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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The Relationship of Microstructure to Fracture and Corrosion Behavior of a Directionally Solidified Superalloy

Trexler, Matthew David 18 December 2006 (has links)
SUMMARY GTD-111 DS is a directionally solidified superalloy currently used in turbine engines. To accurately predict the life of engine components it is essential to examine and characterize the microstructural evolution of the material and its effects on material properties. The as-cast microstructure of GTD-111 is highly inhomogeneous as a result of coring. The current post-casting heat treatments do not effectively eliminate the inhomogeneity. This inhomogeneity affects properties including tensile strength, fracture toughness, fracture path, and corrosion behavior, primarily in terms of the number of grains per specimen. The goal of this work was to link microstructural features to these properties. Quantitative fractography was used to determine that the path of cracks during failure of tensile specimens is influenced by the presence of carbides, which are located in the interdendritic regions of the material as dictated by segregation. The solvus temperature of the precipitate phase, Ni3(Al, Ti), was determined to be 1200C using traditional metallography, differential thermal analysis, and dilatometry. A heat-treatment was designed to homogenize the microstructure for tensile testing that isolates the carbide by dissolving all of the eutectic Ni3(Al, Ti) precipitate phase, which is also found in the interdendritic areas. High temperature oxidation/sulfidation tests were conducted to investigate the corrosion processes involved when GTD-111 DS is utilized in steam and gas combustion turbine engines. The kinetics of corrosion in both oxidizing and sulfidizing atmospheres were determined using thermogravimetric analysis. Additionally, metallography of these samples after TGA revealed a correlation between the presence of grain boundaries and sulfur attack, which led to catastrophic failure of the material under stress-free conditions in a sulfur bearing environment. In summary, this work correlates the inhomogeneous microstructure of GTD-111 DS to tensile fracture, and the corrosion process in turbine engines.
2

Oxidation and corrosion fatigue aspects of cast exhaust manifolds

Ekström, Madeleine January 2015 (has links)
Emission regulations for heavy-duty diesel engines are becoming increasingly restrictive to limit the environmental impacts of exhaust gases and particles. Increasing the specific power output of diesel engines would improve fuel efficiency and greatly reduce emissions, but these changes could lead to increased exhaust gas temperature, increasing demands on the exhaust manifold material. This is currently the ferritic ductile cast iron alloy SiMo51, containing about 4 wt% Si and ~1 wt% Mo, which operates close to its fatigue and oxidation resistance limits at peak temperature (750C). To ensure high durability at higher temperatures, three different approaches to improving the life of exhaust manifolds were developed in this thesis. The first approach was to modify SiMo51 by adding different combinations of Cr and Ni to improve its high-temperature strength and oxidation resistance, or by applying a thermal barrier coating (TBC) to reduce the material temperature and thereby improve fatigue life. In the second approach, new materials for engine components, e.g. austenitic ductile iron and cast stainless steel, were investigated for their high-temperature fatigue and oxidation properties. In order to identify the most suitable alloys for this application, in the third the environmental effects of the corrosive diesel exhaust gas on the fatigue life of SiMo51 were investigated. The high-temperature oxidation resistance of SiMo51 at 700 and 800C in air was found to be improved by adding Cr, whereas Ni showed adverse effects. The effects of solid-solution hardening from Ni and precipitation hardening from Cr were low at 700C, with improvements only at lower temperatures. Applying a TBC system, providing thermal protection from a ceramic topcoat and oxidation protection from a metallic bond coat, resulted in only small reductions in material temperature, but according to finite element calculations still effectively improved the fatigue life of a turbo manifold. Possible alternative materials to SiMo51 identified were austenitic cast ductile iron Ni-resistant D5S and austenitic cast stainless steel HK30, which provided high durability of exhaust manifolds up to 800 and 900C, respectively. Corrosion fatigue testing of SiMo51 at 700C in diesel exhaust gas demonstrated that the corrosive gas reduced fatigue life by 30-50% compared with air and by 60-75% compared with an inert environment. The reduced fatigue life was associated with a mechanism whereby the crack tip oxidized, followed by crack growth. Thus another potential benefit of TBC systems is that the bond coat may reduce oxidation interactions and further improve fatigue life. These results can be used for selecting materials for exhaust applications. They also reveal many new research questions for future studies. Combining the different approaches of alloy modification, new material testing and improving the performance using coatings widened the scope of how component life in exhaust manifolds can be improved. Moreover, the findings on environmental interactions on SiMo51 fatigue provide a completely new understanding of these processes in ductile irons, important knowledge when designing components exposed to corrosive environments. The novel facility developed for high-temperature corrosion fatigue testing can be useful to other researchers working in this field. / <p>QC 20150507</p>
3

