Parametric study of pilot-scale biomass torrefaction

1. HHV LHV Carbon Klason lignin 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 Increase with torrefaction Ash-Glucose-Cellulose Torre Torrefaction No effect Hydrogen Oxygen Volatiles Massyield Energy yield Extractives Xylose Manose Galactose Arabinose Hemicellulose Decrease with torrefaction 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 300°C, which cost efficiently facilitate the above fuel quality improvement. Solved! Untreated biofuel Torrefied biofuel 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%. Problems • High density, densification • Dry and hydrophobic • Low grinding costs • Feedable (spheric particles) • Higher energy density – improved logistics • Homogeneous • No bio contamination • Large bulk volume • Wet, high wettability • Expensive grinding • Non feedable • Low energy content • Inhomogeneous • Risk of bio contamination 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 low value heat via process integration further refinement Torrefied biomass powder Biomass Figure 2. Effects on some of the many analyzed responses 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. 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. 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. Wood Chips Torrefied Wood Chips 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. Raw Low Medium High 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 E-Post: Martin.nordwaeger@chem.umu.se Martin.nordwaeger@chem.umu.se katarina.hakansson@chem.umu.se Ingemar.olofsson@chem.umu.se susanne.wiklundlindstrom@chem.umu.se anders.nordin@chem.umu.se linda.pommer@chem.umu.se