| 1. |
- Hildor, Fredrik, 1992, et al.
(författare)
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Steel converter slag as an oxygen carrier for chemical-looping gasification
- 2020
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 210
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Tidskriftsartikel (refereegranskat)abstract
- Chemical Looping Gasification (CLG) is a dual fluidized bed gasification technique where an oxygen carrier is used as bed material instead of sand. An optimized process could have several advantages, including i) one concentrated CO2 stream, amiable for carbon capture, ii) less tar formation, iii) additional reaction pathways for syngas production, iv) less corrosion and v) CO2 is generated in one stream from the fuel reactor that could be captured. Steel converter slag, also called LD slag, is a by-product from the steel industry which, besides iron, contains significant fractions of Ca, Mg, Al and Mn in a complex matrix of phases. The low cost and presence of known catalytic solid phases in the slag makes it interesting as an oxygen carrier in CLG. In this work, LD slag was investigated using a batch reactor with gaseous and solid fuel as well as with TGA. It was found that during gasification with LD slag, the material can i) transfer oxygen to the fuel, ii) catalyze the water-gas-shift reaction, iii) react with CO2 forming carbonates and iv) split water to hydrogen. The overall result was a raw gas with a higher H2/CO ratio for LD slag than the other tested materials.
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| 2. |
- Eliasson Störner, Felicia, 1994, et al.
(författare)
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Potassium Ash Interactions with Oxygen Carriers Steel Converter Slag and Iron Mill Scale in Chemical-Looping Combustion of Biomass - Experimental Evaluation Using Model Compounds
- 2020
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 34:2, s. 2304-2314
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Tidskriftsartikel (refereegranskat)abstract
- Chemical-looping combustion (CLC) is a combustion technology in which a solid oxygen carrier is used to convert fuel. The oxygen carrier is oxidized in air and subsequently transferred to a separate reactor in which it reacts with the fuel. The produced CO2 is inherently separated from the air components, making CLC a promising technology for carbon capture and storage (CCS). CLC of biomass combined with CCS (bioenergy CCS; BECCS) is a way to generate negative CO2 emissions and thus interesting for climate change mitigation. Undesirable chemical reactions between ash and oxygen carriers are a challenge in BECCS because of the reactive nature of biomass ash. This article examines two low-cost steel industry byproducts that have shown desirable fuel conversion properties in CLC: iron mill scale (Glödskal B) and steel converter slag (LD-slag). Their interactions with potassium ash model compounds (KCl, K2CO3,K2SO4, and KH2PO4) in a reducing atmosphere have been investigated. Mixtures of oxygen carriers and potassium salt have been reduced for 6 h in CO and steam in a laboratory-scale fixed-bed reactor at 850 °C. The reduced samples have been analyzed with SEM/EDS and XRD. The reactivity of the mixtures during reduction and oxidation has also been examined by thermogravimetric analysis (TGA). K2CO3 increased the reaction rate for the reduction of Glödskal and inhibited the reactivity of LD-slag. KH2PO4 formed a K−P−Fe component with apparent low melting temperature with Glödskal, causing agglomeration, and decreased the reduction/oxidation rate in TGA. KH2PO4 formed a K−P−Ca component with apparent high melting temperature with LD-slag causing agglomeration but the reduction rate was not affected. The study suggests that the iron mill scale and LD-slag should not be rejected as oxygen carriers for CLC based on potassium ash interaction.
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| 3. |
- Hildor, Fredrik, 1992, et al.
