A temperature zoning based ammonia decomposition reactor mitigation corrosion control method

Abstract

This invention proposes a corrosion mitigation control method for ammonia decomposition reactors based on temperature zoning. The method is characterized by: establishing a "material-temperature-weight change rate" mapping spectrum to divide corrosion characteristic zones; and using this spectrum to formulate temperature control strategies for the corrosive environment of the high-temperature ammonia atmosphere inside the ammonia decomposition reactor. Simultaneously, based on the non-monotonic temperature-dependent corrosion law of stainless steel in an ammonia environment, material selection is optimized to reduce the weight change rate of structural components in the ammonia decomposition reactor, thereby extending the overall service life of the reactor and improving the safety margin and economy of the ammonia decomposition reactor system. This invention, by establishing a "material-temperature-weight change rate" mapping spectrum to divide corrosion characteristic zones and using this as the core to formulate temperature control strategies, significantly reduces the weight change rate of key structural components, extends the overall service life of the reactor, and improves the safety margin and economy of the system operation.

Description

Technical Field

[0001] This invention relates to the field of ammonia decomposition reaction technology, and in particular to a method for slowing down corrosion control in an ammonia decomposition reactor based on temperature zoning. Background Technology

[0002] The ammonia decomposition reactor is the core device in the ammonia-hydrogen energy conversion route, and its long-term safe and stable operation has a significant impact on the economy and reliability of the hydrogen energy system. Currently, austenitic stainless steels such as 304 and 310S are commonly used as structural materials for this type of reactor. In a high-temperature ammonia atmosphere, stainless steel materials undergo severe nitriding corrosion, leading to the formation of a brittle nitride layer on the material surface, causing cracks and spalling, and significantly reducing the material's yield strength, tensile strength, and elongation, seriously threatening the structural integrity and service safety of the reactor.

[0003] In existing technologies, reactor operating temperature settings are primarily based on chemical reaction kinetics and energy efficiency considerations, generally lacking systematic research on the differences in corrosion behavior of structural materials within specific temperature ranges. For example, neither published literature nor engineering practice clearly indicates that there exists a specific "accelerated corrosion temperature range" for 304 stainless steel and 310S stainless steel, within which operation drastically shortens equipment lifespan. Currently published studies on high-temperature ammonia corrosion only provide scattered temperature point data, lacking systematic temperature-dependent patterns. Empirical temperature control is used in engineering practice, failing to accurately identify the critical temperature range for accelerated corrosion of materials, leading to the risk of unexpected reactor failure.

[0004] Current reactor temperature control strategies are mostly based on simple feedback from process parameters, failing to respond to changes in material corrosion states. There is a lack of a temperature optimization method based on material corrosion characteristics to proactively avoid high-corrosion-risk zones and achieve a balance between safety and economy. Existing detection methods rely solely on weight gain methods or surface observation, lacking the establishment of a multi-scale evaluation system that combines microstructure characterization, phase analysis, and mechanical property degradation assessment. This fails to provide comprehensive data support for the structural integrity management of ammonia decomposition reactors, encompassing corrosion kinetics, microscopic damage mechanisms, and mechanical property degradation.

[0005] Traditionally, it has been believed that 310S stainless steel, with its high Cr and Ni content, exhibits superior corrosion resistance compared to 304 stainless steel. However, the impact of Cr and Ni elements on corrosion behavior in high-temperature ammonia environments has not been clearly understood, leading to misconceptions in material selection. In high-temperature ammonia environments, 310S actually exhibits more severe accelerated corrosion due to the synergistic effect of Cr and Ni, with its maximum weight change rate reaching twice that of 304, and the corrosion layer is accompanied by severe cracking.

[0006] This invention proposes a solution to the above problems. Summary of the Invention

[0007] This invention proposes a corrosion mitigation control method for ammonia decomposition reactors based on temperature zoning. It systematically applies the kinetic research results on high-temperature ammonia corrosion in materials science to the engineering design and operation control of the reactor. By establishing a "material-temperature-weight change rate" mapping spectrum, corrosion characteristic intervals are divided, and a temperature control strategy is formulated based on this. This significantly reduces the weight change rate of key structural components, extends the overall service life of the reactor, and improves the safety margin and economy of the system operation.

