| 1. |
- Hildor, Fredrik, 1992, et al.
(författare)
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Effect of Weathering on Steel Converter Slag Used as an Oxygen Carrier
- 2023
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Ingår i: ACS Omega. - 2470-1343. ; 8:50, s. 47472-47481
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Tidskriftsartikel (refereegranskat)abstract
- Steel converter slag, also called LD slag, is a material that has been suggested for use as a low-cost oxygen carrier for chemical looping applications. Low-cost oxygen carriers are especially relevant for the conversion of solid fuels, which may contain large amounts of reactive ashes. Ash may limit the lifetime of the bed material, which is why a high-cost oxygen carrier will likely not be competitive. Applying LD slag on an industrial scale as an oxygen carrier makes the storage properties of the material highly interesting. LD slag has been known to be affected by weathering, thus limiting the possibilities of the material to be used in construction, e.g., as fillers in concrete. In this study, pretreated LD slag for use as an oxygen carrier was weathered outdoors for roughly 1.5 years in southwest Sweden. Afterward, the particles were characterized and used in a laboratory batch fluidized bed reactor system to evaluate the effects of storage on the oxygen carrier properties. It was found that the reactivity with the fuel of the weathered LD slag was similar to that of the original sample when used in a laboratory fluidized bed. However, the physical properties were severely degraded due to weathering. Dissolved CaO formed CaCO3, agglomerating the top layer of the sample. The particles in the bulk of the sample were found to have decreased density and increased attrition rate. This suggests that LD slag particles for use as oxygen carriers should be stored dry to avoid weathering of the particles.
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| 2. |
- Hildor, Fredrik, 1992, et al.
(författare)
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Metal impregnation on steel converter slag as an oxygen carrier
- 2023
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Ingår i: Greenhouse Gases: Science and Technology. - : Wiley. - 2152-3878. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen carriers used in chemical looping processes operated with biofuel are affected by the inorganic matter of the fuel. It is therefore expected that the lifetime of the oxygen carrier is limited, and preferably low-cost oxygen carriers should be used. Oxygen carriers based on iron ore or steel manufacturing waste products are available in significant quantities at low cost. However, it is common for these types of materials that their reactivity is low. This study investigates the effect of adding small amounts of more reactive elements into steel converter slag, also called LD slag. Slag particles were wet impregnated with 2 or 5 wt.% of Ni, Cu, Mn, or Ce. The new material’s morphology was evaluated using X-Ray Diffraction and SEM-EDS. Changes in reactivity towards CO, CH4 and the model tar molecule benzene were evaluated using a bench-scale laboratory fluidized bed reactor. It was observed that even small amounts of either Ni, Cu, or Mn could increase reactivity toward CO. Both Cu and Mn formed phases with LD slag that released oxygen via CLOU (chemical looping with oxygen uncoupling) and increased the conversion of methane and benzene. Ni and Ce doping also increased methane conversion but had only a minor effect on the benzene conversion.
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| 3. |
- 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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| 4. |
- Baena-Moreno, Francisco, 1992, et al.
(författare)
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Biogas upgrading through calcium looping: Experimental validation and study of CO 2 capture
- 2023
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Ingår i: Biomass and Bioenergy. - 1873-2909 .- 0961-9534. ; 176
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Tidskriftsartikel (refereegranskat)abstract
- The calcium looping technology is one of the most promising technologies for capturing and storing CO2. This technology has been evaluated with a variety of sorbents and conditions in previous works, but the inlet CO2-ladden gas has typically been a flue gas from combustion, which typically has a composition of 10–20% CO2 and 80–90% N2. On the other side, the performance of the calcium looping process for CO2 capture of other gases (i.e., biogas or gases resulting from hydrothermal carbonization) remains largely unstudied. In this work, this knowledge gap is assessed through evaluating the performance of the calcium looping process for biogas (synthesized as 40% CO2, 60% CH4) in terms of carbonation conversion. This experimental study investigates the impact of: (1) using an inlet gas composition representative for biogas instead of combustion flue gas; (2) different biogas compositions; (3) the carbonation temperature; (4) the cooling-down and heating-up of the sorbent material between the reactor and ambient temperatures within cycles; (5) the atmosphere composition during calcination; and (6) the solids particle size. The main result obtained is that the overall CO2-capture performance of calcium looping improves when using biogas as inlet CO2-ladden gas, in comparison with combustion flue gas. One main contribution to this improved performance is shown to be the presence of secondary reactions (i.e., dry reforming, methanation). The impact of the CH4 to CO2 ratio tested is not remarkable, showing that the potentialities of the process in this aspect can be adapted to several biogas producing feedstocks.
