| 1. |
- Adanez-Rubio, Inaki, et al.
(författare)
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Cu-Mn oxygen carrier with improved mechanical resistance: Analyzing performance under CLC and CLOU environments
- 2021
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 217
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Tidskriftsartikel (refereegranskat)abstract
- Chemical Looping Combustion process allows combustion of gaseous, liquid or solid fuels with CO capture. The oxygen necessary for combustion can be supplied using lattice oxygen (CLC) or oxygen uncoupling (CLOU) mechanisms. The present work studies the effects of kaolin addition on Cu–Mn oxygen carrier behavior for CLC and CLOU processes. Cu–Mn oxygen carrier was prepared by granulation with a composition: 27.2 wt% CuO, 52.8 wt% Mn O and 20 wt% kaolin. Oxygen release rates and fluidization behavior were analyzed by TGA and batch fluidized bed reactor. The oxygen carrier was studied for CH and synthetic biogas combustion in a 500 W CLC continuous unit for 50 h of combustion at temperatures up to 930 °C. No agglomeration problems were observed. Results found during biogas combustion were similar to methane combustion. The addition of 20 wt% kaolin changed the mixed oxide chemical composition generating Cu Mn O and improved significantly the oxygen carrier mechanical resistance, increasing the extrapolated lifetime to 19,000 h, 3.6 times over the value found for any Cu based oxygen carrier in CLC. However, the oxygen carrier reactivity had an important decrease with respect to a similar oxygen carrier without kaolin addition, whose fraction in oxygen carrier must be optimized. 2 3 4 4 th 1.2 1.8 4
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| 2. |
- Adanez-Rubio, Inaki, et al.
(författare)
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Development of new Mn-based oxygen carriers using MgO and SiO 2 as supports for Chemical Looping with Oxygen Uncoupling (CLOU)
- 2023
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 337
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Tidskriftsartikel (refereegranskat)abstract
- Chemical Looping with Oxygen Uncoupling (CLOU) is a technological adaptation of CLC, most applicable for the combustion of solid fuels. In the CLOU process, an oxygen carrier in the fuel reactor, avoiding the direct contact of the fuel with the air, releases the oxygen needed for the fuel combustion. The oxygen carrier is regenerated with air in the interconnected air reactor. The present work explores the behavior of the system Mn/Mg/Si as oxygen carriers for chemical-looping with oxygen uncoupling (CLOU). Six different mixed oxides of the system Mn/Mg/Si were investigated for the CLC/CLOU process. Materials were prepared by spray drying with different metal ratios used in the investigation. The properties of interest for the viability of these materials are the lattice oxygen supply for CLC and the gaseous oxygen release for CLOU, properties that were explored in a TGA. Further, the fluidization behavior and the mechanical resistance were investigated in a batch fluidized bed reactor. In the TGA it was observed that the most reactive oxygen carriers for the CLOU process were materials without Si in the structure, more specifically M24Mg76 and M48Mg51 which had a molar ratio of Mn/Mg of 0.17 and 0.51 respectively. It was also observed that for the oxygen carriers with Si in the composition, the regeneration was very poor. Oxygen carriers M24Mg76 and M48Mg51 were selected for batch fluidized bed reactor testing showing good behavior with respect to the CLOU reactivity, and mechanical stability. One of the materials, the M24Mg76 showed activation during the experiments in the batch fluidized bed reactor experiments, increasing the oxygen transport capacity by 20 % during the experiment. However, 10 vol% of O2 was needed to regenerate both oxygen carriers at 850 °C. No agglomeration tendencies were seen, and the attrition rate was low, obtaining high-extrapolated lifetime values. The fact that highly reactive oxygen carriers can be made with cheap and highly available metals oxides, i.e. Mn and Mg, makes this system very promising and a possible alternative to benchmark Cu-based CLOU materials.
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| 3. |
- Adanez-Rubio, Inaki, et al.
(författare)
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Use of a high-entropy oxide as an oxygen carrier for chemical looping
- 2024
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Ingår i: Energy. - 0360-5442. ; 298
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Tidskriftsartikel (refereegranskat)abstract
- One mixed oxide with 5 cations in equimolar proportions in the sublattice, to fulfil high-entropy oxide (HEO) criteria, has been developed and investigated as oxygen carrier for chemical looping combustion processes. As far as we know, nobody has explored this class of material for chemical looping combustion. Material is prepared by direct mixing of five metal oxides (CuO, Mn2O3, Fe2O3, TiO2, MgO), followed by calcination at 1000, 1100 and 1200 °C for 6 h in air. XRD characterization provides strong evidence that the synthesized oxygen carriers possess the hallmark properties of HEO, and SEM-EDX analysis shows an overall homogeneous metal distribution. Materials have one main cubic phase with the empirical formula MnCuMgFeTiO7, dominating under all conditions. One of the key objectives of this study is achieved, reduce chemical stress during redox cycles. Oxygen transfer capability is investigated by thermogravimetric analysis and batch fluidized bed reactor experiments for different fuels and atmospheres. Mass-based oxygen transport capacities for lattice oxygen and oxygen uncoupling are around 5.5 wt% and 1.1 wt%, respectively. This work opens up a new dimension for the future preparation of oxygen carriers for chemical looping processes, since the vast compositional space of HEO provides opportunities to tune both chemical and physical characteristics.
