| 1. |
- Kong, Xiangrui, et al.
(författare)
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Phase recognition in SEM-EDX chemical maps using positive matrix factorization
- 2023
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Ingår i: Methodsx. - 2215-0161. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Images from scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spec- troscopy (EDX) are informative and useful to understand the chemical composition and mixing state of solid materials. Positive matrix factorization (PMF) is a multivariate factor analysis tech- nique that has been used in many applications, and the method is here applied to identify factors that can describe common features between elemental SEM-EDX maps. The procedures of con- verting both graphics and digital images to PMF input files are introduced, and the PMF analysis is exemplified with an open-access PMF program. A case study of oxygen carrier materials from oxygen carrier aided combustion is presented, and the results show that PMF successfully groups elements into factors, and the maps of these factors are visualized. The produced images provide further information on ash interactions and composition of distinct chemical layers. The method can handle all types of chemical maps and the method is not limited solely to SEM-EDX although these images have been used as an example. The main characteristics of the method are:center dot Adapting graphics and digital images ready for PMF analysis.center dot Conversion between 1-D and 2-D datasets allows visualization of common chemical maps of elements grouped in factors.center dot Handles all types of chemical mappings and large data sets.
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| 2. |
- Stanicic, Ivana, 1994, et al.
(författare)
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Combined manganese oxides as oxygen carriers for biomass combustion — Ash interactions
- 2019
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Ingår i: Chemical Engineering Research and Design. - : Elsevier BV. - 0263-8762 .- 1744-3563. ; 149, s. 104-120
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 Institution of Chemical Engineers Carbon capture and storage (CCS) has been acknowledged as an important strategy for mitigation of climate change. Although highly applicable for fossil fuels, CCS with biomass could have the added advantage of resulting in negative emissions of carbon dioxide. One promising carbon capture technology is chemical-looping combustion (CLC). In CLC the reactors are filled with metal oxide bed material called oxygen carriers. Before CLC can be implemented for biomass combustion at a large scale, biomass ash components interaction with oxygen carriers needs to be further understood. Four combined manganese oxides Mn3O4-SiO2, Mn3O4-SiO2-TiO2, Mn3O4-Fe2O3 and Mn3O4-Fe2O3-Al2O3 were exposed to common biomass ash components K, Ca and P. The ash components can exist in many forms, but here the compounds CaCO3, K2CO3 and CaHPO4 were used. Exposures were performed at 900 °C for six hours in oxidising, reducing and inert conditions. Crystalline phases were analysed by XRD and morphology examined with SEM-EDX. Results show that oxygen carrier particles containing silicon were more likely to form agglomerates, especially in combination with potassium, whereas the particles including iron were more stable. MnFeAl was the oxygen carrier that showed least agglomerating behaviour while simultaneously showing a propensity to absorb some ash components. Some inconsistencies between thermodynamic predictions and experimental results is observed. This may be explained by lack of relevant data in the used databases, were only a few of the oxygen carrier-ash systems and subsystems have been optimised. Further optimisation related to manganese rich systems should be performed to obtain reliable results.
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| 3. |
- Andersson, Viktor, 1983, et al.
(författare)
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Alkali desorption from ilmenite oxygen carrier particles used in biomass combustion
- 2024
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Ingår i: Fuel. - 0016-2361 .- 1873-7153. ; 359
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen-carrying fluidized bed materials are increasingly used in novel technologies for carbon capture and storage, and to improve the efficiency of fuel conversion processes. Potassium- and sodium-containing compounds are released during biomass combustion and may have both negative and positive effects on conversion processes. Ilmenite is an important oxygen carrier material with the ability to capture alkali in the form of titanates. This is a desirable property since it may reduce detrimental alkali effects including fouling, corrosion, and fluidized bed agglomeration. This study investigates the interactions of alkali-containing compounds with ilmenite particles previously used in an industrial scale (115 MWth) oxygen carrier aided combustion system. The ilmenite samples were exposed to temperatures up to 1000 °C under inert and oxidizing conditions while the alkali release kinetics were characterized using online alkali monitoring. Alkali desorption occurs between 630 and 800 °C, which is attributed to loosely bound alkali at or near the surface of the particles. Extensive alkali release is observed above 900 °C and proceeds during extended time periods at 1000 °C. The release above 900 °C is more pronounced under oxidizing conditions and approximately 9.1 and 3.2 wt% of the alkali content is emitted from the ilmenite samples in high and low oxygen activity, respectively. Detailed material analyses using scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were conducted before and after temperature treatment, which revealed that the concentrations of potassium, sodium and chlorine decrease at the outermost surface of the ilmenite particles during temperature treatment, and Cl is depleted to a deeper level in oxidizing conditions compared to inert. The implications for ilmenite-ash interactions, oxygen carrier aided combustion and chemical looping systems are discussed.
