August 22, 2007 | General

Turning Limbs And Chips Into Energy Biomass Humus

BioCycle August 2007, Vol. 48, No. 8, p. 56
Biomass is converted to bundles as part of strategy to economically recover logging residues.

WHILE lumber and pulp mills have been using forest residuals to produce power, most of the leftover remains have been underutilized in the United States. An estimated 67.1 million dry tons of logging residues are generated annually, but the main challenge is a lack of cost-effective recovery techniques. Composed of limbs, twigs, foliage and nonsalable timber, these residues represent a substantial amount of available biomass.
Logging residue lacks uniformity and has a significantly lower density thansolid wood thereby decreasing productivity of its recovery. One of the most common methods of residuals recovery is comminution (pulverize). After materials are brought to a central point, they are ground/chopped and transported to generation facilities. Comminution minimizes transportation problems – turning limbs and tops into more easily transportable chips.
But the primary problem is poor storage ability. High surface area and nutrient content lead to rapid decomposition and dry matter loss. To become a suitable energy source, forest residuals need to be available for power generation all year regardless of weather conditions. Therefore, the storage capacity of comminuted materials is currently limited. An alternative process for utilizing forest residue is bundling. Packaging coarser pieces of debris into bundles can reduce dry matter storage loss.
One machine designed to collect forest biomass is the John Deere 1490D slash bundler. Developed to work in conjunction with cut to length machines, this unit collects forest debris, compresses material, and binds it into six to ten feet long bundles that are two feet in diameter. Several studies have investigated performance of the slash bundler in gathering forest residue from harvested sites, but so far none have looked at Deep South conditions. With the South providing about 60 percent of U.S. timber products (i.e., logging residues, timberland clearing, etc.) it’s important to evaluate productivity in southern timberlands.
The bundler demonstrated its operational effectiveness in southeastern Arkansas on loblolly pine stands last July using the ratio-delay method. Ratio delay analyzes machine operations to figure the ratio between delay time and actual productivity. Materials are loaded onto the feed tray, and feed rollers begin intake of the materials into the presses, which reduce volume by about 80 percent. A three minute time frame was used, enabling the observer to monitor different activities – recording what was being done. Bundling activities included: gather, load, bundling, cut/unload, and downtime. Total number of each activity were divided by total observations at the site and then multiplied by 100 to yield the percent of time that the machine spent on a given activity. Overall, the machine was involved in productive work 68 percent of the time. Gathering and loading accounted for the highest proportion of productive work.
Authors of this report include David Patterson of the Arkansas Forest Resources Center at University of Arkansas, Rebecca Montgomery of the Arkansas Forestry Commission, Matthew Pelkki, Professor at the Arkansas Forest Resources Center, and Philip Steele of Mississippi State University’s Forest Products Department.

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