Flue gas heat exchanger low-temperature dew-point flow corrosion experimental device and method

Abstract

The invention discloses a low-temperature dew-point flow corrosion experimental device and method for a flue gas heat exchanger. A single-tube flue gas heat exchanger test system of the device performs a low-temperature dew-point flow corrosion experiment of a test piece, a gas distribution system provides flue gas, a circulating water system provides water and exchanges heat with the flue gas, a tail gas treatment system recycles tail gas generated by the experiment, and a data acquisition system acquires and displays experimental data. The device is simple and convenient to operate, the low-temperature flow corrosion of the flue gas heat exchanger in a real working environment is simulated, and a low-temperature dew point corrosion mechanism and a corrosion rate model are researched; the device realizes accurate measurement and analysis of the corrosion process by controlling parameters such as flue gas components, temperature, flow and the like in combination with microstructure scanning, material component analysis and a weighing method of a corrosion test piece.

Description

Technical Field

[0001] The invention relates to a corrosion test device and the technical field of low-temperature dew-point flow corrosion, in particular to a low-temperature dew-point flow corrosion test device and method for a flue gas heat exchanger. Background Art

[0002] Flue gas heat exchangers are widely used in industrial production to recover waste heat from flue gas. They are widely used in the fields of electricity, chemical industry, metallurgy, etc. However, during operation in the low-temperature section, acidic gases (such as SO2, SO3) in the flue gas combine with water vapor to form sulfuric acid or sulfurous acid. When the flue gas temperature is lower than the dew point temperature, the acidic liquid condenses on the surface of the heat exchanger, causing serious dew point corrosion problems. In addition, the high-speed flow of flue gas will aggravate corrosion and destroy the protective film on the metal surface, resulting in a significant shortening of equipment life and a decrease in operating efficiency. In the existing technology, the corrosion problem has been alleviated to a certain extent by adopting corrosion-resistant materials (such as stainless steel, nickel-based alloys), surface coatings (such as ceramic coatings, polymer coatings), and optimizing the structure of the heat exchanger. However, the existing flow corrosion experimental equipment does not include an actual flue gas heat exchanger test section. Summary of the Invention

[0003] To address the problems presented in the prior art, the present invention provides a low-temperature dew-point flow corrosion test apparatus and method for flue gas heat exchangers. Combining flow corrosion with a flue gas heat exchanger test section, the present invention simulates the flow heat transfer corrosion of a flue gas waste heat recovery heat exchanger under real-world operating conditions, addressing both flow corrosion and waste heat recovery issues in flue gas heat exchangers under low-temperature dew-point conditions.

[0004] The technical solution adopted in the present invention is:

[0005] 1. Flue gas heat exchanger low temperature dew point flow corrosion test device, including:

[0006] Single-tube flue gas heat exchanger test system used to conduct low-temperature dew point flow corrosion experiments on specimens.

[0007] Gas distribution system used to provide flue gas to the single-tube flue gas heat exchanger test system.

[0008] A circulating water system used to supply water to the single-tube flue gas heat exchanger test system and exchange heat with the flue gas.

[0009] Exhaust gas treatment system used to recover exhaust gas generated by low-temperature dew point flow corrosion experiments.

[0010] A data acquisition system used to collect and display experimental data from low-temperature dew-point flow corrosion experiments.

[0011] The data acquisition system includes a data acquisition instrument, a flow meter, several corrosion-resistant pressure gauges, several corrosion-resistant thermocouples and a rotor flow meter. The data acquisition instrument is electrically connected to the flow meter, each corrosion-resistant pressure gauge, each corrosion-resistant thermocouple and the rotor flow meter. The flow meter is located between the circulating water system and the single-tube flue gas heat exchanger test system. One group of corrosion-resistant pressure gauges and corrosion-resistant thermocouples are located at the air inlet of the single-tube flue gas heat exchanger test system, and another group of corrosion-resistant pressure gauges and corrosion-resistant thermocouples are located at the air outlet of the single-tube flue gas heat exchanger test system. Two of the corrosion-resistant thermocouples are respectively located at the water inlet and water outlet of the single-tube flue gas heat exchanger test system. Several test specimens are arranged in the single-tube flue gas heat exchanger test system, and each test specimen is provided with its own corrosion-resistant thermocouple; the rotor flow meter is located in the gas distribution system.

[0012] The single-tube flue gas heat exchanger test system is a single-tube flue gas heat exchanger, including a single-tube heat exchanger cavity and a square-section water pipe. The square-section water pipe is horizontally and coaxially sleeved in the single-tube heat exchanger cavity. A gap is left between the outer wall of the square-section water pipe and the inner wall of the single-tube heat exchanger cavity as an air chamber, and each test piece is arranged at intervals on the outer wall surface of the square-section water pipe; an air inlet and an air outlet communicating with the air chamber are respectively opened at both ends of the single-tube heat exchanger cavity, and the two ends of the square-section water pipe serve as a water inlet and a water outlet respectively. Two sets of corrosion-resistant pressure gauges and corrosion-resistant thermocouples are respectively located at the air inlet and air outlet of the single-tube heat exchanger cavity, of which two corrosion-resistant thermocouples are respectively located at the water inlet and water outlet of the square-section water pipe.

