Thermal power plant boiler exhaust smoke waste heat recovery and cyclic utilization system

Abstract

The embodiment of the invention provides a heat-engine plant boiler exhaust smoke waste heat recovery and cyclic utilization system. The system comprises a boiler, an air supply assembly, a heat exchange assembly and a chimney, wherein the air supply assembly and the heat exchange assembly are connected to an air inlet of the boiler and a smoke exhaust pipeline respectively. The air supply assembly comprises an air feeder used for receiving cold air, a cold air conveying pipeline, an air preheater and a hot air pipeline, wherein the cold air conveying pipeline, the air preheater and the hot air pipeline are sequentially connected with an outlet of the air feeder, and an outlet of the hot air pipeline is connected with an air inlet of the boiler. The heat exchange assembly comprises a dust remover, an induced draft fan, a high-temperature heat exchanger, a medium-temperature heat exchanger and a deep recovery heat exchanger which are sequentially connected with a smoke exhaust pipeline of the boiler, an outlet of the deep recovery heat exchanger is connected with an inlet of the chimney, and the chimney is used for exhausting smoke subjected to heat exchange into the atmosphere. Stepped recovery of boiler exhaust smoke waste heat is achieved through the heat exchange assembly, energy matching is carried out through the smoke temperature grade, the waste heat recovery efficiency is greatly improved, and meanwhile efficient cyclic utilization of energy is achieved.

Description

Technical Field

[0001] The embodiments disclosed herein belong to the field of thermal energy engineering and energy recovery technology, specifically relating to a waste heat recovery and recycling system for flue gas from a thermal power plant boiler. Background Technology

[0002] Thermal power generation is the main form of electricity supply in my country, and its energy conversion efficiency is crucial to the sustainable development of the entire energy system. In coal-fired power units, the boiler is the core energy conversion equipment. However, a large amount of low-temperature waste heat carried by boiler flue gas has not yet been fully recovered and utilized, resulting in significant energy waste and environmental heat load.

[0003] Conventional thermal power plant boiler systems are typically designed to have flue gas temperatures between 120°C and 150°C. This design temperature is primarily to avoid the dew point of sulfuric acid vapors in the flue gas, preventing the formation of acid condensation in the tail flue and chimney, which could corrode equipment and ensure safe system operation. However, the direct release of this high-temperature flue gas into the atmosphere means that a significant portion of energy (approximately 5% to 10% of the total calorific value of the fuel) is wasted. This not only reduces the overall thermal efficiency of the power plant and increases coal consumption for power generation but also releases a large amount of waste heat into the environment, exacerbating thermal pollution.

[0004] To recover this waste heat, the commonly used method in existing technology is to install a low-pressure economizer (or flue gas cooler). This system uses the condensate from the low-pressure regenerative extraction steam of the turbine, or part of the main condensate, as the working fluid. This condensate exchanges heat with the boiler exhaust in the flue gas waste heat recovery unit, reducing the exhaust temperature to around 90°C. The heated condensate is then returned to the thermal system, thereby reducing the amount of low-pressure regenerative extraction steam, increasing the turbine's work output, and ultimately improving unit efficiency.

[0005] Although low-pressure economizer technology has achieved certain energy-saving effects, the following prominent problems and limitations still exist in practical applications and system integration: (1) The contradiction between the depth of waste heat recovery and corrosion risk is prominent: In order to pursue higher heat recovery efficiency, it is desirable to reduce the flue gas temperature to a lower level (such as 80°C or even lower). However, as the flue gas temperature decreases, the temperature of the metal wall of the heated surface will approach or even fall below the acid dew point of the flue gas, causing acidic substances such as sulfuric acid and nitric acid to condense, resulting in severe low-temperature corrosion of the heat exchanger tube wall, greatly shortening the equipment life and threatening operational safety. This contradiction seriously restricts the further exploration of the potential of waste heat recovery.

[0006] (2) Inadequate utilization of energy grade: Boiler flue gas waste heat is a low-temperature heat source, and existing systems usually only use it to heat condensate at a lower temperature. This utilization method is relatively simple and fails to "utilize in stages" according to the temperature level (grade) of the heat energy. For example, higher-temperature waste heat could be used to heat air or feedwater with higher parameters, while lower-temperature waste heat could be used for non-power generation purposes. Existing systems lack this kind of refined energy matching and integration.

[0007] (3) Poor system flexibility and poor adaptability to unit load: When the unit load changes, parameters such as flue gas flow rate and temperature, condensate flow rate and other parameters will change. The existing low-pressure economizer system has limited adjustment means, making it difficult to maintain an efficient and safe operating state under various working conditions. It is prone to problems such as "under-recovery" (decreased energy-saving effect) or "over-recovery" (increased corrosion risk).

