| 1. |
- Jing, Dazheng, 1986, et al.
(författare)
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Examination of oxygen uncoupling behaviour and reactivity towards methane for manganese silicate oxygen carriers in chemical-looping combustion
- 2014
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 29, s. 70-81
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Tidskriftsartikel (refereegranskat)abstract
- Cheap and environmental friendly Mn-Si oxygen carriers manufactured from Mn3O4 and SiO2 by spray-drying have been investigated with respect to properties for chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). Fifteen oxygen carriers with SiO2 content varying from 2wt% to 75wt% were prepared and calcined at 1050°C and 1150°C. The ability of material to release O2 and their reactivity towards CH4 were examined in the temperature range 900-1100°C. Particles with a SiO2 content of more than 45wt% and calcined at 1150°C showed limited CLOU behaviour and poor reactivity towards CH4 at all temperatures investigated. The rest of the materials had significant CLOU properties and provided high conversion of CH4 under the experimental conditions chosen. Increasing the temperature of operation enhanced the CLOU behaviour and reactivity towards CH4. At temperatures above 950°C, the CH4 conversion was 90-100% for these materials. Crystalline phases identified by XRD in the oxidized samples with more than 45wt% SiO2 and calcined at 1150°C were mainly rhodonite MnSiO3. For materials with SiO2 content below 45wt%, braunite Mn7SiO12 was detected as the main phase in most of the samples after oxidation. This indicates that braunite Mn7SiO12 is the main active phase for oxygen transfer in CLC and CLOU, which is supported by thermodynamic calculations. The reactivity of all of the materials were also studied with syngas (50% CO and 50% H2), showing complete gas conversion at 950°C, except for materials with a SiO2 content of more than 45wt% and calcined at 1150°C. The mechanical integrity and attrition resistance of the oxygen carriers were examined in a jet-cup attrition rig, and although the attrition rates varied, some reactive material showed low rates of attrition, making them very promising oxygen carrier materials for applications related to CLC and CLOU. However, measures should probably be taken to improve the crushing strength to some extent. © 2014 Elsevier Ltd.
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| 2. |
- Sundqvist, Sebastian, 1986, et al.
(författare)
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Screening of different manganese ores for chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU)
- 2014
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Ingår i: 11th International Conference on Fluidized Bed Technology, CFB 2014; Beijing; China; 14 May 2014 through 17 May 2014. ; , s. 893-898
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Konferensbidrag (refereegranskat)abstract
- Oxygen carriers based on manganese oxides have recently shown great promise for use in chemicallooping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). In this work, different manganese ores have been investigated for application in CLC and CLOU. The reactivity towards methane and synthesis gas (50% CO in H2) and the oxygen uncoupling behaviour at 900, 950 and 1000°C have been investigated. The mechanical stability and integrity of the ores were also evaluated in a jet-cup attrition rig. It was found that some of the ores could convert approximately 70-80% of methane added to carbon dioxide, and most of them achieved almost complete gas yield for synthesis gas. The materials released small amounts of oxygen during the inert cycles. Some of the investigated ores also exhibited low rates of attrition. The combination of high reactivity with different fuel gases, relatively low attrition rates and low cost make these manganese ores highly interesting for a CLC process based on interconnected fluidized beds.
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| 3. |
- Sundqvist, Sebastian, 1986, et al.
(författare)
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Screening of different manganese ores for chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU)
- 2015
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 43, s. 179-188
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen carriers based on manganese oxides have recently shown great promise for use in chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). In this work, eleven different manganese ores have been investigated for application in CLC and CLOU. The reactivity towards methane and synthesis gas (50% CO in H-2) and the oxygen uncoupling behaviour at 900,950 and 1000 degrees C have been investigated. The mechanical stability and integrity of the ores were also evaluated in a jet-cup attrition rig. It was found that some of the ores could convert approximately 70-80% of the added methane to carbon dioxide, and most of them provided almost complete conversion of synthesis gas. In these experiments the bed mass was 15 g for experiments with methane and 2 g for experiments with syngas, corresponding to a specific solids inventory of 57 and 25 kg/MW, respectively. All of the oxygen carrier materials released small amounts of gas phase oxygen via CLOU, between 0.01 and 0.03 mass% of the oxygen carrier during the inert period. Some of the investigated ores also exhibited low rates of attrition. The combination of high reactivity with different fuel gases, relatively low attrition rates and low cost make some of these manganese ores highly interesting for a CLC process based on interconnected fluidized beds.
