| 41. |
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| 42. |
- Cho, Paul In-Young, 1970, et al.
(författare)
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Defluidization conditions for fluidized-bed of iron, nickel, and manganese oxide containing oxygen-carriers for chemical-looping combustion
- 2006
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 45:3, s. 968-977
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Tidskriftsartikel (refereegranskat)abstract
- For combustion with CO2 capture, chemical-looping combustion with inherent separation Of CO2 is a promising technology. Chemical-looping combustion uses oxygen carriers that are composed of metal oxide to transfer oxygen from the combustion air to the fuel. The defluidization of oxygen-carrier particles was investigated to improve the understanding of when particle agglomeration may occur. The study was made in a laboratory fluidized-bed reactor at 950 degrees C, simulating a chemical-looping combustion system by exposing the sample to reducing and oxidizing conditions in an alternating manner. The oxygen-carrier particles used were based on oxides of iron, nickel, and manganese and produced by freeze granulation. For iron oxide particles, there was no defluidization of the bed when the content of available oxygen in the particle was high. The defluidization occurred during the oxidation period after long reduction periods, in which a significant reduction of the magnetite to wustite occurred. This is an important observation, because the reduction to wustite is not expected in chemical-looping combustion with high fuel conversion. Thus, laboratory experiments with iron oxide performed with long reduction times may give an unduly exaggerated impression of the risks of agglomeration. For nickel oxide, the defluidization was dependent on the sintering temperature with no defluidization in experiments conducted with particles sintered at 1300 and 1400 degrees C. The nickel oxide particles that were sintered at 1500 degrees C only defluidized once in a total of 49 cycles, whereas the particles that were sintered at 1600 degrees C defluidized already in the first cycle. For the nickel oxide particles, it was not possible to see any effect of the length of the reducing period on the defluidization. There was no defluidization of the manganese oxide particles. The defluidization of the bed leads to agglomeration for the iron oxide particles, but not for the particles of nickel oxide, where the bed was still loosely packed. Carbon was formed on the particles based on nickel oxide and manganese oxide.
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| 43. |
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| 44. |
- Cuadrat, Ana, 1982, et al.
(författare)
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Influence of limestone addition in a 10 kWth Chemical-Looping Combustion unit operated with petcoke
- 2011
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 25:10, s. 4818-4828
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Tidskriftsartikel (refereegranskat)abstract
- Ilmenite, a natural mineral composed of FeTiO3, is a low cost material suitable as oxygen-carrier for Chemical-Looping Combustion (CLC) with solid fuels. One option when using the CLC technology with solid fuels is to introduce the fuel directly into the fuel-reactor. There the fuel is gasified and volatiles and gasification products react with the oxygen-carrier. In this study the influence of limestone addition to ilmenite as oxygen-carrier was tested in a continuous 10 kWth CLC pilot for solid fuels. The fuel fed was a petcoke and the gasifying agent was steam. Tests with an ilmenite-limestone mixture as bed material were performed, and also tests using only ilmenite as bed material were carried out for comparison. Global solids circulation was varied as it is an important operational parameter, which determines the solid fuel residence time. The experiments were made at two fuel-reactor temperatures: 950ºC and 1000ºC. Generally, higher residence time of the fuel and higher temperature increased both gasification and combustion efficiencies. This was seen for both with and without limestone addition. The addition of limestone, gave a significant improvement of gas conversion at 950ºC, which could be explained by lime catalyzing the water-gas shift reaction. Moreover, the presence of limestone significantly increased the char conversion both at 950ºC and 1000ºC.
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| 45. |
- Dubey, Ashwani, 1985, et al.