[0008] (4) Lack of coordinated utilization of water resources and waste heat: Thermal power plants are major industrial water users, especially the circulating cooling water system, which evaporates heat into the atmosphere through cooling towers, consuming a large amount of water resources and discharging waste heat. In the existing technology, the boiler flue gas waste heat recovery system and the power plant's water resource circulation and waste heat discharge system are usually independent of each other. The recovery of flue gas waste heat is not effectively coupled with the power plant's water conservation and the comprehensive utilization of cooling tower waste heat. The system integration and resource recycling rate need to be improved.

[0009] Therefore, there is an urgent need for a new type of waste heat recovery and recycling system for boiler flue gas in thermal power plants. Summary of the Invention

[0010] The embodiments disclosed herein aim to at least solve one of the technical problems existing in the prior art, and provide a system for recovering and recycling waste heat from boiler flue gas in thermal power plants.

[0011] The embodiments of this disclosure provide a waste heat recovery and recycling system for boiler flue gas in a thermal power plant. The system includes a boiler, an air supply assembly and a heat exchange assembly respectively connected to the boiler air inlet and the flue gas duct, and a chimney. The air supply assembly includes a blower for receiving cold air, a cold air delivery pipe connected in sequence to the outlet of the blower, an air preheater, and a hot air pipe, the outlet of which is connected to the air inlet of the boiler. The heat exchange assembly includes a dust collector, an induced draft fan, a high-temperature heat exchanger, a medium-temperature heat exchanger, and a deep recovery heat exchanger, which are connected in sequence to the flue gas duct of the boiler. The outlet of the deep recovery heat exchanger is connected to the inlet of the chimney, and the chimney is used to discharge the heat-exchanged flue gas into the atmosphere. The system also includes an air inlet pipe, a return air pipe, a condensate inlet pipe, a condensate outlet pipe, a cooling water inlet pipe, and a cooling water outlet pipe. The inlet and outlet of the air inlet pipe are respectively connected to the cold air delivery pipeline and the high-temperature heat exchanger, and the inlet and outlet of the return air pipe are respectively connected to the high-temperature heat exchanger and the hot air pipeline. The inlet and outlet of the condensate inlet pipe are respectively connected to the upstream low-pressure heater and the intermediate-temperature heat exchanger of the turbine regenerative system, and the inlet and outlet of the condensate outlet pipe are respectively connected to the intermediate-temperature heat exchanger and the downstream low-pressure heater of the turbine regenerative system. The inlet and outlet of the cooling water inlet pipe are respectively connected to the cooling tower and the deep recovery heat exchanger, and the inlet of the cooling water outlet pipe is connected to the deep recovery heat exchanger, and its outlet is connected to the cooling tower and the plant heating network.

[0012] Optionally, a diversion baffle is installed at the connection between the air inlet pipe and the cold air delivery pipe.

[0013] Optionally, the system further includes a preheating branch pipe, the inlet and outlet of which are connected to the return air duct and the denitrification system, respectively.

[0014] Optionally, the high-temperature heat exchanger is a spiral finned tube structure, the medium-temperature heat exchanger is a shell-and-tube structure, and the deep recovery heat exchanger is a glass tube bundle structure.

[0015] Optionally, the system further includes a bypass pipeline, the inlet and outlet of which are respectively connected to the condensate inlet pipe and the condensate outlet pipe.

[0016] Optionally, the system further includes a bypass flue, the inlet of which is connected to the pipeline between the medium-temperature heat exchanger and the deep recovery heat exchanger, and the outlet of which is connected to the chimney.

[0017] Optionally, butterfly valves are installed on both the air inlet pipe and the air return pipe; check valves are installed on the air inlet pipe, the air return pipe, and the preheating branch pipe; and an electric switching valve is installed on the bypass pipe. An electromagnetic flow valve and a pressure sensor are installed on the condensate inlet pipe, and a temperature sensor is installed on the condensate outlet pipe; a filter device, a flow regulating valve, and a temperature sensor are sequentially installed on the cooling water inlet pipe.

[0018] Optionally, the system further includes a flue gas flow balancing module, a working fluid flow distribution module, a waste heat recovery status monitoring module, and a system linkage control platform; The flue gas flow equalization module is installed in the flue section between the induced draft fan and the high-temperature heat exchanger; the working fluid flow distribution module is connected to the air inlet pipe, condensate inlet pipe and cooling water inlet pipe respectively; the waste heat recovery status monitoring module collects the operating parameters of each device in real time through a sensor network; the system linkage control platform dynamically regulates the entire system based on the monitoring data.

[0019] Optionally, the flue gas flow balancing module includes an adjustable guide plate and a flue gas flow sensor disposed in the exhaust duct.

[0020] The waste heat recovery and recycling system for boiler flue gas in thermal power plants according to the embodiments of this disclosure has the following beneficial effects: (1) Through multi-stage heat exchange components, the waste heat of boiler flue gas is recovered in stages, which can significantly reduce the flue gas temperature from 120~150℃ to about 75℃, greatly improving the waste heat recovery efficiency.

