High-temperature Gas Environment Research Articles

The corrosion behavior of Al2O3-SiO2 refractory in reducing atmosphere

Hydrogen metallurgy technology is essential for reducing CO2 emissions. Hydrogen (H2) serves as an ideal energy carrier to replace carbon-based fuels, producing only water as a byproduct. Al2O3-SiO2 refractories are commonly used in hydrogen metallurgy technology, including in technologies like HyCROF(Hydrogen-enriched Carbonic oxide Recycling Oxygenate Furnace) and gas heating furnaces. It is important to systematically study their corrosion in high-temperature reducing gas environments. The results indicated that the Al2O3-SiO2 refractory remained stable in pure H2 atmosphere at temperatures below 1200 °C. However, SiO2 and mullite were reduced by H2 when the temperature was increased above 1200 °C. Carbon precipitation was observed in both pure CO atmosphere and H2-CO mixed atmosphere, resulting in an increase weight of the sample. Additionally, the sample developed mullite whiskers after heating treatment at 1200 °C in H2-CO mixed atmosphere. This study aims to clarify the corrosion mechanism of Al2O3-SiO2 refractory in reducing atmosphere and to provide a theoretical basis for the selecting and optimizing refractories for hydrogen metallurgy technology.

Modeling of the separation process of a two-phase liquid in a high-temperature gas environment

Obtaining a high-quality highly dispersed salt solution can be realized from a salt solution by the method of ultrasonic exposure. As you know, concentrated salt solutions can be presented in the form of a gas-liquid medium. The influence of ultrasound, in the case of wetting a surface vibrating with an ultrasonic frequency by a thin layer, leads to the formation of a cavitation layer in the liquid layer and capillary waves on its surface, from the ridges of which, at a certain intensity of oscillations, finely dispersed aerosol droplets are detached.The detachment of droplets from the vibrating surface leads to the formation of finely dispersed salt aerosol, which saturates the heated air, which is tangentially fed into the cylindrical working chamber with further separation of hydrodynamic processes. Part of the aerosol wets the heated inner surface of the cylindrical chamber with the formation of a thin film, which gravitationally flows down the vertical solid surface and is subjected to active evaporation with the removal of the salt phase, and the second part is subjected to additional grinding and active evaporation in the central turbulent flow and centrifugal turbulent flow of hot air with additional by removing the salt phase. In order to intensify the salt removal process, the surface on which the film is formed can be profiled. Ultrasonic dispersion of the salt solution to a finely dispersed state allows to significantly increase the surface of contact with the heated air, which allows to intensify the diffusion process.

Evaluation of droplet evaporation characteristics and its influencing factors in high-temperature gaseous environment

Droplet evaporation is widely present in nature and industrial production, involving heat and mass transfer between the droplet and the surrounding gas environment. This study investigates the evaporation of individual spherical droplets in a high-temperature gas environment under both stationary and forced convection conditions, using theoretical and numerical approaches. The results show that the established evaporation model can effectively reflect the temperature change during droplet evaporation. When the droplet evaporates in a gaseous environment, the equilibrium temperature of the droplet is influenced by environmental parameters such as temperature and humidity. Compared to environmental temperature, humidity has a more significant impact on the equilibrium temperature of the droplet, making it the dominant factor affecting the evaporation temperature. The evaporation rate of the droplet is influenced by environmental humidity. When the air humidity is below 0.5, the variable-rate evaporation aligns closely with the numerical simulation results (droplet lifetime). When the air humidity is above 0.5, the simulation results are slightly higher but still have a small relative error. As the environmental humidity increases, the evaporation rate of the droplet is suppressed, leading to an increase in its lifetime. Establishing an appropriate droplet evaporation model not only deepens our understanding of the internal mechanisms of droplet evaporation but also provides practical guidance for enhancing heat and mass transfer in droplets.

Thermal Protection Performance of Biomimetic Flexible Skin for Deformable High-Speed Vehicles (DHSV-bio-FS) under Uniaxial Tensile Strain.

