Waste heat recovery device resistant to low-temperature dew point corrosion and corrosion early warning method thereof

Abstract

The application discloses a waste heat recovery device resistant to low-temperature dew point corrosion and a corrosion early warning method thereof, and relates to the technical field of low-temperature dew point corrosion; in order to be able to monitor and early warn the corrosion state of the waste heat recovery device in real time and accurately; specifically comprising a shell, a flue gas inlet and a flue gas outlet are arranged at both ends of the shell respectively, heat exchange pipes are arranged on the inner wall of the shell, a gas inlet is arranged at one end of the heat exchange pipes, a gas outlet is arranged at the other end of the heat exchange pipes, and a first temperature sensor is arranged on the region of the outer wall of the heat exchange pipes close to the gas inlet. The corrosion rate prediction model capable of accurately predicting the low-temperature dew point corrosion rate prediction value of the outer wall of the heat exchange pipes covers the correlation law of the temperature, the HCl concentration and the corrosion rate, provides accurate low-temperature dew point corrosion early warning for the waste heat recovery device in operation, then the cooling mechanism is used to reduce the flue gas temperature entering the inside of the shell, reduce the low-temperature dew point corrosion rate of the outer wall of the heat exchange pipes, and improve the service life of the heat exchange pipes.

Description

Technical Field

[0001] This invention relates to the field of low-temperature dew point corrosion technology, and in particular to a waste heat recovery device and a corrosion early warning method for resisting low-temperature dew point corrosion. Background Technology

[0002] In energy-intensive industries such as petrochemicals and oil refining, heating furnaces (such as catalytic reforming furnaces) are critical energy-consuming equipment. The high-temperature flue gas they discharge carries a large amount of waste heat. By installing waste heat recovery devices such as air preheaters, the flue gas can be used to heat the combustion air, significantly improving the furnace's thermal efficiency and reducing fuel consumption—an important energy-saving measure. However, when the flue gas temperature drops below its acid dew point (especially the condensation temperature of acidic gases such as sulfuric acid and hydrochloric acid), the acidic components in the flue gas (such as SO3, SO2, and HCl) condense to form an acidic liquid film that adheres to metal surfaces such as heat exchanger tubes, causing severe low-temperature dew point corrosion. This not only leads to equipment perforation and leakage, and reduced heat exchange efficiency, but also poses safety hazards and requires frequent maintenance and replacement, severely restricting the long-term, efficient, and safe operation of waste heat recovery systems.

[0003] Traditional solutions often focus on material upgrades, such as using more corrosion-resistant metal or non-metal coatings. However, these methods are costly and may fail under certain extreme conditions. Furthermore, existing technologies lack the ability to monitor and warn of corrosion status in real time and accurately. Repairs are often carried out only after the equipment has been obviously damaged or leaked, which is a passive maintenance approach and cannot achieve proactive prevention and intelligent management of corrosion risks.

[0004] Therefore, there is an urgent need to develop a waste heat recovery device and corrosion early warning method that can effectively resist low-temperature dew point corrosion and monitor and warn of corrosion risks in real time. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a waste heat recovery device and a corrosion early warning method that resists low-temperature dew point corrosion.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A waste heat recovery device resistant to low-temperature dew point corrosion includes a shell with a flue gas inlet and a flue gas outlet at both ends. A heat exchange tube is installed on the inner wall of the shell, with an inlet at one end and an outlet at the other. A first temperature sensor is installed on the outer wall of the heat exchange tube near the inlet, and a second temperature sensor is installed on the outer wall of the outlet. A first electrically controlled three-way valve is connected to one end of the flue gas inlet, with a first and a second flue gas guide pipe connected to both ends. A cooling mechanism is installed on the outer wall of the second flue gas guide pipe, and a second electrically controlled three-way valve is connected to one end of both pipes. A flue gas discharge pipe is connected to one end of the second electrically controlled three-way valve. A liquid collection tank is installed on the bottom outer wall of the shell, with a one-way valve at the bottom.

