Effect of High Speed Blowing on the Bulk Density of Ground Residues
Abstract
Transportation costs of ground forest residues can be reduced by increasing the dry wood bulk density per trailer per trip. Increasing the dry wood bulk density can be achieved by compacting the material into the trailer after it is processed by a grinder. However, increasing load density is often difficult to achieve in conventional conveyor-fed, gravity drop loading methods. The effect of high speed blowing during loading of low moisture wood grindings on the final bulk density was analyzed for two feedstock piece sizes, branches-and-tops and pulpwood. A structured fully randomized field test was implemented with two factors: loading method (high speed blowing and conveyor fed) and bit type (carbide hammer bits and knife-edge bits). The high speed blowing of grindings was made using a blower system to pack the material into the trailer during loading. The resulting bulk density using high speed blowing was compared against the results obtained from the conventional conveyor-fed (gravity drop) loading. The high speed blowing method produced a significant increase in bulk density ranging between 24 and 35 percent more than the conventional conveyor-fed loading. In terms of grinding configuration, knife-edge bits produced a higher bulk density (9%) compared with carbide hammer bits but only for the pulpwood piece size class. The use of high speed blowing during loading was the most powerful factor impacting truckload bulk density in these trials and demonstrated promising results that can lead to significantly lower transportation costs when processing low moisture content harvest residues.
(a) Conveyor-fed loading method into a chip van in a grinding operation; (b) horizontal blowing of wood chips into trailers.
Diagram illustrating the potential increase in truck volumetric capacity by increasing bulk density of the comminuted material. As long as the material is dry enough such that the truck is not at legal weight limit, more material can be added to the more compacted load.
High speed blowing test procedure.
(a) Near-vertical high speed blowing of grindings during truck loading; (b) conveyor-fed truck loading.
Particle size distribution per treatment (bit type loading method) for standard residue size class.
Particle size distribution for each treatment on pulpwood size class residue.
Effect of the treatment bit type loading method on the bulk density for material processed from branches-and-tops and pulpwood size classes.
Transportation cost for each of the two loading methods on branches-and-tops size class material.
Transportation cost for each of the two loading methods on pulpwood size class residue.