[0008] The present invention adopts the following technical solution.

[0009] A temperature-zone-based corrosion control method for ammonia decomposition reactors is proposed. This method systematically applies the kinetic research results on high-temperature ammonia corrosion in materials science to the engineering design and operation control of the reactor. By establishing a "material-temperature-weight change rate" mapping spectrum, corrosion characteristic zones are divided, and temperature control strategies are formulated for the corrosive environment of the high-temperature ammonia atmosphere inside the ammonia decomposition reactor. At the same time, based on the temperature-dependent corrosion non-monotonic law of 304 and 310S stainless steel in the ammonia environment revealed by the multi-factor experimental design system, material selection optimization is carried out to significantly reduce the weight change rate of key structural components of the ammonia decomposition reactor, thereby extending the overall service life of the reactor and improving the safety margin and economy of the ammonia decomposition reactor system.

[0010] The method includes the following steps;

[0011] Step 1: Corrosion experiments were conducted using an ammonia decomposition reaction simulation device to simulate the ammonia decomposition reactor and establish a multi-scale synergistic characterization system.

[0012] Step 2: Corrosion kinetics modeling;

[0013] Step 3: Material selection decision.

[0014] In step one, based on the corrosion experiment results, the following are performed: analysis of material weight gain changes, observation of microstructure in the corrosion assessment area, quantitative analysis of element diffusion, identification of phase transformation of corrosion products, and assessment of mechanical property degradation.

[0015] In step one, the corrosion environment in the corrosion experiment is a high-temperature ammonia atmosphere inside the ammonia decomposition reactor, with an ammonia purity ≥99.8%. The ammonia flow rate is controlled at 2L / min during the corrosion process, the corrosion test time is set to 80h, and the pressure inside the reaction tube is atmospheric pressure.

[0016] The ammonia decomposition reaction simulation device consists of a Hastelloy reaction tube with a height of 600 mm and an inner diameter of 60 mm and a three-section heating furnace with a height of 500 mm. The reaction tube is equipped with a sample support frame, and the three-section heating furnace is equipped with three independently adjustable heaters.

[0017] In step one, the microstructure observation of the microstructure corrosion evaluation area is conducted in an area with dimensions of 15×15×3mm. 3 The upper surface and cross section of the stainless steel block sample were examined. After the upper surface of the block sample was polished with 180-2000# sandpaper and ultrasonically cleaned and dried, it was placed on the sample support frame inside the reaction tube of the ammonia decomposition reactor for corrosion. The surface of the corroded block sample was observed. After the cross section sample was made by resin embedding and curing, the cross section was polished, cleaned and dried before the cross section reaction layer was observed.

[0018] The mechanical property degradation assessment was performed by suspending a plate-shaped tensile specimen on a support frame inside the ammonia decomposition reactor and conducting tensile tests on the corroded tensile specimen.

[0019] Material weight gain analysis includes macroscopic weight gain analysis.

[0020] In step one, the experimental materials for the multi-scale synergistic characterization system are 304 austenitic stainless steel and 310S austenitic stainless steel samples with a sample size of 15mm × 15mm × 3mm; the multi-scale synergistic characterization system is obtained in an ammonia decomposition reaction simulation device (see...). Figure 2 ),

[0021] The ammonia purity was ≥99.8%, the corrosion time was 80 hours, and the corrosion temperature of 304 stainless steel was set at 8 characteristic temperature points: 400℃, 450℃, 500℃, 550℃, 575℃, 600℃, 650℃, and 700℃. The corrosion temperature of 310S stainless steel was set at 9 characteristic temperature points: 400℃, 450℃, 470℃, 500℃, 530℃, 550℃, 600℃, 650℃, and 700℃. Two sets of parallel samples were set at each temperature point.

[0022] The macroscopic weight gain analysis was performed using an electronic balance (accuracy 0.0001g) to weigh the samples and calculate the weight change rate (g / h). The average weight change rate of two parallel samples was taken as the final result.

[0023] In step one, the macroscopic weight gain analysis uses a high-precision balance (accuracy 0.0001g) to weigh and calculate the corrosion kinetic curve;

[0024] The formula for calculating the rate of weight change is: ;

[0025] In the formula, V is the rate of weight change of the metal; M0 is the weight before corrosion (g); M1 is the weight after corrosion (g); and t is the corrosion time (h).

