Temperature High Pressure Water Research Articles

Hydrogen Production from Glucose by Partial Oxidation in High Temperature High Pressure Water -2: Reaction Mechanism and Rate of HCOOH Decomposition

By partial oxidation of glucose with ZnO in high pressure high temperature water at 300°C, glucose was converted into H2 with relatively high yield and without CH4 formation. In order to understand the reaction mechanism and the optimum condition of the process, we performed glucose partial oxidation at 200-300°C to analyse an intermediate of H2, without ZnO, which probably promotes the intermediate into H2. As a result, we detected a high yield of HCOOH. The formation of HCOOH was sensitive to reaction temperature and the yield was the highest at 200°C among the experimental conditions. It was confirmed that the role of ZnO was a promoter of HCOOH decomposition into H2 and CO2 through HCOOH conversion experiments with and without ZnO at 200-300°C. The conversion of HCOOH with ZnO was within a few minutes at 300°C. Through the study, we suggested that two-stage reaction is effective for H2 formation from glucose partial oxidation: the partial oxidation of glucose is conducted at 200°C and the conversion of HCOOH is achieved over 300°C. To confirm the idea, the two-stage reaction was performed: the partial oxidation of glucose was conducted at 200°C with ZnO followed to increase temperature up to 300°C for promotion of H2 formation. The H2 yield was less amount than expected. This was probably due that ZnO prohibited the formation of HCOOH on glucose partial oxidation at 200°C.

Hydrogen Production from Glucose by Partial Oxidation in High Temperature High Pressure Water -1: Study on Reaction Condition and Effect of ZnO

Hydrogen formation from glucose was examined using a batch reactor in high temperature high pressure water at 300°C. Homogenous catalysts (H2SO4 and NaOH) were not effective for H2 formation from glucose at this condition. Heterogeneous catalysts: Ag2O, CuO, Cr2O3, Fe2O3, MgO, MnO2, MoO3, NiO, rutile TiO2, and ZnO, were applied and then it was found that MnO2 and ZnO effectively promoted H2 formation. In order to enhance H2 yield, glucose in high pressure high temperature water was partially oxidized in the presence of ZnO. As a result, 25 % H2 (glucose mole basis) was obtained. In this reaction, by-production of methane was not observed. The enhancement of H2 yield was not observed when ZnO was located at gas phase. It suggested that a precursor of H2 formed in the aqueous phase.

High Temperature Corrosion Behaviors of Carbon Steels by A Pressurized Water

The long-term corrosion resistances for the carbon steels have been investigated under high temperature pressurized water atmosphere, in the conjunction with the analysis of nondestructive properties by the ultrasonic wave. The corrosion test for carbon steels was carried out at the temperature of 200 °C under a water pressure of 10 MPa. The corrosion test cycles for carbon steels were changed up to 65 weeks. The mechanical properties of carbon steel suffered from the corrosion cycle were investigated by a tensile test, attaching an acoustic emission sensor on the test sample. The tensile strength of carbon steels greatly decreased beyond the corrosion cycle of 35 weeks, accompanying the increase of weight loss by the creation of corrosion damages. The attenuation coefficient of carbon steels by the ultrasonic wave increased with the increase of corrosion cycles.

Wear damage resulting from sliding impact kinematics in pressurized high temperature water: energetical and statistical approaches

Specific wear of rod cluster control assemblies (RCCA) in pressurized water nuclear reactors (PWR) results from contacts with their guides due to flow-induced vibration. Particular sliding impact contact conditions and the specific environment in PWR coupling temperature and solution chemistry involve original mechanisms of wear. A specific tribometer has been developed during recent years by FRAMATOME-ANP. This simulator operates in experimental conditions close to the sliding impact motion of RCCA assemblies against guides and under a similar environment (temperature, pressure and water chemistry). Numerous and various wear tests were realized in order to study the influence of the sliding impact parameters on wear loss and wear scars. Specific tests with continuous data acquisition were realized. Different wear scars were observed. An analogy with erosion was done. An erosion model was used to determine critical conditions concerning friction coefficient and incidence angle values leading to wear. Considering these critical conditions, it was possible to explain the observed difference of wear loss and facies.

Water chemistry effect on the wear of stainless steel in nuclear power plant

A specific tribometer equipped for electrochemical measurements in pressurized high temperature water (PHTW) is being used to study the effect of the water chemistry on the wear rate of a stainless steel. First results indicate that a slightly acidic pH increases drastically the wear rate compared to slightly alkaline pH. However, this result could not be correlated to an oxidation process due to a lower current value measured during friction. Some hypothesis are presented on the influence of short-length attractive forces in the contact.

