| 1. |
- Cheng, M., et al.
(författare)
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Oxidation of Ammonia by Ilmenite under Conditions Relevant to Chemical-Looping Combustion
- 2015
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 29:12, s. 8126-8134
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of ammonia to NOx and N-2 was investigated under conditions that pertain to the fuel reactor during the chemical-lopping combustion of coal with ilmenite. The catalytic decomposition of NH3, the oxidation of NH3 over ihnenite, and the reduction of NO by reduced ilmenite and NH3 were studied experimentally. The catalytic decomposition of NH3, NO reduction by NH3, and reduced ilmenite were found to be important for N-2 formation. NH3 oxidation over ilmenite was the only way in which NO could be formed in this systerri, with around 18% the NH3 being converted to NO at 850-950 degrees C, The oxidation of NH3 was only slightly influenced by the reactor temperature but was strongly influenced by the concentrations of NH3 and syngas. NO formation was,promoted by high concentrations of NH3 and decreased by high concentrations of syngas. The selectivity of the NH3 toward-NO formation was favored at low concentrations of NH3 and syngas. The conversion of NH3 was complete in most cases, although 15-25% of the NH3 was not converted when the inlet syngas concentration increased to levels higher than 10-30%.
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| 2. |
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| 3. |
- Hua, X. N., et al.
(författare)
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The behaviour of multiple reaction fronts during iron (III) oxide reduction in a non-steady state packed bed for chemical looping water splitting
- 2017
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 193, s. 96-111
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Tidskriftsartikel (refereegranskat)abstract
- Owing to the unclear temporal and spatial variations of axial solid conversion in a packed bed using iron (III) oxide as an oxygen carrier, we directly observe these variations by means of a sub-layer approach. The results indicate that the behaviour of the multiple reaction fronts during iron (III) oxide reduction by CO or H-2 within a packed bed for chemical looping water splitting (CLWS) is strongly dependent on the reaction temperature. When the reaction temperature is lower than the merging temperature, three reaction fronts, i.e., Fe2O3-Fe3O4, Fe3O4-Fe0.947O and Fe0.947O-Fe, and three product zones, i.e., Fe3O4, Fe0.947O and Fe, will appear in the packed bed. In contrast, when the reaction temperature is higher than the merging temperature, the Fe2O3-Fe3O4 and Fe3O4-Fe0.947O fronts merge, leading to the disappearance of the Fe3O4 zone. As a result, only the Fe2O3-Fe0.947O and Fe0.947O-Fe fronts, as well as Fe0.942O and Fe zones will appear in the packed bed. These reduction behaviours are verified by two breakthrough curves, one for T T-m, from the thermodynamically controlled reduction of iron (III) oxide in the packed bed. The reaction front movement model, which is proposed based on the reduction behaviour, can be used to determine the maximum solid conversion of the reduction step, i.e., the thermodynamic limitation of the reduction step, in the packed bed CLWS. The maximum solid conversion can reach 0.409 for the CO case and 0.554 for the H-2 case. The first discovery of both the behaviours of the reaction fronts movement and the thermodynamic limitations of the reduction step standardizes the criteria for both the oxygen carrier evaluation and the optimization of the operating conditions and provides theoretical support for scaling up the packed bed and developing new technology for packed bed CLWS.
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| 4. |
- Härelind Ingelsten, Hanna, 1973, et al.
(författare)
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Mechanistic Study of the Influence of the Surface Acidity on Lean NO2 Reduction by Propane in HZSM-5
- 2005
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 232:1, s. 68-79
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on the mechanism of lean NO x reduction by propane, over acidic zeolites (HZSM-5), and the influence of surface acidity. In situ FTIR measurements of ammonia adsorption indicate a higher number of Brønsted acid sites for a sample with a low SiO 2 /Al 2 O 3 ratio. The activity for NO x reduction and the selectivity for N 2 formation correlate well with the Brønsted acidity. Step-response experiments with NO 2 and propane show the formation of surface-bound NO + , isocyanate, unsaturated hydrocarbons, and amine species. Formation of the latter two seems to be closely related to the Brønsted acidity. In the NO 2 reaction with propane, the NO + species seem to play a vital role, probably reacting with carbenium ions (from propane cracking) to form isocyanates, which may be hydrolysed to amine species. Step-response experiments with isopropylamine and NO 2 indicate a fast reaction, where the amine and NO + species react over Brønsted acid sites. Hence, amine species are possible reaction intermediates in the lean reduction of NO 2 by saturated hydrocarbons, such as propane, over HZSM-5. © 2005 Elsevier Inc. All rights reserved.
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| 5. |
- Normann, Fredrik, 1982, et al.
