Changes in the Composition and Surface Properties of Torrefied Conifer Cones

Abstract

The paper investigated the torrefaction of cones from three tree species: Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.), and European larch (Larix decidua Mill.). The objective was to determine the effects of torrefaction temperature on the properties of cones with a view to their further use as a renewable energy source. Torrefaction was conducted at 200, 235, 275, and 320 °C for 60 min under an inert gas atmosphere. Elemental composition, ash content, and lower heating value (LHV) were measured for the original and torrefied samples. Torrefaction performance was evaluated using formulas for solid yield, higher heating value (HHV), HHV enhancement factor, as well as energy yield. Scanning electron microscopy (SEM) was used to assess elemental composition and structural changes at the surface of the torrefied material. For all the studied conifer species, the higher the torrefaction temperature, the greater the carbon and ash content and the higher the LHV (a maximum of 27.6 MJ·kg−1 was recorded for spruce and larch cones torrefied at 320 °C). SEM images showed that an increase in process temperature from 200 to 320 °C led to partial decomposition of the scale surface as a result of lignin degradation. Cone scales from all tree species revealed C, O, N, Mg, K, and Si at the surface (except for pine scales, which did not contain Si). Furthermore, the higher the temperature, the higher the enhancement factor and the lower the energy yield of the torrefied biomass. Under the experimental conditions, spruce cones were characterized by the lowest weight loss, the highest HHV, and the highest energy yield, and so they are deemed the best raw material for torrefaction among the studied species.

Use of Spent Coffee Ground as an Alternative Fuel and Possible Soil Amendment

“…Together with moisture, the hydrogen and oxygen level also decreased with the increase in torrefaction temperature, as expected [ 24 , 68 ]. The hydrogen level decreased from 6.29% wt.…”

Substituting Solid Fossil Fuels with Torrefied Timber Products

“…According to Jeníček et al [21], Chen et al [22], and Gendek et al [23], torrefied biomass has three main advantages over unprocessed biomass-increased heating value, increased energy density, and improved physical characteristics, such as shape retention [24], homogeneity [23], and hydrophobic behaviour [25]. The heating value may increase from 17 up to 27 MJ kg −1 [26] through torrefaction, which is enabled by the decrease in oxygen content [27][28][29]. Simultaneously, hydrogen content decreases [30] and the decrease in the hydroxyl groups in the material contributes to its hydrophobic behaviour [17].…”

Energy Efficiency of Conifer Cones and Seed Extraction Residue Biomass

“…The HHV and LHV of conifer cones were higher than the values noted in pinewood chips, other types of sawmill waste (sawdust, woodchips) from coniferous trees, and the biomass of forest residues [10,47,52]. These parameters can be increased through torrefaction [53].…”