[0007] Preferably, the heat exchange tube is composed of an inner tube, a corrosion-resistant alloy layer and a nano-composite coating. The corrosion-resistant alloy layer is hot-rolled and bonded to the outer wall of the inner tube, and the nano-composite coating is sprayed onto the outer wall of the corrosion-resistant alloy layer. The thickness of the corrosion-resistant alloy layer is 0.5-2 mm, and the thickness of the nano-composite coating is 10-20 μm. The inner tube is made of Q345R steel, the corrosion-resistant alloy layer is made of 09CrCuSb steel, and the nanocomposite coating is made of fluorosilicone resin, nano-silica and silicon carbide particles.

[0008] Furthermore: the cooling mechanism includes a heat sink, heat dissipation fins and a coolant circulation pipe. The two ends of the heat sink are connected to the second smoke guide pipe. Multiple heat dissipation fins are equidistantly arranged on the outer walls of both sides of the heat sink. The coolant circulation pipes are respectively arranged on the other two outer walls of the heat sink.

[0009] A further preferred embodiment: The corrosion early warning method for the waste heat recovery device resistant to low-temperature dew point corrosion according to claim 1, characterized in that it includes the following steps:

[0010] S1: Training and deployment of the corrosion rate prediction model; S2: The temperature of the gas flowing in each area of ​​the heat exchange tube is monitored in real time by using a first temperature sensor and a second temperature sensor installed at multiple locations on the outer wall of the heat exchange tube. S3: Detect the HCl concentration of the condensate on the outer wall of the heat exchange tube using a testing instrument; S4: Input the real-time temperature of the gas flowing in each area of ​​the heat exchange tube and the HCl concentration of the condensate into the corrosion rate prediction model to calculate the predicted corrosion rate of the corresponding area of ​​the heat exchange tube at that temperature and concentration. S5: When the real-time temperature and HCl concentration exceed the threshold, the first and second electrically controlled three-way valves are closed at one end connected to the first flue pipe and opened at the other end connected to the second flue pipe. The cooling mechanism cools the flue gas entering the shell in time, reduces the internal temperature of the shell, and reduces the corrosion rate of the heat exchange tubes located inside the shell.

[0011] As a preferred embodiment of the present invention: in step S1, the weight loss corrosion rate of Q345R steel at three temperatures of 60°C, 75°C, and 90°C is collected using a low-temperature dew point corrosion test platform.

[0012] As a further preferred embodiment of the present invention: In step S1, the weight loss corrosion rate of Q345R steel in HCl liquids of three concentrations of 0.1, 0.5, and 1.0 mol / L is collected using a low-temperature dew point corrosion test platform. Based on the above two types of data, a corrosion rate prediction model is trained, and then the trained model is deployed to the intelligent corrosion status diagnosis module on site.

[0013] As a further embodiment of the present invention: the low-temperature dew point corrosion test platform includes an oil bath, a multi-necked evaporator, a third temperature sensor, a straight condenser, a plate, and an electrochemical workstation. The oil bath heats the multi-necked evaporator placed inside. The third temperature sensor is inserted into one end opening of the multi-necked evaporator to monitor the internal temperature of the multi-necked evaporator. The straight condenser is inserted into the top opening of the multi-necked evaporator. The plate is inserted into the top of the straight condenser. The electrochemical workstation detects the rate of weight loss corrosion of the plate.

[0014] Based on the aforementioned scheme: the straight condenser tube is provided with a circulating water pipe inlet, a circulating water pipe outlet and a pressure limiting valve at both ends, one end of the pressure limiting valve is connected to a tail gas conduit, the bottom end of the tail gas conduit is connected to a tail gas absorption bottle, and a support is provided on the outer wall of the straight condenser tube and the multi-port evaporator.

[0015] Based on the aforementioned scheme, the preferred embodiment is as follows: in S3, the detection instrument is an electrochemical workstation; in S5, the threshold value is 125-180 g / (m2·h).

[0016] The beneficial effects of this invention are as follows: 1. When the predicted low-temperature dew point corrosion rate exceeds the threshold, the control terminal will control the first and second electrically controlled three-way valves to close at the end connected to the first flue pipe and open at the end connected to the second flue pipe. This allows the high-temperature steam entering through the flue gas exhaust pipe to dissipate some heat through the heat dissipation fins on the outer wall of the heat exchanger box before entering the shell for heat exchange. This effectively reduces the temperature of the flue gas entering the shell and decreases the low-temperature dew point corrosion rate on the outer wall of the heat exchange tube, thus achieving timely early warning and improving the service life of the heat exchange tube.

