Ash-Forming Matter in Torrefied Birch Wood: Changes in Chemical Association

Abstract

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 torrefied at either 240 or 280 °C. These results give a first understanding of the changes in the association of ash-forming elements during torrefaction. The most significant changes can be seen in the distribution of calcium, magnesium, and manganese, with some change in water solubility seen in potassium. These changes may, in part, be due to the destruction of carboxylic acid groups, which were measured by both potentiometric titration and methylene blue sorption. In addition to some changes in water and acid solubility of phosphorus, a clear decrease in the concentration of both chloride and sulfur was measured. The results provide new data about chemical changes with regards to the inorganic elements during torrefaction. The decrease in the chloride content should be investigated further with high-chloride-containing fuels. If a significant level of chloride is removed by torrefaction, this would be a significant additional benefit for the combustion of torrefied biomass.

Effect of Torrefaction on Physicochemical Properties and Steam Gasification Reactivity of Chars Produced from the Pyrolysis of Typical Food Wastes

“…In comparison to the raw food wastes, almost no AAEM species are released during the torrefaction of the food wastes. However, it can be found that the transformation of AAEM species takes place during torrefaction, which is consistent with the results by Shoulaifar et al . During the torrefaction of LC and WP, almost no transformation of alkali metals is observed, while a portion of water-soluble K (12.1%) is transformed into CH 3 COONH 4 -soluble K during the torrefaction of LP.…”

Oxytree Pruned Biomass Torrefaction: Mathematical Models of the Influence of Temperature and Residence Time on Fuel Properties Improvement

“…The AC in the torrefied pruned Oxytree biomass ranged from 7% to 1% [19]. This is a much higher value than that found in torrefied wood from torrefied pine 0.15%–0.21% [25] and birch 0.23%–0.38% [26]. The AC values obtained for Oxytree were closer to the corn stover 10%–12% [27].…”

Correlations to Predict Elemental Compositions and Heating Value of Torrefied Biomass

“…The sources of the collected experimental data are also provided in Table 1. For instance, the torrefaction data for birch were obtained from four different sources [20][21][22][23][24] with a minimum and a maximum torrefaction temperature of 200 • C and 280 • C respectively, and the residence times varying between 10 and 60 min. Table 2 presents an overview of the compiled data based on the wood type including the number of measurements (n), the minimum (Min), maximum (Max), and mean of experimentally measured Y s , C, H, N contents, and the HHV.…”