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- Gall, Dan, et al.
(författare)
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Online Measurements of Alkali and Heavy Tar Components in Biomass Gasification
- 2017
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 31:8, s. 8152-8161
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Tidskriftsartikel (refereegranskat)abstract
- Tar and alkali metal compounds are released during biomass gasification and have a major impact on the operation and performance of gasification processes. Herein we describe a novel method for characterization of alkali and heavy tar compounds in the hot product gas formed during gasification. Gas is continuously extracted, cooled and diluted, which results in condensation of tar and alkali into aerosol particles. The thermal stability of these particles is subsequently evaluated using a volatility tandem differential mobility analyzer (VTDMA) method. The technique is adopted from aerosol science where it is frequently used to characterize the thermal properties of aerosol particles. Laboratory studies show that pure and mixed alkali salts and organic compounds evaporate in well-defined temperature ranges, which can be used to determine the chemical composition of particles. The performance of the VTDMA is demonstrated at a 4 MWth dual fluidized bed gasifier using two different types of online sampling systems. Alkali metal compounds and a wide distribution of heavy tar components with boiling points above 400°C are observed in the product gas. Implications and potential further improvements of the technique are discussed.
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| 5. |
- Moradian, Farzad, 1981-, et al.
(författare)
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Thermodynamic equilibrium prediction of bed agglomeration tendency in dual fluidized-bed gasification of forest residues
- 2016
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Ingår i: Fuel processing technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 154, s. 82-90
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Tidskriftsartikel (refereegranskat)abstract
- Dual fluidized-bed (DFB) gasification is one of the recently developed technologies for production of heat, power, transportation fuels and synthetic chemicals through steam gasification of biomass. Bed agglomeration is a serious ash-related problem that should be taken into account when biomass-based fuels are selected for fluidized-bed gasification and combustion. This study developed a thermodynamic equilibrium model to assess the risk of bed agglomeration in gasification and combustion reactors of a DFB gasifier using biomass (forest residues) as feedstock. The modelling approach combined thermodynamic equilibrium calculations with chemical fractionation technique to predict the composition and melting behaviour of the fuel-derived ash as well as bed particles coating layer in the gasification and combustion reactors. FactSage was employed for the thermodynamic equilibrium calculations. The modelling results were then compared with experimental data obtained from a full-scale DFB gasifier to estimate the reliability and validity of the predictive model. In general, a good agreement was found between the modelling results and experimental observations. For the forest residues as feedstock and olivine as bed material, the modelling results indicate a low risk of bed agglomeration in the DFB gasifier, as long as the dominant temperature in the combustion zone is below 1020 °C. In contrast, quartz as bed material in the DFB gasifier was shown to significantly increase the risk of bed agglomeration through coating-induced agglomeration mechanism.
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| 8. |
- Svenson, Jenny, 1975, et al.
(författare)
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Fast pyrolysis of the main components of birch wood
- 2004
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 176:5-6, s. 977-990
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Tidskriftsartikel (refereegranskat)abstract
- The pyrolysis kinetics of cellulose, birch hemicellulose, and birch lignin are studied in a single particle reactor under inert atmosphere. Experiments are carried out with samples of 1-5 mg and mass loss data are measured at constant reactor temperature in the range 225-650degreesC. Arrhenius parameters are determined and are comparable with previous studies. The char yield for cellulose, hemicellulose, and lignin is about 5, 10, and 15%, respectively, at temperatures above 400degreesC. Calculations, where the results for the three independent materials are added together in the proportions of birch wood, give good agreement with birch wood data. This supports the assumption that the three materials act independently during pyrolysis. The results also indicate that above 400degreesC 70% of the char formed during birch wood pyrolysis originates from hemicellulose. visual observations show that lignin melts and boils at high temperatures, whereas hemicellulose expands considerably during the pyrolysis process.
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| 9. |
- Tchoffor Atongka, Placid, 1981, et al.
(författare)
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Influence of Fuel Ash Characteristics on the Release of Potassium, Chlorine, and Sulfur from Biomass Fuels under Steam-Fluidized Bed Gasification Conditions
- 2016
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Ingår i: Energy & Fuels. - : American Chemical Society. - 0887-0624 .- 1520-5029. ; 30:12, s. 10435-10442
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Tidskriftsartikel (refereegranskat)abstract
- Steam-fluidized bed gasification of biomass, which produces combustible gases from which transportation fuels can be synthesized, is a promising option for replacing the use of fossil fuels in the transportation sector. Similar to other thermal conversion processes, the release of potassium (K), chlorine (Cl), and sulfur (S) from biomass fuels to the gas phase during this process may be conducive to ash-related problems. Catalytic tar and char conversion by K has also been observed. In addition to operational conditions, the extent to which these elements are released to the gas phase may be affected by fuel ash characteristics such as the ash composition and the speciation (or association) of ash-forming elements in the fuel matrix. In the present work, the influence of these fuel ash characteristics on the extent to which K, Cl, and S are released from biomass fuels to the gas phase was studied under steam-fluidized bed gasification. The aim was to assess whether these fuel ash characteristics provide information that could be useful in making a quick judgment as to what extent K, Cl, and S would be released to the gas phase. To this end, the release of K, Cl, and S from forest residues and wheat straw during devolatilization and steam gasification of the char was quantified in a laboratory-scale bubbling fluidized bed reactor. The speciation of these elements in the virgin fuels was studied with chemical fractionation. The results reveal that the extent to which S is released from biomass fuels to the gas phase mainly depends on its speciation in the fuel matrix. While both the ash composition (mainly the Cl/K molar ratio) of the fuel and the speciation of K in the fuel matrix are relevant for the release of K, they appear to be unimportant with respect to the release of Cl.
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