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| 5. |
- Brorsson, Joakim, 1988, et al.
(författare)
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Discovery of Oxygen Carriers by Mining a First-Principle Database
- 2023
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Ingår i: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 127:20, s. 9437-9451
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Tidskriftsartikel (refereegranskat)abstract
- Chemical looping is an innovative technique that relies, to a large extent, on the possibility of finding new oxygen carriers. Until now, these materials have primarily been identified via experimental techniques and therefrom derived insights. However, this is both costly and time-consuming. To speed-up this process, we have applied a computational screening approach based on energetic data retrieved from the Open Quantum Materials Database. In particular, we have considered combinations of all mono-, bi-, and trimetallic alloys and mixed oxides with up to three distinctive phases. Here, we specifically focus on a technique referred to as chemical looping oxygen uncoupling, which is especially suitable for solid fuels, e.g., combustion of biomass for negative CO2 emissions. The formation energies obtained for the materials of interest were used to identify phase transitions that are likely to occur under conditions relevant for chemical looping oxygen uncoupling. Given these criteria, the initial list of 300000 materials is reduced by a factor of 20, and after filtering out rare, radioactive, toxic, or harmful elements only 1000 remain. When considering the abundance of elements in the ranking criteria, most of the highest ranking phases include Cu, Mn, and Fe. This adds credibility to the procedure, as many viable oxygen carriers for chemical looping oxygen uncoupling that have been studied experimentally contain these elements. While Cr-based materials have not been widely explored for this application, our study suggests that this might be worthwhile since these occur more frequently than Fe. Other elements that would be interesting as additional components include Ba, K, Na, Al, and Si.
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| 6. |
- Eliasson Störner, Felicia, 1994, et al.
(författare)
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An improved method for feeding ash model compounds to a bubbling fluidized bed – CLC experiments with ilmenite, methane, and K 2 CO 3
- 2023
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Ingår i: Greenhouse Gases: Science and Technology. - 2152-3878. ; 13:4, s. 546-564
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Tidskriftsartikel (refereegranskat)abstract
- Biomass conversion with carbon capture and storage (Bio-Energy CCS; BECCS) is one of the options considered for mitigating climate change. In this paper, the carbon capture technology chemical-looping combustion (CLC) is examined in which the CO2 is produced in a stream separate from the combustion air. A central research topic for CLC is oxygen carriers; solid metal oxides that provide oxygen for the conversion process. Biomass and waste-derived fuels contain reactive ash compounds, such as potassium, and interactions between the oxygen carrier and the ash species are critical for the lifetime and performance of the oxygen carrier. This work develops and demonstrates an improved method for studying the interactions between ash species and oxygen carriers. The method uses a lab-scale reactor operating under fluidized conditions, simulating CLC batch-wise by switching between feed gas. The novelty of the setup is the integrated system for feeding solid particles of ash model compounds, enabling the simulation of ash species accumulating in the bed. Ilmenite is a benchmark oxygen carrier for solid fuel conversion and was used in this study to evaluate the method using K2CO3 as a model ash compound. Experiments were done at 850 and 950°C. Methane conversion in CLC cycles and fluidization was evaluated with gas analysis and pressure drop measurements. Scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD) analysis of bed particles were done after the experiments to establish changes in the morphology and composition of the ilmenite. The method for feeding the ash model compound was concluded to be satisfactory. At 950°C, K accumulated in the particles forming K-titanates and agglomeration was enhanced with K2CO3 addition. The agglomeration mechanism was solid-state sintering between the Fe-oxides forming on the particle surfaces. The bed defluidized at 950°C, but no such effect was seen at 850°C. The method is suitable for studying the Fe-Ti-K system with ilmenite and potassium without the influence of other ash species. © 2023 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.
