| 11. |
- 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. - : American Chemical Society (ACS). - 1520-5029 .- 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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| 12. |
- Arjmand, Mehdi, 1986, et al.
(författare)
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Screening of Combined Mn-Fe-Si Oxygen Carriers for Chemical Looping with Oxygen Uncoupling (CLOU)
- 2015
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 29:3, s. 1868-1880
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Tidskriftsartikel (refereegranskat)abstract
- Combined oxygen carriers of Mn, Fe, and Si were screened for the chemical looping with oxygen uncoupling process with the objective of identifying materials with high reactivity and sufficient attrition resistance. Eleven oxygen carrier materials were produced by spray-drying and then calcined for 4 h at 1100 and 1200 degrees C. The ability of the oxygen carriers to release oxygen and to convert gaseous fuels was investigated in a batch fluidized-bed reactor under alternating reducing and oxidizing conditions for temperatures ranging from 850 degrees C to 1050 degrees C. The attrition behavior of the different materials was evaluated in a jet-cup attrition rig. All investigated oxygen carriers proved to release oxygen and showed high reactivity toward synthesis gas (50% CO in H-2). Oxygen carrier materials with comparably lower mechanical stability were found to have a higher reactivity toward methane. One of the investigated formulations showed to have both high mechanical stability and resistance toward attrition, as well as good methane conversion and oxygen release.
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| 13. |
- Arjmand, Mehdi, 1986, et al.
(författare)
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Sulfur Tolerance and Rate of Oxygen Release of Combined Mn-Si Oxygen Carriers in Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2014
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 53:50, s. 19488-19497
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Tidskriftsartikel (refereegranskat)abstract
- Sulfur tolerance and rate of oxygen release of combined Mn-Si oxygen carriers for chemical-looping with oxygen uncoupling (CLOU) is investigated. The oxygen carriers were produced by spray-drying and calcined at 1150 degrees C. The resistance toward sulfur and the rates of oxygen release were evaluated in a laboratory-scale fluidized-bed reactor. It was found that the combined Mn-Si oxygen carrier is tolerant to SO2, at least up to a partial pressure of 5000 vppm. The rates of oxygen release were determined in the temperature range of 975 to 1100 degrees C using devolatilized wood char as fuel while fluidizing with N-2, to maintain a low oxygen partial pressure surrounding the particles. The Arrhenius parameters k(o) and E-app for the release of oxygen were estimated for the investigated materials assuming a zero-order reaction with respect to oxygen. The rates of oxygen release were relatively high, particularly at above 1050 degrees C. From the obtained reaction rates, the solids inventory required for combustion of coal was determined to be as low as 40 kg/MWth in the fuel reactor at 1100 degrees C. The results indicated that combined Mn-Si oxygen carriers could be interesting materials for the CLOU process by virtue of their resistance to sulfur deactivation and high rate of oxygen release.
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| 14. |
- Arjmand, Mehdi, 1986, et al.
(författare)
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Sulfur Tolerance of CaxMn1–yMyO3−δ (M = Mg, Ti) Perovskite-Type Oxygen Carriers in Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2014
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 28:2, s. 1312-1324
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Tidskriftsartikel (refereegranskat)abstract
- Perovskite-structured oxygen carriers of the type CaxMn1–yMyO3−δ (M = Mg, Ti) have been investigated for the CLOU process. The oxygen carrier particles were produced by spray-drying and were calcined at 1300 °C for 4 h. A batch fluidized-bed reactor was used to investigate the chemical-looping characteristics of the materials. The effect of calcium content, dopants (Mg and Ti), and operating temperature (900, 950, 1000, and 1050 °C) on the oxygen uncoupling property and the reactivity with CH4 in the presence and absence of SO2 was evaluated. In addition, the attrition resistance and mechanical integrity of the oxygen carriers were examined in a jet-cup attrition rig. All of the investigated perovskite-type materials were able to release gas phase oxygen in inert atmosphere. Their reactivity with methane was high and increased with temperature and calcium content, approaching complete gas yield at 1000 °C. The reactivity decreased in the presence of SO2 for all of the investigated oxygen carriers. Decreasing the calcium content resulted in a less severe decrease in reactivity in the presence of SO2, with the exception of materials doped with both Mg and Ti, for which a higher resistance to sulfur deactivation could be maintained even at higher calcium contents. The drop in reactivity in the presence of SO2 also decreased at higher temperatures, and at 1050 °C, the decrease in the reactivity of the Mg- and Ti-doped material was minimal. Sulfur balance over the reactor system indicated that the fraction of the introduced SO2 that passed through the reactor increased with temperature. It was shown that it is possible to regenerate the oxygen carriers during reduction in the absence of SO2. Most of the materials also showed relatively low attrition rates. The results indicate that it is possible to modify the operating conditions and properties of perovskite-type oxygen carriers to decrease or avoid their deactivation by sulfur.