[0021] (2) Energy matching is carried out according to the temperature and grade of flue gas: high-temperature waste heat is used to heat the boiler air supply and improve the boiler combustion efficiency; medium-temperature waste heat is used to heat the condensate of the turbine regenerator system and increase the turbine's work; low-temperature waste heat is used to heat the circulating cooling water and realize the resource utilization of waste heat. This cascade utilization mode overcomes the shortcomings of the single energy utilization of existing technologies and realizes the efficient recycling of energy.

[0022] (3) Through the flue gas flow balancing module, working fluid flow distribution unit, bypass pipeline (such as condensate bypass and flue gas bypass) and automatic control valve (such as butterfly valve, electric switching valve, etc.), the working fluid flow and flue gas distribution can be adjusted in real time according to the unit load changes, avoiding the problems of "under-recovery" or "over-recovery", and ensuring that the system maintains efficient and stable operation under various working conditions.

[0023] (4) Integrating flue gas waste heat recovery with power plant water resource management: Deeply recovering the circulating cooling water heated by the heat exchanger reduces the water consumption of the cooling tower evaporation in summer, and uses the heated cooling water for heating the plant area in winter, replacing traditional heating energy. This not only reduces the power plant's water consumption, but also achieves comprehensive utilization of waste heat, achieving the dual goals of energy conservation and water conservation.

[0024] (5) The system is equipped with a waste heat recovery status monitoring module and a system linkage control platform. It collects operating parameters (such as temperature, pressure, flow rate, etc.) in real time through a sensor network and dynamically adjusts the equipment based on data analysis. When an abnormality is detected (such as temperature approaching the acid dew point, abnormal pressure difference, etc.), the system automatically triggers protection measures (such as adjusting the working fluid flow rate, activating the bypass, etc.) to improve the reliability and safety of the system. Attached Figure Description

[0025] Figure 1This is a schematic diagram of a waste heat recovery and recycling system for boiler exhaust in a thermal power plant, according to an embodiment of the present disclosure. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] like Figure 1 As shown, this disclosure provides a waste heat recovery and recycling system for boiler flue gas in a thermal power plant. It includes a dust collector 2, an induced draft fan 3, and a high-temperature heat exchanger 7, a medium-temperature heat exchanger 12, and a deep recovery heat exchanger 16, all sequentially connected to the flue gas duct of boiler 1. The high-temperature heat exchanger 7, the medium-temperature heat exchanger 12, and the deep recovery heat exchanger 16 are connected in series through the flue gas duct and ultimately connected to the chimney 5. Furthermore, it includes a flue gas flow balancing module, a working fluid flow distribution module, a waste heat recovery status monitoring module, and a system linkage control platform. These structures form a complete closed-loop system for preheating recovery and recycling. The flue gas flow balancing module is installed in the flue gas section between the induced draft fan 3 and the high-temperature heat exchanger 7. The working fluid flow distribution module is connected to the air inlet pipe 8, the condensate inlet pipe 13, and the cooling water inlet pipe 17, respectively. The waste heat recovery status monitoring module collects the operating parameters of each device in real time through a sensor network. The system linkage control platform dynamically regulates the entire system based on the monitoring data.

[0028] An air preheater 6 for heat recovery is installed at the tail end of the boiler. It utilizes the high-temperature heat (usually 250℃~350℃) in the boiler flue gas that is not fully utilized to preheat the cold air required for boiler combustion. One end of the device is connected to the cold air delivery pipe 4 of the blower 11, and the other end is connected to the air inlet pipe (air inlet) of the boiler burner. It usually adopts a shell-and-tube or rotary heat exchange structure. Through indirect heat exchange between flue gas and air, it can preheat the cold air at ambient temperature to 150℃~250℃ before sending it into the boiler 1.

[0029] The high-temperature heat exchanger 7 is located in the section with higher flue gas temperature, specifically in the flue gas duct after the air preheater 6. The inlet flue gas temperature is between 120°C and 150°C. In the embodiments disclosed herein, the air preheater 6 and the high-temperature heat exchanger 7 form a synergistic mode of "traditional preheating + deep recovery," which can further tap the remaining waste heat potential in the flue gas and achieve cascaded energy utilization. The high-temperature heat exchanger 7 adopts a spiral finned tube structure (fin spacing 8mm, tube outer diameter 51mm), and the tube material is selected from 20G boiler steel to enhance heat transfer effect and high-temperature resistance.