High Temperature Corrosion Of Steels Used In Petroleum Refinery Heaters

Sultan, Abdelrahman Saleh 01 July 2005 (has links) (PDF)
The oxidation of three different steels used in the construction of petroleum refineryheaters was investigated by using thermogravimetric analysis technique (TGA). C-5,P-11, and P-22 steel samples were tested in two different oxidizing environments / air and CO2+N2+H2O (that simulates the combustion products of natural gas) at two different temperatures / 450oC and 500oC. In air oxidation P-22 had the best oxidation resistance among the three steels at two temperatures. In CO2+N2+H2O environment,C-5 possessed better oxidation resistance than P-22 and P-11. Analyses of oxidation products by using optical microscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were carried out to correlate TGA results to oxide composition and morphology. Lower oxidation rate of P-22 in air was explained with reference to the formation of Cr-O phase. Analytical rate equations showed that all the steels obeyed parabolic rate equation during oxidation and no transition was observed
4

Improved interconnect materials for next-generation Solid Oxide Fuel Cells

Collantes, Pablo January 2019 (has links)
Solid Oxide Fuel Cells (SOFC) are attractive candidates in the search for cleaner and energy efficient production due to their numerous advantages such as fuel flexibility, modularity and exceptional efficiencies when combined heat and power is harnessed. A key element in its design are the interconnects which are mainly manufactured from custom ferritic stainless steels to carry the electricity between two adjacent cells. However, the high operation temperatures increase the chromia scale thickness in those steels, which reduces their conductivity. At the same time, chromium (VI) volatilization due to the wet atmosphere poisons the electrodes and reduces the cell life. Therefore, the narrow of the selection of suitable materials and high production costs have hindered their commercialization. Recent advances in lower temperature SOFC operation have opened a window for new interconnect materials and innovative processes. A Ce/Co nanocoating can be applied in the readily available AISI 441 ferritic steel to form a protective spinel oxide layer that reduces the effect of both degradations in the interconnects. The coating is applied in a continuous roll-to-roll process and then the interconnect shape is pressed in the material, manufactured as Sanergy HT 441 by Sandvik. However, mechanical stresses cause microcracks that expose the substrate material, which can impact the oxidation behaviour negatively. Fortunately, pre-treatments can achieve the spinel to diffuse over short distances and combine with elements in the substrate, homogenizing the protective effect. This phenomenon known as self-healing has not been studied with sufficient depth for the Sanergy HT 441. Thus, different series of temperature and short pre-treatments times were tested, and self-healing properties were observed by means of SEM surface characterization and chemical analysis. The results indicate that self-healing can be obtained within short times using isothermal pre-treatments at temperatures over 750 °C. / Solid Oxide Fuel Cells (SOFC) är attraktiva kandidater i jakten på renare och energieffektiv produktion på grund av deras många fördelar som bränsleflexibilitet, modularitet och exceptionella effektivitet när kombinerad värme och kraft utnyttjas. Ett viktigt element i dess utformning är sammankopplingar som huvudsakligen tillverkas av anpassade ferritiska rostfria stål för att transportera elektricitet mellan två angränsande celler. De höga driftstemperaturerna ökar emellertid tjockleken på kromskalan i dessa stål, vilket minskar deras konduktivitet. Samtidigt förorenar krom (VI) på grund av den våta atmosfären elektroderna och reducerar celllivslängden. Därför har det smala urvalet av lämpliga material och höga produktionskostnader hindrat deras kommersialisering. De senaste framstegen inom SOFC-drift med lägre temperatur har öppnat ett fönster för nya sammankopplingsmaterial och innovativa processer. En Ce / Co-nanocoating kan appliceras i det lättillgängliga AISI 441 ferritstålet för att bilda ett skyddande spinelloxidskikt som minskar effekten av båda nedbrytningarna i sammankopplingarna. Beläggningen appliceras i en kontinuerlig rulle-till-rullningsprocess och sedan pressas sammankopplingsformen in i materialet, tillverkat som Sanergy HT 441 av Sandvik. Mekaniska spänningar orsakar emellertid mikrokrackar som exponerar underlagsmaterialet, vilket kan påverka oxidationsbeteendet negativt.Lyckligtvis kan förbehandlingar uppnå att spinellen diffunderar över korta avstånd och kombineras med element i underlaget och homogeniserar den skyddande effekten. Detta fenomen som kallas självhelande har inte studerats med tillräckligt djup för Sanergy HT 441. Således testades olika serier av temperatur och korta förbehandlingstider, och självhelande egenskaper observerades med hjälp av SEM-ytkarakterisering och kemisk analys. Resultaten indikerar att självläkning kan uppnås inom korta tider med användning av isotermisk förbehandling vid temperaturer över 750 ° C.
5

