| 1. |
- 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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| 2. |
- Attah, Martin, et al.
(författare)
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Vanadium recovery from steel converter slag utilised as an oxygen carrier in oxygen carrier aided combustion (OCAC)
- 2021
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Ingår i: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526. ; 293
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates vanadium extraction from steel converter slag from the LD (Linz-Donawitz) process. This slag has been used as an active bed material in a biomass boiler in a combustion technique called oxygen carrier aided combustion (OCAC). This usage in the boiler could be compared to the roasting step in the common roasting-leaching method for vanadium extraction. Leaching of LD slag prior to use as an oxygen carrier is undesirable as the materials active in OCAC are removed. This study successfully leached the slag following use in the combustion process. Two methods of leaching were utilised to compare the OCAC slag against traditional methods of vanadium extraction; a continuous flow leaching procedure and a microwave-assisted leaching procedure. It was found that a vanadium extraction efficiency of 22.1% could be achieved from the OCAC slag using 5 M sulphuric acid as a leaching solution following 30 min water leaching followed by 30 min of continuous acid leaching. Using the microwave-assisted method and further optimising leaching conditions, a final efficiency of 49.1% was achieved with 4 M sulphuric acid and particle size within the range of 44–74 μm.
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| 3. |
- Darwish, Esraa, 1986, et al.
(författare)
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Effect of mn and cu substitution on the srfeo 3 perovskite for potential thermochemical energy storage applications
- 2021
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Ingår i: Processes. - : MDPI AG. - 2227-9717. ; 9:10
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Tidskriftsartikel (refereegranskat)abstract
- Perovskites are well-known oxides for thermochemical energy storage applications (TCES) since they show a great potential for spontaneous O2 release due to their non-stoichiometry. Transition-metal-based perovskites are particularly promising candidates for TCES owing to their different oxidation states. It is important to test the thermal behavior of the perovskites for TCES applications; however, the amount of sample that can be used in thermal analyses is limited. The use of redox cycles in fluidized bed tests can offer a more realistic approach, since a larger amount of sample can be used to test the cyclic behavior of the perovskites. In this study, the oxygen release/consumption behavior of Mn-or Cu-substituted SrFeO3 (SrFe0.5M0.5O3; M: Mn or Cu) under redox cycling was investigated via thermal analysis and fluidized bed tests. The reaction enthalpies of the perovskites were also calculated via differential scanning calorimetry (DSC). Cu substitution in SrFeO3 increased the performance significantly for both cyclic stability and oxygen release/uptake capacity. Mn substitution also increased the cyclic stability; however, the presence of Mn as a substitute for Fe did not improve the oxygen release/uptake performance of the perovskite.
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| 4. |
- Lidman Olsson, Emil O., et al.
(författare)
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Release of P from Pyrolysis, Combustion, and Gasification of Biomass - A Model Compound Study
- 2021
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 35:19, s. 15817-15830
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Tidskriftsartikel (refereegranskat)abstract
- Phosphorus-rich biomass can cause operational problems in combustion units. Na-phytate, a model compound used to simulate phosphorus in biomass, was studied in a laboratory-scale reactor under temperature and gas atmosphere conditions relevant for pyrolysis, combustion, and gasification in fixed bed or fluidized bed reactors to understand the P and Na release behavior. Solid residues from Na-phytate thermal conversion were analyzed using ICP with optical emission spectrometry in order to quantify the P and Na release. The release mechanism was evaluated based on FTIR spectroscopy analysis of the residues, measurement of the flue gas CO/CO2 concentration, characterization of flue gas particles using SEM with EDS, and thermodynamic equilibrium calculations. Na-phytate decomposed in several steps under a nitrogen atmosphere, starting with condensation of the phosphate OH groups, followed by carbonization in the temperature range 300-420 °C. In the carbonization process, the phosphate units detached from the carbon structure and formed cyclic NaPO3. Above 800 °C, the C in the char reacted with the melted NaPO3 to form CO and gaseous elemental P. When the char produced from flash pyrolysis of Na-phytate at 800 °C for 10 min was exposed to 1% O2, 10% CO2, or 10% H2O (in N2), the release of Na and P to the gas phase in the temperature range 800-1000 °C was around 0-7%. However, the release of P in an inert atmosphere, with a holding time of 2 h or until full char conversion had been achieved, increased from around 4% at 800 °C to almost 30% at 1000 °C. The results indicated that carbothermic reduction reaction is responsible for the release of P and that NaPO3 vaporization is not the dominating mechanism for P and Na release at temperatures below 1000 °C. A small amount of P was released in the O2, CO2, and H2O containing gases because these gas species consumed the char and thereby inhibited the release of P.
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| 5. |
- Mayrhuber, Stefan, 1993, et al.
