A flue gas heat exchanger efficient operation maintenance and leakage prevention treatment method

Abstract

The present application belongs to the technical field of flue gas waste heat recovery equipment maintenance, and discloses a flue gas heat exchanger efficient operation maintenance and leakage prevention treatment method. In the method, the filter screen aperture is optimized to 1mm to form double-layer filtration, an online and shutdown combined ash removal system is designed, precise single tube bundle leakage detection and online plugging of the conical copper plug during operation are realized, double-mode anti-freezing and emptying by using waste heat steaming and compressed air water topping is adopted, dosing and sampling temperature control are optimized to realize precise water quality control, and standardized dry burning, starting, shutdown and conventional operation processes are formulated. The present application solves the problems of existing flue gas heat exchanger, such as impurity wear, ash accumulation, leakage detection difficulty, incomplete anti-freezing and emptying, etc., maintains the heat exchange efficiency of the heat exchanger at 99%, prolongs the service life of the heat exchange tube to more than 20 years, greatly reduces the equipment failure rate and operation and maintenance cost, improves the stability and energy utilization efficiency of the flue gas waste heat recovery system, and is suitable for operation and maintenance of the flue gas heat exchanger at the inlet of the desulfurization tower of the power plant.

Description

Technical Field

[0001] This invention belongs to the field of flue gas waste heat recovery equipment maintenance technology, specifically involving a comprehensive treatment for the operation, maintenance, leakage prevention, antifreeze and water quality control of flue gas heat exchangers applied to the inlet of desulfurization towers in power plants. Specifically, it is a method for efficient operation, maintenance and leakage prevention of flue gas heat exchangers. Background Technology

[0002] In power plant flue gas waste heat recovery systems, the flue gas heat exchanger is the core equipment, primarily used to recover and utilize waste heat from the flue gas, thereby improving energy efficiency. Currently, most mainstream flue gas heat exchangers use fluoroplastic heat exchange tubes, which, while possessing corrosion resistance, still present several technical challenges in actual operation. Welding slag, rust and other impurities in the circulating water pipes can easily enter the tube bundle, wear down the fluoroplastic heat exchange tubes, and cause tube leakage. The existing filter screen has a larger pore size (2-3mm) and poor filtration effect. Dust in flue gas tends to adhere to the outer wall of heat exchange tubes, forming hard ash deposits that are difficult to remove completely by online water rinsing alone. The ash deposits will increase the flow velocity between tubes, causing the heat exchange tubes to rub against each other and leak. In addition, the cleaning hoses are prone to aging and leakage, affecting the cleaning effect. Detecting leaks in heat exchangers requires a complete shutdown for investigation, which is time-consuming and labor-intensive. The sealing process after a leak occurs is complex and cannot be completed while the unit is running. When the equipment is shut down in winter, it is difficult to completely drain the water from the U-shaped fluoroplastic heat exchange tubes. Conventional draining methods can easily cause the tubes to freeze and crack, affecting the service life of the equipment. The pH value of circulating water drops rapidly due to the infiltration of acidic substances from flue gas. The existing dosing system simply adds alkali solution, and the high temperature of the sampled water will cause the pH and conductivity measuring instruments to be distorted, making it impossible to accurately control the water quality and causing corrosion of carbon steel pipes. Fluoroplastic heat exchange tubes are prone to vibration and wear when dry-burned. Existing technology has not established standardized dry-burning operation control measures, and excessive dry-burning time will significantly reduce the tube life.

