Biomass arises in many forms and can be converted readily into solid, liquid, or gaseous fuels and products. Most commonly, wood is chopped into chunks or chipped for ease of handling or even pelletised so that it can be bagged and stored. Biomass can also be pyrolysed or gasified in specific ways to give liquids or fuel gases. All forms of biomass can in turn be burned to raise heat, such as hot water or steam, or to produce electricity or both in a combined heat and power facility (Atchison and Montgomery 1986, Kaminsky 2004). Some biomass is far too wet to be burned successfully and so biological fermentation processes are used. Using containers that exclude air, biomass is digested to produce a methane rich gas called biogas or fermented to produce alcohols or other specialised chemicals. There is increasing interest in using biofuels for transport and the number of alcohol or biodiesel-fueled vehicles around the world is growing (Chum and Power 1992, Hakkila 1989).

Many believe that hydrogen used in fuel cells will be the ultimate clean method of transport since using this fuel produces virtually nothing more than water vapor (Babu 2002, Chornet et al. 1996). Biomass may have a key role to play in the long-term future through producing hydrogen directly by biological processing or through providing sustainable energy for other methods of production such as electrolysis. This section briefly covers the conversion and production processes for obtaining bio-based products and energy.

• Bio-Chemical Processes
• Thermochemical Processes
• Fiber Composite Manufacturing

These processes depend on the use of biological and chemical components for extracting products.

• Aerobic Digesting - Composting
• Anaerobic Digestion
• Fermentation

Sawdust and wood chips are the most common sources of woody biomass waste used in aerobic digestion. This commercially established process collects organic wastes in lagoons, where naturally occurring bacteria use oxygen to convert the waste into carbon dioxide, water, energy, and more bacteria. Daily additional feedstock and water mixes with aerators to ensure constant turnover of the sludge. This constant mixing requires large energy demands because aerators require regular maintenance thus making the process somewhat expensive (Chynoweth et al. 1992)

Nutrient-rich fertilizers and composts are the major product that results from aerobic digestion of woody biomass. Plant covers, mulch, and recycled residues are also large commercial products both nationally and internationally.

Aerobic Digestion Pathway

Fermentation is a biological process in which enzymes produced by microorganisms catalyze chemical reactions. An enormous variety of bacteria, yeasts, and fungi exist to ferment these sugars. These microorganisms digest sugars to produce the energy and chemicals they need for survival while giving off byproducts such as carbon dioxide, organic acids, hydrogen, ethanol, and other products. Producing commercial products through fermentation of lignocellulosic material is a multi-step process involving pre-treatment and hydrolysis of the material with acid to release fermentable simple sugars, fermentation of these sugars by living organisms to produce hydrocarbons, recovery from the fermentation broth of the desired products, and utilization of the byproducts (Van Hoek et al. 2003).

Biorefineries are examining a wide variety of bacteria, yeasts, and fungi because they are capable of producing dozens of chemicals with significant market potential (Energetics 2003). In addition to ethanol, fermentation is already producing commercial levels of therapeutic and research enzymes, antibiotics, and many more intermediate and specialty chemicals to produce even more industrial and consumer products. The byproducts of lignocellulosic fermentation are nearly as valuable as the target products. Residual cellulose and lignin serve as boiler fuel for electricity or steam production and gases such as carbon dioxide are often captured for sale to the beverage industry. Some recovery methods generate large volumes of solid materials such as gypsum that is used as a soil amendment. Very promising research has shown that ethanol production, by means of lignocellulosic fermentation, has an energy output to input ratio of 2.6 to 1 with respect to short rotation woody crops (Lorenz and Morris 1995).

Large-scale fermentation of ethanol from lignocellulose has been possible for decades but has only proven to be commercially attractive during times of shortage, such as wartime. Intense research is being conducted in two critical needs areas: the need to develop cost-efficient processes for hydrolyzing fermentable sugars from cellulose and the need for robust microorganisms to ferment non-glucose sugars from hemicellulose (Gantz 2003, Kerr 2004, LaPlaza and Jeffries 2004).

Iogen operates a demonstration facility in Ontario, Canada that is proposing a US$250 million plant that can handle all functions involved in lignocellulosic fermentation from a variety of biomass feedstocks.

