Supercritical Environment Research Articles

Domain knowledge-guided interpretive machine learning: formula discovery for the oxidation behavior of ferritic-martensitic steels in supercritical water

A general formula with high generalization and accurate prediction power is highly desirable for science, technology and engineering. In addition to human beings, artificial intelligence algorithms show great promise for the discovery of formulas. In this study, we propose a domain knowledge-guided interpretive machine learning strategy and demonstrate it by studying the oxidation behavior of ferritic-martensitic steels in supercritical water. The oxidation Cr equivalent is, for the first time, proposed in the present work to represent all contributions of alloying elements to oxidation, derived by our domain knowledge and interpretive machine learning algorithms. An open-source tree classifier for linear regression algorithm is also, for the first time, developed to materialize the formula with collected data. This algorithm effectively captures the linear correlation between compositions, testing environments and oxidation behaviors from the data. The sure independence screening and sparsifying operator algorithm finally assembles the information derived from the tree classifier for linear regression algorithm, resulting in a general formula. The general formula with the determined parameters has the power to predict, quantitatively and accurately, the oxidation behavior of ferritic-martensitic steels with multiple alloying elements exposed to various supercritical water environments, thereby providing guidance for the design of anti-oxidation steels and hence promoting the development of power plants with improved safety. The present work demonstrates the power of domain knowledge-guided interpretive machine learning with respect to the data-driven discovery of physics-informed formulas and the acceleration of materials informatics development.

Electrochemical, Mechanical, and Tribological Properties of Corrosion Product Scales Formed on X65 Steel Under Co2 Supercritical Pressure Environments

Electrochemical, Mechanical, and Tribological Properties of Corrosion Product Scales Formed on X65 Steel Under Co2 Supercritical Pressure Environments

Wellbore stability in high-temperature granite under true triaxial stress

Supercritical/superhot geothermal success depends on successful drilling. However, wellbore stability in supercritical environments has not been investigated because imposing sufficient stress on high-temperature granite with true triaxial loading is difficult. We conducted wellbore failure experiments on 200–450 °C granite under true triaxial stress, including deformation and acoustic emission measurements, and post-experiment thin section observations. Wellbore failure initiated at stress states consistent with existing brittle failure criterion at the studied temperatures. Using breakout geometry for in situ stress estimation may be difficult as shear failure propagation is suppressed at high temperatures; however, boreholes may be inherently stable in high-temperature environments.

Atomic insight into iron corrosion exposed to supercritical water environment with an improved Fe-H2O reactive force field

Waterside anti-corrosion of Fe-based alloys is one of the great challenges for supercritical water reactors. Herein, an improved Fe-H2O reactive force field (ReaxFF) is constructed to understanding the Fe corrosion mechanism at the atomic scale. Using molecular dynamics simulations, the corrosion of Fe (100) and Fe (110) in supercritical water was investigated. It was found that oxidation and hydrogen evolution reactions occurred along with Fe dissolution; the corrosion rate on Fe (100) was faster than that on Fe (110) in the early stage, but the reverse occurred on a longer time scale; and the precipitation of ferrous hydroxide at the initial stage led to the formation of an oxidation layer, where FeO and Fe3O4 were the dominant products. The present ReaxFF can become a crucial tool for corrosion research on Fe-based alloys.

Comparison of evaporation rate constants of a single fuel droplet entering subcritical and supercritical environments

This work compares the evaporation rate constants of a single fuel droplet under subcritical and supercritical environments by experimental visualizations (in millimeter scale) and molecular dynamics simulations (in nanometer scale). The objection is to understand the differences of fuel droplet evaporation rate constant variations under the subcritical and supercritical environments. Firstly, an experimental apparatus is designed to study the diesel droplet evaporation under subcritical and supercritical environments. The results show that the droplet evaporation obeys the D2 law in subcritical environments, while the D2 law is no longer strictly applicable in supercritical environments and the evaporation rate constant isn’t a constant but a variable that increases with the evaporation time. Secondly, the molecular dynamics simulations are applied to investigate the evaporation of diesel surrogate n-dodecane under subcritical and supercritical environments. The results show that the droplet temperature keeps at the equilibrium temperature in subcritical environments, but keeps increasing in supercritical environments. In supercritical environments, the reason for the evaporation rate constant keeps increasing is that the droplet density keeps decreasing with the increase of droplet temperature. The droplet surface tension will rapidly vanish in supercritical environments, which implies that the formation of fuel–air mixture is no longer dominated by the surface tension, but is the turbulent diffusion in diesel trans/supercritical injection conditions. It can deduce that the evaporation rate constants of a fuel droplet in micrometer scale (that is commonly generated in engines) will follow the same trend and within the same variation scale at the same ambient pressures and temperatures.

