Supercritical Water Research Articles

Experimental Investigation on the Pyrolysis and Conversion Characteristics of Organic-Rich Shale by Supercritical Water.

Organic-rich shale oil reservoirs with low-medium maturity have attracted increasing attention because of their enormous oil and gas potential. In this work, a series of experiments on pyrolysis of the particle and core samples were carried out in a self-made supercritical water pyrolysis apparatus to evaluate the feasibility and benefits of supercritical water in promoting the transformation efficiency and oil yield of the low-medium maturity organic-rich shale. Core samples had a mass loss of 8.4% under supercritical water pyrolysis, and many microcracks were generated, which increased the pyrolysis efficiency substantially. The oil yield of shale pyrolysis could reach 72.40% under supercritical water conditions at 23 MPa and 400 °C, which was 53.02% higher than that under anhydrous conditions. In supercritical water conditions, oxygen-containing compounds are less abundant than in anhydrous conditions, suggesting that supercritical water can inhibit their formation. Also, supercritical water conditions produced higher yields for light fraction, medium fraction, and heavy fraction shale oil than those under anhydrous conditions. These results indicate that supercritical water pyrolysis is feasible and has excellent advantages for low-medium maturity organic-rich shale.

Pulsation effects on mixing behaviour of binary particles with different densities in supercritical water fluidized bed reactors: A CFD-DEM study

A coupled computational fluid dynamics - discrete element method (CFD-DEM) model for simulating supercritical water fluidized bed reactors (SCWFBR) is established and verified using the previous correlations based on experimental data. The CFD-DEM model is then adopted to investigate the pulsation effects on the mixing behaviour of binary particles with different densities in the SCWFBR. Numerical results show that external energy pulses can be effective in promoting the mixing of binary particle systems with different densities in SCWFBR which cannot be achieved by simply increasing the flow rate constantly. Within the current parameter range: low-frequency pulses are favored to promote particle mixing rather than high-frequency pulses, and an optimal frequency exists. The role of low amplitudes in influencing mixing degree is slight, but the particle mixing degree can be greatly enhanced by increasing the pulse amplitude beyond a certain value. The mechanism that pulsed inlet fluid promotes particle mixing is to raise the heavy particles which are inclined to stay at low positions during the fluidization. The Fast Fourier Transform (FFT) method to predict the optimal frequency established for size-induced segregation can be applicable to solve the problem of the density-induced segregation.

REMOTE MONITORING OF RADIATION TEST TEMPERATURE REGIME AT A HIGH-CURRENT ELECTRON ACCELERATOR

Methods for evaluating the radiation resistance of structural materials of nuclear reactors have been developed and research is being carried out in NSC KIPT. As a part of these studies, a supercritical water convection loop with a chamber for irradiation of the tested samples by electron beam of the accelerator LU-10 (beam energy of 8…10 MeV, beam power up to 10 kW) was developed. A pyrometric system based on a DSLR camera (Digital Single-Lens Reflex Camera) has been created for the remote continuous non-intrusive control of the surface temperature of the irradiation cell in the range of 350…550°С. The work presents the results of calibration and use of the developed system in the conditions of a 500-hour run of sample irradiation in the loop.

Thermodynamic and environmental analysis of an integrated multi-effect evaporation and organic wastewater supercritical water gasification system for hydrogen production

Organic wastewater poses significant environmental and human health risks. Supercritical water gasification (SCWG) presents a promising approach for converting organic waste into hydrogen-rich mixed gases. Nevertheless, the high moisture content present in organic wastewater hampers the energy efficiency of the SCWG process. To tackle this challenge, we have designed and developed an organic wastewater SCWG hydrogen production system incorporating a multi-effect evaporator. The developed system demonstrates the ability to achieve autothermal conditions for the treatment of swine wastewater with a solids concentration of 4.3%. Notably, this system exhibits impressive energy efficiency, reaching a maximum value of 44.88%, along with an exergy efficiency of 33.90% when processing 7% swine wastewater. Exergy analysis further reveals that the incorporation of a multi-effect evaporator leads to a reduction in exergy destruction within the gasification unit, oxidation unit, and heat exchanger. These improvements highlight the positive impact of the multi-effect evaporator on the overall performance of the supercritical water gasification system. Sensitivity analysis indicated that suitable concentrated concentration and an appropriate amount of preheated water can improve hydrogen production. The system minimum GWP reaches 5.27 kgCO2-eq/kgH2 after adding the CCUS. This work expands the range of applicable feedstocks for the autothermal SCWG process.