Silicon Carbide - Nanostructured Ferritic Alloy Composites for Nuclear Applications

Bawane, Kaustubh Krishna 10 January 2020 (has links)
Silicon carbide and nanostructured ferritic alloy (SiC-NFA) composites have the potential to maintain the outstanding high temperature corrosion and irradiation resistance and enhance the mechanical integrity for nuclear cladding. However, the formation of detrimental silicide phases due to reaction between SiC and NFA remains a major challenge. By introducing a carbon interfacial barrier on NFA (C@NFA), SiC-C@NFA composites are investigated to reduce the reaction between SiC and NFA. In a similar way, the effect of chromium carbide (Cr3C2) interfacial barrier on SiC (Cr3C2@SiC) is also presented for Cr3C2@SiC-NFA composites. Both the coatings were successful in suppressing silicide formation. However, despite the presence of coatings, SiC was fully consumed during spark plasma sintering process. TEM and EBSD investigations revealed that spark plasma sintered SiC-C@NFA and Cr3C2@SiC-NFA formed varying amounts of different carbides such as (Fe,Cr)7C3, (Ti,W)C and graphite phases in their microstructure. Detailed microstructural examinations after long term thermal treatment at 1000oC on the microstructure of Cr3C2@SiC-NFA showed precipitation of new (Fe,Cr)7C3, (Ti,W)C carbides and also the growth of existing and new carbides. The results were successfully explained using ThermoCalc precipitation and coarsening simulations respectively. The oxidation resistance of 5, 15 and 25 vol% SiC@NFA and Cr3C2@SiC-NFA composites at 500-1000oC temperature under air+45%water vapor containing atmosphere is investigated. Oxidation temperature effects on surface morphologies, scale characteristics, and cross-sectional microstructures were investigated and analyzed using XRD and SEM. SiC-C@NFA showed reduced weight gain but also showed considerable internal oxidation. Cr3C2@SiC-NFA composites showed a reduction in weight gain with the increasing volume fraction of Cr3C2@SiC (5, 15 and 25) without any indication of internal oxidation in the microstructure. 25 vol% SiC-C@NFA and 25 vol% Cr3C2@SiC-NFA showed over 90% and 97% increase in oxidation resistance (in terms of weight gain) as compared to NFA. The results were explained using the fundamental understanding of the oxidation process and ThermoCalc/DICTRA simulations. Finally, the irradiation performance of SiC-C@NFA and Cr3C2@SiC-NFA composites was assessed in comparison with NFA using state-of-the-art TEM equipped with in-situ ion irradiation capability. Kr++ ions with 1 MeV energy was used for irradiation experiments. The effect of ion irradiation was recorded after particular dose levels (0-10 dpa) at 300oC and 450oC temperatures. NFA sample showed heavy dislocation damage at both 300oC and 450oC increasing gradually with dose levels (0-10 dpa). Cr3C2@SiC-NFA showed similar behavior as NFA at 300oC. However, at 450oC, Cr3C2@SiC-NFA showed remarkably low dislocation loop density and loop size as compared to NFA. At 300oC, microstructures of NFA and Cr3C2@SiC-NFA show predominantly 1/2<111> type dislocation loops. At 450oC, NFA showed predominantly <100> type loops, however, Cr3C2@SiC-NFA composite was still predominant in ½<111> loops. The possible reasons for this interesting behavior were discussed based on the large surface sink effects and enhanced interstitial-vacancy recombination at higher temperatures. The molecular dynamics simulations did not show considerable difference in formation energies of ½<111> and <100> loops for NFA and Cr3C2@SiC-NFA composites. The additional Si element in the SiC-NFA sample could have been an important factor in determining the dominant loop types. SiC-C@NFA composites showed heavy dislocation damage during irradiation at 300oC. At 450oC, SiC-C@NFA showed high dislocation damage in thicker regions. Thinner regions near the edge of TEM samples were largely free from dislocation loops. The precipitation and growth of new (Ti,W)C carbides were observed at 450oC with increasing irradiation dose. (Fe,Cr)7C3 precipitates were largely free from any dislocation damage. Some Kr bubbles were observed inside (Fe,Cr)7C3 precipitates and at the interface between α-ferrite matrix and carbides ((Fe,Cr)7C3, (Ti,W)C). The results were discussed using the fundamental understanding of irradiation and ThermoCalc simulations. / Doctor of Philosophy / With the United Nations describing climate change as 'the most systematic threat to humankind', there is a serious need to control the world's carbon