Influence of cyclic water content changes during long-term storage on the mechanical stability of wood pellets

Abstract

In the case of wood pellets, a water content >10 wt.-% should not be exceeded, as they begin to break even under low mechanical loads. However, during storage, they are exposed to different environmental conditions, including rising and falling humidity. In this study, by humidifying and re-drying wood pellets, it was found that their loss of stability at high humidity is reversible and they can recover to a high degree at subsequent low humidity. However, exceeding the saturation vapor pressure and a pellet water content >12 wt.-% leads to much greater swelling and loss of stability. In this case, pellets recover significantly less during subsequent drying. Long-term tests with multiple cycles of humidification <12 wt.-% have shown that pellets with high density and stability in their original state suffer a significant loss of stability within the first 10 cycles, while pellets with high porosity didn't change during long-term storage.