Unlike aerobic digestion, anaerobic digestion is the decomposition of biomass by bacteria in the absence of oxygen. Biogas, or methane, is the primary product produced with digestion effluent being sold as fertilizer and bedding materials. Anaerobic digestion is governed by temperature, retention time, chemical composition of the influent, and presence of toxicants, and as each influence changes, so does the quantity and quality of biogas produced. Fluctuation from a high temperature gradient to a lower one during digestion has shown to produce 25 percent more biogas than maintaining a single steady heat (Mathews 2004). Retention times typically range from 25 to 35 days and pH levels must remain relatively steady at around 7 (Simons 2004).

Not all waste streams are appropriate for anaerobic digestion. The higher the fat content in the feedstock the more biogas can be produced. Other feedstocks, such as lignin, require longer retention times and/or higher concentrations of bacteria in the substrate (Simons 2004). New technologies are looking to increase yields and decrease time by adding ultrasound to the process. Called sonication, the waves disintegrate the solids in the influent, increasing surface area and allowing for more complete digestion (Yoshitani 2003).

Anaerobic Digestion Pathway

These processes require various levels of heat and chemicals to extract bio-based products.

• Biomass Gasification
• Combustion
• Fast Pyrolysis
• Lipid Extraction
• Thermochemical Liquefaction
• Black Liquor Gasification
• Vitrification
• Hydrothermal Upgrading Process
• Fischer-Tropsch Process

Modern chemical pulp mills produce black liquor that is roughly 80 percent solids. This solid is burned in recovery boilers to provide the steam needed to run the mills or to produce electricity through turbines. Another critical task of burning the solids in specialty Tomlinson boilers is to begin the process of recovering pulping chemicals to reduce the economic costs of operation. Black liquor gasification is an emerging commercial technology founded on decades of research and development. Its goal is to produce a combustible mixture of raw gases as well as separate out the inorganic pulping chemicals for recycling for the pulping process. The processes can take place at low, 600 degrees Celsius, or high temperatures around 1000 degrees Celsius (Larson et al. 2003).

ThermoChem Recovery International has commercialized the low-temperature process, where black liquor is indirectly heated to produce a hydrogen-rich gas. This process also produces a dry solid inorganic smelt that reduces the potential for smelt-water explosion hazards. ThermoChem has two commercial plants installed; Trenton, Ontario and one in partnership with Georgia Pacific in Big Island, Virginia. A Swedish company, Chemrec AB, uses a high temperature gasification system. This system can work in parallel with existing Tomlinson recovery boilers or serve as a replacement for old boilers. This replacement system has the capacity to double the biobased electricity produced and increase pulping capacity by 5 percent. Chemrec systems have been used across Sweden as well as in partnership with the Weyerhaeuser mill in New Bern, North Carolina.

The raw gases produced by the system can be converted in biobased syngas which can be used on-site or sold to the market (Brown 2003). The soilds that are produced in the black liquor can be problematic, particularly if the pulping chemicals were high in sulfur and sodium content. Gasification of black liquor has shown significant improvements over Tomlinson boilers with regards to SOx and NOx emissions and total reduced sulfur levels, thus improving future pulp yields. Detailed studies have also demonstrated that, when combined with a gas turbine, black liquor gasification can produce enough energy to make the pulping industry a net exporter of energy (Larson et al. 2003).

Chemrec AB's Black Liquor Gasifier

Vitrification is the process by which minerals are melted into glass. After the feedstock is dried to 10 percent moisture content, it is heated in a furnace at very high temperatures, around 2800 degrees Fahrenheit, to destroy harmful organic compounds and trap trace metals in the resulting liquid mixture. This mixture is then quickly cooled to form a solid sheet of glass that is crushed into aggregates of various size, dependent upon the intended use. The organic compounds that are burned off can be captured and become a significant part of the fuel needed to run the system, thus making it nearly self-sustaining. Feedstocks that are high in ash content, such as paper mill residues, require supplemental heating to vitrify the ash but this exothermic process still results in net energy production (Mauro 1996).

Vitrification plants have been operating in the United States since the early 1990s. Minergy, based in Wisconsin, even offers modular vitrifacation units that can be incorporated into existing biomass-fed processes.

Minergy Vitrification Process

The HTU process converts a large variety of biomass feedstocks into a liquid fuel that can be upgraded to a high quality diesel fuel. The HTU process heats the feedstock in water to 300-350 Celsius at 100-180 bars pressure for 5 to 20 minutes in order to facilitate the removal of oxygen. Typically, 85 percent of the oxygen is removed in equal parts of carbon dioxide and water (Goudriaan et al. 2005).