emissions. The ever increasing global energy needs can be fulfilled by the development of clean energy technologies. Nuclear power is an attractive option as it can produce low cost electricity on a large scale with greenhouse gas emissions per kilowatt-hour equivalent to wind, hydropower and solar. The problem with nuclear power is its vulnerability to potentially disastrous accidents. Traditionally, fuel claddings, rods which encase nuclear fuel (e.g. UO2), are made using zirconium based alloys. Under 'loss of coolant accident (LOCA) scenarios' zirconium reacts with high temperature steam to produce large amounts of hydrogen which can explode. The risks associated with accidents can be greatly reduced by the development of new accident tolerant materials. Nanostructured ferritic alloys (NFA) and silicon carbide (SiC) are long considered are leading candidates for replacing zirconium alloys for fuel cladding applications. In this dissertation, a novel composite of SiC and NFA was fabricated using spark plasma sintering (SPS) technology. Chromium carbide (Cr3C2) and carbon (C) coatings were employed on SiC and NFA powder particles respectively to act as reaction barrier between SiC and NFA. Microstructural evolution after spark plasma sintering was studied using advanced characterization tools such as scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) techniques. The results revealed that the Cr3C2 and C coatings successfully suppressed the formation of detrimental reaction products such as iron silicide. However, some reaction products such as (Fe,Cr)7C3 and (Ti,W)C carbides and graphite retained in the microstructure. This novel composite material was subjected to high temperature oxidation under a water vapor environment to study its performance under the simulated reactor environment. The degradation of the material due to high temperature irradiation was studied using state-of-the-art TEM equipped with in-situ ion irradiation capabilities. The results revealed excellent oxidation and irradiation resistance in SiC-NFA composites as compared to NFA. The results were discussed based on fundamental theories and thermodynamic simulations using ThermoCalc software. The findings of this dissertation imply a great potential for SiC-NFA based composites for future reactor material designs.
6

EB-PBF additive manufacturing of Alloy 718 : Effect of shot peening on surface characteristics and high temperature corrosion performance

Mohandass, Venkataramanan January 2019 (has links)
There is an upsurge of research interest on Alloy 718 additively manufactured (AM) by electron beam powder bed fusion (EB-PBF) technique in aero and land-based gas turbine engines. However, the surface quality of the manufactured components has always been a major challenge. Several factors, including powder particle size, layer thickness, beam parameters, scanning strategies, and inclination angle of the build, govern the surface characteristics. Along with surface roughness resulted from partially melted powder particles, surface defects such as balls, satellites, microcracks as well as up-skin and down-skin surfaces can enhance the vulnerability of the manufactured parts to corrosion. When the surface is unable to withstand the exposed environment adequately, corrosion can be triggered. The surface-induced corrosion failures are increasingly becoming more challenging as the AM components often have complex geometries that render them even more difficult to finish. So, the relatively poor surface finish is the barrier to the full exploitation of the AM industry. In the present study, to achieve the desired surface quality, hence an improved high temperature corrosion performance, shot peening was implemented on Alloy 718 parts manufactured by EB-PBF. The high temperature corrosion behavior of the parts was investigated in an ambient air environment at 650 and 800 °C for up to 336 h. The underlying physical and chemical factors at play of the parts exposed to the corrosive environment were investigated too. The effect of topographical features (e.g., surface roughness) and microstructural characteristics (e.g., grain structure, phases, and defects) on high temperature corrosion behavior were analyzed by 3D surface profilometry, hardness test, optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy disperse spectroscopy (EDS), X-ray diffractometry (XRD) and electron backscatter diffraction (EBSD). The surface roughness and high temperature corrosion rate of the parts was significantly reduced after shot peening.
7

