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Physical and Chemical Characterization of Aerosol Particles Formed during the Thermochemical Conversion of Wood Pellets Using a Bubbling Fluidized Bed Gasifier
Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Bioenergi. (Bioenergiteknik)
Linnaeus University, Faculty of Science and Engineering, School of Engineering. (Bioenergiteknik)
Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Bioenergi.
2007 (English)In: Energy Fuels, ISSN 0887-0624, Vol. 21, no 6, p. 3660-3667Article in journal (Refereed) Published
Abstract [en]

Product gas obtained through biomass gasification can be upgraded to hydrogen-rich synthesis gas. The synthesis gas can be further converted to liquid or gaseous fuels. However, the raw product gas contains both gas- and particle-phase impurities that can negatively affect both catalysts and hot-gas filters used for upgrading and cleaning. The present study aimed to characterize, both physically and chemically, aerosol particles formed during the steam- and oxygen-blown biomass gasification of wood pellets in an atmospheric 20 kW bubbling fluidized bed (BFB) gasifier. The product gas from the gasifier was sampled upstream from the cyclone at 500 °C. The particle number size distribution determined using a scanning mobility particle sizer (SMPS) was bimodal, with modes at 20–30 and 400 nm, mobility equivalent diameters (dB). The total mean number concentration of particles with dB = 15–670 nm was approximately 7 × 10^5 particles/cm3; however, the concentration of particles with dB < 80 nm fluctuated. The particle mass size distribution determined using a low-pressure impactor (LPI) was bimodal, and the total mass concentration of particles with aerodynamic diameters (dae) < 5 µm was 310 mg/m3. Microscopy analysis of particulate matter on the lower LPI stages, expected to sample particles with dae < 0.4 µm, revealed structures approximately 10 µm in diameter. In addition, the mass concentration of particles with dae < 0.5 µm determined using a LPI was higher than that estimated using a SMPS, possibly because of the bounce-off or re-entrainment of coarser particles from higher LPI stages. Elementary analysis of the particulate matter indicated that it was dominated by carbon. The collected particulate matter was stable when heated in nitrogen to 500 °C, indicating that the carbon was not present as volatile tars but more likely as char or soot. The particulate matter collected on all LPI stages contained a small percentage of ash (noncarbonaceous inorganic material), with calcium as the dominant element.

Place, publisher, year, edition, pages
American Chemical Society, Washington DC , 2007. Vol. 21, no 6, p. 3660-3667
Research subject
Technology (byts ev till Engineering), Bioenergy Technology
Identifiers
URN: urn:nbn:se:vxu:diva-2764DOI: doi:10.1021/ef7002552OAI: oai:DiVA.org:vxu-2764DiVA, id: diva2:202720
Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2011-04-27Bibliographically approved
In thesis
1. Characterization of particulate matter from atmospheric fluidized bed biomass gasifiers
Open this publication in new window or tab >>Characterization of particulate matter from atmospheric fluidized bed biomass gasifiers
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Through biomass gasification, biomass can be converted at high temperature to a product gas rich in carbon monoxide, hydrogen, and methane. After cleaning and upgrading, the product gas can be converted to biofuels such as hydrogen; methanol; dimethyl ether; and synthetic diesel, gasoline, and natural gas. Particulate matter (PM) is formed as a contaminant in the gasification process, and the aim of this work was to develop and apply a method for sampling and characterization of PM in the hot product gas.

 

A particle measurement system consisting of a dilution probe combined in series with a bed of granular activated carbon for tar adsorption was developed, with the aim of extracting a sample of the hot product gas without changing the size distribution and composition of the PM. The mass size distribution and concentration, as well as the morphology and elementary composition, of PM in the size range 10 nm to 10 µm in the product gas from a bubbling fluidized bed (BFB) gasifier, a circulating fluidized bed (CFB) gasifier and an indirect BFB gasifier using various types of biomass as fuel were determined.

 

All gasifiers and fuels displayed a bimodal particle mass size distribution with a fine mode in the <0.5 µm size range and a coarse mode in the >0.5 µm size range. Compared with the mass concentration of the coarse mode the mass concentration of the fine mode was low from all gasifiers. The evaluation of the results for the fine-mode PM was complicated by condensing potassium chloride for the CFB gasifier when using miscanthus as fuel and by condensing tars for the indirect BFB gasifier when using wood C as fuel. The mass concentration of the coarse-mode PM was higher from the CFB gasifier than from the two BFB gasifiers. The coarse-mode PM from the BFB gasifier when using wood A as fuel was dominated by char. In the CFB gasifier the coarse-mode PM was mainly ash and bed material when using all fuels. The coarse-mode PM from the indirect BFB gasifier when using wood C as fuel was mainly ash.

Place, publisher, year, edition, pages
Växjö, Kalmar: Linnaeus University Press, 2011
Series
Linnaeus University Dissertations ; 50/2011
Keywords
biomass gasification, fluidized bed, particulate matter, particle morphology, particle elementary composition
Research subject
Technology (byts ev till Engineering), Bioenergy Technology
Identifiers
urn:nbn:se:lnu:diva-11473 (URN)978-91-86491-80-2 (ISBN)
Public defence
2011-05-27, Wicksell, Linnéuniversitetet, 351 95 Växjö, Växjö, 10:00 (English)
Opponent
Supervisors
Available from: 2011-04-27 Created: 2011-04-27 Last updated: 2011-05-02Bibliographically approved

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Gustafsson, EvaStrand, MichaelSanati, Mehri

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