| 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. |
- 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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| 4. |
- Hildor, Fredrik, 1992, et al.
(författare)
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Steel converter slag as an oxygen carrier in a 12 MWth CFB boiler – Ash interaction and material evolution
- 2019
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 88, s. 321-331
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 Elsevier Ltd Steel converter slag or LD slag is a byproduct of the basic oxygen steel production process, where raw iron from the blast furnace is converted to steel. LD slag contains mainly calcium and iron compounds and smaller amounts of magnesium, silicon, manganese and vanadium. The iron content, about 17 wt.% of the slag, makes this material a potential oxygen carrier for combustion processes such as Oxygen Carrier Aided Combustion (OCAC) or Chemical Looping Combustion (CLC). This study will present an investigation of the use of LD slag as an oxygen carrier in OCAC at semi-industrial scale. The Chalmers 12 MWth biomass circulating fluidized bed boiler was operated using LD slag as bed material under OCAC conditions. During the operation, bed samples from the boiler were extracted and analyzed with ICP-SFMS, SEM-EDS, XRD and different mechanical tests to analyze chemical and physical changes of the bed material as a function of time. The samples were also investigated in a laboratory fluidized bed reactor to determine the change in reactivity towards common volatile fuel components, i.e. CO, H2, CH4 and C6H6. It was found that LD slag can be utilized as an oxygen carrier in a combustion process for biofuel. However, the reactivity towards syngas, CH4 and C6H6 is reduced as a function of time in the boiler, which is believed to be caused by accumulation of, and interaction with, alkali from the biofuel ash. Sulfur addition may decrease the adverse effects of alkali on combustion efficiency, but not eliminate them completely.
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| 5. |
- Mattisson, Tobias, 1970, et al.
(författare)
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Chemical-Looping Technologies using Circulating Fluidized Bed Systems: Status of Development
- 2017
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Ingår i: 12th International Conference on Fluidized Bed Technology, CFB 2017. ; , s. 11-22
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Konferensbidrag (refereegranskat)abstract
- In chemical-looping combustion (CLC), an oxygen carrier provides lattice oxygen for complete combustion of a fuel for heat and power production. The reduced metal oxide is then oxidized in a separate reactor. The combustion products CO2 and H2O are obtained in pure form, without any nitrogen in the gas. As no gas separation work is needed, this could be a breakthrough technology for carbon capture (CCS). Normally, the fuel- and air-reactor are designed utilizing inter-connected fluidized beds. The same underlying reversible redox reactions of CLC can be used for other fuel conversion technologies. These include fluidized bed processes for gas, solid and liquid fuels for heat, power, syngas or hydrogen production. Some of these concepts were suggested as far back as the 1950’s, while others have just recently been proposed. Chalmers University of Technology has been involved in CLC research for over 18 years, and this paper will provide a review of some recent developments with respect to CLC with gaseous, liquid and solid fuels. Further, the paper will provide an overview some related technologies where Chalmers is conducting research: i) Chemical-looping gasification (CLG), ii) Chemical-looping reforming (CLR) and iii) Chemical-looping tar reforming (CLTR). In these processes, a pure syngas/hydrogen can be produced effectively, which could be utilized for chemical or fuel production.
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| 6. |
- Mattisson, Tobias, 1970, et al.
(författare)
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Chemical-looping technologies using circulating fluidized bed systems: Status of development
- 2018
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 172, s. 1-12
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Forskningsöversikt (refereegranskat)abstract
- In chemical-looping combustion (CLC), an oxygen carrier provides lattice oxygen for complete combustion of a fuel for heat and power production. The reduced metal oxide is then oxidized in a separate reactor. The combustion products CO 2 and H 2 O are obtained in pure form, without any nitrogen in the gas. As no gas separation work is needed, this could be a breakthrough technology for carbon capture (CCS). Normally, the fuel- and air-reactor are designed utilizing inter-connected fluidized beds. The same underlying reversible redox reactions of CLC can be used for other fuel conversion technologies. These include fluidized bed processes for gas, solid and liquid fuels for heat, power, syngas or hydrogen production. Some of these concepts were suggested as far back as the 1950's, while others have just recently been proposed. This paper will provide a review of some recent developments with respect to CLC with gaseous, liquid and solid fuels, with focus on operational experience. Today, more than 35 continuous units have been used worldwide, with over 9000 h of operational time. Although most experience has been reported for methane and natural gas, significant testing has now also been performed with various solid fuels. Some recent developments include i) shift from Ni-based materials to more benign metal oxide oxygen carriers, ii) use of different types of biomass and iii) operation at semi-commercial scale. Furthermore, this paper will also provide an overview some related technologies which also utilize oxygen carriers in interconnected fluidized beds: i) Chemical-looping gasification (CLG), ii) Chemical-looping reforming (CLR) and iii) Chemical-looping tar reforming (CLTR). In these processes, a pure syngas/hydrogen can be produced effectively, which could be utilized for chemical or fuel production.