[0003] Meanwhile, the existing flue gas heat exchangers lack a standardized operating system for startup, shutdown, and routine operation, resulting in poor inter-system coordination, low equipment stability, high maintenance costs, and easy degradation of heat exchange efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide a method for efficient operation, maintenance, and leak prevention of flue gas heat exchangers, solving problems such as wear from impurities, ash accumulation and blockage, difficulty in leak detection, incomplete antifreeze venting, distorted water quality control, and easy damage from dry burning in existing flue gas heat exchangers. This method enables standardized, intelligent, and efficient operation and maintenance of flue gas heat exchangers, improves equipment operational stability, extends the service life of heat exchange tubes, reduces operation and maintenance costs, and ensures the heat exchange efficiency of the flue gas waste heat recovery system.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows: A method for efficient operation, maintenance, and leak prevention of a flue gas heat exchanger is applied to a flue gas waste heat recovery system consisting of the flue gas heat exchanger body, an HRS circulating water system, an HRS chemical sampling and dosing system, and a flue gas heat exchanger cleaning system, including: S1. Set up a high-precision filtration and pipeline pretreatment system; S2. Establish a routine operation and maintenance mechanism for the composite dust removal system and cleaning system; S3. Design and operation leakage detection and online sealing process; S4. Equip a dual-mode anti-freeze and venting system; S5. Establish a precise circulating water quality control and sampling detection system; S6. Standardized operation and management system; Furthermore, S1 includes optimizing the pore size of the inlet filter screen of the water filling pump and cleaning pump in the circulating pump room and the filter screen on the cleaning platform to 1mm, and fixing the 1mm filter screen to the inner wall and bottom of the existing filter screen cylinder to form a double-layer filtration structure, which effectively blocks impurities such as welding slag and rust from entering the tube bundle. A segmented cleaning process for the pipeline was developed. The pipelines were flushed in segments before connection. After the system was initially filled with water, the tube bundles, pressure stabilization system and dosing equipment were isolated. The circulation pump was started to flush the pipeline. The degree of blockage was judged by the pressure difference before and after the filter. The filter screen was repeatedly cleaned until the pressure difference was <30 kPa to prevent impurities from wearing the heat exchange tubes from the source.

[0006] Furthermore, S2 includes a composite cleaning system that combines online water flushing with manual cleaning during shutdown: When the unit is running, the DCS sequentially controls the cleaning system, with each tube bundle being flushed online for 4 minutes per day, consuming 12 tons of water per tube bundle, and the pressure of the cleaning main pipe is controlled at 3.0-3.5 bar; during shutdown maintenance, if hard ash is found, fire water flushing combined with tapping with wooden sticks is used for cleaning, and in severe cases, the tube bundle is lifted out for manual cleaning. Establish a routine operation and maintenance mechanism for the cleaning system: clean the main cleaning pipe filter every two weeks, and replace all cleaning water spray hoses every 1-2 years as they are vulnerable parts; check the cooler cleaning branch valves for leaks every month, and use a water flow observer to determine the internal leakage of the valves, and repair or replace the leaking valves in a timely manner.

[0007] Furthermore, S3 includes a leak detection process: when the pressure stabilizing system is frequently replenished with water, it is determined that there is a leak in the system. During unit operation, the inlet and outlet valves of the single tube bundle water side are closed, and the local pressure gauge values ​​are read. If the pressure drops, it is determined that there is a leak in the tube bundle. All tube bundles are checked in turn to achieve accurate location. Online sealing process: After depressurizing the leaking pipe bundle, remove the end cap of the water manifold, fill the U-shaped pipe with water, determine the location of the leaking pipe by the drop in liquid level, squeeze the water out of the leaking pipe with compressed air, and use conical copper plugs to knock into both ends of the leaking pipe to seal it. Record the position of the plugs, and put the pipeline into operation after restoring the pipeline connection.

[0008] Furthermore, the S4 is designed with two anti-freeze venting modes for different shutdown conditions in winter: waste heat evaporation and compressed air top-water evaporation. In the event of a short-term shutdown or when the water temperature drops to 5°C, the waste heat drying mode should be used first. Close the isolation valves on both sides of the heat exchanger and open the anti-freeze vent valve to use the waste heat of the flue gas to dry the water in the tube bundle. When the machine is shut down for a long period of time or is undergoing major repairs, use the compressed air water-push mode. Close the isolation valve, open the vent valve and drain valve to release the water in the pipeline, then close the vent valve and drain valve again. Use temporary compressed air to pressurize the pipe bundle system to 2-2.5 bar, open the drain valve to push the water out, and repeat 2-3 times to achieve complete drainage. Meanwhile, auxiliary antifreeze measures are adopted, namely, closing all manholes in the flue and the dampers leading from the reheater outlet to the chimney to avoid convection caused by the chimney's self-pulling force and reduce the probability of circulating water freezing.