[0030] The working fluid loop of the high-temperature heat exchanger 7 is connected in parallel with the boiler air supply system, forming a first-stage waste heat recovery loop through the inlet air pipe 8 and the return air pipe 9. Specifically, one end of the inlet air pipe 8 is connected to the working fluid side inlet of the high-temperature heat exchanger 7, and the other end is connected to the cold air delivery pipe 4 of the blower 11. One end of the return air pipe 9 is connected to the working fluid side outlet of the high-temperature heat exchanger 7, and the other end merges with the outlet hot air pipe 20 of the air preheater 6, ultimately connecting to the air inlet of the boiler burner air inlet pipe. A diversion baffle 10 is installed at the connection between the air inlet duct 8 and the cold air delivery duct 4 of the blower 11. The diversion baffle 10 is electrically connected to the working fluid flow distribution module and can automatically adjust its opening according to system instructions to achieve cold air flow distribution. The cold air from the blower 11 is divided into two paths by the diversion baffle 10. One path enters the high-temperature heat exchanger 7, and the other path directly enters the air preheater 6. The air volume of the two paths can be dynamically adjusted according to the boiler combustion efficiency, the hot air temperature at the outlet of the air preheater, and the flue gas temperature at the inlet of the high-temperature heat exchanger.

[0031] Meanwhile, adjustable flow butterfly valves are installed on both the inlet air duct 8 and the return air duct 9 to assist in controlling the working fluid flow. The hot air from the outlet of the high-temperature heat exchanger 7 is also branched off and sent to the denitrification system via the preheating branch pipe 21, forming a hot air reuse branch. A temperature regulating valve is installed on this branch, linked to the waste heat recovery status monitoring module, to ensure minimal temperature fluctuations in the hot air supplied to the denitrification system. Check valves are installed on the inlet air duct 8, return air duct 9, and preheating branch pipe 21 to prevent backflow of the working fluid, which could lead to system parameter malfunctions or equipment damage.

[0032] The intermediate-temperature heat exchanger 12 is located downstream of the high-temperature heat exchanger 7, with an inlet flue gas temperature of 90℃~120℃. This heat exchanger adopts a shell-and-tube structure, and the tubes are made of corrosion-resistant steel. The working fluid side of the intermediate-temperature heat exchanger 12 is connected to the condensate pipeline of the turbine regenerative system via a condensate inlet pipe 13 and a condensate outlet pipe 14.

[0033] The working fluid loop of the intermediate-temperature heat exchanger 12 is connected in series to the condensate pipe of the turbine regenerative system, forming a second-stage waste heat recovery loop through the condensate inlet pipe 13 and the condensate outlet pipe 14. Specifically, one end of the condensate inlet pipe 13 is connected to the working fluid inlet of the intermediate-temperature heat exchanger 12, and the other end is connected to the outlet condensate pipe of the previous-stage low-pressure heater (an existing component of the turbine regenerative system) in the turbine regenerative system. One end of the condensate outlet pipe 14 is connected to the working fluid side outlet of the intermediate temperature heat exchanger 12, and the other end is connected to the inlet condensate pipe of the next stage low-pressure heater in the turbine regenerative system (the low-pressure heater is an existing component of the turbine regenerative system). Part of the condensate from the previous stage low-pressure heater in the turbine regenerative system enters the intermediate temperature heat exchanger 12 through the condensate inlet pipe 13, absorbs the waste heat of the flue gas, and then returns to the next stage low-pressure heater in the turbine regenerative system through the condensate outlet pipe 14, thus achieving deep integration of the intermediate temperature heat exchange structure and the turbine regenerative system.

[0034] To cope with changes in unit load or equipment maintenance needs, a bypass pipeline 15 is also provided. The two ends of the bypass pipeline 15 are connected to the condensate inlet pipe 13 (before the inlet of the intermediate temperature heat exchanger) and the condensate outlet pipe 14 (after the outlet of the intermediate temperature heat exchanger), respectively. An electric switching valve is installed on the bypass pipeline 15. When the unit load fluctuates significantly, causing abnormal condensate flow, or when the intermediate temperature heat exchanger 12 needs maintenance, the system linkage control platform can automatically open the electric switching valve to allow the condensate to bypass the intermediate temperature heat exchanger 12, ensuring the stable operation of the turbine regenerative system.

[0035] In addition, an electromagnetic flow valve and a pressure sensor are installed on the condensate inlet pipe 13. The electromagnetic flow valve is controlled by the working fluid flow distribution module and can adjust the condensate flow rate in real time according to the load changes of the turbine regenerative system and the flue gas temperature at the inlet and outlet of the intermediate temperature heat exchanger 12. A temperature sensor is installed on the condensate outlet pipe 14 to provide real-time feedback on the temperature data of the condensate after heating. This data is transmitted to the waste heat recovery status monitoring module as one of the bases for adjusting the opening of the electromagnetic flow valve. A differential pressure sensor is installed on the intermediate temperature heat exchanger 12. When ash accumulation or blockage occurs, the differential pressure sensor will issue a warning signal to remind the staff to clean or repair in time to avoid affecting the overall heat exchange efficiency.