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| 15. |
- 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. - : Elsevier BV. - 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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| 16. |
- Arjmand, Mehdi, 1986, et al.
(författare)
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ZrO2-Supported CuO Oxygen Carriers for Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2013
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Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 37, s. 550-559
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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 zirconia (ZrO2) and stabilized by calcia (CaO), magnesia (MgO) and ceria (CeO2) are investigated. The oxygen carriers were produced by freeze-granulation and calcined at 950 and 1050 °C. Their chemical-looping performance was evaluated in a laboratory-scale fluidized-bed reactor at 900 and 925 °C under cyclic oxidizing, inert (N2) and reducing (CH4) conditions. Five out of six oxygen carriers exhibited rapid release of oxygen in the inert environment (CLOU). Also, complete conversion of methane was obtained for three out of the six oxygen carriers. However, only in the case of MgO-stabilized ZrO2 as support and calcined at 950 °C, the oxygen carrier exhibited intact active CuO phase; agglomeration and particle fragmentation were also not observed. Thus, the use of this material could be suggested as a suitable oxygen carrier for the CLOU process.
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| 17. |
- Aronsson, Jesper, 1985, et al.
(författare)
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Effects of the Choice of Gas on the Hydrodynamics of Fluidized Beds
- 2019
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 58:20, s. 8847-8855
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Tidskriftsartikel (refereegranskat)abstract
- Using a cold-flow model, this work examines how the hydrodynamics in the dense region of a fluidized bed are affected when the gas acting as the fluidizing agent is changed. While the focus here is on the use of a gas other than that suggested by scaling laws in cold-flow models, the study also has relevance for fluidized bed processes in which different fluidization agents can be used, such as drying or coating. For cold-flow models, the scaling criteria for the hydrodynamics of the fluidized bed prescribe certain properties of the gas to be used as the fluidizing agent. In certain scenarios, air does not match the suggested properties, and other gases must be used, which increases the complexity and cost. In the worst-case scenario, no gas will fulfill the prescribed properties, and experimentation under strictly scaled conditions will be impossible. Assessing the impact of not using the correct gas allows researchers to evaluate the reliability of their findings when there is no compliance with the scaling laws. In this work, experiments were carried out in a hydrodynamically down-scaled model of a 100 kW chemical looping combustion (CLC) unit, which under hot conditions contains metal oxide particles fluidized with steam. If the hydrodynamic properties are to be resembled at ambient temperature with the same solids, a gas lighter than air, e.g., helium, must be used according to the scaling laws. This entails an experimental setup with gas recycling, adding cost and complexity to the system in comparison to using air. This work investigates how fluidization with air, instead of helium, affects the hydrodynamics of the cold-flow model based on two different approaches: (i) maintained superficial gas velocity and (ii) maintained decay constant in the splash zone. The results show that air does not adequately substitute for helium in a bubbling bed with respect to the following key hydrodynamic properties: pressure fluctuations were 30% lower; the bubble fraction was up to 36% smaller; bubble frequency was up to 17% lower; and the solids concentration was up to 10% higher. It was also found that the use of air yields a poorer horizontal distribution of the gas injected from the reactor side-walls, which affected the cross-sectional distributions of the solids concentration, bubble fraction, and bubble frequency.
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| 18. |
- Aronsson, Jesper, 1985, et al.