Probing lattice dynamics in ST 12 phase germanium nanowires by Raman spectroscopy

Germanium (Ge) plays a crucial role in setting up important functionalities for silicon-compatible photonics. Diamond cubic germanium is an extensively studied semiconductor, although its other exotic forms, like BC8, ST8, ST12 phases, may possess distinct electronic properties. We have fabricated stable ST12-Ge nanowires via a self-seeded bottom-up three phase growth in a confined supercritical toluene environment. Here, we report on the direct evidence of the presence of the ST12 phase by a combination of Raman spectroscopy and first-principles calculations using density functional theory (DFT). It is important to remark that the DFT calculation predicts all the Raman active optical phonon modes of the P 4321 structure, and it is in very good agreement with the experimental results. The phonon dynamics as a function of temperature is investigated through Raman measurements at temperatures varying from 80 to 300 K. First-order temperature coefficients for all the observed Raman modes are estimated from the linear temperature dependence of the phonon shifts. A complete set of isobaric Grüneisen parameters is reported for all Raman modes of ST12-Ge nanowire, and the values are lower compared to the same for Si, dc-Ge bulk, and Ge nanowire. These results have important implications for understanding thermal properties of ST12-Ge nanowire.

Effect of Flow Rate on the Corrosion Behavior of API 5L X80 Steel in Water-Saturated Supercritical CO2 Environments

The effect of the water-saturated supercritical carbon dioxide (scCO2) flow rate on the corrosion behavior of API 5L X80 steel at a temperature of 35°C and pressure of 80 bar was investigated. Tests were performed with the samples attached to a rotating shaft inside an autoclave. Results indicate that increasing the scCO2 flow rate had no significant influence on the general/localized corrosion rate under the various dynamic conditions considered. The average general corrosion rate was 0.064 mm/y, while the average measured pitting penetration rates were one order of magnitude higher. The size of the corrosion features on the surface of the samples, which were believed to provide an indication as to the size of the condensed water droplets, was much smaller than the calculated critical droplet size needed to be displaced by the flow, supporting the theory as to why flow rate had little effect on the corrosion response.

Oxidation behavior of Al0.2CoCrFeNi high-entropy alloy film in supercritical water environment

Oxidation behavior of Al0.2CoCrFeNi high-entropy alloy film in supercritical water environment

Oxidative coupling of methane over MnO2/ZrO2 catalyst in supercritical water: A parametric study

Hydrocarbons production with carbon numbers above C2 through methane coupling has been a target of many researches in the past decades. Recently we discovered that the reaction also occurs under supercritical water conditions. In this work, effects of reaction parameters such as catalyst Mn loading, charged catalyst amount, reaction time as well as reaction pressures and temperatures on the catalytic methane coupling under sub- and supercritical water environment were explored over MnO2/ZrO2 catalyst using a batch reactor. It was found within the investigated parameters that methane coupling activity was maximum at 12–35 MPa, 365–400 °C, 10 wt% Mn loading on ZrO2, reaction time 5 min and 1.0 g catalyst charging. It was conjectured from the temperature–pressure mapping of products that the reaction pathway of hydrocarbon formation over MnO2/ZrO2 is not the same with methanol formation pathway.

