The aim of this work was to rationalize the corrosion resistance of candidate austenitic iron-chromium-nickel (Fe-Cr-Ni) alloys in supercritical water (SCW) for use as fuel claddings within the in-core structure of the Canadian supercritical water-cooled reactor (SCWR) concept. High chromium (Cr)-containing alloys (Alloy 800HT with 20.6 wt.% Cr and 30.7 wt.% Ni and Alloy 33 with 33.4 wt.% Cr and 31.9 wt.% Ni) in the mill annealed condition were chosen for this purpose. Coupons were exposed on a short-term basis (500 h) in a static autoclave containing 25 MPa SCW at 550 °C and 625 °C. Gravimetric measurements and electron microscopy techniques were then used to study the oxidation/corrosion resistance of two alloys. Alloy 33 was found to exhibit the higher corrosion resistance at both temperatures. The improved corrosion resistance of Alloy 33 was attributed to two factors: (i) the formation of a continuous Cr-rich corundum-type M2O3 (M= Cr and Fe) oxide layer that prevented the diffusion of Fe and the formation of a less-protective Fe/Mn-Cr spinel ([Fe,Mn]Cr2O4) outer layer, (ii) a sufficient residual bulk Cr in the Cr-depleted layer adjacent to the alloy/scale interface that prevented any localized internal oxidation from occurring. A mass balance conducted on the corroded Alloy 33 material suggested that volatilization of the corundum-type oxide layer did not occur, at least not within the short-term exposure in the essentially deaerated SCW. A key issue requiring further study was the observation of intermetallic precipitates that formed below the Cr-depleted zone adjacent to the alloy/scale interface in both alloys when exposed for 500 h at 625 °C and their possible influence on the in-service mechanical integrity. / Thesis / Master of Applied Science (MASc) / The supercritical water-cooled reactor (SCWR) is one of the six reactor design concepts developed by the Generation-IV International Forum (GIF). Canada is planning to build the SCWR within the next decades. However, selection of proper materials that perform well within such high pressure high temperature circumstances inside the reactor core with minimum degradation is a very imperative challenge. The current work has addressed this issue by studying the corrosion behaviour of Fe-Cr-Ni alloys in similar environment using electron microscopy techniques.

The objective of this work was to study the effect of supercritical water on coke formed on ZSM-5 during its use as a dodecane cracking catalyst. ZSM-5 coking was quantified at different reaction times, finding that the presence of supercritical water reduced coke formation by an order of magnitude or more. Coked samples were analyzed using several methods, including temperature programmed oxidation (TPO), attenuated total reflectance infrared (ATR-IR) spectroscopy, carbon-13 nuclear magnetic resonance (13C NMR), diffuse reflectance ultraviolet-visible spectroscopy (DR-UV-vis) and UV-Raman. Coked produced in the absence of SCW was formed by polycyclic aromatic hydrocarbons (PAHs) with more than 4 aromatic rings containing alkyl side chains. Coke produced in the presence of SCW was formed by aromatics with 1 to 3 aromatic rings. The characteristics of coke formed in the absence of water on ZSM-5 that had been pretreated in SCW were intermediate to those of coke formed on fresh ZSM-5 in the presence and absence of water, suggesting that the presence of water influences coke properties. It was also verified that SCW can decrease coke formation due to its effect on Bronsted acidity of the catalyst and ability to promote coke gasification. The effect of coke deposits produced in the presence and absence of SCW on the rate of ethanol dehydration, a model reaction studied under diffusion-controlled conditions, indicated that SCD/SWC coke deactivated less the catalyst than SCD coke.

