Article Number 200601, May 2006

Evaporation and Combustion Characteristics of Biomass Vacuum Pyrolysis Oils.

M. Garcìa Pérez^1,5, P. Lappas², P. Hughes ², L. Dell², A. Chaala¹, D. Kretschmer³ & C. Roy^1,4

¹ Chemical Engineering Department,
Université Laval, Québec,
Canada

² Energy Research Laboratories,
CANMET, Ottawa,
Canada

³ Mechanical Engineering Department,
Université Laval, Québec,
Canada

⁴ Now at Pyrovac International,
Québec, Canada

⁵ Now at University of Georgia (See Below)

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ABSTRACT:

The evaporation behaviour at high heating rates of vacuum pyrolysis oils obtained from Softwood Bark Residue (SWBR) and from Hardwood Rich in Fibres (HWRF) was studied photographically at the CANMET laminar Entrained Flow Reactor (EFR). For low heating rates, the evaporation and combustion characteristics for each bio-oil were studied by observing the mass loss in pure nitrogen and in air using thermogravimetry. The bio-oil combustion process starts with the evaporation of light compounds followed by the pyrolysis of heavy fractions yielding charcoal. In the final step, the oxygen reacts with charcoal to yield ash. Tests in the EFR were performed using initial droplet diameters between 58 and 62 µm. These diameters fall within the range of sizes observed in SWBR bio-oil sprays. The droplets were generated in a piezo-electric droplet generator and injected into a quartz tube reactor placed inside the furnace. Two furnace wall temperatures (700 ^oC and 800 ^oC) were used during EFR experiments. For evaporation studies, the EFR was operated in an inert environment (using Ar) while for combustion studies various Ar-O2 mixtures were used (O2 concentration between 20 and 50 vol. %). The photographic results showed that the formation of bubbles inside bio-oil droplets was influenced by heat transfer rates. For the experimental conditions used, no micro-explosions were observed. The solid residues obtained at the furnace exit were collected and analysed by Scanning Electron Microscopy. Two different morphologies of residual particles were observed depending on the frequency of droplet generation: a) compact and mechanically resistant spheres obtained at low electrical pulse frequencies (less than 500 Hz) with typical diameters of 20-30 µm and b) fragile “glass like” cenospheres with thin walls and diameter between 60 and 90 µm obtained at higher droplet generation frequencies (more than 500 Hz).

Keywords:

Combustion, evaporation, droplets, bio-oils, pyrolysis.

Corresponding Author:

Manuel Garcìa - Pérez
University of Georgia
Biological and Agricultural Engineering Department
Driftmier Engineering Center
Athens, GA, 30602
USA

Phone: (706)-254-7704
FAX : (706)-542-8806

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