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| 7. |
- Hildor, Fredrik, 1992, et al.
(författare)
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Interaction behavior of sand-diluted and mixed Fe-based oxygen carriers with potassium salts
- 2023
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 339
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen carriers, in the form of metal oxide particles, are bed materials that transport oxygen in solid form in fluidized bed applications, such as in chemical-looping applications. In biofuel applications, it is well known that alkali from the fuel ash can react with the bed material and cause, among other operation issues, agglomeration. When using oxygen carriers in a fluidized bed, it is likely that the bed material is either a mixture of different metal oxide materials or partly diluted with sand. This is to improve or combine the chemical properties of the materials used or simply for economic reasons. This work investigates how three potassium salts K2CO3, K2SO4 and KH2PO4 interact with the oxygen carriers: Steel converter slag (LD slag), ilmenite, mixtures of the two and each carrier diluted with silica sand. The salts were used as model compounds that can occur in biofuel ash. The set-up used was a fixed bed where a small sample of bed material is mixed with a potassium salt equivalent to 4 wt-% of potassium. The mixture was then exposed to reducing (H2 in steam) conditions at 900 °C during several hours in a tubular furnace. This provides a worst-case scenario for solid–solid interaction in a fluidized bed. If a solid–solid reaction does not take place in this setup, it will most likely never occur in a fluidized bed. When LD slag and ilmenite were combined, the potassium from the salts would prefer to accumulate in the ilmenite rather than the LD slag. Ca from LD slag interacted with KH2PO4 resulting in a less severe agglomeration than when ilmenite was used separately with the same salt. When the oxygen carriers were diluted with silica sand, potassium salt interaction resulted in agglomeration for both the oxygen carriers with all potassium salts. K2CO3 and K2SO4 formed potassium silicates, while KH2PO4 formed a phosphorus-containing melt. When LD slag was present, phosphorus was located in a K-Ca-P phase that was not present if ilmenite was present.
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| 8. |
- Hildor, Fredrik, 1992, et al.
(författare)
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Tar characteristics generated from a 10 kW th chemical-looping biomass gasifier using steel converter slag as an oxygen carrier
- 2023
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 331
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Tidskriftsartikel (refereegranskat)abstract
- Tar management is one of the key components to achieve high energy efficiency and low operational costs connected to thermal gasification of biomass. Tars contain a significant amount of energy, and unconverted tars result in energy efficiency losses. Also, heavy tars can condense downstream processes, resulting in increased maintenance. Dual fluidized beds for indirect gasification operated with active bed material can be a way to better convert and control the tar generated in the process. Using an active material to transport oxygen in an indirect dual reactor gasification setup is referred to as chemical-looping gasification (CLG). A higher oxidative environment in the gas phase, in addition to possible catalytic sites, could mean lower yields in comparison to normal indirect gasification. This paper investigates the effect of using Steel converter slag (LD slag), a byproduct of steel manufacturing, as an oxygen-carrying bed material on tar species generated in a 10 kWth dual fluidized bed biomass gasifier. The results are compared to the benchmark oxygen carrier ilmenite and conventional silica sand. Three different solid biofuels were used in the reactor system: steam exploded pellets, pine forest residue and straw. Tar was absorbed from the raw syngas using a Solid Phase Adsorption (SPA) column and was analyzed using GC-FID. Bench-scale experiments were also performed to investigate benzene conversion of LD slag and ilmenite at different oxidation levels. The findings of this study suggest that oxygen carriers can be used to decrease the tars generated in a dual fluidized bed system during gasification. Phases in LD slag possess catalytic properties, resulting in a decreased ratio of heavy tar components compared to both ilmenite and sand. Temperature and fuel load showed a significant effect on the tar generation compared to the circulation and steam ratio in this reactor system. Increased temperature generated lower tar yields and lower ratios of heavy tar components for LD slag in contrast to sand.