(författare)
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Understanding the Interaction of Potassium Salts with an Ilmenite Oxygen Carrier under Dry and Wet Conditions
- 2020
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:36, s. 22966-22977
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Tidskriftsartikel (refereegranskat)abstract
- This study describes how potassium salts representative of those in bio ash affect the reactivity of the oxygen carrier ilmenite under moist and dry conditions. Ilmenite is a bench-mark oxygen carrier for chemical-looping combustion, a technique that can separate CO2 from flue gases with minimal energy penalty. Different potassium salts were mixed with ilmenite to a concentration of 4 wt % potassium. The salts used were K2CO3, K2SO4, KCl, and KH2PO4. Experiments were performed at 850 °C under alternately oxidizing and reducing conditions in a dry atmosphere or in the presence of steam. Analyses of the oxygen carrier regarding changes in reactivity, structure, and composition followed the exposures. This study showed that salts such as K2CO3, K2SO4, and KCl increase the reactivity of the ilmenite. For the samples mixed with KCl, most of the salt was evaporated. KH2PO4 decomposed into KPO3, forming layers around the ilmenite particles that lead to agglomeration. Additionally, the KPO3 layer was more or less nonpermeable for CO and decreased the reactivity toward H2 significantly in both dry and wet conditions. This decreased reactivity indicates that the concentration of phosphorus in biofuel may have a significant effect on oxygen carrier degradation. It was also observed that the presence of steam changed the chemistry drastically for the nonphosphorus-containing salts. Alkali salts may react with steam, forming volatile KOH that evaporates partly. KOH may also form K-titanates by reaction with the oxygen carrier, leading to segregation of iron and titanium phases in the ilmenite. ©
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| 4. |
- Stanicic, Ivana, 1994, et al.
(författare)
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Interaction of oxygen carriers with common biomass ash components
- 2020
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 200
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Tidskriftsartikel (refereegranskat)abstract
- Carbon capture and storage (CCS) has been proposed as a bridging technology between the current energy production and a future renewable energy system. One promising carbon capture technology is chemical-looping combustion (CLC). In CLC the reactors are filled with metal oxide bed material called oxygen carriers. The interaction between oxygen carriers and biomass ashes is a poorly explored field. To make CLC a viable process, and thereby creating carbon emission reductions, more knowledge about the interactions between biomass ashes and oxygen carriers is needed. This study investigated solid-state reactions of three promising oxygen carriers, hematite, hausmannite and synthesised ilmenite with different biomass ash components. Oxygen carriers were exposed with the ash components: calcium carbonate, silica and potassium carbonate at 900 °C and at different reducing potentials. Crystalline phases of the exposed samples were determined using powder x-ray diffraction (XRD). Results showed that the oxygen carriers hausmannite and hematite interact to a higher extent compared to synthesised ilmenite regarding both physical characteristics and detectable phases. Synthesised ilmenite formed new phases only in systems including potassium. Thermodynamic calculations were performed on the multicomponent system and compared with experimental results. The results suggest that optimisation of systems involving manganese and potassium should be performed.
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| 5. |
- Wang, Baoyi, et al.
(författare)
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Using Mn-Si oxygen carriers supported with CaO or Al 2 O 3 for converting methane and syngas in chemical-looping with oxygen uncoupling (CLOU)
- 2020
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 201
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Tidskriftsartikel (refereegranskat)abstract
- Facing increasingly severe environmental problems and substantial energy demand, chemical-looping with oxygen uncoupling (CLOU) is regarded as a highly promising technique to facilitate the application of carbon capture storage and utilization (CCS & U) due to its inherent gas separation. Thus, feasible oxygen carriers for continuous operation on the industry scale are essential. A combination of Mn and Si, which is not only economic but also has few adverse effects on the environment, has been tested and found to provide satisfactory CLOU behavior. But the results are relevant for several oxygen carrier applications. However, the mechanical properties of these Mn-Si oxygen carriers require further improvement. Thus, two kinds of support materials are chosen in this study, CaO and Al2O3, to enhance the physical strength of the Mn-Si oxides. Twelve samples with a CaO content ranging from 2 wt% to 41 wt% and twelve samples with an Al2O3 content, ranging from 2 wt% and to 36 wt%, were produced using spray-drying at three sintering temperatures, 1100 °C, 1150 °C, and 1200 °C. The aim is to identify oxygen carriers, which exhibit high reactivity and strong mechanical properties. The oxygen release ability and gas-fuel conversion of these oxygen carriers are examined. In general, the particles with a lower content of support materials (≤5 wt%) calcined from lower temperatures (≤1150 °C) show better CLOU behavior and higher reactivity, regardless of the support material. Attrition resistance was assessed with surprisingly good results for an oxygen carrier with a low content of support materials (≤5 wt%). The material with 74% Mn 24% Si and 2% Al was further tested in a continuous 300 W. This was done to test the oxygen carrier capability under more conditions closer to a real circulating CLOU unit. In the 300 W unit the material release oxygen in inert atmosphere and converted up to 99.98%, of the syngas and 70% of the methane. However, under certain conditions with syngas as fuel the physical structure of the oxygen carriers were destroyed as the particles degraded to fines.
