The Right Moisture Content For The Wood Pellet Mill

Before we get into the detail its important to cover the basics. Water within the raw material is a requirement, however it can also be an issue with most fresh raw materials. Take for instance fresh timber, chipped and milled this will have a moisture content around 55%. This needs to be reduced dramatically before you can even consider putting it in the wood pellet mill. To produce a fuel pellet you want to get the moisture down as much as possible, however moisture is required for compression, temperature and for binding. In the pellet mill it is the moisture that gets hot, melts the lignin and spreads it across the pellet. Once the pellet cools the lignin sets, the result is a highly durable pellet. However the exact percentage of moisture effects the temperature achieved. What you will also find is that the large wood pellet mills can produce a high density pellet from a material with less moisture. This is because a large pellet mill will achieve a higher operating temperature and requires less moisture to achieve the same results. For instance a large wood pellet could process wood fibre with a moisture content below 10%, however the process is also sometimes aided by the introduction of super heated dry steam. Steam introduction on small wood pellet mills is not practical or cost effective, therefore the raw material is generally required to have a higher moisture content at around 15%. Something that many people forget is controlling moisture can only do so much, not every pellet mill can produce a high density wood pellet. The die is the most important factor. The speed of the die and its rotation speed are highly influential factors which are often forgotten about. A wood pellet mill generally requires the die to turn slower and the die to be deeper than most other pellet mills. Rotation speed and die depth are to do with compression. The longer the material spends in the die the better the quality of the pellet. We produce special dies for wood pellets where other pellet mill manufacturers just provide one die for all materials, which is simple not acceptable.

 The Wood Pellet Production Guide © PelHeat Ltd - The Right Moisture Content For The Wood Pellet Mill