Effect of exposure temperature on the corrosion behavior of a FeNiCrCuAl high entropy alloy in supercritical water

The corrosion behavior of a FeNiCrCuAl high entropy alloy exposed to supercritical water at 380–650 °C and 25 MPa was investigated. The weight gain exhibited a nearly parabolic kinetics. At 380 °C, Al2O3 precipitated on Fe3O4 particles in FeCr-rich regions and intensified as the temperature increased to 650 °C, eventually resulting in an Al2O3 particle. A mixed Fe3O4 and NiAl2O4 outer layer developed on NiAl-rich regions at 380 °C, whereas an Al2O3 layer formed at 650 °C. Cu2O formed along the boundaries of NiAl-rich regions, regardless of exposure temperatures. The corrosion mechanism at different temperatures was elucidated.

Supercritical water gasification of microalgae: The impact of the algal growth water

Investigation into the supercritical water gasification (SCWG) of microalgae has largely used deionized water as the reaction medium. However, real systems would use the algal growth water directly, containing ions that have been known to catalyse SCWG (K+, Na+, OH-, Fe3+, Cl-). Investigation into the effect of the growth water on SCWG was carried out for a range of temperatures (450–550), biomass concentrations (1–3wt%) and catalysts (KOH, Ru/C), using glucose or Chlorella vulgaris as the feedstock was performed. A significant increase in CO2 and reduction in CO content in the gas was observed without a catalyst and with a Ru/C catalyst. An increase in char/tar was also observed without a catalyst. As a result, the impact of the growth water should be considered for the SCWG of microalgae, in laboratory experiments and the selection of algal growth media in industrial applications.

Hydrogen donation of supercritical water in asphaltenes upgrading by deuterium tracing method

Hydrogen donation is the key to supercritical water upgrading of heavy oil, because it benefits light distillate production and inhibits condensation, but the mechanism is still unclear. In this work, an isotope tracing method, combined with Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy analyses, was used to elucidate the hydrogen donation mechanism in supercritical water upgrading of asphaltenes. In asphaltenes upgrading, it was found that the aliphatic carbon at the end of the side chain of asphaltene macromolecules could capture deuterium from supercritical heavy water via free radical reactions, and the deuteration ratio at this position was 11 %. For supercritical water upgrading of vacuum residue which is generally considered as a system of asphaltenes dissolved in maltenes, the existing maltenes enhanced hydrogen donation to asphaltenes. Further, a possible hydrogen donation pathway was proposed. This work provides an in-depth understanding of the hydrogen donation mechanism for supercritical water upgrading.

Efficient coal-based power generation via optimized supercritical water gasification with chemical recuperation

Supercritical water gasification (SCWG) is promising as a clean coal technology and is an emerging topic of interest in sustainable energy. Here, we introduce a clean and efficient power generation system that optimizes SCWG of coal through chemical recuperation. Central to our approach is the innovative utilization of both exhaust and a portion of the syngas as dual heat sources for gasification, simultaneously producing the requisite supercritical water. This chemical recuperation strategy effectively enhances the transformation of coal chemical energy into syngas. The introduced system achieves power generation and exergy efficiencies of 56.64 and 55.30%, respectively, outperforming those of a baseline system by 8.43 and 8.23%, respectively. This gain is primarily attributed to the irreversible losses in the gasification, air separation, and heat-exchange processes of the introduced system, which were reduced by 8.75, 2.47, and 4.17%, respectively, compared with the corresponding values of the baseline system. In order to elucidate and validate the reduced irreversible losses in the introduced system compared with those in the baseline system, we incorporated the energy utilization diagram methodology into our analysis. In summary, the introduced system represents a pivotal advancement in clean and efficient coal-based power generation and underscores the need for continuous innovation in this sector.

