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- 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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| 2. |
- Hanning, Malin, 1987, et al.
(författare)
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CaMn0.9Mg0.1O3-δ as Oxygen Carrier in a Gas-Fired 10 kWth Chemical-Looping Combustion Unit
- 2013
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 52:21, s. 6923-6932
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Tidskriftsartikel (refereegranskat)abstract
- Spray dried particles of the perovskite material CaMn0.9Mg0.1O3-δ have been examined as oxygen carrier for chemical-looping combustion of natural gas. The experiments have been conducted in a continuously operating reactor with the nominal size 10 kWth. The oxygen carrier particles showed excellent ability to convert fuel and complete combustion was reached at certain conditions. In general, the CO2 yield increased with increased fuel reactor temperature and with increased circulation rate. The oxygen carrier was able to release gaseous oxygen through the so called CLOU-mechanism (Chemical-Looping with Oxygen Uncoupling). When the fuel reactor was fluidized by inert gas, there was oxygen release at temperatures above 700°C, reaching a maximum of more than 3% for temperatures above 850°C. Gas phase oxygen was also measured during operation with fuel, as long as the fuel conversion was complete. When the fuel reactor temperature was above 900°C and a high enough circulation rate was maintained, complete combustion of the fuel was achieved with an oxygen concentration in the outlet stream from the fuel reactor of more than 1%. This suggests that a substantial part of the fuel is converted by gaseous oxygen released from the particles. The oxygen carrier particles were subject to more than 350 h of fluidization, of which more than 175 h was at high temperature and more than 55 h with addition of fuel. The particles did not show any tendencies to form hard agglomerations or break down to fines due to attrition during the experiments. Operational problems included high rate of particle elutriation, which was likely an effect of a mismatch between the size and density of the particles, the air flow and the cyclone.
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| 3. |
- Linderholm, Carl Johan, 1976, et al.
(författare)
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Chemical-looping combustion of solid fuels in a 10 kW reactor system using natural minerals as oxygen carrier
- 2013
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Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 37, s. 598-607
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Konferensbidrag (refereegranskat)abstract
- Chemical-looping combustion (CLC) is an unmixed combustion concept where fuel and combustion air are kept separate by means of an oxygen carrier, and the CO2 capture is inherently achieved. This work presents findings from a continuously operated 10 kW pilot for solid fuels. Using petcoke as fuel, the following oxygen carriers are compared: (a) ilmenite, (b) ilmenite + lime, (c) manganese ore, and (d) manganese ore + lime. Compared to ilmenite, the use of manganese ore as oxygen carrier greatly enhanced the rate of gasification. By adding lime particles to the Mn ore, performance improved further. The addition of lime to ilmenite had a small beneficial effect on gas conversion and char gasification rate.
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