Heats of wetting and sorption for wood pellets

Abstract

Wood pellets have become a flagship biofuel in transitioning from coal-based heat and power generation to renewable energy. However, the hygroscopic nature of wood pellets is a long-standing challenge in storing and transporting this commodity. The heat of moisture sorption contributes to the self-heating and spontaneous combustion of wood pellets. The objective of this paper is to investigate the evolution of heat in moistened pellets and to compare them to that of wood chips. Wood pellets at several moisture content levels were immersed in liquid water and the rise in the pellets’ temperature was recorded. The calorimetric method was used to calculate the heat of wetting for the immersed pellets. The heat of wetting was at its maximum for completely dry pellets. The heat of wetting decreased linearly as the moisture content increased towards a fiber saturation point of about 0.17 (decimal dry basis). Statistically, the maximum heat of wetting of pellets is the same as that of wood chips. However, the rate of heat release of pellets is twice of that of chips.