EFFECT of surface treatment on corrosion control of P91 hydrothermal aqueous solutions

ABSTRACT The proven efficacy of surface treatment on ferritic-martensitic (F/M) steels in subcritical and supercritical water environments has spawned interest in its application for the construction of biomass hydrothermal liquefaction (HTL) conversion reactors. The objective of this paper is to determine the relative extent to which well-established surface treatments, including mechanical abrasion (baseline), sandblasting, shot peening, and pickling, affect corrosion of the steels in a simulated HTL biomass conversion environment. These treatments were administered to P91 steel for the purpose of improving corrosion resistance towards that exhibited by Type 304 austenitic stainless steel. Samples were immersed in a simulated HTL conversion environment at 310 °C and 10 MPa for 10 days using a static autoclave testing system. None of the surface treatments administered improved corrosion control of P91. The structure and chemistry of the oxide scale formed during immersion were not altered by the surface treatments administered, i/e., none of which promoted of the formation of a more protective Cr-enriched scale. Shot peening was particularly problematic as it promoted the formation of Cr-rich carbides in the near-surface region, which, when incorporated into the oxide scale that formed during high temperature immersion, served to reduce the amount Cr available for oxidization.

Effect of thickness on degradation of austenitic 347H steel by direct-fired supercritical CO2 power cycle environment

Austenitic 347H steel of two thicknesses (2.54 and 0.6 mm) was exposed to a simulated direct-fired supercritical CO2 (sCO2) power cycle environment at 650 °C and 1 atm for 1000 h then tensile stressed at room temperature to study the deformation behavior. The thicker 347H formed a protective chromia scale over most of the surface, which minimized carburization of the underlying steel and resulted in no change in mechanical performance. In stark contrast, the thinner 347H formed non-protective Fe-rich oxides over the entire surface, resulting in extensive carburization of the underlying steel. This led to increased strength but significantly reduced ductility, resulting in partially brittle failure. Data availabilityAll relevant data that support this study are available from the corresponding author upon request.

Comparison of the corrosion of materials in supercritical carbon dioxide, air, and argon environments

The corrosion resistance of structural alloys was investigated in conditions that simulate supercritical carbon dioxide sCO2 power fluid environments at 20 MPa and 550°C. Complementary air and Ar experiments were conducted at 1 atm. The alloys investigated in this study were as follows: Gr. 91, ferritic martensitic steel; 316L, austinetic stainless steel; HR 120, Ni-Fe based superalloy; and IN625, Ni based superalloy. The results for the air and sCO2 exposed samples indicated parabolic mass-gain with respect to time and sCO2 was more aggressive. The austinetic alloys exposed to sCO2 developed recrystallized zones under the oxide. The same alloys exposed to air showed signs of recrystallization that was detectable with TEM.

Cement with bacterial nanocellulose cured at reservoir temperature: Mechanical performance in the context of CO[formula omitted] geological storage

Storing CO2 in deep underground reservoirs is key to reducing emissions to the atmosphere and standing against climate change. However, the risk of CO2 leakage from geological reservoirs to other rock formations requires a careful long-term analysis of the system. Mostly, oil well cement used for the operation must withstand the carbonation process that changes its poromechanical behavior over time, possibly affecting the system’s integrity.This work focuses on the microstructure and mechanical behavior of cement modified with bacterial nanocellulose (BNC) cured at 90 °C, simulating temperature at the reservoir level. The chemo-hydro-mechanical (CHM) coupled behavior of the cement–rock interface is also investigated through numerical analyses.Mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), ultrasonic wave velocity measurement, and unconfined compressive strength (UCS) tests were performed on cement samples subjected to a supercritical CO2 environment. After carbonation, BNC samples show a lower mass gain and lower porosity compared to PC. Permeability based on MIP results indicate that the BNC reduces the permeability of the specimen. XRD quantification shows no substantial difference between the crystalline phases of the two samples. Samples with BNC have lower absolute strength but higher relative increase during carbonation.The numerical study includes a homogenization of the medium considering the contribution of all components. CHM behavior of the cement with BNC is analyzed, and the results show the variations of the physical and chemical properties across the sample. The numerical study shows the advantage of using this type of tool to study realistic CO2 injection scenarios in deep wells.