[0036] The deep recovery heat exchanger 16 is located at the end of the entire heat exchange sequence, with an inlet flue gas temperature ranging from 70℃ to 90℃. This heat exchanger adopts a glass tube bundle structure, with the tube bundles arranged in parallel and the tube spacing designed to be 1.8 to 2.2 times the tube diameter, which ensures both heat transfer efficiency and effectively prevents ash accumulation.

[0037] The working fluid loop of the deep heat recovery heat exchanger 16 is connected in parallel to the power plant's circulating cooling water system, forming a third-stage waste heat recovery loop through the cooling water inlet pipe 17 and the cooling water outlet pipe 18. Specifically, one end of the cooling water inlet pipe 17 is connected to the working fluid inlet of the deep heat recovery heat exchanger 16, and the other end is connected to the return water pipe of the cooling tower. One end of the cooling water outlet pipe 18 is connected to the working fluid outlet of the deep heat recovery heat exchanger 16, and the other end is divided into two paths through a three-way valve. One path connects to the cooling tower's inlet water pipe, and the other path connects to the plant's heating network. The return water from the cooling tower is divided into two paths through the cooling water inlet pipe 17. One path enters the deep heat recovery heat exchanger 16 to absorb waste heat, and the other path returns directly to the cooling tower. The water volume of the two paths can be dynamically adjusted according to the inlet flue gas temperature of the deep heat recovery heat exchanger, the return water temperature of the circulating cooling water system, and the heating demand of the plant area.

[0038] A filter, flow regulating valve, and temperature sensor are sequentially installed on the cooling water inlet pipe 17. The filter removes impurities from the circulating cooling water, preventing blockage of the glass tube bundle, and has a periodic automatic backwashing function. The flow regulating valve is linked to the working fluid flow distribution module to precisely control the amount of cooling water entering the deep recovery heat exchanger 16. The three-way valve on the cooling water outlet pipe 18 is automatically controlled by the system linkage control platform according to seasonal changes and heating load. During the heating season, heated cooling water is prioritized for delivery to the plant's heating network to meet heating needs. When heating demand is low, the remaining hot water is returned to the cooling tower. During the non-heating season, the three-way valve switches to full return mode, sending all hot water back to the cooling tower to reduce evaporation water consumption. Simultaneously, an emergency shut-off valve is installed on the connecting pipe between the circulating cooling water system and the deep recovery heat exchanger 16. In the event of a system leak or other emergency, the emergency shut-off valve can be quickly closed to prevent the accident from escalating.

[0039] The flue gas flow balancing module includes adjustable guide vanes and a flue gas flow sensor. The adjustable guide vanes are evenly distributed across the cross-section of the exhaust duct. By changing the angle of the adjustable guide vanes, the flue gas is evenly distributed before entering the high-temperature heat exchanger 7, avoiding uneven heat exchange in some areas due to flue gas flow deviation. The flue gas flow sensor collects the flue gas flow data in the exhaust duct in real time and transmits it to the waste heat recovery status monitoring module. If the flow fluctuation exceeds the preset range, the system linkage control platform will adjust the speed of the induced draft fan 3 to ensure stable flue gas flow and provide stable heat source conditions for the multi-stage heat exchange device.

[0040] The waste heat recovery status monitoring module includes a built-in data acquisition terminal and data analysis software. It collects system operating data in real time through sensors installed in the flue, at the inlet and outlet of each heat exchanger, and on the working fluid pipeline, measuring temperature, pressure, flow rate, and differential pressure. The data analysis software processes and analyzes the collected data to generate waste heat recovery efficiency curves and operating status reports for each piece of equipment. Simultaneously, this module has an early warning function. When a parameter exceeds a safety threshold (such as flue gas temperature approaching the acid dew point or an abnormal increase in heat exchanger differential pressure), it immediately issues an audible and visual warning and transmits the warning information to the system's linkage control platform, triggering corresponding protective measures.

[0041] The system's integrated control platform is built on a PLC control system, integrating control functions for various devices. Based on data transmitted from the waste heat recovery status monitoring module and the overall load demand of the power plant units, the platform can formulate optimal control strategies. For example, when the unit load increases and the flue gas temperature and flow rate rise, the platform will instruct the working fluid flow distribution module to increase the working fluid flow rate of each heat exchanger, thereby improving waste heat recovery. When the inlet flue gas temperature of the deep recovery heat exchanger 16 is detected to be close to the acid dew point, the platform will automatically open the electric damper of the bypass flue 19 and simultaneously reduce the cooling water flow rate to ensure that the heat exchanger wall temperature is at least 5°C above the acid dew point. It's easy to understand why an electric damper is installed in the bypass flue 19. Furthermore, the platform also has remote monitoring and operation functions. Operators can view the system's operating status in real time through the control room's interface and manually intervene in the system operation when necessary.