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| 6. |
- Yilmaz, Duygu, 1987, et al.
(författare)
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Experimental and Thermodynamic Study on the Interaction of Copper Oxygen Carriers and Alkaline-Containing Salts Commonly Present in Ashes
- 2020
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 34:4, s. 4421-4432
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Tidskriftsartikel (refereegranskat)abstract
- As CO2 emission is one of the most critical issues that causes global warming, methods have been developed for carbon capture and storage. Chemical looping combustion (CLC) and chemical looping oxygen uncoupling (CLOU) are unique and useful methods for direct separation of carbon dioxide in combustion. In CLC and CLOU, metal oxides are used as an oxygen carrier to transfer oxygen between an air and a fuel reactor. The fuel is oxidized with the released oxygen by the oxygen carrier used. When coal or any ash-containing fuels are used an interaction between ash-forming matters and oxygen carrier can occur which can cause to deactivation or agglomeration of the oxygen carriers. The composition of species in the ash and their amount can vary widely and also depend on the fuel used. Thermodynamic equilibrium calculations (TEC) can be used to predict the resulting compounds during in CLC and CLOU. This can help choosing the right fuel for the right oxygen carrier or vice versa. In this study, the interaction between common salt-based ash-forming matters present in ash and the widely used CuO oxygen carriers was studied both experimentally and thermodynamically. Experiments were carried out at 900 °C under both oxidizing and inert atmospheres using CuO or Cu2O (CuO/Cu2O) as the oxygen carrier and K- and Na-based carbonate, chloride, nitrate, phosphate, and sulfate to represent salt compounds present in the ashes. To observe the interaction of the oxygen carriers with each salt compound used, equal moles of copper oxide and a salt compound were mixed. In addition to this, the effect of salt compounds used for the interaction between oxygen carrier and a model ash was also investigated. NaSO4 showed the harshest effect among the salts used since it caused a strong agglomeration. Generally, potassium-based salts did not affect the oxygen carriers directly and the results were consistent with the TEC. However, sodium-based salts showed significant effect on the system which differed from the TEC results.
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| 7. |
- Yilmaz, Duygu, 1987, et al.
