Supercritical Water Research Articles

Numerical Investigation on the Heat Transfer Characteristics of Supercritical Water in a Non-Uniformly Heated Tube for a Supercritical CFB Boiler

Numerical Investigation on the Heat Transfer Characteristics of Supercritical Water in a Non-Uniformly Heated Tube for a Supercritical CFB Boiler

Evolution of Recrystallization Texture in A286 Iron-Based Superalloy Thin Plates Rolled via Various Routes

The A286 iron-based superalloy has wide-ranging applications in replacing expensive nickel-based and cobalt-based superalloy to manufacture the turbine disk as well as the pipelines and valves of the fourth-generation supercritical water reactor (SCWR) working below 650 °C. The recrystallization texture importantly affects the mechanical properties and oxidation resistance of superalloys. However, very few investigations are available on the recrystallisation texture of A286 alloy. The current work reports the texture of A286 alloy fabrication using various rolling routes, including one-stage cold rolling with the rolling rates of 83% (Route I) and 91% (Route II), and two-stage cold rolling with the rolling rate of 83% + 50% (Route III). Route III is preferentially recommended to manufacture A286 alloy thin plates due to the obviously reduced work hardening as well as the weakened recrystallization texture and anisotropy; moreover, compared with other routes, the recrystallized grain size of Route III did not significantly coarsen. We also revealed the mechanism for the effect of cold rolling textures on the final recrystallization texture and the role of the deformation twin in {110} <115> grain. In this study, recrystallization texture develops through two independent mechanisms related to different deformation microstructures, including the recrystallization texture inherited from deformation texture and the recrystallization texture depended on deformation twins.

Interior–atmosphere modelling to assess the observability of rocky planets with JWST

Context. Super-Earths present compositions dominated by refractory materials. However, there is a degeneracy in their interior structure between a planet that has no atmosphere and a small Fe content, and a planet that has a thin atmosphere and a higher core mass fraction. To break this degeneracy, atmospheric characterisation observations are required. Aims. We present a self-consistent interior–atmosphere model to constrain the volatile mass fraction, surface pressure, and temperature of rocky planets with water and CO2 atmospheres. The parameters obtained in our analysis can be used to predict observations in emission spectroscopy and photometry with JWST, which can determine the presence of an atmosphere and, if present, its composition. Methods. We coupled a 1D interior model with a supercritical water layer to an atmospheric model. In order to obtain the bolometric emission and Bond albedo for an atmosphere in radiative-convective equilibrium, we used a low-resolution k-correlated atmospheric model. We generated emission spectra with the same atmospheric model at a higher resolution (R = 200–300). An adaptive Markov chain Monte Carlo was employed for an efficient sampling of the parameter space at low volatile mass fractions. Results. From our interior structure retrieval, we conclude that TRAPPIST-1 c most likely has a bare surface, although the presence of an atmosphere cannot be ruled out. We estimate a 1σ confidence interval of the surface pressure for a water-dominated atmosphere of Psurf = 40 ± 40 bar. We generated spectra for these two scenarios to compare with the emission flux of TRAPPIST-1 c recently observed in the MIRI F1500W filter. This is compatible with bare rock surfaces or a thin atmosphere with little or no CO2. In the case of 55 Cancri e, a combined spectrum with NIRCam and MIRI LRS may present high uncertainties at wavelengths between 3 and 3.7 µm. However, this does not affect the identification of H2O because it does not present spectral features in this wavelength range.

Technology Development for Hydrogen Production Using Nuclear Energy

Nuclear energy is a low-carbon energy source which can provide both electricity and high-temperature heat. Nuclear-based hydrogen production offers a unique opportunity to mitigate carbon emissions. Canadian Nuclear Laboratories (CNL) has been actively developing technologies for nuclear hydrogen production. This poster will highlight CNL’s capability and achievements on the Cu-Cl thermochemical process (CNL trademarked as HCuTECTM) and Solid oxide electrolysis (SOE).HCuTECTM has four main steps in the process: Electrolysis, Separation, Hydrolysis and Thermolysis. The maximum temperature of the HCuTECTM process is 530 oC, which is lower than other thermochemical processes and makes its coupling with some small modular reactors and the supercritical water nuclear reactor ideal since these reactors can supply heat above 600 oC. CNL has extensively studied these individual steps and demonstrated an integrated laboratory system (shown in Figure 1) with a hydrogen production capacity of 100 g/d. CNL is interested in scaling up the process with industrial partners.SOE is also being researched and advanced for hydrogen and clean fuel production at CNL. Current effort is focused on the materials development for oxygen conducting cells. Several CNL cells were made with in-house materials and tested on single cell stations. Preliminary results of CNL cells showed very promising performance for hydrogen production. In the meantime, CNL is assessing the economic benefit of different options to integrate SOE with high-temperature nuclear reactors for both hydrogen and clean fuel production. Figure 1

