| 1. |
- Stanicic, Ivana, 1994, et al.
(författare)
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Combined manganese oxides as oxygen carriers for biomass combustion — Ash interactions
- 2019
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Ingår i: Chemical Engineering Research and Design. - : Elsevier BV. - 0263-8762 .- 1744-3563. ; 149, s. 104-120
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 Institution of Chemical Engineers Carbon capture and storage (CCS) has been acknowledged as an important strategy for mitigation of climate change. Although highly applicable for fossil fuels, CCS with biomass could have the added advantage of resulting in negative emissions of carbon dioxide. One promising carbon capture technology is chemical-looping combustion (CLC). In CLC the reactors are filled with metal oxide bed material called oxygen carriers. Before CLC can be implemented for biomass combustion at a large scale, biomass ash components interaction with oxygen carriers needs to be further understood. Four combined manganese oxides Mn3O4-SiO2, Mn3O4-SiO2-TiO2, Mn3O4-Fe2O3 and Mn3O4-Fe2O3-Al2O3 were exposed to common biomass ash components K, Ca and P. The ash components can exist in many forms, but here the compounds CaCO3, K2CO3 and CaHPO4 were used. Exposures were performed at 900 °C for six hours in oxidising, reducing and inert conditions. Crystalline phases were analysed by XRD and morphology examined with SEM-EDX. Results show that oxygen carrier particles containing silicon were more likely to form agglomerates, especially in combination with potassium, whereas the particles including iron were more stable. MnFeAl was the oxygen carrier that showed least agglomerating behaviour while simultaneously showing a propensity to absorb some ash components. Some inconsistencies between thermodynamic predictions and experimental results is observed. This may be explained by lack of relevant data in the used databases, were only a few of the oxygen carrier-ash systems and subsystems have been optimised. Further optimisation related to manganese rich systems should be performed to obtain reliable results.
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| 2. |
- 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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| 3. |
- 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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| 4. |
- Mei, Daofeng, 1986, et al.
(författare)
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Investigation of LD-slag as oxygen carrier for CLC in a 10 kW unit using high-volatile biomasses
- 2023
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier Ltd. - 1750-5836 .- 1878-0148. ; 127
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Tidskriftsartikel (refereegranskat)abstract
- A steel slag from the Linz-Donawitz process, called LD-slag, having significant calcium and iron-fractions, was investigated as an oxygen carrier in a recently developed 10 kWth chemical-looping combustor with three high-volatile biomass fuels. In order to improve operability, the LD-slag was found to require heat-treatment at high temperatures before being used in the unit. In total, operation with the biomasses was conducted for more than 26 h at temperatures of 870–980 °C. The fuel thermal power was in the range of 3.4–10 kWth. The operation involved chemical looping combustion (CLC), chemical looping gasification (CLG) and oxygen carrier aided combustion (OCAC). Around 12 h was in CLC operation, 13.3 h was conducted in CLG-conditions, while the remaining 0.7 h was OCAC. Here, the results obtained during the CLC part of the campaign is reported. Increased temperature in the fuel reactor and higher airflows to the air reactor both lead to better combustion performance. Steam concentration in the fuel reactor has little effect on the performance. The LD-slag showed higher oxygen demand (31.0%) than that with ilmenite (21.5%) and a manganese ore (19.5%) with the same fuel and normal solids circulation. However, with the LD-slag, there is possibility to achieve a lower oxygen demand (15.2%) with high solids circulation. © 2023 The Author(s)
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| 5. |
- 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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| 6. |
- Stanicic, Ivana, 1994, et al.
(författare)
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Thermodynamic Analysis on the Fate of Ash Elements in Chemical Looping Combustion of Solid Fuels Iron-Based Oxygen Carriers
- 2022
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 36:17, s. 9648-9659
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Tidskriftsartikel (refereegranskat)abstract
- Chemical looping combustion (CLC) enables efficient combustion of hydrocarbon fuels while also producing a gas stream with high CO2 concentrations, suitable for carbon capture and storage (CCS). CLC of biomass in combination with CCS results in efficient removal of carbon dioxide from the atmosphere, i.e., negative emissions. However, biomass and waste-derived fuels can contain significant fractions of aggressive ash precursors, which can affect the operability and functionality of oxygen carriers. In this paper, the fate of common ash elements will be investigated thermodynamically in a system utilizing iron-based oxygen carriers: ilmenite and iron oxide. Multiphase, multicomponent equilibrium calculations were performed using databases from FACT and a user-defined database, with a specific focus on alkali (K and Na) and heavy metals (Cu, Zn, and Pb). A detailed and comprehensive comparison with available literature data from experimental investigations was performed, and compounds not available in the databases were identified. Due to a lack of thermodynamic data in the literature, thermodynamic properties for four compounds, K0.85Fe0.85Ti0.15O2, K0.4Fe0.4Ti0.6O2, KTi8O16, and KTi8O16.5, were obtained from first-principles calculations. The fate of ash elements is studied for CLC of three biomass and waste-derived solid fuels under relevant CLC conditions: 950 °C in the fuel reactor and 1050 °C in the air reactor. Results show that the choice of the oxygen carriers largely influences the behavior of the ash elements. Compared to CLC with iron oxide, ilmenite is more beneficial with respect to high-temperature corrosion since less potassium is released into the gas phase since the titanium content in ilmenite immobilizes both potassium and calcium. For both oxygen carriers, the most corrosive compounds are expected to leave with the gas in the fuel reactor, keeping the air reactor free from chlorides. It was found that the compound KTi8O16 is stable in reducing conditions and low potassium concentrations. This is in conformity with previous experimental data, where this phase has been identified in the interior of ilmenite particles used in oxygen carrier aided combustion of wood chips.
