Leaching and drying of herbaceous bales with different density to improve their combustion performance

Abstract

This study investigates the industrial production of high-quality herbaceous biomass through leaching, using an integrated strategy that combines the use of low-density bales with the avoidance of biomass grinding prior to leaching. Large commercial herbaceous biomass bales (≈2.1 m3, ≥200 kg) were subjected to water leaching in order to improve their combustion performance. Bales with three different densities (100, 140 and 190 kg/m3) were submerged in 1800 L of water, corresponding to biomass-to-water ratios of 120, 160 and 220 g/L. Leaching duration was investigated, followed by an outdoor drying study over one year. Both bales and leachates were analysed to assess the removal of potassium, phosphorus and other soluble elements, as well as the potential reduction of sintering and corrosion phenomena. The results show that effective drying of leached bales is only achieved during the warmest summer months (Tmax >30 °C). The diffusion of alkaline compounds from straw fibres into water exhibits a conductivity limit of approximately 8 mS/cm, corresponding to about 220 g of straw per litre of water. Bale density strongly influences drying behaviour, and a density of around 140 kg/m3 is recommended to reach moisture contents below 20 wt%. Potassium removal of approximately 70% was achieved after 5 h of leaching, which could result in a comparable reduction in fouling and particulate emissions. In addition, corrosion severity was reduced by more than 50%. Although ash melting behaviour improved slightly, deformation and fluid temperatures remained below the thresholds required to fully eliminate sintering risks.