[0017] 2. Through hot rolling composite process, a corrosion-resistant alloy layer made of 09CrCuSb steel is bonded to the outer wall of the inner tube. This layer is the main barrier against corrosion by acidic condensate. On the outer surface of the corrosion-resistant alloy layer, a hydrophobic nanocomposite coating is further coated. This coating is prepared by plasma spraying process and its main components are a composite material of fluorosilicone modified resin and nano-silica and silicon carbide particles. This nanocomposite coating can reduce the adhesion of condensate to the tube wall, making it difficult for droplets to stay and allowing them to slide off quickly, reducing the contact time and area between the corrosive medium and the metal surface, and improving the overall resistance of the heat exchange tube outer wall to low-temperature dew point corrosion.

[0018] 3. When the predicted low-temperature dew point corrosion rate of the heat exchange tube has not yet decreased to below the threshold, the two ends of the coolant circulation pipe can be connected to an external coolant circulation and delivery device. The coolant flowing inside the coolant circulation pipe, in conjunction with the heat dissipation fins, cools the flue gas flowing through the heat dissipation box, thereby quickly reducing the temperature of the flue gas entering the shell and allowing the low-temperature dew point corrosion rate of the heat exchange tube to quickly decrease to below the threshold.

[0019] 4. In this solution, the corrosion rate is monitored at various temperatures and HCl concentrations using a low-temperature dew point corrosion test platform. Based on this precise data, a corrosion rate prediction model is trained that can accurately predict the low-temperature dew point corrosion rate of the outer wall of the heat exchange tube. This model accurately covers the correlation between temperature, HCl concentration, and corrosion rate, providing accurate low-temperature dew point corrosion early warning for the waste heat recovery device in operation, while also improving the service life of the waste heat recovery device. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the main structure of the waste heat recovery device resistant to low-temperature dew point corrosion proposed in this invention. Figure 2 This is a side view of the waste heat recovery device for resisting low-temperature dew point corrosion proposed in this invention. Figure 3 This is a schematic diagram of the low-temperature dew point corrosion test platform structure for the corrosion early warning method of the waste heat recovery device for resisting low-temperature dew point corrosion proposed in this invention. Figure 4 This diagram illustrates the corrosion rate of Q345R steel at different temperatures for the corrosion early warning method of the waste heat recovery device for resisting low-temperature dew point corrosion proposed in this invention. Figure 5 This is a schematic diagram showing the fitting results of the polarization curves of Q345R steel immersed in different temperatures for the corrosion early warning method of the waste heat recovery device for resisting low-temperature dew point corrosion proposed in this invention. Figure 6SEM images of the surface morphology of Q345R steel after immersion corrosion at different temperatures, which is used in the corrosion early warning method of the waste heat recovery device for resisting low-temperature dew point corrosion proposed in this invention. Figure 7 This is a schematic diagram showing the corrosion rate of Q345R steel under different HCl concentrations for the corrosion early warning method of the waste heat recovery device for resisting low-temperature dew point corrosion proposed in this invention. Figure 8 This is a schematic diagram showing the fitting results of the polarization curves of Q345R steel under different HCl concentrations for the corrosion early warning method of the waste heat recovery device for resisting low-temperature dew point corrosion proposed in this invention. Figure 9 This is a schematic SEM image of the surface morphology of Q345R steel after corrosion by liquids of different HCl concentrations, which is used in the corrosion early warning method of the waste heat recovery device for resisting low-temperature dew point corrosion proposed in this invention.