[0026] In the microstructure observation of the corrosion assessment area, the microstructure observation uses SEM to analyze the surface microstructure and cross-sectional reaction layer morphology and crack characteristics after corrosion, and measures the reaction layer thickness at different temperatures.

[0027] The quantitative elemental diffusion method uses EDS surface scanning to obtain nitrogen elemental distribution and line scanning to obtain nitrogen elemental concentration gradient;

[0028] The phase transformation identification was performed using XRD analysis to determine the precipitation patterns of the brittle phases of CrN and Fe4N at different corrosion temperatures.

[0029] The mechanical property degradation assessment obtains data on the decrease in yield strength, tensile strength, and elongation through tensile tests.

[0030] The microstructure observation was performed using a QUANTA 250 tungsten filament scanning electron microscope (SEM) to analyze the corroded surface and the cross-section of the corroded layer, focusing on the crack propagation characteristics, spalling behavior, and nitriding layer thickness.

[0031] The quantitative elemental diffusion analysis included nitrogen atom diffusion detection, using a QUANTA 250 tungsten filament scanning electron microscope for line scanning and area distribution analysis to obtain nitrogen elemental distribution and quantitatively characterize nitriding behavior. The phase transformation identification employed a RIGAKUSmartlab X-ray diffractometer (XRD) to analyze the phase composition of the corrosion layer, with a scanning angle of 10-90 degrees and a scanning speed of 10 degrees / minute, focusing on identifying the precipitation patterns of brittle phases such as CrN and Fe4N. The mechanical property degradation assessment used an ETM204C microcomputer-controlled electronic universal testing machine to conduct tensile tests at a tensile rate of 0.001 / s, testing the yield strength, tensile strength, and elongation of the corroded specimens and comparing them with uncorroded specimens.

[0032] In step two, a three-stage corrosion mode classification and alloy composition influence mechanism analysis are performed. Based on the multi-scale characterization data obtained in step one, non-monotonic curves of weight change rate-temperature for 304 and 310S stainless steel are plotted (see...). Figure 3 );

[0033] The three-stage corrosion mode is divided as follows:

[0034] Slight corrosion stage: 304 stainless steel: 400℃-500℃; 310S stainless steel: 400℃-450℃;

[0035] Accelerated corrosion stage: 304 stainless steel: 550℃-600℃; 310S stainless steel: 470℃-530℃;

[0036] Corrosion slowdown stage: 304 stainless steel: 650℃-700℃; 310S stainless steel: 550℃-700℃.

[0037] The mechanism of influence of alloy composition reveals that: high Cr content in 310S stainless steel promotes rapid nucleation of CrN, and Ni reduces nitrogen solid solubility, leading to premature saturation. The synergistic effect of the two causes the accelerated corrosion range to shift to a lower temperature and exacerbates the peak weight change rate.

[0038] The corrosion kinetics modeling is based on multi-scale characterization data, and non-monotonic curves of weight change rate versus temperature are plotted for 304 and 310S stainless steel (see [reference]). Figure 3 Based on the combined corrosion kinetics and multi-scale characterization results, the three-stage corrosion mode was identified as follows: for 304 stainless steel, the corrosion was characterized by a slight corrosion stage (400-500℃), an accelerated corrosion stage (550-600℃), and a slowing corrosion stage (650-700℃); for 310S stainless steel, the corrosion was characterized by a slight corrosion stage (400-450℃), an accelerated corrosion stage (470-530℃), and a slowing corrosion stage (550-700℃).

[0039] In step three, a material with a lower degree of corrosion at the system operating temperature of the ammonia decomposition reaction simulation device is selected.

[0040] In step three, when the material of the ammonia decomposition reactor has been determined to be 304 or 310S stainless steel, the operating temperature should be set to avoid the accelerated corrosion temperature range of each of these two steel types. When the designed operating temperature is consistently in the range of 470℃-530℃, 310S stainless steel should be used with caution. When the operating temperature is in the range of 550℃-600℃, 304 stainless steel should be used with caution.