[0009] Furthermore, the S5 circulating water quality control method includes: setting up an HRS chemical sampling and dosing system, which precisely controls the pH value of the circulating water at 9-9.5 by adding 30% NaOH solution; when the conductivity rises to 5000µS / cm, the drain valve and filling pump are opened to replace the water until the conductivity drops to 800µS / cm; the dosing system is only operated when the circulating pump is running to avoid local accumulation of chemicals; The sampling and testing optimization methods include: designing a sampling water cooling and temperature control structure, using industrial water to cool the sampling water, controlling the temperature of the sampling water flowing through the pH and conductivity measuring elements at 40-50℃, triggering a DCS alarm when the sampling water temperature exceeds 60℃, and closing the sampling water valve; ensuring that the pH electrode head is always immersed in water to prevent instrument inaccuracy and damage.

[0010] Furthermore, S6 includes control over dry burning: the flue gas temperature should not exceed 180°C when the fluoroplastic heat exchange tube is dry burning, the dry burning time should not exceed one week, and debris in the flue should be cleaned before dry burning, and all exhaust valves should be opened to avoid tube vibration and wear. Control over startup and shutdown: Establish a standardized system startup procedure, and operate in the following order: water filling, flushing, water filling of the pressure stabilizing system, water filling of the tube bundle, and trial operation of the circulating pump; when shutting down, the circulating water system shall be shut down half an hour after the desulfurization system is shut down, and the circulating pump shall be kept running to prevent freezing during short-term shutdowns in winter. Routine operation and management: A comprehensive inspection of the system is carried out every shift, monitoring the temperature and pressure of flue gas and water, the water tank level, and the inlet filter of the circulating pump is inspected monthly. The operating status of the pressure stabilization system is judged in real time by the water tank level.

[0011] The beneficial effects of this invention are: Improve equipment operation stability: Through 1mm high-precision filtration and pipeline pretreatment, impurities are prevented from wearing heat exchange tubes at the source. Combined with a composite ash removal system, the problem of ash accumulation and blockage is completely solved, so that the pressure drop on the flue gas side of the flue gas heat exchanger is ≤400Pa and the pressure drop on the water side is ≤0.03Mpa, and the heat exchange efficiency is maintained at 99% of the design value for a long time. Achieve rapid leak handling: The single-tube bundle isolation detection method during operation can accurately locate the leaking tube, and the online sealing process with conical copper plugs does not require overall shutdown, which greatly shortens the leak handling time and reduces the rate of unplanned equipment downtime; Completely solve the antifreeze problem: The dual-mode antifreeze and venting solution of waste heat evaporation and compressed air top water is adapted to different winter shutdown conditions, realizes venting of U-shaped fluoroplastic heat exchange tubes without dead angles, and utilizes the characteristics of fluoroplastic material to completely avoid tube body freezing and cracking. Precise water quality control to prevent pipe corrosion: The optimized dosing system and sampling water temperature control structure ensure the accuracy of pH and conductivity detection, stabilize the pH of circulating water at 9-9.5, effectively prevent carbon steel pipe corrosion, and avoid rust entering the pipe bundle and causing blockage. Extending equipment lifespan: Standardized dry burning control, routine cleaning system maintenance, and standardized operating procedures enable modified fluoroplastic heat exchange tubes to have a lifespan of over 20 years. The replacement cycle for vulnerable parts such as cleaning water spray hoses is clearly defined, reducing equipment replacement costs. Reduced operation and maintenance costs: All processes in this invention are standardized and streamlined, requiring no new large-scale equipment. By optimizing existing systems and establishing operation and maintenance mechanisms, the time spent on manual troubleshooting and fault handling is significantly reduced, thereby lowering overall operation and maintenance costs. Improving energy efficiency: The long-term stable and efficient operation of the flue gas heat exchanger ensures the heat exchange effect of the flue gas waste heat recovery system, effectively recovers waste heat from the flue gas, improves the overall energy efficiency of the power plant, and conforms to the industry development trend of energy conservation and consumption reduction. Attached Figure Description

[0012] Figure 1 This is a system architecture diagram established by the method of this invention. Detailed Implementation

[0013] The present invention will be further described below with reference to the embodiments and accompanying drawings: The waste heat recovery system of the 300MW Units 1 and 2 of the company's power plant is equipped with two flue gas coolers. The heat transfer medium and water are combined and share a common main pipe. The flue gas heat exchanger body is three sets of parallel U-shaped modified fluoroplastic heat exchange tubes with a total heat exchange area of ​​about 3635m². The designed flue gas flow rate is 1,100,000 Nm³ / h, and the cooling water flow rate is 400t / h.

