Properties of Biomass Pellets

Biomass pellets are generally a superior fuel when compared to their raw feedstock. Not only are the pellets more energy dense, they are also easier to handle and use in automated feed systems. These advantages, when combined with the sus-tainable and ecologically sound properties of the fuel, make it very attractive for use.

The standard shape of a fuel pellet is cylindrical, with a diameter of 6 to 8 millimeters and a length of no more than 38 millimeters. Larger pellets are also occasionally manufactured; if they are more than 25 millimeters in diameter, they are usu-ally referred to as “briquettes.”

Table 1.   Typical properties of biomass pellets  from different sources.

Note: to convert from MJ kg-1 to btu/lb, multiply by 430. To convert from kg/m3 to lb/ft3, multiply by 0.0624279.

A high-quality pellet is dry, hard, and durable, with low amounts of ash remaining after combustion. According to the Pellet Fuels Institute, “premium” pellets (which are the most common pellets currently on the market) must have an ash content of less than 1 percent, whereas “standard” pellets may have as much as 2 percent ash. All pellets should have chloride levels of less than 300 parts per million and no more than 0.5 percent of fines (dust). Many biomass feedstocks have a higher ash content than the standard allows. In addition, some grasses and other materials gener-ate ash that tends to form clumps and deposits at high temperatures. Because of this, most wood pellet stoves are not suitable for burning fuel pellets made from materials other than wood. Instead, “biomass pellet” stoves, which are designed especially for those fuels, should be used.