[0042] The above system operates as follows: Under normal operating conditions, boiler flue gas, after being pressurized by induced draft fan 3, first passes through a flue gas flow equalization module for uniform distribution, and then flows sequentially through high-temperature heat exchanger 7, medium-temperature heat exchanger 12, and deep recovery heat exchanger 16. The flue gas temperature drops from an initial approximately 130℃ to approximately 75℃ after three stages of heat exchange, and finally is discharged into the atmosphere through chimney 5. Throughout the entire operation, the waste heat recovery status monitoring module collects data from each stage in real time, and the system linkage control platform dynamically adjusts equipment operating parameters based on the data to ensure the system always operates in a highly efficient and safe state.

[0043] In the first-stage heat exchange process, the high-temperature heat exchanger 7 heats the cold air from ambient temperature to 80-100℃. The working fluid flow distribution module adjusts the opening of the diversion baffle 10 based on the total air volume supplied by the blower 11, the inlet cold air temperature of the air preheater 6, and the inlet flue gas temperature of the high-temperature heat exchanger 7, ensuring that the amount of cold air entering the high-temperature heat exchanger 7 matches the heat of the flue gas. The hot air heated by the high-temperature heat exchanger 7 enters the boiler for combustion, increasing the boiler's inlet air temperature and reducing fuel consumption. Tests have shown that for every 50℃ increase in inlet air temperature, boiler efficiency can increase by approximately 1.5%-2%. Simultaneously, the temperature of the hot air supplied to the denitrification system is controlled by a temperature regulating valve to ensure efficient denitrification reaction and reduce nitrogen oxide emissions.

[0044] During the second-stage heat exchange process, the intermediate-temperature heat exchanger 12 raises the condensate temperature by 8-15°C. The system's integrated control platform, based on the turbine's power generation load, the outlet condensate temperature of the previous-stage low-pressure heater, and the inlet flue gas temperature of the intermediate-temperature heat exchanger 12, instructs the working fluid flow distribution module to adjust the opening of the electromagnetic flow valve on the condensate inlet pipe 13, precisely controlling the condensate flow rate. After the condensate temperature is raised, the steam extraction rate of the low-pressure heater is correspondingly reduced. This increased steam continues to expand and perform work in the turbine, increasing the unit's power generation by 0.8%-1.2%.

[0045] In the third-stage heat exchange process, the deep recovery heat exchanger 16 raises the temperature of the circulating cooling water by 5-10°C. In summer, the system's linkage control platform controls the three-way valve on the cooling water outlet pipe 18 to return most of the heated cooling water to the cooling tower. Due to the increased cooling water temperature, the heat dissipation temperature difference of the cooling tower decreases, reducing evaporation water consumption by approximately 15%-20%. Simultaneously, the filter device automatically backwashes periodically to ensure the cleanliness of the circulating cooling water. In winter, the three-way valve switches to heating mode, delivering the heated cooling water to the plant's heating network to meet the plant's heating needs and save significant heating energy. Furthermore, the return water temperature of the heating network is monitored by a temperature sensor. If the return water temperature is too low, the system will appropriately increase the amount of cooling water entering the deep recovery heat exchanger 16 to raise the hot water temperature and ensure heating efficiency.

[0046] To ensure the safe operation of the system, the present invention has set up the following protection measures, all of which are automatically triggered by the system linkage control platform or manually controlled: A bypass flue 19 is installed before the deep heat recovery heat exchanger 16, and an electric damper and a manual backup damper are installed on the bypass flue 19. When the waste heat recovery status monitoring module detects that the flue gas temperature is too low (below 70℃), or when the deep heat recovery heat exchanger 16 needs maintenance, the system linkage control platform will automatically open the electric damper to directly guide the flue gas to the chimney 5. If the electric damper malfunctions, the operator can manually operate the backup damper to ensure normal flue gas discharge and avoid affecting boiler operation.

[0047] Each heat exchanger inlet and outlet is equipped with temperature monitoring instruments, and the temperature data is transmitted in real time to the waste heat recovery status monitoring module. When the flue gas temperature is detected to be close to the acid dew point (the acid dew point varies depending on the type of coal, typically 90℃~110℃), the system linkage control platform will automatically adjust the working fluid flow rate of the corresponding heat exchanger. For example, if the flue gas temperature at the inlet of the medium-temperature heat exchanger 12 is close to the acid dew point, the condensate flow rate will be increased to raise the heat exchanger wall temperature, ensuring that the wall temperature is always more than 5℃ above the acid dew point. If the flow rate adjustment cannot meet the requirements, the corresponding bypass device will be further opened to reduce the amount of flue gas entering the heat exchanger and prevent acidic substances from condensing and corroding the equipment.

