| 1. |
- Mei, Daofeng, 1986, et al.
(författare)
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Modelling of gas conversion with an analytical reactor model for biomass chemical looping combustion (bio-CLC) of solid fuels
- 2022
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 433
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Tidskriftsartikel (refereegranskat)abstract
- Manganese ores are promising oxygen carriers for chemical looping combustion (CLC), due to their high reactivity with combustible gases. In this work, a manganese ore called EB (Elwaleed B, originating from Egypt) is studied for its reaction rate with CH4, CO and H2 and the data are used in an analytically solved reactor model. The reactivity of fresh and three used EB samples from previous operation in a 10 kWth pilot was examined in a batch fluidized bed reactor with CH4 and syngas (50%CO + 50%H2). In comparison with other manganese ores, the EB ore has a lower rate of reaction with CH4, while showing a significantly higher reactivity with syngas. Nevertheless, this manganese ore always presents a better conversion of CH4 and syngas than the benchmark ilmenite. Mass-based reaction rate constants were obtained using a pseudo first-order reaction mechanism: 1.1·10-4 m3/(kg·s) for CH4, 6.6·10-3 m3/(kg·s) for CO and 7.5·10-3 m3/(kg·s) for H2. These rate constants were used in an analytical reactor model to further investigate results from previous operation in the 10 kWth unit. According to the analytical model, in the 10 kWth operation, 98% of the char in the biomass fuels was gasified before leaving the fuel reactor, while the char gasification products (CO and H2) have a 90% contact efficiency with the bed material. On the contrary, the volatiles have a much lower contact efficiency with the oxygen carrier bed, i.e. 20%, leading to low conversion of volatiles released. Thus, the results emphasize the importance of improving the contact between volatiles and bed material in order to promote combustion performance in the CLC process.
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| 2. |
- Mei, Daofeng, 1986, et al.
(författare)
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Oxygen Carrier and Alkali Interaction in Chemical Looping Combustion: Case Study Using a Braunite Mn Ore and Charcoal Impregnated with K 2 CO 3 or Na 2 CO 3
- 2022
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 36:17, s. 9470-9484
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Tidskriftsartikel (refereegranskat)abstract
- Alkali is a problematic component in biomass and may create various operation issues in normal combustion as well as chemical looping combustion using biomass fuels (bio-CLC). To investigate the interaction of alkali with an oxygen carrier, a methodology has been developed where alkali salts are added with impregnated charcoal particles. This work studies the effect of K2CO3 and Na2CO3 on the fluidization/agglomeration behavior and reactivity as well as the interaction of a braunite manganese ore oxygen carrier with K and Na in a batch fluidized bed reactor. Charcoal impregnated with K2CO3 (K-charcoal) and charcoal impregnated with Na2CO3 (Na-charcoal) were used as solid fuels in the reduction step of the simulated CLC cycles. CH4 and syngas (50% CO + 50% H2) were periodically used to evaluate the reactivity of braunite before and after solid fuel experiments. In total, more than 50 cycles were performed for both K-charcoal series and Na-charcoal series tests, while some additional cycles with non-impregnated charcoal were conducted and considered as a reference. Partial agglomeration and partial defluidization were found after cycles with K-charcoal and Na-charcoal, and the use of K-charcoal tends to lead to the partial agglomeration/defluidization faster than the use of Na-charcoal. K, Na, Si, and Ca were found at a higher concentration on the surface of the agglomerated particles and can be assumed to be responsible for the partial agglomeration. The partial agglomeration with K-charcoal happened likely as a result of surface melting of the braunite particles, whereas the formation of the low-melting-point Na-Si-Ca system could be responsible for agglomeration in the Na-charcoal experiments. The concentration of K and Na in the braunite bed was found to increase during cycles with the alkali charcoals. In total, the added masses of K and Na were 0.8 and 1.2% of the bed, and around 40 and 80% of added K and Na were found, respectively, in the used oxygen carrier particles. Although partial agglomeration and accumulation were observed in the presence of these alkalis, the reactivity of used braunite was scarcely changed in comparison to the fresh sample.