Vehicle skin is the key component in maintaining the aerodynamic shape of the vehicle. A deformable high-speed vehicle needs to adjust its shape in real time to realize optimum aerodynamic efficiency and to withstand extreme heat flow induced by high-speed flight, which requires the skin to possess large strain and high-temperature resistance. Traditional vehicle skin cannot satisfy both of the requirements. Biomimetic flexible skin for deformable high-speed vehicles (DHSV-bio-FS) combines flexible material fabrication with transpiration cooling technology, which can simulate human skin sweat cooling, and has the characteristics of large strain and high-temperature resistance. The thermal protection performance of the prepared prototype of DHSV-bio-FS was evaluated by simulation and wind tunnel experiments at 40% tensile strain with liquid water as coolant. Simulation results suggest that the surface temperature of the DHSV-bio-FS at 40% tensile strain is consistent with the temperature of the coolant (350 K) in a 3,000 K high-temperature gas environment. In addition, the prepared prototype DHSV-bio-FS survived for 1,200 s in a high-temperature gas environment of 200 kW/m2 in wind tunnel experiments. This paper verifies the reliability of DHSV-bio-FS in a high-temperature gas environment and can be deployed in applications of flexible skin for deformable high-speed vehicles (DHSV-FS).

Failure analysis on tube weldment cracking of a high-temperature carbon black air preheater

In this study, the failure analysis on weldment joining the medium-to-high temperature steel tube (the jointed materials are S30815 and HK40Nb, respectively) sections of a high-temperature carbon black air preheater was conducted. The root cause of the cracking is identified as metal dusting appearing in the high-temperature carbon black flue gas environment, as indicated by the result of the macroscopic analysis, the chemical composition analysis, the metallographic examination, and the corrosion product analysis. As revealed by the result, the metal was directly exposed to the flue gas due to the damage of the surface protective film (i.e., Cr2O3) of the stainless-steel tube weldment. The result suggested that elemental sulfur within the flue gas and overheating in the operation destroyed the oxide film. Under the effect of the high carbon activity in the flue gas, carbon atoms were driven to attack metals. The accumulated carbon particles arising from weld reinforcement promoted the failure of the weldment. To prevent metal dusting, it is recommended to increase the amount of water vapor in the flue gas for the reduction of the carbon activity, choose high-temperature resistant materials for the prevention of direct contact between the flue gas and the material, and improve the welding quality to prevent the flue gas from being disturbed.

Dust removal ash coupled with high-temperature exhaust gas to produce energy gas CO and remove the heavy metals synchronously

In order to solve the utilization problem of dry quenching coke dust removal ash (DRA) and high-temperature exhaust gas (HTEG) at the same time, this study proposes a new technology that combines DRA and high-temperature exhaust gas to produce energy gas CO and realize the removal of heavy metals in dust removal ash. The reaction properties of DRA and high-temperature exhaust gases, as well as the migration law of heavy metals, are preliminarily evaluated using thermodynamic simulation software (FactSage) and a combination of thermogravimetric mass spectrometry (TG-MS). The dropper furnace (DF) experiments are used to verify the feasibility of the new technology by simulating the high-temperature flue gas environment. The findings reveal that as pressure rises, the content of gas products namely CO2 and CH4 rises while the content of gas products CO and H2 falls. At the same time, when the temperature rises, the CO and H2 contents rise. Heavy metals such as Cd, Pb, and Zn are also more volatile, whereas heavy metals such as Ni, Cr, and Cu, require higher temperatures to volatilize. As the temperature increases from 800 to 1200 °C, the Pb removal rate climbs from 34.6% to 92.5%, the Cd removal rate increases from 46.5% to 95.6%, and the Zn removal rate increases from 13.4% to 80.5%. The new technology captures CO2 from high-temperature exhaust gases and converts them into CO energy gases, simultaneously realizing the removal of heavy metals. This provides an innovative solution for the treatment of organic solid waste.

Dependence of microstructural evolution on the geometric structure for serviced DZ125 turbine blades

The turbine blades were directionally solidified by a high-rate solidification process by the Bridgman technique using directional solidified Ni-based master superalloy DZ125 and operated on the engine bench with a high-temperature gas environment of more than 1500 °C from combustor and high-speed rotation of more than 13500 rpm for 400 h. A service-environment-based model was put forward to simulate the distribution of temperature and stress on the DZ125 blade in service. It was found that the distribution of temperature and stress on the serviced DZ125 blade was closely related to its geometric structure. The microstructural evolution of the serviced DZ125 blade was analyzed and the variations of microstructures with temperature and stress were investigated by using a scanning electron microscope. The results revealed that the evolution process of microstructures on the serviced DZ125 blade was different from that of the standard sample tested at constant temperature and uniaxial tensile stress. The reason for this discrepancy was explored using a combination of finite-element calculation and diffusion coefficient calculation.

