Influence of oscillating water content on the structure of biomass pellets

When handling wood pellets, the main challenge arises during storage, where the physical properties of the pellets are affected by fluctuating relative humidity (RH). With increasing RH, the water content of the pellets increases, which leads to swelling and higher porosity as well as crack formation on the surface. However, these changes are reversible to a certain extent and the pellets can recover fully or to a certain extent when the RH subsequently decreases again. The permanent damage caused by fluctuating RH is shown in the form of larger gaps between the wood chips within the pellets. As a result, the pellets have a larger volume and higher porosity as well as higher surface roughness than in their initial state before storage. In particular, when the saturation vapor pressure was exceeded to reach a water content of over 12 wt.-%, the reversibility of the structural changes appeared to be lower.

Subjects

Biomass pellet

Microcomputed tomography

Porosity

Reversibility

Storage effect

Water content

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Influence of oscillating water content on the structure of biomass pellets