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| 3. |
- 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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| 4. |
- Hildor, Fredrik, 1992, et al.
(författare)
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Steel Converter Slag as an Oxygen Carrier-Interaction with Sulfur Dioxide
- 2022
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 15:16
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Tidskriftsartikel (refereegranskat)abstract
- Steel converter slag, also called Linz-Donawitz (LD) slag, has been considered as an oxygen carrier for biofuel chemical looping applications due to its high availability. In addition to its content of iron which contributes to its oxygen-carrying capacity, LD slag also contains a significant amount of calcium. Calcium, however, is known to interact with sulfur, which may affect the usability of LD slag. To get a better understanding of the interaction between sulfur and LD slag, batch scale experiments have been performed using solid and gaseous fuel with or without sulfur dioxide, together with LD slag as an oxygen carrier. The reactivity and sulfur interaction were compared to the benchmark oxygen carrier ilmenite. Sulfur increases the gasification rate of biofuel char and the conversion of CO for both LD slag and ilmenite. However, no effect of sulfur could be seen on the conversion of the model tar species benzene. The increased gasification rate of char was suspected to originate from both surface-active sulfur and gaseous sulfur, increasing the reactivity and oxygen transfer of the oxygen carrier. Sulfur was partly absorbed into the LD slag particles with calcium, forming CaS and/or CaSO4. This, in turn, blocks the catalytic effect of CaO towards the water gas shift reaction. When the SO2 vapor pressure was decreased, the absorbed sulfur was released as SO2. This indicates that sulfur may be released in loop-seals or in the air reactor in a continuous process.
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| 5. |
- Mei, Daofeng, 1986, et al.
(författare)
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Batch fluidized bed study of the interaction between alkali impurities and braunite oxygen carrier in chemical looping combustion
- 2022
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Chemical looping combustion (CLC) is a novel technology for heat and power generation with low-penalty CO2 capture. Using biomass in CLC (bio-CLC), negative CO2 emission can be attained. Alkali (mainly K and Na) in biomass can be problematic in bio-CLC, as it can interact with the oxygen carrier bed. The current work used charcoal and four charcoal samples impregnated with K2CO3, Na2CO3, KCl and NaCl, respectively, to study alkali interaction with a low-alkali braunite manganese ore oxygen carrier. The experiments were successfully carried out at 950°C in a quartz batch fluidized-bed reactor. For each alkali-fuel sample, more than 30 cycles of redox were performed. Using the solid fuel impregnated with K2CO3, Na2CO3, KCl and NaCl, char gasification was improved by a factor of 10, 8, 4 and 3 as compared to the non-impregnated fuel. Partial-defluidization of the braunite particles was found with all the alkali-fuels, although the extent differed, e.g. K2CO3 and KCl resulted in earlier onset of partial defluidization than Na2CO3 and NaCl. Hard agglomeration was never observed, while soft partial agglomeration was seen. Accumulation of K, Si, and Ca in agglomerates and particle boundary was found after cycles with K2CO3- and KCl-charcoal, while Na, Si and Ca was found after the Na2CO3- and NaCl-charcoal cycles. The mechanism of agglomeration formation seems different for these alkali-charcoals. For K2CO3- and KCl-charcoal, it seems the potassium reacted with Fe and Mn in the braunite, forming low-melting point components and thus led to agglomeration. In the case of Na2CO3- and NaCl-charcoal, direct reaction with the braunite was not seen, and it seems as if other reactive species combined were formed, which acted as a binder between particles to form agglomerates. In addition, after cycles with the K2CO3- and Na2CO3- charcoals, 80% K and 40% Na were retained in the oxygen carrier particles. After the use with all the alkalis, the braunite reactivity with CH4, CO and H2 was similar to the fresh particles. It is clear that alkali species could react with the braunite oxygen carriers, and this could affect reactivity and fluidization tendency in the long run. Still, only soft agglomerates and partial defluidization were found, which may not be the case in a real CLC system operating at higher fluidizing velocities.
