| 44161. |
- Knutsson, Pavleta, 1980, et al.
(författare)
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Oxidation and alkali sulfate-induced corrosion of aluminide diffusion coating with and without platinum
- 2008
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Ingår i: Materials and Corrosion - Werkstoffe und Korrosion. - : Wiley. - 1521-4176 .- 0947-5117. ; 59:6, s. 484-488
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Tidskriftsartikel (refereegranskat)abstract
- A platinum-free (MDC210) and a platinum-rich (MDC150L) aluminide diffusion coating applied to a CMSX4 single crystal Ni-based superalloy were investigated after exposure to sulfate-induced corrosion and oxidation at 900 degrees C for a total of 100 h. Weight changes, microstructural, and microchemical analyses of the products were performed by the means of gravimetry, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD). Platinum was found to have a beneficial effect on both the oxidation and corrosion resistance of the coating. In both cases the scale was thicker on the platinum-free coating. However, the difference in the extent of oxidation of the two coatings was small.
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| 44162. |
- Knutsson, Pavleta, 1980, et al.
(författare)
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Oxidation and alkali sulphate-induced corrosion of aluminide diffusion coatings with and without platinum
- 2023
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Ingår i: Protective Systems for High Temperature Applications EFC 57: From Theory to Industrial Implementation. ; , s. 191-199
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Ni-based superalloys are extensively used as components in stationary gas turbines. The most frequently encountered form of such corrosion is alkali sulphate hot corrosion. Aluminide coatings are widely used to improve the oxidation resistance of Ni-base superalloy turbine components during high-temperature oxidation and/or corrosion. The environmental conditions of turbines have been simulated by salt deposition and subsequent tube-furnace laboratory experiments. Corrosion and oxidation exposures were performed on platinum-rich and platinum-free coatings. Traces of transient alumina were detected on platinum-rich samples during corrosion but were difficult to quantify. The aluminium oxide scale is thicker in the case of corrosion, which causes more spallation. In the platinum-rich coating, the depletion of the aluminium reservoir to 32% was first observed after 500 h of oxidation at 1050 °C. Corrosion and oxidation exposures were performed on platinum-rich and platinum-free coatings.
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| 44163. |
- Knutsson, Pavleta, 1980, et al.
(författare)
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Phycoremediation of heavy metals
- 2016
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Ingår i: Energy and Clean Technologies Conference Proceedings, Sgem 2016, Vol I. - 9786197105636 ; , s. 533-540
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Konferensbidrag (refereegranskat)abstract
- Increasing amounts of heavy metals is a growing societal problem. By using ion exchangers, heavy metals can be captured and thereby their environmental impact can be decreased. Microalgae have been shown to adsorb metals; the algal cell wall contains functional groups, such as amino-, carboxyl-, hydroxyl- and sulphate groups, to which the various metal ions could bind [1]. This makes them suitable as a sustainable alternative for environmental remediation. Removal of pollutants with algae is called phycoremediation and is well studied for e.g. waste water [2]. Within this project, we study the potential of microalgae for remediating heavy metals in low concentration originating from leaching of combustion ashes, by measuring the metal binding capacity by three phytoplankton species: Chlorella sauna, Dunaliella sauna and Scendesmus obliquus. The heavy metals assessed are divalent ions of copper (Cu), cadmium (Cd), zinc (Zn), mercury (Hg) and lead (Pb). The effect of pH has been determined, as well as binding over time.
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| 44164. |
- Knutsson, Pavleta, 1980, et al.
(författare)
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Phycoremediation of heavy metals in ashes
- 2014
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Ingår i: Chalmers Life Science Area of Advance Meeting, May 5, Göteborg.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A growing problem in today’s society is the increasing amount of ash from the production of electricity and heat. Ash contains heavy metals that may be harmful to the environment. By using algae as ion exchangers, the ashes can be purified from certain heavy metals before deposit and its environmental impact is decreased [1]. Algal cell wall contains functional groups, such as amino-, carboxyl-, hydroxyl- and suphate groups, to which the various metal ions can bind bind [3]. An ion exchange of bound metal ions toward heavy metal ions can occur when the cell wall comes in contact with, for example, leachate from the ashes [1]. The process of using algae for environmental remediation is called phycoremediation.Within this project, we study the potential of microalgae for remediating ash from heavy metals, by measuring the metal binding capacity by three phytoplankton species: Chlorella salina, Dunaliella salina and Scendesmus obliquus. The heavy metals assayed are divalent ions of mercury (Hg), cadmium (Cd), copper (Cu), lead (Pb), zinc (Zn). The effect of pH has been investigated as well as total binding over time. To apply the method on a more authentic situation, the binding of metals from combustion ash was investigated.
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| 44165. |
- Knutsson, Pavleta, 1980, et al.