Performance assessment of an energetically self-sufficient system for hydrogen production from oilfield wastewater treated by supercritical water gasification

Oilfield wastewater with high moisture content can be efficiently treated by supercritical water gasification (SCWG) technology to produce hydrogen. This paper conducted a thermodynamic and environmental analysis of the oilfield wastewater SCWG system to provide optimization strategies. The waste heat utilization technology can enhance the heat integration of the system to reduce the exergy destruction and increase the H2 yield. Sensitivity analysis showed that a ratio of preheating water to emulsion 3 can promote water-sensitive reactions to produce H2 and save the H2 needed to maintain the energetically self-sufficient system. Low system pressures, high feedstock preheating temperatures, and low oxidation reactor temperatures can reduce system energy destruction to obtain high H2 yield and system efficiency. Meantime, the developed SCWG system has the potential to achieve natural enrichment of greenhouse gases after the H2 separation has been completed. The use of waste heat utilization technology and carbon capture and storage (CCS) technology is expected to increase system efficiency to 53.43 % and reduce global warming potential (GWP) of 5.52 kg CO2-eq/kg H2. This work would be of great value to the process design and optimization for the SCWG system of oilfield wastewater.

Hydrogen-rich gas production via supercritical water gasification (SCWG) of oily sludge over waste tire-derived activated carbon impregnated with Ni: Characterization and optimization of activated carbon production

In this study, the production of activated carbon (AC) through the chemical activation of waste tire (WT) using H3PO4 and KOH for H2 production by SCWG of oily sludge (OS) donated by Persian Gulf Star Oil Company was investigated. H3PO4 was the best activating agent based on some pretests results, and then the synthesis of AC was optimized using Response Surface Methodology. Based on BET surface area of synthesized ACs, thirty combinations of the four variables namely; activation temperature (350–550 °C); activation time (1–4 h); H3PO4 to WT ratio (1–3 w.w−1); and H3PO4 concentration (20–40 wt%) were optimized. CHNS, TGA, FE-SEM, and EDS-mapping analyses were used to characterize the AC and catalyst synthesized in optimum condition (activation temperature: 450 °C; activation time: 2.5 h; H3PO4 to WT ratio: 2 w.w−1; and H3PO4 concentration: 40 wt%), which presented a surface area of 170 m2 g−1. Finally, Ni was impregnated on the optimized AC with different loadings (5–15 wt%) to evaluate its performance in H2 production by SCWG of OS. Although H2 yield in catalytic experiments was higher than that observed in non-catalytic experiment, results showed that the maximum H2 selectivity was 66% in SCWG of OS using AC impregnated with 10 wt% Ni.

Experimental investigations of flow dynamics in the riser of supercritical water circulating fluidized bed

Experimental investigations of flow dynamics in the riser of supercritical water circulating fluidized bed

Numerical Simulation of Membrane Separation Characteristics of Supercritical Carbon Dioxide and Water.

To solve the problem of water carryover in the supercritical CO2 separation and mining process in the CO2 plume geothermal system, a three-dimensional shell-tube hollow fiber membrane absorption separator is designed in this study. A coupled species transport model, a porous medium model, and an absorption mathematical model are established, and the flow field and separation characteristics in the circular and flat tubes are analyzed using numerical simulation. The results show that the membrane separation efficiency increases with an increase in the flatness and membrane tube length. When the inlet velocity of the mixture is 0.1 m/s, the separation efficiency can reach 75.92%. Selecting a smaller flow Reynolds number and a more significant membrane tube flatness will reduce the water mass fraction at the outlet. When adding baffles of different shapes to the membrane tube, the mixture fluid in the membrane tube meanders forward and flows in the shape of "Z" under the blocking effect of the arcuate baffles. With an increase in the number of arcuate baffles in the membrane tube, the membrane separation efficiency of the separator increases continuously. The mixture fluid flows in the membrane tube with the built-in torsional baffles in a spiral manner, and the separation efficiency of the membrane separator increases with a torsion ratio reduction in the membrane tube.

Review of SCWR research in Japan

SCWR (supercritical water cooled reactor) is one of the Generation IV reactors. This review summarizes the results of SCWR design concept development through numerical simulations carried out by the author-led team at the University of Tokyo and Waseda University from 1989 to 2014. They are core design, subchannel analysis, statistical thermal design, fuel rod design, development of fuel integrity criteria, plant system and heat balance, plant dynamics analysis, plant control, startup system, stability analysis, safety principle, safety criteria, safety analysis, transient subchannel analysis and fast reactor SCWR. A brief summary of experimental results on thermal hydraulics, materials and water chemistry follows. Discussion includes SCPR study by Japanese BWR manufacturers, comments on the 2005 INEEL SCWR report, misconceptions about SCWR and commercialization challenges. The SCWR is an innovation in light water reactors based on supercritical coal-fired power plant technology that has been in use worldwide for over half a century. This review covers most of the SCWR design and analysis. For researchers, it is a good subject to understand the design and analysis of light water reactors.