[0014] like Figure 1As shown, a system for implementing efficient operation, maintenance, and leak prevention of flue gas heat exchangers is constructed, including a high-precision filtration and pipeline pretreatment system, a composite ash removal and cleaning system, a leak detection and online sealing system, a dual-mode antifreeze and venting system, a precise water quality control and sampling detection system, and a standardized operation and management module.

[0015] The steps for implementing efficient operation, maintenance, and leak prevention methods for flue gas heat exchangers include: S1. Set up a high-precision filtration and pipeline pretreatment system; Install 1mm pore size filters on the inlet filters of the water filling pump and cleaning pump in the circulating pump room, as well as the filters on the cleaning platform. Tie them to the inner wall and bottom of the existing filter cylinder with wire. Perform segmented flushing before pipeline installation. After the system is filled with water for the first time, isolate the pipe bundle, pressure stabilization system and dosing equipment, start the circulating pump to flush the pipeline, and check the pressure difference before and after the filter every 2 minutes. When the pressure difference reaches 20m, shut down the circulating pump, clean the filter, and restart it. Repeat the operation until the pressure difference is <30Kpa. The pipeline flushing process lasts for 1.5 days to thoroughly remove welding slag and rust from the pipeline.

[0016] S2. Establish a routine operation and maintenance mechanism for the composite dust removal system and cleaning system; During unit operation, the DCS sequential cleaning system performs online water flushing on three tube bundles daily, with each bundle flushed for 4 minutes. The throttle valve on the main cleaning pipe is adjusted to a downstream pressure of 3.2 bar, and the water consumption for flushing a single bundle is 12 tons. The filter on the main cleaning pipe is disassembled and cleaned every two weeks, and all cleaning water spray hoses are replaced after 1.5 years of operation. Leak checks are performed monthly on the branch valves, and the impeller rotation is checked using a water flow observer. If any valve is found to have internal leakage, it is replaced promptly to ensure cleaning effectiveness. During shutdown maintenance, a small amount of hardened ash was found on the outer wall of the heat exchange tubes. The ash was successfully removed by flushing with fire water and tapping with a wooden stick, without any wear and tear on the tubes.

[0017] S3. Design and operation leakage detection and online sealing process; During operation, frequent water replenishment of the pressure stabilization system was detected, indicating a leak in the system. Under normal unit operation, the water-side inlet and outlet valves of the three sets of tube bundles were closed in sequence, and the local pressure gauges were read. It was found that the pressure of tube bundle No. 2 continued to drop, indicating a leak in this tube bundle. After depressurizing tube bundle No. 2, the end cover of the water header was removed, and the U-shaped pipe was filled with water. It was observed that the liquid level in one U-shaped pipe dropped rapidly, thus determining the location of the leak. Compressed air was used to squeeze the water out of the leaking pipe, and conical copper plugs were knocked into both ends of the leaking pipe. The plug positions were recorded, and after the pipeline connection was restored, tube bundle No. 2 was put back into operation. The entire leak handling process took 2 hours and did not affect the normal production of the unit.

[0018] S4. Equip a dual-mode anti-freeze and venting system; During a short-term winter shutdown (3 days), when the water temperature dropped to 4℃, a waste heat drying mode was used for freeze protection: the isolation valves on both sides of the heat exchanger were closed, the antifreeze vent valve was opened, and the waste heat of the flue gas was used to evaporate the water in the tube bundle. During the shutdown, there was no water in the tube bundle and no freezing or cracking occurred. During the major overhaul the following winter, when the unit was shut down for a long period, a compressed air water-pumping mode was used: the isolation valve was closed, the vent valve and drain valve were opened to drain the water in the pipeline, the vent valve and drain valve were closed, the tube bundle system was pressurized to 2.3 bar with temporary compressed air, and the drain valve was opened to push the water out. This was repeated 3 times to completely empty the tube bundle. After the overhaul, the equipment started normally.