[0041] The selection decision is based on the reactor's designed operating temperature range (see [link]). Figure 4 When the reactor operates continuously at a temperature between 400℃ and 450℃, 304 stainless steel is preferred, but 310S stainless steel can also be used. When the operating temperature is between 450℃ and 530℃, 304 stainless steel is preferred, as 310S stainless steel exhibits severely accelerated corrosion behavior due to its high chromium content in this range; therefore, 310S stainless steel should be used with caution. When the operating temperature is between 530℃ and 650℃, 310S stainless steel can be used, but 304 stainless steel should be used with caution. When the operating temperature is between 650℃ and 700℃, either 304 or 310S stainless steel can be used.

[0042] This invention provides a corrosion mitigation control method for ammonia decomposition reactors based on temperature zoning. It systematically applies the kinetic research findings on high-temperature ammonia corrosion from materials science to the engineering design and operation control of the reactor. By establishing a "material-temperature-weight change rate" mapping spectrum, corrosion characteristic zones are defined, and a temperature control strategy is formulated based on this. This significantly reduces the weight change rate of key structural components, extends the overall service life of the reactor, and improves the safety margin and economy of the system operation.

[0043] The selection and optimization method provided by this invention reveals the non-monotonic temperature-dependent corrosion law of 304 and 310S stainless steels in ammonia environments through a multi-factor experimental design system. The multi-scale characterization system achieves cross-scale analysis from macroscopic weight gain to microscopic damage mechanisms, supplementing the corrosion data of austenitic stainless steel in pure ammonia environments. The synergistic effect mechanism of Cr / Ni content corrects the technical bias that "high alloy content necessarily means high corrosion resistance," providing a theoretical basis for the cautious use of 310S stainless steel in the 470-530℃ range, and improving the safety and economic efficiency of ammonia-to-hydrogen systems. Attached Figure Description

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0045] Appendix Figure 1 This is a schematic diagram of the method flow of the present invention;

[0046] Appendix Figure 2 This is a schematic diagram of the experimental setup;

[0047] Appendix Figure 3 Schematic diagram of the non-monotonic curves of weight change rate-temperature for 304 and 310S stainless steel.

[0048] Appendix Figure 4 This is a diagram illustrating the selection and decision-making process; Figure 4 Medium: Temperature zones 400℃-450℃, 450℃-530℃, 530℃-600℃, 600℃-700℃; Material recommendations: A (preferred), B (usable), C (use with caution).

[0049] In the diagram: 1. Ammonia cylinder; 2. Pressure reducing valve; 3. Flow control panel; 4. Ammonia decomposition reaction tube; 5. Sample; 6. Heating furnace; 7. Heating furnace thermocouple; 8. Temperature control panel. Detailed Implementation

[0050] As shown in the figure, a corrosion control method for an ammonia decomposition reactor based on temperature zoning is presented. This method systematically applies the kinetic research results on high-temperature ammonia corrosion in materials science to the engineering design and operation control of the reactor. By establishing a "material-temperature-weight change rate" mapping spectrum, corrosion characteristic intervals are divided, and a temperature control strategy is formulated for the corrosive environment of the high-temperature ammonia atmosphere inside the ammonia decomposition reactor. At the same time, based on the non-monotonic temperature-dependent corrosion law of 304 and 310S stainless steel in the ammonia environment revealed by the multi-factor experimental design system, material selection optimization is carried out to significantly reduce the weight change rate of key structural components of the ammonia decomposition reactor, thereby extending the overall service life of the reactor and improving the safety margin and economy of the ammonia decomposition reactor system operation.

[0051] The method includes the following steps;

[0052] Step 1: Corrosion experiments were conducted using an ammonia decomposition reaction simulation device to simulate the ammonia decomposition reactor and establish a multi-scale synergistic characterization system.

[0053] Step 2: Corrosion kinetics modeling;

[0054] Step 3: Material selection decision.

[0055] In step one, based on the corrosion experiment results, the following are performed: analysis of material weight gain changes, observation of microstructure in the corrosion assessment area, quantitative analysis of element diffusion, identification of phase transformation of corrosion products, and assessment of mechanical property degradation.

[0056] In step one, the corrosion environment in the corrosion experiment is a high-temperature ammonia atmosphere inside the ammonia decomposition reactor, with an ammonia purity ≥99.8%. The ammonia flow rate is controlled at 2L / min during the corrosion process, the corrosion test time is set to 80h, and the pressure inside the reaction tube is atmospheric pressure.