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| 9. |
- Lidman Olsson, Emil O., et al.
(författare)
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An exploratory study of phosphorus release from biomass by carbothermic reduction reactions
- 2023
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Ingår i: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 39:3, s. 3271-3281
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Tidskriftsartikel (refereegranskat)abstract
- Phosphorus (P) from biomass can cause operational problems in thermal conversion processes. In order to explore the release mechanism of P to the gas phase, carbothermic reduction of meta-, pyro-, and orthophosphates of ash elements commonly found in biomass; sodium, potassium, magnesium, and calcium was investigated. Mixtures of each phosphate and activated carbon were heated to 1135 °C in a laboratory-scale reactor, with the CO and CO2 evolving from the sample monitored, and the chemical composition of selected residues analyzed to quantify the release of P. Thermal gravimetric analysis was also performed on selected samples. The alkaline earth phosphates were reduced in steps, following the sequence meta → pyro → ortho → alkaline earth oxide. However, the alkali metaphosphates appear to be reduced in one step, in which both alkali and P are released. Alkali pyro- and orthophosphate appear to undergo a two-step process. In the first step, mainly alkali is released and in the second step both alkali and P. An intermediate is produced in the first step, which has a K:P:O atomic ratio of about 2:1:2.7, indicating it might be a phosphite with the overall stoichiometry; K4P2O5. The reduction of alkaline earth phosphates could be interpreted using available thermodynamic data, whereas thermodynamic equilibrium calculations for the alkali phosphates did not correspond well to the experimental observations. Kinetics were derived for the different reduction reactions, and can be used to compare the reactivity of the phosphates. The work suggests that carbothermic reduction reactions are important for the release of P in the temperature range 850-1135 °C and relevant for biomass combustion, pyrolysis and gasification.
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| 10. |
- Lidman Olsson, Emil O., et al.
(författare)
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Release of phosphorus from thermal conversion of phosphorus-rich biomass chars – Evidence for carbothermic reduction of phosphates
- 2023
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 341
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Tidskriftsartikel (refereegranskat)abstract
- Biomass can be used to generate heat, power, or biofuels in thermal conversion processes such as combustion, gasification and pyrolysis. However, some types of biomass contain high levels of phosphorus, which can be released to the gas phase and cause operational or environmental problems. The mechanism(s) responsible for phosphorus release has not been convincingly established. Understanding the high-temperature phosphorus chemistry is also important in order to enable efficient recovery of phosphorus in residues from thermal conversion of biomass. In this work, the release of phosphorus from wheat bran char and sunflower seed char in different gas environments (100 % N2, 1–20 % O2, and 10 % CO2) and temperatures (900–1100 °C) was studied. The chars were converted in a horizontal tube reactor and characterized using ICP-OES, XRD, SEM-EDS, and 31P NMR. The release of ash-forming elements was determined using ICP-OES analysis of the char and sample residues, whereas the release of carbon was determined using CO and CO2 gas analysis. In both chars, phosphorus was present primarily together with potassium and magnesium, mainly as pyrophosphates in the wheat bran char, and largely as orthophosphates in the sunflower seed char. For wheat bran char, the release of phosphorus increased from 27 % at 900 °C to 71 % at 1100 °C in N2, whereas the release was at least 20 % lower in the oxidizing atmospheres (1–20 % O2, or 10 % CO2). The sunflower seed char reached a maximum release of 55 % at 1100 °C in N2. For wheat bran char, the molar ratio of released carbon/phosphorus was close to 2.5, which fits well with the theoretical value for carbothermic reduction of phosphates (P2O5(s, l) + 5C(s) → P2(g) + 5CO(g)). At 1100 °C, in N2, the release of phosphorus, potassium and sodium occurred mainly during the first 10 min. It was shown that KMgPO4, used as a model compound, could be reduced by carbon starting from 950 °C, but that some of the phosphorus remained in the condensed phase. The work provides a better understanding of phosphorus release and presents evidence showing that carbothermic reduction reactions can be an important phosphorus release mechanism for seed- and grain-based biomass char.
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