Production of wood pellets
Pellets are produced by compressing the wood material (sawdust and/or wood shavings) which has first passed through a hammer mill to provide a uniform dough-like mass. This mass is fed to a press where it is squeezed through a die having holes of the size required (normally 6 mm diameter, sometimes 8 mm, 10 mm or larger). The high pressure of the press causes the temperature of the wood to increase greatly, and the lignin plastifies slightly forming a natural 'glue' that holds the pellet together as it cools.
Pellets can be made from nearly any wood variety, provided the pellet press is equipped with good instrumentation, the differences in feed material can be compensated for in the press regulation. Recycled materials such particle board, treated or painted wood, melamine resin-coated panels and the like are particularly unsuitable for use in pellets, since they may produce noxious emissions and / or uncontrolled variations in the burning characteristics of the pellets.
New pellet mills are being opened in the United States, Europe and other countries on a rapid basis, decreasing the price of a tonne of pellets to new lows. The scarcity and unreliable supply that used to come with the dependence on wood pellets has almost vanished. The higher production capacity brings the price of wood pellets to levels below the price of oil or natural gas on a per BTU-basis.
Prices for US pellets surged during the fossil fuel price inflation of 2007 - 2008, but subsequently have decreased significantly in late 2008 and early 2009, and are generally lower than most fossil fuels, excluding coal, which is not an option highly favored for heating by many residential and commercial consumers, due to frequent maintenance/tending requirements for end users, high carbon emissions, air pollution (often leading to nuisance complaints from neighbors and/or investigation by boards of health and environmental agencies), the mess generated by coal dust and/or improper storage, as well as potentially dangerous fly ash.
The opening of new mills for the production of woof pellets for pellet stoves and boilers will contributed to these realtive low prices.