The corrosion behavior of Fe-Cr-Ni alloys in complex high temperature gaseous atmospheres containing the reactants oxygen, sulphur and carbon

Kneeshaw, Jonathan Andrew January 1987 (has links)
A systematic in-depth study has been undertaken to establish the corrosion mechanism of a Model 25Cr-35Ni-Fe alloy and four commercial alloys HP40Nb, AISI314, HP40Al and Alloy 800H in low oxygen, high sulphur and carbon containing environments typically found in coal gasification and fluidised bed combustion processes. A review of present knowledge of corrosion processes in purely oxidizing, sulphidizing and carburizing environments and multiple reactant carburizing/ oxidizing, carburizing/sulphizing and oxidizing/sulphidizing environments is given. The experimental programme was designed to establish the role of sulphur on the corrosion process by studying corrosion mechanisms in a sulphurfree H2-7%C0-1.5%H2o gas, a low sulphur H2-7%C0-1.5%H20-0.2%H 2 S gas (pS2_8= 10 bar), and a high sulphur H 2 -7%C0-1.5%H 2 0-0.6%H 2 S gas (pS = lO bar) at 800'C. All_21j_hree environments had a constant partiaf pressure of oxygen (po2 = 10 bar) and carbon activity (ac = 0.3). In the sulphur-free gas the Model alloy formed a thin uniform cr 2 o 3 layer which grew at a constant parabolic rate throughout the exposure period of 0 - 5000 hours. Surface working increased the growth rate and thickness of the Cr 2 o 3 layer but created a large number of cracks and pores which allowed carbon containing gaseous species to diffuse through the oxide to form carbide precipitates in the alloy substrata. Alloying additions of Si promoted the formation of an inner SiO layer which reduced the corrosion rate by cutting off the outward diffusion of Cr, Mn and Fe. Alloying additions of Mn promoted the formation of an additional outer (Mn, Fe )Cr 2o 4 layer. The 3. 5% Al content of the HP40Al was insufficient to form a complete Al 2 o3 layer. Alloy 800H was susceptible to localised internal oxidation. Adding a low level of sulphur (0.2% H 2 S) to the gas increased the corrosion rate of the Model alloy in the 1nitial stages. This rate gradually slowed down before becoming parabolic after 1000 - 2000 hours. This was due to the nucleation of sulphides in addition to oxides. The oxides and sulphides grew side by side until the oxides overgrew the sulphides to form a complete Cr 2o3 layer which cut off further ingress of sulphur from the gas. The entrapped sulphides promoted localized thickening of the oxide layer. Eventually the sulphur redistributed from the sulphides in the scale to internal sulphide precipitates in the alloy with the corrosion rate returning to that of the sulphur-fre,e gas for the rest of the exposure period (5000 hours total). In the commercial alloys the internal sulphide precipitates prevented the inner Si02 layer becoming complete. Sulphur doped the (Mn, Fe) Cr 2 0 4 outer layer ana the intermediate Cr 2o3 layer formed from the spinal layer, increasing the number of cation . vacancies and the growth rate of the scale. These factors caused a massive Cr depletion of the alloy substrata after several thousand hours. The internal carbides became unstable which led to a massive amount of internal attack and a dramatic increase (breakaway) in the corrosion rate. Due to its thickness and the presence of Si02 inner layer the external scale became susceptible to spallation. If this occurred the oxides and sulphides nucleated on the alloy surface again but sulphides. protective alloy. insufficient Cr was available for the oxides to overgrow the The sulphides therefore grew to form a fast growing nonsulphide scale which soon led to catastrophic failure of the Increasing the level of sulphur in the gas to 0.6% H2S caused oxides and sulphides to nucleate on the surface, but in this case the sulphides overgrew the oxides to form thick fast growing non-protective sulphide scales on all the alloys.
8