Molecular Dynamics Investigation of the Gasification and Hydrogen Production Mechanism of Phenol in Supercritical Water

Supercritical water gasification is an efficient and clean method for converting biomass into hydrogen-rich gas. Phenol plays a crucial role as an intermediate product in biomass supercritical water gasification, and studying its reaction pathway in supercritical water is essential for understanding the chemical reaction mechanism and optimizing biomass energy conversion processes. In this paper, we investigated the conversion mechanism of phenol gasification and hydrogen production in supercritical water using a combined approach of reactive force field (ReaxFF) and density functional theory (DFT). We determined the decomposition pathways and product distribution of phenol in supercritical water. The calculation results demonstrate that in the supercritical water system, the efficiency of phenol conversion for hydrogen production is approximately 27 times higher than that of hydrogen production through gasification in the pyrolysis state. Moreover, both the carbon conversion rate and hydrogenation rate in the supercritical water system are significantly higher compared to those in the pyrolysis system. Furthermore, we found that the energy in the supercritical system is approximately half that of the pyrolysis system, favoring the ring-opening reactions of phenol and promoting hydrogen production. In contrast, the pyrolysis system produces a greater quantity of aromatic compounds, leading to tar formation and having significant implications for both the reaction process and reactor design. Additionally, we conducted comparative experiments between the supercritical water gasification process and the pyrolysis process to explore the advantages of supercritical water gasification.

Direct steam reforming of the product gas from ethanol gasification with supercritical water

A continuous process for producing hydrogen from the gasification of ethanol with supercritical water (SCWG) is investigated, which involves a fixed bed steam methane reforming (SMR) reactor downstream of the SCWG reactor. Increasing temperature and decreasing space velocity in the SMR reactor resulted in increased hydrogen concentration and methane conversion. The catalyst activity was more affected at low than high pressures, presumably due to the kinetics of the SMR reaction. The significant increase in total hydrogen yield based on ethanol in the feed showed the importance of installing the reformer after gasification. The excessive steam from the SCWG reactor helped to prevent carbon formation, but it might have resulted in the sintering of the active metal. A long-time experiment proved the stability of the catalyst up to 49 h of time on stream (TOS) with a minor decrease in methane conversion from 84% to 78%.

Detached eddy simulation of the heat release characteristics of H2-O2 reacting flow in supercritical water

The mild H2-O2 reaction is critical for coal-gasification-based polygeneration of power and heat in supercritical water. Time-averaged methods turbulence studies cannot accurately predict the flow, reaction, and heat release during the start-up of the H2-O2 reaction, which was crucial for the start-up and safe operation of supercritical water environment oxidation reactors (SCOR). In contrast, ordinary time-accurate method studies require a tremendous computational effort. Detached eddy simulation (DES), a hybrid model, could balance numerical simulation's computational accuracy and speed. Consequently, this paper has conducted a DES investigation on the start-up process of H2-O2 reaction in SCW with detailed kinetics. Through this article, the spatio-temporal distribution and reaction structure of the H2-O2 reaction start-up process had been unveiled. The process could be divided into the transition and the steady stage, with H2 mass fraction (XH2) and inlet temperature significantly affecting the H2-O2 reaction start-up process. Moreover, the stability of the H2-O2 reaction start-up process was heavily influenced by the XH2. This numerical study could guide the design, scale-up and optimization of SCOR.

Hydrogen production by kraft black liquor supercritical water gasification: Reaction pathway and kinetic

Kraft black liquor (KBL) supercritical water gasification (SCWG) has significant implications for carbon emission reduction and energy efficiency improvement in the pulp industry. This research focuses on investigating the SCWG of KBL under different reaction conditions, including reaction times (5–30 min), temperatures (450–650 °C), and feed concentrations (5%–20%), utilizing a high heating rate batch reactor. The performance of the gasification process is evaluated by analyzing gaseous, liquid, and solid products. Remarkable achievements in carbon gasification efficiency (CGE) of 95.28% and COD removal of 99.90% are attained at 650 °C, 30 min, and 10 wt% feed concentration. The liquid-phase products primarily comprise aromatic compounds, particularly phenolics, with the possible presence of reactive nonaromatic compounds such as cyclopentanone. Lower temperatures favor the formation of solid products, which result from phenolic agglomeration reactions leading to char formation. The research also explores the SCWG reaction pathway of KBL and develops a comprehensive twelve-lumped quantitative kinetic model. This work provides valuable engineering parameters for reactor design, optimization, and numerical simulations, facilitating advancements in SCWG of KBL technology.

