and the waste heat driven pump according to the operating strategy, includes: When the actual outlet flue gas temperature is greater than the preset outlet flue gas temperature, the operating frequency of the waste heat recovery pump is controlled to increase by a preset frequency range until the operating frequency reaches the rated operating frequency or the actual outlet flue gas temperature is not higher than the preset outlet flue gas temperature. When the actual outlet flue gas temperature is greater than the preset outlet flue gas temperature and the operating frequency of the waste heat recovery pump reaches the rated operating frequency, the operating power of the heat pump is controlled to increase by a preset power range to reduce the water temperature in the first waste heat recovery flow path until the actual outlet flue gas temperature is not higher than the preset outlet flue gas temperature.

[0027] By adopting the above technical solution, a graded control method is used, prioritizing the adjustment of the operating frequency of the waste heat-driven pump and then adjusting the power of the heat pump. First, heat exchange is enhanced by increasing the circulation flow rate, which results in a small increase in energy consumption and a rapid adjustment response. When the operating frequency of the waste heat circulation pump reaches the rated value but still cannot meet the requirements, the inlet water temperature is further reduced by increasing the power of the heat pump. This is because the power consumption of the pump is much smaller than that of the heat pump, and prioritizing the adjustment of the pump frequency can achieve enhanced heat exchange with minimal energy consumption. At the same time, by controlling the adjustment range of frequency and power, the stability of the system is improved, and overshoot and oscillation are avoided. The entire control process achieves refined management and minimizes system energy consumption while ensuring the waste heat recovery effect. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of an embodiment of the boiler flue gas heat recovery system provided in this application; Figure 2 yes Figure 1 A top view of the boiler flue gas heat recovery system at the first heat exchanger. Figure 3 yes Figure 1 A side view of the first heat exchanger in the diagram; Figure 4 yes Figure 1 A top view of the boiler flue gas heat recovery system at the second heat exchanger. Figure 5 yes Figure 1 A side view of the second heat exchanger in the diagram; Figure 6 This is a schematic diagram of another embodiment of the boiler flue gas heat recovery system provided in this application; Figure 7 This is a schematic diagram of the structure of the control device for the hardware operating environment involved in the embodiments of this application; Figure 8 A schematic diagram of the boiler flue gas heat recovery method provided in this application.

[0029] Explanation of reference numerals in the attached figures: 100. Boiler flue gas heat recovery system; 1. Heating device; 11. Boiler; 12. Boiler inlet pipe; 13. Boiler outlet pipe; 2. Smoke exhaust system; 2a. Chimney; 21. Flue; 22. First heat exchanger; 221. Main water inlet pipe; 222. Main drain pipe; 223. Coil; 23. Second heat exchanger; 231. Baffle plate; 232. Smoke duct; 233. Ventilation passage; 3. First waste heat recovery device; 31. First waste heat recovery flow path; 311. Waste heat inlet water pipe; 3111. First waste heat inlet water pipe; 3112. Second waste heat inlet water pipe; 312. Waste heat return water pipe; 3121. First waste heat return water pipe; 3122. Second waste heat return water pipe; 313. First waste heat circulation pipe; 3131. First circulation inlet water pipe; 3132. First circulation return water pipe; 314. Second waste heat circulation pipe; 3141. Second circulation inlet water pipe; 3142. Second circulation return water pipe; 32. Heat pump; 33. Waste heat recovery pump; 34. First waste heat circulation pump; 35. Second waste heat circulation pump; 4. Second waste heat recovery device; 41. Second waste heat recovery flow path; 42. Fan; 51. First calorimeter; 52. Second calorimeter; 61. First smoke temperature sensor; 62. Second smoke temperature sensor; 63. Third smoke temperature sensor. Detailed Implementation

[0030] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are only possible technical implementations of this application and not all possible implementations. Those skilled in the art can obtain other embodiments in conjunction with the embodiments of this application without creative effort, and these embodiments are also within the protection scope of this application.

[0031] Because existing heat recovery systems cannot simultaneously achieve cascaded energy recovery from both high-temperature and low-temperature sections of flue gas while ensuring system safety, resulting in poor heat recovery efficiency, this application provides a boiler flue gas heat recovery system. Among other things, Figures 1 to 8 This is a schematic diagram of the turning composite spindle and recycling method provided in this application.

