Hot Water Extracted and Non-extracted Willow Biomass Storage Performance: Fuel Quality Changes and Dry Matter Losses

Abstract

Dry matter losses (DML) and fuel quality changes occurring in storage piles are important parameters for the management of any biomass supply system. This study evaluates the effect of a hot water extraction pretreatment, harvest season, depth in storage pile and initial moisture content on willow biomass fuel quality [moisture, ash, higher (HHV) heating value and lower (LHV) heating value] during storage, and models DML in storage piles based on experimental data. For the summer storage (SS) pile, mesh bags containing freshly harvested chips (FC) were inserted at 0.5–1 m deep in the pile. For the winter storage pile (WS), the mesh bags were filled with FC and hot water extracted chips (HC) with three different initial moisture contents inserted in the shell (<0.45 cm) and the core (1–1.5 m) of the pile. The ash contents through all sampling periods were in the range of 1.1–2.2% for FC and 0.6–2.1% for HC from both the shell and core of the WS pile. Higher ash contents, in the range of 2.1–3.4%, were observed in SS pile. Moisture contents of the storage piles had differing patterns over time. DML was the highest in the SS pile, reaching up to 33.6% after 140 days in storage; in contrast, there was no significant increase in DML over the first winter season. Although DML of FC and HC were in the same range during the initial storage period, DML of HC was 40% lower than FC after 180 days of storage. Higher DML was observed in the core (e.g., 17.3% for FC) compared to the shell (e.g., 12.1% for FC) at the end of the WS trial. There was no particular trend observed between initial moisture and DML. This study suggests that a linear model is sufficient to estimate DML, but a non-linear model may be needed for chips stored in SS piles for 6 months or longer. It also suggests that DML is reduced in storage piles created in winter, and that willow chips kept in SS should be utilized within 2 months for a DML below a 10% threshold.