[0013] The test pieces are made of the same or different corrosion-resistant steel materials, and the test pieces made of the same corrosion-resistant steel materials are sprayed with or not sprayed with an anti-corrosion layer.

[0014] The gas distribution system includes four first pressure reducing valves, four first ball valves, four second pressure reducing valves, four mass flow controllers, four one-way valves, an atomizing heating chamber, a heating element, a container tank, a two-fluid atomizing nozzle, a preheating chamber, a mixing chamber, four high-pressure gas cylinders and a third ball valve. The first, second, third and fourth high-pressure gas cylinders are respectively filled with the first gas, the second gas, the third gas and the fourth gas. Specifically, the first gas, the second gas, the third gas and the fourth gas container tanks are respectively filled with sulfuric acid. The outlet of each high-pressure gas cylinder is connected in sequence to the first pressure reducing valve, the first ball valve, the second pressure reducing valve, the mass flow controller and the first, second, third and fourth gas where the one-way valve is located. Four branches, a dual-fluid atomizing nozzle is installed at the inlet of the atomizing heating chamber, the first high-pressure gas cylinder is connected to the inlet of the atomizing heating chamber through the first branch, the second, third and fourth high-pressure gas cylinders are connected to the mixing chamber through the second, third and fourth branches respectively, the fourth high-pressure gas cylinder is connected to the container tank through the fourth branch and the third ball valve in turn, the mixing chamber, the preheating chamber and the dual-fluid atomizing nozzle are connected in sequence, the sulfuric acid in the container tank is connected to the dual-fluid atomizing nozzle, and the rotor flowmeter is located between the container tank and the dual-fluid atomizing nozzle; the heating element includes an electrically connected heater and a power controller, the heater is electrically connected to the atomizing heating chamber, and the outlet of the atomizing heating chamber is connected to the air inlet of the single-tube heat exchanger cavity.

[0015] The circulating water system includes a circulating pump, a constant-temperature circulating water tank, and a second ball valve. The outlet of the square-section water pipe is sequentially connected to the circulating pump and the inlet of the constant-temperature circulating water tank, which in turn is connected to the second ball valve and the inlet of the square-section water pipe. A flow meter is located between the second ball valve and the inlet of the square-section water pipe. The water in the constant-temperature circulating water tank in the circulating water system is controlled by the second ball valve and flow meter. The water flows through the square-section water pipe, passes through the single-tube flue gas heat exchanger, exchanges heat with the flue gas, and then returns to the constant-temperature circulating water tank through the circulating pump.

[0016] The exhaust gas treatment system includes a chimney and an exhaust gas purification tank. The air outlet of the single-tube heat exchanger cavity is connected to the air inlet of the exhaust gas purification tank, and the air outlet of the exhaust gas purification tank is connected to the external atmosphere through the chimney.

[0017] 2. An experimental method for a low-temperature dew point flow corrosion test device for a flue gas heat exchanger, comprising:

[0018] Before the experiment, dilute sulfuric acid with a preset concentration must be prepared and placed in a container. At the same time, the data acquisition system must be installed and debugged.

[0019] Step 1: After numbering each specimen, perform morphology scanning with a scanning electron microscope (SEM) and weigh the specimen to obtain the initial morphology and initial weight, respectively.

[0020] Step 2: Start the circulation pump. When the constant temperature circulating water tank reaches the preset first temperature, install each test piece in the single-tube flue gas heat exchanger test system and arrange their own corrosion-resistant thermocouples.

[0021] Step 3: Open each high-pressure gas cylinder and adjust the flow on the four branches to their respective preset first flow rates through each mass flow controller. The preset first flow rates on each branch can be the same or different.

[0022] Step 4: Open the preheating chamber and the atomizing heating chamber and adjust the power of the power controller of the heating element to heat the preheating chamber and the atomizing heating chamber until the inlet temperature of the single-tube heat exchanger cavity reaches the preset second temperature; adjust the flow rate of the dilute sulfuric acid in the container tank entering the two-fluid atomizing nozzle to the preset second flow rate through the third ball valve and the rotor flowmeter.

[0023] Step 5: Continue to operate the corrosion test device for more than the preset time period, which is more than 5 hours in specific implementation; then turn off the heating element and each high-pressure gas cylinder until each test piece cools down to room temperature, and turn off the circulation pump.

[0024] Step 6: Take out each specimen, clean and dry it, and then perform morphology scanning with a scanning electron microscope (SEM) and weigh it to obtain the corrosion morphology and corrosion weight respectively. According to the initial morphology and corrosion morphology, use the energy dispersive spectrometer EDS (Energy Dispersive Spectrometer) to perform energy spectrum analysis to obtain the morphology change results of each specimen before and after corrosion; according to the initial weight and corrosion weight, obtain the weight change results of each specimen before and after corrosion; according to the morphology change results and weight change results, use the multivariate nonlinear fitting method to obtain the corrosion rate of each specimen, and realize the low-temperature dew point flow corrosion experiment of the specimen.

