Biomass Pellet Maker-Fines

As the biomass pellet maker compresses the raw material into pellets some material is not compressed into pellets, this dust is referred to as fines. Fines are particles of material that failed to bind to the pellet during pellet formation; this could be due to lack of pressure in the biomass pellet maker or a lack of binding. If the pellets produced are not mechanically strong, as the pellets move and rub against other pellets and surfaces particles break away from the pellet, again these are described as fines. So the performance of the biomass pellet maker and the quality of the finished pellets affect the percentage of fines.

Pellets are very strong with vertical pressure, but all pellets break fairly easily under horizontal pressure. Pellet breaking is not that important, but how the pellet breaks is. When horizontal pressure is applied to quality pellets the pellet should break cleanly. Pellets made by poor quality biomass pellet making machine however under horizontal pressure will break into several pieces and produce many fine particles.

With regards to how important the percentage of fines is depends on the target market for the pellets produced by pellet maker. Fines can interfere with the pellet feed system into the pellet stove/boiler; this is more of an issue with small residential units. Also pellet stoves and boilers have the feed rate and fan speed set for burning pellets. However fines burn faster than pellets, in some pellet burners this can cause the ash to melt and sinter. In the premium wood pellet industry the target is for fines to be less than 1% by weight. The European CEN standard has specifications for the maximum allowance of fines, and in many cases the percentage of fines must be stated when sold. Pellets in bags tend to have fewer fines than those sold in bulk sacks. Pellets that are stored in silos generally have more fines on delivery.