Mechanism of supercritical water gasification of corn stover for hydrogen-rich syngas: Composition of reaction products

Hydrogen-rich syngas from supercritical water gasification (SCWG) of renewable biomass is a promising technology. However, due to the complexity of the biomass structure, there is limited research on the liquid and solid products generated by SCWG of real biomass, and the related hydrolysis and gasification mechanisms are not yet clear. In this study, SCWG experiments were carried out on corn stover through a batch reactor, and the products were analyzed by gas-phase GC, liquid-phase GC-MS, UV spectroscopy, ultimate analysis, FTIR, PY-GC/MS, BET specific surface area, and SEM. The mechanism of corn stover SCWG was revealed by qualitative and quantitative analyses of gas products, the composition of liquid products, and the functional groups, carbon skeleton, surface morphology and specific surface area of solid products. The results showed that the aliphatic groups were hydrolyzed and gasified first at 400–500 °C. When the temperature rose to 600 °C, the aromatic groups were also gradually hydrolyzed and gasified, and the remaining aromatic groups underwent condensation and dehydrogenation to produce large molecular naphthalene, phenanthrene, pyrene, etc. The optimal biomass concentration was between 10.5 and 1 g/100 g water during the corn stover SCWG, and the reaction was completed in 15 min.

Experimental study on particle deposition of Fe3O4 in supercritical heat exchange tube

Particle deposition poses a significant challenge to the economics and safety of supercritical boilers. Understanding the deposition behavior of particles on the steam-water side wall is essential. A supercritical particle deposition system was designed and build according to the actual conditions. The effects of fluid thermal state, flow rate and exposure time on particle morphology, deposition layer morphology and deposition distribution were investigated. The results showed that FeCl2 was oxidized to micron sized Fe3O4 particle, and the salt crystals had a redissolution behavior in supercritical water. The particle deposition layer was a three-layer structure, possibly related to the gas-like fluid clusters and turbulence. The deposition distribution was related to the flow state, and there was a forward shift of the peak point with exposure time. Our results help to understand the particle deposition behavior in supercritical heat exchangers.

Energy yield from wastewater by supercritical water oxidation process: Experimental validation and simulation from the viewpoint of energy system

The degradation of high concentration organic wastewater and the recovery of energy using supercritical water oxidation (SCWO) technology have the potential to become viable in the future. High concentration organic wastewater contains a significant amount of energy. This paper focuses on utilizing high concentrated wastewater as a renewable energy source, from an energy system perspective, an experimental rig was designed to determine the optimal working conditions. The experiments were conducted with an oxidation coefficient of 1.1, a flow rate of high concentration organic wastewater of 9 ml/min, a heating temperature of 400 °C, and a reaction pressure of 25 MPa. Under these conditions, the COD and TOC removal rates of the high concentration organic wastewater were found to be 99.383 % and 99.876 % respectively. Additionally, the phenomenon of “Abnormalities in pressure sensitivity” observed during high concentration organic wastewater the experiment was further explained through additional experiments. Finally, by comparing the experimental energy recovery with the simulation results, an energy recovery efficiency of 78.95 % was achieved. The feasibility of the simulated energy recovery in practice was verified, confirming the potential to convert the previous energy-consuming wastewater treatment process into a productive one. This study provides a theoretical and experimental foundation for further related research.

Numerical study on particle behavior in a Y-junction mixer for supercritical water hydrolysis

In the continuous-type supercritical water hydrolysis process, rapid mixing of supercritical and subcritical streams is important to maximize yield and minimize degradation from over-reaction. This work investigated the particle behavior in a Y-junction mixer using large eddy simulation coupled with a discrete phase model, aiming to optimize the supercritical hydrolysis process for biomass conversion. A series of numerical simulations analyzed the influence of the mixer’s orientation, flow directions, and flow rates on effective mixing and backflow prevention.The results demonstrated that the most effective mixing occurred in a vertically oriented Y-junction mixer with an upward-directed supercritical water inlet, aligning the momentum direction of natural and forced convection effectively. Consequently, over 80% of particles reached the temperatures close to the mixing temperature of supercritical and subcritical water within the Y-junction mixing zone, indicating enhanced mixing effectiveness and potential for efficient hydrolysis. This configuration also minimized backflow.