Statistical lifetime modeling of FeNiCr alloys for high temperature corrosion in waste to energy plants and metal dusting in syngas production plants / Modélisation statistique de la durée de vie des alliages Fe-Ni-Cr soumis à la corrosion à haute température en environnement UVEOM et metal dusting en installations Syngas

Camperos Guevara, Sheyla Herminia 20 January 2016 (has links)
Au cours des dernières décennies, le contrôle de la corrosion des alliages exposés à des conditions sévères et complexes a été un grand défi pour les applications industrielles. Les coûts de la corrosion sont élevés et les stratégies de prévention sont devenues une demande industrielle importante. Le projet SCAPAC financé par l’ANR, a proposé d’étudier la corrosion lors de deux procédés industriels: le vapo-réformage du méthane et l’incinération des déchets ménagers. Bien que les conditions de fonctionnement de ces deux procédés soient différentes, les approches de modélisation peuvent être similaires. Dans le procédé de vapo-réformage du méthane, les composants métalliques sont soumis à la corrosion par « metal dusting », qui est une forme d’endommagement catastrophique qui affecte les alliages exposés à des températures élevées (400-800 °C) et des atmosphères sursaturées en carbone. De même, les composants métalliques des incinérateurs de déchets qui sont exposés à des atmosphères de combustion sont soumis à la corrosion à haute température sous dépôts de cendres. Le « metal dusting » est un phénomène critique qui a mené à des pertes matérielles importantes et à l’arrêt d’installations industrielles pendant les 50 dernières années. Les mécanismes de cette dégradation ont été identifiés et sont disponibles dans la littérature. Cependant, l'effet de certains paramètres des procédés ne sont pas encore bien compris et nécessitent des compléments d'études. En ce qui concerne la corrosion à haute température, les mécanismes sont bien documentés et une quantité considérable de travaux ont été publiés au cours des dernières décennies. De nombreux matériaux et revêtements ont été développés. Cependant, la performance des matériaux dans des environnements différents n'est pas assez bien comprise pour créer des modèles de prédiction de durée de vie. Une revue bibliographique de ces deux domaines a révélé qu’il existait des approches de modélisation. Néanmoins, il n'y a pas actuellement de modèle prédictifs fiables de durée de vie qui soit disponible dans la littérature pour les alliages commerciaux, et pour une gamme étendue de conditions expérimentales. La présente étude présente une méthodologie pour développer des modèles statistiques de prévision de durée de vie. Il s’agit d’évaluer la performance de matériaux soumis au « metal dusting » et à la corrosion à haute température sous dépôt. Deux bases de données ont été construites pour intégrer les résultats expérimentaux du projet SCAPAC, aussi bien que résultats de la littérature. Ceci afin d’avoir suffisant des données pour la modélisation. Ces bases de données ont permis d'analyser plus de 4000 vitesses de corrosion à l’aide de méthodes statistiques appliquées à différents scénarios. La méthodologie de l’Analyse des Composantes Principales (ACP) a été utilisée pour identifier les paramètres clés des mécanismes de corrosion, qui ont été ensuite utilisés pour construire des modèles de prédiction de durée de vie par Régression Linéaire Multiple (RLM). Pour la corrosion à haute température, trois modèles ont été obtenus dans le scénario de gradient thermique pour trois familles d'alliages: des aciers ferritiques, des alliages austénitiques à base de fer et nickel et des alliages à base de nickel, en montrant des résultats encourageants. Pour la corrosion par « metal dusting », deux