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| 4. |
- Brorsson, Joakim, 1988, et al.
(författare)
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Thermodynamic properties for metal oxides from first-principles
- 2024
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Ingår i: Computational Materials Science. - 0927-0256. ; 233
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Tidskriftsartikel (refereegranskat)abstract
- In this study, an efficient first-principles approach for calculating the thermodynamic properties of mixed metal oxides at high temperatures is demonstrated. More precisely, this procedure combines density functional theory and harmonic phonon calculations with tabulated thermochemical data to predict the heat capacity, formation energy, and entropy of important metal oxides. Alloy cluster expansions are, moreover, employed to represent phases that display chemical ordering as well as to calculate the configurational contribution to the specific heat capacity. The methodology can, therefore, be applied to compounds with vacancies and variable site occupancies. Results are, moreover, presented for a number of systems of high practical relevance: Fe–K–Ti–O, K–Mn–O, and Ca–Mn–O. For the reference materials, the agreement with experimental measurements is exceptional in the case of ilmenite (FeTiO3) and good for CaMnO3. When the generated data is used in multi-phase thermodynamic calculations to represent materials for which experimental data is not available, the predicted phase-diagrams for the K–Mn–O and K–Ti–O systems change dramatically. The demonstrated methodology is highly useful for obtaining approximate values on key thermodynamic properties in cases where experimental data is hard to obtain, inaccurate or missing.
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| 5. |
- Faust, Robin, 1992, et al.
(författare)
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Thermodynamic Modeling and Experimental Investigation of the System Fe-Ti-O-K for Ilmenite Used as Fluidized Bed Oxygen Carrier
- 2024
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Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- The capability of ilmenite for potassium uptake in a simulated oxygen carrier-aided combustion environment has been investigated. The maximum uptake of potassium and the effect of potassium inclusion on the Fe-Ti-O system was analyzed. Through laboratory experiments and thermodynamic calculations, it was found that a molar ratio of 1:1 can be formed spontaneously for both the K-Ti-system (where the formation of K2Ti2O5 was found) and the K-Fe-system (where KFeO2 was found). K2Ti2O5 was identified as an unstable phase, undergoing decomposition into K2Ti4O9. The study demonstrates that the maximum K uptake, through forming K2Ti4O9 and KFeO2, reaches 25 wt %─a notably higher value than ilmenite exposed to biomass in a fluidized bed. The research concludes that the lifetime of ilmenite is therefore rather dependent on its mechanical integrity than its maximum potassium uptake.
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| 6. |
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| 7. |
- Purnomo, Victor, 1992, et al.
(författare)
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Effect of the Conversion Degree on the Apparent Kinetics of Iron-Based Oxygen Carriers
- 2024
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Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 38:13, s. 11824-11836
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Tidskriftsartikel (refereegranskat)abstract
- The role of the oxygen carrier is important in energy conversion processes with fluidized beds, particularly chemical looping technology. It is necessary to establish the relevant kinetics of oxygen carriers that can be applicable for various chemical looping processes. In this study, we analyzed the apparent kinetics of three iron-based oxygen carriers, namely, ilmenite, iron sand, and LD slag, during the conversion of CO, H2, and CH4 in a fluidized bed batch reactor. The effect of both the oxidation degree, presented as the mass conversion degree, and temperature was considered. The results show that the changing grain size (CGS) model is generally applicable in predicting the apparent kinetics of reactions between the investigated iron oxygen carriers and gaseous fuels even at lower oxidation degrees (3-5 wt % reduction). The activation energies of the investigated materials in the conversions of CO, H2, and CH4 obtained from the fittings of the CGS model are about 51-92, 55-251, and 72-211 kJ/mol, respectively. Both the mass conversion degree and temperature influence the reactivity of oxygen carriers in a directly proportional way, especially at temperatures higher than 925 °C. The results of this study are useful for reaction engineering purposes, such as designing a reactor, in chemical looping units, or in any other processes that use oxygen carriers as a bed material.
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| 8. |
- Purnomo, Victor, 1992, et al.
(författare)
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Performance of iron sand as an oxygen carrier at high reduction degrees and its potential use for chemical looping gasification
- 2023
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 339
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Tidskriftsartikel (refereegranskat)abstract
- Iron sand as an industrial by-product has a reasonable iron content (35 wt% Fe) and low economical cost. The reactivity of iron sand as an oxygen carrier was examined in a bubbling fluidized bed reactor using both gaseous and solid fuels at 850–975 °C. Pre-reductions of iron sand were performed prior to fuel conversion to adapt the less-oxygen-requiring environment in chemical looping gasification (CLG). Based on the investigations using CO and CH4, iron sand has an oxygen transfer capacity of around 1 wt%, which is lower than that of ilmenite. The conversion of pine forest residue char to CO and H2 was higher when using iron sand compared to ilmenite. Depending on the mass conversion degree of iron sand, the activation energy of pine forest residue char conversion using iron sand was between 187 and 234 kJ/mol, which is slightly lower than that of ilmenite. Neither agglomeration nor defluidization of an iron sand bed occurred even at high reduction degrees. These suggests that iron sand can be utilized as an oxygen carrier in CLG. Furthermore, this study presents novel findings in the crystalline phase transformation of iron sand at various degrees of oxidation, altogether with relevant thermodynamic stable phases.
