| 1. |
- Bécoulet, A., et al.
(författare)
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Science and technology research and development in support to ITER and the Broader Approach at CEA
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10
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Tidskriftsartikel (refereegranskat)abstract
- In parallel to the direct contribution to the procurement phase of ITER and Broader Approach, CEA has initiated research & development programmes, accompanied by experiments together with a significant modelling effort, aimed at ensuring robust operation, plasma performance, as well as mitigating the risks of the procurement phase. This overview reports the latest progress in both fusion science and technology including many areas, namely the mitigation of superconducting magnet quenches, disruption-generated runaway electrons, edge-localized modes (ELMs), the development of imaging surveillance, and heating and current drive systems for steady-state operation. The WEST (W Environment for Steady-state Tokamaks) project, turning Tore Supra into an actively cooled W-divertor platform open to the ITER partners and industries, is presented.
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| 2. |
- Azimi, Golnar, 1985, et al.
(författare)
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Experimental evaluation and modeling of steam gasification and hydrogen inhibition in Chemical-Looping Combustion with solid fuel
- 2012
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 11, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- A Chemical-Looping Combustion (CLC) system is composed of two fluidized bed reactors, an air reactor and a fuel reactor. Oxygen is transferred from the air to the fuel by solid oxygen carrier particles circulating between these two reactors. By this arrangement, the N2 from the air is kept separated from the fuel gases as a part of the process and an almost pure stream of CO2 is obtained from the fuel reactor.This work investigates and models the influence of the steam and hydrogen concentration in the fuel reactor on the rate of solid fuel conversion in Chemical-Looping Combustion. Two kinds of fuel were examined, Swedish wood char and El Cerrejon bituminous coal (Colombian coal). Four different bed materials have been used in the reactor, ilmenite, nickel and oxide scales as an oxygen carrier and quartz sand for gasification experiments. The temperature was 970 °C for all experiments. Different fractions of steam and hydrogen were added to the fluidizing stream. Additionally, gasification experiments of fuel particles pretreated in mixtures of H2 and N2 were performed in order to determine the reversibility of the observed hydrogen inhibition.The results show that the best models for describing the behavior of steam gasification and fuel conversion in Chemical-Looping Combustion for a Swedish wood char and the El Cerrejon coal is the oxygen exchange model. For both fuels, it can be seen that higher steam concentration increases the rate of char conversion and, higher hydrogen concentration decreases the rate as a result of hydrogen inhibition. No irreversible hydrogen inhibition could be observed.
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| 3. |
- Keller, Martin, 1985, et al.
(författare)
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Chemical Looping Tar reforming with Fe,Sr-doped La2Zr2O7 pyrochlore supported on ZrO2
- 2018
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Ingår i: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 550, s. 105-112
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Tidskriftsartikel (refereegranskat)abstract
- Chemical Looping Reforming (CLR) has been proposed as a new technology for tar removal from hot raw gas derived from biomass gasification. In this two-reactor fluidized bed process at atmospheric pressure, the bed material is circulating between a reformer, in which the bed material is in contact with the raw synthesis gas, and a regenerator, in which the bed material is regenerated by oxidizing coke deposits and sulfides with air. In this study Fe,Sr-doped La 2 Zr 2 O 7 pyrochlores supported on ZrO 2 with different Fe and Sr loadings were investigated for their use as a catalyst in CLR. By decreasing the Fe loading to Fe/La = 0.25 the benzene-to-syngas conversion could be improved by about 50% at T = 800 °C in comparison with the reference material with Fe/La = 1.25. With this material, benzene and ethylene conversion could be further improved by co-feeding O 2 with the gasification gas, achieving a benzene conversion of up to 80% and an ethylene conversion of about 95% at a temperature of 850 °C and a Gas Hourly Space Velocity of 6800 h −1 . The performance of the bed material was found stable over at least 3 redox cycles. Considering the expected lower costs and non-toxicity of this material compared to precious metal- and Nickel-containing catalysts, normally used in fixed-bed systems, it is a promising material for a fluidized CLR system for tar removal.