High value-added syngas production by supercritical water gasification of biomass: Optimal reactor design

Supercritical water gasification (SCWG) emerges as a highly encouraging technique for the efficient generation of syngas from biomass feedstock. The performance of the SCWG reactor plays a pivotal role in determining the overall success of the process. This study employs a mathematical modeling and optimization method to design an optimal tubular-type reactor for the SCWG of biomass. First, the reactor is divided into cells, and mathematical models are established to describe the reactions within each cell, as well as the mass balances between cells. Afterwards, the optimal reactor design problem is formulated as a non-linear optimization problem, which involves integration of all the individual models along the reactor length. The objective is to maximize the high heating value (HHV) of gaseous products and simultaneously satisfying multiple constraints. Once the problem is solved, the optimal decision variables (i.e., reactor axial fluid temperature profiles, diameter and length) are obtained. Here, two reactor design scenarios are investigated to showcase the adaptability of this optimization method. The obtained outcomes indicate that non-isothermal reactors with a zigzag-shaped temperature profiles are more advantageous than traditional isothermal ones for high value-added syngas production. Specifically, optimal non-isothermal reactors can achieve a remarkable increase of 50.08% (i.e., 26.94 vs 17.95 MJ/kg glycerol) in the HHV of gaseous products compared to isothermal reactors. These findings provide valuable insights on designing efficient SCWG reactors for industrial high value-added syngas production.

Hydrogen production from supercritical water gasification of canola residues

Canola hull, meal and straw are abundantly available as low-value agricultural residues in Canada. These lignocellulosic feedstocks have the potential for the generation of biofuels as alternatives to fossil fuels. Supercritical water gasification is an emerging hydrothermal process for the conversion of recalcitrant biomasses into value-added hydrogen with the application of water beyond its critical temperature and pressure. This study focuses on the comparative investigation of supercritical water gasification of canola residues for H2 production through optimization of process temperature (350–500 °C), reaction time (20–80 min) and feedstock concentration (10–25 wt%) at a constant pressure of 23–25 MPa. Supercritical water gasification of canola straw resulted in a high H2 yield of 7.1 mmol/g to 6.2 mmol/g of H2 from canola hull and 5.5 mmol/g of H2 from canola meal at a temperature, reaction time and feedstock concentration of 500 °C, 40 min and 20 wt%, respectively. Furthermore, H2 yield and total gas yield from canola straw were maximized to 8.1 mmol/g and 29.7 mmol/g at the optimized supercritical water gasification conditions of 500 °C, 60 min and 10 wt%. Hydrochar obtained at high gasification temperatures also revealed aromatic carbon structures and thermal stability due to dehydrogenation, decarboxylation, deamination and aromatization. The overall results demonstrated the potential of supercritical water gasification as an evolving hydrothermal process to convert lignocellulosic biomass into high-value H2-rich gas.

Supercritical water gasification of waste R410A refrigerant mixture for the resource utilization: ReaxFF reactive molecular dynamic simulation and density functional theory calculation study

Harmless treatment and resource utilization of the waste HFC refrigerants have gradually become the focus of attention. As a clean waste resource utilization technology, supercritical water gasification has good potential in converting waste refrigerant into high value-added chemicals and fuels. In this study, the supercritical water gasification mechanism of R410A, and the interaction mechanism between R125 and R32, and between H2O and R410A during the gasification process are investigated by using ReaxFF reactive molecular dynamic simulation and density functional theory calculation study. The results show that the main products obtained from the supercritical water gasification of R410A are HF, H2, CO and CO2. More than 90 % of F atoms in R410A can be mineralized to form HF molecules. H2 and CO are two important syngas products during the supercritical water gasification process. Hydrogen bonds are generated between R125 and H2O molecules and between R125 and R32 molecules, which leads to the decomposition of R125 molecules more easily, and the decomposition of R32 molecules more difficult. This work provides a possible way to convert waste HFC refrigerant mixture into high value-added chemicals and syngas.