Small hardwood chips, known as pellet chips, were characterized and combusted in two different pellet burners, installed in a residential boiler specially designed for pellet combustion. The average particle mass was about 10 percent of the mass of an 8-mm pellet, with a similar surface-to-volume ratio. The bulk density of pellet chips was 160 to 170 kg m−3 at 10 percent moisture content (about 25% to 35% of 8-mm pellet bulk densities). The combustion performance was good, with average O2 and CO values (by volume) at 17.6 percent (SD, 0.6%) and 200 ppm (SD, 210 ppm), respectively, for the bottom-fed burner and 14.2 percent (SD, 1.1%) and 330 ppm (SD, 93 ppm), respectively, for the top-fed burner. Thus the study indicates that pellet chips produced with commercially available equipment can be used in ordinary pellet combustors, provided that the fuel feeding rates are increased and the moisture content well below 20 percent. More accurate market assessments will require the investigation of the performance of different types of combustion equipment with fuels of different qualities.
Contributor Notes
The authors are, respectively, Postdoctoral Student, Forest Resource Management, Swedish Univ. of Agric. Sci., Umeå, Sweden (Gunnar.Eriksson@slu.se); Assistant Professor, Energy Technol. and Thermal Process Chemistry, Dept. of Applied Physics and Electronics, Umeå Univ., Umeå, Sweden (Christoffer.Boman@chem.umu.se); and Professor, Dept. of Forest Ecology and Management (Urban.Bergsten@slu.se) and Researcher, Forest Planning and Operations Management, Forest Resource Management (Dan.Bergstrom@slu.se), Swedish Univ. of Agric. Sci., Umeå, Sweden. This article was received for publication in December 2010. Article no. 10-00074.