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| 9. |
- Stanicic, Ivana, 1994
(författare)
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Chemical Transformation of Inorganic Species in Thermochemical Conversion of Waste-Derived Fuels - The Role of Oxygen Carriers
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Waste-derived fuels are used increasingly in heat and power production systems in Sweden. Thermal conversion of waste-derived and biomass fuels offers the possibility of achieving carbon dioxide-neutral or even negative emissions. To limit global warming, it is essential to integrate these systems with carbon capture and storage. However, using alternative fuels raises challenges due to their complex compositions and their contents of heavy metals and other inorganic species. Chemical looping technologies have great potential for lowering costs for CO2 capture and reducing emissions of pollutants, such as NOx. These processes utilize metal oxides, or oxygen carriers (OCs), to transfer oxygen from air to fuel. However, the fates of the inorganic ash species in the presence of OCs are not well understood. The aim of this thesis is to provide a better understanding of the chemical transformations that occur in chemical looping applications, focusing on the heavy metals Zn, Cu, and Pb. In this thesis, the reaction pathways of Zn, Cu and Pb are studied using combined theoretical and experimental approaches. Samples derived from combustion and gasification processes that utilize OCs are studied in detail by XRD, SEM-EDX and XPS. Zn and Cu are observed to interact with the OC and form ferrites under both combustion and gasification conditions. The formation of ferrites is shown to play an important role in the pathways for these elements. For the Fe-Ti-based OC ilmenite, Zn is incorporated into the ash layer while Cu is found to accumulate inside the ilmenite particles. The interaction between Zn and ilmenite is studied in greater detail in laboratory-scale experiments. It is observed that reaction with Zn is promoted after ilmenite has undergone consecutive reduction and oxidation cycles, owing to the formation of an Fe-rich layer on the external surface. Pb is concentrated in the fly ash regardless of the chemical looping technology and OC types investigated in this thesis. The chemical speciation of Zn, Cu, and Pb in chemical looping processes is further considered with respect to the oxygen carrier type, temperature, reduction potential, and other ash components. The correlation of theoretical and experimental observations enables the identification of systems that were not well-described by thermodynamic equilibrium calculations (TECs). To improve the predictive potentials of TECs, thermodynamic databases are expanded by incorporating data i) available in the literature, and ii) from first principle calculations. For the latter, thermodynamic data is obtained for experimentally identified crystalline phases that are not available in the literature. This expansion has contributed to the updated and most comprehensive thermodynamic database for combined OC and ash systems. The database was implemented to study the phase stability during chemical looping combustion (CLC) of waste-derived fuels, providing the first insights into the chemical speciation of inorganic ash species. The results indicate that a major fraction of the problematic compounds exits the fuel reactor with the gas, preventing corrosion of the heat transfer surfaces in the air reactor.
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| 10. |
- Stanicic, Ivana, 1994, et al.
(författare)
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Fate of lead, copper, zinc and antimony during chemical looping gasification of automotive shredder residue
- 2021
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 302
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Tidskriftsartikel (refereegranskat)abstract
- Gasification experiments in this study were performed in a 2–4 MW indirect gasifier coupled to a semi-commercial CFB combustor at Chalmers University of Technology. Experiments were carried out during 13 days with automotive shredder residue (ASR), giving a unique opportunity to investigate the bed material under realistic conditions and with long residence times. The metal rich ash was accumulated in the bed, gaining some oxygen carrying capabilities, creating a chemical looping gasification (CLG) process. This study aims to expand the knowledge about the chemistry of zinc, copper, lead and antimony during CLG of ASR. Several experimental methods have been utilized, such as XRD, SEM-EDX and XPS along with detailed thermodynamic calculations to study chemical transformations that can occur in the system. Thermodynamic calculations showed that the reduction potential affect the phase distribution of these elements, where highly reduction conditions result in heavy metals dissolving in the slag phase. Copper and zinc ferrites, lead silicates and antimony oxides were identified at the particle surfaces in the bottom ash. The formation of an iron rich ash layer plays an important role, especially for copper and zinc speciation. The main pathways in the complex CLG system have been discussed in detail.
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