The wood pellet machine is only a part of the wood pellet equipment needed for the pellet making process. You will need some way of making the wood particle size of your raw material smaller than about 3 mm. or the wood pellet mill will be under unnecessary stress.
Wood pellets for pellet stoves should be a quarter of an inch in diameter and about an inch long to be usable by the majority of pellet stoves. Ash content is specified to be less than 1% for premium grade pellets, and less than 3% for standard grade pellets. Simply removing the bark from the timber will achieve premium grade pellets in wood.
Other potential pellet materials such as grass and paper have higher levels of impurities and so a higher ash content. These materials are usable, but only in stoves designed to cope with high levels of ash. See the links at the bottom of the page for making wood pellets and wood pellet mills for more information.
The tool that most reliably pulverizes timber to a pelletable size is the hammer mill. This machine usually consists of a rotating axle to which metal 'hammers' are attached and allowed to slide so that as the axle turns, the hammers flail down on the raw wood waste. They are equipped with mesh screens that allow material of the desired finished size to fall through into a collection drum.
Moisture content for the wood pulp is important to the wood pellet machine operation. Ideal water content for pelletizing is from 12 to 14%. Larger scale machines have dispensers which can automatically add moisture in the form of steam to dry raw materials as well as conditioning/binding agents. The moisture content needed to make the material malleable will later need to be reduced.
The heat produced by larger wood pellet machines is enough to allow the lignin content of the timber to plasticize and become a glue to hold the pellets together. Smaller machines need a binder, (usually a vegetable oil), to hold the pellets together. Pellets which don't hold together produce excessive fines, (dust), and can clog the auger mechanism in pellet stoves.
Small Pellet Machines
Wood pellet machines come in two configurations: flat die and ring die. In flat die machines, the die is stationary and rollers push the material through. In ring die machines, a drum-like die rotates round the rollers. A knife cuts the pellets to length after they emerge from the die.
Most of the small wood pellet machines available originate from GEMCO, a Chinese company. These same machines are offered by a number of companies in China and marketed under different names by Western companies. Originally designed as small scale animal feed mills, they have been successfully used for wood pelletizing. GEMCO offer complete systems including hammer mills and dryers.
Drying Wood Pellets
After pellets emerge from the machine, they will need cooling to give them physical strength, and drying to enable them to be burnt in pellet stoves. Dryers are available but economics of heating a dryer may not be cost effective. If covered space is available, with a good airflow, pellets can simply be spread out to dry, turning as needed until moisture content is down to 10%.
Larger Wood Pellet Machines
CPM (California Pellet Mill) is the largest manufacturer of pellet mills in the world , based in Indiana.
Sprout is the second largest, based in Pennsylvania.
Bliss Industries are based in Oklahoma.
For second hand machinery, Freedom Equipment of Rockford, Illinois has a good inventory of pelletizing equipment.
Dies and Lubrication
Wood pulp for pelletizing is an abrasive substance and the dies used to produce wood pellets have to be viewed as consumable items. The natural resins present in softwoods are easier on dies than hardwood pulp, and a high moisture content keeps the material soft, helping to prevent wear. As well as helping as a binder, vegetable oil can also help to reduce wear on the die.
A source of replacement dies is a priority to keep the machine running.
Wood Pellet Mills
Making Wood Pellets
Pellet Stove Pellets
Alternative Pellet Stove Fuels
What is Biomass
Pages Related to Wood Pellet Machines