| 1. |
- Purnomo, Victor, 1992, et al.
(författare)
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Effect of oxidation degree of iron-based oxygen carriers on their mechanical strength
- 2024
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Ingår i: Powder Technology. - 1873-328X .- 0032-5910. ; 438
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Tidskriftsartikel (refereegranskat)abstract
- Iron-based oxygen carriers are currently one of the most popular choices for chemical looping processes. In order to minimize losses of oxygen carrier materials in the system, it is important to assess attrition characteristics. Furthermore, in chemical looping gasification where the oxygen transfer capacity needs to be limited, a higher reduction degree of oxygen carriers can be expected. As different oxidation degrees lead to different phase compositions, this study aimed to investigate the correlation between mechanical strength of iron-based oxygen carriers and the phase composition, which is the result of oxidation degree change. Our findings demonstrate that how the phase composition may affect the attrition rate of oxygen carriers depends largely on the type of the material itself. In this study, the presence of Fe-Ti and Fe-Si combinations contribute to a generally stable attrition rate, while Fe-Ca system exhibits a decreasing attrition rate. Furthermore, attrition rate shows a more conclusive trend compared to crushing strength. Among the investigated materials, both ilmenite ore and iron sand showed a robust, stable mechanical stability with an attrition rate of approximately 0.5–1 wt%/h, which is on par with that of sand (0.5 wt%/h). The attrition rates of LD slag and mill scale are lower, about 1–3 wt%/h.
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| 2. |
- Purnomo, Victor, 1992, et al.
(författare)
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Effect of the Conversion Degree on the Apparent Kinetics of Iron-Based Oxygen Carriers
- 2024
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Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- The role of the oxygen carrier is important in energy conversion processes with fluidized beds, particularly chemical looping technology. It is necessary to establish the relevant kinetics of oxygen carriers that can be applicable for various chemical looping processes. In this study, we analyzed the apparent kinetics of three iron-based oxygen carriers, namely, ilmenite, iron sand, and LD slag, during the conversion of CO, H2, and CH4 in a fluidized bed batch reactor. The effect of both the oxidation degree, presented as the mass conversion degree, and temperature was considered. The results show that the changing grain size (CGS) model is generally applicable in predicting the apparent kinetics of reactions between the investigated iron oxygen carriers and gaseous fuels even at lower oxidation degrees (3-5 wt % reduction). The activation energies of the investigated materials in the conversions of CO, H2, and CH4 obtained from the fittings of the CGS model are about 51-92, 55-251, and 72-211 kJ/mol, respectively. Both the mass conversion degree and temperature influence the reactivity of oxygen carriers in a directly proportional way, especially at temperatures higher than 925 °C. The results of this study are useful for reaction engineering purposes, such as designing a reactor, in chemical looping units, or in any other processes that use oxygen carriers as a bed material.
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| 3. |
- Purnomo, Victor, 1992, et al.
(författare)
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Effect of the Mass Conversion Degree of an Oxygen Carrier on Char Conversion and Its Implication for Chemical Looping Gasification
- 2022
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Ingår i: Energy & Fuels. - : American Chemical Society. - 0887-0624 .- 1520-5029. ; 36:17, s. 9768-9779
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Tidskriftsartikel (refereegranskat)abstract
- Chemical looping gasification (CLG) is an emerging process that aims to produce valuable chemical feedstocks. The key operational requirement of CLG is to limit the oxygen transfer from the air reactor (AR) to the fuel reactor (FR). This can be accomplished by partially oxidizing the oxygen carrier in the AR, which may lead to a higher reduction degree of the oxygen carrier under the fuel conversion. A highly reduced oxygen carrier may experience multiple issues, such as agglomeration and defluidization. Given such an interest, this study examined how the variation of the mass conversion degree of ilmenite may affect the conversion of pine forest residue char in a fluidized bed batch reactor. Ilmenite was pre-reduced using diluted CO and then underwent the char conversion at 850, 900, 950, and 975 °C. Our investigations showed that the activation energy of the char conversion was between 194 and 256 kJ/mol, depending upon the mass conversion degree of ilmenite. Furthermore, the hydrogen partial pressure in the particle bed increased as the oxygen carrier mass conversion degree decreased, which was accompanied by a lower reaction rate and a higher reduction potential. Such a hydrogen inhibition effect was confirmed in the experiments; therefore, the change in the mass conversion degree indirectly affected the char conversion. Langmuir-Hinshelwood mechanism models used to evaluate the char conversion were validated. On the basis of the physical observation and characterizations, the use of ilmenite in CLG with biomass char as fuel will likely not suffer from major agglomeration or fluidization issues.
