BioEnergy Conference & Exhibition

Safety in handling wood pellets

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Canada is primarily a bulk producer and exporter of pellets with large mills that make, on average, 56,000 tonnes per year, said Staffan Melin. When shipped in large volumes, pellets are classified as hazardous material, although wood pellets in consumer bags are benign. For example, carbon monoxide (CO) gas emissions released by pellets killed a person in the cargo hold of a ship in 2002.

A research project was undertaken to examine gas concentration on board ocean vessels. “Astonishingly high levels of CO” were found in six vessels, in addition to dangerous levels of CO2, methane, and oxygen, Melin said. UBC launched an extensive research program to verify off-gassing in vessels. Corresponding values in closed reactors were found: after about five days, in excess of 12,000 parts per million (ppm) of CO existed—“a deadly dose.”

“We have now installed a large research reactor at UBC to look at stratification,” Melin said. “When we fill up the holds with layers of pellets, we may get heated zones.” Heat is produced by bacteria and fungi through microbial oxidation and through chemical oxidation. Ultimately, as the temperature increases, an “exothermic situation,” or explosion, can occur. This happened in Denmark and northern Sweden, where silos holding pellets burned for months. WPAC is funding fire-extinguishing research at the laboratory scale to examine the effects of nitrogen and CO2.

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