(författare)
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Effect of the oxygen carrier ilmenite on NO X formation in chemical-looping combustion
- 2021
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 222
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Tidskriftsartikel (refereegranskat)abstract
- The formation of NOx from fuel-bound nitrogen is important for the design of chemical-looping combustion (CLC) power plants. This work studied to what extent NO and NH3 reacts with the perovskite-like oxygen carrier ilmenite under conditions relevant to CLC. Based on mass balance calculations, N2 was the major outlet N-species in all experiments. More NO was measured at lower temperatures and at a higher oxidation level of the oxygen carrier. The presence of syngas hindered the reduction of NO by ilmenite. There were significant differences between the two ilmenites studied with respect to N-species selectivity. Norwegian (rock) ilmenite reduced NO efficiently and showed a stable reaction behavior compared to Australian (sand) ilmenite. This could be attributed to the higher titanium content of Norwegian ilmenite.
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| 6. |
- 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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| 7. |
- Yaqub, Zainab Temitope, et al.
(författare)
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Experimental Evaluation Using Plastic Waste, Paper Waste, and Coal as Fuel in a Chemical Looping Combustion Batch Reactor
- 2021
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Ingår i: Chemical Engineering and Technology. - : Wiley. - 0930-7516 .- 1521-4125. ; 44:6, s. 1075-1083
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Tidskriftsartikel (refereegranskat)abstract
- A comparative study of chemical looping combustion (CLC) with paper, plastic, and coal as fuel was carried out. Experiments were performed in a laboratory fluidized-bed reactor by alternating between reduction and oxidation cycles. The results obtained indicated that a higher temperature leads to an increase in the CO yield and carbon conversion for all fuels. Paper had the highest fractional conversion of CO to CO followed by polyvinyl chloride (PVC) and coal. This was due to the higher fraction of volatiles in paper compared to PVC and coal. Scanning electron microscopy (SEM) analysis of the oxygen carrier particle after each of the solid fuel experiment was carried out. For the used ilmenite, there was a slight difference in the morphology for the three different fuels.
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| 8. |
- Yilmaz, Duygu, 1987, et al.
(författare)
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Comparative Study: Impacts of Ca and Mg Salts on Iron Oxygen Carriers in Chemical Looping Combustion of Biomass
- 2021
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 6:25, s. 16649-16660
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Tidskriftsartikel (refereegranskat)abstract
- Chemical looping combustion (CLC) is one of the most promising methods for carbon capture and storage (CCS). An oxygen carrier, i.e., a mineral that can be oxidized and reduced, is used to convert the fuel in the process. The produced CO2 is inherently separated from the air components that enables easier CCS. The use of biomass-based fuels is desirable since it can lead to negative CO2 emissions. On the other hand, alkali compounds from the biomass may interact with the oxygen carrier causing problems, such as deactivation of the oxygen carrier. The most common oxygen carriers contain iron, since iron-based ores and industrial waste materials are readily available and cost-efficient. Therefore, the interaction between the iron oxygen carriers and the biomass ash-forming compounds needs to be investigated. Since Ca/Mg are abundant in biomass, it is important to clarify how their compounds interact with the oxygen carrier. In this study, the effect of Ca/Mg carbonates, chlorides, nitrates, sulfates, and phosphates along with synthetic biomass-derived ash on iron oxides was investigated. Redox reactions were investigated at 950 degrees C during 5 h under both oxidizing and reducing atmospheres. The results showed that the effect of Ca/Mg salts on the oxygen carrier varied depending on the anion of the salt. Generally, the nitrate- and phosphate-based salts of both Ca and Mg showed the harshest effect regarding agglomeration of the oxygen carriers. It was shown that the Ca/Mg-based compounds interacted differently with iron oxides, which was an unexpected result.
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| 9. |
- Yilmaz, Duygu, 1987, et al.
(författare)
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Utilization of promising calcium manganite oxygen carriers for potential thermochemical energy storage application
- 2021
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 60:3, s. 1250-1258
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Tidskriftsartikel (refereegranskat)abstract
- In this study, oxygen release/consumption behavior of calcium manganese-based oxides (CaMn1-xBxO3, where B: Cu, Fe, Mg and x = 0.1 or 0.2) used in a chemical looping oxygen uncoupling (CLOU) application was investigated. The effect of B-site dopants such as Fe, Mg, and Cu on the oxygen release behavior was also investigated with the aim to use these materials in thermal energy storage (TES). Previous literature studies about CLOU performance of doped calcium manganites were taken into consideration for dopants selection. Calcium manganite-based oxides have been used in chemical looping oxygen uncoupling (CLOU) applications owing to their oxygen release behavior to the gas phase. Studies have revealed that calcium manganite-based oxides show a promising nonstoichiometry over a range of temperatures and oxygen partial pressures, which makes them useful for thermochemical energy storage applications. However, the related literature studies have been mainly focused on their nonstoichiometric characteristics related to temperature and oxygen partial pressure and thermodynamic properties. In this work, thermal analysis and fluidized bed tests were carried out as complementary techniques. CaMn0.8Cu0.2O3 showed the highest oxygen release performance in fluidized bed tests, while CaMn0.9Mg0.1O3 had the best cyclic stability overall among the samples used in the study.
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