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| 4. |
- Purnomo, Victor, 1992, et al.
(författare)
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Performance of iron sand as an oxygen carrier at high reduction degrees and its potential use for chemical looping gasification
- 2023
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 339
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Tidskriftsartikel (refereegranskat)abstract
- Iron sand as an industrial by-product has a reasonable iron content (35 wt% Fe) and low economical cost. The reactivity of iron sand as an oxygen carrier was examined in a bubbling fluidized bed reactor using both gaseous and solid fuels at 850–975 °C. Pre-reductions of iron sand were performed prior to fuel conversion to adapt the less-oxygen-requiring environment in chemical looping gasification (CLG). Based on the investigations using CO and CH4, iron sand has an oxygen transfer capacity of around 1 wt%, which is lower than that of ilmenite. The conversion of pine forest residue char to CO and H2 was higher when using iron sand compared to ilmenite. Depending on the mass conversion degree of iron sand, the activation energy of pine forest residue char conversion using iron sand was between 187 and 234 kJ/mol, which is slightly lower than that of ilmenite. Neither agglomeration nor defluidization of an iron sand bed occurred even at high reduction degrees. These suggests that iron sand can be utilized as an oxygen carrier in CLG. Furthermore, this study presents novel findings in the crystalline phase transformation of iron sand at various degrees of oxidation, altogether with relevant thermodynamic stable phases.
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| 5. |
- Purnomo, Victor, 1992, et al.
(författare)
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Study of defluidization of iron- and manganese-based oxygen carriers under highly reducing conditions in a lab-scale fluidized-bed batch reactor
- 2021
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 219
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen carriers play an important role in chemical looping processes to transport oxygen for fuel conversion. In this study, the defluidization phenomena of oxygen carriers were examined under highly reducing conditions in a fluidized-bed batch reactor. This is highly relevant to chemical-looping gasification, where oxygen carriers could be reduced to a significant extent compared to that in chemical-looping combustion. Only a few studies have reported the physical phenomena in a fluidized bed system under highly reducing conditions. Three iron- and two manganese-based oxygen carriers were investigated at 900 ◦C at several degrees of reduction in this study. Some oxygen carriers that have been exposed to several hours of operation in a 300 W chemical-looping reactor unit were also included in this study to provide a comparison to the fresh-calcined materials. Defluidization of particle beds occurred with the iron-based oxygen carriers, except for LD slag, which has a low content of iron. The defluidization was caused by the formation of elemental iron on the oxygen carriers' surface at high degree of reduction. All defluidizations occurred at a mass-based conversion (Δω) between 3.2–5.0%. The manganese based materials were found to be less prone to defluidization.
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| 6. |
- Rahpeymai Bogestål, Yalda, 1977, et al.
(författare)
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Signaling through C5aR is not involved in basal neurogenesis.
- 2007
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Ingår i: Journal of neuroscience research. - : Wiley. - 0360-4012 .- 1097-4547. ; 85:13, s. 2892-7
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Tidskriftsartikel (refereegranskat)abstract
- The complement system, an important part of the innate immune system, provides protection against invading pathogens, in part through its proinflammatory activities. Although most complement proteins are synthesized locally in the brain and the relevant complement receptors are expressed on resident brain cells, little is known about brain-specific role(s) of the complement system. C3a and C5a, complement-derived peptides with anaphylatoxic properties, have been implicated in noninflammatory functions, such as tissue regeneration and neuroprotection. Recently, we have shown that signaling through C3a receptor (C3aR) is involved in the regulation of neurogenesis. In the present study, we assessed basal neurogenesis in mice lacking C5a receptor (C5aR(-/-)) and mice expressing C3a and C5a, respectively in the CNS under the control of glial fibrillary acidic protein (GFAP) promoter (C3a/GFAP and C5a/GFAP, respectively) and thus without the requirement for complement activation. We did not observe any difference among C5aR(-/-), C3a/GFAP and C5a/GFAP mice and their respective controls in the number of newly formed neuroblasts and newly formed neurons in the subventricular zone (SVZ) of lateral ventricles and hippocampal dentate gyrus, the two neurogenic niches in the adult brain, or the olfactory bulb, the final destination of new neurons formed in the SVZ. Our results indicate that signaling through C5aR is not involved in basal neurogenesis in adult mice and that basal neurogenesis in adult C3a/GFAP and C5a/GFAP mice is not altered. (c) 2007 Wiley-Liss, Inc.