Corrosion behavior and failure mechanism of SiC whisker and c-AlPO4 particle-modified novel tri-layer Yb2Si2O7/mullite/SiC coating in burner rig tests

The corrosion behavior of environmental barrier coatings (EBCs) directly affects the service life and stability of ceramic matrix composite (CMC) structural parts in the aero-engines. The silicon carbide (SiC) whisker toughening phase and c-AlPO4 bonding phase are firstly used to improve the service life of novel tri-layer Yb2Si2O7/mullite/SiC EBCs in the burner rig test. The formation of penetrating cracks in Yb2Si2O7/mullite/SiC coating caused the failure of coating at 1673 K. The SiC whiskers in mullite middle coating significantly inhibited the formation of penetrating cracks in Yb2Si2O7/mullite/SiC coating, and efficiently prevented the oxidation of carbon fiber reinforced silicon carbide (Cf/SiC) samples for 360-min thermal cycles (24 times) with a weight loss of 6.19×10−3 g·cm−2. Although c-AlPO4 particles further improved the service life of SiCw-mullite (SM) coating, the overflow of POx gas aggravated the formation and expansion of cracks in the Yb2Si2O7 outer coating, and caused the service life of overall Yb2Si2O7/c-AlPO4-SiCw-mullite (ASM)/SiC coating to be slightly lower than that of Yb2Si2O7/SM/SiC coating. This study guides the design of modified tri-layer EBCs with long service life in high-temperature and high-speed gas environment.

A Comparative Study of Protective Film Formation of Additively Manufactured 316L SS and Conventional Wrought 316L SS in Aqueous, Gaseous and Steam Environments

Additively prepared 316L SS using selective laser melting technique has been found to possess better passivation behavior in relation to its wrought counterpart in aqueous media such as chloride solutions, despite having cast structure. This has been attributed to the absence of manganese sulfide inclusions and higher chromium content of the passive film formed on the former. Not much work has been published on the behavior of this alloy in high temperature gaseous and steam environments though it is expected to be employed in such environments. Our studies show that the nature of the oxides formed on oxidation on the additively formed alloy has been found to be notably different from that formed on its wrought alloy counterpart. A talk will bring out the salient differences shown by these two types of alloys and their implication on the protection behavior.

Performance assessments of porous FeCoNiCrAlx high-entropy alloys in high-temperature oxidation, carbonization and sulfidation atmospheres

Porous FeCoNiCrAlx high-entropy alloys (HEAs) with different atomic fraction of Al were developed as potential candidates for high-temperature filter materials by reactive synthesis using blended elemental Fe/Co/Ni/Cr/Al powders. This method combines the creation of porous structure with the direct synthesis of HEAs, and takes the advantage of the role of Al in enhancing the porosity of porous materials. The effects of Al atomic fraction on the pore structure parameters, phase compositions, microstructures and mechanical strengths of porous FeCoNiCrAlx were investigated, and a comprehensive assessment of the high-temperature corrosion resistances of these materials was carried out. The results showed that the increase of Al atomic fraction not only improved the porosity and intrinsic mechanical performance of porous FeCoNiCrAlx, but also provided enhanced protection against high-temperature corrosions such as oxidation, carbonization and sulfidation. The optimal atomic fraction range of Al in porous FeCoNiCrAlx HEAs was 0.6–1.0, which could make this material keep structural and chemical stability in potential high-temperature flue gas environment.

Collisions between liquid droplets during the intersection of aerosol flows in a heated gas

• A rise in the gas temperature led to an increase in the number of secondary fragments. • At T g = 300–400 °C droplets with r d = 0.075–0.1 mm prevail. • A temperature rise contributed to a 2–3 times increase in area ratios S 1 / S 0. • At T g = 100–400 °C, droplets increased in size due to expansion of liquid on heating. • The motion of droplets in a heated gas led to a 10–30% change in their size due to evaporation. The paper presents the experimental findings on the water droplet collision behavior during the intersection of two aerosol flows in a high-temperature gas environment. Aerosol flows were produced by two strip pattern nozzles angled at 45° towards each other in the same plane. The resulting flow had an opening angle of 60°. The droplet impact angle (α d ) was varied from 0 to 90°, droplet radii ( R d1 , R d2 ) from 0.1 to 1.2 mm, and droplet velocities ( U d1 , U d2 ) from 2 to 12 m/s. The gas temperature in the droplet collision zone was varied using an induction heater with an internal volume of about 0.13 m 3 with viewing windows to record the key parameters (number, size, velocities, and trajectories) of liquid fragments before and after collision. The air temperature ranged from 20 to 400 °C in the experiments. Using a high-speed video camera, we recorded four collision regimes: coalescence, separation, disruption, and bounce. We also identified the main differences in the number and size of secondary droplets formed in an aerosol flow after the collision of two primary ones. A temperature rise led to an increase in the number of secondary fragments. The size distributions of secondary fragments are presented for three ranges of size ratios of initial droplets: Δ < 0.3; 0.3 < Δ < 0.7; Δ > 0.7. The impact of droplet collisions on their size variation rates was estimated at the gas temperature T g = 20–400 °C. Finally, we compared the contribution of this factor and evaporation without droplet-droplet collisions.