[0019] S5. Establish a precise circulating water quality control and sampling detection system; The HRS chemical sampling and dosing system was activated, and a 30% NaOH solution was prepared in the dosing tank. The solution was then added to the circulating water via a metering pump to stabilize the pH value between 9.2 and 9.4. During operation, when the conductivity of the circulating water reached 5000 µS / cm, a DCS alarm was triggered, and the drain valve and filling pump were opened to replace the water. Simultaneously, the opening of the water supply pipeline valve was adjusted to maintain a balance between inlet and outlet water. After two hours of water replacement, the conductivity dropped to 780 µS / cm, and the drain valve was closed. The sampling water cooling system maintained the sampling water temperature at approximately 45℃. The pH and conductivity data were measured accurately and in real-time, with no instrument distortion observed. No corrosion was observed in the circulating water pipeline after six months of operation.

[0020] S6. Standardized operation and management system; During operation, the flue gas heat exchanger underwent dry-burning operation for maintenance. Before dry-burning, debris inside the flue was cleaned, all exhaust valves were opened, the flue gas temperature was controlled at 175℃, and the dry-burning time was 5 days. After maintenance, water supply was restored, and there was no shaking or wear on the heat exchange tubes. The system startup followed the standardized sequence of water filling-flushing-pressure stabilization system water filling-tube bundle water filling-circulating pump trial operation. The startup process was smooth and without faults. During normal operation, the system temperature, pressure, and liquid level were checked every shift. The inlet filter of the circulating pump was disassembled and inspected once a month. The operating status of the pressure stabilization system was judged in real time by the liquid level in the water tank. There were no abnormal alarms during equipment operation.

[0021] After the implementation of this method, the power plant's flue gas heat exchanger operated continuously for 12 months, with the flue gas side pressure drop stabilizing at 240-260 Pa and the water side pressure drop stabilizing at 0.025-0.03 MPa, and the heat exchange efficiency consistently maintained at 99%. Only one pipe leak occurred, which took 2 hours to resolve, and the unplanned equipment downtime rate was 0%. There were no freezing and cracking failures during winter shutdowns, no corrosion in the circulating water pipes, and no significant wear on the modified fluoroplastic heat exchange tubes. The equipment's operational stability was significantly improved, maintenance costs were reduced by 35% compared to before, and flue gas waste heat recovery efficiency was increased by 5%, achieving the dual effects of energy saving, cost reduction, and efficiency improvement.

Claims

1. A method for efficient operation, maintenance, and leak prevention of a flue gas heat exchanger, applied to a flue gas waste heat recovery system consisting of a flue gas heat exchanger body, an HRS circulating water system, an HRS chemical sampling and dosing system, and a flue gas heat exchanger cleaning system, characterized in that: Includes the following steps: S1. Set up a high-precision filtration and pipeline pretreatment system; S2. Establish a routine operation and maintenance mechanism for the composite dust removal system and cleaning system; S3. Design and operation leakage detection and online sealing process; S4. Equip a dual-mode anti-freeze and venting system; S5. Establish a precise circulating water quality control and sampling detection system; S6. Standardized operation and management system.

2. The method for efficient operation, maintenance, and leak prevention of a flue gas heat exchanger according to claim 1, characterized in that: S1 includes optimizing the pore size of the inlet filter screen of the water filling pump and the cleaning pump in the circulating pump room and the filter screen on the cleaning platform to 1mm, and fixing the 1mm filter screen to the inner wall and bottom of the existing filter screen cylinder to form a double-layer filtration structure. Before connecting the pipeline, perform segmented flushing. After the system is filled with water for the first time, isolate the pipe bundle, pressure stabilization system and dosing equipment, start the circulation pump to flush the pipeline, judge the degree of blockage by the pressure difference of the pressure gauges before and after the filter, and repeatedly clean the filter until the pressure difference is <30Kpa.