[0025] The device of the present invention uses a high-pressure gas pipe equipped with actual flue gas components, which enter the flue gas heat exchanger test section after atomization and heating. It is equipped with a corrosion test piece made of basic steel and sprayed with PPS coating. The corrosion test piece is installed and fixed on the square cross-section water pipe in the heat exchanger. The water in the constant temperature water tank flows into the heat exchanger to exchange heat with the flue gas and then returns to the constant temperature water tank through a circulation pump. The measurement data of the flow meter, corrosion-resistant pressure gauge, and corrosion-resistant thermocouple installed in the test section are collected by a data acquisition instrument. After completing all planned working condition experiments, a data set consisting of images and numerical values ​​of the experimental control parameters, test piece temperature, mass change rate, micromorphology, material composition and content of each numbered test piece is obtained. A flow-heat transfer-mass transfer multi-field coupling model is constructed in combination with the experimental data, and a corrosion rate model is obtained through multivariate nonlinear fitting to obtain the experimental results.

[0026] The beneficial effects of the present invention are:

[0027] The present invention is easy to operate and simulates the low-temperature flow corrosion of the flue gas heat exchanger under a real working environment. It can accurately simulate the actual flue gas environment, build a reliable corrosion rate model based on the actual working environment, and study the low-temperature dew point corrosion mechanism and corrosion rate model. The device controls the flue gas composition, temperature, flow rate and other parameters, combines the microscopic morphology scanning of the corrosion specimen, material composition analysis and weighing method, to achieve accurate measurement and analysis of the corrosion process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the flue gas flow corrosion experimental device of the present invention;

[0029] In the figure: 1. First pressure reducing valve, 2. First ball valve, 3. Second pressure reducing valve, 4. Mass flow controller, 5. Check valve, 6. Circulation pump, 7. Constant temperature circulating water tank, 8. Data acquisition instrument, 9. Flow meter, 10. Test piece, 11. Single tube heat exchanger cavity, 12. Square cross-section water pipe, 13. Chimney, 14. Exhaust gas purification tank, 15. Corrosion-resistant pressure gauge, 16. Corrosion-resistant thermocouple, 17. Atomizing heating chamber, 18. Heating element, 19. Rotor flowmeter, 20. Container tank, 21. Two-fluid atomizing nozzle, 22. Preheating chamber, 23. Mixing chamber, 24. Gas cylinder, 25. Second ball valve, 26. Third ball valve. DETAILED DESCRIPTION

[0030] The principles and features of the present invention are described in detail below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0031] like Figure 1 As shown, the low-temperature dew point flow corrosion experimental device for a flue gas heat exchanger of the present invention includes a single-tube flue gas heat exchanger test system, an air distribution system, a circulating water system, an exhaust gas treatment system and a data acquisition system. The single-tube flue gas heat exchanger test system performs a low-temperature dew point flow corrosion experiment on a test piece 10. The air distribution system provides flue gas to the single-tube flue gas heat exchanger test system. The circulating water system provides water to the single-tube flue gas heat exchanger test system and exchanges heat with the flue gas. The exhaust gas treatment system recovers the exhaust gas generated by the low-temperature dew point flow corrosion experiment. The data acquisition system collects and displays the experimental data of the low-temperature dew point flow corrosion experiment.

[0032] The data acquisition system includes a data acquisition instrument 8, a flow meter 9, several corrosion-resistant pressure gauges 15, several corrosion-resistant thermocouples 16 and a rotor flow meter 19. The data acquisition instrument 8 is electrically connected to the flow meter 9, each corrosion-resistant pressure gauge 15, each corrosion-resistant thermocouple 16 and the rotor flow meter 19. The flow meter 9 is located between the circulating water system and the single-tube flue gas heat exchanger test system. One group of corrosion-resistant pressure gauges 15 and corrosion-resistant thermocouples 16 are located at the air inlet of the single-tube flue gas heat exchanger test system, and another group of corrosion-resistant pressure gauges 15 and corrosion-resistant thermocouples 16 are located at the air outlet of the single-tube flue gas heat exchanger test system. Two corrosion-resistant thermocouples 16 are respectively located at the water inlet and water outlet of the single-tube flue gas heat exchanger test system. Several test specimens 10 are arranged in the single-tube flue gas heat exchanger test system, and each test specimen 10 is provided with its own corrosion-resistant thermocouple 16; the rotor flow meter 19 is located in the gas distribution system. The data acquisition system is connected to the single-tube flue gas heat exchanger test system. A corrosion-resistant pressure gauge 15 and a corrosion-resistant thermocouple 16 are installed at the flue gas inlet and outlet to measure the flue gas pressure and temperature at the inlet and outlet, respectively. A corrosion-resistant pressure gauge 15 and a corrosion-resistant thermocouple 16 are also installed at the inlet and outlet of the square-section water pipe 12 to measure the inlet and outlet pressure and water temperature of the square-section water pipe 12. Furthermore, four corrosion test specimens 10 are fixed on the upper surface of the square-section water pipe 12, each connected to a corrosion-resistant thermocouple 16 to measure the temperature of the test specimen 10. A data acquisition instrument 8 is used to collect the measurement data of all flow meters 9, corrosion-resistant pressure gauges 15, and corrosion-resistant thermocouples 16 of the single-tube flue gas heat exchanger test system to facilitate simultaneous testing.