(författare)
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Examination of chemical-looping combustion of gaseous fuels by 1-dimensional modeling and experiments
- 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. 673-678
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Konferensbidrag (refereegranskat)abstract
- This work presents a 1-dimensional model for the fuel reactor in chemical looping combustion (CLC) with gaseous fuels. Modeled fuel conversion is in good agreement with experimental data from a 300W CLC unit using syngas as fuel and ilmenite as oxygen carrier. The sub-model for the solids fluid dynamics is based on semi-empirical expressions derived and typically used in regular fluidized bed air combustion. These expressions have here been experimentally validated for conditions relevant to chemical looping combustion with data from a 100 kW CLC unit and a cold flow model of the same unit. Fuel conversion is modeled accounting for both heterogeneous and homogeneous kinetics and assuming a classical twophase flow approach for which the influence of the correlation chosen for the gas interchange coefficient is found to have a slight influence the results.
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| 19. |
- Aronsson, Jesper, 1985, et al.
(författare)
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Improved Gas-Solids Mass Transfer in Fluidized Beds: Confined Fluidization in Chemical-Looping Combustion
- 2019
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 33:5, s. 4442-4453
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 American Chemical Society. Fluidized bed processes with reactive bed material have become increasingly popular as research topics, with applications such as chemical-looping technologies, oxygen carrier aided combustion, and fluidized bed gasification being extensively investigated. When used at commercial scale the performance of such processes may be limited not by gas-solid reactivity, but by mass transfer of reactants from bubbles to the emulsion phase. In an effort to break down the two-phase flow structure, and thereby increase the bubble-emulsion mass transfer coefficient, spherical packing material was added to a fluidized bed using ilmenite as bed material. Two types of packing were tested: expanded clay aggregate (ECA) and aluminum silicate balls (ASB). Both packings had a diameter of about 12 mm but drastically different bulk densities of 240 kg/m 3 and 1400 kg/m 3 , respectively. These were tested in chemical-looping-combustion batch experiments using a stainless-steel reactor with a diameter of 78 mm, with syngas or carbon monoxide as fuel at 915 °C. The lighter packing formed a floating plug while the heavier remained stationary at the reactor bottom. To compare the confined fluidized bed to a reference conventional one, a simple reaction model was implemented based on the experiments. It showed that in the confined fluidized bed the associated effective reaction rate constant increased by up to a factor of 2 for a given bed mass. Further, up to 4 times less oxygen carrier bed mass was needed to achieve the same gas conversion, at a lower total pressure drop. Experiments with only carbon monoxide showed similar gains when using aluminum silicate balls, indicating that catalysis of the water gas shift reaction was not the main factor for improved gas conversion. It can be concluded that the concept of confined fluidization has great potential to increase mass transfer in fluidized beds with active bed material.
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| 20. |
- Aronsson, Jesper, et al.
(författare)
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Increasing gas-solids mass transfer in fluidized beds by application of confined fluidization-A feasibility study
- 2019
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 9:4
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Tidskriftsartikel (refereegranskat)abstract
- Fluidized bed applications where the bed material plays an active role in chemical reactions, e.g. chemical looping combustion, have seen an increase in interest over the past decade. When these processes are to be scaled up to industrial or utility scale mass transfer between the gas and solids phases can become a limitation for conversion. Confined fluidized beds were conceptualized for other purposes in the 1960's but are yet to be applied to these recent technologies. Here it is investigated if they can prove useful to increase mass transfer but also if they are feasible from other perspectives such as pressure drop increase and solids throughflow. Four spherical packing solids, 6.35-25.4 mm in diameter at two different densities, were tested. For mass transfer experiments the fluidizing air was humidified and the water adsorption rate onto silica gel particles acting as fluidizing solids was measured. Olivine sand was used in further experiments measuring segregation of solids and packing, and maximum vertical crossflow of solids. It was found that mass transfer increased by a factor of 1.9-3.8 with packing solids as compared to a non-packed reference. With high-density packing, fluidizing solids voidage inside the packing was found to be up to 58% higher than in a conventional fluidized bed. Low density packing material favoured its flotsam segregation and with it higher fluidization velocities yield better mixing between packing and fluidizing solids. Maximum vertical cross-flow was found to be significantly higher with low density packing that fluidized, than with stationary high-density packing. Conclusively, the prospect of using confined fluidized beds for improving mass transfer looks promising from both performance and practical standpoints.
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