[0057] The ammonia decomposition reaction simulation device consists of a Hastelloy reaction tube with a height of 600 mm and an inner diameter of 60 mm and a three-section heating furnace with a height of 500 mm. The reaction tube is equipped with a sample support frame, and the three-section heating furnace is equipped with three independently adjustable heaters.

[0058] In step one, the microstructure observation of the microstructure corrosion evaluation area is conducted in an area with dimensions of 15×15×3mm. 3 The upper surface and cross section of the stainless steel block sample were examined. After the upper surface of the block sample was polished with 180-2000# sandpaper and ultrasonically cleaned and dried, it was placed on the sample support frame inside the reaction tube of the ammonia decomposition reactor for corrosion. The surface of the corroded block sample was observed. After the cross section sample was made by resin embedding and curing, the cross section was polished, cleaned and dried before the cross section reaction layer was observed.

[0059] The mechanical property degradation assessment was performed by suspending a plate-shaped tensile specimen on a support frame inside the ammonia decomposition reactor and conducting tensile tests on the corroded tensile specimen.

[0060] Material weight gain analysis includes macroscopic weight gain analysis.

[0061] In step one, the experimental materials for the multi-scale synergistic characterization system are 304 austenitic stainless steel and 310S austenitic stainless steel samples with a sample size of 15mm × 15mm × 3mm; the multi-scale synergistic characterization system is obtained in an ammonia decomposition reaction simulation device (see...). Figure 2 ),

[0062] The ammonia purity was ≥99.8%, the corrosion time was 80 hours, and the corrosion temperature of 304 stainless steel was set at 8 characteristic temperature points: 400℃, 450℃, 500℃, 550℃, 575℃, 600℃, 650℃, and 700℃. The corrosion temperature of 310S stainless steel was set at 9 characteristic temperature points: 400℃, 450℃, 470℃, 500℃, 530℃, 550℃, 600℃, 650℃, and 700℃. Two sets of parallel samples were set at each temperature point.

[0063] The macroscopic weight gain analysis was performed using an electronic balance (accuracy 0.0001g) to weigh the samples and calculate the weight change rate (g / h). The average weight change rate of two parallel samples was taken as the final result.

[0064] In step one, the macroscopic weight gain analysis uses a high-precision balance (accuracy 0.0001g) to weigh and calculate the corrosion kinetic curve;

[0065] The formula for calculating the rate of weight change is: ;

[0066] In the formula, V is the rate of weight change of the metal; M0 is the weight before corrosion (g); M1 is the weight after corrosion (g); and t is the corrosion time (h).

[0067] In the microstructure observation of the corrosion assessment area, the microstructure observation uses SEM to analyze the surface microstructure and cross-sectional reaction layer morphology and crack characteristics after corrosion, and measures the reaction layer thickness at different temperatures.

[0068] The quantitative elemental diffusion method uses EDS surface scanning to obtain nitrogen elemental distribution and line scanning to obtain nitrogen elemental concentration gradient;

[0069] The phase transformation identification was performed using XRD analysis to determine the precipitation patterns of the brittle phases of CrN and Fe4N at different corrosion temperatures.

[0070] The mechanical property degradation assessment obtains data on the decrease in yield strength, tensile strength, and elongation through tensile tests.

[0071] The microstructure observation was performed using a QUANTA 250 tungsten filament scanning electron microscope (SEM) to analyze the corroded surface and the cross-section of the corroded layer, focusing on the crack propagation characteristics, spalling behavior, and nitriding layer thickness.

[0072] The quantitative elemental diffusion analysis included nitrogen atom diffusion detection, using a QUANTA 250 tungsten filament scanning electron microscope for line scanning and area distribution analysis to obtain nitrogen elemental distribution and quantitatively characterize nitriding behavior. The phase transformation identification employed a RIGAKUSmartlab X-ray diffractometer (XRD) to analyze the phase composition of the corrosion layer, with a scanning angle of 10-90 degrees and a scanning speed of 10 degrees / minute, focusing on identifying the precipitation patterns of brittle phases such as CrN and Fe4N. The mechanical property degradation assessment used an ETM204C microcomputer-controlled electronic universal testing machine to conduct tensile tests at a tensile rate of 0.001 / s, testing the yield strength, tensile strength, and elongation of the corroded specimens and comparing them with uncorroded specimens.

