THE NITTY GRITTY ON WOOD PELLETS ood pellets and briquettes are produced from a variety of feedstock materi-als such as sawdust, planers shavings, cut blocks from lumber production, bush grind (harvest residue), bark and even higher quality hogfuel materials. The feedstock preparation involves separation of contaminants, grinding, drying, hammer milling to size before compression to a commercial products, which in turn are screened and cooled before storage and transportation to the end user. The large majority of the pellets made in Canada are sold and transported in large bulk volumes and used for electrical power production or heat. Smaller volumes are packaged in bags and sold for residential space heaters or boilers. Briquettes are also produced in small volumes. The quality of pellets and briquettes are specified by ISO Standards, currently being rolled out in Canada as a voluntary CSA Standard. These standards specify the mechanical and chemical composition as well as the acceptable feedstock materials. There are six different qualities for wood pellets and an additional five qualities for non-woody (agricultural) pellets. Woody briquettes are specified in three different qualities and non-woody briquettes are specified in five different qualities. The common denominator for all these biofuel products is that the feedstock has to be reduced to particles before compression to a commercial product. For some of the products, such as industrial quality pellets, the maximum allowable particle size is stipulated in the ISO Standards. The pellets are crushed to a powder during the fuel preparation in the power plants before sprayed into the furnaces for combustion, much like coal powder or fuel oil. W facilities. In North America guidelines are published by NFPA (National Fire Protection Association), FM (Factory Mutual Insurance Company), OHS (Occupational Health and Safety), local fire codes, etc., some of which are voluntary and others are mandatory. In Europe, ATEX (Atmospheres Explosibles) is universally accepted as the guideline miti-gation of risk of explosions. Equipment in-stalled in a facility has to be rated in accor-dance with a risk zone classification. In North America, feedstock is dried at high temperatures up to 450ºC, which is a critical ignition temperature for lofted mate-rial (as mentioned above). To prevent igni-tion, the oxygen in the dryer is kept below 10 per cent: the limiting oxygen concentra-tion for wood dust. The thermal balance in the dryer is critical and needs special control strategies, particularly during shutdown or loss of electrical power to the drive system. Hot particle detectors are installed along the material’s path as it makes its way to be-come the final product. Some brands of de-tectors have a temperature set-point capabil-ity as low as 250ºC to monitor hot particles destined to land on dust layers. A set-point firefly EXIMIO FIRE PROTECTION SOLUTIONS FOR PORT FaCILITIES aNd ThE PELLET INdUSTRY VIsIt us at wPaC aGM November 17-19, 2014 | Vancouver, Canada www.fIrEfly.sE 14 Canadian BIOMASS SEPTEMBER/OCTOBER 2014
Canadian Biomass September October 2014: Page 14
