| 1. |
- Engkvist, Josefin, 1972, et al.
(författare)
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The initial effect of KCl deposit on alumina scales characterized by ToF-SIMS and AES
- 2013
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Ingår i: Surface and Interface Analysis. - : Wiley. - 1096-9918 .- 0142-2421. ; 45:1, s. 445-448
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Tidskriftsartikel (refereegranskat)abstract
- A FeCrAl alloy was preoxidized to form a protective alumina scale, and the effect of KCl deposits on the alumina scale was investigated while exposed during 1 and 24 h at 600 degrees C. However, impurity concentrations in the alumina scale change the ion conductivity and hence affect its protective properties. Therefore, Auger electron spectroscopy and time-of-flight secondary ion mass spectrometry were used to characterize the alumina scales and detect traces of K and Cl. The results showed that K and Cl existed as large sharp-edged crystals surrounded by a dendritic network after 1 h. However, after 24 h, those were dissolved, and K together with Cl was detected only in the outer layer of the duplex alumina scale, which was formed during preoxidation.
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| 2. |
- Hagman, Henrik, 1980-
(författare)
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Co-firing animal waste, sludge, residue wood, peat and forest fuels in a 50MWth CFB boiler : ash transformation, availability and process improvements
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The direct variable costs for heat and electricity production based on solid biomass fuel combustion is approximately 3-5 times lower than the costs in a fossil fuel-oil based boiler in Sweden. In addition waste derived biomass fuels are typically much cheaper than biomass not classified as waste. The introduction of the waste derived fuels; wastewater treatment sludge, demolition wood, and animal waste in a 50MWth circulating fluidized bed (CFB) biomass boiler located in Perstorp, Sweden, led to rapid deposit buildup in superheaters, heavy ash accumulation in economizers and failing boiler tubes and vortex finders that forced frequent boiler shutdowns. This in turn increased the use of expensive oil (fossil fuel) in backup boilers and the CO2 footprint of the on-site energy conversion system. This work aims to increase the general mechanistic understanding of combustion systems using complex fuels, and includes: A mapping of the boiler failure and preventive maintenance statistics; elemental composition analysis of ash, deposits and fuel fractions; flue-gas composition measurements; chemical speciation analysis; an attempt to describe the overall ash transformation reactions and mass balance throughout the combustion process. Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) was used to analyze the elemental composition of ash and deposits. The SEM-EDS results were used together with data from X-ray powder diffraction (XRD) analysis, thermodynamic phase data, and equilibrium calculations in an attempt to quantify the crystalline phases and the overall ash transformation of the process. Based on the findings concerning ash transformation and the failure statistics, it has been possible to identify generic key parameters regarding boiler design and process parameters, enabling major improvements of the CFB boiler availability, a lower overall energy conversion cost and a reduced CO2 footprint.
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| 3. |
- Lindgren, Mikaela, 1987, et al.
(författare)
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Confinement dependence of electro-catalysts for hydrogen evolution from water splitting
- 2014
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Ingår i: Beilstein Journal of Nanotechnology. - : Beilstein Institut. - 2190-4286. ; 5:1, s. 195-201
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory is utilized to articulate a particular generic deconstruction of the electrode/electro-catalyst assembly for the cathode process during water splitting. A computational model was designed to determine how alloying elements control the fraction of H2 released during zirconium oxidation by water relative to the amount of hydrogen picked up by the corroding alloy. This model is utilized to determine the efficiencies of transition metals decorated with hydroxide interfaces in facilitating the electro-catalytic hydrogen evolution reaction. A computational strategy is developed to select an electro-catalyst for hydrogen evolution (HE), where the choice of a transition metal catalyst is guided by the confining environment. The latter may be recast into a nominal pressure experienced by the evolving H2 molecule. We arrived at a novel perspective on the uniqueness of oxide supported atomic Pt as a HE catalyst under ambient conditions.
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| 4. |
- Lindgren, Mikaela, 1987, et al.