[0033] The single-tube flue gas heat exchanger test system is a single-tube flue gas heat exchanger, including a single-tube heat exchanger cavity 11 and a square-section water pipe 12. The square-section water pipe 12 is horizontally and coaxially sleeved in the single-tube heat exchanger cavity 11. A gap is left between the outer wall of the square-section water pipe 12 and the inner wall of the single-tube heat exchanger cavity 11 as an air chamber. The test pieces 10 are arranged at intervals on the outer wall of the square-section water pipe 12; the single-tube heat exchanger cavity 11 has an air inlet and an air outlet connected to the air chamber at both ends, and the square-section water pipe 12 has two ends as a water inlet and a water outlet. Two sets of corrosion-resistant pressure gauges 15 and corrosion-resistant thermocouples 16 are respectively located at the air inlet and air outlet of the single-tube heat exchanger cavity 11, of which two corrosion-resistant thermocouples 16 are respectively located at the water inlet and water outlet of the square-section water pipe 12. The test section of the present invention uses water on the tube side and flue gas on the shell side. The square-section water pipe 12 is designed to facilitate the installation and fixation of the corrosion test specimen 10 on the upper surface of the pipe wall. The square-section water pipe 12 of the present invention is made of 20G steel sprayed with PPS coating. The single-tube heat exchanger cavity 11 and the connecting pipe are made of carbon steel Q235B with PPS coating on the inner wall.

[0034] During the specific experiment, the cross-sectional side length of the square cross-sectional water pipe 12 of the single-tube flue gas heat exchanger test system is 20mm-40mm, which can ensure sufficient heat exchange area and avoid excessive flow resistance; the length of the square cross-sectional water pipe 12 is 0.5m-1m, which can provide sufficient heat exchange length; the wall thickness of the square cross-sectional water pipe 12 is controlled at 2mm-4mm, which can withstand the corrosion and pressure in the experiment while avoiding being too heavy or too thick. The square cross-sectional water pipe 12 is assembled in the single-tube heat exchanger cavity 11. The square cross-sectional water pipe 12 is for water on the tube side, and the single-tube heat exchanger cavity 11 is for flue gas on the shell side. The channel cross-sectional size of the single-tube heat exchanger cavity 11 is a rectangle of 100mm×100mm-300mm×300mm. The square cross-sectional water pipe 12 adopts a square cross-sectional design, which is convenient for the corrosion specimen 10 to be installed and fixed on the upper surface of the tube wall of the square cross-sectional water pipe 12. The heat exchange area of ​​the single-tube heat exchanger cavity 11 is approximately 0.1m 2 -0.5m 2 . The square-section water pipe 12 is made of 20G steel sprayed with PPS coating, and the cavity 11 and the connecting pipe of the single-tube heat exchanger are made of carbon steel Q235B and the inner wall is sprayed with PPS coating to achieve the purpose of corrosion resistance. The corrosion test piece 10 is prepared by common basic steel materials such as 20G steel and carbon steel Q235B, and each of them is sprayed with PPS coating. The length of the corrosion test piece 10 is selected from 50mm-100mm, the width is selected from 50mm-100mm, and the thickness is selected from 2mm-5mm. The corrosion test piece 10 is clamped on the surface of the square-section water pipe 12 with a corrosion-resistant clamp. A corrosion test piece 10 is fixed every 100mm-200mm along the length direction of the square-section water pipe 12, and a total of four corrosion test pieces 10 are fixed.

[0035] The test piece 10 is made of the same or different corrosion-resistant steel materials, and the test piece 10 made of the same corrosion-resistant steel material is sprayed with or not sprayed with the anti-corrosion layer polyphenylene sulfide (PPS); the basic steel material of the corrosion test piece 10 and the sprayed PPS coating are selected as experimental samples, and the corrosion test piece 10 is prepared by common basic steel materials such as 20G steel, carbon steel Q235B, etc. and their respective sprayed PPS coatings.