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| 4. |
- Adanez-Rubio, Inaki, et al.
(författare)
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Investigation of Combined Supports for Cu-based Oxygen Carriers for Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2013
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 27:7, s. 3918-3927
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Tidskriftsartikel (refereegranskat)abstract
- The chemical-looping with oxygen uncoupling (CLOU) process is a novel solution for efficient combustion with inherent separation of carbon dioxide. The process uses a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor. In the fuel reactor, the metal oxide releases gas phase oxygen which oxidizes the fuel through normal combustion. In this study, Cu-based oxygen carrier materials that combine different supports of MgAl2O4, TiO2 and SiO2 are prepared and characterized with the objective of obtaining highly reactive and attrition resistant particles. The oxygen carrier particles were produced by spray-drying and were calcined at different temperatures ranging from 950 to 1030oC for 4 h. The chemical-looping performance of the oxygen carriers was examined in a batch fluidized-bed reactor in the temperature range of 900-950oC under alternating reducing and oxidizing conditions. The mechanical stability of the oxygen carriers was tested in a jet-cup attrition rig. All of the oxygen carriers showed oxygen uncoupling behaviour with oxygen concentrations close to equilibrium. During reactivity tests with methane, oxygen carriers with lower mechanical stability showed higher reactivity, yielding almost complete fuel conversion. Oxygen carrier materials based on support mixtures of MgAl2O4/TiO2, MgAl2O4/SiO2 and TiO2/SiO2 showed a combination of high mechanical stability, low attrition rates, good reactivity with methane and oxygen uncoupling behaviour.
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| 5. |
- Arjmand, Mehdi, 1986, et al.
(författare)
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CaxLa1−xMn1−yMyO3−δ (M = Mg, Ti, Fe or Cu) as Oxygen Carriers for Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2013
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 27:8, s. 4097-4107
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Tidskriftsartikel (refereegranskat)abstract
- Perovskite materials of the type CaxLa1−xMn1−yMyO3−δ (M = Mg, Ti, Fe or Cu) have been investigated as oxygen carriers for the chemical-looping with oxygen uncoupling (CLOU) process. The oxygen carrier particles were produced by mechanical homogenization of primary solids in a rotary evaporator followed by extrusion and calcination at 1300°C for 6 h. The chemical-looping characteristics of the substituted perovskites developed in this work were evaluated in a laboratory-scale fluidized-bed reactor in the temperature range of 900−1000°C during alternating reducing and oxidizing conditions. The oxygen carriers showed oxygen releasing behaviour (CLOU) in inert atmosphere between 900−1000°C. In addition, their reactivity with methane was high, approaching complete gas yield for all of the materials at 950°C, the exception being the Cu-doped perovskite which defluidized during reduction. The rates of oxygen release were also investigated using devolatilized wood char as solid fuel, and were found to be similar. The required solids inventory in the fuel reactor for the perovskite oxygen carriers is estimated to be 325 kg/MWth. All of the formulations exhibited high rates of oxidation and high degree of stability with no particle fragmentation or agglomeration. The high reactivity and favourable oxygen uncoupling properties make these oxygen carriers promising candidates for the CLOU process.
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| 6. |
- Arjmand, Mehdi, 1986, et al.
(författare)
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CaZrO3 and SrZrO3-based CuO Oxygen Carriers for Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2014
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Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 51, s. 75-84
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Konferensbidrag (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. In this work, oxygen carriers based on CuO supported by zirconates of SrZrO3 and CaZrO3 are investigated. The oxygen carriers were produced by mechanical homogenization of primary solids in a rotary evaporator followed by extrusion, drying and calcination at 950 and 1030 degrees C for 6 h. Their chemical-looping performance was evaluated in a laboratory-scale fluidized-bed reactor at 900 and 925 degrees C under cyclic oxidizing, inert (N-2) and reducing (CH4) conditions. All oxygen carriers exhibited rapid release of oxygen in the inert environment (CLOU) with high conversion of methane. The carrier calcined at 1030 degrees C with SrZrO3 as support showed no agglomeration or deactivation and exhibited the highest reactivity. Thus, the use of this oxygen carrier could be of interest for the CLOU process.