[0073] In step two, a three-stage corrosion mode classification and alloy composition influence mechanism analysis are performed. Based on the multi-scale characterization data obtained in step one, non-monotonic curves of weight change rate-temperature for 304 and 310S stainless steel are plotted (see...). Figure 3 );

[0074] The three-stage corrosion mode is divided as follows:

[0075] Slight corrosion stage: 304 stainless steel: 400℃-500℃; 310S stainless steel: 400℃-450℃;

[0076] Accelerated corrosion stage: 304 stainless steel: 550℃-600℃; 310S stainless steel: 470℃-530℃;

[0077] Corrosion slowdown stage: 304 stainless steel: 650℃-700℃; 310S stainless steel: 550℃-700℃.

[0078] The mechanism of influence of alloy composition reveals that: high Cr content in 310S stainless steel promotes rapid nucleation of CrN, and Ni reduces nitrogen solid solubility, leading to premature saturation. The synergistic effect of the two causes the accelerated corrosion range to shift to a lower temperature and exacerbates the peak weight change rate.

[0079] The corrosion kinetics modeling is based on multi-scale characterization data, and non-monotonic curves of weight change rate versus temperature are plotted for 304 and 310S stainless steel (see [reference]). Figure 3Based on the combined corrosion kinetics and multi-scale characterization results, the three-stage corrosion mode was identified as follows: for 304 stainless steel, the corrosion was characterized by a slight corrosion stage (400-500℃), an accelerated corrosion stage (550-600℃), and a slowing corrosion stage (650-700℃); for 310S stainless steel, the corrosion was characterized by a slight corrosion stage (400-450℃), an accelerated corrosion stage (470-530℃), and a slowing corrosion stage (550-700℃).

[0080] In step three, a material with a lower degree of corrosion at the system operating temperature of the ammonia decomposition reaction simulation device is selected.

[0081] In step three, when the material of the ammonia decomposition reactor has been determined to be 304 or 310S stainless steel, the operating temperature should be set to avoid the accelerated corrosion temperature range of each of these two steel types. When the designed operating temperature is consistently in the range of 470℃-530℃, 310S stainless steel should be used with caution. When the operating temperature is in the range of 550℃-600℃, 304 stainless steel should be used with caution.

[0082] The selection decision is based on the reactor's designed operating temperature range (see [link]). Figure 4 When the reactor operates continuously at a temperature between 400℃ and 450℃, 304 stainless steel is preferred, but 310S stainless steel can also be used. When the operating temperature is between 450℃ and 530℃, 304 stainless steel is preferred, as 310S stainless steel exhibits severely accelerated corrosion behavior due to its high chromium content in this range; therefore, 310S stainless steel should be used with caution. When the operating temperature is between 530℃ and 650℃, 310S stainless steel can be used, but 304 stainless steel should be used with caution. When the operating temperature is between 650℃ and 700℃, either 304 or 310S stainless steel can be used.

[0083] Example:

[0084] See Figure 1 A corrosion control method for ammonia decomposition reactor based on temperature zoning is proposed, which includes a multi-scale synergistic characterization system, corrosion kinetic modeling, and selection decision.

[0085] Furthermore, the experimental materials for the multi-scale synergistic characterization system were 304 austenitic stainless steel and 310S austenitic stainless steel samples with a sample size of 15mm × 15mm × 3mm. The multi-scale synergistic characterization system was conducted in an ammonia decomposition reaction simulation apparatus (see...). Figure 2The ammonia purity was ≥99.8%, and the corrosion time was 80 hours. For 304 stainless steel, eight characteristic temperature points were set: 400℃, 450℃, 500℃, 550℃, 575℃, 600℃, 650℃, and 700℃. For 310S stainless steel, nine characteristic temperature points were set: 400℃, 450℃, 470℃, 500℃, 530℃, 550℃, 600℃, 650℃, and 700℃. Two sets of parallel samples were set for each temperature point. The macroscopic weight gain analysis was performed using an electronic balance (accuracy 0.0001g) to weigh the samples and calculate the weight change rate (g / h). The average weight change rate of the two sets of parallel samples was taken as the final result.