[0036] The gas distribution system includes four first pressure reducing valves 1, four first ball valves 2, four second pressure reducing valves 3, four mass flow controllers 4, four one-way valves 5, an atomizing heating chamber 17, a heating element 18, a container tank 20, a two-fluid atomizing nozzle 21, a preheating chamber 22, a mixing chamber 23, four high-pressure gas cylinders 24 and a third ball valve 26. The first, second, third and fourth high-pressure gas cylinders 24 are respectively filled with the first gas, the second gas, the third gas and the fourth gas. Specifically, the first gas, the second gas, the third gas and the fourth gas container tank 20 are respectively filled with sulfuric acid. The outlet of each high-pressure gas cylinder 24 is connected in sequence to the first, second, third and fourth branches where the respective first pressure reducing valve 1, the first ball valve 2, the second pressure reducing valve 3, the mass flow controller 4 and the one-way valve 5 are located. The two-fluid atomizing nozzle 21 is atomized and heated. A two-fluid atomizing nozzle 21 is installed at the inlet of the atomizing heating chamber 17. The first high-pressure gas cylinder 24 is connected to the inlet of the atomizing heating chamber 17 via a first branch. The second, third, and fourth high-pressure gas cylinders 24 are connected to the mixing chamber 23 via the second, third, and fourth branches, respectively. The fourth high-pressure gas cylinder 24 is connected to the container tank 20 via the fourth branch and the third ball valve 26. The mixing chamber 23, preheating chamber 22, and two-fluid atomizing nozzle 21 are connected in sequence. The sulfuric acid in the container tank 20 is connected to the two-fluid atomizing nozzle 21. A rotor flowmeter 19 is located between the container tank 20 and the two-fluid atomizing nozzle 21. The heating element 18 includes an electrically connected heater and a power controller. The heater is electrically connected to the atomizing heating chamber 17. The outlet of the atomizing heating chamber 17 is connected to the air inlet of the single-tube heat exchanger cavity 11. The atomizing heating chamber 17 is made of carbon steel Q235B with an enameled inner wall for corrosion resistance.

[0037] The gas distribution system uses high-pressure gas cylinders 24 to supply actual flue gas components including sulfur dioxide, carbon dioxide, oxygen, nitrogen, water vapor, and sulfur trioxide. When the temperature falls below a preset threshold, sulfur trioxide exists as sulfuric acid vapor and is blown into the single-tube flue gas heat exchanger from the atomizing and heating chamber 17. The experiment of the present invention prepares a mixed gas based on the actual range of flue gas components, and uses a mass flow controller 4 to control and meter the flow rates of nitrogen, oxygen, carbon dioxide, and sulfur dioxide. Dilute sulfuric acid is atomized through a two-fluid atomizing nozzle 21, and the flow rates of dilute sulfuric acid, water vapor, and sulfuric acid vapor are controlled and metered using a nitrogen bypass ball valve 2 and a rotor flowmeter 19. The concentration of dilute sulfuric acid is determined and adjusted based on the ratio of water vapor to sulfur trioxide in the flue gas.

[0038] The circulating water system includes a circulating pump 6, a constant temperature circulating water tank 7 and a second ball valve 25. The outlet of the square cross-section water pipe 12 is connected to the circulating pump 6 and the water inlet of the constant temperature circulating water tank 7 in sequence, and the outlet of the constant temperature circulating water tank 7 is connected to the water inlet of the square cross-section water pipe 12 in sequence; the flow meter 9 is located between the second ball valve 25 and the water inlet of the square cross-section water pipe 12. The water in the constant temperature circulating water tank 7 in the circulating water system is controlled by the second ball valve 25 and the flow meter 9, passes through the square cross-section water pipe 12 through the single-tube flue gas heat exchanger, exchanges heat with the flue gas, and then returns to the constant temperature circulating water tank 7 through the circulating pump 6. During the experiment, the water temperature of the constant temperature circulating water tank 7 of the circulating water system was between 30℃ and 50℃, and the water flow rate flowing into the square cross-section water pipe 12 was about 0.5m 3 / h-5m 3 / h, with a flow rate of 0.5m / s-2m / s. Water in the constant-temperature circulating water tank 7 flows in through ball valve 2 and is further controlled by flowmeter 9 to enter square-section water pipe 12. After heat exchange, the water returns to the constant-temperature circulating water tank 7 through circulation pump 6. The outlet temperature of square-section water pipe 12 is between 40°C and 70°C.

[0039] The exhaust gas treatment system includes a chimney 13 and an exhaust gas purification tank 14. The air outlet of the single-tube heat exchanger cavity 11 is connected to the air inlet of the exhaust gas purification tank 14, and the air outlet of the exhaust gas purification tank 14 is connected to the outside atmosphere through the chimney 13. The exhaust gas purification tank 14 is filled with an acidic neutralizing liquid to neutralize nitrogen oxides and sulfides in the flue gas. The exhaust gas purification tank 14 of the exhaust gas treatment system is filled with an acidic neutralizing liquid to recover nitrogen oxides and sulfides from the flue gas at the outlet of the single-tube heat exchanger cavity 11. The outlet flue gas temperature is reduced to 30°C-80°C, and the purified harmless gas is discharged into the atmosphere through the chimney 13.