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| 6. |
- Olsson, Emil O. Lidman, et al.
(författare)
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Thermal Conversion of Sodium Phytate Using the Oxygen Carrier Ilmenite Interaction with Na-Phosphate and Its Effect on Reactivity
- 2022
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Chemical looping combustion (CLC) can be used to convert biomass for heat and/or power production while efficiently capturing the produced CO2. This is possible because the biomass is oxidized by an oxygen carrier instead of directly by air. However, the ash species in biomass can interact with the oxygen carrier causing agglomeration and/or reducing its reactivity. One of the ash elements previously reported to cause problems is phosphorus and especially in combination with alkali. In this work, the interaction between a benchmark oxygen carrier, ilmenite, and a phosphorus model compound, sodium phytate, was studied up to a temperature of 1100 degrees C in N-2 using a fixed bed setup. Activated carbon and NaH2PO4 (thermally decomposing to NaPO3) were also used to study the individual effect of carbon and inorganic Na-phosphate. The CO and CO2 concentration in the flue gas was measured to monitor the oxidation of the samples, which showed that ilmenite participated in the conversion of Naphytate starting from about 600 degrees C. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy analysis of cross sections of the ilmenite residues revealed that Na-phosphate (forming from Na-phytate) penetrates porous ilmenite particles to a greater extent compared to denser particles, which may reduce the agglomeration tendencies since a lower amount of sticky Naphosphate melt will coat the particle surface. The effect of Na-phytate on the reactivity of ilmenite was quantitatively determined in a fluidized bed using 50% syngas or CO in N-2. For a loading of 1.5 wt % Na-phytate, the reactivity toward CO decreased to only 20% of the reference sample. The reason was partly attributed to a decreased surface area but is likely also due to the formation of less reactive Na-Fe-phosphates. A compilation of thermodynamic data relevant for the NaPO3-FeOx (x = 1 or 1.5) system shows that NaPO3 can form a melt containing dissolved iron starting from around 600 degrees C and that sodium and phosphorus are present solely in this form above approximately 930 degrees C at equilibrium.
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| 7. |
- 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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| 8. |
- Zichen, Di, 1992, et al.
(författare)
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Spinel ferrite-contained industrial materials as oxygen carriers in chemical looping combustion
- 2022
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 307
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Tidskriftsartikel (refereegranskat)abstract
- Spinel ferrites (MxFe3-xO4) as oxygen carriers (OC) in chemical looping combustion (CLC) process have drawn significant interest owing to unique lattice structure and oxygen transfer properties. However, their employment in practice is likely cost prohibitive due to the complicated synthesis processes compared to natural occurring materials. In the work, several of the low-cost industrial materials naturally containing ferrite spinel structure (MxFe3-xO4, M = Cr and Mn) were, for the first time, investigated to explore the possibility as an alternative of synthetic OCs. The reactivity and their cyclic performance during the chemical looping combustion were examined by lab-scale fluidized bed and TGA. It was demonstrated that all the tested materials contain spinel structures, especially after CLC cycles. They exhibited almost the same reactivity and stability, and less agglomeration occurred when compared to the synthetic materials contain the same kind of spinel structure. But the tested materials presented lower oxygen transport capacity than the synthetic ones. Specifically, the FM1 material containing MnFe2O4 showed best reactivity towards CH4 and syngas conversion, which may attribute to the oxygen uncoupling ability of Mn based species and the formation of spinel ferromanganese structure. But the stability was not good enough. It may because of the cracked particles attributing to the shrinking during the reduction of Mn2O3 to Mn3O4. The Fe-Cr based sample showed more superior stability and improved performance due to the formation of (Fe,Mg)(Cr,Fe)2O4 spinel structure. The Fe-Cr based samples exhibit poor performance for complete combustion of fuel; however, it appears to convert more CH4 to CO which may be desirable for hydrogenation, gasification, and cracking processes. It is worth noting that these industrial materials did not show significant difference in reactivity and stability when compared to the same kind of synthetic materials, presenting a possibility of potential substitution, especially taking its low cost into account.
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