| 1. |
- Azad, Abdul-Majeed, 1957, et al.
(författare)
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Examining the Cu-Mn-O Spinel System as an Oxygen Carrier in Chemical Looping Combustion
- 2013
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Ingår i: Energy Technology. - : Wiley. - 2194-4296 .- 2194-4288. ; 1:1, s. 59-69
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Tidskriftsartikel (refereegranskat)abstract
- Chemical-looping combustion (CLC) and chemical-looping combustion with oxygen uncoupling (CLOU) are attractive alternatives to conventional combustion that provide efficient and direct separation of CO2. Both processes use metaloxides as oxygen carriers to transfer oxygen between two reactor vessels: the air and fuel reactors. Although monometallic oxides (such as Mn3O4, Fe2O3, NiO, and CuO) have been successfully employed as oxygen carriers, double oxides of the general formula CuxMn3_xO4 in the CuO–Mn2O3 system are examined in this work. The carrier was produced by mixing, extruding, and calcining a 1:1 molar (30.8:69.2 mass ratio) mixture of CuO and Mn2O3 at 950 8C for 6 or 12 h in static air. XRD analysis revealed that spinels of the general formula CuxMn3_xO4 were formed with 0.1_x_2.5 in which x=3Cu/(Cu+Mn). The chemical-looping performance was evaluated in a laboratory-scale fluidized-bed reactor from 800–850 8C over several alternating redox cycles using CH4 as the fuel. The oxygen carrier exhibited reproducible and stable reactivity behavior for both reducing and oxidizing periods in this temperature range. This characteristic makes the system an ideal oxygen-carrier material for CLOU. Moreover, the spinels in the CuxMn3_xO4 series are endowed with favorable physicochemical attributes (such as fast redox processes, high crushing strength, and demonstrated CLOU behavior) and may be viable alternatives to CuO–Cu2O and Mn2O3–Mn3O4 as potential CLOU materials.
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| 2. |
- 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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| 3. |
- Li, Hailong, 1976-, et al.
(författare)
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Using the solid digestate from a wet anaerobic digestion process as an energy resource
- 2013
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Ingår i: Energy technology. - : Wiley. - 2194-4296 .- 2194-4288. ; 1:1, s. 94-101
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Tidskriftsartikel (refereegranskat)abstract
- The wet anaerobic digestion process is a widely used method to produce biogas from biomass. To avoid the risks involved with using the digestion waste as a fertilizer, this work investigates the possibilities to use the solid digestate as an energy resource to produce heat and electricity, which could save some energy currently consumed by the plant and, therefore, may increase the overall efficiency of a biogas plant. Simulations were conducted based on real data from the Växtkraft biogas plant in Västerås, Sweden as a case study. Results show that it is necessary to dry the solid digestate before combustion and include flue-gas condensation to recover enough heat for the drying process. When a steam turbine cycle is integrated, the generated electricity could cover 13–18 % of the total electricity consumption of the plant, depending on the degree of dryness. In addition, reducing the digestion period can increase the carbon content (ultimate analysis), the heating value, and the mass flow of the solid digestate. As a result, the production of electricity and heat is augmented in the steam turbine cycle. However, the production of biogas is reduced. Therefore, a comprehensive economic evaluation is suggested to optimize a biogas plant that uses the solid digestate from a wet anaerobic digestion process as an energy resource.
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| 4. |
- Mohammad Pour, Nasim, 1986, et al.
(författare)
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Investigation of manganese-iron oxide materials based on manganese ores as oxygen carrier in chemical-looping with oxygen uncoupling (CLOU)
- 2014
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Ingår i: Energy Technology. - : Wiley. - 2194-4296 .- 2194-4288. ; 2:5, s. 469-479
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen carrier materials were synthesized using five different types of manganese ores with addition of iron oxide (Fe2O3), and they were investigated for their reactivity and properties in chemical looping with oxygen uncoupling (CLOU). Two different Mn/Fe molar ratios (1:2 and 2:1) were examined. The samples were manufactured by using a lab-scale extrusion method followed by sintering at 950 degrees C for 4 h. To measure their reactivity, the materials were exposed to gaseous CH4 and syngas (50:50 CO/H-2) as well as solid fuel (petroleum coke), in a batch fluidized-bed reactor. With CH4, the materials based on ores from Brazil and Gabon with a Mn/Fe molar ratio 2:1 showed the best reactivity. For reduction using syngas, samples based on Eastern European and South African ores provided higher amounts of oxygen equivalent, up to 3-5% of their mass. To investigate the ability of the samples to release gas-phase oxygen, solid fuel experiments using 0.1 g of petroleum coke in a bed of 10 g oxygen carrier were performed at 950 degrees C with Brazilian, Gabon, and Eastern European ores. In these solid fuel tests samples with a Mn/Fe molar ratio of 1:2 showed higher uncoupling rates. Based on X-ray diffraction analysis, the primary phase detected in all fresh particles was the oxidized form of MnyFe1-yOx, that is, bixbyite [(Mn,Fe)(2)O-3]. All of the particles showed sufficiently high crushing strength (> 2N) and a reasonable attrition resistance (attrition index
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| 5. |
- Sundqvist, Sebastian, 1986, et al.
(författare)
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CaMn0.875Ti0.125O3-δ as oxygen carrier in Chemical-Looping with Oxygen Uncoupling (CLOU) - solid fuel testing and sulphur interaction
- 2013
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Ingår i: Energy Technology. - : Wiley. - 2194-4296 .- 2194-4288. ; 1:5-6, s. 338-344
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Tidskriftsartikel (refereegranskat)abstract
- Particles of the perovskite material CaMn0.875Ti0.125O3-δ have been examined as oxygen-carrier material for chemical-looping with oxygen uncoupling (CLOU). The aim of the work has been to determine the effect of the fuel to bed mass ratio when oxidizing solid fuels, and to determine the influence of SO2 on the reactivity with fuel. Two solid fuels have been used, a Mexican petroleum coke and a Colombian coal. The oxygen carrier material used in this study was CaMn0.875Ti0.125O3-δ and was developed and manufactured by the Norwegian research institute SINTEF. The experiments were conducted in a discontinuous quartz glass batch fluidized-bed reactor with an inner diameter of 10 mm. The particle bed rests on a porous plate and thermocouples 5 mm under and 10 above the plate was used for measuring the temperature. In the oxidation phase a flow of 1000 ml/min with 5% oxygen in nitrogen was used. During the solid fuel experiments the bed was fluidized with 600 ml/min nitrogen while 0.1 g of solid fuel added to the reactor from the top. Two solid fuels were used; petroleum coke and Colombian coal. In the experiments with gaseous fuels the bed was fluidized with 900 ml/min consisting of 450 ml/min CH4 and 450ml/min with 0.25-0.5% SO2 in nitrogen.It was found that the Colombian coal was oxidized considerably faster than the petroleum coke, which is unexpected since it could be expected that the kinetics for O2 release from the oxygen carrier should determine conversion rate rather than the reactivity of the fuels. The overall rate of conversion increased for experiments with larger bed mass though, which was expected. SO2 seems to have had a negative effect on the reactivity of the oxygen carrier, likely because of formation of CaSO4.
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