[0021] In the diagram: 1. Shell, 2. Inlet, 3. Outlet, 4. Flue gas inlet, 5. First electrically controlled three-way valve, 6. First flue gas duct, 7. Second flue gas duct, 8. Flue gas exhaust pipe, 9. Second electrically controlled three-way valve, 10. Heat sink, 11. Heat dissipation fins, 12. Coolant circulation pipe, 13. First temperature sensor, 14. Heat exchanger tube, 15. Second temperature sensor, 16. Electrochemical workstation, 17. Oil bath, 18. Multi-port evaporator, 19. Tail gas absorption bottle, 20. Support, 21. Tail gas duct, 22. Pressure limiting valve, 23. Hanging plate, 24. Straight condenser tube, 25. Circulating water pipe inlet, 26. Third temperature sensor, 27. One-way valve, 28. Liquid collection tank, 29. Flue gas outlet, 30. Circulating water pipe outlet. Detailed Implementation

[0022] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0023] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0024] Example 1: Waste heat recovery device resistant to low-temperature dew point corrosion, such as Figure 1-2As shown, the device includes a housing 1, with a flue gas inlet 4 and a flue gas outlet 29 at its two ends. A heat exchange tube 14 is installed on the inner wall of the housing 1, with an air inlet 2 at one end and an air outlet 3 at the other end. A first temperature sensor 13 is installed on the outer wall of the heat exchange tube 14 near the air inlet 2, and a second temperature sensor 15 is installed on the outer wall of the air outlet 3. A first electrically controlled three-way valve 5 is connected to one end of the flue gas inlet 4, and a first smoke guide pipe 6 and a second smoke guide pipe 7 are connected to both ends of the first electrically controlled three-way valve 5. A cooling mechanism is installed on the outer wall of the second smoke guide pipe 7, and a second electrically controlled three-way valve 9 is connected to one end of the first smoke guide pipe 6 and the second smoke guide pipe 7. A flue gas exhaust pipe 8 is connected to one end of the second electrically controlled three-way valve 9.

[0025] The cooling mechanism includes a heat sink 10, heat sink fins 11, and coolant circulation pipes 12. The two ends of the heat sink 10 are connected to the second smoke guide pipe 7. Multiple heat sink fins 11 are equidistantly arranged on the outer walls of both sides of the heat sink 10, and the coolant circulation pipes 12 are respectively arranged on the other two outer walls of the heat sink 10.

[0026] The high-temperature flue gas first enters the first flue pipe 6, which is connected to the second electrically controlled three-way valve 9, through the flue gas discharge pipe 8. Then, it flows into the flue gas inlet 4 through the first electrically controlled three-way valve 5 at the other end of the first flue pipe 6. After entering the shell 1, the high-temperature flue gas exchanges heat with the air flowing inside the heat exchange tube 14. The heated flue gas is discharged out through the outlet 3. The flue gas cooled down by heat exchange is discharged through the flue gas outlet 29 on the other side of the shell 1. The first temperature sensor 13, located at multiple positions on the outer wall of the heat exchange tube 14, can monitor the air temperature near the air inlet 2 and the air temperature about to be discharged through the second temperature sensor 15 in real time. A corrosive liquid will condense on the outer wall of the heat exchange tube 14 inside the housing 1. This liquid drips and collects in the collection tank 28. Operators can periodically open the one-way valve 27 to remove some liquid for HCl content testing. Then, the temperature data and HCl content data for the corresponding time period are input into the trained and deployed corrosion rate prediction model to obtain the predicted low-temperature dew point corrosion rate of the outer wall of the heat exchange tube 14 at that time. When this value... Once the threshold is exceeded, the control terminal located outside the device and electrically connected to the first electrically controlled three-way valve 5 and the second electrically controlled three-way valve 9 will control the first electrically controlled three-way valve 5 and the second electrically controlled three-way valve 9 to close the end connected to the first flue pipe 6 and open the end connected to the second flue pipe 7. This allows the high-temperature steam entering through the flue gas exhaust pipe 8 to dissipate some heat through the heat dissipation fins 11 on the outer wall of the heat dissipation box 10 before entering the interior of the shell 1 for heat exchange. This effectively reduces the temperature of the flue gas entering the interior of the shell 1, thereby reducing the low-temperature dew point corrosion rate of the outer wall of the heat exchange tube 14, achieving the effect of timely warning and improving the service life of the heat exchange tube 14. When the predicted low-temperature dew point corrosion rate of the heat exchange tube 14 has not yet decreased to below the threshold, the two ends of the coolant circulation pipe 12 can be connected to an external coolant circulation and delivery device. The coolant flowing inside the coolant circulation pipe 12, together with the heat dissipation fins 11, cools down the flue gas flowing through the heat dissipation box 10, thereby quickly reducing the temperature of the flue gas entering the shell 1, so that the low-temperature dew point corrosion rate of the heat exchange tube 14 can quickly decrease to below the threshold.