[0048] The medium-temperature heat exchanger 12 is equipped with a corrosion monitoring sensor to regularly detect the corrosion of the pipes. If the corrosion rate exceeds the allowable range, a replacement warning will be issued in time to prevent the heat exchanger from leaking working fluid due to corrosion damage.

[0049] Pressure protection valves and check valves are installed on all working fluid pipelines (air inlet pipe 8, return air pipe 9, condensate inlet pipe 13, condensate outlet pipe 14, cooling water inlet pipe 17, and cooling water outlet pipe 18). When the pressure inside the pipeline exceeds the design pressure (0.15 MPa for the air inlet and return air pipes, 1.2 MPa for the condensate pipeline, and 0.8 MPa for the cooling water pipeline), the pressure protection valve automatically opens to release pressure and prevent pipeline rupture. The check valve prevents backflow of the working fluid, avoiding equipment damage or system parameter malfunctions caused by backflow.

[0050] The waste heat recovery status monitoring module is equipped with an emergency shutdown button. When a major fault occurs in the system (such as heat exchanger leakage, sudden drop in flue gas flow, or rupture of working fluid pipeline), and the automatic protection measures cannot control the risk, the staff can press the emergency shutdown button. The system linkage control platform will immediately close the inlet and outlet valves of each heat exchanger, cut off the working fluid circuit, and open all bypass devices to ensure the safe operation of the boiler and other equipment. The system will be restarted after the fault is eliminated.

[0051] The system provided in this invention is illustrated below with a specific embodiment: This system was applied in the retrofitting of a 300MW coal-fired power unit. Specific parameters are as follows: After the retrofit, the system operated stably, and all indicators met the design requirements. High-temperature heat exchanger 7: with a heat exchange area of ​​800 m², equipped with two electric butterfly valves (adjustment accuracy ±2%) and one set of diversion baffles 10 (automatic adjustment range 0~100%), it can heat 20,000 Nm³ / h of supply air from 25℃ to 95℃. The total supply air volume of the blower 11 is 50,000 Nm³ / h. After being distributed by the diversion baffles 10, the cold air volume entering the high-temperature heat exchanger 7 is 20,000 Nm³ / h, the cold air volume entering the air preheater 6 is 30,000 Nm³ / h, the hot air from the outlet of the high-temperature heat exchanger 7 is sent to the denitrification system at a flow rate of 5,000 Nm³ / h, and the remaining 15,000 Nm³ / h is merged into the hot air duct at the outlet of the air preheater.

[0052] Medium-temperature heat exchanger 12: Composed of 6 independent heat exchange modules, each with a heat exchange area of ​​200 m², for a total heat exchange area of ​​1200 m². Each module is equipped with one electromagnetic flow valve (flow adjustment range 0~60 t / h) and one differential pressure sensor (measurement accuracy ±0.5 kPa), capable of heating 300 t / h of condensate from 60℃ to 72℃. The design pressure of the condensate inlet pipe 13 is 1.2 MPa, with a stable operating pressure of 0.9~1.0 MPa and a pressure fluctuation range of ±0.05 MPa.

[0053] Deep recovery heat exchanger 16: With a heat exchange area of ​​1500 m², it is equipped with one filtration unit (100 μm filtration accuracy), one flow regulating valve (adjustment range 0~500 t / h), and one three-way valve (switching response time ≤5 s). It can heat 400 t / h of circulating water from 40℃ to 48℃. During the winter heating season, the hot water flow rate delivered to the plant's heating network is 150~200 t / h, meeting the heating needs of a 25,000 square meter building area, with a stable heating temperature of 18~22℃. During the summer non-heating season, all hot water is returned to the cooling tower, reducing the cooling tower makeup water rate by 18%.

[0054] The flue gas flow balancing module ensures a flue gas flow distribution uniformity of over 90% within the flue, preventing localized overheating or insufficient heat exchange in the high-temperature heat exchanger 7. The waste heat recovery status monitoring module can collect over 200 operating parameters in real time, with a data acquisition frequency of once per second and an early warning response time of ≤10 seconds. The system's linkage control platform achieves a control accuracy of ±1℃ (temperature control) and ±5t / h (flow control), ensuring stable system operation under various working conditions.

[0055] After implementation, the unit's coal consumption for power generation decreased by approximately 2.1 g / kWh, saving about 2,100 tons of standard coal annually. Based on a standard coal price of 1,000 yuan / ton, this translates to annual fuel cost savings of approximately 2.1 million yuan. The cooling tower water replenishment rate decreased by 18%, saving approximately 150,000 tons of water annually. Based on an industrial water price of 3 yuan / ton, this translates to annual water cost savings of approximately 450,000 yuan. Simultaneously, it provides a winter heating source for the plant, saving approximately 500,000 yuan in heating costs annually. The overall annual economic benefit is approximately 3.05 million yuan. Furthermore, no equipment corrosion or leakage occurred during system operation. The boiler flue gas temperature was stably controlled at around 75℃, and nitrogen oxide emission concentration decreased by approximately 8%, achieving multiple goals of energy saving, water saving, environmental protection, and safe operation.