(författare)
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Interaction Between Alkali Chlorides and Ilmenite in Chemical Looping Combustion
- 2024
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Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Chemical looping combustion (CLC) is an emerging combustion technology recognized for its high efficiency and minimal environmental impact in terms of CO2 emissions. When biomass is used in CLC, the process referred to as Bio-CLC, it can result in negative CO2 emissions. However, the presence of alkalis (K and Na) in biomass can pose operational challenges. To better understand how alkalis interact with oxygen carriers, this study utilized a method involving the impregnation of charcoal particles with alkali salts (KCl or NaCl or both). The influence of alkali chlorides on fluidization/agglomeration, reactivity, and interaction with ilmenite was investigated in a batch fluidized bed reactor operating at 950 °C. During the reduction step of the simulated CLC cycles with solid fuels, charcoal impregnated with KCl (K-charcoal), NaCl (Na-charcoal), and a combination of both (Na-K charcoal) was used. A total of 33 alkali cycles were performed with K-charcoal, Na-charcoal, and Na-K charcoal with calcined ilmenite, as well as Na-K charcoal with synthetic ilmenite, including additional cycles using nonimpregnated charcoal as a reference. Na-K charcoal with calcined ilmenite led to an earlier onset of agglomeration and defluidization than single-impregnated charcoal. In contrast, no defluidization was observed in the case of synthetic ilmenite with Na-K charcoal. EDX analyses revealed minimal Na and no K accumulation in the particle bridges of the final Na-ilmenite and K-ilmenite samples. Conversely, Na and K were found together with Si and Al in the particle bridges of the final Na-K ilmenite, while no accumulation of Na and K was observed in the final Na-K synthetic ilmenite. ICP-OES analyses showed that approximately 28% of K and 49% of Na were retained in the final K-ilmenite and Na-ilmenite, respectively. Negative K retention and 40% Na were observed in the final Na-K ilmenite, whereas 35% K and 40% Na retention were found in the final Na-K synthetic ilmenite. This research significantly enhances our understanding of the interactions between alkali chlorides and ilmenite.
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| 46. |
- Dueso, Cristina, 1977, et al.
(författare)
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Reactivity of a NiO/Al2O3 oxygen carrier prepared by impregnation for chemical-looping combustion
- 2010
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 89:11, s. 3399-3409
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Tidskriftsartikel (refereegranskat)abstract
- The reactivity of a Ni-based oxygen carrier prepared by hot incipient wetness impregnation (HIWI) on alpha-Al2O3 with a NiO content of 18 wt% was studied in this work. Pulse experiments with the reduction period divided into 4-s pulses were performed in a fluidized bed reactor at 1223 K using CH4 as fuel. The number of pulses was between 2 and 12. Information about the gaseous product distribution and secondary reactions during the reduction was obtained. In addition to the direct reaction of the combustible gas with the oxygen carrier, CH4 steam reforming also had a significant role in the process, forming H-2 and CO. This reaction was catalyzed by metallic Ni in the oxygen carrier and H-2 and CO acted as intermediate products of the combustion. No evidence of carbon deposition was found in any case. Redox cycles were also carried out in a thermogravimetric analyzer (TGA) with H-2 as fuel. Both tests showed that there was a relation between the solid conversion reached during the reduction and the relative amount of NiO and NiAl2O4 in the oxygen carrier. When solid conversion increased, the NiO content also increased, and consequently NiAl2O4 decreased. Approximately 20% of the reduced nickel was oxidized to NiAl2O4, regardless DXs. NiAl2O4 was also an active compound for the combustion reaction, but with lower reactivity than NiO. Further, the consequences of these results with respect to the design of a CLC system were investigated. When formation of NiAl2O4 occurred, the average reactivity in the fuel reactor decreased. Therefore, the presence of both NiO and NiAl2O4 phases must be considered for the design of a CLC facility. (C) 2010 Elsevier Ltd. All rights reserved.
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| 47. |
- Eide, Lars, et al.
(författare)
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Novel Capture Processes
- 2005
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Ingår i: Oil and Gas Science and Technology. ; 60:3, s. 497-508
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Tidskriftsartikel (refereegranskat)
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| 48. |
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| 49. |
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| 50. |
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