Fuel pellet production from reed canary grass

• Main Author: Larsson, Sylvia
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2008
• Subjects: Northern Sweden
• Online Access: https://pub.epsilon.slu.se/1786/; https://pub.epsilon.slu.se/1786/1/Kappa_080904_Sylvia.pdf

This thesis focuses on two main areas: methods for assessing regional supply potentials of reed canary grass (Phalaris arundinacea L.) (RCG); and process technology for the production of high-quality RCG pellets. Partial equilibrium modelling, incorporating a break-even price approach, was used to examine supply potentials for RCG in Västerbotten County, northern Sweden. A remote sensing method, using black and white orthophoto interpretation, was developed, by which abandoned fields with low preparation costs (on average 173 SEK (ha)-1) could be distinguished from fields with high preparation costs (on average 3990 SEK (ha)-1). Based on the assumptions made, RCG production would predominantly be viable in the coastal area of Västerbotten County, and production equal to 1.3 TWh could be supplied at a farmgate fuel price of 116 SEK MW-1h-1. Pelletizing RCG allows it to be transported, stored and handled more easily. To determine the optimum conditions for RCG pelletizing, experiments were performed in an experimental design incorporating the factors: moisture content, steam addition, raw material density, and die temperature. Pre-compaction of the raw material was an efficient method for avoiding uneven pellet production. Through multiple response optimization, process settings were identified for the production of RCG pellets with a bulk density ≥ 650 kg m-3 and a durability ≥ 97.5%. To clarify the underlying mechanisms in the pelletizing process, the influences of moisture content and normal stress on the kinematic wall friction properties of RCG powder were studied. A steep increase in the kinematic wall friction with increasing normal stress was found in the normal stress interval 50-150 MPa. Multiple linear regression modelling of kinematic wall friction measurements at high normal stresses (65 to 376 MPa) revealed a local maximum at moisture contents of 13–16% and normal stresses of 150–225 MPa. Kinematic wall friction and pellet durability maxima occurred in overlapping moisture content ranges; it was, therefore, hypothesised that the two properties were correlated.