Oxidation of plasma surface modified zirconium alloy in pressurized high temperature water

Oxidation of a zirconium-alloy, zircaloy-2 in the untreated (non-surface treated) condition and after ion implantation with nitrogen, carbon, and oxygen has been examined after exposure for 168 h to an environment of pressurized water at 25 MPa at temperatures of 300 and 500 °C. At this pressure, water is in subcritical state at 300 °C and supercritical state at 500 °C. Cross-sectional scanning electron microscopy showed that oxidation occurred in the form of mainly an oxygen diffusion layer for the 300 °C exposure, but for the 500 °C exposure a uniform stoichiometric oxide layer and a sub-surface oxide diffusion layer were observed. For the 300 °C exposure, carbon and nitrogen ion implantation resulted in a thinner oxygen affected layer compared to the untreated alloy. The oxygen ion implanted samples showed a thicker oxygen affected layer, but this included the thickness contributions from both thermal oxidation and prior oxygen ion implantation. After exposure at 500 °C, the carbon and nitrogen ion implanted samples exhibited a thicker, and the oxygen ion implanted samples a thinner oxygen affected layer compared to the untreated alloy. A separate experiment involving exposure to supercritical water at 400 °C for 168 h showed lower levels of oxidation in zircaloy-2 samples that were sputter coated with an yttrium film and subsequently bombarded with xenon ions prior to exposure.

In situ generation of hydrogen for continuous hydrogenation reactions in high temperature water

The thermal decomposition of HCO2H or preferably, HCO2X (X = Na or NH4) can be used to generate H2 for the continuous hydrogenation of aromatic and cyclic aldehydes, ketones and nitroaromatics in high temperature pressurised water (HTPW). This means that hydrogenation reactions can be carried out in exactly the same equipment as has previously been used for selective oxidation in HTPW, thus facilitating relatively simple application of these reactions for non-specialists.

Erosion corrosion in stainless steel pipe under water vapour two-phase flow conditions

High-speed two-phase water vapour flows in the outlet portion pipes of nuclear power stations. Erosion corrosion experiments of stainless steel were performed by the use of Component Test Loop, in which high-temperature pressurized water vapour is circulated, under test conditions of all volatile treatment with steam phase velocities 10–40 m/s (steam quality 15%). The erosion corrosion losses were estimated by weight differences of pipe specimens before and after tests. Erosion corrosion losses are very small and almost constant for velocities of two-phase flow.

Isothermal and non-isothermal oil–water flow and viscous fingering in a porous medium

Immiscible flow of heavy oil in a porous formation by high temperature pressurized water has been numerically studied. The physical region is a square domain in the horizontal plane with low and high pressure points at the opposite corners along one of the diagonals. Water, the invading fluid, when introduced at high pressure displaces the in situ oil towards the low pressure production zone. The extent of displacement of oil by water through the porous medium in a given amount of time and the appearance of preferential flow paths ( fingers) is the subject of the present investigation. The resistance to water–oil movement arises from the viscous forces in the fluid phases and the capillary force at their interface. Based on their relative magnitudes, various forms of displacement mechanisms can be realized. As the viscosity ratio of heavy oil to water is large, viscous forces in the oil phase become dominant and constitute the major factor for controlling the flow distortions in the porous formation. A mathematical model that can treat the individual fluid pressures, capillary effects and heat transfer has been employed in the present work. A fully implicit, two-dimensional numerical model has been used to compute the pressure and temperature fields. The domain decomposition technique has been adopted in the numerical solution since the problem is computationally intensive. Naturally occurring oil-rich reservoirs to which the present study is applicable are inhomogeneous and layered. A qualitative study has been carried out to explore the effect of permeability variations on the flow patterns. Numerical calculations show that non-isothermal effects as well as layering promote the formation of viscous fingers and consequently the sweep efficiency of the high pressure water front.

Characterisation by neutron diffraction in high temperature pressurised water of the surface corrosion and hydrogen embrittlement of zircaloy-4

Zircaloy-4 foils were analysed by in situ neutron diffraction experiments when submitted to a water corrosion process simulating PWR conditions (high temperature and high steam pressure). The oxidation process takes place through two steps and layers. First, a layer of dense tetragonal β-zirconia is formed when the metal external surface is corroded, then it transforms progressively to an α-zirconia external layer. Advancement of the oxidation layer is accompanied by the penetration of some hydrogen in the first metal layers. High temperature formation of a ternary intermetallic hydride involves the fine Zr(Cr,Fe) 2 particles of the C14 Laves phase type which are randomly distributed as precipitates in the zirconium matrix. The hydrides become unstable when the sample is cooled to room temperature. Precipitation of binary ϵ-ZrH 2 grains occurs only when the sample is cooled down to 200 °C. A posteriori experiments reveal some possible local correlation between these two transformations, so an impact of the formation of hydrides on the corrosion process is suggested from the present experiment. The zircaloy-4 was cold-rolled first, and found to be highly textured even after annealing. However, the two types of corroded zirconia formed at the surface were found to have a texture correlated with the metal substrate, and texture effect was observed also for the precipitates.

