| 1. |
- Andersson, Viktor, 1994, et al.
(författare)
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A Novel Method for On-Line Characterization of Alkali Release and Thermal Stability of Materials Used in Thermochemical Conversion Processes
- 2022
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 15:12
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Tidskriftsartikel (refereegranskat)abstract
- Alkali metal compounds are released during the thermal conversion of biofuels and fossil fuels and have a major impact on the efficiency of conversion processes. Herein, we describe a novel method for the simultaneous characterization of alkali release and mass loss from materials used in combustion and gasification processes including solid fuels, fluidized bed materials, and catalysts for gas reforming. The method combines the thermogravimetric analysis of selected samples with the on-line measurement of alkali release using a surface ionization detector. The technique builds on the careful treatment of alkali processes during transport from a sample to the downstream alkali monitor including the losses of alkali in the molecular form to hot walls, the formation of nanometer-sized alkali-containing particles during the cooling of exhaust gases, aerosol particle growth, and diffusion losses in sampling tubes. The performance of the setup was demonstrated using biomass samples and fluidized bed material from an industrial process. The emissions of alkali compounds during sample heating and isothermal conditions were determined and related to the simultaneous thermogravimetric analysis. The methodology was concluded to provide new evidence regarding the behavior of alkali in key processes including biomass pyrolysis and gasification and ash interactions with fluidized beds. The implications and further improvements of the technique are discussed.
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| 2. |
- Andersson, Viktor, 1983, et al.
(författare)
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Alkali desorption from ilmenite oxygen carrier particles used in biomass combustion
- 2024
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Ingår i: Fuel. - 0016-2361 .- 1873-7153. ; 359
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen-carrying fluidized bed materials are increasingly used in novel technologies for carbon capture and storage, and to improve the efficiency of fuel conversion processes. Potassium- and sodium-containing compounds are released during biomass combustion and may have both negative and positive effects on conversion processes. Ilmenite is an important oxygen carrier material with the ability to capture alkali in the form of titanates. This is a desirable property since it may reduce detrimental alkali effects including fouling, corrosion, and fluidized bed agglomeration. This study investigates the interactions of alkali-containing compounds with ilmenite particles previously used in an industrial scale (115 MWth) oxygen carrier aided combustion system. The ilmenite samples were exposed to temperatures up to 1000 °C under inert and oxidizing conditions while the alkali release kinetics were characterized using online alkali monitoring. Alkali desorption occurs between 630 and 800 °C, which is attributed to loosely bound alkali at or near the surface of the particles. Extensive alkali release is observed above 900 °C and proceeds during extended time periods at 1000 °C. The release above 900 °C is more pronounced under oxidizing conditions and approximately 9.1 and 3.2 wt% of the alkali content is emitted from the ilmenite samples in high and low oxygen activity, respectively. Detailed material analyses using scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were conducted before and after temperature treatment, which revealed that the concentrations of potassium, sodium and chlorine decrease at the outermost surface of the ilmenite particles during temperature treatment, and Cl is depleted to a deeper level in oxidizing conditions compared to inert. The implications for ilmenite-ash interactions, oxygen carrier aided combustion and chemical looping systems are discussed.
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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- Andersson, Viktor, 1983, et al.
(författare)
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Gaseous alkali interactions with ilmenite, manganese oxide and calcium manganite under chemical looping combustion conditions
- 2024
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Ingår i: Fuel Processing Technology. - 0378-3820 .- 1873-7188. ; 254
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Tidskriftsartikel (refereegranskat)abstract
- Alkali species present in biomass pose significant challenges in chemical looping combustion (CLC) processes and other thermal conversion applications. The interactions between different alkali species and three common oxygen carrier (OC) materials that are considered to be state of the art in CLC applications have been investigated. A dedicated fluidized bed laboratory reactor was used to study interactions of KCl, NaCl, KOH, NaOH, K2SO4 and Na2SO4 with manganese oxide, calcium manganite and ilmenite. Alkali vapor was generated by injecting alkali salts under reducing, oxidizing and inert conditions at 900 °C. Gaseous species were measured online downstream of the reactor, and the efficiency of alkali uptake was determined under different conditions. The result show significant alkali uptake by all OCs under the studied conditions. Ilmenite shows near complete alkali uptake in reducing conditions, while manganese oxide and calcium manganite exhibited less effective alkali uptake, but have advantages in terms of fuel conversion and oxidizing efficiency. Alkali chlorides, sulfates and hydroxides show distinctly different behavior, with alkali hydroxides being efficiently captured all three investigate OC materials. The findings contribute to a deeper understanding of alkali behavior and offer valuable guidance for the design and optimization of CLC with biomass.
