Development of laboratory studies on the off-gassing of wood pellets Jaya Shankar Tumuluru 1,2* , Xingya Kuang 1,3 , Shahab Sokhansanj 1,4 , C. Jim Lim 1 , Tony Bi 1 and Staffan Melin 1,5 1 2360, East Mall, Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, Canada, V6T 1Z3; 2 Biofuels & Renewable Energy Technologies Department, Energy Systems & Technologies, Division, Idaho National Laboratory, P.O. Box: 1625, Idaho Falls, Idaho 83415-2025, USA; 3 Department of Occupational Medicine, Yangpu, District Central Hospital, Shanghai 200090, China; 4 Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831; and 5 Delta Research Corporation, 501 Centennial Parkway, Delta, British Columbia V4L 2L5, Canada. Note: This work was done by the corresponding author while working as a postdoctoral researcher in the Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, Canada. *E-mail: JayaShankar.Tumuluru@inl.gov. Tumuluru, J.S., X. Kuang, S. Sokhansanj, C.J. Lim, T. Bi, and S. Melin. 2010. Development of laboratory studies on the off- gassing of wood pellets. Canadian Biosystems Engineering/Le ge´nie des biosyste`mes au Canada. 52: 8.18.9. In the present study three sealed containers (304.8 mm inside diameter and 609.6 mm height) were developed to investigate the concentration of off-gases accumulated in the headspace as well as changes in some of the physical properties of wood pellets during storage. Pellets occupied 75% of the container volume leaving 25% headspace. The outside wall of the steel containers was wrapped with electric heating tapes and fiber glass insulation. The storage studies were carried out at room temperature of about 228C and at elevated temperatures of 30, 40 and 508C. The off-gases were collected and analyzed using micro gas chromatography. The accumulations of CO (5000 ppmv) and CO 2 (10000 ppmv) were relatively high at room temperature of about 228C for a storage period of 24 days. These accumulations increased sharply at storage temperatures 308C. At 508C, the maximum measured concentration of CO, CO 2 and CH 4 was about 17,000, 70,000 and 3,000 ppmv, respectively. Storage temperature had a significant effect (PB0.01) on all of the pellet properties, including pellet durability, which dropped by about 20% at the end of 60 days of storage. Keywords: Wood pellets, off-gas, gas chromatography, moisture content, durability, pellet density, bulk density, storage temperature. Trois contenants herme´tiques (304,8 mm de diame`tre in- te´ rieur et 609,6 mm de hauteur) ont e´ te´ de´ veloppe´ s aux fins de la pre´ sente e´ tude dans le but mesurer la concentration ainsi que les proprie´te´s physiques des gaz e´mis par des granules de bois dans l’espace libre a` l’inte´rieur des contenants durant l’entreposage. Les granules occupaient 75% du volume du contenant laissant un espace libre de 25%. Les parois exte´ rieures des contenants en acier inoxydable e´taient recouvertes avec du ruban e´lectrique chauffant et de l’isolation en fibre de verre. Les e´tudes d’entre- posage ont e´te´ re´alise´es a` une tempe´rature ambiante d’environ 228C de meˆme qu’a` des tempe´ratures plus e´leve´es de 30, 40 et 508C. Les gaz e´mis ont e´te´ recueillis et analyse´s a` l’aide d’un micro chromatographe analyseur de gaz. Les accumulations de CO (5 000 ppmv) et de CO 2 (10000 ppmv) e´ taient relativement e´leve´es dans le cas de granules entrepose´es a` la tempe´ra- ture ambiante pour une pe´riode de 24 jours. Ces accumula- tions augmentaient de manie`re importante a` des tempe´ratures d’entreposage supe´rieures a` 308C. A ` 508C, les concentrations maximales mesure´ es de CO, CO 2 et CH 4 e´ taient d’environ 17000, 70000 et 3000 ppmv respectivement. La tempe´ rature d’entrepo- sage avait un effet significatif (PB0,01) sur toutes les proprie´te´s des granules incluant la durabilite´ des granules qui diminuait d’environ 20% apre`s une pe´riode d’entreposage de 60 jours. Motscle ´s: granules de bois, gaz e´mis, chromatographie en phase gazeuse, teneur en eau, durabilite´, densite´ des granules, tempe´rature d’entreposage. INTRODUCTION The use of wood pellets as solid biofuel is increasing as the cost of fossil fuels rises and as environmental concerns regarding greenhouse gas emissions are growing. The raw materials used in wood pellets vary depending upon the logging residues and source of sawdust and shavings from saw mills. In Europe, Scots pine and Norway spruce (Lehtikangas 2000) and in North America both softwood and hardwood species are ground to make pellets (Zaini et al. 2009). Currently, in Canada, most wood pellets are made from relatively dry planer shavings or sawdust. As part of the pelletization process, sawdust is dried at temperatures ranging from 100 to 4008C to a moisture content of less than 10%, and hammer-milled to fractions less than 2 mm. During the drying process, monoterpenes and other volatile compounds are released (McGraw et al. 1999; Banerjee 2001). The dried sawdust is pressed through holes in a die to form pellets. The high pressure in the die develops a temperature sufficient to soften the wood lignin to make pellets self-binding (Mani and Sokhansanj 2008). Therefore, no binders are used in Canadian wood pellets. The wood pellets are 6.4 mm in diameter with a length varying from 6 to 18 mm. The warm pellets exiting from the pellet press are cooled to room temperature and stored in steel bins or warehouses until shipping. Levitt et al. (1995) observed that organic matters, when stored at room temperature, particularly in the presence of air and light, emit small amounts of CO, and the emission rate increases at elevated temperature. During storage, the extractives in the wood pellets are reduced and the Volume 52 2010 8.1 CANADIAN BIOSYSTEMS ENGINEERING