Removal of Metal-Oxide Layers Formed on Stainless and Carbon Steel Surfaces by Excimer Laser Irradiation in Various Atmospheres

To apply the laser ablation technique for decontamination of metal wastes contaminated with radioactive nuclides, the effect of irradiation atmospheres on removal of oxide layers on steel surfaces by laser ablation was studied. Based on the assumption that the absorption of laser light follows the Lambert-Beer law, ablation parameters, such as absorption length and threshold fluence for ablation, of sintered Fe2O3 and stainless and carbon steels were measured in He, O2, Kr, or SF6 atmospheres. The results indicated that SF6 was the most effective gas of all irradiation atmospheres studied for the exclusive removal of oxide layers formed on stainless and carbon steel samples in high-temperature pressurized water. Secondary ion mass spectroscopic measurement and scanning electron microscopic observation confirmed that no oxide layer existed on the steel samples after the exclusive removal with laser irradiation.

Potassium Persulfate as Oxidant in Pressurized Hot Water

Sub- and supercritical water oxidation are quite new techniques for wastewater treatment. Temperatures must be high enough and reaction times long enough that the organic compounds are completely oxidized into carbon dioxide and water. The critical temperature and pressure of water are 374 °C and 22.1 MPa. The primary aim of the study was to determine whether potassium persulfate is a feasible choice for oxidant in work clearly below the critical temperature of water. Because potassium persulfate is water soluble, it can be added directly to water containing organic compounds. Simple equipment was constructed for oxidation in high-temperature pressurized water, and oxidation of phenol, 2,3-dichlorophenol, and 1-naphthol was carried out in aqueous environment at 75−340 °C with potassium persulfate used as oxidant. The pressure was adjusted to 25−45 MPa. The concentration of the organic compounds was 1.0 mM, and that of the oxidant was 1.0−10.0 mM. Study was made of the effects of concentration, temperature...

Correlation between High Temperature-High Pressure Water Corrosion Behaviors and Microstructural Changes and Residual Strength Characteristics of ZrO2-Particle-Dispersed Al2O3.

High temperature and high pressure water corrosion behaviors of ZrO2-particle-dispersed Al2O3 composites were investigated in terms of with the microstructural changes and residual strength characteristics. Sintered Al2O3 bodies with 5, 15, and 30 wt.% 3 mol% Y2O3-doped tetragonal ZrO2 were made using a pressureless sintering method at 1 550. 1 600 and 1 650°C, respectively. These Al2O3/ZrO2 ceramic composites were corroded in high temperature and high pressure deionized water at 200°C∼300°C. Corrosion damage of the Al2O3/ZrO2 ceramic composites occurred preferentially on ZrO2 particles after long-term immersion in deionized water. The tetragonal to monoclinic phase transformation occurred in yittria-doped tetragonal ZrO2 polycrystals due to high temperature and high pressure deionized water corrosion. For improvement of the corrosion characteristics of the composites, are important increasing the ZrO2 content within a range in which no remarkable residual strength degradation is recognized and lowering of the sintering temperature. Al2O3/ZrO2 ceramic composites also have superior residual strength characteristics compared to monolithic ZrO2 ceramics. The residual strength characteristics are improved by increasing the ZrO2 particle concentration. and loweringthe sintering temperature. The fracture surface morphology change from transgranular to intergranular was brought about by increasing the ZrO2 content. Improvement in residual strength characteristics of Al2O3/ZrO2 composites was realized. due to intergranular crack propagation, crack pinning caused by remarkable grain bridging by Al2O3 and stress-induced transformation from tetragonal ZrO2 to stable monoclinic in the vicinity of the crack tip. Then, the necessary manufacturing conditions for sustaining the improved strength characteristics after high pressure and high temperature water immersion were clarified. In addition design concepts used to obtain water-corrosion-resistant high strength and high toughness particle dispersed ceramic composites were proposed.

SUS316鋼の高温高圧水中低ひずみ速度試験における電気化学的ノイズ

SUS316鋼の高温高圧水中低ひずみ速度試験における電気化学的ノイズ

Chemical Processing in High-Pressure Aqueous Environments. 5. New Processing Concepts

A combination of fundamental and applied process research at Pacific Northwest National Laboratory resulted in the development of several new processing concepts. These concepts have in common the use of high-temperature pressurized water as a unique reaction medium for carrying out chemical reactions. Typical operating conditions of these processes range from 300 to 360 °C and have pressures to above 200 bar. Investigation of the process chemistry and engineering for these new processing concepts required the development and scale-up of several high-pressure reactor systems which are described. Several new processes involving catalysts and the distinctive properties of pressurized water were patented as part of this effort. These processes, which are at various stages of development, address a broad mix of energy and environmentally related problems. Chemical processing in a high-temperature liquid water environment remains a relatively untapped area for commercial application.