[0027] The heat exchange tube 14 is composed of an inner tube, a corrosion-resistant alloy layer and a nano-composite coating. The corrosion-resistant alloy layer is hot-rolled and bonded to the outer wall of the inner tube, and the nano-composite coating is sprayed onto the outer wall of the corrosion-resistant alloy layer. The thickness of the corrosion-resistant alloy layer is 0.5-2 mm, and the thickness of the nano-composite coating is 10-20 μm. The inner tube is made of Q345R steel, the corrosion-resistant alloy layer is made of 09CrCuSb steel, and the nanocomposite coating is made of fluorosilicone resin, nano-silica and silicon carbide particles.

[0028] Through a hot-rolling composite process, a corrosion-resistant alloy layer made of 09CrCuSb steel is bonded to the outer wall of the inner tube. This layer is the main barrier against corrosion by acidic condensate. On the outer surface of the corrosion-resistant alloy layer, a hydrophobic nanocomposite coating is further coated. This coating is prepared by plasma spraying and its main components are a composite material of fluorosilicone modified resin and nano-silica (SiO2) and silicon carbide (SiC) particles. This nanocomposite coating can reduce the adhesion of condensate to the tube wall, making it difficult for droplets to stay and allowing them to slide off quickly, reducing the contact time and area between the corrosive medium and the metal surface, and improving the overall resistance of the outer wall of the heat exchange tube 14 to low-temperature dew point corrosion.

[0029] Example 2: Corrosion early warning method for waste heat recovery devices resistant to low-temperature dew point corrosion, such as... Figure 3-9 As shown, it includes the following steps: S1: Training and deployment of the corrosion rate prediction model. Using a low-temperature dew point corrosion test platform, the weight loss corrosion rate of Q345R steel at three temperatures of 60°C, 75°C, and 90°C was collected. The weight loss corrosion rate of Q345R steel in HCl liquids of three concentrations of 0.1, 0.5, and 1.0 mol / L was also collected. Based on the above two types of data, the corrosion rate prediction model was trained, and then the trained model was deployed to the intelligent corrosion status diagnosis module in the field. S2: The temperature of the gas flowing in each area of ​​the heat exchange tube 14 is monitored in real time by using the first temperature sensor 13 and the second temperature sensor 15 installed at multiple locations on the outer wall of the heat exchange tube 14. S3: Detect the HCl concentration of the condensate on the outer wall of the heat exchange tube 14 using the electrochemical workstation 16; S4: Input the real-time temperature of the gas flowing in each area of ​​the heat exchange tube 14 and the HCl concentration of the condensate into the corrosion rate prediction model to calculate the predicted corrosion rate of the corresponding area of ​​the heat exchange tube 14 at that temperature and concentration. S5: When the real-time temperature and HCl concentration exceed the threshold, which is 125-180 g / (m2·h), the first electrically controlled three-way valve 5 and the second electrically controlled three-way valve 9 are controlled to close one end connected to the first flue pipe 6 and open one end connected to the second flue pipe 7. The flue gas entering the shell 1 is cooled in time by the cooling mechanism to reduce the internal temperature of the shell 1 and reduce the corrosion rate of the heat exchange tube 14 located inside the shell 1.

[0030] The low-temperature dew point corrosion test platform includes an oil bath 17, a multi-necked evaporator 18, a third temperature sensor 26, a straight condenser tube 24, a hanging plate 23, and an electrochemical workstation 16. The oil bath 17 heats the multi-necked evaporator 18 placed inside. The third temperature sensor 26 is inserted into one end opening of the multi-necked evaporator 18 to monitor the internal temperature of the multi-necked evaporator 18. The straight condenser tube 24 is inserted into the top opening of the multi-necked evaporator 18. The hanging plate 23 is inserted into the top of the straight condenser tube 24. The electrochemical workstation 16 detects the rate of weight loss corrosion of the hanging plate 23. The model of the electrochemical workstation 16 is CorrTest-CS350M.