[0032] Please see Figure 1 and Figure 6The boiler flue gas heat recovery system 100 includes a heating device 1, a flue gas exhaust device 2, a first waste heat recovery device 3, and a second waste heat recovery device 4. The heating device 1 includes a boiler 11 and heating pipelines. The heating pipelines include a boiler inlet pipe 12 and a boiler outlet pipe 13 connected to the boiler 11. The boiler inlet pipe 12 is used to inject water into the boiler 11, and the boiler outlet pipe 13 is used to discharge the water in the boiler 11. The flue gas exhaust device 2 forms a flue 21, which is arranged sequentially along the flue gas flow direction. There are a first heat exchanger 22 and a second heat exchanger 23. The first waste heat recovery device 3 includes a first waste heat recovery flow path 31 and a heat pump 32. The first waste heat recovery flow path 31 connects the first heat exchanger 22 and the boiler inlet pipe 12. The heat pump 32 is located in the first waste heat recovery flow path 31. The second waste heat recovery device 4 includes a second waste heat recovery flow path 41. The inlet of the second waste heat recovery flow path 41 is connected to the outside air, and the outlet is connected to the boiler 11. The second heat exchanger 23 is located in the second waste heat recovery flow path 41.

[0033] In this embodiment, the flue gas is continuously cooled through staged heat exchange by setting up a first heat exchanger 22 and a second heat exchanger 23, along with corresponding first and second waste heat recovery structures. This method fully considers the heat transfer characteristics between the flue gas and the heat exchange fluid at different temperature states. At high temperatures, it utilizes the good heat transfer performance between the high-temperature flue gas and the heat exchange fluid, while at low temperatures, it utilizes a low-temperature fluid (such as cold air) to ensure the heat transfer effect of the flue gas after the temperature decreases, greatly improving the waste heat utilization rate. At the same time, the warm air after heat exchange is introduced into the boiler 11, reducing the fuel consumption for heating the cold air. In addition, the first heat exchanger 22 and the second heat exchanger 23 adopt indirect heat exchange and are connected to the heat exchanger through the first waste heat recovery flow path 31 and the second waste heat recovery flow path 41, which can avoid the acidic corrosion problem caused by the precipitation of condensate in the flue gas and its mixing with intermediate water. Meanwhile, by setting a heat pump 32 on the first waste heat recovery flow path 31, on the one hand, the water temperature entering the heat exchanger can be actively reduced, thereby increasing the heat transfer temperature difference and enhancing the heat exchange efficiency when the flue gas temperature is high, so as to achieve efficient recovery of sensible heat and even latent heat of flue gas. On the other hand, the recovered heat can be flexibly adjusted according to the load change of boiler 11, which can avoid the "small load, large power" operation problem caused by load change. Thus, the boiler flue gas heat recovery system 100 can adapt to the load change of the system output under different conditions, and improve the economy and stability of system operation.

[0034] In one embodiment of this application, the heat pump 32 includes an evaporator and a condenser. The first waste heat recovery flow path 31 includes a waste heat inlet water pipe 311 and a waste heat return water pipe 312. The evaporator is located in the waste heat inlet water pipe 311 to cool the waste heat inlet water pipe 311, and the condenser is located in the waste heat return water pipe 312 to heat the waste heat return water pipe 312. Thus, by setting up the waste heat inlet water pipe 311 and the waste heat return water pipe 312, a circulation loop is formed to guide the return water from the boiler inlet water pipe 12 into the first heat exchanger 22 to exchange heat with the flue gas, and then guide the water after heat exchange back into the boiler 11 return water pipe. By setting up the evaporator to cool the water in the waste heat inlet water pipe 311, and by setting up the condenser to heat the water in the waste heat return water pipe 312, the overall waste heat recovery efficiency can be greatly improved.

[0035] Understandably, when the heat pump is not working, the water in the boiler inlet pipe 12 can be input into the first heat exchanger 22 through the waste heat pipe 311 to exchange heat with the flue gas, so that the boiler flue gas heat recovery system 100 can still form a two-stage heat exchange cascade energy recovery mode. However, the heat recovered in this way is less and it is only suitable for situations where the boiler 11 has a small load. When the heat pump is working, the evaporator of the heat pump 32 can cool down the waste heat inlet pipe 311 in order to increase the heat transfer temperature difference, enhance the heat exchange efficiency, and achieve efficient recovery of the sensible heat and even the latent heat of the flue gas.

