Temperature patterns in large scale wood pellet silo storage

Over a 7month period, temperatures were monitored in six large scale (approximately 4500 metric tons) silos for wood pellet storage. Each silo had 124 temperature sensors mounted on cables for an even distribution within the volume. During the study, silos were charged and discharged several times, creating different scenarios. Under certain circumstances, pellet temperatures increased vertically from bottom to top in an additive way, and temperatures around 65–70°C were reached at the top of the silos. At some occasions, temperatures were increasing uncontrollably and silos were emptied due to the risk of fire. In an additive scenario, a maximum heat front velocity of 12cm/h and a maximum temperature increment for a specific sensor of 2.4°C/h was found. To avoid condensation of moisture from the ventilation air on stored pellets fan operation is suggested to be controlled by a dew point algorithm.