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| 7. |
- 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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| 8. |
- Kong, Xiangrui, et al.
(författare)
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Phase recognition in SEM-EDX chemical maps using positive matrix factorization
- 2023
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Ingår i: Methodsx. - 2215-0161. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Images from scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spec- troscopy (EDX) are informative and useful to understand the chemical composition and mixing state of solid materials. Positive matrix factorization (PMF) is a multivariate factor analysis tech- nique that has been used in many applications, and the method is here applied to identify factors that can describe common features between elemental SEM-EDX maps. The procedures of con- verting both graphics and digital images to PMF input files are introduced, and the PMF analysis is exemplified with an open-access PMF program. A case study of oxygen carrier materials from oxygen carrier aided combustion is presented, and the results show that PMF successfully groups elements into factors, and the maps of these factors are visualized. The produced images provide further information on ash interactions and composition of distinct chemical layers. The method can handle all types of chemical maps and the method is not limited solely to SEM-EDX although these images have been used as an example. The main characteristics of the method are:center dot Adapting graphics and digital images ready for PMF analysis.center dot Conversion between 1-D and 2-D datasets allows visualization of common chemical maps of elements grouped in factors.center dot Handles all types of chemical mappings and large data sets.
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| 9. |
- Hedayati, Ali, 1984, et al.
(författare)
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Experimental evaluation of manganese ores for chemical looping conversion of synthetic biomass volatiles in a 300 W reactor system
- 2021
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Ingår i: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437 .- 2213-2929. ; 9:2
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Tidskriftsartikel (refereegranskat)abstract
- Two manganese ores with different iron content were investigated as oxygen carriers for chemical looping conversion of simulated biomass volatiles. The aim was to study the performance of the oxygen carriers with regards to combustion and potential use for chemical-looping gasification of wood-based biomass. The oxygen carriers were studied in a 300 W chemical-looping reactor system with circulation of oxygen carriers between the fluidized air and fuel reactors. The temperature was 850-900 °C and the fuel flow rates were 0.6-3 Lmin-1. The Mn ore with higher iron content showed significant oxygen release at 900 °C under inert conditions, as well as full conversion of CO, H2 and methane at low fuel flow. The other Mn ore showed little methane conversion and poorer conversion of the other gases when compared at similar fuel flows. However, the gas composition attained was rather similar if compared for a similar overall gas conversion. Nonetheless, a slightly higher syngas fraction and H2 to CO ratio in the product stream was obtained with the Mn ore with lower iron content. In all cases the syngas fraction in the product gas increased with temperature and fuel flow. The formation of fines (attrition rate), particle size distribution, and the bulk density of the oxygen carriers were measured to evaluate their mechanical properties during chemical looping of biomass volatiles.
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| 10. |
- Hedayati, Ali, 1984, et al.
(författare)
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Thermochemical conversion of biomass volatiles via chemical looping: Comparison of ilmenite and steel converter waste materials as oxygen carriers
- 2022
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 313
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Tidskriftsartikel (refereegranskat)abstract
- Two oxygen carriers were tested with respect to chemical looping combustion (CLC) and chemical looping gasification (CLG). Ilmenite, a natural ore composed mainly of iron–titanium oxide, and LD Slag, an iron-based industrial waste, were investigated at 850 and 900 °C in a continuous operation in a 0.3 kW chemical-looping reactor system using synthetic biomass volatiles as fuel. CLC and CLG conditions were simulated in the fuel reactor by changing the fuel flow rates. In the case of ilmenite the syngas yield and methane conversion increased with fuel flow rate. Consequently, the syngas to hydrocarbon ratio was higher for ilmenite. Methane conversion improved for both tested oxygen carriers with increasing the operating temperature. Oxygen release was observed in the case of LD Slag. The H2/CO ratio was between 0.7 and 0.8 for both oxygen carriers at the higher fuel flows. With respect to CLC, ilmenite showed higher gas conversion than LD slag. Analysis of the particles revealed that ilmenite possessed better mechanical properties and formed less dust compared to LD Slag during the continuous operation with fuel.
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