Neste trabalho apresentamos alguns estudos teóricos sobre propriedades eletrônicas de sistemas atômicos e moleculares em fase líquida e ambiente supercrítico. A utilização dos fluidos supercríticos têm atraído muito interesse como meio solvente para propriedades moleculares, reações químicas e são vistos como alternativa aos solventes orgânicos t´óxidos. Assim como nos solventes convencionais, descrever suas propriedades por meio de estudos em n´nível molecular tem se tornado tão interessante quanto seu uso prático. Primeiramente realizamos o estudo da polarizabilidade estática do argônio e como esta propriedade se comporta em função da variação de pressão. Fizemos também um estudo deste sistema em torno do ponto crítico e região supercrítica. Dentro do intervalo de pressão que estudamos, não observamos variações significativas na polarizabilidade, embora no regime de baixas densidades este sistema apresentou certa dependência da polarizabilidade com a densidade. Neste estudo, também calculamos a constante dielétrica no ponto crítico. Em seguida estudamos o espectro de absorção do ´átomo de xenônio em ambiente formado por argônio líquido. Nesta parte, realizamos várias simulações com o objetivo de verificar o deslocamento da linha de absorção 5p 6s deste ´átomo em relação `a densidade, explorando também as condições supercríticas. Observamos que o deslocamento do espectro ocorrido em meio solvente é para maiores energias (blue shift) `a medida que a densidade aumenta, e obtemos bom acordo com os valores medidos. Por ultimo, realizamos um estudo da mudança de um espectro eletrônico molecular onde o solvente é a ´agua supercrítica. Utilizamos a molécula paranitroanilina como sonda solvatocromica, e observamos que mesmo no regime de alta temperatura e baixa densidade ainda ocorre a formação de ligações de hidrogênio entre soluto e solvente. Obtemos um red shift para a transição eletrônica em agua supercrítica. Este resultado é medido experimentalmente tanto para ´agua em condições ambiente como em condição supercrítica, mas em ´agua supercrítica o deslocamento ´e menor. Nosso resultado para a agua supercrítica está em bom acordo com o resultado experimental e mostra que a maior contribuição para este deslocamento ´e devido ao efeito das interações eletrostáticas. Porém, ao compararmos os resultados da ´agua em condições supercríticas com as condições normais de temperatura e pressão e o dióxido de carbono supercrítico como solventes, os resultados indicam que a aproximação de incluir apenas interações eletrostáticas ´e menos satisfatória e fornece somente parte do efeito de solvente. / In this work we present some theoretical studies of the electronic properties of atomic and molecular systems in liquid and supercritical environments. The study of supercritical fluids is a interesting topic in solvent effects on molecular properties and chemical reactions. Their use can be an alternative to organic toxic solvents. Describing their molecular solvent properties, as opposite to conventional solvents, has become important as of pratical use. First we study the static polarizability of atomic argon and its behavior with pressure. The critical and near critical points also were considered in this study. In the range of pressures used, it is not observed significant changes in the polarizability, although the system present some dependence with density in the supercritical region. We have then determined the dielectric constant at the critical point. Next we study the absorption electronic spectra of xenon atom in liquid argon environment. In this part, we performed several simulations with the aim of verifying the density dependence of the spectral shift of the 5p 6s line of xenon. The supercritical region was also explored. We obtain the spectral blue shift in solvent environment for increasing density in good agreement with experiments. Finally, we study the electronic spectra of a solvatochromic probe molecule, the paranitroaniline, in supercritical water and supercritical carbon dioxide. We observe that even for high temperature hydrogen bond persists between the solute and the water molecules. A red shift in the transition of the electronic spectra of paranitroaniline is well described. This red shift is observed experimentally in water, but in supercritical water it is less pronounced. Our results for supercritical water is in good agreement with the experimental result and show that the long-range electrostatic contribution dominates the solute-solvente interaction and gives the largest influence in the calculated spectrum. Water in normal conditions and supercritical carbon dioxide were also considered for comparison and the results indicates that including only the electrostatic contribution is less satisfactory and gives only part of the total solvent effect.

No description available.

The efficiency of nuclear reactors can be improved by increasing the operating pressure of current nuclear reactors. Current CANDU-type nuclear reactors use heavy water as coolant at an outlet pressure of up to 11.5 MPa. Conceptual SuperCritical Water Reactors (SCWRs) will operate at a higher coolant outlet pressure of 25 MPa. Supercritical water technology has been used in advanced coal plants and its application proves promising to be employed in nuclear reactors. To better understand how supercritical water technology can be applied in nuclear power plants, supercritical water loops are used to study the heat transfer phenomena as it applies to CANDU-type reactors. A conceptual design of a loop known as the Supercritical Phenomena Experimental Apparatus (SPETA) has been done. This loop has been designed to fit in a 9 m by 2 m by 2.8 m enclosure that will be installed at the University of Ontario Institute of Technology Energy Research Laboratory. The loop include components to safely start up and shut down various test sections, produce a heat source to the test section, and to remove reject heat. It is expected that loop will be able to investigate the behaviour of supercritical water in various geometries including bare tubes, annulus tubes, and multi-element-type bundles. The experimental geometries are designed to match the fluid properties of Canadian SCWR fuel channel designs so that they are representative of a practical application of supercritical water technology in nuclear plants. This loop will investigate various test section orientations which are the horizontal, vertical, and inclined to investigate buoyancy effects. Frictional pressure drop effects and satisfactory methods of estimating hydraulic resistances in supercritical fluid shall also be estimated with the loop. Operating limits for SPETA have been established to be able to capture the important heat transfer phenomena at supercritical conditions. Heat balance and flow calculations have been done to appropriately size components in the loop. Sensitivity analysis has been done to find the optimum design for the loop. / UOIT