[0036] Further, in this embodiment, please refer to Figure 1 The waste heat inlet water pipeline 311 includes a first waste heat inlet water pipe 3111 and a second waste heat inlet water pipe 3112. The first waste heat inlet water pipe 3111 connects the boiler inlet water pipe 12 to the inlet of the evaporator of the heat pump 32, and the second waste heat inlet water pipe 3112 connects the outlet of the evaporator of the heat pump 32 to the inlet of the first heat exchanger 22. In this way, the water in the boiler inlet water pipe 12 first enters the evaporator through the first waste heat inlet water pipe 3111. After being cooled by the evaporator, it is then input into the first heat exchanger 22 through the second waste heat inlet water pipe 3112. This can significantly reduce the water temperature entering the first heat exchanger 22 and significantly increase the heat transfer temperature difference with the high-temperature flue gas. This not only absorbs more sensible heat but also reduces the flue gas temperature below the dew point, thereby recovering the latent heat that was previously difficult to utilize.

[0037] Furthermore, the waste heat return water pipeline 312 includes a first waste heat return water pipeline 3121 and a second waste heat return water pipeline 3122. The first waste heat return water pipeline 3121 connects the outlet of the first heat exchanger 22 to the inlet of the condenser, and the second waste heat return water pipeline 3122 connects the outlet of the condenser to the boiler inlet pipe 12. Thus, the water after heat exchange in the first heat exchanger 22 first enters the condenser through the first waste heat return water pipeline 3121, and after being heated by the condenser, it is then fed into the boiler inlet pipe 12 through the second waste heat return water pipeline 3122, thereby increasing the inlet water temperature of the boiler 11.

[0038] In one embodiment of this application, the first waste heat recovery device 3 further includes a waste heat recovery pump 33 disposed in the first waste heat recovery flow path 31. Thus, by setting the waste heat recovery pump 33, the circulation flow rate on the first waste heat recovery flow path 31 can be independently controlled, so that the flow rate can be flexibly adjusted according to the flue gas temperature and waste heat recovery requirements. When the flue gas temperature is high, the flow rate can be increased to increase the heat exchange capacity, and when the flue gas temperature is low, the flow rate can be reduced to ensure the heat exchange temperature difference. Furthermore, by precisely controlling the flow rate, the flow velocity of the water in the first heat exchanger 22 can be optimized to keep it in the optimal heat exchange efficiency range, thereby avoiding the problem of increased pressure loss due to excessive flow velocity or decreased heat exchange coefficient due to excessively low flow velocity.

[0039] In one embodiment of this application, the first waste heat recovery device 3 further includes a first calorimeter 51 disposed on the waste heat inlet water pipe 311. The first calorimeter 51 is located between the heat pump 32 and the first heat exchanger 22. Thus, by setting the first calorimeter 51 on the waste heat inlet water pipe 311, the first calorimeter 51 can measure the heat of the water entering the first heat exchanger 22 after being cooled by the heat pump 32, thereby facilitating real-time monitoring of the heat recovery status of the first waste heat recovery device 3.

[0040] Please see Figure 1 The first waste heat recovery device 3 also includes a second calorimeter 52 installed in the waste heat return water pipeline 312. The second calorimeter 52 is located between the heat pump 32 and the boiler inlet pipe 12. By installing the second calorimeter 52 in the waste heat return water pipeline 312, it can measure the heat of the water after heat exchange and heating by the heat pump 32, thus facilitating real-time monitoring of the heat recovery status of the first waste heat recovery device 3. Furthermore, by setting the first calorimeter 51 and the second calorimeter 52, the heat on the waste heat inlet pipe 311 and the waste heat return water pipeline 312 can be determined. The difference between the two is the actual heat recovered by the first waste heat recovery device 3. This not only provides accurate data support for system operation but also allows for timely detection of problems such as scaling in the first heat exchanger 22 or decreased efficiency of the heat pump 32. Long-term data accumulation can establish system performance curves, providing a basis for predictive maintenance. It can also be used to optimize control strategies, dynamically adjusting the power and circulation flow of the heat pump 32 based on the actual recovered heat, achieving intelligent system operation and maximizing energy recovery efficiency.

[0041] It should be noted that the two related technical features mentioned above, namely, "the first waste heat recovery device 3 further includes a first calorimeter 51 disposed in the waste heat inlet pipe 311" and "the first waste heat recovery device 3 further includes a second calorimeter 52 disposed in the waste heat return pipe 312", can be set either one or both, and the embodiments of this application do not limit this.

