| 1. |
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| 2. |
- Abad, Alberto, 1972, et al.
(författare)
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The use of iron oxide as oxygen carrier in a chemical-looping reactor
- 2007
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 86:7-8, s. 1021-1035
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Tidskriftsartikel (refereegranskat)abstract
- Chemical-looping combustion (CLC) is a method for the combustion of fuel gas with inherent separation of carbon dioxide. This technique involves the use of two interconnected reactors, an air reactor and a fuel reactor. The oxygen demanded in the fuel combustion is supplied by a solid oxygen carrier, which circulates between both reactors. Fuel gas and air are never mixed and pure CO2 can be obtained from the flue gas exit. This paper presents the results from the use of an iron-based oxygen-carrier in a continuously operating laboratory CLC unit, consisting of two interconnected fluidized beds. Natural gas or syngas was used as fuel, and the thermal power was between 100 and 300 W. Tests were performed at four temperatures: 1073, 1123, 1173 and 1223 K. The prototype was successfully operated for all tests and stable conditions were maintained during the combustion. The same particles were used during 60 h of hot fluidization conditions, whereof 40 h with combustion. The combustion efficiency of syngas was high, about 99% for all experimental conditions. However, in the combustion tests with natural gas, there was unconverted methane in the exit flue gases. Higher temperature and lower fuel flows increase the combustion efficiency, which ranged between 70% and 94% at 1123 K. No signs of agglomeration or mass loss were detected, and the crushing strength of the oxygen carrier particles did not change significantly. Complementary experiments in a batch fluidized bed were made to compare the reactivity of the oxygen carrier particles before and after the 40 h of operation, but the reactivity of the particles was not affected significantly.
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| 3. |
- Abanades, J. C., et al.
(författare)
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Emerging CO2 capture systems
- 2015
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 40, s. 126-166
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Tidskriftsartikel (refereegranskat)abstract
- In 2005, the IPCC SRCCS recognized the large potential for developing and scaling up a wide range of emerging CO2 capture technologies that promised to deliver lower energy penalties and cost. These included new energy conversion technologies such as chemical looping and novel capture systems based on the use of solid sorbents or membrane-based separation systems. In the last 10 years, a substantial body of scientific and technical literature on these topics has been produced from a large number of R&D projects worldwide, trying to demonstrate these concepts at increasing pilot scales, test and model the performance of key components at bench scale, investigate and develop improved functional materials, optimize the full process schemes with a view to a wide range of industrial applications, and to carry out more rigorous cost studies etc. This paper presents a general and critical review of the state of the art of these emerging CO2 capture technologies paying special attention to specific process routes that have undergone a substantial increase in technical readiness level toward the large scales required by any CO2 capture system.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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 .- 1873-6785. ; 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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| 7. |
- Andersson, Viktor, 1983, et al.
(författare)
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Alkali desorption from ilmenite oxygen carrier particles used in biomass combustion
- 2024
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Ingår i: Fuel. - 0016-2361 .- 1873-7153. ; 359
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen-carrying fluidized bed materials are increasingly used in novel technologies for carbon capture and storage, and to improve the efficiency of fuel conversion processes. Potassium- and sodium-containing compounds are released during biomass combustion and may have both negative and positive effects on conversion processes. Ilmenite is an important oxygen carrier material with the ability to capture alkali in the form of titanates. This is a desirable property since it may reduce detrimental alkali effects including fouling, corrosion, and fluidized bed agglomeration. This study investigates the interactions of alkali-containing compounds with ilmenite particles previously used in an industrial scale (115 MWth) oxygen carrier aided combustion system. The ilmenite samples were exposed to temperatures up to 1000 °C under inert and oxidizing conditions while the alkali release kinetics were characterized using online alkali monitoring. Alkali desorption occurs between 630 and 800 °C, which is attributed to loosely bound alkali at or near the surface of the particles. Extensive alkali release is observed above 900 °C and proceeds during extended time periods at 1000 °C. The release above 900 °C is more pronounced under oxidizing conditions and approximately 9.1 and 3.2 wt% of the alkali content is emitted from the ilmenite samples in high and low oxygen activity, respectively. Detailed material analyses using scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were conducted before and after temperature treatment, which revealed that the concentrations of potassium, sodium and chlorine decrease at the outermost surface of the ilmenite particles during temperature treatment, and Cl is depleted to a deeper level in oxidizing conditions compared to inert. The implications for ilmenite-ash interactions, oxygen carrier aided combustion and chemical looping systems are discussed.
