Ash-Forming Matter in Torrefied Birch Wood: Changes in Chemical Association
Torrefaction is heat treatment of biomass at relatively low temperatures (∼240–300 °C) in the absence of air. The torrefied fuel offers advantages to traditional biomass, such as higher energy density, better grindability, and reduced biological decay. These factors could, for example, lead to increased use of biomass in pulverized coal boilers. Ash-forming elements are present in biomass as water-soluble salts, ion-exchangeable elements, included or excluded minerals, and covalently bound sulfur and chlorine. In this work, we have studied the change in the chemical association of ash-forming elements in birch wood as a function of the extent of torrefaction. The birch wood was torrefied at 240, 255, 270, or 280 °C at ECN, The Netherlands. The raw and torrefied birch wood samples were studied using three different techniques: chemical fractionation, potentiometric titration, and methylene blue sorption. Chemical fractionation was performed on the original wood sample, and the samples of wood were torrefie...