Parametric study of pilot-scale biomass torrefaction Martin
Nordwaeger, Ingemar Olofsson, Katarina Hkansson, Linda Pommer,
Susanne Wiklund Lindstrm, Anders Nordin Energy Technology and
Thermal Process Chemistry, Ume University Energy Technology and
Thermal Process Chemistry Ume University SE-901 87 Ume, Sweden
Phone: +46 (0)70-239 26 91 E-Post: [email protected]
Results The torrefaction temperature generally effected the results
more than the torrefaction time. The results also show that HHV,
LHV, carbon and klason lignin increased with increased degree of
torrefation. On the other hand, hydrogen, oxygen, volatiles,
massyield, energy yield, extractives, xylose, manose, galactose,
arabinose, and hemicellulose decreased with an increasing degree of
torrefaction. Ash, glucose and cellulose were not effected with
increased degree of torrefaction (Figure 2). Hydrophobicity
measurements indicated that the torrefied fuel absorbed less
moisture and dried faster than the raw biofuel after one month of
outdoor storage in pooring rain (Figure 3). Additional proofs of
hydrophobicity in torrefied fuel could be seen by the differences
in contact angle between the raw biofuel and the torrefied biofuel
(Figure 4). Energy consumption during grinding is another important
property for biofuels. In Figure 5 it is seen that torrefaction
will reduce electricity consumption by at least 80%. Background
Biomass is a widespread source of renewable energy, and has the
potential to play a significant role in the energy conversion
decreasing the fossil fuel dependency. However, a number of fuel
characteristic properties could be significantly improved. The
pretreatment method torrefaction significantly decreases; bulk
volume, water affinity, risk of bio contamination, and increases
heating value, homogeneity and ease of grinding and feeding.
Torrefaction is a mild thermal process requiring an inert
environment and low temperatures typically ranging from 220 to
300C, which cost efficiently facilitate the above fuel quality
improvement. Figure 1. Pilot-scale torrefaction facility Figure 5.
Grinding energy demand for different torrefied biomass samples.
Method The torrefaction experiments were carried out in BioEndevs
pilot-scale torrefaction facility located at BTC in Ume, Sweden
(Figure 1). The maximum capacity is 30 kg biomass per hour, and it
is specially designed with maximum flexibility and control
possibilities to allow for parametric torrefaction and pyrolysis
studies. After torrefaction, the product material is rapidly
quenched by an indirectly cooled screw and is collected for further
analysis. Wood chips from small birch trees in the Vsterbotten
region was used as the feedstock for torrefaction. By
systematically varying torrefaction time and temperature, different
degrees of torrefied fuel was obtained. The material was classified
as low, medium and high degree of torrefied wood chips. The
responses mass yield, energy yield, hydrophobicity, composition of
solid residue, HHV, LHV, milling cost, sugars, klason lignin,
cellulose and hemicellulose was measured on the raw and the
torrefied biofuel for statistical evaluation. Increase with
torrefaction Decrease with torrefaction HHV LHV Carbon Klason
lignin Hydrogen Oxygen Volatiles Massyield Energy yield Extractives
Xylose Manose Galactose Arabinose Hemicellulose
Ash-Glucose-Cellulose No effect Wood ChipsTorrefied Wood Chips
Objective To evaluate the effect on mass yield, energy yield,
hydrophobicity, composition of solid residue, heating value,
milling cost, klason lignin, sugars, cellulose and hemicelulose
when varying the degree of torrefaction Untreated biofuelTorrefied
biofuel Low Medium High Raw Figure 2. Effects on some of the many
analyzed responses Figure 3. Drying pattern for wood chip piles
(torrefied and raw) after being exposed to simulated rain fall.
Figure 4. Contact angle for raw biofuel and for all different
degrees of torrefaction. Conclusions The parameter study proved the
concept of torrefied biomass as an efficient measure to obtain
improved product properties, for example increased hydrophobicity,
grindabity and heating value. low value heat via process
integration further refinement Biomass Torrefied biomass powder
Large bulk volume Wet, high wettability Expensive grinding Non
feedable Low energy content Inhomogeneous Risk of bio contamination
Torr e Torrefaction High density, densification Dry and hydrophobic
Low grinding costs Feedable (spheric particles) Higher energy
density improved logistics Homogeneous No bio contamination
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