Effects of the Ar flow rate on the composition, structure, and properties of near-stoichiometric SiC fibres that were annealed at 1600°C

SiC fibres are widely used in the aerospace and nuclear fields due to their unique high-temperature resistance. Maintaining excellent high-temperature resistance is necessary for the application of fibres. This study involved processing nearly stoichiometric SiC fibres in Ar at 1600 °C for 1 h. The effects of the Ar flow rate on the composition, structure, and properties of fibres after high-temperature treatment were investigated by elemental analysis, SEM, EDS, TEM, XRD, and Raman spectroscopy. The results showed that the nearly stoichiometric SiC fibres did not undergo noticeable pyrolysis or active oxidation at a low Ar flow rate (<0.2 L/min) with a weight loss rate of less than 1% and that the tensile strength retention rate was as high as 86%. As the Ar flow rate was gradually increased above 0.2 L/min, an active oxidation reaction occurred, and the reaction products of SiO and CO were deposited on the fibre surfaces to form large SiC grains. The fibres gradually evolved into a skin-care structure, and the mechanical properties degraded rapidly. A high-temperature inert gas environment with a low flow rate is very important for preserving the mechanical properties of near-stoichiometric SiC fibres at high temperatures.

Failure analysis of reheater tubes in a 350 MW supercritical circulating fluidized bed boiler

This work aimed to analyze a failure that occurred on the TP347H reheater tube in a supercritical circulating fluidized bed boiler from a thermal power plant. Optical microscopy (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), electron probe micro-analysis (EPMA), digital microhardness tester (DMT), X-ray fluorescence spectroscopy equipment (XRF), and carbon sulfur analyzer (CSA) were used to characterize the failed tubes. The results show that the cracks originated in the heat-affected zone and simultaneously propagated in the circumferential and radial directions. There is a multilayered structure in the crack under the effect of the thermal cycle and preferential oxidation. The failure mechanism was identified as stress corrosion cracking (SCC). The cracks were produced under the combined effects of the tensile stress and the high-temperature flue gas environment. Related improvement measures have been implemented to prevent further failures.

Oxidation Behaviors of Different Grades of Ferritic Heat Resistant Steels in High-Temperature Steam and Flue Gas Environments

Oxidation Behaviors of Different Grades of Ferritic Heat Resistant Steels in High-Temperature Steam and Flue Gas Environments

Front Cover: Metastable Nanoporous Palladium Evolving from Palladium Nanocrystals (ChemNanoMat 10/2021)

Palladium nanocrystals can be structurally evolved into metastable nanoporous palladium with catalytic activity toward ethanol electrooxidation. The resultant palladium structure has bimodal pore distribution and a large electrochemically active surface, and its catalytic activity can be enhanced through the structural evolution of palladium nanocrystals. The proposed method is simple and based on an easy process that excludes treatments in high temperature, high vacuum, or inert gas environments, and is thus suitable for mass production of palladium electrocatalyst. More information can be found in the Communication by Nakanishi et al.

Degradation of nickel-based alloys for precise casting in high-temperature gas environment

The corrosion resistance of the alloys designed for precise casting Inconel 713LC and Inconel 738 in high temperature gas environment were tested. The environments during tests simulated helium coolant of advanced gas cooled reactors and high temperature carbon capture storage environment (CO2). The specimens were exposed in helium containing 500 vppm CO, 100 vppm CH4, 100 vppm H2 a 10 vppm H2O at 900 °C for 1000 hours and in CO2 at 900 °C during 200 hours. After exposure weight changes were investigated, the corrosion damage was observed by optical and electron microscope, the samples exposed in CO2 were investigated by XPS (X-ray Photoelectron Spectroscopy), GD-OES (Glow Discharge Optical Emission Spectrometry). After exposure in helium, 2 types of scales with different composition were observed on the sample surface. The depth corrosion damage was up to 20 μm, on the alloy Inconel 738 was deep corrosion damage only local, on the alloy Inconel 713LCcontinuous. After exposure in CO2 the surface corrosion layer was compact and almost uniform, corrosion interfered up to 30 μm under the surface layer. In high temperature helium, the alloy Inconel 738 could be said to bo more corrosion resistant than Inconel 713LC. In high temperature CO2 both tested alloys performed almost the same corrosion resistance.