[0056] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. A system for recovering and recycling waste heat from boiler flue gas in a thermal power plant, characterized in that, The system includes a boiler, an air supply assembly and a heat exchange assembly respectively connected to the boiler air inlet and the flue gas duct, and a chimney; The air supply assembly includes a blower for receiving cold air, a cold air delivery pipe connected in sequence to the outlet of the blower, an air preheater, and a hot air pipe, the outlet of which is connected to the air inlet of the boiler. The heat exchange assembly includes a dust collector, an induced draft fan, a high-temperature heat exchanger, a medium-temperature heat exchanger, and a deep recovery heat exchanger, which are connected in sequence to the flue gas duct of the boiler. The outlet of the deep recovery heat exchanger is connected to the inlet of the chimney, and the chimney is used to discharge the heat-exchanged flue gas into the atmosphere. The system also includes an air inlet pipe, a return air pipe, a condensate inlet pipe, a condensate outlet pipe, a cooling water inlet pipe, and a cooling water outlet pipe. The inlet and outlet of the air inlet pipe are respectively connected to the cold air delivery pipeline and the high-temperature heat exchanger, and the inlet and outlet of the return air pipe are respectively connected to the high-temperature heat exchanger and the hot air pipeline. The inlet and outlet of the condensate inlet pipe are respectively connected to the upstream low-pressure heater and the intermediate-temperature heat exchanger of the turbine regenerative system, and the inlet and outlet of the condensate outlet pipe are respectively connected to the intermediate-temperature heat exchanger and the downstream low-pressure heater of the turbine regenerative system. The inlet and outlet of the cooling water inlet pipe are respectively connected to the cooling tower and the deep recovery heat exchanger, and the inlet of the cooling water outlet pipe is connected to the deep recovery heat exchanger, and its outlet is connected to the cooling tower and the plant heating network.

2. The waste heat recovery and recycling system for boiler flue gas in a thermal power plant according to claim 1, characterized in that, A flow divider is installed at the connection between the air inlet pipe and the cold air delivery pipe.

3. The waste heat recovery and recycling system for boiler flue gas in a thermal power plant according to claim 2, characterized in that, The system also includes a preheating branch pipe, the inlet and outlet of which are connected to the return air duct and the denitrification system, respectively.

4. A waste heat recovery and recycling system for boiler flue gas in a thermal power plant according to claim 3, characterized in that, The high-temperature heat exchanger has a spiral finned tube structure, the medium-temperature heat exchanger has a shell-and-tube structure, and the deep recovery heat exchanger has a glass tube bundle structure.

5. A waste heat recovery and recycling system for boiler flue gas in a thermal power plant according to claim 4, characterized in that, The system also includes a bypass pipeline, the inlet and outlet of which are connected to the condensate inlet pipe and the condensate outlet pipe, respectively.

6. A waste heat recovery and recycling system for boiler flue gas in a thermal power plant according to claim 5, characterized in that, The system also includes a bypass flue, the inlet of which is connected to the pipeline between the medium-temperature heat exchanger and the deep recovery heat exchanger, and the outlet of which is connected to the chimney.

7. A waste heat recovery and recycling system for boiler flue gas in a thermal power plant according to claim 6, characterized in that, Both the air inlet pipe and the air return pipe are equipped with butterfly valves; both the air inlet pipe, the air return pipe, and the preheating branch pipe are equipped with check valves; and an electric switching valve is installed on the bypass pipe. An electromagnetic flow valve and a pressure sensor are installed on the condensate inlet pipe, and a temperature sensor is installed on the condensate outlet pipe; a filter device, a flow regulating valve, and a temperature sensor are sequentially installed on the cooling water inlet pipe.

8. A waste heat recovery and recycling system for boiler flue gas in a thermal power plant according to claim 7, characterized in that, The system also includes a flue gas flow balancing module, a working fluid flow distribution module, a waste heat recovery status monitoring module, and a system linkage control platform; The flue gas flow equalization module is installed in the flue section between the induced draft fan and the high-temperature heat exchanger; the working fluid flow distribution module is connected to the air inlet pipe, condensate inlet pipe and cooling water inlet pipe respectively; the waste heat recovery status monitoring module collects the operating parameters of each device in real time through a sensor network; the system linkage control platform dynamically regulates the entire system based on the monitoring data.

9. A waste heat recovery and recycling system for boiler flue gas in a thermal power plant according to claim 8, characterized in that, The flue gas flow equalization module includes an adjustable guide plate and a flue gas flow sensor installed in the exhaust duct.

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