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| 7. |
- Samprón, Iván, et al.
(författare)
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Catalytic Activity of Oxygen Carriers on the Removal of Tar Byproducts for Biomass Chemical Looping Gasification Application
- 2023
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Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 37:21, s. 16629-16638
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Tidskriftsartikel (refereegranskat)abstract
- One of the main advantages of chemical looping gasification (CLG) in comparison to conventional gasification technologies is its potential to enhance in situ tar removal. This is due to the catalytic properties of the oxygen carrier used in the CLG process, which can facilitate tar oxidation, cracking, and reforming reactions under specific operating conditions. Furthermore, this catalytic effect can be harnessed to convert hydrocarbons (C1-C3), thereby increasing syngas production during the process. In this study, the catalytic activity of eight different oxygen carriers (two ores, two wastes, and four synthetic materials) was examined in a batch fluidized bed reactor. The reactions were mainly conducted at three temperatures (850, 900, and 950 °C), utilizing benzene and ethylene as model compounds. The results revealed that the ores and wastes exhibited a low catalytic effect over benzene and ethylene conversion at low temperatures, although this effect was increased with a rising temperature. Conversely, the synthetic materials demonstrated higher catalytic activity in the benzene and ethylene conversion reactions, which also increased with higher temperatures. It should be noted that the Cu/Al oxygen carrier achieved nearly complete conversion of benzene and ethylene at temperatures exceeding 900 °C. Methane production was observed in most of the experiments, indicating its role as an intermediate in the conversion of tar byproducts. Additionally, the Cu/Al oxygen carrier exhibited a promising catalytic performance in methane conversion. These findings highlight the potential of certain synthetic oxygen carriers, such as the Cu/Al oxygen carrier, to serve as effective catalysts for the removal of tar byproducts and light hydrocarbons during CLG processes.
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| 8. |
- Thacher, Jesse D., et al.
(författare)
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Exposure to long-term source-specific transportation noise and incident breast cancer : A pooled study of eight Nordic cohorts
- 2023
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Ingår i: Environment International. - : Elsevier. - 0160-4120 .- 1873-6750. ; 178
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Tidskriftsartikel (refereegranskat)abstract
- Background: Environmental noise is an important environmental exposure that can affect health. An association between transportation noise and breast cancer incidence has been suggested, although current evidence is limited. We investigated the pooled association between long-term exposure to transportation noise and breast cancer incidence.Methods: Pooled data from eight Nordic cohorts provided a study population of 111,492 women. Road, railway, and aircraft noise were modelled at residential addresses. Breast cancer incidence (all, estrogen receptor (ER) positive, and ER negative) was derived from cancer registries. Hazard ratios (HR) were estimated using Cox Proportional Hazards Models, adjusting main models for sociodemographic and lifestyle variables together with long-term exposure to air pollution.Results: A total of 93,859 women were included in the analyses, of whom 5,875 developed breast cancer. The median (5th–95th percentile) 5-year residential road traffic noise was 54.8 (40.0–67.8) dB Lden, and among those exposed, the median railway noise was 51.0 (41.2–65.8) dB Lden. We observed a pooled HR for breast cancer (95 % confidence interval (CI)) of 1.03 (0.99–1.06) per 10 dB increase in 5-year mean exposure to road traffic noise, and 1.03 (95 % CI: 0.96–1.11) for railway noise, after adjustment for lifestyle and sociodemographic covariates. HRs remained unchanged in analyses with further adjustment for PM2.5 and attenuated when adjusted for NO2 (HRs from 1.02 to 1.01), in analyses using the same sample. For aircraft noise, no association was observed. The associations did not vary by ER status for any noise source. In analyses using <60 dB as a cutoff, we found HRs of 1.08 (0.99–1.18) for road traffic and 1.19 (0.95–1.49) for railway noise.Conclusions: We found weak associations between road and railway noise and breast cancer risk. More high-quality prospective studies are needed, particularly among those exposed to railway and aircraft noise before conclusions regarding noise as a risk factor for breast cancer can be made.
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