Isothermal and Morphological Studies of the Torrefaction of Spruce Wood

The replacement of fossil fuels by biofuel for decreasing the action of greenhouse gases on the global climate is encouraged in industrially developed countries. A promising trend in the refining of waste biomass is torrefaction—a mild pyrolysis process in which biomass is heated to 250–350°C without the access of oxygen at low heating rates; as a result, biocoal with improved chemical and physical properties is formed. The torrefaction (mild pyrolysis at 250–300°C) of spruce stem wood was studied in a fixed-bed reactor at different temperatures. The mass and energy yields of biocoal, its specific heat of combustion, and morphological changes in the biomass structure in the course of spruce wood torrefaction were determined. It was established that the torrefied samples began to decompose at higher temperatures, as compared with the nontorrefied biomass. The torrefied fuel had a higher heat of combustion, which increased with the temperature of torrefaction. Conclusions on the restructuring of test samples and the formation of a porous structure at different temperatures depending on exposure time were made.