(Table:Typical HTU product distribution)

The biocrude readily separates from water and can be separated into light and heavy crude through extraction. The light crude is mineral-free and can be used for high-efficiency electricity production. For large-scale applications, the light crude is upgraded to produce a premium gasoil that has excellent ignition properties and can be blended directly with conventional diesel (Naber and Goudriaan 2003). There are no adaptations needed for engines to use this fuel. The heavy crude fraction is formed as a coal-like solid that can be co-combusted for power production. The heavy faction may also be gasified to produce ‘green hydrogen’ for use in catalytic hydrodeoxygenation.

The first commercial HTU plant demonstration is being conducted by Total France and NV Huisvuilcentrale Noord Holland. The capital investment for the plant is estimated at US$25 million. Currently, the HTU process can compete with premium diesel made from petroleum when crude prices are near US$50/barrel and biomass can be obtained for US$2.50/GJ. When the process is coupled in a bio-refinery concept with protein extraction, HDO upgrading, and gasification, the products that can be produced expand beyond the biocrude and energy production to include premium cattle fodder, green kerosene for aviation fuel, and naphtha feedstocks for chemical plants (Naber et al. 2004).

Fischer-Tropsch Process

The Fischer-Tropsch process is an established technology, first used in Germany in the 1920s, that converts carbon monoxide and hydrogen into oils or fuels that can substitute for petroleum products. The reaction uses a catalyst based on iron or cobalt and is fueled by the partial oxidation of coal or wood-based fuels such as ethanol, methanol, or syngas typically coming from an adjacent gasifier. The current research indicates that combining woody biomass gasification processes with Fisher-Tropsch synthesis is preferred over the use of natural gas, and shows a promising route to producing economical renewable transportation fuels (Benham and Bohn 1983). By carefully controlling the temperature and oxygen content, resulting products can range from pure syngas to "green diesel" or even used to increase the hydrogren byproduct that can be used for the production of ammonia or for fuel cells (USEPA 2002).

Changing World Technologies, Shell, and Choren have all invested in Fischer-Tropsch technologies. In late 2005, Shell licensed technology to Waste Management and Processors in Pennsylvania to construct a plant that will use the process to convert slag-coal into low-sulfer diesel fuel that has shown to be an effective alternative fuel in the trucking industry. The use of these fuels has shown a dramatic reduction in the amount of NOx and SOx emissions compared to traditional diesel emissions (Norton 1998).

The gasification process occurs at temperatures between 600-1000 degrees Celsius and decomposes the complex hydrocarbons of wood. Gasification products can not be easily stored and thus the system is often integrated with other conversion processes to utilize the outputs in the form of various bio-based syngases. The gasification process produces ash and char, tars, methane, charcoal and other hydrocarbons. Most of the time these byproducts are acceptable if the gases are to be combusted, but in fuel synthesis or fuel cells, they must be reduced by using scubbers or filters (Stevens 2001).

Studies have shown that gasification systems can be as much as 20 percent more efficient than direct combustion systems (Bain and Amos 2003) thus potentially making them more economical for power production. Biomass gasification is an emerging technology; most developers are still in the prototype or first commercial demonstration stage, but research is ongoing worldwide. The Community Power Corporation of Littleton, Colorado is currently testing a small scale unit and larger systems are coming online in Skive, Denmark. SilvaGas is being promoted worldwide by FERCO, the Atlanta-based Future Energy Resources Corporation.

The chemical composition of the feedstock influences the constituents of the product gas, the gasification design, and the clean-up methods that must be used, thus some types of biomass may prove more costly to gasify than others. For example, wood residues high in sodium or potassium will require pre-cleaning prior to utilization. In general, feedstocks should have a high carbon-to-nitrogen ratio, relatively low sulfur content, and a low moisture content (Bain and Amos 2003).

Gasification is a relatively old technology that was widely used during World War II. The Germans, when faced with a lack of petrol, gasified coal using the Fischer-Tropsch process to produce diesel. The pollution from this created vast forest destruction in eastern Germany, Poland and the Czech Republic.