[0031] The straight condenser tube 24 is provided with a circulating water pipe inlet 25, a circulating water pipe outlet 30 and a pressure limiting valve 22 at both ends. One end of the pressure limiting valve 22 is connected to a tail gas conduit 21, and the bottom end of the tail gas conduit 21 is connected to a tail gas absorption bottle 19. The straight condenser tube 24 and the multi-port evaporator 18 are clamped by a support 20 on their outer walls.

[0032] The lower end of the straight condenser tube 24 is assembled and sealed with the multi-necked evaporator 18, which is placed inside the oil bath 17. The multi-necked evaporator 18 contains a liquid mixture of water and oil. The straight condenser tube 24 has a circulating water pipe inlet 25 through which cooling water flows. The upper end of the straight condenser tube 24 is connected to the tail gas absorption bottle 19 via a tail gas conduit 21 with a pressure limiting valve 22. The test plate 23 is inserted into the top of the straight condenser tube 24, thus forming the dew point corrosion weight loss test device.

[0033] The mixed liquid is placed in a multi-necked evaporator 18 and heated at an oil bath temperature of 135±1℃. The liquid evaporates to produce a continuous mixed steam containing hydrogen chloride, water, and oil. The steam flows through a straight condenser 24 and is cooled by circulating water at 28±1℃ in the circulating water pipe between the inlet 25 and the outlet 30. The steam condenses into droplets that adhere to the surface of the fins 23, causing corrosion. This process simulates the dew point corrosion formation process of heat exchange equipment. The temperature variable is controlled by controlling the temperature of the circulating water in the condenser, and the concentration variable is controlled by changing the concentration of the corrosive solution in the evaporator 18.

[0034] Effect of dew point temperature on corrosion rate: A 0.5 mol / L HCl solution was used as the immersion corrosion solution inside the multi-necked evaporator 18. Three temperature gradients of 60℃, 75℃ and 90℃ were set to study the corrosion rate of the Q345R steel hanging plate 23 under different temperature environments.

[0035] Figure 4 This demonstrates the dew point corrosion rate of the specimens calculated from the results of the weightlessness experiment. Figure 4 It can be seen that as the temperature increases, the corrosion rate of the plate 23 gradually increases. The corrosion rate of the plate 23 is 125.088 g / (m2·h) at 60℃, 205.240 g / (m2·h) at 75℃, and 234.704 g / (m2·h) at 90℃.

[0036] Dew point corrosion weight loss experiments were conducted at different temperatures under the same operating conditions, and the experimental data were fitted to obtain... Figure 5 The electrochemical parameters of the polarization curve of Q345R steel shown in the figure, combined with the graph, show that the trends of the weight loss experiment and the electrochemical experiment are consistent. As the temperature increases, the corrosion rate of the specimen increases.

[0037] Figure 6 The microstructure of the plate 23 after corrosion in solutions at different temperatures is shown. It can be seen that at 60℃, some areas on the surface of the plate 23 are still not completely corroded. As the temperature increases, the corrosion area begins to spread. By 75℃, the uncorroded area on the surface of the plate 23 is extremely small, and the area and depth of the corrosion pits gradually increase.

[0038] The surface of the 90℃ corrosion plate 23 was completely corroded, and it was covered with fine and uniform corrosion spots. The larger but shallow corrosion pits at 75℃ transformed into a denser and deeper corrosion morphology, and the uniform corrosion morphology became more pronounced with increasing temperature. Furthermore, the microscopic images show that the surface of the 90℃ corrosion plate 23 exhibited increased unevenness and numerous depressions. Increased temperature increases the percentage and number of activated molecules, leading to increased effective collisions between molecules and a faster chemical reaction rate. This results in changes in the corrosion morphology and an increase in the degree of corrosion.

[0039] Effect of HCl concentration on corrosion rate: With the temperature variable constant, the temperature of the solution inside the multi-necked evaporator 18 is heated and maintained at 90℃. The concentration of HCl solution inside the multi-necked evaporator 18 is varied to study the corrosion rate of the Q345R steel hanging plate 23 in different concentration environments.