modèles ont été obtenus pour expliquer le temps d'incubation et la cinétique croissance de profondeur de piqures, avec des résultats satisfaisants. Les modèles statistiques dans les deux cas ont été comparés avec deux résultats expérimentaux et théoriques montrant un bon accord, qui permet l'évaluation de la durée de vie des matériaux dans les conditions définies. / Over the last decades, the corrosion control of alloys exposed to severe and complex conditions in industrial applications has been a great challenge. Currently, corrosion costs are increasing and preventive strategies have become an important industrial demand. The SCAPAC project funded by the French National Research Agency has proposed to study the corrosion for two separate processes: Steam Methane Reforming (SMR) and Waste to Energy (WtE). Although the operating conditions of both processes are different, the modeling approaches can be similar. Metallic components in the SMR process are subjected to metal dusting corrosion, which is a catastrophic form of damage that affects alloys exposed to highly carburising gases (aC>1) at high temperatures (400–800 °C).[1]. Likewise, metallic components in the Waste to Energy (WtE) process are subjected to high temperature corrosion under deposit that takes place in equipment exposed to atmospheres with high content of corrosive products of combustion. Metal dusting corrosion is considered as a critical phenomenon that has led to worldwide material loss for 50 years. A basic understanding of the degradation mechanisms is available. However, the effect of some process parameters is still not well understood in current literature and requires further study. Otherwise for high temperature corrosion, a considerable amount of literature has been published over the last few decades and the mechanisms are well documented. Also many materials and coatings have been developed. However, the material performance in different environments has not been sufficiently well understood to define suitable criteria for lifetime prediction models regarding operating conditions, due to the high complexity of the corrosion phenomena involved. Literature research in both fields revealed modeling approaches in different kinds of complex conditions and applications. Nevertheless, there are no lifetime models currently available in the open literature for commercial materials that consider a wide range of conditions and the relative weight of the variables involved in the corrosion processes. This dissertation presents a methodology to develop lifetime prediction models to evaluate materials performance under metal dusting and high-temperature corrosion conditions. Two databases were created to integrate experimental results from the SCAPAC project, as well as results from literature to enable sufficient amount of data for modeling. The databases allowed analyzing approximately 4000 corrosion rates by different statistical methods over different scenarios. The Principal Component Analysis (PCA) methodology was performed to identify the key parameters to create lifetime prediction models using Multiple Linear Regressions (MLR). For high-temperature corrosion, three models were obtained in the thermal gradient scenario for three families of alloys: low alloyed steels, Fe/Ni-based high temperature alloys and Ni-based alloys, showing agreeable results. For metal dusting corrosion, two models were obtained to explain the incubation times and the kinetic of pit depth growing, showing satisfactory results. The statistical models in both cases were compared with experimental and theoretical results showing good agreement with experimental findings, which allows performing the lifetime assessment of materials under defined conditions.
9