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| 7. |
- Arjmand, Mehdi, 1986
(författare)
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Copper and Manganese-based Oxygen Carriers in Chemical-Looping Combustion (CLC) and Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) processes are attractive 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 to a fuel reactor where the fuel, or gasification products of the fuel, is converted. When solid fuel is used in CLC, the char needs to be gasified, by e.g. steam, to form H2 and CO that can subsequently be oxidized to H2O and CO2 by the oxygen carrier. In the case of CLOU, the oxygen carrier releases gas-phase oxygen in the fuel reactor. This enables a high rate of conversion of char from solid fuels, as CLOU eliminates the need for the gasification step required in normal CLC with solid fuels.In this work, copper- and manganese-based oxygen carriers were investigated for the CLC and the CLOU processes. Their chemical-looping performance was examined in a laboratory-scale fluidized-bed reactor under alternating reducing and oxidizing conditions at different temperatures. The materials were generally evaluated with respect to oxygen release, reactivity and performance. Detailed material analysis and characterization of various oxygen carriers were carried out. Different gaseous fuels such as methane and synthesis gas (50% CO in H2) as well as solid fuels such as petroleum coke and wood char were used.As copper-based materials, freeze-granulated Al2O3 and MgAl2O4-supported CuO oxygen carriers were investigated for CLC and CLOU applications using methane. In order to establish the phase relationships in the Cu–Al–O system, the standard enthalpy of formation, ΔH_f^0, of CuAl2O4 was reassessed using differential scanning calorimetry (DSC). The reducing and oxidizing pathways in the Cu−Al−O system and the reversibility of the phases during the redox process were also studied. As manganese-based materials, various manganese-based perovskite-type oxygen carriers produced by extrusion and spray-drying and different manganese ores were studied. The effect of dopants, operating temperature and calcium content on the reactivity of oxygen carriers towards methane and the stability of the perovskite-structured materials as well as tolerance towards deactivation with sulphur were examined for the CLOU process. The reactivity of manganese ores with gaseous fuels and their influence on the rate of char gasification was scrutinized for CLC application with gasification of solid fuels. A method for obtaining the rate of oxygen release for CLOU by utilizing a devolatilized wood char has been developed and was applied to the MgAl2O4-supported CuO oxygen carrier and the extruded perovskite-type materials. Furthermore, the oxidation rate of the MgAl2O4-supported CuO oxygen carrier for CLOU was studied. Based on the obtained rates, the minimum solids inventories using these oxygen carriers were determined for a CLOU unit.
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| 8. |
- Arjmand, Mehdi, 1986
(författare)
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Copper in Chemical-Looping Combustion (CLC) and Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) processes are attractive 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 to a fuel reactor where the fuel, or gasification products of the fuel, reacts with the oxygen carrier. The feasibility of Al2O3 and MgAl2O4-supported CuO oxygen carriers for CLC and CLOU processes are investigated in this work. The reactivity of these oxygen carriers was evaluated in a laboratory-scale fluidized-bed at 900 and 925°C under alternating reducing and oxidizing conditions. For Al2O3-supported oxygen carriers, CuO reacted with the support forming copper(II) aluminate (CuAl2O4), which is also a viable oxygen carrier, although it has no oxygen uncoupling properties. In the case of MgAl2O4 as support, the oxygen carrier exhibited stable oxygen release due to the presence of intact CuO. In order to establish the phase relationships in the Cu–Al–O system, the standard enthalpy of formation, ΔH_f^0, of CuAl2O4 was reassessed using thermogravimetry and differential scanning calorimetry (TGA/DSC) due to discrepancy in thermodynamic databases. The reducing and oxidizing pathways in the Cu−Al−O system and the reversibility of the phases during the redox process were also investigated. Here, the phase transformations were examined as a function of duration of the reduction period and oxygen concentration during the re-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 re-oxidation into CuO and CuAl2O4. The rate of oxygen release and the rate of oxidation of the MgAl2O4-supported CuO oxygen carrier were determined in the temperature range of 850−900°C. Devolatilized wood char was used to facilitate oxygen release from the oxygen carrier in N2-fluidization by maintaining low oxygen concentration around the particles. The Avrami-Erofeev mechanism was used to model the rates of oxygen release. However, during oxidation it was observed that the rate is limited by the oxygen supply, indicating rapid conversion of the oxygen carrier. From the obtained reaction rates, the total amount of the investigated oxygen carrier needed in the air and the fuel reactor is estimated to be between 73−147 kg MW_th^(-1).
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| 9. |
- 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. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 51:43, s. 13924-13934
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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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| 10. |
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