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| 7. |
- Andersson, Viktor, 1994, et al.
(författare)
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Online Speciation of Alkali Compounds by Temperature-Modulated Surface Ionization: Method Development and Application to Thermal Conversion
- 2024
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Ingår i: ENERGY & FUELS. - 0887-0624 .- 1520-5029. ; 38:3, s. 2046-2057
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Tidskriftsartikel (refereegranskat)abstract
- A novel method for online speciation of potassium- and sodium-containing compounds has been described and demonstrated. The method is based on a temperature-modulated surface ionization (TMSI) technique and may be used to determine the concentrations of alkali chlorides, hydroxides, carbonates, and sulfates in high-temperature processes. The measurement device is a further development of a surface ionization detector (SID) commonly used for online alkali measurements in combustion, gasification, and pyrolysis research. Discrimination between sodium and potassium compounds is made possible by differences in their aerosol evaporation characteristics as a function of temperature combined with the desorption kinetics of alkali on a hot platinum filament. The method is evaluated in laboratory experiments with known alkali salt concentrations. An experimental procedure where the platinum filament in the SID is regularly shifted between three temperatures is concluded to provide sufficient selectivity and time resolution for common applications. The TMSI method is successfully applied to characterize the emission of alkali compounds during pyrolysis of pine wood. The emissions during low-temperature pyrolysis are dominated by KOH, while similar amounts of KOH and NaOH are subsequently emitted from the remaining char and ash. The ability of real-time characterization of individual sodium and potassium compounds opens up new means to understand and optimize solid fuel conversion of common fuels such as low-grade biomass, waste, and coal.
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| 8. |
- Bartels-Rausch, T., et al.
(författare)
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Interfacial supercooling and the precipitation of hydrohalite in frozen NaCl solutions as seen by X-ray absorption spectroscopy
- 2021
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Ingår i: Cryosphere. - : Copernicus GmbH. - 1994-0416. ; 15:4, s. 2001-2020
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Tidskriftsartikel (refereegranskat)abstract
- Laboratory experiments are presented on the phase change at the surface of sodium chloride-water mixtures at temperatures between 259 and 241 K. Chloride is a ubiquitous component of polar coastal surface snow. The chloride embedded in snow is involved in reactions that modify the chemical composition of snow as well as ultimately impact the budget of trace gases and the oxidative capacity of the overlying atmosphere. Multiphase reactions at the snow-air interface have been of particular interest in atmospheric science. Undoubtedly, chemical reactions proceed faster in liquids than in solids; but it is currently unclear when such phase changes occur at the interface of snow with air. In the experiments reported here, a high selectivity to the upper few nanometres of the frozen solution-air interface is achieved by using electron yield near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy. We find that sodium chloride at the interface of frozen solutions, which mimic sea-salt deposits in snow, remains as supercooled liquid down to 241 K. At this temperature, hydrohalite exclusively precipitates and anhydrous sodium chloride is not detected. In this work, we present the first NEXAFS spectrum of hydrohalite. The hydrohalite is found to be stable while increasing the temperature towards the eutectic temperature of 252 K. Taken together, this study reveals no differences in the phase changes of sodium chloride at the interface as compared to the bulk. That sodium chloride remains liquid at the interface upon cooling down to 241 K, which spans the most common temperature range in Arctic marine environments, has consequences for interfacial chemistry involving chlorine as well as for any other reactant for which the sodium chloride provides a liquid reservoir at the interface of environmental snow. Implications for the role of surface snow in atmospheric chemistry are discussed. © 2021 BMJ Publishing Group. All rights reserved.
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| 9. |
- Ding, Saiman, et al.
(författare)
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Time-resolved alkali release during steam gasification of char in a fixed bed reactor
- 2024
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 356, s. 129528-
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Tidskriftsartikel (refereegranskat)abstract
- In this study time-resolved char conversion and alkali release under steam gasification conditions were investigated using a fixed bed reactor. The behaviour of an industrial char and chars produced from straw and furniture waste was investigated. For woody chars, an increase in gasification reactivity is observed together with a notable alkali release as the gasification approaches completion (degree of conversion > 0.8). In contrast, straw char exhibited a decrease in conversion rate and alkali release throughout the gasification process, attributed to the formation of catalytically inactive potassium silicates inhibiting the catalytic role of alkali. Aerosol particles in the 0.01–22 µm size range are emitted during the char conversion. A fraction is formed by nucleation of alkali compounds and other condensable gases. A wide particle distribution that extends over the whole size range is also observed, and the particles are likely to consist of solid char fragments. The study concludes on the importance of alkali release, illustrating the difference in alkali release pattern for high and low ash char.
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| 10. |
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