Low Cycle Fatigue Behavior of Superalloy GH4169 in High Temperature Gas Environment

Turbine components (blades, guides and casing) of gas turbine engine usually suffer from fatigue load in company with a HTG environment in service. The corrosive substances in HTG can deposit on the surface of turbine components and induce accelerated damage known as hot corrosion. In this study, an experimental system is designed and built up to conduct LCF tests of superalloy in HTG environment. The influence of HTG on the LCF behavior of the nickel-base superalloy GH4169 at 650°C is studied. According to the test results, the average fatigue life of the specimens in HTG environment (22270 cycles) is about 31.5% less than that in air (32496 cycles). The protective oxide film on the surface of the specimen can be destroyed by the electrochemical reaction between HTG and oxide film. Compared with the specimen tested in air, there are more fatigue sources in the specimen tested in HTG environment, and the transgranular–intergranular transition occurs in the crack growth area.

Effect of Local Corrosion Caused by Inclusions and Surface Scratches of Steel in High Temperature and Pressure Flue Gas Environment

By simulating the high temperature and high pressure flue gas environment in heavy oil thermal recovery, the influence of two kinds of surface defects, steel inclusions and surface scratches, on local corrosion of steel was studied. And the mechanism of local corrosion caused by inclusions and surface scratches was analysed steel #20 and 26CrMo4 were used as experimental materials, and reacted in a 9 MPa flue gas environment for 24h. The reaction temperatures were 120 °C and 250 °C. The results show that the non-metallic inclusions in the steel are weak parts of the passivation film on the surface of the sample and are easily corroded by corrosive media. The scratched area is more likely to cause aggregation of corrosive media than other parts of the steel surface, and the iron elements in the metal in this area are more likely to reach the surface and react with the corrosive medium.

Effect of the Kinetic Model of Pyrolysis on Prognostic Estimates of Ignition Characteristics of Wood Particles

The effect of the kinetic model of the thermal decomposition of wood on the results of prognostic modeling of the ignition of wood particles was analyzed. The results of mathematical modeling were verified by experimental studies of the ignition of wood particles in a high-temperature environment. Comparative analysis of theoretical and experimental ignition delays shows that they are in good agreement. The prognostic potential of three substantially different kinetic models of wood pyrolysis was analyzed. The model of one-step pyrolysis involving the formation of gaseous reaction products adequately describes thermal decomposition during thermal preparation in the whole range of heating conditions (the deviation from the times obtained using the three-step pyrolysis model does not exceed 5%). Numerical simulation results show that accounting for the thermal decomposition reactions of the second and third levels with the formation of intermediate (liquid and solid) pyrolysis products does not have a significant influence on the characteristics and conditions of ignition of wood particles in a high-temperature gas environment.

Evaluation of Droplet Evaporation Models and the Incorporation of Natural Convection Effects

Evaporation of fuel droplets in high temperature gas environment is of great importance in many engineering applications. There are already several theoretical models proposed in the literature to represent this phenomenon by considering mass and energy transfer between the droplet and the surrounding gas. For that reason, this work aims to evaluate droplet evaporation models that are usually used in spray combustion calculations, including equilibrium and non-equilibrium formulations. In order to validate and assess these theoretical models predictions, an in-house code was developed and diameter evolution results from the numerical simulations are compared against experimental data. First, the models performance are evaluated for water in a case of low evaporation rate and; then, they are evaluated for n-heptane moderate and high evaporation rates using recent experimental data acquired with a new technique. Furthermore, the incorporation of natural convection effects on the droplet evaporation rate by using an empirical correlation is investigated. The Abramzon-Sirignano model is the only one which does not overestimate the evaporation rate for any ambient conditions tested when compared with experimental rate. The results also reveal that when a correction factor for energy transfer reduction due to evaporation is incorporated in the classical evaporation model, the predictions from this model and the non-equilibrium one cannot be differentiated, even if the initial droplet diameter is small. Additionally, taking natural convection effects into account by adding the Grashof number into the Ranz-Marshall correlation for Nusselt and Sherwood calculations actually overestimates the evaporation rate for droplet evaporation under atmospheric pressure.