[0086] The formula for calculating the rate of weight change is as follows:

[0087]

[0088] In the formula, V is the rate of weight change of the metal; M0 is the weight before corrosion (in g); M1 is the weight after corrosion (in g); and t is the corrosion time (in h).

[0089] Furthermore, the microstructure observation employed a QUANTA 250 tungsten filament scanning electron microscope (SEM) to analyze the corroded surface and cross-section of the corrosion layer, focusing on crack propagation characteristics, spalling behavior, and nitriding layer thickness. Nitrogen atom diffusion detection utilized a QUANTA 250 tungsten filament SEM for line scanning and area distribution analysis to obtain nitrogen elemental distribution and quantitatively characterize nitriding behavior. Phase transformation identification used a RIGAKU Smartlab X-ray diffractometer (XRD) to analyze the phase composition of the corrosion layer, with a scanning angle of 10-90 degrees and a scanning speed of 10 degrees / minute, focusing on identifying the precipitation patterns of brittle phases such as CrN and Fe4N. Mechanical property degradation assessment involved tensile testing using an ETM204C microcomputer-controlled electronic universal testing machine at a tensile rate of 0.001 / s, testing the yield strength, tensile strength, and elongation of the corroded specimen and comparing them with uncorroded specimens.

[0090] Furthermore, the corrosion kinetics modeling is based on multi-scale characterization data, and non-monotonic curves of weight change rate versus temperature for 304 and 310S stainless steel are plotted (see...). Figure 3 Based on the combined corrosion kinetics and multi-scale characterization results, the three-stage corrosion mode was identified as follows: for 304 stainless steel, the corrosion was characterized by a slight corrosion stage (400-500℃), an accelerated corrosion stage (550-600℃), and a slowing corrosion stage (650-700℃); for 310S stainless steel, the corrosion was characterized by a slight corrosion stage (400-450℃), an accelerated corrosion stage (470-530℃), and a slowing corrosion stage (550-700℃).

[0091] Furthermore, the selection decision is based on the reactor's designed operating temperature range (see...). Figure 4 When the reactor operates continuously at a temperature between 400℃ and 450℃, 304 stainless steel is preferred, but 310S stainless steel can also be used. When the operating temperature is between 450℃ and 530℃, 304 stainless steel is preferred, as 310S stainless steel exhibits severely accelerated corrosion behavior due to its high chromium content in this range; therefore, 310S stainless steel should be used with caution. When the operating temperature is between 530℃ and 650℃, 310S stainless steel can be used, but 304 stainless steel should be used with caution. When the operating temperature is between 650℃ and 700℃, either 304 or 310S stainless steel can be used.

Claims

1. A method for mitigating corrosion in an ammonia decomposition reactor based on temperature zoning, characterized in that: The method establishes a "material-temperature-weight change rate" mapping spectrum to divide corrosion characteristic intervals, and formulates temperature control strategies for the corrosive environment of high-temperature ammonia atmosphere inside the ammonia decomposition reactor based on this. At the same time, it optimizes material selection based on the non-monotonic temperature-dependent corrosion law of stainless steel in the ammonia environment, so as to reduce the weight change rate of structural components of the ammonia decomposition reactor, extend the overall service life of the reactor, and improve the safety margin and economy of the ammonia decomposition reactor system.

2. The corrosion control method for an ammonia decomposition reactor based on temperature zoning according to claim 1, characterized in that: The method includes the following steps; Step 1: Corrosion experiments were conducted using an ammonia decomposition reaction simulation device to simulate the ammonia decomposition reactor and establish a multi-scale synergistic characterization system. Step 2: Corrosion kinetics modeling; Step 3: Material selection decision.

3. The corrosion control method for an ammonia decomposition reactor based on temperature zoning according to claim 2, characterized in that: In step one, based on the corrosion experiment results, the following are performed: analysis of material weight gain changes, observation of microstructure in the corrosion assessment area, quantitative analysis of element diffusion, identification of phase transformation of corrosion products, and assessment of mechanical property degradation.

