| 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. |
- 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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| 3. |
- Ge, Yaxin, 1992
(författare)
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Alkali Release and Effects on Biomass Thermal Conversion Processes
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High alkali content is an important feature of biomass, and it has a series of implications for thermal conversion processes. This thesis focuses on the release of alkali during various biomass thermal conversion processes, including biomass pyrolysis, char gasification, co-conversion of different types of biomass, and thermal conversion of biomass mixed with fresh and used bed materials. Alkali release is also studied in combination with fuel conversion, to elucidate the underlying relationships. In addition, particle release during steam gasification of char is investigated. The studies were carried out on different reactor scales, ranging from the micro scale to pilot scale. A reliable methodology for simultaneous monitoring of alkali release and sample mass was developed based on the application of a thermogravimetric analyzer in combination with a surface ionization detector (TGA-SID). Using TGA-SID, a significant level of alkali release was observed when wood char conversion approaches completion during CO2 gasification, while the level of alkali release from straw char decreased continuously throughout the process. Alkali migration from straw to wood was observed at temperatures above 600°C during co-pyrolysis, based on online alkali measurements. Positive and negative synergistic effects were observed during the co-gasification at low and high conversions of char, respectively. This is attributed to alkali and silicon migration from the straw to the wood. Fresh bed materials affect wood and straw char gasification reactivities and rates of alkali release, and different bed materials may play different roles. For example, an alkali-containing bed material can enhance char gasification in the initial stage, a Si-containing bed material inhibits char gasification and alkali release at high conversions of char, an Al-containing bed material can inhibit char conversion when the char has a high silicon content, and Mg- and Ca-containing bed materials ensure that alkali persists in releasable form, thus favoring substantial alkali release from the char. Used silicon bed material has a coating layer that is abundant in Ca, Si, K, and Mg. These elements can migrate to the char surface during thermal conversion processes and affect char gasification. In addition, a comprehensive system based on diluters, particle sizers, and SID has been successfully used for particle and alkali measurements in laboratory- and pilot-scale reactors. The laboratory-scale steam gasification system shows that the released levels of alkali and particles significantly increase when char conversion approaches completion. Using steam as the gasifying agent instead of CO2 results in a higher level of alkali release during most of the gasification stage. Aerosol particles are also released during steam gasification, at rates that vary by more than one order of magnitude depending on the char composition. The present study improves our understanding of alkali release, migration, and reaction during biomass thermal conversion processes. The acquired fundamental knowledge can be used for reactor design, co-gasification optimization, and selection of bed materials.
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| 4. |
- Ge, Yaxin, 1992, et al.
(författare)
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Effect of fresh bed materials on alkali release and thermogravimetric behavior during straw gasification
- 2023
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 336
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Tidskriftsartikel (refereegranskat)abstract
- Alkali-associated problems are key issues for the efficient use of straw that is available as a major renewable energy resource worldwide. The effects of six bed materials commonly used in fluidized bed reactors on straw pyrolysis and char gasification were evaluated using online monitoring of alkali release and thermogravimetric analysis. Scanning electron microscopy with energy dispersive spectroscopy was used to determine the elemental composition of the char surface. In the straw pyrolysis stage, alkali release is reduced by the addition of dolomite and silica due to alkali adsorption on the bed materials, and enhanced by the addition of alumina because of its high sodium content. In the char gasification stage, silica, sea sand, olivine, and ilmenite reduce the char reactivity and alkali release, which is attributed to transfer of Si and Ti from the bed materials to the char and reaction with alkali to form stable and catalytically inactive compounds. Alumina also reduces the char conversion rate by transfer of Al to the char and formation of K-Al-Si and Ca-Al-Si compounds, while alkali release from the straw and alumina blend remains high due to the high Na content in alumina. Dolomite initially appears to increase the char gasification reactivity, but the results are affected by conversion of volatile matter that deposited on the dolomite in the straw pyrolysis stage. Dolomite also significantly increases the alkali release, which is attributed to Ca reactions with aluminosilicate compounds that allow potassium to remain in volatile form. Fresh bed materials are concluded to have significant effects on straw conversion depending on their chemical composition, and the results can contribute to the understanding required for efficient use of straw in commercial applications of biomass thermochemical conversion.
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| 5. |
- Ge, Yaxin, 1992, et al.
(författare)
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Emission Characteristics of NOx and SO2 during the Combustion of Antibiotic Mycelial Residue
- 2022
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Ingår i: International Journal of Environmental Research and Public Health. - : MDPI AG. - 1661-7827 .- 1660-4601. ; 19:3
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Tidskriftsartikel (refereegranskat)abstract
- The antibiotic mycelial residue (AMR) generated from cephalosporin C production is a haz-ardous organic waste, which is usually disposed of by landfilling that causes potential secondary environmental pollution. AMR combustion can be an effective method to treat AMR. In order to develop clean combustion technologies for safe disposal and energy recovery from various AMRs, the emission characteristics of NOx and SO2 from AMR combustion were studied experimentally in this work. It was found that the fuel-N is constituted by 85% protein nitrogen and 15% inorganic nitrogen, and the fuel-S by 78% inorganic sulfur and 22% organic sulfur. Nitrogen oxide emissions mainly occur at the volatile combustion stage when the temperature rises to 400◦C, while the primary sulfur oxide emission appears at the char combustion stage above 400◦C. Increasing the combustion temperature and airflow cause higher NOx emissions. High moisture content in AMR can significantly reduce the NOx emission by lowering the combustion temperature and generating more reducing gases such as CO. For the SO2 emission, the combustion temperature (700 to 900◦C), airflow and AMR water content do not seem to exhibit obvious effects. The presence of CaO significantly inhibits SO2 emission, especially for the SO2 produced during the AMR char combustion because of the good control effect on the direct emission of inorganic SO2. Employing air/fuel staging technologies in combination with in-situ desulfurization by calcium oxide/salts added in the combustor with operation temperatures lower than 900◦C should be a potential technology for the clean disposal of AMRs. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
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| 6. |
- Ge, Yaxin, 1992, et al.
