Today a new paper (Article Number 200601, May 2006) has been published in the IFRF Combustion Journal (http://www.journal.ifrf.net), entitled:
Evaporation and Combustion Characteristics of Biomass Vacuum Pyrolysis Oils
by: M. Garcìa – Pèrez, P. Lappas, P. Hughes, L. Dell, A. Chaala, D. Kretschmer and C. Roy
Manuel Garcìa – Pérez
University of Georgia
Biological and Agricultural Engineering Department
Driftmier Engineering Center
Athens, GA, 30602
FAX : (706)-542-8806
In this paper the results of droplet vaporization and combustion studies of pyrolysis oils from softwood bark residue and hardwood are discussed. The techniques used include a TGA and an entrained flow reactor (drop tube furnace) to study the mechanisms involved in the combustion of these liquids in an atomized type flame. These pyrolysis oils typically consist of an emulsion of waxy-like “crystals” in an oily matrix. The unique feature of this work is that the vaporization and combustion properties are studied for fine droplet sizes of these oils (54 – 60 µm). Because of the nature of these oils it is difficult to generate consistent droplets of the sizes found in atomization sprays for single droplet studies. The results presented here will assist in the understanding and modeling of pyrolysis oil combustion.
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).
Combustion, evaporation, droplets, bio-oils, pyrolysis.
The full paper may be downloaded from the server, in the “New Papers” section (http://www.journal.ifrf.net/articles.html), by clicking on the Acrobat PDF icon alongside the title.
Publication in the Journal
The Editor-in-Chief would like to remind all potential authors that publication in the Journal is open to all. If you have interesting results to publish in the field of, or related to, industrial combustion, we invite you to prepare a paper according to the guidelines given in the Author’s Guide on the website (http://www.journal.ifrf.net/).
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