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| 4. |
- Arjmand, Mehdi, 1986, et al.
(författare)
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Oxygen Release and Oxidation Rates of MgAl2O4-Supported CuO Oxygen Carrier for Chemical-Looping Combustion with Oxygen Uncoupling (CLOU)
- 2012
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 26:11, s. 6528-6539
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Tidskriftsartikel (refereegranskat)abstract
- The chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) processes are novel solutions for efficient combustion with inherent separation of carbon dioxide. These processes use a metal oxide as an oxygen carrier to transfer oxygen from an air reactor to a fuel reactor, where the fuel reacts with the solid oxygen carrier. When solid fuel is used in CLC, the char must be gasified by, e.g., steam to form H2 and CO, that can be subsequently oxidized to H2O and CO2 by the oxygen carrier. In the case of CLOU, the oxygen carrier releases oxygen gas in the fuel reactor. This enables a high rate of conversion of char from solid fuels, because it eliminates the need for the gasification step needed in normal CLC with solid fuels. In this work, the rate of oxygen release and oxidation of an oxygen carrier consisting of CuO supported by MgAl2O4 (40/60 wt %) for the CLOU process is investigated. The oxygen carrier was produced by freeze-granulation, calcined at 950 °C, and sieved to a size range of 125–180 μm. The reaction rates were obtained in a laboratory-scale fluidized-bed reactor in the temperature range of 850–900 °C, under alternating reducing and oxidizing conditions. The rate of oxygen release was obtained using devolatilized wood char as the fuel in N2 fluidization. Care was taken to obtain reliable measurements not affected by the availability of the fuel and temperature increase in the bed during combustion of the fuel with the released oxygen from the carrier. The Avrami–Erofeev mechanism was used to model the rates of oxygen release and the values of ko and Eapp were estimated to be 2.5 × 105 s–1 and 139.3 kJ mol–1, respectively. The rates of Cu2O oxidation were investigated in a flow of 5% O2 at the inlet of the reactor. However, it was observed that the oxidation rate is limited by the oxygen supply, indicating rapid conversion of the oxygen carrier. From the obtained reaction rates, the minimum total amount of the investigated oxygen carrier needed in the air and the fuel reactor is estimated to be between 69–139 kg MWth–1.
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| 5. |
- Keller, Martin, 1985, et al.
(författare)
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Chemical looping tar reforming using La/Sr/Fe-containing mixed oxides supported on ZrO2
- 2016
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 183, s. 298-307
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Tidskriftsartikel (refereegranskat)abstract
- Biomass gasification gas contains condensable hydrocarbons usually referred to as "tars". The use of chemical-looping reforming (CLR) has been proposed as a downstream technology for tar removal from the hot raw gasification gas. In this work two different ZrO2 support materials impregnated with La, Sr, Fe and mixtures thereof have been investigated as bed material for this proposed CLR process, with benzene and ethylene as tar surrogates. It was found that only combinations of La and Fe yielded significant catalytic activity for benzene conversion that could be further improved by adding Sr. Over this material, the benzene conversion reaction was found to be of first order with respect to benzene, and a simple kinetic model indicates that a high degree of benzene conversion can be obtained at reasonable residence times when the reactor temperature is sufficiently high (T= 850 degrees C). It was also observed that this material exhibited some activity for selective catalytic oxidation of benzene, which could further increase the tar conversion when either the bed material provided oxygen to the gas or a small stream of molecular O-2 was added to the gasification gas feed. XRD analysis of the used bed materials revealed that a pyrochlore phase and SrZrO3 perovskite were formed during the experiment.
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| 6. |
- Keller, Martin, 1985, et al.
