Composition, Utilization and Economic Assessment of Torrefaction Condensates

The aim of this study was to determine the yields and chemical compositions of condensates formed at torrefaction conditions with different kinds of feedstocks and to assess their utilization from an economic perspective. Test runs for spruce and bamboo were carried out with a slow pyrolysis test rig, and the liquids collected at 20–105, 105–240, and 240–300 °C temperature ranges were analyzed for chemical characteristics and compositions. The results were compared with those obtained earlier for a birch condensate. The mass yields and compositions of condensates differed between the feedstocks and the temperature ranges. The amount of organic compounds in the total condensates was 12–19 wt %. The main compounds were acetic acid, 1-hydroxy-2-propanone, methanol, furfural, and 2-hydroxyacetaldehyde. Total condensates formed at ≤280 °C are promising to be utilized for different purposes, for example as a biopesticide. Higher temperatures are critical, because at 290 °C, strong exothermic reactions occur, which decreases considerably the yield of torrefied material and produces tar containing condensates. It is possible to produce, in addition to biocoal, valuable liquids. Economic assessments were performed for three torrefaction cases without and with the recovery of condensates. The production costs of torrefied pellets can be lowered significantly, for example on the order of 5–10 € MWh–1 in medium scale pellet production, by recovering and selling the condensates to new applications.