(författare)
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Impact of Additives on Zirconium Oxidation by Water: Mechanistic insights from first principles
- 2013
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Ingår i: RSC Advances. - 2046-2069. ; 3:44, s. 21613-21619
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Tidskriftsartikel (refereegranskat)abstract
- Zirconium alloys are widely used as cladding materials employed to contain the fission fuel in nuclear power plants. A limiting factor for fuel longevity is the corrosion property of the zirconium alloys. In the reactor, the main corrodent is water. The oxide forms thermodynamically during hydrogen evolution. Due to the corrosion mechanism, a fraction of the hydrogen is transferred to the alloy. It has long been known that the alloying elements actually control the hydrogen pick-up fraction, HPUF. A mechanism that explains these observations by means of density functional theory calculations is presented and validated. A hydroxylated grain boundary model decorated by various transition metal, TM, ions is employed to study the dependence of the hydrogen evolution reaction, HER, on the choice of TM ion and spin state along the hydride-proton recombination pathway. The efficiency of the system to utilize the overpotential for hydrogen evolution, originating from the overall corrosivity of the alloy, is found to be decisive for the HPUF. A dual origin of the detrimental effects of Co and Ni additives on the HPUF is identified.
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| 5. |
- Lindgren, Mikaela, 1987, et al.
(författare)
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On the fate of hydrogen during zirconium oxidation by water: Effect of oxygen dissolution in α-Zr
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:22, s. 11050-11058
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Tidskriftsartikel (refereegranskat)abstract
- Zirconium oxidation by water is accompanied by hydrogen conversion, either H2 is released or hydrogen is picked up by the alloy. Strategies are sought to mitigate the detrimental hydrogen uptake into the metal. The corrosion phenomenon is subdivided into anode and cathode processes caused by electron release upon O2- oxidation at the metal/oxide interface in case of the former and electron-proton recombination resulting in hydrogen pick-up or H2 evolution in case of the latter. In a previous study, the additive dependence of the cathodic hydrogen evolution reaction was analysed. The present study contributes the oxygen concentration dependence of the anode potential, presents the impact of oxygen concentration on the co-absorption of hydrogen and merges the anode and cathode processes. The computational model is validated by semi-quantitatively reproducing the experimental solubility limit for oxygen in α-Zr. The impact of the emerging conceptual understanding for material development is discussed.
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| 6. |
- Alipour, Yousef
(författare)
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High temperature corrosion in a biomass-fired power boiler : Reducing furnace wall corrosion in a waste wood-fired power plant with advanced steam data
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of waste (or recycled) wood as a fuel in heat and power stations is becoming more widespread in Sweden (and Europe), because it is CO2 neutral with a lower cost than forest fuel. However, it is a heterogeneous fuel with a high amount of chlorine, alkali and heavy metals which causes more corrosion than fossil fuels or forest fuel.A part of the boiler which is subjected to a high corrosion risk is the furnace wall (or waterwall) which is formed of tubes welded together. Waterwalls are made of ferritic low-alloyed steels, due to their low price, low stress corrosion cracking risk, high heat transfer properties and low thermal expansion. However, ferritic low alloy steels corrode quickly when burning waste wood in a low NOx environment (i.e. an environment with low oxygen levels to limit the formation of NOx). Apart from pure oxidation two important forms of corrosion mechanisms are thought to occur in waste environments: chlorine corrosion and alkali corrosion.Although there is a great interest from plant owners to reduce the costs associated with furnace wall corrosion very little has been reported on wall corrosion in biomass boilers. Also corrosion mechanisms on furnace walls are usually investigated in laboratories, where interpretation of the results is easier. In power plants the interpretation is more complicated. Difficulties in the study of corrosion mechanisms are caused by several factors such as deposit composition, flue gas flow, boiler design, combustion characteristics and flue gas composition. Therefore, the corrosion varies from plant to plant and