The impact of a combined pre-treatment on the combustion performance of various biomass wastes and their blends with lignite

Two pre-treatment techniques, water leaching and torrefaction, as well as a combination of these were applied to a variety of biomass wastes in order to get improved quality products in terms of composition, energy density and content of problematic inorganic constituents. Upgraded materials were blended with lignite and tested by thermogravimetric analysis. Devolatilization and combustion characteristics, thermal behaviour, reactivity and the role of ash were determined. The results showed that both pre-treatment methods improved the quality of biomass fuels, increased the FC/VM, decreased the H/C and O/C ratios, enhanced the energy density and provided materials with composition closer to the lignite, thus allowing better performance of the co-combustion process than that of raw blends. The slagging/fouling propensity of lignite/leached biomass mixtures was lowered. The combined leaching/torrefaction pre-treatment could facilitate the handling and feeding of fuels by delaying ignition and increase the reactivity and performance of the co-combustion process, but not to the same extent as solely torrefaction, because minerals removed by washing acted either as diluents or as catalysts during the thermal treatment.