The interactions between mixed waste from discarded surgical masks and face shields during the degradation in supercritical water

The widespread use of surgical masks made of polyolefin and face shields made of polyester during pandemics contributes significantly to plastic pollution. An eco-friendly approach to process plastic waste is using supercritical water, but the reaction of mixed polyolefin and polyester in this solvent is not well understood, which hinders practical applications. This study aimed to investigate the reaction of waste surgical masks (SM) and face shields (FS) mixed in supercritical water. Results showed that the optimal treatment conditions were 400 °C and 60 min, achieving a liquid oil yield of 823.03 mg·g−1 with 25 wt% FS. The interaction between polypropylene (PP), polyethylene terephthalate (PET), and iron (Fe) in SM and FS mainly determined the production of liquid oil products such as olefins and benzoic acid. The methyl-branched structure of PP enhanced PET hydrolysis, resulting in higher production of terephthalic acid (TPA). The degradation of PP was facilitated by the acidic environment created by TPA and benzoic acid in the reaction. Moreover, the hydrolysis of PET produced carboxylic acid, which coordinated with Fe3+ to form Fe-H that catalyzed the polymerization of small olefins, contributing to higher selectivity for C9 olefins. Therefore, this study provides valuable insights into the degradation mechanism of mixed PPE waste in supercritical water and guidance for industrial treatment.

A surrogate model for the economic evaluation of renewable hydrogen production from biomass feedstocks via supercritical water gasification

Supercritical water gasification is a promising technology for renewable hydrogen production from high moisture content biomass. This work produces a machine learning surrogate model to predict the Levelised Cost of Hydrogen over a range of biomass compositions, processing capacities, and geographic locations. The model is published to facilitate early-stage economic analysis (doi.org/10.6084/m9.figshare.22811066). A process simulation using the Gibbs reactor provided the training data using 40 biomass compositions, five processing capacities (10–200 m3/h), and three geographic locations (China, Brazil, UK). The levelised costs ranged between 3.81 and 18.72 $/kgH2 across the considered parameter combinations. Heat and electricity integration resulted in low process emissions averaging 0.46 kgCO2eq/GJH2 (China and Brazil), and 0.37 kgCO2eq/GJH2 (UK). Artificial neural networks were most accurate when compared to random forests and support vector regression for the surrogate model during cross-validation, achieving an accuracy of MAPE: <4.6%, RMSE: <0.39, and R2: >0.99 on the test set.

AI Prediction of H2 Production in a Biomass Supercritical Water Gasification Fluidized Bed under Pulsating Inlets

AI Prediction of H₂ Production in a Biomass Supercritical Water Gasification Fluidized Bed under Pulsating Inlets

Experimental investigation on the supercritical water gasification of coal by integrating the hydrogen oxidation process into a supercritical water fluidized bed

The autothermal gasification process is crucial for the industrial application of supercritical water gasification (SCWG) in a supercritical water (SCW) fluidized bed. However, researchers often consider providing external heat to investigate the gasification process and seldom achieve autothermal gasification. Herein, the hydrogen oxidation process was integrated into an SCW fluidized bed to provide heat for the gasification process and to investigate gasification results under various experimental conditions. Using this method, a carbon gasification efficiency of 98.6% and a H2 yield of 68.03 mol/kg were obtained at an experimental temperature of 690 °C. After the gasification products were partially oxidized in the oxidation zone, a H2 yield of 13.6 mol/kg and a total carbon content of <10 ppm in the liquid products were obtained. Compared with the uniform electrical heating method, the heating method based on the hydrogen oxidation process in SCW has obvious advantages, can improve the coal slurry concentration and mass ratio of coal to SCW in the reactor, and maintain a milder temperature under near-complete gasification conditions. This work provides a basis for heat supply in the industrial application of SCWG technology.