4. The corrosion control method for an ammonia decomposition reactor based on temperature zoning according to claim 3, characterized in that: In step one, the corrosion environment in the corrosion experiment is a high-temperature ammonia atmosphere inside the ammonia decomposition reactor, with an ammonia purity ≥99.8%. The ammonia flow rate is controlled at 2L / min during the corrosion process, the corrosion test time is set to 80h, and the pressure inside the reaction tube is atmospheric pressure. The ammonia decomposition reaction simulation device consists of a Hastelloy reaction tube and a three-stage heating furnace. The reaction tube is equipped with a sample support frame, and the three-stage heating furnace is equipped with three independently adjustable heaters.

5. The corrosion control method for an ammonia decomposition reactor based on temperature zoning according to claim 3, characterized in that: In step one, the microstructure corrosion assessment area is the upper surface and cross-section of the stainless steel block sample. After the upper surface of the block sample is polished with sandpaper, ultrasonically cleaned and dried, it is placed on the sample support frame inside the reaction tube of the ammonia decomposition reactor for corrosion. The surface of the corroded block sample is observed, and after being made into a cross-sectional sample by resin embedding and curing, the cross-section is polished, cleaned and dried before the cross-section reaction layer is observed. The mechanical property degradation assessment was performed by suspending a plate-shaped tensile specimen on a support frame inside the ammonia decomposition reactor and conducting tensile tests on the corroded tensile specimen. Material weight gain analysis includes macroscopic weight gain analysis.

6. The corrosion mitigation control method for an ammonia decomposition reactor based on temperature zoning according to claim 5, characterized in that: In step one, the experimental materials for the multi-scale synergistic characterization system are 304 austenitic stainless steel and 310S austenitic stainless steel samples; the multi-scale synergistic characterization system is obtained in an ammonia decomposition reaction simulation device.

7. The corrosion mitigation control method for an ammonia decomposition reactor based on temperature zoning according to claim 5, characterized in that: The macroscopic weight gain analysis was performed using an electronic balance to weigh the samples and calculate the rate of weight change. The average of the rates of weight change of two sets of parallel samples was taken as the final result. In step one, the macroscopic weight gain analysis uses a high-precision balance to calculate and obtain the corrosion kinetic curve; The formula for calculating the rate of weight change is: ; In the formula, V is the rate of weight change of the metal; M0 is the weight before corrosion (in grams); and M1 is the weight after corrosion (in grams). t is the corrosion time, in hours (h). In the microstructure observation of the corrosion assessment area, the microstructure observation uses SEM to analyze the surface microstructure and cross-sectional reaction layer morphology and crack characteristics after corrosion, and measures the reaction layer thickness at different temperatures. The quantitative elemental diffusion method uses EDS surface scanning to obtain nitrogen elemental distribution and line scanning to obtain nitrogen elemental concentration gradient; The phase transformation identification was performed using XRD analysis to determine the precipitation patterns of the brittle phases of CrN and Fe4N at different corrosion temperatures. The mechanical property degradation assessment obtains data on the decrease in yield strength, tensile strength, and elongation through tensile tests.

8. The corrosion control method for an ammonia decomposition reactor based on temperature zoning according to claim 3, characterized in that: In step two, a three-stage corrosion mode classification and alloy composition influence mechanism analysis are performed; based on the multi-scale characterization data obtained in step one, non-monotonic curves of weight change rate-temperature for 304 and 310S stainless steel are plotted. The three-stage corrosion mode is divided as follows: Slight corrosion stage: 304 stainless steel: 400℃-500℃; 310S stainless steel: 400℃-450℃; Accelerated corrosion stage: 304 stainless steel: 550℃-600℃; 310S stainless steel: 470℃-530℃; Corrosion slowdown stage: 304 stainless steel: 650℃-700℃; 310S stainless steel: 550℃-700℃.

9. The corrosion control method for an ammonia decomposition reactor based on temperature zoning according to claim 3, characterized in that: In step three, a material with a lower degree of corrosion at the system operating temperature of the ammonia decomposition reaction simulation device is selected.

10. The corrosion control method for an ammonia decomposition reactor based on temperature zoning according to claim 9, characterized in that: In step three, when the material of the ammonia decomposition reactor has been determined to be 304 or 310S stainless steel, the operating temperature should be set to avoid the accelerated corrosion temperature range of each of these two steel types.

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