As a means to produce high pressure hydrogen in order to reduce compression penalty, we propose to reform liquid fuel (e.g., bio-ethanol) in supercritical water (pressure above 221 bar and temperature greater than 374°C). Catalytic ethanol reforming in supercritical water for hydrogen production has been carried out in a high pressure packed bed reactor made of Inconel-625. Since Inconel-625 contains mainly nickel, it is expected that the reactor itself can be active toward ethanol reforming. Therefore, a series of tests were first performed in the empty reactor, whose results are a benchmark when studying reforming in the presence of a catalyst. Ethanol reforming in the empty reactor was studied in the temperature range of 450 to 600°C and showed coking/plugging problem at 575°C and above. The ethanol conversion with the empty reactor could be as high as 25% at 550°C and residence time of about one minute. The main reaction products with the empty reactor were H2, CO and CH4. A catalyst screening study was performed to investigate the performance of nickel and cobalt as active metals, supported on γ-Al2O3, α-Al2O3, ZrO2 and YSZ for temperatures between 475°C and 550°C. The presence of the catalyst did increase the activity of ethanol reforming, especially at higher temperatures. All experiments in the catalyst screening study were carried out with non-reduced catalysts. Nickel catalysts were found more active than cobalt, likely because of higher reducibility. Indeed, the higher amount of oxygen in Co3O4 compared to NiO requires more hydrogen to fully reduce the metal oxides. Both Ni/γ-Al2O3 and Co/γ-Al2O3 showed little activity below 500°C, and led to failed experiments due to coking/plugging at temperatures of 525°C and above. The strong acid sites on γ-Al2O3 are responsible for high selectivity toward ethylene, a known coke precursor. The support α-Al2O3 in combination with Ni was active, but yielded lower H2 selectivity and higher CH4 selectivity than the zirconia-based catalysts. The Co/α-Al2O3 shows low activity. The ZrO2-based catalysts were active and yielded high H2 selectivity, but were found very fragile. Finally, the YSZ support was strong and yielded good conversion. Below 550°C the activity of Ni/YSZ is higher than that of Co/YSZ, but at 550°C both catalysts yield nearly complete conversion. The advantage of Co/YSZ is then higher H2 selectivity and lower CH4 selectivity compared to Ni/YSZ. Therefore, Co/YSZ was selected for a more detailed study. The effect of temperature, flowrate, residence time, catalyst weight, Co loading, concentration, and pretreatment with H2 were considered. Two methods for catalyst reduction were applied: ex-situ reduction where the catalyst is reduced in a different reactor and in-situ reduction where the catalyst is reduced in the SCW reactor prior to ethanol reforming. At 550°C, Co/YSZ converts all ethanol for residence times as low as 2 s, even with non-reduced catalyst. At 500°C the activity of the in-situ and ex-situ reduced catalysts were similar and greater than for the non-reduced catalyst. At 475°C the ex-situ reduced catalyst showed low activity, comparable to that of the non-reduced catalyst, but the in-situ reduced catalyst yielded much higher conversion. The better performance of the in-situ reduced catalyst was attributed to active metal sites on the reactor’s wall after pre-treatment in H2. The low activity of the ex-situ reduced catalyst is due to the fact that, when exposed to supercritical water for less than 30 minutes, it re-oxidized to CoO. The temperature of 475°C is then too low to generate sufficient hydrogen that will start reducing the catalyst. Finally, analysis of reaction pathways for ethanol reforming over Co/YSZ showed that the reaction proceeds mostly via ethanol dehydrogenation to form acetaldehyde, the latter species reacting with lattice oxygen on the catalyst to produce acetone and CO2. Acetone is then reformed by water into CO and H2. Finally, H2 and CO react via the methanation reaction to form CH4. Over Co/YSZ it was found that the water-gas shift reaction is fast (CO selectivity most of the time is less than 0.5%), but the methanation reaction is kinetically controlled. Stopping the methanation reaction before equilibrium allowed for H2 selectivity higher than what is expected at equilibrium (likewise, CH4 selectivity is smaller than equilibrium value). For well-controlled reaction Co/YSZ is a promising catalyst that can be highly selective toward hydrogen during ethanol reforming in supercritical water.

