PelletizationWhat are Pellets? Pellets are a carbon neutral fuel source made from compressed woody or herbaceous material, generally measuring 6-8 mm in diameter and 2 cm in length. Wood pellets are commonly made from sawdust and other wood waste from processing mills, however, additional feedstocks can include forest origin wood (tops and branches, unmarketable species, undersized material) and short rotation woody crops (willow, hybrid poplar). Pellets can also be made from other non-woody materials such as herbaceous crops (Miscanthus, Switchgrass) and agricultural residues (oat husks, corn stover). Pellets are classified into premium, standard, and utility categories. Factors in this classification system include

bulk density, ash content, moisture content, and heating value among others. Pellets are commonly used in pellet stoves and commercial or industrial boilers as a main fuel source or co-fired with fossil fuels.

How Does Pelletizing Work?The pelletizing process generally involves:

• Initial grinding of the biomass material.

• Drying the material to approximately 10% moisture content.

• Secondary hammering and grinding of the dried material.

• Sending the ground material through a high pressure, high-temperature press where the high temperatures cause the release of natural lignin in the wood, which acts as a glue to hold the pellets together.

• Cooling and packaging of pellets.

PelletizationNo artificial binders are used in the pelletizing process so pellets need to be stored in a cool, dry place. Moisture will cause the pellets to expand and lose their burning capabilities.

AdvantagesPelletizing woody and herbaceous feedstock offers a number of advantages:

• High energy content and low moisture content allows fuels to burn more efficiently and reliably.

• There are no contaminants as the biomass has been screened and processed.

• Lower transport costs due to compact size and higher energy density.

• Uniform size allows them to be used in automated feed systems.

Pellets are growing in popularity as fossil fuel costs rise and concerns about climate change increase. When raw materials are harvested sustainably, pellets are considered to be carbon neutral. Pellet stoves and boilers are simple to use and therefore, offer an environmentally friendly alternative to fossil fuel heating systems. Pellet systems function much like regular heating systems, requiring only minimal maintenance and re-fuelling.

Information Sources:

AKG BiofuelTech Co. Ltd. (2011) Wood Pellet Mills Production Line. Retrieved May 25, 2012, from http://www.pelletmillguide.com

Åsman, P. (2011) Wood pellet production & technology [PowerPoint slides]. Retrieved from http://www.biomassinnovation.ca/pdf/HarnessingBiomassII/SE_Asman.pdf.

Go Pellets Canada (2012) Pellet information. Retrieved May 25, 2012, from http://www.gopelletscanada.com/article/pellet-information-5.asp

Pellet Fuels Institute (2011) Pellets. Retrieved May 25, 2012, from http://pelletheat.org/pellets/

Wood Pellet Association of Canada (2012) Publications: Presentations and Reports. Retrieved May 25, 2012, from http://www.pellet.org/publications