(författare)
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Cu-impregnated alumina/silica bed materials for Chemical Looping Reforming of biomass gasification gas
- 2016
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 180, s. 448-456
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Tidskriftsartikel (refereegranskat)abstract
- Raw gas derived from low-temperature biomass gasification usually contains condensable hydrocarbons referred to as "tars" as well as other hydrocarbons such as ethylene and other olefins. Reforming of these compounds via Chemical Looping Reforming has been recently proposed. In this work Cu supported on four different Al2O3/SiO2-based porous support materials were investigated for reforming of ethylene. The investigated particles were manufactured by incipient wetness impregnation of the porous support with a copper nitrate solution followed by calcination, and then tested in a small-scale fluidized bed reactor at temperatures between 600 degrees C and 850 degrees C. The ethylene conversion was found to be strongly inhibited by the presence of aromatics in the gas. However, it was found that Cu supported on commercial PURALOX transition alumina catalyst exhibited superior properties, with high degrees of ethylene conversion achievable even in the presence of aromatic compounds. Under the experimental conditions in this work, up to 90% ethylene conversion was obtained at T = 850 degrees C in the presence of high concentrations of benzene. For the other prepared materials, the ethylene conversion was drastically reduced when monoaromatic compounds were present in the feed.
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| 7. |
- Keller, Martin, 1985, et al.
(författare)
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Gasification inhibition in chemical-looping combustion with solid fuels
- 2011
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Ingår i: Combustion and Flame. - : Elsevier BV. - 1556-2921 .- 0010-2180. ; 158:3, s. 393-400
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Tidskriftsartikel (refereegranskat)abstract
- Chemical-looping combustion (CLC) is a novel technology that can be used to meet growing demands on energy production without CO2 emissions. The CLC process includes two reactors, an air and a fuel reactor. Between these two reactors oxygen is transported by an oxygen carrier, which most often is a metal oxide. This arrangement prevents mixing of N-2 from the air with CO2 from the combustion giving combustion gases that consist almost entirely of CO2 and H2O. The technique reduces the energy penalty that normally arises from the separation of CO2 from other flue gases, hence, CLC could make capture of CO2 cheaper. For the application of CLC to solid fuels, the char remaining after devolatilization will react indirectly with the oxygen carrier via steam gasification. It has been suggested that H-2, and possibly CO, has an inhibiting effect on steam gasification in CLC. In this work experiments were conducted to investigate this effect. The experiments were conducted in a laboratory fluidized-bed reactor that was operating cyclically with alternating oxidation and reduction periods. Two different oxygen carriers were used as well as an inert sand bed. During the reducing period varying concentrations of CO or H-2 were used together with steam while the oxidation was conducted with 10% O-2 in N-2. The temperature was constant at 970 degrees C for all experiments. The results show that CO does not directly inhibit the gasification whereas the partial pressure of H-2 had a significant influence on fuel conversion. The results also suggest that dissociative hydrogen adsorption is the predominant hydrogen inhibition mechanism under the laboratory conditions, thus explaining why char conversion is much faster in a bed of oxygen carrying material, compared to an inert sand bed. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 8. |
- Keller, Martin, 1985, et al.
(författare)
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Interaction of mineral matter of coal with oxygen carriers in chemical-looping combustion (CLC)
- 2014
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Ingår i: Chemical Engineering Research and Design. - : Elsevier BV. - 0263-8762 .- 1744-3563. ; 92:9, s. 1753-1770
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Tidskriftsartikel (refereegranskat)abstract
- The chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) processes are novel solutions for efficient combustion with direct separation of carbon dioxide. These processes use a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor, where the fuel reacts with the solid oxygen carrier. When utilizing coal in CLC, the oxygen carrier particles could be affected through interaction with the ash-forming mineral matter found in coal, causing deactivation and/or agglomeration. In this work, possible interactions between minerals commonly encountered in coal and several promising oxygen carriers that are currently under investigation for their use in CLC are studied by both experiment and thermodynamic equilibrium calculations. Possible interaction was studied for both highly reducing and oxidizing conditions at 900 °C. Under highly reducing conditions pyrite was found to have by far the most deteriorating effect on the oxygen carrier particles, as the sulfur in the pyrite reacted with the oxygen carrier to form sulfides. Quartz and clay minerals were found to have a rather low influence on the oxygen carriers. Out of the oxygen carriers investigated, CuO/MgAl2O4 and the Mn3O4/ZrO2 oxygen carriers tended to be quite reactive towards mineral matter whereas ilmenite has been shown to be the most robust oxygen carrier. Although sulfur can clearly deactivate Ni, Cu and Mn based oxygen carriers under sub-stoichiometric conditions, when the fuel is converted fully to CO2 and H2O, sulfides are only expected for Ni-based oxygen carriers.