As a means to produce high pressure hydrogen in order to reduce compression penalty, we propose to reform liquid fuel (e.g., bio-ethanol) in supercritical water (pressure above 221 bar and temperature greater than 374°C). Catalytic ethanol reforming in supercritical water for hydrogen production has been carried out in a high pressure packed bed reactor made of Inconel-625. Since Inconel-625 contains mainly nickel, it is expected that the reactor itself can be active toward ethanol reforming. Therefore, a series of tests were first performed in the empty reactor, whose results are a benchmark when studying reforming in the presence of a catalyst. Ethanol reforming in the empty reactor was studied in the temperature range of 450 to 600°C and showed coking/plugging problem at 575°C and above. The ethanol conversion with the empty reactor could be as high as 25% at 550°C and residence time of about one minute. The main reaction products with the empty reactor were H2, CO and CH4. A catalyst screening study was performed to investigate the performance of nickel and cobalt as active metals, supported on γ-Al2O3, α-Al2O3, ZrO2 and YSZ for temperatures between 475°C and 550°C. The presence of the catalyst did increase the activity of ethanol reforming, especially at higher temperatures. All experiments in the catalyst screening study were carried out with non-reduced catalysts. Nickel catalysts were found more active than cobalt, likely because of higher reducibility. Indeed, the higher amount of oxygen in Co3O4 compared to NiO requires more hydrogen to fully reduce the metal oxides. Both Ni/γ-Al2O3 and Co/γ-Al2O3 showed little activity below 500°C, and led to failed experiments due to coking/plugging at temperatures of 525°C and above. The strong acid sites on γ-Al2O3 are responsible for high selectivity toward ethylene, a known coke precursor. The support α-Al2O3 in combination with Ni was active, but yielded lower H2 selectivity and higher CH4 selectivity than the zirconia-based catalysts. The Co/α-Al2O3 shows low activity. The ZrO2-based catalysts were active and yielded high H2 selectivity, but were found very fragile. Finally, the YSZ support was strong and yielded good conversion. Below 550°C the activity of Ni/YSZ is higher than that of Co/YSZ, but at 550°C both catalysts yield nearly complete conversion. The advantage of Co/YSZ is then higher H2 selectivity and lower CH4 selectivity compared to Ni/YSZ. Therefore, Co/YSZ was selected for a more detailed study. The effect of temperature, flowrate, residence time, catalyst weight, Co loading, concentration, and pretreatment with H2 were considered. Two methods for catalyst reduction were applied: ex-situ reduction where the catalyst is reduced in a different reactor and in-situ reduction where the catalyst is reduced in the SCW reactor prior to ethanol reforming. At 550°C, Co/YSZ converts all ethanol for residence times as low as 2 s, even with non-reduced catalyst. At 500°C the activity of the in-situ and ex-situ reduced catalysts were similar and greater than for the non-reduced catalyst. At 475°C the ex-situ reduced catalyst showed low activity, comparable to that of the non-reduced catalyst, but the in-situ reduced catalyst yielded much higher conversion. The better performance of the in-situ reduced catalyst was attributed to active metal sites on the reactor’s wall after pre-treatment in H2. The low activity of the ex-situ reduced catalyst is due to the fact that, when exposed to supercritical water for less than 30 minutes, it re-oxidized to CoO. The temperature of 475°C is then too low to generate sufficient hydrogen that will start reducing the catalyst. Finally, analysis of reaction pathways for ethanol reforming over Co/YSZ showed that the reaction proceeds mostly via ethanol dehydrogenation to form acetaldehyde, the latter species reacting with lattice oxygen on the catalyst to produce acetone and CO2. Acetone is then reformed by water into CO and H2. Finally, H2 and CO react via the methanation reaction to form CH4. Over Co/YSZ it was found that the water-gas shift reaction is fast (CO selectivity most of the time is less than 0.5%), but the methanation reaction is kinetically controlled. Stopping the methanation reaction before equilibrium allowed for H2 selectivity higher than what is expected at equilibrium (likewise, CH4 selectivity is smaller than equilibrium value). For well-controlled reaction Co/YSZ is a promising catalyst that can be highly selective toward hydrogen during ethanol reforming in supercritical water.