[0040] This study aims to better simulate the actual flue gas environment by designing and constructing a flow corrosion experimental apparatus for a single-tube flue gas heat exchanger based on the actual main components and temperature conditions of flue gas. This experimental apparatus combines scanning electron microscopy (SEM) to scan the micromorphology of the corrosion specimens, energy dispersive spectrometer (EDS) analysis of the material's micro-region composition and elemental analysis, and specimen weighing to investigate the low-temperature dew-point corrosion mechanism and corrosion rate model under flue gas flow conditions. Actual flue gas' main components include sulfur dioxide, carbon dioxide, oxygen, nitrogen, water vapor, and sulfur trioxide. At low temperatures, sulfur trioxide exists as sulfuric acid vapor. The gas distribution system configures the mixed gas according to the actual flue gas component range, with the volume fraction of H2SO4 being 0.001%-0.005%, the volume fraction of H2O being 5%-10%, the volume fraction of SO2 being 0.05%-0.1%, the volume fraction of O2 being 5%-10%, the volume fraction of CO2 being 10%-15%, the volume fraction of SO3 being 0.0001%-0.005%, and the remainder being the volume fraction of nitrogen gas; sulfur dioxide, carbon dioxide, oxygen, and nitrogen are all controlled by a primary pressure reducing valve 1 to control the pressure of the gas flowing out of the gas tank, and then the gas circulation is controlled by a ball valve 2, and the gas pressure is further controlled by a secondary pressure reducing valve 3, the flow of sulfur dioxide, carbon dioxide, oxygen, and nitrogen is controlled and metered by a mass flow controller 4, and the gas circulation is controlled by a one-way valve 5.

[0041] Carbon dioxide, oxygen, and nitrogen flow into mixing chamber 23, where they are evenly mixed before flowing into preheating chamber 22 for preheating and then into atomizing and heating chamber 17. Sulfur dioxide flows directly into atomizing and heating chamber 17. Dilute sulfuric acid in sulfuric acid container tank 20 is atomized by a two-fluid atomizing nozzle 21 and then sprayed into atomizing and heating chamber 17. The flow rates of dilute sulfuric acid, water vapor, and sulfuric acid vapor are regulated and measured using ball valve 2 and rotor flowmeter 19 in the nitrogen branch. The dilute sulfuric acid flow rate ranges from 0.1 L / h to 1 L / h. The appropriate dilute sulfuric acid concentration in sulfuric acid container tank 20 is determined and adjusted based on the ratio of water vapor to sulfur trioxide in the flue gas, approximately 5% to 3%.

[0042] The mixed gas flows into the atomizing heating chamber 17, and the temperature of the mixed gas is controlled by the heater and power controller 18. Then, the mixed gas flows into the flue gas inlet of the single-tube heat exchanger cavity 11. The inlet flue gas flow rate is 1m / s-5m / s, the inlet flue gas flow rate is 35L / min-175L / min, and the inlet flue gas temperature is 80℃-160℃. The outlet flue gas temperature after heat exchange is 30℃-80℃.

[0043] The key experimental steps of the low-temperature dew point flow corrosion test method for flue gas heat exchangers of the present invention are as follows:

[0044] Before the experiment, dilute sulfuric acid of a preset concentration must be prepared and placed in the container tank 20. At the same time, the data acquisition system must be installed and debugged.

[0045] Step 1: After numbering the different test pieces 10 , perform morphology scanning using a scanning electron microscope (SEM) and weigh them to obtain their initial morphology and initial weight.

[0046] Step 2: Start the circulation pump 6 . When the constant temperature circulation water tank 7 reaches the preset first temperature, install each test piece 10 in the single-tube flue gas heat exchanger test system and arrange respective corrosion-resistant thermocouples 16 .

[0047] Step 3: Open each high-pressure gas cylinder 24 and adjust the flow on the four branches to their respective preset first flow rates through each mass flow controller 4. The preset first flow rates on each branch can be the same or different.

[0048] Step 4: Open the preheating chamber 22 and the atomizing heating chamber 17 and adjust the power of the power controller of the heating element 18 to heat the preheating chamber 22 and the atomizing heating chamber 17 until the inlet temperature of the single-tube heat exchanger cavity 11 reaches the preset second temperature; adjust the flow rate of the dilute sulfuric acid in the container tank 20 entering the two-fluid atomizing nozzle 21 to the preset second flow rate through the third ball valve 26 and the rotor flowmeter 19.

[0049] Step 5: Continue to operate the corrosion test device for more than a preset time period, specifically more than 5 hours; then turn off the heating element 18 and each high-pressure gas cylinder 24 until each test piece 10 cools down to room temperature, specifically below 40°C, and turn off the circulation pump 6.

[0050] Step six: Take out each specimen 10 and clean and dry it, then perform morphology scanning with a scanning electron microscope (SEM) and weigh it to obtain the corrosion morphology and corrosion weight respectively. Based on the initial morphology and corrosion morphology, use an energy dispersive spectrometer (EDS) to perform energy spectrum analysis to obtain the morphology change results of each specimen 10 before and after corrosion; based on the initial weight and corrosion weight, obtain the weight change results of each specimen 10 before and after corrosion; based on the morphology change results and the weight change results, use a multivariate nonlinear fitting method to obtain the corrosion rate of each specimen 10, and realize the low-temperature dew point flow corrosion experiment of the specimen 10, where the low temperature is specifically below 160°C.