Clean conversion of pig manure via supercritical water gasification: Hydrogen-enriched syngas generation, mechanisms analysis, and environmental impacts

The energy potential of pig manure (PM) has garnered attention. Supercritical water gasification (SCWG) is proposed to convert PM to H2-enriched syngas without the drying process for wet materials. This paper studied the effect of diverse parameters on H2-enriched syngas production. The results revealed that higher temperatures and alkaline catalysts elevated total gas yield and H2 yield, with the addition of K2CO3 at 620 °C, 30 min, and 6 wt% feed concentration generating the highest total gas yield (36.55 mol/kg), H2 yield (18.89 mol/kg), and mole fraction (51.55%), accompanied by a high gasification efficiency (87.59%). Based on product characterization and thermodynamic analysis, reaction mechanisms were proposed to provide insight into enhancing syngas production, indicating that the suppression of polymerization reactions between cyclic compounds and the promotion of CH4, C2H6, and long-chain alkanes conversion were essential. Further, the environmental impact evaluation showed that heavy metals (Cu, Cr, As, and Zn) were concentrated in solid products by adsorption and passivation. The solid products exhibited negligible environmental hazards. This work showed that PM SCWG realized syngas production as well as heavy metals enrichment and stabilization, which could provide an alternative solution to the clean conversion of other types of organic wastes, especially with high heavy metals content, such as oily sludge and sewage sludge.

A slow positron beam study of the oxidation behaviour of 310S stainless steel and alloy 800HT exposed to supercritical water

This paper reports a variable-energy slow positron beam characterisation of the surface oxide films in 310 S stainless steel and 800HT nickel-based alloy exposed to 550 °C supercritical water for 1000–4392 h. The evolution of the oxide layer was depth-profiled using positron beam energies from 0.5 to 20 keV, which enabled a probe of up to 2 mm of the near-surface region. SEM/EDS was used as a complementary characterisation tool to support and comprehend the positron annihilation spectroscopy data. A strong dependency on the positron trapping rate and the effective positron diffusion length on the microstructure of the studied materials enabled us to identify up to three non-bulk layers, which were preliminarily attributed to different oxide layers and Fe/Cr depletion regions. By calculating the effective positron diffusion length in the given multi-layer systems, we obtained the thicknesses of individual layers, which are in good agreement with the EDS analysis.

Supercritical water oxidation for the destruction of spent media wastes generated from PFAS treatment

Granular activated carbon (GAC) and anion exchange resin (AIX) have been successfully demonstrated to remove per- and polyfluoroalkyl substances (PFAS) from contaminated water and wastewater. These treatment technologies, when applied for PFAS removal, generate spent media loaded with a high mass of PFAS requiring further treatment and disposal. This project is the first study on the use of supercritical water oxidation (SCWO) to destroy both the spent media and the PFAS adsorbed onto it. One sample of spent GAC and one sample of spent AIX were collected from full-scale groundwater remediation systems treating PFAS. A second spent AIX sample was collected from a mobile PFAS treatment unit. The total PFAS concentrations reported in the GAC, AIX and second AIX feedstock slurries were 0.21 mg/kg, 1.3 mg/kg and 0.9 mg/kg, respectively. Each feedstock was processed separately in a one (1) wet metric ton per day tubular reactor SCWO system. The study demonstrated that SCWO is a very effective PFAS destruction technology for spent GAC and AIX, derived from water remediation systems treating PFAS. The spent media were completely mineralized to water, carbon dioxide (CO2) and a negligible amount of residual minerals. Total target PFAS compound concentrations in the SCWO system effluents after treating spent GAC, AIX and second AIX feedstocks were 548, 77 and 796 ng/L, respectively. The results indicated that the percentage elimination of perfluorocarboxylic acids (PFCAs) was better than that of perfluosulfonic acids (PFSAs) and long-chain PFAS elimination was better than short-chain PFAS.

Simultaneous recycling of waste solar panels and treatment of persistent organic compounds via supercritical water technology

The study addresses the application of the supercritical water technology in the simultaneous recycling of obsolete solar panels and treatment of persistent organic compounds. The obsolete solar panels samples were characterized by TEM-EDS, SEM, TG-DTA, XRD, WDXRF, MP-AES and elemental analysis. Initially, the optimized parameters for the degradation of solid organic polymers present in residual solar panels via oxidation in supercritical water were defined by an experimental design. Under optimized conditions, 550 °C, reaction time of 60 min, volumetric flow rate of 10 mL min−1 and hydrogen peroxide as oxidant agent, real laboratory liquid wastewater was used as feed solution to achieve 99.6% of polymers degradation. After the reaction, the solid product free of organic matter was recovered and characterized. On average, a metal recovery efficiency of 76% was observed. Metals such as aluminum, magnesium, copper, and silver, that make up most of the metallic fraction, were identified. Only H2, N2 and CO2 were observed in the gaseous fraction. Then, initial data on the treatment of the liquid decomposition by-products, generated during ScW processing, were reported. A total organic carbon reduction of 99.9% was achieved after the subsequential treatment via supercritical water oxidation using the same experimental apparatus. Finally, insights on the scale-up, energy integration and implementation costs of a ScW solid processing industrial unit were presented using the Aspen Plus V9 software.