[0042] In one embodiment of this application, please refer to Figure 6 The heat pump 32 includes an evaporator and a condenser. The first waste heat recovery flow path 31 includes a first waste heat circulation pipe 313 and a second waste heat circulation pipe 314. The condenser is located in the first waste heat circulation pipe 313 to heat the first waste heat circulation pipe 313, and the evaporator is located in the second waste heat circulation pipe 314 to cool the second waste heat circulation pipe 314.

[0043] In this embodiment, by setting up a first waste heat circulation pipeline 313 and a second waste heat circulation pipeline 314, the heat source side and the cold source side are completely isolated. The first waste heat circulation pipeline 313 directly heats the boiler 11 inlet water through the condenser, avoiding the influence of the water quality of the first waste heat recovery device 3 on the boiler 11 system. The second waste heat circulation pipeline 314 forms an independent closed loop, which can use special antifreeze or treated water, improving the system's adaptability to low-temperature environments. At the same time, this design allows the two circulation systems to use different operating pressures and flow rates, making the system design more flexible. In particular, the second circulation pipeline can use a lower operating pressure, reducing the strength requirements of the heat exchanger and pipeline, reducing equipment investment, and the independent circulation systems facilitate separate water treatment and maintenance, improving the system's maintainability.

[0044] Furthermore, the first waste heat circulation pipeline 313 includes a first circulation inlet pipe 3131 and a first circulation return pipe 3132. The first circulation inlet pipe 3131 connects the boiler inlet pipe 12 and the condenser inlet, and the first circulation return pipe 3132 connects the condenser outlet and the boiler inlet pipe 12. Thus, the water in the boiler inlet pipe 12 enters the condenser through the first circulation inlet pipe 3131, is heated by the condenser, and then enters the boiler inlet pipe 12 through the first circulation return pipe 3132, thereby increasing the inlet water temperature of the boiler 11.

[0045] The second waste heat circulation pipeline 314 includes a second circulation inlet pipe 3141 and a second circulation return pipe 3142. The second circulation inlet pipe 3141 connects the outlet of the evaporator to the inlet of the first heat exchanger 22, and the second circulation return pipe 3142 connects the outlet of the first heat exchanger 22 to the inlet of the evaporator. Thus, the water after waste heat exchange in the first heat exchanger 22 enters the evaporator through the second circulation return pipe 3142. After being cooled by the evaporator, it is then input into the first heat exchanger 22 through the second circulation inlet pipe 3141. This can significantly reduce the water temperature entering the first heat exchanger 22 and significantly increase the heat transfer temperature difference with the high-temperature flue gas. This not only absorbs more sensible heat but also reduces the flue gas temperature below the dew point, thereby recovering the latent heat that was previously difficult to utilize.

[0046] In one embodiment of this application, please refer to Figure 6The first waste heat circulation pipeline 313 is equipped with a first waste heat circulation pump 34. By setting the first waste heat circulation pump 34, power is provided to the first waste heat circulation pipeline 313, so that the first waste heat circulation pipeline 313 can adjust the water flow speed according to its own heat exchange, which is conducive to accurately controlling the heat exchange process of the condenser, thereby ensuring effective preheating of the boiler 11 inlet water.

[0047] Please continue reading. Figure 6 The second waste heat circulation pipeline 314 is equipped with a second waste heat circulation pump 35. By setting up the second waste heat circulation pump 35, power can be provided to the second waste heat circulation pipeline 314, so that the second waste heat circulation can adjust the water flow rate according to its own heat exchange. This is beneficial for accurately controlling the heat exchange process of the evaporator, which can not only fully absorb the heat of the flue gas, but also avoid corrosion problems caused by direct contact between acidic gases and circulating water, thus helping to extend the service life of the equipment.

[0048] It should be noted that the two related technical features mentioned above, namely, "the first waste heat circulation pipeline 313 is provided with a first waste heat circulation pump 34" and "the second waste heat circulation pipeline 314 is provided with a second waste heat circulation pump 35", can be set either one or both, and the embodiments of this application do not limit this.

[0049] In one embodiment of this application, please refer to Figure 1 The exhaust device 2 includes a chimney 2a, which forms an exhaust channel. The flue 21 includes an exhaust channel. The first heat exchanger 22 and the second heat exchanger 23 are both located in the exhaust channel. In this way, the vertical space of the chimney 2a is fully utilized, reducing the additional floor space and pipe connections, and lowering the investment cost of the system. At the same time, the natural upward flow of flue gas in the chimney 2a helps to enhance heat exchange. The draft effect generated by the height difference of the chimney 2a can reduce the power consumption of the fan 42.

