Abstracts Biological Sciences

Evaluating factors that influence the feedstock quality of comminuted forest residues

by Joel Anthony Bisson

Woody biomass residues generated from timber harvest or fuel reduction thinning operations are a potential feedstock for emerging biomass conversion technologies. However, forest residues typically produce a low quality feedstock which may not be suitable for certain biomass conversion technologies. In an effort to increase feedstock quality, this study separated non-merchantable trees and tops from piled limbs during a timber harvest operation. A portion of the separated material was further processed to remove limbs to create five material types: processed and unprocessed, conifer and hardwood stems, and slash (limbs and chunks). These materials were comminuted with a disc-chipper, grinder, and micro-chipper, two and 12 months after harvest. The quality of the feedstock produced from each machine was characterized by moisture content, particle size distribution, bulk density and ash content. Chapter one reviews the comminution of 2-month old material. There was no difference in moisture content between the chipped materials, however, slash material was significantly lower. Processing material did not have an effect on the size distribution nor bulk density of chips. A lower ash content was observed in the conifer type material after processing. Overall, we learned that through sorting and chipping, we were able to improve feedstock quality compared to ground slash. An improvement in feedstock quality may justify the additional cost to sort. In Chapter two, 12-month old material was comminuted and results were compared to those found in Chapter one. The moisture content of chips collected in the study ranged between 18% and 29%. There was a 7.25% decrease in moisture content across all material types. The size distribution of chip samples were dependent on tree type, moisture content and treatment. The bulk density of the 12-month chips decreased by 12% over the 2-month period due to moisture loss. Results show that additional processing (i.e., delimbing stems) does not have a big impact on ash content, bulk density, nor moisture content. Allowing the material to sit for an additional 10 months did have a significant influence on moisture content, which contributed to changes in particle size and bulk density. The chipper produced 30.1 bone dry metric tonne (BDmT)/productive machine hour (PMH) at an estimated cost of $11.87/BDmT. In Chapter three, 12-month material was comminuted using a micro-chipper designed to produce a 3 mm chip. Micro-chips had a smaller particle size distribution, which raised the bulk density 13% over bulk density results found in Chapter 2. The micro-chipper produced 33.9 BDmT/PMH at an estimated cost of $11.16/BDmT. Our findings show that with proper handling and comminution methods, forest residues, once considered a waste bi-product, have the potential to be a high quality feedstock for biomass conversion technologies. These technologies may provide added value and different options for land managers to handle forest residues. Advisors/Committee Members: Han, Han-Sup.