the laboratory experiments should be complemented with field tests. The present project may thus contribute to fill the power plant corrosion research gap.In this work, different kinds of samples (wall deposits, test panel tubes and corrosion probes) from Vattenfall’s Heat and Power plant in Nyköping were analysed. Coated and uncoated samples with different alloys and different times of exposure were studied by scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), X-ray diffraction (XRD) and light optical microscopy (LOM). The corrosive environment was also simulated by Thermo-Calc software.The results showed that a nickel alloy coating can dramatically reduce the corrosion rate. The corrosion rate of the low alloy steel tubes, steel 16Mo3, was linear and the oxide scale non-protective, but the corrosion rate of the nickel-based alloy was probably parabolic and the oxide much more protective. The nickel alloy and stainless steels showed good corrosion protection behavior in the boiler. This indicates that stainless steels could be a good (and less expensive) alternative to nickel-based alloys for protecting furnace walls.The nickel alloy coated tubes (and probe samples) were attacked by a potassium-lead combination leading to the formation of non-protective potassium lead chromate. The low alloy steel tubes corroded by chloride attack. Stainless steels were attacked by a combination of chlorides and potassium-lead.The Thermo-Calc modelling showed chlorine gas exists at extremely low levels (less than 0.1 ppm) at the tube surface; instead the hydrated form is thermodynamically favoured, i.e. gaseous hydrogen chloride. Consequently chlorine can attack low alloy steels by gaseous hydrogen chloride rather than chlorine gas as previously proposed. This is a smaller molecule than chlorine which could easily diffuse through a defect oxide of the type formed on the steel.
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| 7. |
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| 8. |
- Alipour, Yousef, 1979-, et al.
(författare)
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The analysis of furnace wall deposits in a low-NOx waste wood-fired bubbling fluidised bed boiler
- 2012
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Ingår i: VGB PowerTech Journal. - : VGB Power Tech. - 1435-3199. ; 92:12, s. 96-100
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Increasing use is being made of biomass as fuel for electricity production as the price of natural wood continues to rise. Therefore, more use is being made of waste wood (recycled wood). However, waste wood contains more chlorine, zinc and lead, which are believed to increase corrosion rates. Corrosion problems have occurred on the furnace walls of a fluidised bed boiler firing 100 % waste wood under low-NOx conditions. The deposits have been collected and analysed in order to understand the impact of the fuel.
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| 9. |
- Alipour, Yousef, 1979-, et al.
(författare)
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The effect of a nickel alloy coating on the corrosion of furnace wall tubes in a waste wood fired power plant
- 2014
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Ingår i: Materials and corrosion - Werkstoffe und Korrosion. - : Wiley. - 0947-5117 .- 1521-4176. ; 65:2, s. 217-225
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Tidskriftsartikel (refereegranskat)abstract
- The use of waste wood as a fuel in power plants is becoming more widespread in Europe, because it is a renewable energy source with a lower cost than forest fuel. However it is more corrosive than coal and corrosion problems have arisen in the furnace wall area of a low NOx heat and power boiler. The furnace walls are made of a low alloy steel which has been coated in some parts with a nickel alloy to reduce corrosion. In this work, furnace tubes coated with a nickel alloy were compared to the uncoated tubes of the low alloy steel 16Mo3 after 3 years of exposure in the boiler. The nickel alloy coating and uncoated material were also compared with more controlled testing on a corrosion probe lasting for about 6 weeks. The corrosion rates were measured and the samples were chemically analysed by SEM/EDS/WDS and XRD methods. The corrosive environment was also modelled with Thermo-Calc software. The corrosion rates measured from the probe and tube samples of 16Mo3 agreed well with each other, implying linear corrosion rates. The results also showed that the use of nickel alloy coatings changes the corrosion mechanism, which leads to a dramatic reduction in the corrosion rate. The results are discussed in terms of the corrosion mechanisms and thermodynamic stability of the corrosion products.
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| 10. |
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