Transcript PowerPoint-presentation

Parametric study of pilot-scale biomass
torrefaction
Martin Nordwaeger, Ingemar Olofsson, Katarina Håkansson, Linda Pommer,
Susanne Wiklund Lindström, Anders Nordin
Energy Technology and Thermal Process Chemistry, Umeå University
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.
Untreated biofuel
Torrefied biofuel
Results
Problems
Solved!
Large bulk volume
Wet, high wettability
Expensive grinding
Non feedable
Low energy content
Inhomogeneous
Risk of bio contamination
High density, densification
Dry and hydrophobic
Low grinding costs
Feedable (spheric particles)
Higher energy density –
improved logistics
Homogeneous
No bio contamination
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).
further refinement
Torrefied biomass powder
Biomass
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
HHV
LHV
Carbon
Klason lignin
Ash-Glucose-Cellulose
No effect
Decrease with torrefaction
low value heat via
process integration
Increase with torrefaction
Torrefaction is a mild thermal process requiring an inert environment and low temperatures typically ranging from 220 to 300°C, which cost efficiently facilitate the above fuel quality
improvement.
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%.
Hydrogen
Oxygen
Volatiles
Massyield
Energy yield
Extractives
Xylose
Manose
Galactose
Arabinose
Hemicellulose
Figure 2. Effects on some of
the many analyzed responses
Contact angle
180
Method
The torrefaction experiments were carried out in BioEndev´s pilot-scale torrefaction
facility located at BTC in Umeå, 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.
160
140
120
100
80
60
40
Wood chips from small birch trees in the Västerbotten 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.
Wood Chips
20
0
Raw
Low
Medium
High
Figure 4. Contact angle for raw biofuel
and for all different degrees of
torrefaction.
Figure 3. Drying pattern for wood chip piles
(torrefied and raw) after being exposed to
simulated rain fall.
Torrefied Wood Chips
7.0
6.0
0.25mm
Milling cost [kJe/MJth]
5.0
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.
0.5mm
4.0
0.75mm
3.0
2mm
2.0
1.0
0.0
N/A
Raw
Ref
264/10
N3
270/10
Low N5
284/16
N6
285/18
Medium
N1
294/10
313/18
N8
N4
318/22
High
N7
320/18
N2
Figure 5. Grinding energy demand for different
torrefied biomass samples.
Figure 1. Pilot-scale torrefaction facility
Energy Technology and
Thermal Process Chemistry
Umeå University
SE-901 87 Umeå, Sweden
Phone: +46 (0)70-239 26 91
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