The moisture content of the pellet directly affects the pellet’s final quality and combustion efficiency (including the amount of smoke it admits). According to our years’ of study and experience, the optimal moisture content wood and biomass materials is from 10 to 15 percent. Most materials produce the highest quality pellets when the amount of moisture is around 15 percent, but varies for each raw material. If the raw material has a moisture percentage above 15-20% it must be dried or mixed with a dryer material. A rotary drum dryer is often a good option for this process. By controlling for the proper moisture content, you can cut down on overall costs and on energy consumption.
The wet milled material is transferred via screw auger to the rotary dryer. Hot air is generated at one end of the drum; at the other end a fan pulls the hot air and material through the drum up to a cyclone separator. The drum rotates as hot air is pulled over the material. The rotating action produces a more effective drying process. Light, dry particles are pulled through the pipe, and heavy wet particles remain in the drum until dry.
Pipe dryers
The wet material is placed into the pipe dryer. Hot air is generated at one end of the pipe and pulled through the pipe system by a fan; the material then leaves the dryer via a cyclone separator.
Heat sources
Some dryers source their heat using oil or gas burners, however in today’s market this can be very expensive and reduces the green credentials of the biomass fuel pellet. Therefore the cheapest solution is to generate heat through burning pellets or unprocessed biomass waste.
Increasing productivity
Another advantage by using heat to dry the material is once the material leaves the dryer the heat has made the material more malleable. This can therefore increase the productivity through the pellet mill of all materials but particularly dense materials like hard woods. The heat makes the material more malleable, and begins the process of melting the material’s natural lignin.