[0040] Figure 7 This demonstrates the dew point corrosion rate of the specimen calculated from the corrosion weight loss experiment results. Figure 7 It can be seen that as the concentration of HCl in the solution increases, the corrosion rate of the weightless coupon 23 gradually increases.

[0041] The corrosion rate of 0.1 mol / L HCl solution on the surface of the pad 23 is 28.176 g / (m2·h), the corrosion rate of 0.5 mol / L HCl solution on the surface of the pad 23 is 234.704 g / (m2·h), and the corrosion rate of 1 mol / L HCl solution on the surface of the pad 23 is 424.968 g / (m2·h).

[0042] Corrosion electrochemical experiments with different HCl concentrations were conducted simultaneously, and the experimental data were fitted to obtain... Figure 8 The electrochemical parameters of the polarization curve of Q345R steel shown are combined with... Figure 8 The data shown indicates that the corrosion rate of the specimen increases with the increase of HCl concentration in the immersion solution.

[0043] The microstructure of the surface of the 23-piece plate after corrosion by HCl solutions of different concentrations is as follows: Figure 9 As shown. Observing the microstructure of the pad 23 after corrosion by 0.1 mol / L HCl solution, it can be found that the corrosion on the surface of the pad 23 is relatively uniform, with dense and uniform small corrosion spots all over it.

[0044] As the concentration of HCl in the solution increases, the surface of the corrosion plate 23 becomes uneven in the 0.5 mol / L HCl solution, with large pits appearing. The surface of the corrosion plate 23 becomes uneven, and the corrosion points on the surface of the corrosion plate 23 become more concentrated. The depth of the corrosion points also increases with the increase of HCl concentration.

[0045] When the HCl concentration in the solution reaches 1 mol / L, the 23 pads corrode and fall off under the high-intensity corrosion reaction. As the chloride ion concentration increases, its penetrating corrosion characteristics also increase, thus forming hollow corrosion pits on the 23 pads.

[0046] This embodiment demonstrates that by adjusting the temperature inside the shell 1, the low-temperature dew point corrosion of the outer wall of the heat exchange tube 14 can be effectively resisted. Furthermore, the corrosion risk of the heat exchange tube 14 can be predicted in advance by using the real-time temperature inside the shell 1 and the HCl concentration of the condensed liquid. The flue gas temperature inside the shell 1 can be timely adjusted by the cooling mechanism, thereby achieving the purpose of timely warning and improving the overall service life of the heat exchange tube 14.

[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A waste heat recovery device resistant to low-temperature dew point corrosion, comprising a shell (1), characterized in that, The casing (1) has a flue gas inlet (4) and a flue gas outlet (29) at both ends. A heat exchange tube (14) is provided on the inner wall of the casing (1). One end of the heat exchange tube (14) is provided with an air inlet (2), and the other end of the heat exchange tube (14) is provided with an air outlet (3). A first temperature sensor (13) is provided on the outer wall of the heat exchange tube (14) near the air inlet (2), and a second temperature sensor (15) is provided on the outer wall of the air outlet (3). One end of the flue gas inlet (4) is connected to the first... An electric three-way valve (5) is provided. The first electric three-way valve (5) is connected to a first smoke guide pipe (6) and a second smoke guide pipe (7) at both ends. A cooling mechanism is provided on the outer wall of the second smoke guide pipe (7). A second electric three-way valve (9) is connected to one end of the first smoke guide pipe (6) and the second smoke guide pipe (7). A flue gas discharge pipe (8) is connected to one end of the second electric three-way valve (9). A liquid collection tank (28) is provided on the bottom outer wall of the housing (1). A one-way valve (27) is provided at the bottom of the liquid collection tank (28).

2. The waste heat recovery device resistant to low-temperature dew point corrosion according to claim 1, characterized in that, The heat exchange tube (14) is composed of an inner tube, a corrosion-resistant alloy layer and a nano-composite coating. The corrosion-resistant alloy layer is hot-rolled and bonded to the outer wall of the inner tube. The nano-composite coating is sprayed onto the outer wall of the corrosion-resistant alloy layer. The thickness of the corrosion-resistant alloy layer is 0.5-2 mm, and the thickness of the nano-composite coating is 10-20 μm. The inner tube is made of Q345R steel, the corrosion-resistant alloy layer is made of 09CrCuSb steel, and the nanocomposite coating is made of fluorosilicone resin, nano-silica and silicon carbide particles.