[0050] Please continue reading. Figure 1 The second waste heat recovery flow path 41 is equipped with a fan 42. By setting up the fan 42, the air flow can be actively controlled to ensure the heat exchange effect of the second heat exchanger 23. Especially when natural ventilation is insufficient, the fan 42 can provide a stable air flow to ensure the stable operation of the system. This active control can also adjust the amount of preheated air according to seasonal changes. In winter, the air volume is increased to raise the temperature of the preheated air for heating, and in summer, the air volume is reduced to reduce system resistance.

[0051] It should be noted that the two related technical features mentioned above, "the first heat exchanger 22 and the second heat exchanger 23 are both located in the flue gas passage" and "the second waste heat recovery flow path 41 is equipped with a fan 42", can be set either one or both, and this application embodiment does not limit this.

[0052] In one embodiment of this application, a first flue gas temperature sensor is provided in the flue 21. The first flue gas temperature sensor 61 is located in front of the first heat exchanger 22. By setting the first flue gas temperature sensor 61, the flue gas temperature in the flue 21 can be detected, thereby providing a basis for system start-up and power regulation.

[0053] In one embodiment of this application, a second flue gas temperature sensor 62 is provided in the flue 21. The second flue gas temperature sensor 62 is located between the first heat exchanger 22 and the second heat exchanger 23. In this way, by setting the second flue gas temperature sensor 62, the temperature of the flue gas after heat exchange by the first heat exchanger 22 can be detected, and the working status and efficiency of the first heat exchanger 22 can be evaluated in real time. When the temperature rises abnormally, it may indicate that the heat exchanger is fouling or the circulation system is malfunctioning.

[0054] Please see Figure 1 In this embodiment, a third flue gas temperature sensor 63 is provided in the flue 21. The third flue gas temperature sensor 63 is located on the rear side of the second heat exchanger 23. In this way, by setting the third flue gas temperature sensor 63, the temperature of the flue gas after heat exchange in the second heat exchanger 23 is detected, thereby determining the final emission temperature of the flue gas and ensuring that it meets the requirements.

[0055] It should be noted that the above three related technical features, namely, "a first smoke temperature sensor is provided in the flue 21", "a second smoke temperature sensor 62 is provided in the flue 21", and "a third smoke temperature sensor 63 is provided in the flue 21", can be selected as one, two, or simultaneously. This application embodiment does not limit this.

[0056] Please refer to the following: Figures 1 to 3 The first heat exchanger 22 includes an inlet main pipe 221, a drain main pipe 222, and multiple coils 223 connecting the inlet main pipe 221 and the drain main pipe 222. The inlet main pipe 221 and the drain main pipe 222 are connected to the heat pump 32 through the first waste heat recovery flow path 31. Each coil 223 extends vertically and bends back and forth horizontally. Adjacent coils 223 are spaced apart horizontally to form an air passage that allows flue gas to flow. In this way, the parallel structure of multiple coils 223, with each coil 223 bending back and forth horizontally and arranged vertically, can increase the heat exchange area and form an air passage between the coils 223, which can facilitate the flow of flue gas and fully exchange heat with the circulating water.

[0057] In one embodiment of this application, please refer to the following: Figure 1 , Figure 4 and Figure 5The second heat exchanger 23 includes multiple baffles 231 and multiple flue pipes 232. The baffles 231 are spaced vertically within the flue 21, and a ventilation channel 233 for external air to flow in is formed between adjacent baffles 231. Each baffle 231 has multiple through holes, and each flue pipe 232 passes through the through holes of the baffles 231 to allow flue gas to flow. In this way, by setting multiple flue pipes 232, external air and flue gas can form indirect heat exchange, avoiding direct contact between flue gas and external air. This can prevent acidic gases such as sulfur oxides and nitrogen oxides in the flue gas from corroding the equipment, extend the service life of pipes and equipment, and reduce system maintenance costs. At the same time, by setting multiple baffles 231, the heat exchange area of ​​the second waste heat recovery device 4 is increased, and the waste heat recovery efficiency is improved. After the flue gas has been heat-exchanged by the first heat exchanger 22, the remaining heat can be further recovered and utilized, minimizing heat waste.

