Densification of loose forest residuals
The forest industry in the western United States is phasing out slash pile and broadcast burning due to concerns about smoke, risk of fire escapes, and burn-pile heat effects on soil quality. The alternatives are to chip and scatter the material back across the harvest unit or to haul the slash off the site in either whole or ground form.
The Biomass Research and Development Initiative (BRDI) funded project, led by Han-Sup Han at Humboldt State University, is creating new knowledge and understanding about solutions to the slash pile problem by exploring ways to reduce the cost of in-woods collection and hauling (such as baling) to centralized sites for processing into biofuels and bioproducts. The baling task specifically explores the design and potential benefits of special-purpose forestry balers that compact forest residuals into large rectangular bales to be transported, stored, and processed similar to common large square hay bales.
Baling as a part of the solution
Forest residuals contain small diameter roundwood (often including non-target hardwoods), short sub-merchantable lengths of logs, trim (butt sections), tops, branches, and brush. Previous characterizations by Forest Concepts found that forest residuals contain 50-70% wood if the wood fiber content can be separated from bark, needles, soil, etc. Sorting prior to hauling (as detailed in Subtask 1.1) enables separate handling and transport of high-fiber poles, logs, and chunks which have the potential for positive revenue streams for the landowner and contractors.
Long poles and pulpwood quality logs are amenable to transport using conventional flatbed-with-racks and log trucks. Chunk-wood, trim ends and the like have high enough density to be hauled in roll-off containers and dump body trucks.
However, it is the branches, brush, and tops that are most expensive to transport. Such material can be ground on-site into hog-fuel/mulch and transported in specialized trailers, or potentially baled for high density transport with conventional flatbed trucks and trailers. A key part of the BRDI project is to evaluate baling as an alternative to bulk hauling and in-woods grinding.
Background on baling of woody biomass
The concept of baling for woody biomass was developed by Forest Concepts in 2005, under funding from USDA/NIFA/SBIR, to enable collection and delivery of urban woody biomass to biopower facilities in distant communities. Collection and transport of wood chips from conventional chippers used by landscapers, arborists, and municipalities was deemed too expensive and logistically challenging.
Baling was proposed as an alternative that would enable urban woody biomass to be collected and transported just like other baled urban recyclables – cardboard, paper, aluminum cans, etc. Baling had the added advantages of low-noise in neighborhoods, no dust production as with chippers, and the end user benefit of receiving the woody material basically intact. Thus, end users could chip or grind baled biomass to their own optimal feedstock size.
A full-scale engineering prototype was designed and built in 2008 and has been operated on many urban, suburban, and forest sites. The Forest Concepts woody biomass baling technology is covered by three U.S. patents.
This BRDI project will directly benefit from Forest Concepts’ past baler research and engineering efforts. Bale densities up to 25 pounds per cubic foot enable high payload hauling on flatbed trucks and trailers. Productivity data from prior field studies is informing the design and specification of larger, higher horsepower balers more appropriate for use with forest residuals. Field trials in coordination with other processing equipment has led to a sense of where baling makes the most sense as part of a biomass collection system.
If baling can be made sufficiently agile and low cost, bales of forest residuals could be transported on conventional flat-bed trucks and trailers to centralized sites for grinding.
Task 1.2 objectives
Forest Concepts’ engineers and biomass specialists will advise the project team on biomass characterization, conduct laboratory experiments on forest biomass to derive baler engineering properties, and use their engineering prototype biomass baler to create dense bales for use by other team members in drying, transport, and grinding experiments.
By the end of the three-year project, Forest Concepts and the Feedstock Development team will define the technical and operating conditions that would make baling economical for recovery of forest residuals for use with centralized in-woods grinding operations, and for longer hauls to centralized power plants and industrial end-user sites. Experiments and computer simulations will be used to generate operating data, expected fuel and labor consumption, hauling payloads with alternative bale configurations, and other important data for use by the forest operations, biomass fuel economics, and life cycle analysis teams. Three different baler models will be defined to the point of mock-up product specifications and data sheets. Forest Concepts’ role with the other teams (economics, life cycle analysis, and conversion) is to provide plausible and defensible data for their use.
Forest Concepts will be conducting engineering-science research both at their Auburn, Washington facility and in the field to develop platen pressure/bale density relationships for various forest residual types, effect of moisture content on baling energy consumption, and other data needed to design commercially viable balers for use by the forest industry in the near future.
Mike Perry, CEO, and Jim Dooley, CTO
Office phone: 253-333-9663