Biomass Gasification

BioMax5

The Community Power Corporation has constructed a fully automated, portable gasifier that ranges from 5 to 50 kW. Demonstrations of the units are currently being conducted in partnership with SBS Wood Shavings, the USDA Forest Services Forest Products Lab in Madison, WI, and the National Renewable Energy Lab. The units run on a wide variety of dry biomass feedstocks that are fed into the unit and combust in oxygen-deprived environments. The systems can be connected to regional electricity grids or serve as a stand-alone generator for stationary engines, microturbines, and solid oxide fuel cells. The system has a wood energy conversion efficiency of 80 percent. Using woody biomass or the husks of coconut shells, it is estimated that 1.3 kg of feed-stock will produce one kilowatt-hour and the smaller BioMax5 , designed for residental use, could provide the daily power requirements of an average-sized house on as little as 45 kg of wood pellets daily (Bilek et al. 2005)

Almost anything organic will burn, but low moisture-content biomass is best suited for combustion. Combustion refers to the rapid oxidation of the feedstock as it is exposed to high heat.  Most of todays biomass-powered plants are direct-fired systems, similar to fossil-fueled plants. The feedstock is burned in a boiler to produce high-pressure steam that is pumped into a turbine, over a series of blades that roate and power an electric generator. There are three general areas of combustion technology that are being used: Fixed-bed combustion, fluidised-bed combustion, and dust combustion.

Steam powered technologies have proven to be very dependable, but efficiency has at times been limited. Biomass power boilers typically are in the production range of 20-50 MW compared with coal-fired plants in the 100-1500 MW range. Small-capacity plants generally have lower efficiencies because the equipment needed to increase energy-efficiency is not economically viable (Brown 2003). The most economic near-term solution is co-firing furnaces with fossil and biomass feedstocks. Much of the existing power plant equipment can be used with little to no major modifications thus making this much more economically attractive than building new plants. Compared to the coal it might replace, biomass use reduces sulfur dioxide, nitrogen oxide, and other harmful air emissions resulting from combustion (Hustad et al. 1998).  

Many power plants have been burning or co-firing biomass for decades. Most recently the Dunkirk Power Station in New York has started producing energy from local willow plantations, assisting the regional forest products economy (Spaeth 2004). Advances in fluidized beds that promote full oxidation of the feedstock have seen energy efficiencies increase, but one of the largest impacts has been the adoption of pelletized biomass as a commodity fuel. Bixby Energy Systems has desinged a furnace especially for pellets with a 99.7 percent fuel combustion ratio, maximizing value at the same time as limiting emissions and ash residue. The UK-based Talbotts has been a world leader in the development of biomass generators, producing its first wood-fired system during the mid 1970s.

Talbott's Biomass Generator

Talbotts is currently promoting their biomass generator, BG100. The BG 100 is capable of producing 100kW of electricity and 150 kW of heat, utilizing a wide range of fuels including wood chips, pellets, and waste. With a potential reduction of 600 tonnes per unit of carbon dioxide per year compared with an equivalent amount of energy produced from fossil fuels, the BG100 can greatly benefit the environment and take advantage of a common fuel source. The system is small and compact and designed for on-site power production making it ideal for farms, hotels, estates, or commerical properties. Each system can be operational for approximately 8000 hours per year, making it 92% efficient.

A fully-automated, continuous system ensures proper fuel feeding to maintain the required energy output and the step-grate system helps to ensure even burn thoughout the combustion chamber to improve the units efficiency. For more information about the Talbott system and to review the companys past successes, please visit their website here.

In fixed-bed combustion systems, primary air passes through a fixed bed, in which drying, gasification, and charcoal combustion takes place. The combustible gases produced are burned after addition air has been introducted in a combustion zone separated from the fuel bed. When biomass fuels have a high moisture content, varying particle sizes, or high-ash content, grate furnaces can be utilized. Mixtures of wood fuels can be used, but current technology does not allow for mixtures of wood fuels and straw, cereals and grass, due to their different combustion behavior, low moisture content, and low ash-melting point (van Loo and Koppejan 2003).

A homogeneous distribution of the fuel and layer of embers over the whole grate surface is important in order to guarantee an equal primary air supply across the grate surface. Heterogeneous air supply may cause slagging, higher fly-ash amounts, and may increase the excess oxygen needed for complete combustion (Baxter and Koppejan 2004). There are various grate furnace technologies available that will guide the complete combustion of fuel while minimizing the negative externalities.