Chemical processing in high-pressure aqueous environments. 1. Historical perspective and continuing developments

Use of high-temperature pressurized liquid water has been investigated as a reaction medium for conducting chemical reactions and conversion. Results of these studies have demonstrated that high-temperature pressurized liquid water, especially in the presence of suitable catalysts, has unique chemical and physical properties. An overview of fundamental investigations and processing considerations in this environment is presented including details regarding the effects of temperature, pressure, and catalysis. The reactivities of various feedstocks tested are discussed along with the development and scale-up of high-pressure reactor systems used to investigate the process chemistry and engineering. Several new processing concepts were developed for gasification, destruction, and gas processing based on these findings. Most of the research has centered on catalytic processing for the production of liquid and gaseous fuels from biomass and wastes at lower temperatures and higher pressures than conventionally used. Other studies have investigated new methods for carrying out chemical reactions, separations, and the destruction of hazardous organic materials. All of this research has in common the use of high-pressure, water systems operating at below and above critical conditions.

Hydrothermal Corrosion of Si-Ti-C-O System (Tyrano) Fibers.

The wet corrosion by high temperature-high pressure water has been studied on the three types of Si-Ti-C-O system (Tyrano) fibers at 300∼800°C under 100 MPa for 2h. The X-ray diffraction analysis and SEM observation of the scale layers and the measurement of the mass change of reaction products revealed that the pyrolysis together with forming β-SiC crystal took place in lower temperatures, while the hydro-thermal oxidation with following the formation of amorphous silica films propagated in higher temperatures. The oxidation reaction was sharply reduced as the amor-phous silica crystallizes to form cristobalite, whence the porous oxide layer is densified. The densification hindered the gaseous diffusion through the oxide film. The fiber containing 18% O (rich type), where atomic arrangement was disordered, showed a comparatively rapid pyrolytic rate. On the contrary, the fiber containing 12% O (poor type) showed a rapid oxidation rate.

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Wet corrosion by high temperature-high pressure water has been studied on CVD coated Ti base ceramic films (thickness ca. 10μm, TiC, TiN, TiC0.3N0.7, TiC0.3N0.7O0.1) at 300-680°C under 100MPa for 2h. The order of corrosion resistance was obtained as TiN>TiCN>TiCNO>TiC from the X-ray diffraction analysis of scale layers and the reaction ratio calculated from the weight gain. The order was discussed on the volume ratio φ defined by Pilling-Bedworth, the internal stress within the coated films, and the dissolution behavior of gaseous species at the interface of ceramic film-oxide scale. The oxide scale crystallized as anatase in TiC and transformed into rutile at higher temperatures. On the other hand, rutile deposited directly in other samples having a higher corrosion resistance.

The formation of a barrier oxide layer on a Zr-2.5wt.%Nb alloy during corrosion in high temperature pressurized water

Zr-2.5wt.%Nb alloy specimens, and for comparative purposes pure zirconium, were exposed to a pressurized lithiated water environment containing 4.8 g of LiOH per litre of H 2O at 300°C, and the oxides at the oxide-metal interface were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). TEM and SEM studies show that the barrier oxide layer formed on a Zr-2.5wt.%Nb alloy in the aqueous environment has a complex structure. The structure of the barrier oxide layer on Zr-2.5wt.%Nb consists of two parts, namely one resulting from corrosion of grain boundary phases and the other resulting from corrosion of the bulk α-Zr grains. The former consists mainly of tetragonal ZrO 2 crystallites. The latter consists of amorphous or mosaic layers and transformed tetragonal ZrO 2. In contrast, the oxide at or near the oxide-metal interface on pure zirconium specimens exposed to the same environment consists only of amorphous and mosaic structures which are relatively continuous.

Optical observations of fatigue crack growth behaviour of a low-alloy pressure vessel steel in high-temperature pressurized water: Katada, Y., Nagata, N. and Sato, S. Int. J. pressure Vessels Piping Oct. 1991 48 (1) 37–52

This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using `small-crack theory' for various materials and loading conditions. Crack-tip constraint factors, to account for three-dimensional state-of-stress effects, were selected to correlate large-crack growth rate data as a function of the effective-stress-intensity factor range (ΔKeff) under constant-amplitude loading. Some modifications to the ΔKeff rate relations were needed in the near-threshold regime to fit measured small-crack growth rate behavior and fatigue endurance limits. The model was then used to calculate small- and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens made of two aluminum alloys and a steel under constant-amplitude and spectrum loading. Fatigue lives were calculated using the crack-growth relations and microstructural features like those that initiated cracks for the aluminum alloys and steel for edge-notched specimens. An equivalent-initial-flaw-size concept was used to calculate fatigue lives in other cases. Results from the tests and analyses agreed well.