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| 7. |
- 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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| 8. |
- 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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| 9. |
- Cuadrat, Ana, 1982, et al.
(författare)
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Influence of limestone addition in a 10 kWth Chemical-Looping Combustion unit operated with petcoke
- 2011
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 25:10, s. 4818-4828
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Tidskriftsartikel (refereegranskat)abstract
- Ilmenite, a natural mineral composed of FeTiO3, is a low cost material suitable as oxygen-carrier for Chemical-Looping Combustion (CLC) with solid fuels. One option when using the CLC technology with solid fuels is to introduce the fuel directly into the fuel-reactor. There the fuel is gasified and volatiles and gasification products react with the oxygen-carrier. In this study the influence of limestone addition to ilmenite as oxygen-carrier was tested in a continuous 10 kWth CLC pilot for solid fuels. The fuel fed was a petcoke and the gasifying agent was steam. Tests with an ilmenite-limestone mixture as bed material were performed, and also tests using only ilmenite as bed material were carried out for comparison. Global solids circulation was varied as it is an important operational parameter, which determines the solid fuel residence time. The experiments were made at two fuel-reactor temperatures: 950ºC and 1000ºC. Generally, higher residence time of the fuel and higher temperature increased both gasification and combustion efficiencies. This was seen for both with and without limestone addition. The addition of limestone, gave a significant improvement of gas conversion at 950ºC, which could be explained by lime catalyzing the water-gas shift reaction. Moreover, the presence of limestone significantly increased the char conversion both at 950ºC and 1000ºC.
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| 10. |
- Gogolev, Ivan, 1984, et al.
(författare)
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Chemical-looping combustion in a 100 kW unit using a mixture of synthetic and natural oxygen carriers - Operational results and fate of biomass fuel alkali
- 2019
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 88, s. 371-382
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Tidskriftsartikel (refereegranskat)abstract
- Biomass fuel use in chemical looping combustion enables negative CO2 emissions through BECCS (Bio-Energy Carbon Capture and Storage). Effective biomass utilization in CLC requires an economical and effective oxygen carrier to achieve high fuel conversion, effective CO2 capture, and management of the harmful effects of biomass alkali release (bed agglomeration, oxygen carrier deactivation, fouling and corrosion). These issues were addressed in 100 kW CLC pilot experiments. Building on previous work, a mixture of a synthetic calcium manganite perovskite and natural ilmenite was used as the oxygen carrier. Four biomass fuels of varied alkali content were tested: black pellets of steam-exploded stem wood (BP), BP impregnated with K2CO3, a mixture of 50% BP with 50% straw pellets, and wood char. Experiments showed high fuel conversion and very high CO2 capture, with overall performance exceeding that of ilmenite and manganese ore. More than 95% gas conversion was achieved with black pellets at around 950 degrees C. The fate of biomass alkali, previously virtually unknown in CLC research, was explored by implementing online surface-ionization-based measurement of alkali released in the flue gases of the fuel reactor (FR) and air reactor (AR). Release levels were found to correlate with the fuel alkali content. The flue gas measurements and bed material elemental analyses suggest that most of the fuel alkali are accumulated in the oxygen carrier. Unexpectedly, it was found that flue gas alkali release occurs in both the FR and AR, with AR exhibiting an equal or higher rate of release vs. the FR.
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