Moisture sorption isotherm study of Sitka spruce, larch, willow and miscanthus chips and stems

• Moisture sorption isotherm data were presented at 4 °C and 15 °C.
• These data are essential for the ambient drying of woody biomass fuels.
• There was large variability in initial moisture content of individual chips and stems.
• There was much less variability in corresponding equilibrium moistures.
• Moisture sorption during cold damp Irish winter did not impact much on heating value.

Moisture sorption isotherms were measured using saturated salt solutions in airtight Kilner jars. Data were presented at 4 °C and 15 °C for Sitka spruce and larch woodchips obtained from forest thinnings and for willow woodchips and miscanthus stems obtained from short rotation plantations. These data are essential for the ambient drying of biomass fuels because they provide an estimate of how low a moisture content that can be attained. There was large variability in initial moisture content of individual chips and stems, although this variability reduced as the biomass dried, yet there was still significant variability in the equilibrium moisture contents. The sorption isotherm data were applied to a case-study to investigate the influence on moisture content of storing freshly harvested willow chips and dried miscanthus stems during a cold damp Irish winter.