[0051] According to the above process, all planned working condition experiments were completed, and a data set consisting of images and numerical values ​​of the experimental control parameters, temperature, mass change rate, micromorphology, material composition and content of each numbered specimen 10 was obtained. The heat exchanger flow-heat transfer-mass transfer multi-field coupling calculation model and method constructed by the above research plan were used to carry out experimental working condition modeling and numerical simulation. The measurement data such as the inlet and outlet flue gas temperature and pressure of the single-tube heat exchanger cavity 11, the inlet and outlet temperature and pressure of the square cross-section water pipe 12, and the temperature of the specimen 10 can be used as a basis for verifying the accuracy of the model and numerical method. On this basis, the local component concentration, wall shear stress and its average value of each numbered specimen 10 were obtained, and combined with the above experimental data set to form a complete data set for corrosion mechanism analysis and corrosion rate model construction. Among them, the corrosion rate model intends to obtain the optimal expression through the multivariate function nonlinear fitting method, as follows:

[0052]

[0053] Where f() is the nonlinear fitting of multivariate function; T f is the initial fluid temperature of the wall of the square cross-section water pipe 12, which is taken as the test temperature of the specimen 10; τ f is the average shear stress on specimen 10, and the local average values ​​of the concentrations of each component are determined by numerical calculations; and are the average local concentrations of H2SO4, CO2, N2, and SO2, respectively.

[0054] Through the specific operation of this experimental example, it was found that this method is suitable for studying low-temperature flow corrosion of flue gas. The required measurement parameters are simple and easy to implement, the measurement process is concise and easy to master, and the evaluation indicators are objective. In addition, this experimental device simulates the low-temperature flow corrosion of flue gas heat exchangers under real working conditions, and a reliable corrosion rate model is constructed based on actual working conditions.

[0055] The above description is only a preferred experimental example of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A low-temperature dew point flow corrosion test device for flue gas heat exchangers, characterized in that: include: A single-tube flue gas heat exchanger test system for conducting a low-temperature dew point flow corrosion test on a test piece (10); Gas distribution system for supplying flue gas to the single-tube flue gas heat exchanger test system; Circulating water system used to supply water to the single-tube flue gas heat exchanger test system and exchange heat with the flue gas; Exhaust gas treatment system for recovering exhaust gas generated by low-temperature dew-point flow corrosion experiments; A data acquisition system used to collect and display experimental data from low-temperature dew-point flow corrosion experiments.

2. The low-temperature dew point flow corrosion test device for flue gas heat exchangers according to claim 1 is characterized in that: The data acquisition system includes a data acquisition instrument (8), a flow meter (9), a plurality of corrosion-resistant pressure gauges (15), a plurality of corrosion-resistant thermocouples (16) and a rotor flow meter (19), wherein the data acquisition instrument (8) is electrically connected to the flow meter (9), each corrosion-resistant pressure gauge (15), each corrosion-resistant thermocouple (16) and the rotor flow meter (19), and the flow meter (9) is located between the circulating water system and the single-tube flue gas heat exchanger test system, wherein a group of corrosion-resistant pressure gauges (15) and corrosion-resistant thermocouples (16) are connected to the flow meter (9). Located at the air inlet of the single-tube flue gas heat exchanger test system, another set of corrosion-resistant pressure gauges (15) and corrosion-resistant thermocouples (16) are located at the air outlet of the single-tube flue gas heat exchanger test system, wherein two corrosion-resistant thermocouples (16) are respectively located at the water inlet and water outlet of the single-tube flue gas heat exchanger test system. Several test pieces (10) are arranged in the single-tube flue gas heat exchanger test system, and each test piece (10) is provided with its own corrosion-resistant thermocouple (16); a rotor flowmeter (19) is located in the gas distribution system.

3. The low-temperature dew point flow corrosion test device for flue gas heat exchangers according to claim 2 is characterized by: The single-tube flue gas heat exchanger test system is a single-tube flue gas heat exchanger, comprising a single-tube heat exchanger cavity (11) and a square-section water pipe (12), wherein the square-section water pipe (12) is horizontally coaxially sleeved in the single-tube heat exchanger cavity (11), and a gap is left between the outer wall of the square-section water pipe (12) and the inner wall of the single-tube heat exchanger cavity (11) as an air chamber, and each test piece (10) is arranged at intervals on the outer wall surface of the square-section water pipe (12); an air inlet and an air outlet communicating with the air chamber are respectively opened at both ends of the single-tube heat exchanger cavity (11), and the two ends of the square-section water pipe (12) serve as a water inlet and a water outlet, respectively. Two sets of corrosion-resistant pressure gauges (15) and corrosion-resistant thermocouples (16) are respectively located at the air inlet and the air outlet of the single-tube heat exchanger cavity (11), wherein two corrosion-resistant thermocouples (16) are respectively located at the water inlet and the water outlet of the square-section water pipe (12).

4. The low-temperature dew point flow corrosion test device for flue gas heat exchangers according to claim 2 is characterized by: The test piece (10) is made of the same or different corrosion-resistant steel materials, and the test piece (10) made of the same corrosion-resistant steel material is sprayed with or not sprayed with an anti-corrosion layer.

