By Dan Burden, content specialist, AgMRC, Iowa State University, email@example.com.
Profile reviewed October 2015.
Various industrial and consumer products can be derived from many common wood wastes. They have applications in composite wood products, as fillers in plastics and adhesives, and for a number of other industrial and consumer products. Wood wastes frequently are combusted (burned), fermented (to create methane or alcohol) or used in bioreactors (to make carbon and hydrogen) for the production of energy, fuels or industrial chemicals.
With respect to energy production, the forest products industry consumes 85 percent of all wood waste used for energy production in the United States. Wider use of biomass resources will directly benefit many forest product companies whose growth generates more residues than they internally use. These excess materials have the potential to be the basis upon which businesses support expansion into composite-material product manufacturing and similar value-added co-product utilization schemes.
Most power production from biomass is consumed on-site, with some manufacturers selling excess power into the public grid. Overall, 70 percent or more of wood waste power is co-generated with industrial process heat. Wood-fired systems using sawdust account for 88 percent of power production, including use of shavings or shop-produced wood waste. Landfill gas accounts for 8 percent, agricultural waste 3 percent and anaerobic digesters 1 percent of power production (NREL data). Some power companies co-fire biomass with coal to save fuel costs and earn emissions credits. Using wood waste or other biomass in the fuel mix enhances their competitiveness in the marketplace. The cost of electricity from wood-fired plants ranges from $0.06 to more than $0.11 per kWh.
Various social impacts result from biomass use for power generation. Market forces are changing how the U.S. electricity industry fundamentally operates. Wood-waste and agricultural biomass, wind power, municipal wastes and a number of other feedstock materials are reshaping how electricity is produced, distributed, bought and sold. Power marketers are being forced to offer environmentally friendly electricity, including bio-power that is, at least in part, co-generated from the combustion of urban yard and construction wood wastes.
Shavings and sawdust may be reground into wood flours, or the wood flour may be recovered as sized “dust” materials that have been screened and separated. Wood flour has major industrial markets in industrial fillers, binders and extenders in industrial products like epoxy resins, fertilizers, adhesives, absorbent materials, felt roofing, inert explosive components, ceramics, floor tiles, cleaning products, wood fillers, caulks and putties, soil extenders and a vast array of plastics. Some wood flours like mesquite may be used in edible flavorings for human or pet consumption.
Shavings and sawdust can be marketed for use in molded or laminated composite wood products (e.g., toilet seats, countertops) in automotive materials and in oil and water isolation and solidification products for the environmental control industry. Other uses include fillers, bulk shavings, sawdust, hog fuel (dried bark shavings), meat-smoking chips, barbeque cooking fuels and composite fireplace logs. Landscaping applications include playground “footing,” equestrian arena and other “wood edge footing” (safety margin and walkway material) and some exhibit and tradeshow applications. A few manufacturers are using post-consumer plastic waste mixed with a sawdust extender to make high-value extruded composite decking lumber and similar products for the home improvement market.
Currently, a primary use of baled dry shavings is for equine and livestock bedding or small pet bedding applications. This usually takes the form of aromatic material from eastern red cedar, soft ponderosa pine, chlorophyll pine and aspen. In some cases, these wood products are mixed with “non-wood” agricultural residues like corncobs. These products may be prepared for specific pets such as dogs, cats, gerbils and hamsters or for other small animals. Related products may include litter box liners, all natural wipes, and odor and stain eliminators.
At this time and in the near future, wood wastes are and probably will be the most commonly used biomass fuel for heat and power. The most economic sources of wood fuels are usually wood residues from manufacturers (mill residues), discarded wood products or woody yard trimmings diverted from landfills, and non-hazardous wood debris from construction and demolition activities. A significant environmental benefit of using these materials for generating electricity is that their energy value is utilized while landfill disposal is avoided. As long as clean-burning combustion technologies are employed, carbon emissions to the atmosphere can be minimized.
Recent studies indicate that quantities of available (presently unused) mill and urban wood residues exceed 39 million dry tons per year in the United States. This is enough material to supply more than 7,500 MW, doubling the existing U.S. bio-power capacity in the United States. To illustrate this point, this amount of power could supply the yearly electricity demand of the residential customers in all six New England states.