Unpicking the interplay of turbulence, diffusion, and thermophysics in cryogenic jets at supercritical pressures

Cryogenic supercritical fluids represent an intriguing category of fluids that combine mechanical and thermophysical properties of both ultralow temperature conditions and phenomena taking place well above the critical point. Recent research has demonstrated that it is a common misconception to consider the supercritical state as one homogeneous state. Instead, these fluids consist of two to four liquid and gas like phases, each with their own unique characteristics. In our work, we investigate numerically single-specie cryogenic fluid jets—initially at subcritical temperatures—which are injected into a supercritical environment (both the pressure and temperature exceed the thermodynamic critical state). For the investigation, a new solver, namely, “CoolFoam,” has been developed, which is designed for compressible non-isothermal two-fluid simulations where diffusive transport of heat and/or mass is accounted for. Real fluid thermodynamics are modeled using a polynomial fitting approach developed in our previous work. We introduce also a new phase characterization framework based on the association of phases with specific temperature ranges (rather than using a single line like the Widom line), which allowed us to better identify the similarity effects between the various conditions. We analyze the inter-dependence of the underlying phenomena: density gradient and diffusive mass transport [molecular and thermo(Soret)-diffusion] and turbulence. We also compared supercritical N2 with subcritical liquid and gas jets to highlight potential differences with respect to how these jets behave. We find that the jet dynamics are largely dictated by the thermodynamic transition of the injected fluid and the associated variation in thermophysical properties.

Influence of elemental sulfur on the corrosion mechanism of X80 steel in supercritical CO2-saturated aqueous phase environment

The corrosion mechanisms of X80 steel under conditions containing elemental sulfur (S) were investigated in a supercritical CO2-saturated aqueous phase environment. The uniform corrosion rate slightly increased with immersion time in the absence of S, while it decreased with immersion time in the presence of S, and pitting was induced. There were two polymorphs of FeOOH in this study: α-FeOOH, which formed in an S-free environment by conversion of Fe(NO3)3; γ-FeOOH, which formed in the presence of S by conversion of FeSO4. There were also two polymorphs of Fe2O3: α-Fe2O3 could be formed by Fe(OH)3 in both environments, while γ-Fe2O3 could be formed from α-FeOOH in an S-free environment or γ-FeOOH in the presence of S. The S could cause pitting through the acid regeneration cycle reaction and occluded corrosion defects. Moreover, FeS gradually replaced FeCO3 to protect the substrate in the S-containing environment.

Droplet evaporation and phase transition modes in supercritical environment by molecular dynamic simulation

The phase change process of a single hydrocarbon droplet in a supercritical environment has different features compared with subcritical evaporation. In this study, droplets surrounded by supercritical nitrogen are investigated by molecular dynamic simulation. Dodecane droplets are considered in order to reproduce the phase change process of actual fuel, and the radius ranges from 10 nm to 25 nm under various subcritical, transcritical, and supercritical conditions. The emphasis is to describe the entire phase change process and distinguish its different stages. Under supercritical conditions, traditional D2-law theory is invalid and the radius of droplets increases dramatically accompanied by huge fluctuation after a special time. Based on analysis toward fluid properties crossing this time point, the phases classification for supercritical mixture is provided and three phase change stages are distinguished in order, which can be divided by the onset time of supercritical transition, the disappearance of surface tension, and one-phase diffusion, respectively. Additionally, gas/liquid-like features have been observed in the supercritical binary dodecane–nitrogen coexisting system and the defined pseudo-boiling mole fraction (Xpb) is introduced to clarify such deviation in properties of supercritical mixture. At last, by judging whether supercritical transition and undroplet phenomenon will happen, three phase transition modes are summarized for droplets under supercritical conditions.