5. The low-temperature dew point flow corrosion test device for flue gas heat exchangers according to claim 3 is characterized by: The gas distribution system comprises four first pressure reducing valves (1), four first ball valves (2), four second pressure reducing valves (3), four mass flow controllers (4), four one-way valves (5), an atomizing heating chamber (17), a heating element (18), a container tank (20), a two-fluid atomizing nozzle (21), a preheating chamber (22), a mixing chamber (23), four gas cylinders (24) and a third ball valve (26). The first, second, third and fourth gas cylinders (24) are respectively filled with the first gas, the second gas, the third gas and the fourth gas. The container tank (20) is filled with sulfuric acid. The outlet of each gas cylinder (24) is connected in sequence to the first, second, third and fourth branches where the first pressure reducing valve (1), the first ball valve (2), the second pressure reducing valve (3), the mass flow controller (4) and the one-way valve (5) are located. The two-fluid atomizing nozzle (21) is installed. At the inlet of the atomizing heating chamber (17), the first gas cylinder (24) is connected to the inlet of the atomizing heating chamber (17) through the first branch, the second, third and fourth gas cylinders (24) are connected to the mixing chamber (23) through the second, third and fourth branches respectively, the fourth gas cylinder (24) is connected to the container tank (20) through the fourth branch and the third ball valve (26) in sequence, the mixing chamber (23), the preheating chamber (22) and the two-fluid atomizing nozzle (21) are connected in sequence, the sulfuric acid in the container tank (20) is connected to the two-fluid atomizing nozzle (21), and the rotor flowmeter (19) is located between the container tank (20) and the two-fluid atomizing nozzle (21); the heating element (18) includes an electrically connected heater and a power controller, the heater is electrically connected to the atomizing heating chamber (17), and the outlet of the atomizing heating chamber (17) is connected to the air inlet of the single-tube heat exchanger cavity (11).

6. The low-temperature dew point flow corrosion test device for flue gas heat exchangers according to claim 3 is characterized by: The circulating water system comprises a circulating pump (6), a constant temperature circulating water tank (7) and a second ball valve (25); the water outlet of the square cross-section water pipe (12) is sequentially connected to the circulating pump (6) and the water inlet of the constant temperature circulating water tank (7); the water outlet of the constant temperature circulating water tank (7) is sequentially connected to the second ball valve (25) and the water inlet of the square cross-section water pipe (12); and the flow meter (9) is located between the second ball valve (25) and the water inlet of the square cross-section water pipe (12).

7. The low-temperature dew point flow corrosion test device for flue gas heat exchangers according to claim 3 is characterized by: The exhaust gas treatment system comprises a chimney (13) and an exhaust gas purification tank (14); the air outlet of the single-tube heat exchanger cavity (11) is connected to the air inlet of the exhaust gas purification tank (14); and the air outlet of the exhaust gas purification tank (14) is connected to the external atmosphere through the chimney (13).

8. The experimental method of the low-temperature dew point flow corrosion experimental device for flue gas heat exchangers according to any one of claims 1 to 7, characterized in that: include: Step 1: After numbering each different specimen (10), perform morphology scanning using a scanning electron microscope (SEM) and weigh the specimen to obtain the initial morphology and initial weight, respectively; Step 2: Start the circulation pump (6), and when the constant temperature circulation water tank (7) reaches a preset first temperature, install each test piece (10) in the single-tube flue gas heat exchanger test system and arrange respective corrosion-resistant thermocouples (16); Step 3: Open each gas cylinder (24), and adjust the flow rate on the four branches to the respective preset first flow rates through each mass flow controller (4); Step 4: opening the preheating chamber (22) and the atomizing heating chamber (17) and adjusting the power of the power controller of the heating element (18) to heat the preheating chamber (22) and the atomizing heating chamber (17) until the inlet temperature of the single-tube heat exchanger cavity (11) reaches a preset second temperature; regulating the flow rate of the dilute sulfuric acid in the container tank (20) entering the two-fluid atomizing nozzle (21) to the preset second flow rate through the third ball valve (26) and the rotor flowmeter (19); Step 5: Continuously operate the corrosion test device for a predetermined period of time, then turn off the heating element (18) and each gas cylinder (24), until each test piece (10) cools down to room temperature, and then turn off the circulation pump (6); Step 6: Each specimen (10) is taken out and cleaned and dried, and then scanned and weighed using a scanning electron microscope (SEM) to obtain the corrosion morphology and corrosion weight, respectively. Based on the initial morphology and corrosion morphology, an energy dispersive spectrometer (EDS) is used to perform energy spectrum analysis to obtain the morphology change results of each specimen (10) before and after corrosion; based on the initial weight and corrosion weight, the weight change results of each specimen (10) before and after corrosion are obtained; based on the morphology change results and the weight change results, the corrosion rate of each specimen (10) is obtained using a multivariate nonlinear fitting method to realize the low-temperature dew point flow corrosion experiment of the specimen (10).

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