Comparison of Experimental Results with Thermodynamic Equilibrium Simulations of Supercritical Water Gasification of Concentrated Ethanol Solutions with Focus on Water Splitting

Comparison of Experimental Results with Thermodynamic Equilibrium Simulations of Supercritical Water Gasification of Concentrated Ethanol Solutions with Focus on Water Splitting

Thermodynamic analysis of the series system for the supercritical water gasification of coal-water slurry

Supercritical water gasification (SCWG) is a potential clean technology for utilizing solid fuel or waste without producing gaseous pollution. Efficient energy integration and recovery strategies play an essential role in the endothermal gasification process. Previous approaches have only focused on the heat source or heat transfer with very little attention to the utilization of the abundant supercritical water in the product gas. This paper proposes an innovative series design for heat integration in the SCWG system while taking the gasification process into account. Notably, the first-stage oxidized hot fluid containing abundant water is directly utilized as the gasification agent for the second-stage gasification reactor. The thermodynamic analysis shows that the cold gas and exergy efficiency in the two-stage series system is 17.4% and 15.0% higher than in the previous single-stage gasification reactor. The sensitivity analysis illustrates that increasing series stages and feedstock concentration while decreasing oxidation proportion and the agent-slurry ratio can improve the overall system efficiency by decreasing the demand for oxygen, power consumption, and heat transfer rate. The series design should offer an innovative and practical approach for the heat supply in the industrial SCWG plant.

A high-temperature and high-pressure cell for in situ visualization of reaction processes by neutron imaging

This study developed a high-temperature and high-pressure (HTHP) cell for in situ neutron imaging of hydrothermal reactions. The cell’s maximum temperature and pressure were 500 °C and 50 MPa, respectively, and its vessel for observing reactions comprised SUS316 stainless steel. Neutron transmission images were obtained to observe the behavior of sub- and supercritical water and the decomposition of two plastics (polypropylene and polyethylene) at HTHP. The images showed that water’s density and phase changed with temperature and pressure, affecting neutron transmission (and thus image brightness). The plastics began to melt and change shape at 150–200 °C, and they decomposed at 500 °C and 20 MPa. This study provides a basis for future research using the HTHP cell to examine various reactions such as the decomposition of biomass samples, the reforming of heavy oil, and the synthesis of nano-materials using sub- and supercritical water.

High Dimensional Model Representation Approach for Prediction and Optimization of the Supercritical Water Gasification System Coupled with Photothermal Energy Storage

Supercritical water gasification (SCWG) coupled with solar energy systems is a new biomass gasification technology developed in recent decades. However, conventional solar-powered biomass gasification technology has intermittent operation issues and involves multi-variable characteristics, strong coupling, and nonlinearity. To solve the above problems, firstly, a solar-driven biomass supercritical water gasification technology combined with a molten salt energy storage system is proposed in this paper. This system effectively overcomes the intermittent problem of solar energy and provides a new method for the carbon-neutral process of hydrogen production. Secondly, the high dimensional model representation (HDMR) approach, as a surrogate model, was used to predict the production and lower heating value of syngas developed in Aspen Plus, which were validated using experimental data obtained from the literature. The ultimate analysis of biomass, temperature, pressure, and biomass-to-water ratio (BWR) were selected as input variables for the model. The non-dominated sorted genetic algorithm II (NSGA II) was considered to maximize the gasification yield of H2 and the LHV of syngas in the SCWG process for five different types of biomass. Firstly, the results showed that HDMR models demonstrated high performance in predicting the mole fraction of H2, CH4, CO, CO2, gasification yield of H2, and lower heating value (LHV) with R2 of 0.995, 0.996, 0.997, 0.996, 0.999, and 0.995, respectively. Secondly, temperature and BWR were found to have significant effects on SCWG compared to pressure. Finally, the multi-objective optimization results for five different types of biomass are discussed in this paper. Therefore, these operating parameters can provide an optimal solution for increasing the economics and characteristics of syngas, thus keeping the process energy efficient.