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- Arjmand, Mehdi, 1986-, et al.
(författare)
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Evaluation of CuAl2O4 as an Oxygen Carrier in Chemical-Looping Combustion
- 2012
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Ingår i: Industrial & Engineering Chemistry Research. - 1520-5045. ; 51:43
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Tidskriftsartikel (refereegranskat)abstract
- The chemical-looping combustion (CLC) process is a novel solution for efficient combustion with intrinsic separation of carbon dioxide. The process uses a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor where the fuel, or gasification products of the fuel, reacts with the solid oxygen carrier. In this work, copper(II) aluminate (CuAl2O4) was assessed as a potential oxygen carrier using methane as fuel. The carrier particles were produced by freeze–granulation and calcined at 1050 °C for a duration of 6 h. The chemical-looping characteristics were evaluated in a laboratory-scale fluidized-bed reactor in the temperature range of 900–950 °C during 45 alternating redox cycles. The oxygen carrier exhibited reproducible and stable reactivity behavior in this temperature range. Neither agglomeration nor defluidization was noticed in any of the cycles carried out at 900–925 °C. However, after reactivity tests at 950 °C, soft agglomeration and particle fragmentation were observed. Systematic phase analysis of the Cu–Al–O system during the redox cycle was carried out as a function of duration of reduction and oxygen concentration during the oxidation period. It was found that the CuAl2O4 is reduced to copper(I) aluminate (CuAlO2; delafossite), Cu2O, and elemental Cu. The CuAlO2 phase is characterized by slow kinetics for oxidation into CuO and CuAl2O4. Despite this kinetic limitation, complete conversion of methane with reproducible reactivity of the oxygen carrier is achieved. Thus, CuAl2O4 could be a potential oxygen carrier for chemical-looping combustion.
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- Arjmand, Mehdi, 1986-, et al.
(författare)
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Investigation of CuO-based Oxygen Carriers as CLOU Materials for Solid Fuels
- 2011
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Ingår i: Proceeding of the 2011 AIChE Fall Annual Meeting. - 978-0-8169-1070-0
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Konferensbidrag (övrigt vetenskapligt)abstract
- Chemical-looping combustion (CLC) is a promising combustion technique with efficient CO2-capture at low cost due to inherent gas separation. In a CLC process, a metal oxide is circulated between two reactors, wherein they undergo changes from an oxidized form in the air reactor to a reduced one in the fuel reactor. In the case of chemical-looping with oxygen uncoupling (CLOU), the oxygen carrier releases oxygen in the gas phase in the fuel reactor as shown in the figure. This enables a high rate of conversion of char from solid fuels, as it eliminates the need for the gasification step needed in normal CLC with solid fuels. Only certain pure metal oxides of Co, Cu and Mn have an equilibrium partial pressure of oxygen suitable for CLOU. Due to its favorable thermodynamics (facile redox properties) and agile kinetics (high reactivity), CuO is a promising CLOU material, in addition to being an excellent oxygen carrier in the combustion of gaseous fuels. In this work, the performance of CuO-based oxygen carriers supported on ZrO2 stabilized by calcium oxide, magnesia and ceria will be presented to assess their suitability as oxygen carriers for solid fuel combustion. The samples were prepared by freeze-granulation and the reactivity was examined in a laboratory fluidized bed reactor under cyclic oxidizing and reducing conditions, simulating the CLOU process. Owing to the fast release of oxygen by CLOU particles, the reaction rates were investigated using coke as the fuel of choice. The influence of reaction temperature and oxygen concentration on the rate of reaction was also studied.
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- 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. - 0887-0624. ; 26:11
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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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- Arjmand, Mehdi, 1986-, et al.
(författare)
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Prospects of Al2O3 and MgAl2O4-Supported CuO Oxygen Carriers in Chemical-Looping Combustion (CLC) and Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2011
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Ingår i: Energy & Fuels. - 0887-0624. ; 25:11, s. 5493-5502
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Tidskriftsartikel (refereegranskat)abstract
- The chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) processes are attractive solutions for efficient combustion with direct separation of carbon dioxide. In this work, the feasibility of CuO supported on Al2O3 and MgAl2O4 for CLC and CLOU processes is investigated. The oxygen carriers were produced by freeze-granulation and calcined at 950 and 1050 degrees C. The chemical-looping characteristics were evaluated in a laboratory-scale fluidized bed at 900 and 925 degrees C under alternating reducing and oxidizing conditions. Tendencies toward agglomeration, defluidization, and loss of active phase were analyzed by changing the experimental process variables, such as reaction time, temperature, and reducing and inert environments. Complete conversion of methane was obtained for all oxygen carriers investigated in this work Three out of four oxygen carriers also featured the rapid release of oxygen in an inert environment (CLOU). In the case of Al2O3) as support, a CLC and a CLOU oxygen carrier were obtained depending on the calcination temperature. In addition, analyses of the CuO-Al2O3 phase equilibria system under oxidizing and reducing conditions have been carried out. At the investigated temperatures, it is inferred for the case of Al2O3 as support that part of the active phase (either CuO or CuAl2O4 is bound as CuAlO2 during incomplete reduction with slow kinetics for reoxidation. However, when complete reduction is attained, the original active phase composition is rejuvenated upon oxidation. As a result, the use of CuAl2O4 is suggested for CLC processes from the point of agglomeration and attrition-free functioning of the oxygen carrier. In the case of MgAl2O4 as support, the oxygen carrier exhibited a stable oxygen-releasing behavior due to the existence of relatively intact CuO. Together with the absence of agglomeration and major morphological changes, the use of MgAl2O4-supported CuO is suggested as a suitable oxygen carrier for CLOU processes.
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- Arjmand, Mehdi, 1986-, et al.
(författare)
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Use of manganese ore in chemical-looping combustion (CLC) – Effect on steam gasification
- 2012
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Ingår i: International Journal of Greenhouse Gas Control. - 1750-5836. ; 8, s. 56-60
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Tidskriftsartikel (refereegranskat)abstract
- The chemical-looping combustion (CLC) process is a novel solution for efficient combustion with direct separation of carbon dioxide. The process uses 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 solid fuel is used in CLC, the char needs to 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 this work, the influence of the oxygen carrier on the rate of steam gasification is studied, by comparing the conversion of petcoke in the presence of manganese ore to that of ilmenite. The experiments were carried out in a fluidized-bed reactor at 970 °C using a fluidization gas of 50% steam in nitrogen. The manganese ore shows an increase by a factor five in the rate of steam gasification of char as compared to ilmenite. The dramatic increase in rate of steam gasification, in combination with potentially low costs of this material suggests that manganese ore could be an interesting material for CLC with solid fuels.
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