[0058] In one embodiment of this application, in order to recover heat from the flue gas of boiler 11, the boiler flue gas heat recovery system 100 further includes a control device, such as... Figure 4 As shown, the control device may include: a processor 1001, such as a central processing unit (CPU), a communication bus 1002, a user interface 1003, a network interface 1004, and a memory 1005. The communication bus 1002 is used to enable communication between these components. The user interface 1003 may include a display screen or an input unit such as a keyboard; optionally, the user interface 1003 may also include a standard wired interface or a wireless interface. The network interface 1004 may optionally include a standard wired interface or a wireless interface (such as a Wireless-Fidelity (Wi-Fi) interface). The memory 1005 may be high-speed random access memory (RAM) or stable non-volatile memory (NVM), such as a disk drive. The memory 1005 may also optionally be a storage device independent of the aforementioned processor 1001.

[0059] like Figure 4 As shown, the memory 1005, which serves as a storage medium, may include an operating system, a network communication module, a user interface module, and a control program for a control device.

[0060] exist Figure 4In the control device shown, the network interface 1004 is mainly used for data communication with the network server; the user interface 1003 is mainly used for data interaction with the user; the processor 1001 and the memory 1005 in the control device of this application can be set in the control device. The control device calls the control program of the control device stored in the memory 1005 through the processor 1001 and executes the control method of the control device provided in the embodiment of this application.

[0061] Those skilled in the art will understand that Figure 4 The structure shown does not constitute a limitation on the control device and may include more or fewer components than shown, or combine certain components, or have different component arrangements. Based on the above hardware structure, this application also provides a method for boiler flue gas heat recovery. Please refer to [link to relevant documentation]. Figure 8 , Figure 8 A schematic diagram of the boiler flue gas heat recovery method provided in this application.

[0062] Boiler flue gas heat recovery methods include: S10: Obtain the actual inlet flue gas temperature of the first heat exchanger 22; S20: When the actual inlet flue gas temperature is greater than the preset inlet flue gas temperature, control the heat pump 32 and the waste heat drive pump to work.

[0063] In this embodiment, when the actual outlet flue gas temperature is greater than the preset inlet flue gas temperature, it indicates that the flue gas temperature is too high. It is difficult to reduce the flue gas temperature below the dew point by relying solely on the water intake of boiler 11. At this time, it is necessary to start the heat pump 32 to reduce the water temperature entering the first heat exchanger 22, so as to increase the heat transfer temperature difference and enhance the heat exchange efficiency. In this way, by monitoring the inlet flue gas temperature of the first heat exchanger 22 in real time, it is determined whether to start the waste heat recovery system, avoiding the energy waste caused by operating the first waste heat recovery device 3 when the flue gas temperature is too low. When the flue gas temperature is too high, the heat pump 32 and the waste heat recovery pump 33 are started, so that the boiler flue gas heat recovery system 100 can quickly respond to the load changes of boiler 11 and ensure that the system always operates under the best conditions. At the same time, the preset temperature value can be adjusted according to the season and the type of boiler 11, improving the adaptability of the system and minimizing the energy consumption of auxiliary equipment while ensuring the waste heat recovery effect.

[0064] It should be noted that the waste heat driven pump is related to the first waste heat recovery flow path 31. When the first waste heat recovery flow path 31 includes a waste heat inlet water pipe 311 and a waste heat return water pipe 312, the waste heat driven pump is the waste heat recovery pump 33. When the first waste heat recovery flow path 31 includes a first waste heat circulation pipe 313 and a second waste heat circulation pipe 314, the waste heat driven pump is the second waste heat circulation pump 35. Furthermore, there are various preset inlet flue gas temperatures, which can be a fixed value or a range of values, etc., and can be adjusted as needed. The embodiments of this application do not limit this.

[0065] Further, step S20 includes: S21: Obtain the actual outlet flue gas temperature of the first heat exchanger 22; S22: Determine the operating strategy of heat pump 32 and waste heat drive pump based on the actual outlet flue gas temperature and the preset outlet flue gas temperature, and control the operation of heat pump 32 and waste heat drive pump according to the operating strategy.

[0066] In this embodiment, when the actual outlet flue gas temperature is greater than the preset outlet flue gas temperature, it indicates that the heat exchange is insufficient. At this time, it is necessary to adjust the power of the heat pump 32 and the operating frequency of the waste heat drive pump so that the circulating water can carry away more heat to form a closed-loop control. This adaptive adjustment can cope with the dynamic changes in flue gas flow and temperature as well as the gradual decline of heat exchanger performance, ensuring the long-term stable and efficient operation of the system.