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| 8. |
- Andersson, Viktor, 1983, et al.
(författare)
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Alkali interactions with a calcium manganite oxygen carrier used in chemical looping combustion
- 2022
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 227
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Tidskriftsartikel (refereegranskat)abstract
- Chemical-Looping Combustion (CLC) of biofuels is a promising technology for cost-efficient CO2 separation and can lead to negative CO2 emissions when combined with carbon capture and storage. A potential challenge in developing CLC technology is the effects of alkali metal-containing compounds released during fuel conversion. This study investigates the interactions between alkali and an oxygen carrier (OC), CaMn0.775Ti0.125Mg0.1O3-δ, to better understand the fate of alkali in CLC. A laboratory-scale fluidized bed reactor is operated at 800–900 °C in oxidizing, reducing and inert atmospheres to mimic CLC conditions. Alkali is fed to the reactor as aerosol KCl particles, and alkali in the exhaust is measured online with a surface ionization detector. The alkali concentration changes with gas environment, temperature, and alkali loading, and the concentration profile has excellent reproducibility over repeated redox cycles. Alkali-OC interactions are dominated by alkali uptake under most conditions, except for a release during OC reduction. Uptake is significant during stable reducing conditions, and is limited under oxidizing conditions. The total uptake during a redox cycle is favored by a high alkali loading, while the influence of temperature is weak. The implications for the understanding of alkali behavior in CLC and further development are discussed.
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| 9. |
- Andersson, Viktor, 1983, et al.
(författare)
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Alkali-wall interactions in a laboratory-scale reactor for chemical looping combustion studies
- 2021
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 217
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Tidskriftsartikel (refereegranskat)abstract
- Alkali metal-containing compounds are readily released during thermal conversion of solid fuels, and may have both detrimental and beneficial effects on chemical looping combustion. Here, we characterize alkali interactions with the inner walls of a laboratory-scale reactor under oxidizing, reducing and inert conditions at temperatures up to 900 °C. KCl aerosol particles are continuously introduced to the stainless steel reactor and the alkali concentration is measured on-line with a surface ionization detector. Aerosol particles evaporate at temperatures above 500 °C and KCl molecules rapidly diffuse to the reactor wall. Up to 92% of the alkali reaching the wall below 700 °C remains adsorbed, while re-evaporation is important at higher temperatures, where up to 74% remains adsorbed. Transient changes in alkali concentration are observed during repeated redox cycles, which are associated with changes in chemical composition of the wall material. Metal oxides on the reactor wall are partially depleted under reducing conditions, which allow for the formation of a new potassium-rich phase that is stable in a reducing atmosphere, but not under inert conditions. The observed wall effects are concluded to be extensive and include major transient effects depending on gas composition, and the implications for laboratory studies and improved experimental methodology are discussed.
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| 10. |
- Andersson, Viktor, 1983, et al.
(författare)
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Design and first application of a novel laboratory reactor for alkali studies in chemical looping applications
- 2023
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Ingår i: Fuel Processing Technology. - 0378-3820. ; 252
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Tidskriftsartikel (refereegranskat)abstract
- Alkali compounds are readily released during biomass conversion and their complex interactions with reactor walls and sampling equipment makes detailed investigations challenging. This study evaluates a novel laboratory-scale fluidized bed reactor for chemical looping combustion (CLC) studies. The reactor design is based on detailed consideration of the behavior of alkali-containing molecules and aerosol particles and is guided by computational fluid dynamic simulations. The design allows for interactions between gaseous alkali and a fluidized bed, while minimizing alkali interactions with walls before and after the fluidized bed. The function of the laboratory reactor is demonstrated in experiments using online gas and alkali analysis. Alkali is continuously fed to the reactor as KOH or KCl aerosol with and without a fluidized bed of the oxygen carrier CaMn0.775Ti0.125Mg0.1O3-δ present in inert, reducing and oxidizing conditions at temperatures up to 900 °C. Alkali uptake by the OC is characterized in all conditions, and observed to sensitively depend on gas composition, reactor temperature and type of alkali compound. The experimental setup is concluded to have a significantly improved functionality compared to a previously used reactor, which opens up for detailed studies of interactions between alkali compounds and oxygen carriers used in CLC.
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