(författare)
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Interaction of Iron Oxygen Carriers and Alkaline Salts Present in Biomass-Derived Ash
- 2020
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 34:9, s. 11143-11153
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Tidskriftsartikel (refereegranskat)abstract
- Chemical-looping combustion (CLC) is a unique method that is developed for carbon capture and storage (CCS) to mitigate the climate change. In CLC, an oxygen carrier is used to convert the fuel and the produced CO2 is inherently separated from air components, which makes it suitable for CCS. The CLC of biomass is a way to generate negative CO2 emissions. However, interactions between ash and oxygen carriers are a tough challenge as biomass-derived ashes consist of large amounts of reactive ash-forming matter such as alkaline and alkali earth metals. As iron-based oxygen carriers are one of the most commonly used ones, the interaction of the pure iron oxide and biomass-derived ash-forming matter needs to be further understood to overcome the deactivating effects of ash components on the oxygen carriers. Even though ash components may exist in different forms, the effects of K- and Na-based carbonates, chlorides, nitrates, phosphates, and sulfates on the pure iron oxide were mainly investigated in this study. The effect of synthetic biomass-derived ash on the iron oxygen carriers was also investigated to reveal the phases causing agglomeration or deactivation of the oxygen carriers. Experiments were performed at 950 °C for 5 h under both oxidizing and reducing atmospheres. After experiments, the obtained phases were analyzed by X-ray diffraction, and elemental mapping was performed by using scanning electron microscopy–energy-dispersive X-ray spectroscopy. Results showed that the Fe oxygen carrier was worst affected by KCl, KH2PO4, and NaNO3 in terms of agglomeration among the used salts. The presence of K and Si together in the ash caused a “bridge” formation between the oxygen carrier and the ash constituent, which increased the agglomeration. A strong Ca deposit on the outer layer of the Fe oxygen carrier was also observed when a mixture of salt was used to mimic ash. Even though some discrepancies were observed, generally thermodynamic calculations were successful in estimating the experimentally observed phases.
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| 8. |
- Yilmaz, Duygu, 1987, et al.
(författare)
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Investigation of the combined Mn-Si oxide system for thermochemical energy storage applications
- 2020
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Ingår i: Journal of Energy Storage. - : Elsevier BV. - 2352-152X. ; 28
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Tidskriftsartikel (refereegranskat)abstract
- Combined manganese-silicon oxides are promising candidates for thermochemical energy storage (TCES) since they show a great potential for spontaneous O2 release as utilized in chemical-looping with oxygen uncoupling (CLOU). For both concepts, as well as mechanical strength, cyclic stability of oxidation and reduction are very important. The high reaction enthalpy of the material at high temperature conditions is one of the most important issues for TCES. Agglomeration and destabilization of the material can occur during redox cycles which results in decreased cyclic stability. In this study, thermal analyses were carried out to investigate the phase transitions and changes of manganese-silicon oxide by comparably slow heating and cooling rate during the thermal cycling. This was conducted in a packed bed reactor to identify the oxygen releasing and consuming stability versus temperature and number of cycles. Phase analyses were carried out to reveal the phase changes during cycling or new formed phase due to side reactions. Results showed that both thermal cyclic stability and oxygen coupling-uncoupling ability increased with increased silica content, from 2 to 10% wt., and the poorest stability was obtained from the sample which has the highest silica content.
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| 9. |
- Yilmaz, Duygu, 1987, et al.
(författare)
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Thermochemical energy storage performance of copper oxides: Effect of support materials
- 2020
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Ingår i: Journal of Energy Storage. - : Elsevier BV. - 2352-152X. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- Thermochemical energy storage (TCES) is one of the most promising methods for utilization of solar energy. Metal oxides can exhibit reversible redox reactions that are useful for TCES applications. Especially, transitional metal oxides can undergo reduction reactions at high temperatures while absorbing energy given to the system. Later on, when the temperature goes down below a phase-transition temperature, exothermic re-oxidation reactions can take place. Air can be used both as oxygen source and heat transfer medium during the redox reactions. Recently, several studies have been published about the utilization of metal oxides for TCES applications. Among these metal oxides, copper oxides received a great attention owing to its cyclic stability and suitable redox temperature. In this study, copper oxides are used as energy storage material in combination with ZrO2, ZrO2-La2O3, MgAl2O4, Mg2Al2O4-La2O3, CeO2, CeO2-La2O3 as support materials. The best results were obtained from samples supported with MgAl2O4, Mg2Al2O4-La2O3. This most likely eventuated due to the other reversible phase transformations that take place in these systems such as formation of LaAlO3 and Cu2Al2O4. Especially Mg2Al2O4-La2O3 addition improved the system, both in terms of cyclic stability and heat capacity.
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