(författare)
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Oxidation of ammonia over a copper oxide-containing solid oxygen carrier with oxygen uncoupling capability
- 2016
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Ingår i: Combustion and Flame. - : Elsevier BV. - 1556-2921 .- 0010-2180. ; 165, s. 445-452
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Tidskriftsartikel (refereegranskat)abstract
- Measurements and modelling of the oxidation of ammonia over copper oxide (CuO) under conditions relevant to chemical-looping combustion with oxygen uncoupling show that CuO fully converts NH3 into NO or N-2 under most of these conditions. Our experiments demonstrate that considerable amounts of NO are formed when the oxygen carrier is fully oxidised. Decreasing the degree of oxidation of the oxygen carrier affected the selectivity of the NH3 oxidation towards NO. Ageing of the oxygen carrier had a similar effect. Modelling suggests that these results reflect a change in the rate of oxygen release from the CuO particles.
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| 6. |
- Paz, Maria Dolores, 1982, et al.
(författare)
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Investigating corrosion memory: The influence of previous boiler operation on current corrosion rate
- 2017
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 156, s. 348-356
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Tidskriftsartikel (refereegranskat)abstract
- The selection of fuel is crucial for a Combined Heat and Power (CHP) plant in terms of cost and corrosion and the fuel will vary over time. The corrosiveness of different fuels has been studied extensively, however, not how a current corrosion attack is influenced by corrosion history (i.e. previous deposit buildup and oxide scale formation) instead of the influence of the current flue gas composition (i.e. the current fuel mix being used). This influence of the corrosion history effect can be called "corrosion memory". To investigate the corrosion memory effect on boilers, a novel setup was used. Air-cooled probe AISI304L samples were exposed in two different boilers to mimic different fuels. One boiler was a biomass-fired boiler representing a moderate corrosive fuel and the other was a waste-fired boiler representing a highly corrosive fuel. A three-step exposure program was performed in which a reference probe was exposed in the biomass-fired boiler for all three steps while another probe was exposed in the biomass-fired boiler for steps 1 + 3 and in the waste-fired boiler for the second step. All samples were investigated with material-loss measurements and SEM/EDX. The findings show that the deposit and oxide scales formed on the samples in the biomass-fired boiler had a mitigating effect on the corrosion attack. Consequently, corrosion history affects the future corrosion rate.
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| 7. |
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| 8. |
- Xu, L. H., et al.
(författare)
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Cu-Modified Manganese Ore as an Oxygen Carrier for Chemical Looping Combustion
- 2014
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 28:11, s. 7085-7092
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Tidskriftsartikel (refereegranskat)abstract
- A new type of Mn-based oxygen carrier was prepared by impregnating manganese ore with copper nitrate solution. Cyclic reduction and oxidation reactivity of the materials was investigated in a fluidized-bed reactor. The potential use of these oxygen carriers for chemical looping combustion (CLC) was examined. The reactivity of the manganese ore can be highly improved by impregnation of copper. The reactivity of the oxygen carrier reduction is higher with a larger amount of copper impregnated. However, the degree of the reactivity enhancement is not proportional to the amount of copper doped on the oxygen carriers. An important finding is that, even with low Cu loading, such as 0.5 wt % copper impregnated on manganese, the period with full CO conversion can be enhanced 6 times. A very interesting phenomenon is that the Cu-modified manganese ore can completely convert CO, even at a low temperature, such as 500 degrees C. This study proves that the reactivity of the manganese ore could be significantly improved by impregnating copper, even with a small amount. The copper impregnation method could be very promising to improve the reactivity of the manganese ore as oxygen carriers for CLC.
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| 9. |
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| 10. |
- Zhao, Dongmei, 1963, et al.
(författare)
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Catalytic and mechanistic study of lean NO2 reduction by isobutane and propane over HZSM-5.
- 2006
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Ingår i: Journal of Molecular Catalysis A: Chemical. - : Elsevier BV. - 1381-1169. ; 249:1-2, s. 13-22
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Tidskriftsartikel (refereegranskat)abstract
- saturated hydrocarbons, propane and isobutane, has been investigated over acidic zeolite HZSM-5. The activity for NO2 reduction and the selectivity for N-2 formation correlate well with the intracrystalline acidity (Bronsted acid sites) of the zeolite. Isobutane is a more efficient reducing agent than propane due to its tertiary hydrogen being more readily activated than the secondary hydrogen in propane. In situ DRIFT step-response experiments with NO2 and isobutane show formation of surface bound NO+, isocyanate, unsaturated hydrocarbons and amine species. The NO+ species seems to play an important role in the reduction of NO2 probably by reacting with alkenes formed from carbenium ion adsorbates. These species likely form isocyanates, amine species and finally nitrogen.
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