Process line Type Moisture (%, wet basis) n = 30 Ash (%, dry basis) n = 30 1.0 (0.7) 0.4 (0.2) 0.4 (0.1) 2.8 (1.4) 1.7 (1.0) 1.2 (0.7) Bulk density (kg/m 3 ) n = 30 232 (53) 73 (29) 279 (74) 270 (76) 209 (62) 231 (70) Gross calorific value (MJ/kg, dry basis) n = 30 20.2 (0.8) 20.0 (0.5) 20.1 (0.5) 20.6 (1.0) 20.3 (0.3) 20.2 (0.5) Smoking temperature (°C) 1 n = 20 164 (9) 162 (6) 162 (7) 158 (6) 172 (6) 167 (4) Woody biomass feedstock at the plant gate Infeed to the dryer 1 Sawdust Shavings Chips Hog Bush grind Infeed mix 44 (6) 11 (3) 27 (14) 50 (9) 32 (11) 39 (14) Smoking temperature is the minimum temperature at which feedstock particles start to devolatilize and generate visible smoke. Table 2 -Mean moisture, ash, bulk density, gross calorific value and onset smoking temperature of the received and analyzed samples. n is the number of samples for all types of tested samples. Values in brackets indicate the standard deviations. is critical to safe operation of a belt dryer in which the biomass is in contact with hot surfaces for extended periods. The biomass in contact with hot surface may smoulder and eventually combust when it reaches to other enclosed areas such as a cyclone. EXTRANEOUS MATERIAL Extraneous materials (EM) are foreign ma-terials that do not come from plant origin. Stones and pellets are among the EMs. In the samples we tested, hog had an EM con-tent of up to eight per cent. The other three infeed types – sawdust, bush grind, and in -feed mix – had the maximum EM content of one per cent or less. Not all extraneous materials among biomass particles were detectable with the naked eye. In the frac -tion smaller than 3.15 mm, small stones were not detected by the method specified by ISO 19743 and instead were identified in the microscopic image. Our analysis showed that besides rocks and metals, bark contributed to the higher ash content of the infeed material. CONCLUSIONS The wood pellet plants follow site-specific procedures for cleaning their infeed ma-terial. The suite of equipment may vary from one plant to the next, but all have several magnets and density separators to remove heavy and non-woody objects. The current cleaning processes reduce the dirt content and upgrade the feedstock quality. The ranges of moisture content, ash content, bulk density, and particle size are very wide. Smoking temperatures are considerably lower than the ignition tem-peratures that are usually used for equip-ment and process design. It appears that small articles like stones remain in the feedstock even after several segregations. On-line instruments are required to sense extraneous objects in the feedstock. Jun Sian Lee, Hamid Rezaei, Omid Ghola-mi Banadkoki, Fahimeh Yazdanpanah, and Shahab Sokhansanj are members of the Biomass and Bioenergy Research Group at the University of British Columbia. FIKE DFI™ An Explosion Isolation Flap Valve You Can Trust / Flexible Installation / Wide Application Range / Real-World Testing Fike.com / Fike Canada Inc. 4400 Mainway, Burlington, Ontario, L7L 5Y5, Canada Toll free: 800-363-8116 / Main: 905-681-3100 CB_Fike_Summer23_CSA.indd 1 Canadian BIOMASS 2023-07-07 12:07 PM 15
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