3. The waste heat recovery device resistant to low-temperature dew point corrosion according to claim 1, characterized in that, The cooling mechanism includes a heat sink (10), heat sink fins (11) and a coolant circulation pipe (12). The two ends of the heat sink (10) are connected to the second smoke pipe (7). Multiple heat sink fins (11) are equidistantly arranged on the outer walls of the two sides of the heat sink (10). The coolant circulation pipes (12) are respectively arranged on the other two outer walls of the heat sink (10).

4. A corrosion early warning method for a waste heat recovery device resistant to low-temperature dew point corrosion, characterized in that, Includes the following steps: S1: Training and deployment of the corrosion rate prediction model; S2: The temperature of the gas flowing in each area of ​​the heat exchange tube (14) is monitored in real time by using a first temperature sensor (13) and a second temperature sensor (15) installed at multiple locations on the outer wall of the heat exchange tube (14). S3: Detect the HCl concentration of the condensate on the outer wall of the heat exchange tube (14) using a testing instrument; S4: Input the real-time temperature of the gas flowing in each area of ​​the heat exchange tube (14) and the HCl concentration of the condensate into the corrosion rate prediction model to calculate the predicted corrosion rate of the corresponding area of ​​the heat exchange tube (14) at the temperature and concentration. S5: When the real-time temperature and HCl concentration exceed the threshold, control the first electric three-way valve (5) and the second electric three-way valve (9) to close the end connected to the first flue pipe (6) and open the end connected to the second flue pipe (7). The cooling mechanism will cool down the flue gas entering the shell (1) in time, reduce the temperature inside the shell (1), and reduce the corrosion rate of the heat exchange tube (14) located inside the shell (1).

5. The corrosion early warning method for the waste heat recovery device resistant to low-temperature dew point corrosion according to claim 4, characterized in that, In S1, the weight loss corrosion rate of Q345R steel at three temperatures of 60°C, 75°C, and 90°C is collected using a low-temperature dew point corrosion test platform.

6. The corrosion early warning method for the waste heat recovery device resistant to low-temperature dew point corrosion according to claim 5, characterized in that, In step S1, the weight loss corrosion rate of Q345R steel in HCl liquids of three concentrations (0.1, 0.5, and 1.0 mol / L) is collected using a low-temperature dew point corrosion test platform. Based on the above two types of data, a corrosion rate prediction model is trained, and then the trained model is deployed to the intelligent corrosion status diagnosis module on site.

7. The corrosion early warning method for a waste heat recovery device resistant to low-temperature dew point corrosion according to claim 6, characterized in that, The low-temperature dew point corrosion test platform includes an oil bath (17), a multi-necked evaporator (18), a third temperature sensor (26), a straight condenser (24), a plate (23), and an electrochemical workstation (16). The oil bath (17) heats the multi-necked evaporator (18) placed inside. The third temperature sensor (26) is inserted into one end of the multi-necked evaporator (18) to monitor the internal temperature of the multi-necked evaporator (18). The straight condenser (24) is inserted into the top opening of the multi-necked evaporator (18). The plate (23) is inserted into the top of the straight condenser (24). The electrochemical workstation (16) detects the rate of weight loss corrosion of the plate (23).

8. The corrosion early warning method for the waste heat recovery device resistant to low-temperature dew point corrosion according to claim 7, characterized in that, The straight condenser tube (24) is provided with a circulating water pipe inlet (25), a circulating water pipe outlet (30), and a pressure limiting valve (22) at both ends. One end of the pressure limiting valve (22) is connected to a tail gas conduit (21), and the bottom end of the tail gas conduit (21) is connected to a tail gas absorption bottle (19). The straight condenser tube (24) and the multi-mouth evaporator (18) are clamped with a support (20).

9. The corrosion early warning method for the waste heat recovery device resistant to low-temperature dew point corrosion according to claim 4, characterized in that, In S3, the detection instrument is an electrochemical workstation (16), and in S5, the threshold is 125-180 g / (m2·h).

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