ИССЛЕДОВАНИЕ МЕТОДОВ ПОДГОТОВКИ ОРГАНОСОДЕРЖАЩИХ СЕЛЬСКОХОЗЯЙСТВЕННЫХ ОТХОДОВ ДЛЯ ИХ ДАЛЬНЕЙШЕЙ ПЕРЕРАБОТКИ В СВЕРХКРИТИЧЕСКОЙ ВОДНОЙ СРЕДЕ

The problem of waste disposal is always acute in all areas of production activity, especially for the agro-industrial complex. Supercritical water oxidation is the most environmentally friendly method for processing organic waste and persistent organic pollutants. In the process of recycling and disposal, along with the harmfulness, one of the main indicators is the initial state of the waste and its suitability for different disposal technologies. (Research purpose) The research purpose is in choosing and justifying the most energy-efficient method of grinding, taking into account the fact that the organ-containing waste under study (buckwheat husk, sunflower, rice) is soft, elastic and fibrous materials. (Materials and methods) The crushing of organic waste to prepare it for further processing was carried out by different methods in roller, ball, knife and colloid mills. A set of sieves with square cells according to GOST 2715-75, a drying cabinet SHS-80-01 SPU, analytical scales Acculab ALC-210d4 (weighing error of no more than 0.5 percent of the sample weight) were used to evaluate the fractional composition of the obtained material. (Results and discussion) At a concentration of 100 grams of husk per 1 liter of water after 30 minutes of wet grinding, the passage of particles through the sieve is 87.1 percent. The article presents the advantage of wet grinding in a knife mill, reveals mathematical dependencies that allow predicting the grinding process to obtain the product of the required dispersion. (Conclusions) The grinding of organ-containing waste in a knife mill by wet grinding is the most optimal technology for preparing this waste for further processing in a supercritical water environment. The obtained mathematical dependencies allow us to predict the grinding process.

Heterogeneous yielding mechanisms of body centered cubic iron for high resistance to chemical reaction-induced deterioration in supercritical water environments: A reactive molecular dynamics study

The atomic-scale yielding mechanisms of body centered cubic (BCC) iron in supercritical water have been an elusive problem that requires understanding the roles of chemical reactions with supercritical water in the mechanical behavior of iron. This work shows the combined effect of the supercritical water and tensile direction on the yielding mechanism of BCC iron using reactive molecular dynamics simulations. Our simulation results show that tensile strain along the [11¯0] direction of BCC iron may potentially exhibit much higher tensile strength and lower sensitivity to the environment compared with other directions. This is because yielding of iron along the [11¯0] direction originates from the homogenous generation of HCP precursors inside the iron bulk rather than at the surface, which limits the effects of surficial chemical reactions with supercritical water on the yielding behavior. This work is expected to contribute to the theoretical design of high-strength alloys in supercritical water.

Supercritical water partial oxidation mechanism of ethanol

In recent years, supercritical water as a green reaction medium to convert organic matter to produce hydrogen has attracted significant attention. At present, the mechanism of the supercritical water partial oxidation (SCWPO) process is still unknown when complete gasification is achieved. In this paper, a detailed mechanism for SCWPO of ethanol was proposed by establishing a novel kinetic model with a wide reaction temperature range. This model described the formation and consumption of gas products (H2, CO, CH4, and CO2) from ethanol by partial oxidation in the supercritical water environment through nine reactions. The results showed that the dehydrogenation and pyrolysis of ethanol were the main ways to generate H2 in the early stage, and the water-gas shift reaction had the most significant impact on hydrogen production in the later stage. The hydrogenation reaction of the intermediate product ethane was a key step for complete conversion into combustible gas products. The steam reforming reaction of a large amount of CH4 produced by ethanol and intermediate product will become the rate-determining step for hydrogen production.

Analysis of internal corrosion of supercritical CO2 pipeline

Abstract Carbon capture and storage (CCS) technology is considered to be one of the key technologies to reduce CO2 emissions. This paper reviews the industry corrosion accidents of CCS transportation system, in which the pipeline corrosion risk is analyzed, and the pipeline corrosion theory is summarized. Also, the effect of impurities on gas phase properties is discussed. We analyze the corrosion mechanism of multicomponent impurities on metals in a supercritical CO2 environment from the aspects of corrosion rate and corrosion products. We also describe the mechanism of pitting and stress corrosion of metals in a supercritical CO2 environment. Besides, the formation mechanism of FeCO3 protective layer and the research status of corrosion resistant alloys in supercritical CO2 are reviewed and analyzed. Finally, a series of shortcomings and prospects of the current research are put forward.