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| 4. |
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| 5. |
- Abad, Alberto, 1972, et al.
(författare)
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Fuel reactor model validation: Assessment of the key parameters affecting the chemical-looping combustion of coal
- 2013
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 19, s. 541-551
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Tidskriftsartikel (refereegranskat)abstract
- The success of a Chemical Looping Combustion (CLC) system for coal combustion is greatly affected by the performance of the fuel reactor. When coal is gasified in situ in the fuel reactor, several parameters affect the coal conversion, and hence the capture and combustion efficiencies. In this paper, a mathematical model for the fuel reactor is validated against experimental results obtained in a 100 kW(th) CLC unit when reactor temperature, solids circulation flow rate or solids inventory are varied. This is the first time that a mathematical model for Chemical Looping Combustion of coal with in situ gasification (iG-CLC) has been validated against experimental results obtained in a continuously operated unit. The validated model can be used to evaluate the relevance of operating conditions on process efficiency. Model simulations showed that the reactor temperature, the solids circulation flow rate and the solids inventory were the most relevant operating conditions affecting the oxygen demand. However, high values of the solids circulation flow rate must be prevented because they cause a decrease in the CO2 capture. The high values of CO2 capture efficiency obtained were due to the highly efficient carbon stripper. The validated model is a helpful tool in designing the fuel reactor to optimize the CLC process. A CO2 capture efficiency of eta(CC) = 98.5% and a total oxygen demand of Omega(T) = 9.6% is predicted, operating at 1000 C and 1500 kg/MWth in the fuel reactor.
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| 6. |
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| 7. |
- Cuadrat, Ana, 1982, et al.
(författare)
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Influence of limestone addition in a 10 kWth Chemical-Looping Combustion unit operated with petcoke
- 2011
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 25:10, s. 4818-4828
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Tidskriftsartikel (refereegranskat)abstract
- Ilmenite, a natural mineral composed of FeTiO3, is a low cost material suitable as oxygen-carrier for Chemical-Looping Combustion (CLC) with solid fuels. One option when using the CLC technology with solid fuels is to introduce the fuel directly into the fuel-reactor. There the fuel is gasified and volatiles and gasification products react with the oxygen-carrier. In this study the influence of limestone addition to ilmenite as oxygen-carrier was tested in a continuous 10 kWth CLC pilot for solid fuels. The fuel fed was a petcoke and the gasifying agent was steam. Tests with an ilmenite-limestone mixture as bed material were performed, and also tests using only ilmenite as bed material were carried out for comparison. Global solids circulation was varied as it is an important operational parameter, which determines the solid fuel residence time. The experiments were made at two fuel-reactor temperatures: 950ºC and 1000ºC. Generally, higher residence time of the fuel and higher temperature increased both gasification and combustion efficiencies. This was seen for both with and without limestone addition. The addition of limestone, gave a significant improvement of gas conversion at 950ºC, which could be explained by lime catalyzing the water-gas shift reaction. Moreover, the presence of limestone significantly increased the char conversion both at 950ºC and 1000ºC.
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| 8. |
- 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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| 9. |
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| 10. |
- Linderholm, Carl Johan, 1976, et al.
(författare)
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Chemical-Looping Coal Combustion – Results from the ACCLAIM project
- 2014
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Ingår i: 3rd International Conference on Chemical Looping.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This work concerns the first 22 months of the 30-month ACCLAIM project. The project has involved both experimental activities in CLC pilots of 1.5 kW, 10 kW and 100 kW, as well as laboratory investigations and studies in a cold-flow model. Furthermore, investigations have been made using modelling with different approaches and with different aims.The main result of the pilot operation is that several low-cost materials should be able to improve gas conversion significantly as compared to previously tested ilmenite. Promising low cost materials include iron and manganese ores. Two manganese ores were evaluated by operation in a 10 kW CLC reactor system. These materials are called Sinfin, and Mangagran. Both materials performed well with respect to gas conversion, and oxygen demand was clearly lower as compared to ilmenite. The production rate of fines suggested an expected lifetime of around 300 h for one of the manganese materials, Sinfin, which is a distinct improvement as compared to the Buriturama ore previously tested in the 10 kW unit.Further, the fate of fuel contaminants like sulphur and nitrogen has been investigated. Models to describe fluidization and to predict conversion have been developed and are validated against operational data. Mathematical modelling and cold-flow modelling show possible ways of increasing process performance by modification of process or reactor design.A 100 kW CLC unit was operated with a mixture of ilmenite and a Brazilian manganese ore called Buritirama, which had been tested in a previous project and had been found to be much more reactive than ilmenite, although concerns had been raised regarding the attrition resistance. The mixture of ilmenite and Buritirama gave significant improvements in gas conversion in comparison to ilmenite.
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