Fuel Pellet Production from Reed Canary Grass

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)) could be distinguished from fields with high preparation costs (on average 3990 SEK (ha)). 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 MWh. 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 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.