Mill residues from pulp and paper manufacturing, lumber mills and other industrial wood users are frequently used for producing biomass electricity. These materials typically are very clean residues and can be used as fuel in a wide range of biomass and conventional combustion power systems. Currently, most mill residues are used to generate steam and electricity at the manufacturing facilities where they are produced. Urban wood residues consist of large quantities of urban wood waste presently sent to landfills. These include post-consumer wood products, broken wood pallets and crates, untreated clean construction and demolition debris, and ward-waste from trees. Increasingly, urban wood residues are being diverted from landfill disposal at materials recovery facilities and are being co-fired with coal and other fuels, including combustible municipal garbage waste, to generate power. This clean wood also can be productively used in non-combustion biomass fuel production, chipped for landscape mulch products, or chipped or milled into “dust” and recycled for use in composite materials for industrial markets.
Tree and yard trimmings and those generated from right-of-way trimming near roads, railways and utility systems also currently are sent to landfills. In some cases, these materials are converted to mulch, used in compost or are ground and used as a component in landfill cover layering. Energy and “new-use” material projects can be steady users of these materials. Additionally, forest residue wastes including underutilized logging residues, imperfect commercial trees, dead wood, fire-damaged trees and other non-commercial forest growth are non- or under-utilized woody biomass materials that could be used for biomass power or biofuels production, or as a fibrous material source. Because of the low-value quality of these materials, coupled with the potentially high transportation costs associated with extracting them from remote or difficult to access locations, these residues are much more expensive to recover than urban wood residues. An active commitment to the use of these material sources, including new utilization strategies, e.g., processing on-site at the collection point, identification of high-value markets for the material and building of an infrastructure that understands the qualities of the materials and facilitates supplying them, are necessary first steps in expanding the uses of sawdust, shavings and wood wastes.
An important new player may be the agricultural community. The use of crop residues, livestock manures and short-rotation-intensive-culture (SRIC) plantings of fast-growing “wood grass” tree species as fuel resources can improve the economics of farming while solving some of the most intractable environmental problems in agriculture today. In SRIC systems, “wood grass” species are cultivated and then chipped on-site for use in energy production (by combustion) or wood-product manufacturing (composites). The advent of energy crops for power production is a new agricultural market. However, these crops provide soil conservation and nutrient management benefits for the land and may be compatible with government conservation set-aside incentive programs. Increased woody-biomass utilization will impact other groups including architectural and engineering firms, consultants, and processing and handling equipment vendors.
Since the summer of 2008, "clean" sawdust has been a high-priced market, averaging $50 or more and ranging from $600 to $1,200 per truckload of material. There have been several reasons for this. Foremost, there has been less production of sawdust "co-product" from the primary manufacturing of lumber and other forest products. This is partly due to the national downturn in new-home construction. In 2006, U.S. mills were producing 135-million board-feet of material per day; in 2008, production had dropped to around 114-million board-feet of material per day (U.S. Forest Products Laboratory, Madison, WI). As of 2010, sawdust was selling for approximately $45 a dry ton. In 2015 NBC News reported prices in Maine at over $50 per dry ton; and Howmuchisit.org reported retail pricing ranging from $5 to $15 per bag depending on the quality of sawdust and perhaps the type of wood, with bulk purchases from $2 to $6 per pound. They report “horse-stall” bedding prices anywhere from $125 to $200 per stall. This greatly depends on geographic location and whether the material can be locally sourced at greatly reduced cost.
Added to decreased production and less supply to meet what had been the demand, there has been increasing demand for sawdust from the bio-energy sector as more consumers are incorporating pellet stoves and pellet-fueled hot-water boilers into their homes. This has led to increasing numbers of wood-pellet producers, especially in the northern and northeastern states. The increased demand for sawdust and increased price for the commodity has primarily impacted livestock producers, particularly dairy farmers and hog producers who use sawdust as part of a composting system for decomposing quarantined carcasses.
Resources / Other Links
Production of Electricity from Biomass Crops - U.S. Perspective, Ralph Overend, NREL.
The Unintended Ripples from the Biomass Subsidy Program, The Washington Post, January 10, 2010.
Wood Biomass for Energy, Techline, Forest Product Laboratory, 2004.
Forest Biomass & Wood Wastes, Energy Efficiency & Renewable Energy, U.S. Department of Energy (DOE).
U.S. Billion-Ton Update. Biomass Supply for a Bioenergy & Bioproducts Industry, Energy Efficiency & Renewable Energy, U.S. DOE.
Wood Energy Markets - 2010-2011, UNECE/FAO Forest Products Annual Market Review.