A Productivity and Cost Comparison of Two Systems for Producing Biomass Fuel from Roadside Forest Treatment Residues

Forest operations generate large quantities of forest biomass residues that can be used for production of bioenergy and bioproducts. However, a significant portion of recoverable residues are inaccessible to large chip vans, making use financially infeasible. New production systems must be developed to increase productivity and reduce costs to facilitate use of these materials. We present a comparison of two alternative systems to produce biomass fuel (i.e., ‘‘hog fuel’’) from forest residues that are inaccessible to chip vans: (1) forwarding residues in fifth-wheel end-dump trailers to a concentration yard, where they can be stored and then ground directly into chip vans, and (2) grinding residues on the treatment unit and forwarding the hog fuel in high-sided dump trucks to a concentration yard, where it can be stored and then reloaded into chip vans using a frontend loader. To quantify the productivity and costs of these systems, work study data were collected for both systems on the same treatment unit in northern Idaho in July 2009. With standard machine rate calculations, the observed costs from roadside to loaded chip van were $23.62 per bone dry ton (BDT) for slash forwarding and $24.52 BDT 1 for in-woods grinding. Results indicate that for harvest units with conditions similar to the test area, slash forwarding is most appropriate for sites with dispersed residues and long-distance in-woods grinder mobilization. For sites with densely piled roadside residues, in-wood grinding is likely to be a more productive and less costly option for residue recovery. Forest operations for timber harvest, precommercial thinning, fuels management, and other vegetation treatments generate large quantities of treatment residues (also called ‘‘slash’’), including tops, limbs, cull sections, and unmerchantable roundwood. These by-products are a promising source of biomass for the production of energy, fuels, and products because they are widespread, renewable, and can be used to produce products that offset the use of fossil fuels and reduce greenhouse gas emissions (Jones et al. 2010). Use of forest residues can also improve the financial feasibility of some silvicultural prescriptions by reducing site preparation costs and can improve air quality in areas where open burning is a common method of residue disposal (Gan and Smith 2007, Jones et al. 2010). The most prevalent use of forest residues is as hog fuel for combustion boilers used in the generation of heat and electricity. In this article, the term ‘‘hog fuel’’ denotes woody biomass fuel produced from forest residues, fuelwood, and wood waste by all methods of comminution, including grinding, chipping, and shredding. Combustion of hog fuel and other by-products by the forest industry accounts for more than 50 percent of all biomass energy in the United States (US Department of Energy 2011). In some regions, electric utilities, industrial boilers, and institutions with wood-fired heating systems represent additional hog fuel demand outside the forest sector. To meet this demand, The authors are, respectively, Research Forester, USDA Forest Serv., Rocky Mountain Research Sta., Missoula, Montana ([email protected] [corresponding author]); Associate Professor and Research Associate, Univ. of Montana, Missoula ([email protected], [email protected]); and Supervisory Research Forester, USDA Forest Serv., Rocky Mountain Research Sta., Missoula, Montana ([email protected]). This paper was received for publication in September 2011. Article no. 11-00113. Forest Products Society 2012. Forest Prod. J. 62(3):222–233.