Roštový kotel na spalování kontaminovaného dřeva / Grate Biomass Boiler

Dražka, Ondřej January 2020 (has links)
The aim of the thesis is a design of a grate steam boiler with capacity of 35 t/h and output steam parameters with temperature 430 °C and pressure 4,1 MPa. The first part of the thesis deals with stoichiometric calculations and boiler efficiency. The theses mainly focuses on the heat transfer calculation and the geometric design of individual heat transfer surfaces. The specifics of fuel are taken into consideration. The drawing of the basic boiler scheme is a part of the thesis.
10

Effects of Different Fuels on Combustion Boiler Processes : The analysis of alternative fuel mixtures

Stauber Alfredsson, Malin January 2018 (has links)
The objective of this study is to investigate the eect of dierent fuels on two uidized bed boiler systemsat the energy company Soderenergi's site in Igelsta, called IKV and IGV P3. Today, recovered wastewood (RWW) is the major fuel share fed into the boilers. However, with an insecure fuel supply in thefuture, other fuel types must be considered. Based on knowledge from previous fuel usage in the boilers,an evaluation of how other potential fuel mixtures may eect the operation is conducted. The additionalfuels considered in the fuel blends are; stem wood chips, cutter shavings, solid recycled fuel (SRF) andrubber.With elemental analysis of the fuels and established key numbers, the previous fuel mixtures are evaluated.The indications by the guiding parameters are compared with experienced problems and the formercondition of the boilers, and the risk limits for the key numbers are adjusted to a suitable level. Thepotential mixtures are evaluated with the key numbers and the updated limits. In addition to the keynumbers, the heavy metal concentration, the heating value, the moisture content and the ash content ofthe fuel blends are included in the evaluation. The considered damages in the boilers caused by the fuelblends are corrosion, sintering and fouling.The damage level from the current fuel usage for IKV and IGV P3 is fairly low. The results from theanalyzed fuel mixtures show an increased damage risk in the boilers. Additionally, adjustments of theboiler systems are required by some of the analyzed fuel mixtures. In general, the corrosion risk andthe heavy metal content will increase in comparison with today's fuel. The fouling and slagging are aswell expected to increase for the assessed fuel mixtures. Moreover, the result illustrates an increased ashgeneration, which demands a reconstruction of the ash cooling system for IKV. Furthermore, the increaseof LHV in the assessed fuel mixtures to IGV P3, is likely to require an increased capacity of the ue gasrecirculation pump.In the analysis of the potential fuel mixtures it is found that the corrosion risk expressed by the keynumbers is reduced with a higher share of rubber. The heavy metal content is, however, increased,leading to e.g. an enhanced risk for formation of eutectic salts, which as well are corrosive. On thecontrary, the fuel mixtures with a high risk expressed by the key numbers, have the lowest concentrationsof heavy metals. Due to the results are con icting, a balance between the risk indicated by the keynumbers and the heavy metal concentration must be considered in the evaluation. The fuel mixturesconsidered causing least damage to IKV are a mixture of 42% RWW, 48% wood fuel and 15% SRF, and amixture of 70% wood fuel, 20% SRF and 10% rubber. The fuel mixtures considered causing least damageto IGV P3 are a mixture of 85% RWW and 15% rubber and a mixture of 70% RWW and 30% SRF. / Syftet med studien var att undersoka branslets paverkan pa tva uidbaddpannor, IKV och IGV P3, hos energiforetaget Soderenergi. Idag ar det huvudsakliga branslet i dessa pannor returtra (RT). Med en standigtrorlig branslemarknad kravs kunskap av alternativa branslen. Baserat pa tidigare bransleanvandning,har paverkan fran potentiella bransleblandningar pa pannan undersokts. Utover returtra ar stamveds is,span, papper-plast-tra (SRF) och gummi med i de analyserade blandningarna.Med elementaranalyser pa branslen och etablerade nyckeltal utvarderades de tidigare anvanda branslena.Indikationen fran nyckeltalen ar jamford med upplevda problem och risknivaerna for nyckeltalen arandrade till passande nivaer. De framtida bransleblandningarna analyserades med hjalp av nyckeltalenoch de uppdaterade risknivaerna. Utover nyckeltalen analyserades tungmetallhalten, varmevardet, fukthaltenoch askhalten i bransleblandningarna. De pannskador orsakade av bransleblandningarna somundersokts ar korrosion, sintring och paslag.Det nuvarande branslet till IKV och IGV P3 ger en relativt lag skadeniva. Resultaten fran de analyseradebransleblandningarna visar att skaderisken i pannorna kommer att oka och forandringar av pannan kankomma att kravas. Generellt kommer korrosionsrisken och tungmetallinnehallet att oka i jamforelse meddagens bransle. Okat paslag och slaggning ar ocksa forvantat. Vidare visar resultatet att askproduktionenkommer att oka, vilket gor att IKVs kylsystem for bottenaskan kommer behovas byggas ut. LHV for deanalyserade bransleblandningarna for IGV P3 okar, vilket innebar att kapaciteten for returgas aktarnatroligen maste okas.I jamforelsen av de olika bransleblandningarna visas att korrosionsrisken, forutspadd av nyckeltalen,minskar med en hogre andel gummi. Daremot okar tungmetallinnehallet, vilket leder till en okad riskfor bildning av eutektiska salter, vilka ocksa ar korrosiva. Bransleblandningarna med en indikerad hogrisk av nyckeltalen, har tvartemot den lagsta koncentrationen av tungmetaller. Eftersom resultatenar motsagande, kravs en avvagning mellan riskerna indikerade av nyckeltalen och tungmetallshalten.De bransleblandningar som ar ansedda att vara minst skadliga for IKV ar en blandning av 42% RT,48% tradbransle och 15% SRF, och en blandning av 70% tradbransle, 20% SRF och 10% gummi. Debransleblandning som ar ansedda att vara minst skadliga for IGV P3 ar en blandning av 85% RT och15% gummi, och en blandning av 70% RT och 30% SRF.

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