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| 9. |
- Keller, Martin, 1985, et al.
(författare)
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Investigation of Natural and Synthetic Bed Materials for Their Utilization in Chemical Looping Reforming for Tar Elimination in Biomass-Derived Gasification Gas
- 2014
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 28:6, s. 3833-3840
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Tidskriftsartikel (refereegranskat)abstract
- The removal of condensable hydrocarbons or tars from raw gas derived from biomass gasification presents an obstacle in the widespread application of biomass gasification. Hot catalytic tar cleaning as a secondary tar removal strategy is discussed as a tar cleaning technology. This can be realized in a dual-fluidized-bed reactor system, in which a catalytically active bed material is continuously regenerated. Such a process is termed chemical looping reforming (CLR). In such a process, it has been suggested that oxygen carrier particles employed for chemical looping combustion may be used, with the oxygen transfer from the particles to the gas promoting tar decomposition. Experiments were conducted in a small-scale, batch-wise fluidized-bed reactor with the aim of investigating a variety of bed materials for this process. The purpose of the present work is thus to conduct a screening study of a variety of bed materials based on the transition metals Fe, Mn, Ni, and Cu. The experiments were conducted in a batch fluidized bed, where the particles are exposed to reformer and regenerator conditions alternatingly. The conversion of ethylene from a synthetic gasification gas mixture was used as an indicator for the suitability of the materials for tar conversion. It was found that the natural material bauxite and the synthetic bed materials NiO/alpha-Al2O3, CuO/MgAl2O4, and La0.8Sr0.2FeO3/gamma-Al2O3 exhibit high ethylene conversion rates and, thus, possess promising properties for their application in CLR
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| 10. |
- Keller, Martin, 1985, et al.
(författare)
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Mechanisms of Solid Fuel Conversion by Chemical-Looping Combustion (CLC) using Manganese Ore: Catalytic Gasification by Potassium Compounds
- 2013
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Ingår i: Energy Technology. - : Wiley. - 2194-4296 .- 2194-4288. ; 1:4, s. 273-282
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Tidskriftsartikel (refereegranskat)abstract
- Chemical-looping combustion (CLC) is an emerging technology that can be used to meet the growing demands for electrical energy production without CO2 emissions. In CLC with solid fuels, the gasification of the carbonaceous fuel by steam is envisaged to be performed directly in the fuel reactor. This requires high steam-gasification rates for the effective use of the solid fuel. Recently, it has been observed that the choice of oxygen carrier can have a profound effect on the char-conversion rates in the fuel reactor. More specifically, the charconversion rate with a Brazilian manganese ore was a factor of five higher than that with ilmenite. In this work, the reaction mechanism of the char gasification was investigated in the presence of this manganese ore with the aim to explain the high rates observed. Steam-gasification experiments with petroleum coke were performed by using a batch fluidized-bed reactor with manganese ore as the bed material. In addition, partial gasification experiments of petroleum coke were conducted, and detailed energy-dispersive X-ray spectroscopy (EDX) analyses were performed on the surface and interior of the fuel and manganese-ore particles. The effect of the possible gas-phase release of oxygen from the manganese ore was also investigated. It was found that the release of gas-phase oxygen by the oxygen carrier does not explain the high gasification rates observed. Instead, the transfer of a catalytically active material, potassium, from the bed material to the solid fuel was observed, which in turn catalysed the steam-carbon-gasification reaction. As the catalytically active compound is included in this naturally occurring bed material, it may offer cost-efficient, catalytic gasification in a CLC process.
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