[0067] It should be noted that there are various adjustment strategies for the heat pump 32 and the waste heat driven pump. For example, the power of the heat pump 32 can be adjusted first, and then the operating frequency of the waste heat driven pump can be adjusted. Alternatively, the operating frequency of the waste heat driven pump can be adjusted first, and then the power of the heat pump 32 can be adjusted. The embodiments of this application do not limit this.

[0068] In one embodiment of this application, step S22 includes: S221: When the actual outlet flue gas temperature is greater than the preset outlet flue gas temperature, control the operating frequency of the waste heat drive pump to increase by the preset frequency range until the operating frequency reaches the rated operating frequency or the actual outlet flue gas temperature is not higher than the preset outlet flue gas temperature. It should be noted that there are various preset frequency amplitudes, such as 1% or 5%, which can be adjusted as needed. The embodiments of this application do not limit this.

[0069] S222: When the actual outlet flue gas temperature is greater than the preset outlet flue gas temperature and the operating frequency of the waste heat drive pump reaches the rated operating frequency, the operating power of the heat pump 32 is increased by a preset power range to reduce the water temperature on the first waste heat recovery flow path 31 until the actual outlet flue gas temperature is not higher than the preset outlet flue gas temperature.

[0070] It should be noted that there are various preset power amplitudes, such as 1% or 5%, which can be adjusted as needed. The embodiments of this application do not limit this.

[0071] In this embodiment, when the actual outlet flue gas temperature is greater than the preset outlet flue gas temperature, it indicates that the heat exchange is insufficient. At this time, the operating frequency of the waste heat drive pump is increased by a preset frequency range to increase the flow rate on the first waste heat recovery flow path 31, thereby increasing the heat exchange capacity. The outlet flue gas temperature of the first heat exchanger 22 is continuously monitored. If the actual outlet flue gas temperature is equal to or less than the preset outlet flue gas temperature, the waste heat drive pump maintains the current operating frequency and is no longer adjusted. If the actual outlet flue gas temperature is still greater than the preset outlet flue gas temperature, the operating frequency of the waste heat drive pump is continuously adjusted until the rated operating frequency is reached. When the actual outlet flue gas temperature is greater than the preset outlet flue gas temperature and the operating frequency of the waste heat drive pump reaches the rated operating frequency, it indicates that simply increasing the operating frequency of the waste heat drive pump is no longer sufficient to meet the requirements. At this point, it is necessary to increase the power of heat pump 32 to reduce the circulating water temperature. Thus, a graded control method is adopted, prioritizing the adjustment of the operating frequency of the waste heat drive pump and then adjusting the power of heat pump 32. First, heat exchange is enhanced by increasing the circulation flow rate. This method results in a smaller increase in energy consumption and a faster adjustment response. When the operating frequency of the waste heat circulation pump reaches the rated value and still cannot meet the requirements, the power of heat pump 32 is then increased to further reduce the inlet water temperature. This is because the power consumption of the pump is much smaller than that of heat pump 32. Prioritizing the adjustment of the pump frequency can achieve enhanced heat exchange at the lowest energy cost. At the same time, by controlling the adjustment range of frequency and power, the stability of the system is improved, and overshoot and oscillation are avoided. The entire control process achieves refined management and minimizes system energy consumption while ensuring the waste heat recovery effect. The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A boiler flue gas heat recovery system, characterized in that, include: The heating device (1) includes a boiler (11) and a boiler inlet pipe (12) and a boiler outlet pipe (13) connecting the boiler (11). The boiler inlet pipe (12) is used to inject water into the boiler (11), and the boiler outlet pipe (13) is used to discharge water from the boiler (11). The exhaust device (2) has a flue (21) and a first heat exchanger (22) and a second heat exchanger (23) are arranged sequentially along the flue gas flow direction. A first waste heat recovery device (3) includes a first waste heat recovery flow path (31) and a heat pump (32). The first waste heat recovery flow path (31) connects a first heat exchanger (22) and a boiler inlet pipe (12). The heat pump (32) is located in the first waste heat recovery flow path (31). The second waste heat recovery device (4) includes a second waste heat recovery flow path (41), the inlet of which is connected to the outside air and the outlet is connected to the boiler (11), and the second heat exchanger (23) is located in the second waste heat recovery flow path (41).