(författare)
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Impacts of fresh bed materials on alkali release and fuel conversion rate during wood pyrolysis and char gasification
- 2023
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 353
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Tidskriftsartikel (refereegranskat)abstract
- Bed materials provide efficient heat transfer and catalytic function in the thermochemical conversion of biomass, but their interactions with the fuel remain incompletely understood. In this study, the effects of bed materials on alkali release and fuel conversion during wood pyrolysis and CO2 gasification are investigated by online alkali detection combined with thermogravimetric analysis. The investigated bed materials include silica, sea sand, alumina and the natural ores olivine, ilmenite and dolomite. Only dolomite has a significant effect on fuel mass loss and alkali release during wood pyrolysis, while all bed materials influence char reactivity and alkali release during gasification. Sea sand, alumina and dolomite enhance the char gasification during the whole or most of the gasification process, which is related to alkali migration from the bed materials. All bed materials affect char reactivity and alkali release when the conversion approaches completion, and small amounts of some bed materials reduce the alkali release by an order of magnitude. The findings can be understood based on the chemical composition of the different materials. Silicon-rich materials reduce the levels of catalytically active alkali by formation of stable alkali silicates, and a similar explanation applies for ilmenite that captures alkali efficiently. Magnesium and calcium in contrast promote alkali release through their influence on alkali silicate chemistry. Analysis of char surfaces using scanning electron microscopy with energy dispersive spectroscopy indicates that low amounts of several elements are transferred from the bed material to the char where they may be directly involved in the char conversion process. The transferred elements are specific for each bed material and relates to their chemical composition. Mechanisms for material exchange between bed material and char are discussed.
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| 7. |
- Ge, Yaxin, 1992, et al.
(författare)
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Online monitoring of alkali release during co-pyrolysis/gasification of forest and agricultural waste: Element migration and synergistic effects
- 2023
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Ingår i: Biomass and Bioenergy. - : Elsevier BV. - 0961-9534 .- 1873-2909. ; 172, s. 106745-106745
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Tidskriftsartikel (refereegranskat)abstract
- Fuel blends may be used to meet several operational needs in thermal conversion of biomass waste, including optimization of ash properties and fuel conversion efficiency. In this study, online alkali measurements using surface ionization are employed to study synergistic effects produced by inorganic elements during co-pyrolysis/gasification of wood and straw waste. Synergistic effects on the fuel conversion behavior are not observed during co-pyrolysis, while alkali migration from straw to wood is clearly observed above 600 °C by online alkali monitoring. In contrast, synergistic effects on char conversion and alkali release are substantial during co-gasification. Positive effects on char reactivity during most of the gasification process are attributed to alkali migration from the straw to the wood char, and the most pronounced effect occurs at a gasification temperature of 900 °C and a straw content of 25%. Negative effects on char reactivity are observed at the final gasification stage, which is associated with a significantly reduced alkali release from fuel blends compared to pure wood char. The effect is attributed to the migration of silicon, phosphorus, and aluminum to the wood char, as revealed by scanning electron microscopy with energy dispersive spectroscopy, where the elements react with alkali to form catalytically inactive compounds. The mixing of biofuels is concluded to result in substantial effects on the fuel conversion efficiency, which should be taken into consideration in thermochemical conversion of biomass.
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| 8. |
- Ge, Yaxin, 1992, et al.
(författare)
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Real-time monitoring of alkali release during CO2 gasification of different types of biochar
- 2022
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 327
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Tidskriftsartikel (refereegranskat)abstract
- Potassium and sodium compounds play both positive and negative roles during biomass gasification, but the detailed behavior of alkali metal compounds remain incompletely understood. In this study, alkali release during CO2 gasification of biochar is characterized online with a surface ionization method in combination with thermogravimetric analysis of the char samples undergoing gasification. For wood chars, the alkali release rate follows a slowly decreasing trend as the char conversion proceeds, but increases by up to two orders of magnitude when the conversion approaches completion. In contrast, the alkali release from straw char is 40-50 times higher than observed for wood char and decreases continuously during the whole gasification process. A high temperature and a high CO2 concentration enhance both alkali release and char reactivity. The char preparation method also influences the alkali release from pine char, while the char reactivity is less affected. Alkali release and char reactivity are linked, but other factors including mineral content, surface area and char structure may play important roles for the observed reactivity. The results provide a basis for understanding of alkali behavior during gasification and may help optimize catalytic effects and reduce detrimental issues in biomass gasification.
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