In recent years, technologies using supercritical water have gained considerable attention, mainly due to versatility and uniqueness of water at elevated temperatures and pressures. The physical conditions required to generate supercritical water also make it prone to large intrinsic thermal and density fluctuations, exacerbated if there are impurities present in the system. These fluctuations induce nucleation, the initial stage of a first-order phase transition, and subsequent mixing of the new phase within the original phase. When this new phase reaches its critical size it grows irreversibly to macroscopic proportions, otherwise, tending to disintegrate. The presence of a polydispersed solid phase within the supercritical phase is responsible for unfavorable phenomena such as particle deposition and corrosion of structural components, both of which result in decreased efficiency and reliability of the supercritical water employing process. Molecular Dynamics (MD) simulation method has been the primary tool of investigation. Molecular motions are tracked on the femto and picosecond time-scales which are particularly important for the study of nucleation. Sodium chloride has been chosen in this research since it is computationally tractable and is unavoidably involved in most industrial water based applications. Cluster size distributions, the size of critical nuclei and cluster life-times are reported. The size distribution of emerging clusters shows a very strong dependence on the system’s density, with larger clusters preferentially formed at lower densities. Also, a materials science application is presented where the rapid quenching of hydrothermally formed sodium chloride clusters leads to a variety of nanostructures, characterizable by prominent vibrational modes. And lastly, during the conditions prior to crystallization, water is not only physically adsorbed to the cluster’s surface but also exists in a “confined” state within subsurface regions for several picoseconds during the nucleation process. A mechanism for the sodium chloride hydrolysis reaction is presented as well as showing that asymmetric electrostatic fields generated by the coalescing ions are on the order of 1010 V/m, sufficient to drive the hydrolysis of confined water molecules. The HCl molecule and hydroxide ions are formed, with the latter segregating preferentially to sub-surface regions in the amorphous NaCl particles. Both HCl and hydroxide are implicated in corrosion. / Thesis (Master, Chemistry) -- Queen's University, 2008-11-03 13:54:56.021

Supercritical water gasification (SCWG) is an innovative hydrothermal technique, employing supercritical water (SCW, T≥374oC, P≥22.1 MPa) as the reaction media, to convert wet biomass or aqueous organic waste directly into hydrogen (H2)-rich synthetic gas (syngas). In the first stage of this research, a secondary pulp/paper-mill sludge (SPP, provide by AbitibiBowater Thunder Bay Operations) was gasified at temperatures of 400-550oC for 20 to 120 min in a high-pressure batch reactor for H2 production. The highest H2 yield achieved was 14.5 mol H2/kg SPP (on a dry basis) at 550oC for 60 min. In addition, SPP exhibited higher H2-generation potential than sewage sludges, likely attributed to its higher pH and higher volatile matter and alkali salt contents. In the second stage, a novel two-step process for sludge treatment was established. The first step involved the co-liquefaction of SPP with waste newspaper in a batch reactor at varying mixing ratios, aimed at converting the organic carbons in the feedstocks into valuable bio-crude and water-soluble products. The highest heavy oil (HO) yield (26.9 wt%) was obtained at 300oC for 20 min with a SPP-to-newspaper ratio of 1:2. This co-liquefaction process transformed 39.1% of the carbon into HOs, where 16.3% of the carbon still remained in the aqueous waste. Next, an innovative Ru0.1Ni10/γ-Al2O3 catalyst (10 wt% Ni, Ru-to-Ni molar ratio=0.1), with long-term stability and high selectivity for H2 production, was developed for the SCWG of 50 g/L glucose, where no deactivation was observed after 33 h on stream at 700oC, 24 MPa and a WHSV (weight hourly space velocity) of 6 h-1. The H2 yield was maintained at ~50 mol/kg feedstock. The addition of small amounts of Ru to Ni10/γ-Al2O3 was found to be effective in enhancing Ni dispersion and increasing the reducibility of NiO. Finally, the Ru0.1Ni10/γ-Al2O3 catalyst together with an activated carbon (AC) supported catalyst (Ru0.1Ni10/AC) were utilized for treating the aqueous by-product from sludge-newspaper co-liquefaction using a continuous down-flow tubular reactor. More than 90% of the carbon in the waste was destroyed at 700oC with the highest H2 yield of 71.2 mol/kg carbon noted using Ru0.1Ni10/AC. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2011-04-27 17:20:49.193

This thesis was the report of the research done on the near-critical water gasification (NCWG) as an application for activated sludge treatment. The research started with the use of model compounds and binary mixtures of these compounds as feeds for the NCWG. High gasification yields were obtained using a commercial catalyst (Raney nickel), and it was found that interactions between model compounds in the binary mixtures resulted in lowering the gasification efficiencies. The research then shifted to the use of actual activated sludge samples and the search for novel catalysts for that application. Almost 70% of the sludge was gasified in the presence of the high amounts of Raney nickel. Hydrogen was the main product in the gas phase. However, Raney nickel lost half its activity after only 8 minutes of exposure to supercritical water. For some model compounds, novel catalysts formulated in our laboratories had better activities than the commercial ones. This was not the case for the NCWG of activated sludge.