3. The method for efficient operation, maintenance, and leak prevention of a flue gas heat exchanger according to claim 1, characterized in that: The S2 includes a composite cleaning system that combines online water flushing with manual cleaning during shutdown: when the unit is running, the DCS sequentially controls the cleaning system, and each tube bundle is flushed online for 4 minutes every day, with the cleaning pressure of the main tube controlled at 3.0-3.5 bar; during shutdown maintenance, if hard ash is found, fire water flushing is combined with tapping with wooden sticks to clean it, and if the ash is severe, the tube bundle is lifted out for manual cleaning. Establish a routine operation and maintenance mechanism for the cleaning system: clean the main pipe filter every two weeks, and replace all cleaning water spray hoses every 1-2 years; check the cooler cleaning branch valves for leaks every month, and use water flow observers to determine the internal leakage of valves, and repair or replace leaking valves in a timely manner.

4. The method for efficient operation, maintenance, and leak prevention of a flue gas heat exchanger according to claim 1, characterized in that: The S3 includes a leak detection process: when the pressure stabilizing system is frequently replenished with water, it is determined that there is a leak in the system. During unit operation, the inlet and outlet valves of the single tube bundle water side are closed, and the local pressure gauge values ​​are read. If the pressure drops, it is determined that there is a leak in the tube bundle. All tube bundles are checked in sequence to achieve accurate location. Online sealing process: After depressurizing the leaking pipe bundle, remove the end cap of the water manifold, fill the U-shaped pipe with water, determine the location of the leaking pipe by the drop in liquid level, squeeze the water out of the leaking pipe with compressed air, and use conical copper plugs to knock into both ends of the leaking pipe to seal it. Record the position of the plugs, and put the pipeline into operation after restoring the pipeline connection.

5. The method for efficient operation, maintenance, and leak prevention of a flue gas heat exchanger according to claim 1, characterized in that: The S4 is designed with two anti-freezing and venting modes for different shutdown conditions: waste heat evaporation and compressed air top-water discharge. In the event of a short-term shutdown or when the water temperature drops to 5°C, the waste heat drying mode should be used first. Close the isolation valves on both sides of the heat exchanger and open the anti-freeze vent valve to use the waste heat of the flue gas to dry the water in the tube bundle. When the machine is shut down for a long period of time or is undergoing major repairs, use the compressed air water-push mode. Close the isolation valve, open the vent valve and drain valve to release the water in the pipeline, then close the vent valve and drain valve again. Use temporary compressed air to pressurize the pipe bundle system to 2-2.5 bar, open the drain valve to push the water out, and repeat 2-3 times to achieve complete drainage. The auxiliary antifreeze measures adopted are: closing all manholes in the flue and the dampers leading from the reheater outlet to the chimney.

6. The method for efficient operation, maintenance, and leak prevention of a flue gas heat exchanger according to claim 1, characterized in that: The S5 circulating water quality control method includes: setting up an HRS chemical sampling and dosing system, which precisely controls the pH value of the circulating water at 9-9.5 by adding 30% NaOH solution; when the conductivity rises to 5000µS / cm, the drain valve and filling pump are opened to replace the water until the conductivity drops to 800µS / cm; the dosing system is only operated when the circulating pump is running. The sampling and testing optimization methods include: designing a sampling water cooling and temperature control structure, using industrial water to cool the sampling water, controlling the temperature of the sampling water flowing through the pH and conductivity measuring elements at 40-50℃, triggering a DCS alarm when the sampling water temperature exceeds 60℃, and closing the sampling water valve; ensuring that the pH electrode head is always immersed in water.

7. The method for efficient operation, maintenance, and leak prevention of a flue gas heat exchanger according to claim 1, characterized in that: The S6 includes control over dry burning: the flue gas temperature should not exceed 180°C when the fluoroplastic heat exchange tube is dry burning, the dry burning time should not exceed one week, and debris in the flue should be cleaned before dry burning and all exhaust valves should be opened. Control over startup and shutdown: Establish a standardized system startup procedure, and operate in the following order: water filling, flushing, water filling of the pressure stabilizing system, water filling of the tube bundle, and trial operation of the circulating pump; when shutting down, the circulating water system shall be shut down half an hour after the desulfurization system is shut down, and the circulating pump shall be kept running to prevent freezing during short-term shutdowns in winter. Routine operation and management: A comprehensive inspection of the system is carried out every shift, monitoring the temperature and pressure of flue gas and water, the water tank level, and the inlet filter of the circulating pump is inspected monthly. The operating status of the pressure stabilization system is judged in real time by the water tank level.

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