2. The boiler flue gas heat recovery system according to claim 1, characterized in that, The heat pump (32) includes an evaporator and a condenser; The first waste heat recovery flow path (31) includes a waste heat inlet water pipe (311) and a waste heat return water pipe (312). The evaporator is located in the waste heat inlet water pipe (311) to cool the waste heat inlet water pipe (311), and the condenser is located in the waste heat return water pipe (312) to heat the waste heat return water pipe (312).

3. The boiler flue gas heat recovery system according to claim 2, characterized in that, The first waste heat recovery device (3) also includes a waste heat recovery pump (33) disposed in the first waste heat recovery flow path (31).

4. The boiler flue gas heat recovery system according to claim 2, characterized in that, The first waste heat recovery device (3) further includes a first calorimeter (51) disposed in the waste heat inlet water pipeline (311), the first calorimeter (51) being located between the heat pump (32) and the first heat exchanger (22); and / or, The first waste heat recovery device (3) further includes a second calorimeter (52) installed in the waste heat return water pipeline (312); the second calorimeter (52) is located between the heat pump (32) and the boiler inlet pipe (12).

5. The boiler flue gas heat recovery system according to claim 1, characterized in that, The heat pump (32) includes an evaporator and a condenser; The first waste heat recovery flow path (31) includes a first waste heat circulation pipeline (313) and a second waste heat circulation pipeline (314). The condenser is located in the first waste heat circulation pipeline (313) to heat the first waste heat circulation pipeline (313), and the evaporator is located in the second waste heat circulation pipeline (314) to cool the second waste heat circulation pipeline (314).

6. The boiler flue gas heat recovery system according to claim 5, characterized in that, The first waste heat circulation pipeline (313) is equipped with a first waste heat circulation pump (34); and / or, The second waste heat circulation pipeline (314) is equipped with a second waste heat circulation pump (35).

7. The boiler flue gas heat recovery system according to claim 1, characterized in that, A first flue gas temperature sensor (61) is provided inside the flue (21), and the first flue gas temperature sensor (61) is located on the front side of the first heat exchanger (22); and / or, A second flue gas temperature sensor (62) is provided inside the flue (21), and the second flue gas temperature sensor (62) is located between the first heat exchanger (22) and the second heat exchanger (23); and / or, A third flue temperature sensor (63) is provided inside the flue (21), and the third flue temperature sensor (63) is located on the rear side of the second heat exchanger (23).

8. A method for recovering heat from boiler flue gas, based on the boiler flue gas heat recovery system according to claim 1, characterized in that, The first waste heat recovery device (3) also includes a waste heat drive pump; The boiler flue gas heat recovery method includes: Obtain the actual inlet flue gas temperature of the first heat exchanger (22); When the actual inlet flue gas temperature is greater than the preset inlet flue gas temperature, the heat pump (32) and the waste heat drive pump are controlled to work.

9. The boiler flue gas heat recovery method according to claim 8, characterized in that, The step of controlling the operation of the heat pump (32) and the waste heat recovery pump (33) when the actual inlet flue gas temperature is greater than the preset inlet flue gas temperature includes: Obtain the actual outlet flue gas temperature of the first heat exchanger (22); Based on the actual outlet flue gas temperature and the preset outlet flue gas temperature, the operating strategy of the heat pump (32) and the waste heat drive pump is determined, and the operation of the heat pump (32) and the waste heat drive pump is controlled according to the operating strategy.

10. The boiler flue gas heat recovery method according to claim 9, characterized in that, The step of determining the operating strategy of the heat pump (32) and the waste heat driven pump based on the actual outlet flue gas temperature and the preset outlet flue gas temperature, and controlling the operation of the heat pump (32) and the waste heat driven pump according to the operating strategy, includes: When the actual outlet flue gas temperature is greater than the preset outlet flue gas temperature, the operating frequency of the waste heat drive pump is controlled to increase by a preset frequency range until the operating frequency reaches the rated operating frequency or the actual outlet flue gas temperature is not higher than the preset outlet flue gas temperature. When the actual outlet flue gas temperature is greater than the preset outlet flue gas temperature and the operating frequency of the waste heat drive pump reaches the rated operating frequency, the operating power of the heat pump (32) is controlled to increase by a preset power range to reduce the water temperature on the first waste heat recovery flow path (31) until the actual outlet flue gas temperature is not higher than the preset outlet flue gas temperature.

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