Underfeed stokers represent a cheap and operationally safe technology for small-and medium-scale systems up to a nominal boiler capacity of 6 MWth (Knoef 2003). They are suitable for biomass fuels with low ash content such as wood chips, sawdust, pellets and particle sizes to 50 mm. An advantage of underfeed stokers is their good partial-load behaviour and their simple load control. Load changes can be achieved more easily and quickly than in grate combustion plants because the fuel supply can be controlled more easily The fuel is fed into the combustion chamber by screw conveyors from below and is transported upwards on an inner or outer grate. Outer grates are more common in modern combustion plants because they allow for more flexible operation and an automatic ash removing system can be attained easier. Primary air is supplied through the grate, and secondary air usually at the entrance to the secondary combustion chamber. A new development is an underfeed stoker with a rotational post-combustion, in which a strong vortex flow is achieved by a specially designed secondary air fan equipped with a rotating chain (van Loo and Koppejan 2003).

Fixed Fuel Beds

Circulating Fluidized Bed

Within a fluidised bed furnace, biomass fuel is burned in a self-mixing suspension of gas and solid material into which combustion air enters from below. A fluidised bed consists of a cylindrical vessel with a perforated bottom plate that is filled with a suspension bed of hot, inert, granular materials, commonly silica sand and dolomite (van Loo and Koppejan 2003). Primary combustion air enters the furnace from below through the air distribution plate and fluidises the bed so that it becomes a mass of particles and bubbles. The intense heat transfer and mixing provides good conditions for a complete combustion with low excess air demand. The combustion temperature has to be kept low, usually between 800-900°C, in order to prevent ash sintering in the bed. This can be achieved by internal heat exchanger surfaces, by flue gas recirculation, or by water injection (Orjala et al. 2000). Fixed-bed combustion plants usually have operating temperatures 100 to 200°C higher than fluidised bed combustion systems (van Loo and Koppejan 2003).

Due to the good mixing achieved, fluidised bed combustion plants can deal flexibly with various fuel mixtures such as mixtures of wood and straw, but are limited when it comes to fuel particle size and impurities contained in the fuel. Therefore, appropriate fuel pre-treatment system achiving particle size reduction and separation of metals is necessary for low-maintenance operation (Nieminen 2004).

Fuel materials with an average diameter smaller than 2 mm are suited for dust combustion. This includes fine shavings and sawdust that can be pneumatically blown into a furnace. Combustion occurs while the fuel is in suspension, thus a constant and regular fuel-to-air mixture must be maintained. Dust furnaces are using waste mainly from the chipboard industry. A thermal capacity of 2 to 8 MW is possible with this technology (van Loo and Koppejan 2003).

Dust Combustion Plant

Fast pyrolysis is the process of rapid thermal decomposition of biomass in the absence of oxygen. This produces energy, liquids, gases, and char. Small particles, less than a quarter inch in size, are delivered to a high-heat reactor where essentially no combustion occurs. The fuel must be small in size to assure high heat transfer rates during the process. Around 500 degrees Celcius, the material is transformed into a vapor, which in turn is cooled, condensed, and recollected as a liquid bio-oil or converted to hydrogen through a reforming process (Day et al. 2003). Gases that are non-condensable are recycled for co-firing into the reactor while the char is removed for fuel, or as a commercial product. In order to ensure a high yield of bio-oil, the processing time from introducing the feedstock to quenching is typically less than two seconds. Thus the name fast pyrolysis. Prior to recent advancements, pyrolysis was a relatively slow cooking process of producing oils that were thick, low quality, tar-aqueous mixtures in low yields. Processing time took minutes to hours. This traditional slow pyrolysis had been used by industries to produce char and extracts such as turpentine, but has been displaced by fast pyrolysis for biorefining (Bridgewater 2002).

The primary products formed by fast pyrolysis are pyrolytic bio-oils, a combustible mixture of oxygenated hydrocarbons, and char. Reactor design and feedstock characteristics influence yield and quality. Assuming that the feedstock has been dried to less than 10 percent moisture, the process will yield approximately 150 gallons per ton (Brown 2003). Roughly 10 to 20 percent of the product will be in the form of a non-condensable combustible gas, mainly carbon monoxide, hydrogen, and methane and is recycled into the reactor for process heating (Agblevor et al. 1995).