(författare)
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Potassium speciation and distribution for the K2CO3 additive-induced activation/deactivation of olivine during gasification of woody biomass
- 2019
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 248, s. 538-544
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Tidskriftsartikel (refereegranskat)abstract
- The GoBiGas plant, which comprises a 32-MW th dual fluidized bed gasifier, was constructed as a demonstration unit for converting biomass to biomethane via gasification. On several occasions during the commissioning of the plant, low activity of the olivine bed generated a high content of tar in the produced gas, which was deleterious to the downstream equipment. The problem was attributed to a deficiency of ash constituents, and the solution was to control activation of the bed material through the addition of K 2 CO 3 to the process. This enabled extended operational periods without tar-related issues. The achieved activity could be lost during interrupted operation at which time the activation procedure had to be repeated. In the present paper analysis of the bed material samples extracted upon activation and after loss of activity using Scanning Electron Microscopy coupled with Energy Dispersive X-ray spectroscopy (SEM-EDS)showed similar morphologies for the ash layers formed around the olivine particles. The observed differences mainly related to the distributions of potassium (K)across the layers. Furthermore, surface analysis showed differences in K speciation within the outer regions. K solubility tests and X-ray photoelectron spectroscopy analyses indicated that K was present as an oxide/hydroxide rather than as a silicate on the surface of the active olivine. The presented results are of major relevance for the operation of dual fluidized bed gasifiers with fuels that are potassium-lean when ash components need to be supplied as additives.
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| 44166. |
- Knutsson, Pavleta, 1980, et al.
(författare)
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Role of potassium in the enhancement of the catalytic activity of calcium oxide towards tar reduction
- 2018
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 229, s. 88-95
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Tidskriftsartikel (refereegranskat)abstract
- Gasification in fluidized bed systems is considered to be a highly promising alternative for the thermal conversion of biomass. A major challenge for this process is the formed tars, which represent a loss of energy from the product gas and entail additional costs for their removal. Olivine is considered to be the most effective catalytic bed material in terms of its impact on tar levels in the product gas. Additions and modifications to olivine have revealed the potential to enhance its catalytic activity. In the present study, the effect of the addition of K 2 CO 3 to the gasification process on the tar decomposition capability of olivine were evaluated. The effect of the added K 2 CO 3 on the product gas was assessed in the 30-MWth pilot gasification plant GoBiGas. Once dec reases in the tar level were detected, samples of the bed material were extracted from the system and evaluated for morphological and chemical changes related to the observed catalytic effect. SEM-EDX and XPS analyses of the surfaces of the olivine particles indicate that the additive is involved in the formation of mixed oxides of Ca and K within the outermost layer of the olivine particles. DFT modeling showed that the formation of mixed Ca and K oxides changes the oxidation potential of the surface, which may explain the increased activity of ash-coated olivine towards tar reduction.
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| 44167. |
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| 44168. |
- Knutsson, Pavleta, 1980, et al.
(författare)
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Use of natural ores and waste materials as oxygen carriers for chemical-looping combustion
- 2014
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Ingår i: International Multidisciplinary Scientific GeoConference Surveying Geology and Mining Ecology Management, SGEM. - 1314-2704. ; 1:4, s. 597-604
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Konferensbidrag (refereegranskat)abstract
- The increasing CO2 levels in the atmosphere require an immediate action in order to avoid irreversible climate changes. Chemical-looping combustion (CLC) is an innovative technology that provides an energy and cost-effective separation of CO2 for further capture and storage and thereby helps to mitigate the anthropogenic CO2 emissions from thermochemical fuel conversion. The solid oxygen carrier is a core component of every CLC system and the choice of the oxygen carrier depends on the fuel and operation conditions. Low-cost oxygen carriers tend to be more suitable for the process as the lifetime of the oxygen carrier material is often limited by side reactions with fuel ash, or by carryover losses in the ash separation. A series of natural ores and waste products have been investigated as potential oxygen cares, such as Mn-ore, Fe-ore, ilmenite. The materials are chosen based on their content of oxides that have proven to have promising oxygen transporting capabilities. The results lead to summary of criterion for further screening of the existing materials for more reactive and better suited candidates for the process.
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| 44169. |
- Knutsson, Pavleta, 1980, et al.
(författare)
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Use of natural ores in thermal conversion of biomass
- 2018
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Ingår i: International Multidisciplinary Scientific GeoConference Surveying Geology and Mining Ecology Management, SGEM. - 1314-2704. ; 18:4.1, s. 791-798
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Konferensbidrag (refereegranskat)abstract
- To decrease the CO2 levels in the atmosphere without compromising with the electricity production and energy security two different issues have to be addressed – replacement of the current use of fossil fuels with CO2-neutral fuels and increase in the efficiency of the existing processes for thermal conversion. Fluidized bed (FB) thermal conversion is usually considered as the most energy efficient choice when biomass and municipal solid waste are used as fuels. The bed material that is used commonly within FB boilers is sand. With the demand to increase the efficiency of the electricity generation process, alternative bed materials have been tested. These materials are usually naturally occurring minerals containing transient oxides, most often Fe or Mn. The present paper presents three naturally occurring minerals that may be utilized as bed materials – olivine, ilmenite and manganese ore, while comparing with industrial silica sand for reference. The feasibility of their utilization as bed materials in thermal conversion of biomass on their further use is discussed.
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| 44170. |
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