Forest Bioenergy Products
Four types of energy products can be derived from forest biomass as follows:
Thermal energy includes the heating of buildings, heating of water, and heating that is required for certain manufacturing processes. It also includes the production of heat for drying materials, such as lumber, paper, clay, and other products. The heating is produced by direct combustion within boilers, gasifiers and furnaces. Steam boilers and hot water boiler systems fired by wood chips or bark are often used. Wood pellets can be used in furnaces, heaters, and in the larger boiler systems.
Electricity can be generated through the use of steam turbines powered by steam from boilers using wood chips, bark, or wood pellets as fuel. Cogeneration is achieved by producing electricity in this manner while also using the steam for a thermal energy need. The wood fuel can also be combusted within gasification systems to produce a synthetic gas, similar to natural gas. The synthetic gas is then combusted to produce steam and electricity, or the gas can be used directly in a gas turbine for electricity production.
Ethanol, methanol, butanol, and BTL diesel are all liquid fuels that can be produced from cellulosic biomass. The two general conversion technologies used are enzymatic hydrolysis and thermo chemical. Clean wood chips can be converted to alcohol fuels (ethanol, etc.) using enzymatic hydrolysis. Biomass-to-liquid diesel and alcohol fuels can be produced through thermo chemical conversion of any forest biomass material. Gasification and pyrolosis can be used within the thermo chemical conversion methods.
Although wood pellets are a product, they are actually a fuel that can be used to produce the energy types above. They are most easily produced from sawdust and other mill residues. However, small diameter trees can also be chipped and utilized for wood pellets. Wood pellets are produced using pellet presses that force the sawdust through holes in a die using rollers. The natural resins in the wood provide the "glue' necessary to hold the pellets together. Wood moisture content must be in the 10-12% range, so drying is often required during the process. Wood pellets can be used in pellet heaters, furnaces, and boilers. The major use of wood pellets is by European-based utilities that co-fire wood pellets with coal to produce electricity. Large quantities of pellets are also used in residential heaters and furnaces in Europe, Canada, and the northern U.S. Georgia has the potential to use pellets within several industries, such as the poultry industry to provide heat to poultry houses. Pellets have the advantages of being uniform for ease of fuel handling (conveying), dense for ease of transport, and low in moisture to produce more energy.