The Ensyn Company announced a US$9 million plant to be built in Renfrew, Ontario. In 2003, Ensyn had 6 plants operating and reported producing 19 million liters of bio-oil per year. Other companies such as the DynaMotive Corporation and BTG Biomass are making great strides in pyrolysis technologies. PyNe, a global network of active researchers and developers, also exchange information and developements related to the production of liquid fuels, electricity, and chemicals.

Fast Pyrolysis

Lipid extraction involves removing compounds, such as terpenes, esters and triglycerides, from the other constituents of an organic feedstock in a non-destructive manner. Lipid extraction is typically conducted using solvents such as alcohol. The desired compounds are dissolved in the solvent for later separation. The process can be complicated since the solvent must saturate the feedstock through its natural pores and pathways to reach the lipids, and then carry the dissolved compounds out the same way. The rate at which the compounds are removed from the biomass is the major process bottleneck, and so processes are designed to maximize diffusivity, including heating and pressurizing the solvent. However, lipids may be damaged by prolonged exposure to heated solvent (Topfer et al. 1995). 

Microwave extraction is an alternative approach. It saves energy by not heating the solvent but instead heating only the biomass, rapidly exciting whatever water remains inside. This increases the pressure within the biomass particles and thus expels the desired chemicals, sometimes by exploding cell walls. With this method, diffusion is no longer the limiting factor. Expelling chemicals into unheated solvent also preserves them. Additionally, microwave extraction is a single-stage process and greatly reduces overall extraction time (Armstrong 1999).

Once the lipids are extracted, they can undergo esterification or transesterification to become biodiesel, or they might be used as pharmaceuticals, flavorings, fragrances, colorings, or oils. Radient Technologies has licensed the microwave extraction technology and a new company, NaturNorth Technologies is looking at lipid extraction from birch bark.

Whereas nature converts biomass into fossil fuels by applying heat and pressure over millions of years, thermochemical liquefaction can convert a liquid slurry of organic material into hydrocarbon oils and products  to produce fuel in a matter of minutes. Water, injected into a feedstock slurry under pressures of up to 200 atmospheres and temperatures near 350 degrees Celcius, facilitates a chemical reaction that increases the hydrogen to carbon ratio, thereby improving hydrocarbon yields (Zhang et al. 1999). Direct liquefaction, or thermal depolymerization, has been successful in producing a liquid oil while the newer indirect liquefaction has had success producing syngas, ethanol, and methanol (PETC 1985).

Changing World Technologies has a process in which their feedstock, mainly turkey grease and oil, is pulped and heated under pressure to initiate the chemical reactions. First stage oils are removed and the heat is increased to produce a light hydrocarbon and char. The technology is roughly producing 500 barrels of bio-derived oil daily and has an energy efficiency of 85 percent measured by the energy of combustible products that leave the Carthage, Missouri plant divided by the total energy input.

Much more research and technological testing is needed to make this process work more efficiently with woody biomass, but the future is promising (BROKEN-LINKDuncan and White 2002).

Cellulose fibers have inherent properties, such as tensile strength and density, that can add considerable value to durable materials. These include products ranging from fiberboard, whose solids are almost entirely wood-based, to siding composed of wood-cement mixtures. Such wood composites have been manufactured for decades, but have primarily used virgin fiber supplies. A number of technologies are being developed that can produce high-quality materials with low-value lignocellulose feedstocks that have previously not been exploited by industry (Hunt and Scott 1988).

Argonne National Laboratory has developed phosphate ceramics, known as Ceramicrete, that can replace traditional cement in durable building products such as sheathing and door cores, and offer mechanical advantages over existing products including strength, density and flame resistance. Phosphate ceramics can encapsulate low-level hazardous wastes without leaching, which allows for safe recycling of paper mill residue and treated wood. Because of the cement-like nature of the ceramic, wood wastes utilized do not have to be dry. The moisture present in the wood wastes can be beneficial because it helps to moisten the ceramic. This innovative process joins established wood waste recycling products, such as the use of sawdust in extruded plastic composites (Wagh 2005).

Much of the development of novel wood composite manufacturing is focused on maintaining compatibility with current industrial infrastructure. These composites are gaining in popularity mainly because the net energy required to produce them is expected to be less than that needed to make similar products from solid wood. These composites would be made from harvesting residues.  The University of Minnesota-Duluths Natural Resources Research Institute and the Argonne National Laboratory are leading the way domestically in developing commercially acceptable products.